安徽省岳西县碧溪岭片麻岩地球化学和锆石U-Pb年龄研究

本文通过对碧溪岭片麻岩综合研究表明,岩石化学成分高硅(SiO₂=73.18%～75.60%)、低铝(Al₂O₃=11.93%～12.79%)、富碱(Na₂O+K₂O=6.11%～7.23%)和高钠(Na₂O/K₂O=1.51～1.94); 微量元素富集大离子亲石元素Rb、Ba、Th、U等和Pb,贫Nb、Ta、Zr、Hf、Ti等高场强元素; 稀土元素含量范围变化较大(TREE=142.38～308.44×10^-6),富集轻稀土(LREE/HREE=5.93～6.01),和铕负异常明显(δEu=0.42～0.64)等。造岩矿物中斜长石聚片双晶常垂直晶体延长方向,以及继承锆石大部分是不同时代的岩浆碎屑锆石等,暗示其寄主岩是沉积岩; 锆石LA-ICP-MS定年结果: 1)获得超高压变质锆石U-Pb年龄为242 Ma; 2)继承锆石U-Pb年龄,除了有比较多的属于元古代(768～639 Ma),还有大量的属于古生代(590～358 Ma)等,表明其寄主岩的时代不会早于古生代。

The geochemical characteristic and zircons U-Pb age of gneiss in Bixiling area, Anhui Province

According to the comprehensive research in this paper,the chemical composition of the gneiss in Bixiling represents high Si(SiO₂=73.18%～75.60%),low Al(Al₂O₃=11.93%～12.79%),rich alkali(Na₂O+K₂O=6.11%～7.23%)and high Na(Na₂O/K₂O=1.51～1.94).And for the trace elements,large-ion lithophile elements such as Rb,Ba,Th,U and Pb are rich,while high field strength elements such as Nb,Ta,Zr,Hf and Ti are poor.For the rare earth elements(TREE=142.38～308.44×10^-6),the gneiss represents relatively rich LREE(LREE/HREE=5.93～6.01) enrichments and obvious Eu(δEu=0.42～0.64)negative abnormality.The country rock of gneiss is sedimentary because of the polysynthetic twin of plagioclase grew along the vertical direction of crystal extension and most of inherited zircons were magmatic clastic zircons of different times.The date of zircon LA-ICP-MS U-Pb is 242 Ma which belongs to Indo-Chinese epoch and is equal to the Early Triassic.According to the "inheritance zircon" U-Pb different age(Proterozoic eon 768～639 Ma and Palaeozoic era 590～358 Ma),the country rock of gneiss in Bixiling is felsic sedimentary rock which is rich in Na whose formation age is not earlier than Palaeozoic.