Large-scale subduction controls three-dimensional mantle flow beneath the European Alps

Abstract The European Alps formed at the boundary between the European plate and Adriatic microplate within a complex system of collision and subduction. However, the large-scale three-dimensional mantle-flow field related to the underlying geodynamic processes has not yet been resolved. Here, we present the first analysis of layered anisotropy for the complete Alpine range from shear-wave splitting measurements at 591 seismic stations of the AlpArray experiment. Our findings suggest that a three-dimensional asthenospheric flow field is required to explain the complexities in the data which is in contrast to the previously reported models of single-layer anisotropy. The additional vertical resolution reveals the dominant role of the larger scale Mediterranean subduction systems, including the Apenninic and Hellenic slabs, on mantle dynamics. The splitting observations also provide supporting evidence that the European slab has broken off at its western and eastern boundaries and that the resulting gaps channel mantle flow from the European plate to the Apennines and Hellenic subduction systems. Among the features in this region, only the Rhine Graben shows evidence of significant distinct lithospheric anisotropy. The findings provide new constraints for the geodynamic processes involved in the formation of the European Alps and their modelling.