The association of potassic trachytes and carbonatites at the Dicker Willem Complex, southwest Namibia; coexisting, immiscible, but not cogenetic magmas

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doi: 10.1007/s004100000157
Authors:Cooper, Alan F.; Reid, D. L.
Author Affiliations:Primary:
University of Otago, Geology Department, Dunedin, New Zealand
Other:
University of Cape Town, South Africa
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 139(5), p.570-583. Publisher: Springer International, Heidelberg - New York, International. ISSN: 0010-7999
Publication Date:2000
Note:In English. 46 refs.; illus., incl. 3 tables, sketch map
Summary:Trachyte and carbonatite magmas at Dicker Willem are imtimately associated in space and time. From physical interrelationships they were probably immiscible, but geochemical characteristics, particularly their Sr, Nd and Pb isotope ratios, suggest that they were not consanguineous. Their association is considered to have arisen because the formation of trachyte was dependent on the metasomatic interaction of carbonatitic fluid on basement rock types to form fenite. During this process there was a general conversion of fenite isotope ratios towards those of the mantle-derived carbonatites which represent the source of the fenitizing fluids. The end product of fenitization was an ultrapotassic alkali feldspar-rich rock which, with continued fluid fluxing and advective heat input, underwent extensive melting. The ultrapotassic trachyte melt was then emplaced as a series of sills, dykes and plugs into the surrounding fenitized basement collar surrounding the Dicker Willem complex. Emplacement also occurred through a mixed trachyte-carbonatite-fluidized system forming distinctive pellet breccias. [R.A.H.]
Sections:Petrology
Subsections:Igneous petrology
Subjects:Alkaline earth metals; Carbonatites; Chemical composition; Geochemistry; Igneous rocks; Immiscibility; Intrusions; Isotope ratios; Isotopes; Lead; Magmas; Major elements; Metals; Mineral assemblages; Mineral composition; Mixing; Mobilization; Nd-144/Nd-143; Neodymium; Nepheline syenite; Pb-206/Pb-204; Petrology; Phase equilibria; Plutonic rocks; Potassic composition; Radioactive isotopes; Rare earths; Sr-87/Sr-86; Stable isotopes; Strontium; Syenites; Textures; Trace elements; Trachytes; Volcanic rocks; Africa; Namibia; Southern Africa; Dicker Willem Complex
Coordinates:S262900 S262700 E0160200 E0160000
Abstract Numbers:01M/2160
Record ID:2008074030
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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