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