The gneiss of Zabargad Island: deep crust of a rift

Abstract

The gneisses of the Zabargad Island are in contact with lherzolites that were emplaced by mantle diapirism during the early rifting of the Red Sea. The gneisses and the peridotites at their contact develop similar structures, kinematics and common granulite metamorphism. Away from the contact, the shear strain and associated recrystallizations decrease rapidly. Thus the Zabargad gneisses are metamorphosed and deformed by the mantle diapiric intrusion. This is confirmed by preliminary isotopic dates. The gneisses have a tripartite polygenic composition of felsic granulites, metagabbros and amphibolites. The metagabbros and amphibolites are metamorphosed only by the mantle diapir intrusion, which also induces a partial anatexis of the gneisses. The felsic granulites record a proceeding high- P granulite facies metamorphism. They are assumed to represent screens of ancient continental crust.