Protolith age and composition of the north Shahrekord Jurassic eclogite in SW Iran: Correlation with the Permian flood basalts across Asia

The Zayanderud high-pressure metamorphic complex in the Sanandaj-Sirjan zone, north of the Neotethyan Zagros suture in Iran, includes Jurassic eclogites that have been the subject of multiple studies aiming at deciphering their metamorphic history. However, determination of the protolith age has remained ambiguous due to subsequent thermal overprint. This study investigates the protolith ages and characteristics of metabasites from outcrops north of Shahrekord that are older than the Zagros blueschist association. Through U-Pb zircon ages, whole rock analysis, and Sr-Nd-Hf isotope data for metabasites, new insights into their age, chemical composition, and tectonic setting have been achieved. Ion microprobe U-Pb geochronology of rare zircons in thin section permits extracting Early Permian protolith ages for eclogite, despite textural evidence for metamorphic, low-U zircon overgrowths on the zircon crystals. These protolith ages align with the well-studied Permian flood basalts associated with Pangea breakup and Neotethys opening. Remnants of coeval flood basalts are preserved in Oman, the Himalayas, and the Asian Large Igneous Provinces in Tarim, Tianshan, and Emeishan. Elemental and Sr-Nd-Hf isotopic compositions of Zayanderud eclogites and amphibolites confirm a continental flood basalt affinity. Earlier investigations suggested that the eclogitization occurred in the Early- to Middle Jurassic time. Our findings put forward a scenario that the Permian volcanic passive margin of this Neotethyan segment sank into the mantle at the onset of subduction in the Jurassic. The studied example advocates a previously unexplored possibility of deep sinking of a passive continental margin at the beginning of subduction. Another important aspect of the studied metabasites is that they have recorded two major rifting events in the history of Pangea, namely the Permian rifting which caused the separation of the Cimmeria continental ribbon and the Jurassic opening of the southern hemisphere oceans in connection with initiation of subduction within the Neotethys domain.