Fluid-bearing and fluid-absent invariant points in the system CaO-MgO-Al2O3-SiO2-CO2-H2O for a greenschist facies assemblage |
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| Authors: | B J Watts |
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| Institution: | 1. Geological Survey of N.S.W., 2000, Sydney, Australia
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| Abstract: | An outline for a metamorphic grid involving a greenschist facies assemblage is presented in Watts (1973). This grid is derived from a theoretical determination of all possible P-T dependent (solid-solid) reactions and invariant points as well as those in which a fluid, containing CO2, H2O and other unspecified components, takes part. The thermodynamic data in Watts (1973) were accidentally calculated at 425° K and not at 425° C. Since 425° K is an unreasonably low temperature for greenschist facies equilibria, these data have been recalculated at 700° K (427° C) and a new topology of fluid-absent (solid-solid) reactions and invariant points in P-T space results, since the slopes of such reactions change under conditions at the higher temperature. The slopes of the fluid-bearing reactions are independent of P, T and remain unchanged. However, for each different P-T grid of solid-solid reactions, a new set of chemographic arrangements is valid for the fluidbearing invariant points. A set of μH2O-μCO2 diagrams consistent with, and dependent on the new P-T grid is presented. |
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