The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

Abstract

P and S relative arrival time residuals from teleseismic earthquakes recorded on over 60 temporary AfricaArray broadband seismic stations deployed in Uganda, Tanzania, and Zambia between 2007 and 2011 have been inverted, together with relative arrival time residuals from earthquakes recorded by previous deployments, for a tomographic image of mantle wave speed variations extending to a depth of 1200 km beneath eastern Africa. The image shows a low‐wave speed anomaly (LWA) well developed at shallow depths (100–200 km) beneath the Eastern and Western branches of the Cenozoic East African rift system and northwestern Zambia, and a fast wave speed anomaly at depths ≤ 350 km beneath the central and northern parts of the East African Plateau and the eastern and central parts of Zambia. At depths ≥350 km the LWA is most prominent under the central and southern parts of the East African Plateau and dips to the southwest beneath northern Zambia, extending to a depth of at least 900 km. The amplitude of the LWA is consistent with a ∼150–300 K thermal perturbation, and its depth extent indicates that the African superplume, originally identified as a lower mantle anomaly, is likely a whole mantle structure. A superplume extending from the core‐mantle boundary to the surface implies an origin for the Cenozoic extension, volcanism, and plateau uplift in eastern Africa rooted in the dynamics of the lower mantle.

Multiscale Seismic Tomography

“…The MTZ exhibits a normal thickness beneath Cameroon (Reusch et al 2011). Mulibo and Nyblade (2013) determined P and S wave tomography under East Africa down to 1200 km depth (Fig. Mulibo and Nyblade (2013) determined P and S wave tomography under East Africa down to 1200 km depth (Fig.…”

“…5.7), which are associated with the African superplume (Maruyama 1994;Montelli et al 2006;Chang and Van der Lee 2011;Davies et al 2012;Hansen et al 2012;Brandt 2013;Mulibo and Nyblade 2013;. 5.7), which are associated with the African superplume (Maruyama 1994;Montelli et al 2006;Chang and Van der Lee 2011;Davies et al 2012;Hansen et al 2012;Brandt 2013;Mulibo and Nyblade 2013;.…”

“…Mulibo and Nyblade (2013) determined P and S wave tomography under East Africa down to 1200 km depth (Fig. A superplume extending from the CMB to the surface implies an origin for the Cenozoic extension, volcanism and plateau uplift in eastern Africa rooted in the dynamics of the lower mantle (Mulibo and Nyblade 2013). Their images show a low-V anomaly well developed at 100-200 km depths beneath the Eastern and Western branches of the Cenozoic East Africa rift system and northwestern Zambia, and a high-V zone at depths < 350 km beneath the central and northern parts of the East African Plateau and the eastern and central parts of Zambia.…”

Hotspots and Mantle Plumes

“…5.7), which are associated with the African superplume (Maruyama 1994;Ritsema et al 1999;Zhao 2001bZhao , 2004Montelli et al 2006;Chang and Van der Lee 2011;Davies et al 2012;Hansen et al 2012;Brandt 2013;Mulibo and Nyblade 2013;. Large low-V zones are visible from the surface down to about 1000 km under the Afar, Lake Victoria, and East Africa hotspots, which seem to connect with the low-V zones in the lower mantle (Fig.…”

“…The excess temperature in the low-V zone is ~ 150-300 K. The depth extent of the low-V anomaly indicates that the African superplume is likely a whole mantle structure. A superplume extending from the CMB to the surface implies an origin for the Cenozoic extension, volcanism and plateau uplift in eastern Africa rooted in the dynamics of the lower mantle (Mulibo and Nyblade 2013). Hilton et al (2011) reported helium isotope ratios of lavas and tephra of the Rungwe Volcanic Province in southern Tanzania.…”