论文部分内容阅读
The geochronology and genesis of the Qingyang batholith were investigated using ~(40)Ar/~(39)Arand Rb-Sr isotopic techniques.The Qingyang is a composite batholith consisting of two majorrock types granodiorite and granite in the Yangtze fold belt.~(40)Ar/~(39)Ar 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 ~(40)Ar/~(39)Ar 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 ~(40)Ar/~(39)Ar 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 ~(87)Sr/~(86)Sr ratio(about 0.7085).The high initial Sr ratios suggest that themagmas were formed by anatexis of older crustal materials.
The geochronology and genesis of the Qingyang batholith were investigated using ~ (40) Ar / ~ (39) Arand Rb-Sr isotopic techniques. Qingyang is a composite batholith consisting of two major types of granodiorite and granite in the Yangtze fold belt. 40) Ar / ~ (39) Ar spectra for biotite and amphibole 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 myand the granite 122.7 ± 1.2 myWhole-rock Rb-Sr analysis results consistent with the ~ (40) Ar / ~ (39) Ar 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. Specially ~ (40) Ar / ~ (39) Ar analysis of two granodiorite samples has preciseIy documented a 1.0 myapparent 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 the initial ~ (87) Sr / ~ (86) Sr ratio (about 0.7085). The high initial Sr ratios suggest that themagmas were formed by anatexis of older crustal materials.