Publication Date

Spring 2020

Advisor(s) - Committee Chair

Nahid Gani (Director), Stuart Foster, M. Royhan Gani, and Jason Polk

Degree Program

Department of Geography and Geology

Degree Type

Master of Science

Abstract

The Ethiopian Plateau in East Africa features dynamic topography, deep river incision (~1.5 km), active tectonics, continental rifting, volcanic terrain and ~2 km of plateau uplift. Situated on the northwestern part of the Ethiopian Plateau, the Tekeze River is one of the two major rivers associated with incising and documenting the recent geologic history of the uplifted plateau landscape. The consequential Tekeze River incision into the uplifted Ethiopian Plateau is associated with the arrival and impingement of the Afar mantle plume as evidenced by the presence of thick sheets of Cenozoic flood basalts (~30 Ma). However, the Cenozoic to present-day incision history on the Ethiopian Plateau is poorly constrained relative to the number of published studies in the past few decades. In this study, the Cenozoic to present-day incision of the plateau is quantified from the Tekeze River by integrating low-temperature apatite (U-Th)/He and fission-track thermochronologic dating of crystalline basement rocks exhumed from the deep incisions carved out by the Tekeze River. Four samples were collected along a vertical section of the Tekeze River Canyon. Apatite (U-Th)/He and fission-track thermochronologic dating techniques were chosen specifically for their low closure temperatures and helium partial retention zone (PRZ), which better constrain the low-temperature cooling history of rocks to understand the Ethiopian Plateau incision. Inverse thermal history models were generated from HeFTy and QTQt modeling software. New thermochronologic data from this study provides the youngest cooling ages to date in the study area. Results from the thermal history models indicate that the Cenozoic incision within the Tekeze River initiated ~28 Ma after the 30 Ma flood basalt event. Following this onset, incision continued until an ensued transition to exasperated incision rates occurred ~12 Ma, when the bulk of incision occurred, which is likely attributed to the base level perturbations. Incision timing remain unclear after the ~12 Ma due to model directional uncertainties.

Disciplines

Geochemistry | Geology | Geomorphology | Tectonics and Structure

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