13
腊腟腒腝腣腟腈腢腗腢腡腆腐腠腛腙腃腦腎腑腚腁腋腞腜腙 Fold structures and basal fault of the Upper Cretaceous Tochiya Formation in the northeastern Kanto Mountains 腏腕腓腥* Shirou Chikashige* Abstract : Geological structures of the Upper Cretaceous Tochiya Formation, once regarded as one of the member of the Atokura Nappe, were carefully investigated in order to clarify the geotectonic evolution of the the Yorii-Ogawa area in the northeast- ern Kanto Mountains. A macroscopic overturned anticline verging northward was recognized as well as upright folds. Their axes trend N2*2/W and plunge /+*. A basal thrust between the allochthonous Tochiya Formation and the underlying Mikabu greenstones cuts the fold structures and exhibits fault-rock fabrics, suggesting a top to the north sense of shear. These evidences for the northward movement suggest that the Tochiya Formation in the study area was a di#erent nappe from the southward-verging Atokura Nappe of the type locality. Key words : Tochiya Formation, Atokura Nappe, overturned fold, basal fault, paleocurrent 腄腀腅腂 腍腺腺腚腣膯膶膒臧腘腍臉膬 膶膮腇腍腏腮腥臉膬膶膢膨臙臲膌腢腤膥膷腟 腨腄腴膉腢腗腱臠膤腐腯膹臊膤腣膉自腣腑臊膻膗腹膈臡膠腣膿臻臝膈腢腓腎腲腯腤 臰臶腾腼膁腟臹臛腕腲腝腌腱 Fig. +腇腆腏腤+33, ; 臉膬臹膙膹臬膜腸膆膂腹腵膃臩 臦膙+33/腇腁 腔腲腯腣膉腣膰臫膘腧腼膋腙腬腈臌腴臀腎腱臝腞腅腵腞腋 腔腲腩腞腢腓腣膵膧腑臁腳腲腝腌腱 腝腼腨腐+3/- ; 臣膋腨腐+30-+300 ; 臙臘腨腐+31* ; 腤腘+312 ; 臙臈+313 ; +323 腡腠腇腁 +33* 膺腐腯膠臸膓膞臵臫腨腄Sr 腁腮臖臬 腢腮腰腔腲腯腣腣膣臼腑腯腐腢腕腲腚 +32- ; +323 ; +323 ; 腨腐+323 ; +33* ; 腏腤腻腼+33+ ; 腏腤腻腼+33/ 腡腠腇腁 腕腯腢腾腼膁腣膡腔腋臷腣 臷膠腣膿臻膚臮腢腮腜腝膒腗腱臝腣臸腂腖 腡膊腻膆腺腑膦腫腯腲 腵腶腃膅腺腨腐+33* ; +33+ ; +33/ ; Kobayashi, +330 腡腠腇腀 腈臰臶 腾腼膁腣臒腡膿臫膄膆膀腃腞腋腱臰臶臷腣腥腸腣膑膫腑臄腕腲腝腌腱 臣膋+332腇腁 膢膨臙臲膌腣臰臶臷臸臷腟腕腲腱腣腉+3/.膒臧腘腍膌腣臰臶臷腢腧腝膼腡腑臚腡腓膫膿臻腭膡腔腋臷腣膿臻膚臮腡腠腣膴腑臥腖腝腌腡腌臆膭腣腉腴腱膌腣腳腍 膌腞臇臯臞腣膖腑臥腪腅膍腟腑臕膸腖臏膿臻腣 臅腢膁膄腡臟膩腑膸臕腖腚膵膧腞腤臯膋腨腐 +33*腢腮腰腟腕腲腱膌腴臗腓腣腉腴腱 膌腣腳腍膌腴臜腢腖腝膫膿臻腏腮腥膟腗腱臷腴臢腢腴臁腜腚腙腣膲膕腳腫膇膱腣腉臷腤臰臶臷腟腤膉腡腱膎臺腴腗腱 腾腼膁 腆腈腣腉腾腼膁腉腇 腞腋腱腔腟腑腯腐腢腡腜腚 腣腞臄腗腱腌腍腖腘腝腇腃腝腔腉腤 膢膨臙臲膌腣臏膝臨腴 Fig. , 腢臍腗腔腣 膌腞腤腐腯臊膻膗腹膈臡膠膢膨膪膛膠膢膨臷膻膗腹膈臡膠腟膮臘臋臯膏至腣腉腐腲腃腣膠臯臷腑腴腱腖腝腌腱腲腯腣膠臯臷腣腍腛膢膨膲膪膛膠膢膨臷膮臘臋臯膏至腣腉臷腤膻膗腹膈臡膠腣臝腢 腾腼膁腟腖腝膊腖腝腒腚膉自膠腞腋腰膒臧腇腍膌腟腟腬腢 臰臶腾腼膁腴膿臫腖腝腌 * ,*** 1 . ,*** ++ +/ 腧腼腅膞膍膽膞膵膧膔腍膅膞臱膾 Geography Major, Graduate School of Science and Technology, Nihon University, -,/.* Sakurajosui, Setgaya-ku, Tokyo +/02//*, Japan 膿臻.. --./,*** Structural Geology, No. .., --./, ,***33

日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

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Page 1: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

������������ �����������

Fold structures and basal fault of the Upper Cretaceous Tochiya

Formation in the northeastern Kanto Mountains

����*

Shirou Chikashige*

Abstract : Geological structures of the Upper Cretaceous Tochiya Formation, once

regarded as one of the member of the Atokura Nappe, were carefully investigated in

order to clarify the geotectonic evolution of the the Yorii-Ogawa area in the northeast-

ern Kanto Mountains. A macroscopic overturned anticline verging northward was

recognized as well as upright folds. Their axes trend N2*��2/�W and plunge /��+*�.A basal thrust between the allochthonous Tochiya Formation and the underlying

Mikabu greenstones cuts the fold structures and exhibits fault-rock fabrics, suggesting

a top to the north sense of shear. These evidences for the northward movement

suggest that the Tochiya Formation in the study area was a di#erent nappe from the

southward-verging Atokura Nappe of the type locality.

Key words : Tochiya Formation, Atokura Nappe, overturned fold, basal fault, paleocurrent

����

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������ +33/ghAM =#�789�u./v�/v,�-.wx��y>0�1��/0�k1�gz2{F|(}~#3 @I���|`"� +33* ; �3� +33+ ; �3� +33/ ; Kobayashi, +330ghA� 456

789: ��#g-P�F��VX�56v�45���6�7�(8�=3>?� @ab�e&� +332AM��������56vk9v�=3�:;v @i

�� +3/.A �� ����56v�)�><�g=>(�g[7�-.�u./v�-.wxgh��?(�@1>?g?M ��� :;vAB��������V�����C(��!=>(��1� �'-.�D��EFg��(��1sM �\]V�� �b`"@+33*A ��Y�aG�=3�����[:;vAB���������1��1>� 7�-.����H��/v����D���?�^ysM 2� ¡� /�I¢£:;v�56v���g�¤2¥�E��789 @4:;789:A VX�N�(+#"�gys�V8���M

!�"#�$��%&'

���������'¦J§� Fig. ,�¨�M N���V�� �"#% ��)*��+,�� ��K ©ª,�� ��v� )*��+,���c��«¬�,� :;v� LM��,���v(AB1>?�M N3#�,���v�­®��K ©ª,�� ��v��c��«¬�,� :;v�)*��+,��/�789�1>z21>¯s��&,�VXY� ���� ������°� 456789: �-P1>?

*

,***� 1± .�²NM ,***� ++± +/�²OM��!m!m³O´m\]µ�Om¶·Geography Major, Graduate School of Science and

Technology, Nihon University, -�,/�.* Sakurajosui,

Setgaya-ku, Tokyo +/0�2//*, Japan

-.�'� � ..¸� --�./� ,*** @Structural Geology, No. .., --�./, ,***A

¹ 33 ¹

Page 2: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

� ������� +33,�� ��� � �������������������� �!��"#�+323�� WNW-ESE�$% N-S�$�!&'()*+�,-./0�12�3�4(56�(7���8

9��:;)�<0 ������� +33,�� <=� >?(�@0/�� A4B%��C �D�E;� +3/* ; FG� +3/. ; HIE;� +31* ; 3JE;� +33*� K��LIM3NO���PQ�� ,/+ Ma �H��

+32-� K�0� ,/,Ma �RM�SG� +33*� )�TUVW.� ��� �XY;:Z[��\������]&'()��%^_`a� �Hb� +313 ; �c�+32. ; ������ +33,�� >?(�� ��� d�=efd�g�6(;:<�hijklm)K� ������� +33,�� 6(n�g�;:�oUpq�rst�lm-3� uv-3Vw. ���E;� +33* ; D�E;� +33*�� xy.14zQ� Turonian{Cam-panian �=e| 3*{1.Ma� %}~:a/0� �����n�����s��������� +33/�� �1�>?(����3��s��35������V��/0� �Hb� +313 ; �c� +32.�� ���������� ���z�����)K�� �� s�¡¢��£s�m¤�,Q� /3.0 MaVW� ������� +33+�� ��(�� ¥¦���§���(%¨�;:<�©�()K�� �§���(���;:� ¨����=efd�;:<� ������� +33,�� ��(¨��ª��«��������� s�¡¢��£s�m¤�,Q� 0/..MaVW� � ��������%�(789V}��a¬� ��(�4zQ��oU��­®�)K¯�%`a/0� ������� +33,���\�°¤s�± >?(��²� �. ������� +33,�� ³²�´��%µ��� �¶ ��� ��c� +32. ; ������ +33,�� �\�°¤s�±�&O�;: .*,Ma� K-ArQ ·:

Fig. , Geological outline of the Atokura Nappe in the

Yorii-Ogawa area. Simplified after Makimoto and Take-

uchi (+33,).

Fig. + Geological sketch map of the northern Kanto Mountains. Simplified after the Geological

Sheet Map + : ,**,*** “Nagano” (+332) and “Utsunomiya” (+33*) of the Geological Survey of Japan.

MTL : Median Tectonic Line. ISTL : Itoigawa-Shizuoka Tectonic Line. TTL : Tanagura Tectonic Line.

¸¹º

» 34 »

Page 3: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

���� ������� +33/��� ������������������������ ���!�"#��� ��$%&'()* ��� �+ �,-��.���� ���%� /�"��� 012345� ,-��.��012 �� �6 �7�� +33+�� ���� ��,-8�%9�:; �<=�7�� +332� %� 012345� >?@A5 � �B$� �� CDEFG�HIJ�%KL�MNO �� KL$�HIJ�%��P�:; ������� +33,� %QR��� ����S�T'������ ��U��9�VW<X��$QKL$YRZ� [\� ��Q]<�^2$_�?Z�`+��a��b%,-� c<d �� 0*Ma� ,-]']<d �+0Ma� �eYR�������� +33,� [\� � ��U��9� 3��$�fgKL�MNO �%KL$�� h��i�j,-k������l9����%�m.���� ������� +33,� .-�012345� � ��$�no���pq%9�:; ����+32.�� ��$�rsUno���tu�:; �vwJxyz,� +33* ; 6 � +33-�� ��$�{��,-| X\%9�:; �Kobayashi, +330� �� CDEFG�no���l9�%9�:; ���� +32. ; ������ +33/�� 012345� �}�~�* ���!""���#���l9�%�f:; ��

$�7�� +323� WR��� /�-��l������:�p������8�

������

�B$�� %!z, �+3/*� �?Z��$%&'.�� &$ �+3/.� ��(�U��X��B$%&'X\ 61z, �+31*� �.-��(�U��X��B$U���X� ��$���"!(���$ �<=z,� +30-� %�)X\ �B$��(��*����� h%*+�3,-��X�,-�U]<�%9�:; �3=z,� +33*� QR�b%U�.X�� ���Y�]�k!��Y/�� m$8�����!������U��\�B$�� ���{��� "������� R���012345� %/���7A�m$Y�X� �"� +�, km�0YWNW-ESE1 �� 2 km�¡¢8�(U£9 ����¤�X\]�k!���,k� - km�*�YRZ� �$�¥ ��(�1 ���Y N 1*¦�2*¦WYR� �Fig. -���� §¨©KLª2L��«3¬� KLª­®¯���­�¯� �Fig. -�� ( b�����B$�� "�>?@��%Wm$�?���� CDEFG%�9�$ ° 2L��� ­®¯��%W±²$!Y .**m

Fig. - Geological map of the western part of the Tochiya Formation. Modified after Makimoto

and Takeuchi (+33,).

³,2�",´!"!(��B$�/��!%µ2m$�!�� ¶ ..·

¸ 35 ¸

Page 4: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

��� ������� 2** m����� ��� �������� +** m� ������������� +** m� ����������������� ,** m���� ������� !"�#$� �%&'(�)�$"�*� �+�,��-.���( /� 0%1��234�� 5678�34�� 9:;<8� � *�� ��� ��=$���>?:@8A<@B<8�"?,�%� CFig. +,

e� fD ��E� ����� C+33,D %F���=GH�I���JK%���> �*�*� �L�1MNO( +* cm���� PQ�9RS7TQ�U����� ����������� -* cmV, m����� - cmV,/ cm� ����%W�%�( / : +

��%������ ���H�X�(YZ�� ���%� � .!% +���M������������(!""� # � .!% -�����������(!"���[\$]�� ������������M����������%!"^�_��$%%`&��'Ha(�(b)��� [\$]%��"?������%��%*+H,c� 1defg�?(� 0 ��hR78i6T8� j-i6T8 Clongtitudal

scourD CCollinson & Thompson, +323D� klmTi6T8$� ����n.H/"?o,p�1qNErSW�s� CFig. .D� t%o,p��0u�v1C+312D %s�o,p ESErWNW Cw,D H2�� ,H2x"� ��Hyz����%���������{%�%3p� p|w� P*4�%5p� �67|%8}w%5pM~�9|������:$]�� ���%� � .!% +����

# � .!% -�����������(!"����������������;�R78H�)�<=(>?"�*�*?�fg��*� !"^#������ @�� ?a(�M~�%#�|%&'+A���

��������

+ �;�$^%���H�� ���Bp|��B7

|��67|(C��� CFigs. /&0D�[\$]�� � H!"����#=����������������H�����������#�|$� ������%����#��%�������� 0%# �������������|����%�����s�� D��0 � �Bp|%�E� #E���� t%p|%� +** m# H�B7|(C���� t%7|%#E� +** m�#�|�#��%������������ 0%# � /* m���FGHI� ���JK�� 0%# � -* m���|������ t �%�B8}% p�<9�;�����?8}w�� N 2*�W%3pH +*�:;m��� CFig. /bD� ��H# H� +* mL%@��(C��� CFig. +*D� t%@��# %~�� +,* m#�3p� ,** m%M<=��f������ CFig. 1D �PH������%5p�?O)���"?T��5 CFig. 3D� #=��<=��� +-* m#3��H� /* mN~%~*[O%�-� ¡¢ CN~� ,-* mD �� #�3p%~�� -V/ m%£¤+H� � ��# {��|����� 1qn.� #�|�#��{MP¥��������(fg��tM CFig. 2D ���67|(¦M�� �� t%�67|�� 1qQ§3p%5p#{RV'��|��8}w+�¨©� �E('�9��"� #E(R�9�|��Eª�� 2/�%!S�¨« CFig. 3D� >?� t%�68}%¬T!��� 2de%<=H#­�������%®��� p

�<9�;�H=$��?8}w�� N 2/�W%3pH /�:;m��� CFig. /bD���:$] CFig. 0D ���!"^#¯��#3

+**V,** m%ª������(#�|�#������|����H���%� t%ªHp|(C���� ��#¯��#3� -/* mU°%$%���|(±²�H�$� .** m$%�1qn. C/�V1�ND H�$� � +* cmL%4�³l���E� + mL%@��HA��� @���#%� .* m�#�|����%��"?����������(?/� �Bp|#=��B7|%�E��´m�TH�­��VW���%%� �B7|%#E�µW��¶­� CFig. 0bD� [\$]%8}·X��¦��t%�

Fig. . Restored paleocurrent directions on the over-

turned strata in the Tochiya Formation. Arrows show the

directions of paleocurrent.

`¸¹Y

º 36 º

Page 5: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

�������� ����� ������������������� ������ ����������� !� "�#���������� ���$�%�& p'()*+, �-./01�2

34� 2*5W�6�# -57+89��&:;<=> ?Fig. -@ A�� BC�DEF�G�HI �����JK�����LM�NOP/& �Q� RS�TU ?+33,@ �� JV� -WXYZ�BC

Fig. / Route map in the qarry of the Sankyo area (a) (Locality showing in Fig. -), and cross section (b) along the A-B,C-D sections and attitudes of fold axis.

[\]=�\^_J_`abBC��23cd�efg�cd=h i ..j

k 37 k

Page 6: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

������� .���� � ��������������������������� !,� � ��+� ��������"#$%&'� ��()*+,-./0� -./12345� ���6���7 ! 89:;<=>?@��A��*+,-./0 -./12345BCD�E'� N .2FW 1*FS&� -./12345�

GH .* m�IJK�LMNO�� ! -./12345 ���P/� BCD�E'89:;<=>?@�&'N 1.FW 2,FS&Q<� -./12345'H +* mR�IJK�LMNO�� !����S-./12345� BCD�'�TUV$%&WX&Y� ���Z/[\Z/]/^�G N .*FW 0,FSBCE&LMNOJ_`/�a7 ! LMNOJ_`/'���H .* mbc!

Fig. 0 Route map in the Gonotsubo area (a) (Locality showing in Fig. -), and cross section(b)along the A-B, C-D

sections and attitudes of fold axis.

defg

h 38 h

Page 7: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

Fig. 2 Photographs of the outcrops of the southern limb of the overturned anticline in the

southern area of the Tochiya Formation. (a) Normal strata dipping north in the northern

part. (b) Subhorizontal normal strata in the middle part.

Fig. 1 Photograph of the outcrop of the southward dipping reverse beds, forming the northern limb

near the hinge of the overturned anticline in the southern area of the Tochiya Formation.

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� 39 �

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����������� ���� ��������������� ��� !"#$%& '�� ��()* +* m+,�������������-�.* +/ cm�/0123456� 7N 2,8W

,+8S9 :;"# 7Fig. ++c9 <���% 7Fig. ++a� b9&56��=>?�* -* m@A:B%& /01C�DEFGH�I�JKLM:NO� PQ)�RSG�TUVWXYZ()� -K��?4 7top-to-

the-north9 [5\E]2^_`-56:N% 7Fig.

++d9& ab�/01c;_%��������N .*8E>?�56��]defEghE2iYZc_%XZ

jI��� �Qk��lmnopqg]r�TUVYZ�-K��?4\E]2^" 7Fig. ++e9� -s�tu]vweqxyQ�\E]cz{_%& ,)�P�| cmJ����������}~�c�H���234�YZ�56�����WX_% 7Fig. +,a�

b9& -K���6�����������������)Q% 7Fig. +,c� d9& ��`-56� N 108W 228S��� N 2-8E 118S�+��56:�)Q#$%&��`-56�����=>* -* m� * /* m� *

1* m� -���� ��() 0�+* m+,���,Q� /�,/ cm.�/01234�?���N 1*8�1/8W ,*8�,.8S�56:N% 7Fig. +-9& 56�-�]defEghE�56���?� -*8�.*8�� ¡O��¢"� JK�/01C�DEFGH�I�TUVWXYZ()-K�£¤NE>?�?4[5\E]2^_&�Q)� .���£¤¥z¦§�56�2¨©� 56���?�U"#�� ªO>?��¢_%>?�]defEghE2¨«`-56�� ��������-��%��6���56:N%c¬5,Q%&�,� �������

Fig. +* Fracture zone cutting the overturned north limb at To-- in the southern area of the Tochiya Formation.

The overturned strata dipping south in the right hand of fracture zone,the normal strata dipping north in the left

hand of fracture zone are observed. Bag in front of the outcrop for scale.

Fig. 3 Outcrop sketch showing the fold profile of the hinge part of the overturned anticline.

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± 40 ±

Page 9: 日本地質学会 構造地質部会+33, ˘ˇˆ˙˝˛˚˜ ! "# +323 WNW-ESE $%N-S $ !&’()* + ,-./012 3 4(56 (7 ˘8 9 :;)

���������� ���� To--�� /

m���������� +* m������ !"�# ���$%� &� '(�)�*�+,-,./�012 N /.342*3W 0/3N 5Fig. +*6# ���$%�)&�)'(�)�*�+,-,./�012N0*3W /23N789:�� To--�;<����2# %� N 0.3W=>�

�� To-1?7@A�A9 5Fig. /a6: ?�# �� To--$�� To-1�B���� 5����CD2 N 003W

1*3S6 E�FGHIJ,K�L< S-CIMNOPQRSTU<9$# )& 5�V6 W=# & 5WV6 �=X�YZ�;�[U/$\]S^9 5Fig. +.6: �� _�# '(�)�*�`a/$ '(� �*�[b/�B�# '(�)�*�./�)'(�)�*�./�cdef�[U/�gh�ij�$\]S^9kl mn7o9:

Fig. ++ Outcrop of the basal fault of the Tochiya Formation. The hanging wall rock is conglomerate of the Tochiya Formation

and the footwall rock, Mikabu greenstone complex. � Whole view of the basal fault. Black line shows the fault trace. �Central part of the basal fault shown in (a). � Close-up view of the fault gauge zone of about +/ cm in width. � Asymmetric

imbrication structure made by crushed lens-shaped fragments,showing top-to-the-north shear. � XZ thin section of footwall

rock (Mikabu greenstone complex). Asymmetric epidote augen with asymmetric porphyroclast tails indicates top-to-the-north

shear (This is a s-type object of mantled porphyroclast (Passchier & Trouw, +330).

pq��)q�r�rstuvw/�xyz{$|}U/z{�~ � ..�

� 41 �

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� �

+� ����������������� �� �������

������������������� !�"�#$��%&'(�����)*'

+,-�./0�12����.�.�3�4�25678��� 9:';<�=6>?+@A�BCDEFGHIJKLMN8OP�Q� R.ST�.U(28VWX�NEYSW�Z.[T+,� \]<��^;_`a�bc�� WX+CDNGMDdMN#efg_hij�k�lQ�6B ,� � ���������

Fig. +, Photomicrographs of textures near the basal fault. (a) and (b) show the recrystallizied texture in XZ thin section of

Mikabu greenstone complex (left : plane-polarized light and right : crossed nicols). Both s-type winged porphyroclasts in the

central part and anthetic o#set of displaced grains in lower right corner indicate the sense of the dextral share. (c) and (d) show

grain size reduction of quartzes in the matrix of conglomerate in XZ thin section in the Tochiya Formation (left : plane-polarized

light and right : crossed nicols). (e) and (f) show the protomylonitized granite pebble in the Tochiya Formation. The boundary

between granite pebble and the matrix is viewd left to lower right corner (left : plane-polarized light and right : crossed nicols).

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������� ������ +,***m����� �������������������N 2/�W�� /������ !�� ���� N2*�W�� +*������ "��� "���#$� ����%� #&'(�)* + ,-��./� !��� �����01 �2)345678 �( 9:;�< =�>?)@�� AB�CDEF��G��� H *� N-S��I�JK> F��G��>L#$M-ENOP�- +"��Q>R"��S� !�N�D>.�< =�> @��AB� H *��� N-S��I�JK �T��U�#$M-ENOP�- + M�� < =�>?)@�� AB�CDEF��G���V�"��� "���I�JK �T��U�#$M-EW�XSH + � �� ,-��*Y- �$Z>?)���#$M-E�)S� �[;�!���\]^_�`�01'ab,N��cL(*+

-� ��������� ����defg��[;��h��ij�� �;�kl'(�mno;�� n���p��oq�r's�+ tE� o;uv��U��wx��yz����)QL� n��k{�|}�~���mno;���>L#$M-ENOP�- + M�� o;�n�� uv�� U� ��- ���E�#!����� |}������> ~�����(��� ��-(*��� ,-���#��X"h�#$M-ENOP�- +tE� ,�klo;�#z ��z$1#z�z�;�@� f�%��)* ,N �� "����&'�?)* ,N�� �HL� f;��%X'O'� Nf{o�� �Fig. /� �2)!��"��� "��'� N(oM- + ,�,N �� klo;���������#$���N*P + M�� ��n�����oq�r��[;�!��s��\]^_�`�����N )��H +!��¡!�E�&'� "o;������!��#$VNOP�- + ,�"o;Nklo;�������V¢£�*+�H �� klo;��������H?EN� (�¤� ,�o;¥¦S�[;NNS�� �@��)§EW�X�H +.� ������������������U¨,fh�©ª;b*)�� ��«¬�­-�+332� >L E-W(*� ENE-WSW��'ab�\]^_�`�F��G��N�-'��MG "��� �( <.����'s�,N�+� (?)* + ,-®�)� ¯efh�� E-W��'abF��G��N"��� �( ���°j� �� F��G���\]^_�`��*)* ��±( +�[;�� ©ª;®/M-©ª²0;NM-)*

Fig. +. S-C structure in the fracture zone cutting the

overturned north limb of the Tochiya Formation. Arrows

show the sense of shear. Hummer circled for scale.

Fig. +- The another outcrop of the basal fault. Black line shows the fault trace. Toc : Conglomerate of the

Tochiya Formation Sm : Mikabu greenstone complex

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f�� ������ +332� ¡�t�� ���g � !�� : "�#�$��¢9 �K�� +*.� 20+�2109

Collinson, J. D. and Thompson, D. B, +323, Sedimen-

tary structures ,nd ed. The University Printing

House, Oxford, ,*1 p.

^�}£��M¤ �| ��� +3/-� ¡�t��M����# !9 ��ghwjH�9 no. -, +�.+9

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Kobayashi, K., +330, Rotation of slip directions of

the Atokura Nappe viewed from micro-

structural analyses of brittle shear zones in the

Sambagawa belt, Southwest Japan. Jour,

Struct. Geol., +2, /0-�/1+.

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�!� 67� 12� -2�-3�Passchier, C. W. and Trouw, R. A. J., +330, Microtect-

onics. Springer-Verlag, Berlin Heidelberg, ,23

p.

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