Partitioning of rare Earths and other trace elements between sanidine and coexisting volcanic glass

Authors:
  • WLWilliam P. Leeman
    William P. Leeman
  • DPDavid W. Phelps
    David W. Phelps
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Abstract
Major and trace element contents have been measured for sanidine‐glass pairs separated from eight high‐SiO2 rhyolite lavas from the Yellowstone volcanic field. Sanidine/glass partition coefficients for most elements based on these data are uniform to within the cumulative analytical errors. This uniformity reflects similarities in major element compositions and inferred physical conditions for the analyzed samples, which are considered representative of most Yellowstone rhyolites. Of particular note are very high partition coefficients for Ba (∼22), Sr (∼28), and Eu (∼9), relative to the sparse data for other rhyolites available in the literature. With the exception of Na, K, and Pb, which have sanidine/glass partition coefficients of approximately unity, all other elements determined are strongly fractionated into the melt phase relative to sanidine. These data may be used in modeling crystallization of sanidine from Yellowstone or other rhyolites or anatexis of crustal rocks containing sanidine (or K‐feldspar sensu lato), but only with due caution. In particular, the wide range in reported partition coefficients for those elements (Sr, Ba, Eu) strongly incorporated in sanidine suggests that compositional and physical characteristics exert significant influence on these values. Accordingly, applicable partition coefficients are poorly known for these elements in most systems. Care must be taken to select appropriate values or to measure these partition coefficients directly in specific suites of rocks. Difficulties with direct experimental studies in silicic magmas seemingly preclude systemization of element partitioning at present.

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