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Experimental Studies of Fe-Mg Carbonates and Their Role in Petrogenesis
The occurrence of carbonate minerals in rocks and sediments is a mark of the interaction of the biosphere, hydrosphere, and atmosphere with the lithosphere. The studies described in this proposal will help geologists understand the conditions of formation of banded iron formations, carbonatites, and magnesite-bearing eclogites, among other parageneses.

The objectives of this study are to determine siderite (FeCO3), magnesite (MgCO3), and CO2 thermodynamic properties and the mixing relations of siderite-magnesite solid solutions. Selected carbonate univariant equilibria, experimentally reversed over a wide range of pressure and temperature, will provide this information. The equilibria siderite + hematite = magnetite + CO2, when displaced downwards in pressure by magnesite solution in the siderite, will provide the constraints on siderite-magnesite mixing. In effect the principal investigator will be calibrating a geothermobarometer for use in a number of parageneses.

Piston-cylinder experiments will be performed at the University of Dayton High Pressure Laboratory, which has been established by the principal investigator. She will use appropriate experimental techniques to ensure that equilibrium is closely approached. Experimental products will be analyzed by weight loss measurements, X-ray diffraction analysis, and when appropriate, electron microprobe analysis.

Results of this study will be applicable to carbonate globules in Martian meteorite ALH84001, which are composed of Fe-Mg carbonate with variable Ca content. The interpretation of the history and significance of these carbonate globules. The results of the principal investigator's experiments will help determine whether a high temperature origin for these globules is allowable or whether a low temperature environment is indicated.

These studies will also provide tight constraints on the fugacity of CO2 at upper mantle pressure-temperature conditions. A clearer understanding of the stability of magnesite with typical mantle phases olivine and enstatite affects our understanding of the conditions of diamond formation and bears on discussion of the oxidation state of the mantle. It will also determine the free energy of formation of siderite and the mixing properties of magnesite-siderite solid solutions. This work lays the foundation for further research on Fe-Mg mixing in other minerals and for defining an accurate equation of state for CO2.

Completion of this research will establish the principal investigator as an independent scientist. It will enhance her role as a mentor of undergraduates pursuing research experiences.
Publication Date
October, 1998
Dr. Koziol was the principal investigator for this research project. This project received funding from the National Science Foundation's Division of Earth Sciences from October 1998 to September 2000 for the amount of $55,674.00. The abstract number is 9805873.

Citation Information
"Experimental Studies of Fe-Mg Carbonates and Their Role in Petrogenesis" (1998)
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