T149 Tortoise to Hare Tectonics: Steady and Transient Deformation

Monday, 1 November 2010
1:30 PM - 5:30 PM
Lobby F

UPLIFT OF THE ETHIOPIAN PLATEAU: A COMPLEX INTERACTION BETWEEN TECTONICS AND INCISION

Paper number: T149-5
Program: Technical Sessions
Time: 2:30 PM – 2:45 PM

Authors

Abstract

The Ethiopian Plateau in East Africa is undergoing uplift, incision and continental rifting, holding invaluable potential to understand landscape evolution in an active geodynamic context. The plateau has been unroofed through deep incision by two major river systems of the Nile, the Blue Nile in the south and the Tekeze in the north. Here we presented new quantitative estimates of the Blue Nile and its major tributaries to explain the spatial and temporal breaks in tectonic uplift rates in a poorly investigated area like the Ethiopian Plateau. The 1.6 km deep incision resulted in numerous knickpoints distributed throughout the plateau that are identified in tributary longitudinal profiles extracted from SRTM derived DEMs using stream power model. In their long profiles, these tributaries preserved at least two major knickpoints, which resulted in a new equilibrium slope, separating the upstream older channel profiles from the downstream younger channel profiles. This supports our previously documented three phases of incision of the plateau, much of which are uplift related.

We analyzed more than fifty major knickpoints, which are crucial in explaining topographic evolution of the plateau. These are transient knickpoints with mean reliefs of >200 m, demarcating the boundary between steady-state and transient channel reaches within the profiles. Existence of these knickpoints at similar elevations within the plateau likely indicates that pulses of incision propagated at nearly similar vertical rates, marking the breaks in plateau uplift rates. One key question to ask is whether these pulses of incision are migrating faster through time; the answer could be critical to explain differential uplift rates in the region. Although these knickpoints require further investigation, we separated out these knickpoints as they are unassociated with local stream capture, normal faulting, or varied bedrock lithology. Therefore, these major knickpoints are likely related to differential uplift (mantle plume and flexural rift-flank related) of the plateau.