, - { y /0 z ,**0%y+| +2  0 ῑῒ῔ΐ῍ῐῌῒ῏῎ῑ+NPO  ,     + ,+ +2  .  / !"#  +2  /  +* !"$%

Geological Structure of Arima Hot-spring
Susumu NISHIMURA+, Ikuo KATSURA+ and Junichi NISHIDA,+

NPO Think-tank Kyoto Institute of Natural History, , Otani University

Abstract
Arima Spa, situated at the northern part of Kobe City, is one of well-known hotsprings in Japan. There are various kinds of chemical type hot-springs. One of them iswell-known as “Arima-type deep thermal water”. It has very high Cl concentration andextremely high dD and d+2O values, and -He/.He ratio. Such high values in water isotope
composition imply that these saline waters are originated from andesite-magmatic steam
or mantle-derived water. Almost all hot and cold spring water at Arima Spa are gradual,
mixted with deep originated CO, (magmatic or mantle-derived). In this region, there are
no volcanic activities, so that the Arima type steam is containe the ﬂuid devolatilized
from the subducting slab of oceanic plate as pieced together from the various accounts.
Geological and geophysical surveys evidenced that location of springs and the ﬂowof thermal waters in this area are controlled by the deep developed fault system andrelated upwelling pipe.
Key words : Arima Spa, Arima-type deep thermal water, isotopic ratio, subducting slabderived ﬂuid, fault system&'(') : *+,- *+./0 1234 567689:;0<3 =>?@+ῌ ῏ ῍ ῐ ῎*+,-ABCDEFGHIDJKL2MN OPQ*RGST,-UVWX YZ[ῌ\]^[G_`GabcTdefgVWX hiῌjklmnP*+,-LopqrstuP!vwx
3.`4  12   ++3,   ! " #$%&' ()* ++/30 , -' ./&0 1&2 3   !4"/5 6  (#$6 78%9 &'(:&;)* + 1%, 79.%- +<.=#./,  >.0123  
?@4 + A +3.0 BC 01.. m &5. /,D E675 3., gῌl 
% 8  +32* 9 ClF 75: +gῌl, . ./.1D ;G +<=>
+321, HI
3*D M+3//  &5 +0/,2/ m  +, J?@ ? 0 JKL.5'  Nῌ@.A8BCODEPQ FR: .** m G@ H> HIJ KS E6;.ῌTLM9 Nakamura and Maeda++30+,  (NEOOPUQR SV TWUVPQTW,XXY

TYQR Z-Z["6 [\ HI )]^_`\&a]
+Okamoto, +30, ; ^b&1+30. ; _`a>+31. ; bJῌc+312 ; Masuda andTsurumaki, +32, ; Masuda et al., +32/ ; +320 ; Sano and Wakita, +32-,

dῌe ++320,  (UcῌdefPf3ghghi6  i + A%jjklmn k1 opqr! mnstkuvwxy-Uz*lYmno .
+320+33/  pB  q&g{X| r}~s'Ft

Ymnouv -Z&.7" .PRw.23w^xy`\hi z ++30,,  d +,*** a ; ,**+, {]/7&]/  '4 /1 .`=|  } ~ ]>no 8 H } a] ,ῌ ῕ΐ῎ῑῐ῔῍ῒ῏.R _P;%  R&3&& 3R&]  ++30,, <= ῌ ++32-, Masuda et al. ++320,  R7ODEA0\&RXf-HDE A23wDT

 Masuda et al. ++320, R 1&+ +,.@ Pj7¡@,9BCO6 +¢£¤O , X (A86 DE s'BCO¥(¦§O66 DE  4¨©Oῌ OX (fªA86  A8ῌ§O '¡a«j7~¢¬¢£­¤¥x®W¤¥x (4¯¨6DE
.¦U§A sBCO@¨°©iª&I.±A A«'KS«: +¬² ³. ²a , A KS´µ&;, DE ¦§
OBCO&'A­®o1 A¶¯°±·
²P¸ ³¹´ µ¶¸ºE·¯,·3¸0 A«'HIJ/z23 .P xy-0 ¨s¨A®o1 + +,¢» N. sQA¹¼D'+ ,, A8N.

;;;;;;;;;¹ /0 º ,**0¡±¸5;;
Fig. +

Geological map around Arima Spa (modiﬁed from Masuda et al., +320).
 +  Masuda et al., +320 ´µ¶ : Z·v

 -   +3/.  !" +30,  #$%&'( +32-  #$%)*+,-.( +3/-῏,**, /012345?/@?45

 65789/0 : ;<= - >A + ῌ B,C ῍ D ῎ EF GH  IJKLG ῌ B,C ῌ῏+ MNOPQ GRS5

TUV ῌ῏, B@PQ B?/W@?45 XYZ:

[\]^_/`a :=/ [\]ῌbc]^_[bdGefgcd/hi ῌ῏,bc]^_/`a

0j/kl45m , no pqCr sH1 t/ou,Q vH GwxGy  z 3,*** lῌ@G6j{B,Cz +*῍ z 3** lῌ@:kl45

 POB,C|B,CMN NaCl Po}~z ,  G~y5G<y GH ZyvA , /Q 657A , /ῌBMNv/  +331 /0 : =Gs/** m G v:v:G ῌBMNv75 55N 3*./ 3..0 GH \+322  v 3..0 GH:2  ,**-  ¡KLG

v¢£¤1 vs¥¦  £ 657ῌB? U v§/ + J¨NpqC©ª«¬­®G<y . @?¯ ῍ : ῎ EF °± ῌ B,C:²t/³y  ῌῌ῏῍῎6Fig. ,Distribution of faults and the hot area, estimated by the results of g-ray survey.
 ,  

» /0 ¼ b,**0cDkºTable +7Hot- and mineral springs around Arima Spa.
 +ῌJKo!

CDAD<  CD , u'C HD ῌῌ
 + ,D b­c|bgῌlc|-bmgῌlc

ClHCO

01SO.

,|bmgῌlc
bmgῌlck\D

GHGH:;<)*= ?@2*4*+®*4*,3*®32.-®---,®

,-4*®.-42,4-®-+4*+41®.-4/+4+®.42

0*®+1*-/*®/**/**®,5.**+/*®+5***°±./1/*®+5-**®+5-**-**®+50**

nd. -tr.

/®-/nd. -tr.

*®+,*®+**²hb²c h¯

³01|´hµ¶01

:B

High temperature and NaCl springs in Arima.
 ,£¤¥ῌ¦§US V¨U©
+ ,ªῌ«¬¡l¢

Table ,

JK·~¸~ bmc

JKnD b­c + ,+3/+3/++3//+3.2+3//+3/-,,+2,+2/,*0,11,1*

31
31
32
32
3+3,

JKn bm-ῌ¹c,*/*0*.*+2-1   !" #$%&'( ῌ  ῍ )*+,-./ ῌ 012345667898:;<)*=  >695?@2A ῍:B- (/ /+CῌADCDAE .** m FGHIA( JKL MN O2*P2 .Q RSTUVWXAYZ[\ῌ [\]^_ -`a-.( Nakamura and Maeda b+30+c adef gDh2
ijkl mn.opq\rsq+.\tjkuMvwxy z{( Okamoto b+30,c D Cl| }~+,-bX8    ῌ     +30.   ῌ  ! Cl"#$  % &    HCO-  Mg") CO, #$*+ ῌ / ῍ 01/ ῎ 1

 Br, B(,'CO, ,  -.

2ῌ

34 CO, 56

839:7

8/ ῏ !746

CO, "# $;%<#7/  =>&'() +31.

*ῌ<* +?,- @A./#/01) +321  23  B
..-2 gῌlC( D, 4E5 / F+?,6G dDH"-*I",*J d OH'2J 1 7KL MN

ῌCl"/ 23+28 OP7

9: Q/ Masuda and Tsurumaki +32, ; Masuda et al. +32/ ; +320 23
R;ST<=>U V WX- Y?+?,- $Z6@
7[\ -#$AU 23  ]^_B`CBDVDWX#aY?+?,bXcdUU 23  e1 Kfg#/ WXKf hi23  7=>jE4 B>F kDGXlHm#4#/ In

opqrstrut\ῌvwxJ

cd

Nishimura +332 #$) vwyz{r)D|)  vwxJ #}xJ~ xJ   K46/ Sano and Wakita +32- L M~23

-Heῌ.He 6`7 i

{r&NOPK

6/ Tatsumi +323  In  QRSh,\ T &E ShhM5U( T VW3) 0* km[ῌ\][ ;T +/* km X
{rX4)"> Y T +** km

Z^_ ;T F {r 5`U/+,-** E5{r>$a  7bK

/ 0* km E" opqr\ 5> {r >$aU#> #( c 5`U 6 d -/  c e, ~fgXh#i
5` OP - j#kl~  `K6 mn,*** a ; ,*** b ; ,**+/ F V o 23  / pq ,**.  rsP

cdX>B¡cd¢{£q ¤q¥¦q§ X>t, e123¨ e1+?,- ©ª u«) 2Ue1OP
K4/ i#  ¬ vwX U}  ­ 2OPv$#/ ®N #23¨X>5`¯° /23¨X>5` Oe±U  ¬ L$Z!

>ῌ=Dῌ&=

L >²w4/ xyzI  Sh°D{opqr  +** km«T F {r>$aR/  +** km )"}T6|P QR³! T)R6 } +* km
ZZ5`({opqriF#iKL/  /  ´2  Sh,D0* km )">T6c {ri5`  # 5` µX>Z ~U¶7U KL/23  RῌNakm X

WD ? y·¸¹{D{opqr Shh X4º» /*/ F  F #B>F 2UilU¼ /¢ /0 £ Q,**0T9Fig. - The hydrated peridotite is formed by addition of slab-derived H,O (solid arrows) beneath theforearc region and should be dragged on the slab by the subduction of oceanic lithosphere(Nishimura, +332).
AM-CHL : Amphibole and chlorite.
PH : Philogopite.
 - !"#$%&'()*+,+-./01234506" H,O QT
AM-CHL : ῎
PH :  ¡/, 
$   ! "#%&'( '!' )*+,"-,%./ 012"#$&'

CSA-MT $&341$ 56 78'( ,**- 9+ 341$ :;<012&%=>?/@A'( ,**0 9 BCDEFG HI) ῌ J)K)341$&CSA-MT $ @A'( 341$LM+NOP' QNishimura and Katsura, +33* ;JRῌS +333T /%%/+UV - ῌ WX-YZ'G [\'G ]^ῌ_`ab$ ῍ cd)!eWXfg)*$

%&-01/F(;<h+ Aloka i NaI QTlT jklmnjokpnqrsnt&H341;u/+ Aloka ig vwntxyz{|}~snt 6(/,+  jklmnjokpnqrsnt+ ++./ rkl NaI QTlT h E/  g v;<'( ;v +/ m  %'G ) c) / & +,G!e ῌ , ;   +*  ' ;<&'( Q%»¼10 ῌ  #$῍        . "     !

%& "'$ (ῌ)  ,* *  $++ ,-./0123$   4' 56 78 9    :;<1=>:?@A  B CD EF!": !G H,,- m ##$ I%:&J'$B  "K>BL/** m EF3*./M 3..0M :'@AN(%)G 3 ,**- * "'$>$
῎ +,

-OPQRB@./S 01S234T 5/,,g g -UVWXY
,.* _`aY

Z6[6 7\+,*** 9 Hb^cQ^d e!

"'$ ++8 ]^-.0 MeV  _`aY g -faYgR:$;h/ "  i !j/:kl ῌ <:mG <:$UVWXbd:nA'$ ῍ =G(<)G  obpodS> ,+.Bi, XqodS> ,*2Tl
rsRW:?   @6t!Au' ,*2Tlῌ,+.Bi A:$ ,+.Bi  ,,,RnHBvw -.2,,3 C +xDE2 ,*2Tl  ,,*Rn HBvw /+./ 9 +xDE 3?@A   Rn
:5(<yF:<!$/zB@{GH'$ /|  B }@B~I  J:&J bH3J+ B:!$bH:>G> B$AB z=῎ %& 8KL UVWXbd()G 8Au' .*K rsRW:G %& MUVWXbd "'$  /AN()O b(P:<$/ "'$ /- 

Q R  ASQ0' CSA-MT

8, "  &T:U A ":$VASQ "  + 23WM  =G(<@3VASQ "  B 23WM X/   <Y$+,Q " : 1=>ZF:[@ VAS "HMogi et al., +33+
CSA-MT 0 8 , 1 0 "  \]^ pRY _8B@`A/z

a6:   

8¡B@ SE +*¢X£ -./km ^ NE +*¢ + km e¤bC c^ \]¥B@ /+,* ,/0* +,2* 0.* -,*
+0* 2* .* ,* +* / ,./ Hz ¦debZbCfZ gb§d  b@\]X£+¨ +/©,* m e¤¬R­^Y c^''X£§@«UQ®¯°'±  +, ²¦de12f +=3Q³´Y'µ!"AS ± '@A?BASB@3 AS2,c^ /AYª , hH/!

¶· ;·B@  µ´RQi"

:L'$ / ¸B
!B@¹  ῌ8 M+  M. $  jº:

/0,**0

Fig. . Distribution of hot-springs and faults and the hot area in the center of Arima Spa., estimated by
the results of g-ray radioactivity and CSA-MT surveys.
 . g mSVῌh CSA-MT !11,-9:12

Fig. / g-ray spectrum at the main hot-springs.
 /  g ῌ M0M2, M++   !"#$%&'( )*+,-./  01 2345$ 67 .8"

3 /0 4 ,**0Fig. 0/012

13

Cross-sectional resistivity view, around the south-west region of central region of Arima Spa.
 0 CSA-MT 

/. 
ῌ He .

    ῌ -He!"#$%&&' Sano and Wakita, +32,( ῍ )*+,-.

¼

14

 ,  
0* km     ,**. ῎  /*!"#$%&'()*+,-./0* km 0 123*+,-  (-9 -He :;57!"!*+,- .*4 5 36 785< = ,*** a>?@ 1 ABC1:D 5  0**+,/** m 
FGH"IJK LM>NE)G O>PQRSIJKTUJ VWL> XYZ[= N  X\2] XV :^5!
" 77  7>YZ[ _`Kab#cG $d:5e f%c,**- &V 'g ῌ Xh!iWSjIXXV :^ (k 7lUJ mmno87 :^ ῍ V )UJ *p +=p
>  ,qYZ<bUJ VWL>-rf%c,**/ &V 'gstu CSA-MT 'gUJ Xno8v*p +=p>

w.xG >p+*y/L. U ez{VWL>
|F6} ~.
ῐ῏012:|I.3/ 'g345UJ6<K3e:

7

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Masuda, H., Sakai, H., Chiba, H., Matsuhisa, Y. and Nakamura, T. (+320) : Stable isotopic andmineralogical studies of hydrothermal alteration at Arima Spa, Southwest Japan,
Geochim. Cosmochim. Acta, /*, +3῏,2.
Masuda, H., Sakai, H., Chiba, H. and Tsurumaki, M. (+32/) : Geochemical characteristics ofNa-Ca-Cl-HCO- type waters in Arima and its vicinity in the western Kinki district, Japan,Geochem. Jour. +3, +.3῏+0,.
Masuda, H. and Tsurumaki, M. (+32,) : Geochemical study of mineral springs in southeasternpart of Hyogo Prefecture, Southwest Japan, J. Geosci., Osaka City Univ., ,/, +῏+1.

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Mogi, T., Katsura, I. and Nishimura, S. (+33+) : Magnetotelluric survey of an active fault
system in the northern part of Kinki District, Southwest Japan, J. Struct. Geol., +-, ,-/῏ /0  ,**0./%&'15,.*.
Nakamura, H. and Maeda, K. (+30+) : Thermal waters and hydrothermal activities in Arima
hotspring area, Hyogo Prefecture,  +, .23ῌ.31.
Nishimura, S. (+332) : Quaternary arc volcanism of Sunda and Southwest Japan Arcs, Proc.
Symp. Japan-Indonesia IDNDR Project, Sept. ,+ῌ,-, +332, Bandung, Indonesia, ,/ῌ-1.
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Nishimura, S. and Katsura, I. (+33*) : Radon in soil gas : Applications in exploration and earthquake prediction, in Geochemistry of gaseous elements and compounds, edits Durrance
et al., .31ῌ/--.
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Okamoto, N. (+30,) : Research on hotspring group in Arima, Geophys., Magazine, -+, ,1/ῌ-+,.
Sano, Y. and Wakita, K. (+32-) : Geographic distributions of the -He/.He ratios in Japan :Implications for arc tectonics and incipient magmatism, J. Geophys. Res., 3*, 21,3ῌ21.+.
Tatsumi, Y. (+323) : Migration of ﬂuid phases and genesis of basalt mjagmas, J. Geophys. Res.,3., .031ῌ.1*1.

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