Contrastive Research Of Ophiolite M�lange Belts In The Central-east Of Xing'an-mongolian Orogenic Belt

The research area is located in the central of Inner Mongolia.Its geotectonic position is the mid-east region of Xing'an-Mongolian Orogenic Belt(XMOB)between the North China Craton(NCC)and Siberian Plate.The study region can be divided into three belts from north to south:Hegenshan Ophiolitic M�lange Belt(HOMB),Diyanmiao-Daqing Pasture Ophiolite M�lange Belt(DOMB)and Xar Moron Ophiolite M�lange Belt(XOMB).In this paper,we present sampling and indoor analysis of geological samples in key areas by the field geological survey.In additional,integration of the previous research results,regional tectonics,sedimentology,petrology,geochemistry,geochronology are used to find that the XMOB has the characteristics of multiphase tectonic activities in the Late Paleozoic.There are two types of basalt in HOMB.A kind of metamorphic basalt,with the characteristics of IAT and N-MORB in the rare earth and trace elements,is the composition of the Hegan Mountain ophiolite,which forms in the age of 403Ma-354 Ma.Duing the period,there are no arc magma records,so we can speculate that it form in the Mid Ocean Ridge(MOR)environment,which is influenced by the early ancient Asian ocean subduction plate and has the nature of the island arc.Another basalt,with the rare earth element characterized by light-rare earth-enriched right-leaning,which is similar to the continental crust type(C-crust)basalt.Thus,it indicates that it is formed in the continental rift environment,and its formation age is about 300Ma-292 Ma.The Diyanmiao ophiolite has the characteristics of IAT and N-MORB,and it is found that there is the presence of boninite presumably formed in the island arc environment.According to this paper,the age of the Diyanmiao cumulate gabbro is 345.6�2.3Ma.Based on the previous research results,it is presumed that the formation age of the Diyanmiao ophiolite is in the Early Carboniferous Early-Early Carboniferous Late(356Ma-320Ma).Daqing pasture ophiolite has two types of basalt.One is pillow basalts which is likely N-MORB of lithogeochemistry.The other one is foliated basalt.It has low ?REE.The characteristic of trace elements like Continent-crust basalt.So I speculate that the basalt is formed in continent rift.In XOMB,The metabasalt in Xiaoweitang ophiolite has the characteristic of N-MORB,which contains radiolarian chert.It is speculate that Xiaoweitang ophiolite is formed in mid-ocean rige.The Middle Permian radiolarian fossils and associated conodonts are found in the siliceous rocks.Therefore it is suggested that the Xiaoweitang ophiolite is form in early to mid Permian.Age with the characteristics of younger from north to south,may represent the XMOB in the eastern part of the north to south,followed by the opening and closing process of the ocean.