Age, petrogenesis and tectonic implications of the Early Cretaceous magmatism in the Huanggangliang area, southern Da Hinggan Mountains

The Early Cretaceous porphyroclastic lava and K-feldspar granite in the Huanggangliang area of southern Da Hinggan Mountains both yielded LA-ICP-MS zircon U-Pb ages of 137.7±1.2Ma, which represent a widespread magmatic episode in the southern Da Hinggan Mountains. They are characterized by high content of SiO2, K2O and low content of CaO, MgO, and Al2O3 indicating high evolution magma. ASI values of the studied rocks are from 1.06 to 1.33, suggesting that they are metaluminous-weakly peraluminous, and belong to the high-K calc-alkaline to alkaline series. The total rare earth elements (ΣREE) vary in the range of 116.98×10-6 to 350.51×10-6, with strong negative Eu anomalies. The samples are enriched in large ion lithophile elements (LILE, e.g., Rb, Ba, Th, U) and high field strength elements (HFSEs, e.g., Nd, Zr, Hf), but depleted in incompatible elements, such as Ba, Sr, P, Ti and Nb. These characteristics indicate that they are mainly highly fractionated I-type granites. The Early Cretaceous magmatism has slightly high whole-rock εNd(t) values (-0.8 to +0.9）and positive zircon εHf(t) values (+1.9 to +18.3), with the young Nd modal ages (TDM=993-855Ma) and Hf modal ages (TDM2=888-561Ma), indicating that they were probably derived from juvenile crust, with minor old crustal materials. In view of the regional geology and the magmatic evolution in the southern Da Hinggan Mountains, the authors hold that these Early Cretaceous magmtic activities took place in a regional extensional setting. They were possibly related to the post-orogenic extension under the Mongolia-Okhotsk tectonic regime.