Experimental investigation of the stability of Fe-rich carbonates in the lower mantle | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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

Type de publication:

Journal Article

Source:

Journal of Geophysical Research-Solid Earth, Volume 117 (2012)

ISBN:

0148-0227

Numéro d'accès:

WOS:000300231100001

URL:

http://www.agu.org/pubs/crossref/2012/2011JB008733.shtml

Mots-clés:

UMR 7154 ; Géobiosphère Actuelle et Primitive ; carbon cycle ; carbonates ; diamonds ; experimental geochemistry ; phase transition ; redox interaction

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.

Notes:

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