groenewald et al

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Journal of the Geological Society

doi: 10.1144/gsjgs.148.6.11151991, v.148; p1115-1123.Journal of the Geological Society

P. B. GROENEWALD, G. H. GRANTHAM and M. K. WATKEYS

southeastern Africa and Dronning Maud Land, AntarcticaGeological evidence for a Proterozoic to Mesozoic link between

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2/10

Journal ofth e Geological Sociely,

London, Vol. 148

1991, pp. 1115-1123, 1 fig, 2 tables. Printed in Northern Ireland

Geological evidence for a Proterozoic to Mesozoic link between southeastern

Africa and Dronning Maud Land, Antarctica

P . B . GROENEWALD,G . H . GRANTHAMlY3 M. K . WATKEYS

Departm ent of G eolog y, University of Natal, Box

375

Pietermaritzburg

3200

South Africa

Department of Geology and Applied Geology, University of Natal, Durban, South Africa

3 P r e ~ e n tddress: Department of Geology, University of Pretoria, Pretoria, South Africa

Abstmft: Comparison of crustal provinces in Southeastern Africa and Dronning Maud Land, Antar-

ctica, eveals onsiderable imilarity

in

their volution romheArchaeanuntilheMesozoic

separation. Archaean granites and mid-Proterozoic supracrustal successions

in

these regions are so

comparable hatcorrelation is uggested.

A

major mid- to lateProterozoicorogenic errain in

Dronning Maud Land, comprising he H . U . Sverdrupfjella and Heimefrontfjella subprovinces and

termed the Maudheim Province, is very similar in age, lithology, structural style and metamorphic

history to the Mozambique and Natal orogenic provinces of Kibaran age

l o o 0 Ma) in

southeastern

Africa. Deformed supracrustal sequences in

all

three provinces host syn-tectonic granites ntruded

during upper amphibolite- to granulite-facies metamorphism. Isoclinal folding was accompanied

by

thrusting owardsadjacentcratonicareas.Development of orogenicprovinces of Kibaranage in

southeastern Africa and Antarctica reflects accretion of marginal basin-volcanic arc sequences onto

older continents. The500Ma Pan African event was a widespread, predominantly thermal, overprint-

ingof parts of the older orogenic provinces. Faulting

and

rifting of the supercontinent preceded

break-up and influenced the stratigraphy of Phanerozoic sedimentary successions in SE Africa.

Recent reconstructions

of

Gondwana place Dronning Maud

Land, Antarctica and the Mozambique coast of Africa into

juxtaposition at

c.

145 Ma on the basis of marine geophysical

evidence (Martin Hartnady 1986; Lawver Scotese

1987). The geological similarities

of

these regions, remarked

on earlier by du Toit (1937), Grantham

et

al. (1988) and

many others, may benlarged onhe basis of new

information from Antarctica. A major problem in

reassembling Gondwana is the precise juxtapositioning of

Antarctica and Africa. This stems partly from masking of

the original contact areas, inMozambique by a thick

Cretaceous-Tertiary sequence,and in Antarctica by ice.

The new datarom Antarctica allow more detailed

comparison of the marginal regions and offer strong support

for the reassembly proposed by Martin Hartnady (1986).

Studies

of

Phanerozoic crustal evolution in SE Africa have

demonstrated that syn-depositional tectonism in the Karoo

basin was rela ted o earlystages

of

Gondwanabreak-up

(Cox

et

al. 1967; Flores 1970). Theseuthors also

recognized early rifting (220-145 ma) andranscurrent

faulting, which initiated partial separation of Antarctica and

Africa prior to drifting. Geological evidence for correlation

of events in Africa and Antarctica from early Proterozoic

(and possibly Archaean)o mid-Phanerozoic will be

synthesized here. Implications of the extent andevolution of

Proterozoic orogenic provinces will also be discussed.

Southeastern Africa and Dronning Maud Land may be

considered in terms of ancient, cratonic nuclei separated by

orogenic belts

of

various ages (Fig. 1). The Kaapvaal and

Zimbabwe ratonic terrains comprisegranite-greenstone

provinces overlain by supracrustal sequences ranging in age

from late Archaean to mid-Proterozoic. In Dronning Maud

Land,herchaeano mid-Proterozoic Grunehogna

Province shows similarities to these provinces in having

3.0Ga granites and.7Ga red-coloured tenigenous

sediments. Around the cratonic provinces are the accreted

mid- to ate Proterozoicorogenic provinces which have

been the focus of several recent studies. It isnow known

that the 1OOOMa Kibaranectonic vent xtended from

centralMozambique, hrough Malawi into Zambia in the

west, and orthwards into Tanzania and Kenya (Daly

1986a;hackleton 1986). The Mozambiquerovince,

important in the presentcontext,hasbeen described in

some detail by Sacchi et

al.

(1984). Their data are used here.

The Namaqua-Natal orogenic belt, situated some distance

tohe south

of

and geographically discreterom the

Mozambique Province, is of similar age andeneral

lithological character. The ast coast Natal Province is

particularly relevant to this discussion and haseen

described in general terms by Cain (1975), Matthews (1981)

andhomas (1989). More specific aspects of the

geochronology, give by Eglington et al. (1989), reveal that

deformation,metamorphismandgraniteemplacement n

this area occurred synchronously with the same processes in

Mozambique Province.

In DronningMaud Land, a high-grade structuraland

metamorphic errain lies to heeast, south and west

of

Grunehogna Province (Fig. 1). Two sectors of this orogenic

province have been investigated. The eastern sector, first

examined by Roots (1953), consists of

H . U . Sverdrupfjella

and Kirwanveggen, described by Grantham et al. (1988) and

Wolmarans Kent (1982) respectively. The Heimefront-

fjella sector, situated to the west, has been reported on by

Juckes (1972), Spaeth Fielitz (1987) and Weber

et

al.

(1987). The geology of these areas is sufficientlywell

constrained to allow their interpretation in terms

of

a single

orogenic belt, henceforth termed the Maudheim Province.

This name is proposed in view

of

the former existence of

Maudheim base, used by the Norwegian-British-Swedish

Antarctic Expedition from 1950 to 1953. In age, lithology,

1115

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3/10

1116

P. B .

G R O E N E W A L D

E T AL .

deformation and metamorphism, theastern sector of

Maudheim Province shows significant similarities to he

Mozambiquerovince. Inddition, correlation of the

Heimefrontfjellasector with the Natal Province hasbeen

proposed(Spaeth Fielitz 1987; Weber et

al.

1987). The

parallel tectonic evolution of the late Proterozoic provinces

in the Mozambique, Natal-Namaqua and Dronning Maud

Land regions allows more detailed interpretation of their

evolution and identification of their original tectonic

settings. Furthermore, some inferences made regarding the

extent of this loo0Maectonothermal province have

implications for the original assembly of Gondwana.

A tectonothermal overprinting, spanning the period

600

to 450 Ma, is widely recognized in Africa as the Pan African

and in Antarctica ashe RossOrogeny. It as been

sueprimposed on he Mozambique and Maudheim Prov-

inces, but has not been recognized in Natal Province. It is

characterized by folding, thermal resetting

of

some isotopic

systems and the generation and emplacement of granites.

Development of predominantly sedimentary successions

across the older terrains occurred in the Phanerozoic. The

widespread Karoo Sequence in southern Africa comprises a

thick succession

of

sedimentsccumulated in diverse

environments. Its deposition terminated with widespread

emplacement of doleritic ntrusions and tholeiitic volcanic

rocks. A similar, albeit much thinner, succession is present

in the Heimefrontfjella and Kirwanveggen areas

of

the

Maudheimrovince. Likewise, post-Karoolkaline

intrusions are presentboth n theJutulstraumenarea of

Dronning Maud Land and in the northeastern sector of the

Karoo basin in Africa (Fig. 1). The similarity between the

patterns

of

jointing and faulting post-dating these intrusions

in both settings has been recognized by Grantham Hunter

(1991).

Linked cratonic fragm ents

In Dronning Maud Land, relatively undeformed and

unmetamorphosed Archaean and Proterozoicrocks n the

Ahlmannryggen, Straumsnutanend Borgmassivet areas

constitute the Grunehogna Province. This

is

bounded to the

east and south by the Maudheim Province (Fig. 1).The

Archaean ocks,occurringonly in theAnnandagstoppane

area, are c. 3000 Ma granites (Barton et

al.

1987). These are

of the same age as some granitic intrusions in the eastern

Kaapvaal and ZimbabweProvinces, but he limited data

available suggest slightly different geochemical characteris-

tics and provenance (Barton

et al.

1987).

Proterozoicedimentary and volcanic rocks of the

Ritscherflya Supergroup occupy the remainder of Gruneh-

ogna Province and have been extensively intruded by mafic

and ultramafic bodies. Ferreira (1986) interpretedhe

sedimentary rocks as a sequence, from the base upwards, of

shallow marine, tidal flat, braided stream, and alluvial fan

deposits. Measured palaeocurrent directionswere highly

variablebut thedepocentre was probablysituated to he

northeast

of

Grunehogna. The sediments ar e characteristi-

cally immature and red in colour. A sequence of continental

tholeiitic basalts overlies the sedimentary rocks (Watters et

al. 1991). The geochronological dataare equivocal, with

reported ages ranging from 800 Ma to 1800 Ma (Moyes

Barton 1990). Watters et al. (1991) obtained Sm-Nd

zhur

model ages in the range 1300-1620Ma for the basalts and

interpreted these as representative of the crystallization age,

and ascribed an Rb-Sr age of 876 Ma to later ectonothermal

overprinting.

The sediments of the Ritscherflya Supergroup ave

several possible correlates in southeastern Africa such as the

Umkondo, Waterberg andSoutspanberg Groups (Fig. 1).

Farther afield, the Volop Group and theNtingwe Formation

are situated along the southern margin of the Kaapvaal

Province adjacent o he Namaqua and Natal Provinces

respectively. All thesemid-Proterozoic equencescontain

immature fluvial to shallow marine sediments with distinct

ferric pigmentation. However, tholeiitic volcanic rocks are

present only in the Soutpansberg andUmkondo Groups.

Tankard

et al.

(1982) reported predominantlysouthwards

palaeocurrent directions in the Soutpansberg Group, which

is opposite to those in the Grunehogna area. The sediments

were depositedn andy,braided alluvial plain settings,

within either an aulacogen or a yoked basin. The Umkondo

Group situated onhe astern flank of the Zimbabwe

Province, has close similarity to the Ritscherflya Supergroup

in terms of sedimentary characteristics, which led Ferriera

(1986) to suggest correlation. Themkondoroup

sediments, described by Button (1977), represent tidal

flat-lacustrine, progradationalan delta, andmeandering

river depositional nvironments.Palaeocurrentdirections

are to the SE,N and E in the lower, middle and upper parts

of the sequence respectively.

Despite the similarities of the sedimentary sequences in

theUmkondo,Waterberg nd Soutpansberg Groups o

those of the Ritscherflya Supergroup, it is impossible to

correlate them with any certainty. It is significant, however,

thatmid-Proterozoicsequences in this part of Gondwana

are of similar character and re situatedn easonable

proximity to one another in the reconstruction (Fig. 1). The

fact that Soutspanbergediments have been observed

overlying Waterberg Group sediments (Jansen 1976) points

tohe development of severalntracratonic basins

or

aulacogens in the mid-Proterozoic. Certainly, the in-

tracratonic basins on the Kaapvaal craton had a long history

as Jansen (1982) recognized a much more complex

stratigraphy in theWaterbergGroup than previously

reported. However, heir chronology is not unequivocal.

Allsopp

et

al. (1989) presenteda well constrainedage

of

1080Ma forhe UmkondoGroup. Ageserivedor

lowermost parts of theWaterbergGroup range from

1790Ma o1420Ma (Oosthuyzen Burger 1964), which

conflictswith its correlation with the Umkondo Group on

the basis of similar palaeomagnetic poles (Jones

McElhinny 1967). The proximity of all these sequences to

orogenic provinces, which developed subsequently in the

mid- to late Proterozoic, suggests that initial crustal buckling

and the development

of

intracratonic basins was a

consequence of widespread tectonic processes prior to the

onset of the Kibaranorogenesis, itself a widespread and

long-lived collisional tectonic regime.

Comparison of the

loo0

Ma terrains

The geological characteristics of the 1000 Ma orogenic

terrains in SE Africa andAntarctica arecomparable, as

summarized in Table 1and discussed in more detail below,

and broad correlation of these is almost certain.

The Natal Province may be considered in terms of four

zones (Matthews 1981; Tankard et

al.

1982) or terranes

(Thomas 1989). Thenorthern marginal zone

or

Tugela

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ANTARCTICA-AFRICA:ROTEROZOIC-MESOZOICINKAGE 1117

Fig 1. Simplified geological map of SE Africa and Dronning Maud Land, Antarctica.The continents are juxtaposed asn the reconstruction

of Martin Hartnady (1986). The continental outline projection is hat used by de Wit

et

al. (1988). Bathograds at

3000

m depth areshown

using short solid dashed line for Africa and longer dashed line for Antarctica.

Terrane, where the orogenicelt abutshe Kaapvaal

amphibolite facies. They host severalayered mafic-

Province, comprises a narrow, southward dipping thrust belt

ultramafic and interleavedraniticntrusions. ectonic

of low-grade metasediments along its northernextremity,

transport was towards theorth. Thisequence is

and a wider, westward plunging nappe complex farther

considered to beophiolitic n character (Matthews

1972).

south. These nappes consists of a supracrustal suite of basic

Thenorthern marginal zone is succeeded outhwards by

lavas and clastic and chemical sediments metamorphosed at

one in which synformal structures consisting of paragneiss



5/10

1118 P. B . GROENEWALD E T A L .

sequences are separated by augen gneisses. This is followed

toheouth by anrea in which granulite facies

paragneisses,ranites and charnockites predominate.

Thomas (1989) hasargued hat NatalProvincecomprises

three

or

four sectors, consisting of calc-alkaline granitoid

rocks andsubordinate metasedimentary lithologies, which

represent different accreted sequences.

The lithostratigraphy

of

theeastern Mozambiquebelt

comprises a migmatitic gneiss basement and a

volcano-sedimentary cover sequence that includes carbonate

and quartzitic units, all having undergone amphibolite facies

metamorphism (Sacchi et

al.

1984). Much

of

the succession

was interpreteds calc-alkaline volcanic inrigin.

Interlayering

of

mafic, ultramafic and sedimentary protoliths

gives parts of the Mozambique rovince an ophiolitic

character.

A

nappe of granulite facies paragneisses, which

was thrust over the volcano-sedimentary succession, consists

of metamorphic rocks ranging from rhyolitic to ultramafic in

composition.everalraniteswere intrudednto this

sequence.

In eastern Maudheim Province, H.U. Sverdrupfjella and

Kirwanveggen are underlain by ortho- and paragneisses of

the Sverdrupfjella Group(Roots 1953, 1969; Hjelle 1974;

Wolmarans Kent 1982; Grantham

et al.

1988). In H.U.

Sverdrupfjella,orthogneisses predominateadjacent o he

Grunehogna cratonic province. They display layering on a

variety of scales but are generally of rather monotonous,

intermediate composition. These gneisses have calc-alkaline

geochemical characteristics andare nterpreted obe of

volcanic origin. Fartherastre paragneissic meta-

carbonates and pelites interlayered with grey orthogneisses.

These are followed eastwards by paragneisses which are

predominantlyquartzofeldspathic but containwidespread

metapelites, iron-rich amphibolites, uartzitic and semi-

pelitic gneisses. This part of the succession is characterized

by granulite facies mineral assemblages. Rocksn

Kirwanveggen haveeennterpreted asredominantly

volcanic in origin (Wolmarans Kent 1982). Heimefront-

fjella is still relatively unknown,but mphibolite facies

carbonates,para- and orthogneisses have been reported

(Juckes 1972). Pre- and syn-orogenic mafic intrusions,

represented by amphibolite and pyroxene-garnet boudins o r

lenses are also common throughout Maudheim Province.

Several generations

of

syn-tectonic intrusions have been

recognized in the Maudheim Province. Grantham et al.

(1988) described tabular syn-tectonic granitesn H.U.

Sverdrupfjella subprovince. Charnockites are present in the

Kirwanveggen, but the contact relations are ambiguous in

being gradational Wolmarans Kent 1982). Relatively

extensive,oarse-grained, gneissic granitesccurn

HeimefrontfjellaJuckes 1972). Similarly, therere

numerousgranites and charnockites nNatalProvince, in

tabular and batholitic forms of pre-, syn- and late-tectonic

character (Thomas 1989). In MozambiqueProvince, the

c. loo0 Ma granites are domical and migmatitic (Sacchi et al.

1984).

Table

1. Summary and compar i son

of

Kibaran and R oss lPan Afr i can l i thos t ratigraphy and t ec tonotherm al hi s tor i es

Maudheim Province

Mozambiquerovince

Sverdrupfjella/Kirwanveggen

Heimefrontfjella Natal Province

Lithostrat igraphy

Gneiss-migmatite basement. Meta-

sedimentary

meta-volcanic

cover

sequence. Minor carbonates, Fe-

quartzites, greywackes, dominantly

calcalkaline meta-volcanic rocks.

Overthrust granulitemetasedimentary

nappe.

Deformat ion

Intense early folding and thrusting.

Main thrusts to N W in western parts,

to

SE in southern zone. Wide thrust

belts

and

shear zones. Later more

gentle

folding,

possibly accompanied

by thrusting.

Metamorphism

Regional mid-amphibolite facies n

southern

zone

with klippen of gra-

nulites. InNW widespread granulites,

partly retrogressed.

Magmat i sm

Early deformed

and

relatively unde-

formed granites, later with migmatitic

aureoles. Late

porphyritic

granites

are Pan African.

Migmatitic volcano-sedimentary

succession. No

basement-cover

relations. Minor carbonate,

quartzite, greywacke pelites.

Orthogneisses

calcalkaline vol-

canic

rocks Overthrust granulite

sequence

in

the east.

Early coaxial

isoclinal

folding

events

accompanied by thrusting.

Main

thrusts towards N W. Later

open

to close

folding

with

minor

thrusts. Major shear zones (?).

Regional

amphibolite

facies met-

amorphism in west,

granulites

above main thrusts

to

northeast

and in

the south.

Widespread

retrogression

of

granulites.

Suitesof megacrystic, sheeted

highly deformedearly granites

(S-type and calcalkaline?). Char-

nockites

in south. Sheeted

grano-

toid suites

Pan African.

Metamorphosed volcano-

sedimentary sequence.

Basement cover relation

reported.

Metavolcanic

rocks

are

calcalkaline.

Abundant mafic dykes.

Early isoclinalfolding

with

thrust component

to

NE

(Kibaran age). Younger

folding, thrusting toNW

of

Pan African age. Major

shear zone

between

cover

and

basement.

Regional

mid-amphibolite

facies. Granulites in

NW.

Retrogressed and over-

printed

during Pan

African.

Numerous early granite

intrusions.

Metavolcanic-dominated north-

ern

zone, southwards various

metasediments with numerous

intrusive granitoids. Ophiolitic

affinity

of

amphibolites.

Intense

early

thrust and fold

nappe development. Abundant.

evidence for thrusting towards

and NW. Local backthrusts.

No

post-Kibaran

deformation.

Dominantly amphibolite facies in

north, granulite zonen south.

Local

granulites throughout.

No

evidence for post-Kilbaran

retrogression/rehydration.

Abundant graniteand charnock-

ite batholiths and sheets. S-type,

calcalkaline and A-type bodies.



6/10

A N T A R C T I C A - A F R I C A :R O T E R O Z O I C - M E S O Z O I CINKAGE 1 1 1 9

Available geochronological data from the various prov-

inces reveal near contemporaneity of tectonothermal events

(Table

2).

In all the Kibaran provinces considered here, the

marginal basin-volcanic arc successions accumulated before

about200Ma, when metamorphism and deformation

began. The orogeny was particularly prolonged, as revealed

by the presence of granites with ages ranging from 1163 Ma

to 850 Ma.Althoughhesentrusionsange from syn-

orogenic to anorogenic alkaline character, all show evidence

of some metamorphic/deformational history. The ages

may, therefore, represent metamorphic resetting rather than

Table 2. G e o c h r o n o l o g y

of

he Kibaran orogenic provinces ( M S W D

values in brackets if k n own )

Mozambique Province

Basement :Rb-Sr1200 MaR,

=

0.7060 (3 point isochron)

Cover :Rb-Sr950

f

0 Ma R,

=

0.7091

Rb-Sr lo o0 Ma

R,

= 0.7013

Early grani te : Rb-Sr 1100 M u R, = 0.7027

Amphibo1ites :Rb-Sr whole rock 1391 f 8 Ma R,

=

0.707 (0.3)

Granulites : Rb-Sr wh ole rock 1073

f

5Ma

R,

= 0.707 (0.59)

Maudheim Province

Sverdrupj j e l la Group, Kirwanveggen

orth~gneisses(?)~

zirconb-Pbircon U-Pb:

1071

f

4 Ma 90) 112

f

2 Ma (9.5)

1075

f

0Ma (127)1107

f

27 Ma (2 60)

1061f 6 Ma (108 ) 1045

f

93 Ma (548)

Rb-Sr whole rock3 1015f 4 Ma R, = 0.704 (1.04)

1164

f

8 Ma

R, =

0.704 (11.2)

Rb-Sr whole rock-biotite ages 460-485 Ma

Sverdrupj j e l la Group, H .U . Sverdrupfjella

Amphibolite facies orthognei~ses~

Rb-Sr whole rock 1141 f 3 Ma R, = 0.708 (0.4)

Granulite facies paragneisses4

Rb-Sr whole rock 1170

f

6 Ma R, = 0.7040 (0.76)

Syn-orogenic granite4


f

9Ma

R,

= 0.7036 (8.88)

Late syn-orogenic granitoids3


f

7 Ma

R , =

0.708 (1.7)

whole rock-biotite ages4 430-480 Ma

Heimefr~ntfjella~

Volcanism: 1100-1200 Ma

Metamorphism: 1OOO-1100 Ma

Natal

Province

All Rb-Sr whole rock6

Northern marginal area metavolcanic rocks

1240

f

3 Ma

R ,

=

0.704 (2.2)

Northern marginal area, granites

1194f83MaRO=0.7017 0.8); 0 6 7 f 2 0 M a R 0 = 0 . 7 0 6 ( 1 . 7 2 )

examples

of

granites further south

calc-alkalin e 981 f 1 Ma R, = 0.7032 (11.3)

A-type 1089

f

4 Ma

R, =

0.7038 (1.73);

1003 f 9 Ma R,

=

0.7054 (0.75)

transitional 1011 f 9 Ma R , = 0.7063 (2.36)

syn-orogenic metabasite 1024

f

2 Ma

R , =

0.7026 (2.21)

tonalitic basement Nd 7

=

1405 Ma

Data

source

references:

'

Sacchi etal. 1984; *Cahen etal. 1984; 3M oyes Barton1990;

4M oyes Groene wald, unpublished;Weber et

al.

1987;

1065

f

1 Ma

R ,

=

0.707 (0.21)

Eglington et al. 1989.

emplacement, especially as mostwere determined using

Rb-Sr isotopes. Nonetheless, the initial

87Sr/86Sr

atios ( R , )

may be particularly significant. Many

of

the isochrons

(Table 2) have

R ,

values between 0.703 and 0.705 indicative

of a relatively short crustal esidence ime of the source

rocks.

Metamorphic histories were similar in all the 1000 Ma

terrains. In NatalProvince,amphibolite facies conditions

predominatedn theorthern marginal zone with

P >4.5 kbar, T

=

550 600 C and at higher temperature but

lower pressure in the northern zone (Rhodes Leith 1971).

In the southern part

of

Natal conditions of

P

= 4.8-6.8 kbar

at T

=

650-850C persisted hrough much

of

the early

tectonic history (Talbot Grantham 1987). In outhern

Mozambique Province, amphibolite facies rocks predomin-

ate except in klippen consisting

of

granulite facies gneisses

(Sacchi et

al.

1984). Andreoli (1984) documented granulite

facies conditions

of P

= 7-9 kbar, T = 725-800C in

southern Malawi. Maudheim Province also underwent

predominantly high-grade metamorphism.uckes (1972)

found that Heimefrontfjella had undergonelmandine-

amphibolite facies metamorphism, and Weber et

al.

(1987)

identified a granulite facies basement underlying amphibol-

ite facies cover. Wallace (in Wolmarans Kent 1982) has

identified granulite and amphibolite facies assemblages in

Kirwanveggen. Groenewald Hunter (1991) have recog-

nized earlygranulite facies conditions of relatively high

pressure ( P = 8-10 kbar) and temperature T = 800 C),

followed by amphibolite-facies retrogressionand ehydra-

tion ( P = 6 kbar, T = 600C) in the main range of H.U.

Sverdrupfjella. Generally lower grade conditions applied in

the west, closer tohe adjacentGrunehognaratonic

province, where epidote-amphibolite facies conditions were

never exceeded.

The deformational histories of the reas were also

similar (Table1).Structuralevolution in the Mozambique

Province, as documented by Sacchi

et

al.

(1984), was

dominated by thrust-nappe tectonics at c. 1000Ma which

produced strongly linear frontal ramps and imbricate stacks

in areas of morentenseeformation.lsewhere,

recumbent folds are typical. The thrust system had a root

zone in southern Malawi, from which tectonic transport was

towards theSE. Outside his hrustsystem,NW-trending

folds predating the thrusting were superimposed on earlier

structures. In the southeast , widespread gentle deformation

with a WNW trend may represent a late tage of the

thrusting event. This folding is more intense locally where it

gave rise to new foliation.Kibaran tectonics inAfrica,

described in general terms by Daly (1986a, b 1988) and

Shackleton (1986), involved considerable crustal shortening

through NW- and SE-directed hrusting.This divergence

was related to a postulated regional pop-up ooted in a

mid-crustal shearor decoupling one. The NW-verging

structures are considered to represent the main thrust

system whereas those tohe SE are thought to be

backthrusts (Daly 19866).

A similar orogenic history haseen identified in

Maudheim Province. The granulite facies paragneisses in

H.U.' Sverdrupfjellawere eformed by almost co-axial

isoclinal folding events and ater thrustover the adjacent

amphibolite facies succession (Groenewald

Hunter 1991).

The sense of movement on thrustlanes, which are

subparallel to the general SE to E dip of layering, is towards

the northwest. The transgression of thrust planes across the



7/10

1120 P. B . G R O E N E W A L D E T A L .

tectonic foliation indicates that the thrusting postdated much

of the folding. Open to close folding superimposed on the

earlier structures makes interpretation difficult. In Heimefr-

ontfjella older folds trend NW with N E vergence, nd

younger folds trend NE and verge NW Spaeth Fielitz

1987). An older granulite facies basement is separated from

the amphibolite terrain by a major hear zone.Several

flat-lying thrust faults are present in NE Heimefrontfjella.

The Natal orogenic province also underwent thrust and

nappe-dominatedectonism. The orthern arts

of

this

terrain are inferred to be obducted ophiolites in a series of

N-verging thrust nappes (Matthews 1981). The central part

is characterized by upright ynformal structures, whereas

thrust faulting and isoclinal folding occurred in thesouth

(Thomas 1989).

Summary of the

10o0

Mu provinces

The hree provinces describedabove appear o constitute

parts of a single, extensive orogenic province on the basis of

similarities in lithology, tectonic style (Table

1)

and age

(Table 2). Thrust faulting in Natal Province and Dronning

Maud Land involved tectonic transport towards the cratons,

whereas that in the Mozambique Province was bi-directional.

Thrusting in Mozambique and.U. Sverdrupfjella

emplaced granulite-facies successions aboveamphibolites.

The lithologies in all three provinces are interpreted tohave

been volcanic and sedimentary deposits typical of marginal

basins, with aense of polarity in that metavolcanics

predominate close to, nd metasediments further away

from, theadjacent cratonic areas. Geochronological data

suggest contemporaneity.Metamorphism shows the same

general pattern of initial granulite and amphibolite facies,

followed by amphibolite facies retrogression.irect

correlation of lithostratigraphicunits is not possible, and

variations in level of exposure may account for some

of

the

major differences. If the nterpretation

of

the lithological

sequences as marginal basin-volcanic arc deposits is correct,

the Kibaran orogeny was one of accretion of newly formed

crust onto an older continental nucleus.

It is therefore suggested thathe Kibaran Province

encompassessub-provinces neast Africa, Antarctica and

southAfrica, and was thus

of

considerable extent.t

represents major accretion at a relatively early stage in the

construction of Gondwana.Groenewald Hunter (1991)

reported the

P-T-t

path

of

H.U. Sverdrupfjella and argued

that the metamorphism was related to pla te collision. The

generally low PIT conditions, which applied in Natal, may

be at variance with collision orogeny, and Tankard et

al

(1982) argued for an ensialic rather than ensimatic marginal

basin,although more hanone accretionarysegment was

recognized by Thomas (1989). Isotopicvidence that

supports accretion

of

juvenile sialic crust was presented by

Eglington et

al.

(1989). The ophiolitesnNatal and

Mozambique Provinces are also evidence that accretion

occurred through collision of segments

of

continental crust

that were once separated by oceanic crust.

Pan African and

Row

orogenic events

A widespread tectonothermal event affected Gondwana in

the period 600-450Ma, resulting in several fold belts. The

Gariep,Damara nd Saldanian rogenic rovinces and

pervasive thermaloverprinting

of

larger racts

of

Africa

(Fig.

1

are ascribed to he PanAfricanevent, whilst the

extensive tectonothermal province in Antarctica is termed

the Ross Orogeny. In SE Africa evidence for tectonother-

mal overprinting is restricted to the Mozambique Province

where Sacchi

et

al. (1984) recognized that gentle refolding

was related to the emplacement of

500

Ma granites. Despite

the limited new fabrics and etrogression associated with

this event, widespread resetting

of

isotope systems occurred,

particularly Rb-Sr andK-Ar, which resultedn the

Mozambique Province being considered as entirely

of

Pan

African age in somearly publications (for example

Bloomfield 1981).

Orogenesis also occurred in the Maudheim Province at

this time. Many of the granitic intrusions in H.U.

Sverdrupfjella weremplaceduring D3, which was

characterized by open to close folding and minor reverse or

thrust faulting. These granites form subhorizontal to

subvertical tabular bodies highly variable in thickness and

associated with NW-directed thrust faulting. The Brattskar-

vet alkalic granitoidbody, the largest of these intrusions

(100km), has yielded a well constrained whole rock Rb-Sr

age of 519 17 Ma (MSWD = 1.7,

R,,

= 0.708) (Moyes

Barton 1990). Otherate granites,haracterized by

tourmaline or magnetite phenocrysts, are considered to be

younger because theyut monzonitic dykes of the

Brattskarvet uite. The atterpredates a poorly defined

tectonic foliation in which biotite crystallized. This biotite,

in conjunction with whole-rock data, has provided Rb-Sr

ages of 460-490 Ma in the Brattskarvet intrusion (Moyes

Groenewald, unpublished data), similar to biotite blocking

temperature ages of 475 Ma from Kirwanveggen (Elworthy,

in

Wolmarans Kent 1982). Most of the K-Ar age

determinations by Russian workers in the 1960s ranged from

400-500Ma throughout the region (Ravich Solovev

1966), suggesting that the thermal effect

of

this orogeny was

pervasive isotopic resetting, perhaps through retrogressive

rehydration.

In Heimefrontfjella,a rnafic dykedisturbed by one of

the thrust faults provided an age of 450 Ma (Juckes 1972).

Spaeth Fielitz (1987) and Weber et al. (1987) recognized

folding younger than the main 1000Ma deformation. These

folds, which trend NW and verge NE, are associated with

thrust faulting. Extensive etrogression ccompanied this

deformation. Weber et al. (1987) interpreted these events to

be of Pan African age. The vast extent

of

this thermal event

in Antarctica is revealed by the occurrence

of

gneisses

of

this age in the Shackleton Range, at he western limit of

Dronning Maud Land, and in the S c Rondane, to the east

(Fig. 1 as described by Rex (1972) and Picciotto et al

(1964), respectively, and the considerable extent of the Ross

Orogeny outlined by Craddock (1972). In the case of

S0r

Rondane, 1OOOMa ages havebeen suggested recently by

Shiraishi Kagami (1989), which reveal difficulties similar

to those experienced in earlier dating

of

the Mozambique

and Maudheim Provinces.

There is no evidence that the Pan African orogeny had

any effect on Natal Province as isotopic data reveal no ages

younger than 850 Ma. Nor is there any published evidence

foreformation

or

retrogression post-dating the main

orogeny, which was entirelyKibaran in age. Theres,

however, an orogenic province

of

Pan African age in the

southernmost part of Africa, termed the Saldanian, in which

thrust aulting, ntense folding and granite mplacement

have beenocumented (see Tankard et al. 1982, for



8/10

ANTARCTICA-AFRICA:ROTEROZOIC-MESOZOICINKAGE

1121

references). It would therefore seem likely that he Pan

African swathe of tectonism passed from the Mozambique

Province through the MaudheimProvince, thenextended

southwest, but it did not reach westwards into Natal

Province.

Phanerozoic-Palaeozoic deposition, volcanism and

tectonism

Majorntracratonicepositional basins developed in

Gondwana after the Ross/Pan African orogeny. The Karoo

Sequence of southern Africa (Fig. 1 is of particular interest

because its accumulation spanned the critical period during

which initial stages of rifting began.Tectonic adjustments

which heralded the main phase of continental fragmentation

influenced depositional patterns hroughout he develop-

ment of theKaroo basin. These tectonic ontrols also

applied to the succeeding Karoo volcanism which has been

related, in theLebomboarea, o a failed triple unction

(Burke Dewey 1973). These volcanic rocks erupted

between 200-175 Ma (Erlank 1984) andare significantly

older than the earliest marine geophysical anomaly used in

the econstruction

of

Gondwana by Martin Hartnady

(1986).

The KarooSequence of centraland outhern Africa

represents a Carboniferous to Triassic sedimentary succes-

sion capped by late Triassic to Jurassic flood basalts

(Tankard et al. 1982; Dingle

et

al. 1983; Erlank 1984).

Karoo sedimentation proceeded after accumulation of the

Cape Sequence and, in the main basin in southern Africa,

was influenced by deformation in the Cape fold belt (Rust

1975). Termination

of

activity in the fold belt was followed

closely by eruption

of

theKaroo basalts, anvent

considered to be closely relatedohereak-up of

Gondwana (Cox 1970; Eales et al. 1984).

The stratigraphy

of

Karoo sediments in southern Africa

will be described in terms

of

lower and upper subdivisions

for the purposes

of

this paper (using Tankard et al. 1982

and references cited therein as sources). The lower sequence

has a basal succession

of

tillites, diamictites and associated

sediments which reaches its maximum thickness

of

750 m in

the southwestern Karoo basin, but which is absent n the

extreme northeast. This succession is overlain by lower

Permian basinal mudstonesdeposited in a large, possibly

marine, body of water. In the ortheast art of the

depository alluvial sandstones are present at this strat-

igraphic level and hostoaleposits. Overlying the

mudstones and sandstones is asequence of upward-fining

fluviatile cycles which may once have exceeded 5000111 in

thickness in the outhernKaroo basin,but which thins

considerably towards the northeast.

The upper Karoo sedimentary succession commences

with a middle to upper Triassic coarse sediment wedge, up

to 500m thick in the south-central part of the basin, which

is overlain by laterally persistent red mudstone up to 490 m

thick. Thisas low sandstone/mudstoneatios, lacks

carbonaceous shales, and marked the onset

of

aridity which

culminated in deposition of sandstones under aeolian

conditions during the upper Triassic. Although the aeolian

sandstones attain maximum thickness in the southwestern

Karoo basin, they do not become thinner to the northeast s

is characteristic of the other units. In contrast , they occupy a

NE-trending trough within which there are a variety of local

thickness variations. Outside the trough, an approximately

constant thickness of 150 m is present throughout almost the

entire region affected by Karoo sedimentation, making this

the most widely developed sedimentary unit of the Karoo

Sequence.

Deposition

of

theKaroo Sequenceoccurrednwo

broadly different tectonic settings (Rust 1975). South of the

Limpopo River, a marginal cratonic shelf to miogeosynclinal

trough environmentxisted,hereas toheorth

sedimentationook place in separate, fault-controlled

troughs. Although complicated by fault control which led to

considerable thickness variation and intra-strata1 unconfor-

mities, the stratigraphicsequences in the two terrains are

very similar. In the northeast there s, however, evidence for

a long-lived palaeo-high where the late Karoovolcanic rocks

rest directly upon basement. This is the Nuanetsi Igneous

Province, situated in the Limpopo region (Fig. 1). Nearby,

in the Lebombo region, there is a hin veneer

of

aeolian

arenitesbetween the basement and he volcanic rocks,a

feature particularly relevant in the presentontext of

correlatingetween theKaroo Sequence and Permian

sedimentary rocks of Maudheim Province. In Heimefrontj-

fella, the thin (


9/10

1122

P . B . G R O E N E W A L D E T A L .

probably situated between Grunehogna Province and he

Kirwanveggen, but is not yet sufficiently well-constrained to

contribute precision to the Gondwana reconstruction.

Discussion

The reconstruction and geological parallelism of these parts

of Gondwana have implications for an understanding

of

its

crustal evolution from Mid-Proterozoic until Mesozoic time.

Much

of

the supercontinent, in particular the parts adjacent

to

SE

Africa, was almost certainly complete 1000Ma ago.

Subsequently, about hree Wilson cycles occurred n the

northernhemisphere,but he evidence from this part of

Gondwana indicatesredominantly ensialic orogenesis.

Repeated accretion of continentalrustragments and

intervening volcanic arc-marginal basin complexes onto

Africa requiresvaluations viable mechanism for

assembly, oronstruction, of the supercontinent.

continuous record of geological evolution after Gondwana

assembly provides insights into hebreakup mechanism.

This may have broader implications for the current cycle

of

plate tectonic activity from which almost all understanding

of the hypothesis stems.

Similarities between therunehogna supracrustal

succession andhat of the Kaapvaalrovince suggest

continuity between theseerrainsuringhe mid-

Proterozoic. This continuity could possibly have existed as

early as the Archaean if the Annandagstoppane granite is

equivalent to granites of the Swaziland region.his

correlation should perhaps be approached with caution, but

the proposedid-Proterozoicuxtaposition

of

these

terrains requireshat it be considered. If these crustal

segments were originally separate and only juxtaposed after

deposition of the Soutspanberg and Ritscherflya Super-

groups, then a sutureone of some kindhould be

recognizable. There is no direct evidence that such a zone

exists in theeastern Kaapvaalprovince,although Stettler

et al.

(1989) haveeconized variety of very early

discontinuities in the patterns defined by magnetic trends in

KaapvaalProvince. Thereason why the line ollowed by

subsequent breakup passed through this crustal fragment of

considerable longevity requires further investigation.

The similarities between the provinces of Kibaran age

have been detailed above. Clearly, their correlation would

provide evidence for one of the largest orogenic provinces

onarth, extendingouthward from Kenya through

Mozambique intoAntarctica, hen back into Africa in a

westerly direction, and across southern Africa intoSouth

America.

Of

significance in thisproposed correlation

is

evidence thatatere-breakup tectonics modified the

original construction, leading to non-linear fracturing across

the Gondwanaupercontinent and complicating the

present-day reassembly. Furthermore , the Muhlig Hofmann

mountains,extendingeastwards from heH.U. Sverdrup-

fjella tohebrondanerea (Fig. l) , have

lithostratigraphy, metamorphic history and age closely

similar to hose

of

the Maudheim Province (Ravich

Solov'ev 1966; Asami

et d .

1989; Shiraishi Kagami 1989),

which suggests an even greaterextent or thisorogenic

province. Kibaran orogenesis is also known in Madagascar

(Cahen et al. 1984), andBerhe (1990) argued hat he

Mozambique rovince and Arabian-Nubian Shield may

have been contiguous.

On a regional scale, the tectonic history

of

the Karoo

basin reflects jostling of crustal segments prior to and during

the break-up of Gondwana as different crustal blocks were

subjected to the vast stress field associated with this event.

Karooedimentation and magmatism in the Limpopo

region were ontrolled by faults which were, in part,

reactivated structures of Archaeanand earlyProterozoic

age. Flores (1970) recognized a transcurrent component to

some of these faults which suggests that they may have been

related toreak-upnd excision of theGrunehogna

segment from Kaapvaal Province.

Much of theAntarcticdatareported here were acquiredduring

work on the South African National Antarctic Research Program,

supportedby

the

Department

of

EnvironmentAffairs, owhom

P.B.G. and G.H.G. are grateful for sponsorship. D . Hunter s

thanked for his

help

andguidance.Wegratefully cknowledge

constructive analysis

of

the manuscript by

A.

B . Moyes and T.

S

Brewer.

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