Study On The Geological Characteristics And Tectonic Of Hengxianhe Melanges Belt In Mianlue Tectonic Zone

Mian Lue structural belt is the main combination zone of the main body of China's mainland,and also the basic component of the Qinling Mountains orogenic belt.The Mianxian Lueyang section is an important part of the belt,and is represented by the Mianxian Lueyang ophiolite tectonic melange belt.Based on the combination of field geological survey and indoor research,this paper focuses on the study of the"dabaoyan formation"metamorphic sedimentary volcanic rock series,Zhujiashan formation and qiaozigou structural rock sheet shallow metamorphic strata,hengxianhe serpentinite in the area of hengxianhe in the Lueyang area of Mian Lue structural belt,and obtains some new understandings and achievements(1)According to the strength of deformation,the weak deformation"rock block"and the strong deformation"matrix"are divided from the hengxianhe structural melange belt,and six different types of structural rock blocks,including volcanic rock block,serpentine rock block,siliceous rock block,limestone block,marble block and dolomite block,as well as sericite phyllite,sericite quartz phyllite and pebbly sericite phyllite,are identified There are 4 types of matrix rock series,such as rock and medium fine sandstone.(2)Based on the U-Pb geochronology of zircon,it is found that the middle and shallow metamorphic sedimentary rock series of Zhujiashan formation and qiaozigou structural rock sheet in hengxianhe area of Mian Lue structural belt may be formed in the middle and late Devonian,and the sedimentary environment is rifted basin and the extension rifting is transformed into stable platform basin platform sedimentation.The provenance mainly comes from Mian Lue structural belt,Bikou micro block and hannan-mi in the northern margin of Yangtze plate Judging from the chronological data and the distribution scale of magmatic rocks,the provenance provided by Mian Lue structural belt and Bikou micro block is limited,and the Hannan Micangshan micro block on the northern margin of Yangtze plate may be the main provenance area.(3)According to LA-ICP-MS zircon U-Pb isotopic dating,the diagenetic age of metabasic volcanic rocks in"Dabao formation"is 451.9±3.9Ma,which defines the formation age and sedimentary age of metabasic volcanic rocks in"Dabao formation"of Mian Lue structural belt in Hebei Province.The metamorphic basic volcanic rocks in the dabaoyan formation are oceanic island alkaline basalts,which are the product of 1%?10%spinel garnet lherzolite and garnet lherzolite mixed with low degree partial melting in the mantle source area,and formed in the rift environment of the inland margin of the plate,indicating that the Mian Lue structural belt was in the cracking system in the middle and late Early Paleozoic Fang began to be in the tectonic environment of a small rift basin.(4)The serpentine protolith in the north of hengxianhe river is a kind of depleted mantle peridotite after partial melting to some extent,which is MORB type mantle peridotite.Serpentine was formed in the expanding environment of mid ocean ridge at first,experienced about 10%?15%partial melting,then entered the subduction zone environment in the ocean,and was later transformed by the fluid brought by the subduction zone.(5)The deformation sequence of structural melange belt in hengxianhe area is divided.The first stage is the formation of early permeable structural foliation(S₁),which is formed under the subduction compression structural system,and is the early deep-seated plastic deformation;the second stage is the early formed foliation(S₁),which is formed by the later thrust shearing,such as discordant fold,rootless hook fold,structural lens,etc.,which is formed in the early collision compression structural stage,and is the middle deep-seated plastic deformation Deformation:in the third stage,the north to South thrust nappe structure is formed in the migmatite and the boundary of both sides,which is superimposed on the early thrust ductile shear deformation structure,and non permeable axial fold cleavage(S₂)is generated,which is formed in the late collision stage;in the fourth stage,the brittle thrust deformation in the late shallow layer is superimposed on the previous deformation.(6)According to the material composition,structural and structural characteristics of hengxianhe structural melange belt,combined with the latest research results published by Mian Lue structural belt and adjacent areas,the structuralevolution process of Mian Lue structural belt is discussed.It can be divided into three stages in detail:subduction,collision and orogeny of the early Neoproterozoic mianlueyang,intracontinental disintegration of the middle and late Neoproterozoic(Nanhua),stable deposition of Sinian,early Paleozoic,early Paleozoic(Devonian)and opening of the finite ocean basin,Late Paleozoic(Early Carboniferous Early Permian)and expansion of the finite ocean basin,and plate tectonics Block convergence and subduction stage(early Middle Triassic),comprehensive collisional orogeny stage(middle Late Triassic),intracontinental orogenicsuperimposition and reconstruction stage(after late Triassic).On the whole,Mian Lue structural belt is characterized by multi-stage,intermittent cracking and stable sedimentary alternation.