Gravity Effect of Alpine Slab Segments Based on Geophysical and Petrological Modelling

Abstract. We study the potential gravity effect of suggested slab configurations beneath the Alpine mountain belt. The opposing slab configurations are based on seismic crustal thickness estimates and high-resolution upper mantle tomographies. Direct conversion of upper mantle seismic velocities to densities results in a gravity response that reflects results in a gravity field that may be interpreted as related to the effect of subducting lithosphere, however the different contributing slab segments cannot be clearly identified. Therefore, we define the geometry of the upper slab interface by using the crustal thickness at 40 km depth as upper starting point. Based on seismic tomography, the slab interface is followed down to 200 km depth. We define two alternative models for the slab configuration in the Alpine region in line with recently proposed hypotheses. The gravity effect of these alternative models is calculated for (i) a simple constant density distribution in the slab and (ii) accounting for compositional and thermal variations with depth. The forward calculations predict a gravity effect of the slab up to 40 mGal and significant differences in the pattern of the anomalies.