The North American continent consists of a set of Archean cratons, Proterozoic orogenic belts and a sequence of Phanerozoic accreted terranes. We present an ~1250 km long seismological profile that crosses the Superior craton, Grenville province, and Appalachian domains, with the goal of documenting the thickness, internal properties and the nature of the lower boundary of the North American crust using uniform procedures for data selection, preparation and analysis to ensure compatibility of the constraints we derive. Crustal properties show systematic differences between the three major tectonic domains. 2 The Archean Superior Province is characterized by thin crust, sharp Moho and low values of Vp/Vs ratio. The Proterozoic Grenville Province has some crustal thickness variation, near-uniform values of Vp/Vs, and consistently small values of Moho width. Of the three tectonic domains in the region the Grenville Province has the thickest crust. Vp/Vs ratios are systematically higher than in the Superior Province. Within the Paleozoic Appalachian Orogen all parameters (crustal thickness, Moho width, Vp/Vs ratio) vary broadly over distances of 100 km or less, both across the strike and along it. Internal tectonic boundaries of the Appalachians do not appear to have clear signatures in crustal properties. Of the three major tectonic boundaries crossed by our transect, two have clear manifestations in the crustal structure. The Grenville Front is associated with a change in crustal thickness and crustal composition (as reflected in Vp/Vs ratios). The Norumbega Fault Zone is at the apex of the regional thinning of the Appalachian crust. The Appalachian Front is not associated with a major change in crustal properties, rather it coincides with a zone of complex structure resulting from prior tectonic episodes, and thus presents a clear example of tectonic inheritance over successive Wilson Cycles.

The Superior Province of North America has not experienced major internal deformation for nearly 2.8 Gyr, preserving the Archean crust in its likely original state. We present seismological evidence for a sharp (less than 1 km) crust‐mantle boundary beneath three distinct Archean terranes and for a more vertically extensive boundary at sites likely affected by the 1.2–0.9 Ga Grenville orogeny. At all sites crustal thickness is smaller than expected for the primary crust produced by melting under higher mantle potential temperature conditions of Archean time. Reduced thickness and an abrupt contrast in seismic properties at the base of the undisturbed Archean crust are consistent with density sorting and loss of the residues through gravitational instability facilitated by higher temperatures in the upper mantle at the time of formation. Similar sharpness of crust‐mantle boundary in disparate Archean terranes suggests that it is a universal feature of the Archean crustal evolution.

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