Geochronology And Geochemistry Of The Early Jurassic Volcanic Rocks In The Manzhouli-Erguna Area, NE China

The Mongol-Okhotsk suture belt played an important role in the tectonic evolution ofthe NE Asia during the Mesozoic. However, few studies involve the influence of thistectonic belt to NE China. In this paper, we present LA-ICP-MS and SIMS zircon U-Pbdating results, major and trace element datas, Hf and O isotope datas for Early-MiddleJurassic volcanic rocks in the Erguna Massif of NE China, with the aim of constraining thetectonic evolution and spatial extent of influence of the Mongol-Okhotsk suture belt onNE China in the Early Jurassic.Zircon U-Pb dating indicates that the trachybasalts and basaltic andesites in the studyarea formed in193±5Ma,182±2Ma, and181±9Ma, implying the existence of theEarly Jurassic volcanism.The Early Jurassic volcanic rocks have SiO2=49.83~63.45wt.%, Al2O3=15.84~17.86wt.%, MgO=1.97~4.36wt.%, CaO=3.66~7.63wt.%, Na2O=2.82~4.69wt.%, K2O=1.37~2.72wt.%, Na2O/K2O=1.18~4.68wt.%and Mg#=28~57,belonging chemically to the high-K calc-alkaline series. They are enriched in LILEs andLREEs, and depleted in HREEs and HFSEs such as Nb and Ta, with a weak negativeanomaly of Eu or no anomaly. Their zircon εHf (182Ma) values range from-1.9to+12.3,corresponding TDM1and TDM2values range from640to1079Ma and from895to1345Ma, respectively. The δ18O values of zircons from two volcanic rocks are (7.2±1.5)‰(n=19) and (6.6±0.7)‰(n=35), respectively. Geochemically, these Early Jurassicvolcanic rocks are similar to those from the active continental margin setting, and theirprimary magma could been derived from partial melting of a lithospheric mantle wedge modified by fluid from a subducted slab.The discovery of the Early Jurassic calc-alkaline volcanic rocks in the Erguna Massif,combined with the existence of the coeval porphyry Cu-Mo deposits, indicates that anactive continental margin setting occurred in the Erguna area during Early Jurassic. Takentogether, we conclude that a southward subduction of the Mongol-Okhotsk oceanic platetook place beneath the Erguna Massif during the Early Jurassic.