Pre-eruptive processes of Goshikidake pyroclastic rocks in Zao volcano, NE Japan

Abstract

We performed petrologic examination on pre-eruptive process of upper most unit of Goshikidake pyroclastic rocks of Zao volcano. The products were calk-alkaline andesite and were formed by mixing between two end-members. The estimated time scale from mixing to eruption based on zoning profiles of opx thin and relatively broad reverse zoned rims are 1.5 days to several weeks and 5 to 20 years respectively. Meanwhile, the time scale magma scent from shallow chamber to the surface, based on the decompression rate meter using microlite density and composition was estimated to several days.