Geophysical characterization of the different heterogeneities that subduct with the Nazca Plate beneath the central Andes

Abstract

Using information from the Earth magnetic anomaly model (EMAG2), gravity (global vertical gravity gradient), Geoid (Eigen6C4), and heat flow, complemented with seismological data (NEIC), we were able to analyze sublithospheric and lithospheric processes beneath the South American plate in the Central Andes where the Nazca Plate experiences a strong transition from horizontal, from the Chilean-Pampean flat subduction zone in the south to steep in the north beneath the southern Altiplano, a region characterized by delamination. This section of the Nazca Plate presents several heterogeneities, such as the transform Challenger Fault Zone, and three aseismic volcanic chains originated in hot spots, the Juan Fernández Ridge, Copiapó Ridge, and Taltal Ridge that were signaled as sources for subducted plate tearings, abnormal heat flow, volatile injection and asthenospheric upwellings from tomographic and volcanological studies. Besides, associated sub-lithospheric viscosity drop has been linked to lithospheric delamination. Geoid residuals confirm the existence of thinned sectors of the over-thickened southern Altiplano crust, in coincidence with low seismicity and high heat flow zones at the site of subduction of the Challenger fault zone and Copiapó and Taltal aseismic Ridges, which supports former proposals of subducted slab tearings at these heterogeneities controlling lithospheric drippings and retro arc volcanism.