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1、第42卷第4期Vol.42,No.4,361~3722013年7月GEOCHIMICAJuly,2013西准噶尔白杨河地区早二叠世闪长岩的年代学和地球化学:岩石成因和构造意义1,2*1222尹继元,陈文,龙晓平,袁超,张运迎,22王毓婧,关义立(1.中国地质科学院地质研究所大陆构造与动力学国家重点实验室同位素热年代学实验室,北京100037;2.中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640)摘要:西准噶尔白杨河地区的莫合台西北岩体是一个以闪长岩为主的小岩体。该闪长岩由斜长石(65%~7
2、0%)、角闪石(10%~15%)和辉石(10%~15%)组构,其全岩SiO2含量在55.1%~57.0%之间。该闪长岩富集大离子亲石元素(LILE)(如Ba、K、Rb和U)和轻稀土元素(LREE),相对亏损Nb、Ta、Ti等高强场元素,显示了与俯冲带相关的岩浆特征。这些闪长岩可能是由俯冲的板片流体/沉积物交代的地幔楔部分熔融而成。全岩Ar-Ar测年获得了(283±3)Ma的坪年龄,显示其形成于早二叠世,在321Ma,西准噶尔地区开始洋脊俯冲活动,其至少持续到292Ma;在283Ma时,西准噶尔处于正常的俯冲体系或后碰撞
3、环境。关键词:闪长岩;Ar-Ar年代学;早二叠世;地球化学;西准噶尔中图分类号:P59;P597;P58文献标识码:A文章编号:0379-1726(2013)04-0361-12AgeandgeochemicalcharacteristicsofEarlyPermiandioriteintheBaiyangheregion,WestJunggar:Petrogenesisandtectonicimplication1,2*1222YINJi-yuan,CHENWen,LONGXiao-ping,YUANChao,ZHA
4、NGYun-ying,22WANGYu-jingandGUANYi-li1.LaboratoryofIsotopeThermochronology,StateKeyLaboratoryofContinentalTectonicsandDynamics,InstituteofGeology,ChineseAcademyofGeologicalSciences,Beijing100037,China;2.StateKeyLaboratoryofIsotopeGeochemistry,GuangzhouInstituteof
5、Geochemistry,ChineseAcademyofSciences,Guangzhou510640,ChinaAbstract:Ar-ArdatingonMohetaixibeidioriticrockchipsfromBaiyangheregion,westernJunggar,hasyieldedaplateauageof(283±3)Ma,i.e.,EarlyPermian.Thedioritemainlycontainsplagioclase(60%–65%),pyroxene(10%–15%)andh
6、ornblende(15%~20%).TheSiO2contentsvarybetween55.1%–57.0%suggestingthattheyaredioriteratherthangabbroordoleriteasmarkedinthegeologicalmap(1∶200000)ofBaiyanghe,Xinjiang.Thedioritesarecharacterizedbyenrichmentsinlargeionlithophileelements(LILE)(e.g.,Ba,K,RbandU)and
7、lightrareearthelements(LREE)anddepletionsinhighfieldstrengthelements(HFSE)(e.g.,Nb,TaandTi),whichareconsistentwithgeochemicalcharacteristicsofsubduction-relatedmagmas.Thedioritescanbegeneratedbypartialmeltingofthemantlewedgemetasomatizedbyslabreleasedfluid/sedim
8、entmelts.HightemperaturemagmatismintheWestJunggarlikelybeganat321Ma.Therefore,ridgesubductioninthewesternJunggarlikelyoccurredbetween321–292Ma.At283Ma,thewesternJungg
