K-Ar. K-Ar Ages of Hakone Volcano, Japan

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1 /* (,**/) /,2/,33 K-Ar,**/ - ++,**/ 3. K-Ar Ages of Hakone Volcano, Japan Kazuo HAKAMATA, Shigeo SUGIYAMA, Isamu IMANAGA, Kazutaka MANNEN and Yasue OKI Hakone Volcano is an active volcano located near the northern end of the Izu-Bonin volcanic arc. Kuno (+3/*) reconstructed the evolution of this volcano based on detailed study on topography and volcano stratigraphy as follows: +) development of a large stratovolcano (OS : Old Somma),,) collapse of the stratovolcano and formation of the first stage caldera, -) renewed volcanism leading to the formation of a shield volcano (YS : Young Somma) inside the first caldera,.) collapse of the shield volcano resulting to the formation of the second stage caldera, /) growth of Central Cones (CC) inside the second caldera. Our K-Ar dating performed on several lava flows, lava domes, and dykes revealed the following interpretations : +) Ages between parasitic volcanoes on the flank of OS and YS are overlapping.,) Ages of Yugawara volcano presumed to be pre-hakone edifice by Kuno (+3/*) and that of OS are indistinguishable. -) A lava of CC obtained from a deep well shows close age to Hk-TP eruption, later stage of which is thought to be initiation of the CC stage (Hirata, +333). From these results and previous tephrochronological and geological studies (e.g. Machida, +311 ; Takahashi et al., +333), we propose a new classification of the edifices of the Hakone Volcano and their ages as follows: +) formation of the Lower Older Edifice [LOE] which constitute the main part of Kuno s OS lasted until the eruption of TCu-+ tephra (*.,/ Ma).,) Upper Older edifice [UOE], the parasite volcanoes on LOE, was erupted from *.,/ Ma to *.++ Ma. -) Activity of the Younger Edifice [YE ; corresponding to Kuno s YS] was initiated since the emplacement of Hk-TAu+, tephra (*.+- Ma) and ended at *.*2 Ma..) CC erupted from *.*0/ Ma to the present. Key words : Hakone volcano, K-Ar dating, stratovolcano, parasitic volcano, caldera forming + (Fig. +) (Kuno, +3/*),/* *-32,/0 Municipal Government of Hakone Town,,/0 Yumoto, Hakone, Kanagawa,/* *-32, Japan.,.- **+0,,2 Improvement O$ce of Sagami River, Kanagawa Prefecture,,,2 Tamura, Atsugi, Kanagawa,.- **+0, Japan.,/* ** ; +302 (+333) (+333) K-Ar Natural History Museum of Kanagawa Prefecture,.33 Iriuda, Odawara, Kanagawa,/* **-+, Japan.,/* **-+ /20 Hot Springs Research Institute of Kanagawa Prefecture, /20 Iriuda, Odawara, Kanagawa,/* **-+, Japan.,**- +,+,**-. +.,+ deceased Corresponding author: Kazutaka Mannen mannen@onken.odawara.kanagawa.jp

2 286 ;;;;;; ;;;;;;; ;;;;;; ;;;;;; ;;;;;; ;;;; ;;;;; ;;;;; ;;;;; ;;;; ;;; ;;;; ;;;;; ;;;;; ;;;;;;; ;;;;;;; ;;;;;;;;; ;;;;;;;;;; ;;;;;;;;;;; ;;;;;;;;;;;;;;; ;;;;;;;;;;;;; ;;;;;;;;;;;;; ;;;;;;;;;; ; ;;;;;;;; ;;;;;;;;; ;;; ;;; ;;; ;; Fig. +. Index map of Hakone Volcano. K-Ar, +),) -).) Kuno, +3/* ; +31, ++ km 3 km 3** +,** m (+31,) 2 +33* ; , Kuno, +3/* ; +31, Kuno, +3/* ; +31,

3 K-Ar Kuno(+3/*), - +31, (+31,) OS / ; ; +32* Kato, +32/MS ; +333 ; +333 ; +333 ; , (+311) (,**-) TCu-+ TAm-/, TAm-+, TB-+, TCu TCu- + TCu-+ TCu-+ 2 Aso-+ *.,/ Ma Hk-TAu+, ; MnP Hk-OP Hk-OP Hk-OP /a 2* 2/ ka,**- TCu-+ Hk-OP, -AP, -MP, -TP, -S Hk-OP, -MP, -TP Hk-CC+ K-Ar +333 ; +333

$(+31,) "#$%&'()* (+32*) +, QS +YJ T UV W VX Z[\]^_`abc\] defg h i^ jkl m8nopqjrs Table, m8nojr t"#$%uvw -.$

4 < 2 < < < 288.ῌ K-Ar ῑ ῐ ῒ Fig., Table +! (+31,) "#$%&'()* (+32*) +, QS +YJ T UV W VX Z[\]^_`abc\] defg h i^ jkl m8nopqjrs Table, m8nojr t"#$%uvw -./ : x< yzi{ }~ > Jr ; 912<78=<>?@AB C4562 DE1 XRF-+/** H<,*** FB GHI JKL MNO PQ Fig.,. R- Index maps of sampling locations.

$1 K-Ar yz.ῌ+.ῌ+ῌ+? @A B, - mm C DEFGH9IJK+ L -*1 289 % MMNO$PQR + mm ST UO9IJK+ DE F (+* +/ῌ) QVWXYZYF (- /ῌ) [\ GH ]GH^ [D_FGH(`a+ XYZYFGHBbP N0*W!$

5 1 K-Ar B, - mm C DEFGH9IJK+ L -*1 289 % MMNO$PQR + mm ST UO9IJK+ DE F (+* +/ῌ) QVWXYZYF (- /ῌ) [\ GH ]GH^ [D_FGH(`a+ XYZYFGHBbP N0*W! "#$%&'()* cd e mm 9fg$Ph 9 ijbkl : + F $% (Fig.,i)+,- (+31,)./01 2 &3& mb *.+/ mm C no DEF6 *.*+ mm C _ (YV+) 45$%&'6789: &; <= + > FQVWpqrstXZu intergranular vw(x + Fig.,. continued.

6 290 Table +. Summary of sampling locations. Table,. Bulk rock chemistry of samples for K-Ar dating.. +, -*2 -*1 -** m (Fig.,i) +31, ; +32* + - mm (+* +/ ) (- / ) (+ - ) (+ - ) *.*+ mm hyalo-ophitic *3 (Fig.,i) +31, ; +32*, mm (+/,* ) (- / ) (- / ) (+ - ) *.*/

7 K-Ar 291 mm intergranular * (Fig.,j) +31, ; +32*. / mm (+/,* ) (- / ) *.,/ mm *.*/ mm intergranular.,., +,*3,** m (Fig.,a) (+31,) OS,, - mm - mm (/ +* ) (+ - ) (+ - ) *.+ mm hyalo-ophitic.,, -*.,/* m (Fig.,i) (+31,) OS,,. mm, mm (+* +/ ) (- / ) (+ - ) (+ - ) *.+ mm *.*+ mm intersertal ,*0 (Fig.,c) (+31,) - mm,* (- / ) (+ - ) *.,/ *./ mm intersertal. -,,*1, (Fig.,j) (+31,) OS, (+32*) (+31,) OS - OS, OS, OS - mm cm, mm (/ +* ) (+ - ) (+ - ) *.+ mm hyaloophitic. - -,* ** m +33+ (Fig.,d) + mm *./ mm *.,/ mm hyalo-ophitic *./ mm intergranular, mm , - km

8 * (Fig.,b), mm + mm, *./ mm *.+ mm. - / ; -+. (Fig.,l) (+31,) OS, (+32*) (OS -) (OS,) OS,, - mm (+/,* ) (+ - ) *.+ mm *.*+ mm intergranular intersertal. - 0 ; -+/ JR 1** m (Fig.,n) (+31,) OS, (+32*) (OS -) 2-* m +31, + mm (/ +* ) (+ - ) *.,/ mm *./ mm , (Fig.,h) (YS) +31, ; +32* + mm (+ - ) *.+ mm *.*- mm *.*+ mm intergranular.., -+1 (Fig.,e) (YS) +31, ; +32* + mm (- / ) *.+ mm mm intergranular intersertal. /. / + 0**.3/ m -+2 0**.3/ m (Fig.,f) 2*0 m,*/ m 0*2 m,*** (+/,* ) (- / ) (+ - ) (+ - ), mm *., mm *.*/ mm *.*- mm intergranular / K-Ar -2 Ar +s Nagao et al. (+330) 0* 2*,

9 K-Ar 293 VA-2// +s l e *./2+x +* +* yr + l b..30,x+* +* yr + K.* K *.*++01 (Steiger and Jäger, +311) Table - t av) (s av) ; t av s av Fig. - Table -. K-Ar ages for Hakone volcano.

10 294 Table -. continued (+31,) (*.,- *.-2 Ma) (*.,0 *.-, Ma) (+33.) (+33-) (+31,) K-Ar

11 K-Ar 295 Fig. -. K-Ar ages in this study and proposed classification of the Hakone volcano edifice. Eruption stages and classification of edifice in previous studies are also shown.

12 296 0, (+31,),*1 ; *.+. *.*+ Ma,*0 ; *.,* *.*, Ma -*. *.-, *.*, Ma ;,*3 *.,0 *.*+ Ma (+333) *.. *./ Ma +33* ; , ; *.++ *.*+ Ma,*2 ; *.,0 *.*+ Ma (TB-3),-, ; *.+/ *.*+ Ma -+/ ; *.,* *.*+ Ma,*0 ; *.,* *.*, Ma,*1 ; *.+. *.*+ Ma -+. ; *.+/ *.*+ Ma (MnP Hk-TAu+,) *.+.- *.++ Ma *.+.1 *.**3 Ma ; +311 *.+,/ *.+-* Ma ;,**- (+31,) (+32*) (,***) Hirata (+330) (+333) K-Ar /,*1,*2 -+, / ; *.++ *.,0 Ma ; *.*2 *.+, Ma +333 Hirata (+330) (+333) (*.+2 *.+. Ma).**** 0 - (+33+) (Hk-TP) (Hk-TPfl) -+2 ; *.*1 Ma -+0 ; *.*2 *.*+ Ma Hk-TP (+31+) Hk-TPfl.3*** /*** (+322) +. C Hk-TPfl /*+**,1**,*** (,s) (+33,) +. C Hk-TPfl /,-+* -+*(+s) (,**-) Hk-TP Hk-TP. 0 0./ *.*1 *.*+ Ma Hk-TPfl,**- Table -.* Ar Ar 33.* Ar.* Ar

13 K-Ar Picea, Pinus, Abies, Tsuga Alnus, Lepidobalanus, Carpinus-Ostrya,*** Hk-TP Hk-AP ; 1* ka ;,**- (Tsuji et al., +32.) Hk-TP Hk-AP Hk-AP (*.*2 *.*+ Ma) Hk-TP -+2 (+33+) 1 +),) -) (+333) (+333) (+311) Fig , (+333) (+33-) (+33.) (+333) (+32*) OS - (+333) (+333),0 TCu-+ TCu- + TCu-+ TCu-+ *.,/ Ma (+332MS ; +333) (+310) Tm-, ( TCu-+) Tm-- ( TCu-,) (+333) *.+/ Ma (*.++ Ma) (+333) (+333) *.,1 Ma TCu-+ Aso-+,**- *.,/ *.,1 Ma (+333) ; *.,1 *.+2 Ma (,***) K-Ar *.,+ *.*, Ma (,***) (+333)

14 298,* (+333) TCu-+ (*.,/ Ma) (+311) 1, (+311) Hk-TAu+, *.+- Ma ;,**- *.*2 Ma (+333) Hk-TP *.*0 *.*0/ Ma,**- *.*0/ Ma (+333) *.+/ Ma,** ; +31* (+333) (+333) 2 K-Ar +),) -) Hk-TP (+333) (+333) *.,/ Ma *.,/ *.++ Ma *.+- *.*2 Ma *.*0/ Ma., (+33*) (+33+) +*

15 K-Ar 299 (,***) -, (+33+) TP +* (+33.) +33. p +.0. Hirata, Y. (+330) Geology and volcanic activity of Hakone volcano, Japan. IBM arc system symposium - program with abstracts, +*- +*0. (+333) 3 +/ (,***) K-Ar /+.+1.,*. (+32*) Kato, T. (+32/MS) Geology and petrology of the north and west old somma of Hakone volcano, Japan. Master thesis, Univ. Tokyo, +*0 p. (,***) X,1 +*1 +,/. Kuno, H. (+3/*) Geology of Hakone volcano and adjacent areas. Part I. J. Fac. Sci. Univ. Tokyo Sec. II, 1,,/1,13. (+31,) (+311) -,. p (,**-) --0 p. (+302) tephrochronology.+,.+,/1. (+31+).+,0 1*. (+31.) 2- -*, --2. (,***) *. (+333) ++ (+333-W-*3) Nagao, K., Ogata, A., Miura, Y. N. and Yamaguchi, K. (+330) Ar Isotope analysis for K-Ar dating using two modified-vg/.** mass spectrometers - I: Isotope dilution method. J. Mass Spectorom. Soc. Jpn.,.., (+333) ++ (+333-W-*3).1 /0. (+33,) 32 3*/ 3*2. (+33-) +*, (+31*) Steiger, R. A. and Jäger, E. (+311) Subcommission on geochronology convention on the use of decay constants in geo- and cosmochronology. Earth. Planet. Sci. Lett., -0, -/3-0,. (+332MS),. p. (+333),+.-1../. (+322). / +. C -3 /,/ /-/. Tsuji, S., Minaki, M. and Osawa, S. (+32.) Paleobotany and paleoenvironment of the Late Pleistocene in the Sagami region, central Japan. Quaternary Res.,,,,13,30. (+310) -,2-2.

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