New kinematic data from the Sierra Castillo Fault at Quebrada del Carrizo, Precordillera of Atacama Region, Chile.

Abstract

The Sierra Castillo Fault and its associated mesoscopic structures were studied at Quebrada del Carrizo. Here the fault juxtaposes Triassic and Paleozoic rocks on the east with Bajocian rocks on the west. The Sierra Castillo Fault serves as a master fault of its associated mesoscopic structures. It is inferred that a sinistral traspression occurred along it during the Eocene-Oligocene. This inference is based on S-C structures and a drag fold directly observed on the trace of the fault. This deduction is also based on other associated structures such as reverse faults, ptygmatic folds, tensional gashes and cleavage. Subvertical veins and faults in positions T (tension) and R (Riedel) were also identified. Transport directions and sense were determined studying the kinematics of reverse faults and the intersection between reverse faults and cleavage. A 65° clockwise rotation of the shortening direction from a west position to a north-northwest position is detected. An alternative solution considered is the anticlockwise rotation of the rocks, with the shortening direction remaining constant.