Abstract

Reconstructions of the inland branch of the Late Proterozoic Damara orogen in Namibia indicate rifting and show a marked asymmetry in both sedimentary facies and structural styles from north to south. Early synrift sequences comprising terrigenous siliciclastics, minor carbonates, and local volcanics vary markedly within two initial half-grabens. With later subsidence, postrift sequences became laterally more continuous when sedimentation coalesced; they vary from carbonate-dominated in the north to siliciclastic in the south. This indicates sedimentation on a broad epicontinental shelf. Gentle open folds in the north increase in complexity southward, culminating in a fold-thrust belt. These tectonic styles are believed to be a direct result of reactivation of early extensional faults. Although most did not address this point, previous models for the development of Damara rift structures assumed pure-shear homogeneous stretching of the crust to produce the graben systems. These models, however, fail to account satisfactorily for observed asymmetries. Early rifting in the inland arm of the Damara orogen is proposed to have been controlled by two down-to-the-northwest low-angle detachment faults. Asymmetry in basin configuration was a direct consequence of this crustal thinning mechanism, which we believe controlled the depositional environments. This model is more appropriate in explaining the asymmetrical relations observed.

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