Reexamination of magnetotelluric responses and electrical anisotropy of the lithospheric mantle in the Grenville Province, Canada

Ademola Q. Adetunji, Ian J. Ferguson, Alan G. Jones

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Magnetotelluric (MT) responses at the Proterozoic Grenville Front in Canada have been interpreted as being caused by lithospheric electrical anisotropy, and the area is often noted as a classic example of lithospheric anisotropy. This study reevaluates evidence for the electrical anisotropy using 56 MT stations. The spatially uniform MT responses noted at the Grenville Front extend to ~200 km southeast and for at least 400 km along strike and are associated with rocks at less than 150 km depth. Examination of induction arrows at longer periods shows arrows at high angle to the MT conductive direction consistent with the presence of macroscopic resistivity structures. New 2-D anisotropic inversions show that electrical anisotropy is not required to fit the MT data. The results indicate that in the resistive mantle lithosphere beneath the Grenville Front, and in conductive lithosphere in adjacent areas, the maximum horizontal resistivity anisotropy is <10%, much less than the factor of 15 determined in earlier 1-D studies. The results suggest that the upper lithospheric mantle in the area is devoid of significant electrical anisotropy and that the observed MT response directionality is due to large-scale resistivity structure. We interpret the spatially consistent MT responses observed at the Grenville Front as being associated with the resistive Archean lithosphere extending southeast beneath the Grenville Front. The obliquity between seismic and MT responses arises because the Superior fabric is oblique to the seismic fast direction. If dextral shearing occurred, it appears to have not caused any significant shape preferred electrical anisotropy.

Original languageEnglish
Pages (from-to)1890-1908
Number of pages19
JournalJournal of Geophysical Research: Solid Earth
Volume120
Issue number3
DOIs
Publication statusPublished - Mar 1 2015

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Keywords

  • electrical anisotropy
  • electrical resistivity
  • Grenville Province
  • magnetotelluric

ASJC Scopus subject areas

  • Geophysics
  • Oceanography
  • Forestry
  • Ecology
  • Aquatic Science
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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