New insights into the Andean crustal structure between 32° and 34°S from GOCE satellite gravity data and EGM2008 model

Abstract

The subduction of the Nazca oceanic plate under the South American plate in the south-central Andes region is characterized by the oblique collision of the Juan Fernandez Ridge against the continental margin. The upper plate is characterized by a broken foreland, a thrust-and-fold belt and eastward migration of the volcanic arc promoted by the flattening of the slab. Topographic load, thermal state and plate rheology determine the isostatic state of the continental plate. We calculated the vertical gravity gradient from GOCE satellite data in order to delineate the main tectonic features related to density variations resulting from internal and external loads. Then, using the Bouguer anomaly, we calculated the crust–mantle discontinuity and the elastic thickness in the frame of the isostatic lithospheric flexure model applying the convolution method approach. The results obtained show substantial variations in the structure of the continental lithosphere related to variations in the subduction angle of the Nazca plate. These variations are reflected in the varying Moho depths and in the plate rigidity, presenting a distinct behaviour in the southern zone, where the oceanic plate subducts with an approximate ‘normal’ angle with respect to the northern zone of the study area where the flat slab occurs.