Murphy, J. B., Pisarevsky, S. A., Nance, R. D. and Keppie, J. D. 2001. Animated History of Avalonia in Neoproterozoic-Early Palaeozoic. In: Jessell, M. J. 2001. General Contributions: 2001. Journal of the Virtual Explorer , 3, 45 - 58. Animated History of Avalonia in Neoproterozoic-Early Palaeozoic J. B. MURPHY1, S. A. PISAREVSKY2, R. D. NANCE3 AND J. D. KEPPIE4 1Department of Geology, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada email: [email protected] 2Tectonics Special Research Centre, University of Western Australia, Nedlands, WA, Australia 3Department of Geological Sciences, Ohio University, Athens, Ohio 45701 U.S.A 4Instituto de Geología, Universidad Nacional Autónoma de México, México D.F., 04510 México. Abstract: Current debate regarding the configuration and breakup history of the late Precambrian supercontinent Rodinia has focused on the development of Grenville-aged orogenic belts and the evolution of Neoproterozoic passive margin sequences. However, supercontinent amalgamation and breakup also have profound tectonic effects on the evolution of continental margins that continuously faced oceans as the supercontinent assembled and dispersed. This evolution is commonly recorded by exotic terranes along the continental margin. For Rodinia, these would include exotic terranes within the Appalachian, Caledonide and Variscan orogens that are interpreted to have evolved along an active margin of Neoproterozoic Gondwana. Isotopic data indicate that some of these peri- Gondwanan terranes originated from ca. 1.2 to 1.0 Ga juvenile crust within a Panthalassa-type ocean that surrounded Rodinia and became accreted to the Gondwanan margin by 650 Ma. Other terranes, however, formed along this margin by recycling ancient Gondwanan crust. These interpretations require specific relationships with Gondwana that can be tested against the paleomagnetically constrained movements of Laurentia and Gondwana from ca. 800-500 Ma. Problematically, Amazonia is unconstrained paleomagnetically, and there is a lack of reliable paleomagnetic data from Laurentia between 720 and 615 Ma. In addition, some models favour a high latitude for Laurentia around 570 Ma whereas others favour a low latitude. To these two models we apply two approaches, which we present in four animations. The first approach assigns the minimum movement to Laurentia and Gondwana required to satisfy the paleomagnetic data and examines the relationship between this motion and the contemporaneous tectonothermal evolution of the peri- Gondwanan terranes. The second approach again satisfies the paleomagnetic data but in time periods where there is no data Laurentia and Gondwana are permitted to migrate in a fashion that would make them compatible with the tectonothermal history of peri-Gondwanan terranes. The available paleomagnetic data from both West and East Avalonia, although not of high quality, show systematically lower paleolatitudes than predicted by these models. Hence, a suggestion from both approaches is that either Laurentia had a more complicated movement history between 720 and 615 Ma than is currently constrained by the available data, or the configuration of Laurentia-W. Gondwana-Avalonia on many reconstructions is incorrect. Although the Laurentia-W.Gondwana fit shown in this paper is constrained by the abundant Neoproterozoic paleomagnetic poles for Laurentia and Baltica, several tests of this configuration, including the correlation between Dalradian Scotland and the Peruvian Arequipa massif and the discovery of the Neoproterozoic Marañon belt in the northern Andes, have failed to provide conclusive proof. Introduction supercontinent assembly and dispersal. As a result, efforts to The amalgamation and breakup of the supercontinent constrain its history and configuration have focused on the Rodinia has influenced global-scale tectonothermal events distribution of Grenville-aged orogenic belts and the in the Neoproterozoic in much the same way that the evolution of Neoproterozoic passive margin sequences. amalgamation and breakup of Pangea influenced the However, continental margins that continuously faced Phanerozoic. Although the configuration and breakup oceans as the supercontinent assembled and dispersed history of Rodinia is controversial (e.g., Hoffman, 1991; preserve tectonothermal histories that provide additional Dalziel, 1992, 1997; C. Powell et al, 1993; Karstrom et al., geologic constraints on the timing of supercontinent 1999; Loewy et al., 2000; Wingate and Giddings, 2000; Li assembly and fragmentation. For Rodinia, the history of and Powell, 2001), the consensus is that Rodinia was a such margins is collectively recorded in those peri- relatively long-lived (c. 1100-755 Ma) supercontinent Gondwanan terranes, such as Avalonia, Carolina and produced by collisional events of broadly Grenvillian age Cadomia, that are believed to have occupied peripheral (McMenamin and McMenamin, 1990; offman, 1991; positions with respect to the supercontinent. Hence, the Wingate and Giddings, 2000). Neoproterozoic tectonothermal evolution of these terranes Studies of the amalgamation and breakup of Rodinia have may provide further insights into the configuration of centred on the evolution of its continental margins during Rodinia and the timing of its breakup. 45 Murphy et al., 2001 Journal of the Virtual Explorer In this paper, we test the relationship between the peri-Gondwanan terranes and Gondwana implied by a wealth of diverse geologic data against paleomagnetically constrained movements of Laurentia and Gondwana from ca. 800-500 Ma. Using this approach, we can show that if a tectonothermal linkage existed between the peri-Gondwana terranes and Gondwana during the late Neoproterozoic, then a linkage between Laurentia and Gondwana is unlikely. Geologic Setting The peri-Gondwanan terranes are exotic terranes within the Appalachian, Caledonide, and Variscan orogens (Fig. 1A) that are interpreted to have evolved along an active continental margin of Neoproterozoic Gondwana (Fig. 1B, e.g., O’Brien et al., 1983; Rast and Skehan, 1983; Quesada, 1990; Nance et al., 1991). Early Paleozoic shallow-marine successions within these terranes contain peri-Gondwanan faunas (e.g., Theokritoff, 1979; Keppie, 1985; Nance and Thompson,1996). Avalonia, the largest peri-Gondwanan terrane, extends from New England and Atlantic Canada (West Avalonia) into southern Britain and Brabant (East Avalonia). Other peri-Gondwanan arc terranes include Carolina and related terranes in the southern Appalachians and the subsurface of Florida, and Cadomia, a group of related terranes in northwestern France and Bohemia, the age and evolution of which resembles those of parts of Iberia and the Pan-African belts of West Africa (Fig. 1B). In Figure 1. A: Early Mesozoic reconstruction showing the locations of Middle America, peri-Gondwanan terranes include Precambrian peri-Gondwanan terranes. B. Late Neoproterozoic (635-590 Oaxaquia and the Yucatan block of Mexico, and the Chortis Ma) reconstruction showing the location of Avalonia and related peri- block of Honduras and Guatamala. The geology of these Gondwanan terranes (modified after Nance and Murphy, 1996; Linneman terranes has been reviewed in several recent publications et al., 2000; Nance et al. in press) relative to the continental reconstruction (e.g. Nance et al., in press; Keppie and Ramos 1999, Nance of Dalziel (1997). (Ch = Chortis Block, Ox = Oaxaquia, Y = Yucatan Block, and Thompson, 1996) and is briefly outlined here. F = Florida). Figure modified after Nance and Murphy (1994, 1996) and Murphy et al. (1999) to accommodate (1) subduction polarities proposed Avalonia for West Avalonia (Dostal et al., 1996; Keppie and Dostal, 1998; Murphy et al., 1999), Cadomia (e.g., Chantraine et al., 1994), and Iberia (Quesada, The evolution of Avalonia has seven main elements (e.g. 1990; Eguíluz et al., 2000), (2) the present position of Carolina relative to Nance et al., in press); (1) the development of juvenile crust West Avalonia and the preponderance of early Proterozoic and Archean at ca. 1.2 to 1.0 Ga, (2) an early arc phase (pre 650 Ma) , (3) ages among its detrital zircon population (Samson et al., 1999), (3) accretion to Gondwana at ca. 650 Ma, (4) a main arc phase Neoproterozoic correlations of Florida and West Africa (Dallmeyer, 1989), (640-570 Ma), (5) its transition to a platform (570-540 Ma), (4) late Neoproterozoic paleomagnetic evidence for the relative positions of (6) the rifting of Avalonia from Gondwana (ca. 515 Ma), and Baltica-Laurentia (Meert et al., 1996) and West Avalonia-Gondwana (7) its accretion to Laurentia (ca. 440 Ma). (MacNamara et al., 2001), (5) the Neoproterozic Cadomian/Baikalian belt Although Avalonia developed along a continental margin of eastern Baltica (Roberts and Siedlecka 1999), and (6) the peri- subduction zone, the basement upon which the main Gondwanan basement terranes of Middle America (Keppie and Ramos, Avalonian arc was developed is nowhere unequivocally 1999). Not included are peri-Gondwanan fragments of Amazonian affinity exposed. Fragments of this basement may occur in recently identified within the European Variscan belt of Iberia (Fernández- northwestern Cape Breton Island (Keppie and Dostal, 1991) Suárez et al., 2000) and Bohemia (Friedl et al., 2000). and in the Goochland terrane of the southern Appalachians (Hibbard and Samson, 1995), but the provenance of these ranging in age from 740 to 370 Ma. These igneous rocks regions is controversal (e.g., Farrar, 1984; Barr