Cretaceous thermal evolution of the closing Neo-Tethyan realm revealed by multi-method petrochronology

A Cretaceous paleo-accretionary wedge, the Ashin Complex, now exposed along Zagros suture zone in southern Iran, exhibits mafic, metasedimentary and ultramafic lithologies. Field, geochemical petrological observations point to an anomalous high-temperature event that gave rise formation of peritectic (trondhjemitic) melts associated with restitic garnet-bearing amphibolites. Lu-Hf isotopic dating centimetre-sized garnet amphibolite-facies metasediments yielded a crystallization age 113.10 ± 0.36 Ma, possibly representing prograde near-peak metamorphic conditions. SHRIMP U-Th-Pb zircon from trondhjemitic leucosomes yields ages 104 1 interpreted as temperature peak, which occurred upper (c. 650–680 °C at 1.1–1.3 GPa), according thermodynamic modelling Ti-in-zircon thermometry. Rutile crystals two yield Zr-in-rutile temperatures range 580–640 LA-ICP-MS U-Pb 85 112 consequence partial re-equilibration during incipient cooling. late static recrystallization is indicated by presence sodic-calcic clinopyroxene, sodic amphibole, Si-rich phengite, titanite overgrowths after rutile lawsonite within former fractures. This mineral assemblage typical blueschist-facies (high pressure-low temperature) paragenesis reflecting long-term isobaric cooling until end increasing slab thermal age. first report melting wedge reveals transient, abnormally high gradient c. 18 °C/km 105–113 Ma. We speculate this could be explained subduction anomaly such seamount chain, transform fault system or, more likely, spreading ridge under Iranian margin. Indeed, paleogeographic reconstructions Tethyan realm suggest entrance Northern basin into shortly 120