北疆卡鲁安Li-Be-Nb-Ta伟晶岩岩浆-热液过渡过程与晶体-熔体-流体相互作用:锆石矿物学记录  

Zircon as a recorder of magmatic-hydrothermal transition and crystal-melt-fluid interaction in Kaluan Li-Be-Nb-Ta pegmatites,northwestern Xinjiang,China

作　　者：冯浩轩 罗耀清 白应雄 曹冲 武阳 FENG HaoXuan;LUO YaoQing;BAI YingXiong;CAO Chong;WU Yang(CAS Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Innovation Academy of Earth Science,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;North China University of Science and Technology,Tangshan 063210,China)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院矿产资源研究重点实验室,北京100029 [2]中国科学院地球科学研究院,北京100029 [3]中国科学院大学地球与行星科学学院,北京100049 [4]华北理工大学,唐山063210

出　　处：《岩石学报》2023年第11期3353-3368,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金重大研究计划重点支持项目(91962213);上海合作组织国际科技合作计划项目(2020E01043);中国科学院国际伙伴计划项目(132A11KYSB20190070)联合资助。

摘　　要：新疆卡鲁安伟晶岩型Li-Be-Nb-Ta矿床是阿尔泰造山带内重要的锂矿床之一。本文研究发现,卡鲁安富锂伟晶岩的各内部结构带,即钠长石-石英-白云母带(Ⅰ)、锂辉石-钠长石-石英带(Ⅱ)和锂云母-锂辉石-钠长石-石英带(Ⅲ)中的锆石结构和成分变化复杂,均发育三类、不同世代的锆石:Zr-P、Zr-A和Zr-O。Zr-P为原生岩浆锆石,它们具有均匀或振荡CL结构,相似的低HfO_(2)和Li、Be、Al、P、Ca、Fe、Nb、Cs、Ta含量。Zr-P_(Ⅰ)和Zr-P_(Ⅱ)的稀土元素配分模式呈左倾型,而Zr-P_(Ⅲ)的稀土配分模式呈平坦型,这与磷灰石和锰铝榴石分离结晶或熔-流体相互作用有关。Zr-A的CL结构不均匀,发育孔洞、微小富U/Th矿物包裹体,并含较高的Be、Al、P、Ca、Fe、Nb、Cs和Ta含量。Zr-A_(Ⅰ)和Zr-A_(Ⅱ)锆石显示相似的富集轻稀土、平坦式重稀土的M型稀土元素配分模式,而Zr-A_(Ⅲ)显示与Zr-P_(Ⅲ)相同的平坦型稀土配分模式。显微结构和成分差异表明,Zr-A是由原生岩浆锆石溶解-再沉淀而来,其中Zr-A_(Ⅰ)、Zr-A_(Ⅱ)锆石形成于岩浆热液过渡阶段的晶体-熔体-流体相互作用,而Zr-A_(Ⅲ)为流体交代的产物。Zr-O形成最晚,它们的CL结构均匀且强度最高,含最低UO_(2),而HfO_(2)、Li、Be、Al、P、Ca、Fe、Nb、Cs和Ta含量与原生岩浆锆石Zr-P相似,为热液成因。因此,卡鲁安富锂伟晶岩经历了岩浆、岩浆-热液过渡和热液多阶段演化,流体出溶后的晶体-熔体-流体相互作用活化早期锂辉石中的Li为伟晶岩晚期锂云母矿化(锂再富集)提供了重要物质条件。The Kaluan rare metal pegmatites in Altai orogeny belt,northwestern Xinjiang host importantly economic Li,Be,Nb and Ta resources.This study shows zircon in Albite-quartz-muscovite zone(Ⅰ),Spodumene-albite-quartz zone(Ⅱ),and lepidolite-spodumene-albite-quartz zone(Ⅲ) from these Li-rich pegmatites with complex textures and compositions.Three types of zircon(Zr-P,Zr-A and Zr-O) have been recognized in each internal zones.Zr-P zircons are homogeneous and/or oscillatory zoned under CL images,and have similar low contents of HfO_2,Li,Be,Al,P,Ca,Fe,Nb,Cs and Ta.The Zr-P_(I) and Zr-P_Ⅱ zircons are sligtly enriched heavy REEs in chondrite-normalized REE patterns,while Zr-P_Ⅲ zircons show flat REE patterns with convex tetrad effects.These zircons are interpreted to represent primary magmatic zircon formed in evolved melt with fractional crystallization of apatite and garnet,as well as melt-fluid interaction.Zr-A zircons are characterized by inhomogeneous CL intensity,porous texture,and containing numerous tiny U-and/or Th-rich mineral inclusions.They contain higher Be,Al,P,Ca,Fe,Nb,Cs and Ta concentrations.Zr-A_Ⅱ and many Zr-A_Ⅰ zircons are sligtly enriched light REEs and show M-type REE patterns,while Zr-A_Ⅲ zircon shares same REE patterns with Zr-P_Ⅲ.The distinct textures and compositions are thought to reflect the alteration of primary magmatic zircons due to a dissolution-reprecipitation mechanism.It is interpreted that Zr-A_Ⅰ and Zr-A_Ⅱ zircons are formed in magmatic-hydrothermal transition process via crystal-melt-fluid interaction,and that Zr-A_Ⅲ zircons are product of hydrothermal metasomatism.Zr-O zircons are late phase with homogeneously high CL intensity,low UO_(2 )content,and similar HfO_2,Li,Be,Al,P,Ca,Fe,Nb,Cs and Ta contents to primary magmatic Zr-P zircon.The REE patterns of Zr-O_Ⅰ,Zr-O_Ⅱ and Zr-O_Ⅲ are different.These zircons are explained to be deposited from hydrothermal fluids that possibly exsolved from the evolved melt at different stages.Consequently,it is suggestted mag

关 键 词：锆石 岩浆-热液过渡 晶体-熔体-流体相互作用 富锂伟晶岩 卡鲁安 

分 类 号：P578.941[天文地球—矿物学] P588.131[天文地球—地质学] P618.71