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Neoproterozoic Allochthonous Salt Tectonics During the Lufilian Orogeny
in the Katangan Copperbelt, Central Africa
Martin P. A. Jackson, O. N. Warin, G. M. Woad, and Michael R. Hudec

Abstract
The Neoproterozoic Katangan rocks in the Copperbelt of Shaba (Democratic Republic of the Congo) and Zambia contain the world's largest concentration of stratiform copper-cobalt ores. We propose that during the Lufilian orogeny, the Katangan basin was radically transformed first by extrusion of allochthonous evaporites then by orogenic shortening. Salt tectonics plausibly explains spectacular breccias underlying 25,000 km2 and containing gigaclasts up to 10 km long. The brecciated Shaban Roan Supergroup-the lowermost Katangan unit-forms regional detachments and diapirs. The former existence of Roan evaporites is indicated by sabkha facies, crystals and pseudomorphs of gypsum and anhydrite, stratigraphic gaps underlain by collapse breccias, chloride inclusions in ores, hydrothermally propylitized ore hosts, and saline springs. Salt tectonics began during deposition of the Roan Supergroup between 1050 and 950 Ma. In mid-Roan time, small walls and extrusions of evaporite-gigabreccia began to be emplaced. In early Kundelungu time (940-850 Ma), evaporitic diapirs enlarged. Lufilian deformation began between 850 and 650 Ma by laterally squeezing diapirs to form salt welds. Then, a large sheet of commingled Roan evaporite and carbonate-dominated sediments and ores was extruded northward by ~65 km. Extrusion was fast enough to blanket a uniform preorogenic footwall unit without overriding any synorogenic deposits. Continued shortening then emplaced large thrust sheets, lubricated by the pre-existing salt-sediment extrusive sheet. Restoration suggests that the Lufilian foreland in this area shortened from 193 km to 85 km.

The depositional northern edge of the evaporite basin controlled the shape of the Outer Lufilian Arc. We infer three original salt provinces. The large-scale salt tectonics inferred here has implications for ore genesis and may yet be recognized in other Precambrian basins.

O. N. Warin, Consultant, 910 Butterfield Rd, San Anselmo, CA 94960 (formerly BHP Minerals, Senior Vice-President for Exploration)
G. M. Woad, BHP Billiton, Suite 1400, 1111 W. Georgia St., Vancouver BC, V6E M43, Canada

For more information, please contact Martin Jackson. Telephone 512-471-9548; e-mail martin.jackson@beg.utexas.edu
March 2003
 
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