Petrogenesis of Early-Orogenic Diorites, Tonalites and Post-Orogenic Trondhjemites in the Nubian Shield

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Abstract
The gabbro-diorite-quartz diorite-tonalite (GDT) suite represents the oldest crustal component in northeastern Egypt; it was emplaced at 881±58 Ma during the early stage of the Pan-African orogeny. Renewed tectono-magmatic processes at the post-orogenic stage produced the 516±7 Ma trondhjemite (TR) suite that was emplaced into GDT host rocks. The GDT suite is compositionally broad, with a wide range of SiO2 contents (50–64 wt.%), and is depleted in K, Rb, Y, Nb, Hf, and REE. The suite shows a smooth variation in both major and trace elements from gabbro to tonalite and has a very low Rb/Sr ratio (0·05) and a low initial 87Sr/86Sr ratio (0·7042). It is calc-alkaline and shows the petrological characteristics of M-type granites and the trace-element characteristics of arc-lavas. The GDT suite exhibits REE profiles typical of island-arc basalt (IAB), with an (La/Yb)N ratio of 5·5.

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