PROVENANCE AND TECTONIC RECONSTRUCTION OF THE NEOTETHYAN MARGIN OF NE AFRICA, WESTERN DESERT OF EGYPT, BY HIGH-DENSITY DETRITAL ZIRCON (U-TH)/HE THERMOCHRONOMETRY

The subsurface of the Western Desert of Egypt contains multiple stacked sedimentary basin deposits reflecting the long-lived tectonic evolution of the Neotethyan continental margin in eastern North Africa and the transition from rifted to passive continental margin. High-resolution zircon (U/Th)/He (ZHe) data on over 50 samples were collected from boreholes penetrating Tertiary and Cretaceous strata of the rifted margin to elucidate the thermal evolution of the borehole and constrain the thermal history of detrital provenance. ZHe ages are significantly older than depositional ages, suggesting detrital ZHe ages that were not reset subsequent to deposition. In detail, ZHe ages form Cretaceous strata above the unconformity show the following trends. (1) ZHe ages from Jurassic strata show a strong Hercynian input as well as Late Triassic and Early Jurassic components of Tethyan rift affinity; (2) ZHe ages from Aptian-Early Cenomanian strata are characterized by a ZHe age peak at ~450 Ma and a minor Albian peak; (3) samples from Late Hauterivian-Barremian strata show two major detrital ZHe age peaks at ~450 and 350 Ma; while (4) samples from Early Hauterivian rocks exhibit three dominant ZHe age components at ~450 Ma, 350 Ma, and 170-200 Ma. These ZHe age peaks display provenance characteristics typical for cooling signatures of rocks from the eroding Arabian-Nubian Shield, a North-African Hercynian source, and eroded material from exhumed fault blocks along the Triassic-Jurassic Neotethyan rifted margin. Although Hercynian ZHe ages dominate in Jurassic strata, the occurrence of Triassic or Early Jurassic suggest the presence of eroding rapidly cooled and exhumed Tethyan normal fault blocks. At decreasing depth, first Jurassic-Triassic, and then Hercynian source input disappears and the arrival of detritus from the Arabian-Nubian Shield begins to dominate the North African passive continental margin in the Western Desert in the middle to late Cretaceous. This data set illustrates the power of ZHe thermochronometry as a high-resolution thermochronometric detrital provenance tool, not constraining crystallization ages, but rather shedding light on the cooling and exhumation history of the source terrane and the tectonic/geological environment of the basin deposits.