Abstract

Deep inside the Earth, just above the core-mantle boundary at ∼2700 km depth, large-scale mantle structures are assumed to play a key role in global geodynamic processes. While unusual hot regions are attributed with feeding rising mantle plumes and volcanic hotspots, the accumulation of subducted lithospheric plates is associated with colder-than-average features. In both environments, the appearance of dynamic-driven processes such as deformation and mantle flow can directly be inferred by the presence of seismic anisotropy. However, the geometries as well as the interactions of these massive anomalous structures with the surrounding mantle material are still under debate. Based on new seismic data from a dense and large-aperture recording network in Scandinavia, we characterize the anisotropic signatures of two so-far unexplored regions in the lowermost mantle by using observations of clearly discrepant SKS-SKKS shear-wave splitting measurements. Thereby we can demonstrate that anisotropy is located along the northern edges of the large low-shear-velocity province beneath Africa. Furthermore, we recover an anisotropic structure in a region of fast seismic velocity underneath Siberia that provides additional evidence for widespread deformation caused by a deeply subducted slab.

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