  º .1 » +ῌ+, ,**- &Japanese Journal of Structural Geology, No. .1, +ῌ+,, ,**-'

123῍
Some Considerations on the Research History of the Paleo-Ryoke Belt(-) The Median Tectonic Line of Pre-Ichinokawa Stage *ῌ !"**
Ikuo Hara* and Takami Miyamoto**
Abstract : Recent research history of Mesozoic tectonics of the Median Tectonic Line
(MTL) is brieﬂy described in this paper. Some authors pointed out that MTL has to be
distinguished four di#erent faults with reference to tectonic signiﬁcance, time andplace : MTL-* (suture zone between the accretionary complex of the Inner zone and theKurosegawa-Paleo-Ryoke continent beneath which plate subduction responsible forthe formation of the Sambagawa schists occurred), MTL-I (great mylonite zones related
to exhumation of high-temperature parts of the Ryoke metamorphic rocks just after
intrusion of the older Ryoke granites), MTL-II (great mylonite zones developed along
the southern boundary of intrusion ﬁeld of the younger Ryoke granites) and MTL-III(faulting related to exhumation of the Sambagawa schists). While some others assumed that tectonics described in terms of MTL-*, MTL-I, MTL-II and MTL-III occurredin the same place (MTL as a single fault).
Key words : Median Tectonic Line, Kurosegawa-Paleo-Ryoke continent, Ryoke granites,
Izumi Group

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+
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  ! " #$ % &MTL' ()*+),"-.! /012 &,**+' 34567289:;<=)>?@)AB,CDEF GH >IJKLM NOP -QR" MTL ()*STUVWJ+),"XYZ J[N \]^_`a-JbVc
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Oyo Corporation, -ῌ+ῌ-* Minaga, Saeki-ku, Hiroshima 1-+ῌ/+,., Japan** ±²²³²XY´µ¶·,(B²¸¹
Department of Earth and Planetary Systems Science,
Graduate School of Science, Hiroshima University, +ῌ-ῌ+Kagamiyama, Higashi-Hiroshima 1-3ῌ2/,0, Japan

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¥¦ §  >ῌ¨©>3¼ 1 ¼

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 MTL    +3.3 !"#$
 %&#$'&#$() *+, " #$-, .)(/01234 * , %&#$'&#$-56(7.-8923-:,  MTL !, #$.)(;(<=* >?*+@A23.-B*/
CD, Hara et al., +32* b  E ῌF +330 -,"%&#$  "'&#$MTL-I , "'&(/G 23
MTL-II !
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L "%&M N#$O
 (PH"'&'Q#$RS
 89, TUL V WLXY$ῌ"%&Z#$(G H"'&[\]$89! ^_`ab
cdecdfg-, h#$(G H"'&#$!+3iῌ MTL-I ῌ῍῎ MTL jk-, l(mn MTL (loH:23p! CD, Haraet al., +32* b ; `ῌqr, +330, ,*** , * , .s-? t* Fu* ,**, a , ru* ,**, -, .v wx@A , " (yz MTL-I  MTL-II jk-{| B MTL-I (}-, TUL K~ VL-mn MTL (loH!, TUL K~ g-mn MTL *+f3_ T e_LX   Okudaira et al.,+33- ( H! 
TUL K~ g-, mn MTL (/, "!O# " #$Y$  $ %    x (, . 3   ; .  :MTL-I &z"%&#$
 n {'(B  +  !/TUL K~ g-, MTL-I jk-, p)(-{| B=Bz3DB+B TUL K~ g MTL-I jk {| H  x ( -, "    ( $ % 2 3    :MTL-I jk |(*!+, J.
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"%&#$Y$(-, §x
23¨© ªH&! J3­-  « ¬   ¡ Y 4 

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MTL-I  
Sakakibara
et al +323 Sakakibara +33/  ῍  !"#῍$% &'() MTL * +, -. X /01/2ῌ345678
9:;<=>?@ ?8A '& +320 +33* CDB῍E B
FGH/IJIK ῌ LM7
NOPIK Q#RAS ?8A '& TUFVWX& +320 %ῌV
W +321 +33* Ohtomo +33- Yamamoto +33.
 YZGH8H [BR\]^A9 + _8`abc XdQR#!e  MTL-I ?8Af ?g'F !e
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+30+ n +30/ oX& ,*** p@qf
Tgpgs :;tu rgw,
() MTL v`#q e 8!e p+,xy z῍ jk:;lm:;  z ,Xdhi`# +{ :;() MTL vS `#*+ ?8
Okudaira et al +33-  !|frg

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&'#'g MTL-I `#$%_& jk:;lm:;8 j/IJIK   8#:;e 9 :;e @
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
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"#$"%&' ()*+,-()*.
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0!1" +,-()*.
 #$ῌ2%/3 4!"#$"%& #56'  (7(&')*
80ῌ9 +323 ; Okudaira et al., +33- ;  + : !"#$"%& ;<=!>+ ,?@AB
top-to-the southwest  Okudaira et al., +33-C&' DE!-F.GH/ I,' +,!"#$"%&' ()*.
 /JK<'L MN MTL OGHPC0
Q GR &' 1!O2D(S'0! T 36 )*,R:4U4
 + DE!-F.GH/ IV 5W XY,(Z6X.
3R[R \] I,'
 7&'.,(^8 5,(9 Suwa, +30+ ; _ +30/ ; `:,*** ;  ,  DE!-F.GH/ IV 5
W XY,(Z6
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+30+ _ +30/ `: ,*** GQ
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36 ?;
7(
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/ MTL-I Bm4nC oDpE qOQ. $cd7(r .s4tF&',  . uv%tF - 7( $cd 7(,R^? M
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tF GHy $cd 7( T Mw4jOQ:( 9 +33+ )gI&',  z&'
9 : GR/MwO MTL JK4LO
/ &',  .s tFJKOQ  Suzuki et al., +330 0! IV
MTL-I {M 3* Ma | A'lQ}Nῌ9 +330 z&' Oῌ~P ,*** )=

L GR ',  MTL  {M&'k,Q .
QlQ', !"#$"% 4  
-+) MTL R'MC<',=ST4  z: .,(Z6 vzQ
@C tF k( MTL  { M  ? ;  V  z k   CHIME J K
Suzuki and Adachi, +332 O +** Ma ,ῌ MTL-II : ῔ῑῒ῎῍ΐῐ῏.
DE!-f< MN MTL ;<'s MN MTL DU ,V!"#$"%&',  G &=GR   s_ Hara et al., +32* b :Q4 MTL-II  .X9 5 W H Michi
X&!"#$"%(V',
bayashi and Masuda, +33- ; 9 +330 4 5X[R &
 zQ4 MTL-II YZ& MTL-II 4 DE!-/.f/) MTL-I ;<')*,R [y MTL-I ;<=.s !"#$"%&=,R\O
Q',/, .s 0!"#!# <   MTL-II YZ$"%&\OQ/, : : MTL-II M
 zQGH1 <=
N MTL  ^]:(¡¢&',  ^!,( tF&=£¤ )*!"#$"%& _OP +33,

MTL-IIYZ- ST4 
MTL-II ?;z ¥%¦B(LO:4nC pE qOQ 
 \]ODE!-/. !
G
 MTL-I 1MN MTL ;<'?@
 +  ,  DE!-F.f<
R
YZ  U§! Yoshizawa etal., +300 ¨j! Yoshizawa et al., +300 ©ª#%! «0 +310 +311 ; Ohtomo, +33-:4`OQ',  U§! 9ῌ¬­ +31.
¨j!  O +32/ ; Sakakibara, +33/  ©
 MTL-I !"#$"%)ª#%! MN MTL 1  .&©
a& 6 $cd&'bHU GR )*Hara et al., +32* b ; Ohtomo, +33- 4 : bHU&.
YZ ®¯°cd  4
«0 +310 +311 ; Ohtomo, +33-
©ª#% MTL-I N+ 1 bHU&.
YZ )  e±²³­ f­³´«0+310+311 ; Ohtomo, µ,(4+33-g¶GR/· 1! I,')\OQ  ::e±²³­  1¸T³­  MTL-I !"#$"%& .
 1  .s(¹º

¼ 4 ¼

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 MTL-I 
    +321 ; ! +33+ ;  - "# $ MTL-I  % &*+,ῌ'(ῌ)
-./ 01234+2*5. % 31 Ma 
K-Ar 67 89:;!"*+,<#=    +321# >, MTL-I % '($? @%/ 0,>A  , " - "#  
%)B 0 )%C
D E=5F  +321# *G,HI: JK LMN &N
)O'* . LM%( EF)O'% +* )(PQR3*ST 1 )U*Vῌ B= (PQR%W ,/*X/** m Y +,ZX+,[\Z 0 - +331# % ].)E^MZ_8'($/0` '(
$/81a2b3 *K4:> $/8MZ_c0:E'($/%85de6 0
f2  - "#
ghijkhXlmnokh)&8B:&*% ;! *&X78
9ῌE^*:: 03; pq %rsjkhX\hjkh<=:)J'>8B:&*  3
>;!ῌ&ῌtu 03
; vw +31* ; L? +31-# x@
,***# % >3+2E;!& +*-X+*0 Ma  K-Ar yzh{|h}  +*2 Ma  K-Ar

 - " MTL-I  *5.'(
+ : '(@%±h , : B[/ A : gh²³
)
# B : ij? )# C :  )# D : ¯´<= kV#

67 89:38A *> 3 %
MTL-I  '($? @%/ <=)3 *T ~,>389:B
0  - "# 31 Ma  K-Ar 67 89:;!
"*+,<#=>H+2E89:)8 'C pqD'*~: '($?
F8 , MTL-I +F *8 MTL-I +F3  -$/#  %?;!*+,
<#=>ZE 0%A*$ <=)F GH῍I῍J
%'($?T  @%/0 L2  +33- ; K@ῌLM +332 ; ?
  +332#
J.>NxO%N'   E Yamamoto, +30, ; wP +323# >, C'D Q>MTL-I K40 d> pq*5.
MTL-I K4% J+F 30A - RS T
0f2  , " . "# 2 0:
MTL-I +F  pq %A *61῍U*V:# T> 3 *NxON' @῍J ;  . "#0,  *NxOx' GH῍I# 0F 3x'_*;! Hayama and Yamada +32*# 
H<W +330# *+X # 8Y2῍Z
B[/:3*E ῍Z B[/*%'(*%NxO8.E E61῍U0 $ ῍Z B[/\ j m% '($?
<=)89¡¢$ vw +31* ; vwῌ£¤+33/# 0 2]% '(¥*+F3
t3,> MTL-I  ¦§^#*_¨=  0
EGH῍I῍J῍@8`a rsjkh©b)89  . "# >, eastward younging
89Ersjkh lmnokhT89c  vw +311 ; 3ῌ<d ,***# >/% '($? @%/ 0,>1234+2 ª« MTL +F3 % ?;! T> eastward younging
89:3;  = +31* ; v
w +311 ; Nakajima et al., +33*# ;!
eastward younging ©b)῍<=)῍) eastward younging *¬­*®>%vw
+311# 0f2 ¯e^ %¬K 8B:¯ef°
T> eastward young-¼ 5 ¼

¸ ¹PῌºQR»

ing  Hara et al., +33,    !"# $%&'()*+,-./012 3# 45
6 7 
 MTL-I 489:# ;<=>$?@ABCῌDBCῌEBCF 9:
GH,-:I  + J >89KLM $ ? ./012
N H=H# .OH,I
P# ./012 3 F N# @ABCῌDBCῌEBCF N-Q+:4-R:S  @ABCῌD
BCῌEBC 3T# ./012
GUV
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Y Z9:R:*+,-:6 7 =I QH,# [\ 45]^#=+_  + J # MTL-II # .
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+ 8@Pxv y?w<'x?[X jk# _i?i&'q 88
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Y MTL-II }# MTL-II (P: 9P+ MTL-III ?
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+ MTL-III jk# o?[X jk#
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(. ῌ   :MTL-*
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a ° .1 »,  yzl ª!®º¯ῌ ,**, b  
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!"!#$  +33* ; +33+ ,**, a ; %ῌ +330 &#'!01
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0U1 2VWXYZX[ \3C]%^ῌ*
4 ++* Ma 5%]C67^ῌ%J<_`a>
C ; b8 ,***  & ='c9% :;C6'< HN=#CD"#
C>?%,G4 @de 3A ,*** " =#C fB!/g
CDECFGHI +0. Ma Rb-Sr HI J 
 +33- '=G ++,h+*- Ma K-Ar HI KA+321 ; DL ,*** +*1 Ma SHRIMP HI DL ,**+ '!e =#CC$i
5 ='c9% & ,**, b j=k5 i"Ml.RN' OPQ ' % ,*** m3nopqR#C>
()S  r Tf#C>st MTL-* '
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Cuv#C>' ' pqR#C>$i5 wk 345'c9% & = wk 345c9{%Vx=yz &i'F
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Z[=|P'dῌ῏῎῍\]^ MTL [  _H 
5'Gyz- k yz4 {5'c d i" Y`8ab oe 4=  f5$ yz k{5' ghig'=k5&6 y=k j6k=k5' 
zl6gh b'  =mn Yyz|P=' &6 5'+ opq)()rsi' MTL [  MTL-I MTL-II MTL-III  MTL-* tu4, MTL-I [ ,gCC>[vfB k $545wD#xyDz6 Z)3 k {| @ /5$' MTL-I 1'
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ABGdH +33, +** IJ + KABL M - N6
e fO +330 *PgQ*R῍hSij9:kj6 TUV@ W lmnmo pX YZ ,*,῍,+*.
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Kd>| no. +,*, 2.
Hara, I., Sakurai, Y., Arita, S. and Paulitsch, P., +32*
a, Distribution pattern of quartz in granitesEvidence of their high-temperature deformation during cooling. N. Jb. Miner. Mh. +, ,*῍-*.
e fO ῌ }~g ῌ h ῌ i[ ῌ jῌ῎e!O +33+ *Rlmnmo6 K
AB{|M 33 8{k|!{l=mn +῍,*.
e fOῌx#^_ +330 oR -/ km pq
lmnmo X4R 6 {A{rs< no. ,2, +῍10.
Hara, I., Shiota, T., Hide, K., Kanai, K., Goto., M.,
Seki, S., Kaikiri, K., Takeda, K., Hayasaka, Y.,
Miyamoto, T., Sakurai, Y. and Ohtomo, Y., +33,,
Tectonic evolution of the Sambagawa schists
and its implications in convergent margin processes. Jour. Sci. Hiroshima Univ. Ser. C, 3, .3/῍/3/.
Hara, I., Shyoji, K., Sakurai, Y., Yokoyama, S. andHide, K., +32* b, Origin of the Median Tectonic
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e fOῌrs +31. =]`Ce t %0c* h6 u no. +, 3῍+..
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#k{ ῌ u!|{ ῌ }#O ῌ ~~?
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