Precambrian Research

Precambrian Research 75 ( 1995) 23 I-250

East Antarctic crustal evolution: geological constraints and modelling in western Dronning Maud Land

P.B. Groenewald”, A.B. Moyesb, G.H. Granthamc, J.R. Krynauw’ “Depwttnent of Ceolo~y, Universiry @‘Natal, Private Bag X01, Scottsville 3209, South Africu

“Bernard Price Institute, University ofthe Witwatersrand. Johannesburg, South Africa

“Department of Geology, University of Pretoria, Pretoria, South Africa

Received 28 January 1994; revised version accepted 20 August 1994

Abstract

Two geological provinces of western Dronning Maud Land provide constraints which allow preliminary modelling of crustal

evolution in this part of East Antarctica. The Grunehogna province comprises a 3000 Ma granitic basement overlain by a 1000 Ma sequence of sedimentary and volcanic rocks which accumulated in a foreland basin. Juxtaposed with this cratonic province is the Mesoproterozoic Maud erogenic belt. The H.U. Sverdrupfjella portion of this belt consists of two lithostratigraphic assemblages: (i) adjacent to the suture are amphibolite facies talc-alkaline metavolcanic rocks suggesting a volcanic arc environment; (ii) further to the east and southeast are granulite facies para- and ortho-gneisses compatible with a retro-arc marginal basin heritage. Both assemblages were intruded by Proterozoic and lower Phanerozoic granitoids and provide evidence of two distinct major events in the erogenic history. In the eastern assemblage, the first event (1200-900 Ma) involved metamorphism with initial high pressures ( 12-15 kbar, 750°C) followed by decompression and thermal relaxation (8 kbar, 85O”C), a path attributed to continental collision with deep burial of a marginal basin characterised by an elevated geotherm. The second event ( - 500 Ma), also under medium- to high-grade metamorphic conditions ( - 6OO”C, 5-6 kbar), caused tectonic inversion of the metamorphic profile by thrusting followed by rapid uplift and exhumation. Tectonothermal overprinting of the Maud Belt and folding of the 1000 Ma supracrustal sequence near boundaries between the cratonic and erogenic terrains suggest that a Cambrian-Ordovician suture is close to (within?) the 1000 Ma belt. Geological correlation of the two Antarctic provinces with those in southeastern Africa identifies this area as a portion of the Kalahari Craton detached during Gondwana break-up. Similar overprinting of the Proterozoic belts in Africa, such as the Mozambique belt, suggests that these zones of crustal disequilibrium were the loci of repeated continental break-up and convergence.

1. Introduction

The sparse outcrops of East Antarctica have revealed that this enormous Precambrian shield comprises sev- eral Archaean cratons surrounded by Proterozoic and younger erogenic belts. Although the understanding of crustal evolution in this shield is developing sporadi- cally and in local areas as a result of logistical difficul- ties, progressively more detailed work is proving that

the geological history is complex because several stages of crustal reworking occurred in many areas. An example of this complexity is provided by the juxta- posed Grunehogna Craton and Maud Belt in western Dronning Maud Land (Fig. 1) , for which the recent work synthesized here provides some insight and con- straints on crustal evolution.

The first geological work in this region (Roots, 1953) identified the major division stemming from the

030 l-9268/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved

.SsO/O301-9268(95)00032-l

500

km

I I

GR

UN

EH

OG

NA

\

\ Lt

ilrow

-Hel

m

‘\ > “’

D

ron

nin

g

I

AF

RIC

A

+ f

i+

+ +

+

Mau

d

L

a

Bel

gic

afje

lla

0

nd

LO

CA

LIT

IES

/

A

An

nan

dag

sto

pp

ane;

B

A

hlm

ann

ryg

gen

; S

S

trau

msn

uta

ne;

U

U

rfje

lla;

JP

Jutu

lstr

aum

en-P

enck

sijk

ket

GE

OC

HR

ON

OL

OG

Y

SY

MB

OL

S

$#

Arc

hae

an

fi

Mes

op

rote

rozo

ic

* N

eop

rote

rozo

ic-C

amb

rian

LE

GE

ND

F

OR

b

. (in

set)

450~

550M

a er

og

enic

b

elts

900-

I 20

0Ma

ero

gen

ic

bel

ts

I+‘il

Cra

ton

b

efo

re

1 O

OO

Ma

Fig

. I.

(a)

Map

of

wes

tern

D

ronn

ing

Mau

d La

nd,

End

erby

La

nd

and

Mac

R

ober

tson

La

nd

part

s of

th

e E

ast

Ant

arct

ic

Shi

eld

show

ing

the

loca

litie

s re

ferr

ed

to i

n th

e te

xt.

The

ag

es

indi

cate

d by

sym

bols

fo

r ea

ch

loca

lity

are

liste

d in

Tin

gey

( 19

91).

w

ho

prov

ided

al

l re

leva

nt

refe

renc

es.

(b)

The

in

set

is a

sch

emat

ic

map

of

the

maj

or

geol

ogic

al

prov

ince

s in

a

Gon

dwan

a re

asse

mbl

y w

hich

br

ings

w

este

rn

Dro

nnin

g M

aud

Land

in

to j

uxta

posi

tion

with

so

uthe

aste

rn

Afr

ica

P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250 233

different tectonothermal histories of two areas. A cen- tral area of low-grade, flat-lying, sedimentary and vol- canic rocks was found to be adjacent to a belt of predominantly high-grade metamorphic rocks (Roots, 1969). Reconnaissance mapping of Dronning Maud Land by geologists from the former USSR provided further information about the regional distribution and relative ages of the rock types (Ravich and Solov’ev, 1966). South African and German work led to further understanding of the petrogenetic and geochronologi- cal evolution of the rock sequences (Wolmarans and Kent, 1982; Grantham et al., 1988; Moyes and Barton,

1990; Arndt et al., 1991) and separation of the Archaean to Mesoproterozoic Grunehogna Craton from the Mesoproterozoic to Phanerozoic Maud oro- genie belt (Groenewald et al., 1991; Jacobs, 1991;

Jacobs et al., 1993). Clarification of the terminology used in this paper is

thought necessary because of the variety of names used in previous publications. The area of low-grade Meso- proterozoic supracrustals and Archaean granites was recognised as cratonic by Wolmarans and Kent ( 1982) and interpreted as a possibly detached portion of the Kalahari Craton. Krynauw et al. ( 1987) referred to the area as the Grunehogna Province. Although the term ‘Maudheim platform’ was used by Ravich and Solo- v’ev ( 1966) for the supracrustals of Dronning Maud Land, the subsequent publications (cited above) intro- duced other names and this application of ‘Maudheim’ may be redundant. For example, Groenewald et al. ( 199 1) combined the metamorphic complexes adja- cent to the Grunehogna Craton as the ‘Maudheim Prov- ince’. Therefore, the erogenic terrain comprising the H.U. Sverdrupfjella, Kirwanveggen and Heimefro- ntfjella areas (Fig. 1) is here termed the Maud Belt.

The Maud Belt was principally the product of the first of two major erogenic periods in western Dronning Maud Land. This involved high-grade metamorphism, recumbent folding and thrusting of a supracrustal suc- cession during the accretion of relatively juvenile crust on to the Grunehogna Craton in the period 120@-900 Ma (Grantham et al., 1988; Moyes et al., 1993a). Tec- tonothermal events occurred synchronously with this in much of East Antarctica, in particular over the tract extending eastward from Heimefrontfjella through the Gjelsvikfjella (Ohta et al., 1990; Moyes, 1993), the Sor Rondane (Shiraishi and Kagami, 1992), Ltitzow- Holm Bay (Yoshida et al., 1983)) the Rayner complex

of Enderby Land (Sheraton et al., 1987) to Prydz Bay (Tingey, 1991). The extent and continuity of Meso- proterozoic erogenic belts on all the continents reflects an epoch of continental collision represented by the Kibara, Irumide, Namaqua-Natal and Lurio belts of Africa, the Grenvillean of North America, the Svecon- orwegian of Europe, the Rodinia-Sunsas of South

America and the Albany-Fraser in Australia. Linking of these belts allowed definition of the Neoproterozoic supercontinent, Rodinia (Hoffman, 199 1). The term ‘Grenvillean’ for the belts of this age is widely used as it is the most thoroughly investigated of these oroge-

nies, although ‘Kibaran’ as applied widely in Africa (e.g. Thomas, 1988) has also been used in Antarctica (Jacobs et al., 1993). In order to introduce a clear, concise and independent term for the Mesoproterozoic tectonothermal event in western Dronning Maud Land, the name ‘Maud Orogeny’ is used here.

Cambrian- to Ordovician-age tectonic overprinting in the region is now recognised as being of greater intensity and importance than was previously realised (Groenewald, 1991; Shiraishi et al., 1992; Dirks et al., 1993). Dirks et al. ( 1993) recognised this in the Prydz Bay region and used the term ‘Pan-African’, whereas Moyes et al. ( 1993b) viewed the ‘Ross event’ in west- ern Dronning Maud Land as predominantly thermal in

character. In view of the numerous tectonothermal events ranging in age from 400 Ma to 800 Ma for which these names have been used, the 550-450 Ma over- printing in East Antarctica will be termed the ‘500 Ma event’ in this paper.

2. The Grunehogna Craton

2.1. Lithostratigraphy

The Grunehogna Craton (Fig. 1) comprises Archaean basement granites and the Mesoproterozoic Ritschertlya Supergroup. Exposure of the basement is limited to three small outcrops at Annandagstoppane, a group of nunataks at the western extremity of the province. The Archaean age of the Annandagstoppane granite was first suggested by Halpern (1970) who determined a model Rb-Sr whole-rock age of approx- imately 2960 Ma (“Rb decay constant 1.42 X lo-” a-‘). Barton et al. ( 1987) reported a whole-rock Rb- Sr date of 2823 f 100 Ma and Rb-Sr model ages of six

234 P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250

Annandagstoppane AHLMANNRYGGEN

1 JUTULSTRAUMEN

. . . . . . Y”f ’ ?_,....................

c-_. .-t..

+ + + + + + + + + +- + + -7. . . . . . .

++++++++++++++ +++++++++++++

++++++++++++++ +++++++++++++

+++++++++++++++++++ +++++++++t ++++++++

25 km 1 I

1

W E

k Thrust system inferred from field ‘, f Normal fault inferred from geological

relations and geophysical data \? ., and geophysical data

Ice cover /base from radio-echo sounding]

Maud erogenic belt Sverdrup#ella Group

Jutulstraumen Group sedimenrary/volcanoganic Ritscherflya

El

Ahlmannryggen Group Supergroup Archaean basement regressive sedimentary ssguence

+ Annadagstoppane granites

Fig. 2. A schematic cross-section of the Grunehogna Craton, from Annandagstoppane in the west to the H.U. Sverdrupfjellaportion of the Maud

Belt in the east. Radio-echo sounding dataare from Wolmarans ( 1982) and aeromagnetic interpretation from B. Comer (pers. commun., 1993).

Modified after Krynauw et al. ( 1991).

muscovite separates ranging from 3048 to 2828 Ma. Barton et al. ( 1987) also derived a secondary error-

chron of 2945’:: Ma (2a) from 207Pb/204Pb and

2”7Pb/204Pb data.

The Ritscherflya Supergroup, which extends across all exposures in the Grunehogna province (Figs. 1,2),

consists of the sedimentary Ahlmannryggen and sedi-

mentary-volcanogenic Jutulstraumen groups (Wol- marans and Kent, 1982). The voluminous mafic Borgmassivet sills which were emplaced into the

sequence before the completion of diagenesis were found to be consanguineous with the volcanics of the

Jutulstraumen Group on geochemical grounds (Kry- nauw et al., 1988, 1991). Although the basal and upper- most contacts of the Ritscherllya Supergroup have not been identified, Wolmarans and Kent ( 1982) assumed it to be underlain by Archaean granites or granite-

greenstones and interpreted emplacement of the vol-

canic rocks as the final stage of accumulation.

The Ahlmannryggen Group represents a regressive depositional cycle from marine to braided river envi- ronments (Ferreira, 1988). The lowermost grey-

wackes, interlayered with subordinate arenites and siltstones, represent deposition in a marine bay. The

overlying sequences of alternating arenites, siltstones

and mudstones have intraformational (clay pebble) conglomerates and sedimentary structures which sug-

gest a tidal flat environment. At a similar stratigraphic level are conglomerates, greywackes and argillites

interpreted as the deposits of environments ranging from braided to meandering river systems. Both of

these sedimentary rock sequences are conformably overlain by an extra- and intra-formational conglom-

crate-uartz wacke-shale sequence representing dep-

P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250 235

osition in a low-sinuosity braided stream complex. Palaeocurrent directions suggest that the provenance terrains lay to the southwest. Roots (1969) remarked on the likelihood that the provenance was little weath- ered and rapidly eroded because of the immature nature of many of the sedimentary rocks.

The Jutulstraumen Group consists of a sequence of basaltic to andesitic lava flows with minor intercalated volcaniclastic and sihcic beds (Watters et al., 1991). Although lava flows were emplaced in a dominantly subaerial environment, the presence of some bodies of water is reflected by the local presence of pillow lava, hyaloclastite beds and tuffaceous sedimentary layers which have ripple marks and desiccation structures. In the eastern Ahlmannryggen (Fig. 2)) the group consists of a sequence of sedimentary breccia deposits and tuff, overlain conformably by another consisting of arenites interbedded with agglomerate and tuff. Watters et al.

( 1991) considered these two sequences to be alluvial fan deposits associated with active fault scarps.

The extensive and widespread Borgmassivet intru- sions form most of the outcrops in northern parts of Grunehogna province. The sills are up to 400 m thick and the range in composition includes Iherzolite, pyrox-

enite, norite, gabbro and quartz monzodiorite. Although generally conformable with the enclosing

sedimentary rocks, the sills are locally discordant. At Grunehogna, the sedimentary rocks adjacent to a cross- cutting sill were deformed into disharmonic folds 15 m in amplitude during emplacement, and a 3 m thick zone along the intrusive contact is characterised by numer- ous vugs and partial destruction of the sedimentary structures. Small ( <3 m3) granitic segregations are present and the sedimentary rocks reveal the small- scale anatectic production of granitic melt in thin-sec- tion. This zone was interpreted by Krynauw et al. ( 1988) as evidence of intrusion into wet, partially lith- ified sediments at very shallow levels, suggesting that the sill should be close in age to the sedimentary rocks.

The geochemistry of the mafic sills and lavas has been studied in detail ( Krynauw et al., 1991; Watters et al., 1991; Peters et al., 1991). AIM, Jensen cation and Y /Nb diagrams indicate that the rocks are tholei- ites, with minor talc-alkaline characteristics. The chon- drite-normalised REE diagrams and spidergrams for the lavas and gabbros have identical patterns and over- lap extensively, a geochemical coherence which sug- gests that the intrusions and lavas were magmatically

consanguineous. Krynauw et al. ( 1991) found that the patterns resemble those of continental tholeiites such as lavas from the Karoo (Marsh and Eales, 1984) and Kirkpatrick basalts from Victoria Land (Kyle et al., 1983). Although the data of Peters et al. ( 1991) yield La/I% ratios of 3.3u.l and suggest that a thoieiitic island arc setting cannot be excluded, the data of Kry- nauw et al. ( 1991) and Watters et al. (1991) provide values of 1.4-2.9 which support the inferred continen- tal setting.

2.2. The age of the Ritscherjlya Supergroup

Geochronological constraints on the Ritscherflya Supergroup have been diverse and contradictory. Rav- ich and Solov’ev ( 1966) reported algae (Rifenites) and spores in the area identical to those in Late Precam- brian sedimentary rocks of the Russian Platform, an interpretation supported by K-Ar isotope ages of 1050 and 860 Ma determined on siltstones. Eastin et al. (1970) analysed eight lavas for Rb-Sr isotope ratios which provided an isochron of 821+ 58 Ma, and Bow- man ( 197 1) derived a Rb-Sr model age of 1169 + 35 Ma from andesites. The intrusions provided a consid- erable range of ages in the Rb-Sr system (954-1798 Ma, Wolmarans and Kent, 1982; Moyes and Barton, 1990), which led to confusion about the age of the sediments intruded by these sills. Continued research using Sm-Nd and Rb-Sr systematics has led to provi- sional conclusions that the sediments are - 1080 Ma in age and the mafic magmatism occurred in the period 800-1000 Ma, all older ages being attributed to isotopic pseudo-isochrons caused by crustal contamination (Moyes et al., 1995).

2.3. The structure of the Ritscherjiya Supergroup

The Pencksokket-Jutulstraumen glaciers occupy a major physiographic divide between the Grunehogna

Craton and the high-grade metamorphic rocks of the H.U. Sverdrupfjella and Kirwanveggen terrains (Fig. 2). Mapping of the Maud Belt has suggested that this boundary represents original major thrusting in a con- tinental collision setting, possibly with multiple sub- sequent reactivations (Grantham et al., 1988; Grantham and Hunter, 1991). Previous authors (Wol- marans and Kent, 1982; Decleir and Van Autenboer, 1982) considered the boundary to be the site of major

236 P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250

rifting on the basis of gravity and magnetic anomalies and the presence of alkaline complexes along its mar- gins. This older idea cannot be rejected and it is likely that rifting was superimposed on the older thrust zones during the break-up of eastern Gondwana (Grantham

and Hunter, 1991). The Ritscherflya Supergroup is weakly deformed and the strata generally dip between 2” and 1O”NE or SE. However, a ‘pronounced mono-

clinal downwarp to the east’ occurs in the vicinity of the boundary with the Maud Belt, with strata dipping up to 50”SE in eastern parts of the craton (Neethling, 1970). In the southeastern parts, large open synclines

with limbs dipping at up to 30” trend towards the north- east and east-northeast. Watters ( 1972; pers. commun., 1984) noted folding of volcanic rocks in the northeast of the craton, with the intensity of deformation increas- ing from west to east. Steep shear zones parallel to the Jutulstraumen in the eastern nunataks of this area pro- vided K-Ar isotopic ages of 522 f 11 and 526 f 11 Ma (muscovite concentrates, Peters et al., 1989). The ori- entation of the folds and shear zones, and their occur- rence along the eastern margin of the Grunehogna Craton, suggests a relation to the PencksGkket-Jutul- straumen boundary-line.

3. The Maud Belt

The Maud Belt comprises three geographical areas, the H.U. Sverdrupfjella, Kirwanveggen and Heimefro- ntfjella, which abut on the eastern, southern and south- western boundaries (respectively) of the Grunehogna Craton (Fig. 1). All three areas consist of intensely deformed granulite and amphibolite facies gneisses for which the older isotope ages range from 1200 to 900 Ma. The isotopic characteristics (initial ratios, model ages) suggest that the precursors of the gneisses were relatively young at the time when they underwent high- grade metamorphism.

The H.U. Sverdrupfjella terrain has been studied in the greatest detail and provides representative infor- mation about the Maud province. Gneisses of this area, the Sverdupfjella Group of Hjelle (1974), consist of an amphibolite facies rock assemblage in the west, and partially retrogressed granulites in the east (see Gran- tham et al., 1995). There is also a structural difference in that the main eastern outcrops (Fig. 3) are charac- terised by an east- to southeast-dipping series of thrusts

sub-parallel to the general layering and foliation, whereas the west is complexly folded in a variety of orientations. The northwestward transport on the south- east-dipping thrusts suggests that the high-grade rocks in the east have been thrust over the lower-grade rocks

to the west.

3. I. Lithostratigraphy and protoliths

The protoliths of gneisses in metamorphic terrains

provide important constraints on the tectonic settings in which they evolved. In the Maud Belt, only the gneisses of the Sverdrupfjella Group have been inves- tigated in detail thus far, although work is in progress in the other areas.

Hornblende biotite gneisses of intermediate com- position, the predominant rock types along the western margin of the area (Fig. 3)) were ascribed to the Jutul- r&a Formation by Hjelle ( 1974) and Grantham et al. ( 1988). These gneisses are regularly and conformably layered in compositionally homogeneous units 1 to 50 m in thickness, which supports interpretation as orthog-

neisses of volcanic rather than intrusive origin. The layering is inferred to be primary because blastopor- phyritic plagioclase and autolithic enclaves have sur- vived the deformation, proof that transpositioning was not pervasive. The volcanic origin inferred from this field evidence is supported by the geochemistry of these rocks. The ranges in SiOZ (53-73%) and NazO + K,O (5-7%) are typical of basaltic andesites, andesites and dacites on the classification diagrams of Cox et al. ( 1979)) and a distinctly talc-alkaline trend is evident on the AFM diagram (Fig. 4). On CaO/ (Na,O + K,O) and K,O vs SiO, diagrams the bulk of the samples plot in the fields of normal talc-alkaline andesites (Fig. 5a) of the high-K series (Fig. 5b). In addition, the REE patterns (Fig. 6) of these gneisses are similar to those typical of high-K erogenic andesites reported by Gill ( 1981). These data thus support the interpretation of these gneisses as being derived from a talc-alkaline volcanic arc sequence. The distribution of the data on the AIM diagram (Fig. 4) close to the trends of arcs of intermediate maturity (after Brown, 1982) suggests that this volcanic arc developed on or near a continental margin where subduction continued for a lengthy period.

Although no geochemical studies have been pub- lished, metavolcanic protoliths have also been inferred

P. B. Gmenewuld et al. / Precumbrian Research 75 (1995) 231-250 231

72”s

Jutulrbra

72”30’5

IbE

SYENITE OF JURASSIC AGE

BRATTSKARVET INTRUSIVE SUITE 72”s

SVEABREEN GNEISSIC GRANITES

ROOTSHORGA PARAGNEISS

FUGLEFJELLET METACARBONATES

JUTULRdRA METAVOLCANICS

Kvitskarvet

D Outcrop

/ Thrust fault

// Normal fault

A Strike and dip of foliation /banding

* eclogites

0 coronas

a hypersthene

A epidote

0 15 30 km

‘Z”3O’S

0" .&; :. :::::’ l- l”E

I :::. I

Fig. 3. Simplified geological map of the H.U. Sverdrupfjella area.

238 P. B. Groenewald et al. /Precambrian Research 75 (1995) 231-250

A/M

Fig. 4. The AFM diagram indicating talc-alkaline chemical charac-

teristics of the Jutulriira gneisses in western Sverdrupfjella. The

trends are those of Brown ( 1982): A = Tonga-Mariana-S Sandwich;

B = Aleutians-Lesser Antilles; C = New Zealand-Mexico;

D = Cascades-N Chile-New Guinea.

for gneisses in the Kirwanveggen (G. Ferrar and M. Knoper, pets. commun., 1993) and Heimefrontfjella (Weber et al., 1987; R.J. Thomas, pers. commun., 1994). This suggests that a significant portion of the

Maud Belt originally consisted of volcanic arcs, a fea- ture of other Proterozoic accretionary provinces (Tho- mas, 1989; Condie, 1992).

Marbles and associated talc-silicates are present in the H.U. Sverdrupfjella, Kirwanveggen (Wolmarans

and Kent, 1982; G. Ferrar pers. commun., 1993) and Heimefrontfjella (Juckes, 1972) terrains. The meta-

carbonates of the Fuglefjellet paragneisses in H.U. Sverdrupfjella, which are the most extensive ( > 300

(4 1(

1 0.1 L

50

I

55 60 65

Si02 wl.%

lb) 6

l- 5

m thick, 5 km strike length), lie immediately east of

the Jutulrora metavolcanic rocks (Fig. 3) and represent

shallow-marine deposits. Lenses and boudins of calc-

silicates, although sparse, are widely distributed in the

Sverdrupfjella Group and occur in association with

most other lithologies. Calc-silicates may not be proof

of a sedimentary protolith assemblage, but the observed range, from those occurring with substantial marbles to

small lenses within quartzofeldspathic gneisses, sup-

ports a sedimentary heritage.

East of the carbonates is the most substantial rock

assemblage of the Sverdrupfjella Group, the Root-

shorga Formation paragneiss complex. These gneisses

were derived from pelites, arenites and greywackes,

with the resulting diverse range in compositions. Abun-

dant intermediate gneisses, although geochemically similar to talc-alkaline volcanic rocks, are interlayered

with aluminous and quartzose gneisses and have gra- dational variation in composition and banding on a

scale of a few metres. These characteristics support

interpretation as metagreywackes, as do geochemical

discriminant diagrams (Fig. 7a). On the discriminant

diagram devised by Bhatia ( 1983) from a geochemical

study of greywackes deposited in known geological settings, the Rootshorga metagreywackes plot predom-

inantly as active continental margin deposits, with the

remainder as oceanic island arc greywackes (Fig. 7b).

Mafic rocks, although a volumetrically small pro-

portion ( < 5%) of the Sverdrupfjella Group, occur as

Si02 wt.%

7

++ , Acid

Basic / +

+ =*

: +++g+ +

+ HiP( K 1 + _ _ i__;,-.-a+ -. Ic+

,-c /

ME&-K I ____----

__-.-!’

Low:K

+ + +

I

55 60 65 70

Fig. 5. Discriminant diagrams suggesting that the Jutulrijra gneisses are of normal talc-alkaline geochemistry (a), and plot as a high-K series (b). Fields and trends after Gill (1981) and Brown (1982). respectively.

P. B. Groenewald et al. /Precambrian Research 75 (I 995) 231-250 239

looQo 1001

10:

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb

Fig. 6. The REE patterns of the Jutulrijra gneisses shown in compar- ison to those of typical c&-alkaline volcanic suites (shaded area,

fromGill, 1981).

lenses, boudins or layers on almost all nunataks. Their range in composition includes gabbro, pyroxenite, oli- vine gabbronorite and dunite. In several cases the lenses show fractionation-cumulatecharacteristicsout ofpro-

portion to their size, suggesting an origin through tec- tonic fragmentation of larger bodies. Although no ophiolitic characteristics were found, the geochemistry of the mafic rocks suggests genesis through primitive

K,O

MN

a. A Na,O

mantle melting. On the discriminant diagram of Mes- chede ( 1986), the mafic rocks plot predominantly in the N-type MORB field, with most of the remainder of samples plotting in the within-plate tholeiite field (Fig. 8a), a distribution typical of volcanic arc basalts. The rocks are tholeiitic, and thus the absence of LREE enrichment typical of continental magmatism (Fig. 8b)

supports a MORB origin. The protolithologies of the eastern H.U. Sverdru-

pfjella are regarded as a metamorphosed retro-arc mar- ginal basin succession. This interpretation is based on the presence of metagreywackes having an active con- tinental margin signature in association with metabas- ites of MORB affinity, as mentioned above, in close proximity to talc-alkaline metavolcanics.

3.2. Granitoids

The numerous granitoids in the H.U. Sverdrupfjella terrain provide further constraints on the crustal evo- lution. Field relations prove that the several periods of granitic magmatism produced pre-tectonic pegmatites, tabular granites of talc-alkaline, S- and within-plate types during the early deformation history, an A-type batholith between the two main erogenic events, S-type leucogranites during the second event, and syenitic batholiths during the break-up of Gondwana (Gran- tham et al., 1991; Grantham, 1992; Moyes et al., 1993a; Harris and Grantham, 1993).

b . 4-

=

5 2- ‘Z P 2 E o- 2 .- E ‘Z z -2.

6

-4.

-64 I \ -6 -4 -2 0 2 4

Discriminant fu&tion I

Fig. 7. The semi-pelitic-intermediate gneisses of the Rootshorga paragneiss complex on: (a) the K,O-MgO-NazO discriminant diagram of La

Roche ( 1966); (b) the diagram devised by Bhatia ( 1983) for the identification of the sedimentary provenance of greywackes.

240 P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250

a.

Y I-’ ’ ’ c I La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb

Fig. 8. (a) Mafic gneisses and granofelses collected from boudins and lenses in the Rootshorga paragneiss complex on the diagram for

discrimination between oceanic and continental tholeiites formulated by Meschede ( 1986). Fields: A = within-plate alkali basalts; B = P-type

MORB; C= within-plate tholeiites and volcanic arc basal&; D= N-type MORB and volcanic arc basalts. (b) REE patterns of the matic and

uhramafic lithologies from fragments within the Rootshorga paragneiss complex in comparison to the averages of normal and enriched mid-

ocean ridge basalts. These averages and the chondrite values used for normalizing are from Sun and McDonough ( 1989).

All the early granites are highly deformed and

gneissose but are recognised as intrusions, on the grounds of transgressive contacts, xenolithic enclaves,

microstructures and geochemistry. The ages of these granites relative to each other are difficult to interpret, but the order of emplacement inferred provisionally

from field relations and isotope data is used in the following description, beginning with the earliest gran- ites.

(i) Leucogranite veins and sills, which were gener- ated during the early metamorphism, are sparse in the

eastern parts of H.U. Sverdrupfjella. Given the great

crustal depth and high temperatures of the early meta- morphism in this area (Groenewald and Hunter, 199 1)) the earliest syn-erogenic leucogranite magmas were probably able to rise to substantially higher crustal lev- els. The leucogranite sills in the western parts of the terrain are geochemically compatible with the interpre- tation as being generated locally at this time.

(ii) Garnet biotite granites containing abundant xen- olithic enclaves (the Fugitive granites) are identified as predating most of the deformation. The presence of relict garnet indicates that this mineral predated or grew during early stages of the melting. Although the con- tacts of these granites are locally transgressive to the banding in the country rock gneisses, proving that they

were mobile, the granites are geochemically very sim-

ilar to the metagreywackes. On discriminant diagrams they plot as within-plate granites, with many A-type characteristics. This is attributed to these being the product of progressive melting, with the earliest melts segregating to form the leucogranites, leaving restite-

dominated bodies in which melt proportions in a second stage of anatexis exceeded the critical melt fraction (i.e.

mobile restite?) . (iii) The Sveabreen and Roerkulten granites are also

of inferred early syn-tectonic origin and occur as tab- ular units 0.1-3 km thick and up to 30 km in strike

length (Fig. 3). The contacts are most commonly thrust-bounded, although at some localities there appear to be gradational contacts with country rock gneisses. These monzogranites are typically megacrys- tic and have S-type characteristics; they carry garnet

and sillimanite (locally), have A/CNK ratios > 1.1 and normative corundum > 5%. The absence of mus- covite and high temperatures of melting (850-950°C

calculated using the Zr and P saturation thermometers) suggest that these granites were produced by decom- pression melting in a low-volatile environment (PBG,

unpubl. data). (iv) Leucogranodiorites which postdate the granites

described above but predate much of the intense defor-

P. B. Groenewald et al. /Precambrian Research 75 (I 995) 231-250 241

mation are tabular in form (up to 300 m thick) or occur as narrow transgressive (folded) dykes. In terms of discriminants such as the tectonic setting identification diagrams of Pearce et al. ( 1984)) these granites have volcanic arc geochemical characteristics.

In summary, these early granites are typical of a lengthy period of collision tectonism in that they show a progressive change from early near minimum melt compositions to decompression melts, and finally to volcanic arc types which may represent second-stage melting of subducted rocks.

Granitic magmatism during the 500 Ma event com- prises two distinct categories. The first produced the Brattskarvet monzonites and monzogranites, a suite of -520 Ma alkaline to peralkaline A-type granites

emplaced in response to a major heating event, possibly related to extension or underplating (Moyes et al., 1993a). The deformation of these rocks, although less intense than that of the - 1100 Ma granites, is also

characterised by recumbent folding and sub-horizontal foliation in the same orientation as the major thrust faults which brought granulites to high structural levels in this terrain.

The second stage of late granitic magmatism occurred during the final phase of minor ductile defor- mation in the area and resulted in abundant leucogranite sills and dykes throughout the H.U. Sverdrupfjella ter- rain. This suite includes two-mica S-type granites which Grantham et al. ( 1991) interpreted as hydrous melts produced at a depth of 15-20 km which could not have moved far upward without meeting the water-

saturated solidus. The nepheline syenite batholiths at Straumsvola and

Tvora (Fig. 3) represent the final stage of magmatism in the terrain. They are located close to the Jutulstrau- men boundary between the cratonic and erogenic prov- inces. These intrusions were intruded at - 170 Ma in an extensional setting related to the break-up of Gond- wana (Harris and Grantham, 1993).

3.3. Geochronology and isotope chemistry of the Mud Belt

Isotopic characteristics of the rocks in erogenic ter- rains contribute critical constraints on their origins and subsequent history. The work summarized here (Table 1) is principally that in the H.U. Sverdrupfjella area (with some advances on the data and interpretations

presented by Moyes and Barton, 1990; Moyes et al., 1993a, b) , although information from Kirwanveggen (Wolmarans and Kent, 1982) and Heimefrontfjella (Arndt et al., 1991) is included.

The Rb-Sr isotopic dates of the Sverdrupfjella Group metavolcanic ( 1124 k 38 Ma) and metagrey- wacke ( 1183 k 27 Ma) gneisses and the earliest granite

in eastern H.U. Sverdrupfjella (the Fugitive granite 1161& 98 Ma) are statistically indistinguishable. These effectively synchronous ages suggest that the prograde metamorphism which resets the Rb-Sr sys- tem in the gneisses also produced the granites, and thus that the first erogenic event involved high temperatures in the period 120&l 100 Ma. The initial “Srl%r ratios (Ra) of the Rootshorga paragneisses (0.7034) and Fugitive granite (0.7036) are close to that of bulk earth at 1175 Ma, suggesting that the protoliths of the gneisses were young at the time of the orogeny. The higher RO value of the metavolcanics (0.7076) is enig- matic and it is possible that the greywackes were derived from a source less evolved than the metavol- canics present in outcrop. In addition, Nd model ages (depleted mantle) of the Sverdrupfjella paragneisses ( 1495 Ma, Moyes et al., 1993a) and Fugitive granite ( 1498 Ma, ABM and PBG unpubl. data) also suggest relatively juvenile protoliths.

The other early intrusions, the Sveabreen ( 1028 + 94 Ma) and Roerkulten (905 +51 Ma) granites, have higher RO and E values (Table 1). It is possible that these were generated during the post-collisional decompression and thermal relaxation, as the highest

temperatures attained ( - 850°C Groenewald and Hunter, 199 1) would have allowed substantial melting of pelites and greywackes under vapour absent condi- tions (Patiiio Deuce and Johnston, 1991) because the applicable phase boundary has a positive slope. It is possible that the decompression may have been related to gravitational collapse of the orogen or the beginning of extension; as noted above, continental tholeiites were being emplaced at this time in the adjacent Gru- nehogna province.

The next intrusions in the Sverdrupfjella terrain, emplaced between the two orogenies, are predomi- nantly mafic or intermediate in composition. A mafic dyke at Roerkulten, dated at 789 & 90 Ma (Rb-Sr) and 85 1 + 220 Ma (Sm-Nd), clearly postdates the early foliations but is itself intensely deformed and foliated (Grantham, 1992). This provides a critical constraint

242 P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250

Table I

Geochronological data from the Maud province

Locality and lithology n MSWD Age *Ma R0 E Av. TDM

Rb-Sr and Sm-Nd isotopes Kirwanveggen ( I ) : Heksegryta gneiss

Halgrenskarvet gneiss

Neumayerskarvet leucogranite

Sverdrupfjella (2):

Rootshorga paragneiss

Jutulrljra metavolcanic

Fugitive granite

Sveabreen granite

Roerkulten granite

Roerkulten mafic dyke

Midbresrabben diorite

Brattskarvet suite

Rootshorga mafic

Dalmatian granite (3):

Sr 5 11 1164 76 0.70463 17 Sr 10 6.5 1035 18 0.70463 17

Sr 6 1.6 1007 51 0.70407 8.4

Sr 6 2.8

Sr 25 (f) Sr 5 8.9

Nd 3 (It) Sr 5 86

Sr 12 (*) Sr 11 2.4

Nd 16 1.9

Sr 6 1.6

Sr 18 (It) Nd 13 5.4

Nd 3 (k) Sr 7 1.3

1183 27 0.70341 2

1124 38 0.70756 60

1161 98 0.70356 4

1087 (Zt) 0.51126 2 1498

1028 94 0.70647 43

905 51 0.70951 84

789 90 0.70486 16

851 220 0.51139 - 3.6 1516 788 110 0.7065 1 39

518 15 0.70784 53

522 120 0.51111 - 17.5 1905

479 (f) 0.51112 - 17.8 2301 469 5 0.73530 434

Locality and lithology Method Date MSWD

U-Pb, Pb-Pb and K-Ar isotopes Kirwanveggen ( I, 2 ) : Neumeyerskarvet

Heksegryta

Armalsryggen

Heimefrontfjella (4):

Metarhyolite

Garnet amphibolite

Granulite paragneiss

Granites (amphibolite terrain)

Mafic dyke (5) (post-meta, pre-

thrust)

Mylonites (6)

PbPb

U-Pb

PbPb

U-Pb

Pb-Pb

U-Pb

U-Pb zircon

U-Pb zircon

U-Pb zircon

U-Pb range

K-Ar

K-Arrange

1071*74 90

1112*32 9.5

1075 *60 127

1107k 127 260

1061 rt66 127

1045 * 193 548

1093*038

1031+24

1060 $3

1104*5, 1215f15

1048*8to 1104*4

452 f 15,458 + 15

484508

Source references: I = Wolmarans and Kent, 1982; 2=Moyes and Barton, 1990, Moyes et al., 1993a. b; 3=Grantham et al., 1991; 4 = Amdt etal.. 1991; 5=Rex, 1972; 6=Jacobs, 1991.

on the minimum age of the Maud Orogeny, and sug- gests that by - 800 Ma compression had ceased and deep fracturing allowed the emplacement of mafic

dykes. A significant constraint on the 500 Ma orogen is

revealed by the isotope chemistry of the Brattskarvet

granite suite, the main pluton of which intruded at 518+15 Ma (Rb-Sr) or 522+120 Ma (Sm-Nd)

(Moyes et al., 1993a) and was probably emplaced syn- chronous to the deformation. The A-type characteris- tics of this suite (PBG, unpubl. data) and the Nd model ages of 1900-2300 Ma (Moyes et al., 1993a) indicate

P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250 243

that a major thermal perturbation occurred in this event and led to melting of lower crustal rocks older than the surrounding Rootshorga paragneisses (Moyes et al., 1993a). In contrast, the oldest post-tectonic granites in the area, which have an age of 469 + 5 Ma and a higher

R. value (0.7 IO), are peraluminous granites derived from water-rich magmas which could not have trav- elled far from their source (Grantham et al., 1991), and were thus generated locally in response to the influx of water (see below).

Mineral isotope chemistry also contributes to the understanding of crustal evolution in the area. Almost all biotite separates from the terrain provide ages in the range 440-480 Ma (Moyes et al., 1993b), indicating that cooling to temperatures less than 400-450”C occurred rapidly after generation of the S-type granites. Similarly, garnets from both the gneisses and the early granites have Sm-Nd isotope ratios indicative of clo- sure to diffusion of these elements at about 500 Ma (ABM unpubl. data) which supports the inference that temperatures during the 500 Maevent exceeded 600°C.

3.4. Deformation and metamorphism

Details of the thermotectonic history in the H.U. Sverdrupfjella and Kirwanveggen parts of the Maud province are given by Grantham et al. ( 1995), and the

limited available detail from Heimefrontfjella by Juckes ( 1972) and Jacobs (1991). Throughout the belt, the multiple stages of intense deformation

involved thrusting and recumbent folding with predom- inantly northwestward transport directions. Although separation of the stages is imprecise at present, Gran- tham ( 1992) established that intense deformation

occurred both before and after the emplacement of an 800 Ma mafic dyke in the central part of H.U. Sverdru-

pfjella. High-grade metamorphism (see below) asso- ciated with the earlier deformation suggests that the first (Maud) orogeny involved considerable crustal thickening. The early folding and thrusting with NW vergence is thus attributed to a collision orogeny in the period 1200-800 Ma.

In the 520 Ma Brattskarvet intrusion, recumbent folding has the same vergence and orientation as the major early thrusting in the H.U. Sverdrupfjella (PBG unpublished information) and indicates that major deformation which occurred during the 500 Ma orog-

eny was in the same orientation as that in the earlier event.

Jacobs et al. ( 1993) suggested that the initial stage of collision in the Heimefrontfjella part of the belt was northeastward and orthogonal to the southern margin

of the Grunehogna Craton. Subsequent deformation in this area produced major NE-striking shear zones attributed to dextral transpression. Minor NNE-verging thrusts and recumbent folds are also present.

Aspects of the metamorphic history of the Maud Belt have been reported by Groenewald and Hunter ( 1991)) Groenewald (1991, 1993b) and Grantham et al. ( 1995). The H.U. Sverdrupfjella terrain underwent a complex evolution, with a P-T path in which the rela- tive timing of events is significant, even if lacking in absolute-age precision. Evidence that high pressures applied in the eastern part of H.U. Sverdrupfjella at an early stage is preserved in unfoliated boudins of meta- basite. The relict assemblages of gamet-augite-rutile- quartz and garnet-olivine-hypersthene-spinel- hornblende have allowed thermobarometric work (Groenewald, 1993b; Grantham et al., 1995) to iden- tify peak pressures greater than 12 kbar at temperatures of 750-790°C. This was followed by the medium-pres- sure granulite facies conditions (P= 8-10 kbar, T = 850°C) in the later part of the first event (Groene- wald and Hunter, 199 1) which led to the generation of

the Sveabreen granites through decompression melt- ing.

In spite of the early high-grade conditions, most of the gneisses in eastern H.U. Sverdrupfjella are hom- blende- and biotite-bearing, with abundant evidence of decompressive retrograde rehydration such as augite relicts within hornblende, local replacement of garnet by biotite-cordierite-sillimanite, of kyanite by silli- manite, and the local production of muscovite by reac- tion of sillimanite, microcline and water. The garnets in these gneisses have a Sm-Nd isotope chemistry indi- cating re-equilibration at N 500 Ma (ABM and PBG unpubl. data).

This decompressive retrogression in eastern H.U. Sverdrupfjella is interpreted as the result of tectonic exhumation through thrusting and emplacement of these rocks above a lower-grade tectonostratigraphic unit. This occurred at relatively high temperatures, as indicated by the generation of granites, the stability of cordierite-sillimanite-garnet assemblages, and the conversion of kyanite to sillimanite.

244 P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250

4. A preliminary model of crustal evolution in western Dronning Maud Land

The research reviewed above provides several con- straints on crustal evolution in this portion of East Ant- arctica. The preliminary model which follows (Fig. 9) is based on these constraints in conjunction with data from the cratonic and erogenic provinces of southeast- ern Africa which Groenewald et al. (1991) and Gro- enewald ( 1993a) correlated with those in western Dronning Maud Land.

Little can be inferred about the Archaean history of Dronning Maud Land because only a small area of outcrop ( < 10 km2) consists of gneissic granite of established Archaean-age. Barton et al. (1987) inferred that the granite is of S-type because it is per- aluminous, has a high Si02 content, lacks hornblende and sphene, and contains accessory monazite and mus- covite. They suggested that the granite is unlike any granite of this age documented in southern Africa or East Antarctica, and speculated that the Grunehogna

crustal fragment originated as a microcontinent rather than a fragment of the Kalahari Craton. The ‘unique- ness’ of the granite is equivocal; Barton et al. (1987) based their interpretation on limited geochemical and petrographic data ( 10 samples), and D.R. Hunter

(pers. commun., 1987) has confirmed that some gran- ites in the Barberton Mountainland area are geochem- ically similar to the Annandagstoppane granite. The continuity of the Mesoproterozoic belts in Mozam- bique, Dronning Maud Land and Natal is highly likely and this constrains the Grunehogna province to being part of the Kalahari Craton prior to the Mesoproterozoic orogeny which formed these belts (Grantham et al., 1988; Groenewald et al., 1991; Groenewald, 1993a). There is, thus, little support for the existence of the Grunehogna microplate.

The sedimentary and volcanic rocks of the Ritsch- erflya Supergroup accumulated on the platform pro- vided by the Kalahari Craton in a period which ended in an 800-1000 Ma magmatic event (Fig. 9). A con- tinental basin succession in eastern Zimbabwe and southwestern Mozambique, the Umkondo Group, is of similar lithostratigraphy, age and setting to the Ritsch- erflya Supergroup (Ferreira, 1988). The contempora- neity of accumulation of these sequences with collision orogeny around the eastern and southern margins of the platform suggests that a foreland basin succession

should be identifiable. However, in the Ritscherflya Supergroup, the paucity of the alluvial fans which should predominate in the proximal part of such basins is significant; outcrops of Ritscherflya sedimentary

rocks closest to the high-grade terrain are no different from other, more distal, parts of the sequence. The occurrence of jasperlitic banded chert clasts in the con-

glomerates suggests an intracratonic provenance because the deposits of such rock types are predomi- nantly banded iron formations of Palaeoproterozoic continental platform deposits. The palaeoslope indi- cated by the dominance of northeastern palaeocurrent directions in the Ritschefiya sediment rocks may sup- port the interpretation of Jacobs et al. ( 1993) that ini- tial, orthogonal, collision occurred on the southwest

edge of the Grunehogna Craton. The characteristics of the Maud Belt are compatible

with an origin through Mesoproterozoic collision and1 or accretion of a volcanic arc and retro-arc marginal basin to the Kalahari Craton, although there is evidence of modification in later events. Constraints provided by the Sverdrupfjella terrain are important with regard to timing, setting and the distinctions between the two orogenies.

The limited spread in the oldest isotopic ages, be they of metamorphic rocks or crystallization ages of

granites, indicates that high temperatures reset the sys- tem in the period 1100-1200 Ma. The terrain was rel- atively juvenile at the time of resetting, as indicated by the low “Sr/%r initial ratios close to the bulk earth value of N 0.7035 at 11.50 Ma, suggesting a brief crustal residence time. The Nd model ages (depleted mantle) of - 1500 Ma suggest that the volcanic arc and the provenance of the greywackes were no older than Mesoproterozoic in age. The mafic magmatism at N 800 Ma in the Maud Belt and in the adjacent cratonic area at 800-1000 Ma indicates the onset of extension at the end of the Maud Orogeny and constrains its duration to 200-400 m.y.

The earliest recognised structures in the Maud Belt are recumbent isoclinal folds, commonly reduced to limbless intrafolial structures by intense refoliation. The metamorphic P-T path involved initial high pres- sures followed by decompression and thermal relaxa- tion (to the higher temperatures of the equilibrium geotherm), more typical of continental collision than of simple accretion. The high early metamorphic pres- sures in the eastern parts of the H.U. Sverdrupfjella are

P.B. Groenewuld et al. /Precambrian Research 75 (1995) 231-250 245

a.

b. e.

MAUD BELT I.

d.

@ Continental basement -@ Volcanic arc @&JJ Retro-arc deposits

@& 11 OOMa Molasse m_ 400Ma Urfjell Group \,I_

1 OOOMa Tholeiites rt Eclogite remnants

Fig. 9. Crustal evolution in western Dronning Maud Land. (a) The inferred setting of the Grunehogna part of the Kalahari Craton in the period

1200-l 600 Ma. (b) Collision and compression of the retro-arc marginal basin ( 1100-l 200 Ma). The elevated isotherms beneath the floor of

the marginal basin are based on the presence of MORB-like mafic dyking in the paragneisses and the early medium-temperature eclogites

suggest that crustal thickening forced the deepest part of the marginal basin succession down into thermally perturbed lithospheric mantle. (c)

The decompression and thermal relaxation to medium-pressure granulite facies conditions which followed produced the voluminous Sveabreen

granites at this stage ( - 1050 Ma). (d) Extension in the period 800-1000 Ma is suggested by the mafic igneous activity in both the Grunehogna

(continental tholeiites) and Sverdrupfjella terrains (malic and intermediate dykes). (e) The - 500 Ma tectonothermal overprinting event.

Initial heating led to the emplacement of the A-type Brattskarvet granite suite at - 520 Ma. This may have been virtually synchronous with or

was immediately followed by renewed thrusting and folding towards the northwest. Post-tectonic granite dyking with S-type characteristics

followed. (f) Dramatic exhumation occurred, before deposition of the Urtjell Group, with the removal of IO-15 km of crust as a result of

isostatic rebound. (g) Late Jurassic extension and magmatism (the Kirwanveggen basalts followed by Straumsvola nepheline syenite pluton)

reflects the break-up of Gondwana.

246 P.B. Gmenewaid et al. /Precambrian Reseurch 75 (1995) 231-250

problematic in that, if this was a retro-arc basin, sub- duction would not have contributed the high pressures. It would thus seem likely that this orogeny involved collision and sandwiching of a young arc-complex between colliding continents, in a fashion similar to the Kohistan portion of the Himalayan belt (Bard, 1983). The arc and basin were no older than 300 m.y. at the time of collision. Although no older continental crust has been identified east or south of the erogenic belt, zircons greater than 2000 Ma in age have been found only in metasediments in the southern part of the Hei- mefrontfjella, that is, the area furthest from the Gru- nehogna province ( Arndt et al., 199 1) This is an aspect impossible to investigate further without geophysical research because of the absence of outcrops to the

southeast of the belt. Furthermore, the inferred lateral equivalent of the Maud Belt in southeastern Africa, the Natal belt (Groenewald et al., 1991), has been inter- preted as accretionary, with addition of volcanic arc terrains to the southern margin of the Kalahari Craton without any identifiable continental province to the south (Thomas, 1989).

The supercontinent assembled at - 1100 Ma entered a period of extension marked by the 1000-800 Ma mafic magmatism, possible (albeit tenuous) evidence of some break-up and dispersal (Fig. 9d). The next

marker is provided by the Brattskarvet alkaline granite suite which reflects high heat flow and thermal pertur- bation of the lower crust at - 520 Ma. Deformation of

these granitoids suggests thrusting and folding with NW vergence. This deformation probably reflects another compressive or collisional orogeny in the early Cambrian. The intensity of late deformation increases to the northeast, and in the Gjelsvikfjella (Fig. la), intense refoliation accompanied whole-rock Rb-Sr iso- tope resetting at about 500 Ma in gneisses which have retained Mesoproterozoic Sm-Nd isotope characteris- tics (Moyes, 1993). Still further east is the Fimbulhei- men (Fig. I a), where all published isotopic dates fall

in the range 600-400Ma (Ravich and Solov’ev, 1966). S-type granites generated at a late stage (470 Ma)

provide evidence for an influx of water, suggesting that prograde metamorphism involving devolatization reac- tions occurred as a result of thrusting of the granulites over the lower-grade rocks in the west leading to ther- mal inversion (Fig. 9e). Significantly, the Brattskarvet intrusion provides evidence of the involvement of older crust as it has Nd model ages around 2 Ga (Moyes et

al., 1993a), indicating that this A-type granite was pro- duced from Palaeoproterozoic crust in depth. It is pos- sible that thrusting towards the northwest had been so extensive that crust of the GrunehognaCraton was pres- ent beneath the eastern H.U. Sverdrupfjella by 520 Ma. This would require overthrusting of crust at least 15 km thick (the depth of emplacement of this intrusion) in excess of 100 km westward onto the Grunehogna province, thus providing an immense source of hydrous fluid after the thrusting. Two aspects support this pos- tulated overthrusting. Firstly, the 500 Ma event was followed by rapid cooling as shown by the age of iso- topic closure of several minerals only 20 m.y. after the anatectic melting had produced the late granites (Gran- tham et al., 199 1) . Secondly, and relatedly, rapid exhu- mation occurred. Grantham et al. ( 1991) inferred a

minimum depth of emplacement for the Dalmatian granites of about 15 km, yet the pre-Permian Urfjell Group in southwestern Kirwanveggen consists of aren- ites and conglomerates derived from a high-grade met- amorphic provenance (Aucamp et al., 1972), suggesting that the SverdrupfjellaGroup gneisses were being eroded in the early Palaeozoic (Fig. 9f). Such rapid uplift after the 500 Ma event has been noted in several parts of East Antarctica, and was attributed by Stiiwe and Sandiford ( 1993) to this event being the result of major mafic underplating rather than a colli- sion orogeny. Although it is beyond the scope of this paper to dispute this, the evidence of a distinct 500 Ma orogeny in western Dronning Maud Land suggests that overthrusting of the Sverupfjella terrain onto the adja- cent craton could have led to greatly overthickened crust with the resulting isostatic rebound causing the rapid exhumation.

5. Discussion

Jacobs et al. ( 1993) suggested that the initial move- ment in Heimefrontfjella was northeastward and involved orthogonal collision onto the southern margin of the Kalahari Craton followed by dextral transpres- sion along the eastern margin. In the H.U. Sverdru- pfjella and Kirwanveggen areas, transport directions are overwhelmingly towards the northwest, despite the evidence for intense multiple deformation. Although the reworking renders interpretation of the earliest structural history difficult, the Maud Belt almost cer-

P. B. Gmenewnld et al. /Precambrian Research 75 (1995) 231-250 241

tainly represents collision of continents. The metamor- phic and structural evidence of a collision setting is substantial and isotope data prove that juvenile crust was reworked in the Mesoproterozoic.

The second erogenic event involved northwestward thrusting onto the eastern margin of the Grunehogna part of the Kalahari Craton. It is possible that consid- erable shortening of the Sverdupfjella terrain occurred in this event with major decompression of the 1100 Ma eastern granulites through thrusting and inversion of the metamorphic profile. Major thermal disturbances would have accompanied such thrusting as the granu- lite terrain was still deep crust and its emplacement above the western amphibolites would have caused significant heating of these. The decompression would have caused melting in the granulites and production of the 520 Ma A-type granites (A-type does not nec- essarily imply anorogenic, see Eby, 1992). Abundant hydrous fluid became available as prograde reactions progressed in the now deeply buried frontal portion of the Kalahari Craton, leading to the production of 470 Ma S-type granites.

As noted by Windley ( 1992)) Proterozoic erogenic belts range from those in which juvenile volcanic arcs

and accretionary prisms built on to continents to those involving collision and reworking of older crust. An intermediate scenario applied in the Maud Orogeny: the continental margin developed a volcanic arc-mar- ginal basin complex while an ocean between the con- verging continents was consumed prior to collision. The second orogen is more difficult to classify, but the reworking of older crust may possibly represent simple collision. Ring ( 1993) suggested that the Proterozoic erogenic belts of central East Africa may have been structurally weak because they represented disturbance of equilibrium density gradients and were thus favou- red loci of break-up. This means that margins of frag-

ments of the Mesoproterozoic supercontinent may have been parts of the Mesoproterozoic erogenic belts. Reas- sembly, or closure of substantial rifts, would then have juxtaposed portions of the older erogenic belts.

Western Dronning Maud Land is particularly rele- vant to recent interpretations of the Neoproterozoic continental assemblies. The SWEAT hypothesis (Moores, 199 1; Dalziel, 199 1) suggests that East Ant- arctica, or part thereof, was attached to western North America in the Neoproterozoic. The extension sug-

gested by the 1000-800 Ma tholeiitic magmatism in

the Grunehogna and Maud provinces may imply that break-up occurred between the two orogenies and that an ocean existed between the Kalahari and East Ant- arctic cratons/continents, the Mozambique ocean needed in the hypothetical SWEAT reconstruction of Dalziel ( 1991, 1992). This requires that Cambrian reassembly be represented by a major - 500 Ma oro- genie belt. Such a belt may exist: the Saldanian at the southern extremity of Africa, if extrapolated on the Gondwana assembly, could be envisaged as crossing Dronning Maud Land south and east of the Maud Belt to join the Pan-African collision belt of East Africa (Fig. lb).

Acknowledgements

This research in Antarctica has been funded by the South African Department of Environment Affairs. We thank Prof. Branko Corner for providing his interpre- tations of geophysical data from western Dronning Maud Land. Gavin Ferrar, Chris Jackson, Mike Knoper and Phil Harris shared preliminary research findings from their work in the Kirwanveggen with us. Dr. R.J. Thomas gave us a detailed description of the Heimer- fontfjella after working there in December 1993. We are grateful to Professors I.W.D. Dalziel and M. Yosh- ida for reviewing this paper and making constructive comments and suggestions.

References

Amdt, N.T., Todt, W., Chauvel, C., Tapfer, M. and Weber, K., 1991.

U-Pb zircon age and Nd isotopic composition of gmnitoids,

chamockites and supracrustal rocks from Heimefrontfjella, Ant-

arctica. Geol. Rundsch., 80: 759-777.

Aucamp, A.P.H., Wolmarans, L.C. and Neethling, D.C., 1972. The

UrfJell Group, a deformed (?) early Palaeozoic sedimentary

sequence, Kitwanveggen, Western Dronning Maud Land. In:

R.J. Adie (Editor), Antarctic Geology and Geophysics. Univ-

ertetsforlaget, Oslo, pp. 557-562. Bard, J.P., 1983. Metamorphism of an abducted island arc: example

of the Kohistan sequence (Pakistan) in the Himalayan collided

range. Earth Planet. Sci. L&t., 65: 133-144.

Barton, J.M., Jr., Klemd, R., Allsopp, H.L., Auret, S.H. and Cop-

perthwaite, Y.L., 1987. The geology and geochronology of the Annandagstoppane granite, western Dronning Maud Land, Ant-

arctica. Contrib. Mineral. Petrol., 97: 488496. Bhatia, M R., 1983. Plate tectonics and geochemical composition of

sandstones. J. Geol., 91: 661627.

248 P.B. Gmenewuld et al. /Precambrian Research 75 (1995) 231-250

Bowman J.R., 1971. Use of the Isotopic Composition of Strontium evolution of the Kirwanveggen-Sverdrupfjella terrains, Dron-

and SiOl Content in determining the Origin of Mesozoic Basalt ning Maud Land, Antarctica. In: P. Dirks, C.W. Passchier and

from Antarctica. M.Sc thesis, Ohio State University, unpubli- J.D. Hock (Editors), Tectonics of East Antarctica. Precambrian

shed. Res., 75: 209-229 (this issue).

Brown, G.C.. 1982. Calc-alkaline intrusive rocks: their diversity,

evolution, and relation to volcanic arcs. In: R.S. Thorpe (Editor),

Andesites. Wiley, London, pp. 437-46 I.

Condie, K.C., 1992. Proterozoic terranes and continental accretion

in southwestern North America. In: K.C. Condie (Editor), Prot-

erozoic Crustal Evolution. Elsevier, Amsterdam, pp. 463480.

Cox, K.G., Bell, J.D. and Pankhurst, R.J., 1979. The Interpretation

of Igneous Rocks. Allen and Unwin, London, 450 pp.

Dalziel. I.W.D., 1991. Pacific margins of Laurentia and East Antarc-

tica-Australiaas aconjugaterift pair: evidence and implications

for an Eocambrian supercontinent. Geology, 19: 598-601.

Dalziel. I.W.D., 1992. Antarctica-a tale of two supercontinents?

Annu. Rev. Earth Planet. Sci., 20: 501-526.

Decleir, H. and Van Autenboer, T.. 1982. Gravity and magnetic

anomalies across Jutulstraumen, a major geologic feature in west-

ern Dronning Maud Land. In: C. Craddock (Editor), Antarctic

Geoscience. The University of Wisconsin Press, Madison, pp.

941-948.

Groenewald, P.B., 1991. Metamorphic evolution of H.U. Sverdru-

pfjella in the context of Maudheim erogenic province, western

Dronning Maud Land, Antarctica. 6th Int. Symp. Antarctic Earth

Sciences, NIPR, Tokyo, p. 194.

De La Roche, H.. 1966. Sur I’existence de plusieurs facies geochi-

miques dans les schistes paleozdiques des Pyretrees Luchon-

naises. Geol. Rundsch., 55: 274-301.

Dirks, P.H.G.M.. Carson, C.J. and Wilson, C.J.L., 1993. The defor-

mational history of the Larsemann Hills, Prydz Bay: the impor-

tance of the Pan-African (500 Ma) in East Antarctica. Antarc.

Sci.. 5: 179-192.

Groenewald, P.B., 1993a. Correlation of cratonic and erogenic prov-

inces in southeastern Africa and Dronning Maud Land, Antarc-

tica. In: R.H. Findlay, R. Unrug, M.R. Banks and J.J. Veevers

(Editors), Gondwana 8. Balkema, Rotterdam, pp. 11 I-123.

Groenewald, P.B., 1993b. Eclogites in Dronning Maud Land, Ant-

arctica: evidence of mid-crustal detachment during metamorphic

inversion. Terra Nova, Abstr. SuppI., 5: 13.

Groenewald, P.B. and Hunter, D.R.. 1991. Granulites of northern

Sverdrupfjella, western Dronning Maud Land: metamorphic his-

tory from garnet-pyroxene assemblages, coronas and rehydra-

tion reactions. In: M.R.A. Thomson, J.A. Crame and J.W.

Thomson (Editors), Geological Evolution of Antarctica. Cam-

bridge University Press, Cambridge, pp. 61-66.

Groenewald, P.B., Grantham, G.H. and Watkeys, M.K., 1991. Geo-

logical evidence for a Proterozoic to Mesozoic link between

Dronning Maud Land, Antarctica, and southeastern Africa. J.

Geol. Sot. London, 148: 1115-l 123.

Eastin, R., Faure, G. and Neethling, D.C., 1970. The age of the

Trollkjellrygg volcanics of western Queen Maud Land. Antarc.

J. U.S.. 5: 157-158.

Eby, G.N., 1992. Chemical subdivision of the A-type granitoids:

petrogenetic and tectonic implications. Geology, 20: 64-644.

Ferreira, E.P., 1988. ‘n Sedimentologies-Stratigrafiese Ondersoek

van die Sedimentere Gesteentes in die Ahlmannryggen, Antark-

tika. Thesis, University of Stellenbosch. 193 pp., unpublished.

Gill, J.. 1981. Orogenic Andesites and Plate Tectonics. Springer,

Berlin. 390 pp.

Halpem, M., 1970. Rubidium-strontium date of possibly 3 billion

years for a granitic rock from Antarctica. Science, 169: 977-978.

Harris, C. and Grantham, G.H., 1993. Geology and petrogenesis of

the Straumsvola nepheline syenite complex, Dronning Maud

Land, Antarctica. Geol. Msg., 130: 523-532.

Hjelle, A., 1974. Some observations on the geology of the H.U.

Sverdrupfjella, Dronning Maud Land, Antarctica. Nor. Polarinst.

Arbor, 1972: 7-22.

Grantham, G.H., 1992. Geological Evolution of Western H.U. Sver-

drupfjella, Dronning Maud Land, Antarctica. Thesis, University

of Natal, Pietermaritzburg. 32 I pp., unpublished.

Grantham, G.H. and Hunter, D.R., 1991. The timing and nature of

faulting and jointing adjacent to the Pencksokket. western Dron-

ning Maud Land, Antarctica. In: M.R.A. Thomson, J.A. Crame

and J.W. Thomson (Editors), Geological Evolution of Antarc-

tica. Cambridge University Press, Cambridge, pp. 47-5 I.

Grantham, G.H., Groenewald, P.B. and Hunter, D.R., 1988. Geology

of the northern H.U. Sverdrupfjella, western Dronning Maud

Land and implications for Gondwana reconstructions. S. Afr. J.

Antarc. Res.. 18: 2-10

Grantham, G.H., Moyes, A.B. and Hunter, D.R., 1991. The age,

petrogenesis and emplacement of the Dalmatian granite, H.U.

Sverdrupfjella. Dronning Maud Land, Antarctica. Antarc. Sci.,

3: 197-204.

Grantham, G.H., Jackson, C.. Moyes. A.B., Groenewald, P.B., Har-

ris, P.D., Ferrar, G. and Krynauw, J.R., 1995. The tectonothermal

Hoffman, P.F., 1991. Did the breakout of Laurentia turn Gondwan-

aland inside out? Science, 252: 1409-1412.

Jacobs, J., 1991. Strukturelle Entwicklung und Abktihlungsgeschi-

chte der Heimefrontfjella (Westliches Dronning Maud Land/

Antarctica). Ber. Polarforsch., 97: 1-141.

Jacobs, J., Thomas, R.J. and Weber, K., 1993. Accretion and inden-

tation tectonics at the southern edge ofthe Kaapvaal craton during

the Kibaran (Grenville) orogeny. Geology, 21: 203-206.

Juckes, L.M., 1972. The geology of north-eastern Heimefrontfjella,

Dronning Maud Land. Br. Antarc. Surv., Sci. Rep.. 65.44 pp.

Krynauw, J.R., Hunter, D.R. and Wilson, A.H., 1987. A review of

the field relationships, petrology and geochemistry of the Borg-

massivet intrusions in the Grunehogna Province, western Dron-

ning Maud Land, Antarctica. 5th Int. Symp. Antarctic Earth

Sciences, Cambridge, Abstr. Vol., p. 83.

Krynauw, J.R., Hunter, D.R. and Wilson, A.H.. 1988. Emplacement

of sills into wet sediments at Grunehogna, western Dronning

Maud Land, Antarctica. J. GeoI. Sot. London, 145: 1019-1032.

Krynauw, J.R., Watters, B.R., Hunter, D.R. and Wilson, A.H., 1991.

A review of the field relations, petrology and geochemistry of

the Borgmassivet intrusions in the Grunehogna Province, west-

em Dronning Maud Land, Antarctica. In: M.R.A. Thomson, J.A.

Crame and J.A. Thomson (Editors), Geological Evolution of

Antarctica. Cambridge University Press, Cambridge, pp. 33-39.

P.B. Groenewald et al. /Precambrian Research 75 (1995) 231-250 249

Kyle, P.R., Pankhurst, R.J. and Bowman, J.R., 1983. Isotopic and

chemical variations in Kirkpatrick Basalt Group rocks from

southern Victoria Land. In: R.L. Oliver, P.R. James and J.B. Jago

(Editors), Antarctic Earth Science. Australian Academy of Sci-

ence Press, Canberra, pp. 234237.

Marsh, J.S. and Eales, H.V., 1984. The chemistry and petrogenesis

of igneous rocks of the Karoo central area, southern Africa. Spec.

Publ. Geol. Sot. S. Afr., 13: 27-67.

Meschede, M., 1986. A method of discriminating between different

types of mid-ocean ridge basalts and continental tholeiites with

the NbZr-Y diagram. Chem. Geol., 56: 207-218.

Moore% E.M.. 1991. The southwest U.S.-East Antarctica

(SWEAT) connection: a hypothesis. Geology, 19: 425428.

Moyes, A.B., 1993. The age and origin of the Jutulsessen granitic

gneiss, Gelsvekfjella, Dronning Maud Land. S. Afr. J. Antarc.

Res.. 23: 25-32.

Moyes. A.B. and Barton. J.M., Jr., 1990. A review of isotopic data

from western Dronning Maud Land, Antarctica. Z. Geol. Palbn-

to]., I: 19-31.

Moyes, A.B.. Groenewald, P.B. and Brown, R.W., 1993a. Isotopic

constraints on the age and origin of the Brattskarvet intrusive

suite, Dronning Maud Land. Antarctica. Chem. Geol. (Isot.

Geosci. Sect.), 106: 453466.

Moyes, A.B., Barton. J.M. and Groenewald, P.B.. 1993b. Late Prot-

erozoic to early Palaeozoic tectonism in Dronning Maud Land,

Antarctica: its bearing on supercontinental fragmentation and

amalgamation. J. Geol. Sot. London, 150: 833-842.

Moyes, A.B., Krynauw, J.R. and Barton. J.M.. 1995. The age of the

Ristcherflya Supergroup and Borgmassivet intrusions, Dronning

Maud Land (Antarctica). Antarct. Sci., 7: 87-97.

Neethling, D.C., 1970. South African Earth Science Exploration of

Western Queen Maud Land, Antarctica. PhD Thesis, University

of Natal, Durban, 139 pp., unpublished.

Ohta, Y., Torudbakken, B.O. and Shiraishi, K., 1990. Geology of

Gjelsvikfjella and western Muhlig-Hofmannfjella, Dronning

Maud Land. Antarctica. Polar Res., 8: 99-126.

Patiiio Deuce, A.E. and Johnston, A.D., I99 I. Phase equilibria and

melt productivity in the pelitic system: implications for the origin

of peraluminous granitoids and aluminous granulites. Contrib.

Mineral. Petrol.. 107: 202-2 18.

Pearce, J.A.. Harris, N.B.W. and Tindle, A.G., 1984. Trace element

discrimination diagrams for the tectonic interpretation of granitic

rocks. J. Petrol., 25: 956-983.

Peters, M., Lippolt, H.J., Rittmann, U. and Weber, K., 1989. Field

relations, petrography and K-Ar age determinations on mag-

matic rocks from Neuschwabenland, Antarctica. Polarforschung,

59: 35-44.

Peters, M.. Haverkamp, B.. Emmermann, R., Kohnen, H. and Weber,

K., I99 I. Paleomagnetism, K-Ar dating and geodynamic setting

of igneous rocks in western and central Neuschwabenland, Ant-

arctica. In: M.R.A. Thomson, J.A. Crame and J.A. Thomson

(Editors), Geological Evolution of Antarctica. Cambridge Uni-

versity Press, Cambridge, pp. 549-555.

Ravich, M.G. and Solov’ev, D.S., 1966. Geology and petrology of

the mountains of central Queen Maud Land (eastern Antarctica). Transactions of the Scientific Research Institute of Arctic Geol-

ogy, Ministry of Geology of the USSR, Vol. 141. (Translation-

Israel Program for Scientific Translations, Jerusalem, 1969) 348

PP. Rex, D.C., 1972. K-Ar determinations on volcanic and associated

rocks from the Antarctic Peninsula and Dronning Maud Land.

In: R.J. Adie (Editor), Antarctic Geology and Geophysics. Univ-

ertetsforlaget. Oslo, pp. 133-136.

Ring, U., 1993. Aspects of the kinematic history and mechanisms of

superpositioning of the Proterozoic mobile belts of eastern Cen-

tral Africa (northern Malawi and southern Tanzania). Precam-

brian Res.. 62: 207-226.

Roots, E.F., 1953. Preliminary note on the geology of western Dron-

ning Maud Land. Nor. Geol. Tidsskr., 32: 17-33.

Roots, E.F., 1969. Geology of western Dronning Maud Land. Expla-

nation of Plate VI, Folio 12, Antarctic Map Series, American

Geophysical Union.

Sheraton, J.W., Tingey, R.J., Black, L.P.. Offe, L.A. and Ellis, D.J.,

1987. Geology of Enderby Land and western Kemp Land, Ant-

arctica. BMR Bulletin 223, Australian Government Publishing

Service, Canberra, 5 1 pp.

Shiraishi, K. and Kagami, H., 1992. Sm-Nd and Rb-Sr ages of

metamorphic rocks from the Ser Rondane mountains, East Ant-

arctica. In: Y. Yoshida, K. Kaminumashiraishiand K. (Editors),

Recent Progress in Antarctic Earth Science. Terrapub, Tokyo,

pp. 29-36

Shiraishi, K., Hiroi, Y., Ellis, D.J., Fanning, C.M., Motoyoshi, Y.

and Nakai, Y., 1992. The first report of a Cambrian erogenic belt

in East Antarctica-an ion microprobe study of Liitzow-Helm

complex. In: Y. Yoshida, K. Kaminuma and K. Shiraishi (Edi-

tors), Recent Progress in Antarctic Earth Science. Terrapub,

Tokyo, pp. 67-74.

Stiiwe, K. and Sandiford, M., 1993. A preliminary model for the 500

Ma event in the East Antarctic shield. In: R.H. Findlay, R. Unrug,

H.R. Banks and J.J. Veevers (Editors), Gondwana, 8. Assembly,

Evolution and Dispersal. Balkema, Rotterdam, pp. 125-130.

Sun, S.-S. and McDonough, W.F., 1989. Chemical and isotopic sys-

tematics of oceanic basalts: implications for mantle compositions

and processes. In: A.D. Saunderand M.J. Norry (Editors), Mag-

matism in Ocean Basins. Geol. Sot. London, Spec. Publ., 42:

3 13-345.

Thomas, R.J., 1988. The petrology of the Oribi Gorge Suite: Kibaran

charnockitic granites from southern Natal. S. Afr. J. Geol., 91:

275-29 1. Thomas, R.J., 1989. A tale of two tectonic terranes. S. Afr. J. Geol.,

92: 306-321.

Tingey, R.J., 1991. The regional geology of Archaean and Protero-

zoic rocks in Antarctica. In: R.J. Tingey (Editor), The Geology

of Antarctica. Clarendon, Oxford, pp. l-73.

Watters, B.R., 1972. The Straumsnutane volcanics, western Dron-

ning Maud Land. S. Afr. J. Antarc. Res.. 2: 23-31.

Watters,B.R., Krynauw,J.R.andHunter, D.R., 1991. Volcanicrocks

of the Proterozoic Jutulstraumen Group in western Dronning

Maud Land, Antarctica. In: M.R.A. Thomson, J.A. Crame and

J.W. Thomson (Editors), Geological Evolution of Antarctica.

Cambridge University Press, Cambridge, pp. 41-46.

Weber, K.. Amdt, N.T.. Behr, H.J., Emmerman, R., Schenk, V. and

Tapfer, M., 1987. Age and geodynamic setting of the vulcanite

250 P.B. Gmenewcdd el al. /Precambrian Research 75 (1995) 231-250

series in Western Neuschwabenland. 5th Int. Symp. Antarctic

Earth Science, Cambridge, Abst. Vol., p. 168.

Windley, B.F.. 1992. Proterozoic collisional and accretionary oro-

gem. In: K.C. Condie (Editor), Proterozoic Crustal Evolution,

Elsevier, Amsterdam, pp. 419446.

Wolmarans, L.C., 1982. Subglacial morphology of the Ahlmannryg-

gen and Borgmassivet, western Dronning Maud Land. In: C.

Craddock (Editor). Antarctic Geoscience. The University of

Wisconsin Press. Madison, pp. 963-968.

Wolmarans, L.C. and Kent, K.E., 1982. Geological investigations in

western Dronning Maud Land, Antarctica-a synthesis. S. Afr.

J. Antarc. Res., Suppl., 2.93 pp.

Yoshida, M., Suzuki, M., Shirahata, H., Kojima, H. and Kizaki, K.,

1983. A review of the tectonic and metamorphic history of the

Liitzow-Holm Bay region, East Antarctica. In: R.L. Oliver, P.R.

James and J.B. Jago (Editors), Antarctic Earth Science. Austra-

lian Academy of Science Press, Canberra, pp. 36-39.