(1. 湖南省国土资源规划院 国土资源评价与利用湖南省重点实验室，长沙 410007；
2. 中南大学 有色金属成矿预测与地质环境监测教育部重点实验室，长沙410083)
摘 要: 选择钦-杭成矿带中段当家冲铜矿区白石峰岩体为研究对象开展岩相学、地球化学、锆石U-Pb-Hf同位素方面研究。结果显示：白石峰岩体岩性为黑云母二长花岗岩，具有富Si(w(SiO2)为70.95%~72.12%)、富碱(w(Na2O+K2O)为8.48%~8.99%)、弱过铝质(A/CNK为1.07~1.09)特征，成岩温度变化范围较大(锆石Ti温度计为658~816 ℃)，指示其I型花岗岩属性。LA-ICP-MS锆石U-Pb定年结果((135.4±0.8) Ma，平均标准权重偏差为1.9, N=14)显示白石峰岩体形成于早白垩纪，与华南地区燕山晚期大规模岩浆活动事件吻合。另外，白石峰岩体中Mg#(35~38)、Co(3×10-6~4×10-6)、Ni(3×10-6~5×10-6)、Sr(111×10-6~131×10-6)和Yb(1.13×10-6~1.36×10-6)的含量较低，具有明显的负Eu异常(δEu=0.33~0.40)和低Nb/Ta比值(6.29~8.07)，且Hf同位素显示亏损(εHf(t)= -4.73~-0.58)，Hf模式年龄年龄(tDM2)范围为1484~1228 Ma，指示白石峰岩体来源中元古代含石榴石-斜长石岩石部分熔融形成的。结合区域地质资料和前人相关研究成果，推测白石峰花岗岩体形成于太平洋板块由俯冲转为回撤，构造应力由挤压向拉张伸展转换的环境中。
关键字: 白石峰岩体；锆石U-Pb年龄；地球化学；锆石Hf同位素；当家冲铜矿；钦杭成矿带
（1. Hunan Key Laboratory of Land Resources Evaluation and Utlization, Hunan Land and Resources Planning Institute, Changsha 410007, China;
2. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitor, Ministry of Education, Central South University, Changsha 410083, China）
Abstract:Mesozoic tectonic-magmatism events with a wide range of magma and a large numbers of deposits strongly occur in the Qin-Hang metallogenic belt (QHMB) within the South China, which is significant for further insight into the geological evolvement in the South China Plate. The whole rock geochemical data, zircon U, Pb and Hf isotopes of Baishifeng stock in the Dangjiachong Cu deposit were determined, within the middle part of the QHMB. The lithology of the Baishifeng granitic samples are biotite adamellite, enriched in Si (w(SiO2)=70.95%-72.12%), alkali (w(Na2O+K2O)=8.48%-8.99%), weakly peraluminous (A/CNK=1.07-1.09) and have zircon saturation temperature ranging from 658 ℃ to 816 ℃, which are identical with the features of the I-type granite. LA-ICP-MS zircon dating of Baishifeng granite samples yield an age of (135.4±0.8) Ma (MSWD=1.9, N=14), i.e., Early Cretaceous. The lower Mg# values (35-38), Co (3×10-6-4×10-6), Ni (3×10-6-5×10-6), Sr (111×10-6-131×10-6) and Yb (1.13×10-6- 1.36×10-6) contents, the weakly negative Eu anomalies (δEu=0.33－0.40), lower Nb/Ta ratios (6.29-8.07), depletion of Hf isotopes (εHf(t)=-4.73- -0.58) and Hf model ages of 1484-1228 Ma indicate that the Baishifeng granitic body is derived from partial melting of the Mesoproterozoic rocks containing garnets and plagioclase. In conjunction with previous and our studies, the Baishifeng granitic body is formed under a transition environment from squash to stretch, which is associated with transition from subduction to rollback of the Pacific Ocean.
Key words: Baishifeng stock; Zircon U-Pb age; geochemistry; zircon Hf isotope; Dangjiachong deposit; QHMB
