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Laser-fusion .*Ar/ -3Ar Dating on Sanidine Phenocrysts from Toga Pumice,
Toga Volcano, Oga Peninsula, Northeast Japan, ῍
Kozo UTO῍῍, Kazuhiko KANO῍ and Osamu ISHIZUKA῍

Toga volcano is a tu# ring, located at Toga Bay of Oga Peninsula, NE Japan. The crater is ,.* km by ,..
km in dimension, ﬁlled with K-rich rhyolite pumice-bearing tephra (Toga Pumice). The crater rim deposit has
been almost entirely lost and Late Pliocene shallow marine terrace deposits overlie the crater inﬁllings. In orderto determine the eruption age of Toga volcano, a laser-fusion .*Ar/ -3Ar dating was successfully applied to sanidine
phenocrysts extracted from pumice lapilli of the Toga Pumice. Measurement was made 1 times by fusion of
single, , or . grains, resulting in mutually consistent dates with a weighted average .*Ar/ -3Ar age of *..,*.*+Ma. This result coincides with *..,*.*. Ma, the ﬁssion-track age of zircon crystals from the same sample.
Key words : laser-fusion .*Ar/ -3Ar dating, sanidine, pumice, Quaternary, Toga volcano

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P¹01?5 ¢7gfA K DEY'()"- +ῌ+ῌ+-*/ῌ2/01
%&
Institute of Geology and Geo-information, Geological
Survey of Japan, AIST, +ῌ+, Higashi +-chome, Tsukuba-*/ῌ2/01, Japan.

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 :  !"#$
Present address : Kyushu Center, AIST
Corresponding author : Kozo Uto
e-mail : k.uto@aist.go.jp

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Fig. +. Geologic map of the western part of Oga Peninsula and the locality of dating sample TOGA-/(modiﬁed after Kano et al., ,**,). The inset shows the location of the Toga Bay and exposures of the
Oga Pumice Tu#.

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ῐ ῕ ῔ ῑBassinot, F.C., Labeyrie, L.D., Vincent, E., Quidelleur, X.,
Shackleton, N. J. and Lancelot, Y. (+33.) The atronomical theory of climate and the age of the BrunhesMatsuyama magnetic reversal. Earth Planet. Sci. Lett.,Arῌ -3Ar 

.*

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!"#?@A (,**/)  $%&'(),-.CDE - $%&' (),  F/0,
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!"#?@AD EFGB*]^H_ I(,**,)  : NO$%  PQefg
STh'ijgk  .1 -1-ῌ-30.
Kuiper, K.F., Deino, A., Hilgen, F. J., Krijgsman, W.,
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]^ _`}ab (+33,) ~eN $%8
cd  N #|0,E ,10 p.
#?@Afgh (+32.)  ijk(,J6ijn $%&'|ENOop no. +. +1ῌ+2#> (+3-*)  &' &' -1 1.*ῌ1/*.
#> (+3-2) t &u| 0 ,,+ῌ,-,.
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l}K;^h·¢FG (+331) ODP $%zY7B(Y¸= ¹^º»`
¼½

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(+33/) !" : K-Ar, .*Arῌ -3Ar "#$%& ! .* S,1-S.0.
  (+330) '()*+,-./012
.*Arῌ -3Ar ",?@ ;ABC(D no. /*.1ῌ+2.
   (+333) '()WX .* Ar ῌ -3 Ar "-./ !`ab+c ;def -- +.+ῌ+/..
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Togashi, S. (+331) Laser-fusion .*Ar/ -3Ar dating systemof the Geological Survey of Japan : System outline andpreliminary results. Bull. Geol. Surv., Japan, .0, ,-ῌ.0.
 345678 9 (+33.) !:;<=>
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