Major and trace-element classification of Rand Granite lithologies: a Ab-An-Or diagram after O’Connor (1965). b Q-A-P diagram after Streckeisen (1974) and Le Maitre (1989). c A/CNK-diagram (molar proportions) after Maniar and Piccoli (1989). d Ocean ridge granite (ORG) normalized chemical patterns after Pearce et al. (1984). e Rb vs. (Y+Nb) diagram after Pearce et al. (1984)
The Rand Granite Complex consists of meta-granites,
meta-trondhjemites and biotite augen gneisses (orthogneisses) (for
sample locations see insets in Fig. 2 and Table 1 ; for
modal compositions see Fig. 3 b and Table 2 ).
All studied lithologies lie within the granitoid band in the
Streckeisen diagram (Fig. 3 b).
In the Ab-An-Or diagram (O’Connor 1965 ), the three rock types
discriminate as granite, trondhjemite and adamellite (Fig. 3
The Q-A-P plot (Streckeisen 1974 ; Le Maitre 1989 ) also shows good
discrimination between granites and trondhjemites (Fig. 3 b).
Based on major elements that are often problematic in metamorphosed
terrains, granites and trondhjemites display a peraluminous
character and cluster in and around the overlapping area of
continental arc and collision granites (Fig. 3 c).
However, the more reliable trace element patterns also show
far-reaching congruence with volcanic arc or syn-collisional
granites (Fig. 3 d,e).
Where appropriate, the trondhjemites discriminate as volcanic arc
granites with generally lower abundances in both the large-ion
lithophile and the high field strength elements, whereas the
granites to granodiorites show a trend towards the syn-collisional
granite field (Fig. 3 d,e).
Although the diagrams shown in Fig. 3 c–e are not designed
for intermediate rocks such as the biotite augen gneiss, this
lithology is also plotted to show its close chemical relationship
to the granites, as it becomes also evident by its normative and
modal composition (Fig. 3 a,b)..
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