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ONE-ATMOSPHERE MELTING EXPERIMENTS ON BASALTS OF
OGINOSEN VOLCANO: PHASE RELATIONSHIP AND ELEMENTPARTITIONING OF AN ALKLIC BASALT AND THOLEIITIC
BASALTU. Honma

130 E134 E

Oginosen37 E

Oki-Dog
Daisen34 E

Kannabe

Sanbe
Aono
Abu
Himeshima

Philippine
Sea Plate31 E130 E134 E

Depth distribution of Quertanary
volcanoes and upper boundary of
the subducting Philippine Sea
plate (Ishida, 1989; Kimura et al., 2003;
Sakiyama et al., 1995; Fruyama et al.,
1993; Zhao et al., 1992; Tsukui et al.,
1985; Matsui and Inoue. 1971).

Type-1 Type-2
SiO2 48.86 48.84
1.42
TiO2 1.96
Al2O3 16.98 16.85
Fe2O3 10.42 11.95
MnO 0.15 0.17
MgO.21 6.61
CaO
7.89 9.42
Na2O 3.95 3.39
2.10 0.85
K2O
P2O5 0.91 0.36
Total 99.43 99.85

2.5

absarokite

Type-1 basaltTomieda unit
Alkalic basalt,
silicaundersaturated
Type-2 basaltIshiidani-1 unit
Tholeiitic basalt,
silica saturated

High-K suite

K2 O wt%

Starting Materials (1)

2.0
1.5

Mid-K suite

1.00.545

SiO2 wt%
5055

6065

Starting Materials (2)Type-2 basalt
ol : pl : gm = 3.6 : 13.4 : 83.0

Type-1 basalt ol : pl : gm = 0.7 : 3.7 : 95.6

plol

plolplol

1 mm1510Frequency

15100Mg/ (Mg+Fe)Fo) in olivine

540

50556065

100Ca/ (Ca+Na+K)
An#) inplagioclase

105045

40

45

5055

60

65

70

75

80

85

90

75

80

8501510   70



5015

Olivine phenocrystCore   

100Mg/ (Mg+Fe)Fo) in olivine

10   1 mm

5900

Rim
Ground mass

40455055606570

100Ca/ (Ca+Na+K)
An#) inplagioclase

75808590

Plagioclase phenocryst   CoreRim
Ground mass

40455055606570

Histograms of mineral compositions

7580

8590

Experimental Method:
Electronic furnace (SiC heating elements)

Befor Quenchedglass

Wire loop method (Donaldson et al., 1975)
AtmosphereH2-CO2 Mixed gas NNO redox conditions
Temperature calibrationmelting point of Au (1064. 43 )
TPt wiret
1quenchFusion experimentt1t

PressedPowdersample

2quenchGrowth experimenttimehrSample assemblage

H2+CO2Mixed gas

ol olivinepl plagioclase
cpx clinopyroxene

Growth experiment Fusion experiment

Run products (110010 hrol
pl
pl

50 μm

ol

cpx
50 μm

ol
plol

Type-1

50 μm

plType-250 μm

Fusion experiment1240 An64
Pl
1200
Fo781160
1120
Cpx
1080
Solidus1040
110melt
olivineclinopyroxene
plagioclase

Growth experiment

Ol Fo85
1230
An68
1190
1150

Fo80
Ol11101070

1001030

PlAn52

Fo73
Cpx

An480Timeh110100melt pigeonite?
clinopyroxene
olivineplagioclase magnetite

Temperature-Time diagram (Type-1)

Fusion experiment

1240
An73
1200
Fo75
1160
1120
1080

OlAn66
1230
Fo80
1190

Cpx

1150

Growth experiment
PlSolidus

1040
1melt
olivine10
clinopyroxene
plagioclaseTimeh

Fo74

OlCpx
Ol

1110

An62
1070 Fo73
1030
0100

An68

1

10100melt pigeonite?
clinopyroxene
olivineplagioclase magnetite

Temperature-Time diagram (Type-2)

Mineral-melt partition coefficients
Run products

Ol  Liq
Kd Fe2+ Mg

Kd (Takahashi, 1986)

Type-1

Kd (Carmichael and Ghiorso, 1990)

Type-2

Kd (Gee and Sack, 1988)

0.50

Pl  Liq
Kd Ca
 Na

2.00.40
0.30
0.20

1.5
1.0

0.10

0.50.00
1050 1100 1150 1200 1250

0.0Melt An#1050

11001150 1200

Temperature (1250

Origin of high-An plagioclase (An87) in Type-2 basalt
An87

An#

90
80
7060
504040Mg#

2002

FeO wt%

100.8

0.6

0.4

0.2

distancemm0Pl  Liq
Kd Ca Na  Type-1

!10

An87
Type-2

Ca/Na plagioclase155   

2% H2O
4% H2O 

6% H2O

0012

Ca/Na glass

3

Type-1 plagioclasebulk rock composition
Type-2plagioclasebulk rock compositions

SummaryPhase relations and element partition relations were examine
experimentally under NNO redox conditions at 1 atm. for bothalkalic and tholeiitic basalts of Oginosen volcano.
Fusion experiments gave equilibrium liquidus, whereas thegrowth experiments show markedly undercooled conditions withdendritic crystal texturesAn (Ca/Ca+Na ratio) content of plagioclase in Type-1 basalt
corresponds to that of experimental charges, while An content ofplagiolcase in Type-2 basalt is much higher than that ofexperimental plagioclase, suggesting high H2O content of melt
during crystallization of the plagioclase phenocryst.