Grain-size variations of cumulus plagioclase in the Main Zone of the Bushveld Complex
Maier, Wolfgang D.; Mitchell, Andrew A.
European Journal of Mineralogy Volume 7 Number 1 (1995), p. 195 - 204
published: Feb 8, 1995
manuscript accepted: Sep 1, 1994
manuscript received: Jan 26, 1994
ArtNo. ESP147050701017, Price: 29.00 €
Abstract At Union Section in the northwestern Bushveld Complex the Main Zone is ca. 2700 m thick. Borehole core and surface traverses yielded 150 samples of cumulate rock which were analysed for grain sizes of cumulus plagioclase. Grain size and geochemical variation is coupled in large parts of the Main Zone in that the smaller grain sizes are associated with the more primitive orthopyroxenes. At the same time, grain size varies independently of modal proportions. The data support the stratigraphic sub-division of Mitchell (1990) and indicate that grain-size variation is mainly controlled by differentiation and magma replenishment. Postcumulus textural modification of the cumulates is shown to be of relatively minor importance.