YOUNG COOLING HISTORY OF THE TEKEZE RIVER CANYON, ETHIOPIAN PLATEAU DEDUCED FROM NEW APATITE (U-TH)/HE AGES

The Ethiopian Plateau (divided into Northwestern and Southeastern Plateaus) in East Africa features dynamic topography, active tectonics, continental rifting, volcanism and plateau uplift. Deeply incised canyons carved by the Blue Nile and Tekeze River drainage network also characterize the plateau, which is situated north of the Kenya Dome. The arrival and impingement of the Afar mantle plume beneath the Ethiopian Plateau resulted in a ~2 km thick flood basalts around 30 Ma (Early Oligocene). A handful of research efforts have been made to ascertain the timing of incision and uplift of the Ethiopian Plateau since 30 Ma, yielding conflicting results that involve either a steady-state old (>20 Ma) incision or an episodic young (<15 Ma) incision. In an effort to clear these controversies, the ~1.5 km deep canyon incision carved by the Tekeze River on the Northwestern Ethiopian Plateau was investigated as a proxy for deciphering the plateau uplift.

In this study, we present new single-grain apatite (U-Th)/He thermochronologic dates from a total of 16 grains extracted from four basement rock samples along a vertical transect of the Tekeze River Canyon. The apatite (U-Th)/He data from this transect yield a range of cooling ages as young as 12.27 Ma. With the lack of a systematic cooling age gradient with increasing sample elevation, these cooling ages show a positive correlation with effective uranium concentration indicating radiation damage.

Thermal histories were generated by RDAAM (Radiation Damage Accumulation Annealing model) in HeFTy guided by reasonable geologic constrains. Initial results suggest that during the Early Cretaceous (130–80 Ma), the plateau underwent gradual cooling associated with Mesozoic rift-related exhumation followed by burial-related heating around 30 Ma related to the flood basalt eruption. This reheating event is followed by complex young cooling history showing two rapid pulses. The first phase of rapid cooling started during the beginning of the Late Miocene while the second rapid cooling initiated during the Pliocene continuing into the present day. Our previous studies within the Blue Nile Canyon also shares this young cooling and incision history of the Ethiopian Plateau.