大兴安岭南段道伦达坝黑云母花岗岩成岩时代、锆石微量元素、Lu-Hf同位素特征及地质意义

Geochronology, Zircon Trace Element and Lu-Hf Isotope Characteristics of the Biotite Granite and Their Geological Significance from Daolundaba Cu Polymetallic Deposit, Southern Great Hinggan Ling,China

道伦达坝铜多金属矿床位于大兴安岭成矿带南段,对道伦达坝矿床黑云母花岗岩开展了锆石U-Pb测年、锆石微量元素和Lu-Hf同位素研究.锆石U-Pb LA-ICP-MS测年结果显示黑云母花岗岩形成时代为282.2±4.5~287.0±3.7 Ma.锆石LuHf同位素研究结果显示黑云母花岗岩锆石均具有较高的176Hf/177Hf(平均值分别为0.282770和0.282769)和低的176Lu/177Hf(平均值分别为0.002224和0.001984)同位素组成,εHf(t)值变化范围为3.05~8.58之间和2.31~7.36,二阶段模式年龄分别为730.22~1083.46 Ma和812.42~1134.56 Ma,暗示其来源为年轻的新生下地壳,可能遭受了古老地壳的混染.锆石微量元素研究显示,黑云母花岗岩的锆石具有低的Nb含量(<2×10-6)和强烈的Eu异常,符合S型花岗岩特征.锆石的Ti饱和温度平均值为770℃和785℃,指示其源区经历了水近饱和情况下的部分熔融,暗示其可能形成于俯冲环境下.

Daolundaba Cu polymetallic deposit islocated in southern segment of Great Hinggan Ling metallogenic belt.In this study,we carried out chronological studies of LA-ICP-MS zircon U-Pb ages,zircon trace element and Lu-Hf isotope for the biotite granites in Daolundaba deposit.LA-ICP-MS zircon U-Pb dating results suggested that the formation age of the biotite granites range from 282.2±4.5-287.0±3.7 Ma.Lu-Hf isotope analysis of the biotite granite showed that the biotite granites had high isotopic compositions of176 Hf/177 Hf(mean values of 0.282770 and 0.282769)and low isotopic compositions of176 Lu/177 Hf(mean values of 0.002224 and 0.001984),εHf(t)values range from 3.05-8.58 and 2.31-7.36,with older two-stage ages(730.22-1083.46 Ma and 812.42-1134.56 Ma).Zircon trace element results suggest eda S-type granites characteristic with al ow Nb(<2×10-6)values and large negative Euanomalies.The forming mean temperatures of the biotite granite calculated by zircon Tithermometer are 770℃and 785℃,indicated that its magmas is like lytorelate to a subducted environment,and the source region probably experienced partial melting with water nearly saturation.The Daolundaba copper polymetallic deposit was formed in the Late Permian subduction environment.