Diamonds: the oceanic lithosphere connection with special reference to Beni Bousera, North Morocco

Abstract

Outside cratonic areas where kimberlites typically occur, diamonds have been recorded in alpine peridotites and gravels associated with them. Graphite pseudomorphs after diamonds occur in the Beni Bousera peridotite massif within garnet pyroxenites or eclogites. They have cubic morphology and contain cpx inclusions of high pressure cubo-octahedral morphology similar to those in natural diamonds. They possess isotopically light δ13C values. The garnet pyroxenites have similar mineralogy to diamond bearing eclogite xenoliths and have a wide oxygen isotope variation (δ18O = 4.9 to 9.3%) - much greater than that of the associated peridotites. They are believed to represent portions of hydrothermally altered subducted oceanic lithosphere that resided at great depth (≫ diamond stability limit) before diapiric uprise and final cumulate segregation. -from Authors