标题：Emplacement of granites in a transitional regime from volcanic arcs to post-collisional: an evidence from the Gabal El-Zeit block, Gulf of Suez region, Egypt .
摘要：Gabal El-Zeit block at the western coast of the Gulf of Suez region in Egypt consists of twovarieties of Precambrian granites, namely monzogranite and a peripheral zone of alkali granite.Both granitic varieties display moderate (60.1-68.5 wt%) and high silica (73.36-76.16 wt%)contents with high Na2O+K2O (7.21-8.61 wt%), respectively. The investigated monzogranite iscalc-alkaline metaluminous whereas the alkali granite is peralkaline. The primordial mantlenormalized plots of the Gabal El-Zeit granites indicate that they are characterized by Ba, Sr, P andTi negative anomalies and a moderate to weak negative Nb anomaly. These geochemical featuresare similar to those expected for magmas extracted during post-collisional high-K granites from thelate Neoproterozoic Arabian Nubian Shield. Tectonic discrimination diagrams show that themonzogranite is formed in a volcanic-arc setting, whereas the alkali granites is a characteristic ofpost-collisional tectonics. The geochemical characteristics of the monzogranite are consistent withmagmatism derived by partial melting of a slightly LILE-enriched amphibole-bearing (i.e.hydrated) mafic source. However, the studied alkali granite perhaps was originated by fractionalcrystallization process from the monzogranite due to the relative depletion in the contents of Al2O3,MgO, CaO, Ba, and Sr with increasing silica which is also strengthened by other geochemicalrelationships. The collective field investigations and available geochemical data are consistent witha late- to post-collisional stage magmatism formed at the transition from volcanic-arc to withinplatetectonics. The monzogranite is ilmenite- and magnetite-bearing, either homogenous or asexsolution, whereas alkali granites contains homogeneous magnetite only. Therefore, the Fe-Ticontent is a very useful tool to distinguish the two granitic varieties.
