Zircon U-Pb ages, Hf isotope and extensional tectonics of monzogranite in the Hansumu area of southern Great Khingan

Large area of monzogranite is outcropped in the Hansumu area of southern Great Khingan. In order to recognize the formation age of the rock and its tectonic significance, samples were collected from the monzogranite pluton to study its petrography, zircon LA-MC-ICP-MS age and Hf isotope. The results show that the pluton is composed of fine-grained porphyritic amphibolit-biotite monzogranite and fine-grained porphyritic biotite monzogranite with porphyritic and porphyritic structures and massive structures. The zircons from the monzogranite is of magmatic origin, and yields ²⁰⁶Pb/²³⁸U age of 136±1 Ma (MSWD=1.4), which suggests that the pluton was formed in the late Early Cretaceous. This result is strongly consistent with the study area and its surrounding areas, and even with the 114-145 Ma magmatic activities in the northeastern of China, indicating the products of the same magmatic activity stage. The monzogranite in the Hansumu area has positive ε_Hf (t) values of 7.1 to 14.4 and young Hf two-stage model ages, and T_DM2 is 324 to 959 Ma. Young Hf isotope model ages imply that this area could have experienced an important crustal accretion event during the Neoproterozoic-Late Proterozoic. Combined with regional geology, it is suggested that the monzogranite was likely derived from the partial melting of young mantle, and possibly was formed in a lithosphere extensional tectonics environment related to the subduction of the Paleo-Asian plate to Eurasia Plate.