Magma evolution of Changbaishan Tianchi volcano:Evidences from the main phenocrystal minerals
长白山天池火山岩浆演化——来自主矿物成分的证据

The main phenocrysts of Changbaishan Tianchi volcanic rocks were olivines, pyroxenes, feldspars and Ti-Fe oxides, which had clear characteristics of components evolution by electron microprobe analysis. From shield-forming stage, cone-forming stage to Holocene eruptions, the content of iron in olivines kept increasing till it almost reached the end-member of fayalite; iron and sodium contents also increased in clinopyroxene. In the meantime, feldspars evolved from labradorite to anorthoclase and sanidine which had more potassium and sodium, and the contents of Fe-Ti oxides in rocks were reduced cleary. The evolution of phenocrysts in three stages of Tianchi volcanic rocks reflected the complete series of Tianchi magma evolution in 2 Ma, which was in conformity with the evolution tide of fractional crystallization.