DEVELOPMENT CHARACTERISTIC AND MAIN CONTROLLING FACTORS OF THE ORDOVICIAN KARST CAVES IN LIUHUANGGOU, KEPING AREA

This study aims to characterize the main factors controlling the development of the Ordovician karst cave in Liuhuanggou, the Keping area, China. Tape, compass, portable GPS and camera were used to conduct the field work and measure length, orientation, accurate location and distribution of fracture sets and cavities. Unmanned Aerial Vehicle (UAV) was used to build 3D digital models of the cave structure and fracture sets. The study of thin sections, testing of fluid inclusions, composition of C, O and Sr isotopes was conducted to characterize fracture and cavity development. Key parameters controlling karst development were identified through the application of multiple linear regressions, and neural network and discriminate classification techniques (facilitated by SPSS Statistic 17.0 software). Four fracture sets have been distinguished in the Ordovician limestone of the karst cave. Set 1 includes subhorizontal(dip = 0-10°) intermittently filled fractures, 0.25-1 m-long, striking NNE 40° that are interpreted being formed during the Middle-Late Caledonian orogeny. Set 2 involves inclined (dip = 30-60°) tensile-shear fractures, 0.5-2.5 m-long, striking NNE330° and NEE70° that likely formed in the Early Hercynian orogeny. Set 3 includes variably oriented (dip = 0-50°), fully filled conjugate shear fractures 0.25-1.25 m-long, striking NEE 70° that developed during the Indo-Yanshanian orogeny. Set 4 involves high angle(dip = 50-90°) shear fractures, 0.3-3 m-long, striking NNE30° and NWW310° that formed during the Himalayan orogeny. The cave is filled by the debris and chemical deposits, including sulfur-rich, giant crystal calcite, travertine, sand mud, and gypsum. Two stages of cave filling deposition are distinguished. Stage I was coeval with the Middle-Late Caledonian Set 1 fractures and is attributable to deep hydrothermal fluid circulation. Stage II was coeval with the Early Hercynian Set 2 fractures and is attributable to the circulation of freshwater fluid. The karst caves are connected by and aligned along a fault zone. The Ordovician limestone is characterized by high permeability that facilitates karst development. The wider the fault core or fracture zones, the larger the cave size. Away from the fault, the limestone dissolution is reduced and the karst development less pronounced. At the distance of greater than 1000 m from the fault, only regional factors (lithology and climate) control the cave development.