| The complex geological structure and tectonically deformed coal of the Enhong syncline are currently the primary geological factors restricting the safe and efficient production of mines and the commercial development of coalbed methane.On the basic of the regional geological background and the tectonic evolution,the field tectonic observation and survey data are analyzed systematically,and the structural characteristics,distribution law,combination style and formation mechanism of Enhong syncline are deeply studied.The development types,deformation characteristics and distribution laws of tectonically deformed coal in Enhong syncline are studied,and the geological model and structural control laws of structural coal development are further discussed based on the underground observation of coal structure,the comprehensive identification method of multi-parameters with three different amplitudes based on the combination characteristics of geophysics logging curves and the ternary diagram of deformation combination of different coal structure,Furthermore,the geological model and structural control law of tectonically deformed coal are discussed.The results show that the Enhong syncline has complex geological structures,with complex combinations of multi-level and multi-directional folds and faults,showing the development law of plane zoning,distribution direction,structural difference,and genetic differences.The NW trending folds and faults are mainly developed in the the northeastern part of the study area,which which are strongly reconstructed in the late period.While the other areas are dominated by NNE-NE trending folds and faults.The structural complexity in the study area is enhanced due to the development of co-directional accompanying structures and NNE trending,NNS trending,NEE trending,and NEW trending derived structures.The fractal dimension of the fault calculated by the “oblique high-precision fine grid” division scheme has a good quantitative characterization for the fault complexity.The Enhong syncline mainly experienced three tectonic activities in the Indosinian,Yanshanian and Himalayan periods.During the the Indosinian period,the NW trending structure was formed in the middle and northeast areas of the Enhong syncline due to the NE-SW trending compression,which was deflected from the NS trending stress under the influence of the NW directing Youjiang fault in the northeast of the study area.During the Yanshanian period,a large number of NE trending structures developed under the NW-SE trending compression.During the Himalayan period,the study area was subjected to EW trending compression stress,resulting in the formation of a small amount of NS-trending structure.Meanwhile,the previous NE trending and NNE trending boundary faults occurred dextral strike-slip,which derived secondary structures such as NNE-trending secondary drag folds and reverse faults,as well as the NEE and NW-trending tension-shear faults.In the late Himalayan period,the strikeslip and extensional tectonics caused the negative inversion of some faults,thus the extensional tectonics developed in the south.The deformation degree of the tectonically deformed coal in the Enhong syncline are strong,mainly type II and III coal,which is consistent with the characteristics of strong structural deformation and multi-phase tectonic activity in the study area.The ternary diagram of deformation combination of different coal structure is proposed,and the deformation combination is divided into 7types of weak deformation type A,medium deformation type B,stronger deformation type C,locally strong deformation type D,strong deformation type E,and strong deformation type F of the whole coal.The structural deformation of different coal seams has obvious vertical differentiation phenomenon,and the deformation of the coal seam at the bottom is weaker than that of the middle and upper coal seam.The development of tectonically deformed coal in the study area has the law of plane zoning.The deformation degree of tectonically deformed coal is the strongest in the western Fuyuan-Mile thrust fault zone,followed by the southern extensional fault block zone,and the structure deformation is relatively weaker in the eastern Youjiang fault fold zone.The structural control law of tectonically deformed coal in the study area is further discussed.Eight types of development models are proposed,containing primary weak structural deformation zone,bedding bending-slip shear zone,strong structural deformation zone of gangue layer,bedding plastic flow zone,compression-shear fragmentation flow zone,fault weak structural deformation zone,fault strong structural deformation zone and mylonitized coal zone between translation faults.The paper has 40 pictures,17 tables,and 141 references. |
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