【摘要】 山西早前寒武系分布区的吕梁期凤凰山花岗岩，给出的透明、自形的单颗粒锆石Ｕ．Ｐｂ年龄为１７５８±１４Ｍａ（２ａ），地质解释认为是该岩体的成岩年龄，为研究华北陆台的吕梁运动时限提供了一个翔实的年龄证据。更多还原

【Abstract】 The granitoids of Wutaishan area, characterized by a great variety and Widedistribution, cover one third area of the Whole exposed Late Archean terrain and are assigned toArcheozoic Wutaiian and Proterozoic Luliangian stage respectively.This paper obtaines samples of U-Pb single zircon isotope age from the Fenghuangshan,Dingxiang County of Shanxi Province. It is located about 1. 5kin northwest of Xiangyang village.Well-idetified the Fenghuangshan Granite invades Hutuo Group assigned to Early Proterozoic.Hutuo Group is composed of low-grade metasedimentary rocks. It unconformably overlies rocks ofLate Archean Wutai Group that is mainly composed of medium-grade metavolcanic rocks. All ofthese rock systems are overlain by unmetamorphosed, little deformed siliceous dolomites of MiddeProterozoic Changcheng System. The metasediments for Fenghumpshan sector can be correlated,at leaast in part,Hutuo Group but no reliable estimates of thiCkness can be given for more of thedivision.Two populations of zircons were separated from metamorphic basalt of the HebinacunFormation in the type section of Hutuo Group. One population of zircons yields an age of 2358 ±96Ma(Za) (Wang Ruzheng and Li Huimin, 1992).We selected zircons from the granite with the gravimetric concentration means, appraisedthem with the microscope and the scanning electron microscope, analyzed their REE composition,and initally discussed their formation regularity 60 kg-sized rock Samples from about a 0. lm3volum of the granite produced the zircons that are colourless, transparent and euhedral grains witha U-Pb sigle zircon uppercocordia intercept age of 1758 ±14Ma (2a). Unfortunately, thisexamination of the data and a k-Ar age reveals a number of factual inconsistencies. The K-Arbiotite date of 1810 ±29Ma have been reported from the Fenghuangshan Granite (Bai Jin, 1986)but there is no detailed documentation of the K-Ar isotope analysis results. It is the U-Pb age thatis believed to approximate to the time of Fenghuangshan Granite emplacement. Because of thefact of the matter in that K-Ar system appears to be susceptibler to isotop resetting than U-Pbsystem.更多还原