湖南锡田晚侏罗世花岗岩成因及其地质意义

Petrogenesis of Late Jurassic Xitian granite,Hunan Province and its geological implications

为探讨湘东锡田地区晚侏罗世花岗质岩浆作用及其与成矿作用的相互关系,本文对锡田垄上黑云母二长花岗岩进行了矿物学和LA-ICP-MS锆石U-Pb年代学及Hf同位素组成研究。锆石U-Pb年代学研究表明花岗岩形成于~150 Ma,为晚侏罗世,与锡田钨锡多金属矿床具有一致的形成时代。锆石原位Hf同位素的研究结果表明锡田晚侏罗世花岗岩主要来源于古老地壳物质的重熔,同时有少量地幔物质的加入。花岗岩黑云母的化学成分特征显示其具有高的含铁指数和低的氧逸度,暗示其有利于钨锡成矿。综合相关区域地质资料,表明锡田晚侏罗世花岗岩的形成与中生代时期华南发生的岩石圈伸展与减薄作用有关,本区晚侏罗世花岗质岩浆活动与区内钨锡多金属矿床的形成具有密切联系。

Zircon U-Pb geochronological,Hf isotopic and petrological analyses have been carried out on the Late Jurassic Xitian granite emplaced in the middle part of Shiwandashan-Hangzhou belt,which is closely related to the economically important Xitian tungsten-tin deposit in eastern Hunan Province,Southeast China.LA-ICP-MS zircon U-Pb dating of one representative granite sample yields weighted means;Pb/;U age of~150 Ma,suggesting that both the Xitian granite and Xitian tungsten-tin deposit have the same formation age.In-situ zircon Hf isotope analysis indicates that the Late Jurassic Xitian granite mainly originated from partial melting of metamorphic basement rocks with a small amount of mantle materials.Electron microprobe analyzer(EMPA)analysis suggests that biotite has high Fe/(Fe+Mg)values and low oxygen fugacities,which are in favor of W-Sn mineralization.The above data and regional geological data indicate that large scale of crustal extension and thinned would be the most important mechanism to result in the Mesozoic magmatism in South China,which is also the key reason why abundant polymetallic deposits developed in South China during Late Mesozoic.The Late Jurassic magmatism shows a close relationship with the Xitian tungsten-tin deposit.