Synthetic fluid inclusions XXIII. Effect of temperature and fluid composition on rates of serpentinization of olivine

Serpentinization, i.e. the hydrothermal alteration of ultramafic rocks, is an important and ubiquitous geologic process that occurs at slow- ultraslow-spreading mid-ocean ridges, magma-poor passive margins, subduction zones. While serpentinization over a wide temperature range involves diverse fluid compositions, few experimental studies systematically examined effects composition on kinetics olivine, published rates diverge greatly. We present results study using synthetic inclusions in Mg-rich olivine as micro-batch reactors to monitor (100–350 °C), (H2O-MgCl-NaCl, H2O-NaCl, H2O-MgCl), total salinity under closed system conditions. Petrographic observations Raman analyses run products revealed produce serpentine minerals, brucite, magnetite. The aqueous increased H2O was removed from solution incorporated into hydrous product phases served proxy for reaction progress. fastest were found 250 °C presence seawater-like solution. This result further suggests lower temperatures (?250 °C) shallower depths oceanic lithosphere than suggested by previous (?300 °C). Moreover, our experiments show decrease several orders magnitude concentration dissolved Mg increase. These may reconcile some differences observed when comparing previously obtained involving fluids different compositions. constructed quantitative model based principle detailed balance predict variations (J±) low 320 °C. It 25 °C, are 4 5 slower dependence has been coupled with kinetic derived calculate amount time required having reactive surface areas. shows between 200 300 fast timescales rocks large areas interact (complete days decades).