Carbon-fluid equilibria and the oxidation state of the upper mantle

摘要: IT has been proposed that the oxidation state of Earth's upper mantle is buffered by C–O fluids in equilibrium with elemental carbon1,2. A large body data on oxygen fugacities (fo2) recorded rocks and their derivative melts now allows us to test this proposal. By comparing measured fo2 values those calculated for carbon–CO2–CO–carbonate equilibria along appropriate geotherms, we find be wholly consistent hypothesis. Moreover, variation temperature pressure accounts much observed correlation between samples tectonic provenance3,4. The apparent buffering requires modest quantities carbon fluid, which do not exceed independently estimated values. proposal compromised if parts are fluid-undersatu rated, or fluid phase diluted other volatile.