TY - JOUR
T1 - Co2+ as a chemical analogue for Fe2+ in high-temperature experiments in basaltic systems
AU - Coons, William E.
AU - Holloway, John R.
AU - Navrotsky, Alexandra
N1 - Funding Information:
We thank Mr. Edward Holdsworth for the microprobe analyses used in this paper, and Dr. Peter Buseck and Mr. Henry Westrich for helpful comments during the writing of this manuscript. We gratefully acknowledge the National Science Foundation which provided funds through grant DES 72-01357 AO1.
PY - 1976/5
Y1 - 1976/5
N2 - High-temperature experiments on ferromagnesian compositions have been hampered by the rapid absorption of up to 95% of the original iron by platinum and 40% by silver-palladium capsules. Molybdenum or iron capsule materials can decrease or alleviate iron loss, but restrict oxygen fugacities to values near the iron-wustite buffer. Because Co2+ is stable at f{hook}O2 = HM and because the solubility of Co in platinum in this range of f{hook}O2 is ∼0.05% at temperatures to 1350°C, its use as an analogue for Fe2+ is possible. In addition, experiments simulating various Fe2+ ratios can be easily performed by choosing appropriate Co2+/Fe3+ ratios. The cobalt phases produced possess brilliant and distinctive colors which are valuable aids in optical identification of minute phases. The cobalt analogue hypothesis was tested with atmospheric pressure experiments in air on the cobalt analogue of the 1921 Kilauea basalt at three simulated Fe2+/Fe3+ ratios. The results were compared with those of R.E.T. Hill (1969) for the natural 1921 basalt. The phase relations were the same, with the cobalt system stability fields systematically shifted by about +50°C. Microprobe analysis of olivines and the coexisting glasses indicate that the distribution of Co2+ between olivine and melt is independent of temperature and liquid composition. Although the analogue liquid composition differs from the equilibrium composition of the natural system, it may be corrected be employing distribution coefficients (KD = 0.61 for the Co system; KD = 0.33 for the Fe system) to closely approximate what the natural system would yield if iron loss did not occur.
AB - High-temperature experiments on ferromagnesian compositions have been hampered by the rapid absorption of up to 95% of the original iron by platinum and 40% by silver-palladium capsules. Molybdenum or iron capsule materials can decrease or alleviate iron loss, but restrict oxygen fugacities to values near the iron-wustite buffer. Because Co2+ is stable at f{hook}O2 = HM and because the solubility of Co in platinum in this range of f{hook}O2 is ∼0.05% at temperatures to 1350°C, its use as an analogue for Fe2+ is possible. In addition, experiments simulating various Fe2+ ratios can be easily performed by choosing appropriate Co2+/Fe3+ ratios. The cobalt phases produced possess brilliant and distinctive colors which are valuable aids in optical identification of minute phases. The cobalt analogue hypothesis was tested with atmospheric pressure experiments in air on the cobalt analogue of the 1921 Kilauea basalt at three simulated Fe2+/Fe3+ ratios. The results were compared with those of R.E.T. Hill (1969) for the natural 1921 basalt. The phase relations were the same, with the cobalt system stability fields systematically shifted by about +50°C. Microprobe analysis of olivines and the coexisting glasses indicate that the distribution of Co2+ between olivine and melt is independent of temperature and liquid composition. Although the analogue liquid composition differs from the equilibrium composition of the natural system, it may be corrected be employing distribution coefficients (KD = 0.61 for the Co system; KD = 0.33 for the Fe system) to closely approximate what the natural system would yield if iron loss did not occur.
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U2 - 10.1016/0012-821X(76)90257-0
DO - 10.1016/0012-821X(76)90257-0
M3 - Article
AN - SCOPUS:0042336080
SN - 0012-821X
VL - 30
SP - 303
EP - 308
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 2
ER -