Magma mixing in mantle xenolith-bearing calc-alkalic ejecta, ichinomegata volcano, Northeastern Japan

摘要: Abstract The latest Pleistocene ejecta from the Ichinomegata volcano, NE Japan, (composed of three maars), show a wide compositional variation ranging basalt (51% SiO 2 ) to dacite (65% ). These have same phenocryst assemblage olivine, augite, hornblende, biotite, quartz, plagioclase and titanomagnetite. Upper-mantle peridotite xenoliths are found not only in basalts but also andesite. Whole-rock major chemistry modal compositions indicate that chemical variations been caused by mixing magmatic components; primitive high-alumina (SiO ∼ 51 wt.%, MgO 8.5 wt.%) with olivine (Fo 88) augite phenocrysts; differentiated basaltic andesite 54 5 which has same, slightly Fe-rich phases as basalt; porphyritic 65 2.0 phenocrysts upper-mantle peridotite-bearing may be derived directly upper mantle its carried magma. estimated density for end components requires high flow velocity magma small volume ( m 3 body facilitate breaking stratification body. This is consistent retention mixed preserved disequilibrium petrographic features.