Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms
| dc.contributor.author | Basson, I | |
| dc.contributor.author | Viola, G | |
| dc.date.accessioned | 2016-07-21T14:13:33Z | |
| dc.date.available | 2016-07-21T14:13:33Z | |
| dc.date.issued | 2003 | |
| dc.date.updated | 2015-12-18T15:03:38Z | |
| dc.description.abstract | Group II kimberlite dykes occur in small, dominantly en-echelon dyke- fracture arrays, with individual dyke-fractures showing small angular variations from their array trends (5° to 15°). The analysed dyke systems are characterized by closely matching opposing dyke contacts, "in-situ" breccia, multiple kimberlite stringers within a dilated dyke-parallel fracture cleavage, wedge-shaped apophyses in bent bridges at dyke- fracture offsets/overlaps, kimberlite-free offset/overlap areas and calcite vein fibres orthogonal to dyke contacts. Commonly found microscopic structures include syn-emplacement/syn-crystallization calcite veinlets, containing high aspect ratio stretched fibrous calcite, and elongate phlogopite phenocrysts and serpentinized olivine phenocrysts growing across the width of these veins. Both macro- and microscopic structures support a model of orthogonal host rock dilation during kimberlite emplacement. Terminations of dyke-fracture segments show minimal curvature or overlap, suggesting that remote horizontal stresses dominated during their emplacement ("passive" intrusion), as opposed to magma overpressured systems wherein dyke or dyke-fracture overlaps curve strongly towards each other ("active" intrusion). The application of Mohr diagrams suggests that low differential stresses, with no or only a very minor shear component, prevailed at the time of emplacement. The dominance of remote horizontal forces, imparting small differential stresses to the brittle portions of the crust, a closely-spaced, dilating dyke-parallel fracture cleavage ahead of the dyke tip (imparting a local suction) and the low-volume, low-viscosity, highly volatile nature of kimberlitic magmas may explain their empirically-constrained high emplacement velocities. This, in turn, explains the means by which such magmas may entrain significant volumes of high specific-gravity mantle material. Mobile hydrofracturing in the fringe zones around dilated... [ABSTRACT FROM AUTHOR] | |
| dc.identifier.apacitation | Basson, I., & Viola, G. (2003). Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms. <i>South African Journal of Geology</i>, http://hdl.handle.net/11427/20588 | en_ZA |
| dc.identifier.chicagocitation | Basson, I, and G Viola "Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms." <i>South African Journal of Geology</i> (2003) http://hdl.handle.net/11427/20588 | en_ZA |
| dc.identifier.citation | Basson, I. J., & Viola, G. (2003). Structural overview of selected group II kimberlite dyke arrays in south africa: Implications for kimberlite emplacement mechanisms. South African Journal of Geology, 106(4), 375-394. Retrieved from http://search.ebscohost.com/login.aspx?direct=true&db=aph&AN=13157171&site=ehost-live | |
| dc.identifier.issn | 1012-0750 | |
| dc.identifier.ris | TY - Journal Article AU - Basson, I AU - Viola, G AB - Group II kimberlite dykes occur in small, dominantly en-echelon dyke- fracture arrays, with individual dyke-fractures showing small angular variations from their array trends (5° to 15°). The analysed dyke systems are characterized by closely matching opposing dyke contacts, "in-situ" breccia, multiple kimberlite stringers within a dilated dyke-parallel fracture cleavage, wedge-shaped apophyses in bent bridges at dyke- fracture offsets/overlaps, kimberlite-free offset/overlap areas and calcite vein fibres orthogonal to dyke contacts. Commonly found microscopic structures include syn-emplacement/syn-crystallization calcite veinlets, containing high aspect ratio stretched fibrous calcite, and elongate phlogopite phenocrysts and serpentinized olivine phenocrysts growing across the width of these veins. Both macro- and microscopic structures support a model of orthogonal host rock dilation during kimberlite emplacement. Terminations of dyke-fracture segments show minimal curvature or overlap, suggesting that remote horizontal stresses dominated during their emplacement ("passive" intrusion), as opposed to magma overpressured systems wherein dyke or dyke-fracture overlaps curve strongly towards each other ("active" intrusion). The application of Mohr diagrams suggests that low differential stresses, with no or only a very minor shear component, prevailed at the time of emplacement. The dominance of remote horizontal forces, imparting small differential stresses to the brittle portions of the crust, a closely-spaced, dilating dyke-parallel fracture cleavage ahead of the dyke tip (imparting a local suction) and the low-volume, low-viscosity, highly volatile nature of kimberlitic magmas may explain their empirically-constrained high emplacement velocities. This, in turn, explains the means by which such magmas may entrain significant volumes of high specific-gravity mantle material. Mobile hydrofracturing in the fringe zones around dilated... [ABSTRACT FROM AUTHOR] DA - 2003 DB - OpenUCT DP - University of Cape Town J1 - South African Journal of Geology LK - https://open.uct.ac.za PB - University of Cape Town PY - 2003 SM - 1012-0750 T1 - Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms TI - Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms UR - http://hdl.handle.net/11427/20588 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/20588 | |
| dc.identifier.vancouvercitation | Basson I, Viola G. Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms. South African Journal of Geology. 2003; http://hdl.handle.net/11427/20588. | en_ZA |
| dc.language.iso | eng | |
| dc.publisher | Geological Society of South Africa | |
| dc.publisher.department | Department of Geological Sciences | en_ZA |
| dc.publisher.faculty | Faculty of Science | en_ZA |
| dc.publisher.institution | University of Cape Town | |
| dc.source | South African Journal of Geology | |
| dc.source | http://sajg.geoscienceworld.org/ | |
| dc.source.uri | http://sajg.geoscienceworld.org/ | |
| dc.title | Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms | |
| dc.type | Journal Article | en_ZA |
| uct.type.filetype | Text | |
| uct.type.filetype | Image | |
| uct.type.publication | Research | en_ZA |
| uct.type.resource | Article | en_ZA |