LAUSR

The present work concerns two occurrences of Neoproterozoic volcaniclastic metasediments in the Central Eastern Desert (CED) of Egypt namely Alam occurrence and Atalla occurrence. They are mainly composed of bedded successions of feldspathic and feldspathic-lithic metagreywackes, arkosic metagreywackes, metasiltstones, and subordinate metaconglomerates. The rocks have been subjected mainly to various ductile deformational events (D1 and D2) due to NE–SW compression and later deformation (D3). The D1 deformation is synchronous with greenschist facies metamorphism (M1). The Alam metagreywackes show oceanic arc tectonic setting. The greywackes have clasts of quartz, feldspar, and metamorphic amphibole after pyroxene and show variable abundances of Cr, Ni, and V. Their provenance components are mainly of evolved felsic and mafic (bimodal) island arcs. The rocks are suggested to be deposited in a localized “intra-arc basin.” The metagreywackes of Atalla show tectonic setting affinity similar to continental sland arc or active continental margin. Their geochemical characteristics reflect the presence of felsic rocks as the main sources, together with minor inputs of intermediate rocks and reworked mineral grains of quartz and feldspar. They are deposited in a localized “retro-arc basins” of an active continental margin. The whole sequences of both Atalla and Alam sediments have been subjected to deformation and contemporaneous regional metamorphism during arc-arc or arc-continent collision. Newproterozoic clastic metasedimentary rocks in the CED appear to have been deposited in arc-related basins, including interarc or back-arc basins, intra-arc basins, and retro-arc basin of active continental margin.