Major Tectonic Features arid Struc Elemerats in the Northwest r ,£1 ,'f the Greenville Quadrangle,

I .

.. I • '· Major Tectonic Features and Structural Elements in the Northwest Part of The Greenville Quadrangle, Georgia

By ARTHUR E. NELSON

A study of major structural features, tectonic fabrics, and fold analyses of polydeformed metamorphic rocks comprising three major thrust sheets that together form a large part of the southern Appalachian Mountains in northeast Georgia

U.S. GEOLOGICAL SURVEY BULLETIN 1643 DEPARTMENT OF THE INTERIOR DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1985

For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304

Library of Congress Cataloging in Publication Data Nelson, Arthur E. (Arthur Edward), 1922- Major tectonic features and structural elements in the northwest part of the Greenville quadrangle, Ga. (U.S. Geological Survey bulletin; 1643) Bibliography: p. Supt. of Docs. no.: I 19.3:1643 1. Geology-Georgia-Greenville region. 2. Geology, structural. I. Title. II. Series: Geological Survey bulletin; 1643. QE75.B9 no. 1643 557.3 s [557.58'455] 85-600011 [QE102.G73] CONTENTS

Abstract 1 Introduction 1 Previous work 1 General geology 1 Great Smoky thrust sheet 2 Hayesville thrust sheet 2 Mafic and ultramafic rocks 3 Helen-Coweeta terrane 4 Metamorphism 4 Structural geology 5 Faults, joints, and lineament trends 5 Folding and related deformation 6 Fold analyses 12 Area I 12 Area II 12 Area III 12 Area IV 14 Area V 14 The northwest subdivision 14 Helen-Coweeta terrane 14 East part of Hayesville sheet 16 Brasstown Bald window 16

Crenulation cleavage (S3) 16 F J fold analysis 18 Summary and conclusions 18 References cited 21

FIGURES 1. Maps showing (A) location of report area and generalized tectonic features of northeast Georgia and (B) generalized lithotectonic features of the northwest part of the Greenville 2-degree quadrangle, Georgia 2,3 2. Landsat image of the northwest part of the Greenville 2-degree quadrangle and approximate boundaries of the major lithotectonic units of the area 6 3. Photograph showing three fold phases at an exposure in Brasstown Creek, Georgia 8 4. Photograph showing type 3 fold interference pattern at an outcrop along the Richard Russell Highway, Georgia 9 5. Photograph showing outcrop that contains hinge of an F1 isoclinal fold in siliceous metasandstone and schist in the Hayesville thrust sheet, Georgia 9 6. Photograph showing F2 fold that is overturned to the northwest, western Union County, Georgia 9

7. Photograph showing an exposure that displays S0, S~, and S3 foliation, Brass­ town Bald, Georgia 10

Contents Ill 8. Photograph showing exposure that displays a rootless F2 fold and an F3 fold with an axial planar crenulation cleavage, southeast of Young Harris, Georgia 10 9. Photograph showing gently inclined saprolite exposure that shows a small conjugate F3 fold pair, north of Ebenezer Church, Georgia 10 10. Map showing generalized structure of the report area as displayed by folia­ tion form lines 11 11. Map showing structural areas in northwest Greenville quadrangle, Georgia, that were used for statistical analyses of fold events 12 12. Contoured equal area projections of poles to s. and F2 and F3 fold attitudes for areas shown in figure 11 13 13. Contoured equal area projections of various planar and linear features in northwest Greenville quadrangle, Georgia 15 14. Contoured equal area projections of various planar and linear features in the Brasstown Bald area and northwest Greenville quadrangle, Georgia 17

15. Diagram depicting deformed S1 surface in the area southeast ofthe Hayes­ ville fault, Georgia 20

IV Contents Major Tectonic Features and Structural Elements in the Northwest Part of the Greenville Quadrangle, Georgia

By Arthur E. Nelson J)Orthwest part of the Greenville 2-degree quadrangle in northeast Georgia (fig. 1). Because most earlier Abstract geologic investigations of the area were of a recon­ naissance nature and because many remote sections The rocks underlying the northwest part of the Green­ ville 2-degree quadrangle form parts of three lithotectonic were not previously mapped, the geologic detail of units. From northwest to southeast, they are the Great much of the study area has not been well understood. Smoky thrust sheet, the Hayesville thrust sheet, and the My investigation indicates that the rocks underlying Helen-Coweeta terrane, which divides the Hayesville the report area are allochthonous. They have been sheet diagonally southwest to northeast. The Hayesville folded during at least four and possibly six folding thrust sheet was transported westward over the Great phases, and they have been locally deformed by duc­ Smoky thrust sheet along the Hayesville thrust fault. The tile and brittle faulting. Hayesville fault is part of a major fault system in the south­ ern Appalachian Mountains; in the study area, the Hayes­ ville fault also forms the contact around several windows Previous work of the Great Smoky thrust sheet through the Hayesville thrust sheet. Yeates and McCallie (1896) and Park (1953) landsat images show that each lithotectonic unit is described some of the gold deposits and mining characterized by lineaments with distinct trends. The lin­ properties of Georgia. One of the major gold produc­ eaments probably represent fracture zones. They suggest ing zones, the Dahlonega gold belt, extends northeast that rocks of each lithotectonic unit yielded differently to stress or that lineaments were present before thrust em­ from Dahlonega and forms part of the Helen­ placement, and they imply different prethrust tectonic his­ Coweeta terrane, defined later in this report (see p. tories for the different thrust sheets. 4). Hopkins (1914) described soapstone, and Fur­ Rocks in the study area were deformed by at least four cron and Teague (1943) reported on the mica-bearing phases of folding; the second generation folds (Fv form pegmatites within the study area. Crickmay (1952) the dominant folds and have northeast-trending axes. and Hurst (1973) described rocks in this area as part Northwest of the Hayesville fault, the F2 fold axial surfaces of their general descriptions of the Blue Ridge crys­ are upright to steeply inclined; southeast of the fault, the talline rocks. Hartley (1973) reported on the ul­ F2 axial surfaces range from recumbent to steeply inclined. tramafic rocks present in the north part of the area, A set of conjugate folds {F3) whose axes trend north­ and Hatcher ( 1971) described the geology of Rabun northeast and west-northwest refolds the F2 folds. The F 3 and Habersham Counties, Ga. Hatcher also reported fold axial surfaces are upright to steeply inclined. on the various aspects of the tectonic history of Analysis of conjugate folds (F3) shows that the direction of maximum compression during F3 folding was northeast­ northern Georgia and surrounding areas (1974, 1976, southwest, almost parallel to the regional (S1) foliation 1978a, c). The general geology of the area is shown on trend. This direction is nearly normal to the maximum the Geologic Map of Georgia (Georgia Geological compression direction during F2 folding. The F3 maximum Survey, 1976). Dupuis (1975) and Wooten (1980) compression direction probably is due to a relaxation of mapped adjoining areas to the west and north, re­ compressive stress or due to elastic rebound after F2 spectively, of the report area, and Shellebarger ( 1980) folding. and Gillon (1982) mapped parts of the study area as part of the U.S. Geological Survey Greenville 2-de­ gree quadrangle mapping project. INTRODUCTION GENERAL GEOLOGY This report describes and interprets the general structure and deformation chronology of Three lithotectonic units underlie the northwest polydeformed metamorphic rocks underlying the part of the Greenville 2-degree quadrangle in north-

Abstract 1 east Georgia. From northwest to southeast, these units are the Great Smoky thrust sheet, the Hayes­ ville thrust sheet, and the Helen-Coweeta terrane. The Hayesville sheet was transported westward over the Great Smoky sheet along the Hayesville fault, a major Appalachian tectonic feature (Williams, 1978). Rocks of the Great Smoky sheet underlie the Hayes­ ville fault and are exposed in several windows through the Hayesville sheet. The Helen Group (in­ formal usage of Gillon, 1982) and the Coweeta Group of Hatcher ( 1979) form a long narrow lithotectonic unit herein called the Helen-Coweeta terrane that divides diagonally from southwest to northeast the Hayesville sheet in northeast Georgia and adjacent North Carolina.

Great Smoky thrust sheet

Rocks of the Great Smoky thrust sheet consist chiefly of interbedded feldspathic and argillaceous 0 10 20 30 KILOMETERS· I I I I metasandstone, metaconglomerate, muscovite schist, and calc-silicate granofels that together form various A groups and formations of the Ocoee Supergroup (Higgins and Zietz, 197 5) of Late Proterozoic age. Figure lA. location of report area and generalized tecton­ ic map of northeast Georgia. B, Blairsville; C, Canton; D, Although the Great Smoky sheet rocks have been Dahlonega; H, Helen; GSTS, Great Smoky thrust sheet; metamorphosed and polydeformed, original bedding, HTS, Hayesville thrust sheet; H-C, Helen-Cowetta terrane; even at sillimanite grade, is preserved locally. Middle DF, Dahlonega fault; SFF, Shope Fork fault; HF, Hayesville Proterozoic plutonic rocks and variably layered fault; A-HF, Allatoona-Hayesville fault; BZ, Brevard zone. paragneisses form the basement rocks in parts of the Great Smoky thrust sheet, but they are not exposed in the report area. Hayesville fault, some diamictite is exposed. Al­ though the diamictite is not widespread, its presence suggests that it probably formed as the Hayesville Hayesville thrust sheet sheet advanced northwesterly. Some Grenville (Mid­ dle Proterozoic) basement rocks are exposed east of the report area (in the eastern part of the Hayesville Two formations make up the Hayesville thrust thrust sheet), but they have not been observed in the sheet in the report area; (1) the Tallulah Falls Forma­ study area. tion (Hatcher, 1971; Bell and Luce, 1983), which oc­ Rocks of the Hayesville sheet, particularly units cupies most of the eastern part, and (2) the Richard of biotite gneiss, mica schist, and metasandstone, are Russell Formation (informal usage of Gillon, 1982), variably layered. Compositional layering, which re­ which occupies the western part. The Richard Russell sults from metamorphic differentiation and transpo­ Formation probably is equivalent to the Tallulah sition of bedding into the regional foliation, is wide­ Falls Formation of probable late Precambrian age spread in the report area. Hatcher (1976) described (Hatcher, 1971; Bell and Luce, 1983). similar transposed bedding farther east in the Hayes­ The Richard Russell Formation consists pri­ ville sheet. The transposition and metamorphic dif­ marily of biotite gneiss and lesser amounts of mica ferentiation probably destroyed most of the primary schist, fine-grained feldspar gneiss, metasandstone, sedimentary features that may have existed in the quartzite, hornblende gneiss, amphibolite, and some rocks. Layers in most of the rocks range from 2 to 15 calc-silicate layers. Granitic and granodiorite gneisses em in thickness; rarely are rock layers greater than 1 are interlayered with these rocks. Numerous discon­ m thick. As a result of interlayering, metamorphic tinuous pegmatite veins and pods of various sizes are differentiation, and transposition of rock units, con­ dispersed widely throughout the Hayesville sheet, tacts between mapped units in the Hayesville thrust and migmatitic biotite gneiss and granitic gneiss are sheet are commonly gradational (Nelson, 1982, abundant. In the Hayesville thrust sheet near the 1983a and b; Nelson and Koeppen, 1984).

2 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. EXPLANATION Shooting Creek IGsrsJ window GSTS, Great Smoky thrust sheet: Undivided metasandstone, schist, and metasiltstone

I HTS I HTS, Hayesville thrust sheet: Undi­ vided metasandstone, biotite gneiss and schist, amphibolite, hornblende gneiss, granitic gneiss, mafic and ultramafic rocks, and some Grenville age basement rocks

H-C, Helen-Coweeta terrane: Undi­ vided metasandstone, metasiltstone, massive biotite gneiss and schist, aluminous and graphitic schist, granitic gneiss, quartzite, amphibo­ lite, and some ultramafic rocks HTS Thrust fault

Kyanite ~ HTS Isograd Approximate position adopted frorri Hatcher (1971), Shellebarger (1980), and Gillon (1982)

0 10 15 KILOMETERS

DAHLONEGA A

B

Figure 1 8. Generalized lithotectonic map of the northwest part of the Greenville 2-degree quadrangle, Georgia.

Mafic and ultramafic rocks certain. The ultramafic rocks have chemical affinities with mantle rocks (Hartley, 1973, p. 59) and, as such, A wide variety of ultramafic and mafic rocks is may represent fragments of oceanic crust caught up present in the Hayesville sheet, some as small discon­ in the Hayesville sheet during or before westward tinuous pods, some as large mappable units (Hadley emplacement of the Hayesville sheet. Some ul­ and Nelson, 1971; Nelson, 1982, 1983a and b). These tramafic rocks are believed to represent small sepa­ rocks are chiefly serpentinite, dunite, pyroxenite, rate thrust slices of oceanic crust underlying the gabbro, and amphibolite (Hartley, 1973). Locally, Hayesville sheet. some of these rocks are magnetite rich. The relation Ultramafic and mafic rocks that surround the of the ultramafic rocks to the Hayesville sheet is un- Brasstown Bald window (in the north-central portion

General Geology 3 of the study area) are believed to form a separate and the Helen-Coweeta terrane has been deformed thrust slice of oceanic crust between the Hayesville by faulting. Nevertheless, recent investigations by K. and Great Smoky thrust sheets (fig. lB). Some ul­ I. McConnell and J. 0. Costello (1981, oral com­ tramafic and mafic rock bodies high in the thrust mun.) indicate that some units in the terrane do cor­ sheet may represent diapirs or small intrusives. Other relate with units of the New Georgia Group to the ultramafic and mafic rocks are exposed along strike southwest (Abrams and McConnell, 1981 ). northeast of the report area, and some ultramafic bodies are probably present locally but concealed While some rock assemblages of the Helen­ within the Hayesville sheet elsewhere in the study Coweeta terrane appear to correlate with rocks of the area. Canton area, part of the terrane resembles Ocoee rocks of the Great Smoky thrust sheet. Incomplete studies by me suggest that some Ocoee rocks may be Helen-Coweeta Terrane present in the terrane, either as a window or as a tectonically emplaced unit. Ocoee rocks are exposed Rocks of the Helen Group (informal usage of in the Brasstown Bald and Shooting Creek windows Gillon, 1982) and the overlying Coweeta Group to the northwest in the Hayesville sheet; the Brass­ (Hatcher, 1979) form the Helen-Coweeta terrane (fig. town Bald window is about 12 km northwest of the 1B) that extends northeastward from Dahlonega, Ga. Helen-Coweeta terrane. Because the Helen-Coweeta This terrane varies in width and divides the Hayes­ terrane has been deformed by faulting, some Ocoee ville thrust sheet diagonally into almost equal areas rock units may have been tectonically emplaced. This (fig. lB). The Helen Group contains numerous rock emplacement is plausible because part of the Great types, including metagraywacke, quartzite, graphite­ Smoky thrust sheet is exposed along the trend of the bearing garnet-muscovite-biotite schist, metasilt­ Helen-Coweeta terrane just west and southwest of stone, phyllite, and impure feldspathic metasand­ Dahlonega (fig. lA). Rocks of the Great Smoky sheet stone that is locally conglomeratic and interlayered are in this location because of a southerly bend of the with thin muscovite schist beds. Thin to thick layers Hayesville fault (Williams, 1978) in the adjoining of amphibolite also are present, as are some granitic Rome 2-degree quadrangle (fig. 1A). Current field gneiss and ultramafic bodies. Rocks of the Helen­ studies should help resolve this problem. Coweeta terrane range from garnet(?)-staurolite to kyanite grade; locally they are retrograded. The Coweeta Group includes feldspar quartz­ biotite-epidote gneiss, metasandstone, granofels, Metamorphism quartzite, aluminous sch~~t:L __gametiferous biotite schist, and minor amphibolite. Granitic gneiss and -some ultra mafic rocks also are present. Rocks of the A Paleozoic Barrovian-type prograde regional Coweeta Group overlie the Helen Group and range metamorphism affected the southern Blue Ridge from staurolite-kyanite to sillimanite grade; locally rocks (Hadley and Goldsmith, 1963; Carpenter 1970; they are retrograded. Butler 1972; Dallmeyer 1975). This metamorphic Although some rock types in both the Coweeta event probably occurred during the Taconic orogeny and Helen Groups are similar, their overall lithology about 450 m.y. to 480 m.y. ago (Butler, 1972; Dall­ differs significantly. Rocks in the Coweeta- Group meyer 197 5). Much of the report area is within a commonly contain numerous thin layers of calc-sili­ large, elongate, northeast-trending sillimanite-grade cate granofels, which is rarely seen in rocks of the metamorphic zone (fig. lB). However, lower grade Helen Group. The Helen Group contains relatively rocks ( staurolite-kyanite) border the higher grade sil­ thick units of amphibolite, graphite schist, and limanite zone in the northwest part of the area. Low­ metasiltstone units, all of which are much less abun­ er grade rocks also are present in the southeast part of dant or are absent in the Coweeta Group. the area, especially near the Brevard zone (fig. 1B). Correlations of rock units in the Helen-Coweeta The southern part of the Helen-Coweeta terrane, terrane with mapped units along strike in the vicinity which ranges from garnet(?)-staurolite to kyanite of Canton, Ga. (McConnell and Costello, 1980), are grade, is bordered on both sides by sillimanite-grade somewhat tenuous. The Canton area is about 45 km rocks of the Hayesville thrust sheet. southwest of the study area; the area between Canton Within the sillimanite zone, the effects of meta­ and the Helen-Coweeta terrane is unmapped. No morphic differentiation and anatectic melting are one-to-one correlation of mapped units between the particularly noticeable. Biotite gneiss, mica schist, Helen-Coweeta terrane and the Canton area exists, and metasandstone units of the Hayesville sheet have

4 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. been variably migmatized and have been differentiat­ STRUCTURAL GEOLOGY ed to form gneisses of banded leucosomes and mela­ nosomes. Quartz, which is highly mobile, also has been segregated into variably sized veins and pods Faults, joints, and lineament trends that are widespread. Veins and irregular bodies of quartzofeldspathic segregations and anatectic melt Numerous thrust faults characterize the south­ materials and irregular granite bodies also are com­ em Appalachian Mountains (Rodgers, 1953; King, mon. The migmatized and differentiated rocks of the 1964; Hadley and Goldsmith, 1963; Hadley and Nel­ Hayesville sheet contrast strongly with rocks of the son, 1971; Hatcher, 1971, 1972). The Hayesville Great Smoky sheet, which are only slightly migmatit­ thrust sheet was pushed westward over the Great ic and do not have an abundance of feldspathic dif­ Smoky thrust sheet along the Hayesville fault. I be­ ferentiates, even though they are at the same meta­ lieve this fault is premetamorphic to early morphic grade as the Hayesville sheet rocks. Rocks in synmetamorphic. The fault does not offset the silli­ the study area at kyanite grade are essentially manite isograd (fig. 1), and the foliation (S1) attitudes nonmigmatitic; they do not have an abundance of in rocks on either side of the fault do not appear to be feldspathic differentiates, and the effects of metamor­ deflected in the Greenville quadrangle or in the area phic differentiation are rare. to the north (Wooten, 1980). Sillimanite is distributed widely in most pelitic Shellebarger ( 1980) described the Hayesville rocks within the sillimanite zone and is commonly fault and summarized evidence that supports its oc­ present in rocks with a moderate quartz content and currence in the northwestern part of the Greenville a moderate to low muscovite content. Sillimanite lies quadrangle. He indicated that the fault juxtaposes in and most probably grew in the regional foliation rocks of different lithologies and structural style. planes (S1) during the high temperature peak of re­ Southeast of this fault, the Hayesville thrust sheet gional metamorphism. The foliation formed during contains most of the known ultramafic rocks and in­ the 450- to 480-m.y. regional metamorphic event but trusive plutons and volcanic rocks. In addition, the before the high temperature peak. The foliation metasandstones are more garnetiferous, and the planes were later deformed during regional folding schists more mafic, than similar rock types occurring (F2) that probably occurred slightly after the high in the Great Smoky thrust sheet. In places along the temperature peak. Hayesville fault, competent rock types of the Hayes­ Ten1peratures probably remained elevated in ville sheet have been changed to blastomylonite and the study area through an episode of deformation mylonite gneiss. Southeast of the Hayesville fault, the rocks are recumbently folded, whereas the rocks that occurred after the regional F2 folding. The appar­ ent growth of biotite along planes parallel to the third northwest of the fault are folded into upright folds or fold generation (F3) axial surfaces supports this hy­ are only slightly overturned. pothesis. Therefore, I believe that temperatures re­ Many smaller faults also are present in the mained elevated in the study area at least until after study area; they include both thrust and normal the F 3 folding event. faults, as well as ductile shear zones that are present In some places, prograde metamorphic miner­ in individual outcrops. These small faults and shear als have been retrogressively altered. Some, but not zones are not shown in figure 1 of this report because all, of the altered areas appear to be related to shear the paucity of exposures precludes mapping them. zones. The alteration is not intense, nor is it wide­ Both brittle and ductile faulting have deformed spread. Sillimanite alters to sericite or sericitic clus­ the southern part of the Helen-Coweeta terrane. The ters, and garnet and biotite alter to chlorite. Some southeast side of the terrane near Dahlonega (fig. 1) is plagioclase is saussuritized. Most of the ultramafic bounded by a fault, and the Geologic Map of Georgia rocks are extensively chloritized, are serpentinized, (Georgia Geological Survey, 1976) shows a discontin­ and are altered locally to talc schists. The age of ret­ uous fault and a shear zone along the terrane's south­ rogression is uncertain, and several estimates have east side. This fault and the shear zone have been been proposed for the time of retrograde alteration in referred to as the Dahlonega shear zone (Crickmay, the southern Appalachian Mountains. Hatcher 1952, p. 48, and Fairly, 1973, p. 693). The northwest (1972) and Butler (1973) suggested that the alteration side of the terrane is bounded by the Shope Fork was due to a Permian thermal event, probably related fault, which was mapped by Hatcher (1976), near the to late Paleozoic thrusting. Shellebarger ( 1980) be­ Georgia-North Carolina boundary. The Shope Fork lieves that the alteration resulted from uplift and fault is folded by what appears to be F2 folds, and cooling after the last deformation and thus does not Hatcher (1976) suggests that the fault is pre- or necessarily imply a separate thermal event. synmetamorphic. However, a discordance of folia-

General Geology 5 tion attitudes between the Helen-Coweeta terrane ville sheet. The principal lineament trends in the In­ and the Hayesville sheet indicates that later move­ ner Piedmont, southeast of the Brevard zone, do not ment along the Shope Fork fault is post-S 1• Recent have strikes parallel to lineaments in the Hayesville geologic mapping shows that the Shope Fork fault, sheet. which is probably a fault zone, locally extends south­ The contrasting lineament patterns among ad­ westward toward Dahlonega (Gillon, 1982); the jacent major lithotectonic units suggest that each unit Shope Fork fault appears to join the Hayesville fault was subjected to a different history of fracturing west of the Greenville quadrangle. before emplacement along thrust faults. Alternative­ Reconnaissance mapping in the Helen-Coweeta ly, the physical makeup of each unit may have caused terrane shows that shear zones are present along sev­ the units to yield differently to stress. eral prominent northeast-trending topographic linea­ The gently curving west-southwest-trending ments. The shear zone boundaries appear to be gra­ Warwoman lineament (Hatcher, 1974) forms a prom­ dational, and rocks from these zones include button inent Landsat feature (fig. 2). Although bedrock is schist, mylonite, blastomylonite, and mylonite concealed by surficial materials in valleys that form gneiss. These rocks exhibit deformed fabrics that most of the lineament, a siliceous flinty crush rock is range from microscopic to mesoscopic in size; the exposed along part of it west of Clayton, Ga. Hatcher rocks display a prominent mylonitic foliation. The (1974) reports that the lineament is a late fea­ sheared rocks in the Helen-Coweeta terrane are prob­ ture-probably post-Paleozoic-and indicates that ably the northeast continuation of sheared rocks de­ lithologic contacts cross the lineament without being scribed by Bowen (1961) in Dawson County, just offset. west and southwest of Dahlonega. On the Landsat image (fig. 2), the Warwoman Jointing is present throughout the study area, lineament appears to cross the Dahlonega shear zone, but joint patterns have not been studied in detail. which bounds the southeast side of the Helen­ Most joints are steeply inclined and do not seem to Coweeta terrane. A similarly trending, prominent lin­ have well-defined preferred strike orientations. Less eament almost on strike with that of the Warwoman commonly, joints are shallow dipping or are horizon­ lies in the Hayesville sheet, west of the Helen­ tal. Some thin pegmatite and quartz veins occupy Coweeta terrane. Because the lineament's trace is in­ early joint sets. distinct near the Shope Fork fault, we cannot be cer­ Figure 2 is a Landsat image (Georgia Geologic tain that the Warwoman is present west of the fault. and Water Resources Division, 1977) of the north­ If the Warwoman is present to the west, it appears to west part of the Greenville quadrangle; outlines of be displaced about 1.6 km to the right, along the the major lithotectonic units are superimposed on Shope Fork fault. A few kilometers northeast of this the image. Distinct image patterns and lineament locality, reconnaissance mapping shows a small un­ trends show a close correlation with the major metamorphosed diabase dike of probable Triassic­ lithotectonic units. The lineaments follow topograph­ Jurassic age that also appears to be offset about 1.6 ic and geologic features, such as aligned stream val­ km to the right, along the Shope Fork fault. The leys or some distinct lithologic units, and many linea­ apparent similar displacements of the dike and the ments are believed to reflect prominent fracture Warwoman lineament suggest post-Triassic-Jurassic zones. movement along the Shope Fork fault. Several sets of lineament patterns, which do not follow the regional trends of mapped lithologic units, are present in the Hayesville sheet but are not evi­ Folding and related deformation dent in the adjoining lithotectonic units. A north­ trending set appears to end along the Hayesville fault, especially in the Brasstown Bald window area. The In the southern Blue Ridge, the major folds same set ends along the Shope Fork fault to the south trend northeast, and their axes plunge gently north­ and does not appear in the Helen-Coweeta terrane. east or southwest. These folds vary from upright to The same set continues, however, in the Hayesville inclined to recumbent, and, although some of them sheet, south of the Helen-Coweeta terrane. A west­ verge southeast, most verge northwest. Evidence for southwest-trending set also is present in both the polyphase folding is widespread, and the present out­ eastern and western parts of the Hayesville sheet but crop patterns of many large structural features have is not present in the Helen-Coweeta terrane. resulted from superposed folding (Dallmeyer and A faint east-southeast lineament trend is pres­ others, 1978; Hatcher, 1974, 1978b; Wooten, 1980; ent in the Helen-Coweeta terrane and in part of the Shellebarger, 1980). The superposed later fold phases Great Smoky sheet but is not present in the Hayes- have formed large-scale interference patterns of

6 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. EXPLANATION GSTS Great Smoky thrust sheet HTS Hayesville thrust sheet H-C Helen-Coweeta terrane HF Hayesville fault SFF Shope Fork fault BZ Brevard zone BBW Brasstown Bald window WL Warwoman lineament d Approximate position of diabase dike DF Dahlonega shear or fault sew Shooting Creek window

0 5 10 15 20 KILOMETERS

Base from Georgia Department of Natural Resources, Blue Ridge Mountains sheet. 1977.

Figure 2. Landsat image of the northwest part of the Greenville 2-degree quadrangle and approximate boundaries of the major lithotectonic units of the area.

Structural Geology 7 domes and basins, such as the Tallulah Falls dome (Hatcher, 1971) and other similar structures within and adjacent to the study area (Shellebarger, 1980). Within the report area, mesoscopic structures at some exposures show that the rocks have been de­ formed by folding at least four times (fig. 3). Hatcher (1976 and oral commun., 1979) reports six phases of folding in similar rocks exposed farther east in the Hayesville sheet. Fold interference patterns are com­ monly seen at rock exposures; most of these patterns are similar to types 2 and 3 of Ramsay (1967) (fig. 4). The first generation folds (Ft) (fig. 5) are represented as intrafolial, rootless, recumbent isoclinal folds in transposed layers. Second generation folds (F2), which form the major folds, are steeply inclined to recumbent isoclinal folds, with hinges generally plunging gently northeast or southwest (fig. 6). The limbs of F2 folds have been folded locally into two sets of tight to open, upright to overturned flexural folds or crenulations. The axes of one set trends Figure 3. Three fold phases at an exposure in Brasstown north-northeast;· and the axes of the other set trends Creek 2.2 km east-southeast of U.S. Route 76 and south west to northwest. Whether these folds represent sep­ of Young Harris. F1 is present as small rootless isoclines; F2 arate fold phases F 3 and F 4 or whether they form part is overturned and is tight to isoclinal; F3 is an upright fold of a conjugate fold pair (Johnson, 1956) is uncertain. with an almost vertical axial plane (AP). Pencil for scale. Evidence presented below (pg. 18) favors the latter interpretation. Hereafter, the two sets of folds will be is axial planar to the first generation folds (Ft) (fig. 5); referred to collectively as F3 folds and individually as subsequent phases of"deformation refold the regional F3 (northeasterly) and F3 (northwesterly). Generally, foliation into later fold generations (F2 and F3). The the axial surfaces of the F 2 folds are less steep than second generation folds appear to have a poorly de­ those of the later folds, but some F2 folds in the veloped axial plane schistosity (S2), but the later F 3 northwest part of the report area have steeply dipping fold generation locally displays a strong axial plane axial surfaces. Statistical analyses of folds suggest crenulation cleavage (fig. 7). In this report, these sur­ that the flanks of some F 3 folds were gently folded by faces (S~, S2, S3) correspond to the fold phases (F~, F2, a later folding event or events, but axial plane cleav­ F3). Foliated clasts are present in some host metasedi­ ages have not been identified with these later folds or mentary rocks in the Hayesville sheet, and their folia­ flexures. Post-F3 folding appears to be around an tion is across the St foliation in the host gneiss. I east-west axis and a less well defined north-to-north­ interpret this foliation as showing that the clasts were east axis. A late episode of folding along northeast­ probably deformed prior to their incorporation into trending axes in an area east of the study area (Hatch­ the host rocks before the regional foliation S1 formed er, 1978b) may correspond to post-F3 folding along a and, as such, may represent a pre-St deformation northeast-trending axis. Flowage folds characterize fabric. the F1 and F2 folds, and flexure folds are the domi­ Crenulation cleavage (slip cleavage), although nant fold type for the F3 folds in the report area. common, is not uniformly well developed except Bedding (So), metamorphic layering, regional where it locally masks the earlier regional foliation foliation (St), foliation axial planar to F2 folds (S2), (fig. 7). Crenulation cleavage is the most recent pla­ and crenulation cleavage (S3) form the principal pla­ nar structure associated with folding. This cleavage is nar structures in the report area. Bedding can be present in many pelitic units, and, where observed, it identified in most rock units of the Great Smoky is axial planar to either the northwest or northeast F 3 sheet northwest of the Hayesville fault. Farther to the folds (fig. 8). Where the cleavage is well developed, F3 southeast, however, most of the bedding in rock units folds deform the layering and the regional foliation. within the study area appears to be transposed into Two principal crenulation cleavage sets are present. the regional foliation. One set is associated with the northeast-trending F3 Except for a diabase dike and some small peg­ folds; the other set is related to the northwest-trend­ matite and quartz veins, all rocks in the study area ing F3 folds. The northeast-striking set is much more have a pervasive planar foliation (St). This foliation common and widespread than is the northwest set.

8 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. Figure 4. Type 3 fold interference pattern (Ramsay, 1967) Figure 5. Outcrop showing hinge of an F1 isoclinal fold in at an outcrop along the Richard Russell Highway about siliceous metasandstone and schist in the Hayesville thrust sheet and also showing trend of foliation (S1). View is 0.3 km west of Hogpen Gap. F2 folds are refolded by F3 folds. Hammer for scale. northwestward along the shore of Lake Sidney Lanier just south of Highway 369 at Browns Bridge. Pencil for scale.

Locally, small crenulations associated with the two cleavage sets form a conjugate fold pair (fig. 9). These conjugate folds are rare, but they and their related crenulation cleavages suggest that the north­ west-striking folds and the northeast-striking folds

probably formed together as a conjugate F3 fold pair. As such, the F 3 folds probably represent one of the later sets of compressive structures to form during the waning stages of regional metamorphism and de­ formation that affected the southern Appalachians. Throughout most of the study area and else­ where in the Hayesville thrust sheet, satisfactorily defining the chronology and the details of the macro­ scopic folding is difficult. The principal reasons for this difficulty are that ( 1) the original bedding (So) is transposed into the regional foliation (S1); (2) no easi­ ly distinguished marker beds exist; (3) a thick forest cover conceals much of the bedrock; and ( 4) original primary sedimentary features, such as graded bed­ ding, are not well preserved. In the Hayesville sheet, the compositional layering is almost everywhere par­ allel to the pervasive foliation (S1), and this foliation is axial planar to F1 folds (fig. 5). On figure 5, folia­ tion form lines (constructed from foliation (SI) atti­ tudes) were drawn to depict the _general form of the Figure 6. An F2 fold (axial plane (AP) dipping gently south­ post-F1 folds. east) that is overturned to the northwest. View is north­ Figure 10 shows the foliation (SI) form line eastward near the Appalachian Trail in western Union County at an exposure 0.25 km north of Puncheon Gap. trends for the report area. The two major regional Hammer for scale. structures are outlined; they are ( 1) the west part of

Structural Geology 9 Figure 8. Exposure showing a rootless F2 fold and an F3 fold with an axial planar crenulation cleavage S3. View is northwestward 0.35 km west-southwest of Chimney Top about 5 km southeast of Young Harris. Pencil for scale.

Figure 7. Exposure showing So, S1, and 53 foliation. The 53 foliation is the dominant planar feature and almost masks the earlier foliations. A faint 54(?) crenulation cleavage is also present. View is northwestward, just southeast of the crest of Brasstown Bald. Hammer for scale. the Tallulah Falls dome (Hatcher, 1971), which is east of the Helen-Coweeta terrane, and (2) the Chat­ tahoochee basin and synform, which occupies much of the western part of the Hayesville sheet. The Chat­ tahoochee basin is a broad, shallow-dipping, complex structure with a central, shallow-dipping basin that merges to the northeast into a synform with a north­ east-trending axis. Numerous small folds with several distinct trends also are present. Exposures within the Chattahoochee basin and synform commonly show fold interference patterns, and in places as many as four and possibly five episodes of folding are record­ ed in the rocks. In and near the Chattahoochee basin, Figure 9. Gently inclined saprolite exposure showing a one fold set trends west-northwest, and other sets small conjugate F3 fold pair. Exposure is located in a ditch trend north-northeast. next to Smyrna Road 0.15 km north of Ebenezer Church, Folds in the Helen-Coweeta terrane east ofthe in the northwest part of the Greenville quadrangle. Felt Chattahoochee synform trend northeast. pen for scale. The previously mentioned limitations (see p. 9) to fold analysis on a macroscopic scale required equal area projections to make generalized interpre­ tations of the fold chronology. Insofar as possible, the

1 0 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. 0 5 10 15 20 KILOMETERS

Figure 10. Generalized structure of the report area shown by foliation 51 form lines. Regional Appalachian fold structures trend northeast, and later folds are superposed upon them. B, Blairsville; D, Dahlonega; H, Helen; HF, Hayesville fault; SFF, Shope Fork fault; DF, Dahlonega fault; BZ, Brevard zone; GSTS, Great Smoky thrust sheet; HTS, Hayesville thrust sheet; H-C, Helen Coweeta terrane; BBW, Brasstown Bald window; SCW, Shooting Creek window; TFD, Tallulah Falls dome.

Structural Geology 11 study area was divided into structurally homogene­ trend northeast. Figure 12A is an S, pole diagram for ous areas (fig. 11), and the linear and planar fabric area I and shows projections of F2 fold axes. The elements for each area were statistically analyzed by concentrations of poles to S, suggest a weak S, girdle using an equal area net. In the fold analyses that with a ~S, of 060/16 °. The single s, pole maxima follow, the S, attitudes are represented by a five-digit concentration is interpreted to show that significant numeral. The bearing of the strike of fabric elements post-F 2 deformation did not noticeably affect the is given by the first three digits, and the dip or plunge rocks in area I. Together with the observed F2 folds, value by the next two digits. The symbol "nS" refers the concentration suggests that the S, surface in this to a great circle of best fit through poles of measured area was deformed by F 2 folds that are overturned to S surface segments. The normal to nS is represented the southeast. The plotted fold axes are close to the by ~S, which is the statistically defined axes of fold­ statistical axial plane 086/33 o; this proximity sug­ ing (Turner and Weiss, 1963). gests that F2 folds are overturned to the southeast.

Area II Fold Analyses Areal Area II (see fig. 11) lies just north of area I in the Hayesville thrust sheet. The wide dispersal of S, This area (see fig. 11) occupies the southwest poles along a broad girdle (fig. 12B) suggests that area part of the Hayesville sheet northwest of the Helen­ II probably has undergone considerably more post-F2 Coweeta terrane. Here the S, foliation attitudes gen­ deformation than has adjacent area I and that a sin­ erally strike east-west and have moderate north dips gle ~S, probably does not characterize this area. Be­ that reflect the structural attitudes along the southern sides the F2 regional folds whose axes trend north­ boundary area of the Chattahoochee basin (fig. 10). I east, there are also FJ folds with northwest- and observed few F2 folds; they are overturned to the northeast-trending axes. I interpret an S, pole dia­ southeast and are reclined to recumbent. Their axes gram for area II (fig. 12B) as showing a trimodal distribution for S, pole concentrations. This distribu­ tion resulted from a spread of a maxima for north­ west-dipping surfaces into two submaxima, possibly 313110° ~S, AREA V during FJ (northwest) folding. The is close to the plotted mean attitude for axes of 17 northwest-trending FJ folds (fig. 12B). The projec­ tions of the mean attitude for axes of 15 southwest­ and northeast-plunging FJ fold axes have different AREA IV orientations than does the ~S, 07211 oo. However, the ~ 217/05 o ~S, strike is close to the average strike for

~ the axes of northeast-trending F2 and F3 folds, except \AREA Ill'\ it plunges gently southwest instead of northeast; note that some measured FJ folds plunge southwest and \ that others plunge northeast. The ~S, po~itions for AREA II the southeast- and northwest-dipping S, surfaces sug­ gest that the segment of the Chattahoochee synform in area II is folded into upright folds along northeast­ trending axes. The general northeast-southwest strike East part ofthe of S, contrasts strongly with the east-west S, trend in Hayesville thrust sheet area 1.

Area Ill 0 5 KILOMETERS In area III (see fig. 11 ), the regional schistosity L______j (S,) strikes northeast and dips primarily to the north­ west, but some other attitudes are also present. Be­ sides the generally northeast-striking major F2 fold axes, both northeast- and northwest-trending FJ folds Figure 11. Structural areas in northwest Greenville are present. In places throughout the report area, F2 quadrangle that were used for statistical analyses of fold events. and the northeast-trending F3 folds have almost par-

12 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. AP 086/33°N {35 1 060/16°

/35 1 072/1 oo 110 pts 291 pts 23% 6% 18% 4% 13% 3% 6% 2% 1% 1%

A. Area I B. Area II

EXPLANATION EXPLANATION + F2 fold ~::,. Mean altitude for 17 northwest- and southeast-plunging F3 folds + Mean altitude for 15 southwest- and northeast-plunging F3 folds

/35 1 312/30°

91 pts 133 pts 13% 5% 10% 4% 6% 3% 3% 1% 1% /35 1 239/14° •

C. Area Ill D. Area IV

EXPLANATION EXPLANATION + Mean altitude for 15 southwest- and + Mean altitude for 14 northeast- and northeast-plunging FrF3 folds southwest-plunging F2-F3 folds ~::,. Mean altitude for 17 northwest­ ~::,. Mean altitude for 12 northwest- and plunging F3 folds southeast-plunging F3 folds

f3S 1 062/1 oo ++ -i 7TS, 66 pts + 83 pts 9% + 8% 6% 7% 3% 5% 1% 1%

+

E. Area V F. Northwest subdivision

EXPLANATION EXPLANATION Altitude for F -F folds + 2 3 + F3 fold areas

Figure 12. Contoured equal area projections of poles to S, and F2 and F3 fold attitudes for areas shown in figure 11.

Structural Geology 13 allel axes, and, depending on the rock exposure, one dense point maxima, forms a bimodal S, pole distri­ cannot always differentiate an F2 from an F3 fold. bution along the girdle. Figure 12£ also shows the Figure 12C is an S, pole diagram that also gives the projections of axes of northeast undivided F2 and F3 mean attitudes of undifferentiated F2 and F3 folds in folds that plunge either to the northeast or southwest. area III. The S, pole maxima concentrations are The F2 and FJ fold axes have very similar trends. I somewhat elongate and define a 1tS, girdle with a ~S, interpret the bimodal distribution as reflecting F2 of 239/14 o. The pole concentrations are locally dis­ folding. The irregular scatter from the 1tS 1 girdle may persed away from the girdle, especially near the max­ be a result of FJ (northwest) folding. However, I did imum pole density. I believe that the maximum den­ not observe FJ northwest-trending folds within area sity for S, poles approximates S, attitudes prior to F3 v. strain, but the dispersal of the pole concentrations at several points along the girdle may reflect post-F2 The northwest subdivision deformation that is .related to the F3 strain. The ef­ fects of post-F2 strain in area III, however, do not The northwest subdivision (see fig. 11) is north seem to be as widespread as in area II. Figure 12C and west of the Hayesville fault and southeast of the shows that, although some surfaces dip southeast­ Murphy syncline (fig. 1A). Rocks of the Great Smoky ward, most of the surfaces in area III dip to the thrust sheet underlie the subdivision. Structurally, the rocks of this area are overturned. Most of the northwest. This northwest dip suggests that, in this rock units and the included foliations (S,) dip varia­ part of the Chattahoochee synform, the northeast­ bly southeast, but some rock units dip northwest. trending folds are overturned to the southeast. Fold interference patterns (Shellebarger, 1980) show the rocks have been multiply folded. Figure 12F, Area IV which gives the orientations for S, in the northwest Area IV (see fig. 11) contains a wide variety of area, shows a 1tS, girdle with a closely spaced bimodal S, orientations. Figure 12D contains plots of poles to maxima distribution and a ~S, of 062/10 o. The main S, that form a 1tS, girdle with a ~S, of 312/20°. The concentration of points containing the two maxima poles to S, are widespread in the diagram, but a bi­ probably represents the least deformed S, surfaces on modal distribution is indicated by two maxima. Also the southeast flank of the Murphy syncline. The shown in the diagram are the mean trends of fold spread of the maxima, as well as the distribution of axes and their plunges for the undivided F2 and points away from the girdle, probably represents late northeast-trending (FJ) folds, as well as the north­ stage or post-F2 folding. The plots for northeast­ west-trending (F3) folds. plunging F2 folds are widely dispersed, also possibly The bimodal spread of the 1tS, girdle appears to due to post-F2 deformation. be the result of post-F2 deformation. Because the ~S, Shellebarger (1980) reported that rocks in the and the mean fold projections for the northwest­ study area northwest of the Hayesville fault have striking FJ folds are similar, I interpret the post-F2 been folded several times. Wooten (1980) also indi­ strain as resulting from deformation associated with cated that rocks northwest of the Hayesville fault just FJ (northwest-trending) folds. north of the report area are multiply deformed. Both Wooten and Shellebarger report that folds equivalent AreaV to the F2 folds of this report have steeply inclined axial surfaces and are overturned to the northwest. The regional schistosity in area V (see fig. 11) almost uniformly strikes northeast and dips primari­ ly to the northwest, but in some areas it dips to the The Helen-Coweeta terrane southeast. The rocks in this area have been folded The Helen-Coweeta terrane area (see fig. 11) is several times. I observed some type 2 and 3 interfer­ underlain by rocks whose foliation (S,) trends north­ ence patterns (Ramsay, 1967) in the field within area east, parallel to the strike of the terrane. After the V. The F, folds are small rootless isoclinal folds in formation of foliation during F,, the rocks were the foliation; F2 folds plunge to the southwest. These folded around northeast-trending axes, and the folia­ F2 folds, which appear to form part of the major folds tion now dips either northwest or southeast. Within with northeast-trending axes, are reclined and over­ the terrane, differentiating between F 2 and F J folds is turned to the southeast. A few asymmetric northeast­ difficult. Both F2 and FJ folds have axes that strike trending (F 3) folds also were observed. northeast and plunge gently northeast, and some F2 The S, pole concentrations in area V (fig. 12E) folds also plunge south-southwest. define a 1tS 1 girdle with a ~S, of 012/05°. One high Figure 13A illustrates the S, orientations within density pole maxima, which plots together with a less the Helen-Coweeta terrane. Plots of S, pole concen-

14 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. s, 031/10° •

125 pts 70 pts 6% 4% 8% 3% 6% 1% 4%

A. B. 8 1 plots in Helen-Coweeta terrane F2 and F3 fold axes in Helen-Coweeta terrane

327 pts 137 pts 8% 7% 12% 5% 9% 3% 7% 2% 4% 1% 1%

c. D. Plots of s, altitudes in east part of Hayesville sheet S, northeast-trending folds

1rS3_...,.... E. 83 northwest-trending folds

Figure 13. Contoured equal area projections of various planar and linear features in northwest Greenville quadrangle.

trations have a bimodal distribution and form a nS1 showing that the bimodal sl pole distribution proba­ girdle whose ~S1 is 031110°. Figure 13B shows the bly resulted from either F2 or F3 deformation or, bimodal distribution of undivided F2 and F3 fold ax­ more probably, from both. Additionally, the north­ es. The ~s~ of figure 13A would plot within the north­ east maxima is close to the F2 and FJ (northeast­ east maxima for the fold axes. I interpreted this as trending) plots elsewhere in the study area.

Structural Geology 15 East part of the Hayesville sheet maxima away from the girdle may represent post-F3 folding about an east-west axis or may be due to The east part of the Hayesville sheet lies just cleavage fans about F J axes. east of the Helen-Coweeta terrane (see fig. 11) and Figure 13£ shows the S crenulation cleavage covers that part of the Hayesville sheet southwest of 3 orientations for the northwest-trending (F ) folds for the Tallulah Falls structural dome (Hatcher, 1971) 3 the entire study area. Pole plots to S give a 1tS girdle where the rock units and S, surfaces strike primarily 3 3 with a ~SJ of 093/05 o. The pole concentrations along northeast. Most of the dips are to the southeast, but the girdle have a bimodal distribution and probably northwest-dipping foliation is not uncommon. An reflect post- FJ folding about an east-west axis. orientation for poles to S, is shown in figure 13C. The Figure 14C illustrates the SJ cleavage pole con­ poles form a distinct 1tS, girdle with a bimodal maxi­ centrations in the Brasstown Bald area for the F3 ma distribution and a ~S, of 045/05 o. The orienta­ northwest-trending (FJ) folds that define a 1tS3 girdle tion of the girdle and the position of the 1tS 1 are with a ~SJ of 119/30°. The pole density concentra­ similar to those of the Helen-Coweeta terrane (fig. tions form a bimodal distribution, and their separa­ 11 ), where the maximum density concentrations are tion suggests post-FJ deformation, possibly along a more widely dispersed along the 1tS, girdle. Because west-trending axis. fabric orientations in both the Helen-Coweeta ter­ Figure 14D shows the poles to S cleavage asso­ rane and Hayesville sheet (east) are similar, I believe 3 ciated with northeast-trending (FJ) folds in the Brass­ that the S, surfaces in both areas have a similar post­ town Bald area; these plots of SJ cleavage define a S, deformation history. statistical axial plane at 033/34 ofor the maximum S3 pole concentration. The ~S, position for the window Brasstown Bald window plots on the edge of a cluster of several F2 and F3 fold axes (fig. 14B) that are close to the plotted axial Hartley and Penley (1974) and Shellebarger plane-. The maxima concentration, together with the ( 1980) described parts of the Brasstown Bald area axial plane and FJ fold axes plots, suggests that here (see fig. 11). Within the Brasstown window, the re­ the northeast-trending FJ folds plunge northeast and gional foliation has been deformed by F , F3, and 2 are overturned to the northwest. The well-defined S3 later folding. Fabric element diagrams (fig. 14A-D) maxima density suggests minimal post-S3 were made for this area; these include S-pole dia­ deformation. grams, as well as plots of other fabric elements from The bimodal distribution of poles to SJ crenula- rocks along a ridge northwest of Brasstown Bald. tion cleavage for northwest-trending (FJ) folds (figs. An S, pole orientation for the entire window is 14C and 13E) suggests post-FJ folding along east-west shown in figure 14A. Here the S, pole plots define a axes. The pole concentrations (fig. 14D) for FJ north­ 1tS, girdle with a ~S, of 03 7/24 o and define a statisti­ east-trending fold cleavages in the Brasstown Bald cal axial plane that contains the ~S,. Figure 14B area, however, do not suggest significant post-FJ de­ shows the axial plane of a representative F2 fold, its formation, even though post-FJ folding of similar axis, and the axes of several other F2 and F3 folds. cleavages along west-trending axes throughout the The ~S, (fig. 14A) for the window is reasonably simi­ study area is suggested by figure 13D. This lack of lar to the F2 fold axes. The ~S, and F2 fold axes, agreement presents a problem. If both the northwest­ together with the axial plane and the S, pole maxima, and northeast-trending (FJ) folds form a conjugate suggest that the F2 folds are overturned to the west­ pair, their associated rocks also should show evi­

northwest. dences of similar post-F3 deformation. Several expla­ nations for this apparent difficulty are possible. ( 1)

The measured S3 surfaces of northeast-trending folds Crenulation cleavage (S3) in the Brasstown Bald area might have been taken Figure 13D shows the orientations of crenula­ from a position or positions on a relatively on­ tion cleavage for the northeast-trending (FJ) folds deformed part of a fold that would have similar atti­ throughout the study area. Pole concentrations show tudes. (2) The measured crenulation cleavages might a somewhat dispersed maxima within a broad zone be associated with a fold that is younger than the of low pole concentrations that define a questionable northwest-trending (FJ) folds; that is, a fold that has girdle. The distribution of poles to SJ surfaces (axial not been previously recognized. (3) The number of planar to the northeast-trending folds) represents a plotted measured surfaces was insufficient and did wide variety of SJ attitudes. The majority of these S3 not indicate the post-FJ folding. surfaces, however, dip to the southeast and suggest In summary, the post-F, fold analyses show ori­ that most of the axial planes of the northeast-trend­ entations of the principal folds within specific areas ing folds have similar orientations. The spread of the of the report region. In the Great Smoky thrust sheet 16 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. {3S 1 037/24°

49 pts 18% 14% 8% 2%

A. B.

Brasstown Bald window S1 Brasstown Bald F2 axis, its axial plane, and the axes of other F2 folds

34 pts 14 pts 17% 60% 4% 45% 2% 2% 1%

c. D. Brasstown Bald S (northwest­ 3 Brasstown Bald S3 (northeast­ trending) altitudes trending) altitudes

• +

• +

E. F. Brasstown Bald ridge Northwest part of Greenville quadrangle

EXPLANATION EXPLANATION + Intermediate compression axis + Intermediate compression axis • Minimum compression axis • Minimum compression axis • Maximum compression axis 233/10° • Maximum compression axis 200/25°

Figure 14. Contoured equal area projections of various planar and linear features in the Brasstown Bald area and northwest Greenville quadrangle.

northwest of or beneath the Hayesville fault, the re­ The F 3 strain appears to be reflected in the varied gional F2 folds are mostly overturned to the north­ distribution of F2 fold axes and in the diverse atti­ west, and their axial surfaces are steeply inclined. tudes of sl surfaces. Structural Geology 17 In the Hayesville thrust sheet southeast of the statistical maximum compression direction for the Hayesville fault, the F 2 folds are reclined to recum­ northwest area at 200/25 o. This direction almost lies bent and, depending on their location with reference in the regional foliation for that area. These south­ to the Chattahoochee basin (fig. 10), have variable west-striking compression directions are not exactly orientations that reflect considerable FJ (northwest­ parallel, and the slight angular discordances between and northeastward) strain. S, attitudes vary widely. them are probably due to preconjugate deformation In contrast, in both the Helen-Coweeta terrane and that gave the rock units varying orientations. The the southeastern part of the Hayesville thrust sheet, southwest trend of the maximum compressive stress the F2 fold axes generally strike northeast and have axis for the conjugate folds is almost parallel to the steeply dipping axial surfaces. These terranes also ap­ trends of the regional F 2 and F 3 fold hinges in the pear to have been subjected to post-F2 deformation report area (see figs. 12, 13, and 14). that did not change the orientation of F2 fold axes In the southern Appalachian Blue Ridge Moun­ greatly. Throughout the report area, FJ fold axes tains, the regional folds trend northeast-southwest. strike west to northwest and north to northeast, and This trend suggests that the maximum compression their axial surfaces range from gently to steeply in­ axes of the stress ellipsoid had a northwest-southeast clined. Although statistical evidence suggests post-FJ orientation during regional deformation. It has previ­ folding about east-west axes, field observations indi­ ously been shown that the maximum compression cate only gentle warping about east-west axes. I rec­ direction for the conjugate folds in part of the report ognize no significant post-FJ folding in the study area. area was to the southwest. This orientation suggests that the stress field during conjugate folding was ori­ ented almost normal to that which was prevalent dur­ F3 fold analysis ing regional deformation. Tobisch and Fiske (1976) reported on a similar situation in the central Sierra Ramsay ( 1962) used some structural elements Nevada. To explain this anomaly, they suggested a of conjugate folds to determine the principal stress model where the conjugate structures resulted from directions in the formation of a conjugate fold sys­ forces that developed during an elastic recovery stage tem. He discussed a procedure to determine the three that occurred after the main folding event. This ne­ principal stress axes for the deforming forces respon­ cessitated shortening parallel to the regional structur­ sible for conjugate folds. Tobisch and Fiske (1976) al trends. Therefore, applying the Tobisch-Fiske made regional structural interpretations of the cen­ model in the report area, the stress field that pro­ tral Sierra Nevada from maximum compression di­ duced the regional northeast-trending structures was rections (maximum stress of Ramsay) of conjugate not rotated almost 90° to obtain the conjugate fold­ folds. Ramsay and Tobisch and Fiske indicated that ing maximum compression. Instead, the compression the maximum compression directions probably lie direction for conjugate folding probably resulted parallel or subparallel to the surfaces being folded. from forces that developed during elastic recovery Several crenulation cleavage sets are exposed after the main deformation. along a ridge north of Brasstown Bald in the Brass­ town Bald window. Orientations of the axial planes of both sets of crenulation folds were plotted on a stereonet. These data were used to obtain a statistical SUMMARY AND CONCLUSIONS orientation for the principal compression directions (Ramsay, 1962). Figure 14£ shows the statistical The rocks underlying the northwest part of the compression axes for the conjugate (FJ) folds in the Greenville 2-degree quadrangle form parts of three Brasstown Bald window. The maximum compression major lithotectonic units. They are the Great Smoky direction is 233/10° and is subparallel to the regional thrust sheet, the Hayesville thrust sheet, and the foliation on the ridge north of Brasstown Bald. A Helen-Coweeta terrane. Each of these lithotectonic similar study was made of conjugate folds near Ebe­ units is characterized by lineaments with distinct nezer Church, which is 8 km northwest of Blairsville trends; each is allochthonous and bounded by faults. and 1 km east of the quadrangle boundary in the- The Hayesville fault and its northern continua­ northwest part ofthe study area. Figure. 14F shows a tion separate two major terranes in the Appalachian

18 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga. Mountain chain-the Great Smoky thrust sheet and faces. The F3 (northeast- and northwest-trending) the Hayesville thrust sheet (Rankin, 1975; Hatcher, folds are well developed locally, and their axial sur­ 1976, 1978; Williams, 1979). The Hayesville fault is faces range from steeply to gently inclined. In places, pre- or synmetamorphic and is folded. The fault rocks show type 2 and 3 fold interference patterns. forms the contact around several windows in the These patterns result from F3 folds deforming the Hayesville sheet. almost flat-lying F2 and F1 folds. Figure 15 is a sche­ The Shope Fork fault is probably a pre- or matic diagram of a folded regional foliation surface synmetamorphic feature, but some evidence indi­ between the Hayesville fault and the Helen-Coweeta cates a late episode of movement along part of the terrane; the diagram shows the generalized form of fault. Patterns on Landsat imagery suggest possible the F 2 and F 3 folds. right lateral offset of the Warwoman lineament along In the report area, the relations between the the Shope Fork fault. Mapping suggests that a post­ directions of maximum compression for the conju­ metamorphic diabase dike of probable Triassic-Ju­ gate and regional folds seem to agree with the struc­ rassic age(?) is similarly offset along the Shope Fork. tural requirements of the conjugate folding model of The Helen-Coweeta terrane is bounded by Tobisch and Fiske (1976). The analysis of conjugate faults, and numerous topographic lineaments within folds shows that maximum compression directions the terrane are associated locally with mylonitic for conjugate folding nearly parallel the regional foli­ rocks. These lineaments correspond with aer­ ation, as shown in figure 12E and F. omagnetic lineaments in rocks of the Helen Group If all the northeast- and northwest-trending FJ that extend southwest beyond the study area. Bowen folds in the report area are part of a conjugate fold ( 1961) also described a band of sheared rocks that are pair, then one less folding event is required to explain on strike with the Helen Group a few miles to the the fold structures present. This simplifies structural southwest, in Dawson County. Therefore, shear interpretation and eliminates the need for an almost zones in the Helen Group may be part of a larger 90° rotation of the force field after regional F2 defor­ shear zone; that is, the Dahlonega shear zone in mation. Further work is necessary to determine northeast Georgia. whether conjugate folding extends beyond the report Several major lithotectonic units in the study area. area are characterized by distinctive lineament With the inclusion of the conjugate folds, the trends on Landsat images. These lineaments, which following fold phases occur in the report area: are not the northeast-trending lineaments seen on topographic maps, are believed to reflect prominent F1-Rootless recumbent to reclined isoclinal folds fracture zones in the lithotectonic units. Two inter­ that trend northeast. F 1 folds lie in the regional pretations of the lineament trends are possible: ( 1) foliation and may be coplanar with F2 folds. each major lithotectonic unit had different physical characteristics that caused the unit to yield different­ F2-Steep to recumbent isoclinal folds that form ma­ ly to stress or (2) the lineaments were present in each jor folds. F2 folds deformed S1 regional folia­ thrust sheet prior to emplacement into their present tion, probably occurred after peak metamor­ positions. phism, and rarely have well-developed axial The majority of folds in the terrane northwest plane foliations (S2). of (below) the Hayesville fault are F2 folds with northeast-trending axes. These folds are overturned F3-Upright to slightly inclined conjugate fold sets to the northwest, and their axial surfaces are steeply that trend northeast and northwest. F 3 fold sets inclined. F 1 folds are not apparent northwest of the have planar crenulation cleavage in pelitic units Hayesville fault, but F3 folds are present and super­ and probably are late metamorphic. imposed upon the F2 folds. Southeast of the Hayesville fault, most F2 folds F4-Post-F3 folding about east-west and north-north­ have northeast-trending axes. In this area, the F2 east axes, as suggested by statistical fold analy­ folds are overturned, but their axial surfaces are ei­ ses. Field studies, however, have not identified ther gently inclined or nearly horizontal. The imprint axial planar cleavages associated with these lat­ of later folding has variably deformed F2 axial sur- er folds.

Summary and Conclusions 19 ..,. ~ 11(1. ,J~ ~~ Le a 1-;. 4_"\ :7\ ~~ ' ~ 0~ -· ' ,J~ ~ I ' (('ll ~ 'to ~~ ' ' 1/ l ' ~ f "' ?'~ i !1.

Iz

iC') I. f -i l ~~,.o"'~ i ~'2. lf" ~

Figure 15. A deformed S, surface in part of the Hayesville thrust sheet between the Hayesville fault and the Helen terrane. The generalized form of the F1 and F, folds is indicated. REFERENCES CITED Hadley, J. B., and Nelson, A. E., 1971, Geologic map of the Knoxville quadrangle, North Carolina, Tennessee, and Abrams, C. E., and McConnell, K. I., 1981, Stratigraphy of South Carolina: U.S. Geological Survey Miscellaneous the area around the Austell-Frolona antiform, west­ Investigations Map Series I-654, scale I :250,000. central Georgia, in Latest thinking on the stratigraphy Hartley, M. E., 1973, Ultramafic and related rocks in the of selected areas in Georgia: Georgia Geological Sur­ vicinity of Lake Chatuge: Georgia Geological Survey vey Information Circular 54, p. 55-67. Bulletin 85, 61 p. Bell, H., and Luce, R., 1983, Geologic map of the Ellicott Hartley, M. E., and Penley, N. M., 1974, The Lake Chatuge Rock Wilderness and additions: U.S. Geological Sur­ sill outlining the Brasstown antiform: Georgia Geolog­ vey Miscellaneous Field Studies Map MF-1287-B, ical Society Field Trip Guidebook 13, 27 p. scale 1:48,000. Hatcher, R. D., Jr., 1971, Geology of Rabun and Haber­ Bowen, B. M., Jr., 1961, The structural geology of a portion sham Counties, Georgia-A reconnaissance study: of southeastern Dawson County, Georgia: Unpub­ Georgia Geological Survey Bulletin 83, 48 p. lished M.S. thesis, Emory University, 45 p. ___1972, Developmental model for the southern Ap­ Butler, J. R., 1972, Age of Paleozoic regional metamor­ palachians: Geological Society of America Bulletin, v. phism in the Carolinas, Georgia, and Tennessee south­ 83, p. 2735-2760. em Appalachians: American Journal of Science, v. 272, p. 319-333. ___1974, An introduction to the Blue Ridge tectonic ___1973, Paleozoic deformation and metamorphism in history of northeast Georgia: Georgia Geological Soci­ part of the Blue Ridge thrust sheet, North Carolina: ety Field Trip Guidebook 13-A, 60 p. American Journal of Science, v. 273-A, p. 72-88. ___1976, Introduction to the geology for the eastern Carpenter, R. H., 1970, Metamorphic history of the Blue Blue Ridge of the Carolinas and nearby Georgia: Caro­ Ridge province of Tennessee and North Carolina: Ge­ lina Geological Society Guidebook, 53 p. ological Society of America Bulletin, v. 81, p. 749-762. ___l978a, Tectonics of the western Piedmont and Blue Crickmay, G. W., 1952, Geology of the crystalline rocks of Ridge, Southern Appalachians-Review and specula­ Georgia: Georgia Geological Survey Bulletin 58, 54 p. tion: American Journal of Science, v. 278, p. 276-304. Dallmeyer, R. D., 1975, Incremental 40ArP9Ar ages of bio­ __l978b, Structural style of the Blue Ridge: Geologi­ tite and hornblende from retrograded basement cal Society of America, Penrose Research Conference gneisses of the southern Blue Ridge-Their bearing on Field Trip, 12 p. the age of Paleozoic metamorphism: American Journal ___l978c, A structural transect in the southern Ap­ of Science, v. 275, p. 444-460. palachians, Tennessee and North Carolina, in Milici, Dallmeyer, R. D., Courtney, P. S., and Wooten, R. M., R. C., ed., Report of Investigations 37, Field trips in 1978, Stratigraphy, structure, and metamorphism east the southern Appalachians, Tennessee Division of Ge­ of the Murphy Syncline-Georgia-North Carolina: ology, 86p. 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References Cited 21 Nelson, A. E., 1982, Geologic map of the Tray Mountain Shellebarger, J. E., 1980, A preliminary report on the geolo­ Roadless Area, northern Georgia: U.S. Geological Sur­ gy of the Coosa Bald and Jack's Gap quadrangles, vey Miscellaneous Field Studies Map MF-134 7-A, Georgia: Unpublished M.S. thesis, University of Geor­ scale 1:30,000. gia, 209 p. ___ 1983a, Geologic map of the Chattahoochee Tobisch, 0. T., and Fiske, R. S., 1976, Significance of con­ Roadless Area, Towns, Union, and White Counties, jugate folds and crenulation in the central Sierra Neva­ Georgia: U.S. Geological Survey Miscellaneous Field da, California: Geological Society of America Bulletin, Studies Map MF-1502-A, scale 1:30,000. v.87,no. 10,p. 1411-1420. ___ 1983b, Geologic map of the Blood Mountain Roadless Area, Union and Lumpkin Counties, Geor­ Turner, J. J., and Weiss, L. E., 1963, Structural analysis of gia: U.S. Geological Survey Miscellaneous Field Stud­ metamorphic tectonites: New York, McGraw-Hill, 545 ies Map MF-1503-A, scale 1:30,000. p. Park, C. F., 1953, Gold deposits of Georgia: Georgia Geo­ logical Survey Bulletin 60, p. 60-67. Williams, Harold, 1978, Tectonic lithofacies map of the Rankin, D. W., 1975, The continental margin of Eastern Appalachian Orogen: Memorial University of New­ North America in the southern Appalachians-The foundland, St. Johns, Newfoundland, Canada, scale opening and closing of the Proto-Atlantic Ocean: 1:1,000,000. American Journal of Science, v. 275-A, p. 298-336. Wooten, R. M., 1980, Geology of the southern half of the Ramsay, J. G., 1962, The geometry of conjugate fold sys­ Hayesville quadrangle, North Carolina: Unpublished tems: Geological Magazine, v. 99, no. 6, p. 516-526. M.S. thesis, University of Georgia, 276 p. ___ 1967, Folding and fracturing of rocks: New York, McGraw-Hill, 568 p. Yeates, W. S., and McCallie, S. W., 1896, The gold deposits Rodgers, John, 1953, Geologic map of east Tennessee with of Georgia: Georgia Geological Survey Bulletin 4, 542 explanatory text: Tennessee Division Geological Bulle­ p. tin 58, pt. 2, 168 p.

22 Tectonic Features and Structural Elements, Northeast Greenville Quadrangle, Ga.