Provenance of the heavy mineral-enriched alluvial deposits at the west coast of the Red Sea. Implications for evolution of Arabian–Nubian crust

Abstract

Here we present the LA-ICP-MS U–Pb ages and Hf isotopic record of detrital zircons from the active alluvial fans at the west coast of the Red Sea. The Ras Manazal alluvial fan (primarily composed of zircon, magnetite with some rutile, ilmenite and monazite) yielded a relatively restricted age population ranges from 765 to 666Ma. These ages and present-day drainage pattern is consistent that the sediments are primarily derived from erosion of nearby subduction related granitoids in the immediate west (i.e., not more than 50km from the Red Sea coast) of the fan. In contrast, approximately 160km south, at the Egypt–Sudan border, the Wadi Diit fan is relatively more enriched in ilmenite and REE-bearing phases (e.g., thorite, monazite, xenotime, garnet, etc.) and yielded five zircon age populations of (1) 824–733Ma, (2) 730–705Ma, (3) 646–608Ma, (4) 516–500Ma, and (5) 134–114Ma. The age populations 1–3 if coupled with the present-day drainage pattern can be related to the earlier subduction related and later post collision granitoids in the southern part of the South Eastern Desert and Gebeit terrane of northern Sudan. Sparse Early Cretaceous zircons (134–114Ma) are derived from the Mesozoic volcanic suits in the source region. However, the age group 516–500Ma is enigmatic. Wadi Diit zircons are primarily derived from granitoids in the broad S–N directed Hamisana Shear Zone and its subordinate SW to NE directed Onib-Sol-Hamed Suture Zone. These shear zones provided pathways for the present-day drainage system for sediment transportation to the Wadi Diit and adjacent coastal region. We infer that the ca. 500Ma late-stage magmatic zircons represent a hitherto unknown magmatic event, possibly related to the shear heating associated with the crustal scale shear zones. This implies that the shear zones in the South Eastern Desert and northern Sudan remained thermally active as late as ∼500Ma. The time resolved hafnium composition (εHf (t)) of both fans varies from +3.5 to +13.5. Our new U–Pb ages and Hf isotopic composition suggests that the detrital zircons were derived from the Neoproterozoic juvenile crust. This is consistent with the Neoproterozoic juvenile igneous and metamorphic rocks in the Eastern Desert and northern Sudan.