Abstract
The northern Hudson Bay region in Canada comprises several Archean cratonic nuclei, assembled by a number of Paleoproterozoic orogenies including the Trans-Hudson Orogen (THO) and the Rinkian–Nagssugtoqidian Orogen. Recent debate has focused on the extent to which these orogens have modern analogues such as the Himalayan–Karakoram–Tibet Orogen. Further, the structure of the lithospheric mantle beneath the Hudson Strait and southern Baffin Island is potentially indicative of Paleoproterozoic underthrusting of the Superior plate beneath the Churchill collage. Also in question is whether the Laurentian cratonic root is stratified, with a fast, depleted, Archean core underlain by a slower, younger, thermally-accreted layer. Plate-scale process that create structures such as these are expected to manifest as measurable fossil seismic anisotropic fabrics. We investigate these problems via shear wave splitting, and present the most comprehensive study to date of mantle seismic anisotropy in northern Laurentia. Strong evidence is presented for multiple layers of anisotropy beneath Archean zones, consistent with the episodic development model of stratified cratonic keels. We also show that southern Baffin Island is underlain by dipping anisotropic fabric, where underthrusting of the Superior plate beneath the Churchill has previously been interpreted. This provides direct evidence of subduction-related deformation at 1.8 Ga, implying that the THO developed with modern plate-tectonic style interactions.
Highlights
OverviewThe geological record of the northern Hudson Bay region in Canada exceeds 2 billion years, including several Archean nuclei and a series of Paleoproterozoic orogens that culminated in the assembly of the cratonic core of North America, Laurentia
The northern Hudson Bay region in Canada comprises several Archean cratonic nuclei, assembled by a number of Paleoproterozoic orogenies including the Trans-Hudson Orogen (THO) and the Rinkian– Nagssugtoqidian Orogen
Structural and thermobarometric studies suggest the THO was similar in scale and style to the modern-day Himalayan–Karakoram–Tibet Orogen (HKTO) (e.g., St-Onge et al, 2006), a finding corroborated by seismic studies of the crust (Thompson et al, 2010; Pawlak et al, 2011; Gilligan et al, 2016), and recently by the discovery of low-temperature, high-pressure eclogite rocks within the THO indicative of platescale subduction (Weller and St-Onge, 2017)
Summary
The geological record of the northern Hudson Bay region in Canada exceeds 2 billion years, including several Archean nuclei and a series of Paleoproterozoic orogens that culminated in the assembly of the cratonic core of North America, Laurentia. The largest of these is the Trans-Hudson Orogen (THO), which marks the ∼1.8 Ga collision between the Archean Superior craton and the Churchill plate (Fig. 1; Hoffman, 1988). Stations FCC and FRB from the Canadian National Seismograph Network have been active since 1994
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