Abstract:
Three major settings of hydrothermal karst development are: endokarst, deep-seated karst, and shallow karst. Endokarst develops at great depth, where the pressure exceeds the strength of the rock and voids can exist only if they are filled with overpressured fluid, which prevents them from collapse. In the deep-seated setting hydrothermal karst develops in response to changes of pressure and temperature of upwelling fluids. Two large zones: (1) zone of carbonate dissolution and (2) zone of carbonate precipitation form within hydrothermal systems. The shallow setting encompasses the interface between thermal and low-temperature waters or the zone near the upper surface of thermal waters. Four major conditions, which create and enhance solutional capacity in hydrothermal systems are: (1) elevated temperature gradients (for carbonated waters); (2) elevated rate of discharge (for carbonated waters); (3) oxidation of hydrogen sulfide; and (4) mixing waters of contrasting chemistry. These features readily occur in the shallow hydrothermal karst setting; the largest hydrothermal caves are formed there. Morphologies and dimensions of hydrothermal caves range from pores, individual rooms, and single conduit caves to large three-dimensional mazes. Cave deposits hold clues as to their origin in their mineralogy, morphology, chemistry, isotopic properties, and fluid inclusion temperatures.