Character of the Alleghanian orogeny in the southern Appalachians: Part I. Alleghanian deformation in the eastern Piedmont of South Carolina

Abstract

The eastern Piedmont Province in South Carolina contains a sequence of Cambrian volcanic and sedimentary rocks that was penetratively deformed (D1) and regionally metamorphosed (M1) to the greenschist facies during the early and/or middle Paleozoic. The eastern Piedmont was subsequently affected by late Paleozoic (Alleghanian) polyphase deformation (D2–D4) and regional metamorphism. The earliest Alleghanian event (D2) is associated with amphibolite facies regional metamorphism and felsic plutonism in a mid-crustal infrastructure at ca. 295–315 Ma. The gradational interface between infrastructure and overlying suprastructure contained a steep M2 metamorphic gradient (between amphibolite facies below and greenschist facies above), numerous sheets of felsic orthogneiss, and a deformation front marking the upper limit of intense D2 penetrative deformation. D3 is represented by northwestward-vergent folding of S1 and S2 foliations and M2 isothermal surfaces. The Kiokee belt in South Carolina is interpreted as a D2 infrastructure exposed within the core of a D3 antiform. This interpretation suggests that an Alleghanian infrastructure may be present in the subsurface beneath much of the Piedmont and Coastal Plain. The polygenetic Modoc zone forms the northwest boundary of the Kiokee belt. It is interpreted to represent an interface between D2 infrastructure and suprastructure which was rotated into a steep, northwest-dipping attitude during development of the Kiokee belt antiform. Between ca. 267 and 290 Ma, portions of the Kiokee belt, Modoz zone, and Carolina slate belt were overprinted by ductile deformation (D4) along steeply dipping, northeast-trending dextral shear zones.