拉萨地块钾质-超钾质火山岩或为高分异岩石:来自铷、铯富集的证据  

Potassic-Ultrapotassic Volcanic Rocks in the Lhasa Block may be Highly Differentiated Rocks:Evidence from Rubidium and Cesium Enrichment

作　　者：车东 郑绵平[1] 赵元艺[1] 张照志[1] Che Dong;Zheng Mianping;Zhao Yuanyi;Zhang Zhaozhi(Key Laboratory of Saline Lake Resources and Environment(Ministry of Land and Resources),Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院矿产资源研究所自然资源部盐湖资源与环境重点实验室,北京100037

出　　处：《地球科学》2024年第3期850-867,共18页Earth Science

基　　金：国家自然科学基金项目(No.91962219);西藏自治区科技计划重大专项(No.XZ202201ZD0004G01);第二次青藏高原综合科学考察研究专题(No.2022QZKK0201)。

摘　　要：青藏地区拉萨地块、羌塘地块、松潘甘孜-可可西里地块中,广泛发育后碰撞以来的钾质-超钾质火山岩.在上述众多钾质-超钾质火山岩研究数据中,拉萨地块的Rb、Cs等稀碱元素的超常富集程度远高于其他两地块,为了将此现象量化表述,并且尝试对富集原因进行探究.本文通过实测和已公开发表的数据,运用箱线图等统计方法,以及系统的矿物学、地球化学分析手段,量化了三大地块稀碱元素富集程度,对富集成因有了初步认识.结果表明拉萨地块钾质-超钾质火山岩存在较高程度的岩浆分异是导致Rb、Cs等稀碱元素超常富集的主要原因,超常富集区主要分布于火山岩年龄范围为25~13 Ma之间的拉萨地块中西部.并且类比高分异花岗岩的研究成果划分了拉萨地块钾质-超钾质火山岩较高程度分异的Zr/Hf和Nb/Ta判别范围.Post-collisional potassic-ultrapotassic volcanic rocks are widely developed in the Lhasa block,Qiangtang block and Songpan-Ganzi-Kekexili block in the Qinghai-Xizang region.Many previous studies on the potassic-ultrapotassic volcanic rocks in this area show the supernormal enrichment of trace alkali elements such as Rb and Cs in the Lhasa block is much higher than those in other two blocks.In order to quantify this phenomenon and to investigate the causes of enrichment,this paper quantifies the enrichment degree of trace alkali elements in the three blocks,and has attained a preliminary understanding of the causes of enrichment,based on the measured and published data,using statistical methods such as box-plot and systematic mineralogical and geochemical analysis methods,It is concluded that the high degree of magmatic differentiation in the potassic-ultrapotassic volcanic rocks of the Lhasa block is the main cause of the rare alkali elements enrichment of Rb and Cs,and the enrichment zones are mainly located in the central and western part of the Lhasa block,where the volcanic rocks range in age from 25 to 13 Ma.The discrimination range of Zr/Hf and Nb/Ta with high degree of differentiation of potassic-ultrapotassic volcanic rocks in the Lhasa block is also delineated by analogy with the results of highly differentiated granites.

关 键 词：拉萨地块 钾质-超钾质火山岩 稀碱元素富集 高分异 西藏 矿物学 地球化学 

分 类 号：P588[天文地球—岩石学] P595[天文地球—地质学]