CaC12-H20, with application to fluid inclusions from oceanic hydrothermal systems

Ah&act-Halite solubility along part of the vapor-saturated liquidus in the system NaCl-CaClrHzO has been determined using the synthetic fluid inclusion technique. Data allow the construction of liquidus isotherms for temperatures up to 500°C and bulk compositions containing>60 wt % total salt and as much as 25 wt % CaCl2. Combined with previous data for the binary system NaCl-Hz0 and for the ternary system NaCl-CaC&Hz0 in the low-salinity, low-temperature region, apreliminary ternary phase diagram can be constructed that remains incomplete only in the CaC12-rich region. Results are applied to the interpretation f saline fluid inclusions From quartz veins in oceanic metagabbros, and can be applied to many other natural inclusions containing aqueous olutions with NaCl and CaClr the dominant solutes. Microthermometric measurements at equilibrium of the melting temperature of ice [Tm (ice)] and of the dissolution temperature of halite [Tm (halite)] are sufficient o determine the bulk composition of the NaCl-CaClr-Hz0 fluid