An assessment of dip-slip versus strike-slip faulting modes along the Patagonian Andes (39°-50° S) and their related orogenic models

Abstract

The compilation of a database of 225 strain/stress tensors (accounting for ~ 4000 fault-striae data pairs) combined with evidence of syntectonic strata, and a seismotectonic appraisal along the Patagonian Andes (39°-50° S; South America), leads us to assess typical features of Mesozoic to current faulting in this segment of the Andean orogen. At the orogen scale, the fault-slip and focal mechanism database show the prevalence of strike-slip faulting, challenging the classic proposal for the Andean orogen of alternating extensional and contractional deformation phases. However, the wrenching tectonism in Cenozoic times may be explained through a strain partitioning model in the North Patagonian Andes by re-activating a large-scale, inherited anisotropy within the basement (namely the Liquiñe-Ofqui fault system), which is currently the locus of significant seismicity. On the other hand, a non-partitioned context allows explaining the Cenozoic patterns of brittle deformation the South Patagonian Andes. Our results highlight that the classifications of Andean-type orogens should integrate both inherited anisotropies and the heterogeneous distribution of strain across the upper plate in order to address complex patterns of deformation.