The final collision zone between East and West Gondwana: where is it?

Journal o f African Earth Sciences, Vol. 23, No. 3, pp. 271-287, 1996

Pergamon PII:

S0899-5362(97)00002-X

Copyright © 1997 Elsevier Science Ltd Arl rights reserved. Printed in Great Britain 0899-5362/98 $15.00 + 0.00

The final collision zone between East and W e s t Gondwana: where is it? R. M . S H A C K L E T O N The Croft Barn, Church Street. East Hendred, Oxfordshire OX12 8LA, UK

Abstract--The final collisional suture between East and West Gondwana is identified as the Nabitah Zone in Arabia. It can be traced through north central Kenya just east of the Baragoi ophiolite klippe, thence to the Cobu6 and Manica Belts, cutting across the eastern end of the Zambezi Belt, and finally to west Dronning Maud Land. There are misfits across the whole length of the suture. The collisional suturing, from 680 Ma to 550 Ma, involved compression and rotation about a hinge in the south. The rotation was less than the -270 ° or more interpreted from palaeomagnetic data. It is suggested that part of the rotation perhaps took place east of India and western East Antarctica. Copyright © 1997 Elsevier Science Ltd. All rights reserved

R6sum6--La suture qui represente la derni6re collision entre Gondwana de I'est et Gondwana de I'Ouest est identifi~e comme ~tant la Zone de Nabitah d'Arabie. On peut la suivre travers le nord de Kenya central en passant juste & I'est du klippe ophiolitique de Baragoi, de I& aux zones mobiles de Cobue et Manica, & travers I'extr~mite orientale de la chafne de Zambezi puis enfin ~ la Terre de Maud-Dronning Occidentale. II y a des manques d'accord & travers tout le long de la suture. Le collement collisional, de 680 Ma & 550 Ma, necessitait de la compression et de la rotation autour d'une charni~re au sud. La rotation etait moins que I'environ 270 ° ou plus qui a ~te deduit des donn~es pal~omagnetiques. On suggere qu'une partie de la rotation a peut-~tre eu lieu & I'est d'lnde et d'Antarctique de I'est Occidental. Copyright © 1997 Elsevier Science Ltd. All rights reserved (Received 15 March 1996: revised version received 27 April 1996)

INTRODUCTION T h e a i m o f t h i s r e v i e w is t o l o c a t e a n d t r a c e t h e f i n a l c o l l i s i o n a l s u t u r e b e t w e e n East a n d W e s t Gondwana. The Mozambique Belt (Holmes, 1951) and its apparent continuation northwards into the A r a b i a n - N u b i a n S h i e l d - t o g e t h e r k n o w n as t h e East African Orogen (Stern, 1993, 1994) separates East and West Gondwana. The M o z a m b i q u e B e l t is p o l y c y c l i c , t h e c u m u l a t i v e product of a succession of collisional orogenies. Most of these collisions were between preG o n d w a n a p l a t e a s s e m b l a g e s s u c h as t h e - 1 Ga s u p e r c o n t i n e n t o f R o d i n i a . T h e r e is as y e t no certainty as to the relative importance and e x t e n t in t h e E a s t A f r i c a n O r o g e n o f t h e s e p r e Gondwana orogenic Belts - the Ubendian ~2.01 . 8 Ga, ( W e n d t et al., 1 9 7 2 ; G a b e r t a n d W e n d t , 1 9 7 4 ) , t h e L u r i a n , - 1 . 2 - 0 . 9 G a ( S a c c h i e t al., 1 9 8 4 ; P i n n a e t al., 1 9 9 3 ) , t h e S a m b u r u a n Sabachian, -830-820 M a (?) a n d B a r s a l o i a n -

B a r a g o i a n , 6 2 0 - 5 7 0 M a (Key e t a l . , 1 9 8 9 ) . S i n c e superimposed deformations are the normal consequence of the relative weakness of a younger orogenic zone compared to the greater r i g i d i t y o f o l d e r ' c r a t o n i c ' c r u s t : all o f t h e B e l t s may be superimposed o v e r l a r g e a r e a s . Far d e e p e r e r o s i o n in t h e s o u t h m e a n s t h a t y o u n g e r c o m p l e x e s are e x p o s e d , a n d o l d e r o n e s c o v e r e d , in t h e n o r t h . T h e f i n a l s u t u r e b e t w e e n East a n d W e s t G o n d w a n a is j u s t t h e y o u n g e s t o f a s e r i e s o f s u t u r e s , m a n y n o t y e t i d e n t i f i e d . Its p o s i t i o n is c o n t r o v e r s i a l , especially in t h e s o u t h . Continuation westwards through the Zambezi and Damara Belts, or south between Natal and Dronning Maud Land, or through an unexposed a r e a f a r t h e r e a s t in D r o n n i n g M a u d L a n d , o r between India and Madagascar, or eastwards from South Madagascar, have all been p r o p o s e d . It is t h i s u n c e r t a i n t y t h a t it is h o p e d to remove.

Journal o f African Earth Sciences

271

R. M. SHACKLETON

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Figure I. M a p o f the n o r t h e r n p a r t o f the East A f r i c a n Orogen ( G o n d w a n a r e c o n s t r u c t i o n ) .

272 Journal of African Earth Sciences

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Figure 2. Map of the southern part of the East African Orogen (Gondwana reconstruction).

Journal o f African Earth Sciences

273

R. M. SHACKLETON

CRITERIA USED TO IDENTIFY THE E A S T - W E S T G O N D W A N A SUTURE The most obvious indicators for t-he East-West Gonclwana suture might seem to be that it runs between the areas identifiable as parts of East and West Gondwana and that it is the youngest of the sutures in that space. One would expect collisional deformation, but this may be quite weak compared with often much more intense deformation and metamorphism at a distance from the suture, particularly in the footwall plate; thus deformation is quite w e a k along the IndusTsangpo suture but intense in the post-collisional Himalaya. Ophiolites are often preserved only as lenses along the suture, but as much more extensive obducted sheets which are often far from the suture. Palaeomagnetists estimate the date of EastWest G o n d w a n a n collision at - 5 5 0 - 5 2 0 Ma (Li and McPowell, 1993). This is not actually the date of collision as understood by geologists but of plate c o a l e s c e n c e , o f t e n long after collision (India and Eurasia collided a t - 4 5 Ma, but their coalescence and the end of relative plate motion will be sometime in the future). The geologically estimated date of a suture relates to t h e s t a r t of c o l l i s i o n , a l t h o u g h deformation along it may continue after collision. The whole process from collision to coalescence may take more than 1 0 0 Ma. Because the geological evidence dates collision while the the palaeomagnetic evidence dates coalescence they are often difficult to correlate and appear c o n t r a d i c t o r y . D a t i n g c o l l i s i o n is i n e x a c t , whether done stratigraphically (end of ocean sediments), magmatically (change from collisional to p o s t - c o l l i s i o n a l m a g m a t i s m ) , structurally or metamorphically. Therefore one must use all the available evidence to indicate the most plausible answer. Because of the previous collisions, location of the final East-West Gondwana suture by using the extent of reworked marginal cratons or their shelf sediments may be misleading. Rifting after a previous collision of the cratons may have cut through one of them: the next collision would then be b e t w e e n t w o sides misidentified as East and West Gondwana.

POSSIBLE EAST-WEST G O N D W A N A SUTURES IN THE A R A B I A N - N U B I A N SHIELD In the Arabian-Nubian Shield there are at least five or six N e o p r o t e r o z o i c s u t u r e s (Fig. 1) representing successive collisions of juvenile island arcs, Andean arcs or continental terranes. The oldest dated arc magmatism is - 0 . 9 Ga;

2 7 4 Journal o f A f r i c a n Earth Sciences

while dates of ophiolites range from 0 . 8 7 to 0 . 6 9 5 Ga (Pallister et al., 1987; KrSner et al., 1992). These ophiolites were obducted during a succession of c o l l i s i o n s within the ' M o z a m b i q u e Ocean' b e t w e e n pre-Gondwana plates, island arcs, opposite sides of back-arc basins, or East and West Gondwana. The wide spacing of the sutures, the relatively reliable dating of ophiolites and the absence of t h e s u p e r i m p o s e d o r o g e n i e s s e e n in t h e p o l y c y c l i c domains f a r t h e r south make the Arabian-Nubian Shield the best place to look first for the final East-West G o n d w a n a suture. The disadvantage is that there are only a f e w small exposures of Neoproterozoic basement in e a s t e r n m o s t A r a b i a (in s o u t h e a s t Oman), beyond which the nearest intact supposedly East Gondwana basement is over 2 0 0 0 km farther to t h e s o u t h e a s t . F o u r p o s s i b i l i t i e s are considered: from w e s t to east, these are the Onib-Sol Hamed suture, the Nabitah suture, the Urd-AI Amar suture and a hypothetical suture b e t w e e n Madagascar and India. The Onib-Sol Hamed suture Two reasons suggest that the East-West Gondwana suture might lie along the western side of the East African Orogen: firstly, that a l t h o u g h ophiolites on the Onib-Sol Hamed suture have given older dates than the ophiolites on the Nabitah and Urd-AI Amar sutures, the estimates of collision dates on the Onib-Sol Hamed suture, 6 0 0 Ma (Stoeser and Camp, 1985) or 6 1 0 Ma (Shackleton, 1994) are slightly y o u n g e r than the estimated 6 2 0 Ma age of sutures to the east (Stoeser and Camp, 1985). Secondly, the successively younger ages of the juvenile arcs n o r t h w e s t w a r d s from the margin of older continental crust terranes e a s t of the Nabitah suture is to be expected if they evolved successively, above southeast-dipping subduction zones, t o w a r d s an ocean to the northwest, but puzzling otherwise. So the OnibSol Hamed suture is discussed as one possible candidate for the East-West Gondwana suture (Figs 1 and 2). The O n i b - S o l H a m e d s u t u r e in Egypt and Sudan

The Onib-Sol Hamed ophiolite zone trends northnortheast - s o u t h - s o u t h w e s t from the Red Sea to the Hamisama Shear Zone (Fig. 1), into which it bends southwards, to continue south as a series of ultramafic lenses for nearly 100 km (Stern e t al., 1 9 9 0 ) . There are very many o p h i o l i t e s n o r t h w e s t of t h e s u t u r e in the southern and central parts of the Eastern Desert

The final collision zone b e t w e e n East a n d West G o n d w a n a : w h e r e is it?

of Egypt (Fig. 1). Those nearest to the suture, such as Jebel Gerf, are probably klippen or thrust lenses, those farther north occur in an ophiolite m e l a n g e (Ries e t al., 1 9 8 3 ) . T h e r e is no convincing evidence for a younger suture farther north. All of these ophiolites might have been obducted from a s u b d u c t i o n zone along the Onib-Sol Hamed suture zone: the distances are less than that of the Semail ophiolite, which was obducted up to N400 km (Gansser, 1974). W e s t of t h e H a m i s a m a Shear Zone, the ophiolite zone along and north of Wadi Allaqi is generally regarded as the displaced continuation of the Onib-Sol Hamed suture (Kr6ner et al., 1987; Stern et al., 1990). For several reasons, this interpretation is rejected here:i) Continuation of the Onib-Sol Hamed suture along the Allaqi Zone would imply a net dextral displacement of - 7 0 km across the Hamisama Shear Z o n e , w h e r e a s s t r u c t u r a l e v i d e n c e appears to indicate d o m i n a n t sinistral shear (Kr6ner et aL, 1992). ii) A l t h o u g h c o m p l i c a t e d by superimposed deformations, notably a series of n o r t h w e s t s o u t h e a s t - t r e n d i n g t h r u s t s and s o u t h w e s t verging D~ folds, it can be seen, as in the Abu Swayel area (El Shazly et al., 1975; author's observations), that the overall dip of the ophiolite sheets and lenses, and the marbles not far above them, is almost flat for about 25 km across strike. This suggests obduction, rather than a true suture zone dipping d o w n into the crust. iii) The Gabgaba and Gebeit Terranes have been correlated (Stern and KrSner, 1993) and the Onib-Sol Hamed-Allaqi suture assumed to separate them from the younger Gerf Terrane to the north. H o w e v e r , the sparse available geochronological evidence from both the eastern and western parts of the Gabgaba Terrane (Stern and KrSner, 1993; Stern e t al., 1994) indicates that while these dates from the Gabgaba Terrane correlate with those of the Gerf and Midyan Terranes, they do not correlate with those from the Gebeit Terrane (Fig. 3). It is concluded that the Allaqi ophiolites, like the Gerf ophiolites and others east of the Allaqi Zone, are obducted sheets or klippen within the Gerf Terrane. A number of ophiolites (Keraf, Siniat, Atmur, Delgo), structurally overlie a metasedimentary s e q u e n c e w i t h c o n s p i c u o u s marble bands, which in turn overlies the older core of the Bayuda antiform (Fig. 1 ). This series of ophiolites may represent an antiformally folded thrust zone (not s y n f o r m a l , as m i s t a k e n l y s u g g e s t e d [Shackleton, 1994; Fig. 3]). The Delgo ophiolite has been interpreted as subducted w e s t w a r d s i.e. thrust eastwards (Denkler et al., 1994) but

if the Keraf-Siniat-Atmur-Delgo ophiolites are on a single folded thrust or shear zone, the direction of dip of the thrust n o w is no indication of direction of m o v e m e n t . A date of - 7 5 0 Ma obtained from the Delgo ophiolite (Denkler et al., 1993) falls within the range of those from t h e O n i b - S o l H a m e d s u t u r e (Fig. 3). The associated overlying metasediments are also similar. It therefore seems possible that these ophiolites were o b d u c t e d from the Onib-Sol Hamed suture zone. If so the Keraf, Siniat, A t m u r and Delgo ophiolites do not represent the Onib-Sol Hamed suture. Its continuation must be sought to the south-southwest, possibly as the Nuba ophiolite zone (Steiner, 1987) in the northeast Nuba Mountains (Fig. 1). This ophiolite includes meta-ultrabasites and metabasites overlain by a persistent ferruginous metachert, f o l l o w e d by m e t a g r e y w a c k e s . This assemblage is isoclinally folded, with a general n o r t h e a s t - s o u t h w e s t to n o r t h - n o r t h e a s t s o u t h - s o u t h w e s t trend. Immediately south of the Nuba Mountains is the presumed, here unexposed, continuation of the major Akobo Shear Zone (Fig. 1). This shear zone is only exposed in the vicinity of Akobo (Fig. 1 ), where it is seen along a distance of about 250 kin, with an exposed width of - 3 0 kin; the s o u t h w e s t limit is not seen (Davidson et al, 1976). It is clearly a major sinistral strike-slip zone. Assuming a displacement of about 200 kin, the Nuba ophiolite could be correlated, across an exposure gap of about 6 0 0 km, with t h e S e k e r r - K a r a s u k Z o n e of o p h i o l i t e s in n o r t h w e s t Kenya. Like the Nuba ophiolite, the Sekerr ophiolite s h o w s complex structures, the result of a series of superimposed phases of thrusting and folding (Vearncombe, 1983). The Nuba and Sekerr (West Pokot) ophiolites both appear to lie just east of the margin of the Nile C r a t o n (Figs 1 and 3). O t h e r n o r t h w a r d correlations of the Sekerr ophiolite zone have been suggested: with the Ingessena and Keraf ophiolites (Abdelsalam, pers. c o m m . ) or with the A k o b o - Y u b d o and Barka ophiolites (Berhe, 1990). These are unacceptable because they are incompatible with the mapped n o r t h w e s t w a r d continuation of the Sekerr Zone and because they ignore the effects of the major Akobo Shear Zone. South of Sekerr, there are f e w exposures of basement, and no ophiolites are recognized for about 5 0 0 km. However, in the Taita Hill area and s o u t h w e s t of Voi, w e l l - a u t h e n t i c a t e d ophiolites (with N-type mid-ocean ridge basalts) are recognized (Frisch and Pohl, 1986). They occur in a north-northwest - south-southeast

Journal of African Earth Sciences 275

R. M. S H A C K L E T O N

m

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DELGO SUTURE ZONE

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Figure 3. Correlation data o f some sutures and terranes in southern Egypt and northeastern Sudan. Sources." Stern and KrSner ( 1993); Stern e t al. ( 1994); and as c o m p i l e d b y Shackle ton (1994).

276

Journal o f A f r i c a n Earth Sciences

The final collision zone between East and West Gondwana: where is it?

zone named the Voi Suture Zone, some 20 km wide, traceable for about 70 kin. This zone separates the structurally underlying Kurase Group from the overlying Kasigau Group. The Kurase Group consists of m e t a g r e y w a c k e s and metavolcanics w i t h subductional magmatism. The suture zone dips east-northeast, apparently the direction of subduction. From this area, the zone presumably continues, unexposed, to the coast and thence southwards as discussed below for Zone 2. It is c o n c l u d e d that while there are many uncertainties about the continuity or course of the suture from Egypt to n o r t h w e s t Kenya, this is a possible East-West G o n d w a n a Suture. The suggested continuation southwards from Sekerr is unconvincing but no more plausible one can be suggested. The alternative is to interpret the Sekerr and associated ophiolites not as marking a suture, but as obducted from a suture to the east. It is concluded that the Onib-Sol Hamed suture is probably not the EastWest Gondwana suture. The Nabitah Zone Arabia

The Nabitah orogenic zone is distinguished by strong compressive deformation combined with sinistral strike-slip, by m e t a m o r p h i s m up to amphibolite-facies (higher than most of the Arabian Shield), and by voluminous plutonic r o c k s , m o s t l y g r a n i t e s , g r a n o d i o r i t e s and tonalites. It is up to 2 0 0 km wide and can be traced for - 1 5 0 0 km through the whole of the Shield, running into the Red Sea margin near Hajjah in Yemen. In Arabia, some ophiolites occur on both margins of the Nabitah orogenic zone, but most are on the eastern one, the Nabitah suture (the western marginal fault is k n o w n as the Unaynah suture). In the north, the Tuluhah and other ophiolites which appear to be in the Nabitah Zone give ages w h i c h indicate that they are extraneous, dragged into the zone by the sinistral shearing, from the Bir Umq suture (Pallister e t al., 1988). Ophiolitic rocks from a single locality in the Nabitah Zone have been dated at - 7 0 9 - 7 5 0 Ma (Pallister e t al., 1 9 8 8 ) . Collision on the Nabitah suture occurred at about 6 8 0 - 6 4 0 Ma, based on the t e c t o n i c setting (uncertain) of analysed and dated plutonic rocks (Stoeser, 1986). The most striking feature of the Nabitah Zone is that it separates s u t u r e - b o u n d e d terranes trending n o r t h e a s t - s o u t h w e s t to the w e s t of it from terranes and sutures trending nearly northsouth to the east. Those to the w e s t are sharply

truncated (Fig. 1). The terranes on either side cannot be matched. The Nabitah steep reverse faults presumably flatten d o w n w a r d s into major west verging thrusts as suggested by a seismic profile (Prodehl, 1985). Such thrusts could have brought originally distant terranes together. Isotopic (Pb-Pb and Nd TDM) data s h o w an abrupt and f u n d a m e n t a l c h a n g e across the Nabitah Zone from Neoproterozoic juvenile arc crust w e s t of it to crust with Palaeoproterozoic or Archaean signatures to the east (Pallister e t al., 1988, Harris e t al., 1990). Outcropping Palaeoproterozoic ( > 1 8 0 0 Ma) crust has been mapped in the south Afif Terrane. Isotopic data in Yemen (Windley e t al., 1996), in northern Somalia (Lenoir e t al., 1994) and in the HirnaHarar area in east Ethiopia (Mengist Teklay e t al., 1993) confirm that east of the Nabitah Zone and its s o u t h w e s t w a r d projection across the Red Sea Rift (Fig. 1), the underlying crust is still Palaeoproterozoic or Archaean. The continuity of the Nabitah Zone, the strong deformation, the m e t a m o r p h i s m to a higher grade than in any other suture zone in the shield and the fact that it separates t w o domains which are isotopically distinct and in which structural trends are quite different, east-west, and the oceanic MORB Pb isotopic character of the ophiolites (Pallister e t al., 1988) plainly make it a prime candidate for the East-West Gondwana suture. Other evidence that the Nabitah Zone is a transpressive suture is firstly that the huge volume of arc-type plutonic rocks along it, on the western side of the Nabitah suture, implies subduction and secondly that it is parallel to, virtually contemporaneous with and by inference tectonically related to the parallel Urd-AI Amar Andean-type suture zone some 2 0 0 km east (Quick, 1991). It has been argued (Caby, 1982) that the Nabitah Zone is not a suture but a transpressive sinistral shear zone, w i t h serpentinites which are diapirs, not ophiolites, along it. Because the isotopic misfit across it extends for at least 1500 km, a strike-slip of at least this magnitude, far larger than was envisaged by Caby, would be implied by such an i n t e r p r e t a t i o n . For the reasons given above, it is interpreted as a suture and not just a shear zone. The Nabitah Z o n e t r e n d s almost d i r e c t l y southwards (allowing for displacement on the Najd faults) for more than 1 0 0 0 km across Arabia, s o u t h w e s t w a r d s into Yemen before turning to run out to the Red Sea coast at about 16°N, s o u t h w e s t of Hajjah.

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North Somafia-Ethiopia-Kenya-south TanzaniaMozambique After closure of the Red Sea-Ethiopia-Gulf of Aden Tertiary rifts, the expected continuation from the Yemen exposures of the Nabitah Zone is located where Tertiary volcanics cover all Precambrian r o c k s . Its p r e s u m e d c o n t i n u a t i o n f a r t h e r southward remains covered for about 800 km and its probable course can only be estimated from the strikes in the f e w s c a t t e r e d b a s e m e n t exposures on either side of the projected line. At least three unexposed sinistral strike-slip faults of u n k n o w n magnitude are crossed (Fig. 1). It is not until north central Kenya that its possible equivalent can effectively be sought (Fig. 2). There the n o r t h - s o u t h 6 2 0 - 5 7 0 Ma Barsaloi Shear Zone (Mosley, 1993) seems the only possible candidate. This, like the Nabitah Zone, is a zone of strong transpressional deformation. A map of stretching lineations clearly shows major sinistral strike-slip (Shackleton, 1993). The Zone is limited quite sharply on its western side against a wide sector of the East African Orogen where the deformation is > 8 2 0 Ma old and is distinguished by refolded near-recumbent tight folds and foliation, and by stretching lineations, and locally sheath folds, transverse to the orogen (Key et al., 1989). The northern part of the Barsaloi Zone is immediately east of the Baragoi ophiolite. This is a large ( ~ 1 0 0 x 4 0 km) complexly thrust and folded synformal sheet, presumably from its form obducted rather than occurring along a suture. However within the Barsaloi Zone there are many serpentinite lenses w h i c h might be along a suture. The Baragoi ophiolite is not dated. The BaragoJ C o m p l e x is intruded by plutons w h i c h have been correlated w i t h others about 100 km south, one of w h i c h is dated (Rb-Sr) at - 8 2 0 Ma (Key et al., 1989); the structures of the Baragoi ophiolite were correlated with the 8208 3 0 Ma Samburuan-Sabachian d e f o r m a t i o n s because, like those, they are recumbent (Key e t a l . , 1989). If this correlation were accepted, the Baragoi ophiolite would be related to a much earlier tectonism than that in the Nabitah suture. However, it seems probable that the ophiolite is younger than has been supposed. The granites correlated with the - 8 2 0 Ma granites 100 km to the south differ from those to the south in being simple ovoid intrusions rather than folded sheets; there is no e v i d e n c e that - 8 2 0 Ma (Samburuan) r e c u m b e n t structures and high grade metamorphism were superimposed on recumbent obductional structures; metamorphism in the Baragoi Complex appears to be moderate: even garnet is rare (Baker, 1963). Finally, it is

2 7 8 Journa! o f A l n c a n Earth Sciences

significant that the Adola ophiolite (Fig. 2), which is structurally and lithologically similar to the Baragoi ophiolite, has been dated at 700 _+ 10 Ma (Kr6ner, pers. c o m m , ) . It is concluded that the Baragoi ophiolite is probably - 7 0 0 Ma, not more than 820 Ma as previously Supposed (Key et al,, 1989). While the Barsaloi Zone is clearly a major t r a n s p r e s s i v e shear zone, it is not easy to recognise any line in it as separating t w o distinct plates. The line shown (Fig. 2) runs just within the metapelitic Don Dol gneisses w h i c h are interpreted as deeper water sediments separating coarser sediments derived from east and west G o n d w a n a (Key e t a l . , 1 9 8 9 ) . T h i s line corresponds to that s h o w n by Mosley (1993) as a westward-directed thrust. Metamorphism up to amphibolite-facies was associated with the Barsaloian-Baragoian tectonism. The Barsaloi Zone can be traced south to about 1°S, where it curves southeastwards into the wide sinistral ductile shear zones which are on line with the A s w a shear zone in the Nile Craton in Uganda (Fig. 2). South of this shear zone, from about 4°S, the structures then again trend regularly - 1 9 0 °. until they run under younger cover at about 5°S. From there southwards, the position of the suture 'is constrained by the difference b e t w e e n exposures east and west of the exposure gap through which it runs. In south Kenya, the structures on the western side are clearly Samburuan ( - 8 2 0 - 8 3 0 Ma), similar to those described from farther north (Key et al., 1989). In north Tanzania, reworked Archaean and Palaeoproterozoic rocks have been shown to extend close to the eastern limit of exposures w e s t of Dar-es-Salaam (Maboko, 1995) and farther south to the Furua area (Coolen, 1980; Coolen et al., 1982; Fig. 2). In complete contrast to these areas west of the suture line, those east of it, in southeast Tanzania, are almost certainly a continuation of the Mesoproterozoic (1.2-0.9 Ga) Lurian orogen (Pinna et al., 1993). M o z a m b i q u e and n o r t h e a s t Z i m b a b we South and southeast of the unexposed stretch, which extends to about 11°S (Fig. 2), almost the w h o l e w i d t h of n o r t h e a s t M o z a m b i q u e exposes Lurian (1.2-0.9 Ga) structures which trend roughly north-south (Pinna eta~., 1993); these are crossed by the virtually unbroken eastnortheast - w e s t - s o u t h w e s t Lurio Belt. The Lurio Belt deformation is not precisely dated but is interpreted as - 8 5 0 Ma (i.e. not Lurian), although possibly initiated towards the close of the Lurian tectonism (Sacchi e t a / . , 1984; Pinna et al.,

The final collision zone between East and West Gondwana: where is it?

1993); it is thus contemporaneous with the main deformation in the Zambezi Belt, with which it was perhaps originally continuous. The Lurio Belt is p l a i n l y n o t c r o s s e d by t h e m a j o r Neoproterozoic East-West Gondwana suture. That suture must either run west of northeast M o z a m b i q u e , turn s u d d e n l y w e s t into the Zambezi Belt o~ die out altogether. The Cobu~ Zone, about 70 km wide, along the western side of northeast Mozambique (Fig. 2), is a zone of intense Neoproterozoic deformation (Pinna e t al., 1993). Major w e s t - n o r t h w e s t vergent t h r u s t s and r e c u m b e n t folds were followed by folds and a strain-slip cleavage with southeast vergence. This was followed by a phase of sinistral faults and shear zones. It is s u g g e s t e d (Pinna e t a l . , 1 9 9 3 ) t h a t the amphibolite-facies metamorphism during the first phase is dated at 538 Ma (U-Pb lower intercept). This date suggests that the deformation in the Cobu~ Zone is younger than that in the Barsaloi Zone. Since the date is a lower intercept age, it may only represent t h e end of t h e metamorphism. The other similarities are so convincing that it is concluded that the Cobu~ Zone does represent the continuation of the Nabitah and Barsaloi Zones. A suggestion (Pinna e t a l . , 1 9 9 3 ) t h a t the Cobu~ Zone t u r n s northwestwards into the northwest-southeasttrending Ukingan Zone on the northwest side of the Ubendian Belt is not accepted because the major thrust directions are contradictory. South from the Cobue area, the Neoproterozoic structures bend to a north-south trend but soon disappear again under cover east of Tete. The southward rather than westward bend of these structures, and their relation to the structures in the Zambezi Belt (Barton e t al., 1993; Fig. 2), disprove the idea that the East-West Gondwana suture might suddenly turn westward through the Zambezi and Damara Belts. The Tete metamorphic c o m p l e x (Barr and Brown, 1987) is at the northern side of the Zambezi Belt. Basal thrusts dipping inwards on both the northern and s o u t h e r n sides are interpreted as north- and south-vergent (Barr and Brown, 1987), indicating a flower structure, but by analogy with those associated with the Lurio Belt in Mozambique, they may be a synformally folded south-southeast vergent thrust under a klippe. The east-west Neoproterozoic Zambezi Belt separates the Archaean Zimbabwe Craton in the south from Meso- and Palaeoproterozoic terranes to the north. The earliest recognised deformation in the belt, possibly - 9 0 0 Ma, involved recumbent mylonitic zones; it was f o l l o w e d by major s o u t h w a r d t h r u s t i n g at

- 8 2 0 Ma. A later deformation phase led to northwestward back-thrusting and overfolding (Barton e t a l . , 1993). At the eastern end of the area examined by Barton e t al., the southward and southwestward plunging mineral lineations of the Zambezi Belt are abruptly replaced by lineationS plunging eastwards (Fig. 2). This change marks the western limit of the Mozambique Belt (sensu lato). This orientation of stretching lineations continues in the north-south Manica Belt along the eastern margin of the Zimbabwe Craton: it is clearly younger than the east-west trending structures in the Zambezi Belt - sufficiently younger to allow a complete change of relative plate movements. Associated with, and slightly outlasting, the west verging structures, which include many t h r u s t s and t i g h t folds, is a metamorphism which rises to upper amphibolitefacies (sillimanite zone) within about 10 km from the eastern margin of the Zimbabwe Craton (Vail, 1966). The western limit of this deformation -zone is displaced by several faults at the eastern end of the Zambezi Belt (Fig. 2), but the similarly oriented stretching lineations, similar upper amphibolite-facies metamorphism and similar westward and northwestward thrusting, indicate continuity from the Cobu6 Belt to the Manica Belt (Fig. 2). This deformation, at the eastern limit of the Zambezi Belt, occurred after 820 Ma (Barton e t al., 1993), while that in the Cobu~ Zone took place between 900 Ma and 538 Ma (Pinna e t al., 1993). The structural and metamorphic similarities and their alignment leave little doubt that they represent the same Neoproterozoic tectonic zone. The Umkondo Group, unconformable on the A r c h a e a n Z i m b a b w e C r a t o n , c o n s i s t s of s e d i m e n t s and v o l c a n i c s ; the latter, and associated sills, are dated at - 1 0 8 0 Ma (AIIsopp e t a L , 1989). Eastwards from the craton margin, in the Manica Belt, the Umkondo rocks become increasingly deformed (Vail, 1964, 1966), thrust westwards towards the craton with an eastwardplunging stretching lineation, and metamorphosed, reaching sillimanite zone amphibolite-facies within about 10 km of the craton margin. Despite the deformation and metamorphism, they are still r e c o g n i s a b l y u n c o n f o r m a b l e on a gneissic basement (Vail, 1966). There is no apparent evidence that the Umkondo metasediments were subjected to any Lurian deformation before 820 Ma. The gneisses on which they rest, at least near the intact craton, and for an unknown distance eastwards, are probably Archaean, although all are shown as Mozambican gneiss or reworked Lurian on the maps of Pinna e t al.

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( 1 9 9 3 ) and Ferrara and M a r q u e s ( 1 9 9 5 ) . W h e t h e r the line of the a c t u a l E a s t - W e s t Gondwana suture is b e t w e e n the Manica Belt, with Umkondo synforms, and the gneisses east of it (Fig. 2), or farther east in the unexposed tract, is uncertain. West Dronning M a u d Land, A n t a r c t i c a There are no e x p o s u r e s on the s o u t h w a r d projection of the suture line for about 5 0 0 km (on the Gondwana reconstruction, Fig. 2) until Dronning Maud Land. There, across a 30 km wide thrust belt, there seems to be a major misfit. The terrain west of the misfit zone, in w e s t D r o n n i n g M a u d Land, is a s t a b l e c r a t o n i c platform, considered to be part of the Kaapvaal Craton. It consists of a small patch, exposed on the Annadag-Stoppane nunataks, of Archaean rocks (the G r u e n e h o g n a Province), overlain (originally unconformably) by the sediments and voicanics of the Ritscherfyla Supergroup. These are correlated on lithological and palaeomagnetic evidence with the - 1 0 8 0 Ma Umkondo Group of Zimbabwe (Moyes and Knoper, 1995). In west Dronning Maud Land, but south of the cratonic province, rocks are correlated on lithological, structural, metamorphic and most conclusively on geophysical evidence (Corner, 1995), with the - 1 . 0 Ga Namaqua-Natal Belt. Exposures in this area are poor but the trends clearly confirm that this area in west Dronning Maud Land ~s a direct continuation of the Natal Belt. To the east of the misfit zone, stretching for about 1000 km through the MOhlig Hoffman Mountains to Sor Rondane in central Dronning Maud Land, is a little k n o w n belt of high grade (often granulite facies) metamorphic rocks which a p p a r e n t l y have a general e a s t - w e s t trend (Groenewald eta/., 1991, Kamenev, 1993). The rocks in the belt are thought from from their lithostratigraphy, metamorphic history and age to correlate with the -1 Ga Namaqua-Natal Belt (Groenewald et al., 1991). Thus in west Dronning Maud Land a misfit zone a p p e a r s to t r u n c a t e or d i s p l a c e t w o similarly-trending belts so that they are now about 400 km out of line with each other. Within the misfit zone, there are rocks that are similar, except in trend, to those of the Natal Belt. It might thus appear that the 'misfit zone' is simply a sinistral flexure connecting t w o parts of a single belt (although there is at present no evidence that the t w o belts can be correlated. However, the fact that there are t w o major thrusts within the misfit zone, across which structures change suddenly, shows that it is not just a flexure; but

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the most significant evidence is that indications of t r a n s p o r t d i r e c t i o n on t h e t h r u s t s w a s n o r t h w e s t w a r d s ( M a t t h e w s , 1981; Jackson, 1995; Fig. 2), while in the Natal Belt the transport direction was towards the northeast (Jacobs and Thomas, 1994). This difference proves that the thrust tectonics in the Natal Belt and those in the misfit zone cannot, as it is now oriented, be the result of relative motion b e t w e e n the same t w o plates. S u b s e q u e n t t e c t o n i c rotation is implied. The truncation of structures by the thrusts in the misfit zone clearly shows that these are y o u n g e r than those of the Natal Bett (and presumably than those of the central Dronning M a u d Land Belt). The a c t u a l d a t e of the thrusting in the misfit zone is still uncertain but t h e r e is ' o r o g e n e s i s ' , s u g g e s t e d to be - 1 . 0 Ga and - 0 . 5 Ga (Ferrar, 1995; Jackson, 1995). There is no evidence that the deformation occurred at - 0 . 5 Ga rather than - 0 . 6 Ga, the date here t a k e n as t h a t of the East-West Gondwana suture. However, as pointed out to the author by Alfred Kr6ner, a collisional suture may be diachronous, and complex. The exact position of the East-West Gondwana suture might be along either of the t w o thrusts or, less probably, b e t w e e n H.U. Sverdrupfjella and the MQhlig-Hoffman range. Because the eastern thrust is structurally higher, western propagation is most likely so the eastern one is favoured. G e o p h y s i c a l w o r k (Corner, 1 9 9 4 , 1 9 9 5 ) demonstrates the continuity, on the Gondwana reconstruction, from the - 1 . 0 Ga Namaqua-Natal Belt, across the Falkland Plateau microplate, into west Dronning Maud Land. The Kirwan magnetic anomalies which show the continuity of pattern are attributed to deep-crustal magnetization and c r a t o n - d i r e c t e d t h r u s t s . This c o n t i n u i t y of g e o p h y s i c a l p a t t e r n , s h o w n by the Kirwan anomalies, continues for about 500 km into west Dronning Maud Land. Then "the east-trending Kirwan anomalies largely disappear in the regton of Neumayerskarvet and again continue into the H.U. Sverdrupfjella with a changed direction (NNE)" (Corner, 1994). The position of this abrupt change in the trend of the magnetic anomalies is exactly where the line of the EastWest Gondwana suture is postulated on the basis of the structural evidence of a misfit presented here. Despite this evidence, the suture is s h o w n on Fig. 2 along the n o r t h w e s t e r n of the pair of N e o p r o t e r o z o i c thrusts near Heimfrontfjella (H, Fig. 2), firstly because it marks a much more conspicuous structural discontinuity and secondly because it separates areas yielding

The final collision zone between East and West Gondwana: where is it?

1.0 Ga K-Ar ages from those with 0.5 Ga K-Ar ages (Jacobs e t al., 1 9 9 5 ) . The Natal Belt magnetic anomalies continue beyond this thrust. However, these Kirwan magnetic anomalies are thought to originate deep in the crust (Corner, 1994). The lineations along the thrusts plunge at about 30 ° to the southeast (Grantham e t aL, 1995) and the thrusts probably flatten below surface. It is s u g g e s t e d that the Natal Belt structures continue for some distance underneath the thrusts. It is, of course, still possible that the East-West Gondwana suture is farther east. In the northern part of the misfit zone, there is a wedge of low grade rocks, separated by thrusts from a foreland fold and t h r u s t Belt to the s o u t h e a s t ( M o y e s and Knoper, 1 9 9 5 ) . The foreland fold and thrust belt and the low grade rocks appear comparable to those in the Manica Belt, adjacent to the Z i m b a b w e Craton. The Urd-AI Amar Zone The Urd-AI Amar Zone must be considered a possible candidate as the East-West Gondwana suture because the single reliable date, from the Urd ophiolite, is 6 9 4 + 8 Ma, which is slightly younger than those from the Nabitah Zone. The estimated date of collision, 6 7 0 - 6 3 0 Ma, is also slightly younger than that of the Nabitah Zone 6 8 5 - 6 4 0 Ma (Stoeser and Stacey, 1988). It has however also been suggested that the Nabitah and Urd-AI A m a r Zones r e p r e s e n t a single collisional event. Nevertheless, the possible southern continuation of the Urd-AI Amar Zone is discussed below. Arabia-Yemen-northern Somalia To the south, the Urd-AI Amar Zone disappears under Phanerozoic cover, and basement is not exposed again until Yemen, where, east of the Nabitah Zone, there are many ophiolites or ophiolite-like rocks, recognised in three zones, b e t w e e n w h i c h gneisses predominate. From these gneiss terranes, Lower Proterozoic and Archaean Nd TDM dates have been obtained ( W i n d l e y e t a l . , 1 9 9 6 ) , s h o w i n g t h a t preNeoproterozoic crust is either exposed or subsurface for at least 6 0 0 km east of the Nabitah suture. It is not clear w h e t h e r the Urd-AI Amar Zone should be correlated with a zone running towards Sana'a, as tentatively proposed (Windley e t al., 1996) or with one farther east. However, w h e n allowance is m a d e f o r t h e N a j d F a u l t displacements, the distance between the Nabitah and Urd sutures, and the mapped trends to the east of the Nabitah suture, it seems more

probable that the Urd-AI Amar Zone correlates with the AI Bayda arc (Fig. 1). It might even continue as the AI Makalla arc still farther east, which correlates with the AI Maydh ophiolite complex in north Somalia. Thrust westward onto this AI Maydh Complex is the Inda Ad Group with a possible basal conglomerate, just as the strikingly similar Abt Group, with possible basal conglomerate, is thrust w e s t against the Urd ophiolite in Arabia. Difficulties of correlation are aggravated by the complex structures which make the d i s t i n c t i o n even b e t w e e n gneiss t e r r a n e s and i s l a n d arcs in Y e m e n v e r y speculative. H o w e v e r , despite the analogies between the Urd-AI Amar Zone and the AI Maydh Zone, the most plausible equivalent of the UrdAI Amar Zone is t h o u g h t to be the AI Bayda arc. Projection of the AI Bayda arc southwestwards and a l l o w i n g f o r t h e e s t i m a t e d s i n i s t r a l d i s p l a c e m e n t of b e t w e e n 100 and 170 km (Berhe, p e t s . c o m m . ) on the unexposed Marda fault, indicates correlation with the ophiolitic Soka Group (Fig. 1). From the s o u t h w e s t end of the 40 km long Soka Group exposure, the zone may then possibly be correlated, under a 200 km stretch of lava, with the Adola area of southern Ethiopia and the Moyale area (Fig. 2) on the Ethiopia-Kenya border. In the Adola area, over a width of almost 100 km, there are four ophiolitic masses, the largest of which, the Adola mass, s t r e t c h e s - 1 0 0 km n o r t h - s o u t h . All t h e i r b o u n d a r i e s are t h r u s t s , b u t w h e t h e r t h e ophiolites are synformal (klippen) or, possibly in the case of Adola, a flower-structure (Tolessa e t al., 1991) is uncertain. The Kenticha mass is clearly a klippe: the bounding thrusts define it as a north-south synform (Beraki e t al., 1989). The ophiolites of the Adola Group are not dated: but a date of 7 0 0 + 10 Ma has recently been o b t a i n e d from the M o y a l e o p h i o l i t e (Alfred Kr6ner, pets. comm.). This date is indistinguishable from the 694+_8 Ma date of the Urd ophiolite. Structures are complex, with earlier, probably obductional, recumbent folds and t h r u s t s over w h i c h s t r o n g n o r t h - s o u t h trending transpressive structures are superimposed. These structures are correlated w i t h the - 6 2 0 - 5 7 0 Ma Barsaloian-Baragoian structures of north central Kenya (Mulugeta Alene and Barker, 1993) Transport direction on the t h r u s t s is u n c e r t a i n . There is no clear evidence of a suture: rather the thrust geometry suggests that the whole complex was obducted. This north-south zone of ophiolites continues a short distance south from M o y a l e before disappearing under younger cover, and there are no more exposures to the south of this in Kenya

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(Fig. 2). If the line is continued using trends to the west as guide, the next exposures would be in Madagascar. There, across the major sinistral Ranotsara Shear Zone, a possible continuation might appear to be the Vohibory Belt in southwest Madagascar (Windley et aL, 1994). This belt, of which a width of only about 50 km is exposed, differs from others to the east of it. It has given (so far) only Neoproterozoic ages (between 600 and 900 Ma), although the real age is still uncertain. A Rb-Sr age of 811 +_ 153 Ma from the Serie de Vohibory is thought to represent the first metamorphism (Cahen and Snelling, 1984), and perhaps the main deformation. This is later than the 1.0-0.9 Ga anorthosites and probably ended before the 0.65-0.55 Ga granulite-facies metamorphism (Morel et al., 1995). The zone is also distinguished in containing a large number, at least 55, of chromite-layered peridotite lenses, gabbros and pillow-bearing amphibolite (Windley et al., 1994). There are also in the Vohibory Belt many bands and lenses of marble and quartzite and abundant migmatitic ortho- and paragneisses, all complexly folded. The Vohibory Belt is bounded to the east by a now-steep shear zone w h i c h , like o t h e r s in s o u t h w e s t Madagascar, is interpreted as an east-vergent thrust (Morel e t a l . , 1995), athough prevously as a dextral shear zone (Windley et al., 1994). Metamorphism in the Vohibory Belt ranges from greenschist to high-P granulite facies, the latter dated at 650-550 Ma (Windley et al., 1994; Ashwal et al., 1995). Because only Rb-Sr dates are available, the real age of the Vohibory Belt is uncertain. The natural continuation of this belt seems to be into the Lurio Belt in Mozambique (Fig. 2). The Chiure Supergroup in the Lurio Belt contains essentially the same lithologies as those in the Vohibory Belt (Sacchi et al., 1984; Pinna et al., 1993; Windley etal., 1994) and the metamorphic grade is also similar. They differ in that the ages, both U-Pb and Rb-Sr in the Lurio Belt, are mostly between 1.2 and 0 . 9 Ga but c h a r n o c k i t i c gneisses now in the Mugebe klippe are dated at - 6 1 4 _+ 16 Ma (Sacchi and Kr6ner, pets. comm.), whereas dates in the Vohibory Belt (Rb-Sr) are 0.9-0.6 Ga; the trends also differ (Fig. 2). Despite their a p p a r e n t l y d i f f e r e n t oldest ages and different trends, it seems from the regional tectonic pattern (Fig. 2) and because of the similarities discussed above, that the Vohibory Belt probably continues as the Lurio Belt. If so, the Vohibory Belt cannot represent the eventual southern continuation of the Urd-AI Amar suture zone, because the Vohibory-Lurio correlation apparently implies that the deformation in the

2 8 2 Journal o f African Earth Sciences

Vohibory Belt is older than that in the Urd-AI Amar Zone; moreover their transport directions are opposite. However, if the Neoproterozoic age for the Lurio Belt is confirmed, an important reinterpretation will be needed. The Urd-AI Amar suture might run south through the Vohibory Belt, with a failed arm in the Lurio Belt, and a main continuation into East Antarctica. A suture between Madagascar and India? The Archaean of southern India is conspicuously different from that of Madagascar, suggesting that there might be a major suture between them (Fig. 2). The main part of the southern Indian D h a r w a r Craton c o n s i s t s of Neoarchaean granitoids and greenschist-facies greenstone belts which, at least in some places, can be clearly seen to be unconformable on older, > 3 . 0 Ga, gneissose basement. The general trend of the greenstone belts is north-northwest - southsoutheast (Fig. 2). In the south, the grade of m e t a m o r p h i s m rises rather suddenly up to granulite facies, along the northern margin of an east-west Neoarchaean (-2.6 Ga) complex orogenic belt. South, but not north, of the P a l g h a t - C a u v e r y f a u l t t h e r e is a general Neoproterozoic granulite facies overprint (Harris etal., 1995). In Madagascar, no Archaean greenstone belts have been recognised (but they may be exposed in the north IKrhner, pers. c o m m . ] ) ; trends are irregular but dominated by a northsouth axial 100 km wide dextral ductile shear zone, much of it at granulite facies. This shear zone is interpreted as Neoproterozoic (Windley et aL, 1994). However it appears to be older than 734 Ma, (Rb-Sr age of the post-tectonic Carion P l u t o n ) , p r o b a b l y older t h a n 8 8 5 Ma, (metamorphic age), perhaps older than 1191 Ma, (age from the Vendrazo migmatite) and possibly even very much older, since the zone includes rocks still yielding Archaean ages (Cahen and Snelling, 1984). In the zones on either side of this axial zone, there are areas where the north-south trends swing towards east-west, as though this was their original Archaean trend, now generally obliterated by later north-south structures. However some of these east-west trends are here interpreted as reflecting lateral ramps associated with Mesoproterozoic deformation w h i c h p r o d u c e d s i m i l a r t r e n d s in the Mesoproterozoic metasediments west of the axial zone (Fig. 2). There is no structural or metamorphic evidence of a post-Archaean suture zone, either along the eastern side of Madagascar or the western side of the south India Craton. It is, however, quite

The final collision zone between East and West Gondwana: where is it?

likely that there is a fault. If so, it may continue, displaced sinistrally by a northwest-southeast fault, into Antarctica (Fig. 3).

DISCUSSION Palaeomagnetic interpretations: reservations and suggestions Acceptance of the palaeomagnetic evidence that there was a major Mozambique ocean, widest in the north, between East and West Gondwana, d o e s n o t m e a n t h a t all of t h e s u p p o s e d implications are acceptable. In particular, the argument (Li and McPowell, 1993) that East and West Gondwana must have been completely separated by an ocean to allow their relative rotation through more than 270 ° , seems irreconcilable with the geological evidence. There is, according to the evidence assembled here, only a relatively small misfit ( - 2 0 0 km) b e t w e e n the Namaqua-Natal Belt and the central Dronning Maud Belt (if they were originally continuous). It is inconceivable that the t w o continental plates could have moved apart, rotated separately, and then reunited so close to their previous positions. There is even less apparent misfit b e t w e e n the Lurio and Zambezi Belts - again if they were originally continuous. One control, in looking to resolve the conflict between g e o l o g i c and p a l a e o m a g n e t i c interpretations, is the w i d t h of the Mozambique ocean, because this d e t e r m i n e s the rotation n e e d e d to c l o s e it, and g i v e rise to t h e collisional tectonics. On some reconstructions, it is s h o w n as e n o r m o u s : an angular span of - 2 2 0 ° at 7 5 0 Ma (Young, 1 9 9 5 ) , - 2 7 0 ° at 550 Ma (Li and McPowell, 1993) o r - 2 1 0 ° at the start of the Cambrian (Dalziel, 1991). In locating the suture, h o w e v e r , ~t is more important to k n o w the minimum possible angular span of the ocean. The total present width of juvenile arcs, b e t w e e n the Nabitah suture and the eastern margin of the Nile Craton in northeast Egypt is probably 1 0 0 0 km. More arc magmatism was added to the crust east of the Nabitah suture. Thus the width of the ocean there could not have been less than say 2 0 0 0 km. It is about 5 0 0 0 km from the northern margin of the arcs to the Zambezi Belt and about 1 0 0 0 km farther to west Dronning Maud Land. Closing the ocean through 25 ° about a hinge at the eastern end of the Zambezi Belt or 20 ° about a hinge near west Dronning Maud Land might be enough to explain t h e arc m a g m a t i s m and t h e c o l l i s i o n a l d e f o r m a t i o n . The c o r r e s p o n d e n c e of t h e palaeomagnetic data from the Kaapvaal and west Nile Ccratons appear to exclude clockwise rotation

of the Nile Craton away from the Kaapvaal Craton (other than a quick open and shut rotation), so a hinge there w o u l d imply that India rotated r e l a t i v e l y - 2 5 ° a w a y f r o m w e s t e r n East A n t a r c t i c a or both a w a y from eastern East A n t a r c t i c a during t h e N e o p r o t e r o z o i c : not impossible, but not supported by any obvious evidence. The alternative, a rotation of at least 20 ° about a hinge to the south, in or near west Dronning Maud Land, seems more probable. This does not seem incompatible with the amount of deformation in the south. A possible latestage southern hinge position farther west is mentioned later.

Match and mismatch across the suture: interpretation Very detailed geological and geophysical studies d e m o n s t r a t e c o n t i n u i t y , at -1 Ga, of t h e Namaqua-Natal Belt from Natal to west Dronning Maud Land (Groenewald e t a / . , 1991; Corner, 1994, 1995). The fit of the t w o sides there is very tightly constrained. The exact fit of East and West G o n d w a n a is less certain. Three alternatives were recently figured (de Wit e t a / . , 1995). The t w o most recent ones, using some geological constraints, perhaps fit Dronning Maud Land so close to South Africa that there is no room for the continental crust indicated by dredged samples from the 2 0 0 - 3 0 0 km wide Mozambique Ridge b e t w e e n them, but Corner (1995) excludes this ridge because it shows none of the magnetic anomalies which are otherwise continuous on each side. The slightly modified reconstruction of Fig. 2 is not constrained to fit the - 1 . 0 Ga s t r u c t u r e s of Natal and w e s t Dronning Maud Land, but to fit Neoproterozoic Gondwana structures, in particular to align the major Neoproterozoic sinistral strike-slip A s w a shear zone in Uganda and its ductile shear zone in Kenya, the Ranotsara Shear Zone through M a d a g a s c a r , the A c h a n k o v i l Shear Zone in southern India and t w o supposed faults in east Dronning Maud Land. It is also controlled partly by the southeastern India-Antarctica fit. In the s o u t h , t h e d i s t a n c e b e t w e e n A f r i c a and A n t a r c t i c a is c o n t r o l l e d p r i m a r i l y by t h e geophysical data of Corner (1994, 1995). One result is a fit of the western Dronning Maud Land Archaean Terrane to the Kaapvaal Craton. This fit, independently derived from evidence to the north, implies that this Archaean Terrane was part of West Gondwana. It is east of this Archaean Terrane that there appears to be a misfit and it is here that the suture between East and West G o n d w a n a is t h o u g h t to be located.

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If the evidence of transport direction, almost normal to the thrusts in w e s t Dronning Maud Land, is accepted, there was no significant sinistral displacement. The misalignment (if they were f o r m e r l y continuous) of the Natal and central Dronning Maud Land Belts might be attributed to a substantial thrust displacement - perhaps even as much as 1000 km. A still larger westward displacement (plate c o n v e r g e n c e ) is i m p l i e d , 1 0 0 0 km n o r t h , between the Zambezi Belt and the Lurio Belt of northeast Mozambique. This would leave ample room for the w e s t - s o u t h w e s t - east-northeast trending deformation south of, and contemporaneous with, the Lurio Belt, to die out before reaching the Zimbabwe Craton. Several interpretations of the misfit across the East-West Gondwana suture may be considered. The first is to accept the former continuity of the Natal and central Dronning Maud Belts and of the Lurio and Zambezi Belts. These small m i s f i t s s e e m u n l i k e l y if East and W e s t Gondwana were completely separated before colliding, as apparently required by palaeomagnetic evidence; so the palaeomagnetic evidence would need to be re-interpreted. A second interpretation is that the Natal Belt bends to continue northwards into the Lurio Belt. This implies that the east-west trends in the central Dronning Maud Belt cross e a r l i e r - 1 Ga north-south structures. The east-west structures in the central Dronning Maud Belt would be Neoproterozoic, parallel to the major thrust in Sri Lanka, on which Neoproterozoic southward movement, parallel to the fault trend, is intense. This deformation is attributed to translation on a lateral ramp (Kleinschrodt, 1994), but it may represent Neoproterozoic reactivation of an older east-vergent (up-dip) thrust. Parallelism of the fault with the central Dronning Maud Land Belt is therefore difficult to use as an indicator of the age of structures in that belt. However, the major objection to correlation of the Natal and Lurio Belts is that the transport directions in them appear to be incompatible. A third interpretation is that there was a triple junction between the Natal, central Dronning Maud Land and Lurio Belts. This triple junction could have migrated northwards from its initial position. This interpretation would be difficult to reconcile with the postulated suture line. Finally it might be argued that there is no c o r r e l a t i o n at all a c r o s s t h e E a s t - W e s t Gondwana suture. Recognition of the true interpretation requires more data, especially from central Dronning Maud Land, and more palaeomagnetic data from

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India and the western parts of East Antarctica. At present the first interpretation, correlations across a quite small misfit, seems more likely. It almost certainly implies a southern hinge, not independent rotation. However, rejection of any correlations across the misfit l i n e and acceptance of the palaeomagnetic evidence for complete separation cannot yet be ruled out. A latest Proterozoic r o t a t i o n a l pole?

westward

shift

of t h e

While rotation about a pole in the region of west Dronning Maud Land or Natal seems to fit the subductional and collisional structures in the East African Orogen, it may be that at perhaps - 6 5 0 Ma the pole of rotation shifted westwards, possibly as much as 2 0 0 0 km. Such a position might have been the pole of rotation of the a p p r o x i m a t e l y n o r t h w e s t - s o u t h e a s t sinistral s t r i k e - s l i p f a u l t s and s h e a r z o n e s w h i c h represent the major deformations from - 6 4 0 to - 5 5 0 Ma a c r o s s much of e a s t e r n A f r i c a . Relaxation of compression, injection of dyke s w a r m s and erosion to near-peneplain were completed right across northern A f r i c a and southeast Asia before the deposits of the still nearly flat and little-deformed Lower Cambrian w e r e laid d o w n a c r o s s t h e p l a n e d - d o w n Proterozoic structures (Millson e t a l . , 1996). On the opposite, southern, side of Gondwanaland, deformation associated with the 0.5 Ga Ross Orogen affected a large region. It was quite distinct from the earlier north-south trending East African Orogeny.

SUMMARY

Of four possible East-West Gondwana sutures in the East African Orogen, the only acceptable one runs from the Nabitah Belt to west Dronning Maud Land. The small Archaean Terrane and its patch of - 1 . 0 Ga sedimentary cover was part of the West Gondwanan Kaapvaal Craton. The date of collision, in the geological sense, across the Nabitah Zone, and the associated Urd-AI Amar Zone, was between 680 and 630 Ma. It may have been diachronous, later in the south. Collision in the palaeomagnetic sense f i n a l p l a t e c o a l e s c e n c e and t h e end of compressional deformation - was at - 5 5 0 Ma. After relaxation, extension, uplift and erosion, the Lower Cambrian sediments were deposited unconformably on the East African Orogen in Arabia and across north Africa. There are misfits across the suture. In the north, su[ures between juvenile arcs wesL of

The final collision zone between East and West Gondwana: where is it?

the s u t u r e are o b l i q u e l y t r a n s e c t e d by t h e Nabitah Belt. The crust on the eastern side of the suture is isotopically quite different. In it, Anclean arcs are underlain by Archaean or Lower Proterozoic basement. In Kenya, the suture separates metasediments from East and West G o n d w a n a . Farther south the Ubendian Zone has no visible east-side c o u n t e r p a r t and the Lurio Belt seems not to fit the Lufilian w e s t of the suture. Neoproterozoic (-850 Ma) s t r u c t u r e s parallel to, and south of, the Lurio Belt, have no c o u n t e r p a r t w e s t of the suture. In w e s t Dronning M a u d Land, the NamaquaN a t a l B e l t is c u t by w e s t w a r d thrusts incompatible with the northeast-vergent thrusts in Natal. The central Dronning Maud Land Belt may be the displaced c o u n t e r p a r t of the Natal Belt. Direct continuation of the Natal Belt northward into the Lurio Belt is incompatible with the trend of the central Dronning Maud Belt, and with east verging recumbent structures right across northeast Mozambique. A triple junction of the Natal, central Dronning Maud Land and Lurio Belts is a possibility. If the Natal and central Dronning Maud Land Belts are correlated, their misalignment, and their trends oblique to the w e s t w a r d transport on t h e t h r u s t s , i m p l i e s r e l a t i v e w e s t w a r d collisional transport of the East Gondwana plate of perhaps 1 0 0 0 km. This is consistent with the near-alignment of the correlated ( - 8 5 0 Ma) Lurio and Zambezi Belts, because their trends are almost parallel to the collisional transport. H o w e v e r , if the Lurio Belt is s h o w n to be y o u n g e r ( - 0 . 6 Ga), its correlation w i t h the Z a m b e z i B e l t is u n l i k e l y . T h e s i n i s t r a l d i s p l a c e m e n t , as well as major t r a n s v e r s e t h r u s t i n g and c o m p r e s s i o n , on the Nabitah suture is attributed to a late-collisional change to n o r t h w e s t w a r d transport. This change may i m p l y a large w e s t w a r d m i g r a t i o n of t h e rotational pole. The rotational closure of the M o z a m b i q u e ocean and the collisional suturing of East and West Gondwana involved relative rotation about a pole in the Dronning Maud region. There may have been no oceanic separation there, but rather compression at a hinge. If so, because of the limitation of a hinge, the angle of rotation is thought to have been much less than inferred from palaeomagnetic evidence. Palaeomagnetic data from India and western East Antarctica are so scanty that it is unjustifiable to assume that they were part of a single East Gondwana plate. Part of the relative rotation may have been f a r t h e r east. A l t e r n a t i v e l y , if t h e r e is no

recognisable correlation across the misfit line, a wide ocean and independent rotation of East and West Gondwana could be accepted.

ACKNOWLEDGEMENTS The author is particularly grateful to Alfred KrOner, Rosalino Sacchi and Bob Thomas for corrections, suggestions and information. He is also very grateful to John Taylor for drafting the maps and to Peigi for her patience and seemingly endless work.

REFERENCES AIIsopp, H. L., Kramers, J., Jones, D. I. and Erlank, A. V. 1 9 8 9 . The age of t h e U m k o n d o Group, e a s t e r n Z i m b a b w e , and i m p l i c a t i o n s for p a l a e o m a g n e t i c correlations. South African Journal Geology 93, 11-19. Ashwal, L. D., Morel, V. P. and Hamilton, M. A. 1995. RbSr and Sm-Nd geochronology of massif-type anorthosites, southwest Madagascar. Geological Society South Africa Centennial Geocongress (1995). Extended Abstracts 1, 206-209. Baker, B. H. 1963. Geology of the Baragoi Area. Geological Survey o f Kenya. Report 53. 74p, map. Barr, M. W. C. and Brown, M. A. 1987. Precambrian gabbro a n o r t h o s i t e c o m p l e x , Tete Province, M o z a m b i q u e . Geological Journal (thematic issue), 22, 139-159. Barton, C. M., Carney, J. N., Crow, M. J., Evans, J. A. and S i m a n g o , S. 1 9 9 3 . G e o l o g i c a l and s t r u c t u r a l framework of the Zambezi Belt, northeastern Zimbabwe. In: Gondwana Eight. (Edited by Findlay, R. H., Unrug, R., Banks, M. R. and Veevers, J. J.) Balkema, Rotterdam. Beraki, W. H., Bonavia, F. F., Getachew, T., Schnerold, T. and Tarekegh, T. 1989, The Adola fold and thrust Belt, southern Ethiopia: a re-examination with implications for Pan-African evolution. Geological Magazme 126, 647-657. Berhe, S. M. 1990. Ophiolites in northeast and east Africa: implications for Pan-African crustal g r o w t h . Journal Geological Society London 147, 41-57. Caby, R. 1982. Petrological and structural observations from the Nuqrah area and some remarks concerning the crustal history of the northern Najd Province, Saudi Arabia. In: Pan-African Crustal Evolution in Arabia and northeast Africa. (Edited by AI Shanti, A. M.) Precambrian Research 16, A 1 1 - A 1 2 . Cahen, L. and Snelling, N. J. 1984. The Geochronology and Evolution o f Africa. Clarendon Press, Oxford. 512p. Charsley, T. J. 1987. Geology o f the Laisamis area. Report 106. Ministry of Environment and Natural Resources, Republic of Kenya. Coolen, J. J. M. M. M. 1980. Chemical Petrology of the Furua granulite complex, southern Tanzania. Academische Proeschrift. Vreije Universiteit te Amsterdam. 258p. Coolen, J. J. M. M. M., Priem, H. N. A., Verdurmen, E. A. Th. and Verschure, R. H. 1982. Possible zircon U-Pb evidence for Pan-African granulite-facies metamorphism in t h e M o z a m b i q u e Belt of s o u t h e r n T a n z a n i a . Precambrian Research 17, 31-40. Corner, B. 1994. Geological evolution of western Dronning Maud Land within a Gondwana framework: Geophysical subprogramme. Final project report to DEA, Pretoria. 21 p. Corner, B. 1995. The Namaqua-NataI-Maudheim Belt: geophysical signatures within Gondwana. Geological Society South Africa Centennial Geocongress (1995). Extended Abstracts 1, 210-213.

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Dalziel, W. D. 1991. Pacific margins of Laurentia and East Antarctica-Australia as a conjugate rift pair: Evidence and implications for an Eocambrian supercontinent. Geology 19, 598-601. Davidson, A., Shiferaw, A., Davies, J. C., Moore, J. M. and Taferra, M. 1976. Preliminary Report on the Geology and Geochemistry of parts of Gemu Gofa, Kefa and Iluabbor Provinces, Ethiopia. (Ethiopian Government M i n i s t r y of Mines and Power). Omo River Project Preliminary Report I~o. 2. 28p. Denkler, T., Franz, G., Schandelmeier, H., Harms, U., Darbyshire, D. P. E. and Pilot, J. 1993. Evolution of the s o u t h - w e s t e r n part of the A t m u r - D e l g o suture. In: Geotectonic Research in Northeast Africa pp82 89. (Edited by T h o r w e i h e , U. and S c h a n d e l m e i e r , H.) Balkema, Rotterdam. Denkler, T., Franz, G. and Schandelmeier, H. 1994. Tectonometamorphic evolution of the Neoproterozoic Delgo suture zone, N o r t h e r n Sudan. Geo/ogische Rundschau 83, 578-590. De Wit, M., Vitali, S. and Ashwal, L. 1995. Gondwana reconstruction of the East Africa-Madagascar-lndia-Sri Lanka-Antarctica fragments revisited. Geological Society South A f r i c a C e n t e n n i a l G e o c o n g r e s s E x t e n d e d Abstracts, 1 218-221. El Shazly, E. M., Bassyouni, F. A. and Abdel Khalek, M. I. 1975. Geology of the Greater Abu Swayel Area. Egyptian Journal Geology 19, 1-41. Ferrar, G. 1995. Orogenic implications deduced from the metamorphic history of the A r m a l s r y g g e n , western Dronning Maud Land, Antarctica. Geological Society South Africa Centennial Geocongress (1995). Extended Abstracts 1, 222-225. Frisch, W., and Pohl, 1986. Petrochemistry of some mafic and ultramafic rocks from the Mozambique Belt, SE Kenya. M i t t e i l u n g e n . (~sterretchisch g e o l o g i s c h e Gese/Ischaft. 78, 97 114 G a b e r t , G. and W e n d t , E. 1 9 7 4 . D a t i e r u n g y o n granitischen gesteinen im Dodoman und UsagaranS y s t e m und im der N d e m b e r a - S e r i e ( T a n z a n i a ) . Geologische Jahrbuch, B l l , 3-55. Gansser, A. 1974. The ophiolite melange, a world-wide problem on Tethyan examples. Ecologae geologicae Helvetiae 67, 459 507. Grantham, G. H., Jackson, C., Moyes, A. B., Groenewald, P. B., Harris, P. D., Ferrar, G. and Krynauw, J. R. 1995. Tectonothermal evolution of the Kirwanveggan-H.U. Sverdrupfjella areas, Dronning Maud Land, Antarctica. Precambrian Research 75, 209-229. Groenewald, B., Grantham, G. H. and Watkeys, M. K. 1991. Geological evidence for a Proterozoic to Mesozoic link b e t w e e n southeast Asia and Dronning Maud Land, Antarctica. Journal Geological Society London 148, 1115-1123. Harris N. B. W., Gass, I. G. and Hawkesworth, C. J. 1990. A geochemical approach to allochthonous terranes: a PanAfrican case study. Philosophical Transactions Royal Society London A331, 533-548. Harris, N. B. W., Bartlett, J. M. and Santosh, M. 1995. Crustal evolution of high-grade metamorphism in the South India s e g m e n t of G o n d w a n a l a n d . Geological Society South Africa Centennial Geocongress (1995). Extended Abstracts 1, 377. Holmes, A. 1951. The sequence of Pre-Cambrian orogenic belts in south and central Africa. 18th International Geological Congress, Great Britain 1948. Part XlV, 254269. Jackson, C. 1995. Colinear deformation within the MesoNeoProterozoic Kirwanveggan terrain of western Dronning Maud Land, East Antarctica - implications for tectonic models. Geological Society South Africa Centennial Geocongress (1995), Extended Abstracts 1, 244 246.

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Jacobs, J. and Thomas, R. J. 1994. Oblique collision at about 1.1 Ga along the southern margin of the Kaapvaal continent, south-east Africa. Geo/ogische Rundschau 83, 322-333. Jacobs, J., Ahrendt, H., Kreuzer, H. and Weber, K. 1995. K-Ar, 4°Ar 39Ar and apatite ftssnon-track ewdence for Neoproterozobc rejuvenat0on events ~n the Heimfrontfjella and Manifalt Knausana (East Antarctica). Precambrian Research 75, 251-262. Kamenev, N. 1993. Structure and evolution of the Antarctic Shield in Precambrian. In: Gondwana Eight (Edited by Findlay, R. H., Unrug, R., Banks, M. R. and Veevers, J. J.) pp141 151. Balkema, Rotterdam. Key, R. M.. Charsley, T. J., Hackman, B. D., Wilkinson, A. F. and Rundle, C. C. 1 9 8 9 . S u p e r i m p o s e d Upper P r o t e r o z o i c c o l l i s i o n - c o n t r o l l e d o r o g e n i e s Jn the M o z a m b i q u e Orogenic Belt of Kenya. Precambrian Research 44, 197-225. Kleinschrodt, R. 1994. Large scale thrusting in the lower crustal basement of Sri Lanka. Precambrian Research 66, 39-47. Kr6ner, A., Greiling, R., Reischmann, T., Hussein, I. M., Stern, R. J., Durr, S., Kruger, J. and Zimmer, M. 1987. Pan-African microptate evolution in the Nubian segment of northeast Africa. In: Precambrian Lithosphere Evolution (Edited by Kr6ner, A.) American Geophysical Union Geodynamics Series 17, 235-257. Kr6ner, A., Todt, W., Hussenn, I. M., Mansour, M. and Rashwan, A. A. 1992. Dating of late Proterozoic ophiolites in Egypt and the Sudan using the single grain zircon evaporation technique. Precambrian Research 59, 15 32. Lenoir, J. J., KQster, D., Li~geois, J. P., Utke, A., Haider, A. and Matheis, G. 1994. Origin and regional significance of Late Precambrian and early Palaeozoic granitoids in the Pan African Belt of Somalia. Geo/ogische Rundschau 83, 624 641. Li, Z. X. and McPowell, C. 1993. Late Proterozoic to Early Palaeozoic p a l a e o m a g n e t i s m and the f o r m a t i o n of Gondwanaland. In: Gondwana Eight (Edited by Findlay, R. H., Unrug, R., Banks, M. R. and Veevers, J. J.) Balkema, Rotterdam. Maboko, M. A. H. 1995. Neodymium isotopic constraints on the protolith age of rocks involved in Pan African tectonism in the Mozambique Belt of Tanzania. Journal Geological Society London 152, 911 916. Matthews, P. E. 1981. Eastern or Natal Sector of the N a m a q u a - N a t a l mobile belt in southern Africa. In: Precambrian of the Southern Hemisphere. (Edited by Hunter, D. R.) pp705-714. Elsevier, Amsterdam. Mengist Teklay, Kr6ner, A. and OberhAnsli, R. 1993. Reconnaissance Pb Pb zircon ages from the Precarnbrian rocks in eastern and southern Ethiopia and an attempt to define crustal provinces. In: Geoscientific Research in N o r t h e a s t A f r i c a . (Edited by T h o r w e i s e , U. and Schandelmeier, H.} pp133-158. Balkema, Rotterdam. Millson, J. A., Mercadier, C. G. L., Livera, S. E. and Peters, J. M. 1996. The Lower Palaeozoic of Oman and its context in the evolution of the Gondwanan continental margin. Journal Geological Society London 153, 213 230. Morel, V. P. I., Randrianasolo, I. G., de Wit, M. J. and Ashwal, L. D. 1995. Structure and tectonics of the Ampanihy Shear Zone in the vicinity of the Ankafotia anorthosite massif, S.W, Madagascar. Geological Society South Africa Centennial Geocongress (1995). Extended Abstracts 1, 253-256. Mosley, P. N. 1993. Geological evolution of the Late Proterozoic "Mozambique Belt" of Kenya. Tectonophysics 221, 223-250. Moyes, A. B. and Knoper, M. W. 1995. A mesoproterozoic (_+1100 Ma) foreland fold and thrust Belt in Western Dronning Maud Land, Antarctica. Geological Society of South Africa Centennial Geocongress (1995). Extended Abstracts 1, 257-260.

The final collision zone between East and West Gondwana: where is it?

Mulugeta-Alene and Barker, A. 1993. Tectonometamorphic evolution of the Moyale region, southern Ethiopia. Precambrian Research 62, 271-283. Pallister, J. S., Stacey, J. S., Fischer, L. B. and Premo, W. R. 1987. Arabian Shield ophiolites and Late Proterozoic microplate accretion. Geology 15, 320-323. Pallister, J. S., Stacey, J. S., Fischer, L. 8. and Premo, W. R. 1988. Precambrian ophiolites of Arabia: Geologic settings, U-Pb geochronology, Pb-isotope characteristics, and implications for continental accretion. Precambrian Research 38; 1-54 Pinna, P., Jourde, G., Calvez, Y., Mroz, J. P. and Marques, J. M. 1993. The Mozambique Belt in northern Mozambique: Neoproterozoic ( 1 1 0 0 - 8 5 0 Ma) crustal growth and tectogenesls, and superimposed Pan-African (800-550 Ma) tectonism. Precambrian Research 62, 1-59. Prodehl. C. 1985. Interpretation of a seismic refraction survey across the Arabian Shield in western Saudi Arabia. Tectonics 111, 247-282. Quick, J. E. 1991. Late Proterozoic transpression in the Nabitah Fault System and implications for the assembly of the Arabian Shield. Precambrian Research 53, 119-147. Ries, A. C., Shackleton, R. M., Graham, R. H. and Fitches, W. B. 1983. Pan-African structures, ophiolites and melange in the Eastern Desert of Egypt: a traverse at 26°N. Journal Geological Society London 140, 75-95. Ries, A. C., Vearncombe, J. R., Price, R. C. and Shackleton, R. M. 1992. Geochronology and geochemistry of the rocks associated with a Late Proterozoic ophiolite in West Pokot, NW Kenya. Journal African Earth Sciences 14, 25-36. Sacchi, R., Marques, J. M., Costa, M. and Casati, C. 1984. Kibaran events in the southernmost Mozambique Belt. Precambrian Research 25, 141-159. Shackleton, R. M. 1993. Tectonics of the Mozambique Belt in East Africa. In: Precambrian Processes and Plate Tectonics. (Edited by Pritchard, H. M., Alabaster, T., Harris, N. Br W. and Neary, C. R.) Geological Society Special Publication 76, 345-362. Shackleton, R. M. 1994. Review of Late Proterozoic sutures, ophiolite melanges and tectonics of Eastern Egypt and northeast Sudan. Geologische Rundschau 83, 537-546. Steiner, L. 1987. The Nuba ophiolite and its geologic setting. In: Current Research In African Earth Sciences. (Edited by Matheis, G. and Schandelmeier, H.) pp101-108. Balkema, Rotterdam. Stern, R. J. 1993. Tectonic evolution of the Late Proterozoic East African Orogen: constraints from crustal evolution of the Arabian-Nubian Shield and the Mozambique Belt. In: Geoscientific Research in Northeast Africa (Edited by T h o r w e i h e , U. and S c h a n d e l m e i e r , H.) Balkema, Rotterdam. Stern, R. J. 1994. The Assembly and Continental Collision in the Neoproterozoic East African Orogen: Implications for the consolidation of Gondwana. AnnualReview Earth Planetary Sciences 22, 319-333. Stern, R. J. and Kr6ner, A. 1993. Late Precambrian crustal evolution in the NE Sudan; isotopic and geologic contrasts. Journal Geology 101, 555-574.

Stern, R. J., Kr6ner, A., Bender, R., Reischmann, T. and Dawoud, A. S. 1994. Precambrian basement around Wadi Halfa, Sudan: a new perspective on the evolution of the East Saharan Craton. Geologische Rundschau, 83, 564-577. Stern, R. J., Nutsen, K. C., Best, E., Sultan, M., Arundson, R. E. and Kr6ner, A. 1 9 9 0 . O r i e n t a t i o n of late Precambrian sutures in the Arabian-Nubian Shield. Geology 18, 1103-1100. Stoeser, D. B. 1986. Distribution and tectonic setting of plutonic rocks of the Arabian Shield. JournalAfrican Earth Sciences 4, 21-46. Stoeser, D. B. and Camp, V. R. 1985. Pan-African microplate accretion of the Arabian Shield. Bulletin Geological Society America 96, 817-826. Stoeser, D. B. and Stacey, J. S. 1988. Evolution, U-Pb geochronology and isotope geology of the Pan African Nabitah orogenic Belt of the Saudi Arabian shield. In: The Pan-African Belt o f Northeast Africa and Adjacent Areas (Edited by: El Gaby, S. and Greiling, R. O.) pp227288. Vieweg, Braunschweig/Wiesbaden. Tolessa, S., Bonavia, F. F., Solomon, M., Haik-Meskel, A. and Tefera, E. 1991. Structural pattern of Pan-African rocks around Moyale, southern Ethiopia. Precambrian Research 52, 179-186. Vail, J. R. 1964. Aspects of the stratigraphy and structure of the Umkondo System in the Manica Belt of Southern Rhodesia and Mozambique, and an outline of the Regional Geology. Transactions Geological Society South Africa LXVII, 13-30. Vail, J. R. 1 9 6 6 . Zones of p r o g r e s s i v e r e g i o n a l metamorphism across the w e s t e r n margin of the M o z a m b i q u e Belt in Rhodesia and M o z a m b i q u e . Geological Magazine 103, 231-239. Vearncombe, J. R. 1983. A dismembered ophiolite from the Mozambique Belt, West Pokot, Kenya. JournalAfrican Earth Sciences 1, 133-143. Wendt, J., Besang, W., Harre, H., Kreuzer, A., Lenz, H. and MQller, P. 1972. Age determination of granite intrusions and m e t a m o r p h i c e v e n t s in the Early Precambrian of Tanzania. 24th International Geological Congress, Montreal Section 1 295-314. Windley, B. F., Razafiniparany, A., Razakamanana, T. and Ackermand, D. 1994. Tectonic f r a m e w o r k of the P r e c a m b r i a n of M a d a g a s c a r and its G o n d w a n a connections: a review and reappraisal. Geologische Rundschau 83, 642-659. Windley, B. F., Whitehouse, M. J., Mahfood, A. O. and Ba-Bitat, M. A. O. 1996. Early Precambrian gneiss terranes and Pan-African island arcs in Yemen: crustal accretion of the eastern Arabian Shield. Geology 24, 131-134. Young, G. M. 1995. Are Neoproterozoic glacial deposits preserved on the margins of Laurentia related to the fragmentation of t w o supercontinents? Geology 23, 153-156. Tectonic map of Mozambique; 1:2 000 000. 1995. Compiled by Ferrara, M. and Marques, J. M. National Directorate of Geology, Republic of Mozambique.

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