Details

Autor(en) / Beteiligte

• Stagno, V.
• Tange, Y.
• Miyajima, N.
• McCammon, C. A.
• Irifune, T.
• Frost, D. J.

Titel

The stability of magnesite in the transition zone and the lower mantle as function of oxygen fugacity

Ist Teil von

• Geophysical research letters, 2011-10, Vol.38 (19), p.n/a

Ort / Verlag

Washington, DC: Blackwell Publishing Ltd

Erscheinungsjahr

2011

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The oxygen fugacity at which magnesite (MgCO3) is reduced to diamond in a typical mantle assemblage has been determined between 16 and 45 GPa and 1500–1700°C in experiments employing a multianvil device. This oxygen fugacity for carbonate stability, measured using a sliding redox sensor that employs IrFe alloy, was found to be greater than 2 log units above the iron‐wüstite oxygen buffer (ΔIW+2). Reversal experiments employing FeNi alloy confirmed complete oxidation of Ni in the presence of magnesite and diamond even at 45 GPa. As the oxygen fugacity of the transition zone and lower mantle is most likely at or below the IW buffer, mantle carbon, if distributed relatively homogeneously, is unlikely to be hosted in carbonates throughout most of the mantle but is more likely present as diamond, methane, Fe‐rich carbide or as a carbon‐component dissolved in Fe‐Ni metal. The existence of carbonate at these depths would imply the presence of unusually oxidized regions of the deeper mantle. Such regions could form in the deeper mantle from an influx of subduction related carbonate melt, which would reduce by causing oxidation of the surrounding silicates. Due to changes in the degree of oxidation of the surrounding mantle such melts could potentially travel further in the transition zone mantle than in the lower mantle. The results do not exclude the possibility that carbonate could coexist with Fe‐Ni metal or carbide at the very base of the lower mantle. Key Points Oxygen fugacity required for magnesite being stable at high pressure conditions Ferric iron content of mantle minerals coexisting with diamond and magnesite Redox reactions involving ferric iron bearing minerals and diamond/magnesite