Gondwana events and pal˦ogeography:A pal˦omagnetic review

Pergamon Journal o f African Earth Sciences, Vol. 28, No. 1, pp. 53 -59 , 1999

© 1999 Elsevier Science Ltd PII:S0899-5362(99)00019-6 Aii rights reserved. Printed in Great Britain

0899 -5362 /99 $- see f ront mat te r

Gondwana events and palaeogeography: a palaeomagnetic review

ANNE M. GRUNOW Byrd Polar Research Center, Ohio State University, Columbus, Ohio, 43210 USA

ABSTRACT--Several important tectonic episodes stand out in Gondwana's major and microplate motions: (1) Gondwana assembly; (2) the general movement of Gondwana towards higher latitudes in the Palaeozoic; (3) the influence of terranes on Gondwana Mesozoic break-up motions; and (4) Mesozoic-Cenozoic terrane motion along Gondwana's convergent margins. Current palaeomagnetic data indicate that the various fragments of Gondwana were assembled between -900 and -500 Ma. After assembly, the East Gondwana portion of Gondwana moved from more equatorial latitudes in the Early Palaeozoic into much higher latitudes by the Late Palaeozoic, whereas that of West Gondwana was the opposite. This overall motion and concomitant climatic change had a profound influence on the palaeoevolution of different Gondwana faunas and floras in the Palaeozoic. During the Palaeozoic and Mesozoic, convergence along the Gondwana margin resulted in accretion of various microplates. By the Early to Mid- Jurassic, palaeomagnetic data suggest that terrane motion along the palaeo-Pacific margin of Gondwana was related to the initial break-up of the supercontinent. This motion, especially in West Antarctica and New Zealand, caused the intermittent occurrence of palaeoseaways and landbridges between East and West Gondwana. In the Tertiary, collision of India and Africa with Eurasia caused significant local rotations associated with regional deformation. © 1999 Elsevier Science Limited. All rights reserved.

RI~SUMI~--Les mouvements du Gondwana et des microplaques associ~es se distribuent en plusieurs episodes tectoniques majeurs: (1) unification du Gondwana, (2) mouvement g~n~ral du Gondwana vers les hautes latitudes au Paleozo'fque, (3) individualisation de "terrains" Iors de la dislocation du Gondwana au MGsozoi'que, et (4) mouvements des "terrains" le long des marges convergentes du Gondwana. Les donn~es pal6omagnGtiques actuelles indiquent que, environ entre 900 et 500 Ma, les differents fragments du Gondwana 6taient rassemblGs. Apres I'unification du Gondwana, la zone orientale s'est dGplac~e de latitudes proches de I'l~quateur au Paleozo'fque infGrieur vers de plus hautes latitudes au PalGozo'ique sup~rieur, alors que le Gondwana occidental effectuait un mouvement inverse. Le d~placement et le changement climatique qui en a r~sult6 ont eu une profonde influence sur la palGo-~volution des faunes et des faunes du Gondwana au cours du Pal~ozo'i'que. Durant le Pal~ozo'ique et le MGsozofque, la convergence sur les marges du Gondwana a favoris6 I'accr~tion de diff~rentes micro-plaques. Au cours du Jurassique inf~rieur et moyen, les donn~es palGomagn~tiques sugg#rent que le dGplacement des "terrains" le long de la marge palGo-pacifique du Gondwana est lie & la dislocation initiale du super-continent. Le deplacement, surtout dans I'Antarctique occidental et en Nouvelle-ZGlande, a provoqu6 I'apparition intermittente de pal~o-d~troits et de ponts continentaux entre les zones occidentale et orientale du Gondwana. Au cours du Tertiaire, la collision de I'lnde et de I'Afrique avec I'Eurasie s'est accompagn~e d'importantes rotations locales li~es ~ la deformation r~gionale. © 1999 Elsevier Science Limited. All rights reserved.

(Received 20/8/98: accepted 20/10/98)

email: grunow.1 @osu.edu

Journal of African Earth Sciences 53

A. M. G R U N O W

INTRODUCTION

For almost 40 years, palaeomagnetic information has been gathered to better constrain Gondwana's plate motions, and this has led to a first order understanding of Gondwana's movements during the Phanerozoic. Much of this data is of uncertain geological value due to incomplete demag- netisation procedures, lack of precise age dating and insufficient structural analysis at sample sites. Significant palaeomagnetic questions still remain concerning the Neoproterozoic to Cambrian assembly of Gondwana, the break-up of the supercontinent in the Mesozoic-Cenozoic and understanding periods of very rapid polar wander. In this paper, several major palaeomagnetic events in Gondwana's history will be reviewed and some of the outstanding key issues discussed.

GONDWANA ASSEMBLY East Gondwana assembly Limited palaeomagnetic data from Australia and India for the -650 to -850 Ma time period have been interpreted to indicate that East Gondwana (Aus t ra l ia , A n t a r c t i c a , India and part of Madagascar?) was a single entity since -730 Ma (Li and Powell, 1993; Powell et a l . , 1993). Unfortunately, there are no Neoproterozoic poles from Antarctica to demonstrate East Gondwana's coherence. Neoproterozoic palaeomagnetic data from Australia and India are few and of variable quality. In Australia, four Neoproterozoic dykes from the Archean Yilgarn Block (dated at 700- 750 Ma) yielded a pal~eopole with an A95 of 28 ° (Giddings, 1976). Younger poles from the Elatina Formation (600-650 Ma) are better constrained magnetically and stratigraphically (Schmidt and Williams, 1995). The Early-Mid-Neoproterozoic palseomagnetic data from India are from alkali syenite dykes dated at 8 1 4 + 3 4 Ma (Dawson and Hargraves, 1994) and rhyolitic lava flows from the Malani rhyol i tes dated at 7 4 5 + 1 0 Ma, (Klootwijk, 1975). The Yilgarn Dykes pole is tempora l ly and palseomagnet ica l ly broadly equivalent to the Indian Malani rhyolites pole. However, the large error on the Australian pole renders it of uncertain value in constraining the timing of East Gondwana assembly. There are several Late Neoproterozoic and Cambrian Indian poles, i.e. the Bhander Series (Klootwijk, 1974; McEIhinny et al., 1978), the Purple Sandstone (McEIhinny, 1970) and the Salt Beds (Wesink, 1972), which are often used in palaeogeographic reconstructions (Meert et al., 1995). However, the ages of the Bhander Series and Purple

Sandstone are poorly constrained and the Tertiary rotation of the Salt Beds (KIootwijk et al., 1986) makes these poles suspect for use as cratonic reference poles.

The occurrence of 'Pan-African' (-500-600 Ma) deformational belts in East Antarctica, Australia, Madagascar and Sri Lanka may indicate that parts of East Gondwana were not fully assembled until the latest Neoproterozoic to Cambrian (Grunow et al., 1996). Clearly more Neoproterozoic data are needed from East Gondwana, and particularly East Antarctica, to constrain the timing of East Gondwana assembly.

West Gondwana assembly West Gondwana, prior to the Pan-African (or Braziliano) mobile belts, consisted of: Congo, Kalahar i , West A f r i can , A rab ian -Nub ian , Amazonian, Sao Francisco and Rio de la Plata Craton and/or Shield areas (Fig. 1). These areas are usually separated by Neoproterozoic Pan- African (or Braziliano) mobile belts. Neoproterozoic palseomagnetic poles from ~810 and -740 Ma rocks in the Congo Craton are considered well- constrained (Meert eta / . , 1995). With these data, Meert et al. propose that the Congo and Kalahari regions were sutured together between ~800 Ma and -650 Ma. However, the lack of isotopically and palaeomagnetically well-constrained data from the Kalahari Shield restricts the ability of palaeomagnetism to demonstrate the Neoproterozoic coherence of the Congo/Kalahari areas. The similarity of 1.1 Ga palaeomagnetic poles from the Kalahari Shield area and Coats Land, Antarctica indicate that Coats Land was part of the Kalahari Craton rather than East Gondwana (Gose et al., 1997) in the Late Mesoproterozoic (Fig. 1). One Late Neoproterozoic pole from the West African Craton (Morel, 1981) and one from the Arabian- Nubian Shield (Saradeth et al., 1989) are of similar age (-590-600 Ma), but yield very different pole positions.

There are only a few good quality reference poles for the Neoproterozoic from cratonic South America. One of these is the Neoproterozoic La Tinta Formation pole (709 + 24 Ma) from the Rio de la Plata Craton (Valencio e t a l . , 1980). A few poles of uncertain tectonic value have been obtained from Neoproterozoic rocks in the Sao Francisco Craton (D'Agrella-Filho and Pacca, 1988; Renne e t a l . , 1990) . There are no published Neoproterozoic palaeomagnetic poles from the Amazonian Craton to constrain its final assembly with the other cratonic parts of West Gondwana.

54 Journal of African Earth Sciences

Gondwana events and pala~ogeography: a pa/~eomagnetic review

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East-West Gondwana assembly The timing of final East-West Gondwana assembly is not well-constrained by palaeomagnetic data. This is due to the lack of reliable, temporally equivalent palaeopoles from the Gondwana cratonic areas.

Nonetheless, a first order approximation of Gondwana assembly has been proposed in which the Congo and Kalahari Cratons were assembled between -650 and 800 Ma during the East African Orogeny (Meert and van der Voo, 1996). According to Meert and van der Voo, final Gondwana assembly occurred when the regions mentioned above collided with East Gondwana around 550 Ma during the Kuunga Orogeny. Grunow et al. (1996) proposed final East-West Gondwana assembly in the Early Cambrian based primarily upon the comparison of l ithologies, structural histories, isotopic ages and a limited amount of palaeomagnetic data.

Avalon terranes Along the margin of Gondwana, palaeomagnetic data from the Avalon terranes indicate that they were moving away from the Gondwana periphery while the final stages of Gondwana assembly were occurring in the latest Neoproterozoic to Early Cambrian (van der Voo, 1993; Lefort, 1998). Due to the lack of Late Neoproterozoic through Early Palaeozoic poles from within the same terrane, it is unknown whether the Avalon Terrane moved as a single entity or as discrete terranes throughout this interval.

CAMBRIAN GONDWANA TRUE POLAR WANDER

Palaeomagnetic data from many continents have recently been interpreted to indicate that the Earth's lithosphere and mantle rotated -90 ° during a -15 Ma interval between -532 Ma and -517 Ma during a true polar wander (TPW) event (Kirschvink eta/., 1997). This hypothesis has been used to explain very rapid Cambrian plate motions and even the accelerated diversity of fauna in the Cambr ian. The palaeomagnet ic data f rom Gondwana used to support this model come exclusively from Australia: the Lower Cambrian Todd River Formation (earl iest Tommot ian) (Kirschvink, 1978) and the Cambro-Ordovician Black Moun ta in sequence (Ripperdan and Kirschvink, 1992). The plate motions predicted by these two Gondwana palaeopoles, separated in age by approximately 35 Ma, by themselves do not require unusually fast drift rates and can

be explained by regular tectonic mechanisms. The Black Mountain pole is almost identical to the Australian Middle Ordovician Stairway Sandstone pole (Embleton, 1972) (Table 1 ), raising questions about the age of these formations and/or the age of magnetisation. Clearly, the TPW hypothesis is an in t r igu ing proposal w i th wide reaching implications for many areas of Earth Science (Evans, 1998), but much addit ional palaeomagnetic data are needed from Gondwana and elsewhere during the c r i t i ca l -535 t o - 5 1 0 Ma interval to convincingly demonstrate the viability of the true polar wander hypothesis.

Early Ord ~485 l~

Late Ord, 450

Figure 2. Ordovician pa/~eogeographic reconstructions o f Gondwana; the geographic south pole is centred on the Gondwana reference pole (in African co-ordinates) with its associated A95 circle (see Table 1). The position of Laurentia is based on the pala~omagnetic pole of Jackson and van der Voo (1985). Bold line with triangles marks a possible subduction zone along the Gondwana margin (Grunow, 1995). L: Laurentia; G: Gondwana.


Silurian- Devon Gondwana Paleopoles

-'374-438 Ma

[ ~ Early Devonian

[:::] Late Silurian

~'~ Early Silurian

Mean Gondwana pole

t

Figure 3. Silurian and Late Devonian poles from Gondwana. Note the two different apparent polar wander paths. (A) This is based on poles that do not demonstrate fast apparent polar wander. (B) This shows poles that support fast apparent polar wander. The Late Devonian reconstruction shows the geographic south pole centred on the Gondwana reference pole (in African co-ordinates) with its associated A95 circle (see Table 1 for the data and reference sources).

A. M. G R U N O W

GONDWANA MOTIONS DURING THE PALaEOZOIC/EARLY MESOZOIC

The loop in the Siluro-Devonian Gondwana apparent polar wander path In the Early and Late Ordovician, the palaeomagnetic pole was located in northern Africa (Fig. 2), While there is considerable error in the Late Ordovician pole, its position is consistent with the location predicted by the Gondwana glacial deposits (Smith, 1997). By the Late Devonian, the Gondwana pole was located in central Africa (Table 1 ; Fig. 3). A subject of debate in Gondwana palaeomagnetism is the location of the Gondwana pole between the Ordovician and Late Devonian. The pole may have moved slowly from northern Africa to central Africa between -480 Ma and - 3 2 5 Ma (Bachtadse and Br iden, 1991) . Alternatively, some palaeomagnetists believe that the pole moved quickly from northwestern Africa to southernmost South America and back to central Africa, creating a loop in the apparent polar wander path (APWP) (Fig. 3) between the Ordovician and Devonian (Schmidt et al., 1990). The fast motions predicted by this loop would affect climate, palaeodiversity and regional tectonic events.

The similar i ty of Silurian palaeopoles from western and eastern Australia can be used to support the view of slow apparent polar wander, particularly the Early Silurian Cowra Trough, Tumblagooda Sandstone and Mereenie Sandstone poles (Embleton, 1972; Goleby, 1980; Schmidt and Embleton, 1990; Hocking, 1991). The Early Silurian poles fall near to each other and are from w ide l y separa ted regions tha t have not experienced the same tectonic events. A new mean Early Silurian pole calculated here (Table 1 ) places the mean Gondwana pole in north-central Africa. An Australian Late Silurian pole (Goleby, 1980) is located in northeastern South America, while an Early Devonian pole from the Bowning Group is located in southwestern Africa (Luck, 1973) (Table 1; Fig. 3A). These Silurian and Devonian poles shown in Fig. 3A support slow apparent polar wander between the Ordovician and Late Devonian.

Alternatively, limited palaeomagnetic data from rocks within fold belts in eastern Australia and South America have been interpreted to indicate a large loop in the APWP between the Ordovician and Late Devonian (Schmidt et al., 1987). Some of these data place the Gondwana palaeopole in southern South America for the Silurian and Early Devonian (Fig. 3B). The poles used to support the loop are primarily the Late Silurian Laidlaw

Volcanics (Luck, 1973), the Early Devonian Australian Snowy River Volcanics (Schmidt et al., 1987) and the Early Devonian Air Intrusives from Africa (Hargraves et al., 1987; Moreau et al., 1994) (Table 1).

The Laidlaw Vo lcan ics and Snowy River Volcanics poles are from the eastern Australia Fold Belt (Luck, 1973; Schmidt et al., 1987). These poles may have experienced structural rotations associated with the two deformational events that affected these rocks. The Air Intrusive pole comes from intrusive rocks that lack palaeohorizontal control and may have been tilted. Other poles often cited to support the fast APWP loop include the Sierra Grande SG1 pole from South America (Rapalini and Vilas, 1991 a), but this pole is poorly cons t ra ined (Rapal in i , 1998) . Add i t i ona l palaeomagnetic sampling of these rocks has demonstrated at least a partial remagnetisation event in the Permian (Rapalini, 1998). Lastly, the South American Lipe6n Formation pole (Conti et a l . , 1995) fal ls away from all of the other Gondwana Siluro-Devonian palaeopoles, but it is very similar to Gondwana Early Mesozoic poles. Perhaps the Lipe6n Formation C component pole has experienced unidentified rotations due to its location in the Andean Fold and Thrust Belt.

Given that some of the Silurian poles from both the eastern Australian fold belts and from western Australia are similar, it is reasonable to propose that the Early Silurian pole was located in north- central Africa. If the Australian Late Silurian pole from Goleby (1980) and the Early Devonian Bown ing Group pole (Luck, 1973) are representative of Gondwana, then there is no evidence for the fast APWP model. However, if the Early Devonian Snowy River and Air Intrusive poles are representative of Gondwana then there may have been fast APWP between the Early Si lur ian and Late Devon ian . Faunal and sedimentological data could help resolve this controversy.

Permo-Triassic palaeogeographic reconstructions Palaeogeographic reconstruct ions required for evolutionary models of flora and fauna from the Permian through Early Jurassic depend upon reliable palaeomagnetic data from Gondwana. Previous APWP's and associated reconstructions (Scotese and McKerrow, 1990; Powell and Li, 1994) provide a reasonable first approximation of Gondwana palaeolat i tudes for the Late Palaeozoic and Early Mesozoic. However, in this paper the Permo-Triassic Gondwana palaeopoles with well-constrained ages have been re-examined.


Late Permian Early Permian ~275 Ma

Gondwana events and pala~ogeography: a pala~omagnetic rev iew

Early Triassic Late T r ' - - - ' - 240-245 Ma ~220

Figure 4. Permian and Triassic continental reconstruct/ons based on averaging pala~opoles from several Gondwana fragments; the geographic south pole is centred on the Gondwana reference pole (in African co-ordinates) with its associated A95 circle (see Table 1).

The mean Gondwana poles for the Early Permian, Late Permian, Early Triassic, Middle Triassic and Late Triassic periods are listed in Table 1. Each mean pole represents the averaging of equivalent age poles (with a Q factor of 3 or greater; van der Voo, 1993). Most of these poles have large A95 errors associated with them because there are so few temporally well-constrained poles from these

time intervals. The palaeopoles indicate that the South Pole was located over the Transantarctic Mountains in the Early Permian, then in south- central Australia by the Late Permian, and moved over the Pacific Ocean during the Triassic (Fig. 4). These reconstructions differ from those of Powell and Li (1994) in the location of the Late Permian, Early Triassic and Late Triassic poles. In this paper,

Journal of African Earth Sciences 6 1

A. M. GRUNOW

Arequipa Puna Oriental- Famatina

Mejiilonia

Chana

Chilenia

Chiloe

Figure 5. South American blocks that may be Palaeozoic-Mesozoic terranes (modified from Ramos, 1988).

the Late Permian pole is located over south-central Australia/Antarctica with a large A95, rather than over North Victoria Land, Antarctica. The latitudes listed in Table 1 for the Early and Late Triassic poles differ by 16 ° and 12 ° , respectively, from those of Powell and Li (1994). These differences may be significant to those concerned with floral and faunal evolution at high latitudes during the Permo-Triassic (Collinson, 1997).

Gondwana's Pacific margin and Palaeozoic terrane accretion Along the Gondwana margin, Palaeozoic terrane motion has been proposed for West Antarctica/ New Zealand, and along the eastern Australian and South Amer ican cont inenta l margins. Palaeopoles from the Brook Street Terrane in New Zealand do not agree with Permian poles from con t i nen ta l Gondwana and is, the re fo re , considered to be allochthonous (Haston et al.,

1989). In eastern Australia, palaeomagnetic data indicate that there was little signif icant Late Palaeozoic to Mesozoic terrane motion, except for parts of the Hastings Terrane (Schmidt et al., 1994). Permo-Triassic palaeomagnetic data from Timor have been interpreted to indicate that it now represents a displaced terrane from Australia (Wesink and Hartosukohardjo, 1990).

Palaeomagnetic data from the Arequipa Terrane in South America (Forsythe et al., 1993) have been interpreted to indicate rotation of this terrane in the Early Palaeozoic. Based on the new Late Ordovician pole listed in Table 1, it is possible that the Arequipa Terrane did not experience the 60 ° rotation originally predicted, and perhaps very little to no rotation. It is difficult to say whether the Cambro-Ordovician? and pre-Devonian poles used to support movement of the Arequipa Terrane are discordant to the Gondwana APWP because the pole errors are not listed and the rocks are


Gondwana events and pala~ogeography: a pala~omagnetic rev iew

not well-constrained in age. Palaeomagnetic data from Patagonia suggest no significant rotation of this region since at least the Carboniferous (Rapalini et al., 1994) (Fig. 5). The Puna Oriental- Famatina Terrane appears to have been located near the Gondwana margin in the Lower-Middle Ordovician prior to its amalgamation in the Middle Ordovician (Conti et al., 1996). Palaeomagnetic data from the Precordillera Terrane in Argentina suggests that it may have been part of Laurentia in the Cambrian rather than Gondwana (Rapalini and Astini, 1997)(Fig. 5). Rapalini e ta l . (1989) and Rapalini and Vilas (1991 b) suggest that some Late Palaeozoic rocks sampled in western Argentina may represent ter ranes and/or areas that experienced vertical axis rotations.

G O N D W A N A BREAK-UP ( - 1 8 5 MA TO PRESENT)

While there are sea-floor magnetic anomaly and flow line data constraining the break-up geometry of the main Gondwana continents from the Middle to Late Jurassic onward, similar anomalies have not been preserved to document the motion of smaller terranes; particularly along the Pacific margin of Gondwana. Palaeomagnetic data provide the only way to evaluate the kinematics of break- up in these parts of Gondwana.

Mesozoic terrane motion and dispersal of Gondwana's microplates Palaeomagnetic poles from the Falkland Islands (FI) and the West Antarctic terranes [the Antarctic Peninsula (AP), Thurston Island (TI), Marie Byrd Land/New Zealand (MBL/NZ) and the EIIsworth- Whitmore Mountains (EWM)] demonstrate that significant rotations and translations occurred during the Jurassic and Cretaceous break-up of the supercontinent (Taylor and Shaw, 1989; Grunow, 1993a; Luyendyk et al., 1996).

Gondwana palaeomagnetic poles from -180 Ma are well-constrained and pre-date the break-up of the supercontinent (Lanza and Zanella, 1993). Palaeomagnetic data from the EWM block in West Antarctica indicate that this region rotated 90 ° sometime between the Cambro-Ordovician and the Jurassic (Watts and Bramall, 1981; Grunow et al., 1987). Alignment of the Permo-Triassic Gondwanide structural trends in the EWM block with those in the Cape Fold Belt could indicate that rotation occurred after the Permo-Triassic and before -175 Ma. Palaeomagnetic data from dolerite dykes on the FI (Fig. 1) indicate that this block rotated - 1 8 0 ° (Taylor and Shaw, 1987 OR

1987??) since dyke emplacement a t - 1 9 0 Ma. If the EWM and FI rotations are related, they may be tied to pre-sea-floor spreading break-up events between Antarctica, Africa and South America.

Along the Pacific margin of Gondwana, the positions of the West Antarctic blocks are shown in Fig. 6 based primarily on palaeomagnetic data compiled by Grunow (1993 a or b??), but with addi t ional M id -Cre taceous MBL data from DiVenere et al. (1994, 1995) and Luyendyk et al. (1996). Between the Middle and Late Jurassic, pal~eomagnetic data from the AP and TI blocks suggest c lockwise mot ion relat ive to East Antarctica, perhaps associated with opening in the Weddell Sea (Grunow, 1993b) (Fig. 6b). The precise width of the Weddell Sea is dependent on the mean Gondwana reference pole for the latest Jurassic and that is not well-constrained. By the Early Cretaceous, palaeopoles from the AP and TI blocks suggest some counter-clockwise motion re lat ive to East An ta rc t i ca , ref lect ing the southward movement of East Gondwana as the Somali and Mozambique Basins opened (Grunow et al., 1991; Grunow, 1993a) (Fig. 6c). This southward motion of East Gondwana may have caused some closure and collision of the AP with the Weddell Sea and EWM Terrane. By the Mid- Cretaceous, the West Antarctic blocks, apart from MBL/NZ, appear to have been in their present day positions with respect to East Antarctica based on the similarity of these poles with the East Antarctic reference pole (Fig. 6d). Early Cretaceous palaeomagnetic data f rom MBL have been interpreted to indicate that the MBL/NZ crustal block was divided into an eastern MBL/Eastern New Zealand region and a western MBL/western NZ region (DiVenere e ta / . , 1995). These block motions during the Jurassic and Cretaceous caused palaeoseaways and land-bridges to develop at various times between the Pacific Ocean basin and the interior Gondwana seaways, affecting palaeoclimate and palaeobiogeography (Grunow, 1993b).

West Antarctic terrane motion in the Mid-Cretaceous? One of the controversial issues that remains in the Gondwana microplate palaeomagnetic record is whe the r there was pa laeomagnet ica l ly discernible terrane motion in West Antarctica and New Zealand relative to East Antarctica from the M id -Cre taceous onward (Grunow, 1993a; DiVenere et al., 1994; Luyendyk et al., 1996). DiVenere et al. and Luyendyk et al. suggest that there was West Antarctic terrane motion, while


A. M. GRUNOW

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64 Journal o f Afr ican Earth Sciences

Gondwana events and pal~eogeography: a pal~eomagnet ic r ev i ew

Grunow (1993a) argues that the ex is t ing palaeomagnetic database did not convincingly demonstrate such motions. Based on the reference poles and assumed age of magnetisation chosen by DiVenere et al. (1994), there is a statistical difference between the East and West Antarctic poles at the A63 level (but not the A95 level) and this might support palaeomagnetically discernible motion between MBL, TI and the AP blocks with East Antarctica. Based on Grunow's (1993a) choice of reference poles and assigned ages, there was no statistical difference observed between the Mid-Cretaceous East Antarctic, TI and AP poles, and this would indicate no rotation between East An ta rc t i ca and these parts of West Antarctica. It is still felt that the uncertainties associated with the choice of reference poles, isotopic and faunal ages, the age of magnetisation, and the errors associated with the rotation poles are significant enough to question the ability of palaeomagnetism to document small, West Antarctic motions at very high latitudes during such short time intervals (e.g. less than 10 Ma).

Cenozoic terrane motion Vertical axis rotation and translation of blocks have occurred along the Gondwana Pacific margin associated with Pacific-South American convergence, especially in the Arica embayment of Chile, Peru and Bolivia (Beck, 1988; Roperch and Carlier, 1992; Butler eta/. , 1995; MacFadden etal . , 1995). Palaeomagnetic data from these areas indicate that significant vertical axis rotations have occurred in the Cenozoic, especially the Late Cenozoic (Rojas et al., 1994; MacFadden et al., 1995). In northern Chile, similar Mesozoic rotation of the fore-arc region has been docu-mented in several studies (Palmer et al., 1980; Hartley et al., 1988, 1992). In the southern Chilean fore-arc (Jesinkey et al., 1987; Cembrano et al., 1992; Rojas et al., 1994), vertical axis, counter-clockwise rotations in Eocene-Miocene sedimentary rocks have been found along the dextral Liquine-Ofqui Shear Zone. In northern India and

Africa, vertical axis rotations occurred due to the collision of Greater India and Africa with Eurasia (Klootwijk et al., 1986).

FUTURE DIRECTIONS IN GONDWANA PAL~EOMAGNETISM

It is clear from reviewing the Gondwana pala~o- magnetic database that much work remains to be done, particularly with regard to cratonic reference poles. Without high quality and well-dated reference poles it will be very difficult to produce pal~eo- magnetically constrained pal~eogeographic models dealing with Gondwana assembly, break-up and terrane mot ions. Pala~omagnetic data from structurally and temporally well-constrained units can address a number of important questions concerning Gondwana plate motions by:

i) Evaluating the nature of Gondwana assembly, especially:

a) the t iming of East, West and East-West Gondwana assembly

b) the timing and geometry of any connection be tween Laurent ia and Gondwana in the Neoproterozoic; and

c) the plate motions of the Avaton/Cadomian terranes relative to Gondwana.

ii) Obtaining high quality pal~eomagnetic poles from temporally well-constrained Lower-Middle Cambrian rocks in order to evaluate the proposed Cambrian true-polar wander event.

iii) Obtaining cratonic reference poles for the Middle Ordovician through Middle Devonian to document the plate motions for that time. It appears that the proposed large loop in the APWP may not exist.

iv) Refining the Gondwana APWP for the latest Palaeozoic to Early Mesozoic in order to constrain biogeographic models and evaluate the various Pangaea models.

v) Understanding the kinematics of the microplates and what role they played during Gondwana break-up.

Figure 6. Jurassic through Mid-Cretaceous reconstructions showing the break-up of Gondwana and the role that the microplates along the Pacific margin played at this time. The geographic south pole is centred on the Gondwana reference pole (in African co- ordinates) with the associated A95 circle; West Antarctic pala~opoles with A95 circles are identified as: ap: AP block; ewm: EWM block; ti." TI block (see Grunow, 1993a; DiVenere et al., 1995). Abbreviations: AP: Antarctic Peninsula block; MAD: Madagascar; MB: Mozambique Basin; NWS: northern Weddell Sea; RVB: Rocas Verdes Basin; S.A T: South Atlantic Ocean basin; SB: Somafi Basin; SNZ: southern New Zealand; SWS: southern Weddell Sea. (a) - 175 Ma. Initiation o f sea-floor spreading in the Weddell Sea. Clockwise rotation of the AP block relative to East Antarctica due to opening in the Weddell Sea. (b) ~ 155 Ma. Spreading geometry changes in the Weddell Sea such that opening begins along the northern AP block and into the Rocas Verdes Basin. Ocean floor in the southern Weddell Sea may have been subducted beneath the southeastern AP and TI blocks. (c) ~ 130 Ma. AP block near its present-day position with respect to East Antarctica. Dextral strike-slip motion in the southeastern AP block related to movement o f the EWM and TI blocks. (d) - 9 0 Ma. New Zealand and MBL sti l l moving relative to East Antarctica. NZ about to break away from MBL. Other West Antarctic blocks appear to be in position relative to West Antarctica.


A. M. GRUNOW

v) Documenting rotations associated with convergence along the Gondwana margin.

In summary, the palaeomagnetic record over the last 20 years or more has al lowed palaeogeographic reconstructions to be made for most of the Phanerozoic record. The palaeomagnetic data generally provide a good, first order understanding of where most of the main Gondwana fragments were located during the Phanerozoic. Recent studies have started to provide more data on the Gondwana fragments during the Neoproterozoic, but there are not enough data yet to constrain many of these pieces. In order to create more reliable palaeogeographic models, greater emphasis should be placed on determining the age of magnetisation. Many more palaeomagnetic studies need to be undertaken in Gondwana on rocks with w e l l - c o n s t r a i n e d ages, and s t ruc tu ra l and diagenetic histories. In this way, palaeo-magnetic data can help the geological community make new predictions about the tectonic, faunal and climatic history of the Gondwana super-continent.

ACKNOWLEDGMENTS

This work was supported through National Science Foundation sponsored grants: OPP-9317673 and EAR-9526709. The author would like to thank Maarten de Wit and Neil Opdyke for reviewing this paper and Lisa Gahagan (PLATES) at the University of Texas, Austin for helping with the reconstructions.

REFERENCES Aifa, T., 1993. Different styles of remagnetization in Devonian

sed iments f rom the no r th -wes te rn Sahara (Algeria). Geophysical Journal International 115, 529 -537 .

Bachtadse, V., Briden, J.C., 1991. Palaeomagnetism of Devonian ring complexes f rom the Bayuda Desert, Sudan-new cons t ra in ts on the apparen t po lar wande r path for Gondwanaland. Geophysical Journal International 104, 635- 646.

Bachtadse, V., van der Voo, R., H~lbich, I.W., 1987. Paleomagnetism of the western Cape fold belt, South Africa, and its bearing on the Paleozoic apparent polar wander path for Gondwana. Earth Planetary Science Letters 84, 487-499 .

Beck Jr., M.E., 1988. Analysis of Late Jurassic -Recent paleomagnetic data from active plate margins of South America. Journal South American Earth Sciences 1, 39-52 .

Briden, J.C., McClelland, E., 1993. Proving the age of a paleomagnetic pole: the case of the Ntonya ring structure, Malawi. Journal Geophysical Research 98, 1743 -1749 .

Butler, R.F., Richards, D.R, Semper, T., Marshall, L.G., 1995. Paleomagnet ic determinat ions of vert ical-axis tectonic rotations from Late Cretaceous and Paleocene strata of Bolivia. Geology 23, 7 9 9 - 8 0 2 .

Cembrano, J., Beck Jr., M.E., Burmester, R.F., Rojas, C., Garcia, A., Herv~, F., 1992. Paleomagnetism of Lower Cretaceous rocks from east of the Liquine-Ofqui fault zone, southern Chile: evidence of small in-situ clockwise rotations. Earth Planetary Science Letters 113, 539 -551 .

Chen, Z., Li, Z.X., Powell, C. McA., 1995. Palaeomagnetism of the Upper Devonian reef complexes, Canning Basin, Western Australia. Tectonics 14, 154 -167 .

Col l inson, J.W., 1997. Paleoc l imate of Permo-Triassic Antarct ica. In: Ricci, C.A. (Ed.), The Antarct ic Region: Geological Evolut ion and Processes. Terra Antarc t ica Publication, Siena, pp. 1 0 2 9 - 1 0 3 4 .

Conti, C.M., Rapalini, A.E, Coira, B., Koukharsky, M., 1996. Paleomagnetic evidence of an early Paleozoic rotated terrane in nor thwest Argentina: A clue for Gondwana-Laurentia interaction? Geology 24, 9 5 3 - 9 5 6 .

Conti, C.M., Rapalini, A.E., Vilas, J.F., 1995. Palaeomagnetism of the Silurian Lipe6n formation, NW Argentina, and the Gondwana apparent polar wander path. Geophysical Journal International 121, 8 4 8 - 8 6 2 .

Corner, B., Henthorn, D.I., 1978. Results of paleomagnetic survey undertaken in the Damara Mobile Belt, South West Africa, with special reference to the magnetization of the uraniferous pegmatitic granites. Atomic Energy Board Report, PEL-260, Pretoria.

Daly, L., Pozzi, J.P., 1976. Resultats pal6omagnetiques du Permien inf~rieur et du Trias Marocain: comparaison avec les donn6es africaines et sud-americaines. Earth Planetary Science Letters 29, 71 -80 .

D'Agrelho-Filho, M.S., Pacca, I.G., 1988. Paleomagnetism of the Itajai, Castro and Bom Jardim groups from southern Brazil. Geophysical Journal 93, 365 376.

Dawson, E.M., Hargraves, R.B., 1994. Paleomagnetism of Precambrian dike swarms in the Harohalli area, south of Bangalore, India. Precambrian Research 69, 157 -167 .

DiVenere, V., Kent, D.V., Dalziel, I.W.D., 1994. Mid-Cretaceous pa leomagne t i c resul ts f rom Mar ie Byrd Land, West Antarctica: a test of post- lO0 Ma relative motion between East and West Antarctica. Journal Geophysical Research 99, 15 ,115 -15 ,139 .

DiVenere, V., Kent, D.V., Dalziel, I.W.D., 1995. Early Cretaceous pa leomagne t i c resul ts f rom Mar ie Byrd Land, West Antarctica: implications for the Weddellia collage of crustal blocks. Journal Geophysical Research 100, 8 1 4 4 - 8 1 5 1 .

Embleton, B.J.J., 1970. Palaeomagnetic results for the Permian of South America and a comparison with the African and Australian data. Geophysical Journal Royal Astronomical Society 21, 105 -118 .

Embleton, B.J.J., 1972. The paleomagnetism of some Proterozoic- Cambrian sediments from the Amadeus Basin, central Australia. Earth Planetary Science Letters 17, 217-226.

Embleton, B.J.J., McDonnell, K.L., 1980. Magnetostratigraphy in the Sydney Basin, southeastern Austral ia. Journal Geomagnetism Geoelectricity 32 (Sill), 1 -10 .

Embleton, B.J.J., McEIhinny, M.W., 1975. The paleoposition of Madagascar: paleomagnetic evidence from the Isalo group. Earth Planetary Science Letters 27, 3 2 9 - 3 4 1 .

Evans, D.A., 1998. True polar wander, a supercontinental legacy. Earth Planetary Science Letters 157, 1-8 .

Forsythe, R.D., Davidson, J., Mpodozis, C., Jesinkey, C., 1993. Lower Paleozoic relative motion of the Arequipa Block and Gendwana: paleomagnetic evidence from Sierra de Almeida of Northern Chile. Tectonics 12, 2 1 9 - 2 3 6 .

Ghorabi, M., Henry, B., 1991. Analyses pal~omagnetiques darts les formations permo-triasiques du Sud tunisien. Comptes Rendus Acad6mie Science Paris, S~ries II 312, 1527-1530 .

Giddings, J.W., 1976. Precambrian palaeomagnetism in Australia h basic dykes and volcanics from the Yilgarn block. Tectonophysics 30, 9 1 - 1 0 8 .

Goleby, B.R., 1980. Early Palaeozoic palaeomagnetism in southeast Australia. In: McEIhinny, M.W., Khramov, A.N., Ozima, M., Valencio, D.A. (Eds.), Global reconstruction and the Geomagnetic field during the Paleozoic. Advances Earth Planetary Sciences 10, 11-21 .


Gondwana events and pa/aeogeography: a palaeomagnetic review

Gose, W.A., Helper, M.A., Connelly, J.N., Hudson, F.E., Dalziel, I.W.D., 1997. Paleomagnetic data and U-Pb isotopic age determinations from Coats Land, Antarctica: implications for late Proterozoic plate reconstruct ions. Journal Geophysical Research 102, 7887-7902.

Green, R., 1961. Palaeomagnetism of some Devonian rock formations in Australia. Tellus 13, 119-134.

Grunow, A.M., 1993a. New Paleomagnetic data from the Antarctic Peninsula and their Tectonic Implications. Journal Geophysical Research 98, 13,815-13,833.

Grunow, A.M., 1993b. The creation and destruction of Weddell Sea floor in the Jurassic. Geology 21, 647-650.

Grunow, A.M., 1995. Implications for Gondwana of new Ordovician paleomagnetic data from igneous rocks in southern Victoria Land, Antarctica. Journal Geophysical Research 100, 12,589-12,603.

Grunow, A.M., Dalziel, I.W.D., Kent, D.V., 1987. EIIsworth- Whitmore Mountains crustal block, western Antarctica: new paleomagnetic results and their tectonic significance. In: McKenzie, G.D. (Ed.), Gondwana Six: Structure, Tectonics and Geophysics. American Geophysical Union, Geophysical Monograph 40, 161-172.

Grunow, A.M., Hanson, R.E., Wilson, T.J., 1996. Were aspects of Pan-African deformation a result of lapetus opening? Geology 24, 1063-1066.

Grunow, A.M., Kent, D.V., Dalziel, I.W.D., 1991. New paleomagnetic data from Thurston Island and their implications for the tectonics of West Antarctica. Journal Geophysical Research 96, 17,935-17,954.

Hargraves, R.B., Dawson, E.M., van Houten, F.B., 1987. Palaeomagnetism and age of mid-Paleozoic ring complexes in Niger, West Africa, and tectonic implications. Geophysical Journal Royal Astronomical Society 90, 705-729.

Hartley, A.J., Jolley, E.J., Turner, P., 1992. Paleomagnetic evidence for rotation in the Precordillera of northern Chile: structural constraints and implications for the evolution of the Andean forearc. Tectonophysics 205, 49-64.

Hartley, A.J., Turner, P., Williams, G.D., Flint, S., 1988. Palaeomagnetism of the Cordillera de la Costa, northern Chile: evidence for local forearc rotation. Earth Planetary Science Letters 89, 375-386.

Haston, R.B., Luyendyk, B.P., Landis, C.A., Coombs, D.S., 1989. Paleomagnetism and question of original location of the Permian Brook Street Terrane, New Zealand. Tectonics 8, 791-801.

Hocking, R.M., 1991. The Silurian Tumblagooda sandstone, Western Australia. Geological Survey Western Australia, Report 27, 124p.

Irving, E., Parry, L.G., 1963. The magnetism of some Permian rocks from New South Wales. Geophysical Journal Royal Astronomical Society 7, 395-411.

Jackson, M., van der Voo, R., 1985. A Lower Ordovician paleomagnetic pole from the Oneota Dolomite, Upper Mississippi Valley. Journal Geophysical Research 90, 10449-10461.

Jesinkey, C., Forsythe, R.D., Mpodozis, C., Davidson, J., 1987. Concordant late Paleozoic paleomagnetizations from the Atacama Desert: implications for tectonic models of the Chilean Andes. Earth Planetary Science Letters 85,461-472.

Kirschvink, J.L., 1978. The Precambrian-Cambrian boundary problem: paleomagnetic directions from the Amadeus Basin, central Australia. Earth Planetary Science Letters 40, 91- 100.

Kirschvink, J.L., Ripperdan, R.L., Evans, D.A., 1997. Evidence for a large-scale reorganization of Early Cambrian continental masses by inertial interchange true polar wander. Science 277, 541-545.

Klootwijk, C.T., 1974. Paleomagnetic results from some Panchet clay beds, Karanpura Coalfield, northeastern India. Tectonophysics 21,79-92.

KIootwijk, C.T., 1975. A note on the palaeomagnetism of the Late Precambrian Malani rhyolites near Jodhpur-India. Journal Geophysics 41, 189-200.

Klootwi jk, C.T., Nazirullah, R., de Jong, K.A., 1986. Palaeomagnetic constraints on formation of the Mianwali re-entrant, Trans-lndus and western Salt Range, Pakistan. Earth Planetary Science Letters 80, 394-414.

Klootwijk, C.T., Shah, S.K., Gergan, J., Sharma, M.L., Tirkey, B., Gupta, B.K., 1983. A palaeomagnetic reconnaissance of Kashmir, northwest Himalaya, India. Earth Planetary Science Letters 63, 305-324.

Lackie, M.A., 1988. The paleomagnetism and magnetic fabric of the Late Permian Dundee rhyodacite, New England. In: Kteeman, J.D. (Ed.), New England Orogen: Tectonics and Metallogenesis. University of New England, Australia, pp. 157-165.

Lanza, R., Zanella, E., 1993. Palaeomagnetism of the Ferrar dolerite in the northern Prince Albert Mountains (Victoria Land, Antarctica). Geophysical Journal International 114, 501-511.

Lawver, L., Scotese, C.R., 1987. A revised reconstruction of Gondwanaland. In: McKenzie, G.D. (Ed.), Gondwana Six: Structure, Tectonics and Geophysics. American Geophysical Union, Geophysical Monograph 40, 17-23.

Lefort, J.-P., 1998. Palaeozoic splitting, rotation and re- amalgamat ion oat the northern edge of Palaeozoic Gondwana. Where is the mother-country of Armorica? Journal African Earth Sciences 27 (1A), 130-131.

Li, Z.X., Powell, C.McA., 1993. Late Proterozoic to early Paleozoic pa leomagnet ism and the format ion of Gondwanaland. In: Findlay, R.H., Unrug, R., Banks, M.R., Veevers, J.J. (Eds.), Gondwana Eight. A.A. Balkema, Rotterdam, pp. 9-21.

Li, Z.X., Powelt, C.McA., Embleton, B.J.J., Schmidt, P.W., 1991. New palaeomagnetic results from the Amadeus Basin and their implications for stratigraphy and tectonics. In: Korsch, R.J., Kennard, J.M. (Eds.), Geological and Geophysical studies of the Amadeus Basin, central Australia. Bureau Mineral Resources Bulletin 236, 349-360.

Luck, G.R., 1972. Paleomagnetic results from Paleozoic sediments of northern Australia. Geophysical Journal Royal Astronomical Society 28, 475-487.

Luck, G.R., 1973. Palaeomagnetic results from Palaeozoic rocks of southeast Austral ia. Geophysical Journal Royal Astronomical Society 32, 35-52.

Luyendyk, B., Cisowski, S., Smith, C., Richard, S., Kimbrough, D., 1996. Paleomagnetic study of the northern Ford Ranges, western Marie Byrd Land, West Antarctica: motion between West and East Antarctica. Tectonics 15, 122-141.

MacFadden, B.J., Anaya, F., Swisher III, C.C., 1995. Neogene paleomagnetism and oroclinal bending of the central Andes of Bolivia. Journal Geophysical Research 100, 8153-8167.

Manzoni, M., Nanni, T., 1977. Paleomagnetism of Ordovician lamprophyres from Taylor Valley, Victoria Land, Antarctica. Pure Applied Geophysics 115, 961-977.

Martin, D.L., Nairn, A.E.M., Noltimier, H.C., Petty, M.H., Schmitt, T.J., 1978. Paleozoic and Mesozoic paleomagnetic results from Morocco. Tectonophysics 44, 91-114.

McEIhinny, M.W., 1970. The paleomagnetism of the Cambrian purple sandstone from the Salt Range, West Pakistan. Earth Planetary Science Letters 8, 149-156.

McEIhinny, M.W., Cowley, J.A., Edwards, D.J., 1978. Palaeomagnetism of some rocks from Peninsular India and Kashmir. Tectonophysics 50, 41-54.

McEIhinny, M.W., Embleton, B.J.J., Daly, L., Pozzi, J.P., 1976. Paleomagnetic evidence for the location of Madagascar in Gondwanaland. Geology 4, 455-457.

Meert, J.G., van der Voo, R., 1996. Paleomagnetic and 4°Ar/ 39Ar study of the Sinyai dolerite, Kenya: implications for Gondwana assembly. Journal Geology 104, 131-142.


A. M. GRUNOW

Meert, J.G., van der Voo, R., Ayub, S., 1995. Paleomagnetic investigation of the Neoproterozoic Gagwe lavas and Mbozi complex, Tanzania and the assembly of Gondwana. Precambrian Research 74, 225-244.

Moreau, C., Demaiffe, D., Bellion, Y., Boullier, A.M., 1994. A tectonic model for the location of Palaeozoic ring complexes in Air (Niger, West Africa). Tectonophysics 234, 129-146.

Morel, P., 1981. Paleomagnetism of a Pan-African diorite: a late Precambrian pole for western Africa. Geophysical Journal Royal Astronomical Society 65,493-503.

Morel, P., Irving, E., Daly, L., Moussine-Pouchkine, A., 1981. Paleomagnetic results from Permian rocks of the northern Saharan craton and motions of the Moroccan Meseta and Pangea. Earth Planetary Science Letters 55, 65-74.

Nyblade, A.A., Lei, Y., Shive, P.N., Tesha, A., 1993. Paleomag- netism of Permian sedimentary rocks from Tanzania and the Permian paleogeography of Pangea. Earth Planetary Science Letters 118, 181 - 194.

Opdyke, N.D., 1964. The paleomagnetism of the Permian red beds of southwest Tanganyika. Journal Geophysical Research 69, 2477-2487.

Palmer, H.C., Hayatsu, A., MacDonald, W.D., 1980. The Middle Jurassic Camarac Formation, Arica, Chile: palaeomagnetism, K-Ar age dating and tectonic implications. Geophysical Journal Royal Astronomical Society 62, 155-172.

Porada, H., 1989. Pan -African rifting and orogenesis in southern to equatorial Africa and eastern Brazil. Precambrian Research 44, 103-136.

Powell, C.McA., Li, Z.X., 1994. Reconstruction of the Panthalassan margin of Gondwanaland. In: Veevers, J.J., Powell, C. McA. (Eds.), Permian-Triassic Pangean Basins and Foldbelts along the Panthalassan Margin of Gondwanaland. Geological Society America Memoir 184, 5-8.

Powetl, C.McA., Li, Z.X., McEIhinny, M.W., Meert, J.G., Park, J.K., 1993. Paleomagnetic constraints on timing the Neoproterozoic break-up of Rodinia and the Cambrian formation of Gondwana. Geology 21, 889-892.

Ramos, V.A., 1988. Late Proterozoic-Early Paleozoic of South America - a collisional history. Episodes 11, 168-174.

Rapalini, A.E., 1998. Syntectonic magnetisation of the mid- Palaeozoic Sierra Grande Formation: further constraints on the tectonic evolution of Patagonia. Journal Geological Society London 155, 105-114.

Rapalini, A.E., Astini, R.A., 1997. Paleomagnetic confirmation of the Laurentian origin of the Argentine Precordillera. Earth Planetary Science Letters 155, 1-14.

Rapalini, A.E., Tarling, D.H., Turner, P., Flint, S., Viias, J.F., 1994. Paleomagnetism of the Carboniferous Tepuel Group, central Patagonia, Argentina. Tectonics 13, 1277-1294.

Rapalini, A.E., Vilas, J.F., 1991 a. Preliminary paleomagnetic data from the Sierra Grande Format ion: tecton ic consequences of the first mid-Paleozoic paleopoles from Patagonia. Journal South American Earth Sciences 4, 25- 41.

Rapalini, A.E., Vilas, J.F., 1991 b. Tectonic rotations in the Late Palaeozoic continental margin of southern South America determined and dated by palaeomagnetism. Geophysical Journal International 107, 333-351.

Rapalini, A.E., Vilas, J.F., Bobbio, M.L., Valencio, D.A., 1989. Geodynamic interpretations from paleomagnetic data of late Paleozoic rocks in the southern Andes. In: Hillhouse, J.W. (Ed.), Deep Structure and Past Kinematics of Accreted Terranes. Geophysical Monograph Series 50, 41-57.

Renne, P.R., Onstott, T.C., D'Agrella-Filho, M.S., Pacca, I.G., Teixeira, W., 1990. 4°Ar/39Ar dating of 1.0-1.1 Ga magnetizations from the Sao Francisco and Kalahari cratons: tectonic implications for Pan-African and Brasiliano mobile belts. Earth Planetary Science Letters 101, 349-366.

Ripperdan, R.L., Kirschvink, J.L., 1992. Paleomagnetic results from the Cambrian-Ordovician boundary section at Black Mountain, Georgina Basin, western Queensland, Australia. In: Webby, B.D., Laurie, J.R. (Eds.), Global Perspectives on Ordovician Geology. A.A. Balkema, Rotterdam, pp. 93-103.

Rojas, C., Beck, M.E., Burmester, R.F., Cembrano, J., Herv@, F., 1994. Paleomagnetism of the Mid-Tertiary Ayacara Formation, southern Chile: counterclockwise rotation in a dextral shear zone. Journal South American Earth Sciences 7, 45-56.

Roperch, P., Cartier, G., 1992. Paleomagnetism of Mesozoic rocks from the Central Andes of southern Peru: importance of rotations in the development of the Bolivian orocline. Journal Geophysical Research 97, 17,233-17,249.

Royer, J.Y., Sandwell, D.S., 1989. Evolution of the eastern Indian Ocean since the Late Cretaceous: constraints from Geosat altimetry. Journal Geophysical Research 94, 13,755- 13,782.

Saradeth, S., Soffel, P., Horn, P., Muller-Sohnius, D., Schult, A., 1989. Upper Proterozoic and Phanerozoic pole positions and potassium-argon (K-Ar) ages from the East Sahara craton. Geophysical Journal International 97, 209-221.

Schmidt, P.W., Aubourg, C., Lennox, P.G., Roberts, J., 1994. Palaeomagnetism and tectonic rotations of the Hastings Terrane, eastern Australia. Australian Journal Earth Sciences 41, 547-560.

Schmidt, P.W., Embleton, B.J .J., 1990. The palaeomagnetism of the Tumblagooda Sandstone, Western Australia: Gondwana Palaeozoic apparent polar wandering. Physics Earth Planetary Interiors 64, 303-313

Schmidt, P.W., Embleton, B.J.J., Palmer, H.C., 1987. Pre- and post-folding magnetizations from the early Devonian Snowy River Volcanics and Buchan Caves Limestone, Victoria. Geophysical Journal Royal Astronomical Society 91, 155- 170.

Schmidt, P.W., Powell, C.McA., Li, Z.X., Thrupp, G.A., 1990. Reliability of Palaeozoic palaeomagnetic poles and APWP of Gondwanaland. Tectonophysics 184, 87-100.

Schmidt, P.W., Williams, G.E., 1995. The Neoproterozoic climatic paradox: equatorial palaeolatitude for Marinoan glaciation near sea level in South Australia. Earth Planetary Science Letters 134, 107-124.

Scotese, C.R., McKerrow, W.S., 1990. Revised World Maps and Introduction. In: McKerrow, W.S., Scotese, C.R. (Eds.), Palaeozoic Palaeogeography and Biogeography. Geological Society Memoir 12, 1-21.

Smith, A.G., 1997. Estimates of the Earth's spin (geographic) axis relative to Gondwana from glacial sediments and paleomagnetism. Earth Science Reviews 42, 161-170.

Taylor, G.K., Shaw, J., 1989. The Falkland Islands: new paleomagnetic data and their origin as a displaced terrane from southern Africa. In: Hilhouse, J.W. (Ed.), Deep Structure and Past Kinematics of Accreted Terranes. Geophysical Monograph Series 50, 59-72.

Thompson, R., 1972. Paleomagnetic results from the Paganzo Basin of northwest Argentina. Earth Planetary Science Letters 15, 145-156.

Thrupp, G.A., Kent, D.V., Schmidt, P.W., Powell, C.McA., 1991. Palaeomagnetism of red beds of the Late Devonian Worange Point Formation, SE Australia. Geophysical Journal International 104, 179-201.

Van der Voo, R. 1993. Paleomagnetism of the Atlantic, Tethys and lapetus Oceans. Cambridge University Press, Cambridge, 411p.

Valencio, D.A., Mendia, J.E., Vilas, J.F., 1975. Palaeomagnetism and K-Ar ages of Triassic igneous rocks from the Ischiqualasto-lschichuca Basin and Puesto Viejo formation, Argentina. Earth Planetary Science Letters 26, 319-330.


Gondwana events and palaeogeography: a pa/aeomagnetic review

Valencio, D.A., Vilas, J.F.,-1985. Evidence of a microplate in the southern Andes. Journal Geodynamics 2, 183-192.

Valencio, D.A., Vilas, J.F., Mendia, J.E., 1977. Palaeomagnetism of a sequence of red beds of the middle and upper sections of Paganzo Group (Argentina) and the correlation of upper Palaeozoic-lower Mesozoic rocks. Geophysical Journal Royal Astronomical Society 51, 59-74.

Valencio, D.A., Vilas, J.F., Mendia, J.E., 1980. Paleomagnetism and K-Ar ages of Lower Ordovician and Upper Silurian-Lower Devonian rocks from northwest Argentina. Geophysical Journal Royal Astronomical Society 62, 27-39.

Veldkamp, J., Mulder, F.G., Zi jderveld, J.D.A., 1971. Palaeomagnetism of Surinam dolerites. Physics Earth Planetary Interiors 4, 370-380.

Watts, D.R., Bramall, A.M., 1981. Paleomagnetic evidence for a displaced terrain in western Antarctica. Nature 293 ,638 - 641.

Wesink, H., 1968. Paleomagnetism of some Gondwana red beds from central India. Palaeogeography, Palaeoclimatology Pala~oecolgy 5, 323-343.

Wesink, H., 1972. The pa leomagnet ism of the Salt Pseudomorph beds of Middle Cambrian age from the Salt Range, West Pakistan. Earth Planetary Science Letters 16, 189-194.

Wesink, H., Hartosukohardjo, S., 1990. The palaeomagnetism of Late Permian-Early Triassic and Late Triassic deposits on Timor: an Australian origin? Geophysical Journal International 101, 315-328.


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Gondwana events and pal˦ogeography:A pal˦omagnetic review