Clinopyroxene, distribution coefficients

Figure 5,65 Garnet-clinopyroxene geothermometric exchange (Fe +-Mg +). Thermodynamic constant K is compared with distribution coefficient K the difference between the two terms represents the effect of interactions in mixtures. Reprinted from J. Ganguly, Geochimica et Cosmochimica Acta, 43, 1021-1029, copyright 1979, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

Ganguly J. (1979). Garnet and clinopyroxene solid solutions and geothermometry based on Fe-Mg distribution coefficient. Geochim. Cosmochim. Acta, 43 1021-1029. 

McKay G. A., Wagstaff J., and Yang S. R. (1986) Clinopyroxene REE distribution coefficients for shergottites the REE content of the Shergotty melt. Geochim. Cosmochim. Acta 50, 927-937. 

Fig, 20. Lanthanide mineral/mell distribution coefficient values for clinopyroxenes from volcanic rocks, showing the extreme dependence on the composition of the bulk rock. For example, the values for La extend over three orders of magnitude. (Data by courtesy of Dr. A. Ewart, University of Queensland, Australia.)... 

Despite the apparently over-sin lified form of the Berthelot-Nernst distribution coefficient, it has been extensively employed in trace element geochemistry often with considerable success. In this respect it is instructive to compare D. with the true equilibrium constant for a given reaction. As an example the partition of Ni between olivine and clinopyroxene (Hakli and Wright, 1967 Broecker and Oversby, 1971 Banno and Matsui, 1973 Carmichael Consider the following exchange reaction ... 

Ideally a trace element geothermometer should be based upon a reaction with a large AH and small AV and vice versa for a geobarometer. A number of experimental studies have now demons trated the temperature dependence of Berthelot-Nernst distribution coefficients. Noteworthy amongst these are the experiments of Shimizu (l97 ) on the distribution of Sr, Ba, K, Rb, and Cs between clinopyroxenes and liquid and those of Drake and Weill (1973) on the partitioning of Sr, Ba and Eu between plagioclase and liquid. 

Figure 4.11 Monte-Carlo simulation (100 trials) of error propagation for La/Yb fractionation in residual melts by clinopyroxene-garnet removal from a basaltic parent magma (see text for parameter description and distributions used). Top mineral-liquid partition coefficients for La and Yb. Bottom variations of the La/Yb ratio as a function of the fraction F of residual melt.

Figure 10.10 Arrhenius plot of conventional partition coefficient (A) and thermodynamic constant (B) for clinopyroxene/liquid distribution of Ni.

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