内蒙古白云鄂博北部宝音图岩群变质基性火山岩的年龄、构造背景及地质意义  

Ages, tectonic environment and geological significance ofmetabasic volcanic rocks of the Buyant Group-complexin the north of Bayan Obo, Inner Mongolia

作　　者：张玉清[1] 

机构地区：[1]内蒙古自治区地质调查院,内蒙古呼和浩特010020

出　　处：《地质通报》2004年第2期177-183,共7页Geological Bulletin of China

基　　金：中国地质调查局1:25万区域地质调查项目K49C003002(白云鄂博幅)项目编号20001300008051

摘　　要：内蒙古白云鄂博北宝音图岩群变质基性火山岩是白云鄂博幅(1∶25万)区域地质调查时从过去的华力西晚期斜长角闪岩(Ψo43-1)和布龙山组(O1-2b)中解体出来的一个地层单位。通过岩石化学、稀土元素、微量元素分析,确定该岩群的原岩为钙碱性玄武岩。同位素年代测试显示,透辉角闪斜长变粒岩单颗粒锆石U-Pb测年获得的不一致线上交点年龄为(2525±41)Ma代表了基性火山岩即宝音图岩群的形成时代不一致线下交点年龄(460±37)Ma代表了奥陶纪岩浆侵位及宝音图岩群的变质改造年龄。结合其他地质证据,认为散布于内蒙古北部的宝音图岩群可能是古元古代华北克拉通北缘裂解的证据。Metabasic volcanic rocks of the Buyant Group-complex in the north of Bayan Obo, Inner Mongolia, is a stratigraphic unit which was disintegrated from the original late Variscan amphibolite(Ψo43-1) and Bulongshan Formation (O1-2b) during the regional geological survey of the 1∶250000 Bayan Obo Sheet. By the petrological, REE and trace element analyses, this group-complex has been determined to be calc-alkaline basalt. Single-zircon U-Pb dating of diopside-hornblende-plagioclase leptynite yielded an upper intercept age of 2525 Ma±41 Ma and an lower intercept age of 460 Ma±37 Ma, which represent the age of basic volcanic rocks, i.e. the Buyant Group-complex, and the age of emplacement of the Ordovician magma and modification of the Buyant Group-complex, respectively. These ages, coupled with other geological evidence, suggest that the Buyant Group-complex distributed in northern Inner Mongolia might be the evidence of breakup of the northern margin of the Paleoproterozoic North China craton.

关 键 词：宝音图岩群 岩石地球化学 锆石U-PB年龄 内蒙古白云鄂博 

分 类 号：P534.3[天文地球—古生物学与地层学] P588.145[天文地球—地质学]