Experimental studies of condensation processes of silicate materials at low pressures and high temperatures, I. Phase equilibria in the system CaMgSi2O6-H2 in the temperature range 1200-1500°C and the pressure range (PH2) 10-6 to 10-9 bar

Details Experimental studies of condensation processes of silicate materials at low pressures and high temperatures, I. Phase equilibria in the system CaMgSi2O6-H2 in the temperature range 1200-1500°C and the pressure range (PH2) 10-6 to 10-9 bar Experimental studies of condensation processes of silicate materials at low pressures and high temperatures, I. Phase equilibria in the system CaMgSi2O6-H2 in the temperature range 1200-1500°C and the pressure range (PH2) 10-6 to 10-9 bar

Oct 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985e%26psl..75..139m&link_type=abstract

Earth and Planetary Science Letters, Volume 75, Issue 2-3, p. 139-146.

Mathematics

Logic

5

Scientific paper

Phase equilibria in the system CaMgSi2O6-H2 in the pressure and temperature ranges 10-9 to 10-6 bar and 1200-1500°C, respectively, have been experimentally determined. The vaporous curve was determined by monitoring evaporation rate and compositional changes as a function of temperature. Crystalline diopside condenses from a gas phase along a vaporous curve with a positive slope of approximately 16°C/log unit PH2 (bars) from about 1360°C at PH2 = 10-9 bar to 1388°C at 3 × 10-7 bar. Partially evaporated diopside at temperatures above its vaporous shows but systematic increase in Ca/Mg with time (and degree of evaporation). There were no chemical changes with time (and degree of evaporation) of diopside within its own stability field. At higher pressures, a liquid condenses from the vapor, with a slope of the liquid-vapor curve of about 50°C/log unit PH2 (bars). The liquidus temperature decreases from 1388°C near the triple point to about 1350°C at PH2 = 10-6 bar and is nearly vertical to PH2 = 1 bar. The Ca/Mg of the liquid exceeds 1 indicating incongruent melting behavior although no additional crystalline phases were observed. Liquid diopside probably also evaporates incongruently.
Provided that the phase equilibria of the diopside composition mimic those of other refractory phases condensing from the early solar nebula and that only H2 gas was present, the experimental results indicate that the pressures in the nebula during condensation of crystals from vapor were significantly lower (< 10-6 bar) than that frequently suggested (> 10-4 bar). Alternatively, if the higher pressure estimates are correct, liquid silicate will condense from the vapor, and vapor-liquid and crystal-liquid equilibria were more important during the petrogenetic processes resulting in aggregated silicate materials than suggested previously.
Also at: Geological Institute, University of Tokyo, Tokyo, Japan.

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