Expanding the application of the Eu-oxybarometer to the lherzolitic shergottites and nakhlites: Implications for the oxidation state heterogeneity of the Martian interior
Abstract
Experimentally rehomogenized melt inclusions from the nakhlite Miller Range 03346 (MIL 03346) and the lherzolitic shergottite Allan Hills 77005 (ALH 77005) have been analyzed for their rare earth element (REE) concentrations in order to characterize the early melt compositions of these Martian meteorites and to calculate the oxygen fugacity conditions they crystallized under. D(Eu/Sm)pyroxene/melt values were measured at 0.77 and 1.05 for ALH 77005 and MIL 03346, respectively. These melts and their associated whole rock compositions have similar REE patterns, suggesting that whole rock REE values are representative of those of the early melts and can be used as input into the pyroxene Eu-oxybarometer for the nakhlites and lherzolitic shergottites. Crystallization fO_2 values of IW + 1.1 (ALH 77005) and IW + 3.2 (MIL 03346) were calculated. Whole rock data from other nakhlites and lherzolitic shergottites was input into the Eu-oxybarometer to determine their crystallization fO_2 values. The lherzolitic shergottites and nakhlites have fO_2 values that range from IW + 0.4 to 1.6 and from IW + 1.1 to 3.2, respectively. These values are consistent with some previously determined fO_2 estimates and expand the known range of fO_2 values of the Martian interior to four orders of magnitude. The origins of this range are not well constrained. Possible mechanisms for producing this spread in fO_2 values include mineral/melt fractionation, assimilation, shock effects, and magma ocean crystallization processes. Mineral/melt partitioning can result in changes in fO_2 from the start to the finish of crystallization of 2 orders of magnitude. In addition, crystallization of a Martian magma ocean with reasonable initial water content results in oxidized, water-rich, late-stage cumulates. Sampling of these oxidized cumulates or interactions between reduced melts and the oxidized material can potentially account for the range of fO_2 values observed in the Martian meteorites.
Additional Information
© The Meteoritical Society, 2009. (Received 07 July 2008; revision accepted 06 February 2009) The authors are grateful to the ANSMET program, the NASA Antarctic Meteorite Curator, and the Meteorite Working Group for allowing them access to these meteorites. The assistance of Dr. J. Devine with EMP analysis and Dr. Y. Guan with ion probe analysis was greatly appreciated. Critical reviews by A. Irving, K. Stockstill-Cahill, and A. Treiman helped improve and clarify this work. This research was supported by NASA grant NNG06GF12G to M. J. R. and a Mars Fundamental Research Program grant to L. E. T. A portion of this work was done while M. C. M. was a Urey Post-Doctoral fellow at the Lunar and Planetary Institute.Attached Files
Published - McCanta_1038.pdf
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Additional details
- Eprint ID
- 15103
- Resolver ID
- CaltechAUTHORS:20090817-144815604
- NNG06GF12G
- NASA
- Lunar and Planetary Institute
- Created
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2009-09-08Created from EPrint's datestamp field
- Updated
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2019-10-03Created from EPrint's last_modified field