Serpentinization

As serpentinizing the conversion of olivine -containing rocks to serpentinite, or the formation of serpentine minerals from olivine is referred to in the geosciences. Both processes are characterized by different geochemical processes.

Serpentinization of peridotites

Serpentinization in the conversion of peridotites to serpentinites occurs at temperatures between 300 and 500 ° C and pressure in the Earth's mantle. This process is described in detail in Lemma serpentinite.

Serpentinization on the ocean floor

Serpentinization is also called the changes that take place by the decomposition of olivine by hydration ( ie, by absorption of water ) at temperatures up to 260 ° C during the metasomatism. This process occurs, for example, from near mid-ocean ridges, where olivinreiches mantle rock can meet with seawater. The conversion of ferrous olivine under these conditions to serpentine and iron-rich brucite is described by the following equation:

As a further variant water effects are also significant in niedrigmetamorphen conditions of greenschist facies, which leads to Serpentinbildung of olivines.

Serpentinization as hydrogen and methane source

On the ocean floor is at its spreading axis in up to 400 ° C hot thermal springs of black smokers and slightly away from the spreading axis in cooler ( to about 90 ° C), alkaline thermal springs of type Lost -City- Hydrothemalquellen with the thermal water hydrogen ( H2 ) and methane (CH4) promoted. The hydrogen formation is considered as a result of serpentinization. The formed during the serpentinization of iron-rich brucite (see equation above) dissolved in water reacts with silicon dioxide ( SiO2) to serpentine, magnetite ( Fe3O4 ), water and hydrogen to:

In summary, the following equation describes the serpentinization of olivine to form magnetite and hydrogen:

It is believed that methane from carbon dioxide also contained in thermal water produced (CO2 ) and the formed during the serpentinization hydrogen by a Fischer- Tropsch synthesis. A general reaction equation for the formation of alkanes of carbon dioxide and hydrogen in the Fischer- Tropsch synthesis is:

The presence of hydrogen and methane in alkaline thermal waters on the ocean floor will be discussed in the context of the emergence of life: Such an environment is considered favorable condition for it. The formation of methane proceeds according to the reaction formula

It is also assumed that these chemical reactions are one of the possible causes for the detected methane in the Martian atmosphere.