Petrogenesis and evolution of the Dineibit El-Qulieb hyperaluminous leucogranite, Southeastern Desert, Egypt: petrological and geochemical constraints

The Dineibit El-Qulieb Leucogranite exhibits most features of I-type granit oids (calc-alkaline affinity, relatively high Na2O, moderate values of Rb, Ba, LREE, Rb/Sr and low Rbi Ba with the presence of magnetite and titanite as the main accessories). On the other hand, they possess hyperaluminous (m olar A/CNK = 1.22-1.43) and high normative corundum (similar to 5%), which are in contrast to typical I-type granitoids. The REE patterns are characte rised by fractionated LREE and relatively flat HREE with pronounced negativ e Eu anomalies. The investigated rocks have low K/Rb and high Zr/Y ratios r eflecting a typical mature continental-arc environment. The absence of recrystallised phases and the undepleted and flat HREE of th e Dineibit El-Qulieb Leucogranite pattern argue against its formation by pa rtial melting of crustal materials. Based on the petrological and geochemic al features, the Dineibit El-Qulieb Leucogranite can be generated by fracti onal crystallisation of mafic magma. The Qulieb leucogranites are character ised by LILE enrichment, normative corundum-rich, strongly peraluminous com positions and associated with miarolitic cavities and pegmatitic patches su ggesting the role of the aqueous fluids released from the downgoing slab du ring subduction. The main fractionating phases were hornblende, biotite, pl agioclase and alkali feldspars. Based on the modelling of major elements, t he least differentiated adamellite sample requires 91% crystal fractionatio n, mainly of hornblende, plagioclase, K-feldspar and biotite, from dioritic liquid. On the other hand, the most felsic investigated adamellite sample can be generated by 29% fractional crystallisation of plagioclase, K-feldsp ar and biotite from the most basic adamellite sample. (C) 1999 Elsevier Sci ence Limited. All rights reserved.