@article {russell_lithosphere_2021,
	title = {Lithosphere Structure and Seismic Anisotropy Offshore Eastern North America: Implications for Continental Breakup and Ultra-Slow Spreading Dynamics},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {126},
	number = {12},
	year = {2021},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021JB022955},
	month = {11/2021},
	pages = {e2021JB022955},
	abstract = {The breakup of supercontinent Pangea occurred \~{}200 Ma forming the Eastern North American Margin (ENAM). Yet, the precise timing and mechanics of breakup and onset of seafloor spreading remain poorly constrained. We investigate the relict lithosphere offshore eastern North America using ambient-noise Rayleigh-wave phase velocity (12{\textendash}32 s) and azimuthal anisotropy (17{\textendash}32 s) at the ENAM Community Seismic Experiment (CSE). Incorporating previous constraints on crustal structure, we construct a shear velocity model for the crust and upper \~{}60 km of the mantle beneath the ENAM-CSE. A low-velocity lid (VS of 4.4{\textendash}4.55 km/s) is revealed in the upper 15{\textendash}20 km of the mantle that extends \~{}200 km from the margin, terminating at the Blake Spur Magnetic Anomaly (BSMA). East of the BSMA, velocities are fast (>4.6 km/s) and characteristic of typical oceanic mantle lithosphere. We interpret the low-velocity lid as stretched continental mantle lithosphere embedded with up to \~{}15\% retained gabbro. This implies that the BSMA marks successful breakup and onset of seafloor spreading \~{}170 Ma, consistent with ENAM-CSE active-source studies that argue for breakup \~{}25 Myr later than previously thought. We observe margin-parallel Rayleigh-wave azimuthal anisotropy (2\%{\textendash}4\% peak-to-peak) in the lithosphere that approximately correlates with absolute plate motion (APM) at the time of spreading. We hypothesize that lithosphere formed during ultra-slow seafloor spreading records APM-modified olivine fabric rather than spreading-parallel fabric typical of higher spreading rates. This work highlights the importance of present-day passive margins for improving understanding of the fundamental rift-to-drift transition.},
	keywords = {ambient noise, continental rifting, eastern North American margin, oceanic lithosphere, seismic anisotropy, surface-wave tomography},
	issn = {2169-9356},
	doi = {10.1029/2021JB022955},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2021JB022955},
	author = {Russell, J. B. and Gaherty, J. B.}
}
@article {brunsvik_mantle_2021,
	title = {Mantle Structure and Flow Across the Continent-Ocean Transition of the Eastern North American Margin: Anisotropic S-Wave Tomography},
	journal = {Geochemistry, Geophysics, Geosystems},
	volume = {22},
	number = {12},
	year = {2021},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2021GC010084},
	pages = {e2021GC010084},
	abstract = {Little has been seismically imaged through the lithosphere and mantle at rifted margins across the continent-ocean transition. A 2014{\textendash}2015 community seismic experiment deployed broadband seismic instruments across the shoreline of the eastern North American rifted margin. Previous shear-wave splitting along the margin shows several perplexing patterns of anisotropy, and by proxy, mantle flow. Neither margin parallel offshore fast azimuths nor null splitting on the continental coast obviously accord with absolute plate motion, paleo-spreading, or rift-induced anisotropy. Splitting measurements, however, offer no depth constraints on anisotropy. Additionally, mantle structure has not yet been imaged in detail across the continent-ocean transition. We used teleseismic S, SKS, SKKS, and PKS splitting and differential travel times recorded on ocean-bottom seismometers, regional seismic networks, and EarthScope Transportable Array stations to conduct joint isotropic/anisotropic tomography across the margin. The velocity model reveals a transition from fast, thick, continental keel to low velocity, thinned lithosphere eastward. Imaged short wavelength velocity anomalies can be largely explained by edge-driven convection or shear-driven upwelling. We also find that layered anisotropy is prevalent across the margin. The anisotropic fast polarization is parallel to the margin within the asthenosphere. This suggests margin parallel flow beneath the plate. The lower oceanic lithosphere preserves paleo-spreading-parallel anisotropy, while the continental lithosphere has complex anisotropy reflecting several Wilson cycles. These results demonstrate the complex and active nature of a margin which is traditionally considered tectonically inactive.},
	keywords = {anisotropy, continent-ocean transition, eastern North American margin, shear wave splitting, tomography},
	issn = {1525-2027},
	doi = {10.1029/2021GC010084},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2021GC010084},
	author = {Brunsvik, Brennan R. and Eilon, Zachary C. and Lynner, Colton}
}
@article {shuck_role_2019,
	title = {The role of mantle melts in the transition from rifting to seafloor spreading offshore eastern North America},
	journal = {Earth and Planetary Science Letters},
	volume = {525},
	year = {2019},
	month = {nov},
	pages = {115756},
	abstract = {The Eastern North American Margin (ENAM) formed in the early Jurassic (\~{}195 Ma) with the breakup of supercontinent Pangea. This rifting event was accompanied by volcanism along the continental shelf of the eastern United States, giving rise to the East Coast Magnetic Anomaly (ECMA). Numerical models show that magmatic diking can assist rifting by reducing the effective stress required to rupture the lithosphere. Therefore, magma-rich rifts can develop a rapid transition from continental breakup to seafloor spreading. Alternatively, the onset of seafloor spreading may be accompanied by a long period of persistent thermal weakening and erosion of the lithosphere. In this paper we present analyses of active-source wide-angle seismic data collected during the 2014 ENAM Community Seismic Experiment in an area that extends farther offshore than previous seismic surveys along the eastern U.S. Seaward of the ECMA lies a zone of thin oceanic crust with high compressional seismic velocity (up to 7.5 km/s in the lower crust), whereas thicker normal oceanic crust lies \~{}200 km farther offshore along another prominent magnetic anomaly, the Blake Spur Magnetic Anomaly (BSMA). We reconcile our seismic images with a petrologic model to evaluate the mantle melting conditions during the late stages of continental breakup and early seafloor spreading in the Central Atlantic. We propose that the zone of thin crust between the ECMA and BSMA with high seismic velocity is best explained by the presence of a \~{}15{\textendash}20 km thick lithospheric lid at the time of early seafloor spreading, which prevented melting in the shallow mantle. Our analysis suggests that the volcanism that produced the nearshore ECMA did not lead to complete lithospheric breakup of the conjugate North American and African margins. Normal seafloor spreading began at the BSMA under a moderately high mantle potential temperature of \~{}1395{\textendash}1420{\textdegree}C, \~{}25 million years after the initial formation of the volcanic margin. These results imply that stretching, thermal weakening, and rupture of the lithosphere may take millions of years, even in the presence of mantle melts.},
	keywords = {continent-ocean transition, continental rifting, eastern North American margin, mantle melting, oceanic crust, seismic tomography},
	issn = {0012-821X},
	doi = {10.1016/j.epsl.2019.115756},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X19304480},
	author = {Shuck, Brandon D. and Van Avendonk, Harm J. A. and B{\'e}cel, Anne}
}
@article {lynner_crustal_2017,
	title = {Crustal structure across the eastern North American margin from ambient noise tomography},
	journal = {Geophysical Research Letters},
	volume = {44},
	number = {13},
	year = {2017},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL073500},
	pages = {6651{\textendash}6657},
	abstract = {Passive tectonic margins, like the eastern North American margin (ENAM), represent the meeting of oceanic and continental material where no active deformation is occurring. The recent ENAM Community Seismic Experiment provides an opportunity to examine the crustal structure across the ENAM owing to the simultaneous deployment of offshore and onshore seismic instrumentation. Using Rayleigh wave phase and group velocities derived from ambient noise data, we invert for shear velocity across the ENAM. We observe a region of transitional crustal thicknesses that connects the oceanic and continental crusts. Associated with the transitional crust is a localized positive gravitational anomaly. Farther east, the East Coast magnetic anomaly (ECMA) is located at the intersection of the transitional and oceanic crusts. We propose that underplating of dense magmatic material along the bottom of the transitional crust is responsible for the gravitational anomaly and that the ECMA demarks the location of initial oceanic crustal formation.},
	keywords = {ambient noise, crustal structure, eastern North American margin, passive margin},
	issn = {1944-8007},
	doi = {10.1002/2017GL073500},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/2017GL073500},
	author = {Lynner, Colton and Porritt, Robert W.}
}
