Laser Ablation ICPMS study of trace element partitioning between plagioclase and basaltic melts: an experimental approach |
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| Authors: | Mario Aigner-Torres Jon Blundy Peter Ulmer Thomas Pettke |
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| Institution: | (1) Institute of Mineralogy and Petrography, Swiss Federal Institute of Technology, ETH Zentrum NO, 8092 Zürich, Switzerland;(2) CETSEI, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol, BS8 1 RJ, UK;(3) Department of Petroleum Engineering, University of Campinas (DEP-FEM-UNICAMP), 6122 Campinas, 13083-970, Brazil;(4) Present address: Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland |
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| Abstract: | Plagioclase-melt partition coefficients (D) for 34 trace elements at natural concentration levels were determined experimentally in a natural MORB composition at atmospheric
pressure using thin Pt-wire loops. Experiments were carried out at three temperatures (1,220, 1,200, and 1,180°C), and at
three different oxygen fugacities (fO2 = IW, QFM, air) in order to assess the effect of fO2 on the partitioning of elements with multiple valence (Fe, Eu, Cr). Run products were analyzed by laser-ablation ICP-MS.
Most trace element Ds increase slightly as temperature decreases, except for D
Zr, D
Fe, D
Eu and D
Cr that vary systematically with fO2. Applying the Lattice Strain Model to our data suggests the presence of Fe2+ entirely in the octahedral site at highly to moderate reducing conditions, while Fe3+ was assigned wholly to the tetrahedral site of the plagioclase structure. Furthermore, we provide a new quantitative framework
for understanding the partitioning behaviour of Eu, which occurs as both 2+ and 3+ cations, depending on fO2and confirm the greater compatibility of Eu2+, which has an ionic radius similar to Sr, relative to Eu3+ in plagioclase and the higher Eu2+/ Eu3+ under reducing conditions. For petrogenetic basaltic processes, a combined fractionation of Eu2+–Sr and Fe–Mg by plagioclase has considerable potential as an oxybarometer for natural magmatic rocks. |
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| Keywords: | Trace elements Melting experiments Plagioclase LA-ICPMS |
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