Mantle Structure and Flow Across the Continent‐Ocean Transition of the Eastern North American Margin: Anisotropic S‐Wave Tomography

Abstract

Seismic resolution across the rift-drift transition, particularly in the mantle, is extremely limited due to the sparsity of broadband ocean-bottom seismometers (OBSs) offshore at rifted margins.The eastern North American passive margin (ENAM) is an excellent location to study the tectonics of the rifted continent-ocean transition (COT). ENAM is a mature passive margin resulting from the rifting of Pangaea at ∼230-200 Ma (Withjack et al., 2012). There has been relatively little deformation at ENAM since the transition

Plate‐Scale Imaging of Eastern US Reveals Ancient and Ongoing Continental Deformation

“…The Margin crust is also notably thinner than the continental interior ∼34 km on average. Moreover, while the GRP and Grenville regions show no clear crustal radial anisotropy, the Margin region has widespread strong V SH > V SV anisotropy (ξ ∼ 1.07), consistent with previously inferred extensional fabrics (Brunsvik et al., 2021). The Margin 's slowest upper mantle coincides closely with the distribution of CAMP dykes, suggesting that the CAMP's thermal legacy persists today (Figure 1).…”

“…Given our smooth parameterization, we likely underpredict velocity extrema, so melt percentages may be locally higher than stated here. Our lowest velocities span ∼70–∼145 km depth, but body‐wave tomography suggests slow wavespeed may extend to ∼400 km (Biryol et al., 2016; Brunsvik et al., 2021).…”

“…We find three spatially localized, upper mantle low‐velocity anomalies along the Appalachians: the NAA, CAA and Southern Appalachian anomaly (SAA) at the Georgia‐Tennessee border (Figure 2). The SAA, a deeper (130 km) but statistically significant (Section S6; Figure S16 in Supporting Information ) ∼4.5% slow feature, is missing in some tomography models (e.g., Shen & Ritzwoller, 2016), and present in others (e.g., Brunsvik et al., 2021; Schmandt & Lin, 2014). The NAA and CAA are more widely observed (Carrero Mustelier & Menke, 2021; Dong & Menke, 2017; Shen & Ritzwoller, 2016), perhaps because they are shallower.…”

“…The Eastern North American Margin (ENAM) experienced intraplate tectonic activity (Biryol et al, 2016;Brunsvik et al, 2021) and has variable mantle seismic velocity structure (Savage, 2021;Wagner et al, 2018), including several slow anomalies. The Central Appalachian Anomaly (CAA) aligns with intraplate, non-plume volcanism (Long et al, 2021), while the Northern Appalachian Anomaly (NAA) is associated with extensive lithospheric modification and plume influence (Menke et al, 2016(Menke et al, , 2018Tao et al, 2021).…”

Receiver Function Analysis Reveals Lateral Variations in Temperature and Water Content in the Mantle Transition Zone Beneath Eastern North America

“…Finally, we'd like to emphasize that the proposed hydro‐thermal upwelling hypothesis does not rule out the possibility of other coexisting dynamic processes to contribute to the origin of the prominent slow velocity anomaly below central Appalachian Mountains (S1 p /S1 s in Figure 2). Potentially, this slow velocity anomaly may be connected to the positively buoyant material in the deeper mantle beneath the Atlantic ocean, as indicated by the tomographic imaging from the recent deployment of the broadband ocean‐bottom seismometers offshore at the eastern U.S. continental margin (Brunsvik et al., 2021).…”