- Email: [email protected]
U-Pb zircon geochronology and Sr-Nd isotopic composition of the Inchope orthogneiss in Mozambique: Age constraints and petrogenetic implications
Accepted Manuscript U-Pb zircon geochronology and Sr-Nd isotopic composition of the Inchope orthogneiss in Mozambique: Age constraints and petrogenetic implications Vicente Albino Manjate PII:
S1464-343X(17)30154-1
DOI:
10.1016/j.jafrearsci.2017.03.027
Reference:
AES 2874
To appear in:
Journal of African Earth Sciences
Received Date: 5 April 2016 Revised Date:
13 February 2017
Accepted Date: 21 March 2017
Please cite this article as: Manjate, V.A., U-Pb zircon geochronology and Sr-Nd isotopic composition of the Inchope orthogneiss in Mozambique: Age constraints and petrogenetic implications, Journal of African Earth Sciences (2017), doi: 10.1016/j.jafrearsci.2017.03.027. 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.
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
U-Pb zircon geochronology and Sr-Nd isotopic composition of the
2
Inchope orthogneiss in Mozambique: Age Constraints and
3
Petrogenetic implications
4
Vicente Albino Manjate1([email protected])
5
1
RI PT
1
Instituto Nacional de Minas, Av 24 de Julho, 1895 – Maputo, Moçambique
6
SC
7
ABSTRACT
9
The Inchope orthogneiss comprises a mesoproterozoic group of variously deformed and
10
migmatised orthogneisses in the Chimoio group. This area is well known for its
11
numerous, small pegmatite deposits with cassiterite and columbite. Zircon U-Pb
12
geochronological and whole rock Sr-Nd isotope data are reported for five Inchope
13
orthogneiss samples. The zircon U-Pb data exhibit one period of crystallization between
14
1065-1053 Ma and two metamorphic ages of 956 Ma and 484 Ma. The Inchope
15
orthogneiss displays evolved Nd isotopic compositions with ɛNdi between -11.7 and -
16
13.3, 87Sr/86Sri between 0.7117 and 0.7209 and TDM values of between 2.3 and 2.4 Ga..
17
Therefore, the Inchope orthogneiss crystallized in Mesoproterozoic from the
18
paleoproterozoic metapelites along the eastern margin of the archaen Zimbabwean
19
craton. This was followed by pegmatite veins intrusions and Pan-African
20
tectonometamorphic reworking. These features are typical of S-type and calc-alkaline
21
granites in continental margin arcs.
22
Key-words: Inchope orthogneiss; U-Pb geochronology; Sr-Nd isotope data
AC C
EP
TE D
M AN U
8
1
ACCEPTED MANUSCRIPT
1. INTRODUCTION
24
The Inchope orthogneiss comprises a group of variously deformed and migmatised
25
orthogneisses in the Chimoio group (GTK, 2006). Named after Inchope village, the
26
composition of the orthogneisses varies from granodioritic to tonalitic. In type area,
27
around the Inchope village, the orthogneiss is light grey, medium-grained and only
28
slightly foliated granodioritic gneiss with random potassium feldspar phenocrysts. This
29
area is well known for its numerous, small pegmatite deposits with cassiterite and
30
columbite (LKAB, 1979). However, no resource evaluation was made. GTK (2006)
31
dated the Inchope orthogneiss by both monazite conventional and zircon SHRIMP
32
methods. Monazite yielded slightly reversely concordant age data of ~ 530 – 520 Ma.
33
SHRIMP dating, using 17 different zircon domains, yielded an age of ~ 1100 Ma. Seven
34
concordant analyses define an age of 1079±7 Ma. The discordia age formed by the U-
35
Pb data from 12 zoned zircon domains is the same as the concordia age. Three analyses
36
were carried out on high-U CL-dark rims but rejected because of high common lead
37
contents. They are believed to reflect Pan-African reworking as demonstrated by the
38
monazite age. In this paper, we report new zircon U-Pb LA-ICP-MS ages and whole
39
rock Sr±Nd isotopic data to constrain the petrogenesis of the Inchope orthogneiss and
40
discuss its implications for the Proterozoic crustal growth in central Mozambique.
42
SC
M AN U
TE D
EP
AC C
41
RI PT
23
43
44
45 2
ACCEPTED MANUSCRIPT
2. GEOLOGICAL SETTING
47
The study area is composed of intrusive rocks and supracrustal unities of the Chimoio
48
group (GTK, 2006). The intrusive rocks are the Inchope orthogneiss (P2BUig) and
49
gabbro and gabbroic rock (P2BUgb). On the other hand, the supracrustal unities are
50
represented by the mica schist and mica gneiss (P2BCch), migmatitic paragneiss
51
(P2BCmi), Monte Chissui gneiss, felsic biotite gneiss and metagranite (P2BCfg) and
52
siliclastic metasediment (P2BCss) (Fig. 1).
53
The Inchope orthogneiss comprises a group of variously deformed and migmatised
54
orthogneisses in the Chimoio group. Named after Inchope village, the composition of
55
gneisses varies from granodioritic to tonalitic. In type area, around the Inchope village,
56
the gneiss is light grey, medium-grained and only slightly foliated granodioritic gneiss
57
with random potassium feldspar phenocrysts.
M AN U
SC
RI PT
46
TE D
58
The migmatitic paragneisses form the major lithology in the Chimoio Group. Locally,
60
significant amounts of mafic minerals suggest a contribution of calcareous or
61
volcanoclastic material. Due to the primary compositional variation of these rocks,
62
magnetic and radiometric signatures of gneisses are generally rather weak when
63
compared with surrounding rock units. Although placed in the legend at the base of the
64
Chimoio Group, the lithostratigraphical position of these rocks remains doubtful
AC C
65
EP
59
66
Several small, roundish to elongated mafic intrusive bodies of gabbro and gabbroic
67
rocks have been emplaced into migmatitic paragneisses in the Chimoio group. The rock
68
is medium- to coarse-grained and generally massive, although also mildly deformed
69
varieties occur. 3
ACCEPTED MANUSCRIPT 70
The mica schists and mica gneisses occur in the area southeast of the Inchope village.
72
Random outcrops of mica gneisses have also been found within the area largely
73
assigned to the Inchope orthogneisses. The grain-size and fabric vary from rather
74
massive, medium-grained mica gneisses into very fine-grained mica schists with
75
crenulation cleavage often visible. In the western contact zone the rocks are often
76
strongly mylonitized, and in places, they turn there into garnet-bearing chlorite schists.
RI PT
71
SC
77
A large area North of Serra da Gorongosa is composed of gneisses, felsic biotite
79
gneisses, and metagranites, named after Monte Chissui, located some kilometers
80
southwest of the Chimoio town. Small, separate domains of these rock unities are also
81
exposed in the area between Chimoio and the Inchope village. The Monte Chissui
82
gneisses, felsic biotite gneisses, and metagranites are intruded by coarse-grained
83
microcline pegmatite dykes and basaltic Karoo dykes up to ~ 15 m thick.
TE D
M AN U
78
84
A heterogeneous sequence of siliciclastic metasediments is exposed in the eastern part
86
of the Inchope village, where these mostly quartzitic rocks form low hills and elongated
87
ridges within migmatitic paragneisses of the Chimoio Group. Accessory minerals found
88
are amphibole, garnet, sillimanite, and Fe-oxides. Texturally, these rocks are often
89
markedly foliated, stretched or mylonitized; only random saccharoidal varieties have
90
been observed.
AC C
EP
85
91 92 93 94 4
ACCEPTED MANUSCRIPT
3. MATERIALS AND METHODS
96
Five samples were collected (VM-011, VM-015, VM-012, VM-025 and BA-004) from
97
Inchope area (Fig. 1). The sampling criterion consisted of selecting material without
98
alteration, with sizes of 6 to 10 times greater than the major crystal and weighing
99
approximately 3kg. All samples were analyzed for petrography, U-Pb geochronology
100
and Sm-Nd whole rock geochemistry at the Institute of Geosciences Laboratory –
101
University of São Paulo, Brasil.
102
All four samples were analyzed for petrography using thin sections on a polarized light
103
microscope. These analyses were made using plane-polarized light and cross-polarized
104
light on the Olympus BX50 microscope and some important features were then
105
photographed using a digital Olympus E330 camera attached to the microscope. The
106
analysis consisted of texture, fabric and composition studies of the rocks. In addition,
107
modal analyses were made using point counts in each thin section for rock
108
classification.
SC
M AN U
TE D EP
109
RI PT
95
Two rock samples (VM-011 and VM-015) was crushed and heavy minerals were
111
separated on a Wifley table. Further separation of heavy minerals was done using heavy
112
liquid (methylene iodine). A Frantz magnetic separator was used to separate the
113
magnetic and nonmagnetic fractions using 1 and 1.5 A sequentially. Zircons were then
114
hand-picked under a binocular microscope, mounted in epoxy resin and subsequently
115
abraded to remove the exterior portion of the grains (Sato, et al., 2008). Once mounted
116
and polished, zircon grains were studied by cathodoluminescent imaging (Fig. 7) and
117
analyzed for U–Th–Pb using the Laser-ablation multi-collector inductively coupled
AC C
110
5
ACCEPTED MANUSCRIPT 118
plasma mass spectrometer (LA-MC-ICP-MS), Thermo-Fisher Neptune, at the
119
University of São Paulo.
120
LA-MC-ICP-MS U-Pb analyses were acquired using ArF-193 nm Photon laser system
122
(frequency of 6Hz) that produces a spot of 32 µm in diameter. Corrections of laser
123
induced elemental fractionation of
124
referred to the GJ-1 zircon standard (U-Pb mean age of 601 ± 3.5 Ma; Elholou et al.,
125
2006). The analytical data were obtained in sets of 2 sheets including two blanks, four
126
GJ-1 analyses, 13 unknown zircon spots and two more blanks.
127
corrected for
128
Pb (Stacey and Kramers, 1975). Isotopic ratios are reported at the 1σ level. Raw data
129
were processed on-line and reduced in an Excel worksheet adapted from SQUID 1.02
130
(Ludwig, 2001). Data plots on the Concordia diagrams used ISOPLOT/Ex 4.15
131
(Ludwig, 2009).
202
204
Pb values were
Hg/204Hg = 4.345, the blank and common
M AN U
Hg interference assuming
SC
Pb/238U ratio and instrumental discrimination are
TE D
204
206
RI PT
121
132
Another four samples (VM-011, VM-012, VM-015, and VM-025) were powdered and
134
digested in a clean room using ultra-clean reagents (HF+HNO3+HCl) and subject to
135
chromatographic separation of rare earth elements with ion-exchange resins. This was
136
followed by a secondary hydrogen di-Ethylhexyl phosphate (HDEHP) coated Teflon
137
powder column for Rb, Sr, Sm and Nd separation (Sato et al., 1995). The isotope ratios
138
were measured on a Finnigan Mat 262 spectrometer and the quoted errors are given at
139
the 2-sigma level. Concentrations of Rb, Sr, Sm and Nd were obtained by isotope
140
dilution.
141
procedures. The
142
Paolo, 1981). Sm-Nd model ages were calculated using the depleted mantle model
AC C
EP
133
87
Rb/86Sr and 143
147
Sm/144Nd were calculated using Hamilton et al., 1983
Nd/144Nd ratios were normalized for
146
Nd/144Nd = 0.7219 (De
6
ACCEPTED MANUSCRIPT 143
Nd/144Nd of the standard JNDi during
(TDM) of Depaolo (1981). The mean value for
144
January to May/2011 = 0.512098 ± 0.000010. Rb-Sr isotopic ratios were similarly
145
conducted in the Triton-Thermo Fisher mass spectrometer. The acquired 87Sr/86Sr
146
values were normalized to 86Sr/88Sr = 0.1194. The final quoted errors are external values
147
(1σ) based on replicate analyses of NBS-987 SrCO3 standard, which yielded a mean
148
ratio of 0.710251 ±0.000043 (1σ). Mean blank for Sr was 200 pg during the period of
149
analyses. Initial
150
considering the decay constants recommended by Steiger and Jäger (1977).
Sr/86Sr values were calculated based on the Rb and Sr results
SC
87
RI PT
143
M AN U
151
4. RESULTS
153
4.1. Petrography
154
The Inchope orthogneiss is a group of variously deformed and migmatised
155
orthogneisses in the central part of Mozambique (Fig. 1). This orthogneiss crops out at
156
Inchope village and its composition varies from granodioritic to tonalitic. The
157
orthogneiss is light grey, medium-grained and slightly foliated with random potassium
158
feldspar phenocrysts and in some places intruded by pegmatite dykes (Fig. 2). This rock
159
is holocrystalline, light grey with phaneritic and porphiritc textures with fenocrystals of
160
K-feldpar dispersed and with a variable grains sizes from fine to médium being slightly
161
foliated. In thin section, the texture is granular varying from xenomorphic to
162
hypidiomorphic. This rock is composed mainly of quartz, plagioclase, microcline,
163
biotite and muscovite. The accessory minerals are opaques, titanite, hornblende, zircon,
164
apatite and monazite (Fig. 3). The quartz is in the form of whitish grains, anhedral, with
165
limits that frequently adapt to the form of other minerals and presents ondular extinction
AC C
EP
TE D
152
7
ACCEPTED MANUSCRIPT as well as development of sub-grains with indented contacts evidencing recrystallization
167
and deformation processes. The microcline shows cross-hatched twinning and/or
168
mirmeckitic texture. These crystals are idiomorphic to hypidiomorphic. The plagioclase
169
is prismatic and subhedral. The biotite and muscovite are subhedral and in contact with
170
other minerals creating a slightly preferential orientation in the rock.
171
RI PT
166
4.2. In situ zircon U-Pb geochronology
173
Two samples (VM-011 and VM-015) were analyzed by LA-ICP-MS. The analyzed
174
crystals are mostly colorless, euhedral to subhedral with variable grain size from 100-
175
300 µm. Cathodoluminescence (CL) images of some selected zircon grains from each
176
analyzed sample are given in Figure 4. The CL images show low luminescent zircons
177
with inherited nuclei, some of them with sector or faint oscillatory zoning and
178
metamorphic overgrowths formed around inherited cores and by alteration or
179
recrystallization of protolithic zircons. Resorpted and metamict grains are also present.
180
The U–Pb analytical data are presented in Table 1, and plotted in concordia diagrams in
181
Figure 5.
182
The two Inchope orthogneiss samples gave Mesoproterozoic crystallization ages.
183
Twenty-three analyzed grains from the sample VM-011 gave a mean
184
1065±13 Ma (MSWD= 4.4, data-point error ellipses are 68.3%) as shown in Figure 5a.
185
This is considered to be the crystallization age of the Inchope orthogneiss. In the sample
186
VM-015 analysis are from seventeen grains. These analyses resulted in three 207Pb/206Pb
187
age groups of 1053±19 Ma (MSWD=2.9), 958±38 Ma (MSWD=0.39) and 484.2±7 Ma
188
(MSWD=2.6) as shown in Figure 5b.
189
crystallization of the Inchope orthogneiss and other two the metamorphism.
AC C
EP
TE D
M AN U
SC
172
207
Pb/206Pb age of
The first age is considered to date the
8
ACCEPTED MANUSCRIPT 4.3. Whole rock Nd-Sr isotopic systematic
191
Whole-rock Rb-Sr and Sm-Nd isotopic data for the Inchope orthogneiss are listed in
192
Table 2 and plotted in Figure 6. For all samples, their initial 87Sr/86Sr and ɛNd(t) values
193
are calculated at the time of the Inchope orthogneiss crystallization considered to
194
approximately 1050 Ma. The Inchope orthogneiss have high initial 87Sr/86Sr of 0.7117 -
195
0.7209, negative ɛNd(t) values of between -11.7 and -13.3 and depleted mantle Sm-Nd
196
model age (TDM) values between 2.3 and 2.4 Ga. Their Sm/Nd fractionation values are
197
between -0.50 and -0.42.
SC
RI PT
190
M AN U
198
5. DISCUSSIONS
200
5.1. Age Constraints
201
The analyzed samples from Inchope granite show two age groups. The dominant zircon
202
population in one sample of the Inchope granite yielded a weighted mean 206Pb/207Pb of
203
1065±13 Ma. Another sample show well defined cluster on the Concordia diagram with
204
an intercept
205
these zircon populations suggest metasedimentary material and the dates determined
206
constrain the protolith ages. This material resulted from partial melting of crustal
207
material. The above data are broadly consistent with the published ages of the Inchope
208
orthogneiss in Manica Province of 1079±7 Ma (GTK, 2006), Culicui suite orthogneiss
209
in Nampula Province (NE of the study area) ranging from 1087±16Ma to 1057±9Ma
210
(one with metamorphic overgrowths at 1019±18 Ma) reported in Bingen et al. (2009)
211
and Macey et al. (2010). This age group represents the thermal reactivation during the
212
accretion of the Mozambique belt onto the Kalahari craton.
EP
Pb/207Pb age of 1053±19 Ma. The morphology and internal structure of
AC C
206
TE D
199
9
ACCEPTED MANUSCRIPT 213
The Inchope orthogneiss was affected by a polyphase metamorphism. The first
215
metamorphic age of 956±38 Ma is related to pegmatite veins intrusions in Inchope
216
orthogneiss. These pegmatite veins are associated with tin-columbite-tantalite
217
mineralization in the area. Similar ages 996.8 Ma ± 3.4 Ma are found in for the
218
migmatitic veins in Chimoio (West of the study area) which indicate the occurrence
219
strong shearing at the boundary between the Kalahari Craton and Mozambique belt
220
(Manhiça et al., 2001; Grantham et al., 2011). Bingen et al., (2009) determined similar
221
ages of 953±8 Ma interpreted as evidence of a granulite-facies metamorphism for the
222
Marupa and Unango Complexes of Nampula province (NE of the study area). Dewaele
223
et al., (2011) determined emplacement of pegmatites at 969 ± 8 Ma associated with
224
columbite-tantalite and tin mineralization in Kibaran belt and karagoe and Karagwe–
225
Ankole belts. The second metamorphic age of 484.2±7 Ma is related to the final stage of
226
the Pan-African tectonothermal event in Mozambique belt. This age is consistent with
227
the evidence for amphibolite-facies metamorphism as late as 493±8Ma in Nampula
228
Complex (Bingen et al., 2009). Most studies report repeated deformation and
229
reactivation at c.550 Ma and c. 450 Ma (see Manhiça et al., 2001) ages typical of Pan
230
African Orogeny (Kennedy, 1964). GTK (2006) dated the Inchope orthogneiss by
231
monazite conventional method and found slightly reversely concordant age data of ~
232
530 – 520 Ma interpreted to reflect Pan-African reworking.
SC
M AN U
TE D
EP
AC C
233
RI PT
214
234 235 236 237 10
ACCEPTED MANUSCRIPT 5.2. Petrogenesis and geodynamic setting
239
The Inchope orthogneiss, for the crystallization age of approximately 1050 Ma, shows
240
initial values of ɛNd between -11.7 and -13.3 and 87Sr/86Sr between 0.7117 and 0.7209.
241
These features suggest significant contamination of the parental magma by the crustal
242
material. The Sm-Nd model ages provide useful information about the age of the
243
protolith and the petrogenesis of granitic magmas. The Inchope orthogneiss has
244
Paleoproterozoic TDM values between 2.3 and 2.4 Ga. These Sm-Nd model ages are
245
older than the crystallization ages of the Inchope orthogneiss of 1065±13 Ma and
246
1053±19 Ma (This study) and of 1079±7 Ma (GTK, 2006). Consequently, the Nd in the
247
Inchope orthogneiss left the magma sources between 2.3 and 2.4 Ga and resided in the
248
crust for about 1250 Ma before the Inchope orthogneiss formed. These results,
249
therefore, reveal that the study area consists of recycled or rejuvenated rocks of
250
Paleoproterozoic age. These ages are consistent with the maximum sedimentation of the
251
paleoproterozoic Gairezi and Rushinga metapelites along the eastern margin of the
252
archaean Zimbabwean craton (GTK, 2006). This evidence is reinforced by their strong
253
Sm/Nd fractionation values of between -0.50 and -0.42 which are related to the granitic
254
melts and their sources during partial melting.
256
257
SC
M AN U
TE D
EP
AC C
255
RI PT
238
258
259
11
ACCEPTED MANUSCRIPT
6. CONCLUSIONS
261
New zircon U-Pb LA-ICP-MS ages and whole rock Sr±Nd isotopic data permitted to
262
make the following petrogenetic and crustal growth conclusions related to central
263
Mozambique:
RI PT
260
264
(1) The analyzed samples from Inchope granite show two age groups. The dominant
265
zircon population in one sample of the Inchope granite yielded a weighted mean
266
206
267
Concordia diagram with an intercept
268
morphology and internal structure of these zircon populations suggest
269
metasedimentary material and the dates determined constrain the protolith ages.
270
This material resulted from partial melting of the crustal material.
Pb/207Pb of 1065±13 Ma. Another sample shows well-defined cluster on the
SC
Pb/207Pb age of 1053±19 Ma. The
M AN U
206
(2) The first metamorphic age of 956±38 Ma is related to pegmatite veins intrusions
272
in Inchope orthogneiss. These pegmatite veins are associated with tin-columbite-
273
tantalite mineralization in the area.
276 277 278 279 280
Pan-African tectonothermal event in Mozambique belt.
EP
275
(3) The second metamorphic age of 484.2±7 Ma is related to the final stage of the
(4) The ɛNdi between -11.7 and -13.3 and
87
Sr/86Sri between 0.7117 and 0.7209
suggest strong influence of crustal material in the genesis of the Inchope
AC C
274
TE D
271
orthogneiss. This orthogneiss has a hybrid source which involved also Paleoproterozoic magmatic material as shown by TDM values of between 2.3 and 2.4 Ga.
281 282
12
ACCEPTED MANUSCRIPT
ACKNOWLEDGEMENTS: The author thanks the fostering research institutions
284
(Cnpq and PRO-ÁFRICA) and the National Mining Institute for the financial help. To
285
Centro de Pesquisas Geocronológicas (CPGeo) of IGc/USP; Laboratório de
286
Fluorescência de Raios X – FRX; Laboratório de Química e ICP-AES/MS; Laboratório
287
de Tratamento de Amostras – LTA e Laboratório de Preparação de Amostras for the
288
analysis and C.C. G. Tassinari from IGc/USP and I. S. Williams from the National
289
University of Australia for the revisions, criticism and suggestions.
RI PT
283
SC
290
M AN U
291
REFERENCES
293
Baier, J., Audétat, A., Keppler, H., 2008. The origin of the negative niobium tantalum
294
anomaly in subduction zone magmas. Earth and Planetary Science Letters 267, 290–
295
300.
296
Bingen, B., Jacobs, J., Viola, G., Henderson, I.H., Skår, Ø., Boyd, R., Thomas, R.J.,
297
Solli, A., Key, R.M., Daudi, E.X., 2009. Geochronology of the Precambrian crust in the
298
Mozambique Belt of NE Mozambique, and implications for Gondwana assembly.
299
Precambrian Research 170, 231–255.
300
Chappell, B.W., 1999. Aluminium saturation in I- and S-type granites and the
301
characterization of fractionated hapogranites. Lithos 46, 535±551.
302
Chappell, B.W., White, A.J.R., 1992. I- and S-type granites in the Lachlan Fold Belt.
303
Trans. Royal Soc. Edinburgh: Earth Sci. 83, 1±26.
304
DePaolo, D. J., 1988. Neodymium Isotope Geochemistryçan Introduction. Berlin:
305
Springer, 187 pp.
AC C
EP
TE D
292
13
ACCEPTED MANUSCRIPT Dewaele, S., Henjes-Kunst, F., Melcher, F., Sitnikova, M., Burgess, R., Gerdes, A.,
307
Fernandez, M. A., De Clercq, F., Muchez, P., Lehmann, B., 2011. Late Neoproterozoic
308
overprinting of the cassiterite and columbite-tantalite bearing pegmatites of the
309
Gatumba area, Rwanda (Central Africa). Journal of African Earth Sciences 61, 10–26.
310
Gill, R., 2010. Igneous rocks and processes: A practical guide. Willey-Blacwell. First
311
Edition 428p
312
Grantham, G. H., Manhiça, A. D., Armstrong, R. A., Kruger, F. J., & Loubser, M.,
313
2011. New SHRIMP, Rb/Sr and Sm/Nd isotope and whole rock chemical data from
314
central Mozambique and western Dronning Maud Land, Antarctica: Implications for the
315
nature of the eastern margin of the Kalahari Craton and the amalgamation of Gondwana.
316
Journal of African Earth Sciences 59, 74–100.
317
GTK, 2006. Map Explanation; Volume 2: Sheets 1630 – 1934. Geology of Degree
318
Sheets Mecumbura, Chioco, Tete, Tambara, Guro, Chemba, Manica, Catandica,
319
Gorongosa, Rotanda, Chimoio and Beira, Mozambique. Ministério dos Recursos
320
Minerais, Direcção Nacional de Geologia, Maputo p. 499.
321
Irvine, T.N., Barager, W.R.A., 1971. A guide to the chemical classification of the
322
common volcanic rocks. Canadian Journal of Earth Science 8, 523–548.
323
Irvine, T.N., Barager, W.R.A., 1971. A guide to the chemical classification of the
324
common volcanic rocks. Canadian Journal of Earth Science 8, 523–548.
325
Kennedy, W.Q., 1964. The structural differentiation of Africa in the Pan African
326
(‘‘500Ma) tectonic episode. Leeds University Research Institute for African Geology
327
Annual Report 8, 48–49.
328
Kretz, 1983. Symbols for rock forming minerals. American Mineralogist. 68, 277–279.
329
LKAB, 1979. Preliminary exploration work in the Inchope-Doeroi area, Mozambique.
330
Draft final report. Unpubl. Rept., DNG Library No. 973, Maputo.
AC C
EP
TE D
M AN U
SC
RI PT
306
14
ACCEPTED MANUSCRIPT Macey, P. H., Thomas, R. J., Grantham, G. H., Ingram, B. A., Jacobs, J., Armstrong, R.
332
A., Roberts, M. P., Bingen, B., Hollick, L., de Kock, G. S., Viola, G., Bauer, W.,
333
Gonzales, E., Bjerkgard, T., Henderson, I. H. C., Sandstad, J. S., Cronwright, M. S.,
334
Harley, S., Solli, A., Nordgulen, O., Motuza, G., Daudí, E., Manhiça, V., 2010.
335
Mesoproterzoic Geology of the Nampula block, northern Mozambique: Tracing
336
fragments of Mesoproterozoic crust in the heart of Gondwana. Journal of Precambrian
337
Research 182, 124–148.
338
Manhiça, A.S.T.D., Grantham, G.H., Armstrong, R.A., Guise, P.G., Kruger, F.J., 2001.
339
Polyphase deformation and metamorphism at the Kalahari Craton – Mozambique belt
340
boundary. In: Miller, J.A., Holdsworth, R.E., Buick, I.S., Hand, M. (Eds.), Continental
341
Reactivation and Reworking. Geological Society of London 184, 303–321.
342
Maniar, P. D., Piccoli, P. M., 1989. Tectonic discrimination of granitoids. Geological
343
Society of America Bulletin 101, 635-643.
344
O’Connor, J.T., 1965. A classification for quartz-rich igneous rocks based on feldspar
345
ratios. U.S. Geological Survey Professional Paper 525 (B), pp. 79–84.
346
Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimination
347
diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology. 25, 956–
348
983.
349
Steiger, R.H., Jäger, E., 1977. Subcommision on Geochronology convention on the use
350
of decay constants in geo- and cosmochronology. Earth Planetary Science Letters 36,
351
359-362.
352
Sun, S. S., McDonough, W. F., 1989. Chemical and isotopic systematic of ocean
353
basalts: implications for mantle composition and processes. In: Saunders, A. D. &
354
Norry,M. J. (eds) Magmatism in the Ocean Basins. Geological Society, London, Special
355
Publications 42, 313-345.
AC C
EP
TE D
M AN U
SC
RI PT
331
15
ACCEPTED MANUSCRIPT Figure Captions
357
Figure 1. Sketch map of the study area in Central Mozambique modified after GTK
358
(2006). Abbreviations: P2BUig-Inchope orthogneiss (1079 Ma, magmatic U/Pb),
359
P2BCch-mica schist and mica gneiss, P2BUgb-gabbro and gabbroic rock, P2BCmi-
360
migmatitic paragneiss, P2BCfg-Monte Chissui gneiss, felsic biotite gneiss and
361
metagranite, P2BCss-siliclastic metasediment and numbers: (1) normal fault, (2) fault
362
or fracture line, (3) foliation, (4) lineation (5) main road (asphalt), (6) railroad, (7) main
363
river, (8) topographic line, (9) radiometric age in Ma and method, and (10) sampling
364
point.
SC
RI PT
356
M AN U
365
Figure 2. Field photographs of the Inchope orthogneiss. (a) Slight compositional
367
banding in in the Inchope orthogneiss, (b) layered coarse-grained tonalitic orthogneiss
368
of the Inchope orthogneiss, with an audit abandoned mine, (c) pegmatitic veis in the
369
Inchope orthogneiss, (d) Typical Inchope orthogneiss with tonalitic (dark) and
370
granodioritic (light) bodies.
TE D
366
371
Figure 3. Petrographic photographs of the Inchope orthogneiss taken under crossed
373
polars (XP). (a), (b), (c) and (d) quartz, plagioclase, biotite, muscovite and alkali
374
feldspar. Symbols according to Kretz (1983).
AC C
375
EP
372
376
Figure 4. Cathodoluminescence (CL) images of representative zircons from analysed
377
samples, with analytical spots and age results in Ma indicated for samples VM-011 and
378
VM-015.
379
16
ACCEPTED MANUSCRIPT 380
Figure 5. Concordia plots for the Inchope orthogneiss (a) Sample VM-011. (b) Sample
381
VM-015.
382
Figure 6. Plots of the Inchope orthogneiss after Depaolo (1988) in terms of (a) eNd(T)
384
vs. Nd depleted-mantle model ages, (b) Plots of eNd(T) values vs. initial Sr isotope
385
ratios for the samples of the Inchope orthogneiss.
RI PT
383
386
SC
387
Table Captions
389
Table 1. LA-ICP-MS data of zircons from the Inchope orthogneiss
390
Table 2. Whole-rock Sr-Nd data from the Inchope orthogneiss
M AN U
388
AC C
EP
TE D
391
17
Ages and errors (Ga) T206/238 1 sigma T207/235 1 sigma T207/206 1 sigma
1.8607
0.0420
0.1801
0.0040
0.99
5.5517
0.1236
0.0749
0.0007
0.5548
0.2542
1.068
0.022
1.067
0.015
1.067
0.019
2.1
1.8114
0.0194
0.1770
0.0015
0.81
5.6484
0.0490
0.0748
0.0007
0.0386
0.0170
1.051
0.008
1.050
0.007
1.065
0.018
4.1
1.8195
0.0195
0.1756
0.0015
0.80
5.6946
0.0491
0.0756
5.1
1.7182
0.0205
0.1687
0.0018
0.87
5.9275
0.0617
0.0747
6.1
1.7506
0.0187
0.1730
0.0015
0.81
5.7804
0.0501
0.0744
7.1
1.8125
0.0196
0.1760
0.0015
0.80
5.6803
0.0493
0.0743
8.1
1.7658
0.0201
0.1737
0.0015
0.77
5.7578
0.0509
0.0736
10.1
1.7250
0.0213
0.1692
0.0018
0.84
5.9106
0.0613
0.0743
11.1
1.7870
0.0188
0.1744
0.0015
0.81
5.7333
0.0490
13.1
1.8934
0.0208
0.1820
0.0016
0.82
5.4956
0.0493
14.1
1.9151
0.0360
0.1841
0.0032
0.92
5.4330
0.0935
16.1
1.7591
0.0146
0.1695
0.0008
0.56
5.8986
0.0276
17.1
1.7821
0.0123
0.1717
0.0008
0.69
5.8232
18.1
1.8437
0.0268
0.1807
0.0021
0.80
5.5344
19.1
1.6856
0.0128
0.1682
0.0009
0.71
5.9442
20.1
1.8363
0.0127
0.1790
0.0009
0.77
21.1
1.8196
0.0150
0.1775
0.0010
0.66
22.1
1.7944
0.0130
0.1768
0.0011
0.83
24.1
1.7523
0.0112
0.1738
0.0007
0.66
27.2
1.9008
0.0680
0.1836
0.0077
28.1
1.8385
0.0538
0.1789
0.0066
29.1
1.7908
0.0515
0.1750
30.1
1.8725
0.0566
0.1816
M AN U
1.1
EP
SC
Ratios and errors 207/235 1sigma 206/238 1 sigma Rho 238/206 1 sigma 207/206 1 sigma 208/206 1 sigma
AC C
Spot VM-011
RI PT
ACCEPTED MANUSCRIPT
0.0007
0.2005
0.0819
1.043
0.008
1.052
0.007
1.086
0.018
0.0007
0.1704
0.0672
1.005
0.010
1.015
0.008
1.062
0.018
0.0007
0.4872
0.1856
1.029
0.008
1.027
0.007
1.054
0.018
0.0007
0.1176
0.0435
1.045
0.008
1.050
0.007
1.050
0.018
0.0007
0.5627
0.2009
1.032
0.008
1.033
0.007
1.032
0.019
0.0007
0.1293
1.008
0.010
1.018
0.008
1.052
0.020
0.0007
0.0646
0.0211
1.036
0.008
1.041
0.007
1.066
0.018
0.0755
0.0007
0.3228
0.0996
1.078
0.009
1.079
0.007
1.083
0.018
0.0767
0.0005
0.2838
0.0295
1.089
0.017
1.086
0.012
1.117
0.013
0.0764
TE D
0.3848
0.0749
0.0005
0.0267
0.0028
1.010
0.004
1.031
0.005
1.106
0.013
0.0278
0.0762
0.0004
0.5697
0.0594
1.022
0.005
1.039
0.004
1.103
0.011
0.0642
0.0750
0.0004
0.1951
0.0208
1.071
0.011
1.061
0.010
1.071
0.012
0.0320
0.0724
0.0004
0.4864
0.0572
1.002
0.005
1.003
0.005
0.999
0.011
5.5866
0.0296
0.0747
0.0004
-0.2507
0.0462
1.062
0.005
1.059
0.005
1.062
0.011
5.6331
0.0306
0.0746
0.0004
0.2796
0.0294
1.053
0.005
1.053
0.005
1.059
0.011
5.6572
0.0340
0.0744
0.0004
0.0824
0.0087
1.049
0.006
1.043
0.005
1.053
0.011
5.7536
0.0242
0.0738
0.0004
0.0232
0.0026
1.033
0.004
1.028
0.004
1.038
0.011
0.99
5.4468
0.2298
0.0762
0.0006
1.0078
0.3101
1.087
0.042
1.081
0.024
1.101
0.016
0.99
5.5890
0.2067
0.0753
0.0005
0.4571
0.1431
1.061
0.036
1.059
0.019
1.078
0.013
0.0064
0.99
5.7143
0.2086
0.0745
0.0005
1.1861
0.3859
1.040
0.035
1.042
0.019
1.055
0.013
0.0068
0.99
5.5075
0.2061
0.0748
0.0005
0.0421
0.0139
1.076
0.037
1.071
0.020
1.064
0.013
ACCEPTED MANUSCRIPT
VM-015 1.8117
0.0339
0.1776
0.0038
0.99
5.6318
0.1215
0.0758
0.0004
0.0871
0.0435
1.054
0.021
1.050
0.012
1.091
0.012
1.7886
0.0323
0.1744
0.0036
0.99
5.7344
0.1196
0.0755
0.0004
0.0467
0.0243
1.036
0.020
1.041
0.012
1.082
0.012
6.1
1.7554
0.0320
0.1706
0.0036
0.99
5.8628
0.1235
0.0758
0.0004
0.1416
0.0905
1.015
0.020
1.029
0.012
1.093
0.012
8.1
1.6986
0.0312
0.1670
0.0036
0.99
5.9871
0.1273
0.0747
0.0004
0.0931
0.0742
0.996
0.020
1.008
0.012
1.062
0.012
1.2048
1.052
0.021
1.047
0.012
1.067
0.012
0.0096
1.009
0.006
1.014
0.006
1.063
0.004
RI PT
1.1 2.1
1.8050
0.0342
0.1772
0.0038
0.99
5.6427
0.1224
0.0749
0.0004
1.4231
1.7140
0.0151
0.1694
0.0011
0.76
5.9036
0.0392
0.0748
0.0001
0.0837
15.1
1.7403
0.0258
0.1729
0.0023
0.89
5.7835
0.0761
0.0734
0.0002
0.5937
0.0660
1.028
0.012
1.024
0.010
1.027
0.007
4.1
1.9026
0.0346
0.1834
0.0038
0.99
5.4533
0.1145
0.0761
0.0004
0.1867
0.1051
1.085
0.021
1.082
0.012
1.100
0.012
1.7545
0.0322
0.1684
0.0036
0.99
5.9377
0.1257
0.0764
1.7808
0.0237
0.1722
0.0009
0.39
5.8081
0.0301
0.0755
3.1
1.4834
0.0271
0.1516
0.0032
0.99
6.5962
0.1380
0.0738
17.1
1.4338
0.0250
0.1449
0.0015
0.61
6.9006
0.0729
0.0735
19.1
1.3741
0.0231
0.1406
0.0014
0.60
7.1108
0.0721
0.0726
21.1
1.4068
0.0211
0.1444
0.0012
0.54
6.9234
0.0556
0.0725
6.2
0.4836
0.0089
0.0599
0.0013
0.99
16.6889
0.3526
7.2
0.6177
0.0115
0.0788
0.0017
0.99
12.6889
0.2701
9.2
0.5376
0.0104
0.0679
0.0015
0.99
14.7209
0.3225
M AN U
5.1 20.1
0.0004
1.3376
0.8221
1.003
0.020
1.029
0.012
1.108
0.012
0.0003
0.2472
0.0554
1.024
0.005
1.038
0.009
1.083
0.009
0.0004
1.3914
0.7517
0.910
0.018
0.924
0.011
1.036
0.012
0.0006
0.0865
0.0210
0.872
0.009
0.903
0.010
1.028
0.016
0.0769
0.0177
0.848
0.008
0.878
0.010
1.003
0.012
0.0837
0.0184
0.870
0.007
0.892
0.009
1.001
0.009
0.0593
0.0004
0.0127
0.0087
0.375
0.008
0.401
0.006
0.572
0.013
0.0591
0.0003
0.0115
0.0087
0.489
0.010
0.488
0.007
0.565
0.013
0.0586
0.0004
0.0089
0.0081
0.424
0.009
0.437
0.007
0.544
0.014
TE D
0.0004
0.0003
EP AC C
SC
9.1 11.1
ACCEPTED MANUSCRIPT
143
Nd/ Nd (σ) 0.511474 (9) 0.511457 (8) 0.511279 (5) 0.511429 (11) 144
fSm/Nd
ɛNd (0)
-0.42 -0.43 -0.50 -0.43
-22.70 -23;05 -26.51 -23.58
ɛNd at 1050Ma -11.8 -11.7 -13.3 -12.4
TDM (Ga) 2.4 2.4 2.3 2.4
Rb (ppm) 561.2 519.6 438.6 481.9
Sr (ppm) 102.2 106.4 173.3 101.4
RI PT
Sm/ Nd (σ) 0.1148 (7) 0.1113 (7) 0.0977 (6) 0.1124 (7)
SC
147
144
M AN U
Nd (ppm) 34.08 39.44 41.91 36.68
TE D
WR WR WR WR
Sm (ppm) 6.47 7.26 6.77 6.82
EP
VM-025 VM-012 VM-015 VM-011
Mat.
AC C
Sample no.
87
Rb/ Sr 16.284 (61) 14.453 (82) 7.413 (63) 14.047 (39) 86
87
Sr/ Sr 0.953692 (66) 0.936048 (119) 0.828486 (64) 0.925961 (74) 86
(87Sr/86Sr) at 1050 Ma 0.7117 0.7209 0.7170 0.7167
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 (1) The Inchope orthogneiss crystallized in Proterozoic from a hybrid source dominated by crustal material. (2) The Inchope orthogneiss was affected by two metamorphic events. (3) The first metamorphic age is related to pegmatite veins intrusion.
AC C
EP
TE D
M AN U
SC
RI PT
(4) The second metamorphic age is related to Pan-African deformation.
S1464-343X(17)30154-1
DOI:
10.1016/j.jafrearsci.2017.03.027
Reference:
AES 2874
To appear in:
Journal of African Earth Sciences
Received Date: 5 April 2016 Revised Date:
13 February 2017
Accepted Date: 21 March 2017
Please cite this article as: Manjate, V.A., U-Pb zircon geochronology and Sr-Nd isotopic composition of the Inchope orthogneiss in Mozambique: Age constraints and petrogenetic implications, Journal of African Earth Sciences (2017), doi: 10.1016/j.jafrearsci.2017.03.027. 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.
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
U-Pb zircon geochronology and Sr-Nd isotopic composition of the
2
Inchope orthogneiss in Mozambique: Age Constraints and
3
Petrogenetic implications
4
Vicente Albino Manjate1([email protected])
5
1
RI PT
1
Instituto Nacional de Minas, Av 24 de Julho, 1895 – Maputo, Moçambique
6
SC
7
ABSTRACT
9
The Inchope orthogneiss comprises a mesoproterozoic group of variously deformed and
10
migmatised orthogneisses in the Chimoio group. This area is well known for its
11
numerous, small pegmatite deposits with cassiterite and columbite. Zircon U-Pb
12
geochronological and whole rock Sr-Nd isotope data are reported for five Inchope
13
orthogneiss samples. The zircon U-Pb data exhibit one period of crystallization between
14
1065-1053 Ma and two metamorphic ages of 956 Ma and 484 Ma. The Inchope
15
orthogneiss displays evolved Nd isotopic compositions with ɛNdi between -11.7 and -
16
13.3, 87Sr/86Sri between 0.7117 and 0.7209 and TDM values of between 2.3 and 2.4 Ga..
17
Therefore, the Inchope orthogneiss crystallized in Mesoproterozoic from the
18
paleoproterozoic metapelites along the eastern margin of the archaen Zimbabwean
19
craton. This was followed by pegmatite veins intrusions and Pan-African
20
tectonometamorphic reworking. These features are typical of S-type and calc-alkaline
21
granites in continental margin arcs.
22
Key-words: Inchope orthogneiss; U-Pb geochronology; Sr-Nd isotope data
AC C
EP
TE D
M AN U
8
1
ACCEPTED MANUSCRIPT
1. INTRODUCTION
24
The Inchope orthogneiss comprises a group of variously deformed and migmatised
25
orthogneisses in the Chimoio group (GTK, 2006). Named after Inchope village, the
26
composition of the orthogneisses varies from granodioritic to tonalitic. In type area,
27
around the Inchope village, the orthogneiss is light grey, medium-grained and only
28
slightly foliated granodioritic gneiss with random potassium feldspar phenocrysts. This
29
area is well known for its numerous, small pegmatite deposits with cassiterite and
30
columbite (LKAB, 1979). However, no resource evaluation was made. GTK (2006)
31
dated the Inchope orthogneiss by both monazite conventional and zircon SHRIMP
32
methods. Monazite yielded slightly reversely concordant age data of ~ 530 – 520 Ma.
33
SHRIMP dating, using 17 different zircon domains, yielded an age of ~ 1100 Ma. Seven
34
concordant analyses define an age of 1079±7 Ma. The discordia age formed by the U-
35
Pb data from 12 zoned zircon domains is the same as the concordia age. Three analyses
36
were carried out on high-U CL-dark rims but rejected because of high common lead
37
contents. They are believed to reflect Pan-African reworking as demonstrated by the
38
monazite age. In this paper, we report new zircon U-Pb LA-ICP-MS ages and whole
39
rock Sr±Nd isotopic data to constrain the petrogenesis of the Inchope orthogneiss and
40
discuss its implications for the Proterozoic crustal growth in central Mozambique.
42
SC
M AN U
TE D
EP
AC C
41
RI PT
23
43
44
45 2
ACCEPTED MANUSCRIPT
2. GEOLOGICAL SETTING
47
The study area is composed of intrusive rocks and supracrustal unities of the Chimoio
48
group (GTK, 2006). The intrusive rocks are the Inchope orthogneiss (P2BUig) and
49
gabbro and gabbroic rock (P2BUgb). On the other hand, the supracrustal unities are
50
represented by the mica schist and mica gneiss (P2BCch), migmatitic paragneiss
51
(P2BCmi), Monte Chissui gneiss, felsic biotite gneiss and metagranite (P2BCfg) and
52
siliclastic metasediment (P2BCss) (Fig. 1).
53
The Inchope orthogneiss comprises a group of variously deformed and migmatised
54
orthogneisses in the Chimoio group. Named after Inchope village, the composition of
55
gneisses varies from granodioritic to tonalitic. In type area, around the Inchope village,
56
the gneiss is light grey, medium-grained and only slightly foliated granodioritic gneiss
57
with random potassium feldspar phenocrysts.
M AN U
SC
RI PT
46
TE D
58
The migmatitic paragneisses form the major lithology in the Chimoio Group. Locally,
60
significant amounts of mafic minerals suggest a contribution of calcareous or
61
volcanoclastic material. Due to the primary compositional variation of these rocks,
62
magnetic and radiometric signatures of gneisses are generally rather weak when
63
compared with surrounding rock units. Although placed in the legend at the base of the
64
Chimoio Group, the lithostratigraphical position of these rocks remains doubtful
AC C
65
EP
59
66
Several small, roundish to elongated mafic intrusive bodies of gabbro and gabbroic
67
rocks have been emplaced into migmatitic paragneisses in the Chimoio group. The rock
68
is medium- to coarse-grained and generally massive, although also mildly deformed
69
varieties occur. 3
ACCEPTED MANUSCRIPT 70
The mica schists and mica gneisses occur in the area southeast of the Inchope village.
72
Random outcrops of mica gneisses have also been found within the area largely
73
assigned to the Inchope orthogneisses. The grain-size and fabric vary from rather
74
massive, medium-grained mica gneisses into very fine-grained mica schists with
75
crenulation cleavage often visible. In the western contact zone the rocks are often
76
strongly mylonitized, and in places, they turn there into garnet-bearing chlorite schists.
RI PT
71
SC
77
A large area North of Serra da Gorongosa is composed of gneisses, felsic biotite
79
gneisses, and metagranites, named after Monte Chissui, located some kilometers
80
southwest of the Chimoio town. Small, separate domains of these rock unities are also
81
exposed in the area between Chimoio and the Inchope village. The Monte Chissui
82
gneisses, felsic biotite gneisses, and metagranites are intruded by coarse-grained
83
microcline pegmatite dykes and basaltic Karoo dykes up to ~ 15 m thick.
TE D
M AN U
78
84
A heterogeneous sequence of siliciclastic metasediments is exposed in the eastern part
86
of the Inchope village, where these mostly quartzitic rocks form low hills and elongated
87
ridges within migmatitic paragneisses of the Chimoio Group. Accessory minerals found
88
are amphibole, garnet, sillimanite, and Fe-oxides. Texturally, these rocks are often
89
markedly foliated, stretched or mylonitized; only random saccharoidal varieties have
90
been observed.
AC C
EP
85
91 92 93 94 4
ACCEPTED MANUSCRIPT
3. MATERIALS AND METHODS
96
Five samples were collected (VM-011, VM-015, VM-012, VM-025 and BA-004) from
97
Inchope area (Fig. 1). The sampling criterion consisted of selecting material without
98
alteration, with sizes of 6 to 10 times greater than the major crystal and weighing
99
approximately 3kg. All samples were analyzed for petrography, U-Pb geochronology
100
and Sm-Nd whole rock geochemistry at the Institute of Geosciences Laboratory –
101
University of São Paulo, Brasil.
102
All four samples were analyzed for petrography using thin sections on a polarized light
103
microscope. These analyses were made using plane-polarized light and cross-polarized
104
light on the Olympus BX50 microscope and some important features were then
105
photographed using a digital Olympus E330 camera attached to the microscope. The
106
analysis consisted of texture, fabric and composition studies of the rocks. In addition,
107
modal analyses were made using point counts in each thin section for rock
108
classification.
SC
M AN U
TE D EP
109
RI PT
95
Two rock samples (VM-011 and VM-015) was crushed and heavy minerals were
111
separated on a Wifley table. Further separation of heavy minerals was done using heavy
112
liquid (methylene iodine). A Frantz magnetic separator was used to separate the
113
magnetic and nonmagnetic fractions using 1 and 1.5 A sequentially. Zircons were then
114
hand-picked under a binocular microscope, mounted in epoxy resin and subsequently
115
abraded to remove the exterior portion of the grains (Sato, et al., 2008). Once mounted
116
and polished, zircon grains were studied by cathodoluminescent imaging (Fig. 7) and
117
analyzed for U–Th–Pb using the Laser-ablation multi-collector inductively coupled
AC C
110
5
ACCEPTED MANUSCRIPT 118
plasma mass spectrometer (LA-MC-ICP-MS), Thermo-Fisher Neptune, at the
119
University of São Paulo.
120
LA-MC-ICP-MS U-Pb analyses were acquired using ArF-193 nm Photon laser system
122
(frequency of 6Hz) that produces a spot of 32 µm in diameter. Corrections of laser
123
induced elemental fractionation of
124
referred to the GJ-1 zircon standard (U-Pb mean age of 601 ± 3.5 Ma; Elholou et al.,
125
2006). The analytical data were obtained in sets of 2 sheets including two blanks, four
126
GJ-1 analyses, 13 unknown zircon spots and two more blanks.
127
corrected for
128
Pb (Stacey and Kramers, 1975). Isotopic ratios are reported at the 1σ level. Raw data
129
were processed on-line and reduced in an Excel worksheet adapted from SQUID 1.02
130
(Ludwig, 2001). Data plots on the Concordia diagrams used ISOPLOT/Ex 4.15
131
(Ludwig, 2009).
202
204
Pb values were
Hg/204Hg = 4.345, the blank and common
M AN U
Hg interference assuming
SC
Pb/238U ratio and instrumental discrimination are
TE D
204
206
RI PT
121
132
Another four samples (VM-011, VM-012, VM-015, and VM-025) were powdered and
134
digested in a clean room using ultra-clean reagents (HF+HNO3+HCl) and subject to
135
chromatographic separation of rare earth elements with ion-exchange resins. This was
136
followed by a secondary hydrogen di-Ethylhexyl phosphate (HDEHP) coated Teflon
137
powder column for Rb, Sr, Sm and Nd separation (Sato et al., 1995). The isotope ratios
138
were measured on a Finnigan Mat 262 spectrometer and the quoted errors are given at
139
the 2-sigma level. Concentrations of Rb, Sr, Sm and Nd were obtained by isotope
140
dilution.
141
procedures. The
142
Paolo, 1981). Sm-Nd model ages were calculated using the depleted mantle model
AC C
EP
133
87
Rb/86Sr and 143
147
Sm/144Nd were calculated using Hamilton et al., 1983
Nd/144Nd ratios were normalized for
146
Nd/144Nd = 0.7219 (De
6
ACCEPTED MANUSCRIPT 143
Nd/144Nd of the standard JNDi during
(TDM) of Depaolo (1981). The mean value for
144
January to May/2011 = 0.512098 ± 0.000010. Rb-Sr isotopic ratios were similarly
145
conducted in the Triton-Thermo Fisher mass spectrometer. The acquired 87Sr/86Sr
146
values were normalized to 86Sr/88Sr = 0.1194. The final quoted errors are external values
147
(1σ) based on replicate analyses of NBS-987 SrCO3 standard, which yielded a mean
148
ratio of 0.710251 ±0.000043 (1σ). Mean blank for Sr was 200 pg during the period of
149
analyses. Initial
150
considering the decay constants recommended by Steiger and Jäger (1977).
Sr/86Sr values were calculated based on the Rb and Sr results
SC
87
RI PT
143
M AN U
151
4. RESULTS
153
4.1. Petrography
154
The Inchope orthogneiss is a group of variously deformed and migmatised
155
orthogneisses in the central part of Mozambique (Fig. 1). This orthogneiss crops out at
156
Inchope village and its composition varies from granodioritic to tonalitic. The
157
orthogneiss is light grey, medium-grained and slightly foliated with random potassium
158
feldspar phenocrysts and in some places intruded by pegmatite dykes (Fig. 2). This rock
159
is holocrystalline, light grey with phaneritic and porphiritc textures with fenocrystals of
160
K-feldpar dispersed and with a variable grains sizes from fine to médium being slightly
161
foliated. In thin section, the texture is granular varying from xenomorphic to
162
hypidiomorphic. This rock is composed mainly of quartz, plagioclase, microcline,
163
biotite and muscovite. The accessory minerals are opaques, titanite, hornblende, zircon,
164
apatite and monazite (Fig. 3). The quartz is in the form of whitish grains, anhedral, with
165
limits that frequently adapt to the form of other minerals and presents ondular extinction
AC C
EP
TE D
152
7
ACCEPTED MANUSCRIPT as well as development of sub-grains with indented contacts evidencing recrystallization
167
and deformation processes. The microcline shows cross-hatched twinning and/or
168
mirmeckitic texture. These crystals are idiomorphic to hypidiomorphic. The plagioclase
169
is prismatic and subhedral. The biotite and muscovite are subhedral and in contact with
170
other minerals creating a slightly preferential orientation in the rock.
171
RI PT
166
4.2. In situ zircon U-Pb geochronology
173
Two samples (VM-011 and VM-015) were analyzed by LA-ICP-MS. The analyzed
174
crystals are mostly colorless, euhedral to subhedral with variable grain size from 100-
175
300 µm. Cathodoluminescence (CL) images of some selected zircon grains from each
176
analyzed sample are given in Figure 4. The CL images show low luminescent zircons
177
with inherited nuclei, some of them with sector or faint oscillatory zoning and
178
metamorphic overgrowths formed around inherited cores and by alteration or
179
recrystallization of protolithic zircons. Resorpted and metamict grains are also present.
180
The U–Pb analytical data are presented in Table 1, and plotted in concordia diagrams in
181
Figure 5.
182
The two Inchope orthogneiss samples gave Mesoproterozoic crystallization ages.
183
Twenty-three analyzed grains from the sample VM-011 gave a mean
184
1065±13 Ma (MSWD= 4.4, data-point error ellipses are 68.3%) as shown in Figure 5a.
185
This is considered to be the crystallization age of the Inchope orthogneiss. In the sample
186
VM-015 analysis are from seventeen grains. These analyses resulted in three 207Pb/206Pb
187
age groups of 1053±19 Ma (MSWD=2.9), 958±38 Ma (MSWD=0.39) and 484.2±7 Ma
188
(MSWD=2.6) as shown in Figure 5b.
189
crystallization of the Inchope orthogneiss and other two the metamorphism.
AC C
EP
TE D
M AN U
SC
172
207
Pb/206Pb age of
The first age is considered to date the
8
ACCEPTED MANUSCRIPT 4.3. Whole rock Nd-Sr isotopic systematic
191
Whole-rock Rb-Sr and Sm-Nd isotopic data for the Inchope orthogneiss are listed in
192
Table 2 and plotted in Figure 6. For all samples, their initial 87Sr/86Sr and ɛNd(t) values
193
are calculated at the time of the Inchope orthogneiss crystallization considered to
194
approximately 1050 Ma. The Inchope orthogneiss have high initial 87Sr/86Sr of 0.7117 -
195
0.7209, negative ɛNd(t) values of between -11.7 and -13.3 and depleted mantle Sm-Nd
196
model age (TDM) values between 2.3 and 2.4 Ga. Their Sm/Nd fractionation values are
197
between -0.50 and -0.42.
SC
RI PT
190
M AN U
198
5. DISCUSSIONS
200
5.1. Age Constraints
201
The analyzed samples from Inchope granite show two age groups. The dominant zircon
202
population in one sample of the Inchope granite yielded a weighted mean 206Pb/207Pb of
203
1065±13 Ma. Another sample show well defined cluster on the Concordia diagram with
204
an intercept
205
these zircon populations suggest metasedimentary material and the dates determined
206
constrain the protolith ages. This material resulted from partial melting of crustal
207
material. The above data are broadly consistent with the published ages of the Inchope
208
orthogneiss in Manica Province of 1079±7 Ma (GTK, 2006), Culicui suite orthogneiss
209
in Nampula Province (NE of the study area) ranging from 1087±16Ma to 1057±9Ma
210
(one with metamorphic overgrowths at 1019±18 Ma) reported in Bingen et al. (2009)
211
and Macey et al. (2010). This age group represents the thermal reactivation during the
212
accretion of the Mozambique belt onto the Kalahari craton.
EP
Pb/207Pb age of 1053±19 Ma. The morphology and internal structure of
AC C
206
TE D
199
9
ACCEPTED MANUSCRIPT 213
The Inchope orthogneiss was affected by a polyphase metamorphism. The first
215
metamorphic age of 956±38 Ma is related to pegmatite veins intrusions in Inchope
216
orthogneiss. These pegmatite veins are associated with tin-columbite-tantalite
217
mineralization in the area. Similar ages 996.8 Ma ± 3.4 Ma are found in for the
218
migmatitic veins in Chimoio (West of the study area) which indicate the occurrence
219
strong shearing at the boundary between the Kalahari Craton and Mozambique belt
220
(Manhiça et al., 2001; Grantham et al., 2011). Bingen et al., (2009) determined similar
221
ages of 953±8 Ma interpreted as evidence of a granulite-facies metamorphism for the
222
Marupa and Unango Complexes of Nampula province (NE of the study area). Dewaele
223
et al., (2011) determined emplacement of pegmatites at 969 ± 8 Ma associated with
224
columbite-tantalite and tin mineralization in Kibaran belt and karagoe and Karagwe–
225
Ankole belts. The second metamorphic age of 484.2±7 Ma is related to the final stage of
226
the Pan-African tectonothermal event in Mozambique belt. This age is consistent with
227
the evidence for amphibolite-facies metamorphism as late as 493±8Ma in Nampula
228
Complex (Bingen et al., 2009). Most studies report repeated deformation and
229
reactivation at c.550 Ma and c. 450 Ma (see Manhiça et al., 2001) ages typical of Pan
230
African Orogeny (Kennedy, 1964). GTK (2006) dated the Inchope orthogneiss by
231
monazite conventional method and found slightly reversely concordant age data of ~
232
530 – 520 Ma interpreted to reflect Pan-African reworking.
SC
M AN U
TE D
EP
AC C
233
RI PT
214
234 235 236 237 10
ACCEPTED MANUSCRIPT 5.2. Petrogenesis and geodynamic setting
239
The Inchope orthogneiss, for the crystallization age of approximately 1050 Ma, shows
240
initial values of ɛNd between -11.7 and -13.3 and 87Sr/86Sr between 0.7117 and 0.7209.
241
These features suggest significant contamination of the parental magma by the crustal
242
material. The Sm-Nd model ages provide useful information about the age of the
243
protolith and the petrogenesis of granitic magmas. The Inchope orthogneiss has
244
Paleoproterozoic TDM values between 2.3 and 2.4 Ga. These Sm-Nd model ages are
245
older than the crystallization ages of the Inchope orthogneiss of 1065±13 Ma and
246
1053±19 Ma (This study) and of 1079±7 Ma (GTK, 2006). Consequently, the Nd in the
247
Inchope orthogneiss left the magma sources between 2.3 and 2.4 Ga and resided in the
248
crust for about 1250 Ma before the Inchope orthogneiss formed. These results,
249
therefore, reveal that the study area consists of recycled or rejuvenated rocks of
250
Paleoproterozoic age. These ages are consistent with the maximum sedimentation of the
251
paleoproterozoic Gairezi and Rushinga metapelites along the eastern margin of the
252
archaean Zimbabwean craton (GTK, 2006). This evidence is reinforced by their strong
253
Sm/Nd fractionation values of between -0.50 and -0.42 which are related to the granitic
254
melts and their sources during partial melting.
256
257
SC
M AN U
TE D
EP
AC C
255
RI PT
238
258
259
11
ACCEPTED MANUSCRIPT
6. CONCLUSIONS
261
New zircon U-Pb LA-ICP-MS ages and whole rock Sr±Nd isotopic data permitted to
262
make the following petrogenetic and crustal growth conclusions related to central
263
Mozambique:
RI PT
260
264
(1) The analyzed samples from Inchope granite show two age groups. The dominant
265
zircon population in one sample of the Inchope granite yielded a weighted mean
266
206
267
Concordia diagram with an intercept
268
morphology and internal structure of these zircon populations suggest
269
metasedimentary material and the dates determined constrain the protolith ages.
270
This material resulted from partial melting of the crustal material.
Pb/207Pb of 1065±13 Ma. Another sample shows well-defined cluster on the
SC
Pb/207Pb age of 1053±19 Ma. The
M AN U
206
(2) The first metamorphic age of 956±38 Ma is related to pegmatite veins intrusions
272
in Inchope orthogneiss. These pegmatite veins are associated with tin-columbite-
273
tantalite mineralization in the area.
276 277 278 279 280
Pan-African tectonothermal event in Mozambique belt.
EP
275
(3) The second metamorphic age of 484.2±7 Ma is related to the final stage of the
(4) The ɛNdi between -11.7 and -13.3 and
87
Sr/86Sri between 0.7117 and 0.7209
suggest strong influence of crustal material in the genesis of the Inchope
AC C
274
TE D
271
orthogneiss. This orthogneiss has a hybrid source which involved also Paleoproterozoic magmatic material as shown by TDM values of between 2.3 and 2.4 Ga.
281 282
12
ACCEPTED MANUSCRIPT
ACKNOWLEDGEMENTS: The author thanks the fostering research institutions
284
(Cnpq and PRO-ÁFRICA) and the National Mining Institute for the financial help. To
285
Centro de Pesquisas Geocronológicas (CPGeo) of IGc/USP; Laboratório de
286
Fluorescência de Raios X – FRX; Laboratório de Química e ICP-AES/MS; Laboratório
287
de Tratamento de Amostras – LTA e Laboratório de Preparação de Amostras for the
288
analysis and C.C. G. Tassinari from IGc/USP and I. S. Williams from the National
289
University of Australia for the revisions, criticism and suggestions.
RI PT
283
SC
290
M AN U
291
REFERENCES
293
Baier, J., Audétat, A., Keppler, H., 2008. The origin of the negative niobium tantalum
294
anomaly in subduction zone magmas. Earth and Planetary Science Letters 267, 290–
295
300.
296
Bingen, B., Jacobs, J., Viola, G., Henderson, I.H., Skår, Ø., Boyd, R., Thomas, R.J.,
297
Solli, A., Key, R.M., Daudi, E.X., 2009. Geochronology of the Precambrian crust in the
298
Mozambique Belt of NE Mozambique, and implications for Gondwana assembly.
299
Precambrian Research 170, 231–255.
300
Chappell, B.W., 1999. Aluminium saturation in I- and S-type granites and the
301
characterization of fractionated hapogranites. Lithos 46, 535±551.
302
Chappell, B.W., White, A.J.R., 1992. I- and S-type granites in the Lachlan Fold Belt.
303
Trans. Royal Soc. Edinburgh: Earth Sci. 83, 1±26.
304
DePaolo, D. J., 1988. Neodymium Isotope Geochemistryçan Introduction. Berlin:
305
Springer, 187 pp.
AC C
EP
TE D
292
13
ACCEPTED MANUSCRIPT Dewaele, S., Henjes-Kunst, F., Melcher, F., Sitnikova, M., Burgess, R., Gerdes, A.,
307
Fernandez, M. A., De Clercq, F., Muchez, P., Lehmann, B., 2011. Late Neoproterozoic
308
overprinting of the cassiterite and columbite-tantalite bearing pegmatites of the
309
Gatumba area, Rwanda (Central Africa). Journal of African Earth Sciences 61, 10–26.
310
Gill, R., 2010. Igneous rocks and processes: A practical guide. Willey-Blacwell. First
311
Edition 428p
312
Grantham, G. H., Manhiça, A. D., Armstrong, R. A., Kruger, F. J., & Loubser, M.,
313
2011. New SHRIMP, Rb/Sr and Sm/Nd isotope and whole rock chemical data from
314
central Mozambique and western Dronning Maud Land, Antarctica: Implications for the
315
nature of the eastern margin of the Kalahari Craton and the amalgamation of Gondwana.
316
Journal of African Earth Sciences 59, 74–100.
317
GTK, 2006. Map Explanation; Volume 2: Sheets 1630 – 1934. Geology of Degree
318
Sheets Mecumbura, Chioco, Tete, Tambara, Guro, Chemba, Manica, Catandica,
319
Gorongosa, Rotanda, Chimoio and Beira, Mozambique. Ministério dos Recursos
320
Minerais, Direcção Nacional de Geologia, Maputo p. 499.
321
Irvine, T.N., Barager, W.R.A., 1971. A guide to the chemical classification of the
322
common volcanic rocks. Canadian Journal of Earth Science 8, 523–548.
323
Irvine, T.N., Barager, W.R.A., 1971. A guide to the chemical classification of the
324
common volcanic rocks. Canadian Journal of Earth Science 8, 523–548.
325
Kennedy, W.Q., 1964. The structural differentiation of Africa in the Pan African
326
(‘‘500Ma) tectonic episode. Leeds University Research Institute for African Geology
327
Annual Report 8, 48–49.
328
Kretz, 1983. Symbols for rock forming minerals. American Mineralogist. 68, 277–279.
329
LKAB, 1979. Preliminary exploration work in the Inchope-Doeroi area, Mozambique.
330
Draft final report. Unpubl. Rept., DNG Library No. 973, Maputo.
AC C
EP
TE D
M AN U
SC
RI PT
306
14
ACCEPTED MANUSCRIPT Macey, P. H., Thomas, R. J., Grantham, G. H., Ingram, B. A., Jacobs, J., Armstrong, R.
332
A., Roberts, M. P., Bingen, B., Hollick, L., de Kock, G. S., Viola, G., Bauer, W.,
333
Gonzales, E., Bjerkgard, T., Henderson, I. H. C., Sandstad, J. S., Cronwright, M. S.,
334
Harley, S., Solli, A., Nordgulen, O., Motuza, G., Daudí, E., Manhiça, V., 2010.
335
Mesoproterzoic Geology of the Nampula block, northern Mozambique: Tracing
336
fragments of Mesoproterozoic crust in the heart of Gondwana. Journal of Precambrian
337
Research 182, 124–148.
338
Manhiça, A.S.T.D., Grantham, G.H., Armstrong, R.A., Guise, P.G., Kruger, F.J., 2001.
339
Polyphase deformation and metamorphism at the Kalahari Craton – Mozambique belt
340
boundary. In: Miller, J.A., Holdsworth, R.E., Buick, I.S., Hand, M. (Eds.), Continental
341
Reactivation and Reworking. Geological Society of London 184, 303–321.
342
Maniar, P. D., Piccoli, P. M., 1989. Tectonic discrimination of granitoids. Geological
343
Society of America Bulletin 101, 635-643.
344
O’Connor, J.T., 1965. A classification for quartz-rich igneous rocks based on feldspar
345
ratios. U.S. Geological Survey Professional Paper 525 (B), pp. 79–84.
346
Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimination
347
diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology. 25, 956–
348
983.
349
Steiger, R.H., Jäger, E., 1977. Subcommision on Geochronology convention on the use
350
of decay constants in geo- and cosmochronology. Earth Planetary Science Letters 36,
351
359-362.
352
Sun, S. S., McDonough, W. F., 1989. Chemical and isotopic systematic of ocean
353
basalts: implications for mantle composition and processes. In: Saunders, A. D. &
354
Norry,M. J. (eds) Magmatism in the Ocean Basins. Geological Society, London, Special
355
Publications 42, 313-345.
AC C
EP
TE D
M AN U
SC
RI PT
331
15
ACCEPTED MANUSCRIPT Figure Captions
357
Figure 1. Sketch map of the study area in Central Mozambique modified after GTK
358
(2006). Abbreviations: P2BUig-Inchope orthogneiss (1079 Ma, magmatic U/Pb),
359
P2BCch-mica schist and mica gneiss, P2BUgb-gabbro and gabbroic rock, P2BCmi-
360
migmatitic paragneiss, P2BCfg-Monte Chissui gneiss, felsic biotite gneiss and
361
metagranite, P2BCss-siliclastic metasediment and numbers: (1) normal fault, (2) fault
362
or fracture line, (3) foliation, (4) lineation (5) main road (asphalt), (6) railroad, (7) main
363
river, (8) topographic line, (9) radiometric age in Ma and method, and (10) sampling
364
point.
SC
RI PT
356
M AN U
365
Figure 2. Field photographs of the Inchope orthogneiss. (a) Slight compositional
367
banding in in the Inchope orthogneiss, (b) layered coarse-grained tonalitic orthogneiss
368
of the Inchope orthogneiss, with an audit abandoned mine, (c) pegmatitic veis in the
369
Inchope orthogneiss, (d) Typical Inchope orthogneiss with tonalitic (dark) and
370
granodioritic (light) bodies.
TE D
366
371
Figure 3. Petrographic photographs of the Inchope orthogneiss taken under crossed
373
polars (XP). (a), (b), (c) and (d) quartz, plagioclase, biotite, muscovite and alkali
374
feldspar. Symbols according to Kretz (1983).
AC C
375
EP
372
376
Figure 4. Cathodoluminescence (CL) images of representative zircons from analysed
377
samples, with analytical spots and age results in Ma indicated for samples VM-011 and
378
VM-015.
379
16
ACCEPTED MANUSCRIPT 380
Figure 5. Concordia plots for the Inchope orthogneiss (a) Sample VM-011. (b) Sample
381
VM-015.
382
Figure 6. Plots of the Inchope orthogneiss after Depaolo (1988) in terms of (a) eNd(T)
384
vs. Nd depleted-mantle model ages, (b) Plots of eNd(T) values vs. initial Sr isotope
385
ratios for the samples of the Inchope orthogneiss.
RI PT
383
386
SC
387
Table Captions
389
Table 1. LA-ICP-MS data of zircons from the Inchope orthogneiss
390
Table 2. Whole-rock Sr-Nd data from the Inchope orthogneiss
M AN U
388
AC C
EP
TE D
391
17
Ages and errors (Ga) T206/238 1 sigma T207/235 1 sigma T207/206 1 sigma
1.8607
0.0420
0.1801
0.0040
0.99
5.5517
0.1236
0.0749
0.0007
0.5548
0.2542
1.068
0.022
1.067
0.015
1.067
0.019
2.1
1.8114
0.0194
0.1770
0.0015
0.81
5.6484
0.0490
0.0748
0.0007
0.0386
0.0170
1.051
0.008
1.050
0.007
1.065
0.018
4.1
1.8195
0.0195
0.1756
0.0015
0.80
5.6946
0.0491
0.0756
5.1
1.7182
0.0205
0.1687
0.0018
0.87
5.9275
0.0617
0.0747
6.1
1.7506
0.0187
0.1730
0.0015
0.81
5.7804
0.0501
0.0744
7.1
1.8125
0.0196
0.1760
0.0015
0.80
5.6803
0.0493
0.0743
8.1
1.7658
0.0201
0.1737
0.0015
0.77
5.7578
0.0509
0.0736
10.1
1.7250
0.0213
0.1692
0.0018
0.84
5.9106
0.0613
0.0743
11.1
1.7870
0.0188
0.1744
0.0015
0.81
5.7333
0.0490
13.1
1.8934
0.0208
0.1820
0.0016
0.82
5.4956
0.0493
14.1
1.9151
0.0360
0.1841
0.0032
0.92
5.4330
0.0935
16.1
1.7591
0.0146
0.1695
0.0008
0.56
5.8986
0.0276
17.1
1.7821
0.0123
0.1717
0.0008
0.69
5.8232
18.1
1.8437
0.0268
0.1807
0.0021
0.80
5.5344
19.1
1.6856
0.0128
0.1682
0.0009
0.71
5.9442
20.1
1.8363
0.0127
0.1790
0.0009
0.77
21.1
1.8196
0.0150
0.1775
0.0010
0.66
22.1
1.7944
0.0130
0.1768
0.0011
0.83
24.1
1.7523
0.0112
0.1738
0.0007
0.66
27.2
1.9008
0.0680
0.1836
0.0077
28.1
1.8385
0.0538
0.1789
0.0066
29.1
1.7908
0.0515
0.1750
30.1
1.8725
0.0566
0.1816
M AN U
1.1
EP
SC
Ratios and errors 207/235 1sigma 206/238 1 sigma Rho 238/206 1 sigma 207/206 1 sigma 208/206 1 sigma
AC C
Spot VM-011
RI PT
ACCEPTED MANUSCRIPT
0.0007
0.2005
0.0819
1.043
0.008
1.052
0.007
1.086
0.018
0.0007
0.1704
0.0672
1.005
0.010
1.015
0.008
1.062
0.018
0.0007
0.4872
0.1856
1.029
0.008
1.027
0.007
1.054
0.018
0.0007
0.1176
0.0435
1.045
0.008
1.050
0.007
1.050
0.018
0.0007
0.5627
0.2009
1.032
0.008
1.033
0.007
1.032
0.019
0.0007
0.1293
1.008
0.010
1.018
0.008
1.052
0.020
0.0007
0.0646
0.0211
1.036
0.008
1.041
0.007
1.066
0.018
0.0755
0.0007
0.3228
0.0996
1.078
0.009
1.079
0.007
1.083
0.018
0.0767
0.0005
0.2838
0.0295
1.089
0.017
1.086
0.012
1.117
0.013
0.0764
TE D
0.3848
0.0749
0.0005
0.0267
0.0028
1.010
0.004
1.031
0.005
1.106
0.013
0.0278
0.0762
0.0004
0.5697
0.0594
1.022
0.005
1.039
0.004
1.103
0.011
0.0642
0.0750
0.0004
0.1951
0.0208
1.071
0.011
1.061
0.010
1.071
0.012
0.0320
0.0724
0.0004
0.4864
0.0572
1.002
0.005
1.003
0.005
0.999
0.011
5.5866
0.0296
0.0747
0.0004
-0.2507
0.0462
1.062
0.005
1.059
0.005
1.062
0.011
5.6331
0.0306
0.0746
0.0004
0.2796
0.0294
1.053
0.005
1.053
0.005
1.059
0.011
5.6572
0.0340
0.0744
0.0004
0.0824
0.0087
1.049
0.006
1.043
0.005
1.053
0.011
5.7536
0.0242
0.0738
0.0004
0.0232
0.0026
1.033
0.004
1.028
0.004
1.038
0.011
0.99
5.4468
0.2298
0.0762
0.0006
1.0078
0.3101
1.087
0.042
1.081
0.024
1.101
0.016
0.99
5.5890
0.2067
0.0753
0.0005
0.4571
0.1431
1.061
0.036
1.059
0.019
1.078
0.013
0.0064
0.99
5.7143
0.2086
0.0745
0.0005
1.1861
0.3859
1.040
0.035
1.042
0.019
1.055
0.013
0.0068
0.99
5.5075
0.2061
0.0748
0.0005
0.0421
0.0139
1.076
0.037
1.071
0.020
1.064
0.013
ACCEPTED MANUSCRIPT
VM-015 1.8117
0.0339
0.1776
0.0038
0.99
5.6318
0.1215
0.0758
0.0004
0.0871
0.0435
1.054
0.021
1.050
0.012
1.091
0.012
1.7886
0.0323
0.1744
0.0036
0.99
5.7344
0.1196
0.0755
0.0004
0.0467
0.0243
1.036
0.020
1.041
0.012
1.082
0.012
6.1
1.7554
0.0320
0.1706
0.0036
0.99
5.8628
0.1235
0.0758
0.0004
0.1416
0.0905
1.015
0.020
1.029
0.012
1.093
0.012
8.1
1.6986
0.0312
0.1670
0.0036
0.99
5.9871
0.1273
0.0747
0.0004
0.0931
0.0742
0.996
0.020
1.008
0.012
1.062
0.012
1.2048
1.052
0.021
1.047
0.012
1.067
0.012
0.0096
1.009
0.006
1.014
0.006
1.063
0.004
RI PT
1.1 2.1
1.8050
0.0342
0.1772
0.0038
0.99
5.6427
0.1224
0.0749
0.0004
1.4231
1.7140
0.0151
0.1694
0.0011
0.76
5.9036
0.0392
0.0748
0.0001
0.0837
15.1
1.7403
0.0258
0.1729
0.0023
0.89
5.7835
0.0761
0.0734
0.0002
0.5937
0.0660
1.028
0.012
1.024
0.010
1.027
0.007
4.1
1.9026
0.0346
0.1834
0.0038
0.99
5.4533
0.1145
0.0761
0.0004
0.1867
0.1051
1.085
0.021
1.082
0.012
1.100
0.012
1.7545
0.0322
0.1684
0.0036
0.99
5.9377
0.1257
0.0764
1.7808
0.0237
0.1722
0.0009
0.39
5.8081
0.0301
0.0755
3.1
1.4834
0.0271
0.1516
0.0032
0.99
6.5962
0.1380
0.0738
17.1
1.4338
0.0250
0.1449
0.0015
0.61
6.9006
0.0729
0.0735
19.1
1.3741
0.0231
0.1406
0.0014
0.60
7.1108
0.0721
0.0726
21.1
1.4068
0.0211
0.1444
0.0012
0.54
6.9234
0.0556
0.0725
6.2
0.4836
0.0089
0.0599
0.0013
0.99
16.6889
0.3526
7.2
0.6177
0.0115
0.0788
0.0017
0.99
12.6889
0.2701
9.2
0.5376
0.0104
0.0679
0.0015
0.99
14.7209
0.3225
M AN U
5.1 20.1
0.0004
1.3376
0.8221
1.003
0.020
1.029
0.012
1.108
0.012
0.0003
0.2472
0.0554
1.024
0.005
1.038
0.009
1.083
0.009
0.0004
1.3914
0.7517
0.910
0.018
0.924
0.011
1.036
0.012
0.0006
0.0865
0.0210
0.872
0.009
0.903
0.010
1.028
0.016
0.0769
0.0177
0.848
0.008
0.878
0.010
1.003
0.012
0.0837
0.0184
0.870
0.007
0.892
0.009
1.001
0.009
0.0593
0.0004
0.0127
0.0087
0.375
0.008
0.401
0.006
0.572
0.013
0.0591
0.0003
0.0115
0.0087
0.489
0.010
0.488
0.007
0.565
0.013
0.0586
0.0004
0.0089
0.0081
0.424
0.009
0.437
0.007
0.544
0.014
TE D
0.0004
0.0003
EP AC C
SC
9.1 11.1
ACCEPTED MANUSCRIPT
143
Nd/ Nd (σ) 0.511474 (9) 0.511457 (8) 0.511279 (5) 0.511429 (11) 144
fSm/Nd
ɛNd (0)
-0.42 -0.43 -0.50 -0.43
-22.70 -23;05 -26.51 -23.58
ɛNd at 1050Ma -11.8 -11.7 -13.3 -12.4
TDM (Ga) 2.4 2.4 2.3 2.4
Rb (ppm) 561.2 519.6 438.6 481.9
Sr (ppm) 102.2 106.4 173.3 101.4
RI PT
Sm/ Nd (σ) 0.1148 (7) 0.1113 (7) 0.0977 (6) 0.1124 (7)
SC
147
144
M AN U
Nd (ppm) 34.08 39.44 41.91 36.68
TE D
WR WR WR WR
Sm (ppm) 6.47 7.26 6.77 6.82
EP
VM-025 VM-012 VM-015 VM-011
Mat.
AC C
Sample no.
87
Rb/ Sr 16.284 (61) 14.453 (82) 7.413 (63) 14.047 (39) 86
87
Sr/ Sr 0.953692 (66) 0.936048 (119) 0.828486 (64) 0.925961 (74) 86
(87Sr/86Sr) at 1050 Ma 0.7117 0.7209 0.7170 0.7167
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 (1) The Inchope orthogneiss crystallized in Proterozoic from a hybrid source dominated by crustal material. (2) The Inchope orthogneiss was affected by two metamorphic events. (3) The first metamorphic age is related to pegmatite veins intrusion.
AC C
EP
TE D
M AN U
SC
RI PT
(4) The second metamorphic age is related to Pan-African deformation.