Crustal structure of the eastern Piedmont and Atlantic coastal plain in North Carolina and Virginia, eastern North American margin

Abstract

The eastern North American rifted margin is a passive tectonic margin that has experienced Paleozoic ocean closure and Mesozoic continent rifting. To understand evolution of this continental margin, we modeled the two-dimensional P-wave and S-wave seismic velocity structure of the crust with a seismic wide-angle reflection/refraction profile located in North Carolina and Virginia. There is a seismic low-velocity zone (LVZ) at 10-12 km depth beneath the western segment of the profile. We infer the LVZ to be the base of a Paleozoic metasedimentary succession beneath the eastern Piedmont and westernmost coastal plain. The P-wave velocity and Poisson's ratio suggest a felsic composition for the upper and middle crust beneath the seismic profile, and an intermediate composition for the lower crust. Overall, the measured crustal velocities and the lateral homogeneity of the crust, especially the middle and lower crust, indicate that Laurentian middle and lower crust extends beneath the entire coastal plain. The lack of a basal crustal layer with a high seismic velocity indicates that no magmatic intrusions have underplated the eastern Piedmont and coastal plain. The comparison with South China Sea, which is a wide rift, and Kenya Rift, which is a narrow rift, indicates that eastern North American margin has the character of a narrow rift. We infer that narrow rifts and wide rifts may have similar crustal compositions, but show strong differences in crustal thickness and the distribution of basal crustal mafic intrusion. These differences may be related to differences in extensional rate during rifting. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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

“…We observe very low P ‐wave velocities (<5.0 km/s) for the top 8 km depths in the oceanic part (Figure 2a; Cross‐sections AA’ and BB’ in Figure 3), which likely reflect the presence of the water layer and the thick sedimentary layer underneath (Laske et al., 2013). In comparison, the continental part is marked by low P ‐wave velocities (<5.0 km/s) for the top ∼2 km depth (Cross‐sections AA’, BB’, and CC’ in Figure 3), which likely indicates a thin sedimentary layer (Guo et al., 2019; Laske et al., 2013). However, our model resolution tests of P ‐wave velocities show that the seismic structures near the surface cannot be fully resolved (Figures ).…”

Gravity Survey of a Buried Triassic Rift Basin, Bertie County, North Carolina

“…Along these master faults, continental Triassic basins developed sub-parallel to the inherited structural framework as is demonstrated by the Danville and Deep River Triassic basins. The Appalachian gravity gradient, a gravitational feature thought to represent a major crustal transition and/or decollement zone between fault blocks, likely represents one such master fault that can be traced underneath the Piedmont Province in the Carolinas (Longwell, 1943, Guo et al, 2019. Crustal thinning on the southeast side of 7 to 10 km is inferred, a β value of approximately 1.1, to cause the gradient between positive and negative gravity values Hutchinson and others, 1983).…”

“…The boundary between the Blue Ridge and Piedmont provinces is a fault system, the Brevard Fault Zone, and coincides with a significant gravitational anomaly, known as the Appalachian Gravity gradient. This boundary is thought to represent the master detachment fault associated with Triassic crustal thinning and extension and is likely a reactivated over-thrusted package of Paleozoic sedimentary and metamorphic rocks(Guo et al, 2019). The Coastal Plain is furthest east and begins at the Fall Line, where Piedmont rock suites are covered by Cretaceous age coastal sediments and sedimentary rock.…”

Assessing origins of end-Triassic tholeiites from Eastern North America using hafnium isotopes

“…The decoupling toward higher ε Hf relative to the terrestrial array is primarily observed in Proterozoic granulites (Huang et al, 1995;Schmitz et al, 2004;Zartman et al, 2013) and so also may play a role in the Carolina terrane (Ingle et al, 2003). As for major element compositions, while much of the LCC may be mafic, Zhao and Guo (2019) and Guo et al (2019) S1). Several Pb isotopic compositions were tested for the LCC assimilation scenarios to determine the best fit to the measured ENA CAMP data set (see Figure 3 and Tables S1 and S2), considering the large span of Pb isotopic ratios exhibited by the basement terranes previously accreted to ENA (Pettingill et al, 1984;Sinha et al, 1996;Whalen et al, 2015).…”