Kinematic constraints on intra-arc shear and strain partitioning in the southern Andes between 38°S and 42°S latitude

Abstract

On the basis of structural field work, fault kinematic analysis, and the analysis of digital imagery, we describe the northern part of the southern Andean intra-arc Liquiñe-Ofqui Fault Zone (LOFZ) as an SC-like fault zone system accommodating part of the Nazca-South American plate convergence obliquity. Kinematic modeling suggests that the LOFZ accommodated 124 (+24/-21) km of dextral displacement between 40°S and 42°S and 67 (+13/-11) km between 38°S and 40°S since the Pliocene. Associated vertical axis rotations are 31 ± 4° clockwise and 9 ± 1° counterclockwise along synthetic and antithetic faults, respectively. Mean Pliocene to recent shear rates along the LOFZ decrease northward from 32 ± 6 mm/yr to 13 ± 3 mm/yr compatible with partitioning of half of the convergence obliquity into the intra-arc zone north of 40°S and complete partitioning to the south. The displacement gradient along the intra-arc zone results in margin-parallel shortening of the fore arc. Copyright 2006 by the American Geophysical Union.