Geochronological and isotopic constraints on Neoproterozoic crustal growth in the Egyptian Nubian Shield: Review and synthesis

The tectonic evolution of the Neoproterozoic Arabian-Nubian Shield (ANS) is widely held as an example of crustal growth processes. The ANS consists of continental crust formed prior to and during the collision between East and West Gondwana. In this contribution, we compile, review, and synthesize published whole-rock Nd-Sr isotopic and zircon U-Pb-Hf-O-trace element data for granitoids and volcanic rocks from the ANS, with a focus on the Egyptian Nubian Shield which constitutes the north-western part of the ANS. These data indicate that the tectonic evolution of the Egyptian Nubian Shield was dominated by episodes of both crustal formation and reworking during the-800-650 Ma time interval. Magmatism within that interval is characterized by high epsilon Nd(t) (+6.5 to +8.5), low initial 87Sr/86Sr (-0.702), high zircon epsilon Hf(t) (+9 to +13), and mantle-like zircon delta 18O values (-+ 5 parts per thousand), implying magma extraction from a depleted mantle source and/or reworking of juvenile crust. By contrast, Nd-Sr-Hf-O isotopic data for-650-550 Ma igneous rocks indicate this region experienced crustal recycling/reworking during continental collision related to the formation of Gondwana. The Egyptian Nubian Shield crust evolved through three major episodes of magmatism with peaks at-730 Ma,-700 Ma, and -600 Ma and underwent a fundamental transition in tectonic and magmatic styles around-650 Ma, from pre -continental collision (-800-650 Ma, involving arc magmatism, accretion of oceanic lithosphere and oceanic arcs, and reworking of juvenile crust) to syn- and post-collision (-650-550 Ma). The central and western terranes of the Arabian Shield share a similar south to north magmatic age progression, whereas the eastern and southern Arabian Shield has Neoproterozoic magmatism dominated by post ca. 650 Ma events associated with the final assembly of Gondwana. Collectively, the geochronological and isotopic data suggest that magmatism was pro-tracted and occurred in discrete episodes of crustal reworking, that transformed previously accreted juvenile crust into the continental crust of the Egyptian Nubian Shield and the ANS in general.

Automated summary

The tectonic evolution of the Neoproterozoic Arabian-Nubian Shield (ANS) shows examples of crustal growth processes with multiple episodes of crustal formation and reworking. The magmatism within this region occurred in distinct time intervals and underwent a transition in tectonic and magmatic styles around 650 Ma.