TECTONIC SETTING AND PETROGENESIS OF THE KADABORA PLUTON - A LATE PROTEROZOIC ANOROGENIC A-TYPE YOUNGER GRANITOID IN THE EGYPTIAN SHIELD

The Kadabora A-type alkali granite is subsolvus and composed of quartz , alkali feldspar, plagioclase, biotite and small amounts of sodic-cal cic amphibole (ferro-richterite) and ferro-eckermannite alkali amphibo le. Textural relations indicate that the alkali amphibole was the last phase to crystallize. Fe-rich biotite shows no significant variation in the Fe/(Fe + Mg) ratio ranging from 0.752 to 0.767, possibly indica ting nearly constant temperature and oxygen fugacity during the crysta llization of these rocks. The Kadabora granite is metaluminous to slig htly peraluminous in character (A/CNK range from 0.84 to 1.19) and sho ws high contents of SiO2 and Na2O+K2O and low contents of MgO and CaO similar to A-type granites. The REE patterns are characterized by high and fractionated LREE (La=300xchondrite), slightly negative Eu anomal ies and undepleted, flat HREE (Lu=40xchondrite). The Kadabora A-type a lkali granite is generated by fractional crystallization of an I-type ganodioritic magma source in an anorogenic rift-related environment wi th a significant degree of crustal contamination.