Major-, trace-, rare-earth-element, and RbSr and SmNd isotope data of the various low-grade metamorphosed magmatic units in the Pan-African Gariep Belt, southwestern Namibia, presented in this paper, provide the basis for the reconstruction of the evolution of the late Proterozoic Adamastor ocean between the South American and Kalahari Cratons. The Gariep Belt is subdivided into two major zones, a para-autochthonous, predominantly sedimentary rift and passive continental margin succession (Port Nolloth Zone, PNZ) and the allochthonous, predominantly mafic Marmora Terrane. The latter has been thrust in southeasterly direction over the former. All of the magmatic activity in the PNZ can be related to lithospheric stretching. The earliest magmatic activity is expressed as bimodal volcanism with continental within-plate affinity along an embryonic rift graben (Rosh Pinah Formation) and is found within the older sediment package of the para-autochthonous external zone of the orogen. After ∼ 24 Ma, this was followed by the intrusion of mafic, tholeftic dykes into the basement and the lower parts of the PNZ, heralding the opening of the Gariepian basin at 717 Ma. There is evidence of a series of seamounts, or an aseismic ridge, with oceanic within-plate characteristics in the Marmora Terrane. Such volcanic piles make up most of the Schakalsberge Complex and parts of the Chameis Complex. Both complexes are separated by turbidites (Oranjemund Complex), which are interpreted as continental slope deposits. In the Chameis Complex, metagabbros predominate. Most of them are part of the oceanic seamounts, but some have a markedly different chemistry, indicative of a mid-ocean ridge setting. During Pan-African collision, the Marmora Terrane formed an accretionary wedge that was thrust over the passive continental margin succession. Peak metamorphism in the thickened crust was reached at ∼ 545 Ma, with erosion of the orogen having commenced as early as 540 Ma.