Zoisite--Anorthite--Calcite Stability Relations in H2O--CO2 Fluids at 5000 Bars: An Experimental and SEM Study
- 1 May 1982
- journal article
- Published by Oxford University Press (OUP) in Journal of Petrology
- Vol. 23 (2) , 215-239
- https://doi.org/10.1093/petrology/23.2.215
Abstract
The reaction 2 zoisite + CO2 = 3 anorthite + calcite + H2O has been reversed experimentally in cold-seal pressure vessels using natural phases and H2O–C02 fluids generated by water-silver oxalate mixtures. Equilibrium has been determined at 5000 50 bars, 599 9 °C and 0–075 ± 0–010 XCO2. Extrapolation using the MRK equation of Kerrick & Jacobs (1981) gives an equilibrium curve of negative T–X slope consistent with bracketing runs at 500, 550 and 650 °C. The curve agrees only with a new bracket of Nitsch (in Hoschek, 1980), and is at higher XCo2 than all other experimental determinations and at lower XCO2 than those calculated from the thermodynamic data of Helgeson et al. (1978). Discrepancies are attributed to differences in starting materials and small errors in the thermodynamic properties of the phases.Keywords
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