| Abstract: | The intracratonic Bushveld igneous province that formed 2.1–1.9 Ga ago contains three contrasting suites of siliceous rocks that are demonstrably of magmatic origin. The oldest of these are the high-Mg (HMF) and low-Mg (LMF) felsites, which form interstratified flows in the Rooiberg Group. Bushveld granites intrude the Rooiberg Group and constitute the youngest component of the province.Well-defined interelement variation trends illustrate that the granites do not share the same petrogenetic history as the Rooiberg magmas. Nd isotope measurements indicate that the two eruptive suites probably formed under similar differentiation conditions but from parental magmas that were derived from compositionally different sources. On trace-element discrimination diagrams, the Bushveld granites and LMF are usually correctly assigned to a within-plate setting but, conversely, the HMF are generally misclassified as subduction-related eruptives. It is argued that the trace-element signatures of the granites and felsites do not identify their tectonic setting per se, but rather point to the melting and crystallization histories of the source regions from which their parent magmas were extracted. As such, tectonic discrimination diagrams may provide valuable pointers to processes that have affected igneous source materials in much earlier magmatic cycles. |
