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Article Dans Une Revue Journal of Geophysical Research : Solid Earth Année : 2012

Experimental investigation of the stability of Fe-rich carbonates in the lower mantle

Jean-Philippe Perrillat
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Résumé

The fate of carbonates in the Earth's mantle plays a key role in the geodynamical carbon cycle. Although iron is a major component of the Earth's lower mantle, the stability of Fe-bearing carbonates has rarely been studied. Here we present experimental results on the stability of Fe-rich carbonates at pressures ranging from 40 to 105 GPa and temperatures of 1450-3600 K, corresponding to depths within the Earth's lower mantle of about 1000-2400 km. Samples of iron oxides and iron-magnesium oxides were loaded into CO2 gas and laser heated in a diamond-anvil cell. The nature of crystalline run products was determined in situ by X-ray diffraction, and the recovered samples were studied by analytical transmission electron microscopy and scanning transmission X-ray microscopy. We show that Fe-(II) is systematically involved in redox reactions with CO2 yielding to Fe-(III)-bearing phases and diamonds. We also report a new Fe-(III)-bearing high-pressure phase resulting from the transformation of FeCO3 at pressures exceeding 40 GPa. The presence of both diamonds and an oxidized C-bearing phase suggests that oxidized and reduced forms of carbon might coexist in the deep mantle. Finally, the observed reactions potentially provide a new mechanism for diamond formation at great depth.
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Dates et versions

hal-00720913 , version 1 (07-01-2013)

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E. Boulard, N. Menguy, Anne-Line Auzende, K. Benzerara, H. Bureau, et al.. Experimental investigation of the stability of Fe-rich carbonates in the lower mantle. Journal of Geophysical Research : Solid Earth, 2012, 117, pp.B02208. ⟨10.1029/2011JB008733⟩. ⟨hal-00720913⟩
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