AN INVESTIGATION OF ALLEGHANIAN FAULT ZONES NORTH OF ASHEVILLE, NC

North of Asheville, NC, the western Blue Ridge thrust complex consists of a series of thrust sheets that lie NW of the Burnsville fault. These thrust sheets are separated by thick greenschist-facies Alleghanian shear zones. Trupe et al. (2004) suggested that the Sams Gap-Pigeonroost (SGPR) fault, exposed near the TN-NC border, splays off the Fries fault west of the Grandfather Mountain window, and that the Fries fault therefore lies between the Burnsville fault and the SGPR fault. Near the Grandfather Mountain window, the Fries fault is a thick greenschist-facies mylonite zone. Our previous mapping suggests that the Fries fault should extend to into the Sams Gap and Mars Hill quadrangles. Merschat (1977) mapped a stratigraphic discontinuity in the Mars Hill quadrangle, and suggested that it is either a fault or an unconformity. This study was undertaken to locate the Fries fault in the Bald Creek, Sams Gap, and Mars Hill quadrangles, and to determine if Merschat's stratigraphic discontinuity is equivalent to the Fries fault. Basement rocks between the Burnsville fault and the SGPR fault consist of intensely folded, locally migmatitic biotite-hornblende gneiss, biotite gneiss, amphibolite, and calc-silicate rock, intruded by mafic rocks of the Bakersville Intrusive Suite. These mafic rocks contain amphibolite-facies assemblages, with local occurrences of granulite-facies assemblages near the Burnsville fault. Mafic dikes below the SGPR fault are slightly lower grade. We have found no evidence of a greenschist-facies shear zone coincident with the mapped stratigraphic discontinuity in the Mars Hill quadrangle. However, a thick greenschist-facies shear zone occurs ~10 km NW of this contact, in the SE corner of the White Rock quadrangle. This shear zone strikes NE, dips moderately to steeply SE and contains mylonite and ultramylonite with abundant SE-trending lineations. Outcrop-scale kinematic indicators show top-to-NW sense of shear. Mafic dikes within the shear zone have been retrograded to greenschist-facies assemblages and rotated to near concordance with mylonitic foliation. At present, it is unclear whether this shear zone represents the SGPR fault or the Fries fault. Further mapping is in progress to resolve this question.