Stratigraphy, structure, and metamorphism east of the Murphy syncline, Georgia-North Carolina : a field excursion for the Georgia Geological Society, November 3-5, 1978, Blairsville, Georgia

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STRATIGRAPHY, STRUCTURE, AND METAMORPHISM EAST OF
THE MURPHY SYNCLINE: GEORGIA-NORTH CAROLINA
A FIELD EXCURSION FOR THE GEORGIA GEOLOGICAL SOCIETY
NOVEMBER 3-5, 1978 BLAIRSVILLE, GEORGIA
By
R. D. DALLMEYER, P. S. COURTNEY, AND R. M. WOOTEN

CONTENTS

..... ............... . INTRODUCTION .

.

Page
1

.. . ... . . .. .. ......... REGIONAL STRATIGRAPHIC RElATIONS

.

3

. ... .. . .. . ... .. . . . .. ... . . . SUMMARY OF PREVIOUS WORK

5

ACKNOWLEDGMENTS ..................... ................... 9

STRATIGRAPHIC UNITS

Great Smoky Group
Introduction ................................... 10

Copperhi 11 Formation 10

Wehutty Formation . . 11

........ ....... . Hughes Gap Formation
...... ... ... . . Hothouse Formation

11
.. . .. . 13

Dean Formation ................................. 13

. . .. ...... Murphy Group

Nantahala Formation . . ..............

14

.. .. . Tusquitee Quartzite

.. ..

...

...... 15

. MABnruadrpsreshwtyoswMFnaorFrbmoleramt.iao.tnio.n.......................................................................

16 16
16

Nottely Quartzite ............................ 16

Mineral Bluff Formation ........................ 16

Igneous Lithologies
Granitic Dikes and Lenses ...................... 17
Tonalite ....................................... 17
..... Lake Chatuge Ultramafic ............... 18 METAMORPHISM ........................................... 19

STRUCTURE

Folding

Introduction ................................... 27

Pre-Tectonic Fabric ............................ 27

Early Folding ................... ..... 28

Late Folding ................................ 30

... Not e Ill

................

. ..

.... 30

Faulting ........ .................................. 31

CHRONOLOGie RELATIONSHIP BETWEEN DEFORMATION,

METAMORPHISM AND INTRUSION II f II tl f I II I I tl t I I

33

iii

Page
INSTRUCTIONS ............................................. 35

ROAD WG

...... Saturday .. , , ... , .....

37

...... Sunday . , .... o

41

DESCRIPTION OF EXCURSION STOPS

Saturday

Stop 1

t t I t I I I I t t I I I a I a t a' I I I t I I t I aI I t t I

. . . .... . . .. .... . . . .. Stop 2 ... . . . . . . . . . . ..... . .. Stop 3 .. .

. .

....... .."

.. . ... . . . . 0

. . .. .. . .. . . .. . . ... Stop 4 0

o I

. . .....

. .. .... ..... ..... ... .... . Stop 5

. .. . o I

... I 0 0

45 53 54 55 59

Sunday Introduction

...................................

62

Stop 6 a

62

Stop 7 . , , .... , .... o 62

Stop 8 , .... , , , . . . . 63

Stop 9 ....... , . , . . . . . . 64

Stop 10 ......... , . . . 68

.......... . Stop 11 ... , ... ~ .. ".. ~ . . .....

68

.......... . Stop 12 ........................... .

69

REFERENCES I I I 70

iv

Figure

ILLUSTRATIONS

Page

1. Blue Ridge geologic map ....... 2

2. Index of geologic mapping 4

3. Regional correlations of Great Smoky Group rocks 7

4. Map of "first appearance" metamorphic isograds 20

5. Mineral equilibria diagram 22

6. Temperature vs. oxygen fugacity diagram 24

7. Map of proposed Hayesville-Fries fault . 32

8. Relation between deformation, metamorphism,

and intrusion .... e .. 34

9. Road log geologic map with excursion route 36

10. Stratigraphic column for stop 1 46

11. Geologic map of the stop 1 area .. .. .. 47

12. Cross-section along the stop 1 traverse 48

13. Geologic map of the stop 4 area . 56

14. Geologic map of the stop 5 area .. 58

15. Stratigraphic column for stop 9 .. .. .. 66

16. Geologic map of the stop 9 area . . . 67

Photographs From stop 5 area . . . . . . . . . . . . . . . 60

TABLES Table 1. Lithostratigraphic correlations . 6

v

I NIRODUCTI ON

The 1978 Georgia_Geologi(;_g_l_Soci~~t:Y fi~ld__gxcursiol!__R:i.luxamiil_e _I'Q~~ka _

of the Great Smoky and Murphy Groups along the eastern margin of the Murphy

syncline in Georgia and southwestern North Carolina. The excursion has been

organized to:

1. Illustrate lithologic characteristics of formations within the

Great Smoky and Murphy Groups.

2. Analyze the polydeformational history recorded by the internal

fabric and areal distribution of these rocks.

3. Show the effects of progressive regional metamorphism within the

area.

4. Demonstrate the relative chronologie relationship between

metamorphism, deformation, and intrusion within this portion of

the Blue Ridge.

The excursion will cover portions of the following 7~' quadrangle topographic

maps:

Persimmon Creek, N.C. Murphy, N.c. Peachtree, N.C. Hayesville, N.C.

Mineral Bluff, Ga. Nottely Dam, Ga. Blairsville, Ga. Hiawassee, Ga. Culberson, Ga.

We hope that you will find the excursion enjoyable and rewarding.

1

0

mi

20

I

I

0 km 20

GA .

0 UNMETAMORPHOSED PALEOZOIC ROCKS

~'JifrtXJ MURPHY GROUP

~ WEISNER AND ASSOCrATED FORMATIONS

~ CHILHOWEE GROUP

~o)%1 WALDE N CRE E K GROUP

D GREAT SMOKY GROUP
I I SNOWBIR D GROUP

} OCOEE SUPERGRO'JP

~ ~ GRENVILLE BASEMENT TERRAIN

Figure 1. Simplified Blue Ridge geologic map. Adapted from Hadley (1970) and Hadley and Nelson (1971).

2

REGIONAL STRATIGRAPHIC RElATIONS Much of the southwestern Blue Ridge is underlain by a thick sequence of Late Precambrian, predominantly clastic metasedimentary rocks of the Ocoee Supergroup (King and others, 1958; Hadley, 1970). These rocks unconformably overlie an older basement terrain consisting of polymetamorphic gneisses and associated granitic intrusives (Fig. 1). U-Pb zircon ages (Davis and others, 1962) and Rb-Sr whole-rock dating (Fullagar and Odom, 1973) indicates a minimum age of 1.1 b.y. for the basement complex. This date is similar to that recorded in variably retrograded gneissic inliers throughout the Appalachian orogen (Dallmeyer, 1975, 1978) and suggests that the oldest Blue Ridge rocks are part of a widespread basement terrain which is probably continuous into the Adirondack Highlands of New York and the Grenville Province of the Canadian Shield. Both the basement terrain and overlying Ocoee Supergroup are broken by numerous thrust faults in eastern Tennessee and western North Carolina (Fig. 1). Although stratigraphic correlations are difficult in this area, Ocoee rocks have been subdivided into the Snowbird, Great Smoky, and Walden Creek Groups (listed in ascending stratigraphic order). Detailed descript.ions of these groups and the basis for their definition are summarized in King and others (1958) and Hadley (1970). Correlatives of the Snowbird Group have not been recognized southeast of the Great Smoky Mountains (Hadley and Nelson, 1971; Merschat and Wiener, 1978), and the Great Smoky Group directly overlies the Blue Ridge basement terrain. In Georgia and southwestern North Carolina the Great Smoky Group is conformably overlain by Early Paleozoic (?) metasedimentary rocks of the Murphy Group. These lithologies are exposed within the Murphy syncline, a major Blue Ridge structural element which extends from Cartersville, Georgia, to Bryson City, North Carolina (Fig. 1).
3

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o km ro

- ,"

,

,
"

,

,.,.

/ " " "

5

"

9

II

1. Keith, 1907.

2. LaForge and Phalen, 1913.

3. Hurst, 1955.

4. Fairley, 1965.

5. Hernon, 1964 and 1968.

6. Forrest, 197 5.

2

7. Mohr, 1971 and 1973.

8. Dupuis, 1975.

9. Price, 1977.

10. Dougherty, 1977.

ll. Shellebarger and Potter, 1978.

12. Courtney, (in progress).

13. Wooten (in progress). 4

Figure 2. Index of geologic mapping within and contiguous to the Murphy syncline (shaded area includes all Murphy Group lithologies). In addition to the work shown, large-scale maps by Hadley and Nelson (1971) and Merschat and Wiener (1973, 1975) cover the North Carolina portion of the syncline.

4

SUMMARY OF PREVIOUS WORK Keith (1907) and LaForge and Phalen (1913) defined six formations within the Murphy lithologic sequence (Fig. 2; Table 1). Metaconglomeratic rocks which immediately underlie the Murphy sequence were called the Great Smoky conglomerate (Keith) or the Great Smoky formation (LaForge and Phalen). All rocks below this stratigraphic interval were termed Carolina gneiss and considered to be of Archean age. Hurst (1955) revised stratigraphic relations within the Murphy syncline in north-central Georgia (Fig. 2; Table 1). He also proposed that all older rocks in this area be considered part of the Great Smoky Group and defined the Copperhill, Hughes Gap, Hothouse, and Dean formations (listed in ascending stratigraphic order). Hurst noted that the uppermost 50-100m of the Copperhill formation contained abundant dark schists and phyllites which were gradational into the overlying Hughes Gap formation. Hernon (1964, 1968) demonstrated that this transitional zone thickens northward from the area of Hurst's study (Fig. 2). Because of its greater areal extent and distinctive lithologic characteristics, Hernon separated the transitional zone from Hurst's Copperhill formation and named it the Wehutty formation (Table 1). Hurst outlined the overall structural setting of the Murphy syncline and noted locally complex deformational features. However, it was the work of Forrest (1975; published earlier in Power and Forrest, 1971) which first outlined the polydeformational character of the area (Fig. 2) and therefore necessitated minor revisions in the Murphy stratigraphy proposed by Hurst (Table 1). Holcomb (1973) has described a similarly complex folding history within Great Smoky Group rocks along the western limb of the Murphy syncline near Ducktown, Tennessee. Mapping along the northeastern termination of the Murphy syncline in North
5

Keith (1907); LaForge Hurst (1955) and Phalen (1913)

Hernon (1965, 1968)

Mohr (1971, 1973)

Mineral B~uff Fm. Nottely Qtzite.

Mineral Bluff Fm a

Power and Forrest (1971) ; Forrest (1975)
Mineral Bluff Fm.

Nottely Qtzite. Andrews Schist Murphy Marble
Valleytown Fm.
Brasstown Schist
Tu?quitee Qtzite.

Andrews Fm .
' Murphy Marble
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"' Brasstown Frn.
.<a><:.
"'"'
::;: Tusquitee Qtzite.

Nottely Qtzite.
Andrews Schist
......,.
""' Murphy Marble
.."..
.Q
"':'.":' Valleytown and
~ Brasstown Frns. .<a:. ~ :;:
Tusquitee Qtzite.

unexposed
a.
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L'"' ...j.J. OJ r - - - - - - -
"'.<.a>..:<. Brasstown Fm.
"::;:
Tusquitee Member

Nottely Qtzite.

Andrews Fm.

...,

....
OJ

Murphy Marble

Ill

..O..J
.Q
"':':";:' Brasstown Fm.
.<>.a.<:.. f

Tusquitee Qtzite.

Dupuis (1975); Price (1977); Dougherty (1977); Shellebarger and Potter (1978)

1'his report.

Mineral Bluff Fm~
- - ----- - -

14ineral Bluff Fm. Nottely Qtzite.

Andrews Fm~

a.

unexposed

0

a.

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-

--- -

-

"' " .<>a<:. Brasstown Fm.

--

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Tusquitee Qtzite.

Murphy Marble Brasstown Fm. Tusquitee Otzite.

Nantahala Slate

Nantahala Slate

Nantahala Slate

Nantahala Fm.

Nantahala Fm.

Nantahala Fm.

Nantahala Fm ..

Great Smoky Fm. (conglomerate) Cl'
Carolina Gneiss

Dean Fm .
a. Hothouse Fm.
" 0 "'"'
>< Hughes Gap Fm. -"' e 0
Ul
.jJ Transition Zone
"Q..'.) "
Copperhill Fm.

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Dean Fm.
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l)'!ember
mre!l Alnmons Fm.
""'0

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"'"' Grassy Branch
>< Fm,

-s0"'
[fJ
Anakeesta Frn.

not studied

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Dean Fm.
01. Hothouse Frn.
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Dean Frn .

a. a. Hothouse Fm.

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Thunderhead

r- --- - - -

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Fm.

r-- - - - - ---r- - -----

unexposed

r- - - - - - .- -

-~

unexposed

unexposed

Grenville Age

unexposed

Basement

Table 1. Proposed lithostratigraphic correlations within the Murphy and Great Smoky Groups. Refer to Figure 2 for the locations of individual study areas.

GREAT SMOKY GROUP
m0 0 DEAN Fm .
ITITiffi1 HOTHOUSE, AMMONS, lillilliJ GRASSY BRANCH Fms.
[ill] HUGHES GAP Fm.

LAKE CHATUGE
< ~
: ULTRAMAFIC

WEHUTTY, ANAKEESTA Fms.

ltit!11J COPPERHILL Fm .
r q GREAT SMOKY GROUP lii:::J UNDIVIDED

~ GRENVILLE AGE
l!...:J BASEMENT

Figure 3. Proposed regional correlations within the Murphy and Great Smoky Groups. Adapted from Hadley and Nelson (1971), and Merschat and Wiener (1973 , 1975). Location of Blairsville , Ga. is indicated (*).
7

MURPHY GROUP
... MINERAL BLUFF Fm .
:::-: NOTTELY Qtzite.
ANDREWS Fm . MURPHY Marble
G BRASSTOWN Fm .
D TUSQUITEE Qtzite. NANTAHALA Fm.

Carolina (Fig. 2) was carried out by Mohr (1971, 1973). He described the following major Great Smoky Group units from this area (listed in ascending stratigraphic sequence): metasandstone and schist, the Anakeesta formation (predominantly graphitic phyllite and schist interlayered with dark metasiltstone), the Grassy Branch and Ammons formations, and the Dean formation (Table 2). The Ammons formation is litho logically similar to the Hothouse formation defined by Hurst (1955), Merschat and Wiener (1973, 1975) considered the formations correlative in their compilation map of Ocoee rocks in North Carolina and Tennessee (Fig. 3). We suggest that both the stratigraphic position and lithologic characteristics of the Grassy Branch and Anakeesta formations are similar to those of the Hughes Gap and Wehutty formations mapped in Georgia. Therefore, they also may be lithostratigraphic correlatives (Table 1). The relationship between Hurst's Copperhill formation and the metasandstoneschist unit of Mohr is uncertain.
ACKNOWLEDGMENTS Detailed mapping (1:12,000) was initiated in 1973 by University of Georgia students along the eastern margin of the Murphy syncline in north-central Georgia (Fig. 2). This field excursion is largely based on a compilation of this work, including masters theses completed by Dupuis (1975), Price (1977), and Dougherty (1977). Masters work by Courtney and Wooten is currently in progress. Mapping within the southern half of the Blairsville quadrangle formed the basis of an undergraduate thesis by Jeff Shellebarger and Phil Potter (1978 ).
9

STRATIGRAPHIC UNITS Great Smoky Group
Introduction The Great Smoky Group in north-central Georgia and southwestern North
Carolina is a heterogeneous, internally conformable, predominantly clastic metasedimentary succession. Many individual lithologic types are common throughout the sequence. Therefore, formations must be defined and mapped on the basis of distinctive lithologic associations and/or the presence or absence of diagnostic, although possibly minor rock types. In the brief summary of the stratigraphic section which follows, attention will be focused on describing diagnostic lithologic associations and outlining the criteria used to define formation boundaries within the excursion area.
Copperhill Formation The stratigraphically oldest rocks exposed within the excursion area have
been correlated with the Copperhill formation defined by Hurst (1955) along the western limb of the Murphy syncline (excluding the uppermost transitional zone which he included within the formation; Table 1). This formation is distinguished by numerous metaconglomeratic beds which are most abundant and constitute mappable horizons within the upper portion of the unit. Metaconglomerate is interlayered with or gradational into more abundant horizons of metasandstone and conglomeratic metasandstone. The thickness of individual clastic beds varies from 2 em to more than 9 m, but the average is less than l m. Much thinner beds of muscovite schist, biotite-muscovite schist, and, locally, kyanite (sillimanite)-biotite-muscovite schist are interlayered with the clastic rocks. Schist and metasandstone frequently show rhythmic interlayering with considerable intergrading. Calc-silicate granofels (previously referred to as "pseudodiorite" by Keith, 1907, and by Hurst, 1955) although
10

not a major lithologic constituent, is distributed throughout the form~tion and characteristically occurs as ellipsoidal bodies. Overall, the formation consists of approximately 50% metasandstone, 15% metaconglomerate, and 35% schist. However, the relative percentage of clastic rocks gradually increases upsection.
Wehutty Formation The Wehutty formation is characterized by dark, generally graphitic
muscovite-rich schist and/or phyllite. Locally these contain kyanite (sillimanite), garnet, staurolite, plagioclase, and/or biotite. The schist and phyllite is interlayered with much less abundant argillaceous and slightly feldspathic metasandstone and/or metasiltstone. Metaconglomerate is not abundant, but thin horizons are locally found throughout, Those in the lower part of the unit are typically more argillaceous and contain more feldspar and lithic clasts than do those in the upper portion of the formation, Calc-silicate granofels occurs throughout the unit and generally forms bedded horizons.
In general, metasandstone is more argillaceous and feldspathic than that within the Copperhill formation. It also tends to be less thickly bedded, The contact with the Copperhill formation is conformable and marked by a gradual change from a predominance of metasandstone to a predominance of schist and/or phyllite; the latter becoming increasingly more graphitic upsection. The contact has been arbitrarily placed below the last mappable graphitic schist and/or phyllite horizon.
Hughes Gap Formation
A distinctive lithologic association has been mapped in the southwestern
portion of the excursion area which is similar to that described by Hurst (1955)
11

for the Hughes Gap formation. This association includes argillaceous and generally feldspathic metasandstone (60%), a variety of schists (30%), and metaconglomerate (5-10%). Bedded calc-silicate granofels is ubiquitous but nowhere abundant. This association differs from the underlying Wehutty formation in an increased abundance of metasandstone and a lack of graphitic, muscovite-rich schist and/or phyllite. The contact between the two associations has been located at the top of the last mappable graphitic schist and/or phyllite horizon within the Wehutty formation.
Schist within the l-111Ehes Gap formation shows a wide variation in mineralogy and texture. Most common are muscovite- and biotite-muscovite schist with frequently abundant porphyroblasrn of garnet and/or staurolite. Finegrained, sericitic schists with randomly-oriented biotite porphyoblasts locally occur interbedded with metasandstone (locally conglomeratic) in 5-10 m thick intervals throughout the formation. These "cross-biotite" schists are very similar to those which make up a considerable portion of the Dean formation.
In the southwestern portion of the excursion area, the abundance of schist relative to metasandstone increases upward in the Hughes Gap formation. This gradual change culminates in a 20-30 m thick sequence of thinly-bedded schists. This section is overlain by a 15-30 m thick interval of argillaceous metasandstone (in 1-2 m beds) with abundant interbedded feldspathic and lithic metaconglomerate horizons and subordinate schist. In this area, the contact between the Hughes Gap and overlying Hothouse formations has been mapped at the top of the conglomeratic sequence.
The transitional zone between the Hughes Gap and Hothouse formations becomes increasingly less well-defined east and northeastward across the excursion area. In addition, the mineralogic and textural variability of schists within the Hughes Gap stratigraphic interval diminishes. These changes
12

reduce the overall lithologic contrast between the Hughes Gap and Hothouse formations. Therefore, over much of the excursion area the two sequences have not been separated and only the Hothouse formation has been mapped with a lower contact placed at the top of the last mappable graphitic schist and/or phyllite horizon within the underlying Wehutty formation.
Hothouse Formation The Hothouse formation consists predominantly of a repetitive sequence of
variably argillaceous and consistently feldspathic metasandstones which are rhythmically interbedded with coarse-grained, muscovite and biotite-muscovite schists (locally garnet-bearing). Individual clastic beds range in thickness from several millimeters to greater than 2 m, however most are less than 1m. The schists are generally more thinly bedded. Calc-silicate granofels is rare throughout the formation. Approximately 70 m above the lower contact, a 10-20 m sequence of 1-3 m thick quartz-pebble metaconglomerate and conglomeratic metasandstone beds are interlayered with schist forming a mappable horizon. Except for this zone, metaconglomerate is not present within the formation. Because of the relative abundance of non-resistant, feldspathic metasandstone, the Hothouse formation typically underlies belts of low relief within the excursion area.
Dean Formation The Dean formation consists predominantly of biotite-muscovite schists
which locally contain abundant porphyroblasts of garnet, staurolite, chlorite and/ or plagioclase. Particularly di agnostic are fine-grained, seri ci tic schists with randomly-oriented biotite porphyroblasts ("cross-biotite schist"), Several beds of these schists contain abundant staurolite and feldspar and constitute mappable horizons within the middle and upper portions of the
13

formation. Interlayered with the schists are variably argillaceous and generally
feldspathic metasandstone and conglomeratic metasandstone (30-35% of the formation). Metaconglomerate horizons are locally abundant, particularly near the top and bottom of the unit. These are typically gradational into conglomeratic metasandstone. Metaconglomerate within the lower portion of the Dean formation consist largely of quartz-pebble clasts. Those within the upper part of the unit contain, in addition to quartz, detrital plagioclase, microcline, and/or lithic fragments.
The contact between the Dean and Hothouse formations is gradational. It has been arbitrarily placed below a 30-75 m interval of fine-grained, cross-biotite schists which are interlayered with non-feldspathic, quartzpebble metaconglomerates and argillaceous metasandstones.
Murphy Group Introduction
Formations which comprise the Murphy Group are characterized by significantly less internal lithologic variability than those within the Great Smoky Group. Nevertheless, formation boundaries are typically gradational and must be arbitrarily located in most instances. Detailed descriptions of the Murphy Group formations have been presented by Hurst (1955), Hernon (1964, 1968), Power and Forrest (1971), Forrest (1975), and Mohr (1971, 1973). Therefore, only a brief outline of their most distinctive lithologic characteristics will be presented here,
Nantahala Formation The Nantahala formation consists predominantly of interlaminated,
sulfide-rich and graphitic metasiltstone and fine-grained metasandstone. A
14

subordinate amount of graphitic phyllite is locally interbedded with the clastic rocks in the northeastern portion of the excursion area. However, this lithology becomes increasingly more prevalent southwestward across the area. Thin beds of buff-colored, feldspathic metasandstone occur throughout the formation. These increase both in number and thickness as the unit grades upward into the overlying Tusquitee quartzite. In many places this contact fs marked by a 3-10 m hybrid zone of "zebra-striped" rocks consisting of nearly equal proportions of dark- and buff-colored metasandstone. Several thick beds (1-2m) of buff metasandstone occur within a 75-100 m interval near the base of the Nantahala formation. Below this interval the unit is lithologically gradational into the underlying Dean formation. Within this transitional zone the abundance of thinly bedded, graphitic phyllite and/or metasiltstone decreases and the number of more thickly bedded argillaceous metasandstone beds increases. Fine-grained, biotite-muscovite schists also become increasingly more numerous toward the base of the transitional zone. The contact with the Dean formation has been mapped below this transitional interval and above the first appearance of quartz-pebble metaconglomerate and interlayered cross-biotite schist. Tusquitee Quartzite
Although extremely variable in thickness (2-50m), the Tusquitee quartzite is a mappable unit above the Nantahala formation throughout the excursion area. It consists largely of variably argillaceous and generally feldspathic metasandstone with frequent intercalations of dark-colored, graphitic metasiltstone and/or phyllite. The unit is best characterized as the last predominantly metasandstone horizon between the Nantahala and overlying Brasstown formations.
15

Brasstown Formation The Brasstown formation is a thick sequence of dark-gray (~ staurolite)
garnet-biotite-muscovite schists (typically with a cross-biotite texture) which are interlaminated with lighter-colored, argillaceous fine-grained metasandstone and/or metasiltstone. The regular interlayering of these lithologies results in a characteristic laminated appearance which may be recognized even in deeply weathered exposures. The overall percentage of metasandstone and/or metasiltstone increases markedly toward the base of the formation. In general, the schists also become darker and somewhat graphitic downsection.
Murphy Marble The Murphy marble consists of impure, slightly graphitic calcareous
and dolomitic marble. Talc-rich and pelitic horizons are locally abundant.
Andrews Formation The Andrews formation is a thin horizon of interlayered marble and
sulfide-bearing, cross-biotite schist which gradationally overlies the Murphy marble.
Nottely Quartzite The Nottely quartzite is a thi~, locally sericitic white metasandstone.
The quartzite has been mapped for a considerable distance along the western limb of the Murphy syncline but has only been tentatively recognized at one locality along the eastern limb.
Mineral Bluff Formation The Mineral Bluff formation consists predominantly of a thick sequence of
chlorite-sericite phyllites. Horizons of interlayered argillaceous and feldspathic metasandstone, feldspathic and/or quartz-pebble metaconglomerate,
16

graphitic phyllite and/or schist, and chloritoid-bearing phyllite may be mapped locally. Discontinuous and minor horizons of garnet-staurolite-biotitemuscovite schist and garnet-bearing cross-biotite schist have been described from several localities.
Igneous Lithologies Granitic Dikes and Lenses
Several thin dikes of (~ biotite), muscovite, plagioclase, quartz, (perthitic) microcline granite (locally pegmatitic) are found to have generally discordant relations in the western portion of the excursion area. These become increasingly more numerous and less obviously discordant northeastward. In these areas the quartzo-feldspathic material occurs throughout metaclastic horizons, usually as small stringers and more or less pediform, generally coarse-grained segregations. The presence of an irregular, biotite-rich selvage around the perimeter of this material is inferred to represent the resistite mineralogy of the metaclastic host which was largely excluded and thus concentrated during partial melting. Throughout the eastern portion of the excursion area this quartzo-feldspathic material is considered to have been locally derived,
Tonalite Numerous small dikes and sills of tonalite (leucocratic oligoclase-
quartz diorite or "trondhjemite") intrude Great Smoky Group rocks and are locally abundant. Similar rocks have been reported from other Blue Ridge localities by Cameron (1950), Hadley and Goldsmith (1963), Bryant and Reed (1970), Hatcher 0974), and Kish and others (1975). Within the excursion area the tonalites range up to 8 m in thickness but most are less then 2 m, Although contacts are sharp, well-defined contact metamorphic effects are not
17

observed. Several generations of tonalite intrusion are suggested by generally consistent cross-cutting relationships.
The tonalite is variable in grain-size but may be generally classified into two distinct textural types:
1. A porphyritic or microporphyritic, fine-grained variety with oligoclase phenocrysts set in an aphanitic matrix.
2. A mineralogically similar phaneritic variety with roughly equidimensional oligoclase and quartz which generally cross-cuts the porphyritic variety.
The tonalite is composed predominantly of subhedral calcic oligoclase phenocrysts which are both oscillatorily and nom~ally zoned. Rims of the crystals typically have a small overgrowth of less calcic oligoclase. The phenocrysts are set in a groundmass of oligoclase and quartz. Biotite and/or muscovite are locally present as groundmass and/or phenocrystal phases. Where abundant they usually have a preferred orientation which imparts a foliation to the tonalite. Aggreates of coarser-grained micas occur in many intrusions and probably are remnants of partially resorbed xenoliths. Lake Chatuge Ultramafic
In the easternmost part of the excursion area the Lake Chatuge, alpinetype ultramafic intrudes high-grade Great Smoky Group (?) rocks. Lithologies within the ultramafic include dunite, coronite, troctolite, olivine gabbro, and eclogite. Detailed descriptions of the petrologic character of the intrusion and its emplacement history are given by Hartley (1973), Dallmeyer (1974), and Hartley and Penley (1974).
18

METAMORPHISM Mapping in the Great Smoky Mountains by Hamilton (1961), Hadley and Goldsmith (1963), King (1964), and Neuman and Nelson (1965) demonstrated that Blue Ridge rocks were affected by a progressive, Barrovian-type regional metamorphism which generally increased in intensity southeastward. Studies by Hurst and Schlee (1962), Smith and others (1969), Carpenter (1970), and Hurst (1973) approximately located the first appearances of metamorphic index minerals within the Blue Rictge south of the Great Smoky Mountains. These workers outlined an elongate, northeast-trending zone of maximum Blue Ridge metamorphism (sillimanite grade) flanked on the northwest and southeast by lower-grade terrains (see regional geologic map of Hadley and Nelson, 1971). Within the excursion area a somewhat more complicated metamorphic pattern is evident as rocks within the core of the Murphy syncline are markedly lower grade (uppermost greenschist facies) than those exposed on both limbs. Although the first appearances of metamorphic index minerals have been mapped within this area (Fig. 4), these "isograds" show a marked parallelism with lithologic contacts. This suggests significant bulk compositional control on the regional ''isograd" pattern. Detailed petrologic studies have not been carried out in the area and rigorous control on the systematic regional variations in intensive metamorphic parameters is not presently available. The first stop on this excursion will traverse from chloritoid-bearing chlorite-muscovite phyllites within the Mineral Bluff formation into staurolitebearing garnet-biotite-muscovite schists of the Brasstown formation. Mineralogical variations observed along the traverse reflect a change from the uppermost greenschist facies to lower amphibolite facies. The reactions involved in the disappearance of chloritoid along the traverse cannot be established because of the bulk compositional restrictions on its occurence.
19

0

.

mi.

0

km.

10 10

ch

:

:'&:>

.. ~

N 0

Figure 4. Generalized map of the Murphy syncline and contiguous areas showing the first appearance "isograds" of metamorphic index minerals
(G = garnet, S = staurolite, K = kyanite, Sill = sillimanite; letters
are shown on the high-grade side of the isograd). Compiled from Hernon (1964, 1968), Hurst (1973), and Forrest (1975). The Murphy marble (black), Wehutty formation (shaded), and Copperhill formation (ch) are outlined for reference. The contact between Nantahala and Dean formations is also shown (n-d).

Several reactions have been proposed for the prograde breakdown of chloritoid (Richardson, 1968; Ganguly, 1968, 1969, 1972; Hoschek, 1969; Grieve and Fawcett, 1974; Holdaway, 1978). Those which have been experimentally studied by these workers are listed below and are located in Figure 51
Fe-chloritoid + aluminosilicate + 02 :;::::::!:Fe-staurolite +magnetite + quartz (1)
Fe-chlori toid + quartz + o2 ~ Fe-stauroli te + almandine + magnetite + H20 (2)
chloritoid + muscovite + quartz:;::::::!: staurolite + biotite + magnetite (3). Reaction (2) defines the maximum stability of chloritoid in the presence of quartz. However, the reaction involving the disappearance of chloritoid in association with muscovite and quartz (3) is more likely to have limited the upper stability of chloritoid in the muscovite-rich lithologies of the Mineral Bluff and Brasstown formations. Reaction (1) can lead to the prograde formation of staurolite. However, the reaction most often desc.ri bed for the prograde formation of staurolite in pelitic bulk compositions is:
chlorite + muscovite~ staurolite + biotite + quartz + H20 (4).
This reaction has been experimentally located by Hoschek (1969) with a QFM
buffer and a starting composition of Mg/Mg+Fe = 0.4 (Fig. 5), Together with
the overall metamorphic character of the excursion area, reactions (1-4) suggest that temperatures along the Stop 1 traverse could not have exceeded approximately 550C and that pressures below approximately 6 Kb were probably maintained (fig. 5). These conditions are tentatively proposed to characterize the staurolite appearance "isograd" shown in Figure 4.
Kyanite is present throughout the Wehutty formation in the southwestern portion of the excursion area, Fibrolitic to coarse-grained sillimanite occurs in the northeast and an overall northeastward increase in metamorphic grade is indicated. However, muscovite and quartz are mutually compatible throughout the excursion area which indicates that metamorphic conditions appropriate for
21

(I)

(3)

8
-CD
-~
w a::
e=n> ~ 6
a::
a..
4

....
_,(I) :+E ~ + .N... .Q... +0
() .... (I)
500

,:

\:
\ ~
.,':: \ :: \: (Jg,

JS\ .{iD~

. I: lill. ,.-

;~

N

\:Zoo' ....

: II' 0

i:l i

: :

:
(I)

. i :11
:/

. .J.' tl-:

.,:. .1 :., , :.

,:

~ ~

;

.. I.

I .I ~..I

:,. .' ;f.
I , .
0 .5 i

.
;.
;:..

(5)

A I
I

I

I

0.6 I

.. I ,.

I

;~

0.8 I

....... =GRANITE SOLIDUS -- =MUS+QTZ

I

I 1.0

600

700

TEMPERATURE (C)
Figure S. Relevant mineral equilibria for establishing metamorphic pressure and temperature conditions within the excursion area. Aluminosilicate triple point from Holdaway (1971). Numers in parenthesis refer to equations in text. Curves defining the maximum stability of muscovite in association with quartz are shown for several values of XHzO in the fluid phase, The granite solidus is also shown for several fluid compos1tions. Circled numbers refer to excursion stop locations. Those enclosed with a solid circle have limiting assemblages for estimating metamorphic conditions. Those enclosed with a broken circle are only approximately located with respect to temperature and pressure. Refer to text for sources.

the second sillimanite isograd reaction were not attained. Radiating clusters of exceedingly fine-grained (microscopically observable only) sillimanite occur within oligoclase and/or biotite across the south-central portion of the area.
Locally in the Wehutty formation exposed within the south-central portion of the excursion area, non-graphitic schists include horizons with
the assemblage staurolite + quartz + muscovite + biotite ~ garnet~ kyanite
+ sillimanite+ ilmenite. Staurolite within this assemblage typically occurs as large poikiloblasts which are pseudomorphically overgrown by coarse-grained muscovite. Often, only isolated but optically continuous areas of staurolite remain. These characteristics suggest that conditions approaching those of the upper stability limit of staurolite may have been attained during metamorphism. The reaction defining the maximum stability of Fe-staurolite in association with quartz has been experimentally located by Richardson (1968) with a QFM buffer (Fig. 5):
Fe-staurolite + quartz~almandine + aluminosilicate +magnetite (5). However, in pelitic bulk compositions reactions defining the maximum stability of staurolite in the presence of quartz, muscovite and/or biotite are probably more appropriate:
staurolite + muscovite + quartz~ biotite + aluminosilicate + H20 (6) staurolite + biotite + quartz ;;=!:garnet + muscovite + H20 (7). Ganguly (1968) demonstrated that reactions (5-7) may be shown as univariant equilibria which intersect in an invariant point in an isobaric 0 2-T section (Fig. 6). He suggested that an f0 2 within the lower portion of the magnetite stability field is appropriate for the invariant point. The presence of ilmenite within non-graphitic schists of the Wehutty formation suggests that
a similar range of t02 was maintained during their metamorphism. Note from
Figure 6 that at the same value of f0 2 , reactions defining the disappearance 23

(6)

C\l

0

(7)

'+-

TEMP

I
,,,II , '
\
' ' '
0
.....,:..:z:CV
...t.o.
oq"
.,. .,.
~. oq"
(5)

Figure 6. Schematic isobaric diagram illustrating the effect of
temperature and oxygen fugacity on reactions 5-7 discussed in the text. Reactions 6 and 7 more likely defined the maximum stability of staurolite during metamorphism of the pelitic schists within the excursion area. Note that at similar oxygen fugacities, reactions 6 and 7 occur at lower temperatures than reaction 5
which defines the maximum stability of staurolite + quartz.
Therefore, conditions for the upper stability of staurolite within the excursion area have been shifted to slightly lower temperatures than those defined by reaction 5 (dashed line in
= = Fig. 5). Mineral phases indicated by: bi biotite, st = = staurolite, qtz quartz, Alsi aluminosilicate, mus =muscovite, = alm almandine garnet. Figure adapted from Ganguly (1968).

24

of staurolite in association with quartz, muscovite and/or biotite occur at lower temperatures than that which marks the disappearance of the staurolite + quartz association (Fig. 5).
The presence of kyanite and fine-grained sillimanite within graphitic schists interlayered with the staurolite-bearing rocks provides additional control on the intensive parameters of metamorphism within this area because it suggests that conditions were near those required for the kyanite-sillimanite inversion (Fig. 5). In addition, the stable coexistance of muscovite and quartz in all lithologies indicates that temperatures and pressures were below those required for the second sillimanite isograd reaction:
muscovite+ quartz;::!:orthoclase +sillimanite+ H20 (8). Kerrick (1972) demonstrated that the conditions appropriate for this reaction are strongly dependent upon the mole fraction of H20 within interstitial fluids. His work indicated that decreasing the mole fraction of water within the fluids significantly lowersrequisite temperatures and pressures for
reaction (8) (Fig. 5). A variety of gases (co2 , CO, CH4) are produced during
metamorphism of carbonaceous sedimentary rocks. Because of their presence, metamorphic fluids within graphitic rocks such as the Wehutty formation schists
would have a relatively low mole fraction of H2o. Kerrick suggested that meta-
morphic fluids in equilibrium with graphitic pelites would likely have a mole fraction of water in the range of 0.8-0.5. The conditions at which reaction (8) occurs at these fluid compositions (Fig. 5) are considered an upper limit for possible metamorphic parameters in this area. Together with the controls afforded by the apparent proximity to the kyanite-sillimanite inversion and the staurolite+ quartz+ biotite and/or muscovite breakdown reactions, it appears that temperatures on the order of 650-6750 C and total pressures of 6.5-7.5 Kb were attained during metamorphism within this area.
25

The effects of incipient anatexis are obvious in metaclastic rocks of

the Copperhill formation within the south-central and eastern portions of

the excursion area. These include numerous small veins and stringers of

quartzo-feldspathic material and apparently locally-derived pegmatites. The

appearance of anatectic material is also marked by a loss of well-defined

clastic textures because of the nearly complete recrystallization of most

mineral constituents. A drastic change in lithologic character results.

Kerrick (1972) demonstrated that the temperatures and pressures at which melting

begins in granitic bulk compositions is controlled by the composition of the

coexisting fluid phasP.. Increasinely higher temperatures and pressures are

required for melting as the mole fraction of H20 in the fluid phase is
reduced (Fig. 5). Not~ from Figure 5 that when the mole fraction of H2o in
the fluid phase is approximately greater than 0.5, conditions required for

melting are compatible with those defined for metamorphism in this area.

However, when the mole fraction of water in the fluid phase is approximately

less than 0.5, the temperatures and pressures required for melting are greater

than those which appear to have been attained during metamorphism. Deviation

from a granitic bulk composition by the presence of CaO in the natural system

increases

the

melting

conditions

for

all

values

of

XH 2

0



The

relationship

between fluid composition and melting temperatures is particularily significant

throughout the excursion area because during metamorphism of the graphitic
schists of the Wehutty formation, the mole fraction of H2o within the fluid
phase was likely to have been significantly less than 1.0 because of the diluting
affect of co2 , CO, and CH4 , thereby increasing the temperatures and pressures
required for partial melting within these and interlayered lithologies. This

is probably why anatexis is first seen within metaclastic lithologies of the

Copperhill formation.

26

The regional extent and local degree of anatexis increases northeastward across the excursion area which is consistent with the overall increase in metamorphic grade suggested by the disappearance of kyanite (and staurolite) and occurrence of increasingly coarser-grained sillimanite in the Wehutty formation schists. In these areas metaclastic horizons within both the Hothouse and Copperhill formgtions contain abundant, locally-derived quartzo-feldspathic material and show progressively less well-defined clastic textures. A very generalized correlation between approximate metamorphic conditions and the excursion stop locations are shown in Figure S.
STRUCTURE Folding
Introduction Two deformational episodes appear to have regional significance throughout
the Blue Ridge (see, for example, Hadley and Goldsmith, 1963; Butler, 1973; Dabbaga, 1975; Hatcher, 1978). The effects of both periods are recorded within the excursion area and the mapped distribution of litho logic associ ations reflects large-scale interference between both fold generations. This deformation was broadly synchronous with metamorphism and affected rocks of varying metamorphic grade and lithologic character. Therefore, the responses to deformation were variable across the excursion area and diverse local strains are recorded. A thorough description of all fabric elements and their relative geometric relationships within the excursion area is beyond the scope of this guidebook, Only a brief overview of the sequence of plastic deformation events and their most general characteristics will be presented.
Pre-Tectonic Fabric (?) Most previous workers within the area have described a regional foliation
27

which generally parallels the local orientation of bedding (Hurst, 1955; Forrest, 1975; Mohr, 1971, 1973). This has been inferred to be of tectonic
origin (termed s1 by the latter two workers) and was previously asst.nned to
have formed essentially parallel to axial surfaces of early, isoclinal folds. This foliation is not penetrative within the excursion area and is only observed as an alignment of mica along the interface between contrasting lithologies (regardless of the thickness of compositional variations). It is most strongly developed within schists adjacent to metasandstone. These characteristics suggest that the foliation did not form as an axial planar schistosity. Instead, it appears to have developed either by mimetic crystallization (diagenetic and/or metamorphic growth on detrital mica) and/or localized growth or rotation of mica concomitant with interlayer slippage during deformation.
Early Folding Early deformation (D1 ) in the area ultimately produced nearly isoclinal
folds,which occur at all scales (including the Murphy syncline). Complex and locally superposed strains developed during the evolution of D1 folds and a variety of associated fabric elements may be observed throughout the area.
Initial D1 shortening occurred prior to peak metamorphism and was probably largely accomplished by layer slippage (with formation of the nonpenetrative layer-boundary mica alignment ?). Metamorphic intensity increased as D1 shortening continued. Eventually, rotation and/or a preferred growth orientation of metamorphic mica and continued flattening of clastic quartz
grains produced a regional foliation parallel to D1 axial surfaces Cs 1A). This
may be observed as a penetrative schistosity in argillaceous metasandstone and gradually becomes recognizable as a differentiated crenulation cleavage in more
28

micaceous lithologies, Where bedding is distinct, 180XS lA has a generally sub-horizontal plunge, This intersection is locally paralleled by an

elongation direction of flattened quartz grains and/or the axial direction

of differentiated crenulations.

Another, variably penetrative n1 foliation (s 1B) may be observed throughout the excursion area,' Because its orientation is generally very similar to that

of s1A (differing only slightly in strike), a composite n1 foliation is

usually observed,

18

XS lA

lB

is

typically

a

faint

lineation

at

a

large

angle

to 18u XS0 on the composite n1 foliation. Axes of differentiated crenulations

locally parallel the faint lineation. The s1B foliation probably developed

during terminal stages of n1 shortening as progressive rotation of limbs

significantly changed their relative orientation with respect to the plane

of maximum flattening of the finite strain ellipsoid, This produced a trans-

ection of the original axial plane foliation (s 1A). Late-stage o1 rotation
about s1B locally results in a disruption of compositional layering which
resembles an interference pattern generated by two separate deformational

events with subparallel axial surfaces. We tentatively correlate the s2 surface
described by Forrest (1975) with the composite SlA+lB in the excursion area.
He could not define folds at any scale which were associated with his s2 and
it is likely that it also represents an axial planar schistosity which formed

during late-stage closure of the evolving Murphy syncline.

Porphyroblasts of most peak metamorphic index minerals include flattened

quartz grains within their interior. This indicates that the porphyroblasts

nucleated after SlA had begun to develop. Many porphyroblasts contain

helical trains of flattened quartz grains which may be traced toward the

porphyroblast perimeter and into the composite 01 foliation plane. This pattern suggests rotation of the porphyroblasts as they overgrew the evolving

29

o1 composite foliation, Late Folding
Bedding, the pre-tectonic mica alignment, and all o1 structures are
deformed by later folding Co2). Second generation folds occur at all scales
and several megascopic structures trend in a general north-south direction across the excursion area, Their axial surfaces may be followed northward into what Forrest (1975) termed F3 folds. A regionally pervasive, generally southeast-dipping crenulation developed in association with o2 folds and it everywhere deforms peak metamorphic index minerals. Extreme crenulation occurs
within the cores of megascopic o2 folds and this commonly results in nearly
complete transposition of bedding and all early fabric. Regional warping of o2 fabric elements is evident throughout the
excursion area and Forrest (1975) described similar deformation of what he termed F3 axial surfaces. No penetrative fabric elements can be found associated with this event and it was apparently of much less intensity than either o1 or o2 and probably involved little more than regional flexure. Note
A variety of other crenulations have been locally described within the excursion area, These are particularly well-developed in the graphitic, muscovite-rich schists of the Wehutty formation and have been determined to be of variable chronologie development with respect to o2 No mesoor megascopic folds can be associated with any of these crenulations and they
I
do not appear to be of regional significance, We interpret these fabric elements to record only very localized strains which were encountered in particularly incompetent. lithologies during the overall post-01 movement history,
30

Faulting Only one major fault has been mapped within the excursion area. It is continuous with the structure Forrest (1975) named the Mary King Mtn. slide. Throughout its length the fault has a sense of reverse movement and variably juxtaposed any two formations within the stratigraphic interval between the Mineral Bluff and Brasstown formations. Great Smoky Group rocks are in thrust contact with dated Grenville age basement gneisses near Bryson City, N.C. (Kish and others, 1975; Fig. 3). Hadley and Nelson (1971) extended this fault into the excursion area where they reported it to separate Great Smoky Group rocks from possibly older gneisses. However, they were not confident of its location south of Nantahala Lake, over 30 km northeast of the excursion area (Nelson, personal communication, 1978). Hatcher (1978a, 1978b) recently termed this the Hayesville-Fries fault and projected it throughout the trip area and the entire southern Blue Ridge (Fig. 7). He interprets the fault to be a major post-metamorphic thrust which underlies a separate allochthonous sheet within the southern Blue Ridge. We believe that a lithologic continuity exists between rocks exposed on either side of the postulated fault and find no evidence for such a fundamental Blue
I
Ridge structural feature. The approximate position of the proposed fault trace roughly corresponds to the area where abundant sillimanite begins to appear within the Wehutty formation and the initial development of widespread anatectic features within argill~ceous metasandstones within the Copperhill and Hothouse formations. It is apparent that the marked change in lithologic character which occurs as a result of anatexis has been incorrectly used as evidence for the fault which, if it exists, must be located east of the location proposed by Hadley and Nelson and Hatcher.
31

e 7 STOP LOCATION

0

ml

4

bf

I
0

km

mb+nq

N
r
Figure 7. Generalized geologic map of the eastern portion of the excursion area showing the proposed location of the Hayesville-Fries fault (dashed= Hadley and Nelson, 1971; dotted= Hatcher, 1978). Refer to Figure 9 for explanation of symbols.
32

CHRONOLOGie RELATIONSHIP BETWEEN DEFORMATION, METAMORPHISM AND INTRUSION
Formation of the D1 composite foliation in the excursion area was broadly synchronous with attainment of maximum metamorphic condtions. Although D2 creulations rotate and/or break peak metamorphic index minerals, minor lenses of anatectic material are locally aligned along o2 crenulation surfaces indicating that this strain did not occur long after the metamorphic climax. No evidence for brittle deformation between the two folding periods has been recognized and they are considered parts of a deformational continuum which were not separated by a considerable length of time. Pegmatite dikes and most quartzofeldspathic stringers are locally differentiated by o1 and are themselves intruded by the earliest generation of tonalite. In several localities, the younger generation of tonalite is broadly folded along o2 axial surfaces and has a foliation which may be traced into adjacent country rocks. These relations indicate that tonalite intrusion probably occured during terminal
stages of o2 strain.
Placing these relative chronologie relations in a real time framework is hampered by the generally unfossiliferous character of the Great Smoky and Murphy Group rocks and a paucity of systematic isotopic dating in the area. McLaughlin and Hathaway (1973) described articulate brachiopod fragments and a complete gastropod from a core of Murphy Marble from the Hewitt Quarry. They tentatively classified these fossils as Early Paleozoic and suggested that they may be a young as Early Ordovician. On the basis of recent calibration of the Ordovician time scale (Churkin and others, 1977), a maximum age of approximately 480-450 m.y. is therefore defined for regional metamorphism in this area. Similar estimates for the time of Blue Ridge metamorphism have been suggested by Butler (1972) and Dallmeyer (1974). Kish and others (1975) reported a
33

preliminary Rb-Sr whole-rock isochron age of 440 m.y. for a pegmatite near Bryson City, N.C. These workers described the pegmatite as similar to others which cross-cut n2 structures and which clearly post-date regional metamorphism in this area. If deformation and metamorphism were roughly contemporaneous throughout the Blue Ridge, then a minimum date of 440 m.y. is defined for D2 strain in the excursion area. K-Ar and Rb-Sr mineral ages from the southern Blue Ridge are markedly younger than 440 m.y. (430-360 m,y,; Long and others 1959; Dallmeyer 1974, l975b). However, these record the times of cooling through temperatures required for retention of mobile radiogenic products.
A schematic interpretation of the relative chronology of events within the
excursion area compared to a real time framework is presented in Figure 8.
TONALITE INTRUSION
700

500
-u
0
a.
w::E 300
12

- ARGON RETENTION IN HORNBLENDE
ARGON RETENTION IN BIOTITE

100

600

500

400

300

?

?------------~

DEPOSITION OF . DEPOSITION OF

GREAT SMOKY MURPHY GROUP

GROUP

"'TIME (M.Y.)

BLUE RIDGE THRUSTING..._

Figure 8. Schematic diagram illustrating the chronologie relationship between deformation, metamorphism, and intrusion within the high-grade portion of the excursion area. Refer to text for discussion.

34

INSTRUCTIONS
Y:
The excursion will depart from the Milton Inn at 8130 A.M. on Saturday and Sunday. It is imperative that the number of vehicles be kept to an absolute minimum. Therefore, please carry a maximum passenger load if you are driving. All lunch materials must be procured prior to departure.
A generalized geologic map showing the excursion route and stop locations is shown in Figure 9. A cumulative-mileage road log for both days of the excursion is listed in _p_ages_ .1~44. Detaile_d____deacrip_tLons _o tha_indi:viduaL ___ excursion stops are presented in the remaining pages of the guidebook.
35

EXCURSION ROUTE
SATURDAY SUNDAY

e 2 STOP LOCATION

0

.

4

I

ml

1

I

km

I

0

4

mb+nq

I

/ / {/ " I :;::

?

5

~ ~ -

7 ~ ~ X ....

::':==& < -- 1----> L

7 [

I /7 7 C ;,

... :111350

ch

........./. :./,,.

N

. ~,

r

/ hh

I "

Figure 9. Generalized geologic map of the excursion area. The route and stop locations are indicated. Formation
abbreviations: mb+nq =Mineral Bluff fm. and Nottely quartzite; mm+af =Murphy marble and Andrews fm.; bf = Brasstown fm.; tq = Tusquitee quartzite; nf = Nantahala fm.; df =Dean fm.; hh =Hothouse fm.; hg =Hughes Gap fm.; we= Wehutty fm.; ch =Copperhill fm.; um = Lake Chatuge ultramafic. The 7\' quadrangle coverage of the excursion area is outlined: northern row from west to east = Persimmon Creek, Murphy, Peachtree, Hayesville; southern row from west to east = Culberson, Nottely Dam, Blairsville, Hiawassee.

Cumulative Mileage
o.oo
o.os

SATURDAY ROAD LOG
Leave Milton Inn and turn right (SW) onto u.s. 76-19-129.
Excursion originates within the Wehutty formation.
Turn right (NW) and remain on u.s. 19-129 toward Murphy, N.C.

l. 65

Cross the contact between Wehutty and Copperhill formations.

2.3

Saprolite of interbedded argillaceous metasandstone and muscovite

schist within the Copperhill formation in the bank on right

by the Exxon station.

3.45

Cross the contact between Wehutty and Copperhill formations.

4.15

Locally kyanite-bearing, graphitic schists characteristic of the Wehutty formation are exposed on left.

4.65

Cross the contact between Hothouse and Wehutty formations. Descend into broad valley which is typical of the topography underlain by the Hothouse formation.

5.35

Typical exposure of extensively weathered Hothouse formation lithologies in road bank across from Beaver's Grocery.

6.25

View of Gumlog Mtn. to right demonstrates the type of topography which is typically underlain by the Dean formation.

6. 8 0

Outcrop of Wehutty formation on left immediately after crossing Ivylog Creek. This exposure consists predominantly of slightly graphitic muscovite schists which characterize a transitional zone between the Wehutty and overlying Hothouse formations.

7.45 8.95

Saprolite of lithologies within the Hothouse formation on left.
Intersection of u.s. 19-129 and Ga. 325 by Poteet's Grocery.

9.25

Saprolite of lithologies within the Hothouse formation on left.

10.95

Georgia-North Carolina state line.

11.35

Saprolite of lithologies within the uppermost part of the Hothouse formation.

11.50

Outcrop of lithologies within the lowermost Dean formation on left; predominant are cross-biotite sericite schists and quartz-pebble metaconglomerate.

11.70

Excellent exposure of lithologies within the middle portion of the Dean formation on left at the intersection. Rock types include: feldspar and quartz-pebble metaconglomerate, argillaceous metasandstone, and (+garnet) biotite-muscovite schist.

37

12.25

Large exposure of the uppermost Dean formation on right. Predominant lithologies include! slightly graphitic muscovite schist, cross-biotite sericite schist, and minor beds of slightly conglomeratic metasandstone.

12.35

Cross the contact between Dean and Nantahala formations.

12.40

Exposure of buff-colored, feldspathic metasandstone horizon within the lower portion of the Nantahala formation.

12.70

Cross the contact between the Nantahala formation and the Tusquitee quartzite.

12.75

Fresh exposure of feldspathic metasandstone typical of the Tusquitee quartzite behind Exxon station on left.

12.80

Cross the contact between the Tusquitee quartzite and Brasstown formation.

12.85-12.95 Large exposure of Brasstown formation on right.

13.10

Mineral Bluff formation juxtaposed against Brasstown formation along fault located in the small valley.

13.10-14.85 Several exposures of Mineral Bluff formation phyllites occur along the road.

14.85

Intersection with U.S. 64; turn left (SW).

14.85-15.55 Several exposures of Mineral Bluff formation phyllites occur along the road which is located near the axial surface trace of the Murphy syncline.

15.55

Intersection with Rt. 60; turn left (SW) toward Blue Ridge, Ga.

15.55-19.80 Several roadside exposures of the Mineral Bluff formation.

19.80

Turn sharply left (E) on small gravel road immediately before bridge over creek (near Culberson, N.C. post-office). Park along the gravel road between Rt. 60 and first curve.

19.80-22.40 STOP 1; Jonica Gap traverse. To reduce congestion, cars will not be allowed along the traverse route. Drivers will be returned here later by society officers.

22.40

Turn right (SW) at intersection.

22.40-23.10 Road generally parallels and frequently crosses the contact between Nantahala and Dean formations.

23.10

Road turns sharply southeast and away from the contact.

38

23,10-23.90 Staurolite-bearing, cross-biotite muscovite schists of the Dean formation are frequently exposed along the road.

23,90

Exposure of the mapped boundary between the Dean and Hothouse formations. Here cross-biotite muscovite schist and quartzpebble metaconglomerate of the Dean formation become gradually interlayered with argillaceous metasandstone and biotite-muscovite schist without a cross-biotite fabric.

24.10

Intersection with Dooley Creek Road (Union County Road 92325). Note lowland underlain by the Hothouse formation directly ahead. Further in the distance, Lance Mtn, is underlain by the Hughes Gap formation. Turn left (NE) onto Dooley Creek Road,

24.10-26.65

Saprolite of lithologies within the Hothouse formation are exposed in road banks. Road generally parallels lithologic strike until the Zion Hill Church where it swings southeast and into the Hughes Gap formation.

26.65

STOP 2: Uppermost Hughes Gap formation.

26.65-27.20 Contiune on Dooley Creek Road until it intersects Ga. 325 by the Mt, Zion Church. Turn left (NE) onto Ga. 325.

27.20-29.10 Several exposures of locally kyanite-bearing, slightly graphitic muscovite schist of the lower Hughes Gap formation occur along the road,

29.10

Turn right on first gravel road after crossing Nottely Dam.

29.15

Turn right into picnic area.

29.15

STOP 3: Uppermost Wehutty Formation and LUNCH

29.20

Return to intersection with Ga. 325, Turn left. (W) and recross dam.

31.10

Intersection with Dooley Creek Road at Mt, Zion Church. Continue ahead on 325.

32.50

Cross the contact between Wehutty and Copperhill formations.

32.70

STOP 4 Cat Terry's Landing): Uppermost Copperhill formation.

32.70

Continue on Ga. 325.

32.9

Exposure of thickly-bedded, argillaceous metasandstone typical of the Copperhill formation.

34.10

Cross the contact between Wehutty and Copperhill formations.

34.3

Graphitic schists of the Wehutty formation exposed on right.

39

35.65 36.40
36.50 36,50 36.60
37.2
38.65
42,00
42.50 43.00 44.50 44.55

Cross the contact between Wehutty and Copperhill formations.
Intersection at which Ga. 325 turns sharply right (S). Turn LEFT onto small gravel road.
Park along dirt road at loop.
STOP 5: Copperhill formation.
Return to intersection with Ga. 325. Turn left (W) onto Bethlehem- Blairsville Road. DO NOT continue straight on 325.
At crest of hill is a good view ahead of Brasstown Bald, the highest elevation in Georgia (4784').
Exposure just before bridge on left shows typically interbedded lithologies of the Copperhill formation.
Large exposure of Copperhill formation lithologies across creek on right.
Intersection with u.s. 19-129; turn right (SE) toward Blairsville.
Cross the contact between Wehutty and Copperhill formations.
Intersection with u.s. 76; turn left.
Turn left into Milton Inn parking lot,
END OF SATURDAY ROAD LOG

40

Cumulative Mileage
0.00

SUNDAY ROAD LOG Leave Milton Inn and turn right (SW) onto U.s. 76-19-129.

0,05

Turn right (NW) and remain on U.s. 19-129 toward Murphy, N.C.

0.05-5.35 Follow Saturday's road log for description.

5.35

Intersection with Gumlog Road at Beaver's Grocery. Turn right (NE).

5,35-8.05 A series of saprolite exposures within the Hothouse formation.

8,05

Intersection just before Ebenezer Church; turn left.

8.25

Intersection with Smyrna Road; turn left. Saprolite of lithologies within the Hothouse formation in bank across from intersection.

8.35

Beginning of a long exposure on left. First seen are interbedded argillaceous metasandstone and muscovite-schist of the Houthouse formation.

8.55

Contact between the Hothouse and Dean formations is exposed immediately before small driveway on left. The remainder of the exposure consists of cross-biotite muscovite schist interbedded with locally conglomeratic metasandstone.

8.75-12.15 A series of roadside exposures of the Dean formation.

12.15

Georgia-North Carolina state line.

12.50

Intersection with Pinelog Road; turn right (SE).

13.55

Excellent exposure of staurolite-bearing, cross-biotite muscovite schist of the Dean formation on left.

14.75

Bridge over Brasstown Creek; contact between the Dean and Hothouse formations is exposed 0.2 mi. down side road to right just before bridge.

15.15

Feldspar and quartz-pebble metaconglomerate horizon near the base of the Dean formation exposed on left at bend in road.

15.40

Intersection with N.C. Road 1100; turn right (SE).

15.45

Staurolite-bearing, cross-biotite muscovite schist of the Dean formation exposed on left.

16.15

The contact between Dean and Hothouse formations is exposed in low bank behind cleared parking area on left.

41

16.50
16.70 17.85 18.25 18.45
18.55
19.10 19.10 19.10 19.55 19.65 20.20 20.20 21.60
23.40 23.60 24.70
25.20
25.60 25.60 25.60 26.50 26.8 0

Roadcut through uppermost portion of Hothouse formation. Fresh rocks may actually be seen!~t Large valley on right is underlain by the Hothouse formation. Intersection with Route 66 in Warne, N.C.; turn right (S). BEAR LEFT AT FORK. Georgia-North Carolina state line; also the approximate location of the contact between the Wehutty and Hothouse formations. Exposure of graphitic, sillimanite-rich muscovite schists of the Wehutty formation on left. Brasstown Church driveway on right; turn in and park. STOP 6: Wehutty formation. Contiune south on Route 66. Cross contact between Wehutty and Copperhill formations. Intersection with Ga. 339; turn left (NE), STOP 7: Copperhill formation (park along road on right). Continue northeast on Ga. 339. Copperhill formation exposed on left; predominantly argillaceous metasandstone with abundant anatectic material
Intersection with Ga. 17; turn left (N).
Georgia-North Carolina state line; road becomes N.C. 69, Intersection with N.C. county road 1116 (Matheson Cove Road)J turn left (W). Copperhill formation exposed on left; predominantly argillaceous metasandstone with abundant anatectic material
Intersection near dirt-bike track, STOP 8: Wehutty formation (park along road). Continue northeast on Matheson Cove Road. Intersection with N.C. 69; turn left (N). Locally sillimanite-bearing, graphitic schist of the Wehutty formation on left,
42

27.50
27.60 28.10
28.40
29.10 29.70
30.90 31.20
31.20
31.20 34.0
34.10 35.60
35.60 35.60 35.95
36.05
36.35 36,35 36.35 37.30

Argillaceous metasandstone within the Wehutty formation exposed on the right.
Cross the contact between Hothouse and Wehutty formations.
Hothouse formahon exposed on right; predominantly argillaceous metasandstone with abundant anatectic material
Intersection with U.s. 64 bypass; turn left (W) toward Murphy, N.c.
Cross the proposed trace of the Hayesville -Fries fault.
Exposure of saprolite of lithologies within the Hothouse formation on right.
Sweetwater Gap; exposure of Hothouse formation; SLOW DOWN.
Manage a u-turn to park on the left (SW) side of road on broad shoulder.
STOP 9: Traverse of the contact between the Dean and Hothouse formations.
Retrace route eastward on U.s. 64. Intersection of U.s. 64 bypass and N.C. 69; continue east on
the bypass.
Saprolite exposure of Hothouse formation on left.
SLOW DOWN and pull across road to park on broad shoulder. Do not u-turn but maintain an easterly heading.
STOP 10: Hothouse formation.
Pull back into eastbound lane and continue on U.s. 64.
Intersection with N.C. county road 1147; turn right (SE). Cross contact between the Hothouse and Wehutty formations.
Sillimanite-bearing, graphitic muscovite schist of the Wehutty formation exposed in bank on left.
Intersection with N.C. county road 1148 at Oak Forest Church.
STOP 11: Wehutty formation (park in vicinity of church),
Continue ahead on county road 1147 (past church).
Intersection with U.S. 64; turn left (W)

38.10

Intersection with N.C. 69; turn left (S) toward Hiawassee, Ga.

41.60 42.70

Georgia-North Carolina state line; road becomes Ga. 17.
Intersection with u.s. 76; turn right (SW) toward Young Harris
and Blairsville, Ga.

43.70

Large exposure at Brasstown Gap; Copperhill formation (?).

44.50 46.20

Cross the contact with ultramafic rocks of the Lake Chatuge intrusion (see Hartley and Penley, 1974).
Intersection with Rt. 66; continue south on u.s. 76.

46.95

Exposure of foliated (cataclastic) amphibolite associated with the Lake Chatuge ultramafic in bank at intersection on right.

47.95

Cross the contact between ultramafic rocks of the Lake Chatuge intrusion and the Wehutty formation (?).

48.20

Exposure of Wehutty formation on right.

49.40

Cross contact between the Copperhill and Wehutty formations.

48.40-53.45 Copperhill formation exposed in several roadcuts; predominant lithologies are argillaceous metasandstones.

53.45

Pull off onto broad shoulder on right.

53.45 53.45

STOP 12: Copperhill and Wehutty formations.
Continue toward Blairsville on u.s. 76.

54.00

Blairsville city limit.

54.50

Stop sign; turn left,

54.55 54.60

Courthouse circle; turn right.
Stay right on u.s. 76.

54.70

Turn right into Milton Inn parking lot.

END OF SUNDAY ROAD LOG

44

DESCRIPTION OF EXCURSION STOPS Saturday

Traverse across Jonica Gap; Culberson 7~' quadrangle. The locations discussed below refer to red numbers painted on outcrops and/or nearby trees. Because of the ephemeral nature of paint in this area, approximate mileage readings at the locations are included below. A schematic column of the stratigraphic section exposed along the traverse is presented in Figure 10, A generalized geologic map and representative cross-section of the traverse route are shown in Figures 11 and 12.
Purpose L Demonstrate the mappable internal stratigraphy within the Mineral Bluff formation. 2. Examine the lithologic character of Murphy Group formations and the gradational nature of their boundaries. 3. Observe regional fabric elements.

19,80 Traverse mileage starts at the intersection of Rt. 60 and small gravel road immediately north of the bridge before the Culberson, N.C., city limit. Walk southeast from the intersection.

19,95

Location 1 Exposures of chloritoid-bearing chlorite-sericite phyllite of the Mineral Bluff formation. These lithologies define a mappable horizon within the formation (Fig. 11). Hernon (1964, 1968) traced a chloritoid horizon at an equivalent stratigraphic position within the Mineral Bluff formation in the Persimmon Creek quadrangle. Within the Culberson quadrangle, the chloritoid-bearing phyllites typically occur immediately above a mappable conglomeratic horizon which underlie the higher portions of dividing ridge. The dominant fabric element within the exposure is the composite SlA+lB foliation. Locally, appressed crenulation hinges may be observed to plunge very gently southwest along the composite foliation and are paralleled by a fine intersection lineation

45

Mineral Bluff Fm.

A, Gray-green, chlorite-sericite phyllite and fine-grained

schist; reddish-brown weathering color.

B, Thinly bedded, fine-grained mltasandstone (variably

feldspathic and argillaceous) interlaminated with thin beds of

graphitic phyllite and fine-grained schist.

C. Gray to green, chlorite-sericite phyllite and fine-grained

schist (+magnetite, pyrrhotite, and/or biotite or an iron-

E

stained,-pleochroic oxy-chlorite).

~

D. Thin- or medium-bedded, medium-grained quartzite (variably

feldspathic and argillaceous) interlaminated with greenish gray

~

sericite phyllite.
E. Similar to horizon c.
F. Greenish-gray, chloritoid-bearing phyllite.
G, Quartz-pebble metaconglomerate (with a variety of lithic
fragments) interbedded with quartzite and conglomeratic meta-

IJ..

::::>

-eooi

_J
m

sandstone. Grain-size within this horizon diminishes southeastward,

H.Sericite and sericite-chlorite phyllite and fine-grained

schist; occasional interbeds of fine-grained, magnetite-bearing,

feldspathic and argillaceous metasandstone.

Nottely Quartzite (?)
1, Thin- to medium-bedded, medium-grained quartzite with minor feldspar, sericite and magnetite; local thin-beds of sericite phyllite,

Murphy Marble and Andrews Fm. J.lnterbedded blue-gray to white, dolomite and calcite marble (+ talc, quartz, tremolite, tourmaline, pyrrhotite, and/or graphite) with intercalations of sericite phyllite, The upper 2-5 m of this horizon is characterized by interlayered marble and X-biotite muscovite schist (the Andrews Fm,).

Brasstown Fm.

K. Thinly-bedded to laminated, biotite-sericite schist and argi 11-

aceous, fine-grained metasandstone; a gradual increase in the

thickness and preservation of bedding is concommitant with a

down-section increase in the abundance of quartz. The middle

portion of this horizon is characterized by medium-bedded, X-

biotite sericite schist and argillaceous metasandstone (both+

garnet); occasional beds of calc-silicate granofels. The schists

become less abundant but increasingly darker-colored down-section. L, Zone of ductile displacement (7) marked by intense distortion of bedding.

E
IJ..

M. Thinly bedded or laminated, dark gray X-biotite sericite schist (+garnet and/or staurolite) and buff-colored argillaceous meta-

<t
_J

sandstone. There is a general increase in bedding thickness and in the abundance of metasandstone down-section,

<t

:J:

Tusquitee Quartzite N. Medium-bedded, buff to white, pyritic and feldspathic meta-

~

sandstone with minor interbeds of sericite phyllite.

z

Nantaha la Fm, 0. Graphitic and argillaceous metasiltstone (+ garnet, staurolite,

<z t

and/or pyrite-pyrrhotite) and graphitic sericite phyllite locally

interlaminated with slightly argillaceous and feldspahtic meta-

sandstone. Although the abundance of interlaminated metasandstone

decreases down-section, there are local zones with thickly-bedded

metasandstone horizons. Locally within the middle portion of

this unit, graphite sericite phyllite predominates.

P. Thickly-bedded, buff-colored, argillaceous and feldspathic meta-

sandstone interbedded with graphitic sericite phyllite and minor

graphitic and argillaceous metasiltstone.

Q, Argillaceous and slightly feldspathic metasandstone interlayered

with garnet-biotite-muscovite schist and graphitic sericite

phyllite. The abundance of graphite sericite phyllite decreases

down-section.

--""'-'

A

8
c

D

E

F,G

H
I J
K L
~

0

p
a
R

Dean Fm. R, Argillaceous and locally conglomeratic metasandstone in t erlayered with X-biotite sericite schists and garnet-biotitemuscovite schist.

Figure 11. Generalized geologic

Figure 10. Schematic stratigraphic column illustrating the lithologic character of formations along the stop 1 traverse. The approximat e positions

map of the stop 1 traverse area. Stop localities are indicated. North is toward top of the page and the scale is 1:12,000.

of traverse localities within the stratigraphic section are indicated.

46

NANTAHALA Fm.

SE 1700'

1200'

,,

1200'

700'

Figure 12. Representative cross-section along the stop 1 traverse. Vertical exaggeration ~ 2X. The approximate positions of the traverse localities are indicated.

(L8 XS ) Another more steeply plunging lineation is inferred to be tohe lA1ntersect1.on between SlA and SlB' Axes of d.1fferent1 ated crenulations may be observed in association with this lineation.

19,95-20.25 Proceed to location 2. Within this interval, the abundance of chloritoid rapidly decreases and minor metasandstone horizons may be seen, The rocks loose their massive appearance as the degree of D1 differentiation decreases and bedding becomes more dominant.

20.25

I.ocati on 2 Thin- to medium-bedded, medium-grained, slightly feldspathic and argillaceous quartz metasandstones are interbedded with sericite phyllites in ditch east of the intersection. These rocks occupy a similar stratigraphic position within the Mineral Bluff formation as the metasandstones described by Power and Forrest (1975; p. 10) in the Murphy quadrangle and the metasandstones which Hurst (1955; p. 54) called Nottely quartzite in the Mineral Bluff quadrangle. We agree with Power and Forrest and interpret these clastic rocks as stratigraphically above the Nottely quartzite and part of the Mineral Bluff formation. Bedding is oriented NSSE-75SE within this exposure and the composite SlA+lB foliation is developed subparallel to bedding in the phyllites. This foliation is weakly developed within the metasandstones by flattened quartz grains. An approximately horizontal lineation defined by the elongation direction of flattened quartz grains may be observed.

20.25-20.40 Proceed to location 3.

Within this interval, fine.,..grained chlorite-sericite phyllites

predominate. Bedding becomes vague as differentiation along

D1 foliations increases in intensity.

20.40

location 3

At the intersection are exposed a series of slightly graphitic,

dark phyllites which are interlayered with metasandstone. The

metaclastic rocks are distinctly more argillaceous than those

seen at location 2. This interlayered sequence constitutes

the uppermost mappable metaclastic horizon within the Mineral Bluff

49

formation.

20.40-20.80

Proceed to location 4.
The axial trace of the D1 Murphy syncline is crossed within this interval. Predominant lithologies are chlorite-sericite phyllites.

20.80

Location 4 Interbedded graphitic phyllite and very argillaceous metasandstone are exposed along the road. This lithologic association is believed to be stratigraphically correlative with that seen at location 3, here exposed on the overturned, southwestern limb of the Murphy syncline.

20.80-21.10 Proceed to location 5. Chlorite-sericite phyllites characterize this interva1.

21.10

Location 5 Slightly argillaceous, and locally conglomeratic and feldspathic metasandstones are interlayered with magnetite- and pyrrhotitebearing chlorite-sericite phyllites and chloritoid-bearing chlorite-sericite phyllites. This association is correlated with that seen at location 1.

21.10-21.40

Proceed to location 6 Chlorite-sericite phyllites and/or fine-grained schists predominate within this interval.

21.40

wcation 6 Saprolite bank on the southeastern side of the road contains approximately 3 m of deeply-weathered metasandstone which is tentatively correlated with the Nottely quartzite. Immediately following this interval is approximately 3 m of what appears to be saprolite derived from the Andrews formation. It contains contorted sericitic phyllites and large, reddish-spots which are likely the residuum of biotite porphyroblasts within cross-biotite schist. For the next 30-35 m down the road, a dark red, homogeneous saprolite may be observed in the bank. This is interpreted as residuum of Murphy marble.

so

,.

21.45

Location 7 Dark red saprolite of Murphy marble changes to yellowish-brown saprolite of schists within the Brasstown formation (in part colluvial).

21.55

Location 8 Exposure of finely-laminated schist and argillaceous metasiltstone within the uppeunost portion of the Brasstown formation.

Turn right at the intersection and proceed approximately 0,1 mi. to location 9,

Location 9 Chlorite-sericite phyllites within the Mineral Bluff formation. Return to intersection at location 8. Note the dark red saprolite between locations 8 and 9. This appears to be Murphy marble residuum.

If the lithologic inferences suggested by the saprolite between locations 6 and 9 are correct, then the Mary King Mtn, slide mapped by Forrest (1975) in the Murphy quadrangle as faulting the Brasstown formation against the Mineral Bluff formation must locally cut stratigraphy, This is required because in this area the dislocation must occur between the Nottely quartzite and the Mineral Bluff formation (Fig. 12),

21.55-21,90

Proceed to location 10, Nearly a continuous exposure of the Brasstown formation occurs within this interval. Note the change in scale of interlamination between argillaceous metasiltsone and schist along the traverse. It varies from very thinly-laminated at the top of the founation to finelybedded near the base (remember that bedding is overturned along this section of the traverse), Most of the schist within this interval contain garnet and are locally staurolite-bearing. Crossbiotite textures are typical. Elliptical pods of calc-silicate granofels occur throughout, Note the overall increase in the relative proportion of metasiltstane and fine-grained metasandstone downsection.

51

21.90

A non-penetrat:ive alignment of mica occurs along the interface

between compositional layers throughout the Brasstown formation

in the interval between locations 8 and 10. This is interpreted

to be a pre-tectonic feature. Another generally penetrative

schistosity may be observed to make an approximately 300 angle

to bedding. This represents the composite SlA+lB foliation.

A nearly horizontal intersection lineation may be seen on the

composite foliation and represents LS XS Another, nearly
vertical and more faintly defined lin~~tign may be correlated with

L



slAxslB

Location 10

Here the well-defined compositional layering (bedding) of the

Brasstown formation is highly contorted. This may reflect local

intraformational thrusting.

21.90-21.95

Proceed to location 11. This interval exposes the lowermost portion of the Brasstown formation and its gradational contact with the underlying Tusquitee quartzite. Note that the Brasstown formation becomes increasingly more quartz-rich downsection and that the interbedded schists become increasingly darker-colored as a result of the appearance of graphite.

21.95

Location 11 Approximate location of the Brasstown forrnation-Tusquitee quartzite contact. See stratigraphic column in Figure 10 for description.

21.95-22.00

Proceed to location 12. Cross the gradational contact between the Tusquitee quartzite and Nantahala formation.

22.00

Location 12 Laminated argillaceous metasiltstone and fine-grained metasandstone within the uppermost portion of the Nantahala formation are exposed.

22.00-22.40 Proceed to location 13. The Nantahala formation is variably exposed in this interval. Note thick zone of graphitic phyllites in the middle portion of this 52

22.40

'
interval,
location 13 (at intersection) Several thick beds of Tusquitee-type metasandstone are exposed across from the intersection. These constitute a mappable horizon within the Nantahala formation.
Proceed to location 14. This interval represents a transitional zone between the Nantahala and underlying Dean formations. Note the gradual decrease in the abundance of graphitic phyllite and Tusquitee-type metasandstone. Metasandstones become increasingly thicker bedded and argillaceous toward location 14. Thin beds of biotite-muscovite schist also become increasingly more numerous.
location 14 Quartz-pebble metaconglomerate and conglomeratic metasandstone are exposed. These are typical of the upper portion of the Dean formation and the contact between the Dean and Nantahala formations has been mapped at the top of this metaclastic interval. Sericitic crossbiotite schists (locally staurolite-bearing) are interbedded with the metaclastic rocks farther down the road.
Return to location 13 and wait for drivers to return with vehicles.

County road 92325, Union County, Georgia; Nottely Dam 7!z' quadrangle.
The middle portion of the Hughes Gap formation is exposed northwest and southeast of the small side road.
Purpose 1. Demonstrate the lithologic character of the Hughes Gap formation where it is a mappable formation. 2. Show the recognition of facing criteria at middle amphibolite metamorphic grade. 3. Observe intrusive relations of tonalite sill. 4. Introduction to the complexities of deformational fabric within Great Smoky Group rocks at middle amphibolite metamorphic grade.
53

A 10-15 rn horizon of medium- to thick-bedded (3 ern - 2 rn), locally conglomeratic metasandstone occurs in the first exposure uphill from the small side road. Note that individual beds become increasingly more argillaceous in a direction opposed to dip, indicating that they are overturned. The metasandstones are interbedded with garnet-biotite-muscovite schist. Both lithologies
display a well-defined s1A foliation. A pre-tectonic alignment of mica may
also be observed along the base of the metasandstone beds. A 2.5 rn thick tonalite sill intrudes along the bedding plane between a schist and metasandstone bed without noticeable disruption and/or contact metamorphic effects.
Walk uphill and note the consistent orientation of bedding until a 10-15 rn interval of locally graphitic (::!::garnet) biotite-muscovite schists is enountered on the northeast side of the road. Here bedding is obscure and
the s1A foliation may be observed as a strongly differentiated crenulation.
This differentiated foliation is deformed by two crenulations. One has a steeply-dipping axial surface and moderately plunging axis and is thought to
be correlative to s1B seen at stop 1. The other crenulation is more strongly
developed and is a D2 fabric element. A D2 rnesoscopic fold may also be seen. Note that bedding within adjacent rnetasandstones is undeforrned by either of these crenulations.
Stop 1
Picnic area immediately east of Nottely Darn on Ga. 325; Nottely Darn 7~' quadrangle. Exposures of the upper portion of the Wehutty formation occur along the lakeshore around the point below the picnic area.
Purpose 1. Examine the lithologic characteristics of the upper portion of the Wehutty formation, 2. Trace the intensity of D2 crenulation within the hinge area of a megascopic D2 fold.
Starting on the west side of the peninsula, the first lithologies encountered are graphitic (2:_ garnet) kyanite-rnuscovite schist. The most prominent fabric element in this exposure is a differentiated crenulation cleavage Cs1A). Kyani te porphyroblasts can be observed to overgrow this foliation and appear to be most abundant within quartz-rich differentiated compositional layers. A later more open crenulation deforms the differentiated foliation and
54

.
their axes are roughly paralleled by a preferred growth direction of kyanite
porphyroblasts. These are believed to be related to the s1B seen at stop 1.
An even later crenulation may be observed to break kyanite porphyroblasts and locally fragments may be seen rotated into generally parallel alicnment to
their axial surfaces. The youngest crenulations are n2 elements.
Walking around the point, a few layers of calc-silicate granofels (5-20 em thick) are interbedded with schist and minor horizons of argillaceous metasandstone. Below this horizon is a thick sequence of graphitic (~ garnet) kyanite-muscovite schist. The dominant foliation here, as elsewhere, is SlA
and may be seen as a strongly differentiated crenulation. o2 crenulations occur
at all scales and are variably penetrative. Those of larger amplitude appear to locally refold crenulations of smaller amplitude imposed early during D
2
deformation.
Exposures along the southeastern shore of Camp Creek Cove near Terry's Landing, Ga. 325; Nottely Dam 7~' quadrangle. A generalized geologic map of this area is presented in Figure 13.
Purpose 1. Examine lithologic associations typical of the uppermost portion of the Copperhill formation. 2. Observe inferred primary features within these rocks. 3. Demonstrate the textural variability of tonalite. 4. Contrast deformational fabric elements with those previously seen.
Across the store on Ga. 325 is a fresh exposure of argillaceous metasandstone which is representative of those within the Copperhill formation. An ellipsoidal pod of calc-silicate granofels may also be seen and the occurrence of similar non-bedded calc-silicate granofels is common throughout the formation. Walk east and down the small drive toward the lake. Abundant float of typical Copperhill formation lithologies may be seen at the base of the boatramp. These include argillaceous metasandstone, conglomeratic and argillaceous metasandstone, and calc-silicate granofels. Between the boatramp and the small creek abundant tonalite float may be observed. A variety of textural types are present and include~ medium-grained equigranular, aph2nitic porphyry, and medium-grained porphyritic. In the exposure within the small creek occur argillaceous metasand-
55

.
.
.c ... L28
=.J

'f20...

a

1\

~25 28

A"

stone, conglomeratic metasandstone and minor schist. This is part of a mappable, generally conglomeratic horizon within the upper portion of the Copperhill formation (Fig. 13).

:Wcation A Walk along lakeshore to exposure in bank. Here may be observed a thick
tonalite sill (medium-grained porphyritic texture), a o. 5 m bed of calc-silicate
granofels, minor argillaceous metasandstone, and an 8 m thick section of (+ garnet) biotite-muscovite schist. The schists are interlayered at a scale of 2-8 em. Bedding within this exposure is oriented N35-40W and dips 40-SSE. This orientation reflects the relative structural location of this stop; along the upright, northeastern limb of a D1xn2 interference dome (Figure 13). A non-penetrative mica alignment occurs along the contact between contrasting lithologic types throughout the exposure and is a pre-tectonic feature. A generally penetrative schistosity is also developed and trends N70-80W and
dips gently (15-25) no~ th. This schistosity is correlated with the s A 1
foliation seen at previous stops. It is not differentiated here because of an increased arenaceous component within the schists. Well-defined n2 crenulations are present throughout the exposure. They have ccn sistently oriented axial surfaces which trend Nl0-20W and dip steeply east (75-85). In general, the
exposure at location A is regarded as transitional into a Wehutty formation
lithologic assemblage (generally schistose with bedded calc-silicate granofels) and is typical of the uppermost Copperhill formation in the vicinity of the contact. However, the absence of distinctly graphitic lithologies this sequence is included within the Copperhill formation.

:Wcation B

Proceed to location B. Several approximately 0.5 rn thick slightly cong-

lomeratic and argillaceous metasandstone beds display internal size grading

at this exposure. They become increasingly more argillaceous upward and into

a 2-8 ern flaser-bedded zone which culminates in a 4-10 em horizon dominated by

schist which displays an abrupt contact with the overlying metasandstone bed.

These characteristics may be inferred relics of a Bouma cycle. Note also that

Figure 13. Generalized geologic map of the stop 4 area. North is toward top of page and the scale is 1:12,000. RepresentatiNe attitudes of beddding are shown.

an s1A schistosity within the metasandstone
is deformed along with bedding into a meso-
scopic o2 fold in a portion of the exposure at
location B.
57

) ~4

..........:.

~so

f

..

..



..........
...:0pf'~'ONG

... t>.'ttEA \

.. . . . ~ ...'..

Exposures along the southeastern shore of McClure Creek Branch; northeast of Ga. 325, Nottely Dam 7~' quadrangle. A generalized geologic map of this area is presented in Figure 14.

Purpose 1. Examine the change in lithologic character which accompanies
incipient anatexis within the Copperhill formation.
2. Demonstrate the intrusive relations between several generations
of tonalite. 3. Observe the extreme development of D2 crenulations within the core
of a megascopic D2 fold. 4. Resolve the chronologie relationship between metamorphism,
deformation, ~nd tonalite intrusion.

Walk approximately 500 m northeastward along the lakeshore to the first

exposures. Texturally variable tonalite float is abundant along the shore.

The predominant lithology within these exposures is variably argillaceous

metasandstone of the Copperhill formation. Ghost remnants of calc-silicate

granofels are common. Incipient anatexis is suggested by numerous veins and

stringers of quattzo-feldspathic material. Note the general absence of well-

defined clastic textures in the metasandstone. A texturally and mineralogically

zoned pegmatite dike is cross-cut by a fine-grained tonalite dike within the

large exposure. These are both cross-cut by a coarse-grained tonalite dike.

Similar cross-cutting relationships between these tonalite textural varieties

are observed throughout the area and suggest that tbey are of different intrusion

generation (although probably not separated by a significant time interval).

These cross-cutting relations are illustrated in photograph B for stop 5.

D2 crenulations are strongly developed throughout the exposures. Axial surfaces of these and of D2 mesoscopic folds defined by vague compositional differences in the metasandstone trend Nl0-20E and dip 50-60 SE. Note that

a strongly differentiated foliation (SlA+lB) is deformed by the D2 crenulations

(photograph A for stop 5). Country rock

Figure 14. Generalized geologic

map of the stop 5 area. North

xenoliths may locally be seen within the fine-

is toward top of the page and the scale is 1:12,000. Representative attitudes of bedding are shown.

grained tonalite dikes. These typically display D2 crenulations. However, several of the coarse-grained tonalites are folded about D2

59

Stop 5- Photograph A. Illustration of the penetrative development of Dz creulation cleavage (DzS) within the hinge zone of the Nottely anticline. Note that the Dz creulations are deforming a previously differentiated tectonic surface (D1S).
Stop 5- Photograph B. Illustration of the chronological relationship between intrusion of a zoned pegmatite dike and two generations of tonalite dikes. The pegmatite dike (PEG) is cross-cut by a fine-grained tonalite dike (FGT) which is in turn intruded by a coarse-grained tonalite dike (CGT). Note that the small quartz vein is deformed along Dz crenulations.
60

axial surfaces. These folds are rather more open than those defined by
bedding (?). Together these relationships suggest that tonalite intrusion
occurred during later stages of D2 strain. Note that poth the pegmatites and fine-grained quartzo-feldspathic materialare involved in the pre-D2 differentiated crenulation schistosity.
61

Sunday Introduction
Seven stops have been planned for today. Their primary purpose is to show the remarkable change in lithologic character which accompanies the appearance of widespread anatectic features in the northeastern part of the excursion area. The stops are organized to demonstrate that a lithologic continuity within the Great Smoky Group exists across the proposed trace of the Hayesville-Fries fault. Continued reference should be made to Figure 7 in order to maintain a perspective on our location with respect to the proposed fault. Except for stop 9, only a short time is allotted for each locality. Therefore, only a brief description is provided for most stops.
Exposure across from Brasstown Church on Ga. 66; Blairsville 7~' quadrangle.
Purpose l. Examine the Wehutty formation at sillimanite grade of metamorphism. 2. Contrast deformational fabric elements with those seen yesterday.
Predominant lithologies within this exposure are biotite-muscovite schist (+ sillimanite, garnet, and graphite) interlayered with subordinate argillaceous metasandstone and calc-silicate granofels. Several small muscovite-bearing pegmati tes are present .Layers with abundant fibroli tic sillimanite occur through0ut the exposure. This sillimanite-rich zone is part of the lower of two aluminous horizons which may be mapped within the Wehutty formation. They were first described by Hash and VanHorn (1951) in their survey of sillimanite deposits in North Carolina.
Bedding within the metasandstones trends N55-65E and dips steeply (75-85) SE. A penetrative differentiated foliation occurs at a low angle to bedding within the schists. This is interpreted as a composite SlA+lB"
Exposures along Ga. 339 approximately 0.4 mi. east of the intersection with Ga. 66; Blairsville, 7~' quadrangle.
Purpose 1. Demonstrate the widespread development of anatectic features within metaclastic rocks of the Copperhill formation at sillimanite grade 62

of metamorphism. 2. Establish the temporal relationship between deformation and
anatexis.
Several exposures occur along the road and up the bank on the left. Predominant lithologies include variably argillaceous metasandstone and a variety of textural and mineralogical types of generally quartzo-feldspathic material. Thin layers of more schistose lithologies occur throughout. Garnetbearing lithologies and calc-silicate granofels are noticeably absent .
With few exceptions, the quartzo-feldspathic material is deformed by mesoscopic folds of two types:
1. One type has an interlimb angle of approximately 50 and axial surfaces trending N45-SSE and dipping moderately southeast (45-65). Fold axes plunge 10-30 northeast.
2. The other fold set is more open and has axial surfaces which trend N25-75E and dip gently southeast (10-30). These have a subhorizontal plunge.
Upon close inspection both fold sets can be observed to deform a differentiated
foliation (composite s1). Locally, a faint alignment of biotite parallel to
the axial surfaces of both sets occurs. No well-defined interference can be observed between the two fold types and they are both considered products of D2.
Exposures near dirt bike track along County Road 1116 (Matheson Cove Road), Clay County, North Carolina; Hayesville 7%' quadrangle.
Purpose 1. Examine the along strike continuation of the lower sillimanite
horizon within the Wehutty formation. 2. Contrast the degree of anatexis within graphitic schists of the
Wehutty formation with that seen in metaclastic rocks of the Copperhill formation at generally equivalent metamorphic grades.
Examine the saprolite exposure at the intersection. Lithologies here include: feldspathic, conglomeratic and argillaceous metasandstone interlEyered with (+ sillimanite, biotite) garnet-muscovite schist and bedded calc-silicate granofels. Note that this lithologic association is identical to those
63

seen yesterday within the Great Smoky Group. However, stop 8 is located over 4 loo east of the proposed Hayesville-Fries fault which is described as separating Great Smoky Group rocks on the west from older basement gneisses on the east.
Walk approximately 200 m up the small dirt road. Note exposures of feldspathic and argillaceous metasandstone en route, Minor stringers of quartzo-feldspathic material are developed in this 1i thology suggesting incipient anatexis (but noticeably less than at stop 7), At 200 m is a saprolite bank across from a trailer, Here may be seen the following lithologies: sillimanite-rich muscovite schist (locally graphitic) and thinly-bedded calc-silicate granofels horizons. This association is identical to that observed at stop fi,
Throughout the exposures at stop 8 bedding orientations vary from N40E70SE to N50E75NE as a result of D2 folding. D2 crenulations are locally developed and have axial surfaces trending N05-10E and dipping moderately SE (45-65), These crenulations deform a strongly differentiated crenulation
schistosity (composite s1).
Stop 2_
U.s. 64 at Sweetwater Gap; Hayesville 7~' quadrangle. The locations
discussed below refer to red nt.nnbers painted on outcrops. A schematic colt.nnn of the stratigraphic section exposed at this stop is presented in Figure 15. A generalized geologic map of the area is shown in Figure 16,
Purpose 1. Demonstrate the gradational character of the contact between the
Dean and Hothouse formations. 2. Examine the mappable stratigraphic horizons within the Dean formation. 3, Observe the overall lithologic characteristics of both formations.
wcation 1 The cross-biotite schists with interbeds of (+ staurolite)
chloritic sericite schist and feldspathic argillaceous metasandstone which are exposed here correspond to horizon G in Figures 15 and 16. The attitude of bedding is 35-40E 75-85SE. weal attitudes deviate from this general orientation within the hinges of small, nearly isoclinal
D1 folds. A differentiated crenulation schistosity (composite s1 ) is
64

axial planar to these folds. Bedding is at a low angle to this foliation in the limbs of the isoclinal folds and staurolite porphyroblasts appear to have been rotated during development of this surface. location 2
Sericitic schists typical of horizon H of the Dean formation
are exposed here. Note the differentiated schistosity (composite s1).
location 3 Sericitic cross-biotite schists typical of horizon I within the
Dean formation are exposed at this location. location 4
A slightly conglomeratic, feldspathic and argillaceous metasandstone is exposed at this location. This lithology constitutes a mappable unit at the top of horizon J within the Dean formation (Fig. 16). location 5
Within Sweetwater Gap, cross-biotite schists, argillaceous metasandstones, and calc-silicate granofels (horizon J) are exposed on left. Here the transition to the Hothouse formation can be examined by walking through the Gap. The contact is gradational and arbitrarily located below the last occurrence of cross-biotite schist. Note that schists become progressively coarser-grained and that calc-silicate granofels beds decrease in abundance eastward through the Gap. Within the easternmost exposures, a typical Hothouse formation lithologic association of interlayered biotite-muscovite schist and variably feldspathic and argillaceous metasandstones may be observed.
65

Nantahala Fm,
A, Graphitic, argillaceous metasiltstone (accessory pyrite and pyrrhotite; locally garnet-bearing) interlaminated with slightly argillaceous, feldspathic metasandstones; bedding thicknesses 0,5-6_em; metasiltstone comprises 60-70% of the horizon
B. Thickly bedded to massive, variably feldspathic metasandstones; local graphitic, argillaceous metasiltstone intercalations (usually less than 50 em thick),
C, Similar to horizon A,
D, Graphitic, argillaceous metasiltstones (locally garnet- and/or biotite-bearing) rhythmically interlaminated with slightly argillaceous, feldspathic metasandstones; thicker feldspathic metasandstone beds (30-60 em) are interlayered with laminated aequences and comprise 15-20% of the horizon,
Dean Fm.
E. Predominantly thickly bedded (+ staurolite) garnet-mica schist (local X-biotite fabric); minor interbeds (less than 30 em) of variably feldspathic, argillaceous metasandstone, and locally graphitic, sericitic schist,

t

E
LL

A

<{

..J

<{

::r::
~

c

z

z<{ .. :~..,,... ,,,..._,..:::---...;.. :-:: D

~.~r.~,~(l );',Jt(...:.~~....-i~.i : lfr:r.>~
E '/11- J.~'\1_,, ~~ "-f'~fri.v~. 1'-;,.,re}

F. Predominantly thickly bedded, locally chlodtic, sericitic schists; subordinate lithologies include; variably feldspathic, argillaceous metasandstones (2-30 em), feldspathic metasandstones (2-15 em ), and graphitic, sericitic schists,

G, Predominantly thickly bedded garnet-mica schists (commonly with X-biotite fabric); minor thin interbeds of (+ staurolite) locally chloritic, sericitic schists, and variably feldspathic, argillaceous metasandstones.
H. Thickly bedded,locally chloritic, sericitic schists with 15-60 em beds of variably feldspathic, argillaceous metasandstones which comprise less than 257. of the horizon,
I. Predominantly thickly bedded biotite-muscovite schists (locally garnet-bearin~>, r.ornmonly with X-biotite fabric); subordinate lithologies include variably feldspathic, argillaceous metasandstones (less than 20%), and locally chloritic, sericitic schists (25-30%).
J. Predomiantly locally chloritic, sericitic schists, interbedded ~<ith X-biotite schists, variably feldspathic, argillaceous metasandstones, and local calc-silicate granofelsl upper~ of horizon is characterized by several argillaceous, variably feldspathic, slightly conglomeratic metasandstone beds; argillaceous metasandstones and X-biotite schists comprise less than 254 of the horizon, but X-biotite schists are more common near the base,
Hothouse Fm,
K. Upper portion, characteristically interbedded mica schists, and variably feldspathic, argillaceous metasandstones; minor argillaceous metasi ltstones, and bedded calc-silicate granofe ls; bedding averages from 30 c~-1 ~, but varies from less than 10 em to 4 m; calc-silicate granofels beds are locally present, particularly near the upper contact, however they are not typical of the formation,
Figure 15. Schematic stratigraphic column illustrating the lithologic character of the Nantahala, Dean, and Hothouse formations in the vicinity of stop 9, The approximate position of stop 9 localities within the stratigraphic section are indicated.

, -_ " ' ,1 # _ 1 , 1 - , , - ....:;.. ,

E

LL

-- -- Z _ . ' -- .-, -.\~ .Z- J- ~- -

...

........ .,., "-'"1'-.:;~IJ~""'-1---- . tl' ~,.-
..:::::.:::::::: --::::::: -

w .--- ., , --, - ' - ~

0

~! : :. ~~: ~: ;t ..~ ~ ~~:-.,: ~:..~ ';J:. :-" , ..:...:.-...~ _......
.<fi4 ' "''. ::<\"\"'" ....~"?fl!".. . . ~

- .........._

- ----

J

::::--

.. I . , -



~ I _\ , "": ,

t--- _....._.--- - ,......._.. -::_~

- -_- ___. -~

_ ~...._...

-- ---- - -.,. .

HOTHOUSE
Fm.
'

Figure 16. Generalized geologic map of the stop 9 area. Stop localities are indicated. North is toward top of the page and the scale is 1:12,000.

66

...... ,.R...t....6..4.........

Stop 10
u.s. 64 1.6 mi. east of intersection with N.C. 69; Hayesville 7~ 1
quadrangle,
Purpose 1. Demonstrate the marked change in lithologic character of the Hothouse formation which accompanies the development of widespread anatectic features at sillimanite grades of metamorphism. 2. Contrast the deformational fabric with that seen at previous stops.
Argillaceous metasandstone is the predominant lithology in this exposure. Subordinate amounts of biotite-muscovite schist and garnet-bearing, biotitP.quartz-feldspar granofels, (biotite occurs as pseudomorphic (?) aggregates). Veins and stringers of biotite-bearing quartzo-feldspathic material occur at a variety of scales but are not generally abundant.
Anatexis and concomitant recrystallization within the metaclastic rocks have largerly obscured primary detrital textures, however large-scale bedding can easily be observed. Note the general concordance between what is interpreted as metamorphic layering (generally rhythmic interlayering at scales of less than 2 em of quartzo-feldspathic horizons and more biotite and muscovite-rich horizons) and bedding.
Both bedding and the metamorphic layering are isoclinally folded about axes which plunge 30-40 variably northeast or southwest. A differentiated
crenulation schistosity (composite s1 ) is axial planar to these folds.
Intersection lineations between the composite schistosity and bedding and/or metamorphic layerhg are locally visible. Coarser-grained anatectic material is also deformed by these folds and, where abundant, muscovite and/or biotite are aligned subparallel to the differentiated schistosity. Generally nonpenetrative crenulations with nearly horizontal axial surfaces and gently
plunging axes deform the composite s1 foliation.
Stop ll Exposure on N.C. County Road 11Lf8, approximately 100m southeast of
intersection with N.C. County Road ll47; Hayesville 7~' quadrangle. Purpose 1. Examine sillimanite schists within the Wehutty formation which
68

are stratigraphically correlative with those seen at stops 6 and 8. Locally graphitic muscovite schist dominates in this exposure. Coarsegrained sillimanite (locally crystals up to 5 em in length) may be observed within several horizons.
Stop 11. Exposure along u.s. 76, approximately 0.55 mi. northeast of the Blairsville
city limit; Blairsville 7%' quadrangle.
Pur p o s e 1. Examine contact relations between the Wehutty and Copperhill formations at middle amphibolite grades of metamorphism. 2. Relate deformational fabric elements to those seen at stop 5 by observing their chronologie relationship to intrusion,
The exposure along U.s. 76 consists of thickly-bedded argillaceous meta-
sandstone and at least one horizon of quartz-pebble metaconglomerate, Thin dikes and sills of fine-grained, generally equigranular igneous material (most can be termed garnet-bearing muscovite alaskite) are abundant. Bedding appears to be isoclinally folded about a nearly recumbent axial surface. Much of the igneous material occurs generally subparallel to the axial surface orientation but is not significantly deformed by the folds. Another, comparatively open folding is prevalent in the exposure and most of the igneous material is deformed by this event. Although most of the non-pegmatitic igneous lithologies seen at stop 5 were tonalites, it is not unreasonable to assume that the alaskitic material at the present stop were emplaced at approximately the same time. If the igneous events were correlative, then the open folding observed at this stop can be identified as a D2 event,
A small road leads off to the southeast from U.S. 76. At the intersection and several meters up the road is a low exposure of graphitic muscovite schist interlayered with minor argillaceous metasandstone and calc-silicate granofels. This is a typical association within the Wehutty formation and the contact with the underlying Copperhill formation has been mapped through this stop location. Locally in graphitic schists at the intersection kyanite porphyroblasts are pseudomorphically overgrmm with fibrolitic sillimanite,
69

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