Imaging crust and upper mantle beneath southern Africa: The southern Africa broadband seismic experiment

The view from the rim of the Big Hole in Kimberley, South Africa, can only be described as spectacular (Figure 1). Both the size of that legendary kimberlite pipe and the prodigious amount of back breaking labor that went into removing some 27 million tons of dirt to extract 14.5 million carats (2722 kilos) of diamonds are powerful testaments to the timeless allure of diamonds. The Big Hole, the largest hand-dug excavation in the world (820 m deep and 1.6 km across), lies at an improbable elevation above 1100 m (3500 ft) in the heart of the great Archean Kaapvaal craton of South Africa. The Kaapvaal, perforated with thousands of kimberlite pipes similar to that from which the Big Hole was dug, has a rich and colorful history of exhaustive and painstaking geologic study and exploration that the presence of exotic mantle samples and large quantities of gem quality diamonds inspires. In this classic Archean craton we launched the largest seismic investigation ever to probe the deep crust and upper mantly beneath the ancient continental nucleus (Figure 2).