Rheology And Detachment Faulting Of The Upper-Middle Crust

In this paper we aim at the Liaonan metamorphic core complex (MCC). Based on geometric, kinematic and dynamic study, we worked out the main shear type of Jinzhou detachment fault. We carefully researched on the lower plate of detachment fault by using finite strain analysis, kinematic vorticity analysis, quartz dynamic recrystallization thermometer, quartz crystallographic preferred orientation analysis and differential stress piezometer. In this way, we determined the rheology parameters of the Liaonan MCC, and built a model of rheological strength of the Liaonan area.Deformation temperature of the lower plate ranges from 320℃ to 480℃, which is a little lower than temperature inferred by the lattice preferred orientation of recrystallized quartz which ranges from 300℃ to 650℃.Differential stress calculation yield a range of 60.48 MPa to 22.98 MPa. Combine with the temperature data we calculated the strain rate of the Liaonan MCC, and it’s turned out to be 10-12～10-13 s-1.By estimating the geothermal gradient of Liaonan area, we obtain the relationship between the differential stress and the depth (temperature). Since the differential stress is responsible for the deformation extent that rock can suffer, this relationship directly reflects the heterogeneity of the upper-middle crust of the Liaonan area.The model of rheological strength of the Liaonan area fits the model type of "Creme Brulee", which indicates a higher Moho temperature. Based on the kinematic vorticity changing of typical metamorphic core complexes, we infer that the flow of the lower crust might be the drive force for the detachment faulting.MCCs of North China Craton have close relationship with Jurassic magmatic activities. We interpret that the magmatism in the Jurassic age provided heat for the formation of MCC. Jurassic magma increased the geothermal gradient of local crust and shallower the brittle-ductile transition depth by heating the lower crust. This makes it easier for detachment fault to form at where there are Jurassic magmatic activities.