Abstract

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.

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