Fossil seamount in southeast Zagros records intraoceanic arc to back-arc transition: New constraints for the evolution of the Neotethys

Abstract

The Neotethys ocean is transiently involved in two subduction zones during the Late Cretaceous. While the Northern Neotethys subduction zone (below Eurasia) was active from the early Mesozoic until the Eocene, the intra-oceanic Southern Neotethys subduction zone only developed during the Late Cretaceous. We herein document, through a combination of structural, geochemical and geochronological data, the magmatic evolution of a Late Cretaceous supra-subduction ophiolite fragment of the Neotethys (the Siah Kuh massif, Southern Iran), now sandwiched in the Zagros suture zone. Results show that this ophiolite fragment — a subducted yet exceptionally well-preserved seamount — records an evolution from supra-subduction zone magmatism (including island arc tholeiites, boninites and calc-alkaline transitional magmatism) around 87 Ma, to MORB (from E-MORB to N-MORB) magmatism at 78 Ma, and potentially until 73 Ma. We conclude that this seamount initially formed in an arc context and represents either (i) a non-obducted remnant of the Oman ophiolite that experienced a longer-lived magmatic history (prefered hypothesis) or (ii) a piece from the forearc/frontal arc of the Northern margin of the Neotethys. Regardless of its exact original location, the Siah Kuh seamount was later subducted in the Northern Neotethys subduction zone.