Abstract
In this paper we review the dimensions, geometry and architecture of the components of the
Introduction
It is almost 40 years since Clifford (1970) first coined the term Kalahari Craton for the Precambrian shield of Southern Africa. This concept was developed by Hartnady et al. (1985) , who envisaged a Kalahari Craton made up of crustal components of different ages, comprising a composite Archaean nucleus partly surrounded by progressively younger accreted belts of Palaeoproterozoic and Mesoproterozoic age (Fig. 1) . In contrast to this definition, however, a number of authors have used Kalahari Craton for the crust that existed prior to amalgamation into Rodinia, BUT without the extensive Mesoproterozoic rim (e.g. Dalziel, 1991; Powell et al., 2001a) . The term Kalahari Craton has never included the Late Neoproterozoic/Early Palaeozoic ("Pan-African") belts, which were subsequently accreted to the older core.
Introduction
In the late 1980's it became clear that pre-Neoproterozoic crustal fragments, now residing in other continents, might have been contiguous with the southern African part of the Kalahari Craton and subsequently dispersed during the Mesozoic break-up of Gondwana (Martin and Hartnady, 1986; Groenewald et al., 1991) . For example, the Archaean and Mesoproterozoic crust of Western Dronning Maud Land, East Antarctica, was probably juxtaposed against the eastern part of the "African" Kalahari Craton prior to Gondwana break-up (e.g. Groenewald et al., 1991) . Consequently, there is a need to exactly define the term Kalahari Craton. In defining a "craton" as a once-continuous fragment of stabilised continental crust, the Kalahari Craton should encompass all fragments of crust (up to Mesoproterozoic age) of "African" affinity, that were juxtaposed prior to the Neoproterozoic. We do not restrict the term to those areas with a thick lithospheric root, which would only include the Archaean nucleus.
Introduction
In the 1990's it was proposed that the extensive Mesoproterozoic collision belts of the world (including the Grenville Orogen) represent the amalgamation of a pre-Gondwana supercontinent, which was named Rodinia. This major collision orogen included the belts of southern Africa and East Antarctica -the outer "rim" of the Kalahari Craton. It thus appeared that the crustal fragments constituting the "Kalahari Craton" were involved in the assembly and dispersal of two supercontinent cycles, Rodinia in the Mesoproterozoic and Gondwana in the Neoproterozoic, giving rise to a complex history of growth and accretion, rifting and dispersal.
Introduction
In this paper we propose a workable definition of the Kalahari Craton and briefly describe its architecture and growth from Archaean to Mesoproterozoic time when it was incorporated into, and formed as one of the larger fragments of, Rodinia. To illustrate this we present a series of time-slice diagrams, which purport to show the broad "palaeogeography" of the evolving craton and its margins. We review the available palaeomagnetic data from the various fragments of the Kalahari Craton in order to trace its palaeoposition over time and to test which other cratonic fragments may have been adjacent to it in Rodinia, prior to final break-up and separation from Rodinia in the Neoproterozoic.
Introduction
Consequently, we propose using the terms "Proto-Kalahari Craton" for the ArchaeanPalaeoproterozoic core of the craton and "Kalahari Craton" for the African part of the Kalahari Craton as originally defined (i.e. including Mesoproterozoic crust), plus the various non-African fragments that together probably constituted a single crustal fragment during the assembly of Rodinia (Fig. 1) . These include smaller fragments now near South America (Falkland Islands), different parts of Antarctica (Dronning Maud Land, Haag Nunataks) and possible further, as yet 4 nature of the underlying crust. In the Rehoboth area of central Namibia, migmatitic orthogneisses, dated at 1784 ± 45 Ma (Burger and Walraven, 1978) are overlain by an at least 5 km-thick succession of sheared and metamorphosed volcano-sedimentary rocks known as the Rehoboth Group . The volcanic component of this succession is juvenile in character and has given a conventional U-Pb zircon crystallisation age of 1782 +10/-9 Ma (Nagel et al., 1996) . Deposition of the Rehoboth Group was accompanied and followed by major plutonism ranging in composition from ultramafic to mafic (Alberta layered complexes) through intermediate (Weener tonalite) to granitic (Piksteel Suite) at ca. 1780-1765 Ma (Burger and Walraven, 1978; Becker et al., 1996; . The geology of the Rehoboth Group is considered to reflect the transition from a volcanic arc into a back arc setting ). The regional metamorphic event coinciding with the timing of calc-alkaline magmatism has been explained by arc accretion which, at the end of the Palaeoproterozoic, marked the completion of the assembly of the Proto-Kalahari Craton.
Introduction
Further south, Palaeoproterozoic arc-related volcanic and plutonic rocks occur in the Richtersveld Subprovince. These consist of a low-grade (greenschist facies) volcanosedimentary sequence, the Orange River Group, which is intruded by co-genetic, coeval plutonic rocks (Vioolsdrif Suite) with juvenile island-arc geochemistry and ages bracketed between 2000 and 1730 Ma (Reid, 1997) . It is unclear if the rocks of the Richtersveld Subprovince formed in this location or if they represent part of a microcontinental mass accreted during the Mesoproterozoic. It is similarly unknown if the high-grade basement to much of the Mesoproterozoic Namaqua Sector, which is known to be at least partially Palaeoproterozoic in age (e.g. Eglington and Armstrong, 2004) , originated within southern Africa or if these rocks represent parts of exotic fragments accreted during the Mesoproterozoic. Notwithstanding these unknowns, the end of the Palaeoproterozoic marked the beginning of a long period of tectonic quiescence in the geological record of this region. No evidence of Palaeoproterozoic activity is recorded from the SE flanks of the ZKG Craton.
2) From the Proto-Kalahari Craton to the Kalahari Craton
After over 350 Ma of apparent quiescence around the margins of the Proto-Kalahari Craton, renewed tectonic activity during the Mesoproterozoic heralded a major period of crustal growth, during which the area of the Proto-Kalahari Craton almost doubled from ca. 7 x 10 6 to 13 x 10 6 km 2 (Fig. 3) .
The north-western margin: a Mesoproterozoic continental arc
Outboard of the accreted Palaeoproterozoic terranes, the NW flank again became an active continental jeffrey98@example.org. 1400 Ma. Low-grade Mesoproterozoic volcanic and sedimentary rocks occur in a series of poorly-exposed inliers which appear to have been deposited in basins aligned along the western and north-western margins of Proto-Kalahari. These define a magmatic province that, if all the outcrops are considered, measured more than 1000 km in length (Fig. 3) . It includes the Kgwebe Formation of Botswana and the Sinclair and Nauzerus groups of Namibia (Becker et al. 2006 and references therein). The Sinclair Group includes four thick, conformable volcano-sedimentary cycles deposited in north-south elongated basins (Watters, 1974; Borg, 1988; Hoal, 1990; 1993) . These thick sequences are dominated by 5 bimodal volcanic rocks and epicontinental sedimentary clastic rocks. These are mildly deformed and were subsequently intruded by calc-alkaline granite suites of batholithic dimensions, with subordinate gabbro and granodiorite. The minimum age of the lower part of the Sinclair Group in southern Namibia is constrained by the intrusion of the arc-related Aunis tonalite at about 1376 Ma (Hoal and Heaman, 1995) .
The north-western margin: a Mesoproterozoic continental arc
Late-Mesoproterozoic volcanosedimentary rocks crop out in the Rehoboth area of central Namibia, and in Botswana, parallel to the north-western margin of the Proto-Kalahari Craton.
The north-western margin: a Mesoproterozoic continental arc
The sequence consists of low-grade metasedimentary rocks and acid volcanics which have given dates ranging from ca. 1225 Ma up to ca. 1100 Ma (Hegenberger and Burger, 1985; Schwartz et al., 1996; Schneider et al., 2004; Becker et al. 2005) .
The north-western margin: a Mesoproterozoic continental arc
The origin of the Mesoproterozoic basins of north-west Kalahari remains controversial. A variety of settings have been proposed, most of which involve subduction-related active continentalmargin settings (e.g. Hoal, 1990; Pfurr et al., 1991; Hoal and Heaman, 1995 , Becker et al., 2005 .
The southern and eastern margins: a major Mesoproterozoic orogenic belt
The Namaqua-Natal-Maud Province forms a major continuous belt of high-grade rocks that has been modeled as resulting from continent-continent and/or arc-continent-collision, with indentation-escape tectonics along the south-western, southern, south-eastern and eastern side of Proto-Kalahari between ~1.2 to 1.0 Ga (e.g. Jacobs et al., 1993; Thomas et al., 1994; Fig. 3 ).
The southern and eastern margins: a major Mesoproterozoic orogenic belt
In southern Africa, the province is exposed in two areas of outcrop known as the "Namaqua Sector" (in the Northern Cape Province of South Africa and southern Namibia) and the "Natal Sector" (in Kwazulu-Natal). Regional geophysical data, together with crustal xenolith evidence from kimberlite diatremes in Lesotho and deep boreholes, show that the two sectors are the exposed parts of a continuous, 1400 x 400 km wide, arcuate orogenic belt extending beneath the Phanerozoic Karoo Supergroup of central South Africa (Fig. 4) . Both sectors of the province are subdivided into various tectono-stratigraphic blocks, defined by distinctive lithostratigraphic packages bounded by structural discontinuities. The belt can then be traced via the Falkland and Ellsworth-Haag microplates into Dronning Maud Land (East Antarctica) and thence probably northwards into NE Mozambique.
Namaqua Sector
The Namaqua Sector of the Namaqua-Natal Province comprises a number of subprovinces and terranes, the definitions and boundaries of which remain controversial. The main crustal units recognized are the Richtersveld Subprovince and the Bushmanland, Kakamas, Areachap and Kaaien terranes. These terranes are bound by late Mesoproterozoic shear zones. The
Namaqua Sector
Richtersveld Subprovince represents a Palaeoproterozoic arc terrain within the Namaqua Sector that largely escaped Mesoproterozoic reworking (Reid, et al., 1987) . As noted before it is not known if this crustal fragment formed in its present position, or evolved elsewhere and was accreted as a micro-continental block during the Mesoproterozoic. Similarly, the vast proportion of the Namaqua Sector include a high (but unknown) proportion of Palaeoproterozoic rocks that were deformed, subjected to high-grade metamorphism and intruded by voluminous granitoids during the Mesoproterozoic collision. The latter are generally of granite to charnockite 6 composition, ranging in age from ca. 1200 to 1030 Ma (e.g. Robb et al., 1999 ). It appears that only the relatively small Areachap terrane (Fig. 4) is made up of almost entirely juvenile
Namaqua Sector
Mesoproterozoic crust with subduction-related signatures and an age of ca. 1285 Ma (e.g. Cornell et al., 1992 , Geringer et al., 1994 . Recent work however cast doubt on the extent to which Palaeoproterozoic crust forms the "basement" in Namaqualand (e.g. Cornell and Pettersson, 2007) . In the Eastern Namaqua sector, the Koras Group comprises an approximately 7000 m thick succession of bimodal volcanics and immature sedimentary rocks that unconformably overlie the Kheis and Namaqua belts. The sequence is largely undeformed, underwent only very low-grade metamorphism, and was SHIRMP zircon dated at 1171 ± 7 Ma (Gutzmer et al., 2000) .
Namaqua Sector
Structurally, the Mesoproterozoic history of the Namaqua Sector is dominated by SW-directed crustal stacking, followed by prolonged dextral transpressional tectonics (e.g. Colliston et al., 1991; Van Bever Donker, 1991; Jacobs et al., 1993) . The Koras Group represents deposition in a rift basin, which might have evolved within a dextral pull-apart type setting during oblique shearing along the margin of the Namaqua Belt (Jacobs et al., 1993) .
Natal Sector
The Natal Sector of the Namaqua-Natal Province comprises three distinct tectono-stratigraphic terranes (Thomas, 1989; Thomas et al., 1994 ) that were thrust NE over the southern margin of the Kaapvaal Craton at about 1135 . The terranes are made up of juvenile Mesoproterozoic crust (Eglington et al., 1989; Eglington, 2006) , which probably formed in island-arcs crust that evolved during subduction away (southwards) from the Kaapvaal Craton between ca. 1250 and 1100 Ma (see review, McCourt et al., 2006) . Arc-continent collision was oblique and resulted, after initial crustal thickening, in sinistral transpression and crustal escape tectonics along major ductile shear zones (Jacobs and Thomas, 1994) . This event was accompanied by the widespread intrusion of rapakivi-textured granitoids and charnockites in a transcurrent tectonic setting, associated with high-T, moderate-P granulite-grade metamorphism between 1070 and 1030 Ma (e.g. Thomas et al., 1993, Eglington and Armstrong, 2004; Eglington, 2006) . The youngest intrusions in Natal are microgranite dykes which were jeffrey98@example.org. 1020 Ma , though low-temperature thermal perturbations as young as 900 Ma are recorded . Jacobs et al. (1993) pointed out that Proto-Kalahari probably acted as a SW-directed indenter during the accretion of the Namaqua-Natal Province during Mesoproterozoic times (1.2 to 1.0 Ga) and that the contrasting late-tectonic transcurrent shearing along the craton margin in the Namaqua and Natal sectors are a function of the varying orientation of the craton margin, resulting in sinistral transpression in Natal and in dextral transpression in Namaqualand.
Falkland Islands and Haag Nunataks
The Falkland Islands represent the exposed part of the Falkland-Malvinas Plateau, a crustal fragment that in Gondwana and Rodinia, most probably lay between SE South Africa and East Antarctica ( Fig. 1, 4 ). Its position along the SE coast of South Africa was proposed by Adie (1952) for purely geological reasons, although this position requires the rotation of the FalklandMalvinas microplate through 180° with respect to its present position. This rotation was confirmed palaeomagnetically by Mitchell et al. (1986) . This position suggests that the Falkland Island microplate probably formed part of the Kalahari Craton. Crystalline basement rocks are exposed in West Falkland along a 5 km coastal strip at Cape Meredith (Cingolani and Varela, 1976, Thomas et al., 1997) . U-Pb zircon crystallisation ages of igneous rocks from the Cape Meredith Complex were dated between ca. 1120 -1000 Ma (Jacobs et al. 1999a ).
Falkland Islands and Haag Nunataks
Late Mesoproterozoic rocks are also exposed in the Haag Nunataks (West Antarctica).
Falkland Islands and Haag Nunataks
Geophysical data indicate that the Haag Nunataks, together with the Ellsworth-Whitmore
Falkland Islands and Haag Nunataks
Mountains, form an extensive continental fragment that could have resided within the Natal Embayment (Lawver et al., 1991; Dalziel and Grunow, 1992; Grantham et al., 1997) . The main rock type of the small exposures is foliated granodioritic gneiss with calc-alkaline geochemistry, probably representing a volcanic/plutonic island-arc complex (Grantham et al., 1997) . The granodiorite gneiss is intruded by two sets of granite sheets, which gave Rb-Sr isochron dates of 1176 ± 76 Ma and 1058 ± 53 Ma and 1003 ± 18 Ma respectively (Millar and Pankhurst, 1987) . Although these ages have large uncertainties, they can be correlated with similar rocks from the Natal Sector (Mzumbe Terrane) and from western Dronning Maud Land. Thus, it is likely that the Haag Nunataks also formed part of the Kalahari Craton.
Dronning Maud Land, East Antarctica
The ca. 1.2-1.0 Ma Maud Belt represents the continuation of the Namaqua-Natal Province via the Falkland Island and the Haag Nunataks into western Dronning Maud Land (Antarctica) (e.g. Groenewald et al., 1991; Jacobs et al., 1993; Bauer et al, 2003a) . The Maud Belt was widely and intensely overprinted during Pan-African high-grade tectonism along the East AfricanAntarctic Orogen (e.g. Jacobs and Thomas, 2004) .
Dronning Maud Land, East Antarctica
In the westernmost part of Dronning Maud Land (Heimefrontfjella) three distinct discontinuitybound juvenile Mesoproterozoic terranes are recognised (e.g. . The terranes comprise high grade gneisses and granitoids that have been dated between ca. 1160 and 1070 (Arndt et al., 1991; Jacobs et al., , 1999b Bauer et al., 2003b) .
Dronning Maud Land, East Antarctica
Aeromagnetic studies of the area indicate that this part of the Maud Belt is characterised by elongate, high-amplitude, craton-parallel magnetic anomalies, which perfectly correlate with very similar features in the Namaqua-Natal Province in southern Africa (e.g. Golynsky and Jacobs, 2001) . Crust formation was succeeded by high-grade metamorphism between ca.
Dronning Maud Land, East Antarctica
1090-1060 Ma .
Dronning Maud Land, East Antarctica
Further to the NE, in Kirwanveggen and Sverdrupfjella, exposures of high-grade rocks similarly represent juvenile material that probably evolved in island arc settings dated between ca. 1200 and 1050 Ma (e.g. Grantham et al., 1995; Groenewald et al., 1995; Board et al., 2005) .
Dronning Maud Land, East Antarctica
In central Dronning Maud Land (Gjelsvikfjella to Grubergebirge), late Mesoproterozoic basement rocks similar to those of Heimefrontfjella and Sverdrupfjella are exposed, although they are much stronger deformed as a result of Late Neoproterozoic medium to high-grade tectono-metamorphic overprinting during continent-continent collision along the East AfricanAntarctic Orogen. Despite this, SHRIMP zircon studies have allowed resolution of the major components of the Mesoproterozoic history and metavolcanic rocks were jeffrey98@example.org. 1130 Ma, with minimal inheritance up to 1190 Ma being recorded (Jacobs et al., 1998) . Initial Nd-isotopic 8 data of these rocks indicate again relatively juvenile material with little older crustal involvement.
Dronning Maud Land, East Antarctica
An origin along a major volcanic arc has been suggested for this terrane (e.g. Jacobs et al., 1998; Bauer et al., 2003a,b) . Syntectonic granitoid intrusions and high-grade metamorphism were jeffrey98@example.org. 1080 to 1060 Ma and thus correlate well with similar data from western Dronning Maud Land.
Dronning Maud Land, East Antarctica
The easternmost extent of Mesoproterozoic rocks crop out at Sør Rondane, where two distinct tectono-stratigraphic juvenile terranes are recognised, separated by the Sør Rondane suture (Shiraishi and Kagami, 1992; Shiraishi et al., 1999) . U-Pb zircon data from the northern, highgrade terrane give a range of ages from 1100 to 1000 Ma (Grew et al., 1992 , Shiraishi et al., 1999 ). Nd-model ages from mafic granulites and enderbitic gneisses are only slightly older and range from ca. 1300 to 1100 Ma, thus indicating the relatively juvenile character of these rocks.
Dronning Maud Land, East Antarctica
The southern terrane is an amphibolite to greenschist facies block made up of tonalitic gneisses with mafic enclaves jeffrey98@example.org. 980 Ma, whose geochemistry indicates that they were probably derived from the subduction of young hot oceanic crust (Ikeda and Shiraishi, 1998) that could represent the margin of the Kalahari Craton has not unequivocally been identified in the area and, although a number of possibilities have been discussed (e.g. Shiraishi et al., 1994; Kriegsmann, 1995; Fitzsimons 2000; Kleinschmidt et al., 2002; Jacobs et al., 2003b ) no convincing, unequivocal position has been presented at this stage.
Northern Mozambique and Malawi
The Maud Belt probably continued northwards into north-eastern Mozambique, where a collage of discrete gneiss complexes are dominated by late Mesoproterozoic protolith ages that are comparable with those of Dronning Maud Land (e.g. Pinna et al., 1993; NGU-Nordconsult, 2007 . Within the southernmost of these, the Nampula Complex, an upper amphibolite facies supracrustal gneiss/migmatite sequence is intruded by various suites of orthogneisses, dated between ca. 1150 -1000 Ma (Kröner et al., 1997; Jamal and De Wit, 2004, NGU-Nordconsult, 2007) . The Nampula Complex is bound to the north by the Lurio Belt, a structure comprising a zone of highly dismembered and deformed Neoproterozoic granulitegrade gneisses of different composition and protolith ages. The significance of the Lurio Belt is controversial. Some authors believe it represents a major suture zone and forms a connection via the Zambezi Belt with the Damara Orogen (e.g. Grantham et al., 2003 Grantham et al., , 2005 . Others suggest it has a less fundamental significance, especially because some of the metamorphic complexes to the north of the Lurio Belt are quite similar to the rocks of the Nampula Province Viola et al., 2006) , an because of an apparent decrease in strain along the belt from NE to SW. To the north of the Lurio Belt, a number of metamorphic complexes are juxtaposed along NW-verging Neoproterozoic tectonic contacts and are interpreted as a NWdirected sequence of nappes. Two of the larger complexes, the Marrupa and Unango 9 complexes, consist mainly of 1.1-1.0 Ga granitoid gneisses, that represent intrusions into a metasedimentary successions with unknown protolith age . These complexes appear to continue northwards for an unknown distance into Tanzania. In northeastern Mozambique (and southern Tanzania), extensive high-grade re-working and crustal accretion during the Neoproterozoic have largely obscured the true extent and nature of the Mesoproterozoic crust. In Malawi, similar orthogneisses with crystallisation ages of ca. 1040-1000 Ma were interpreted to represent a continental-margin-arc (Kröner, 2001 ).
Northern Mozambique and Malawi
To summarise the complex and fragmentary evidence of the palaeogeographic situation along the southern and eastern margins of the Kalahari Craton during the Mesoproterozoic, the important point to note is that significant portions of juvenile crust formed between ca. 1.3 and 1.0 Ga along subduction-related magmatic arcs along the southern, south-eastern and eastern margin of Proto-Kalahari, while significant proportions of older (Palaeoproterozoic) material incorporated along the Namaqua Sector in the southwest.
The northern margin: Mesoproterozoic remnants
Along the current northern margin of the Proto-Kalahari Craton, in Zimbabwe, there are remnants of Mesoproterozoic rocks in complex, deformed terranes within the Neoproterozoic Zambezi Belt. These include ophiolitic rocks (in the Chewore Inliers) jeffrey98@example.org. 1393 Ma (Oliver et al., 1998) and orthogneisses jeffrey98@example.org. 1080 Ma (Goscombe et al., 2000) . However, Johnson and Oliver (2004) considered that these rocks were accreted to the margin of the (then distant) Congo Craton, and that this part of the northern margin of the Kalahari Craton was a passive margin during the Mesoproterozoic (Fig. 3) .
The northern margin: Mesoproterozoic remnants
West of the Chewore Inliers, the Choma-Kalomo Block probably represents the exposed part of an extensive northeast-trending Mesoproterozoic orogenic belt along the margin of the ProtoKalahari Craton, continuing possibly into Namibia (Hutchins and Reeves, 1980; Hanson et al., 1988; Steven et al., 2000; Singletary et al., 2003 ). An amphibolite facies metasedimentary sequence is exposed that is intruded by at least two distinct granitoid generations (Hanson et al., 1988; Bulambo et al., 2004 ). An older suite of granitic gneisses was jeffrey98@example.org. 1370-1340
The northern margin: Mesoproterozoic remnants
Ma (U-Pb zircon), whilst a second set of foliated granites gave U-Pb zircon ages ranging from ca. 1100-1075 Ma (Hanson et al., 1988; Bulambo et al., 2004) . The Choma-Kalomo Block has undergone polyphase deformation with a dominant north-east trending structural grain. The younger granitoids are regarded as late-tectonic.
The northern margin: Mesoproterozoic remnants
The Choma-Kalomo Block underwent intense late-Mesoproterozoic rifting along the northwest Botswana rift (Key and Mapeo, 1999) . The belt has been penetrated by boreholes in the Kalahari desert, where amphibolite facies gneisses are intruded by granites, the latter of which were U-Pb jeffrey98@example.org. 1108 Ma (Singletary et al., 2003) .
The northern margin: Mesoproterozoic remnants
The north-western margin of this belt, and thus that of the Kalahari Craton, is defined by the Neoproterozoic Matchless-Rooibok zone, which consists of amphibolites and intercalated granitic gneisses (Singletary et al., 2003) . Zircons from the granite gneiss gave an igneous crystallisation age of 716.8 ± 2.2 Ma, which is a minimum estimate for the onset of ocean floor spreading along this part of the Kalahari margin (Singletary et al., 2003) .
Late Mesoproterozoic intraplate magmatism
The Proto-Kalahari Craton was subjected to widespread anorogenic magmatism in the period 1.4 to 1.11 Ga, which has recently been reviewed by Hanson et al. (2006) . The older jeffrey98@example.org. 1.35 Ga is charaterised by alkaline and cabonatite complexes in the southern part of the craton.
Late Mesoproterozoic intraplate magmatism
The ca. 1.1 Ga volcanic rocks of the Oppdam and Kwebe formations along the north-western margin of Proto-Kalahari have widespread, voluminous equivalents throughout the craton and are known as the Umkondo lavas in Africa (e.g. Hanson et al., 1998 Hanson et al., , 2004 and as the Borg lavas in Dronning Maud Land (e.g. Barton and Moyes, 1990) . Together, this Large Igneous
Late Mesoproterozoic intraplate magmatism
Province magmatic event is known as the Umkondo Igneous Province, covering at least 2 million km 2 (Fig. 4) . It is inferred to have resulted from the up-welling of a large mantle plume within a short space of time between ca. 1112 and 1116 Ma. .
Late Mesoproterozoic intraplate magmatism
Summarising, the growth of the Proto-Kalahari Craton during the Mesoproterozoic is recorded by multiple events surrounding the craton and within it: from ca. 1400 to 1000 Ma, large amounts of crust were added and the area of the resulting Kalahari Craton had almost doubled in area to ca. 13 million km 2 .
Late Mesoproterozoic intraplate magmatism
3) The Mesoproterozoic-Neoproterozoic transition (1000-750 Ma): rifting of
Kalahari and Rodinia break-up
The Kalahari Craton is almost completely surrounded by Neoproterozoic rocks, or the products of Neoproterozoic ("Pan-African") tectonic reworking. Early Neoproterozoic rift-related rocks are well preserved along its north-western, western and southern margins. Rifting was eventually superseded by drifting, and finally by the inversion of the rift basins (Fig. 5) . High-grade overprint has obliterated much of the rift-related events along the eastern margin of the Kalahari Craton, along the Late Neoproterozoic/Early Palaeozoic East African-Antarctic Orogen.
The north-western margin (Tsumis, Nosib and Ghanzi groups in Namibia)
Major uplift occurred along the north-western margin of the Kalahari Craton after the extensive ca. 1.1 Ga magmatic event. Rocks of the predominantly sedimentary Tsumis Group rest on the Meso-to Palaeoproterozoic basement along a regional unconformity, with intracontinental redbed successions developed at the base, along with limited contemporaneous volcanic activity.
The north-western margin (Tsumis, Nosib and Ghanzi groups in Namibia)
There is an upward transition into overlying monotonous well-bedded, fine-grained, purplish to greyish sandstone with intercalated red slate more than 4500m thick (e.g. Doornpoort Formation). These pass upwards into fluviatile, lacustrine and aeolian clastic sediments (Klein Aub Formation). In Botswana, a similar succession, up to 13 500 m thick (Ghanzi Group), was deposited in a northeast trending, ca. 100 km wide basin seen in the Ghanzi-Chobe belt. Modie (2000) has correlated these with the Namibian succession.
The north-western margin (Tsumis, Nosib and Ghanzi groups in Namibia)
A second regional unconformity separates the Tsumis Group from overlying sediments of the Nosib Group deposited in braided river systems (Kamtsas Formation) and playas lakes (Duruchaus Formation). The Nosib Group is taken to mark the onset of Neoproterozoic Damara sedimentation although there is no evidence of a major break in the deposition style to the underlying Tsumis Group. Rocks in an apparently similar stratigraphic position have been correlated across the Damara orogen (Porada, 1989) . They are believed to have been deposited in various grabens and half-grabens in a diachronous rift system that was active from at least 900 to 750 Ma. However, Nosib Group rocks deposited into the Sesfontein and northern grabens of the Congo Craton in northern Namibia differ considerably in composition from those deposited onto the Kalahari Craton; here, basal conglomerates and quartzite deposited along active faults are overlain by a succession of alkaline volcanic rocks grouped into the Naauwpoort Formation. Local occurrences of carbonate and dolomite suggest partial submarine deposition. The age of the Naauwpoort volcanic rocks has been determined as 752 ± 7 Ma (UPb SHRIMP zircon, De Kock et al., 2000) .
The western and southern margins (Gariep-Saldania belts)
The Saldania Belt (Hartnady et al., 1985) is a low-grade orogenic belt along the south-western and southern margin of Kalahari that underwent refolding during the Permo-Triassic Cape Fold
The western and southern margins (Gariep-Saldania belts)
Belt orogeny (e.g. Rozendaal et al., 1999) . It is sporadically exposed in isolated windows, with the main exposures north and east of Cape Town. The Neoproterozoic Malmesbury, Kango, Kaaimans and Gamtoos groups are interpreted as distal facies of rift successions (Rozendaal et al., 1999 (Armstrong et al., 1998) .
The western and southern margins (Gariep-Saldania belts)
The Gariep Belt is a low-to medium-grade Neoproterozoic orogen exposed in a small area on the western side of the Kalahari Craton. It consists of two distinct units, the rift-related eastern Port Nolloth Zone and the oceanic western Marmora Terrane, which together document subsequent Neoproterozoic rifting, drifting and final inversion of the Adamaster Ocean (e.g. Frimmel and Frank, 1998) . The 7-12 km thick sequences of the Port Nolloth Zone represent a Neoproterozoic rift succession deposited on Namaquan basement, including rift-related sedimentary rocks, intercalated with bimodal volcanic rocks (Frimmel et al., 1996a) . Rifting was also associated with the intrusion of voluminous mafic dykes. The basal quartzites are intruded by the ca. 780 Ma Lekkersing granite, giving a minimum age for the lower Port Nolloth Zone sedimentary rocks (Allsop et al., 1979 in Frimmel and Frank, 1998) . A Pb-Pb single zircon age from a felsic volcanic rock gave an age of 741 ± 6 Ma, which was interpreted as a crystallisation age (Frimmel et al., 1996b) , therefore giving a good estimate for the onset of rifting of ca. 780-740 Ma. All rift-related igneous rocks have a within-plate geochemistry and continental flood basalts are absent, typical for a non-volcanic margin (Frimmel et al., 1996a) .
The western and southern margins (Gariep-Saldania belts)
The rift volcanics are overlain by the Kaigas Diamictite, which is correlated with the Sturtian jeffrey98@example.org. 720-700 Ma (Von Veh, 1988; Germs, 1995) . In the upper part of this formation, carbonate rocks (Hilda Subgroup) and a second massive diamictite horizon (Numees Formation) are developed (Frimmel et al. 1996b ). The second diamictite horizon is correlated with the Varangian glaciation at 590 to 560 Ma (Frimmel and Jiang, 2001 ).
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The northern margin: relationship between the Kalahari Craton and the Zambezi Belt
The northern margin of Kalahari, adjacent to the Zambezi Belt, is associated with a narrow, but laterally extensive, suite of syn-tectonic granite gneisses and metarhyolites, emplaced between ca. 880-800 Ma. A number of settings for these rocks have been proposed -either in a compressional regime within the Zambezi Belt (e.g. Hanson et al., 1988) , or in an extensional environment. However, Late Neoproterozoic/Early Palaeozoic orogenesis along the Zambezi Belt has largely obliterated the evidence. While a clockwise PT path attaining upper amphibolite facies conditions in the Zambezi Belt argues for crustal thickening due to compressional orogenesis (Munyanyiwa and Blenkinsop, 1994) , extensional tectonics and an anti-clockwise PT path are recognised in northwest Zimbabwe and point to extension and rifting (Dirks and Sithole, 1999) . The latter is supported by the largely A-type geochemistry of the associated granite gneisses and, in the western part of the Zambezi Belt, an extensive supracrustal sequence of bimodal metavolcanic rocks, overlain by metasandstones, metaconglomerates, pelitic schists and extensive metacarbonates is exposed (Hanson, 2003) .
The northern margin: relationship between the Kalahari Craton and the Zambezi Belt
In the Rushinga area, Neoproterozoic metasedimentary rocks are interlayered with felsic gneisses that are interpreted as metavolcanic rocks (Chironga metarhyolites). The latter have an A-type geochemistry and gave a U-Pb zircon date of 795 ± 2 Ma (Hargrove et al., 2003) . A plutonic equivalent of these metavolcanics is probably represented by the Basal Rushinga
The northern margin: relationship between the Kalahari Craton and the Zambezi Belt
Intrusive Complex, that gave a U-Pb zircon date of 805 ± 11 Ma (Vinyu et al., 1999) . Thus, there is some evidence to suggest that the 880 to 800 Ma A-type igneous rocks along the northern margin of Kalahari are indicative of rift tectonics.
The Kalahari Craton as part of Rodinia
Various positions of the Kalahari Craton within Rodinia have been proposed in the past two decades and there is still no consensus (e.g. Hoffman, 1991; Gose et al., 1997; Dalziel et al., 2000; Hanson et al., 1998; Powell et al., 2001a,b; Jacobs et al., , 1997 Jacobs et al., , 2003a Collins and Pisarevsky, 2005) . The available palaeomagnetic data these reconstructions are in part based on are summarized in Tab. 1. In most reconstructions, the southern and southeastern side of the Kalahari Craton are either placed against E Laurentia (in various configurations) or against Western Australia (Powell and Pisarevsky, 2002; Fitzsimons, 2003; Pisarevsky et al., 2003) , though it may transpire that neither is true. There is no reliable indication of what may have lain along the NW flanks of the Kalahari Craton. Available palaeomagnetic data show that between ca. 2100 Ma and 1000 Ma, the Kalahari Craton drifted between the equator and 60º. This is shown in Fig. 6 where it is assumed for simplicity that the Kalahari Craton was in the northern hemisphere, though the southern hemisphere would be an equally valid option.
The Kalahari Craton as part of Rodinia
Hoffman (1991), Jacobs et al. ( , 1997 , Hanson et al. (1998 Hanson et al. ( , 2004 and Dalziel et al. (2000) showed Kalahari adjacent to SW Laurentia with the Umkondo-Borg lavas and dolerites of Kalahari representing an extension of the coeval Keweenawan mafic province of Laurentia (Hanson et al., 1998 (Hanson et al., , 2004 Dalziel et al., 2000) . Dalziel et al. (2000) proposed an elegant model in which the Kalahari Craton was interpreted as an indenter into Laurentia, concordant with the model of Jacobs et al. (1993) that showed the Namaqua-Natal-Maud Belt as the product of continent-arc/continent indentation tectonics (Fig. 2, 3 ). In the model of Dalziel et al. (2000) , the Namaqua-Natal-Maud Belt formed the opposing counterpart of the Grenville Orogen in the area of the Llano uplift, whilst the Umkondo-Borg-Keweenawan LIP was interpreted as representing rift-related rocks along structures that formed at a high angle to the combined GrenvilleNamaqua-Natal-Maud Belt. Dalziel et al. (2000) assumed continent-continent collision between 1150-1120 Ma with continued tectonism until ca. 980 Ma. The timing of the main collision, however, was challenged by palaeomagnetic data that indicated that Kalahari could not have been attached to Laurentia at 1105 Ma (Powell et al., 2001a) . The latter authors showed that there was a latitudinal separation of ca. 30º between Kalahari and the Llano margin of jeffrey98@example.org. 1105 Ma, and at the same time pointed out that Kalahari could have been rotated by 180º, with the Namaqua-Natal Belt facing outboard. Jacobs et al. (2003b) pointed out that, from the Namaqua-Natal-Maud perspective, the main collision orogeny is best dated at 1090-1060 Ma. This is ca. 60 Ma younger than the timing proposed by Dalziel et al. (2000) . However, should the main collision have occurred at 1090-1060 Ma, the palaeomagnetic 30º latitudinal misfit between Kalahari and Laurentia at 1105 Ma would be consistent with a Kalahari-Laurentia collision. In this case, the older Grenville-age metamorphism in the Llano uplift area could represent an early phase of arc-continent collision rather than the main continent-continent collision associated with final Rodinia assembly. It is thus important to note that the collision phase at 1090-1060 Ma recorded in the NamaquaNatal-Maud Belt is similar in age and character to the Ottawan cycle of the Grenville Orogen, which is interpreted as continent-continent collision of Himalayan-style (e.g. Mezger et al., 1992; McLelland et al., 1996) . Hanson et al. (2004) pointed out that the orientation of Kalahari with the Namaqua-Natal-Maud
The Kalahari Craton as part of Rodinia
Belt facing away from the Grenville jeffrey98@example.org. 1105 Ma is strongly supported by the comparison of the palaeomagnetic polarity in Keweenawan and Umkondo igneous rocks. In their opinion, the "reversed" orientation of Kalahari required by the model of Dalziel et al. (2000) is precluded by this analysis. We agree that this is a strong argument in view of available Keweenawan and Umkondo palaeomagnetic data, but it is not absolutely conclusive for the following reasons: 1) Despite that the "normal" polarity is dominant in the upper part of the Keweenawan succession and the "reverse" polarity is dominant in its lower part, there are exceptions, and the possibility that ~90% of the Umkondo palaeomagnetic ("reverse") sites (Hanson et al., 2004) to be correlative with the upper part of those exceptional cases of the "normal" intervals in the lower Keweenawan is unlikely, but yet possible. Hanson et al. (2004) also mentioned that most of the palaeomagnetically studied Umkondo rocks were emplaced in less than 3 Ma, which can explain this possible coincidence. If this is the case, the "reversed" position of Kalahari is justified.
The Kalahari Craton as part of Rodinia
2) Second, if the collision of Kalahari occurred sufficiently after the 1109 Ma Umkondo magmatism, Kalahari could have rotated through 180 degrees and could have collided with Laurentia in a similar fashion as in the model of Dalziel et al. (2000) . This scenario may appear overly complex but it cannot be discounted entirely.
The Kalahari Craton as part of Rodinia
3) Third, if the north-western margin of Kalahari was an active continental margin, it could also have been this margin that collided with Laurentia. In this way a large rotation could be avoided and the north-western margin could be the counterpart to the Grenville orogen. In this scenario one would need another major continent along the Namaqua-Natal-Maud Belt.
The Kalahari Craton as part of Rodinia
The southern margin of the Namaqua-Natal-Maud Belt is not exposed, but it probably represents a Neoproterozoic rifted margin. In Dronning Maud Land however, the Maud Belt is bound by another crustal block to the south. This block is geophysically distinct (Golynsky and Aleshkova, 1997) and is exposed in the Coats Land Nunatak, where it is overlain by unmetamorphosed volcanic rocks that were jeffrey98@example.org. 1112 Ma (Gose et al., 1997) .
The Kalahari Craton as part of Rodinia
These volcanics probably represent part of the Umkondo-Borg-Keewenawan magmatic province. The Coats Land block clearly forms part of the southern foreland of the Maud Belt and is not part of the belt itself. Gose et al. (1997) suggested that the age of their palaeopole from
The Kalahari Craton as part of Rodinia
Coats Land (22.9°N, 80.3°E) is approximated by the U-Pb titanite age of 1106 ± 3 Ma. The
The Kalahari Craton as part of Rodinia
Keweenawan R pole (47°N, 211°E; Green et al., 1987 ) has a very similar estimated age of 1107
The Kalahari Craton as part of Rodinia
Ma (Powell et al., 2001a) . Palaeomagnetic reconstruction based on these two poles gives two sets of possible positions of Coats Land with respect to Laurentia, depending on the chosen polarity option (Fig. 7) . One of these options permits the connection between the two blocks.
The Kalahari Craton as part of Rodinia
The palaeopole from the 1108-1112 Ma Umkondo igneous rocks in Kalahari (63.6°N, 36.2°E), however, rules out the connection with Laurentia at that time in both polarity options ( Fig. 8) , as was also shown by Powell et al. (2001a,b) , and proves that Coats Land had not amalgamated to Kalahari at this time. If the palaeomagnetic data allow Coats Land to be part of Laurentia, then the Coats Land basement could represent an older part of the Grenville Orogen, e.g.
The Kalahari Craton as part of Rodinia
Elzeviran crust, that was not reactivated during later continent-continent collision (OttawanNamaqua-Natal-Maud). Powell et al. (2001b) and Pisarevsky et al. (2003) pointed out that Kalahari could have lain off the western margin of Australia until 800-750 Ma. The problem with this reconstruction is that the eastern, Mozambiquan side of Kalahari would have had to collide obliquely with the western margin of Australia to form the Pinjarra Orogen. The Namaqua-Natal-Maud Belt, however, as the main collision orogen, would have no counterpart (e.g. Jacobs et al., 2003b) . Although this reconstruction is palaeomagnetically permissible, one would need another continental block to the south of Kalahari.
The Kalahari Craton as part of Rodinia
A further test of a possible linkage between Kalahari and Western Australia comes from the comparison of the provenance records in metasedimentary rocks from the Maud Belt and the Pinjarra Orogen (Fitzsimons, 2002 (Fitzsimons, , 2003 . A comparison of SHRIMP U-Pb zircon ages of paragneisses from the Pinjarra Orogen and the Maud Belt indicated that the metasedimentary sequences in both areas have apparently similar detrital age spectra and, besides a number of age groups common to both regions, all show a characteristic lack of a ca. 1500 Ma age population (Fitzsimons, 2002 (Fitzsimons, , 2003 (Ksienzyk, 2006; and unpubl. data) shows distinctly different detrital age components for the two areas for ages > 1300 Ma and no notable lack of ca. 1500 Ma detrital ages in the Northampton Complex. Fitzsimons (2002 Fitzsimons ( , 2003 comparisons are based on a limited dataset, so in our view, the detrital zircon record does not support a Kalahari -West Australia connection.
The Kalahari Craton as part of Rodinia
It was argued that Kalahari could have been attached to Western Australia until 800-750 Ma, when it started to rift away (e.g. Pisarevsky et al., 2003) . The breakup could have been associated with the Mundine Well dyke swarm in Western Australia (Wingate and Giddings, 2000) . Although, a 800-750 Ma rifting event for Kalahari is permissible, the main rift activity along the margin of Kalahari happened along the western margin and not much evidence for rifting along the eastern margin is known, as would be required for the Kalahari-Western Australia model (though the eastern margin is strongly overprinted and therefore rift related rocks might not be preserved).
The Kalahari Craton as part of Rodinia
The proximity of Kalahari to eastern jeffrey98@example.org. 1000 Ma, though permissible by palaeomagnetic data (Powell et al., 2001a) , faces some problems. First, in most reconstructions of Rodinia (e.g., Hoffman, 1991; Dalziel, 1997; Pisarevsky et al., 2003; Grenville province of Laurentia (e.g. Aleinikoff et al., 1995; Tollo and Aleinikoff, 1996; Tollo et al, 2004) , which roughly coincides with the timing of rifting recorded along the margins of Kalahari.
The Kalahari Craton as part of Rodinia
However, most workers interpret the ca. 750 rift event along the margin of Laurentia as a failed rift and it is thought that the rift-drift transition here started much later, at 550-530 Ma (e.g. Cawood et al., 2001 ).
Conclusion
Over the past two decades there has been much interest and research carried out on the Kalahari Craton, including a wealth of new field observations and high-precision geochronological and geophysical data. This has led to a much better understanding of the geological evolution of various components of the craton. During its evolution the craton initiated as an Archaean nucleus with a surface area of ca. 4,500,000 km 2 , grew by successive continental accretion and magmatic events to ca. 7,000,000 km 2 by the end of the Palaeoproterozoic, to eventually cover an area of over 13,000,000 km 2 by the end of the The original extent of Kalahari is difficult to estimate due to the extensive overprint along its margins. Hints for original boundaries are provided by suture zones that are locally preserved.
Conclusion
African geology adapted from Singletary et al. (2003) . 

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