Limited role for the Central Atlantic Magmatic Province in continental breakup along the eastern United States margin

Continental rifting is a fundamental plate tectonic process that leads to the formation of new passive margins and ocean basins. Large igneous provinces have the potential to accelerate the breakup of continents, since they can produce voluminous mantle melts that weaken the extending lithosphere. Here, we present seismic velocity models from a controlled-source seismic dataset across the passive margin of the eastern United States, where the Late Triassic Central Atlantic Magmatic Province (CAMP) impinged on a broad incipient continental rift zone along the eastern flank of the Appalachian orogen. In the Early Jurassic, continued rifting at the present-day outer continental shelf led to complete crustal separation ∼50 km east of where CAMP magmatism intruded the mid-Triassic rift basins. Our results show that the first pulse of breakup magmatism occurred along the present-day East Coast Magnetic Anomaly when the continental crust offshore thinned to ∼15 km, ∼15 m.y. after CAMP. We infer that slow extension rates and a strong mantle lithosphere prevented a rapid continental rupture beneath the present-day coastal plain, despite the previous emplacement of CAMP volcanics in this region.