Kinematic modeling of neotectonic thrusts at the Andean orogenic front (southern Precordillera, Argentina)

Abstract

The south-central Andes located between 32°-33° S are considered to be a transitional zone between the flat-lying and the normal subduction zones of the Nazca Plate. The active mountain-building processes are mainly concentrated between the Andean eastern foothills and the adjacent broken foreland, as highlighted by crustal seismicity, historic destructive earthquakes, and Quaternary-active contractional structures. Between 32° 10′ and 32° 40′ S, the Andean orogenic front is exposed at the Las Peñas-Las Higueras range, where east- and west-verging thrusts interact, resulting in an antithetic linkage transfer zone. We built kinematically-balanced structural sections through the integration of surface and subsurface data (2D seismic lines) to achieve a 3D characterization of the Quaternary-active thrusts and to estimate shortening rates of ∼1.8–3.4 mm/a during the last ∼8.5 Ma, thus extending the spatial and temporal penetration achieved by surface geology data. Our results indicate that the main east-verging thrusts detach at a depth of ∼10 km within Paleozoic basement rocks. This outcome implies larger potential rupture areas than if rooted at Neogene layers. West-verging thrusts present detachment levels at ∼5 km, also linked to Paleozoic basement rocks. The analysis of 2D seismic lines has also contributed to the recognition of blind thrusts without a morphologic signature, which could be regarded as relevant seismogenic structures.