and Planetary Science Letters 154Ž. 1998 13±24

The : paleomagnetically derived reconstructions for 1100 to 800 Ma

Arlo B. Weil a,), Rob Van der Voo a, Conall Mac Niocaill a, Joseph G. Meert b a Department of Geological Sciences, UniÕersity of Michigan, Ann Arbor, MI 48109-1063, USA b Department of , Indiana State UniÕersity, Terre Haute, IN 47809, USA Received 1 January 1997; revised 24 June 1997; accepted 9 July 1997


Well-dated paleomagnetic poles for the interval 1100±800 Ma have been compiled for the , , SaoÄ Francisco, Congo and Kalahari in order to construct apparent polar wander pathsŽ. APWPs for this interval. Laurentia's APWP consists of a well-determined Keweenawan track for 1100±1000 Ma and a 1000±800 Ma Grenville loop. We use a counterclockwise APW loop for the Grenville poles based on ages for post-metamorphic cooling through ;5008C for the Grenville Province between 1000 and 950 Ma, and the temporal and spatial similarities with Proterozoic counterclockwise APWP's for other cratons. Baltica's APWP is comprised of seven dated poles that define a similar loop, counterclockwise and hinged at 950 Ma, that can be superimposed on the Laurentian Grenville loop. This loop is also seen in the seven poles of the APWP for the combined SaoÄ Francisco±Congo ; superposition of these loops leads to a reconstruction in which the SaoÄ Francisco± is to the south-southeast of Laurentia in present-day coordinates. A long 1090±985 Ma APWP track for the Kalahari is in reasonable agreement with the roughly coeval Keweenawan track, when the is rotated ;408 counterclockwise away from the Congo craton while remaining hinged at the Zambezi belt. The resulting Rodinia reconstruction resembles those previously proposed on geological grounds for Laurentia, East , Baltica, SaoÄ Francisco±Congo, and the Kalahari craton. q 1998 Elsevier Science B.V.

Keywords: ; reconstruction; ; upper Proterozoic

1. Introduction paleomagnetic data by Piperwx 2±4 , the more recent reconstructions of a shorter-lived Rodinia have continental reconstructions have re- largely been based on geological evidence linking cently become the subject of renewed interest fol- truncated Meso-Proterozoic mobile beltswx 5±7 . In lowing the proposal that all major continental blocks the latter scenario the assembly of Rodinia is marked were part of a long-lived late Proterozoic superconti- by Grenville-aged deformation Ž.;1.1 Ga on the nent: Rodiniawx 1 . While the existence of a major margins of Laurentia, East Gondwana, Amazonia long-lived Ž.;2500±500 Ma Proterozoic superconti- and Balticawx 8 , with the western margin of Laurentia nent had earlier been advocated on the basis of facing East in the so-called SWEAT con- nectionŽ southwest U.S.A.±East Antarctica;wx 5. . This hypothesis has received partial support from paleo- ) Corresponding author. magnetic data in that the apparent polar wander

0012-821Xr98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S0012-821XŽ. 97 00127-1 14 A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24 pathsŽ. APWPs for Laurentia and East Gondwana tion ages, absence of local structural control, in- are in relatively good agreement for the time period creased scarcity of results per unit of time, and of 1050±750 Ma in a SWEAT fitwx 9,10 . Breakup ambiguous polarity assignments. The most important and redistribution of the continental elements of uncertainty in Proterozoic paleomagnetism is usually Rodinia seems to have been initiated at ;750 Ma the poor control on the age of magnetization; it is with the separation of East Gondwana from the notoriously difficult to date sedimentary sequences western margin of Laurentiawx 9,11,12 . This rifting without faunal data and studies from metamorphic event and subsequent drift of the rifted elements rocks rely heavily on reset isotopic ages, which may eventually led to the amalgamation of East and West or may not record the age of remanence acquisition. Gondwana at ;550 Mawx 13±15 . Incorrect age assignments can therefore lead to mis- However, other links in the Rodinia reconstruc- leading APWPs with inherently negative conse- tion remain poorly substantiated, especially where it quences for the reconstructions derived from those concerns the paleopositions of the individual South paths. American and African elements, for the interval With this in mind, we have reviewed the available following Grenville-aged assembly, i.e., 1100±800 1100±800 Ma paleomagnetic data from the Lauren- Ma. In this paper, we review the existing paleomag- tian, Baltic, Congo, SaoÄ Francisco and Kalahari cra- netic database available for this interval for several tons, paying special attention to the age assignments major Proterozoic cratonsŽ Laurentia, Baltica, Kala- for the individual poles. Nearly all paleopoles so hari, and the SaoÄ Francisco and Congo blocks. , and selected have age uncertainties believed to be less use these compilations to generate independent APW than "80 Myr, and about half of them less than paths for each of them. We then use these APWPs to "40 Myr. The approach we have taken has been to test and modify proposed continental fits for this generate individual APWPs for each of the cratons, time period. with the most accurately dated key poles providing an age calibration, and we have examined these paths for similarities in their geometries and time 2. Assumptions and methods progression. Where these paths exhibited similarities in both their shapes and age progressions, we rotated Testing Precambrian plate reconstructions relies the paths into coincidence with each other and used heavily on paleomagnetic data in addition to correla- the resulting Euler poles to fit the individual cratons tions between the fragmented geological records of into paleomagnetically constrained reconstructions. the various continental nuclei and their deformed This approach differs from that of Piperwx 4 who margins. However, for the use of paleomagnetic data assembled all paleopoles into a single common global for paleogeographic reconstructions for this time pe- APWP for his Proterozoic supercontinent. The con- riod to be valid the following assumptions must be struction of a single global APWP a priori assumes granted:Ž. 1 the geomagnetic field must have been the existence of a supercontinent and forces all avail- that of a geocentric dipole when averaged over a able paleomagnetic poles, regardless of their reliabil- sufficiently long period of time; andŽ. 2 the Earth's ity or age constraints, to fall somewhere on an radius has not changed significantly. These assump- APWP based on a preconceived continental configu- tions have been shown to be reasonable for the ration. When dealing with the Proterozoic data-set it Phanerozoicwx 16 , but are largely untested for the is almost always possible to create a common, albeit Proterozoic. A controversy has arisen, in fact, about convoluted, path that is within theŽ. ample errors that possibly asymmetric reversals at ;1.1 Ga, that will are typical of Precambrian paleomagnetic data be discussed below. wx17,18 . However, Piper's reconstruction has re- Along with these assumptions, one must also mained ambiguous and is unreliable for intervals recognize that there are generally greater uncertain- without intercontinental agreement between well- ties in many of the Precambrian paleomagnetic data dated paleopoles, as shown by Van der Voo and than for paleopoleswx 17,18 . Included in Meertwx 18 , Meert et al. wx 19 and Torsvik and Meert these uncertainties are poorly controlled magnetiza- wx20 . A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24 15

3. A review of 1100±800 Ma paleomagnetic data opoles in this interval are from Keweenawan sedi- mentsŽ Fond du Lac, Eileen, Middle River, Freda, Jacobsville in Table 1. . They differ much more in 3.1. Laurentia declination than inclination, which may suggest some relative rotations between the sampling areasŽ located The Proterozoic data-set for in Minnesota, Wisconsin, Michigan, and Ontario. . Ž.Laurentia constitutes the most complete of any of We have drawn our generalized Laurentian path the major . The Keweenawan sequence through the western part of this grouping, passing the Ž.1.1±1.0 Ga of the Lake Superior has yielded equator at ;1508E. While a more convoluted APWP a fairly long APW track based on the most exten- is not precluded, we note that a smoother APWP at sively studied rocks of the entire Precambrian. Char- ;1.0 Ga will serve our attempts to match APWPs acterized by good stratigraphic, geochronological and just as well. structural control, over 60 paleopoles, forming the The time progression of paleopoles from the well-known ``Logan Loop'', have been compiled Grenville Province of northeastern Laurentia has wx21 . The Keweenawan rocks have experienced very generated considerable debate in the last few decades little penetrative deformation since their formation, wx4,28±33 . While all studies agree that the and magnetizations are generally regarded as pri- Grenville-aged paleopoles Ž.;1.0±0.8 Ga fall in the mary. A good review of the available paleomagnetic southwest Pacific quadrantŽ. Fig. 1 , there are argu- poles of Keweenawan age can be found in Halls and ments about the sense of younging along the APWP, Pesonenwx 21 . either clockwise or anticlockwise, for this period. There may exist, however, a potential problem in The temporal uncertainties arise from the highly the Keweenawan APWP in that some coeval normal metamorphic of the rocks of the Grenville and reversed polarity directionsŽ e.g., at Mamainse Province, as high as amphibolite grade, in which all Point. are distinctly and perhaps repeatedly non-anti- magnetizations must have been thermallyŽ andror podalwx 22±24 , which may indicate asymmetric re- chemically. reset. Consequently, magnetization ages versals of the field. This, in turn, could imply that are not easily obtained; while age constraints for the the geomagnetic field was not, on average, dipolar Grenville APWP limit the ensemble of paleopoles to wx25 . In contrast, Lewchuk and Symons wx 26 and the interval of 1.0±0.8 Ga, ages of individual results Symonswx 27 have argued that their own observations are uncertain. of multiple reversals provide strong evidence against Some researchers have used the ArrAr isotopic the concept of asymmetric reversals and that the system to derive empirical cooling curves based on Mamainse Point record incompletely averaged secu- mineral blocking temperatures as a method for se- lar variation. Regardless of the eventual outcome of quencing Grenville multi-component magnetizations this debate, it appears prudent to keep the possibility wx28,29,32,34±36 . The assumption in this method is of asymmetric reversals in mind when assessing the that, given two or more magnetic components from precision of 1.08±1.11 Ga paleopoles, which may an area that appear to be of different ages, a young- therefore have an inherent uncertainty of about "158. ing sequence of magnetizations can be derived from The combined Keweenawan APW track defines specific mineral cooling historiesŽ e.g., hornblende the earlier part of Laurentia's 1100±800 Ma APWP. and biotite. that relate to unblocking temperatures of Individual paleopoles are listed in Table 1. Cluster- the magnetic minerals. The main problem with this ing of poles and time progression at the older end of technique seems to be with the contradictory results the trackŽ. 1100±1070 Ma is as complete for the of the relative age assignments. Magnetic sequencing Precambrian as can be hoped for and forms a south- tied to cooling curves has produced results showing west-younging path. We assume here that the Pacific APWP younging trends in both clockwiseŽ. Fig. 2 APWP of Laurentia represents northpoles. While this and anticlockwise directions. The inherent difficulty path leads, without discontinuity, into the 1000±800 in obtaining ages of isotopic system closure relative Ma poles from the Grenville ProvinceŽ. Fig. 1 , the to remagnetization ages, especially those of meta- paleopoles for ; 1020±1010 Ma scatter from morphic rockswx 37,38 , does not help resolve APWP ;258N, 1508Eto108S, 1858E. Many of the pale- younging trends. 16 A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24

Table 1 Proterozoic paleomagnetic northpoles used for Rodinia APWP construction

Pole Age Age Pole long. Pole lat. KAQ95 Reference range assignedŽ. E88 Ž. LaurentiarKeweenawan Tracka Seabrook Lake 1077±1149 1113 180 46 13 11 6wx 27 Mean Logan sills 1106±1112 1109 220 49 976 3 5wx 21 Mean Logan dikes ;1100 1100 181 35 165 10 6wx 21 Lower Normal, Upper Osler Group 1095±1101 1098 178 34 82 9 4wx 67 Portage Lake volcanics 1094±1098 1095 181 27 49 2 4wx 68 Mamainse Point volcanics 1083±1097 1090 188 38 28 1 4wx 69 Chipman Lake carbonatites 991 1090 186 38 25 8 5wx 27 Mamainse Point Intrusive Unit 1083±1088 1085 166 24 17 31 3wx 69 Clay±Howells Complex 1060±1090 1075 179 27 26 7 5wx 26 Michipicoten Island volcanics 1088 1075 175 25 9 8 4wx 69 Copper Harbor conglomerate 982±1095 1060 176 35 239 4 5wx 70 Nonesuch 1000±1092 1046 177 10 22 6 5wx 71 K1 Fond du Lac sandstonesrshale 950±1088 1020 160 16 58 61 3wx 37 Eileen 950±1040 1020 156 20 10 10 3wx 37 Middle River sandstonesrshale 950±1041 1020 148 25 16 9 3wx 37 Freda sandstones 982±1075 1020 180 1 31 3 4wx 71 Jacobsville sandstones 950±1040 1010 183 y9296572wx Grenville Thermochron Zone A ;1000 1000 159 1 140 6 3wx 28 Greenschist Reset 950±1000 990 152 y52211173wx Nipissing Reset 950±1000 975 141 y27 12 8 3wx 73 Granodiorites Reset 950±1000 960 150 y37 18 8 2wx 73

Baltica Laanila dyke swarm, Finland 998"80 1020 218 y4296243wx Within Protogine Zone ;950 950 211 y44 86 11 3wx 43 East of Protogine Zone ;950 950 210 y42 ± ± 2wx 43 West of Protogine Zone ;950 950 217 y45 34 5 4wx 43 East of Protogine Zone ;850 850 242 0 ± ± 2wx 43 West of Protogine Zone ;850 850 241 4 66 10 3wx 43 West of Protogine Zone ;850 850 231 y25 131 7 4wx 43

Congo Nyabikere, Burundi ;950 950 137 43 25 14 3wx 74 Gagwe lavas, Tanzania 788±838 813 93 25 5 10 5wx 14 Bukoban intrusives, Tanzania 776±836 806 101 11 5 19 4wx 75

SaoÄ Francisco " y wx Olivenca dikesŽ. OR 1078 18 1078 100 10 17 9 4 46 Calculated mean Itaju do Colonia pole ;1050 1055 111 8 11 10 4wx 46 ; wx Olivenca dikesŽ. ON 1050 1030 107 16 12 8 4 46 Ilheus dikes 1012"24 1012 100 30 79 4 4wx 46

Kalahari Post-Waterberg Diabase, Botswana 1076±1106 1091 231 y65 31 8 5wx 76 q140 y wx Umkondo dolerites, Zimbabwe 1082y25 1080 223 65 66 6 2 77 q140 y wx Umkondo combined, Zimbabwe 1081y25 1075 208 64 20 8 3 78 q140 y wx Umkondo lavas, Zimbabwe 1080y25 1070 196 63 13 15 2 78 A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24 17

Table 1Ž. continued

Pole Age Age Pole long. Pole lat. KA95 QReference range assignedŽ. E88 Ž. Kalahari Kalkpunt Fm.Ž. Koras Grp. 1049±1080 1065 183 y57 67 7 3wx 79 O'Okiep intrusives, S. ;1030 1030 155 y15 28 15 1wx 80 Central Namaqua Metamorphic Zone ;1000 1000 150 y82610355wx Port Edward Charnockite, S. Africa 960±1010 985 148 5 57 9 1wx 55 a Other Grenville poles can be found in Hyodo and Dunlopwx 32Ž. their table 5 . All poles are inferred to be northpoles Q is the quality factor wx16,18 .

The Grenville paleopoles plotted in Fig. 1 have curred between 1000 and 950 Ma in the Grenville been taken from Hyodo and Dunlopwx 32 ; because of Provincewx 39±42 . If this is true, then few or no space restrictions, they have not been listed in Table Grenville A-group poles would be expected to fall 1. The Grenville paleopoles derived from multi-com- on the returnŽ. northward path with an age range ponent magnetizations typically fall into two groups from 950 to 800 Ma. This indeed appears to be the related to their effective magnetic unblocking tem- case if the counterclockwise loop is acceptedŽ see peratures; an ``A Group'' that is thought to reflect Fig. 1. , but does not agree with recent proposals for the time of peak Grenville regional metamorphism or the clockwise loopŽ. Fig. 2 . This argument, com- metamorphic cooling from high temperaturesŽ poles bined with the temporal and geometric progression falling near ;308S. , and a ``B Group'' that includes of poles from Baltica, to be discussed below, leads polesŽ. near the equator thought to be related to the us to prefer a counterclockwise Grenville Loop. later cooling at lower temperatures andror post-oro- genic upliftwx 35 . However, it is generally accepted 3.2. Baltica that post-metamorphic cooling through ;5008Coc- Baltica's APWP for the 1100±800 Ma interval is comprised of seven mean polesŽ Table 1;wx 43. that define a loop, hinged at 950 Ma, similar to the

Fig. 1. Grenville and Keweenawan paleopolesŽ. from Table 1 from Laurentia Ž.white , and Baltica Ž.grey for the 1100±800 Ma time interval. Notice the counterclockwise time progression with the inclusion of Baltic paleopoles. Baltica has been rotated accord- Fig. 2. Grenville poles used by Hyodo and Dunlopwx 33Ž their table ing to Piper'swx 4 Late Precambrian fitŽ. Table 2 . 5. , representative of the alternative clockwise APWP. 18 A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24

Table 2 Euler poles used for Rodinia reconstruction in Fig. 6 Continental blockrw.r.t. other Pole lat. Pole long. Rotation Reference BalticarLaurentia 80.5 274.0 y66.5wx 4 GreenlandrLaurentia 67.5 y118.5 y13.8wx 83 CongorLaurentia 7.0 150.0 185.0 This study SaoÄ FranciscorCongo 53.0 y32.2 57.5wx 50 KalaharirLaurentia y15.0 156.0 147.0 This study Rio PlatarLaurentia 9.5 315.0 y96.5 This study AmazoniarLaurentia 9.5 315.0 y96.5 This study SiberiarLaurentia 29.3 341.2 19.6wx 45 IndiarLaurentia 53.1 145.1 168.0wx 84 MadagascarrLaurentia 28.6 123.8 170.2wx 8 AustraliarLaurentia 28.9 126.1 132.1wx 8 East AntarcticarLaurentia 12.8 119.9 134.8wx 8

Rotation pole to rotate Laurentia in Fig. 6 relative to globe iswx 08, 2308,928, clockwise for 1010 Ma, using the paleopoles for that time wx 32 .

Laurentian loop, as just described. Age assignments wx49 . When restored to their pre-Atlantic configu- are taken from Pesonen et al.wx 43 and define a rationŽ according to de Wit et al.wx 50 or Rabinowitz counterclockwise geometryŽ. Fig. 1 . Superposition of et al.wx 51. , the two cratons are surrounded, but not the Sveco-Norwegian paleopoles of Baltica and the dissected, by Braziliano and Pan-African mobile belts Grenville poles of Laurentia has previously been of late Proterozoic age. attemptedwx 44,33,3,4,16 , and in all cases a juxtaposi- Until recently, the paucity of paleomagnetic poles tion without continental overlap of the two continen- from these two cratons, for the interval 1100±800 tal blocks is achieved. We find that Piper'swx 4 fit for Ma, has made it difficult to make any substantive the Late Precambrian between Baltica and Laurentia comparisons between the APWP of the combined provides the best estimate of the Euler parameters SaoÄ Francisco±Congo craton and those for the re- that superpose the two APWPsŽ. see Table 2 . It mainder of Rodinia. Therefore, reconstructions have differs somewhat from the recent fit of Torsvik et al. been based mainly on geologic similarities and have wx45 , which is based on the less well-constrained been rather different from each otherwx 7,8 . However, paleopoles of Laurentia and Baltica for the interval four paleopoles from mafic dikes in Brazil have now 0.8±0.6 Ga. become availablewx 46 from an area in the SaoÄ Fran- After rotation, Baltica's paleopoles come into cisco craton that is well to the east of the good coincidence with the Laurentian counterclock- EspinhacËo±Sententrional±Paramirim transcurrent wise loopŽ. Fig. 1 . Moreover, the two paths show zone, and therefore a part of the stable SaoÄ Fran- identical time progression, with a correlative hinge at ciscorCongo cratonwx 48 . Two of these dike sets are ;950 Ma. Results from both continents combined well-datedwx 52 so that a well-constrained APWP will be used next in comparisons with APWPs from segment can be constructed. Similarly, three well- other blocks. dated results from the East African part of the Congo craton have become available, although these are for a younger time interval than those from Brazilwx 14 . 3.3. Congo and SaoÄ Francisco blocks Given that the Congo and SaoÄ Francisco cratons were connected throughout the 1100±800 Ma inter- The Congo craton of Central Africa and the SaoÄ val, a common APWP is constructed, after restoring Francisco cratonŽ. SF of the Bahia State region of the two parts to their pre-Atlantic configuration. This Brazil, , have long been recognized as APWP, assumed to be southpoles, reveals a clock- having had a long-lived Precambrian connection wise loop near present-day South AmericaŽ. Fig. 3 . wx46±48 , perhaps extending back as far as ;3.0 Ga The corresponding northpole APWP falls in the cen- A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24 19

bined Laurentia±Baltica APWP in North American coordinatesŽ. Fig. 4 . Agreement between the Congo± SaoÄ Francisco and Laurentia±Baltica poles with sim- ilar ages is generally within 158. The corresponding Congo±SaoÄ Francisco± Laurentia paleoreconstruction, derived from the above rotation with respect to Laurentia, loosely resembles Dalziel'swx 8,53 reconstructionsŽ. Fig. 4 . As seen in Fig. 4, the Congo±SaoÄ Francisco blocks end up east-southeast of Laurentia and differ from Dalziel'swx 8 reconstruction by ;158, which is prob- ably about the minimum accuracy of the paleomag- netic method for the . This similarity is noteworthy in that Dalziel's fit is based on geo- logic similarities, and not on any paleomagnetic pole data. Our fit has lesser similarities with that of Fig. 3. South America is rotated with respect to a fixed AfricaŽ for Hoffmanwx 7 , because he juxtaposes the Irumide and Euler poles, see Table 2.Ž. . The Congo craton of Africa dark grey and the SaoÄ Francisco craton of South America Ž.white are plotted Kibaran belts of East Africa and the Grenville belt of with their respectiveŽ. south paleopoles Ž Table 1 . . southeastern Laurentia. Such a connection has the Congo±SaoÄ Francisco craton rotated by ;1808 from tral-west Pacific and shows a counterclockwise loop. this study. Incidentally, the earlier reconstruction of When rotated about an Euler Pole at 7.08N, 150.08E, Piperwx 3,4 , who inferred that West Gondwana was a with a 1858 counterclockwise angleŽ. Table 2 , a coherent cratonic block during the entire Proterozoic, satisfactory correlation is achieved with the com- had the Congo block much further to the south with

Fig. 4.Ž. A Schematic APWP for Laurentia and Baltica Žgrey swath ., and Congo and SaoÄ Francisco paleopoles Ždots .plotted in a Laurentian reference frame. Congo's APWP has been rotated with respect to Laurentia according to the Euler Pole: 1508,78, 1858 counter clockwise. For pole references see Table 1. Ž.B Corresponding reconstruction of Rodinia according to a 1010 Ma Laurentian pole, with the Congo craton Ž.white rotated as above. Also shown is Dalziel'swx 8 Congo reconstruction Ž.dark grey based on geologic observations. 20 A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24 respect to Laurentia than is the case in the Rodinia into good coincidence with the Laurentia±Baltica configurations; Piper's configuration is not supported APWPŽ. Fig. 5 . Unfortunately, no Kalahari pale- by our study. opoles are available for the upward leg of the Lau- rentia±BalticaŽ. Grenville-aged loop. 3.4. Kalahari The resulting paleogeographic reconstruction of the Kalahari craton with respect to the rest of Ro- The Kalahari craton of southern Africa, like the diniaŽ. Fig. 5 shows a reasonable similarity to previ- Congo, has previously been positioned within Ro- ous reconstructions. Dalzielwx 6 placed the Kalahari dinia with rather large uncertainties. The main issue in juxtaposition with Antarctica, the Ellsworth± of contention stems from two schools of thought Whitmore and southern Laurentia, and regarding the tectonic history of the Damara belt close to its present-day position with respect to the between the Congo and the Kalahari cratons: the Congo cratonŽ. Figs. 4 and 5 . Similarly, Hoffmanwx 7 recently prevailing argument is for an ensimatic ori- places the Kalahari craton near East Antarctica and gin for this Pan-African mobile beltwx 54,55,7,8 , southern Laurentia, matching the Lurian and Na- whereas an earlier model of an ensialic originwx 56±58 maqua±Natal belts of Kalahari with the Grenville- invokes instead a tectonothermal event affecting a aged belts of Antarctica and southeastern Laurentia. previously coherent cratonic Kalahari±Congo block. A third reconstructionwx 52 compared the paleopoles The Kalahari craton has yielded eight paleomag- from the SaoÄ Francisco cratonwx 46 and those from netic poles that are dated between 1100 and 985 Ma the Kalahari, resulting in a counterclockwise rotation Ž.Table 1 . These poles define a long track of APW of ;908 around the edge of the Congo craton. that shows temporal continuity and a reasonable rate Several other recent reconstructionswx 59,60,47 place of continental motion with respect to the pole distri- the Kalahari rotated counterclockwise by ;30±408 bution. When theŽ. presumed north poles are rotated with respect to a similar hinge in the Zambezi belt about an Euler Pole at 15.08S, 156.08E, angle 1478 southeast of the Congo craton. Most recently, Gose counterclockwiseŽ. Table 2 , Kalahari's APWP comes et al.wx 61 have shown that paleomagnetic results

Fig. 5.Ž. A Schematic combined Laurentia±Baltica APWP Žgrey swath ., with the seven Kalahari paleopoles Ždots; Table 1 . for the 1100±950 Ma time interval, rotated into coincidence and plotted in a Laurentian reference frameŽ. refer to Table 2 . Ž.B Corresponding reconstruction of the Kalahari craton with respect to the rest of Rodinia with paleolatitudes according to a 1010 Ma Laurentian pole. Also shown is Dalziel'swx 8 Kalahari fit. A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24 21 from Coats and sections of western Dronning untested, as are the locations of smaller Maud LandŽ. CMG , Antarctica, were linked to the Ž.Arequipa, Precordillera, etc. . Kalahari craton at 1.1 Ga, and not to the East This paper shows that sequential paleopolesŽ when Antarctic Interior as previously suggested. Their sub- dated and numerous enough per unit of time. can sequent Rodinia reconstruction places the Kalahari give sufficient character or ``fingerprint'' to APWPs and CMG near the other cratons of West Gondwana, to generate intercratonic Proterozoic reconstructions similar to the position proposed here, with a later with a resolution of ;158. Congruence of looping suturing to East Gondwana as the Mozambique Ocean APWP tracks suggests that there was no relative closed interior toŽ. present day East Antarcticaw 62± motion between the separate cratonic blocks, and 64x . that they, to first approximation, were part of a The paleopoles used in this studyŽ. Table 1 create single supercontinent during the time involved. Geo- a paleogeographical position for the 1100±950 Ma metric similarities and temporal sequencing of the intervalŽ. Fig. 5 with the Kalahari rotated ;358 individual APWPs have been used in this paper to counterclockwise away from the Congo craton. This demonstrate evidence for a Rodinia reconstruction reconstruction is in good agreement with geologic Ž.Fig. 6 that resembles those previously proposed evidence found in the intervening Pan-African belts wx5±8,53,61 for Laurentia, East Gondwana, Baltica, of southern Africa. There is a recent general consen- Kalahari and SaoÄ Francisco±Congo. sus that a Neoproterozoic westward widening rift structure created an embayment of oceanic floor in the Khomas basin of the Damara belt. This embay- ment terminated at a transform type boundary lo- cated near the Zambezi belt on the northeastern margin of the Kalahari cratonwx 65 . Other geologic evidence, such as sediment transport direction analy- sis, subsidence advancement, and structural evidence also support an eastward narrowing rift between the Congo and Kalahariwx 66,60 .

4. Discussion

The paleomagnetic evidence for Rodinia's config- uration is still quite scant, but steadily improving as new results become available. The Baltica±Laurentia fitwx 4 as supported by this study and the reconstruc- tions between Laurentia and East GondwanaŽ i.e., wx ; 9. and Congo±SaoÄ Francisco as well as Fig. 6. Proposed Rodinia reconstruction with all cratons rotated KalahariŽ. this study are removing some of the previ- with respect to a 1010 Ma Laurentian paleopole according to the ously large uncertainties about the relative positions Euler poles of Table 2. Grenvillian orogenic belts highlighted in wx of Rodinia's continental constituents. The paucity of black stipple after Hoffman 7 . Uncertainties in the position of 8 s paleomagnetic data still plays a limiting role in our the cratons can be as large as 15 . AM Amazonia craton; AsAustralia craton; BAsBalticaŽ. Fennoscandia ; CsCongo ability to test the reconstruction involving other con- craton; CMGsCoates Land±Maudheim±Grunehogna Province tinental blocks, such as , South China, Ama- wx61 ; E s Ellsworth±Whitmore Block; EA s East zonia and the Rio de la Plata craton. In Fig. 6, we Antarctica; GsGreenland; IsIndia; K sKalahari craton; Ms have positioned the latter two South American cra- ; RP sRio de la Plata craton; SsSiberia craton; s s tons adjacent to the Appalachian margin of Lauren- SF SaoÄ Francisco craton; WA West Africa craton. Not in- cluded are the North and South China blocks, believed by some to tia. Given that there are no paleopoles from these border the western margin of Laurentiawx 81,82 . For discussions of cratons, their positions are paleomagnetically proposed fits for Siberia, seewx 45,82 . 22 A.B. Weil et al.rEarth and Planetary Science Letters 154() 1998 13±24

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