Crustal structure across the eastern North American margin from ambient noise tomography

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.

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

“…Seismic data gathered by USGS in Virginia (close to the seismic profile in this study) support this thin-skinned model (Pratt et al 1988). Previous studies also interpret the eastern North Figure: A-A′, a seismic reflection profile of Pratt et al (1988Pratt et al ( , 2015; B-B′, crustal model of Dreiling and Mooney (2015); C-C′, S-wave velocity model of Shen and Ritzwoller (2016); D-D′, P-wave velocity model of Hales et al (1968) and Lewis and Meyer (1977); E-E′, P-wave velocity model of Holbrook et al (1994); F-F′: S-wave velocity model of Lynner and Porritt (2017). Red box in the inset map outlines the study area American margin as a strongly volcanic margin, which are generally indicated by the presence of dipping reflectors within the transitional crust and crustal underplating of igneous materials (Klitgord et al 1988;Tréhu et al 1989;Holbrook et al 1994;White and McKenzie 1989).…”

“…The middle and lower crust extend only as far east as the rifted zone, where they terminate. The offshore ocean-continent transition is 100 km wide, with normal oceanic crust beginning immediately to the east (Holbrook et al 1994;Lynner and Porritt 2017). Beneath the profiles in the SCS rift, there is no distinct oceancontinent transition as seen on the mid-Atlantic margin, and the extended crust is extended from continent to the ocean.…”

“…Red box in the inset map outlines the study area American margin as a strongly volcanic margin, which are generally indicated by the presence of dipping reflectors within the transitional crust and crustal underplating of igneous materials (Klitgord et al 1988;Tréhu et al 1989;Holbrook et al 1994;White and McKenzie 1989). There is also a stark transition in crustal thickness across the margin, and the Moho boundary is sharply uplifted in the transition between continent and ocean crust (Holbrook et al 1994;Lynner and Porritt 2017).…”

“…our study area, Shen and Ritzwoller (2016) present only a rough model. Lynner and Porritt (2017) present the crustal structure across the eastern North American margin from ambient noise tomography and focus on the interpretation of the ocean-continental transitional crust and the East Coast magnetic anomaly. Given the previous seismic data, it is still unclear to what extent the Appalachian and Laurentian terranes exist beneath the coastal plain, or whether the coastal plain is its own unique crustal section.…”

Midcrustal Deformation in the Central Andes Constrained by Radial Anisotropy

“…We invert for V sh and V sv separately using identical starting models and inversion parameters. Our initial model is set to AK135 (Kennett et al, ) below 100 km and 4.5 km/s in the upper 100 km without an artificial jump at the Moho to avoid low velocity artifacts (e.g., Lynner & Porritt, ). We tested several starting models with a spatially varying velocity jump at the Moho and found that the different starting models resulted in only minor deviations.…”