Quaternary fault kinematics and stress tensors along the southern Caribbean from fault-slip data and focal mechanism solutions

Deformation along the southern Caribbean coast, as confirmed by the compilation of stress tensors derived from fault-plane kinematic indicators (microtectonics) and further supported by focal mechanism solutions herein presented, results from a compressive strike-slip (transpressional senso lato) regime characterized by a NNW-SSE maximum horizontal stress (sigma(H)=sigma(1)) and/or an ENE-WSW minimum (sigma(h)=sigma(3) or sigma(2)) horizontal stress, which is responsible for present activity and kinematics of six sets of brittle features: east-west right-lateral faults, NW-SE right-lateral faults-synthetic Riedel shears, ENE-WSW to east-west dextral faults-P shears, NNW-SSE normal faults, almost north-south left-lateral faults-antithetic Riedel shears, and ENE-WSW reverse faults-sub-parallel to fold axes and mostly in the subsurface; the latter ones being associated to ENE-WSW-trending folding. In this particular region, the brittle deformation obeys the simple shear model, although not all the deformation can be accounted for it since partitioning is also taking place (regional folding and thrusting is essentially due to the normal-to-structure component of the partitioned maximum horizontal stress). Conversely, the maximum horizontal stress on the Maracaibo block and south of the Oca-Ancon fault progressively turns counter-clockwise to become more east-west-oriented, allowing left- and right-lateral slip along the north-south-striking and NE-SW-striking faults, respectively. The orientation and space variation of this regional stress field in western Venezuela results from the superposition of the two major neighboring interplate maximum horizontal stress orientations (sigma(H)): roughly east-west-trending stress across the Nazca-South America type-B subduction along the pacific coast of Colombia and NNW-SSE-oriented one across the southern Caribbean boundary zone. (C) 2004 Elsevier B.V. All rights reserved.