The Ethiopian Plateau, situated in the northernmost part of the East African Rift System, has been uplifted and incised by the Blue Nile River, creating the 1.5 km-deep Blue Nile Canyon, the only extensive canyon within the Nile drainage basin. Much of this canyon incision is related to the Ethiopian Plateau uplift, which is due to a combined tectonic influence linked to the East African Rift System and the Afar Mantle Plumerelated upwelling since the Oligocene. The Blue Nile Canyon incision followed this plume-related upwelling, which resulted in extensive flood basalt emplacement around ~30 Ma. This study employs low-temperature apatite (U-Th)/He thermochronology to better understand the timeline and mode of the Blue Nile Canyon incision and the landscape geodynamics of the Ethiopian Plateau. Neoproterozoic basement rocks and Mesozoic sedimentary rock samples were collected in a vertical transect along the Blue Nile Canyon for AHe dating. Euhedral apatite grains that are inclusion-free and fractureless were selected for dating. The Australian Scientific Instrument (ASI) Alphachron and Inductively Coupled Plasma Mass Spectrometer (ICP-MS) measured the concentrations of radiogenic isotopes uranium (U), thorium (Th), and helium (He) to obtain apatite helium (AHe) dates, providing (U-Th)/He cooling ages ranging from 64 to 460 Ma. These AHe dates are much older than the 30 Ma flood basalt event, thus older than the canyon incision. In this study, a cooling/thermal history is suggested by explaining the data dispersion by the radiation damage effect in the dated apatite grains, which is related to He retention with time. The apatite suite has been subjected to protracted cooling, longer residence time in the He partial retention zone, and partial resetting due to Mesozoic rift-related burial and subsidence from deposition of ~1.2 kmthick sedimentary rocks, the extensive emplacement of ~1 km-thick flood basalt at 30 Ma, and differential incision. Radiation Damage Accumulation and Annealing Model (RDAAM) time-temperature thermal models indicate a rapid cooling event, suggesting rapid incision after 10 Ma, which is explained by an increase in uplift of the Ethiopian Plateau, likely due to mantle delamination.

The Ethiopian Plateau is one of the few tectonically-active regions on Earth that is situated in continental rift zones. About 1.6 km deep gorge of the Nile was carved by the Blue Nile River on the Ethiopian Plateau, as the plateau has been experiencing continuous uplift and exhumation in the Cenozoic. Here, we used quantitative analysis of longitudinal rive-profile forms and parameters (knickpoint and normalized steepness-index ksn) of the Blue Nile tributaries to tease out regional tectonic signals. 244 knickpoints were examined in the tributaries, majority (>80%) of which are unassociated with lithology or geological structures. Knickpoint distribution throughout the plateau reveals three incision phases. The novel approach of correlation of ksn with mantle tomography suggests that higher and lower ksn values occur above low-velocity and high-velocity zones, respectively, indicating that thermal upwelling beneath the plateau linked to Afar mantle plume largely controls the uplift thus incision of the plateau.