西昆仑大红柳滩二云母花岗岩地球化学和地质年代学研究及其地质意义  

Geochemistry and geochronology of the Dahongliutan two-mica granite pluton in western Kunlun orogen: Geotectonic implications

作　　者：魏小鹏[1,2] 王核[1] 胡军 慕生禄 丘增旺 闫庆贺[1,2] 李沛[1,2] 

机构地区：[1]中国科学院广州地球化学研究所矿物学与成矿学重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]中国地质调查局武汉地质调查中心,湖北武汉430205

出　　处：《地球化学》2017年第1期66-80,共15页Geochimica

基　　金："十二五"国家科技支撑计划项目(2015BAB05B03-02)

摘　　要：大红柳滩花岗岩体位于康西瓦构造带南侧,甜水海地体的北部,是三十里营房-奇台达坂花岗岩带的主要岩体之一。该岩体具有明显的岩相分带,其东部-东北部为二长花岗岩,而西南部则为二云母花岗岩。本文对西南部二云母花岗岩进行了岩石学、元素和同位素地球化学及同位素年代学综合研究,同时对二长花岗岩进行了元素地球化学研究。二云母花岗岩明显富SiO_2、Al_2O_3和K_2O,贫MgO、CaO和TiO_2,属于高钾钙碱性系列岩石;二云母花岗岩的锆石LA-ICPMS U-Pb年龄为(209.6±1.5)Ma,与东部二长花岗岩年龄一致,表明两者是同一构造事件的产物。二云母花岗岩稀土总量低(∑REE 56.0~66.1μg/g),强烈亏损重稀土元素,Eu负异常不明显(δEu为0.81~0.98),低Y(~7μg/g)和Yb(~0.5μg/g),Sr/Y比值较高(~20),Nb、Ta和Ti含量低,Nb/Ta比值高(21~23),表明其源区有石榴子石和金红石残留,说明二云母花岗岩形成压力可能为1~1.5 GPa,是壳源物质部分熔融形成。研究显示,大红柳滩花岗岩形成于古特提斯洋闭合之后的同碰撞过程,是甜水海地体和西昆仑地体碰撞造山作用的产物,西昆仑造山带东部的古特提斯洋闭合以及碰撞造山时代可能晚于该造山带的中部和西部。In western Kunlun Orogen on the northwestern margin of the Tibetan Plateau are distributed abundant Triassic granitoids in response to the evolution of the Paleo-Tethys Ocean. In this paper, we conducted a combined study on detailed zircon U-Pb geochronology, whole-rock major and trace elements in the Dahongliutan pluton exposed south of the Kangxiwa suture zone. Zircon U-Pb dating demonstrates that the ages of zircons from the two-mica granites distributed in the southwest of the Dahongliutan pluton are around （209.6±1.5） Ma, i.e., the Late Triassic. The two-mica granites are highly peraluminous, belonging to the high-K talc-alkaline series. The two-mica granites are characterized by high SiO2, Al2O3, K2O, Rb, Th, U, and low MgO, CaO, TiO2, Ba, Zr, Hf, Nb, and Ta. The two-mica granites have lower REE（∑REE=56.0-66.1 μg/g）, showing the fractionation between LREE and HREE, and display weak negative Eu anomalies （δEu=0.81-0.98）. The granites are characterized by low Y （-7 μg/g）, Yb （-0.5 μg/g）, Nb（-10 pg/g）, Ta（-0.5 μg/g） and Ti（-900 μg/g）, and high Sr/Y（-20） and Nb/Ta （21-23）. The geochemical features of the two-mica granites indicate that they were derived from partial melting of continental crust, and garnet and rutile in the residues during partial melting. In combination with the regional tectonic evolution and geochemical discrimination, it is suggested that the Dahongliutan granite pluton was formed in a syncollisinal setting after the closure of the Paleo-Tethys Ocean.

关 键 词：锆石U-Pb年龄 古特提斯洋 晚三叠世 大红柳滩 西昆仑造山带 

分 类 号：P597[天文地球—地球化学]