NEW PERSPECTIVES ON THE PETROLOGY AND STRUCTURE AT ELK KNOB STATE PARK, NORTH CAROLINA

Mapping of Elk Knob State Park in northwestern North Carolina reveals that the Park lies wholly within the Ashe Metamorphic Suite (AMS) of the Gossan Lead Block. Three main lithologic units in the park constitute the AMS: (1) a lower amphibolite unit, (2) a middle mixed rock unit, and (3) an upper amphibolite unit. All are overlain only by Quaternary landslide deposits.

The upper two AMS units, viewed at a small scale, are very gently south-dipping, but in more detail exhibit N70°W trending, open to gentle, anticlines and synclines, that refold earlier-formed fold sets. All three units internally exhibit steep foliations and evidence ¬locally of up to three earlier fold generations — in the mixed rock unit, early cm-scale sheath folds; steeply to gently plunging, tight to isoclinal, macro- to mesoscopic N-S folds; and SE, S, and SW, shallow to moderately plunging, gentle to isoclinal, meso- to macroscopic folds. Foliations and mineral lineations were formed early and folded by later deformation. A ductile thrust fault likely separates the upper and middle units.

The lower amphibolite layer consists of biotite hornblende gneisses and schists of the amphibolite facies, partially overprinted by a greenschist facies assemblage of sphene-epidote-chlorite. The mixed rock layer, which may represent a deformed and metamorphosed breccia body beneath the upper, overthrust amphibolite layer, dominantly consists of amphibolite facies, kyanite-bearing, white mica (pelitic) schists with lenses of quartz-feldspar semischist and amphibolite of N- and E-MORB parentage. The upper amphibolite layer consists of upper amphibolite facies, sphene-biotite-plagioclase-garnet-hornblende amphibolites, with retrograde plagioclase coronas on the garnets — a rock likely derived from a pre-existing eclogite.