Anatomy of the Andean subduction zone: three-dimensional density model upgraded and compared against global-scale models

Abstract

We present an upgraded version of a previously published 3-D density model of the Andean subduction zone between 18°S and 45°S. This model consists of 3-D bodies of constant density, which geometry is constrained by independent seismic data and is triangulated from vertical cross-sections. These bodies define the first-order morphology and internal structure of the subducted Nazca slab and South American Plate. The new version of the density model results after forward modelling the Bouguer anomaly as computed from the most recent version of the Earth Gravitational Model (EGM2008). The 3-D density model incorporates new seismic information to better constrain the geometry of the subducted slab and continental Moho (CMH) and has a trench-parallel resolution doubling the resolution of the previous model. As an example of the potential utility of our model, we compare the geometry of the subducted slab and CMH against the corresponding global models Slab1.0 and Crust2.0, respectively. This exercise demonstrates that, although global models provide a good first-order representation of the slab and upper-plate crustal geometries, they show large discrepancies (up to ±40 km) with our upgraded model for some well-constrained areas. The geometries of the slab, lithosphere-asthenosphere boundary below the continent, CMH and intracrustal density discontinuity that we present here as Supporting Information can be used to study Andean geodynamic processes from a wide range of quantitative approaches.