U–Pb zircon geochronology and geochemistry of Late Palaeozoic and Early Mesozoic igneous rocks of the Bujinhei area: implications for the tectonic evolution of south Great Xing'an Range

Abstract

AbstractThe Bujinhei region, situated in the southern reach of the Great Xing'an Range, has experienced multistage tectonic‐magmatic activities, which have led to the formation of different stages and types of magmatic rocks. LA‐ICP‐MS zircon U–Pb dating was performed, and geochemical data were obtained for magmatic rocks samples from the Bujinhei area to analyse the times of magmatic rocks and their tectonic setting. Zircon U–Pb dating indicates that Middle Permian (269.8 Ma) magmatic event formed two‐mica granite, and Middle Jurassic (158–170 Ma) magmatic events formed monzogranite, quartz monzonite‐porphyry and granite porphyry. Chemical analyses indicate that the Middle Permian two‐mica granite is S‐type granite, rich in SiO2, Al2O3and K2O and low in Na2O, A/CNK > 1. Middle Jurassic monzogranite is a metaluminous I‐type granite, rich in SiO2, Al2O3and K2O and low in Na2O and CaO. Quartz monzonite porphyry and granite porphyry are high in K2O and peraluminous and derived from a granitic liquid as a result of strong interaction with hydrothermal fluid during the late magmatic stage; they have high Zr saturation temperature and belong to A‐type granites. Geochemically, two‐mica granite formed in a compressional tectonic regime related to collision, whereas Middle Jurassic intrusive rocks have affinities with intrusive rocks from the extensional environment influenced by post‐collision. Therefore, the southern Great Xing'an Range has experienced the collisional orogenesis of the Central Asian Orogenic Belt in the Middle Permian, whereas in the Middle Jurassic, the southern Great Xing'an Range turned into a post‐collision extensional setting influenced by the Mongol–Okhotsk tectonic regime. Copyright © 2016 John Wiley & Sons, Ltd.