Implications for mélange diapir melting from HT eclogite in refrigerated subduction plate interface

Much debate exists concerning mechanisms of crustal material transfer from subducting slab to overlying mantle. Formation of mélange rocks by physical mixing of slab components within subduction plate interface is predicted to transfer their compositional signal to source of arc magmas by ascending as diapirs from slab-top. Despite being supported conceptually and through modeling, existence of these diapirs in global subduction architecture remains inconclusive. plate interface. Here we present a comprehensive study on eclogites with distinct pressure-temperature-protolith histories from a deeply buried mélange “package” in the Atbashi low-temperature (LT)- high-pressure (HP) metamorphic complex, Kyrgyzstan section of the South Tianshan Metamorphic Complex (STMC), southern Altaids. Recent studies in the Chinese section of the STMC disclose massive sediment accretion at ~80 km depth along the subduction interface, suggesting continuous refrigeration, by incoming cold material from the slab, and juxtaposition to the “cold nose” of mantle wedge. In addition, transient thermal excursion was revealed, in region, from strikingly concordant chemical zonation of garnet in coesite-bearing oceanic eclogites, disclosing the potential translation of ultra-high-pressure rocks (UHP) refrigerated slices near to a relatively hotter mantle wedge. In this study, field mapping, bulk-rock geochemistry, metamorphic petrology, Zr-in-rutile & Ti-in-quartz thermobarometers, thermodynamic modeling, rutile & zircon trace elements, and U-Pb chronology analyses have been conducted to provide the first tangible eclogitic rock evidence recording mélange diapir melting signal (MDP) and experiencing substantial thermal excursion in a well-preserved refrigerated subduction plate interface, as confirmed by the pervasive presence of lowtemperature eclogitic rocks. Additional multi-disciplinary data, especially those Late Carboniferous ones, are also compiled from regional various lithologies to fingerprint the temporal-spatial variations of mantle signal and crustal feedback during which the eclogitic mélange rocks contemporaneously formed and their fate during substantial thermal excursion. Available data provide insights into a model of mélange diapir melting in refrigerated subduction plate interface as substantiated in the STMC. Implications for such process with a momentous contribution in transferring crustal volatile from slab surface to arc lava, regulating terrestrial geochemical cycle, are thus discussed.