40Ar/39ArandRb-SrGeochronologyoftheQingyangBatholith,AnhuiProvince,China

<正> The geochronology and genesis of the Qingyang batholith were investigated using 40Ar/39Arand Rb-Sr isotopic techniques.The Qingyang is a composite batholith consisting of two majorrock types granodiorite and granite in the Yangtze fold belt.40Ar/39Ar spectra for biotite andamphibole separates are internally concordant.The concordance of the minerals and spectra indi-cate no thermal disturbance of the ages,and rapid cooling of the rocks.The granodiorite hasan age of 137.6±1.4 m.y.and the granite 122.7±1.2 m.y.Whole-rock Rb-Sr analysis yieldsages consistent with the 40Ar/39Ar dates.Thus,the Qingyang batholith was formed in two ma-jor stages in the late Jurassic and early Cretaceous.The batholith is not Triassic as was pre-viously proposed.Special 40Ar/39Ar analysis of two granodiorite samples has preciseIy documented a 1.0 m.y.apparent age difference between these samples.Several factors could account for this difference,but different emplacement times seem most convincible.The granodiorite and granite show lit-de variation in initial 87Sr/86Sr ratio（about 0.7085）.The high initial Sr ratios suggest that themagmas were formed by anatexis of older crustal materials.