Evolution of the foreland basins in the Cordillera Principal, at 35º - 36º S. Malargüe

Abstract

The Andean fold-and-thrust belt of Malargüe is located in the foothills of Cordillera Principal at 35º-36º S. The geometry and age of the growth strata preserved in syntectonic basins, recorded the Cenozoic kinematics of the frontal fold-and-thrust belt. The Pincheira-Ventana basin, located at the western edge of the study area, is filled by two syntectonic volcanic and volcaniclastic sequences covered by basalts. In the western part of the basin, growth strata thins toward La Valenciana and Torrecillas anticlines at the west and La Brea backthrusts to the east, showing progressive unconformities observed in the field. In the eastern part the facies arrangement, clast composition and unconformities suggest a provenance area from the Bardas Blancas anticline to the west. Radiometric dating of andesitic lavas at the base of the growth sequence and of basalts at the top, constrain the age of this basin between early middle Miocene and late upper Miocene (15.1 Ma and 6.7 Ma). The Malargüe basin, located at the eastern edge of the area, is filled by two syntectonic volcanic and clastic sequences covered by a postectonic sequence. The seismic analysis of the growth sequence shows a divergent arrangement related to the uplift of the Malargüe anticline to the west and a growth triangle at the flank of Chacay anticline to the east. The radiometric dating of outcropping basal andesitic breccias yielding an age of 5.04 Ma and a Quaternary post tectonic sequence at the top, constrains the age of the basin between late Miocene and Quaternary. These observations indicate that the frontal fold and thrust-belt has a normal propagation toward the foreland during the Cenozoic.