Deformation at the eastern margin of the Northern Canadian Cordillera: Potentially related to opening of the North Atlantic

Abstract

The Northern Canadian Cordillera (NCC) comprises the Mackenzie Mountains, which are characterized by earthquakes occurring ~1,000 km east of the western North American margin. However, no recognized convergence has occurred in this inboard region since the Mesozoic to early Cenozoic formation of the Cordillera. This lack of an obvious driver for the modern NCC deformation has generated considerable debate and various geodynamic models. We show here thermal histories derived from (U‐Th‐Sm)/He data that are interpreted to indicate reactivated deformation and formation of the eastern deformation front beginning ~30 Ma. At that time the western margin of North America was mainly a transform boundary, which typically transmits very limited amount of stress into the continent. Along the northeastern margin of North America, however, the North Atlantic was opening and may have caused horizontal forces that drove deformation far to the west where the rigid craton encountered the weak Cordillera.

Late Devonian magmatism and clastic deposition in the upper Earn Group (central Yukon, Canada) mark the transition from passive to active margin along western Laurentia

“…Modern seismicity and GPS studies indicate that deformation persists at the mountain front today and that central Yukon is translated northeasterly at a rate of 2-5 mm/yr relative to the craton (e.g. Mazzotti and Hyndman 2002;Enkelmann et al 2019).…”

Cenozoic Exhumation History of the Eastern Margin of the Northern Canadian Cordillera

“…However, some pre-existing structures such as White Uplift show a clear influence (Figure 3 and Figure S9). The two thrust faults that bound White Uplift (Figure S9d) are assumed to have formed along an important Paleozoic facies change between carbonates of White Uplift and shales of the surrounding Richardson Trough (Figure 7c; Dyke, 1996). The difference in date dispersion and the stratigraphic separation between the samples collected across the thrusts suggest that the Proterozoic-Cambrian rocks (hanging wall) were buried to temperatures above the ZHe PRZ before being rapidly cooled by thrusting and erosion.…”

“…Two major phases of orogenesis affected the Canadian Arctic margin during the mid-Paleozoic (Lane, 2007). These are the late Early Devonian to earliest Middle Devonian Romanzof Orogeny and the latest Devonian to Early Carboniferous Ellesmerian Orogeny (Figure 2; Dyke, 1996;Lane, 2007;Lane & Mortensen, 2019). The Jurassic and Early Cretaceous were characterized by extension and rifting that culminated in the opening of the Canada Basin (Figure 1).…”

“…Regional extension and thinning of continental lithosphere occurred as early as 195 Ma (Grantz et al, 2011;Pease et al, 2014) with rifting and sea floor spreading during the Early Cretaceous (134-117 Ma; Grantz et al, 2011;Helwig et al, 2011). In the Richardson Mountains, Jurassic Dixon (1996b) and Dyke (1996) Lane (2007). The dark gray shaded area shows the location of latest Carboniferous-early Permian Ancestral Aklavik Arch of Jeletzky (1963).…”

“…The dominantly NNE structural grain roughly parallels the underlying cratonic margin and was additionally inherited from a complex geological and structural history that preceded Cordilleran contraction (Figure 2; Cook et al, 1987;Lane, 1998;Lane & Dietrich, 1995;Norris, 1996). Pre-Cambrian and lower Paleozoic rocks are only exposed along the western flank of a tilted fault block known as White Uplift (Figures 2 and 3; Dyke, 1996). White Uplift originated as an isolated Cambrian-Devonian carbonate platform that developed within the Richardson Trough, a northward-broadening failed rift graben flanked by shallow-water carbonates (Figure 2; Morrow, 1999;Rohr et al, 2011).…”