oa South African Journal of Geology - The Liüderitz Alkaline Province, South West Africa I : descriptive petrology of the Granitberg Foyaite complex

Volume 78 Number 2
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590



The Granitberg foyaite complex is one of three known alkaline igneous complexes, which, together with a dyke swarm, constitute the Liüderitz Alkaline Province of Lower Cretaceous age. The near-circular complex is em placed into dolomites and sandstones of the Bogenfels Formation. A large fragment of these sedimentary rocks, originally forming the roof of the intrusion, is preserved in the centre of the complex. Three major intrusive phases can be recognized. The first phase resulted in the magma chilling at the roof to form porphyritic nepheline syenites. The second phase crystallized as the Inner Foyaite - a cylindrical, zoned plug capped by layered, laminated, and xenolith-rich foyaites. The third phase was the emplacement of the Outer Foyaite magma into which the Roof Zone - Inner Foyaite unit foundered. The Outer Foyaite is zoned with a miaskitic core and agpaitic outer zone. A dyke swarm is developed in the vicinity of the complex and the dominant dyke rocks are tinguaites and quartz-bostonites.

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