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.