鹿児島県野間半島地域の熱水変質安山岩中の変質鉱物

抄録

Alteration minerals in the hydrothermally altered volcanic rocks of the Kasasakurose Andesite distributed in the Noma Peninsula area were studied. Hydrothermally altered rocks could be divided into five altered zones by the differences in the constituent alteration products. They are unaltered zone (Zone I), smectite zone (Zone II), interstratified chlorite/smectite zone (Zone III), chlorite zone (Zone IV) and chlorite+ (sericite and/or interstratified mica/smectite) zone (Zone V).
Trioctahedral smectite in Zone II is often accompanied with mordenite, whereas interstratified mineral of chlorite/smectite is accompanied with laumontite. Smectite, interstratified chlorite/smectite and chlorite were formed from pyroxenes by hydrothermal alteration; mica minerals and calcite, on the other hand, were formed from plagioclases. Smectite was formed not only from pyroxene but also from glasses. Hydrothermal liquid was considered to be alkalic with the addition of K⁺and H₂O and removal of Si, Al and Fe by the hydrothermal alteration.