Electric lithosphere of the Slave craton

The Archean Slave craton in northwestern Canada is an ideal natural laborat ory for investigating lithosphere formation and evolution, and has become a n international focus of broad geoscientific investigation following the di scovery of economic diamondiferous kimberlite pipes. Three deep-probing mag netotelluric surveys have recently been carried out on the craton using nov el acquisition procedures. The magnetotelluric responses reveal an unexpect ed and remarkable anomaly in electrical conductivity, collocated with the k imberlite field that is modeled as a spatially confined upper mantle region of low resistivity (< 30 Omega .m) at depths of 80-100+ km, and is interpr eted to be due to dissolved hydrogen or carbon in graphite form. This geoph ysically anomalous upper mantle region is also spatially coincident with a geochemically defined ultradepleted harzburgitic layer. The tectonic proces ses that emplaced this structure are possibly related to the lithospheric s ubduction and trapping of overlying oceanic mantle at 2630-2620 Ma.