Geochronology and petrogenesis of the Yuanbaoshan leucogranite in southeast Inner Mongolia: Implications for the collision between the Sino-Korean and Siberian paleo-plates

Abstract Leucogranite, typically as an important signature of continent-continent collision, records valuable information on evolution of continental crust and provides an insight into the geodynamic processes during continental collision. Here, we present zircon U-Pb and muscovite Ar-Ar dating, major and trace elements, and Sr-Nd isotope data for the Yuanbaoshan leucogranites in southeast Inner Mongolia, with the aim of discussing its petrogenesis and tectonic implications. Zircon U-Pb dating reveals that the leucogranite formed at 239 ± 3 Ma, similar to the plateau age of 230.9 ± 2.2 Ma given by muscovite 40Ar/39Ar dating, indicating that the leucogranite formed during the period of latest Middle Triassic to earliest Late Triassic, not the early Permian as previously believed. The Yuanbaoshan leucogranites are characterized by containing aluminum-rich minerals of muscovite and garnet, high silica and alkali contents, belonging to weakly peraluminous and high-K calc-alkaline series. Their closed correlation in major elements and high similarity in Nd isotopic compositions (eNd(t) values ranging from −5.08 to −4.59) with the coeval Shuangjingzi granites in the adjacent area, together with the relatively lower TiO2, TFe2O3, MgO, CaO and P2O5 contents and more strongly negative Eu anomalies (Eu/Eu* = 0.27–0.88), indicate a more evolved cogenetic magma probably originated by partial melting of juvenile crustal materials with some old components. Furthermore, the Yuanbaoshan leucogranites show the extreme depletion in total REE contents, serious deviation in Zr/Hf and Nb/Ta ratios from the common range of magmatic rocks, and a tetrad effect of the REE distribution, all of whose specific trace element behaviors typically occur in highly evolved magmatic systems. Taken together, these leucogranites seem to be highly similar in petrological and geochemical characteristics to those of Himalayan leucogranites undergone an intensive crystal fractionation in the later of orogenic period. Combined with regional geological data, we conclude, therefore, that the Yuanbaoshan leucogranites were most probably formed in the post-orogenic tectonic setting, in response to the initial collapse of the thickened lithosphere related to the collision between the Sino-Korean and Siberian paleo-plates, and that a destructive collision, probably similar to Himalayan orogeny, might have occurred after final closure of the Paleo-Asian Ocean between the Sino-Korean and Siberian paleo-plates in the Late Permian, and lasted at least until the middle Triassic.