岡山大学 地球科学研究報告
Published by Okayama University Earth Science Reports Editorial Committee

Chemical composition of clinopyroxenes associated with the gehlenite skarn from the Hirata outcrop, Kushiro, Tojo-Cho, Hiroshima Prefecture, Japan

Kusachi, Isao
Kagetama Tatsuya
Abstract
The clinopyroxenes of the hybrid rocks from the Hirata outcrop, Kushiro, Hiroshima Prefecture, Japan are grouped into(1)diopside, (2)aegirine, and (3)zoned pyroxene. The diopside occurs as isolated crystals enclosed in feldspars. The aegirine occurs along with late hydrous minerals in pore spaces. The zoned pyroxenes occur as discrete cryatals with wide rims growing interstitially between feldspar laths and show a continuous composition-al trend from diopside through hedenbergite and aegirine-augite to aegirine or titanian aegirine. The pyroxenes enclosed in feldspars and the cores of the zoned crystals have nearly same chemical composition. The late stage pyroxenes are characterized by extreme enrichment of sodium and sometimes titanium. The titanian aegirines studied hera are characterized by the predominance of the Na(Fe2+, Mg)0.5Ti0.5Si2O6 component over other Ti-bearing pyroxene components. The compositional trend of clinopyroxenes from the Hirata hybrid rocks follows a typical trend of peralkalne rocks. The peralkaline neture of the Hirata samples is a result of compositional change of magma accompanied by the metasomatic skarn formation.
Keywords
aegirine
aegirine-augite
diopside
pyroxene
hybrid rock
skarn
ISSN
1340-7414
NCID
AN10506284