Source: Journal of Geophysical Research: Solid Earth
Continental breakup involves extensive volcanism and magmatic addition to the continental crust. Once the continent breaks up, the passive margin evolves into a mid-ocean ridge spreading center that forms oceanic crust. Of particular interest is whether segmentation of the later spreading center is inherited from the structure and scale of magmatic focusing along the passive margin.
Brandl et al.  probe the composition and rock types at 10 to 20 kilometers beneath the surface along the east coast passive margin of the United States using ocean bottom seismometer measurements. They find segments of enhanced magmatic addition at 30- to 100-kilometer scales with gaps up to 30 kilometers wide. Although along-strike variability has been observed at other passive margins, small-scale magmatic segmentation has not been documented except at present-day continental rifts.
This study, along with work from the Main Ethiopian Rift, points to oblique rifting as a primary control in focusing extension and small-scale magmatic segmentation. Notably, the magmatic discontinuities align with Mid-Atlantic Ridge fracture zones suggesting that segmentation of the rift controls later segmentation of the spreading center.
Citation: Brandl, C. C., Worthington, L. L., Magnani, M. B., Shillington, D. J., & Luckie, T. W. (2023). Discontinuous igneous addition along the Eastern North American Margin beneath the East Coast Magnetic Anomaly. Journal of Geophysical Research: Solid Earth, 128, e2023JB026459. https://doi.org/10.1029/2023JB026459
—Emilie Hooft, Associate Editor, JGR: Solid Earth