Abstract
Namaqualand is the site of an extensive Proterozoic granulite terrain from which the bulk and mineral chemistry of the mafic specimens shows no consistent variation in the concentrations of Al 2 O 3, Fe 2 O 3, FeO, MgO, and CaO along its ⋍ 85 km length. The Wood and Banno (1973), Saxena (1976) and Wells (1977) methods of determining equilibration temperatures from coexisting ortho- and clinopyroxenes were applied to twelve specimens from the granulite zone. The methods show relatively little variation in temperature for each specimen and there is no consistent variation in computed temperatures throughout the zone. The mean calculated temperature is 830°C with a probable range of 800–860°C and a tentative pressure of approximately 7 kbar as determined from various methods (Currie, 1971; Green, 1976; 1977). The calculated T and P data fall well within a broad field defined by experimentally determined curves taken from the literature. Evidence is presented which suggests that an amphibolite-facies zone adjacent to the granulite zone is the result of later retrogressive metamorphism rather than progressive metamorphism as previously suggested in the literature.
Published Version
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