Morphological And Kinematic Analysis On Geological Structures Of Yeyu Area In Xishan Coalfield, Taiyuan

Located in the eastern side of Luliang Mountain, the northwestern margin of Jinzhong Faulted Basin, Taiyuan Xishan Coalfield is one of the six major coalfields in Shanxi province. Some consistent results on overall geological structural form and evolution of the coalfield have been acquired by the predecessors:the coalfield is overall a multiple syncline with steep west wing, wide and gentle east wing. Strong tectonic movement and magma intrusion during Yanshanian firstly created the overall geological structural form, owing to the influence of multi-phase tectonic superimposition later, the form of the coalfield was made progressively complex. The analysis of supracrustal medium-small structures are mostly neglected during the geological structural research of the coalfield. However, this type of structures is not only the record of the structural formation and evolution, but also the important shallow response to the deep process of the coalfield, even more importantly, these structures have a tremendous negative impact on the efficiency and safety during coal mining. Consequently, making meticulous research on this type of geological structures has both important theoretical and great practical significance.Taking a range of approximately30km2geologic body in Yeyu area of Xishan coalfield as the object,3D structural geology theories as research perspective, and applying coupling geology idea, based on the observation of the outcrops and analysis of3D physical model, the author identifies the geometric morphological and kinematic characteristics of the structural blocks in the study area and established the tectonic relative event-time series of the study geologic body.The major research results acquired in this thesis are as follows:(1) The study area overall is a monocline with dipping to NE as the structural frame, mainly developing32normal faults in the form of graben-and-horst and step faults within it, besides, some other structural phenomenon such as folds, kink zone, joint fractured zone, fault fractured zone and broken-folded structure.(2) By overlay analyzing geological structural characteristics of the outcrops and the situation exposed in the underground of Xiyu coal mine, it is suggested that the surface and the underground geological structures have some relevance. To some extent, the latter could be forecast according to the former. Moreover, it is found that the dominant direction of karst collapse pillars developed within the area is NE, which could indicate that the fault might play a controlling role in the developing of the karst collapse pillar to some extent.(3) The study area could be divided into two one-level blocks and on the base of the faults and morphological characteristics:Xiyu Block and Yeyu Block. The former is overall a monoclinic structural block dipping to NE with faults and folds developed within the block. It could be further divided into two sub-level blocks:Niejiashan Block and Shentanggou Block, between which is the fault F1as the boundary. Both overall are monoclinic structural blocks with dipping to NNE and NEE, respectively. The degree of deformation of Yeyu Block is more stronger, with blocks dipping to NW, NNW, NNE, NEE and more complicated and variable attitude in it. Yeyu Block could be further divided into three sub-level blocks:Shangyeyu Block, Kaihua Block and Shizhuangtou Block. It could be illustrated that the morphology of Shangyeyu Block is an antiform and broken-folded by analyzing the cutting sections and plasticine model. Kaihua Block is gently inclined with stable attitude and weak strata deformation. Shizhuangtou Block is dipping to NNE-NEE. The latter two are both products of the border mount fracture.(4) On the basis of morphological characteristics of the study area, the author explored the kinematics and established a tectonic relative sense of event-time series:in the Yanshanian, when the coalfield began forming syncline, the study area was experiencing compressional stress, leading to fold deformation of local strata. As the tectonic stress changed, the study area turned to under the control of extensional tectonic stress mainly. Xiyu monoclinic tectonic block formed firstly, then planty of faults formed, striking to NEE. Coming to the Pliocene, continued with EW extensional tectonic stress, NNE striking faults developed and the pre-structures were transformed. Simultaneously, Taiyuan basin started to rift.