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Title: Tetrahedrally Coordinated Carbonates in Earth¿s Lower Mantle

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Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 2041-1723
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nature Communications; Journal Volume: 6
Country of Publication:
United States

Citation Formats

Boulard, E, Pan, D, Galli, G, Liu, Z, and Mao, W. Tetrahedrally Coordinated Carbonates in Earth¿s Lower Mantle. United States: N. p., 2015. Web. doi:10.1038/ncomms7311.
Boulard, E, Pan, D, Galli, G, Liu, Z, & Mao, W. Tetrahedrally Coordinated Carbonates in Earth¿s Lower Mantle. United States. doi:10.1038/ncomms7311.
Boulard, E, Pan, D, Galli, G, Liu, Z, and Mao, W. 2015. "Tetrahedrally Coordinated Carbonates in Earth¿s Lower Mantle". United States. doi:10.1038/ncomms7311.
title = {Tetrahedrally Coordinated Carbonates in Earth¿s Lower Mantle},
author = {Boulard, E and Pan, D and Galli, G and Liu, Z and Mao, W},
abstractNote = {},
doi = {10.1038/ncomms7311},
journal = {Nature Communications},
number = ,
volume = 6,
place = {United States},
year = 2015,
month = 2
  • An increase in the ionic character in C-O bonds at high pressures and temperatures is shown by the chemical/phase transformation diagram of CO{sub 2}. The presence of carbonate carbon dioxide (i-CO{sub 2}) near the Earth's core-mantle boundary condition provides insights into both the deep carbon cycle and the transport of atmospheric CO{sub 2} to anhydrous silicates in the mantle and iron core.
  • Pressure-induced electronic spin-pairing transitions of iron and associated effects on the physical properties have been reported to occur in the lower-mantle ferropericlase, silicate perosvkite, and perhaps in post silicate perovskite at high pressures and room temperature. These recent results are motivating geophysicists and geodynamicists to reevaluate the implications of spin transitions on the seismic heterogeneity, composition, as well as the stability of the thermal upwellings of the Earth's lower mantle. Here we have measured the spin states of iron in ferropericlase and its crystal structure up to 95 GPa and 2000 K using a newly constructed X-ray emission spectroscopy andmore » diffraction with the laser-heated diamond cell. Our results show that an isosymmetric spin crossover occurs over a pressure-temperature range extending from the upper part to the lower part of the lower mantle, and low-spin ferropericlase likely exists in the lowermost mantle. Although continuous changes in physical and chemical properties are expected to occur across the spin crossover, the spin crossover results in peculiar behavior in the thermal compression and sound velocities. Therefore, knowledge of the fraction of the spin states in the lower-mantle phases is thus essential to correctly evaluate the composition, geophysics, and dynamics of the Earth's lower mantle.« less
  • The equations of state of perovskite with (Mg{sub 0.75},Fe{sub 0.25})SiO{sub 3} and MgSiO{sub 3} compositions have been investigated by synchrotron X-ray diffraction up to 130 GPa at 300 K in diamond anvil cells. Here we show that the addition of 25% Fe in MgSiO{sub 3} perovskite increases its density and bulk sound velocity (V{phi}) by 4-6% and 6-7%, respectively, at lower-mantle pressures. Based on concurrent synchrotron X-ray emission and Moessbauer spectroscopic studies of the samples, the increase in V{phi} and density can be explained by the occurrence of the low-spin Fe3+ and the extremely high-quadrupole component of Fe{sup 2+}. Combiningmore » these experimental results with thermodynamic modeling, our results indicate that iron-rich perovskite can produce an increase in density and a value of V{phi} that is compatible with seismic observations of reduced shear-wave velocity in regions interpreted as dense, stiff piles in the lower mantle. Therefore, the existence of the Fe-rich perovskite in the lower mantle may help elucidate the cause of the lower-mantle large low-shear-velocity provinces (LLSVPs) where enhanced density and V{phi} are seismically observed to anti-correlate with the reduced shear wave velocity.« less