Coupled reactions and silica diffusion during serpentinization

摘要: Abstract Silica activity is one of the key factors in controlling reaction paths serpentinization. We conducted hydrothermal experiments olivine (Ol)–orthopyroxene (Opx)–H 2 O system at 250 °C and a vapor-saturated pressure 3.98 MPa to explore role silica diffusion aqueous fluids during Olivine (Fo 91 ), orthopyroxene (En or their composite powders (with Ol/Opx/Ol zones) were set tube-in-tube vessels, solution chemistry extent serpentinization analyzed detail. In Ol–H experiments, product changed from serpentine + magnetite serpentine + brucite + magnetite, accompanied by Si-drop solutions. Serpentinization proceeded uniformly throughout tube, indicating that supply water was not rate-determining process. Opx–H orthopyroxenes dissolved along cleavages, amount newly formed serpentine very small. The solutions 1–3 orders higher than experiments. Ol–Opx–H both Ol Opx zones. zone, constant, whereas most extensive boundary between zones, it decreased gradually away boundary. modeled simply coupled processes involving two reactions: silica-consuming after silica-releasing orthopyroxene. spatial pattern controlled coefficient solution, D SiO2,aq , apparent rate constants k ′ zone. Assuming  = 2.0 × 10 −4  cm /s, observed variation run 1512 h best fitted simulation with  = 4.4 × 10  = 3.2 × 10 −5  s −1 constant ∼14 times zone Our experimental results represent an analogue natural systems high porosity, we suggest as function distance source could be useful indicator relative magnitudes reaction, mass transport, fluid flow well temperature alteration oceanic lithosphere.