西藏革吉县一带下白垩统则弄群火山岩地球化学特征及其地质意义  

Geochemical Characteristics and Its Geological Significance of the Lower Cretaceous Zenong Group Volcanic Rocks of Geji Country,Tibet

作　　者：杨永锋 姜亚国 唐静 程犬 YANG Yongfeng;JIANG Yaguo;TANG Jing;CHENG Quan(Shaanxi Mining Technology Industry Co.,Ltd.,Xi’an 710000,Shaanxi,China;Regional Geological Survey Academe of Shaanxi Geology and Mining Group Co.,Ltd.,Xianyang 712000,Shaanxi,China)

机构地区：[1]陕西地矿科技产业股份有限公司,陕西西安710000 [2]陕西地矿区研院有限公司,陕西咸阳712000

出　　处：《西北地质》2024年第6期300-317,共18页Northwestern Geology

基　　金：中国地质调查局项目“西藏革吉县尕尔穷地区4幅1:5万地质矿产调查”(12120113036800)资助。

摘　　要：西藏革吉县一带则弄群(K_(1)Z)广泛发育,自下而上由多爱组(K_(1)d)、拖称组(K_(1)t)和朗久组(K_(1)l)组成。笔者对则弄群(K_(1)Z)火山岩开展了详细的岩相学、地球化学和年代学研究,研究发现这些火山岩存在明显火山喷发不整合,指示火山活动具有脉动特点。主量元素组成显示多爱组(K_(1)d)和拖称组(K_(1)t)火山岩属碱性-钙碱性系列,朗久组(K_(1)l)火山岩则为碱性系列。微量元素蛛网曲线、稀土配分图以及构造差别图解表明多爱组(K_(1)d)和拖称组(K_(1)t)火山岩形成于岛弧环境,朗久组(K_(1)l)火山岩则形成于近活动大陆边缘岛弧环境。多爱组(K_(1)d)角闪安山岩锆石U-Pb加权平均年龄值为(111.2±2.1)Ma。结合前人资料和本研究,笔者认为则弄群(K_(1)Z)火山岩是狮泉河-永珠-纳木错-嘉黎蛇绿混杂岩带所代表的Slainajap洋盆向南俯冲形成的陆缘弧。The Zenong Group is exposed widely in the Geji area of Tibet and is composed of Duo'ai Formation,Tuo'cheng Formation,and Langjiu Formation from bottom to top.This study carried petrography,geochemistry,and chronology on the Zenong Group volcanic rocks.It was found that these volcanic rocks show obvious eruption unconformity and pulsed magmatism.According to the major element composition,the igneous rocks of the Duo'ai,and Tuo'cheng Formations belong to the alkaline-calc-alkaline series,while the rocks of the Langjiu Formation belong to the alkaline series.The trace elements,REE distribution,and tectonic discrimination diagram show that the Duo'ai,and Tuocheng Formation formed in the island arc environment,while the Langjiu formed in the island arc environment near the active continental margin.The average weighted zircon UPb age of the hornblende andesite from the Duo'ai Formation is(111.2±2.1)Ma.Combination with previous work and this study,we suggest the Zenong Group volcanic rocks are the marginal continental arc of the southward subduction of the Slainajap ocean basin represented by the Shiquanhe-Yongzhu-Namco-Jiali ophiolitic melange belt.

关 键 词：早白垩世 则弄群 冈底斯带 地球化学 火山岩 

分 类 号：P56[天文地球—构造地质学]