Some key issues in reconstructions of Proterozoic supercontinents Guochun Zhao a, * , Min Sun a , Simon A. Wilde b , Sanzhong Li c , Jian Zhang a a Department of Earth Sciences, James Lee Science Building, The University of Hong Kong, Pokfulam Road, Hong Kong, China b College of Earth Sciences, Ocean University of China, Qingdao 266603, China c Department of Applied Geology, Curtin University of Technology, G.P.O. Box U1987, Perth WA 6845, Australia Received 24 February 2004; received in revised form 28 May 2004; accepted 20 June 2004 Abstract Supercontinents containing most of the earth’s continental crust are considered to have existed at least twice in Proterozoic time. The younger one, Rodinia, formed at w1.0 Ga by accretion and collision of fragments produced by breakup of the older supercontinent, Columbia, which was assembled by global-scale 2.0–1.8 Ga collisional events. Little consensus has been reached regarding configurations of these supercontinents because of some unresolved issues concerning continental fits. One of these issues concerns how Siberia was related to Laurentia. Previous reconstructions that consider the Aldan Shield of Siberia as a continuation of the Wyoming Province of Laurentia have been largely abandoned in favor of models connecting Siberia to northern Laurentia, but it remains controversial which part of Siberia is contiguous with northern Laurentia. Also at issue is the western Laurentia–Australia–East Antarctica connection. Most Rodinia reconstructions place Australia, together with East Antarctica, adjacent to either western Canada (the SWEAT hypothesis) or the western United States (the AUSWUS hypothesis). However, recent studies combining paleomagnetic and isotopic age data have called into question the validity of SWEAT, AUSWUS and other variants. Another issue is the position of North China in Rodinia/Columbia. Limited paleomagnetic data seem to be consistent with the Paleo-Mesoproterozoic North China–Siberia/Baltica connection, whereas geological data support the recently proposed Archean to Mesoproterozoic North China–India connection. Controversial issues have also been raised about the timing and history of the amalgamation and fragmentation of South America and West Africa. Both geological and paleomagnetic data suggest that South America (Sa ˜o Francisco and Amazonia Cratons) and West Africa (Congo and West African Cratons) coalesced into a single landmass along the 2.1–2.0 Ga Transamazonian/Eburnean orogens. However, whether they were divorced and then re-married to form part of Gondwana, or remained largely coherent from their amalgamation at 2.1–2.0 Ga until their incorporation into Gondwana is unclear. Also little known is the position of Amazonia–West Africa in the proposed supercontinents, with some workers believing that they existed as a separate landmass, whereas others place Amazonia–West Africa adjacent to Baltica. In summary, although geological and paleomagnetic data are supportive of the existence of Proterozoic supercontinents Rodinia and Columbia, they are insufficient to determine their exact geometries. q 2006 Elsevier Ltd. All rights reserved. Keywords: Supercontinent; Paleo-Mesoproterozoic; Geological correlations; Paleomagnetism; Reconstruction 1. Introduction The Earth’s surface consists of a number of rigid plates that either drift apart to create new oceanic crust, or collide to generate mountain belts. A supercontinent forms when most of the earth’s continental blocks collide with each other and coalesce into a single landmass. In Earth’s history, the youngest supercontinent is Pangea which formed by assembly of all continents about 300–250 Ma ago (Lottes and Rowley, 1990; Rogers, 1993, 1996), and which itself consisted of Gondwana (Australia, India, East Antarctica, South America and Africa) as its southern half, and Laurasia (North America, Greenland and Eurasia) as its northern half (Fig. 1a). Since the 1980s, the notion of Proterozoic supercontinents has attracted much attention. Piper (1982, 1987) produced paleomagnetic evidence for the existence of a long-lived Proterozoic supercontinent. Hoffman (1989) and Gower et al. (1990) provided geological evidence for a supercontinent (named Nena) that was assembled in the period 2.0–1.8 Ga. McMena- min and MacMenamin (1990) outlined growing evidence for a Meso-Neoproterozoic supercontinent, named Rodinia, from a Russian word meaning ‘to beget’. Dalziel (1991), Hoffman (1991) and Powell et al. (2001) proposed configurations for Rodinia in which Laurentia (North America and Greenland) Journal of Asian Earth Sciences 28 (2006) 3–19 www.elsevier.com/locate/jaes 1367-9120/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2004.06.010 * Corresponding author. Tel.: C852 28578203; fax: C852 25176912. E-mail address: gzhao@hkucc.hku.hk (G. Zhao).