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 flatlyingand the normal subduction zones of the Nazca Plate. The active mountain-building processes are mainlyconcentrated between the Andean eastern foothills and the adjacent broken foreland, as highlighted by crustalseismicity, historic destructive earthquakes, and Quaternary-active contractional structures. Between 32◦ 10′ and32◦ 40′ S, the Andean orogenic front is exposed at the Las Pe˜nas-Las Higueras range, where east- and westvergingthrusts interact, resulting in an antithetic linkage transfer zone. We built kinematically-balancedstructural sections through the integration of surface and subsurface data (2D seismic lines) to achieve a 3Dcharacterization of the Quaternary-active thrusts and to estimate shortening rates of ~1.8–3.4 mm/a during thelast ~8.5 Ma, thus extending the spatial and temporal penetration achieved by surface geology data. Our resultsindicate that the main east-verging thrusts detach at a depth of ~10 km within Paleozoic basement rocks. Thisoutcome implies larger potential rupture areas than if rooted at Neogene layers. West-verging thrusts presentdetachment levels at ~5 km, also linked to Paleozoic basement rocks. The analysis of 2D seismic lines has alsocontributed to the recognition of blind thrusts without a morphologic signature, which could be regarded asrelevant seismogenic structures.