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 Louzidian metamorphic core complex (LMCC) in southern Chifeng is located on the northern margin of the North China craton. Structural analyses of the LMCC and its extensional detachment system indicate that the LMCC experienced two-stage extension. The ductile regime experienced top-to-northeast shearing extension and the brittle detachment fault underwent top-down-outwards slipping. Between these two stages, a semi-ductile regime recorded the transition from ductile to brittle. The hanging wall of the detachment fault is similar to those classic supradetachment basins in western North America. Analyses of provenance and paleocurrent directions in the basins show that there were two filling stages. In the early stage, materials came from the southwest margin of the basin and the hanging wall of the detachment system and were transported from southwest to northeast; while in the late stage, deposits were derived from the footwall of the detachment fault and transported outwards to the two sides of the core complex. Since the filling period of the basins is from the late Jurassic to the late Cretaceous and it is coeval with the extension, the two filling stages reflect the two-stage history of the detachment fault. The large-scale late Jurassic underplating in the deep crust of the Chifeng area led to thickening and heating of the middle-upper crust and trigged the extension at depths and volcanism on the surface. In the early Cretaceous the upper plate of the detachment fault moved northeastwards and sediments were transported from southwest to northeast, while in the late Cretaceous the core complex was uplifted rapidly, the original basin was separated by the uplifted core, and lower-plate-derived debris was deposited in the adjacent upper-plate basins of the detachment fault. Evidentially, the development of the supradetachment basins were controlled by the extension and in turn the fillings in the basins recorded information of the extension, which has provided new evidence for kinematic interpretation of
