Deformation partitioning during transpressional emplacement of a ‘mantle extrusion wedge': the Ronda peridotites, western Betic Cordillera, Spain

Abstract

Abstract: Composite tectonic emplacement of the world's largest outcropping body of subcontinental mantle rocks, the Ronda peridotites, occurred during Early Miocene continental subduction and as a result of oblique plate convergence. Partitioning of transpressional deformation between coeval orogen-parallel wrenching and orogen-perpendicular, pure thrusting components is recorded by shear zone kinematics and dynamothermal metamorphism in the footwall to the ultramafic rocks. Left-lateral shear, characterizing the deeper, high-pressure (eclogitic) portions of the continental subduction system, propagated through the mantle into the overlying continental crust of the overriding plate, whereas top-to-the-foreland frontal thrusting dominated at the leading edge of the hot peridotite body. Top-to-the-hinterland shear along the upper contact of the peridotites is consistent with the kinematics expected for an extrusion wedge consisting of subcontinental mantle rocks. On the other hand, coeval strike-parallel extension and thinning of the crustal rocks overlying the peridotites confirms that, similarly to other Alpine–Mediterranean examples, partitioned transpression resulted in the development of a complex deformation pattern, with kinematically linked shear zones aiding exhumation. The proposed model provides a new, coherent scenario for syn-convergence peridotite emplacement and exhumation in the western Betic Cordillera.