High-K calc-alkaline leucocratic granites are widespread in the northern half of the Arabian-Nubian Shield
(ANS). Generally, they are considered late to post-orogenic intrusions. These rocks are important because they mark the
transitional stage from subduction-related magmatism to within-plate magmatism in the crustal evolution of the Shield. In this context, granites exposed along Wadi Moqabela and Wadi Tweiba in Taba area, SE Sinai, were chosen for a petrographic and geochemical study aiming at understanding their tectono-magmatic evolution.The studied granites exhibit strongly peraluminous characteristics in both mineralogy and geochemistry. As their colour index is <16% and ΣFeOT+MgO+TiO2 is ~ 1.6 wt%, they are referred to as leucogranites. These rocks are typically mediumto
coarse-grained, composed essentially of K-feldspar, quartz, plagioclase, muscovite, subordinate biotite and chlorite, and
accessory apatite and zircon. Their major element geochemistry indicates that they are normal to highly fractionated calcalkaline granites, characterized by a strong peraluminous affinity (alumina saturation index, ASI, consistently >1, normative corundum). Primitive mantle-normalized spider-diagrams for these rocks reveal negative Sr, Eu, Y anomalies, reflecting fractionation of plagioclase, biotite, and alkali feldspar. Representative chondrite-normalized REE patterns for the analyzed samples are characterized by moderately fractionated light rare earth elements, substantial negative Eu anomalies, and nearly
flat heavy REE patterns. The trace and rare earth element characteristics of these granites suggest a generally post-collision environment. Their high incompatible K, Rb, Ba and Th values, besides being peraluminous, suggest derivation from a crustal source, for which the most appealing potential source is the so-called Taba metamorphic belt (i.e. migmatites).The uniform petrography, low Sr contents and limited variations in compatible elements favour the partial melting of a crustal protolith and proscribe the hypothesis that wall-rock assimilation and magma mixing processes were important in the magmatic evolution of the investigated leucogranites. |
