Alkaline Rocks and Carbonatites of the World

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Nlonako

stripes

Occurrence number: 
030-00-027
Country: 
Cameroon
Location: 
Longitude: 9.95, Latitude: 4.88

An elliptical intrusion 8 km in length, Nlonako is surrounded on its northern and western sides by lavas of the Manengouba centre (No. 26) and consists of gabbro, syenite and granite with some rhyolite. The syenites contain some quartz, alkali feldspar, which in some varieties is dominantly albite, biotite, sodic amphibole, which includes both arfvedsonite and riebeckite, aegirine-augite; fayalite occurs in some rocks. The granites are similar with zoned alkali feldspar, arfvedsonite and aegirine. Rhyolites contain abundant alkali feldspar but pyroxene and amphibole have been completely replaced by iron oxides.

Age: 
A Rb-Sr whole rock isochron gave 43.3(0.3 Ma (Lasserre, 1978). K-Ar determinations on microgabbro and syenite gave 43(2 and 45(1 Ma (Cantagrel et al., 1978).
References: 
CANTAGREL, J.-M., JAMOND, C. and LASSERE, M. 1978. Le magmatisme alcalin de la ligne du Cameroun au Tertiaire inférieur: données géochronologiques K/Ar. Bulletin de la Société Géologique de France Compte Rendu Sommaire des Seances, 20: 300-3.LASSERRE, M. 1978. Mise au point sur les granitoides dits "ultimes" du Cameroun: gisement, pétrographie et géochronologie. Bulletin du Bureau de Recherches Géologiques et Minières. Paris, IV: 143-59.
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith