【作者】 杨奇荻；

【导师】 王涛；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2014， 博士

【摘要】 了解深部物质组成特片和结构是探索地壳深部地质过程和地壳演化基本理论的关键所在,这已经成为当前地学研究的前沿课题。作为大陆地壳重要组成部分的花岗质岩石,在揭示大陆岩石圈结构与反演地球深部演化过程中一直扮演着重要的角色。因此,常用花岗质岩石同位素示踪技术探测地壳深部物质组成,探讨地壳生长,为寻找深部资源提供依据。本文选择中亚造山带东段及与华北克拉通接壤地带,开展花岗质岩石同位素填图,试图揭示花岗质岩石物源时空变化特征,了解该区深部物质组成结构特征,探讨地壳生长及其成矿制约。本文在785个侵入岩(含少量基性侵入岩)U-Pb锆石年龄收集和11件花岗岩类锆石U-Pb年龄实测基础上,初步确定了大兴安岭及邻区显生宙花岗岩的时空演化框架。以此为基础,系统开展了花岗质侵入岩的Nd同位素研究,依据46套实测和675套收集的Nd同位素数据,编制研究区Nd同位素图,圈定了同位素省,揭示了花岗岩的Nd同位组成和演化特征,探讨了地壳深部物质组成结构及地壳生长。在此基础上,进一步探讨了深部地壳结构对岩浆型金属矿产的制约。论文取得以下主要成果：1.初步厘定了大兴安岭及邻区花岗质侵入岩时空分布特征。依据796个锆石年龄,大兴安岭及邻区花岗质侵入岩可以划分为早古生代(517～353Ma)、晚古生代(347～251Ma)、早中生代(250～146Ma)、晚中生代(145～106Ma)四期。其中,早古生代花岗岩主要分布于二连-锡林浩特-乌兰浩特构造带和阴山-燕山构造带,其次为额尔古纳地块周缘。晚古生代花岗岩大多数位于阴山-燕山构造带,少量分布十大兴安岭的北部和额尔古纳地块周缘。早中生代全区皆有分布,早中三叠世花岗岩主要在阴山-燕山构造带,晚三叠-早侏罗世花岗岩主要位于额尔古纳地块。晚中生代花岗岩全区皆发育,其中中晚侏罗世花岗岩主要出露于额尔古纳地块,白垩纪花岗岩大部分出露于大兴安岭地区。2、通过显生宙花岗岩Nd同位素填图,确定了Nd模式年龄同位素省。研究区可以划分为4个同位素省(区)：(1)高正εNd(t)值(多数+3～+8)及年轻模式年龄区(TDM=0.8～0.3Ga),位于二连-贺根山-嫩江-黑河地区及德尔布干断裂带；(2)较高εNd(t)值(多数-1～+3)及较年轻模式年龄区(TDM=1.1～0.8Ga),主要位于中亚造山带,蒙古的大部分地区,俄罗斯部分地区,大兴安岭部分地区；(3)较低εNd(t)值(多数-9～-1)及较老模式年龄区(TDM=1.6～1.1Ga),主要位于锡林浩特微陆块的四周和华北北缘南侧；(4)极低εNd(t)值(多数-23～-9)及老模式年龄区(TDM=3.2～1.6Ga),主要位于华北克拉通北缘、额尔古纳地块、大兴安岭北段、锡林浩特地区、东乌旗地区。3、同位素填图及同位素省确定对研究区深部地壳组成结构特征及构造单元划分提供新依据。高正εNd(t)值(+3～+8)及年轻模式年龄区(TDM=0.8～0.3Ga)带揭示,二连-贺根山-嫩江-黑河地区年轻地壳及幔源物质活动强烈地带,是一条重要的构造边界,可以作为划分大的构造单元的界线。较高εNd(t)值(-1～+3)及及较年轻模式年龄区(TDM=1.1～0.8Ga),位于内蒙古的大部分地区,俄罗斯远东部分地区,大兴安岭部分地区,为较年轻地壳生长区。较低εNd(t)值(-9～-1)及较老模式年龄区(TDM=1.6～1.1Ga)揭示,中蒙占、锡林浩特、华北北缘等地区可能存在古老基底物质被改造的残迹。极低εNd(t)值(-23～-6.3)及老模式年龄区(TDM=3.2～1.6Ga)与华北克拉通古老基底范围完全重合；另外,也显示,在额尔古纳地区、大兴安岭北段、锡林浩特、东乌旗地区可能存在古老基底或微陆块。这揭示,中亚造山带东段比西段可能具有较多的古老微陆块。4、依据同位素填图及同位素省的圈定,确定了研究区陆壳生长的空间范围和相对生长量。上述高εNd(t)值带为显著的陆壳生长区,最显著的生长区发育在线性缝合带。通过同位素省推测的年轻地壳分布区域和范围,特别是与古老地壳分布区面积的比例,大致估算了生长量。较年轻陆壳(TDM=1.1～0.8Ga)所占研究区面积比例为50%,以古老物质循环为主的陆壳(TDM=3.2～1.1Ga)和以幔源物质加入为主的新生陆壳(TDM=0.8～0.3Ga)面积比例各占35%和15%,表明在研究区新元古代-显生宙(TDM=1.1～0.3Ga)地壳生长区面积比例应在65%左右。5、初步探讨了同位素省与成矿的关系。同位素填图揭示的大兴安岭及其邻区深部地壳物质组成结构对不同矿种的分布特征有明显制约关系：铜矿分布于年轻地壳生长区；钨锡、铅锌、铀矿分布于古老陆块区域；钼、金矿分布于壳幔混合区域,但相对倾向于古老陆块区。该研究显示,利用花岗质岩体同位素填图,可以直观显示花岗质岩石物源变化特征,揭示深部地壳组成结构,为划分大地构造单元和了解构造单元属性以及探讨地壳生长提供依据,也可以为认识矿产分布规律提供新的信息。更多还原

【Abstract】 Understanding of the deep composition and structure is a key to study geological processes in deep crust and establish fundamental theory of crust evolution, and has become an important front. Granitoids, as an important part of the continental crust, play an important role in revealing the structure of the lithosphere and the evolution in deep earth. Therefore, the isotope-tracer technique of granitoids is often used to invastigate the composition of deep crus, the crustal growth, and deep mines. This paper, taking the Da Hinggan Moutains and Adjacent Areas as the studied area, carryies out the isotope mapping to approach to the deep composition and structure in the study area, and discusses the relationship between crustal growth and mineralization.In this dissertation, the author has established the temporal and spatial evolution framework of Phanerozoic granitoids in the Da Hinggan Moutains and its adjacent area based on the785published and11newly acquired U-Pb Zircon dating of the granitoids. Then, accoring to675published and46newly acquired Sm-Nd isotopci data of the granitoids, Nd isotopic mapping is made and the isotopic Provinces are determined. These clearly show the composition and evolution of the Nd isotopic characteristics of the study granitoids, reveal the structural compositions of the deep crustal and the models of crustal growth. T the constraints that the deep crustal structure puts on metal deposits is also discussed. Following are the research findings and innovations.First, based on the above datas, the granitoids in this study area are devided into four groups: early Paleozoic (517～353Ma), Late Paleozoic (347-51Ma), early Mesozoic (250～146Ma), and late Mesozoic (145～106Ma). Early Paleozoic granitoid are mainly located in Erlian-xilin-Wulanhaote and Yinshan-yanshan tectonic zone, next for Eerguna tectonic zone. Late Paleozoic granite are mainly located in Yinshan-yanshan tectonic zone, next for the northern of Da Hinggan Moutains. Early Mesozoic granitoid are located in the whole district. The early Triassic granite exposed in the Yinshan-yanshan tectonic zone. The late Triassic and early Jurassic granite are located in Eerguna tectonic zone. Middle-late Jurassic granite are located in Eerguna and the cretaceous granites are in the Da Hinggan Moutains.Second, the Nd isotopic maps of Phanerozoic granitoids show that the study area can be divided into4Isotopic Provinces.(1) The Province with the highest εNd(t)values (+3～+8) and the youngest Nd model ages (TDM=0.8～0.3Ga), that is located in the Erlian-Hegenshan-Heihe area and Derbugan fault.(2) The Province with higher εNd(t) values (-1～+3) and younger TDM ages (TDM=1.1-0.8Ga), which is mainly distributed in the Central Asian, most areas of Mongolia, parts of Russia, and parts of the Great Khingan Mountains.(3) The Province with lower εNd(t) values (-9～1) and older TDM ages (TDM=16～1.1Ga), that is mainly in the periphery of Xilinhot micro-continental and northern margin of North China.(4) The Province with the lowest εNd(t) values (majority,-23～-6.3) and the oldest TDM ages (TDM=3.2～1.6Ga), which is distributed in the northern margin of North China craton, the Ergun block, the northern of Da Hinggan Moutains, the Xilinhot micro-continental, and the Dongwuqi area.Third, the highest εNd (t) value belt reveals that the southern border of CAOB is in Erlian-Ganzhuermiao-Wulanhaote region. The Erlian-hegengshan-nenjiang-heihe zone is the important tectonic boundary as a juvenile crust and strong mantle source activity region. High εNd(t)value (-1～+3) and young model age regions(TDM=1.1～0.8Ga). located in most of southeast of Mongolia, parts of Russian Far East and Da Hinggan Moutains area, are young crustal growth regions., In lower εNd(t) value (-9～-1) and old model age region (TDM=1.6～1.1Ga), such as the center of Mongolia, Xilinhaote and northern of North China craton region, the remnant of transformed old basemen might exist. Furthermore, there are old basements or micro continental massif in Erguna. northern of Da Hinggan Moutains, Xilinhaote and Dong Ujimqin Qi. The lowest εNd(t) value (-23～6.3) and old model age region (TDM=3.2-1.6Ga) is coincide exactly with old basement from northern of North China craton region.Forth, young continental crust (TDM=1.1～0.8Ga) is accounted for50percent of area in eastern section of Central Asian Orogenic Belt. Continental crust of old material cycle (TDM=3.2～1.1Ga) and juvenile crust of mantle material (TDM=0.8～0.3Ga) accounted for35%and15%respectively, which indicate that phanerozoic crust growth area covers65%of eastern section of Central Asian Orogenic Belt. Fifth, significant restrictive correction between the structural composition of deep crustal and the distribution characteristics of different minerals have been revealed by the isotopic maps. Copper is distributed in the young crustal accretion areas. Tungsten-tin, lead-zinc, and uranium deposits are associated with ancient land. However, molybdenum and gold mines are in the crust-mantle mixing zone, tending to the ancient continental relatively.According to the study, the isotopic mapping can show the variation characteristics of sources in granitoid rocks, and reveal the structural composition of deep crust. It provides an evidence for dividing the geotectonic units, understanding the tectonic unit nature, and discussing the crust growth, also providing new information for learning about the distribution of minerals.更多还原