THERMOCHRONOMETRIC DATING OF MUSCOVITE AND ZIRCON FROM THE TALLULAH FALLS DOME, NE GEORGIA

The Tallulah Falls Dome is a 35 km long-axis elliptical foliation dome cored by Neoproterozoic-Ordovician-aged metasedimentary rocks located within the Blue Ridge of northeastern Georgia. Surrounding the dome are bodies of metasedimentary rocks of the Tallulah Falls Formation and elongated Grenvillian-aged gneissic plutons. Previous models suggest that formation of the Tallulah Falls Dome is the result of duplexing during Alleghanian collision. In order to better understand the deformational history of the Tallulah Falls Dome we used two thermochronometers: ⁴⁰Ar/³⁹Ar in muscovite, and fission track in zircon. These thermochronometers have closure temperatures of ~340 ˚C and ~240 ˚C respectively. ⁴⁰Ar/³⁹Ar cooling ages from this study and previously published data indicate that cooling below ~340 ˚C in and around the dome occurred between 321-317 Ma. Because of their age, zircon grains from the Tallulah Falls Dome contain high track densities, which makes the tracks indistinguishable from each other using standard optical counting methods. Instead we use low etching times and scanning electron microscopy to better distinguish fission tracks. We will use these zircon fission-track ages to determine a cooling rate through the zircon fission track closure temperature using both thermochronometers, as well as pre-existing hornblende ⁴⁰Ar/³⁹Ar data where available. This cooling rate will allow us to distinguish between steady and slow cooling rates consistent with erosion, or rapid cooling consistent with tectonic denudation processes.