A Palaeozoic Northwest Passage: incursion of Caledonian, Baltican and Siberian terranes into eastern Panthalassa, and the early evolution of the North American Cordillera

Abstract

Palaeozoic to early Mesozoic terranes of the North American Cordillera mostly originated from three distinct regions in Palaeozoic time: the western peri-Laurentian margin, western (Asian) Panthalassa, and the northern Caledonides–Siberia. A review of geological history, fossil and provenance data for the Caledonian–Siberian terranes suggests that they probably occupied an intermediate position between northern Baltica, northeastern Laurentia and Siberia, in proximity to the northern Caledonides, in early Palaeozoic time. Dispersion of these terranes and their westward incursion into eastern Panthalassa are interpreted to result from development of a Caribbean- or Scotia-style subduction system between northern Laurentia and Siberia in mid-Palaeozoic time, termed here the Northwest Passage. Westward propagation of a narrow subduction zone coupled with a global change in plate motion, related to the collision of Gondwana with Laurentia–Baltica, are proposed to have led to initiation of subduction along the western passive margin of Laurentia and development of the peri-Laurentian terranes as a set of rifted continental fragments, superimposed arcs and marginal ocean basin(s) in mid- to late Palaeozoic time. Diachronous orogenic activity from Late Silurian in Arctic Canada, to Early Devonian in north Yukon and adjacent Alaska, Middle Devonian in southeastern British Columbia, and Late Devonian–Early Mississippian in the western USA records progressive development of the Northwest Passage and southward propagation of subduction along western Laurentia.

U-Pb and Hf isotope analysis of detrital zircons from the Banks Island assemblage (coastal British Columbia) and southern Alexander terrane (southeast Alaska)

“…Given that our geochronologic and Hf isotopic data from the Banks Island assemblage are very similar to data from the Saint Elias Mountains (Beranek et al, 2013a(Beranek et al, , 2013b and share similarities with a variety of circum-Arctic assemblages, we concur with Soja (1994), Bazard et al (1995), Gehrels et al (1996), Blodgett et al (2002), Soja and Krutikov (2008), Grove et al (2008), Blodgett (2010), Miller et al (2010), Colpron and Nelson (2009), and Beranek et al (2012, 2013a, 2013b) that the Banks Island assemblage-Alexander terrane may have formed in proximity to the Arctic margin of Baltica and eastern Laurentia. As shown on Figure 15, however, all portions of the Alexander terrane also record the presence of more juvenile early Paleozoic magmatism than is recorded in any of the circum-Arctic assemblages.…”

Proterozoic Evolution of the North Atlantic–Arctic Caledonides: Insights from Detrital Zircon Analysis of Metasedimentary Rocks from the Pearya Terrane, Canadian High Arctic

“…Placing other elements of the AAC in a similar but more distal position northeast of Greenland provides a potential pathway for Cryogenian grains from the Arctic Alaska igneous units of this age to reach the Pearya Terrane ( fig. 12) and supports the ties between the Arctic Alaska and Pearya Terranes and the Caledonides invoked for various Neoproterozoic to Mesozoic reconstructions of the Arctic (e.g., Miller et al 2006Miller et al , 2010Miller et al , 2011Amato et al 2009;Colpron and Nelson 2009;Beranek et al 2010). Figure 13 depicts a series of latest Mesoproterozoic to Neoproterozoic paleogeographic reconstructions for basin development along the North Atlantic Caledonian margin that attempt to explain the regional variation of detrital zircon signatures observed.…”

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“…The occurrence of off-shelf assemblages with similar age and Hf isotope characteristics cannot be explained by simple westward spilling of sediment into deeper-water settings because the off-shelf sandstones are less mature and coarser grained than their on-shelf counterparts (Ketner, 1968). Possible explanations include: (1) transport of sediment southward along the margin in deep-water settings, perhaps in a trench (Gehrels et al, , 2000b; (2) southward transport of the off-shelf assemblages by tectonic processes, e.g., sinistral transform faults (Wallin et al, 2000;Colpron and Nelson, 2009); (3) deri va tion from basement rocks exposed outboard of the Cordilleran margin (Ketner, 1968); and (4) derivation from regions other than western Laurentia, for example southeast Laurentia (Wright and Wyld, 2006).…”