SEISMIC PROPERTIES OF THE NORTHEASTERN NORTH AMERICAN CRUST FROM ARCHEAN TO PHANEROZOIC: A REVIEW

Over the last 20-30 years, a wealth of new information on crustal thickness, internal structure and composition has become available for northeastern North America, allowing for a detailed comparison of crustal properties over a large portion of Earth’s geological history. Eastern North America is particularly well-placed for such comparisons, as it preserves a geological record of over 3 billion years. The Archean crust of the Superior craton in the centre of the Canadian Shield is bounded to the southeast by the Mesoproterozoic Grenville Province and to the northwest by the Paleoproterozoic Trans-Hudson Orogen. Both of these orogenic belts are comparable in spatial scale to the present-day Himalayan collision zone. Further to the southeast, Phanerozoic continental collision created the Appalachian mountain chain, the edges of which were subsequently affected by rifting, leading to the opening of the North Atlantic Ocean. The region as a whole experienced later tectonic modification, both at a local scale (e.g. the Charlevoix impact crater) and a regional scale (e.g. the proposed interaction with the Great Meteor hotspot).

Here I review a number of recent studies of crustal structure across the Superior-Grenville-Appalachian domains of eastern Canada and the northeasternmost USA. The results are taken from active-source refraction/reflection profiling campaigns (LITHOPROBE) and from receiver function analysis (CNSN, POLARIS, EarthScope Transportable Array, EarthScope QM-III FlexArray). In general, the crust beneath the Appalachian domains of Maine and Maritime Canada is slightly thinner than that of the Archean domains, and significantly thinner than that of the Grenville Province. Vp/Vs ratios suggest a broadly felsic to intermediate crust beneath the Appalachians, whereas Superior crust is almost exclusively felsic and Grenville crust is highly variable, ranging from felsic to strongly mafic in nature. Both receiver function modelling and seismic-reflection images show a high degree of crustal complexity within the Proterozoic and Phanerozoic orogenic belts, and a Moho that ranges in character from sharp to diffuse to doubled across the region.