Different Levels of Exhumation Across the Bucaramanga Fault in The

Volume 3 Chapter 17 <a href="/goto?url=https://doi.org/10.32685/pub.esp.37.2019.17" target="_blank">https:</a><a href="/goto?url=https://doi.org/10.32685/pub.esp.37.2019.17" target="_blank">/</a><a href="/goto?url=https://doi.org/10.32685/pub.esp.37.2019.17" target="_blank">/doi.org/10.32685/pub.esp.37.2019.17 </a>Published online 22 May 2020 Different Levels of Exhumation across the Bucaramanga Fault in the Cepitá Area of the Southwestern Santander Massif, Colombia: Implications for the Tectonic Evolution of the Northern Andes in Northwestern South America <ul style="display: flex;"><li style="flex:1">1</li><li style="flex:1">[email protected], [email protected] </li></ul>Servicio Geológico Colombiano Dirección de Recursos Minerales Diagonal 53 n.° 34–53 Bogotá, Colombia Sergio AMAYA–FERREIRA1* ,<a href="/goto?url=https://orcid.org/0000-0002-1385-2144" target="_blank"> </a><a href="/goto?url=https://orcid.org/0000-0002-1385-2144" target="_blank">C</a>arlos Augusto ZULUAGA2 and Matthias BERNET3 <a href="/goto?url=https://orcid.org/0000-0002-2403-2731" target="_blank">,</a><ul style="display: flex;"><li style="flex:1">2</li><li style="flex:1"><a href="mailto:[email protected]" target="_blank">[email protected] </a></li></ul>Universidad Nacional de Colombia Sede Bogotá Departamento de Geociencias Carrera 30 n.° 45–03 Abstract Apatite and zircon fission–track data from crystalline rocks collected along an east–to–west elevational profile across the Bucaramanga strike–slip fault in the Cepitá area and thermal history modeling show the four–stage thermal history of the southwestern Santander Massif of the northern Andes in Colombia. A 60 my phase of burial heating from the Late Jurassic to the Late Cretaceous was followed by three cooling phases beginning in approximately 65–60 Ma, which were related to regional tectonic events. The Late Cretaceous – early Paleocene accretion of an island arc and interac- tions of the Caribbean Plate with the northwestern South America plate first triggered the surface uplift and erosional exhumation of the Santander Massif. During the late Oligocene – early Miocene, the collision of the Panamá–Chocó Block with northwestern South America caused an acceleration in the cooling and exhumation of the Santander Massif and differential surface uplift to the east and west of the Bucaramanga Fault in the Cepitá area. The present–day topography of the Santander Massif probably formed at that time. Locally recorded late Miocene cooling may be related to movement on the secondary fault pattern in the study area or minor magmatic activity. Bogotá, Colombia 3*<a href="mailto:[email protected]" target="_blank">[email protected] </a>Université Grenoble Alpes Insitut des Sciences de la Terre 1381 rue de la piscine, CS 40700, 38058 Grenoble cedex 9, France Corresponding author Keywords: exhumation, fission–track analysis, Santander Massif, Bucaramanga Fault, thermal modeling. Resumen Datos de huellas de fisión en apatito y zircón de rocas cristalinas colectadas a lo largo de un perfil de elevación este–oeste a través de la Falla de Bucaramanga, falla de rumbo, en el área de Cepitá y el modelamiento de la historia termal muestran una historia termal en cuatro etapas para el suroeste del Macizo de Santander de los Andes del norte en Colombia. A los 60 millones de años, una fase de calentamiento por enterramiento desde el Jurásico Tardío al Cretácico Tardío fue seguida por tres fases de enfriamiento que comenzaron aproximadamente a los 65–60 Ma, y están relacionadas con eventos tectónicos regionales. En el Cretácico Tardío–Paleoceno temprano, la acre- ción de un arco de islas y las interacciones de la Placa del Caribe con el noroccidente de la Placa de Suramérica desencadenaron el primer levantamiento de superficie y la Citation: Amaya–Ferreira, S., Zuluaga, C.A. & Bernet, M. 2020. Different levels of exhumation across the Bucaramanga Fault in the Cepitá area of the southwestern Santander Massif, Co- lombia: Implications for the tectonic evolution of the northern Andes in northwestern South America. In: Gómez, J. & Mateus–Zabala, D. (editors), The Geology of Colombia, Volume 3 Pa- leogene – Neogene. Servicio Geológico Colombiano, Publicaciones Geológicas Especiales 37, p. 491–507. Bogot<a href="/goto?url=https://doi.org/10.32685/pub.esp.37.2019.17" target="_blank">á. https:</a><a href="/goto?url=https://doi.org/10.32685/pub.esp.37.2019.17" target="_blank">/</a><a href="/goto?url=https://doi.org/10.32685/pub.esp.37.2019.17" target="_blank">/doi.org/10.32685/pub.esp.37.2019.17 </a>491 AMAYA–FERREIRA et al. exhumación erosiva del Macizo de Santander. Durante el final del Oligoceno y el Mioceno temprano, la colisión del Bloque Panamá–Chocó con el noroeste de Suramérica provocó la aceleración del enfriamiento y de la exhumación del Macizo de Santander y la elevación diferencial de la superficie al este y al oeste de la Falla de Bucaramanga en el área de Cepitá. Probablemente, la topografía actual del Macizo de Santander se formó en ese momento. El enfriamiento del Mioceno tardío registrado localmente puede estar relacionado con el movimiento en el patrón de falla secundaria en el área de estudio o con la actividad magmática menor. Palabras clave: exhumación, análisis de huellas de fisión, Macizo de Santander, Falla de Bucaramanga, modelamiento termal. 1. Introduction Batholith in the Central Cordillera (Restrepo–Moreno et al., 2009). Parra et al. (2012) argued, on the basis of AFT data from The rise of orogenic mountain belts, particularly in the northern the Nuevo Mundo Syncline sedimentary basin fill and thermal Andes, has a significant influence on regional climate and at- modeling, for a Paleocene – early Eocene (60–50 Ma) phase of mospheric circulation and precipitation patterns, and forms bar -pronounced shortening and cooling of the western margin of riers to species migration and the creation of new habitats and the Eastern Cordillera associated with tectonic inversion and ecological niches (e.g., Hoorn et al., 2010; Mapes et al., 2003). the first surface uplift and erosion of the Eastern Cordillera. For paleogeographic reconstructions, it is important to link the However, the Parra et al. (2012) study lacked information from exhumation of deep–seated crystalline rocks and the formation ZFT or zircon (U–Th)/He thermochronometers and therefore of high orogenic topography with the plate–tectonic evolution the pre–depositional thermal histories in their models were ful- of the area of interest. Here, we present a study on the exhuma- ly unconstrained. Regardless, the absence of Cretaceous sed -tion history of the southern Santander Massif in northeastern imentary cover rocks in large areas of the Santander Massif, Colombia because this mountain belt holds a key position in the which are otherwise widespread in the Eastern Cordillera of northern Andes, forming the northwest–striking continuation of Colombia, suggests erosion was an important process during the Eastern Cordillera at the junction between the Eastern Cor- the exhumation history of the Santander Massif. Evidence of dillera and the Mérida Andes in Venezuela to the east (Figure 1). Paleogene and Neogene erosional exhumation of the Santander The Santander Massif is part of the so–called Maracaibo Block, Massif basement and sedimentary cover rocks is preserved in which is delineated by the Santa Marta–Bucaramanga and Oca the stratigraphic sequences of the Lisama, La Paz, Esmeraldas, strike–slip Fault Systems and the southwestern fold–and–thrust Mugrosa, Colorado, and Real Formations in the Nuevo Mundo, belt of the Mérida Andes (Figure 1; e.g., Colletta et al., 1997; Armas, and Andes Synclines of the Middle Magdalena Valley Mann et al., 2006). The Maracaibo Block also includes the Si- (Figure 1; Caballero et al., 2013; Parra et al., 2012; Sánchez et erra Nevada de Santa Marta and the serranía de Perijá (Figure al., 2012). Deformation of the Middle Magdalena Valley area 1). The cooling history of the crystalline rocks of the central and probably began during the Paleocene, with structures such as southern Santander Massif has been previously studied with the Lisama Anticline (Caballero et al., 2013). low–temperature thermochronology, with apatite fission–track The objective of this study was to more precisely constrain (AFT) ages ranging from 20 to 7 Ma and zircon fission–track the exhumation history of the southwestern Santander Massif (ZFT) ages ranging from 172 to 20 Ma (Amaya et al., 2017; in the Cepitá area, to the east and west of the Chicamocha River Shagam et al., 1984; van der Lelij et al., 2016; Villagómez et (Figure 2). Thus far, very few and spatially dispersed thermoal., 2011). In addition, from outcrops to the east of the city of chronological data have been published from this region (Ca- Bucaramanga and the Bucaramanga Fault, Mora et al. (2015) ballero et al., 2013; Shagam et al., 1984; van der Lelij et al., first presented AHe ages between 8.2 and 16 Ma and ZHe ages 2016). Therefore, we present data of 10 AFT and 9 ZFT sam- between 22.6 and 24.2 Ma. Along the same profile, Amaya et al. ples collected from igneous and metamorphic crystalline rocks (2017) demonstrated an exhumed ZFT partial annealing zone, along a profile across the Chicamocha Canyon and the Buca- which was rapidly exhumed between 25 and 20 Ma. All these ramanga Fault System near Cepitá, referred to here as the west- data show the importance of late Oligocene regional tectonics ern and eastern blocks of the Santander Massif (Figures 2, 3), driving the exhumation of the Santander Massif along the Bu- respectively. The Chicamocha River does not exactly follow the caramanga Fault, which is related to the break–up of the Far- trace of the Bucaramanga Fault System but does mark the presallón Plate and the collision of the Panamá–Chocó Block with ent–day morphologic separation between the two blocks. While northwestern South America (Farris et al., 2011; Taboada et the western block reaches an elevation of only approximately al., 2000; O’Dea et al., 2016). This regional tectonic influence 1600 m in the study area, the eastern block rises to more than has already been shown in the exhumation of the Antioquian 3200 m in this part of the Santander Massif (Figure 3). Expo- 492 Different Levels of Exhumation across the Bucaramanga Fault in the Cepitá Area of the Southwestern Santander Massif, Colombia Lesser Antillas Caribbean Plate OAF <ul style="display: flex;"><li style="flex:1">SSF </li><li style="flex:1">SNSM </li></ul>SP 10° N MTB Mérida Andes Barinas Apure Basin SM <ul style="display: flex;"><li style="flex:1">Cocos Plate </li><li style="flex:1">South American Plate </li></ul>Llanos Orientales Basin NMS 5° N EC MMV Guiana Shield Nazca Plate 0° Caguán–Vaupés Basin Oriente Basin Amazonas Basin <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">200 </li><li style="flex:1">400 km </li></ul>study area Figure 1. Overview map showing the major tectonic features of northern South America (modified from Colmenares & Zoback, 2003). (SCF) Southern Caribbean Marginal Fault; (SNSM) Sierra Nevada de Santa Marta; (OAF) Oca–Ancón Fault; (SSF) San Sebastián Fault System; (LBESF) Los Bajos–El Soldado Fault System; (SP) serranía de Perijá; (MTB) Maracaibo Triangular Block; (SBF) Santa Marta–Bucaramanga Fault; (BF) Boconó Fault; (PSZ) Panamá suture zone; (SM) Santander Massif; (GF) Garrapatas Fault; (IBF) Ibagué Fault; (NMS) Nuevo Mundo Syncline; (EC) Eastern Cordillera; (MMV) Middle Magdalena Valley; (EAFFS) Eastern Andean Front Fault System; (DGM) Dolores–Guayaquil Megashear. sure of crystalline rocks at high surface elevations implies both de Perijá, and the Mérida Andes of Venezuela along two of its exhumation and surface uplift. The thermochronological data of three sides (Figure 1). Even if two of the main bounding faults of this study were used in t–T models to provide constraints on the the Maracaibo Block, the dextral Oca Fault to the north and the timing of cooling. The cooling histories were then interpreted sinistral Santa Marta–Bucaramanga Fault on its western flank, in terms of erosional and tectonic exhumation. To constrain the are strike–slip fault systems with an unknown vertical offset, difference in relative surface uplift between the western and considerable topographic surface elevations have been attained eastern blocks, ZFT cooling ages at similar elevations on both in the Sierra Nevada de Santa Marta and the Santander Massif sides of the Bucaramanga Fault were compared. Furthermore, (up to 4530 m at Paramo del Almorzadero). The Santa Marta– the apparent fission–track cooling ages were translated into ex- Bucaramanga Fault extends for over 600 km from Santa Marta humation rates (e.g., Willett & Brandon, 2013) for the crystal- in the north to the Chicamocha Canyon, approximately 40–70 line rocks that were buried beneath sedimentary rocks at least km south of Bucaramanga, where it ceases defining the western since the Late Jurassic and throughout most of the Cretaceous. margin of the Santander Massif (Figure 1). The Boconó strike– slip fault dominates the late Miocene to Pliocene evolution and 2. Geological Setting exhumation of the Mérida Andes of Venezuela (Bermúdez et al. 2010, 2011, 2013; Kohn et al. 1984), but the southeastern The fault–bounded triangular Maracaibo Block in the northern fold–and–thrust belt is thought to delimit the Maracaibo Block Andes is an interesting geological feature, as this block not only to the southeast against the South American continental plate hosts the highest coastal mountain belt in the world including (e.g., Figure 1; Colletta et al., 1997; Mann et al., 2006). <ul style="display: flex;"><li style="flex:1">the 5700 m–high Pico Cristobal Colón of the Sierra Nevada de </li><li style="flex:1">Late Proterozoic to Paleozoic metamorphic rocks intruded </li></ul>Santa Marta, but also features the Santander Massif, the serranía by Triassic and Jurassic plutonic rocks form the crystalline core 493 AMAYA–FERREIRA et al. Triassic – Jurassic intrusives 7.30° N Guaca–La Virgen (low–grade metamorphic rocks) Páramo Rico Tonalite Silos Berlín Orthogneiss Bucaramanga Paleozoic intrusive rocks Silgará Schists Santa Barbara Quartz Monzonite Bucaramanga Gneiss La Corcova Quartz Monzonite 21.4 Ma 15.7 Ma 93 Ma Zircon fission–track age this study Guaca 13.7 Ma 21.4 Ma 18.9 Ma Apatite fission–track age this study Published zircon fission–track data Published apatite fission–track data 6.86° N 20 Ma 172 Ma 18.5 Ma Cepitá Aratoca 166.7 Ma 18.9 Ma Jordán 25.1 Ma 24.6 Ma 5.4 Ma 6.9 Ma 25.3 Ma 7.3 Ma 34.5 Ma 12.9 Ma 127.5 Ma 88.7 Ma Faults Folds 145.6 Ma 36.2 Ma 264.8 Ma 19.6 Ma 122.8 Ma Mogotes Quartz Monzonite County <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">10 </li><li style="flex:1">20 km </li></ul>Figure 2. Geological map and sample locations. Taken and modified from Zuluaga & López (2018). 3500 3000 2500 2000 1500 1000 500 3500 3000 2500 2000 1500 1000 500 <ul style="display: flex;"><li style="flex:1">Cepitá area apatite fission–track age profile </li><li style="flex:1">Cepitá area zircon fission–track age profile </li></ul>abBucaramanga Fault zone Bucaramanga Fault zone Chicamocha River valley <ul style="display: flex;"><li style="flex:1">Western block </li><li style="flex:1">Eastern block </li><li style="flex:1">Western block </li><li style="flex:1">Eastern block </li></ul>34.5 ± 17.5 18.9 ± 7.1 36.2 ± 5.8 12.9 ± 4.6 25.1 ± 6.3 145.6 ± 25.7 166.7 ± 32.7 <ul style="display: flex;"><li style="flex:1">24.6 ± 3.9 </li><li style="flex:1">5.4 ± 6.3 </li></ul>18.5 ± 4.8 25.3 ± 7.7 <ul style="display: flex;"><li style="flex:1">6.9 ± 2.4 </li><li style="flex:1">88.7 ± 28.3 </li></ul>122.8 ± 18.3 127.9 ± 37.8 142.4 ± 21.2 7.3 ± 4.6 19.6 ± 9.6 264.8 ± 110.9 21.4 ± 5.5 <ul style="display: flex;"><li style="flex:1">Topography </li><li style="flex:1">Topography </li></ul><ul style="display: flex;"><li style="flex:1">AFT age ± 2SE </li><li style="flex:1">ZFT age ± 2SE </li></ul><ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">0</li></ul><ul style="display: flex;"><li style="flex:1">Longitude (W) </li><li style="flex:1">Longitude (W) </li></ul>Figure 3. Topographic profile with sample locations. of the Santander Massif (Goldsmith et al., 1971). In this study, (Figures 2, 3). The Jurassic and Cretaceous sedimentary cover only the late Proterozoic Bucaramanga Gneiss, Paleozoic Sil- rocks, with a cumulative thickness of ca. 2500 to ca. 3500 m gará Schists, Jurassic Mogotes Batholith and Pescadero Granite (Shagam et al., 1984), were used as a constraint for thermal are of interest because samples were only collected from these history modeling for the phase and amplitude of the Jurassic lithological units to the east and west of the Chicamocha River and Cretaceous burial heating in the study area. A zircon fission 494 Different Levels of Exhumation across the Bucaramanga Fault in the Cepitá Area of the Southwestern Santander Massif, Colombia track age in the study area of 172.0 ± 16.4 Ma from the Pes- Our study also employed the most robust and revealing cadero Granite of van der Lelij et al. (2016) indicates that burial method plotting length against a kinetic parameter (Dpar), heating was insufficient to fully reset the zircon fission–track noting whether trends exist and, if possible, defining coherent system to the west of the Bucaramanga Fault. Our samples of kinetic populations (e.g., Burtner et al., 1994). This approach the western profile were collected between 612 and 1347 m not only can result in more accurate age interpretation but also elevation between Cepitá and Aratoca, whereas eastern profile allows length data to be segregated to enable proper inverse samples were collected from elevations ranging between 900 modeling. Because fission–track lengths shorten as a function and 1050 m to the east of Cepitá (Figure 2; Table 1). of the thermal history they have undergone, a set of length mea- The Chicamocha River is a tributary of the Magdalena surements constitutes an integrated record of the temperatures River. In the Cepitá area, the Chicamocha River flows in a experienced by a sample. N–NW direction, before following the secondary NE–SW– oriented fault pattern of the Santander Massif and turning to 3.3. Exhumation Rate Estimates the SW and flowing toward the village of Jordán (Figure 2). In the study area, the Chicamocha Canyon shows at least 1000 First–order exhumation rates based on AFT and ZFT ages can m of incision with respect to the highest elevations of the be estimated from the simple 1–D thermal advection mod- western block (Figure 3). el age2dot created by Mark BRANDON (see Ehlers et al., 2005). For these first–order estimates, we assumed a constant pre–exhumation thermal gradient of 30 °C/km, which we ac- knowledge is a very simplistic assumption but sufficient for the purpose of this study. The AFT model was selected for chlorine apatite, which is justifiable with regard to the measured Dpar 3. Methods 3.1. Fission–Track Analysis Sample preparation for the fission–track analysis was complet- values shown in Table 2. For the ZFT model, we selected an- ed at the Servicio Geológico Colombiano in Bogotá, following nealing parameters for radiation–damaged zircon, given that the methodology described by Amaya et al. (2017). All samples the ZFT cooling ages are on average older than 100 Ma for were irradiated at the FRM II research reactor in Garching, the western block. For the eastern block samples 13SACZ03 Germany. For track length measurements of horizontally con- and 07, we used a zero–damage model, considering that these 252 fined tracks, apatite samples were irradiated with Cf at the zircons rapidly cooled below the zircon fission–track closure University of Melbourne. Samples were analyzed dry at 1250x temperature and through the zircon partial annealing zone bewith an Olympus BX51 optical microscope, using the FTStage tween 25 and 20 Ma (Table 3). 4.04 system of Trevor Dumitru in the fission–track laboratory of the Servicio Geológico Colombiano in Bogotá and in the 4. Results fission–track laboratory at ISTerre, Université Grenoble Alpes. 4.1. Fission–Track Data 3.2. Time–Temperature History Modeling The samples from the western profile, to the west of the For t–T history modeling of the western profile samples, we used Chicamocha River and the Bucaramanga Fault zone, have the QTQt program (v 4.6) of Gallagher (2012) to model age pairs AFT ages between 36 and 7 Ma depending on elevation of samples for which we have AFT and ZFT data and length mea- (Figure 4a). The lowest sample, i.e., 12SACEP11 from the surements of horizontally confined tracks in apatite. The QTQt Silgará Schists, yields a central AFT age of 21.4 ± 5.5 Ma program determines cooling history scenarios using a Bayesian and was collected at 612 m along the secondary fault pat-

Different Levels of Exhumation Across the Bucaramanga Fault in The

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