Stratigraphic Sequence And Basin Properties Of Carboniferous In Northern Greater Xing'an Range,Inner Mongolia

By analyzing the Carboniferous strata of northern Greater Xing'an Range,this thesis divided the study area into Hongshuiquan Formation and Moergenhe Formation,both of which experienced mild metamorphism,appeared in transverse interfingering phase contact,and the sedimentary environment was back-arc basin.From bottom to top,the Hongshuiquan Formation can be divided into three lithological sections:the underpart is conglomerate section,most of them are coarse-grained multi-composite comglomerates and glutenites;the middle part is primarily sandy and argillaceous rocks section which comprise of fine-grained greywackes,siltstones,phyllites,and slates;and the domination of the upper glutenite section are fine-grained anagenites,pebbly coarse-grained sandstones,and mingled with some carbonate rocks.Abundant neritic facies fossils are contained in the middle and upper layers.The Moergenhe Formation also can be divided into three lithologic sections:the lower and upper layers are thick volcanic rocks,basic-acidic volcanic rocks are all outcroped in the study area,and a large number of siliceous rocks crop out partially;carbonate rocks and clastic rocks are in the middle section,includinging bioclastic limestones,marbles,anagenite,greywackes,and this section is rich in fossils of brachiopods,corals,crinoids,etc.Generally,Hongshuiquan Formation was the sedimentation of the coastal and neritic facies clasolite.There were alluvial fan,fan delta sedimentary facies near the island arc side,which were formed by gravity flow.The Moergenhe Formation was the sedimentation of marine facies volcanic rock mingled with shallow marine facies carbonate rocks,clastic rocks,and bathyal facies siliceous-pelitic rocks.By fossil record and zircon U-Pb dating analysis,Hongshuiquan Formation and Moergenhe Formation were corresponding to Tournaisian-Serpukhovian stage of the early Carboniferous epoch,there are clastic rocks and volcanic rocks interbedded,in interfingering contact,indicating that they were deposited synchronously.By analyzing geochemical characteristics of the Early Carboniferous volcanic rocks,the tholeiitic basalt and alkali basalt are symbioses,with the transition trend from sub-alkaline to calc-alkaline.The chondrite-normalized REE patterns is relatively flat incline to right,total REE is on the average level,and LREE is relatively abundant with the HREE loss.The trace elements are characterized by enrichment in Th?U?Pb and large-ion lithophile elements such as Rb,and strongly depletion in high field strength elements such as Nb,Sr,Ti.Through the analysis of comprehensive research,the northern of Greater Xing'an Range was in subduction zone of the oceanic plate and active continental margin during the Early Carboniferous.The area between Toudaoqiao and Wunuer uplifted and formed volcanic island arc,in the northwest of which such as Yakeshi,Ewenki Banner,etc.they were formed in an extensional environment back-arc basin with a great deal of sedimentation from the island arc,submarine volcanic eruption,and a small amount from the continental margin sediments.To the Late Carboniferous-Early Permian,the plate subduction activities terminated,marine sedimentary of the back-arc basin was disappeared,the earth's surface uplifted caused by continental collisions,and then suffering weathering and denudation process.In addition,near the Honghuaerji-Urqihan polymetallic metallogenic belt,the Moergenhe Formation is occurrence of copper mineralization.Perhaps relating to the submarine volcanic eruption-hydrothermal solution,the middle-upper layer's marine facies sodium-rich basic volcanic rocks(spilitic),intercalated with siliceous siltstone and slate are abundant in Cu,Au,Zn,so it is an important target for polymetallic deposits.