新疆北天山东段花岗岩类地球化学特征  

GEOCHEMICAL CHARACTERISTICS OF GRANITOIDS IN THE EASTERN SECTOR OF THE NORTHERN TIANSHAN MOUNTAINS, XINJIANG

作　　者：王碧香[1] 李兆鼐[1] 赵光赞 王富宝[1] 张水哲 费文恒[1] 

机构地区：[1]中国地质科学院地质研究所

出　　处：《地质学报》1989年第3期236-245,共10页Acta Geologica Sinica

摘　　要：本区花岗岩类位于北天山地向斜褶皱带。岩体侵入于石炭纪海相火山-沉积岩系中,呈同期多次侵入的中基性-酸性复式岩体。依据Rb-Sr全岩等时线其年龄为315.7Ma,属于海西中期。SiO_2含量48—78％,钙碱指数为60,硅碱指数ρ为2.2—2.4和σ为1.5—2。稀土元素从基性到酸性,总量从38 ppm增到143ppm,δEu为0.47—0.86,为负铕异常,各岩类标准化曲线相似性很好。上述情况结合微量元素特点,本区为岛弧-陆缘型的钙碱性系列的侵入体。δ^(18)O为5.8—8.9‰,^(87)Sr/^(86)Sr初始值为0.705。岩体物质由上地幔顶部和下地壳岩浆混合组成,可能是同源分异演化的产物。具Ⅰ型花岗岩特征。Gabbros and granitoids in the eastern sector of the Northern Tianshan Mountains, Xinjiang, are tectonically located in the Northern Tianshan geosynclinal fold belt. They, widespread and large in size, extend in an east-west direction, essentially parallel to the regional tectonic trend. The intrusives and their country rocks, the Carboniferous, submarine interinediate, intermediate-acid and acid volcano-sedthentary series, form a volcano-plutonic complex. Two intrusive phases may be distinguished. The first is characterized by intermediate-basic intrusive rocks, and the second, by acid intrusions. They are of middle Hercynian age as shown by a Rb-Sr whole-rock isochron age determination of 315 Ma.The SiO_2 content of gabbros and granitoids of the study area ranges from 48 to 78%. They belong to the calc-alkaline series with a calc-alkali index of 60 and silica-alkaline indices 0=2.2—2.4 and σ=1.5—2. From basic to acid compositions the total REE content increases from 38 to 143 ppm and the LREE content increases from 29 to 125 ppm. δEu ranges from 0.47 to 0.86, the Eu anonmalies are negative. Their normalized curves of REE are very similar. The characteristics of normalized trace elements conform to the shapes of the normalized curves of calc-alkaline island arc-continental margin igneous rocks constructed by J. A. Pearce (1982). This coincides with foregoing calc-alkaline old island arc-continental margin intrusive body in the area. The δ^(18)O values range from 5.8 to 8.9% and the ^(87)Sr/^(86)Sr initial ratio is 0.705. To surh up, the materials of the gabbros and granitoids in the area consist of the top of the upper mantle and the lower crust. This indicates that intrusive zocks might also be consanguineous, gradually differentiated and evolved products and possess the characterics of the Ⅰ-type granite.

关 键 词：花岗岩 地球化学 天山 

分 类 号：P588.121[天文地球—岩石学]