An introduction to the Blue Ridge tectonic history of northeast Georgia [1974]

AN INTRODUCTION TO THE BLUE RIDGE TECTONIC HISTORY OF NORTHEAST GEORGIA by Robert D. Hatcher
Published by the Georgia Geological Survey for the Georgia Geological Society
GUIDEBOOK 13-A
..
Georgia Department of Natural Resources Joe D. Tanner, Commissioner Earth and Water Division
The Geological Survey of Georgia Sam M. Pickering, Jr., State Geologist
ATLANTA 1974

AN INTRODUCTION TO THE BLUE RIDGE TECTONIC HISTORY
OF NORTHEAST GEORGIA. By
Robert D. Hatcher,. Jr. Department of Chemistry and Geology
Clemson University Clemson, South Carolina 29631
Prepared as the gui debook ~or Day 1 of the 1974 Georgi a Geo1ogi ca1 Society Meeting, held October 25-27, 1974 in Clayton, Georgia.

CONTENTS

ABSTRACT . . .

1

INTRODUCTION .

3

ROCK UNITS . .

5

Basement (?) Rocks

5

Wiley Gneiss

6

Rabun Geniss

6

Ta 11 ul ah Fa 11 s Formation . . . . .

9

Graywacke-Schist-Amphibolite Member

9

Ga-rnet-A1umi no us Schist Member

10

Graywacke-Schist Member .

10

Quartzite-Schist Member . . .

10

Coweeta Group . . . . . . .

12

Persimmon Creek Gneiss . . .

13

Coleman River Formation .. .

13

Ridgepole Mountain Formation

14

Igneous and Igneous-Like Rocks .

16

Ultramatic Rocks . . . . . .

16

Trondhjemite Dikes . . . . .

16

Diabase Dikes . . . . . . . . .

17

Pegmatite Dikes and Quartz Veins

17

Speculation on Ages of Igneous Rocks

19

METAMORPHISM . . . .

21

STRUCTURAL ELEMENTS

22

S-Surfaces . .

22

Lineations . . . .

25

Folds . . . . . . . . . .

25

Early Folds (F 1 and F?)

25

Late Faults

.F.old.s.(F.3.a.nd.F.4 J.

.

.

.

.

.

.

.

.

28 30

Speculation on the Timing of Deformational Events

30

LINEAMENTS . . . . . . .

31

DISCUSSION AND SYNTHESIS

32

ACKNOWLEDGEMENTS . .

35

REFERENCES CITED . . . .

37

FIELD TRIP GUIDE . . . .

39

LEGEND FOR FIGURE 2 . . . . . . . . . . . . . . . . . . . 59

; ; i

LIST OF FIGURES
Figure 1 Map showing the location of the map in Figure 2 and the geologic provinces of this area.
Figure 2 - A geologic map representing the present state of knowledge of the Blue Ridge geology of northeast Georgia.
Figure 3 - Typical Wiley gneiss.
Figure 4 - Coarse Rabun gneiss.
Figure 5 - Kyanite-bearing schist of the Garnet-Aluminous Schist Member of the Tallulah Falls Formation.
Figure 6 - Typical Persimmon Creek gneiss from Patterson Gap Road, Dillard Quadrangle.
Figure 7 - Pinstriped quartzite in the Coleman River formation on Ridgepole Mountain, Dillard Quadrangle.
Figure 8 - Contact of fine-grained trondhjemite dike with coarse Persimmon Creek gneiss on Patterson Gap Road, Dillard Quadrangle.
Figure 9 - Exposure of Coleman River formation atop Albert Mountain south of Franklin, North Carolina showing several generations of folds and quartz veins.
Figure 10- Crenulation cleavage in schist of the Graywacke-Schist Member of the Tallulah Falls Formation west of U.S. 441, Prentiss Quadrangle, North Carolina.
Figure 11- A. Flexural flow F? fold at Woodall Shoals on the Chattooga River (Rainy Mounta1n Quadrangle). This fold appears to plunge in two different directions. B. F1 isoclines are present as intrafolial folds in the nose of thi,s fold (to left of hammer).
Figure 12- An F1 isoclinal fold refolded by F2 folds with more upright axial surfaces, at Holcomb Creek Falls on Rabun Bald Quadrangle.
Figure 13- Dome and basin structures produced by interference of F3 and F4 folds at Woodall Shoals on the Chattooga River (Rainy Mountain Quadrangle}.
iv

Figure 14 - Generalized geologic map of the Blue Ridge of northeast Georgia and adjacent North and South Carolina showing field trip .stops.
Figure 15 - Schematic Cross-section of Tiger Mountain. Figure 16 - Porphyroblastic Rabun gneiss exposed in Kelly Quarry.
v

AN INTRODUCTION TO THE BLUE RIDGE TECTONIC HISTORY OF NORTHEAST GEORGIA
by Robert D. Hatcher, Jr.
It has been said that stratigraphy is the basis of all geology (Weller, 1947). This is true of the metamorphic rocks as well as the sedimentary rocks. Cogni~ant of the importance of petrography, physical chemistry, and structural geology, the investigator of metamorphic rocks should nevertheless give more adequate treatment to the fascinating problems in stratigraphy, sedimentation, and paleogeography that await solutions in the interesting rocks to which, perhaps foolishly, he has dedicated his scientific career.
M. P. Billings, 1950
ABSTRACT This guide will serve to introduce the reader to the tectonic
history of the Blue Ridge of part of northeast Georgia. The geologic map which accompanies this guide is based principally upon detailed geologic mapping but some reconnaissance work is involved in the compilation.
Major rock units in this area include the plutonic Rabun and Wiley gneisses, which are probably basement rocks, the Tallulah Falls Formation and the younger (?) Coweeta group. Ultramafic rocks, which were emplaced before or during metamorphism, post metamorphic and post deformational trondhjemite, and mesozoic diabase dikes comprise the igneous intrusiv~of this area. Pegmatites and several generations of quartz veins of local origin are present in these

rocks also. One progressive metamorphic event has been recognized in the Blue
Ridge of northeast Georgia. It is thought to have occurred during the Early Paleozoic.
Four deformational episodes have been recognized in this area. F1 and F2 folds are early flowage folds. F1 is pre- or syn-metamorphic,
F2 is post-metamorphic. s1 and s2 are axial plane foliations. s1 and
compositional layering (So) are parallel. F3 consists of a later set of flexural folds and crenulation cleavage. F4 folds are flexural-slip cross folds. Early lineations, L1 and L2, are mineral elongation lineations. Later lineations are intersections of s-surfaces.
Several topographic lineaments cross this area. The most prominent of them is called the Warwoman lineament. Although siliceous mylonite is present along all the lineaments, bedrock contacts are not offset along any of them.
The unconformity at the base of the Tallulah Falls Formation is a nonconformity. Relief on tnis surface suggests it is also a disconformity. The units in the Tallulah Falls Formation are equivalents of units in the Sandy Springs sequence.
Rocks of the Coweeta group occupy a large previously unknown syncline to the northwest of the Tallulah Falls Dome. Rock units within the syncline may be lithologic correlatives of the Murphy group and possibly the Alligator Back Formation.
2

Thicknesses of rock units cannot be accurately determined due to isoclinal folding and other types of tectonic thickening and thinning, as well as the effects of high grade metamorphism.
INTRODUCTION
The purpose of this guide is to introduce the reader to the Blue Ridge tectonic history of part of northeast Georgia, northwestern South Carolina and adjacent North Carolina (Figure 1). In order to understand the tectonic history of this portion of the Southern Appalachians, it is necessary to gain some insight into the rock units present in this area in the form of their nature and origin. Therefore, we shall begin with a discussion of the rock units and their stratigraphy, then proceed to the deformational history.
Pre~ently, the eastern three-fourths of Rabun County has been mapped in detail, an area of about 736 km2 (265 mi. 2). Previous reconnaissance mapping by Teague and Furcron (1948) and by Hatcher (1971) covered both Rabun and Habersham Counties. Hurst and Crawford (1964) made a deta.iled study of the mineral resources of Habersham County. Giles (1966) made a reconnaissance study of the Rabun Bald area in Rabun County. Livingston and McKniff (1967) speculated that the Tallulah Falls Dome could be a window like the Grandfather Mountain window.
The geologic map (Figure 2) represents the present state of knowledge
3

3J1 ''"45'

5~;;e;;Z0=""""5.._....,..,10""""'~15 Miles
5 0 5 10 15 20 Kilometers

Figure 1. Map showing the location of the map in Figure 2 and the geologic provinces of this area.
4

of the Blue Ridge geology of northeast Georgia. This map is a compilation of the detailed work by my assistants and myself over the past seven years. Most of this mapping has been carried out at a scale of 1/24~000. The Rabun Bald and Dillard Quadrangleswere mapped at a scale of l/12,000, then complied at the l/24,000 scale. Most of the area mapped in detail lies in Rabun County. The geologic map in this report is considered to be factual in this area with few extrapolations of contacts. The contacts to the south and west of the Tallulah Falls Dome are based upon the original reconnaissance data, later reconnaissance and some of the locations of kyanite mica schist from Hurst and Crawford (1964). Contacts in parts of this area are extrapolated, so the map is only an approximation of the geology.
ROCK UNITS
Basement(?) Rocks Two rock units appear to be older than any of the other rocks in
this area. Both occupy the same stratigraphic position but, in the absence of detailed analysis of the structural data, no additional deformational episodes have been recognized in these rocks. Such structural analysis should subsequently yield one .or more additional events.
The names of the two rock units, Wiley gneiss and Rabun gneiss, are used herein as informal names. However, they are distinctly mappable units and there is no reason to believe that they should be abandoned
5

as future formal names for these units.
WILEY GNEISS. The Wiley gneiss is a felsic orthogneiss (Figure 3). It appears to have originated from metamorphism of a coarse-grained granitic rock. It weathers to a light-colored soil, is a good bluff-former and supporter of waterfalls in creeks. It occurs in a single outcrop belt that begins as several smaller subparallel closely spaced belts on the crest of the Tallulah Falls Dome, then extends southwestward crossing to the outer edge of the Dome. It has been traced by reconnaissance into Habersham County.
RABUN GNEISS. The Rabun gneiss, like the Wiley gneiss, is also a felsic orthogneiss. This rock unit contains several textural types ranging from coarse porphyroblastic weakly foliated quartz monozonite gneiss (Figure 4), to a coarse gneiss with either poorly developed porphyroblasts or coarse gneiss with porphyroblasts which have been stretched out during deformation and metamorphism and an even grained leuco-quartz diorite gneiss. The coarse variety may have been completely remobilized during Paleozoic metamorphism.
The Rabun gneiss is in a continuous outcrop belt with rocks mapped as Whiteside Granite by Keith (1907) and Hadley and Nelson (1971). This main belt terminates along the northwest side of the Tallulah Falls Dome. Smaller belts ring the north, east, south, and southwest sides of the Dome.
6

Figure 3. Typical Wiley gneiss. The augen and other coarse feldspars are microcline. Sample from exposures on U.S. 441 near Wiley on the Tiger Quadrangle.
7

Figure 4. Coarse Rabun gneiss. The subhedral porphyroblasts are microcline. Sample from Kelly Quarry on the Rabun Bald Quadrangle. 8

All of these masses of Rabun and Wiley gneiss occur in the same stratigraphic position: beneath the rocks of the Tallulah Falls Formation. They are the oldest rocks of this area and are thought to represent old continental basement rocks.
Tallulah Falls Formation
The Tallulah Falls Formation was defined by this investigator (Hatcher, 1971). This formation name was proposed to raise the name Tallulah Falls to group status, since the Tallulah Falls Quartzite, named by Galpin (1915), is interlayered with and grades into graywackes that either underlie or are facies equivalents of the quartzite. This investigator recognized and named four members in the Tallulah Falls Formation: the lowermost Graywacke-Schist-Amphibolite Member, the Garnet-Aluminous-Schist Member, Graywacke-Schist Member and the QuartziteSchist Member (formerly Tallulah Falls Quartzite). Each will be described briefly.
GRAYWACKE-SCHIST-AMPHIBOLITE MEMBER. The Graywacke-Schist-Amphibolite Member contains the same lithologies as the Graywacke-Schist Member except that amphibolite and/or hornblende gneiss is more prominent in the former.
This member rests upon basement and is therefore considered to be the oldest member. However, it is not present everywhere, being sporadi-
9

cally preserved on the Tallulah Falls Dome, but more consistently preserved elsewhere. This preservation was previously interpreted as nonuniform desposition (Hatcher, 1971, Figure 22). However, this member could have been removed by later erosion. These possibilities will be more thoroughly discussed in a later section.
GARNET-ALUMINOUS SCHIST MEMBER. The Garnet-Aluminous Schist Member consists of one or more zones of silvery muscovite-garnet-kyanite (or sillimanite)-quartz-biotite-plagioclase schist (Figure 5) interlayered with the usual metagraywacke and muscovite-biotite schist of the members above and below.
GRAYWACKE-SCHIST MEMBER. The Graywacke-Schist Member consists of interlayered metagraywacke and muscovite-biotite schist with variable amounts of amphibolite and/or hornblende gneiss. Amphibolite may be quite common in some areas such that distinguishing rocks of this member from those of the Graywacke-Schist-Amphibolite Member is difficult. Structural position may have to be used in those areas.
QUARTZITE-SCHIST MEMBER. The Quartzite-Schist Member consists of medium to thick beds of metaquartzite to metasubgraywacke. Quartz-muscovitebiotite-microcline-plagioclase-carbonate quartzite is most common. The interlayers are muscovite-biotite schist. A genetic connection of the
10

Quartzite-Schist member with the Graywacke-Schist member is suggested by interlayered and gradational lithologies.
Some primary structures are preserved in the Quartzite-Schist Member. Stretched pebble conglomerate is present at one locality along U.S. 441 (see Hatcher, 1971, Figure 6). The same beds appear graded and
Figure 5. Kyanite-bearing schist of the Garnet-Aluminous Schist Member of the Tallulah Falls Formation. Sample from Wolf Creek Church area, Rainy Mountain Quadrangle.
11

upright. Graded beds and possible cross-beds are also present at another locality on U.S. 441 (see Hatcher, 1971, Figure 19). Beds are upright at this locality also.
Coweeta Group
A group of rocks in a stratigraphically and structurally high position was recognized during the summer of 1973 by L. L. Acker. Some of these rocks were observed during the reconnaissance investigation (Hatcher, 1971) and it was recognized that they were lithologically different from the rocks to the southeast and farther northwest. For example, calc-silicate quartzite (quartz-ep1dote-clinozoizite-garnethornblende-plagiaclase quartzite) is more common in these rocks (essentially ubiquitous) than in the rocks of the Tallulah Falls Formation. In the latter it is stratigraphically controlled and serves as a marker.
Detailed mapping placed the rocks of this younger (?) unit high in the section above the rocks of the Tallulah Falls Formation. The name Coweeta group is proposed here as an informal name for these metasedimentary and metaigneous rocks. There is no known previous mention of this assemblage in the literature. These rocks are well exposed in the vicinity of Ball Creek, Coweeta Creek, Henson Creek and Cunningham Creek in the area of the U.S. Forest Service Coweeta Hydrologic Laboratory
12

in the Prentiss Quadrangle in North Carolina north of Dillard Georgia. Several units have been recognized in the Coweeta group. These
include the basal Persimmon Creek gneiss, Coleman River formation and the uppermost Ridgepole Mountain formation. These informal names were proposed by L. L. Acker and the units will be briefly described below.
PERSIMMON CREEK GNEISS. The Persimmon Creek gneiss is an oligoclasequartz-biotite gneiss (Figure 6). In many places it contains abundant epidote. It is poorly folitated and isolated specimens have a distinctly igneous character. Yet the upper part contains interlayered metagraywacke. This unit was named for exposures along Persimmon Creek in northwestern Rabun County.
COLEMAN RIVER FORMATION. The Coleman River formation consists of interlayered impure metasandsmne, musovite-biotite schist and metaconglomerate. Also occurring in this unit and the overlying Ridgepole Mountain formation is some thinly laminated sandstone in which the laminations were probably produced by tectonic transposition of an earlier foliation (S1) or bedding (So) (Figure 7). The rock has a pinstriped appearance. This type of structure has been described by Rankin and others (1973) in the North Carolina-Virginia Blue Ridge.
13

RIDGEPOLE MOUNTAIN FORMATION. The Ridgepole Mountain formation consists of clean quartzite, chlorite-muscovite quartzite and coarse biotitechlorite schist and metagraywacke containing garnets up to 3 em. in diameter. Pinstriping of some of the quartzite may also occur here but
Figure 6. Typical Persimmon Creek gneiss from Patterson Gap Road, Dillard Quadrangle.
14

is not as common as in the Coleman River formation.
Figure 7. Pinstriped quartzite in the Coleman River formation on Ridgepole Mountain, Dillard Quadrangle. Coin (a quarter) is 2.4 em. in diameter.
15

Igneous and Igneous-like Rocks
ULTRAMAFIC ROCKS. Ultramafic rocks are common in this area. They are associated with all rock units. Although they may appear to be crosscutting, close examination indicates these rocks are deformed, foliated and have been through the metamorphic mill. Most are altered to a greater or lesser degree. Dunites seem to be the most common ultramafic rock type although hartzburgite and some pyroxenite make up the remainder.
Some ultramafics occur as isolated bodies. Others appear to be associated in mafic-ultramafic complexes (see also Hartley, 1973; Hartley and Penley, 1974).
TRONDHJEMITE DIKES. Two extensive trondhjemite dikes have been mapped in northwestern Rabun County. They are only a meter or slightly more in thickness, have a near vertical dip, sharp contacts (Figure 8) a northeast strike and a straight outcrop pattern. These two are part of a belt of trondhjemite dikes that occurs in this part of the Blue Ridge of northeast Georgia and southwest North Carolina. These rocks are maficpoor, light in color, fine-grained and a few contain phenocrysts of plagioclase. In thin section quartz dominates in the groundmass over plagioclase (albite-oligoclase). The phenocrysts are zoned plagioclase.
16

The dark mineral is biotite. These rocks are unaltered, have not been metamorphosed and have been folded only by the latest episodes, if at all.
DIABASE DIKES. Diabase dikes cut the Brevard Zone in Habersham County (Lester and Allen, 1950; Pruitt, 1952; Hatcher, 1974) and continue into the Blue Ridge. The same or a different group of dikes appears on the west side of the Tallulah Falls Dome along a parallel trend. These are typical olivine diabase dikes like others of this part of the Appalachians. However, these are the westernmost dikes in the Southern Appalachians south of Virginia. All these dikes have a northwest strike, an almost vertical dip and are unmetamorphosed. Their straight outcrop pattern indicates they have not been folded. They cut rocks folded by earlier episodes.
PEGMATITES AND QUARTZ VEINS. Simple quartz-feldspar and quartz-feldsparmuscovite pegmatites are common in the Blue Ridge of this area. Pegmatites become more common in areas of higher metamorphic grade. They are rare in rocks whose metamorphic grade is below the middle of the kyanite zone. Early pegmatites were also deformed during one or both episodes of flowage folding. Lenticular, folded and boudined pegmatites have all been observed.
17

Figure 8. Contact of fine-grained trondhjemite dike with coarse Persimmon Creek gneiss on Patterson Gap Road, Dillard Quadrangle.
18

However, late crosscutting pegmatites are rare. Therefore I interpret most pegmatites to have formed during metamorphism, as felsic material 11 SWeated out11 of the metasedimentary rocks of the Tallulah Falls Formation. Pegmatites are rare in the rocks of the Coweeta group. They are also not as common in the plutonic gneisses of the basement. However, in the porphyroblastic phase of the Rabun gneiss, there are both early and late pegmatites.
There are several generations of quartz veins in the rocks of this area (Figure 9). Early veins are folded, many are pinched off and all appear highly deformed. A later generation of quartz veins has been slightly deformed by F3 flexural folds and are broken by closely spaced joints or fracture cleavage. A still later set of veins is undeformed and fills planar joints. Latest fractures are not filled.
SPECULATION ON AGES OF IGNEOUS ROCKS. The ultramafic rocks are deformed and metamorphosed. Study of the Lake Chatuge ultramafics indicates they are mantle derived (Hartley, 1973; Jones and others, 1973). It is likely the ultramafic rocks of Rabun County also have their source in the mantle. I believe the ultramafic rocks of this area were emplaced during one of the major early episodes of flowage folding, probably F1 and prior to or during metamorphism. They are likely Early Paleozoic rocks.
The trondhjemites are unmetamorphosed and essentially undeformed.
19

Figure 9. Exposure of Coleman River formation atop Albert Mountain south of Franklin, North Carolina showing several generations of folds and quartz veins.
20

They could have been folded by the later episodes (F3 or F4) without the folding being expressed in their outcrop patterns. However, these rocks appear to have been emplaced later than the last episode of folding. They are likely to be Late Paleozoic and could have been intruded while northeast-trending extension fractures formed as the tectonic forces subsided.
The diabase dikes appear to be part of the general group of Mesozoic dikes that were intruded as the present Atlantic Ocean opened. May (1971) has presented a mechanical model that effectively accounts for their orientations in relation to the stress system that might have existed at that time.
METAMORPHISM
The rocks of the northeast Georgia Blue Ridge have been metamorphosed to amphibolite facies assemblages. The isograds were folded by the second episode of flowage folding (F2) so metamorphism likely was synchronous with or slightly later than the F1 episode.
Inverted metamorphic zones exist on the Tallulah Falls Dome where kyanite grade assemblages dip beneath sillimanite grade rocks. Index minerals in pelitic rocks have shown that this inversion exists. A map showing the distribution of isograds in this area was published by Hatcher (1973, Figure 2). Only one progressive metamorphic event is
21

recognizable in this area.
STRUCTURAL ELEMENTS
The Blue Ridge rocks of northeast Georgia have been subjected to several episodes of deformation. The various fabric elements are summarized in Table 1. It is likely that the two early episodes were not greatly separated in time and the two later sets of folds also formed at closely related times.
S-Surfaces
Bedding (So) is the earliest s-surface formed in this area. How-
ever, So and s1, the earliest foliation, are parallel at present, since So was transposed during formation of s1. s1 was formed as an axial
plane foliation to the F1 folds.
An axial plane foliation, s2, was formed in association with F2 folds. This foliation cuts the s1 foliation in the axial zones of F2 folds, which fold the earlier s1 foliation.
Crenulation cleavage, s3, was fonmed in association with later
generation F3 folds (Figure 10). s3 is commonly observed in schistose
rocks as axial surfaces to F3 crenulations on the mesoscopic scale stnce breakage of the crenulations generally has not taken place. Very weak axial plane or fracture cleavage may be present in more quartzose or quartzofeldspathic rocks in association with more open F3 folds.
22

TABLE 1
MESOSCOPIC-MACROSCOPIC FABRIC ELEMENTS IN THE BLUE RIDGE OF NORTHEAST GEORGIA

Folds S-Surfaces

Lineations

Remarks

Original bedding, transposed to sl or s2

Fl

sl

Ll

Flowage folds, dominantly

(Axial plane to F1)

(elongation)

recumbent isoclines, preor synmetamorphic, north

to west vergent.

F2

s2

L2

Flowage folds, dominantly

upright isoclines, other

(Axial plane to F2)

(elongation) similar folds, northwest vergent.

s3
(Axial plane to F3, Crenulatin cleavage planes)

L3

Flexural and passive slip folds, crenulation cleavage,

(crinkle axes,northwest vergent.

and S3 X S1 or

S2 intersec-

tions)

s4 (weak axial plane foliation)

L4

Flexural slip folds, northwest axial trend

(s4 X s1 or s2

intersections)

23

Figure 10. Crenulation cleavage in schist of the Graywacke-Schist Member of the Tallulah Falls Formation west of U.S.441, Prentiss Quadrangle, North Carolina. Knife is 10 em. long.
24

Weak fracture or axial plane cleavage, s4, has been observed in
association with F4 open folds. This s-surface is seldom observed. The reader is referred to Hatcher (1971, Figure 9) for a complia-
tion of the initial data from different homogeneous subdomains.
Lineations
The lineations associated with early structures (L 1 and L2) are mineral elongation lineations. Those associated with the later episodes of folding are intersections, except the L3 crenulation cleavage.
Folds
The earlier sets of folds, (F 1 and F2), were formed in the realm of flow, while the late sets were produced at lower temperatures and possibly lower confining pressures in the realm of brittle deformation. All four fold sets are observable at Woodall Shoals on the Chattooga River (Figure 11).
EARLY FOLDS (F1 and F2). The first folds (F1) are represented by isoclinal recumbent passive flow folds. These are most easily recognized on the mesoscopic scale where they have been refolded by more upright flowage folds (Figure 12).
Axial orientation of the F1 folds varies from east-west to northwest. These folds probably verge westward or northward. Sense of shear
25

Figure 11. A: Flexu~al flow Fz fold at Hoodall_ ~hoals on the Cltattooga
RlVer (Ra1ny Mounta1n Quadrangle). ffns fold appears to
plunge in two different directions. R : 1 L,oclines are present as intrafolial folds in the nose of this foid (t; 1eft of hammer).
26

Figure 12.

An F1 axia

isoclinal surfaces,

fold refolded by at Holcomb Creek

FF2alflosldosn

with more upright Rabun Bald Quad-

rangle.

27

on most mesoscopic F1 folds is westward or northward. On some, however, it is southeastward. Macroscopic F1 folds are represented by the basement antiforms and syniforms on the Tallulah Falls Dome and the large refolded isocline east of Clayton and north of the Dome (Figure 2). The macroscopic interference pattern northeast of the Dome is produced by refolding of F1 by F2 folds then some modification by F3.
LATE FOLDS (F3 and F4 )~ The later sets of folds (F3 and F4), which are
present in this area were produced after the temperatures of the rocks dropped below the temperatures necessary for metamorphism to occur. These folds are frequently seen as gentle warps and dome and basin interference folds (Figure 13). The Tallulah Falls Dome is probably an F4 X F3 interference structure which is superimposed upon earlier F1 and F2 structures.
Crenulation cleavage in schists is also thought to be associated with the F3 episode. The cleavage surfaces generally dip moderately to steeply southeast indicating a northwest vergence. The F3 flexural slip fold axial surfaces are likewise inclined moderately to steeply to the southeast. This coincident orientation and lack of refolding of the crenulation cleavage by northeast-trending flexural slip folds led to the conclusion that they are part of the same deformational episode. F4 folds fold F3 mesoscopic crinkles on the macroscopic scale. This is shown by the consistent southwest plunge of the
28

Figure 13. Dome and basin structures produced by interference of

F(R3 aainnyd

F4 folds Mountain

at Woodall Shoals Quadrangle).

on

the

Chattooga

River

29

crenulation cleavage crinkles on the southwest flank of the Dome and the northeast plunge of crinkle axes on the north and northeast flank.
FAULTS
Relatively few faults have been mapped in this area. One small fault, which has a northwest strike and strike-slip dominated oblique slip movement, occurs in the area of Rabun Bald (Figure 2). Its offset is on the order of hundreds of meters and is traceable for no more than 2-3 kilometers.
Speculation On The Timing Of Deformational Events
The F1 folds are thought to be pre- or synmetamorphic features. If so, and if Butlers (1972) estimate of an Ordovician-Silurian (Taconic) metamorphism for the Blue Ridge is correct, then these folds could have formed anytime from the Cambrian to the Silurian.
The F2 folds are considered to be post-metamorphic features but the temperature and confining pressures were probably generated no earlier than the Latest Ordovician or Silurian and no later than the Devonian.
F3 and F4 folds are reasonably established as late structures. It is likely that they could be Late Paleozoic features associated with movement and emplacement of the Blue Ridge thrust sheet. The Rabun Bald fault is likewise a late feature.
30

LINEAMENTS
Several topographic lineaments cross the area mapped in northeast Georgia. These are all oriented nearly east-west and each is several kilometers in length (Figure 2).
The most prominent of these lineaments consists of the valleys of Laurel Creek, Warwoman Creek, Timpson Creek and two aligned arms of Lake Burton. This lineament is here named the Warwoman lineament (Figure 2). It is traceable westward 50 kilometers from its eastern end and has been considered to be an eastward extension of the Dahlonea fault on some tectonic maps (see for example Reed, 1970). This is a logical extension of the known extent of the fault since the lineament appears to line up with the fault trace to the west. However, in the area east of Lake Burton that has been mapped in detail, contacts cross the lineament without being offset. Moreover, a siliceous mylonite body is exposed along the lineament at one locality along U.S. 76 west of Clay:on. This material is considered to be very late in terms of its time of formation perhaps post-Paleozoic. Similar lack of displacement of contacts occurs other bodies of silicified microbreccia mapped in the Inner Piedmont by myself indicating very little displacement on these features. Jf the Dahlonega fault is a very late feature, perhaps this is the distal end of it. I prefer to not connect the two features.
Other smaller lineaments with an almost east-west trend occur south of the Warwoman lineament in this area. The most prominent of these is responsible for the straight north shore of parts of Lake Rabun.
31

Siliceous microbreccia occurs along portions of these lineaments.
DISCUSSION AND SYNTHESIS
The stratigraphic section in northeast Georgia has at its base a group of plutonic gneisses upon which the younger Tallulah Falls Formation was deposited. The boundary separating the basement from the cover rocks is therefore a nonconformity. It is also a surface of some relief since the Graywacke-Schist-Amphibolite Member of the Tallulah Falls Formation is discontinuous in some areas but continuous in others. This boundary is likely to be a disconformity as well.
The basement gneisses occupy the axial zones of F1 anticlinal structures. The narrowing and widening of the outcrop belts of Wiley gneiss on the east side of the Tallulah Falls Dome is topographically expressed as narrowing on highs and widening in the creek valleys (Figure 2). This is perhaps due to the topograpic surface residing very close to the updip limit of Wiley gneiss in these folds. This type of outcrop pattern was not noted in other areas with any of the other units.
The belts of Rabun gneiss around the flanks of the Tallulah Falls Dome south of the main body of Rabun gneiss occur in anticlinal F1 axial zones as well. The outcrop pattern and structure interpreted in the area around Tiger Mountain implies that major parts or even all of the large body of Rabun gneiss to the north is not rooted but is part of an al-
32

lochthonous mass brought into its present position by folding (see Hatcher, 1973, Figure 6).
The various units of the Tallulah Falls Formation correspond to units in Higgins (1966) Sandy Springs sequence. His gneiss-schist amphibolite unit corresponds to the Graywacke-Schist Amphibolite Member of the Tallulah Falls Formation. Higgins, (1966, p. 20) interpreted the contact between his lower unit and the lower quartzite to be an unconformity. The large variation in thickness of this unit in the Tallulah Falls Dome area could explained by an unconformity on top of the unit. Relief on the basement unconformity below causing nondepostition has been used here to explain this but an unconformity above could equally well explain it.
The lower quartzite unit of the Sandy Springs sequence is present in northeast Georgia nad northwestern South Carolina but is not persistent enough to serve as a marker horizon. The aluminous schist unit corresponds to the Garnet-Aluminous-Schist Member of the Tallulah Falls Formation.
Higgins upper quartzite may correspond to the Quartzite-Schist Member and the Graywacke-Schist Member could either be missing or a facies equivalent of the upper quartzite unit. The sequence described by Crawford and Medlin (1974) appears inverted when compared to the sequence in northeast Georgia, but the rocks and units are essentially the same.
The rocks of the Coweeta group occupy the axial portion of a large
33

syncline, the Coweeta syncline, whose northeast terminus appears to be just southeast of Franklin, North Carolina. The rock units contained therein are structurally higher and likely stratigraphically younger as well. If the Tallulah Falls Formation rocks are Late Precambrian, as previously suggested (Hatcher, 1971, 1973), the Coweeta group could also be of Late Precambrian or perhaps Early Paleozoic age. The contact between the Coweeta group and the underlying Tallulah Falls Formation does not appear to be an unconformity. However, the Persimmon Creek gneiss is an anomalous unit in the section. Its distinctly igneous character seems to require it to be intrusive. Yet it is in precisely the same stratigraphic position for many square kilometers. Moreover, it is intercalated with graywacke and schist in part of the unit. Could it be a felsic volcanic whose fine grain size favored more cQmplete recrystallization during metamorphism?
Due to their stratigraphic and structural position, the rocks of the Coweeta syncline appear to be the best candidates for Murphy belt equivalents in the eastern Blue Ridge. Also, their symmetry of position relative to the Grandfather Mountain window, as well as the occurrence in this group of certain almost unique lithologic types, such as the pinstripe lithology, there is a chance that these rocks may be a southwestward lithologic and sequential if not time equivalent of the Alligator
34

Back formation of Rankin and others (1973). The top and base of the Tallulah Falls Formation have been mapped
in this area. Yet to say more than that the thickness of this unit is on the order of a thousand meters or more would make the estimate meaningless despite the fact that graded beds are present in some areas (see Hatcher, 1971, Figure 20) and indicate tops at that point. However, isoclinal folding within the rock body and other means of tectonic thickening and thinning prevent accurate estimates of thickness of this or other units in this area.
ACKNOWLEDGEMENTS
The initial reconnaissance study in the area was supported by the Georgia Geological Survey. It was during the reconnaissance study that the stratigraphy of the Tallulah Falls Formation was broken down. The detailed study in Georgia has been supported by National Science Foundation Grant GA-20321. Continuation of the detailed work into North Carolina is being supported by the North Carolina Department of Natural and Economic Resources. The work in South Carolina has been supported by National Science Foundation Grant GA-1409 and the South Carolina Geological Survey.
35

Field assistants J. E. Wright, Jr., D. H. Petree and particularly L. L. Acker have made important contributions to this portion of the study. Acker is responsible for detailed 1:12,000 mapping of the Rabun Bald and Dillard Quadrangles and for r.ecognition and delineation of important facets of the stratigraphic order in this area.
Critical review by B. J. oconnor and editing by Lynda Stafford resulted in considerable improvement of the manuscript. Comments by J. B. Murray have also been helpful and are equally appreciated. However, I remain responsible for all errors and misinterpretations .
. 36

REFERENCES CITED
Billings, M. P., 1950, Stratigraphy and the study of Metamorphic rocks: Geol. Soc. America Bull., v. 61., p. 435-448.
Butler, J. R., 1972, Age of Paleozoic regional metamorphism in the Carolinas, Georgia and Tennessee southern Appalachians: Am. Jour. Sci., v. 272, p. 319-333.
Crawford, T. J., and Medlin, J. H., 1974, Brevard fault zone in western Georgia and eastern Alabama: Geol. Soc. America Southeastern Sect. Mtg. Field Trip Guidebook, Georgia Geol. Survey Guidebook 12, p. l-11-67.
Galpin, S. L., 1915, The feldspar and mica deposits of Georgia: Georgia Geol. Survey Bull. 53, 190 p.
Giles, R. T., 1966, Petrography and petrology of the Rabun Bald area, Georgia-North Carolina [M. S. thesis]: Athens, Univ. Georgia, 7lp.
Hadley, J. B., and Nelson, A. E., 1971, Geologic map of the Knoxville quadrangle, North Carolina, Tennessee and South Carolina: U. S. Geol. Survey Misc. Geol. Inv. Map I-654, scale l/250,000.
Hartley, M. E., III, 1973, Ultramafic and related rocks in the vicinity of Lake Chatuge: Georgia Geol. Survey Bull. 85, 61 p.
Hartley, M. E., III, and Penley, H. M., 1974, The Lake Chatuge sill outlining the Brasstown antiform: Georgia Geol. Society Guidebook 13' 27 p.
Hatcher, R. D., Jr., 1971, Geology of Rabun and Habersham Counties, Georgia: a reconnaissance study: Georgia Geol. Survey Bull. 83, 48 p.
------------ - -- 1973, Basement versus cover rocks in the Blue Ridge of northeast Georgia, northwestern South Carolina and adjacent North Carolina: Am. Jour. Sci., v. 273, p. 671-685.
-- ------------- 1974, Brevard zone tectonics along the Gecrgia-South Carolina border: Geol. Soc. America Abst. with Programs (Southeastern Section), v. 6, p. 362.
Higgins, M. W., 1966, The geology of the Brevard lineament near Atlanta, Georgia: Georgia Geol. Survey Bull. 77, 49 p.
37

Hurst, V. J., and Crawford, T. J., 1964, Exploration for mineral deposits in Habersham County, Georgia: U. S. Dept. Comm. Area Redevel. Adm., 180 p.
Jones, L. M., Hartley, M. E., III, and Walker, R. L., 1973, Strontium isotope compostion of Apline-tupe ultramafic rocks in the Lake Chatuge District, Georgia-North Carolina: Contrib. Mineralogy and Petrology, v. 38, p. 321-327.
Keith, Arthur, 1907, Description of the Pisgah quadrangle (North Carolina-South Carolina): U. S. Geol. Survey Geol. Atlas Folio 148, 8 p.
Lester, J. G., and Allen, A. T., 1950, Diabase of the Georgia Piedmont: Geol. Soc. America Bull., v. 61, p. 1217-1224.
Livingston, J. L., and McKniff, J. M., 1967, Tallulah Falls Dome, northeastern Georgia: another window? [abs.]: Geol. Soc. America Spec. Paper 115, p. 485.
May, P. R., 1971, Pattern of Triassic-Jurassic diabase dikes around the North Atlantic in the context of predrift position of the continents: Geol. Soc. America Bull., v. 82, p. 1285-1292.
Pruitt, R. G., Jr., 1952, The Brevard zone of northeast Georgia [M. S. thesis]: Atlanta, Emory Univ., 71 p.
Rankin, D. W., Espenshade, G. H., and Shaw, K. W., 1973, Stratigraphy and structure of the metamorphic belt in northwestern North Carolina and southwestern Virginia: a study from the Blue Ridge across the Brevard fault zone to the Sauratown Mountains anticlinorium: Am. Jour. Sci., Cooper Vol., v. 273-A, p. 1-40.
Reed, J. C., Jr., 1970, Tectonic map of the central and southern Appalachians, in, Fisher, G. W., Pettijohn, F.J., Reed, J. C., Jr., and Weaver. L.~. eds., Studies in Appalachian geology: central and southern: New York, Intersclence, p. 438.
Teague, K. H., and Furcron, A. S., 1948, Geology and mineral resources of Rabun and Habersham Counties, Georgia: Georgia Geol. Survey, scale l/125,000.
Weller, J. M., 1947, Relations of the invertebrate paleontologist to geology: Jour. Paleontology, v. 21, p. 570-575.
38

ROAD LOG FOR DAY 1, GEORGIA GEOLOGICAL SOCIETY MEETING OCTOBER 26~ 1974 A generalized geologic map showing the stops is contained in Figure 14. 8:00A.M. - Depart Heart of Rabun Motel, Clayton, Georgia, within the Warwoman Lineament.

CUMULATIVE MILEAGE 00.0 0.3 0.4 0.6
0.9 to 2.8
3. 1 3.2

DIFFERENTIAL MILEAGE 0.00 0.3
0. 1 0.2
0.3 to 2.2 0.3
0. 1

Depart Heart of Rabun Motel, head south on U.S. 441. Grassed exposure of Tallulah Falls Formation. U.S. 76 turns left; continue on 441. Exposures of Rabun gneiss saprolite behind shopping center to right. Contact with Tallulah Falls Formation rocks visible on south end of cut. Note the dip here is north or northeast. Weathered Tallulah Falls Formation rocks in grassed and ungrassed cuts. Stekoa (Big) Creek - one of the few badly polluted streams in this area. Weathered Tallulah Falls Formation rocks. Some epidote - rich amphibolite is present here.

39

3.3 3.5 to 3.6

0.1 0.2 to 0.3

Road turns right to Tiger. Weathered Tallulah Falls rocks just up road. Note north dip here also. Draw through which the Garnet-Aluminous Schist Member of the Tallulah Falls Formation crosses the highway. The hillside to the west of the highway is a dipslope containing abundant small garnets and kyanite crystals.

40

3500'

s.J

.,.-'-" .../s-.---

.'> ~

......\ ."'~

\..,

> r.:;
-...._./

~ _.
3445'

)

-7

tf

_ .:;.

,) ./

rr
\.{_
,,
8330'

2

0

2 3 4 5 Miles

2 I 0 I 2 3 4 5 Kilometers

Figure 14. Gen~ralized geoiogic map of the Blue Ridge of northeast Georgia and adjacent
North ar,d South Caroli!1a showing field trip stops. w-Wiley gneiss. r-Rabun gneiss. tf-To.llu1ah Falls Fonnation undivided. tq-Quartzite-Schis~ Member. cgCoweeta group. t-trondhjemite. d-diabase.

3.7

0.1

STOP 1. Cut in fresh rock contains the

Graywacke-Schist-Amphibolite Member

(metagraywacke, amphibolite layers and

boudins, schist interlayers, sparce

kyanite crystals in some schist inter-

layers). Grassed area is Rabun gneiss

(light felsic gneiss). The contact

here is sharp and does not appear

gradational, although the gneiss just

below the contact appears more quartz-

rich (paleosaprolite?). F2 folds, likely rotated by F3 folding, are present on the east side of the highway. Close

inspection of some of the garnets in

the folds will show that they have

been rotated. Please -do-no-t collect ~of these folds. Leave them for

others to enjoy in their present

position (The Georgia Highway Depart-

ment may soon find a way to grass bare

rock. If so, the folds will be removed

then). Foliation strikes about N50W

here, dips about 20NE.

42

3.9
4. 1
4.3 to 4.4
4.5 to 4.8 4.9 5.0 to 5.1 5.4

0.2
0.2
0.2 to 0.3
0.1 to 0.4 0. 1 0.1 to 0.2 0.3

Contact of Rabun gneiss with Graywacke-

Schist-Amphibolite Member on south side

of body.

Garnet-Aluminous Schist Member crosses

highway. It is not easy to find kyanite

crystals here.

Dirt road turns right. Grassed cuts

on highway are in Graywacke-Schist Mem-

ber. Can see red soils on top of cuts.

Grassed cuts in Quartzite-Schist Member.

County road crossing.

Grassed cuts in Quartzite-Schist Member.

STOP 2. Fresh exposure of Quartzite-Schist

Member. Stretched quartz pebbles and

feldspar augen (?) are present. Some

beds appear graded. Which side is up?

The heavy mineral suite present here is

sphene, zircon, tourmaline, and magnetite.

The modal composition of a sample of this

material is:

Quartz

76.5%

Biotite

4.3

Muscovite

4.4

Plagioclase

8.4

43

Microcline

4.3

Tourmaline

0.1

Sphene

0.9

Opaque

0.2

Chlorite

0.1

Garnet

0.1

Zircon

0.1

Carbonate

0.6 100.0%

5.5

0.1

Covered interval where the Graywacke-

Schist Member crosses the highway.

5.7

0.2

STOP 3. Fresh exposure of Wiley gneiss.

Two foliationsappear to be present

here. Is one a basement foliation

cut by s1 or is this s1 cut by s2?
At the south end of this cut is the

contact with the Graywacke-Schist

Member. On a trail turning left off

the highway is some of the garnet-

amphibole - epidote quartzite which

occurs next to the Wiley gneiss con-

tact in this area. Turn around, pro-

ceed north again on U.S. 441 to road to

Tiger.

44

8.4 8.5 to 8.6
8.8 to 9.1 9.2

2.7 0.1 to 0.2
0.2 to 0.5 0.1

Turn west on road to Tiger. Weathered Graywacke-Schist-Amphibolite Member. Can observe weathered folded amphibolite and graywacke here. Cuts of weathered Graywacke-SchistAmphibolite Member. Cut in_weathered Graywacke-SchistAmphibolite Member. Good crosssection view of Tiger Mountain from here Figu~e 15. Rocks on bluffs are Tallulah Falls Formation rocks. On the crest of the mountain is Rabun gneiss underlain by Garnet-Aluminous Schist Member rocks, then the bluffforming Graywacke-Schist-Amphibolite Member rocks. These are underlain by Rabun gneiss .on the 1ower s1opes.

45

s
.s:ll: .........:~.. - 5........e.+
~el.~d
6-r....ywH~- ~ .. "'~' TA , f Jd:u.l:h..
)/e/111/ber

Figure 15. Schematic Cross-section of Tiger Mountain.

9.5

0.3

Elementary school on left. Road turns

right.

9.7

0.2

Intersection (old U.S. 441) in down-

town Tiger. Continue straight ahead

after stop.

46

10.0

0.3

10. 1

o. 1

10.3 to 10.8 11.3 to 11.8 12.0 12. 1 to 12.7

0.2 to 0.7 0. 5 to 1.0 0.2 0.1 to 0.6

12.9 to 13.4 0.2 to 0.7

13.8

0.4

14.2

0.4

Tallulah Falls Formation soil on left. Road to right. Big white farmhouse across road and view of Tiger Mountain behind. Cuts in weathered Tallulah Falls rocks. Cuts in weathered, Rabun gneiss. Liberty Church on right. Cuts in soils and saprolite of Tallulah Falls metagraywackes. The large mountain to the west is Glassy Mountain (3440 +feet). Cuts in the Graywacke-Schist-Amphibolite Member. Driveway turns left with mailbox with W. L. Crunkleton written on it. Turn left here. House on Right. STOP 4. Walk down the hill through the gate and into the pasture. Continue walking southward to exposures of schist on the left. Notice the amount of kyanite concentrated on the surface. This is the GarnetAluminous Schist Member of the Tallulah Falls Formation. There fewer garnets

47

18.5

4.3

19.8

1.3

22.9

3.1

23.1

0.2

23.3

0.2

23.8 to 24.1 0.5 to 0.8

24.4

0.3

24.5 to 25.3 0.1 to 0.9

25.2

0.8

here than normal and the kyanite is coarser. This might rate as commercial kyanite. Return to the bus. Return to paved road and turn right, continue to 4-way stop in Tiger. Intersection in downtown Tiger. Continue straight back to U.S. 441. U.S. 441. Turn left. Proceed northward along highway. Heart of Rabun Motel. Continue northward. Grassed cuts in Rabun gneiss. Grassed cuts in the Graywacke-SchistAmphibolite Member of the Tallulah Falls Formation. Tallulah Falls Formation rocks and grassed saprolite on left. Old U.S. 441 comes in from Clayton on left. Weathered cuts of Tallulah Falls Formation rocks (likely all is Graywacke-SchistAmphibolite Member). Mountain City, Georgia city limits.

48

25.7

0.5

25.8 25.9 26.1 to 26.3

o. 1
0.1 0.2 to 0.4

26.4

0. 1

26.5 26.6 26.7 26.8 to 27.0 27.1 27.2 27.3 to 27.8 27.9 to 28.0 28. 1

0.1
0. 1
0.1 0.1 to 0.3
0. 1
0.1 0.1 to 0.6 0.1 to 0.2
o. 1

28.2

a. 1

28.3

0.1

28.6

0.3

Sign says 11 Black Rock Mountain State Park. 11 Turn left (west). Methodist Church on right. Cut in weathered Tallulah Falls rocks. Cuts in weathered Tallulah Falls rocks, the first is capped by terrace gravel. Tallulah Falls saprolite, some amphibolite boudins are present. Co 11 uvi urn. Rabun gneiss boulders on right. Black Rock Mountain State Park sign.
Rabun gneiss saprolite &soil.
Tallulah Falls saprolite. State Park Gate. Rabun gneiss saprolite. Rabun gneiss saprolite and soils. Tallulah Falls rocks, saprolite. Road to campground turns left. Continue on paved road to right. Rabun gneiss saprolite exposed. Rabun gneiss soil. Tallulah Falls Formation. Rabun gneiss.

49

28.8

0.2

28.9

0. 1

Tallulah Falls Formation. STOP 5. Blackrock Mountain (Elevation: 3440 + feet) Lunch Stop. This stop affords an interesting combination of geomorphic features and a look at some bedrock structures and the Rabun gneiss Tallulah Falls contact. The Warwoman Lineament, the town of Clayton and the north dipping flank of the Tallulah Falls Dome are the most obvious features to be seen. Tiger Mountain can be seen slightly to the southwest. The mountains to the east are part of the range crested by Rabun Bald (not visible). Partially developed Screamer Mountain just east of Clayton is also quite visible. The Rabun gneiss here is quite folded. F1 (?) and F2 mesoscopic folds are visible. One or more pieces of epidote-rich quartzite, which is common just above the contact, are caught up in the basement gneiss. The contact is actually above the rock

50

32.1

3.2

32.3

0.2

32.6

0.3

33.5

0.9

33.6

0. l

33.7

0. 1

pavement exposure below the ditch just b.elow the parking lot. Amphibolite can be seen in the Tallulah Falls Formation just above the contact. Return to U.S. 441. U.S. 441 intersection in Mountain City. Turn left (north). Eastern Continental Divide (Elev. 2165 feet). Rabun gneiss saprolite. Turn right on county road. York House ~ince 1896) advertised here. Notice that we are entering a large open valley. This is the headwaters area of the Little Tennessee River, which drains northward into North Carolina. This valley was swampland when originally settled. The swamps were drained and the rich alluvium makes up most of the farmland in Rabun County. Bridge built in 1938. Rabun gneiss soil.

51

34.0

0.3

34.5

0.5

34.6

0. 1

35.5

0.9

35.9

0.4

36.0

0. 1

36. 1

0. 1

36.2

0.1

36.8 to 36.9 0.6 to 0.7

37.4

0.5

37.8

0.4

York House. Rabun gneiss soil just up road. Rabun gneiss (porphyroblastic) saprolite containing folded garnet-quartzite of the basal part of the Tallulah Falls Formation. Porphyroblastic Rabun gneiss saprolite. Intersection. Turn right. Porphyroblastic Rabun gneiss exposures on right. Creek crossing. Porphyroblastic Rabun gneiss saprolite. Porphyroblastic Rabun gneiss saprolite. Can see high mountains to the west in North Carolina. The highest is Ridgepole Mountain and the next (just to the right) is Pickens Nose. Porphyroblastic Rabun gneiss soil. Turn right toward quarry. Thick soil of porphyroblastic Rabun gneiss on right. STOP 6. Kelly Quarry 16). Exposed here is the porphyroblastic phase of the Rabun gneiss. Foliation is not immediately obvious but can be seen in biotite rich

52

Figure 16. Porphyroblastic Rabun gneiss exposed in Kelly Quarry. Late pegmatite dikes are distinct here.
zones. The coarse porphyroblasts are microcline. Pegmatite re abundant and the late generation provides the most obvious oriented structures in an
53

38.2

0.4

38.3 to 38.9 0.1 to 0.7

39.0

o. 1

39.3

0.3

otherwise homogeneous rock body. To the southwest the porphyroblasts become strongly aligned and more elongate parallel to b. This mass could represent remobilized basement which was emplaced without moving very far as a pre- or synmetamorphic pluton. Attempts to date these rocks using Rb-Sr have been unsuccessful to date because the Rb concentration is too low. NOTE: STAY AWAY FROM THE QUARRY FACE, BENCHES AND ANY UNSTABLE SLOP-ES. THE OWNER HAS DISCLAIMED ANY LIABILITY FOR INJURIES. Return to paved road. Paved road. Turn right (north). Exposures of porphyroblastic Rabun gneiss soil and saprolite. In several, porphyroblasts can be seen weathering out into the soil. Porphroblastic Rabun gneiss saprolite overlain by terrace gravel. Intersection with Georgia State Highway 246. Turn left (west). Eastatoa Falls

54

39.4

0.1

39.9

0.5

40.1

0.2

40.2

0.1

40.3

o. 1

40.5

0.2

41.1

0.6

41.3

0.2

41.5

0.2

41.7

0.2

41.9

0.2

42.4 to 42.6 42.6 to 42.7 42.9 to 43.1

0.5 to 0.7 0.2 to 0.3 0.2 to 0.4

on Mud Creek to the right and exfoliation domes on the higher mountainsides. Porphyroblastic Rabun gneiss. Tallulah Falls Formation rocks and saprolite. Cross Little Tennessee River. U.S. 441. Turn left (south). Folded Tallulah Falls Formation rocks to the right. Dillard city limits. Folded Tallulah Falls Formation rocks on right. Rabun gneiss boulders. Betty Creek Road. Turn right. Rabun gneiss soil~ Tallulah Falls Formation soil. View of Ridgepole Mountain to west. Tallulah Falls Formation saprolite (folds) and terrace gravel on top. Tallulah Falls Formation rocks. Terraces. Tallulah Falls Formation soil.

55

43.6

0.5

43.7 to 44.2 0.1 to 0.6

44.6

0.2

44.8

0.2

45.0

0.2

STOP 7. Tallulah Falls Formation rocks. Metagraywacke, schist and amphibolite are all present here. The folds here are likely F2 folds. The unit has been divided in this area into upper and lewer members based upon the presence or absence of amphibolite. If the subdivision based upon this criterion is correct, as it seems to be, the Garnet-Aluminous Schist Member is absent in the area between the outcrop belt of belt of Rabun gneiss and the Coweeta sycline. Continue westward. Tallulah Falls Formation rocks. West dipping Tallulah Falls Formation rocks. To the south is Scaly Knob and Ledford Mountain. Straight ahead (northwest) is Ridgepole Mountain. Tallulah Falls Formation rocks and saprolite on right. View up Betty Creek valley straight

56

45.1

0.1

45 . 2 to 45. 6 0. 1 to 0. 5

45.7

0. 1

45.8

0.1

45.9

0. 1

50.0

0~ 1

ahead. To the left of the valley is Ridgepole Mountain. To the right is Pickens Nose. Both mountains are i rr North Care1ina. Turn left onto Patterson Gap Road. Cross Betty Creek. Tallulah Falls Formation rocks expo~~d in road and i~ cuts. Trondhjemite dike exposed in road and cut'to right. Patterson Creek crossing (bridge). Leave busses here and walk up road. Persimmon Creek gneiss. STOP 8. Persimmon ereek gneiss and trondhjemite dike. The intrusive contact is visible in the ditch. Note the igneous-looking character of the Persimmon Creek gneiss on the road. However, that just beyond the fence contains some interlayered schist and metagraywacke. What is. its origin? The trondhjemite here looks the same

57

51.1

1.1

54.7

3.6

54.9

0.2

55.3

0.4

61.8

6.5

throughout this area. Seldom does it contain a higher mafic content, but it commonly contains some mafics. Return to bus then to Betty Creek Road. Betty Creek Road - turn right (east}. U.S. 441 intersection in Dillard. Turn right (south}. Road to Dillard House Restaurant, a well known hog down place. Continue south on U.S. 441. Cross Betty Creek. Rabun Gap- Nacoochee School. Home of Foxfire books. Heart of Rabun Motel. End of trip for Day 1.

58

EXPLANATION FOR THE PRELIMINARY GEOLOGIC MAP OF THE BLUE RIDGE OF NORTHEAST GEORGIA, AND ADJACENT NORTH AND SOUTH CAROLINA
MESOZOIC ROCKS d - diabase
LATE PALEOZOIC ROCKS t - trondhjemite
EARLY PALEOZOIC {?} ROCKS urn - ultramafic rocks p - pegmatite
LATE PRECAMBRIAN {?} - EARLY PALEOZOIC {?} ROCKS Coweeta Group rp - Ridgepole Mountain formation cr - Coleman River formation pc - Persimmon Creek Gneiss
TALLULAH FALLS FORMATION tf- undivided Tallulah Falls rocks m - migmatized tq - Quartzite-Schist Member tg - Graywacke-Schist Member a - Garnet-Aluminous Schist Member or garnet schist marker horizon. tl - Graywacke-Schist-Amphibolite Member y- garnet-amphibole-epidote calc-silicate quartzite marker. e - epidote-rich quartzite marker
59

EARLIER PRECAMBRIAN (?) ROCKS r - Rabun gneiss w - Wiley gneiss
Thrust fault or tectonic slide
Transcurrent fault
Topographic Lineament
60

, -NO-RTH- -CA-RO.. LIN..-A - -

GEORGIA

i
o.

u 0

u \z

(f) :>

tr z~i\<m{

1-

FIGURE 2

. ~. . . . . .. ........:......\ .;....'\;......................... ..
. . (

i.. ~4/j . .

!1

ft.4l.ii,~"S1. t. _'.~u..t.4v/1'7cc'oo".,.i.j::..._.'-



~ ,

.r.

/
/

.

.

.

\ \

83151
PRELIMINARY GEOLOGIC MAP 0 1
THE BLUE RIDGE OF NORTHEAST GEOF
AND ADJACENT NORTH AND SOUT~ CAROLINA

Robert D. Hatcher, Jr. and Louis L. Acker ASSISTED BY: James E. Wright, Jr. D. Hoke Petree Steven L. Wood 1968-1974
~t of the geology in the southwest corner of the mop is modified from Hurst and Craw ford (1964).

By
Robert D. Hatcher, Jr. 1974
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