Magnetotelluric data acquired across the Paleoproterozoic Trans-Hudson orogen, northern Saskatchewan, image one of the world's longest crustal features, the North American Central Plains conductivity anomaly. Modeling shows the anomaly at this latitude to comprise two distinct, westward-dipping bodies of high conductivity lying structurally above a late collisional feature, the Guncoat thrust. The shallower of these bodies correlates with the western part of the La Ronge belt; the deeper body at mid-crustal depths underlies the Wathaman batholith, and its western boundary is close to the inferred subsurface extension of the sub-vertical Needle Falls shear zone. The anomaly is identified with interleaved, biotitic, metasedimentary rocks of the Nemeiben zone and Cree Lake belt and is interpreted to have been thrust beneath the margin during collision of the La Ronge arc with the Rae-Hearne continent via westward-directed subduction.

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