Publication Date

Fall 2018

Advisor(s) - Committee Chair

Dr. Nahid D. Gani (Director), Dr. Royhan Gani, and Dr. Joshua Durkee

Degree Program

Department of Geography and Geology

Degree Type

Master of Science

Abstract

The geology of Ethiopia is dominated by the Ethiopian Plateau that is similar in elevation to, but aerially larger than, the Colorado Plateau. Several rivers have incised through the plateau, creating gorges that reach up to 1.5 km in depth. The plateau uplifted to its current elevation and was subsequently incised sometime after the Oligocene flood basalt event that signaled the arrival of the African Superplume below Kenya and Ethiopia. Due to its size and extent, published climate modeling has indicated that Late Cenozoic plateau formation could have been a driving force in the East African Cenozoic climate changes. Although uplift timing has potentially far-reaching impacts to several scientific disciplines, uplift is not well constrained, and several published studies present contradictory data. This study aims to elucidate the uplift timing of the Ethiopian Plateau through the use of river incision timing as a proxy for uplift. Methods employed to accomplish incision timing include low temperature apatite fission track and (U-Th)/He thermochronology, thermal modeling, and scanning electron microscopy backscatter electron detection (SEM-BSE). Basement samples for thermochronologic dating were collected from the Didessa River Canyon near Nekemte. (U-Th)/He dating was conducted at the Arizona State University Group 18 Laboratory where 17 apatite grains were dated, while GeoSeps Services LLC performed the apatite fission track analysis. Results indicate that after crystallization between 797-630 Ma during the East African Orogen, the rocks experienced rapid exhumation to within 1400-3000 m of the surface in the Jurassic. The Cenozoic flood basalt event at 31-29 Ma caused a massive outpouring of basalts that forced the lowest sample into the partial retention zone where it remained for an extended period of time while accumulating radiation damage. Rapid cooling from 8 Ma to present represents a recent exhumation history of the Ethiopian Plateau, suggesting that the plateau’s high elevation gain was achieved within the last 10 Ma. This integrated apatite (U-Th)/He and fission track study is the first of its kind addressing East African Cenozoic tectonics.

Disciplines

Geochemistry | Geology | Geomorphology | Tectonics and Structure

Available for download on Friday, December 10, 2021

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