Hornblende-melt trace-element partitioning measured by ion microprobe
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Abstract
Trace-element abundances were measured in situ by ion microprobe in five samples of hornblende and melt ranging from basaltic andesite to high-silica rhyolite. Except for one sample, for which quench overgrowth or disequilibrium is suspected, the abundance ratios show systematic inter-element and inter-sample variations, and probably approach true partition coefficients. Apparent partition coefficients are reported for La, Ce, Nd, Sm, Dy, Er, Yb, Sc, Ti, V, Cr, Sr, Y and Zr. Rare-earth elements (REE) and Y form smooth convex-upward partitioning patterns that rise to higher D-values and become increasingly convex in more evolved samples. Apparent partition coefficients for REE, Y, Ti, V and Cr can be parameterized as functions of the distribution of Ca between hornblende and melt, giving expressions to predict hornblende-melt trace-element partitioning values. These expressions are used to show that heavy REE-enriched hornblende/whole-rock REE abundance patterns in granitoids may result from partial re-equilibration of hornblende and late-stage residual liquids rather than from anomalous partitioning values.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Hornblende-melt trace-element partitioning measured by ion microprobe |
| Series title | Chemical Geology |
| DOI | 10.1016/0009-2541(94)90135-X |
| Volume | 117 |
| Issue | 1-4 |
| Year Published | 1994 |
| Language | English |
| Publisher | Elsevier |
| Contributing office(s) | Volcano Hazards Program |
| Description | 14 p. |
| First page | 331 |
| Last page | 344 |
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