The Vulcan structure is a major tectonic boundary between the Medicine Hat and Loverna Blocks, Archean crustal domains that are buried beneath the Western Canada Sedimentary Basin. It is characterized by prominent east-trending gravity and magnetic anomalies, more than 350 km in length, which cut across the potential-field fabric of southern Alberta at a high angle. Three decades ago, the Vulcan structure was the target of one of the first deep-crustal seismic profiles, and it has since been variously interpreted as a failed Proterozoic rift, an intraplate collisional zone, and (or) a largely amagmatic Proterozoic suture. Several recent Lithoprobe seismic-reflection profiles, coupled with new, coincident high-resolution gravity data, regional gravity data, and updated aeromagnetic coverage, provide the basis for a revised model of the crustal architecture in this region. We interpret the Vulcan structure to be a relatively narrow (40--70 km) axial zone of a continental collisional belt. The seismic images imply crustal delamination and south-directed subduction of the lower crust of the Loverna Block. The axial gravity low and corresponding magnetic anomaly are interpreted to originate from a large granitic pluton, while prominent gravity highs on the flanks of the structure are modeled as thrust slices of lower-crustal and/or mantle material brought up during the collision. Cross-cutting relationships inferred from aeromagnetic data indicate that the timing of collision postdated formation of Archean fabrics in the Medicine Hat Block but predated terminal collision in the adjacent TransHudson Orogen. The geographic extent, inferred net shortening and tectonic setting of the Vulcan structure appear to resemble the modern Pyrenees belt, although the deep structure appears to be more akin to the Scandinavian Caledonides. Either scenario is consistent with an interpretation of the Vulcan structure as the Proterozoic collisional suture between the Wyoming and Hearne Provinces of the Laurentian craton. ¿ 1999 American Geophysical Union