First‐Order Transition in Appalachian Orogenic Processes Revealed by Along‐Strike Variation of the Moho Geometry

• Published in: Journal of geophysical research. Solid earth 2023-12, Vol.128 (12), p.n/a
• Main Authors: Luo, Yantao, Long, Maureen D., Karabinos, Paul, Rondenay, Stéphane, Masis Arce, Roberto
• Format: Article
• Language: English
• Subjects: Accretion; Appalachians; Arrays; Crustal shortening; Crustal thickness; dense seismic array; Deposition; Depth; Geometry; Imaging techniques; Latitude; Moho; Moho geometry; orogenic plateau; Orogeny; Paleozoic; Precambrian; rifted margin; Seismic arrays; Seismic studies; Seismology; Subduction; Subduction (geology); Tectonics; Variation; wavefield migration
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2023JB027024

Along‐strike variation of the Laurentian rifted margin and the Appalachian orogen has long been recognized in the geologic record. We investigated the manifestation of this along‐strike variation at depth by generating scattered wavefield migration profiles from four dense seismic arrays deployed across the Appalachian orogen at different latitudes. All profiles exhibit a similar crustal thickness decrease of 15–20 km from the Mesoproterozoic Grenville Province to the Paleozoic Appalachian accreted terranes, but the Moho architecture differs dramatically along strike. The profiles beneath the central and southern Appalachians show a smoothly varying Moho geometry; in contrast, there is an abrupt Moho depth offset beneath the New England Appalachians. This contrast in Moho geometry may result from variations in the Laurentian rifted margin architecture, changes in Taconic orogeny subduction polarity, and greater crustal shortening during the Acadian‐Neoacadian orogeny in southern New England and the Alleghanian orogeny in the central and southern Appalachians. A first‐order along‐strike transition in the behavior of Appalachian orogenic processes is located between the central and New England Appalachians. Plain Language Summary The Proterozoic Grenville Province and Paleozoic Appalachian domains are the two major tectonic units in eastern North America, associated with two past supercontinent cycles. The Grenville Province has generally thicker crust than the Appalachian domains, and a Moho depth decrease from Grenville to Appalachians has been observed throughout the Appalachian orogen by previous continental‐scale seismic studies. The Moho beneath the Laurentian margin records how the Proterozoic rifted margin of Laurentia interacted with the Paleozoic Appalachian orogenesis at crustal levels. However, the detailed geometry of the Moho beneath the edge of Laurentia, and how it varies along the margin, have not been resolved by previous work. In this study, we apply a scattered wavefield migration imaging technique to four dense seismic arrays deployed at different latitudes across the Appalachian orogen to investigate the geometry of the Moho across the Grenville‐Appalachian transition. The Moho depth change is smooth beneath the central and southern Appalachians but abrupt beneath New England. This distinction may result from a combination of a non‐uniform Grenville rifted margin, different styles and directions of Appalachian subduction and terrane acc