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| Detailed Reference Information |
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Stimac, J. and Hickmott, D. (1994). Trace-Element Partition-Coefficients for Ilmenite, Ortho-Pyroxene and Pyrrhotite in Rhyolite Determined by Micro-Pixe Analysis. Chemical Geology 117(1-4): 313-330. doi: 10.1016/0009-2541(94)90134-1. |
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Ilmenite is a common accessory mineral in igneous and metamorphic rocks, yet few data are available on its partitioning behavior. We present in situ proton-induced X-ray emission (PIXE) microanalytical data for ilmenite (Ilm), orthopyroxene (Opx), pyrrhotite (Po) and coexisting silicic glass in a rhyolite lava from Clear Lake, California. The rhyolite contains grains of Ilm (X(ilm)=0.96-1.00) associated with Opx and Flag phenocrysts. Po occurs as inclusions in Ilm and Opx, and as rare single grains. Ilmenite concentrates Nb (D=51-71), Ta (64-85), Zn (10-11), Mo (>5) and Zr (1.0-1.4). Opx concentrates Ni (D=similar to 11-25) and Zn (14-16). Po concentrates Mo (D=similar to 161), As (2-3), Se (similar to 36-44), Pb (2), Co (similar to 999), Cu (similar to 459-502) and Ni (similar to 1842) relative to silicic melt, but these coefficients may reflect liquid/liquid rather than solid/liquid partitioning. Ilmenite is the dominant oxide in Clear Lake volcanic rocks, occurring in silicic to intermediate lavas and metasedimentary xenoliths. Silicic volcanic rocks of the area formed by interaction of mafic magmas with deep crustal rocks. The dominance of ilmenite over magnetite reflects the bulk composition and low f(O2) of a metasedimentary source component. The relative abundance of ilmenite in such systems and its high D-Nb- and D-Ta-values suggest that it will strongly influence Nb and Ta concentrations during partial melting of crustal rocks and during crystal fractionation. Similarly Po will exert an important influence on the distribution of chalcophile and siderophile elements. Ilm and Po must be considered in quantitative fractionation models involving HFSE and metals, even if present in trace abundances. |
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Whole-Rock & Glass |
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Pixe Analyses |
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Electron Microprobe |
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Keywords
rare-earth elements, high-silica rhyolites, nuclear microprobe, mare basalts, crater lake, clear-lake, ti, magmas, evolution, minerals |
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Publisher
Elsevier Science
P.O. Box 211
1000 AE Amsterdam
The Netherlands
(+31) 20 485 3757
(+31) 20 485 3432
nlinfo-f@elsevier.com |
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