Geochronology, geochemistry, and Hf isotopic compositions of Middle Jurassic–Early Cretaceous granites in the southern Great Xing’an Range, NE China: implications for magmatism and tectonic evolution

Mesozoic intrusive rocks are widespread in the Great Xing’an Range (GXR) in eastern China. Although the petrogenesis and tectonic setting of these intrusive rocks have been studied, the role of magmatic processes in the geotectonic evolution of the GXR across various tectonic phases in the Late Mesozoic is unclear. In this study, we present new zircon U–Pb dating, Hf isotopic analysis, and whole–rock geochemistry data, together with previously published data, to better constrain the petrogenesis and tectono-magmatic evolution of this area. The newly obtained zircon U–Pb ages, together with previously reported ages from the southern GXR, were classified into Early–Middle Jurassic (182–164 Ma), Late Jurassic (162–146 Ma), and Early Cretaceous (144–125 Ma). The Middle–Late Jurassic granites belong to I-type granites and are enriched in LREE and LILE, but depleted in HREE and HFSE, exhibit negative anomalies in Nb, Ti, and Eu, and positive zircon εHf(t) values, suggesting that magma originated from the partial melting of Meso-Neoproterozoic lower crust. The Early Cretaceous granites are similarly enriched in LREEs and LILEs and depleted in the HREEs and HFSEs, but exhibit distinct negative anomalies in Nb, Ti, and Eu and positive zircon εHf(t) values, indicating that the magma was generated by the partial melting of juvenile lower crust with a minor contribution from mantle-derived material. By combining these results with regional geological and geochemical evidence from Northeast China, we propose that (a) Middle Jurassic granitic magmatism in the GXR was associated with the closure of the Mongol–Okhotsk Ocean; (b) Late Jurassic granitic magmatism occurred in a extensional environment resulting from delamination of the continental crust following the closure of the Mongol–Okhotsk Ocean; and (c) Early Cretaceous intrusive rocks formed in an extensional environment following closure of the Mongol–Okhotsk Ocean, accompanied by significant asthenospheric upwelling.