NEW 1:24,000-SCALE GEOLOGIC MAP COMPILATIONS OF THE BURNSVILLE, MICAVILLE, AND SPRUCE PINE 7.5-MINUTE QUADRANGLES, YANCEY, MITCHELL, AVERY, AND MCDOWELL COUNTIES, NORTH CAROLINA

The North Carolina Geological Survey has produced 1:24,000-scale bedrock geologic map compilations of Burnsville, Micaville, and Spruce Pine 7.5-minute quadrangles in Yancey, Mitchell, Avery, and McDowell counties, cooperatively funded through the STATEMAP component of the National Cooperative Geologic Mapping Program. The compilations are based on mapping by Brobst (1962), Adams (1995), Waters (1999), Borella (2000), and Langille (2023). Over 3,800 measurements from these unpublished sources were digitally processed and added to the NC bedrock geodatabase. Fieldwork in 2022-23 by the NCGS added 3,600 structural measurements and observations at 1,518 stations. These efforts produced the first edge-matched 1:24K-scale geologic map and GeMS Level 3 database of the region.

Bedrock geology of the mapped areas is comprised of Mesoproterozoic gneisses (MG), Neoproterozoic Bakersville Metagabbro, Neoproterozoic to Cambrian Ashe Metamorphic Suite (AMS), and Devonian Spruce Pine Plutonic Suite. New mapping identified several previously unknown granodiorite and ultramafic bodies and confirmed the extent of mylonitization associated with the Burnsville shear zone (BSZ). Whole rock geochemical analyses of 16 samples helped characterize these units. University of Arizona Laserchron Center zircon analyses are pending for crystallization ages of a magnetite-bearing MG unit and an undeformed trondhjemite in the BSZ. Detrital zircon ages are pending for a biotite-hornblende MG unit and a biotite-hornblende AMS unit near the BSZ.

Compositional layering and schistosity are generally subparallel and complexly folded in the study area. Foliations on Burnsville and Micaville quadrangles typically strike NE-SW and dip moderately to steeply to the NW and SE. Foliations on the Spruce Pine quad strike more N-S and dip shallowly to moderately E and W. Southwest plunging antiform-synform pairs were identified within the AMS. Most measured minor fold axes on all three maps have a shallow NE or SW plunge.

Fractures on Burnsville and Micaville quadrangles trend strongly NW-SE but fractures near the prominent Laurel Creek lineament trend E-W on these quadrangles and are parallel to minor brittle faulting. Fractures on the Spruce Pine quadrangle trend strongly WSW-ENE, subparallel to the Laurel Creek lineament in this area.