Magma Evolution and Holocene Eruption Phases of the Tianchi Volcano, Changbai Mountain

Combined with previous researches on the Tianchi volcano, Changbai Mountains, the authors gave a detailed description of magma evolution characteristics of the Tianchi volcano and divided its Holocene eruption phases. The results indicate that the Tianchi volcano underwent shield-forming stage -> cone-forming stage -> Holocene multistage eruption, and the corresponding lithologies of the three stages are potassic trachybasalt -> basaltic trachyandesite -> trachyte, showing characteristics of comagmatic evolution. The Holocene trachyte is characterized by significantly increased SREE as well as negative anomalies of Eu, Sr and Ba, and obvious linear relationship as shown from the major oxides versus SiO2 covariant diagram; these characteristics suggest that the magma evolution of volcanic rocks from the Tianchi volcano, Changbai Mountains is principally controlled by crystal fractionation. Since Holocene, there have been at least four phases of explosive eruption occurring in the Tianchi volcano, two of which are Plinian eruption. On the basis of field geology and volcanic chronology, Holocene volcanic eruption activities were divided into Tianwenfeng Phase, Qixiangzhan Phase, Baiyunfeng phase and Baguamiao Phase.