Geochemistry of island arc assemblage in the Eastern Desert of Egypt and the role of Pan-African magmatism in crustal growth of the Arabian–Nubian Shield: A review

Abstract

Neoproterozoic island arc assemblage of the Arabian–Nubian Shield (ANS) in the Eastern Desert (ED) of Egypt comprises juvenile suites of metavolcanics (MV), large amounts of meta-sedimentary rocks (MS), and voluminous metagabbros-diorites (MGD) and syn-tectonic intrusions of older granitoids (OG). We report here the updates of these four rock units in terms of classification, distribution, chemical characteristics, geodynamic evolution, metamorphism, and ages. In addition, we discuss these integrated data to elucidate a reasonable and reliable model for crustal evolution in the ANS. The main features of these rock units indicate their relation to each other and the geodynamic environment dominated by early immature oceanic island arcs to primitive continental arcs. Integrated information of the island arc metavolcanic and plutonic rocks (gabbros, diorites, tonalites, and granodiorites) furnish evidence of the genetic relationships. These include proximity and a coeval nature in the field; all protolith magmas are subalkaline in nature following calc-alkaline series with minor tholeiitic affinities; common geochemical signature of the arc rocks and subduction-related magmatism; their similar enrichment in LREEs; and similar major element compositions with mafic melts derived from metasomatized mantle wedge. The volcano-sedimentary and the OG rocks underwent multiphase deformation events whereas the MGD complexes deformed slightly. Based on the magmatic, sedimentological, and metamorphic evolutions constrained by geochronological data as well as the progressive evolutionary trend from extensional to compressional regimes, a possible gradual decrease in the subducted slab dip angle is the most influential in any geodynamic model for arc assemblage in the ED of Egypt.