ῒΐ  .3  (,**.)
 /  ,.3ῌ,00 ῕ ῔

,**-  3  3  ,**.  2  ,0 Magmatic Di#erentiation Process Inferred from Plagioclase Zoning and Its Pattern
Akira TSUNE῍ and Atsushi TORAMARU῍
Relationships between whole rock composition of magma and plagioclase zoning were investigated on
volcanic rocks from the Shirahama Group, Izu Peninsula, Japan, which have the various chemical compositionsof tholeiitic series produced only by crystallization di#erentiation. The plagioclase zoning can be divided into thefollowing three zoned regions, (+) oscillatory-zoned, (,) patchy-zoned, and (-) unzoned regions, based onAnderson(+32.)’s classiﬁcation. We described the ﬂatness of zones and the spatial distribution of zoned regions
from core to rim of the phenocrysts, and found the relations between the characteristics of plagioclase zoning andthe whole rock compositions. As the whole rock SiO, increases, (+) the number of resorption zones, deﬁned aszones with resorbed track, increases ; (,) the frequency of plagioclase with patchy-zoned region decreases ; (-) the
frequency of plagioclase with the patchy-zoned region in central parts of crystals increases ; (.) the diversity in thezoning pattern becomes smaller. In basalts, various zoning patterns can be observed whereas in dacite, oscillatory
zoned regions are dominant.
Our observation can be explained by a simple model involving the homogenization processes of heterogeneity
in a magma chamber, associating with the crystal growth or dissolution processes. According to the model andthe observations of natural plagioclase zoning, we can give a constraint on the characteristics of homogenization
process developed in an evolving magma chamber : parameters of the characteristics f, the volume ratio ofrelatively di#erentiated part in the magma to homogenize and g, chemical contrast of the magma. At the initialstage (basalt magma), the homogenization process with large f and large g is dominant. At the later stage (dacite
magma), the homogenization process with large f or small g is dominant.
Key words : plagioclase zoning, heterogeneous magma, homogenization process, the Shirahama group+ῌ ῐ ῎ ῑ ῏

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Wiebe, +302 ; Anderson, +32. ; Stamatelopoulou-Seymour~$mn"v-.M89.:)

et al., +33* ; Pearce and Kolisnik, +33* ; Singer et al., +33/

(Kawamoto, +33, ; Murphy et al., ,***). <=>\]V; OP QR ,+33/ ; Hattori and Sato, +330 ; Umino and

WXA (Shore and Fowler, +330)    EHorio, +332 ; Kuritani, +332 ; Murphy et al., ,*** ; Stewart

F5BC)  (Singer et al., +33/) [ and Fowler, ,**+;!$<=>ῌ/ (L’Heureux, +33-) 3,*ῌ++3, >
##T# ¡
Graduate School of Natural Sciences, Kanazawa University, Kakuma-machi, Kanazawa 3,*ῌ++3,, Japan.
¢ : 2+,ῌ2/2+ £¤£¤¥¦§¨ 0ῌ+*ῌ+©ª###«¬­®¯#°±

Present address : Department of Earth and Planetary
Sciences, Graduate School of Sciences, Kyushu
University, 0ῌ+*ῌ+, Hakozaki, Higashi-ku, Fukuokashi 2+,ῌ2/2+, Japan.
Corresponding author : Akira Tsunee-mail : tsune@geo.kyushu-u.ac.jp

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250

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or irregular zoned region), -  
region).

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BbB¨©ª F s ! (Fig. , d). ®5¨©ª A«ME!K ¨©ª o)6¯@4! ,Fig. +. Schematic illustration showing zoning pattern of u-o-p-o and typical zones (ﬂat, wavy,
and resorption zones) of plagioclase.

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252

ῐ῎ ΐῌῑ῍ῒ῏Fig. ,. Photographs of plagioclase phenocrysts in the Shirahama group volcanic rocks. Photoes (a)-(e) are
NDIC images, and (f), closs-polarized light image. (a) Zoning pattern of u-o-p-o (basalt -+.). (b) Patchy
zoned region in , mm long phenocryst with zoning pattern of u-p-o (basalt -+.). The patchy zoned region
can be recognized at the left crystal face, but not recognized at the right (arrow). (c) Flat zones in /** mmlong phenocryst with zoning pattern of u-o (basalt -+.). (d) Resorption zones deﬁned as eroded-like tracks at
crystal corner (dacite -*+). The phenocryst is /** mm long, with o zoning pattern. (e) Honeycomb structure(andesite -+,ῌ-). The phenocryst is +./ mm long, with zoning pattern of p-o. (f) Dusty zoning (andesite-,0).

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254



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Histograms of An content (mol.ῌ) of plagioclase phenocryst cores in the samples.

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255

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XY -*/B  Z:IO[\]%C8 ;9: <2=> 

3^ *./.*.2 mm5 A[\]_`8 3^ *.-.

45

?*@A?@B%CDE8F#" *@ +*.-**./ mm5 ab:  %C8RSmm 2 , mm GH4IJ KL(D9MF)

cd 3e o5 Bf 9: <ghi4%C

N:IO($%B / PQ2I ?@ 2*.+**
Table +.

Table ,.

"jA

klmnopF#(q(qrs`V 9

Whole-rock major element analyses and modal composition.

Modal composition and area of plagioclase phenocrysts of the samples obtained by image processing.

¢£ ¤¥¦§¨©

256

+* mm , +**

   !"# $%&
 ,* mm '()*+. + ,./012  u-o, p-o 3456 78
<=+-

9:;

mm P 012E?

QRST 7D"JK#!" (p-o) # Kn#/012 (o, u-o) !"(Table -). F

+>?@ABCD" E?$%

$  /Y 7D"JK#g +*+

- mm 

,* 

+F

 GD"   !"# )*



)*

-

-*

++
.  SiO, wt.ῌ 

HIJK#!"
LM -+,῍- 012E? N1O *.+ - mmP+* mm   +/* " |}  

 SiO, wt.ῌ K012ST<=K

QRST 78UV( (Fig. , e), W +** mm XY#e : N+P 012E?F

9ZY[\]^G_#`a8Ub" 9:;)*W Wrcc?d%efaD"JK#gb (p-o) # h SiO, wt.ῌ #bn 012E?Hh")*W#gb

ij%HhUb" (o-p-o, p-o-p-o) JK!" h(Fig. . a). N,P  SiO, wt.ῌ #bn[\]^G_Y c?kKglm#!( [\; +012E?t#/b (Fig. . b).

]^G_no8#pc.Ub"qoer"stuh

c?vwxUyz8Ub"st#!x $%F

tK e/&x (Fig. . c). N-P  (/* ,** mm) 

SiO, wt.ῌ #bn 012ST3456+ / mm 

+ SiO, wt.ῌ Ku9:

+012E?

F{x# ,* +/* !" )* glm8/" (Table -). N.P  SiO, wt.ῌ 

/b# h - "JK#!x bqxU 012E?Hh"9:;-῍- 

012

1O *.+

<=#¡/xUb"
, mm, |} *.+*.- mm ~,YbY + /  N1O +Table -.

Variety of zoning patterns in basalt (-+.), andesite (-*/A) and dacite (-*+).

F& :;!"/ /ῌ+ 

257

Kh!"#i98'<.'/ WX YZ[Z\ ^'jk!"2 , 3lm>9<.'/ + 3

SiO, wt.ῌ 

 FRSOTUV; UV:mn 9: (Fig. /)   !"#$;&'!" oT + 3:;> Fpqrs%&'()* +,#-.'/ 012 , 34:; tu\vwMx (self-mixing) &'!"y'/56789  :;!"#<=>

@b!"mz{z.|  vwSiO, wt.ῌ #?&'@}~ L NF RSO8rJ

#AB'/

C01 J !" D a>9 vw



45 C+D  EFGHIJK;L'!"

Mxn 9rJF Cw:rD %&'!"MN#OPQ RSOTUV:;BWX Y

C01 J!" D '/Z[Z\]^    WX  _`  YZ[Z\ vwh' .| bounda-

abcb :;*> dFe 'fgry layer N (Tait, +322 ; Kuritani, +332), Mx C +320 ; +321D q (Jaupart and Tait, +33/)

Fig. .. (a) Relation between the whole-rock SiO,
contents (wt.ῌ) and the number of resorption
zones in oscillatory zoned regions of plagioclase
phenocrysts. Representative number means the
maximum number for phenocrysts. (b) Frequencyof zoning pattern of o (open square) and thosewith p (solid square) in each sample plottedagainst the SiO, contents. (c) Frequency of zoning pattern with u for plagioclase phenocrysts ineach sample plotted against the whole-rock SiO,
contents.

Fig. /. Schematic illustration showing the characteristics of plagioclase zoning in basalt, andesite
and dacite.

fº g»h¼

258

    # $   % % Z[:y<= f zQ67!"

  Tsuchiyama (+32/)  simple dissolution &'(

$ 3F@ o % %,5# %:y<= f)*+ ,-. /012#
3 4& 567  (Couch etEx%

7$ 323 k,l  W; Table . )R$

al., ,**+). 8)*  9:;3 , K23pqz 4? SiO, wt.ῌ c,-

<=>?@ABCBD)E. F89;L!";  X.

GHIF*(@@JE%  + K

# '$ j Z[YZ ] 89:r

LM'#

6NF%O8(McBirney et al., +32/). PQER !STU

VBDW"XY?#% 9$.&%;<Z

u % S-*&% )* k 

Wl E [f %,y<=Ex% )R u %89:r o[.\]E.^&%DU_` 'a(E8T(Tamura, +33. ; +33/) F@ 

/ῌ,)*)b#$ )R . * +c,- An .

de# (Fig. -), c,-/[CBfg F (Table ,) 5Z[0\ 1RF;hi$ j F23 k+l % )*-*&% mnE8* Z[.
\ )*4mn5g o6IF 723pq $R67

\$% E8

  +6NE%¡<$




% Z[ (a)ῌuDnE¢£U¤ %*]g
W A k-* TA, Z[&% CSA, Z[U¤8
uD&% CLAl ;$ A^.W

B k-* TB k¥TAl uD&% CLB k¥CLAll &'# W M k-* TM, uD&% CLMl gR¦E
 Z[ a §*uDZ[%,:y<=;23 k,l 89:rs# ; o, p t%Z[uDv w 89x%y<=s# k%,yc,- , %WE6N (Fig. 0 a). FM' Z[(
uD&%;

Ca _*E`z¨767<= :y<=l E%  y<=7z

$ W B 67$ o> Z[%,y<= 7zR W B %0¬­®3&% -*;5 Z

%,{?

[¯ x%

|.67Z[©a# M';¡ªb O«
M';67$ K)* +E(Mullins and Sekerka, +30.). Lofgren % H}~#%)= k+l . A kZ[ a uDl°.

,%,y<= k@ *l ;5K+j  B kuD]l M' k±case+² ³´l KuDABC;Z[B[Z[%,;

G#  (Lofgren, +31. ; +32*). )R Tsuchiyama (+32/)

6N;µ k,l . A kuDl°.
B kZ[ b uDl M' k±case,² ³´l K% :y<=7z~+EABC; 89% ¶·$ j +6NE% c¸¹ k^

 kD9l x%;G# $ F F%

du2/Je X.Fl ;67$

:y<=(%,y<=7z+E p

x%

F;EF$ p G  HIgRx;J# F (Anderson, +32.) 5 Z[%,^F
6N;EF$ F67F 89xK;L .^&%!;L ;'M%7  uDABCBNy<=7z !" 867F$ 3;)
 uDABC;*89:rxKs#%
OP8 5 v  89:r%%,5#%:y<= 7z+EQ 7$ oRoD?;5 ABC;<xK;LE8F;67 p S o %:y<=(%,y<=Sf Ex%RT

$ o ;%U%Z[%,y<= fzQ67 $ )R o ;%V

Table .. Relation between the driving forces and theformed zoned regions.

v¨©*¼,>+F§



259



Fig. 0 a  C+:C, C-:C. + ;,<# >? )

  

TM '( A @AB'CD23456 CLA!"# $% &'()*+,

'E CLA* # $ /0FG.?HI

 -. /0 a 123456* CLM $C' 234569+=J!" K*L

 75689+ ; Fig. 0 a  C-:C/ + ;,< $# !M! /0KNO 7()PQ<

=/0 a 234)* TM  789+ ;23456+ RS?TUV,# W$' XQ' K 7Y< Z (*

B[\23456*9+!?% ]^!_ `T# $]^' /0 a 123456 CLA  CLB abc CLM  7Fig. 0 a 
C--C0 def C/ [<# /g!" ( M @A

/0 (C,)h234 (C/)  W.i.j (!"kldmld'n>.?3opaq#$$ /0 a rA( /0K! s 234rA(234Ft

HIC /0+,$ u!"# W!"(M @" /0 a *FK569+/06vwxy$

u,# z! /0 a 1234{|FG. HI(C.)}?T ~ /0 a *Kwx b/0 a 1234*/06vwxb.*C#$$' ( M @A/0h234W.i./0
6vhKwx XQS^, (Fig. 0 a).
/0Kwx 7< ; ) TM 'B'CD/056 CSA*  /056 CSA DCSCSA*CSA

7+<

2346vwx 7F< : 5689+23456 CLM  ) TM 'B'CD23
456 CLA* 
DCLCLMCLA*

7,<l8HM- _, DCL  CLA  CLBSab8$ CLM *?
* DCS  CLM * CLB E#/ῌ- 



,'D?S v>8BHI ,¡  W!"
¢wx DCS £ DCL G¤,# ¥ DCS £ DCL G¦F§ ¤yFig. 0. The binary system of An-Ab and therepresentative composition of crystal andsurrounding melt. The ﬁgures show sequenceof events that the magmas of the local systems
A and B produce the system M by mixing. (a)case +. (b) case ,.

" _,#
9¨©¦F§ ª«¬A­®2o¯ 7XQ°¦F§­®2o¯± ²³< !" + A´µ f 56¶·4®¸4¹ g\º»¬"^,# =^!?( A ( B ´¶· ¸}¹º»¼260 VA, VB  f

-f.fgv+ .CLA/.+vf/g v+ .CLB//vf.g v+ .CLA// (VAVB)  A  VA    g.++/  A  B 

!" #  $% 

DCL-CLM-CLA*f !"-xfCLA.+vf/CLByvg.TM/&' () *+ g ,
f--fCLA.+vf/CLBvg.fTA.+vf/TB/

VA
VAVB

-fCLA.+vf/CLBvg.fgv+.CLA/.+vf/gv+.CLB//

.-/

.+,/

de
g-

CLB
CLA

../

z4mQ f, g

0 1234567 DCL ,
9: ;< VA =VB >4?@A  DCS , 

f 8 *./

BCDf 8EFG> ;< VA 8EFG>4@>70BCDHI DCS, DCL!" CLM

JK {|}~ (+31,) 4S#  Q 4Rc

JKK4, L+ TM M

NOPQ CLA, TA, CLB, TB, f 4RS#%

T8U #FD4 L+ TM VW0XY!

+vem
CSA*-f.TM/- n m
e ve

.+-/

+vem
CLA*-g.TM/-en n m
e ve

.+./

0 " CSA*  !" CLA* AZNOPQ4RS

DSAb.TvTmeltingAb/
RT

.+//

DSAn.TvTmeltingAn/
RT

.+0/

m-m.T/-#% T8U [!"\]^M _!"\]^

n-n.T/-`a  )b(')4Rc !" CLM L+
TM ,

U R ,Q DSAb, DSAn ,' 

TM-fTA.+f/TB.//

CLM-fCLA.+f/CLB.0/

P TmeltingAb, TmeltingAn , Ab  An prq
)L+U lDA,{|}~ (+31,) 4G
DSAb-+*.+*
v+

v+(cal}Kv+}molv+), DSAn-+/.+*

K }mol ), T

de

(cal}

-+2,- (K) -+-3+ (K), T

meltingAbmeltingAn_fg4VW4U, L+ TM 4hG#VW

 mQ f, g 4, lMUXY  !" CSA* CLA* ,ij4k' P!"\]^ `aiA  ll TM  CSA* CLA* mnCl07456G#G8 3 K

CSA*-f.TM/.1/

CLA*-g.TM/.2/

% l4  lD$,L+ TM  L+ TM opq)!" prq)!"mn s  lD$4hG# L+!",itimn4U umQ fv+, gv+ Z>
.3/

TM-gv+.CLA*/.+*/

de lD$ G DCS, DCL ,

DCS-CSA*vCSA-f.fTA.+vf/TB/vf.TA/

DCL  f mn $ .++/ .+,/ 4RS#% l8 Fig. 1 a 4$ .++/ .+,/ JK f  DCS, DCL 

mn s#G CLA-*., CLB-*.2  s#hc l>*+ g-. U DCL , f 8A?@A c DCS , f 8@>70lDmn,13¡ U

TM-fv+.CSA*/

PQ f CLA, CLB d>%w

4,0G .{|}~ +31,/ Rc DCS,

z4$
mn
M 

B¥

G#¢

£ p, o "¤ f, g

 Fig. 1 a Rc DCS¦DCL Ul8"HI DCL

8HI DCS§l©D§RcZ¨4XY¢ £ p ª"4

, DCL RcZ DCS 8«0 ¬ Z­BCD®, DCS, DCL, ¯< DCS 8 ¢ £° k
K±²g0³#3 K
p 8ª" K4T0HI DCS´µ »¼ghMpqp@ S(O DCS 261

  

e f gh[\ p  DCc   %]O^_`"abi*@jDCc

 !"# simple dissolution $% partial dissolution

U3  p  DCS 

(Tsuchiyama, +32/) &'( ) DC *+,W QC Q U3kl ]O^_`"a3klm/

 -./ DCc 012345*637

/1DE f Tn oS(pqp A 1DrA

 7  p 89 DCS:DCc / 2T ns $tHI g   oS(pqp A u;</ o 89 DCS =DCc >?

S(pqp B vE s KL % W @7  DCc 5ABC)1DE fF;<  o  DCS T 3klm/ W Q

fc G@CQ U3kl 1DE f   oS(pqp(Fig. 1 a), f=fc / p  f:fc / o 1DrA2 s HI g T  ovo  p 89 HI g 5J3 C CLA F*./ CLB F*.1 KL*Fig. 1 b M 7

gF+.. /NO gF. KLET s KL % W/ῌ.  A  B b  

EPQ5RST  Fig. 1 b M U g S(pqp A o`wxsyuS(pqp B o b `

T   %V f / DCS=DCc 3 p

wxs KL ocase,s tz case+ {  W3KL 7W

 g 5O| A uS(3| B }LC | M 3~/

I 7 p 89/7 b  b 

X$ YZ

z (Fig. 0 b).

  [\ DCS * ]O^_`"a f, g bc?7d 

case+ {`wxQWW[\*  b /|I'(

`wxv CLM 37

ov2( ; Fig. 0 b  C-C/ '(*sN b, `wxI TM 3 o2( ;Fig. 0 b  C+C, C-C. '(*s @/| B ?/P

I TM`wxv CLB /3n CLB* ocase+  CLA* {/s 3 7   b  `wx

W~

/ case+ J3  2( o`wxv(NCs 7 2( os [\ DCLῌ  `wxv
CLB  I TM //P `wxv CLB* 
DCLῌFCLBCLB*/ 3  b 1

o+1s

W

'(C3

 )/@2(7  o| IZs `wxv'(*U ¡3 Q7/ case+ KL{  |¢£`wxv(C¤¥C ¦§¨*©ª t@ `wxv(«X@/¬n7%3KL*­¥Cz*®¯ U 7¤¥ /  b `wxv CLB $% CLA  CLB °±5 CLM
oFig. 0 b  C--C0 ²Z³ C/s 3  `wx Ca ´

IT n3 Qµ [\ DCLῌ T n
Fig. 1. ºC as a function of f. (a) CLAF*.,, CLB
F*.2. (b) CLAF*./, CLBF*.1.

3  DCL ocase+  DCL { : Fig. 0 bs 3 r¶
·¸¹2~$%z DCLῌ  CLB*  CLA ¶· ¸¹º»¼

262
(Fig. 0 b).  

DCL DCL῍ 

hih A 9D

hih B  7F T

  b   

U 1<) ^n case+ 9op6) 5

 !"#$ %& DCL῍ '() *+, case,5 7q5, _`7STU-./0 p 123 45, DCL 6
 DCL῍ 789:; <)
DCL῍ => f, CLA, CLB ?(9@!A 6)9b^97a )

BCLBCgDfgC+DCLAFED+CfFgC+DCLBFF

D+2F

IJKLMNO f, g

R() Fig. 2 a

f 7S D

hih A _`7j4Y SF TU I t

BCLBCgDfTAED+CfFTBF

9PQ= Fig. 2 acase+ 9 case, @!AIJKLMNO _`DCL῍BCLBCCLB*DCL῍ 9 case+ GH5

p 71< 9Ar case+ 9 case, \s) CLAB*./ CLBB

ih A u a 7v5Jw<hb xy/  0 p D ; z { | / }   ~   ; Tsuchiyama,+32/F 71<7 

hih B 

"J<  b  61 =5  o*.1  Dg 7SF TU9 CLAB*., CLBB*.2  Dg 7

71<)F TU=R5,) f 769 DCL῍ VW_`7j4Y F TU (9APQ $GXY6Z 9[Y)

7v5J< b 1}  b 

case+ 9\ xy/0 p D;zL /}

 DCL῍ 7] DDCc῍ ; ^9_` fBfc῍F !"#TU

p 7a 9:;9 p_`

f 7 D

 ; Lofgren, +32* ; Anderson, +32.F 17^

71( b23cd!A 6) /0 p

7

 DCL῍ 6efd1< g!A6efb  o 71<)IJKLMNO_`f 7 D

ih A _`7j4Y F

klm g 7hih A 

hih B hih A u a h"Jw<6 IJKLMNO lm g 7 D

hih 7F TU x

hih9y/0 p 71<7 o g 7 S D
hih7\sF TU

hih9xy/0 p 1<  /0 o 7
1<) ^^9;9 lm g 7TU

hih A  a /=15 !"{|hih b v5J< =1(7 lm g 7STU 
ih A  a =15 

h

hih

 b 61 =1( 9;) Fig. 2 b
 g 9 DC PQ=R5,7 ^ Dp =1

( b 6F  DC = 
case+ case,

P 

_`

f  P) g ]7^97^97 )c^9=UY :;9 xy/0 p 
1 lm g 789;) o
_`f 9 p PQ=Z( g TU,57 '9  %& !+, p 71
<  9A^97<z case+ case, < 7G g< !+,_`fk,=;^97 ¡)¢£¤ </09c:¥9¦PQk,§< o  ¢£¨'© p  p-o95,ª«5 ¬  o 7) ^^9
Fig. 2. (a) µCL῍ as a function of f.
function of g.

(b) µC as a

IJK tA%&7 ­®S¯ 9°±5 ^9=R²() ³´ SiO, wt.ῌ VW t¨'ST=> ()WXWYZ[\]cd

(Fig. . a), p   (Fig. . b)

 p 

KLMN(OPQR SiO, wt.ῌ ST=>A! 

B$% ! UV9D&WXWYZ[\]^_&"#$$%&'()* +,-. /0&! p

263

+,-.

12/0&3456 7587! `Dabcde]O;+fgh (Fig. 3).
i SiO, wt.ῌ Rjklm  p ST n/ ! \]op qrsRt WXWYZ

 +,-.1&9:;<5=>3?@[&u/;! vw g 12/abcd x[DAB C! /DEF76G (Table .) HIJ

(y)* ZP! rsRNz75 
{|}~=>AB)87! case, a

;/*
/῍/

 SiO, wt.ῌ 
 bcd O;/6 75 qFig. 3 t* case,N ! 

f

12/ p

345

Fig. 3. Schematic illustration showing summarized relationships between the whole rock composition and thecharacteristics of the homogenization process in a magma chamber. See text for details.

º 9»¼

264



/ῌ0 ῑῐ῍῎ῒ  

*2YZ[\!]) K$%  g  !"#$

 Ok3Q]^_` a"j %()J{)K$%$MYZ+ An-Ab, v

*+,-.# case+ !]% Diopside b+"%1+!c,- !"#$

&#$ 'Fig. 3 / case+  f

OF Ok3 % T.$M01) p )2$3 4- .#2K!]%z YZ DC +d\ Ae35 678.# e

9:3;<=>?@) A

b- 6f`J{)4/Ob31Wgp 23X

!% BCD?E g

rh5i3.F% a"j 753F%-  , case G3 H"#8iK$%) An 6_%z #g!"#$ IJ8K$%)&'32( p &# g1+[6 _ An K$%) p +2

$- .# (Fig. /), case+case, LM#)N6

,tMYZ DCS +j-

:;3HO5P-F% !"#$ Fig. 3 * +F I"# % An 6OFK$%$kGJ8&#$K$%3-*), .# QR!S+-.6$3

,.6$3J) lmno#$%K$%T.r
T.U< &#$(Kirkpatrick et al., +313)  p 23X (V/!) (2  T.0%312

W3X/.$%- +Y, +Fp%  -$#T. + r + r)T.*R@+
qF#o r*BE?Z+O¡3*B

H"# . =¢£¤¥x¦@3!].#

E?Z&'#) &'#- 4[lmno#$%T.&5)T.*R@s§, +F \]T^.# _ SiO, wt.ῌ ` 5ot$H"#_ a"j Cashman and Marsh,

SiO, wt.ῌ BCD?Eab67c

+322

)d

89:;

" lmT.rp`%T.

¨u6%rT.

<=46 ef@)>?:;

   <=$%g1p%+e!] hi*>?,$j-%6

Oi/@A3<¨uv§© 

w?0 -- .# JOb xª
*BE?Z) «$¬$8%­y+z!"{  K$%

+Oh5e®,=%1)  g 0P--¬$BC$ kl)o#$%3L+!c,- f`) p 3 -- ) Dm)5 !" E1 kl 78i

i

*

 K$%T.* «$(|z} lmK$%T.
Ander-

son, +32. ; ~¯ +33/ ; Umino and Horio, +332

<,(}L$5#°±g1)FnP-#o pq +320 G*+H$.+!c,- 6f` a"j Pearce et al.,r !"#$ (Singer et al., +33/). r

+321 % 0T.)

ist) <=4
Iu%v

!"O -Ob3

w D?x+yz- )J{|})3
-$4~K3 %J{) LM
NMD@ O[r)!"3 J{AF%Pg1+-Ob31
Q!],-)H"tb # Anderson(+32.) )78K$%S*  *R@

(+T%@K$%.# T.

*BE?Z+i,- 6f` J{)Y3
Xm#)*BE?Z T.

¨+p`%- BC$Ob 0T.²L*B

E?Z&'#F% . 8 SiO, wt.ῌ 6
053) T.

*BE?Zp3 b¨O6)3- +Xm#)³(op2+  )35UV*0ῌ ῏ WXm# G3 -Ob3)AJ{)~K3

}60-

¨

6r¶

ΐ

T.´?&89:;£Zµ+G·¸£¹

vJ8r<¼^_`_Ca b!
  

 

 



  o,   p,   u  - ! "#$%&'()&*+,-., /01234 56


78 
/B4

 SiO, wt.ῌ )9 :;<&)=: /+4 > SiO, wt.ῌ 

?@A + "#)BC,-DE F* GF)
HI-J /E64 K<I9- /,4  SiO, wt.ῌ?@A   p

LMN<9

/-4 > SiO, wt.ῌ ?@A0123O)P=- QR=0123<H,< STUTVRH, 0123@WA o +
RX



/C4

YZ , [)\9  SiO, wt.ῌ ]^-_`_Ca 
b!cSd e  /+4 fg"#5h$ia%=<Q_`_<STUTV_`_CR"# )G +jk- 9F_`_Ca &'^- /,4  l( /o, p4 m9 "#no)pdV q*+),- ) p q*+<.r9sN) o  q*+<tu9sN)^-
/D4

 SiO, wt.ῌ   _`_Ca v )/Fh$b!YZGF)]  _`_fgh$b!
 , 0 _`_ /12)  _`_12

)3 =_`_4 wNb!+=  fgh$b!  _`_4x5 f  , _`_5 g R \*-yzR 4x

5 f, {|5 g <.r9h$b!<6}^-~z) 4x5 f <.r9& C 5 g <tu
9h$b!<6}^-῏῎JAMSTEC 789:;)? < =A P=R >)=

 EPMA )G-?

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 C  @.D

EF{|)G=<H9 IRX-.Jv;) )^- Hr K<L<.rPu,  MNI )K5
cSd)OP Q R¡¢:;)G K.rPu,  £P¤¥C^

265ῌ ῑ ῐ ῍Anderson, A. T. Jr. (+32-) Oscillatory zoning of plagioclase Nomarski interference contrast microscopy ofetched polished sections. Amer. Mineral., 02, +,/῍+,3.
Anderson, A. T. Jr. (+32.) Probable relations between
plagioclase zoning and magma dynamics, Fuego, Volcano, Guatemala. Amer. Mineral., 03, 00*῍010.
Cashman, K. V. and Marsh, B. D. (+322) Crystal size distribution (CSD) in rocks and the kinetics and dynamics
of crystallization II. Makaopuhi lava lake. Contrib. Mineral. Petrol., 33, .*+῍.*/.
Couch, S., Sparks, R. S. J. and Carroll, M. R. (,**+) Mineral disequilibrium lavas explained by convective selfmixing in open magma chambers. Nature, .++, +*-1῍+*-3.
Hattori, K. and Sato, H. (+330) Magma evolution recordedin plagioclase zoning in +33+ Pinatubo eruption products. Amer. Mineral., 2+, 32,῍33..
ST ¦nJ v (+33/) U§¨©Z_ª«¬_`_a­®¯¨©V°±²W­ ¨© .* -1/῍
-3-.
Jaupart, C. and Tait, S. (+33/) Dynamics of di#erentiationin magma reservoirs. J. Geophys. Res., +**, +10+/῍+10-0.
Kano, K. (+323) Interactions between andesitic magma
and poorly consolidated sediments : Examples in the
Neogene Shirahama Group, south Izu, Japan. J.
Volcanol. Geotherm. Res. -1, /3῍1/.
Kawamoto, T. (+33,) Dusty and honeycomb plagioclase :indicators of processes in the Uchino stratiﬁed magma
chamber, Izu Peninsula, Japan. J. Volcanol. Geotherm.
Res., .3, +3+῍,*2.
Kingery, W. D., Bowen, H. K. and Uhlmann, D. R. (+310)
Introduction to ceramics. John Wiley and Sons.
Kirkpatrick, R. J., Klein, J., Uhlmann, D. R. and Hays, J.
F. (+313) Rate and processes of crystal growth in thesystem anorthite ­ albite. J. Geophys. Res., 2., -01+῍-010.
Kuritani, T. (+332) Boundary layer crystallization in abasaltic magma chamber : Evidence from Rishiri volcano, northern Japan. J. Petrol., -3, +0+3῍+0.*.
t³±´; (+320) µXg_`_¶g_`_wN·­fg=_`_¸­ ¨©Y¹ -* .+῍/..
t³±´; (+321) _`_wN)G-fg_`_
b! º»F 3 ./῍.3.
L’Heureux, I. (+33-) Oscillatory zoning in crystal growth :A constitional undercooling mechanism. Phys. Rev. E,.2, ..0*῍..03.
Lofgren, G. E. (+31.) An experimental study of plagioclase
crystal morphology : Isothermal crystallization. Amer. J.
Sci., ,1., ,.-῍,1-.
Lofgren, G. E. (+32*) Experimental studies on the dynamic
crystallization of silicate melts. In Physics of Magmatic
Processes. (Hargraves, E. B. ed.) Princeton University
Press. .21῍//+.

266

FG H$IJKLMcBirney, A. R., Baker, B. H. and Nilson, R. H. (+32/)
Liquid fractionation. Part I : Basic principles and experimental simulations. J. Volcanol. Geotherm. Res., ,., +ῌ
,..
Mullins, W. W. and Sekerka, R. F. (+30.) Stability of aplanar interface during solidiﬁcation of a dilute binary
alloy. J. Appl., phys., -/, ...ῌ./+.
Murphy, M. D., Sparks, R. S. J., Barclay, J., Carroll, M. R.
and Brewer, T. S. (,***) Remobilization of andesite
magma by intrusion of maﬁc magma at the Soufriere
Hills Volcano, Montserrat, West Indies. J. Petrol., .+,,+ῌ.,.
Adobe PhotoshopTM (+330)   3+ ,-/ῌ,.+.
Pearce, T. H., Gri$n, M. P. and Kolisnik, A. M. (+321)
Magmatic crystal stratigraphy and constraints on magma
chamber dynamics : Lazer interference results on individual phenocrysts. J. Geophys. Res., 3,, +-1./ῌ+-1/,.
Pearce, T. H. and Clark, A. H. (+323) Nomarski interference contrast observations of textual details on volcanic
rocks. Geology, +1, 1/1ῌ1/3.
Pearce, T. H. and Kolisnik, A. M. (+33*) Observations ofplagioclase zoning using interference imaging. Ear. Sci.
Rev., ,3, 3ῌ,0.
Shore, M. and Fowler, A. D. (+330) Oscillatory zoning inminerals : A common phenomenon. The Can. Mineral.,-., ++++ῌ++,0.
Singer, B. S., Dungan, M. A. and Layne G. D. (+33/) Textures and Sr, Ba, Mg, Fe, K, and Ti compositonal proﬁlesin volcanic plagioclase : clues to dynamics of calcalkaline magma chambers. Amer. Mineral., 2*, 110ῌ132.
Stamatelopoulou-Seymour, K., Vlassopoulos, D., Pearce,

T. H. and Rice, C. (+33*) The record of magma chamberprocesses in plagioclase phenocrysts at Thera Volcano,Aegean volcanic arc, Greece. Contrib. Mineral. Petrol.,+*., 1-ῌ2..
Stewart, M. L. and Fowler, A. D. (,**+) The nature andoccurrence of discrete zoning in plagioclase from recently erupted andesitic volcanic rocks, Montserrat. J.
Volcanol. Geotherm, Res., +*0, ,.-ῌ,/-.
Tait, S. R.(+322) Sample from the crystallizing boundary
layer of a zoned magma chamber. Contrib. Mineral.
Petrol., +**, .1*ῌ.2-.
Tamura, Y. (+33.) Genesis of island arc magmas bymantle-derived bimodal magmatism : Evidence from the
Shirahama Group, Japan. J. Petrol., -/, 0+3ῌ0./.
Tamura, Y. (+33/) Liquid lines of descent of island arc
magmas and genesis of rhyolites : Evidence from the
Shirahama Group, Japan. J. Petrol., -0, .+1ῌ.-..
Tsuchiyama, A. (+32/) Dissolution kinetics of plagioclasein the melt of the system diopside-albite-anorthite, andorigin of dusty plagioclase in andesites. Contrib. Mineral.
Petrol., 23, +ῌ+0.
Umino, S. and Horio, A. (+332) Multistage magma mixing
revealed in phenocryst zoning of the Yunokuchi Pumice,
Akagi Volcano, Japan. J. Petrol., -3, +*+ῌ+,..
Vance, J. A. (+30,) Zoning in igneous plagioclase : normal
and oscillatory zoning. Amer. J. Sci., ,0*, 1.0ῌ10*.
Wiebe, R. A. (+302) Plagioclase stratigraphy : A record ofmagmatic conditions and events in a granitic stock.
Amer. J. Sci., ,00, 03*ῌ1*-.
!"#$%&'( (+31,) )*+,-./0123
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