Hydrogen partitioning between nominally anhydrous upper mantle minerals and melt between 3 and 5 GPa and applications to hydrous peridotite partial melting

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• 作者：Travis J. Tenner ; Marc M. Hirschmann ; Anthony C. Withers ; Richard L. Hervig
• 关键词：Hydrogen partitioning ; Experimental petrology ; Mantle melting
• 刊名：Chemical Geology
• 出版年：2009
• 出版时间：15 May 2009
• 年：2009
• 卷：262
• 期：1-2
• 页码：42-56
• 全文大小：2435 K

文摘

To extend our knowledge of partitioning of hydrogen between nominally anhydrous mantle minerals and basaltic melts to higher pressures, we conducted 8 experiments at 3–5 GPa and 1350–1440 °C on a modified mid-ocean ridge basalt (MORB) + 2 wt. % H₂O. H contents in olivine, orthopyroxene, clinopyroxene, and garnet were measured by counting ¹⁶O¹H ions with low-blank SIMS, and total H₂O concentrations in coexisting glasses were measured by FTIR, SIMS, and electron microprobe. The glasses have water contents ranging from 4.1 to 8.9 wt. % . Eleven measured pyroxenes have H₂O concentrations ranging from 430 to 1430 ppm, two garnets have concentrations of 73 and 260 ppm, and one olivine has a concentration of 29 ppm. Mineral/melt hydrogen partition coefficients are as follows: D_H^cpx/melt ranges from 0.014–0.021, D_H^opx/melt ranges from 0.009–0.019, D_H^gt/melt ranges from 0.001–0.0033, and D_H^ol/melt has a value of 0.0006. Mineral/mineral hydrogen partitioning data are as follows: D_H^cpx/opxranges from 1.2–2, D_H^cpx/gt has values of 5.5 and 14, and a single D_H^cpx/ol has a value of 27. D_H^pyx/melt correlates with the concentration of Al₂O₃ in pyroxene and with the concentration of Al on tetrahedral sites. Combining the mineral/melt hydrogen partitioning data from this study, and estimates of mineral modes and compositions along the solidus, we estimate that D_H^perid/melt increases from 0.006 at 1 GPa up to 0.01 near the garnet lherzolite/spinel lherzolite transition, owing to the maximum in Al₂O₃ concentration in pyroxenes. With increasing pressure D_H^perid/meltfor garnet lherzolite diminishes to 0.005 at 5 GPa, as pyroxenes become less aluminous and less abundant. As a result, incipient hydrous melts beneath oceanic ridges with bulk mantle H₂O contents of 50–200 ppm will have solidus partial melts with H₂O contents between 0.5 and 3.8 wt. % , while oceanic island mantle with 300–1000 ppm will have solidus partial melts with H₂O content between 3 and 20 wt. % .