TY - JOUR A1 - Sodoudi, Forough A1 - Yuan, Xiaohui A1 - Kind, Rainer A1 - Lebedev, Sergei A1 - Adam, Joanne M-C. A1 - Kästle, Emanuel A1 - Tilmann, Frederik T1 - Seismic evidence for stratification in composition and anisotropic fabric within the thick lithosphere of Kalahari Craton JF - Geochemistry, geophysics, geosystems N2 - Based on joint consideration of S receiver functions and surface-wave anisotropy we present evidence for the existence of a thick and layered lithosphere beneath the Kalahari Craton. Our results show that frozen-in anisotropy and compositional changes can generate sharp Mid-Lithospheric Discontinuities (MLD) at depths of 85 and 150-200 km, respectively. We found that a 50 km thick anisotropic layer, containing 3% S wave anisotropy and with a fast-velocity axis different from that in the layer beneath, can account for the first MLD at about 85 km depth. Significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second MLD led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The deepening of this boundary from 150 to 200 km is spatially correlated with the surficial expression of the Thabazimbi-Murchison Lineament (TML), implying that the TML isolates the lithosphere of the Limpopo terrane from that of the ancient Kaapvaal terrane. The largest velocity contrast (3.6-4.7%) is observed at a boundary located at depths of 260-280 km beneath the Archean domains and the older Proterozoic belt. This boundary most likely represents the lithosphere-asthenosphere boundary, which shallows to about 200 km beneath the younger Proterozoic belt. Thus, the Kalahari lithosphere may have survived multiple episodes of intense magmatism and collisional rifting during the billions of years of its history, which left their imprint in its internal layering. KW - lithospheric layering KW - S receiver functions Y1 - 2013 U6 - https://doi.org/10.1002/2013GC004955 SN - 1525-2027 VL - 14 IS - 12 SP - 5393 EP - 5412 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Heit, Benjamin A1 - Yuan, Xiaohui A1 - Weber, Michael H. A1 - Geissler, Wolfram H. A1 - Jokat, Wilfried A1 - Lushetile, Bufelo A1 - Hoffmann, Karl-Heinz T1 - Crustal thickness and V-p/V-s ratio in NW Namibia from receiver functions: Evidence for magmatic underplating due to mantle plume-crust interaction JF - Geophysical research letters N2 - A seismological network was operated at the junction of the aseismic Walvis Ridge with the northwestern Namibian coast. We mapped crustal thickness and bulk V-p/V-s ratio by the H-k analysis of receiver functions. In the Damara Belt, the crustal thickness is similar to 35km with a V-p/V-s ratio of <1.75. The crust is similar to 30km thick at the coast in the Kaoko Belt. Strong variations in crustal thickness and V-p/V-s ratios are found at the landfall of the Walvis Ridge. Here and at similar to 150km northeast of the coast, the crustal thickness increases dramatically reaching 44km and the V-p/V-s ratios are extremely high (similar to 1.89). These anomalies are interpreted as magmatic underplating produced by the mantle plume during the breakup of Gondwana. The area affected by the plume is smaller than 300km in diameter, possibly ruling out the existence of a large plume head under the continent during the breakup. KW - crustal thickness KW - V-p KW - V-s ratios KW - magmatic underplating KW - Walvis Ridge KW - continental breakup Y1 - 2015 U6 - https://doi.org/10.1002/2015GL063704 SN - 0094-8276 SN - 1944-8007 VL - 42 IS - 9 SP - 3330 EP - 3337 PB - American Geophysical Union CY - Washington ER -