Lithospheric Thermo-Compositional Structure of the Northeastern North American Shield from Rayleigh Wave Dispersion Analysis

The thermal and compositional structure of lithospheric keels underlying cratons, which are stable continental cores formed during the Precambrian, is still an enigma. Recent seismological studies have shown that some regions of cratonic lithosphere are vertically stratified in terms of composition, requiring either fast minerals or metasomatic minerals in order to fit their seismological profiles. Mapping such variations is essential to better understand geodynamical processes that operate beneath cratons as well as their formation and evolution. The northeastern part of North America is ideal to investigate the precambrian lithosphere. The region comprises the Superior Craton, the largest Archean craton in the world, and surrounding orogenic belts from the Proterozoic. To model the thermal and compositional structure of its lithosphere, we used Rayleigh wave dispersion curves. The dispersion curves were divided into groups based on cluster analysis and geological characteristics. For each group, we searched for thermal and compositional structures using constraints from surface heat flow and thermodynamic methods to map thermocompositional structures into seismic velocity to find those that fit the average observed dispersion curve as well as independent constraints on crustal structure. In agreement with previous studies, some regions contain velocity anomalies that cannot be solved with variations in temperature alone and may require a substantial amount of carbonate and/or hydrous minerals in the lithosphere to fit the dispersion curves. We expect that the results will contribute to the geophysical and geological knowledge of the American Continent, and will provide further insights into how continents are formed and how they evolve.