Research ArticleGEOPHYSICS

Stability of Fe,Al-bearing bridgmanite in the lower mantle and synthesis of pure Fe-bridgmanite

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Science Advances  15 Jul 2016:
Vol. 2, no. 7, e1600427
DOI: 10.1126/sciadv.1600427
  • Fig. 1 Stability fields of skiagite garnet, oxides, and bridgmanite.

    Ski, skiagite-majorite garnet Fe2+3(Fe2+0.234(2)Fe3+1.532(1)Si4+0.234(2))(SiO4)3 (25); open triangle with cross, mixture of stishovite (St, SiO2), Fe1−xO, and Fe4O5; empty triangles, mixture of stishovite and Fe4O5. Solid symbols correspond to conditions of the experiments on Mg0.86Fe0.14Al0.04Si0.96O3 (FE14, squares), Mg0.83Fe0.17Al0.06Si0.94O3 (FE17, triangle), and Mg0.60Fe0.40Si0.63Al0.37O3 (FE40, circle) described in table S1. Open circles show conditions at which pure iron bridgmanite (Fe2+0.64(2)Fe3+0.24(2)Si1.00(3)O3) was synthesized. The dark gray area marks pressure-temperature conditions at which experiments on Fe,Al-bearing bridgmanite were conducted. Red solid curve, expected lower mantle geotherm (46). Error bars indicate experimental uncertainty in pressure and temperature.

  • Fig. 2 Examples of parts of the two-dimensional wide-scan x-ray diffraction images of bridgmanite Mg0.86Fe0.14Al0.04Si0.96O3.

    (A to D) Data were collected (A) before and (B to D) after laser heating at the indicated temperatures and pressures. Indices are given for bridgmanite reflections (underlined by boxes). The only observed changes in diffraction patterns upon heating are due to development of additional domains of the same phase (marked in red). Large black spots are due to diamond (D) reflections. Diffraction rings of Ne (pressure transmitting medium), Re (gasket), and Au are also marked. Data were collected at IDD-13 at APS. Yellow circles indicate bad pixels of the detector. (Full high-resolution images are also given in the Supplementary Materials).

  • Fig. 3 Compressibility of (Fe2+0.64(2)Fe3+0.24(2))Si1.00(3)O3 silicate perovskite.

    (A) Unit cell volumes of single crystals of pure iron bridgmanite synthesized at different pressures were measured on compression (red dots with error bars) and decompression (red triangles with error bars). The data are fitted (solid dark red line) with a Birch-Murnaghan equation of state, giving bulk modulus of K300 = 190(4) GPa and unit cell volume at ambient conditions V0 = 178.98(6) Å (K′ = 4). For comparison, compressional curves of pure MgSiO3 (solid purple line) (32, 47), (Mg0.6,Fe0.4)(Si0.63Al0.37)SiO3 (dotted-dashed green line) (12, 34), and (Mg0.86,Fe0.14)(Si0.94Al0.06)SiO3 (dashed dark-blue line) are shown (see also table S3). Insert shows model of perovskite-structured orthorhombic (space group Pbmn, no. 62) bridgmanite with two distinct cation coordinations: distorted bicaped prisms (A-site, brown) and octahedra (B-site, blue). (B) Dependence of A- and B-site polyhedral volumes as a function of unit cell volume for bridgmanite with different compositions (see text for more details and references).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/7/e1600427/DC1

    fig. S1. Parts of the integrated diffraction images of bridgmanite Mg0.86Fe0.14Al0.04Si0.96O3 (FE14) collected before (lower curve) and during (upper curve) laser heating.

    fig. S2. Full high-resolution 2D wide-scan x-ray diffraction images of bridgmanite samples FE14, FE17, and FE40.

    fig. S3. Representative polyhedral structural model of orthorhombic bridgmanite.

    fig. S4. Backscattered electron image of skiagite starting composition at 23 GPa and 1600°C (run S6151).

    fig. S5. Typical powder x-ray diffraction patterns of skiagite-majorite garnet that was laser-heated at different pressures and temperatures (St, stishovite; hFe3O4, orthorhombic CaTi2O4-type Fe3O4; Pv, perovskite-structured phase).

    fig. S6. Crystal structure of Fe4O5 obtained as the product of decomposition of skiagite-majorite garnet in a laser-heated DAC at 39(1) GPa and 2250(100) K (see table S4 for crystallographic data).

    fig. S7. Variation with pressure of the normalized unit-cell parameters for three bridgmanites—Fe-bridgmanite (this study), (Mg0.96,Fe0.04)SiO3 (32), and Mg0.60Fe0.40Si0.63Al0.37O3 (12).

    fig. S8. Effect of FeASiO3, FeAAlBO3, and Fe3+,A2/3SiO3 substitutions in bridgmanite on the bulk modulus (“A” and “B” denote structural positions; see table S3 for references).

    table S1. Crystallographic data for Fe,Al bridgmanite samples FE14, FE17, and FE40 at selected pressures before and after laser heating at different temperatures.

    table S2. Crystallographic data for (Fe2+0.64(2)Fe3+0.24(2))Si1.00(3)O3 bridgmanite at selected pressures.

    table S3. Compressibility of bridgmanite with different compositions.

    table S4. Crystallographic data of Fe4O5.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Parts of the integrated diffraction images of bridgmanite Mg0.86Fe0.14Al0.04Si0.96O3 (FE14) collected before (lower curve) and during (upper curve) laser heating.
    • fig. S2. Full high-resolution 2D wide-scan x-ray diffraction images of bridgmanite samples FE14, FE17, and FE40.
    • fig. S3. Representative polyhedral structural model of orthorhombic bridgmanite.
    • fig. S4. Backscattered electron image of skiagite starting composition at 23 GPa and 1600°C (run S6151).
    • fig. S5. Typical powder x-ray diffraction patterns of skiagite-majorite garnet that was laser-heated at different pressures and temperatures (St, stishovite; hFe3O4, orthorhombic CaTi2O4-type Fe3O4; Pv, perovskite-structured phase).
    • fig. S6. Crystal structure of Fe4O5 obtained as the product of decomposition of skiagite-majorite garnet in a laser-heated DAC at 39(1) GPa and 2250(100) K (see table S4 for crystallographic data).
    • fig. S7. Variation with pressure of the normalized unit-cell parameters for three bridgmanites—Fe-bridgmanite (this study), (Mg0.96,Fe0.04)SiO3 (32), and Mg0.60Fe0.40Si0.63Al0.37O3 (12).
    • fig. S8. Effect of FeASiO3, FeAAlBO3, and Fe3+,A2/3SiO3 substitutions in bridgmanite on the bulk modulus ("A" and "B" denote structural positions; see table S3 for references).
    • table S1. Crystallographic data for Fe,Al bridgmanite samples FE14, FE17, and FE40 at selected pressures before and after laser heating at different temperatures.
    • table S2. Crystallographic data for (Fe2+0.64(2)Fe3+0.24(2))Si1.00(3)O3 bridgmanite at selected pressures.
    • table S3. Compressibility of bridgmanite with different compositions.
    • table S4. Crystallographic data of Fe4O5.

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