M. Hamada 1 *, M. Ushioda 1 , T. Fujii 2,3 and E. Takahashi 1
1
Hydrogen concentration in plagioclase as a hygrometer of magmas: Approaches from melt inclusion analyses and hydrous melting experiments M. Hamada 1 *, M. Ushioda 1 , T. Fujii 2,3 and E. Takahashi 1 1 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan 2 Earthquake Research Institute, University of Tokyo, Tokyo, Japan 3 Crisis & Environmental Management Policy Institute, Tokyo, Japan (*E-mail: [email protected]) V11C- 2776 Plagioclase is one of the nominally anhydrous minerals (NAMs) which accommodates hydrogen, and plagioclase in volcanic rocks essentially contains structural OH in it. Hydrogen concentration in NAMs can be a useful proxy for dissolved H 2 O in silicate melts if the partitioning of hydrogen between plagioclase and melts is known. Here, we performed two parts of studies in order to determine hydrogen partitioning between plagioclase and hydrous basaltic melt: (i) analyses of low-H 2 O melt inclusions (H 2 O ≈ 0.3 wt. %) hosted by plagioclase in mid-ocean ridge basalt (MORB) and (ii) hydrogen partitioning experiments between Ca-rich plagioclase (An 95 ) and hydrous arc basaltic melt (0.8 ~ 5.5 wt.% H 2 O) at 0.35 GPa. Obtained formulation is Hydrogen in plagioclase (wt. ppm water) ≈ 94.3×√(H 2 O in melt, wt.%). This empirical formulation can be used as a practical hygrometer of magmas. In this poster, we apply this formulation to understand the 1986- 1987 summit eruption of Izu-Oshima volcano, a frontal-arc volcano in Izu arc, and discuss eruption process of H 2 O-saturated magma. Purpose and quick summary Part 1) Analyses of plagioclase-melt inclusion pairs from MORB Figure is from Nakamura et al. (2007 Marine Geol.) KH93-3 DR9 50 μm 500 μm Whole-rock composition SiO 2 50.5 TiO 2 1.52 Al 2 O 3 15.1 FeO* 11.1 MnO 0.19 MgO 7.44 CaO 11.1 Na 2 O 2.80 K 2 O 0.10 P 2 O 5 0.15 Total 100 (wt.%) Studied sample: Sample# KH93-3 DR9 from Rodriguez Triple Junction in the Indian Ocean Part 2) Hydrous melting experiments to determine H partitioning between plagioclase and melt 1000 1050 1100 1150 1200 1250 1300 0 1 2 3 4 5 6 Experimental procedures volcanic front 35ºN Izu-Oshima volcano 30º N 45ºN 145ºE 140º E 135º E 130º E Miyakejima volcano SiO 2 TiO 2 Al 2 O 3 FeO* MnO MgO CaO Na 2 O K 2 O Tota l 51.2 0.96 17.5 11.2 0.21 4.9 11.5 2.2 0.25 100 (wt. %)) Starting material of melting experiments (MTL rock, collected from Miyakejima volcano in Izu arc) H 2 O in melt (wt.%) Temperature (℃) plagioclas e-in augite-in magnetite- in plagioclas e-in augite -in magnetite -in Partitioning experiment of hydrogen between An 95 plagioclase and melt Au 80 Pd 20 capsule 200 μm Crushing volcanic rock Separation of An 95 plagioclase Hydrous melting of crushed rock 10 mg of hydrous glass 1 mg of An 95 plagioclase Melting at 0.35 GPa for 24-48 hours using internally- heated pressure vessel Backscattered electron image of the recovered sample (1130℃, 2.6 wt.% in melt) Obtained phase diagram of MTL rock at 0.35 GPa An 95 plagioclase f O 2 ~NNO+3 300 H 2 O in glass (wt.%) 0 50 100 150 200 250 0 0.005 0.010 0.015 0 1 2 3 4 5 6 H in plagioclase (wt.ppm water) D H (plag/melt) C H2O (wt. ppm) ≈94.3× C H2O (wt. %) melt plag Hydrous melting experiments Melt inclusions 0.01±0.00 5 0.008±0.002 0 1 2 3 OH in glass (wt.%) 0 5 10 15 20 25 2500 3000 3500 4000 4500 5000 5500 6000 ☞ Linear correlation between H concentration in plagioclase and OH in melt suggests that H is accommodated in plagioclase as OH. Wavenumber (cm -1 ) Absorption per cm #RTJ-pl20 (11 wt. ppm water, 0.3 wt.% H 2 O in melt inclusion) #RTJ-pl24 (38 wt. ppm water, 0.3 wt.% H 2 O in melt inclusion) #MTL17 (68 wt. ppm water, 0.8 wt.% H 2 O in melt) #MTL05 (153 wt. ppm water, 2.3 wt.% H 2 O in melt) #MTL39 (157 wt. ppm water, 3.5 wt.% H 2 O in melt) #MTL37 (210 wt. ppm water, 4.5 wt.% H 2 O in melt) #MTL41 (225 wt. ppm water, 5.6 wt.% H 2 O in melt) Natural plagioclase in MTL lava (5 wt. ppm water) residual resin? Longer hydrogen bond length d(O⋯O) Shorter hydrogen bond length d(O⋯O) ☞ Peak of infrared absorption spectra of plagioclase shifts from lower wavenumbers (peak position: 3200-3400 cm -1 ) under H 2 O-poor conditions to higher wavenumbers (peak position: 3600 cm -1 ) under H 2 O-rich conditions, meaning expansion of O-H⋯O bond length with increasing H 2 O. These observations suggest that hydrogen site in plagioclase slightly changes with increasing H 2 O, which also changes hydrogen partitioning between plagioclase and melt as shown above. － Representative absorption spectra of plagioclase － ☞ High hydrogen concentration in plagioclase from Izu-Oshima volcano, a frontal-arc volcano in Izu arc (≥200 wt. ppm water, Hamada et al., 2011 EPSL), suggests crystallization of plagioclase from H 2 O-rich (≥4 wt.%) melt. Hamada et al. (2011, EPSL) An80 An85 An90 An95 Anorthite content of plagioclase ☞ Hydrogen partition coefficient D H slightly decreases with increasing H 2 O in coexisting melt. Internally-heated pressure vessel installed at Magma Factory, Tokyo Tech. 40º N 1160 ℃ 1130 ℃ 1050 ℃ 1000 ℃ 1050 ℃ ☞ H concentration in plagioclase can be approximated as a square root of H 2 O in melt. Decreasing temperature lowers H concentration in plagioclase. However, the effect of temperature is minor. Plagioclase (An 95 ) Olivine (Fo 78- 81 ) Clinopyroxen e Orthopyroxen e Magnetite 16 2 0 0 0 (vol.%)) Modal composition 0 20 40 60 80 70 75 80 85 90 0 10 20 30 40 50 0 0.1 0.2 0.3 0.4 0.5 Plagioclase (An 74- 89 ) Olivine (Fo 90 ) 5 1 (vol. %)) Modal composition Cross-Nicol image of studied MORB. Quenched glass contains ~0.3 wt.% H 2 O. Backscattered-electron image of plagioclase and melt inclusion. Analytical result using FT-IR An content of plagioclase Hydrogen concentration in plagioclase (wt. ppm water) H 2 O in plagioclase- hosted melt inclusions (wt.%) Hydrogen concentration in plagioclase (wt. ppm water) ≈ 0.01 Integration of Part 1 and Part 2 Application ☞ Hydrogen concentration in plagioclase and H 2 O concentration in glass was measured using FT-IR.
description
V11C-2776. (*E-mail: [email protected]). Part 2) Hydrous melting experiments to determine H partitioning between plagioclase and melt. Integration of Part 1 and Part 2. 300. Purpose and quick summary. - PowerPoint PPT Presentation
Transcript of M. Hamada 1 *, M. Ushioda 1 , T. Fujii 2,3 and E. Takahashi 1
Hydrogen concentration in plagioclase as a hygrometer of magmas: Approaches from melt inclusion analyses and hydrous melting experiments
M. Hamada1*, M. Ushioda1, T. Fujii2,3 and E. Takahashi1
1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan 2Earthquake Research Institute, University of Tokyo, Tokyo, Japan 3Crisis & Environmental Management Policy Institute, Tokyo, Japan (*E-mail: [email protected])
V11C-2776
Plagioclase is one of the nominally anhydrous minerals (NAMs) which accommodates hydrogen, and plagioclase in volcanic rocks essentially contains structural OH in it. Hydrogen concentration in NAMs can be a useful proxy for dissolved H2O in silicate melts if the partitioning of hydrogen between plagioclase and melts is known. Here, we performed two parts of studies in order to determine hydrogen partitioning between plagioclase and hydrous basaltic melt: (i) analyses of low-H2O melt inclusions (H2O ≈ 0.3 wt.%) hosted by plagioclase in mid-ocean ridge basalt (MORB) and (ii) hydrogen partitioning experiments between Ca-rich plagioclase (An95) and hydrous arc basaltic melt (0.8 ~ 5.5 wt.% H2O) at 0.35 GPa. Obtained formulation is
Hydrogen in plagioclase (wt. ppm water) ≈ 94.3×√(H2O in melt, wt.%).
This empirical formulation can be used as a practical hygrometer of magmas. In this poster, we apply this formulation to understand the 1986-1987 summit eruption of Izu-Oshima volcano, a frontal-arc volcano in Izu arc, and discuss eruption process of H2O-saturated magma.
Purpose and quick summary
Part 1) Analyses of plagioclase-melt inclusion pairs from MORB
Figure is from Nakamura et al. (2007 Marine Geol.)
KH93-3 DR9
50 μm
500 μm
Whole-rock composition
SiO2 50.5 TiO2 1.52 Al2O3 15.1 FeO* 11.1 MnO 0.19 MgO 7.44 CaO 11.1 Na2O 2.80 K2O 0.10 P2O5 0.15 Total 100 (wt.%)
Studied sample: Sample# KH93-3 DR9 from Rodriguez Triple Junction in the Indian Ocean
Part 2) Hydrous melting experiments to determine
H partitioning between plagioclase and melt
1000
1050
1100
1150
1200
1250
1300
0 1 2 3 4 5 6
Experimental procedures
volcanic front
35ºN
Izu-Oshima volcano
30ºN
45ºN145ºE140ºE135ºE130ºE
Miyakejima volcano
SiO2
TiO2
Al2O3
FeO* MnO MgO CaO Na2O K2OTotal
51.2 0.9617.511.2 0.21 4.911.5 2.2 0.25100 (wt.%))
Starting material of melting experiments (MTL rock, collected from Miyakejima volcano in Izu
arc)
H2O in melt (wt.%)
Tem
pera
ture
()
℃
plagioclase-in
augite-inmagnetite-in
plagioclase-in augite-inmagnetite-in
Partitioning experiment of hydrogen between An95 plagioclase and melt
Au80Pd20 capsule
200 μm
Crushing volcanic rock
Separation of An95 plagioclase
Hydrous melting of crushed rock
10 mg of hydrous glass
1 mg of An95 plagioclase
Melting at 0.35 GPa for 24-48 hours using
internally-heated pressure vessel
Backscattered electron image of the recovered sample (1130℃, 2.6 wt.% in melt)
Obtained phase diagram of MTL rock at 0.35 GPa
An95 plagioclase
fO2~NNO+3
300
H2O in glass (wt.%)
0
50
100
150
200
250
0
0.005
0.010
0.015
0 1 2 3 4 5 6
H in
pla
gioc
lase
(w
t.ppm
wat
er)
DH
(pla
g/m
elt)
CH2O (wt. ppm) ≈94.3× CH2O (wt. %)meltplag
Hydrous melting experiments
Melt inclusions
0.01±0.005
0.008±0.002
0 1 2 3OH in glass (wt.%)
0
5
10
15
20
25
25003000350040004500500055006000
☞ Linear correlation between H concentration in plagioclase and OH in melt suggests that H is accommodated in plagioclase as OH.
Wavenumber (cm-1)
Abs
orpt
ion
per
cm
#RTJ-pl20(11 wt. ppm water, 0.3 wt.% H2O in melt inclusion)
#RTJ-pl24(38 wt. ppm water, 0.3 wt.% H2O in melt inclusion)
#MTL17(68 wt. ppm water, 0.8 wt.% H2O in melt)
#MTL05(153 wt. ppm water, 2.3 wt.% H2O in melt)
#MTL39(157 wt. ppm water, 3.5 wt.% H2O in melt)
#MTL37(210 wt. ppm water, 4.5 wt.% H2O in melt)
#MTL41(225 wt. ppm water, 5.6 wt.% H2O in melt)
Natural plagioclase in MTL lava(5 wt. ppm water)
resi
dual
res
in?
Longer hydrogen bond length d(O⋯O) Shorter hydrogen bond length d(O⋯O)
☞ Peak of infrared absorption spectra of plagioclase shifts from lower wavenumbers (peak position: 3200-3400 cm-1) under H2O-poor conditions to higher wavenumbers (peak position: 3600 cm-1) under H2O-rich conditions, meaning expansion of O-H⋯O bond length with increasing H2O. These observations suggest that hydrogen site in plagioclase slightly changes with increasing H2O, which also changes hydrogen partitioning between plagioclase and melt as shown above.
－ Representative absorption spectra of plagioclase －
☞ High hydrogen concentration in plagioclase from Izu-Oshima volcano, a frontal-arc volcano in Izu arc (≥200 wt. ppm water, Hamada et al., 2011 EPSL), suggests crystallization of plagioclase from H2O-rich (≥4 wt.%) melt.
Hamada et al. (2011, EPSL)
An80 An85 An90 An95
Anorthite content of plagioclase
☞ Hydrogen partition coefficient DH slightly decreases with increasing H2O in coexisting melt.
Internally-heated pressure vessel installed at Magma Factory, Tokyo
Tech.
40ºN
1160 ℃
1130 ℃
1050 ℃
1000 ℃
1050 ℃
☞ H concentration in plagioclase can be approximated as a square root of H2O in melt. Decreasing temperature lowers H concentration in plagioclase. However, the effect of temperature is minor.
Plagioclase (An95)Olivine (Fo78-81)ClinopyroxeneOrthopyroxeneMagnetite
16 2 0 0 0 (vol.%))
Modal composition
0
20
40
60
80
70 75 80 85 90 0
10
20
30
40
50
0 0.1 0.2 0.3 0.4 0.5
Plagioclase (An74-89)Olivine (Fo90)
51 (vol.%))
Modal composition
Cross-Nicol image of studied MORB.Quenched glass contains ~0.3 wt.% H2O.
Backscattered-electron image of plagioclase and melt inclusion.
Analytical result using FT-IR
An content of plagioclase
Hyd
roge
n co
ncen
trat
ion
in
plag
iocl
ase
(wt.
ppm
wat
er)
H2O in plagioclase-hosted melt inclusions (wt.%)
Hyd
roge
n co
ncen
trat
ion
in
plag
iocl
ase
(wt.
ppm
wat
er)
≈ 0.01
Integration of Part 1 and Part 2
Application
☞ Hydrogen concentration in plagioclase and H2O concentration in glass was measured using FT-IR.
