Petrogenesis and tectonic evolution of syn-to late granitoid rocks from Um Taghir NE Egyptian Nubian Shield Desert of Egypt: subduction to post-collision magmatism

Abstract

The Pan-African rocks of Um Taghir area encompass metavolcanics, synorogenic granites, Dokhan Volcanics, younger gabbros, post-collision granites, and they are cross-cut by dikes. The current granitoid rocks comprise older weakly deformed tonalite-granodiorites intruded by late tectonic undeformed granite including monzo-syenogranites and alkali feldspar granites. The weakly deformed tonalite-granodiorite is characterized by a restricted range of SiO 2 (65.78-69.43%) with reasonable enrichment in the LILE (Ba, Rb, and K 2 O), small negative Nb anomaly, and low Rb/Sr ratio which is the distinguishing of most of the synorogenic and subducted I-type granitoids in the Egyptian Nubian Shield (ANS). It is supposed that tonalitegranodiorite was formed by fractional crystallization of the Abu Furad metagabbro-diorite which is designated by their more or less lined trend on variation diagrams and their elements contents are ascribed to fractional crystallization of ferromagnesian minerals and feldspars. The monzo-syenogranites and alkali feldspar granites show SiO 2 ranges of 71.86-75.88% and 73.74-78.62%, respectively, formed through limited melting of the tonalite-granodiorite crust by rising of asthenosphere fluids with fractional crystallization of feldspars and amphibole. They are enhanced in LILE and Nb, formed in shallower depth, and categorized as A-type post-collision granite. On the basis of the geodynamic model, granite phases are consistent with the prevalent change from compressional toward post-collisional setting in the North Eastern Desert (NED). The monzosyenogranites were partially transformed into episyenitized rocks (episyenitized monzo-syenogranites) via desilicification, displaying SiO 2 contents of 65.44-66.36%, where gains and losses in mass are generally minimal (7.52 and 8.98%, respectively) and most other elements are close to the isocon line. Both older-and younger-granite types are in harmony with their formation by fractional crystallization process and are dependable with the dominant transitional tectonic setting in NED.

Age and hafnium isotope evolution of Sudanese Butana and Chad illuminates the Stenian to Ediacaran evolution of the south and east Sahara

“…Hafnium and oxygen isotopes in the North Eastern Desert show δ 18 O values (+5.15 to +6.70) and ƐHf(t) values (+6.3 to +10.6), which were interpreted to reflect melting of a juvenile Neoproterozoic mantle source that assimilated slightly older Neoproterozoic crustal material (Ali et al, 2016). The northernmost extent of the Arabian Nubian Shield is defined by the Sa'al metamorphic complex in Sinai (Hassan et al, 2014) which has Mesoproterozoic age (ca. 1100-1000 Ma) and intruded by post-collisional calc-alkaline (ca.…”