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

来自南大西洋和其他洋盆的大洋玄武岩中异常的非放射成因143 Nd/144 Nd和206 Pb/204 Pb同位素组成被认为是古陆下岩石圈地幔（SCLM）的产物，或者最近被认为是下陆壳的产物，后者被认为是在冈瓦纳大陆解体时被引入大洋上地幔的。然而，实际SCLM和下地壳的同位素组成的空间与这些不寻常的海洋玄武岩只有很少的约束。建议测试假设分层SCLM和/或下地壳的海洋玄武岩的来源，通过评估富集的海洋玄武岩在南大西洋和大陆材料可能从亚冈瓦纳岩石圈分层的组合物之间的直接关系。在纳米比亚和南非的一系列地幔捕虏体金伯利岩领域提供了一个独特的机会，直接采样的SCLM和下地壳的关键领域的元古代纳马夸-纳塔尔带以及Kaapvaal盆地。Sr-Nd-Pb同位素组成以及微量元素的矿物分离从地幔捕虏体，浓缩的幔源单斜辉石，下地壳捕虏体和主机金伯利岩从这些位置将被用来约束的组成SCLM和下地壳在南大西洋的开放时间。该项目将与南非开普敦大学的Anton le Roex博士合作完成。

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.