Folding of the Rustenburg layered suite adjacent to the Steelpoort pericline: implications for syn-Bushveld tectonism in the eastern Bushveld Complex

Clarke, Brendan M.

doi:10.2113/108.3.397

Cited by 24 publications

(13 citation statements)

References 20 publications

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“…We have described how the extent of disruption of the layering varies significantly over short stratigraphic distances (as observed at Dwars River, for example): such behaviour is suggestive of brief episodic events which destabilise the mush [such as might be expected during updoming affecting the Dwars River region (Clarke et al 2005)]. We suggest that the welldefined onset of significant dislocation creep near the base of our traverse through Lower Main Zone marks the start of a more regional deformation event.…”

Section: What Caused the Deformation In The Rustenburg Layered Suite?mentioning

confidence: 65%

“…6. Such highly contorted layering demonstrates that deformation and slumping of fluid-rich mush was episodic, with intervening periods of quiescence, suggestive of earthquake-triggered deformation events (Cawthorn 2015) possibly associated with syn-magmatic diapiric updoming of the underlying country rocks (Clarke et al 2005). …”

Section: Field Observations Of Mush Behaviourmentioning

confidence: 99%

“…Field evidence suggests deformation of the intrusion (on scales of the order of tens of km), including updoming of the underlying country rock, may have been episodic, beginning shortly after emplacement and continuing after the intrusion was fully solidified (e.g. Clarke et al 2005;Letts et al 2009;Maier et al 2013).…”

Section: Geological Settingmentioning

confidence: 99%

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The thickness of the crystal mush on the floor of the Bushveld magma chamber

Holness

Cawthorn

Roberts

2017

Contrib Mineral Petrol

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The thickness of the crystal mush on magma chamber floors can be constrained using the offset between the step-change in the median value of dihedral angles formed at the junctions between two grains of plagioclase and a grain of another phase (typically clinopyroxene, but also orthopyroxene and olivine) and the first appearance or disappearance of the liquidus phase associated with the step-change in median dihedral angle. We determined the mush thickness in the Rustenburg Layered Suite of the Bushveld Complex at clinopyroxene-in (in Lower Main Zone) and magnetite-in (in Upper Zone). We also examined an intermittent appearance of cumulus apatite in Upper Zone, using both the appearance and disappearance of cumulus apatite. In all cases, the mush thickness does not exceed 4 m. These values are consistent with field observations of a mechanically rigid mush at the bases of both magnetitite and chromitite layers overlying anorthosite. Mush thickness of the order of a few metres suggests that neither gravitationally-driven compaction nor compositional convection within the mush layer is likely to have been important processes during solidification: adcumulates in the Bushveld are most likely to have formed at the top of the mush during primary crystallisation. Similarly, it is unlikely either that migration of reactive liquids occurs through large stretches of stratigraphy, or that layering is formed by mechanisms other than primary accumulation.

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Section: What Caused the Deformation In The Rustenburg Layered Suite?mentioning

confidence: 65%

Section: Field Observations Of Mush Behaviourmentioning

confidence: 99%

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The thickness of the crystal mush on the floor of the Bushveld magma chamber

Holness

Cawthorn

Roberts

2017

Contrib Mineral Petrol

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“…The presence of these easily and preferentially weathered ultramafic rocks is also responsible for the accentuation in the appearance of the Burgersfort Bulge, an apparent downward transgression of the RLS into the Pretoria Group floor. Recent examination of the "Bulge" (Clarke et al, 2005) indicates that, rather than being a downward transgression of the RLS, it represents a deep trough of RLS rocks that ponded between two upwarps of the metasedimentary floor, the Steelpoort and Derde Gelid periclines. These two structures originated as interfinger deformation zones between intruding Lower Zone magma fingers (Uken and Watkeys, 1997;Clarke et al, 2005).…”

Section: Regional Geological Setting and Previous Investigationsmentioning

confidence: 99%

“…Recent examination of the "Bulge" (Clarke et al, 2005) indicates that, rather than being a downward transgression of the RLS, it represents a deep trough of RLS rocks that ponded between two upwarps of the metasedimentary floor, the Steelpoort and Derde Gelid periclines. These two structures originated as interfinger deformation zones between intruding Lower Zone magma fingers (Uken and Watkeys, 1997;Clarke et al, 2005). Regardless of the true origin of the "Bulge", the ADP results in a prominent eastward shift of the outcrop position of the Pretoria Group-RLS contact (cf.…”

Section: Regional Geological Setting and Previous Investigationsmentioning

confidence: 99%

The Geometry and Emplacement Mechanics of a Bushveld Complex Peridotite Body, South Africa

Clarke

Uken

Reinhardt

2009

South African Journal of Geology

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The Apiesdooringdraai peridotite is a syn-Bushveld Complex, dominantly harzburgitic intrusion of Lower Zone parentage. Detailed mapping and three-dimensional modeling shows the intrusion to comprise several discordant segments linked by concordant, silllike segments. Deformation in the contact aureole is strongly partitioned adjacent to the discordant segments of the intrusion and is detectable at distances from the contact on the order of the intrusion width. In contrast, areas above and below the intrusion, and at greater distances from the discordant intrusive segments, are effectively undeformed. The geometry of structural features suggests that the peridotite is a variably structurally-evolved stepped-sill system that was emplaced as kilometre-scale magma fingers from the northwest to the southeast, a trend heavily utilised by the mafic-ultramafic magmas of the Bushveld Complex. Deformation in the country rock was affected by the lateral expansion of the magma fingers at high postulated strain rates, and linkage of offset fingers formed prominent steps in the intrusion. Emplacement-related country rock deformation is postdated by a shallow dipping foliation that records compaction and crustal loading during contact metamorphism. Figure 5. Simplified geological map of the Burgersfort-Steelpoort area, showing the transgressive nature of the ADP with respect to its country-rock stratigraphy.

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The geology and structure of the Rustenburg Layered Suite in the Potgietersrus/Mokopane area of the Bushveld Complex, South Africa

Merwe¹

2007

Miner Deposita

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Folding of the Rustenburg layered suite adjacent to the Steelpoort pericline: implications for syn-Bushveld tectonism in the eastern Bushveld Complex

Cited by 24 publications

References 20 publications

The thickness of the crystal mush on the floor of the Bushveld magma chamber

The thickness of the crystal mush on the floor of the Bushveld magma chamber

The Geometry and Emplacement Mechanics of a Bushveld Complex Peridotite Body, South Africa

The geology and structure of the Rustenburg Layered Suite in the Potgietersrus/Mokopane area of the Bushveld Complex, South Africa

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