Effects of high pressure and temperature on the properties of nanocrystals in rocks: Evidences from Raman spectroscopy

A search is conducted to detect nanocrystals in a sample of apogranitic pseudotachylite, which is a product of extremely strong crushing of granite in a seismogenic fault. Raman spectroscopy revealed nanocrystals of quartz measuring approximately 17 to 25 nm and low-temperature albite ranging from 8 to 30 nm. The crystallographic cell in the nanocrystals is deformed. The internal stresses which might have been responsible for these deformations vary from approximately −300 (compression) to +480 (tension) MPa. It is found that after having been exposed to high pressure (1 GPa) and temperature (470–500°C for 10 minutes and 550–600°C for 16 minutes), the nanocrystals of quartz reduced in size to ≈10 nm, and the nanocrystals of albite, to 13 nm. At the same time, the level of tension in the lattice spacing of quartz increased.