Abstract:

The Shangdan fault belt as the suture zone of the Yangtze Plate and the North China Plate occupies a significant position in the Qinling Orogen. To study the finestructure of the Shangdan fault belt is a key step in understanding the interaction process of the Yangtze Plate and the North China Plate. The study was implemented at the eastern section of the Shangdan fault belt, in which we carried out the detailed field survey, microstructure analysis, the estimation of temperature of deformed rocks, the finite strain measurement, the calculation of differential stress and the calculation of kinematic vorticity during the mylonitization. The temperature and pressure of the deformation suggested that the mylonites formed in the middlehigh greenschist facies to low amphibolite facies metamorphic conditions. The differential stress indicated that the Shangdan fault belt is a structure belt with largescale dynamic characteristics. The kinematic vorticity suggested that the deformation was mainly the pure shear with the component of simple shear, which proved the boundary between the Yangtze Plate and the North China Plate was an oblique convergence boundary mainly characterized by compression.

Key words: Qinling orogenic belt, Shangdan fault belt, suture zone, flower structure, kinematic vorticity analysis