西藏雅鲁藏布江结合带色吾村白垩纪变基性岩锆石U-Pb年龄、地球化学特征及其地质意义  

Zircon U-Pb age and geochemistry of Cretaceous metabasic rocks in Sewu area, Yarlung Zangbo River junction belt of Tibet, and their geological significance

作　　者：王燚 董磊[2] 叶春林[1] 杨学俊[1] 吕志伟 贾小川[1] 黄波 陈东升 WANG Yi;DONG Lei;YE Chunlin;YANG Xuejun;LüZhiwei;JIA Xiaochuan;HUANG Bo;CHEN Dongsheng(Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province,Sichuan Geological Survey,Chengdu 610081,Sichuan,China;Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China;The Geological Prospecting Team of Sichuan Geological&Mineral Bureau,Chengdu 610032,Sichuan,China)

机构地区：[1]四川省地质调查院稀有稀土战略资源评价与利用四川省重点实验室,四川成都610081 [2]中国地质调查局成都地质调查中心,四川成都610081 [3]四川省地质矿产勘查开发局物探队,四川成都610032

出　　处：《地质通报》2020年第4期459-470,共12页Geological Bulletin of China

基　　金：国家重点研发计划《青藏高原碰撞造山成矿系统深部结构与成矿过程》(编号:2016YFC0600308);中国地质调查局项目《冈底斯-喜马拉雅铜矿资源基地调查》(编号:DD20160015)。

摘　　要：区域地质调查在青藏高原南部曲松县邱多江乡色吾村附近新发现白垩纪变基性岩,呈层状大面积分布于雅鲁藏布江缝合带南侧宋热岩组B岩段中。为查明这些变基性岩形成时代和地球化学特征,在详实的野外工作基础上,进行了LA-ICP-MS锆石U-Pb测年和地球化学分析。所有样品的年龄值均属于早白垩世。主量元素地球化学特征显示,其属于低钾(拉斑)玄武岩系列;稀土元素分析结果显示,原始岩浆岩中晶出的斜长石较少或者未结晶,轻、重稀土元素之间具有相对较高的分馏程度;高场强元素相对明显的富集;大离子亲石元素亏损,Sr和Ba负异常明显;并认为变基性岩可能来自软流圈地幔。根据稳定富集的高场强元素投图,岩浆在就位和形成过程中受到地壳混染。构造环境分析认为,这套变基性岩具有洋中脊玄武岩MORB的特征,其形成可能与新特提斯洋被动大陆边缘热点与洋中脊相互作用有关。由于岩石变质变形作用强烈,镜下无法判断其原岩成分,从野外观察看,较接近火山岩的特征。若为火山喷发形成,将对雅鲁藏布江缝合带南部研究产生重要促进作用,并因此厘定出白垩纪地层。In recent years, new Cretaceous metabasic rocks were found in the vicinity of Sewu, Qiuduojiang Township, Qusong County, southern Tibetan Plateau, by regional geological survey.The rocks are extensively distributed in layers in B rock section of Songre Formation in southern Yarlung Zangbo River suture zone.A series of LA-ICP-MS zircon U-Pb samples, geochemical samples and thin section samples were collected for testing on the basis of detailed field work in order to find out the formation age and geochemical characteristics of these metamorphic rocks.All LA-ICP-MS zircon U-Pb samples belong to the Early Cretaceous.The geochemical characteristics of the major elements show that the rocks belong to the low-K tholeiite basalt series. The rare earth elements show that the plagioclase in the original magmatic rocks was less or not crystallized, and there existed a relatively high degree of fractionation between light rare earth and heavy rare earth.The high field strength elements are relatively obvious;the large ion lithophile elements are deficient, and the negative anomalies of Sr and Ba are obvious.It is considered that the metabasic rocks might have been derived from the soft fluid mantle.According to the high field intensity element diagram of stable enrichment, magma was contaminated by the crust in the process of emplacement and formation.According to the analysis of tectonic environment, the metabasic rocks have MORB characteristics, which might have been related to the interaction between the hot spots and the mid-ocean ridges on the passive continental margin of the New Tethys Ocean.Due to the strong metamorphism and deformation of the rocks, the composition of the original rocks can not be determined under the microscope.Field observation shows that they were probably similar to the characteristics of the volcanic rocks. If they were formed by volcanic eruption, they would play an important role in promoting the study of the southern part of the Yarlung Zangbo Suture Zone and therefore the Cretaceous strat

关 键 词：雅鲁藏布缝合带 朗杰学群 变基性岩 岩石地球化学 锆石U-PB测年 

分 类 号：P534.53[天文地球—古生物学与地层学] P597+.3[天文地球—地质学]