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Distribution of the Transvaal Supergroup within three basins (Transvaal, Griqualand West and Kanye—see inset map), as well as of the carbonate rocks of the Chuniespoort Group and Campbellrand Subgroup. Note Vryburg rise palaeohigh between Transvaal and Griqualand West basins (inset), and two sub-basins of carbonate deposition (Prieska and Ghaap ''facies'') in the latter basin. Modified after Eriksson and Altermann (1998).
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The 2714–2709 Ma Ventersdorp Supergroup overlies Mesoarchaean basement rocks and sedimentary strata of the Neoarchaean Witwatersrand Supergroup. The latter basin was inverted by tectonic shortening and suffered the loss of up to 1.5 km of stratigraphy prior to deposition of the Ventersdorp volcanics. Thermal uplift and fluvial incision prior to the...
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... Ventersdorp Supergroup comprises a 5100 m thick succession of subaerial volcanic rocks, including up to 2900 m of sedimentary units identified in borehole sections. This supergroup occupies an area greater than 300 000 km 2 within the central part of the Kaapvaal craton ( Fig. 1) (Pretorius, 1976;Winter, 1976). A minimum eruptive volume of 0.66Â10 6 km 3 is indicated from these dimensions, which falls within the definition of a superplume (Condie, 2001b) adopted in this paper. However, preserved outcrops fall well short of a plume head diameter in excess of 1500 km assumed for the same definition. White (1997) ...
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... Kaapvaal craton preceded Klipriviersberg volcanism (e.g., Hatton, (1998). Also shown is the preserved Witwatersrand basin, above which the bulk of the Klipriviersberg Group occurs. 1995a; White, 1997) must perhaps be questioned. Thrusting related to shortening of the Witwa- tersrand basin-fill is pre-Klipriviersberg in age in the Klerksdorp (Fig. 1) region, and towards the southeast, late-stage Witwatersrand inversion deformed lower Klipriviersberg lavas (Coward et al., 1995). Although underplating generally significantly reduces post-rift thermal subsidence above a mantle upwelling (White and McKenzie, 1989), it would appear that a tectonically shortened and therefore thickened ...
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... 1980;Grobler et al., 1989); proximal talus scree, debris-flow deposits and alluvial fans developed at graben margins, and passed into central fine-clastic and chemical lacustrine sediments (Buck, 1980), locally exhibiting ooids and stromatolites (van der Westhuizen et al., 1991). In the T'Kuip area in the southwest of the Ventersdorp basin ( Fig. 1), a half-graben geo- metry is preserved for Kameeldoorns clastic sediments, which encompass basal immature boulder beds with granitic megaclasts up to 140 cm diameter ( Grobler et al., 1989). Upwards in the suc- cession at T'Kuip, boulder dimensions decrease and tuffaceous beds associated with immature clastic material (upward-fining ...
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... to remote localities, such as the T'Kuip hills. The sedimentary interbeds include tuffaceous siltstones, arkosic sandstones, gritstones and stromato- litic cherty limestones ( Grobler et al., 1989;van der Westhuizen et al., 1991). Intercalated sedi- mentary layers at T'Kuip indicate continuous tectonic activity during volcanism. At T'Kuip ( Fig. 1), as well as in the northwest of the basin, shallow lakes developed by subsidence as a result of thermal relaxation after the major volcanic events. Karpeta (1989) described bedded cherts overlying tholeiitic flows in the northwest of the Ventersdorp basin which he ascribed to magadiitic alkaline playa lacustrine ...
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... thickness differences and the large spectrum of variable sedimentary and volcanic lithofacies found within the Platberg Group and discussed briefly above, there is a broad regional correlation of the major subdivisions of the group over a large area, including outliers separated from the main Ventersdorp preservational basin, such as at T'Kuip ( Fig. 1). This sug- gests that the control on Platberg grabens was regional and perhaps related to a plume, with periods characterised by eruptive rocks, with interbedded sedimentary units, both thick and thin, reflecting hiatuses in effusive events of large lateral extent. Rift propagation may have been enhanced by adiabatic decompression ...
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... et al., 1984;Henry et al., 1988;Green and Fitz, 1993), as illustrated by the Ventersdorp example displaying a preserved extent and geometry reminiscent of pyroclastic flows, with local lava flows (Meintjies, 1998;van der Westhuizen and de Bruiyn, 2000). The latter authors propose an ignimbritic origin, based on detailed studies at T'Kuip ( Fig. 1) where the presence of lithic fragments and definite flow features have been recorded. Minor thin arkose and tuff interbeds in the Makwassie indicate that volcanism was largely continuous, with few and short hiatuses between eruptive events. The essentially rhyolitic composition of the Makwassie lithologies may be ascribed to the ...
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... Reef lithologies are known from two of the ''fragments'' of Transvaal rocks found within the c. 2053 Ma Bushveld Complex (which intruded into the central part of the Transvaal basin; e.g., Eriksson and Reczko, 1995), where the Wachteenbeetje For- mation in the Crocodile River fragment and the Bloempoort Group in the Dennilton fragment are defined (Fig. 5) (Hartzer, ...
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... Fortescue Group consists of a $7 km thick subaerial sequence of basalts, subordinate komatiitic basalts and felsic volcanic and clastic sedimentary rocks (Fig. 9) that unconformably overlie the southern part of the Pilbara Craton of Western Australia (Fig. 10). The volcanic rocks are essentially bimodal, with predominant tholeiitic basalts and andesites, and minor felsic com- positions (Blake and Groves, 1987). A basal unconformity lies upon a locally rugged palaeoto- pography characterised by relief up to about 500 m (Blake, 1993). Scattered remnants of the lower formation of the Fortescue ...
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... c. 2.4 km thick Hamersley Group conformably overlies the Fortescue Group (Fig. 10), and comprises shales, banded iron formations, volcanic and carbonate rocks (Fig. 11), laid down over an area estimated to have been about 10 5 km 2 . Tuff beds have enabled precise dating of a number of the units, indicating that sedimentation occurred between >2597 and 2449 Ma ( Nelson et al., 1999). There is a general similarity in ...
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... c. 2.4 km thick Hamersley Group conformably overlies the Fortescue Group (Fig. 10), and comprises shales, banded iron formations, volcanic and carbonate rocks (Fig. 11), laid down over an area estimated to have been about 10 5 km 2 . Tuff beds have enabled precise dating of a number of the units, indicating that sedimentation occurred between >2597 and 2449 Ma ( Nelson et al., 1999). There is a general similarity in the lithologies and lithostratigraphy of the Hamerlsey and Chuniespoort-Ghaap Groups ...
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... can be seen from the preceding sections on the Ventersdorp Supergroup (Kaapvaal) and Fortescue Group (Pilbara), and bearing in mind recent geochronological data given above and Fig. 11. Lithostratigraphy of the Hamersley Group (modified after Simonson et al., 1993). discussed further below, there is a great deal of similarity in lithostratigraphy and inferred geological evolution of the two Neoarchaean flood basaltic provinces. Nelson et al. (1992) discuss this comparison in detail, emphasising analogous geochemical ...
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... Ventersdorp Supergroup comprises a 5100 m thick succession of subaerial volcanic rocks, including up to 2900 m of sedimentary units identified in borehole sections. This supergroup occupies an area greater than 300 000 km 2 within the central part of the Kaapvaal craton ( Fig. 1) (Pretorius, 1976;Winter, 1976). A minimum eruptive volume of 0.66Â10 6 km 3 is indicated from these dimensions, which falls within the definition of a superplume (Condie, 2001b) adopted in this paper. However, preserved outcrops fall well short of a plume head diameter in excess of 1500 km assumed for the same definition. White (1997) ...
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... Kaapvaal craton preceded Klipriviersberg volcanism (e.g., Hatton, (1998). Also shown is the preserved Witwatersrand basin, above which the bulk of the Klipriviersberg Group occurs. 1995a; White, 1997) must perhaps be questioned. Thrusting related to shortening of the Witwa- tersrand basin-fill is pre-Klipriviersberg in age in the Klerksdorp (Fig. 1) region, and towards the southeast, late-stage Witwatersrand inversion deformed lower Klipriviersberg lavas (Coward et al., 1995). Although underplating generally significantly reduces post-rift thermal subsidence above a mantle upwelling (White and McKenzie, 1989), it would appear that a tectonically shortened and therefore thickened ...
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... 1980;Grobler et al., 1989); proximal talus scree, debris-flow deposits and alluvial fans developed at graben margins, and passed into central fine-clastic and chemical lacustrine sediments (Buck, 1980), locally exhibiting ooids and stromatolites (van der Westhuizen et al., 1991). In the T'Kuip area in the southwest of the Ventersdorp basin ( Fig. 1), a half-graben geo- metry is preserved for Kameeldoorns clastic sediments, which encompass basal immature boulder beds with granitic megaclasts up to 140 cm diameter ( Grobler et al., 1989). Upwards in the suc- cession at T'Kuip, boulder dimensions decrease and tuffaceous beds associated with immature clastic material (upward-fining ...
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... to remote localities, such as the T'Kuip hills. The sedimentary interbeds include tuffaceous siltstones, arkosic sandstones, gritstones and stromato- litic cherty limestones ( Grobler et al., 1989;van der Westhuizen et al., 1991). Intercalated sedi- mentary layers at T'Kuip indicate continuous tectonic activity during volcanism. At T'Kuip ( Fig. 1), as well as in the northwest of the basin, shallow lakes developed by subsidence as a result of thermal relaxation after the major volcanic events. Karpeta (1989) described bedded cherts overlying tholeiitic flows in the northwest of the Ventersdorp basin which he ascribed to magadiitic alkaline playa lacustrine ...
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... thickness differences and the large spectrum of variable sedimentary and volcanic lithofacies found within the Platberg Group and discussed briefly above, there is a broad regional correlation of the major subdivisions of the group over a large area, including outliers separated from the main Ventersdorp preservational basin, such as at T'Kuip ( Fig. 1). This sug- gests that the control on Platberg grabens was regional and perhaps related to a plume, with periods characterised by eruptive rocks, with interbedded sedimentary units, both thick and thin, reflecting hiatuses in effusive events of large lateral extent. Rift propagation may have been enhanced by adiabatic decompression ...
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... et al., 1984;Henry et al., 1988;Green and Fitz, 1993), as illustrated by the Ventersdorp example displaying a preserved extent and geometry reminiscent of pyroclastic flows, with local lava flows (Meintjies, 1998;van der Westhuizen and de Bruiyn, 2000). The latter authors propose an ignimbritic origin, based on detailed studies at T'Kuip ( Fig. 1) where the presence of lithic fragments and definite flow features have been recorded. Minor thin arkose and tuff interbeds in the Makwassie indicate that volcanism was largely continuous, with few and short hiatuses between eruptive events. The essentially rhyolitic composition of the Makwassie lithologies may be ascribed to the ...
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... Reef lithologies are known from two of the ''fragments'' of Transvaal rocks found within the c. 2053 Ma Bushveld Complex (which intruded into the central part of the Transvaal basin; e.g., Eriksson and Reczko, 1995), where the Wachteenbeetje For- mation in the Crocodile River fragment and the Bloempoort Group in the Dennilton fragment are defined (Fig. 5) (Hartzer, ...
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... Fortescue Group consists of a $7 km thick subaerial sequence of basalts, subordinate komatiitic basalts and felsic volcanic and clastic sedimentary rocks (Fig. 9) that unconformably overlie the southern part of the Pilbara Craton of Western Australia (Fig. 10). The volcanic rocks are essentially bimodal, with predominant tholeiitic basalts and andesites, and minor felsic com- positions (Blake and Groves, 1987). A basal unconformity lies upon a locally rugged palaeoto- pography characterised by relief up to about 500 m (Blake, 1993). Scattered remnants of the lower formation of the Fortescue ...
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... c. 2.4 km thick Hamersley Group conformably overlies the Fortescue Group (Fig. 10), and comprises shales, banded iron formations, volcanic and carbonate rocks (Fig. 11), laid down over an area estimated to have been about 10 5 km 2 . Tuff beds have enabled precise dating of a number of the units, indicating that sedimentation occurred between >2597 and 2449 Ma ( Nelson et al., 1999). There is a general similarity in ...
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... c. 2.4 km thick Hamersley Group conformably overlies the Fortescue Group (Fig. 10), and comprises shales, banded iron formations, volcanic and carbonate rocks (Fig. 11), laid down over an area estimated to have been about 10 5 km 2 . Tuff beds have enabled precise dating of a number of the units, indicating that sedimentation occurred between >2597 and 2449 Ma ( Nelson et al., 1999). There is a general similarity in the lithologies and lithostratigraphy of the Hamerlsey and Chuniespoort-Ghaap Groups ...
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... can be seen from the preceding sections on the Ventersdorp Supergroup (Kaapvaal) and Fortescue Group (Pilbara), and bearing in mind recent geochronological data given above and Fig. 11. Lithostratigraphy of the Hamersley Group (modified after Simonson et al., 1993). discussed further below, there is a great deal of similarity in lithostratigraphy and inferred geological evolution of the two Neoarchaean flood basaltic provinces. Nelson et al. (1992) discuss this comparison in detail, emphasising analogous geochemical ...
Citations
... These local occurrences of high freeboard at 2.8-2.7 Ga and ca. 2.5 Ga have been suggested to reflect mantle plume-related uplift (Eriksson et al., 2002;Eriksson et al., 2005) or the onset of continental emergence (due to changes in crustal thickness and/or density) at different times on different cratons (Campbell & Davies, 2017;Chowdhury et al., 2021). The first re- ...
Geologic observations and numerical models imply that Archean continents were mostly submarine. In contrast, approximately one‐third of modern Earth’s surface area consists of subaerial continental crust. To temporally constrain changes in the subaerial exposure of continents, we evaluate the eruptive environment (submarine vs subaerial) of 3.4‐2.0 Ga continental large igneous provinces (LIPs). Our results indicate that up until 2.4 Ga LIPs predominantly erupted onto submerged continents. This period of low freeboard was punctuated by local subaerial eruptions at 2.8‐2.7 Ga and 2.5 Ga. From 2.4 Ga‐2.2 Ga, extensive subaerial continental volcanism is recorded in six different cratons, supporting widespread subaerial continents at this time. An increase in exposed continental crust significantly impacts atmospheric and oceanic geochemical cycles, and the supply of nutrients for marine bioproductivity. Thus, the 2.4‐2.2 Ga high freeboard conditions may have triggered the earliest global glaciation event and the first significant rise of atmospheric oxygen.
... These include mantle plume-related upwelling and decompression, asthenospheric shear-driven upwelling, decompression melting due to continental extension and attendant lithospheric thinning (especially during continental rifting), decompression melting associated with convective instabilities in the upper mantle caused by lithospheric delamination or initial difference in lithosphere thickness Mckenzie, 1989, 1995;Silver et al., 2006;Conrad et al., 2011;Ernst, 2014;Hole, 2015). Besides, intracontinental mafic magmatism may be closely related to crustal extension and sedimentary basin formation (Zhao et al., 1994;Eriksson et al., 2002;Klocking et al., 2018). ...
The origin of continental intraplate basalts, their role in crust-mantle interaction, and processes of formation of the associated sedimentary rocks have remained important research problems. The poorly-studied Simlipal basin hosts a well-preserved, weakly-metamorphosed ensemble of three bands of mafic volcanic rocks intercalated with shallow marine sandstones and minor phyllites, occurring unconformably over a Paleoarchean continental basement of the Singhbhum Craton. Little is known about the age of the basin, the nature of sediment source and source weathering, petrogenesis of the volcanic rocks, and the tectonic setting of the volcano-sedimentary assemblage. To address these issues, we present whole-rock geochemical data on the Simlipal sediments and volcanic rocks, detrital zircon U-Pb ages and mineral chemical analyses. The sandstones and phyllites are characterized by high K2O/Na2O and chemical index of alteration. The source-indicating elemental ratios and REE patterns (negative Eu anomaly and flat HREE) suggest that felsic rocks, especially the granitoids resulting from shallow crustal melting, were the dominant source. The detrital zircons are mostly rounded with U-Pb ages ranging from 3.63 to 3.17 Ga. All these features suggest that the Simlipal basin formed during the Mesoarchean Era on a slowly subsiding continental platform undergoing extension, which received reworked and recycled sediments from a diverse but granitoid-dominated, intensely-weathered, mostly Paleoarchean source. The mafic volcanic rocks are low-Ti, tholeiitic basalts showing low CaO/Al2O3 and TiO2/Yb values, and flat HREE pattern indicating derivation from a spinel lherzolite mantle at shallow depth (<80 km). The presence of xenoliths of crustal rocks, quartz-normative nature, wide range of magnesium number (39–80), primitive mantle-normalized negative Nb, Ta and Ti anomalies, and high U/Nb and Th/Yb ratios reflect that the magma underwent significant fractional crystallization and crustal assimilation. The Simlipal volcanic rocks are consanguineous with the spatially close and coeval gabbro-anorthosite bodies, layered mafic–ultramafic rocks, and A-type Mayurbhanj Granite of the Singhbhum Craton, together forming an intraplate bimodal volcanic-plutonic association. We construe that the widespread Mesoarchean magmatism and sedimentation was linked to mantle upwelling possibly related to an event of lithospheric delamination and crustal extension.
... Armstrong et al. (1991) reported 2714 ± 16 Ma and 2709 ± 8 Ma ages (Table 1) for the lower (Klipriviersberg Group) and middle (Makwassie Formation of the Platberg Group) part of the Ventersdorp Supergroup, respectively, making the whole volcanic province a single, but pulsed LIP, ∼10 m.y. long, connected with a mantle plume (e.g., Eriksson et al., 2002). However, several authors have argued for a longer and older period of formation between ca. ...
U-Pb geochronology on baddeleyite is a powerful technique that can be applied effectively to chronostratigraphy. In southern Africa, the Kaapvaal Craton hosts a well-preserved Mesoarchean to Paleoproterozoic geological record, including the Neoarchean Ventersdorp Supergroup. It overlies the Wit-watersrand Supergroup and its world-class gold deposits. The Ventersdorp Supergroup comprises the Klipriviersberg Group, Plat-berg Group, and Pniel Group. However, the exact timing of formation of the Ventersdorp Supergroup is controversial. Here we present 2789 ± 4 Ma and 2787 ± 2 Ma U-Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS) baddeleyite ages and geochemistry on mafic sills intruding the Witwatersrand Su-pergroup, and we interpret these sills as feeders to the overlying Klipriviersberg Group flood basalts. This constrains the age of the Witwatersrand Supergroup and gold miner-alization to at least ca. 2.79 Ga. We also report 2729 ± 5 Ma and 2724 ± 7 Ma U-Pb ID-TIMS baddeleyite ages and geochemistry from a mafic sill intruding the Pongola Supergroup and on an east-northeast-trending mafic dike, respectively. These new ages distinguish two of the Ventersdorp Supergroup magmatic events: the Klipriviersberg and Platberg. The Ventersdorp Supergroup can now be shown to initiate and terminate with two large ig-neous provinces (LIPs), the Klipriviersberg and Allanridge, which are separated by Plat-berg volcanism and sedimentation. The age of the Klipriviersberg LIP is 2791-2779 Ma, and Platberg volcanism occurred at 2754-2709 Ma. The Allanridge LIP occurred between 2709-2683 Ma. Klipriviersberg, Plat-berg, and Allanridge magmatism may be genetically related to mantle plume(s). Higher heat flow and crustal melting resulted as a mantle plume impinged below the Kaapvaal Craton lithosphere, and this was associated with rifting and the formation of LIPs.
... But the dichotomy of ages north and south of the retrograde isograd needs explanation. From a Pilbara correlation perspective, a possibility that can be tested by future studies is that the two groups of ages are related to the two episodes of Fortescue flood basalt volcanism at c. 2765 and 2715 Ma in the Pilbara Craton (e.g., Eriksson et al., 2002), leaving behind fragments (the Southern Marginal Zone) that was thrusted onto the lowgrade Pietersburg block of the Kaapvaal Craton. Finally, it should be pointed out that the different age ranges highlighted in this study from the Southern Marginal Zone (see Table 1) have equivalents in the detrital zircon U-Pb age spectra from the Paleoproterozoic Waterberg Group sediments (~3.37-3.28 ...
High-grade terranes along Archean cratonic margins either represent remobilized equivalents of the adjacent low-grade domain or an exotic entity which accreted to the developing craton. This study addresses this debate for the Southern Marginal Zone high-grade terrane along the northeastern margin of the Kaapvaal Craton. The Hout River shear zone separates the high-grade terrane from the adjacent low-grade Pietersburg block of the Kaapvaal Craton. Tonalite-trondhjemites of the Baviaanskloof gneiss unit constitute the dominant rock in the Southern Marginal Zone. Both pyroxene-bearing and pyroxene-absent variants occur. Locally, the granitoids are affected by anatectic and metasomatic overprints. Magmatic textures are better preserved in the massive granitoids. U-Pb zircon analyses of two orthopyroxene-bearing granitoids gave Mesoarchean crystallization ages [3088 ± 11 Ma (massive), 3121 ± 9 Ma (banded)]. However, overprint ages differ, with 2706 + 50/−34 Ma from the massive variety, and 1925 ± 19 Ma, 1976 ± 11 Ma from the banded variety. The syn-tectonic ~2.71 Ga is interpreted as metamorphic overprint age, while the post-tectonic ~2 Ga represent age of local overprint. Available geochemical data on the Baviaanskloof granitoids are similar to Archean TTGs. A possible spatial-temporal transition from ~3.13 Ga low-pressure through ~3.12–2.98 Ga medium-pressure to ~2.92 Ga high-pressure TTG is delineated from the northwest towards the southeastern Southern Marginal Zone. This trend is compatible with the southward directed polarity of accretion events recognised in the adjacent low-grade Pietersburg block. We argue that the northeastern margin of the Kaapvaal Craton, north of the Hout River shear zone, is an exotic terrane because 1) the Baviaanskloof granitoid event (~3.1–2.9 Ga with peak at ~3.1 Ga) is older than the accretion episodes (~2.97–2.92 Ga with peak at ~2.95 Ga, and ~2.87–2.84 Ga with peak at ~2.86 Ga) in the adjacent Pietersburg block, 2) the younger ~2.86 Ga event occurs closer to the Hout River shear zone, while the older ~2.95 Ga event was away from it, and 3) contemporaneous (~3.1–3.0 Ga) detrital zircons are absent in greenstone belts of the Pietersburg block that are proximal to the Hout River shear zone. Possible connection to rocks of similar age from the Pilbara Craton as part of the Vaalbara supercraton is explored.
... This will lay a solid stratigraphic basis for studies focused on the economic potential of the Transvaal Supergroup in Botswana (e.g., Tisane et al., 2019), and for hydrogeological studies aimed at the characterization of aquifers such as the dolomitic aquifers in the LTS (e.g., Baqa, 2017;Nijsten et al., 2018). Franchi (2018); modified from Eriksson et al., 2002;Bumby et al., 2012). Arrow points to the Molepolole-Mochudi depository (after Modie, 1999). ...
... Black Reef Quartzite Formation. The Vryburg Formation (Ghaap Group) is considered the equivalent of the Black Reef Quartzite Formation in the Griqualand West Basin of South Africa (e.g., Eriksson et al., 2002;Mapeo et al., 2006;Bumby et al., 2012). This is the lowest stratigraphic unit above the unconformity that marks the top of the Ventersdorp Supergroup in the Griqualand West Basin and consists of shales, quartzites, siltstones and volcanic rocks. ...
... The protobasinal rocks (sensu Eriksson et al., 1996;Eriksson et al., 2002) include deep subaqueous facies, deltaic-shoreline sediments, volcanic rocks (mainly subaerial lava and subordinate volcaniclastic lithologies; Eriksson et al., 2001) and alluvial braided river sediments. Individual protobasinal successions were deposited in separate faultbounded basins on top of the Kaapvaal Craton (Eriksson et al., 2001. ...
Several lithostratigraphic and radiometric-dating studies over the last half century have generated a robust stratigraphic data set about the Transvaal Supergroup sedimentary deposits throughout southern Africa. The Transvaal Supergroup in southern Africa represents one of the best examples of a Precambrian intracratonic sequence, including one of the best preserved and extensive Archaean/Palaeoproterozoic carbonate platforms. Sediments of the Transvaal Supergroup are hosted on the Kaapvaal Craton in three areas of South Africa and Botswana. Critically, the smallest of the three Transvaal depocentres, the Kanye Basin (including the Molepolole-Mochudi sub-basin), is the least known, and the stratigraphic model is still incomplete. The Kanye Basin in southern Botswana exposes a mixed volcanic-sedimentary succession spanning from the Meso-Neoarchaean to the Palaeoproterozoic, including the complete sequence of the Lower Transvaal Supergroup (LTS) and the lower part of the Upper Transvaal Supergroup (UTS). Although no consensus has been reached so far, the deposition of the Transvaal-age sediments in Botswana likely followed the same thermal and tectonic processes recorded in South Africa, albeit diachronously. The initial stage of rifting was followed by sediments that formed in an epicontinental sea setting that recorded the deepening of the basin. The younger sequence records the reactivation of the extensional tectonics alternating with post-rift thermal subsidence. The nomenclature of the lithostratigraphic units in Botswana is often inconsistent, and the correlations with the main Transvaal basins in South Africa are imprecise. Because of the importance of the Transvaal Supergroup for economic (e.g., skarn deposits and placers) and hydrologic (e.g., the Ramotswa trans-boundary aquifer) reasons, the lack of a consistent nomenclature can introduce ambiguity in the scientific literature and lead to misinterpretations. A thorough lithostratigraphic revision of the Transvaal Supergroup in Botswana will also solve the puzzle of the Transvaal-age deposits in southern Africa, allowing reliable interpretations across the three basins. Here, a comprehensive lithostratigraphic and chronostratigraphic description of the Transvaal Supergroup is provided based on literature data and new observations. New lithostratigraphic charts are produced for the Kanye Basin, revealing the stratigraphic relationships within the different Transvaal basins and the effect of cyclicity in the evolution of this Precambrian basin.
... Fluvial strata are present at the base of the 2.714-2.665 Ga Ventersdorp Supergroup in southern Africa (Eriksson et al. 2002;Schneiderhan et al. 2011), where they underlie flood basalts of the Klipriversberg Group, and overlap strata of the Witwatersrand basin. Krapež (1985) noted that these strata of the Ventersdorp Contact Placer (Venterspost Fm) were concentrated in incised valleys developed on a bedrock pediment. ...
... Rust (1994) suggested that the regional depositional slope beneath the conglomerates was in the order of 2-5 m/km, and that floodplain widths of individual river systems, made up of numerous braid channels, may have been as much as 2 km wide, with peak flow depths of 5-10 m, and flow velocities of 2-3 m/s. Other minor fluvial units may also be present between flood basalts in the overlying,~2 km thick, Klipriversberg Group (Eriksson et al. 2002). Anhaeusser et al. (2010) have suggested that minor layers of laminated granular sandstone, interbedded with conglomerate in the upper part of the fill of the 2.79-2.71 ...
... Strata in the volcaniclastic 2.714-2.709 Ga Kameeldoorns Formation, at the base of the overlying Platberg Group, may include basin margin alluvial fans, which prograded into deeper water mudrocks away from bedrock horsts (Buck 1980;Crow and Condie 1988;Karpeta 1993;Eriksson et al. 2002). In the Hartbeesfontein basin the Kameeldoorns Formation is characterized by massive, very poorly sorted, matrix-supported conglomerate (diamictite), in beds up to 8 m thick, containing clasts up to 2 m in diameter that Myers et al. (1990), and Karpeta (1993), suggested were of mass-flow origin. ...
The recognition of Archean fluvial deposits is complicated in many cases by post depositional deformation and metamorphism. Most surviving deposits can be categorized as deposits of alluvial fans with and without debris flows, and sand and gravel-bed braided rivers. Examples of possible intermediate to high sinuosity meandering systems have been tentatively identified in Africa, Australia and India: all lack clear evidence of lateral migration and can be reinterpreted in terms of esturine deposition, shallow tide-influenced marine, and deep-water mass-flow deposits respectively. Mudstone intervals in Archean fluvial strata are rare, and where present, are typically of silt grade. These may represent ponds developed within channel thalwegs, or where more extensive may be of lacustrine rather than floodplain origin. Prior to 3.2 Ga preserved fluvial deposits appear to be largely confined to the flanks of volcanic cones or plateau, perhaps reflecting globally high sea level combined with the small-scale of cratonic nuclei. The onset of modern style plate tectonics in the early Mesoarchean allowed for more extensive generation and preservation of fluvial strata: most of these are first cycle deposits, preserved in rift, strike-slip, and foreland basins, with rare examples accumulating in forearc and syn-tectonic piggy-back basins.
... The Platberg Group consists of chert, carbonate, and clastic sediments, as well as mafic and felsic volcanic deposits (van der Westhuizen et al., 1991). A lacustrine interpretation for Platberg sediments is supported by deposition in isolated intracratonic grabens within the central Kaapvaal Craton (Grobler and Emslie, 1976;Buck, 1980;Eriksson et al., 2002), intercalated with predominantly subaerial volcanic flows (van der Westhuizen et al., 1991;Altermann and Lenhardt, 2012). The overlying Pniel Group consists of Bothaville Formation conglomerates and Allanridge Formation mafic-intermediate lavas (Clendenin et al., 1988). ...
... Pniel Group deposits of the Bothaville and Allanridge Formations unconformably overlie Rietgat Formation strata (Karpeta, 1993). The interpreted tectonic history of the Hartbeesfontein Basin is similar to other Ventersdorp Supergroup localities (Eriksson et al., 2002). Crustal extension opened the basin through listric faulting, followed by Kameeldoorns alluvial deposition, Makwassie ashes and Rietgat basalt flows (Karpeta, 1993;Tinker et al., 2002). ...
The Hartbeesfontein Basin contains the most extensive deposits of Archean lacustrine stromatolites on the Kaapvaal Craton, with stromatolitic facies occurring over ∼100 km² in beds up to 7 m thick. Stromatolitic dolostones and cherts both preserve evidence of microbial processes. Dolomitic stromatolites have grumelous microspar textures between organic-rich laminae, suggestive of carbonate precipitation within microbial mats. Stromatolitic laminae within chert preserve detrital material beyond the angle of repose, indicating the trapping and binding of grains by microbial mats. Stromatolitic cherts also preserve fenestral textures and filamentous microfossils. Many fenestrae have rounded shapes surrounded by filamentous laminae and appear to have formed in situ within stromatolite fabrics before lithification. Fenestrae within stromatolitic chert resemble “hourglass-associated fenestrae” noted from recent silica stromatolites from Yellowstone National Park, and are interpreted to originate from gas bubbles forming within stromatolite-building mats. The preservation of delicate structures in Hartbeesfontein stromatolitic chert (e.g., filamentous microfossils and gas-related fenestrae) implies rapid lithification of microbial mats, while the mm to cm scale of fenestrae indicate equally rapid rates of microbial gas production. Textural and mineralogical evidence associated with gas-related fenestrae support the presence of oxygenic photosynthesis, which in turn strengthens previous hypotheses on Archean lakes as potential oxygen oases before the Great Oxidation Event.
... The Hekpoort/Ongeluk formation lavas follow this model to some extent. However, for Srivastava (2008) and Srivastava and Ernst (2013) the second step also corresponds to cratonization, which is not the case for the Kaapvaal craton which became stable before 3 Ga and not at the end of the Archean (e.g., de Wit et al., 1992;Eriksson et al., 2002;Schoene et al., 2009). Since ca. ...
The ∼2.23 Ga Hekpoort Formation (Transvaal sub-basin) and the ∼2.43 Ga Ongeluk Formation (Griqualand West sub-basin) represent voluminous Paleoproterozoic igneous events on the Kaapvaal craton of South Africa that predate the emplacement of the ∼2.055 Ga Bushveld Complex, and probably covered most of the craton at the time of their extrusion. In this contribution, we present field, petrological and geochemical studies of the Hekpoort Formation and compare it with the Ongeluk Formation. The Hekpoort Formation consists of a thick subaerial volcanic sequence in which volcanoclastic rocks occur mainly at the base. Rare, localized hyaloclastites and variolitic rocks record the presence of ponded water, while interbedded sedimentary rocks and paleo-weathered flow tops suggest prolonged time-breaks in volcanic activity. The Hekpoort rocks underwent metamorphism up to greenschist facies but also episodes of metasomatism and silicification. Preserved primary magmatic minerals are clinopyroxene (pigeonite, augite and diopside), and rarely plagioclase (labradorite). Both the variable whole rock Mg# (evolving from 69 to 50) and the changes in clinopyroxene composition attest to magmatic fractionation. Lava units of both the Hekpoort and Ongeluk formations are mostly basalts, with silicification responsible for increased SiO2 contents. Lava units of both formations also display remarkably similar trace elements patterns, which is noteworthy for units separated by 200 million years, and unique among the Precambrian mafic magmatic units of the Kaapvaal craton that we evaluated. Similar to other Precambrian mafic magmatic units of the Kaapvaal craton, the Hekpoort Formation shows an arc-like trace element signature, mainly represented by negative Nb-Ta anomalies (in normalized trace element patterns). The Hekpoort (and Ongeluk), together with three other Paleoproterozoic mafic units of the craton older than 2.2 Ga, exhibit relatively high contents of Th and U, which sharply contrasts with Archean units. The data suggest that a subduction process marked the Archean-Proterozoic boundary on the Kaapvaal craton.
... The Platberg Group consists of chert, carbonate, and clastic sediments, as well as mafic and felsic volcanic deposits (van der Westhuizen et al., 1991). A lacustrine interpretation for Platberg sediments is supported by deposition in isolated intracratonic grabens within the central Kaapvaal Craton (Grobler and Emslie, 1976;Buck, 1980;Eriksson et al., 2002), intercalated with predominantly subaerial volcanic flows (van der Westhuizen et al., 1991;Altermann and Lenhardt, 2012). The overlying Pniel Group consists of Bothaville Formation conglomerates and Allanridge Formation mafic-intermediate lavas (Clendenin et al., 1988). ...
... Pniel Group deposits of the Bothaville and Allanridge Formations unconformably overlie Rietgat Formation strata (Karpeta, 1993). The interpreted tectonic history of the Hartbeesfontein Basin is similar to other Ventersdorp Supergroup localities (Eriksson et al., 2002). Crustal extension opened the basin through listric faulting, followed by Kameeldoorns alluvial deposition, Makwassie ashes and Rietgat basalt flows (Karpeta, 1993;Tinker et al., 2002). ...
... The O isotopic signature of zircon during this time frame carries subdued supracrustal signatures (Spencer et al., 2014a;Payne et al., 2015), implying that supracrustal reworking was at a minimum. Therefore if the majority of the continental crust growing during the Neoarchean that carries predominantly a mantle signature, then it is implied this crustal growth episode was dominated by magmatism derived predominantly from the mantle, either within oceanic arc environments, associated with mantle plumes (Condie et al., 2001;Condie, 2004;Eriksson et al., 2002;Condie and Aster, 2009;Condie and Kröner, 2008;Zhai and Santosh, 2011), and/or mantle overturn events (Stein and Hofmann, 1994;Breuer and Spohn, 1995;Bédard and Harris, 2014;Griffin et al., 2014). The geodynamic environment of the Late Archean Eon has been compared to the modern Western Pacific region, being dominated by oceanic arcs within an oceanic realm (Santosh et al., 2009;Sawada et al., 2016). ...
From the scant Hadean records of the Jack Hills to Cenozoic supervolcanoes, the continental crust provides a synoptic view deep into Earth history. However, the information is fragmented, as large volumes of continental crust have been recycled back into the mantle by a variety of processes. The preserved crustal record is the balance between the volume of crust generated by magmatic processes and the volume destroyed through return to the mantle by tectonic erosion and lower crustal delamination. At present-day, the Earth has reached near-equilibrium between the amount of crust being generated and that being returned to the mantle at subduction zones. However, multiple lines of evidence support secular change in crustal processes through time, including magma compositions, mantle temperatures, and metamorphic gradients. Though a variety of isotopic proxies are used to estimate crustal growth through time, none of those currently utilized are able to quantify the volumes of crust recycled back into the mantle. This implies the estimates of preserved continental crust and growth curves derived therefrom represent only a minimum of total crustal growth. We posit that from the Neoarchean, the probable onset of modern-day style plate tectonics (i.e. steep subduction), there has been no net crustal growth (and perhaps even a net loss) of the continental crust. Deciphering changes from this equilibrium state through geologic time remains a continual pursuit of crustal evolution studies.
