Deformation and Metamorphic Constraints on Aluminous Rocks from the Chunky Gal Mountain Fault in the Jake Ridge Exposure, Southwestern North Carolina
College of Liberal Arts and Sciences
The Jake Ridge roadcut in southwestern North Carolina exposes aluminous gneisses, apparently deformed by the Chunky Gal Mountain Fault. The rocks appear compositionally similar to the granulite-facies aluminous rocks at Winding Stair Gap (~10km to the northeast) and preserve textural evidence of a complex deformation and metamorphic history. The relatively larger (2-5mm) garnet grains in the slide preserve complex textural and compositional zoning. Garnet cores (up to 0.5-1.0 mm) display inclusion trails nearly perpendicular to external foliation. A sharp boundary separates the cores from an inclusion-free zone that extends to the rim. The garnets are unusual in that they appear to have continued to grow into the tail regions of the grains creating garnets that look like eyes. The tail portions of the garnet are mostly symmetrical and are loaded with fibrous sillimanite grains that are oriented semi-parallel to the prismatic sillimanite grains of the matrix. Preliminary zoning profiles in garnet show a decrease in Ca from core to rim and relatively flat profiles for other elements, apart from evidence of retrograde zoning near the rims. A final stage of deformation is suggested by fractures in garnet, approximately perpendicular to the matrix fabric. Evaluation of P-T conditions in the context of complex textures in the Jake Ridge samples and comparison with mylonites from the type outcrop of the Chunky Gal Mountain Fault and published P-T-t conditions for granulite facies rocks at Winding Stair Gap may help to better understand the P-T-deformation history of the fault with respect to surrounding rocks.
Geological Society of America Annual Southeastern Section Meeting
Peterson, Virginia and Williams, Chadwick, "Deformation and Metamorphic Constraints on Aluminous Rocks from the Chunky Gal Mountain Fault in the Jake Ridge Exposure, Southwestern North Carolina" (2011). Faculty Scholarly Dissemination Grants. 329.