Important role of magma mixing in generating the late Carboniferous Tayuan Complex during subduction of the Paleo-Asian oceanic plate beneath the Xing'an–Erguna Massif, NE China: Evidence from petrology, geochemistry, and zircon U–Pb–Hf isotopes

Abstract To constrain the processes of mantle–crust interactions during magma generation and reconstruct the tectonic evolution of the Paleo-Asian Ocean, we present an integrated study involving detailed geological field work, petrological observations, zircon U–Pb–Hf isotope analyses, whole-rock geochemistry, and mineral chemistry for the Tayuan Complex in the northern Great Xing'an Range, NE China. The Tayuan Complex is composed mainly of monzogranites (host granitoids) and gabbros with minor amounts of quartz monzonites, and microgranular enclaves (MMEs) are unevenly distributed within the host granitoids. Our new zircon U-Pb dating results show that the host granitoids were emplaced during the late Carboniferous (318 ± 4 Ma and 319 ± 2 Ma). The MMEs yield similar zircon U-Pb ages of 320 ± 2 Ma and 322 ± 5 Ma, within error of the emplacement ages of the host granitoids. In this study, the petrological and geochemical features of the Tayuan Complex indicate disequilibrium conditions, and we favor a magma mixing model to explain the genesis of various rock types within the complex. Combined with the petrological and geochemical observations, we suggest that the host granitoids can be ascribed to felsic end-member and they originated from the partial melting of the Meso–Neoproterozoic medium- to high-K basaltic lower crust. According to the petrological and geochemical features, the gabbros in Tayuan complex are closely related to the mafic end-member, and we conclude that they were derived from the partial melting of depleted mantle that was metasomatized by subducted slab-derived fluids, and that clinopyroxene, hornblende and Fe-Ti oxides were fractionated during magma generation. The MMEs and coeval quartz monzonites in Tayuan complex represent the mixing of felsic and mafic end-member magmas. Our new data, combined with the spatial distribution and temporal evolution of the Carboniferous magmatism in the Great Xing'an Range, indicate the generation of the late Carboniferous Tayuan complex was related to the northwestward subduction of the Paleo-Asian oceanic plate.