湖南锡田花岗岩锆石U-Pb年代学及钨锡成矿时代的探讨

Zircon U-Pb geochronology of Xitian granitic pluton in Hunan Province and its constraints on the metallogenic ages of the tungsten-tin deposit

华南是世界上最大的花岗岩省之一,其中中生代花岗岩最为发育,与之相伴生的是大量钨锡多金属矿床,花岗岩的成因演化因与这些矿床的成矿作用密切相关而备受关注。湖南锡田花岗岩体是该区的一个典型岩体,主要由黑云母花岗岩、黑云母二长花岗岩和细粒花岗岩组成,并伴生有钨锡矿床。本文以湖南锡田花岗岩体为研究对象,对其中不同类型的岩石进行了详细的岩石学和锆石SIMS与LA-ICP-MS U-Pb定年工作。分析结果表明,锡田花岗岩体存在晚三叠世（227~233Ma）和晚侏罗世（150~154Ma）两期岩浆活动,早期的岩浆活动主要分布在岩体北部和中部,晚期岩浆活动仅在岩体中部及东部矿体附近可见,两期岩浆活动具有相同的岩性组合。另外,对含矿花岗岩的锆石U-Pb定年结果表明该地区可能存在晚三叠世的成矿作用,结合前人的工作推断锡田地区钨锡矿的形成受晚三叠世和晚侏罗世两期岩浆事件的影响。

South China is one of the biggest granite provinces worldwide. The widespread Mesozoic granitoids in southeastern China have a close genetic relationship with large amount of ore deposit. As a typical granitic pluton,Xitian granites,which are mainly composed of biotite granite,biotite monzogranite and fine-grained granite,are associated with tungsten-tin deposit. In this study,SIMS and LA-ICP-MS zircon U-Pb dating were performed on the selected Xitian granites,in order to establish the geochronological framework. The zircon U-Pb ages of different granite types from the Xitian pluton indicate that there are two episodes of intrusions. The Late Triassic granites（ 227 ~ 233Ma） mainly crops out along the core and northern part of the Xitian pluton. The Late Jurassic granites（ 150 ~ 154Ma） only occurs in the inner part of the pluton and along the eastern orebody. Granites of both stages are indiscernible in the rock types. SIMS U-Pb zircon analyses yield consistent ages from 227. 7 ± 2. 3Ma to 230. 2 ± 2. 1Ma for the granites with welldeveloped mineralization. Combined with previous studies,we interpret these Late Triassic and Late Jurassic igneous rocks as different magmatism in response to the formation of W-Sn deposit in Xitian pluton.