Fig. 5. Two anoxic mechanochemistry mechanisms leading to hydrogen and oxidant production in subseafloor environments.
The first mechanism is caused by earthquake-derived cataclasis, which forms Si• and SiO• from crushed ≡Si-O-Si≡. Hydrogen is formed at ≤80 °C from Si• and H2O2 is formed from SiO• at 104 °C. This mechanism requires fluctuating temperatures to produce H2O2. The second mechanism results from the formation of SiOH from magma crystallisation, releasing H• (which combine to form H2) when cooled. A peroxy bridge subsequently forms, splitting into two SiO• under mechanical stress. Under stress, an electron from an adjacent O2− site can be transferred to the electron-deficient SiO•, which can be repeated in a chain reaction through the mineral22. This allows the migration of O− defects through the crystal and adjacent crystal boundaries to form surface SiO•6,22, which can then react with water to generate H2O2 at 104 °C.