The Tectonic Evolution And Its Control Action On Coal Deformation In Laochang Anticline Of Eastern Yunnan

The development of tectonically deformed coal?TDC?is one of the important factors affecting CBM exploration and exploitation.Taking the Laochang anticline as research area,this paper analyzed the tectonic evolution and formation mechanism,and discussed the control effects of tectonic evolution on the development and distribution of TDCs,which will provide important application guidance and reference for the CBM exploration in this area.Based on systematic collection and summary of the geological data,regional geological background and evolution history of study area,practical works,such as field observation of structures,restoration of paleo-tectonic stress field macro and micro-deformation observation of TDCs and the research of distribution law of different coal structures,were conducted to deeply discuss the development and distribution rules of various TDCs and its main controlling geological factors.The achieved research results are as follows:1.The deformation characteristics and formation mechanism of the Laochang anticline structure are discussed based on the analysis of regional tectonic background and combined with the typical structures observation and joint system measurement.tThe Laochang anticline and the surrounding faults and folds of different size constitute the Laochang diamond-shaped broken zone.Typically,the Laochang anticline is divided into 6 secondary tectonic zones,the NE fault-fold structural zone in the core,the steeply inclining monoclinic zone in the NW wing,the gently inclining fault zone in the SE wing,the gentle fold zone in the SE wing,the southern complex fault block zone and the eastern complex fault zone.The study area mainly experienced the effects of NNE compression in the Indosinian period,NW-SE compression in the Yanshanian period and EW compression in the Himalayan.The controlling effects of the different tectonic stresses on the structural deformation characteristics of study area were separately discussed in-depth and it is confirmed that the Yanshanian NW-SE tectonic compression has the key control effect on the tectonic framework formation of the Laochang anticline.2.The systematic study on the macroscopic and microscopic deformation characteristics of the Laochang anticline TDC samples reveals the developmental characteristics of tectonic coal in the study area.According to the analysis of macro and micro-degeneration characteristics,the structural coal in the Laochang area is divided into five types:broken coal,broken spot coal,flaky coal,scale coal and wrinkled coal.Among them,fragmented coal,broken plaque coal and flaky coal are brittle deformation series,scale coal is brittle-tough transition series,and wrinkled coal reflects the characteristics of ductile deformation.The TDC in the study area is dominated by brittle deformation series of structural coal,which is widely distributed,while the transitional and ductile deformation series of TDC is weakly developed and limited in layout.3.Based on the identification of selected logging curves,the coal structure types are divided and the development characteristics of different TDCs are discussed.According to the analysis of borehole data and the interpretation of logging curves,the coal structures are divided into three different types:type I coals are mainly composed of primary structural coal and weakly deformed broken coal,type II coals are fragmented coals with strong deformation,flaky coal and broken spot coal,type III coals mainly include scaly coal of transitional series and crumpled coal of ductile series.By comparative analysis of the logging curves of the C₉ and C₁₃ coal seams which are the main mining coal seams of study area,it is found that both of the two coal seams are dominated by type I coal and type II coal while type III coal is relatively weakly developed,and that the proportion of type I coal gradually increases with the increase of coal seam thickness.4.The factors affecting coal deformation of Yuwang block were analyzed and it shows that faults and folds play a key role on coal deformation.The thickness contour maps of different coal structures of Yuwang block are analyzed and the influences of faults and folds on coal deformation are systematically summarized.It is believed that the NE reverse faults formed during the Yanshanian period play a key role in controlling the deformation of coal body and affect the distribution laws of different TDCs.The results show that the developed TDCs gradually transforms from the strongly deformed type III coal to type II and type I coals with the distance to faults increasing.The EW compression during the Indosinian period has a weak influence on the structure development of study area.Specifically,it mainly results the increase of TDCs thickness in partial areas by superposition with the nearby faults.