Geochronology and tectonic settings of Late Jurassic – Early Cretaceous intrusive rocks in the Ulanhot region, central and southern Da Xingan Range

Zircon U-Pb dating and whole-rock geochemical analysis have been performed on Late Jurassic - Early Cretaceous intrusive rocks of the Ulanhot area, NE China, with the aim of constraining the tectonic evolution of the central and southern Da Xingan Range. Zircon U-Pb dating indicates that Late Jurassic - Early Cretaceous magmatic events experienced four stages at: c. 155 Ma; c. 144 Ma; 135-130 Ma; and c. 126 Ma. The c. 155 Ma magmatic event consists of quartz diorite and granite-porphyryp with the geochemical characteristic of high Sr and Sr/Y or high A/CNK (1.38), implying the primary magma was derived from partial melting of a thickened lower crust which induced the closure of the Mongol-Okhotsk Ocean. The c. 144 Ma magmatic event consists of quartz monzodiorite with the geochemical characteristics of alkaline series, and indicates the delamination of a thickened crust. The 135-130 Ma magmatic event consists of syenogranite and granite-porphyry with characteristics of both I-type and A-type granites, which induced both the subduction of the Palaeo-Pacific oceanic plate and the post-orogenic extension of the Mongol-Okhotsk Orogenic Belt. The c. 126 Ma magmatic event consisted of highly fractionated I-type biotite granite and alkaline series gabbro, marking the end of the Mongol-Okhotsk Orogen, and implying that the study area was controlled by the circum-Pacific tectonic system during this stage.