藏东衣珠兴拉地区超基性岩岩石地球化学特征及Pb-Nd-Sr同位素特征  

Petrogeochemical and Pb-Nd-Sr isotope characteristics of ultrabasic rocks in the Yizhuxingla area,Eastern Tibet

作　　者：于涛[1] 周新 樊炳良 石楠 何建娟 余佳树 易金龙 YU Tao;ZHOU Xin;FAN Bingliang;SHI Nan;HE Jianjuan;YU Jiashu;YI Jinlong(College of Science,Tibet University,Lhasa 850000,Tibet,China;Geothermal Geological Survey Party,Tibet Bureau of Geology and Mineral Exploration and Development,Lhasa 850000,Tibet,China;Sichuan Road&Bridge Mining Investment&Development,Co.Ltd.,Chengdu,610039,Sichuan,China)

机构地区：[1]西藏大学理学院,西藏拉萨850000 [2]西藏自治区地质矿产勘查开发局地热地质大队,西藏拉萨850000 [3]四川路桥矿业投资开发有限公司,四川成都610039

出　　处：《地质通报》2021年第5期687-697,共11页Geological Bulletin of China

基　　金：中国地质调查局项目《西藏卡贡地区1∶5万四幅区域地质调查》(编号:DD20160016-21)和《西藏类乌齐县衣珠兴拉镍多金属矿远景调查》(编号:121201010000150007-15)

摘　　要：对出露于班公湖-怒江缝合带东段衣珠兴拉地区超基性岩的野外地质调查,以及岩石学、岩石地球化学、Pb-Nd-Sr同位素等研究表明:岩石类型为强烈蛇纹石化的方辉橄榄岩,具有富MgO(45.33%~47.70%)、贫CaO(0.15%~0.37%)和Al_(2)O_(3)(0.08%~0.39%)、低TiO_(2)(0.011%~0.014%)的特征;稀土元素含量低于原始地幔,稀土元素配分模式呈平缓右倾型,轻、重稀土元素分馏明显,具有明显的正Eu异常和弱负Ce异常;过渡金属元素表现为不对称的配分型式,在Ti和Cu处形成明显的负异常;岩石具有高(87 Sr/86 Sr)i、低εNd(t)的特征。上述特征表明,衣珠兴拉超基性岩相当于SSZ型地幔橄榄岩,由原始地幔经15%~25%部分熔融形成亏损地幔岩,形成于洋内岛弧环境,在俯冲消减作用过程中,混染了20%~40%的地壳物质。The field geological survey and petrology study of the ultrabasic rocks in the Yizhuxingla area of the eastern Bangonghu-Nujiang suture zone show that the rocks in this area are strongly serpentinized peridotite.Geochemical studies show that these rocks are rich in MgO(45.33%~47.70%),poor in CaO(0.15%~0.37%)and Al_(2)O_(3)(0.08%~0.39%),and deficient in TiO_(2)(0.011%~0.014%).Its total content of REE is lower than that in the primitive mantle,and the REE distribution pattern is gentle to the right,the fractionation of light and heavy REE is obvious,and there are obvious positive Eu anomaly and weak negative Ce anomaly.Transition metal elements show an asymmetric W-type distribution pattern,forming obvious negative Ti and Cu anomalies,and the rocks have high(87 Sr/86 Sr)i and lowεNd(t)characteristics.The above characteristics indicate that the ultrabasic rocks in the Yizhuxingla area is similar to SSZ type mantle peridotite.The depleted mantle rocks resulted form the partial meltingof original mantle(15%~25%).These ultrabasic rocks were formed in the oceanic island arc environment and had mixing of 20%~40%crustal material during the subduction process.

关 键 词：岩石地球化学 Pb-Nd-Sr同位素 衣珠兴拉 亏损地幔 

分 类 号：P588.125[天文地球—岩石学] P597[天文地球—地质学]