Receiver Function Imaging of Mantle Transition Zone Discontinuities Beneath the Tanzania Craton and Adjacent Segments of the East African Rift System

Abstract

The mantle transition zone (MTZ) discontinuities beneath the Tanzania Craton and the Eastern and Western Branches of the East African Rift System are imaged by stacking over 7,100 receiver functions. The mean thickness of the MTZ beneath the Western Branch and Tanzania Craton is about 252 km, which is comparable to the global average and is inconsistent with the existence of present-day thermal upwelling originating from the lower mantle. In contrast, beneath the Eastern Branch, an up to 30 km thinning of the MTZ is observed and is attributable to upwelling of higher temperature materials from either the upper MTZ or the lower mantle. The observations are in agreement with the hypothesis that rifting in Africa is primarily driven by gradients of gravitational potential energy and lateral variations of basal traction force along zones of significant changes of lithospheric thickness such as the edges of the Tanzania Craton.

Upper Mantle Earth Structure in Africa From Full‐Wave Ambient Noise Tomography

“…In each following results section, we highlight the details of our isotropic Vs model and provide a brief comparison between our models and prior work. A more detailed comparison between models for Africa, the Mediterranean, and the Middle East is included in the supporting information (Figure S23; Achauer & Masson, ; Ayadi et al, ; Benoit et al, ; Brazier et al, ; Bufford et al, ; Corbeau et al, ; Corchete, ; Dorbath et al, ; Fichtner et al, ; Fichtner & Villaseñor, ; Green et al, ; Hansen et al, ; Houser et al, ; Jakovlev et al, ; Khoza et al, ; Korostelev et al, , ; Leseane et al, ; Mulibo & Nyblade, ; Nita et al, ; Nyblade, ; Nyblade & Brazier, ; Nyblade et al, ; Reed, Gao, et al, ; Reed, Liu, et al, ; Ritsema et al, , ; Slack et al, ; Sun et al, ; Yu et al, ).…”

“…Geochemistry, Geophysics, Geosystems 2013; Khoza et al, 2013;Korostelev et al, 2015Korostelev et al, , 2016Leseane et al, 2015;Mulibo & Nyblade, 2013b;Nita et al, 2016;Nyblade, 2011;Nyblade & Brazier, 2002;Nyblade et al, 2000;Reed, Gao, et al, 2016;Ritsema et al, 2011Ritsema et al, , 1998Slack et al, 1994;Sun et al, 2017;Yu et al, 2015).…”

Topography of the 410 and 660 km Discontinuities Beneath the Cenozoic Okavango Rift Zone and Adjacent Precambrian Provinces

“…Results using the expanded data set suggest that the area has a NE‐SW elongated shape, with a maximum amount of MTZ thinning of 14 km located at (22°E, 22°S) (Figure 6d), which corresponds to a positive thermal anomaly of 120°C if Clapeyron slopes of 2.9 MPa/K (an average value from Bina & Helffrich, 1994) for the d410 and −1.3 MPa/K (determined by Fei et al, 2004) for the d660 are used. MTZ thinning is also suggested beneath the Main Ethiopian and Kenyan rifts and has been interpreted to be possibly related to the African Superplume (Cornwell et al, 2011; Huerta et al, 2009), but such an interpretation has recently been challenged (Sun et al, 2017). Although the magnitude of the thermal anomaly is comparable with what has been proposed for a moderate mantle plume (Farnetani & Richards, 1994), the observations cannot adequately support a mantle plume originated from the lower mantle and extends to the surface, for a number of reasons.…”

Insights Into Deep Mantle Thermochemical Contributions to African Magmatism From Converted Seismic Phases

“…In the southern East African Rift, a thinned MTZ (30–40 km) and associated 200–300 K anomaly below the eastern rift branch is often interpreted as evidence for active upwelling from deeper mantle (Mulibo & Nyblade, 2013; Owens et al., 2000; Sun et al., 2017). Normal thickness MTZ below the western rift branch and Tanzanian craton is inconsistent with present‐day thermal anomalies rooted at/below the MTZ (e.g., Sun et al., 2017).…”