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The Relationship Between Clinopyroxene Fe3+ Content and Oxygen FugacityThe intrinsic oxygen fugacity (fO2) imposed on a magma has the ability to influence the crystallization sequence of the melt, as well as the composition of the resulting minerals. fO2 is an easily controlled parameter in the lab, either through gas-mixing equilibria or with a solid-state buffer assemblage. In nature, the fO2 of a closed system is imposed on the system internally through multivalent equilibria involving the phenocryst-melt assemblage. This results in a characteristic oxidation state. The physical parameter used to quantify oxidation state is oxygen fugacity. Iron is the only major rock forming element in basaltic melts to exist in multiple valence states and, therefore, it is commonly used to assess fO2. Traditional methods to quantify fO2 utilize the ferric content of glasses or coexisting Fe-Ti oxides. However, many rocks, such as the Martian meteorites, do not contain the necessary phases or have oxides which have suffered reequilibration, thereby rendering them unmeasureable by current techniques. For these rocks, new methods, utilizing other phases are needed. Mafic minerals have Fe(3+)/SigmaFe ratios that are a function of two factors: 1) crystal chemistry and 2) their intrinsic fO2 during crystallization. Olivine and orthopyroxene, for example, have steric constraints on the extent to which Fe(3+) can be incorporated in their structures, and may not record changes in magmatic fO2 in a way that can easily be measured. The chemistry of clinopyroxene, however, allows for extensive incorporation of Fe(3+) in its crystal structure, making it a potentially useful oxybarometer. To date, there have been few, if any, systematic experimental studies of the variation of the Fe(3+)/SigmaFe ratio as a function of fO2 in clinopyroxene. This study seeks to address this lack of data.
Document ID
20040056064
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
McCanta, M. C.
(Brown Univ. Providence, RI, United States)
Rutherford, M. J.
(Brown Univ. Providence, RI, United States)
Dyar, M. J.
(Mount Holyoke Coll. South Hadley, MA, United States)
Delaney, J. S.
(Rutgers Univ. Piscataway, NJ, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2004
Publication Information
Publication: Lunar and Planetary Science XXXV: Special Session: Oxygen in the Solar System, II
Subject Category
Lunar And Planetary Science And Exploration
Funding Number(s)
CONTRACT_GRANT: NAG5-12848
CONTRACT_GRANT: NAG5-12687
CONTRACT_GRANT: NAG5-12225
CONTRACT_GRANT: NAG5-10424
CONTRACT_GRANT: NGT-963
Distribution Limits
Public
Copyright
Public Use Permitted.
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