Multiple folding in the Snellville, Luxomni, Suwanee, and Madras quadrangles in the Georgia Piedmont [Mar. 1980]

MULTIPLE FOLDING IN THE SNELLVILLE, LUXOMNI, SUWANEE,
AND MADRAS QUADRANGLES IN THE GEORGIA PIEDMONT
by Robert L. Atkins, Robert E. Dooley, and Stephen W. Kline
OPEN-FILE REPORT 80-6
I i I
In cooperation with the U.S. Geological Survey Grant No. 14-08-0001-G-568
GEORGIA DEPARTMENT OF NATURAL RESOURCES ENVIRONMENTAL PROTECTION DIVISION GEORGIA GEOLOGIC SURVEY
March 1980

MULTIPLE FOLDING IN THE SNELLVILLE, LUXOMNI, SUWANEE,
AND MADRAS QUADRANGLES IN THE GEORGIA PIEDMONT
by Robert L. Atkins, Robert E. Dooley, and Stephen W. Kline
OPEN-FILE REPORT 80-6
In cooperation with the U.S. Geological Survey Grant No. 14-08-0001-G-568
GEORGIA DEPARTMENT OF NATURAL RESOURCES ENVIRONMENTAL PROTECTION DIVISION GEORGIA GEOLOGIC SURVEY
March 1980

CONTENTS
ABSTRACT . . INTRODUCTION
PURPOSE PREVIOUS WORK . METHODS OF INVESTIGATION. ACKNOWLEDGEMENTS . . LITHOLOGIC UNITS . ALLUVIUM. . . . . . IGNEOUS ROCKS .
Pegmatite. Stone Mountain Granite Aplite . . . . . . . . Diabase Altered Ultramafics. METAMORPHIC ROCKS . . . . Sandy Springs Group.
Factory Shoals Formation. Chattahoochee Palisades Quartzite Powers Ferry Formation. . . . . Quartzite, Mica Schist-Amphibolite Quartzite. . . . . . . . . Biotite Gneiss-Amphibolite Muscovite Biotite Gneiss . Granite Gneiss-Amphibolite Mica Quartz Schist Member . Lithonia Gneiss. CATCLASTIC ROCKS Mylonite .. Phyllonite Schist .. Phyllonitized Gneiss . Graphitic Gneiss . . Button Schist-Phyllonite STRUCTURES . . . . . . . . . COMPOSITIONAL LAYERING. SCHISTOSITY LINEATIONS. JOINTS. . . FOLDS . . . . UNCONFORMITY FAULT . . . . STONE MOUNTAIN PLUTON . DIABASE . . HYDROGEOLOGY . . . ECONOMIC RESOURCES . CRUSHED STONE BUILDING STONE SAND . . . .
ii

PAGE
1 4
5
5 6
6 6 7 7 7 7 9 11 .11 11 13 13 . 12
14 14
15 . . 15
16 . . 17 . . . 17
. 17 . . . 18
20 20
20 . 21 . 21 21
22 . 22 . 22 . 23 . 23 . 31 . 36 . . 37
37 . . . 37
39 39 40 40

POTENTIAL GEOLOGIC PROBLEMS

40

PLANAR STRUCTURES

40

LITHOLOGIES

41

Shallow Soil Horizons

Corrosion Characteristics of Graphitic Soils

ADDITIONAL STUDIES

41

SUMMARY OF CONCLUSION

42

APPENDIX

A-1

GEOLOGY OF MADRAS QUADRANGLE

A-1

LIST OF MAPS
Map 1 - Fold Generations of the Stone Mountain Area Map 2 - Geologic Map of the Snellville Quadrangle Map 3 - Geologic Map of the Luxomni Quadrangle Map 4 - Geologic Map of the Suwanee Quadrangle Map 5 - Geologic Map of Madras Quadrangle

32
IN POCKET IN POCKET IN POCKET IN POCKET

LIST OF FIGURES
1. Location map of study area, Atlanta, and Chattahoochee River 2. Location map of study area excluding Madras Quadrangie 3. Explanation and stratigraphic relations of the lithologies in the
study area 4. Modal analysis of Stone Mountain Granite 5. Modal analysis of Quartz Mica Schist from Mica Schist-Amphibolite Unit . 6. Modal analysis of Micaceous Quartzite Unit 7. Modal analysis of Biotite Gneiss from Biotite Gneiss-Amphibolite Unit 8. Modal analysis of Lithonia Gneiss 9. Equal area projection of poles to foliations in the Suwanee Quadrangle 10. Equal area projection of poles to foliations in the Luxomni Quadrangle 11. Equal area projection of poles to foliation in the Snellville Quadrangle 12. Lineations in the Snellville Quadrangle 13. Lineations in the Luxomni Quadrangle 14. Equal area projection of poles to joints in the Snellville Quadrangle 15. Equal area projection of poles to joints in the Luxomni Quadrangle 16. Equal area projection of poles to joints in the Suwanee Quadrangle 17. Equal area projection of poles to joints in the Stone Mountain Granite 18. Equal area projection of poles to axial planes in the Snellville Quadrangle 19. Equal area projection of poles to axial planes in the Luxomni Quadrangle 20. Buck Branch folds at Klondike, Georgia 21. Klondike folds at Klondike, Georgia 22. Opening warping folds of Scott Creek or Tara Generation 23. Ramsey Type I Interference Pattern in Snellville Quadrangle 24. Ramsey Type III Interference Pattern at Dekalb J. College, South Campus 25. Unconformity of Stockbridge, Georgia 26. Shearing along limbs of Klondike fold, Luxomni Quadrangle 27. Diabase outcrop near Snellville, Georgia

ill

APPENDIX A
THE GEOLOGY OF THE MADRAS QUADRANGLE
CONTENTS
APPENDIX INTRODUCTION . LITHOLOGIC UNITS
QUATERNARY ALLUVIUM IGNEOUS ROCKS .
Pegmatite Palmetto Granite METAMORPHIC ROCKS Amphibolite-Hornblende Gneiss Biotite Gneiss Diopside Biotite Gneiss, Biotite Gneiss Amphibolite Biotite Gneiss, Biotite Gneiss Mica Schist, Amphibolite Garnet Quartzite Biotite Gneiss, Amphibolite STRUCTURES LINEATIONS . JOINTS FOLDS FAULTS CONCLUSIONS STRUCTURES ECONOMIC RESOURCES GEOLOGIC HAZARDS .
LIST OF
FIGURES
2A. Diagrammatic description of lithologies in the Madras Quadrangle
3A. Poles perpendicular to foliation planes in the Madras Quadrangle .
4A. Poles perpendicular to joint planes in the Madras Quadrangle
TABLES
1. Modal analysis of the Palmetto Granite 2. Modal analysis of the garnet quartzite 3. Modal analysis of the biotite gneiss .

PAGE
A-1 A-1 A-1 A-1 A-3 A-3 A-3 A-3 A-4 A-5 A-5 A-5 A-6 A-7 A-7 A-7 A-8 A-8 A-10 A-10 A-10 A-10 A-10
A-2
A-9
A-9
A-12
A-13
A-14

iv

ABSTRACT
The structural geology of the Snellville, Luxomni, and Suwanee quadrangles which comprise an area of approximately 300 square kilometers (186 square miles) in portions of Dekalb, Forsyth, Fulton, Gwinnett, and Rockdale Counties was studied for this investigation. Particular emphasis was placed on evaluating the history of multiple phases (or generations) of folding. The quadrangles are almost entirely in the Piedmont Province southeast of the Brevard Zone. Portions of the Brevard Zone and the Piedmont northwest of the Brevard Zone are included in the Suwanee quadrangle. The Madras quadrangle, about 36 kilometers (25 miles) to the southwest of Atlanta, also was evaluated with the results presented in appendix A.
The rocks of these quadrangles have undergone a minimum of five episodes of folding, a period of erosion resulting in a major unconformity, perhaps as many as three intrusive events as well as a minimum of two separate movements involving the Brevard Zone. The interference patterns created by the superimposed folding result in distinctive map patterns. The five fold generations are named for the localities at which they are best exposed. From oldest to youngest, these fold generations are: Buck Branch, Klondike, Elijah Mountain, Scott Creek and Tara. The Buck Branch folds are typically tight to isoclinal, and are characterized by a recrystallized schistosity that parallels compositional layering except in the hinge zones where the schistosity is axial planar. The Buck Branch folds in turn are folded by the Klondike generation folds, which are typically recumbent to reclined folds with an axial plane schistosity. Elijah Mountain (northwest-trending folds) axial traces commonly are perpendicular to the earlier folds. Scott Creek (north-

south trending) and Tara (east-west trending) generations fold all previous folds generations. Both the Scott Creek and Tara fold generations generally are gentle to open folds characterized by a widely spaced, jointlike axial planar cleavage. All five fold generations are present in rocks that are stratigraphically beneath the unconformity; rocks above the unconformity exhibit only the last four.
Fifteen distinguishable rock units have been mapped in this threequadrangle area: The Sandy Springs Group, (Factory Shoals Formation, Chattahoochee Palisades Quartzite and Powers Ferry Formation), granite gneiss-amphibolite, biotite gneiss-amphibolite, epidote biotite granite gneiss, quartzite-mica schist-amphibolite, quartzite, button schistamphibolite, button schist phyllonite-mylonite, Lithonia Gneiss, Stone Mountain Granite, pegmatite dikes, diabase dikes, and alluvial deposits (figure 3).
Certain areas that are underlain by Lithonia Gneiss and Stone Mountain Granite have very shallow soil horizons. These areas have particular problems for landowners and real estate developers by creating difficulties in excavating building foundations. These areas also are generally unsuitable for sewage disposal septic tank methods because of the shallow soil horizon, so an alternate method of sewage disposal must be employed, such as the installation of sewer lines in a rural environment.
As the Metropolitan Atlanta area has grown, so has the demand for crushed aggregate. In the Snellville and Luxomni quadrangles the Lithonia gneiss is a source of crushed aggregate for use as road metal, paving, riprap, and concrete filler.
(2)

LOCATION MAP SHOWING STUDY AREAS, ATLANTA AND THE CHATTAHOOCHEE RIVER

LOCATION MAP OF STUDY AREA \ SUWANEE QUADRANGLE

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GEORGIA
Figure 1. Location map of study areas-Atlanta and Chattahoochee River.

BETHESDA

LUXOMNI QUADRANGLE

:o_.:X')IM~i

SNELLV18

ocE,TERV'CLE I SNELLVILLE QUADRANGLE
----... ",_':.-"<"P~-<o:~:o>~','>-~'~....

Figure 2. Location map of study area excluding the Madras Quadrangle.

INTRODUCTION
The Snellville, Luxomni, and Suwanee quadrangles are located east and northeast of Atlanta, Georgia, and include the cities of Snellville, Suwanee, Sugar Hill, and Buford, and the towns of Centerville and Luxomni (figure 2). These quadrangles encompass an area of approximately 300 square kilometers (62 square miles) and are bordered by 84 and 8407 1 30" west longitudes and 34 07' 30" and 33 45" north latitudes (figure 2). The Madras quadrangle encompasses an area of approximately 100 square kilometers (62 square miles) and is bordered by 8436 1 30" and 8445 1 west longitude and 3322'30 11 and 33"30 1 north latitude. The area lies almost entirely within the Piedmont Province southeast of the Brevard Zone; a small area of the Brevard Zone and the Piedmont northwest of the Brevard Zone occur in the Suwanee quadrangle. Two physiographic districts in the study area are distinguishable: the Winder Slope and the Gainesville Ridge (Clark and Zisa, 1976). The Winder Slope district consists of gently rolling topography varying from approximately 30 to 200 meters (100 to 700 feet) in elevation and is dissected by the headwater tributaries of major streams draining to the Atlantic Ocean and Gulf of Mexico. Numerous dome-shaped mountains occupy the rounded interstream divides. The Gainesville Ridge district consists of a series of low, parallel northeast-trending ridges of quartzite and gneiss ' separated by valleys underlain by phyllonites and schists. Elevation of the ridges varies from 480 meters (1600 feet) to about 210 meters (700 feet). The Chattahoochee River and its tributaries are controlled by these resistant ridges, forming a rectangular drainage pattern (Clark and Zisa, 1976).
(4)

Purpose Information is needed to assess the impact of metropolitan Atlanta's
growth on natural resources. As Atlanta continues to grow, a comprehensive understanding of the geologic regime will be required. The purpose of this investigation, therefore, was to:
1. Perform a detailed structural investigation of the study area. 2. Provide geologic background information that could be made
available to hydrologists, planners, and engineers. 3. Provide geologic information on the trend of rock strata
including potential mineral and rock occurrences such as granite and granite gneiss for crushed aggregate. 4. Outline areas of shallow soil horizons such as those over the Lithonia Gneiss in Rockdale, Gwinnett, and eastern Dekalb Counties. Previous Work Very little work has been done in the Georgia Piedmont, south of the Brevard Zone. Watson (1902) studied the granites and gneisses of the Georgia Piedmont. More recently, multiple folding in the Georgia Piedmont was recognized in the Ben Hill area by Cofer (1948) and in the Stone Mountain and Lithonia areas by Herrmann (1954). Folds in these areas were described as northeast-trending isoclinal folds and open northwest-trending cross folds. The petrology and mechanics of the intrusion of the Stone Mountain granite have been studied by Lester (1938), Herrmann (1954), Grant (1962) and Mohr (1965). Cofer (1948) studied the petrology and mechanics of intrusion of the Ben Hill Granite. The structure and mineralogy of ultramafic bodies in the Georgia Piedmont between the Brevard Zone and Towaliga Faults were studied by Prowell (1972). These investigations have included petrographic studies, chemical analyses, saprolite descriptions, and structural interpretations. The importance of structure and lithology to ground-water occurrence was stressed by Herrick and LeGrand (1949). Fullager (1971), Whitney (1976), (1977),

Dallmeyer (1978) and Dooley (1978) have dated the rocks of the study area. Methods of Investigation
Geologic mapping at a scale of 1:24,000 was conducted. Structural elements such as joints, foliations, axes, and axial planes were plotted on pi diagrams. Trends, plunges, and axial planes were plotted on a separate structural map (map 1) to evaluate whether one folding episode dominates over another within a given area. All the generations of folds have been described using the classification of Donath and Parker (1964). Shallow soil horizons are outlined from observations of pavement outcrops in the field and from studying orthophoto quadrangles. Acknowledgements
Partial support for this study came from the U.S.G.S. grant number 14-08-001-568. The writer is indebted to Ms. Lisa Joyce of West Georgia College, Ms. Pamela Bloss of the University of Georgia, and Mr. Stephen Kline of Georgia Tech. Ms. Joyce assisted in the field and in office compilation. Ms. Bloss described the petrology of the area. Mr. Kline mapped the northern half of the Suwanee quadrangle.
LITHOLOGIC UNITS
Rocks units were separated and defined on the basis of repeated common occurrence or association. Correlation of the lithologies in the Snellville, Luxomni, and Suwanee quadrangles are given in figure 3.
(6)

ALLUVIUM The youngest rock material in the area is alluvium, unconsolidated
recent clay and sand, which was mapped primarily on topographic evidence such as floodplains of existing streams. Terrace deposits, consisting of unconsolidated sand, pebbles, and cobbles were identified on the northwestern side of the Chattahoochee River. IGNEOUS ROCKS
Several intrusive episodes have occurred in the study area. During the history of the Piedmont, pegmatites, granites, and diabase were injected at separate times. Depending on their ages, these igneous rocks may or may not reflect periods of folding and deformation. Pegmatites
Several episodes of pegmatite intrusions have occurred in the Piedmont. The pegmatites typically are coarse grained and appear in outcrop to be less than 5 meters (15 feet) thick. Many pegmatites, however, were found to be less than 10 centimeters thick. None appear to be traceable beyond the outcrop in which they occur. The common minerals in the pegmatites are quartz and feldspar, with biotite, muscovite, garnet, tourmaline and beryl being common accessory minerals. Stone Mountain Granite
The Stone Mountain Granite is located about 25 kilometers (16 miles) east of Atlanta, Georgia in Dekalb and Gwinnett Counties. The pluton as a whole exhibits a roughly elliptical map pattern, elongated in an eastwest direction which cuts across the local and regional structures. Excellent exposures are available; the largest of these is Stone Mountain itself, an impressive erosional remnant of granite standing approximately 250 meters above the surrounding terrain.
(7)

EXPLANATION AND STRATIGRAPHIC RELATIONS OF LITHOLOGIES IN THE STUDY AREA

SNELLVILLE QUADRANGLE
G DIABASE

LUXOMNI QUADRANGLE
G ALLUVIUM

SUWANEE QUADRANGLE

lcl STONE MOUNTAIN LJ GRANITE

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I
Figure 3.

Building stone was quarried from the mountain by the Stone Mountain Granite and Railway Company from 1869 to 1882, when the operation passed into other hands. Purington (1894) reaffirmed the granitic nature of the rock by examination of its texture and quartzo-feldspathic composition. Watson (1902) describes the Stone Mountain granite as a biotite-bearing muscovite granite. Herrmann (1954) determined the feldspar compositions, and as a result placed the Stone Mountain plutonic rock in the adamellite, or quartz-monazite class. The name "Stone Mountain Granite" has been retained, however, owing to prior usage by many sources over many years and its suitability as a general term for a quartzo-feldspathic rock with a coarse granitoid texture.
The Stone Mountain granite is a light grey, fine- to medium-grained, slightly foliated, micaceous rock. Its average mineralogical composition is 30 percent quartz, 31 percent oligoclase, 28 percent microcline, 10 percent muscovite, and 1 percent biotite (Herrmann, 1954). It does, however, become less leucocratic away from Stone Mountain, and may contain up to 3 percent biotite (figure 4). Accessory minerals may include epidote, garnet, apatite, zircon, pyrite, rutile, and tourmaline. Xenoliths of biotite gneiss, amphibolite, and mica quartz schist are present. The microscopic texture is allotriomorphic-granular (aplitic) to hypidiomorphic-granular (granitic). Locally, the micas exhibit a slight foliation. Aplite
Fine- to medium-grained aplite dikes fill joints in the Stone Mountain granite and occur in shear zones in the Lithonia Gneiss. The aplite is composed of quartz, microcline and albite with occasional magnetite and little or no mica (Herrmann, 1954).
(9)

100

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STONE MOUNTAIN GRANITE MODEL ANALYSIS FROM HERRMANN,i954

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STONE MOUNTAIN GRANITE SIX SAMPLES

Figure 4. Modal analysis.

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QUARTZ MICA SCHIST FROM MICA SCHIST

AMPHIBOLITE UNIT

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Figure 5. Modal analysis.

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MICACEOUS QUARTZITE UNIT TWO SAMPLES

Figure 6. Modal analysis.

Diabase Fine-grained, dark-green to black diabase occurs as large and
small dikes in the Stone Mountain granite and the surrounding metamorphic rocks of the area. The width of the dikes varies from less than 10 millimeters to 15 to 20 meters and extends for a maximum length of 5 kilometers, with the majority of the dikes traceable for less than 1 kilometer. Diabase is very resistant to weathering and forms small ridges capped by diabase boulders. Diabase saprolite is bright red to orange with residual spheroidal boulders.
Mineralogically, two types of diabase occur: olivine diabase and pyroxene diabase. Both are fine- to medium-grained rocks with subophitic texture consisting of long narrow laths of plagioclase at random orientation enclosed by anhedral pyroxene or pyroxene and olivine grains. The olivine diabase contains approximately 10 percent olivine, 65 percent plagioclase, and 25 percent pyroxene. The pyroxene diabase contains about 60 percent plagioclase and 35 percent pyroxene. Altered Ultramafic Rocks (Chlorite Schist)
Associated with the more massive amphibolites are altered lenticular ultramafic bodies that typically are less than 20 meters in length. These ultramafic bodies are light green in color and contain altered pyroxene phenocrysts up to 3 centimeters in diameter. Herrmann (1954) described these bodies as talc-actinolite-chlorite schists. The ultramafic rocks have been altered to a chlorite schist and consist of chlorite, amphibole, talc, magnetite, and possibly albite. METAMORPHIC ROCKS
In the Piedmont south of the Brevard Zone, the common rock types are biotite gneiss, granite gneiss, amphibolite or hornblende gneiss, mica schist, and quartzite. These rocks are interlayered in various proportions, but the dominant lithology is a biotite gneiss. The texture
I 1 1 \ \ .J....J...)

and mineralogy of the gneiss vary from a medium-grained gneiss to a porphyroblastic gneiss, and may be rich in either quartz or feldspar. The percent of biotite varies from 5 to 20 percent. Another common rock type is amphibolite or hornblende gneiss, which includes the following lithologies: epidote amphibolite, epidosite, biotite hornblende gneiss, and amphibolite. Where possible, the amphibolites can be broken out and are mapped as lenses within a unit.
The metamorphic rocks of the study area can be divided into 15 lithologic units or formations (figure 3): (A) Rocks north of the Brevard Zone
(1) Sandy Springs Group (a) Factory Shoals Formation (b) Chattahoochee Palisades Quartzite (c) Powers Ferry Formation
(B) Rocks south of the Brevard Zone (2) Quartzite, mica schist-amphibolite (3) Quartzite (4) Biotite gneiss-amphibolite (5) Muscovite biotite gneiss (6) Granite gneiss-amphibolite, with mica quartz schist member (7) Lithonia Gneiss (8) Cataclastic Rocks (a) Mylonite (b) Phyllonitic gneiss, schist, amphibolite (c) Graphitic phyllonite (d) Button schist-phyllonite (e) Button mica schist (f) Button mica schist-amphibolite The quartzite and button mica schist-amphibolite south of the
Brevard Zone in the Suwanee quadrangle and the quartzite, mica schistamphibolite in the Luxomni and Snellville quadrangles may be correlative with the Sandy Springs Group north of the Brevard.
(12)

Sandy Springs Group The rocks northwest of the Brevard Zone belong to the Sandy Springs
Group and have been described by Higgins and McConnell (1978). The Sandy Springs Group in the Suwanee quadrangle consists of the following: Factory Shoals Formation, Chattahoochee Palisades Quartzite, and the Powers Ferry Formation. Factory Shoals Formation:
The rocks of the Factory Shoals Formation mainly consist of kyanite mica schists and biotite gneisses. The typical schist is a kyanite garnet biotite plagioclase quartz muscovite schist with kyanite occurring as blades up to 3 millimeters long. Garnets in the schist are approximately 2 millimeters in diameter. The rock weathers to a bright purplered color. Small and large lensoidal pods of granitic material are common on the outcrop scale. The biotite gneisses are typically medium-grained layered gneisses. Light and dark layers vary from less than a centimeter to over a meter thick. The leucocratic layers commonly are coarse-grained. Chattahoochee Palisades Quartzite:
The Chattahoochee Palisades Quartzite consists of micaeous quartzites, feldspathic quartzites, mica schists, and mica quartz schists. The micaceous quartzite is commonly a medium-grained vitreous muscovite quartzite. The quartz grains average 2 to 3 millimeters in diameter. Muscovite flakes are very thin and are 2 to 5 millimeters across. Thickness of the quartzite varies from .5 to 4 meters (.5 to 12 feet). The unit grades laterally into a mica quartz schist that has approximately 30 percent muscovite and 20 percent garnet. The mica schist is a medium-grained, foliated, quartz muscovite schist in which biotite may or may not be present. This mica schist is locally absent and occurs in places interlayered with quartzite.

Powers Ferry Formation: The Powers Ferry Formation consists of interbedded gneisses, schists
and amphibolites. The gneisses are by far the most abundant of these three lithologies with lenses of schists and amphibolites. The gneiss consists of biotite gneiss and granite gneiss in which layering is common and can be found on all scales (thickness of layers range from a millimeter to several meters). The darker layers are generally fine to medium grained and the lighter layers are medium to coarse grained (6 centimeters or more). The lighter layers are composed of plagioclase, microcline, and quartz with minor amounts of muscovite. Quartzite-mica schist-amphibolite
Interlayered garnet mica schist, amphibolite, biotite gneiss, and micaceous quartzite structurally overlie the contact between the Lithonia Gneiss and biotite gneiss-amphibolite unit, forming small, from 30 to 60 meters (100-200 feet) high, ridges above the surrounding. area. This unit consists of two members: a mica schist-amphibolite member and a quartzite member, and is approximately 30 meters (80 to 100 feet) thick with the quartzite varying from 1 to 3 meters (5 to 10 feet thick).
The larger mica schist-amphibolite member consists of interlayered garnet mica schist and mica schist with subordinate interbedded amphibolite, biotite gneiss, and micaceous quartzite. Amphibolite and biotite gneiss are abundant near the base. This mica schist-amphibolite member is well exposed in stream beds on the northern slope of Snellville Mountain, near Snellville, Georgia. Herrmann (1954) described the mica schist as follows:
"Fresh garnet mica schist is dark grey, and the weathered rock is brown to red. In the final stages of decay the rock changes to a red micaceous saprolite. The schistosity surfaces are sometimes corrugated. In thin section the schistosity
(14)

consists of an alternation of muscovite-biotite and quartzfeldspar bands 1 millimeter thick. The bands are frequently folded into minute crenulations which are ruptured by small shear planes.
The microscopic texture of the schist is granoblastic. Quartz and oligoclase have irregular, polyhedral boundaries. Idiomorphic grains of olive-green tourmaline sometimes exhibit a snowball structure formed by a spiral orientation of inclusions in the centers of the grains. Garnet crystals are usually flattened parallel to the schistosity.
The rock is composed of almost equal amounts of biotite, muscovite, oligoclase, and quartz with accessory amounts of garnet, sillimanite, kyanite, epidote, and tourmaline. Staurolite, zircon, magnetite, and ilmenite are rare." (figure 5).
The second member is the quartzite unit, which consists of micaeous
quartzite with minor mica schist. The quartzite member is only 1 to 3
meters thick, but it is a persistent ridge former. The unit is well
exposed on Elijah Mountain near Klondike, Georgia. Herrmann (1954)
described this member as follows:
"Fresh specimens of quartzite are hard, compact and grey to brownish in color. The quartzite weathers to a light brown friable rock. The rock is fine to medium-grained and well foliated because of subparallel orientation of muscovite flakes between and within quartz grains. A faint banding is sometimes present in the form of color or changes in grain size. The mineralogical composition is similar to that of a metaquartzite." (figure 6).
Quartzite
Four parallel ridges south of the Chattahoochee River near the
intersection of the Gainesville Connector and I-85 are held up by a
thin (less than 2 to 3 meters thick) micaceous to feldspathic
quartzite which has been sheared and is locally mylonitic. Button mica
schist-phyllonites are associated with the quartzite.
Biotite Gneiss-Amphibolite
This unit has been described as a porphyroblastic biotite gneiss
by Herrmann (1954), but it includes other lithologies as well.
Amphibolite is interlayered on the millimeter to the meter scale, and
in places can be mapped as lenses within the gneiss. Fresh exposures
(15)

of the biotite g~eiss ~~e Red mlcaceo:.::s roads.
white bar,ds ~

1::.,,,

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minerals ~~~ri:th (figt~re 7) .

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reeL)

Granite Gneiss-Amphibolite including Mica Schist member Separating the biotite gneiss-amphibolite from the granite gneiss-
amphibolite is a thin micaceous quartzite-mica quartz schist (less than 3 meters thick), which is composed almost entirely of muscovite and quartzite with the percentages varying from outcrop to outcrop. Fresh outcrops are nearly white in color with a distinct foliation resulting in a fine- to very fine-grained lepidoblastic texture.
The granite gneiss-amphibolite is a massive to thinly layered medium-grained gray-banded biotite gneiss interlayered with amphibolite on a centimeter to meter scale. The granite gneiss-amphibolite unit is probably between 150 to 300 meters (500 to 1,000 feet) thick. Lithonia Gneiss
The Lithonia Gneiss is a major rock unit of the Piedmont in Georgia. It is located about 30 kilometers east of Atlanta, Georgia, in Rockdale, Walton, Gwinnett, Dekalb, Bartow, Newton, and Jackson Counties. The outcrop pattern is a broad band elongated in a northeast direction. The Lithonia Gneiss typically forms pavement outcrops throughout the area.
This rock unit originally was described as the "Lithonia area of contorted granite gneiss" by Watson (1902). Crickmay (1939) referred to the body, which he believed to be a metamorphosed granite, as a granite gneiss, Lithonia Type. Herrmann (1954) considered the unit to be a migmatite, and revised its name to Lithonia Gneiss. Herrmann's terminology will be followed in this report.
(17)

"The Lithonia Gneiss is a fine to medium-grained gray biotite quartz feldspar gneiss with a well developed and often contorted gneissic foliation. This gneissic layering is sometimes cut by aplitic or pegmatitic dikes. Occasional garnetiferous layers are present and consist of garnet, oligoclase, and quartz.
The texture of the biotite gneiss is xenoblastic to granoblastic. Poikiloblastic and sympletic textures are common, especially in the feldspars. Grain size is seriate with boundaries which may be straight, curved, sutured, lobate, or serrate. Microcline and plagioclase are present in subequal proportions, and together constitute 50 to 60 percent of the rock. Quartz abundance averages 30. percent or more. Biotite abundance is variable, usually between 0.5 and 4 percent. Garnet is an important accessory mineral; other accessory minerals include epidote, muscovite, sphene, zircon and apatite."
The mineralology is of a high grade gneiss, whether metaigneous
or metasedimentary (figure 8).
CATACLASTIC ROCKS
Two distinct zones of cataclastic rock exist in the Suwanee
quadrangle with the one zone extending into the Luxomni quadrangles;
the first zone consists of button schists, phyllonites, and mylonites,
and the second zone consists of button schist interlayered with am-
phibolites and granite gneiss-biotite gneiss. The first zone is
from 2 to 5 kilometers wide and extends across the Suwanee quadrangle
in a northeasterly direction in the vicinity of the Chattahoochee
River. The second zone extends parallel to the first and extends
into the Luxomni quadrangle.
The cataclastic rocks are divided into the following with no
stratigraphic order implied:
(1) Mylonite
(2) Phyllonitic gneiss, schist, amphibolite
(3) Graphitic phyllonite
(4) Button schist, phyllonite
(5) Button mica schist
(6) Button mica schist, amphibolite

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BIOTITE GNEISS FROM BIOTITE GNEISS-AMPHIBOLITE UNIT FOUR SAMPLES
Figure 7_Modal analysis.

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LITHONIA GNEISS TWO SAMPLES
Figure 8. Modal analysis.
(19)

Mylonite Mylonites of the Brevard cataclastic zone consist of quartz
mylonite, muscovite quartz mylonite, and muscovite quartz feldspar mylonite. The fine-grained quartz varieties are thin (only a few centimeters thick). The muscovite quartz mylonites are generally fine grained with numerous quartz ribbons containing very tiny muscovite grains scattered throughout. The muscovite quartz feldspar varieties appear similar to the muscovite quartz units, but contain feldspar porphyroclasts on the order of 1 millimeter in diameter. Phyllonitic Schist
A fine-grained garnet quartz muscovite (sericite) schist has a well-developed foliation. The phyllonite has a distinctive sheen and grades into a button schist. Phyllonitized Gneiss
Although there is variation, this rock is for the most part phyllonitic, porphyroclastic biotite gneiss. Porphyroclasts of quartz and feldspar (0.5 to 1.5 centimeters) are widely scattered. Some layers of the gneiss are more leucocratic than others. The rock consists of biotite (5 to 20 percent), muscovite (10 to 20 percent), quartz (20 to 30 percent) and feldspar (60 percent). The biotite content is inversely proportional to the muscovite content.
(20)

Graphitic Phyllonite Fine-grained graphite quartz muscovite phyllonite is a distinct
unit within the cataclastic rocks. Graphite comprises approximately 10 percent and muscovite between 40 to 50 percent of the rock. The rock in outcrop has a very distinct gray color and tends to form subtle ridges. Button Schist - Phyllonite
Coarse-grained biotite quartz muscovite schist is a rock with a wavy double cleavage producing lens-shaped porphyroblasts of mica that weather out as "buttons" approximately 5 to 10 millimeters in diameter. Garnet and graphite are common as accessory minerals and the graphite imparts a blue-gray color to the button schist. The button schist grades into a phyllonite. Wit.hin the button schist-phyllonites are thin (less than 1 meter thick) manganese garnet quartzites that are not mappable beyond the outcrop. These manganese quartzites form a distinct black sooty saprolite with blocky cobbles of the quartzite.
STRUCTURES
Prior to 1978, previous work in the Piedmont south of the Brevard in the Atlanta area, recognized only two folding episodes. Atkins and Higgins (1978) described five generations of folds with associated schistosity, cleavages, and lineations. In addition to confirming five generations of folding work, this investigation suggests two possible movements along the Brevard Zone.
(21)

Compositional Layering Metamorphic lithologies throughout the study area exhibit com-
positional layering. The layering is from millimeter to centimeter scale and is well to poorly developed depending upon the mineralogy of the rock. Schistosity
The mica schists and button mica schist exhibit a pronounced schistosity formed by the alternation of micas, quartz, feldspar, garnets, sillimanite, or graphite in bands on millimeter to centimeter scale.
Equal area projections of poles to foliation diagrams of the Suwanee (figure 9), Luxomni (figure 10), and Snellville quadrangles (figure 11), illustrate essentially a flat-lying foliation. The foliations in the Suwanee quadrangle indicate a slight northeast strike with a southeast dip, the Luxomni quadrangle a northwest strike with a south dip, and the Snellville quadrangle a slight east-west strike with a north dip. Locally, steeper foliations are the result of late warping folding. Lineations
Mica lineations are the most consistent. The mica lineations and other mineral lineations are fairly consistent with the trend of later generations of open warping folds. Exclusive of mineral lineations, fold axes are the most consistent. Grouped according to fold generations, east-west, north-south, northwest and northeast trends occur with a lesser number scattered randomly. The
.
northeast-southwest lineations may be the result of late movement along the Brevard Zone or possibly lineations associated with the Newnan-Tucker Synform (Higgins and others, 1980). The random lineations probably are from the interference of several fold
(22)

generations (figure 12, 13). Streaking lineations are present locally, but are not as common as the other lineations. Joints
Four distinct joint sets have been mapped in the metamorphic rocks. A separate joint system was mapped in the Stone Mountain Granite. The joint systems in the metamorphic rocks consist of the following: north-south, east-west, northwest, and northeast. All of the sets have a near-vertical dip. Spacing between the vertical joints in a set varies from a few centimeters in the amphibolites and quartzites to several meters in the granites and gneisses. The joints in the Suwanee and Luxomni quadrangles are not dipping as steeply as in the Snellville quadrangle. (See figures 14, 15, 16). The joint systems in the Stone Mountain granite are predominately northwest striking with the second set striking to the northeast (figure 17). The spacing in both joint sets is of several meters scale. Folds
The rocks in this area have undergone a miniumum of five folding episodes. Generally, the first two folds are tight to isoclinal folds and the last three are upright warping folds (figures 18, 19). Each fold has been named after a type locality in order to avoid confusion of letter-number designations and to provide a "type locality" for the different fold generations (Atkins and Higgins, 1978).
The earliest recognized generation of folds, called the Buck Branch generation, is generally tight to isoclinal passive folds (figure 20). These folds are characterized by a recrystallized schistosity that is generally defined by compositional layering and elongate micas or amphiboles, and which parallels bedding except in the hinge zones where it is axial planar.
(23)

N
"
600 OBSERVATIONS

1%-3% l'l 4%- 9% Ill
10%-15%. 16%-21%. 22%-26%.

0
---------
Figure 9. Equal area projection of poles to foliations in the Suwanee Quadrangle.

N

N

363 OBSERVATIONS

1%-3%1
4%6% lil

7"1.-9"1

10%-11%11

12%

11111

1%-3"10 4%-6"/lllilll 7%-9"111111 10%-ll"I.J!!I
12"111

Figure 10. Equal area projection of poles to foliations in the Luxomni Quadrangle.

Figure 11. Equal area projeclion of poles to foliations in the Snellville Quadrangle.

(24)

N I %-2%0 3%-6%0
7%-9% !'l!lll
11 to%-12%
Figure 12. Lineations in the Snellville Quadrangle.
N 4.8
Figure 13. Lineations in the Luxomni Quadrangle.
(25)

Klondike folds, the second recognized generation) fold Buck Branch folds and are generally flexural flow to passive flow isoclinal folds that are characterized by an axial planar schistosity. The Klondike folds generally are recumbent to slightly inclined and are short limbed folds, which, typically, resemble an accordian (figure 21).
Elijah Mountain folds, the third generation, fold Buck Branch and Klondike and are characterized by their effect on the map patterns. Their axial traces commonly are nearly at right angles to the axial traces of earlier regional folds. The axial traces of the Elijah Mountain generation trend to the northwest and probably are open-warping flexural slip to flexural flow folds. The wave length of these folds varies and is up to two kilometers in length. The northwest trending joints are thought to be axial planar to this fold generation. The fold axes plunge gently to the northwest or southeast in the Snellville quadrangle.
The Scott and Tara fold generations generally are symmetrical, gentle to open upright warping, flexural slip to flexural flow folds with wave lengths that vary from one to 30 meters (figure 22). The axes of these folds are either horizontal or plunge gently (5 to 20 degrees). Locally, the Scott Creek generation has a sillimanite mineral lineation parallel to the fold axis, but generally the minerals warp around the fold nose. The north-south and east-west joints are thought to be an open widely spaced axialplanar cleavage to Scott Creek and Tara generations of folds. The Scott Creek folds trend north-south but may vary in trend as much as fifteen degrees to the west and east. The Tara folds trend east-west and vary in trend as much as fifteen degrees to the north

N

N

1% 2% Ill 3"1.-4% lllll 5%-6% !'I 7%-9% ml
10% 14% llJ

Figure 14. Equal area projection of poles to joints in the Snellville Quadrangle.

Figure 15. Equal area projection of poles to joints in the Luxomni Quadrangle.

N
1%3% Ill 4%6% El
7"/oO

N
1%-3%1!1
4%-6% IIIII
7%-9% 1111!1
D 10%12%
13%0

Figure 16. Equal area projection of poles to joints in the Suwanee Quadrangle.

Figure 17. Equal area projection of poles to joints in the Stone Mountain Granite.

(27)

N 17
..........
N 00 '-"

I%- 10/o~~~ 11%-15%['] 16%-20%1:fuJ 21%-24%0

Figure 18. Equal area projection of poles to axial planes in the Snellville Quadrangle.

N
24 OBSERVATIONS

4%-B%0
B%-12%1'l
12%-13% Ill

J
Figure 19. Equal area projection of poles to axial planes in the Luxomni Quadrangle.

or south. The Tara folds appear to be at right angles to the Scott Creek folds. Reconnaissance mapping in the Newnan North quadrangle has outlined Scott Creek folds that have been refolded by Tara generation folds.
As is evident by the map pati:erns (maps 1, 2, 3, and 4) , the effect of superimposed folding is clearly illustrated. Utilizing Ramsey's classification, the following can be illustrated:
(1) A Ramsey Type I fold occurs when the first folds are refolded at nearly right angles. Where synformal second folds are superimposed, there is a mutual culmination of both sets of folds resulting in a basin-like structure. The same pattern develops for antiforms in which domelike structures form. The Snellville, Suwanee, and Luxomni quadrangles are in the area of a nose of a synform that may have developed in a similar fashion in which an isoclinal Buck Branch Klondike has been cross folded by an Elijah Mountain fold. On outcrop scale, this map interference pattern is illustrated by the intersection of Tara and Scott Creek folds (figure 23).
(2) Ramsey Type II interference pattern~ develop when the axial surface of the first folds become folded within the limbs of the first folds by the second fold. The refolded folds are commonly crescent shaped or mushroom shaped. This interference pattern is illustrated in the geologic map of the Snellville quadrangle by a Klondike fold being crossfolded by a Scott Creek fold 3.5 kilometers (2 miles) east of Centerville.
(29)

Figure 20. Buck branch folds at Cleveland Avenue.
Figure 21. Klondike folds at Klondike, Ga.
2::~
Figure 22. Opening warping folds of Scott Creek or Tara generation.

(3) Ramsey Type III interference patterns commonly develop where recumbent folds are refolded by later structures with steeply inclined axial surfaces. This fold pattern is illustrated on the outcrops scale where recumbent Klondike folds are refolded by Scott Creek or Tara Folds (figure 24).
In studying an area, such as the GeorgiarPiedmont that is complexly deformed, it is apparent that not all fold generations occur throughout the region. Instead, the folds are located in zones. Klondike folds are found throughout the study area; Elijah Mountain folds are most pronounced in the southeast Snellville quadrangle; Scott Creek folds are strong in the south-and central-east Snellville quadrangle; and the Tara generation affects the map pattern most in the central Snellville quadrangle. The Brevard Zone masks the folds in the Suwanee quadrangle, but a fold that appears to be a Buck Branch or Klondike fold is present in the Brevard Zone in the Suwanee quadrangle. Late warping folds occur north of the Brevard Zone in the Suwanee quadrangles. The zoning of the folds also is reflected by the accompanying lineations and joints; such zoning of folds occurs throughout the Piedmont in the Atlanta area south of the Brevard (map 1). Unconformity
Geologic mapping south and east of Atlanta shows map patterns characteristic of an unconformity or fault (figure 25) between a quartzite, mica schist-amphibolite and either the Lithonia Gneiss or biotite gneiss-amphibolite or granite gneiss~amphbilite. The structurally disconformable contact is best exposed at Stockbridge, Georgia (see Higgins and Atkins, 1980~ in press). Here, about a meter (3 feet) of folded garnet sillimanite quartzite overlies
(31)

FOLD GENERATIONS IN THE STONE MOUNTAIN AREA

/( ..
,1;45
16
82
/( "'4'1,_17
24
~3

0

4

5 MILES

b=====~==d===~=d

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27 ~35
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EXPLANATION

30HIT
121-f+--
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23

12~

OPEN WARPING FOLD-
Trends Northeast
TARA GENERATIONBroad open upright warping fold, trends East -West
SCOTT CREEK GENERATIONBroad open upright warping fold, trends North- South
ELIJAH MOUNTAIN GENERATIONBrood open warping fold, trends Northwest
KLONDIKE GENERATIONTight isoclinal reclined to recumbent fold

BUCK BRANCH FOLDMINERAL LINEATION

not present

CRENULATION

QUADRANGLE BOUNDARY

UNCLASSIFIED FOLD AXES ARE NOT NAMED

INTERSTATE 20

I I
Mapl. (32)

finely banded gneiss and amphibolite. There,is a discordance of about 30 degrees between the dip of layering in the biotite gneiss-amphibolite and the quartzite above (figure 25). A similar situation exists in a roadcut along Klondike Road about 1,000 meters (3,200 feet) north of the community of Klondike in the Conyers, Georgia quadrangle where about a meter (3 feet)-thick bed of quartzite dipping about 45 degrees is underlain discordantly by finely banded gneiss and amphibolite.
The map pattern of the quartzite, mica schist-amphibolite unit suggests that it is either thrust upon or lies unconformably upon the other units of the area. It is above different units at different places, and locally, it rests athwart unit contacts, including the contact between the Lithonia Gneiss and rocks of the Atlanta Group (Higgins and Atkins, 1980, in press). Moreover, while folds of the Klondike, Elijah Mountain, Scott Creek, and Tara generations are present in rocks of the quartzite and mica schist-amphibolite units, the early Buck Branch folds are apparently absent (even though they are present in rocks immediately beneath the contact).
Evaluation of all of the available evidence still makes it difficult to decide between a thrust and unconformable contact. The following facts argue for a thrust fault: (1) we have seen no recognizable clasts of country rocks in the quartzite, mica schist-amphibolite rocks above the contact; (2) there is no evidence of a relict regolith in the rocks immediately beneath the contact, although one might expect such a regolith to be eroded away in most cases; (3) 1,100 m.y.-old (or older) detrital zircons are present in the quartzite member of the quartzite mica schist amphibolite unit, but the nearest known 1,0001,100 m.y.-old basement exposed today is about 100 kilometers (62 miles) away; (4) the quartzite, mica schist-amphibolite outcrop area is limited to the area of the Lithonia Gneiss and the easternmost part of the eastern limb
(33)

Figure 23. Ramsey Type I interference pattern in Snellville quadrangle.

Figure 24. Ramsey Type III interference pattern at DeKalb Jr. College, South Campus.

Figure 25. Unconformity at Stockbridge, Ga.

Figure 26. Shearing along limbs of Klondike fold, Luxomni quadrangle.

Figure 27. Diabase outcrop near Snellville, Ga.

of the Newnan-Tucker synform (however, the synform is nearly recumbent and the southeastern limb is the long limb); and (5) the mica schistamphibolite locally is absent and the quartzite rests directly upon the country rock and (or) Lithonia Gneiss, although this could be due to non-deposition. The following facts argue for an unconformity and against a thrust contact: (1) there are no cataclastic rocks of any type (not even gouge or breccia or "healed" cataclastic rocks) at or near the contact between the quartzite, mica schist-amphibolite and the other "older" metamorphic rocks; (2) there is no drag along the contact, even in finely banded biotite gneiss-amphibolite; (3) local irregularities at the base of the quartzite could be interpreted as erosional channels in the underlying country rocks; (4) most thrusts are imbricate, but there is no evidence to suggest more than a single contact surface between the quartzite, mica schist-amphibolite units (in fact, not only are the underlying units not cut, but there is no recognizable debris from an overthrust sheet); (6) most thrust faults have moved on rocks, such as shales (though there are many exceptions), but if the lower contact of the quartzite, mica schistamphibolite unit is a thrust fault it would have had to have moved over folded amphibolite and gneiss without causing drag in these finely banded rocks; (7) no rock units have been found above the quartzite, mica schist-amphibolite unit, and it is difficult to imagine that any rocks once present there would have everywhere been completely removed by erosion if the quartzite, mica schist-amphibolite unit is a thrust sheet; it would have to be almost impossibly thin and almost impossibly far traveled and; (8) if the quartzite, mica schist-amphibolite unit is overthrust upon the country rocks, it should still have been affected by the Buck Branch generation of folding, unless it is almost
(35)

impossibly far travelled. The last two points lose some force because of the presence of the Soapstone Ridge Complex, which is definitely a thin, far-travelled thrust sheet.
Nevertheless, the bulk of the evidence suggests that the quartzite, mica schist-amphibolite unit lies unconformably upon the Lithonia Gneiss and other metamorphic rocks. If this interpretation is correct, it means that there was a break in metamorphism and folding, and a period of uplift and erosion followed by subsidence and deposition of the quartzite, mica schist-amphibolite unit between the Buck Branch and Klondike folds. Fault
The Brevard Zone is two to five kilometers wide in the Suwanee quadrangle. Map patterns and lithologies of the Brevard suggest there has been at least a minimum of two distinct periods of movement. The first movement came before or during Buck Branch folding. Rocks folded by the Newnan-Tucker Synform include rocks with cataclastic texture. This cataclastic texture probably was derived during the early movements along the Brevard. The button schist-amphibolite unit folds around the nose of the Newnan-Tucker synfor~; however, the button schist-amphibolite does not extend into the Snellville quadrangle. The later Brevard movements are either post- or syn-Ben HillPalmetto granite. Brevard movement has sheared the northwest edge of both the Ben Hill and Palmetto Plutons. These granites have a
1
foliation which may or may not be metamorphic; however, they both intrude the axial planes of late-occurring Elijah Mountain and Scott Creek fold generations and definitely are post-folding in the Piedmont.
(36)

Many of the outcrops that exhibit Buck Branch - Klondike folds also illustrate faulting (figure 26). Typically, one limb of the Buck Branch - Klondike fold has been sheared out. These faults are not traceable beyond the outcrop. Stone Mountain Granite Pluton
Based on deformation of a Scott Creek open warping fold, lack of metamorphic minerals and textures, and the presence of igneous textures and minerals, the Stone Mountain granite intrusion is interpreted to have taken place after the last folding and metamorphic event. The granite with numerous sills south of the pluton is discordant to all metamorphic rocks. The form of, the igneous body is thought to be a dike to the west, becoming a loccolith to the east. Structurally, the granite is controlled by pre-existing folding and the sills are emplaced in the limbs and noses of Elijah Mountain and Scott Creek folds. Diabase
Trending in a north to northwest direction is a series of less than 1 centimeter to 30 meters wide diabase dikes. These dikes occupy a zone that is approximately 5 kilometers wide. These dikes pinch and swell and cut across all lithologies except alluvium (figure 27).
HYDROGEOLOGY The occurrence of ground water is largely controlled by the geology. In this study, the detailed geology of the quadrangles is described, but the well inventory necessary for a thorough analysis of ground water is beyond the scope of this report. Nevertheless, it is the intent of this report to provide information regarding potential lithologies and structural controls that may warrant additional study by a hydrologist.
(37)

All of the metamorphic and igneous rocks have little or no primary permeability. However, since this area has undergone polydeformation, secondary openings ~uch as joints will yield ground water, but probably only in small quantities per minute.
The amphibolites, quartzites, and quartz mica schists are the best lithologies for ground water. These lithologies, typically, are highly jointed and fractured on an 8 to 10-centimeter scale. Another lithology, which may produce usable amounts of water, is the amphibolites in the Suwanee and Luxomni quadrangles south-southeast of the wide floodplains.
The following is a list of structures with secondary openings that would be potentially favorable for the occurrence of a viable ground-water supplier:
(1) The Elijah Mountain synform in the southeast corner of the Snellville quadrangle.
(2) The cross-folds west of Snellville in the quartzite, mica schist-amphibolite.
(3) The diabase dikes are highly jointed and appear to be controlled by Elijah Mountain axial planar joints. The joints in the diabase would be particularly favorable for ground water.
(4) The quartzite in the Suwanee quadrangle dips gently to the southeast. The quartzite would be .encountered at depth by drilling southeast of the exposures.
(5) At or near the base of a large sloping pavement outcrop. The gneisses are jointed on a several meter scale; however these joints are connected by exfoliation joints. These joints allow ground water to migrate to the base of the pavement outcrop and may provide higher ground-water yields than one would expect.

ECONOMIC RESOURCES

Crushed Stone

The stone industry of the Atlanta area had its beginnings around

1845 to 1850 when tombstones and building stones were quarried from the

Stone Mountain granite (Watson, 1902). With the introduction of the

railroad, production increased dramatically as the stone could be shipped

relatively long distances. During the late 1800's, Dekalb County

was Georgia's leading producer of stone. In the late 1950's with the

beginnings of the expressway and the explosive growth of Atlanta,

quarries were no longer restricted to a location near a railroad.

Stone could be hauled by truck and compete by locating closer to a

market in the Atlanta area. Quarries with rail facilities neverthe-

less still can compete for markets not available to other quarries

such as railroad ballast and markets in the Coastal Plain.

Atlanta is the only major metropolitan area in the United States

that depends on crushed granite-granite gneiss as its sole source of

local aggregate. Most cities rely on crushed limestone, natural

sands and gravels, or traprock. However, none of these is aYailable
in the immediate Atlanta area. Hence, the greatest concentration

of crushed granite-granite gneiss quarries in the United States

is in the Atlanta area. Within 20 miles of Atlanta are 19

quarries with a capacity of producing 25 million tons of crushed

aggregate a year (Atkins and Power, 1978).

Geologic mapping of the Snellville and Luxomni quadrangles

outlined additional areas for quarries within the Lithonia Gneiss.

Recommended areas for additional studies are east, north, and south

of Snellville. Numerous outcrops of Lithonia gneiss occur in this

area.

(39)

Curbstone, Riprap, and Building Stone Another product derived from the gneisses and granites of the area
are curbstones, riprap, and building stone. These operations that produce these products are usually small and consist of less than ten men and are located on pavement outcrops. From the geologic map, additional areas for quarrying of curbstones, riprap, and building stone may be located in the Stone Mountain granite in the central portion of the Snellville quadrangle and east, north, and south of Snellville. Sand
The Chattahoochee River and a few of its tributaries have fairly extensive floodplains. Present dredging of the river and floodplains produces a product suitable for the building industry in the Atlanta area.
POTENTIAL GEOLOGIC PROBLEMS The geology of a region includes the study of the structures, lithologies, physical, chemical, stratigraphic, and economic potential. In addition, geology may adversely effect construction or development projects. For this reason, geologic maps should be made available to planners and developers to evaluate the geology of the area. Planar Structures Joints in the study area are predominantly vertical and should not present any major problems during construction. However, compositional layering is flat lying or dipping at a low angle which can present problems. If cut slopes are at a higher angle than the dip of the rock,
,.
local slope distress or landslides along layersmay occur.
(40)

Lithologies (Shallow Soil Horizons and Corrosive Characteristics) The Stone Mountain Granite, Lithonia Gneiss, and other more massive
gneisses resist weathering and develop little or no soil horizons. In the areas in which these granites and gneisses crop out, geologic studies prior to construction should be done. An example would be the installation of septic tanks in a subdivision. The shallow soil horizons would not be deep enough to install the septic tank or allow for the proper percolation rate. Also, rock will be encountered at fairly shallow depths and blasting would be required.
In areas in which graphite occurs in the rocks, the soils tend to be corrosive. Pipes that were not treated had to be replaced along I-20 west of Atlanta. If Peachtree Industrial Boulevard is extended northeast, it will. cross a graphitic phyllonite and a potential corrosion problem exists.
ADDITIONAL STUDIES The following warrants additional work:
~)
(1) An inventory of existing wells in the area. (2) The mapping of the Hog Mountain quadrangle. The city
of Lav~enceville has a well that produces several hundred gallons of water per minute, which is unusual for the Piedmont. It appears that a major geologic structure exists north of the city and the well may have been located in this structure. The mapping of the Hog Mountain quadrangle would be invaluable in locating additional high yielding wells in this structure. (3) Quartzite previously unmapped in the Suwanee quadrangle extends northeast into the Hog Moun~ain and Buford quadrangles and continues beyond these quadrangles. These quartzites need to be mapped to determine their extent, possible hydrologic potential and economic resources.
(41)

SUMMARY OF CONCLUSIONS
The complex geologic history of the study area can be simplified as follows:
(1) Folding of the rocks into isoclinal folds by the Buck Branch folding episode which probably represents the first folding after the deposition of the metasedimentary rocks. Before or during this fold generation, fauiting took place along the Brevard. The cataclastic rocks of this movement along the Brevard are folded around the nose of a regional Buck Branch fold in the Suwanee and Luxomni quadrangles.
(2) Uplift and erosion. (3) Deposition of the quartzite, mica schist-amphibolite unconformably
on the other rocks. (4) Folding of the rocks into tight to open, recumbent to slightly
reclined folds of the Klondike folding episode. (5) Cross folding of the previous folds_by the Elijah Mountain fold.
~
(6) Open warping folding by the Scott Creek-Tara generation. (7) Intrusion of the Stone Mountain Granite. (8) Movement along the Brevard Zone. (9) Intrusion of the diabase dikes. (10) Uplift and erosion.
(42)

BIBLIOGRAPHY
Atkins, R.L., 1978. A widespread unconformity in the Georgia Piedmont southeast of the Brevard Zone (abs.): Georgia Jour. Sci., v. 36, no. 2, p. 93.
Atkins, R.L. and Higgins, M.W., 1978. Relationship between superimposed folding and geologic history in the Georgia Piedmont (abs.): Geol. Soc. America abs. with program, v. 10, 7, p. 136.
Atkins, R.L., and Power, W.R., 1976. The crushed granite industry of the Atlanta Metropolitan area: Twelfth forum on the geology of industrial minerals, GeorgiaGeol. Survey, I.e. 49, PP 6-9.
Clark, W.E., and Zisa, A.C., 1976. Physiographic map of Georgia, Georgia Geol. Survey. Scale 1:2,000,000.
Cofer, H.E., Jr., 1948. Petrology, petrography~ mineralogy and structure of the Arabia Mountain Gneiss, Dekalb County, Georgia: Emory University, MS. thesis, 64 p.
, 1958. Structural relations of the granites and the asso ----------~----- ciated rocks of South Fulton County, Georgia:
University of Illinois, Ph.D. Dissertation, 139 p.
Dallmeyer, R.D., 1978, 40Ar/ 39Ar Incremental-release ages of hornblende and biotite across the Georgia Piedmont: their bearing on late Paleozoic-Early Mesozoic tectono thermal history.
Dooley, R.E., and Wampler, J.M., 1978. Low temperature release of excess 40Ar from Georgia dolerites, in R.E. Zartmen, ed., Short papers of the Fourth International Conference of Geochronology, Cosmochronology and Isotope Geology: U.S. Geological Survey Open-File Report 78-701, p. 94-96.
------------~~----------------- 1978. Location of environmental excess 40Ar in dolerites, Ga. Jour. Sci., 35, no. 2, p. 88.
Fullagar, P.D., 1971, Age and origin of plutonic intrusions in the Piedmont of the southeastern Appalachians: Geol. Soc. America Bull., v. 82, p. 2845-2862.
Grant, W.H., 1949. Lithology and structure of the Brevard Schist and the hornblende gneiss in the Lawrenceville, (Gwinnett County) Georgia, area: Emory University, M.S. Thesis, 45 p.
____________, 1962, Field excursion, Stone Mountain-Lithonia district: Guidebook no. 2, Georgia Dept. Min~s, Mining, and Geology, 21 p.
(43)

------S-t-o-n-e--M--o-u-n-t-a~i'n

1969, The intrusion mechanics and cooling history Granite (abs.): Geol. Soc. America Abs. with

of

Progs., pt. 4, Southeastern Sec., p. 28-29.

Herrmann, L.A., 1954. Geology of the Stene Mountain-Lithonia district, Georgia: Georgia Geol. Survey Bull. 61, 139 p.

Higgins, M.W., and McConnell, K.I., 1978. The Sandy Springs Group and

related rocks of the Georgia Piedmont: Nomenclature and stratigraphy,

in Short contributions to the geology of Georgia. Georgia Geol.

Survey, Bull. 93, p. 50-55.

~

Higgins, M.W., and Atkins, R.L., -1980, The stratigraphy of the Piedmont in the Atlanta, Georgia area southeast of the Brevard Zone: Georgia Geol. Survey Bull., in press.

Mohr, D.W., 1965. Regional setting and intrusion mechanics of the Stone Mountain pluton: unpublished master's thesis, Emory University, 68 p.

Purington, C.W., 1894. Geologic and Topographic features of the Region about Atlanta, Georgia: Am. Geol., vol 14, pp. 106-108.

Watson, T.L., 1902. A preliminary report on the granites and gneisses of Georgia: Geol. Survey of Ga., Bull. 9-A, 367 pp.

Whitney, J.A., Jones, L.M., and Walker, R.L., 1976, Age and origin of

the Stone Mountain Granite, Lithonia district, Georgia: Geol.

Soc. America Bull., v. 87, p. 1067-1077.

!

Whitney, J.A., and Stormer, J.C., Jr., 1977, Two-feldspar geothermometry, geobarometry in mesozonal granitic intrusions: Three examples from the Piedmont of Georgia: Contrib. Mineral. Petrol., v. 63, p. 51-64.

i
(44)

APPENDIX A THE GEOLOGY OF THE MADRAS QUADRANGLE
The Madras 7 1/2 minute quadrangle is located in the Piedmont Province approximately 36 kilometers southwest of Atlanta, Georgia (figure 1), and lies in the Greenville physiographic district of the Midland Georgia Subsection (Clark and Zisa, 1976). The area contains the unincorporated communities of Madras and Major, Ga. Interstate 85 diagonallyicuts across the quadrangle. Relief in the quadrangle averages 70 to 73 meters,
Numerous streams and creeks in the quadrangle supply the Chattahoochee and Flint Rivers, and a major stream divide between the headwaters of the Flint and tributaries of the Chattahoochee River is located in the quadrangle. In the Palmetto granite, the streams form a rectangular drainage pattern which is joint controlled. In the metamorphic rocks, the streams .have a dendritic drainage pattern which, locally, is controlled by jointing and foliation.
LITHOLOGIC UNITS Figure 2 is a diagrammatic description of the rock types in the Madras quadrangle. The alluvium and porphyritic granites are in their positions relative to the older metamorphic rocks. A relative stratigraphic sequence of the metamorphic rock units has been established. QUATERNARY ALLUVIUM (Qal) Unconsolidated micaceous clays, silt, sand, pebbles, and gravels constitute the bulk of the alluvium. Colluvium is included under the term alluvium and is not differentiated on the map. Alluvium was mapped using the extent of the flood plains of the rivers and streams in the area and by mapping its widths where roads cross rivers and creeks.
A-1

0

Quaternary alluvium

G

Porphyritic granite

~ Biotite gneiss with amphibolite

GJ Garnetiferous quartzite

,

.X 0

Undif

a0::

~ ~ Mica schist with amphibolite

0 .L:
a.

I ~:~ I Amphibolite with biotite gneiss

'-

0

-E
0
Q) [ : ; ] Diopside

gneiss

with

biotite gneiss

~

I

Amp
hgn bgn
-

Amphibolite with hornblende gneiss and biotite gneiss
(No time sequence implied for the metamorphic rocks)

Figure 2A. Diagrammatic description of lithologies in the Madras Quadrangle.

(A-2)

IGNEOUS ROCKS Pegmatite
Several different generations of pegmatite intrusion have occurred in the Piedmont. Most pegmatites are coarse grGined, appear in outcrop to be less than 5 meters thick, and consist of quartz and feldspar with various accessory minerals such as muscovite, garnet, tourmaline and beryl. Palmetto Granite (Pg)
The Palmetto Granite is a coarse-grained porphyritic granite with an idiomopphic texturewith large euhedral microcline crystals (9 to 25 millimeters). Typically the Palmetto granite forms small pavement rock outcrops with xenoliths or a distinct red to red-orange saprolite with kaolin pseudomorphs after microcline. Locally, microcline crystals cover the saprolite due to incomplete weathering. The essential minerals are microcline, plagioclase, and quartz. Accessory minerals include biotite, muscovite, perthite, sphene, apatite, epidote, and zircon. Allanite, chlorite, hematite, and sericite occur as secondary alteration products in trace amounts.
A modal analysis of an average Palmetto granite is given in table 1. The modal analysis was done on the basis of.l,l45 counted points. The K-feldspar in table 1 includes the microcline in the groundmass and phenocrysts which comprise 35 percent of the granite by volume. METAMORPHIC ROCKS
The metamorphic rocks have been grouped into assemblages based on rock units mapped in the surrounding quadrangles. The metamorphic rocks of the Madras quadrangle can be divided into six mappable units:
(a) Amphibolite-hornblende gneiss, biotite gneiss (Amp-hgn-bgn) (b) Diopside biotite gneiss, biotite gneiss (Dgn-bgn) (c) Amphibolite-biotite gneiss (Amp-bgn)
A-3

(d) Mica Schist, amphibolite (Ms-amp) (e) Garnet quartzite (Gq) (f) Biotite gneiss, amphibolite (Bgn, amp) All the metamorphic rocks consist of lithologies interlayered with biotite gneiss. The texture and mineralogy of these gneisses vary from a medium-grained gneiss to a porphyroblastic gneiss, and may be enriched in either quartz or feldspar. Biotite ranges from 5 to 20 percent. Epidote, garnet, opaque oxides, and sphene occur as accessory minerals in trace amounts in the biotite gneiss. The saprolite typically is red or light brown (depends on the percentages of biotite) and slightly micaceous. The amphibolite varies in composition. Hornblende ranges from 35 to 80 percent, plagioclase from 15 to 40 percent, and quartz from 0 to 30 percent, with traces of epidote and garne.t. Locally, epidote occurs in thin layers and comprises 70 to 80 percent of the layer and is an epidosite. Typically, the texture of the amphibolite is crystalloblastic. Amphibolites weather to a distinct blocky red-orange saprolite with a microboxwork texture. Amphibolite-hornblende gneiss, biotite gneiss (Amp-hgn-bgn) This unit is correlative with the biotite gneiss-amphibolite unit in the Snellville and Luxomni quadrangles. Additional mapping in adjacent quadrangles supports this correlation. Amphibolites and hornblende gneisses are interlayered with a medium-grained biotite gneiss. Amphibolite and hornblende gneisses constitute 70 percent and biotite gneiss 30 percent in the northwest corner of the quadrangle. In the southern half of the quadrangle, the granite gneiss comprises 80 percent and amphibolite 20 percent. The interlayering of the gneiss with the amphibolite
A-4

varies, but typically,each lithology may be several meters thick. Diopside biotite gneiss-biotite gneiss (Dgn-Bgn)
Massive slightly foliated biotite gneiss is interlayered with thin (em) diopside biotite gneiss layers. The diopside gneiss is discontinuous and composes only 10 to 15 percent of the unit. The biotite gneiss and diopside gneiss are characteristically slabby or blocky due to jointing and weathering. The general slabby appearance is a major criterion for recognizing the unit along with the rock units on either side.
The diopside gneiss occurs as a thin unit (varying in thickness from 1 to 10 em) with large euhedral crystals of diopside. Rhombic crystals of calcite are also present in minor amounts. The diopside gneiss is coarser grained than the massive biotite gneiss in which it occurs. The diopside is present in variable amounts from 5 to 10 percent. K-feldspar and plagioclase feldspar comprise 60 percent and quartz about 30 percent. -Calcite occurs as a secondary mineral in varying amounts from 0 to 5 percent.
The biotite gneiss occurs in the northwest corner and across the southern half of the quadrangle. The distinct diopside gneiss only occurs in the biotite gneiss in the northwest corner in the Madras quadrangle. Amphibolite, biotite gneiss (amp-bgn)
This unit consists of interlayered amphibolites and biotite gneiss. Amphibolite comprises 60 percent of the unit with theremainderbiotite gneiss. Thin layers of epidosite occur within the amphibolite. Epidote is found throughout this sequence in both the gneiss and amphibolite. The amphibolite and biotite gneiss are interlayered on meter scale. In other quadrangles lenses of amphibolite and biotite gneiss can be mapped separately. Mica Schist~Amphibolite (Ms-amp)
Mica schist and amphibolite are interlayered on a 1 to 2-meter scale and in equal proportions. The mica schist weathers to a tan or pink micaceous
A-5

saprolite with mica schist fragments. The pink color is due to a small percent of garnets (approximately 5 percent) in the schist. Muscovite or bleached biotite comprises approximately 50 percent of the schist. Garnet Quartzite (Gq)
A thin (less than 3 meters), discontinous, coarse-to medium-grained garnet quartz rock is a distinct mappable unit in the quadrangle and the Atlanta area. This quartzite is the marker bed between two different rock units. The quartzite is resistant to weathering and forms subtle ridges. The saprolite is a distinct black color withweatheredmanganese-coated cobbles of the garnet quartzite.
In thin section, the minerals quartz and garnet comprise the major portion of the rock. Quartz is generally present by 65 percent (average) and garnet in the proportions of 30 percent. Opaque minerals occur in varying degrees of proportion within the quartzite. Many of the opaques preserve the texture of garnets which they replace.
The quartz crystals form a xenoblastic texture and have straight or slightly curved boundaries. The garnets occur in separate layers and are of idioblastic to subidioblastic texture. They are smaller than the quartz crystals but have a bimodal distribution with the quartz. A diffuse banding (millimeter scale) with garnet-quartz layers and quartz-garnet layers is discernible. The accessory minerals include sillimanite, apatite, tourmaline, andalusite, muscovite, biotite and opaques. Sillimanite is tabular to aciclar and shows well-developed cleavage. Opaque and garnet inclusions are common in the sillimanite and andalusite crystals. Muscovite occurs in trace amounts and is always associated with the sillimanite. Biotite is rare and apatite occurs as small inclusions in the quartz crystals.
A-6

A modal analysis (table 2) of the garnet quartzite is from a roof pendant in the Palmetto granite. The sample is slightly oxidized and may not represent the true average composition, but fresh exposures do not exist in this quadrangle. A total of 2196 points were counted in the modal analysis. Biotite gneiss, amphibolite (Bgn-amp)
This unit consists of massive biotite gneiss interlayered with amphibolites which are commonly less than 1 meter thick. The biotite gneiss comprises. 60. to 70 percent of the unit and amphibolite, 30 to 40 percent. A modal analysis (table 3) of the biotite gneiss was done on the basis of 1,135 counted points. The sample was collected from a roof pendant in the granite, but does not appear to be altered by the granite. Local fracturing of feldspars is .att~ibuted to the forceful intrusion of the granite.
STRUCTURES The structures in the Madras quadrangle are similar to the structures in the Snellville, Luxomni, and Suwanee quadrangles. Schistosity and compositional layering have been previously described. The lithologies are essentially flat lying (figure 3A). Locally, the lithologies are cross folded or intruded by the Palmetto granite. Either event locally has caused a steepening of the lithologies. Lineations Fold axes and mineral lineations are the more common lineations in the quadrangle. The mica lineations generally reflect the late warping folds of Elijah Mountain, Scott Creek, and Tara generations of folds. The Tara generation is the strongest lineation and the Scott Creek next; a weak Elijah Mountain (northwest trending) and a northeast generation, probably related
A-7

to late Brevard fault zone movements, also exist in the quadrangle. Joints
Two distinct joint systems occur in the quadrangle, a system associated with the granite, and a system associated with the metamorphic rocks. In the granite, the joints trend northeast and northwest. These joints are steeply dipping and unevenly spaced several meters apart. The joints in the metamorphic rocks trend northeast, northwest, north-south, and east-west and generally are steeply dipping (figure 4A). From outcrop studies, the majority of these joints appear to be axial planar to the late warping folds previously discussed. The spacing of the joints in the metamorphic rocks: varies by lithology. The joints in the amphibolites are spaced closely (less than a meter), whereas joints in t:he massive biotite and granite gneisses may be several meters apart. All of the observed jointing in outcrop appears to be closed rather than open. Folds
The five episodes of folding in the study area have been previously discussed. All folding episodes have been recognized in the Madras quadrangle. A refolded Buck Branch-Klondike fold trends across the quadrangle in a northeast-southwest trend and a southeast dip. This regional fold extends from Tucker to Newnan and is a synform (Higgins and others, '1980, in press). Buck Branch folds are tight isoclinal folds and the Klondike folds are also tight recumbent to reclined isoclinal folds. In the Madras quadrangle, the Buck Branch and Klondike folds are co-axial. The Newnan-Tucker synform is a Buck Branch Fold that has been modified by a Klondike fold. Elijah Mountain folds are the third generation of folds and trend in a northwest direction and are open warping folds. Scott Creek folds are the fourth generation of folds and are gentle to open upright folds which trend in a north-south direction. The Elijah Mountain and Scott Creek folds control the emplacement of the Palmetto Granite, which trends in a
A-8

0 1;2o/o- 2 o/o 0 2/o-4%
up.5i 4/o- 6%
6%8
Figure 3A. Poles perpendicular to foliation planes in the Madras Quadrangle.
1/2/o- 2 /o [] 2/o- 4/o ~ 4/o- 6''/o ~ 6%- 8%1
8% Sup Ill
Figure 4A. Poles perpendicular to joint planes in the Madras Quadrangle.

north to northwest direction. The Tara generation folds are east-west oriented, gentle to open upright folds, which fold the other folds. On map scale in the Madras quadrangle, the Scott Creek folds refold the Newnan-Tucker synform. The other generations are observed in the outcrops. Faults
Many faults were observed in outcrop, but none were traceable beyond the outcrop. Typically, these faults occ:ur on the limbs of Buck Branch or Klondike Folds. No faulting was observed associated with either the Scott Creek, Tara, or Elijah Mountain folds. The shearing probably took place when the Buck Branch folds were tightened by the Klondike folds.
CONCLUSIONS The folding episodes, faulting, etc. are the same as in the Snellville, Luxomni, and Suwanee quadrangles. The only event that may be different is the time of emplacement of the Palmetto granite. The Palmetto granite is probably older than or the same age as the Stone Mountain pluton. If the foliation in the granites is metamorphic, the granite is pre-metamorphic or syn-metamorphic and the Stone Mountain granite is post-metamorphic. However, the feldspars do not appear to have been rotated, which suggests that the foliation is primar~not metamorphic. Economic Resources The Palmetto Granite is currently being quarried as a class A aggregate. Additional quarry sites may be located by utilization of current mapping. Other potential economic resources include the garnet quartzite which may be a source for manganese. Geologic Hazards No geologic hazards exist as such in the Madras quadrangle, but potential geologic problems will arise in the location of septic tanks in
A-10

areas of the Palmetto granite. The Palmetto granite has flat rock outcrops and thin soil horizons. Foundations, septic tanks, and other construction could be expensive in these areas.
A-ll

Table 1--Modal analysis of the Palmetto granite

Mineral species

Plagioclase K-feldspar quartz biotite muscovite myrmekite sphene apatite epidote/allanite

Number of points

I

counted

344

389

204 139

26

13

9

6

10

Percentage of rock

I

:

by volume

30.0

33.9

11.31 12.14 2.27

1.14

0.24 0.52

0.82

I

I
t-' N

I

I

I

I

______J

Total 1,145

Table 2--Modal analysis of garnet quartzite

Mineral species

quartz

garnet

opaques

Fe-oxide

apatite Total

Number of points

Ii 831

207

counted

Percentage of rock

73.5

18.3

Number of points

)>
,.I....

counted

543

379

w

Percentage of rock

51.0

35.6

49 4.33

40 3.54

4 0.35

1,131 quartz-garnet layers estimated 35% of the rock

82 7.70

55 5.16

- - - - - - - - - - - - - - - - - - - - - - - -~

J 6
0.56

1,065 garnet-quartz layers estimated 65% of the rock

2,196

Table 3--Modal analysis of biotite gneiss

Mineral species plagioclase quartz biotite microcline* garnet epidote/allanite opaque

Number of points 638

225 165

44

7

counted

-~

Percentage of rock 60.2

19.8 14.5

3.88

'0.62

I

>---'
+:--

*includes perthite

---------~--------

5 0.44

1
i

0.10

i I

!

I
--- -----------.!

Total 1,135

UN ITED STAT ES

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ALLUVIUM - Terrace and stream deposits
DIABASE DIKE
STONE MOUNTAIN GRANITE medtum grained biotite muscovite granite
MICACEOUS QUARTZITE WITH MINOR MICA SCHIST

Will~rTrs Cl.!~'~

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BIOTITE GNEISS - AMPHIBOLITE

GGN-A

GRANITE GNEISS - AMPHIBOliTE

AMPHIBOLITE - Massive lenses of amphibolit e

A

within either biotite gneiss amphibolit e

or granite . gneiss amphibolite

Lgn

liTHONIA GNEISS -Banded to contorted biotite granite gneiss to biotite gne iss

GGN

GRANITE GNEISS -Medium grained light colored weakly foliated

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SYMBOLS Mineral
Strike and dip of foliation
Strike and dip of axial plane. trend and plunge of ax1s
Axial pl ane and trend and plunge of upr1ght f ol d
Mtn er al l1n ea t 1on Op en1ng warpin g synf orm
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Toor~r:~r.h; frorn aenal photog aphs by Kel sh plo tlP. r Aer <~1 pt-.otog ap!l-:; taken 1955. Field check 1956
PclyJ;:'lfliC projection. 1927 No rth Arn eri ra n drn1m l O.OOCJ- fo0 ! grid ba5ed ()!1 Georgi,; covrdinu t o> ~y~ te -n .
,.,,.,.t ct:ne. 1,000-mP\er Un1verr.;:~l Tr,r.sv.:: rsE> Merca tor
grid t:-:ks, zone 16. ~hown m tlue
Land lmes ar.d De Kalb county l ine f rom mforr1a t 10 n su ppli ed by De Kalb County Department of Plann rng
Rev i sio ns sho wn 10 pu p l c co rn pli ed frcm a!! na l p ho tog rap h s taken 1968 and 19 72 rh1 s 1n for matron not f1eld checke::l

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CONTOUR INTERVAL 20 FFET DATUM IS MEAN SEA LEVlL
THI S M AP COMPLIES Wlr H NII ,. IONA L MAP ACC U RACY SIAN DAR)S FO R SALE BY U . S. GEOLOG ICAL SURVEY. RESTON . VI RGIN IA 22092 A FOLD ER DESCRIBIN G TOPOGRAPHI C MAPS AN D SYMBO LS IS AVAILAB LE ON REQUE.ST

0
QU ADRANGLE LOCATION

ALL CONTACTS ARE APPROXIMATE Geology by :
Ro bert L. Atkins and Lisa G. Joyce
March 1979

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1]7000m (

ROAD C LA SS I F I CATIO~

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U S Route

Stille Route

. 33"45'
8--l '001

SNELLV ILLE. GA .
1956 PHOTOREV ISED 196!1 AND l<.l72
AMS 4 15 ! I SE SEHIES VM S

UNITED STATES DEPARTMENT OF THE INTER IOR
GEOLOGICAL SURVEY
84 07'30" 34 00'
57 ' 30 '' J'l 6l
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LUXOMNI QUADRANGLE
GEORO I A-OW I NNETT CO. 7.5 MINUTE SERIES (TOPOGRAPHIC)
34'"00'

EXPLANATION

1 450 000
D

FORMATIONS
DIABASE DIKE

AI
"64
Q

ALLUVIUM MICACEOUS QUARTZITE

GMS-A GARNET MICA SCHIST - AMPHIBOLITE

BS

BUTTON SCHIST

85-A

BUTTON SCHIST AMPHIBOLITE

BGN-BGGN BIOTITE GNEISS - BIOTITE GRANITE GNEISS

BGN

BIO' TITE GNEISS WITH MINOR AMPHIBOLI TE

57'30' BGN -A GGN-A

BIOTITE GNEISS- AMPHIBOLITE GRANITE GNEISS - AMPHIBOLITE

Lgn

LITHONIA GRANITE GNEISS

GGN

GRANITE GNEISS

J16Q

SYMBOLS

m

Mineral

_1_2.,_

Strike and dip of foliation

+

Strike and dip of 1nclined axial plane of fold , trend and plunge of axis
Strike and dip of vertical ax ial plane, trend and plunge of ax1s
Trend and plunge of mine ral lineat ion. crenulation , or fold axis
Open warping synfo rm

Opening warping antiform

ft

Isoc linal synform

All CONTACTS ARE APPROXIMATE
Geology by: Robert l. Atkins, June 1979

1410000

HET

.....

33 "52'30"

84 "07'3 0 "

Mapped . edited . and pu bl ish ed by t he Geo logical Survey

Con t rol by USGS . USC&GS, and Geo rg ia Geodetic Su rvey

Topography by nro togrammet n c me t hod !'; f rom .:er ta l pho tographs ta ken 1959 F tel d chec o~. e d 1963

P::llyconlc prOJeC t :on 1927 North Amer ica n datum 1J .OOO- foot gn d based on Georg1a coord 1nate s:ystem, west zone 1000 mete r Un1 versa1 Trans verse M erca to r grid t1c ks,
zone 15. show n 1n blue

F1ne red dashed l1nes 1nd1cate se lected fe nce an d f 1e ld l 1nes whe re e~?nPr.'l ly V1<:; 1b l e on ;H?r la l photographs Th1s 1nlormat 1on 15 unchec ked

Revi SIOn s stown n pu1ple co rn p 1l ed f ro m aenal pho tograp~ s take n 197 3 Th 1s Jnfo rmal10n not f 1eld checkec


0' I}.: ."
I.,T M GRID AN D i 91l MA G Nf ' N ORT H DECLINAIIQN AI C: ENTII? U l ~ HE. E r

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~ive Fork~

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!SNELLV I LLE) '72

4 I !) I I Sri

SCALE 124 000

iOJO
!
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CONTOUR I ~ TERVAL 20 FEET DA1U M IS MFIIN '>E.II LFV[l

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1\1111

!HI~ MA P i'U f\11)1 1 -.. WI 1-1 N.\1 1\J N AI MA P A C C UI~A CY !::>IAN D Ar-n~, FOR S ALE BY U _S GEOLOGICi-\L SURVEY . RESTON . VIRG INI A 22092 A FOLOrl~ Df:. L RIB ING I ., i)l,f"I/I, P!J I< MAP ~ ANI"! SYMBO l S IS AVAIL ABI.F ON RLQIHSI

GMS-A /ao 175 - - - - - - - i

Lgn
I
l
~ -,;c-.--+--..::ill 33. 52' 30"
Bl4 oo

RO AD CLASS it-lrAihJ N

Heavy duly Med ~ 't 'n du tv



ln ter:;tnw Route

(.'li/ILIR Ari GU L JC A' .'N

LUXOMN I, GA .
N335:? 5- W8400/7 .5
1963 PHOTOREV ISED 197 3
AMS 4 151 1 NE - SER 1ES V845

UN ITED STATES

DE PARTME NT OF T HE INTE RI OR

GEOLOGICAL SUR VEY

') ''30 11

'68

S UWANEE QU ADRANGLE
GE ORG IA 7.5 MINUTE SERIES (TOPOGRAPH IC)

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3 772

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EXPlANATION

FORMATIONS

A

AI

D

M

(f)
!,!,!
(.!)
0
_J
0 I f-
_J
0 0:::
,, ~ w
0::: CD

Sph
GSA Ph
GrPh B S Ph y

BMS

BMS-A

GGN

AMPHIBOLITE ALLUV IUM DIABASE MYLONITE PHYLLONITIC SCHIST PHY LLONI TIC GN EISS. SC HIST. AMPHIBOLITE GRAPHITIC PHYLLONITE BUTTON SCHIST PHYLLONITE BUTTON MICA SCHIST BUTTON MICA SCHIS T AM PHIBOLITE GRANITE GNEISS

Q

QUARTZITE

Fs

FACTORY SHOALS FORMATION

Qz

CHATTAHOOCHEE PALISADES QUARTZITE-

feldspathic or mic aceou s quartz1te

Pu

POWERS FERRY FORMATION -u nd1fferent1ated

gneis s. schi st. amphibol ite

0

Pggn

POWERS FERRY GRANITE GNEISS

Pms

POWERS FERRY MICA SCHIST

SYMBOLS

...1..8.......

Fo lia tion strike and dip

..1..2....-

Inc lined axia l pl ane

...1.5....--

Vertical axial plane

Li neation : Fold axis. mineral streak1ng

lso cl mal synfor m

Isoc linal antifo rm

'
1767 i '

' 67

Mapped , ed ited, and puol isned by the Geological Su rvey

r'ontro l by Li~GS . USC&G:;, US' E, <WC Georgi.., Geodelrc SLr vey

r o:orr.rphv Ly r'nt- gr.Hnrnetric rnt~U.oos Iron. o.~erial piHJtogrJptrs l K -~< l~hu .rn d 1963. Fre id C1leC""cd J J64

r ' \ ' nr r. rV;f:>(fir;,n . :S27 !~unh 1\tn,. r icm c.1tum l l. rl C 1 .11 gri a t.-rsed on Geo,,a rocHdrn<;te ' \ -l<: n r, WI:'<;! to r.e l r'r( r .t l ' i .l!l l d;"~! r arsJe:<;e !\lercatur gnd !l ck<:; , t:o r~ ~.: J, . ..,., n ,:1 t11 ue

F'l t 11d i r ~ h, d lr r o; l r: : .~h. r:!(d '('Icc nd f: !:, ; 'i rv t. h

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( LU X O M N /)

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SCALE I 24 000

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CO NTOU R I NTERVAL ?(1 rEF: r
DAT.JM l ':i ri! IAN S!. A l!V I l

J]3 ' 1'1

U1 M GRID A N D 19 r-IA G NE I N tliHH DF CLI N Al iON J.l . !'l rfF<' (l f S H!.II

H IS M AP f: 0 !\.1 PLif S WIIH NAllONA.I MAP AI IRA( Y SIANOI"\RrS roR SA l E BY U S GEO LOG ICAL SURVEY Ht':i ON VIRGINIA 2?092 A f OIDfR O[SCHIHING !OfJOl.RAPI!!C MAPS r,N[) SYM!lCH I AVAILA8L 01\i 11(Q1Jl::.T


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ALL CONTACTS ARE APPROXIMATE

Geology by:
J
Robert L. Atkins, Stephen W. Kline , and Lisa G. Joyce

JIG]OOOm N.

August 1979

. -~ .. t 104

. \.15 \.:

.~v 'El: ;

'

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11t'.W) dulv MPdum do\

ROAD CLASSIIICAliON l I~'~ :I \; ll: '
lnH'"I I'I ,r..: J.r
':JtP.k !Route

SUWANEE. GA.
N3400- W8400 7 '>
l%4
AMS 4 5~ II H SERII::S V845

UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOG ICAL SURVEY
0
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,, ,. ' ~ ~\

14

'15

Pg
. .ld '' ....
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~s-qm-p .

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'''o''B gn-oJ!lP /

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98 S! .lnht
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Bgn.ar'Qp



0

"

0
Undif.

l.tm \ '
'
Undif.

tHi Thoma:-;

.

.. . . '=1 ) Cr m;.:;rmuls

I
1~7

~"'

AmFffgn- bgn

'"l6

u :~,

""

84"45'

' II

Mapped ed ted and publsoed by th e Geo logical Survey

Cor1tr o l by USGS. USC&GS . an d Georgta Geodetic Survey

T u po~ r ap'ly by Jho togror>lmetr tC metho<Js from aeron'
ph o t ORr<:~pb!> ta.,;en 1962 Freid cnecked 1965

Poly-:o n rc pro re':ton 1'327 North Amer can datum
10 0 00 foot gnd ba~t>d on GNnga rooo rdtn<lte system.

10 00- mee r Unrvers al Tran:.ver se M ercator grrd t re ks,
!One \6. shown,,, blue
F.,!' re d d ashPd lrnes rn drcate se ec ted fence and fre ld l 11"1 t'S Nhere ; t-nr- rah vS rb l" cr, aeral photographs Th rs rnlormatr Or'! s unchec ked
Re"" S i o n~; sh o"'n m purple cornp 1led m cooper ation w1th S tQit.! of G eo rg1n agenc1e"- lr om aerral photographS takP. n 1973 Trw; rnforma t1on not f1eld c hecked

*
MN I
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Y M il 5 i i, . n.. .L'cl
LJ TM cihtf) ANfJ ::i ~ 1., 1\id~f- Trt N ORTH
(liC:I_ INAII (! r-I Ar ~, !Niir .11 :J !-j f f l

'16
SCALE ! .'I C(J''
.,

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'ONTOUR tNfERVAL 20 FEE T
[)AfLtM 1, f'lf.'ll\ )t,'\ ~E V El

IHI MAl t '.-!lt r S W il H NA JIO NA L MAP A C Cl i~II, L 'l' SIAN( o\1~1 'j
I On S.AU l-iY U S GFOI OGICAL SURVEY . RESTON . VIRGI N I A ?20G2
A rOLI I!R IISt.IIIHI!'<t, IQ t rJG HI<PHi f MAP S "ND SY MBOLS IS fo.Vfl lllll!lf ON RlQLf$1

MADRAS QUADRANG L E

GEORGIA

SERIES (TOPOGRAPHIC)

'10

84" l I lC
! 3J"n "09

v

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p,g -r \ I ,.

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-'i'o,46)

'

EXPlANATION

1 ' J\) 1 ~111 11 lt T

Qal

Quaternary alluvtum

Pg
Bgn-
amp

Porphyritic granite Biotite gneiss with Amph ibolite
Gq

Garnetile rous quartZite

(/.)

>oe
'-'
0

Undif. Und iIfere nti ate d

a:

Garnet quartz1te

Ms
amp

Mica schist wi th Amp hibolite

'-'

::r::

c...

a::

0

~
.<...(.

Dgn-

w.J
:::;:

bgn

Mtca schist
Amphibolite b1ot1te gnetss Amp-
bgn
Oiops1de gne1ss w1th biotite gne1ss

Amphibolite w1t h b1ot1te gne1ss

Amp-
hgnbgn

Amphibolite with hornblende gneiss biotite gneiss

I

NO TIME SEQUENCE IMPLIED (FOR METAMORPHIC ROCKS)

Pg
.,,.,.

Pg

90:.('

-,,04
Foliation

Joint

Lineation

Trend and Plunge

Ax1al plane

i' l1Q2

-ti-

Synform

+

Antiform

Overturned synform

GEOLOGY BY, Robert Dooly, 1979

31 00 2':. '

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11-.8

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H et~ ~y .!ur v M~:> rlru~ 1ul ~

ROAD CLASS IFICA.I tON Lrgn t duty Ummoroved dtrt S:ate RoutE>

MADRAS, GA.
N3322 .5-W8437 5/7 5
19 65 PHOTO REVISED 1973
AMS 4050 I NW- SERJES V845