The Blue Ridge belt in northwestern North Carolina and northeastern Tennessee is composed chiefly of 1,000-million to 1,100-million-year-old metamorphic and plutonic rocks that have been thrust many miles northwestward across unmetamorphosed Cambrian(?) and Cambrian sedimentary rocks of the Unaka belt. The Blue Ridge thrust sheet is rooted on the southeast along the Brevard zone, a zone of strike-slip faulting along which metamorphic and plutonic rocks of the Inner Piedmont belt are juxtaposed with rocks of the Blue Ridge.Near the southeastern edge of the Blue Ridge belt, the Blue Ridge thrust sheet is breached by erosion, and the rocks beneath are exposed in the Grandfather Mountain window, which is 45 miles long and as much as 20 miles wide; it is the only major window so far recognized in the Blue Ridge belt. The rocks exposed within it include 1,000-million-year to 1,100-million-year-old plutonic basement rocks, sedimentary and volcanic rocks of late Precambrian age, and an allochthonous tectonic slice of Lower Cambrian ( ? ) and Cambrian sedimentary rocks identified with the Chilhowee Group and Shady Dolomite in the Unaka belt 20 to 30 miles to the northwest.The Blue Ridge thrust sheet surrounding the Grandfather Mountain window consists largely of schist, gneiss, and amphibolite derived by •metamorphism of sedimentary and volcanic rocks 1,000 to 1,100 m.y. ago, and of Cranberry Gneiss, a complex of migmatite and granitic rocks which underlies the metasedimentary and metavolcanic rocks and which probably formed during the same metamorphic episode. The Cranberry Gneiss is intruded by the Beech Granite, by aegirine-augite granite, and by quartz monzonite, all of which were emplaced during a late stage of or after the plutonic metamorphism. Stocks and dikes of Bakersville Gabbro of late Precambrian(?) age and small bodies of ultramafic rock, granodiorite, and pegmatite of early or middle Paleozoic age intrude the earlier Precambrian rocks. Although all these rocks may have been metamorphosed about 450 nt.y. ago, the principal Paleozoic dynamothermal metamorphism occurred about 350 m.y. ago. At that time new medium-grade minerals, including staurolite, kyanite, monoclinic pyroxene, epidote, and calcic plagioclase, crystallized in the schist, gneiss, and amphibolite. During the late Paleozoic, most of the plutonic rocks were partly reconstituted to low-grade blastomylonitic and phyllonitic gneisses containing new biotite, albite, sericite, chlorite, actinolite, and epidote, whereas the overlying rocks were largely unaffected. The contact between low-and medium-grade rocks may be a fault. vard wa:s contemporaneous with and mechanically related to northwest movement of the Blue Ridge and Tablerock thrust sheets.A dike of unmetamorphosed Upper Triassic(?) diabase cuts the rocks of the Inner Piedmont, the Brevard fault zone, the Blue Ridge thrust sheet, and the Grandfather Mountain window.The rocks of the Blue Ridge thrust sheet moved northwestward at least 35 miles over the Grandfather Mountain window after the clos...
