TIMING AND DEFORMATION CONDITIONS OF THE TALLULAH FALLS DOME, NE GEORGIA; IMPLICATIONS FOR THE ALLEGHANIAN OROGENY

The Tallulah Falls Dome in northeast Georgia is a shear zone-bounded body of metasedimentary rocks that is defined by a foliation pattern that cross-cuts the regional fabric of the Eastern Blue Ridge crystalline nappe in the southern Appalachian Mountains. Previously the Tallulah Falls Dome was interpreted as the expression of duplexed underlying slices of Laurentian margin sediments imbricated during Alleghanian emplacement of the allochthonous Blue Ridge thrust sheet under greenchist-facies conditions.

We provide new observations of quartz and feldspar recrystallization fabrics, and complement existing thermochronometric ages with new ⁴⁰Ar/³⁹Ar ages from muscovite to determine the timing and conditions of doming within the Tallulah Falls Dome. Our microstructural observations are consistent with deformation mechanisms active dominantly at amphibolite-facies conditions, with some samples recording temperatures in excess of 650 °C. Thermochronometric ages define a period of relatively rapid cooling from ~550-340 °C within and around the Tallulah Falls Dome between 321-317 Ma, with differential cooling across the dome bounding shear zone lasting until at least 313 Ma. Our observations reveal a period of early Alleghanian cooling from amphibolite- to greenschist-facies conditions within the Tallulah Falls Dome. This is inconsistent with previous interpretations of doming genetically related to emplacement of the Blue Ridge thrust sheet at greenschist-facies conditions.