The Kunene complex, Angola/Namibia: a composite massif-type anorthosite complex

Abstract

AbstractThe c. 15000 km2, c. 2 Ga Kunene complex of southern Angola and northern Namibia is one of the world's largest occurrences of anorthositic rocks, rivalled only perhaps by the Lac St Jean massif of the Grenville Province in Quebec. We report here the results of a detailed field and laboratory study of a 100 km2 area in the northern part of the complex. Coarse grained (av. 1–2 cm) anorthosite and leucotroctolite are the predominant rock types, although colour index varies between 0 and 50, averaging about 10. Ultramafic rocks are totally absent. Typical mineralogy is: plagioclase (An57–76) + olivine(Fo64–71) + orthopyroxene(En65–74) + clinopyroxene ± Fe—Ti oxides ± apatite. Textures are dominantly massive, although weak, impersistent, magmatic lamination with nearvertical dip and unsystematic strike is also present. Other magmatic features include plagioclase and orthopyroxene megacrysts, block structure, mortar texture, and anorthositic dykes. Metamorphic effects are minimal or absent. All of these attributes are similar to those found in typical massif-type anorthosites. Since comparable features are present over large areas elsewhere in the complex, we suggest that Kunene should be considered analogous to a large, composite, massif-type anorthositic intrusive complex, rather than to a large, single or composite mafic layered intrusion such as Bushveld, as has been previously suggested or assumed. This interpretation is supported by satellite imagery, which shows the outlines of several individual anorthositic plutons, one of which clearly encompasses our field area.