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Kernel density estimation plots for compiled geo‐ and thermochronologic data in the Blue Ridge. (a) Zircon fission track (ZFT) dates for all Blue Ridge (BR) thrust sheets. N equals the number of ZFT central ages of single samples derived from multi‐grain analyses. (b) Rug plots of ZFT dates subdivided into structural zones across the BR. The frontal western Blue Ridge thrust sheets includes the Great Smoky, Maggies Mill‐Citico, and Miller Cove thrust sheets. (c) Muscovite ⁴⁰Ar/³⁹Ar dates for all BR thrust sheets (n = 66). (d) Rug plots of muscovite ⁴⁰Ar/³⁹Ar dates subdivided into selected thrust sheets in the BR. (e) Hornblende ⁴⁰Ar/³⁹Ar dates for all BR thrust sheets (n = 17). (f) Combined rug plots of ZFT, muscovite and hornblende ⁴⁰Ar/³⁹Ar, and monazite data of this study, subdivided into BR and Inner Piedmont dates. For BR ZFT dates, pre‐Paleozoic ages of the frontal BR thrust sheets are not included. Bin and histogram width designated as 20 Myr in all diagrams. All data and references are included in Table S1 in Supporting Information S1. Diagrams produced using IsoplotR (Vermeesch, 2018).
Source publication
The tectonometamorphic evolution of the southern Appalachians, which results from multiple Paleozoic orogenies (Taconic, Neoacadian, and Alleghanian), has lacked a consensus interpretation regarding its thermal‐metamorphic history. The Blue Ridge terranes have remained the focus of the debate, with the interpreted timing of regional Barrovian metam...
Citations
... The Taconic orogeny is recognized throughout the Appalachian orogen, but its timing and style are thought to have varied. Tectonic models of the Taconic orogeny in other parts of the orogen typically invoke east-dipping subduction of the Laurentian margin under arcs or accreted terranes for the Canadian Appalachians ( van Staal & Barr, 2012;van Staal et al., 2007), for the central Appalachians (Hughes et al., 2014;Wise & Ganis, 2009) and for the southern Appalachians (Hatcher, 2010;Thigpen et al., 2022). However, Tull et al. (2014Tull et al. ( , 2018 suggested a northwest-dipping subduction polarity throughout the Taconic orogeny in the Appalachians of Georgia and Alabama (Figure 6d). ...
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 accretion episodes, and varied amount of crustal shortening along the Appalachian orogen.
