Physics
Scientific paper
Jun 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004pepi..143..291s&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 143, p. 291-304.
Physics
8
Scientific paper
We have measured the infrared spectra of two carbonates, FeCO3-siderite and MnCO3-rhodochrosite to pressures of 50GPa at 300K, and taken X-ray diffraction patterns of these phases before and after in-situ laser heating at pressures to 47GPa. Our infrared measurements primarily sample the vibrations of the CO3-2 carbonate unit, particularly its asymmetric stretching vibration and out-of-plane and in-plane bends. In particular, we wish to determine whether any high-pressure polymorphism (metastable or otherwise) is present in these phases. Our X-ray results for FeCO3 and MnCO3 demonstrate that the calcite structure is stable for each of these materials to 50GPa at 300K, and following heating to 2000K at pressures to 47GPa; similarly, within the infrared spectra, all vibrations are observed to shift monotonically with pressure, with no splitting observed. This behavior is in marked contrast to that of dolomite, in which splitting of the infrared vibrations is observed above ~20-30GPa. Our results demonstrate that carbonates are stable in the calcite structure at lower mantle pressures if the carbonates' divalent cations have zero pressure radii of less than 1Å. Accordingly, the crystal structure of carbonates within the lower mantle will critically depend on the amount of calcium that enters into carbonates within lower mantle assemblages.
Santillán Javier
Williams Quentin
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