喜马拉雅东段库局中新世淡色花岗岩-伟晶岩中电气石的元素和硼同位素变化:对岩浆熔体演化的见解  

Elemental and boron isotopic variations of tourmalines from the Miocene leucogranite-pegmatite in Kuju,eastern Himalaya:Implications for the evolution of magmatic melts

作　　者：张凯 刘欣 赵葵东[1] 刘行 陈浩然 张向飞 邹灏[3] 曹华文[3] ZHANG Kai;LIU Xin;ZHAO KuiDong;LIU Hang;CHEN HaoRan;ZHANG XiangFei;ZOU Hao;CAO HuaWen(Faculty of Earth Resources,China University of Geosciences,Wuhan 430074,China;Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu 610218,China;College of Earth and Planet Sciences,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]中国地质大学(武汉)资源学院,武汉430074 [2]中国地质调查局成都地质调查中心(西南地质科技创新中心),成都610218 [3]成都理工大学地球与行星科学学院,成都610059

出　　处：《岩石学报》2024年第8期2334-2352,共19页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2021YFC2901803);国家自然科学基金项目(92055314、42321001、41802095);国际地球科学计划项目(IGCP-741)联合资助。

摘　　要：喜马拉雅广泛分布的高分异淡色花岗岩与稀有金属成矿具有密切成因联系,岩浆岩中电气石的元素与硼同位素可以有效示踪岩浆演化过程,因此电气石的研究对示踪稀有金属元素迁移和富集过程具有重要指示意义。本文聚焦于喜马拉雅东段库局(库曲)中新世淡色花岗岩和伟晶岩,综合野外地质特征和独居石U(-Th)-Pb年代学,分析白云母花岗岩和伟晶岩之间的时空演化关系;利用电子探针和LA-(MC)-ICP-MS重点研究白云母花岗岩中团块状电气石(Tur-GI)、脉状电气石(Tur-GⅡ)以及伟晶岩中电气石(Tur-P)的元素地球化学和硼同位素特征。独居石^(208)Pb/^(232)Th加权平均结果显示白云母花岗岩年龄为16.8Ma,伟晶岩为15.8Ma,两者形成时代在误差范围内一致;伟晶岩是白云母花岗岩高分异演化的产物。三类电气石Fe/(Mg+Fe)变化范围为0.64~0.91,Na/(Na+Ca)变化范围为0.93~0.96。库局白云母花岗岩和伟晶岩中的电气石均属于碱性基团的黑电气石,主要结晶于岩浆熔体中。电气石微量元素含量主要受岩浆熔体成分和局部围岩混染控制。三类电气石的硼同位素组成在-13.7‰~-7.6‰之间,并且越晚结晶的电气石δ^(11)B值更高。电气石δ^(11)B值与其他地球化学比值和微量元素含量之间存在相关性,这种相关性进一步反映岩浆的连续演化过程。电气石中微量元素含量模拟显示单次岩浆结晶分异作用可以促进熔体中稀有元素的富集。The high-differentiated leucogranites widely distributed in the Himalayas are closely related to rare metal mineralization.The elements and boron isotopes of tourmaline in magmatic rocks can effectively trace magma evolution,which is significant for rare metal migration and enrichment.This study focuses on the Miocene leucogranite and pegmatite in Kuju(Kuqu),eastern Himalaya.It presents a comprehensive analysis of the geological characteristics and monazite U(-Th)-Pb chronology to determine the temporal and spatial evolution relationship between muscovite granite and pegmatite.Subsequently,this paper uses electron microprobe and LA-(MC)-ICP-MS to investigate the elemental geochemical and boron isotope characteristics of agglomerated allotriomorphic tourmaline(Tur-GI)and veined self-shaped tourmaline(Tur-GII)in muscovite granite,as well as agglomerated self-shaped tourmaline(Tur-P)in pegmatite.The study aims to determine the origin of tourmaline and its implications for rare metal mineralization.The muscovite granite and pegmatite have similar ^(208)Pb/^(232)Th weighted average ages of 16.8Ma and 15.8Ma,respectively.The pegmatite is the product of the highly differentiated evolution of muscovite granite.The Fe/(Mg+Fe)and Na/(Na+Ca)ratios of the three types of tourmalines vary from 0.64 to 0.91 and 0.93 to 0.96,respectively,with compositions similar to black tourmaline.The black tourmaline with alkaline groups found in the leucogranite and pegmatite in Kuju is crystallized directly from the magmatic melt.The trace element content is mainly controlled by the composition of the magmatic melt and the contamination of the local surrounding rock contamination.The boron isotope composition of tourmaline ranges from-13.7‰to-7.6‰,with higherδ^(11) B values observed for later crystallization series.A correlation exists between theδ^(11) B value of tourmaline and other geochemical ratios or trace element contents,which further reflects the continuous evolution process of magma.Single magmatic crystallization differenti

关 键 词：喜马拉雅 淡色花岗岩-伟晶岩 电气石 硼同位素 稀有金属 

分 类 号：P578.953[天文地球—矿物学] P588.121[天文地球—地质学] P597.3P618.6