Supplementary Information

SUPPLEMENTARY INFORMATION
DOI: 10.1038/NGEO2306
Lower mantle water reservoir implied by the
extreme
stability of water
a hydrous
aluminosilicate
Lower-mantle
reservoir
implied by the
extreme stability of a hydrous aluminosilicate
Supplementary Information
Martha G. Pamato, Robert Myhill*, Tiziana Boffa Ballaran, Daniel J. Frost, Florian Heidelbach
and Nobuyoshi Miyajima
Corresponding author: bob.myhill@uni-bayreuth.de
1
Bayerisches Geoinstitut, University of Bayreuth, 95440 Bayreuth, Germany
Experimental details
The starting compositions for the synthesis of Al-phase D are shown in Supplementary Table 1.
The oxide and hydroxide reagents were first dried, then weighed in the required proportions and
ground under ethanol. The powdered samples were loaded into platinum capsules that were sealed
by arc welding. Capsules were made of 1 mm outer diameter platinum tubing and had initial
lengths of 1.0–1.2 mm. High pressure experiments were carried out using 1200t and 1000t 6-8
Kawai type multianvil apparatuses at the Bayerisches Geoinstitut (BGI). For pressures up to 24 GPa
10 mm edge length Cr2 O3 -doped MgO octahedra were used as pressure media in combination with
tungsten carbide cubes of 32 mm edge length and 4 mm truncation edge length (10/4 assembly).
The temperature was measured using W3%Re/W25%Re (type D) thermocouple wires (0.13 mm
thick). The thermocouple was inserted axially into the octahedral assembly within a 4-hole alumina
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1
tube (d=1.2 mm, 2.6 mm in length, with the hot junction in contact with the capsule. A 7/3
(octahedral edge length/ truncation edge length) type assembly was used at pressures of 26 GPa.
In this type of assembly, the LaCrO3 tube was placed directly into the octahedron and no insulting
ZrO2 sleeves were used (due to the reduced space in the assembly). Type D thermocouple wires
(0.07 mm thick) were inserted longitudinally through the wall of the heater, with the hot junction
at the center of the assembly. The pressure calibrations for the assemblies used in this study
are reported in the literature1 . After heating at high pressure, the experiments were quenched by
shutting off the power. The samples were recovered after a 15 hour decompression phase.
Sample analysis
a. XRD
Experimental runs performed at lower temperatures and pressures resulted in a fine
grained powder. For phase identification of these run products, powder X-ray diffraction patterns
were collected using a PHILIPS Xpert diffractometer, operating at 40 kV and 40 mA with CoKα
radiation (λ=1.78897 Å). Diffraction patterns were collected in the 2Θ range from 15◦ to 90◦ .
Phase identification was carried out using the WinXPow Stoe program.
b. SEM/EBSD
The run products were characterized using a GEMINI LEO (now Zeiss) 1530
scanning electron microscope operating at 20 kV accelerating voltage, a beam current of about 2
nA and a working distance of 14 mm. Preliminary phase identification was performed by means
of EDS (energy dispersive spectroscopy) analysis using a Si(Li) detector (Oxford INCA). EBSD
patterns were recorded in the SEM with a Nordlys detector and indexed with the Channel software
2
Figure 1: Raw (a) and indexed (b) EBSD patterns of Al-phase D.
package (both Oxford Instruments; see Supplementary Figure 1). The indexing of the diffraction
patterns was based on the 100 strongest reflections calculated with kinematic theory2 from the
structural model of the new Al-rich form of phase D previously reported3 .
c. EPMA
The chemical compositions of the run products (Supplementary Table 3) were mea-
sured with a JEOL JXA-8200 electron probe microanalyser operating at 15 kV and 5 nA. The
low beam current reduced the level of electron beam damage to the sensitive hydrous phases. The
electron beam size was approximately 1-2 µm in diameter and the peak counting times were 20 s.
The concentrations of Si and Al were determined using diopside and pyrope as standards.
d. TEM
The samples were prepared for TEM investigation by crushing crystal fragments be-
tween two glass slides. The powdered samples were then dispersed in ethanol and loaded on a
Lacey carbon TEM grid. The samples were studied using an analytical transmission electron mi3
croscope (ATEM, Philips CM-20FEG) operating at 200 kV. The crystals were characterised by
selected area electron diffraction (SAED), bright-field (BF) imaging and EDXS spectra, collected
using an energy dispersive X-ray spectrometer (NORAN Ge detector).
e. Raman spectroscopy
Raman spectroscopy was performed on single-crystals of Al-phase D
(S5113) with a Dilor XY system. The system was operated with a 514 nm Ar+ ion laser and a
liquid nitrogen-cooled CCD detector. The resulting spectrum can be compared to Mg,Fe-bearing
superaluminous phase D (Supplementary Figure 2). Stishovite crystals were also analysed (Supplementary Figure 3).
Water contents of phases
The hydrogen contents in Supplementary Table 3 were derived from the deficits in microprobe totals. Hydrous phases tend to show the same systematic behaviour, with hydrogen contents decreasing with increasing temperature. In contrast, nominally anhydrous stishovite exhibits a marked
increase in deficits at around 1460◦ C, implying an increase in hydrogen solubility in the phase.
Aluminous stishovite with 5 at. % Al has previously been synthesised with ∼2 at. % H at 20 GPa,
1400◦ C4 . Water contents should increase with pressure and temperature5 until the melting point
is reached. Raman spectra collected from stishovite synthesised at 2100◦ C qualitatively reveal the
presence of significant hydrogen in the structure via a broad peak at ∼3000 cm−1 (Supplementary
Figure 3). A further study will quantitatively investigate the incorporation of water in stishovite
under lower mantle conditions.
4
Normalised Intensity
a. S4430 (superaluminous phase D)
0
500
1000
1500
2000
2500
3000
3500
4000
3000
3500
4000
Wavenumber (cm−1)
Normalised Intensity
b. S5113 (Al−phase D; Mg,Fe free)
0
500
1000
1500
2000
2500
Wavenumber (cm−1)
Figure 2: Raman spectra of synthesised phase D crystals. Comparison of background-corrected
Raman spectra from a) superaluminous phase D (Mg0.20 Fe0.11 Al1.50 Si0.92 H3.1 O6 )3 synthesised at
1500◦ C and b) Al-phase D synthesised at 2100◦ C. The background intensities were approximated
with manually determined Akima spline functions. Note the similar wavenumbers and breadth of
the OH peak at ∼2900 cm−1 . Note also the side lobes at 3000-3200 cm−1 , which are present in
both samples but are much more pronounced in the Mg,Fe-free Al-phase D.
5
2000
Intensity (a.u.)
1600
1200
800
400
0
0
1000
2000
Wavenumber
3000
4000
(cm−1)
Figure 3: Raman spectra of synthesised stishovite. Raman spectra from stishovite synthesised
at 2100◦ C and ∼26 GPa. Note the broad peak attributed to OH at ∼3000 cm−1 .
Structural refinement of Al phase D
A crystal of Al-phase D with dimensions of about 15 x 15 x 30 µm was selected from run product S4517 1. Intensity data were collected from the crystal mounted on a glass fiber at ambient
conditions using an Xcalibur diffractometer with MoKα radiation operated at 50 kV and 40 mA,
equipped with a CCD detector and a graphite monochromator. Combined omega and phi scans
provided a coverage of the half reciprocal sphere up to 2θmax = 70◦ . Given the very small crystal
dimensions the exposure time was 60 s/frame. Lorentz and polarization factors were taken into account for the correction of the reflection intensities using the CrysAlis package (Oxford Diffraction
2006). The set of {hkl} reflections in the trigonal symmetry of Mg-phase D6 which had similar,
although not equal, intensities in superaluminous phase D3 are identical in this study, suggesting
6
that the structure of pure Al-phase D is hexagonal. Analysis of the extinction conditions indicate
a Laue class 6/mmm and possible space groups P63 /mcm and P63 cm. Given the small number of
unique reflections that could be observed due to the small dimension of the crystal, we were unable
to use direct methods to solve the structure. The space group P63 /mcm (S.G. # 193) has similar
structural positions to those of the cations in Mg-phase D (space group P-31m; S.G. # 162), so this
space group was chosen for structural refinement. Structure refinements were performed based on
F2 using the SHELX97 program package7 in the WingX System8 . The occupancy of Al and Si
was allowed to vary in the 2b and 4d Wyckoff positions (see following paragraph). Total Al and Si
contents were constrained to agree with the content determined from electron probe microanalysis
for the same sample. The position of the oxygen atoms were deduced from the residual peak in
the difference-Fourier map. In order to reduce the number of refined parameters only isotropic
displacement parameters were refined. Data collection and refinement details, fractional atomic
coordinates and isotropic displacement parameters are reported in Supplementary Table 4.
The crystal structure of Al phase D
The crystal structure of Mg-phase D (ideal formula MgSi2 H2 O6 ) is based on a hexagonal closepacked array of oxygen atoms6 . The SiO6 and MgO6 octahedra occur in two separated layers
stacked along c (Supplementary Figure 4). The symmetry of this endmember is trigonal (space
group P-31m; S.G. # 162). Mg and Si cations occupy the 1a (M1) and 2d (M2) Wyckoff positions
respectively. The remaining octahedral sites corresponding to the 2c (M3) and 1b (M4) Wyckoff positions are vacant. In endmember Al-phase D (analysed composition Al1.54 Si0.98 O6 H3.5 ), a
7
completely random distribution of Si and Al on the octahedral sites increases the symmetry from
trigonal to the hexagonal space group P63 /mcm (S.G. # 193). In this structure, the M1 and M4
sites become equivalent (Wyckoff position 2b for this space group), as do the M2 and M3 sites
(Wyckoff position 4d). All six octahedral sites are partially occupied.
8
Figure 4: The structure of Al phase D. Al phase D has a structure corresponding to hexagonal
space group P63 /mcm, shown here projected down the a axis. The octahedral sites are named
according to the structure of Mg-phase D in trigonal space group P-31m3 . In the Mg endmember,
Mg and Si exclusively occupy the M1 and M2 sites respectively, with the M3 and M4 sites vacant.
In pure Al-phase D the M1 and M4 sites are equivalent, as are the M2 and M3 sites. All six
octahedral sites are partially occupied by a random distribution of Si and Al.
9
Table 1: Nominal compositions of starting materials expressed in wt. %.
Starting composition
Al2 O3
Al(OH)3
SiO2
Mixture 1
19.24
55.5
25.27
Mixture 2
13.59
39.27
47.15
Table 2: Experimental details (st=stishovite, egg=phase Egg, D=Al-phase D).
starting comp.
assembly
P (GPa)
T (◦ C)
t(min)
Analytical tools
Run products
H3061
mixture 1
10/4
22
1050
150
XRD
δ-AlOOH,st
H3067
mixture 1
10/4
24
1150
150
XRD
δ-AlOOH,st
H3073 1
mixture 1
7/3
26
1200
30
XRD
δ-AlOOH,st
S4517 2
mixture 1
7/3
26
1460
30
XRD,EBSD,EPMA,TEM
δ-AlOOH,D,st
S4523 1
mixture 1
7/3
26
1700
30
XRD,EBSD,EPMA
D
S5050 1
mixture 1
7/3
26
1600
30
XRD,EBSD,EPMA
D
S5081
mixture 1
7/3
26
1730
30
XRD,EBSD,EPMA,TEM
D
H3073 2
mixture 2
7/3
26
1200
30
XRD
δ-AlOOH,st
S4517 1
mixture 2
7/3
26
1460
30
TEM,EBSD,XRD,EPMA
egg,D,st
S4523 2
mixture 2
7/3
26
1700
30
XRD,EBSD,EPMA
D,st
S4976
mixture 2
10/5
18
1100
60
XRD
egg,st
S4988
mixture 2
10/5
18
1100
60
XRD
egg,st
S4992 2
mixture 2
7/3
26
1460
30
EPMA
egg,st
S5021 2
mixture 2
7/3
26
1200
30
EBSD,EPMA
δ-AlOOH,egg,st
S5050 1
mixture 2
7/3
26
1600
30
XRD,EBSD,EPMA
egg,D,st
S5081
mixture 2
7/3
26
1730
30
XRD,EBSD,EPMA,TEM
D,st
S5113
mixture2
7/3
26
2100
10
XRD,EPMA,EBSD
D,st,melt
S4992 1
egg
7/3
26
1460
30
EPMA
egg,st
S5021 1
egg
7/3
26
1200
30
EBSD,EPMA
egg,st
Run no.
Al-rich system
Si-rich system
Egg
10
Table 3: Electron probe microanalysis of experimental run products. The number after
the phase name is the number of analyses. The number after each value is the standard
deviation referring to the last digit.
Weight percent
Experiment
Cation totals
SiO2
Al2 O3
Total
Al/Si
Si
Al
H
Tot
50.4(6)
40.7(5)
91.1(3)
0.95(1)
1.00(1)
0.95(1)
1.18(4)
3.14(3)
phase Egg (20)
47(1)
43(1)
89.8(6)
1.08(2)
0.92(2)
1.00(2)
1.34(8)
3.26(6)
stishovite (14)
97.3(7)
3.3(4)
100.6(4)
phase Egg (5)
49(1)
40.7(5)
89.7(8)
0.98(1)
0.96(3)
0.94(1)
1.4(1)
3.25(7)
d AlOOH (19)
17(2)
66(2)
82.6(4)
4.7(5)
0.16(2)
0.75(3)
1.12(2)
2.02(2)
stishovite (10)
98(1)
1.5(2)
100(1)
phase Egg (21)
49.2(8)
41.8(7)
91.0(4)
1.00(2)
0.97(2)
0.97(2)
1.19(5)
3.14(4)
stishovite (5)
96(1)
3.4(7)
99.9(7)
Egg composition
S5021 1 (26 GPa, 1200◦ C)
phase Egg (15)
stishovite (0)
S4992 1 (26 GPa, 1460◦ C)
Si-rich system
S5021 2 (26 GPa, 1200◦ C)
S4992 2 (26 GPa, 1460◦ C)
S4517 1 (26 GPa, 1460◦ C)
Al-phase D (41)
35(1)
46.7(9)
82(1)
1.58(4)
0.98(4)
1.54(4)
3.5(2)
5.98(16)
phase Egg (42)
47.8(8)
42.1(6)
89.8(7)
1.04(2)
0.94(2)
0.97(2)
1.33(8)
3.24(6)
stishovite (13)
96(3)
3(1)
99(2)
Al-phase D (19)
38.2(5)
46.7(6)
84.9(7)
1.44(2)
1.09(2)
1.58(3)
2.9(1)
5.56(9)
Egg (11)
46.9(5)
42.4(2)
89.3(4)
1.06(1)
0.92(1)
0.98(1)
1.39(5)
3.29(4)
stishovite (19)
92(1)
6.4(8)
98(1)
Al-phase D (31)
39.5(5)
47.8(5)
87.3(4)
1.43(2)
1.15(2)
1.64(2)
2.46(8)
5.26(5)
stishovite (19)
87(1)
10.6(6)
97.6(9)
S5050 2 (26 GPa, 1600◦ C)
S4523 2 (26 GPa, 1700◦ C)
11
S5081 (26 GPa, 1730◦ C)
Al-phase D (32)
39.1(6)
48.3(3)
87.4(5)
1.46(1)
1.14(2)
1.66(1)
2.46(9)
5.26(6)
stishovite (22)
84(1)
9.2(9)
93.1(9)
Al-phase D (11)
40.5(8)
49.2(4)
89.7(6)
1.43(1)
1.20(3)
1.72(2)
2.0(1)
4.96(9)
stishovite (11)
77.9(8)
15.6(4)
93.5(5)
Al-phase D (55)
27(1)
55(1)
82.9(8)
2.38(6)
0.78(3)
1.87(4)
3.26(14)
5.9(1)
d AlOOH (31)
16.5(7)
68.6(8)
85.0(5)
4.9(1)
0.16(1)
0.79(1)
0.98(3)
1.93(2)
stishovite (13)
95(1)
3.8(2)
99(1)
27(1)
57.1(9)
84.5(4)
2.45(5)
0.79(3)
1.94(3)
2.99(8)
5.73(6)
Al-phase D (16)
29(1)
57(1)
86.4(4)
2.31(6)
0.85(4)
1.98(4)
2.66(7)
5.49(6)
stishovite (1)
87.74
9.46
97.20
26.5(4)
59.0(3)
85.4(4)
2.63(2)
0.77(1)
2.03(2)
2.84(8)
5.63(5)
S5113 (26 GPa, 2100◦ C)
Al-rich system
S4517 2 (26 GPa, 1460◦ C)
S5050 1 (26 GPa, 1600◦ C)
Al-phase D (14)
S4523 1 (26 GPa, 1700◦ C)
S5081 (26 GPa, 1730◦ C)
Al-phase D (16)
12
Table 4: Unit-cell lattice parameters, atomic coordinates and displacement parameters, Al
and Si occupancy and structural refinements details for superaluminous phase D. Standard
deviations are in parentheses.
Measured reflections
587
M1
Unique reflections
85
Wyckoff position
2b
Fo >4s(Fo )
63
x
0
Rint
4.46%
y
0
Rw for Fo >4s(Fo )
6.70%
z
0
Rall
8.45%
Uiso
0.0202 (9)
wR2
20.60%
Al occupancy
0.335 (8)
GooF
1.334
Si occupancy
0.108 (8)
Nr. parameters
9
Space group
P63 /mcm
M2
Z
1
Wyckoff position
4d
F(000)
85
x
-0.3333
Absorption coefficient
1.03 mm−1
y
0.3333
z
0
Uiso
0.0143 (10)
Al occupancy
0.216 (8)
Si occupancy
0.188 (8)
Unit-cell parameters
a (Å)
4.7114 (6)
Oxygen
c (Å)
4.3039 (7)
Wyckoff position
6g
V (Å3 )
82.74 (9)
x
0.3349 (6)
y
0.3349 (6)
z
0.25
Uiso
0.0202 (9)
13
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