Late Cryogenian-Ediacaran history of the Arabian-Nubian Shield: A review of depositional, plutonic, structural, and tectonic events in the closing stages of the northern East African Orogen

https://cyberleninka.org/article/n/966601.pdf

Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution.

Geochemistry, Nd isotopes and U–Pb SHRIMP zircon dating of Neoproterozoic volcanic rocks from the Central Eastern Desert of Egypt: New insights into the ∼750 Ma crust-forming event

Ages are used to constrain the temporal evolution of the Meatiq Gneiss Dome, Eastern Desert, Egypt, by dating (ID-TIMS) pre-, syn-, and post-tectonic igneous rocks in and around the dome. The Um Ba’anib Orthogneiss, comprising the deepest exposed structural levels of the dome, has a crystallization age of 630.8 ± 2 Ma. The overlying mylonites are interpreted to be a thrust sheet/complex (Abu Fannani Thrust Sheet) of highly mylonitized metasediments (?), migmatitic amphibolites, and orthogneisses with large and small tectonic lenses of less-deformed intrusives. Two syn-tectonic diorite lenses in this complex have crystallization ages of 609.0 ± 1.0 and 605.8 ± 0.9 Ma, respectively. The syn-tectonic Abu Ziran diorite, cutting across the tectonic contact between mylonite gneisses of the Abu Fannani Thrust Sheet and a structurally overlying thrust sheet of eugeoclinal rocks (“Pan-African nappe”), has a magmatic emplacement age of 606.4 ± 1.0 Ma. Zircons from a gabbro (Fawakhir ophiolite) within the eugeoclinal thrust sheet yielded a crystallization age of 736.5 ± 1.2 Ma. The post-tectonic Fawakhir monzodiorite intrudes the ophiolitic rocks and has an emplacement age of 597.8 ± 2.9 Ma. Two other post-tectonic granites, the Arieki granite that intrudes the foliated Um Ba’anib Orthogneiss, and the Um Had granite that cuts the deformed Hammamat sediments, have emplacement ages of 590 ± 3.1 and 596.3 ± 1.7 Ma, respectively. We consider formation of the Meatiq Gneiss Dome to be a young structural feature (<631 Ma), and our preferred tectonic interpretation is that it formed as a result of NE–SW shortening contemporaneous with folding of the nearby Hammamat sediments around 605–600 Ma, during oblique collision of East and West Gondwana.

U–Pb TIMS age constraints on the evolution of the Neoproterozoic Meatiq Gneiss Dome, Eastern Desert, Egypt

Review of the Late Neoproterozoic history of the northern Arabian–Nubian Shield (ANS) reveals that rapid and extensive erosional denudation, widespread late-orogenic calc–alkaline and alkaline igneous activity and intramontane basin formation affected this terrane at 630–590 Ma. Core-complex extension is also recorded at this time interval. To account for this coupling it is suggested that the mantle lithosphere was removed/delaminated from below the northern ANS subsequent to significant crust–mantle thickening in the course of the Late Neoproterozoic orogeny. Because the physical properties of the delamination process are not clear, we use it as a conceptual term accounting for the replacement of mantle lithosphere by an asthenosphere. Removal and replacement of the thickened lithospheric mantle roots potentially caused uplift of the northern ANS to elevations of more than 3 km, thus triggering exceptionally-rapid erosional unroofing of a ca. 10 km thick rock carapace, and some lateral extension. Delamination and erosional decompression potentially caused partial melting of ANS residual upper mantle and lower crust to produce the widespread post-orogenic magmas. We emphasize that removal of the lithospheric mantle also played a key role in lowering ANS topography to sea level. Our data show that lowering ANS down to sea level was significantly accelerated by post-delamination cooling and thermal subsidence. Unlike erosional denudation which is followed by isostatic uplift, thermal contraction causes net surface lowering. We show that thermal subsidence plays a critical role in lowering mountain belts, particularly in the latest stages, when the topography reaches a threshold of ∼ 1.0 km and erosion rates greatly decrease. Post-delamination thermal subsidence can cause 1.3 km of net surface lowering within 100 m.y. regardless of the state of relief and elevation. Therefore, orogenic belts that experienced removal or delamination of their mantle lithosphere (hot orogens) would rapidly rise, but would relatively rapidly fall too.

Late Neoproterozoic rise and fall of the northern Arabian-Nubian Shield: The role of lithospheric mantle delamination and subsequent thermal subsidence

A late Neoproterozoic magmatic core complex in the Eastern Desert of Egypt: emplacement of granitoids in a wrench-tectonic setting

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A late Neoproterozoic magmatic core complex in the Eastern Desert of Egypt: emplacement of granitoids in a wrench-tectonic setting