The late stage of retreating subduction in the Alpine-Mediterranean region: constraints from travel time seismic tomography

Abstract

Seismological modelling of the upper mantle of the Africa-Eurasia collision region has given images of its structure which can be used to supplement surface (geologic) information in the attempt to understand past and active tectonic processes. A foremost feature of the region is given by the sinuous Alpine-Mediterranean thrust belt, under which subducted lithosphere is imaged by seismic tomography as seismically fast material (colder than ambient rock). Several arcuate structures are present, combining an external thrust front with an internal extensional basin, originated by slab rollback: the Hellenic arc with the Aegean basin, the Calabrian arc with the Tyrrhenian Sea, the Betic-Rif with the Alboran Sea, and the Carpathians with the Pannonian basin. These systems are at different stages of their life, and all but the Hellenic-Aegean appear close to their terminal phase. Shape and extent of subducted slabs provide constraints on their evolution. Tomographic results, in all but the Hellenic-Aegean system, show a general lack of overall continuity of the subducted bodies, and in many cases support the idea that other processes, such as slab detachment or mantle delamination, contributed to shape the present day tectonics. Although tomographic results have steadily improved image resolution with time, differences between studies may lead to different interpretations. Better understanding of processes active at the late phases of subduction needs a close interplay between tomography, geology, and mantle dynamics calculations.