STATISTICAL EVALUATION OF POSSIBLE TECTONIC SETTINGS FOR THE BUSHVELD COMPLEX

The Archaean Kaapvaal Craton in South Africa hosts several extensive ultramafic to mafic complexes, including both extrusive and intrusive components. The 2.0 Ga Bushveld Complex is the most extensive mafic layered intrusion on the planet, with a wide range of magmas (from Fe-rich to Si-rich). This research project looks to provide tectonic constraints on the origin of the magma emplaced in the uppermost portion of the Bushveld Complex through statistical analysis of geochemical whole rock trace element data and apatite REE data. In this approach, the geochemistry of basaltic rocks is considered a predictive indicator in determining the likely tectonic setting in which the parental magma originated. For this project, a global database of basaltic rock data, namely Georoc, subdivided by tectonic setting (convergent plate margin, oceanic island, submarine ridge, and oceanic plateau), is compared to that of the Bushveld Complex. A principal component analysis (PCA) of the Bierkraal trace element data, sampled in the western limb of the complex, suggests that the settings and locations most similar geochemically to the Bushveld data seem to be that of the Hawaiian Islands Kaula and Nihau, as well as overlapping with Fiji and Tonga. Hawaii does exhibit more depletion in elements like Nb and Y relative to the Bushveld data, but the inference would be that mantle hotspots/plumes may be involved with the Bushveld magmatism. On the other hand, the REE apatite data shows an overlap with the arc-related settings. By far, the most similar geochemical signature exists between the lower 300m segment of the Upper Zone, characterized by multiple magnetite layers, and the East Scotia Ridge. This ridge is a back-arc tectonic environment associated with diverging plate motions and subsequent rifting. Therefore, more work is required to investigate this contradictory set of findings.