Structural and geochronological constraints on the Pan‐African tectonic evolution of the northern Damara Belt, Namibia

Abstract

The Pan-African Orogen formed by convergence of numerous continental blocks during the Neoproterozoic to early Cambrian. This convergence eventually led to amalgamation of Gondwana, a supercontinent crosscut by a network of highly oblique linear orogenic belts that locally intersect each other, as in NW Namibia, where the NNW trending Kaoko Belt joins the NE trending Damara Belt. The northern Damara Belt has preserved well three regional Pan-African tectonic events due to the dominance of weak Neoproterozoic marine sediments (Damara Supergroup) that have been affected by low-grade metamorphism. A newly discovered early N-S horizontal contraction, dated by 40 Ar/ 39 Ar at~590 Ma, is tentatively linked to convergence between the Congo and Kalahari cratons. This was superseded by collision between the Congo and Rio de la Plata cratons between 580 and 530 Ma that thickened and exhumed the orogenic crust of the Kaoko Belt and produced upper crustal N-S oriented folds of earlier fold trains and associated axial planar schistosities in the northern Damara Belt. A switch from E-W to NW-SE horizontal shortening occurred at 530 Ma as a result of collision with the Kalahari Craton, triggering extensive syn-orogenic magmatism in the entire Damara Belt. During this last event, southward indentation and underthrusting of the Congo Craton promontory below the Neoproterozoic cover sequences produced a deformation front in the northern Damara Belt. Our results show that highly oblique convergent processes competed over a period of~120 Ma to build Gondwana in Namibia during the late Neoproterozoic to early Cambrian.The Damara Orogen is composed of three highly oblique branches, the NNW trending Kaoko and Gariep belts and the NE trending Damara Belt [Martin and Porada, 1977;Coward, 1981;Miller, 1983;Gray et al., 2008] that were at least partly active at the same time [e.g., Miller et al., 2009] during mutual convergence of three cratonic blocks, the Rio de la Plata, Congo, and Kalahari cratons (Figure 1). Despite the Damara Orogen being extensively LEHMANN ET AL.TECTONIC EVOLUTION NORTHERN DAMARA BELT 103

Seawater-buffered diagenesis, destruction of carbon isotope excursions, and the composition of DIC in Neoproterozoic oceans

“…2A), providing a reliable basis for correlation (25,(31)(32)(33)(34)(35)(36). The Otavi/Swakop Group is disconformably overlain by foredeep clastic deposits and both were folded during collisional orogeny to the south (Damara Belt) and west (Kaoko Belt) starting at 0.59 Ga (37,38). We relate platform destruction to subduction at a trench, initiating collisional tectonism.…”

Timing of deformation in the Sarandí del Yí Shear Zone, Uruguay: Implications for the amalgamation of western Gondwana during the Neoproterozoic Brasiliano‐Pan‐African Orogeny

“…The onset of subduction at approximately 595–590 Ma along the northern margin of the Khomas Ocean and/or the southernmost margin of Adamastor Ocean [ Prave , ; Gray et al ., ; Rapela et al ., ] due to the convergence of the Kalahari Craton may provide a satisfactory explanation for this process (Figure c), as documented by Lehmann et al . []. This plate reorganization could be further supported by the sudden change in the apparent polar wander path of the Congo Craton observed after approximately 590 Ma [ Moloto‐A‐Kenguemba et al ., ].…”

Sedimentology and chemostratigraphy of the late Neoproterozoic carbonate ramp sequences of the Hüttenberg Formation (northwestern Namibia) and the C5 Formation (western central Democratic Republic of Congo): Record of the late post-Marinoan marine transgression on the margin of the Congo Craton

“…The Hüttenberg Formation is constrained by the stratigraphically-equivalent Kuiseb Formation in south-central Namibia, which yielded U-Pb detrital zircon ages between 606 ± 24 Ma and 587 ± 9 Ma (Foster et al, 2015). 40 Ar-39 Ar metamorphic ages of 590 Ma were obtained in the Kuiseb Formation in the Austerlitz area (Lehmann et al, 2016). The C5 Formation is constrained between ~575 Ma and 566 ± 42 Ma, based on 87 Sr/ 86 Sr ratios in carbonate rocks of the underlying C4 Formation (Poidevin, 2007) and 40 Ar-39 Ar metamorphic ages obtained in the Mpioka Subgroup (Frimmel et al, 2006) respectively.…”

“…Based on lithostratigraphic and radiometric data, the Tsumeb Subgroup in Namibia and the Gombela Subgroup of the Central Africa Copperbelt (CAC) in DRC and Zambia were considered as coeval (Miller, 2013). The Tsumeb Subgroup succession is constrained by an U-Pb zircon age of 635 ± 1.2 Ma on an ash layer interbed in the Ghaub Formation (Hoffmann et al, 2004), and U-Pb detrital zircon ages on metasediments between 606 ± 24 Ma and 587 ± 9 Ma in the Kuiseb Formation (Foster et al, 2015;Lehmann et al, 2016), considered as stratigraphic-equivalent with the Hüttenberg Formation (Miller, 2008). The youngest age is confirmed by 40 Ar-39 Ar metamorphic ages of 590 Ma obtained in the Kuiseb Formation (Lehmann et al, 2016).…”

“…The Tsumeb Subgroup succession is constrained by an U-Pb zircon age of 635 ± 1.2 Ma on an ash layer interbed in the Ghaub Formation (Hoffmann et al, 2004), and U-Pb detrital zircon ages on metasediments between 606 ± 24 Ma and 587 ± 9 Ma in the Kuiseb Formation (Foster et al, 2015;Lehmann et al, 2016), considered as stratigraphic-equivalent with the Hüttenberg Formation (Miller, 2008). The youngest age is confirmed by 40 Ar-39 Ar metamorphic ages of 590 Ma obtained in the Kuiseb Formation (Lehmann et al, 2016). A minimum deposition age for the top of the Swakop Group in Northern Zone of Namibia, intruding the Karibib and Kuiseb formations, is constrained by granite and metamorphic age determinations of ~585-F. Delpomdor, S. Schröder, A. Préat, P. Lapointe, C. Blanpied 570 Ma (Bergemann et al, 2014;Milani et al, 2014;Forster et al, 2015).…”