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

• Published in: Journal of African earth sciences (1994) 1999-04, Vol.28 (3), p.703-720
• Main Authors: El-Sayed, Mohamed M., Nisr, Said A.
• Format: Article
• Language: English
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/S0899-5362(99)00040-8

The Dineibit El-Qulieb Leucogranite exhibits most features of l-type granitoids (calc-alkaline affinity, relatively high Na 2O, moderate values of Rb, Ba, LREE, Rb/Sr and low Rb/Ba with the presence of magnetite and titanite as the main accessories). On the other hand, they possess hyperaluminous (molar A/CNK = 1.22−1.43) and high normative corundum (∼ 5%), which are in contrast to typical l-type granitoids. The REE patterns are characterised by fractionated LREE and relatively flat HREE with pronounced negative Eu anomalies. The investigated rocks have low K/Rb and high Zr/Y ratios reflecting a typical mature continentalarc environment. The absence of recrystallised phases and the undepleted and flat HREE of the Dineibit El-Qulieb Leucogranite pattern argue against its formation by partial melting of crustal materials. Based on the petrological and geochemical features, the Dineibit El-Qulieb Leucogranite can be generated by fractional crystallisation of mafic magma. The Qulieb leucogranites are characterised by LILE enrichment, normative corundum-rich, strongly peraluminous compositions and associated with miarolitic cavities and pegmatitic patches suggesting the role of the aqueous fluids released from the downgoing slab during subduction. The main fractionating phases were hornblende, biotite, plagioclase and alkali feldspars. Based on the modelling of major elements, the least differentiated adamellite sample requires 91% crystal fractionation, 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-feldspar and biotite from the most basic adamellite sample. Le leucogranite de Dineibit El-Qulieb montre la plupart des caractères des granitoïdes de type l: affinité calco-alcaline, teneurs assez élevées en Na 2O, veleurs modérées des teneurs en Rb, Ba, terres rares légères et du rapport Rb/Sr, basses valeurs du rapport Rb/Ba, présence de magnétite et titanite comme minéraux accessoires. D'un autre côté, il est hyperalumineux (rapport molaire A/CNK = 1.22−1.43) et contient du corindon normatif (∼ 5%), ce qui contraste avec les granitoïdes classiques de type l. Les spectres de terres rares sont caractérisés par le fractionnement des terres rares légères, un spectre plat des terres rares lourdes et une anomalie négative en Eu prononcée. Les roches étudiées ont des rapports K/Rb faibles et Zr/Y élevés