PRESERVED LARGE GARNET ZONING, PSEUDOSECTION THERMOBAROMETRY, AND LOCALIZED DEFORMATION CONSTRAIN P-T PATH AND EXTEND GRANULITE FACIES REGION IN THE SOUTHERN APPALACHIAN CENTRAL BLUE RIDGE, NORTH CAROLINA

Preservation of features that provide T-P constraints on metamorphic conditions within and near the Chunky Gal Mountain Fault (CGMF) are influenced by garnet size and strain intensity. The CGMF, located in the southern Appalachian Central Blue Ridge, partly bounds the Buck Creek-Chunky Gal mafic-ultramafic (BC) complex in rocks previously mapped as amphibolite facies. Published peak T-P conditions in Taconian granulite facies rocks at Winding Stair Gap (WSG) (~ 10 km east) are 850^oC, 0.7-0.9GPa and in meta-troctolites at BC are 825-850^oC, 0.9-1.4GPa. Pseudosection thermobarometry of CGMF samples constrains peak T-P at ~ 800-850^oC, 0.8-0.9GPa, suggesting these rocks reached peak granulite facies.

Garnet zoning in CGMF rocks is preserved as a function of grain size. Smaller garnets have flat chemical profiles due to diffusion. Larger garnets preserve apparent prograde zoning with a moderate outward increase in Mg and a distinct decrease in Ca. Garnet rims show a retrograde drop in Mg and increase in Ca and Mn. Some larger garnets from WSG show similar zoning patterns. Garnet isopleths define clockwise PT-paths in CGMF samples. The well constrained prograde part of the paths are consistent with observed assemblages. More variable and less constrained retrograde paths (near isobaric) may be better determined by considering garnet fractionation effects during growth.

Differing matrix assemblages (sil vs. ky-ms) observed in high-Al CGMF samples from the Jake Ridge outcrop may result from variations in deformation. These samples have similar bulk compositions and garnet interior assemblages (including sil). Shearing appears to have facilitated the growth of ky-ms at lower temperatures.

Garnets in ms-st schists collected ~1.5 km west of CGMF outcrops preserve distinctly different zoning patterns. Large garnets show strong core-rim zoning (incr. Mg, decr. Mn and Ca) more typical of amphibolite facies. Deformation appears to locally influence garnet zoning patterns in these rocks.

Our results expand the region of southern Blue Ridge granulite facies metamorphism. Constraints on the PT-path and peak conditions in these high-T rocks are facilitated by preserved zoning in large garnets, low variance assemblages, pseudosection thermobarometry, and localized influence of deformation on metamorphic preservation.