THE LIQUINE OFQUI FAULT ZONE - A LONG-LIVED INTRAARC FAULT SYSTEM IN SOUTHERN CHILE

Plate reconstructions for the Cenozoic document relatively steady righ t-oblique subduction of the Farallon (Nazca) plate beneath the Chilean continental margin, The kinematic signature recorded along the intra- arc Liquine-Ofqui fault zone (LOFZ), a major feature of the southern A ndes, may help to understand the way in which the Nazca-South America slip vector has been partitioned into strain and displacement along an d 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 tow ard the northwest. The LOFZ runs mostly through heterogeneously deform ed Cenozoic plutonic rock of the North Patagonian Batholith and patchy metamorphic wall rock. Early Cenozoic volcano-sedimentary rocks and d yke swarms, found in close spatial association with the strike-slip du plex, are believed to have developed in strike-slip-related basins. Qu aternary volcanoes are aligned parallel to the LOFZ. Both ductile and brittle kinematic indicators within centimeter-to-meter-wide high-stra in zones, document late Cenozoic dextral shear deformation. Contrastin g left-lateral deformation recorded on older and wider mylonitic zones , suggests that the LOFZ may be a long-lived shear zone that accommoda ted continental-scale deformation arising from the Farallon (Nazca)-So uth America plate convergence. A block rotation pattern, as indicated by paleomagnetic data, is consistent with the geometry and Cenozoic ki nematics of the LOFZ.