Geochronology,Geochemistry And Tectonic Significance Of Paleozoic And Mesozoic Granitoids In The Southern Area Of Da Hinggan Mountains,China

Southern areas of Da Hinggan Mountains are located in the conversion superimposed parts of the Paleo-Asian tectonic domain and the Pacific tectonic domain,and are affected by the major geological events such as lithospheric thinning in eastern China.These major geological events lead to frequent occurrence of the structure-magmatic events.In order to solve relevant scientific problems,the petrotectonic assemblage was considered as the main line,and the petrology,geochemistry and geochronology of the southern areas of Da Hinggan Mountains were deeply analyzed,according to different eras and different tectonic units.Meanwhile,combined with research findings from contemporaneous volcanic activity,stratigraphy,paleontology,paleomagnetism,and geophysics,the regional geochronological framework of intrusive rocks from Paleozoic to late Mesozoic era was built based on regional tectonic structure,which aimed to restore the tectonic evolution history from Paleozoic to late Mesozoic era in this region.By using precise zircon U-Pb isotopic dating techniques,the geochronological framework of granitoid intrusive rocks in the southern areas of Da Hinggan Mountains from Paleozoic to Mesozoic era was established.This geochronological framework was divided into four major stages of magmation.At each stage,there was a good correspondence between the petrotectonic assemblage and rock geochemistry,which could reasonably reflect the tectonic evolution history of the regionIn this study,based on the combination of the chronology framework and the petrotectonic assemblage,the spatial and temporal distribution of granitoid intrusive rocks was explored,and the tectonic evolution history of the southern areas of Da Hinggan Mountains was analyzed Certain understandings of the research were as follows.The Hegenshan ocean drove bidirectionally in both south and north sides from early Paleozoic to early Carboniferous period From the mid-Carboniferous to early Permian period,there were obvious differences in the petrotectonic assemblage of the Hegenshan tectonic zone and Xilamulun tectonic zone.During this period,the Hegenshan ocean tended to be closed,while Xilamulun ocean was in the stage of driving bidirectionally in both south and north sides.Late Permian to mid-Triassic period represented the orogenic stage after closure of Xilamulun ocean.The period from middle to late Triassic period,was the orogenic collapse phase after the collisional orogenesis of the Xilamulun tectonic belts.This post-orogenic extension in some areas was continued to early Jurassic.Late Jurassic to early Cretaceous period represented intense magmatism period of the southern areas of Da Hinggan Mountains in the late Mesozoic under the mantle background.