Summary of Mesozoic and Tertiary igneous activity

In his 1972 paper on the Karoo Volcanic Cycle, Cox (p.330) concluded, inter alia, that ‘all the Mesozoic igneous rocks of southern Africa… belong to a single long cycle of igneous activity’. He might have added Tertiary igneous rocks to this scheme as well because they are clearly associated with the kimberlite volcanism that forms the last gasp of the cycle. This statement may be justified in terms of the overall geochemical evolution of the magmas Cox envisaged, but to avoid oversimplification in a complex area further cognizance must be taken of the ages of the main centres of igneous activity and their relationship to local phenomena associated with the breakup of Gondwanaland. Sufficient data, both in terms of age determinations and regional setting are now available to make such a regional survey possible, and to discern tectonic/igneous relationships, even if it is beyond the scope of this book to propose geochemical models to link the various phenomena.