Age determination of nephrite by in-situ SIMS U-Pb dating syngenetic titanite:A case study of the nephrite deposit from Luanchuan,Henan,China
作者单位：State Key Laboratory of Lithospheric EvolutionInstitute of Geology and GeophysicsChinese Academy of Sciences School of Gem StudiesChina University of Geoscience Gem Appraisal CenterPeking University
会议名称：《中国科学院地质与地球物理研究所2015年度（第15届）...》
会议日期：2016年
学科分类：070902[理学-地球化学] 081803[工学-地质工程] 0709[理学-地质学] 07[理学] 08[工学] 0818[工学-地质资源与地质工程]
基 金：supported by the National Natural Science Foundation of China(grant41303042,41222023,41221022) the State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences(Grant 201301)
关 键 词：Nephrite Geochronology Titanite Tremolite SIMS U-Pb dating
摘 要：Nephrite is a kind of valuable jade which forms during metamorphism under greenschist facies *** investigations focus on the genesis of nephrite,however,the formation age of nephrite remains poorly constrained due to the lack of suitable dating *** this paper,the petrological,chemical characteristics,and mineral inclusions of nephrite collected from Luanchuan,Henan,China have been studied by optical and electron microscopy and wavelength-dispersive electron microprobe(EMP).The petrological observations show that nephrite consists mainly of tremolite,minor calcite and titanite,occasionally with rutile,quartz,serpentine,chlorite,pyrite,and *** titanite and tremolite which are intergrown with each other share low-energy grain *** indicates that the two phases are equilibrated and can be considered as *** chemical composition of tremolite is high in Si,Mg,Ca,but low in Fe,Cr,and Ni,which indicates that the nephrite from Luanchuan belongs to the dolomite type rather than the serpentinite *** petrography of different nephrite structures suggests that the grain size of tremolite was determined by the stress intensity undergone during the nephrite formation ***-situ Secondary Ion Mass Spectrometer(SIMS)U-Pb dating of titanite from nephrite yielded an age of 361±4 Ma,which is the first estimate for the time of formation of the Luanchuan nephrite *** investigation provides a powerful in-situ dating method to unravel the age of nephrite,which could be served as a tool for future research on other nephrite deposits.