The Appalachian-Caledonian orogen records a complex history of the closure of the Cambrian-Ordovician Iapetus Ocean. The Dunnage Zone of Newfoundland preserves evidence of an Ordovician arc-arc collision between the Red Indian Lake Arc, which forms part of the peri-Laurentian Annieopsquotch accretionary tract (ca. 480–460 Ma), and the peri-Gondwanan Victoria Arc (ca. 473–453 Ma). Despite the similarity in age, the coeval arc systems can be differentiated on the basis of the contrasts that are apparent across the suture zone, the Red Indian Line. These contrasts include structural and tectonic history, stratigraphy, basement characteristics, radiogenic lead in mineral deposits, and fauna. The arc-arc collision is considered in terms of modern analogues (Molucca and Solomon Seas) in the southwest Pacific, and the timing is constrained by stratigraphic relations in the two arc systems. The Victoria Arc occupied a lower-plate setting during the collision and underwent subsidence during the collision, similar to the Australian active margin and Halmahera arcs in the southwest Pacific. The timing of the subsidence is constrained by three new ages of volcanic rocks in the Victoria Arc (457 ± 2; 456.8 ± 3.1; 457 ± 3.6 Ma) that immediately predate or are coeval with deposition of the Caradoc black shale. In contrast the Red Indian Lake Arc contains a sub-Silurian unconformity and a distinct lack of Caradoc black shale, suggesting uplift during the collision. The emergent peri-Laurentian terranes provided detritus into the newly created basin above the Victoria Arc. The evidence of this basin is preserved in the Badger Group, which stratigraphically overlies the peri-Gondwanan Victoria Arc but incorporated peri-Laurentian detritus. Thus the Badger Group forms a successor basin(s) over the Red Indian Line. Following the collision, subduction stepped back into an outboard basin, the Exploits-Tetagouche backarc, closing the Iapetus Ocean along the Dog Bay Line in the Silurian. Correlative tracts in the Northern Appalachians and British Caledonides support the Ordovician arc-arc collision; however, the evidence is less obvious than in Newfoundland.

The Taconic orogeny in Newfoundland consisted of three accretionary events (Taconic 1, 2, and 3). Taconic 1 is represented by ca. 495 Ma, west-directed obduction of the infant-arc Lushs Bight oceanic tract (510–501 Ma) onto the peri-Laurentian Dashwoods microcontinent. Subduction is inferred to have initiated at a spreading center abandoned during an inboard ridge jump responsible for separation of Dash-woods from Laurentia and opening of the Humber seaway. Clogging of the subduction zone by Dashwoods forced subduction to step back into the Humber seaway. Inception of the new subduction zone led to formation of the ca. 490 Ma Baie Verte oceanic tract. Closure of the Humber seaway formed the Notre Dame arc (489–477 Ma) built on Dashwoods and the coeval Snooks Arm arc built on the Baie Verte oceanic tract. Sea-way closure led to collision (Taconic 2) between the arcs and Laurentia, which caused significant shortening of the Notre Dame arc. After a magmatic gap of 7–10 m.y., the Notre Dame arc records a voluminous flare-up of predominantly tonalite magmatism (464–459 Ma) during the waning stages of Taconic 2. Magmatism overlaps with deformation and includes both arc and non-arc-like tonalite. This flare-up was related to break-off of the oceanic lithosphere of the downgoing slab. The rapidly upwelling asthenosphere that replaced the broken-off slab induced melting in the subarc mantle and arc infrastructure. Taconic 3 is represented by 455–450 Ma accretion of a peri-Laurentian arc that had formed after the ca. 480 Ma initiation of west-directed subduction in the Iapetus Ocean outboard of the Dashwoods microcontinent.