Greater Avalonia—latest Ediacaran–Ordovician “peribaltic” terrane bounded by continental margin prisms (“Ganderia,” Harlech Dome, Meguma): Review, tectonic implications, and paleogeography

Distinctive uppermost Ediacaran–Ordovician rocks (Avalonian overstep sequence) were key in definition of Avalonia, which comprises large areas the NE Appalachians and Caledonian Variscan mountains (Britain western Europe). This siliciclastic-dominated cover succession unconformably overlies a Neoproterozoic pre-Avalonian basement collage (arc, continental, oceanic fragments; Gwna-type melanges [now Rhode Island–Maritime Canada–North Wales]). Rather than an arc–transform transition, our new model proposes that Avalonian was amalgamated after inferred late Ediacaran ridge-trench collision initiated northerly–southerly trending transform fault (Atf, new). Avalonia is commonly regarded as originating arc marginal to Gondwana early Paleozoic detached only Ordovician. We review multiple lines evidence show it insular microcontinent; this require revisions Ediacaran–early paleogeography plate tectonics models. Detrital zircon isotopic data Avalonia–Baltica link Timanian orogen, with peribaltic, not perigondwanan, terrane. The from Baltica rotated parallel Atf, its origin similar modern Scotia Sea (i.e., North Ridge transform) by accumulation continental fragments on transform. Deposition sequence beginning ca. 552 Ma pull-apart basins marked ribbon-microcontinent. succession, ten unconformity-bounded depositional sequences, extends for 5000 km (eastern Massachusetts–Silesia). bounded NW SE siliciclastic Gander Meguma belts Ordovician Gander) margin prisms coeval sequence. Endemic lower Lower Cambrian (Terraneuvian–lower Series 2, 538–510 Ma) faunas, dropstones, absence archaeocyaths, minor shallow-water carbonates suggest isolated location at ≥50° S. Only latest Early (ca. 506 do faunas African, “Gondwanan” affinities Avalonia-Gondwana convergence Atf. A longer 28 Ma, Middle Cambrian–Tremadocian) faunal similarity links temperate terranes same plate. An consistent Cambrian, 49° S latitude (Cape Breton Island) location—its reliable paleomagnetic datum. Meso- Paleoproterozoic zircons record nearby West margins, but eroded basement. Purported “Ganderian” plutonic whole rock signatures SW New Brunswick indicate heterogeneity between blocks, “Ganderia” affinity before purported transfer parts “Ganderia.” Coeval extensional collisional igneous along Atf seen regions faulting allow reference should be shown part or separating