U-Pb zircon ages for granitoid gneisses in northern Namibia and their significance for proterozoic crustal evolution of southwestern Africa

Abstract

The pre-Damara (> 900 Ma) basement gneisses and granitoids of northern Namibia and southern Angola constitute the southern margin of the Congo craton and are poorly known geochronologically. We report U-Pb zircon concordia intercept ages for an augengneiss of the Epupa Complex (∼ 1800 Ma), a banded quartzofeldspathic gneiss of the Huab Complex (∼1810 Ma), a post-Huab granitic gneiss (∼1750 Ma) and for inherited zircons (∼2120 Ma) from a Damaran syenite that has a true emplacement age of 800–840 Ma. These ages suggest that the Epupa and Huab Complexes are broadly coeval, and their formation, together with the emplacement of the widespread Fransfontein granitoid suite, constitutes a significant and regionally extensive crust-forming event in northern Namibia and southern Angola (the Huabian Episode) that corresponds to the Eburnian event in western, central and eastern Africa. Older crust in excess of 2120 Ma is likely to be present in the region but has not been documented geochronologically. Similarities in age, rock association and broad geologic evolution for pre-Damara basement complexes in northern, central and southern Namibia suggest that the entire territory may have been part of the Congo craton in mid-Proterozoic times, whose southwestern portion was largely reworked during the late Precambrian Namaqua and Pan-African events.