南秦岭铧厂沟碧口群玄武岩LA-ICP-MS锆石U-Pb年龄及岩石成因研究  

LA-ICP-MS zircon U-Pb dating and petrogenesis of the Bikou Group basalt in Huachanggou area,South Qinling

作　　者：吴杰[1,2] 刘家军[1,2] 李静贤[1,2] 贾磊[1,2] 刘冲昊[1,2] 杨尚松[1,2] 王立新 余康伟 李志国[4] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质大学(北京)地球科学与资源学院 [3]陕西省略阳县铧厂沟金矿,陕西略阳724312 [4]中国黄金集团公司,北京100011

出　　处：《中国地质》2014年第4期1341-1355,共15页Geology in China

基　　金：国家自然科学重点基金项目(41030423);中国地质调查局地质调查工作项目(1212011220924);111计划(B07011);中国黄金集团公司及中国人民武装警察部队黄金研究所委托项目(武黄研WHY(05)-03)联合资助

摘　　要：铧厂沟地区碧口群玄武岩呈带状和透镜状分布于凝灰岩和凝灰质千枚岩中。在详细野外观察基础上,利用显微镜观察、主微量元素及放射性同位素分析等综合分析技术对玄武岩的岩石学、地球化学以及年代学特征进行了研究。结果表明：碧口群玄武岩普遍经历了绿片岩相的变质作用,主要矿物为斜长石、绿泥石和绿帘石；SiO2（44.67%~49.76%）、TiO2（1.14%~1.34%）含量较低, TFe2O3（12.03%~15.47%）、MgO（7.57%~9.3%）、CaO（7.29%~10.54%）含量较高。稀土总量较低,轻稀土亏损,重稀土富集。岩石微量元素和锆石Hf同位素特征显示玄武岩形成环境可能类似N-MORB,起源于软流圈,并在上升过程中混入了古老的地壳物质。LA-ICP-MS锆石测年结果显示玄武岩的形成年龄为（316.3±6.0） Ma （MSWD=0.78；n=7）,表明碧口群火山岩系至少是两期（新元古代时期和晚古生代时期）火山作用的产物。其大规模形成时期为新元古代,后经晚古生代火山作用的叠加改造而成。The Bikou Group basalt lenticular or banded in form is distributed in tuffs and tuffaceous phyllites of Huachanggou area. Based on detailed field geological survey and systematic laboratory studies including microscope observation, major and trace element analysis and radioactive isotope analysis, the authors investigated the petrological, geochemical and chronological characteristics of the basalt. The result shows that the basalt in Bikou Group has been subjected to metamorphism of greenschist facies, and mainly consists of plagioclase, chlorite and epidote. The basalt exhibits low SiO2 （44.67%-49.76%）, TiO2 （1.14%-1.34%） and REE, high TFe2O3 （12.03%-15.47%）, MgO （7.57%-9.3%） and CaO （7.29%-10.54%）, with LREE depletion and HREE enrichment. It originated from asthenosphere, occurred in N-MORB setting and was mixed with the old crust. The basalt sample yielded zircon LA-ICP-MS U-Pb age of （316.3±6.0） Ma （MSWD=0.78;n=7）, which indicates that the Bikou Group volcanic rocks are products of at least two periods of volcanic activities, i.e., Neoproterozoic and late Paleozoic. They were formed massively in Neoproterozoic and reformed by the volcanic activity in late Paleozoic.

关 键 词：碧口群 玄武岩 锆石U-PB定年 HF同位素 岩石成因 铧厂沟 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]