Crustal structure beneath the Ethiopian Plateau and adjacent areas from receiver functions: Implications for partial melting and magmatic underplating

Abstract

Receiver function measurements of crustal thickness (H) and Vp/Vs provide important information on the formation and evolution of continental plateaus and rift zones such as the Ethiopian Plateau, the Afar and Main Ethiopian Rifts in northeastern Africa. Unfortunately, the presence of a low-velocity sedimentary layer atop most of the Cenozoic rift basins may lead to strong reverberations that can mask the P-to-S conversions from the Moho, resulting in unreliable H and Vp/Vs measurements. Here we estimate H and Vp/Vs beneath the Afar Depression (AD), Ethiopian Plateau (EP), and the Main Ethiopian Rift (MER) by stacking receiver functions. Reliable H and Vp/Vs measurements are obtained at a total of 69 stations, among which 18 stations are pre-processed by applying the reverberation removal technique. In comparison to the MER and EP, the AD is characterized by a thinner crust and higher Vp/Vs, and the thinnest crust and highest Vp/Vs are found in the Red Sea Rift (RSR) in central AD. Gradual variations of H and Vp/Vs between the previous and present axes of the RSR support a gradual rather than jumpy migration model of the axis. The overall high Vp/Vs values in the study area can be interpreted as a combined result of continental flood basalts at the surface, magmatic intrusion, and crustal partial melting. The relatively low amplitude of the P-to-S converted phases from the Moho observed in the southern part of the western Ethiopian Plateau and the AD with the exception of the RSR may be attributed to magmatic underplating.