Defining the Timing, Extent, and Conditions of Paleozoic Metamorphism in the Southern Appalachian Blue Ridge Terranes of Tennessee, North Carolina, and Northern Georgia

J. Ryan Thigpen, David P. Moecher, Harold H. Stowell, Arthur Merschat, Robert D. Hatcher, Nicholas E. Powell, Brandon M. Spencer, Calvin A. Mako, Elizabeth M. Bollen, Andrew Kylander-Clark

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

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 metamorphism and associated deformation ranging from early (Taconic) to late Paleozoic (Alleghanian). New monazite U-Pb geochronology and thermobarometric data are integrated with previously reported geo- and thermochronology to delimit the Paleozoic thermal-metamorphic evolution of these terranes. Monazite compositional, textural, and U-Pb age systematics are remarkably consistent for all samples, yielding a single dominant age mode for each sample. The western, central, and eastern Blue Ridge terranes yield weighted mean monazite U-Pb ages of 450–441, 459–457, and 458–453 Ma, respectively. Thermodynamic modeling using mineral assemblages yields peak conditions of 600°C–650°C and 5.8–8.9 kbar for staurolite and kyanite grade western Blue Ridge units, including the stratigraphically youngest unit in the Murphy syncline, which also yields a weighted mean monazite U-Pb age of 441 Ma. The Taconic metamorphic core of the central Blue Ridge yields peak conditions of 775°C and ∼11.5 kbar. Combined, these ages indicate that the relatively intact Barrovian metamorphic progression mapped across the Blue Ridge of Tennessee, North Carolina, and northern Georgia is solely of Ordovician (Taconic) age. Synthesis of this new data with existing geo- and thermochronology support a model of Barrovian metamorphism resulting from construction of a Taconic accretionary wedge and subduction complex, followed by post-Taconic unroofing during Neoacadian and Alleghanian thrusting.

Original languageEnglish
Article numbere2022TC007406
JournalTectonics
Volume41
Issue number10
DOIs
StatePublished - Oct 2022

Bibliographical note

Funding Information:
This work was supported by the NSF-EAR 1802730 to JRT. NSF-EAR 1551342 to DM supported instrumentation used in the analyses presented here. Our work in the Blue Ridge has benefitted greatly from discussions with numerous colleagues. Mike Jercinovic is thanked for helping with WDS mapping at UMass. Comments by Jacob Forshaw, Gabe Casale, associate editor Eva Enkelmann, and editor Jonathan Aitchison greatly improved a previous version of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Funding Information:
This work was supported by the NSF‐EAR 1802730 to JRT. NSF‐EAR 1551342 to DM supported instrumentation used in the analyses presented here. Our work in the Blue Ridge has benefitted greatly from discussions with numerous colleagues. Mike Jercinovic is thanked for helping with WDS mapping at UMass. Comments by Jacob Forshaw, Gabe Casale, associate editor Eva Enkelmann, and editor Jonathan Aitchison greatly improved a previous version of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Publisher Copyright:
© 2022. American Geophysical Union. All Rights Reserved.

Keywords

  • Alleghanian
  • Blue Ridge
  • Neoacadian
  • Taconic
  • metamorphism
  • monazite

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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