Solubility of molecular hydrogen in silicate melts and consequences for volatile evolution of terrestrial planets
By M. Hirschmann, A. Withers, P. Ardia, N. Foley. 2012
196 citations recorded by the source corpus.
Abstract We present experiments from 0.7 to 3 GPa that quantify solubility of H 2 in silicate melts under controlled hydrogen fugacities ( f H2 ). Two experimental series, one on synthetic basalt+COH and other with a synthetic andesite+OH, were conducted using a double capsule technique to impose a range of f H2 , on the samples. Quenched glasses were analyzed by FTIR and SIMS. Both series follow simple solubility laws in which molecular H 2 concentrations are proportional to f H2 and with a partial molar volume of molecular H 2 of 11 cm 3 /mole. Solubilities in andesitic melt are systematically greater than in basaltic liquid in a relationship consistent with control by the ionic porosity (IP) of the melts. Extrapolation based on IP allows estimation of the solubility of H 2 in peridotitic melts applicable to magma oceans. The H 2 /(H 2 +H 2 O) ratio in silicate melts (where H 2 O includes molecular H 2 O and OH − ) increases as conditions become more reduced, with increasing pressure, and with increasing total H. Under some conditions prevailing in the early Earth and terrestrial planets as well as in the deep Earth today, H 2 can be a significant fraction of the dissolved H and at high pressure it may exceed “water” (H 2 O and OH − ). Therefore, magmatic H 2 may influence the initial distribution of volatiles and the redox evolution of terrestrial planets, as well as the ongoing formation and fate of hydrous melts in the deep Earth today. Hydrous species in melts in equilibrium with Fe-rich alloy at high pressure, for example during core formation from a magma ocean, could be chiefly H 2 , rather than H 2 O. Hence, delivery of H 2 to the core by removal of Fe hydride need not be coupled to oxidation of the residual mantle. Although lunar basalts are much reduced, the fraction of H dissolved as molecular H 2 is small owing to low total H concentrations. Extrapolation to conditions of potential hydrous partial melting in the deep Earth suggests that the chief magmatic volatile may be H 2 rather than H 2 O. The very small partial specific density of magmatic H 2 (0.18 g/cm 3 at low pressure) may provide significant positive buoyancy to deep partial melts.
Subfields: Ceramics and Composites, Geophysics
View Paper: https://www.semanticscholar.org/paper/3ed7103c892996cf5da4e8ff9679718270d420a4
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Citations in the corpus
- Heterogeneous distribution of H2O in the Martian interior: Implications for the abundance of H2O in depleted and enriched mantle sources (2016, background): “…high pressure is much higher than previously estimated (Hirschmann et al. 2012), and the oxidation process described by Dreibus and Wanke (1985) is likely applicable only to the outermost portions of a planet (Sharp et al. 2013), where H2 solubility decreases substantially (Hirschmann et al. 2012).”
- The abundance, distribution, and isotopic composition of Hydrogen in the Moon as revealed by basaltic lunar samples: Implications for the volatile inventory of the Moon (2013, unknown): “, 2008, 2013), in nominally anhydrous minerals from the lunar highlands (Hui et al., 2013), and in the mineral apatite present in both lunar basalts and magmatic rocks comprising the lunar highlands (Boyce et al., 2010, 2013; McCubbin et al., 2010b, 2010c, 2011; Greenwood et al., 2011, 2012; Barnes ”
- A hydrogen-based oxidation mechanism relevant to planetary formation (2013, background): “(1997) proposed that metal blebs found in glass beads are a result of oxidation of graphite to CO, although it is equally likely (and in fact expected) that iron reduction would be accomplished by decompression of an H2-bearing magma as the H2:OH ratio in the melt at a given f O2 decreases with decr”