Central Baffin electromagnetic experiment (CBEX): Mapping the North American Central Plains (NACP) conductivity anomaly in the Canadian arctic

• Published in: Physics of the earth and planetary interiors 2005-05, Vol.150 (1), p.107-122
• Main Authors: Evans, Shane, Jones, Alan G., Spratt, Jessica, Katsube, John
• Format: Article
• Language: English
• Subjects: Electromagnetic induction; Magnetotelluric technique; North American Central Plains conductivity anomaly (NACP); Paleoproterozoic orogeny; Petrophysical conductivity measurements; Trans-Hudson orogen
• ISSN: 0031-9201; 1872-7395
• DOI: 10.1016/j.pepi.2004.08.032

Over the summers of 2001 and 2002, a 45 station, 500-km-long regional magnetotelluric (MT) profile was acquired on central Baffin Island in the eastern Canadian arctic. This Central Baffin electromagnetic experiment (CBEX) profile traverses the northern margin of the Paleoproterozoic Trans-Hudson Orogen (THO). In its southern segment, within the juvenile rocks of the orogen, the profile lies on Paleoproterozoic meta-sedimentary strata known as the Piling Group, and the profile extends northwards onto the Archean Rae craton. The primary goal of the experiment was to determine the subsurface geometry of major geological boundaries and to define regional electrical structures. Field observations and laboratory analyses show that one particular horizon within the Piling Group, the sulphidic–graphitic Astarte River formation, is highly conductive and can be mapped and used as structural proxy for the base of the Piling Group. The laboratory results imply that the source of the enhanced conductivity in the Astarte River formation is the high content of interconnected graphite, and that the host rocks are highly anisotropic due to bedding. Mapping this formation in depth images the base of the Piling Group basin well. There is high contrast in electrical conductivity between the Piling Group meta-sedimentary rocks and the Archean granites and gneissic complexes of the Rae craton to the north. The lower crust of the Rae craton in this area is moderately conductive (some 100 s Ω m), in contrast to Rae lower crust observed elsewhere in Canada, and this observation is not readily explained. The lithospheric mantle beneath the profile exhibits a strong north-to-south gradient in decreasing resistivity, suggesting resistive Archean mantle (>3000 Ω m) subducted beneath moderately resistive Proterozoic mantle (300 Ω m).