The amalgamation and breakup of the supercontinent Rodinia has influenced global-scale tectonothermal events in the Neoproterozoic in much the same way that the amalgamation and breakup of Pangea influenced the Phanerozoic. Although the configuration and breakup history of Rodinia is controversial (e.g., Hoffman, 1991; Dalziel, 1992, 1997; C. Powell et al, 1993; Karstrom et al., 1999; Loewy et al., 2000; Wingate and Giddings, 2000; Li and Powell, 2001), the consensus is that Rodinia was a relatively long-lived (c. 1100-755 Ma) supercontinent produced by collisional events of broadly Grenvillian age (McMenamin and McMenamin, 1990; Hoffman, 1991; Wingate and Giddings, 2000).
Studies of the amalgamation and breakup of Rodinia have centred on the evolution of its continental margins during supercontinent assembly and dispersal. As a result, efforts to constrain its history and configuration have focused on the distribution of Grenville-aged orogenic belts and the evolution of Neoproterozoic passive margin sequences.
However, continental margins that continuously faced oceans as the supercontinent assembled and dispersed preserve tectonothermal histories that provide additional geologic constraints on the timing of supercontinent assembly and fragmentation. For Rodinia, the history of such margins is collectively recorded in those peri-Gondwanan terranes, such as Avalonia, Carolina and Cadomia, that are believed to have occupied peripheral positions with respect to the supercontinent. Hence, the Neoproterozoic tectonothermal evolution of these terranes may provide further insights into the configuration of Rodinia and the timing of its breakup.
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.
| Figure 1 (a) Early Mesozoic reconstruction showing the locations of Precambrian peri-Gondwanan terranes. (b) Late Neoproterozoic (635-590 Ma) reconstruction showing the location of Avalonia and related peri-Gondwanan terranes (modified after Nance and Murphy, 1996; Linneman et al., 2000; Nance et al. in press) relative to the continental reconstruction of Dalziel (1997). (Ch = Chortis Block, Ox = Oaxaquia, Y = Yucatan Block, F = Florida). Figure modified after Nance and Murphy (1994, 1996) and Murphy et al. (1999) to accommodate (1) subduction polarities proposed 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, 1990; Egu’luz et al., 2000), (2) the present position of Carolina relative to West Avalonia and the preponderance of early Proterozoic and Archean ages among its detrital zircon population (Samson et al., 1999), (3) Neoproterozoic correlations of Florida and West Africa (Dallmeyer, 1989), (4) late Neoproterozoic paleomagnetic evidence for the relative positions of Baltica-Laurentia (Meert et al., 1996) and West Avalonia-Gondwana (MacNamara et al., 2001), (5) the Neoproterozic Cadomian/Baikalian belt of eastern Baltica (Roberts and Siedlecka 1999), and (6) the peri-Gondwanan basement terranes of Middle America (Keppie and Ramos, 1999). Not included are peri-Gondwanan fragments of Amazonian affinity recently identified within the European Variscan belt of Iberia (Fernandez-Suarez et al., 2000) and Bohemia (Friedl et al., 2000). Click to enlarge |  |
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 Middle America, peri-Gondwanan terranes include Oaxaquia and the Yucatan block of Mexico, and the Chortis block of Honduras and Guatamala. The geology of these terranes has been reviewed in several recent publications (e.g. Nance et al., in press; Keppie and Ramos 1999, Nance and Thompson, 1996) and is briefly outlined here.