Structures and transport properties of supercritical SiO2-H2O and NaAlSi3O8-H2O fluids

Abstract

Speciation and transport properties of supercritical fluids is critical for understanding their behaviour in the Earth's interior. Here, we report a systematic first principles molecular dynamics simulation study of the structure, speciation, self-diffusivity (D) and viscosity (η) of SiO 2 melt, NaAlSi 3 O 8 melt, SiO 2 -H 2 O and NaAlSi 3 O 8 -H 2 O fluids at 2000 -3500 K with 0 -70 wt% H 2 O. Our calculations show that as the water content increases, the proportion of Q 0 species (Q n species, where n is the number of bridging oxygens in an individual Si/Al-O polyhedra) increases while Q 4 decreases. The proportions of Q 1 , Q 2 and Q 3 species first increase and then decrease with increasing water content. The diffusivity sequence for the supercritical SiO 2 -H 2 O fluids is D H > D O > D Si , and for the supercritical NaAlSi 3 O 8 -H 2 O fluids, on the whole, is

Mobility of Magmas Within the Earth: Insights From the Elasticity and Transport Properties of Hydrous Albitic Melts

“…Our results therefore highlight that the hydrous melt structure is relatively depolymerized compared to the anhydrous melt at crustal to upper mantle conditions (Karki & Stixrude, 2010). Sun et al, 2023). Solid circles and squares are taken from (a) to (c).…”

“…The faded bands show ±95% confidence in the trends. The lines for 2500–4000 K are calculated by $${\log }_{10}(\eta )\left(T,{X}_{{\mathrm{H}}_{2}\mathrm{O}}\right)={\log }_{10}\left({\eta }_{0}\right)+{\left(\partial {\log }_{10}(\eta )/\partial {X}_{{\mathrm{H}}_{2}\mathrm{O}}\right)}_{T}\cdot d{X}_{{\mathrm{H}}_{2}\mathrm{O}}+{\left(\partial {\log }_{10}(\eta )/\partial T\right)}_{{X}_{{\mathrm{H}}_{2}\mathrm{O}}}\cdot dT$$, where log 10 ( η 0 ) = 1.1 (±0.6) Pa s, $${\left(\partial {\log }_{10}(\eta )/\partial {X}_{{\mathrm{H}}_{2}\mathrm{O}}\right)}_{T}=-5.5\,(\pm \,0.3)$$ Pa s per mole fraction H 2 O, and $${\left(\partial {\log }_{10}(\eta )/\partial T\right)}_{{X}_{{\mathrm{H}}_{2}\mathrm{O}}}=-1.6\,(\pm \,0.2)\times {10}^{-3}$$ Pa s K −1 , based on our and earlier work (Sun et al., 2023). The dashed lines at 1300 and 1823 K are linear interpolations between extrapolated η of the anhydrous and hydrous melts (Equations and ; Table 3).…”

“…The “amb.” indicates ambient pressure and temperature for reference. Open circles indicate FPMD predictions for silicate‐rich fluids (S23; Sun et al., 2023). Solid circles and squares are taken from (a) to (c).…”

“…• dT, where log 10 (η 0 ) = 1.1 (±0.6) Pa s, ∂log 10 (η)/∂X H 2 O ) T = 5.5 (± 0.3) Pa s per mole fraction H 2 O, and ∂log 10 (η)/∂T) X H 2 O = 1.6 (± 0.2) × 10 3 Pa s K 1 , based on our and earlier work (Sun et al, 2023). The dashed lines at 1300 and 1823 K are linear interpolations between extrapolated η of the anhydrous and hydrous melts (Equations 7 and 8; Table 3).…”

“…Increasing the temperature of melts yields viscosities comparable to H 2 O-rich fluids at significantly lower temperatures (Figure 4). As a result, H 2 Orich melts or fluids should be highly mobile even at low temperatures and high pressures (Audétat & Keppler, 2004;Sun et al, 2023). Geochemistry, Geophysics, Geosystems 10.1029/2024GC011510…”