Testing the Rodinia hypothesis: Records in its building blocks

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Precambrian Research 160 (2008) 1–4

Preface

Testing the Rodinia hypothesis: Records in its building blocks

“Did Rodinia ever exist?” is still a question in many geoscientists’ minds. This Special Issue focuses on recent data and ideas relating to the Precambrian supercontinent Rodinia, and presents the first Geodynamic Map of Rodinia (Appendix I in Li et al., this issue)—a final product of the UNESCO/IUGSsponsored IGCP-project 440 “Rodinia Assembly and Breakup”. The first suggestion of a late Precambrian supercontinent was made by Valentine and Moores (1970). It came out of the Asilomar Penrose conference on “The Meaning of the New Global Tectonics for Geology”, which was held in December 1969. This hypothesis was building on ideas that Alpine- and Appalachian-style orogenic belts were from the collision of previously separate continents and generalized from the global distribution of late Precambrian Pan-African-Baikalian orogenic belts demonstrated by Dewey and Horsfield (1970). Valentine and Moores suggested that the break-up of a supercontinent, which they called Pangaea I had, by the Cambrian, led to a divergence of environments and characteristics among the daughter continents and a sudden prominence of shallow, nutrient-rich shelves and coastal areas, all factors conductive to the diversification of life forms on the Earth. Piper (1976) published a Precambrian supercontinent fit with continents in fairly conventional positions and argued that this supercontinent had lasted from about 2 Ga until the Permian. Subsequently, McMenamin and McMenamin (1990) coined the names “Rodinia” (from the Russian word “rodit”’ = to beget) for that supercontinent and “Mirovia” (from Russian “mirovoy” = “world-wide”) for the surrounding world ocean. To them, Rodinia was the motherland of all subsequent continents separated during its break-up, which can also explain the explosion of life at the end of the Proterozoic and in the early Cambrian. During the early search of geological evidence for Rodinia, three papers by Moores (1991) and Dalziel (1991) in Geology, and Hoffman (1991) in Science were published nearly simultaneously, showing the first Rodinia configurations, its break-up and the formation of the Gondwana daughter-continental assembly. These approaches and a growing paleomagnetic database have underlain all subsequent Rodinia reconstructions (see Dalziel, 1997; Powell and Meert, 2001, and references therein). 0301-9268/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2007.06.010

In the mid 1990s, it became clear that conjectural data on the tectonic evolution of continental blocks in the Meso- and Neoproterozoic, and the absence of reliable geochronological and paleomagnetic constraints hampered progress in the search for Rodinia. Reconstructions often contradicted each other, which sometimes created doubts on the existence of this supercontinent. This confusion was partly due to later tectonic overprinting on the geological records of Rodinia history, but still more due to the lack of high-quality paleomagnetic and geological (particularly geochronological) data for each of the Meso- and Neoproterozoic continental blocks. In order to improve knowledge of Rodinia, IGCP-project 440 “Rodinia Assembly and Break-up” was launched in 1999. The initial project co-leaders were Rafael Unrug from Wright State University, Dayton, OH, USA, and Chris M.A. Powell of the Tectonics Special Research Centre, University of Western Australia, who were inspired by the achievements made during the reconstruction of Gondwana (IGCP 288; Unrug, 1997). The objective of IGCP 440 was to obtain a robust database and framework for the interpretation of the geodynamic evolution of the continental lithosphere during the late Mesoproterozoic and Neoproterozoic. In particular, the project aimed at the compilation of the “Geodynamic Map of Rodinia” (Rodinia Map hereafter). The untimely loss of the two principal co-leaders of IGCP 440 in the first 3 years of the life of the project seriously challenged the compilation of the Rodinia Map. During the Rodinia symposium organized by the Tectonics Special Research Centre in Perth in 2001, the Rodinia Map Committee nevertheless decided to continue the mapping project but with a simplified legend, which focuses on first-order tectonic settings relevant to the assembly and break-up of Rodinia (Li et al., Appendix I). As different from common geological and tectonic maps, colors in the Rodinia Map describe tectonic settings between 1600 and 700 Ma with their tones reflecting the ages. Pre-1600 Ma rocks are marked in grey in order to highlight Rodinia-related features. Rock ages are shown using 100 Ma as a unit instead of 1 Ma. Thus, for instance, the number 22 labels ages of ca. 2200 Ma. Between 2001 and 2004, the project was led by Svetlana Bogdanova (Lund University, Sweden), Henri Kampunzu (University of Botswana) and Zheng-Xiang Li (Tectonics Special Research Centre, University of Western Australia), and the project secretary Sergei Pisarevsky (also Tectonics Special

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Preface / Precambrian Research 160 (2008) 1–4

Research Centre, University of Western Australia). Over 300 geoscientists from 40 countries participated in the project. In 2004, the project suffered again when Professor Henri Kampunzu passed away without having been able to see the final results of the project as presented in the present volume. Various results from IGCP 440 were published in a number of special issues of scientific journals (cf. below), over 150 individual papers and PhD theses, and ca. 350 conference abstracts. They were also demonstrated at a number of international and national conferences, and finally during the Rodinia session at the 32nd International Geological Congress in Florence, Italy, in August 2004 and at the Supercontinents and Earth Evolution Symposium in Fremantle, Western Australia, in October 2005. Journal special issues sponsored by IGCP 440 or with a significant portion of papers by project participants include: • Neoproterozoic of Australia (Guest Editor: Malcolm R. Walter), Precambrian Research, Vol. 100 (2000). • Crustal Evolution in South and Southeast Asia (Co-editors: S. Hada, M. Yoshida, Z.X. Li, and X. Wang), Gondwana Research, Vol. 4 (2001). • Assembly and Break-up of Rodinia (Guest Editors: C.McA. Powell and J. Meert), Precambrian Research, Vol. 110 (2001). • Rodinia and the Mesoproterozoic Earth–Ocean System (Coeditors: L.C. Kah and J.K. Bartley), Precambrian Research, Vol. 111 (2001). • Mantle plumes: their identification through time (Co-editors: R.E. Ernst and K.L. Buchan), GSA Special Paper Series, Vol. 352 (2001). • Precambrian Tectonics of East Asia and Relevance to Supercontinent Evolution (Guest Editors: Z.X. Li, M. Cho, and X.H. Li), Precambrian Research, Vol. 122 (2003). • Orogenic Belts, Regional and Global Tectonics (Guest Editors: K. Sircombe and M.W. McElhinny), Tectonophysics, 375 (2003). • Proterozoic East Gondwana: Supercontinent Assembly and Break-up (Editors: M. Yoshida and B.F. Windley), Geological Society of London Special Publication, No. 206 (2003). • Assembly and Break-up of Rodinia and Gondwana: Evidence from Eurasia and Gondwana (Guest Editors: M. Yoshida, A.B. Kampunzu, Z.X. Li and T. Watanabe), Gondwana Research, Vol. 6 (2003). • The present volume. The present Special Issue sums up the evolving knowledge of the Meso- and Neoproterozoic history of the lithosphere obtained during the work of IGCP 440 on the Rodinia reconstruction, employing a range of direct and circumstantial evidence. The presence of ca. 1.3–1.0 Ga belts of continent–continent collision, the 1.2 Ga peak of global-scale growth of juvenile crust (Condie, 2001), platformal basins extending across several continental blocks and similar Mesoto Neoproterozoic apparent polar wandering paths (APWPs) for many continents can all be considered as direct evidence of Rodinia’s existence. However, defining the positions of the different continental blocks within Rodinia rests on many indirect indications. Among these, signals of simultaneous Neoprotero-

zoic supercontinent break-up such as mafic dike swarms, large igneous provinces, extended rifted/passive margins comparable in different continents, and the appearance of glacial rocks, are of great importance. Preserved fragments of Mesoproterozoic continental assemblies within later supercontinents or in orogenic belts are also helpful in the paleogeographical reconstructions. The “Geodynamic Map of Rodinia” (Li et al., Appendix I) summarizes the new scientific findings and will facilitate further tests of the Rodinia hypothesis by presenting all the information in GIS-format compilations. The Precambrian geological and tectonic features of each continental block were depicted employing a uniform legend and were then put together to form a consistent Rodinia reconstruction. The present Special Issue is thus designed to provide an update of the records of Rodinia assembly in the Mesoproterozoic and its Neoproterozoic break-up. By combining the global geological records and the case histories of the various crustal provinces and orogenic belts with the time-space diagrams for the cratons and craton margins, and with the paleomagnetic constraints, we provide a qualified synthesis of Rodinia history. Specific considered aspects include basin development, analyzes of sediment provenances, mantle-plume events, glaciations, etc. The issue begins with a paper by A. Davidson on Laurentia (including western Greenland). This largest Rodinia continent, which formed the core of the supercontinental assembly with the extensive Grenville orogen to its south-east, is a cornerstone for all Rodinia reconstructions. Before the Grenvillian Orogeny, this part of Laurentia was affected by several orogenic events during the late Paleoproterozoic and the early Mesoproterozoic. In the stable northern part of Laurentia, intracontinental and passivemargin sedimentation along with mafic igneous activity, mainly in the mid-Mesoproterozoic, were related to some extension. In Laurentia, the earliest signs of Rodinia break-up appeared in the west at ca. 0.8 Ga, earlier than along the southeast side, while the age of initial rifting along the northern margin is not known. Two papers shed light on the Mesoproterozoic and Neoproterozoic evolution of the East European Craton (Baltica), another important and well-defined continental block in the Rodinia framework. Bogdanova et al. document different tectonothermal histories of crust development in the western and eastern parts of the East European Craton from ca. 1.6 Ga onwards. While accretionary growth dominated the west, intense rifting and formation of passive margins occurred in the east. New seismic profiling across the major rift systems demonstrates very thick sedimentary sequences, which are more extensive than has been known previously. Such differences persisted even during the Sveconorwegian Orogeny, which can be subdivided into four different phases related to Baltica’s movements. The two early ones, at 1.14–1.10 and 1.05–0.98 Ga, had much in common with Grenvillian orogenic events in Laurentia and took place in the course of the collision of Baltica with southeastern Laurentia and southern Amazonia (present coordinates). The later phases, at 0.98–0.96 and 0.96–0.90 Ga, were much associated with movements of Baltica to the south, rotation and oblique juxtaposition with western Amazonia and its Oaxaquia terrane. Simultaneously, strong shearing of the lithosphere in Baltica took place along Paleo- to Mesoproterozoic terrane boundaries.

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With regard to the reconstruction of the positions of Baltica both within Rodinia and after its break-up, Pease et al. provide comprehensive information about the development of Baltica’s principal margins between ca. 800 and 550 Ma. In the northwest, rifting to break away from Rodinia was unsuccessful until ca. 620–550 Ma, whereas its Cryogenian-Ediacaran northeastern edge was an ocean-facing passive margin of Rodinia and remained so until the onset of the Timanian Orogeny at ca. 615 Ma. Along Baltica’s southern and southwestern margins, the Paleo- to Mesoproterozic basement is covered by thick successions of a Ediacaran and younger platform sediments. The authors infer that Cryogenian rifting may have occurred there before the formation of an Ediacaran passive margin at ca. 550 Ma. They argue that paleomagnetic and paleontological data are consistent with Baltica and Laurentia drifting together between ca. 750 and 550 Ma. In view of several recent publications on the Precambrian geology of Siberia, Pisarevsky et al. critically analyze various Rodinia-time reconstructions of this craton with respect to Laurentia. They also review the late Paleoproterozoic assembly of Siberia and its Mesoproterozoic to early Neoproterozoic history and emphasize the development of passive continental margins along most of the Siberian edges. In the authors’ opinion, the combined geological, geochronological, and paleomagnetic evidence support the concept that Siberia was an integral part of Rodinia. However, they also argue against a tight connection between Siberia and Laurentia, requiring a “missing link” between southern Siberia and northern Laurentia. They suggest that Precambrian fragments of the Arctic parts of Eurasia and North America once formed a single continental block. Two papers consider the Meso- and Neoproterozoic developments of the North China and Tarim cratons, which are markedly different. As shown by Lu, Zhao et al., the North China Craton as well as the Siberian Craton appears not to have been affected by noticeably convergent tectonics during the assembly of Rodinia. However, in Mesoproterozoic to Cambrian times, several sedimentary basins developed along the margins of the North China Craton. These basins are characterized by thick Tonian- to Ediacaran carbonates with numerous stromatolites and terrestrial clastic beds. Employing new SHRIMP zircon ages, the authors dispute and discard a previous model which assumed the presence of a Mesoproterozoic ophiolite belt along the northern margin of this Craton. The early Paleozoic ages of these rocks additionally argue against an active involvement of the North China Craton in the assembly and break-up of Rodinia. As different from the North China Craton, the Tarim Craton features clear signs of Rodinia-related orogenic and break-up processes. Lu, H. Li et al. review geochronological and petrological studies suggesting the existence of an active margin of the Tarim Craton with a ca. 1.2 Ga island arc affected by metamorphism and partial melting at 1.05–0.90 Ga. A belt of syn to postorogenic granitic gneisses and the presence of highpressure metamorphic rocks of similar age indicate subduction and collision during the assembly of Rodinia. Coeval carbonates containing abundant stromatolites were deposited along its northern passive margin. During the break-up of Rodinia, bimodal plutonic and volcanic rocks accumulated in rift basins,

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were formed during two episodes at ca. 820 Ma and again ca. 740 Ma. Terrestrial clastic and volcanic rocks of Cryogenian (Nanhua) age and thick Ediacaran (Sinian) marine carbonates with abundant stromatolites and associated glacial deposits characterize the Tarim Craton. The authors note distinct similarities between the Tarim and Yangtze cratons and discuss their possible connections with Australia and other, smaller Precambrian blocks. Concerning Rodinian parts in present South America, Fuck et al. emphasize the Amazonian belts of 1.5–1.0 Ga as well as small Rodinian blocks within the ca. 600 Ma Brasiliano orogens in the present east of South America. In addition, there are numerous scattered basement exposures within the Andes, in a belt from Venezuela and Colombia in the north to northwestern Argentina in the south. The reconstructions of these authors picture Amazonia of much larger dimensions, which are more relevant regarding the syn-Rodinia paleogeographic position of Amazonia in relation to Laurentia and Baltica. This is also important when discussing the position of the CongoS˜ao-Francisco craton in Rodinia. De Waele et al. consider the Paleo- to Mesoproterozoic amalgamation of the Congo-S˜ao-Francisco Craton and conclude that this process terminated after peak compressional tectonism in the Kibaran Belt at 1.38 Ga. They note that late Mesoproterozoic tectonism along the southern margin of this Craton may have been linked to its participation in Rodinia. These authors discuss two paleomagnetically permissible positions of the Congo-S˜aoFrancisco Craton within Rodinia which are either in conflict with the geological evidence or necessitate overlap with other cratons, which suggests that the Congo Craton was independent at that time. However, they also note that by reckoning with minor movements between the West Africa and Amazonia cratons, a permissible fit can still be proposed between the Congo-S˜ao-Francisco and Amazonia cratons. In this scenario, the 880 Ma Roan rifting event along its southern margin could indicate the beginning of Rodinia break-up. The growth of the Kalahari Craton by accretion of Paleoproterozoic and Mesoproterozoic crust to its composite Archean core and the ∼1000 Ma drift history of this Craton are the subject of a review by Jacobs et al. These authors suggest that the Kalahari Craton could have joined Rodinia by collision along the Namaqua-Natal-Maud Belt at ∼1100–1000 Ma. In their opinion, the indicated position of Kalahari in Rodinia is also consistent with the evidence of ca. 800–750 Ma rifting and break-up preserved in the western part of this Craton. Jacobs et al. admit, however, that their model is not unique in view of recent paleomagnetic studies and that more research is required. Nevertheless, they notice that alternative models still meet difficulties when the late rifting history and the subsequent incorporation of the Kalahari Craton into Gondwana are considered. Ernst et al. review known and suspected large igneous provinces (LIPs) for the 1600–700 Ma interval and take up their implications for the reconstruction of both the late Paleoproterozoic Nuna (Columbia) supercontinent and the early Neoproterozoic Rodinia. They associate regional-scale magmatic events at 1460, 1380, and 1280 Ma with the break-up of

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Nuna (Columbia), and those at 825, 800, 780, 755, and possibly 720 Ma with the break-up of Rodinia. Even though the possibility of spatial separation of the coeval LIPs complicates their use in the constraining reconstructions, regionally grouped LIPs possibly representing superplume events (e.g. at 825–755 Ma and 1280–1235 Ma) could guide the first-order regional grouping of continents into reconstructed supercontinents. Obviously, the knowledge of the LIP records assists the reconstruction of Rodinia and will be more helpful in the future as additional magmatic units are dated precisely. To complete the volume, Li et al. provide a brief synthesis on the formation and break-up of Rodinia, the subsequent assembly of Gondwana, and the rationale for the compilation of the Geodynamic Map of Rodinia (Li et al., Appendix I). In addition to arguing that the assembly of Rodinia had not been complete before ca. 900 Ma, they also present a conceptual model in which a mantle superplume, caused by possible mantle avalanches surrounding the supercontinent, eventually led to its destruction ca. 150 Ma after it formed. In doing so, they draw parallels to events during the evolution of the supercontinent Pangaea in that mantle superplumes and whole-mantle convection are primarily driven by subduction processes (a kind of whole-mantle “top-down tectonics”), but not by stationary heat sources at the core-mantle boundary as commonly assumed, and that mantle superplumes move relative to the Earth’s axis of rotation together with supercontinents. An animation of global paleogeography, from the assembly of Rodinia to the formation of Gondwana, is provided in their Appendix II, available online as supplementary material. Acknowledgements The guest editors are much indebted to the reviewers, whose thorough and timely reviews made the present issue possible. They are: P.-G. Andr´easson (Lund University, Sweden), V. Bachtadse (Munich University, Germany), W. Bauer (Mainz University, Germany), T.S. Brewer (Leicester University, UK), P.A. Cawood (University of Western Australia), She Fa Chen (Geological Survey of Western Australia), N. Chumakov (GIN, Moscow, Russia), K. Condie (New Mexico Tech, USA), J. Connelly (University of Texas at Austin, USA), I.W.D. Dalziel (University of Texas at Austin, USA), M. De Wit (University of Cape Town, RSA), B. Eglington (University of Saskatchewan, Canada), R. Hanson (Texas Christian University, USA), A. Kr¨oner (Mainz University, Germany), B. Murphy (Saint Francis Xavier University, Antigonish, Canada), J.P. Nystuen (University of Oslo, Norway), G. Oliver (University of St. Andrews, UK), V. Pavlov (Institute of Physics of the Earth, Moscow,

Russia), R. Rainbird (Geological Survey of Canada), T. Rivers (Memorial University of Newfoundland, St. Johns, Canada), V. Ramos (University of Buenos Aires, Argentina), J. Rogers (University of North Carolina, USA), Wenjiao Xiao and F.-Yu. Wu (Institute of Geology and Geophysics, Beijing, China). References Condie, K.C., 2001. Continental growth during formation of Rodinia at 1.35–0.9 Ga. Gondwana Res. 4, 5–16. Dalziel, I.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. Dalziel, I.W.D., 1997. Neoproterozoic–Paleozoic geography and tectonics: review, hypothesis, environmental speculation. Geol. Soc. Am. Bull. 109, 16–42. Dewey, J.F., Horsfield, B., 1970. Plate tectonics, orogeny and continental growth. Nature 225, 521–525. Hoffman, P.F., 1991. Did the breakout of Laurentia turn Gondwanaland insideout? Science 252, 1409–1412. McMenamin, M.A.S., McMenamin, D.L.S., 1990. The Emergence of Animals: The Cambrian Breakthrough. Columbia University Press, New York, 217 pp. Moores, E.M., 1991. Southwest U.S.–East Antarctic (SWEAT) connection: a hypothesis. Geology 19, 425–428. Piper, J.D.A., 1976. Paleomagnetic evidence for a Proterozoic supercontinent, A280. Phil. Trans. Roy. Soc. Lond., pp. 469–490. Powell, C.M., Meert, J.G., 2001. Assembly and break-up of Rodinia: introduction to the special volume. Precambrian Res. 110, 1–8. Unrug, R., 1997. Rodinia to Gondwana: the geodynamic map of Gondwana supercontinent assembly. GSA Today 7, 1–6. Valentine, J.W., Moores, E.M., 1970. Plate-tectonic regulation of animal diversity and sea level: a model. Nature 228, 657–659.

Guest Editors S.V. Bogdanova ∗ Department of Geology, Lund University, S-223 62 Lund, Sweden E-mail address: [email protected] (S.V. Bogdanova) Z.-X. Li Department of Applied Geology, Curtin University of Technology, Perth, WA 6845, Australia E.M. Moores Department of Geology, University of California at Davis, Davis, CA 95616-8605, USA S.A. Pisarevsky School of GeoSciences, Grant Institute, The University of Edinburgh, Edinburgh EH9 3JW, UK