Ediacaran–middle paleozoic oceanic voyage of avalonia from baltica viagondwana to laurentia: Paleomagnetic, faunal and geological constraints

Abstract

Current Ediacaran–Cambrian, paleo-geographic reconstructions place Aval-onia, Carolinia and Ganderia (Greater Avalonia) at high paleolatitudes off northwestern Gondwana (NW Africa and/or Amazonia), and locate NW Gondwana at either high or low paleo-latitudes. All of these reconstructions are incompatible with 550 Ma Avalon-ian paleomagnetic data, which indicate a paleolatitude of 20–30ºS for Greater Avalonia and oriented with the present-day southeast margin on the northwest side. Ediacaran, Cambrian and Early Ordovician fauna in Avalonia are mainly endemic, which suggests that Greater Avalonia was an island micro-continent. Except for the degree of Ediacaran deformation, the Neopro-terozoic geological records of mildly deformed Greater Avalonia and the intensely deformed Bolshezemel block in the Timanian orogen into eastern Baltica raise the possibility that they were originally along strike from one another, passing from an island micro-continent to an arc-continent collision-al zone, respectively. Such a location and orientation is consistent with: (i) Ediacaran (580–550 Ma) ridge-trench collision leading to transform motion along the backarc basin; (ii) the reversed, ocean-to-continent polarity of the Ediacaran cratonic island arc recorded in Greater Avalonia; (iii) derivation of 1–2 Ga and 760–590 Ma detrital zircon grains in Greater Avalo-nia from Baltica and the Bolshezemel block (NE Timanides); and (iv) the similarity of 840–1760 Ma TDM model ages from detrital zircon in pre-Uralian–Timanian and Nd model ages from Greater Avalonia. During the Cambrian, Greater Avalonia rotated 150º counterclockwise ending up off northwestern Gondwana by the beginning of the Ordovician, after which it migrated orthogonally across Iapetus to amalgamate with eastern Laurentia by the Late Ordovician–Early Silurian.