R6: Plutonic rocks, volcanic rocks and subduction factory

[R6P-09] Mineralogical occurrence of alunite-supergroup minerals in the 1895 CE eruption product at Zao Volcano, NE Japan

*Takumi Imura¹, Masao Ban¹, Tsukasa Ohba² (1. Yamagata Univ. Sci., 2. Akita Univ.)

Keywords:Alunite-supergroup minerals, Zao Volcano, Subvolcanic hydrothermal system, Lithic ash, Hydrothermal alteration

This study mineralogically investigated alunite-supergroup minerals in the clayish pyroclastic deposit from the 1895 CE magmatic-hydrothermal eruption in Zao Volcano. The subjected deposit is divided into six units (Layer 1 to Layer 6) based on increase of eruptive intensity with a sequence. Towards Layer 5 and 6, the alunite-supergroup minerals became dominant in huangite with natroalunite-2c. This trend represents the drastic change of the hydrothermal fluid sourced for the minerals, caused by a flux increase of the magmatic vapor separated from the1895 CE degassed magma.