Modification of Crust and Mantle Lithosphere Beneath the Southern Part of the Eastern North American Passive Margin

Abstract

The eastern North American margin (ENAM; Figure 1a) represents an archetypical passive margin, which experienced the assembly and breakup of the supercontinent Pangea over the last 500 Ma (Thomas, 2006). During the assembly of Pangea between ∼495 Ma and ∼270 Ma, a sequence of tectonic terranes progressively accreted onto the North American craton (namely Laurentia) (Hatcher, 2010;Thomas, 2006). Extensive rifting along the ENAM started at ∼230 Ma (Withjack et al., 2012), and was accompanied by short-lived igneous activities. Enormous postrifting magmatism occurred over a period of less than 1 million years at ∼200 Ma and formed one of the Earth's largest igneous provinces, the Central Atlantic Magmatic Province (Marzoli et al., 1999(Marzoli et al., , 2018. Rifting led to the breakup of Pangea at ∼185 Ma, and the modern passive margin was ultimately established (Withjack et al., 2012).The southern segment of the ENAM is characterized by a variety of tectonic features associated with both syn-and postrifting tectonic events. For example, a positive magnetic anomaly (namely the East Coast Magnetic Anomaly) aligns approximately in the SW-NE direction (Figures 1 and S1a). The East Coast Magnetic Anomaly likely represents volcanism that was associated with the initial rifting at ∼230 Ma, and thus marks the boundary between the oceanic and continental lithosphere (Austin et al., 1990;Klitgord

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

“…The gradient in velocity between fast values inboard of the ECMA and slow values seaward of this lineament is suggestive of a relatively rapid contrast in lithospheric thickness (Figures 3, 5, and 7). This is consistent with localized crustal thinning observed by Lynner and Porritt (2017) and C. Li and Gao (2021). We are hesitant to over-interpret small-scale velocity anomalies beneath the ocean in our models.…”

“…Utilizing ENAM-CSE OBSs, recent Rayleigh wave ambient noise phase velocity tomography has shown crustal thinning across the margin and a correlation between the East Coast Magnetic Anomaly (ECMA) and a region of thinned crust (Lynner & Porritt, 2017). Full-waveform ambient-noise tomography reinforced these results (C. Li & Gao, 2021). The presence of the ECMA at the edge of the margin suggests that it is correlated with the first oceanic material emplaced after rifting.…”

“…The ENAM-CSE constitutes one of the only rifted-margin crossing broadband OBS datasets, which is capable of interrogating a rifted COT in the mantle. This data set has already been utilized for crustal-scale ambient noise tomography (C. Li & Gao, 2021;Lynner & Porritt, 2017), shear-wave splitting analyses (Lynner & Bodmer, 2017), multi-channel reflection imaging (Bécel et al, 2020), and crustal to uppermost-mantle tomography based on wide-angle seismic data (Shuck et al, 2019). However, no margin-spanning body-wave velocity or 3-D anisotropy models have been developed…”

Seismic Evidence for Crustal Magmatic Intrusion Beneath the Southern Part of the Eastern North American Margin

“…Our new tomographic model shows well‐constrained velocity structures of the crust and uppermost mantle beneath the SENAM, with better lateral and vertical imaging resolution compared to previous studies. For example, our model provides a tighter constraint on the sedimentary thickness variation in the SENAM compared to previous tomographic studies (Figures S22 and S23 in Supporting Information S1; e.g., Li & Gao, 2021; Lynner & Porritt, 2017; Shen & Ritzwoller, 2016). The fast‐to‐slow velocity transition from ocean to continent at the depth of 20–40 km revealed in our model is generally consistent with the observations from previous tomographic studies (e.g., Li & Gao, 2021; Lynner & Porritt, 2017) and matches with the Moho depth variations defined by receiver function studies and active‐source surveys (Guo et al., 2019; Holbrook et al., 1994; Li et al., 2020; Ma & Lowry, 2017).…”

Three‐Dimensional Variation of the Slab Geometry Within the South American Subduction System

“…We calculate the three‐dimensional finite‐frequency sensitivity kernels of Rayleigh waves and apply a damped least squares scheme to invert for the velocity perturbations (Gao & Shen, 2014; Li & Gao, 2021; Yang & Gao, 2020). The inversion approach is fully described in Supporting Information .…”