[1] 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

SUMMARY Seismic anisotropy within the lithosphere of cratons preserves an important record of their ancient assembly. In southern Africa, anisotropy across the Archean Kaapvaal Craton and Limpopo Belt has been detected previously by observations of SKS‐wave splitting. Because SKS‐splitting measurements lack vertical resolution, however, the depth distribution of anisotropy has remained uncertain. End‐member interpretations invoked the dominance of either anisotropy in the lithosphere (due to the fabric formed by deformation in Archean or Palaeoproterozoic orogenies) or that in the asthenosphere (due to the fabric formed by the recent plate motion), each with significant geodynamic implications. To determine the distribution of anisotropy with depth, we measured phase velocities of seismic surface waves between stations of the Southern African Seismic Experiment. We applied two complementary measurement approaches, very broad‐band cross‐correlation and multimode waveform inversion. Robust, Rayleigh‐ and Love‐wave dispersion curves were derived for four different subregions of the Archean southern Africa in a period range from 5 s to 250–400 s (Rayleigh) and 5 s to 100–250 s (Love), depending on the region. Rayleigh‐wave anisotropy was determined in each region at periods from 5 s to 150–200 s, sampling from the upper crust down to the asthenosphere. The jackknife method was used to estimate uncertainties, and the F‐test to verify the statistical significance of anisotropy. We detected strong anisotropy with a N–S fast‐propagation azimuth in the upper crust of the Limpopo Belt. We attribute it to aligned cracks, formed by the regional, E–W extensional stress associated with the southward propagation of the East African Rift. Our results show that it is possible to estimate regional stress from short‐period, surface wave anisotropy, measured in this study using broad‐band array recordings of teleseismic surface waves. Rayleigh‐wave anisotropy at 70–120 s periods shows that the fabric within the deep mantle lithosphere of the Limpopo Belt and northern Kaapvaal Craton is aligned parallel to the Archean–Palaeoproterozoic sutures at block boundaries. This confirms that the fabric within the lithosphere created by pervasive ancient deformation is preserved to this day. Suture‐parallel fabric is absent, however, in the deep lithosphere of the western Kaapvaal Craton, suggesting that it was not reworked in the collision with the craton’s core, either due to its mechanical strength or because the deformation mechanism was different from those that operated in the north. Anisotropy at periods greater than 120–130 s shows fast directions parallel to the plate motion and indicates shear wave anisotropy in the asthenosphere. The depth distribution of anisotropy revealed by surface wave measurements comprises elements of both end‐member models proposed previously: anisotropy in the asthenosphere shows fast‐propagation directions parallel to the plate motion; anisotropy in the Limpopo and northern Kaapvaal lithosphere shows fast ...

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Seismic‐wave velocities offer essential constraints on the temperature, thickness, and composition of the lithosphere of cratons. We invert broadband, Rayleigh‐wave phase and Love‐wave phase velocities measured across the Kaapvaal Craton and Limpopo Belt for depth distributions of shear‐wave velocity and radial anisotropy, from the upper‐crust down to deep upper mantle. Our probabilistic, Bayesian inversion addresses model nonuniqueness by means of direct parameter‐space sampling. An increase in Vs between the Moho and 100–150 km depths occurs across the region and can be explained by the gradual emergence of garnet below 80 km, due to the spinel peridotite‐garnet peridotite transformation and due to the exsolution of garnet from mantle orthopyroxene. Lateral variations in this Vs gradient can provide new information on lateral compositional variations. Cold cratonic lithosphere is manifest in very high shear velocities, up to 4.8 km/s. The depth extent of the shear‐velocity anomaly and the inferred lithospheric thickness increase from ∼200 km beneath the central and southwestern Kaapvaal to ∼300 km beneath the Limpopo Belt. Curiously, surface elevation decreases monotonically with the increasing lithospheric thickness. The relationship between the lithospheric thickness and topography depends on the lithospheric composition and, with the crustal structure taken into account, our results imply that the bottom part of the Limpopo lithosphere (200–300 km) is weakly‐to‐moderately depleted (Mg# 89.7–90.8). Our results also show that the central‐southwestern Kaapvaal lithosphere is thinner than it was (according to kimberlites) 100–200 m.y. ago. It may have been thinned by the same mantle plume that, initially, triggered the kimberlite eruptions.