Late precambrian volcanism in NE Sudan and the evolution of the Nubian shield

Abstract

Two recent models: the intra-cratonic and the ensimatic island-arc for the evolution of the “Pan-African” (1200-500 M.a) Arabian-Nubian Shield have emerged from work mainly in Arabia and Eastern Egypt. To test these models, this study has focused on some of the late Precambrian metavolcanics and associated batholithic granitoids of the Nubian Shield, NE Sudan. New geochemical and mineralogical data indicate that the volcanism was predominantly calc-alkaline, representing a mature island-arc that evolved above possibly a westerly-dipping subduction zone. This tectonic setting is emphasised on a new discriminant diagram by the geochemical pattern displayed by the metavolcanic rocks occurring in the main study area, here named the Gebeit Mine arc. Trace and REE studies suggest that the rocks were derived from partial melting of modified garnet-free peridotite. The batholithic granitoids, dominated by tonalites, are geochemically similar to the metavolcanic rocks. A plate-tectonic evolutionary model for the Nubian Shield is devised in relation to the whole of the Arabian-Nubian Shield. Within-plate magmatism, the younger “granites” were formed in the late stage of cratonisation. Evidence for mineralisation related to plate-tectonic regimes in the Nubian Shield is also reported.