Characteristics of rock magnetic fabric in middle Wahongshan fault zone and its geological significance

The Wahongshan fault zone in Qinghai province is one of the most important faults in western China. Magnetic fabric of the tectonites and some plutons and veins along the middle segment of the fault are studied. The characteristics of the tectonites from the faults are: (1) the values of H , which symbolize the degree of the magnetic anisotropy, are high (5% in general and 10% in fault zone); (2) the magnetic susceptibility ellipsoid is flattened; (3) the magnetic foliation is well developed ,but the magnetic lineation is poor developed. The orientation of the maximum principal stress inferred from the minimum magnetic susceptibility is nearly E-W,so the horizontal movement sense of the shear zones is sinistral.The variations of H,P,F,L,E values along the strike of the fault zones show that the deformation characteristics are different along the fault.The ductile deformations in Ayixiang and Wayanhe-Bayinggeligou-Jiamuen are stronger than the deformations in Hongliugou-Menggao and Laoyan. Because of the low H values of the plutons and veins formed in or after late Hercynian, these rocks have no significant ductile deformation, which indicates that the rocks formed after the formation of the Wahongshan ductile shear zone.