Using Infrared Spectroscopy to Study the Mineral Composition of Shear Fracture Surfaces in Rocks

Infrared-reflection and transmission spectroscopy was used to study the mineral composition of a shear fracture surface in a core recovered from a well in the seismically active Koyna-Varna region in western India, which is associated with reservoir-induced seismicity. Methods for conducting comprehensive experimental studies of the mineral composition of shear fracture surfaces in rocks are described. The experiments demonstrated the wide possibilities of these techniques and allowed us to obtain new results on shear fractures, which are important for further research on the physics of earthquake foci. It is established that the shear fracture surface is a three-layer structure. The upper layer contains only glauconite nanocrystals. The layer beneath it contains, in addition to glauconite, calcite and montmorillonite crystals. The total thickness of these layers is about 600 µm. Below these layers is the host rock, which contains calcite, dolomite, and glauconite. The number of illite–smectite layers in glauconite nanocrystals has been determined. The upper layer contains nanocrystals consisting of ∼30 layers. In the second layer, the crystals of this mineral contain ∼25 layers. Finally, in the host rock, glauconite crystals make up ∼20 layers.