How far can we trust provenance and crustal evolution information from detrital zircons? A South African case study

    How far can we trust provenance and crustal evolution information from detrital zircons? A south African case study Tom Andersen, Magnus Kristoffersen, Marlina Elburg PII: DOI: Reference:

S1342-937X(16)30026-0 doi: 10.1016/j.gr.2016.03.003 GR 1591

To appear in:

Gondwana Research

Received date: Revised date: Accepted date:

20 November 2015 8 March 2016 13 March 2016

Please cite this article as: Andersen, Tom, Kristoffersen, Magnus, Elburg, Marlina, How far can we trust provenance and crustal evolution information from detrital zircons? A south African case study, Gondwana Research (2016), doi: 10.1016/j.gr.2016.03.003

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How far can we trust provenance and crustal evolution information from detrital zircons? A South African case study.

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Tom Andersen1,2, Magnus Kristoffersen1, Marlina Elburg2 1: Department of Geosciences, University of Oslo, PO Box 1047 Blindern, N-0316

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Oslo, Norway

2: Department of Geology, University of Johannesburg, South Africa ABSTRACT

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U-Pb and Lu-Hf data are routinely used to trace detrital zircon in clastic sediments to their original source in crystalline bedrock (the protosource), to map out paths of sediment

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transport, and characterize large-scale processes of crustal evolution. For such data to have a provenance significance, a simple transport route from the protosource in which the zircon formed to its final site of deposition is needed. However, detrital zircon data from

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Phanerozoic sedimentary cover sequences in South Africa suggest that this ―source to sink‖

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relationship has been obscured by repeated events of sedimentary recycling. Phanerozoic sandstones (Cape Supergroup, Karoo Supergroup, Natal Group, Msikaba Formation) and

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unconsolidated, Cenozoic sands in South Africa share major detrital zircon fractions of late Mesoproterozoic (940-1120 Ma, Hf≈0 to +15) and Neoproterozoic age (470-720 Ma, Hf≈ -10 to +8). A Permian age fraction (240-280 Ma, Hf≈ -8 to +5) is prominent in sandstones from

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the upper part of the Karoo Supergroup. All of these sequences are dominated by material derived by recycling of older sedimentary rocks, and only the youngest, late Palaeozoic fraction has a clear provenance significance (Gondwanide orogen). The virtual absence of Archaean zircon is a striking feature in nearly all suites of detrital zircon studied in the region. This indicates that significant events in the crustal evolution history of southern African and western Gondwana are not represented in the detrital zircon record. South Africa provides us with a record of recycling of cover sequences throughout the Phanerozoic, and probably back into the Neoproterozoic, in which the ―sink‖ of one sedimentary cycle will act as the ―source‖ in subsequent cycles. In such a setting, detrital zircon may give information on sedimentary processes rather than on provenance.

Keywords: Zircon; U-Pb; Lu-Hf; Provenance; Crustal evolution, South Africa

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1. Introduction The use of combined U-Pb and Lu-Hf data from detrital zircon to identify the provenance of clastic sediments (e.g. Gehrels, 2012 and references therein) and to unravel

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first-order features of evolution of the continental crust (e.g. Iizuka et al., 2010, 2013; Condie

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et al., 2011; Belousova et al., 2010, Roberts and Spencer, 2015) counts among the success

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stories of geochronology in recent years. These applications are based on the assumption that the U-Pb and Lu-Hf isotope systems of a detrital zircon grain retrieved from a sediment or a sedimentary rock preserve information about the properties of its original source (the protosource). This is not unreasonable, given the robustness of zircon (e.g. Fedo et al., 2003).

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The ideal aim of detrital zircon geochronology is to trace the transport of clastic material (represented by detrital zircon) from its source in crystalline bedrock to the final

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resting place in a sedimentary basin, commonly referred to as "from source to sink‖. As the amount of detrital zircon data has increased, some observations challenging its power as provenance indicator have been made (e.g. Dickinson et al., 2009; Thomas, 2011; Andersen,

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2014; Hadlari et al., 2015, Zimmermann et al., 2015). The most serious problem may be that

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recycling of detrital zircons through successive erosion-transport-deposition cycles may homogenize material from different protosources over long time intervals and large distances.

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Such homogenization is detrimental to the power of detrital zircon as an indicator of sedimentary provenance, but, the same effect ideally allows detrital zircon to be used as an indicator of large-scale processes such as the extraction, growth and preservation of

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continental crust (e.g. Griffin et al., 2004; Belousova et al., 2010; Condie et al., 2011). For this to be possible, the detrital zircon population must retain age- and isotopic memory of all of the major crustal extraction events in the history of the continental source. Quantitative (in the sense of Fedo et al., 2003) representation of age components in the source terrane is unlikely to be achievable, even for large sample sizes (e.g. Andersen, 2005). The best place to test the performance of detrital zircon as a provenance and crustal evolution indicator is a geological environment where all of the controlling factors are known in advance: i.e. the age and nature of the continental reservoirs, the sources and transport ways of detritus, and the evolutionary history of the sedimentary basin where final deposition has taken place. The well-preserved and well-studied Phanerozoic sedimentary basins in southern Africa provide a suitable target for such a test study. The aim of this paper is to review the existing detrital zircon data from the region and add to these by presenting new UPb and Lu-Hf isotope data on three of the sequences in the region, and thereby to explore

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some of the limits for the applicability of detrital zircon as an indicator of sedimentary provenance and continental evolution. The main focus of this paper is on U-Pb ages and Lu-Hf isotopic signatures of detrital

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zircons from sandstones in the northeastern part of the late Palaeozoic to Mesozoic Main

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Karoo Basin (MKB) of South Africa (Fig. 1a). The target has been chosen because the depositional history is well understood, and sediment transport directions and hence source

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areas have changed with time (Smith et al., 1993; Veevers et al., 1994; Catuneanu et al., 1998, 2005). To be able to compare data from the northeastern MKB to data from the underlying sedimentary rocks of the Palaeozoic Cape Supergroup (CSG), from which U-Pb but no Lu-Hf

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isotope data have been published (Fourie et al., 2011; Vorster, 2013), and to older sequences (e.g. the Neoproterozoic Saldania Belt; Frimmel et al., 2013; Naidoo et al., 2013), we also

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present new detrital zircon data from the CSG, and from the Msikaba Formation, located northeast of the main outcrop of the Cape Supergroup (Fig. 1b), which is thought to be an

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equivalent of the Witteberg Group of the CSG (Shone and Booth, 2005).

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2. Geological Setting

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Southern Africa has a history of evolution from the Palaeoarchaean to the Mesozoic, which has involved assembly and breakup of (at least) two supercontinents, the late Mesoproterozoic Rodinia and the Neoproterozoic-Phanerozoic Gondwana / Pangea (Evans, 2009; Torsvik and Cocks, 2011). Present-day southern Africa (Fig. 1a) consists of the Archaean to

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Palaeoproterozoic nucleus of the Kaapvaal and Zimbabwe Cratons, surrounded by belts of Late Archaean and Palaeoproterozoic crust (Kramers et al., 2006; Jacobs et al., 2008; van Schijndel et al., 2011). Before breakup of Gondwana, the Grunehogna Craton of Dronning Maud Land was continuous with the Kaapvaal Craton (e.g. Mendonidis et al., 2015). The late Mesoproterozoic Namaqua-Natal Belt with distinct Namaqua and Natal sectors (Cornell et al., 2006) borders the cratonic core in the south and southwest (Fig. 1a), and presumably continues into East Antarctica (Jacobs et al., 1998; Mendonidis et al., 2015). This mobile belt is related to formation of the Rodina supercontinent, and forms part of a global system temporally equivalent to the Grenville belts of the northern hemisphere (Dalziel et al., 2000; Li et al., 2007; Lindeque et al., 2011). During assembly of Gondwana in the Neoproterozoic, Pan-African mobile belts (ca. 870 to ca. 550 Ma; Kröner and Stern, 2004) formed around the Archaean to Mesoproterozic core of southern Africa: The Mozambique Belt (as part of the East African-Antarctic orogen) in the east, Saldania Belt in the south, Gariep and Damara

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Belts in the west and northwest (Stern, 1994; Kröner and Stern, 2004; Frimmel et al. 2011; Jacobs et al., 2015). Prior to Gondwana breakup in the Jurassic (Watkeys, 2006), southern Africa was situated adjacent to (from east to west): East Antarctica (including Dronning

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Maud Land), the Falklands Plateau, several blocks now forming part of West Antarctica, and

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Patagonia (Fig. 1a). Convergence and subduction of oceanic lithosphere in the Paleozoic caused development of the Gondwanide orogen along the Panthalassan margin of Gondwana,

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of which the Cape Fold Belt in South Africa is a distal expression (Johnston, 2000; Milani and De Wit, 2008; Tankard et al., 2012). In South Africa, this mainly involved folding and thrusting of sedimentary rocks of the Palaeozoic Cape Supergroup over its Mesoproterozoic

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to Neoproterozoic basement (Newton et al., 2006). Peaks of deformation in the Cape Fold Belt have been dated by Ar-Ar to 245-270 Ma (Hansma et al., 2015). Sedimentation

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continued with deposition of the Karoo Supergroup (Johnson et al., 2006) in Carboniferous to early Jurassic time. The Cape and Karoo Supergroups have commonly been seen as distinct entities, with the Cape Supergroup being deposited in passive margin basins (Shone and

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Booth, 2005 and references therein), and the Karoo Supergroup in a retroarc foreland basin

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behind an emerging Gondwanide orogen (Veevers et al., 1994; Catuneanu et al., 2005 and references therein). Some later studies, based on more refined plate reconstructions,

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interpretation of basement structures and geophysical data, have questioned both of these interpretations, and instead proposed different basin evolution models, common to which is a continuous evolution of an intracontinental Cape-Karoo basin inboard from, but ultimately related to the convergent plate margin (Milani and de Wit, 2008; Lindeque et al., 2011;

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Tankard et al., 2012). Around 180 Ma, extensive basaltic magmatism gave rise to the lavas of the Drakensberg Group and equivalent intrusive rocks of the Karoo Igneous Province, signalling the breakup of the Gondwana supercontinent (Elburg and Goldberg, 2000; Duncan and Marsh, 2006; Watkeys, 2006). Late Mesoproterozoic sedimentary cover sequences in southern Africa and adjacent parts of Gondwana (Fig. 1a) include the 1130-1100 Ma Ritscherflya Supergroup deposited on Archaean basement of the Grunehogna Craton in Dronning Maud Land (Marschall et al., 2013), and the 1170-1090 Ma Koras Group overlying Mesoproterozoic rocks of the Namaqua-Natal Belt near the western boundary of the Kaapvaal Craton (Gutzmer et al., 2000; Pettersson et al., 2007; Bailie et al., 2012). Neoproterozoic sedimentary sequences are recorded in all of the Neoproterozoic mobile belts in the region (Kröner and Stern, 2004). Neoproterozoic to Cambrian sedimentary rocks of the Saldania Belt form part of the depositional basement of the Cape Supergroup. In the Gariep Belt of northwestern South

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Africa and western Namibia, a Neoproterozoic sequence with quartzites and glacial diamictite is preserved. Sedimentary rocks of the Nama and Vanrhynsdorp Groups rest unconformably on rocks of the Gariep Belt and on Namaqua-Natal basement, and underlie the Cape

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Supergroup in the western parts of its outcrop area (Gresse et al., 2006; Hofmann et al., 2014,

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2015).

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2.1. The Cape Supergroup and equivalents.

The early Ordovician to early Carboniferous Cape Supergroup consists of sandstones and lesser amounts of shale and glaciogenic sediments deposited on Mesoproterozoic

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basement and rocks of the Saldania Belt in extensional basins inboard from the margin of the Gondwana supercontinent (Fig. 1a; Veevers et al., 1994; Shone and Booth, 2005; Tankard et

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al., 2012). The maximum thickness is ca. 8000 m, wedging out from south to north and east. Three main stratigraphic units (Fig. 2) are recognized (Shone and Booth, 2005; Thamm and Johnson, 2006): the Ordovician to Silurian Table Mountain Group (sandstones,

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conglomerates, siltstones and minor glacial diamictite), the middle Devonian Bokkeveld

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Group (argillaceous rocks with minor sandstone), and the late Devonian to early Carboniferous Witteberg Group (mudstones, siltstones, sandstones). The Ordovician Natal

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Group (Marshall, 2002) and the Devonian Msikaba Formation (Shone and Booth, 2005) occur east of the outcrop area of the Cape Supergroup (Fig. 1b), but are generally regarded as equivalents of the Table Mountain and Witteberg Groups, respectively, although probably deposited in separate basins (Vorster et al., 2015). The Natal Group was deposited on

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Mesoproterozoic rocks of the Natal sector of the Namaqua-Natal Belt, and in the northeast, on Archaean rocks of the Kaapvaal Craton (Marshall, 2002). The CSG sediments were derived from continental sources to the (present day) north (Fig. 1b), including the late Mesoproterozoic rocks of the Namaqua-Natal Belt and Neoproterozoic cover rocks (Shone and Booth, 2005; Thamm and Johnson, 2006). The presence of boulders of Nama Group origin in diamictite of the Table Mountain group (Shone and Booth, 2005) demonstrates that recycling of Neoproterozoic to Cambrian deposits into the Cape Basin took place. The Kaapvaal craton is well within the potential area of source rocks (Veevers et al., 1994), but U-Pb data from CSG sandstones suggest that they are devoid of Archaean detrital zircon, leading Fourie et al. (2011) to suggest that the Namaqua-Natal Belt acted as a topographic barrier against southward transport of detritus from the craton in Palaeozoic time. The Natal Group sandstones have been interpreted to come from sources in the Neoproterozoic Mozambique Belt and the Kaapvaal Craton (Veevers et al., 1994;

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Marshall, 2002). This interpretation is not uneqivocally supported by detrital zircon data, which suggest that the most important sources of zircons were Mesoproterozoic rocks reworked in the Pan-African orogeny; potential sources of such material are widespread

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2.2. The Karoo Supergroup in the Main Karoo Basin

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within Gondwana (Kristoffersen et al., 2016).

The evolution, stratigraphy and sedimentology of the Main Karoo Basin (Fig. 1a, c, Fig. 2) have been the subject of many studies (e.g. Smith et al., 1993; Cadle et al., 1993;

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Veevers et al., 1994; Catuneanu et al., 1998, 2002, 2005; Tankard et al., 2012 and others). These studies provide a large amount of relevant sedimentary provenance information derived

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from sedimentary structures, palaeocurrent indicators and general basin geometry and development. The stratigraphy of the Karoo Supergroup was reviewed by Johnson et al. (2006). The following summary is drawn from these sources.

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The oldest sediments in the basin are glaciogenic deposits of the late Carboniferous to

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early Permian Dwyka Group, consisting of glaciomarine deposits in the south and southwest (e.g. Tankard et al., 2012 and references therein), but on-shore glacial sediments and

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glaciofluvial deposits in the northeast (Smith et al., 1993; Cadle et al., 1993). In the south, the Dwyka Group rests unconformably on the CSG, in the east and northeast on the Natal Group, or directly on Proterozoic and Archaean basement. Material transport was from surrounding highlands in the south (CFB), east (―Eastern Highlands‖) and the ―Cargonian Highlands‖ -

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―Witwatersrand Arch‖ in the north (Fig. 1b; Veevers et al., 1994), comprising exposed rocks of the Kaapvaal Craton and surrounding Proterozoic mobile belts, but which must also have included any cover sequences accumulated before glaciation that have since been removed. In the south, the Ecca Group consists of shales, mudstones and turbidite fans deposited mainly in a marine environment (Tankard et al., 2012 and references therein), from sources to the south of the basin (CFB). In the northeast, the shales of the marine Pietermaritzburg Formation and the marine to freshwater Volksrust Formation are separated by deltaic and fluvial sandstones of the Vryheid Formation, hosting coal deposits and originating from sources in the north and northeast (Christie, 1988; Cadle et al., 1993; Veevers et al., 1994, Green and Smith, 2012; Tankard et al., 2012). The upper boundary of the Ecca Group is diachronous, ranging in age from ca. 265 Ma in the south to 255 Ma in the north (Catuneanu et al., 1998; Cole, 2007). By the start of sedimentation of the Beaufort Group (comprising Adelaide and Tarkastad Subgroups), conditions were non-marine across

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the basin, but differences in provenance persisted between northeast and south / southwest (Smith et al., 1993; Catuneanu et al., 1998). The main source to almost the entire basin was now in the CFB, except for the most northeasterly part, where eastern sources were still

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delivering material (Veevers et al., 1994). In the northeast, the Adelaide Subgroup is

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represented by shales interlayered with sandstones of the Normandien Formation. The area that has been sampled for this study (Fig. 1a) lies in the boundary zone between domains

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dominated by transport from the south and east, respectively (Fig. 1c, cf. Fig. 17G in Veevers et al., 1994). The overlying Tarkastad Subgroup (ca. 240 Ma) consists mainly of sandstones deposited from meandering rivers, again with differences between north(eastern) and southern

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facies and presumably sources (Catuneanu et al., 1998). The three upper sedimentary formations (Molteno, Elliot and Clarens Formations) making up the Stormberg Group were

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deposited in freshwater (Molteno Formation sandstone, siltstone and shale; Elliot Formation redbeds and sandstones) and in a desert environment (Clarens Formation, mainly aeolian sandstone).

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Based on evidence from sequence stratigraphy, palaeocurrent indicators, basin

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geometry and depositional environments, the provenance regime of the Karoo Supergroup sediments in the northeastern part of the MKB changed with time from one dominated by

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sources in the north or northeast to one sourced in the CFB. The change between the two transport regimes has been suggested to have taken place during deposition of the upper part of the Beaufort Group (Catuneanu et al., 1998). Zircon-bearing volcanic ash beds of Carboniferous to Permian age occur interbedded

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with strata of the Dwyka Group, Ecca Group (Collingham Formation, ca. 270 Ma, Cole, 2007) and Beaufort Group in the southwestern part of the MKB, and in equivalent deposits in Namibia. Because of their potential importance for the dating of Palaeozoic glaciations in Gondwana, and for the definition of the Permian-Triassic boundary, zircons from these ash beds have been subject to several U-Pb dating studies (Bangert et al., 1999; Werner, 2006; Fildani et al., 2009; Rubidge et al., 2013; Lanci et al., 2013;, Dean, 2014;, McKay et al., 2015). The pooled data from these studies are shown as a histogram in Fig. 2. Two isolated occurrences of volcanic ash layers have been reported from lower Beaufort Group strata in the northern part of the basin (Keyser and Zawada, 1988), but these have not been dated by the U-Pb method..

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3. A review of published detrital zircon data Several studies have reported U-Pb zircon ages from the Cape and Karoo Supergroups and other sedimentary sequences in the region (Table 1, Fig. 3). Published Hf isotope data

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are fewer, but still make up a reasonable set of data for comparison (Fig. 4).

3.1. Detrital zircon U-Pb data

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Two independent sets of detrital zircon data from the Natal Group have recently been published by Vorster et al. (2015, U-Pb ages only) and Kristoffersen et al. (2016, U-Pb and Lu-Hf data). Although the two studies agree on the presence of late Mesoproterozoic (1000-

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1100 Ma) and late Neoproterozoic to early Palaeozoic (450-700 Ma) age fractions, their age distribution patterns are strikingly different. Kristoffersen et al. (2016) found a sparsely

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populated 800 to 1000 Ma interval, which appears as low-slope segments of the cumulative distribution curves (Fig. 3). In contrast, the data of Vorster et al. (2015) suggest a continuum of ages throughout the Neoproterozoic, reflected by evenly sloping distribution patterns (Fig

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3). Vorster et al. (2015) reported larger uncertainties on the individual analyses than did

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Kristoffersen et al. (2016), which applies in particular to ratios involving 207Pb (see Figure 7 of Vorster et al., 2015). The large errors on the 207Pb/235U ratio may have caused grains that

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have considerable normal discordance to appear concordant. We therefore suspect that the age distribution patterns reported by Vorster et al. (2015) may suffer from a significant amount of undetected lead loss, and that the appreciable abundance of 800-1000 Ma ages reflects this. Accordingly, we find it reasonable to exclude these data from further consideration. The same

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concern applies to the data on the Msikaba Formation reported by Vorster et al. (2015), and data from sandstones of the Cape and Karoo Supergroups by Vorster (2013) and Bowden (2013).

From overlapping segments with consistently steep slopes in the cumulative age distribution curves in Fig. 3, five more or less well-defined age groups or "components" can be defined from the published detrital zircon age data. The late Palaeozoic (ca. 250-300 Ma) component a is found as a major constituent in sandstones of the Ecca and Beaufort Groups from the southern part of the Main Karoo Basin, and as a minor component in Cenozoic sediments (Fig. 3a, b). It is, however, absent from Permian sandstones of the Vryheid Formation (Ecca Group) from the northeastern part of the basin (Fig. 3a, b). Component b consists of late Neoproterozoic to early Palaeozoic zircons (450-700 Ma), and is observed in all of the sandstones shown in Fig. 3. Component c is late Mesoproterozoic (1000-1100 Ma), and is most clearly defined in Cenozoic sediments, in the Cape and Karoo Supergroups and in

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the Natal Group data of Kristoffersen et al. (2016), but it is present in at least some samples in all of the data considered here. This is not the case with the older (1100 Ma to 1250 Ma) component d, which has not been recorded in the Cenozoic sediments, Karoo and Cape

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Supergroups and Natal Group, but which is prominent in the Gariep Belt, in some samples

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from the Nama Group and Damara Belt, as well as in the Ritscherflya Supergroup in Dronning Maud Land. The Palaeoproterozoic e-component is prominent in the Gariep Belt, it

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is also seen in the Damara Belt and in some samples from the Nama Group, but it is only an accessory component in the Phanerozoic sequences, and in the Saldania Belt (except for one single conglomerate clast reported by Frimmel et al., 2013). Archaean zircon is scarce, and

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only found in the basal beds of the Natal Group, in Permian sandstone in the Ellisras Basin (Veevers and Saeed, 2007) and in diamictite of the Dwyka Group from western South Africa

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(Jansson, 2010). Further afield, component a makes up a dominant fraction in Permian – Jurassic sandstones in Patagonia and the Antarctic peninsula (Fanning et al. 2011), whereas components b, c and e are prominent in Phanerozoic sedimentary rocks of the Congo Basin

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(Linol et al., 2016).

3.2. Detrital zircon Hf isotope data

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Common to all of the studies reporting Hf isotope data (Fig. 4) are significant ranges of epsilon Hf in both late Mesoproterozoic component c (ca. -30 to +15) and Neoproterozoic component b (ca. -25 to +10, but some zircons from the Saldania Belt have epsilon Hf ≤ -30, Fig. 4b; Frimmel et al., 2013). With ranges from -8 to +12 in the Mesoproterozoic zircon and

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-8 to +8 in the Neoproterozoic grains, the Natal Group (Fig. 4b) shows less spread towards highly negative values than do the other deposits (Kristoffersen et al., 2016). Archaean zircons in the basal units of the Natal Group and a minor Archaean age fraction in the Saldania Belt have epsilon Hf in the range from -10 to 0, and the same range is observed in the sparse Palaeoproterozoic zircon reported from these sequences. Hf isotope data for late Palaeozoic zircons (component a) have so far only been reported from the Cenozoic sediments (Andersen et al., 2015), in which they straddle the composition of the chondritic uniform reservoir (CHUR) at that time (epsilon Hf= -5 to +5). The Neoproterozoic sedimentary rocks from Namibia differ from the South African samples in having a broader age range in the Mesoproterozoic (1000 to 1500 Ma), but show ranges of epsilon Hf mimicking their South African counterparts in each of the age intervals found in both. Furthermore, the Namibian samples show a larger Archaean age fraction (epsilon Hf = -10 to +10), and have a prominent late Palaeoproterozoic to early

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Mesoproterozoic age fraction spanning a range of epsilon Hf from -25 to +5. The few Palaeoproterozoic zircons found in the South African samples fall well within this range (Fig.

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4a).

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3.3. Basement rocks

Zircon from Archaean crystalline rocks and metasediments of the Kaapvaal Craton

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show a broad range of ages and epsilon Hf, compatible with primary crystallization at epsilon Hf ≥0 in the Neoarchaean to late Palaeoarchaean (Fig. 4b, data from Zeh et al. 2007, 2009, 2011, 2013a, b; Frimmel et al., 2009; Koglin et al., 2010; Hicks et al., 2015; Reinhardt et al.,

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2015).

A pronounced tail towards post-Archaean 207Pb/206Pb ages and low epsilon Hf values

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probably reflects Phanerozoic lead loss in these zircons, most likely caused by thermal events related to Karoo magmatism and/or Gondwana breakup. There is very limited overlap between the fields of zircon originating in rocks of the Kaapvaal Craton and published detrital

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zircon from Neoproterozoic to Recent cover sequences, suggesting that Archaean zircons that

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have lost lead in post-Archaean events can only account for the most strongly negative epsilon Hf part of the detrital zircon distribution observed in the sediments (Fig. 4).

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In Fig. 5, the main age components a, b, c, d and e are compared to the "barcode" of dated magmatic events in southern Africa and Gondwana neighbours (for sources of rock age data, see Supplementary Table S1). The late Palaeozoic component a is coeval with magmatism in the Gondwanide orogen (Patagonia, Antarctic Peninsula; Flowerdew et al.

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2006; Fanning et al., 2011; Pankhurst et al., 2014). Component b overlaps in age with magmatic events in all of the Neoproterozoic belts surrounding southern Africa and in Argentina (e.g. Hongn et al. 2014, Ducea et al. 2010). Component c corresponds to the last period of magmatism in the Namaqua-Natal Belt and to basement components in the Mozambique and Damara orogens, as well as to magmatic provinces in Dronning Maud Land (e.g. Elburg et al., 2016). It should be noted that in general magmatism in the Namaqua-Natal Belt starts earlier than 1100 Ma and in some terranes terminates before 1100 Ma (Mc Court et al., 2006; Spencer et al., 2015; Mendonidis et al., 2015), thus corresponding to age component d. Component d is otherwise found in some of the older accreted terranes in the Namaqua Sector of the Namaqua-Natal Belt (Kakanas, Kaien, Areachap; Cornell et al., 2012, and references therein), and in the Rheoboth Province and Konkiep terrane of Namibia (van Schijndel et al., 2014; Mapani et al., 2014; Cornell et al., 2015). The Palaeoproterozoic e-

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component corresponds to magmatic ages recorded in the Rehoboth Province (Fig. 1; van Schijndel et al., 2011). The age distribution patterns in Fig. 5 suggest that zircon derived directly from

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bedrock sources in the Namaqua-Natal Belt should include ages between ca. 1000 and ca.

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1250 Ma, i.e. a broadening of the late Mesoproterozoic-early Neoproterozoic age fraction to comprise both components c and d. This is not observed in the published data from any of the

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Phanerozoic sandstones (Fig. 3), in which component d is virtually absent.

4. New detrital zircon data from Phanerozoic sandstones in South Africa

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4.1. The material studied

17 samples of the Karoo Supergroup (Fig. 2, Table 2, Supplementary Fig. S1) were

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collected from exposures in KwaZulu-Natal and the Free State provinces of South Africa. The suite of samples span the full extent of the Karoo Supergroup in the northeastern part of the basin, from Dwyka Group diamictite to the top of the Clarens Formation. Except for sample

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SA12/09, which is the fine-grained matrix of a diamictite of the Dwyka Group, the samples

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all come from sandstones, or from sandy interlayers in the mainly shaly Normandien Formation of the Adelaide Subgroup (lower Beaufort Group). Three samples of the

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Normandien Formation were collected in a single profile along road P263 east of Colling’s Pass. SA13/111 is a sandy layer near the base of the formation, SA13/112 comes from a similar unit higher in the formation, and SA13/113 from one near the top. SA13/130 and SA13/132 were taken from sandy units further south (Frere-Estcourt area), in the lower and

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upper parts of the Normandien Formation, respectively. Three samples from the Table Mountain Group (Peninsula, Rietvlei and Skurveberg Formations, respectively) and two from the lower part of the overlying Bokkeveld group (Gydo and Gamka Formations of the Ceres Subgroup) of the Cape Supergroup (Fig. 2, Table 2, Supplementary Fig. S2) were collected from exposures in the Western Cape province. Except for SA14/239, which is a sandy interlayer in the otherwise shaly Gydo Formation of the Bokkeveld Group, the samples come from massive sandstone units, which range from gritty (SA14/240) to fine-grained (SA14/229, SA14/234, SA14/238). Two samples from the Msikaba Formation were collected from exposures in southeastern KwaZulu Natal (Table 2, Supplementary Fig. S1). SA12/55 is a sandy unit with quartz pebbles from the upper part of the preserved sequence, and SA12/61 is a medium to fine grained sandstone near the base of the formation.

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Detrital zircons in the samples range from angular to well-rounded, short prismatic crystals, ranging in size from <50 to >200 m in size (Fig. 6). Some irregular fragments are probably derived from larger crystals that were broken up during crushing (Fig. 6c, i). Internal

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structures include short wavelength oscillatory, "magmatic" zoning (Fig. 6a, b, c) with (Fig.

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6b) or without cathodoluminescence (CL) bright rims, moderate CL amplitude sector zoning (Fig. 6d, e), and patchily developed CL bright domains (Fig. 6f, g, h, i). There is no

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systematic relationship between grain-shape or internal structure and age, as both oscillatory zoning and patchy variations in CL intensity can be observed in all age groups detected by UPb dating (in Fig. 6, compare frames j and k with a and b, and l with e) for U-Pb data, see

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below).

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4.2. Analytical methods

The samples were crushed in a jaw crusher, sieved to <250 m grain size, after which

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heavy minerals were separated by manual pan-washing. Zircon was handpicked from the

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heavy mineral fractions under a binocular microscope. Cathodoluminescence (CL) imaging was done with a JEOL JSM 6460LV scanning electron microscope in the Department of Geosciences, University of Oslo and with a Tescan scanning electron microscope at the

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Spectrum Analytical Facility, University of Johannesburg. U-Pb and Lu-Hf isotope analysis was done by laser ablation, inductively coupled plasma source mass spectrometry (LA-ICPMS), using Nu Plasma HR multicollector and

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Bruker Aurora quadrupole mass spectrometers at the Department of Geosciences, University of Oslo. Ablations were made with 213 nm Nd:YAG CETAC LSX-213 G2+ laser microprobes with dual volume, Helex cells. All ablations were made in helium, which was mixed with argon within the plumbing system of the cell. For U-Pb analysis with the multicollector instrument, analytical protocols described by Andersen et al. (2009) were used. Standards used for calibration were GJ-1 (609±1 Ma, Belousova et al. 2006), 91500 (1065±1 Ma, Wiedenbeck et al., 1995) and A382 (1877±2 Ma, Huhma et al., 2012). On the Bruker Aurora instrument, a fast scanning protocol was employed, measuring masses 29 (Si), 91(Zr), 202 (Hg), 204 (Pb+Hg), 206 (Pb), 207 (Pb), 208 (Pb), 232 (Th), 235 (U), 238(U), 248 (ThO), and 254 (UO). Dwelltimes were 10 ms, except for 20 ms at masses 204, 207 and 235. 235U used in geochronological calculation was, however, calculated from 238U assuming 238U/235U =138.77. Raw data were reduced in an inhouse interactive spreadsheet program written in VBA for Microsoft Excel 2003, using the

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linear calibration curve option of Andersen et al. (2009). Common lead was estimated from Hg-corrected measurement of 204Pb, using a common lead composition given by the Stacey and Kramers (1975) model at the observed 206Pb/238U age of the zircon. Standards used for

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calibration were the same as for the Nu Plasma instrument. The age used to recalculate Hf 206

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isotope data and plot age distribution diagrams is the most precise of the 207Pb/206Pb or Pb/238U ages. When relative uncertainty of the calculated ages is used as a criterion, the

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turnover value from one to the other is not fixed, but tends to lie between 900 and 1000 Ma. For Lu-Hf analysis, analytical protocols described by Elburg et al. (2013) were used. Interference from 176Yb on mass 176 was corrected using the measured signal on mass 172

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(interference-free 172Yb) and mass discrimination factors for Yb determined from measurement of 174Yb/172Yb ratio, after correction for interference from 174Hf. Interference

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from 176Lu was corrected from observed 175Lu, using mass discrimination factor of Hf as a proxy. Reference zircons run during the period these analyses were made gave (all errors quoted at the 2-sigma level): Mud Tank: 176Hf/177Hf= 0.282508 ± 0.000034 (published value: 176

Hf/177Hf = 0.282682 ± 0.000042 (published value: 0.282686, Woodhead & Hergt,

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2:

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0.282507, Woodhead and Hergt, 2005), 178Hf/177Hf = 1.46726 ± 0.00008, n = 1168; Temora 2005), 178Hf/177Hf = 1.46726 ± 0.00009, n = 51 (initial 176Hf/177Hf at 417 Ma: 0.282672 ±

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0.000042); LV11: 176Hf/177Hf = 0.282828 ± 0.000061 (published solution analysis: 0.282830±0.000028, Heinonen et al., 2010), 178Hf/177Hf = 1.46724 ±0.00008, n = 647 (initial 176

Hf/177Hf at 290 Ma: 0.282816±0.000061). The Lu-Hf model age is calculated assuming a two-stage evolution since extraction of

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the crustal protolith from depleted mantle. The first stage is represented by a crustal protolith whose 176Lu/177Hf ratio is assumed to represent average continental crust, for which 176

Lu/177Hf =0.015 is used (Griffin et al., 2004). The zircon formed from this protolith in

some later event whose age is given by the U-Pb age of the zircon itself. The model age is calculated from the initial 176Hf/177Hf of the zircon at its time of crystallization by extrapolating along the growth-curve of the assumed crustal protolith until its intersection with the depleted mantle growth curve. A crustal residence age calculated from Hf isotopes in zircon may be less accurate than one based on whole-rock Sm-Nd isotope data, but this is of little consequence for the present study, as the main reason to apply model ages is to allow comparison between sedimentary sequences and between these and potential bedrock sources.

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4.3. Results LA-ICMPS U-Pb and Lu-Hf analyses of zircons are given in Supplementary Tables S2 and S3, and plotted in age and epsilon Hf distribution diagrams for the individual samples in

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Supplementary Figures S3 to S26.

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Common to all Karoo Supergroup samples (Figs. 7, 8) are significant age fractions in the late Mesoproterozoic to earliest Neoproterozoic (940 to 1120 Ma, epsilon Hf = 0 to +15,

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but with a sparsely populated tail to ca. -20) and in the Neoproterozoic to early Palaeozoic (470 to 720 Ma, epsilon Hf= -10 to +8, again with a tail, to ca. -30). The age ranges of these fractions correspond to components b and c in the published data (Fig. 3). The proportion of

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these two groups varies between samples, with the Mesoproterozoic fraction being least abundant in the samples from the Tarkastad Subgroup. Strongly negative Mesoproterozoic

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zircon (epsilon Hf < -10) is more abundant in the lower (Dwyka Group, Vryheid Formation, lower part of the Normandien Formation) than in the stratigraphically higher units. Cumulative distribution patterns (Fig. 8) suggest that these two groups are well separated in

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most of the samples, but that there is a tendency towards a more continuous range of ages in a

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few samples, most notably in sandstone SA13/124 of the Clarens Formation. The main variation in the samples of the Karoo Supergroup is the appearance of a late Palaeozoic

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fraction (300 to 240 Ma, epsilon Hf= -8 to +5, corresponding to component a in Fig. 3) from the higher part of the Normandien Formation (samples SA13/112, SA13/113 and SA13/132), which persists in variable amounts to the end of sedimentation. This late Palaeozoic age fraction mimics the complete age range of magmatic zircon that has been dated from volcanic

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ash-layers in Dwyka, Ecca and Beaufort Group strata from the southwestern part of the main Karoo basin. In these samples, the late Palaeozoic zircons occur as ordinary detrital grains, albeit with less rounding than seen in other age groups (Fig. 6). The young zircons appear in our samples at a stratigraphic level above the Ecca-Beaufort boundary, which in the northeast has been estimated to be ca. 255 Ma by Cole (2007). For most of these zircons, there is thus a time-lag between crystallization and deposition that may be as short as a few million years in the lower samples, to 80 Ma (or more) in the Clarens Formation (Fig. 9). Zircons older than late Mesoproterozoic are very scarce in the Karoo samples, and amount to a few early Mesoproterozoic, Palaeoproterozoic and late Archaean grains, most of which are found in samples of the Dwyka Group and the Tarkastad and Clarens Formations (Fig. 8), with epsilon Hf between -5 and +5. Hf model ages of detrital zircons reflect the average time Hf has resided in a continental reservoir. Model ages (Fig. 8b) range from late Neoproterozoic to early

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Mesoproterozoic, with minor Palaeoproterozoic and Archean fractions observed only in diamictite of the Dwyka Group SA12/09. The late Palaeozoic zircons stand out with model ages in the range 600-800 Ma, which is noticeable in the cumulative distribution curves for

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samples SA13/112, SA13/113, SA13/132 and, to a certain degree, SA13/114.

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The samples from the Cape Supergroup and the Msikaba Formation show an age and epsilon Hf distribution that mimics the Neoproterozoic and Mesoproterozoic fractions in the

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Karoo samples (Fig. 10a, b, c). Sample SA14/240 (from a coarse-grained bed in the Skurveberg Formation of the Table Mountain Group) shows a higher proportion of Neoproterozoic zircon than the other samples. There is no apparent difference between

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samples of the Table Mountain and Bokkeveld Groups. The samples analysed in this study come from part of the sequence only (Table Mountain Group and lower part of the Bokkeveld

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Group), but show age distribution patterns that are similar to those published by Fourie et al. (2011), which include data on other parts of the Bokkeveld Group and from the Witteberg Group. Another feature in common with the Karoo samples and the samples of Fourie et al.

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(2011) is the almost complete absence of Archaean zircon from the CSG and its complete

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absence from Msikaba Formation samples (in agreement with the data presented by Vorster et al., 2015). Hf model ages are mainly late Mesoproterozoic, but with minor Neoproterozoic

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5. Discussion

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and Palaeoproterozoic contributions in the Cape Supergroup (Fig. 10d)

5.1. Similarities, groups and significant features of detrital zircon in the Cape and Karoo sandstones.

Simple visual inspection of the detrital zircon age vs. Hf isotope patterns and the cumulative age distributions in Figs. 7, 8 and 10 suggest extensive similarity within the Cape and Karoo Supergroups individually, but also between the two supergroups, and between these and Neoproterozoic sedimentary rocks of the Saldania Belt, Damara Belt and possibly also the Nama Group, although so far Hf isotope data have only been published from one single sample of that group (Figs. 3, 4). From the upper part of the Normandien Formation and upwards, late Palaeozoic zircon appears as an obviously significant feature of the distribution patterns of the Karoo sandstones. Different statistical parameters can be used to quantify similarities and differences in detrital zircon distribution patterns between samples (e.g. Vermeesch, 2013; Saylor et al.,

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2013; Satkoski et al., 2013). None of these take the uncertainty caused by random sampling of relatively small sample sizes explicitly into account, although this can be considerable (Andersen, 2005). To minimize the risk of "distinguishing the indistinguishable" (i.e. making

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the classical Type I Error of statistics), we will use the degree of overlap of 95% confidence

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intervals around cumulative age distribution patterns based on the Dvoretzky-KieferWolfowitz inequality (e.g. Wassermann, 2006) as a measure of similarity between samples, as

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proposed by Andersen et al. (2015). If O represents the part of the cumulative age distribution curve over which the confidence intervals of two samples overlap (0≤O≤1), 1-O is a measure of difference between the two that takes sampling error into account, O=1.0 indicating that the

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samples have indistinguishable age distribution patterns. A table of pairwise O values is given in Supplementary Table S4, and a graphical representation of the similarity pattern

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represented by 1-O is shown in Fig. 11, with samples listed in stratigraphic sequence (younging from bottom to top, and from left to right). Two samples stand out as consistently different from the others: SA13/113 and SA13/132, and to a lesser extent, SA13/114. These

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are the samples having the largest fractions of late Palaeozoic zircon. Although such zircon is

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present in all but one of the samples from the upper part of the Normandien Formation and higher levels, their abundance is not sufficiently high in those samples to prevent overlap

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between the 95% confidence intervals in the young part of the age range. Four stratigraphically defined groups stand out as internally indistinguishable based on detrital zircon ages (outlined in blue in Fig. 11): (1): The Cape sandstones, except for SA14/240. (2): Vryheid Formation and lower part of the Normandien Formation. (3): Molteno

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Formation. (4): Elliot and Clarens Formations. However, similarity is not restricted to these groups; in fact, most samples dominated by Mesoproterozoic and Neoproterozoic-Cambrian age fractions appear as indistinguishable in Fig. 11.

5.2. Detrital zircon fractions with and without provenance significance

The late Palaeozoic age fraction carries significant provenance information. In the samples analysed for this study, the late Palaeozoic zircons occur as detrital grains in sandstones that are not associated with preserved layers of volcanic ash. Although these zircons had a limited life-span prior to final deposition compared to Neoproterozoic and older zircons, the time-gap between crystallization and deposition is still in excess of 50 Ma in the younger of the units (Fig. 9), which indicates that most of the young zircons encountered in this study must have been stored in some intermediate source-rock outside of the basin, or

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recycled within the basin itself for a significant time before final deposition. The protosources of late Palaeozoic zircons are most probably igneous rocks within the Gondwanide orogen , although volcanoes along the northern basin margin may also have contributed (Keyser and

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Zawada, 1988). The appearance of the young zircons in sediments in the northeast reflects a

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situation in which clastic material could cross the basin from south to north, either by water or by wind. Linol et al. (2016) invoked wind-blown transport from volcanic centres in the proto-

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Andean part of the Gondwanides to account for minor fractions of 200-300 Ma zircons in Jurassic to Cenozoic sediments in the Congo Basin, but even there, a time-lag between crystallization and deposition indicates that the zircons must have been kept in some

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intermediate reservoir for considerable time before final deposition. A significant proportion of the late Palaeozoic zircons in the younger strata predates

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deposition of the Vryheid Formation and lower part of the Normandien Formation (ca. 240260 Ma). The absence of these zircons in the older units and their presence in the younger strata must therefore reflect changes in transport regime with time, and cannot be used to

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constrain the age of deposition of any of the units. One possible consequence is that the

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dominance of southern sources, as envisaged by Catuneanu et al. (1998), coincided with deposition of the upper part of the Normandien Formation, rather than the Beaufort Group -

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Molteno Formation boundary.

5.3. Recycling of Cape sandstone?

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The general evolution of the Cape Fold Belt and the Main Karoo Basin suggests that sedimentary rocks of the Cape Supergroup and the early Karoo Supergroup affected by thrusting and folding would be exposed to erosion and recycling into the basin (Catuneanu et al., 1998; Johnson et al., 2006). At the time of deposition of the Molteno Formation, or possibly earlier, southern sources were dominant also in the northeast (Catuneanu et al., 1998; this work). However, older sandstones of the Vryheid and lower Normandien Formations also have detrital zircon distribution patterns similar to the Cape Supergroup, suggesting that a recycling regime may have existed in the northeast much earlier. This is difficult to reconcile with sedimentological evidence of general transport directions from the north and east in he area at this early stage of basin evolution (Christie, 1988; Smith et al., 1993; Veevers et al., 1994; Green and Smith, 2012). Sedimentary structures indicating palaeocurrent directions (channel orientations, crossbeds etc.) may give biased information on sediment transport, as they only record the last stage of movement before final deposition (e.g. Thomas, 2011).

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However, even when disregarding indications from sedimentary structures, there remains overwhelming independent evidence from stratigraphy, general basin geometry and from studies of the depositional environment of coal in the Vryheid Formation to conclude that

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these sandstones were deposited along the northern basin margin and fed by rivers flowing

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from exposed highland areas to the north and northeast (Cadle et al., 1993; Smith et al., 1993; Veevers et al., 1994; Catuneanu et al., 1998, 2005). Because significant transport of sand from

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south to north across the underfilled, Karoo basin in Ecca time is unlikely, the presence of rocks with this kind of detrital zircon signature in areas that received sediment from the north remains an enigmatic feature of the Karoo Supergroup that needs to be explained. Vryheid

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Formation sandstones in eastern South Africa and Permian sandstones in Dronning Maud Land have similar age and Hf isotope distribution patterns, which led Veevers and Saeed

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(2007) to suggest transport from sources in central Antarctica. If this is interpretation is correct, similarity in detrital zircon patterns would imply that such sources also contributed to the older Natal Group and CSG. However, this is in conflict with the general agreement that

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CSG sediments were derived from sources in the north, i.e. from areas on the African

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mainland (Shone and Booth, 2005). If sources in central Antarctica contributed to the early Karoo in the northeast, and to the Natal Group, but not to the Cape Supergroup, the two

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source terranes involved (Central Antarctica and southern Africa) must have contributed Neoproterozoic and Mesoproterozoic detrital zircon loads that were indistinguishable in terms age and Hf isotope distribution. This is, of course, not impossible, given the common history of these continental terranes (Andersen, 2014). Detrital zircon data from Mesoproterozoic

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sandstones in Dronning Maud Land (Ritscherflya Supergroup) show a dominance of pre-1100 Ma zircon ages (Fig. 3) which suggests that bedrock sources in at least some parts of eastern or central Antarctica have provided a distinct age signature that is not of major importance in the deposits studied here. Kristoffersen et al. (2016) evaluated the provenance model of Veevers and Saeed (2007) in the light of more recently published detrital zircon data, and found a great degree of similarity between sedimentary rocks in southern Africa and adjoining parts of Gondwana, concluding that the late Mesoproterozoic and Neoproterozoic age and Hf isotope signature (b and c in Fig. 3) is a common feature for western Gondwana that cannot be assigned to a specific source terrane with any degree of confidence. The data reviewed in this paper support this assessment, as does the presence of the same (b + c) zircon age components in the Congo Basin (Linol et al., 2016).

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5.4. The problem of the missing Archaean

The virtual absence of Archaean detrital zircon is a common feature for all samples of

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this study, and indeed for all Phanerozoic sediments from the region that have so far been

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studied. The only exceptions are the basal layers of the Natal Group (Kristoffersen et al., 2016), Permian sandstones in the Ellisras basin (southern part of the Kalahari basin; Veevers

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and Saeed, 2007) and some of the samples of Dwyka diamictite from western South Africa analysed by Jansson (2010).

Possible explanations for the lack of Archaean detrital zircon include: (1) The sources

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were outside of southern Africa, for example in central Antarctica (Veevers and Saeed, 2007), or in other parts of former Gondwana (Fourie et al., 2011). Such sources are, however, in

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some conflict with the pattern of sediment transport discussed above. (2): The NamaquaNatal Belt acted as a topographic barrier during deposition of the Cape Supergroup, preventing material from farther north (e.g. Kaapvaal Craton) from reaching the basin (Fourie

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et al., 2011). This requires the barrier to have persisted for 500 Ma, surviving even the

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formation and denudation of the Neoproterozoic mobile belts which eventually provided the depositional basement for the Cape basin. (3): The Kaapvaal Craton was submerged or

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unexposed during the early stages of Karoo sedimentation. This is in conflict with evidence that deposits of the Dwyka and Ecca Groups along the northern margin of the basin were fed by material from northern and northeastern sources, including the Cargonian Highlands, situated well within the Kaapvaal Craton (Fig. 1b). (4): Archaean zircon has been exposed to

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radiation damage and physical abrasion for a longer time than younger zircon, and may thus have been selectively removed during erosion and transport. If this has been the reason, the effect must have been applicable only to the sediments deposited in the Main Karoo Basin. Permian sandstones (Vryheid Formation equivalents) in the Ellisras basin are dominated by Archaean age fractions (Veevers and Saeed, 2007), which suggests that selective removal cannot be invoked as a general explanation. (5): Changes in sea level caused stronger incision of rivers in lower reaches of the continent, thereby swamping the Archaean signal (e.g. Cawood et al., 2003). This is a model that cannot be tested from the data available at present. However, such a mechanism certainly does not control the detrital zircon budget of Cenozoic sediments along the coast of eastern South Africa, in which recycled Karoo material from the higher reaches of the rivers feeding the deposits dominate over material from Archaean basement eroded in the lower reaches (Andersen et al., 2015). None of these five hypotheses can be considered entirely satisfactory.

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5.5. Recycling of a common precursor?

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An alternative scenario which may reconcile the palaeocurrent and transport patterns

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with the similarity of detrital zircon signatures in the lower part of the northeastern Karoo and the Cape sandstones, and may explain the lack of Archaean zircon in both, would be that both

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sequences contain recycled material from a common Neoproterozoic sedimentary precursor that partly covered the Kaapvaal Craton, but which was removed by glacial and fluvial erosion in the Palaeozoic and early Mesozoic (Fig. 12). The Namaqua-Natal Belt formed in

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the late Mesoproterozoic as an orogenic belt during assembly of Rodinia, which involved accretion and trusting of exotic terranes over Archaean and Palaeoproterozoic basement and

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eventually collision with another continental block (Cornell et al., 2006; McCourt et al., 2006; Mendonidis et al., 2015). This must have resulted in a topographic high bordering against the Kaapvaal Craton, the denudation of which will have yielded significant amounts of

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Mesoproterozoic detritus (Fig. 12a, b). The system of Neoproterozoic mobile belts

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surrounding the cratonic core were also high-relief areas that had to be denuded before they could act as depositional basement for the Cape Supergroup. Part of the detritus shed during

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denudation of these mountain ranges must have been deposited on Kaapvaal Craton basement (Fig. 12 c, d). The only preserved remnants of Neoproterozoic to Cambrian sedimentary cover in the region are the Gariep Supergroup and the Nama and Vanrhynsdorp Groups of southern Namibia and western South Africa, of which the detrital zircon age patterns of the Nama

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Group are compatible with what can be predicted for a precursor for the Cape and Karoo Supergroup sandstones (Figs. 3, 4). How far east such cover sequences may have existed in the past is unknown. Glaciogenic Dwyka Group deposits on the craton mainly consist of valley fills made up by material abraded off topographic highs. The valleys filled by this material were also the natural pathways for post-glacial rivers that delivered sediment to delta deposits of the Vryheid Formation along the northern basin margin. It is therefore a possible scenario that the Cape basin in the early Palaeozoic and the northern rim of the Main Karoo basin in Permian time both received material recycled from older sedimentary sequences on mainland southern Africa (Fig. 12 e, f). This would be an ancient parallel to the situation in Cenozoic sediments in eastern South Africa studied by Andersen et al. (2015), which are almost devoid of Archaean zircon even where deposited by rivers eroding Archaean basement, because any Archaean component is camouflaged by an overwhelming amount of material from Karoo sandstones. Like some other models that have been proposed (Veevers

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and Saeed, 2007; Fourie et al., 2011), this hypothesis is based only on detrital zircon data without support from independent evidence. However, systematic detrital zircon studies on

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the valley fill facies of the northeastern Dwyka Group could test this as a feasible scenario.

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5.6. Consequences for application of detrital zircon data

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Continental evolution. If the data from the present study - or in fact data from almost any of the published studies on detrital zircon in Neoproterozoic and Phanerozoic sediments and sedimentary rocks in southern Africa reviewed above, including sediments in the Zambezi

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and Orange rivers (Iizuka et al., 2013), were used to derive a first history of continental evolution, a highly biased model neglecting Archean crustal growth would result. Regardless

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of the reason for the scarcity or absence of Archaean zircon in the vast majority of samples studied until now, the Kaapvaal Craton would be unlikely to figure as a significant feature of southern African geology or of Gondwana. Since few, if any, attempts to test the robustness

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of the crustal evolution signal from detrital zircon have been carried out in geological settings

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that are equally well constrained by independent data, it remains unknown whether this mismatch between bedrock geology and detrital zircon patterns of sedimentary cover is a

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general feature, or something specific to southern Africa. Sedimentary deposits in the region ranging in age from Neoproterozoic to Recent certainly do not reflect all of the important crustal extraction processes recorded by the regional bedrock that is required for detrital zircon to be a reliable indicator of crustal evolution. A message to take home from this study

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is that any research on the extraction, evolution and preservation of continental crust based on detrital zircon without solid support by independent information should be regarded with a certain amount of scepticism. Detrital zircon may still have potential to contribute to the understanding of such processes, but only when the external framework of basement and surface geology and its evolution through time are understood in advance.

Provenance analysis. One reason why detrital zircon has become such a popular tool in sedimentary provenance studies is that no detailed knowledge of the geology and geochemistry of the actual source regions seems to be required, beyond a broad control of the chronology of rock-forming processes. In contrast, the use of heavy mineral assemblages to fingerprint sources requires knowledge of the petrography of the major rock types in the potential source terranes and their relative distribution. Detrital zircon is insensitive to chemical alteration during erosion and transport, both of which can modify the major and

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trace element composition of bulk sediments and other constituent minerals. This was pointed out in a recent multi-method study by Vermeesch and Garzanti (2015), who proposed that detrital zircon age distributions carry more directly source-related information than

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petrography and whole rock geochemistry. However, this is true only if the link to

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protosources has not been obscured by recycling and mixing of material from different sources. The problem becomes especially grave if detritus has had a long lifetime in

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successive cover sequences in a continental or supercontinental environment. In the case of southern Africa, a large proportion of the detritus making up Palaeozoic to Recent cover sequences must have remained in the recycling mill since Neoproterozoic time. This adds

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another disturbing effect: because of the physical and chemical robustness of zircon, it may be significantly enriched with respect to less resistent minerals in such a chain of processes, and

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in the end it may have been sufficiently enriched in the heavy fraction to obscure any firstgeneration contribution from bedrock sources (Andersen et al., 2015; this study).

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6. Conclusions

Sandstones from three important Phanerozoic sedimentary sequences in South Africa, the

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Cape Supergroup, the Msikaba Formation and the Karoo Supergroup show similar detrital zircon age and Hf isotope distribution patterns, with major late Neoproterozoic-early Phanerozoic and late Mesoproterozoic components in common. These patterns have features in common with the detrital zircon populations of Neoproterozoic sedimentary rocks in the

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region, but they lack the specific age and Hf isotope characteristics expected from bedrock sources within the late Mesoproterozoic Namaqua-Natal Belt. The late Mesoproterozoic and late Neoproterozoic-early Palaeozoic zircon fractions are much more likely to have been derived by recycling of earlier cover sequences on Mesoproterozoic to Archaean basement than directly from first-generation sources. They carry no specific and interpretable provenance information, and the sandstones hosting the zircons represent more or less homogenized mixtures of detritus from Mesoproterozoic and Neoproterozoic mountain belts that were denuded before deposition of the Cape Supergroup in the early Palaeozoic. Late Palaeozoic detrital zircon in the higher part of the succession in the northeastern part of the Karoo basin does carry provenance information, suggesting a scenario in which southern sources had become dominant and material transport across the basin was possible. However, these zircons are significantly older their host sediments, and thus give no useful limits for the timing of deposition.

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A crustal evolution model built on the detrital zircon data presented in this study, and of published studies that have been reviewed, would fail to detect the existence of the Kaapvaal Craton and the entire Archaean crustal evolution of southern Africa. Although

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detrital zircon may contribute to the understanding of continental evolution, using them in

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unknown territory may have little meaning.

Whereas the findings in this study suggest that detrital zircon is a less robust

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provenance indicator than commonly believed, this does not imply that the zircons should in general be left to rest in peace. The Phanerozoic basins of southern Africa represent a situation in which a face-value interpretation of detrital zircon data cannot easily be

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reconciled with existing sedimentary transport paths based on interpretation of sound geological data. In such a context, geological information must take precedence, but detrital

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zircons can be used to point to aspects of currently accepted models that need further research, such as the possible existence of cover sequences that have not survived erosion.

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Acknowledgements.

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This study received economic support from the University of Oslo through Småforsk grants from the Department of Geosciences to TA. The authors thank Siri Simonsen for skilled

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assistance in the lab. Nigel Hicks was instrumental in obtaining the samples from the Msikaba Fmt. Helpful comments from Henning Dypvik and Johan Petter Nystuen are gratefully acknowledged, as are critical but helpful reviews by Bastien Linol, Steve McCourt and two anonymous reviewers. T.A. wants to express his gratitude to the University of Johannesburg

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for the opportunity to work with the Department of Geology as a visiting professor.

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References Andersen, T., 2005. Detrital zircons as tracers of sedimentary provenance: limiting conditions from statistics and numerical simulation. Chemical Geology 216, 249–270.

T

Andersen, T., 2014. The detrital zircon record: Supercontinents, parallel evolution - or

IP

coincidence? Precambrian Research 244, 279-287.

Andersen, T., Andersson, U.B, Graham, S., Åberg, G., Simonsen, S.L., 2009. Granitic

SC R

magmatism by melting of juvenile continental crust: New constraints on the source of Palaeoproterozoic granitoids in Fennoscandia from Hf isotopes in zircon. Journal of the Geological Society, London 166, 233-248.

NU

Andersen, T., Elburg, M., Cawthorn-Blazeby, A., 2015. U–Pb and Lu–Hf zircon data in young sediments reflect sedimentary recycling in eastern South Africa. Journal of the

MA

Geological Society XXX, xxx-xxx, in press, doi:10.1144/jgs2015-006. Bangert, B., Stollhofen, H., Lorenz, V., Armstrong, R., 1999. The geochronology and significance of ash-fall tuffs in the glaciogenic Carboniferous-Permian Dwyka Group of

D

Namibia and South Africa. Journal of African Earth Sciences 29, 33-49.

TE

Bailie, R., Rajesh, H.M., Gutzmer, J., 2012. Bimodal volcanism at the western margin of the Kaapvaal Craton in the aftermath of collisional events during the Namaqua-Natal Orogeny:

CE P

The Koras Group, South Africa. Precambrian Research 200-203, 163-183. Belousova, E.A., Griffin, W.L., O'Reilly, S.Y., 2006. Zircon crystal morphology, trace element signatures and Hf isotope composition as a tool for petrogenetic modelling: Examples from eastern Australian granitoids. Journal of Petrology 47, 329-353.

AC

Belousova, E.A., Kostitsyn, Y.A., Griffin, W.L., Begg, G.C., O’Reilly, S.Y., Pearson, N.J., 2010. The growth of the continental crust: constraints from zircon Hf-isotope data. Lithos 119, 457–466.

Blanco, G., Germs, G.J.B., Rajesh, H.M., Chemale, F., Jr., Dussin, I.A., Justino, D., 2011. Provenance and paleogeography of the Nama Group (Ediacaran to early Palaeozoic, Namibia): Petrography, geochemistry and U–Pb detrital zircon geochronology. Precambrian Research 187, 15–32. Bouvier, A., Vervoort, J.D., Patchett, P.J., 2008. The Lu-Hf and Sm-Nd isotopic composition of CHUR: Constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters 273, 48-57. Bowden, L.L., 2013. A comparative study of detrital zircon ages from river sediment and rocks of the Karoo Supergroup (late Carboniferous to Jurassic), Eastern Cape Province, South Africa: Implications for the tectono-sedimentary evolution of Gondwanaland’s

ACCEPTED MANUSCRIPT

25

southern continental margin. Unpublished M.Sc. thesis, University of Johannesburg, South Africa. Retrieved from: https//ujdigispace.uj.ac.za, Cadle, A.B., Cairncross, B., Christie, A.D.M., Roberts, D.L., 1993. The Karoo Basin of

T

South Africa: type basin for the coal-bearing deposits of southern Africa. International

IP

Journal of Coal Geology 23, 117-157.

Catuneanu, O., Hancox, P.J., Rubidge, B.S., 1998. Reciprocal flexural behaviour and

SC R

contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa. Basin Research 10, 417-439.

Catuneanu, O., Hancox, P.J., Cairncross, B., Rubidge, B.S., 2002. Foredeep submarine fans

African Earth Sciences 35, 489–502.

NU

and forebulge deltas: orogenic off-loading in the underfilled Karoo Basin. Journal of

MA

Catuneanu, O., Wopfner, H., Eriksson, P.G., Cairncross, B., Rubidge, B.S., Smith, R.M.H., Hancox, P.J., 2005. The Karoo basins of south–central Africa. Journal of African Earth Sciences 43, 211–253.

D

Cawood , P. A., Nemchin, A. A., Freeman, M., Sircombe, K., 2003. Linking source and

TE

sedimentary basin: Detrital zircon record of sediment flux along a modern river system and implications for provenance studies. Earth and Planetary Science Letters 210, 259-268.

CE P

Christie, A.D.M., 1988. Sedimentary models for coal formation in the Klip River Coalfield. Unpublished PhD thesis, University of Natal, Durban, South Africa. Cole, D.I., 2007. Late Carboniferous to Permian sequence stratigraphy in the main Karoo Basin of South Africa and its application in Southwestern Gondwanaland. In: Iannuzzi, R.,

AC

Boardman, D.T. (Eds.), Problems in Western Gondwana Geology, I. Workshop ―South America – Africa correlations: du Toit revisited, 26-33. http://www.ufrgs.br/alpp/Problems_Gondwana.pdf Condie, K.C., Bickford, M.E., Aster, R.C., Belousova, E.A., Scholl, D.W., 2011. Episodic zircon ages, Hf isotopic composition, and the preservation rate of continental crust. Geological Society of America Bulletin 123, 951–957. Dean, J.R., 2014. U-Pb Detrital Zircon Geochronology within the Cape Fold Belt/Karoo Basin System. Unpublished M.Sc. thesis, West Virginia University. Dickinson, W.R., Lawton, T.F., Gehrels, G.E., 2009. Recycling detrital zircons: A case study from the Cretaceous Bisbee Group of southern Arizona. Geology 37, 503-506. Dorland, H.C., 2004. Provenance ages and timing of sedimentation of selected Neoarchaean and Palaeoproterozoic successions on the Kaapvaal Craton. Unpublished PhD thesis, Rand Afrikaans University, Johannesburg.

ACCEPTED MANUSCRIPT

26

Ducea, M.N., Otamendi, J.E., Bergantz, G., Stair, K.M., Valencia, V.A., Gehrels, G.E., 2010. Timing constraints on building and intermediate plutonic arc crustal section: U-Pb zircon geochronology of the Sierra Valle Fértil – La Huerta, Famantinian arc, Argentina. Tectonics

T

29, TC4002, doi: 10.1029/2009TC002615

IP

Duncan, A.R., Marsh, J.S., 2006. The Karoo igneous province. In: Johnson, M.R, Anhaeusser, C.R., Thomas, R.J. (Eds.), The Geology of South Africa. Geological Society of South

SC R

Africa and Council for Geosciences, Johannesburg and Pretoria, South Africa, 501-520. Eglington, B.M., Armstrong, R.A., 2003. Geochronological and isotopic constraints on the Mesoproterozoic Namaqua–Natal Belt: evidence from deep borehole intersections in South

NU

Africa. Precambrian Research 125, 179-189.

Elburg, M., Andersen, T., Bons, P.D., Simonsen, S.L., Weisheit, A., 2013. New constraints on

MA

Phanerozoic magmatic and hydrothermal events in the Mt Painter Province, South Australia. Gondwana Research 24, 700-712.

Elburg, M.A., Goldberg, A., 2000. Age and geochemistry of Karoo dolerite dykes from NE

D

Botswana. Journal of African Earth Sciences 31, 539-554.

TE

Evans, D.A.D., 2009. The palaeomagnetically viable, long-lived and all-inclusive Rodinia supercontinent reconstruction. In: Murphy, J.B., Keppie, J.D., Hynes, A.J. (Eds.), Ancient

371–404.

CE P

Orogens and Modern Analogues. Geological Society, London, Special Publications 327,

Fanning, C.M., Hervé, F., Pankhurst, R.J.,Rapela, C.W., Kleiman, L.E., Yaxley, G.M., Castillo, P., 2011. LueHf isotope evidence for the provenance of Permian detritus in

AC

accretionary complexes of western Patagonia and the northern Antarctic Peninsula region. Journal of South American Earth Sciences 32,485-496. Fildani, A., Weislogel, A., Drinkwater, N.J., McHargue, T., Tankard, A., Wooden, J., Hodgson, D., Flint, S., 2009. U-Pb zircon ages from the southwestern Karoo Basin, South Africa: Implications for the Permian-Triassic boundary. Geology 37, 719-722. Flowerdew, M.J., Millar, I.L., Vaughan , A.P.M., Horstwood, M.S.A., Fanning, C.M., 2006. The source of granitic gneisses and migmatites in the Antarctic Peninsula: a combined U– Pb SHRIMP and laser ablation Hf isotope study of complex zircons. Contributions to Mineralogy and Petrology 151, 751-768. Foster, D.A., Goscombe, B.D., Newstead, B., Mapani, B., Mueller, P.A., Gregory, L.C., Muvangua, E., 2015. U–Pb age and Lu–Hf isotopic data of detrital zircons from the Neoproterozoic Damara Sequence: implications for Congo and Kalahari before Gondwana. Gondwana Research 28, 179–190. http://dx.doi.org/10.1016/j.gr.2014.04.011.

ACCEPTED MANUSCRIPT

27

Fourie, P.H., Zimmermann, U., Beukes, N.J., Naidoo, T., Kobayashi, K., Kosler, J., Nakamura, E., Tait, J.,Theron, J.N., 2011. Provenance and reconnaissance study of detrital zircons of the Palaeozoic Cape Supergroup in South Africa: revealing the interaction of the

T

Kalahari and Río de la Plata cratons. International Journal of Earth Sciences, 100, 527-541.

IP

Frimmel, H.E., Xeh, A., Lehrmann. B., Hallbauer, D., Frank, W., 2009. Geochemical and Geochronological Constraints on the Nature of the Immediate Basement next to the

SC R

Mesoarchaean Auriferous Witwatersrand Basin, South Africa. Journal of Petrology 50, 2187-2220.

Frimmel, H.E., Basei, M.S., Gaucher, C., 2011. Neoproterozoic geodynamic evolution of

NU

SW-Gondwana: a southern African perspective. International Journal of Earth Sciences 100, 323-354

MA

Frimmel, H.E., Basei, M.A.S., Gorrea,V.X., Ndawedapo, M., 2013. A new lithostratigraphic subdivision and geodynamic model for the Pan-African western Saldania Belt, South Africa. Precambrian Research 231, 218–235.

D

Garzanti, E., Vermeesch, P., Padoan, M., Resentini, A., Vezzoli, G., Andò, S., 2014.

TE

Provenance of Passive-Margin Sand (Southern Africa). The Journal of Geology 122, 17-42. Green, A.N., Smith, A,M., 2012. Can ancient shelf sand ridges be mistaken for Gilbert-type

CE P

deltas? Examples from the Vryheid Formation, Ecca Group, KwaZulu-Natal, South Africa. Journal of African Earth Sciences, 76, 27-33. Gehrels, G.E., 2012. Detrital zircon U-Pb geochronology: current methods and new opportunities. In: Busby, C., Azor, A. (Eds.), Tectonics of sedimentary basins: Recent

AC

advances. Blackwell Publishing Ltd., Oxford, UK, 47-62. Gresse, P.G., von Veh, M.W., Frimmel, H., 2006. Namibian (Neoproterozoic) to early Cambrian successions. In: Johnson, M.R, Anhaeusser, C.R., Thomas, R.J. (Eds.), The Geology of South Africa. Geological Society of South Africa and Council for Geosciences, Johannesburg and Pretoria, South Africa, 395-420. Griffin, W.L., Pearson, N.J., Belousova, E., Jackson, S.E., van Achterbergh, E., O’Reilly, S.Y., Shee, S.R., 2000. The Hf isotope composition of cratonic mantle: LAM-MC-ICPMS analysis of zircon megacrysts in kimberlites. Geochimica et Cosmochimica Acta 64, 133147. Griffin, W.L., Belousova, E.A., Shee, S.R., Pearson, N.J., O’Reilly, S.Y., 2004. Archean crustal evolution in the northern Yilgarn Craton: U–Pb and Hf-isotope evidence from detrital zircons. Precambrian Research 131, 231–282.

ACCEPTED MANUSCRIPT

28

Gutzmer, J., Beukes, N.J., Picard, A., Barley, M.E., 2000. 1170 Ma SHRIMP age for Koras Group bimodal volcanism, Northern Cape Province. South African Journal of Geology 103, 32-37.

T

Hadlari, T.,Swindlee, G.T., Galloway, J.M., Bell, K.M.,Sulphur, K.C., Heaman, L.M.,

IP

Beranek, L.P., Fallas, K.M., 2015. 1.8 billion years of detrital zircon recycling calibrates a refractory part of Earth’s sedimentary cycle. PLoS ONE 10(12):e0144727, doi:

SC R

10.1271/journal.pone.0144727

Hansma, J., Tohver, E., Schrank, C., Jourdan, F., Adams, D., 2015. The timing of the Cape Orogeny: New 40Ar/39Ar age constraints on deformation and cooling of the Cape Fold Belt,

NU

South Africa. Gondwana Research, in press. doi:10.1016/j.gr.2015.02.005 Heinonen, A.P., Andersen, T., Rämö, O.T., 2010. Re-evaluation of rapakivi petrogenesis:

MA

Source constraints from the Hf isotope composition of zircon in the rapakivi granites and associated mafic rocks of southern Finland. Journal of Petrology 51, 1687-1709. Hicks, N., Elburg, M., Andersen, T., 2015. U-Pb and Hf isotope constraints for emplacement

TE

of Geology 118, 119-128.

D

of the Nkandla granite, southeastern Kaapvaal Craton, South Africa. South African Journal

Hongn, F.D., Tubía, J.M., Esteban, J.J., Arganguren. A., Vegas, N., Sergeev, S., Larionov, A.,

CE P

Basei, M. 2104. The Sierra de Cachi (Salta, NW Argentina): geological evidence about a Famatinian retro-arc at mid crustal levels. Journal of Iberian Geology 40, 225-240. Hofmann, M., Linnemann, U., Hoffmann, K.-H., Gerdes, A., Eckelmann, K., Gärtner, A., 2014. The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton,

AC

Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana. International Journal of Earth Sciences 103, 1187–1202. Hofmann, M., Linnemann, U., Hoffmann, K.H., Germs, G., Gerdes, A., Marko, L., Eckelmann, K., Gärtner, A., Krause, R., 2015. The four Neoproterozoic glaciations of southern Namibia and their detrital zircon record: The fingerprints of four crustal growth events during two supercontinent cycles. Precambrian Research 259, 176-188. Hole, M.J., Ellam, R.M., Macdonald, D.I.M, Kelly, S.P., 2015. Gondwana break-up related magmatism in the Falkland Islands. Journal of the Geological Society XXX, xxx-xxx. in press. doi:10.1144/jgs2015-027 Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halkoaho, T., Hanski, E., Hokkanen, T., Hölttä, P., Juopperi, H., Konnunaho, J., Layahe, Y., Luukkonen. E., Pietikäinen. K., Pulkkinen, A., Sorjonen-Ward, P., Vaasjoki, M., Whitehouse, M., 2012. The age of the

ACCEPTED MANUSCRIPT

29

Archaean greenstone belts in Finland. Geological Survey of Finland, Special Paper 54, 74−175. Iizuka, T., Komiya, T., Rino, S., Maruyama, S., Hirata, T., 2010. Detrital zircon evidence for

T

Hf isotopic evolution of granitic crust and continental growth. Geochimica et

IP

Cosmochimica Acta 74, 2450–2472.

Iizuka, T., Campbell, I.H., Allen, C.M., Gill, J.B., Maruyama, S., Makoka, F., 2013.

SC R

Evolution of the African continental crust as recorded by U-Pb, Lu-Hf and O isotopes in detrital zircons from modern rivers. Geochimica et Cosmochimica Acta 107, 96-120. Jacobs, J., Fanning, M., Henjes-Kunst, F., Olesch, M., Paech, H.-J., 1998. Continuation of the

NU

Mozambique Belt into East Antarctica: Grenville-Age Metamorphism and Polyphase PanAfrican High-Grade Events in Central Dronning Maud Land. The Journal of Geology 106,

MA

385-406.

Jacobs, J., Pisarevsky, S., Thomas, R.J., Becker, T., 2008. The Kalahari Craton during the assembly and dispersal of Rodinia. Precambrian Research 160, 142–158.

D

Jacobs, J., Elburg, M., Laeufer, A., Kleinhanns, I.C., Henjes-Kunst, F., Estrada, S., Ruppel,

TE

A., Damaske, D., Montero, P., Bea, F., 2015. Two distinct Late Mesoproterozoic/Early Neoproterozoic basement provinces in central/eastern Dronnning Maud Land, East

CE P

Antarctica: the missing link, 15-21°E. Precambrian Research 265, 249-272. Jansson, E., 2010. What lies under the Kalahari sand ? U/Pb dating of Dwyka tillites, South Africa. Unpublished M.Sc. thesis, University of Gothenburg, Sweden. Johnson, M.R., van Vuuren, C.J., Visser, J.N.J, Cole, D.I., Wickens, H. de V., Christie,

AC

A.D.M., Roberts, D.L., Brandl, G., 2006. Sedimentary rocks of the Karoo Supergroup. In: Johnson, M.R, Anhaeusser, C.R., Thomas, R.J. (Eds.), The Geology of South Africa. Geological Society of South Africa and Council for Geosciences, Johannesburg and Pretoria, South Africa, 461-499. Johnston, S.T., 2000. The Cape Fold Belt and Syntaxis and the rotated Falkland Islands: dextral transpressional tectonics along the southwest margin of Gondwana. Journal of African Earth Sciences 31, 51–63. Keyser, N., Zawada, P.K., 1988. Two occurrences of ash-flow tuff from the lower Beaufort Group in the Heilbron-Frankfort area, northern Orange Free State. South African Journal of Geology 91, 509-521. Klama, K.O., 2008. U-Pb Geochronologie, Hf Isotopie und Spurenelementgeochemie detritischer Zirkone aus rezenten Sedimenten des Orange- und Vaal River Flusssystems in

ACCEPTED MANUSCRIPT

30

Südafrika. Unpublished PhD thesis, Johann Wolfgang Goethe-Universität Frankfurt am Main, Germany. Koglin, N., Zeh, A., Frimmel, H.E., Gerdes, A., 2010. New constraints on the auriferous

T

Witwatersrand sediment provenance from combined detrital zircon U–Pb and Lu–Hf

IP

isotope data for the Eldorado Reef (Central Rand Group, South Africa). Precambrian Research 183, 817-824.

SC R

Kositcin, N., Krapež, B., 2004. Relationship between detrital zircon age-spectra and the tectonic evolution of the Late Archaean Witwatersrand Basin, South Africa. Precambrian Research 129, 141-168.

NU

Kramers, J.D., McCourt, S. & van Reenen, D.D., 2006. The Limpopo Belt. In: Johnson, M.R, Anhaeusser, C.R., Thomas, R.J. (Eds.), The Geology of South Africa. Geological Society of

MA

South Africa and Council for Geosciences, Johannesburg and Pretoria, South Africa, 209– 236.

Kristoffersen, M., Andersen, T., Elburg, M.A., Watkeys, M.K., 2016. Detrital zircon in a

D

supercontinental setting: locally derived and far-transported components in the Ordovician

TE

Natal Group, South Africa. Journal of the Geological Society, London. 2015–012. Published online 27. Oct. 2015. doi:10.1144/jgs2015-012

CE P

Kröner, A., Stern, R.J., 2004, Pan African Orogeny. Encyclopedia of Geology, Elsevier, Amsterdam, The Netherlands. Vol 1, pp. 1-12. doi:10.1016/B0-12-369396-9/00431-7 Lanci, L., Tohver, E., Wilson, A., Flint, S., 2013. Upper Permian magnetic stratigraphy of the lower Beaufort Group, Karoo Basin. Earth and Planetary Science Letters 375, 123-134.

AC

Macdonald, D.I.M., Gomez-Perez, I., Franzese, J., Spalletti, L., Lawver, L., Gahagan, L., Dalziel, I., Thomas, C., Trewin, N., Hole, M., Paton, D., 2003. Mesozoic break-up of SW Gondwana: Implications for regional hydrocarbon potential of the southern South Atlantic. Marine and Petroleum Geology 20, 287–308. Marschall, H.R., Hawkesworth, C.J., Leat, P.T., 2013. Mesoproterozoic subduction under the eastern edge of the Kalahari-Grunehogna Craton preceding Rodinia assembly: The Ritscherflya detrital zircon record, Ahlmannryggen (Dronning Maud Land, Antarctica). Precambrian Research 236, 31-45. Marshall, C.G.A., 2002. The Stratigraphy, Sedimentology and Basin Evolutionof the Natal Group. Council for Geosciences Memoir 91. McKay, M., P., Weislogel, A.L., Fildani, A., Brunt, R.L., Hodgseon, D.M., Flint, S.S., 2015. U-Pb zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls. International Geology Review 57, 393-410.

ACCEPTED MANUSCRIPT

31

Mendonidis, P., Thomas, R.J., Grantham, G.H., Armstrong, R.A., 2015. Geochronology of emplacement and charnockite formation of theMargate Granite Suite, Natal Metamorphic Province, South Africa:Implications for Natal-Maud belt correlations. Precambrian

T

Research 265, 189-202.

IP

Milani, E.J., De Wit, M.J., 2008. Correlations between the classic Parana and Cape–Karoo sequences of South America and southern Africa and their basin infills flanking the

SC R

Gondwanides: du Toit revisited. In: Pankhurst, R.J., Trouw, R.A.J., Brito Neves, B.B., De Wit, M.J. (Eds.), West Gondwana: Pre-Cenozoic Correlations Across the South Atlantic Region. Geological Society, London, Special Publications 294, 319–342.

NU

Naidoo, T., Zimmermann, U., Chemale, F. 2013. The evolution of Gondwana: U–Pb, Sm–Nd, Pb–Pb and geochemical data from Neoproterozoic to Early Palaeozoic successions of the

MA

Kango Inlier (Saldania Belt, South Africa). Sedimentary Geology 294, 164-178. Newton, A.R., Shone, R.W., Booth, P.W.K., 2006. The Cape Fold Belt. In: Johnson, M.R, Anhaeusser, C.R., Thomas, R.J. (Eds.), The Geology of South Africa. Geological Society of

D

South Africa and Council for Geosciences, Johannesburg and Pretoria, South Africa, 521-

TE

530.

Pankhurst, R.J., Rapela, C.W., Lópes de Luchi, M.G., Rapalini, A.E., Fanning, C.M.,

CE P

Galindo, C., 2014. The Gondwana connections of northern Patagonia. Journal of the Geological Society, London 171, 313-328 Pettersson, Å., Cornell, D.H., Moen, H.F.G., Reddy, S., Evans, D., 2007. Ion-probe dating of 1.2 Ga collision and crustal architecture in the Namaqua-Natal Province of southern Africa.

AC

Precambrian Research 158, 79-82. Poma, S., Zappettini, E.O., Quenardelle, S., Santos, J.O., Kukaharsky, M., Belousova,E., McNaughton, N. 2014. Geochemistry, U-Pb SHRIMP zircon dating and Hf isotopes of the Gondwanan magmatism in NW Argentina: petrogenesis and geodynamic implications. Andean Geology 41, 267-292. Reinhardt, J., Elburg, M.A., Andersen, T., 2015. Zircon U-Pb age data and Hf isotope signature of Kaapvaal basement granites from the Archaean White Mfolozi Inlier, northern KwaZulu-Natal. South African Journal of Geology 118, 473-488. Roberts, N.M.W., Spencer, C.J., 2015. The zircon archive of continent formation through time. In: Roberts, N.M.W., van Kranendonck, M., Parman.S., Shirey, S., Clift, P.D., (Eds), Continent formation through time. Geological Society, London, Special Publication 389, 197-225.

ACCEPTED MANUSCRIPT

32

Rubidge, B.S., Erwin, D.H., Ramezani, J., Bowring, S.A., de Klerk, W.J. 2013. Highprecision temporal calibration of Late Permian vertebrate biostratigraphy: U-Pb zircon constraints from the Karoo Supergroup, South Africa. Geology 41, 363-366.

T

Satkoski, A.M., Wilkinson, B.H., Hietpas, J.H., Samson, S.D., 2013. Likeness among detrital

IP

zircon populations - An approach to the comparison of age frequency data in time and space. Geological Society of America Bulletin 125, 1783-1799.

SC R

Saylor, J.E., Knowles, J.N., Horton, B.K., Nie, J., Mora, A., 2013. Mixing of source populations recorded in detrital zircon U-Pb age spectra of modern river sands. The Journal of Geology 121, 17-33.

NU

Shone, R.W., Booth, P.W.K., 2005. The Cape Basin, South Africa: A review. Journal of African Earth Sciences 43, 196-210.

MA

Smith, R.M.H., Eriksson, P.G., Botha, W.J., 1993. A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa. Journal of African Earth Sciences 16, 143-16.

D

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a

TE

two-stage model. Earth and Planetary Science Letters 26, 207– 221. Stern, R.J. 1994. Arc assembly and continental collision in the Neoproterozoic East African

CE P

Orogen: Implications for the consolidation of Gondwanaland. Annual Reviews Earth and Planetary Science 22, 319-351. Tankard, A., Welsink, H., Aukes, P., Newton, R., Stettler, E., 2012. Geodynamic interpretation of the Cape and Karoo basins, South Africa. In: Roberts, D.G., Bally, A.W.

AC

(Eds.): Phanerozoic Passive margins, Cratonic Basins and Global Tectonic Maps Vol 1c Elsevier, Amsterdam, 869-945. DOI: 1016/8978-0-444-5637-6.00022-6. Thamm, A.G., Johnson, M.R. 2006. The Cape Supergroup. In: Johnson, M.R, Anhaeusser, C.R., Thomas, R.J. (Eds.), The Geology of South Africa. Geological Society of South Africa and Council for Geosciences, Johannesburg and Pretoria, South Africa, 443-460. Thomas, R.J., Jacobs, J., Horstwood, M.S.A., Ueda, K., Bingen, B., Matola, R., 2010. The Mecubúri and Alto Benfica Groups, NE Mozambique: Aids to unravelling ca. 1 and 0.5 Ga events in the East African Orogen. Precambrian Research 178, 72-90. Thomas, W.A., 2011. Detrital zircon geochronology and sedimentary provenance. Lithosphere 3, 304-308. Torsvik, T.H., Cocks, L.R. 2011. The Palaeozoic palaeogeography of central Gondwana. In: Van Hinsbergen, D.J.H., Buiter, S.H.H., Torsvik, T.H., Gaina, C., Webb, S.J. (Eds.) The

ACCEPTED MANUSCRIPT

33

formation and evolution of Africa: A synopsis of Earth history. Geological Society of London Special Publications 357, 137-166. van Niekerk, H.S., 2006. The origin of the Kheis Terrane and its relationship with the

T

Archaean Kaapvaal Craton and the Grenvillian Namaqua Province in southern Africa.

IP

Unpublished PhD thesis, University of Johannesburg.

van Schijndel, V., Cornell, D.H., Hoffmann, K.-H., Frei, D., 2011 Three episodes of crustal

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development in the Rehoboth Province, Namibia. Geological Society, London, Special Publications 357, 27-47.

van Staden, A., 2011. Provenance analyses of Neoproterozoic/ Early Palaeozoic glacial (?)

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deposits from southwestern Gondwana. Unpublished PhD thesis, University of Johannesburg, South Africa.

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Veevers, J.J., Saeed, A., 2007. Central Antarctic provenance of Permian sandstones in Dronning Maud Land and the Karoo Basin: integration of U-Pb age and TDM ages and hostrock affinity from detrital zircons. Sedimentary Geology 202, 653-676.

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Veevers, J.J., Cole, D.I., Cowan, E.J., 1994. Southern Africa: Karoo Basin and Cape Fold

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Belt. In: Veevers, J.J., , Powell, C.McA. (Eds.), Permian-Triassic Pangean basins and foldbelts along the Panthalassan margin of Gondwanaland. Geological Society of America

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Memoir 184, 223-280

Vermeesch, P. 2013. Multi-sample comparison of detrital age distributions. Chemical Geology 341, 140-146.

Vermeesch, P. & Garzanti, E. 2015. Making geological sense of 'Big Data' in sedimentary

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provenance analysis. Chemical Geology, 409, 20-27. Vorster, C. 2013. Laser ablation ICP-MS age determination of detrital zircon populations in the Phanerozoic Cape and lower Karoo Supergroups (South Africa) and correlatives in Argentina. Unpublished PhD thesis, University of Johannesburg, South Africa. Vorster, C., Kramers, J., Beukes, N., van Niekerk, H., 2015. Detrital zircon U–Pb ages of the Palaeozoic Natal Group and Msikaba Formation, Kwazulu-Natal, South Africa: provenance areas in context of Gondwana. Geological Magazine XXX, xxx-xxx , in press. doi:10.1017/S0016756815000370 Wassermann, L. 2006. All of nonparametric statistics. Springer , New York. Watkeys, M.K. 2006. The break-up of Gondwana: a South African perspective. In: Johnson, M.R, Anhaeusser, C.R., Thomas, R.J. (Eds.), The Geology of South Africa. Geological Society of South Africa and Council for Geosciences, Johannesburg and Pretoria, South Africa, 531-539.

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Werner, M., 2006. The stratigraphy, sedimentology, and age of the Late Palaeozoic Mesosaurus Inland Sea, SW-Gondwana. New implications from studies on sediments and altered pyroclastic layers of the Dwyka and Ecca Group (lower Karoo Supergroup) in

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southern Namibia. Unpublished PhD thesis, University of Würtzburg, Germany.

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Wiedenbeck, M., Allé, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., Von Quadt, A., Roddick, J.C.,Spiegel, W., 1995. Three natural zircon standards for U-Th-Pb, Lu-Hf, trace

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element and REE analysis. Geostandards Newsletter 19, 1-23.

Woodhead, J.D., Hergt, J.M., 2005. A preliminary appraisal of seven natural zircon reference materials for in situ Hf isotope determination. Geostandards and Geoanalytical Research 29,

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183-195.

Zeh, A., Gerdes, A., 2012. U–Pb and Hf isotope record of detrital zircons from gold-bearing

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sediments of the Pietersburg Greenstone Belt (South Africa)—Is there a common provenance with the Witwatersrand Basin? Precambrian Research 204-205, 46-56. Zeh, A., Gerdes, A., Heubeck, C., 2013b. U−Pb and Hf isotope data of detrital zircons from

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the Barberton Greenstone Belt: constraints on provenance and Archaean crustal evolution.

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Journal of the Geological Society 170, 215-223 Zeh, A., Gerdes, A., Klemd, R., Barton Jr., J.M., 2007. Archean to Proterozoic crustal

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evolution of the Limpopo Belt (South Africa/Botswana): constraints from combined U–Pb and Lu–Hf isotope zircon analyses. Journal of Petrology 48, 1605–1639. Zeh, A., Gerdes, A., Barton Jr., J.M., 2009. Archean accretion and crustal evolution of the Kalahari Craton—the zircon age and Hf isotope record of granitic rocks from

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Barberton/Swaziland to the Francistown Arc. Journal of Petrology 50, 933–966. Zeh, A., Jaguin, J., Poujol, M., Boulvais, P., Block, S. & Paquette, J., 2013a. Juvenile crust formation in the northeastern Kaapvaal Craton at 2.97 Ga—Implications for Archean terrane accretion, and the source of the Pietersburg gold. Precambrian Research 233, 20–43. Zeh, A., Gerdes, A., Barton Jr., J.M., Klemd, R., 2010. U–Th–Pb and Lu–Hf systematics of zircon from TTG’s, leucosomes, anorthosites and quartzites of the Limpopo Belt (South Africa): constraints for the formation, recycling, and metamorphism of Paleoarchean crust. Precambrian Research 179, 50–68. Zeh, A., Gerdes, A., Klemd, R., Barton, J.M. Jr, 2008. U–Pb and Lu–Hf isotope record of detrital zircon grains from the Limpopo Belt – Evidence for crustal recycling at the Hadean to early-Archean transition. Geochimica et Cosmochimica Acta 72, 5304-5329. Zeh, A., Gerdes, A., Millonig, L., 2011. Hafnium isotope record of the Ancient Gneiss Complex, Swaziland, southern Africa: evidence for Archaean crust–mantle formation and

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crust reworking between 3.66 and 2.73 Ga. Journal of the Geological Society, London 168, 953–963. Zimmermann, U., Andersen, T., Madland, M.V., Larsen, I.S., 2015. The role of U-Pb ages of

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provenance interpretation. Sedimentary Geology 320, 38–50.

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detrital zircons in sedimentology—An alarming case study for the impact of sampling for

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Figure captions Figure 1

a: Schematic plate reconstruction of western Gondwana after Macdonald et al. (2003) and

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Hole et al. (2015). Abbreviations: E: Ellisras Basin, EW: Ellsworth-Whitmore Mountains,.F: Falklands Plateau, G: Grunehogna Craton, Ga: Gariep Belt, Ko: Koras Group, KVC:

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Kaapvaal Craton, L: Limpopo Belt, ME: Maurice-Ewing Bank, NQ: Namaqua and NA: Natal sectors of the Namaqua-Natal Belt, Nm: Nama Group, R: Rehoboth province, Vr: Vanrhynsdorp basin, ZC: Zimbabwe Craton. Latitude and longitude refer to the present-day

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grid for Africa. Dots: Sample localities (Red: Karoo Supergroup, Purple: Msikaba Formation,

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Blue: Cape Supergroup), see further detail in Supplementary Figures S1 and S2. b The situation in the early Palaeozoic with deposition of the Cape Supergroup, Msikaba

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Formation (MSI) and Natal Group (NAT) in basins on a continental basement, and with sources in the north (Cape) and northeast (Natal) indicated by ruling. Arrows are palaeocurrent vectors from Veevers et al. (1994) c: The situation during deposition of the Karoo Supergroup, with the preserved extent of the

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Karoo and coeval intracontinental basins indicated by shading, and possible source regions Cargonian Higlhands / Witwatersrand Arch (Car/WA) and Eastern Highlands (EH). Arrows show the main main sedimetnary transport directions in the Ecca Group (brown) and the lower part of the Beaufort Group (blue), after Veevers et al. (1994).

Figure 2 Generalized stratigraphic column of Neoproterozoic and Phanerozoic deposits of South Africa. Mainly derived from Catuneanu et al. (1998). The approximate stratigraphic positions of samples in the present study are indicated along the right margin. Further details are shown in Supplementary Figures S1 and S2. The histogram along the left margin is a compilation of zircon U-Pb ages from volcanic ash-layers in the southern part of the basin; for sources of data, see Table 1. Timing for deposition of the Karoo sequence follows Cole (2007); for units older than the Dwyka Group, the time scale is relative and uncalibrated. TAR = Tarkastad

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Subgroup; AD/Nor = Normandien Formation of the Adelaide Subgroup; VRY = Vryheid Formation; MSI = Msikaba Formation; NQ-NA = Namaqua-Natal Belt; KVC = Kaapvaal

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Craton.

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Figure 3

A survey of published detrital zircon U-Pb ages from southern Africa and adjoining parts of

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Gondwana. Sources of data from southern Africa, see Table 1. Data for the Congo Basin are from Linol et al. (2016), Patagonia from Fanning et al. (2011) and Poma et al. (2014), and Antarctic Peninsula from Fanning et al. (2011) . The black, vertical bars in the two uppermost

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frames show the width of the 95% confidence interval around a cumulative distribution curve based on 100 analysed grains (Andersen et al., 2015). Shaded background fields denoted a, b,

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c, d are intervals of high frequency of zircon ages observed in all or some of the age groups of sedimentary rocks. See further explanation in the text.

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Figure 4

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Survey of published Hf isotope data of zircon from sedimentary and igneous rocks of Western Gondwana, represented by the 1% of maximum height of Kernel Density Estimation (KDE)

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surfaces (bandwidths: 30 Ma, 1.5 epsilon Hf units). For sources of data, see Table 1. DM = depleted mantle; CHUR = chondritic uniform reservoir. a: Published data from the Karoo Supergroup and the Precambrian basement of South Africa. b: Rocks from Neoproterozoic belts of Namibia and western South Africa.

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c: Sedimentary rocks and Cape Granite Suite of the Saldania Belt, with rocks from the Mozambique Belt and granites from Dronnng Maud Land, Eastern Antarctica. d: Sedimentary rocks from Western Antarctica and Patagonia.

Figure 5 The geochronological "barcode" of southern Africa and neighbouring parts of Gondwana, compared to the main age groups (colour bands) of detrital zircon extracted from the published data in Fig. 4. The height of the bars represents the relative number of dates in each 20 Ma interval (maximum mumber: full scale). Sources of data are listed in Supplementary Table S1. *: Basement samples in deep drillcores through Karoo cover in the central part of the Namaqua-Natal Belt (Eglington and Armstrong, 2003).

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Figure 6 Representative cathodoluminescence images of zircons. Each grain is identified with its

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analysis number from Supplementary Table S2 and U-Pb age. The images have been chosen

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to give an impression of the variation of shape and internal structures seen in the samples. a: Sample SA13/113, upper Normandien Formation. Sub-rounded prismatic grain showing a

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combination of short-wavelength oscillatory zoning and sector zoning, with no evidence of secondary overprint.

b: Sample SA13/111, lower Normandien Formation. Doubly terminated, euhedral grain with

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osciallatory magmatic zoning overprinted by BSE-bright alteration discordant to the oscillatory zoning. The central part of the grain shows patchy zoning; this is not a xenocrystic

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core but is caused by intersecting the zircon subparallel to one of the narrow, magmatic zones. c: Sample 12/114, Tarkastad Subgroup. Angular fragment of a large, late Palaeozoic grain showing short wavelength magmatic zoning and no evidence of alteration.

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zoning as well as sector zoning.

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d: Sample SA13/114, Tarkastead Subgroup. Euhedral crystal with low amplitude oscillatory

e: Sample SA13/108, Vryheid Formation. Rounded grain showing a sector-zoning, and an

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outer, discontinuos rim of BSE bright, probably altered zircon. f: Sample SA13/114, Tarkastead Subgroup. Euhedral, angular crystal with short-wavelength oscillatory zoning and sector zoning. g: Sample SA13/111, lower Normandien Formation. Crystal fragmennt in which oscillatory

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and sector zoning (lower tip) has been altered to patchy, BSE bright zircon. h: Sample SA13/114, Tarkastad Subgroup. Rounded grain showing pronounced alteration to BSE bright zircon along the rims. The central part of the grain retains low-amplitude oscillatory magmatic zoning. i: Sample SA13/114, Tarkastad Subgroup. Irregular crystal fragment showing diffuse areas with variable BSE brightness, relict orscillatory zoning can be seen in the intermediate, darker part of the crystal. j: Sample SA13/129, top of Clarens Formation. Oscillatory zoned, subangular grain of Permian age. k: Sample SA13/129, top of Clarens Formation. Subangular grain of Permian age showing less well-developed oscillatory zoning that the one shown in j. l: Sample SA13/129, top of Clarens Formation Subrounded Permian grain without internal oscillatory zoning, but with a BSE bright outer zone that is only partly preserved

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Figure 7

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Age vs. epsilon Hf distribution patterns for detrital zircon from sandstones in the northeastern

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part of the Karoo Basin, data from supplementary Table S2.

The contours represent the KDE surface of the entire set of data from the Karoo Supergroup,

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calculated using bandwidths of 30 Ma (0.03 Ga) for age and 1.5 epsilon units for epsilon Hf. Blue lines are CHUR and Depleted Mantle curves, from Bouvier et al. (2008) and Griffin et

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al. (2000), respectively

Figure 8

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Cumulative distribution patterns for the samples from the Karoo Supergroup, grouped by stratigraphy.

a: Concordant (i.e. < 10% discordant) zircon ages. Shaded background fields (in yellow and

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grey) are as in Figure 3.

Figure 9

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b: Hf isotope depleted mantle model ages.

Detailed age distribution of the late Palaeozoic age fraction in the Karoo sandstones, shown as a histogram with 5 ma bin width, compared to the timing of deposition of the individual host

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rock, after Cole (2007).. Shaded fields in the upper bar represent ages of deposition of Karoo sediments, V: Vryheid Formation, N: Normandien Formation, T: Tarkastad Subgroup. M: Molteno Formation, E: Elliot Formation, C: Clarens Formation. Note that these zircons only occur in sedimentary rocks of the upper part of the Normaniden Formation and higher, i.e. in strata deposited after ca. 250 Ma.

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Figure 10 Data from Cape Supergroup and Msikaba Formation sandstones. The contours shown as a background in (a) and(b) represent the KDE surface of the entire set of data from the Karoo

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Supergroup as in Fig. 7..

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a: Age vs. epsilon Hf for the Cape Supergroup. b: Age vs. epsilon Hf for the Msikaba Formation

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c: Cumulative zircon age distribution patterns for the Msikaba Formation (SA12/55 and SA12/61) and Cape Supergroup.

d: Cumulative Hf model age distribution patterns for the Cape Supergroup and Msikaba

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Formation (samples SA12/55 and SA12/61, broken, black curves) and Cape Supergroup (Table Mountain Group: SA14/229, SA14/238, SA14/240, red curves, Bokkeveld Group:

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SA14/234, SA14/239, blue curves).

Figure 11

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Similarities and differences in detrital zircon age among the Cape and Karoo sandstones as

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defined by the overlap parameter O for age distributions defined by Andersen et al. (2015). The figure is a graphical representation of the numeric overlap matrix in Supplementary Table

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S4. Green colour represent sample pairs that are fully indistinguishable (1-O= 0.0), white squares sample pairs having 0.0<1-O<0.05 and red 1-O > 0.05. Blue outlines mark stratigraphically consistent groups that are internally homogeneous in terms of detrital

Figure 12

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zircons.

Cartoon illustrating a multi-stage recycling model that can account for the detrital zircon UPb and Lu-Hf characteristics of the Cape and Karoo Supergroups in South Africa. Colour coding is as in Figure 1. a: Buildup of a topographic high associated with terrane accretion and colision of continental blocks along the Namaqua-Natal Belt to form the Rodinia supercontinent in late Mesoproterozoic time. b: Denudation of the elevated Namaqua-Natal Belt left a sedimentary cover containing late Mesoproterozoic – earliest Neoproterozoic material both on the Kaapvaal Craton and on the opposing block.

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c: After breakup of Rodinia, Pan African orogeny in the Neoproterozoic lead to buildup of mobile belts and new topographic highs surrounding the continental nucleus of Kaapvaal Craton and Mesoproterozoic domains.

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d: Denudation of the Pan African belts yielded a new load of detritus to continental cover

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sequences

e: Formation of the Cape Basin in the early Palaeozoic lead to partial removal of preexisting

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continental cover and parts of Namaqa-Natal basement to be deposited in the Cape Supergroup.

f: Formation of the Cape Fold Belt (GondwanideOrogeny) caused uplift of the rocks of the

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Cape Supergroup in the south, and recycling of these into the Main Karoo Basin. Concomitant erosion in the north removed the last remains of cover left at the Kaapvaal Craton, that was

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also recycled into the basin. Tables

Table 1 Published detrital zircon data from southern Africa

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Table 2 Samples analysed in the present study

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Tom Andersen, Dr. Philos. (University of Oslo, 1987), Phil. Dr. H.C. (University of Gothenburg, 2013), Professor of Geochemistry at the Department of Geosciences, University of Oslo and Distinguished Visiting Professor at the Department of Geology, University of Johannesburg. Research interests include the mineralogy and petrology of alkaline igneous rocks, the application of radiogenic isotope data to the evolution of the continental crust, and fundamental aspects of detrital zircon geochronology.

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Magnus Kristoffersen got his MSc from the University of Oslo in 2011, and is currently working on a PhD project related to sedimentary provenance analysis of Archaean to Phanerozoic sedimentary rocks in South Africa, as well as being research technician in charge of the multicollector ICPMS laboratory at the Department of Geosciences, University of Oslo.

Marlina Elburg, PhD (Monash University, 1996), Associate Professor at the Department of Geology, University of Johannesburg. Research interests include the petrogenesis of granites, arc volcanics and alkaline rocks, high-temperature geochronology and ―zirconology‖, and the application of geochemical techniques to different fields of the (earth) sciences.

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Table 1 Published detrital zircon data from southern Africa Age Group Domain

Unit

Depositional Uage Pb

LuHf

Reference

Unconsolidate d sediments Unconsolidate d sediments

20 to 0 ka

Yes

Andersen et al. (2015) Garzanti et al. (2014)

Mesozoic Beaufort

South Africa

Ecca

South Africa

Ecca (Vryheid Fm). Dwyka-Ecca

AC

TE

CE P

South Africa

No

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Recent

Triassic

D

Late Palaeozoic

Recent

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South Africa

Ye s Ye s

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Namibia, Mozambique , South Africa Orange River River sediments Orange River River sediments

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South Africa

T

Cenozoic

Permian Permian CarboniferousPermian

Namibia

Dwyka-Ecca

South Africa

Dwyka

Carboniferous

South Africa

Natal Group

Ordovician

South Africa

Natal Group

Ordovician

South Africa

Msikaba Formation Cape Supergroupo

Devonian

Ye s Ye s

Yes

Klama ( 2008)

Yes

Iizuka et al. (2013)

Ye s

No

Dean (2014), McKay et al. (2015)

Ye s Ye s Ye s

No

Ye s Ye s

No

Dean (2014), Vorster (2013) Veevers and Saeed (2007) Bangert et al. (1999), Fildani et al. (2009), Lanci et al. (2013), Rubige et al. (2013), McKay et al. (2015) Werner (2006)

No

Jansson (2010), Vorster (2013)

Ye s Ye s Ye s Ye s

Yes

Kristoffersen et al. (2015) Vorster et al. (2015) Vorster et al. (2015) Fourie et al. (2011), Vorster (2013)

Ye

Yes

Yes No

Early Palaeozoic

South Africa

OrdovicianCarboniferous

No No No

Neoproter ozoic Namibia

Nama

Hofmann et al.

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South Africa

Saldania Belt

South Africa / Namibia

Nama Group

Namibia

Gariep belt

Namibia

Damara Belt

Antarctica

Ritscherflya supergroup

No Yes No

Yes

Ye s

No

Ye s

No

Ye s Ye s

No

Kaapvaal Craton

Ye s

No

Kaapvaal Craton

Ye s

Yes

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TE

D

South Africa

Palaeopro terozoic South Africa

AC

Namibia

NU

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Mesoprote rozoic

Namibia

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Ye s Ye s Ye s Ye s

Mozambique

Archaean

Ye s Ye s Ye s

T

Saldania Belt

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South Africa

Yes No Yes

No

55 (2015), Foster et al. (2015) Naidoo et al. (2013) Frimmel et al. (2013) van Staden (2011), Blanco et al. (2011) Hoffmann et al. (2014, 2015) Foster et al. (2015) Marschall et al. (2013) Thomas et al. (2010)

Petterson et al. (2007), van Niekerk (2006) van Schijndel et al. (2011)

van Niekerk (2006) van Schijndel et al. (2011) Kositcin and Krapež (2004), Dorland (2004) Zeh and Gerdes (2012), Zeh et al. (2008, 2010, 2013), Koglin et al. (2011)

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Tarkast ad

Stormbe rg Stormbe rg

Elliot

Ecca

Vryheid

Molteno

SA13/1 13

SA13/1 14

SA13/1 16

SA13/1 23

Roadside ditch on road to Colling's pass Roadcut, road to Colling's pass Roadcut, road to Colling's pass Roadside w. Colling's pass Off road to Fricksbur g Roadcut profile at top of

29°35.142' S

2948.746'E

28°30'21.9 9''S 28°33'59.6 4''S

28°37'7.29'' E 29°8'1.38''E

Vryheid

Descripti on Matrix of diamictit e Sandston e Sandston e Sandston e

27°41.95'S

30°52.235'E Sandston e, lower part of section, interlaye red with mudston e 28°15'7.34' 30°19'10.83 Sandston 'S ''E e 28°14.278' 29°42.243'E Fine, xS bedded sst

Beaufor t

Adelai de

Normand ien

Beaufor t

Adelai de

Normand ien

28°13.439' S

29°38.847'E Sandston e

Beaufor t

Adelai de

Normand ien

28°12.922' S

29°38.093'E Sandston e

Beaufor t

Tarkast ad

CE P

SA13/1 12

S. Dundee Ecca

AC

SA13/1 08 SA13/1 11

TE

D

SA13/1 06

Beaufor t

East

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SA12/C L1 SA12/C L2

W. Nottingha m Road Golden Gate E. Oliviersh oek Pass Zingua Mnt railway cut

South

30°14'20.3' 30°47'9.4''E 'S

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SA12/1 5

Formatio n

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Table 2,Samples analysed in this study Group Subgro up Karoo Supergroup SA12/0 Clansthal Dwyka 9 Beach

56

28°11'30.2' 29°32'21.9'' 'S E

Sandston e

Stormbe rg

Molteno

28°40.779' S

28°7.568'E

Sandston e

Stormbe rg

Elliot

28°33.322' S

28°24.96'E

Red sandston e

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Stormbe rg

Clarens

28°36.519' S

SA13/1 26 SA13/1 29

Roadcut, R74 Champag ne Castle

Stormbe rg Stormbe rg

Molteno

28°27.483' S 29° 3.459' S

SA13/1 30

Riverbed, Frere

Beaufor t

Adelai de

Normand ien

28°53.152' S

SA13/1 32

Roadcut S Beaufor Estcourt t

Adelai de

Normand ien

29°1.678'S

IP

SC R

NU

MA

D

30°51'16.6' 30°2254.5'' 'S E

CE P

Margate

AC

SA12/6 1

30°38'10.4' 30°15'41.3'' 'S

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Msikaba Formation SA12/5 Rock of 5 Gibraltar

Clarens

Cape Supergroup SA14/2 East of 29 Citrusdal

28°23.333'E Massive, finegrained sst 29°3.402'E Sandston e 29°23.886'E Fine grained sandston e, top of Clarens Fm. 29°46.305'E Sanstone interlaye r in shales 29°54.286'E Sst interlaye r in shale

T

SA13/1 24

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Top unit with quartz pebbles Beach outcrop lowest part of Msikaba Fmt

Peninsula 32°37'50.0 1"S

"19°5'47.35 "E

Sandston e

32°8'52.08 "S

"18°54'4.07 "E

Sandston e

Rietvlei

"31°34'38. 8"S

"19°10'38.5 8"E

Sandston e

SA14/2 39

Table Mountai n NE Bokkev Ceres Clanwillia eld m Table Nardou Mountai w n Bokkev Ceres eld

Gydo

"31°32'53. 7"S

"19°11'18.3 "E

SA14/2 40

Roadcut, R27

Skurvebe rg

"31°22'29. 9"S

"19°1'3.45" E

Sandy interlaye r in shale Gritty sandston e

SA14/2 34 SA14/2 38

Table Nardou Mountai w n

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Graphical abstract

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● Clastic ediments in southern Africa have been recycling since the Neoproterozoic ● Detrital zircon distributions are controlled by recycling, not by the primary sources ● Detrital zircon does not catch the Archaean history of southern Africa ● Detrital zircon is a less robust indicator of provenance than commonly believed ● Detrital zircon is a less useful indicator of crustal evolution than commonly thought

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