ИСТИНА

The mechanism of fracture of surface layer of basalt and tonalite (granodiorite), with thickness of 1-2 mcm, under friction was investigated by fracto- and photoluminescence, Raman and infrared spectroscopy methods. The samples were taken from borehole drilled in Killari (Latur) earthquake area, Maharashtra, from depth of 209 m (basalt) and 614 m (tonalite). Tonalite consist of quartz and plagioclases (albite and labrador). The crystallographic lattices of these minerals contain many defects: Fe3+● ions, oxygen vacancies, electron traps and self-trapped excitons. Concentration of quartz crystals after friction of tonalite decreased by an order of magnitude. Concentration of plagioclase decreased 2-3 times in both rocks. The concentration of the defects increased several times in these minerals. Upon friction, microcracks with several nanometer sizes are formed in the surface layer of basalt and tonalite. Crack growth time is about several nanoseconds. The distribution of cracks by sizes obeys to known in seismology power-law relation (Gutenberg–Richter law) between the numbers of cracks and the energy of their formation. It is assumed that the result indicates the border where the power-law is still observed, because nanometers defects in the crystal lattices of minerals correspond to the dislocation scale. The work was carried out in partial fulfillment of the State Institution contracts; the experimental part of the study was supported by the Russian Foundation for Basic Research (project no. 20-05-00155a).