Diachronous Paleozoic accretion of peri-Gondwanan terranes at the Laurentian margin

Abstract

In the original Wilson cycle, the northern Appalachian–Caledonide orogen resulted from the collision of two continental masses separated by a single ocean. One of these corresponds to the modern concept of Laurentia, but the colliding continent to the east has been variously subdivided into many smaller terranes and domains, including Ganderia, Avalonia and Megumia. Using published stratigraphic evidence and detrital zircon provenance data from units of known depositional age, the timing of arrival of these units at the Laurentian margin between the Early Ordovician and Early Devonian can be constrained. Several of the accreted terranes do not extend over the entire length of the orogen, with the result that the lines separating them change character along strike from terrane-bounding sutures to simple accretionary faults. The Ganderia domain consists of at least four separate terranes that share a common origin on the continental margin of Gondwana, but were separated by back-arc oceanic crust as they crossed the Iapetus Ocean and collided diachronously with the Laurentian margin.

Fifty years of the Wilson Cycle concept in plate tectonics: an overview

“…The Avalonia block records multiple tectonostratigraphic events throughout the Neoproterozoic-Early Paleozoic, which ultimately led to the closure of the proto-Atlantic (Iapetus) Ocean as Avalonia docked with Laurentia. Waldron et al (2018) provide a detailed analysis of the collision and docking of various microplates (including Ganderia and Avalonia) with Laurentia that now outcrop in Eastern Canada and Newfoundland. They describe the diachronous nature of individual microplate and arc-terrane convergence and ultimate collision.…”

Anticosti foreland basin offshore of western Newfoundland: Concealed record of northern Appalachian orogen development

“…By ca.451 Ma, subduction polarity reversal ) had placed the Anticosti Basin entirely in an upperplate retro-arc setting. (a) Present-day geometry of eastern North America showing major Appalachian boundaries after Hibbard et al (2006) and Waldron et al (2018). 450 Ma and continued until suturing in the Wenlock (Pollock, Wilton, Van Staal, & Morrissey, 2007) along the Dog Bay Line (Williams, Currie, & Piasecki, 1993), after which break-off of the west-dipping subducting slab occurred (van Staal et al, 2009;Whalen et al, 2006) at ca, 433-425 Ma.…”

“…In Newfoundland, 39 Ar/ 40 Ar and U-Pb metamorphic ages associated with Taconian orogenesis and ophiolite obduction are relatively scarce (van Staal et al, 2009). Ar-Ar ages of 481-465 Ma from amphiboles at the structural base of obducted ophiolites are interpreted (Castonguay, Van Staal, Waldron et al, 2018) Joyce, Skulski, & Hibbard, 2014) to date underthrusting of the leading edge of Laurentia. Following Taconian collision at a SE-dipping subduction zone, a NW-dipping subduction zone was initiated outboard of the accreted Dashwoods block by at least ca.…”

“…After collision, there was another phase of slab break-off and re-initiation of NW-dipping subduction (Zagorevski et al, 2008), along the Dog Bay Line (Reusch & van Staal, 2012). These accretion events were responsible for an extended Silurian (440-422 Ma) orogenic episode, involving magmatism, metamorphism and deformation, recognized in central Newfoundland as the Salinian Orogeny (Cawood et al, 1994;Dunning et al, 1990;van Staal et al, 2009;Waldron, Schofield, & Murphy, 2018).…”

“…It is likely that the Clam Bank unconformity represents a period F I G U R E 1 2 Comparison of Middle to Late Ordovician Laurentian margin with present-day northern Australian margin using topography and bathymetry after Amante and Eakins (2009). (a) Present-day geometry of eastern North America showing major Appalachian boundaries after Hibbard et al (2006) and Waldron et al (2018). (b) Present-day tectonic map of northern Australian margin showing northward subduction at Timor Trough concurrent with southward subduction at New Guinea Trench following arc-continent collision and subduction polarity reversal at a promontory underlying Papua.…”