Computer Science
Scientific paper
Nov 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003gecoa..67.4389g&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 67, Issue 22, pp.4389-4409
Computer Science
7
Scientific paper
The critical role of iron on crystal-silicate liquid relationships and melt differentiation is mainly controlled by the redox conditions prevailing in magmas, but the presently available database merely constrains the thermodynamic properties of iron-bearing components in strongly reduced and anhydrous molten silicate where iron is in the ferrous form. This paper provides new standard states for pure ferrous (FeO liq ) and ferric (Fe 2 O 3 liq ) molten iron oxides and extends the experimental database towards oxidizing and water-bearing domains. Iron-iridium, iron-platinum alloys, magnetite or hematite were equilibrated with synthetic silicic liquids at high temperature and high pressure under controlled oxygen fugacity (fO 2 ) to determine activity-composition relationships for FeO liq and Fe 2 O 3 liq . Between 1000 and 1300°C, the fO 2 ranges from that in air to 3-log units below that of the nickel-nickel oxide buffer (NNO). Experiments were performed on both anhydrous and hydrous melts containing up to 6-wt.% water. Incorporation of water under reducing conditions increases the activity coefficient of FeO liq but has an opposite effect on Fe 2 O 3 liq . As calcium is added to system, the effect of water becomes weaker and is inverted for Fe 2 O 3 liq . Under oxidizing conditions, water has a negligible effect on both activities of FeO liq and Fe 2 O 3 liq . In contrast, changes in redox conditions dominate the activity coefficients of both FeO liq and Fe 2 O 3 liq , which increase significantly with increasing fO 2 . The present results combined with the previous work provide a specific database on the energetics of iron in silicate melts that cover most of the condition prevailing in natural magmas.
Gaillard Fabrice
Pichavant Michel
Scaillet Bruno
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