Comment on 'Mexican peridotite xenoliths and tectonic terranes: Correlations among vent location, texture, temperature, pressure and oxygen fugacity by J.F. Luhr & J.J. Aranda-Gomez (1997)

This comment addresses the interpretation of oxygen fugacity data for spine l peridotite xenoliths from five Mexican volcanic fields presented by Luhr & Aranda-Gomez (Journal of Petrology, 38, 1075-1112, 1997). The postulated east-west increase of the Delta FMQ ('relative oxygen fugacity', where FMQ is fayalite-magnetite-quartz) values is inherent to the method and therefor e of questionable geological significance. Increases in Delta FMQ do not ne cessarily mirror oxidation processes in the mantle controlled by subduction -related fluids.