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Evolution of the Oxidation State of the Earth's MantleThe oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3(+) at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. In our previous experiments on shergottite compositions, variable fO2, T, and P less than 4 GPa, Fe3(+)/sigma Fe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3(+)/sigma Fe decreased as well, but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3(+). Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Preliminary multi-anvil experiments with Knippa basalt as the starting composition were conducted at 5-7 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal to Fe3(+)/2(+). Experiments are underway to produce glassy samples that can be measured by EELS and XANES, and are conducted at higher pressures.
Document ID
20150009507
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Danielson, L. R. (Jacobs Technology, Inc. Houston, TX, United States)
Righter, K. (NASA Johnson Space Center Houston, TX, United States)
Keller, L. (NASA Johnson Space Center Houston, TX, United States)
Christoffersen, E. (Jacobs Technology, Inc. Houston, TX, United States)
Rahman, Z. (Jacobs Technology, Inc. Houston, TX, United States)
Date Acquired
June 4, 2015
Publication Date
August 16, 2015
Subject Category
Geophysics
Report/Patent Number
JSC-CN-33552
Meeting Information
Meeting: Goldschmidt Conference (Goldschmidt2015)
Location: Prague
Country: Czechoslovakia
Start Date: August 16, 2015
End Date: August 21, 2015
Sponsors: Geochemical Society, European Association of Geochemistry
Distribution Limits
Public
Copyright
Public Use Permitted.

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