中蒙边界英巴地区元古宙杂岩的时代及其对南戈壁微陆块分布范围的限定
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摘要
中亚造山带可能存在具有前寒武纪基底的微陆块。中国境内亚干地区新元古代片麻状花岗岩的存在可能表明南戈壁微陆块延伸到了中国境内,但南戈壁微陆块在中国境内的分布范围还不能准确限定。在内蒙古西部靠近中蒙边界的英巴地区可能存在元古宙变质杂岩,岩性主要有片麻岩、石英岩、云母石英片岩和碳酸盐岩等。其中产出在岩体内部的一个花岗质片麻岩岩块主要由斜长石、石英和黑云母组成,LA-ICP-MS锆石U-Th-Pb定年给出复杂的年龄结果,岩浆成因的锆石核的年龄分散,207Pb/206Pb年龄在2.5-1.0Ga之间,暗色锆石幔给出的206Pb/238U加权平均年龄为417.2Ma±3.5Ma,可能代表早古生代晚期一次构造热事件。花岗岩体内另外一处片麻岩岩块主要由斜长石、黑云母和石英组成,206Pb/238U加权平均年龄为905.2Ma±6.1Ma,与亚干新元古代片麻状花岗岩的时代非常接近。并且,亚干和英巴地区元古代杂岩具有相似的岩石组合。表明南戈壁微陆块向南至少延伸到中国境内的亚干—英巴一带,显生宙强烈的构造-岩浆活动对微陆块产生了重要的改造或破坏,造成了目前不连续出露的状况。
Micro-continents with Precambrian basement are developed in the Central Asian orogenic belt.In southern Mongolia,the Toto Shan and South Gobi miro-continents are characterized by Neoproterozoic magmatism.The South Gobi micro-continent might extend into China,as evidenced by the discovery of Neoproterozoic granitoid in Yagan area.However,the distribution of the South Gobi micro-continent is not well constrained in China.Regional geological data reveal that there are some Proterozoic rocks in Yingba area of western Inner Mongolia.They are regarded as the relict blocks in and around the Yingba granitoid pluton and are mainly composed of gneiss,quartzite,mica and quartz schist and carbonate.In a Proterozoic block,the felsic gneiss composed of plagioclase,quartz and biotite gave complex U-Pb age results from the LA-ICP-MS zircon dating.The zircon cores with the igneous origin provided a wide range of207Pb/206Pb ages from 2.5Ga to 1.0Ga,while the igneous zircon mantles generated a weighted mean206Pb/238U age of 417.2Ma±3.5Ma,indicating an early Paleozoic tectonic event.In another block,the gneiss is crosscut by leucogranite veins,one of which gave a weighted mean206Pb/238U age of 905.2Ma±6.1Ma.The age is close to the emplacement time(916Ma±16Ma) of Neoproterozoic gneissic granite pluton in Yagan.Therefore,the South Gobi micro-continent extended southward at least to the YaganYingba area in China and were strongly modified and destroyed by the Phanerozoic tectonic-igneous activities.
Micro-continents with Precambrian basement are developed in the Central Asian orogenic belt.In southern Mongolia,the Toto Shan and South Gobi miro-continents are characterized by Neoproterozoic magmatism.The South Gobi micro-continent might extend into China,as evidenced by the discovery of Neoproterozoic granitoid in Yagan area.However,the distribution of the South Gobi micro-continent is not well constrained in China.Regional geological data reveal that there are some Proterozoic rocks in Yingba area of western Inner Mongolia.They are regarded as the relict blocks in and around the Yingba granitoid pluton and are mainly composed of gneiss,quartzite,mica and quartz schist and carbonate.In a Proterozoic block,the felsic gneiss composed of plagioclase,quartz and biotite gave complex U-Pb age results from the LA-ICP-MS zircon dating.The zircon cores with the igneous origin provided a wide range of207Pb/206Pb ages from 2.5Ga to 1.0Ga,while the igneous zircon mantles generated a weighted mean206Pb/238U age of 417.2Ma±3.5Ma,indicating an early Paleozoic tectonic event.In another block,the gneiss is crosscut by leucogranite veins,one of which gave a weighted mean206Pb/238U age of 905.2Ma±6.1Ma.The age is close to the emplacement time(916Ma±16Ma) of Neoproterozoic gneissic granite pluton in Yagan.Therefore,the South Gobi micro-continent extended southward at least to the YaganYingba area in China and were strongly modified and destroyed by the Phanerozoic tectonic-igneous activities.
引文
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[26]Helo C,Hegner E,Kroner A,et al.Geochemical signature of Pale-ozoic accretionary complexes of the Central Asian Orogenic Belt inSouth Mongolia:Constraints on arc environments and crustalgrowth[J].Chemical Geology,2006,227:236-257.
[2]Sengor A M C,Natal’in B A.Paleotectonics of Asia:fragments of asynthesis[C]//Yin A,et al.(Eds.).The Tectonic Evolution of Asia.Cambridge University Press,Cambridge,1996:486-640.
[3]Yakubchuk A,Cole A,Seltmann R,et al.Tectonic Setting,Charac-teristics,and Regional Exploration Criteria for Gold Mineralization inthe Altaid Tectonic Collage:The Tien Shan Province as a Key Ex-ample[J].Society of Economic Geologists,2002,(9):177-201.
[4]Windley B P,Alexeiev D V,Xiao W,et al.Tectonic models for ac-cretion of the Central Asian Orogenic Belt[J].J.Geol.Soc.Lond.2007,164:31-47.
[5]Yarmolyuk V V,Kovalendo E B,et al.U–Pb age of syn-andpost-metamorphic granitoids of South Mongolia:evidence for thepresence of Grenvillides in the Central Asian foldbelt[J].Doklady EarthSciences,2005,404:986–990.
[6]Yarmolyuk V V,Kovach V P,Kovalendo E B,et al.Isotopic Com-position of the Hercynian Crust of Southern Mongolia:Substantiationof the Hercynian Juvenile Crust-Forming Event[J].Doklady EarthSciences,2007,417:1178–1182.
[7]Yanshin A L.Map of geological formation of the Mongolian People’sRepublic:Moscow[M].Academica Nauka USSR,2 sheets,scale1:1.500.000.1989.
[8]Tomurtogoo O.Geological Map of Mongolia,Map Scale 1:1000000General Directorate of Mineral Research and Exploration[M].Ankara,Turkey,1999.
[9]Badarch G,Cunningham W D,Windley B F.A new terrane subdi-vision for Mongolia:implications for the Phanerozoic crustal growthof Central Asia[J].Journal of Asian Earth Sciences,2002,21:87-110.
[10]Graham S A,Hendrix M S,Johnson C L,et al.Sedimentary recordand tectonic implications of Mesozoic rifting in southeast Mongolia[J].Geological Society of America Bulletin,2001,113:1560-1579.
[11]Blight J H S,Petterson M G,Crowley Q G,et al.The Oyut UlaanVolcanic Group:Stratigraphy,magmatic evolution and timing ofCarboniferous arc development in southeast Mongolia[J].Journal ofthe Geological Society,London,2010,167:491-509.
[12]Wang T,Zheng Y,Gehrels G E,et al.Geochronologic evidence forthe existence of micro-continent in the southern Mongolia:zirconU-Pb age of granitic gneiss from the Yagan Onch Hayrhan meta-morphic core complex[J].Chin.Sci.Bull.,2001,46:1220-1223.
[13]Demoux A,Kroner A,Hegner E,et al.Devonian arc-related mag-matism in the Tseel terrane of SW Mongolia:chronological andgeoche mical evidence[J].Journal of the Geological Society,London,2009,166:459-471.
[14]Wang T,Zheng Y,Li T,et al.Mesozoic granitic magmatism in ex-tensional tectonics near the Mongolian border in China and its im-plications for crustal growth[J].Journal of Asian Earth Sciences,2004,23:715-729.
[15]Wang T,Zheng Y,Zhang J,et al.Pattern and kinematic polarity oflate Mesozoic extension in continental NE Asia:Perspectives frommetamorphic core complexes[J].Tectonics,2011,30,TC6007,doi:10.1029/2011TC002896.
[16]沈其韩,耿元生,王新社,等.阿拉善地区前寒武纪斜长角闪岩的岩石学、地球化学、形成环境和年代学[J].岩石矿物学杂志,2005,24(1):21-31.
[17]耿元生,周喜文.阿拉善地区新元古代岩浆事件及其地质意义[J].岩石矿物学杂志,2010,29(6):779-795.
[18]内蒙古自治区地质矿产局.内蒙古自治区区域地质志[M].北京:地质出版社,1991:725.
[19]Zhou Y,Han B,Zhang B,et al.The Yingba shear zone on theSino-Mongolian border:Southwestern extension of the ZuunbayanFault from Mongolia to China and implications for Late Mesozoicintracontinental extension in Eastern Asia[J].Tectonophysics,2012,(574/575):118-132.
[20]付国斌,李罡,任玉光,等.内蒙古呼伦陶勒盖下白垩统巴音戈壁组的叶肢介化石[J].古生物学报,2007,46(2):244-248.
[21]韩宝福,张臣,赵磊,等.内蒙古西部呼伦陶勒盖地区花岗岩类的初步研究岩[J].岩石矿物学杂志,2010,29(6):741-749.
[22]Andersen T.Correction of common lead in U–Pb analyses that donot report 204Pb[J].Chemical Geology,2003,192:59-79.
[23]Ludwig K R.Isoplot 3.0-A geochronological toolkit for MicrosoftExcel[J].Special publication No.4.Berkeley Geochronology Cen-ter,Berkeley,Calif.,2003:71.
[24]Corfu F,Hanchar J M,Hoskin P W O,et al.Atlas of Zircon Textures[J].Reviews in Mineralogy and Geochemistry,2003,53:469-500.
[25]Zhang J,Santosh M,Wang X,et al.Tectonics of the northern Hi-malaya since the India-Asia collision[J].Gondwana Research,2012,21:939-960.
[26]Helo C,Hegner E,Kroner A,et al.Geochemical signature of Pale-ozoic accretionary complexes of the Central Asian Orogenic Belt inSouth Mongolia:Constraints on arc environments and crustalgrowth[J].Chemical Geology,2006,227:236-257.