The Louzidian ductile shear zone at the south of Chifeng strikes NE-SW and dips SE at low-medium- angles. This ductile shear zone is mainly composed of granitic mylonite, which grades structurally upward into a chloritized zone, a microbreccia zone, a brittle fault and a gouge zone. All these zones share similar planar attitudes, but contain different linear attitudes and kinematic indicators. Finite strain measurements were performed on feldspar porphyroclasts using the Fry method. These meas- urements yield Fulin indexes of 1.25―3.30, Lode's parameters of -0.535―-0.112 and strain parameters of 0.41―0.75 for the protomylonite, respectively. These data are plotted within the apparent constric- tional field in Fulin and Hossack diagrams. In contrast, for the mylonite, corresponding parameters are 0.99―1.43, -0.176―-0.004 and 0.63―0.82, respectively, and located in the apparent constrictional field close to the plane strain. The mean kinematic vorticity numbers of the protomylonite and mylonite by using three methods of polar Mohr circle, porphyroclast hyperbolic and oblique foliation, are in the range of 0.67―0.95, suggesting that the ductile shearing is accommodated by general shearing that is dominated by simple shear. Combination of the finite strain and kinematic vorticity indicates that shear type was lengthening shear and resulted in L-tectonite at the initial stage of deformation and the shear type gradually changed into lengthening-thinning shear and produced L-S-tectonite with the uplifting of the shear zone and accumulating of strain. These kinds of shear types only produce a/ab strain facies, so the lineation in the ductile shear zone could not deflect 90° in the progressively deformation.
The Mohr-Coulomb criterion has been widely used to explain formation of fractures. However, it fails to explain large strain deformation that widely occurs in nature. There is presently a new theory, the MEMC, which is mathematically expressed as Meff = ((σ1 ? σ3) L·sin 2α sin α)/2, where σ1?σ3 represents the yield strength of the related rock, L is a unit length and α is the angle between σ1 and deformation bands. This criterion demonstrates that the maximum value appears at angles of ±54.7° to σ 1 and there is a slight difference in the moment in the range of 55°±10°. The range covers the whole observations available from nature and experiments. Its major implications include: (1) it can be used to determine the stress state when the related deformation features formed; (2) it provides a new approach to determine the Wk of the related ductile shear zone if only the ratio of the vorticity and strain rate remains fixed; (3) It can be used to explain (a) the obtuse angle in the contraction direction of conjugate kink-bands and extensional crenulation cleavages, (b) formation of low-angle normal faults and high-angle reverse faults, (c) lozenge ductile shear zones in basement terranes, (d) some crocodile structures in seismic profiles and (e) detachment folds in foreland basins.
