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Published 1969 | public
Journal Article

Liquidus Phase Relationships in the System CaO-CO_2-H_2O to 40 Kilobars Pressure with Petrological Applications

Abstract

Two melting reactions, (i) CaCO_3 + Ca(OH)_2 = liquid and (ii) CaCO_3 + Ca(OH)_2 + vapor = liquid, have been extended from 4 kb to 40 kb using piston-cylinder apparatus. Points measured for reaction (i) are: 655°C at 4 kb, 659°C at 15.5 kb, 662°C at 25 kb, and 666°C at 40.7 kb; and for reaction (ii): 630°C at 4 kb, 565°C at 15.5 kb, 537°C at 25 kb, and 524°C at 40.8 kb. A pressure-temperature projection for the system CaO-CO_2-H_2O is presented, in part schematic, from 300°C to 1500°C and from l bar to 40 kb. The carbonate phase changes from calcite to aragonite with increasing pressure. The compositions of the liquid and vapor phases appear to remain quite distinct up to 40 kb, hut conditions above a hypothetical second critical endpoint for reaction (ii) are illustrated. Textures observed in the quenched liquids are compared with textures described in carbonatites and adduced as evidence supporting a magmatic origin for these carbonatites.

Additional Information

© 1969 American Journal of Science. We are grateful to R. C. Newton for advice and assistance in setting up piston-cylinder apparatus, and to R. C. Newton and J. R. Goldsmith for reviews of the manuscript. The research was supported by National Science Foundation Grants GP-4910 and GA-1289, using apparatus supplied by ARPA Contract SD-89 awarded to the Division of Physical Sciences, University of Chicago.

Additional details

Created:
August 23, 2023
Modified:
October 17, 2023