Research ArticleEARTH SCIENCES

Recovery of an oxidized majorite inclusion from Earth’s deep asthenosphere

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Science Advances  07 Apr 2017:
Vol. 3, no. 4, e1601589
DOI: 10.1126/sciadv.1601589
  • Fig. 1 Majoritic inclusions in garnet with Raman spectra.

    (A) Backscattered electron (BSE) image of majorite inclusion (Maj) in the host garnet (Grt-II). (B) Superposed Fe and Al x-ray mapping shows higher Fe and lower Al contents in majorite inclusion than those in the host garnet. (C) The Raman spectrum of the inclusion in garnet compared with that of the synthetic majorite and garnet (Grt-I or Grt-II).

  • Fig. 2 Mössbauer spectrum and XRD pattern of the separated majorite inclusions.

    (A) The fitted Mössbauer spectrum, yielding quadrupole splittings and isomer shifts of 3.567(9) and 1.275(5) mm/s for Fe2+, respectively, and 0.580(3) and 0.388(2) mm/s for Fe3+, respectively. The area fraction Fe3+/∑Fe is 0.81(1). (B) XRD pattern of the separated inclusions, labeled with Miller indices (hkl). The vertical ticks at the bottom of the diffraction pattern indicate the calculated peaks with a cubic unit cell parameter, a = 11.5675 Å.

  • Fig. 3 Estimated pressures for the formation of the majoritic garnets.

    The relationship between pressure and composition parameter XcatMj defined by Collerson et al. (6) is experimentally determined for Fe3+-bearing majorite. The crosses represent the experimental data of the synthetic majorites (table S1). The solid line represents the best fit to the data with an average Fe3+/∑Fe of 0.55. The calculated pressures for the natural samples are indicated by solid hexagons. The relationship between pressure and cation substitutions in the majoritic garnet without considering the effect of ferric iron (6) is also shown for comparison (dashed line).

  • Table 1 Compositions of garnets (Grt-I and Grt-II) and majorite.

    Compositions for synthetic majorites at 12.5 and 14 GPa are also listed for comparison.

    Natural samplesSynthetic majorite
    Grt-I(6)*Grt-II(4)Majorite(6)P = 12.5 GPaP = 14 GPa
    SiO240.31(17)42.40(46)44.20(38)43.89(24)44.03(16)
    TiO20.06(4)0.10(2)0.10(2)00
    Al2O322.54(21)22.13(118)7.09(41)10.75(65)10.80(93)
    Cr2O30.04(4)1.09(85)1.10(44)1.69(5)1.61(9)
    FeO17.05(24)7.71(9)18.47(103)15.94(75)15.58(81)
    MnO0.71(11)0.30(3)0.32(5)00
    MgO11.39(27)20.79(35)27.16(28)25.10(22)25.25(16)
    CaO8.01(27)5.06(43)1.35(32)1.28(7)1.31(4)
    Na2O0.02(1)0.02(1)0.03(1)00
    Total100.14(29)99.60(20)99.83(6)98.71(33)98.63(32)
    Cations per 12 oxygen atoms§
    Si3.003(11)3.014(36)3.181(28)3.192(8)3.199(19)
    Ti0.003(2)0.006(1)0.005(1)00
    Al1.979(13)1.854(97)0.602(35)0.921(52)0.925(76)
    Cr0.002(2)0.061(48)0.063(25)0.097(3)0.092(5)
    Fe3+0.005(15)0.046(32)0.963(69)0.598(44)0.585(46)
    Fe2+1.057(5)0.413(39)0.148(54)0.371(9)0.362(17)
    Mn0.045(7)0.018(2)0.020(3)00
    Mg1.265(27)2.203(38)2.914(26)2.721(14)2.735(12)
    Ca0.639(23)0.385(31)0.104(24)0.100(5)0.102(4)
    Na0.003(1)0.002(1)0.004(2)00
    Fe3+/∑Fe0.02(2)0.11(8)0.87(5)0.62(2)0.62(2)
    XcatMj0.022(10)0.193(29)0.192(21)0.199(32)
    P(GPa)||6.4(0.4)12.9(1.1)12.9(0.8)13.2(1.3)

    *Number of electron microprobe analyses.

    †1 SD in the rightmost digit.

    ‡Total iron oxide.

    §Fe3+ and Fe2+ are calculated using the charge balance method.

    XcatMj = 0.5 × (XMj1 + XMj2), where XMj1 = (Si + Ti − 3) + Na and XMj2 = 1 − 0.5 × (Al + Cr + Fe3+) + 1.25 × Na.

    ||The pressures were calculated using our calibrated equation P(GPa) = 5.61 + (37.98 × XcatMj), with Fe3+/∑Fe ~ 0.55.

    • Table 2 The indexed peaks of the XRD pattern of the majorite (Mj) inclusion and synthetic majorite recovered from 14 GPa.

      The calculated d spacings (dcalc) with a cubic unit cell parameter, a = 11.5675(2) Å, agree well with the observed d spacings (dobs) for the natural majorite inclusion. The synthetic majorite has a comparable unit cell parameter, a = 11.5688(54) Å.

      Natural MjSynthetic Mj
      hkldobs (Å)dcalc (Å)dobsdcalc (Å)dobs (Å)
      4002.89212.89190.00022.8957
      4202.58622.5866−0.00042.5912
      3322.46672.46620.00052.4627
      4222.36132.36120.00012.3615
      4312.26862.26860.00002.2742
      5212.11222.11190.00032.1116
      4402.04482.0449−0.0001
      5321.87671.87650.00021.8759
      6201.82901.82900.00001.8324
      4441.66971.66960.00011.6704
      6401.60411.60410.00001.6033
      6421.54571.5458−0.00011.5456
      8001.44591.44590.00001.4465
      7411.42421.42390.00031.4223
      6531.38231.3826−0.00031.3821
      8401.29331.29330.00001.2928
      8421.26201.2621−0.00011.2624
      7611.24741.24740.00001.2471
      6641.23321.23310.00011.2337
      8511.21931.21930.00001.2188
      8531.16851.16850.00001.1674
      10201.13431.13430.00001.1345
      8641.07391.0740−0.00011.0734
      10421.05611.05600.00011.0556
      8801.02241.02240.00001.0226

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1601589/DC1

      table S1. Compositions of synthetic majorites.

      fig. S1. Field observations of eclogite xenoliths associated with carbonatite in the North China Craton.

      fig. S2. BSE image of a representative run product at 12.5 GPa and 1600°C, showing the majoritic garnet (Maj) in equilibrium with pyroxene (Px) and olivine (Ol).

    • Supplementary Materials

      This PDF file includes:

      • table S1. Compositions of synthetic majorites.
      • fig. S1. Field observations of eclogite xenoliths associated with carbonatite in the North China Craton.
      • fig.S2. BSE image of a representative run product at 12.5 GPa and 1600°C, showing the majoritic garnet (Maj) in equilibrium with pyroxene (Px) and olivine (Ol).

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