Lithospheric Formation and Evolution of Eastern North American Continent.

Lithospheric layering contains critical information about continental formation and evolution. However, discrepancies on the depth distributions of lithospheric layers have significantly limited our understanding of possible tectonic connections among the layers. Here, we construct a high‐resolution shear velocity model of eastern North America using full‐wave ambient noise simulation and inversion by integrating onshore and offshore seismic datasets. Our new model reveals large lateral variations of lithosphere thickness approximately across the major tectonic boundaries, strong low‐velocity anomalies underlying the thinner lithosphere, and multiple low‐velocity layers within the continental lithosphere. We suggest that the present mantle lithosphere beneath eastern North America was formed and modified through multiple stages of tectonic processes, among which metasomatism may have significantly contributed to the observed intralithospheric low‐velocity layers. The sharp thickness variation of lithosphere promoted edge‐driven mantle convection, which has been consequently modifying the overlying mantle lithosphere and further sharpening the gradient of lithosphere thickness Plain Language Summary: Eastern North America provides a complete record of the eastward growth of the continent, from the breakup of one supercontinent (Rodinia), 1 billion years ago, through the multistage assembly of the supercontinent of Pangea to the formation of the modern Atlantic Ocean. Eastern North America provides an excellent setting to advance our understanding of lithosphere (i.e., tectonic plate) evolution through geologic time. Using an advanced seismic imaging method, we constructed a detailed model of the mantle lithosphere beneath eastern North America. Our new model demonstrates three key features: (1) strong lateral variations of lithosphere thickness from the North American craton (∼200–250 km) to the Grenville Province (∼150–200 km) and the Appalachian Province (∼100 km); (2) multiple low‐velocity layers within the continental lithosphere; and (3) low‐velocity anomalies at the base of the Grenville and Appalachian lithosphere. Our seismic observations suggest that the eastern North American continent was likely established and modified through multiple stages of tectonic events. The sharp thickness variation of lithosphere triggered upwelling of deep mantle materials, which has been consequently modifying the overlying mantle lithosphere. Our findings shed light on the nature of mantle lithosphere and our understanding of continental growth and evolution in general. Key Points: Strong lateral variations of lithosphere thickness is revealed roughly across the tectonic boundaries in eastern North AmericaMultiple nearly parallel low‐velocity layers are observed within the interior of the continental lithosphere of eastern North AmericaThe interior of the Grenville Province is characterized by strong variations of seismic characteristics from north to south [ABSTRACT FROM AUTHOR]

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