  .3  (,**.)
 .  +2+ῌ+21     ,**-  .

K-Ar





+/  ,**.  0+1 

K-Ar Ages of the Teragi Cauldron
Katsuhiko FURUYAMA and Keisuke NAGAOK-Ar ages of volcanic rocks from the Teragi cauldron were determined. The earliest volcanic products were
the Lower Tu# (about +** km-), which erupted -.+ Ma, and was succeeded by the Teragi cauldron subsidence (+1km+. km). The Yudani conglomerate and overlying Haruki mud deposited in the northeast part of thecauldron, and andesitic volcanism (Terada volcanics) began ,.2 Ma in the southwest part. The upper and lower
parts of the Haruki mud were intruded or intercalated by andesitic sheet or lava of ,.0 and ,.- Ma, which show
an approximate period of deposition of the mud. The latest volcanic activity was ,., Ma, which wascharacterized by rhyolitic volcanism forming domes and pyroclastic ﬂows mainly around the northeasterncauldron rim. The period of volcanic activity related to the Teragi cauldron was about *.3 Ma (-.+ to ,., Ma).
Key words : rhyolites, Teragi cauldron, North Kinki, K-Ar ages, Pliocene+  

~iA/xIJ2 Furuyama (+323)      !"wu5 (+300) "|/x#J b#

#$%&'()*+ /01'(2 345

$IJ2 \b Furuyama (+323) O(|/,- .

(,**,)

/0"67789:"";

# /,8(2<=>?'(@AB-+ CDEFGHAI,ῌ+ 

J2 KL"MNOP/0>Q'(#$B- ,.2R

/0"$$!bY@l$% &,., Ma " K-Ar ST1UVW,(1X5

b'Q$ z"5"|6b*!/0+33. ; Y5 +33/ 7Z [\>Q'(\]^"( ) */bc(2 (*/i$"_SU`a72 b c-Jd,

R#$ )*/+$$ */

/0[\>Q'($e#fgh"STA$B->QVW( tuvw +3/22 z"5&"Ai /0"#$ /0 jW()*k,-".b*/   + /0"#$ /0 lmnopqpr7Z"+ /0$/ b jW(k$e$ "b+

6 "#$" K-Ar ST   ,**+ b/0\]^$ jW(/k$e$7Zs  U'(2I`  a"B-¡k$e$1¢£¤0¥'

(2
,



 '(+ /0 (Fig. +) t,ῌ, 

uvw (+3/2) OPx1y7jWJ2 z!"b¦|'($"@l$ b"{wu5 (+300) /06"!""|e}l@l$+§A'(+$/ wu5 +300 b ¨//2ῌ2/2/ ©ª«¬x­©ª1®®¯®MN°±|²³´
Department of Bio- and Geosciences, Graduate Schoolof Science, Osaka City University, Sumiyoshi-ku,
Osaka //2ῌ2/2/, Japan.
 ¨++-ῌ**-- "µ2µx¶"µ®®¯®MN°|·¸®¹º»¼
Laboratory for Earthquake Chemistry, Graduate
School of Science, University of Tokyo, Hongo,
Bunkyo-ku, Tokyo ++-ῌ**--, Japan.
Corresponding author : Katsuhiko Furuyama
e-mail : furuyama@sci.osaka-cu.ac.jp

182

῏ῐῑ῔ῌῒΐ῎῍Fig. +. Index and geological map of the Teragi cauldron. The geological map is simpliﬁed based on Furuyama (+323).

&'QMO K-Ar 

Fig. ,. Sampling points (X) for K-Ar age.
Northeast part of the Teragi cauldron. + :,/*** digital map (Tottori), Geographical
Survey Institute is used.

Fig. .. Sampling points (X) for K-Ar age. Southpart of the Teragi cauldron. + : ,/*** digitalmap (Tottori), Geographical Survey Institute isused.

Fig. -. Sampling points (X) for K-Ar age. Westpart of the Teragi cauldron. + : ,/*** digitalmap (Tottori), Geographical Survey Institute isused.

Fig. /. Sampling points (X) for K-Ar age.
Southeast part of the Teragi cauldron. + :,/*** digital map (Tottori), Geographical
Survey Institute is used.

n _^ /** m  


183

opqVWrs!t?uiv$



ῌῐΐῒ῍


twxU : y

 :     !"#$% &';zm{]|}!89 "~VbYZ[ fW)(% +32-g xU()*'()+,()-.(/012)13!45

?y=>tw= 

67% 

~%   X*'  !$

89:;<=>?@ABC"

DEFG (Fig. +) HIJK/$LMN~twVbYZ[67% OP)QRSTUVWXYZ[ \/]!v$/~)VbYZ[/0^ .** m_` aVbYZ[c% de45

8 f _^ +** mg

hi?% Kjkl/m?

\$
ῑ῏῔῍῎

<

¹Yº9?):»¼

184
Table +.

K-Ar ages of volcanic rocks from Teragi cauldron and others.

 

  !

& '()  *+"#$%et al., +33-) ~E
I  
cded<(|!

NE-SW, - ./01&  $234x) -./ km,  +./ km{ 5*67 89  %

 *?9Wcded %:; <=m >?@ABCDE >< ,** m

:F%hij+@Y ^

`a> ,** m+@Y

XYO,G# I_$% H<[|<_H: G#)HH ? <= mm8+ cm >IJ
KL MNOPQ8RS*

Furuyama (+323)<+@YL~+@YG#hij-S .L/cdedm

TTOU VWDE<XYOZ[\ +* m ]YP[^I_H

X`a> /** m%- K-Ar -ῌ+ 

01<  
+,


XYbScded

?XY !n

XY?cded* Furuyama (+323)i}$+,I_L@Y ! }$
/cded hij



%



 f g *@Yhij@YAklm %G#< !S!n?n op"q _ abOXY (Furuyama, +323)

 #r <s$ tuv

1 ¡|2 Fig. + x¢1{  Fig. ,8/ x|3{H 

 <s$  ^w% 
,ῌ-

 

-ῌ, !"

 xyYz,@YhijbO{|n}$G#£L
1<4A ,/*8+/* mm ¤53 6¥

H  ,* b

W?d¦§d¨©ª«¬­[®[ ¯¥°±7

Oz,@YS* yYz,@Y (+.,8*.. Ma ;²±¡³HLW&01L 

Furuyama et al., +33-) ~ <´µ¶·? *0 $|&<'*bOz,@Y (+./8*.1 Ma ; Furuyama < *d¦§d¨©ª«¬­[®[¸8 33./ῌ ]¹ºw»¼

K-Ar 

185:A.;!"A*A56FG [$  (+33.)
 (TG+++)
p

+323

" !"A*A

B<A

eFuruyama,'ApR=!%^&.; >? @ /+/.2 m .OPQNh  HI() AB X

.!; TG+++

Y ; ,.-*/*.+*Ma (TRG*.h ,..,/*.,+ Ma (TRG*/)
K-Ar .'b! N.FG4CLQN  e DEh 4 (Fig. ,) : FG ; B
<A.;A*A e@ /1/./ m
Fig. 0. Stratigraphy and K-Ar ages of the Teragi
cauldron.

,.0+/*.*1 Ma (TG,*+)h 56.+ J 

\*A56 [$  (+33.) (TRG*, : ,.0*/*.*2 Ma) \HQN I  1** m B<A K






 Ar "#$%& Ar  (+32.)










!

'()

Nagao et al. (+330) ,& -*

*+
K



 ()./,./ῌ !-* >JA,./1/*.*1 Ma (TG.2

+*.)7 eKL; C!; MC; h 4 (Fig. -) :KLN MRAS>.OPQNOA 

,.2//*.*2 Ma (TG-3) W& 

 (+33/)

C@ 00* m FGA-ῌ- 

*A56 ,.2//*.*2 Ma e OG,hTable + 01.2 Fig. 0  34b! N Jc6 , s ,MRA56+

56758! 9 :.2; 
01.<=


6cT&TU WN *A (TG-3)"(Fig. ,)

>?@A : 3 ; BCDEFG*.*2 Ma .2 J-.+-/

 K>LMN3.

R]AP¡gcNKL¢QApA56,.11/*.*1 (TG-2)

>?@A HI (TGLTb)

K-Ar .'C
mh.+ £ R]A

T; R¤S +** m e@ +,,.*

C!R]A¥¡gcNA*A

K-Ar 

,.1//*.*1 Ma (TG+*1) WN Jc

OPQNRA STUV; >?@A,9

6 RA.¦TY7§¨;{=6cN*A,

3 S>WNJT XY 

KL  ©>NQN Jc6 *A 

?@A 'Z  !"A# : ?@AHI

,.,2/*.*1 Ma (TGUTb)

9>"56"ª ,.01/*.*1 Ma eTG+*3 ; ¢.2

QApAh; ,.0,/*.*1 Ma eTG-/ ; A +h; ,.02

 [$  (+33.) T\R]!%^& HI/*.*1 Ma eTG+*0 ; A ,h; ,.03/*.*1 Ma eTG-1 ; 56_`a (TRG*- : ,.,2/*.,. Ma) .'b

A .h U« ,.01 Ma

! N Zc6(%^&d) *0 efg /*῍ Jc6( eMC!h+** cmh

ijk56 llU  (TGUTg : ,./,/*.*1 Ma) .+ m> *0ijk perlitic crack,n6cNT-o.pq& ,n6cY  HI/r*0ijk,llU .2Q
TstukvwxWN

ijk56

ijk
K

*

0 N K 1 2>3QNy4z,{=6cN
J nHI+.?@A 5+} ¬­QN.2
@ 2.* m FGMRA VW®p¯°±° eTG,/ ;,.,//*.*0Ma, Furuyama (+323)  X.s8!

Y  ² ¯°±° ³h  'DE@ 1** m B<A ¥¡gcNA*A(TG++, ; ,.-//*.+- Ma) ´V; FG4 !

"A# WN
4 (Fig. .) : µ¶C!4QNHI

|YQ } 6c!; 9~ 7

 O¯°±° (TG++-)YL

8Y!"A*A , 

 A  . 7 § ¨  ;  ,; J7 § ¨ . Furuyama

01Zcc ,.,0/*.*0 Ma (TG+++); ,.-//*.*0 Ma (TG+*/)WN J

 TG+++

d9

# 

JA

d)

MR

(+323)MRAB ¦TY7§¨{=MRA 5·¸01º <»¼

186(+.1**.*/ Ma)  

   jm AB*  . "/ ,.0 Ma =/kBm ,.- Ma f l (Fig. /)

 d



n"m"ST/5 67"45icj ! "#$ %& " '(")* +,,-". "  -".
"  K-Ar / -.-3*.*3 Ma (TG11)01M*k*=o {f1 0yt n"m"
#||tp"ST/ 5  7
.

"

/
 

.ῌ+

hk*

bY qm ,.1 Ma{f18| ,.- Ma

mST#l8%*.*3 Ma)

 4%$%9 R`"  "db 'RST6-". " (TG11 ; -.-3

Yst/%d   abcdKLu $2",,-". "%9 @vR`" " "w 'RST6H! )*" !3"#4% 5 67" $ )*8$%9

!3"-". " */ :;<"&'=; (>?")*

-

 (-.2@,./M a ; Furuyama et al.,

+9 AB* 
H3I  JKL#M*

9 . "2
8

:; / NO  45456P

icjRx;

#s9AB*  

7YstabcdKL/ -.+ Ma 5
67"45 ^ticju_ {f _*m"<"ST ,.2 Ma//f ,.0 MaRm. " #8 ,.-ῌ,., Ma  #y9/CD,<E-./#FG0  1
2 
67

"P

 ,.-ῌ,., Ma rPabcdKL

.

+33-)

& "R5 m"#||tNO" Q2 < 9

abcdKLu R`" q #zB
{B|}&'/3'=;E +*** ~8 +*  km 

icj

,**+ ::;;;  0  18  <9 +323 ;/3I  JKLR

cjvP5 67"t45Q/* 
vicj 9  S=

< S=9 T>?0 

.ῌ, +33, ; +33. i/  j JKL< 

0 {@A<9 (,**,) /B!$%CUVD" 

Bicj !S= JKL^E +*@+/ mgal F%GHIJKLMWN$

P9 0 m#m%B  Z |%8% 0 LMWNXO /B!VD"OE

m20/% icj /icjM*o=YZ[\]^P9  B!R5  Q

. "  0  abcdKL'RST67 _*< " 

/EM 0  4%Rx;R`" 

 B!`U#abcdKL ,e f

8%gh / M/V)*8% W:icjM*k*,**, HL Lbicj Smith

8%lX  /YZ#m B

and Bailey, +302 ; O +33- 29 !#`*9Fig. 0nM*;o#p[9 qr\#s9

-.+ Ma0PHIFLMWN#s9 @A < 9!
Q567" ]T 1*@+** km ; @-K-Ar Yst/



¡

¢£¤L

A<9 ,**, 45 45 ^tu_ icj¥b:¢£8|1 Andrew J. Martin

E +.v+1 km M*k* ¦ /§¨©#8%e% ª« ¦| ¬,.-ῌ,., Ma

R`" /VDwt"#tm0 i^­ / B®#¯9 7 L\cjx R5 0yt5 67"/aP bc°#%e% j  /±bL²³´µk*AB*/d}f

 icju_=om% ,.2 Ma

 . "
e 01 ,.0 Ma/m ~

1 abcdKL f8& "7 
gh.

"$%9

¶·#%e% 7j ¸9 

z{8| ,.0Maq*Y/ ,.0ῌ,./ Mam0 i <9 +33/ :; /. "

" # $ %
Furuyama, K. (+323) Geology of the Teragi Group, Southwest Japan ¹with special reference to the Terada Vol- `abcd
canics. J. Geosci. Osaka City Univ., -,, +,-ῌ+1-.
 (+32-)    12 ,3/ῌ-*/.
  (,**+)   !" #$ ,*** %#&'( )*,.,.
Furuyama, K., Nagao, K., Mitsui, S., Kasatani, K. (+33-)
K-Ar ages of Late Neogene monogenetic volcanoes inthe east San-in district, Southwest Japan. Earth Science(CHIKYU KAGAKU), .1, /+3ῌ/-,.
+,-./ 0123 (+323) 456
789:;<=>  ?8@A
B 6C#* -, .*3ῌ.,3.
D /EF     G-   H(,**+) IJKLMNK67 6C 676COPQ
R/  + 6CST 6CUVW +,3 p.
XY    Z[ 3  \!]^  _(,**,)  `abcd e"fg h .1 3ῌ+/.
ijklm #no$p% (+300)  
6Cq8 r? stuv &w'x%8@AB 6Uy +1 0/ῌ1..
  z{(-|}~)3 (+32.) K-Ar
*8:  +,OQ 3 +3ῌ-2.
Nagao, K., Ogata, A., Miura, Y. and Yamaguchi, K.
(+330) Ar isotope analysis for K-Ar dating using two

K-Ar



187

modiﬁed-VG/.** mass spectrometersῌ : isotope dilution method. J. Mass Spectrom.Soc. Japan, .., -3ῌ0+.
 |  i/   <,   ,-(+33/) >hK-Ar6#   R.
  /T 0 +.3ῌ+1*.
Smith, R. L. and Bailey, R. A. (+302) Resurgent Cauldrons. Geol. Soc. Amer. Memo., ++0, 0+-ῌ00,.
Steiger, R. and Jäger, E. (+311) Subcommission on geochronology : convention on the use of deacay constantsin geo- and cosmochronology. Earth Planet. Sci. Lett.,-0, -/3ῌ-0,.
l (+33-)   OP y6 +/ 001ῌ01+.
¡¢£/n¤¥¦ - (+33.) §6)4 r?h K-Ar ¨M©ª«¬­d®«¯  6C° +** 121ῌ132.
j¦±i 0 (+3/2) ²167 .³r´µ  .³ OP R¶ +T 6C° 0.
0,/ῌ0-1.
_·¤ (+33,) $K67 <=;
h? 6C° 32 ,+ῌ-2.
_·¤ (+33.) ¸267 <=;¹ h? 6CUVWy ./ +-/ῌ+//.
R3*º» 4 ¼%T