Results of NFP 20 seismic reflection profiling along the Alpine section of the European Geotraverse (EGT)

Abstract

SUMMARY Recent deep-crustal seismic reflection profiling across the central Alps of eastern and southern Switzerland has provided a detailed image of this continental collision zone. As part of the Swiss National Science project NFP 20, a series of reflection profiles was recorded during two phases along N-S transects crossing the Alpine edifice. The eastern and southern profiles coincide with the Alpine segment of the European Geotraverse (EGT) and in part with the earlier Swiss Geotraverse. These data together with other geophysical and extensive geologic information form a unique and comprehensive volume of crustal information for this region of the Alps. On a larger scale, the new reflection data also add to a growing set of profiles crossing the Alpine fold belt which includes an additional traverse carried out by NFP 20 across the western Swiss Alps and the ECORS-CROP profile across the western Alps. The initial results of the reflection data across the central Alps outline a crustal framework involving northward indentation of the Adriatic hinterland into the subducting European foreland. This occurs beneath the collapsed oceanic basins of the Penninic allochthon which is defined by its highly reflective crystalline nappes. The present crustal thickness within the Alpine collision zone has doubled to about 60 km by both vertical and horizontal displacements along an inferred complex detachment system controlled by the Adriatic wedge. The south-plunging European foreland implies that portions of the thickened crust have been subducted into the upper mantle. This general framework of flake tectonics is laterally consistent with the ECORS-CROP results, from the western Alps. However, the western Alps show a higher degree of crustal imbrication which may be related to the presence of the rigid Ivrea body and an overall greater amount of crustal shortening compared to the central Alps.