Precambrian crustal evolution: Seismic constraints from the Canadian Shield D.A. Thompson a, ⁎, I.D. Bastow a , G. Helffrich a , J-M. Kendall a , J. Wookey a , D.B. Snyder b , D.W. Eaton c a Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK b Geological Survey of Canada, Natural Resources Canada, 615 Booth Street, Ottawa, Ontario K1A 0E9, Canada c Department of Geoscience, University of Calgary, Calgary, Alberta T2N 1N4, Canada abstract article info Article history: Received 2 February 2010 Received in revised form 23 June 2010 Accepted 7 July 2010 Available online 1 August 2010 Editor R.D. van der Hilst Keywords: continental crust moho discontinuity Precambrian receiver function Canadian Shield Whether or not plate tectonic processes operated on a younger, hotter Earth remains ambiguous. Seismic data from new networks in the Hudson Bay region of the Canadian Shield, where the Precambrian geological record spans more than 2 billion years, offer fresh scope to address this problem. Using receiver function analyses we show that the crust of the Rae domain, which exhibits ages of Paleo- to Neoarchean (3.9–2.7 Ga), is likely felsic-to-intermediate in composition (average Vp/Vs b 1.73) and seismically transparent with a sharp Moho. There is little evidence for modern-style plate tectonics, and based on the simplicity and spatial extent of the felsic crust, models favouring vertical tectonic processes such as crustal delamination or plume activity appear better suited to the results. Data from the Hearne domain, which exhibits widespread ~ 2.7 Ga granite-and-greenstone geology, show a more complex crust with higher Vp/Vs ratios, consistent with a greater mafic component. The Trans-Hudson Orogen (THO), proposed to be a Himalayan-scale mountain belt during the Paleoproterozoic, is thought to have formed during the ~1.8 Ga collision of the Superior and Churchill plates. Results from the Quebec–Baffin Island segment of the THO appear to map out the first-order shape of the underthrusting Superior plate, with elevated Vp/Vs ratios likely representing the rifted margin of the Superior craton. Consistently thicker crust is observed beneath central and southern Baffin Island (~43 km), coincident with widespread high-grade metamorphic surface geology. These features can be explained by crustal thickening due to stacking of accreted terranes during continent–continent collision, analogous to the present-day Tibetan Plateau, followed by erosion. When reviewed in light of age and compositional constraints from the geological record, our seismic observations point towards secular crustal evolution from non-plate tectonic during the Paleo- to Mesoarchean evolving towards fully-developed modern-style plate tectonics during the Paleoproterozoic. © 2010 Elsevier B.V. All rights reserved. 1. Introduction 1.1. Overview The processes that formed and shaped the early Earth's crust are still poorly understood. For example, the onset of plate tectonics has been estimated as being as early as the Hadean, or as late as the Neoproterozoic (Hamilton, 2003; Stern, 2005; Cawood et al., 2006; Furnes et al., 2007; Hopkins et al., 2008). During the Archean, models varying from plume interactions in oceanic plateau environments (e.g., Bédard, 2006), crustal delamination (Zegers and Van Keken, 2001) or slab melting during flat subduction (Martin, 1999) have been invoked to explain the abundance of tonalite–trondjhemite–granodiorite (TTG) series rocks during this time period. These models are based on geochemical controls on the conditions under which TTG is formed (namely the melting of hydrated basalt within the garnet stability field), but without further constraints on the deep structure of the crust and upper mantle it is difficult to discriminate between these competing models. Seismic methods provide a means of imaging these regions with sufficient resolution, making them a useful diagnostic tool. The Hudson Bay region (Fig. 1) presents the opportunity to probe crustal formation during the Precambrian. It records tectonic events leading to the formation and stabilisation of the Laurentian continent including the proposed Himalayan-scale Trans-Hudson Orogen (THO) during the Paleoproterozoic. It also preserves crust with ages spanning around 2 billion years (~ 3.9–1.7 Ga), making it an ideal place to investigate secular crustal evolution. Until now, much of the region has been sparsely studied due to its inaccessible location and harsh climate, leading to few constraints on the deep structure. To address this, the Hudson Bay Lithospheric Experiment (HuBLE) was initiated by researchers in Canada and the United Kingdom with the aim of investigating lithospheric structure for constraints on the evolutionary models of the region. This contribution presents results from teleseismic receiver function (RF) analysis, providing the most spatially extensive information to date on the bulk crustal geophysical properties of the Western Churchill craton. Through the analysis of P-to-S converted energy at the Moho and the subsequent free-surface reverberations, crustal thickness and Earth and Planetary Science Letters 297 (2010) 655–666 ⁎ Corresponding author. E-mail address: gldat@bristol.ac.uk (D.A. Thompson). 0012-821X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2010.07.021 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl