Western Mediterranean Subcontinental Mantle Emplacement by Continental Margin Obduction

Abstract

Obduction is the tectonic process that results from thrusting of an oceanic lithosphere section (ophiolite) onto a continent. In contrast, thrusting of subcontinental mantle, observed in several mountain belts, remains a major unknown of plate tectonics. In the western Mediterranean, the Ronda and Beni Bousera peridotites are the largest worldwide subcontinental mantle exposure. From a geological point of view, the Ronda peridotites are exhumed by hyperstretching of the continental lithosphere in a back-arc immediately followed by thrusting, explaining their present-day position inside the Alboran crust. Using 2-D and 3-D modeling of new gravimetric data combined with local seismic tomography, we show that the Ronda peridotites are rooted inside the Alboran mantle along the entire Gibraltar arc. On these bases, we propose that the emplacement of the Ronda peridotites occurred in a back-arc setting and corresponds to the thrusting of an entire hyper-stretched continental margin onto a continent, a process that we define as continental margin obduction. This results from two successive deformation events: continental upper plate extension driven by slab roll-back, immediately followed by upper plate shortening, likely triggered when a buoyant continental domain enters the subduction. We propose that this process affected the entire western Alboran domain, with peridotite bodies embedded within the crust along the whole Gibraltar Arc. We suggest that other examples such as the Alps Ivrea mantle body could likely represent continental margin obduction at the onset of continental collision. ©2019. American Geophysical Union. All Rights Reserved.