25-2 Alleghenian Overprint of the Taconic Basement of Central Blue Ridge (Winding Stair Gap, NC, US)

Session: New Research in the Appalachian-Ouachita Orogen: Integrated studies from the Foreland to the Hinterland (Posters)

Presenting Author:

Authors:

Abstract:

Multiple overprinting collision and accretion events during the Paleozoic Era comprise the Appalachian Orogeny. One such event, the Taconic Orogeny, consists of subduction of the Iapetus Ocean underneath Laurentia with accretion of various oceanic arcs and oceanic lithosphere. Peak metamorphism during the Taconic Orogeny is well preserved within the exposed basement of the Central Blue Ridge (CBR) at the Winding Stair Gap (WSG) (North Carolina, USA). The WSG basement suite contains numerous meta- pelitic and mafic lithologies, including biotite-garnet granulite, quartzo-feldspathic gneiss, sillimanite-garnet schist and amphibolites. Here, we present U-Pb ages of zircons from a biotite-garnet granulite and zircons and rutiles from an amphibolite lens encompassed within, providing critical insights into the complex tectonic evolution of the CBR.

The zircons analyzed in the present study are all euhedral, with CL imaging of the zircons revealing high U and Th content, with no zoning patterns present, indicating complete metamictization. Ex-situ analysis of zircons from the amphibolite and the biotite-garnet granulite sample yielded concordia ages of 453.1±2.0 Ma (n=32, MSWD=1.8) and 457.4±3.0 Ma (n=28, MSWD=1.2), respectively. These ages are interpreted to record peak Taconic metamorphism and are consistent with previously reported U-Pb ages of igneous zircons from partial melt lenses exposed at the WSG. Furthermore, these ages indicate coeval metamorphism of the basement assemblage exposed at the WSG.

The rutiles separated from the amphibolite lens are all prismatic, and EDS imaging revealed all rutiles to be located within grain boundaries of the amphibole and plagioclase phases. These rutiles yielded a lower intercept age of 318±15 Ma (n=38, MSWD=0.57) and a weighted mean ²⁰⁶Pb/²³⁸U age of 323±15 Ma (n=38, MSWD=0.56). This age provides the first ever reported evidence for Alleghenian overprinting of the Taconic basement of CBR and is interpreted to suggest polymetamorphism, requiring reconsideration of the tectonothermal evolution of this terrane.

Future work will integrate additional geochemical and geo- and thermo-chronological constraints, attempting to resolve the petrogenesis of these lithologies prior to their metamorphism, and temporal and thermal evolution of the Central Blue Ridge basement post-Taconic Orogeny.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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