Ja. Dalton et Bj. Wood, THE STABILITY OF CARBONATE UNDER UPPER-MANTLE CONDITIONS AS A FUNCTION OF TEMPERATURE AND OXYGEN FUGACITY, European journal of mineralogy, 7(4), 1995, pp. 883-891
The stability of carbonate in the upper-mantle is a function of oxygen
fugacity. Carbon-carbonate buffers such as EMOG (enstatite-magnesite-
olivine-graphite) provide a lower fO(2) limit for carbonate stability.
We have experimentally calibrated, for mantle compositions, the posit
ion of the carbonate-oxide equilibrium: GRAPHICS at 20 kbar and 1000
degrees C at graphite saturation. This equilibrium constrains the upp
er fO(2) limit for carbonate stability given that Fe contents are much
less than Mg in both carbonate and spinel. We find that the experimen
tal results are in good agreement with calculations based on existing
thermodynamic data. Using appropriate upper-mantle compositions and ac
tivity models for carbonate and spinel, we are thus able, at any press
ure, to constrain the stability field of carbonate as a function of te
mperature and oxygen fugacity. The calculated stability field is gener
ally compatible with current estimates of upper-mantle fO(2) (FMQ +/-
1.5 log units). In P-T-fO(2) space the upper temperature limit of carb
onate stability is controlled by intersection of carbon-carbonate and
carbonate-oxide oxygen buffer planes. With decreasing magnetite activi
ty the carbonate stability field is restricted to lower temperatures r
esulting in a shift in the carbonate stability field. At upper-mantle
pressure carbonate melts can only be produced without the carbonate br
eaking down when the fO(2) is above FMQ-0.5 log units.