TECTONIC IMPLICATIONS OF GRAPHITIZED DIAMONDS FROM THE RONDA PERIDOTITE MASSIF, SOUTHERN SPAIN

Octahedral graphite aggregates are present in garnet pyroxenites from the Ronda peridotite massif, southern Spain. In the aggregates, basal {0001} planes of graphite are parallel to {111} of the octahedra, demo nstrating that the graphite is pseudomorphic after a cubic mineral. Th e aggregates contain clinopyroxene inclusions that have a morphology a typical of a monoclinic phase, demonstrating that the precursor diamon d has imposed a cubic symmetry. Graphitized diamonds at Ronda and Beni Bousera (northern Morocco) establish that mantle-derived material is brought to the surface from great depths by a method other than kimber litic volcanism. A tectonic model is proposed to explain how diamond-f acies rocks were emplaced into the crust on both sides of an orogen.