| 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. |
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