Record of the Damaran Khomas Hochland accretionary prism in central Namibia: Refutation of an "ensialic" origin of aLate Proterozoic orogenic belt

Abstract

Sedimentation patterns in multiply deformed and highly metamorphosed sedimentary rocks of the Khomas trough indicate deposition on an elongate submarine-fan system that developed in a Late Proterozoic depository forming part of the inland branch of the Damara orogen. Structural patterns exhibit mainly compressional features and indicate that the Damara Sequence metasedimentary rocks and interposed amphibolites, metagabbros, and ultramafic rocks lie within several imbricate thrust slices, floored by relatively thick pelitic units. The highly deformed Matchless amphibolite and associated pelagic sedimentary rocks are interpreted as the upper parts of an oceanic crustal sequence. These features are explained in a model that interprets the sediments as accumulating in a Late Proterozoic accretionary prism developed during convergence of the Congo and Kalahari cratons. Preservation of original sedimentary structures and coherent structural profiles allow the documentation of what may be the best preserved Precambrian accretionary prism yet described. Our interpretation helps to resolve some earlier speculation concerning an ensialic origin for this fold and thrust belt.