Arc-trench-back arc systems in the Mediterranean area: examples of extrusion tectonics

Abstract

The hypothesis that trench-arc-back arc migrating systems in the Mediterranean area developed as extrusion processes, driven by the convergence of the confining plates, i.e. Africa, Arabia and Eurasia is discussed. This kind of process occurs in the zones where an accretionary belt obliquely collides with a strong buoyant block. This collision induces in the belt a compressional regime parallel to its main trend, which is accommodated by an outward extrusion/bending of the belt (arc), at the expense of an adjacent low buoyancy domain. In the zone where the bending arc separates from the overriding plate, crustal extension occurs, with the generation of a back arc basin. It is argued that the dynamic and structural conditions implied by the proposed mechanism may be recognized in the Mediterranean tectonic contexts which led to the strong distortion and migration of orogenic systems, both in the western and eastern Mediterranean regions, and to the consequent generation of the Balearic, Tyrrhenian, Aegean and Pannonian basins, in the wake of the respective migrating arcs. The proposed interpretation allows to find simple, coherent and plausible explanations for the complex space-time distribution of tectonic events observed in the study area. It is also argued that the implications of the most quoted alternative explanation of back arc opening, i.e. the slab pull model, cannot easily be reconciled with several major features of the observed deformation pattern.