Crustal structure across the southern Appalachians and Atlantic Coastal Plain
Parker, Elias Horry
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The Southeastern Suture of the Appalachian Margin Experiment (SESAME) is an 85-station broadband seismometer array deployed across the southern Appalachians and Atlantic Coastal Plain. Receiver functions analyzed in this study complement previous active-source reflection and refraction experiments and provide new constraints on crustal structure across the crystalline southern Appalachians. Receiver function Ps conversions combined with previous wide-angle results confirm the presence of a localized crustal root (up to ~58-km crustal thickness) beneath the high elevations of the Blue Ridge province in northern Georgia and western North Carolina. Low average crustal Vp/Vs ratios (1.69-1.72) determined from H-k stacking indicate that the continental crust across the Carolina terrane and parts of the Inner Piedmont has a felsic average composition. Forward modeling of Ps conversions in relatively high-frequency (2-3 Hz) receiver functions provides new constraints on the nature of velocity contrasts along the Appalachian detachment. In the Blue Ridge, a 3.5-km-thick, high shear-wave velocity layer (Vs=3.9 km/s) is consistent with underlying passive-margin metasedimentary rocks dominantly comprised of quartzite and/or dolostone. In the Inner Piedmont, conversions from the top and base of a low-Vs zone (3.1 km/s) at depths of 5-9 km are interpreted as a package of metasedimentary rocks or a shear zone characterized by radial anisotropy. High-amplitude negative conversions beneath the Carolina terrane at 10-13 km depth are consistent with high-Vs arc rocks (4.0 km/s) overlying sheared rocks with lower Vs (3.2 km/s). H-k stacking results and forward modeling are consistent with models showing that the Alleghanian detachment extends southeastward beneath the peri-Gondwanan Carolina terrane. Beneath the Atlantic Coastal Plain, the Suwannee suture zone is interpreted to mark the Late Paleozoic Alleghanian collision between Laurentia and Gondwana, though the coincident Brunswick Magnetic Anomaly (BMA) is interpreted to result from Central Atlantic Magmatic Province intrusions. New magnetic models assuming a contrast in remanent magnetization between two crustal blocks suggest that the anomaly can also be explained as an effect of continental suturing. Additional constraints on the velocity structure across the Atlantic Coastal Plain from the SESAME array are needed to differentiate between models for the source of the BMA.