Temporal and spatial relationship between thick- and thin-skinned deformation in the Malargüe fold and thrust belt, southern Central Andes

LAURA BEATRIZ GIAMBIAGI; FLORENCIA BECHIS; VÍCTOR HUGO GARCÍA; ALAN CLARK

Barcelona, España

Simposio; 6th International Symposium on Andean Geodynamics (ISAG); 2005

Institut de recherche pour le développement - Universitat de Barcelona - Instituto Geológico y Minero de España

Abstract   A new kinematic model, which integrates original detailed structural data and new Ar/Ar dating with previous surface and subsurface data, is proposed for the Malargüe fold and thrust belt. The aim of this research was to define the structural geometry and kinematics of Neogene deformation and to identify the way thin-skinned and thick-skinned related structures interact in space and time. The Malargüe fold and thrust belt can be divided into a western sector of thick-skinned deformation related to inversion of Jurassic normal faults, and an eastern sector characterized by thin-skinned deformation. The question as to whether shortening in the basement occurred first and was transmitted to the cover, or the cover detached first and basement thrusting occurred afterwards, has been addressed by detailed field structural data combined with Ar/Ar dating of pre- and post-tectonic volcanic and subvolcanic rocks. Comparison of the timing of deformation in the thick- and thin-skinned deformational sectors strongly supports the hypothesis that the reactivation of normal faults was coeval with the activation of shallow detachments and low-angle thrusting in this belt. Within the belt thrust front detachments occur at several stratigraphical horizons: a deep basement detachment related to the basement-involved thrusting, and shallow detachments located within Jurassic and Cretaceous sedimentary sequences. We propose that these detachments were coevally active during the complex deformation of the thrust front, which occured between 15 and 7 Ma.