Journal
PHYSICS OF THE EARTH AND PLANETARY INTERIORS
Volume 168, Issue 3-4, Pages 191-203Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.pepi.2008.06.018
Keywords
magnesite; equation of state; synchrotron X-ray diffraction; mantle; subduction
Categories
Funding
- Ministry of Education, Culture, Sports, Science and Technology, Japan [14102009, 16075202]
- Japan Society for Promotion of Science [17740344]
- Carnegie/Department of Energy Alliance Center (CDAC) [DE-FC03-03NA0014]
- NSF [EAR 051055]
- Grants-in-Aid for Scientific Research [17740344, 14102009, 16075202] Funding Source: KAKEN
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Pressure-volume-temperature relations have been measured to 32 GPa and 2073 K for natural magnesite (Mg(0.975)Fe(0.015)Mn(0.006)Cao(0.004)CO(3)) using synchrotron X-ray diffraction with a multianvil apparatus at the SPring-8 facility. A least-squares fit of the room-temperature compression data to a third-order Birch-Murnaghan equation of state (EOS) yielded K-0 = 97.1 +/- 0.5 GPa and K' = 5.44 +/- 0.07, with fixed V-0 = 279.55 +/- 0.02 A(3). Further analysis of the high-temperature compression data yielded the temperature derivative of the bulk modulus (partial derivative K-T/partial derivative T)(P) = -0.013 +/- 0.001 GPa/K and zero-pressure thermal expansion alpha = a(0) + a(1) T with a(0) = 4.03 (7) x 10(-5) K-1 and a(1) = 0.49 (10) x 10(-8) K-2. The Anderson-Gruneisen parameter is estimated to be delta(T) = 3.3. The analysis of axial compressibility and thermal expansivity indicates that the c-axis is over three times more compressible (K-TC = 47 +/- 1 GPa) than the a-axis (K-TC = 157 +/- GPa), whereas the thermal expansion of the c-axis (a(0) = 6.8 (2) X 10(-5) K-1 and a(1) = 2.2 (4) x 10(-8) K-2) is greater than that of the a-axis (a(0) = 2.7 (4) x 10(-5) K-1 and a(1) = -0.2 (2) x 10(-8) K-2). The present thermal EOS enables us to accurately calculate the density of magnesite to the deep mantle conditions. Decarbonation of a subducting oceanic crust containing 2 wt.% magnesite would result in a 0.6% density reduction at 30 GPa and 1273 K. Using the new EOS parameters we performed thermodynamic calculations for magnesite decarbonation reactions at pressures to 20 GPa. We also estimated stability of magnesite-bearing assemblages in the lower mantle. (C) 2008 Elsevier B.V. All rights reserved.
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