Evolution of the Blue Ridge basement complex in the eastern Great Smoky Mountains: Evidence from zircon U-Pb geochronology and Nd-Pb isotope geochemistry of basement gneisses

D. P. Moecher, E. D. Anderson, D. F. Loughry, R. J. Quinn, E. A. Larkin, K. B. Walsh, S. D. Samson, A. M. Satkoski, E. Tohver

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations

Abstract

The eastern Great Smoky Mountains basement complex consists of the following components: (1) ca. 1350-1325 Ma orthogneiss and mafic xenoliths that represent some of the oldest crust in Appalachian Grenville massifs (similar to “pre-Grenville” basement components in the Adirondack, Green Mountain, Hudson Highland, and Shenandoah massifs); (2) ca. 1150 Ma augen orthogneisses and granitic orthogneisses correlating with the Shawinigan phase of Grenville magmatism; and (3) paragneisses (cover rocks) that have either pre- or syn-Grenville (i.e., Mesoproterozoic) versus post-Grenville (Neoproterozoic) depositional ages, and that experienced Taconian metamorphism and migmatization. Mesoproterozoic paragneisses contain major zircon age modes that require a component of Proterozoic crust in the source region. The Neoproterozoic paragneisses exhibit the archetypical “Grenville doublet” in detrital zircon age distributions that matches the age distribution of Ottawan and Shawinigan magmatic/metamorphic events in eastern Laurentia. Most zircon U-Pb age systematics exhibit variable lead loss interpreted to result from high-grade Taconian (ca. 450 Ma) regional metamorphism and migmatization. Neodymium mantle model ages (T DM ) for ortho- and paragneisses range from 1.8 to 1.6 Ga, indicating that all rocks were derived from recycling of Proterozoic crust (i.e., they are not juvenile), which is consistent with Proterozoic detrital zircon ages in pre- to syn-Grenville paragneisses. Lead isotope compositions confi rm the presence of an exotic (Amazonian) crustal component in the source region for the protoliths of the pre-Grenville orthogneisses and xenoliths, and that this exotic component was incorporated to varying degrees in the evolution of the basement complex. The oldest age component may represent an Amazonian pre-Grenville analog to the ca. 1.35 Ga native Laurentian crust present in Adirondack and northern Appalachian basement massifs.

Original languageEnglish (US)
Title of host publicationGSA Field Guides
PublisherGeological Society of America
Pages121-139
Number of pages19
ISBN (Electronic)9780813756509
DOIs
StatePublished - Mar 29 2018

Publication series

NameGSA Field Guides
Volume50

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ASJC Scopus subject areas

  • Geology
  • Earth-Surface Processes
  • Stratigraphy
  • Palaeontology

Cite this

Moecher, D. P., Anderson, E. D., Loughry, D. F., Quinn, R. J., Larkin, E. A., Walsh, K. B., Samson, S. D., Satkoski, A. M., & Tohver, E. (2018). Evolution of the Blue Ridge basement complex in the eastern Great Smoky Mountains: Evidence from zircon U-Pb geochronology and Nd-Pb isotope geochemistry of basement gneisses. In GSA Field Guides (pp. 121-139). (GSA Field Guides; Vol. 50). Geological Society of America. https://doi.org/10.1130/2018.0050(08)