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Part 5. The Paleoarchean Kaapvaal Craton, Southern Africa

Part 5. The Paleoarchean Kaapvaal Craton, Southern Africa

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Earth’s Oldest Rocks

Edited by Martin J. Van Kranendonk, R. Hugh Smithies and Vickie C. Bennett

Developments in Precambrian Geology, Vol. 15 (K.C. Condie, Series Editor)

© 2007 Elsevier B.V. All rights reserved.

DOI: 10.1016/S0166-2635(07)15051-9



453



Chapter 5.1



AN OVERVIEW OF THE PRE-MESOARCHEAN ROCKS

OF THE KAAPVAAL CRATON, SOUTH AFRICA

MARC POUJOL

Géosciences Rennes, UMR 6118, Université de Rennes 1, Avenue du Général Leclerc,

35 042 Rennes Cedex, France



5.1-1. INTRODUCTION

The Kaapvaal Craton of Southern Africa (Fig. 5.1-1) is one of the oldest and bestpreserved Archean continental fragments on Earth. Its assembly during the Archean took

place episodically over a 1000 million year period (3500 to 2500 Ma) and involved magmatic arc formation and accretion as well as tectonic amalgamation of numerous discrete

terranes or blocks (de Wit et al., 1992; Lowe, 1994; Poujol and Robb, 1999). Delineation of

these domains, and constraining the timing and duration of the principal magmatic events

within them, is best achieved by the craton-wide application of accurate and precise U-Pb

dating (Eglington and Armstrong, 2004; Poujol et al., 2003; Schmitz et al., 2004), together

with appropriate tectonic and metamorphic studies. This paper summarizes some of the

recent age data that identify the main tectono-magmatic events that have contributed to the

assembly of the craton prior to 3200 Ma.

Based on geological, structural or aeromagnetic lineaments, faults and thrusts, the Kaapvaal Craton has been divided into three main blocks separated by major, craton-wide,

lineaments (Fig. 5.1-1; Schmitz et al., 2004): the Witwatersrand Block in the east, the

Kimberley Block in the west and the Pietersburg Block in the north. To the north, the

Thabazimbi–Murchison lineament (TML) separates the Witwatersrand Block from the

Pietersburg Block. To the west, the Colesberg lineament separates the Witwatersrand and

Kimberley blocks. Eglington and Armstrong (2004), however, identified the Kimberley

terrain, Witwatersrand terrain and Pietersburg terrain and describe two additional terrains,

the Swaziland terrain to the south-east and an unnamed terrain to the north-west, separated from the Kimberley and Pietersburg terrains by the Palaba Shear Zone (PSZ). For

the purposes of this paper, however, the Kaapvaal Craton has been subdivided (Fig. 5.1-2)

into eastern, central, northern and western domains as in Poujol et al. (2003). These four

domains are not intended to represent geological terranes, although each does have its own

identifiable geological and chronological characteristics.

Much of the Kaapvaal Craton is covered by Neoarchean-to-Palaeoproterozoic volcanosedimentary sequences and good exposures of basement exist in only a few areas. Of these,

the Barberton Mountain Land is a region of superb three-dimensional exposure and repre-



454

Chapter 5.1: An Overview of the Pre-Mesoarchean Rocks of the Kaapvaal Craton, South Africa



Fig. 5.1-1. Simplified diagram showing the outline of the Kaapvaal Craton and the main geological components referred in the paper. (TML):

Thabazimbi–Murchison lineament, (HRSZ): Hout River Shear Zone and (PSZ): the Palaba shear zone.



5.1-2. Overview of the Pre-Mesoarchean Evolution of the Kaapvaal Craton



455



Fig. 5.1-2. Simplified diagram showing the locations of the eastern, central, northern and western

domains of the Kaapvaal Craton as used in this paper.



sents the type area for Archean crustal evolution in the craton. The majority of all studies

and age dating of the crust has also been carried out in the Barberton region and, accordingly, crust-forming processes are best described from this portion of the craton. As

emphasized by Schmitz et al. (2004), much of the geochronological data to the west of

the craton concerns mantle xenoliths. Consequently, the direct comparison between the

crustal evolution of the eastern, central and northern domains and the mantle evolution of

the western domain is equivocal. This may, at least in part, be responsible for the discrepancies between the geochronological records.

In this paper, we synthesize the accurate geochronological data applicable to the Barberton Mountain Land as well as three other geographic domains of the craton where a

useful body of data has now been generated.

5.1-2. OVERVIEW OF THE PRE-MESOARCHEAN EVOLUTION OF THE

KAAPVAAL CRATON

5.1-2.1. Eoarchean (>3600 Ma)

5.1-2.1.1. Barberton Mountain land

The oldest rock yet dated on the Kaapvaal Craton is a sample of banded tonalite gneiss

from part of the Ancient Gneiss Complex (AGC) in northwest Swaziland (Fig. 5.1-1). This

sample provided a population of zircons which yielded an U-Pb isotope age of 3644 ±



456



Chapter 5.1: An Overview of the Pre-Mesoarchean Rocks of the Kaapvaal Craton, South Africa



4 Ma (Compston and Kröner, 1988). Crystallization and recrystallization of other zircons

in the same sample indicate that this rock has been affected by subsequent events, the most

notable of which are at 3504 ± 6 Ma and 3433 ± 8 Ma. Other evidence for the existence of

Eoarchean crust in the Kaapvaal Craton is provided by the presence of xenocrystic zircons

in the Vlakplaats weakly foliated to massive granodiorite and the Ngwane gneiss, dated at

3702 ± 1 Ma and 3683 ± 10 Ma, respectively (Kröner et al., 1996; Kröner and Tegtmeyer,

1994). There are no other Eoarchean intrusions that have yet been found in the craton as a

whole.

5.1-2.2. Palaeoarchean (3600 to 3200 Ma)

5.1-2.2.1. Eastern Domain

(i) 3600 to 3400 Ma tonalite-trondhjemite-granodiorite (TTG) gneiss plutons and volcanism Tonalite and trondhjemite gneisses occur as discrete plutons along the southwestern

part of the Barberton Greenstone Belt (BGB). They contain greenstone xenoliths of variable size, which are thought to be mainly remnants, but could also partly represent infolded

material. Some of the plutons are unequivocally intrusive into the adjacent greenstones,

whereas others display sheared margins indicating that they were structurally emplaced

into their present position. A granitoid gneiss clast found in the Moodies Formation was

dated at 3570 ± 6 Ma (Kröner and Compston, 1988). A zircon xenocryst found in the

Hooggenoeg Formation was dated at 3559 ± 27 Ma while an age of 3563 ± 3 Ma was also

determined for a well foliated tonalitic gneiss (Kröner et al., 1989) in the Ancient Gneiss

Complex (AGC). A weakly foliated porphyritic granodiorite (Vlakplaats) yielded a Pb-Pb

zircon age of 3540 ± 3 Ma (Kröner et al., 1996). A tonalitic gneiss wedge in the Theespruit

Formation, described as a possible basement for the BGB, was dated at 3538 +4/−2 Ma

and 3538 ± 6 Ma respectively (Armstrong et al., 1990; Kamo and Davis, 1994). This age

is identical within error to the age of 3531 ± 4 Ma of a granitoid gneiss clast found in the

Moodies Group (Kröner and Compston, 1988). In the AGC, the Ngwane tonalic gneiss was

dated at 3521 ± 23 Ma and 3490 ± 3 Ma (Kröner and Tegtmeyer, 1994), while a granite

boulder from the Moodies conglomerate in the BGB yielded an age at 3518 ± 11 Ma.

The Steynsdorp Pluton, a banded trondhjemitic gneiss, yielded ages between of 3510 ±

4 Ma and 3505 ± 5 Ma (Kamo and Davis, 1994; Kruger, 1996). A granodioritic phase

of the pluton has been dated at 3502 ± 2 Ma (Kröner et al., 1996). An identical age of

3504 ± 24 Ma was found for a trondhjemitic gneiss from the AGC (Kröner et al., 1989).

Younger ages at 3490 Ma have also been reported for both the trondhjemitic and tonalitic

phases of the pluton (Kröner et al., 1991a, 1992). Three zircon xenocryst found in the

gneiss were dated at 3553 ± 4 Ma, 3538 ± 9 Ma and 3531 ± 3 Ma, respectively (Kröner et

al., 1991, 1996).

The Stolzburg Pluton, which comprises a biotite-bearing trondhjemitic gneiss which

is intrusive into the lower part (Theespruit Formation) of the BGB, was dated at 3460

+5/−4 Ma by Kamo and Davis (1994) and 3445 ± 3 Ma (Kröner et al., 1991). An age of

3431 ± 11 Ma (Dziggel et al., 2002) has also been reported, a range interpreted to reflect

the age of crystallization of the gneisses. A pebble found in the Moodies Group was dated



5.1-2. Overview of the Pre-Mesoarchean Evolution of the Kaapvaal Craton



457



at 3474 + 35/−31 Ma (Tegtmeyer and Kröner, 1987). A quartz-feldspar porphyry dyke

cutting the Komati Formation in the BGB was dated at 3470 + 39/−9 Ma on zircons and

3458 ± 1.6 Ma on titanites, while metagabbros from the Komati Formation were dated at

3482 ± 5 Ma (Armstrong et al., 1990). Within the AGC, Kroner et al. (1989) reported an

age of 3458 ± 3 Ma for a tonalitic gneiss, while the Tsawela Gneiss, a foliated tonalite,

was dated between at 3455 and 3436 Ma (Kröner and Tegtmeyer, 1994).

The trondhjemitic Theespruit Pluton unequivocally intrudes and cross-cuts the adjacent

lower portion (Sandspruit and Theespruit Formations) of the BGB. The reported singlezircon U-Pb ages vary only slightly, between 3443 and 3437 Ma (Armstrong et al., 1990;

Kamo and Davis, 1994; Kamo et al., 1990; Kröner et al., 1991, 1992), and are indistinguishable from the age for the Stolzburg Pluton, indicating that both bodies belong to the

same igneous event.

The Doornhoek Pluton is the smallest (4 × 2 km) of the intrusive trondhjemite gneiss

bodies and is entirely surrounded by greenstones of the Theespruit Formation of the BGB.

U-Pb isotopic determinations on single zircons yielded an age of 3448 + 4/−3 Ma (Kamo

and Davis, 1994). A titanite U-Pb age (∼3215 Ma; Kamo and Davis, 1994) has also been

obtained from the Doornhoek Pluton, as well as imprecise Rb-Sr whole-rock ages (Barton

et al., 1983) of 3176 ± 203 Ma (coarse-grained phase) and 3191 ± 46 Ma (fine-grained

variety). Both the titanite and Rb-Sr ages are interpreted as thermal re-setting, possibly

manifest as numerous quartz veins especially in the western portions of the body.

The Theeboom Pluton comprises two varieties of gneiss, an early well-foliated trondhjemite and a younger cross-cutting, more homogeneous variety. For the older phase a

single zircon U-Pb age of 3460 + 5/−4 Ma, and for the younger variety titanite and zircon

ages of 3237–3201 Ma were reported by Kamo and Davis (1994). These workers regarded

the Theeboom Pluton as the southern extension of the Stolzburg Pluton.

The TTG gneisses southwest of the BGB are virtually unmetamorphosed and are now

interpreted to be the plutonic equivalents of, and hence comagmatic with, felsic volcanics

and shallow subvolcanic intrusions occurring in the stratigraphically lower portions of

the adjacent greenstone belt (de Wit et al., 1987a). The age correlation between plutonic and extrusive components of this magmatic suite have been confirmed by Kröner

and Todt, (1988), Armstrong et al. (1990) and Kroner et al. (1991, 1992), who showed

that felsic rocks of the Theespruit and Hooggenoeg Formations, with zircon U-Pb ages of

3453–3438 Ma, overlap with the 3460–3430 Ma ages of the Doornhoek, Theespruit and

Stolzburg plutons. The one exception to this is the ca. 3510 Ma old Steynsdorp pluton

which is clearly older than most of the metavolcanic sequences in the southwestern part of

the BGB, but is broadly coeval with an adjacent suite of felsic volcanics previously correlated with the Theespruit Formation and dated between 3548 and 3530 Ma (Kröner et al.,

1992, 1996). These observations are central to the hypothesis by Lowe (1994) that the BGB

comprises a series of discrete tectono-stratigraphic blocks that were progressively accreted

to one another between 3550 and 3220 Ma to form a composite granite-greenstone terrane

that represents the core of an ancient continental fragment now referred to as the Kaapvaal

Craton.



458



Chapter 5.1: An Overview of the Pre-Mesoarchean Rocks of the Kaapvaal Craton, South Africa



(ii) 3400–3250 Ma rocks This period experienced very little plutonic or volcanic activity

within this part of the craton. In south-central Swaziland, the granodiorite of the Usuthu

suite in the south central Swaziland was dated at 3306 ± 4 Ma (Maphalala and Kröner,

1993). Activity was also recorded in the BGB where pegmatitic to medium grained gabbros and metagabbros present in the Komati Formation were dated at around 3350 Ma

(Armstrong et al., 1990; Kamo and Davis, 1994). Within the Medon Formation in the

BGB, a volcanic unit has been dated at 3298 ± 3 Ma (Byerly et al., 1996). A coarsegrained granodiorite described as the older part of the Stentor Pluton yielded a U-Pb age

of 3347 + 67/−60 Ma (Tegtmeyer and Kröner, 1987), whereas zircon xenocrysts found

mostly in volcanic rocks from the Fig Tree Group gave ages between 3334 and 3310 Ma

(Byerly et al., 1996; Kröner et al., 1991). Finally, a pebble found in the Moodies Group

yielded a poorly constrained age of 3306 + 65/−57 Ma (Tegtmeyer and Kröner, 1987).

(iii) Circa 3250 Ma tonalite-trondhjemite-granodiorite (TTG) gneiss plutons and associated volcanism During this period, volcanic activity was recorded with the deposition

of the Fig Tree Group in the central part of the BGB, consisting mostly of dacitic tuffs

and agglomerates interbedded with ferruginous cherts. Several publications (Armstrong et

al., 1990; Byerly et al., 1996; Kamo and Davis, 1994; Kohler et al., 1993; Kröner et al.,

1991, 1992) indicate that the deposition of the Fig Tree Group took place between 3259

and 3225 Ma. A feldspar-quartz porphyry that intrudes the Fig Tree Group metasediments

dated at 3227 ± 3 Ma provides a minimum age of the Fig Tree Group (de Ronde, 1991).

Gneisses flank the western and northwestern margin of the Barberton Greenstone Belt

and include the Nelshoogte, Kaap Valley and Stentor plutons. They are generally larger

bodies than the older intrusions that are found along the southern and southwestern flank

of the belt.

The Kaap Valley Pluton is the largest of the three bodies. Towards the centre, the pluton displays only a weakly developed fabric. It contains a number of mafic and ultramafic

xenoliths. The Kaap Valley Pluton differs significantly from most of the other gneiss plutons in the region in that it is entirely tonalitic and is one of the best-dated granitoids in the

Barberton region. Results of precise single-grain U-Pb zircon dating by various workers

differ only slightly, ranging from 3229 to 3223 Ma (Armstrong et al., 1990; Kamo and

Davis, 1994; Layer et al., 1992; Tegtmeyer and Kröner, 1987). 40 Ar/39 Ar hornblende and

biotite ages are slightly lower, being 3214 and 3142 Ma, respectively, which can be attributed to variable closure temperature effects in the slowly cooling pluton (Layer et al.,

1992).

The Nelshoogte Pluton is an oval-shaped body of trondhjemitic gneiss, situated between

the Badplaas domain and Kaap Valley pluton. A Pb-Pb zircon age of 3212 ± 2 Ma for the

intrusion has been obtained by York et al. (1989). Studies by these authors on muscovite

and biotite separates gave 40 Ar/39 Ar ages of 3080–2860 Ma, suggesting that the pluton

experienced a prolonged cooling history. An imprecise Rb-Sr whole-rock age of 3180 ±

75 Ma was reported by Barton et al. (1983) while an U-Pb age of 3236 ± 1 Ma was found

for a strongly foliated sample (Kamo and Davis, 1994).

The Stentor Pluton occurs as an elongate intrusion of trondhjemitic to granodioritic

gneisses that intrudes between the BGB and the Nelspruit batholith. Conventional zircon



5.1-2. Overview of the Pre-Mesoarchean Evolution of the Kaapvaal Craton



459



dating yielded U-Pb ages of 3250 ± 30 Ma (Tegtmeyer and Kröner, 1987). A more recent

U-Pb zircon age of 3107 ± 5 Ma obtained by Kamo and Davis (1994) from the eastern

portion of the pluton suggests that certain parts of the body should be attributed to the

Nelspruit Suite.

The Dalmein Pluton is granodioritic in composition and is situated at the southeastern

end of the BGB, where it cuts into both the older (ca. 3450 Ma) TTG gneiss plutons as

well as the various lithologies of the BGB. Single zircon U-Pb dating has yielded an age

of 3216 + 2/−1 Ma (Kamo and Davis, 1994).

The poorly documented Badplaas domain, located to the south of the Barberton Greenstone Belt, is made up of a variety of compositionally and texturally distinct, variably

gneissose trondhjemites. Geochronological work on the five main TTG phases (Kisters et

al., 2006) reveals that the Badplaas domain was assembled over a period of ca. 50 Ma between ca. 3290 and 3240 Ma. This is interpreted as a 50 Ma record of convergence-related

TTG plutonism.

Other intrusive bodies that fall into the ca. 3230 Ma category are; the tonalitic to granodioritic Wyldsdale pluton that occurs along the Mgudugudu thrust in the Piggs Peak area

of northern Swaziland, that yielded a single zircon U-Pb isotope age of 3234 + 17/−4 Ma

(Fletcher, 2003); a granodiorite from the Usuthu Suite in North-Central Swaziland (Maphalala and Kröner, 1993) dated at 3231 ± 4 Ma and 3224 ± 4 Ma, suggesting that this body

is not equivalent to the Usuthu Suite dated farther south; a K-feldspar-rich granitic gneiss

from the AGC dated at 3227 ± 21 Ma (Kröner et al., 1989); and, a tonalitic intrusion in the

Weltevreden area of the BGB, as well as a tonalitic dyke dated at ca. 3229 Ma (de Ronde

and Kamo, 2000). In the Tjakastad schist belt (TSB), a 10 km long N–S trending extremity

of the BGB that occurs along the southern margin of the belt, titanites have been dated

at 3229 ± 25 Ma in a garnet-bearing metabasite (Diener et al., 2005). This age has been

interpreted as dating the peak of the metamorphism in the TSB. Similar results have been

found by Dziggel et al. (2005) for a greenstone remnant located 10 km to the west of the

TSB. Titanites extracted from a clastic metasedimentary unit yield an upper intercept age

of 3229 ± 9 Ma, providing a minimum age for the peak of metamorphism (∼650–700 ◦ C)

while zircons separated from the same unit record a range of 207 Pb/206 Pb dates between

∼3560 and 3230 Ma, the youngest group yielding a weighted mean age of 3227 ± 7 Ma.

They also defined a minimum age for the timing of deformation with the emplacement age

of 3229 ± 5 Ma found for a late-kinematic trondhjemite.

Finally, a series of granitoid samples were dated around 3.2 Ga. A pebble found in

the Moodies Group yielded an age of 3224 ± 6 Ma (Tegtmeyer and Kröner, 1987), and a

porphyry intrusion from the Stolzburg Syncline was dated at 3222 + 10/−4 Ma (Kamo

and Davis, 1994). In the AGC, a tonalitic gneiss was dated at 3214 ± 20 Ma (Kröner et al.,

1989) and an unfoliated granodiorite intrusive into the Dwazile greenstone belt yielded an

age of 3213 ± 10 Ma (Kröner and Tegtmeyer, 1994).

In the southeastern part of the Kaapvaal Craton, pre-3200 Ma granitoids occur in two

areas: one in the vicinity of Piet Retief, and the other adjacent to the Nondweni greenstone

belt (Fig. 5.1-1). In the Piet Retief-Paulpietersburg region, Hunter et al. (1992) reported the

presence of layered granitoid rocks consisting of alternating light and dark TTG gneisses



460



Chapter 5.1: An Overview of the Pre-Mesoarchean Rocks of the Kaapvaal Craton, South Africa



and amphibolites preserved as inliers in younger granitoids. The gneisses are described as

similar to the ca. 3640 to 3460 Ma layered gneisses of the bimodal suite of the Ancient

Gneiss Complex in Swaziland. South and west of the Assegaai and Commondale Archean

greenstone remnants (Fig. 5.1-1) are exposures of Luneburg gneisses (Hunter et al., 1992),

which consist of medium-grained tonalitic to trondhjemitic rocks described as chemically

and mineralogically indistinguishable from the ca. 3458–3362 Ma Tsawela gneisses of

southwestern Swaziland dated by Kröner et al. (1991). A third variety of gneiss (referred

to as the De Kraalen gneiss), consists of layered tonalitic rocks and occurs southeast of the

De Kraalen greenstone remnant in the valley of the Assegaai River. No precise radiometric

ages are available for the various gneisses previously described, but they have been intruded

by the ca. 3250 Ma Anhalt Granitoid Suite described below.

The Anhalt Granitoid Suite (Fig. 5.1-1) comprises the most extensive development of

granitoid rocks in the southeastern part of the Kaapvaal Craton. The Anhalt granitoids can

be subdivided into a number of different phases, including trondhjemites, granodiorites

and quartz monzonites (Hunter et al., 1992). A Rb-Sr whole-rock age of 3250 ± 39 Ma

for the Anhalt Suite rocks has been documented by (Farrow et al., 1990). In the area adjacent to the Nondweni greenstone belt, a homogeneous, fine- to medium-grained rock

of batholithic proportions, known as the Mvunyana Granodiorite, is the most widespread

granitoid (Matthews et al., 1989). Rb-Sr, Pb-Pb and limited U-Pb zircon isotopic data obtained for the Mvunyana granodiorite yielded an age of ca. 3290 Ma (Matthews et al.,

1989). Further south, in the Natal Spa, a granite sensus-stricto was dated at 3210 ± 25 Ma

(Reimold et al., 1993).

In the southeastern region of the Kaapvaal Craton, only the Commondale and Nondweni

greenstone belts have been dated. The Commondale greenstone belt yielded a precise SmNd age of 3334 ± 18 Ma on an exceptionally well preserved peridotite suite of komatiitic

affinity (Wilson and Carlson, 1989). An age of 3406 ± 6 Ma was obtained on zircons

from a rhyolite flow in the uppermost Witkop Formation of the Nondweni Group (Versfeld

and Wilson, 1992) while a Re-Os isochron regression age of 3321 ± 62 Ma was obtained

for komatiite and komatiitic basalt flows collected from the same formation (Shirey et al.,

1998).

5.1-2.2.2. Northern part of the craton

Very little pre-Mesoarchean geochronological data are available for this part of the craton. This area is characterized by the widespread occurrence of the Goudplaats-Hout

River Gneiss Suite, which comprises a wide spectrum of granitoid gneisses, types and

compositions. These gneissic bodies range from homogeneous to strongly layered, from

leucocratic to dark grey, and from fine-grained to pegmatoidal varieties. They underlie

both the high-grade (“Southern Marginal Zone”) and low-grade terranes of the northern

part of the Kaapvaal Craton, mainly to the north of the Pietersburg and Giyani greenstone

belts (Fig. 5.1-1). The oldest known age in this region comes from a 3364 ± 18 Ma zircon

xenocryst found in the Mac Kop conglomerate from the Murchison greenstone belt (Poujol

et al., 1996).



5.1-2. Overview of the Pre-Mesoarchean Evolution of the Kaapvaal Craton



461



In most of the area around the Giyani greenstone belt (GGB, Fig. 5.1-1), mediumgrained, whitish, or locally pinkish, tonalitic or trondhjemitic gneisses are the dominant

phase, with the exception of the southern boundary of the GCB where massive granites

are developed. Ages of ca. 3282.6 ± 0.4 and 3274 + 56/−45 Ma from dark-grey tonalitic

gneisses located to the north of the GGB have been obtained (Kröner et al., 2000). Within

the GGB, a meta-andesite was dated at 3203.3 ± 0.2 Ma (Kröner et al., 2000) while a felsic

metavolcanic yielded an age of 3203 ± 4 Ma (Brandl and Kröner, 1993).

At the Goudplaats locality (Fig. 5.1-1), light-to dark-grey gneisses, together with minor

leucocratic gneisses and hornblende amphibolite and hornblende-biotite tonalitic gneisses,

are prominently exposed in a river section. A dark-grey migmatitic tonalitic gneiss from

this locality has been dated at 3333.3 ± 5 Ma (Brandl and Kröner, 1993).

In the Lowveld, south of the Murchison greenstone belt, two principal types of gneisses

are present; a layered composite variety termed the Makhutswi Gneiss and a “homogeneous gneiss” which has not yet been named. The Makhutswi Gneiss extends from

the Murchison greenstone belt southwards for some 50 km, and then forms another

smaller occurrence still further to the south. Limited geochemical data suggest that the

Makhutswi Gneiss has a tonalitic to granodioritic composition. A single zircon U-Pb age

of 3228 ± 12 Ma, has been obtained for a gneiss sampled close to the contact with the

Murchison greenstone belt (Poujol et al., 1996). An imprecise Rb-Sr whole-rock age of

3268 ± 113 Ma was also reported from the Phalaborwa area (Barton, 1984).

5.1-2.2.3. Central domain

Very few Paleoarchean ages have been documented in this part of the Craton. The oldest

granitoid phase recognised so far is a Palaeoarchean trondhjemite gneiss from the Johannesburg Dome (Fig. 5.1-1) that yielded an age of 3340 ± 3 Ma (Poujol and Anhaeusser,

2001). Still older xenocrystic zircon ages, of ca. 3425 Ma (Hart et al., 1999) and 3310 Ma

(Kamo et al., 1996), have, however, been reported from a paragneiss and a pseudotachylitic

breccia, respectively, sampled on the Vredefort Dome, and from the Neoarchean Makwassie Quartz Porphyry of the Ventersdorp Supergroup, with a zircon xenocryst age of ca.

3480 Ma (Armstrong et al., 1991). Two additional zircon xenocrysts found in the highly

amygdaloidal volcanic horizon of the Crown Lava from the Witwatersrand Supergroup

have been dated at 3259 ± 9 and 3230 ± 8 Ma, respectively (Armstrong et al., 1991). Finally a tonalitic gneiss from the Johannesburg Dome has been dated at 3199.9 ± 2 Ma

(Poujol and Anhaeusser, 2001).

5.1-2.2.4. Western domain

The Archean crystalline basement of this part of the Kaapvaal Craton is only poorly exposed as it is covered by Neoarchean to Phanerozoic sedimentary and volcanic strata.

Consequently, it has produced very little geochronology. Indication of old crust is provided by the presence of several zircon xenocrysts. Two xenocrysts from a felsic schist

collected in the Western succession of the Madibe greenstone belt (Fig. 5.1-1) provided

ages of 3428 ± 11 and 3201 ± 4 Ma (Hirner, 2001). Tonalitic and trondhjemitic gneisses

and migmatites occur as windows in Karoo cover rocks in the Kimberley–Boshoff–



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Chapter 5.1: An Overview of the Pre-Mesoarchean Rocks of the Kaapvaal Craton, South Africa



Fig. 5.1-3. Compilation of the geochronological constraints on the evolution of the Kaapvaal craton

(see text for source references). Dotted line compiles the geochronological data relative probability

for the entire craton (N = 122). D1 (development of an active margin) and D2 (main “orogenic”

stage) refer to the main deformation events in the Barberton granitoid-greenstone terrain.



Koffiefontein area of the Northern Cape and Free State Provinces. Zircon cores from samples of these rocks from the Bultfontein diamond mine in the Kimberley area (Fig. 5.1-1)

defined a mean 207 Pb/206 Pb age of circa 3250 Ma (Drennan et al., 1990). A peraluminous

tonalitic gneiss obtained from the Bultfontein diamond mine dump yielded abundant prismatic zircons with 207 Pb/206 Pb dates ranging from 3246 to 3069 Ma (Schmitz et al., 2004).

The proposed crystallization age for this tonalite is ca. 3.22 Ga.



5.1-3. CONCLUSIONS

As illustrated in this paper, the Kaapvaal Craton of Southern Africa experienced a

protracted evolution with different terrains exhibiting distinct histories (Eglington and

Armstrong, 2004). The magmatic record for the four Kaapvaal domains has been plotted



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Part 5. The Paleoarchean Kaapvaal Craton, Southern Africa

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