MULTIDISCIPLINARY STUDIES OF ANDEAN SYNOROGENIC DEPOSITS, UNRAVELING THE UPLIFT SEQUENCES IN THE TRANSITION ZONE BETWEEN FLAT AND NORMAL SUBDUCTION

Stratigraphic analyses of Neogene retroarc basins provide insight into temporal and spatial variations in magmatic activity, deformation, and exhumation along the continental margin. Sedimentological, structural, thermochronological and geophysical analysis from proximal to distal areas of the foreland basin system at different latitudes (Manantiales, Penitentes, Uspallata, Tunuyán, Cacheuta, Las Peñas and Atuel) provide a three-dimensional view for the structural and depositional evolution. Using a number of complementary techniques (U/Pb geochronology, sedimentary analysis of provenance, facies analysis, thermochronology) we can reconstruct the episodes of uplift of the different ranges and the pattern of deposition in the basin through time. This multidisciplinary approach allows us challenging previous evolutionary models. Our results indicate that the Precordillera uplift is synchronic along strike since 14-13 Ma. On the other hand, different blocks from Cordillera Frontal where activated from north to south at different ages during the Early to Late Miocene. This suggests that the uplifting sequence in the southern Central Andes is not controlled by the flattening of the slab (~10 Ma), as previously proposed. Unconformities in the wedgetop (Penitentes and Tunuyán basins) can be correlated with conformities within the foredeep area (Cacheuta and Tupungato areas) and sedimentation in the intermontane basins appears strongly controlled by the effectiveness of the structural barriers in some cases (Uspallata). In this way, we can obtain new insight on the evolution of a key segment of the Andes and the role of flat-slab subduction in orogenic evolution.