Note on the genesis of brucite in contact metamorphism of dolomite |
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| Authors: | Professor Dr Francis J Turner |
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| Institution: | (1) Department of Geology and Geophysics, University of California, Berkely/California, USA |
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| Abstract: | Consideration of available thermodynamic data and the published results of direct experiments relating to (1) formation. of periclase from dolomite and (2) hydration of periclase to brucite, permits the following conclusions to be drawn: (1) At very low partial pressures of CO2 (perhaps of the order of 1 bar) and relatively high partial pressures of water (up to 2000 bars), dolomite can break down directly to brucite and calcite at temperatures above about 400° C, and below temperatures on the brucite dehydration curve. (2) The reaction dolomite  calcite + periclase + CO2 in contact metamorphism near granitic bodies is likely to occur only at low partial pressures of CO2 (perhaps 10 or 20 bars); this can be achieved without direct formation of brucite, by maintaining a partial pressure of water of the order of 1000 bars or more. (3) At low CO2 pressures dolomite may re-form in the cooling stages of metamorphism by reaction between calcite, brucite, and CO2 at temperatures below about 400° C. |
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