With a detailed study on petrology, mineralogy and geochemistry of some important Ordovician carbonate well core samples in Tazhong uplift of Tarim Basin, the distinguishing symbols of hydrothermal karstification are first put forward as the phenomena of rock hot depigmentation, hot cataclasm and the appearance of typical hydrothermal minerals such as fluorite, barite, pyrite, quartz and sphalerite. The main homogenization temperatures of primary fluid inclusions in fluorite are from 260 to 310 , ℃ indicating the temperature of hydrothermal fluid. The fluid affected the dissolved rocks and showed typical geochemistry features with low contents of Na and Mg, and high contents of Fe, Mn and Si. The ratio of 3 He/ 4 He is 0.02R a , indicating the fluid from the typical continental crust. The hydrothermal fluid karstification pattern may be described as follows: the hot fluid is from the Permian magma, containing dissolving ingredients of CO 2 and H 2 S, and shifts along fault, ruptures and unconformity, and dissolves the surrounding carbonates while it flows. The mechanism of hydrothermal karstification is that the mixture of two or more fluids, which have different ion intensity and pH values, becomes a new unsaturated fluid to carbonates. The hydrothermal karstification is an important process to form hypo-dissolved pinholes in Ordovician carbonates of Tazhong uplift of Tarim Basin, and the forming of hydrothermal minerals also has favorable influence on carbonate reservoirs. hydrothermal karstification, hydrothermal mineral, carbonate reservoir, Ordovician, Tazhong regionThe study of hydrothermal fluid is the frontier field of modern geosciences [1,2] . It has been deeply studied in metal mineralization both at home and abroad, and less involved in the study of sedimentary basins. In recent years, the research of hydrothermal fluid in sedimentary basins has been mainly concentrated on the hydrothermal activities affecting the reservoir and organic hydrocarbonization [3][4][5] . The hydrothermal fluids often contain abundant ingredients with strong chemical activity such as CO 2 , H 2 S, and SO 2 [6] , release large amounts of heat, impel various physical chemistry reactions between the hydrothermal fluid and its surrounding carbonates, and dissolve the carbonates, namely hydrothermal karstification. These processes have greatly improved the reservoir quality and thus have been paid great attention to in recent years. But many major problems are devoid of systemic research, especially the features of hydrothermal karstification, the identifying symbols, the hydrothermal karstification pattern and so on. In that the carbonate reservoir is tightly associated with the magma fluid in Tazhong uplift of Tarim Basin, this article provides a detailed and systemic study on petrology, mineralogy and geochemistry in order to reveal the feature of hydrothermal karstification, its identifying symbols, the hydrothermal karstification pattern and its influence on carbonate reservoirs.
