The geochemical characteristic and zircons U-Pb age of gneiss in Bixiling area, Anhui Province
Xia Bin1,2, Huang Qiangtai2,4, Zhang Yuquan2, Cui Shasha3, Dong Binghua2,4, Li He2,4, Zhang Hong2,4
1. Sun Yat-Sen University, Guangzhou 510275;
2. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640;
3. Geological Engineering Center of Geology Bureau for Nonferrous Metals of Guangdong Province, Guangzhou 510080;
4. Graduate University of Chinese Academy of Sciences, Beijing 100049
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.