Morpho-tectonics and mechanism of emplacement of the dolerite rings and sills of the western Karoo, South Africa

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Authors:Chevallier, L.; Woodford, A.
Author Affiliations:Primary:
Council for Geoscience, Bellville, South Africa
Other:
Directorate of Geohydrology, South Africa
Volume Title:South African Journal of Geology
Source:South African Journal of Geology, 102(1), p.43-54. Publisher: Bureau for Scientific Publications, Pretoria, South Africa. ISSN: 1012-0750
Publication Date:1999
Note:In English. 34 refs.; illus., incl. sects., geol. sketch maps
Summary:The dolerite sill and ring-like structures of the Karoo Basin have been a matter of debate for a considerable period of time. However, the mechanism for their emplacement still remains an enigma. A review of the available literature shows that very little structural work has been carried out on these intrusions, which outcrop over two thirds of South Africa. A large quantity of geological information, maps, and field data have become available over the last 15 years. A comparative morphotectonic analysis of three sill-ring systems of the western Karoo, that is, Williston, Fraserburg, and Victoria West complexes, indicates that their shape is saucer-like with an inner sill at the bottom, an arcuate inclined sheet (the ring) on the periphery, and an outer sill on the rim. Many arcuate dykes are seen branching onto the ring structures. A mode of emplacement is proposed whereby dolerite dykes feed into the inclined sheets, which then propagate into an outer sill and thereafter into an inner sill.
Sections:Petrology
Subsections:Igneous petrology
Subjects:Arcuate structures; Complexes; Diabase; Dikes; Emplacement; Igneous rocks; Intrusions; Mechanism; Outcrops; Plutonic rocks; Ring structures; Shape analysis; Sills; Tectonics; Africa; Karoo Basin; South Africa; Southern Africa; Fraserburg Complex; Victoria West Complex; Williston Complex
Coordinates:S345000 S193000 E0295000 E0180500
Abstract Numbers:99M/4261
Record ID:1999070719
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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