川西李家沟锂多金属矿区晚三叠世花岗细晶岩脉的成因:地球化学、锆石U-Pb年龄和Hf同位素的证据  

Petrogenesis of granite aplite in the Lijiagou lithium polymetallic ore district in western Sichuan:constraints from geochemistry,zircon U-Pb geochronology and Hf isotope

作　　者：罗伟 彭静 金廷福 杨波 庞良武 LUO Wei;PENG Jing;JIN Tingfu;YANG Bo;PANG Liangwu(College of Engineering and Technology,Zunyi Normal University,Zunyi 563002,China;College of Mining Engineering,Guizhou University of Engineering Science,Bijie 551700,China;Geochemical Exploration Brigade of Sichuan Provincial Geology&Mineral Resources Bureau,Deyang 618000,China)

机构地区：[1]遵义师范学院工学院,贵州遵义563006 [2]贵州工程应用技术学院矿业工程学院,贵州毕节551700 [3]四川省地质矿产勘查开发局化探队,四川德阳618000

出　　处：《沉积与特提斯地质》2023年第1期36-47,共12页Sedimentary Geology and Tethyan Geology

基　　金：贵州省省级科技计划项目(黔科合基础-ZK[2021]一般204);贵州省教育厅项目(黔教合KY字[2020]100);遵义师范学院项目(遵师BS[2020]5号、遵师XM[2020]1号-01);毕节市科学技术联合基金项目(毕科合字[2019]22号)联合资助。

摘　　要：李家沟锂多金属矿床位于松潘-甘孜褶皱造山带东南缘,是近年来在区内发现的超大型锂多金属矿床,矿区内广泛发育花岗细晶岩脉。本文对花岗细晶岩脉进行了全岩地球化学测试、锆石U-Pb定年和Hf同位素分析,探讨其岩石成因及地质意义。花岗细晶岩锆石U-Pb加权平均年龄为200±2 Ma,属晚三叠世—早侏罗世。岩石具高硅(w(SiO_(2))=73.27%~75.14%)、富铝(w(Al_(2)O_(3))=14.8%~15.25%)、富碱(w(Na_(2)O+K_(2)O)=4.86%~8.08%)、贫钙(w(CaO)=0.45%~1.45%)的特征,A/CNK值均大于1.1,属中钾-高钾钙碱性强过铝质S型花岗岩。微量元素表现出Rb、Th、U、K的正异常和Ba、Sr、P、Ti相对负异常。稀土元素显示轻稀土富集、重稀土亏损及弱的负Eu异常(δEu=0.68~0.81)。岩石中锆石ε_(Hf)(t)值和对应的二阶模式年龄(t_(DM2))较为均一,分别为-6.36~-3.39和1 424~1 616 Ma。研究表明,花岗细晶岩脉形成的构造背景为松潘-甘孜洋(古特提斯支洋)闭合后的后碰撞造山阶段,源岩为古老地壳变杂砂岩。结合前人研究成果,认为锂矿化花岗伟晶岩与花岗细晶岩为同一源区不同源岩(变泥质岩和变杂砂岩)部分熔融的产物。The Super-large Lijiagou lithium polymetallic deposit is a newly discovered deposit in the southeastern margin of Songpan-ganzi Fold Orogenic Belt and has widespread outcrops of granite aplite veins.whole-rock geochemical analysis,zircon UPb dating and zircon Hf isotopic analysis for granite aplite are performed to explore its petrogenesis and geological significance.Zircons yielded weighted mean U-Pb age of 200±2 Ma for granite aplite,indicating that it was emplaced in the Late Triassic to Early Jurassic.The rocks exhibit high SiO_(2) concentration(73.27%~75.14%),high Al_(2)O_(3) concentration(14.8%~15.25%),high total alkali concentration(4.86%~8.08%) and low CaO concentration(0.45%~1.45%) with A/CNK ratios1.1,which are defined as median-K to high-K calc-alkaline strongly peraluminous S-type granites.Trace elements of the granite aplite show positive anomalies for Rb,Th,U,K and relative negative anomalies for Ba,Sr,P,Ti.The granite aplite display enrichment of LREE,depletion of HREE,and weak negative Eu anomalies(δEu=0.68~0.81).zircon ε_(Hf)(t) values range from -6.36 to -3.3 9 with t_(DM2) varying from 1 424 Ma to 1 616Ma.The study shows that the granite aplite veins were formed in the post-collision orogenic stage after the closure of the SongpanGanzi ocean(a branch of the Paleo-Tethys Ocean),and the source rocks are the ancient crustal meta-grey wacke.Combined with the previous research results,it is considered that the lithium mineralized granitic pegmatites and the granite aplites are the products of partial melting of different source rocks(meta-argillite vs meta-graywacke) in the same source area.

关 键 词：锆石U-Pb-Hf同位素 S型花岗岩 后碰撞 古特提斯 李家沟锂多金属矿床 四川可尔因地区 

分 类 号：P581[天文地球—岩石学] P611.12[天文地球—地质学]