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Discontinuous Igneous Addition along the Eastern North American Margin beneath the East Coast Magnetic Anomaly
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  • Collin Brandl,
  • Lindsay L. Worthington,
  • Maria Beatrice Magnani,
  • Donna Shillington,
  • Thomas W Luckie
Collin Brandl
University of New Mexico

Corresponding Author:collincbrandl@gmail.com

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Lindsay L. Worthington
University of New Mexico
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Maria Beatrice Magnani
Southern Methodist University
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Donna Shillington
Northern Arizona University
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Thomas W Luckie
University of Southern California
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Detailed models of crustal structure at volcanic passive margins offer insight into the role of magmatism and distribution of igneous addition during continental rifting. The Eastern North American Margin (ENAM) is a volcanic passive margin that formed during the breakup of Pangea ~200 Myr ago. The offshore, margin-parallel East Coast Magnetic Anomaly (ECMA) is thought to mark the locus of synrift magmatism. Previous widely spaced margin-perpendicular studies seismically imaged igneous addition as seaward dipping reflectors (SDRs) and high velocity lower crust (HVLC; >7.2 km/s) beneath the ECMA. Along-strike imaging is necessary to more accurately determine the distribution and volume of igneous addition during continental breakup. We use wide-angle, marine active-source seismic data from the 2014-2015 ENAM Community Seismic Experiment to determine crustal structure beneath a ~370-km-long section of the ECMA. P-wave velocity models based on data from short-period ocean bottom seismometers reveal a ~21-km-thick crust with laterally variable lower crust velocities ranging from 6.9 to 7.5 km/s. Sections with HVLC alternate with two ~30-km-wide areas where the velocities do not exceed 7.0 km/s. This variable structure indicates that HVLC is discontinuous along the margin. Velocity-thickness analysis indicates that the HVLC discontinuity is the result of variable intrusion along-strike. Our results suggest that magmatism during early rifting was segmented and was lower in volume than previously thought. The HVLC discontinuities roughly align with locations of Mid-Atlantic Ridge fracture zones, which may indicate that early rift segmentation influenced later segmentation of the Mid-Atlantic Ridge.
17 Feb 2023Submitted to ESS Open Archive
20 Feb 2023Published in ESS Open Archive
Aug 2023Published in Journal of Geophysical Research: Solid Earth volume 128 issue 8. 10.1029/2023JB026459