Geochronology And Geochemistry Of The Early Cretaceous Intrusion In The Northeastern Tahe,Northern Dahinggan Mountain

The Mongol-Okhotsk orogeny and Paleo-pacific plate subduction played an important role in the tectonic evolution of the NE Asia during the Mesozoic,the study that the influence of this tectonic belt to NE China has been paid more and more attention.In this paper,by studying systematically U-Pb isotopic dating,major and trace element datas for the intrusive rocks in the northeastern Tahe,North Da Hinggan Mountain,we identified the time of the intrusive rocks,discussed the nature of magma sources of the rocks in the study area and their tectonic setting.We reveal the tectonic evolution and influence of the Mongol-Okhotsk suture belt on NE China together with regional tectonic analysis.Zircon U-Pb dating indicates that the monzonite,granodiorite and granodiorite porphyry in the study area formed in 138.2±2.9Ma.136.9±4.8Ma and 135.0±4.2Ma respectively,implying the existence of the Early Cretaceous magmatic event.In general,the intrusive rocks in the northeast of Tahe,the northen part of Greater Khingan Range have similar geochemical characteristics,the content of SiO₂ in the is between 67.87%and 74.14%,TiO₂ is 0.11%⁰.27%,Al₂O₃ is 14.39%¹5.78%,MgO is 0.19%⁰.96%,K₂O/Na₂O is 0.56⁰.90,The content of TiO2is higher than that in granites,and the content is between 15.00 and 15.26%.Rock geochemical characteristics indicated that the early Cretaceous intrusive rocks in northeastern Tahe belong to the high potassium calc alkaline series,They are enriched in LILEs and LREEs,and depleted in HREEs and HFSFs,with no anomaly or a weak negative anomaly of Eu.The rock has a resemble that high content of Sr and low content of Y,Yb which is similar to adakites rocks,speculate that it may originated from partial melting of the thickened lower crust.Combined with regional geological investigations,we belive that the Early Cretaceous intrusive rocks in the northeastern Tahe was closely related to lithospheric extension caused by closure of the Mongol-Okhotsk Ocean.During middle-late Jurassic,NE China went through paleo-pacific plate subduction in SE Asia and subdution and collision of Mongol-Okhotsk Ocean.In late Jurassic-Cretaceous,the extension of thickened lithosphere and deep unerplating,a large area of magmatic events in Da Hinggan Mountain was formed by partical melting of the mafic lower crust.