Transpression and the build-up of the Cordillera: the example of the Bucaramanga fault (Eastern Cordillera, Colombia)

Abstract

Widespread wrench tectonics have been described along the northern Andes. The Bucaramanga fault, described as sinistral strike-slip, bounds the high Santander Massif. We combine structural and thermochronological data from the centralsouthern portion of the fault to investigate the vertical displacement. The structural survey data show old phases of activity preserved in the host rocks along the fault trace, with the superimposition of different generations of slickenlines, and both strike-slip and dip-slip kinematics indicators. New and previous thermochronological data show that differential exhumation of the fault walls has been ongoing for the last 50 Ma. The hanging wall, the Santander Massif, records, in the central portion, decreasing exhumation rates from the early Miocene to the mid- to late Miocene and, in the southern portion, constant rates from the Late Oligocene to the Pliocene. Combining such observations, the thermochronological offset resulting from the relative motion of the two fault walls is comparable with the observed drop in elevation across the fault, suggesting that the present topography of the Santander Massif is related to vertical movement along the Bucaramanga fault. We infer that the fault has a significant Neogene reverse component, consistent with the present day horizontal global positioning system vector data, longterm exhumation rates and the structural assemblage.