Imaging the subducted slab under the Calabrian Arc, Italy, from receiver function analysis

Abstract

We use data from the CAT/SCAN seismic deployment in southern Italy to reconstruct the crust and uppermost mantle structure above one of the narrowest active subduction zones worldwide, the Calabrian Arc, where the last fragment of the former Tethys ocean is being subducted. An E-W time-domain profile composed of teleseismic receiver functions shows the geometry of the main seismic discontinuities beneath Calabria. It provides a clear two-dimensional (2-D) image of the subducting Ionian plate at shallow depth where it bends and starts to descend into the mantle. In the profile the Moho of the subducting Ionian plate lies at ~35 km and gently dips westward beneath the eastern part of Calabria. Then the depth increases steeply to ~80 km below western Calabria. The locus where the Ionian plate changes its dip and starts to subduct corresponds to the transition from an uplifted plateau to an extensional basin at the surface. It suggests that the Ionian plate has not rolled back relative to Calabria since it slowed. This implies the uplift of the Sila Plateau is more likely due to under-plating than eastward growth of the mantle wedge. When projected on a map, the depths of the Ionian Moho beneath each seismic station reveal a more complex geometry for the subducting plate, including an unexpected deepening northward. This may be related to a tear in the plate or other tectonic motions between Calabria and the Southern Apennines. Thus the relationship between the imaged geometry of the subducting plate and structural elements at the surface provides new knowledge about the geodynamic evolution of the subduction system and the tectonics of the Calabrian Arc.