Along-Margin Variations in Breakup Volcanism at the Eastern North American Margin

We model the magnetic signature of rift-related volcanism to understand the distribution and volume of magmatic activity that occurred during the breakup of Pangaea and early Atlantic opening at the Eastern North American Margin (ENAM). Along-strike variations in the amplitude and character of the prominent East Coast Magnetic Anomaly (ECMA) suggest that the emplacement of the volcanic layers producing this anomaly similarly varied along the margin. We use three-dimensional magnetic forward modeling constrained by seismic interpretations to identify along-margin variations in volcanic thickness and width that can explain the observed amplitude and character of the ECMA. Our model results suggest that the ECMA is produced by a combination of both first-order (similar to 600-1,000 km) and second-order (similar to 50-100 km) magmatic segmentation. The first-order magmatic segmentation could have resulted from preexisting variations in crustal thickness and rheology developed during the tectonic amalgamation of Pangaea. The second-order magmatic segmentation developed during continental breakup and likely influenced the segmentation and transform fault spacing of the initial, and modern, Mid-Atlantic Ridge. These variations in magmatism show how extension and thermal weakening was distributed at the ENAM during continental breakup and how this breakup magmatism was related to both previous and subsequent Wilson cycle stages.