Moho depths and Poissonʹs ratios of Precambrian crust in East Africa: Evidence for similarities in Archean and Proterozoic crustal structure

We investigate the structure of Precambrian crust in East Africa by using estimates of Moho depth and Poissonʹs ratio for 37 new seismic stations in Uganda and Tanzania and for 32 previously deployed seismic stations in Kenya and Tanzania. The dataset includes estimates of crustal structure distributed between all of the major Archean and Proterozoic terrains obtained from modeling P-wave receiver functions. The average crustal thickness for the Ubendian belt is 42 km and between 37 and 39 km for all of the terrains. The average Poissonʹs ratio for all of the terrains is either 0.25 or 0.26, indicating a felsic to intermediate bulk crustal composition. A similar composition and thickness of the crust in East Africa for terrains spanning some 4 byr of Earth history is different than in many other Precambrian regions. Our results suggest that there may have been few changes over Earthʹs history in the processes that formed the East African crust, or else that processes have been at play to homogenize crustal structure, such as the flow of lower crustal material in orogenic systems or through the foundering of eclogites into the mantle. The finding that crustal structure is similar between the Archean and Proterozoic terrains indicates that crustal structure, through its influence on lithospheric rheology and strength, has not had a first-order effect on the location of rifting. We also find that there is little correlation between Moho depth and elevation across the East African Plateau, indicating that variations in crustal thickness exert few, if any, influences on topography in East Africa. This conclusion lends support to many studies arguing that mantle structure and processes provide the primary buoyant support for the plateau.