Neoproterozoic island arcs evolution and recycling in the northern Arabian-Nubian Shield: U-Pb-Hf-O isotopes in detrital zircon from Eilat metasediments

The Arabian-Nubian Shield is a vast, juvenile continental crust province that formed during the Neoproterozoic by accretion of intra-oceanic island arcs. Sediments eroded from these arcs are preserved in the Eilat Metamorphic Complex in the northernmost part of the Arabian-Nubian Shield. We present a coupled U-Pb-Hf-O study of detrital zircons from metasedimentary units from Eilat area, intended to assess the juvenile nature of the island arcs and to detect crustal recycling processes involved in their formation. Detrital zircon geochronology places island arcs magmatism in this region at 1040-740 Ma, peaking between 850-750 Ma. Arc crustal evolution is demonstrated by coupling Hf and O isotopes in the detrital zircons. Zircons with mantle-like δ¹⁸O (5.0-6.5‰) have predominantly positive εHf_(t) values of +6 to +12 that principally reflect late-Stenian to late-Tonian juvenile crust formation. A temporally decreasing trend in εHf_(t) values implies ~80 m.y. of crustal reworking of the juvenile arcs. The contribution of reworked older crust was minor, as just two Paleoproterozoic grains and a small number of Neoproterozoic grains with lower εHf_(t) values were detected. Crustal reworking is further demonstrated by abundant zircons with elevated δ¹⁸O values of mostly 6.5‰ to 9‰, indicating assimilation of ¹⁸O-rich supracrustal components in the arc magmas starting from ~930 Ma. Since the εHf_(t) values of zircon grains with elevated δ¹⁸O are positive and high, we assign this ¹⁸O-enrichment to juvenile sediments that were recycled shortly after crust formation, suggesting a self-recycling island arcs system. Mixing calculations show that at least 20% and up to 40% of juvenile sediments with δ¹⁸O of 14‰ were assimilated in the melts sampled by our zircons. These results imply that reworking of arc terranes and the incorporation of supracrustal components played a fundamental role in the evolution of island arcs in the northern Arabian-Nubian Shield.