CENOZOIC INCISION OF THE ETHIOPIAN PLATEAU FROM THERMAL MODELING

Situated along the East African Rift, the Ethiopian Plateau has undergone uplift, and incision by the Blue Nile River. Recent tectonic activity associated with the Afar Mantle Plume and the discoveries of some of the earliest human remains have fueled interest in the area’s shifting environment. Apatite-helium dating technique has been employed to better understand the timeline and mode of this incision, thus the landscape dynamics of the region. In this process, ASI Alphachron and ICP-MS measure the concentrations of radiogenic isotopes Uranium, Thorium, and Helium for age calculation. 55 single apatite grains were analyzed from a vertical profile of 9 sample locations, providing (U-Th)/He ages ranging from 64 to 460 Ma. The radiation damage accumulation and annealing model (RDAAM) calibration to the HeFTy modeling software incorporates fission track density as a factor of (U-Th)/He age calculation based on its affect on helium diffusion kinetics in apatite grains. Due to the complex geologic history of the region, the RDAAM provides suitable parameters for analysis of this apatite suite, which has been subjected to conditions prone to partial resetting as a result of the deposition of the overlying 1km-thick flood basalt at 30 Ma and ensuing temperature increase. Employing HeFTy software, age and isotope concentration data were processed in an effort to establish thermal history. The time-temperature models constructed using local geologic constraints suggest multiple phases of Cenozoic uplift and variable incision rates.