Serpentinite - Formation and Petrology

Formation and Petrology

Serpentinization is a geological low-temperature metamorphic process involving heat and water in which low-silica mafic and ultramafic rocks are oxidized (anaerobic oxidation of Fe2+ by the protons of water leading to the formation of H₂) and hydrolyzed with water into serpentinite. Peridotite, including dunite, at and near the seafloor and in mountain belts is converted to serpentine, brucite, magnetite, and other minerals — some rare, such as awaruite (Ni₃Fe), and even native iron. In the process large amounts of water are absorbed into the rock increasing the volume and destroying the structure.

The density changes from 3.3 to 2.7 g/cm3 with a concurrent volume increase on the order of 30-40%. The reaction is exothermic and large amounts of heat energy are produced in the process.

Rock temperatures can be raised by about 260 °C, providing an energy source for formation of non-volcanic hydrothermal vents. The magnetite-forming chemical reactions produce hydrogen gas under anaerobic conditions prevailing deep in the mantle, far from the Earth atmosphere. Carbonates and sulfates are subsequently reduced by hydrogen and form methane and hydrogen sulfide. The hydrogen, methane, and hydrogen sulfide provide energy sources for deep sea chemotroph microorganisms.