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Fractional Crystallization in the “Carbonatite Systems” CaO-MgO-CO_2-H_2O and CaO-CaF_2-P_2O_5-CO_2-H_2O

Wyllie, P. J. and Biggar, G. M. (1966) Fractional Crystallization in the “Carbonatite Systems” CaO-MgO-CO_2-H_2O and CaO-CaF_2-P_2O_5-CO_2-H_2O. In: International Mineralogical Association - Papers and proceedings of the fourth general meeting. International Mineralogical Association , pp. 92-105. ISBN 0579-5559. https://resolver.caltech.edu/CaltechAUTHORS:20160307-134420161

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Abstract

Many carbonatite masses exhibit inhomogeneities on both large and small scales. Evidence for large scale differentiation is offered by the successive intrusion of sövite, ankeritic sövite, and finally siderite carbonatites at complexes such as Chilwa Island. On a smaller scale, the segregation of minerals is illustrated by the development of apatite-rich bands and lenses in the carbonatite. In the system CaO-MgO-FeO-H_2O, the minerals calcite, portlandite, periclase, and iron oxide are stable on the vapor-saturated liquidus above 600°C at pressures below about 900 bars, with brucite, dolomite (or ankerite), and sidcrite appearing on this liquidus only at successively higher pressures. In the system CaO-CaF_2-P_2O_5-CO_2-H_2O, apatite and calcite may crystallize simultaneously through a wide range of pressures and temperatures (as low as 575°C). However, any liquid containing initially more than a small percentage of P_2O_5 precipitates apatite before calcite. The synthetic carbonatite magmas are very fluid, and crystal settling occurs within a few minutes. Paths of crystallization and the sequence of minerals precipitated are dependent upon several variables, including changes in temperature, in pressure, and in the composition of the vapor phase (CO_2-H_2O) in equilibrium with liquid and crystals. It can be shown from the phase relationships in these systems that fractional crystallization of synthetic carbonatite magmas is capable of producing differentiation sequences similar to those occurring at Chilwa Island and elsewhere.


Item Type:Book Section
Alternate Title:Fractional Crystallization in the “Carbonatite Systems” CaO-MgO-CO2-H2O and CaO-CaF2-P2O5-CO2-H2O
Additional Information:© 1966 International Mineralogical Association. We are grateful to O.F. Tuttle for his comments during preparation of the manuscript, to D.K. Bailey and H.J. Greenwood for their review of part of the manuscript. Research in the "dolomite" system was supported by National Science Foundation Grants G 19588 and GP-1870, and research in the "apatite" systems was supported by the Department of Scientific and Industrial Research.
Funders:
Funding AgencyGrant Number
NSFG 19588
NSFGP-1870
Department of Scientific and Industrial Research (UK)UNSPECIFIED
Record Number:CaltechAUTHORS:20160307-134420161
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160307-134420161
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ID Code:65131
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:14 Mar 2016 21:54
Last Modified:03 Oct 2019 09:44

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