A minimum Thanetian (Paleocene) age for the African Surface in the Eritrean highlands, Northeast Africa

Abstract

Supergene alunite from a supergene leached capping zone in the Daero Paulos area near Asmara, Eritrea yields Thanetian (late Paleocene) K–Ar ages of 58.6 ± 2.3 and 59.4 ± 2.3 Ma. The leached capping is exposed in an erosional window through a laterite profile, with the supergene alunite forming by oxidation of pyrite contained in quartz veinlet stockworks hosted by porphyry copper-related, felsic porphyry and adjacent volcano-sedimentary country rocks. Geologic relationships show that the leached capping and contained supergene alunite formed simultaneously with the lateritic weathering event that accompanied regional planation of equatorial and subequatorial Afro-Arabia to form the African Surface. Landscape modification of the central Ethiopian-Eritrean plateau by incision of transverse valleys and canyons commenced in the Oligocene, with a principal exhumation event occurring in the Miocene in response to swell-induced rift-flank uplift during Red Sea opening.