The relative roles of inheritance and long-term passive margin lithospheric evolution on the modern structure and tectonic activity in the southeastern United States

Abstract

We perform inversions for the shear-wave velocity structure of the southeastern United States (SEUS) using Rayleigh-wave phase and amplitude data from the broadband stations of the South Eastern Suture of the Appalachian Margin Experiment (SESAME) and EarthScope Transportable Array (TA). Our tomographic images of shear-wave velocities in the upper mantle beneath the SEUS provide new constraints on the evolution of mantle lithosphere, both from the inheritance of structures from repeated Wilson cycles and from processes that have occurred while at a passive margin setting. Our images also allow us to correlate these structures to evidence of Eocene to recent tectonism observed at the surface. We find evidence for both inherited structures and more recently evolved structures, both of which bear some correlation to observations of ongoing tectonism. Our results suggest that lithospheric mantle continues to evolve while in a passive margin setting and that even relatively "stable" continental mantle lithosphere is subject to episodes of delamination, foundering, and erosion due to processes that are still not well under stood. Our results provide structural constraints on the types of processes that may be ongoing and on possible explanations for the numerous observations of comparatively recent tectonic activity occurring along this passive margin setting. Tectonic History The geologic history of our study area begins with the formation of Rodinia, the supercontinent that juxtaposed the Granite Rhyolite Province of the Laurentian basement against cratons found in present-day South America, Africa, GEOSPHERE

Synthesizing Seemingly Contradictory Seismic and Magnetotelluric Observations in the Southeastern United States to Image Physical Properties of the Lithosphere

“…Resistive upper mantle beneath the SEUS also appears in the global geomagnetic depth sounding (GDS) results of Sun et al (2015). (Pollitz & Mooney, 2016;Porter et al, 2016;Schmandt et al, 2015;Shen & Ritzwoller, 2016;Wagner et al, 2018) and geometric mean resistivity (Murphy & Egbert, 2017) over the same depth range. (Pollitz & Mooney, 2016;Porter et al, 2016;Schmandt et al, 2015;Shen & Ritzwoller, 2016;Wagner et al, 2018) and geometric mean resistivity (Murphy & Egbert, 2017) over the same depth range.…”

“…The lithosphere in the SEUS has been imaged by numerous surface-wave tomography studies that used a variety of data sets and inversion approaches (e.g., Pollitz & Mooney, 2016;Porter et al, 2016;Savage et al, 2017;Schmandt et al, 2015;Shen & Ritzwoller, 2016;Wagner et al, 2018). These surface-wave imaging results generally show heterogeneous, small-amplitude deviations from reference models in the Piedmont Figure 2.…”

“…The Piedmont physiographic region comprises the low-relief region between the Coastal Plain and the modern Appalachian Mountains (high-relief, high-elevation region shown on base map). They have further been used to argue that the mantle lithosphere in this region has been modified since opening of the Atlantic by passive continental margin processes such as delamination and lithospheric erosion by edge convection (e.g., Wagner et al, 2018). The white line shows the cross-section location for subsequent figures.…”

“…Figures 4 and 5 compare five of these surface-wave tomography models to each other and to the MT results. The black line in the lower plot is drawn to follow the 0% Vs anomaly contour (reference value is 4.5 km/s, as used by Wagner et al (2018) in their imaging study). Body-wave tomography studies similarly show mottled small-amplitude deviations from standard velocity reference models (Biryol et al, 2016;Schmandt & Lin, 2014).…”

“…Spatially limited outcrops of late-Jurassic-and Eocene-aged volcanic rocks along the border between Virginia and West Virginia (Mazza et al, 2014;Meyer & van Wijk, 2015;Mazza et al, 2017; see Figure 2) that are coincident with both a slow seismic anomaly (e.g., Wagner et al, 2018) and a conductive geoelectric anomaly (Evans et al, 2016) in the mantle lithosphere provide evidence for postrifting lithospheric modification, although more consideration is needed to determine whether such modification is due to hot spot impingement (e.g., Chu et al, 2013), to a delamination event (e.g., Mazza et al, 2014;Meyer & van Wijk, 2015;Schmandt & Lin, 2014), to localized thermal erosion (e.g., Evans et al, 2016), to a combination of such processes, or to some completely other process. Spatially limited outcrops of late-Jurassic-and Eocene-aged volcanic rocks along the border between Virginia and West Virginia (Mazza et al, 2014;Meyer & van Wijk, 2015;Mazza et al, 2017; see Figure 2) that are coincident with both a slow seismic anomaly (e.g., Wagner et al, 2018) and a conductive geoelectric anomaly (Evans et al, 2016) in the mantle lithosphere provide evidence for postrifting lithospheric modification, although more consideration is needed to determine whether such modification is due to hot spot impingement (e.g., Chu et al, 2013), to a delamination event (e.g., Mazza et al, 2014;Meyer & van Wijk, 2015;Schmandt & Lin, 2014), to localized thermal erosion (e.g., Evans et al, 2016), to a combination of such processes, or to some completely other process.…”