Integrated Studies of Diamond Age and Composition: Constraints on Continental Lithospheric Evolution, Kaapvaal-Zimbabwe Craton, Southern Africa

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EAR-0310059ShireyThe stable interiors of continents (cratons or shields) are composed of 35 to 40 km thick continental crust overlying up to 180 km of ancient lithospheric mantle root. In certain cratonic regions such as southern Africa, volcanic eruptions of kimberlite have sampled and brought to the surface, rocks (e.g. peridotites and eclogites) and minerals (e.g. diamonds) found in the man-tle root. These samples provide an important direct record of some of Earth's earliest continent-building. Diamonds and the silicate and sulfide minerals that they sometimes include are espe-cially unique as they are the most robust capsules of geochemical and geochronological informa-tion in the mantle.Seven mines in kimberlites (Bobbejaan/Bellsbank, Helam/Swartruggens, Palmietgat, Premier, Orapa, Star, and Venetia) from the Kaapvaal-Zimbabwe craton will provide sulfide-inclusion-bearing diamonds that will be used to expand our knowledge of the geological history of the mantle keel beneath this ancient southern African continent. The broad goals of the re-search are to determine the ages of diamonds at each kimberlite with the Re-Os method on sul-fide inclusions and to relate the ages and the compositions of both inclusions and their host dia-monds to the geologic setting of the diamond source region in the lithospheric mantle. More than three episodes of diamond formation are currently seen to match major episodes of creation (3.2-3.3 billion years ago), amalgamation (2.9-3.1 billion years ago) and magmatic modification of the craton (1-2 billion years ago). The new data will test the extent of these episodes, especially in areas like the eastern craton that have the oldest crustal history (3.3-3.5 billion years) or the Limpopo mobile belt that has been subject to craton collision. Supporting xenolith age and geo-chemistry studies will yield new information on the emplacement of diamondiferous protoliths or the source of the carbon-rich diamond fluids. The broader impacts of the research are in the training and scientific development of a postdoctoral associate and two students. The postdoctoral associate will join the academic teach-ing community and his training will contribute directly to his supervision of students. Both stu-dents reside in South Africa and would otherwise have little chance to train and learn at a high-level research facility in the United States. One student, a female African geochemist, is so un-der-represented as to be unique at the current time in southern Africa. The development of new analytical protocols is proposed; these will improve infrastructure for diamond research in gen-eral. The research will strengthen partnerships with the academic community (Universities of Glasgow, Cape Town, Witwatersrand) and the mining community (DTC - De Beers, Helam Mining). Dissemination of the research will enhance our background understanding of how dia-monds, economically important in stable countries and a problematic resource in areas of con-flict, were created. The project is partially supported by NSF's Office of International Science and Engineering.