Karst abnormal development and origin of the Tianxingzhou carbonate rook belt in the Wuhan area

This work studied the characteristics of the Tianxingzhou carbonate zone adjacent to the Xiangfan-guangji fault, located at the middle-north Wuhan. A comparison was made to this rock zone and the Daqiao and Baishazhou carbonate zones to the south in some aspects including rock chemical and mineral composition，lithology and the degree of karst development，karst cave scale，burial depth of karst cave roof under bedrock surface，karst vertical zoning and cave fillings. The results show great differences among them. The development of karst in the Tianxinzhou zone was associated with the activity of the Xiangfan-guangji fault. The first karstification of this zone took place during Late Triassic and Jurassic period. In the Cretaceous and Paleogene period，the extension dominated by the Xiangfan-Guangji fault resulted in fractures and cracks, providing channels for the basaltic magma eruption and tectonic hydrothermal activity. Because of widespread tectonic hydrothermal dolomitization and silicification，the raw rock of the Tianxingzhou carbonate zone suffered reformation，leading to rock combination dominated by dolomite containing silicite with weak dissolution. At the same time，the karstification interrupted due to the broad coverage of red beds. Neogene and early Pleistocene，the carbonate rock zone once again exposed on the surface，suffered second karstification. Due to change of lithology and weakened solubility, the karstification of the Tianxingzhou rock zone became diminished compared with other carbonate belts.