Remnants of a Mesozoic Rift in a Subducted Terrane of the Alpujarride Complex (Betic Cordilleras, Southern Spain)

Abstract

Amphibolite bodies with eclogite relics are interlayered at different levels in the Ojen nappe (Alpujarride Complex) below the Ronda peridotites of the Betic Cordilleras in southern Spain. We present an integrated structural, petrological, and geochemical study of such amphibolites, from which it is possible to deduce a gabbroic origin for the amphibolite protoliths, and we propose that their intrusion into the continental crust took place in a rift setting of Jurassic to lower Cretaceous age. The geochemical data are consistent with basaltic magmas produced by partial melting of an enriched or transitional mantle source (E- or T-MORB [mid-ocean ridge basalt]) and reflect plagioclase accumulation and weak crustal contamination processes. The structures associated with the rifting stages are obliterated by deformation and metamorphism related to subduction at depths of 60 km and later exhumation of the amphibolite bodies during the complex convergence of the Iberian and African plates from upper Cretaceous onward. The recognition of this Mesozoic rift is of great interest in studies of the tectonic evolution of the Betic Cordilleras and places new constraints on paleogeographic reconstructions of the western Mediterranean. We suggest that such a Mesozoic rift would correspond to the transform seaway linking the Neo-Tethys realm with the Atlantic Ocean.