Profs John Clemens, Alex Kisters and Ian Buick, with honours students are nearing completion in their three-year, NRF-funded study of the gigantic Donkerhuk granite batholith in Namibia (200 km long, 25 to 50 km wide and at least 1 km thick). The work, over 3 field seasons has involved mapping, geochemical sampling, computer modelling of mineral assemblages, chemical and isotopic analysis and U-Pb dating of the minerals in the rocks. Great progress has been made in understanding the conditions under which the magmas were formed and their mode of emplacement as thousands of magma sheets into the surrounding Kuiseb formation. Interestingly, emplacement occurred only slightly higher in the crust (at about 15 km depth) than where they were formed (at about 20 km). This is now understood in terms of the geological structures that prevented the Donkerhuk magmas from moving to shallower levels. What remains to be worked out is how this extremely heterogeneous and long-lived (perhaps about 20 Myr long) plutonism fitted into the overall tectonic development of the Damara Belt in the Early Cambrian, around 530 million years ago.
Clik here to view.
