Geochronology And Geochemistry Of Late Mesozoic Volcanic Rocks In Zhalantun Region,Central Great Xing'an Range

Research area located at central part of Great Xing'an Range and with abundant late Mesozoic volcanic rocks.The central part of Great Xing'an Range relatively lack research files.As a result,the questions about late Mesozoic volcanic rocks at central part of Great Xing'an Range such as Formation age,petrogenesis and tectonic setting are still controversial today.So,it is necessary to carry out geochronology and geochemistry to the late Mesozoic volcanic rocks about central part of Great Xing'an Range.This paper take late Mesozoic volcanic rocks at central part of Great Xing'an Range in Zhalantun area as research object.Based on field geological survey carried out recent years,selecting typical section and take systematically sampling,then use multiply methods including petrography,isotopic geochronology and geochemistry to determine the genetic age,petrogenesis and tectonic setting.Key opinions stated bellow.Based on field geological survey,profile survey and petrography,the main rock types of each formation were identified,volcanic cycles?volcanic rhythms and volcanic facies were divided.The main lithology of Tamulan and Meiletu Formation is intermidiate basic volcanic and volcano clastic rocks,the main lithology of Manketouebo and Baiyingaolao Formation is acidic volcanic and volcano clastic lava,the main lithology of Manitu Formation is intermidiate volcanic and volcano clastic rocks.The study area of Late Mesozoic volcano activity is divided into 3 cycles,from early to late respectively Tamulangou cycles,the manketouebo and manitu cycle,Baiyingaolao and Meiletu cycle.6 volcanic lithofacies have been divided in study area,they are Explosive facies,overflow facies,volcanic channel facies,eruptive sedimentary facies,volcanic clastic flow facies and subvolcanic facies.Depend on zircon LA-ICP-MS U-Pb ages,the age of late Mesozoic volcanic rocks in study area from late Jurassic to middle Early Cretaceous.Tamulangou Formation formed during 158?150Ma which belong to late Jurassic,Manketouebo Formation formed during 152?135Ma which belong to Late Jurassic to Early Cretaceous,Manitu Formation formed during 149?131Ma which belong to Late Jurassic to Early Cretaceous,Baiyingaolao Formation formed during 129?118Ma which belong to Early Cretaceous and Meiletu Formation formed during 130-118Ma which belong to Early Cretaceous.Geochemistry characteristics indicate that the magma source of late Mesozoic volcanic rocks in study area is very complex,some derived from partial melting of enriched lithospheric mantle,others derived from partial melting of crust.Primary magma of Tamulangou Formation and Meiletu Formation derived from enriched lithospheric mantle,and surfed certain crust material contamination.Primary magma of Manketouebo Formation,Manitu Formation and Baiyingaolao Formation derived from partial melting of crustal rocks.The late Mesozoic volcanic activity in study area started from Late Jurassic,lasting to middle Early Cretaceous.The generation of Late Jurassic-early Early Cretaceous volcanic rocks influenced by extension tectonic background after the closure of Mongolia-Okhotsk Ocean.The generation of middle Early Cretaceous volcanic rocks also influenced by extension tectonic background,but influenced by the closure of Mongolia-Okhotsk Ocean and subduction of Paleo-pacific at the same time.The volcano activity of Late Mesozoic in study area is part of the volcano activities of the Great Xing'an Range,but due to the impact of the Mongolia-Okhotsk ocean's subduction to the South,the volcano activity in study area is later than north of Great Xing'an Range,and at the same time with the south of Great Xing'an Range basically,which is starting from Late Jurassic to middle Early Cretaceous.