The Question of Delaminated Continental Lithosphere in South Atlantic Oceanic Basalt Sources - A Study of Mantle and Lower Crustal Samples from Southern Africa

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ClassEAR-0207311Unusual unradiogenic 143Nd/144Nd and 206Pb/204Pb isotopic compositions of oceanic basalts from the South Atlantic and other ocean basins have been attributed to ancient subcontinental lithospheric mantle (SCLM), or, more recently, to lower continental crust, which is thought to have been introduced into the oceanic upper mantle at the time of the breakup of Gondwana. However, the isotopic composition of the actual SCLM and lower crust spatially associated with those unusual oceanic basalts is only poorly constrained. It is proposed to test the hypotheses of delaminated SCLM and/or lower crust in the source of oceanic basalts by evaluating a direct relationship between the composition of enriched oceanic basalts in the South Atlantic and continental material potentially delaminated from the sub-Gondwana lithosphere. A series of mantle xenolith-bearing kimberlite fields in Namibia and South Africa provide a unique opportunity to directly sample the SCLM and lower crust in the critical area of the Proterozoic Namaqua-Natal Belt as well as the Kaapvaal Craton. Sr-Nd-Pb isotopic compositions as well as trace elements on mineral separates from mantle xenoliths, concentrates of mantle-derived clinopyroxenes, lower crustal xenoliths and host kimberlites from these locations will be used to constrain the composition of the SCLM and lower crust at the time of the opening of the South Atlantic. This project will be done in collaboration with Dr. Anton le Roex, University of Capetown, South Africa.