Detailed mapping of a terrane boundary, and structure and origin of block-in-matrix structures, central and eastern Blue Ridge, Jackson County, North Carolina

Detailed geologic mapping of the Sylva South and Tuckaseegee quadrangles reveals the southern extent of the Great Balsam Mountains window (Great Balsam Mountains Window), which exposes the northeastern extension of the Dahlonega gold belt in western North Carolina. The Great Balsam Mountains Window is framed by the Soque River fault to the NW and SW, and by the Chattahoochee-Holland Mountain (Chattahoochee-Holland Mountain) fault to the SE. Emplacement and tight folding of the Chattahoochee-Holland Mountain fault is interpreted as an early Alleghanian (D₄) post-peak metamorphic, ductile event because it crosscuts the Rabun Granodiorite (335 Ma) south of the Great Balsam Mountains Window.The Soque River fault is a postmetamorphic late Taconic(?) fault separating two central Blue Ridge terranes: the Cartoogechaye terrane of upper amphibolite to granulite paragneisses, mafic and ultramafic rocks, pelitic schist and Grenvillian basement; and the Dahlonega gold belt of middle to upper amphibolite facies metasedimentary rocks and lesser mafic and altered ultramafic (soapstone to metaperidotite). The Chattahoochee-Holland Mountain fault separates Dahlonega gold belt rocks from Tallulah Falls-Ashe Formation middle to upper amphibolite facies rocks of the Tugaloo terrane in the eastern Blue Ridge and truncates the Soque River fault in the SW part of the window. The tripartite stratigraphy of the Tallulah Falls Formation was identified and mapped in the study area, along with the northern extent of the Walnut Creek granodiorite (355 Ma), Rabun Granodiorite (335 Ma), and Looking Glass granodiorite (333 ± 2 Ma).Geochemistry of felsic igneous rock samples indicates they are typical eastern Blue Ridge plutonic rocks that are likely derived from repeated intracrustal melting of accretionary wedge rocks. Geochemistry of mafic rocks collected from block-in-matrix structures have a geochemical signature typical of an igneous protolith and fall in the tholeiitic basalt field with a strong affinity for a MORB protolith. Penetrative (D₂) structures are dominant in the study area and probably formed during the Taconic orogeny. Rocks in the study area contain amphibolite facies assemblages (sillimanite-kyanite and sillimanite-kyanite-staurolite).