SANTANDER MASSIF
Description
Determine the importance of the tectonic control in the exhumation and uplift of Santander Massif from Eocene to late Miocene; and assess if erosion (unloading) also played an important role in the history of exhumation and uplifting of Santander Massif during this time. A compilation of published and new apatite and zircon fission-track and (U-Th)/He cooling ages along a transect between the Bucaramanga and the Guaicáramo faults is presented here to support the interpretation of Pre-Pleistocene episodic exhumation and deformation during the evolution of the central part of the Santander Massif's. The Pamplona Wedge controls the structural evolution of the central part of the Santander Massif producing a set of north to south trending transpressional faults and curved oblique faults with a dextral (NE-SW) and sinistral (NW-SE) slip component in a regional framework developed by indentation tectonics. The whole database points to three tectonic events: (i) exhumation during the Late Cretaceous, (ii) exhumation and uplifting of the western flank of the Santander Massif from Eocene to early Miocene times, and (iii) exhumation and uplifting associated to increasing deformation toward the central part of the Santander Massif from late Miocene to Recent times. The first phase was associated with shortening and reactivation of intraplate structures as consequence of the interaction of the Nazca, Caribbean Plate and South America Plates. The second phase was related to tectonic activity of the Bucaramanga Fault and structures as the Suratá Fault, in turn caused by the onset and final closure of the collision of the Panamá-Chocó Block; this phase was characterized by fast erosion with isostatic response of the massif. The third phase was related to westward motion of the Pamplona Wedge. Our and published thermochronological data agree with quantitative geomorphological and structural data suggesting that the current geomorphology reflects the tectonic control from the late Miocene to the Recent, associated with the most recent phase of exhumation, surface uplift and rejuvenation of deformation toward central part of the Santander Massif.
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For estimating patterns of deformation and associated exhumation samples were collected for AFT and ZFT analysis from crystalline basement rocks of the Pamplona Indenter and the SM along a transect between Toledo and Bucaramanga. The stress tensors analysis was based on a structural map obtained from the published geological maps (Ward et al., 1977), the interpretation of digital terrain models (12.5 m resolution, NASA – Alaska Satellite Facility, 2015), and fieldwork in the study area. Data from twenty observation sites were selected for stress tensor analysis. Measured data consist of orientation of planes marked with slickensides as main slip indicators. Movement sense was determined for each striated plane from kinematic criteria of Petit (1987) and Doblas (1998), considering especially the associated Riedel fractures. The slickensides were also analyzed from a quality point of view checking striation sharpness, type of slip, outcrop weathering, lithology, and mineral patinas. Data was also controlled using relations of crosscutting planes and superimposing of slickensides to examine slip confidence and relative timing. Fault slip data were collected from the central part of the SM, crossing the main structures of the study area, i.e., Suratá, Río Charta, Mutiscua, and Chitagá faults. For quantitaive geomorphology we obtained the steepness index (ks), a geomorphometric proxy to analyse erosional patterns (Kirby and Whipple, 2001, 2012; Wobus et al., 2006). We obtained the index for the catchment of the Caraba River (including the Berlín Plateau), where the younger exhumation ages were obtained. The Win-Tensor software (Delvaux and Sperner, 2003) was used for stress tensor analysis. For fission-track analysis, the samples were prepared and analyzed at the fission-track laboratories of the Servicio Geológico Colombiano and ISTerre, Université Grenoble Alpes, France. Using the external detector method, all grain mounts were covered with low-U muscovite sheets and irradiated together with Durango apatite and Fish Canyon Tuff apatite and zircon age standards, as well as IRMM540R (for apatite) and IRMM541 (for zircon) dosimeter glasses at the well-thermalized FRMII research reactor of the Technische Universität München in Garching, Germany. For quantitive geomorphology, the index for the catchment (Ks) of the Caraba River, is calculated as follows: S = ks * A-θ, where S is the channel gradient and θ is the concavity index. We obtained a normalized form of the ks index (ksn) by introducing a reference concavity (θref=0.15), which is a common standard value (Wobus et al., 2006). The ksn index was computed using a minimum drainage area of 1x106 m2. We obtained the knickpoints pattern with the aim of the knickpointfinder Matlab function included in the TopoToolbox package (Schwanghart and Scherler, 2014).