The Superior Boundary Zone (SBZ) forms the northwestern margin of the Archean Superior craton and constitutes a tectonic foreland of the ~1.8 Ga Trans-Hudson Orogen. The Superior Boundary Fault (SBF) separates the SBZ from the adjacent Reindeer Zone, a collage of Paleoproterozoic juvenile intraoceanic rocks. Lithoprobe seismic reflection and magnetotelluric data were acquired along two profiles crossing the SBZ in an attempt to better constrain the deformation and crustal geometry resulting from Trans-Hudson orogeny. Analysis and interpretation of spatially coincident regional seismic and magnetotelluric data acquired along the southern 200 km profile indicate the following: (1) the Reindeer Zone accretionary collage forms an east dipping, eastward steepening, crustal-scale tectonic stack of moderately conductive rocks near the SBZ. (2) The SBZ is characterized at shallow depths (1.88--1.81 Ga, through lithospheric delamination at ~1.82--1.80 Ga to a steep transpressive plate boundary at 1.80--1.72 Ga. ¿ 1999 American Geophysical Union