Late Mesozoic tectonic evolution of the southern Great Xing'an Range, NE China: Evidence from whole-rock geochemistry, and zircon U[sbnd]Pb ages and Hf isotopes from volcanic rocks

Abstract

The large-scaled Mesozoic volcanic activities in the Great Xing'an Range, northeastern (NE) China, have received extensive attention recently. However, the details of the tectonic setting and geodynamic processes of the Late Mesozoic time are still controversial. In this paper, we examined the geochronology and geochemistry of the Late Mesozoic volcanic rocks collected from the southern Great Xing'an Range, in order to constrain the tectonic evolution of the Great Xing'an Range in the Late Mesozoic time. The compiled data show that the Late Mesozoic volcanic rocks can be divided into three stages: Middle-Late Jurassic felsic volcanic rocks (174–148 Ma), Early Cretaceous intermediate and intermediate-felsic volcanic rocks (142–125 Ma, peak at 138 Ma) and Early Cretaceous felsic volcanic rocks (140–120 Ma, peak at 125 Ma). The Middle-Late Jurassic felsic volcanic rocks in the southern Great Xing'an Range are geochemically similar to A-type granite or highly fractionated granite, which have εHf(t) values of (−0.7 to +12.1) and Hf two-stage model (TDM2; 549–1714 Ma), indicating they are derived from the magma generated by partial melting of thickened juvenile lower crust and formed in a post-collisional extensional setting related to subduction of the Mongol–Okhotsk oceanic plate. The Early Cretaceous intermediate and intermediate-felsic volcanic rocks have the characteristics of active continental margin arc, which have εHf(t) values of −11.6 to +13.0 and TDM2 ages of 449–2670 Ma, suggesting that these rocks are the product of partial melting of lithospheric mantle. They are metasomatized by subduction-derived fluids or melts and related to the flat-slab subduction of the Mongol-Okhotsk oceanic plate beneath the Great Xing'an Range after the rapid closure of the Mongol-Okhotsk Ocean. The Early Cretaceous felsic volcanic rocks in the study are dominated by A-type rhyolite, which are associated with coeval A-type granites, metamorphic core complexes and rift basins, suggesting they formed in an extensional environment related to either the subduction of the Paleo-Pacific oceanic plate beneath the Eurasian continent or the massive upwelling of the asthenosphere following the collapse of the Mongol–Okhotsk oceanic plate.