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Melting relationships in the system CaO-MgO-SiO_2-H_2O at 1 kilobar pressure

Franz, G. W. and Wyllie, P. J. (1966) Melting relationships in the system CaO-MgO-SiO_2-H_2O at 1 kilobar pressure. Geochimica et Cosmochimica Acta, 30 (1). pp. 9-22. ISSN 0016-7037. doi:10.1016/0016-7037(66)90088-3.

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Solid-liquid-vapor phase relationships in the system CaO-MgO-SiO_2-H_2O have been determined at 1 kilobar pressure using the quench technique in cold-seal pressure vessels. The phase fields intersected by the composition joins Ca(OH)_2-Mg_2SiO_4 and Ca(OH)_2-MgSiO_3 have been delineated in the temperature range 700–950°C. From these results and from previous work in the bounding systems, a schematic diagram for the phase relationships on the vapor-saturated liquidus surface has been prepared. A thermal divide exists on this surface, corresponding to the melting of mixtures on the join Ca_2SiO_4-MgO in the presence of H_2O vapor. Original liquids with compositions on the SiO_2 side of the divide yield anhydrous crystalline phases and vapor on fractional crystallization, whereas original liquids with compositions on the CaO side of this divide yield hydrated crystalline phases (calciochondrodite and portlandite) plus vapor. The estimated compositions of isobaric invariant liquids at 1 kilobar pressure for the reactions: portlandite + calciochondrite + periclase + vapor ⇌ liquid, at 725°C calciocondrite + periclase + vapor ⇌ dicalcium silicate + liquid, at 875°C, are Ca(OH)_2−92.7%, Ca_2SiO_4−4.3%, MgO−2.5%, H_2O−0.5%, and Ca(OH)_2−62.1%, Ca_2SiO_4−25.6%, MgO−11.3%, H_2O−1.0%. These results provide a basis for interpretation of the phase relationships in the more complex system CaO-MgO-SiO_2-CO_2-H_2O which have bearing on the petrogenetic relationships between kimberlites and carbonatites.

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Alternate Title:Melting relationships in the system CaO-MgO-SiO2-H2O at 1 kilobar pressure
Additional Information:© 1966 Published by Elsevier Ltd. Received 17 June 1965. We would like to thank D. M. Roy for her assistance at various stages during the work, W. C. Luth for a critical review of the manuscript, and the National Science Foundation for supporting the research at the Pennsylvania State University with Grants G-19588 and GP-1870.
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Official Citation:G.W Franz, P.J Wyllie, Melting relationships in the system CaO-MgO-SiO2-H2O at 1 kilobar pressure, Geochimica et Cosmochimica Acta, Volume 30, Issue 1, January 1966, Pages 9-22, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63576
Deposited By: Ruth Sustaita
Deposited On:12 Jan 2016 18:15
Last Modified:10 Nov 2021 23:18

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