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Title: Constraints on the oxidation state of the mantle: An electrochemical and sup 57 Fe Moessbauer study of mantle-derived ilmenites

Abstract

Ilmenite samples from four kimberlite localities were studied using electrochemical, Moessbauer spectroscopic, and microprobe analytical techniques in order to infer the oxidation state of their source regions in the mantle. The values of Fe{sup 3+}/{Sigma}Fe calculated from analyses, using three different electron microanalytical instruments assuming ilmenite stoichiometry, are consistently higher than those derived from the Moessbauer data, by as much as 100%. Furthermore, the range in Fe{sup 3+}/{Sigma}Fe calculated using the analyses from different instruments and/or different correction schemes is nearly as large. Thus Fe{sup 3+}/{Sigma}Fe calculated from microprobe analyses should be taken with caution, even if the precision appears high. {sup 57}Fe Moessbauer spectroscopy on the electrochemical experiment run products demonstrates that Fe{sup 3+}/{Sigma}Fe is significantly lower than it is for the natural C-bearing ilmenites. In contrast, the ilmenite that lacked C did not change Fe{sup 3+}/{Sigma}Fe during the electrochemical experiment. Examination of the reduced samples with SEM established that the natural, single-phase ilmenites exsolved during the electrochemical experiment to form ilmenite{sub ss} + spinel{sub ss}. The initial, reduced trends in the electrochemical experiments for the C-bearing ilmenites are attributed to disequilibrium interactions between the decomposing sample and the evolved gas in the electrochemical cell and do not representmore » the quenched mantle memory nor the intrinsic f{sub O{sub 2}} of the sample prior to reduction. Furthermore, the oxidized f{sub O{sub 2}} trend is interpreted, for the carbon-bearing samples, are representing the f{sub O{sub 2}} of the ilmenite{sub ss} + spinel{sub ss} assemblage and not the intrinsic f{sub o{sub 2}} of the mantle-derived ilemnite{sub ss}.« less

Authors:
;  [1]; ;  [2]
  1. Geophysical Laboratory, Washington, DC (USA)
  2. Temple Univ., Philadelphia, PA (USA)
Publication Date:
OSTI Identifier:
5152842
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta; (USA)
Additional Journal Information:
Journal Volume: 52:7; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ILMENITE; MINERALIZATION; PETROGENESIS; QUANTITATIVE CHEMICAL ANALYSIS; VALENCE; CHEMICAL COMPOSITION; CHEMICAL REACTION KINETICS; EARTH MANTLE; ELECTROCHEMISTRY; EQUILIBRIUM; GEOCHEMISTRY; MAGMA; OXIDATION; REDOX REACTIONS; STOICHIOMETRY; THERMODYNAMIC ACTIVITY; CHALCOGENIDES; CHEMICAL ANALYSIS; CHEMICAL REACTIONS; CHEMISTRY; IRON COMPOUNDS; IRON OXIDES; KINETICS; MINERALS; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; REACTION KINETICS; TITANIUM COMPOUNDS; TITANIUM OXIDES; TRANSITION ELEMENT COMPOUNDS; 580000* - Geosciences

Citation Formats

Virgo, D, Luth, R W, Moats, M A, and Ulmer, G C. Constraints on the oxidation state of the mantle: An electrochemical and sup 57 Fe Moessbauer study of mantle-derived ilmenites. United States: N. p., 1988. Web. doi:10.1016/0016-7037(88)90003-8.
Virgo, D, Luth, R W, Moats, M A, & Ulmer, G C. Constraints on the oxidation state of the mantle: An electrochemical and sup 57 Fe Moessbauer study of mantle-derived ilmenites. United States. https://doi.org/10.1016/0016-7037(88)90003-8
Virgo, D, Luth, R W, Moats, M A, and Ulmer, G C. 1988. "Constraints on the oxidation state of the mantle: An electrochemical and sup 57 Fe Moessbauer study of mantle-derived ilmenites". United States. https://doi.org/10.1016/0016-7037(88)90003-8.
@article{osti_5152842,
title = {Constraints on the oxidation state of the mantle: An electrochemical and sup 57 Fe Moessbauer study of mantle-derived ilmenites},
author = {Virgo, D and Luth, R W and Moats, M A and Ulmer, G C},
abstractNote = {Ilmenite samples from four kimberlite localities were studied using electrochemical, Moessbauer spectroscopic, and microprobe analytical techniques in order to infer the oxidation state of their source regions in the mantle. The values of Fe{sup 3+}/{Sigma}Fe calculated from analyses, using three different electron microanalytical instruments assuming ilmenite stoichiometry, are consistently higher than those derived from the Moessbauer data, by as much as 100%. Furthermore, the range in Fe{sup 3+}/{Sigma}Fe calculated using the analyses from different instruments and/or different correction schemes is nearly as large. Thus Fe{sup 3+}/{Sigma}Fe calculated from microprobe analyses should be taken with caution, even if the precision appears high. {sup 57}Fe Moessbauer spectroscopy on the electrochemical experiment run products demonstrates that Fe{sup 3+}/{Sigma}Fe is significantly lower than it is for the natural C-bearing ilmenites. In contrast, the ilmenite that lacked C did not change Fe{sup 3+}/{Sigma}Fe during the electrochemical experiment. Examination of the reduced samples with SEM established that the natural, single-phase ilmenites exsolved during the electrochemical experiment to form ilmenite{sub ss} + spinel{sub ss}. The initial, reduced trends in the electrochemical experiments for the C-bearing ilmenites are attributed to disequilibrium interactions between the decomposing sample and the evolved gas in the electrochemical cell and do not represent the quenched mantle memory nor the intrinsic f{sub O{sub 2}} of the sample prior to reduction. Furthermore, the oxidized f{sub O{sub 2}} trend is interpreted, for the carbon-bearing samples, are representing the f{sub O{sub 2}} of the ilmenite{sub ss} + spinel{sub ss} assemblage and not the intrinsic f{sub o{sub 2}} of the mantle-derived ilemnite{sub ss}.},
doi = {10.1016/0016-7037(88)90003-8},
url = {https://www.osti.gov/biblio/5152842}, journal = {Geochimica et Cosmochimica Acta; (USA)},
issn = {0016-7037},
number = ,
volume = 52:7,
place = {United States},
year = {Fri Jul 01 00:00:00 EDT 1988},
month = {Fri Jul 01 00:00:00 EDT 1988}
}