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.
With analytical data by P. Mielke
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Winkler, H.G.F. (1983). A Survey of Granitic Rocks of the Damara Orogen and Considerations on Their Origin. In: Martin, H., Eder, F.W. (eds) Intracontinental Fold Belts. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-69124-9_35
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DOI: https://doi.org/10.1007/978-3-642-69124-9_35
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