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ID 13941
Eprint ID
13941
FullText URL
Thumnail ESR_2_23.pdf 2.34 MB
Title Alternative
A suggestion on the origin of biotite gneisses of the Ryoke belt in the Seto Inland Sea (Seto-nai-kai) region : Some biotite gneisses were derived from a different geologic unit to the Kuga froup
Author
Nureki, Terukazu
Abstract
The Kuga group is a Jurassic accretional complex that has been believed by many workers to be a unique geologic unit transformed into the Ryoke gneisses in the Seto Inland Sea region. I will now suggest the presence of a different geologic unti in addition to the Kuga group. Most of the biotite gneisses found at the Iwakuni-Yanai area are probably derived from rocks of the Kuga group, but the rest biotite gneisses that occur in the Murotu Peninsula, the Yashiro-jima, the E-no-shima, and the other several islands in the Seto Inland Sea region were derived from a un-known and a different geologic unit to the Kuga froup. Some pieces of evidence proving the distinct origin of the latter biotite gneisses are: (1) the biotite gneisses commonly occur as small to large fusiform bodies generally enclosed in the older Ryoke granite or as large masses contacting only with the older Ryoke granite; (2) tight folds with parallel axial surfaces are very common, and dupli-cated fold systems are found in many localities; (3) microtextures of some minerals, e.g. garnet and K-feldspar, often suggest a plural metamorphic history of the gneisses (Nuraki et al., 1982a; Miyashita % Komatsu,1993); and (4) the sillimanite zone (Ikeda,1991 : Okudaira et al.,1993) is only a metamorphic zone that can be found. The sillimanite zone is interpreted to be excluded from the progressive metamorphism in the Iwakauni-Yanai area (Wallits et al.,1992). Biotite gneisses of the sillimanite zone are found here and there and show no zonal arrangement of distribu-tion in the Ryoke belt. The estimated metamorphic temperature and pressures for the biotite gneisses of the silliman-ite zone are 530-710℃ and 2-4kb respectively, both of which are lower than of the peak metamorphism, estimated as 550-820℃ and 5-6kb, at the Iwakuni- Yanai area.
Keywords
Kuga group
Ryoke belt
biotie gneisses
Sillimanite Zone
Iwakuni-Yanai area
Published Date
1995-09-20
Publication Title
Okayama University Earth Science Report
Publication Title Alternative
岡山大学地球科学研究報告
Volume
volume2
Issue
issue1
Publisher
岡山大学理学部地球科学教室
Publisher Alternative
Department of Earth Sciences Faculty of Science, Okayama University
Start Page
23
End Page
54
ISSN
1340-7414
NCID
AN10506284
Content Type
Departmental Bulletin Paper
language
日本語
Copyright Holders
岡山大学地球科学研究報告編集委員会
File Version
publisher
Refereed
False
Eprints Journal Name
esr