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1 SUPPLEMENTARY INFORMATION DOI: /NGEO2306 Lower-mantle water reservoir implied by the extreme stability of a hydrous aluminosilicate 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, 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 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 Cr 2 O 3 -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 NATURE GEOSCIENCE 1

2 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 LaCrO 3 tube was placed directly into the octahedron and no insulting ZrO 2 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 literature 1. 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= 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

$The indexing of the diffraction patterns was based on the 100 strongest reflections calculated with kinematic theory2 from the structural model of the new Al-rich form of phase D previously reported3.$

3 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

4 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 C 4. Water contents should increase with pressure and temperature 5 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

5 a. S4430 (superaluminous phase D) 0 b. S5113 (Al phase D; Mg,Fe free) Normalised Intensity Normalised Intensity Wavenumber (cm 1 ) Wavenumber (cm 1 ) Figure 2: Raman spectra of synthesised phase D crystals. Comparison of background-corrected Raman spectra from a) superaluminous phase D (Mg 0.20 Fe 0.11 Al 1.50 Si 0.92 H 3.1 O 6 ) 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 cm 1, which are present in both samples but are much more pronounced in the Mg,Fe-free Al-phase D. 5

6 Intensity (a.u.) Wavenumber (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 S 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 D 6 which had similar, although not equal, intensities in superaluminous phase D 3 are identical in this study, suggesting 6

7 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 P6 3 /mcm and P6 3 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 P6 3 /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 F 2 using the SHELX97 program package 7 in the WingX System 8. 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 MgSi 2 H 2 O 6 ) is based on a hexagonal closepacked array of oxygen atoms 6. The SiO 6 and MgO 6 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 Al 1.54 Si 0.98 O 6 H 3.5 ), a 7

8 completely random distribution of Si and Al on the octahedral sites increases the symmetry from trigonal to the hexagonal space group P6 3 /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 P6 3 /mcm, shown here projected down the a axis.

9 Figure 4: The structure of Al phase D. Al phase D has a structure corresponding to hexagonal space group P6 3 /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-31m 3. 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

10 Table 1: Nominal compositions of starting materials expressed in wt. %. Starting composition Al 2 O 3 Al(OH) 3 SiO 2 Mixture Mixture Table 2: Experimental details (st=stishovite, egg=phase Egg, D=Al-phase D). Run no. starting comp. assembly P (GPa) T ( C) t(min) Analytical tools Run products Al-rich system H3061 mixture 1 10/ XRD δ-alooh,st H3067 mixture 1 10/ XRD δ-alooh,st H mixture 1 7/ XRD δ-alooh,st S mixture 1 7/ XRD,EBSD,EPMA,TEM δ-alooh,d,st S mixture 1 7/ XRD,EBSD,EPMA D S mixture 1 7/ XRD,EBSD,EPMA D S5081 mixture 1 7/ XRD,EBSD,EPMA,TEM D Si-rich system H mixture 2 7/ XRD δ-alooh,st S mixture 2 7/ TEM,EBSD,XRD,EPMA egg,d,st S mixture 2 7/ XRD,EBSD,EPMA D,st S4976 mixture 2 10/ XRD egg,st S4988 mixture 2 10/ XRD egg,st S mixture 2 7/ EPMA egg,st S mixture 2 7/ EBSD,EPMA δ-alooh,egg,st S mixture 2 7/ XRD,EBSD,EPMA egg,d,st S5081 mixture 2 7/ XRD,EBSD,EPMA,TEM D,st S5113 mixture2 7/ XRD,EPMA,EBSD D,st,melt Egg S egg 7/ EPMA egg,st S egg 7/ EBSD,EPMA egg,st 10

11 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 Cation totals Experiment SiO 2 Al 2 O 3 Total Al/Si Si Al H Tot Egg composition S (26 GPa, 1200 C) phase Egg (15) 50.4(6) 40.7(5) 91.1(3) 0.95(1) 1.00(1) 0.95(1) 1.18(4) 3.14(3) stishovite (0) S (26 GPa, 1460 C) 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) Si-rich system S (26 GPa, 1200 C) 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) S (26 GPa, 1460 C) 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) S (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) S (26 GPa, 1600 C) 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) S (26 GPa, 1700 C) 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) 11

12 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) S5113 (26 GPa, 2100 C) 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-rich system S (26 GPa, 1460 C) 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) S (26 GPa, 1600 C) Al-phase D (14) 27(1) 57.1(9) 84.5(4) 2.45(5) 0.79(3) 1.94(3) 2.99(8) 5.73(6) S (26 GPa, 1700 C) 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) S5081 (26 GPa, 1730 C) Al-phase D (16) 26.5(4) 59.0(3) 85.4(4) 2.63(2) 0.77(1) 2.03(2) 2.84(8) 5.63(5) 12

13 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 2 b Fo >4s(Fo) 63 x 0 R int 4.46% y 0 Rw for Fo >4s(Fo) 6.70% z 0 R all 8.45% U iso (9) wr % Al occupancy (8) GooF Si occupancy (8) Nr. parameters 9 Space group P6 3 /mcm M2 Z 1 Wyckoff position 4 d F(000) 85 x Absorption coefficient 1.03 mm 1 y z 0 U iso (10) Al occupancy (8) Si occupancy (8) Unit-cell parameters a (Å) (6) Oxygen c (Å) (7) Wyckoff position 6 g V (Å 3 ) (9) x (6) y (6) z 0.25 U iso (9) 13

14 1. Keppler, H. & Frost, D. J. Introduction to minerals under extreme conditions. In Miletich, R. (ed.) Mineral Behaviour at Extreme Conditions, vol. 7 of Lecture Notes in Mineralogy, 1 30 (European Mineralogical Union, 2005). 2. Thomas, G. & Goringe, M. Transmission electron microscopy of materials (John Wiley and Sons, 1979). 3. Boffa Ballaran, T., Frost, D. J., Miyajima, N. & Heidelbach, F. The structure of a superaluminous version of the dense hydrous-magnesium silicate phase D. Am. Mineral. 95, (2010). 4. Litasov, K. D. et al. High hydrogen solubility in Al-rich stishovite and water transport in the lower mantle. Earth Planet. Sci. Lett. 262, (2007). 5. Panero, W. R. & Stixrude, L. P. Hydrogen incorporation in stishovite at high pressure and symmetric hydrogen bonding in δ-alooh. Earth Planet. Sci. Lett. 221, (2004). 6. Yang, H., Prewitt, C. T. & Frost, D. J. Crystal structure of the dense hydrous magnesium silicate, phase D. Am. Mineral. 82, (1997). 7. Sheldrick, G. M. A short history of SHELX. Acta Crystallographica Section A 64, (2008). 8. Farrugia, L. J. WinGX suite for small-molecule single-crystal crystallography. J. App. Cryst. 32, (1999). 14

Redox-induced lower mantle density contrast and effect on mantle structure and primitive oxygen

SUPPLEMENTARY INFORMATION DOI: 10.1038/NGEO2772 Redox-induced lower mantle density contrast and effect on mantle structure and primitive oxygen Tingting Gu, Mingming Li, Catherine McCammon and Kanani K.