The Hudson Bay Lithospheric Experiment (HuBLE): insights into Precambrian plate tectonics and the development of mantle keels

Abstract

Hudson Bay Lithospheric Experiment (HuBLE) was designed to understand the processes that formed Laurentia and the Hudson Bay basin within it. Receiver function analysis shows that Archaean terranes display structurally simple, uniform thickness, felsic crust. Beneath the Palaeoproterozoic Trans-Hudson Orogen (THO), thicker, more complex crust is interpreted as evidence for a secular evolution in crustal formation from non-plate-tectonic in the Palaeoarchaean to fully developed plate tectonics by the Palaeoproterozoic. Corroborating this hypothesis, anisotropy studies reveal 1.8 Ga plate-scale THO-age fabrics. Seismic tomography shows that the Proterozoic mantle has lower wavespeeds than surrounding Archaean blocks; the Laurentian keel thus formed partly in post-Archaean times. A mantle transition zone study indicates 'normal' temperatures beneath the Laurentian keel, so any cold mantle down-welling associated with the regional free-air gravity anomaly is probably confined to the upper mantle. Focal mechanisms from earthquakes indicate that present-day crustal stresses are influenced by glacial rebound and pre-existing faults. Ambient-noise tomography reveals a low-velocity anomaly, coincident with a previously inferred zone of crustal stretching, eliminating eclogitization of lower crustal rocks as a basin formation mechanism. Hudson Bay is an ephemeral feature, caused principally by incomplete glacial rebound. Plate stretching is the primary mechanism responsible for the formation of the basin itself.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.

Layered structure in the upper mantle across North America from joint inversion of long and short period seismic data

“…The last and stronger drop in velocity occurs at 240 km depth and is interpreted as the LAB, in agreement with other studies of this part of the craton (e.g. Bastow et al, 2013).…”

“…This can be addressed by averaging data collected over a wide range of azimuths, via harmonic decomposition (e.g. Girardin and Farra, 1998;Bianchi et al, 2010 and reference therein). However in Appendix 1 we show, through tests performed at three stations, that the structure recovered using our simplified approach is only marginally biased by structural variations between different azimuth/distance bins.…”

Inverting magnetic meridian data using nonlinear optimization

“…The Polaris geophysical project emplaced geophysical instruments in several locations in Canada (Bastow et al 2015) including the east shore of Hudson Bay and southward, as the Hudson Bay Lithospheric Experiment (HuBLE). The instruments included magnetometers producing high cadence data, available with gaps during the first years (2007)(2008)(2009)(2010)(2011)(2012) of the THEMIS (Angelopoulos 2008) mission.…”

Continent formation through time

“…Numerous mechanisms are proposed, but at present, the dominant mechanism is not constrained; these include episodic subduction, mantle avalanches and dynamics in the basalt-eclogite transition. Bastow et al (2013) present a geophysical study of Precambrian continental crust that contributes to our understanding of the crustal structure of Archaean to Proterozoic regions; this study reviews the results from a seismic network deployed over little-known Precambrian crust of the Canadian Shield in the Hudson Bay area (the Hudson Bay Lithospheric Experiment). Receiver function analysis reveals a different structure between Archaean and Proterozoic lithosphere, with the Archaean having a simple, uniformly thick felsic crust (37 km), and the Palaeoproterozoic crust (that of the Trans Hudson Orogen) having a thicker (46 km) and more complex structure.…”

“…A higher degree of mantle involvement in magmatism resulted in the formation of anomalously thick portions of continental lithosphere via construction as volcanic plateaux (e.g. Bastow et al 2013;Van Kranendonk et al 2014). As a counterpart, high-grade gneiss terranes were forming in settings where crust was recycling back into the mantle (e.g.…”