ῒΐ  /0  (,*++)
 0  +23ῌ,** ῕ ῔
 : !"
¼ ½,*++ 0 0 1 ,- 234 ,*++ 0 ++ 1 +2 23ῌMagmatic Evolution in the Initial Products of Bandai Volcano, NE Japan :Geochemical Results from the Ura-Bandai-Kogen Core on the Northern Flank
Takahiro YAMAMOTO῍
Bandai volcano is one of active volcanoes in the southern part of the NE Japan. The Japan Metrological
Agency made a new +**.0-m-deep borehole (JMA-V+3) within the +222 collapse crater of this volcano in ,**3.
I analyzed bulk chemical compositions of the core samples. This core consists of three units as follows : the
Ura-Bandai-Kogen core lower unit (UBL ; +**.0 to 1,.2 m in depth), the Ura-Bandai-Kogen core middle unit
(UBM ; 1,.2 to ,*.- m in depth) and the +222 debris avalanche deposit (,*.- to -./ m in depth), in ascendingorder. UBL is made up of andesite to dacite pyroclastic ﬂow and debris ﬂow deposits, showing a distal volcanic
fan facies. UBM is composed of a basal basaltic andesite lava ﬂow and overlying andesite lava ﬂows, showing a
proximal volcanic cone facies. Geochemical features of UBL are well reconciled with the calc-alkalic rocks
corresponding to the medium-K series of Nekoma volcano, which is older than Bandai volcano. On the other
hand, UBM is made up of unique tholeiitic rocks, although the superﬁcial products of Bandai volcano (AkahaniKushigamine, Kobandai and Obandai ediﬁces) consist solery of calc-alkalic andesite. UBM is regarded asconcealed initial products of Bandai volcano. 21Sr/20Sr and +.-Nd/+..Nd ratios for the basal basaltic andesite in
UBM are *.1*.*0 and *./+,2,, respectively. These values are further depleted than those of the younger ediﬁcesof Bandai volcanoes and other frontal volcanoes in the southern part of NE Japan, and manifest the beginning ofBandai volcano. Trace element variations of the subsequent tholeiitic andesite samples in UBM show that thetholeiitic andesite was not derived from the initial basaltic andesite, but was generated by a partial melting of acrustal material. Such geochemical change presumably implies temperature-increasing processes caused byintrusion of depleted melt from the mantle into the lower crust.
Key words : Bandai volcano, JMA-V+3, core, geochemistry567 89: ;<=>?@ABCDEF+ῌ ῐ ῎ ῑ ῏

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9|: ; +222 0BC:

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B*

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 (+33.)

 -*/ῌ2/01  +ῌ+ῌ+ 1!"#$%&'() *+,-'(./
Geological Survey of Japan, AIST, Higashi +ῌ+ῌ+Central 1, Tsukuba -*/ῌ2/01, Japan.

 (+33.)

 (+330)

Corresponding author : Takahiro Yamamoto
e-mail : t-yamamoto@aist.go.jpAbstract



190

 (,**+)  !"

1234 (+32+) !523 (+32,) %&'(
(+322) #$ (+322) %&'()*+,-./

0)678 9 :;)<8 = (+33.) >?@ ABC @ADEF : Fig. + )GH"IJ

KL (+330) %&'(

M+N!OG-PQ

O:R-)NSTUOVW<8 XYZ[ \]67)^_

0`+aObcd)ef

Fig. +. Geologic map of Bandai volcano and localities for analyzed samples. Numerals are thesample numbers. A
Mt. Akahani ; K Mt. Kushigamine ; O Mt. Obandai ; JMA-V+3
borehole. Modiﬁed from Yamamoto and Suto (+330). QVF-I, -II and ῌIII in the index map
are three groups in Nd-Sr isotopic space (Kimura and Yoshida, ,**0).

6Q3R,- STDED145U6V : WXYIVZ7[\9;#5 8

9: 5+  6  5

]

+33*

=_>?5`1aE@bAB%& ( C -+222

D, +33/), EFG-=(RcHIdJ

#, 6^;<191,  !(ELK) ! (LK)  ,;&<KLeMf'N, 

!Og ;#hP%&'( -D, +33,+(MK)  +  !;dJ ij]kQ%&'S , 4lm 

<YI7[\no'pq;#(NEDO, +33*) #, +..-  *./+ Ma # *.02  *.*. Ma ++.++*.0* Ma  2 " K-Ar

 , ,**, $%&'(+ ), 

K-Ar, 

 !  *  

6 Rr 1+* km, SWT + km 4Ma  K-Ar

  

*..1*.+*

$%&'( (NEDO, +33*)+

U65 (Fig. +), * VW +2+2.0 m -stW






VW +0-0 m-XY VW +.-* m  Wu4%-&'( (Fig. +)+ +222

/01 2 +.**.῍+,.+, 3 -1-2῍**./

=_>?

, v'Z#wx&9[N , *y ]VWOO

VW 3*,.+m

S('\% +**.0 m YI (JMA-V+3)

(]^5f9;#, ,6z_O{|}`a y,**3b:%&'( Yonechi, +321 ; cE, +323+ dkQ%&'( (Fig. ,)+ YI

ef~YIBHB1 g%&'S , z]= _5 hi 9 fjT +./ km- =&ef~YIk/ 1/5AB9+ YI 4lf'm<nooX-Zpq-r:=8 . M *st5, 4u 6,v<i4 ##] , w&#wx&Z

6xyzYI7E1 (,*++)+222<{| 49 (Nakamura, +312)+ w&E58}
T& , dE ]'(  =& : , +312+^ -./ m  ,*.- m >5 , ῌYI=l 8(], EFE#N

64 , ~ O= ])'(T5 =(, /
R< %5H v¡5R *s ;# v(' £¤el%&'(+z%&'(+EF~^ -./ m >5 ,  5+=¥, XY.stW<k=YI8}, +222

=&#&+^ ,*.- m  1,.2 m >5 , . U¢( w<
#, 4U6u4l=+ ^ ,*.- m ¦, *#,65*&9/-.* m >5 , ¢% 1+2 m §0§0

ZH( (Fig.+)+ :- (+330)   w=+ ¨ , U w

U<©

ª ¡ 5, 67  «¬ (clastogenic) 

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 w #&- U #]¢£, ­¤'¥¦j +*=& /  + 67, *,-,,* ῌ (Table +), 0F GHIJKAL@LMN12§X¨E, ©ª«=&, +222

OAP®@LMN12<¬v+ ^ /-.* m  /1.. m,-<¯°QHR,-­ = E®5 

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,6<Q± ¡./, T 2   , 67

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..0  5+  + 67.,ka  AMS !"#&'(9 $% AB,*+ : :, ,**-, ;&< Fairbanks et al. (,**/) <[u y=w±Po&+ >+/,*ῌ5 (Table +), 0F²³=H

^ ,+.2ῌ,,.*m   , Bn *1

, Bn*0+^ .*.*ῌ.*.+ m  , Bn*0

^ .1./ ῌ .1.0 m ^ -,.1 ῌ -,.3 m   , Bn */&(' () # .0 cal ka #=+ >9, * ?

dJ

+ Tn @ABC8 

DED,-<./'(+J ©µ9+

 6   ;,    4U 6    6 

, Bn*/+

^ 0,.3 ῌ 0-.* m^ 03.3ῌ1*.* m d^ 1,.2 m µR +**.0 m >5 ,  6d¨, ,**, ¶E= , U ¶0wO067w·, 6XY.stW M&+ ;6

<·°4U6¸¸l5+ ¨E  , )N¹º 3i=6E¹ »£ºῌ=0w#W¼^»½w , ¡¼7%&'(+ Kimura et al. (,**+)½U5u4%&'(+ ¶0w ^ 2-., m 

Nakamura, +312 ; Kimura et al., ,**+ ;

y

192

345
2..2 m 678) 9:;<=>;=?@A@B

CDE1F)GHI J*  "# 3*.3/ m %& 33.0 m 678) K$
LMN 

!

O P;<=>;=  ῌQRRST)*U:" V"W%&XY G
HI Z[%ῌQX\:!]^ F)_`J.]KOaXP Rbc
d

Pe.f

O .*  // ῌ   Bn*-  1/.2-1/.3 m(Table +)



! Bn*+  3..,-3..- m

"# $!%&'()*. 

EXg7hijklmnF Nd-Sr /012+,Dop* h ijklmnqr 2 [%
ds6t7uvwxyῌz{|1F}w~11K.. 0 DF)* /012+,qr , Fvwxyῌz{|1%&
 + DF)* mn Activation Laboratories6) Elm3 Sc, V, Ba, Sr, Y, Zr 6P_ Thermo Jarrell-Ash ENVIRO II ICP Z.&Olm6P_ Perkin Elmer SCIEX ELAN 0***
ICP-MS +,-.* Sr-Nd /012 Finningan MaT,0+ 2-collector Mass spectrometer mn-._P '(0 Appendix + 6)_P mn
6P_ Bn*+ F Bn*-  UBL qr
 Bn*/ %& Bn*2  UBM qr 6m^-. xyz{|1D AK ~1D OK Fu/  
JMA-V +3   UBM  Bn */ F Bn */+ ] SiO,

`O /,.1/-.+ wtῌ  Y/0.20+.0wtῌ  (Table ,)  kl" ]u ds"g7 AK 
 OK F¡¢uf £ElmF2¤m^)*¥¦§B¨6kl©P]ª«&. (Fig. -)
uX¬­ SiO,-FeO*/MgO ® UBM ] ¯&%X°±r@B²³´µ6¶·§B-.6)_ AK °±r@B¸¹ºr¹¸»²³¼½ UBL F OK
¸¹ºr¹¸»²³´µ6¶·§B-. J*

Fig. ,. Lithofacies of the JMA-V+3 core. Bn*+ to Bn*2 show the sample positions. UBL the UraBandai-Kogen core lower unit ; UBM the UraBandai-Kogen core middle unit.

:2;<=>?@ABA  CD) : EFGH )*IJ

193

Table +. Modal compositions of phenocrysts.
Pl  plagioclase ; Cpx  clinopyroxene ; Opx  orthopyroxene ; Opq  opaque minerals ;gmgroundmass ; trtrace (*.+ῌ).

SiO,-K,O %"

 R SiO, $ 

K.LMNO0&%

K,O $ " UBM OK 4 

UBL AK  !"#

Nd-Sr U!"" #$%&V 'WP:24T

"XYTZ .' %0 [\] ^UBM

839123" #$%&V _`a :2( )* +, -./%0(b,7 QVF-I +, QVF-III c4)!+Ud UBM * )+,[4 

!-  ./  01- *(Fig. .) % & 'S QVF-II  T T+T UBM 8391
23%(Fig. -)Rb $ 

MgO TiO, $

P:2>" Q7& Kimura and Yoshida (,**0)83912341234%" SiO,

h.3ij@%
Ba $

ef

 k5lm6.839123S&1231 
1ῌ+ 

% 7nIo)%"8p+,qp.9@^
4v=Trs

JMA-V+3:): ,** m U;[ <tu*wxyz{S +33* > |}67Z BD-+ ?@~ A B m 6 (REE)  + , [  4 UBL
AK! (Fig. + ; Kimura andYoshida, ,**0) +,"2,+g7?R ^4.24%0 (Fig. .)
%0"Q



UBM

OK 4&~AC ~A"_  DV+**.* m %" rs GH4 UBM 8391

23E3% 35F.  G%567

:23H-.(b,7 D% I J +33/ I J (+33/) S4 ?@"4 (Fig. /) UBM

0. m K "J4 Eu

8 39123L M. ^7"NO

R.5S-6+Z^4 T74,7

Ma

123E 3+, *.+.

K-Ar >PQ ?@ 2+

23 E 3 - K  +, *..+*.*0 Ma*.+/*.,0 Ma*.20*.-3 Ma

K-Ar >PQ.567 ZjT?@ 0. m
0 Nd-SrUBL

Bn*+( 123 ) " +.-Nd/+..Nd*./+,0/ 4 21Sr

/ Sr*.1*/+, UBM
20

3
Bn*/ 839123 " +.-Nd/+.. Nd  *./+,2, 421 Sr /20 Sr  *.1*.*0 AK+**/-*-+

K-Ar >PQ" UV_U

XY ῌ  Z 2 !

Z 839123>P ,/ [>8  8 ; 2

K-Ar >PQ& ¡.3i

>>P

4eb67Z (Table -) Z OK¦fS4 G%

3>+,12

W>PQ+,

m \] +330 S&v ^_`aT

( 123 ) "+.- Nd/+.. Nd  *./+,01 421 Sr/20 Sr  *.1*/*0"¨ +.-Nd/+..Nd*./+,1, 421 Sr/20Sr*.1*.02*.*1R 8391

32 m

b"cT ¢£J (+33/)¤)d¥

839123$§ BD-+Q.

GH"  ©Mª« g ¤¬= S" 67

567 (Kimura and Yoshida, ,**0) UBL 4 AK­ ^ 839123 >P" =®hi8j"+B¯TZ Nd-Sr U!"&°&4 UBM 839123 ®" OK ^7,
Nd-Sr U!

 Q7+ C=%T+±²b ³k(+33.) " +222 >l´m

" ¶Z"3i Z ·T

E3+, *.1 (Fig. 0) UBM g¼s:2

:2¹º»r'W*., Ma:nµop>[123K-Ar >PQq ^7¸

t½#uT BD-+ G

839

194

῏ῌ῍῎



 :  !"#

195

Fig. -. Bulk major element variations of the products of Bandai and Nekoma volcanoes. SiO, versus K,O, FeO*/MgO,
Al,O-, Fe,O-, MgO, TiO,, CaO and Na,O. The boundaries deﬁning the low-, middle- and high-K ﬁelds in the
K,O-SiO, diagram are from Gill (+32+), and that between tholeiitic and calc-alkalic ﬁelds in the FeO*/MgO-SiO,
diagram is from Miyashiro (+31.). AKthe Akahani-Kushigamine ediﬁce, OKthe Obandai-Kobandai ediﬁce ; UBL
the Ura-Bandai-Kogen core lower unit ; UBMthe Ura-Bandai-Kogen core middle unit. Data for the extreme-low K(ELK), low K (LK) and medium K rocks (MK) of Nekoma volcano are taken from Kimura et al. (,**+).

196



Fig. .. Bulk trace element variations of the products of Bandai and Nekoma volcanoes. SiO,
versus Rb, Ba, Sr and Zr. Data for ELK, LK and MK of Nekoma volcano are taken from
Kimura et al. (,**+ ; ,**,).

Fig. /. Chondrite-normalized rare earth element patterns for UBL, UBM, AK and OK.
Chondrite-normalized values are after Sun and McDonough (+323).

  '() *+,+ (+33/) -./012
:;< +**0*+-+ = >?@A4 AK B!"#$%&'
JMA-V+3  34 567 (UBL) (893"

CDEFGH ,7 (UBM) ("IJK3AL"

MNOPQR @ASTU1VWX-YZ[A\ (Fig. ,) UBL DEFGH]

UBM OK ^_`.ab" MK -4c)de-fg^.4h1ij.ab"Yk

1l'm nm :;<Y4*+ (+33.) op :q ]dJK3(krstXp!"Q :  !"#$%
Table -.

197

Sr and Nd isotopic ratios.

Fig. 0. 21Sr/20Sr versus +.-Nd/+..Nd diagram. Data of Quaternary volcanoes, including OK and
Nekoma, in NE Japan are from Kimura and Yoshida (,**0) and Kersting et al. (+330).
Symbols are same in Fig. -. QVF-I, -II and ῌIII ﬁelds are shown in Figure +.

&'()*++,-. /012345627

89 :;<= 6> 45?@A3> BC

DE'F 4+* UBL G"H"7

()'IJKL@ A , < MN7

O

XY (+32-) Z[@ \]^

PQ RS,TUVWR /* 

cde MK ;9fghFi  AK 37_`abjk3l  mnoR*'F p@ Fujinawa

qrL5? (Figs. - .) p@ Nd-Sr stuvw(+322) 7 P =`x  ?5 89 :;<?5* UBL 7 MK +Siy?z3S{5? (Fig.

3|k}k|~<

' Sr stuv>D0) AL-!mS7 UBL VO 0Si

1Q3RA33 4S?  y2- P] mS6!

'F UBM w?57 !' UBM R
7S /"7 u&p{ >DSA3V -+45? K

mbjkV5@ Kimura and Yoshida (,**0) 7
6 Nd-Sr-Pb stuvV f;k

5?@A37I'F {5  t"3 Q¡"3¢'£ '¤A3V¥45?

¦' §¨>©p{@7 UBM +-3Si AL>

 Aª[[« QVF-II ¬Rs ­

(AK  OK) ²³45stum´µ4@> 'F3®¯'¤°±1ῌ, 

7 |k}

45?@A37 (Fig. 0) f;k"3 Qk|~<=6¶·R¡"3¢¸?> _`a?54 ¹ºmS\]^ 'F 4+4S>- /@A3 RS,T

RA3Sf;k"> '¤@*> 

7 stum´µ4@»¼6E= 6½

7 Q¡">Fpi¢



198

Fig. 1. Reciprocal plots of trace element abundances for UBL, UBM, AK and OK. Solidstraight lines are the linear correlation lines for the UBM andesite.

   !"#$%&'(")9: ; !<(4=>)Kimura et al. (,**,) B *+CD4,-./014239K ; L  !M(GH3
4 T

84=; !A

*+,-./0123 4 K 56478
Sisson et al. (,**/) 4?@A ")9

E+4F3GH3 K 9

I;9"J47

N OP= 9 UBM 234QRBS
LU484"#8VU ,4WX5YZ9

UBM 4,-./01423B *+4[1% \]\F4 64V^!A ;4423"#8 K _ Rb 9 ` :aJb9Bcd

")d 6V^0-efB [ghij4kl

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./CD E0 F (+32,) 1ῑ%2G>=    no.- ,+ῌ-,.
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j .*-p
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I .9S ῍8 4567 0 (+33.)
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&'() (+32-)   /0# +-/p&'() (+322) ; <=
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o9 pq rs (+33,) ;!CDEF
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$% 13ῌ20
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1+23456789:  (+33/) +222
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 mQn!
h 0ijklGl0"t /. -,-ῌ-.*
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 * (+330) bhwy;£+= mQn¤¥" .1, --/ῌ-/3
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, -. (+323) ¨©ª# «. ¬;­ +222    , .+, +--ῌ+.1.
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no. , +/ῌ,0.

Appendix. Sample localities.

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