Island-arc magmatism marked the initial step of continental crust formation in the Arabian-Nubian Shield (ANS). Coupling U-Pb-Hf-O data with trace element analyses in detrital zircons from Eilat metasedimentary units that store arc detritus advances our understanding of the arc-system evolution. U-Pb geochronology of these zircons points to mainly early- to late-Tonian island-arc activity, peaking between 740-870 Ma. Combined with Hf-O isotope data, the results suggest that the arcs evolved and matured through juvenile magmatism, crustal reworking, and widespread assimilation of juvenile, ¹⁸O-rich sediments.
Ti-in-zircon thermometry of pristine zircons retaining magmatic, unaltered trace-element signatures, indicates crystallization at mostly 660-820°C. Whereas pre-870 Ma zircons crystallized at ~700-820°C, a significant subset of the 740-870 Ma zircons crystallized at lower temperatures of ~660-700°C, suggesting more evolved magmas. Similarly, zircons with elevated δ¹⁸O (mostly post-870 Ma) generally crystallized at ~670-780°C, implying that sediment assimilation lowered magma temperatures, or that sediment-assimilating magmas crystallized at lower temperatures, consistent with intra-crustal recycling. Zircon U-Ti-Ce oxy-barometry suggests temporally evolving redox conditions within the arc system. Pre-870 Ma grains crystallized at fO₂ between +1 and -1.2 log units relative to FMQ, consistent with a primitive arc only slightly affected by oxidized and reduced components, respectively. In contrast, 790-870 Ma and 740-790 Ma zircons crystallized at fO₂ of -3 to +2.3, and +0.8 to +2.8 log units relative to FMQ, respectively, suggesting more reduced and oxidized conditions, and later a distinctly more oxidized magmatic system. These changes may reflect an evolving subduction system with increasing fluid input, coinciding with declining crystallization temperatures and enhanced crustal reworking. A negative ΔFMQ-δ¹⁸O correlation suggests that ¹⁸O-enrichment of arc magmas resulted from reduced sediments assimilation. Our results highlight the importance of sediment assimilation in the ANS island-arc evolution and demonstrate the effectiveness of coupling isotopic and trace-element analyses of detrital zircons for crustal evolution studies.