Effects of hydrous minerals in subduction-zones
In subduction zones, one tectonic plate plunges beneath another into the Earth's interior. Some of the earthquakes that occur at subduction zones are unusual due to their occurrence at depths of 70 to 300 km (intermediate depths), deeper than the expected limit of brittle failure.
However, this might be explained through the unique properties of hydrous minerals. Seawater penetrates deep into these faults and forms new, hydrous minerals, but these new minerals are not stable deeper in the subduction zone. Laboratory experiments show that breakdown of these hydrous minerals can cause seismicity at depths of 70–300 km. Seismicity is correlated with the faults that formed due to plate bending. This observation can be explained if the amount of faulting prior to subduction controls the amount of hydrous mineral formation, which subsequently determines the intensity and rate of subduction zone‐related intermediate‐depth earthquakes.
Deformation experiments of talc (hydrous mineral expected in subduction-zones) at high pressures show its strength evolution which is both temperature and pressure dependent with brittle and ductile characteristics.
Optical image of talc polycrystalline
Talc sample, covered by silver jacket, after deformation experiment in the Griggs apparatus (background)