Formation of the eclogites of the Atbashi complex, Kyrgyzstan, in a subduction zone mélange diapir

Abstract

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. Here we use petrological observations, thermometry and thermodynamic modeling, combined with geochemical constraints and compilation of massive existing data, to investigate eclogites from a deeply buried mélange “package” in Kyrgyz Tianshan, southern Altaids. We find that various slab components physically mixed to form eclogitic mélange rocks at threshold depth of the subarc (i.e., ≥85 km). Index mineralogical and Pressure-Temperature records indicate a thermal history with substantial heating after peak burial to condition crossing wet solidus. Such translation, toward hot corner of mantle wedge, is short-lived around several hundred thousand to few million years, serving as first tangible evidence substantiating mélange diapirs propagate and dynamically mix with overlying mantle. Contemporaneous Late Carboniferous flare-up of regional arc magmatism with mélange diapir melting signal also advocates that non-negligible process of mantle wedge hybridization by buoyant mélange materials, to transfer volatile, generate arc lavas and regulate terrestrial geochemical cycles, stands.