Stability of hydrous silicate at high pressures and water transport to the deep lower mantle

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1 Stability of hydrous silicate at high pressures and water transport to the deep lower mantle Supplementary Figure 1: Compositions of dense hydrous magnesium silicates on the H2O-MgO-SiO2 diagram. PhH, phase H; PhD, phase D; PhA, phase A; shb super hydrous phase B; Pv, MgSiO3 perovskite. DHMSs phases A G and superhydrous phase B have been reported 8. However, phase F and phase G were found to be identical to phase D 27, and it has been common practice that these three phases are called phase D. We named the new DHMS phase discovered here phase H to avoid possible confusion, as the names phase F and phase G were already used elsewhere, although these phases do not actually exist. NATURE GEOSCIENCE 1

2 Supplementary Figure 2: X-ray diffraction patterns of phase H at 42.0 GPa and 1000 C. The diffraction peaks were obtained by assuming orthorhombic symmetry with a space group P21nm (red lines), and cell parameters with theoretically predicted monoclinic symmetry (sub blue lines) are shown for comparison. PhH, phase H; St, stishovite; Br, brucite; Pe, periclase; D, phase D; *, Characteristic lines of Au (67.0 kev and 68.9 kev) and La (33.0 kev, 33.4 kev, and 37.8 kev). 2 NATURE GEOSCIENCE

3 SUPPLEMENTARY INFORMATION Supplementary Figure 3: Plots of Si and Mg against Al, based on 4 Oxygens showing the Tschermak substitution between phase H and -AlOOH (Si 4+ + M g2+ 2Al 3+ ). NATURE GEOSCIENCE 3

4 Supplementary Figure 4: Cross-sections of the sample assemblages used for quench experiments and in situ X-ray diffraction measurements. 4 NATURE GEOSCIENCE

5 SUPPLEMENTARY INFORMATION Supplementary Table 1: Experimental conditions and run products Run No. Mg(OH) 2 :SiO 2 : P (GPa) T ( C) t (hour) Run products in-situ, MgSiH 2 O 4 (Ph H) M : PhH M : PhH, Br*, St* quench, MgSi 1.5 H 2 O 5 (Ph D) MII193D 1 : PhD, Pe* MII197D 1 : Pv, St, Br, fluid MII213D 1 : PhD, PhH, St MII198D 1 : Pv, St, fluid MII203D 1 : PhH, St MII196D 1 : Pv, St, fluid quench, MgSiH 2 O 4 (Ph H) MII193H 1 : PhD, Br, Pe MII204H 1 : PhD, Br, Pv, fluid MII201H 1 : PhH, Pv* MII198H 1 : Pv, fluid MII199H 1 : PhH, Pe*, Pv* PhH, phase H; PhD, phase D; St, Stishovite; Br, Brucite; Pv, perovskite; *, trace amount. NATURE GEOSCIENCE 5

6 Supplementary Table 2: Experimental conditions and chemical compositions of phase H, phase D, and MgSiO 3 perovskite in the system Mg(OH) 2 -SiO 2 -Al 2 O 3 Run No. P (GPa) T ( C) Run products (chemical compositions) Partition MII214A 1) H ( Mg 0.49 Al 0.77 Si 0.58 H 2.4 O 4 ), Pv ( Mg 0.9 Al 0.16 Si 0.93 O 3 ) Al H /Al Pv = ~3.6 MII213A 2) H ( Mg 0.60 Al 0.71 Si 0.65 H 2.1 O 4 ), Pe*, St* MII199A 3) H ( Mg 0.26 Al 1.24 Si 0.33 H 2.4 O 4 ), D ( Mg 0.77 Al 0.27 Si 1.08 H 3.3 O 5 ), St Al H /Al D = ~6 The solubility of -AlOOH into phase H was investigated using the starting materials with various amounts of Al 2 O 3 added to the mixtures of Mg(OH) 2 and SiO 2. We confirmed that phase H can accommodate the -AlOOH component up to ~70 %. It is also found that alumina can be strongly partitioned into phase H relative to MgSiO 3 perovskite and phase D. Starting compositions: 1, 2) Mg(OH) 2 : SiO 2 : Al 2 O 3 = 1 : 1 : 1, 3) Mg(OH) 2 : SiO 2 : Al 2 O 3 = 1 : 2 : 0.5. Heating durations were 3-9 hours. H, aluminous phase H; D, aluminous phase D; Pv, MgSiO 3 perovskite; St, Stishovite; Pv, perovskite; *, trace amount; Al H, mol fraction of Al in aluminous phase H; Al D, mol fraction of Al in aluminous phase D; Al Pv, mol fraction of Al in perovskite. 6 NATURE GEOSCIENCE

7 SUPPLEMENTARY INFORMATION Supplementary Notes: X-ray diffraction pattern of phase H A clear X-ray profile of phase H at ambient conditions was only obtained immediately after pressure release (Fig. 3E), and the diffraction peaks weakened with time after retrieval from the high-pressure cell. Moreover, attempts to observe the electron diffraction pattern with a transmission electron microscope failed because of rapid amorphization of the sample during observations. Formation of phase H in the subducting plates Phase H should be formed by the reaction of phase D and MgO periclase somewhere between ~33 and 48 GPa if MgO-saturated systems such as pyrolite are assumed, while the direct transformation of phase D to phase H plus stishovite is expected to occur at pressures of ~48 GPa in MgO-undersaturated systems such as oceanic and continental crusts, which are more relevant to the present composition (A). Supplementary references: 28. Liu, L. Irifune, T. Comment on A new hydrous silicate, a water reservoir, in the upper part of the lower mantle by Eiji Ohtani, Hiroki Mizobata, Yasuhiro Kudoh, Toshiro Nagase, Haruo Arashi, Hisayoshi Yurimoto, and Isoji Miyagi. Geophy. Res. Lett. 25, 979 (1998). NATURE GEOSCIENCE 7