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| Titel |
Experimental study of carbonate-silicate-metal equilibria at pressures to 30 GPa: New insights into deep volatile cycles |
| VerfasserIn |
Konstantin Litasov, Anton Shatskiy, Yingwei Fei, Eiji Ohtani |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038165
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| Zusammenfassung |
| Carbon and hydrogen are among the most important, but uncertain constituents
in the Earth’s deep interior. In this presentation we will review resent results on
carbonate-silicate-metal equilibria at pressures up to about 30 GPa using multianvil
technique. In situ X-ray diffraction experiments were performed at the synchrotron radiation
facility SPring-8. We have studied the following systems: MgCO3+SiO2, CaCO3+SiO2,
MgCO3+Fe, and CaCO3+Fe. Preliminary results from in situ measurements for the
MgCO3+H2O+Fe and CaCO3+H2O+Fe systems and from laboratory experiments on
peridotite and eclogite, coexisting with ultra-reduced C-O-H fluids, will also be
discussed.
The reaction of MgCO3+SiO2 = MgSiO3+CO2 was studied using both the multianvil and
diamond anvil cell (DAC) technique. We observed melting reaction at pressures up to about
32 GPa. Decarbonation was observed at pressures below 6 GPa and, surprisingly, in the short
pressure interval of wadsleyite + stishovite stability (in MgSiO3 system) near 16 GPa. In all
other experiments reaction proceeds with the formation of MgSiO3 phase and melt. The
Mg/Si ratio of partial melt, coexisting with Mg-perovskite, was 1.7-2.0, whereas at lower
pressures this ratio is 2.3-2.5. Formation of Mg-perovskite was observed in DAC
experiments at pressures 25-100 GPa, however, CO2 was not detected by in situ X-ray
diffraction or in situ Raman spectroscopy, which may indicate melting reaction at
higher pressure also. The reaction CaCO3+SiO2 = CaSiO3+CO2 was studied at
pressures 3-22 GPa. In contrast to the Mg-system we observed the formation of
CO2 fluid at 6-10 GPa and melting at 16-17 GPa. The partial melt has a Ca/Si ratio
of 2.3-3.0. The reactions MgCO3+Fe and CaCO3+Fe were also studied at 6 and
15-16 GPa. We observed fast formation of Fe3C in the Mg-system at 900-1000oC,
according to the reaction MgCO3+5Fe=Fe3C+3(Fe0.67Mg0.33)O. In the Ca-system the
reaction proceeds with formation of Fe3C and Ca-rich melt with a Ca/Fe ratio of near
4.
In discussion, we outline (a) relative stability of Fe-hydride and Fe-carbide and their role
in core formation and metal precipitation, (b) possibility of carbonate reduction during deep
subduction, (c) possible role of melting in COH-fluid equilibria with mantle assemblages, (d)
comparison of mantle solidi under reduced and oxidized conditions up to lower mantle P-T
conditions. |
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