Abstract:

 It is proposed for the first time that the three forms (Th>Tm, Th=Tm and Th<Tm) of moderate and highsalinity NaClH2O fluid inclusions trapped homogenously are mainly determined by their phase states (homogeneous or inhomogeneous) and the relationships between ΔVl (variation in volume of NaClH2Osaturated fluids) and ΔVs (variation in volume of salts) caused by the process of temperature decrease and increase after entrapment of the inclusions. During homogeneous entrapment of NaClH2Osaturated fluids, if ｜ΔVl｜＞｜ΔVs｜, i.e. the inclusions trapped at the temperature less than the temperature range at the Tr point (which is the temperature at ｜ΔVl｜＝｜ΔVs｜) on the NaCl saturation curve, the inclusions have Th=Tm, where Th or Tm is the temperature during their entrapment. If ｜ΔVl｜≤｜ΔVs｜, i.e. the inclusions trapped at the temperatures equivalent to or higher than the temperature range at the Tr point on the NaCl saturation curve, the inclusions have Th＜Tm, where Tm is the temperature during their entrapment and Th has a negative correlation with pressures during entrapment. During homogeneous entrapment of NaClH2Oundersaturated fluids, i.e. when the temperature is higher than that at the saturation point and the inclusions trapped at the densities less than the density ranges at the saturation point, the inclusions have Th＞Tm, where Th is the lowest temperature during entrapment of this type of inclusion. When the inclusions trapped at the temperatures and densities less than those on the isochore at the Tr point, the inclusions have Th<Tm, where Tm is the lowest temperature during entrapment of this type of inclusion and Th has a negative correlation with the pressures during entrapment. When the inclusions trapped at the temperatures and densities greater than those on the isochore at the Tr point, the inclusions have Th=Tm, where Th or Tm is the lowest temperature during entrapment of this type of inclusion. During inhomogeneous entrapment of NaClH2Osaturated fluids, both Th and Tm are higher than or equal to the entrapment temperature. The relationship between Th and Tm is determined by the volume ratio of crystals to vapor bubbles. In this paper the Tr value under the standard conditions (one atmospheric pressure and 25 ℃) of vaporliquid equilibrium is determined through thermodynamic calculations to be 335 ℃. It is suggested that the entrapment environments of this type of inclusion (homogeneous or inhomogeneous) can be distinguished by calculations of Tr values at different temperatures and the ratios of Vl, Vs and Vg at normal temperatures and pressures.

Key words: moderate and highsalinity NaClH2O fluid inclusions, three forms, formation mechanism, physicochemical condition during entrapment