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タイトル :Middle Miocene back-arc volcanism in the Tappi-zaki area, Northeast Japan arc : plagioclase K-Ar age constraints
著者 :Watanabe, Naoki
Itaya, Tetsumaru
Ohki, Jun'ichi
Shuto, Kenji
公開者・出版者 :新潟大学理学部
刊行年月 :2009-3
掲載誌名 :Science reports of Niigata University. (Geology)
巻 :24
開始ページ :91
終了ページ :108
ISSN :1349-1237
抄録 :K-Ar ages of whole rock and plagioclase separates were determined for Miocene volcanic rocks from the Tappi-zaki area, Tsugaru Peninsula in the Northeast Japan arc. Whole rock and plagioclase K-Ar ages for the basalt with subophitic groundmass are identical within analytical errors. On the other hand, whole rock K-Ar ages for the basalt, andesite and dacite with intersertal or hyalopilitic groundmass tend to be younger than those of plagioclase separates from the same samples. The discordance between whole rock and plagioclase K-Ar ages may be caused by radiogenic 40Ar loss from whole rock due to alteration and hydration of glass in the groundmass. These suggest that the plagioclase K-Ar ages can be regarded as the formation ages of older volcanic rocks in the study area. The obtained plagioclase K-Ar ages show that the extrusive rocks from the Tappi-zaki area, with a total thickness of about 1,500 m, were formed during 16.5-10 Ma(Middle to Late Miocene), and the dikes and sheets intruded these volcanic piles during the same period of 15-11 Ma. This implies that both the extrusive and intrusive rocks were produced by the same magmatic episode during the Middle to Late Miocene. The younger Minmaya rhyolites yielded a whole rock age of 7.9 Ma.
キーワード :K-Ar dating
Minmaya rhyolites
Northeast Japan arc
Tappi-zaki
volcanic rocks
資料種別 :紀要論文
言語 :eng
フォーマット :application/pdf
URI :http://hdl.handle.net/10191/12944
fullTextURL :http://dspace.lib.niigata-u.ac.jp/dspace/bitstream/10191/12944/1/24_91-108.pdf
出現コレクション:02 Science reports of Niigata University. (Geology)

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