A viable Labrador Sea rifting origin of the Northern Appalachian and related seismic anomalies

The Northern Appalachian Anomaly (NAA) is a prominent low-seismic-velocity zone, similar to 400 km in diameter, in the asthenosphere beneath New England (northeastern USA). Previous studies interpreted this shallow feature, occurring at a depth of similar to 200 km, as a thermal anomaly tied to edge-driven convection along the North American continental margins. Those studies recognized, however, that upwelling here is highly unusual given that the passive margin has been tectonically quiescent for similar to 180 m.y. We propose an alternative model, based on geologic observations, geotectonic reconstructions, and geodynamic simulations, that the anomaly instead represents a Rayleigh-Taylor instability linked to the breakup of the distant Labrador Sea continental margin. A Labrador Sea origin at breakup, ca. 85-80 Ma, would imply the migration of a chain of Rayleigh-Taylor instabilities at a rate of similar to 22 km/m.y., close to expected rates from geodynamic models. A migrating-instability origin for the anomaly can reconcile its spatial characteristics, depth profile, and position near a long-inactive continental margin. A corollary is that the north-central Greenland anomaly, a mirror-image of the NAA, also potentially originated at the time of breakup. Further, The Central Appalachian Anomaly may fit this model if it represents an early-stage instability linked to rifting onset in the Labrador Sea. The NAA and other associated anomalies viably represent a legacy of continental rifting and breakup along the distant Labrador Sea margins.