Petrological characteristics of the eruption products in early part of the Goshikidake activity of the Zao volcano.

Abstract

Zao volcano is one of representative active stratovolcanoes in NE Japan. The Goshikidake, the youngest cone in this volcano, started its activity at about ca. 2 ka. We examined geologic and petrologic features of the initial stage eruption products of this cone. Eruption products are divided into four units. All rocks are cpx-opx andesites, which belong to medium-K, calc-alkaline series. Many phenocrysts have dissolution textures. Bulk SiO₂ contents vary from 56 to 58%, and all samples are plotted in same variation trends in silica variation diagrams.