The Fault System And Its Evolution Mechanism Of Huaibei Coalfield

The special structural location of Huaibei coalfield leads to the complicated fault structure through the long-time geological evolution. A lot of geological data have been taken to show the development characteristics, geometric characteristics, kinematic characteristics of the fault structure of the region; the process of evolution of fault in Huaibei coalfield has been reproduced and the mechanism of fault structure has been got from regional geological background, distribution of structure stress field as well as activity of fault, what’s more, sand box analog models and numeric simulation have been combined. On the basis of finding out the fault system, the engineering geological impact of fault structure which is decided by the characteristics of fault structure has been discussed from hydrogeological condition and current geothermal field. The results and cognitions include the following aspects:(1) The growth characteristics of fault structure of Huaibei coalfield have been shown comprehensively:The growth degree of fault structure of Huaibei coalfield is high and there is five groups of the distribution in space as well as the faults in NE and NEE develop the best; normal faults with large angles are the main part in the region and the drop of faults is in accordance with its length of extension in the plane on the whole.(2) The difference of the growth of fault structure in each mining area has been got: There is different characteristic of the growth of fault in each mining area such as that the tectonic deformation in Linhuan and Guoyang mining area is intense and normal faults in the region develop very well. There are two entensional faults which are near south-north and east-west in Guoyang mining area; normal faults of NE with large angle and large drop tend to cover the whole Linhuan mining area; the development of fault in Suixiao, Zhahe and Suxian mining area is relatively weak but many reserve faults of nappe of Xuzhou-Suxian arcuate structure have grown.(3) The fault system of Huaibei coalfield has been classified and the structure unit has been divided. The basic structure situation of that south and north should be divided into region and east as well as west should be divided into band has been assured. The morphology of fault structure in the region is complicated and the style of fault structure has been concluded into extensional fault, compression fault, wrench fault and inverted structure. The typical ideograph of each structure style has been established. The dominant structure style of coal control in Huaibei coalfield is extensional structure; the controlling-depression fault is mainly the straight fault with large angle, rotating plane-like and spade-like are mainly in nappe area of east or partial area of complicated structure; Xuzhou-Suxian arcuate nappe structure could represent compressive fault, especially, the imbricate thrust structure is the most characteristic; the reverse faults develop in the front and nearby area of Xuzhou-Suxian arcuate structure and detachment structure develops partly; wrench faults mainly include EW,NNE and NE as well as they are mostly deep and large faults; inverted structure develops mostly in the front area of Xuzhou-Suxian arcuate nappe structure and they are mainly positive and negative going faults. Different characteristics of fault structure show the generation and pleiotropy of structure stress and the complexity of fault evolution.(4) Strike-slip and stretch movement of Tanlu fault zone from Mesozoic have shown an important effect in the evolution of structure of Huaibei coalfield and the influential periods could be divided into four parts and they are sinistral rotation transform faults period in Indosinian(orogenic period of Dabie-Sulu), large scale strike-slip in early Yanshanian, extensional period of late Yanshanian and the extruding period from Neogene period. In addition, strike-slip movement of Tanlu fault zone and the orogenic movement of Dabie-Sulu are the main factors of the formation of Xuzhou-Suxian arcuate nappe structure.(5) Structure of Huaibei coalfield is structure of coal control of rift and it develops from the latticed broken base, its formation and development is the structure deformation in plate and the boundry of plate which are controlled by regional geological structure. The fault system is very complicated and there is mainly five periods of tectonic deformation, which are Indosinian, early Yanshanian, late Yanshanian, North China period, Xishan Epoch. Structures formed in the early times get to be active in the later period, which leads to the characteristic with the structure activity of later period; the repeated structure activities in the later period let them show the characteristics of early structure from crosscuting relationship.(6) Active faults in the region are mainly large scale normal faults near east-west, especially Subei fault. They have made luffing and translation movement of different scales from Anthropogene, and there exists the possibility of further activity. The fault activity and the style of activity of faults are decided mainly by modern structural stress field.(7) Sand-box analog models experimental results show that,Xusu arc nape structure is the structure style of plane arc and imbrication in profile, and its fault group of thrust is side jointed to the curve in the direction of sliding, as well as it is influenced by the heterogeneous distribution of stress on base and the restriction of Fengpei, Banqiao and Guzhen fault under the shrinking of base and the extruding whose active force came from eastFault system of Linhuan is not only the simple extension structure or pressure shear structure,but pressure shear fault which formed in the compressed obliquely from two directions with contractive substrate,and finally formed by extension and fault depression.(8) Tectonic stress field numerical simulation results show that, the tectonic deformation of the area mainly comes from horizontal stress, tectonic stress field has a fundamental effect on the formation of tectonic framework. Stress field features showed a larger partition In Huaibei, the stress distribution controlled by fault and lithology. The combined analysis of numeric simulation of stress field in plane and profile not only shows the mechanism of strain of detachment fault and extensional fault basin but also show the characteristics of sedimental strata extruding with base.(9) Faut has significant control effect on regional hydrogeological conditions and the groundwater migration. Fault structures controlling water include fault block water model, water diversion fault model and fault storage model,which shown as the demarcation of hydrogeological unit, fault conduction effect and abnormal water-rich of fault development zones.(10) The distribution of current geothermal field in Huaibei coalfield is mainly controlled by regional geological background and regional tectonic framework, And the maldistribution of heat flow in study area is mainly because of the influence of the geological structure on the geothermal field. Especially, the influence of Insulation fault, water heat transfer fault and nappe tectonic is very obvious.