THE KAAPVAAL CRATON PROJECT: ORIGIN AND EVOLUTION OF CONTINENTAL LITHOSPHERE

The Kaapvaal and Zimbabwe cratons of southern Africa preserve a record of the processes that formed some of Earth's first continental lithosphere. To read and understand this record, the CD-sponsored Kaapvaal project undertook; installation and operation of a 55 station broad-band seismic array; detailed petrologic, geochemical and isotope studies of lower-crustal and mantle xenoliths and diamonds and their inclusions from across southern Africa; and geologic mapping, petrologic, geochemical and isotopic study of high degree mantle melts (komatiites) found throughout the old crust of southern Africa. Scientific results from the project are summarized in three special journal volumes: GRL 28 (13), 2001; Lithos 71, 2003; and the South African J. Geology 107 (1, 2), 2004. Highlights of the project include: 1) the construction of a 4-D image of the structure of the crust and upper mantle beneath the southern African cratons and their surrounding accretionary belts (GRL 28 (13) cover page), 2) direct comparison of the seismic velocities measured in the upper mantle with those calculated for mantle xenoliths (James et al., G-cubed 5, 2004) and the paragenesis of silicate inclusions in diamond (Shirey et al., Science 297, 2002), 3) evidence for a subduction-related origin for large crustal sutures (Schmitz et al., EPSL 222, 2004), diamonds (Richardson et al. EPSL, 191, 2001; Shirey et al., Lithos 77, 2004) and komatiites (Parmen et al., EPSL 150, 1997; Wilson et al., Nature 423, 2003), and 4) insight into the time-scales for attainment of cratonic geotherms after post-formational tectonic and thermal disturbances (Schmitz and Bowring, Chem. Geol, 172, 2001; Bell et al., Lithos 71, 2003; Silver et al., EPSL, 245, 2006). The project involved a large number of southern African collaborators and students (from a total of 28 different industry, government and academic institutions) who made critical contributions to the success of the project and broadened its scope tremendously. This aspect of the Kaapvaal project illustrates the added value obtained from CD-Program sponsorship of research efforts of sufficient size to focus a diverse, multidisciplinary and international, group of geoscientists on a fundamental system-level problem of geodynamics.