Magnetotelluric and teleseismic study across the Snowbird Tectonic Zone, Canadian Shield: A Neoarchean mantle suture?

Abstract

The Snowbird tectonic zone (STZ) is a fundamental boundary within Canada's Western Churchill Province, one of the world's largest yet poorly‐known fragments of Archean crust. Geophysical data from a collocated magnetotelluric and teleseismic transect across the northeastern segment of the STZ provide an image of its subsurface geometry and indicate that it may have been previously mislocated. The model suggests that (1) the STZ has played a major role in the Neoarchean assembly and Paleoproterozoic reworking of the western Canadian Shield, (2) it was reactivated in a manner comparable to other crustal‐scale features such as the Kapuskasing zone of the Superior Province, Canada, and the Redbank thrust of the Arunta block, central Australia, and (3) it juxtaposes mantle blocks with contrasting geophysical properties, revealing a lithosphere‐scale overlap of the leading edges of the Rae and Hearne domains. The STZ thus records plate interactions in the Neoarchean comparable in scale with that of modern orogenic belts.

Heterogeneity and anisotropy in the lithospheric mantle

“…Lateral and vertical variations in electrical conductivity by up to 2 orders of magnitude were nevertheless mapped in the Slave and Kaapvaal cratonic lithosphere (Jones et al, 2001;Evans et al, 2011). Large lateral variations in electrical conductivity have also been observed beneath plate-scale shear zones with ages ranging from Archean to Cenozoic, such as the Great Slave and Snowbird tectonic zones in Canada (Jones et al, 2002;Eaton et al, 2004), the Pernambuco shear zone in northeast Brazil (Santos et al, 2014), the North Pyrenean fault (Pous et al, 2004), and the Tien Shan fault in the Himalaya (Bielinski et al, 2003). Electrical conductivity signatures of shear zones in the lithospheric mantle vary.…”

Retro-arc extension and continental rifting: a model for the Paleoproterozoic Baker Lake Basin, Nunavut1Geological Survey of Canada Contribution 20100436.

“…Faults with significant offset during Baker Sequence time have been identified regionally (e.g., the Tyrrell shear zone, MacLachlan et al 2005b). Magnetotelluric data have illuminated the conductive structure of the Rae-Hearne crust, providing estimates on the depth of the Moho in the vicinity of Baker Lake Basin (Jones et al 2002). A Moho depth of 36-40 km allows for zero net crustal thickening between metamorphism of Kramanituar Complex at pressures of 12-15 kbar (1 kbar = 100 MPa; ∼36-45 km depth) at ∼1.9 Ga (Sanborn- Barrie et al 2001) and deposition of Thelon Formation at ca.…”

The elusive lithosphere–asthenosphere boundary (LAB) beneath cratons

“…In some places, however, there are resistive crustal "windows" through which the lithospheric mantle resistivity-depth profile can be reasonably well resolved although, once again, determining the actual resistivity of the most resistive part of the profile is virtually impossible -only a lower bound can be put on it. The most resistive upper mantle reported in the literature is that beneath the Rae Province of the Canadian Shield, adjacent to the Slave craton, where resistivities in excess of 65,000 m have been ⋅ reported by Jones et al (2002) in a region of little crustal conductance.…”