Lithospheric architecture and tectonic evolution of the Hudson Bay region

Hudson Bay conceals several fundamental tectonic elements of the North American continent, including most of the ca. 1.9–1.8 Ga Trans-Hudson orogen (THO) and the Paleozoic Hudson Bay basin. Formed due to a collision between two cratons, the THO is similar in scale and tectonic style to the modern Himalayan–Karakorum orogen. During collision, the lobate shape of the indentor (Superior craton) formed an orogenic template that, along with the smaller Sask craton, exerted a persistent influence on the tectonic evolution of the region resulting in anomalous preservation of juvenile Proterozoic crust. Extensive products of 2.72–2.68 Ga and 1.9–1.8 Ga episodes of subduction are preserved, but the spatial scale of corresponding domains increases by roughly an order-of-magnitude (to 1000 km, comparable to modern subduction environments) from the Archean to the Proterozoic. Based on analysis of gravity and magnetic data and published field evidence, we propose a new tectonic model in which Proterozoic crust in the southeastern third of Hudson Bay formed within an oceanic or marginal-basin setting proximal to the Superior craton, whereas the northwestern third is underlain by Archean crust. An intervening central belt truncates the southeastern domains and is interpreted to be a continental magmatic arc.Thick, cold and refractory lithosphere that underlies the Bay is well imaged by surface-wave studies and comprises a large component of the cratonic mantle keel beneath North America. The existence of an unusually thick mantle root indicates that subduction and plate collision during the Trans-Hudson orogeny were ‘root-preserving’ (if not ‘root-forming’) processes. Although the Hudson Bay basin is the largest by surface area of four major intracratonic basins in North America, it is also the shallowest. Available evidence suggests that basin subsidence may have been triggered by eclogitization of lower-crustal material. Compared to other basins of similar age in North America, the relatively stiff lithospheric root may have inhibited subsidence of the Hudson Bay basin.