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

作　　者：孙文礼[1,2] 刘益 张照伟[4,5,6] SUN Wenli;LIU Yi;ZHANG Zhaowei(Gansu Industry Polytechnic College,Tianshui 741025,Gansu,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Kunming University of Science and Technology,Kunming 650093,Yunnan,China;Xi'an Center of China Geological Survey,Xi'an 710054,Shaanxi,China;Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,MNR,Xi'an 710054,Shaanxi,China;Northwest China Center for Geoscience Innovation,Xi'an 710054,Shaanxi,China)

机构地区：[1]甘肃工业职业技术学院,甘肃天水741025 [2]北京大学地球与空间科学学院,北京100871 [3]昆明理工大学国土资源工程学院,云南昆明650093 [4]中国地质调查局西安地质调查中心,陕西西安7410054 [5]自然资源部岩浆作用成矿与找矿重点实验室,陕西西安7410054 [6]西北地质科技创新中心,陕西西安7410054

出　　处：《西北地质》2022年第2期35-55,共21页Northwestern Geology

基　　金：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。

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3040~7 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SiO_(2)、Na_(2)O、K_(2)O、Li、Cs、Ta和Nb,亏损Fe_(2)O_(3)、CaO、MgO、TiO_(2)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≥10000×10^(-6))受控于深部岩浆房总分配系数(D_(Li)<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。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 SiO_(2),Na_(2)O,K_(2)O,Li,Cs,Ta,Nb and depletion of Fe_(2)O_(3),CaO,MgO,TiO_(2),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≥10000×10^(-6))is controlled by the total distribution coefficient(D_(Li)<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 o

关 键 词：LCT型伟晶岩 基本特征 岩浆起源 岩浆演化 富锂机制 

分 类 号：P618.71[天文地球—矿床学] P581[天文地球—地质学]