Abstract
Attempts have been made in the recent literature to constrain major element mobility in altered basalts and komatiites using the molecular proportion ratio (MPR) diagrams developed by T.H. Pearce (1970). The method involves ratioing the molecular proportions of two oxides against a third oxide and presenting the results as an oxide-oxide ratio plot. The transformation appears to ‘clean up’ scatter plots with low correlations and produces highly correlated ratio plots. These plots have been taken to be indicative of igneous fractionation trends and thus of minimal bulk chemical change during alteration. There are however inherent statistical problems in ratio correlation which have received much attention in the mathematical literature. This paper explains the implications of enhanced correlations for work on altered rocks using ratio plots and suggests that extreme caution must be exercised in the interpretation of MPR diagrams.
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Rollinson, H.R., Roberts, C.R. Ratio correlations and major element mobility in altered basalts and komatiites. Contr. Mineral. and Petrol. 93, 89–97 (1986). https://doi.org/10.1007/BF00963587
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DOI: https://doi.org/10.1007/BF00963587