Magma genesis of silicic and mafic magmas in large eruption cycles at Aso volcano

Abstract

Mamga genesis of silicic and mafic magmas in three large pyroclasitic eruption cycles at Aso volcano between 150 ka and 90 ka has been investigated on the basis of geochemical data. In each large eruption cycle, the silicic and mafic magmas have identical isotope ratios of Sr so that they were generated from the same source material, whereas they do not have parent-daughter relationships by simple fractionation. Petrogenesis of these two magmas can be explained by partial melting of mafic lower crust due to injection of hot, mantle-derived magma. The mafic magma was produced by fractionation of partial melt with higher degree of lower mafic crust. The silicic magma is partial melt with lower degree of the lower mafic magma. Generation of these two magmas occurred in every large pyroclastic eruption cycle at Aso volcano.