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Character of the Alleghanian Orogeny in the Southern Appalachians: Part I

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Character of the Alleghanian Orogeny in the Southern Appalachians: Part I Character of the Alleghanian orogeny in the southern Appalachians: Part I. Alleghanian deformation in the eastern Piedmont of South Carolina DONALD T. SECOR, JR. Department of Geology, University of South Carolina, Columbia, South Carolina 29208 ARTHUR W. SNOKE Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071 KENNETH W. BRAMLETT Shell Western E and P, Inc., Box 831, Houston, Texas 77001 OLIVER P. COSTELLO Samson Resources, 801 Travis Street, Suite 1630, Houston, Texas 77002 OLLIE P. KIMBRELL Soil & Material Engineers, Inc., 3025 McNaughton Drive, Columbia, South Carolina 29223 ABSTRACT ward, 1957) is a fundamental problem. This report summarizes results of new field work and outlines interpretations concerning late Paleozoic de- The eastern Piedmont Province in South Carolina contains a formation along the Fall Line in west-central South Carolina. This infor- sequence of Cambrian volcanic and sedimentary rocks that was pene- mation is essential to development of a more general analysis of the tratively deformed (Dj) and regionally metamorphosed (Mi) to the Alleghanian orogeny in the southern Appalachians (Secor and others, greenschist facies during the early and/or middle Paleozoic. The east- 1986). era Piedmont was subsequently affected by late Paleozoic (Allegha- nian) polyphase deformation (D2-D4) and regional metamorphism. The OVERVIEW earliest Alleghanian event (D2) is associated with amphibolite facies regional metamorphism and felsic plutonism in a mid-crustal infra- In the southeastern Piedmont, late Paleozoic deformation events af- structure at ca. 295-315 Ma. The gradational interface between infra- fected a region that had previously been strongly deformed in the early structure and overlying suprastructure contained a steep M2 and/or middle Paleozoic. Some aspects of the pre-late Paleozoic geologic metamorphic gradient (between amphibolite facies below and green- history are important in this discussion and are included in the following schist facies above), numerous sheets of felsic orthogneiss, and a de- overview. formation front marking the upper limit of intense D2 penetrative Our geological studies have been conducted along the Fall Line in deformation. D3 is represented by northwestward-vergent folding of west-central South Carolina in an area that includes parts of the Piedmont St and S2 foliations and M2 isothermal surfaces. The Kiokee belt in and Atlantic Coastal Plain Provinces (Figs. 1 and 2; for Fig. 2, see folded South Carolina is interpreted as a D2 infrastructure exposed within insert accompanying this issue). Here, crystalline rocks of the Piedmont are the core of a D3 antiform. This interpretation suggests that an Alle- unconformably overlain by semi-consolidated Upper Cretaceous and Ter- ghanian infrastructure may be present in the subsurface beneath much tiary strata of the Coastal Plain. The unconformity at the base of the of the Piedmont and Coastal Plain. The polygenetic Modoc zone Coastal Plain sequence dips gently southeast at ~2 m/km. The outcrop forms the northwest boundary of the Kiokee belt. It is interpreted to trace of the contact between the Piedmont and Coastal Plain is extremely represent an interface between D2 infrastructure and suprastructure irregular because it is maturely dissected and has a local topographic relief which was rotated into a steep, northwest-dipping attitude during of -75 m. Coastal Plain sequences cap hills and ridges in the central part development of the Kiokee belt antiform. Between ca. 267 and 290 of the study area. In the southeast, Piedmont crystalline rocks are exposed Ma, portions of the Kiokee belt, Modoz zone, and Carolina slate belt in numerous erosional inhere through the Coastal Plain. Additional infor- were overprinted by ductile deformation (D4) along steeply dipping, mation on the Coastal Plain is available in Siple (1967), Smith (1980), northeast-trending dextral shear zones. Bramlett and others (1982), Nystrom and Willoughby (1982), and Colqu- houn and others (1983). INTRODUCTION Previous investigators have subdivided the Piedmont Province into several northeast-trending lithotectonic belts (Crickmay, 1952; King, Geological and geochronological studies have recently indicated that 1955; Hatcher, 1972). In South Carolina, belts characterized by low- to an important belt of late Paleozoic (Alleghanian) penetrative deformation medium-grade regional metamorphism (Belair, Carolina slate, Kings and amphibolite facies metamorphism is present along the southeastern Mountain, Chauga; see Fig. 3 of Secor and others, 1986) alternate with edge of the Piedmont Province and beneath the adjacent Atlantic Coastal medium- to high-grade belts (Kiokee, Charlotte, Inner Piedmont). Our Plain (Secor and Snoke, 1978; Durrant and others, 1980; Snoke and study area includes parts of the Carolina slate and Kiokee belts. others, 1980a; Pavlides and others, 1982; Glover and others, 1983; Farrar, In west-central South Carolina, metavolcanic and metasedimentary 1985; Russell and others, 1985; see Fig. 1 of Secor and others, 1986). The map units trend obliquely across the Carolina slate belt and intersect the uncertain relationship of this deformed belt in the eastern Piedmont to the bordering Charlotte and Kiokee belts. classical Alleghanian deformation in the western Appalachians (Wood- The oldest stratigraphic unit recognized in the South Carolina slate Geological Society of America Bulletin, v. 97, p. 1319-1328, 8 figs., November 1986. 1319 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/11/1319/3445129/i0016-7606-97-11-1319.pdf by guest on 26 September 2021 1320 SECOR AND OTHERS belt is the Persimmon Fork Formation (Secor and Wagener, 1968), Carolina slate belt, the Asbill Pond contains layers and lenses of quartz which is exposed in the core of the F! Emory anticlinorium (Fig. 2). The siltstone and quartz sandstone displaying sedimentary structures suggestive Persimmon Fork exceeds ~3 km in thickness and is predominantly an of deposition on a tidal shelf (Secor and Snoke, 1978). The upper part of intermediate to felsic ashflow tuff. Geochronological studies of rocks that the Asbill Pond contains a mudstone sequence which has yielded several are considered equivalent to the Persimmon Fork Formation indicate genera of late Middle Cambrian trilobites, some of which are diagnostic of deposition during ca. 530-580 Ma (Butler and Fullagar, 1975; Carpenter the Atlantic faunal province (Secor and others, 1983; Samson, 1984). In and others, 1982; Dallmeyer and others, 1986). the Kiokee belt, mudstone sequences of the Asbill Pond are metamor- A sequence of thin-bedded to massive mudstone and siltstone, with phosed to biotite schist and biotite paragneiss. subordinate greenstone, occurs in the core of the Fi Saluda synclinorium The oldest recognizable deformation phase (Dj) in the study area was in the northwestern corner of the study area (Fig. 2). Sedimentary struc- an episode of tight to isoclinal folding with attendant development of slaty tures in these rocks suggest turbidite deposition below wave base (Brown, cleavage under conditions of greenschist facies regional metamorphism. F| 1971; Kearns and others, 1981). These rocks are here correlated with the folds occur at a variety of scales, and the S] slaty cleavage is generally Richtex Formation of Secor and Wagener (1968) because of lithological penetrative. Major F] fold structures occur which have wavelengths of as similarity. Structural data and meager sedimentary younging criteria sug- much as several kilometres (Saluda synclinorium, Emory anticlinorium, gest that the Richtex overlies the Persimmon Fork, although it is uncertain Delmar synclinorium) and are primarily responsible for the outcrop pat- whether the contact is depositional or tectonic. The thickness of the Rich- tern of stratigraphic units in the Carolina slate belt. Stratigraphic and tex probably exceeds 3 km; however, precise measurement is precluded by structural evidence (Costello and others, 1981; Fig. 2) indicates that a postdepositional penetrative strain. major south westward-plunging Fj synclinal fold (the Delmar synclino- The Asbill Pond formation (informal usage) conformably overlies the rium) occurs in the Carolina slate belt between Lake Murray and Bates- Persimmon Fork Formation in the southeastern part of the study area. It burg. Southwest of Batesburg (Figs. 2 and 3), the axis of the Delmar has a thickness in excess of 5 km and is represented by a sequence of synclinorium can be traced into the Kiokee belt. In this region, mudstone metasedimentary rocks locally interbedded with mafic to felsic metavol- canic rocks. The Asbill Pond is exposed in the northeast-trending F[ Delmar synclinorium, which crosses from the Kiokee belt to the Carolina 34° 30' slate belt between Johnston and Batesburg, South Carolina (Fig. 2). In the kilometers Figure 1. Generalized geologic map of west-central South Carolina showing some geographic and geologic features referred to in the text. Modified from Figure 2 and from Wagener (1977), Secor and others (1982), Halik (1983), Hauck (1984), and Kirk (1985). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/11/1319/3445129/i0016-7606-97-11-1319.pdf by guest on 26 September 2021 ALLEGHANIAN OROGENY, APPALACHIANS, PART I 1321 and quartz-rich siltstone and sandstone units in the Asbill Pond formation Di fabric (Butler and Fullagar, 1978; Fullagar, 1981). Recent studies by can be traced into the Kiokee belt where they
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