【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。更多还原

【Abstract】 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 relatively high such as Rb, Li, F, B, Sn and W. The initial 87Sr/86Sr ratio (0.7349) and δ18O values (9.54%-11.05‰) are high or very high; the Rb-Sr age is 98.17 Ma. All this indicates that the Qiboxiari series belongs to continental crustal transformation-type grainte, formed in a tectonic environment of a collisional orogenic belt, possessing high to very high Sn mineralizing potentiality.更多还原