Crustal structure in Ethiopia and Kenya from receiver function analysis: Implications for rift development in eastern Africa

Abstract

[1] Crustal structure in Kenya and Ethiopia has been investigated using receiver function analysis of broadband seismic data to determine the extent to which the Cenozoic rifting and magmatism has modified the thickness and composition of the Proterozoic crust in which the East African rift system developed. Data for this study These results indicate that the crust beneath the Ethiopian Plateau has not been modified significantly by the Cenozoic rifting and magmatism, even though up to a few kilometers of flood basalts have been added, and that the crust beneath the rifted regions in Ethiopia has been thinned in many places and extensively modified by the addition of mafic rock. The latter finding is consistent with models for rift evolution, suggesting that magmatic segments with the Main Ethiopian Rift, characterized by dike intrusion and Quaternary volcanism, act now as the locus of extension rather than the rift border faults.

The development of extension and magmatism in the Red Sea rift of Afar

“…In support of this model, high-resolution magnetic and gravity surveys (Bridges et al, 2012) reveal the presence of mafic dikes through the upper crust. Receiver function evidence for elevated bulk-crustal Vp/Vs ratios (Dugda et al, 2005;Hammond et al, 2011), and controlled-source seismic imaging of gabbroic intrusions Makris and Ginzburg, 1987) provide evidence for magma intrusion into the lower crust as well. Evidence for localised dike intrusion accommodating significant crustal strain has important subsequent implications for basin morphology.…”

“…In general, the plateaus have Vp/Vs of 1.7-1.9, whereas localised regions of thicker (~30 km-thick) crust within Afar have Vp/Vs of 1.8-1.9 (Dugda et al, 2005;Hammond et al, 2011). Vp/Vs ≤ 1.85 can be explained compositionally, but observations of Vp/Vs > 1.85 strongly suggest present-day melt.…”

“…Vp/Vs ≤ 1.85 can be explained compositionally, but observations of Vp/Vs > 1.85 strongly suggest present-day melt. Near the active Quaternary-Recent magmatic segment and beneath the Miocene Dahla basalts, where crustal thickness is b 30 km, Vp/Vs is high at 1.9-2.1 -also strong evidence for partial melt in the crust (Dugda et al, 2005;Hammond et al, 2011).…”

“…Discussion has often focussed on whether the crust is completely new oceanic crust, or whether it is stretched and thinned continental crust, heavily intruded by magma (transitional crust). Constraints on crustal structure primarily come from wide-angle seismic studies (Berckhemer et al, 1975;Maguire et al, 2006;Makris and Ginzburg, 1987;Prodehl et al, 1997), teleseismic receiver function studies (Ayele et al, 2004;Dugda et al, 2005;Hammond et al, 2011;Stuart et al, 2006), and from gravity analysis (Redfield et al, 2003;Tessema and Antoine, 2004;Tiberi et al, 2005). Results achieved using these different methods are broadly consistent (e.g., Fishwick and Bastow, 2011).…”

Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers

“…increasingly point to the influential role of melt products on the evolution of continental rifting (e.g. Ebinger & Casey 2001;Corti et al 2003;Dugda et al 2005;Kendall et al 2005;Buck 2006;Bastow & Keir 2011;Armitage et al 2015). However, many ancient and active rift systems display evidence of volumetrically limited magmatic activity, for example, the Western Branch of the East African Rift System (EARS ;Furman 2007) and the Newfoundland-Iberia rifted margins (e.g.…”