The style of the Tyrrhenian subduction

Abstract

Momentum and energy equations are solved simultaneously for an incompressible viscous fluid in order to model the changes in the shape of a subducted slab when active convergence between the subducting and overriding plates comes to the end and slab pull becomes the dominant tectonic mechanism. This model can be applied to the Tyrrhenian domain, where it has been suggested that active convergence terminated about 7–9 Myr ago. During the active phase the angle of immersion of the slab at intermediate depths between 100 and 270 km is small, about 45°–50°, and large, about 80°–90°, at depths greater than 300 km. The phase of passive gravitational sinking is characterized by a substantial modification in the shape of the slab, with a large angle of immersion of 70° now at intermediate depths, decreasing to 50° in proximity of the tip of the slab. When the shape of the modelled slab is compared with the seismogenic portion of the subducted Ionian lithosphere in the Tyrrhenian, our results are consistent with subduction driven by slab pull and with cessation of active convergence between 7–9 Myr before present.