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标题：Contrasting partition behavior of F and Cl during hydrous mantle melting: implications for Cl/F signature in arc magmas
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作者：Célia Dalou ; Kenneth T Koga ; Marion Le Voyer 等
期刊名称：Progress in Earth and Planetary Science
电子版ISSN：2197-4284
出版年度：2014
卷号：1
期号：1
页码：1-17
DOI：10.1186/s40645-014-0026-1
出版社：Springer Verlag
摘要：We present the results of five experiments on F and Cl partitioning during hydrous mantle melting under conditions relevant to subduction zone magmatism (1.2–2.5 GPa, 1,180°C–1,430°C).For each experiment, we determined the F and Cl partition coefficients between lherzolitic mineral phases (olivine, orthopyroxene (opx), clinopyroxene (cpx), and garnet), amphibole, and hydrous basaltic melts (0.2–5.9 wt.% dissolved H2O).At constant pressure, \( {D}_{\mathrm{F}}^{\mathrm{opx}/\mathrm{melt}}\;\mathrm{and}\;{D}_{\mathrm{Cl}}^{\mathrm{opx}/\mathrm{melt}} \) show contrasting response to the combined effects of decreasing temperature from 1,310°C to 1,180°C and increasing H2O content in the melt from 0.2 to 5.9 wt.%: \( {D}_{\mathrm{F}}^{\mathrm{opx}/\mathrm{melt}} \) .decreases from 0.123 ± 0.004 to 0.021 ± 0.014 while \( {D}_{\mathrm{Cl}}^{\mathrm{opx}/\mathrm{melt}} \) increases from 0.0021 ± 0.0031 to 0.07 ± 0.01.Similar results are observed for clinopyroxene: \( {D}_{\mathrm{F}}^{\mathrm{cpx}/\mathrm{melt}} \) decreases from 0.153 ± 0.004 to 0.083 ± 0.004 while \( {D}_{\mathrm{Cl}}^{\mathrm{cpx}/\mathrm{melt}} \) increases from 0.009 ± 0.0005 to 0.015 ± 0.0008.Experimentally determined F and Cl partition coefficients were used in a hydrous melting model of a lherzolitic mantle metasomatized by slab fluid.In this model, we vary the amount of metasomatic slab fluid added into the mantle while its composition is kept constant.Increasing the amount of fluid results in an increase of both the degree of melting (due to the effect of H2O addition) and the F and Cl input in the mantle wedge.Because of the change of F and Cl partition coefficients with the increase of H2O, the observed variation in the F and Cl contents of the modeled melts is produced not only by F and Cl input from the fluid, but also by the changes in F and Cl fractionation during hydrous melting.Overall, the model predicts that the Cl/F ratio of modeled melts increases with increasing fluid fraction.Therefore, a variation in the amount of fluid added to the mantle wedge can contribute to the variability in Cl/F ratios observed in arc melt inclusions.
关键词：Fluorine ;Chlorine ;Partition coefficients ;Lherzolite minerals ;Hydrous silicate melt ;Fluid induced melting ;Subduction