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Title Transcription
オキ ドウゴ マッキ チュウシンセイ ツズラオソウ カドウカクレキガン ト ソメンガン ガンペンチュウ ノ アルカリ チョウセキ K AR ネンダイ
Title Alternative (English)
Geology and petrography of vent breccias of the Latest Miocene Tsuzurao Formation, and alkali feldspar K-Ar age from a trachyte essential fragment, Oki-Dogo Island, SW Japan
File
language
jpn
Author
Sawada, Yoshihiro
Tome, Akane
Kitagawa, Hiroya
Kobayashi, Shinji
Imaoka, Teruyoshi
Itaya, Tetsumaru
Description
 The Tsuzurao Formation is distributed in the northeastern part of Oki-Dogo Island in an area about 4.5 km E-W by 6 km N-S. It unconformably covers the Oki metamorphic rocks and the Tokibariyama Formation(Figs. 1 and 2). The Tsuzurao Formation consists mainly of rhyolitic pyroclastic flow deposits, with a small volume of rhyolitic air fall deposits and associated rhyolite lavas, dikes, and trachyte essential fragments and xenoliths. Vent breccias and feeder dikes are distributed in the eastern and southwestern parts of the Tsuzurao Formation(Figs. 2 and 3). Vent breccias are intruded into the basement as a fissure vent 1500 m long and 400 m wide. The vent breccias are massive, and are composed of rhyolite and trachyte essential fragments and accidental fragments derived from the basement. The vent breccia matrix consists of rhyolitic pyroclastic material. Many trachyte fragments are elongated, and some are enclosed by rhyolite fragments or are mixed with them. Trachyte fragments consist of alkali feldspar, fayalite, hedenbergite, alkali amphiboles(arfvedsonite, riebeckite), magnetite, and apatite. Rhyolite is composed of alkali feldspar, quartz, alkali amphiboles(arfvedsonite, riebeckite), annite, magnetite, apatite. The alkali feldspars in rhyolite are albite(An1.8-1.7 Ab90.4-93.0 Or7.8-5.3)and anorthoclase - sanidine(An0.0-2.0 Ab34.6-58.2 Or41.8-86.0). In trachyte they are anorthoclase - sanidine(An3.8-6.4 Ab36.0-50.9 Or41.5-52.0 and An0.0 Ab46.8 Or53.2).
 Alkali feldspar from a trachyte essential fragment in the vent breccia yields a K-Ar age of 5.45±0.17 Ma. This is similar to the radiometric ages of the Omosu Formation and Hei Trachyte Group in Oki-Dogo Island.
Journal Title
島根大学地球資源環境学研究報告
Volume
27
Start Page
11
End Page
20
ISSN
13439774
Published Date
2008-12-25
NCID
AA11455176
Publisher
島根大学総合理工学部地球資源環境学教室
Publisher Aalternative
Department of Geoscience, Interdisciplinary Faculty of Science and Engineering, Shimane University
NII Type
Departmental Bulletin Paper
OAI-PMH Set
Interdisciplinary Graduate School of Science and Engineering
Remark
12-14,16+ / 1993+
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