A three-dimensional model of the crust and upper mantle along the Alpine part of the European Geotraverse (EGT)

Abstract

We investigated the structure of the crust and the upper mantle in the Alpine part of the European Geotraverse by integrating gravity and seismic refraction data into a three-dimensional (3-D) model of the crust. The gravity data came from Swiss, Italian and German sources. The study area included the Swiss Molasse Basin north of the Alps and the Po Plain in the south. To enhance the resolving power of this data for short wavelength anomalies in the Alps, 550 additional stations were surveyed on a 10 km wide swath from Lake Constance (bordering Switzerland and the Federal Republic of Germany) to Bergamo (Italy). The Bouguer anomalies were reduced with 3-D models for the effect of the sediments of the Swiss Molasse Basin, the Po Plain and other bodies of known geometry such as the Quaternary sediments of the Alpine valleys and the mafic and ultramafic rocks of the Ivrea body. This resulted in a map of stripped Bouguer anomalies. A 3-D model of the crust was built using seismic data. The densities were determined by a least-squares inversion technique. After subtraction of the model effect from the stripped Bouguer anomalies we found a residual gravity anomaly of more than 400 km length that can be explained with a positive density anomaly in the upper mantle which is in agreement with seismological results. These findings fit well into a tectonic model with subducted material of higher density and seismic velocity in the upper mantle beneath the boundary between the European plate and the Adriatic Promontory (African plate).