柴北缘大柴旦电气石花岗岩成因及富硼机制研究  

Genesis and mechanism of tourmaline granite in the Da Qaidam area,northern margin of the Qaidam Basin

作　　者：赵春涛 王建萍[1,2] 李斌凯 张西营[1,2] 余冬梅 马海州[1,2] 韩文华 陈亮[1,2,3] ZHAO ChunTao;WANG JianPing;LI BinKai;ZHANG XiYing;YU DongMei;MA HaiZhou;HAN WenHua;CHEN Liang(Key Laboratory of Green and High-end Utilization of Salt Lake Resources,Qinghai Institute of Salt Lakes,Chinese Academy of Sciences,Xining 810008,China;Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes,Xining 810008,China;University of Chinese Academy of Sciences,Beijing 110034,China)

机构地区：[1]盐湖资源绿色高值利用重点实验室,中国科学院青海盐湖研究所,西宁810008 [2]青海省盐湖地质与环境重点实验室,西宁810008 [3]中国科学院大学,北京110034

出　　处：《岩石学报》2025年第2期711-736,共26页Acta Petrologica Sinica

基　　金：第二次青藏高原综合科学考察研究(2022QZKK0201);国家自然科学基金项目(U24A20598);青海省自然科学基金项目(2024-ZJ-722);盐湖资源绿色高值利用重点实验室开放基金(ISL2024-07);中科院特别研究助理项目(E410DZ01)联合资助.

摘　　要：柴达木盆地北缘地处青藏高原东北部,受多期岩浆-构造活动的影响发育有众多侵入岩和关键金属矿产。B作为挥发性元素,在全球花岗岩-伟晶岩成矿系统中广泛发育,可能是促进稀有金属成矿的关键挥发组份。但是,目前有关稀有金属超常富集过程中挥发组份的起源及其控制机制仍不清楚。近期我们在柴北缘的大柴旦北部发现大量电气石花岗岩体,厘清该岩体的成因和富硼机制有助于区域岩浆热液型硼矿床和稀有金属成矿作用的整体认识。因此,我们选取了塔塔楞和居红土电气石花岗岩体为研究对象,对其开展了详尽的野外地质调研、岩石地球化学、矿物地球化学、Lu-Hf同位素地球化学和锆石U-Pb年代学等工作,获得以下主要认识:(1)大柴旦湖区电气石花岗岩体属于富钾(2.09%~7.04%)、富硅(68.35%~79.42%)、过铝质(A/CNK=1.00~1.50)的高分异花岗岩,具有富集大离子亲石元素和硼、氟等流体活动性元素、亏损高场强元素的特征;(2)电气石花岗岩体形成于~438Ma,适值柴北缘洋俯冲结束、柴达木地块向南祁连地块俯冲的陆-陆碰撞环境;(3)电气石花岗岩的形成与洋-陆俯冲向陆-陆碰撞转换过程中,洋壳发生蛇纹石化使流体活动性元素富集,进而引发地壳物质重熔有关。即:柴北缘洋洋壳俯冲时发生蛇纹岩化,该过程使硼、氟等流体活动性元素在其中富集,然后继续俯冲造成蛇纹岩脱水,脱水过程促进富硼流体进入地幔楔并造成地壳物质的重熔。富矿的重熔岩浆在上升过程中受到了少量地幔物质的混染,在后续的演化过程经历了钾长石、斜长石、磷灰石、褐帘石和独居石等矿物的分离结晶作用,最终在地壳浅部成岩。B,as a volatile element,is widely developed in the global granite pegmatite mineralization system and may be a key volatile component that promotes rare metal mineralization.However,the origin and control mechanism of volatile components during the abnormal enrichment process of rare metals are still unclear.The northern margin of the Qaidam Basin is located in the northeastern Qinghai-Tibet Plateau.Influenced by multistage magmatic-tectonic activities,many intrusive rocks and rare metal deposits are present.Recently,we found many B-rich granites in the Da Qaidam area on the northern margin of the Qaidam Basin.Identifying the genesis of these tourmaline granites can provide a reference for solving the scientific problem of the origin and control mechanism of volatile components in the process of rare metal enrichment.Therefore,we investigated two tourmaline granites plutons,Tataleng and Juhongtu,and carried out detailed field geological surveys,element geochemistry,Hf isotopes and zircon U-Pb chronology and obtained the following findings:(1)The tourmaline granites in the Da Qaidam area belong to a highly differentiated granite rich in potassium,silicon,and peraluminium.(2)Tourmaline granites were formed~438Ma in a continental collisional environment where the Qaidam block subducted under the South Qilian block after the end of northern Qaidam marginal ocean subduction.(3)The formation process of B-rich granites is as follows:serpentinisation occurs during the subduction of oceanic crust,in which fluid-mobile elements are enriched,and then continuous subduction causes the dehydration of ophiolite.The dehydration process promotes the B-rich fluid to enter the mantle wedge and causes the remelting of crustal materials.The B-rich magma is contaminated by upper mantle crystals to form the ore-bearing parent magma.In the subsequent evolution process,the magma experiences the fractional crystallization of K-feldspar,plagioclase,hornblende,allanite,and monazite.

关 键 词：电气石花岗岩 Lu-Hf同位素地球化学 锆石U-Pb年代学 大柴旦 柴北缘 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]