LCT型伟晶岩及其锂矿床成因概述
A review of LCT pegmatite and its lithium ore genesis
查看参考文献86篇
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文摘
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花岗伟晶岩具有与低共熔花岗岩相似的矿物和化学组成,通常与高分异花岗岩具有成因联系。花岗伟晶岩划分为富Li-Cs-Ta(LCT)、富Nb-Y-F(NYF)和混合的LCT+NYF型,其中LCT型伟晶岩以过铝质,富集助熔组分(H_2O、F、P、B)、稀有元素(Li、Rb、Cs、Nb、Ta、Be、Sn),极其低的Nb/Ta比值(<5)为特征。通常LCT型伟晶岩显示内部分带,主要包括边界带、壁带、中间带和核部带;此外,可能还发育交代体、层状细晶岩和晶洞。大多数LCT型伟晶岩形成与(同造山)-晚造山的过铝质S型、I型或混合的S+I型花岗岩具有成因联系。对于壳源沉积岩小比例部分熔融直接形成的伟晶岩,通常形成于伸展背景下的晚造山和造山后阶段,侵入于典型的低压角闪岩-高绿片岩相的变沉积岩中。伟晶岩外带(包括边缘带、壁带、细晶岩)中的细粒和细晶岩结构、UST(单向固结结构)是液相线过冷所致,而伟晶岩内带(中间带、核部带)中粗大矿物形成、矿物分带以及稀有金属矿物的饱和结晶是助熔组分(H_2O、B、P、F)、稀有金属(Li、Rb、Cs、Be、Nb、Ta)通过组成带状纯化方式在边界层聚集的结果。伟晶岩分离结晶作用的开始与液相线过冷状态密切相关,晶体成核延迟、晶体生长速率、晶体成核密度取决于液相线过冷程度(!T)。针对LCT型伟晶岩,已提出的稀有金属成矿机制主要有分离结晶作用、岩浆不混溶、超临界流体和组成带状纯化。对于全脉矿化锂辉石伟晶岩成因,尚不清楚是岩浆液态分离还是Li强烈分配进入流体相所致? |
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其他语种文摘
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Granitic pegmatite shares similar modal and chemical compositions with eutectic granite,and has a genetic links with the highly fractionated granite.The LCT-family,NYF-family,and mixed LCT+NYFfamily pegmatites were classified petrogenetically,in which LCT pegmatites are peraluminous, characterized by enrichment of rare and alkali elements(Li,Rb,Cs,Be,Sn)and fluxing components (H_2O,F,P,B),and very low Nb/Ta ratios(<5).In general,LCT pegmatite shows internal textural zonation,including the border,wall,intermediate and core zones;in addition,some of pegmatites maybe develop replacement bodies,layered aplites and miarolitic cavities.Most of LCT pegmatites intruded into metasedimentary rocks,typically at low-pressure amphibolite to upper greenschist facies under tectonic setting of late syn-collision to early post-collision with respect to enclosing rocks.Aplitic textures in the outer zone(including border,wall zones and aplite)of pegmatites and UST (unidirectional solidification texture)have resulted from the liquidus undercooling of viscous granitic liquids prior to the onset of crystallization,while increasing crystal size in the internal zones(including intermediate and core zones), mineral zonations and crystallization of rare metal minerals have originated from a flux-enriched(H_2O,F, P,B)and pile-up of rare metal(Li,Rb,Cs,Be,Nb,Ta)boundary layer of liquid developed adjacent to the crystallization front by constitutional zone refining CZR mechanism.The onset of crystallization is closely related to liquidus undercooling state,while nucleation delay,crystal growth rate and nucleation density are dependent on the degree of liquidus undercooling.Up to now,the four main metallogenic mechanism proposed for pegmatite-type rare metal deposits include fractional crystallization,magmatic immiscibility,supercritical fluids and constitutional zone refining (CZR).For unzoned Li pegmatitic deposit(or whole vein Li-mineralized pegmatite),ore genesis is unclear as it could have resulted either from the magmatic immiscibility or Li strongly partitioning into magmatic fluids. |
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来源
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地质学报
,2021,95(10):2955-2970 【核心库】
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DOI
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10.19762/j.cnki.dizhixuebao.2021093
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关键词
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组成特征
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结构分带
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岩石成因
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成矿机制
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LCT型伟晶岩
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地址
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中国科学院地球化学研究所, 地球内部物质高温高压中国科学院重点实验室, 贵州, 贵阳, 550081
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语种
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中文 |
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文献类型
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研究性论文 |
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ISSN
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0001-5717 |
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学科
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地质学 |
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基金
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国家自然科学基金委“战略性关键金属超常富集成矿动力学”重大研究计划
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国家自然科学基金
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文献收藏号
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CSCD:7077093
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