孙文礼,刘益,张照伟.LCT型花岗伟晶岩岩石成因和锂富集机制研究进展[J].西北地质,2022,55(2):35-55 SUN Wenli,LIU Yi,ZHANG Zhaowei.Research Progresson Petrogenesis of LCT-type Granitic Pegmatite and Lithium Enrichment Mechanism[J].Northwestern Geology,2022,55(2):35-55
LCT型花岗伟晶岩岩石成因和锂富集机制研究进展
Research Progresson Petrogenesis of LCT-type Granitic Pegmatite and Lithium Enrichment Mechanism
投稿时间:2021-09-23  修订日期:2022-01-10
DOI:10.19751/j.cnki.61-1149/p.2022.02.003
中文关键词:  LCT型伟晶岩;基本特征;岩浆起源;岩浆演化;富锂机制
英文关键词:LCT-type pegmatite;essential feature;pegmatite-forming magma origin;pegmatite-forming magma evolution;lithium enrichment mechanism
基金项目:国家自然科学基金“柴北缘花岗伟晶岩型锂铍等关键金属超常富集成矿的可能机制”(92062217);甘肃省教育厅高等学校创新基金项目“天水温泉岩体放射性元素生热特征与干热岩潜力评价”(2021A-230);天水市科技支撑项目“锆石Zr同位素分馏与关键金属超常富集耦合关系研究”(2022-FZJHK-3012);甘肃省青年博士基金项目“高分卫星特征参数反演算法系统集成研究”(2021QB-141)联合资助。
作者单位
孙文礼 甘肃工业职业技术学院, 甘肃 天水 741025
北京大学地球与空间科学学院, 北京 100871 
刘益 昆明理工大学国土资源工程学院, 云南 昆明 650093 
张照伟 中国地质调查局西安地质调查中心, 陕西 西安 7410054
自然资源部岩浆作用成矿与找矿重点实验室, 陕西 西安 7410054
西北地质科技创新中心, 陕西 西安 7410054 
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中文摘要:
      LCT型花岗伟晶岩是全球重要的锂资源寄主岩石之一。基于近40年全球LCT型花岗伟晶岩年代学、地球化学、包裹体、数值模拟和岩石实验学研究成果,笔者梳理总结LCT型花岗伟晶岩时空分布特征、温压条件、岩浆起源与演化过程和锂富集机制,以期为今后花岗伟晶岩型锂矿找矿工作提供理论依据。研究表明,全球LCT型花岗伟晶岩形成于3 040~7 Ma,成岩峰期与超大陆存在期具有较好耦合性;其侵位压力为250~350 MPa,液相线温度与助溶剂含量有关(650~750℃),固相线温度约为425℃。相比于大陆地壳,不同时代LCT型花岗伟晶岩均具有富集SiO2、Na2O、K2O、Li、Cs、Ta和Nb,亏损Fe2O3、CaO、MgO、TiO2和Zr,低Nb/Ta值、Zr/Hf值等特征。LCT型花岗伟晶岩岩浆可能起源于花岗质岩浆高程度(>90%)结晶分异、地壳物质小比例(5%~20%)深熔作用、富F-Li花岗质岩浆熔离作用或超临界流体(T≈731±21℃)。LCT型伟晶岩岩浆侵位后在较短时间内冷却固结,具体演化过程存在不平衡结晶和不混溶之争。伟晶岩岩浆起源和演化过程均有Li富集效应,其中结晶分异成因的LCT伟晶岩Li超常富集(Li≥10 000×10-6)受控于深部岩浆房总分配系数(DLi<0.5)、分异程度(F>99%)和Li初始浓度(>100×10-6);深熔成因LCT型伟晶岩Li超常富集受控于源区Li含量和残余相黑云母所占比例;不混溶成因LCT伟晶岩Li超常富集受控于含Li络合物/化合物进入富挥发分贫硅熔体相能力。伟晶岩岩浆不平衡结晶演化的Li富集与组成带状优化过程有关,而不混溶演化的Li富集受控于富挥发分熔体相温度和含水量。
英文摘要:
      LCT-type granitic pegmatite is one of the important host rocks of lithium resources in the world. Based on research results of geochronology, geochemistry, inclusion, numerical simulation and petrological experiments on LCT-type pegmatite in the past 40 years, this paper summarizes its the temporal-spatial distribution characteristics, temperature-pressure conditions, magma origin and evolution process and lithium enrichment mechanism, which is aim to provide theoretical reference for future prospecting work. Studys show that the global LCT-type granitic pegmatite was formed at 3040~7Ma, showing a good coupling between the peak of diagenesis and the supercontinent existence. The pressure of pegmatite emplacement is 250~350 MPa, and its liquidus temperature (650~750℃) is related to the abundance of fluxing-element while solidus temperature is about 425℃. Compared with the average composition of continental crust, LCT-type granitic pegmatite is characterized by enrichment of SiO2, Na2O, K2O, Li, Cs, Ta, Nb and depletion of Fe2O3, CaO, MgO, TiO2, Zr, Lower Nb/Ta and Zr/Hf ratios. LCT-type granitic pegmatite-froming magma is derived from granitic magma with high degree crystallization differentiation (>90%), from partial melting of crustal material with low degree (5%~20%), from immiscibility of F-Li-rich granitic magma and from a supercritical fluid(T≈731±21℃). It cooled and consolidated in a short time after emplacement, howere, its evolution process is debatable, including dynamic crystallization and melt-melt immiscibility. Both origin and evolution of pegmatite-forming melt can cause lithium enrichment. The crystallization differentiation origin modle proposes that the supernormal lithium enrichment (Li ≥ 10 000×10-6) is controlled by the total distribution coefficient (DLi<0.5), degree of crystallization differentiation (>99%) and initial lithium concentration (>100×10-6) in deep magma chamber; however, the partial melting origin modle suggests that the lithium abundance in LCT type pegmatite is related to the abundance of lithium in its source component and the proportion of biotite in the residual phase. The immisible origin modle point out that lithium enrichment is affected by the ability of lithium complexes/compounds entering the volatile-rich and silicion-poor melt phase. The enrichment of lithium during the dynamic crystallization evolution of pegmatite-forming magma is related to constitunent zoning-refining process, however, the lithium abundacne is associated with the temperature and water content of volatile-rich melt in the immiscible evolution model.
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