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Mineralogy and cryptic layering of the Kunene anorthosite complex of SW Angola and Namibia

Published online by Cambridge University Press:  05 July 2018

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

layeringlayered anorthosite'massive' anorthositeKuneneAngolaNamibia
Type
The Hallimond Lecture
Information
Mineralogical Magazine , Volume 56 , Issue 384 , September 1992 , pp. 319 - 327
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1992

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References

Atkins, F.B. (1969) Pyroxenes of the Bushveld Intrusion. South Africa. J. Petrol., 10, 22249.CrossRefGoogle Scholar
Barnes, S.J. (1989) Are Bushveld U-type parent magmas boninites or contaminated komatiites? Con-trib. Mineral. Petrol., 101, 447–57.CrossRefGoogle Scholar
Bartolomé, P. (1961) Co-existing pyroxenes in igneous and metamorphic rocks. Geol. Mag., 98, 346–8.CrossRefGoogle Scholar
Beetz, P.F.W. (1933) Geology of South West Angola, between Kunene and Lunda Axis. Trans. Geol. Soc.South Africa, 36, 137–76.Google Scholar
Brown, G.M. (1957) Pyroxenes from the early and middle stages of fractionation of the Skaergaard intrusion. Mineral. Mad., 31, 511–41.Google Scholar
Brown, G.M. and Vincent, E.A. (1963) Pyroxenes from the late stage of fractionation of the Skaergaard intrusion, East Greenland. J. Petrol., 4, 175–97.CrossRefGoogle Scholar
Cameron, A.N. (1978) The lower zone of the eastern Bushveld Complex in the Olifants River trough. Ibid. 19, 437-52.CrossRefGoogle Scholar
Cawthorn, R.G., Meyer, P.S., and Kruger, F.J. (1991) Major addition of magma at the Pyroxenite Marker in the Western Bushveld Complex, South Africa. Ibid. 32, 739-63.CrossRefGoogle Scholar
Chalokwu, C.I. and Grant, N.K. (1990) Petrology of the Partridge intrusion, Duluth Complex, Minesotta. Relationship between mineral composition, density and trapped liquid abundance. Ibid. 31, 265-93.Google Scholar
Eales, H.V., March, J.S., Mitchel, A.A. De Klerk, W. J. Kruger, F.J., and Field, M. (1986) Some geochemical constraints upon models for the crystallisation of the upper critical zone-main zone interval, northwestern Bushveld complex. Mineral. Mag., 50, 567–82.CrossRefGoogle Scholar
Eales, H.V., March, J.S., Mitchel, A.A. De Klerk, W. J. Kruger, F.J., and Field, M. De Klerk, W. J., and Butcher, A.R. (1990) The cyclic unit UG1 ehromitite (UG1FW unit) at RPM Union Section Platinum Mine-Rosetta Stone of the Bushveld Upper Critical Zone? Ibid. 54, 23-43.Google Scholar
Hess, H.H. (1960) Stillwater igneous Complex, Montana. Geol. Soc. Amer. Memoir, 80, 230.p.Google Scholar
Hess, H.H. and Phillips, A.H. (1940) Optical properties and chemical composition of magnesian orthopyroxenes. Amer. Mineral., 25, 271–85.Google Scholar
Irvine, T.N. (1982) Terminology for layered intrusions. J. Petrol., 23, 127–62.CrossRefGoogle Scholar
Irvine, T.N. Keith, D.W., and Todd, S.G. (1983) The J-M platinum-palladium Reef of the Stillwater Complex, Montana: II. Origin by diffuse convective magma mixing and implications for the Bushveld Complex. Econ. Geol., 78, 1287–334.CrossRefGoogle Scholar
Köstlin, E. C. (1967) Geology of part of the Kunene basic Complex, Kaokoveld, South West Africa. M.Sc. Thesis, Univ. Cape Town, South Africa.Google Scholar
Köstlin, E. C. (1974) The Kunene Basic Complex, northern South West Africa. In Contributions to the Precam-brian Geology of Southern Africa: a volume in honour of John de VUliers. (Kroner, F.) Univ. of Cape Town, Chamber of Mines Precambrian Research Unit Bull. 15, 123-35.Google Scholar
Kretz, R. (1961) Co-existing pyroxenes. GeoL Mag., 98, 345.CrossRefGoogle Scholar
Kruger, F.J. and Marsh, J.S. (1982) Significance of 87Sr/86Sr ratios in the Merensky cyclic unit of the Bushveld Complex. Nature, 298, 53–5.CrossRefGoogle Scholar
Kushiro, I. (1960) Si-AI relations in clinopyroxenes from igneous rocks. Amer. J. Sci., 258, 548–54.CrossRefGoogle Scholar
Lindsley, D.H. (1983) Pyroxene thermometry. Amer. Mineral., 68, 477–93.Google Scholar
LeBas, M.J. (1962) The role of aluminium in igneous clinopyroxenes with relation to their parentage. Amer. J. Sci., 280, 267–88.CrossRefGoogle Scholar
Markgraaff, J. (1976) Pyroxenes of the Western Bushveld Complex, South Africa. Trans. GeoL Soc. South Africa, 79, 217–24.Google Scholar
McBirney, A. and Noyes, R.M. (1979) Crystallisation and layering of the Skaergaard intrusion, or. Petrol., 20, 487–554.CrossRefGoogle Scholar
Miller, J.D. and Weiblen, P.W. (1990) Anorthositie rocks of the Duluth Complex: Example of rocks formed from plagioclase crystal mush. Ibid. 31, 295-339.Google Scholar
Paixão, J. C. C. Noticia Explicativa da Folha 397-Ompupa, da Carta Geológica de Angola. Servigos de Geologia e Minas de Angola (unpublished).Google Scholar
Philpotts, A.R. (1966) Origin of the anorthosite-mangerite rocks in southern Quebec. J. Petrol, 7, 1–64.CrossRefGoogle Scholar
Ramberg, H. and De Vore, G. W. (1951) The distribution of Fe++ and Mg+ + in co-existing olivines and pyroxenes. J. Geol., 59, 193–210.CrossRefGoogle Scholar
Romey, W.D. (1968) An evaluation of some ‘differences’ between anorthosite in massifs and in layered complexes. Lithos, 1, 23040.CrossRefGoogle Scholar
Santos, L. (1969) Ocorr∼ncias de ilmenites no Sul de Angola. Bol. Servi∼os de Geol. Minas de Angola, 20, 21–8.Google Scholar
Silva, Z.C.G. (1987) Plagioclases of the anorthosites from Southwest Angola. In Current Research in African Earth Sciences (Matheis, J. and Schandel-meier, H., eds.), 41-4. Balkema, Roterdam.Google Scholar
Silva, Z.C.G. (1988) Estudo petroqu[mico do Complexo gabro-anortositico de Angola. PhD. Thesis, Univ. of Lisbon, Portugal.Google Scholar
Silva, Z.C.G. (1990) Geochemistry of the Gabbro-anorthosite Complex of Southwest Angola. J. African EarthSciences, 10, 683–92.Google Scholar
Silva, Z.C.G. and Silva, M.A.J.G. (1990) Subsídio estatístico à interpretação de dados do Complexo gabro-anor- tosítico de Angola. Rev. Bras. Geol., 20, 122–32.CrossRefGoogle Scholar
Simpson, E.S.W. (1970) The anorthosite of southern Angola: a review of present data. In African Magmatism and Tectonics (Clifford, T. N. and Gass, I. G., eds.), 89-96. Oliver & Boyd Ltd., Edinburgh.Google Scholar
Smith, J.V. and Gay, P. (1958) The powder patterns and lattice parameters of plagioclase feldspars II. Miner. Mag., 31, 47.Google Scholar
Stone, P. and Brown, G. M. (1958) The Quihita- Cunene layered gabbroic intrusion of Southwest Angola. Geol. Mag., 95, 195–206.CrossRefGoogle Scholar
Streckeisen, A. (1976) To its plutonic rock its proper name. Earth Sci. Review, 12, 1–33.CrossRefGoogle Scholar
Wager, L.R. and Brown, G.M. (1968) Layered Igneous Rocks. Oliver & Boyd Ltd., Edinburgh.Google Scholar
Wager, L.R. and Brown, G.M. and Wadsworth, W.J. (1960) Types of igneous cumulates. J. Petrol., 1, 73–85.CrossRefGoogle Scholar
Weiblen, P.W. and Morey, G.B. (1980). A summary of the stratigraphy, petrology, and structure of the Duluth Complex. Amer. J. Sci., 280-A, 88–188.Google Scholar