SOME BASIC PROBLEMS ON DUCTILE SHEAR ZONES ALONG COAL SEAMS WITHIN SHALLOW AND SUPERFICIAL TECTONIC LAYERS

摘要

In the shallow and superficial tectonic levels, ductile shear zones have been surveyed for the past years and it was called coal-seam fault because it always exists in and extends along coal-seam. The further study shows that most of them have characteristics of ductile deformation and we named it as coal-seam ductile shear zone in this paper. The cross section structure of coal-seam ductile shear is divided into main shear zone and secondary zone. Main shear zone was made of mylonitic coal with flake and foliated texture. Both kinds of tectonic coal are the result of ductile deformation. But on the secondary shear zone, there is mainly cataclastic coal which is considered as the result of brittle-ductile deformation. The cross-section structure of coal-seam ductile shear zone is asymmetric. The main shear zone is not in the midst of the structure zone but always on the secondary shear zone and contacts directly with the upper normal zone (undamaged zone). The secondary shear zone is always beneath the main shear zone and contacts directly with lower normal zone. Three shear planes have been discovered in the shear zone. They exist between normal zone and shear zone, and between main shear zone and secondary shear zone. It is the three shear planes that make us can tell shear zone from the normal zone and distinguish main shear zone from secondary shear zone. As mentioned above, from upper to lower, by structure feature, the structure sequence are as follows: roof, upper normal zone, main shear zone, secondary shear zone and lower normal zone or floor. Obviously, the structure feature in the cross section is asymmetic. But, in this kind of coal field where coal series has undergone intensive deformation, coal was damaged very intensely and all of them became mylonitic coal. The occurence of almost all of the coal-seam ductile shear zone stretched parallel to coal seam.