Crustal Evolution of Southern Africa

Tankard, A. J.; Jackson, Marion; Eriksson, Kenneth A.; Hobday, D. K.; Hunter, D.R.; Minter, W. E. L.

doi:10.1007/978-1-4613-8147-1

Cited by 250 publications

(77 citation statements)

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“…An angular unconformity is also reported between the lower Witwatersrand and the overlying Ventersdorp Supergroup, in the west of the basin (Tankard et al, 1982;Winter, 1987). However, the Ventersdorp Supergroup may rest conformably on the Witwatersrand in the Central Rand (Linton et al, 1990), East Rand, the Heidelberg area (Nel and Jansen, 1958), and the Orange Free State Goldfield (Coetzee, 1960).…”

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confidence: 83%

The volcano-sedimentary succession of the Archean Sodium Group, Ventersdorp Supergroup, South Africa: Volcanology, sedimentology and geochemistry

Altermann

Lenhardt

2012

Precambrian Research

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Section: Insert Figure 1 Herementioning

confidence: 83%

The volcano-sedimentary succession of the Archean Sodium Group, Ventersdorp Supergroup, South Africa: Volcanology, sedimentology and geochemistry

Altermann

Lenhardt

2012

Precambrian Research

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“…2). The Prince Albert Formation was deposited as syn-to post-glacial suspension fall-out and flocculation of fines from large inflows of sedimentladen water (Domack, 1983;Smith and Ashley, 1985), with some input by periodic turbidites and mud flows of semi-consolidated sediments (Tankard et al, 1982;Visser, 1991).…”

Section: Geological Settingmentioning

confidence: 99%

Depositional environments of the lower Permian Dwyka diamictite and Prince Albert shale inferred from the geochemistry of early diagenetic concretions, southwest Karoo Basin, South Africa

Herbert

Compton

2007

Sedimentary Geology

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The upper Dwyka and lower Ecca Groups in the Karoo Basin of South Africa document the climatic and palaeoenvironmental changes associated with the final Permo-Carboniferous deglaciation of the Gondwana supercontinent. The depositional environments of these groups have, until recently, been interpreted on the basis of sedimentological and palaeontological evidence. Here we use the geochemistry of early diagenetic concretions -septarian calcite concretions from the upper Dwyka Group and phosphatic chert concretions and beds from the lower Ecca Group -to infer the depositional environment of these rocks in the southwestern Karoo Basin. δ 18 O values (7.8 to 8.9‰ SMOW) suggest that the calcite concretions precipitated from a mixture of meteoric and glacial melt waters rather than Permian seawater. δ 13 C values (−15 to − 3‰ PDB) indicate that the carbon was derived from a mixture of craton-derived calcareous material and organic matter, bacterially degraded in the lower sulphatereduction to upper methanogenesis zones during early burial diagenesis. The rare-earth element (REE) patterns, Sr concentrations and 87 Sr/ 86 Sr ratios (0.716-0.737) significantly greater than Permian seawater (0.708), together also support the interpretation that calcite and phosphatic concretions formed in glacial, fresh water sediments.

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“…It contains a highly metamorphosed volcano-sedimentary sequence arranged in approximately east-west trending belts in'a terrain dominated by granitic gneisses (Tankard, Jackson, Eriksson, Hobday, Hunter & Minter, 1982). Highgrade metamorphism in western Namaqualand, at about 1150 Ma, produced a symmetrical metamorphic zonation (Fig.…”

Section: Regional Settingmentioning

confidence: 99%

Partial melting and the formation of granulite facies assemblages in Namaqualand, South Africa

Waters

1988

Journal Metamorphic Geology

227

124

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Abstract. Dehydration-melting reactions, in which water from a hydrous phase enters the melt, leaving an anhydrous solid assemblage, are the dominant mechanism of partial melting of high-grade rocks in the absence of externally derived vapour. Equilibria involving melt and solid phases are effective buffers of uHzO. The element-partitioning observed in natural rocks suggests that dehydration melting occurs over a temperature interval during which, for most cases, aHZO is driven to lower values. The mass balance of dehydration melting in typical biotite gneiss and metapelite shows that the proportion of melt in the product assemblage at T s 850°C is relatively small (10-20%), and probably insufficient to mobilize a partially melted rock body.Granulite facies metapelite, biotite gneiss and metabasic gneiss in Namaqualand contain coarse-grained, discordant, unfoliated, anhydrous segregations, surrounded by a finer grained, foliated matrix that commonly includes hydrous minerals. The segregations have modes consistent with the hypothesis that they are the solid and liquid products of the dehydration-melting reactions: Bt + Sil + Qtz + PI = Grt ? Crd + Kfs + L (metapelite), Bt + Qtz + P1 = Opx + Kfs + L (biotite gneiss), and Hbl + Qtz = Opx + Cpx + PI + L (metabasic gneiss). The size, shape, distribution and modes of segregations suggest only limited migration and extraction of melt. Growth of anhydrous poikiloblasts in matrix regions, development of anhydrous haloes around segregations and formation of dehydrated margins on metabasic layers enclosed in migmatitic metapelites all imply local gradients in water activity. Also, they suggest that individual segregations and bodies of partially melted rock acted as sinks for soluble volatiles. The preservation of anhydrous assemblages and the restricted distribution of late hydrous minerals suggest that retrograde reaction between hydrous melt and solids did not occur and that This model, combined with the natural observations, suggests that it is possible to form granulite facies assemblages without participation of external fluid and without major extraction of silicate melt.

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Crustal Evolution of Southern Africa

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Cited by 250 publications

References 0 publications

The volcano-sedimentary succession of the Archean Sodium Group, Ventersdorp Supergroup, South Africa: Volcanology, sedimentology and geochemistry

The volcano-sedimentary succession of the Archean Sodium Group, Ventersdorp Supergroup, South Africa: Volcanology, sedimentology and geochemistry

Depositional environments of the lower Permian Dwyka diamictite and Prince Albert shale inferred from the geochemistry of early diagenetic concretions, southwest Karoo Basin, South Africa

Partial melting and the formation of granulite facies assemblages in Namaqualand, South Africa

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