A deep seismic reflection profile across the Archean-Proterozoic Witwatersrand basin, South Africa

Durrheim, Raymond; Nicolaysen, L. O.; Corner, B.

doi:10.1029/gd022p0213

Cited by 21 publications

(13 citation statements)

References 28 publications

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“…Published seismic reflection data were used to pregauge the characteristics of the seismic reflections of the various stratigraphic groups across the craton (Durrheim, 1986;Pretorius et al, 1987;1994;Durrheim et al, 1991;Weder, 1994;Stettler et al, 1998a;b). Timedepth conversions were made using published P-wave velocities (Table 4).…”

Section: Methodsmentioning

confidence: 99%

“…These reflectors are more numerous and of higher amplitude along the Rz lines than along the interior and western margin seismic profiles. Alternative origins of such reflectors within the basement are discussed in Blundell and Raynaud (1986), Klemperer et al (1987), Durrheim et al (1991), Corner (1998). In summary the interpreted tectonic history of this area begins with a period of extension, resulting in Ventersdorp extrusion and sediment deposition in discrete, predominately east to west listric-fault-bounded half-grabens.…”

Section: Stratigraphic and Structural Interpretations Of Seismic Linementioning

confidence: 98%

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Seismic Stratigraphic Constraints on Neoarchean - Paleoproterozoic Evolution of the Western Margin of the Kaapvaal Craton, South Africa

Tinker

Wit

Grotzinger

2002

South African Journal of Geology

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The Kaapvaal Craton is partially covered by the supracrustal sequences of remnants of the Witwatersrand, Ventersdorp and Transvaal-correlated Griqualand West Basins that span about 800 million years (~3.0 to 2.2 Ga). This study describes and interprets eight newly available seismic reflection profiles of the Ventersdorp and younger cover sequences, acquired by the vibroseis method to 6 seconds TWT (~ 17km), and totalling ~720km in length. New stratigraphic and structural features are identified across three main regions: the Kaapvaal Craton's western margin, the craton's northern margin, (southwards from the Thabazimbi-Murchison Lineament across the western extremity of the Bushveld Igneous Complex) and the craton's interior.Across the craton's western margin, the volcano-sedimentary succession is shown to thicken towards its edge from 0 km to >17km over 150km. The Ventersdorp Supergroup underlies the Transvaal Sequence right to the western extremity of the craton. Close to the margin, we recognise a normal fault, here named the Moshaweng fault, with >6km normal displacement and an unknown distance of strike-slip displacement. Three prominent unconformities are identified, as well as ~300% tectonic thickening of the Hartley Formation in response to east-verging, Paleoproterozoic (~1.8 Ga) thrusting across the craton. Folding and thrusting of Griqualand West and Olifantshoek Supergroups across the craton are also apparent.A tectonic model for the evolution of the craton's western margin involves the formation of an Atlantic-type margin by extension, volcanism and rifting over ~70 Ma, followed by 160 Myrs of thermal subsidence. Subsequently, Paleoproterozoic (1.7 to 1.9 Ga) compression involved folding and thrusting eastward across the margin.Along the northern margin of the craton, the seismic profiles traverse a syncline which trends east to west over several hundred kilometers and involves mainly Transvaal-aged rocks and sporadic Bushveld outcrop. Evident from these profiles are discrete Ventersdorp half grabens, up to 3km in depth, with bounding listric normal faults that trend east to west, subparallel to the Thabazimbi-Murchison Lineament (TML), and downthrow predominantly to the north. These faults are truncated by the well-imaged Black Reef unconformity.Across the craton interior, horst and graben structures, involving the Witwatersrand and lower Ventersdorp Formations, dominate the seismic profiles. Bounding listric normal faults (one example with minimum throw of 9.5km), trend east to west and northeast to southwest and downthrow to the north, south, northwest and southeast. The Black Reef unconformity is again distinctive, as is a Paleozoic unconformity (the Beaufort unconformity).The orientation of boundary faults of Ventersdorp-aged half-grabens along the craton's margins and interior, south of the TML, suggests a complex process of extension tectonism for ~70 Myrs that overlaps in time with northward thrusting of volcano-sedimentary sequences to the north of the TML. On a regional scale, the data pres...

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Section: Methodsmentioning

confidence: 99%

Section: Stratigraphic and Structural Interpretations Of Seismic Linementioning

confidence: 98%

Seismic Stratigraphic Constraints on Neoarchean - Paleoproterozoic Evolution of the Western Margin of the Kaapvaal Craton, South Africa

Tinker

Wit

Grotzinger

2002

South African Journal of Geology

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“…First, thrusting away from the centre of impact is suggested by previous investigators (Brink et al, 2000, Fletcher and Reimold, 1989, Durrheim et al, 1991 with thrusting evidently more apparent than normal faulting (Brink et al, op. cit., Durrheim et al, op.…”

Section: Size Of Transient Cratermentioning

confidence: 82%

The Roodekraal Complex as a constraint on the size of the Vredefort impact crater, South Africa

Waal

2008

South African Journal of Geology

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The volcanic Roodekraal Complex, situated about 40 km from the proposed center of the ~2.02 Ga Vredefort cratering event, overlies the rocks of the Pretoria Group with an angular unconformity. The unsheared basal contact of the Roodekraal Complex, a succession of alkaline basic lava intruded by diorite sills, defines an ~2.05 Ga palaeosurface and as such constrains the size of the transient Vredefort crater to a maximum of ca. 80 km in diameter. A group of concentric thrust and normal faults with listric characteristics, the Ensel Thrust System, probably represents the expected normal faults that caused collapse of the transient crater rim during the modification stage of the cratering event. A series of semi-concentric thrust faults of the order of 200 km diameter and centered on the point of impact may define the total size of the Vredefort astrobleme (taken to be the entire area of impactinduced deformation). The indicated diameters of the transient and final craters agree well with those suggested by recent numerical models.

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“…In contrast to the other domes that have been produced by poly-phase tectonics, the Vredefort Dome displays both a more pronounced circular geometry and more extreme uptilting of the Late Archean to Paleoproterozoic supracrustal succession. Regional seismic sections (e.g., Durrheim et al 1991) indicate that the base of the supracrustal sequence is raised by more than 10 km between the rim syncline and the dome. It is, however, the unusual deformation and metamorphic phenomena observed in rocks in the dome and its immediate vicinity that point to its origin as the central uplift of a large impact structure.…”

Section: Impact-related Features In the Vredefort Domementioning

confidence: 99%

“…1, 2). Although several workers have attempted to explain the dome in terms of polyphase tectonics or ballooning intrusions (see review in Reimold and Gibson 1996), its geometry and the scale of structural uplift documented by seismic studies (Durrheim et al 1991) cannot be explained by such conventional geological processes, particularly in the light of the regional geological history. Nonetheless, the irregular shape of the core-collar contact in the southeast of the dome (Fig.…”

Section: Recognition Of Deeply Eroded Impact Structures -The Way Forwardmentioning

confidence: 99%

Deeply exhumed impact structures: A case study of the Vredefort structure, South Africa

Gibson

Reimold

Impacts and the Early Earth

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The main evidence in the Vredefort Dome and surrounding parts of the Witwatersrand Basin is presented, which indicates that this terrain represents the deeply exhumed root zone of a large, 2023 _+ 4 Ma, complex impact structure.Shock metamorphic features such as impact melt, shatter cones, high-pressure quartz polymorphs and shock microdeformation features are restricted to the Vredefort Dome, which constitutes the central uplift of the impact structure. High strain rate brittle deformation features, including pseudotachylites and clastic breccias, are found over a larger radial distance of at least 100 km from the center of the structure. Low-temperature (~300 °C) hydrothermal effects occur up to a similar radial distance but, in the central uplift, metamorphic mineral parageneses overprinting the shock and brittle deformation features in pelites indicate a strong radially-inward increase in temperature to between 700 and 900 °C. Pressure estimates of 0.2-0.3 GPa obtained from these mineral parageneses indicate that the Vredefort structure has been eroded by between 7 and 10 kin. The original depth of burial of these rocks after the impact and their elevated temperatures explain the anomalous appearance and restricted distribution of many of the shock features compared to other, less eroded, structures. The metamorphism and hydrothermal activity are attributed to the combined effects of exhumation of deep (hot) crustal levels by the cratering event and formation of the central uplift, and shock heating, possibly with a minor component of heating caused by an overlying impact melt volume. The structural, shock and thermal impact-related features in the Vredefort Dome and Witwatersrand Basin provide a case study that should assist in the identification of other deeply exhumed impact structures. 250 Gibson and Reimold

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A deep seismic reflection profile across the Archean-Proterozoic Witwatersrand basin, South Africa

Cited by 21 publications

References 28 publications

Seismic Stratigraphic Constraints on Neoarchean - Paleoproterozoic Evolution of the Western Margin of the Kaapvaal Craton, South Africa

Seismic Stratigraphic Constraints on Neoarchean - Paleoproterozoic Evolution of the Western Margin of the Kaapvaal Craton, South Africa

The Roodekraal Complex as a constraint on the size of the Vredefort impact crater, South Africa

Deeply exhumed impact structures: A case study of the Vredefort structure, South Africa

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