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1 SUPPLEMENTARY INFORMATION doi: /nature11294 Review of previous works on deep-liquid properties The major parameters controlling the buoyancy of deep-mantle melts are (i) the changes in atomic packing between solid and liquid phases that can contribute to a volume increase of 3-4 % 1,2, (ii) the Fe partitioning coefficient between solid and liquid mantle fractions and (iii) the MgO/SiO 2 ratio in the liquid phase 3. For a pyrolitic mantle composition, the evolution with pressure of the liquid MgO/SiO 2 ratio has been discussed previously, based on the nature of the solid phase at the liquidus 4 ; the liquidus phase changes from majoritic garnet 5 to ferropericlase 6 at GPa, before becoming Mg-Pv at ~32 GPa 7. Coexistence with the melt of crystalline Mg-Pv is expected to raise significantly the MgO/SiO 2 ratio in the melt, compared to the SiO 2 -rich melts found in the upper mantle 4. This should contribute to relatively denser liquids in the lower mantle 3. Moreover, the Fe partitioning coefficient between solid and liquid phases has been measured using large volume press apparatus up to ~35 GPa and varies from about 0.3 to 0.7 4,7-12 (Figure 4). On this basis, Fe is generally recognized as an incompatible element in the deep mantle, with a concentration of approximately 1.5 to 3 times higher in the melt. For lower mantle pressures, partitioning data on partially molten mantle materials are extremely scarce. Phase relations were recently investigated up to 160 GPa on samples recovered from LH-DAC 13. In this study, the authors used olivine as a starting material, Ar as a pressure transmitting medium in the LH-DAC experiments, and analyzed the recovered samples using highresolution field-emission-type EPMA. The authors report a decrease of D Fe from ~0.4 to ~0.07, with increasing pressures from 35 to 85 GPa, respectively. Then, they suggest that D Fe remains almost constant up to 160 GPa. This suggests an extremely strong incompatible character of Fe in the lowermost mantle, with a concentration ~14 times higher in the melt at 85 GPa. In order to corroborate their observations, the authors invoke an abrupt spin cross-over in the Fe-rich silicate melt. While they clearly demonstrate a spin transition at 300 K between 59 and 77 GPa during compression of a (Mg,Fe)SiO 3 glass, we note that their argument differs from another study showing that the spin cross-over in Fe should be progressive and extend over a large pressure range at high temperature 14. Discussion about potential Soret diffusion in our experiments One could invoke artefacts generated by chemical diffusion induced by strong thermal gradient such as those generated in the LH-DAC 15,16. The Soret effect can be particularly efficient to produce Fe heterogeneities when the sample configuration is not adequate. From an experimental point of view, great care was taken for (a) minimizing axial and vertical temperature gradients and (b) checking the sample homogeneity after laser heating. In a previous work devoted to the analysis of this effect, it has been shown that NaCl acts as a very good thermal insulator, especially when 1

2 RESEARCH SUPPLEMENTARY INFORMATION samples are coated with a thin metallic layer 16. While we used NaCl pressure medium, we did not coated our samples with metal, since it can be an additional source of chemical reactions with the sample. In their study on olivine, Nomura et al. 13 also avoided metallic coating. Another dominant parameter to prevent major axial temperature gradients is the thickness of the thermal insulator. In our experiments, X-ray diffraction evidences a major NaCl contribution at all sample positions (Figure 2a), a sign of good thermal insulation relative to the diamond anvils. Afterwards, we checked our samples and analyzed the chemical heterogeneities. Optical (Figure 1a) and XRF (Figure 3a and 3c, Suppl. Figures 1) observations evidence highest Fecontents at the centre of the laser hot spot (CLHS). Thus, Fe-diffusion took place toward the sample region heated to the highest temperature. Higher Fe concentration in the molten sample at the CLHS is compatible with the relatively incompatible behaviour of Fe (Figure 4). This observation is in sharp contrast with what can be expected in case of major Soret-diffusion, since Fe was reported to diffuse away from the peak temperature when a silicate samples is subject to excessive thermal gradients 16. While we can hardly say that there was no Soret diffusion at all in our samples, it is not a major cause of chemical segregation, and therefore major artefacts are most likely prevented. X-ray fluorescence results We present typical XRF patterns recorded in the two different region of interests that are the liquid (Liq.) and the Mg-Pv solid residue (Suppl. Figures 2 and 3). The measurement quality is very similar in both sample regions, at both beamlines. Together with the raw experimental spectra, we present a fit to the profiles optimized using the PyMCA software 17, which allows retrieving the XRF intensities emitted by each specific element. The fits yield the total XRF-intensities emitted by Fe in both Liq and Pv sample regions, together with their uncertainties (Suppl. Table 1). At each pixel, we obtained more than ~4 10 4, or ~ counts, with an uncertainty of less than 0.2%, or 0.6%, for Fe XRF-signal recorded at ID27, or ID21, respectively. The XRF mapping obtained with a spatial resolution of 0.5x0.5 microns shows chemical heterogeneities within the quenched-liquid ball at the CLHS (Suppl. Figure 3). These heterogeneities are most likely due to the rapid crystallization of the melt during quenching. Since the melt composition is intermediate between Mg-Pv, Ca-Pv and Fp, such mantle phases are expected to occur. Since Fp is known to be the richest in Fe 18, the regions with highest Fe-content within the CLHS are likely to be the ones where Fp grains have grown. It is also possible that other phases such as the so-called new aluminous phase appear in the CLHS upon quenching, due to the enriched liquid composition 19. Unfortunately, we could not analyze the phase content in the CLHS, because of very thin samples and probable phase amorphization during pressure release. We could not measure Mg, Si and Ca fluorescence with sufficient accuracy to draw major consequences for their repartition within the melted region. This is due to excessively low Mg and 2

3 SUPPLEMENTARY INFORMATION RESEARCH Si fluorescence energies and too low Ca-content in our starting material. At low energy, the XRF signals are strongly reabsorbed by any material. While the presence of a thin layer of NaCl pressure medium reduces XRF signals at all sample positions, presence of Fe within the sample could strongly reabsorb the XRF signal arising from Si and Mg in some sample areas, especially at the CLHS where the Fe-content is maximum. Based on the intensity of the Cl fluorescence signal, we estimated that the NaCl thickness can reach 10 µm at low pressures. It induces ~65% or ~20% absorption of the XRF signal intensity for Ca and Fe, respectively. At high pressures, a NaCl-layer of ~5 µm induces ~40% or ~10% absorption for Ca and Fe XRF signals, respectively. Beside these limitations, the chemical maps recorded at ID21 are compatible with a lower Ca content where X- ray diffraction shows a maximum of Mg-Pv. Electron probe micro-analyzes Some of our samples could be extracted from their gasket for electron probe micro-analyzes (Cameca SX100 using wavelength-dispersive spectrometry). Before EPMA analyzes, the NaCl pressure medium was removed by immersion in water (we note that dissolution of a very thin sample surface can occur, producing preferential leaching of some elements). We used accelerating voltage of 15 kv, beam current of 40 na, and a counting time of 10 sec. at each spectrometer positions. The EPMA calibration was based on wollastonite for Ca and Si, corundum for Al, forsterite for Mg and fayalite for Fe. No electron-beam damage was observed at the sample surface. Spatial resolution of the EPMA analyses is of ~1 micron. For the sample synthesized at 78.5 GPa and 3650 K, chemical analyses performed in sample regions corresponding to Mg-Pv, quenchedliquid and un-heated material are reported (Suppl. Table 2). A D Fe value of 0.56(3) was calculated, fully compatible with our XRF results of 0.5(5). 3

4 RESEARCH SUPPLEMENTARY INFORMATION References cited: 1 Mosenfelder, J. L., Asimow, P. D., Frost, D. J., Rubie, D. C. & Ahrens, T. J. The MgSiO 3 system at high pressure: Thermodynamic properties of perovskite, postperovskite, and melt from global inversion of shock and static compression data. Journal of Geophysical Research 114, B01203 (2009). 2 Stixrude, L., de Koker, N., Sun, N., Mookherjee, M. & Karki, B. B. Thermodynamics of silicate liquids in the deep Earth. Earth and Planetary Science Letters 278, , doi: /j.epsl (2009). 3 Funamori, N. & Sato, T. Density contrast between silicate melts and crystals in the deep mantle: An integrated view based on static-compression data. Earth and Planetary Science Letters 295, , doi: /j.epsl (2010). 4 Liebske, C., Corgne, A., Frost, D. J., Rubie, D. C. & Wood, B. J. Compositional effects on element partitioning between Mg-silicate perovskite and silicate melts. Contribution in Mineralogy and Petrology 149, (2005). 5 Ito, E. & Takahashi, E. Melting of peridotite at uppermost lower-mantle conditions. Nature 328, (1987). 6 Zhang, J. & Herzberg, C. Melting experiments on anhydrous peridotite KLB-1 from 5.0 to 22.5 GPa. Journal of Geophysical Research 99, (1994). 7 Ito, E., Kubo, A., Katsura, T. & Walter, M. J. Melting experiments of mantle materials under lower mantle conditions with implications for magma ocean differentiation. Physics of The Earth and Planetary Interiors , (2004). 8 Ohtani, E., Moriwaki, K., Kato, T. & Onuma, K. Melting and crystal-liquid partitioning in the system Mg2SiO4-Fe2SiO4 to 25 GPa. Physics of The Earth and Planetary Interiors 107, (1998). 9 Hirose, K., Shimizu, N., van Westrenen, W. & Fei, Y. Trace element partitioning in Earth's lower mantle and implications for geochemical consequences of partial melting at the coremantle boundary. Physics of the Earth and Planetary Interiors 146, (2004). 10 Walter, M. J., Nakamura, E., Trønnes, R. G. & Frost, D. J. Experimental constraints on crystallization differentiation in a deep magma ocean. Geochimica et Cosmochimica Acta 68, (2004). 11 Corgne, A., Liebske, C., Wood, B. J., Rubie, D. C. & Frost, D. J. Silicate perovskite-melt partitioning of trace elements and geochemical signature of a deep perovskitic reservoir. Geochimica et Cosmochimica Acta 69, (2005). 12 Tronnes, R. G. & Frost, D. J. Peridotite melting and mineral melt partitioning of major and minor elements at GPa. Earth and Planetary Science Letters 197, (2002). 13 Nomura, R. et al. Spin crossover and iron-rich silicate melt in the Earth's deep mantle. Nature 473, (2011). 14 Lin, J. F. et al. Spin transition zone in Earth's lower mantle. Science 317, , doi: /science (2007). 15 Lesher, C. E. & Walker, D. Cumulate maturation and melt migration in a temperature-gradient. Journal of Geophysical Research-Solid Earth and Planets 93, (1988). 16 Sinmyo, R. & Hirose, K. The Soret diffusion in laser-heated diamond-anvil cell. Physics of the Earth and Planetary Interiors, doi: /j.pepi (2010). 17 Solé, V. A., Papillon, E., Cotte, M., Walter, P. & Susini, J. A multiplatform code for the analysis of energy-dispersive X-ray fluorescence spectra. Spectrochimica Acta Part B: Atomic Spectroscopy 62, (2007). 18 Murakami, M., Hirose, K., Sata, N. & Ohishi, Y. Post-perovskite phase transition and mineral chemistry in the pyrolitic lowermost mantle. Geophysical Research Letters 32, L03304 (2005). 19 Miyajima, N., Fujino, K., Funamori, N., Kondo, T. & Yagi, T. Garnet-perovskite transformation under conditions of the Earth's lower mantle: an analytical transmission electron microscopy study. Physics of the Earth and Planetary Interiors 116, (1999). 4

5 SUPPLEMENTARY INFORMATION RESEARCH Supplementary Table 1: Details of the XRF analysis and its associated uncertainties Pressure (GPa) Sample Region Typical XRF pattern Intensity of Fe peaks Error of fit Statistical analysis of the XRF maps Number of points XRF Intensity (normalized) Standard deviation 41.5 Pv 4.1E+04 4.E Liq 6.9E+04 9.E Pv 7.4E+05 4.E Liq 1.2E+06 8.E Pv 4.0E+04 8.E Liq 7.4E+04 2.E Pv 5.5E+05 3.E Liq 8.3E+05 5.E Pv 3.9E+04 7.E Liq 7.1E+04 1.E Pv 2.8E+03 2.E Liq 5.3E+03 3.E Pv 2.3E+04 2.E Liq 4.8E+04 3.E Pv 4.0E+05 5.E Liq 6.7E+05 9.E Pv 4.2E+04 4.E Liq 7.5E+04 7.E Supplementary Table 2: Results of the EPMA analyses for the sample synthesized at 78.5 GPa. SiO 2 CaO FeO Al 2 O 3 MgO Pv 54.5 (8) 3.3 (5) 5.7 (3) 2.7 (2) 33.7 (7) Liq 63.2 (8) 4.7 (5) 10.3 (3) 5.1 (8) 16.8 (12) Bulk 51.0 (8) 3.5 (3) 8.2 (3) 4.1 (3) 33.3 (6) 5

6 RESEARCH SUPPLEMENTARY INFORMATION Supplementary Figure 1: Maps of the Fe-XRF emission intensity measured for the 9 samples considered in this study. They all present a region with a higher Fe-content located at the CLHS, which corresponds to the quenched liquid (Liq). This central region is surrounded by a region depleted in Fe, corresponding to the Al-bearing (Mg,Fe)SiO 3 perovskite (Pv). Our knowledge of this sample configuration is based on the analysis of the XRD signal (see Figure 3). Superimposed on the maps, we draw sample regions (Liq and Pv) where the statistical analysis of the Fe-XRF signals (Suppl. Table 1) provides mean values and standard deviations of the Fe-XRF intensities (Table 1). Colours (blue = minimum, red = maximum) represent the photon counts in the regions of interest of Fe for each pixel.. 6

7 SUPPLEMENTARY INFORMATION RESEARCH Supplementary Figure 2: Detailed analysis of the sample recovered after laser-heating at 57.5 GPa and 3250 K. An optical image of this sample is presented in the upper-left corner. The central frame presents a typical Fe-XRF map recorded at the ID27 beamline. Upper-right profile represents the changes in Fe-XRF emission intensity for a traverse across the grey area reported on the XRF-map. It is normalized to 1 for the highest Fe-intensity to enlighten changes in Fe-XRF amplitude between the CLHS and the surrounding sample regions. Left and right lower frames show typical XRF patterns recorded in the Liq and Pv sample regions, respectively. The Fe-XRF signal arises from more than photon counts at each pixel (Suppl. Table 1). 7

8 RESEARCH SUPPLEMENTARY INFORMATION Supplementary Figure 3: Detailed analysis of the sample synthesized at 105 GPa and 4150 K. The upper-right frame presents a typical Fe-XRF map recorded at the ID21 beamline. Upper-left profile represents the changes in Fe-XRF intensity for a traverse across the grey area reported on the XRFmap (normalized to 1 for the highest Fe-intensity). The left and right lower frames show typical XRF patterns recorded in the Liq and Pv sample regions, respectively. The XRF signal of Fe arise from more than counts at each pixel (Suppl. Table 1). A most noticeable feature is the chemical heterogeneity within the CLHS, as evidenced by significant changes in Fe-XRF intensities within the "Liq" zone of the XRF-profile. This feature is likely to be due to liquid crystallization in a mixture of Mg-Pv, Fp and Ca-Pv upon quenching. 8

9 SUPPLEMENTARY INFORMATION RESEARCH Supplementary Figure 4: Detailed analysis of the sample synthesized at 78.5 GPa and 3650 K. For this sample, we present spatial distributions of (a) the Al-bearing (Mg,Fe)SiO 3 perovskite content and (b) the Fe-XRF intensity. Integration of the Fe XRF intensity along the grey strip in (b) is presented in frame (c). The Fe-XRF intensity in the quenched-liquid at the CLHS is found about twice the value found in Mg-Pv. 9

10 RESEARCH SUPPLEMENTARY INFORMATION Supplementary Figure 5: Detailed analysis of the sample synthesized at 113 GPa and 4250 K. We present (a) an optical microphotograph and (b) spatial distributions of the Fe-XRF intensity. Integration of the Fe XRF intensity along the grey strip in (b) is presented in frame (c). 10