Tectonothermal evolution of a hyperextended continental rift margin, Egypt, Red Sea

Scientific understanding of the mechanics of continental breakup in the absence of voluminous magmatism has dramatically evolved over the past decades. Numerical and conceptual rift models have elucidated the temporal and spatial evolution of crustal structures and the processes operating during the onset and evolution of lithospheric extension. Critical questions remain, however, regarding the strain and thermal evolution of the lower crust during progressive rifting, particularly during hyperextension and the transition to oceanic spreading. The Gulf of Suez and Red Sea – one of the conceptually most influential continental rifts – define a Miocene rift system that preserves segments of the proximal and distal hyperextended rift margin and presents unique opportunities to study the extensional thermal history without the influence of subsequent orogenic overprinting. This study presents new basement U-Pb and (U-Th)/He data from both the proximal Egyptian margin and the distal hyperextended margin, exposed on Zabargad Island, to reconstruct the thermal evolution during progressive continental rifting. Apatite (U-Th)/He data from transects across the length of the Egyptian margin record fault-controlled rift initiation, erosional retreat of the escarpment, and necking in the proximal margin at 23-19 Ma. Integrated structural and low-temperature thermochronometric data suggest that the Northern Red Sea is a late-stage continental rift currently experiencing hyperextension caused by a kinematic shift to oblique rifting at 14 Ma. The data also suggest that the multi-phase structural evolution of the Northern Red Sea is variably influenced by inherited basement structures, with structural inheritance being more determinative in the stretching and exhumation phases, while deformation in the thinning phase cuts across older structures uniformly along strike. In the distal domain, zircon U-Pb data from Zabargad — an exhumed portion of the highly-attenuated distal margin — record coeval Miocene hyperextension at ~23-19 Ma. In contrast, rutile and apatite U-Pb data from Zabargad document a significant tectono-thermal event during the Late Miocene (~7 Ma). Integrating apatite U-Pb and trace and rare earth element (TREE) analysis with prior geochemical studies suggest that this high-temperature metamorphic event was accompanied by hydrothermal alteration in the basement. Zircon (U-Th)/He likely record cooling after the high-temperature hydrothermal pulse as the Zabargad block continues to exhume during the Pliocene. This is the first documentation of reheating of a distal continental margin incipient oceanization. These data provide critical new insights into the thermal evolution of the crust and role of reheating during the transition from initial rifting, to hyperextension, and ultimately to seafloor spreading