Abstract
By observing a large number of conjugate shear joint data in the field and underground of the study area, the conjugate shear joint data is analyzed by the stereographic projection method, and the paleo-tectonic stress field experienced in the mining area since the Mesozoic is inferred. Based on the above research, the tectonic evolution process of the eastern mining area of Pingdingshan is discussed from the aspect of dynamic mechanism. The results show that: (1) The eastern mining area of Pingdingshan experienced the Indosinian, Yanshan early-middle, Yanshanian, and Xishanian tectonic stress fields, with the directions of NS, NW, NE, and NNE, respectively. (2) The tectonic evolution of the mining area can be divided into four stages: (a) The Indosinian tectonic stress field has the weakest effect on the study area, the coal-bearing strata are gradually uplifted by the stress field in this period, and some small structures are formed in the coal-bearing strata; (b) The early-middle Yanshanian tectonic stress field has a certain transformation effect on the coal-bearing strata in the eastern part of Pingdingshan. It mainly forms the secondary structure of the mining area such as Huoyan normal fault and small fault-fracture structure; (c) The late Yanshanian tectonic stress field has the strongest effect, and the control complex fold structure with the axis near NW direction is formed under the tectonic stress field of this period, such as Likou syncline, Baishishan anticline, Lingwushan syncline, Guozhuang anticline, Niuzhuang syncline, etc. The near-NW direction of the control fault structure is also formed under the action of the late Yanshanian tectonic stress field, such as the Niuzhuang reverse fault, the original No.11 mine reverse fault, etc.; (d) The Himalayan tectonic stress field mainly forms some secondary and small structures in the mining area and has a certain transformation effect on the structure formed by the early tectonic stress field. The tectonic pattern of the eastern mining area of Pingdingshan is the result of the above-mentioned tectonic stress field acting in sequence with the coal-bearing strata, causing structural deformation of the coal seam.
Highlights
China is the world’s largest coal-producing country with abundant coal resources
(2) The tectonic evolution of the mining area can be divided into four stages: (a) The Indosinian tectonic stress field has the weakest effect on the study area, the coal-bearing strata are gradually uplifted by the stress field in this period, and some small structures are formed in the coal-bearing strata; (b) The early-middle Yanshanian tectonic stress field has a certain transformation effect on the coal-bearing strata in the eastern part of Pingdingshan
It mainly forms the secondary structure of the mining area such as Huoyan normal fault and small fault-fracture structure; (c) The late Yanshanian tectonic stress field has the strongest effect, and the control complex fold structure with the axis near NW direction is formed under the tectonic stress field of this period, such as Likou syncline, Baishishan anticline, Lingwushan syncline, Guozhuang anticline, Niuzhuang syncline, etc
Summary
China is the world’s largest coal-producing country with abundant coal resources. The country’s proven coal geological reserves are 114 billion tons, and its associated coalbed methane (mainly gas) is rich in resources, reaching 36.8 trillion m3, ranking third in the world. Due to the lack of corresponding magmatic activity in the mining area, it is difficult to determine the tectonic deformation period by the traditional isotope dating method, which makes the formation order and evolution law of the fault-fold structure always unclear In this case, it is a more effective way to demonstrate the tectonic evolution process through the inversion of the tectonic stress field. Based on the above situation, this paper carried out extensive field and underground observations on the joint structure of the eastern Pingdingshan mining area, obtained a large number of conjugate shear joint data. The distribution of joints produced by the same tectonic stress field has a certain regularity, usually a large area is developed in the rock mass to form a specific structural pattern.
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