3D data-derived lithospheric structure of the Central Andes and its implications for deformation: Insights from gravity and geodynamic modelling

Abstract

We present a new three-dimensional density model of the CentralAndes characterizing the structure and composition of the lithospheretogether with a geodynamic simulation subjected to continental intraplateshortening. The principal aim of this study is to assess the link betweenheterogeneities in the lithosphere and different deformation patterns andstyles along in the orogen-foreland system of the Central Andes. First,we performed a 3D integration of new geological and geophysical data withprevious models through forward modelling of Bouguer anomalies.Subsequently, a geodynamic model was set-up and parametrized from thepreviously obtained 3D structure and composition. We do not find aunambigous correlation between the resulting density configuration andterrane boundaries proposed by other authors. Our models reproduce theobserved Bouguer anomaly and deformation patterns in the foreland. Wefind that thin-skinned deformation in the Subandean fold-and thrust beltis controlled by a thick sedimentary layer and coeval underthrusting ofthin crust of the foreland beneath the thick crust of the Andean Plateau.In the adjacent thick-skinned deformation province of the invertedCretaceous extensional Santa Barbara System sedimentary strata are muchthinner and crustal thickness transitions from greater values in theAndean to a more reduced thickness in the foreland. Our results show thatdeformation processes occur where the highest gradients of lithosphericstrength are present between the orogen and the foreland, thus suggestinga spatial correlation between deformation and lithospheric strength.