Studies on the textures of some eruption products of the Fuji volcano.

Abstract

We note an example of eruption processes of basaltic magmas generated in a subduction factory. The Younger Fuji volcano (ca. 11ka to present) produced mostly basaltic ejecta. Some are explosive (A.D.1707 Hoei, ca. 3000ybp Omuroyama etc), and others are effusive (A.D.864 Aokigahara lava flow, Omuroyama lava flow, Mishima lava flow, Saruhashi lava flow etc). All the basaltic eruption products are mildly evolved (FeO*/MgO=2.0-2.8). Some of the explosive eruption products are sparsely-phyric with calcic plagioclase and olivine, and most of the effusive eruption products are porphyritic with 15-30 vol% plagioclase and associated olivine, augite, and orthopyroxene. Sodic compositions of abundant plagioclase phenocrysts suggest they crystallized by degassing of water at shallow depth.