Quaternary Collision-Zone Magmatism of the Greater Caucasus

Abstract The Greater Caucasus mountains (Cavcasioni) mark the northern margin of Arabia–Eurasia collision zone. Magmatism in central part began Pleistocene, up to ~25 Myr after initial collision. This paper presents bulk-rock and Sr–Nd–Pb isotope geochemistry from 39 Quaternary volcanic rock samples (<450 Ka) recovered Mt. Kazbek (Kasbegui) region Caucasus, Georgia, assess sources magmatic evolution these lavas possible triggers for melting context their regional tectonics. Compositions are dominantly calc-alkaline basaltic andesite dacite (57–67 wt % SiO2). Although were erupted through thick continental crust, there is little evidence extensive modification by crustal contamination. Trace element isotopic systematics indicate that have supra-subduction zone signatures, most likely reflecting derivation a lithospheric source had been modified melts and/or fluids material subducted before during collisional event. Mass-balance modelling Sr–Nd data indicates require significant input slab, with deep-sourced fluxing slab into region. In contrast published Lesser magmatism, suggest compositionally distinct sediment resides beneath producing characteristic trace Pb signatures. Two compositional groups therefore primary liquids can be discerned various centres, both derived light rare-earth enriched sources, but differences Th/Yb Dy/Yb ratios isotopes. Rare-earth lava consistent 3–4% starting garnet peridotite continuing spinel facies or, potentially, sited garnet-spinel transition Small-scale convection related mantle upwelling provides plausible mechanism magmatism explains random aspect distribution across