Potassium–argon ages of volcanic rocks from northeast of Lake Turkana, northern Kenya

Abstract

AbstractThe Asille Group, a 1500 m succession comprising dominantly basaltic lavas but with interbedded sediments and silicic volcanics, lies unconformably upon metamorphosed basement northeast of Lake Turkana. Concordant K–Ar ages on alkali feldspars from pantelleritic units in the succession show that the Langaria Formation erupted 26.9±0.3 Ma ago in late Oligocene time, that Gum Dura Formation volcanism occurred at 15.8±0.2 Ma (early Miocene), and that there was widespread middle Miocene silicic volcanism at 13.0±0.3 Ma. Younger basaltic volcanism producing the flood lavas of the Gombe Group commenced at least 6.16±0.09 Ma ago in late Miocene time. These results, based upon 20 K–Ar age determinations, provide good numerical age control for much of the sequence developed within a little known sector of the Eastern Rift of Africa between the Ethiopian and Kenyan domes.