k-arkazan.or.jp/cgi-bin/dpdf.cgi?q=51.1.3.pdf · fig. +. topography and geologic map of kimpo...

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ῒΐ /+ (,**0) + -+.* ῎ῒ῍῏ῌ K-Ar ῑῐ 至膼臯 膣 膀臱膮膶 腆腆 臮腽 腆腆腆 ,**/ 0 ,1 臺臂,**0 + +* 臺臂K-Ar Dating of Kimpo Volcano, Northern Ryukyu Arc Kiyoshi TOSHIDA , Kozo UTO ῍῍ and Akikazu MATSUMOTO ῍῍῍ Kimpo volcano is a distinct volcano in central Kyushu, western Japan, and is located -* km west of the active volcanic front of Ryukyu arc. In order to determine the growth history of the volcano, systematic K-Ar dating has been performed. The activity of Kimpo volcano has been divided into three stages. The oldest activity formed the andesitic stratovolcano in the southern part (Older stage). Six ages are concentrated between +.-2 and +.+/ Ma. The horseshoe shaped caldera was formed before the middle stage activity. The middle stage activity formed the andesitic volcano in the northern part (Sannotake-Ninotake). Ages between *./2 and *./* Ma are obtained from six samples. The youngest activity formed a dacite lava dome (Ichinotake), which is located within the caldera of the first stage activity. Two samples gave consistent ages of *., Ma. The total duration of the volcanism at Kimpo volcano exceeds one million years. However, long periods of repose existed between each active stage : about 0**,*** years between the first and the second stages, and about -**,*** years between the second and the third stages. These inactive periods are much longer than the durations of volcanic activities of each stage. It is therefore important to determine the duration of each active and inactive period of the volcanoes that have longer than a few thousand years of growth history. Key words : Kimpo volcano, K-Ar dating, Ryukyu arc, Quaternary, long term eruption rate +ῐ῎ῑ῏ 膠臃臦膜膪腚腙腻臧腏膑臷臭膊膷腋臹 腙膃腝腧膊膷腰腶腷腮腩膭臏腑腧腽臵臑腙膆臥 腑腧腊腅致膨臦膯膄腉腙腢臢膹膘膊膷腋腀腚腏腕腉腧膊膷腛腸臙膊膷腚臑腎腓 -* km膁臕膊膷腗腚臨膓 腙腻臧腏膻臑腇腄臨臋腗腑腧臢膹膘臏臚膊膷 腖腈腧 (Fig. +)膩膴腛膗腣膊膷臎臦臍臶膊膷膑臷 腚臩膫腛腽臔臻腡腥腨腘腉膜膪腙臬腟膳腠腰腪腴腯 腷膍腱腵腃腮腛膊膷腰腶腷腮臫膇腖臌臲+** km 臣腏腓腦腊腥臬腟膳腠膎臲腋膛臜腏膊膷腚腻臧 腖腛臌臲-** km 腙臣腏腒腨腤腦臑腖腛臌臦臍腩 臐腏腘腌腘腧 ( 臒膨膚臯+33,腅腁 腍腚腓腡膷腤腦臑腙腻臧腑腧膁臕膊膷腣臟膐膊膷腚膇腖腛腰腪腴腯腷膍腱腵腃腮腙腤腧臌臦臍腛臐腏腕腉腘 膊膷腚膔臒腛膎臖臒腹膷膔腩臁臠腗腑腧腍腗 腣膈膏臘臏腚臸自腋腊腅致膨臦膯膄腉腙腇腄腑腧膠 臄膊膷腣膁臕膊膷腗膽腑腧腍腗腋膲腎腨腕腉腧 ( +320腅腁 膊膷腚臠臓腛,/ km - 腖腈腦腞腓膢臏膾膖腙 腔腉腕Takai et al. (+32.) 腛腰腪腭腬腲腷腮腳腭腫 (FT) 臼臡腗臦膿膗腻腩腢腗腙+** 臼臗腊腥+/ 臼臗腞腖 2* 臼膓腺臈腖腈腧腗腐腓腍腨腩臞 腆腆 ,1*++3. 膋臝膺膻膋臝膺 +0.0 腄膵腅臰臨膅膦膝臆 臦膜膬膏膦膝臆臦膥膉膏Geosphere Science Sector, CRIEPI, +0.0 Abiko, Abiko-shi, Chiba ,1*++3., Japan. -*/2/02 腾臉膧腔腌腜膻+++ 腔腌腜臨膅 , 膸膞膙臅臛膱膦膝臆膕膌腐腆 Planning Headquarters, AIST, Tsukuba Central ,, +++ Umezono, Tsukuba-shi, Ibaraki -*/2/02, Japan. 腆腆腆 -*/2/01 腾臉膧腔腌腜膻臵 +++ 腔腌腜臨膅臢 1 膸膞膙臅臛膱膦膝臆 臦臀臊膦膝腆腒 Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Tsukuba Central 1, +++ Higashi, Tsukuba-shi, Ibaraki -*/2/01, Japan. Corresponding author : Kiyoshi Toshida e-mail : [email protected]

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Page 1: K-Arkazan.or.jp/cgi-bin/dpdf.cgi?q=51.1.3.pdf · Fig. +. Topography and geologic map of Kimpo volcano. (a) Location of Kimpo volcano in Kyushu. (b) Bird’s eye view of Kimpo volcano

� �� ��� � /+� (,**0)� +� -+�.*�

�����K-Ar��

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K-Ar Dating of Kimpo Volcano, Northern Ryukyu Arc

Kiyoshi TOSHIDA�, Kozo UTO��and Akikazu MATSUMOTO���

Kimpo volcano is a distinct volcano in central Kyushu, western Japan, and is located -* km west of the activevolcanic front of Ryukyu arc. In order to determine the growth history of the volcano, systematic K-Ar dating

has been performed.

The activity of Kimpo volcano has been divided into three stages. The oldest activity formed the andesitic

stratovolcano in the southern part (Older stage). Six ages are concentrated between +.-2 and +.+/Ma. The

horseshoe shaped caldera was formed before the middle stage activity. The middle stage activity formed the

andesitic volcano in the northern part (Sannotake-Ninotake). Ages between *./2 and *./*Ma are obtained fromsix samples. The youngest activity formed a dacite lava dome (Ichinotake), which is located within the caldera

of the first stage activity. Two samples gave consistent ages of *.,Ma.The total duration of the volcanism at Kimpo volcano exceeds one million years. However, long periods of

repose existed between each active stage : about 0**,*** years between the first and the second stages, and about-**,*** years between the second and the third stages. These inactive periods are much longer than the durations

of volcanic activities of each stage. It is therefore important to determine the duration of each active and inactive

period of the volcanoes that have longer than a few thousand years of growth history.

Key words : Kimpo volcano, K-Ar dating, Ryukyu arc, Quaternary, long term eruption rate

+� � � ������������ !"#� $%&'()*� +,-'(./012345-��6� 78 9:5-�;<�=>? @�AB'()��#C?-DE '(�FG'(�8�� -* km� HI'(J�KL !"#� M�N8�2��KOJ5-�AB4P'(6Q- (Fig. +)D RS��TU'(V�WX� '($%�YZ��[\]^_`?D ��� abcd.efg0hijk1�� '(./01lm6no� +** km p#q�rs^abcdto)uv#� E '(�!"6�no� -** km p#� w_xr86�n��W2

�y#`z`- ({<|�� +33,�D }�q]� E '(xr8� !"5-HI'(U~��'(�m6��.efg0hijk1 x-n��W��y#C?`?D E '(��{�� t�{�(�2��J5-}JU���4���)� �;<�=>? ��5-��'(UHI'(J��5-}J)���_C?- (K�� +320�DE '(����� ,/ km-6Qr� �q� �4�� �?C� Takai et al. (+32.)�.e���01���(FT)��J��T�!2@J � � +**���s^�+/����6 2*��L��6Q-J��qD }_2�

��

 ,1*�++3. ¡¢£N¡¢£ +0.0�¤�¥�K¦§¨© ��ª�§¨©�«¬��­Geosphere Science Sector, CRIEPI, +0.0 Abiko,

Abiko-shi, Chiba ,1*�++3., Japan. -*/�2/02 ®¯°�z±N�² +�+�+ �z±K¦� ,³´µ¶·¸§¨©¹º��Planning Headquarters, AIST, Tsukuba Central ,, +�+�+Umezono, Tsukuba-shi, Ibaraki -*/�2/02, Japan.

��� -*/�2/01 ®¯°�z±N7 +�+�+�z±K¦� 1³´µ¶·¸§¨© �»¼�§¨��Institute of Geology and Geoinformation, Geological

Survey of Japan, AIST, Tsukuba Central 1, +�+�+Higashi, Tsukuba-shi, Ibaraki -*/�2/01, Japan.

Corresponding author : Kiyoshi Toshida

e-mail : [email protected]

Page 2: K-Arkazan.or.jp/cgi-bin/dpdf.cgi?q=51.1.3.pdf · Fig. +. Topography and geologic map of Kimpo volcano. (a) Location of Kimpo volcano in Kyushu. (b) Bird’s eye view of Kimpo volcano

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Page 3: K-Arkazan.or.jp/cgi-bin/dpdf.cgi?q=51.1.3.pdf · Fig. +. Topography and geologic map of Kimpo volcano. (a) Location of Kimpo volcano in Kyushu. (b) Bird’s eye view of Kimpo volcano

Fig. +. Topography and geologic map of Kimpo volcano. (a) Location of Kimpo volcano in Kyushu. (b)

Bird’s eye view of Kimpo volcano with the dip angle of ,/ degrees. Vertical enlargement ratio is , : +. (c)

Geologic map of Kimpo volcano (after Hoshizumi et al., ,**.). K-Ar ages by mass fractionation correction

method are shown (average, in Ma). Contour line interval is +** m.

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Page 4: K-Arkazan.or.jp/cgi-bin/dpdf.cgi?q=51.1.3.pdf · Fig. +. Topography and geologic map of Kimpo volcano. (a) Location of Kimpo volcano in Kyushu. (b) Bird’s eye view of Kimpo volcano

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Page 5: K-Arkazan.or.jp/cgi-bin/dpdf.cgi?q=51.1.3.pdf · Fig. +. Topography and geologic map of Kimpo volcano. (a) Location of Kimpo volcano in Kyushu. (b) Bird’s eye view of Kimpo volcano

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Table +. K-Ar ages of Kimpo volcano.

����������� 36

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Takai et al. (+32.)�� ��������� - ����� *.3.�*.+/Ma, +.+,�*.,*Ma, +.*+�*.*3Ma

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Fig. ,. Three active stages of Kimpo volcano and comparison of K-Ar ages. K-Ar ages of this study are plotted

by their measurement methods. Error bars represent + sigma for K-Ar ages and , sigmas for FT ages. The

radiometric ages are concentrated into three groups ; +..�+.+Ma (Older stage), *./Ma (Middle stage ;

Sannotake-Ninotake), and *.,Ma (Younger stage ; Ichinotake).

st���K-Ar�� 37

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ments in seventeen GSJ Geochemical Reference Samples,

“Igneous Rock Series”. Geostandard Newsletter, +3, +-/�,+-.

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Reference Samples, “Sedimentary Rock Series”. Geostandard

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Geostandard Newsletter, ,-, ,,-�,/*.��[�.§T�P (+33,)¨©dª«¬­¥�®(¯����,���� ,�� ./� ./�/+.

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Japan.°Part / Yoshino area (Middle Pleistocene)°. J.

Geol. Soc. Japan, 32, ,*/�,,+.pI�= (+323) K-Ar�2�{�Q��%¬±@{���\�� ,~²�� .*� 0/�1*.

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“mass fractionation correction procedure” : application

to the Younger Ontake Volcano, central Japan. Chem.

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applicable to rocks younger than *./Ma. Bull. Geol.

Surv. Japan, .*, /0/�/13.³´GU� (+32-)�I� �,�� ?µ9p4�¶�

+-/ p.�T�� (+320)¨©�|�`��w.9�� ��+��Cp���7_vw� � � ,�� -+� 3/�++*.�Ty� (+333) �+�·���+��¡��E¸¹� fX�Avw+�º� U33*10� pp /�0.

Nier, A.O. (+3/*) A redetermination of the relative abun-dances of the isotopes of carbon, nitrogen, oxygen, argon

»T¼.�s�2.pI�=38

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and potassium. Phys. Rev., 11, 123�13-.Steiger, R.H. and Jager, E. (+311) Subcommision on geo-chronology : convention on the use of decay constants in

geo- and cosmochronology. Earth Planet. Sci. Lett., -0,-/3�-0,.

Sudo, M., Tagami, T., Sato, K., Hasebe, N. and Nishimura,

S. (+330) Calibration of a new Ar analytical system forthe K-Ar dating method and analytical results of K-Ar

age known samples. Mem. Fac. Sci. Kyoto Univ., Ser.

Geol. and Mineral., /2, ,+�.*.Sudo, M., Uto, K., Anno, K., Ishizuka, O. and Uchiumi, S.

(+332) SORI3- biotite : a new mineral standard forK-Ar dating. Geochem. J., -,, .3�/2.

Takai, M., Miyachi, M. and Hirano, I. (+32.) Paleomagnet-ism and fission-track ages of Kimbo volcano, southwest

Japan. Rock Magnetism and Paleogeophysics, ++, ,+�,/.���� (+33+)�������� ���������������� ��� -0� ,++�,,+.��� (,**-)!"�#�K-Ar$%&'()��*'+,-��./� 0�12345�6� U*-*,.�,2 p.

Tsukui, M., Sakuyama, M., Koyaguchi, T. and Ozawa, K.

(+320) Long-term eruption rates and dimensions of magmareservoirs beneath Quaternary polygenetic volcanoes in

Japan. J. Volcanol. Geotherm. Res., ,3, +23�,*,.78 �+9� : (+32*) K-Ar$%&';<�=>?@A� B,C�� -+� ,01�,1-.DEFG+R.M. H�I�+��JK+78 � (+33/)BL,M5;<�NOPQR�K-Ar$%&'STUV�W"XYZL[\]^\&_`;#a�bc��dTe�fgh��i�Z� B,C�� .0�,-3�,.3.j kl (+332)mGn BLo�� pq�rK�stuv�� pq�rK� wK�� m +x ]y+z{+|%� pp 12�+*2.

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