[S-MP33] Physics and Chemistry of Minerals

[SMP33-P04] The occurrence combinations of Zeolites at Chichijima, Ogasawara Islands

Michiharu Ito¹, *Yuki Inoue¹, Mana Yasui², Atsushi Yamazaki², Hiroshi Hagiya¹ (1. Tokyo City University, 2.Waseda research institute for science and engineering)

Keywords:Zeolite, boninite, hydrothermal activity, occurrence combinations

The Ogasawara Islands are located in the Pacific Ocean about 1000 km
south of Tokyo, Japan. These Islands are situated in the outer of the
Izu-Bonin-Mariana Arc. The Ogasawara Islands are composed by paleogene
submarine volcanic formation, and is well known by andesitic volcanic
rock called boninite. Boninite is a feldspar-free and glass-rich
olivine-bronzite andesite with higher MgO, SiO₂, H₂O and Cr contents.
Zeolites, co-exist with calcite, quartz/chalcedony and celadonite,
fill the vesicles of volcanic gas, radial and columnar cooling joint
of pillow lava, and also occur in interpillow sediment with large
aggregate of crystals.

In this study, various habits of zeolites at Chichijima, Ogasawara
Islands are obtained, also more than two-step growth of zeolites in
amygdale were confirmed. Between these two-step growth, cation ratio
have changed at the border of two faces.

These cation's contents are similar to neighboring rock. It is
considered that there is another hydrothermal activity after the
first-step growth.