Abstract
The composition of magmas proposed as parental to the layered suite of the
Bushveld Complex, and some models for the manner of their emplacement, are
reviewed briefly. Included are some contributions published in South Africa, with
which overseas readers might be less familiar. Emphasis is given to the broader
features of the cumulates, and the contradictions raised by whole-rock
compositional, Sr-isotopic, and trace-element data that cloud their correlation
with proposed parental magmas. It is concluded that the Lower, Critical and Main
Zones are the derivatives of only two primary magmatic lineages, while a third was
added to residual liquids from which the layered rocks above the Pyroxenite Marker
were formed. Excessive amounts of olivine and chromium in the cumulates of the
Lower and Lower Critical Zones in the northern sector of the Western Limb can
seemingly not be accounted for by the composition and volume of the putative
magmas. This is attributed to (1) this sector being a proximal facies located
close to the original feeder, and/or (2) crystal-charged magma batches, expelled
from a lower magma chamber, being periodically injected into and dispersed within
the liquids already in place in the Bushveld chamber. Thus, ongoing changes in the
bulk composition of the liquids within the chamber would not be reflected in the
rinds of earlier, chilled-facies rocks. The expulsion of significant volumes of
liquid residua from the chamber during cumulate deposition is not ruled
out.
Microtextural characterisation of the Lower Zone in the western limb of the Bushveld Complex, South Africa: evidence for extensive melt migration within a sill complex
