DUCTILE SHEAR ZONES IN EARLY PRECAMBRIAN POLYPHASE DEFORMATION AND METAMORPHISM AREAS

Early Precambrian polyphase deformation and metamorphism zones may be classified accord-ing to their relations with deformation and metamorphism into: (1) ductile shear zones formed byprincipal deformation and metamorphism at the early stage, called principal-stage ductile shearzones for short, and (2) ductile shear zones formed by superimposed deformation and metamor-phism at the late stage, called superimposed ductile shear zones for short. No mylonite retrogres-sive metamorphism and neofliation are developed in the principal stage ductile shear zones andtheir high-strain features are mainly manifested by the degree of developmnent of schisosity andlineation in rocks, orientation of minerals, grain size of minerals and strain magnitude. As theschistosity lineation and mineral assemblage of the rocks in the principal-stage ductile shear zonesare the same as those of their surrounding rocks, the comparison of the same strain intensity ofrocks is an effective means for recognizing them. In comparison, the physical parameters that canreflect the intensity of rock deformation such as n (the specific ratio of mineral grains in the direc-tions parallel and vertical to X on the XZ plane), S (the surface area of mineral grains in unit vol-ume) and Rs (strain of mineral forms) are used.