Delamination and asymmetric lithospheric thickening in the development of the Tyrrhenian Rift

Abstract

Summary Late tectonic extensional basins are superimposed on the continental collision suture at certain points along the Alpine belt. The onset of extension in these basins (Alboran, Tyrrhenian, Pannonian and Aegean) postdates the continental collision by only a few million years. In the case of the Tyrrhenian region, the rifting of the collision suture is accompanied by contemporaneous shortening in the Sicilian/southern Apennine thrust belt. We use finite element models to test whether the rapid evolution of the collision suture into a zone of rifting, and the development of closely juxtaposed regions of compression and extension, can be explained by a mechanism involving collision-induced delamination of continental mantle lithosphere. With delamination underway, the models predict the development of a region of contraction flanked by regions of extension, but no appreciable migration of the delamination front. Investigation of various initial lithospheric geometries shows that a uniformly thickened lithosphere will not readily delaminate, and that delamination is triggered if crustal and lithospheric thickening are offset. Asymmetric, or offset, lithospheric thickening produces an asymmetry in underlying mantle flow which gives rise to extension which is largely restricted to one side of the region of compression. The juxtaposition of extension and shortening in the Tyrrhenian/Calabrian region, as well as the greater degree of extension in the Tyrrhenian relative to the Ionian basin, may be a result of asymmetric lithospheric thickening in the initial collision suture.