Origin of Neoproterozoic metamorphic suites along the Western Segment of Allaqi Shear Zone, Southern Egyptian Nubian Shield

Abstract

The Neoproterozoic basement complex of the western segment of the Allaqi Shear Zone (ASZ) in the extreme southern part of the Egyptian Nubian Shield comprises four main lithologic units: gneisses, amphibolites, island arc metasediments, and intrusives. In the present study, these units investigated at the outcrop scale, as well as petrographically and geochemically. Gneisses are subdivided into three types: hornblende, muscovite, and biotite gneisses. The hornblende and muscovite gneisses have para-gneissic origin, while the biotite gneiss has igneous protolith. Amphibolites have intermediate andesitic to basaltic andesite composition, with igneous origin, and were formed in island-arc environments. The metagabbros are subalkaline and have within-plate geochemical characteristics. The metasediments involve graphite-muscovite, albite, chlorite, biotite-muscovite, carbonate, and tremolite-actinolite schists, in addition to metagreywackes. The bulk chemistry of metasedimentary succession revealed their formation within active continental margin setting with pelitic to semi-pelitic and psammitic precursor. The previously mentioned lithologic units are poly deformed and intensively affected by shearing and thrusting. These structures strike in various direction: WNW-ESE, NNE-SSW, NW-SE, NW-SE, and E-W, which are consistent with the automatic and manual principal component analyses (PCA) lineament extraction.