The structure of the northern Austral Basin: Tectonic inversion of mesozoic normal faults

Abstract

This paper analyzes the style, distribution, mechanics, and timing of deformation of the Andean retroarc zone between 47° and 50°S, in the southern Patagonian Andes during the Mesozoic times. This northern sector of the Austral Basin records almost the entire Meso-Cenozoic evolution of the Patagonia western margin. Two balanced cross sections were constructed in the north and south of the study area to show the contrasting structural styles of the fold and thrust belt and the foreland sector. The westernmost internal sector is characterized by a thick-skinned structure associated with a deep decollement, over which late Paleozoic rocks (basement) are uplifted. Towards the foreland, the external fold and thrust belt is dominated by partial positive tectonic inversion of normal faults that gently fold the Cretaceous cover. The restoration of the external fold and thrust belt structural sections has yielded a total minimum shortening of less than 3 km produced since the Cretaceous contractional stage continuing until the more recent Andean deformation. The age, distribution, and compositional features of the middle Early Cretaceous - Late Cretaceous magmatic rocks show a relative shift of the volcanic arc location, indicating interactions between the extensional and contractional regimes associated with different geodynamic settings.