Modification of Crust and Mantle Lithosphere Beneath the Southern Part of the Eastern North American Passive Margin

The eastern North American passive margin was modified by Mesozoic rifting. Seismic data from recent deployment of onshore and offshore stations offer a unique opportunity for studying the signature of syn-rifting and postrifting in lithospheric structures. Using full-wave ambient noise tomography, we construct a new seismic velocity model for the lithosphere of the southeastern United States. Our model confirms an oceanic-continental transitional crust over a ∼70 km wide zone across the coastline. Our model reveals (a) a patch of lower-than-average mantle lithospheric velocities underlying this transitional crust and (b) a low-velocity column in the mantle lithosphere beneath the Virginia volcanoes. We propose that anomaly 1 represents cooled enriched mantle that underplated the thinning crust during the initial stages of rifting around 230 Ma. Anomaly 2 likely has a more recent origin in the Eocene and may result from an asthenospheric upwelling induced by a localized lithospheric delamination.