Journal of Biology and Earth Sciences (Jan 2012)
The Pan-African calc-alkaline granitoids and the associated mafic microgranular enclaves (MME) around Wadi Abu Zawal area, North Eastern Desert, Egypt: geology, geochemistry and petrogenesis
Abstract
Introduction: The area around Wadi Abu Zawal is occupied by gneisses-migmatites, island arcs metavolcanics, Dokhan volcanics, Hammamat sediments, intrusive rocks of granitic and gabbroic composition and dyke swarms.Materials and Methods: The present work concerning on the geology, geochemistry and petrogenesis of the MME and the host granitoid rocks of that area. The analytical methods for major and trace elements of some representative samples were carried out by XRF technique at the Institute of BGR in Hannover, Germany.Results: Mineralogically, MME are composed mainly of plagioclase, hornblende, biotite and quartz with accessory of sphene, acicular apatite and opaque oxides, while chlorite and epidote are secondary ones. Whereas Abu Zawal granitoid rocks are subsolvus and consist of variable contents of plagioclase, K-feldspar, quartz, and biotite, with accessory sphene, zircon and opaque oxides, typical of I-type granites. The studied Abu Zawal area represents part of the northeastern Egypt which formed by regional crustal extension and magmatic-arc regimes during Pan-African orogenic event.The MME display major, trace element contents and tectonic setting comparable with the end members of (GDT) and (IAG) of the Eastern Desert which produced (by fractionation) from a mantle-derived tholeiitic magma in an island-arc tectonic environment. Abu Zawal granitoid rocks exhibit trace element characteristics of volcanic-arc granites, and formed in an Andean-type setting.Conclusions: On the variation diagrams, major and trace element contents of the MME and granitoid rocks display conspicuous gap and two distinct trends one for the MME, (IAG) and the other for the Abu Zawal granitoid rocks, which indicates that they are not genetically related and suggest the crustal source for the host granitoid rock.
