Comparisons of Slave and Superior electric lithosphere. Presented at the Slave-Kaapvaal workshop, Merrickville

Active or ancient tectonomagmatic processes operating within the crust and upper mantle may in-troduce electrical charge carriers into an insulating sub-continental lithosphere mantle (SCLM). Long period magnetotellurics (MT), a deep-probing, natural-source electromagnetic geophysical method, offers a complementary technique to seismics for obtaining in-situ physical property infor-mation about the SCLM. Carbon-based conductors are an attractive explanation for the conductive features observed in the Slave and Superior lithospheres above the graphite-diamond stability field (~150 km depth). Given our understanding of the conductivity of olivine from laboratory studies, features in our models of the Slave and Superior SCLM are too conductive, by orders of magnitude, for an olivine-dominant mantle without the addition of an interconnected minor conducting phase. Grain boundary carbon or graphite is the most likely minor conductive phase in the SCLM (Duba & Shankland 1982). Spatially correlated with the surface Eocene aged kimberlite field, the Central Slave Mantle Con-ductor (CSMC) also correlates in depth with a geochemically-imaged ultra-depleted harzburgitic region (Griffin et al. 1999). The CSMC at 80-100 km depth has a minimum thickness of 20 km, and an internal isotropic (1-D) conductivity of the order of 0.03 S/m or greater. The elongated axis of th