A Survey of Granitic Rocks of the Damara Orogen and Considerations on Their Origin

  • H. G. F. Winkler

Abstract

The compositions of 32 granitic rocks of the Damara Orogen (red granites, grey granites, Donkerhoek granites, and Salem granites) show that there is a very broad spectrum of granitic and granodioritic rocks that have been intruded during the long lasting magmatic activity in the Central Zone of the Damara Orogen. No compositional grouping can be made according to the type of granite.

As has been shown earlier by the author the system Qz-Ab-Or-An-H2O is the petrogenetically relevant system for granitic rocks. For each granitic rock of the Damara Orogen the crystallization history is deduced from this system. The reliability of the deductions is proven by a comparison with experimentally determined crystallization histories for some rocks.

Two different cases of magmatic behaviour can be distinguished: (a) The compositions are such that the total rock has been completely or almost completely liquid at low temperatures, or (b) the composition are such that the total rock has not been completely or almost completely liquid at low temperatures. Instead, in the latter case the total magma consists of a liquid part and substantial amounts of suspended solids. The suspended solids amount to about 20–40 % and consist of one of the three leucocratic minerals plagioclase, quartz, and alkali feldspar, plus more or less biotite, plus a few percent accessories. In both cases of compositions a magma genesis other than anatexis of metasediments does not seem to be possible.

Keywords

Crystallization Quartz Siliceous Recrystallization Dolomite 

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References

  1. Barth, T.F.W. (1963) The Precambrium of Southern Norway.– In: The Geologic System. The Precambrium (Rankana, K. ed.) Vol. 1, 29–64.Google Scholar
  2. Blaxland, A., Gohn, E., Haack, U. & Hoffer, E. (1979) Rb/Sr ages of the late tectonic granites in the Damara Orogen, Southwest Africa/Namibia.– N.Jb.Miner.Mh. 1979, 498–508.Google Scholar
  3. Brown, P.E. (1971) The origin of the granitic sheets and veins in the Loch Coire migmatites.– Min.Mag. 38, 446–450.CrossRefGoogle Scholar
  4. Faupel, J. (1974) Geologisch-mineralogische Untersuchungen am Donkerhoek-Granit (Karibib-District, Südwestafrika).– Göttinger Arb.Geol.Paläont. 15, 95 pp.Google Scholar
  5. Germantzides, C. (1980) Experimentelle Anatexis von häufigen Metasedimenten aus dem Damara-Orogen (Südwest-Afrika).– Dissertation, Göttingen.Google Scholar
  6. Haack, U. & Martin, H. (1982) Geochronology of the Damara Orogen.– This vol..Google Scholar
  7. Hoernes, S. & Hoffer, E (1979) Equilibrium relations of prograde metamorphic assemblages. A stable isotope study of rocks of the Damara Orogen, from Namibia.– Contrib.Mineral.Petrol. 68, 377–389.CrossRefGoogle Scholar
  8. Hoffer, E. (1982) Compositional variations of minerals in metapelites involved in low- to medium grade isograd reactions in the southern Damara Orogen, South West Africa/Namibia.– This vol..Google Scholar
  9. Hoffmann, C. (1976) Granites and migmatites of the Damara Belt, South West Africa. Petrography and melting experiments.– Geol.Rdsch. 65, 939–966.CrossRefGoogle Scholar
  10. Luth, W.C., Jahns, R.H. & Tuttle, O.F. (1964) The granite system at pressures of 4 to 10 Kilobars.– Journ. Geophys. Res. 69, 759–773.CrossRefGoogle Scholar
  11. Martin, H. (1965) The Precambrian geology of South West Africa and Namaqualand.– Precambrian Res. Unit, Univ. Cape Town, 159 pp.Google Scholar
  12. Mielke, P. & Winkler, H.G.F. (1979) Eine bessere Berechnung der Mesonorm für granitische Gesteine.– N.Jb.Miner.Mh. 1979, 471–480.Google Scholar
  13. Nieberding, F. (1976) Die Grenze der zentralen Granitzone südwestlich Otjimbingwe (Karibib-District, Südwestafrika): Intrusionsverband, Tektonik, Petrographie.– Göttinger Arb.Geol.Paläont. 19, 78 pp.Google Scholar
  14. Orville, P.M. (1963) Alakli ion exchange between vapour and feldspar phases.– Am.J.Sci. 261, 201–237.CrossRefGoogle Scholar
  15. Puhan, D. (1979) Petrologische und geothermometrische Untersuchungen an silikat – führenden Dolomit-Calcit Marmoren zur Ermittlung der Metamorphosebedingungen im zentralen Damara- Orogen (Südwest-Afrika).– Habilitationsschrift, Göttingen.Google Scholar
  16. Puhan, D. (1982) Metamorphism of siliceous dolomites of the central and southern part of the Damara Orogen.– This vol..Google Scholar
  17. Reinhard, M. (1931) Universal-Drehtischmethoden.– Verlag Weph & Cie, Basel.Google Scholar
  18. Storre, B. & Karotke, E. (1971) Experimentelle Anatexis von Glimmerschiefern in Modellsystemen.– Fortschr.Miner. 49, Beiheft 1, 56–58.Google Scholar
  19. Tuttle, O.F. & Bowen, N.L. (1958) Origin of granite in the light of experimental studies in the system NaAlSi3O8 – KalSi3 O8 – SiO2 – H2O.– Geol.Soc.Amer.Memoir 74, 153 pp.Google Scholar
  20. Winkler, H.G.F. (1976) Petrogenesis of metamorphic rocks, 4 th ed., 334 pp. Springer-Verlag, New York/Heidelberg/Berlin.Google Scholar
  21. Winkler, H.G.F. (1979) Petrogenesis of metamorphic rocks, 5 th ed., 348 pp. Springer-Verlag, New York/Heidelberg/Berlin.Google Scholar
  22. Winkler, H.G.F., Boese, M. & Marcopoulos, T. (1975) Low temperature granitic melts.– N.Jb.Miner.Mh. 1975, 245–268.Google Scholar
  23. Winkler, H.G.F. & Breitbart, R. (1978) New aspects of granitic magmas.- N.Jb.Miner.Mh. 1978, 463–480.Google Scholar
  24. Winkler, H.G.F. Das, B.K. & Breitbart, R. (1977) Further data of low temperature melts existing on the quartz + plagioclase + liquid + vapour isobaric cotectic surface within the system Qz-Ab-Or-An-H2O.– N.Jb.Miner.Mh. 1977, 241–247.Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1983

Authors and Affiliations

  • H. G. F. Winkler
    • 1
  1. 1.Mineralogisch-Petrologisches InstitutGöttingenGermany

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