GGG:D30 The Andean Gravity Field, Forward Modelling and Determination of Lithospheric Rigidity

Abstract

The gravity field of the geologically contrasting Central and Southern Andes has been investigated with regard to isostatic state, crustal density structure and rigidity of the lithosphere. The gravity database, together with other geophysical data, is a product of several years of field data acquisition in the Central and Southern Andes as part of the German Collaborative Research Centre SFB267 (``Deformation Processes in the Andes'). All gravity data are tied to the IGSN71 gravity datum and are terrain-corrected. The gravity effect of the subducting Nazca Plate was removed from both Bouguer and isostatic residual anomalies and then correlated with mean topographic heights to identify areas of disturbed isostatic equilibrium. The abundance of geophysical information obtained by the SFB267 and its partners (e.g. geological, structural, seismic and magnetotelluric data) allows the development of well-constrained 3D forward gravity models. These models allow estimation of subsurface loading and, therefore, permit more rigorous estimation of lithospheric rigidity than if topographic loading alone were considered. To date we have used estimates of surface and subsurface loading from such 3D models with a 2D coherency method to estimate lithospheric rigidity in the central Andes.