DIKE ROCK GENERATION AND MAGMA INTERACTIONS IN THE BIR-SAFSAF IGNEOUSCOMPLEX, SOUTH-WEST EGYPT - IMPLICATIONS FOR THE PAN-AFRICAN EVOLUTION IN NORTHEAST AFRICA

The geological setting, ages, petrography and geochemistry of late Pan -African (almost-equal-to 580 Ma) calc-alkaline and tholeiitic dike ro cks in the Bir Safsaf igneous complex of south - west Egypt are discus sed. These basaltic to rhyolitic dikes intruded contemporaneously and shortly after the intrusion of granitoids. The major and trace element data, Sr and Nd isotope relations, in combination with textural obser vations, confirm complex interactions between most of the intermediate calc-alkaline dike melts and plutonic melts, with different degrees o f mixing, assimilation, replenishment and tapping of magma chambers. T rachytic and rhyolitic dikes are strongly differentiated melts from th e granitic pluton. The tholeiitic dikes evolved dominantly by fraction al crystallization processes. It is inferred that open system and clos ed system processes operated in calc-alkaline magma chambers, and that the calc-alkaline melts came from a garnet-and amphibole-bearing mant le, modified by a subduction component. Tholeiitic rocks were formed l ater by fractional crystallization and assimilation processes. Magma a scent of both dike types took place in an extensional environment and the presumed subduction zone has to be seen in connection with the Atm ur-Delgo suture zone.