Lithospheric density structure of the Southern Central Andes and their forelands constrained by 3D gravity modelling

CONSTANZA RODRIGUEZ PICEDA; BOTT, JUDITH; MAGDALENA SCHECK-WENDEROTH; CLAUDIA PREZZI; MARÍA LAURA GÓMEZ DACAL; MANFRED STRECKER

Viena

Congreso; EGU General Assembly; 2020

T he Andean orogeny is a ~7000 km long N-S trending mountain range developed along the SouthAmerican western margin. The formation of this mountain range is driven by the subduction ofthe oceanic Nazca plate beneath the continental South American plate, being the only knownpresent-day case of subduction-type orogeny. In this tectonic setting, the intrinsic physicalproperties of the overriding plate govern the formation of zones of crustal strength and weaknessand control the localization and the style of deformation. Furthermore, the dynamics of thesubducting oceanic lithosphere is strongly conditioned by the properties of the continentalcounterpart. The southern segment of the Central Andes (29°S-39°S) is a suitable scenario toinvestigate the relationship between the two plates for several reasons. It is characterized by acomplex deformation pattern with variations in horizontal shortening, crustal thickening andmean topographic elevation. In addition, the subduction angle changes at 33°S-35°S latitude fromflat in the North to normal in the South. To gain insight into this geodynamic system, a detailedcharacterization of the lithosphere is needed. Therefore, we constructed a 3D model of the entiresegment of the Southern Central Andes that is consistent with the available geological, seismic andgravity data in order to assess the geometry and density variation within the lithosphere. Thederived configuration shows a spatial correlation between density domains and known tectonicfeatures. It is also consistent with other independent observations such as S wave velocityvariation and surface deformation. The generated structural model allows us to reach the firstconclusions about the relationship between the characteristics of the overriding plate and thecrustal deformation and dynamics of the subduction system. It is also useful to constrainthermomechanical experiments and therefore contributes to discussions about the crustalthermal and rheological fields within the region.Powered by