Evidence for an upper mantle plume beneath the Tanzanian craton from Rayleigh wave tomography

Abstract

[1] The Archean Tanzanian craton, nestled between the eastern and western branches of the East African Rift, presents a unique opportunity to study the interaction of active rifting with stable cratonic lithosphere. The high density of Rayleigh wave paths recorded in a regional seismic array yields unusually precise determinations of phase velocity within the Tanzanian craton. Shear velocities in the cratonic lithosphere are higher than a global average to a depth of 150 ± 20 km. Beginning at 140 km, shear velocity decreases sharply, reaching a minimum of 4.20 ± 0.05 km/s at depths of 200-250 km. The base of the lithosphere, identified by the depth to the center of the maximum negative velocity gradient, is similar to that found beneath other Archean lithospheres. Where Cenozoic rifting crosscuts the southern corner of the craton, velocities up to 130 km depth are reduced, indicating recent disruption of the lithosphere. The anomalously low velocities beneath the Tanzanian craton indicate high temperatures and the presence of melt, consistent with the spreading of a mantle plume head beneath the craton. Tests for the possibility of a radial pattern of azimuthal anisotropy that may indicate outward flow from a plume show that a model with average anisotropy of 0.71 ± 0.17% centered SE of Lake Victoria fits the data significantly better than a uniform, single direction of anisotropy. Thus our results agree with the suggestion that an upper mantle plume, centered beneath the Tanzanian cratonic lithosphere, provides the buoyancy required for uplift of the East African Plateau.

Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa

“…13). Finally, the presence of a low-velocity mantle beneath the region is consistent with previous seismological results that demonstrated a marked decrease of surface waves velocity between ∼60 and 100 km depth (Fishwick & Bastow 2011;Weeraratne et al 2003;O'Donnell et al 2013).…”

Lithospheric instability and the source of the Cameroon Volcanic Line: Evidence from Rayleigh wave phase velocity tomography

“…Values and one standard deviation uncertainties for Table 3. Formal standard deviations from model parameters calculated using this methodology are frequently very small [e.g., Weeraratne et al, 2003;Adams et al, 2012;O'Donnell et al, 2013]. Therefore, for estimates on uncertainty that are likely more realistic, we refer the reader to the two sigma error estimates of our two-dimensional models ( Figure 5).…”

Long lasting epeirogenic uplift from mantle plumes and the origin of the Southern African Plateau

“…A region of low seismic wave speeds has been imaged in the upper mantle beneath much of East Africa, providing strong evidence for thermally perturbed structure [e.g., Fuchs et al, 1977, and references therein; Ritsema et al, 1998;Nyblade et al, 2000;Ritsema and van Heijst, 2000;Debayle et al, 2001;Nyblade, 2002;Weerarantne et al, 2003]. Numerous hot spots, manifest as seamount chains, ridges and rises, are found within the southeastern Atlantic Ocean basin, and provide evidence of lithospheric reheating.…”