THE TIMING AND CONDITIONS AND METAMORPHISM AND ASSOCIATED FLUID-ROCK INTERACTION OF ULTRAMAFIC BODIES WITHIN THE ASHE METAMORPHIC SUITE, NORTH CAROLINA APPALACHIANS

Metasomatic reaction zones can provide a window into mass transfer processes at high pressure. These fluid-rock interactions can generate hybrid lithologies, e.g. chlorite- and talc-rich rocks, which can affect rock mechanical properties at mid-crustal depths. However, determining the conditions at which these reactions occur and the sources of fluid can be challenging.

This work highlights an ultramafic body located within the Ashe Metamorphic Suite (AMS) of the North Carolina Appalachians. The AMS has been recognized as a unit predominantly made up of pelitic and amphibolite schist containing pods of variably altered mafic and ultramafic bodies, that has been interpreted to be an accretionary complex related to Taconic subduction. Previous work has highlighted a metasomatic reaction between a dunite pod and the host pelitic schist in the locality of Greer Hollow, however, the protolith of metasomatized rocks and the nature of fluid-rock interaction remains enigmatic. Exposures within the Greer Hollow body are largely comprised of three rock types, a tremolite schist, a magnetite chlorite schist, and a garnet magnetite chlorite schist. These lithologies incorporate a reaction zone between the ultramafic pod and the pelitic (AMS) host rock. Bulk Lu-Hf garnet geochronology on the garnet-chlorite-magnetite schist provides an age of 455 ± 2 Ma, in line with Taconic subduction. Laser fluorination δ¹⁸O values obtained from the core and rim of the garnets reveal low δ¹⁸O (~0.9 ‰) in garnet cores, suggesting incorporation of a low-temperature serpentinization (protolith) signature. In contrast, garnet rims exhibit higher δ¹⁸O values (~1.8 ‰), possibly influenced by high-pressure fluid infiltration, as quartz veins cutting through the reaction zone give δ¹⁸O values of ~9.0 ‰.

Ongoing work involves microsampling garnet growth zones for geochronology in order to determine the duration of metamorphism. Additionally, phase equilibria modeling is being performed to constrain the conditions at which this rock underwent metamorphism and metasomatism and the element fluxes necessary to create these hybrid lithologies.