闽中梅仙铅锌多金属矿区花岗岩锆石U-Pb年龄、Sr-Nd同位素组成特征及其地质意义

Zircon U-Pb age, Sr-Nd isotopic characteristics and its geological significance of the granites from the Meixian zinc-lead polymetallic deposit, central Fujian Province

为探讨闽中梅仙矿区花岗岩的成因,对小焦、寨头、根竹园花岗岩体的岩相学、年代学和Sr-Nd同位素特征进行研究。LA-ICP-MS锆石U-Pb测年结果显示,小焦花岗岩体的结晶年龄为158±3Ma,形成于燕山中期晚侏罗世。同位素分析显示,样品具有高ISr(0.707099~0.710082)和低εNd(t)(-9.79^-10.92)的特点,显示明显的壳源特征,其岩石成因类型属高分异的I型花岗岩。结合前人最新的研究成果表明,梅仙矿区燕山中期花岗岩形成于古太平洋板块向欧亚板块的俯冲-消减的伸展拉张环境,是板内伸展造山阶段的产物。

In order to discuss the genesis of the granites in the Meixian orefield of central Fujian Province,this paper reports petrography,geochronology and Sr-Nd isotope data.Zircon U-Pb dating yielded an age of 158±3Ma for the Xiaojiao granites,indicating that they were formed in Late Jurassic in the middle Yanshanian period.Isotopically,sample analyses show high and variable initial ISr ratios(0.707099~0.710082)but low and constantεNd(t)(-9.79^-10.92),showing crust source characteristics obviously and indicating that Meixian granites are highly fractionated I-type granites.Combined with previous research results,it is held that the granites of the middle Yanshanian period in Meixian area were formed by the sub-reduction stretching and extension of the paleo-Pacific plate to the Eurasian plate,and were emplaced at the extention orogenic stage within the plate.