- Email: [email protected]
yr slip rate for the Bucaramanga-Santa Marta Fault, Colombia
Accepted Manuscript Magnetic stratigraphy of the Bucaramanga alluvial Fan: Evidence for a ≤ 3 mm/yr slip rate for the Bucaramanga-Santa Marta Fault, Colombia Giovanny Jiménez Diaz , Fabio Speranza , Claudio Faccena , German Bayona , Andres Mora PII:
S0895-9811(14)00154-0
DOI:
10.1016/j.jsames.2014.11.001
Reference:
SAMES 1341
To appear in:
Journal of South American Earth Sciences
Received Date: 13 March 2014 Revised Date:
24 October 2014
Accepted Date: 7 November 2014
Please cite this article as: Diaz, G.J., Speranza, F., Faccena, C., Bayona, G., Mora, A., Magnetic stratigraphy of the Bucaramanga alluvial Fan: Evidence for a ≤ 3 mm/yr slip rate for the BucaramangaSanta Marta Fault, Colombia, Journal of South American Earth Sciences (2014), doi: 10.1016/ j.jsames.2014.11.001. 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.
1
ACCEPTED MANUSCRIPT 1
Magnetic stratigraphy of the Bucaramanga alluvial Fan: Evidence for a ≤ 3
2
mm/yr slip rate for the Bucaramanga-Santa Marta Fault, Colombia
3 Giovanny Jiménez Diaz 1, 2, Fabio Speranza 2, Claudio Faccena 1, German
5
Bayona 3, Andres Mora 4
RI PT
4
6 1 Università di Roma TRE, Roma, Italy
8
2 Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy
9
3 Corporación Geológica ARES, Bogota, Colombia
M AN U
10
SC
7
4 Instituto Colombiano del Petróleo, Ecopetrol-ICP, Bucaramanga, Colombia
11 12
16 17 18 19 20 21 22 23 24 25
EP
15
AC C
14
TE D
13
2
ACCEPTED MANUSCRIPT 26 27 28
Abstract
RI PT
29 The 550 km long Bucaramanga-Santa Marta Fault is one of the main active tectonic
31
features of NW South America. It is a left-lateral strike-slip fault bounding the
32
Maracaibo block, and straddling northern Colombia from the Caribbean Sea to the
33
Eastern Cordillera. Variable total displacement values (from 40 to 110 km), and
34
present-day slip rates (from 0.01 to 10 mm/yr) have been proposed so far for the
35
Bucaramanga Fault. Here we report on the paleomagnetic investigation of a Plio-
36
Pleistocene (?) continental alluvial fan juxtaposed to the Bucaramanga Fault, and
37
horizontally displaced by 2.5 km with respect to its feeding river. Nine (out of
38
fourteen) reliable paleomagnetic directions define a succession of six different
39
magnetic polarity zones that, lacking additional age constraints, can be correlated
40
with several tracks of the Plio-Pleistocene magnetic polarity time scale. If the
41
youngest age model is considered, most recent sediments of the fan can be
42
reasonably dated at 0.8 Ma (Brunhes-Matuyama chron transition), translating into a
43
maximum 3 mm/yr slip rate for the Bucaramanga Fault. Older age models would
45 46
M AN U
TE D
EP
AC C
44
SC
30
obviously yield smaller slip rates. Our paleomagnetic sites, located at 4-10 km from the fault, do not show significant rotations, implying weak fault coupling and/or ductile upper crust behavior adjacent to the Bucaramanga Fault.
47 48 49 50
Keywords: Paleomagnetism, Bucaramanga Fan, Bucaramanga Fault, Slip rate.
3
ACCEPTED MANUSCRIPT 51
Introduction
52 The NW margin of South America is characterized by a complex pattern of
54
mountain ranges (Western, Central, and Eastern Cordillera of Colombia, Fig. 1),
55
and by a puzzle of crustal blocks undergoing independent movements (Kellogg et
56
al., 1982; Taboada et al., 2000; Trenkamp et al., 2002). The eastward subduction of
57
the Nazca Plate beneath South America at a rate of 6 cm/yr is well documented
58
(Trenkamp et al., 2002), while the existence of an ESE-ward directed subduction of
59
the Caribbean plate is debated (Pindell et al., 1988). A well-developed accretionary
60
wedge (Fig. 1) is exposed at the boundary between the Caribbean and South
61
American plate (e.g., Flinch et al., 2003).
62
The Maracaibo block, the biggest semi-rigid block of the Colombian tectonic
63
puzzle, is bounded by three major wrench faults: the dextral Boconó and Oca
64
faults, and the sinistral Bucaramanga-Santa Marta Fault (Fig. 1). The relevance,
65
age, and displacement rate of these major strike-slip faults have been widely
66
discussed in the past (Irving, 1971; Toro, 1990; Ujueta, 2003; Mora and Garcia,
67
2006; Lopez et al., 2008), and a consensus on the whole block and fault kinematics
68
has not been reached so far.
71
AC C
EP
TE D
M AN U
SC
RI PT
53
72
1), where it crosses the city of Bucaramanga (ca. 500,000 inhabitants). It can be
73
divided along strike into three major zones (Northern, Central and Southern zone),
74
where it bounds several distinct geological provinces. The Northern zone, or Santa
75
Marta section (Paris, 2000; Ingeominas, 2001a), corresponds to a 140 km long
69 70
The Bucaramanga-Santa Marta Fault system juxtaposes basement rocks to the east and sedimentary Jurassic to Cenozoic rocks to the west. This fault system extends for a distance of 550 km from the Caribbean coast to the Eastern Cordillera (Fig.
4
ACCEPTED MANUSCRIPT
topographic lineament juxtaposing old crystalline rocks of the Santa Marta Massif
77
to Neogene deposits of the Lower Magdalena Valley basin (Fig. 1). The 100 km
78
long Central zone is covered by alluvial deposits of the Lower Magdalena Valley
79
basin (Ariguani graben) and Cesar Valley basin (Mora and García, 2006; Fig.1).
80
The Southern zone corresponds to Bucaramanga section (Paris, 2000; Ingeominas,
81
2001a), a 310 km long outstanding linear topographic feature separating the
82
Santander Massif from the Middle Magdalena Valley basin (Fig. 1). At the city of
83
Bucaramanga, the fault clearly left-laterally displaces a 10-15 km wide continental
84
alluvial fan of presumable Plio-Pleistocene age, produced by debris carried by the
85
Suralá river from the adjacent Santander Massif (Fig. 2). The zone is well known
86
for the high seismic activity of the “Bucaramanga nest” (Taboada et al, 2000; Zarifi
87
et al, 2007; Fig. 3), but earthquakes are deep (from 100 to 200 km), thus they
88
should not be related to the activity of the Bucaramanga Fault.
89
In this paper we report on a paleomagnetic investigation of the Bucaramanga Fan to
90
constrain its age by magnetic stratigraphy, one of the few viable method to
91
dategravel-size alluvial fan deposits. The results allow the documentation of when
92
fan displacement occurred, and unravel recent and present-day slip rate of the
93
Bucaramanga Fault. The city of Bucaramanga has not been struck by devastating
96
AC C
EP
TE D
M AN U
SC
RI PT
76
97
Bucaramanga Fault, as GPS data of Trenkamp et al. (2002) might suggest (Fig. 1).
94 95
98 99 100
earthquakes since when historical accounts are available (XVII century AD), thus it is unclear whether we are living an inter-seismic interval preceding a future strong earthquake, or in fact there is no significant present-day activity of the
5
ACCEPTED MANUSCRIPT 101
Characteristics of the Bucaramanga-Santa Marta Fault
102 Previous work around the City of Bucaramanga has been done in the frame of
104
regional and local cartography projects (Ward et al., 1973; Ingeominas, 2001b;
105
Diedrix et al., 2009; Fig. 2). In the Santander Massif, which is bounded to the west
106
by the Bucaramanga Fault system, Precambrian, Paleozoic, and Mesozoic intrusive
107
and metamorphic rocks (schists and gneisses) are exposed. According to Cediel et
108
al. (2003), the Bucaramanga-Santa Marta Fault was active during the Precambrian
109
Grenville - Orinoco continental collision, and reactivated in the Aptian-Albian
110
times. The Bucaramanga Fault bounds a thick deposition of upper Jurassic and
111
Cretaceous rocks to the south and west (Kammer and Sanchez, 2006), whereas to
112
the north and east the deposition of Jurassic rocks is more condensed and in some
113
areas lowermost Cretaceous strata are lacking (Ward et al, 1973).
114
Provenance analysis indicates that the Santander Massif and its sedimentary cover
115
were uplifted since Paleogene time (Ayala et al, 2012). Paleocene movements may
116
be related to other structures in the Cobardes Anticline (Parra et al, 2012, Fig. 1).
117
Mora and García (2006) using extensive seismic profile analysis and well data in
118
the Central zone, proposed that the Bucaramanga-Santa Marta Fault was
121
AC C
EP
TE D
M AN U
SC
RI PT
103
122
activity ended after Oligocene, as the Lower Magdalena Valley and Cesar basins
123
have been connected without tectonic disturbances.
119 120
responsible for the intense structural deformation that affected pre-Oligocene units, indicating that it was an active boundary between the Lower Magdalena Valley and Cesar basins during the late Eocene-early Oligocene. They also suggested that fault
124 125
Ross et al. (2009) using Apatite fission track analysis (AFTA) of Precambrian to
6
ACCEPTED MANUSCRIPT
Neogene rocks from the Santander Massif and Middle Magdalena Valley proposed
127
three paleothermal episodes (interpreted as erosional phases) in the Paleocene (65
128
to 60 Ma), Early Miocene (20 to 18 Ma) and Middle Miocene (12 to 9 Ma). This
129
evidence provides age clues for the uplift of the Santander Massif with respect to
130
the adjacent Magdalena Valley that likely occurred along the Bucaramanga Fault.
131
As the Bucaramanga Fault is a recent geomorphological feature, it was likely
132
activated in the last phase of deformation of late Miocene age, as suggested by
133
AFTA data. Finally, Pindell et al. (1988) proposed that the Bucaramanga – Santa
134
Marta fault is the western limit of the Maracaibo Block since Miocene times.
M AN U
SC
RI PT
126
135
Reported total displacement values of the Bucaramanga – Santa Marta fault vary
137
from 45 to 110 km. Toro (1990) using structural reconstructions proposed for the
138
southern fault portion a displacement of 45 km. According to Campbell (1968), the
139
total displacement is more than 100 km, relying on a regional scale correlation
140
between rocks from the Central Cordillera and the Santa Marta Massif. Other
141
authors (Irving, 1971; Tschantz, 1974) proposed 110 km of displacement after the
142
analysis of samples drilled in oil wells. Montes et al. (2010) and Bayona et al.
143
(2010) considered the Bucaramanga-Santa Marta Fault system as western boundary
146
AC C
EP
TE D
136
147
evaluated after regional geology considerations (Rivera, 1989).
144 145
of the Maracaibo block clockwise rotation during the Cenozoic. Reported values for the fault slip rate range between 0.01-0.2 mm/yr, calculated on the basis of geomorphic offset features (Paris, 2000; Ingeominas, 2001a), to 10 mm/yr,
148 149
López et al., (2008) reported the occurrence of Pseudotachylite associated to
150
cataclasites in the southern sector of the Bucaramanga Fault, that they interpreted
7
ACCEPTED MANUSCRIPT
as an evidence for paleoseismicity along the fault. Diedrix et al. (2009) using
152
paleoseismological investigation and radiocarbon dating of paleosols trenched
153
adjacent to the fault proposed eight Holocene seismic events during the last 8300
154
years and magnitudes in the order of 6.5-7.0, associated to the Bucaramanga Fault
155
activity.
RI PT
151
156
Ujueta (2003) made an extensive review of the previous works on the Bucaramanga
158
Santa Marta Fault available since 1933, and observed that some authors consider
159
the Bucaramanga Santa Marta fault as a reverse fault, others as left lateral strike-
160
slip fault, while few works propose two different and independent faults.
161
Concerning the age of the Bucaramanga Fault activity, a late Mesozoic, Paleocene,
162
Eocene or Pliocene-Quaternary age are proposed (Ujueta, 2003). Finally, using
163
seismic profiles, he discussed the continuity of the fault Central zone, and proposed
164
two different but related faults, with absence of connection between the southern
165
and the northern zone.
166
The deep seismicity of the Bucaramanga Nest
M AN U
TE D
No significant shallow crustal seismicity has been recorded along the Santa Marta-
171
AC C
168
EP
167
SC
157
172
nests by its high rate of activity in a volume much smaller than the other nests at
173
similar intermediate depths (Schneider et al., 1987; Zarifi and Harsco, 2003; Prieto
174
et al., 2012). The Bucaramanga nest has been mostly related to tectonic processes
175
occurring in the oceanic subducting plates beneath Colombia (Zarifi and Havskov,
169 170
Bucaramanga Fault (Fig. 3), but at depth a remarkable cluster of subcrustal earthquakes in the 100-200 km depth interval is observed in the so-called “Bucaramanga nest”, centered at 7°N 73°W (Fig 3). It differs from other worldwide
8
ACCEPTED MANUSCRIPT
2003). Taboada et al. (2000) proposed that the Bucaramanga Nest is due to the
177
interaction between the subducting Nazca and paleo-Caribbean plates, while Zarifi
178
et al. (2007) suggested a simultaneous subduction process and collision between
179
two subducted slabs. Conversely, Cediel et al. (2003) proposed that the seismic
180
activity recorded in the Bucaramanga Nest represents a zone of tectonic detachment
181
associated with NW-ward migration of the Maracaibo subplate, while Rivera
182
(1989) proposed that there is a relationship between the Bucaramanga Fault and
183
Nest.
SC
RI PT
176
185
The Bucaramanga Fan
186
M AN U
184
The Bucaramanga Fan is limited to the east by the Santander Massif and the
188
Bucaramanga Fault, and to the west by the Suárez Fault (Fig. 2). The Suárez Fault
189
is a west-dipping reverse fault with sinistral displacement and Quaternary activity
190
(Page, 1986; Paris et al., 2000; Ingeominas, 2001a) that terminates northward
191
against the Bucaramanga Fault. In the study area, the Suárez Fault juxtaposes
192
Jurassic and Cretaceous strata against the Bucaramanga Fan. Locally, the
193
Bucaramanga Fan is folded with vertical to overturned beds by the effect of the
196
AC C
EP
TE D
187
197
De Porta (1959) defined the Bucaramanga Fan as a sedimentary deposit of
198
Quaternary age with an alluvial fan morphological shape (Fig. 2).
199
According to Julivert (1958) The E-W creeks and the shape of the Bucaramanga
200
Fan can be related, but the present-day drainage network can't explain the
194 195
Suárez Fault (Ingeominas, 2008).
9
ACCEPTED MANUSCRIPT
Bucaramanga Fan location. Ingeominas (2001b and 2008) suggested that the Suratá
202
River is the feeder of the Bucaramanga Fan, although it is presently shifted by 2.5
203
km with respect to fan apex. According to Ingeominas (2008) the southern part of
204
the Bucaramanga Fan has been more faulted than the northern part, and seems to be
205
diachronous. Thus the progressive northward migration of the fan apex has been
206
related to the sinistral shear along the Bucaramanga Fault.
207
RI PT
201
According to Ingeominas (2001b) the thickness of the Bucaramanga Fan increases
209
from east to west with an average thickness of 250 m, and from base to the top it
210
has been subdivided into, the Organos, Finos, Gravoso, and Limos Rojos member
211
(Fig. 2).
212
The Organos Member was first defined by Hubach (1952), and according to Bueno
213
and Solarte (1994) is a monotonous sequence of conglomerates with intercalations
214
of fine sandstones. Conglomerate clasts are 10 - 30 cm in diameter (and in some
215
cases more than 1 m) and include gneisses and schists fragments. This member is
216
clast supported, contains a clay matrix (Ingeominas, 2001b), and crops out to the
217
west of the study area with a maximum thickness of 180 m (Mancera and
218
Salamanca, 1994). The Finos Member (Hubach, 1952) is a continuous sub-
221
AC C
EP
TE D
M AN U
SC
208
222
m thick, matrix supported level of gravel-size clasts overlying the Finos Member
223
along a net contact. The clasts are on average 15 cm in diameter (cobble size), and
224
the matrix includes a mixture of clay- and sand-size fragments. Finally, the
225
Gravoso Member transitionally passes upward into the 15 m thick Limos Rojos
219 220
horizontal 15 m thick bed overlying the Organos member along a net discontinuity, and it consists of clays evolving upsection into fine-grained sandstone beds (Ingeominas, 2001b). The Gravoso Member (Vargas and Niño, 1992) is an 8 to 30
10
ACCEPTED MANUSCRIPT
Member (Julivert, 1963); this unit consists of argillaceous sandstones and
227
conglomeratic sandstones, interbeded with layers of siltstones. Locally, block
228
fragments (meter scale in diameter) of sandstone texture are supported by the red
229
silty matrix (Ingeominas, 2001b).
230
The Bucaramanga Fan is generally referred to a Plio-Pleistocene age (Ingeominas,
231
2001b), although no conclusive age constraints were gathered from the continental
232
succession so far.
RI PT
226
SC
233
235 236
Sampling and Methods
237
M AN U
234
We collected sandy-silty samples for paleomagnetic analysis in fourteen sites (154
239
cores, Table 1) from the Bucaramanga Fan, using a petrol-powered portable drill
240
cooled by water. Ten sites were gathered in the Organos Member, two in the Finos
241
Member, and two in the Gravoso Member (Figure 2 and Table 1). At each site we
242
collected 6–12 cores (11 on average), spaced in at least two outcrops in order to try
243
to average out secular variation of the geomagnetic field. All samples were oriented
246
AC C
EP
TE D
238
247
Cores were prepared into standard cylindrical specimens of 22 mm height, and
248
rock magnetic and paleomagnetic measurements were done in the shielded room of
249
the paleomagnetic laboratory of the Istituto Nazionale di Geofisica e Vulcanologia
250
(Roma, Italy). All samples were thermally demagnetized through 11–12 steps up to
244 245
using a magnetic compass, corrected to account for the local magnetic field declination value at the sampling area (about 7º W) according to NOAA’s National Geophysical Data Center (http://www.ngdc.noaa.gov).
11
ACCEPTED MANUSCRIPT
680°C by a shielded oven, and the natural remanent magnetization (NRM) of the
252
specimens was measured after each step with a DC- SQUID cryogenic
253
magnetometer (2G Enterprises, USA). Thermal demagnetization data were plotted
254
on orthogonal diagrams (Zijderveld, 1967), and the magnetization components
255
were isolated by principal component analysis (Kirschvink, 1980). The site-mean
256
directions were evaluated by Fisher’s (1953) statistics.
257
On a set of selected specimens, magnetic mineralogy analyses were carried out to
258
identify and characterize the main magnetic carriers using the thermal
259
demagnetization of a three-component isothermal remanent magnetization (IRM)
260
imparted on the specimen axes, according to the method of Lowrie (1990). Fields
261
of 2.7, 0.6, and 0.12 T were successively imparted on the z, y, and x sample axes
262
(respectively) with a pulse magnetizer (Model 660, 2G Enterprises). The
263
generalized stratigraphic column of the Bucaramanga Fan was made using field
264
data and previous geological maps (Ingeominas, 2001b). The stratigraphic position
265
for all sampled sites was calculated using a cross section.
SC
M AN U
TE D
271
AC C
268
Results
EP
266 267
RI PT
251
272
samples both the medium coercivity and the hard fractions are demagnetized
273
between 600 and 680°C (Fig. 4), pointing to hematite as the main magnetic carrier
274
of our samples. In almost all sites, a drop of the medium coercivity and hard
275
fraction occurring before 100º shows that a small amount of goethite is also
269 270
Magnetic Mineralogy
The thermal demagnetization of a three-component IRM shows that for most of the
12
ACCEPTED MANUSCRIPT 276
associated to hematite.
277 278
Paleomagnetism
RI PT
279 Only 9 (out of 14) sites yielded reproducible paleomagnetic directions during
281
cleaning, while the remaining 5 sites showed scattered demagnetization diagrams
282
(Figure 5 and Table 1). For most of the sites, a characteristic magnetization
283
component (ChRM) was isolated between 550 and 680°C, confirming that hematite
284
represents the main magnetic carrier. For about 10% of the samples, a ChRM is
285
isolated between 380 and 680°C, suggesting the coexistence of hematite and
286
maghaemite (Fig. 5). Mean paleomagnetic directions are reasonably well
287
constrained, the α95 values being comprised between 8.4° and 22.4° for all sites but
288
one yielding a value of 48.2 (Fig. 6 and Table 1). Three sites are of normal polarity
289
(D = 356.1, I = 9.4, K = 136.76 and α95 = 10.6 ) and the other six are of reverse
290
polarity (D = 178.2, I =1.8, K = 36.20, and α95 = 11.3 ); the reversal test (according
291
to McFadden and McElhinny (1990), is positive of Class “c”.
292
The fact that our results yielded reverse polarity directions indicate that the
293
Bucaramanga Fan should be older than the Bruhnhes polarity chron (0 to 0.8 Ma)
296
AC C
EP
TE D
M AN U
SC
280
297
direction, except the youngest magnetozone R3, which is corroborated by four
298
different site results. As the age of the Bucaramanga Fan is vaguely inferred to be
299
Plio-Pleistocene, several different correlations with the global magnetic polarity
300
time scale (GPTS, Cande and Kent, 1995) are possible (Fig. 8). If we assign the
294 295
When plotted according to their stratigraphic position, the sites from the Bucaramanga Fan yield a succession of three normal- and three reverse-polarity magnetozones (Fig. 7). Each magnetozone is defined by one paleomagnetic
13
ACCEPTED MANUSCRIPT
youngest possible age to the succession (Fig. 8a), R3 correlates with upper
302
Matuyama polarity chron (C1r.1r), and N3, N2, and N1 with the Jaramillo,
303
Olduvai, and Gauss chron, respectively. In a slightly older age model (Fig. 8b), R3
304
correlates with the mid Matuyama chron (C1r.2r), N3 with Olduvai chron, and N2
305
and N1 fall both within the Gauss chron. It is not possible at present to indicate a
306
preferred age model using calculated sedimentation rates that vary irregularly
307
(considering both age models of Figure 8) between 30 and 300 mm/kyr. In fact in
308
this kind of deposits the sedimentation is expected to be highly irregular and
309
discontinuous, and the thickness of some magnetozones (such as N3) is poorly
310
constrained due to the occurrence of several failed sites located below and above it
311
(Fig. 7).
M AN U
SC
RI PT
301
312 313
315
Discussion and Conclusions
TE D
314
The slip rate of the southern segment of the Bucaramanga Fault can be in principle
317
calculated by dividing its along-fault displacement by the age of the displaced
318
rocks. Left-lateral displacement is well known, and equates the 2.5 km distance
321
AC C
EP
316
322
magnetozone succession gathered from the Bucaramanga Fan (Fig. 7).
319 320
from the mouth of the Suralá river to the apex of the Bucaramanga Fan (Ingeominas 2008, Figs. 9 and 10). Conversely, the age of the displaced sediments is not firmly constrained, as several different age models can equally fit the
323 324
However, a maximum possible slip rate can be calculated assigning the youngest
325
possible age of the succession, i.e. inferring that magnetozone R3 corresponds to
14
ACCEPTED MANUSCRIPT
the top of the Matuyama polarity chron (Fig. 8a). In this case, a 0.8 Ma age
327
(Brunhes-Matuyama boundary, Cande and Kent, 1995) can be reasonably assigned
328
to the youngest sediments of the Bucaramanga Fan, by considering that: 1) we did
329
not reach the normal-polarity magnetozone above R3, thus the youngest sampled
330
sediments (site GJ192) might fall in the lower-medium part of chron C1r.1r, and be
331
0.9-1 Ma old; 2) the upper member of the Bucaramanga Fan is the Limos Rojos
332
Member, but the youngest paleomagnetic directions were obtained in the
333
underlying Gravoso Member; 3) the Limos Rojos Member is only 15 m thick, and
334
shares the same fan morphology with the underlying Finos-Gravoso members (Fig.
335
2). This suggests that the Limos Rojos Member was rapidly emplaced, and that no
336
significant time gap (and displacement of the fan feeding source) occurred with
337
respect to the Gravoso Member.
338
A 0.8 Ma age of the top of the Bucaramanga Fan translates into a maximum slip
339
rate of 3 mm/yr for the Bucaramanga Fault. Obviously, progressively smaller slip
340
rates would arise by considering progressively older age models for the
341
Bucaramanga Fan. Our slip rate estimate is in rough agreement with conclusions by
342
Diedrix et al. (2009), who documented by paleosismology eight main earthquakes
343
in the last 8300 years, with 400 to 1300 years recurrence intervals, and estimated
346
AC C
EP
TE D
M AN U
SC
RI PT
326
347
seismogenic fault is expected to be associated with 7-7.5 M earthquakes (Wells and
348
Coppersmith, 1994), slightly greater than Diederix et al. (2009) estimates. We note
349
however that older age models for the Bucaramanga Fan would give smaller slip
350
rates, thus better agreement with Diederix et al. (2009) calculated values.
344 345
magnitude values of 6.5 to 7.0. Average recurrence interval documented by Diedrix et al. (2009) is 1000 years, which would translate into an accumulated displacement of 3 m, if our 3 mm/yr spreading rate is considered. A 3 m displacement along a
15
ACCEPTED MANUSCRIPT
Considering that the city of Bucaramanga has a documented history of 390 years
352
without any catastrophic earthquake occurrence, a 1.2 m displacement could have
353
been accumulated since then, if the 3 mm/yr slip rate is considered.
354
Sediments of the Bucaramanga Fan have been clearly displaced by left-lateral fault
355
shear, thus counterclockwise rotations are expected at fault walls, as already
356
observed in several strike-slip fault settings (Sonder et al., 1994; Kimura et al.,
357
2011). On the other hand, our sites from the Bucaramanga Fan, located at 4-10 km
358
from the fault, do not show significant rotations (Fig. 6).
359
Using the power law rheology model (England et al., 1985), in which the relation
360
between distance from a fault trace y (km) and vertical-axis relative rotation θ
361
(rad.) is expressed as:
362
364
θ=arctan (((4Dsπ √n)/L) exp((−4π √ny)L))
TE D
363
M AN U
SC
RI PT
351
Ds (km) is the displacement in one side of the fault, L/2 (km) is the length of the
366
fault, and n is the stress exponent and describes the average mechanical behavior of
367
the lithosphere (Sonder and England, 1986). Clearly, the lack of observed rotations
368
may imply that 1) fault locking is extremely weak, whereas fault walls are
371
AC C
EP
365
372
understand this issue, and better constrain the seismic hazard assessment related to
373
the Bucaramanga Fault activity.
369 370
374 375
extremely rigid and undergo minimal internal deformation, and/or 2) the upper crust west of the Bucaramanga Fault has a ductile behavior. Additional geophysical data (e.g. a high-resolution GPS network across fault zone) are needed to fully
16
ACCEPTED MANUSCRIPT 376 377 378
Acknowledgements: Many thanks to Ecopetrol-ICP and the project: “Cronologia de
380
la deformación en las cuencas Subandinas” for funding and supporting the field
381
work. Danilo Seccia (INGV) helped to realize Figure 3. GB acknowledges
382
Colciencias for continuing support ARES. Thanks to Omar Montenegro for
383
logistical and field work. We are grateful to two anonymous referees and to JSAES
384
Editor James Kellogg for providing careful reviews of our work.
M AN U
SC
RI PT
379
AC C
EP
TE D
385
17
ACCEPTED MANUSCRIPT 386
References
387 Ayala-Calvo, C., G. Bayona, A. Cardona, C. Ojeda, O. Montenegro, C. Montes, V.
389
Valencia and C. Jaramillo (2012), The Paleogene synorogenic succession in the
390
northwestern Maracaibo block: Tracking intraplate uplifts and changes in
391
sediment-delivery systems. Journal of South America Earth Sciences, Special
392
Edition on Tectonic and climatic shaping of the northern Andes and southern
393
Caribbean margin 39, 93-111. Doi: 10.1016/j.jsames.2012.04.005
SC
RI PT
388
Bayona, G., Jimenez, G., Silva, C., Cardona, A., Montes, C., Roncancio, J., and
395
Cordani, U., (2010), Paleomagnetic data and K.Ar ages from Mesozoic units of
396
the Santa Marta Massif: A preliminary interpretation for block rotations and
397
translations: Journal of South American Earth Sciences, v. 29, p. 817-831.
M AN U
394
Bueno. E and A. Solarte (1994), Geología, Geotecnia y Comportamiento Erosivo
399
del Área de Reserva Forestal de Bucaramanga. Tesis para optar al título de
400
Geólogo. Escuela de Geología, UIS, Bucaramanga.
TE D
398
Cande, S.C. and D.V. Kent (1995), Revised calibration of the geomagnetic polarity
402
timescale for the late Cretaceous and Cenozoic. Journal Geophys. Res., 100,
403
6,093-6,095.
405 406
AC C
404
EP
401
Campbell, C. J (1965), The Santa Marta wrench fault of Colombia and its regional setting. Fourth Caribbean Geological Conference. Memoir: 247-261. Trinidad.
Cediel, F., R. Shaw, and C. Cáceres (2003), Tectonic assembly of the northern
407
Andean Block, in Bartolini, C., Buffler, R. T., and Blickwede, J., eds., The
408
Circum-Gulf of Mexico and the Caribbean: Hydrocarbon habitats, basin
409
formation and plate tectonics, American Association of Petrolum Geologists
410
Memoir 79, p. 815-848.
18
ACCEPTED MANUSCRIPT 411 412
De Porta. J (1959), La Terraza de Bucaramanga. UIS. Bol. de Geología No. 3. p.p: 5-13, Bucaramanga. Diederix. H, C. Hernandez, M. T. Eliana, J. A. Osorio, P. Botero (2009), Memorias
414
Congreso Colombiano de Geología, Paipa- Boyaca.́ Resultados preliminares del
415
primer estudio paleosismológico a lo largo de la falla de Bucaramanga.
RI PT
413
England. P, G. Houseman and L. Sonder (1985), Length scales for continental
417
deformation in convergent, divergent, and strike–slip environments: analytical
418
and approxi- mate solutions for a thin viscous sheet model. J. Geophys. Res. 90,
419
3551–3557.
M AN U
SC
416
Fisher, R. A. (1953), Dispersion on a sphere, Proc. R.Soc. London, 217, 295–305.
421
Flinch, J.F. (2003), Structural evolution of the Sinu-Lower Magdalena area(
422
Northern Colombia), in Bartolini, C., Buffler, R., and Blickwede, J., eds., The
423
Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin
424
Formation and Plate Tectonics, American Association of Petroleum Geologists
425
Memoir 79, p. 776-796.
TE D
420
Hubach. E (1952), Interpretación Geológica de la erosión y de los deslizamientos
427
en Bucaramanga y medidas de defensa, Serv. Geol. Nal. Bogotá. Informe 867
428
(inédito), 2-4.
430 431 432
AC C
429
EP
426
Ingeominas (2008), Modelo de evolución morfotectónica cuaternaria basado en evidencias estructurales, neotectónicas y paleosismológicas de los principales sistemas de falla en la región de Bucaramanga. Diederix. H, Torres. E. M, Hernández. C and Botero. P. A. Bogotá
433
Ingeominas (2001a), Base de datos de fallas activas. Recopilación Bibliográfica.
434
Proyecto Compilación y Levantamiento de la Información Geodinámica, Montes
435
N., Sandoval A., Bogotá.
19
ACCEPTED MANUSCRIPT 436
Ingeominas (2001b), Zonificación Sismo Geotécnica Indicativa del Área
437
Metropolitana de Bucaramanga, Fase II. Convenio realizado entre la CDMB e
438
Ingeominas, Bucaramanga.
440 441 442
Irving. E. M (1971), La evolución estructural de los Andes mas septentrionales de
RI PT
439
Colombia. Boletín Geológico, Ingeominas, Bogotá. 19 (2), 1-90
Julivert. M (1958), La morfoestructura de la zona de Mesas al SW de Bucaramanga. UIS. Bol. de Geología No. 1. p.p: 7-43, Bucaramanga.
Julivert, M. (1963), Nuevas observaciones sobre la estratigrafía y tectónica del
444
Cuaternario de los alrededores de Bucaramanga. UIS. Bol. de Geología No. 15.
445
p.p: 41-56, Bucaramanga.
M AN U
SC
443
Kammer, A., and J. Sanchez (2006), Early Jurassic rift structures associated with
447
the Soapaga and Boyacá faults of the Eastern Cordillera, Colombia:
448
Sedimentological inferences and regional implications: Journal of South
449
American Earth Sciences, v. 21, p. 412-422.
TE D
446
Kellogg. J. N. and W. E. Bonini (1982), Subduction of the Caribbean Plate and
451
basement uplifts in the over- riding South American Plate: Tectonics, v. 1, no. 3,
452
p. 251–276.
454 455 456 457 458 459 460
Kimura, H. N. Ishikawa, and H. Sato (2011),
AC C
453
EP
450
Estimation of total lateral
displacement including strike-slip offset and broader drag deformation on an active fault; tectonic geomorphic and paleomagnetic evidence on the Tanna fault zone
in
central
Japan
Tectonophysics,
501(1-4):87-97
doi:
10.1016/j.tecto.2011.01.016 Kirschvink, J. L (1980), The least-squares line and plane and the analysis of paleomagnetic data, Geo- phys. J. R. Astron. Soc., 62, 699–718. López, J. A, M. A. Cuéllar, J. A Osorio, L. E. Bernal and E. Cortés (2008),
20
ACCEPTED MANUSCRIPT 461
Pseudotaquilitas y el carácter paleosísmico de un segmento del Sistema de Fallas
462
de Bucaramanga (SFB), noreste del Muncipio de Pailitas, Departamento del
463
Cesar, Colombia. Boletín de Geología, Bucaramanga. 30 (2), 79-92.
465
Lowrie, W. (1990), Identification of ferromagnetic minerals in a rock by coercivity
RI PT
464
and unblocking temperature properties, Geophys. Res. Lett., 17, 159 – 162.
Marcera. M and P. Salamanca (1993), Cartografía geológica y estratigráfica a
467
detalle y Zonificación geotécnica del sector oriental del Área Metropolitana de
468
Bucaramanga. Tesis para optar al título de Geólogo. Escuela de Geología, UIS,
469
Bucaramanga.
471
M AN U
470
SC
466
McFadden, P. L., and M. W. McElhinny (1990), Classification of the reversal test in paleomagnetism, Geophys. J. Int., 103, 725–729.
Montes, C., Guzman, G., Bayona, G., Cardona, A., Valencia, V., and C. Jaramillo
473
(2010), Clockwise Rotation of the Santa Marta Massif and Simultaneous
474
Paleogene to Neogene Deformation of the Plato-San Jorge and Cesar-Ranchería
475
Basins: Journal of South American Earth Sciences, v. 29, p. 832-848.
TE D
472
Mora, A. and Garcia A. (2006), Cenozoic Tectono-Stratigraphic Relationships
477
between the Cesar Sub-Basin and the Southeastern Lower Magdalena Valley
478
Basin of Northern Colombia. AAPG 2006 Annual Convention. Houston, Texas.
481
AC C
EP
476
482
París, G. M, Machette. R, Dart and K. Haller (2000), Map and Database of
483
Quaternary Faults and Folds in Colombia and its Offshore Regions. U.S.
484
Department of the Interior U.S. Geological Survey. 66 p.
479 480
485
Parra, M., Mora, A., Lopez, C., Rojas, L.E., and K.B. Horton (2012), Detecting earliest shortening and deformation advance in thrust-belt hinterlands: Example from the Colombian Andes: Geology, v. 40, p. 175-178.
Pindell, J. L., S. C. Cande, W. C. Pitman III, D. B. Rowley, J. F. Dewey, J.
21
ACCEPTED MANUSCRIPT 486
LaBrecque, and W. Haxby (1988), Plate- kinematic framework for models of
487
Caribbean evolution: Tectonophysics, v. 155, p. 121–138. Prieto. G. A, Gregory C. Beroza . G. Cb, Barrett. S. A, López. G.A and M. Florez
489
(2012), Earthquake nests as natural laboratories for the study of intermediate-
490
depth earthquake mechanics. Tectonophysics 570-571, 42–56
RI PT
488
Rivera. L. A (1989), Inversion du Tenseur des Contraintes et des Mechanismes au
492
Foyer a partir des Donnees de Polarite pour une Population de Seismes:
493
Applicaton a l’Etude du Foyer de Sismicite Intermediaire de Bucaramanga
494
(Colombie): Doctoral Thesis, Universite de Strasbourg, France, 266 p.
M AN U
SC
491
Ross, I., P. Parra, C. Mora and C. Pimentel (2009), AFTA apatite fission track
496
analysis constraints on the Mesozoic to Quaternary thermal and tectonic evolution
497
of the Middle Magdalena Basin and Santander Massif, Eastern Cordillera,
498
Bucaramanga area, Colombia. X Simposio Bolivariano: Exploración Petrolera en
499
Cuencas Subandinas. Cartagena, Colombia. Memoir.
TE D
495
Schneider, J., Pennington, W., Meyer, R., (1987), Microseismicity and focal
501
mechanisms of the intermediate depth Bucaramanga nest, Colombia. J. Geophys.
502
Res. 92, 13913–13926.
504 505 506
Sonder. L and P. England (1986), Vertical averages of rheology of the continental
AC C
503
EP
500
lithosphere: relation to thin sheet parameters. Earth Planet. Sci. Lett. 77, 81–90.
Sonder. L, J. Jones, C.H. Salyards, S.L and K. M. Murphy (1994), Vertical axis rotation in the Las Vegas Valley shear zone, southern Nevada: paleomagnetic
507
constraints on kinematics and dynamics of block rotations. Tectonics 13, 769–
508
788.
509
Taboada, A., L. A. Rivera, A. Fuenzalida, A. Cisternas, H. Philip, A. Bijwaard, J.
510
Olaya, and C. Rivera (2000), Geodynamics of the northern Andes: Sub- ductions
22
ACCEPTED MANUSCRIPT 511
and intracontinental deformation (Colombia), Tectonics, 19, 787–813. Toro, J. (1990), The termination of the Bucaramanga Fault in the Cordillera
513
Oriental, Colombia: Masters Thesis, University of Arizona, Department of
514
Geosciences, Tucson: 60.
RI PT
512
515
Trenkamp, R., J. N. Kellogg, J. T. Freymueller, and H. P. Mora (2002), Wide plate
516
deformation, south- ern Central America and northwestern South America, CASA
517
GPS observations, J. S. Am. Earth Sci., 15, 157–171.
Tschanz. C, R. Marvin, J. Cruz, H. Mennert, and E. Cebula (1974), Geologic
519
evolution of the Sierra Nevada De Santa Marta. Geol. Soc. Am. Bull., 85, 269-
520
276.
M AN U
SC
518
521
Ujueta, G. (2003), La Falla de Santa Marta-Bucaramanga no es una sola falla; son
522
dos fallas diferentes: La Falla de Santa Marta y la Falla de Bucaramanga:
523
Geología Colombiana No. 28, Universidad Nacional de Colombia, Bogotá.
525
Vargas, A., G and A. Niño (1992), Patrones de fracturamiento asociados a la Falla
TE D
524
Bucaramanga. Tesis, Universidad Industrial de Santander, Bucaramanga. Ward, D., Goldsmith, R., Cruz, J., and H. Restrepo (1973), Geología de los
527
Cuadrángulos H-12, Bucaramanga y H-13, Pamplona, Departamento de
528
Santander, Boletín Geológico Ingeominas 21(1-3), 132 p.
530 531 532
AC C
529
EP
526
Wells, D.L and K. J. Coppersmith (1994), New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement. Bulletin of the Seismological Society of America, Vol. 84, No. 4, pp. 974-1002
533
Zijderveld, J. D. A. (1967), A.C. demagnetization of rocks: Analysis of results, in
534
Methods in Palaeomagnetism, edited by D. W. Collinson, K. M. Creer, and S. K.
535
Runcorn, pp. 254–286, Elsevier, New York.
23
ACCEPTED MANUSCRIPT
537 538 539
Zarifi, Z., and J. Havskov (2003), Characteristics of dense nests of deep and intermediate-depth seismicity. Adv. Geophys. 46, 237–278. Zarifi, Z., J. Havskov and A. Hanyga (2007), An insight into the Bucaramanga nest Tectonophysics 443, 93–10.
RI PT
536
AC C
EP
TE D
M AN U
SC
540
24
ACCEPTED MANUSCRIPT 541
Figure captions
542 Figure 1. Major tectonic and structural features of the NW margin of South
544
America. Plate velocity vectors with respect to stable South America are from
545
Trenkamp et al. (2002). WC = Western Cordillera, CC = Central Cordillera, EC =
546
Eastern Cordillera, SMF = Santa marta Fault, BF = Bucaramanga Fault.
RI PT
543
547
Figure 2. Geological map of the Bucaramanga Fan (scale 1:25,000, modified from
549
Ingeominas, 2001b) and location of the 14 paleomagnetic sites. See Figure 1 for
550
location.
M AN U
SC
548
551
Figure 3. Seismicity in NW South American Plate recorded during 2006-2009 by
553
the Red Sismica Nacional de Colombia (RSNC)-Ingeominas.
554
TE D
552
Figure 4. Thermal demagnetization of a three-component IRM according to the
556
method of Lowrie (1990) for six representative specimens.
557
Figure 5. Orthogonal vector diagrams of typical demagnetization data, in situ
561
AC C
558
EP
555
562
Figure 6. Equal-area projections of the site-mean paleomagnetic directions from the
563
study area. Solid (open) symbols represent projection onto the lower (upper)
564
hemisphere. Open ellipses are the projections of the α95 cones about the mean
565
directions. The star represents the normal polarity geocentric axial dipole (GAD)
559 560
coordinates. Solid and open dots represent projections on the horizontal and vertical planes, respectively. Demagnetization step values are in °C.
25
ACCEPTED MANUSCRIPT 566
field direction (D=0°, I=14°) calculated for the Bucaramanga latitude (7.1° N).
567 Figure 7. Stratigraphic column of the Bucaramanga Fan, and stratigraphic variation
569
of magnetic polarity zones. Magnetic polarity zones are progressively numbered
570
from the section bottom. Uncertain polarity intervals are grey and cross-hatched.
571
The crosses indicate failed sites.
RI PT
568
572
Figure 8. Stratigraphic distance versus age correlation plots. Magnetic polarity
574
zones are correlated to polarity chrons from the GPTS (Cande and Kent, 1995).
575
Sloping lines are average sediment accumulation rates. Two different possible
576
correlations are shown (see text for explanation).
M AN U
SC
573
577 578
Figure 9. (a) Geomorphological context in the study area, where the Suárez and
579
Bucaramanga faults are located.
580
Bucaramanga Fan apex and the Suratá River. (b) Elevation contours around the
581
area. Three zones are well defined (from E to W), the eastern wall of the
582
Bucaramanga Fault with high topographic expression, the Bucaramanga Fan, and
583
the hanging wall of the Suárez Fault. Finally, three topographic profiles across the
585 586
TE D
EP
AC C
584
A distance of 2.5 km occurs between the
Suratá River, the apex and Bucaramanga Fan are shown. BF = Bucaramanga Fault, SF = Suárez Fault.
587
Figure 10. Scheme showing the displacement of the Bucaramanga Fan apex from its
588
feeding Suratá River along the Bucaramanga Fault.
589
Table 1. Paleomagnetic results
RI PT
ACCEPTED MANUSCRIPT
N/n 10/8 11/6 12/0 12/0 11/9 6/0 12/5 12/0 11/0 12/12 11/8 12/8 12/8 11/5
M AN U
TE D
Finos Finos Gravoso Organos Organos Organos Gravoso Organos Organos Organos Organos Organos Organos Organos
Geographic coordinates Longitude ºW Latitude ºN 73.132033 7.075063 73.132031 7.075061 73.143939 7.075496 73.168091 7.036684 73.174056 7.049284 73.138192 7.067906 73.132332 7.097189 73.133936 7.090153 73.138862 7.087891 73.138862 7.087891 73.162533 7.088209 73.161192 7.101659 73.165264 7.100704 73.148797 7.066336
EP
Member
AC C
Site GJ186 GJ187 GJ188 GJ189 GJ190 GJ191 GJ192 GJ193 GJ194 GJ195 GJ196 GJ197 GJ198 GJ199
SC
Table 1 Paleomagnetic results from Bucaramanga Fan
D (º) 179.0 176.4 353.5 176.7 188.1 181.5 357.9 356.9 167.9
In Situ I (º) 13.4 9.0 4.0
k 7.75 14.9 9.14
9.2 -19.0 -0.6 7.6 16.7 -1.3
12.61 12.79 11.63 44.45 13.37 3.47
α95 (º) 21.2 17.9 18.0 22.4 12.6 18.5 8.4 15.7 48.2
The geographic coordinates are referred to WGS84 datum. Bedding is sub-horizontal. D and I are in situ declination and inclination; K and α95 are statistical parameters after Fisher (1953).
73º ACCEPTED MANUSCRIPT
74º
80º
75º
N
ut So
OF
C o c o s P la te
N a z c a P la te
me n
e
TE D
o BF thern Z Sou
S a n ta n d e r M a s s if
C u c u ta
n o c o o B
Me
t u l F a
ri d
EP AC C
FIGURE 2
RION E a s te rn C o r d ille r a
Figure 1
c o b u c a r A
tic A n
lin
es
0
nt ro st f ru Th
75 Km
150 Km
Plate velocity Vectors 1 cm/yr
Seismic lines (Ujueta, 2003) a F a u lt
e
Y o p a lF au lt
6º
Km
Reverse fault strike-slip fault
L o s C A n tic o b a r d e s lin e
M e d e llin
B u c a ra m a n g a
C h u c a ri m
nd aA
URIB
ne
C e n tr a l C o r d ille r a
M id d le M a g d a le n a V a lle y B a s in
S o u th A m e r ic a n P l a t e 500
M a r a c a ib o B lo c k
BUCM
7º
0
E C
ra
W C
M AN U
Z on
r El Ca t F aul
t ra l
0º
C C
ille
w e r C R B g d a le n a Ariguani lle y graben s in
MONT
8º
5º
n accretionary wedge
rd
P e r ija R a n g e
ea
Co
VDUP
Cen
9º
bb
rn
S a n ta M a rta M a s s if
Z one
L o M a V a B a
10º
65º
M a r a c a ib o B lo c k
RI PT
CART
h
ri Ca
10º
SC
SMFNothern
11º
70º
15º
Ea ste
75º
1000
73º 11´0" W
73º 9´0" W
73º 7´0" W
0
73º 5´0" W
2 Km
4 Km
7º 12´0" N
Santander Massif ACCEPTED MANUSCRIPT 7º 10´0" N
er
Riv
7º 8´0" N
GJ198
7º 6´0" N
TE D
GJ192
GJ195 GJ194
GJ196
7º 4´0" N
aF au lt
AC C
GJ187 GJ186 GJ191
ri d
GJ199
GJ193
F lo
EP
GJ188
Suarez Fault system
em
GJ197
yst tS
M AN U
aul
SC
aF
Apex
ang
Su a
ra m
re
zF
ca Bu
au
RI PT
lt s ys
te
m
Su
á ra t
GJ190
GJ189
7º 2´0" N
Cretaceous
Flow deposits
Triassic-Jurassic
Limos rojos Member
Precambric to Paleozoic
Finos and Gravoso Member
Fault Covered Fault or lineament
Organos Member
Paleomagnetic sites
Figure 2
Bucaramanga Fan
79º W
70º
ACCEPTED MANUSCRIPT
75º
200 km
RI PT
depth[km]
B u c a ra m a n g a N e s t
N a z c a P la te
AC C
EP
5º
S o u th A m e r ic a n P la te 0º Figure 3
40 80 120
TE D
M AN U
SC
10º N
0
160 200
ACCEPTED MANUSCRIPT
10E-1 A/m
1 A/m
0.6 T < coer.< 2.7 T 0.12 T < coer. <0.6 T coer. < 0.12 T
10E-1 A/m
4
4 1 3 GJ194
RI PT
3 GJ197
2
SC
2
GJ194
0
0 20
100
200
300
400
500
600
20
T (xC)
10E-1 A/m
100
200
10E-1 A/m
5
5
4 GJ186
4
400
500
600
3
20
T (xC)
100
200
300
400
500
600
500
600
T (xC)
10E-2 A/m
3 GJ190
GJ192 2
AC C
3
EP
6
300
1
0
TE D
7
M AN U
1
2
2
1
1
1 0
0 20
100
200
300
400
500
600
Figure 4
T (xC)
0 20
100
200
300
400
500
600
T (xC)
20
100
200
300
400
T (xC)
N Up
N Up
N MANUSCRIPT Up ACCEPTED
200º
500º 600º
Unit= 537.e-06 A/m Unit= 508.e-06 A/m
Unit= 411.e-06 A/m
GJ192-9
600º
W
680º
500º
W
500º
E
W
E
W
600º
200º
(b)
500º
W
E
W
680º 680º
E
600º 500º
200º
S Down N Up200º 460º
E
600º
(c)
M AN U
380º
E
SC
(a)
250º
GJ195-1
200º
RI PT
GJ190-2
250º
S Down
S Down
N Up
N Up
200º
TE D
600º
380º
600º
680º
W 680º 460º 200º
(d)
GJ198-2 E
W
E
W
680º
S Down
E
W
E
W
Unit= 83.9e-06 A/m E E 550º
380º
(f)
460º
200º
S Down
Figure 5
380º
GJ199-3
Unit= 258.e-06 A/m
(e)
AC C
W
Unit= 266.e-06 A/m
EP
GJ197-3
460º
S Down
ACCEPTED N MANUSCRIPT 197
190
M AN U
SC
RI PT
198
90
AC C
EP
TE D
270
195 186
192 187
199
196
180
Geocentric axial dipole field direction expected at Bucaramanga (Lat 7.13º N) Mean paleomagnetic direction (D = 357.5 I = 2.0 K = 41.63 a 95 = 8.1)
Figure 6
188 192
200
ACCEPTED MANUSCRIPT
186 187
180
160
SC
195 191
140
M AN U
190
120
TE D EP
80
60
40
20
0 Figure 7
N3
193 194
AC C
Organos Member
100
R3
RI PT
Limos Rojos Member Gravoso Member Finos Member
220
189 199
R2
197
N2
196
R1
198
N1
ACCEPTED MANUSCRIPT
B
60
120
193 194 189 199
R2
197
N2
196
R1
198
N1
100
40
20
Za nc l e an
Late Pliocene
Piacenzian
RI PT 195 191
190
N3
193 194 189 199
R2
197
N2
196
R1
198
N1
20
SYSTEM Stages
0 P LI OC E NE E ar l y Pl i oc e n e Middle Pliocene Za nc l e an
G A U S S
Gelasian
Santern. Emilian Sicilian 1
G I L B E R T
Late Pliocene
P LE I S TOC E N E Early Pleistocene M. Pleistocene
2
BRUNHES
POLARITY CHRONS
Piacenzian 3
Ma
5
M A T U Y A M A
R3
4
1
G A U S S
Santern. Emilian Sicilian
2
3
4
5
G I L B E R T
Gelasian
P LE I S TOC E N E Early Pleistocene M. Pleistocene
60
186 187
M A T U Y A M A
POLARITY CHRONS POLARITY
Jaramillo
Olduvai
Kaena
Mammoth
Cochiti
Nunivak
Sidufjall
Thvera
Jaramillo
Olduvai
Kaena
Mammoth
Cochiti
Nunivak
Sidufjall
Thvera
Figure 8
Polarity Subchrons
Stages
Ma BRUNHES
POLARITY
SYSTEM
Chrono
P LI OC E NE E ar l y Pl i oc e n e Middle Pliocene
80
188 192
40
Chrono
0
Organos Member
80
M AN U
100
180
140
N3
TE D
120
190
200
160
195 191
EP
140
R3
220
SC
180
186 187
160
Organos Member
Limos Rojos Member
188 192
Finos Member
200
Gravoso Member
220
AC C
Finos Member
Gravoso Member
Limos Rojos Member
A
Polarity Subchrons
ACCEPTED MANUSCRIPT
(b)
(a) 73º 9' W
73º 5' W
73º 1' W
RI PT
7º 10' N
2.5 km
C
A` B`
M AN U
SC
7º 8' N
A
AC C
EP
TE D
7º 6' N
Reverse fault Strike-slip fault
B C`
7º 4' N
A 950 m 850 m 750 m 650 m
1050 m
BF
SF B
950 m 850 m 750 m 650 m 1050 m 950 m 850 m 750 m 650 m
Figure 9
A’
1050 m
Apex
B’
BF C
C’
r ve
at
á
Ri
ACCEPTED MANUSCRIPT
Su r
Stage A
Su r
at
TE D
á
Ri
Stage B
M AN U
ve r
SC
D
RI PT
Bucaramanga Fault
D
AC C
EP
2.5 Km
Figure 10
Bucaramanga Fault
ACCEPTED MANUSCRIPT Highlights
Paleomagnetic investigation of a Plio-Pleistocene (?) continental alluvial fan juxtaposed to the Bucaramanga Fault, and horizontally displaced by 2.5 km with respect to its feeding river. Nine reliable paleomagnetic directions define a succession
RI PT
of magnetic polarity zones, correlated with several tracks of the Plio-Pleistocene magnetic polarity time scale. If the youngest age model is considered, most recent sediments of the Bucaramanga Fan can be reasonably dated at 0.8 Ma (BrunhesMatuyama chron transition), translating into a maximum 3 mm/yr slip rate for the
AC C
EP
TE D
M AN U
SC
Bucaramanga Fault.
S0895-9811(14)00154-0
DOI:
10.1016/j.jsames.2014.11.001
Reference:
SAMES 1341
To appear in:
Journal of South American Earth Sciences
Received Date: 13 March 2014 Revised Date:
24 October 2014
Accepted Date: 7 November 2014
Please cite this article as: Diaz, G.J., Speranza, F., Faccena, C., Bayona, G., Mora, A., Magnetic stratigraphy of the Bucaramanga alluvial Fan: Evidence for a ≤ 3 mm/yr slip rate for the BucaramangaSanta Marta Fault, Colombia, Journal of South American Earth Sciences (2014), doi: 10.1016/ j.jsames.2014.11.001. 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.
1
ACCEPTED MANUSCRIPT 1
Magnetic stratigraphy of the Bucaramanga alluvial Fan: Evidence for a ≤ 3
2
mm/yr slip rate for the Bucaramanga-Santa Marta Fault, Colombia
3 Giovanny Jiménez Diaz 1, 2, Fabio Speranza 2, Claudio Faccena 1, German
5
Bayona 3, Andres Mora 4
RI PT
4
6 1 Università di Roma TRE, Roma, Italy
8
2 Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy
9
3 Corporación Geológica ARES, Bogota, Colombia
M AN U
10
SC
7
4 Instituto Colombiano del Petróleo, Ecopetrol-ICP, Bucaramanga, Colombia
11 12
16 17 18 19 20 21 22 23 24 25
EP
15
AC C
14
TE D
13
2
ACCEPTED MANUSCRIPT 26 27 28
Abstract
RI PT
29 The 550 km long Bucaramanga-Santa Marta Fault is one of the main active tectonic
31
features of NW South America. It is a left-lateral strike-slip fault bounding the
32
Maracaibo block, and straddling northern Colombia from the Caribbean Sea to the
33
Eastern Cordillera. Variable total displacement values (from 40 to 110 km), and
34
present-day slip rates (from 0.01 to 10 mm/yr) have been proposed so far for the
35
Bucaramanga Fault. Here we report on the paleomagnetic investigation of a Plio-
36
Pleistocene (?) continental alluvial fan juxtaposed to the Bucaramanga Fault, and
37
horizontally displaced by 2.5 km with respect to its feeding river. Nine (out of
38
fourteen) reliable paleomagnetic directions define a succession of six different
39
magnetic polarity zones that, lacking additional age constraints, can be correlated
40
with several tracks of the Plio-Pleistocene magnetic polarity time scale. If the
41
youngest age model is considered, most recent sediments of the fan can be
42
reasonably dated at 0.8 Ma (Brunhes-Matuyama chron transition), translating into a
43
maximum 3 mm/yr slip rate for the Bucaramanga Fault. Older age models would
45 46
M AN U
TE D
EP
AC C
44
SC
30
obviously yield smaller slip rates. Our paleomagnetic sites, located at 4-10 km from the fault, do not show significant rotations, implying weak fault coupling and/or ductile upper crust behavior adjacent to the Bucaramanga Fault.
47 48 49 50
Keywords: Paleomagnetism, Bucaramanga Fan, Bucaramanga Fault, Slip rate.
3
ACCEPTED MANUSCRIPT 51
Introduction
52 The NW margin of South America is characterized by a complex pattern of
54
mountain ranges (Western, Central, and Eastern Cordillera of Colombia, Fig. 1),
55
and by a puzzle of crustal blocks undergoing independent movements (Kellogg et
56
al., 1982; Taboada et al., 2000; Trenkamp et al., 2002). The eastward subduction of
57
the Nazca Plate beneath South America at a rate of 6 cm/yr is well documented
58
(Trenkamp et al., 2002), while the existence of an ESE-ward directed subduction of
59
the Caribbean plate is debated (Pindell et al., 1988). A well-developed accretionary
60
wedge (Fig. 1) is exposed at the boundary between the Caribbean and South
61
American plate (e.g., Flinch et al., 2003).
62
The Maracaibo block, the biggest semi-rigid block of the Colombian tectonic
63
puzzle, is bounded by three major wrench faults: the dextral Boconó and Oca
64
faults, and the sinistral Bucaramanga-Santa Marta Fault (Fig. 1). The relevance,
65
age, and displacement rate of these major strike-slip faults have been widely
66
discussed in the past (Irving, 1971; Toro, 1990; Ujueta, 2003; Mora and Garcia,
67
2006; Lopez et al., 2008), and a consensus on the whole block and fault kinematics
68
has not been reached so far.
71
AC C
EP
TE D
M AN U
SC
RI PT
53
72
1), where it crosses the city of Bucaramanga (ca. 500,000 inhabitants). It can be
73
divided along strike into three major zones (Northern, Central and Southern zone),
74
where it bounds several distinct geological provinces. The Northern zone, or Santa
75
Marta section (Paris, 2000; Ingeominas, 2001a), corresponds to a 140 km long
69 70
The Bucaramanga-Santa Marta Fault system juxtaposes basement rocks to the east and sedimentary Jurassic to Cenozoic rocks to the west. This fault system extends for a distance of 550 km from the Caribbean coast to the Eastern Cordillera (Fig.
4
ACCEPTED MANUSCRIPT
topographic lineament juxtaposing old crystalline rocks of the Santa Marta Massif
77
to Neogene deposits of the Lower Magdalena Valley basin (Fig. 1). The 100 km
78
long Central zone is covered by alluvial deposits of the Lower Magdalena Valley
79
basin (Ariguani graben) and Cesar Valley basin (Mora and García, 2006; Fig.1).
80
The Southern zone corresponds to Bucaramanga section (Paris, 2000; Ingeominas,
81
2001a), a 310 km long outstanding linear topographic feature separating the
82
Santander Massif from the Middle Magdalena Valley basin (Fig. 1). At the city of
83
Bucaramanga, the fault clearly left-laterally displaces a 10-15 km wide continental
84
alluvial fan of presumable Plio-Pleistocene age, produced by debris carried by the
85
Suralá river from the adjacent Santander Massif (Fig. 2). The zone is well known
86
for the high seismic activity of the “Bucaramanga nest” (Taboada et al, 2000; Zarifi
87
et al, 2007; Fig. 3), but earthquakes are deep (from 100 to 200 km), thus they
88
should not be related to the activity of the Bucaramanga Fault.
89
In this paper we report on a paleomagnetic investigation of the Bucaramanga Fan to
90
constrain its age by magnetic stratigraphy, one of the few viable method to
91
dategravel-size alluvial fan deposits. The results allow the documentation of when
92
fan displacement occurred, and unravel recent and present-day slip rate of the
93
Bucaramanga Fault. The city of Bucaramanga has not been struck by devastating
96
AC C
EP
TE D
M AN U
SC
RI PT
76
97
Bucaramanga Fault, as GPS data of Trenkamp et al. (2002) might suggest (Fig. 1).
94 95
98 99 100
earthquakes since when historical accounts are available (XVII century AD), thus it is unclear whether we are living an inter-seismic interval preceding a future strong earthquake, or in fact there is no significant present-day activity of the
5
ACCEPTED MANUSCRIPT 101
Characteristics of the Bucaramanga-Santa Marta Fault
102 Previous work around the City of Bucaramanga has been done in the frame of
104
regional and local cartography projects (Ward et al., 1973; Ingeominas, 2001b;
105
Diedrix et al., 2009; Fig. 2). In the Santander Massif, which is bounded to the west
106
by the Bucaramanga Fault system, Precambrian, Paleozoic, and Mesozoic intrusive
107
and metamorphic rocks (schists and gneisses) are exposed. According to Cediel et
108
al. (2003), the Bucaramanga-Santa Marta Fault was active during the Precambrian
109
Grenville - Orinoco continental collision, and reactivated in the Aptian-Albian
110
times. The Bucaramanga Fault bounds a thick deposition of upper Jurassic and
111
Cretaceous rocks to the south and west (Kammer and Sanchez, 2006), whereas to
112
the north and east the deposition of Jurassic rocks is more condensed and in some
113
areas lowermost Cretaceous strata are lacking (Ward et al, 1973).
114
Provenance analysis indicates that the Santander Massif and its sedimentary cover
115
were uplifted since Paleogene time (Ayala et al, 2012). Paleocene movements may
116
be related to other structures in the Cobardes Anticline (Parra et al, 2012, Fig. 1).
117
Mora and García (2006) using extensive seismic profile analysis and well data in
118
the Central zone, proposed that the Bucaramanga-Santa Marta Fault was
121
AC C
EP
TE D
M AN U
SC
RI PT
103
122
activity ended after Oligocene, as the Lower Magdalena Valley and Cesar basins
123
have been connected without tectonic disturbances.
119 120
responsible for the intense structural deformation that affected pre-Oligocene units, indicating that it was an active boundary between the Lower Magdalena Valley and Cesar basins during the late Eocene-early Oligocene. They also suggested that fault
124 125
Ross et al. (2009) using Apatite fission track analysis (AFTA) of Precambrian to
6
ACCEPTED MANUSCRIPT
Neogene rocks from the Santander Massif and Middle Magdalena Valley proposed
127
three paleothermal episodes (interpreted as erosional phases) in the Paleocene (65
128
to 60 Ma), Early Miocene (20 to 18 Ma) and Middle Miocene (12 to 9 Ma). This
129
evidence provides age clues for the uplift of the Santander Massif with respect to
130
the adjacent Magdalena Valley that likely occurred along the Bucaramanga Fault.
131
As the Bucaramanga Fault is a recent geomorphological feature, it was likely
132
activated in the last phase of deformation of late Miocene age, as suggested by
133
AFTA data. Finally, Pindell et al. (1988) proposed that the Bucaramanga – Santa
134
Marta fault is the western limit of the Maracaibo Block since Miocene times.
M AN U
SC
RI PT
126
135
Reported total displacement values of the Bucaramanga – Santa Marta fault vary
137
from 45 to 110 km. Toro (1990) using structural reconstructions proposed for the
138
southern fault portion a displacement of 45 km. According to Campbell (1968), the
139
total displacement is more than 100 km, relying on a regional scale correlation
140
between rocks from the Central Cordillera and the Santa Marta Massif. Other
141
authors (Irving, 1971; Tschantz, 1974) proposed 110 km of displacement after the
142
analysis of samples drilled in oil wells. Montes et al. (2010) and Bayona et al.
143
(2010) considered the Bucaramanga-Santa Marta Fault system as western boundary
146
AC C
EP
TE D
136
147
evaluated after regional geology considerations (Rivera, 1989).
144 145
of the Maracaibo block clockwise rotation during the Cenozoic. Reported values for the fault slip rate range between 0.01-0.2 mm/yr, calculated on the basis of geomorphic offset features (Paris, 2000; Ingeominas, 2001a), to 10 mm/yr,
148 149
López et al., (2008) reported the occurrence of Pseudotachylite associated to
150
cataclasites in the southern sector of the Bucaramanga Fault, that they interpreted
7
ACCEPTED MANUSCRIPT
as an evidence for paleoseismicity along the fault. Diedrix et al. (2009) using
152
paleoseismological investigation and radiocarbon dating of paleosols trenched
153
adjacent to the fault proposed eight Holocene seismic events during the last 8300
154
years and magnitudes in the order of 6.5-7.0, associated to the Bucaramanga Fault
155
activity.
RI PT
151
156
Ujueta (2003) made an extensive review of the previous works on the Bucaramanga
158
Santa Marta Fault available since 1933, and observed that some authors consider
159
the Bucaramanga Santa Marta fault as a reverse fault, others as left lateral strike-
160
slip fault, while few works propose two different and independent faults.
161
Concerning the age of the Bucaramanga Fault activity, a late Mesozoic, Paleocene,
162
Eocene or Pliocene-Quaternary age are proposed (Ujueta, 2003). Finally, using
163
seismic profiles, he discussed the continuity of the fault Central zone, and proposed
164
two different but related faults, with absence of connection between the southern
165
and the northern zone.
166
The deep seismicity of the Bucaramanga Nest
M AN U
TE D
No significant shallow crustal seismicity has been recorded along the Santa Marta-
171
AC C
168
EP
167
SC
157
172
nests by its high rate of activity in a volume much smaller than the other nests at
173
similar intermediate depths (Schneider et al., 1987; Zarifi and Harsco, 2003; Prieto
174
et al., 2012). The Bucaramanga nest has been mostly related to tectonic processes
175
occurring in the oceanic subducting plates beneath Colombia (Zarifi and Havskov,
169 170
Bucaramanga Fault (Fig. 3), but at depth a remarkable cluster of subcrustal earthquakes in the 100-200 km depth interval is observed in the so-called “Bucaramanga nest”, centered at 7°N 73°W (Fig 3). It differs from other worldwide
8
ACCEPTED MANUSCRIPT
2003). Taboada et al. (2000) proposed that the Bucaramanga Nest is due to the
177
interaction between the subducting Nazca and paleo-Caribbean plates, while Zarifi
178
et al. (2007) suggested a simultaneous subduction process and collision between
179
two subducted slabs. Conversely, Cediel et al. (2003) proposed that the seismic
180
activity recorded in the Bucaramanga Nest represents a zone of tectonic detachment
181
associated with NW-ward migration of the Maracaibo subplate, while Rivera
182
(1989) proposed that there is a relationship between the Bucaramanga Fault and
183
Nest.
SC
RI PT
176
185
The Bucaramanga Fan
186
M AN U
184
The Bucaramanga Fan is limited to the east by the Santander Massif and the
188
Bucaramanga Fault, and to the west by the Suárez Fault (Fig. 2). The Suárez Fault
189
is a west-dipping reverse fault with sinistral displacement and Quaternary activity
190
(Page, 1986; Paris et al., 2000; Ingeominas, 2001a) that terminates northward
191
against the Bucaramanga Fault. In the study area, the Suárez Fault juxtaposes
192
Jurassic and Cretaceous strata against the Bucaramanga Fan. Locally, the
193
Bucaramanga Fan is folded with vertical to overturned beds by the effect of the
196
AC C
EP
TE D
187
197
De Porta (1959) defined the Bucaramanga Fan as a sedimentary deposit of
198
Quaternary age with an alluvial fan morphological shape (Fig. 2).
199
According to Julivert (1958) The E-W creeks and the shape of the Bucaramanga
200
Fan can be related, but the present-day drainage network can't explain the
194 195
Suárez Fault (Ingeominas, 2008).
9
ACCEPTED MANUSCRIPT
Bucaramanga Fan location. Ingeominas (2001b and 2008) suggested that the Suratá
202
River is the feeder of the Bucaramanga Fan, although it is presently shifted by 2.5
203
km with respect to fan apex. According to Ingeominas (2008) the southern part of
204
the Bucaramanga Fan has been more faulted than the northern part, and seems to be
205
diachronous. Thus the progressive northward migration of the fan apex has been
206
related to the sinistral shear along the Bucaramanga Fault.
207
RI PT
201
According to Ingeominas (2001b) the thickness of the Bucaramanga Fan increases
209
from east to west with an average thickness of 250 m, and from base to the top it
210
has been subdivided into, the Organos, Finos, Gravoso, and Limos Rojos member
211
(Fig. 2).
212
The Organos Member was first defined by Hubach (1952), and according to Bueno
213
and Solarte (1994) is a monotonous sequence of conglomerates with intercalations
214
of fine sandstones. Conglomerate clasts are 10 - 30 cm in diameter (and in some
215
cases more than 1 m) and include gneisses and schists fragments. This member is
216
clast supported, contains a clay matrix (Ingeominas, 2001b), and crops out to the
217
west of the study area with a maximum thickness of 180 m (Mancera and
218
Salamanca, 1994). The Finos Member (Hubach, 1952) is a continuous sub-
221
AC C
EP
TE D
M AN U
SC
208
222
m thick, matrix supported level of gravel-size clasts overlying the Finos Member
223
along a net contact. The clasts are on average 15 cm in diameter (cobble size), and
224
the matrix includes a mixture of clay- and sand-size fragments. Finally, the
225
Gravoso Member transitionally passes upward into the 15 m thick Limos Rojos
219 220
horizontal 15 m thick bed overlying the Organos member along a net discontinuity, and it consists of clays evolving upsection into fine-grained sandstone beds (Ingeominas, 2001b). The Gravoso Member (Vargas and Niño, 1992) is an 8 to 30
10
ACCEPTED MANUSCRIPT
Member (Julivert, 1963); this unit consists of argillaceous sandstones and
227
conglomeratic sandstones, interbeded with layers of siltstones. Locally, block
228
fragments (meter scale in diameter) of sandstone texture are supported by the red
229
silty matrix (Ingeominas, 2001b).
230
The Bucaramanga Fan is generally referred to a Plio-Pleistocene age (Ingeominas,
231
2001b), although no conclusive age constraints were gathered from the continental
232
succession so far.
RI PT
226
SC
233
235 236
Sampling and Methods
237
M AN U
234
We collected sandy-silty samples for paleomagnetic analysis in fourteen sites (154
239
cores, Table 1) from the Bucaramanga Fan, using a petrol-powered portable drill
240
cooled by water. Ten sites were gathered in the Organos Member, two in the Finos
241
Member, and two in the Gravoso Member (Figure 2 and Table 1). At each site we
242
collected 6–12 cores (11 on average), spaced in at least two outcrops in order to try
243
to average out secular variation of the geomagnetic field. All samples were oriented
246
AC C
EP
TE D
238
247
Cores were prepared into standard cylindrical specimens of 22 mm height, and
248
rock magnetic and paleomagnetic measurements were done in the shielded room of
249
the paleomagnetic laboratory of the Istituto Nazionale di Geofisica e Vulcanologia
250
(Roma, Italy). All samples were thermally demagnetized through 11–12 steps up to
244 245
using a magnetic compass, corrected to account for the local magnetic field declination value at the sampling area (about 7º W) according to NOAA’s National Geophysical Data Center (http://www.ngdc.noaa.gov).
11
ACCEPTED MANUSCRIPT
680°C by a shielded oven, and the natural remanent magnetization (NRM) of the
252
specimens was measured after each step with a DC- SQUID cryogenic
253
magnetometer (2G Enterprises, USA). Thermal demagnetization data were plotted
254
on orthogonal diagrams (Zijderveld, 1967), and the magnetization components
255
were isolated by principal component analysis (Kirschvink, 1980). The site-mean
256
directions were evaluated by Fisher’s (1953) statistics.
257
On a set of selected specimens, magnetic mineralogy analyses were carried out to
258
identify and characterize the main magnetic carriers using the thermal
259
demagnetization of a three-component isothermal remanent magnetization (IRM)
260
imparted on the specimen axes, according to the method of Lowrie (1990). Fields
261
of 2.7, 0.6, and 0.12 T were successively imparted on the z, y, and x sample axes
262
(respectively) with a pulse magnetizer (Model 660, 2G Enterprises). The
263
generalized stratigraphic column of the Bucaramanga Fan was made using field
264
data and previous geological maps (Ingeominas, 2001b). The stratigraphic position
265
for all sampled sites was calculated using a cross section.
SC
M AN U
TE D
271
AC C
268
Results
EP
266 267
RI PT
251
272
samples both the medium coercivity and the hard fractions are demagnetized
273
between 600 and 680°C (Fig. 4), pointing to hematite as the main magnetic carrier
274
of our samples. In almost all sites, a drop of the medium coercivity and hard
275
fraction occurring before 100º shows that a small amount of goethite is also
269 270
Magnetic Mineralogy
The thermal demagnetization of a three-component IRM shows that for most of the
12
ACCEPTED MANUSCRIPT 276
associated to hematite.
277 278
Paleomagnetism
RI PT
279 Only 9 (out of 14) sites yielded reproducible paleomagnetic directions during
281
cleaning, while the remaining 5 sites showed scattered demagnetization diagrams
282
(Figure 5 and Table 1). For most of the sites, a characteristic magnetization
283
component (ChRM) was isolated between 550 and 680°C, confirming that hematite
284
represents the main magnetic carrier. For about 10% of the samples, a ChRM is
285
isolated between 380 and 680°C, suggesting the coexistence of hematite and
286
maghaemite (Fig. 5). Mean paleomagnetic directions are reasonably well
287
constrained, the α95 values being comprised between 8.4° and 22.4° for all sites but
288
one yielding a value of 48.2 (Fig. 6 and Table 1). Three sites are of normal polarity
289
(D = 356.1, I = 9.4, K = 136.76 and α95 = 10.6 ) and the other six are of reverse
290
polarity (D = 178.2, I =1.8, K = 36.20, and α95 = 11.3 ); the reversal test (according
291
to McFadden and McElhinny (1990), is positive of Class “c”.
292
The fact that our results yielded reverse polarity directions indicate that the
293
Bucaramanga Fan should be older than the Bruhnhes polarity chron (0 to 0.8 Ma)
296
AC C
EP
TE D
M AN U
SC
280
297
direction, except the youngest magnetozone R3, which is corroborated by four
298
different site results. As the age of the Bucaramanga Fan is vaguely inferred to be
299
Plio-Pleistocene, several different correlations with the global magnetic polarity
300
time scale (GPTS, Cande and Kent, 1995) are possible (Fig. 8). If we assign the
294 295
When plotted according to their stratigraphic position, the sites from the Bucaramanga Fan yield a succession of three normal- and three reverse-polarity magnetozones (Fig. 7). Each magnetozone is defined by one paleomagnetic
13
ACCEPTED MANUSCRIPT
youngest possible age to the succession (Fig. 8a), R3 correlates with upper
302
Matuyama polarity chron (C1r.1r), and N3, N2, and N1 with the Jaramillo,
303
Olduvai, and Gauss chron, respectively. In a slightly older age model (Fig. 8b), R3
304
correlates with the mid Matuyama chron (C1r.2r), N3 with Olduvai chron, and N2
305
and N1 fall both within the Gauss chron. It is not possible at present to indicate a
306
preferred age model using calculated sedimentation rates that vary irregularly
307
(considering both age models of Figure 8) between 30 and 300 mm/kyr. In fact in
308
this kind of deposits the sedimentation is expected to be highly irregular and
309
discontinuous, and the thickness of some magnetozones (such as N3) is poorly
310
constrained due to the occurrence of several failed sites located below and above it
311
(Fig. 7).
M AN U
SC
RI PT
301
312 313
315
Discussion and Conclusions
TE D
314
The slip rate of the southern segment of the Bucaramanga Fault can be in principle
317
calculated by dividing its along-fault displacement by the age of the displaced
318
rocks. Left-lateral displacement is well known, and equates the 2.5 km distance
321
AC C
EP
316
322
magnetozone succession gathered from the Bucaramanga Fan (Fig. 7).
319 320
from the mouth of the Suralá river to the apex of the Bucaramanga Fan (Ingeominas 2008, Figs. 9 and 10). Conversely, the age of the displaced sediments is not firmly constrained, as several different age models can equally fit the
323 324
However, a maximum possible slip rate can be calculated assigning the youngest
325
possible age of the succession, i.e. inferring that magnetozone R3 corresponds to
14
ACCEPTED MANUSCRIPT
the top of the Matuyama polarity chron (Fig. 8a). In this case, a 0.8 Ma age
327
(Brunhes-Matuyama boundary, Cande and Kent, 1995) can be reasonably assigned
328
to the youngest sediments of the Bucaramanga Fan, by considering that: 1) we did
329
not reach the normal-polarity magnetozone above R3, thus the youngest sampled
330
sediments (site GJ192) might fall in the lower-medium part of chron C1r.1r, and be
331
0.9-1 Ma old; 2) the upper member of the Bucaramanga Fan is the Limos Rojos
332
Member, but the youngest paleomagnetic directions were obtained in the
333
underlying Gravoso Member; 3) the Limos Rojos Member is only 15 m thick, and
334
shares the same fan morphology with the underlying Finos-Gravoso members (Fig.
335
2). This suggests that the Limos Rojos Member was rapidly emplaced, and that no
336
significant time gap (and displacement of the fan feeding source) occurred with
337
respect to the Gravoso Member.
338
A 0.8 Ma age of the top of the Bucaramanga Fan translates into a maximum slip
339
rate of 3 mm/yr for the Bucaramanga Fault. Obviously, progressively smaller slip
340
rates would arise by considering progressively older age models for the
341
Bucaramanga Fan. Our slip rate estimate is in rough agreement with conclusions by
342
Diedrix et al. (2009), who documented by paleosismology eight main earthquakes
343
in the last 8300 years, with 400 to 1300 years recurrence intervals, and estimated
346
AC C
EP
TE D
M AN U
SC
RI PT
326
347
seismogenic fault is expected to be associated with 7-7.5 M earthquakes (Wells and
348
Coppersmith, 1994), slightly greater than Diederix et al. (2009) estimates. We note
349
however that older age models for the Bucaramanga Fan would give smaller slip
350
rates, thus better agreement with Diederix et al. (2009) calculated values.
344 345
magnitude values of 6.5 to 7.0. Average recurrence interval documented by Diedrix et al. (2009) is 1000 years, which would translate into an accumulated displacement of 3 m, if our 3 mm/yr spreading rate is considered. A 3 m displacement along a
15
ACCEPTED MANUSCRIPT
Considering that the city of Bucaramanga has a documented history of 390 years
352
without any catastrophic earthquake occurrence, a 1.2 m displacement could have
353
been accumulated since then, if the 3 mm/yr slip rate is considered.
354
Sediments of the Bucaramanga Fan have been clearly displaced by left-lateral fault
355
shear, thus counterclockwise rotations are expected at fault walls, as already
356
observed in several strike-slip fault settings (Sonder et al., 1994; Kimura et al.,
357
2011). On the other hand, our sites from the Bucaramanga Fan, located at 4-10 km
358
from the fault, do not show significant rotations (Fig. 6).
359
Using the power law rheology model (England et al., 1985), in which the relation
360
between distance from a fault trace y (km) and vertical-axis relative rotation θ
361
(rad.) is expressed as:
362
364
θ=arctan (((4Dsπ √n)/L) exp((−4π √ny)L))
TE D
363
M AN U
SC
RI PT
351
Ds (km) is the displacement in one side of the fault, L/2 (km) is the length of the
366
fault, and n is the stress exponent and describes the average mechanical behavior of
367
the lithosphere (Sonder and England, 1986). Clearly, the lack of observed rotations
368
may imply that 1) fault locking is extremely weak, whereas fault walls are
371
AC C
EP
365
372
understand this issue, and better constrain the seismic hazard assessment related to
373
the Bucaramanga Fault activity.
369 370
374 375
extremely rigid and undergo minimal internal deformation, and/or 2) the upper crust west of the Bucaramanga Fault has a ductile behavior. Additional geophysical data (e.g. a high-resolution GPS network across fault zone) are needed to fully
16
ACCEPTED MANUSCRIPT 376 377 378
Acknowledgements: Many thanks to Ecopetrol-ICP and the project: “Cronologia de
380
la deformación en las cuencas Subandinas” for funding and supporting the field
381
work. Danilo Seccia (INGV) helped to realize Figure 3. GB acknowledges
382
Colciencias for continuing support ARES. Thanks to Omar Montenegro for
383
logistical and field work. We are grateful to two anonymous referees and to JSAES
384
Editor James Kellogg for providing careful reviews of our work.
M AN U
SC
RI PT
379
AC C
EP
TE D
385
17
ACCEPTED MANUSCRIPT 386
References
387 Ayala-Calvo, C., G. Bayona, A. Cardona, C. Ojeda, O. Montenegro, C. Montes, V.
389
Valencia and C. Jaramillo (2012), The Paleogene synorogenic succession in the
390
northwestern Maracaibo block: Tracking intraplate uplifts and changes in
391
sediment-delivery systems. Journal of South America Earth Sciences, Special
392
Edition on Tectonic and climatic shaping of the northern Andes and southern
393
Caribbean margin 39, 93-111. Doi: 10.1016/j.jsames.2012.04.005
SC
RI PT
388
Bayona, G., Jimenez, G., Silva, C., Cardona, A., Montes, C., Roncancio, J., and
395
Cordani, U., (2010), Paleomagnetic data and K.Ar ages from Mesozoic units of
396
the Santa Marta Massif: A preliminary interpretation for block rotations and
397
translations: Journal of South American Earth Sciences, v. 29, p. 817-831.
M AN U
394
Bueno. E and A. Solarte (1994), Geología, Geotecnia y Comportamiento Erosivo
399
del Área de Reserva Forestal de Bucaramanga. Tesis para optar al título de
400
Geólogo. Escuela de Geología, UIS, Bucaramanga.
TE D
398
Cande, S.C. and D.V. Kent (1995), Revised calibration of the geomagnetic polarity
402
timescale for the late Cretaceous and Cenozoic. Journal Geophys. Res., 100,
403
6,093-6,095.
405 406
AC C
404
EP
401
Campbell, C. J (1965), The Santa Marta wrench fault of Colombia and its regional setting. Fourth Caribbean Geological Conference. Memoir: 247-261. Trinidad.
Cediel, F., R. Shaw, and C. Cáceres (2003), Tectonic assembly of the northern
407
Andean Block, in Bartolini, C., Buffler, R. T., and Blickwede, J., eds., The
408
Circum-Gulf of Mexico and the Caribbean: Hydrocarbon habitats, basin
409
formation and plate tectonics, American Association of Petrolum Geologists
410
Memoir 79, p. 815-848.
18
ACCEPTED MANUSCRIPT 411 412
De Porta. J (1959), La Terraza de Bucaramanga. UIS. Bol. de Geología No. 3. p.p: 5-13, Bucaramanga. Diederix. H, C. Hernandez, M. T. Eliana, J. A. Osorio, P. Botero (2009), Memorias
414
Congreso Colombiano de Geología, Paipa- Boyaca.́ Resultados preliminares del
415
primer estudio paleosismológico a lo largo de la falla de Bucaramanga.
RI PT
413
England. P, G. Houseman and L. Sonder (1985), Length scales for continental
417
deformation in convergent, divergent, and strike–slip environments: analytical
418
and approxi- mate solutions for a thin viscous sheet model. J. Geophys. Res. 90,
419
3551–3557.
M AN U
SC
416
Fisher, R. A. (1953), Dispersion on a sphere, Proc. R.Soc. London, 217, 295–305.
421
Flinch, J.F. (2003), Structural evolution of the Sinu-Lower Magdalena area(
422
Northern Colombia), in Bartolini, C., Buffler, R., and Blickwede, J., eds., The
423
Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin
424
Formation and Plate Tectonics, American Association of Petroleum Geologists
425
Memoir 79, p. 776-796.
TE D
420
Hubach. E (1952), Interpretación Geológica de la erosión y de los deslizamientos
427
en Bucaramanga y medidas de defensa, Serv. Geol. Nal. Bogotá. Informe 867
428
(inédito), 2-4.
430 431 432
AC C
429
EP
426
Ingeominas (2008), Modelo de evolución morfotectónica cuaternaria basado en evidencias estructurales, neotectónicas y paleosismológicas de los principales sistemas de falla en la región de Bucaramanga. Diederix. H, Torres. E. M, Hernández. C and Botero. P. A. Bogotá
433
Ingeominas (2001a), Base de datos de fallas activas. Recopilación Bibliográfica.
434
Proyecto Compilación y Levantamiento de la Información Geodinámica, Montes
435
N., Sandoval A., Bogotá.
19
ACCEPTED MANUSCRIPT 436
Ingeominas (2001b), Zonificación Sismo Geotécnica Indicativa del Área
437
Metropolitana de Bucaramanga, Fase II. Convenio realizado entre la CDMB e
438
Ingeominas, Bucaramanga.
440 441 442
Irving. E. M (1971), La evolución estructural de los Andes mas septentrionales de
RI PT
439
Colombia. Boletín Geológico, Ingeominas, Bogotá. 19 (2), 1-90
Julivert. M (1958), La morfoestructura de la zona de Mesas al SW de Bucaramanga. UIS. Bol. de Geología No. 1. p.p: 7-43, Bucaramanga.
Julivert, M. (1963), Nuevas observaciones sobre la estratigrafía y tectónica del
444
Cuaternario de los alrededores de Bucaramanga. UIS. Bol. de Geología No. 15.
445
p.p: 41-56, Bucaramanga.
M AN U
SC
443
Kammer, A., and J. Sanchez (2006), Early Jurassic rift structures associated with
447
the Soapaga and Boyacá faults of the Eastern Cordillera, Colombia:
448
Sedimentological inferences and regional implications: Journal of South
449
American Earth Sciences, v. 21, p. 412-422.
TE D
446
Kellogg. J. N. and W. E. Bonini (1982), Subduction of the Caribbean Plate and
451
basement uplifts in the over- riding South American Plate: Tectonics, v. 1, no. 3,
452
p. 251–276.
454 455 456 457 458 459 460
Kimura, H. N. Ishikawa, and H. Sato (2011),
AC C
453
EP
450
Estimation of total lateral
displacement including strike-slip offset and broader drag deformation on an active fault; tectonic geomorphic and paleomagnetic evidence on the Tanna fault zone
in
central
Japan
Tectonophysics,
501(1-4):87-97
doi:
10.1016/j.tecto.2011.01.016 Kirschvink, J. L (1980), The least-squares line and plane and the analysis of paleomagnetic data, Geo- phys. J. R. Astron. Soc., 62, 699–718. López, J. A, M. A. Cuéllar, J. A Osorio, L. E. Bernal and E. Cortés (2008),
20
ACCEPTED MANUSCRIPT 461
Pseudotaquilitas y el carácter paleosísmico de un segmento del Sistema de Fallas
462
de Bucaramanga (SFB), noreste del Muncipio de Pailitas, Departamento del
463
Cesar, Colombia. Boletín de Geología, Bucaramanga. 30 (2), 79-92.
465
Lowrie, W. (1990), Identification of ferromagnetic minerals in a rock by coercivity
RI PT
464
and unblocking temperature properties, Geophys. Res. Lett., 17, 159 – 162.
Marcera. M and P. Salamanca (1993), Cartografía geológica y estratigráfica a
467
detalle y Zonificación geotécnica del sector oriental del Área Metropolitana de
468
Bucaramanga. Tesis para optar al título de Geólogo. Escuela de Geología, UIS,
469
Bucaramanga.
471
M AN U
470
SC
466
McFadden, P. L., and M. W. McElhinny (1990), Classification of the reversal test in paleomagnetism, Geophys. J. Int., 103, 725–729.
Montes, C., Guzman, G., Bayona, G., Cardona, A., Valencia, V., and C. Jaramillo
473
(2010), Clockwise Rotation of the Santa Marta Massif and Simultaneous
474
Paleogene to Neogene Deformation of the Plato-San Jorge and Cesar-Ranchería
475
Basins: Journal of South American Earth Sciences, v. 29, p. 832-848.
TE D
472
Mora, A. and Garcia A. (2006), Cenozoic Tectono-Stratigraphic Relationships
477
between the Cesar Sub-Basin and the Southeastern Lower Magdalena Valley
478
Basin of Northern Colombia. AAPG 2006 Annual Convention. Houston, Texas.
481
AC C
EP
476
482
París, G. M, Machette. R, Dart and K. Haller (2000), Map and Database of
483
Quaternary Faults and Folds in Colombia and its Offshore Regions. U.S.
484
Department of the Interior U.S. Geological Survey. 66 p.
479 480
485
Parra, M., Mora, A., Lopez, C., Rojas, L.E., and K.B. Horton (2012), Detecting earliest shortening and deformation advance in thrust-belt hinterlands: Example from the Colombian Andes: Geology, v. 40, p. 175-178.
Pindell, J. L., S. C. Cande, W. C. Pitman III, D. B. Rowley, J. F. Dewey, J.
21
ACCEPTED MANUSCRIPT 486
LaBrecque, and W. Haxby (1988), Plate- kinematic framework for models of
487
Caribbean evolution: Tectonophysics, v. 155, p. 121–138. Prieto. G. A, Gregory C. Beroza . G. Cb, Barrett. S. A, López. G.A and M. Florez
489
(2012), Earthquake nests as natural laboratories for the study of intermediate-
490
depth earthquake mechanics. Tectonophysics 570-571, 42–56
RI PT
488
Rivera. L. A (1989), Inversion du Tenseur des Contraintes et des Mechanismes au
492
Foyer a partir des Donnees de Polarite pour une Population de Seismes:
493
Applicaton a l’Etude du Foyer de Sismicite Intermediaire de Bucaramanga
494
(Colombie): Doctoral Thesis, Universite de Strasbourg, France, 266 p.
M AN U
SC
491
Ross, I., P. Parra, C. Mora and C. Pimentel (2009), AFTA apatite fission track
496
analysis constraints on the Mesozoic to Quaternary thermal and tectonic evolution
497
of the Middle Magdalena Basin and Santander Massif, Eastern Cordillera,
498
Bucaramanga area, Colombia. X Simposio Bolivariano: Exploración Petrolera en
499
Cuencas Subandinas. Cartagena, Colombia. Memoir.
TE D
495
Schneider, J., Pennington, W., Meyer, R., (1987), Microseismicity and focal
501
mechanisms of the intermediate depth Bucaramanga nest, Colombia. J. Geophys.
502
Res. 92, 13913–13926.
504 505 506
Sonder. L and P. England (1986), Vertical averages of rheology of the continental
AC C
503
EP
500
lithosphere: relation to thin sheet parameters. Earth Planet. Sci. Lett. 77, 81–90.
Sonder. L, J. Jones, C.H. Salyards, S.L and K. M. Murphy (1994), Vertical axis rotation in the Las Vegas Valley shear zone, southern Nevada: paleomagnetic
507
constraints on kinematics and dynamics of block rotations. Tectonics 13, 769–
508
788.
509
Taboada, A., L. A. Rivera, A. Fuenzalida, A. Cisternas, H. Philip, A. Bijwaard, J.
510
Olaya, and C. Rivera (2000), Geodynamics of the northern Andes: Sub- ductions
22
ACCEPTED MANUSCRIPT 511
and intracontinental deformation (Colombia), Tectonics, 19, 787–813. Toro, J. (1990), The termination of the Bucaramanga Fault in the Cordillera
513
Oriental, Colombia: Masters Thesis, University of Arizona, Department of
514
Geosciences, Tucson: 60.
RI PT
512
515
Trenkamp, R., J. N. Kellogg, J. T. Freymueller, and H. P. Mora (2002), Wide plate
516
deformation, south- ern Central America and northwestern South America, CASA
517
GPS observations, J. S. Am. Earth Sci., 15, 157–171.
Tschanz. C, R. Marvin, J. Cruz, H. Mennert, and E. Cebula (1974), Geologic
519
evolution of the Sierra Nevada De Santa Marta. Geol. Soc. Am. Bull., 85, 269-
520
276.
M AN U
SC
518
521
Ujueta, G. (2003), La Falla de Santa Marta-Bucaramanga no es una sola falla; son
522
dos fallas diferentes: La Falla de Santa Marta y la Falla de Bucaramanga:
523
Geología Colombiana No. 28, Universidad Nacional de Colombia, Bogotá.
525
Vargas, A., G and A. Niño (1992), Patrones de fracturamiento asociados a la Falla
TE D
524
Bucaramanga. Tesis, Universidad Industrial de Santander, Bucaramanga. Ward, D., Goldsmith, R., Cruz, J., and H. Restrepo (1973), Geología de los
527
Cuadrángulos H-12, Bucaramanga y H-13, Pamplona, Departamento de
528
Santander, Boletín Geológico Ingeominas 21(1-3), 132 p.
530 531 532
AC C
529
EP
526
Wells, D.L and K. J. Coppersmith (1994), New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement. Bulletin of the Seismological Society of America, Vol. 84, No. 4, pp. 974-1002
533
Zijderveld, J. D. A. (1967), A.C. demagnetization of rocks: Analysis of results, in
534
Methods in Palaeomagnetism, edited by D. W. Collinson, K. M. Creer, and S. K.
535
Runcorn, pp. 254–286, Elsevier, New York.
23
ACCEPTED MANUSCRIPT
537 538 539
Zarifi, Z., and J. Havskov (2003), Characteristics of dense nests of deep and intermediate-depth seismicity. Adv. Geophys. 46, 237–278. Zarifi, Z., J. Havskov and A. Hanyga (2007), An insight into the Bucaramanga nest Tectonophysics 443, 93–10.
RI PT
536
AC C
EP
TE D
M AN U
SC
540
24
ACCEPTED MANUSCRIPT 541
Figure captions
542 Figure 1. Major tectonic and structural features of the NW margin of South
544
America. Plate velocity vectors with respect to stable South America are from
545
Trenkamp et al. (2002). WC = Western Cordillera, CC = Central Cordillera, EC =
546
Eastern Cordillera, SMF = Santa marta Fault, BF = Bucaramanga Fault.
RI PT
543
547
Figure 2. Geological map of the Bucaramanga Fan (scale 1:25,000, modified from
549
Ingeominas, 2001b) and location of the 14 paleomagnetic sites. See Figure 1 for
550
location.
M AN U
SC
548
551
Figure 3. Seismicity in NW South American Plate recorded during 2006-2009 by
553
the Red Sismica Nacional de Colombia (RSNC)-Ingeominas.
554
TE D
552
Figure 4. Thermal demagnetization of a three-component IRM according to the
556
method of Lowrie (1990) for six representative specimens.
557
Figure 5. Orthogonal vector diagrams of typical demagnetization data, in situ
561
AC C
558
EP
555
562
Figure 6. Equal-area projections of the site-mean paleomagnetic directions from the
563
study area. Solid (open) symbols represent projection onto the lower (upper)
564
hemisphere. Open ellipses are the projections of the α95 cones about the mean
565
directions. The star represents the normal polarity geocentric axial dipole (GAD)
559 560
coordinates. Solid and open dots represent projections on the horizontal and vertical planes, respectively. Demagnetization step values are in °C.
25
ACCEPTED MANUSCRIPT 566
field direction (D=0°, I=14°) calculated for the Bucaramanga latitude (7.1° N).
567 Figure 7. Stratigraphic column of the Bucaramanga Fan, and stratigraphic variation
569
of magnetic polarity zones. Magnetic polarity zones are progressively numbered
570
from the section bottom. Uncertain polarity intervals are grey and cross-hatched.
571
The crosses indicate failed sites.
RI PT
568
572
Figure 8. Stratigraphic distance versus age correlation plots. Magnetic polarity
574
zones are correlated to polarity chrons from the GPTS (Cande and Kent, 1995).
575
Sloping lines are average sediment accumulation rates. Two different possible
576
correlations are shown (see text for explanation).
M AN U
SC
573
577 578
Figure 9. (a) Geomorphological context in the study area, where the Suárez and
579
Bucaramanga faults are located.
580
Bucaramanga Fan apex and the Suratá River. (b) Elevation contours around the
581
area. Three zones are well defined (from E to W), the eastern wall of the
582
Bucaramanga Fault with high topographic expression, the Bucaramanga Fan, and
583
the hanging wall of the Suárez Fault. Finally, three topographic profiles across the
585 586
TE D
EP
AC C
584
A distance of 2.5 km occurs between the
Suratá River, the apex and Bucaramanga Fan are shown. BF = Bucaramanga Fault, SF = Suárez Fault.
587
Figure 10. Scheme showing the displacement of the Bucaramanga Fan apex from its
588
feeding Suratá River along the Bucaramanga Fault.
589
Table 1. Paleomagnetic results
RI PT
ACCEPTED MANUSCRIPT
N/n 10/8 11/6 12/0 12/0 11/9 6/0 12/5 12/0 11/0 12/12 11/8 12/8 12/8 11/5
M AN U
TE D
Finos Finos Gravoso Organos Organos Organos Gravoso Organos Organos Organos Organos Organos Organos Organos
Geographic coordinates Longitude ºW Latitude ºN 73.132033 7.075063 73.132031 7.075061 73.143939 7.075496 73.168091 7.036684 73.174056 7.049284 73.138192 7.067906 73.132332 7.097189 73.133936 7.090153 73.138862 7.087891 73.138862 7.087891 73.162533 7.088209 73.161192 7.101659 73.165264 7.100704 73.148797 7.066336
EP
Member
AC C
Site GJ186 GJ187 GJ188 GJ189 GJ190 GJ191 GJ192 GJ193 GJ194 GJ195 GJ196 GJ197 GJ198 GJ199
SC
Table 1 Paleomagnetic results from Bucaramanga Fan
D (º) 179.0 176.4 353.5 176.7 188.1 181.5 357.9 356.9 167.9
In Situ I (º) 13.4 9.0 4.0
k 7.75 14.9 9.14
9.2 -19.0 -0.6 7.6 16.7 -1.3
12.61 12.79 11.63 44.45 13.37 3.47
α95 (º) 21.2 17.9 18.0 22.4 12.6 18.5 8.4 15.7 48.2
The geographic coordinates are referred to WGS84 datum. Bedding is sub-horizontal. D and I are in situ declination and inclination; K and α95 are statistical parameters after Fisher (1953).
73º ACCEPTED MANUSCRIPT
74º
80º
75º
N
ut So
OF
C o c o s P la te
N a z c a P la te
me n
e
TE D
o BF thern Z Sou
S a n ta n d e r M a s s if
C u c u ta
n o c o o B
Me
t u l F a
ri d
EP AC C
FIGURE 2
RION E a s te rn C o r d ille r a
Figure 1
c o b u c a r A
tic A n
lin
es
0
nt ro st f ru Th
75 Km
150 Km
Plate velocity Vectors 1 cm/yr
Seismic lines (Ujueta, 2003) a F a u lt
e
Y o p a lF au lt
6º
Km
Reverse fault strike-slip fault
L o s C A n tic o b a r d e s lin e
M e d e llin
B u c a ra m a n g a
C h u c a ri m
nd aA
URIB
ne
C e n tr a l C o r d ille r a
M id d le M a g d a le n a V a lle y B a s in
S o u th A m e r ic a n P l a t e 500
M a r a c a ib o B lo c k
BUCM
7º
0
E C
ra
W C
M AN U
Z on
r El Ca t F aul
t ra l
0º
C C
ille
w e r C R B g d a le n a Ariguani lle y graben s in
MONT
8º
5º
n accretionary wedge
rd
P e r ija R a n g e
ea
Co
VDUP
Cen
9º
bb
rn
S a n ta M a rta M a s s if
Z one
L o M a V a B a
10º
65º
M a r a c a ib o B lo c k
RI PT
CART
h
ri Ca
10º
SC
SMFNothern
11º
70º
15º
Ea ste
75º
1000
73º 11´0" W
73º 9´0" W
73º 7´0" W
0
73º 5´0" W
2 Km
4 Km
7º 12´0" N
Santander Massif ACCEPTED MANUSCRIPT 7º 10´0" N
er
Riv
7º 8´0" N
GJ198
7º 6´0" N
TE D
GJ192
GJ195 GJ194
GJ196
7º 4´0" N
aF au lt
AC C
GJ187 GJ186 GJ191
ri d
GJ199
GJ193
F lo
EP
GJ188
Suarez Fault system
em
GJ197
yst tS
M AN U
aul
SC
aF
Apex
ang
Su a
ra m
re
zF
ca Bu
au
RI PT
lt s ys
te
m
Su
á ra t
GJ190
GJ189
7º 2´0" N
Cretaceous
Flow deposits
Triassic-Jurassic
Limos rojos Member
Precambric to Paleozoic
Finos and Gravoso Member
Fault Covered Fault or lineament
Organos Member
Paleomagnetic sites
Figure 2
Bucaramanga Fan
79º W
70º
ACCEPTED MANUSCRIPT
75º
200 km
RI PT
depth[km]
B u c a ra m a n g a N e s t
N a z c a P la te
AC C
EP
5º
S o u th A m e r ic a n P la te 0º Figure 3
40 80 120
TE D
M AN U
SC
10º N
0
160 200
ACCEPTED MANUSCRIPT
10E-1 A/m
1 A/m
0.6 T < coer.< 2.7 T 0.12 T < coer. <0.6 T coer. < 0.12 T
10E-1 A/m
4
4 1 3 GJ194
RI PT
3 GJ197
2
SC
2
GJ194
0
0 20
100
200
300
400
500
600
20
T (xC)
10E-1 A/m
100
200
10E-1 A/m
5
5
4 GJ186
4
400
500
600
3
20
T (xC)
100
200
300
400
500
600
500
600
T (xC)
10E-2 A/m
3 GJ190
GJ192 2
AC C
3
EP
6
300
1
0
TE D
7
M AN U
1
2
2
1
1
1 0
0 20
100
200
300
400
500
600
Figure 4
T (xC)
0 20
100
200
300
400
500
600
T (xC)
20
100
200
300
400
T (xC)
N Up
N Up
N MANUSCRIPT Up ACCEPTED
200º
500º 600º
Unit= 537.e-06 A/m Unit= 508.e-06 A/m
Unit= 411.e-06 A/m
GJ192-9
600º
W
680º
500º
W
500º
E
W
E
W
600º
200º
(b)
500º
W
E
W
680º 680º
E
600º 500º
200º
S Down N Up200º 460º
E
600º
(c)
M AN U
380º
E
SC
(a)
250º
GJ195-1
200º
RI PT
GJ190-2
250º
S Down
S Down
N Up
N Up
200º
TE D
600º
380º
600º
680º
W 680º 460º 200º
(d)
GJ198-2 E
W
E
W
680º
S Down
E
W
E
W
Unit= 83.9e-06 A/m E E 550º
380º
(f)
460º
200º
S Down
Figure 5
380º
GJ199-3
Unit= 258.e-06 A/m
(e)
AC C
W
Unit= 266.e-06 A/m
EP
GJ197-3
460º
S Down
ACCEPTED N MANUSCRIPT 197
190
M AN U
SC
RI PT
198
90
AC C
EP
TE D
270
195 186
192 187
199
196
180
Geocentric axial dipole field direction expected at Bucaramanga (Lat 7.13º N) Mean paleomagnetic direction (D = 357.5 I = 2.0 K = 41.63 a 95 = 8.1)
Figure 6
188 192
200
ACCEPTED MANUSCRIPT
186 187
180
160
SC
195 191
140
M AN U
190
120
TE D EP
80
60
40
20
0 Figure 7
N3
193 194
AC C
Organos Member
100
R3
RI PT
Limos Rojos Member Gravoso Member Finos Member
220
189 199
R2
197
N2
196
R1
198
N1
ACCEPTED MANUSCRIPT
B
60
120
193 194 189 199
R2
197
N2
196
R1
198
N1
100
40
20
Za nc l e an
Late Pliocene
Piacenzian
RI PT 195 191
190
N3
193 194 189 199
R2
197
N2
196
R1
198
N1
20
SYSTEM Stages
0 P LI OC E NE E ar l y Pl i oc e n e Middle Pliocene Za nc l e an
G A U S S
Gelasian
Santern. Emilian Sicilian 1
G I L B E R T
Late Pliocene
P LE I S TOC E N E Early Pleistocene M. Pleistocene
2
BRUNHES
POLARITY CHRONS
Piacenzian 3
Ma
5
M A T U Y A M A
R3
4
1
G A U S S
Santern. Emilian Sicilian
2
3
4
5
G I L B E R T
Gelasian
P LE I S TOC E N E Early Pleistocene M. Pleistocene
60
186 187
M A T U Y A M A
POLARITY CHRONS POLARITY
Jaramillo
Olduvai
Kaena
Mammoth
Cochiti
Nunivak
Sidufjall
Thvera
Jaramillo
Olduvai
Kaena
Mammoth
Cochiti
Nunivak
Sidufjall
Thvera
Figure 8
Polarity Subchrons
Stages
Ma BRUNHES
POLARITY
SYSTEM
Chrono
P LI OC E NE E ar l y Pl i oc e n e Middle Pliocene
80
188 192
40
Chrono
0
Organos Member
80
M AN U
100
180
140
N3
TE D
120
190
200
160
195 191
EP
140
R3
220
SC
180
186 187
160
Organos Member
Limos Rojos Member
188 192
Finos Member
200
Gravoso Member
220
AC C
Finos Member
Gravoso Member
Limos Rojos Member
A
Polarity Subchrons
ACCEPTED MANUSCRIPT
(b)
(a) 73º 9' W
73º 5' W
73º 1' W
RI PT
7º 10' N
2.5 km
C
A` B`
M AN U
SC
7º 8' N
A
AC C
EP
TE D
7º 6' N
Reverse fault Strike-slip fault
B C`
7º 4' N
A 950 m 850 m 750 m 650 m
1050 m
BF
SF B
950 m 850 m 750 m 650 m 1050 m 950 m 850 m 750 m 650 m
Figure 9
A’
1050 m
Apex
B’
BF C
C’
r ve
at
á
Ri
ACCEPTED MANUSCRIPT
Su r
Stage A
Su r
at
TE D
á
Ri
Stage B
M AN U
ve r
SC
D
RI PT
Bucaramanga Fault
D
AC C
EP
2.5 Km
Figure 10
Bucaramanga Fault
ACCEPTED MANUSCRIPT Highlights
Paleomagnetic investigation of a Plio-Pleistocene (?) continental alluvial fan juxtaposed to the Bucaramanga Fault, and horizontally displaced by 2.5 km with respect to its feeding river. Nine reliable paleomagnetic directions define a succession
RI PT
of magnetic polarity zones, correlated with several tracks of the Plio-Pleistocene magnetic polarity time scale. If the youngest age model is considered, most recent sediments of the Bucaramanga Fan can be reasonably dated at 0.8 Ma (BrunhesMatuyama chron transition), translating into a maximum 3 mm/yr slip rate for the
AC C
EP
TE D
M AN U
SC
Bucaramanga Fault.