The Liquiñe Ofqui fault zone: a long-lived intra-arc fault system in southern Chile

Abstract

Plate reconstructions for the Cenozoic document relatively steady right-oblique subduction of the Farallon (Nazca) plate beneath the Chilean continental margin. The kinematic signature recorded along the intra-arc Liquiñe-Ofqui fault zone (LOFZ), a major feature of the southern Andes, may help to understand the way in which the Nazca-South America slip vector has been partitioned into strain and displacement along and across the continental margin. The LOFZ consists of two NNE-trending right-stepping straight lineaments, a strike-slip duplex at the right step, and curved features which splay off the straight lineaments toward the northwest. The LOFZ runs mostly through heterogeneously deformed Cenozoic plutonic rock of the North Patagonian Batholith and patchy metamorphic wall rock. Early Cenozoic volcano-sedimentary rocks and dyke swarms, found in close spatial association with the strike-slip duplex, are believed to have developed in strike-slip-related basins. Quaternary volcanoes are aligned parallel to the LOFZ. Both ductile and brittle kinematic indicators within centimeter-to-meter-wide high-strain zones, document late Cenozoic dextral shear deformation. Contrasting left-lateral deformation recorded on older and wider mylonitic zones, suggests that the LOFZ may be a long-lived shear zone that accommodated continental-scale deformation arising from the Farallon (Nazca)-South America plate convergence. A block rotation pattern, as indicated by paleomagnetic data, is consistent with the geometry and Cenozoic kinematics of the LOFZ.