- Email: [email protected]
New age constraints on the palaeoenvironmental evolution of the late Paleozoic back-arc basin along the western Gondwana margin of southern Peru
Accepted Manuscript New age constraints on the paleoenvironmental evolution of the late Paleozoic backarc basin along the western Gondwana margin of southern Peru F. Boekhout, M. Reitsma, R. Spikings, R. Rodriguez, A. Ulianov, A. Gerdes, U. Schaltegger PII:
S0895-9811(17)30128-1
DOI:
10.1016/j.jsames.2017.12.016
Reference:
SAMES 1859
To appear in:
Journal of South American Earth Sciences
Received Date: 24 March 2017 Revised Date:
3 November 2017
Accepted Date: 24 December 2017
Please cite this article as: Boekhout, F., Reitsma, M., Spikings, R., Rodriguez, R., Ulianov, A., Gerdes, A., Schaltegger, U., New age constraints on the paleoenvironmental evolution of the late Paleozoic back-arc basin along the western Gondwana margin of southern Peru, Journal of South American Earth Sciences (2018), doi: 10.1016/j.jsames.2017.12.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
1 2 3
New age constraints on the paleoenvironmental evolution of the late Paleozoic backarc basin along the western Gondwana margin of southern Peru F. Boekhouta,1,†, M. Reitsmaa,2, R. Spikingsa, R. Rodriguezb, A. Ulianovc, A. Gerdesd, and U.
5
Schalteggera
6
a
7
b
8
c
9
d
Department of Earth Sciences University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland INGEMMET, Av. Canadá 1470, Lima, Perú
SC
Institute of Earth Sciences, University of Lausanne, BFSH 2, CH-1015 Lausanne, Switzerland University of Frankfurt, Institute of Geosciences, Altenhofer Allee 1, D-60431, Germany
1
Present address: Institute for Geology and Paleontology, westfälische Wilhelms-Universität, 48149 Münster, Germany
13
2
14
†
M AN U
10 11 12
RI PT
4
Present address: HRH Geology, 19 Silverburn Place, Aberdeen AB23 8EG, UK
Corresponding author, [email protected]
15
Keywords: zircon geochronology, Oqoruro Formation, Ene Formation, Ambo Formation, Tarma-Copacabana
17
Group, back-arc basin
18
TE D
16
Abstract
20
The tectonic evolution of the western Gondwana margin during Pangaea amalgation is recorded in variations in
21
the Permo-Carboniferous back-arc basin sedimentation of Peru. This study provides the first radiometric age
22
constraints on the volcanic and sedimentary sequences of south-central eastern Peru up to the western-most tip
23
of Bolivia, and now permits the correlation of lateral facies variations to the late Paleozoic pre-Andean orogenic
24
cycle. The two phases of Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260 Ma are reflected in
25
two major changes in this sedimentary environment.
AC C
EP
19
26
1
ACCEPTED MANUSCRIPT
Our detrital U-Pb zircon ages demonstrate that the timing of Ambo Formation deposition corroborates the Late
28
Mississipian age estimates. The transition from the Ambo to the Tarma Formation around the Middle
29
Pennsylvanian Early Gondwanide Orogeny (c. 315 Ma) represents a relative deepening of the basin. Throughout
30
the shallow marine deposits of the Tarma Formation evidence for contemporaneous volcanism becomes gradually
31
more pronounced and culminates around 312 - 309 Ma. Continuous basin subsidence resulted in a buildup of
32
platform carbonates of the Copacabana Formation. Our data highlights the presence of a previously unrecognized
33
phase of deposition of mainly fluvial sandstones and localized volcanism (281 – 270 Ma), which we named
34
´Oqoruro Formation´. This sedimentary succession was previously miss-assigned to the so-called Mitu Group,
35
which has recently been dated to start deposition in the Middle Triassic (~ 245–240 Ma). The emersion of this
36
marine basin coincides with the onset of a major plutonic pulse related to the Late Gondwanide Orogeny (c. 260).
37
Exhumation lead to the consequent retreat of the epeiric sea to the present-day sub-Andean region, and the
38
coeval accumulation of the fluvial Oqoruro Formation in south eastern Peru. These late Paleozoic
39
paleoenvironmental changes in the back-arc basins along the western Gondwana margin of southern reflect
40
changes in tectonic plate reorganization in a long-lived Paleozoic accretionary orogeny.
41 42 43
1.
44
Sedimentation within the Permo-Carboniferous back-arc basin of Peru reflects temporal
45
changes in subduction parameters during the amalgamation of Pangaea. This study is the first
46
large-scale chronostratigraphic reconstruction of the paleogeography of south-central eastern
47
Peru during this time period. Two phases of late Paleozoic metamorphism and magmatism at c.
48
315 Ma and c. 260 Ma have so far been recognised in the central and southern Eastern
49
Cordillera of Peru (Chew et al., 2016). These Gondwanide orogenic cycles can be correlated into
50
the Proto-Andean margin of Argentina and Chile (Chew et al., 2016 and refs therein). Phases of
AC C
EP
Introduction
TE D
M AN U
SC
RI PT
27
ACCEPTED MANUSCRIPT
advance and retreat in the evolution of this long-lived Paloezoic accretionary orogeny resulted
52
in magmatic pulses and tectonic phases that can be correlated along the plate boundary
53
(Cawood 2005). This study now links the sedimentary sequences of the Eastern Cordillera of
54
southern Peru to the pre-Andean orogenic cycle.
55
The Permo-Carboniferous sedimentary sequences in the Eastern Cordillera of Peru (Fig. 1) are
56
subdivided into three formations that, in ascending stratigraphic order, are: The Ambo
57
Formation, the Tarma Formation, and the Copacabana Formation (Azcuy and di Pasquo, 2005;
58
Azcuy et al., 2002; Cárdenas et., 1997; Doubinger and Marocco, 1981; Iannuzzi et al., 1998).
59
Previous age constraints were mostly based on palaeobotany and marine biostratigraphy fossils
60
(Azcuy and Di Pasquo, 2005; Azcuy et al., 2002; Cárdenas et al., 1997; Doubinger and Marocco,
61
1981; Iannuzzi et al., 1998). This study combines stratigraphic observations with, (U-Pb zircon)
62
geochronology, whole rock geochemistry and isotopic (Hf-zircon) data from volcanic and
63
sedimentary units at 8 different localities in the central Eastern Cordillera of Peru to the
64
western-most tip of Bolivia (Fig. 1). These new data bracket the time and duration of the
65
different palaeoenvironments, providing age constraints on lateral facies variations in the
66
Eastern Cordillera of southern Peru.
68 69
SC
M AN U
TE D
EP
AC C
67
RI PT
51
3
ACCEPTED MANUSCRIPT
2.
Geological setting
71
During the final stages of assembly of Pangaea (320–250 Ma; Cawood and Buchan, 2007), major
72
plate boundary reorganization was accompanied by orogenic events that affected the central
73
and southern Pacific margin of Pangaea (Chew et al., 2016). A Permo-Carboniferous (340–285
74
Ma) belt of intrusive rocks is exposed along orogenic strike of the Peruvian Eastern Cordillera
75
from the Ecuadorian border (6°S) to southern Peru (14°S; Chew et al., 2008; Miskovic et al.,
76
2009). Two Gondwanide orogenic phases accompanied by magmatism and metamorphism
77
have been identified. A Carboniferous (Early Gondwanide) event affected most of the Proto-
78
Andean margin of South America (Pankhurst et al., 1998; Thomas et al., 2004), and recently a
79
second c. 260 Ma (Late Gondwanide) metamorphic event in the Eastern Cordillera of Peru was
80
documented by Chew et al., (2016). Coeval with these tectono-magmatic events, thick
81
sedimentary sequences were accumulating in the south-central Peruvian Eastern Cordillera.
82
The Carboniferous sedimentary sequences are represented by the Ambo (Lower Carboniferous)
83
and Tarma (Upper Carboniferous) lithostratigraphic units. These sequences were originally
84
assigned a Group status in Peru, but without adhering to the accepted norms or codes of
85
stratigraphy, they have always been used as lithostratigraphic units without further internal
86
subdivision (Azcuy and di Pasquo, 2005). Therefore, in Peru these sequences are now assigned
87
to formations, as proposed by Azcuy and di Pasquo (2005). However, the Ambo Group has also
88
been identified in Bolivia, and authors there correctly make reference to the Ambo with Group
89
status, as it is subdivided in three units: Cumaná, Kasa and Siripaca Formations (Díaz Martínez,
90
1991).
AC C
EP
TE D
M AN U
SC
RI PT
70
ACCEPTED MANUSCRIPT
The Carboniferous sedimentary rocks in south-eastern Peru overlie metamorphic basement or
92
are in faulted or unconformable contact with the locally underlying sedimentary Devonian
93
Cabanillas Formation (Azcuy and di Pasquo, 2005, Boekhout et al., 2013; Zumsprekel et al.,
94
2015). Generally, Carboniferous sedimentation started within a fluvial setting (Ambo Fm.). The
95
sea progressively transgressed along a narrow, subsiding depression, which was centred at the
96
location of the present-day Eastern Cordillera (Fig. 1). The sea regressed during the Visean (347
97
– 331 Ma; Cohen et al., 2013), giving way to subaerial sedimentation and contemporaneous
98
volcanism in eastern central Peru (Dalmayrac et al., 1980).
99
A marine transgression from the north-west or north covered a significant part of Peru in the
100
Pennsylvanian (323 – 299 Ma), and largely overflowed the limits of the Mississippian (359 – 323
101
Ma) basin and initiated deposition of the Tarma Fm. (Laubacher, 1978). The transition between
102
the Tarma and younger Copacabana Fm. is gradual, and consequently the boundary between
103
the two is arbitrary. Therefore, we will refer to the singular Tarma-Copacabana Group, or to the
104
resolved Tarma and Copacabana Fms, as suggested by Azcuy and Di Pasquo (2005). Azcuy et al.
105
(2002) assigned a middle Pennsylvanian (315 – 307 Ma) age to the palynological assemblages at
106
the location which they judge to be the boundary between the Tarma and Copacabana Fms at
107
Pongo de Mainique (Fig. 2). The carbonates of the Copacabana Fm. are conformably overlain by
108
organic-rich shales interbedded with minor sandstone and limestone layers of the Ene
109
Formation in the subandean fold and thrust belt and the foreland basin of north and central
110
Peru (Fig. 1; Azcuy and Di Pasquo, 2005; Mathalone and Montoya, 1995). The Ene Fm. is
111
interpreted as a hypersaline, restricted marine basin marking a marine regression. In south-
AC C
EP
TE D
M AN U
SC
RI PT
91
5
ACCEPTED MANUSCRIPT
eastern Peru we identify a previously unrecognised possible lateral equivalent of the Ene Fm.
113
which we named Oqoruro Formation, after its type location.
114
Coeval late Palaeozoic sedimentation in the Coastal Cordillera of Peru (Fig. 1) consists of the
115
Yamayo Group (Boekhout et al., 2013a). This is a sedimentary succession of variable thickness
116
(up to 2 km) interpreted as a back-arc basin environment, with facies varying from alluvial fan
117
and alluvial plain to shallow-marine and deltaic. Because of the small dimensions of the
118
dispersed outcrops, these unit are not indicated on this large overview map (Fig. 1).
SC
RI PT
112
M AN U
119
2.1 Sedimentary units
121
2.1.1 Ambo Formation
122
The Ambo Fm. is mainly composed of sub-aerial basins and contains plant remains that are
123
preserved at several locations in Peru and Bolivia, indicating a warm-temperate, humid climate
124
during the late Visean – earliest Serpukhovian (Azcuy and Di Pasquo, 2005; Iannuzzi and
125
Pfefferkorn, 2002). Sandstones and conglomerates of the Ambo Fm. host numerous
126
metamorphic basement clasts, and the youngest rocks are tuffs and ignimbrites in central Peru
127
(Mégard, 1978). The Ambo Fm. near Pongo de Mainique (Fig. 2) consists of quartz arenites,
128
lutites, conglomerates and volcanic tuffites, with a palynoflora that is exclusively composed of
129
continental elements of late Viséan age (Azcuy and Di Pasquo, 2005). Abundant plant fossils
130
found in outcrops on the Altiplano indicate that deposition was fully subaerial in this region
131
(Laubacher, 1978), although both marine and fluvial deposits are exposed within the Cordillera
132
de Carabaya (Macusani area, Fig. 2). Sandstone beds containing marine fossils such as
133
brachiopods and crinoids are intercalated with pelites in the middle part of the sequence
AC C
EP
TE D
120
ACCEPTED MANUSCRIPT
(Laubacher, 1978). In Bolivia, where the Ambo sediments have a group status, the oldest
135
formation of the Ambo Group (Cumaná Fm.) on the Bolivian shore of Lake Titicaca is marine,
136
while the overlying Kasa and Siripaca Formations are interpreted as a prograding delta and a
137
fluvial and/or delta plain, respectively (Iannuzzi et al., 1998).
138
RI PT
134
2.2.2 Tarma-Copacabana Group
140
A marine transgression from the north-west or north covered a significant part of Peru in the
141
Pennsylvanian (323 – 299 Ma), and largely overflowed the limits of the Mississippian (359 –
142
323) basin and initiated deposition of the Tarma Fm. (Laubacher, 1978). The marine basin
143
deepens towards the east, and mainly consists of fossiliferous limestone, shale, marl, siltstone
144
and sandstone (Azcuy et al., 2002; Laubacher, 1978; Marocco, 1978; Mégard, 1978). Evidence
145
for explosive volcanism can be found in reworked tuffs, tuffaceous sandstones and
146
volcanoclastic deposits (Dalmayrac et al., 1980; Laubacher, 1978). Overall, the transition to the
147
Copacabana Fm. can be considered as a continuous marine transgression that reached its
148
maximum extent in the lower Permian (Marocco, 1978); at this time the sea covered most of
149
Peru except for the Arequipa Terrane (Fig. 1; Dalmayrac et al., 1980). The lower part of the
150
Copacabana Fm. mainly consists of platform carbonates, which contain abundant fossils such as
151
fusulinida, brachiopods, corals, bryozoans and gastropods (Dalmayrac et al., 1980; Marocco,
152
1978), with some intercalations of sandstone and shale. In the sections where the upper levels
153
of the Copacabana Fm. are still present, it is observed that siliciclastic input becomes more
154
dominant during the final stages, indicating a partial retreat of the vast inland sea. The
155
limestones become sandier with time in the Macusani area, and the sequence ends with
AC C
EP
TE D
M AN U
SC
139
7
ACCEPTED MANUSCRIPT
deposition of continental red beds (Laubacher, 1978). In the upper part of the Tarma-
157
Copacabana Group, 10 km north of Abancay (Fig. 2), black shales and intercalated fine
158
sandstone beds contain small fossilized trunks and acicular leaves identified as Lycopsidropsis
159
pedroanus, and a palynological assemblage indicating an Artinskian age (290 – 284 Ma;
160
Doubinger and Marocco, 1981). Fusulinida-bearing strata in the upper part of the Copacabana
161
Fm. are also indicative of an Artinskian age (290 – 284 Ma; Dalmayrac et al., 1980). Evidence for
162
volcanism is scarce, although two volcanic intervals have been identified in the dominantly
163
calcareous sequence in the Vilcabamba area (Marocco, 1978; Fig. 2). Even though volcanic
164
activity is not very pronounced in the Tarma-Copacabana Group, the presence of plutons
165
suggests that the magmatic activity that originated in the Mississippian continued
166
intermittently into the Pennsylvanian and early Permian (340-271 Ma; Miskovic et al., 2009; Fig.
167
1).
SC
M AN U
TE D EP
169
AC C
168
RI PT
156
ACCEPTED MANUSCRIPT
3. Analytical methods and sampling
171
3.1 Sampling
172
Geochronological data have been obtained using U–Pb analyses (CA-ID-TIMS and LA-ICPMS) of
173
zircon. Geochemical analyses includewhole rock major oxides, trace and REE data, which have
174
been obtained using XRF and LA-ICPMS.Nd (whole rock) and Hf (zircon) isotopic data were
175
acquired using ID-TIMS (Nd) and LA-MC-ICPMS (Hf). Methodological details are summarized in
176
Table 1 and are presented in Appendix A.
M AN U
177
SC
RI PT
170
Sections through the Ambo successions were investigated at three locations: i) Hacienda
179
Huanca, near Cerro de Pasco in central Peru, ii) Mamuera, near Sicuani in south-eastern Peru,
180
and iii) Kellay-Bélen, on the Copacabana Peninsula at Lake Titicaca, western Bolivia (Figs. 1 and
181
2).
182
The Tarma-Copacabana Group was studied at seven different localities. A continuous section
183
stratigraphically above the Ambo Fm., can be found in the Hacienda Huanca and Kellay-Bélen
184
sections (Fig. 3). Four of these locations are located in the Sacred Valley (Ollantaytambo,
185
Oqoruro, Pisac, Caicay; Figs. 1, 2 and 4b), of which only the Pisac section was previously
186
correctly mapped as part of the Copacabana Fm. (Carlotto et al., 1996). The Ollantaytambo,
187
Oqoruro and Caicay sections were formerly attributed to the Mitu Group (now dated to be
188
~ 245–240 to ~ 220 Ma; Spikings et al., 2016). Likewise, the Vilcabamba section in the Machu
189
Picchu Inlier (Fig. 2) was presumed to belong to the Mitu Group (Carlotto et al., 1999). The U-Pb
190
zircon data presented in this study shows all these sections are part of the Tarma-Copacabana
191
Group.
AC C
EP
TE D
178
9
ACCEPTED MANUSCRIPT
Three volcanic intervals in the Ollantaytambo, Oqoruro and Kellay-Bélen sections were selected
193
for U-Pb zircon dating and whole rock geochemistry (MR29, MR230, MR143; Fig. 3). Four
194
different volcanic horizons were sampled for geochemistry from the sections at Hacienda
195
Huanca (GR6-0311) and Ollantaytambo (MR32), and two other volcanic outcrops in the lateral
196
extension of the Oqoruro Fm. (MR173) and Tarma Fm. (MR208). Seven maximum deposition
197
ages were obtained from U-Pb dating of detrital zircons from sedimentary rocks in part of the
198
sequences (Vilcabamba, Pisac, Caicay, Mamuera and Kelley-Bélen) where no volcanic intervals
199
were found (GR6-0511, MR26, MR84, MR11, MR98, MR140, MR144). Lava flows were sampled
200
for whole rock geochemistry throughout the sections, and in the surrounding regions.
M AN U
SC
RI PT
192
201
4. Results
203
Eight sites were studied in south-central eastern Peru and the western most tip of Bolivia, four
204
of which are located in the Sacred Valley (Figs. 1 and 2). All locations are discussed below in
205
geographic order, from north-west to south-east (Fig. 3). A summary of the results of the
206
magmatic and detrital U-Pb zircon geochronology and Hf isotopic analyses is shown in Table 1.
207
Data from individual detrital and magmatic zircons are listed in Supplementary Tables 2 and 3.
EP
AC C
208
TE D
202
209
4.1 Stratigraphy and geochronology
210
4.1.1 Hacienda Huanca (-10.651, -76.0915)
211
The Ambo Fm. and Tarma-Copacabana Group in the Hacienda Huanca section near the city of
212
Cerro de Pasco (Fig. 4a) are described in detail by Rodriguez et al. (2011). The Ambo Fm. in this
213
location is entirely volcanic and consists of a ~500 m pile of volcanic deposits. The sequence
ACCEPTED MANUSCRIPT
begins with rhyolitic ignimbrites, and the upper units are dominated by dacitic lava flows with
215
plagioclase and biotite phenocrysts. Dacite GR6-0311 was sampled for geochemistry 60 m
216
below the top of the Ambo Fm. (Fig 3a), and did not
217
The overlying Tarma-Copacabana Group consists of near shore deposits, varying from
218
limestones, shales and sandstones to conglomerates (Rodriguez et al., 2011). Medium-grained,
219
white sandstone GR6-0511 was sampled after the first conglomeratic interval (Fig. 3a). Ninety
220
eight zircon grains were dated by LA-ICPMS, 16 of which yield discordant dates. All concordant
221
zircon grains (n = 82) yield Carboniferous ages that range between 308.2 ± 6.2 Ma and 341.1 ±
222
17 Ma (Fig. 5a). Slight bimodal behaviour can be observed, and the most prominent mode
223
corresponds to 319 Ma. Towards the top of the section, the depositional environment evolves
224
from alluvial and shallow marine deposits to fluvial sedimentation.
M AN U
SC
RI PT
214
TE D
225
4.1.2 Vilcabamba (-13.108, -72.938)
227
The outcrops in the Vilcabamba area (Fig. 2) are too fragmented to construct a coherent
228
stratigraphic column (Fig. 3b). Red clastic rocks which were previously assigned to the Mitu
229
Group are unconformably underlain by massive limestone deposits of the Copacabana Fm.
230
(Doubinger and Marocco, 1981). Subaerial deposits include fine to medium red sandstones and
231
coarse, poorly sorted sandstones and pebble beds. Pebbles are mainly volcanic in origin but
232
vein quartz, chert and limestone pebbles are also observed. Cross bedding and current ripples
233
are preserved. Coarse red sandstone MR26 was sampled for detrital zircon analysis, and 56
234
zircon grains yield concordant U-Pb ages. The youngest zircon grains are the dominant
AC C
EP
226
11
ACCEPTED MANUSCRIPT
population, with the youngest grain giving a maximum depositional age of 277.1 ± 7.3 Ma, with
236
the most prominent mode peaking (youngest cluster) at 282 Ma (Fig. 5b).
237
4.1.3 Ollantaytambo (-13.258, -72.237)
238
A discontinuous section of red clastic sedimentary rocks and a few interbedded lava flows
239
(MR29 and MR32) in the northwestern corner of the Sacred Valley was sampled near the village
240
of Ollantaytambo (Fig. 4b). The section mainly consists of conglomerates that contain up to 30
241
cm long clasts of rhyolite, basalt and red siltstone (Fig. 3c). MR32 was sampled for geochemistry
242
at the base of the section. Rhyodacite MR29 was sampled at the top of the section (Fig. 3c) for
243
geochemistry and geochronology. Evidence of minor Pb-loss was found in 4 of 18 dated zircon
244
grains, while the remaining 14 yielded concordant U-Pb zircon ages with a weighted mean age
245
of 308.6 ± 3.1 Ma (MSWD = 6.6; Fig. 5c).
TE D
246
M AN U
SC
RI PT
235
4.1.4 Oqoruro (-13.444, -71.7658)
248
The sedimentology of the 2.7 km long section in the valley of the village of Oqoruro (Fig. 4b) has
249
been studied in detail by Panca (2010). He suggested the entire sequence formed part of the
250
Mitu Group, overlying limestones of the Copacabana Fm. Based on U-Pb zircon data from
251
Spikings et al. (2016) and this study, we reinterpret the upper part of this section as a newly
252
recognised formation, which will is discussed below. The rocks are sandstones, lava flows and
253
ignimbrites (Fig. 3d). Zircon grains were extracted from andesitic ignimbrite MR230 (Fig. 3d),
254
which yields 21 concordant U-Pb ages (n = 24), with a weighted mean average of 281.3 ± 1.5
255
Ma (MSWD = 3.6; Fig. 5d).
256
AC C
EP
247
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
257
13
ACCEPTED MANUSCRIPT
4.1.5 Pisac (-13.452, -71.824)
259
A 20 meter long section of evaporites, marls, and white sandstones containing bivalve
260
fragments located to the south-east of the village of Pisac is interpreted as a lagoonal sequence
261
(Fig. 3e; 4b). Detrital zircon grains were extracted from white sandstone MR84, which hosts
262
well-rounded quartz grains and shows planar lamination. Seventy seven concordant U-Pb ages
263
were obtained out of a total of 96 analysed zircon grains. The youngest grain yields an earliest
264
Permian age of 296.2 ± 3.4 Ma. The majority of the zircon grains yield Carboniferous ages (301
265
– 325 Ma; Fig. 5e), and the most prominent mode corresponds to 304 Ma.
266
M AN U
SC
RI PT
258
4.1.6 Caicay (-13.581, -71.686)
268
The Caicay section is located in the south-eastern corner of the Sacred Valley, near the village
269
of Caicay, and forms part of the same thrust sheet that is preserved in the Oqoruru section (Fig.
270
4b). The sedimentary succession is dominated by red clastic rocks and lacks volcanic deposits
271
(Fig. 3f). Some sandstones contain abundant detrital muscovite. Ninety eight detrital zircon
272
grains from medium red sandstone MR111 were dated by LA-ICP-MS, of which 82 grains give
273
concordant ages. Only 3 zircon grains yield Permian ages, and the youngest grain yields an age
274
of 270 ± 3.7 Ma. The majority of the zircon grains are Cambro-Ordovician. The data also shows
275
a noteworthy Late Mesoproterozoic peak (Fig. 5f).
276 277 278
4.1.1 Mamuera (-14.361, -71.084)
279
The Mamuera section is located 20km south-east of the city of Sicuani, near the village of
280
Mamuera (Fig. 2). Here, the Ambo Fm. unconformably overlies schists and meta-siltstones of
AC C
EP
TE D
267
ACCEPTED MANUSCRIPT
the Siluro-Devonian metamorphic basement. The Ambo Fm. consists of 70 meters of siliciclastic
282
deposits ranging in grain size from siltstone to coarse sandstone, with a general coarsening
283
upward trend (Fig. 3g). Cross-bedding is widely recognized as well as ca. 5 meter wide
284
conglomeratic channel fills. Clasts and pebbles are mainly quartzite and vein quartz. We
285
interpret the depositional environment of this section as a fluvial plain setting. Medium-
286
grained, cross-bedded sandstone MR98, located near the stratigraphic top of the section, was
287
sampled for detrital zircon geochronology (Fig. 3g). Concordant ages were obtained for 71 out
288
of 80 grains. The dominant age groups are Carboniferous, Cambro-Ordovician and
289
Mesoproterozoic, while the youngest zircon has an age of 315.2 ± 12.1 Ma (Fig. 5g), suggesting
290
an earliest Pennsylvanian maximum depositional age for the top of the Ambo Fm. exposed in
291
this section. The youngest mode (age cluster) corresponds to 332 Ma. The Ambo Fm. is
292
unconformably overlain by continental sedimentary rocks and alkaline lava flows of the Middle
293
to Upper Triassic Mitu Group (Spikings et al., 2016) in the Mamuera valley. The presence of
294
sandstones and shales of the Copacabana Fm. elsewhere in the Sicuani region, containing
295
abundant corals, crinoids and bivalves, suggests that the Copacabana Fm. has not been
296
preserved in the Mamuera section.
SC
M AN U
TE D
EP
AC C
297
RI PT
281
298
4.1.2 Kellay-Bélen (-16.110, -69.045)
299
The Kellay-Bélen section is located on the Copacabana Peninsula on the Bolivian side of Lake
300
Titicaca, near the village of Kellay-Bélen (Fig. 3h). Fossil flora indicative of the upper Ambo
301
Group have been identified at this locality (Iannuzzi et al., 1998). The Ambo succession has a
302
Group status in this area and is divided into three formations (Fig. 3h). The Cumaná Fm. is the
15
ACCEPTED MANUSCRIPT
oldest formation and consists of glacio-marine deposits, while the overlying Kasa Fm.
304
represents a prograding delta sequence. The youngest is the Siripaca Fm., which was deposited
305
within a fluvial or delta plain environment and contains coal beds with abundant plant fossils
306
(Iannuzzi et al., 1998). We sampled medium grained, poorly cemented, white sandstone
307
(MR144), which preservesmeter-scale crossbedding, from the very top of the Kasa Fm. (Fig. 3h).
308
One hundred and two detrital zircon grains were dated. The youngest grain (Fig. 5h) has an age
309
318.2 ± 16.2 Ma, while the youngest prominent mode has an age of 341 Ma. Sandstone MR144
310
contains only 7 Carboniferous grains, and mostly grains with a Cambro-Ordovician age (Fig. 5h).
311
An erosional hiatus separates the Ambo Group from the overlying Titicaca Group (Bolivian
312
equivalent of the Peruvian Tarma-Copacabana Group, Fig. 3h). The oldest rocks of the Titicaca
313
Group were deposited across a coastal plain, overlain by shallow marine deposits. The shallow
314
marine deposits consist of alternating sand- and siltstone versus limestones intervals, both of
315
which host abundant bivalve fossils. Several tuffaceous ash beds were discovered within the
316
sequence. Dacitic tuff MR143 with biotite crystals was sampled in the first sandy interval (Fig.
317
3h) and 8 zircon grains were dated by ID-TIMS. The youngest zircon grain yielded a concordant
318
age of 312.14 ± 0.29 Ma (Fig. 5i). The exposed top of the Tarma-Copacabana Group near Kellay-
319
Bélen consists of sub-aerial, red sandstone. Finely laminated sandstone (Fig. 3h) was sampled
320
for U-Pb dating of detrital zircon grains and 77 out of 95 grains yielded concordant dates. One
321
third of the zircon grains yield an Early Permian age with a prominent mode corresponding to
322
288 Ma (Fig. 5i). The youngest grain has an age of 270 ± 10.6 Ma.
323 324
AC C
EP
TE D
M AN U
SC
RI PT
303
ACCEPTED MANUSCRIPT
4.2 Hf-isotopic ratios of zircon
326
Hf istopic analyses were performed on both volcanic and detrital concordant zircon grains from
327
the south Peruvian Eastern Cordillera. Raw data is listed in Supplementary Table 4. The results
328
are plotted together with Hf isotopic data from Permo-Carboniferous detrital zircon grains from
329
the coeval Yamayo Group in coastal Southern Peru (Boekhout et al., 2013a; Fig. 6). Hf-isotopic
330
results from volcanic rocks are indicated in red, and data from detrital zircons are shown in
331
grey, black and dark blue (Fig. 6). The volcanic zircon grains have a relatively narrow Hf-isotopic
332
range. Rhyodacite MR29 (n=6; Ollantaytambo) yielded a εHfi ranging between -0.5 ± 0.7 and 1.1
333
± 0.6. Zircon grains from ignimbrite MR230 (n=6; Oqoruro) range between εHfi -0.7 ± 0.7 and
334
1.4 ± 0.6, and zircon grains from tuff MR143 (n=9) yielded Hf-isotopic ratios that range between
335
εHfi -4.1 ± 0.3 and -2.9 ± 0.4.
336
Detrital zircons from seven sedimentary rocks were analysed for Hf isotopic analyses, and 5 to
337
14 concordant zircon grains in the Permo-Carboniferous age range were selected per rock.
338
Overall, the εHfi values range between -20.4 and +3.4. Sandstones MR26 and GR6-0511 yield
339
the smallest intra-sample variation. The Upper Cisuralian zircon grains (275.6 ± 0.7 Ma – 284.4 ±
340
0.7 Ma) of sandstone MR26 (n=10) yielded only positive εHfi values that range between 0.8 ±
341
0.9 and 3.2 ± 0.9, while the Carboniferous zircon grains of GR6-0511 (n=13) yielded solely
342
negative εHfi values that range between -4.6 ± 0.8 and -2.1 ± 0.6. The Carboniferous zircon
343
grains from sandstone MR98 are also restricted to a negative εHfi range (-8.7 ± 0.9 - -2.9 ± 0.7, n
344
= 5). Zircon grains extracted from sandstones within the Kellay-Bélen section extend to the
345
most negative values and display the largest spread in εHfi values. The Mississippian (359 – 323
346
Ma) zircon grains from MR144 range from -20.4 ± 0.6 to 1.4 ± 0.7 (n=6) and the Early Permian
AC C
EP
TE D
M AN U
SC
RI PT
325
17
ACCEPTED MANUSCRIPT
and Mississippian zircon grains from MR140 vary between -9.0 ± 1.0 and 2.2 ± 0.9 (n=10). The
348
εHfi data of sandstone MR84 from the Pisac section forms two clusters that both span the
349
Carboniferous – earliest Permian; 3.4 ± 1.3 – 0.4 ± 1.0 (n=10) and -3.7 ± 1.1 – -5.9 ± 0.8 (n=4).
350
The Hf-isotopic compositions of Pennsylvanian - Early Permian zircon grains within sandstone
351
MR111 range from -4.8 ± 0.6 to 2.9 ± 0.7 (n=5).
SC
352
RI PT
347
4.3 Whole rock geochemistry
354
Whole-rock XRF and LA-ICP-MS analyses of 7 samples are listed in Supplementary Table 5.
355
Three volcanic intervals in the Ollantaytambo, Oqoruro and Kellay-Bélen sections that were also
356
dated by U-Pb zircon geochronology, were analysed for whole rock geochemistry (MR29,
357
MR230, MR143; Fig. 3). Additionally, four undated volcanic levels were sampled for
358
geochemistry from the Hacienda Huanca section (GR6-0311), the Ollantaytambo section
359
(MR32), and two other volcanic outcrops in the lateral extension of the Oqoruro Fm. (MR173)
360
and Tarma Fm. (MR208).
361
Volcanic rocks of the Carboniferous Ambo Fm. and Tarma Fm. are mainly lava flows with
362
phenocrysts of quartz and feldspar, except at the Kellay-Bélen section in Bolivia where 10-cm
363
thick green ash beds with biotite crystals are found (sample MR143). In contrast, volcanic rocks
364
from the Oqoruro Fm. in the Sacred Valley (samples MR173 and MR230) are ignimbrites.
365
Volcanic rocks are intermediate to felsic in composition (61 - 77 wt% SiO2), calc-alkaline and
366
classify as andesites, dacites and rhyolites (Fig. 7), with a chemical index of alteration (CIA)
367
between 50.4 and 69.6. The Permian ignimbrites are significantly richer in Fe (6.4 – 6.7 wt%)
368
than the Carboniferous lavas (2.2 - 3.4 wt% ; Supplementary Table 5).
AC C
EP
TE D
M AN U
353
ACCEPTED MANUSCRIPT
The primitive mantle-normalized spider diagram reveals negative anomalies for Ba, Nb, Ta, Sr, P
370
and Ti and elevated LILE/HFSE ratios (Fig. 8a). Chondrite-normalized REE plots show that the
371
volcanic rocks are LREE enriched and have flat HREE patterns, except andesite MR230, which is
372
the least evolved and does not yield a negative Eu anomaly (Fig. 8b). Rhyodacite MR29 and
373
rhyolite MR208 have strongly negative Eu anomalies, indicating significant feldspar
374
fractionation.
SC
RI PT
369
375
5. Discussion
377
5.1 Ambo Formation
378
The Ambo Fm. was studied in three sections. Our findings corroborate previous observations
379
that there was significantly less volcanism in the sedimentary record of the southern Eastern
380
Cordillera of Peru (Dalmayrac et al., 1980; Iannuzzi et al., 1998; Laubacher, 1978) compared to
381
the Ambo Fm. in the Eastern Cordillera of central Peru (Mégard, 1978). Scarce geochronological
382
information is available on the onset of the Ambo Fm. This sedimentary sequence locally
383
overlies schist with a maximum depositional age of 317 ± 7 Ma, 30 km south-west of the
384
Hacienda Huanca section (Cardona et al., 2009), giving a local maximum age constraint on the
385
oldest part of this sedimentary unit.
386
Towards the Bolivian border the onset of Ambo sedimentation seems to be earlier.
387
Geochronology of an ash bed from the lower Tarma-Copacabana Group (Kellay-Bélen section)
388
suggests the Ambo Group near the Bolivian border was deposited before 312.1 ± 0.3 Ma. Plant
389
fossils observed in this section between dated sandstones MR144 and ash bed MR143 (Fig. 3h)
390
assign this part of the section to the late Viséan-earliest Serpukhovian (325-335 Ma; Iannuzzi
AC C
EP
TE D
M AN U
376
19
ACCEPTED MANUSCRIPT
and Pfefferkorn, 2002). Identical plant fossils (Nothorhacopteris, Tomiodendron) have been
392
identified in the coeval Yamayo Group (Boekhout et al., 2013a) in coastal southern Peru
393
(Pfefferkorn and Alleman, 2001; Pino et al., 2004), indicating a similar depositional environment
394
in large parts of the back-arc basin, that lies within a late Visean warm temperate floral belt
395
that runs through Gondwana (Iannuzzi and Pfefferkorn, 2002).
SC
396
RI PT
391
Regarding the termination of the Ambo Fm., more geochronological data is available. The Ambo
398
Fm. of south-eastern Peru terminated around the Middle Pennsylvanian (~ 315 Ma). Maximum
399
depositional ages for the upper levels of the Ambo Fm. from our two southern most sections
400
overlap and are 315 ± 12 Ma (MR98; Mamuera section) and 318 ± 16 Ma (MR144; Kellay-Bélen
401
section; Fig. 5a). Lavas of the Ambo Fm. in the Hacienda Huanca section were not directly
402
dated, but sandstone GR6-0511 of the overlaying Tarma-Copacabana Group yields exclusively
403
Carboniferous zircon grains (308.2 ± 6.2 – 341.1 ± 17.0 Ma; Fig. 5a) with a narrow range in εHfi
404
values (-4.6 ± 0.8 to -2.1 ± 0.6; Fig. 6), suggesting they could be derived from reworking of a
405
single source. Conglomerates bracketing this sandstone contain volcanic clasts which suggest
406
they may be reworked remnants of underlying lava flows (Rodriguez et al., 2011). The Kernel
407
density curve for this sandstone (GR6-0511) has a prominent mode corresponding to 319 Ma
408
(Fig. 5a) and overlaps with the maximum depositional ages of the Ambo Fm. that were obtained
409
in the two more southern sections discussed above.
410
Overall, the duration of Ambo Fm. deposition appears to have initiated in the Early
411
Mississippian in western Bolivia, and terminated in the Middle Pennsylvanian (~315 Ma). It
412
should however be noted that there may be a faulted contact between the Ambo Fm. and the
AC C
EP
TE D
M AN U
397
ACCEPTED MANUSCRIPT
413
metamorphic basement or underlying sedimentary Devonian Cabanillas Fm. (Boekhout et al.,
414
2013a and refs therein).
RI PT
415
5.2 Tarma-Copacabana Group
417
A marine transgression formed an epeiric sea along the axis of the present-day Eastern
418
Cordillera of Peru, initiating deposition of the Tarma Fm. in the Early Pennsylvanian (Azcuy et
419
al., 2002). Dacitic tuff MR143 indicates that marine conditions initiated just prior to 312.1 ± 0.3
420
Ma in the Titicaca area (Fig. 3h). If the maximum detrital age of sandstone GR6-0511 of 308 ± 6
421
Ma (Hacienda Huanca) approaches the depositional age of the rock, it reveals a comparable age
422
for marine transgression in central Peru (Fig. 3a). Submarine conditions are reported for the
423
same period in Pongo de Mainique (Fig. 2), where palynological analyses assign a Moscovian
424
age (315-307 Ma) to the upper Tarma Fm. (Azcuy et al., 2002). Marine conditions however did
425
not prevail during deposition of the Ollantaytambo section in the Sacred Valley, where
426
rhyodacite MR29 indicates subaerial deposition at and prior to 309 ± 3 Ma (Fig. 3c). Although
427
marine limestones of the Tarma-Copacabana Group are present in the south-eastern Sacred
428
Valley, their stratigraphic relationship to the Ollantaytambo section is unknown. Subaerial
429
deposition may have been a localized phenomenon related to a volcanic edifice built above the
430
Nevado Chicon pluton (Fig. 4b). The Nevado Chicon alkali granite (304.3 ± 0.1 Ma (U-Pb zircon);
431
Reitsma, 2012), located 10 km to the north-east may be genetically related to the rhyodacites
432
and rhyolites (MR29, MR32 and MR208) at Ollantaytambo (Fig. 4b). The highly silicic nature of
433
the lavas suggests that were highly viscous during eruptions, and thus a volcanic vent must
AC C
EP
TE D
M AN U
SC
416
21
ACCEPTED MANUSCRIPT
have been located nearby where these lavas were deposited. We suggest that subaerial
435
sedimentation of the Ollantaytambo Fm may have occurred along a volcanic flank.
436
Azcuy et al. (2002) report that siliciclastic input into the marine Tarma-Copacabana basin
437
diminished after the Moscovian (315 – 307 Ma) at Pongo de Mainique. According to Marocco
438
(1978) and Dalmayrac et al. (1980), the epicontinental sea reached its maximum extent in the
439
earliest Permian when it covered most of Peru. The only earliest Permian age obtained in this
440
study is from a lagoonal sequence near Pisac in the Sacred Valley (Fig. 3e). Here, zircon ages
441
from white sandstone MR84 indicate a maximum depositional age of 296.2 ± 3.4 Ma. Almost
442
half of the detrital zircon grains in sandstone MR84 have ages between 301 Ma and 325 Ma.
443
These dates overlap with the age of rhyodacite MR29 and plutons exposed in the same area
444
(Reitsma, 2012; Fig. 5c), suggesting they may have been a source for sandstone MR84. Some of
445
the detrital zircon grains have εHfi values that overlap with values obtained from the plutons,
446
although several grains in the same age range have significantly lower εHfi values (Fig. 6).
447
Therefore, an additional source may have supplied detritus to sandstone MR84, which may
448
have consisted of volcanic deposits that are similar to dacitic tuff MR143.
SC
M AN U
TE D
EP
449
RI PT
434
5.3 Oqoruro Formation
451
Several authors (Carlotto et al., 2004; Doubinger and Marocco, 1981; Laubacher, 1978) already
452
recognized that a few sections through the Copacabana Fm. become increasingly rich in
453
siliciclastic material towards the top, and culminate with subaerial deposition. For example, 10
454
km north of Abancay, the upper levels of the Tarma-Copacabana Group consist of sandstones
455
and black shales containing abundant plant fossils (Pecopteris sp., Sphenopteris sp.,
AC C
450
ACCEPTED MANUSCRIPT
Gangamopterus sp., Lycopsidropsis pedroanus) assigned to the Artinskian (290 – 284 Ma),
457
indicating deposition occurred in a swamp-like environment (Doubinger and Marocco, 1981).
458
Using the age constraints obtained in this study, we demonstrate that the subaerial deposition
459
environments, as recognised by the authors cited above, the Tarma-Copacabana Group was
460
more widespread during the final stages of than previously thought. It appears that oxidized
461
clastic rocks have often been confused with, and attributed to the significantly younger Mitu
462
Group (~ 245–240 to ~ 220 Ma; Spikings et al., 2016).
463
Direct age constraints on the Oqoruro Fm. are obtained by ignimbrite MR230, which indicates a
464
transition to significant subaerial volcanism and sedimentation from a phase of marine
465
deposition in the Oqoruro section at 281.3 ± 1.5 Ma (Fig. 3d). This period of explosive volcanism
466
coincides with a major pulse of local plutonism in the Vilcabamba area that lasted from 282.2 ±
467
0.1 Ma to 271.3 ± 0.3 Ma (U-Pb zircon; Reitsma, 2012; Fig. 2).
468
Detrital age information was obtained from the other sections. The upper levels of the Kellay-
469
Bélen and Hacienda Huanca sections and the deposits at the Vilcabamba and Caicay localities
470
(Figs. 4a and 4b) have similar sedimentary characteristics and maximum detrital zircon ages,
471
suggesting that they are possibly lateral equivalents of the Oqoruro section (Fig. 3). Red
472
sandstone MR26 from the Vilcabamba area yielded a maximum depositional age of 277.1 ± 7.3
473
Ma (Fig. 5b). The deposits were previously assigned to the Pennsylvanian-Permian, based on
474
the presence of thin marine intervals with brachiopods (Linoproductus cora d’Orbigny)
475
intercalated with red clastic rocks in the same region (Cárdenas et al., 1997). Therefore, we
476
conclude that the maximum detrital age of sandstone MR26 approaches the biostratigraphic
477
age. However, sandstone MR26 belongs to the final stages of the Tarma-Copacabana Group
AC C
EP
TE D
M AN U
SC
RI PT
456
23
ACCEPTED MANUSCRIPT
rather than the Mitu Group (Spikings et al., 2016). Red sandstone MR111 (Fig. 3f) is a Middle
479
Permian fluvial sandstone with a maximum depositional age of 270 ± 3.7 Ma in the Caicay
480
section. Other outcrops known in this same region studied by Carlotto et al. (2004) include a
481
200m long section of dolomite and black shale, assigned to the Middle Permian based on the
482
occurrence of brachiopods, which grades into fluvial sandstones and can probably also be
483
assigned to the Oqoruro Fm.. The marine deposits of the Copacabana Fm. in the Kellay-Bélen
484
section also appear to undergo a gradual transition towards fluvial sandstone at the top, with
485
no hiatuses or faulting observed in the field. The youngest detrital zircon within red sandstone
486
MR140, taken from the top of the Kellay-Bélen section, has a U-Pb age of 270 ± 10.6 Ma (Fig.
487
3h), and overlaps (within 2σ) with the (maximum) depositional ages for the Lower Permian sub-
488
aerial Tarma-Copacabana Group.
489
The Hacienda Huanca section in central Peru also terminates with fluvial sandstones and shales
490
(Fig. 3a), which are separated from the overlying coarse, red clastics of the Mitu Group by an
491
unconformity (Rodriguez et al., 2011). Although age data for the fluvial sandstones is lacking,
492
we tentatively assign them to the Lower Permian based on the radiometric ages obtained for
493
the fluvial sandstones in the sections discussed above.
494
On a regional scale, our data demonstrates a previously unrecognized depositional phase
495
between 281 and 270 Ma of mainly fluvial sandstones and localized volcanism. Given the
496
lithological contrast with the underlying marine deposits of the Copacabana Fm., we consider
497
this phase of subaerial deposition to constitute a stratigraphic formation. Since the only direct
498
age data was obtained from ignimbrite MR230 in the Oqoruro section, we refer to this
AC C
EP
TE D
M AN U
SC
RI PT
478
ACCEPTED MANUSCRIPT
499
depositional unit as the Oqoruro Fm., although it is likely that the volcanism observed in the
500
Oqoruro section is not representative of the entire formation.
501
5.4 Summary of new age constraints on late Paleozoic stratigraphic units
503
Table 6 summarizes the new geochronological constraints on the late Paleozoic (Permo-
504
Carboniferous) back-arc basin sedimentation of Peru. Our detrital U-Pb zircon ages
505
demonstrate that the timing of Ambo Fm. deposition corroborates the Late Mississipian age
506
estimates from plant fossils and palynology. The transition from the Ambo to the Tarma Fm.
507
occurred close to the Middle Pennsylvanian (~ 315 Ma) and reveals deepening of the basin.
508
Evidence for contemporaneous volcanism becomes gradually more pronounced throughout the
509
shallow marine deposits of the Tarma Fm., and culminates at approximately 312 - 309 Ma.
510
Continuous basin subsidence resulted in a buildup of platform carbonates of the Copacabana
511
Fm. in a depositional environment that remained stable from remained stable until ~ 281 Ma.
512
Our data highlights the presence of a previously unrecognized phase of deposition between 281
513
and 270 Ma of mainly fluvial sandstones and localized volcanism, which we named ´Oqoruro
514
Formation´. This sedimentary succession was previously incorrectly assigned to the so-called
515
Mitu Group, which commenced in the Middle Triassic (Spikings et al., 2016).
516
5.5 Correlation between the Oqoruro and Ene Formations
517
The hypersaline, organic-rich black shales of the restricted marine Ene Fm., exposed in the
518
subandean fold and thrust belt and buried in the foreland basin (Fig. 1), are considered to be
519
one of the major source rocks for Peruvian hydrocarbons (Mathalone and Montoya, 1995). The
520
Ene Fm. is observed to conformably overlie the Copacabana Fm. in north-eastern Peru (Azcuy
AC C
EP
TE D
M AN U
SC
RI PT
502
25
ACCEPTED MANUSCRIPT
and Di Pasquo, 2005; Martinez et al., 2003; Mathalone and Montoya, 1995), and was deposited
522
during shallowing of the basin. There is confusion in the literature about the relationship
523
between the Ene Fm. and the sedimentary rocks that crop out in the southern Peruvian Eastern
524
Cordillera. Some authors have suggested that the Ene Fm. pre-dates the Mitu Group and is
525
separated from it by an unconformable contact (Carlotto et al., 2010; Rosas et al., 2007), while
526
others consider it equivalent to the older part of the Mitu Group (Sempere et al., 2002). A
527
combination of the U-Pb zircon data discussed in this manuscript, and age data reported by
528
Spikings et al. (2016) for the Mitu Group sheds light on this discussion. By dating the base of the
529
Mitu Group at four different locations in central and south-eastern Peru, Spikings et al. (2016)
530
have demonstrated that deposition of the Mitu Group did not start until the Middle Triassic
531
(~240 Ma). Age data from this study show that the Tarma-Copacabana Group ends with
532
deposition of fluvial sandstones (Oqoruro Fm), and occasional volcanism from 281 to 270 Ma.
533
These sedimentary units were previously assigned to the Mitu Group. The subaerial deposits of
534
the Oqoruro Fm. reveal a retreat of the Copacabana sea to the subandean region by the end of
535
the Lower Permian. The Ene Fm., that conformably overlies the Copacabana Fm., also marks a
536
marine regression. Although direct age data for the Ene Fm. is lacking, it could very well be a
537
time equivalent to the Oqoruro Fm..
SC
M AN U
TE D
EP
AC C
538
RI PT
521
539
5.6 Permo-Carboniferous geodynamic evolution
540
Figure 9 illustrates three time slices for the Permo-Carboniferous paleogeographic evolution of
541
Peru at approximately 330 Ma, 310 Ma and 270 Ma. Both the present-day margin and late
542
Paleozoic Peruvian margin are indicated. The latter does not include the Arica bend, which may
ACCEPTED MANUSCRIPT
have formed during the Paleogene (Arriagada et al., 2008). Also, significant Late Mesozoic and
544
Cenozoic subduction erosion has modified the coastline, resulting in the present morphology
545
(Clift et al., 2003; Stern, 2011).
546
5.6.1 Mississippian
547
Permo-Carboniferous subduction was active along the entire length of the Peruvian margin
548
(Cawood, 2005, Chew et al., 2008, Miskovic et al., 2009; Reitsma, 2012). However, the
549
abundance of magmatism varies significantly when comparing the southern and northern
550
Eastern Cordillera. Smaller volumes of volcanic rocks are recorded in the sedimentary record of
551
the Ambo Fm. in southern Peru, whereas intrusions and volcanic rocks are restricted to a
552
narrow zone centred along the axis of the present-day Eastern Cordillera in northern and
553
central Peru (Fig. 9a). There, Carboniferous granitoids were emplaced in a back-arc setting, as
554
defined by their chemical composition, extensional tectonic setting and distance to the inferred
555
paleo-trench (Reitsma, 2012). Serpukhovian and Bashkirian ages were established in the
556
southern Eastern Cordillera, for part of the Machu Picchu Batholith (324.1 ± 5.3 Ma – 320.1 ±
557
1.8 Ma; Miskovic et al., 2009; Reitsma, 2012; Fig. 2). These intrusives show a similar
558
geochemical signature as the magmatic rocks in the Eastern Cordillera of northern Peru. Apart
559
from these intrusion ages, so far only detrital Mississippian age data for volcanism were found
560
in both south-eastern and south-western Peru (this study; Boekhout et al., 2013a). We
561
obtained geochemical data from one lava flow of the Ambo Fm. (Figs. 7 and 8), which also
562
shows a similar geochemical signature as reported for the lavas in the northern Eastern
563
Cordillera (Reitsma, 2012).
AC C
EP
TE D
M AN U
SC
RI PT
543
27
ACCEPTED MANUSCRIPT
Integrating all available data on Mississippian sedimentation in southern Peru, it can be
565
concluded that the present-day Eastern Cordillera of southern Peru was not experiencing the
566
same amount of extension during deposition of the Ambo Fm. as the Eastern Cordillera in
567
northern and central Peru (Fig. 9a). Variations in sedimentation and the volumes of preserved
568
magmatism throughout the present-day Eastern Cordillera of Peru suggest there was increased
569
extension in the northern half of Peru. Mississippian detrital zircon grains from sandstone
570
MR98 from the Ambo Fm. suggests reworking of a contemporaneous volcanic source similar to
571
dacitic tuff MR143 (Fig. 7). The small percentage of Carboniferous zircon grains in sandstone
572
MR144 of the Kellay-Bélen section (< 8%; Fig. 5b) indicates that there was limited volcanic
573
material available to be reworked in this region, or at least that limited material was preserved.
574
Similarly, Mississippian zircon grains form a subordinate population in the sandstones of the
575
Yamayo Group (Boekhout et al., 2013a). Detrital zircon grains from both the Yamayo Group and
576
the Ambo Fm. do show similar εHfi values, and therefore they possibly had similar sources (fig.
577
6). The presence of air fall deposits with similar εHfi isotopic values in both the Coastal and
578
Eastern Cordillera of southern Peru could suggest that these two locations were part of the
579
same sedimentary basin (Boekhout et al., 2013b).
SC
M AN U
TE D
EP
AC C
580
RI PT
564
581
5.6.2 Pennsylvanian
582
The transition from the Ambo Fm. to the Tarma-Copacabana Group at approximately 315 Ma
583
and is marked by a marine transgression that coincides with a global rise in sea level (Haq and
584
Schutter, 2008). The plutonic record in northern Peru on the other hand continues into the
585
Pennsylvanian (323 – 299 Ma) without any noticeable change in petrological signature
ACCEPTED MANUSCRIPT
(Miskovic et al., 2009). There is an increase of reworked volcanic material in the Tarma-
587
Copacabana Group compared to the Ambo Fm. in south-eastern Peru (Dalmayrac et al., 1980;
588
Laubacher, 1978). Volcanic activity was most pronounced at the end of the Lower
589
Pennsylvanian, giving rise to dacitic tuffs (e.g. MR143; 312.1 ± 0.3 Ma) that are now exposed
590
along the shores of Lake Titicaca, and rhyodacites and rhyolites in the Sacred Valley (e.g. MR29,
591
MR32, MR208; 309 Ma). This increase in volcanism in south-eastern Peru coincides with
592
migmatisation, granitoid plutonism and deformation at 312.9 ± 3 Ma in central Peru (Chew et
593
al., 2007). Interpretation of this tectono-thermal event coincides with the onset of the Early
594
Gondwanide Orogeny that occurred as a consequence of the assembly of Pangaea (e.g.
595
Cawood, 2005). Closure of the Rheic Ocean between Gondwana and Laurussia may have driven
596
increased convergence rates between the eastern Panthallasic Ocean and western Gondwana.
597
The abrupt change from limestone to conglomerate in the Hacienda Huanca section (Fig. 3a),
598
located 80 kilometre north-west of the migmatites studied by Chew et al., 2007, could be the
599
result of eroding relief that formed during this ca. 315 Ma tectonothermal event. The Early
600
Gondwanide orogeny, that is recognized in the Huánuco–La Unión and Tarma–La Merced
601
sectors of the Eastern Cordillera (c. 315 Ma; Chew et al., 2016), is contemporaneous with the
602
high-pressure, low-temperature Toco tectonic event that folded the Sierra del Tigre turbidites
603
in northern Chile (Bahlburg and Breitkreuz, 1991), with an upper age limit provided by the
604
emplacement of c. 310–290 Ma plutons into the folded turbidites (Bahlburg and Hervé, 1997).
605
However, the temporal evolution of the basin which hosts the Tarma-Copacabana Group is
606
marked by a gradual decrease in siliciclastic detritus at Pongo de Mainique (Azcuy et al., 2002),
607
and an unchanged depositional environment is observed at Kellay-Bélen (Fig. 3h). This implies
AC C
EP
TE D
M AN U
SC
RI PT
586
29
ACCEPTED MANUSCRIPT
that depo-centres located further afield were not disturbed by this tectonothermal event,
609
which is best expressed in central Peru in the Late Carboniferous (Fig. 9b).
610
The continuous build-up of platform carbonates may reflect basin subsidence due to flexure of
611
the crust, as a consequence of deformation. The continuous sea-level rise throughout the
612
Pennsylvanian (Haq and Schutter, 2008) renders it difficult to resolve the effects of either
613
process.
SC
RI PT
608
614
5.6.3 Permian
616
The newly described Oqoruro (this study) and Ene Formations (if coeval deposition is assumed,
617
as discussed in section 5.5) collectively reveal a shift from marine to continental depositional
618
environment with respect to the preceding Copacabana Fm. Emersion of the region of the
619
Eastern Cordillera and retreat of the epeiric sea to the sub-Andean region cannot be explained
620
by a global sea level low (Haq and Schutter, 2008). Instead, basin emersion coincides with a
621
major pulse of plutonism in south-eastern Peru (Figs. 2 and 9c; Reitsma, 2012). Early Permian
622
plutons in the Machu Picchu Inlier and the Cordillera de Andahuaylas (Fig. 2) are calc-alkaline,
623
metaluminuous and peraluminious gabbros to alkali granites (Reitsma, 2012). Kemp et al.
624
(2009), and Collins and Richards (2008) observed granitoids with similar geochemical signatures
625
in incipient back-arcs. Lower Permian alkaline granitoids and lava flows with an intraplate
626
signature, that could suggest continental rifting, have not been detected (Fig. 8; Reitsma, 2012).
627
The U-Pb ages and εHfi values of some of the Early Permian detrital zircon grains overlap with
628
the plutonic rocks exposed in the Machu Picchu Inlier (Fig. 6), indicating a possible source
629
region.
AC C
EP
TE D
M AN U
615
ACCEPTED MANUSCRIPT
The plutons were emplaced in an extensional back-arc setting leading to lithospheric thinning
631
and resultant doming of the crust. This doming resulted in the emersion of the Tarma-
632
Copacabana basin in the Eastern Cordillera and retreat of the epicontinental sea to the present-
633
day foreland basin (Fig. 9c) where the Ene Fm. accumulated under restricted marine conditions.
634
Considering the late Paleozoic metamorphic event at c. 260 defined in the northern and central
635
eastern Cordillera of Peru (Chew et al., 2016), the Oqoruro might well be the southern Peruvian
636
sedimentary expression of this Gondwanide orogenic phase. Late Gondwanide (c. 260 Ma)
637
metamorphism in the Eastern Cordillera of Peru is identified in the Huaytapallana Complex (in
638
the southern portions of the Maraynioc–Marairazo massif, the Huaytapallana massif, and the
639
north part of the Huaytapallanakaru massif). This high-grade metamorphic event is
640
contemporaneous with a Late Permian deformation phase that truncates the Copacabana
641
Group below the overlying 240–217 Ma Mitu Group (Chew et al., 2016; Rosas et al., 2007). Late
642
Gondwanide metamorphism in the Eastern Cordillera of Peru is broadly contemporaneous with
643
the mid-Permian San Rafael event (Bahlburg and Herve, 1997 and Ramos, 2000). The San
644
Raphael event is marked by intense folding and thrusting, resulting in a pronounced angular
645
unconformity between Late Carboniferous to Early Permian turbidites and the extensive
646
Permo-Triassic Choiyoi Volcanics in Argentina and Chile (Kay et al., 1989; Ramos, 2000;Ramos
647
and Aleman, 2000; Chew et al., 2016).
648 649
In summary, the evolution of the marginal basins of the Proto-Andean margin reflects changes
650
subduction parameters in a long-lived Paleozoic accretionary orogeny. The two phases of
651
Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260 Ma are reflected in two
652
major facies changes in the sedimentary environment of southern Eastern Peru. Interestingly,
AC C
EP
TE D
M AN U
SC
RI PT
630
31
ACCEPTED MANUSCRIPT
the Hf data obtained in this study on detrital and volcanic zircons also show both the Late as
654
well as the Early Gondwanide events. Hf isotopic values on zircon can be used as a tool to trace
655
episodes of crustal growth through time along the Peruvian (Boekhout et al., 2013b). The
656
interpretation of the Hf isotopic data on zircon is that of a correlation with trends in isotope v.
657
time space; extensional geodynamic settings see excursions to more primitive Hf isotopic
658
compositions, and compressional settings see excursions to more evolved Hf isotopic
659
compositions (Fig. 6).
SC
RI PT
653
661
M AN U
660
6. Conclusions
1. U-Pb zircon dates from the Ambo Formation corroborate stratigraphic age estimates
663
obtained from fossils and palynology, and show initiation in the Early Mississippian in
664
western Bolivia, and terminated in the Middle Pennsylvanian (~ 315 Ma).
TE D
662
2. The Mississippian back-arc basin of southern Peru experienced less extension during
666
deposition of the Ambo Formation than the Eastern Cordillera in north and central Peru.
667
3. The transition from the Ambo Formation to the Tarma Formation reveals deepening of
668
the basin. Evidence for volcanism becomes gradually more pronounced and culminated
669
at ~312 - 309 Ma, temporally correlating with the onset of the Early Gondwana Orogeny
671 672
AC C
670
EP
665
(~315 Ma). Erosion of the newly created relief gave rise to the initiation of deposition of coarse-grained clastic rocks in central Peru. Continuous subsidence in more distal basins resulted in an accumulation of platform carbonates of the Copacabana Formation.
673
4. Our data demonstrates a previously unrecognized depositional phase of mainly fluvial
674
sandstones and localized volcanism between 281 – 270 Ma. We refer to this phase of
ACCEPTED MANUSCRIPT
subaerial deposition as the Oqoruro Formation. This sedimentary succession was
676
previously miss-assigned to the Mitu Group, which has recently been constrained to 245
677
– 220 Ma (Spikings et al., 2015). The Oqoruro Formation may have been
678
contemporaneous with the Ene Formation because it conformably overlies the
679
Copacabana Formation, and reveals a marine regression.
RI PT
675
5. Late Paleozoic paleoenvironmental changes in the back-arc basins along the western
681
margin of Gondwana of southern Peru are contemporaneous with northern Peru,
682
Argentina and Chile. The evolution of the back-arc basins of the Proto-Andean margin
683
reflects changes subduction parameters in a long-lived Paleozoic accretionary orogeny.
684
The two phases of Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260
685
Ma are reflected in two major facies changes in the sedimentary environment of
686
southern Eastern Peru, and can also be recognised in the Hf isotopic record.
TE D
M AN U
SC
680
Figure captions
688 689 690
Figure 1. Map of Peru showing major tectonic features and Carboniferous-Permian sedimentary and plutonic units, which are described in the text. The study locations are labelled. The green rectangles highlight the regions shown in Figures 2 and 4a.
691 692
Figure 2. Geological map of the study area in south-eastern Peru. Study locations are labeled and the green rectangle shows the region that was studied in detail.
693 694 695 696 697 698 699
Figure 3. Stratigraphic sections through the Ambo Fm. and Tarma-Copacabana groups (for locations see Figs. 1 and 2). (a) Hacienda Huanca section, Cerro de Pasco (after Rodriguez et al., 2011). (b) Vilcabamba section, Machu Picchu Inlier. (c). Ollantaytambo section, Sacred Valley. (d) Oqoruro section, Sacred Valley (after Panca, 2010). (e) Pisac section, Sacred Valley. (f) Caicay section, Sacred Valley. (g) Mamuera section, Sicuani. (h) Kellay-Bélen section, Lake Titicaca (modified after Iannuzzi et al., 1998). Stars indicate locations of analysed samples. Note that sections are not drawn to the same vertical scale.
700 701 702 703
Figure 4. Zoomed maps of the field work areas indicated in green squares in Figs. 1 and 2. a) Geological map of the Cerro de Pasco area indicating the location of Hacienda Huanca section. b) Geological map of the Sacred Valley indicating the location of the Ollantaytambo, Pisac, Oqoruro and Caicay sections (indicated in yellow). For legend see Fig. 2.
AC C
EP
687
33
ACCEPTED MANUSCRIPT
Figure 5. U-Pb zircon geochronology of detrital and magmatic zircon grains from late Paleozoic sequences in southcentral eastern Peru (all plots show LA-ICP-MS data, except 5i, which was measured using CA-ID-TIMS). The data is discussed in order of sample location, from NE to SW. Kernel density curves are shown in the case of detrital zircons, n = number of concordant grains plotted. Data from magmatic rocks is shown in Concordia space. Ellipses are 2 sigma and data points demonstrating inheritance are not plotted. (a) Kernel-density plot of concordant zircon U-Pb data of white sandstone GR6-0511, Hacienda Huanca section. (b) Red sandstone MR26, Vilcabamba section. (c) Concordia plot, rhyolite MR29, Ollantaytambo section, analyses used in weighted mean calculation indicated by black ellipses. (d) Concordia plot, Ignimbrite MR230, Oqoruro section. (e) Kernel-density curve of white sandstone MR84, near Pisac. (f) Kernel-density curve of red sandstone MR111, Caicay section. (g) Kernel-density curve of yellow sandstone MR98, Mamuera section. (h) Kernel-density curve of white sandstone MR144, Kellay-Bélen section. (i) ID-TIMS data from dacitic ash MR143 represented in a concordia diagram, Kellay-Bélen section. Black bold ellipse indicates age of the youngest concordant zircon grain. (j) Kernel-density curve of red sandstone MR140.
717 718 719 720 721 722 723
Figure 6. Hf isotopic results from Permo-Carboniferous volcanic and detrital zircon grains. Two grains with significantly lower εHfi values fall outside of the figure (see supplementary Table 2). Red symbols represent volcanic zircon grains, grey and blacks symbols are detrital zircon grains from this study, and dark blue diamonds are detrital grains from the Coastal Cordillera of southern Peru (Yamayo Group; Boekhout et al., 2013b). Dotted fields represent εHfi values of Carboniferous and Permian plutonic rocks in south-east Peru (data from Reitsma, 2012). The timing of the Late and Early Gondwanide Orogeny are highlighted by grey fields. CHUR = Chondritic Uniform Reservoir.
724 725 726 727 728
Figure 7. Whole rock geochemistry for volcanic samples of the Ambo, Tarma and Oqoruro Fms plotted on the rock type discrimination diagram of Winchester and Floyd (1977) based on immobile elements. Numbers in graph refer to the following sample names. Oqoruo Fm.: (1) MR230; (2) MR173; Tarma Fm.: (3) MR208; (4) MR29; (5) MR32; (6) MR143; Ambo Fm.: (7) GR6-0311. Com/Pant = Comendite Pantellerite; TrachyAnd = Trachy Andesite; Bsn/Nph= Basanite Nephelinite.
729 730 731 732
Figure 8. Whole rock geochemistry for volcanic rocks from the Ambo, Tarma and Oqoruro Fms. (a) Trace elements normalized to primitive mantle values and (b) REE normalized to chondritic values from Sun and McDonough (1989). Numbers in graph refer to the following sample names. Oqoruo Fm.: (1) MR230; (2) MR173; Tarma Fm.: (3) MR208; (4) MR29; (5) MR32; (6) MR143; Ambo Fm.: (7) GR6-0311.
733 734 735 736 737 738 739 740 741
Figure 9. Paleogeographic reconstruction of Peru during the Carboniferous and Early Permian. The paleo-Peruvian margin (Pre-Andean Orogeny; indicated by a thick black line) does not show the Arica bend, which formed later during the Andean Orogeny (Arriagada et al., 2008). Back-arc magmatism is based on data from (Miskovic et al., 2009; Chew et al., 2007; Reitsma, 2012 and this study). The distribution of sedimentary units in eastern Peru is based on this work and data from Mathalone and Montoya (1995). The Yamayo Group on the Arequipa Terrane is modified after Boekhout et al. (2013a). No Permo-Carboniferous data are available for the white regions. a) Mississippian paleogeography. b) Pennsylvanian paleogeography, clastic sediments indicate region that was tectonically disturbed at ~312 Ma. c) Lower Permian paleogeography.
742
Table captions
743 744 745 746 747 748 749
Table 1: Overview of U-Pb ages and Hf isotope data of A. zircons in magmatic rocks and B. detrital U-Pb zircons
AC C
EP
TE D
M AN U
SC
RI PT
704 705 706 707 708 709 710 711 712 713 714 715 716
a – number of analyses included in weighted mean calculation over total number of analyses. Discordant analyses, xenocrystic cores and analyses demonstrating slight inheritance or Pbloss are not used in the weighted mean. b – LA: Laser Ablation ICP-MS; TIMS: Isotope Dilution Thermal Ionization MS. c – number of concordant analyses used in probability-density over total number of analyses.
ACCEPTED MANUSCRIPT
750 751 752
d – T/C: Tarma or Copacabana Fm.
753
Acknowledgements
754 755 756 757 758 759
We first of all want to express our gratitude two the reviewers of this manuscript for their input and comments. We thank Fernando Panca for his assistance in the field in the Sacred Valley, INGEMMET for the logistical support in Peru and members of the geochemistry and geochronology groups of the universities of Geneva and Lausanne for their analytical support. We would also like to express our gratitude to C. Heineke for her comments and suggestions. This project was funded by Swiss SNF projects 200020_116572 and 200020_124332.
AC C
EP
TE D
M AN U
SC
RI PT
Table 6. Summary of geochronological results of the late Paleozoic sedimentary units of southern Peru.
35
ACCEPTED MANUSCRIPT
References Arriagada, C., Roperch, P., Mpodozis, C., and Cobbold, R., 2008. Paleogene building of the Bolivian Orocline: Tectonic restoration of the central Andes in 2-D map view. Tectonics 27, TC6014.
RI PT
Azcuy, C.L., and Di Pasquo, M., 2005, Early Carboniferous palynoflora from the Ambo formation, Pongo de Mainique, Peru: review of palaeobotany and palynology 134, 153-184. Azcuy, C.L., Di Pasquo, M., and Valdivia Ampuero, H., 2002, Late Carboniferous miospores from the Tarma Formation, Pongo de Mainique, Peru: review of palaeobotany and palynology 118, 1-28. Bahlburg, H and Herve, F., 1997. Geodynamic evolution and tectonostratigraphic terranes of northwestern Argentina and northern Chile. Geological Society of America Bulletin, 109, 869–884.
M AN U
SC
Bahlburg, H., Vervoort, J.D., DuFrane, S.A., Carlotto, V., Reimann, C.R., and Cárdenas, J., 2011, The U-Pb and Hf isotope evidence of detrital zircons of the Ordovician Ollantaytambo Formation, southern Peru, and the Ordovician provenance and paleogeography of southern Peru and northern Bolivia: Journal of South American Earth Sciences 32, 196-209. Blichert-Toft, J. & Albarède, F. 1997. The Lu–Hf isotope geochemistry of chondrites and the evolution of the mantle–crust system. Earth and Planetary Science Letters 148, 243–258. Boekhout, F., Sempere, T., Spikings, R., and Schaltegger, U., 2013a. Late Paleozoic to Jurassic chronostratigraphy of coastal southern Peru: temporal evolution of sedimentation along an active margin: Journal of South American Earth Sciences 47, 179-200.
TE D
Boekhout, F., Roberts, N.M.W., Gerdes, A., Schaltegger, U., 2013b. A Hf-isotope perspective on continent formation in the south Peruvian Andes. Geological Society of London, Special Publications 389, 305–321. Bouvier, A., Vervoort, J., Patchett, P.J., 2008. The Lu-Hf and Sm-Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters 273, 48-57.
EP
Cárdenas, J., Carlotto, V., Romero, D., Jaimes, F., and Valdivia, W., 1997. Geología de los Cuadrángulos de Chuanquiri y Pacaypata. Hojas 26-p y 27-p., Carta Geolólogica Nacional, 69, Lima-Perú, INGEMMET. Cardona, A., Cordani, U.G., Ruiz, J., Valencia A., Armstrong, R., Chew, D.M., Nutman, A., and Sanchez, A.W., 2009. U-Pb Zircon geochronology and Nd Isotopic Signatures of the Pre-Mesozoic metamorphic basement of the Eastern Peruvian Andes: Growth and Provenance of a Late Neoproterozoic to Carboniferous accretionary orogen on the northwest margin of Gondwana. The journal of Geology 117, 285-305.
AC C
760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810
Carlotto, V., Gill, W., Cárdenas, J. and Chávez, R., 1996. Geología de los Cuadrángulos de Quillabamba y Machupicchu. Hojas 26r-q y 27-q., Carta Geolólogica Nacional, 127, Lima-Perú, INGEMMET. Carlotto, V., Cárdenas, J., Romero, D., Valdivia, W. and Tintaya, D., 1999. Geología de los Cuadrángulos de Urubamba y Calca. Hojas 27r-p y 27-s., Carta Geolólogica Nacional, 65, Lima-Perú, INGEMMET. Carlotto , Cardenas, J., Carlier, G., Diaz-Martinez, E., Cerpa, L., Valderrama , and Robles, T., 2004. Evolucion Tectonica y sedimentaria de la cuenca Mitu (Permo-Triasico) de la region de Abancay-Cusco-Sicuani (sur de Peru), XII Congreso Peruano de Geologia: Lima, Peru, Sociedad Geologica del Peru, 412-415.
ACCEPTED MANUSCRIPT
Carlotto , Cárdenas, J., Reitsma, M., and Rodriguez, R., 2010. Las edades de la formación Ene y del Grupo Mitu: Propuesta de cambios en la cartografía regional: Abancay-Cusco-Sicuani, XV Congreso Peruano de Geología, Cusco, Peru, 830-833. Cawood, A., 2005, Terra Australis Orogen: Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic: Earth Science Reviews 69, 249-279.
RI PT
Cawood, P.A., Buchan, C, 2007. Linking accretionary orogenesis with supercontinent assembly (vol 82, pg 217, 2007). Earth-Science Reviews 85, p.82 Chew, D.M., Schaltegger, U., Kosler, J., Whitehouse, M.J., Gutjahr, M., Spikings, R.A., and Miskovic, A., 2007. U-Pb geochronologic evidence for the evolution of the Gondwanan margin of the north-central Andes: Geological Society of America Bulletin 119, 697-711.
M AN U
SC
Chew, D.M., Magna, T., Kirkland, C.L., Miskovic, A., Cardona, A., Spikings, R., and Schaltegger, U., 2008. Detrital zircon fingerprint of the Proto-Andes: Evidence for a Neoproterozoic active margin? Precambrian Research, 167, 186-200. Clift, D., and Hartley, A.J., 2007. Slow rates of subduction erosion and coastal underplating along the Andean margin of Chile and Peru. Geology 35, 503-506. Chew, D.M., Pedemonte, G., and Corbett E., 2016. Proto-Andean evolution of the Eastern Cordillera of Peru. Gondwana Research 35, 59-78. Clift, D., Pecher, I., Kukowski, N., and Hampel, A., 2003. Tectonic erosion of the Peruvian forearc, Lima basin, by subduction and Nasca Ridge collision. Tectonics 22, 1-16.
TE D
Cohen, K.M., Finney, S.C., Gibbard, P.L. and Fan, J-X., 2013; updated). The ICS International Chronostratigraphic Chart. Episodes 36, 199-204. Collins, W.J., and Richards, S.W., 2008. Geodynamic significance of S-type granites in corcum pacific orogens. Geology 36, 559-562.
EP
Chu, N.C., Taylor, R.N., Chavagnac, V., Nesbitt, R.W., Boella, R.M., Milton, J.A., German, C.R., Bayon, G., and Burton, K., 2002. Hf isotope ratios analyses using multi-collector inductively coupled plasma mass spectrometry: An evaluation of isobaric interference corrections: Journal of Analytical Atomic Spectrometry 17, 1567-1574. Dalmayrac, B., Laubacher, G., and Marocco, R., 1980. Caractères généraux de l'evolution géologique des Andes péruviennes, Géologie des Andes péruviennes 122. Paris, ORSTOM, 501.
AC C
811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860
Díaz Martínez, E., 1991. Litoestratigrafía del Carbonífero del Altiplano de Bolivia. Revista Técnica de Yacimientos Petroliferos Fiscales Bolivianos 12, 295– 302. Doubinger, J., and Marocco, R., 1981. Contenu palynologique du groupe Copacabana (Permien Inférieur et Moyen) sur la bordure sud de la Cordillère de Vilcabamba, région de Cuzco (Pérou). International Journal of Earth Sciences 70, 1086-1099. Gerdes, A., and Zeh, A., 2006. Combined U-Pb and Hf isotope LA-(MC-)ICP-MS analyses of detrital zircons: Comparison with SHRIMP and new constraints for the provenance and age of an Armorican metasediment in central Germany. Earth and Planetary Science Letters 249, 47-61.
37
ACCEPTED MANUSCRIPT
Gerdes, A., and Zeh, A., 2009. Zircon formation versus zircon alteration - new insights from combined U-Pb and LuHf in-situ LAICP-MS analyses, and consequenses for the interpretation of Archean zircon from the Central Zone of the Limpopo Belt. Chemical Geology 261, 230-243. Haq, B. U., and Schutter, S.R.,schre 2008. A chronology of Paleozoic sea-level changes. Science 322, 64-68.
RI PT
Hessler, A. M., and Fildani, A., 2015. Andean forearc dynamics, as recorded by detrital zircon from the Eocene Talara Basin, northwest Peru. Journal of Sedimentary Research 85, 646-659. Iannuzzi, R., and Pfefferkorn, H.W., 2002. A Pre-glacial, warm-temperate floral belt in Gondwana (Late Visean, Early Carboniferous). Palaios 17, 571-590.
SC
Iannuzzi, R., Pfefferkorn, H.W., Diaz-Martinez, E., Alleman, V., and Suarez-Soruco, R., 1998. La flora eocarbonifera de la formacion Siripaca (grupo Ambo, Bolivia) y su correlacion con la flora de Paracas (Grupo Ambo, Peru). Boletin de la Sociedad Geologica del Peru 88, 39-51.
M AN U
Kay, S.M. Ramos, V.A., Mpodozis, C., Sruoga, P., 1989. Late Paleozoic to Jurassic silicic magmatism at the Gondwana margin: analogy to the middle Proterozoic in North America? Geology 17, 324–328. Kemp, A.I.S., Hawkesworth, C.J., Collins, W.J., Gray, C.M., and Blevin, L., 2009. Isotopic evidence for rapid continental growth in an extensional accretionary orogen: The Tasmanides, eastern Australia. Earth and Planetary science letters 284, 455-466. Laubacher, G., 1978. Geologie des Andes Peruviennes. Géologie de la Cordillère orientale et de l'Altiplano au nord et nord-ouest du lac Titicaca, Pérou. Paris, O.R.S.T.O.M., 217. Marocco, R., 1978, Géologie des Andes Péruviennes: Paris, O.R.S.T.O.M.
TE D
Martinez, E., Fernandez, J., Calderon, Y., and Galdos, C., 2003. Reevaluation defines attractive areas in Peru's Ucayali-Ene basin. Oil & Gas Journal 10, 32-38. Mathalone, J.M.P., and Montoya, M., 1995. Petroleum geology of the Sub-Andean basins of Peru, in Tankard, A., Suarez, R., and Welsink, H.J., eds., Petroleum basins of South America, American Association of Petroleum Geology Memoir 62, 423-444.
EP
Mégard, F., 1978. Etude géologique des Andes du Pérou central. Paris, O.R.S.T.O.M. Miskovic, A., Spikings, R., Chew, D.M., Kosler, J., Ulianov, A., and Schaltegger, U., 2009. Tectonomagmatic evolution of Western Amazonia: Geochemical characterization and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran granitoids. Geological Society of America Bulletin 121, 1298-1324.
AC C
861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913
Panca, F., 2010. The late Permian - lower Triassic Mitu Group, SE of Cusco (Peru). Field relations, volcanosedimentary facies and geochemistry. Freiberg, Technische Universität Bergakademie. Pankhurst, R.J., Rapela, C.W., Saavedra, J., Baldo, E., Dahlquist, J., Pascua, I., Fanning, C.M., 1998. The Famatinian magmatic arc in the central Sierras Pampeanas: an Early to Mid-Ordovician continental arc on the Gondwana margin. In: Pankhurst, R.J., Rapela, C.W. (Eds.), The Proto-Andean Margin of Gondwana. London, Special Publications, Geological Society, pp. 343–367. Pearce, N.J.G., Perkins, W.T., Westgate, J.A., Gorton, M.P., Jackson, S.E., Neal, C.R., and Chenery, S.P., 1997. A compilation of new and published major and trace element data for NIST SRM 610 and NIST SRM 612 glass reference materials. Geostandards Newsletter 21, 115-144.
ACCEPTED MANUSCRIPT
Pfefferkorn, H.W., and Alleman, V., 2001. The Carboniferous of Paracas - A synthesis. In: XI Congreso Peruano de Geologia, Lima, 43. Pfefferkorn and Alleman 2002
RI PT
Pino, A., Sempere, T., Jacay, J., and Fornari, M., 2004. Estratigrafia, Paleogeografia y paleotectonica del intervalo paleozoico superior - cretaceo inferior en el area de Mal Paso - Palca (Tacna). In: Jacay, J., and Sempere, T., eds., Nuevas contrubuciones del IRD y sus contrapartes al conocimiento geologico del sur del Peru, 5, Lima, Sociedad geologica del Peru, 15-44. Ramos, V.A., 2000.The Southern Central Andes. In: Cordani,U.G., Milani, E.J., Thomaz Filho, A.,x Campos, D.A. (Eds.). Tectonic Evolution of South America. 31st International Geological Congress, Rio de Janeiro, 561–604.
SC
Ramos, V.A and Aleman, A. Tectonic evolution of the Andes. In: Cordani,U.G., Milani, E.J., Thomaz Filho, A.,x Campos, D.A. (Eds.). Tectonic Evolution of South America. 31st International Geological Congress, Rio de Janeiro, 635-685.
M AN U
Reitsma, M.J., 2012. Reconstructing the Late Paleozoic: Early Mesozoic plutonic and sedimentary record of southeast Peru: Orphaned back-arcs along the western margin of Gondwana, University of Geneva (Ph.D. Thesis). Rodriguez, R., Cueva, E., and Carlotto, V., 2011. Geología del cuadrángulo de Cerro de Pasco (22-k), Carta Géologica Nacional, 144, INGEMMET, 164. Romero, D., Valencia, K., Alarcόn, P., Ramos, V.A., 2013. The offshore basement of Peru: evidence for different igneous and metamorphic domains in the forearc. Journal of South American Earth Sciences 42, 47-60.
TE D
Rosas, S., Fontboté, L., and Tankard, A., 2007. Tectonic evolution and paleogeography of the Mesozoic Pucara Basin, central Peru. Journal of South American Earth Sciences 24, 1-24. Schaltegger, U., Brack, P., Otcharova, M., Peytcheva, I., Schoene, B., Stracke, A., Marocchi, M., and Bargossi, G., 2009. Zircon and titanite recording 1.5 million years of magma accretion, crystallization and initial cooling in a composite pluton (southern Adamello botholith, northern Italy). Earth and Planetary Science Letters 286, 208-218. Scherer, E., Münker, C. & Mezger, K. 2001. Calibration of the lutetium–hafnium clock. Science, 293, 683–687.
EP
Schoene, B., Latkoczy, C., Schaltegger, U., and Gunther, D., 2010. A new method integrating high-precision U-Pb geochronology with zircon trace element analysis (U-Pb TIMS-TEA). Geochimica et Cosmochimica acta 74, 71447159.
AC C
914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964
Sempere, T., Carlier, G., Soler, P., Fornari, M., Carlotto, V., Jacay, J., Arispe, O., Néraudeau, D., Cardenas, J., Rosas, S., and Jiménez, N., 2002. Late Permian-Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on the Andean-age tectonics. Tectonophysics 345, 153-181. Spikings, R., Reitsma, M.J., Boekhout, F. Mišković, A., Ulianov, A., Chiaradia, M., Gerdes, A., and Schaltegger, U., 2016. Characterization of Triassic Rifting in Peru and implications for the early disassembly of western Pangaea. Gondwana Research 35, 124–143. Sláma, J., Kosler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S.A., Morris, G.A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M.N., and Whitehouse, M.J., 2008. Plesovice zircon - a new natural reference material for U-Pb and Hf isotopic microanalysis. Chemical Geology, 249, 1-35.
39
ACCEPTED MANUSCRIPT
Sun, S., and McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., and Norry, M.J., eds., Magmatism in the ocean basins, Geological Society of London 42, 313-345.
RI PT
Thomas, W.A., Astini, R.A., Mueller, P.A., Gehrels, G.E., Wooden, J.L., 2004. Transfer of the argentine Precordillera terrane from Laurentia: constraints from detrital-zircon geochronology. Geology 32, 965–968. Torsvik, T.H., and Cocks, R.M., 2013. Gondwana from top to base in space and time. Gondwana Research 24, 9991030.
SC
Ulianov, A., Müntener, O., Schaltegger, U., and Bussy, F., 2012. The data treatment dependent variability of U-Pb zircon ages obtained using mono-collector, sector field, laser ablation ICP-MS. Journal of Analytical Atomic Spectrometry 27, 663-676.
M AN U
Vervoort, J. D., Patchett, P. J., Blichert-Toft, J. and Albered, F., 1999. Relationships between Lu–Hf and Sm–Nd isotopic systems in the global sedimentary system. Earth and Planetary Science Letters 168, 79–99. Winchester, J.A., and Floyd, A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology 20, 325-343. Woodhead, J. D. & Hergt, J. M., 2005. A preliminary appraisal of seven natural zircon reference materials for in situ Hf isotope determination. Geostandards and Geoanalytical Research, 29, 183–195.
TE D
Zumsprekel, CRR., Bahlburg, H., Carlotto, V., Boekhout, F., Bernt, J. and Lopez, Shirley, L., 2015. Multi-method provenance model for early Paleozoic sedimentary basins of southern Peru and northern Bolivia (13°–18°S). Journal of South American Earth Sciences, 64, 94-115.
EP
994
Stern, C.R., 2011. Subduction erosion: Rates, mechanisms, and its role in arc magmatism and the evolution of the continental crust and mantle. Gondwana Research 20, 284-308.
AC C
965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993
ACCEPTED MANUSCRIPT A.1 Methodology A.1.1 Whole rock geochemistry All geochemical analyses were carried out at the Institute of Mineralogy and Geochemistry, University of Lausanne. Seven whole rock samples were crushed and grinded using a jaw
RI PT
crusher and agate ring mill, lithium tetraborate glass discs were prepared and major and some trace elements were determined by X-ray fluorescence spectrometry (XRF) using a Philips PW 2400 spectrometer. The BHVO-1 basaltic and NIM-G granitic standard were used
SC
for accuracy control. Abundances of REE and additional trace elements (e.g. Th, U, Ta, Cs, Hf)
M AN U
were analysed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on the lithium tetraborate discs using an Elan 6100 DRC quadrupole mass spectrometer (Perkin Elmer) interfaced to a GeoLas 200M 193 nm excimer ablation system (Lambda Physik). Operating conditions of the ablation system included a 10 Hz repetition rate, 120
TE D
mm spot size and ca. 10 J/cm2 on-sample energy density. Helium was used as the carrier gas. The acquisition times for the background and the ablation interval were ca. 70 and 35 s, respectively. The SRM 612 synthetic glass standard from NIST was used for external
EP
standardisation. The average element abundances were taken from Pearce et al. (1997). Ca42
AC C
served as an internal standard. Raw data was reduced off-line, using LAMTRACE, a Lotus 1-23 spreadsheet written by Simon Jackson (Macquarie University, Australia). For each sample 3 measurements were acquired and results were then averaged.
A.1.2 Zircon U-Pb geochronology Several kilograms of rock were crushed and zircon grains were extracted from the sub-300 µm size fraction using a Wilfley table, Frantz horizontal magnetic separator with a side slope of 10° and dense liquid (di-iodomethane, ρ = 3.32 g/cm3). Zircon grains extracted from the
ACCEPTED MANUSCRIPT samples to be dated by ID-TIMS were additionally run on the Frantz horizontal magnetic separator with the side slope reduced to 2° to obtain the least magnetic zircon grains. All zircon grains selected for analysis were handpicked in ethanol using a binocular microscope.
RI PT
A.1.2.1 Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on zircon
Zircon grains were extracted from three volcanic rocks and seven sedimentary rocks and
SC
handpicked with a preference for euhedral grains for volcanic samples and a random
M AN U
population was selected for detrital samples. Zircon grains were subsequently mounted in epoxy and polished with diamond paste to expose the internal surface of the grains. 18-24 zircon grains per plutonic and volcanic sample and 79-102 zircon grains per detrital sample were mounted into epoxy resin blocks (a total of 792 for this study) and polished to obtain
TE D
flat surfaces. The zircon grains were characterized by cathodoluminescence (CL) imaging on a CamScan MV2300 SEM (Institute of Geology and Paleontology, University of Lausanne) to reveal their internal structure.
EP
Pb-U238 and Pb-U235 dates were obtained using a 193-nm excimer ablation system UP-193FX
AC C
(ESI) interfaced to an Element XR sector field, singlecollector inductively coupled plasmamass spectrometry (ICP-MS; Thermo Scientific) at the Institute of Mineralogy and Geochemistry, at the University of Lausanne. Operating conditions were similar to those described in Ulianov et al. (2012) and included a 35 µm spot size combined with a relatively low on-sample energy density of 2.2-2.3 J/cm2 and a repetition rate of 5 Hz to minimize fractionation. A GJ-1 standard zircon was used for external standardisation. The 91500 standard was measured as an unknown on a routine basis to control accuracy.
ACCEPTED MANUSCRIPT Discordant ages, inherited zircon grains and zircon grains showing signs of Pb-loss were discarded from the age calculation. For volcanic zircon grains a weighted mean age was calculated using the
206
Pb/238U ratio of analytically concordant zircon grains. U–Pb data is
206
Pb/238U ages are plotted as probability-density distributions.
RI PT
plotted on concordia diagrams as 2σ error ellipses. For detrital zircon grains concordant
A.1.2.1 Chemical abrasion-isotope dilution-thermal ionisation mass spectrometry (CA-ID-
SC
TIMS)
M AN U
Eight zircon grains from dacitic tuff MR143 were dated by CA-ID-TIMS, following the methodology described in Schoene et al. (2010). Because of the high precision of chemical abrasion ID-TIMS analyses, only the youngest concordant
206
Pb/238U date was taken as the
age of the sample (Schaltegger et al., 2009; Schoene et al., 2010). Zircon grains were
TE D
analyzed at the University of Geneva on a TRITON thermal ionization mass spectrometer using the EARTHTIME 205Pb-238U-235U tracer solution.
EP
A.1.3 Lu-Hf isotope analyses of zircon
AC C
Lu–Hf isotope analyses were performed with a Thermo-Scientific Neptune multi-collector inductively coupled plasma mass spectrometer (ICPMS) at the Goethe-University Frankfurt (GUF) coupled to a RESOlution M50 193 nm ArF Excimer (Resonetics) laser system following the method described in Gerdes and Zeh (2006, 2009). A Lu–Hf laser spot of 40 µm was drilled on top or directly next to the U–Pb laser spot. To correct for the isobaric interferences of Lu and Yb on mass 176, isotopes The
176
and a
Yb and
176
176
172
Yb,
173
Lu were calculated using a
Yb and
176
175
Lu were monitored simultaneously.
Yb/173Yb ratio of 0.796218 (Chu et al. 2002)
Lu/175Lu ratio of 0.02658 (GUF in-house value). The instrumental mass bias for Hf
ACCEPTED MANUSCRIPT isotopes was corrected using an exponential law and a 179Hf/177Hf value of 0.7325. For Yb isotopes the mass bias was corrected using the Hf mass bias of the individual integration step multiplied by a daily βHf/βYb offset factor. All zircon laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analyses were adjusted 176
Hf/177Hf ratio of 0.282160, and the reported uncertainties (2σ)
RI PT
relative to the JMC 475
were propagated by quadratic addition of the reproducibility of JMC 475 (2 standard deviations, SD = 0.0028%, n = 8) and the within-run precision of each analysis (2 standard
SC
errors, SE). The accuracy and external reproducibility of the method were verified by
material),
which yielded
176
M AN U
repeated analyses of reference zircon GJ-1, Plesovice and Temora2 (see Supplementary Hf/177Hf values of 0.282008±0.000025
(2SD, n=41),
0.0282478±0.000018 (n= 9) and 0.282675±0.000022 (n= 11), respectively. This is in perfect agreement with previously published results (Woodhead & Hergt 2005; Sláma et al. 2008;
TE D
Gerdes & Zeh 2009) and with the LA-MC-ICP-MS long-term averages of GJ-1 (0.282010±0.000025; n > 800), Plesovice (0.282478±0.000025, n> 450) and Temora2 (0.282683±0.000026; n>200) reference zircon at GUF. Initial 176Hf/177Hf values are expressed
EP
as εHf(t), which is calculated using a decay constant value of 1.867 × 10-11 yr-1 (Scherer et al.
AC C
2001), giving 176Hf/177HfCHUR,today and 176Lu/177HfCHUR,today of 0.282772 and 0.0332, respectively (Blichert-Toft & Albarède 1997). For the calculation of Hf two-stage model ages (T*DM), a 176
Lu/177HfCrust,today value of 0.0113 was used for the average continental crust, and depleted
mantle 176Lu/177HfDM,today and 176Hf/177HfDM,today values of 0.03813 and 0.283224, respectively (Vervoort et al. 1999) were used. For detailed results from Hf isotopic analyses, see the online supplementary Tables A1 and A2. For the sample MR143 Hf isotopic compositions were measured on the same volume of zircon dated by CA-IDTIMS techniques at GUF. This involves retaining the waste eluted
ACCEPTED MANUSCRIPT solution obtained from ion exchange chemistry. The dried residue was dissolved in 500 to 700 μl 2% HNO3(aq) and introduced into the plasma with an Aridus II desolvating nebulizer, and analyzed for Hf isotope composition using the same multicollector ICP-MS techniques as described above for laser ablation analyses. Data acquisition of the solution analyses lasted
RI PT
for 5 minutes per sample (55 ratios) and was performed in automatic mode, bracketing groups of 5 unknowns by JMC-475 standard measurements. Six solution aliquots of standard
AC C
EP
TE D
M AN U
SC
zircon GJ-1 were analyzed as an external control (0.282016 ± 0.000002, 2σ).
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
Table 1 ɛHfi
Location
MR29
Ollantaytambo
Tarma
13.28 72.20 rhyodacite
308.6
MR143
Kellay-Bélen
Tarma
16.09 69.04 dacite
312.14
0.29
MR230
Oqoruro
13.45 71.53 andesite
281.3
1.5
B Sample
Location
MR26
Vilcabamba
MR84
Pisac
MR98
Mamuera
MR111
CaiCay
Oqoruro
13.59 71.69 red sandstone
MR140
Kellay-Bélen
Oqoruro
16.09 69.04 red sandstone
MR144
Kellay-Bélen
Ambo
16.11 69.05 white sandstone
T/C
10.82 76.07 white sandstone
Oqoruro
Long. (°W) Rock type
Youngest zircon Age (Ma)
13.12 72.94 red sandstone
277.1
Copacabana 13.46 71.82 white sandstone Ambo
14.36 71.09 yellow sandstone
296.2
3.6
ɛHfi
low ± 2σ high ± 2σ
n
-0.5
0.7
1.1
0.6
6
Methodb LA
1/8
-4.1
0.3 -2.9
0.4
9
ID-TIMS
21 / 24
-0.7
0.7
0.6
6
LA
low ± 2σ high ± 2σ
n
Methodb LA
MSWD n / Ntot 3.1 6.6 14 / 18
ɛHfi
± 2σ 7.3
n / Ntot 56 / 79
c
1.4 ɛHfi
0.8
0.9
3.2
0.9 10
3.4 1.30 14
3.4
76 / 96
-5.9
0.8
12.1
71 / 80
-8.7
0.9 -2.9
0.7
5
LA
270.0
3.7
82 / 98
-4.8
0.6
2.9
0.7
5
LA
270.0
10.6
77 / 95
-9.0
1.0
2.2
0.9 10
LA
318.2
16.2
90 / 102 -20.4 0.6
1.4
0.7
6
LA
308.2
6.2
82 / 98
0.6 13
LA
315.2
M AN U
GR6-0511 Hd. Huanca
Formation
Lat. (°S)
Age (Ma) ± 2σ
a
RI PT
Oqoruro
Long. (°W) Rock type
SC
Formation
Lat. (°S)
Concordia
A Sample
-4.6
0.8 -2.1
TE D
Table 1: Overview of A. magmatic and B. detrital U-Pb zircon and Hf isotope data
AC C
EP
a – number of analyses used in weighted mean calculation over total of analyses done. Discordant analyses, xenocrystic cores and analyses demonstrating slight inheritance or Pb-loss are not used in the weighted mean. b – LA: Laser Ablation ICP-MS ; ID-TIMS: Isotope Dilution Thermal Ionization MS. c – number of concordant analyses used in probability-density over total of analyses done. d – T/C: Tarma or Copacabana Formation
LA
ACCEPTED MANUSCRIPT
Summary of geochronological results of the Late Paleozoic sedimentary units Unit Studied section
Tarma-Copacabana Group
Termination
Sample
315 ± 12 Ma < 318 ± 16 Ma 319 Ma prominent age mode
Paleoenvironment
Sample #
subaerial
MR98 MR144 GR6-0511
no direct dating of the onset
312.1 ± 0.3 < 308 ± 6.2 Ma
marine conditions marine conditions subaerial
309 ± 3 Ma
Oqururo Formation 218.3 ± 1.5 Ma
subaerial & volcanism subaerial
AC C
EP
TE D
M AN U
SC
< 270 ± 11 Ma
RI PT
Ambo Formation
Onset
GR6-0511 MR29
MR230
ACCEPTED MANUSCRIPT
Table 6. Summary of geochronological results of the Late Paleozoic sedimentary units of southern Peru. Unit
Onset
Termination
Paleoenvironment
Oqoruro Formation
Kungurian (~281 Ma)
Roadian (~270 Ma)
Subaerial fluvial conditions and localized volcanism
Kungurian (~281 Ma)
Basin deepening to marine conditions
Middle Pennsylvanian (~315 Ma)
Subaerial fluvial conditions with sporadic volcanism
Tarma-Copacabana Group
AC C
EP
TE D
M AN U
SC
RI PT
Ambo Formation
Early Pennsylvanian (~315 Ma) Initiation in the Early Mississippian in western Bolivia (325-335 Ma)
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT Highlights
• •
AC C
EP
TE D
M AN U
SC
•
The Ambo Formation terminated around the Mississippian-Pennsylvanian boundary The transition from Ambo Formation to Tarma Formation represents basin deepening We describe a previously unrecognized phase of Artinskian to Roadian deposition The basin sedimentology of southern Peru reflects two Godwanide orogenic phases
RI PT
•
S0895-9811(17)30128-1
DOI:
10.1016/j.jsames.2017.12.016
Reference:
SAMES 1859
To appear in:
Journal of South American Earth Sciences
Received Date: 24 March 2017 Revised Date:
3 November 2017
Accepted Date: 24 December 2017
Please cite this article as: Boekhout, F., Reitsma, M., Spikings, R., Rodriguez, R., Ulianov, A., Gerdes, A., Schaltegger, U., New age constraints on the paleoenvironmental evolution of the late Paleozoic back-arc basin along the western Gondwana margin of southern Peru, Journal of South American Earth Sciences (2018), doi: 10.1016/j.jsames.2017.12.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
1 2 3
New age constraints on the paleoenvironmental evolution of the late Paleozoic backarc basin along the western Gondwana margin of southern Peru F. Boekhouta,1,†, M. Reitsmaa,2, R. Spikingsa, R. Rodriguezb, A. Ulianovc, A. Gerdesd, and U.
5
Schalteggera
6
a
7
b
8
c
9
d
Department of Earth Sciences University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland INGEMMET, Av. Canadá 1470, Lima, Perú
SC
Institute of Earth Sciences, University of Lausanne, BFSH 2, CH-1015 Lausanne, Switzerland University of Frankfurt, Institute of Geosciences, Altenhofer Allee 1, D-60431, Germany
1
Present address: Institute for Geology and Paleontology, westfälische Wilhelms-Universität, 48149 Münster, Germany
13
2
14
†
M AN U
10 11 12
RI PT
4
Present address: HRH Geology, 19 Silverburn Place, Aberdeen AB23 8EG, UK
Corresponding author, [email protected]
15
Keywords: zircon geochronology, Oqoruro Formation, Ene Formation, Ambo Formation, Tarma-Copacabana
17
Group, back-arc basin
18
TE D
16
Abstract
20
The tectonic evolution of the western Gondwana margin during Pangaea amalgation is recorded in variations in
21
the Permo-Carboniferous back-arc basin sedimentation of Peru. This study provides the first radiometric age
22
constraints on the volcanic and sedimentary sequences of south-central eastern Peru up to the western-most tip
23
of Bolivia, and now permits the correlation of lateral facies variations to the late Paleozoic pre-Andean orogenic
24
cycle. The two phases of Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260 Ma are reflected in
25
two major changes in this sedimentary environment.
AC C
EP
19
26
1
ACCEPTED MANUSCRIPT
Our detrital U-Pb zircon ages demonstrate that the timing of Ambo Formation deposition corroborates the Late
28
Mississipian age estimates. The transition from the Ambo to the Tarma Formation around the Middle
29
Pennsylvanian Early Gondwanide Orogeny (c. 315 Ma) represents a relative deepening of the basin. Throughout
30
the shallow marine deposits of the Tarma Formation evidence for contemporaneous volcanism becomes gradually
31
more pronounced and culminates around 312 - 309 Ma. Continuous basin subsidence resulted in a buildup of
32
platform carbonates of the Copacabana Formation. Our data highlights the presence of a previously unrecognized
33
phase of deposition of mainly fluvial sandstones and localized volcanism (281 – 270 Ma), which we named
34
´Oqoruro Formation´. This sedimentary succession was previously miss-assigned to the so-called Mitu Group,
35
which has recently been dated to start deposition in the Middle Triassic (~ 245–240 Ma). The emersion of this
36
marine basin coincides with the onset of a major plutonic pulse related to the Late Gondwanide Orogeny (c. 260).
37
Exhumation lead to the consequent retreat of the epeiric sea to the present-day sub-Andean region, and the
38
coeval accumulation of the fluvial Oqoruro Formation in south eastern Peru. These late Paleozoic
39
paleoenvironmental changes in the back-arc basins along the western Gondwana margin of southern reflect
40
changes in tectonic plate reorganization in a long-lived Paleozoic accretionary orogeny.
41 42 43
1.
44
Sedimentation within the Permo-Carboniferous back-arc basin of Peru reflects temporal
45
changes in subduction parameters during the amalgamation of Pangaea. This study is the first
46
large-scale chronostratigraphic reconstruction of the paleogeography of south-central eastern
47
Peru during this time period. Two phases of late Paleozoic metamorphism and magmatism at c.
48
315 Ma and c. 260 Ma have so far been recognised in the central and southern Eastern
49
Cordillera of Peru (Chew et al., 2016). These Gondwanide orogenic cycles can be correlated into
50
the Proto-Andean margin of Argentina and Chile (Chew et al., 2016 and refs therein). Phases of
AC C
EP
Introduction
TE D
M AN U
SC
RI PT
27
ACCEPTED MANUSCRIPT
advance and retreat in the evolution of this long-lived Paloezoic accretionary orogeny resulted
52
in magmatic pulses and tectonic phases that can be correlated along the plate boundary
53
(Cawood 2005). This study now links the sedimentary sequences of the Eastern Cordillera of
54
southern Peru to the pre-Andean orogenic cycle.
55
The Permo-Carboniferous sedimentary sequences in the Eastern Cordillera of Peru (Fig. 1) are
56
subdivided into three formations that, in ascending stratigraphic order, are: The Ambo
57
Formation, the Tarma Formation, and the Copacabana Formation (Azcuy and di Pasquo, 2005;
58
Azcuy et al., 2002; Cárdenas et., 1997; Doubinger and Marocco, 1981; Iannuzzi et al., 1998).
59
Previous age constraints were mostly based on palaeobotany and marine biostratigraphy fossils
60
(Azcuy and Di Pasquo, 2005; Azcuy et al., 2002; Cárdenas et al., 1997; Doubinger and Marocco,
61
1981; Iannuzzi et al., 1998). This study combines stratigraphic observations with, (U-Pb zircon)
62
geochronology, whole rock geochemistry and isotopic (Hf-zircon) data from volcanic and
63
sedimentary units at 8 different localities in the central Eastern Cordillera of Peru to the
64
western-most tip of Bolivia (Fig. 1). These new data bracket the time and duration of the
65
different palaeoenvironments, providing age constraints on lateral facies variations in the
66
Eastern Cordillera of southern Peru.
68 69
SC
M AN U
TE D
EP
AC C
67
RI PT
51
3
ACCEPTED MANUSCRIPT
2.
Geological setting
71
During the final stages of assembly of Pangaea (320–250 Ma; Cawood and Buchan, 2007), major
72
plate boundary reorganization was accompanied by orogenic events that affected the central
73
and southern Pacific margin of Pangaea (Chew et al., 2016). A Permo-Carboniferous (340–285
74
Ma) belt of intrusive rocks is exposed along orogenic strike of the Peruvian Eastern Cordillera
75
from the Ecuadorian border (6°S) to southern Peru (14°S; Chew et al., 2008; Miskovic et al.,
76
2009). Two Gondwanide orogenic phases accompanied by magmatism and metamorphism
77
have been identified. A Carboniferous (Early Gondwanide) event affected most of the Proto-
78
Andean margin of South America (Pankhurst et al., 1998; Thomas et al., 2004), and recently a
79
second c. 260 Ma (Late Gondwanide) metamorphic event in the Eastern Cordillera of Peru was
80
documented by Chew et al., (2016). Coeval with these tectono-magmatic events, thick
81
sedimentary sequences were accumulating in the south-central Peruvian Eastern Cordillera.
82
The Carboniferous sedimentary sequences are represented by the Ambo (Lower Carboniferous)
83
and Tarma (Upper Carboniferous) lithostratigraphic units. These sequences were originally
84
assigned a Group status in Peru, but without adhering to the accepted norms or codes of
85
stratigraphy, they have always been used as lithostratigraphic units without further internal
86
subdivision (Azcuy and di Pasquo, 2005). Therefore, in Peru these sequences are now assigned
87
to formations, as proposed by Azcuy and di Pasquo (2005). However, the Ambo Group has also
88
been identified in Bolivia, and authors there correctly make reference to the Ambo with Group
89
status, as it is subdivided in three units: Cumaná, Kasa and Siripaca Formations (Díaz Martínez,
90
1991).
AC C
EP
TE D
M AN U
SC
RI PT
70
ACCEPTED MANUSCRIPT
The Carboniferous sedimentary rocks in south-eastern Peru overlie metamorphic basement or
92
are in faulted or unconformable contact with the locally underlying sedimentary Devonian
93
Cabanillas Formation (Azcuy and di Pasquo, 2005, Boekhout et al., 2013; Zumsprekel et al.,
94
2015). Generally, Carboniferous sedimentation started within a fluvial setting (Ambo Fm.). The
95
sea progressively transgressed along a narrow, subsiding depression, which was centred at the
96
location of the present-day Eastern Cordillera (Fig. 1). The sea regressed during the Visean (347
97
– 331 Ma; Cohen et al., 2013), giving way to subaerial sedimentation and contemporaneous
98
volcanism in eastern central Peru (Dalmayrac et al., 1980).
99
A marine transgression from the north-west or north covered a significant part of Peru in the
100
Pennsylvanian (323 – 299 Ma), and largely overflowed the limits of the Mississippian (359 – 323
101
Ma) basin and initiated deposition of the Tarma Fm. (Laubacher, 1978). The transition between
102
the Tarma and younger Copacabana Fm. is gradual, and consequently the boundary between
103
the two is arbitrary. Therefore, we will refer to the singular Tarma-Copacabana Group, or to the
104
resolved Tarma and Copacabana Fms, as suggested by Azcuy and Di Pasquo (2005). Azcuy et al.
105
(2002) assigned a middle Pennsylvanian (315 – 307 Ma) age to the palynological assemblages at
106
the location which they judge to be the boundary between the Tarma and Copacabana Fms at
107
Pongo de Mainique (Fig. 2). The carbonates of the Copacabana Fm. are conformably overlain by
108
organic-rich shales interbedded with minor sandstone and limestone layers of the Ene
109
Formation in the subandean fold and thrust belt and the foreland basin of north and central
110
Peru (Fig. 1; Azcuy and Di Pasquo, 2005; Mathalone and Montoya, 1995). The Ene Fm. is
111
interpreted as a hypersaline, restricted marine basin marking a marine regression. In south-
AC C
EP
TE D
M AN U
SC
RI PT
91
5
ACCEPTED MANUSCRIPT
eastern Peru we identify a previously unrecognised possible lateral equivalent of the Ene Fm.
113
which we named Oqoruro Formation, after its type location.
114
Coeval late Palaeozoic sedimentation in the Coastal Cordillera of Peru (Fig. 1) consists of the
115
Yamayo Group (Boekhout et al., 2013a). This is a sedimentary succession of variable thickness
116
(up to 2 km) interpreted as a back-arc basin environment, with facies varying from alluvial fan
117
and alluvial plain to shallow-marine and deltaic. Because of the small dimensions of the
118
dispersed outcrops, these unit are not indicated on this large overview map (Fig. 1).
SC
RI PT
112
M AN U
119
2.1 Sedimentary units
121
2.1.1 Ambo Formation
122
The Ambo Fm. is mainly composed of sub-aerial basins and contains plant remains that are
123
preserved at several locations in Peru and Bolivia, indicating a warm-temperate, humid climate
124
during the late Visean – earliest Serpukhovian (Azcuy and Di Pasquo, 2005; Iannuzzi and
125
Pfefferkorn, 2002). Sandstones and conglomerates of the Ambo Fm. host numerous
126
metamorphic basement clasts, and the youngest rocks are tuffs and ignimbrites in central Peru
127
(Mégard, 1978). The Ambo Fm. near Pongo de Mainique (Fig. 2) consists of quartz arenites,
128
lutites, conglomerates and volcanic tuffites, with a palynoflora that is exclusively composed of
129
continental elements of late Viséan age (Azcuy and Di Pasquo, 2005). Abundant plant fossils
130
found in outcrops on the Altiplano indicate that deposition was fully subaerial in this region
131
(Laubacher, 1978), although both marine and fluvial deposits are exposed within the Cordillera
132
de Carabaya (Macusani area, Fig. 2). Sandstone beds containing marine fossils such as
133
brachiopods and crinoids are intercalated with pelites in the middle part of the sequence
AC C
EP
TE D
120
ACCEPTED MANUSCRIPT
(Laubacher, 1978). In Bolivia, where the Ambo sediments have a group status, the oldest
135
formation of the Ambo Group (Cumaná Fm.) on the Bolivian shore of Lake Titicaca is marine,
136
while the overlying Kasa and Siripaca Formations are interpreted as a prograding delta and a
137
fluvial and/or delta plain, respectively (Iannuzzi et al., 1998).
138
RI PT
134
2.2.2 Tarma-Copacabana Group
140
A marine transgression from the north-west or north covered a significant part of Peru in the
141
Pennsylvanian (323 – 299 Ma), and largely overflowed the limits of the Mississippian (359 –
142
323) basin and initiated deposition of the Tarma Fm. (Laubacher, 1978). The marine basin
143
deepens towards the east, and mainly consists of fossiliferous limestone, shale, marl, siltstone
144
and sandstone (Azcuy et al., 2002; Laubacher, 1978; Marocco, 1978; Mégard, 1978). Evidence
145
for explosive volcanism can be found in reworked tuffs, tuffaceous sandstones and
146
volcanoclastic deposits (Dalmayrac et al., 1980; Laubacher, 1978). Overall, the transition to the
147
Copacabana Fm. can be considered as a continuous marine transgression that reached its
148
maximum extent in the lower Permian (Marocco, 1978); at this time the sea covered most of
149
Peru except for the Arequipa Terrane (Fig. 1; Dalmayrac et al., 1980). The lower part of the
150
Copacabana Fm. mainly consists of platform carbonates, which contain abundant fossils such as
151
fusulinida, brachiopods, corals, bryozoans and gastropods (Dalmayrac et al., 1980; Marocco,
152
1978), with some intercalations of sandstone and shale. In the sections where the upper levels
153
of the Copacabana Fm. are still present, it is observed that siliciclastic input becomes more
154
dominant during the final stages, indicating a partial retreat of the vast inland sea. The
155
limestones become sandier with time in the Macusani area, and the sequence ends with
AC C
EP
TE D
M AN U
SC
139
7
ACCEPTED MANUSCRIPT
deposition of continental red beds (Laubacher, 1978). In the upper part of the Tarma-
157
Copacabana Group, 10 km north of Abancay (Fig. 2), black shales and intercalated fine
158
sandstone beds contain small fossilized trunks and acicular leaves identified as Lycopsidropsis
159
pedroanus, and a palynological assemblage indicating an Artinskian age (290 – 284 Ma;
160
Doubinger and Marocco, 1981). Fusulinida-bearing strata in the upper part of the Copacabana
161
Fm. are also indicative of an Artinskian age (290 – 284 Ma; Dalmayrac et al., 1980). Evidence for
162
volcanism is scarce, although two volcanic intervals have been identified in the dominantly
163
calcareous sequence in the Vilcabamba area (Marocco, 1978; Fig. 2). Even though volcanic
164
activity is not very pronounced in the Tarma-Copacabana Group, the presence of plutons
165
suggests that the magmatic activity that originated in the Mississippian continued
166
intermittently into the Pennsylvanian and early Permian (340-271 Ma; Miskovic et al., 2009; Fig.
167
1).
SC
M AN U
TE D EP
169
AC C
168
RI PT
156
ACCEPTED MANUSCRIPT
3. Analytical methods and sampling
171
3.1 Sampling
172
Geochronological data have been obtained using U–Pb analyses (CA-ID-TIMS and LA-ICPMS) of
173
zircon. Geochemical analyses includewhole rock major oxides, trace and REE data, which have
174
been obtained using XRF and LA-ICPMS.Nd (whole rock) and Hf (zircon) isotopic data were
175
acquired using ID-TIMS (Nd) and LA-MC-ICPMS (Hf). Methodological details are summarized in
176
Table 1 and are presented in Appendix A.
M AN U
177
SC
RI PT
170
Sections through the Ambo successions were investigated at three locations: i) Hacienda
179
Huanca, near Cerro de Pasco in central Peru, ii) Mamuera, near Sicuani in south-eastern Peru,
180
and iii) Kellay-Bélen, on the Copacabana Peninsula at Lake Titicaca, western Bolivia (Figs. 1 and
181
2).
182
The Tarma-Copacabana Group was studied at seven different localities. A continuous section
183
stratigraphically above the Ambo Fm., can be found in the Hacienda Huanca and Kellay-Bélen
184
sections (Fig. 3). Four of these locations are located in the Sacred Valley (Ollantaytambo,
185
Oqoruro, Pisac, Caicay; Figs. 1, 2 and 4b), of which only the Pisac section was previously
186
correctly mapped as part of the Copacabana Fm. (Carlotto et al., 1996). The Ollantaytambo,
187
Oqoruro and Caicay sections were formerly attributed to the Mitu Group (now dated to be
188
~ 245–240 to ~ 220 Ma; Spikings et al., 2016). Likewise, the Vilcabamba section in the Machu
189
Picchu Inlier (Fig. 2) was presumed to belong to the Mitu Group (Carlotto et al., 1999). The U-Pb
190
zircon data presented in this study shows all these sections are part of the Tarma-Copacabana
191
Group.
AC C
EP
TE D
178
9
ACCEPTED MANUSCRIPT
Three volcanic intervals in the Ollantaytambo, Oqoruro and Kellay-Bélen sections were selected
193
for U-Pb zircon dating and whole rock geochemistry (MR29, MR230, MR143; Fig. 3). Four
194
different volcanic horizons were sampled for geochemistry from the sections at Hacienda
195
Huanca (GR6-0311) and Ollantaytambo (MR32), and two other volcanic outcrops in the lateral
196
extension of the Oqoruro Fm. (MR173) and Tarma Fm. (MR208). Seven maximum deposition
197
ages were obtained from U-Pb dating of detrital zircons from sedimentary rocks in part of the
198
sequences (Vilcabamba, Pisac, Caicay, Mamuera and Kelley-Bélen) where no volcanic intervals
199
were found (GR6-0511, MR26, MR84, MR11, MR98, MR140, MR144). Lava flows were sampled
200
for whole rock geochemistry throughout the sections, and in the surrounding regions.
M AN U
SC
RI PT
192
201
4. Results
203
Eight sites were studied in south-central eastern Peru and the western most tip of Bolivia, four
204
of which are located in the Sacred Valley (Figs. 1 and 2). All locations are discussed below in
205
geographic order, from north-west to south-east (Fig. 3). A summary of the results of the
206
magmatic and detrital U-Pb zircon geochronology and Hf isotopic analyses is shown in Table 1.
207
Data from individual detrital and magmatic zircons are listed in Supplementary Tables 2 and 3.
EP
AC C
208
TE D
202
209
4.1 Stratigraphy and geochronology
210
4.1.1 Hacienda Huanca (-10.651, -76.0915)
211
The Ambo Fm. and Tarma-Copacabana Group in the Hacienda Huanca section near the city of
212
Cerro de Pasco (Fig. 4a) are described in detail by Rodriguez et al. (2011). The Ambo Fm. in this
213
location is entirely volcanic and consists of a ~500 m pile of volcanic deposits. The sequence
ACCEPTED MANUSCRIPT
begins with rhyolitic ignimbrites, and the upper units are dominated by dacitic lava flows with
215
plagioclase and biotite phenocrysts. Dacite GR6-0311 was sampled for geochemistry 60 m
216
below the top of the Ambo Fm. (Fig 3a), and did not
217
The overlying Tarma-Copacabana Group consists of near shore deposits, varying from
218
limestones, shales and sandstones to conglomerates (Rodriguez et al., 2011). Medium-grained,
219
white sandstone GR6-0511 was sampled after the first conglomeratic interval (Fig. 3a). Ninety
220
eight zircon grains were dated by LA-ICPMS, 16 of which yield discordant dates. All concordant
221
zircon grains (n = 82) yield Carboniferous ages that range between 308.2 ± 6.2 Ma and 341.1 ±
222
17 Ma (Fig. 5a). Slight bimodal behaviour can be observed, and the most prominent mode
223
corresponds to 319 Ma. Towards the top of the section, the depositional environment evolves
224
from alluvial and shallow marine deposits to fluvial sedimentation.
M AN U
SC
RI PT
214
TE D
225
4.1.2 Vilcabamba (-13.108, -72.938)
227
The outcrops in the Vilcabamba area (Fig. 2) are too fragmented to construct a coherent
228
stratigraphic column (Fig. 3b). Red clastic rocks which were previously assigned to the Mitu
229
Group are unconformably underlain by massive limestone deposits of the Copacabana Fm.
230
(Doubinger and Marocco, 1981). Subaerial deposits include fine to medium red sandstones and
231
coarse, poorly sorted sandstones and pebble beds. Pebbles are mainly volcanic in origin but
232
vein quartz, chert and limestone pebbles are also observed. Cross bedding and current ripples
233
are preserved. Coarse red sandstone MR26 was sampled for detrital zircon analysis, and 56
234
zircon grains yield concordant U-Pb ages. The youngest zircon grains are the dominant
AC C
EP
226
11
ACCEPTED MANUSCRIPT
population, with the youngest grain giving a maximum depositional age of 277.1 ± 7.3 Ma, with
236
the most prominent mode peaking (youngest cluster) at 282 Ma (Fig. 5b).
237
4.1.3 Ollantaytambo (-13.258, -72.237)
238
A discontinuous section of red clastic sedimentary rocks and a few interbedded lava flows
239
(MR29 and MR32) in the northwestern corner of the Sacred Valley was sampled near the village
240
of Ollantaytambo (Fig. 4b). The section mainly consists of conglomerates that contain up to 30
241
cm long clasts of rhyolite, basalt and red siltstone (Fig. 3c). MR32 was sampled for geochemistry
242
at the base of the section. Rhyodacite MR29 was sampled at the top of the section (Fig. 3c) for
243
geochemistry and geochronology. Evidence of minor Pb-loss was found in 4 of 18 dated zircon
244
grains, while the remaining 14 yielded concordant U-Pb zircon ages with a weighted mean age
245
of 308.6 ± 3.1 Ma (MSWD = 6.6; Fig. 5c).
TE D
246
M AN U
SC
RI PT
235
4.1.4 Oqoruro (-13.444, -71.7658)
248
The sedimentology of the 2.7 km long section in the valley of the village of Oqoruro (Fig. 4b) has
249
been studied in detail by Panca (2010). He suggested the entire sequence formed part of the
250
Mitu Group, overlying limestones of the Copacabana Fm. Based on U-Pb zircon data from
251
Spikings et al. (2016) and this study, we reinterpret the upper part of this section as a newly
252
recognised formation, which will is discussed below. The rocks are sandstones, lava flows and
253
ignimbrites (Fig. 3d). Zircon grains were extracted from andesitic ignimbrite MR230 (Fig. 3d),
254
which yields 21 concordant U-Pb ages (n = 24), with a weighted mean average of 281.3 ± 1.5
255
Ma (MSWD = 3.6; Fig. 5d).
256
AC C
EP
247
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
257
13
ACCEPTED MANUSCRIPT
4.1.5 Pisac (-13.452, -71.824)
259
A 20 meter long section of evaporites, marls, and white sandstones containing bivalve
260
fragments located to the south-east of the village of Pisac is interpreted as a lagoonal sequence
261
(Fig. 3e; 4b). Detrital zircon grains were extracted from white sandstone MR84, which hosts
262
well-rounded quartz grains and shows planar lamination. Seventy seven concordant U-Pb ages
263
were obtained out of a total of 96 analysed zircon grains. The youngest grain yields an earliest
264
Permian age of 296.2 ± 3.4 Ma. The majority of the zircon grains yield Carboniferous ages (301
265
– 325 Ma; Fig. 5e), and the most prominent mode corresponds to 304 Ma.
266
M AN U
SC
RI PT
258
4.1.6 Caicay (-13.581, -71.686)
268
The Caicay section is located in the south-eastern corner of the Sacred Valley, near the village
269
of Caicay, and forms part of the same thrust sheet that is preserved in the Oqoruru section (Fig.
270
4b). The sedimentary succession is dominated by red clastic rocks and lacks volcanic deposits
271
(Fig. 3f). Some sandstones contain abundant detrital muscovite. Ninety eight detrital zircon
272
grains from medium red sandstone MR111 were dated by LA-ICP-MS, of which 82 grains give
273
concordant ages. Only 3 zircon grains yield Permian ages, and the youngest grain yields an age
274
of 270 ± 3.7 Ma. The majority of the zircon grains are Cambro-Ordovician. The data also shows
275
a noteworthy Late Mesoproterozoic peak (Fig. 5f).
276 277 278
4.1.1 Mamuera (-14.361, -71.084)
279
The Mamuera section is located 20km south-east of the city of Sicuani, near the village of
280
Mamuera (Fig. 2). Here, the Ambo Fm. unconformably overlies schists and meta-siltstones of
AC C
EP
TE D
267
ACCEPTED MANUSCRIPT
the Siluro-Devonian metamorphic basement. The Ambo Fm. consists of 70 meters of siliciclastic
282
deposits ranging in grain size from siltstone to coarse sandstone, with a general coarsening
283
upward trend (Fig. 3g). Cross-bedding is widely recognized as well as ca. 5 meter wide
284
conglomeratic channel fills. Clasts and pebbles are mainly quartzite and vein quartz. We
285
interpret the depositional environment of this section as a fluvial plain setting. Medium-
286
grained, cross-bedded sandstone MR98, located near the stratigraphic top of the section, was
287
sampled for detrital zircon geochronology (Fig. 3g). Concordant ages were obtained for 71 out
288
of 80 grains. The dominant age groups are Carboniferous, Cambro-Ordovician and
289
Mesoproterozoic, while the youngest zircon has an age of 315.2 ± 12.1 Ma (Fig. 5g), suggesting
290
an earliest Pennsylvanian maximum depositional age for the top of the Ambo Fm. exposed in
291
this section. The youngest mode (age cluster) corresponds to 332 Ma. The Ambo Fm. is
292
unconformably overlain by continental sedimentary rocks and alkaline lava flows of the Middle
293
to Upper Triassic Mitu Group (Spikings et al., 2016) in the Mamuera valley. The presence of
294
sandstones and shales of the Copacabana Fm. elsewhere in the Sicuani region, containing
295
abundant corals, crinoids and bivalves, suggests that the Copacabana Fm. has not been
296
preserved in the Mamuera section.
SC
M AN U
TE D
EP
AC C
297
RI PT
281
298
4.1.2 Kellay-Bélen (-16.110, -69.045)
299
The Kellay-Bélen section is located on the Copacabana Peninsula on the Bolivian side of Lake
300
Titicaca, near the village of Kellay-Bélen (Fig. 3h). Fossil flora indicative of the upper Ambo
301
Group have been identified at this locality (Iannuzzi et al., 1998). The Ambo succession has a
302
Group status in this area and is divided into three formations (Fig. 3h). The Cumaná Fm. is the
15
ACCEPTED MANUSCRIPT
oldest formation and consists of glacio-marine deposits, while the overlying Kasa Fm.
304
represents a prograding delta sequence. The youngest is the Siripaca Fm., which was deposited
305
within a fluvial or delta plain environment and contains coal beds with abundant plant fossils
306
(Iannuzzi et al., 1998). We sampled medium grained, poorly cemented, white sandstone
307
(MR144), which preservesmeter-scale crossbedding, from the very top of the Kasa Fm. (Fig. 3h).
308
One hundred and two detrital zircon grains were dated. The youngest grain (Fig. 5h) has an age
309
318.2 ± 16.2 Ma, while the youngest prominent mode has an age of 341 Ma. Sandstone MR144
310
contains only 7 Carboniferous grains, and mostly grains with a Cambro-Ordovician age (Fig. 5h).
311
An erosional hiatus separates the Ambo Group from the overlying Titicaca Group (Bolivian
312
equivalent of the Peruvian Tarma-Copacabana Group, Fig. 3h). The oldest rocks of the Titicaca
313
Group were deposited across a coastal plain, overlain by shallow marine deposits. The shallow
314
marine deposits consist of alternating sand- and siltstone versus limestones intervals, both of
315
which host abundant bivalve fossils. Several tuffaceous ash beds were discovered within the
316
sequence. Dacitic tuff MR143 with biotite crystals was sampled in the first sandy interval (Fig.
317
3h) and 8 zircon grains were dated by ID-TIMS. The youngest zircon grain yielded a concordant
318
age of 312.14 ± 0.29 Ma (Fig. 5i). The exposed top of the Tarma-Copacabana Group near Kellay-
319
Bélen consists of sub-aerial, red sandstone. Finely laminated sandstone (Fig. 3h) was sampled
320
for U-Pb dating of detrital zircon grains and 77 out of 95 grains yielded concordant dates. One
321
third of the zircon grains yield an Early Permian age with a prominent mode corresponding to
322
288 Ma (Fig. 5i). The youngest grain has an age of 270 ± 10.6 Ma.
323 324
AC C
EP
TE D
M AN U
SC
RI PT
303
ACCEPTED MANUSCRIPT
4.2 Hf-isotopic ratios of zircon
326
Hf istopic analyses were performed on both volcanic and detrital concordant zircon grains from
327
the south Peruvian Eastern Cordillera. Raw data is listed in Supplementary Table 4. The results
328
are plotted together with Hf isotopic data from Permo-Carboniferous detrital zircon grains from
329
the coeval Yamayo Group in coastal Southern Peru (Boekhout et al., 2013a; Fig. 6). Hf-isotopic
330
results from volcanic rocks are indicated in red, and data from detrital zircons are shown in
331
grey, black and dark blue (Fig. 6). The volcanic zircon grains have a relatively narrow Hf-isotopic
332
range. Rhyodacite MR29 (n=6; Ollantaytambo) yielded a εHfi ranging between -0.5 ± 0.7 and 1.1
333
± 0.6. Zircon grains from ignimbrite MR230 (n=6; Oqoruro) range between εHfi -0.7 ± 0.7 and
334
1.4 ± 0.6, and zircon grains from tuff MR143 (n=9) yielded Hf-isotopic ratios that range between
335
εHfi -4.1 ± 0.3 and -2.9 ± 0.4.
336
Detrital zircons from seven sedimentary rocks were analysed for Hf isotopic analyses, and 5 to
337
14 concordant zircon grains in the Permo-Carboniferous age range were selected per rock.
338
Overall, the εHfi values range between -20.4 and +3.4. Sandstones MR26 and GR6-0511 yield
339
the smallest intra-sample variation. The Upper Cisuralian zircon grains (275.6 ± 0.7 Ma – 284.4 ±
340
0.7 Ma) of sandstone MR26 (n=10) yielded only positive εHfi values that range between 0.8 ±
341
0.9 and 3.2 ± 0.9, while the Carboniferous zircon grains of GR6-0511 (n=13) yielded solely
342
negative εHfi values that range between -4.6 ± 0.8 and -2.1 ± 0.6. The Carboniferous zircon
343
grains from sandstone MR98 are also restricted to a negative εHfi range (-8.7 ± 0.9 - -2.9 ± 0.7, n
344
= 5). Zircon grains extracted from sandstones within the Kellay-Bélen section extend to the
345
most negative values and display the largest spread in εHfi values. The Mississippian (359 – 323
346
Ma) zircon grains from MR144 range from -20.4 ± 0.6 to 1.4 ± 0.7 (n=6) and the Early Permian
AC C
EP
TE D
M AN U
SC
RI PT
325
17
ACCEPTED MANUSCRIPT
and Mississippian zircon grains from MR140 vary between -9.0 ± 1.0 and 2.2 ± 0.9 (n=10). The
348
εHfi data of sandstone MR84 from the Pisac section forms two clusters that both span the
349
Carboniferous – earliest Permian; 3.4 ± 1.3 – 0.4 ± 1.0 (n=10) and -3.7 ± 1.1 – -5.9 ± 0.8 (n=4).
350
The Hf-isotopic compositions of Pennsylvanian - Early Permian zircon grains within sandstone
351
MR111 range from -4.8 ± 0.6 to 2.9 ± 0.7 (n=5).
SC
352
RI PT
347
4.3 Whole rock geochemistry
354
Whole-rock XRF and LA-ICP-MS analyses of 7 samples are listed in Supplementary Table 5.
355
Three volcanic intervals in the Ollantaytambo, Oqoruro and Kellay-Bélen sections that were also
356
dated by U-Pb zircon geochronology, were analysed for whole rock geochemistry (MR29,
357
MR230, MR143; Fig. 3). Additionally, four undated volcanic levels were sampled for
358
geochemistry from the Hacienda Huanca section (GR6-0311), the Ollantaytambo section
359
(MR32), and two other volcanic outcrops in the lateral extension of the Oqoruro Fm. (MR173)
360
and Tarma Fm. (MR208).
361
Volcanic rocks of the Carboniferous Ambo Fm. and Tarma Fm. are mainly lava flows with
362
phenocrysts of quartz and feldspar, except at the Kellay-Bélen section in Bolivia where 10-cm
363
thick green ash beds with biotite crystals are found (sample MR143). In contrast, volcanic rocks
364
from the Oqoruro Fm. in the Sacred Valley (samples MR173 and MR230) are ignimbrites.
365
Volcanic rocks are intermediate to felsic in composition (61 - 77 wt% SiO2), calc-alkaline and
366
classify as andesites, dacites and rhyolites (Fig. 7), with a chemical index of alteration (CIA)
367
between 50.4 and 69.6. The Permian ignimbrites are significantly richer in Fe (6.4 – 6.7 wt%)
368
than the Carboniferous lavas (2.2 - 3.4 wt% ; Supplementary Table 5).
AC C
EP
TE D
M AN U
353
ACCEPTED MANUSCRIPT
The primitive mantle-normalized spider diagram reveals negative anomalies for Ba, Nb, Ta, Sr, P
370
and Ti and elevated LILE/HFSE ratios (Fig. 8a). Chondrite-normalized REE plots show that the
371
volcanic rocks are LREE enriched and have flat HREE patterns, except andesite MR230, which is
372
the least evolved and does not yield a negative Eu anomaly (Fig. 8b). Rhyodacite MR29 and
373
rhyolite MR208 have strongly negative Eu anomalies, indicating significant feldspar
374
fractionation.
SC
RI PT
369
375
5. Discussion
377
5.1 Ambo Formation
378
The Ambo Fm. was studied in three sections. Our findings corroborate previous observations
379
that there was significantly less volcanism in the sedimentary record of the southern Eastern
380
Cordillera of Peru (Dalmayrac et al., 1980; Iannuzzi et al., 1998; Laubacher, 1978) compared to
381
the Ambo Fm. in the Eastern Cordillera of central Peru (Mégard, 1978). Scarce geochronological
382
information is available on the onset of the Ambo Fm. This sedimentary sequence locally
383
overlies schist with a maximum depositional age of 317 ± 7 Ma, 30 km south-west of the
384
Hacienda Huanca section (Cardona et al., 2009), giving a local maximum age constraint on the
385
oldest part of this sedimentary unit.
386
Towards the Bolivian border the onset of Ambo sedimentation seems to be earlier.
387
Geochronology of an ash bed from the lower Tarma-Copacabana Group (Kellay-Bélen section)
388
suggests the Ambo Group near the Bolivian border was deposited before 312.1 ± 0.3 Ma. Plant
389
fossils observed in this section between dated sandstones MR144 and ash bed MR143 (Fig. 3h)
390
assign this part of the section to the late Viséan-earliest Serpukhovian (325-335 Ma; Iannuzzi
AC C
EP
TE D
M AN U
376
19
ACCEPTED MANUSCRIPT
and Pfefferkorn, 2002). Identical plant fossils (Nothorhacopteris, Tomiodendron) have been
392
identified in the coeval Yamayo Group (Boekhout et al., 2013a) in coastal southern Peru
393
(Pfefferkorn and Alleman, 2001; Pino et al., 2004), indicating a similar depositional environment
394
in large parts of the back-arc basin, that lies within a late Visean warm temperate floral belt
395
that runs through Gondwana (Iannuzzi and Pfefferkorn, 2002).
SC
396
RI PT
391
Regarding the termination of the Ambo Fm., more geochronological data is available. The Ambo
398
Fm. of south-eastern Peru terminated around the Middle Pennsylvanian (~ 315 Ma). Maximum
399
depositional ages for the upper levels of the Ambo Fm. from our two southern most sections
400
overlap and are 315 ± 12 Ma (MR98; Mamuera section) and 318 ± 16 Ma (MR144; Kellay-Bélen
401
section; Fig. 5a). Lavas of the Ambo Fm. in the Hacienda Huanca section were not directly
402
dated, but sandstone GR6-0511 of the overlaying Tarma-Copacabana Group yields exclusively
403
Carboniferous zircon grains (308.2 ± 6.2 – 341.1 ± 17.0 Ma; Fig. 5a) with a narrow range in εHfi
404
values (-4.6 ± 0.8 to -2.1 ± 0.6; Fig. 6), suggesting they could be derived from reworking of a
405
single source. Conglomerates bracketing this sandstone contain volcanic clasts which suggest
406
they may be reworked remnants of underlying lava flows (Rodriguez et al., 2011). The Kernel
407
density curve for this sandstone (GR6-0511) has a prominent mode corresponding to 319 Ma
408
(Fig. 5a) and overlaps with the maximum depositional ages of the Ambo Fm. that were obtained
409
in the two more southern sections discussed above.
410
Overall, the duration of Ambo Fm. deposition appears to have initiated in the Early
411
Mississippian in western Bolivia, and terminated in the Middle Pennsylvanian (~315 Ma). It
412
should however be noted that there may be a faulted contact between the Ambo Fm. and the
AC C
EP
TE D
M AN U
397
ACCEPTED MANUSCRIPT
413
metamorphic basement or underlying sedimentary Devonian Cabanillas Fm. (Boekhout et al.,
414
2013a and refs therein).
RI PT
415
5.2 Tarma-Copacabana Group
417
A marine transgression formed an epeiric sea along the axis of the present-day Eastern
418
Cordillera of Peru, initiating deposition of the Tarma Fm. in the Early Pennsylvanian (Azcuy et
419
al., 2002). Dacitic tuff MR143 indicates that marine conditions initiated just prior to 312.1 ± 0.3
420
Ma in the Titicaca area (Fig. 3h). If the maximum detrital age of sandstone GR6-0511 of 308 ± 6
421
Ma (Hacienda Huanca) approaches the depositional age of the rock, it reveals a comparable age
422
for marine transgression in central Peru (Fig. 3a). Submarine conditions are reported for the
423
same period in Pongo de Mainique (Fig. 2), where palynological analyses assign a Moscovian
424
age (315-307 Ma) to the upper Tarma Fm. (Azcuy et al., 2002). Marine conditions however did
425
not prevail during deposition of the Ollantaytambo section in the Sacred Valley, where
426
rhyodacite MR29 indicates subaerial deposition at and prior to 309 ± 3 Ma (Fig. 3c). Although
427
marine limestones of the Tarma-Copacabana Group are present in the south-eastern Sacred
428
Valley, their stratigraphic relationship to the Ollantaytambo section is unknown. Subaerial
429
deposition may have been a localized phenomenon related to a volcanic edifice built above the
430
Nevado Chicon pluton (Fig. 4b). The Nevado Chicon alkali granite (304.3 ± 0.1 Ma (U-Pb zircon);
431
Reitsma, 2012), located 10 km to the north-east may be genetically related to the rhyodacites
432
and rhyolites (MR29, MR32 and MR208) at Ollantaytambo (Fig. 4b). The highly silicic nature of
433
the lavas suggests that were highly viscous during eruptions, and thus a volcanic vent must
AC C
EP
TE D
M AN U
SC
416
21
ACCEPTED MANUSCRIPT
have been located nearby where these lavas were deposited. We suggest that subaerial
435
sedimentation of the Ollantaytambo Fm may have occurred along a volcanic flank.
436
Azcuy et al. (2002) report that siliciclastic input into the marine Tarma-Copacabana basin
437
diminished after the Moscovian (315 – 307 Ma) at Pongo de Mainique. According to Marocco
438
(1978) and Dalmayrac et al. (1980), the epicontinental sea reached its maximum extent in the
439
earliest Permian when it covered most of Peru. The only earliest Permian age obtained in this
440
study is from a lagoonal sequence near Pisac in the Sacred Valley (Fig. 3e). Here, zircon ages
441
from white sandstone MR84 indicate a maximum depositional age of 296.2 ± 3.4 Ma. Almost
442
half of the detrital zircon grains in sandstone MR84 have ages between 301 Ma and 325 Ma.
443
These dates overlap with the age of rhyodacite MR29 and plutons exposed in the same area
444
(Reitsma, 2012; Fig. 5c), suggesting they may have been a source for sandstone MR84. Some of
445
the detrital zircon grains have εHfi values that overlap with values obtained from the plutons,
446
although several grains in the same age range have significantly lower εHfi values (Fig. 6).
447
Therefore, an additional source may have supplied detritus to sandstone MR84, which may
448
have consisted of volcanic deposits that are similar to dacitic tuff MR143.
SC
M AN U
TE D
EP
449
RI PT
434
5.3 Oqoruro Formation
451
Several authors (Carlotto et al., 2004; Doubinger and Marocco, 1981; Laubacher, 1978) already
452
recognized that a few sections through the Copacabana Fm. become increasingly rich in
453
siliciclastic material towards the top, and culminate with subaerial deposition. For example, 10
454
km north of Abancay, the upper levels of the Tarma-Copacabana Group consist of sandstones
455
and black shales containing abundant plant fossils (Pecopteris sp., Sphenopteris sp.,
AC C
450
ACCEPTED MANUSCRIPT
Gangamopterus sp., Lycopsidropsis pedroanus) assigned to the Artinskian (290 – 284 Ma),
457
indicating deposition occurred in a swamp-like environment (Doubinger and Marocco, 1981).
458
Using the age constraints obtained in this study, we demonstrate that the subaerial deposition
459
environments, as recognised by the authors cited above, the Tarma-Copacabana Group was
460
more widespread during the final stages of than previously thought. It appears that oxidized
461
clastic rocks have often been confused with, and attributed to the significantly younger Mitu
462
Group (~ 245–240 to ~ 220 Ma; Spikings et al., 2016).
463
Direct age constraints on the Oqoruro Fm. are obtained by ignimbrite MR230, which indicates a
464
transition to significant subaerial volcanism and sedimentation from a phase of marine
465
deposition in the Oqoruro section at 281.3 ± 1.5 Ma (Fig. 3d). This period of explosive volcanism
466
coincides with a major pulse of local plutonism in the Vilcabamba area that lasted from 282.2 ±
467
0.1 Ma to 271.3 ± 0.3 Ma (U-Pb zircon; Reitsma, 2012; Fig. 2).
468
Detrital age information was obtained from the other sections. The upper levels of the Kellay-
469
Bélen and Hacienda Huanca sections and the deposits at the Vilcabamba and Caicay localities
470
(Figs. 4a and 4b) have similar sedimentary characteristics and maximum detrital zircon ages,
471
suggesting that they are possibly lateral equivalents of the Oqoruro section (Fig. 3). Red
472
sandstone MR26 from the Vilcabamba area yielded a maximum depositional age of 277.1 ± 7.3
473
Ma (Fig. 5b). The deposits were previously assigned to the Pennsylvanian-Permian, based on
474
the presence of thin marine intervals with brachiopods (Linoproductus cora d’Orbigny)
475
intercalated with red clastic rocks in the same region (Cárdenas et al., 1997). Therefore, we
476
conclude that the maximum detrital age of sandstone MR26 approaches the biostratigraphic
477
age. However, sandstone MR26 belongs to the final stages of the Tarma-Copacabana Group
AC C
EP
TE D
M AN U
SC
RI PT
456
23
ACCEPTED MANUSCRIPT
rather than the Mitu Group (Spikings et al., 2016). Red sandstone MR111 (Fig. 3f) is a Middle
479
Permian fluvial sandstone with a maximum depositional age of 270 ± 3.7 Ma in the Caicay
480
section. Other outcrops known in this same region studied by Carlotto et al. (2004) include a
481
200m long section of dolomite and black shale, assigned to the Middle Permian based on the
482
occurrence of brachiopods, which grades into fluvial sandstones and can probably also be
483
assigned to the Oqoruro Fm.. The marine deposits of the Copacabana Fm. in the Kellay-Bélen
484
section also appear to undergo a gradual transition towards fluvial sandstone at the top, with
485
no hiatuses or faulting observed in the field. The youngest detrital zircon within red sandstone
486
MR140, taken from the top of the Kellay-Bélen section, has a U-Pb age of 270 ± 10.6 Ma (Fig.
487
3h), and overlaps (within 2σ) with the (maximum) depositional ages for the Lower Permian sub-
488
aerial Tarma-Copacabana Group.
489
The Hacienda Huanca section in central Peru also terminates with fluvial sandstones and shales
490
(Fig. 3a), which are separated from the overlying coarse, red clastics of the Mitu Group by an
491
unconformity (Rodriguez et al., 2011). Although age data for the fluvial sandstones is lacking,
492
we tentatively assign them to the Lower Permian based on the radiometric ages obtained for
493
the fluvial sandstones in the sections discussed above.
494
On a regional scale, our data demonstrates a previously unrecognized depositional phase
495
between 281 and 270 Ma of mainly fluvial sandstones and localized volcanism. Given the
496
lithological contrast with the underlying marine deposits of the Copacabana Fm., we consider
497
this phase of subaerial deposition to constitute a stratigraphic formation. Since the only direct
498
age data was obtained from ignimbrite MR230 in the Oqoruro section, we refer to this
AC C
EP
TE D
M AN U
SC
RI PT
478
ACCEPTED MANUSCRIPT
499
depositional unit as the Oqoruro Fm., although it is likely that the volcanism observed in the
500
Oqoruro section is not representative of the entire formation.
501
5.4 Summary of new age constraints on late Paleozoic stratigraphic units
503
Table 6 summarizes the new geochronological constraints on the late Paleozoic (Permo-
504
Carboniferous) back-arc basin sedimentation of Peru. Our detrital U-Pb zircon ages
505
demonstrate that the timing of Ambo Fm. deposition corroborates the Late Mississipian age
506
estimates from plant fossils and palynology. The transition from the Ambo to the Tarma Fm.
507
occurred close to the Middle Pennsylvanian (~ 315 Ma) and reveals deepening of the basin.
508
Evidence for contemporaneous volcanism becomes gradually more pronounced throughout the
509
shallow marine deposits of the Tarma Fm., and culminates at approximately 312 - 309 Ma.
510
Continuous basin subsidence resulted in a buildup of platform carbonates of the Copacabana
511
Fm. in a depositional environment that remained stable from remained stable until ~ 281 Ma.
512
Our data highlights the presence of a previously unrecognized phase of deposition between 281
513
and 270 Ma of mainly fluvial sandstones and localized volcanism, which we named ´Oqoruro
514
Formation´. This sedimentary succession was previously incorrectly assigned to the so-called
515
Mitu Group, which commenced in the Middle Triassic (Spikings et al., 2016).
516
5.5 Correlation between the Oqoruro and Ene Formations
517
The hypersaline, organic-rich black shales of the restricted marine Ene Fm., exposed in the
518
subandean fold and thrust belt and buried in the foreland basin (Fig. 1), are considered to be
519
one of the major source rocks for Peruvian hydrocarbons (Mathalone and Montoya, 1995). The
520
Ene Fm. is observed to conformably overlie the Copacabana Fm. in north-eastern Peru (Azcuy
AC C
EP
TE D
M AN U
SC
RI PT
502
25
ACCEPTED MANUSCRIPT
and Di Pasquo, 2005; Martinez et al., 2003; Mathalone and Montoya, 1995), and was deposited
522
during shallowing of the basin. There is confusion in the literature about the relationship
523
between the Ene Fm. and the sedimentary rocks that crop out in the southern Peruvian Eastern
524
Cordillera. Some authors have suggested that the Ene Fm. pre-dates the Mitu Group and is
525
separated from it by an unconformable contact (Carlotto et al., 2010; Rosas et al., 2007), while
526
others consider it equivalent to the older part of the Mitu Group (Sempere et al., 2002). A
527
combination of the U-Pb zircon data discussed in this manuscript, and age data reported by
528
Spikings et al. (2016) for the Mitu Group sheds light on this discussion. By dating the base of the
529
Mitu Group at four different locations in central and south-eastern Peru, Spikings et al. (2016)
530
have demonstrated that deposition of the Mitu Group did not start until the Middle Triassic
531
(~240 Ma). Age data from this study show that the Tarma-Copacabana Group ends with
532
deposition of fluvial sandstones (Oqoruro Fm), and occasional volcanism from 281 to 270 Ma.
533
These sedimentary units were previously assigned to the Mitu Group. The subaerial deposits of
534
the Oqoruro Fm. reveal a retreat of the Copacabana sea to the subandean region by the end of
535
the Lower Permian. The Ene Fm., that conformably overlies the Copacabana Fm., also marks a
536
marine regression. Although direct age data for the Ene Fm. is lacking, it could very well be a
537
time equivalent to the Oqoruro Fm..
SC
M AN U
TE D
EP
AC C
538
RI PT
521
539
5.6 Permo-Carboniferous geodynamic evolution
540
Figure 9 illustrates three time slices for the Permo-Carboniferous paleogeographic evolution of
541
Peru at approximately 330 Ma, 310 Ma and 270 Ma. Both the present-day margin and late
542
Paleozoic Peruvian margin are indicated. The latter does not include the Arica bend, which may
ACCEPTED MANUSCRIPT
have formed during the Paleogene (Arriagada et al., 2008). Also, significant Late Mesozoic and
544
Cenozoic subduction erosion has modified the coastline, resulting in the present morphology
545
(Clift et al., 2003; Stern, 2011).
546
5.6.1 Mississippian
547
Permo-Carboniferous subduction was active along the entire length of the Peruvian margin
548
(Cawood, 2005, Chew et al., 2008, Miskovic et al., 2009; Reitsma, 2012). However, the
549
abundance of magmatism varies significantly when comparing the southern and northern
550
Eastern Cordillera. Smaller volumes of volcanic rocks are recorded in the sedimentary record of
551
the Ambo Fm. in southern Peru, whereas intrusions and volcanic rocks are restricted to a
552
narrow zone centred along the axis of the present-day Eastern Cordillera in northern and
553
central Peru (Fig. 9a). There, Carboniferous granitoids were emplaced in a back-arc setting, as
554
defined by their chemical composition, extensional tectonic setting and distance to the inferred
555
paleo-trench (Reitsma, 2012). Serpukhovian and Bashkirian ages were established in the
556
southern Eastern Cordillera, for part of the Machu Picchu Batholith (324.1 ± 5.3 Ma – 320.1 ±
557
1.8 Ma; Miskovic et al., 2009; Reitsma, 2012; Fig. 2). These intrusives show a similar
558
geochemical signature as the magmatic rocks in the Eastern Cordillera of northern Peru. Apart
559
from these intrusion ages, so far only detrital Mississippian age data for volcanism were found
560
in both south-eastern and south-western Peru (this study; Boekhout et al., 2013a). We
561
obtained geochemical data from one lava flow of the Ambo Fm. (Figs. 7 and 8), which also
562
shows a similar geochemical signature as reported for the lavas in the northern Eastern
563
Cordillera (Reitsma, 2012).
AC C
EP
TE D
M AN U
SC
RI PT
543
27
ACCEPTED MANUSCRIPT
Integrating all available data on Mississippian sedimentation in southern Peru, it can be
565
concluded that the present-day Eastern Cordillera of southern Peru was not experiencing the
566
same amount of extension during deposition of the Ambo Fm. as the Eastern Cordillera in
567
northern and central Peru (Fig. 9a). Variations in sedimentation and the volumes of preserved
568
magmatism throughout the present-day Eastern Cordillera of Peru suggest there was increased
569
extension in the northern half of Peru. Mississippian detrital zircon grains from sandstone
570
MR98 from the Ambo Fm. suggests reworking of a contemporaneous volcanic source similar to
571
dacitic tuff MR143 (Fig. 7). The small percentage of Carboniferous zircon grains in sandstone
572
MR144 of the Kellay-Bélen section (< 8%; Fig. 5b) indicates that there was limited volcanic
573
material available to be reworked in this region, or at least that limited material was preserved.
574
Similarly, Mississippian zircon grains form a subordinate population in the sandstones of the
575
Yamayo Group (Boekhout et al., 2013a). Detrital zircon grains from both the Yamayo Group and
576
the Ambo Fm. do show similar εHfi values, and therefore they possibly had similar sources (fig.
577
6). The presence of air fall deposits with similar εHfi isotopic values in both the Coastal and
578
Eastern Cordillera of southern Peru could suggest that these two locations were part of the
579
same sedimentary basin (Boekhout et al., 2013b).
SC
M AN U
TE D
EP
AC C
580
RI PT
564
581
5.6.2 Pennsylvanian
582
The transition from the Ambo Fm. to the Tarma-Copacabana Group at approximately 315 Ma
583
and is marked by a marine transgression that coincides with a global rise in sea level (Haq and
584
Schutter, 2008). The plutonic record in northern Peru on the other hand continues into the
585
Pennsylvanian (323 – 299 Ma) without any noticeable change in petrological signature
ACCEPTED MANUSCRIPT
(Miskovic et al., 2009). There is an increase of reworked volcanic material in the Tarma-
587
Copacabana Group compared to the Ambo Fm. in south-eastern Peru (Dalmayrac et al., 1980;
588
Laubacher, 1978). Volcanic activity was most pronounced at the end of the Lower
589
Pennsylvanian, giving rise to dacitic tuffs (e.g. MR143; 312.1 ± 0.3 Ma) that are now exposed
590
along the shores of Lake Titicaca, and rhyodacites and rhyolites in the Sacred Valley (e.g. MR29,
591
MR32, MR208; 309 Ma). This increase in volcanism in south-eastern Peru coincides with
592
migmatisation, granitoid plutonism and deformation at 312.9 ± 3 Ma in central Peru (Chew et
593
al., 2007). Interpretation of this tectono-thermal event coincides with the onset of the Early
594
Gondwanide Orogeny that occurred as a consequence of the assembly of Pangaea (e.g.
595
Cawood, 2005). Closure of the Rheic Ocean between Gondwana and Laurussia may have driven
596
increased convergence rates between the eastern Panthallasic Ocean and western Gondwana.
597
The abrupt change from limestone to conglomerate in the Hacienda Huanca section (Fig. 3a),
598
located 80 kilometre north-west of the migmatites studied by Chew et al., 2007, could be the
599
result of eroding relief that formed during this ca. 315 Ma tectonothermal event. The Early
600
Gondwanide orogeny, that is recognized in the Huánuco–La Unión and Tarma–La Merced
601
sectors of the Eastern Cordillera (c. 315 Ma; Chew et al., 2016), is contemporaneous with the
602
high-pressure, low-temperature Toco tectonic event that folded the Sierra del Tigre turbidites
603
in northern Chile (Bahlburg and Breitkreuz, 1991), with an upper age limit provided by the
604
emplacement of c. 310–290 Ma plutons into the folded turbidites (Bahlburg and Hervé, 1997).
605
However, the temporal evolution of the basin which hosts the Tarma-Copacabana Group is
606
marked by a gradual decrease in siliciclastic detritus at Pongo de Mainique (Azcuy et al., 2002),
607
and an unchanged depositional environment is observed at Kellay-Bélen (Fig. 3h). This implies
AC C
EP
TE D
M AN U
SC
RI PT
586
29
ACCEPTED MANUSCRIPT
that depo-centres located further afield were not disturbed by this tectonothermal event,
609
which is best expressed in central Peru in the Late Carboniferous (Fig. 9b).
610
The continuous build-up of platform carbonates may reflect basin subsidence due to flexure of
611
the crust, as a consequence of deformation. The continuous sea-level rise throughout the
612
Pennsylvanian (Haq and Schutter, 2008) renders it difficult to resolve the effects of either
613
process.
SC
RI PT
608
614
5.6.3 Permian
616
The newly described Oqoruro (this study) and Ene Formations (if coeval deposition is assumed,
617
as discussed in section 5.5) collectively reveal a shift from marine to continental depositional
618
environment with respect to the preceding Copacabana Fm. Emersion of the region of the
619
Eastern Cordillera and retreat of the epeiric sea to the sub-Andean region cannot be explained
620
by a global sea level low (Haq and Schutter, 2008). Instead, basin emersion coincides with a
621
major pulse of plutonism in south-eastern Peru (Figs. 2 and 9c; Reitsma, 2012). Early Permian
622
plutons in the Machu Picchu Inlier and the Cordillera de Andahuaylas (Fig. 2) are calc-alkaline,
623
metaluminuous and peraluminious gabbros to alkali granites (Reitsma, 2012). Kemp et al.
624
(2009), and Collins and Richards (2008) observed granitoids with similar geochemical signatures
625
in incipient back-arcs. Lower Permian alkaline granitoids and lava flows with an intraplate
626
signature, that could suggest continental rifting, have not been detected (Fig. 8; Reitsma, 2012).
627
The U-Pb ages and εHfi values of some of the Early Permian detrital zircon grains overlap with
628
the plutonic rocks exposed in the Machu Picchu Inlier (Fig. 6), indicating a possible source
629
region.
AC C
EP
TE D
M AN U
615
ACCEPTED MANUSCRIPT
The plutons were emplaced in an extensional back-arc setting leading to lithospheric thinning
631
and resultant doming of the crust. This doming resulted in the emersion of the Tarma-
632
Copacabana basin in the Eastern Cordillera and retreat of the epicontinental sea to the present-
633
day foreland basin (Fig. 9c) where the Ene Fm. accumulated under restricted marine conditions.
634
Considering the late Paleozoic metamorphic event at c. 260 defined in the northern and central
635
eastern Cordillera of Peru (Chew et al., 2016), the Oqoruro might well be the southern Peruvian
636
sedimentary expression of this Gondwanide orogenic phase. Late Gondwanide (c. 260 Ma)
637
metamorphism in the Eastern Cordillera of Peru is identified in the Huaytapallana Complex (in
638
the southern portions of the Maraynioc–Marairazo massif, the Huaytapallana massif, and the
639
north part of the Huaytapallanakaru massif). This high-grade metamorphic event is
640
contemporaneous with a Late Permian deformation phase that truncates the Copacabana
641
Group below the overlying 240–217 Ma Mitu Group (Chew et al., 2016; Rosas et al., 2007). Late
642
Gondwanide metamorphism in the Eastern Cordillera of Peru is broadly contemporaneous with
643
the mid-Permian San Rafael event (Bahlburg and Herve, 1997 and Ramos, 2000). The San
644
Raphael event is marked by intense folding and thrusting, resulting in a pronounced angular
645
unconformity between Late Carboniferous to Early Permian turbidites and the extensive
646
Permo-Triassic Choiyoi Volcanics in Argentina and Chile (Kay et al., 1989; Ramos, 2000;Ramos
647
and Aleman, 2000; Chew et al., 2016).
648 649
In summary, the evolution of the marginal basins of the Proto-Andean margin reflects changes
650
subduction parameters in a long-lived Paleozoic accretionary orogeny. The two phases of
651
Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260 Ma are reflected in two
652
major facies changes in the sedimentary environment of southern Eastern Peru. Interestingly,
AC C
EP
TE D
M AN U
SC
RI PT
630
31
ACCEPTED MANUSCRIPT
the Hf data obtained in this study on detrital and volcanic zircons also show both the Late as
654
well as the Early Gondwanide events. Hf isotopic values on zircon can be used as a tool to trace
655
episodes of crustal growth through time along the Peruvian (Boekhout et al., 2013b). The
656
interpretation of the Hf isotopic data on zircon is that of a correlation with trends in isotope v.
657
time space; extensional geodynamic settings see excursions to more primitive Hf isotopic
658
compositions, and compressional settings see excursions to more evolved Hf isotopic
659
compositions (Fig. 6).
SC
RI PT
653
661
M AN U
660
6. Conclusions
1. U-Pb zircon dates from the Ambo Formation corroborate stratigraphic age estimates
663
obtained from fossils and palynology, and show initiation in the Early Mississippian in
664
western Bolivia, and terminated in the Middle Pennsylvanian (~ 315 Ma).
TE D
662
2. The Mississippian back-arc basin of southern Peru experienced less extension during
666
deposition of the Ambo Formation than the Eastern Cordillera in north and central Peru.
667
3. The transition from the Ambo Formation to the Tarma Formation reveals deepening of
668
the basin. Evidence for volcanism becomes gradually more pronounced and culminated
669
at ~312 - 309 Ma, temporally correlating with the onset of the Early Gondwana Orogeny
671 672
AC C
670
EP
665
(~315 Ma). Erosion of the newly created relief gave rise to the initiation of deposition of coarse-grained clastic rocks in central Peru. Continuous subsidence in more distal basins resulted in an accumulation of platform carbonates of the Copacabana Formation.
673
4. Our data demonstrates a previously unrecognized depositional phase of mainly fluvial
674
sandstones and localized volcanism between 281 – 270 Ma. We refer to this phase of
ACCEPTED MANUSCRIPT
subaerial deposition as the Oqoruro Formation. This sedimentary succession was
676
previously miss-assigned to the Mitu Group, which has recently been constrained to 245
677
– 220 Ma (Spikings et al., 2015). The Oqoruro Formation may have been
678
contemporaneous with the Ene Formation because it conformably overlies the
679
Copacabana Formation, and reveals a marine regression.
RI PT
675
5. Late Paleozoic paleoenvironmental changes in the back-arc basins along the western
681
margin of Gondwana of southern Peru are contemporaneous with northern Peru,
682
Argentina and Chile. The evolution of the back-arc basins of the Proto-Andean margin
683
reflects changes subduction parameters in a long-lived Paleozoic accretionary orogeny.
684
The two phases of Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260
685
Ma are reflected in two major facies changes in the sedimentary environment of
686
southern Eastern Peru, and can also be recognised in the Hf isotopic record.
TE D
M AN U
SC
680
Figure captions
688 689 690
Figure 1. Map of Peru showing major tectonic features and Carboniferous-Permian sedimentary and plutonic units, which are described in the text. The study locations are labelled. The green rectangles highlight the regions shown in Figures 2 and 4a.
691 692
Figure 2. Geological map of the study area in south-eastern Peru. Study locations are labeled and the green rectangle shows the region that was studied in detail.
693 694 695 696 697 698 699
Figure 3. Stratigraphic sections through the Ambo Fm. and Tarma-Copacabana groups (for locations see Figs. 1 and 2). (a) Hacienda Huanca section, Cerro de Pasco (after Rodriguez et al., 2011). (b) Vilcabamba section, Machu Picchu Inlier. (c). Ollantaytambo section, Sacred Valley. (d) Oqoruro section, Sacred Valley (after Panca, 2010). (e) Pisac section, Sacred Valley. (f) Caicay section, Sacred Valley. (g) Mamuera section, Sicuani. (h) Kellay-Bélen section, Lake Titicaca (modified after Iannuzzi et al., 1998). Stars indicate locations of analysed samples. Note that sections are not drawn to the same vertical scale.
700 701 702 703
Figure 4. Zoomed maps of the field work areas indicated in green squares in Figs. 1 and 2. a) Geological map of the Cerro de Pasco area indicating the location of Hacienda Huanca section. b) Geological map of the Sacred Valley indicating the location of the Ollantaytambo, Pisac, Oqoruro and Caicay sections (indicated in yellow). For legend see Fig. 2.
AC C
EP
687
33
ACCEPTED MANUSCRIPT
Figure 5. U-Pb zircon geochronology of detrital and magmatic zircon grains from late Paleozoic sequences in southcentral eastern Peru (all plots show LA-ICP-MS data, except 5i, which was measured using CA-ID-TIMS). The data is discussed in order of sample location, from NE to SW. Kernel density curves are shown in the case of detrital zircons, n = number of concordant grains plotted. Data from magmatic rocks is shown in Concordia space. Ellipses are 2 sigma and data points demonstrating inheritance are not plotted. (a) Kernel-density plot of concordant zircon U-Pb data of white sandstone GR6-0511, Hacienda Huanca section. (b) Red sandstone MR26, Vilcabamba section. (c) Concordia plot, rhyolite MR29, Ollantaytambo section, analyses used in weighted mean calculation indicated by black ellipses. (d) Concordia plot, Ignimbrite MR230, Oqoruro section. (e) Kernel-density curve of white sandstone MR84, near Pisac. (f) Kernel-density curve of red sandstone MR111, Caicay section. (g) Kernel-density curve of yellow sandstone MR98, Mamuera section. (h) Kernel-density curve of white sandstone MR144, Kellay-Bélen section. (i) ID-TIMS data from dacitic ash MR143 represented in a concordia diagram, Kellay-Bélen section. Black bold ellipse indicates age of the youngest concordant zircon grain. (j) Kernel-density curve of red sandstone MR140.
717 718 719 720 721 722 723
Figure 6. Hf isotopic results from Permo-Carboniferous volcanic and detrital zircon grains. Two grains with significantly lower εHfi values fall outside of the figure (see supplementary Table 2). Red symbols represent volcanic zircon grains, grey and blacks symbols are detrital zircon grains from this study, and dark blue diamonds are detrital grains from the Coastal Cordillera of southern Peru (Yamayo Group; Boekhout et al., 2013b). Dotted fields represent εHfi values of Carboniferous and Permian plutonic rocks in south-east Peru (data from Reitsma, 2012). The timing of the Late and Early Gondwanide Orogeny are highlighted by grey fields. CHUR = Chondritic Uniform Reservoir.
724 725 726 727 728
Figure 7. Whole rock geochemistry for volcanic samples of the Ambo, Tarma and Oqoruro Fms plotted on the rock type discrimination diagram of Winchester and Floyd (1977) based on immobile elements. Numbers in graph refer to the following sample names. Oqoruo Fm.: (1) MR230; (2) MR173; Tarma Fm.: (3) MR208; (4) MR29; (5) MR32; (6) MR143; Ambo Fm.: (7) GR6-0311. Com/Pant = Comendite Pantellerite; TrachyAnd = Trachy Andesite; Bsn/Nph= Basanite Nephelinite.
729 730 731 732
Figure 8. Whole rock geochemistry for volcanic rocks from the Ambo, Tarma and Oqoruro Fms. (a) Trace elements normalized to primitive mantle values and (b) REE normalized to chondritic values from Sun and McDonough (1989). Numbers in graph refer to the following sample names. Oqoruo Fm.: (1) MR230; (2) MR173; Tarma Fm.: (3) MR208; (4) MR29; (5) MR32; (6) MR143; Ambo Fm.: (7) GR6-0311.
733 734 735 736 737 738 739 740 741
Figure 9. Paleogeographic reconstruction of Peru during the Carboniferous and Early Permian. The paleo-Peruvian margin (Pre-Andean Orogeny; indicated by a thick black line) does not show the Arica bend, which formed later during the Andean Orogeny (Arriagada et al., 2008). Back-arc magmatism is based on data from (Miskovic et al., 2009; Chew et al., 2007; Reitsma, 2012 and this study). The distribution of sedimentary units in eastern Peru is based on this work and data from Mathalone and Montoya (1995). The Yamayo Group on the Arequipa Terrane is modified after Boekhout et al. (2013a). No Permo-Carboniferous data are available for the white regions. a) Mississippian paleogeography. b) Pennsylvanian paleogeography, clastic sediments indicate region that was tectonically disturbed at ~312 Ma. c) Lower Permian paleogeography.
742
Table captions
743 744 745 746 747 748 749
Table 1: Overview of U-Pb ages and Hf isotope data of A. zircons in magmatic rocks and B. detrital U-Pb zircons
AC C
EP
TE D
M AN U
SC
RI PT
704 705 706 707 708 709 710 711 712 713 714 715 716
a – number of analyses included in weighted mean calculation over total number of analyses. Discordant analyses, xenocrystic cores and analyses demonstrating slight inheritance or Pbloss are not used in the weighted mean. b – LA: Laser Ablation ICP-MS; TIMS: Isotope Dilution Thermal Ionization MS. c – number of concordant analyses used in probability-density over total number of analyses.
ACCEPTED MANUSCRIPT
750 751 752
d – T/C: Tarma or Copacabana Fm.
753
Acknowledgements
754 755 756 757 758 759
We first of all want to express our gratitude two the reviewers of this manuscript for their input and comments. We thank Fernando Panca for his assistance in the field in the Sacred Valley, INGEMMET for the logistical support in Peru and members of the geochemistry and geochronology groups of the universities of Geneva and Lausanne for their analytical support. We would also like to express our gratitude to C. Heineke for her comments and suggestions. This project was funded by Swiss SNF projects 200020_116572 and 200020_124332.
AC C
EP
TE D
M AN U
SC
RI PT
Table 6. Summary of geochronological results of the late Paleozoic sedimentary units of southern Peru.
35
ACCEPTED MANUSCRIPT
References Arriagada, C., Roperch, P., Mpodozis, C., and Cobbold, R., 2008. Paleogene building of the Bolivian Orocline: Tectonic restoration of the central Andes in 2-D map view. Tectonics 27, TC6014.
RI PT
Azcuy, C.L., and Di Pasquo, M., 2005, Early Carboniferous palynoflora from the Ambo formation, Pongo de Mainique, Peru: review of palaeobotany and palynology 134, 153-184. Azcuy, C.L., Di Pasquo, M., and Valdivia Ampuero, H., 2002, Late Carboniferous miospores from the Tarma Formation, Pongo de Mainique, Peru: review of palaeobotany and palynology 118, 1-28. Bahlburg, H and Herve, F., 1997. Geodynamic evolution and tectonostratigraphic terranes of northwestern Argentina and northern Chile. Geological Society of America Bulletin, 109, 869–884.
M AN U
SC
Bahlburg, H., Vervoort, J.D., DuFrane, S.A., Carlotto, V., Reimann, C.R., and Cárdenas, J., 2011, The U-Pb and Hf isotope evidence of detrital zircons of the Ordovician Ollantaytambo Formation, southern Peru, and the Ordovician provenance and paleogeography of southern Peru and northern Bolivia: Journal of South American Earth Sciences 32, 196-209. Blichert-Toft, J. & Albarède, F. 1997. The Lu–Hf isotope geochemistry of chondrites and the evolution of the mantle–crust system. Earth and Planetary Science Letters 148, 243–258. Boekhout, F., Sempere, T., Spikings, R., and Schaltegger, U., 2013a. Late Paleozoic to Jurassic chronostratigraphy of coastal southern Peru: temporal evolution of sedimentation along an active margin: Journal of South American Earth Sciences 47, 179-200.
TE D
Boekhout, F., Roberts, N.M.W., Gerdes, A., Schaltegger, U., 2013b. A Hf-isotope perspective on continent formation in the south Peruvian Andes. Geological Society of London, Special Publications 389, 305–321. Bouvier, A., Vervoort, J., Patchett, P.J., 2008. The Lu-Hf and Sm-Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters 273, 48-57.
EP
Cárdenas, J., Carlotto, V., Romero, D., Jaimes, F., and Valdivia, W., 1997. Geología de los Cuadrángulos de Chuanquiri y Pacaypata. Hojas 26-p y 27-p., Carta Geolólogica Nacional, 69, Lima-Perú, INGEMMET. Cardona, A., Cordani, U.G., Ruiz, J., Valencia A., Armstrong, R., Chew, D.M., Nutman, A., and Sanchez, A.W., 2009. U-Pb Zircon geochronology and Nd Isotopic Signatures of the Pre-Mesozoic metamorphic basement of the Eastern Peruvian Andes: Growth and Provenance of a Late Neoproterozoic to Carboniferous accretionary orogen on the northwest margin of Gondwana. The journal of Geology 117, 285-305.
AC C
760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810
Carlotto, V., Gill, W., Cárdenas, J. and Chávez, R., 1996. Geología de los Cuadrángulos de Quillabamba y Machupicchu. Hojas 26r-q y 27-q., Carta Geolólogica Nacional, 127, Lima-Perú, INGEMMET. Carlotto, V., Cárdenas, J., Romero, D., Valdivia, W. and Tintaya, D., 1999. Geología de los Cuadrángulos de Urubamba y Calca. Hojas 27r-p y 27-s., Carta Geolólogica Nacional, 65, Lima-Perú, INGEMMET. Carlotto , Cardenas, J., Carlier, G., Diaz-Martinez, E., Cerpa, L., Valderrama , and Robles, T., 2004. Evolucion Tectonica y sedimentaria de la cuenca Mitu (Permo-Triasico) de la region de Abancay-Cusco-Sicuani (sur de Peru), XII Congreso Peruano de Geologia: Lima, Peru, Sociedad Geologica del Peru, 412-415.
ACCEPTED MANUSCRIPT
Carlotto , Cárdenas, J., Reitsma, M., and Rodriguez, R., 2010. Las edades de la formación Ene y del Grupo Mitu: Propuesta de cambios en la cartografía regional: Abancay-Cusco-Sicuani, XV Congreso Peruano de Geología, Cusco, Peru, 830-833. Cawood, A., 2005, Terra Australis Orogen: Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic: Earth Science Reviews 69, 249-279.
RI PT
Cawood, P.A., Buchan, C, 2007. Linking accretionary orogenesis with supercontinent assembly (vol 82, pg 217, 2007). Earth-Science Reviews 85, p.82 Chew, D.M., Schaltegger, U., Kosler, J., Whitehouse, M.J., Gutjahr, M., Spikings, R.A., and Miskovic, A., 2007. U-Pb geochronologic evidence for the evolution of the Gondwanan margin of the north-central Andes: Geological Society of America Bulletin 119, 697-711.
M AN U
SC
Chew, D.M., Magna, T., Kirkland, C.L., Miskovic, A., Cardona, A., Spikings, R., and Schaltegger, U., 2008. Detrital zircon fingerprint of the Proto-Andes: Evidence for a Neoproterozoic active margin? Precambrian Research, 167, 186-200. Clift, D., and Hartley, A.J., 2007. Slow rates of subduction erosion and coastal underplating along the Andean margin of Chile and Peru. Geology 35, 503-506. Chew, D.M., Pedemonte, G., and Corbett E., 2016. Proto-Andean evolution of the Eastern Cordillera of Peru. Gondwana Research 35, 59-78. Clift, D., Pecher, I., Kukowski, N., and Hampel, A., 2003. Tectonic erosion of the Peruvian forearc, Lima basin, by subduction and Nasca Ridge collision. Tectonics 22, 1-16.
TE D
Cohen, K.M., Finney, S.C., Gibbard, P.L. and Fan, J-X., 2013; updated). The ICS International Chronostratigraphic Chart. Episodes 36, 199-204. Collins, W.J., and Richards, S.W., 2008. Geodynamic significance of S-type granites in corcum pacific orogens. Geology 36, 559-562.
EP
Chu, N.C., Taylor, R.N., Chavagnac, V., Nesbitt, R.W., Boella, R.M., Milton, J.A., German, C.R., Bayon, G., and Burton, K., 2002. Hf isotope ratios analyses using multi-collector inductively coupled plasma mass spectrometry: An evaluation of isobaric interference corrections: Journal of Analytical Atomic Spectrometry 17, 1567-1574. Dalmayrac, B., Laubacher, G., and Marocco, R., 1980. Caractères généraux de l'evolution géologique des Andes péruviennes, Géologie des Andes péruviennes 122. Paris, ORSTOM, 501.
AC C
811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860
Díaz Martínez, E., 1991. Litoestratigrafía del Carbonífero del Altiplano de Bolivia. Revista Técnica de Yacimientos Petroliferos Fiscales Bolivianos 12, 295– 302. Doubinger, J., and Marocco, R., 1981. Contenu palynologique du groupe Copacabana (Permien Inférieur et Moyen) sur la bordure sud de la Cordillère de Vilcabamba, région de Cuzco (Pérou). International Journal of Earth Sciences 70, 1086-1099. Gerdes, A., and Zeh, A., 2006. Combined U-Pb and Hf isotope LA-(MC-)ICP-MS analyses of detrital zircons: Comparison with SHRIMP and new constraints for the provenance and age of an Armorican metasediment in central Germany. Earth and Planetary Science Letters 249, 47-61.
37
ACCEPTED MANUSCRIPT
Gerdes, A., and Zeh, A., 2009. Zircon formation versus zircon alteration - new insights from combined U-Pb and LuHf in-situ LAICP-MS analyses, and consequenses for the interpretation of Archean zircon from the Central Zone of the Limpopo Belt. Chemical Geology 261, 230-243. Haq, B. U., and Schutter, S.R.,schre 2008. A chronology of Paleozoic sea-level changes. Science 322, 64-68.
RI PT
Hessler, A. M., and Fildani, A., 2015. Andean forearc dynamics, as recorded by detrital zircon from the Eocene Talara Basin, northwest Peru. Journal of Sedimentary Research 85, 646-659. Iannuzzi, R., and Pfefferkorn, H.W., 2002. A Pre-glacial, warm-temperate floral belt in Gondwana (Late Visean, Early Carboniferous). Palaios 17, 571-590.
SC
Iannuzzi, R., Pfefferkorn, H.W., Diaz-Martinez, E., Alleman, V., and Suarez-Soruco, R., 1998. La flora eocarbonifera de la formacion Siripaca (grupo Ambo, Bolivia) y su correlacion con la flora de Paracas (Grupo Ambo, Peru). Boletin de la Sociedad Geologica del Peru 88, 39-51.
M AN U
Kay, S.M. Ramos, V.A., Mpodozis, C., Sruoga, P., 1989. Late Paleozoic to Jurassic silicic magmatism at the Gondwana margin: analogy to the middle Proterozoic in North America? Geology 17, 324–328. Kemp, A.I.S., Hawkesworth, C.J., Collins, W.J., Gray, C.M., and Blevin, L., 2009. Isotopic evidence for rapid continental growth in an extensional accretionary orogen: The Tasmanides, eastern Australia. Earth and Planetary science letters 284, 455-466. Laubacher, G., 1978. Geologie des Andes Peruviennes. Géologie de la Cordillère orientale et de l'Altiplano au nord et nord-ouest du lac Titicaca, Pérou. Paris, O.R.S.T.O.M., 217. Marocco, R., 1978, Géologie des Andes Péruviennes: Paris, O.R.S.T.O.M.
TE D
Martinez, E., Fernandez, J., Calderon, Y., and Galdos, C., 2003. Reevaluation defines attractive areas in Peru's Ucayali-Ene basin. Oil & Gas Journal 10, 32-38. Mathalone, J.M.P., and Montoya, M., 1995. Petroleum geology of the Sub-Andean basins of Peru, in Tankard, A., Suarez, R., and Welsink, H.J., eds., Petroleum basins of South America, American Association of Petroleum Geology Memoir 62, 423-444.
EP
Mégard, F., 1978. Etude géologique des Andes du Pérou central. Paris, O.R.S.T.O.M. Miskovic, A., Spikings, R., Chew, D.M., Kosler, J., Ulianov, A., and Schaltegger, U., 2009. Tectonomagmatic evolution of Western Amazonia: Geochemical characterization and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran granitoids. Geological Society of America Bulletin 121, 1298-1324.
AC C
861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913
Panca, F., 2010. The late Permian - lower Triassic Mitu Group, SE of Cusco (Peru). Field relations, volcanosedimentary facies and geochemistry. Freiberg, Technische Universität Bergakademie. Pankhurst, R.J., Rapela, C.W., Saavedra, J., Baldo, E., Dahlquist, J., Pascua, I., Fanning, C.M., 1998. The Famatinian magmatic arc in the central Sierras Pampeanas: an Early to Mid-Ordovician continental arc on the Gondwana margin. In: Pankhurst, R.J., Rapela, C.W. (Eds.), The Proto-Andean Margin of Gondwana. London, Special Publications, Geological Society, pp. 343–367. Pearce, N.J.G., Perkins, W.T., Westgate, J.A., Gorton, M.P., Jackson, S.E., Neal, C.R., and Chenery, S.P., 1997. A compilation of new and published major and trace element data for NIST SRM 610 and NIST SRM 612 glass reference materials. Geostandards Newsletter 21, 115-144.
ACCEPTED MANUSCRIPT
Pfefferkorn, H.W., and Alleman, V., 2001. The Carboniferous of Paracas - A synthesis. In: XI Congreso Peruano de Geologia, Lima, 43. Pfefferkorn and Alleman 2002
RI PT
Pino, A., Sempere, T., Jacay, J., and Fornari, M., 2004. Estratigrafia, Paleogeografia y paleotectonica del intervalo paleozoico superior - cretaceo inferior en el area de Mal Paso - Palca (Tacna). In: Jacay, J., and Sempere, T., eds., Nuevas contrubuciones del IRD y sus contrapartes al conocimiento geologico del sur del Peru, 5, Lima, Sociedad geologica del Peru, 15-44. Ramos, V.A., 2000.The Southern Central Andes. In: Cordani,U.G., Milani, E.J., Thomaz Filho, A.,x Campos, D.A. (Eds.). Tectonic Evolution of South America. 31st International Geological Congress, Rio de Janeiro, 561–604.
SC
Ramos, V.A and Aleman, A. Tectonic evolution of the Andes. In: Cordani,U.G., Milani, E.J., Thomaz Filho, A.,x Campos, D.A. (Eds.). Tectonic Evolution of South America. 31st International Geological Congress, Rio de Janeiro, 635-685.
M AN U
Reitsma, M.J., 2012. Reconstructing the Late Paleozoic: Early Mesozoic plutonic and sedimentary record of southeast Peru: Orphaned back-arcs along the western margin of Gondwana, University of Geneva (Ph.D. Thesis). Rodriguez, R., Cueva, E., and Carlotto, V., 2011. Geología del cuadrángulo de Cerro de Pasco (22-k), Carta Géologica Nacional, 144, INGEMMET, 164. Romero, D., Valencia, K., Alarcόn, P., Ramos, V.A., 2013. The offshore basement of Peru: evidence for different igneous and metamorphic domains in the forearc. Journal of South American Earth Sciences 42, 47-60.
TE D
Rosas, S., Fontboté, L., and Tankard, A., 2007. Tectonic evolution and paleogeography of the Mesozoic Pucara Basin, central Peru. Journal of South American Earth Sciences 24, 1-24. Schaltegger, U., Brack, P., Otcharova, M., Peytcheva, I., Schoene, B., Stracke, A., Marocchi, M., and Bargossi, G., 2009. Zircon and titanite recording 1.5 million years of magma accretion, crystallization and initial cooling in a composite pluton (southern Adamello botholith, northern Italy). Earth and Planetary Science Letters 286, 208-218. Scherer, E., Münker, C. & Mezger, K. 2001. Calibration of the lutetium–hafnium clock. Science, 293, 683–687.
EP
Schoene, B., Latkoczy, C., Schaltegger, U., and Gunther, D., 2010. A new method integrating high-precision U-Pb geochronology with zircon trace element analysis (U-Pb TIMS-TEA). Geochimica et Cosmochimica acta 74, 71447159.
AC C
914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964
Sempere, T., Carlier, G., Soler, P., Fornari, M., Carlotto, V., Jacay, J., Arispe, O., Néraudeau, D., Cardenas, J., Rosas, S., and Jiménez, N., 2002. Late Permian-Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on the Andean-age tectonics. Tectonophysics 345, 153-181. Spikings, R., Reitsma, M.J., Boekhout, F. Mišković, A., Ulianov, A., Chiaradia, M., Gerdes, A., and Schaltegger, U., 2016. Characterization of Triassic Rifting in Peru and implications for the early disassembly of western Pangaea. Gondwana Research 35, 124–143. Sláma, J., Kosler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S.A., Morris, G.A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M.N., and Whitehouse, M.J., 2008. Plesovice zircon - a new natural reference material for U-Pb and Hf isotopic microanalysis. Chemical Geology, 249, 1-35.
39
ACCEPTED MANUSCRIPT
Sun, S., and McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., and Norry, M.J., eds., Magmatism in the ocean basins, Geological Society of London 42, 313-345.
RI PT
Thomas, W.A., Astini, R.A., Mueller, P.A., Gehrels, G.E., Wooden, J.L., 2004. Transfer of the argentine Precordillera terrane from Laurentia: constraints from detrital-zircon geochronology. Geology 32, 965–968. Torsvik, T.H., and Cocks, R.M., 2013. Gondwana from top to base in space and time. Gondwana Research 24, 9991030.
SC
Ulianov, A., Müntener, O., Schaltegger, U., and Bussy, F., 2012. The data treatment dependent variability of U-Pb zircon ages obtained using mono-collector, sector field, laser ablation ICP-MS. Journal of Analytical Atomic Spectrometry 27, 663-676.
M AN U
Vervoort, J. D., Patchett, P. J., Blichert-Toft, J. and Albered, F., 1999. Relationships between Lu–Hf and Sm–Nd isotopic systems in the global sedimentary system. Earth and Planetary Science Letters 168, 79–99. Winchester, J.A., and Floyd, A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology 20, 325-343. Woodhead, J. D. & Hergt, J. M., 2005. A preliminary appraisal of seven natural zircon reference materials for in situ Hf isotope determination. Geostandards and Geoanalytical Research, 29, 183–195.
TE D
Zumsprekel, CRR., Bahlburg, H., Carlotto, V., Boekhout, F., Bernt, J. and Lopez, Shirley, L., 2015. Multi-method provenance model for early Paleozoic sedimentary basins of southern Peru and northern Bolivia (13°–18°S). Journal of South American Earth Sciences, 64, 94-115.
EP
994
Stern, C.R., 2011. Subduction erosion: Rates, mechanisms, and its role in arc magmatism and the evolution of the continental crust and mantle. Gondwana Research 20, 284-308.
AC C
965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993
ACCEPTED MANUSCRIPT A.1 Methodology A.1.1 Whole rock geochemistry All geochemical analyses were carried out at the Institute of Mineralogy and Geochemistry, University of Lausanne. Seven whole rock samples were crushed and grinded using a jaw
RI PT
crusher and agate ring mill, lithium tetraborate glass discs were prepared and major and some trace elements were determined by X-ray fluorescence spectrometry (XRF) using a Philips PW 2400 spectrometer. The BHVO-1 basaltic and NIM-G granitic standard were used
SC
for accuracy control. Abundances of REE and additional trace elements (e.g. Th, U, Ta, Cs, Hf)
M AN U
were analysed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on the lithium tetraborate discs using an Elan 6100 DRC quadrupole mass spectrometer (Perkin Elmer) interfaced to a GeoLas 200M 193 nm excimer ablation system (Lambda Physik). Operating conditions of the ablation system included a 10 Hz repetition rate, 120
TE D
mm spot size and ca. 10 J/cm2 on-sample energy density. Helium was used as the carrier gas. The acquisition times for the background and the ablation interval were ca. 70 and 35 s, respectively. The SRM 612 synthetic glass standard from NIST was used for external
EP
standardisation. The average element abundances were taken from Pearce et al. (1997). Ca42
AC C
served as an internal standard. Raw data was reduced off-line, using LAMTRACE, a Lotus 1-23 spreadsheet written by Simon Jackson (Macquarie University, Australia). For each sample 3 measurements were acquired and results were then averaged.
A.1.2 Zircon U-Pb geochronology Several kilograms of rock were crushed and zircon grains were extracted from the sub-300 µm size fraction using a Wilfley table, Frantz horizontal magnetic separator with a side slope of 10° and dense liquid (di-iodomethane, ρ = 3.32 g/cm3). Zircon grains extracted from the
ACCEPTED MANUSCRIPT samples to be dated by ID-TIMS were additionally run on the Frantz horizontal magnetic separator with the side slope reduced to 2° to obtain the least magnetic zircon grains. All zircon grains selected for analysis were handpicked in ethanol using a binocular microscope.
RI PT
A.1.2.1 Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on zircon
Zircon grains were extracted from three volcanic rocks and seven sedimentary rocks and
SC
handpicked with a preference for euhedral grains for volcanic samples and a random
M AN U
population was selected for detrital samples. Zircon grains were subsequently mounted in epoxy and polished with diamond paste to expose the internal surface of the grains. 18-24 zircon grains per plutonic and volcanic sample and 79-102 zircon grains per detrital sample were mounted into epoxy resin blocks (a total of 792 for this study) and polished to obtain
TE D
flat surfaces. The zircon grains were characterized by cathodoluminescence (CL) imaging on a CamScan MV2300 SEM (Institute of Geology and Paleontology, University of Lausanne) to reveal their internal structure.
EP
Pb-U238 and Pb-U235 dates were obtained using a 193-nm excimer ablation system UP-193FX
AC C
(ESI) interfaced to an Element XR sector field, singlecollector inductively coupled plasmamass spectrometry (ICP-MS; Thermo Scientific) at the Institute of Mineralogy and Geochemistry, at the University of Lausanne. Operating conditions were similar to those described in Ulianov et al. (2012) and included a 35 µm spot size combined with a relatively low on-sample energy density of 2.2-2.3 J/cm2 and a repetition rate of 5 Hz to minimize fractionation. A GJ-1 standard zircon was used for external standardisation. The 91500 standard was measured as an unknown on a routine basis to control accuracy.
ACCEPTED MANUSCRIPT Discordant ages, inherited zircon grains and zircon grains showing signs of Pb-loss were discarded from the age calculation. For volcanic zircon grains a weighted mean age was calculated using the
206
Pb/238U ratio of analytically concordant zircon grains. U–Pb data is
206
Pb/238U ages are plotted as probability-density distributions.
RI PT
plotted on concordia diagrams as 2σ error ellipses. For detrital zircon grains concordant
A.1.2.1 Chemical abrasion-isotope dilution-thermal ionisation mass spectrometry (CA-ID-
SC
TIMS)
M AN U
Eight zircon grains from dacitic tuff MR143 were dated by CA-ID-TIMS, following the methodology described in Schoene et al. (2010). Because of the high precision of chemical abrasion ID-TIMS analyses, only the youngest concordant
206
Pb/238U date was taken as the
age of the sample (Schaltegger et al., 2009; Schoene et al., 2010). Zircon grains were
TE D
analyzed at the University of Geneva on a TRITON thermal ionization mass spectrometer using the EARTHTIME 205Pb-238U-235U tracer solution.
EP
A.1.3 Lu-Hf isotope analyses of zircon
AC C
Lu–Hf isotope analyses were performed with a Thermo-Scientific Neptune multi-collector inductively coupled plasma mass spectrometer (ICPMS) at the Goethe-University Frankfurt (GUF) coupled to a RESOlution M50 193 nm ArF Excimer (Resonetics) laser system following the method described in Gerdes and Zeh (2006, 2009). A Lu–Hf laser spot of 40 µm was drilled on top or directly next to the U–Pb laser spot. To correct for the isobaric interferences of Lu and Yb on mass 176, isotopes The
176
and a
Yb and
176
176
172
Yb,
173
Lu were calculated using a
Yb and
176
175
Lu were monitored simultaneously.
Yb/173Yb ratio of 0.796218 (Chu et al. 2002)
Lu/175Lu ratio of 0.02658 (GUF in-house value). The instrumental mass bias for Hf
ACCEPTED MANUSCRIPT isotopes was corrected using an exponential law and a 179Hf/177Hf value of 0.7325. For Yb isotopes the mass bias was corrected using the Hf mass bias of the individual integration step multiplied by a daily βHf/βYb offset factor. All zircon laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analyses were adjusted 176
Hf/177Hf ratio of 0.282160, and the reported uncertainties (2σ)
RI PT
relative to the JMC 475
were propagated by quadratic addition of the reproducibility of JMC 475 (2 standard deviations, SD = 0.0028%, n = 8) and the within-run precision of each analysis (2 standard
SC
errors, SE). The accuracy and external reproducibility of the method were verified by
material),
which yielded
176
M AN U
repeated analyses of reference zircon GJ-1, Plesovice and Temora2 (see Supplementary Hf/177Hf values of 0.282008±0.000025
(2SD, n=41),
0.0282478±0.000018 (n= 9) and 0.282675±0.000022 (n= 11), respectively. This is in perfect agreement with previously published results (Woodhead & Hergt 2005; Sláma et al. 2008;
TE D
Gerdes & Zeh 2009) and with the LA-MC-ICP-MS long-term averages of GJ-1 (0.282010±0.000025; n > 800), Plesovice (0.282478±0.000025, n> 450) and Temora2 (0.282683±0.000026; n>200) reference zircon at GUF. Initial 176Hf/177Hf values are expressed
EP
as εHf(t), which is calculated using a decay constant value of 1.867 × 10-11 yr-1 (Scherer et al.
AC C
2001), giving 176Hf/177HfCHUR,today and 176Lu/177HfCHUR,today of 0.282772 and 0.0332, respectively (Blichert-Toft & Albarède 1997). For the calculation of Hf two-stage model ages (T*DM), a 176
Lu/177HfCrust,today value of 0.0113 was used for the average continental crust, and depleted
mantle 176Lu/177HfDM,today and 176Hf/177HfDM,today values of 0.03813 and 0.283224, respectively (Vervoort et al. 1999) were used. For detailed results from Hf isotopic analyses, see the online supplementary Tables A1 and A2. For the sample MR143 Hf isotopic compositions were measured on the same volume of zircon dated by CA-IDTIMS techniques at GUF. This involves retaining the waste eluted
ACCEPTED MANUSCRIPT solution obtained from ion exchange chemistry. The dried residue was dissolved in 500 to 700 μl 2% HNO3(aq) and introduced into the plasma with an Aridus II desolvating nebulizer, and analyzed for Hf isotope composition using the same multicollector ICP-MS techniques as described above for laser ablation analyses. Data acquisition of the solution analyses lasted
RI PT
for 5 minutes per sample (55 ratios) and was performed in automatic mode, bracketing groups of 5 unknowns by JMC-475 standard measurements. Six solution aliquots of standard
AC C
EP
TE D
M AN U
SC
zircon GJ-1 were analyzed as an external control (0.282016 ± 0.000002, 2σ).
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
Table 1 ɛHfi
Location
MR29
Ollantaytambo
Tarma
13.28 72.20 rhyodacite
308.6
MR143
Kellay-Bélen
Tarma
16.09 69.04 dacite
312.14
0.29
MR230
Oqoruro
13.45 71.53 andesite
281.3
1.5
B Sample
Location
MR26
Vilcabamba
MR84
Pisac
MR98
Mamuera
MR111
CaiCay
Oqoruro
13.59 71.69 red sandstone
MR140
Kellay-Bélen
Oqoruro
16.09 69.04 red sandstone
MR144
Kellay-Bélen
Ambo
16.11 69.05 white sandstone
T/C
10.82 76.07 white sandstone
Oqoruro
Long. (°W) Rock type
Youngest zircon Age (Ma)
13.12 72.94 red sandstone
277.1
Copacabana 13.46 71.82 white sandstone Ambo
14.36 71.09 yellow sandstone
296.2
3.6
ɛHfi
low ± 2σ high ± 2σ
n
-0.5
0.7
1.1
0.6
6
Methodb LA
1/8
-4.1
0.3 -2.9
0.4
9
ID-TIMS
21 / 24
-0.7
0.7
0.6
6
LA
low ± 2σ high ± 2σ
n
Methodb LA
MSWD n / Ntot 3.1 6.6 14 / 18
ɛHfi
± 2σ 7.3
n / Ntot 56 / 79
c
1.4 ɛHfi
0.8
0.9
3.2
0.9 10
3.4 1.30 14
3.4
76 / 96
-5.9
0.8
12.1
71 / 80
-8.7
0.9 -2.9
0.7
5
LA
270.0
3.7
82 / 98
-4.8
0.6
2.9
0.7
5
LA
270.0
10.6
77 / 95
-9.0
1.0
2.2
0.9 10
LA
318.2
16.2
90 / 102 -20.4 0.6
1.4
0.7
6
LA
308.2
6.2
82 / 98
0.6 13
LA
315.2
M AN U
GR6-0511 Hd. Huanca
Formation
Lat. (°S)
Age (Ma) ± 2σ
a
RI PT
Oqoruro
Long. (°W) Rock type
SC
Formation
Lat. (°S)
Concordia
A Sample
-4.6
0.8 -2.1
TE D
Table 1: Overview of A. magmatic and B. detrital U-Pb zircon and Hf isotope data
AC C
EP
a – number of analyses used in weighted mean calculation over total of analyses done. Discordant analyses, xenocrystic cores and analyses demonstrating slight inheritance or Pb-loss are not used in the weighted mean. b – LA: Laser Ablation ICP-MS ; ID-TIMS: Isotope Dilution Thermal Ionization MS. c – number of concordant analyses used in probability-density over total of analyses done. d – T/C: Tarma or Copacabana Formation
LA
ACCEPTED MANUSCRIPT
Summary of geochronological results of the Late Paleozoic sedimentary units Unit Studied section
Tarma-Copacabana Group
Termination
Sample
315 ± 12 Ma < 318 ± 16 Ma 319 Ma prominent age mode
Paleoenvironment
Sample #
subaerial
MR98 MR144 GR6-0511
no direct dating of the onset
312.1 ± 0.3 < 308 ± 6.2 Ma
marine conditions marine conditions subaerial
309 ± 3 Ma
Oqururo Formation 218.3 ± 1.5 Ma
subaerial & volcanism subaerial
AC C
EP
TE D
M AN U
SC
< 270 ± 11 Ma
RI PT
Ambo Formation
Onset
GR6-0511 MR29
MR230
ACCEPTED MANUSCRIPT
Table 6. Summary of geochronological results of the Late Paleozoic sedimentary units of southern Peru. Unit
Onset
Termination
Paleoenvironment
Oqoruro Formation
Kungurian (~281 Ma)
Roadian (~270 Ma)
Subaerial fluvial conditions and localized volcanism
Kungurian (~281 Ma)
Basin deepening to marine conditions
Middle Pennsylvanian (~315 Ma)
Subaerial fluvial conditions with sporadic volcanism
Tarma-Copacabana Group
AC C
EP
TE D
M AN U
SC
RI PT
Ambo Formation
Early Pennsylvanian (~315 Ma) Initiation in the Early Mississippian in western Bolivia (325-335 Ma)
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT Highlights
• •
AC C
EP
TE D
M AN U
SC
•
The Ambo Formation terminated around the Mississippian-Pennsylvanian boundary The transition from Ambo Formation to Tarma Formation represents basin deepening We describe a previously unrecognized phase of Artinskian to Roadian deposition The basin sedimentology of southern Peru reflects two Godwanide orogenic phases
RI PT
•