METAMORPHISM AND GEOCHEMICAL ASPECTS ON NEOPROTEROZOIC SERPENTINITES HOSTED CHROME SPINEL FROM GABAL AL-DEGHEIMI, EASTERN DESERT, EGYPT

Petrographic and geochemical studies of the chrome (Cr)-spinel in serpentinites from the Gabal Al-Degheimi, in the central Eastern Desert of Egypt, are made to evaluate their textural and compositional variations Cr-spinel cores do not appear to have re-equilibrated completely with the metamorphic spinel rims and surrounding silicates, suggesting relic magmatic composition unaffected by metamorphism. Accessory Cr-spinel in the serpentinites is characterized by Cr (0.60-0.78) and Mg (0.54-0.68). Normalized REE patterns and the low abundances of Ti, Na, Nd, Sm, Lu and Hf of serpentinites and Cr-spinel core compositions suggest that Gabal Al-Degheimi serpentinites are of ophiolitic origin and represent relicts of a reduced depleted harzburgite to dunite mantle peridotites formed in an oceanic suprasubduction zone (marginal-basin) tectonic environment that experienced high degrees of partial melting in excess of 22%. Textural and compositional features of the Cr-spinels suggest transitional greenschist-amphibolite up to lower amphibolite facies metamorphism, which is isofacial with the country rocks.