西藏班戈花岗岩成因、构造环境及其含锡性  

ORIGIN,TECTONIC SETTING AND TIN POTENTIAL OF THE BAINGOIN GRANITE,NORTHERN XIZANG(TIBET)

作　　者：王洁民[1] 雍永源[1] 李永灿[1] 

机构地区：[1]中国地质科学院成都地质矿产研究所

出　　处：《地质论评》1994年第2期173-182,共10页Geological Review

摘　　要：西藏班戈花岗岩基可划分为五个单元,属于二个花岗岩序列。其中班戈序列主要为花岗闪长岩类,以含普通角闪石为特征,地球化学特征表明其属同熔型花岗岩,形成于发育不完善的火山岩浆弧,含锡性较弱。期波下日序列主要是黑云母花岗岩,地球化学特征显示为陆壳改造型花岗岩,形成于碰撞造山带,具有良好的含锡性。The Baingoin granite is a gigantic batholith in the Nyainqentanglha granite belt of northern Xizang (Tibet). It is composed of many complex plutons which are either independent or penetrate and intertongue into each other. Based on the mineral composition and rock textures, the plutons can be divided into five grainte units, which are grouped into two series (superunits), i. e. :Ⅰ. Baingoin series; Hornblende granodiorite unitMedium-grained biotite-granodiorite unit Macrophyric biotite-monzonitic granite unitⅡ. Qiboxiari series: Macrophyric biotite-granite unitFine-grained biotite-granite unitThree granite units in the Baingoin series are characterized by medium to a bit higher SiO2 contents (66.1%-73.36%) and differentiation indices (DI 67.7-88.3), higher Na2O/K2O ratios (0.58-1.46) and lower alkali indices (A. R 1.81-2.73), higher MF values (0.38-0.60) and aluminum unsaturation to oversatura-tion. Biotites are commonly rich in MgO(6.72%-14.91%, average 9.28%)and poor in FeO (13.0%-18.9%, average 16.49%). The REE patterns show LREE enrichment and weak Eu depletion. The superunit is relatively rich in Sr, Zr, Ba, Cr, Co and Ni, and has lower initial 86Sr/87Sr ratios (0.7065-0.7079), δ18O values of 8.54‰-9.82‰ and Rb-Sr ages of 131-121 Ma. According to the above-mentioned geochemical properties, it is believed that the three units belong to syntectic granite resulting from strong contamination of continental crust and were formed in a tectonic environment of immature volcanic-magma arc, belonging to Sn-poor granite.Two granite units in Qiboxiari series are characterized by high SiO2 contents (73.39%-77.3%), high differentiation indices (DI 87.05-96.09), alkali indices (A. R. 3.08-5.19), low Na2O/K2O ratios (0.39-0.74) and aluminum over saturation. Biotites are obviously rich in FeO (17.61%-25.72%, average 23.13%), poor in MgO (0.9%-7.24%, average 4.2%), belonging to siderophyllite and lepidome- lane. REE patterns of all rocks show HREE enrichment and strong Eu depletion. Certain trace elements are relativ

关 键 词：花岗岩 成因 构造环境 含锡性 

分 类 号：P588.121[天文地球—岩石学]