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

L. GIAMBIAGI, F. BECHIS, V. GARCÍA Y A. CLARK

Barcelona, España

Simposio; VI International Symposium on Andean Geodynamics; 2005

IRD

The question 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 volcanics and subvolcanic rocks in the MFTB. Comparison of the timing of deformation in the thick- and thin-skinned deformational areas strongly supports the hypothesis that the reactivation of normal faults was coeval with the activation of shallow detachments and low-angle thrusting in the thrust front of the MFTB. Low-angle thrusting interacted with high-angle faulting related to reversal of basement normal faults inherited from the extensional history of the foreland, indicating a deformation mode characterized by superimposed shallow and deep detachment tectonics. Within the thrust front of the MFTB, detachments occur at several stratigraphic horizons: a deep basement detachment related to the basement-involved thrusting, and shallow detachments located within the Jurassic and Cretaceous sequences. We propose that these detachments were active during the complex deformation of the thrust front, between 14 and 9 Ma.