Research On Magmatism And Basin Formation And Evolution In The Western Basin Group Of The Greater Xing'an Mountains

The western basin group of Greater Xing'an Mountains,including the Erlian Basin,Hailaer Basin,Labudalin Basin,Genhe Basin and Mohe Basin.The research area is located in the west of Greater Xing'an Mountains in Heilongjiang Province and Inner Mongolia Autonomous Region of China,with a length of 1650km from north to south.Among them,there are several fault depression basins with mainly Mesozoic sedimentary deposits.The total area of the basin is about 20.0×10~4km~2.The tectonic structure and strata of the basin are controlled by Mongolian-Ekhutsk suture zone in the west and north,the Greater Xing'an Mountains fault zone and Heihe-Hegenshan suture zone in the east,the Ondor Sum-Xar Moron suture zone and northern marginal fault zone of North China craton in the south.In the Paleozoic,the tectonic evolution in Northeast China is characterized by the fusion of several continental blocks and the final closure of the Paleo-Asian oceans.And in the Mesozoic,the tectonic processes and evolution are related to the circum Pacific tectonic belt.Since the Middle to Late Mesozoic,the tectonic evolution of Northeast China mainly affected by the subduction of the Paleo-Pacific plate and the closure of the Mongolia-Okhotsk ocean.The study area is complex in tectonic structure,influenced by deep structures and multiple tectonic systems.Whether the formation and evolution of the western basin group have a unified geological background?What the tectonic setting among the formation and evolution of the western basin groups are in?and What the relationship among the magmatism of the western basin groups,and What is the difference in the formation and evolution of the western basin group of oil and gas resources potential?All these problems need to be resolved.Based on the previous research,geophysical data,zircon U-Pb chronology and rock geochemistry were used to study the magma sequence and magmatism in the western basin group of Greater Xing'an Mountains,and analyze the interrelationship among magmatism in the western basin group.Comparing the formation and evolution of the Songliao Basin,the potential of oil and gas resources in the western basin group is discussed,which provides a theoretical basis for oil and gas exploration.The zircon U-Pb geochronology of igneous rocks in the western part of the Greater Xing'an Mountains revealed that six magmatic events occurred in the Ordovician of Paleozoic to Early Cretaceous of the Mesozoic.Stage?:510~450Ma,cracking and extension environment;Stage?:330~300Ma,collision and extrusion environment;Stage?:290~270Ma,stretching and extension environment;Stage?:255~230Ma,collision and extrusion environment;Stage?:200~170Ma,stretching and extension in the early stage,and squeezing and uplifting in the late stage;Stage?:150~110Ma,stretching and extension environment.The latter two magmatic events are closely related to regional western basin group.The basement of the Hailaer Basin and the Labudalin Basin were formed in Stage?;the closure of the Paleo-Asian Ocean and the collision of the North China Craton and the Siberian Craton were related to the magmatic events of Stage?;the strata of Hailar Basin,Labdalin Basin and Genhe Basin began to sediment,and the basement of the Erlian Basin formed during the Stage?.At this stage,the Mongolian-Okhotsk Ocean in the north began to close;the strata of Erlian Basin began to deposit,and the Hailaer Basin,Labudalin Basin,Genhe Basin and the Mohe Basin in the northern were reconstructed by tectonic movement,with extensional subsidence or extrusion uplift,forming a complex fault basin in the basement during the magmatic event of Stage?;the Paleo-Pacific plate subducted to the North Asia region,and the basement and sedimentary strata of the western basin group of Greater Xing'an Mountains were further reconstructed during the magmatic event of Stage?.The third and the magmatism and the magmatic events in the Songliao Basin occurred at the same period with the western Greater Xing'an Mountains.In the Late Paleozoic,the western basin group was controlled by the Paleo-Asian tectonic domain,and in the Late Mesozoic to Cenozoic,it was controlled by the cumulated influence of Mongolian-Okhotsk and the Paleo-Pacific tectonic domain.The Erlian Basin mainly experienced five stages,compressional uplifting stage-extensional fault depression stage-extrusion sediment stage-extensional fault depression stage-tectonic inversion stage,which was related to the fifth and sixth magmatic events in the western Greater Xing'an Mountains,thus forming a complex fault basin.The Hailaer Basin experienced six stages,Initial cracking stage-fault depression expansion stage-continuous and stable fault depression stage-fault-depression transition stage-depression stage-atrophy stage.The basin basement was formed and reconstructed,and the sedimentary strata were tectonic uplifted or subsided,which was related to the second to sixth magmatic events in the western Greater Xing'an Mountains.The Mohe Basin experienced five stages,extension stage-fault depression stage-uplift stage-extrusion stage-extension stage,which was related to the fifth and sixth magmatic events in the western Greater Xing'an Mountains.The Labudalin Basin and Genhe Basin mainly experienced four stages of magmatism,related to the second and third and sixth magmatic events in the western Greater Xing'an Mountains.After the last magmatic event,each basin has been relatively stable.According to the rocks geochemical characteristics,the magmatic rocks in the western Greater Xing'an Mountains Basin are mostly aluminum-alkaline rocks,and high-potassium and calcium-alkaline rocks.Trace elements show chondrite-normalized REE patterns are LREE-rich,and Eu element generally shows weak losses and weak enrichment,and features such as enrichment of high field strength elements(HFSE),poor large ion lithophile elements(LILE),and rich high field strength elements.It indicates that magma may have fractional crystallization and magmatic mixing of mantle and crustal materials.It is formed by the partial melting of oceanic and continental,or continental and continental tectonic movement or post-orogenic movement.It is characterized by complexity and diversity.The beginning of magmatism in the Hailaer Basin is about the Late Paleozoic,mainly due to the tectonic movement caused by the closure of the Paleo-Asian Ocean.The other four basins are mainly controlled by close of the Mongolian-Okhotsk Ocean and the movement of the Paleo-Pacific Ocean in the Jurassic or Cretaceous.Combined with the previous research of evaluation of the source rocks in the western basin group,and comparing the oil and gas formation conditions in the Songliao Basin,the western basin group has good source rock distribution and hydrocarbon generation potential,and should has good potential for oil and gas resources.