Strain partitioning in the Patagonian Broken Foreland: influence of structural inheritance of Early Andean deformation

Abstract

In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well-documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW-SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with E-W to NE-SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems.