LATE PROTEROZOIC MAGMATISM IN THE NAKASIB SUTURE, RED-SEA HILLS, SUDAN

The south-western part of the NE-SW-trending Nakasib suture in the Red Sea Hills of Sudan is characterized by a distinct lithostratigraphic and geochemical zonation from north to south. The southern part of the suture zone is underlain by the Ariab volcanic arc which is separated from the adjacent Osbib ophiolitic melange to the north by a major NW -verging thrust. Basalts of the Oshib ophiolite complex vary from nort h to south from typical mid-ocean-ridge (MORB) through oceanic island (OIB) to boninitic lavas. The volcanic sequences of the Ariab island a rc consist of minor tholeiitic and major calc-alkaline intermediate to felsic volcanic and plutonic rocks. Approximately 810 Ma old, subduct ion-related calc-alkaline granitoid rocks have been intruded into the northern margin of the 890-840 Ma old Haya terrane along the southern boundary of the Nakasib suture zone. This lithostratigraphic arrangeme nt and the geochemical zonation of the ophiolites indicate that the Na kasib ocean basin was consumed in the Late Proterozoic by a southerly dipping subduction zone.