西南日本内帯の古生界火山岩の変成作用 : 変成作用研究における火山岩の重要性

抄録

Three types of metamorphic mineral parageneses are developed in basic volcanic rocks of the so-called “unmetamorphosed” Paleozoics of the Inner Zone of Southwest Japan. These rocks are characterized by the mineral associations of 1. Chlorite-calcite, 2. Prehnite-pumpellyite-chlorite, and 3. Epidote-actinolite-chlorite. In the former two clinopyroxene of the original rocks does not suffer the recrystallization, while in the latter the mineral is entirely replaced by actinolite. Olivine is always recrystallized into chlorite. The parageneses 1 and 2 may correspond to the prehnite-pumpellyite metagreywacke facies, and 3 to the greenschist facies. The absence of any critical Ca-Al silicates in type 1 may be due to the effects of variation of H₂O and CO₂ pressure in metamorphism or due to the lack in rocks of suitable chemical composition.