Hydrogen partition coefficients between nominally anhydrous minerals and basaltic melts

We have measured hydrogen partition coefficients between nominally anhydrous minerals ( olivine, pyroxenes) and basaltic melts in 13 hydrous melting experiments performed at upper mantle P-T conditions ( 1 - 2 GPa and 1230 - 1380 degreesC). Resulting liquids have 3.1 - 6.4 wt.% H2O and average mineral/melt partition coefficients as follows: D-H(ol/melt) = 0.0017 +/- 0.0005 ( n = 9), D-H(opx/melt) = 0.019 +/- 0.004 ( n = 8), and D-H(cpx/melt) = 0.023 +/- 0.005 (n = 2). Mineral/mineral partition coefficients are D-H(ol/opx) = 0.11 +/- 0.01 ( n = 4), D-H(ol/cpx) = 0.08 +/- 0.01 ( n = 2) and D-H(cpx/opx) = 1.4 +/- 0.3 ( n = 1). These measurements confirm that water behaves similarly to Ce during mantle melting (D-H(peridotite/melt) is similar to 0.009). For mantle water concentrations of 50 - 200 ppm, the onset of melting is 5 - 20 km deeper than the dry solidus, less than previous estimates.