The Karasugasen lava dome is part of the Daisen – Hiruzen Volcanic complex and was the source of a large number of Block and Ash flows. Products directly overlie the Aira Tanzawa tephra (AT), and the majority of erupted material is preserved in three voluminous lobes to the south and southeast of Mt Daisen. Dacitic magmas with adakitic characteristics were sourced from a large magma chamber in the shallow crust crystallizing between 4 and 12 km depth, at temperatures between 803 and 920 ˚C and oxygen fugacities of Δlog +1.7 to +1.8 above the NNO buffer. Cores of magnesium rich orthopyroxene phenocrysts are not in equilibrium with the host dacite and may be a rare evidence for insipient mafic replenishment of the voluminous magma chamber beneath the Daisen Volcanic complex.