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Spatial and temporal variation of tectonic uplift in the southeastern Ethiopian Plateau from morphotectonic analysis

Xue, Liang, Alemu, Tadesse, Gani, Nahid D., Abdelsalam, Mohamed G.
Geomorphology 2018 v.309 pp. 98-111
Advanced Spaceborne Thermal Emission and Reflection Radiometer, basalt, cartography, digital elevation models, plateaus, tectonics, temporal variation
We use morphotectonic analysis to study the tectonic uplift history of the southeastern Ethiopian Plateau (SEEP). Based on studies conducted on the Northwestern Ethiopian Plateau, steady-state and pulsed tectonic uplift models were proposed to explain the growth of the plateau since ~30 Ma. We test these two models for the largely unknown SEEP. We present the first quantitative morphotectonic study of the SEEP. First, in order to infer the spatial distribution of the tectonic uplift rates, we extract geomorphic proxies including normalized steepness index ksn, hypsometric integral HI, and chi integral χ from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model (DEM). Second, we compare these rates with the thickness of flood basalt that we estimated from geological maps. Third, to constrain the timing of regional tectonic uplift, we develop a knickpoint celerity model. Fourth, we compare our results to those from the Northwestern Ethiopian Plateau to suggest a possible mechanism to explain regional tectonic uplift of the entire Ethiopian Plateau. We find an increase in tectonic uplift rates from the southeastern escarpments of the Afar Depression in the northeast to that of the Main Ethiopian Rift to the southwest. We identify three regional tectonic uplift events at ~11.7, ~6.5, and ~4.5 Ma recorded by the development of regionally distributed knickpoints. This is in good agreement with ages of tectonic uplift events reported from the Northwestern Ethiopian Plateau.