Geochemistry and spatial variation in dolerites of the Drakensberg Group, Karoo Supergroup, South Africa

Abstract

The Karoo Large Igneous Province (KLIP) in South Africa comprises a spatially limited basalt suite (Drakensberg Group) and a spatially extensive dolerite suite. This study aims to establish a tectonic regime that could have facilitated the KLIP and the extent of geochemical variation in the dolerite suite. Principal component analysis (PCA) is used to identify trends as this multivariate statistical operation is particularly well suited to identifying possible petrological processes. Major and trace element chemistry is interpreted from data made available by GeoROC, a public geochemical data depository. This study observed 139 samples of which 49 were basalts and 90 were dolerites, sampled along a c. 1500 km E-W tract along the southern margins of the Karoo basin. Disassociations between the KLIP and surficial manifestations of mantle plumes are discussed. Transition metal chemistry is described using Co, Cr, Cu, Ni, V, and Zn; however, anomalies in the transition metal data resulted in only LILs (Ba, Sr, and Rb) and HFSEs (Nb and Zr, and the REEs Ce, La, Nd, and Y) being used to investigate spatial variation in the KLIP. Spatial variation could not be inferred with major element chemistry nor with trace element chemistry, and the data is remarkably compatible to the lower crust. Although it is suggested that gravity could have been a driving force behind the KLIP, further studies must be done to provide a better understanding of the relationships between the KLIP and its host geology.