Neoproterozoic arc sedimentation, metamorphism and collision: evidence from the northern tip of the Arabian-Nubian Shield and implication for the terminal collision between East and West Gondwana

Abstract

In the Wadi Um Had area, Central Eastern Desert, Egypt, NE-trending metapelitic and molasse-type successions are exposed. The metasediments bear the geochemical signature of a first depositional cycle in two distinct continental island arc settings that derived from incipiently-to moderately-weathered intermediate to felsic sources under generally warm and humid conditions. The metapelitic succession records three distinct episodes of metamorphism, M1–M3, whereas the molasse-type succession records only the last metamorphic episode, M3. M1/D1 records an amphibolite facies tectono-metamorphic event that has been dated at 625\u202f±\u202f5\u202fMa, whereas M2/D2 records a greenschist facies subduction-related event. Collision of the two domains during a NE–SW shortening D3, culminated in formation of the macroscopic NW–SE-trending folds. D2 and D3 correlate with the gneiss-forming event, which is constrained at <609\u202fMa, and doming of the nearby Meatiq gneiss dome, respectively. M3 is a hornblende hornfels facies thermal metamorphism related to the intrusion of the post-orogenic, Neoproterozoic (596.3\u202fMa) Um Had granite. This study records, for the first time, a tectono-metamorphic phase predating the gneiss-forming event in the Meatiq gneiss dome, and pushes the boundary of the Late Ediacaran terminal collision between East and West Gondwana to ≤600\u202fMa.