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 Witwatersrand Supergroup and its world-class gold deposits. The Ventersdorp Supergroup comprises the Klipriviersberg Group, Platberg 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 Supergroup, and we interpret these sills as feeders to the overlying Klipriviersberg Group flood basalts. This constrains the age of the Witwatersrand Supergroup and gold mineralization 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 igneous provinces (LIPs), the Klipriviersberg and Allanridge, which are separated by Platberg 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, Platberg, 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.Major intraplate magmatic events, many of which generate large igneous provinces (LIPs), are globally becoming better understood through U-Pb dating of their magmatic feeders: mafic dike swarms and sill provinces. Although the definition of LIPs has become increasingly complex, a LIP is typically defined as a mainly mafic magmatic province that is >0.1 Mkm2 in area, with volumes >0.1 Mkm3 (Ernst, 2014). Usually, LIPs are emplaced within 1–5 m.y. or consist of multiple short pulses over a maximum of a few tens of millions of years (Ernst and Youbi, 2017) and geochemically have intraplate characteristics. Additionally, many mafic dike swarms and sill provinces connected with LIPs intrude supracrustal successions and can be crucial temporal markers in the stratigraphic record or help to constrain the timing of critical events in the Earth’s history (e.g., Ernst and Youbi, 2017; Gumsley et al., 2017).The Ventersdorp Supergroup (Fig. 1) on the Kaapvaal Craton in southern Africa is the largest and oldest predominantly volcanic supracrustal succession in the world and has been linked to the slightly lower volume Fortescue Group on the Pilbara Craton; both may have been contiguous in the hypothetical Vaalbara Supercraton (de Kock et al., 2009; Evans et al., 2017). The Ventersdorp Supergroup overlies the world-class gold- and uranium-bearing conglomerate reefs of the Witwatersrand Supergroup. However, the exact timing of the formation of the Ventersdorp Supergroup has been a matter of controversy, with implications for the termination of Witwatersrand Supergroup and gold deposition (Armstrong et al., 1991; Wingate, 1998; de Kock et al., 2012; Cornell et al., 2017). 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. 2.78 Ga and ca. 2.71 Ga (Wingate, 1998; de Kock et al., 2012; Cornell et al., 2017). For example, Cornell et al. (2017) re-dated the quartz porphyry of the Makwassie Formation at 2720 ± 2 Ma (Table 1), calling into question the age of ca. 2709 Ma obtained by Armstrong et al. (1991) for the same unit, as well as the ca. 2714 Ma age for underlying flood basalts of the Klipriviersberg Group. Similarly contradicting ages (i.e., older than ca. 2714 Ma) were determined from units that are lithostratigraphically similar to the Ventersdorp Supergroup from the northwestern and western regions of the Kaapvaal Craton (Table 1; e.g., Wingate, 1998; de Kock et al., 2012). The exact correlation of these units to the Ventersdorp Supergroup, however, has yet to be confirmed. It has also been argued that Ventersdorp Supergroup magmatism represent three pulses, or potentially three different LIP events (Ernst and Buchan, 2001; Ernst, 2014).In this study, mafic sills and dikes intruding units older than the Ventersdorp Supergroup (i.e., the Witwatersrand Supergroup, the Pongola Supergroup, and the basement granitoids and granitic gneisses of the Kaapvaal Craton) provide new chronostratigraphic information for the Ventersdorp Supergroup. This information further constrains the timing and formation of the Ventersdorp Supergroup and temporally related units. For the first time, in conjunction with previous studies, we can now define LIPs as initiating, developing, and terminating the formation of the Ventersdorp Supergroup over a period of ∼100 m.y. (e.g., Ernst and Buchan, 2001). The Witwatersrand Supergroup and its world-class gold deposits can also now be shown to have formed by ca. 2.79 Ga.The Kaapvaal Craton in southern Africa preserves over ca. 3.6 Ga of geological history and is world renowned for its record of well-preserved Archean rocks. Following the stabilization of the proto-craton around ca. 3.1 Ga, a series of five supracrustal successions developed unconformably on a peneplaned basement terrain of greenstone belts and greenstone fragments, granitic gneisses, and granitoid plutons before the intrusion of the Bushveld Complex between 2056 Ma and 2055 Ma (Zeh et al., 2015). These five supracrustal successions, in chronological order, include the Dominion Group, Pongola Supergroup, Witwatersrand Supergroup, Ventersdorp Supergroup, and Transvaal Supergroup. The Mesoarchean Dominion Group and the Witwatersrand Supergroup can be regarded as stratigraphic equivalents of the Pongola Supergroup (Beukes and Cairncross, 1991; Cole, 1994).The ∼300,000 km2 Neoarchean Ventersdorp Supergroup (e.g., van der Westhuizen et al., 1991, 2006) is a supracrustal volcanic-sedimentary succession (Fig. 1). The development of the Ventersdorp Supergroup has been attributed to a mantle plume arising from the core-mantle boundary, which led to the formation of a LIP that was distinctly pulsed (Hatton, 1995; Ernst, 2014). In Olsson et al. (2011), a mantle plume center for the Ventersdorp LIP was proposed beneath the Bushveld Complex. The Ventersdorp Supergroup comprises the basal Klipriviersberg Group, followed by the Platberg Group, the Bothaville Formation, and finally the Allanridge Formation. The last two formations comprise the Pniel Group (South African Committee for Stratigraphy (SACS), 1980). At its base, the Ventersdorp Supergroup is separated from the Witwatersrand Supergroup by an unconformity in the central part of the Kaapvaal Craton (e.g., van der Westhuizen et al., 2006). However, in isolated parts of the center of the basin, a conformable relationship exists where conglomerates of the Venterspost Formation (also known as the Ventersdorp contact reef or VCR) are sporadically developed (e.g., Pelletier, 1937; Chunnett, 1994). This formation gives way to the ca. 2714 Ma Klipriviersberg Group flood basalts (Winter, 1976; Armstrong et al., 1991). In the North West Province of South Africa, and southwestern Botswana (Fig. 1), a lithostratigraphically similar succession of flood basalts within the Derdepoort Formation was correlated to the Klipriviersberg Group (e.g., Tyler, 1979). The Derdepoort Formation, however, was inferred by Wingate (1998) at 2782 ± 5 Ma, leading him to regard the 2714 ± 16 Ma age of Armstrong et al. (1991) as a minimum age for Klipriviersberg Group volcanism. The Derdepoort Formation is also coeval to nearby bimodal volcanic rocks and plutonic units in southwestern Botswana and the North West Province of South Africa. In this area (Fig. 1), the Lobatse Group and Kanye Formation have also been dated between ca. 2785 Ma and ca. 2781 Ma (Table 1; Grobler and Walraven, 1993; Moore et al., 1993; Walraven et al., 1996), while the Modipe Complex gabbro and Gabarone Complex granite (Fig. 1) have yielded ages between 2784 Ma and 2779 Ma, respectively (Grobler and Walraven, 1993; Moore et al., 1993; Mapeo et al., 2004; Denyszyn et al., 2013). The only indication that this dated series of coeval magmatic events may have been spatially more significant is an age of 2781 ± 5 Ma for a dacite in a drill core ∼480 km to the southwest, near Kimberley (Fig. 1; Cornell et al., 2017). It has thus been speculated that the Klipriviersberg Group forms part of this ca. 2.78 Ga magmatic pulse (Wingate, 1998; de Kock et al., 2012), but prior to this study, such ages were not reported from the central region of the Kaapvaal Craton, which is the type area of the Klipriviersberg Group.An unconformity separates the Klipriviersberg Group from the Platberg Group (van der Westhuizen et al., 2006); the Platberg Group formed within numerous grabens and half grabens following the termination of Klipriviersberg Group volcanism (Winter, 1976; Stanistreet and McCarthy, 1991). The Platberg Group is best developed over the western Witwatersrand Supergroup in the central part of the Kaapvaal Craton and farther westward (Fig. 1; e.g., Tankard et al., 1982). The typical Platberg Group graben-fill succession consists of basal, coarse-grained sedimentary rocks of the Kameeldoorns Formation, followed by predominantly more mafic volcanic rocks of the Goedgenoeg Formation and more felsic volcanic rocks of the Makwassie Formation (Winter, 1976; Armstrong et al., 1991; van der Westhuizen et al., 2006). In some instances, interbedded mafic volcanic and sedimentary rock (i.e., the Rietgat Formation) is developed overlying the typical successions, but its occurrence is limited to reactivated grabens (van der Westhuizen et al., 2006). Graben-fill is characterized by rapid facies changes and wedge-shaped geometries (de Kock et al., 2012), with possible caldera formation accounting for the excessively thick formations (Meintjes and van der Westhuizen, 2018a). The Makwassie Formation has been dated by Armstrong et al. (1991) at 2709 ± 8 Ma and more recently by Cornell et al. (2017) at 2720 ± 2 Ma at several localities (Table 1). Cornell et al. (2017) further presented an age for the underlying Goedgenoeg Formation of 2746 ± 9 Ma (Table 1). These ages by Cornell et al. (2017) for the Platberg Group are in agreement with age constraints from many lithological correlatives of the Ventersdorp Supergroup that have been described under various names due to non-continuous outcrop in isolated grabens (Fig. 1; van der Westhuizen et al., 2006). These include the 2739 ± 10 Ma Sodium Group (Altermann and Lenhardt, 2012), the 2714 ± 3 Ma Zoetlief Group (Walraven et al., 1991), the 2729 ± 3 Ma Amalia Group (Poujol et al., 2005), and the 2733–2724 Ma Hartswater Group (de Kock et al., 2012) (see Table 1). It has been suggested that the age differences between Platberg Group equivalents is a result of diachronous graben development across the Kaapvaal Craton (de Kock et al., 2012). All these U-Pb ages are in disagreement with the younger ca. 2714 Ma age for the Klipriviersberg Group, which is stratigraphically beneath the Platberg Group.The so-called Pniel Group overlies the Platberg Group with an unconformity (Winter, 1976) that followed the cessation of graben development (Stanistreet and McCarthy, 1991). The Pniel Group covers an extensive area in the central and western parts of the Kaapvaal Craton (van der Westhuizen et al., 2006). The base of the Pniel Group, the Bothaville Formation, is composed of an upward-fining succession of conglomerates and sandstones (Visser and Grobler, 1985). The basaltic andesites of the Allanridge Formation (Winter, 1976) are conformable with the underlying Bothaville Formation (van der Westhuizen et al., 2006). The Pniel Group has not been dated directly, but a maximum age constraint of 2720 ± 4 Ma is available for the lithostratigraphically equivalent Zeekoebaart Formation of the southwestern margin of the Kaapvaal Craton (Fig. 1 and Table 1; Cornell et al., 2018). A minimum age constraint comes from a 2664 ± 1 Ma age for volcanic rocks at the base of the overlying Transvaal Supergroup in the Buffelsfontein Group (Table 1; Barton et al., 1995). The Allanridge Formation is ascribed to renewed rifting and thermal subsidence of the Kaapvaal Craton after the cessation of volcanism in the Platberg Group (Burke et al., 1985; Clendenin et al., 1988).Mafic dike emplacement on the stabilized Kaapvaal Craton is summarized in de Kock et al. (2019), and the first known dike swarm occurred between ca. 2980 Ma and ca. 2966 Ma, with the southeast–trending Badplaas Dike Swarm on the southeastern region of the Kaapvaal Craton (Olsson et al., 2010; Gumsley et al., 2015). These dikes are temporally and spatially associated with the Nsuze Group of the Pongola Supergroup and the Piet Retief Suite of the Usushwana Complex (Olsson et al., 2010; Gumsley et al., 2015). Further mafic magmatism was manifest later in a mafic sill province hosted within the Pongola Supergroup, which includes the 2866 ± 2 Ma Hlagothi Complex (Gumsley et al., 2013; 2015). The Modipe Complex was then emplaced at 2784 ± 1 Ma (Fig. 1 and Table 1; Denyszyn et al., 2013), which is temporally associated with the Gabarone Complex granite and volcanism within the nearby Derdepoort and Kanye Formations (Grobler and Walraven, 1993; Moore et al., 1993; Walraven et al., 1996; Wingate, 1998; Mapeo et al., 2004) on the northwestern region of the Kaapvaal Craton. Approximately 80 m.y. later, mafic magmatism was again documented between ca. 2701 Ma and ca. 2654 Ma on the eastern and southeastern regions of the Kaapvaal Craton (Fig. 1 and Table 1; Olsson et al., 2010, 2011; Gumsley et al., 2016). This includes the 2701 ± 11 Ma to 2659 ± 13 Ma Rykoppies Dike Swarm, which appears to radiate out from beneath the 2056–2055 Ma Bushveld Complex (Olsson et al., 2011; Zeh et al., 2015) and the 2664–2654 Ma northeast–trending White Mfolozi Dike Swarm (Table 1; Gumsley et al., 2016). The Rykoppies and White Mfolozi Dike Swarms potentially mark the termination of Ventersdorp Supergroup-related magmatism at ca. 2.65 Ga, as these dike swarms are also coeval with 2664 ± 1 Ma proto-basinal volcanism to the Transvaal Supergroup in the Buffelsfontein Group (Barton et al., 1995), as well as other proto-basins. Lastly, there are the so-called Kopenang dikes, which were documented by Meier et al. (2009) on the central region of the Kaapvaal Craton within the Witwatersrand Supergroup, although they have random trends. Meier et al. (2009) linked these mafic dikes geochemically to the Klipriviersberg Group. However, their exact relationship remains to be confirmed.In this study, three samples of mafic sills and one sample from a mafic dike are examined (Table DR11). Two samples, named AM1 and VJ1, were collected from drillcore near one of the type areas of the Ventersdorp Supergroup in the central region of the Kaapvaal Craton in the Free State Province of South Africa (Fig. 1). Another two samples, PRGE and ENED08, were collected from outcrops in the southeastern (Mpumalanga Province) and southeasternmost (KwaZulu-Natal Province) regions of the Kaapvaal Craton in South Africa (Fig. 1).Mafic intrusive rocks are commonly intersected in boreholes through Precambrian strata and especially within the Witwatersrand Supergroup on the central region of the Kaapvaal Craton. Many are sills that are over ∼100 m thick, including the studied sills, which are stratigraphically below the flood basalts of the Klipriviersberg Group. The sills are weakly metamorphosed and deformed along with the Witwatersrand Supergroup strata they intruded. The AM1 and VJ1 mafic sills are located east of Klerksdorp and Welkom but south of the Vredefort Dome. The sills intruded into the Government Subgroup of the upper West Rand Group from the Witwatersrand Supergroup (Fig. 2). Sample VJ1 was collected from drill core ∼10 km northeast of Edenville from a ∼200-m-thick mafic sill at ∼1400 m depth, which intruded into sandstones of the Palmietfontein Formation. Sample AM1 was collected from a drill core ∼10 km north of Steynsrus (Fig. 2) and comes from a ∼110-m-thick mafic sill at ∼1800 m depth that intruded into sandstones of the Afrikaner Formation.Another mafic sill, PRGE, was sampled near the road between Piet Retief and Amsterdam in southeast Mpumalanga (Fig. 3A). The outcrop is on the border between the Evergreen and Redcliff Farms, with the mafic sill intruding into the Redcliff Formation. The Redcliff Formation, comprising shales and banded iron formation, and has been assigned to the Mozaan Group of the Pongola Supergroup. The mafic sill itself was previously ascribed to the 2990–2978 Ma Piet Retief Suite of the Usushwana Complex (Hammerbeck, 1982; Gumsley et al., 2015).Sample ENED-08 is from an east-northeast–trending mafic dike that was sampled near the White Mfolozi River between Ulundi and Vryheid (Fig. 3B). The dike intrudes the 3254–3234 Ma granitoid gneiss basement in the White Mfolozi inlier of northern KwaZulu-Natal (Reinhardt et al., 2015) and is part of a mafic dike swarm, herein termed the Ulundi Dike Swarm. This dike swarm is in turn cut by the 2664–2654 Ma plagioclase–megacrystic, northeast–trending White Mfolozi Dike Swarm (Gumsley et al., 2016). Further, the sampled dike cuts an undated southeast–trending mafic dike; both are in turn cut by a ca. 2423 Ma mafic sheet (Gumsley et al., 2017). Some geochemistry and paleomagnetism on these mafic units was conducted by Klausen et al. (2010) and Lubnina et al. (2010).Petrographic analysis of thin sections was undertaken at the Institute of Earth Sciences in the University of Silesia in Katowice using an Olympus BX-51 optical microscope. Mineral chemical analysis of the main rock-forming and accessory minerals was carried out at the Inter-Institutional Laboratory of Microanalyses of Minerals and Synthetic Substances, University of Warsaw, using a CAMECA SX-100 electron microprobe. The analytical conditions employed an accelerating voltage of 15 kV, a beam current of 20 nA, counting times of 4 s for the peaks and background, and a beam diameter of 1–5 μm. Reference materials, analytical lines, and mean detection limits (in wt. %) can be found in Table DR2 (see footnote 1). Diffracting crystals include LIF, PET, TAP, and LPET.For whole-rock geochemistry, samples were selected from the most homogenous parts of the sampled mafic sills and dike after the weathered material was removed. They were then hand crushed and milled in a tungsten-carbide ring mill. The resulting material was then coned and quartered before being dispatched for analysis of major, minor, and trace elements at Bureau Veritas Laboratories in Vancouver, Canada. Analyses were made on glass beads prepared from the powdered samples with a sample-to-flux (lithium tetraborate) ratio of 1:10, and the resulting molten bead was rapidly digested in weak nitric acid solution. Inductively coupled plasma emission spectroscopy (ICPES) was used for major and minor elements, and inductively coupled plasma mass spectrometry (ICPMS) was used for trace elements, including rare-earth elements (REE). The volatile content of each sample was determined by loss on ignition (LOI). The data were plotted in diagrams using the GeoChemical Data toolkit (GCDkit; Janoušek et al., 2006).The sampled units were processed for baddeleyite U-Pb dating by the isotope dilution-thermal ionization mass spectrometry (ID–TIMS) and laser ablation (LA)–ICPMS analytical methodologies. The LA–ICPMS methodology was deployed to test the reproducibility between the two independent methods at the LA–ICPMS Laboratory at Lund University. Samples were hand crushed and ground to a coarse-grained powder using a chrome-steel ring mill in the Department of Geology, Lund University. The water-based separation process developed by Söderlund and Johansson (2002) was used to extract baddeleyite grains for ID-TIMS; however, only VJ1 yielded suitably sized baddeleyite grains for LA-ICPMS (greater than 60 μm long and 20 μm wide).The extracted baddeleyite grains were split into fractions that were transferred in ethanol to pre-cleaned Teflon capsules. The fractions were washed for several cycles in ultrapure HNO3 and H2O. A small amount of a 236–233U-205Pb tracer solution and an ultrapure HF:HNO3 (10:1) mixture was added to each Teflon capsule. The baddeleyite fractions were completely dissolved in an oven after three days at ∼190 °C. The capsules were placed on a hotplate at ∼100 °C until the HF solution had evaporated. A mixture of ultrapure 0.25 M H3PO4 and 6.2 M HCl was added to each capsule and dried again on a hotplate. The remaining sample droplet in the Teflon capsules was mixed with 2 μl of a prepared Si gel and placed on an outgassed Re filament. The samples on the outgassed Re filaments were heated until the H3PO4 burnt off. The resultant filaments were then placed in a carousel inside a Finnigan TRITON thermal ionization mass spectrometer at the Department of Geosciences, Swedish Museum of National History in Stockholm. The mass spectrometer is equipped with a secondary electron multiplier and Faraday Cups.The Re filaments and samples were heated to temperatures between ∼1210 °C and ∼1250 °C, where the intensities of the isotopic masses of 204Pb, 205Pb, 206Pb, 207Pb, and 208Pb were measured in cycles of between 20 and 140 at gradually increasing temperatures. The Pb signal intensities were measured in either static mode with Faraday Cups or in dynamic mode with peak-switching using the secondary electron multipliers. The isotopic masses of 233U, 236U, and 238U were measured as oxides at temperatures of ∼1300 °C to ∼1340 °C at increasing temperatures. The 235U was calculated from 238U, using 238U/235U = 137.818, following Hiess et al. (2012). No significant differences due to interferences from 18O were detected, and therefore corrections were not made. The measurements were made in dynamic mode for between 40 and 80 cycles. Initial data reduction was made using an “in-house” Microsoft Excel program using algorithms from Ludwig (2003). However, the Microsoft Excel macro, Isoplot 4.15, from Ludwig (2012) using U decay constants from Jaffey et al. (1971), was used for final data calculations and concordia diagrams. Initial common Pb corrections were made using the isotopic compositions from the global common Pb evolution model of Stacey and Kramers (1975) at the age of the sample. Error propagations in dates are given at 2σ and do not include decay constant errors.Baddeleyite grains from sample VJ1 were placed on double-sided adhesive tape and mounted into epoxy resin in a 1-inch-wide Teflon ring and left to harden for three days. The hardened epoxy mount was then separated from the tape and polished for between 20 s and 140 s, with 9 μm, 3 μ, and 1 μm diamond paste using a Struers Rotopol-22 automated polisher. The mount was subsequently cleaned with ethanol. The reference material used was baddeleyite from the Phalaborwa Complex, which was dated to 2059.60 ± 0.35 Ma (Heaman, 2009).The analyses were carried out at the LA-ICPMS Laboratory in the Department of Geology at Lund University. The LA-ICPMS uses a 193 nm Analyte G2 laser ablation unit with a two volume HelEx sample holder and an Aurora Elite quadrupole inductively coupled plasma mass spectrometer. Ablation was done with a 5 Hz repetition rate, a fluence of ∼4 j/cm2, using 20 μm spot diameters. The total acquisition time for each analysis was 55 s, of which the first 20 s were used to determine the Ar/He/N2 gas blank, followed by 28 s of laser ablation and 3–4 s of wash-out delay. The He carrier gas was mixed downstream with Ar and N2 before entering a “squid” signal smoothing device made up of several tubes that split the stream and re-joined it before entering the plasma. The mass spectrometer was calibrated using NIST612 glass to give stable 206Pb, 207Pb, and 238U signals and low oxide production rates (238U16O/238U below 0.5%) and a 232Th/238U ratio of ∼1. The 202Hg, 204(Pb + Hg), 206Pb, 207Pb, 208Pb, 232Th, 235U, and 238U intensities were determined using secondary electron multipliers. The interference of 204Hg on 204Pb was monitored by measuring 202Hg, assuming a 202Hg/204Hg ratio of 4.36 (natural abundance). Although 235U was measured, the 207Pb/235U was calculated from 238U, using 238U/235U = 137.818 following Hiess et al. (2012). The laser-induced elemental fractionation and instrumental mass bias on measured isotopic ratios were corrected through standard-sample bracketing using the Phalaborwa baddeleyite standard (Heaman 2009). A total of 36 analyses were made in the following order: six standards followed by seven unknowns (i.e., VJ1), four standards, six unknowns, four standards, five unknowns, and four standards. Data reduction was done using the Iolite software (Paton et al., 2011) with the U-Pb geochronology data reduction scheme routine of Paton et al. (2010). Correction routines for downhole fractionation and instrumental drift were applied in the Iolite software. Common-Pb correction was done in the Iolite software using VizaulAge by Petrus and Kamber (2012) from the terrestrial Pb-isotope composition of Stacey and Kramers (1975). All age data were calculated using Isoplot 4.15 (Ludwig, 2012), which was also used to plot and evaluate data. Error propagation in dates reported are given at 2σ and do not include decay constant errors.The four samples investigated have a mineral assemblage typical of mafic intrusions (Table DR1). The primary rock-forming minerals are mostly zoned plagioclase feldspar (An41Ab59–An18Ab82; Fig. 4A), zoned diopside (Fe2+/Mg from 0. 46 in cores to 0.82 at rims; Table DR3 (see footnote 1); Fig. 4B), and ilmenite (Ti0.96–1.00Fe0.90–1.00Mn0.04–0.07O3), intergrown with Ti-bearing magnetite (Fe2+1.08–1.13Fe3+1.69–1.80Ti0.09–0.14O4; Table DR3; Figs. 4B–4C, and 4E). Fluorapatite and baddeleyite are common accessory minerals. Pyrite and chalcopyrite grains were noted as inclusions in pyroxene. The metamorphic overprint is observed by the partial to complete replacement of pyroxene (diopside) by amphibole (actinolite) and rims of ferrian-ferro-hornblende (Figs. 4A–4B; Table DR3). Further evidence of metamorphic alteration is provided by secondary Al-bearing titanite rims on ilmenite and ilmenite-magnetite intergrowths (Fig. 4D). Locally, secondary biotite (Ti = 0.37–0.43 a.p.f.u.; #fm = 0.64–0.67; Table DR3) was formed at the expense of opaque minerals (Fig. 4B). Late chlorite-epidote veins cut the rocks. The metamorphic alteration is typical of greenschist facies metamorphic conditions. Samples also show secondary, low-temperature alteration manifest by the sericitization of plagioclase feldspar and chloritization of mafic silicates and aluminosilicates. The least altered samples are PRGE and AM1, while the other two samples show pervasive alteration (Table DR1). Sample PRGE displayed graphic intergrowths of quartz and alkali feldspar (Or79–56, Ab36–17An1–5), forming a groundmass between the clusters of mafic phases (Figs. 4C and 4E).Whole-rock major and trace element compositions for the studied mafic sills and dike are listed in Table DR4 (see footnote 1). Data from previous studies (Crow and Condie, 1988; Marsh et al., 1992; Nelson et al., 1992; Meier et al., 2009; Klausen et al., 2010; Gumsley et al., 2016; Meintjes and van der Westhuizen, 2018b) are used for comparison and are shown in Table DR5 (see footnote 1). Data were filtered using an LOI of less than 10% to account for extensive alteration. A thorough review of the geochemistry and petrogenesis of the Ventersdorp Supergroup can be found in Humbert et al. (2019). The mafic sills in this study (AM1 and VJ1) straddle the basalt and the basaltic andesite/andesite fields in the Zr/Ti-Nb/Y classification diagram (Fig. 5A; Pearce, 1996, after Winchester and Floyd, 1977), and are similar to the Klipriviersberg Group basalts and Kopenang dikes, with the lowest Nb/Y and Zr/Ti. The mafic sill PRGE and mafic dike ENED08 are within the basalt and basaltic andesite/andesite range of the Platberg Group volcanic rocks (and Rykoppies Dike Swarm), which are bimodal in Zr/Ti and show greater Zr/Ti in the dacites/rhyolites of the Makwassie Formation. The Allanridge Formation basaltic andesites have a slightly higher Nb/Yb but are equivalent to the lower Zr/Ti grouping from the Platberg Group. The White Mfolozi Dike Swarm, however, is geochemically distinct from the other groupings, having lower Zr/Ti and Nb/Yb. In the AFM diagram (Irvine and Baragar, 1971), samples AM1 and VJ1 and the basalts of the Klipriviersberg Group and the Kopenang dikes plot in the field of tholeiitic basalts with slight calc-alkaline affinities (Fig. 5B). Samples PRGE and ENED08 again show more similarities to the Platberg Group mafic volcanic rocks, Rykoppies Dike Swarm, and Allanridge Formation basaltic andesites, which have a more calc-alkaline differentiation trend. Using the Th/Yb-Nb/Yb diagram (Pearce, 2008), AM1 and VJ1 are in close proximity to the Kopenang dikes and the Klipriviersberg Group basalts, whereas samples PRGE and ENED08 plot near the mafic volcanic rocks of the Platberg Group, Rykoppies Dike Swarm, and Allanridge Formation basaltic andesites (Fig. 5C). These samples show greater Th/Yb than the mid-oceanic ridge basalt–oceanic island basalt (MORB-OIB) array of oceanic basalts toward the modern volcanic arc array except for the White Mfolozi Dike Swarm, which plots in the MORB–OIB array. Th/Yb is slightly higher in the Platberg Group volcanic rocks, Rykoppies Dike Swarm, and Allanridge Formation basaltic andesites as well as in the dike (ENED08) and sill (PRGE) in this study, compared to the Klipriviersberg Group basalts and Kopenang dikes, including the mafic sills (AM1 and VJ1). Finally, in the Th/Ta–La/Yb diagram (Fig. 5D; Ernst, 2014, after Condie, 2003), samples AM1 and VJ1, including the Klipriviersberg Group basalts and Allanridge Formation basaltic andesites, plot in the continental flood basalt (or CFB field). However, samples from Allanridge Formation basaltic andesites and Rykoppies Dike Swarm, as well as ENED08 and PRGE, have higher La/Yb. The Kopenang dikes have similar values of La/Yb as the Klipriviersberg Group basalts, as well as the VJ1 and AM1 samples, but have higher Th/Ta values, which results in a shift of their location above the CFB field. Samples ENED08 and PRGE have a higher Th/Ta and La/Yb than samples VJ1 and AM1 and plot above the Platberg Group volcanic rocks. At this time, samples from the White Mfolozi Dike Swarm are clearly geochemically distinct from any other unit on the Kaapvaal Craton.In the chondrite normalized REE diagram and the primitive mantle normalized multi-element plot (Figs. 6A–6D; McDonough and Sun, 1995), samples AM1 and VJ1 are broadly similar to the Klipriviersberg Group basalts and Kopenang dikes. These samples are slightly enriched in light REE relative to heavy REE with no significant anomalies. PRGE and ENED08, however, have elevated levels of REE compared to AM1 and VJ1 and the Klipriviersberg Group basalts and Kopenang dikes. Sample PRGE has a diagnostic enriched REE pattern like that of the Platberg Group volcanic rocks and especially the Makwassie Formation rhyolites and dacites, whereas ENED08 has a similar pattern but is only slightly more enriched as compared to VJ1 and AM1, comparable to the Rykoppies Dike Swarm and the Allanridge Formation basaltic andesites. Only PRGE shows a negative Eu anomaly, and both PRGE and ENED08 are more enriched in light REE compared to heavy REE. Excluding the mobile elements such as Cs, Rb, Ba, Th, and U, all samples have negative Nb and Ta anomalies, as well as negative Ti and slightly negative Eu anomalies.The water-based separation process of Söderlund and Johansson (2002) yielded ∼40 grains of baddeleyite each for VJ1 and PRGE, and 30 grains for AM1, whereas only 20 grains of ENED08 were recovered. The best-quality grains analyzed in the VJ1, AM1, and ENED08 samples were light brown and generally clear with some slight to moderate frostiness with a length of between 50 μm and 60 μm for VJ1 and ∼30 μm for AM1. ENED08 baddeleyite grains were between 20 μm and 30 μm long. Sample PRGE had baddeleyite grains that were dark brown and generally clear with some slight frostiness with lengths of ∼40 μm. U and Pb isotopic measurements are listed in Tables DR6 and DR7 (see footnote 1), and data are plotted on Wetherill concordia diagrams in Figures 7 and 8.Four fractions of baddeleyite from VJ1 were analyzed, which were composed of between two and three baddeleyite grains each (Fig. 7A). Regression of these fractions produced a precise upper intercept date of 2787 ± 2 Ma (mean square of weighted deviates [MSWD] = 1.5). Three fractions are between 2% to 1% discordant and a fourth fraction is 6% discordant, likely due to zircon alteration. The most discordant fraction constrains the lower intercept of 295 ± 98 Ma. A weighted mean 207Pb/206Pb date of the three least discordant fractions is 2785 ± 1 Ma (MSWD = 0.67). The fourth fraction is excluded because it is not within error of the 207Pb/206Pb dates of the other three fractions. Two fractions of AM1, composed of six baddeleyite grains each, produced a preliminary upper intercept date of 2789 ± 4 Ma (Fig. 7B), which is within error of the date of VJ1. Regression yields a preliminary lower free intercept date of 106 ± 190 Ma. The two fractions were 5% and 2% discordant, with 207Pb/206Pb dates between ca. 2788 Ma and ca. 2786 Ma. For sample ENED08, three baddeleyite fractions were analyzed, with three grains in each (Fig. 7C). Free regression yields upper and lower intercept dates of 2729 ± 5 Ma and 228 ± 57 Ma, respectively (MSWD <0.1). Two fractions plot between 6% and 5% discordant and have 207Pb/206Pb dates between ca. 2723 Ma and ca. 2722 Ma, and a third fraction is 16% discordant, likely as a result of zircon alteration, and constrains the lower intercept.Sample PRGE yielded an upper intercept date of 2727 ± 3 Ma and a lower intercept date of 540 ± 280 Ma (MSWD = 0.71) from analysis of four fractions of baddeleyite (Fig. 7D). The discordance varies between 10% and 0%, with the three least discordant fractions being between 1% and 0% discordant. A weighted mean 207Pb/206Pb age calculated on these three least discordant dates is 2724 ± 7 Ma (MSWD = 3.3). The fourth fraction is excluded due to not being within error of the 207Pb/206Pb dates of the other three fractions.Analytical results from the Phalaborwa Complex reference material (Heaman, 2009) are presented in Table DR7 (see footnote 1). No significant difference was observed between 207Pb/206Pb ratios of VJ1 measured in the sequence, but the isotopic data show variable discordance (between ∼17% and ∼1%), forming a discordant array in a Wetherill concordia diagram (Fig. 8A). Using all data (Table DR8; see footnote 1), we obtain an upper intercept date of 2799 ± 15 Ma (MSWD = 3.4) and a weighted mean 207Pb/206Pb date of 2796 ± 6 Ma (MSWD = 3.2; Fig. 8B).Difficulties in determining the true U-Pb dates of grains analyzed using LA–ICPMS might arise from difficulties with correction of common Pb. In the presented data, the average mass 204 background signal was relatively high, around 1900 counts per second, which increases the risk that small amounts of common Pb cannot be detected. When detecting isotopes close to the detection limit, it is not possible to quantify concentrations; however, by plotting the 206Pb/204Pb against common Pb corrected and uncorrected 207Pb/206Pb dates, we observe an increasing age difference for analyses with low 206Pb/204Pb, which mainly shows up in decreasing common Pb corrected dates. This supports the idea that some grains contain a small amount of common Pb but also that we seemingly overcorrect the data, as observed when 206Pb/204Pb ratios are below 9000. Using all uncorrected data, we obtain an upper intercept date of 2799 ± 15 Ma (MSWD = 3.4) and a weighted mean 207Pb/206Pb date of 2796 ± 6 Ma (MSWD = 3.2). Using only uncorrected data from analyses with 206Pb/204Pb above 9000, we obtain an upper intercept date of 2798 ± 12 Ma (MSWD = 1.9) and a weighted mean 207Pb/206Pb date of 2793 ± 7 Ma (MSWD = 1.7; Fig. 8B). As observed, there is, within the limits of uncertainty, no significant difference between these age estimates. We, however, prefer to use the data that are arguably least affected by common Pb, and thus our best date estimate of VJ1 is 2798 ± 12 Ma, using the upper intercept, as with the ID-TIMS data.Regression of the U-Pb ID–TIMS data for VJ1 yields an upper intercept date of 2787 ± 2 Ma (MSWD = 1.5) and is within analytical uncertainty of the LA–ICPMS result as well as the preliminary AM1 date of 2789 ± 4 Ma, both of which are also obtained by free regression. This is preferred age over a weighted mean 207Pb/206Pb age on the three least discordant analyses at 2785 ± 1 Ma (MSWD = 0.67), as no data overlap the concordia, making the weighted mean date a minimum age. Although the lower intercept is close to 0 Ma, which indicates recent Pb disturbance, it is still beyond uncertainty at 295 ± 98 Ma, and therefore an isotopic disturbance at an earlier time is possible. This is interpreted as likely belonging to the Karoo magmatic event at 183–179 Ma (Duncan et al., 1997). The relatively precise 2787 ± 2 Ma date is our preferred crystallization age, since ID–TIMS normally allows for robust common-Pb correction. Noteworthy is that the discordance of ID–TIMS fractions is ∼3%, i.e., much less than for the LA–ICPMS analyses. The crystallization age of ENED08 is also interpreted as 2729 ± 5 Ma (MSWD < 0.01) using a free regression, as no analyses overlap with the concordia, with Pb disturbance again likely attributed to Karoo magmatism. The upper intercept date of PRGE is 2727 ± 3 Ma (MSWD = 0.71). However, a weighted mean 207Pb/206Pb date on the three least discordant fractions, which overlap the concordia, is 2724 ± 7 Ma (MSWD = 3.3). The weighted mean 207Pb/206Pb date is thus our preferred crystallization age for PRGE.The incompatible element patterns of all the magmatic events presented in Figure 6 are different, but with the exception of the White Mfolozi Dike Swarm, they all show “subduction-related” or “arc-like” signatures (e.g., Pearce, 2008; Ernst, 2014; O’Neill and Jenner, 2016; Humbert et al., 2018; 2019) that are notably marked by negative Nb and Ta anomalies. These signatures are common in many Archean and Paleoproterozoic mafic rocks of the Kaapvaal Craton (e.g., O’Neill and Jenner 2016; Humbert et al., 2018; 2019) and in other intraplate events (including LIPs) in the rest of the world (e.g., Pearce, 2008; Ernst, 2014). These events also plot higher Th/Yb and Th/Nb values than the MORB-OIB array (Fig. 5C). According to Pearce (2008), this preferential enrichment in Th over Nb may either indicate crustal contamination or assimilation of the magma and/or a lithospheric mantle source that was fluid-metasomatized by past subduction. Substantial crustal contamination actually has been inferred through whole-rock Sm-Nd isotopic data in the case of the Platberg Group (average εNd2720Ma = –3.4) and Allanridge Formation (average εNd2700Ma = –3.0), with an average εNd2780Ma = 0 for the source of the Klipriviersberg magmas probably also possibly contaminated to a lesser extent (Humbert et al., 2019). Note that no isotopic data exist for the other events so far. In addition, the quartz and alkali feldspar groundmass in the PRGE sample can be interpreted as the result of local mixing-mingling phenomena (e.g., Burda et al., 2011) from assimilation of silica-rich material. It can also simply represent the highly fractionated portions of rift-related intracontinental basaltic magma.Samples from the White Mfolozi Dike Swarm are clearly geochemically distinct from any other unit on the Kaapvaal Craton (Figs. 5 and 6). They notably present lower Th/Yb, Nb/Yb, Th/Ta, and La/Yb ratios, as well as “flat” and moderately enriched signatures compared to chondrite/primitive mantle in REE/trace-element diagrams. The White Mfolozi Dike Swarm samples plot close to primitive mantle in Figures 5C and 5D and might be from such a source. On the contrary, they also may have been generated from a depleted mantle source (i.e., NMORB-like) that later underwent minor crustal contamination.The herein dated 2787 ± 2 Ma and 2789 ± 4 Ma mafic sills VJ1 and AM1 are the first documented occurrence of this magmatic event from the central region of the Kaapvaal Craton (Fig. 9). These sills are situated stratigraphically beneath the Klipriviersberg Group flood basalts of the Ventersdorp Supergroup in the Witwatersrand Supergroup and are interpreted as likely related to them. Further, these mafic sills closely resemble the flood basalts of the Klipriviersberg Group geochemically (Figs. 5 and 6; e.g., Winter, 1976; Marsh et al., 1992; Humbert et al., 2019). Meier et al. (2009) has already shown the similar geochemical characteristics of mafic feeders to the Klipriviersberg Group flood basalts in the form of the Kopenang dikes intruding the Witwatersrand Supergroup in the same area (Fig. 1). Therefore, it is reasonable to interpret that the mafic sills AM1 and VJ1 analyzed in this study belong to a single magmatic system represented by mafic intrusions that fed the overlying flood basalts of the Klipriviersberg Group.As shown in Figure 9, we now recognize a widespread 2791–2779 Ma magmatic event across the central, western, and northwestern regions of the Kaapvaal Craton. The mafic sills from the central region of the Kaapvaal Craton in this study, AM1 and VJ1, are coeval with the bimodal volcanic Kanye Formation and its plutonic equivalent, the Gabarone Complex granites. The Kanye Formation has been considered a proto-basinal or precursor phase to the Ventersdorp Supergroup in the Swartruggens Trough (Tyler, 1979; Ernst, 2014). The nearby Derdepoort Formation and Modipe Complex gabbro was dated to 2782 ± 5 Ma and 2784 ± 1 Ma, respectively (Table 1; Wingate, 1998; Denyszyn et al., 2013). These units were originally correlated with the Klipriviersberg Group flood basalts and other units of the Ventersdorp Supergroup (Tyler, 1979). Similarly aged units are documented in the Amalia–Kraaipan granite-greenstone terrane of the western and northwestern regions of the Kaapvaal Craton (Figs. 9A and 9B). These include the Mosita, Mmathete, and “red” granites, as well as the Turfloop and Rooibokvlei granites in the Makoppa Dome (e.g., Grobler and Walraven, 1993; Moore et al., 1993; Mapeo et al., 2004; de Kock et al., 2012; Denyszyn et al., 2013; Ernst, 2014). This magmatic event is also recorded in detrital zircon data from the Ventersdorp and Transvaal supergroups (Figs. 9A and 9B; Tables DR9 and DR10; see footnote 1).Furthermore, the ages proposed for the Klipriviersberg Group flood basalts in this study do not agree with the 2714 ± 16 Ma age obtained by Armstrong et al. (1991) from the type locality of the Klipriviersberg Group flood basalts. This is the only volcanic event occurring in the region of the mafic sills dated in this study other than the ca. 2914 Ma Crown Formation lava of the Witwatersrand Supergroup (Armstrong et al., 1991; Fig. 9A). However, the age presented by Armstrong et al. (1991) for the Klipriviersberg Group flood basalts has been questioned by Wingate (1998), de Kock et al. (2012), Cornell et al. (2017), and Humbert et al. (2019). A recalculation of the Armstrong et al. (1991) isotopic data using the least discordant analyses at ca. 2.7 Ga and ca. 1.0 Ga results in an upper intercept date of 2757 ± 57 Ma and a lower intercept date of 1082 ± 140 Ma. This result, as originally shown by Wingate (1998), indicates that the magmatic/metamorphic event that formed the younger ca. 1.0 Ga generation of zircons may have affected the ca. 2.7 Ga zircons and should be regarded as a minimum age of crystallization for the flood basalts. Recent geochronological studies on the Platberg Group (in the Makwassie Formation) and one of its stratigraphic equivalents (i.e., the Hartswater Group) also add temporal constraints on the age of the Klipriviersberg Group, indicating an older age (e.g., de Kock et al., 2012; Cornell et al., 2017). Furthermore, Barton et al. (1989) analyzed detrital zircons from the Venterspost Formation, which constitutes the base of the Klipriviersberg Group, and obtained a maximum age of 2780 ± 5 Ma for deposition of the formation from the youngest concordant zircon grains.The magmatic event described above meets the criteria for a LIP, as specified by Ernst (2014). As illustrated in Figure 9, we can now redefine this event to encompass the Klipriviersberg Group flood basalts and coeval mafic sills, the Kanye and Derdepoort bimodal volcanic rocks, and the temporally related Gabarone Complex and Modipe Complex granites and gabbros as well as granites farther afield to the west (Fig. 9B). The LIP had an area of ∼250,000 km2, with the thickness of the flood basalt package up to 2 km. Further material from the magmatic province has likely eroded away, as shown by the extensive detrital zircon spectra peak at ca. 2.78 Ga. An age range for all units belonging to this newly defined Klipriviersberg LIP is 2791–2779 Ma, although through more modern methodology, this age range can likely be narrowed further. Additionally, the lack of any intervening sedimentary layers or unconformities in the flood basalts provides further evidence of the short-lived duration of the magmatic event.Following a magmatic hiatus from the Klipriviersberg LIP, large-scale rifting, sedimentation, and volcanism dominated the western and central Kaapvaal Craton between 2754 Ma and 2709 Ma (de Kock et al., 2012; Cornell et al., 2017). In the eastern Kaapvaal Craton, numerous granites were emplaced simultaneously (e.g., Hofmann et al., 2015), which Taylor et al. (2010) argued were likely related to the extension and magmatism that deposited the Ventersdorp Supergroup (Figs. 9A and 9B; Tables DR9 and DR10). In this study, the mafic sill PRGE from the southeastern part of the Kaapvaal Craton intruding into the Pongola Supergroup was dated to 2724 ± 7 Ma, and thus it is coeval with this widespread magmatic event. Geochemically, this sill resembles volcanic rocks within the Platberg Group, specifically the Makwassie Formation (Figs. 5 and 6). Near the sill, the Amsterdam Formation is the only unit with which it may be linked. The Amsterdam Formation unconformably overlies the Pongola Supergroup and is a volcanic succession composed of the Gobosha Member dacites near Amsterdam and the Vaalkop Member rhyolites near Piet Retief (Hammerbeck, 1982). The sill geologically and geochemically resembles the Gobosha dacites of the Amsterdam Formation (Hammerbeck, 1982), and therefore it is hypothesized as a likely part of a feeder system to the volcanic rocks of the Amsterdam Formation. This interpretation implies that the Amsterdam Formation is the easternmost equivalent of the Platberg Group (Fig. 9B). Additionally, farther to the east in the Mkondo Suite, leucosomes dated to 2730 ± 5 Ma have been reported to date granulite facies metamorphism (Taylor et al., 2010).To the south of the dated sill, our age of 2729 ± 5 Ma for ENED08 on a coeval east-northeast–trending dike establishes a newly identified dike swarm on the southeasternmost part of the Kaapvaal Craton. This dike swarm, which we name the “Ulundi Dike Swarm” (Figs. 1 and 3), is the first recognized dike swarm associated with the Platberg Group of the Ventersdorp Supergroup and extends this magmatic event further to the southeast. The ENED08 dike is cut by plagioclase megacrystic northeast-trending dikes of the 2664–2654 Ma White Mfolozi Dike Swarm (Gumsley et al., 2016) as well as by a mafic sheet dated at 2420 ± 3 Ma (Gumsley et al., 2017).Using the new age constraints presented in this study of 2729 ± 5 Ma for ENED08 and 2724 ± 7 Ma for PRGE, and age constraints of 2733–2724 Ma in de Kock et al. (2012) and 2720 ± 2 Ma in Cornell et al. (2017), the Platberg volcanic province (or possibly a LIP pulse of a combined Platberg–Allanridge LIP) is constrained to between ca. 2754 Ma and ca. 2709 Ma. For the Makwassie Formation, the Cornell et al. (2017) age of 2720 ± 2 Ma replaces the original 2709 ± 8 Ma age presented by Armstrong et al. (1991). A detrital zircon-spectra peak again provides evidence of magmatism and erosion at ca. 2.71 Ga.These new data for samples ENED08 and PRGE help to refine the minimum and maximum age constraints on the Allanridge Formation basaltic andesites, which unconformably overlie the Platberg Group along with the Bothaville Formation (both part of the Pniel Group). The Allanridge Formation basaltic andesites are sufficiently voluminous to be defined as a LIP according to Ernst (2014), being over 200,000 km2 in area and up to 1 km thick. Age constraints on the Allanridge LIP bracket its deposition between ca. 2709 Ma, which is the age of the underlying Makwassie Formation of the Platberg Group (Cornell et al., 2017), and ca. 2664 Ma, which corresponds to the age of the Buffelsfontein Group in the overlying proto-basins of the Transvaal Supergroup (Barton et al., 1995).However, the Rykoppies Dike Swarm, emplaced between ca. 2701 Ma and ca. 2664 Ma, may also be linked to the Allanridge LIP and appears geochemically similar (Figs. 5 and 6). This mafic magmatism documents peaks at 2701–2692 Ma, 2686–2683 Ma, and 2664–2659 Ma (Gumsley et al., 2016). Reinterpretation of the complex discordant U-Pb isotopic data and Pb loss histories of these dike swarms appears to indicate two magmatic events at 2701–2683 Ma and 2664–2654 Ma using only the least discordant U-Pb baddeleyite isotopic data from the Rykoppies and White Mfolozi dike swarms. If this is correct, the age of the Allanridge LIP may reflect this older pulse at 2701–2683 Ma in the Rykoppies Dike Swarm, with further magmatism at 2664–2654 Ma represented by the geochemically distinct White Mfolozi Dike Swarm, which is coeval to parts of the Rykoppies Dike Swarm (despite being geochemically different) and volcanism and renewed rifting in proto-basinal fills to the Transvaal Supergroup, such as the bimodal volcanic rocks of the Buffelsfontein Formation at 2664 ± 1 Ma (Barton et al., 1995). The White Mfolozi Dike Swarm may then be regarded as a separate magmatic event, potentially another LIP, especially when including coeval parts of the Rykoppies Dike Swarm. The White Mfolozi Dike Swarm has a unique geochemical signature but has an approximately orthogonal linear trend to the Rykoppies Dike Swarm, which is radiating (Fig. 1). While the White Mfolozi Dike Swarm could represent part of a separate linear or radiating swarm, we speculate that the White Mfolozi Dike Swarm could alternatively be evidence for a giant circumferential swarm (Buchan and Ernst 2018, 2019) that circumscribes the plume center at the focus of the Rykoppies Dike Swarm.In summary, Ventersdorp magmatism can be divided into distinct volcanic/magmatic events, some of which are of LIP scale, including the 2791–2779 Ma Klipriviersberg LIP and the 2701–2683 Ma Allanridge LIP, which are separated from the 2664–2654 Ma White Mfolozi/Rykoppies magmatic province, which may also be a LIP. Despite the unconformity between the Platberg Group and the Pniel Group, the Allanridge LIP was closely preceded by the 2754–2709 Ma Platberg volcanic province, which is composed of a mixed succession of sedimentary and bimodal volcanic rocks. The Platberg Group was, therefore, likely genetically related to a mantle plume responsible for the emplacement of the Allanridge LIP beneath the lithosphere, making the plume distinctly pulsed (with fractionation or arc-related magmatism, with a crustal contribution, as seen from geochemistry; Humbert et al., 2019). The mantle plume center for the Allanridge LIP is well defined by the radiating Rykoppies Dike Swarm. In addition, the associated Ventersdorp rift zone trends approximately from this plume center, suggesting that this rifting was in part coeval with the Allanridge LIP. The location of a plume center for the 2791–2779 Ma Klipriviersberg LIP and 2664–2654 Ma White Mfolozi volcanic province remains unconstrained.The 2787 ± 2 Ma and 2789 ± 4 Ma mafic sills reported in this study intrude and crosscut the gold-bearing Witwatersrand Supergroup successions, indicating that the placer gold deposits must predate the mafic dikes and sills as suggested by Meier et al. (2009). This makes the minimum depositional age for placer gold and the Witwatersrand Supergroup greater than ca. 2.79 Ga and is in agreement with the ca. 2.78 Ga and ca. 2.76 Ga diagenetic ages reported from xenotime (England et al., 2001; Kositcin et al., 2003) as well as a ca. 2.78 Ga detrital zircon age for the Venterspost Formation of the Klipriviersberg Group, which conformably overlies the Witwatersrand Supergroup (Barton et al., 1989). This further confirms the approximate minimum and maximum age constraints for the cessation of the Witwatersrand Supergroup deposition and the initiation of the Ventersdorp Supergroup. The Venterspost Formation was deposited conformably onto the Witwatersrand Supergroup, with the sedimentary rocks still unconsolidated with the eruption of the Klipriviersberg Group flood basalts (Chunnett, 1994). Diagenesis occurred between ca. 2.78 Ga and ca. 2.76 Ga (England et al., 2001; Kositcin et al., 2003). This has implications for gold metallogeny, indicating that the Witwatersrand Supergroup sedimentary rocks were deposited within a maximum timespan of ∼180 m.y., as opposed to the previously suggested maximum timespan of ∼256 m.y., dating gold metallogeny to ca. 2.78 Ga (Armstrong et al., 1991; Meier et al., 2009).Using the chronostratigraphic constraints above (Figs. 9A and 9B), at 2791–2779 Ma, large amounts of magmatic material were preserved in the central and northwestern regions of the Kaapvaal Craton, such as the Klipriviersberg LIP. This LIP incorporates the Klipriviersberg flood basalts that flowed across the central Kaapvaal Craton and the Kanye and Derdepoort basalts and rhyolites on the northwestern Kaapvaal Craton. This was accompanied by the emplacement of anorogenic granites, which were likely produced from crustal melting associated with an underlying mantle plume responsible for the Klipriviersberg LIP (Grobler and Walraven, 1993). These granites were emplaced along the Colesberg and Thabazimbi–Murchison lineaments, which likely reflected suture zones of thin, weaker crust susceptible to higher heat flows (e.g., Ernst, 2014). A mantle plume is shown in LIP-scale magmatism, incorporating mantle-derived komatiites and high-MgO basalts at the base of the Klipriviersberg Group as well as uplift and erosion of unconsolidated Witwatersrand Supergroup and Venterspost Formation sediments before deposition of the Klipriviersberg Group flood basalts.As extensive, short-lived magmatism of the Klipriviersberg LIP terminated, the impact of the same or potentially a different mantle plume some ∼30 m.y. later led to extension and graben development associated with volcanism and sedimentation across the central and western Kaapvaal Craton; this is now preserved as the Platberg Group between ca. 2754 and ca. 2709 Ma. In the southeastern Kaapvaal Craton, this magmatism is also now documented in the 2729 ± 5 Ma east-northeast–trending Ulundi Dike Swarm and possibly in the Amsterdam Formation, which accompanied metamorphism, core complex emplacement, and granite formation in Swaziland and adjacent areas of South Africa. Mafic magmatism in this area is also evident in sills in the Pongola Supergroup dated here to 2724 ± 7 Ma.As the grabens were filled with the Platberg Group, sedimentation and volcanism continued after a small hiatus in the Pniel Group sometime after ca. 2709 Ma, with basaltic andesites preserved as the Allanridge LIP likely erupted between ca. 2709 Ma and ca. 2683 Ma, which was possibly related to the same mantle plume responsible for the Platberg volcanic province. Once again, the LIP itself, uplift and erosion of the Platberg Group rocks, and emplacement of komatiites and high-MgO basalts at the base of the Allanridge Formation basaltic andesites provide evidence for a mantle plume. These volcanic rocks blanketed the underlying western regions of the Kaapvaal Craton, while mafic dike swarms were emplaced at 2701–2683 Ma on the eastern region of the Kaapvaal Craton in the Rykoppies Dike Swarm. The Rykoppies Dike Swarm radiates out from a focus underneath the eastern Bushveld Complex and was likely produced by a mantle plume at 2701–2683 Ma (Olsson et al., 2011), if the three pulses of magmatism proposed by Gumsley et al. (2016) are reinterpreted and reduced to two (Olsson et al., 2010, 2011) at 2701–2683 Ma and at 2664–2654 Ma, with the older pulse being responsible for the Allanridge LIP. The 2664–2654 Ma pulse was possibly associated with another LIP and renewed rifting in the so-called proto-basins to the Transvaal Supergroup and the White Mfolozi Dike Swarm, with some magma injected along the same trends as those of the Rykoppies Dike Swarm, possibly under the same stress regime or lines of weakness in the crust. This terminated volcanism on the Kaapvaal Craton during the proto-basinal phases to the Transvaal Supergroup, which included failed rifting.Baddeleyite from two mafic sills interpreted as feeders of Klipriviersberg magmatism, hosted within the Witwatersrand Supergroup on the central Kaapvaal Craton, yields U-Pb ID-TIMS crystallization ages of 2787 ± 2 Ma and 2789 ± 4 Ma. Complementary U-Pb LA–ICPMS analysis of baddeleyite grains from one of the sills yielded an similar crystallization age of 2793 ± 7 Ma. All dates above overlap within error, and a 2791–2779 Ma age is interpreted for emplacement of these sills and the larger Klipriviersberg LIP. Baddeleyite from a mafic sill in the Pongola Supergroup on the southeastern Kaapvaal Craton yielded a crystallization age of 2724 ± 7 Ma. This extends magmatism associated with the Platberg Group farther east to the southeastern Kaapvaal Craton. Additionally, an east-northeast–trending mafic dike from the southeasternmost Kaapvaal Craton, part of the newly defined Ulundi Dike Swarm, produced a U-Pb baddeleyite crystallization age of 2729 ± 7 Ma, which makes it part of the first dike swarm directly related to the Ventersdorp Supergroup (specifically the Platberg Group). Our results extend the 2791–2779 Ma magmatic event into the central Kaapvaal Craton and 2754–2709 Ma magmatism into the southeastern Kaapvaal Craton.These new data, combined with previous data associated with the 2701–2654 Ma Rykoppies and White Mfolozi magmatism, allow us to distinguish two separate LIPs within the Ventersdorp Supergroup and shortly thereafter: at 2791–2779 Ma in the Klipriviersberg LIP, at 2701–2683 Ma in the Allanridge LIP, and potentially at 2664–2654 Ma in the White Mfolozi Dike Swarm after the formation of the Ventersdorp Supergroup but before formation of the Transvaal Supergroup. The first two LIPs initiated and terminated Ventersdorp Supergroup development across the entire Kaapvaal Craton, which can be associated with magmatism of the Klipriviersberg Group and the Pniel Group, respectively. These LIPs are separated by rifting and graben development with associated sedimentation and bimodal volcanism during the formation of the 2754–2709 Ma Platberg Group during the arrival of the Allanridge mantle plume at the base of the lithosphere. These new ages also allow us to reinterpret the timing of gold deposition within the Witwatersrand Supergroup, with gold deposition in the conglomerates occurring before ca. 2.79 Ga.The authors would like to thank the staff at GSA Bulletin and editor Rob Strachan for all their assistance throughout the publication process. The authors are also grateful to the detailed and constructive review of Steve Denyszyn. Ashley Gumsley acknowledges financial support through a grant from the National Science Centre, Poland (POLONEZ grant no. UMO-2016/23/P/ST10/02423). This grant has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Actions COFUND-2014 (grant no. 665778). Funding for the U-Pb geochronology by De Beers is gratefully acknowledged. Richard Ernst was partially supported by Russian Federation mega-grant 14.Y26.31.0012. Michiel de Kock acknowledges support from the DST-NRF Centre of Excellence in Mineral and Energy Resource Analysis (CIMERA) as well as NRF incentive funding. This article is a contribution to International Geoscience Programme (IGCP) 648: Supercontinents and Global Geodynamics.

中文翻译：

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南部非洲Kaapvaal Craton上的新archean火成岩大省重新定义了Ventersdorp超群的形成及其时间上的等价物

铅锌矿上的U-Pb地质年代学是一项强大的技术，可以有效地应用于年代地层学中。在南部非洲，Kaapvaal Craton拥有保存良好的中元古代至古元古代的地质记录，其中包括Neoarchean Ventersdorp超群。它覆盖了Witwatersrand Supergroup及其世界一流的金矿床。Ventersdorp超级集团包括Klipriviersberg集团，Platberg集团和Pniel集团。但是，成立Ventersdorp Supergroup的确切时间是有争议的。在这里，我们介绍了侵入威特沃特斯兰超群的基性基岩上的2789±4 Ma和2787±2 Ma铀-Pb同位素稀释-热电离质谱（ID-TIMS）斑状沸石年龄和地球化学，我们将这些基石解释为上覆的Klipriviersberg的馈线群洪玄武岩。这将Witwatersrand超群的年龄和金矿化的年龄至少限制在了大约50岁。2.79 Ga。我们还报告了从侵入Pongola超群的基性基岩和向东-东北趋势的基性岩脉中分别获得2729±5 Ma和2724±7 Ma的U-Pb ID-TIMS年龄和地球化学。这些新时代区分了Ventersdorp超群岩浆事件中的两个：Klipriviersberg和Platberg。现在可以显示出Ventersdorp超级集团以两个大的火成岩省（LIP）开始和终结，这两个大的火成岩省是Klipriviersberg和Allanridge，被Platberg火山作用和沉积作用分开。Klipriviersberg LIP的年龄为2791-2779 Ma，而Platberg火山活动发生在2754-2709 Ma。Allanridge LIP发生在2709-2683 Ma之间。克拉普里维斯贝格，普拉特贝格，阿兰里奇岩浆作用可能与地幔柱成因有关。地幔柱撞击Kaapvaal Craton岩石圈以下导致较高的热流和地壳融化，这与裂谷和LIP的形成有关。主要的板内岩浆事件在全球范围内变得越来越好，其中许多产生了较大的火成岩省（LIP）。通过对岩浆馈层的U-Pb定年了解：铁镁质堤防群和坎ill省。尽管LIP的定义变得越来越复杂，但LIP通常被定义为面积大于0.1 Mkm2，体积大于0.1 Mkm3的主要镁铁质岩浆省（Ernst，2014）。通常，LIP放置在1-5 my内，或由多个短脉冲组成，最长可达几千万年（Ernst和Youbi，2017）和地球化学具有板内特征。此外，许多与LIP相连的黑手性堤防群和基石省都侵入了地壳上演替，并且可能是地层记录中的关键时间标志或有助于限制地球历史上关键事件的发生时间（例如，Ernst和Youbi，2017年; Gumsley等人） （2017年）。南部非洲Kaapvaal克拉顿的Ventersdorp超级群（图1）是世界上最大，最古老的主要火山上覆层演替，并且与Pilbara克拉顿的Fortescue群体积较小有关; 两者都可能在假设的Vaalbara Supercraton中是连续的（de Kock等，2009; Evans等，2017）。Ventersdorp超级集团位于Witwatersrand超级集团的世界级含金和铀的砾岩礁上。但是，建立Ventersdorp超级集团的确切时机一直是一个有争议的问题，它对Witwatersrand超级集团的终止和金矿的沉积产生了影响（Armstrong等，1991； Wingate，1998； de Kock等，2012； Amstrong等，1991）。 Cornell等人，2017）。阿姆斯特朗等。（1991年）报道了Ventersdorp超群的下部（Klipriviersberg组）和中部（Platberg组的Makwassie组）的年龄分别为2714±16 Ma和2709±8 Ma（表1），使整个火山省成为一个单一的，但脉冲状的LIP（约10我长）与地幔柱相连（例如Eriksson等，2002）。但是，有几位作者争辩说，大约在大约30年之间，形成时间更长，更老。2.78 Ga和ca. 2.71 Ga（Wingate，1998; de Kock等，2012; Cornell等，2017）。例如，康奈尔（Cornell）等人。（2017）将Makwassie组的石英斑岩重新定年为2720±2 Ma（表1），这引起了人们的质疑。Armstrong等人获得的2709Ma。（1991）对于相同的单位，以及 Klipriviersberg集团的潜在洪流玄武岩为2714 Ma年龄。从Kaapvaal Craton西北和西部地区的地层学上与Ventersdorp超群相似的单元，确定了相似的矛盾年龄（即，大于2714 Ma）（表1；例如，Wingate，1998； de Kock等。 ，2012）。这些单元与Ventersdorp Supergroup的确切相关性尚未得到证实。也有人认为Ventersdorp超群岩浆作用代表了三个脉冲或潜在的三个不同的LIP事件（Ernst和Buchan，2001; Ernst，2014）。黑手党人的门槛和堤坝侵入比Ventersdorp超级集团更早的单位（即Witwatersrand超级集团，Pongola超级集团以及Kaapvaal Craton的基底花岗岩和花岗片麻岩）为Ventersdorp超级集团提供了新的年代地层信息。此信息进一步限制了Ventersdorp超群和与时间相关的单元的时间安排和形成。结合先前的研究，我们现在第一次可以将LIP定义为在约100 my的时间内启动，发展和终止Ventersdorp超群的形成（例如，Ernst和Buchan，2001）。威特沃特斯兰德超级集团及其世界级的金矿床现在也可以证明是由约旦河的形成。约2.79加仑。南部非洲的Kaapvaal Craton保留超过 3。地质历史6 Ga，以保存完好的太古代岩石而闻名世界。随着原始克拉通稳定在约。3.1 Ga，在2056 Ma至2055 Ma期间，在布什维尔德（Bushveld）复合体侵入之前，绿岩带，绿岩碎片，花岗片麻岩和花岗岩类岩体的通透的地下基底地形上发育了一系列的五个上壳演替，不一致（Zeh et al。，2015） 。按时间顺序排列的这五个超壳层继承包括Dominion组，Pongola超级组，Witwatersrand超级组，Ventersdorp超级组和Transvaal超级组。中上古统统和威特沃特斯兰超统可以看作是Pongola上超统的地层等值（Beukes and Cairncross，1991; Cole，1994）。约300,000平方公里的新上统Ventersdorp上超统（e。例如，van der Westhuizen等人（1991，2006）是地壳上的火山－沉积层序（图1）。Ventersdorp超级群的发展归因于地幔柱边界产生的地幔柱，这导致形成了明显脉动的LIP（Hatton，1995； Ernst，2014）。在奥尔森等。（2011年），在布什维尔德综合体下提议建立一个Ventersdorp LIP地幔柱中心。Ventersdorp超级集团包括基底的Klipriviersberg组，其次是Platberg组，Bothaville组，最后是Allanridge组。最后两个编队包括Pniel组（南非地层委员会（SACS），1980年）。在其基地，Ventersdorp超级集团与Witwatersrand超级集团因Kaapvaal Craton中部的不整合而分开（例如，van der Westhuizen等，2006）。但是，在盆地中心的偏远地区，零星发育的Venterspost组砾岩（也称为Ventersdorp接触礁或VCR）存在一致关系（例如，Pelletier，1937； Chunnett，1994）。这种形式让位于ca。2714 Ma Klipriviersberg组洪水玄武岩（Winter，1976； Armstrong等，1991）。在南非的西北省和博茨瓦纳西南部（图1），Derdepoort组内岩性地层学上类似的洪水玄武岩序列与Klipriviersberg组有关（例如，Tyler，1979年）。然而，温盖特（1998）在2782±5 Ma推断出了Derdepoort组，使他认为Armstrong等人的年龄为2714±16 Ma。（1991年）作为克里夫里斯堡山群火山活动的最低年龄。Derdepoort组也与博茨瓦纳西南部和南非西北省附近的双峰火山岩和深成岩单元同生。在该地区（图1），Lobatse组和Kanye组的年代也已定为约3个月。2785 Ma and约。2781 Ma（表1; Grobler和Walraven，1993; Moore等，1993; Walraven等，1996），而Modipe Complex长辉岩和Gabarone Complex花岗岩（图1）的年龄介于2784 Ma和2779 Ma之间，分别（Grobler和Walraven，1993； Moore等，1993； Mapeo等，2004； Denyszyn等，2013）。唯一的迹象表明，这个年代久远的岩浆事件系列在空间上可能更有意义，这是在西南约480 km的金伯利附近钻芯中的一个钠铁矿的年龄为2781±5 Ma（图1; Cornell等。 ，2017）。因此，据推测，克利普里斯堡银行集团是该公司的一部分。2.78 Ga岩浆脉动（Wingate，1998; de Kock等，2012），但在此研究之前，Kaapvaal Craton的中部地区（Klipriviersberg群的典型地区）未报告过这样的年龄。将Klipriviersberg集团与Platberg集团分开（van der Westhuizen等，2006）；克利普里维斯贝格集团的火山活动终止后，普拉特贝格集团在众多抓斗和一半抓斗中形成（Winter，1976； Stanistreet和McCarthy，1991）。普拉特贝格组最好在Kaapvaal Craton中部和更西端的西部Witwatersrand超群之上发展（图1；例如Tankard等，1982）。典型的普拉特伯格集团（Platberg Group）抢夺型接班人包括基础，Kameeldoorns组的粗粒沉积岩，然后是Goedgenoeg组的镁铁质火山岩和Makwassie组的长胶质火山岩（Winter，1976; Armstrong等，1991; van der Westhuizen等，2006） ）。在某些情况下，层状的镁铁质火山岩和沉积岩（即Rietgat组）在典型的演替层之上发育，但其发生仅限于重新活化的grab石（van der Westhuizen等，2006）。Graben-fill的特征是快速的相变和楔形的几何形状（de Kock等人，2012），可能的破火山口形成解释了过厚的地层（Meintjes和van der Westhuizen，2018a）。Makwassie组已由Armstrong等人定年。（1991）在2709±8 Ma，最近由Cornell等人。（2017）在几个地方在2720±2 Ma（表1）。康奈尔等。（2017）进一步提出了潜在的Goedgenoeg形成年龄2746±9 Ma（表1）。这些年龄由康奈尔等。（2017）Platberg组与Ventersdorp超级组的许多岩性相关物的年龄限制相一致，这些年龄限制因孤立grab沟中非连续露头而以各种名称描述（图1； van der Westhuizen等人，2006年）。 ）。这些包括2739±10 Ma的钠基团（Altermann和Lenhardt，2012），2714±3 Ma的Zoetlief组（Walraven等，1991），2729±3 Ma的Amalia组（Poujol等，2005），以及2733–2724 Ma Hartswater Group（de Kock等，2012）（见表1）。有人提出，Platberg集团同等人之间的年龄差异是整个Kaapvaal Craton grab抓发展的结果（de Kock等，2012）。所有这些U-Pb年龄都与年轻的ca. 2714年Klipriviersberg集团的年龄，该集团位于Platberg集团的地层之下。所谓的Pniel集团以不整合（Winter，1976年）的形式覆盖了Platberg集团（Stanistreet and McCarthy，1991年）。Pniel集团覆盖了Kaapvaal Craton中部和西部的广阔地区（van der Westhuizen等，2006）。Pniel集团的基础是Bothaville地层，由向上聚集的砾岩和砂岩组成（Visser和Grobler，1985年）。Allanridge组的玄武质安山岩（Winter，1976年）与下层的Bothaville组一致（van der Westhuizen等人，2006年）。Pniel组尚未直接标出日期，但Kaapvaal Craton西南边缘的岩体-地层学上等效的Zeekoebaart组可使用的最大年龄限制为2720±4 Ma（图1和表1; Cornell等人，2018） 。最小年龄限制来自布佛斯方丹组中上覆的德兰士瓦超级组底部火山岩的2664±1 Ma年龄（表1； Barton等，1995）。阿拉根里奇组归因于普拉特贝格组火山活动停止后，Kaapvaal Craton再次裂陷和热沉降（Burke等，1985； Clendenin等，1988）。de Kock等人总结了在稳定的Kaapvaal Craton上的黑手党堤防安置。（2019），第一个已知的堤防群发生在大约 约2980 Ma 2966 Ma，东南向的Kadvaal Craton东南地区有Badplaas Dike Swarm（Olsson等，2010； Gumsley等，2015）。这些堤防在时间和空间上与庞哥拉超群的Nsuze群和Usushwana复杂群的Piet Retief套房相关（Olsson等，2010； Gumsley等，2015）。后来在庞古拉超级集团（Pongola Supergroup）内的镁铁基石省发现了进一步的镁铁质岩浆作用，包括2866±2 Ma Hlagothi Complex（Gumsley et al。，2013; 2015）。然后将Modipe复合体放置在2784±1 Ma处（图1和表1； Denyszyn等，2013），在时间上与附近的Derdepoort和Kanye组内的Gabarone Complex花岗岩和火山作用有关（Grobler和Walraven，1993; Moore等，1993; Walraven等，1996; Wingate，1998; Mapeo等，2004）。在Kaapvaal Craton的西北地区。大约在我后来的80年代，铁镁质岩浆作用被再次记录下来。2701 Ma和大约。Kaapvaal Craton东部和东南部地区的2654 Ma（图1和表1; Olsson等，2010，2011; Gumsley等，2016）。这包括2701±11 Ma至2659±13 Ma Rykoppies Dike Swarm，似乎从2056-2055 Ma Bushveld复杂构造的下方放射出去（Olsson等，2011； Zeh等，2015）和2664-2654 Ma东北趋势的白色Mfolozi堤防群（表1； Gumsley等，2016）。Rykoppies和White Mfolozi Dike Swarms可能标志着与Ventersdorp超群有关的岩浆作用终止于大约。2.65 Ga，因为这些堤防群还与Buffelsfontein组（Barton等，1995）的德兰士瓦超级组以及其他原流域同时具有2664±1 Ma的原始基底火山活动。最后，有所谓的Kopenang堤防，由Meier等人记录在案。（2009年）在Witwatersrand超群内的Kaapvaal Craton的中部地区，尽管它们具有随机趋势。Meier等。（2009年）将这些铁基岩堤在地球化学上与Klipriviersberg集团联系起来。然而，它们的确切关系尚待证实。在这项研究中，检查了三个铁镁基石样品和一个来自铁基岩堤的样品（表DR11）。两个样本，分别为AM1和VJ1，采自南非自由州省Kaapvaal Craton中部地区Ventersdorp超群类型区域之一附近的钻芯（图1）。另外两个样本是PRGE和ENED08，它们是从南非Kaapvaal Craton的东南部（普马兰加省）和最东南部（夸祖鲁-纳塔尔省）的露头中收集到的（图1）。前寒武纪地层，尤其是在Kaapvaal Craton中部地区的Witwatersrand超群内。许多基岩厚约100 m以上，其中包括所研究的基岩，其地层在Klipriviersberg组的洪水玄武岩之下。基石与它们侵入的Witwatersrand超群地层一起微弱地变形和变形。AM1和VJ1铁基石门槛位于Klerksdorp和Welkom以东，但在Vredefort Dome圆顶以南。窗台从威特沃特斯兰德超级集团侵入西兰德集团的政府子集团（图2）。样品VJ1是从伊甸维尔东北约10 km的钻芯中收集的，深度约1200 m，基岩厚度约1400 m，并侵入了Palmietfontein组的砂岩中。AM1样品是从Steynsrus以北约10 km的钻芯中收集到的（图2），来自一个约110 m厚的镁铁基岩，深度约1800 m，该基岩侵入了Afrikaner地层的砂岩中。 ，是在东南部的普马兰加省Piet Retief和阿姆斯特丹之间的道路附近采样的（图3A）。露头在常绿农场和雷德克里夫农场之间的边界上，镁铁基岩侵入雷克利夫组。雷德克里夫地层，由页岩和带状铁地层组成，已被归类为庞哥拉超群的莫扎恩集团。黑手党窗台本身以前归因于Usushwana建筑群的2990–2978 Ma Piet Retief套房（Hammerbeck，1982； Gumsley等人，2015）。样品ENED-08来自东-东北向的黑手党堤防。靠近乌伦迪和弗赖海德之间的怀特·姆福洛兹河（图3B）。堤防侵入了夸祖鲁-纳塔尔省北部的白色姆福洛兹内陆地区的3254-3234 Ma花岗片麻岩基底（Reinhardt等人，2015），是黑手党堤防群的一部分，在这里被称为乌伦迪堤防群。反过来，该堤防群被2664–2654 Ma斜长石-大晶，东北-趋势的白色Mfolozi堤防群（Gumsley等人，2016）切断。进一步，采样的堤防切割了一条未标注日期的东南趋势的铁镁质堤防；两者依次被约割。2423 Ma Mafic sheet（Gumsley等，2017）。这些铁镁质单元上的一些地球化学和古磁性学由Klausen等人进行。（2010）和Lubnina等。（2010）。薄切片的岩石学分析是在卡托维兹西里西亚大学地球科学研究所进行的，使用了Olympus BX-51光学显微镜。使用CAMECA SX-100电子微探针在华沙大学矿物与合成物质微分析机构间实验室进行了主要成岩矿物和副矿物的矿物化学分析。分析条件采用加速电压15 kV，束电流20 nA，峰和背景的计数时间为4 s，束直径为1-5μm。参考物质，分析线和平均检出限（以重量％计）可见表DR2（见脚注1）。衍射晶体包括LIF，PET，TAP和LPET。对于全岩石地球化学，样品选自镁铁基石和风化岩去除后的堤坝中最均匀的部分。然后将它们手工压碎并在碳化钨环磨机中研磨。然后，将所得的材料锥化并切成四等分，然后发送到加拿大温哥华的必维国际检验集团进行主要，次要和痕量元素的分析。对由粉末状样品制成的玻璃微珠进行分析，样品与助熔剂（四硼酸锂）的比例为1:10，然后将所得的熔融微珠在弱硝酸溶液中快速消解。电感耦合等离子体发射光谱法（ICPES）用于主要和次要元素，电感耦合等离子体质谱法（ICPMS）用于痕量元素，包括稀土元素（REE）。每个样品的挥发物含量通过灼烧损失（LOI）确定。使用地球化学数据工具包（GCDkit；Janoušek等人，2006）将数据绘制在图表中。通过同位素稀释-热电离质谱（ID-TIMS）和激光烧蚀对采样单元进行了斑脱石U-Pb定年处理。 （LA）–ICPMS分析方法。在隆德大学的LA-ICPMS实验室中，使用LA-ICPMS方法论来测试两种独立方法之间的可重复性。手工粉碎样品，并使用地质学系的铬钢环磨机将其研磨成粗粒粉末，隆德大学。Söderlund和Johansson（2002）开发的水基分离工艺用于提取ID-TIMS的斑脱钙石颗粒。然而，只有VJ1可以产生适合LA-ICPMS尺寸的长晶钙锰矿晶粒（长于60μm，宽20μm）。提取的阔晶锂晶粒被分成几部分，然后在乙醇中转移到预先清洗的特富龙胶囊中。将级分在超纯HNO 3和H 2 O中洗涤数个循环。将少量的236–233U-205Pb示踪剂溶液和超纯的HF：HNO3（10：1）混合物添加到每个特富龙胶囊中。在约190°C下放置三天后，该脱钙沸石级分完全溶解在烤箱中。将胶囊放在约100°C的加热板上，直到HF溶液蒸发为止。超纯0.25 M H3PO4和6。向每个胶囊中加入2 M HCl，并在电热板上再次干燥。将聚四氟乙烯胶囊中剩余的样品液滴与2μl制备的Si凝胶混合，并置于脱气的Re灯丝上。加热脱气的Re灯丝上的样品，直到H3PO4烧尽。然后将所得的细丝放在斯德哥尔摩瑞典国家历史博物馆地球科学系Finnigan TRITON热电离质谱仪内的转盘中。质谱仪配备有二次电子倍增器和法拉第杯，将Re灯丝和样品加热到约1210°C至约1250°C之间的温度，其中同位素质量的强度为204Pb，205Pb，206Pb，207Pb，在逐渐升高的温度下，在20至140之间的循环中测量了208Pb和208Pb。使用法拉第杯在静态模式下或使用二次电子倍增器进行峰值切换的动态模式下测量Pb信号强度。233U，236U和238U的同位素质量在约1300°C至约1340°C的温度下以升高的温度测量为氧化物。遵循Hiess等人的方法，使用238U / 235U = 137.818由238U计算得出235U。（2012）。未检测到由于18O的干扰引起的显着差异，因此未进行更正。在动态模式下进行了40至80个循环的测量。使用Ludwig（2003）的算法，使用“内部” Microsoft Excel程序进行初始数据缩减。但是，Ludwig（2012）的Microsoft Excel宏Isoplot 4.15使用了Jaffey等人的U衰减常数。（1971），用于最终数据计算和协和图。使用来自Stacey and Kramers（1975）的全球通用Pb演化模型的同位素组成，在样品年龄时进行了初始通用Pb校正。日期中的误差传播以2σ给出，不包括衰减常数误差。将样品VJ1中的辉绿岩晶粒放在双面胶带上，并安装在1英寸宽的特氟龙环中的环氧树脂中，使其硬化三天。然后将硬化的环氧树脂支座与胶带分离，并使用Struers Rotopol-22自动抛光机用9μm，3μ和1μm的金刚石浆料抛光20 s至140 s。随后用乙醇清洁底座。使用的参考物质是来自Phalaborwa配合物的Baddeleyite，其年代为2059.60±0.35 Ma（Heaman，2009）。分析是在隆德大学地质系的LA-ICPMS实验室进行的。LA-ICPMS使用193 nm Analyte G2激光烧蚀单元，带有两个体积的HelEx样品架和Aurora Elite四极杆电感耦合等离子体质谱仪。使用20μm的光斑直径，以5 Hz的重复频率进行消融，通量约为4 j / cm2。每次分析的总采集时间为55 s，其中前20 s用于确定Ar / He / N2气体空白，然后进行28 s激光烧蚀和3-4 s冲洗延迟。将氦气载流子在下游与Ar和N2混合，然后进入“蠕动”信号平滑装置，该装置由几根管子组成，这些管子将气流分开并在进入等离子体之前重新加入。使用NIST612玻璃对质谱仪进行校准，得到稳定的206Pb，207Pb，238U信号和低氧化物生成率（低于0.5％的238U16O / 238U）和232Th / 238U比约为1。使用二次电子倍增器确定202Hg，204（Pb + Hg），206Pb，207Pb，208Pb，232Th，235U和238U的强度。假设202Hg / 204Hg比为4.36（自然丰度），则通过测量202Hg来监控204Hb对204Pb的干扰。尽管测量了235U，但根据Hiess等人的方法，使用238U / 235U = 137.818从238U计算出207Pb / 235U。（2012）。激光诱导的元素分馏和仪器对测得的同位素比率的质量偏差通过使用Phalaborwa baddeleyite标准品进行的标准样品包围校正（Heaman 2009）。按照以下顺序总共进行了36次分析：六个标准，然后是七个未知数（即VJ1），四个标准，六个未知数，四个标准，五个未知数和四个标准。使用Iolite软件（Paton等人，2011）和Paton等人的U-Pb年代学数据缩减方案例程完成数据缩减。（2010）。井下分级和仪器漂移的校正程序已在Iolite软件中应用。使用Stacey和Kramers（1975）的陆地Pb同位素组成，使用Petrus和Kamber（2012）的VizaulAge在Iolite软件中进行了常见Pb校正。所有年龄数据均使用Isoplot 4.15（Ludwig，2012）进行计算，该数据也用于绘制和评估数据。报告数据中的误差传播以2σ给出，不包括衰减常数误差。研究的四个样本具有典型的镁铁质侵入岩的矿物组合（表DR1）。主要的成岩矿物主要是斜生长石（An41Ab59–An18Ab82；图4A），带透辉石的区域（Fe2 + / Mg从核中的0. 46到边缘的0.82；表DR3（参见脚注1）；图4B）和钛铁矿（Ti0.96-1.00Fe0.90-1.00Mn0）。 04–0.07O3）与含钛磁铁矿（Fe2 + 1.08–1.13Fe3 + 1.69–1.80Ti0.09–0.14O4；表DR3；图4B–4C和4E）共生。氟磷灰石和baddeleyite是常见的辅助矿物。黄铁矿和黄铜矿晶粒被认为是辉石中的夹杂物。通过角闪石（阳起石）和ferrian-ferro-hornblende的边缘部分完全取代辉石（透辉石）观察到了变质的叠印（图4A-4B；表DR3）。钛铁矿和钛铁矿-磁铁矿共生体上的次生含铝钛矿轮缘提供了进一步的变质证据（图4D）。局部黑云母（Ti = 0.37–0.43 apfu； #fm = 0.64–0.67；表DR3）的形成是以不透明矿物质为代价的（图4B）。后期的亚氯酸盐-静电石脉切开了岩石。变质作用是绿片岩相变质条件的典型特征。样品还显示了斜长石的绢云母化和镁铁硅酸盐和铝硅酸盐的氯化作用后，出现了二次低温变化。变化最小的样本是PRGE和AM1，而其他两个样本显示出普遍的变化（表DR1）。PRGE样品显示了石英和碱长石（Or79–56，Ab36–17An1–5）的图形共生关系，在镁铁质相簇之间形成了地基（图4C和4E）。整个岩石主要和微量元素组成表DR4中列出了铁镁基石和堤坝（请参见脚注1）。先前研究的数据（Crow和Condie，1988年； Marsh等人，1992年。Nelson等，1992；Meier等，2009；Klausen等，2010；Gumsley等人，2016；Meintjes和van der Westhuizen，2018b）用于比较，并在表DR5中显示（见脚注1）。使用小于10％的LOI过滤数据以说明广泛的变化。可以在Humbert等人的文章中找到对Ventersdorp超群的地球化学和岩石成因的全面回顾。（2019）。本研究中的镁铁质基岩（AM1和VJ1）跨越Zr / Ti-Nb / Y分类图中的玄武岩和玄武质安山岩/安山岩田（图5A; Pearce，1996; Winchester and Floyd，1977），和与Klipriviersberg Group的玄武岩和Kopenang堤防相似，Nb / Y和Zr / Ti最低。基性基岩PRGE和基性岩堤ENED08处于Platberg Group火山岩（和Rykoppies Dike Swarm）的玄武岩和玄武质安山岩/安山岩范围内，在Zr / Ti中为双峰，而在Dacites / Rhyolite中的Zr / Ti较大。 Makwassie组。阿拉兰奇组玄武质安山岩的Nb / Yb稍高，但与Platberg组的Zr / Ti组较低。但是，白色Mfolozi堤防群在地球化学上与其他族群不同，其Zr / Ti和Nb / Yb较低。在原子力显微镜图中（Irvine and Baragar，1971），样品AM1和VJ1以及Klipriviersberg组的玄武岩和Kopenang堤防在钙碱性较弱的胆甾型玄武岩田中绘图（图5B）。样本PRGE和ENED08再次显示出与Platberg Group基性火山岩的相似之处，Rykoppies Dike Swarm和Allanridge形成的玄武安山岩，具有更多的钙碱性分化趋势。使用Th / Yb-Nb / Yb图（Pearce，2008），AM1和VJ1紧邻Kopenang堤防和Klipriviersberg组玄武岩，而PRGE和ENED08样本则位于Platberg Group Rykoppies的镁铁质火山岩附近。 Dike Swarm和Allanridge组玄武质安山岩（图5C）。这些样本显示的Th / Yb值比朝向现代火山弧阵列的大洋中脊玄武岩-海洋岛玄武岩（MORB-OIB）阵列更大，除了白色Mfolozi Dike Swarm（在MORB-OIB阵列中绘图）。在Platberg Group火山岩，Rykoppies Dike Swarm，与Klipriviersberg Group玄武岩和Kopenang堤防（包括镁铁基石（AM1和VJ1））相比，本研究中的Alanridge组玄武质安山岩以及堤坝（ENED08）和窗台（PRGE）。最后，在Th / Ta–La / Yb图（图5D； Ernst，2014，Condie，2003年之后）中，样本AM1和VJ1（包括Klipriviersberg组玄武岩和Allanridge组玄武岩安山岩）在大陆洪水玄武岩中作图（或CFB字段）。然而，来自Allanridge组玄武质安山岩和Rykoppies Dike Swarm以及ENED08和PRGE的样品的La / Yb较高。Kopenang堤的La / Yb值与Klipriviersberg组的玄武岩以及VJ1和AM1样品相似，但Th / Ta值较高，这导致其位置移到CFB场上方。ENED08和PRGE样品的Th / Ta和La / Yb高于VJ1和AM1样品，并且位于Platberg Group火山岩上方。这时，白色Mfolozi堤防群的样品在地球化学上明显不同于Kaapvaal Craton上的任何其他单元。在球粒陨石归一化REE图和原始地幔归一化多元素图中（图6A-6D； McDonough和Sun， （1995年），样品AM1和VJ1与Klipriviersberg Group玄武岩和Kopenang堤防大致相似。相对于重稀土元素，这些样品在轻稀土元素中略有富集，而没有明显异常。然而，与AM1和VJ1以及Klipriviersberg Group玄武岩和Kopenang堤防相比，PRGE和ENED08的REE水平升高。样品PRGE具有诊断丰富的REE模式，如Platberg Group火山岩，尤其是Makwassie组流纹岩和dacites，而ENED08具有类似的模式，但与VJ1和AM1相比，其富集程度略强于Rykoppies Dike Swarm和阿拉兰奇组玄武岩安山岩。只有PRGE表现出负Eu异常，与重REE相比，PRGE和ENED08的轻REE含量都更高。除Cs，Rb，Ba，Th和U等可移动元素外，所有样本均具有负Nb和Ta异常，负Ti和负Eu异常.Söderlund和Johansson（2002）的水基分离过程VJ1和PRGE分别产生约40粒斑竹，而AM1则产生30粒，而ENED08仅得到20粒。在VJ1，AM1和ENED08样品中分析出的最佳品质谷物为浅棕色，通常是透明的，有一些轻度至中度的霜冻，VJ1的长度在50μm至60μm之间，AM1的长度在30μm之间。ENED08的块状钙钛矿晶粒长在20μm至30μm之间。样品PRGE的斑脱钙石晶粒为深棕色，通常澄清，略微结霜，长度约为40μm。表DR6和DR7中列出了U和Pb同位素测量值（见脚注1），图7和8中的数据绘制在Wetherill共生图上。分析了VJ1中的4种残渣，由2至3种残渣组成。每粒（图7A）。这些分数的回归产生了2787±2 Ma的精确上截距数据（加权平均偏差[MSWD] = 1.5）。可能由于锆石的变化，三部分之间的不一致程度在2％至1％之间，第四部分之间的不一致之处为6％。最不协调的分数限制了295±98 Ma的较低截距。三个最不协调的分数的加权平均207Pb / 206Pb日期为2785±1 Ma（MSWD = 0.67）。排除第四部分，因为它不在其他三个部分的207Pb / 206Pb日期的误差之内。AM1的两个部分分别由六个斑晶石颗粒组成，产生的初步上截距日期为2789±4 Ma（图7B），这在VJ1日期的误差范围内。回归得出的初步较低的自由截距数据为106±190 Ma。这两个部分的不一致性为5％和2％，其中207Pb / 206Pb的日期介于大约之间。2788 Ma和大约。2786马。对于样品ENED08，分析了三个斑脱钙石馏分，每个都有三个晶粒（图7C）。自由回归的截距上限和下限分别为2729±5 Ma和228±57 Ma（MSWD <0.1）。两个分数在6％和5％之间不一致，并且在大约之间存在207Pb / 206Pb日期。2723 Ma和大约。2722 Ma，第三部分分数不一致，可能是锆石改变的结果，并限制了较低的截距，样品PRGE的最高截距为2727±3 Ma，较低的截距为540±280 Ma（MSWD = 0.71）的分析方法是对4种残次钙铝石进行分析（图7D）。不一致性在10％和0％之间变化，三个最小不一致性分数介于1％和0％之间。在这三个最不协调的日期计算出的加权平均207Pb / 206Pb年龄为2724±7 Ma（MSWD = 3.3）。由于不在其他三个馏分的207Pb / 206Pb日期的误差范围内，因此排除了第四馏分。表DR7给出了Phalaborwa Complex参考材料（Heaman，2009）的分析结果（参见脚注1）。在序列中测得的VJ1的207Pb / 206Pb比率之间没有观察到显着差异，但是同位素数据显示出可变的不一致性（在〜17％和〜1％之间），在Wetherill Concordia图中形成了不一致的阵列（图8A）。使用所有数据（表DR8；请参见脚注1），我们获得较高的截距日期2799±15 Ma（MSWD = 3.4）和加权平均207Pb / 206Pb日期2796±6 Ma（MSWD = 3.2；图8B）。 。使用LA–ICPMS分析确定晶粒的真实U-Pb日期的困难可能是由于校正常见Pb的困难。在显示的数据中，平均质量204背景信号相对较高，约为每秒1900个计数，这增加了无法检测到少量普通Pb的风险。当检测到接近检测限的同位素时，无法量化浓度。但是，通过将206Pb / 204Pb与常见的Pb校正日期和未校正的207Pb / 206Pb日期作图，我们发现对于206Pb / 204Pb较低的分析，年龄差异有所增加，这主要表现为减少的常见Pb校正日期。这支持以下观点：一些晶粒包含少量的常见Pb，但是我们似乎对数据进行了过度校正，如206Pb / 204Pb比率低于9000时所观察到的。使用所有未校正的数据，我们得出的最高截距日期为2799±15 Ma （MSWD = 3.4），加权平均207Pb / 206Pb日期为2796±6 Ma（MSWD = 3.2）。仅使用来自高于9000的206Pb / 204Pb的分析中的未校正数据，我们获得了2798±12 Ma（MSWD = 1.9）的较高截距日期和2793±7 Ma（MSWD = 1.7）的加权平均值207Pb / 206Pb日期；图8B ）。如所观察到的，在不确定性的范围内，这些年龄估计之间没有显着差异。但是，我们更喜欢使用可以说受普通Pb影响最小的数据，因此，与ID-TIMS数据一样，使用较高的截距，我们对VJ1的最佳日期估计为2798±12 Ma。 VJ1的Pb ID–TIMS数据产生的最高截距日期为2787±2 Ma（MSWD = 1.5），且在LA–ICPMS结果的分析不确定性以及2789±4 Ma的初步AM1日期范围内也可以通过自由回归获得。在三个最不协调的分析中，这是首选年龄，而不是加权平均207Pb / 206Pb年龄，即2785±1 Ma（MSWD = 0.67），因为没有数据与协和重叠，使得加权平均日期成为最小年龄。尽管较低的截距接近于0 Ma，这表明最近有Pb扰动，但仍超出295±98 Ma的不确定性，因此可能在更早的时间发生同位素扰动。这被解释为可能是183-179 Ma的Karoo岩浆事件（Duncan等，1997）。相对精确的2787±2 Ma日期是我们首选的结晶年龄，因为ID–TIMS通常可以进行可靠的common-Pb校正。值得注意的是，ID-TIMS分数的不一致性约为3％，即比LA-ICPMS分析的相差小得多。ENED08的结晶年龄也被解释为2729±5 Ma（MSWD <0。01）使用自由回归，因为没有分析与一致意见重叠，铅的干扰也可能归因于Karoo岩浆作用。PRGE的上限拦截日期为2727±3 Ma（MSWD = 0.71）。但是，与协和重叠的三个最不协调的分数的加权平均207Pb / 206Pb日期为2724±7 Ma（MSWD = 3.3）。因此，加权平均207Pb / 206Pb日期是PRGE的首选结晶年龄。图6所示的所有岩浆事件的不相容元素模式都不同，但是除了白色Mfolozi堤堰群以外，它们都显示出与俯冲有关。 ”或“类似弧的”签名（例如，Pearce，2008年； Ernst，2014年； O'Neill和Jenner，2016年； Humbert等人，2018年； 2019年），其特征是负Nb和Ta异常。这些特征在Kaapvaal Craton的许多太古代和古元古代镁铁质岩石中很常见（例如，O'Neill和Jenner，2016年; Humbert等，2018年; 2019年）以及世界其他地区的其他板内事件（包括LIP）（例如，Pearce，2008； Ernst，2014）。这些事件还绘制了比MORB-OIB阵列更高的Th / Yb和Th / Nb值（图5C）。根据Pearce（2008）的研究，Th比Nb的优先富集可能表明地壳受到污染或被过去俯冲作用流体化的岩浆和/或岩石圈地幔源的同化。实际上，通过Platberg组（平均εNd2720Ma= –3.4）和Allanridge组（平均εNd2700Ma= –3.0）的全岩石Sm-Nd同位素数据可以推断出严重的地壳污染，Klipriviersberg岩浆来源的平均εNd2780Ma= 0也可能受到较小程度的污染（Humbert等人，2019）。请注意，到目前为止，尚无其他事件的同位素数据。另外，PRGE样品中的石英和长石的碱土可以解释为富硅物质同化引起的局部混合混合现象的结果（例如Burda等，2011）。它也可以简单地代表与裂谷有关的大陆内玄武岩浆的高度分离部分。白色Mfolozi Dike Swarm的样品在地球化学上明显不同于Kaapvaal Craton上的任何其他单元（图5和6）。它们的Th / Yb，Nb / Yb，Th / Ta和La / Yb之比特别低，以及与稀土/痕量元素图中球粒陨石/原始地幔相比的“平坦”和适度丰富的特征。White Mfolozi堤防群样本在图5C和5D中绘制为接近原始地幔，并且可能来自此类来源。相反，它们也可能是由贫化的地幔源（即类似NMORB的地幔源）产生的，后来该地壳受到了轻微的地壳污染。此处首次记载的日期为2787±2 Ma和2789±4 Ma的铁镁基石VJ1和AM1 Kaapvaal Craton中心地区发生了该岩浆事件（图9）。这些窗台位于地层上，位于维特沃特斯兰德超级集团的温特斯多普超级集团的Klipriviersberg集团洪水玄武岩之下，并被解释为可能与它们有关。进一步，这些镁铁质基岩在地球化学上与克里夫里斯堡山群的玄武岩极为相似（图5和图6；例如，Winter，1976； Marsh等，1992； Humbert等，2019）。Meier等。（1）（2009）已经显示了镁铁质馈线的地球化学特征与Klipriviersberg群洪水玄武岩相似，其形式为Kopenang堤防侵入了同一地区的Witwatersrand超群（图1）。因此，可以合理地解释，本研究中分析的镁铁基岩AM1和VJ1属于以镁铁质侵入体为代表的单一岩浆系统，该侵入体为Klipriviersberg组上覆的玄武岩提供了营养。如图9所示，我们现在已经认识到发生在Kaapvaal Craton中部，西部和西北地区的2791–2779 Ma岩浆事件。在这项研究中，来自Kaapvaal Craton中部的镁铁质基岩AM1和VJ1与双峰式火山岩Kanye地层及其深成等量的Gabarone Complex花岗岩同时存在。Kanye组被认为是Swartruggens槽中Ventersdorp超群的原始基性或前体相（Tyler，1979； Ernst，2014）。附近的Derdepoort组和Modipe Complex辉长岩的年代分别为2782±5 Ma和2784±1 Ma（表1; Wingate，1998; Denyszyn et al。，2013）。这些单位最初与Klipriviersberg Group洪水玄武岩以及Ventersdorp Supergroup的其他单位相关（Tyler，1979年）。在Kaapvaal Craton西部和西北地区的Amalia-Kraaipan花岗岩-绿岩地层中也记录了类似的老化单元（图9A和9B）。这些包括Mosita，Mmathete和“红色”花岗岩，以及Makoppa圆顶中的Turfloop和Rooibokvlei花岗岩（例如Grobler和Walraven，1993； Moore等，1993； Mapeo等，2004； de Kock）。等人，2012； Denyszyn等人，2013； Ernst，2014）。该岩浆事件也记录在来自Ventersdorp和Transvaal超群的碎屑锆石数据中（图9A和9B;表DR9和DR10;见脚注1）。此外，本研究为Klipriviersberg Group洪水玄武岩提议的年龄不同意。由Armstrong等人获得的2714±16 Ma年龄。（1991年）来自Klipriviersberg Group洪水玄武岩的类型区域。这是除本研究之外，在本研究中日期的镁铁质基岩区域中唯一发生的火山事件。Witwatersrand超群的2914 Ma Crown地层熔岩（Armstrong等，1991;图 9A）。然而，阿姆斯特朗等人提出的年龄。Wingate（1998），de Kock等人（1991）对Klipriviersberg Group的洪水玄武岩提出了质疑。（2012），康奈尔（Cornell）等人。（2017）和Humbert等人。（2019）。阿姆斯特朗等人的重新计算。（1991年）的同位素数据使用最少不一致性分析。2.7 Ga和ca. 1.0 Ga的最高截距为2757±57 Ma，较低的截距为1082±140 Ma。如Wingate（1998）最初显示的，该结果表明形成较年轻ca的岩浆/变质事件。1.0 Ga锆石的生成可能影响了ca。2.7 Ga锆石，应视为洪泛玄武岩的最低结晶年龄。Platberg组（位于Makwassie组）及其地层等值之一（例如，Hartswater组）也对Klipriviersberg组的年龄增加了时间限制，表明年龄较大（例如，de Kock等，2012； Cornell等，2017）。此外，巴顿等。（1989年）分析了构成Klipriviersberg组基础的Venterspost组的碎屑锆石，并获得了最大年龄2780±5 Ma来沉积最年轻的一致锆石颗粒。上述岩浆事件符合标准根据Ernst（2014）的规定，适用于LIP。如图9所示，我们现在可以重新定义此事件，以包括Klipriviersberg Group洪水玄武岩和中世纪基性基石，Kanye和Derdepoort双峰火山岩以及与时间相关的Gabarone Complex和Modipe Complex Complex花岗岩和辉长岩以及更远的花岗岩向西（图9B）。LIP的面积约为250,000 km2，玄武岩包裹的厚度可达2 km。岩浆区域的更多物质可能已被侵蚀掉，如大约在加利福尼亚州的广泛碎屑锆石光谱峰所示。2.78 Ga。属于这个新定义的Klipriviersberg LIP的所有单位的年龄范围是2791-2779 Ma，尽管通过更现代的方法，该年龄范围可能会进一步缩小。此外，洪水玄武岩中没有任何中间的沉积层或不整合面，这进一步提供了岩浆事件持续时间短的证据.Klipriviersberg LIP发生岩浆裂隙之后，西部的大规模裂谷，沉积和火山作用占主导地位以及2754 Ma和2709 Ma之间的Kaapvaal Craton中部（de Kock等，2012; Cornell等，2017）。在东部的Kaapvaal Craton，同时放置了许多花岗岩（例如，Hofmann等，2015），Taylor等（2015）。（2010年）认为可能与沉积Ventersdorp超群的延伸和岩浆作用有关（图9A和9B；表DR9和DR10）。在这项研究中，来自Kaapvaal Craton东南部侵入Pongola超群的基性基岩PRGE的年代为2724±7 Ma，因此与这一广泛的岩浆事件相吻合。从地球化学角度看，该基岩类似于普拉特贝格组内的火山岩，特别是马克瓦西组（图5和6）。在门槛附近，阿姆斯特丹编队是唯一可以与其联系的单位。阿姆斯特丹地层不整合地覆盖在Pongola超群之上，是由阿姆斯特丹附近的Gobosha成员dacites和Piet Retief附近的Vaalkop成员流纹岩组成的火山演替（Hammerbeck，1982）。该基石在地质和地球化学上类似于阿姆斯特丹地层的戈博夏（Gobosha dacites）（Hammerbeck，1982），因此被认为是阿姆斯特丹地层火山岩馈线系统的可能部分。这种解释意味着阿姆斯特丹组与普拉特伯格组最东端等效（图9B）。此外，据报道，在Mkondo Suite的更东边，日期为2730±5 Ma的隐性粒体表明粒岩相变质了（Taylor等，2010）。我们在一个古老的东西方趋势大堤上对ENED08的年龄为2729±5 Ma，在Kaapvaal Craton的最东南部建立了一个新发现的大堤群。这种堤防群，我们称为“乌伦迪堤防群”（图1和图3），是第一个与Ventersdorp超群的普拉特伯格群相关的堤防群，并将这一岩浆事件扩展到了东南部。ENED08堤防被2664–2654 Ma White Mfolozi堤防群（Gumsley等人，2016）的斜长石巨晶东北趋势堤防（以及Gumsley等人，2016）和镁铁质片材切割而成（2420±3 Ma）（Gumsley等人，2017）。 ）。使用本研究中提出的新年龄限制，即ENED08为2729±5 Ma，PRGE为2724±7 Ma，de Kock等人的年龄限制为2733–2724 Ma。（2012）和Cornell等人的2720±2 Ma。（2017），Platberg火山省（或可能是Platberg-Allanridge LIP组合而成的LIP脉冲）被限制在大约2个之间。2754 Ma and ca. 2709马。对于Makwassie组，康奈尔等。（2017）2720±2 Ma年龄取代了Armstrong等人提出的原始2709±8 Ma年龄。（1991）。碎屑的锆石光谱峰再次提供了岩浆和侵蚀的证据。2.71 Ga.ENED08和PRGE样品的这些新数据有助于完善Allanridge组玄武质安山岩的最小和最大年龄约束，该约束不合规地覆盖了Platberg组和Bothaville组（均为Pniel组的一部分）。艾伦里奇组的玄武质安山岩体积足够大，根据恩斯特（Ernst）（2014）的定义为LIP，面积超过200,000 km2，最大厚度为1 km。在Allanridge LIP上的年龄限制将其沉积在大约2到3之间。2709 Ma，这是普拉特贝格组下伏的Makwassie组的年龄（Cornell等，2017），大约是 2664 Ma，相当于上层瓦斯超群原始盆地中的Buffelsfontein群的年龄（Barton等，1995）。但是，Rykoppies Dike Swarm位于 2701 Ma和大约。2664 Ma，也可能与Allanridge LIP连锁，并且在地球化学上看起来相似（图5和6）。该镁铁质岩浆作用记录的峰值在2701–2692 Ma，2686–2683 Ma和2664–2659 Ma（Gumsley等，2016）。这些堤防群的复杂不一致的U-Pb同位素数据和Pb损失历史的重新解释似乎表明，仅使用来自Rykoppies和White的最少不一致的U-Pb铅锌矿同位素数据，就在2701–2683 Ma和2664–2654 Ma发生了两次岩浆事件。 Mfolozi堤防群。如果这是正确的话，那么阿兰里奇LIP的年龄可能反映了Rykoppies Dike Swarm中2701–2683 Ma处的较早脉冲，并在2664–2654 Ma处出现了岩浆作用进一步的岩浆作用，这是地球化学上独特的Mfolozi Dike Swarm组，这与部分地区相同Rykoppies Dike Swarm（尽管在地球化学上有所不同）和火山活动，以及在原始基底充填中重新裂谷到Transvaal超群，例如Buffelsfontein组的双峰火山岩在2664±1 Ma（Barton等，1995）。白色Mfolozi堤防群可能会被视为单独的岩浆事件，可能是另一个岩浆事件，尤其是在包括Rykoppies堤防群的同时期部分时。白色Mfolozi堤防群具有独特的地球化学特征，但与辐射的Rykoppies堤防群具有近似正交的线性趋势（图1）。尽管白色Mfolozi堤防群可以代表单独的线性或辐射群的一部分，但我们推测白色Mfolozi堤防群可以替代地证明是巨大的周围群（Buchan和Ernst 2018，2019），其将烟羽中心定为焦点总而言之，Ventersdorp的岩浆活动可分为不同的火山/岩浆事件，其中一些属于LIP规模，包括2791–2779 Ma Klipriviersberg LIP和2701–2683 Ma Allanridge LIP，它们与2664–2654 Ma White Mfolozi / Rykoppies岩浆省（也可能是LIP）分开。尽管Platberg集团与Pniel集团之间存在不整合，但Allanridge LIP紧随其前的2754-2709 Ma Platberg火山省，该省由一系列沉积和双峰火山岩混合而成。因此，普拉特伯格群很可能与地幔柱在遗传上有关，而地幔柱负责在岩石圈下方安放阿兰德里奇LIP，使该羽流脉动明显（具有分馏作用或与弧有关的岩浆作用，具有地壳作用，从地球化学中可以看出）。 Humbert等人，2019年）。散发着辐射的Rykoppies Dike Swarm很好地定义了Allanridge LIP的地幔柱中心。此外，相关的Ventersdorp裂谷带大致从该羽流中心开始趋向，这表明该裂谷与Allanridge LIP在一定程度上是相同的。2791–2779 Ma Klipriviersberg LIP和2664–2654 Ma White Mfolozi火山省的羽状中心位置仍然不受限制。本研究报告的2787±2 Ma和2789±4 Ma基性基岩侵入并横切了含金的Witwatersrand超群演替，表明如迈耶等人的建议，砂金沉积必须早于铁镁质堤防和基石。（2009）。这使得砂金和维特沃特斯兰德超群的最小沉积年龄大于约。2.79 Ga，并与ca. 2.78 Ga和ca. 2.xenotime报道了2.76 Ga的成岩年龄（England等，2001； Kositcin等，2003），以及约有一个。2。Klipriviersberg群的Venterspost组的78 Ga碎屑锆石年龄，适形地覆盖了Witwatersrand超群（Barton等，1989）。这进一步证实了维特沃特斯兰德超群沉积的停止和温特斯多普超群的开始的大约最小和最大年龄限制。Venterspost组被一致地沉积在Witwatersrand超群上，但随着Klipriviersberg群洪水玄武岩的喷发，沉积岩仍未固结（Chunnett，1994）。成岩发生在约。2.78 Ga和ca. 2.76 Ga（England等，2001； Kositcin等，2003）。这对金成矿意义重大，表明维特沃特斯兰德超群沉积岩的最大沉积时间约为180 my，与先前建议的最大时间跨度为256 my相对，金成矿时间约为ca。2.78 Ga（Armstrong et al。，1991; Meier et al。，2009）。利用上面的年代地层约束（图9A和9B），在2791-2779 Ma处，中部和西北部地区保留了大量岩浆物质。 Kaapvaal Craton之类的产品，例如Klipriviersberg LIP。该LIP包括流经中部Kaapvaal Craton的Klipriviersberg洪水玄武岩以及西北Kaapvaal Craton上的Kanye和Derdepoort玄武岩和流纹岩。这伴随着食源性花岗岩的进入，这可能是由于地壳融化产生的，而地壳融化则与负责Klipriviersberg LIP的地幔柱有关（Grobler和Walraven，1993）。这些花岗岩沿Colesberg和Thabazimbi–Murchison线排列，可能反映了薄而弱的地壳的缝合带，易受较高的热流影响（例如，Ernst，2014年）。在LIP级岩浆作用中显示出地幔柱，在Klipriviersberg组底部合并了源自地幔的科马提岩和高MgO玄武岩，以及在Klipriviersberg组洪水玄武岩沉积之前对未固结的Witwatersrand超群和Venterspost组沉积物进行了抬升和侵蚀。随着Klipriviersberg LIP广泛的，短暂的岩浆作用终止，大约30年代以后相同或可能不同的地幔柱的撞击导致了中部和西部Kaapvaal Craton火山和沉积作用的扩展和and发发展；现在，它被保留为大约 2754年及以后 2709马。在东南部的Kaapvaal Craton地区，这种岩浆作用也记录在2729±5 Ma的东西北趋势的Ulundi Dike Swarm中，也可能在阿姆斯特丹组中，伴随着变质作用，岩心复合体的形成以及斯威士兰及其邻近地区的花岗岩形成。南非。该地区的母岩性岩浆作用也见于此处的庞戈拉超级群中的窗台，其日期为2724±7 Ma。由于grab陷中充满了普拉特堡群，在大约20年后的某个时间，Pniel群中的一个小裂隙后沉积和火山作用继续。2709 Ma，玄武质安山岩保存完好，因为大约在两次之间的Allanridge LIP爆发。2709 Ma和大约。2683 Ma，可能与负责Platberg火山省的同一地幔柱有关。LIP本身，Platberg Group岩石的隆起和侵蚀，以及在Allanridge组玄武质安山岩底部的科莫铁矿和高MgO玄武岩的位置提供了地幔柱的证据。这些火山岩覆盖了Kaapvaal Craton的下部西部地区，而镁铁岩堤防群则位于Rykoppies Dike Swarm的Kaapvaal Craton东部地区的2701–2683 Ma。如果古姆斯利等人提出的三个岩浆脉动，雷科比山脉的堤防群会从东部布什维尔德综合体下方的一个焦点散发出来，很可能是由地幔柱在2701-2683 Ma产生的（Olsson等，2011）。（2016）被重新解释为2701–2683 Ma和2664–2654 Ma时减少为两个（Olsson等人，2010，2011），其中较旧的脉冲负责Allanridge LIP。2664年至2654年的Ma脉冲可能与另一个LIP有关，并在所谓的原始盆地中重新裂陷了德兰士瓦超级集团和怀特·姆福洛兹·迪克群，并注入了一些岩浆，其趋势与雷科皮斯·迪克群的趋势相同，可能处于相同的应力状态或地壳的弱线下。这终止了卡瓦瓦族克拉通火山在原基伏期至特兰斯瓦特超级集团的火山爆发，其中包括裂谷失败;来自两个基性基岩的辉石，被解释为克利普里斯堡山岩浆岩的馈线，位于基普瓦瓦尔克拉通中部的威特沃特山脉超群内，产出U-Pb。 ID-TIMS的结晶年龄为2787±2 Ma和2789±4 Ma。对其中一种基石中的斑脱钙石晶粒进行U-Pb LA-ICPMS补充分析，得出相似的结晶年龄2793±7 Ma。以上所有日期均在误差范围内重叠，并且解释了这些基岩和较大的Klipriviersberg LIP的位置是2791–2779 Ma年龄。Kaapvaal Craton东南部Pongola超群中的铁镁质基石中的Baddeleyite的结晶年龄为2724±7 Ma。这将与普拉特堡群有关的岩浆作用扩展到更远的东面，到东南的卡普瓦瓦尔克雷顿。此外，来自最东南的Kaapvaal Craton的东北趋势黑铁岩堤，是新定义的Ulundi Dike Swarm的一部分，产生了2729±7 Ma的U-Pb Baddeleyite结晶年龄，这使其成为第一批直接相关的堤防群的一部分。到Ventersdorp超级集团（特别是Platberg集团）。我们的研究结果将2791–2779 Ma岩浆事件扩展到了Kaapvaal Craton的中部，并将2754–2709 Ma岩浆作用扩展到了Kaapvaal Craton的东南部。这些新数据，再加上与2701–2654 Ma Rykoppies和White Mfolozi岩浆作用有关的先前数据。以便在Ventersdorp超群中区分两个单独的LIP，并在此后不久进行区分：Klipriviersberg LIP中的2791–2779 Ma，Allanridge LIP中的2701–2683 Ma，以及白Mfolozi Dike Swarm形成后的2664–2654 Ma Ventersdorp超级集团，但在成立Transvaal超级集团之前。前两个LIP启动和终止了整个Kaapvaal Craton的Ventersdorp超级集团的发展，这可能分别与Klipriviersberg集团和Pniel集团的岩浆作用有关。在2754-2709 Ma Platberg群的形成过程中，阿拉兰里奇地幔柱流到达岩石圈底部时，这些裂谷通过裂谷和grab陷发育以及相关的沉积和双峰火山作用而分离。这些新时代也使我们能够重新解释维特沃特斯兰德超群内金矿的沉积时间，大企业集团中的金矿沉积发生在约公元前。2.79加。作者要感谢GSA公报的工作人员和编辑Rob Strachan在整个出版过程中提供的所有帮助。作者还感谢Steve Denyszyn进行的详细而建设性的评论。阿什利·古姆斯利（Ashley Gumsley）通过波兰国家科学中心的一笔赠款（POLONEZ赠款，编号UMO-2016 / 23 / P / ST10 / 02423）表示感谢。该赠款已从欧盟2020年“地平线2020”研究与创新计划中获得了资助，该计划由MarieSkłodowska-CurieActions COFUND-2014（拨款号665778）提供。非常感谢戴比尔斯（De Beers）为U-Pb年代学提供的资金。理查德·恩斯特（Richard Ernst）得到了俄罗斯联邦超级拨款14.Y26.31.0012的部分支持。米歇尔·德·科克（Michiel de Kock）感谢DST-NRF矿产和能源资源分析卓越中心（CIMERA）的支持以及NRF激励资金。本文是对国际地球科学计划（IGCP）648：超大陆和全球地球动力学的贡献。理查德·恩斯特（Richard Ernst）得到了俄罗斯联邦超级拨款14.Y26.31.0012的部分支持。米歇尔·德·科克（Michiel de Kock）感谢DST-NRF矿产和能源资源分析卓越中心（CIMERA）的支持以及NRF激励资金。本文是对国际地球科学计划（IGCP）648：超大陆和全球地球动力学的贡献。理查德·恩斯特（Richard Ernst）得到了俄罗斯联邦超级拨款14.Y26.31.0012的部分支持。米歇尔·德·科克（Michiel de Kock）感谢DST-NRF矿产和能源资源分析卓越中心（CIMERA）的支持以及NRF激励资金。本文是对国际地球科学计划（IGCP）648：超大陆和全球地球动力学的贡献。