The carbon speciation in the Earth’s interior as function of pressure, temperature and oxygen fugacity
type: CreativeWork
description: The redox state of the Earth’s interior will influence the speciation of volatile elements both in the mantle and in mantle derived magmas. Carbon is one of the principal elements to be affected in this way because under reducing conditions it forms graphite or diamond, and under oxidizing conditions carbonate (or CO2-bearing) minerals and melts. The cycling and residence time of carbon in the mantle can be strongly effected by the oxygen fugacity because reduced phases such as diamond and graphite are immobile and likely to remain within the mantle and potentially within subducting slabs, while at more oxidizing conditions CO2-rich fluids or melts can migrate and escape from the interior. The carbon cycle in the Earth may therefore depend on the redox state of mantle rocks. Conversely, an influx of CO2-rich fluids or melts may act to oxidize the mantle as an additional aspect of metasomatism. In the first part of this study experiments were performed to measure the oxygen fugacity at which carbon (graphite or diamond) oxidises to carbonate minerals or melts within mantle peridotite assemblages between 2.5 and 11 GPa at 1100-1600 °C. The experiments were performed up to temperatures where carbonate melts evolve towards more silicate-rich compositions. The dilution of the carbonate melt component was found to lower the relative fo2, expanding the melt stability field with respect to reduced carbon. The results allow the fo2 of the diamond formation process to be determined both as a function of pressure, temperature and melt CO2 concentration. These results also have implications for the onset of melting within up welling mantle material. Several studies have indicated that the mantle may become more reduced with depth. This means that the oxidation of elemental carbon (graphite or diamond) may occur in up welling rocks where the oxidized product is a carbonate bearing magma. When the experimental data are compared with current estimates for the fo2 of mantle rocks t…
abstract: The redox state of the Earth’s interior will influence the speciation of volatile elements both in the mantle and in mantle derived magmas. Carbon is one of the principal elements to be affected in this way because under reducing conditions it forms graphite or diamond, and under oxidizing conditions carbonate (or CO2-bearing) minerals and melts. The cycling and residence time of carbon in the mantle can be strongly effected by the oxygen fugacity because reduced phases such as diamond and graphite are immobile and likely to remain within the mantle and potentially within subducting slabs, while at more oxidizing conditions CO2-rich fluids or melts can migrate and escape from the interior. The carbon cycle in the Earth may therefore depend on the redox state of mantle rocks. Conversely, an influx of CO2-rich fluids or melts may act to oxidize the mantle as an additional aspect of metasomatism. In the first part of this study experiments were performed to measure the oxygen fugacity at which carbon (graphite or diamond) oxidises to carbonate minerals or melts within mantle peridotite assemblages between 2.5 and 11 GPa at 1100-1600 °C. The experiments were performed up to temperatures where carbonate melts evolve towards more silicate-rich compositions. The dilution of the carbonate melt component was found to lower the relative fo2, expanding the melt stability field with respect to reduced carbon. The results allow the fo2 of the diamond formation process to be determined both as a function of pressure, temperature and melt CO2 concentration. These results also have implications for the onset of melting within up welling mantle material. Several studies have indicated that the mantle may become more reduced with depth. This means that the oxidation of elemental carbon (graphite or diamond) may occur in up welling rocks where the oxidized product is a carbonate bearing magma. When the experimental data are compared with current estimates for the fo2 of mantle rocks t…
author: Stagno, Vincenzo
date published: 2011-05-30
date modified: 2026-07-27T18:49:09Z
provider: Universität Bayreuth
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Universität Bayreuth