内蒙狼山北部古元古代变质花岗岩地球化学特征、锆石U-Pb年代学——哥伦比亚超大陆裂解事件的岩浆记录  

Geochemical characteristics and zircon U-Pb geochronology of Paleoproterozoic metamorphic granites from northern Langshan,Inner Mongolia: Magmatic response to the breakup of Columbia supercontinent

作　　者：孙立新 张云 胡晓佳 任邦方 王树庆 张天福 SUN LiXin;ZHANG Yun;HU XiaoJia;REN BangFang;WANG ShuQing;ZHANG TianFu(Tianjin Centre,China Geological Survey,Tianjin 300170,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170

出　　处：《岩石学报》2018年第10期3116-3136,共21页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41572172);中国地质调查局地质调查项目(121201006000172007)联合资助

摘　　要：内蒙狼山宝音图地区前寒武纪地质体由古元古代宝音图群、片麻状花岗岩、混合岩和斜长角闪岩等组成。锆石LA-MC-ICP-Ms U-Pb测年获得了宝音图变质花岗岩的形成年龄为1644±11Ma^1710±20Ma。岩石学、地球化学研究表明片麻状钠长花岗岩具有高Si O_2(77.08%~79.96%)、高碱(K_2O+Na_2O)(4.46%~7.26%),低Ti O_2(0.088%~0.17%)、MgO(0.036%~0.37%)、Ca O(0.17%~1.19%)及中等Al_2O_3含量(12.12%~14.10%);Na_2O>>K_2O,A/CNK为0.88~1.09<1.1,属弱铝质;里特曼指数б=0.54~1.55<1.8,表明属于钙质系列;10000Ga/Al=3.43~12.46(均值为5.18>2.6)及较高的含铁指数[Fe O/(Fe O+MgO)=0.57~0.94],显示了低钾钙性A型花岗岩的特点。片麻状二长花岗岩具有高Si O_2(73.65%~77.63%),低Ti O_2(0.11%~0.27%)、MgO(0.25%~0.80%)、Al_2O_3(11.68%~12.72%)、Ca O(0.24%~0.99%)含量,基本与片麻状钠长花岗岩相近;同时具有高碱(K_2O+Na_2O)含量(6.84%~9.31%),低的Na_2O/K_2O比值(0.53~1.62),钾含量明显高于与片麻状钠长花岗岩;A/NCK为0.96~1.86,б=2.06~2.80<1.8~3.3为钙碱性系列,显示高钾钙碱性A型花岗岩的特点。两类片麻状花岗岩均具有稀土总量较高,轻稀土富集而重稀土亏损的特征,具有明显Eu的负异常;构造判别图解均指示为陆内非造山型A型花岗岩。全岩同位素分析表明具有弱富集-亏损的同位素组成,其中ε_(Nd)(t)为小的负值到小的正值(-4.91^+2.41),两阶段Nd模式年龄t_(DM2)为1.95~2.58Ga;锆石ε_(Hf)(t)均为正值(+1.5^+8.0),两阶段Hf模式年龄t_(DM2)(1.73~2.31Ga),Nd-Hf模式年龄均高于其形成年龄,揭示源自古元古代新生下部陆壳物质的部分熔融,并有少量幔源物质的加入。与华北北缘、欧美大陆的古元古代非造山作用形成的岩浆岩相似,宝音图变质花岗岩时代上与哥伦比亚超大陆的裂解事件(1.7~1.6Ga)具有一致性,可能是全球哥伦比亚超大陆裂解事件的构造岩浆响应。The Precambrian Ba0yintu terrain in Langshan,Inner Mongolia,is composed of the Paleoproterozoic Baoyintu Group,gneissic granites,migmatite and amphibolite.LA-MC-ICP-MS zircon U-Pb dating of the Baoyingtu metamorphic granites give ages from1644±11Ma to 1710±20Ma.Petrological and geochemical studies of albite granites show that they have contents of high Si O2（77.08%-79.96%）and alkali（K2O＋Na2O）（4.46%-7.26%）with ratios of Na2O/K2O1,moderate Al2O3（12.12%-14.10%）,low Ti O2（0.088%-0.17%）,MgO（0.036%-0.37%）and Ca O（0.17%-1.19%）,indicating that they belong to calcium（Ritman indexδ=0.54-1.551.8）and metaluminum series（A/NCK=0.88-1.091.1）.High 10000Ga/Al（3.43-12.46,averaged at 5.182.6）and iron content index（Fe O/（Fe O＋MgO）=0.57-0.94）further suggest that they are lowpotassium calcium A-type granite.The gneissic monzonite show high Si O2（73.65%-77.63%）and alkali（K2O＋Na2O）（6.84%-9.31%）,low Ti O2（0.11%-0.27%）,MgO（0.25%-0.80%）and Ca O（0.24%-0.99%）contents,which is similar with those of gneissic albite granites except that they have a lower Na2O/K2O ratio（0.53-1.62）and a higher metaluminous-strong peraluminous index（A/CNK range from 0.96 to 1.86）and calc-alkaline features（δ=2.06-2.801.8-3.3）,showing characteristics of highpotassium calc-alkaline A-type granite.All granites are characterized by high total REE,enrichment of LREE and depletion of HREE,with obvious negative Eu anomaly.Discriminant diagrams suggest that these gneissic granites are intracontinental non-orogenic A-type granites.Whole rock isotopic analysis show slight negative to positiveε（Nd）（t）（-4.91-＋2.41）and positive zirconε（Hf）（t）（＋1.5-＋8.0）,with Paleoproterozoic t（2DM）（Nd）（1.95-2.58Ga）,and t（2DM）（Hf）（1.73-2.31Ga）,which is older than the formation age,indicating they are sourced from the Paleoproterozoic lower continental crustal materials together with small amounts of mantle materials.Compared with the non-orogenic P

关 键 词：古元古代 A-型花岗岩 哥伦比亚超大陆裂解事件 内蒙古狼山地区 

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