Lithospheric architecture beneath Hudson Bay

Abstract

Hudson Bay overlies some of the thickest Precambrian lithosphere on Earth, whose internal structures contain important clues to the earliest workings of plate formation. The terminal collision, the Trans-Hudson Orogen, brought together the Western Churchill craton to the northwest and the Superior craton to the southeast. These two Archean cratons along with the Paleo-Proterozoic Trans-Hudson internides, form the core of the North American craton. We use S to P converted wave imaging and absolute shear velocity information from a joint inversion of P to S receiver functions, new ambient noise derived phase velocities, and teleseismic phase velocities to investigate this region and determine both the thickness of the lithosphere and the presence of internal discontinuities. The lithosphere under central Hudson Bay approaches 350 km thick but is thinner (200-250 km) around the periphery of the Bay. Furthermore, the amplitude of the LAB conversion from the S receiver functions is unusually large for a craton, suggesting a large thermal contrast across the LAB, which we interpret as direct evidence of the thermal insulation effect of continents on the asthenosphere. Within the lithosphere, midlithospheric discontinuities, significantly shallower than the base of the lithosphere, are often imaged, suggesting the mechanisms that form these layers are common. Lacking time-history information, we infer that these discontinuities reflect reactivation of formation structures during deformation of the craton.

Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

“…The recognition of at least two temporally distinct lithospheric zones in our model endorses the idea that cratonic keel growth is not due to one particular dominant tectonic process and, most importantly, is not exclusively an Archean phenomenon. Previous seismic studies postulated a Paleoproterozoic origin for the lower layer beneath Hudson Bay and surrounding terranes [e.g., Darbyshire et al , ; Porritt et al , ], supporting episodic formation of cratonic roots in the Precambrian.…”

Precambrian Plate Tectonics in Northern Hudson Bay: Evidence From P and S Wave Seismic Tomography and Analysis of Source Side Effects in Relative Arrival‐Time Data Sets

“…This change may be distinguished by a change in anisotropic fast direction (e.g., Darbyshire et al, ; Liddell et al, ; Petrescu et al, ). Sharp discontinuities imaged at midlithospheric depths by receiver function studies throughout cratonic North America (Abt et al, ) and within northern Hudson Bay have supported this episodic growth theory (e.g., Porritt et al, ; Rychert & Shearer, ).…”

Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

“…King and Ritsema, 2000), in a chemically buoyant plume (e.g. Simmons et al, 2007;Dannberg and Sobolev, 2015), or due to thermal insulation beneath large continental plates (Andersen and King, 2014;Porritt et al, 2015). In contrast, kimberlite formation may additionally require excess T P (thermal plume) enabling upwelling mantle to be above the carbonated peridotite solidus over a large enough pressure interval to dissolve SiO 2 (Dasgupta, 2013), and/or enriched conditions (high CO 2 -H 2 O contents; section 4.1.3).…”

“…4) helps explain the seismic complexity of cratonic lithospheric mantle and the occurrence of multiple, spatially distributed MLDs with both negative and positive velocity phases that appear only when short-period filtering is applied (Selway et al, 2015). A major argument in favour of MLDs being caused by processes dating back to cratonic lithosphere construction is that these discontinuities sometimes appear to be correlated with tectonic units and truncated at craton margins (Porritt et al, 2015). They show steep-sided seismic velocity offsets that therefore have persisted for billions of years (Poupinet al, 2003).…”