LA-ICP-MS zircon U-Pb dating and Hf isotope study of the plagioclase granite porphyry in the Lianhuashan Cu-Ag deposit of Inner Mongolia and its geological significance

Abstract：The Lianhuashan Cu-Ag deposit of Inner Mongolia is an important deposit in southern Da Hinggan Mountains metallogenic belt, and its mineralization is closely related to the plagioclase granite porphyry. Zircon LA-MC-ICP-MS dating of the plagioclase granite porphyry shows that its formation ages range from 236.8±0.77Ma (MSWD=0.85) to 237.9±0.71Ma (MSWD=1.02), suggesting that it is a product of the Triassic magmatism rather than the Middle Jurassic magmatic activity. The Lianhuashan plagioclase granite porphyry has εHf(t) values range from +5.6 to +11.5 with relatively high 176Hf/177Hf values and younger two-stage model ages (477~810Ma), indicating that it was mainly derived from the partial melting of the new-born lower crust that originated from the depleted mantle, and that there probably existed an important crustal growth event in Hinggan massif which occurred in the early Paleozoic-late Proterozoic period. Based on a systematical study of ~1100 zircon Hf isotope data from the magmatic rocks in the Xingmeng orogenic belt, the authors found that the Hinggan, Songnen and Jiamusi massifs have similar properties, and these three massifs, the Ergun massif and the North China plate margin have their respective crustal accretion histories, revealing that they had different early crustal evolution processes.