Contribution of pre Pan-African crust to formation of the Arabian Nubian Shield: New secondary ionization mass spectrometry U-Pb and O studies of zircon

Abstract

New secondary ionization mass spectrometry U-Pb and O isotope analyses of detrital zircons from the Sa'al schist in Sinai coupled with whole-rock Nd isotopic analyses provide new evidence of pre- Neoproterozoic crust in the northernmost Arabian-Nubian Shield (ANS). The detrital zircon age population is bimodal, with concordia ages of 1029 ± 7 Ma and 1110 ± 8 Ma. The whole-rock ϵ_Nd(t = 1.0 Ga) value of +2 is significantly lower than found for juvenile Neoproterozoic rocks in the region. Thus, the Sa'al schist is interpreted to represent Kibaran (Grenville) age crust incorporated into the northernmost ANS. The δ¹⁸O (zircon) values (6.1‰–9.4‰) imply that supracrustal recycling was involved in the formation of this ca. 1.0–1.1 Ga crust. A compilation of reported xenocrystic and detrital pre-ANS zircons and the variability of Nd, Sr, Pb, and O isotopic compositions within the shield suggests that its northernmost and eastern margins were more strongly contaminated by older crust ca. 0.9–3.0 Ga old. The distribution of 0.9–1.1 Ga xenocrystic and detrital zircons mainly in the east and north of the ANS suggests that such crust characterized parts of the northeastern margin of western Gondwana prior to ANS formation, and that 0.9–1.1 Ga old zircons detected in lower Paleozoic sandstone cover may have a proximal provenance.