Chapter 31 A Palaeozoic NW Passage and the Timanian, Caledonian and Uralian connections of some exotic terranes in the North American Cordillera

Abstract

Exotic terranes of inferred Arctic affinity form an outer belt within the North American Cordillera extending from Alaska to northern California. The geological history, fossil and detrital zircon data for these terranes show strong correlations and linkages among them, and many features in common with the northern Caledonides, the Timanide orogen and the Urals. They probably occupied an intermediate position between Baltica, Laurentia and Siberia, in proximity to the northern Caledonides in Early Palaeozoic time. Westward dispersion of these terranes is interpreted to result from development of a Scotia-style subduction system between Laurentia–Baltica and Siberia in Mid-Palaeozoic time – the NW Passage – following closure of the Iapetus ocean. Diachronous orogenic activity from Late Silurian in Arctic Canada to Early Devonian in north Yukon and Alaska records passage of some of these terranes. Westward propagation of a narrow subduction zone coupled with a global change in plate motion, linked to closure of the Rheic Ocean are proposed to have led to initiation of subduction along the western margin of Laurentia. This is recorded by the Late Devonian initiation of arc magmatism along western Laurentia, and the Late Devonian–Early Mississippian Antler orogeny in the western US and Ellesmerian orogeny in the Canadian Arctic.

Neoproterozoic–early Paleozoic provenance evolution of sedimentary rocks in and adjacent to the Farewell terrane (interior Alaska)

“…Detrital zircon data provide useful information that bears on terrane definitions and aids in interpreting terrane associations and histories within the complex tectonic collage of Alaska. Our data suggest modifications to previously proposed paleogeographic positions of the Farewell terrane (Colpron and Nelson, 2011;Beranek et al, 2013a) during the early Paleozoic.…”

“…Terra Cotta Mountains Sandstone sedimentation coincided with the main ScandicSalinian phase of the Caledonian orogeny (440-400 Ma), during which Baltica collided with Laurentia (Beranek et al, 2013b, and references therein). We interpret this correlation as evidence for a position near this collision zone for the Farewell terrane during the Silurian (Koroleski, 2014), rather than adjacent to Siberia (e.g., Colpron and Nelson, 2011), and for a linkage between generation of Terra Cotta Mountains Sandstone flysch and Caledonian orogenic processes. We show this alternative Silurian position in Figure 17C (adapted from Colpron and Nelson, 2011).…”

“…We interpret this correlation as evidence for a position near this collision zone for the Farewell terrane during the Silurian (Koroleski, 2014), rather than adjacent to Siberia (e.g., Colpron and Nelson, 2011), and for a linkage between generation of Terra Cotta Mountains Sandstone flysch and Caledonian orogenic processes. We show this alternative Silurian position in Figure 17C (adapted from Colpron and Nelson, 2011).…”

“…The few speculative reconstructions that include displaced Arctic terranes discussed herein typically show the Farewell terrane more closely associated with Siberia through much of the Paleozoic (Colpron and Nelson, 2011;Beranek et al, 2013a). The Arctic Alaska-Chukotka and Alexander terranes are more commonly shown in association with the Timanide orogen, a late Neoproterozoic belt that formed along the eastern margin of Baltica (e.g., Gee and Pease, 2004;Amato et al, 2009;Beranek et al, 2013a;Ayuso and Till, 2014;Till et al, 2014a).…”

Age and provenance of a Paleoproterozoic to Devonian Canadian Cordilleran sequence of metasedimentary rocks, Thor-Odin dome, southeastern British Columbia

“…Upper Jurassic to mid-Cretaceous strata in the Gravina belt in southeastern Alaska contain 400-560 Ma zircon grains, which have been interpreted as having been derived from igneous rocks in the Alexander terrane (Kapp and Gehrels, 1998), an alternative source for our similar-aged zircon. Sources may also include the 565-570 Ma tonalitic intrusions in the Ykera and Trinity terranes in northern California (Wallin, 1990;Colpron and Nelson, 2011), the Shoo Fly terrane in California, and possibly the Okanagan terrane southwest of the Monashee complex in British Columbia (Colpron and Nelson, 2011;Miller et al, 2011). The position of these terranes relative to North America before the Late Cretaceous is somewhat poorly known (e.g., Butler et al, 1997;Kapp and Gehrels, 1998).…”