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, demonstrating that the graphite is pseudomorphic after a cubic mineral. The aggregates contain clinopyroxene inclusions that have a morphology atypical of a monoclinic phase, demonstrating that the precursor diamond 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 kimberlitic volcanism. A tectonic model is proposed to explain how diamond-facies rocks were, emplaced into the crust on both sides of an orogen.