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 - Roux, E. A1 - Moorkamp, Max A1 - Jones, Alan G. A1 - Bischoff, Monika A1 - Endrun, Brigitte A1 - Lebedev, Sergei A1 - Meier, Thomas T1 - Joint inversion of long-period magnetotelluric data and surface-wave dispersion curves for anisotropic structure application to data from Central Germany JF - Geophysical research letters N2 - Geophysical datasets sensitive to different physical parameters can be used to improve resolution of Earth's internal structure. Herein, we jointly invert long-period magnetotelluric (MT) data and surface-wave dispersion curves. Our approach is based on a joint inversion using a genetic algorithm for a one-dimensional (1-D) isotropic structure, which we extend to 1-D anisotropic media. We apply our new anisotropic joint inversion to datasets from Central Germany demonstrating the capacity of our joint inversion algorithm to establish a 1-D anisotropic model that fits MT and seismic datasets simultaneously and providing new information regarding the deep structure in Central Germany. The lithosphere/asthenosphere boundary is found at approx. 84 km depth and two main anisotropic layers with coincident most conductive/seismic fast-axis direction are resolved at lower crustal and asthenospheric depths. We also quantify the amount of seismic and electrical anisotropy in the asthenosphere showing an emerging agreement between the two anisotropic coefficients. Y1 - 2011 U6 - https://doi.org/10.1029/2010GL046358 SN - 0094-8276 VL - 38 IS - 3 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Endrun, Brigitte A1 - Lebedev, Sergei A1 - Meier, Thomas A1 - Tirel, Celine A1 - Friederich, Wolfgang T1 - Complex layered deformation within the Aegean crust and mantle revealed by seismic anisotropy JF - Nature geoscience N2 - Continental lithosphere can undergo pervasive internal deformation, often distributed over broad zones near plate boundaries. However, because of the paucity of observational constraints on three-dimensional movement at depth, patterns of flow within the lithosphere remain uncertain. Endmember models for lithospheric flow invoke deformation localized on faults or deep shear zones or, alternatively, diffuse, viscous-fluid-like flow. Here we determine seismic Rayleigh-wave anisotropy in the crust and mantle of the Aegean region, an archetypal example of continental deformation. Our data reveal a complex, depth-dependent flow pattern within the extending lithosphere. Beneath the northern Aegean Sea, fast shear wave propagation is in a North-South direction within the mantle lithosphere, parallel to the extensional component of the current strain rate field. In the south-central Aegean, where deformation is weak at present, anisotropic fabric in the lower crust runs parallel to the direction of palaeo-extension in the Miocene. The close match of orientations of regional-scale anisotropic fabric and the directions of extension during the last significant episodes of deformation implies that at least a large part of the extension in the Aegean has been taken up by distributed viscous flow in the lower crust and lithospheric mantle. Y1 - 2011 U6 - https://doi.org/10.1038/NGEO1065 SN - 1752-0894 VL - 4 IS - 3 SP - 203 EP - 207 PB - Nature Publ. Group CY - New York ER -