ῒΐ /* (,**/)
/ ,03ΐ,2- ῕ ῔
῏
,**. 1 2 ,**/ 2 + ῐ
Genetic Relationships of the Compositionally Diverse Magmas
from Aso Post-caldera Volcanism
Masaya MIYOSHI῍, Toshiaki HASENAKA῍῍ and Takashi SANO῍῍῍
Between ,1* and 3*ka, Aso volcano produced four large caldera-forming pyroclastic flows, all of which
probably derived from a single zoned magma chamber, as suggested by previous geological and geochemical
studies. On the other hand, after 3*ka, for the post-caldera activities, it is di$cult to create a wide compositional
range of post-caldera magmas from a single magma chamber model, when the following observations are
considered. (+) Seven distinct magma groups with distinct petrographic and compositional characteristics are
found ; ῌ. ,px-rhyolite, ῍. bt-rhyolite, ῎. hb-dacite, ῏. ,px-dacite, ῐ. aphyric andesite, ῑ. porphyritic andesite, ῒ. basalt-basaltic andesite. (,) Incompatible trace element plots show that the seven magma groups were
formed by at least four end-member magmas that do not show parent-daughter relationships. (-) Vents
extruding basaltic magmas are centered in the caldera, whereas those extruding andesitic, dacitic, and rhyolitic
magmas are distributed around them. These observations indicate that several (at least four) magma chambers
are developed during the post-caldera activities, and that the compositional diversity of the magmas can be
explained by magma mixing among the end-member magmas in addition to fractional crystallization.
Key words : Aso caldera, post-caldera volcanic products, compositional variation of magma, vent distribution
+ῌ ῐ ῎ ῑ ῏
.0)€).'(‚ƒ„.'(#-.%&'(*+
!"#$%&'()*+, !"-
H…†e‡ˆ‰;h& Š
‹Œ +32/B !"
./0123 , 4)5'6789:;<&=>?@
-. (Aso-+ŽAso-.) H, 5R.H‘’:;
AB C4, !"-.)D2E><&FGHIJK<
“”’ •–,“”’:;‘’>A†–—˜™ ?š
5' LMC4, !"-.0)N'OP:;)
›d–=>:; Š
‹Œ (+32-) ,|}<„C)
῍Qῒ)ῒR<S)TUKVW<'(*+1X&B =)
zoned magma chamber œ! #žd–B Ÿ;H Hunter
5'ῌY)Z[,\])^_^`ab)Z[#cdeA
(+332) )Q ¡K¢£, z)œ! )¤¥¦#ῑ‰
&>fg;h& (Hunter and Blake, +33/)B ijkHl
–B
m%&no'(,pqr ,/ km, str +2 km )
!
C§ !"-.0)'(*+1L@ῌ<.)^
"#$%&uvwx) !"'(1Xy z)'(
_^?*+deA&? !"-.)…M<5R
*+L !"-.{)|}'~ῒ5'> !"-
.—˜™ ,¨ΐ1,<AB ©›\ª1«;h&a¬
­20*ῌ2/// ®¯°±² ,ῌ-3ῌ+
®¯¡¡³´µ¶¡¢£¶
Graduate School of Science and Technology Kumamoto
University, Kurokami ,ῌ-3ῌ+, Kumamoto 20*ῌ2///,
Japan.
­20*ῌ2/// ®¯°±² ,ῌ-3ῌ+
Faculty of Science, Kumamoto University, Kurokami
,ῌ-3ῌ+, Kumamoto 20*ῌ2///, Japan.
­.+1ῌ*2*+ ·¸°῔ -,/
·¸G῎¡¹º»¼¡i
College of Environment and Disaster Research, Fuji
Tokoha University, Ohbuchi -,/, Fuji .+1ῌ*2*+, Japan.
Corresponding author : Masaya Miyoshi
e-mail : miyoshim@es.ssi.kumamoto.ac.jp