Zr-in-Rutile Thermometry of the Bakersville, NC Eclogite: Constraining Prograde and Peak Temperatures Prior to Overprinting

Author ORCID Identifier

0009-0000-3009-8588

Degree Year

2026

Document Type

Thesis - Oberlin Community Only

Degree Name

Bachelor of Arts

Department

Geology

Advisor(s)

Zeb Page

Committee Member(s)

Zeb Page
Megan Flansburg
Maximiliano Paz

Keywords

Geology, Metamorphic petrology, Geochemistry, Eclogite, Appalachian Mountains, Taconian orogeny, Eclogite

Abstract

An eclogite associated with the Taconian orogeny from the Eastern Blue Ridge in Bakersville, North Carolina records evidence of two episodes of metamorphism, one during the rock’s initial burial and another during its subsequent exhumation. The eclogite, metamorphosed from a basaltic protolith, consists of garnet + clinopyroxene + plagioclase + hornblende + quartz + ilmenite + rutile +/– apatite +/– orthopyroxene. A limitation of major element thermometry methods is their susceptibility to diffusion and subsequent resetting. In contrast, trace elements such as Zr can be more resistant to diffusion and therefore may be able to record their host crystal’s formation temperatures more accurately. This study applies Zr-in-rutile thermometry and equilibrium assemblage diagrams (EADs) in combination with garnet compositional isopleth modeling to three samples of the Bakersville eclogite in order to constrain peak and prograde temperatures. Zr-in-rutile analysis yields the following matrix and inclusion temperatures at a minimum pressure of 10 kbar: 765 ± 42°C and 805 ± 42°C in the first sample, 759 ± 29°C and 791 ± 62°C in the second, and 731 ± 24°C and 748 ± 23°C in the third sample. The similarity between inclusion and matrix rutile temperatures suggests that both populations record peak or near-peak temperature conditions of the rock’s metamorphism. These temperatures partially overlap with previous upper temperature estimates produced by cation exchange thermometry and EADs, yet Zr-in-rutile thermometry pushes the constraint of peak temperatures higher. The high temperatures obtained via Zr-in-rutile thermometry align with the post-peak stability of orthopyroxene indicated by EADs. These revised, higher temperature estimates approach those of the known thermal maximum of the southern Appalachians — the ~850°C Winding Stair Gap migmatites and granulites, providing insight into the conditions of the Taconian orogeny. The high temperatures yielded by Zr-in-rutile thermometry suggest that the method is well suited to reconstruct conditions of peak metamorphism in rocks, such as the Bakersville eclogite, that have undergone multiple pulses of metamorphism like those of the Appalachians.

Notes

Department: Geosciences

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