Characterization of hyperalkaline fluids produced by low-temperature serpentinization of mantle peridotites in the Oman and Ligurian ophiolites

摘要: A regional survey of alkaline springs in Oman and Ligurian ophiolites shows that the water compositions significantly vary from one ophiolite to other within same ophiolite. The first-order correlation between Na (and K) Cl concentrations points fluid only partly due evaporation. scatter around evaporation line implies may not be conservative during alteration ultramafic rocks. Mg is almost entirely depleted at pH > 10.5 as a result serpentine formation body brucite minor hydrotalcite) precipitation springs. Ca accumulates high-pH fluids consumed by Ca-carbonate springs, mixing with river waters or CO2 supply atmosphere. Thermodynamic calculations show saturation reached values which triggers major changes composition. evolve quartz-saturated low-pH continental environment brucite-dominated serpentinizing system low temperature. highest salinities are found located along basal thrust plane Al some on crustal side mantle/crust boundary. This poses question hydrologic pathways role mineralogical composition altered formations. Key Points New temperature Brucite chemical Relationship