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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

By
D.P. Moecher
D.P. Moecher
University of Kentucky, Department of Earth and Environmental Sciences, Lexington, Kentucky 40506, USA
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E.D. Anderson
E.D. Anderson
University of Kentucky, Department of Earth and Environmental Sciences, Lexington, Kentucky 40506, USA
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D.F. Loughry, Jr.
D.F. Loughry, Jr.
University of Kentucky, Department of Earth and Environmental Sciences, Lexington, Kentucky 40506, USA
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R.J. Quinn
R.J. Quinn
University of Kentucky, Department of Earth and Environmental Sciences, Lexington, Kentucky 40506, USA
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E.A. Larkin
E.A. Larkin
University of Kentucky, Department of Earth and Environmental Sciences, Lexington, Kentucky 40506, USA
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K.B. Walsh
K.B. Walsh
University of Kentucky, Department of Earth and Environmental Sciences, Lexington, Kentucky 40506, USA
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S.D. Samson
S.D. Samson
Syracuse University, Department of Earth Sciences, Syracuse, New York 13244, USA
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A.M. Satkoski
A.M. Satkoski
Syracuse University, Department of Earth Sciences, Syracuse, New York 13244, USA
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E. Tohver
E. Tohver
Instituto de Geosciências, Universidade de São Paolo, 05508-080 São Paolo, Brazil
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Published:
March 29, 2018
Publication history
08 January 2018

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 (TDM) 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 confirm 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.

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GSA Field Guides

Geology at Every Scale: Field Excursions for the 2018 GSA Southeastern Section Meeting in Knoxville, Tennessee

Annette Summers Engel
Annette Summers Engel
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Robert D. Hatcher, Jr.
Robert D. Hatcher, Jr.
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Geological Society of America
Volume
50
ISBN electronic:
9780813756509
Publication date:
March 29, 2018

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