The Feature Of The Fengning-Chicheng Ductile Shear Zone

This paper mainly focuses on the geometry and kinematics of the Fengning Chicheng ductile shear zone, Hebei province. The study of ductile shear zone is one of the hot points in structural geology recently. In this area,we had been taken four muscovite samples of mylonite in the ductile shear zone to test their ages in the way of Ar-Ar.Integrated with the isotope-dating data of different researchers,the ductile shear age should be druring 237~232Ma according to the result of intrusive geochronology and the relationship between the structural deformation and intrusive rocks.Compared with a new geologic times scale provided by ICS,2004,the geologic age of thrusting activity should be Middle Trias. More and more people are focus on the ductile shear zone,especially on the relationship between the ductile shear zone and metallo- genesis.It has always made great progress. The author has researched on the mutual relationship among fault, magmatism and ductile shear activities. Several pieces of new achievements and fresh ideas have been arrived as follows:1,The north of mylonite is mainly composed of no deformed or little deformed granite and diorite.2,The mylonite is mostly distributed in the granite/diorite and gneiss/chorismite, which have characteristic of the middle-lower crust. The lower plate of thrust fault has an extrusion from north to south.3,There is no evidence to show left/right lateral strike-slip faults, only has a fierce squeezing from north to south..4,There is no lower crust substance in the north of the Fengning-Longhua fault, but in the south.5,The Dantazi group which is composed of kalifeldspar-granite and quartz granite, is not deformed.6,Nearby the Chicheng, the north of the ductile shear zone has happened thrusted deformation, and part of diorite severely suffered mylonization.7,A great deal of faults with NS strike have characteristic of left-lateral shear movement.8,It is proved that there is no strike-slip faulting in Chicheng-Shangyi fault.9,The ductile deformation happened during 237 -232 Ma.