喜马拉雅东段库曲锂辉石伟晶岩锡石研究及指示意义
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2024/040(02):0433 0449ActaPetrologicaSinica 岩石学报doi:10.18654/1000 0569/2024.02.04周起凤,秦克章,刘宇超等.2024.喜马拉雅东段库曲锂辉石伟晶岩锡石研究及指示意义.岩石学报,40(02):433-449,doi:10.18654/1000-0569/2024.02.04
喜马拉雅东段库曲锂辉石伟晶岩锡石研究及指示
意义
周起凤1 秦克章2,3 刘宇超2,3 何畅通2 赵俊兴2,3 李俊瑜2 朱丽群2,3 赵永能2,3 张昕2,3
ZHOUQiFeng1,QINKeZhang2,3,LIUYuChao2,3,HEChangTong2,ZHAOJunXing2,3,LIJunYu2,ZHULiQun2,3,ZHAOYongNeng2,3andZHANGXin2,3
1 中国冶金地质总局矿产资源研究院,北京 101300
2 中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京 100029
3 中国科学院大学地球与行星科学学院,北京 100049
1 InstituteofMineralResourcesResearch,ChinaMetallurgicalGeologyBureau,Beijing101300,China
2 KeyLaboratoryofMineralResources,InstituteofGeologyandGeophysics,ChineseAcademyofSciences,Beijing100029,China
3 CollegeofEarthandPlanetarySciences,UniversityofChineseAcademyofSciences,Beijing100049,China
2023 10 05收稿,2023 12 11改回
ZhouQF,QinKZ,LiuYC,HeCT,ZhaoJX,LiJY,ZhuLQ,ZhaoYNandZhangX 2024 CassiteriteoftheKuquspodumene bearingpegmatitesintheeasternHimalaya,Tibet,anditsimplication.ActaPetrologicaSinica,40(2):433-449,doi:10.18654/1000 0569/2024.02.04
Abstract Cassiteriteisoneofthemostimportanttin bearingmineralsingraniticpegmatite,whichcanbeobservedinmanyleucogranite pegmatitesystemsintheHimalaya Themicrostructuresandchemicalcompositionsofcassiteritefromthelithium richpegmatitesinthisregionhavenotbeenrevealedsofaranditssignificanceonmagmafractionationandevolutionrequiresfurtherstudy Inthefieldwork,thespodumene bearingpegmatitedykesintheKuquintrusionintheeasternHimalayawereidentifiedandinvestigated,whicharesimplyzonedandmainlycomposedofspodumene quartz albitezoneorspodumene blockyfeldspar quartz (muscovite)zonewithalbiteaplite Thecassiteritecrystalsfromthreespodumene bearingpegmatitedykeswerestudiedbycathodoluminescence(CL)andin situEMPAandLA ICP MSanalyses,demonstratingthatthemechanismsofthecassiteritesubstitutionaredominantof2(Nb,Ta)5++Fe2+→3Sn4+togetherwithahomovalentsubstitutionof(Ti4+,Zr4+,Hf4+,U4+)→Sn4+ Insomeofthecassiteritecrystalsinonepegmatitedyke,SnandNbwerereplacedbyFe Black,grey,oscillatoryandwhitedomainsaredisplayedonCLimagesofcassiterite,andtheresultsshowthattheblackdomainshavehighNb,Ta,Fe,Zr,UandGacontentswitharelativelyhighHfcontentandalargerTicontentrange,thegreyzonesdisplaysimilarcomponentstotheoscillatoryzoneswhichareslightlyrichinNb,TaandFeanddepletedinU,whilethewhitedomainsaremainlypoorinNb,Ta,Fe,Zr,U,GaandHf TheCLcharacteristicsofcassiteriteareinfluencedbyitscompositions,i e ,Zr,U,GaandHfarerelatedwithCLofcassiteriteinsomedegree TheCLstructuresarehomogeneouscrystals,includingblack,greyandoscillatorygrains,andheterogeneouspatternswhicharecore rimnormalzoning,patchandcore rimreversezoning Theyareblackcore+oscillatory/greyborder/patch,greycore+oscillatory/greyborder/patch,oscillatory/blackcore+whiteconvoluterim/patch,oscillatory/grey/blackcore+blackborder,etc ThesequenceofthecassiteriteCLstructureisblackcore/crystal→greyoroscillatorydomain/crystal→(white/blackdomain),andgeochemically,theevolutiontrendisagradualdecreaseofNb,Ta,Fe,U,Ga,aslightlossofZr,Hf,Y,Ti,anincreasingofTa/(Nb+Ta)andZr/Hfvalues,andfinallyfollowedbyanFeenrichment ComparisonsonCLstructuresandchemicalcompositionsofcassiteriterevealthattheevolutiondegreeofthepegmatitewithsporadicsmallspodumenecrystalsislowerthanthatofthepegmatitehostingcoarsespodumenegrains,competenceofcoexistingmineralsmightproduceNb richandTa richcassiteriteinonepegmatitesample,anddifferentspodumene bearingpegmatitedykesarediversifiedintheircompositionsandevolutionofmagmas Thus,CLstructureandchemicalcompositionofcassiteritecouldreflectthecharacteristicsofmagmachemistryandformationprocessinaspodumene bearingpegmatite
本文受第二次青藏高原综合科学考察研究项目(2019QZKK0802、2019QZKK0806)、国家重点研发计划青年科学家项目(2023YFC2908400)和国家自然科学基金项目(42272101)联合资助
第一作者简介:周起凤,女,1985年生,博士,高级工程师,主要从事花岗伟晶岩及稀有金属矿床研究,E mail:zhouqifeng85@163 com