Evidence for Mesoproterozoic Components in the Arabian-Nubian Shield

Abstract

AbstractThis chapter reviews and summarizes the early ideas on the existence of Mesoproterozoic components in the Arabian-Nubian Shield (ANS). It sheds more light on their significance in crustal evolution of the ANS. Nowadays, there is a general agreement among geologists that the Late Mesoproterozoic to Cambrian period bears the most remarkable geological record in Earth’s history. It began with the assembly of Rodinia supercontinent (1300–900 Ma) and ended by the amalgamation of Gondwana supercontinent (around 550 Ma). It is widely accepted that the ANS were formed by juvenile magmatic arc accretion and subsequent shield-wide post-tectonic magmatism. However, the recorded Mesoproterozoic crust, with subordinate Palaeoproterozoic and rare Archaean components, proves that ANS is less juvenile than previously thought, and may provide important clues for the reconstruction of the crustal evolution of the ANS. Recent studies by several workers have shown that inherited zircon grains from igneous rocks within the ANS may provide evidence for Mesoproterozoic crustal growth. The Mesoproterozoic components of the ANS were interpreted as pervasively reworked pre-existing crust during the Pan-African orogeny, which was responsible for the final juxtaposition of the collage of terranes now seen, e.g. reworked pre-Neoproterozoic crustal fragments at Sa’al Mesoproterozoic rocks, Wadi Rutig volcano-sedimentary succession and Wadi Solaf metapsammitic and granodioritic biotite gneisses in Sinai (Egypt); Khida subterrane in eastern Saudi Arabia; the arc–gneiss collages of the Precambrian basement of Yemen and the eastern Ethiopian–northwestern Somalian crustal block. Sediments are good natural samplers of the existing continental crust at the time of erosion and sedimentation. Several workers have presented detrital zircon isotopic dataset from the Palaeozoic sedimentary sequences of the ANS (e.g. Meinhold et al. 2020). They interpreted the Ediacaran to middle Tonian zircon grains as being derived from igneous rocks of the ANS, whereas Palaeoproterozoic and Archaean grains were interpreted as a primary derivation from Palaeoproterozoic and Archaean basement found in some parts of the ANS or crustal components of the eastern Saharan Metacraton. This is consistent with palaeocurrent indicators, which suggest sediment transport from the hinterland of Gondwana. In the light of the above, future efforts to understand ANS crustal evolution will require more zircon geochronology and related studies to answer two main questions: (1) how isotopically juvenile Neoproterozoic magmas were contaminated with pre-Neoproterozoic zircon? and (2) was zircon assimilated from unexposed older crust that underlies the contaminated shield or derived from Neoproterozoic sediments sourced from a neighbouring pre-Neoproterozoic craton?KeywordsMesoproterozoicGondwana supercontinentNeoproterozoic magmasZircon geochronology