Constraining the timing and migration of collisional tectonics in the Damara Belt, Namibia: U-Pb zircon ages for the syntectonic Salem-type Stinkbank granite

Abstract

A U-Pb zircon LAM-ICP-MS age of 549 ± 11 Ma from the Stinkbank granite in the south Central Zone of the Damara belt represents the first robust age for the crystallization of a member of the regionally widespread suite of syntectonic Salem-type granites. This age confirms previous assertions that suggest that the main phase of crustal shortening related to the collision between the Congo and Kalahari Cratrons occurred between 550 and ~540 Ma in the south Central Zone, the leading edge of the Congo Craton. Ages from syntectonic granites reported in the literature from the north Central and the Northern Zone record progressively younger ages of ~530 to ~515 Ma and late-stage folding in the Northern Zone is suggested to have occurred between ~510 to ~500 Ma. The younging of ages that date the main collisional phase towards the north is interpreted to track the northward propagation of the deformation and metamorphic front from the main suture zone to the northern foreland of the Damara belt. Geochronological data are sparse, and the lack of detailed structural data precludes the retrodeformation of the fold-and-thrust belt along this 250 km long section. However, the age brackets suggest a migration of the orogenic front at a rate of at least 5 to 7 mm/a, but more likely in the order of several centimetre per year, if the internal strain is removed.