PandSwave upper mantle seismic velocity structure beneath the northern Apennines: New evidence for the end of subduction

Abstract

Orogeny in the geologically young northern Apennines is explained by the eastward retreat of a convergence zone in which Adriatic lithosphere subducts to the west. It is unclear, however, whether all of the lithosphere or only the lower portion has subducted since 15 Ma, when the convergence zone lay near Corsica. We combine teleseismic P and S wave arrival time data from the RETREAT seismic network (2003–2006) and surrounding permanent stations to estimate tomographic images of the upper mantle structure beneath the northern Apennines. We image a vertically oriented slab that that extends to only ∼300 km depth. Our slab termination is shallower than previous studies but is confirmed by resolution tests. Furthermore, our images resolve the southern edge of the northern Apennines slab at ∼43°N, with no deep continuity with any slab segment to the south, as earlier proposed. Our results suggest that only a 300–400 km strip of lithosphere has subducted since 15 Ma beneath the northern Tyrrhenian Sea, a length roughly equivalent to the distance from the present-day west coast of Corsica to the crest of the northern Apennines. Although not a definitive indicator, the largely aseismic vertical slab configuration and its limited extent, coupled with other volcanic and geophysical indicators, suggests the delamination scenario of Bird (1979), in which only the lower portion of the continental lithosphere subducts.