Formation and properties of water from quartz and hydrogen at high pressure and temperature

Z Futera and X Yong and YM Pan and JS Tse and NJ English, EARTH AND PLANETARY SCIENCE LETTERS, 461, 54-60 (2017).

DOI: 10.1016/j.epsl.2016.12.031

Quartz, as the most stable low-pressure polymorph of silica (SiO2), is widely abundant in Earth's crust and mantle, exhibiting relatively high chemical stability. Although silica is only slightly soluble in water at ambient conditions, producing silicon-based weakly acidic compounds, Shinozaki et al. (2014) have shown recently that water itself can be formed by dissolution of SiO2 in H-2 fluid under high-temperature and pressure conditions. Here, we have simulated this process via molecular- dynamics techniques based on a reactive force-field description of the SiO2/H-2 interface. Diffusion of the H-2 fluid into the quartz crystal lattice was observed upon increasing temperature and pressure, followed by interaction of dissociated, atomic hydrogen with oxygen atoms in the SiO2 lattice, disrupting the lattice and leading to the formation of water. Interestingly, water is evolved in the subsurface region of the silica, and it remains confined there, isolated from the hydrogen fluid, which corresponds precisely to the ice-like spectroscopic patterns observed experimentally. The over-pressured water formed from quartz and H-2 is a possible trigger for nucleating enigmatic deep earthquakes in the continental mantle lithosphere. (C) 2016 Elsevier B.V. All rights reserved.

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