[SMP32-P21] Dissolution kinetics of forsterite olivine at >200 °C: implication for the kinetics of serpentinization.
キーワード：蛇紋岩、反応速度、かんらん石、溶解速度
Serpentinization (hydration of mantle peridotite) gives significant changes to both chemical and physical properties of the oceanic lithosphere. Several studies suggested that the rate of serpentinization is maximized at 250-300°C, and the rate-limiting process of serpentinization is the dissolution of primary mineral (e.g., Malvoisin et al., 2012). Therefore, the dissolution rate of olivine at 250-300°C is consequently a critical parameter to understand the progress of serpentinization in the oceanic lithosphere. However, the olivine dissolution rates at > 150°C have never been measured (Rimstidt et al. 2012), and the olivine dissolution rate extrapolatory calculated at 300°C was inconsistent with the olivine serpentinization kinetics (Malvoisin et al., 2012). Towards the improved understanding of serpentinization kinetics, measuring dissolution rates of olivine as a function of solution composition and the temperature is required.
In this study, the dissolution rate of natural olivine ((Mg0.91, Fe0.09)2SiO4) was measured at 200-400 °C and 50 MPa using a flow-through reactor (Suzuki et al., 2015). A 0.5 mol/kg NaCl solution was introduced at a constant rate of 2.0 mL/min during experiments. A preliminary experiment revealed that steady-state dissolution rate of olivine at 200 °C and far-from-equilibrium conditions was ca. -4.8 [mol/m2/s] in log units. The obtained dissolution rate was consistent with the extrapolated dissolution rate (log10(Rate) = ca. -4.72 [mol/m2/s]), which was extrapolated from their pH-temperature dependence at 25-150 °C (Rimstidt et al., 2012). Based on dependences of temperature, salinity, and ΔG on dissolution rate, the timescales on hydrothermal alteration of peridotite will be discussed.
References
Malvoisin B, Brunet F, Carlut J, et al (2012) Serpentinization of oceanic peridotites: 2. Kinetics and processes of San Carlos olivine hydrothermal alteration. J Geophys Res Solid Earth 117:1–13. doi: 10.1029/2011JB008842
Rimstidt JD, Brantley SL, Olsen AA (2012) Systematic review of forsterite dissolution rate data. Geochim Cosmochim Acta 99:159–178. doi: 10.1016/j.gca.2012.09.019
Suzuki K, Kato S, Shibuya T, et al (2015) Development of Hydrothermal and Frictional Experimental Systems to Simulate Sub-seafloor Water–Rock–Microbe Interactions. In: Subseafloor Biosphere Linked to Hydrothermal Systems. Springer Japan, Tokyo, pp 71–85
In this study, the dissolution rate of natural olivine ((Mg0.91, Fe0.09)2SiO4) was measured at 200-400 °C and 50 MPa using a flow-through reactor (Suzuki et al., 2015). A 0.5 mol/kg NaCl solution was introduced at a constant rate of 2.0 mL/min during experiments. A preliminary experiment revealed that steady-state dissolution rate of olivine at 200 °C and far-from-equilibrium conditions was ca. -4.8 [mol/m2/s] in log units. The obtained dissolution rate was consistent with the extrapolated dissolution rate (log10(Rate) = ca. -4.72 [mol/m2/s]), which was extrapolated from their pH-temperature dependence at 25-150 °C (Rimstidt et al., 2012). Based on dependences of temperature, salinity, and ΔG on dissolution rate, the timescales on hydrothermal alteration of peridotite will be discussed.
References
Malvoisin B, Brunet F, Carlut J, et al (2012) Serpentinization of oceanic peridotites: 2. Kinetics and processes of San Carlos olivine hydrothermal alteration. J Geophys Res Solid Earth 117:1–13. doi: 10.1029/2011JB008842
Rimstidt JD, Brantley SL, Olsen AA (2012) Systematic review of forsterite dissolution rate data. Geochim Cosmochim Acta 99:159–178. doi: 10.1016/j.gca.2012.09.019
Suzuki K, Kato S, Shibuya T, et al (2015) Development of Hydrothermal and Frictional Experimental Systems to Simulate Sub-seafloor Water–Rock–Microbe Interactions. In: Subseafloor Biosphere Linked to Hydrothermal Systems. Springer Japan, Tokyo, pp 71–85