Oxidation state of mantle xenoliths from British Columbia,Canada |
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| Authors: | Dante Canil David Virgo Christopher M Scarfe |
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| Institution: | (1) Experimental Petrology Laboratory, Department of Geology, University of Alberta, T6G 2E3 Edmonton, Canada;(2) Geophysical Laboratory, Carnegie Institution of Washington, 20008 Washington DC, USA;(3) Present address: Bayerisches Geoinstitut, Universität Bayreuth, Postach 101251, D-8580 Bayreuth, Federal Republic of Germany |
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| Abstract: | Mössbauer spectra for 17 spinels separated from mantle xenoliths from six different eruptive centers in southern British Columbia, Canada were measured in an effort to accurately determine their Fe3+/total Fe ratios, and to examine lateral and vertical variations in oxygen fugacities (f
o2's) calculated for these samples using published thermobarometric methods. Spectra acquired at 298 and 77 K suggest that both Fe2+ and Fe3+ are tetrahedrally coordinated in lherzolite spinels from this alkaline province. Calculatedf
o2's for spinel lherzolites from British Columbia range from about 0.5 to 1.5 log units below the fayalite-magnetite-quartz (FMQ) oxygen buffer at 15 kbar using the thermobarometric method of O'Neill and Wall. Thesef
o2's are on average more reducing than those reported for the upper mantle beneath the Massif Central and Japanese Arc and fall within the range for fresh MORB glasses and for lherzolite xenoliths from the southwestern United States and Mongolia. Significant variations inf
o2 between samples from different eruptive centers with varying ages are absent, indicating that the oxidation state of the upper mantle was not affected by Cenozoic magmatism within this alkaline province. |
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