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1、第25卷第1期岩石矿物学杂志Vol.25,No.12006年1月ACTAPETROLOGICAETMINERALOGICAJan.,2006内蒙古集宁新生代玄武岩中橄榄岩包体和巨晶的发现及意义杜蔚,韩宝福,张文慧,刘志强(北京大学造山带与地壳演化教育部重点实验室地球与空间科学学院,北京100871)摘要:内蒙古集宁新生代玄武岩产于华北克拉通北缘,属于广义的汉诺坝玄武岩。首次在三义堂附近的碱性玄武岩中发现了大量的橄榄岩包体、辉石和长石以及少量的含钛磁铁矿巨晶。包体主要是尖晶石二辉橄榄岩,造岩矿物为橄榄石+斜方辉石+单斜辉石+
2、尖晶石,辉石巨晶主要为透辉石和普通辉石,长石巨晶主要是歪长石和少量斜长石。1.5GPa条件下,尖晶石二辉橄榄岩样品所记录的平衡温度与汉诺坝相近,集中于950!左右,大体上反映了华北克拉通北缘大陆岩石圈地幔尖晶石相部分的温度状态。单斜辉石巨晶的结晶温压大于幔源包体的平衡温压,表明巨晶的来源深度可能大于包体。包体的结构及矿物成分分析表明,这些包体是玄武质岩浆上升过程中偶然捕#获岩石圈地幔的岩石碎块。二辉橄榄岩包体中橄榄石高Mg值(89.5~91.7)和较高的NiO含量(0.29%~0.55%),暗示集宁玄武岩中的橄榄岩包体来自较高熔融程度的岩石圈地幔。关键词:新
3、生代玄武岩;橄榄岩包体;巨晶;岩石圈地幔;集宁+中图分类号:P588.145文献标识码:A文章编号:1000-6524(2006)01-0013-12ThediscoveryofperidotitexenolithsandmegacrystsinJining,InnerMongoliaDUWei,HANBao_fu,ZHANGWen_huiandLIUZhi_qiang(KeyLaboratoryofOrogenicBeltsandCrustalEvolution,SchoolofEarthandSpaceSciences,Pekin
4、gUniversity,Beijing100871,China)Abstract:LocatedinInnerMongolia,thenorthernedgeoftheNorthChinacraton,JiningCenozoicbasaltsbelongtothegeneralized∀HannuobaBasalts".Alotofperidotitexenolithsaswellassomepyroxene,feldsparandtitanomagnetitemegacrystswerediscoveredforthefirsttimeinthealk
5、alibasaltsoutheastofSanyitang.Mostofthesexenolithsarespinellherzoliteswiththeassemblageofolivine+orthopyroxene+clinopyroxene+spinel.Thepyroxenemegacrystsaremostlydiopsideandaugiteincomposition.Feldsparmegacrystsaremainlyanorthoclaseandminorplagioclase.Theequilibriumtemperaturerepre
6、sentedbythesespinellherzolitexenolithsisabout950!at1.5GPa,whichisalmostthesameasthatoftheHannuobaxenolithsandreflectsthetemperatureofspinelphaseinthelithosphericmantlebeneaththenorthernedgeoftheNorthChinacraton.Thecrystallizationtemperatureandpressureofclinopyroxenemegacrystsareh
7、igherthanthoseoflherzolitexenoliths,implyinganorigindeeperthanthatoftheperidotitexenoliths.Petrographyandmineralchemistryofthesexenolithsindicatethattheyarefragmentsoftheuppermantlecapturedbybasalticmagmasalongtheascendingway.#ThehighMg(89.5~91.7)andhighNiO(0.29%~0.55%)contentsof
8、olivinesdemonstratethatJin
