Carbon isotopes, chemotrophs, hydrogen, hydrothermal vents, methane, ultramafic rocks

Serpentinization is the process of hydrothermal alteration that transforms Fe-Mg-silicates such as olivine, pyroxene, or amphiboles contained in ultramafic rocks into serpentine minerals. Much of the uppermost mantle in oceanic setting is so altered, as are the cumulus parts of layered intrusions. Serpentine is a soft ductile mineral and its presence in the mantle wedge lubricates subduction of the oceanic plate. Production of serpentine in the oceanic crust produces hydrothermal fluids and releases gaseous methane and hydrogen, as observed along mid-ocean ridges. The pH of the hydrothermal fluids is generally low but under some conditions, notably at low temperature, may be high enough to be favorable to life.