Diamond and coesite in ultrahigh-pressure-ultrahigh-temperature granulites from Ceuta, Northern Rif, northwest Africa

Diamond and coesite occur in granulites of the Internal Zone of the Rif belt in northwest Africa. Diamond, identified by optical microscopy, electron microprobe analysis, Raman spectroscopy, cathodoluminescence and microstructural electron backscattered diffraction, is present as inclusions up to 20 pm across in garnet, K-feldspar, coesite relics and quartz. Thermobarometric estimates yield P >4.3 GPa and T>1100 degrees C, which corresponds to a depth of formation >150 km. The estimates suggest that the diamond-bearing peridotites and adjacent crustal rocks experienced similar P-T conditions. If this is correct, there is an old (undated) core in the Betic-Rif cordillera and the current models of the tectonic evolution of the area, which are based on 'full Alpine' evolution, must be revised. This discovery provides further valuable information about the complex geotectonic environment of the southeast Spain and north Moroccan collisional orogen.