Skip to main content
eScholarship
Open Access Publications from the University of California

UCLA

UCLA Electronic Theses and Dissertations bannerUCLA

Experimental determination of quartz solubility in KCl-H2O solutions at 7.5 and 10 kbar and 600-800°C

  • Author(s): Pempeña, Napoleon;
  • Advisor(s): Manning, Craig E;
  • et al.
Abstract

Brines are potentially important agents of mass transfer in the lower crust and subduction zones. Experiments and models typically assume that alkali-halide solutions can be approximated by the system NaCl-H2O. However, KCl is also likely to be abundant in high pressure and temperature fluids, and the effect of this solute is unknown. We experimentally determined the solubility of quartz in H2O-KCl solutions at 7.5 and 10 kbar and 600-800°C. We used hydrothermal piston cylinder methods and determined solubility by weight loss.

At 10 kbar and 800°C, quartz solubility is 1.23 mol SiO2/kg H2O in pure H2O. Quartz solubility increases slightly with addition of a small amount of KCl up to 0.06 bulk KCl mole fraction (XKCl). At higher XKCl, quartz solubility decreases exponentially to 0.19 mol SiO2/kg H2O at sylvite saturation (XKCl = 0.70). Quartz solubility decreases with T at constant XKCl. At 700°C and 600°C, quartz solubility at sylvite saturation (XKCl = 0.60 and 0.54, respectively) is 0.22 and 0.17 mol SiO2/kg H2O. At 7.5 kbar, “salting in” or silica solubility enhancement is observed at XKCl < 0.025. Solubility then decreases monotonically.

Solubility variations at different P, T and salt types can be compared using the relative solubility (i.e., observed solubility divided by that in pure H2O at P, T). In H2O-NaCl solutions at 10 kbar, relative solubility decreases with rising NaCl mole fraction independent of temperature. This is not seen at high P in KCl-H2O solutions. Relative quartz solubility measurements in KCl-H2O solutions at 7.5 and 10 kbar are higher than in NaCl-H2O solutions at any given salt mole fraction. Values in KCl-H2O solutions are comparable to those in NaCl-H2O solutions at lower P of ~5 kbar. This could be a result of the formation of hydrated KCl-SiO2 complexes.

Textural and geochemical analyses of many petrologic examples indicate mass transport of silicates and mineral paragenesis enabled by alkali-rich, low-a(H2O) fluids. This newly discovered enhancement of silica solubility in KCl-H2O solutions implies the possibility of significant silica metasomatism involving potassic salt solutions in deeper environments.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View