Crustal evolution across the southern Appalachians: Initial results from the SESAME broadband array

Abstract

Receiver functions from the EarthScope Southeastern Suture of the Appalachian Margin Experiment broadband deployment and U.S. Transportable Array were analyzed to constrain average crustal thickness and composition across the southern Appalachians. Low Vp/Vs ratios (1.69–1.72) across the Carolina terrane and parts of the Inner Piedmont indicate that the crust has a felsic average composition. The results are consistent with models of thin‐skinned thrusting of Carolina arc fragments over Laurentian basement, whereas arc collision models require significant crustal modification to explain the low Vp/Vs. New crustal thickness estimates provide constraints on the extent of the Blue Ridge crustal root. The present root may be a remnant of a broader structure formed by Alleghanian thrust loading. Root preservation is attributed to Mesozoic heating and thinning of the lower crust beneath outboard terranes, leaving colder Blue Ridge crust largely intact. However, thickened crust (50–55 km) across the region may also be inherited from continental collision during the Proterozoic Grenville orogeny.

Constraining lithologic variability along the Alleghanian detachment in the southern Appalachians using passive-source seismology

“…The velocity inversion at depths of 12-13 km beneath stations D03 and D04 in the Carolina terrane is interpreted as the interface between high-Vs rocks at the base of the Carolina terrane allochthon and the top of this shear zone. Well-constrained, low average crustal Vp/ Vs ratios previously reported from SESAME stations in the Carolina terrane also support the interpretation that arc rocks overlie relatively felsic Laurentian basement (Parker et al, 2013).…”

Shallow mantle velocities beneath the southern Appalachians from Pn phases

“…One interpretation of reflection profiles in northern Georgia is that the deep crust and mantle lithosphere of Laurentia extend far to the east beneath the Coastal Plain, and that the Blue Ridge, Inner Piedmont, and Carolina terranes are thin crustal slivers that were thrust hundreds of kilometers to the northwest over the Laurentian crust and mantle [e.g., Cook and Vasudevan , ]. This view is consistent with the absence of intact arc crust beneath the Carolina terrane inferred from constraints on crustal thickness and V P / V S from Ps phases at SESAME and TA stations [ Parker et al , ]. In an alternative model, Hibbard et al [] suggest that northwest directed subduction created a suture between the lower crusts of Laurentia and the Carolina terrane in the vicinity of the transition from high to low Pn mantle velocities.…”

Estimating crustal thickness using SsPmp in regions covered by low‐velocity sediments: Imaging the Moho beneath the Southeastern Suture of the Appalachian Margin Experiment (SESAME) array, SE Atlantic Coastal Plain

“…One possibility is that the basic features of the crustal architecture were in place by the Jurassic, with the Blue Ridge root either a remnant of a much broader zone of crustal thickening formed during Alleghanian collision and thinned by Mesozoic extension, or an earlier structure associated with Taconic or Grenville collision [Parker et al, 2013]. One possibility is that the basic features of the crustal architecture were in place by the Jurassic, with the Blue Ridge root either a remnant of a much broader zone of crustal thickening formed during Alleghanian collision and thinned by Mesozoic extension, or an earlier structure associated with Taconic or Grenville collision [Parker et al, 2013].…”

“…The Southeastern Suture of the Appalachian Margin Experiment (SESAME) array consists of 85 broadband stations along three transects crossing parts of the ACP and southern Appalachians [Parker et al, 2013] ( Figure 1). A primary objective of SESAME is to determine the relationship between the Late Paleozoic Suwannee-Wiggins suture (SWS) and the Triassic-Jurassic South Georgia basin (SGB).…”