Alkaline Rocks and Carbonatites of the World

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Noqui

stripes

Occurrence number: 
038-00-020
Country: 
Comoros
Location: 
Longitude: 13.48, Latitude: -5.87

The Noqui peralkaline granite covers some 9 km2, but extends over a much bigger area to the south in Angola (see Angola No. 1). It intrudes Zadinian mica schists and quartzites in the Matadi anticline which are feldspathised at the contact. The granite comprises abundant quartz, generally >30%, perthitic alkali feldspar, riebeckite, aegirine, a little biotite and magnetite and accessory orthite, calcite, parisite and zircon. Some facies may be syenitic. Petrographic, modal and chemical data will be found in Holmes (1915) and Mortelmans (1948).

Age: 
U-Pb measurements on three zircon fractions did not furnish a well established age, but indicated a date of at least 760 Ma (Delhal et al., 1971), while Cahen et al. (1984) report that four zircon fractions defined a chord with an upper intercept of 733 Ma. A six point Rb-Sr isochron defined an age of 536(10 Ma (Cahen et al., 1984).
References: 
CAHEN, L., SNELLING, N.J., DELHAL, J. and VAIL, J.R. 1984. The geochronology and evolution of Africa. Clarendon Press, Oxford. 512 pp.DELHAL, J., LEDENT, D., PASTEELS, P. and VERNIER, J. 1971. Étude du comportement isotopique de systèmes Rb/Sr et U/Pb dans le granite hyperalcalin de Noqui (République Démocratique du Congo et Angola). Annales de la Société Géologique de Belgique, Liège 94: 223-36.HOLMES, A. 1915. A contribution to the petrology of north-western Angola. Geological Magazine, 6: 228-32 and 267-72. MORTELMANS, G. 1948. Le granite de Noqui et ses phénomènes de contact. Bulletin de la Société Belge de Géologie de Paléontologie et d'Hydrologie, 57: 519-39.
Location: 
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