Solubility of water-hydrogen fluid in haplogranite, albite, and sodium disilicate melts

Abstract

Solubility curves of water-hydrogen fluid were studied using a high-pressure gas apparatus at a pressure of 200 MPa under variable fluid composition in haplogranite (Ab39Or32Qtz29, 950°C), Na-disilicate (Na2Si2O5, 950°C), and albite melts (1200°C). The mole fraction of hydrogen in experiments was controlled directly by Ar-H2 mixtures using a specially designed cell with a Shaw membrane. \( X_{H_2 }^{Ar - H_2 } \) ranged from 0 to 1. In some experiments with haplogranite and Na-disilicate melts under oxidizing conditions, in order to increase the accuracy of experimental parameters, the fugacities of oxygen and hydrogen were controlled using the double-capsule technique and the solid-phase buffer mixtures Ni-NiO (NNO) and Co-CoO (CCO). The addition of H2 to the H2O-saturated systems (\( X_{H_2 }^{H_2 O - H_2 } \) ≥ 0.012) results in the appearance of a distinct maximum on the solubility curves at \( X_{H_2 }^{H_2 O - H_2 } \) = 0.05–0.07 (H2 mole fractions were calculated for real H2O-H2 mixtures of real gases), and the maximum content of H2O-H2 fluid increases relative to the H2O-saturated melts by 1.51 wt % for haplogranite melt at \( X_{H_2 } \) = 0.063, 2.68 wt % for albite melt at \( X_{H_2 } \) = 0.066, and 3.54 wt % for Na-disilicate melt at \( X_{H_2 } \) = 0.067. A further increase in H2 content in the gas mixture decreases the solubility of H2O-H2 fluid in the melts, and under pure H2 pressure, the contents of fluid components are 0.08 wt % in haplogranite melt and 0.06 wt % in albite melt. The 1H NMR study of aluminosilicate and Na-silicate glasses obtained under the pressure of H2O and H2O-H2 fluids suggests different mechanisms of the dissolution of H2O and H2O-H2 fluids in magmatic melts. In addition to the spectra of dissolved water fluid, the spectra of quenched glasses synthesized under H2O-H2 fluid pressure exhibited a narrow line of molecular hydrogen with a width at half height of 1.8–2.0 kHz at \( X_{H_2 } \) ≥ 0.653 for albite and \( X_{H_2 } \) ≥ 0.063 for Na-disilicate and two lines at \( X_{H_2 } \) ≥ 0.063 for the haplogranite composition.