ZIRCON U-PB AND (U-TH)/HE DOUBLE DATING OF TETHYAN SYNRIFT IN WESTERN DESERT, EGYPT – INSIGHTS INTO CRUSTAL STRUCTURE AND TECTONIC EVOLUTION OF NE AFRICA

The NE African Neotethyan continental margin in the Western Desert of Egypt, formed during Triassic-Jurassic rifting, is characterized by multiple stacked Phanerozoic sedimentary sequences, overlying crystalline basement. The age, nature, and tectonic origin of the Western Desert basement is unknown and could either be associated with the Archean-Paleoproterozoic “Saharan Megacraton” or the juvenile Neoproterozoic Pan-African Arabian-Nubian Shield. In order to elucidate the age and tectonic affinity of the Western Desert basement, we employed detrital zircon double dating on subsurface Neotethyan synrift strata, combining zircon U-Pb LA-ICP-MS and (U-Th)/He dating. Detitral zircon U-Pb-He double dating is a powerful tool as it not only provides zircon crystallization ages, but (U-Th)/He dating of the same zircon allows for robust determination of both source terrain and thermal/tectonic history; thus narrowing the potential source terrane and shedding light on the Precambrian basement and Phanerozoic basin development in NE Africa. Conventional zircon (U-Th)/He ages from subsurface synrift strata of the Faghur basin, located in the Western Desert, exhibit two distinct age populations with respect to their thermal evolution, with ages of ~180-210 Ma and ~350 Ma. While the younger ages likely represent input of rapidly cooled crystalline basement fault blocks exhumed during the Neotethyan rifting, the ~350 Ma ages are sourced from recycled Paleozoic sedimentary strata that were thermally reset during Carboniferous tectonism. In contrast, preliminary U-Pb zircon data from the same Jurassic and Cretaceous subsurface well intervals show detrital signatures dominated by multiple Pan-African, Grenvillian, and multiple Archean crystallization age populations. (U-Th)/He dating of the same U-Pb dated zircons will allow differentiation between locally-derived and rapidly-exhumed zircons from the Neoethyan fault blocks and recycled Cambro-Ordovician sediments and thus, should shed light on the age and tectonic affinity of the Western Desert basement in the Faghur area. Future isotopic study of two additional wells that directly penetrate basement rocks along the Mediterranean coast of the Western Desert will further elucidate the age and evolution of the NE African basement.