Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
11024667 | Tectonophysics | 2018 | 46 Pages |
Abstract
Dolerite sills in the central parts of the Karoo large igneous province on the Kalahari Craton in South Africa record the emplacement of magic magmas over 350,000â¯km2, but the feeders to the voluminous magmatism have yet to be identified. Extensive exploration and mining data across a 7400â¯km2 area and to a depth of 2.5â¯km in the northern Karoo Basin provide unprecedented access to the subsurface geometry of dolerite sills and their relationship to underlying basement strata. The data show saucer-shaped sills in the Karoo Supergroup with distinctly funnel-shaped geometries along their base that are seated within basement rocks. The funnel-shaped dolerite structures are interpreted to represent the feeders to the overlying regional-scale sill-saucer complexes. Four distinct saucer geometries can be identified (1) cone-shaped saucers that extend outwards from a single funnel-shaped point (Type A), (2) elongated saucers that dip towards multiple aligned funnel-shaped points (Type B), (3) the more commonly described elongated saucers with flat inner sills (Type C) and (4) elongated saucers with a combination of Type B and C geometries (Type D). Type A and C saucer geometries and point-like contacts are consistent with analogue models of saucers for respective pipe-like and linear feeders. However, the multiple pipe-like feeders associated with Type B and combination thereof with sheet-like feeders (Type D) represent saucer-feeder relationships thus far not modelled. Notably, the lower dolerite funnels are commonly rooted in older faults and/or dykes within the basement rocks. This spatial correlation emphasizes the significance of pre-existing basement structures in the Kalahari craton for the long-range transfer of the magmas through the crust. The distributed occurrence of numerous magma feeders across much of the craton is more consistent with thermal incubation of the sub-lithospheric mantle beneath Gondwana than the impact of a mantle plume.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth-Surface Processes
Authors
André Coetzee, Alexander F.M. Kisters,