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

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Character of the Alleghanian Orogeny in the Southern Appalachians: Part II Character of the Alleghanian orogeny in the southern Appalachians: Part II. Geochronological constraints on the tectonothermal evolution of the eastern Piedmont in South Carolina R. DAVID DALLMEYER Department of Geology, University of Georgia, Athens, Georgia 30601 JAMES E. WRIGHT Department of Geology, Stanford University, Stanford, California 94305 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 ABSTRACT Piedmont at ca. 315 Ma (prior to or during GEOLOGIC OVERVIEW the early stages of the Alleghanian orogeny). A nearly concordant U-Pb zircon age of The thermal maximum of Alleghanian re- Early workers subdivided the southeastern 550 ± 4 Ma is interpreted to closely date crys- gional metamorphism (amphibolite facies in Piedmont into several northeast-trending litho- tallization of the epizonal Little Mountain the Kiokee belt; greenschist facies in the tectonic belts (Crickmay, 1952; King, 1955; metatonalite in the southeastern part of the southeastern part of the Carolina slate belt) Hatcher, 1972; see Fig. 3 of Secor and others, Charlotte belt in South Carolina. This con- occurred during ca. 295-315 Ma. During the 1986b). In South Carolina, belts characterized firms field studies which indicate that the late Carboniferous and Early Permian, the by low- to medium-grade regional metamor- Charlotte belt contains a plutonic metaigne- eastern Piedmont experienced differential up- phism (Belair, Carolina slate, Kings Mountain, ous complex that developed as a sub-vol- lift, erosion, and relatively rapid postmeta- Chauga) alternate with medium- to high-grade canic-arc infrastructure, contemporaneous morphic cooling. Isothermal surfaces were belts (Kiokee, Charlotte, Inner Piedmont). Strat- with vulcanism manifested in the Carolina folded into an antiform-synform-antiform igraphic sequences within the Belair, Kiokee, slate belt. Both paleontological and geochron- configuration corresponding to the Kiokee, Carolina slate, and Charlotte belts are generally ological controls indicate that the South Carolina slate, and Charlotte belts, respec- similar (Maher, 1978; Secor and others, 1982; Carolina slate belt is mostly younger than tively. Hauck, 1984; Secor and others, 1986a). Each is 570 Ma (Cambrian?), whereas the slate belt in The geochronological data provide the fol- represented by an association of intermediate to North Carolina and Virginia is mostly of late lowing calibration for the late Paleozoic de- felsic, epizonal, metaplutonic rocks and/or in- Proterozoic age. formational chronology recorded in the Kio- termediate to felsic metavolcanic rocks which is A regionally significant mid-Paleozoic (ca. kee and Carolina slate belts: D2 (Lake overlain by metasedimentary sequences includ- 340-360 Ma) thermal event is suggested by Murray deformation), ca. 295-315 Ma; D3 ing mudstone, siltstone, wacke, and/or feld- discordant ^Ar/^Ar whole-rock age spectra (Clarks Hill deformation), ca. 285-295 Ma; spathic sandstone. In central South Carolina, of slate/phyllite in the northwestern Carolina and D4 (Irmo deformation), ca. 268-290 field studies suggest that the Charlotte belt in- slate belt and from hornblende in the south- Ma. cludes a sub-volcanic-arc infrastructure, which eastern Charlotte belt. It is uncertain if this likely developed contemporaneously beneath event was associated with deformation in the INTRODUCTION extrusive arc sequences of the Carolina slate belt eastern Piedmont; however, mid-Paleozoic (Secor and others, 1982). Geochronological studies in South Carolina (Butler and Fullagar, deformation has been previously documented The relationship of late Paleozoic deforma- 1975) and Georgia (Carpenter and others, elsewhere in the western Piedmont. tion and metamorphism recorded in the eastern 1982) suggest a Cambrian age for at least some A slightly disconcordant U-Pb zircon age Piedmont (Secor and others, 1986a) with the of these arc sequences. The report of the occur- of 317 ± 4 Ma is interpreted to closely date Alleghanian orogenic development of the west- rence of Atlantic province Middle Cambrian initial crystallization of the deformed Edge- ern Appalachian foreland (Woodward, 1957) trilobites in metasedimentary rocks within the field granite and confirms a record of late has long been uncertain. This report presents Carolina slate belt (Secor and others, 1983; Paleozoic penetrative deformation in the Ki- U-Pb zircon and 40Ar/39Ar geochronological Samson, 1984) suggests that the Belair, Kiokee, okee belt of South Carolina. U-Pb isotope results from the eastern Piedmont in South Car- Carolina slate, and Charlotte belts likely origi- data for the Lake Murray orthogneiss and olina. The thermal evolution suggested by these nated in environments spatially distant from Clouds Creek granite are discordant and sug- data provides controls essential to a more North America and should be considered an ex- gest that the magmas of these plutons were general analysis of the Alleghanian orogeny in otic Appalachian terrane (the Carolina terrane). derived by partial melting of a sialic Precam- the southern Appalachians (discussed by Secor Structural and paleomagnetic evidence suggests brian source and then emplaced in the eastern and others, 1986b). Additional material for this article (tables and appendices) may be secured free of charge by requesting Supplementary Data 86-25 from the GSA Documents Secretary. Geological Society of America Bulletin, v. 97, p. 1329-1344, 10 figs., 2 tables, November 1986. 1329 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/11/1329/3445149/i0016-7606-97-11-1329.pdf by guest on 23 September 2021 1330 DALLMEYER AND OTHERS Figure 1. Generalized geo- logic map of the Piedmont in west-central South Carolina. Modified from Wagener (1977), Secor and others (1982), Halik (1983), Hauck (1984), Kirk (1985), and Secor and others (1986a). Localities sampled for U-Pb zircon geochronological analysis are indicated by numbered stars. CAROLINA SLATE BEL.T^ KIOKEE BELT BELAIR BELT that the Carolina cerrane was accreted to North 1983; Dallmeyer and others, 1985b). A predom- related to initial phases of extension during America in the ea rly or middle Paleozoic (Ell- inantly felsic magmatic arc developed within the opening of the present Atlantic Ocean. The wood, 1982; Barton and Brown, 1983; Dooley, eastern Piedmont between ca. 285 and 325 Ma crystalline rocks in the study area are uncon- 1983; Secor and others, 1983). Predominant (Sinha and Zietz, 1982). Northwest of the Kio- formably overlain by Late Cretaceous and Ter- lithologies within, the Kings Mountain belt kee belt, these plutons are not regionally duc- tiary sediments of the Atlantic Coastal Plain. (phyllite, manganiferous schist, amphibolite, tilely deformed; however, within or adjacent to marble, metacongi omerate) and Inner Piedmont the Kiokee belt, the 285- to 325-Ma plutons PREVIOUS GEOCHRONOLOGY AND (sillimanite schist, biotite paragneiss, felsic or- display regionally penetrative ductile deforma- ITS GEOLOGICAL SIGNIFICANCE thogneiss) are unlike those in the Carolina ter- tion fabrics (Snoke and others, 1980). Geologi- rane. The northwest edge of the Carolina terrane cal and geochronological studies (Kish, 1983; During the past 25 yr, there have been nu- is interpreted to be within or adjacent to the Secor and others, 1986a) indicate that the Kio- merous geochronological attempts to determine Kings Mountain belt on the basis of geological kee belt and the southeastern edge of the Caro- initial crystallization or eruption ages of plu- and geophysical evidence (Glover and Sinha, lina slate belt underwent polyphase deforma- tonic, metaplutonic, or metavolcanic rocks in 1973; Hatcher ar d Zietz, 1980; Williams and tion (D2-D4) and a greenschist to amphibolite the eastern Piedmont. The ages reported are Hatcher, 1983). facies metamorphism (M2) during the late Pa- separable into three groups: late Precambrian- The study area of this report (Fig. 1) was leozoic. The rocks in the study area are de- Cambrian1 (520-740 Ma; Fullagar, 1971; penetratively defarmed (Dj) and regionally formed by a series of northeast-trending, Glover, 1971; Glover and Sinha, 1973; Briggs metamorphosed (Mi) to the greenschist and post-D4 brittle faults with small to moderate amphibolite facies in the early and/or middle displacement (see Fig. 2 of Secor and others, 1986a, the folded insert accompanying this Paleozoic (Kish and others, 1979; Fullagar, 'This paper uses the 1983 Decade of North Ameri- 1981; Secor and e thers, 1982; Sutter and others, issue). These are likely of Mesozoic age and can Geology time scale (Palmer, 1983). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/11/1329/3445149/i0016-7606-97-11-1329.pdf by guest on 23 September 2021 GEOCHRONOLOGICAL CONSTRAINTS ON EVOLUTION OF PIEDMONT, SOUTH CAROLINA 1331 TABLE 1. Rb-Sr WHOLE-ROCK AGES FOR SELECTED PLUTONS and others, 1978; Wright and Seiders, 1980; ciated with well-developed contact metamor- IN THE EASTERN PIEDMONT OF SOUTH CAROLINA THAT Black, 1980; Carpenter and others, 1982; phism aureoles. Along the east side of the arc, HAVE EXPERIENCED EPISODES OF ALLEGHANIAN . PENETRATIVE DUCTILE DEFORMATION McConnell and Glover, 1982), Silurian and however, some of the plutons have locally expe- rienced penetrative ductile deformation and Devonian (385-415 Ma; Butler and Fullagar, Name Age (Ma) 1978; Fullagar,
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