第３期刘晓阳等青海多彩地区龙墨沟辉绿岩脉锆石ＵＰｂ年代学及其地质意义４５多群Ｐｔ２３Ｎ是区内露的最老地层岩性组合为一套高绿片岩低角闪岩相变质岩与上覆巴塘群火互层组Ｔ３Ｂｔ３与下伏结隆组呈断层接触

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1 GeologicalScienceandTechnologyInformation Vol.37 No.3 May 2018 doi: /j.cnki.dzkq ,,,. U-Pb [J].,2018,37(3): U-Pb 1, 1, 2, 3, 2 2, (1. ( ), ;2., ; 3., ) :, -, LA-ICP-MS U-Pb, (248.3±2.6)Ma, ;, - : U-Pb ; ; - ; :P :A : (2018) [18],, -, [1-4], LA-ICP-MSU-Pb,,, -, - [5-6] [7], 1 -,, - [8-11] [12] [19-20] -, [21-22] (375~345 Ma) - -, (245~226 Ma) ( ) - - [13-17] -, ( 1-a), - - [29], - - -,, -, - (, 1-a), : : : ( [2014] ) : (1993 ),,, xihai-fire- work@foxmail.com : (1982 ),,, tanjunalan@163.com

第３期刘晓阳等青海多彩地区龙墨沟辉绿岩脉锆石ＵＰｂ年代学及其地质意义４５多群Ｐｔ２３Ｎ是区内露的最老地层岩性组合为一套高绿片岩低角闪岩相变质岩与上覆巴塘群火互层组Ｔ３Ｂｔ３与下伏结隆组呈断层接触火山岩灰岩组Ｔ３Ｂｔ２岩性组合较为复杂主要为泥晶

2 第３期刘晓阳等青海多彩地区龙墨沟辉绿岩脉锆石ＵＰｂ年代学及其地质意义４５多群Ｐｔ２３Ｎ是区内露的最老地层岩性组合为一套高绿片岩低角闪岩相变质岩与上覆巴塘群火互层组Ｔ３Ｂｔ３与下伏结隆组呈断层接触火山岩灰岩组Ｔ３Ｂｔ２岩性组合较为复杂主要为泥晶山岩组和查涌蛇绿混杂岩为断层接触关系三叠系地层广泛分布主要出露中三叠统结隆组Ｔ２ｊ中灰岩粉细砂岩英安岩英安质凝灰岩安山岩等其中Ｙａｎｇ等１３测得该组英安岩年龄为２１３± ２Ｍａ并认为其成因与甘孜理塘洋的俯冲消减作上三叠统巴颜喀拉山群Ｔ２３Ｂ上三叠统巴塘群Ｔ３Ｂｔ和结扎群Ｔ３Ｊ呈北西西向分布于区内图１ｂ巴塘群地层在研究区分布最为广泛图１ｃ呈ＮＷＳＥ向带状展布从下至上分为变砂岩夹板岩组Ｔ３Ｂｔ１火山岩灰岩组Ｔ３Ｂｔ２和变砂岩板岩用有关区内断裂构造十分发育ＮＷＮＷＷ向断裂为区内的主干断裂如玉树乌兰乌拉湖可可西里金沙江深大断裂二叠纪三叠纪火山岩类印支期中酸性侵入岩类和镁铁质岩类均有分布图１青藏高原构造框架图ａ多彩地区地质简图ｂ和采样位置地质简图ｃａ据文献１９２７修改ｂ据文献２８修改Ｆｉｇ１Ｓｉｍｐｌｉｆｉｅｄｔｅｃｔｏｎｉｃｍａｐｏｆｔｉｂｅｔｐｌａｔｅａｕａｓｉｍｐｌｉｆｉｅｄｍａｐｏｆｔｈｅｄｕｏｃａｉａｒｅａｂａｎｄｒｅｇｉｏｎａｌｍａｐｏｆｔｈｅｓａｍｐｌｉｎｇｌｏｃａｔｉｏｎｃ２岩体地质特征及样品描述辉绿岩样品手标本呈灰黑灰绿色图２ｂ后期蚀变较弱镜下呈辉绿结构图２ｃ辉绿辉本文研究的辉绿岩脉位于多彩地区龙墨沟以东区域采样位置经纬度坐标为Ｅ３３４８４８Ｎ９５０７长结构局部见嵌晶含长结构块状构造主要由斜长石 φｂ５０单斜辉石 φｂ３５黑云母 φｂ４１宏观上主要以岩脉形式呈ＮＷＳＥ向带状产出与区域构造线方向一致岩脉规模沿走向方向上变化稳定脉宽２１５ｍ延伸１００１０００ｍ不等１０及少量不透明矿物 φｂ５组成斜长石多为自形半自形板状可见聚片双晶发育粒径０１１ｍｍ部分发生绢云母化仅保留斜长石假象主要分布在上三叠统巴塘群火山岩灰岩组内图２ａ与围岩呈断层接触关系项目组测得围岩中英安图２ｄ单斜辉石多色性不明显少数可见两组岩年龄２２７Ｍａ谭俊等未发表数据本次定年样品Ｂ６０１９２采自新鲜露头的格架中构成典型辉绿结构个别单斜辉石晶体内含针板状斜长石嵌晶其粒径０１０５ｍｍ部分近正交解理多呈它形颗粒充填在斜长石晶体搭成

地质科技情报４６２０１８年Ｃｐｘ单斜辉石Ｐｌ斜长石Ｓｅｒ绢云母Ｃｈｌ绿泥石图２龙墨沟辉绿岩宏观照片及镜下照片Ｆｉｇ２Ｍａｃｒｏｓｃｏｐｉｃａｎｄｍｉｃｒｏｓｃｏｐｉｃｐｈｏｔｏｓｏｆｔｈｅｌｏｎｇｍｏｇｏｕｄｉａｂａｓｅｍｓ实验原理和详细的测试方法见文献３０分析数据通过即时分析软件ＧＬＩＴＴＥＲ计算获得同位

3 地质科技情报４６２０１８年Ｃｐｘ单斜辉石Ｐｌ斜长石Ｓｅｒ绢云母Ｃｈｌ绿泥石图２龙墨沟辉绿岩宏观照片及镜下照片Ｆｉｇ２Ｍａｃｒｏｓｃｏｐｉｃａｎｄｍｉｃｒｏｓｃｏｐｉｃｐｈｏｔｏｓｏｆｔｈｅｌｏｎｇｍｏｇｏｕｄｉａｂａｓｅｍｓ实验原理和详细的测试方法见文献３０分析数据通过即时分析软件ＧＬＩＴＴＥＲ计算获得同位发生绿泥石化蚀变３分析方法素比值年龄和误差分析结果通过ＩＳＯＰＬＯＴ软件版本４１５完成加权平均年龄计算和ＵＰｂ谐和图锆石挑选在河北省廊坊市区域地质矿产调查研究所实验室完成先经破碎浮选电磁选等方法清洗后手工挑出晶形透明度较好的单颗粒锆石将的绘制对年龄小于１０００Ｍａ的锆石采用２０６ＰｂＵ年龄表示而对年龄大于１０００Ｍａ的锆石则采用Ｐｂ２０６Ｐｂ年龄表示３１２３８２０７锆石固定于环氧树脂上制靶并抛光首先进行透射光反射光观察照相然后通过阴极发光显微照相观４分析结果察锆石内部结构锆石ＣＬ照相在北京锆年领航科技有限公司完成锆石ＵＰｂ同位素定年在南京大学内生金属矿床成矿机制研究国家重点实验室利用ＬＡＩＣＰＭＳ分析完成激光剥蚀系统为ＮｅｗＷａｖｅ公司产的ＵＰ２１３固体激光剥蚀系统激光束斑直径３０μｍＩＣＰＭＳ为Ａｇｉｌｅｎｔ７５００ａ型四级杆质谱仪采用Ｈｅ气作为载气质量分馏校正采用标样２０７ＧＥＭＯＣＧＪ１Ｐｂ２０６Ｐｂ年龄为６０８５±０４本次辉绿岩样品Ｂ６０１９２共进行１６个点的激光剥蚀ＵＰｂ同位素定年分析锆石ＣＬＵＰｂ同位素分析结果分别见图３及表１样品中锆石均呈无色透明浅黄色ＣＬ图像下样品中锆石可分为２种类型大部分锆石呈自形半自形板状没有或仅发育微弱的振荡环带如图３中４５１４等测点的锆石内部较均匀个别沿晶面包裹体发育在ＣＬ图每轮ＭａＰｂＵ年龄为５９９８±４５Ｍａ测试约分析１５个点开始和结束前分别分析ＧＪ１标样２４次中间分析未知样品１０１２次其中包像中颜色较暗表明Ｕ含量高锆石长度８０１２０ μｍ宽度４０μｍ长宽比接近３１整体符合基性岩括１次已知年龄的锆石样品ＭｕｄＴａｎｋ７３５Ｍａ仪器工作参数为波长２１３ｎｍ剥蚀孔径２５μｍ剥蚀时间６０ｓ背景测量时间４０ｓ激光脉冲重复频率龄ｗＵ为１２８１０６６６１１０６ｗＴｈ为６５１０６２７４２１０６ＴｈＵ比值为０５１２０６２３８３０ｃｍ２停留时间２０６Ｐｂ５Ｈｚ脉冲能量为１０２０Ｊ２０７２０８２３２２３８ＰｂＰｂＴｈＵ依次为１５３０１０１０１５锆石的典型特征３２可以代表基性岩脉形成的年６６５均大于０１显示岩浆结晶锆石特点３３所有数据点都位于谐和线上或附近图４ｂ无明显Ｐｂ２０６丢失Ｐｂ２３８Ｕ年龄变化在２５０±３２４５±３

4 3 : U-Pb 47 Ma (248.3±2.6) Ma 982 Ma 2440 Ma (MSWD=0.26),,,2,3, 1 Th/U 0.98,, 206 Pb/, -, 207 Pb/ 238 U 434 Ma, Liu [23] 206 Pb 1056,2513Ma( 4-a),,, [34], ; 1000 Ma 1000 Ma 207 Pb/ 206 Pb 206 Pb/ 238 U 3 (B6019-2) (CL) Fig.3 Cathodoluminescence(CL)imagesforzirconsoftheLongmogoudiabaseinDuocaiarea Fig.4 4 U-Pb U-PbconcordiadiagramforzirconsoftheLongmogoudiabaseinDuocaiarea - -, (248.3± - 2.6)Ma, -, [24,36],, - ( 268 Ma) (258~253 Ma) (236~ Ma) ( 213 Ma) [25-26,35], - [17,35,37] - -, [38],, (230~201 Ma) [3,39-41] 5

5 Th U w B / (B6019-2) LA-ICP-MSU-Pb Table1 LA-ICP-MSzirconU-PbdatingresultsoftheLongmogoudiabase(B6019-2)inDuocaiarea Th U-Th-Pb t/ma /U 207 Pb/ 206 Pb 1σ 207 Pb/ 235 U 1σ 206 Pb/ 238 U 1σ 207 Pb /206 Pb 1σ 207 Pb/ 235 U 1σ 206 Pb/ 238 U 1σ B B B B B B B B B B B B B B B B [12] -,Liu [23], - ((234±3)Ma), [42], E-MORB Nb Ta (282±3)Ma( ), -,Sr-Nd, Ce/Nb-Th/ Nb Al 2O 3-(TiO 2+Cr 2O 3 ) ( ), (BABB), (230~213 Ma) -, - [13-17],,, -, - -, -,,, -, - [43], - Zhai [4] - SHRIMP U-Pb 357~345 Ma,, - -, -,, Yang [36] - - (275~248 Ma), -, - [44] -,Liu 6 [24] ((258± 1)Ma) - (1) LA-ICP-MS, ((257±1) U-Pb (248.3± Ma), 2.6)Ma(MSWD=0.26), (245~ (2), 226 Ma), - -

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7 (3/4): rogenicbelt,southwestchina[j].geologicalsocietyofameri- [34],,,. [40]ChenJL,XuJF,RenJB,etal.Geochronologyandgeochemi- 4.0Ga [J].,2011,56(8): [36]YangT N,ZhangH R,LiuY X,etal.Permo-Triassicarcmag- try[j].chemicalgeology,2011,284(3): matismincentraltibet:evidencefromzircon U-Pbgeochro- nology,hfisotopes,rareearthelements,andbulkgeochemis- [37]YangT N,DingY,Zhang H R,etal.Two-phasesubduction andsubsequentcolisiondefinesthepaleotethyantectonicsof thesoutheasterntibetanplateau:evidencefromzircon U-Pb dating,geochemistry,andstructuralgeologyofthesanjiango- cabuletin,2014,126(11/12): [38],,,. basinsofthesouth Philippine Sea[J].Oceanologica Acta, : SHRIMP 1981,4: [J].,2005,50(2): [39]ReidA,WilsonCJL,ShunL,etal.Mesozoicplutonsofthe YidunArc,SW China:U/Pbgeochronologyand Hfisotopic signature[j].oregeologyreviews,2007,31(1/4): calcharacteristicsoflatetriassicporphyriticrocksfromthe matismandporphyrycoppermineralization[j].lithos,2011, 127(1/2): [42],,,. [J].,2009,23(6): [43]ScotRB,KroenkeL.Periodicityofremnantarcsandback-arc [44],,,. - Ar-Ar [J].,2007,26(6): ZirconU-PbGeochronologyandGeologicalImplicationsofthe LongmogouDiabaseinDuocaiArea,QinghaiProvince LiuXiaoyang 1,TanJun 1,WangFenglin 2,ZhaoShaoqing 3,WuYuan an 2,LiXiaoliang 2 (1.FacultyofEarthResources,ChinaUniversityofGeosciences(Wuhan),Wuhan430074,China; 2.QinghaiInstituteofGeologyforMineralResources,Xining810007,China; 3.SchoolofEarthSciences,YangtzeUniversity,Wuhan430100,China) [35]. - Zhongdianarc,eastern Tibet,andtheirtectonicand metalo- [D]. : ( ),2014. genicimplications[j].gondwana Research,2014,26(2): [41] WangB Q,Zhou M F,LiJ W,etal.LateTriassicporphyritic intrusionsandassociatedvolcanicrocksfrom theshangri-la region,yidunterrane,easterntibetanplateau:adakiticmag- Abstract:TheDuocaiareaislocatedinthenortheastern marginoftheqiangtangterrane.inthisarea, PermiantoTriassicmagmaticrocksarewidespreadbecauseofthesubductionofPalaeo-Tethyanoceansand thefinalclosure.wetakethelongmogoudiabaseastheresearchobject,anddetailstheresearchesonits zirconu-pbgeochronology.theresultshowsthatthediabasehascrystalineageof(248.3±2.6)maand thusconstrainsitsformationtimetotheearlytriassic.cosideringpreviouslypublisheddata,wesuggest thatthelongmogoudiabasemighthaveformedinacontinentalback-arcspreadingenvironmentoflong- mucuo-shuanghuoceansubduction. Keywords:zircon U-Pbgeochronology;diabase;Longmucuo-Shuanghu Ocean;Duocaiarea;QinghaiProv- ince

Q. ;J. ;C-P. - ; -O. - ;Qb. ;Ar. ; ;γδ5. Q2m. ;C2-P1t. ;P1-2s. ;P2y. ;1. ;2. 1 [25] (a) (b) - (c)(a [10] ;b [7] ) Fig.1 Schematicgeologicalmap

Q. ;J. ;C-P. - ; -O. - ;Qb. ;Ar. ; ;γδ5. Q2m. ;C2-P1t. ;P1-2s. ;P2y. ;1. ;2. 1 [25] (a) (b) - (c)(a [10] ;b [7] ) Fig.1 Schematicgeologicalmap 36 4 2017 7 GeologicalScienceandTechnologyInformation Vol.36 No.4 Jul. 2017 doi:10.19509/j.cnki.dzkq.2017.0404. : [J]. 201736(4):29-35. : ab b ab ( )a. ;b. 430074) : : 330~300 Ma 310 Ma U-Pb 330~300 Ma