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Eruption History in the Post-caldera Stage of Akita-Komagatake Volcano,
Northeastern Japan Arc: Correlation between
Eruptives Constituting Volcanic Edifices and Air-fall Tephra Layers
Akihiko FUJINAWA�, Masayuki IWASAKI�, Kyoko HONDA�, Akemi NAGAO�,
Takeshi WACHI��and Shintaro HAYASHI���
Akita-Komagatake volcano is situated at about -* km west of volcanic front in the northeastern Japan arc.Development history of the volcano is divided into - stages ; main strato cone, syn-caldera formation, andpost-caldera eruption stages, in descending order. In order to reveal the comprehensive eruption history in the
post-caldera stage of the volcano, correlation between eruptives constituting the volcanic edifices and dispersed
air-fall tephra are investigated, along with re-examining geology of the volcanic edifices formed in the concurring
stage. Petrological a$nities such as whole rock major-element chemistry and mineral assemblages includingmodal abundances of phenocrystic phases are utilized in identifying the contemporaneous eruptives of various
modes of emplacement. To avoid the e#ect of phenocryst-matrix separation, coarse-grained tephra samples wereselected to the whole rock chemical analysis.
The revealed outline of eruption history is as follows : Tholeiitic magmatism has been dominant through the
stage, with episodic calc-alkalic magmatism at the final activitiy in the northern region (ca. .,***�-,+** y.B.P.).Relatively large eruptions occurred at the beginning of the stage (ca. +-,*** to +*,*** y.B.P.), resulting in calderaand probably large horse-shoe shaped crater as well, rather than forming volcanic edifices. Formation of the
northern volcanic edifice began ca. +*,*** y.B.P. Five pyroclastic cones were built up successively, and subordi-
nate lava flows or pyroclastic flows accompanied with them. Composition of magma was abruptly changed from
andesitic to basaltic around 2,*** y.B.P., and the basaltic volcanism lasted to 1,*** y.B.P. After ca. -,*** yearsof dormancy, phreatic explosions occurred successively, probably giving rise to horse-shoe shaped crater at the
center of the northern area. Calc-alkali andesitic magma e#used to build up a small pyroclastic cone immediatelyafter the major explosion event. After ceasing the magmatism in the northern area, volcanism in the southern
area was initiated by phreato-magmatic explosion in the floor of the south caldera about ,,/** y.B.P., followed byvulcanian eruptions, lasting until ca. +,0** y.B.P. About +,/** y.B.P., eruption center was localized to two majorvents at northern part of the caldera. Repeated eruptions from the vents have built up Medake and Kodake cones
and their associated lava flows. The latest eruption occurred at the summit of Medake in +31* AD.Key words : Akita-Komagatake vocano, eruption history, tephra, basaltic volcanism, island-arc tholeiite
&-+*�2/+, '()*+,-./$/01234567/7Department of Environmental Sciences, Ibaraki
University, Bunkyo, Mito -+*�2/+,, Japan.&,.-�**+0 89:;<=)�>?@A@BC�D%Asia Air Survey Co. Ltd., Tamura-Cho, Atsugi ,.-�**+0, Japan.
&*+*�2/*, E�)FG/H?E�./IJ*K/01/ILDepartment of Earth Sciences, Faculty of Education
and Human Studies, Akita University, Tegata-Gakuen-
Cho, Akita *+*�2/*,, Japan.Corresponding author : Akihiko Fujinawa
e-mail : [email protected]
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Fig. +. Index map and topographic outline of Akita-Komgatake volcano. Triangles show localities of Quaternary
volcanoes in the Tohoku region of Japan. Point marked with star (�) indicates the site of drilling (see text).
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§ ,� ®q¯°f%�(%���C�§�Fig. ,. Geomorphological map of Akita-Komagatake volcano.
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Fig. -. Geologic map showing the eruptives at the post-caldera stage of the Akita-Komagatake volcano. + :Tertiary sediments and volcanics, , : Quaternary volcanics erupted prior to the formation of the
Akita-Komagatake volcano, - : Eruptives in the main strato cone stage, . : epiclastic sediments. Other
abbreviations refer to those in the text and also appeared in Fig. .. Solid curves show the caldera or crater
walls, whereas the broken curve indicates the inferred location of the step on the caldera floor.
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stage of the Akita-Komagatake volcano. LF:
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fall, DK: dyke.
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mm�� ��6`a./�'�AK-+, : '(�� (YP) �+QR��� OY=�%[)�6bcd�%[\ (Y-P)� e*f'��g�h� ��5�� LY,P, �] 2* cmP� Z2� ��-d����� ���i� (Y+P)49��� ^_ Y,P=��+-+* mm��� ����� L�� 2 : ,P 6./�'�AK-++ : �]% ,/ cm�Z2� ��5��6�� ��% +-. mm�Z2� ��6./�'�AK-+* : AK-++�+j��]% +/ cm�Z2� ��5��69� �� +-- mm,��Z2� ��6./�'�AK-3 : ,(�� (AP)�+kl� - +./����0$1�� m�6bc�]�% 0* cm, OY�n� � �������� L�]% /* cm, �� 0 : .P� d�%[\��m��234�o�&��� ����g��0�6./�'�AK-2 : 56�� (HP)�+QR��� �]% +1* cm��-��d7�p�� qOY�rst�%[\� (H-P)�u�j�� ������ LH,P, �] /* cm, �� 1 :
-P� qjY�% +** cm]�d�� 8�� ���i�LH+P, 0�./���]� +- cmP 4&��� H,P=��% ,-,* mm, H+P=���% +-/ mm�0�6./�'�AK-1 : OY�n� ]&% 2 cm�vtZ2� ����]& 2 cm,�9std����� &��9��'w\t%[\�4&��� :�]% .* cm6�� OY ,�=�u�x�� vt� �� L�% +-- mmP� g�hd��� L�% +-. mmP 6./�'�AK-0 : ��% +-2 mm�� �����65���L�� 0 : .P� �] 0* cmy� j#�m�g�h23s
t44������AK-/� AK-. : ;��+��]% / cm, \t-r\t�d�%[\�n9���� �2�2�������� �� +-- mm�%[\6./�'�AK-- : Z2� ��-Z2%[\65���� OY�nwvtZ2%[\ L�]% / cmP� st8�Z2%[\L�]% +*-+/ cmP� rstd�%[\� vtZ2%[\�g�hz\t234=�9��- ,�- -./�g��� OY�Z2� �� L+-- mm�P g�hst8�Z2%[\ L+-0 mm�P 6./�'�AK-, : �]% +* cm�Z2� ��-Z2%[\65���� ,./�g��� �� +-2 mmZ2%[\-� ��6./�'�AK-+ : O#�<st-9st8��Z2%[\� j#��v-v\tZ2� ��49�8=6���]� +/-,* cm�� �� +-+/ mm�Z2� ��6./�'�AK--� AK-.{�� ��>|# : - +./�� AK-.�j?% , cm LAK--�O?% - cmP �� q@] - cm�� ��>|#4}��p'� ��� ,-1 mm�B�� �~���7�� ��+� A�()*���+�./�7��� B��C6�f'� NO� AK--./�����
/� ��������� ��[�89������ D�0�=�EF6�9�� ���'� ��4q+8��G��<H��� �����q@��4 *.*/ mm, I< �� *.*- mm6J��7�4��� �f�� ����� q@K4 *.*/ mmNj��36�L���M����7���'� �F�N9�� EF0�O�O{����� ,,***P��Q��=���� FR�%T�� G��<H� S#- .%T��"��������� +0�� u�N������� ,
--0���F��Q6�f'� ��� FR�SI< �S#- .%T��TU�V- +I< � J�- ,I< �J�%T������ ()*��BWX�'��� Y2M�¡#�N96� P7���nQZ�'� �Q�¢£@¤[\� SEM-EDS��(¥ (JEOL-JSM /0**
LV-Oxford) 6]�� +/ KV, +¦+*§2 A, �Q¨{ +**^�©ª��f'��%[89��«���M��@p&�¬�_f���� ®K�M��`¯XC°±� *.--+ mm,�� q@��mm�� �#0��� + cm6J��7�+B�� Y2M���� `¯C°±4 *.--*./ mm,�� q@�+ , mm6J������²��B�� ²'� ³Y�Labc��P �� q@�+ *.+ mm,��B��
/�+ �������
´dµ¶�%[� ·"!V*¸�¹�gº��%» : %[�89����¼O()*��B 341
��� �������� �������������������� +� � ,���� - !"��#$���� %&'���(� )*�� ������ )���� +)����,� ��� %&'��-./������012 ��345�� �#' !"�6#$ !�78�(������� ��� - !"��#'����/� ������9:3���������345� ;< ,=� �>( /*?1/ ;@8= �-ABCD�� ����(� �#'����-.EFGHIJKLKMNOP/QD4R�� S-T-���(2:RU�>VW/X� Y�Z?[YZOP\,�� !�-�>��]�VW(^_�`X� EFGHIJKLKMN?EFGHabLKMNOP\,�;< ,=���� , !"��#$����(� c��d�Oefg�h/i2� j,� ;k /lgm=��#'����m-+)���(� no�pqrFq5� (Wo)/ -1?.+ (mol)��Mg� (+***Mg�(MgsFe) atomic) �t-uv/QD4R� w�pxxFq5� (En) ( -3?./ (mol)�-AByz ;k 0 a=� {|,�)���-Wo( -.3�� En( 0,./?1*�-O5}, ;k 0 a=� ^�� ��� . !"m-+)���(
En/ .*?.0�-AB�,�/� Wo( -3?.+���Mg~�-uv(QD4R12 ;k 0 b=� {|,�)���(Wo�-.+?-./�� En�/1?/3./����#'���m-�u��SR�R����2 ;k 0 b=�
/�, �����������-���(� �Oef-����� ;<
,=� &' !"����'� ,���/��Oefl��U���1����� ��345�� 0�� ������ +)��� )������ ������/��,� ;����� +���� �'���� �'� +
���� �'�����78�� �' !"=� ����� ,������&' +31*����(��������5�R� ���(�X0R������/�0R���>OP(���� !��UVW(����Y�Z?EFGHabLKMNOP0������ ;< ,=��U���1�Oef�,����(� m���� ,� ;< ,� k .=� 0�� �'� +�����'������(� c��14����h/� i2� j,� ;k 1=������ +���m-+)��(� Wo, En/¡�
.-?./ mol�},¢Mg-O5�� Wo�.*?.+��En�.*�£W-O5�� ,��R� ;k 0 c=� {|,�
< ,� �@�5���-¤¥��¦§¨©���ª«¬O5�Table ,. Petrographic features and modal compositions of the eruptives constituting volcanic edifices.
opx : )���� cpx : +)��� ol : ������ bg� : ��� H-P: EFGHabLKMN� H-O: EFGHIJKLKMN� I-G: Y�Z� I-S : [YZ� SE: bFMq� P-T: aHx®LKMNopx : orthopyroxene, cpx : clinopyroxene, ol : olivine, bg. : bearing, H-P : hyalopilitic, H-O: hyaloophitic, I-G:
intergranular, I-S : intersertal, SE : seriate, P-T : pilotaxitic
¯°�±g��²³g�´µ¶g*·�¸g�¹ ºg�»¼�342
��������Wo�--..� En�/21*���� ��� �� 0 c�� ������������ �!����Wo�-..-� En�.,/+��""#$���� ��� �� 0 d�� ��% ,��� &�'���� �()*)�+�Mg�, 13-*././ 01�
0� ��������� ��������2345*6��78 9���:;<�� AK-/
AK-. =>?6�.@$ABCDEF GH1� I�78 AK-+- (K+P) +, 3 2 0 -./ - ,� 26�+�?JK L�. ,MNO01�PQ R -.S'�TUV��WX�YZ+[�� 6� \]0A^_ 3Z=>� I�` abcde �*.-*.0 mmfg� .�h Iij�1�. 45* klm+n>11o pq'r7.�s T�01� T�` Jt. ,**�uv0 wxNyz{|X+}_~ �F01� �F��1����cd}_��r�����/�+[�� ����/�� ��0A�*����;<�Z ��cd+[���}_�0�0������ @�Z ��+���}_cd !L�s.���T�+o� ���/�.��A$�� �h���.��HA$�$, �<���s� �� ������ � ��}_ =oab�� �cd����"cd}_������ R'�¡�,¢£���� N¤ EFPQ+� ����/��r��¥���� ���� ��,I�¦� //1/�fg ,*�.*�fg �R -� � �y&�_����r��¥�cd�BCD���§�'��cde�()*)��,¨©��145*ª� AK-
+-� AK-3;< AK-+�+�« 3ª+[�� ����
� /� �¬������% ,���&����r� AK-0�BCD��� opx : ���� cpx :
!��� ol : ()*)� opq : ��}_�Fig. /. Modal compositions of the Katakurazawa
lava flow, Hokubu second pyroclastic cone and
AK-0 tephra. opx : orthopyroxene, cpx :
clinopyroxene, ol : olivine, opq : opaque minerals.
� 0� ®¯��1�y&�°v_���cd���Fig. 0. Chemical compositions of the phenocrystic
pyroxenes in the selected samples of the
eruptives composing volcanic edifices.
±²³´��� `(µ¶*·¸¢.�¹�°�º : ��y&�°v_�»X45*ª�¼� 343
� 1� ���������� �������������� ���� /���
Fig. 1. Modal compositions of the Kodake first lava
flow and the Kodake-Ohyakisuna pyroclastics.
Abbreviations refer to those in Fig. /.
� 2� �� !"#$%&�'����a()d( &�*+�,!-! KK, HO., HI+,
KDP&�'���.*/01 2� 034(�Fig. 2. Chemical compositions of the phenocrystic
pyroxenes in the selected samples of the tephras.
Enveloped areas in the a) to d) indicate the
concurring phenocrystic compositions in the KK,
HO., HI+, and KDP, respectively (see Fig. 0).
5 -� #$%�������Table -. Modal compositions of the tephra.
K+P� AK-+-&� 6789:;< H,P� AK-
2&�789:=>�;/01� s-sc : 6789:< sc : 789:< pu : >�< s-ash : 6�?@2AB=C< +331/DE(� FGH�IJ�KL34�K+P and H,P indicate the sandy scoria layer of
the AK-+- and mixed pumice/scoria layers of the
AK-2, respectively. s-sc : sandy scoria, sc : scoria,
pu : pumice, s-ash : scoriaceous ash (referred from
Wachi et al., +331). Detailed analytical method
is shown in the text.
MNOP=QRST=KUVW=XYOZ=AB [=\]^_344
��������������� ��� AK-+*
� AK-1� AK-0�� AK-+*������� � ,�������� � � ����� AK-,���������� ������ ������� !���� AK-2 (H,
P)� AK--./� AK--� AK-,� AK-+�"� � !���� #$����%��&�� AK-2� AK--./� AK--
�'�(����������� AK-,��)*+*��AK-+������%� � ��,&�� AK-2��������Wo--1.-3�� En-.+..-�� ������Wo--.2�� En-0-.0.��� � /�&� 01 2
a2� AK--./���������Wo--3..+�� En-.*..0�� ��� �����Wo--.+.-..�� En-/2./.0*��34�01 2 b2� AK--�������Wo--0..*�� En-.,..-���%5�� 678��� Wo
-.-�� En-.0��� Mg��9�:;��� � 012 c2� <��������Wo� -.0..��/�&� En
� 0+.1-���=%5�� 01 2 c2� AK-,��)*+*��Mg�� 12...13.-�3�� AK-+�������Wo--1..../�� En-.,./..2� ��=%5��01 2 d2�
1� ������������>�?��� �@�A�BC�����3�� �D %E!�FG&�HIJ%K"L�M&� #N$OP�� Q%RS�� T�Q%HIJ%� UV*WU&'�>���� X*YUV*)Z[\]^
_Z`a`��>&��b�� Vc+�'�(�� ()&�*+d,e%FG������ fg�hi��>�?�%j4�� Vc+C�%kZ)Z�- (./&� l0m%n(�op%� m0��q����rs1�� t�� K"L%2��#N$OP%uvrs1�� Q%�� wxg��Vc+�:��8��D�:dy �:%E!�FG��� Ti&(� zv{|&�C�8�� }��~3��:%4�T����� �>5�� B�HIJ����3��B��6C��� U�����`� 0�����H��2 � + : +*�������&� �+UkZ]�&���� �����7� RIGAKU-,1*��� X��,87�hs��&�� 9�C��� ��:�;����<��h��bC��rs1&=��%> .� �� rs1&�¡Rq� �5���:��¢� £� ��?¤¥�� ¦§<�@¨���T�A��
1�+ �� ��BC©�Dª�� «W¬\�E 0F®£
1 3� ¯G°±²A�� �)`³+´Dª�!BFeO*�MgO-SiO,1� Hµ�1 .��¶� ��Hµ�I���Dª�
Fig. 3. Whole rock FeO*/MgO vs. SiO, for the
eruptives at the post-caldera stage of the
Akita-Komagatake volcano. Abbreviations
refer to those in Fig. .. Italic characters imply
the eruptives of the northern volcanic edifice.
> .� XRF�,§<�Table .. Accuracy and precision of the XRF analysis.
³ZX�� ·¸ 0+331� MS2� JK 0,**,� MS2�Data are from Togari (+331, MS) and Saito
(,**,, MS).
¯G°±²A�� �)`³+¹L´��º�DA» : A���Dª�¼gVc+M�;� 345
Miyashiro, +31.� ��Gill (+32+) ��� low-K����� �� �� 3� +*�� ��� ��� .������� Medium-K������������ !�� "#$���%���� &'���(�)&'������� *+� ��� +,� ,(�)� -���� -.'��� &/��� (�)-.' 0� 1�2345� �� +* a�� ��������� !���� .���0��6� SiO,�4���&'���7&'�����8� FeO*� TiO,(�)Na,O
�0�9� MgO��:; �� +*� b-d�� <=>�?@0� ����A�BC�(D�EF�GH� ���������I�JK���%��� ��LMKawano et
al., +30+ ; Fujinawa, +322��*+� N�O�� �O����6P+� &/��%��� ,���%0�Q23R�STUQ�VW��XY�Z[\]^_H�>3�-.'��0� 23�`77a;� &'�bc �de /Z[\]^_H 0� Rf�g�; FeO*�MgO��Rhig��j>=+ �� /��
1�, ����������k��l 0�ST�8m��Miyashiro (+31.)
�EF�GH(�)Gill (+32+) ��� low-K�!k"�#5n=� �� 3�� SiO,� /,�$%�1��>�0*����* � SiO,��o&W23pq_r0W;� .'���(�)s'� ,��0� "#$%���� t�� SiO,�� (�) FeO*�MgO�45��*+� Q23R�u'� ��LM Basaltic Volcanism
Study Project, +32+� `� "#$�'�%(vPW;���k�l �w>=�)xig �� +* a-e� 0�����A�BC��Z[yH*z�{�������EF�GH����+�ig%��� ��LM� Kawano
et al., +30+�� +|� SiO,� /3�0*�,-��� 0�./"}� ,���� .' +31*0���~`K,O
�1�� TiO,, FeO*, Na,O�2P; �� +* a-d�� *+��O� 2��,����6P+� s'���%s'�+��%0� Q23`ST�3���
1�- �4�5����O��'6���� Q23��T
���4�7��+j� �8��� ��1� AK-3�AK-0��Z��94:6P� 8-;�Q234<����P+� ��,��n�+�94 .mm�R� ,mm�R .mm$%� +mm�R ,mm$%� +mm$%� .Z����y�8-�'P+� �Z����y%`������=�P� <�'���P+� *+� AK-3� AK-0%` ¡�� �¢£8� %¤ �¥£8� �¦§���
¨£8©I�23���+j�¦�?�ª� �;«=`¬.mm�R�� ¢£8,¥£8���Z����y`3� <�'�4®¯+�°�4� 0�5�� >e%`�¦�? �8¬ .mm
�R�Z����y%� ,±.mm�?²�Z����y
� +*� ���³�´�l �Q SiO,)x��"µ0� 3%@¶�
Fig. +*. Whole rock silica variation diagrams for
the eruptives at the post-caldera stage. Symbols
are same as those in Fig. 3.
ABCD,EF·¸,�G¹©,HICJ,K º,L»¼M346
����� ������� � �� +mm���������������� ������ +�,mm����������� !� ""#�������$%������ &��'( �)*+,-�� ./0�����123-4553�6�7�8.9 (AK-3) :$;<�9 (AK-0) ����� => ++� +,?� �� @ABC �DE FG���HI� *+,-$%JKL� SiO,� �M�123-4553�6$% CaO, Na,O, K,O���N� OP� #��QRS�� QT��U��� ��V��QRWX�� ""*+,-��$%������ => ++�+,? ��Y��QRS��$%Y���Z[�*+,-\ABQRW(]^EP���_` =� 0?�aX(]� bcUd�P���e� f���g9���� �h +mm����V�:Ni� �j�Bk��l N�AB\*+,-N^E�J�� �m�V�Q��no�KL�&��'( � &�no� +�, mm������Jpq�r]E � �� ,mmaX��V��NEsXt�no��uv � $wi� �xy�� h , mmaX��V��Ni�z{��U|�P� AK--�AK-+�`Ni�} ,\} -� ,��� ~E
a��} +��(]�{��z���P� �:� ���.��/� AK-/:$; AK-.�`Ni�� �z��'�N�AK-+,� AK-++:$; AK-2�� N^EJ*+,-�
1�aX��r *+,-\ABQRS���� AK-3�0�Xt� %QRS�� *+,-\AB~E�E���� AK-1����(]���P*+,-� AB~E�E���� AK-+-� AK-+*� AK--./� AK--�+�*+,-�1�S����)�!��P�./0��"#� $�f��J23-45�%9����� ���-��,9� AK--./��l � f���g9���:� ��%���� a��$��O�r]E �
+) ��$%� AK-+-(] AK-+*O� SiO,�� /,�/-�&'�<�9� SiO,� /0�&'�<�9�8.9����$�� => ++� +,?� <�9�(�� SiO,���� ./0��$%�N FeO*�MgO���� =>++?�
,) AK-3� 2�KL��N FeO*�MgO����� �)������ �i¡��P*¢���� AK-3�SiO,� /,�/-�&'�<�9� � AK-2�� SiO,J
� /� +£¤�¥�7�:� ¦§¤,9-��¨©ª«¬5�g9����� � .®���X� X���¯�°��
Table /. Relationship between flow sequence and whole-rock compositional variation among the Onamedake
lava flow at the rim of the Katakuradake crater. Arrows show the ascending order of stratigraphy.
� 0� AK-3� AK-0f���/�HI� *+,-\AB:$;QRS�g9��±��� QRS��'�$% .��� �²��z�P�
Table 0. Whole sample major element chemical compositions of the scoria, pumice and mixtures in the AK-3and AK-0. As for the mixtures, four fractions sifted in size were separately analyzed.
³0´µ¤�.� ¶��·�¸1¹�:� $�º : �./0�$���»�f����¼� 347
/3����� ������� ������������������� � ++!"
-) AK-1� 0#$�%&� ' FeO*�MgO����()�*+ � ++!" AK-1#$� ,-�./012�3 SiO,
� /.�45�6��789�� :-�;/<�=>$SiO,�� /*��6��()���" AK-0$� ./012��?�()#$ SiO, � /,�� @AB#$ SiO, �/*�45�6��()#� AK-1�;/=>��C�()���" ./012�$���� � ��' FeO*�MgO��� D�()$9EF) ��' FeO*�MgO��GH�� � ��I ,JKL�MN%O�+"
.) AK--./$��%�PQmedium-K�RST�SR289�()��� � +, a!"
/) AK-- UV AK-+W#$� XYZ�9EF)3[)�+� \]^ low-K��������()��+ � ++!" AK--$ SiO, 3 /1�45�6��789�� AK-,$ SiO,_/+�45�6��� W AK-+$��`� a� SiO,_/.�45�6��789�()#b+"
2� � �2�+ ������� ������� c�def +(Yg� hi�jkl� him�n*Vlfo�()�pC�� JKq�� �(rs3tuVZ+" ��I ,JKL��GH�� � jkl� vwxyz�>�vwI +�� #b+ � /�1!" {ZV�(rs$� |Xf�}~�-�� �-����+" ��I ,JKL� �GH�� ��f� �}~3��I ,��J~�f���Z� �GwJKLjkl��I +JKL����+" %�� vwxyz�>�vwI +�� ����}�$��fvw#b+" W�vwxyz�>��73vw9E���f�VZ*X�$� {Z3���}���� vw,�f�A�+u����Z+" gW�� �`��� vw����}���� �-3%O�+���3�X" ���� :� ,
(��}$DZ�Z� �%�J#���� �*+�������f���+�}���# +"
2�, ��� ��������9EF)����()¡n�¢£f¤�¥� 012��=>@A�f¦�� ��*o�()���;/0
++" §RS¨���}���o� FeO*�MgO-SiO, " ©?$ª�*9EF)�()«©���" ¬$�%��� �AK-3, AK-0! ��012��=>�@rB�@r���"
Fig. ++. Whole sample FeO*/MgO vs. SiO, for the tephra erupted at the post-caldera stage. Enveloped areas
indicate the compositional variation ranges for the representative eruptives composing volcanic edifices.
Dashed lines indicate the mixing lines between the coexisting scoria, pumice and mixtures within a single
tephra layers AK-3 and AK-0, respectively.
®¯�°���±²��³´µ�¶·�¸� ¹ º�!»¼"348
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¬ +,� P�Bvp��3��p�� SiO,�M¬� µ2� H¶� I·�¬ ++����
Fig. +,. Whole sample silica variation diagrams for
the tephra erupted at the post-caldera stage.
Envelops, dashed lines and abbreviations are
same as those in Fig. ++.
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-./)���� .��� (HO.)�P������� ,62�TU7�V � .�0� HO.0#��� <A7�AK-.¡¢� £V¤�A�y�¥¦§%&��2*�89A]� � D&.�0� AK-.�&¨<AHO.7� hP(���y�:%&'���� *�!7�A]� �� � A�©� HO.7 AK-.&¨Q�� <� *�!89A�<�D� 9§1=ª�«����7:1=�� R¬0�0C�� � ���� AK-/� .&¨Q� HO
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Fig. +-. Modal compositions for the pairs of
eruptives and bulk chemically resembled tephra
layers. Abbreviations refer to those in Fig. /.
� +.� �[���\�� �[�����345AK-2�XYZPP� >³0� /��´�
Fig. +.. Modal compositions of the Katakuradake
pyroclastic cone, Katakuradake-kita lava flow
and the tephra AK-2. Abbreviations refer to
those in Fig. /.
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Fig. +/. Subdivision of formative history in the post-caldera stage. Numbers at the top show the assumed order
of formation. Abbreviations are same as those in Fig. ., and AK-+ to AK-+- are the names of tephra layers
defined by Wachi et al. (+331).
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Basaltic Volcanism Study Project (+32+) Island arc basalts.
In Basaltic volcanism on the terrestrial planets, +3-�,+-.
2q34 (+330) Mo��)��`CLDEFP���RG� ���HI}�/&���R& +/*.
2q34�JK-���L�M (+32-) MoLD& NO�L��PQR$� +. C�S� �Mo�L�ST+1��UP�VWT� +. C�S (1� +��� Mo�XYT�bcZ�& no +, ,3�-..
Fujinawa, A. (+322) Tholeiitic and calc-alkaline magma
series at Adatara volcano, northeast Japan : +. Geochem-
ical constraints on their origin. Lithos, ,,, +-/�+/2.
:[�\�]^_`�a)�� (,**+) Kb_c�L�K-Ar�S : Kb_c�L(� ���d� �L& .0&3/�+*0.
:e�l�U]f4 (+331)Ng`��� � �L& .,&+3/�,+,.
Gill, J. B. (+32+) Orogenic andesites and plate tectonics.
Springer, Berlin, -3* pp.
qK� (+312)�)��`�L�ST� +. C�S� ¡¢g& -,& ,,+�,,-.
Inoue, K. (+32*) Stratigraphy, distribution, mineralogy
and geochemistry of late Quaternary tephras erupted
from tne Akita-Komagatake volcano, notheastern Japan.
Soil Sci. Plant. Nutr., ,0, .,�0+.
£ h (+310) MoLCD��L¤G� /& (g¥i�}& no ++, +-*�+-+.
Itaya, T., Nagao, K., Nishido, H. and Ogata, K. (+32.)
K-Ar age determination of late Pleistocene volcanic
rocks. J. Geol. Soc. Japan, 3*, 233�3*3.
Kawano, Y., Yagi, K. and Aoki, K-I. (+30+) Petrography
and petrochemistry of the volcanic rocks of Quaternary
volcanoes of northeastern Japan. Sci. Rep. Tohoku Univ.,
Ser. III, 1, +�.0.
Miyashiro, A. (+31.) Volcanic rock series in island arcs
and continental margins. Am. J. Sci., ,1., -,+�-//.
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Fig. +0. Eruption history in the post-caldera stage.
Abbreviations are same as those in Fig. .. AK-+to AK-+- excluding AK--./ were quoted from
Wachi et al. (+331). The AK--./ was tentatively
named in this study (see text).
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