Abstract
Stratigraphy of northern Kita-Hakkoda volcano, consisting of Mae-dake, Tamoyachi-dake, Narusawa-daichicones, was established. Combined with the stratigraphy, differentiation process was investigated from whole-rock chemistry and mineralogy. The activity initiated with the effusion of differentiated tholeiitic basaltic magma around 0.4Ma. After a dormancy, the activity resumed around 0.2Ma with effusion of andesitic magma, followed by a series of lavas with a successive decrease in SiO2 from andesite to basalt. Then, the magma composition jumped to high silica andesite. Disequilibrium mineral assemblages in calc-alkaline rocks imply open system processes. As indicated by linear trends between basalt and the high-silica andesite, magma mixing is a plausible process to produce the series. Stratigraphic chemical variation might be caused by temporal variation in mixing ratios.
