Mineralogy and Cryptic Layering of the Kunene Anorthosite Complex of SW Angola and Namibia

Zenaide C. G. Silva
Departmento de Geologia, Universidade de Lisboa, Campo Grande, Ed. C2, 5 Piso. 1700 Lisboa, Portugal

Abstract: The gabbro-anorthosite complex of SW Angola and Namibia (Kunene Complex) is dominated by anorthosite-troctolite cumulates. Other broadly gabbroic rock types are subordinate. An-rich plagioclase (max. An85) and Fo-rich olivine (max. Fo79) are common in the western area of the complex with plagioclase becoming gradually less anorthitic (min. An45) and olivine less forsteritic (min. Fo62) toward the east. This cryptic change is more pronounced in the northern half of the complex where rocks are darker, fresh, and the rhythmic layering is also more conspicuous. Within the white ‘massive’ anorthosite type, which is largely restricted to the southern half of the intrusion, cryptic layering is less pronounced. Textures indicate that rocks cooled very slowly and the co-existing mineral compositions indicate re-equilibration to usually low temperatures.

Keywords: layering • layered anorthosite • ‘massive’ anorthosite • Kunene • Angola • Namibia

Mineralogical Magazine; September 1992 v. 56; no. 384; p. 319-327; DOI: 10.1180/minmag.1992.056.384.03
© 1992, The Mineralogical Society
Mineralogical Society (www.minersoc.org)