STRUCTURE WITHIN THE ASHE METAMORPHIC SUITE, BUNCOMBE COUNTY, NORTH CAROLINA: EXAMPLES FROM THE USFS BENT CREEK RESEARCH AND DEMONSTRATION FOREST AND THE NPS BLUE RIDGE PARKWAY

Mapping by the North Carolina Geological Survey on the USFS Bent Creek Research and Demonstration Forest (BCRDF) and the Blue Ridge Parkway (BRP) demonstrates that the dominant structural style within the Ashe Metamorphic Suite (AMS) consists of as many as five fold events in the vicinity of Asheville. On the BCRDF (11 km SW of Asheville), S1 and S3 foliation orientations in metagraywacke and sillimanite-garnet-chlorite-mica schist define a first-order, closed to tight, upright to inclined, gently to moderately SW-plunging, non cylindrical F4 antiform with parasitic folds on its limbs. Metagraywacke crops out on the fold limbs, whereas sillimanite-garnet-chlorite-mica schist marks its core. Dome-and-basin interference patterns on the NW limb suggest deformation by gentle to open, upright to inclined, NW- and SE-plunging F5 folds. This deformation style continues along the BRP from Craggy Gardens to Black Mountain Gap (~24 km NE of Asheville), where extensive exposures allow for an analysis of structures and timing. Near Pinnacle Gap, a dominant S3 schistosity in kyanite-garnet-mica schist encloses metagraywacke boudins containing intrafolial F2 folds defined by the orientation of S1 compositional bands. Metagraywacke boudins are several meters to hundreds of meters in length, and have aspect ratios of ~4:1. F2 axes and axial planes in the boudins are nearly perpendicular to S3. Metagraywacke boudins and early-formed migmatite and pegmatite are also folded (F3 folds) and transposed into the regionally penetrative S3 schistosity. Locally, a younger suite of pegmatite and quartz veins crosscuts both S1 and S3. Elsewhere along the BRP in this area, S1 generally parallels S3. Together, S1 and S3 orientations define N-S and NW-plunging first- and higher-order F4 folds similar to the F4 antiform observed at BCRDF. F1 folds and S2, S4, and S5 foliations have not yet been recognized in outcrop. Westward deflection of F4 fold hinges and subhorizontal, strike-parallel mineral stretching lineations along the BRP may be due to local overprinting by second- and higher-order, E-W and N-S plunging, gentle to open, upright to inclined and reclined F5 folds (observed in outcrop along the BRP and also at map-scale at BCRDF), but may also reflect dextral movement within the entire AMS related to the Burnsville fault zone ~11 km to the NW.