Multiple volcanic episodes of the Kermanshah forearc basin, SW Iran: a record of the deactivation and re-initiation of Neotethyan subduction involving a mid-ocean ridge

Abstract

Numerical simulations and theoretical analyses predict that forearc ophiolites probably record the end of subduction followed by re-initiation. We report here the results of a field study and new geochronological data that enable identification of the Kermanshah forearc basin, SW Iran. This basin is filled with two terrestrial volcaniclastic successions separated by an Upper Cretaceous reef facies limestone. Early Late Cretaceous ocean island basalts, early Eocene incompatible element-enriched mid-ocean ridge basalts/normal-type mid-ocean ridge basalts and late Eocene arc basalts of the basin indicate that Neotethyan subduction ended during the early Late Cretaceous and then re-initiated during the late Eocene. We suggest that the Neotethyan Ocean between the Iranian and Arabian continents consisted of leading and trailing oceanic plates separated by a mid-ocean ridge (MOR). Subduction of the leading plate generated the Jurassic–Early Cretaceous Sanandaj–Sirjan arc, which was ended by MOR–trench collision. The Zagros late Early Cretaceous forearc ophiolites represent the youngest/hottest segments of the leading plate emplaced during the MOR–trench collision. Subsequently, subduction of the MOR generated the forearc basin and basalts with diverse geochemistry. After c. 60 myr, the cooled trailing plate started to subduct, generating the late Eocene arc basalts. This model has significant implications for investigating and understanding other fossil subduction zones elsewhere in the world. Supplementary material: Supplementary material is available at https://doi.org/10.6084/m9.figshare.c.6086586