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Static compressibility of magnesite to 20 GPa: Implications for MgCO 3 in the lower mantle
Author(s) -
Redfern S. A. T.,
Wood B. J.,
Henderson C. M. B.
Publication year - 1993
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/93gl02507
Subject(s) - magnesite , mantle (geology) , compressibility , bulk modulus , geology , solidus , thermodynamics , transition zone , mineralogy , materials science , geochemistry , physics , magnesium , composite material , alloy , metallurgy
The bulk modulus of MgCO 3 magnesite has been measured to 20 GPa at room temperature using X‐ray powder diffraction. Since the response to pressure is primarily compression of the MO 6 octahedron, magnesite is substantially less compressible than Ca‐carbonates of similar structure type. Using the Birch equation of state, with K T′ of 4.0, we obtain K T of 142 (±9) GPa at room temperature. The full Birch‐Murnaghan equation of state yields K T of 151 (±7) GPa and K T′ of 2.5. These results, together with other thermodynamic data, have been applied to calculate the stability of magnesite under lower mantle conditions. Assuming lower‐mantle saturation in (Mg,Fe)O, magnesite should be stable to temperatures well in excess of 6000 K at the core‐mantle boundary, i.e. at least up to the solidus of peridotitic or pyroxenitic compositions. This confirms that magnesite is a stable host for carbon in the mantle.