(1. 湖南省國土資源規(guī)劃院 國土資源評價與利用湖南省重點實驗室，長沙 410007；
2. 中南大學 有色金屬成礦預測與地質(zhì)環(huán)境監(jiān)測教育部重點實驗室，長沙410083)
摘 要: 選擇欽-杭成礦帶中段當家沖銅礦區(qū)白石峰巖體為研究對象開展巖相學、地球化學、鋯石U-Pb-Hf同位素方面研究。結果顯示：白石峰巖體巖性為黑云母二長花崗巖，具有富Si(w(SiO2)為70.95%~72.12%)、富堿(w(Na2O+K2O)為8.48%~8.99%)、弱過鋁質(zhì)(A/CNK為1.07~1.09)特征，成巖溫度變化范圍較大(鋯石Ti溫度計為658~816 ℃)，指示其I型花崗巖屬性。LA-ICP-MS鋯石U-Pb定年結果((135.4±0.8) Ma，平均標準權重偏差為1.9, N=14)顯示白石峰巖體形成于早白堊紀，與華南地區(qū)燕山晚期大規(guī)模巖漿活動事件吻合。另外，白石峰巖體中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)的含量較低，具有明顯的負Eu異常(δEu=0.33~0.40)和低Nb/Ta比值(6.29~8.07)，且Hf同位素顯示虧損(εHf(t)= -4.73~-0.58)，Hf模式年齡年齡(tDM2)范圍為1484~1228 Ma，指示白石峰巖體來源中元古代含石榴石-斜長石巖石部分熔融形成的。結合區(qū)域地質(zhì)資料和前人相關研究成果，推測白石峰花崗巖體形成于太平洋板塊由俯沖轉(zhuǎn)為回撤，構造應力由擠壓向拉張伸展轉(zhuǎn)換的環(huán)境中。
關鍵字: 白石峰巖體；鋯石U-Pb年齡；地球化學；鋯石Hf同位素；當家沖銅礦；欽杭成礦帶
（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
