The Central Main Ethiopian Rift is younger than 8 Ma: confirmation through apatite fission-track thermochronology

An isolated block of Precambrian basement rocks and Mesozoic sediments is exposed at Kella along the western margin of the Central Main Ethiopian Rift (MER), surrounded by Tertiary to Quaternary volcanic rocks. Apatite fission-track thermochronology on two basement samples yielded ages of 7.2 +/- 1.0 Ma and 6.7 +/- 3.0 Ma and a long mean track length (>14.5 mu m). Rapid Late Miocene cooling is attributed to denudation related to rifting. Despite the paucity of data, due to the absence of suitable lithologies in the area, our data confirm that the Central MER is younger than 8 Ma as recently proposed on the basis of field evidence and radiometric dating of volcanics. This implies that the Central MER formed after the Northern MER, indicating a diachronous development of this third arm of the Red Sea-Gulf of Aden-Ethiopian Rift system.