Experimental water-rock interaction; silica geothermometers in the temperature range 100-350C
Experimental water-rock interaction; silica geothermometers in the temperature range 100-350C
European Journal of Mineralogy (February 1992) 4 (1): 53-65
The reliability of silica geothermometers for different natural mineral assemblages and fluid compositions has been experimentally assessed in the P-T range 185-435 bar, 100-350 degrees C with the Barnes hydrothermal apparatus, using twomica schists and a dolomitic limestone from central Italy and fluids of pure sea- water composition. Silica geothermometry is poorly applicable to carbonate rock. For the feldspar-free mica schists, both the rock chemistry and the fluid composition affect silica solubility at any given P-T. The effect of rock composition is greatly diminished when saline fluids are used. Three new silica geothermometers were calibrated: two for oxidized and reduced silicate assemblages and pure water fluids and one for a variety of silicate assemblages interacting with marine fluids. Combined equations allow a reliable chemical geothermometry over the range 25-350 degrees C provide that the redox conditions of the reservoir and the composition of the initial fluid are known approximately.