1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. College of Geography Sciences, Harbin Normal University, Harbin 150023, China;
3. State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130012, China;
4. Provincial Key Laboratory of Oil & Gas Chemical Technology, College of Chemistry & Chemical Engineering, Northeast Petroleum University, Daqing 163318, Heilongjiang, China

Montmorillonite was selected as the initial material to simulate the transformation process of montmorillonite into illite by hydrothermal experiments in different temperautres and pressures. The mineralogical and chemical evolution,crystal structure and morphology of the clay minerals were analyzed using X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results showed that:�� the transformation process of montmorillonite illitization depends on the temperature and pressure;�� with the increasing of temperature and pressure,the transformation sequence was from montmorillonite to disordered I/S, ordered I/S, and to illite;�� the transformation process mainly involved dissolution and recrystallization mechanism. The experiment is helpful to the understanding of the transformation process of montmorillonite illitization under the condition of burial and very low-grade metamorphism, and provides basic parameters for the transformation of clay minerals contained in fault gouge during fault activity, as well as the temperature and pressure conditions for the inversion of fault formation.