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Single-crystal elasticity of hydrous wadsleyite and implication for the Earth’s transition zone. Zhu Mao 1 , Steven D. Jacobsen 1 , Fuming Jiang 1 , Joseph R. Smyth 3 , Christopher Holl 2 , Daniel J. Frost 4 Thomas Duffy 1 - PowerPoint PPT Presentation
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Single-crystal elasticity of hydrous wadsleyite and implication for the Earth’s
transition zone
Zhu Mao1, Steven D. Jacobsen1, Fuming Jiang1, Joseph R. Smyth3, Christopher Holl2, Daniel J. Frost4
Thomas Duffy1
1Princeton University, Department of Geosciences, Princeton, NJ, 085402Northwestern University, Department of Geological Sciences, Evanston, IL 60208
3University of Colorado, Department of Geological Sciences, Boulder, CO 803094Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany
2
Estimate of water content in the mantle
MORB source from 0.005 to 0.02 wt% (e.g. Saal et al.2002)
OIB source from 0.03 to 0.1 wt% (e.g. Dixon et al.2002)
Shear wave velocity anomaly 0.3 wt% from 300-500 km in central and eastern Europe (Nolet and Zielhuis 1994)
Width of 410-km discontinuity 0.02-0.07 wt% (Wood 1995; van de Meijde et al., 2003)
Transition zone electrical conductivity 0.1-0.2 wt% (Huang et al., 2005)
3
Model for global water circulation
Ohtani 2005
4
transition zone
Li et al., 2001Fei and Bertka 1999
ri
5
Wadsleyite ( -Mg2SiO4)
• Has the greatest hydrogen storage capacity among the olivine polymorphs (e. g., Smyth 1987).
• Including ringwoodite, transition zone could contain a large water reservoir perhaps exceeding the mass of the hydrosphere (Smyth et al., 2006).
• Small amounts of water can strongly influence physical properties of mantle minerals (e. g., Wood 1995).
• The bulk modulus of hydrous wadsleyite was studied by static compression studies (Yusa and Inoue 1997; Smyth et al., 2005; Holl 2006).
• Pressure derivatives of bulk and shear moduli are needed to extrapolate elastic moduli to high pressures.
6
1. Ambient conditions measurements:
0.37 wt%, 0.84 wt% and 1.67 wt% H2O content
2. High-pressure measurements to 12 GPa:
0.84 wt% H2O content
Single-crystal elasticity measurements for hydrous wadsleyite by Brillouin scattering:
7
Example of Brillouin spectrum at ambient conditions for sample containing 0.84 wt% H2O.
-10 -5 0 5 10
LA LA
TA2 TA2TA1
Velocity (km/s)
R
TA1
1. Ambient conditions measurements
8
RMS: 49 m/s0.84 wt% water:
0 50 100 150
6
8
10
(0.56, 0.42, 0.71)
0 50 100 150
6
8
10
(0.84, 0.36, 0.42)
0 50 100 150
6
8
10
(0.15, 0.90, 0.42)
0 50 100 150
6
8
10
(1.00, 0, 0)
Azimutha angle (degree)
Velocity (km/s)
(b)
Measured compressional and shear wave velocities as a function of direction by Brillouin scattering.
9
Single-crystal elastic moduli of Mg2SiO4 hydrous wadsleyite as a function of water content.
Elasticity of anhydrous wadsleyite:
Sawamoto et al., 1984
Zha et al., 1997
110
100
90
80
70
60
Cij (GPa)
1.51.00.50.0
Water (wt%)
C13
C23
C12
120
110
100
90
1.51.00.50.0Water (wt%)
C55
C44
C66
400
350
300
250
Cij (GPa)
1.51.00.50.0
C22
C11
C33
10
is the water weight percent.OHX 2
OHOHS XGXK22
)1(9.7)1(8.111)6(4.12)7(3.1700 −=−=
180
160
140
120
100
80
Modulus (GPa)
2.52.01.51.00.50.0
Water (wt%)
KS
G
Yusa and Inoue 1997 Smyth et al., 2005. Wa II Zha et al., 1997 Sawamoto et al., 1984
11
VP and VS calculated for three olivine polymorphs at ambient conditions
Sawamoto et al., 1984; Zha et al., 1996 Inoue et al., 1998; Jackson et al., 2000 Li et al., 2003; Wang et al., 2003; Sinogeikin et al., 2003
See also: Fe-bearing hydrous ringwoodite Jacobsen et al., 2004.
0.0 0.4 0.8 1.2 1.6 2.0 2.48.4
8.6
8.8
9.0
9.2
9.4
9.6
9.8
10.0
Vp (km/s)
H2O (wt%)
olivine
Wadsleyite
Ringwoodite Mg#100
0.0 0.4 0.8 1.2 1.6 2.0 2.4
5.0
5.2
5.4
5.6
5.8
olivine
Wadsleyite
Ringwoodite Mg#100
Vs (km/s)
H2O (wt%)
12
2. High-Pressure measurements
Photo of hydrous wadsleyite crystal at 12 GPa
mμ250
ruby
ruby
13
450
400
350
300
250
Modulus (GPa)
14121086420
Pressure (GPa)
C22C11 C33
Open symbol: Zha et al., 1997Filled symbol: This study
140
130
120
110
100
90
Modulus (GPa)
14121086420
Pressure (GPa)
C55C44 C66
160
140
120
100
80
60
Modulus (GPa)
14121086420
Pressure (GPa)
C12 C13 C23
Single-crystal elasticity of wadsleyite with 0.84 wt% H2O as a function of pressure
14
240
220
200
180
160
140
120
100
80
Modulus (GPa)
14121086420
Pressure (GPa)
KS
G
KS'=4.2(1)
G'=1.4(1)
Aggregate bulk and shear moduli as a function of pressure
Anhydrous wadsleyite (Zha et al., 1997)
Wadsleyite with 0.84 wt% H2O (this study)
15
Application to the Earth’s mantle
1. Velocity jump at 410-km depth
2. Velocity gradient in the transition zone
16
)()()()( 0000 TTT
KTKTK P
SSS −
∂∂
+=
)]4(2
31[)21)((3 '2
5
0 SS KfTfKP −−+=
]1))(
)([(
2
1 3/2
0
−=TT
fρρ
∫=
−T
T
dTT
eTT 0
')'(
000 )()(α
ρρ
GVGKV SSP =+= 22 3/4 ρρ
Hydrous olivine
Hydrous wadsleyite
PS
T
K)(
∂∂
(GPa/K)
-0.0164(5)
-0.0175(3)
SS
P
K)(
∂∂
4.2(2)
4.2(1)
)10( 15 −−× Kα
WX
T
162.04.3
1022.273.2 3
−×+ −
Table. Thermal elastic parameters
Liu et al., 2005; Mayama et al., 2004;
Zha et al., 1996;
Inoue et al., 2004
0 200 400 600 800 10005
6
7
8
9
10
11
12
VP (km/s)
Depth (km)
AK135)]35(1)[()21( '0
2/5SSS KfTKfK −−+=
17
wdolP
seisPfrac V
Vol
−
−
ΔΔ
=
200 300 400 500 600
8.0
8.4
8.8
9.2
9.6
10.0
VP (km/s)
Depth (km)
VP at 410 km
Wadsleyite
olivine
200 300 400 500 600
8.0
8.4
8.8
9.2
9.6
10.0
AK135
VP (km/s)
Depth (km)
VP at 410 km
18
1. Velocity jump at 410-km depth
360 400 440 4806.6
6.9
7.2
7.5
0.8 wt% H2O
410 km
olivine
wadsleyite
VB (km/s)
Depth (km)
VK= 7.7%
VK= 6.7%
VK= 5.7%
dry conditions
0.4 wt% H2O
Frost and Dolejš 2007
19
360 380 400 420 440 460 480
4.6
4.8
5.0
5.2
5.4
0.8 wt% H2O
0.4 wt% H2O
Dry conditions
Olivine
Wadsleyite
410 km
VS (km/s)
Depth (km)
VS=12.1%
VS=10.8%
VS=9.4%
20
Olivine fraction as a function of water in wadsleyite
0.0 0.4 0.8 1.2 1.6
40
50
60
70
80
90
100
olivine volume fraction %
H2O in wadsleyite (wt%)
Pyrolite
determined by VB contrast at 410 km
reference seismic model: AK135
21
Olivine fraction as a function of water in wadsleyite
0.0 0.4 0.8 1.2 1.6
40
50
60
70
80
90
100
olivine volume fraction %
H2O in wadsleyite (wt%)
Pyrolite
determined by VB contrast at 410 km
reference seismic model: AK135
wdolS
seisS
V
V
−−
−
ΔΔ
22
2. Velocity gradient in the transition zone
Speziale, unpublished
23Li et al., 2001
24
Litasov and Ohtani 2003
Demouchy et al. 2005
~0.9 wt%~0.3 wt%
25
AK135 : 0.24 wt%
njpb: 0.4 wt%
PA5: 0.7 wt%
TNA-GCA: 0.5 wt%
SNA-S25: 0.8 wt%
Estimates of the reduction of water content:
Grand and Helmberger 1984; Walck 1984; Lefevre and Helmberger 1989
Kennett et al., 1994; Kennett et al., 1995; Gaherty et al., 1996
400 425 450 475 500 525 550
7.0
7.2
7.4
7.6
wd with 0.1 wt% H2O
VB (km/s)
Depth (km)
AK135
dry wd
wd with 0.34 wt% H2O
26
AK135 : 0.25 wt%
njpb: 0.4 wt%
PA5: 0.7 wt%
TNA-GCA: 0.5 wt%
SNA-S25: 0.8 wt%
Estimates of the reduction of water content:
Grand and Helmberger 1984; Walck 1984; Lefevre and Helmberger 1989
Kennett et al., 1994; Kennett et al., 1995; Gaherty et al., 1996
400 420 440 460 480 500 520
7.2
7.3
7.4
7.5
7.6
VB(km/s)
Depth(km)
AK135
njpb
TNA-GCA
SNA-S25
PA5
27
Conclusions
• Aggregate bulk and shear moduli of hydrous wadsleyite vary linearly as function of water content:
• For iron-free olivine polymorphs, water has a greater (or similar) effect on the elasticity of wadsleyite than the other two polymorphs.
• The high pressure measurements of hydrous wadsleyite show pressure derivative of bulk modulus, KS’ and shear modulus, G’ is similar to its anhydrous phase: KS’ = 4.2(1), G’ = 1.4(1).
OHOHS XGXK22
)1(9.7)1(8.111)6(4.12)7(3.1700 −=−=
28
Conclusions
• For a pyrolite upper mantle (60 vol% olivine), 0.8 wt% H2O in wadsleyite is required to match the velocity contrast given by seismic model AK135.
• Transition zone seismic velocity gradient (AK135) can be matched by ~0.3 wt% H2O reduction in wadsleyite from 410 to 520 km. Regional model needs more water reduction to match the velocity gradient than AK135.
29
30
Frost and Dolejš 2007
31
120
110
100
90
80
70
60
Cij (GPa)
1.51.00.50.0
C55
C44
C66
wadsleyite
olivine
400
350
300
250
200
Cij (GPa)
1.51.00.50.0
C22
C11
C33
olivine
wadsleyite
110
100
90
80
70
60
Cij (GPa)
1.51.00.50.0H2O (wt%)
C13
C23
C12
olivine
wadsleyite
32
0.0 0.4 0.8 1.2 1.6 2.0 2.4
80
90
100
110
120
G (GPa)
H2O (wt%)
0.0 0.4 0.8 1.2 1.6 2.0 2.4120
140
160
180
Forsterite
Wadsleyite
rw Mg#90
Ringwoodite(rw) Mg#100
H2O (wt%)
KS (GPa)
33
Table. Water storage capacity of olivine polymorphs with pressure and temperature
Litasov et al., 20030.8021.51200
Ohtani et al., 20000.2918.51600rw
0.2918.51600
0.4618.51400
Litasov et al., 20030.72161400
0.93151400
Demouchy et al., 20052.68141200wd
0.40121400
Smyth et al., 20060.89121200ol
ReferenceH2O (wt%)P (GPa)T (oC)
Litasov et al., 20030.8021.51200
Ohtani et al., 20000.2918.51600rw
0.2918.51600
0.4618.51400
Litasov et al., 20030.72161400
0.93151400
Demouchy et al., 20052.68141200wd
0.40121400
Smyth et al., 20060.89121200ol
ReferenceH2O (wt%)P (GPa)T (oC)
34
200
180
160
140Bulk Modulus (GPa)
4.44.24.03.83.63.43.2
Density (g/cm3)
Ringwoodite
Wadsleyite
Olivine
T=300K
P=10-4
GPa
Mg#100
Mg#90
120
100
80
60Shear Modulus (GPa)
4.44.24.03.83.63.43.2
Density (g/cm3)
Olivine
Ringwoodite
Wadsleyite T=300K
P=10-4
GPa
Mg#100
Mg#90Effect of composition and structure on the elasticity of olivine (Mg, Fe)2SiO4 polymorphs
Birch’s plot
35
200
180
160
140
120
KS (GPa)
4.44.24.03.83.63.43.2
Density (g/cm3)
Ringwoodite
Wadsleyite
Olivine
Chondrodite
Clinohumite
hy-ol hy-wa this study hy-ri
120
100
80
60
G (GPa)
4.44.24.03.83.63.43.2
Density (g/cm3)
RingwooditeWadsleyite
OlivineClinohumite
Chondrodite
hy-ol hy-wa this study hy-ri
Effect of hydration
36
• Elasticity of hydrous olivine Jacobsen et al., 2006.
• Elasticity of hydrous ringwoodite Inoue et al., 1998 and Wang et al., 2003
• Assuming a linear relationship between aggregate moduli and water content for three olivine polymorphs.
Effect of water on the elasticity of iron free olivine polymorphs
Thus, water has a greater (or similar) effect on the elastic moduli of wadsleyite than the other two polymorphs.
14
12
10
8
6
4
2
0
G/G
2.01.51.00.50.0
Water (wt%)
olivine
ringwoodite
wadsleyite
1.6%
5%
7.1%
14
12
10
8
6
4
2
0
K0S
/K0S
2.01.51.00.50.0
Water (wt%)
wadsleyite
ringwoodite
olivine2.9%
4.5%
7.3%7.4%
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