A PE'E‘ROGRAF‘HIC AND" SWUCTURAL STUDY
OF A PORFiON OF THE PALMER GNEI$S AREA,
MARQUETTE DISTRICT, MEWGAN

Thesis for HM 0.0qu0 of M. 5.
MICHIGAN STATE UNIVERSITY

Arman Sahakian

1959

 

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A PETROGRAPHIC AND STRUCTURAL STUDY
OF A PORTION OF THE PALMER GNEISS AREA,

MARQUETTE DISTRICT, MICHIGAN

By

ARMEN SAHAKIAN

A THESIS

Submitted to the School of Science and Arts of Michigan
State University of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Geology

1950

A Petrographic and Structural Study
of a Portion of the Palmer Gneiss Area,

Marquette District, Michigan

Armen Sahakian
ABSTRACT

Section 36, T47N, R26w3 constitutes a portion of what is
known as the Palmer gneiss. The Palmer gneiss and, to a
larger extent, the Southern Complex south of the Marquette
synclinorium in Michigan have been a point of controversy
during the last one hundred years. A petrographic and
structural examination, in addition to the mapping of the
area, point to certain possible conclusions regarding the

geologic interpretations of observed phenomena.

Three major rock types comprise the area: (1) hornblende
gneiss, (2) granites and pegmatites, and (3) metabasalts.
The gneiss appears to have deve10ped through liquid injections
or, less probably, through metamorphic differentiation. The
original rock was basalt, later metamorphosed to amphibolite
schist. The amphibolite was in turn intruded, it is suggested,
by Algoman granite in the late pre-Huronian. The post-
Algoman granitic and pegmatitic intrusions are related to
the latest major orogenic period, the Killarney Revolution.

The metabasalts might be Huronian in age.

The joint patterns present suggest an anticlinal belt
trending E-W to NW—SE, with a general N-S stress field.
The major stress direction is generally perpendicular to
the direction of the foliation, the latter striking roughly
N45w to N8SW. Stress differentials appear to have played a

ii

significant role in the preferential alignment of the mafic

minerals prior to the intrusion of the Algoman granite.

All evidence of this study points to a Precambrian

origin for the major lithologic units of the area.

iii

ACKNOWLEDGMENTS

The writer is deeply indebted to Dr. J. Zinn
for the original conception of this problem, as
well as for his unselfish aid in directing the
project. Sincere thanks also go to Dr. J. W. Trow
and Dr. B. T. Sandefur and Dr. H. B. Stonehouse
for their constructive criticism and helpful

suggestions.

iv

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . . . . . .
Location and Accessibility . . . . .
Physical Features and Climate . . . .
Regional Geologic Background . . . .
Purpose and Scope . . . . . . . . . .

PETROGRAPHY AND PETROLOGY . . . . . . . .
Rock Types . . . . . . . . . . . . .
The Gneiss . . . . . . . . . . . . .

Sample 5b . . . . . . . . . . . .
Sample 6b . . . . . . . . . . . .
Sample 12a . . . . . . . . . . . .
Observations and Interpretations .
The Granite . . . . . . . . . . . . .
Late Granite . . . . . . . . . .
Porphyritic Granite . . . . . . .
Sample 2 . . . . . . . . . . . . .
Non-Porphyritic Granite . . . . .
Sample 6a . . . . . . . . . . . .
Sample 15 . . . . . . . . . . . .

Observations and Interpretations .

Metadiabases and Associated Basic Rocks .

Sample 19b . . . . . . . . . . . .

Sample 22 . . . . . . . . . . . .
PETROGENIC AND PETROLOGIC INTERPRETATIONS
Sericitization and Paragonitization .
Plagioclases . . . . . . . . . . . .
Perthites . . . . . . . . . . . . . .

Plagioclase and epidote . . . . . . .

V

Page

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b-I» c» L».Lo u: n: N>Iw to to no n: N>uv to r- r- rd
C) a: Osnd rd <3 \o C» ~4 0‘ U1 Ovid rd c> c: b-cv <3

Page

DIFFERENTIATION OF ZIRCONS FOR
CORRELATION PURPOSES . . . . . . . . . . . . . . . . 43

STRUCTURAL GEOLOGY . . . . . . . . . . . . . . . . . 46
Structural Setting . . . . . . . . . . . . . . 46
Joints and Acute Bisectrices . . . . . . . . . 51
Quartzo-feldspathic Ellipsoids . . . . . . . . 54
Banding and Foliation . . . . . . . . . . . . . 56

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . 6O

SUGGESTIONS FOR FURTHER RESEARCH . . . . . . . . . . 63

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . 64

vi

LIST OF TABLES

Table Page
I Modal Analyses of Gneiss 8
II Modal Analyses of Granite 24

vii

LIST or FIGURES

Figure

l.
2.
3.

10.

ll.

12.

Location map of problem area in Southern
Typical appearance of the gneiss . . . .

Photomicrograph of sphene stringers
between subhedral, prismatic sections
of hornblende . . . . .'. . . . . . . .

Illustrative photomicrograph showing
profusion of sphene stringers in the
vicinity of intrusives (sample 6b) . . .

Photomicrograph showing euhedral

pyrite in intrusive zone. Partial
replacement by quartz. Epidote
inclusions . . . . . . . . . . . . . . .

Photomicrograph exhibiting myloni-
tization of quartz at contact zone

of acidic intrusive and gneiss

(sample 6b) . . . . . . . . . . . . . .

Photomicrograph of patch perthite
from microcline (sample 6b) . . . . . .

Photomicrograph showing epidote veins
adjacent to quartzo-feldspathic in-
trusive (sample 12a) . . . . . . . . . .

Photomicrograph exhibiting chlorite

as alteration product of biotite and
pseudomorphous after it. Sub-parallel
arrangement evident (sample 3) . . . . .

Photomicrograph of secondary carbonate
vein with chlorite pseudomorphous after
biotite (sample 20) . . . . . . . . . .

Photomicrograph of microcline surrounded

.by perthites, quartz and various types

of intergrowths (sample 2) . . . . . . .

Photomicrograph of examples of graphic
intergrowth(sample 2) . . . . . . . . .

viii

Page

11

12

13

l4

16

22

22

Figure

13.

14.

15.

l6.

17.

18.

19.

20.

21.

22.

23.

Photomicrograph of vein and string
perthite. Orthoclase is at ex-
tinction (sample 2) . . . . . . . . .

Photomicrograph of thin section
showing breakdown of magnetite and
pyrite into martite and hematite in
granite (sample lc) . . . . . . . . .

Photomicrograph illustrating diabasic
texture (sample 12c) . . . . . . . .

Photomicrograph illustrating felsitic
texture in metabasalt (sample 22) . .

Photomicrograph exhibiting sericiti-
zation along twinning lamellae
(sample 4) . . . . . . . . . . . . .

Photomicrograph showing partial
development of twinning lamellae
in plagioclase crystal (sample lc) .

Photomicrograph exhibiting different
zones and intensities of sericiti-
zation in plagioclase crystal (sample

Photomicrograph of perthitic inter-
growth, probably due to exsolution
(sample 1a) . . . . . . . . . . . . .

Photomicrograph of malacon-type
zircon, typically cloudy in appear-
ance, occuring in granite. Alter-
ation zone along borders (sample 19a)

Photomicrograph of rounded zircon
with breakdown along periphery in
granite (sample 14) . . . . . . . . .
Minor drag phenomena. Fold axis
roughly parallel to gneissosity . . .

ix

12b)

Page

23

27

28

29

33

34

38

'44

44

47

Figure Page

24. Quartzose elliptical concentrations
along gneissOSity O O C C O O O O O O O O O O O O O 48

25. Photomicrograph showing quartzose
ellipsoids in biotite displaying
flow structure (sample 20) . . . . . . . . . . . . 48

26. Strike frequency diagram of I68 joints . . . . . . 49

27. Strike frequency diagram of acute
bisectrices . . . . . . . . . . . . . . . . . . . . 49

28. Contour diagram of poles to 168 joints . . . . . . 50
29. Fissures ascribed to tension . . . . . . . . . . . 51
30. Contour diagram of acute bisectrices . . . . . . . 53

31. Contour map of angles of conjugate
jaint systems 0 O O O O O O O O O O O O O O O O O O 55

32. Acute bisectrices of assumed conjugate
joint systems . . . . . . . . . . . . . . . . . . . 58

33. Photomicrograph showing fracture and
diSplacement of twinning lamellae.
Quartz crystallization in fracture
zone (sample 14). . . . . . . . . . . . . . . . . . 59

34. Photomicrograph showing diaplacement
of twinning lamellae through stress
differentials (sample 14) . . . . . . . . . . . . . 59

INTRODUCTION

Location and Accessibility

Section 36, T47N, R26w, of the Palmer-Sands Quadrangles,
is located in Marquette County of Michigan, roughly twelve
miles southeast of Palmer (Figure l). The area under study
extends from the fire lane running approximately parallel to
the southern border of Section 36 to the northernmost boundary
of the major outcrops in the section.

The site of this study is readily accessible as major
highways (connecting Palmer, Negaunee and Marquette) surround
this area, and the interior is well traversed by numerous auto
trails, permitting motoring throughout the area during the

summer months.

Physical Features and Climate

The terrain is composed ofrolling, terraced and pitted
sand outwash, with rounded rock-cored hills and occasional
outcrops protruding above the comparatively flat landscape.
The immediate vicinity is thickly wooded with jack pine trees
and a dense growth of underbrush. Glacial scouring and
polishing is evident on the outcrops.

The summers are temperate to hot. There is a consider-
able amount of rainfall during the summer months and nights
tend to be cool. Winters are commonly severe, with heavy
snowfalls and recorded low temperatures of -3OF.

The principal industry of the Marquette area is the
mining and shipping of iron ores and concentrates. In the
immediate map area occasional pulp wood cutting serves as

the only economic activity.

 

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LOCATION MAP OF PROBLEM AREA IN SOUTHERN COMPLEX.

 

 

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3

Regional Geologic Background

Section 36 constitutes a small segment of what is known
as the Southern Complex bordering the Marquette iron-bearing
District. The geology of the igneous and metamorphic rocks
of the Southern Complex, situated directly south of the
Marquette synclinorium, has been a point of controversy since
the middle of the 19th Century. Various postulations as to
the age of the granitic rocks and gneisses in the Complex
have been recorded, with a notable lack of agreement on the
part of the researchers.

In 1851, Foster and Whitney (1851, Vol. 111, No. 4)
suggested that the granite south of the Marquette synclin-
orium was an intrusive into what were called Huronian rocks.
There followed, in the ensuing years, references by different
investigators to the age of the rocks. They were variously
regarded as Archean, Archean and post-Huronian, post-Huronian
and post-Cambrian. Van Hise, Bayley and Smyth (1897, p. l-
148), summarized the arguments from 1851 to 1897, and Van Hise
and Leith in 1909 (1909, p. 104) arrived at the conclusion
that the granites of the Marquette District, including the
Southern Complex, belonged to two separate ages, the Archean
and the post-Huronian.

This train of thought continued until challenged by
Lamey, in a series of articles (1931, p. 288-295; 1933, p. 487-
500; 1934, p. 248-263), who postulated that the entire Southern
Complex was predominantly made up of post-Huronian granite. He
recognized one major period of granitic intrusion. Referring
to the Palmer gneiss, Lamey considers that "at least a part of
the Palmer gneiss in this area near Palmer may represent Lower

Huronian formations..."

Finally, in 1936, Dickey (1936, p.317-340) attempting
to reconcile the divergent views on the subject, concluded
that there were three distinct periods of Precambrian
intrusions in the Complex. Two of these are Archean and one
post-Huronian. Thus, he regards the Southern Complex as
made up dominantly of Archean rocks, and not as Lamey and
others have proposed, compoSed of predominantly post-Huronian

granite. There stands the essential difference.
Purpose and Scope

The basic reason underlying the undertaking of this
project was to map and examine, lithologically and structur-
ally, a hitherto unmapped portion of the so called Southern
Complex in the Palmer gneiss area. It was hoped at the out-
set that this project would shed additional light on the
complexities of this region and perhaps indicate opportunities
for further research in this direction. The thesis presents
the results of a combined field and laboratory examination
of Section 36 of the Palmer-Sands Quadrangles. The field
work, consisting of mapping of outcrops, study of joints-and
foliation and collection of samples, was completed during the
summer of 1958. A petrographic examination was made of 29
thin sections cut from 29 of the 55 samples collected (see
location map in back pocket).

Furthermore, the information gained by Messrs. Long and
Vehrs, in their investigations of adjacent areas, may be
applied in collective correlation with the results of this
paper to gain a broader and more complete perspective of the
geOIOgic history of the area. However, many deductions ex-
pressed here should be regarded as still tentative, rather

than comprehensive and final.

5
PETROGRAPHY AND PETROLOGY

Rock Types

The dominant rock type in Section 36 is a hornblende
gneiss (Figure 2), which is similar to what Dickey (1936,
p. 323) refers to as the Archean injection gneiss. The
original country rock, thought to be basalt flows, was ap-
parently altered to gneiss during severe folding and intru-

sions by granitic magma.

 

 

 

 

Figure 2. Typical appearance of the gneiss.

Associated with the gneiss are several varieties of
granitic intrusions. It is convenient to divide these into
three groups. What appears to be the youngest granite is
typically coarse to pegmatitic in texture and is bright pink.
The pegmatites are a part of the youngest granitic intrusion,

and as a rule, appear in an extremely irregular and erratic

pattern and are of little value to the investigator except
for possible metamorphic effects. Consequently, they will
not be discussed in detail. A second type consists of a
relatively equi-granular, medium—grained, grayish-pink
granite. The remaining granites diSplay a porphyritic tex-
ture and range from pink in the feldspars to the blacks of
the ferromagnesians.

Intruding the above described rocks are metamorphosed
dikes or sills which are predominantly basic in composition.

Metadiabases and metabasalts are the common representatives.
The Gneiss

The hornblende gneiss, characterized by alternating
dark bands of ferromagnesian minerals and light bands of
granitic material, constitutes the most prevalent lithologic
unit. Its banding strikes from E-w to Nw-SE, with an average
dip of 55° to the south, and is indiscriminately intruded by
numerous quartzo-feldspathic dikes and veins. The contacts
between these intrusions and the gneiss are often sharp and

show little gradational phenomena.

Sample 5b. Megasc0pically, the rock is a dark green, medium
grained amphibolite converted into a gneiss as a consequence
of quartzo-feldSpathic intrusions. The acidic bands vary in
thickness (.05-.25 in.) and are parallel to cleavage planes.
Under the microscope the texture is hypautomorphic-
granular to xenomorphic. The thin section shows two bands.
The dark band of the gneiss is predominantly composed of
hornblende, while the light band is quartzo-feldspathic in
composition. The hornblende, some showing prismatic cleavage,

commonly appears anhedral to subhedral. The crystals often

display inclusions of quartz, zircon and magnetite. Sphene
overgrowths on magnetite are relatively common. The Sphene
is frequently observed surrounding a core of magnetite, this
phenomenon being quite representative of the gneissic rocks.
It is eSpecially abundant in the vicinity of veins and
intrusives (Figure 3). Epidote, in the form of clinozoisite
and pistacite, occurs in small quantities as formless aggre-
gates or intrusive veinlets. The feldspar determination is
complicated by the advanced stage of sericitization and pro-
fuse quantities of clinozoisite and piedmontite. The plagio-
clase appears more distinctly in the light intrusive band,
although again exhibiting advanced paragonitization. The
Ab.An content was determined to be Ab54An46 in the light band,
.and Ab46An54 in the dark band. Undulatory extinction is a

characteristic of the quartz. It is frequently fractured.

  
  

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Figure 3. Photomicrograph of Sphene
stringers between subhedral, prismatic
sections of hornblende (sample 5b).
Plain light, x54 diameters.

TABLE I

 

 

 

 

 

 

 

MCDAL ANALYSES CF CNEISS
Sample No.
Analysis

5b 6b 12b
Hornblende . . . . . . . . . . . . . . 6O 3O 4O
Chlorite . . . . . . . . . . . . . . . 5 2? 3
K-feldspar . . . . . . . . . . . . . . 15 5 15
Plagioclase (andesine) . . . . . . . 10 15 25
Quartz . . . . . . . . . . . . . . . . 5 20 10
Biotite . . . . . . . . . . . . . . 2 3
Epidote* . . . . . . . . . . . . . . . 3 5 3
Pyrite . . . . . . . . . . . . . . tr. tr. tr.
Magnetite' . . . . . . . . . . . . . . tr. tr. tr.
Sericite and/or paragonite** . . . . . ** ** ** '
Sphene . . . . . . . . . . . . . . . tr. tr. tr.
Apatite . . . . . . . . . . . . . . . tr. tr. tr.
Zircon . . . . . . . . . . . . . . . . tr. tr. tr.
Carbonate. . . . . . . . . . . . . . . tr.
Leucoxene . . . . . . . . . . . . . . tr. tr.
Total . . . . . . . . . . . . . . . . 98 99 99
A clinozoisite, pistacite, zoisite (2)
** percentage of feldSpar altered 25 25 15

A.

A‘L

 

‘53

— .__—__———— __ ~ _ , —. —-._.

 

 

 

v— v I . * j

Figure 4. Illustrative photomicrograph
showing profusion of Sphene stringers in
the vicinity of intrusives (sample 6b).
Plain light. x54 diametersi___1

 

 

Figure 5} Photomicrograph showing euhedral
pyrite in intrusive zone. Partial replace-
ment by quartz. Epidote inclusions (sample 6b).
Crossed nicols, x54 diameters.

10

Sample 6b. The rock consists of alternate hornblende
(chloritic) and quartzo-feldspathic bands. The acidic bands
range in width from .05 to .10 inches, while the dark bands
average .40 inches.

Microsc0pically, the texture ranges from hypautomorphic-
granular to xenomorphic. Hornblende and chlorite form the
bulk of the ferromagnesian minerals in the mafic bands of the
gneiss. Hornblende occurs in quantities up to 30 per cent,
and chlorite, showing characteristic Berlin blue under crossed
nicols, up to a maximum of 25 per cent. The chlorite appears
to be an alteration product of and pseudomorphous after biotite.
Unaltered flakes of biotite are still present but rare. Profuse
quantities of Sphene in the form of stringers, or anhedral to
subhedral crystals, occur at contact zones with the granitic
bands (Figure 4). Also associated are large formless aggre-
gates of epidote (clinozoisite, pistacite). Pyrite appears
in large subhedral to euhedral crystals, partially altering
to hematite (Figure 5). The plagioclase (15 per cent) is
extensively replaced by piedmontite and clinozoisite. .Some
secondary calcite is present. The quartz, constituting up to
20 per cent of the sample, is often severely shredded and
fractured, with granulation at grain boundaries and liquid
inclusions not uncommon. Mylonitization is suggested by the
intensive dragging out of the constituent minerals into
streaks, apparently during the intrusion of the youngest
granitic intrusive, and is observed running roughly parallel
to the contact of the gneiss and the intrusive (Figure 6).

The light bands exhibit comparatively little alteration of
major constituents. Quartz (35 per cent) and plagioclase
(AbSBAn42) are the major constituents of the acidic bands.

The plagioclase runs up to 50 per cent. Accessory minerals

ll .

 

 

 

Figure 6. Photomicrograph exhibiting
mylonitization of quartz at contact zone
of acidic intrusive and gneiss (sample 6b).
Crossed nicols, x21 diameters.

are at a minimum. Undulatory extinction is present in the
quartz, and although fracturing and granulation of grain
boundaries is observed, most of the quartz appears rela-
tively fresh and undisturbed. Phenocrysts of micro-perthite
are common as patch perthite, with microcline remnants in
plagioclase host (Figure 7). Subhedral to euhedral apatite

is present.

12

 

 

 

 

Figure 7. Photomicrograph of patch
perthite from microcline (sample 6b).
Crossed nicols, x54 diameters.

Sample 12a. The megascopic description of this rock is very
similar to the preceding two samples mentioned above. It is
medium-grained, granular, dark green and cut by two sets of
acidic intrusions. One set is parallel to the gneissic
pattern. The youngest intrusion, mainly quartzose in compo-
sition, cuts the rock at an angle of 50 degrees with sharp
contact.

In the thin section, the texture is xenomorphic-granular
to hypautomorphic. Hornblende is again the most important
mafic constituent. Prismatic sections are common. Chlorite
is observed, probably as an alteration product of biotite.
The feldSpars are sericitized to an advanced stage. There is a

smattering of biotite, often in a partial alteration condition.

Sphene appears frequently, anhedral and commonly associated
with magnetite. The malacon zircon is rounded to subhedral,
clouded and colorless. Prismatic and hexagonal sections of
apatite are observed, mainly subhedral. Reaction strips of
epidote at the contacts of basic and acidic bands are noted
(Figure 8). Pyrite is infrequent and sometimes altering to

hematite. Cataclasis and mashing is widespread.

 

 

Figure 8. Photomicrograph showing epidote
veins adjacent to quartzo-feldspathic
intrusive (sample 12a). Crossed nicols,
x21 diameters.

General Observations and Possible Interpretations. The
dominance of hornblende in the gneisses studied, comprising
35 to 65 per cent of the rock, suggests an original rock of
basalt or basic tuff in composition. The hornblende commonly
appears in prismatic sections, mostly subhedral, light yellow
to brownish yellow and is of the uralitic variety. It is

often accompanied by chlorite which appears to be an altera-

tion product of biotite (Figure 9), possibly as a result of

J.

 

 

 

Figure 9. Photomicrograph exhibiting
chlorite as alteration product of biotite
and pseudomorphous after it. Sub-parallel
arrangement evident (sample 3). Crossed
nicols, x54 diameters.

retrograde metamorphism. The chlorite content varies from
5 to 25 per cent, and is sometimes associated with small

quantities of relatively unaltered biotite. Another possible
indicator of the basic origin of the country rock is the pro-

fusion of sphene at the contacts of light and dark bands.

15

Epidote is also locally abundant, as clinozoisite and
pistacite, particularly where associated with mylonitiza-
tion of quartz. The presence of epidote may be explained

by the process of saussuritization, a retrograde effect,
which involves the breakdown of the Ca content of the
plagioclase with concurrent separation of the Na content.
This phenomenon is prevalent in the dark amphibolite bands
of the gneiss which show an Ab46An54 ratio in the plagio-
clase. This contrasts with the Ah54An46 ratio of the
andesine in the light bands, in which the An content is sub-
ordinate. Civen the extra Ca content of the dark bands,
epidote may form through hydrothermal activity, often ac-
companied by uralitization of pyroxene into hornblende.
Large euhedral crystals of pyrite are present at contact
zones of acidic intrusions and are another evidence of
hydrothermal activity. The feldSpar in the light bands is
dominantly plagioclase. Andesine comprises up to 30 per
cent of the rock, while orthoclase runs to about 15 per cent.
The feldspars, as a rule, are heavily sericitized and/or
paragonitized and are difficult to identify in the dark bands,
while in the light bands they appear relatively fresh. The
albite, Carlsbad and occasional pericline twinning is more
distinct in the light bands. Zircon is present in subhedral
to rounded crystals of the malacon type. The presence of
some secondary calcite (Figure 10) may be associated with
the general process of saussuritization encountered in the
gneisses, as a result of the breakdown of the plagioclase
into Ca and Na. Quartz appears mylonitized at contact zones
of the amphibolite and the youngest granitic intrusions.

The mylonitization can be attributed to strong differential

movement in the stress field. It is noteworthy that the

 

 

 

 

 

Figure 10. Photomicrograph of secondary
carbonate vein with chlorite pseudomor-
phous after biotite (sample 20). Crossed
nicols, x21 diameters.

pulverization of quartz is restricted to the vicinity of the
youngest acidic intrusive contacts with the gneiss. There is
comparatively little deformation displayed in the intrusive
-itself. Thus the mylonitization may represent the last major
period of structural deformation. As the epidote occurrence
is strongly associated with these youngest intrusives, it

may also be regarded as a late event.

-According to Turner and Verhoogen (1951), metamorphic
differentiation may account for veins or laminae of simple
compositon in initially homogeneous rocks. An example of
this are the epidosite (epidote and quartz) veins in amphi-
bolites, and quartz-calcite veins in various kinds of low

grade schists. Epidosite and quartz-calcite veins, which

17

are common in the gneiss studied, may be due to metamorphic
differentiation and derived from the rock in which they occur.
This is eXplained by the property of the particular mineral

to be readily dissolved and redeposited under low-grade meta-
morphic conditions, which appear to be applicable to the meta-
morphic rank of the area under study. Turner and Verhoogen
(1951) regard metamorphic differentiation as "a result of dif-
ferential migration of the component ions of the metamorphic
system through short distances, under-the influence of local
gradients in chemical potential."

The foliation observed in the gneiss can also be attri-
buted to segregation resulting from metamorphic differentiation.
The differentiation involves mechanical deformation synchronous
with chemical activity, the former agent being subordinate.
Mechanical activity results in shear surfaces from the induced
rotation and gliding of crystals, thus facilitating passage of
pore solution. Since minerals such as quartz and calcite de-
form with ease, they are conducive to the develOpment of layers
and bands due to segregation. The subparallel arrangment of
the platy or prismatic crystals of the dominant constituents
is achieved through flow movement accompanying deformation.
Cataclasis, in the form of extreme shredding and mashing, is
amply evidenced in the hornblende gneiss of the area, although
relatively absent in the youngest granites. If the deve10pment
of the layered structures were attributed to the interplay of
mechanical deformation, solution and crystallization, i.e.,
metamorphic differentiation, one period of metamorphism would
be sufficient. However, the writer questions the probability
of metamorphic differentiation as the chief agent in the
development of the gneiss. It is doubtful whether the original

basaltic rock included the necessary amounts of quartz and

18

calcite to provide for the essential preperty of comparatively
high solubility, thus facilitating segregation of the minerals
into bands and layers and accounting for the prevalence of

the quartz, calcite, epidote and granite in veins, stringers
and dikes.

An interesting sidelight on the issue of diffusion and
differentiation is Barth's description (1952) of what he calls
secretion pegmatities. These form, in his view, first, through
the formation of fissures and open cracks by stress differen-
tials, and second, through the action of the gradients in the
chemical activities set up by mechanical pressure gradients.
The haphazardness of the youngest quartzose and pegmatitic
bodies cutting the gneiss, and their extreme irregularity in
the area studied by this writer, could perhaps be explained
by advocating the absence of ducts leading to magmatic sources.
Rather, since stress differentials have existed in this area,
the lack of any order to the youngest acidic bodies may be due
to their dependence on the presence of fissures and cracks,
and consequent filling of these cavities by secretion or
excretion. This, in fact, appears to be a possibility since
'a definite zoning in the pegmatite is noticeable. The marg-
inal zone displays crystals of quartz and plagioclase up to
.6 inch in length embedded in a fine-to-medium grained matrix,
often showing graphic intergrowths. The inner zone appears
more coarse-grained; single crystals of microcline attain
1.6 inches in length.

If the injection of the acidic intrusives were regarded
as the agent reSponsible for the genesis of the hornblende
gneiss, then two major periods of metamorphism would have to
be postulated, plus a minor one as a result of various periods

of granitic "intrusions" on a smaller scale, giving rise to

19

stringers and veins of epidote and calcite. These, when in
any type of linear aggregates, appear closely associated with
the contacts of the younger acidic bodies and the gneiss.

The writer would suggest the following sequence for the
genesis of the hornblende gneiss in the area, which is, for
all practical purposes, part of the Palmer gneiss nearby.

The first major period of metamorphism could coincide with
the Laurentian disturbance and result in the alteration of
the original Keewatin basic flows to amphibolite. The form-
ation of the gneiss could be attributed to late pre-Huronian
granitic activity and the Algoman Revolution. This is in
view of the predominance of the malacon-type zircons, and the
conclusions of Tyler and Marsden (1940). The important point
to bear in mind, however, is that the formation of the gneiss
involved a second major period of metamorphism in the late
pre-Huronian. A third period of metamorphism could be rela-
ted to the Killarney Revolution which led to the haphazard
pattern of the youngest quartzo-feldSpathic and pegmatitic
intruding bodies. The solutions in turn, it is suggested,
were instrumental in the formation of epidote and calcite
stringers and veins, through the.hydrotherma1 alteration of
Ca bearing minerals, particularly the plagioclase, and for
the retrograde minerals such as chlorite.

Distortion of laminae, drag effects, crenulations and
the like make some type of injection of the gneiss, or per-
haps lateral secretion, as a likely process. The acidic bands
in the gneiss, however, are not the uniform, lit par lit type,
but tend to differ in their concentrations. The thin sections
display a (subparallel) preferred orientation in the hornblende.
Cataclasis, in the form of extreme shredding and mashing

rw’

evident in the dark bands, also appears to favor the intrusion

of relatively solid strata by foreign bodies. This extreme
form of cataclasis is absent in the younger granitic intru-
sions. The role of cataclasis in the deve10pment of the
gneiss will be further explored in the succeeding section
when its correlation with the granites is discussed.

The gneiss is similar to what Dickey (1936, p. 323)
described as the Archean injection gneiss:

" (developing) through the intimate
intrusion of Keewatin-type schists,
generally along cleavage planes, by
granite."
Observed relationships he saw led him to regard the intrusive

granite as belonging to the older or Laurentian granite.

The Granite

Late'Granite

The characteristic properties of what is probably the
youngest granitic intrusion make easy its recognition and dif-
ferentiation from other varieties of granite in the map area.
-The orthoclase crystals are conSpicuously red to pink and may
appear as intergrowths with quartz. The texture ranges from
coarse to pegmatitic. As a rule, the granite is distributed
Sporadically in irregular masses, crosscutting dikes and vein-
lets, and is observed intruding the earlier rocks in a hap-
hazard manner. This rock is comparatively devoid of mashing
and cataclasis and appears to have been introduced concurrently
with the last major period of orogeny. The above description
is not unlike the Killarney granite described by Dickey (1936,
D. 333).

21
Porphyritic Granite

A porphyritic granite, very similar to what Dickey refers
to as the Laurentian granite porphyry, is "characteristically
‘pink to gray in color, and where not deformed subsequent to
its emplacement, bears large phenocrysts of orthoclase, micro-
(Cline, and microperthite, in‘a groundmass of quartz and biotite,
xvith lesser amounts of oligoclase, apatite, zircon and muscov-
:ite (Dickey, 1936)". The porphyry appears deformed to a
rnedium degree, and displays some realignment of the constit—
tient minerals. It should be noted that Dickey considers the
Imaurentian granite porphyry as younger than the Laurentian

granite reSponsible for the Archean gneiss.

Sample 2. In the hand Specimen, a porphyritic granite
similar to Dickey's Laurentian granite porphyry is seen to
have a granophyric texture. The pink feldspar phenocrysts
range from .10 inch to .30 inch in length, against a dark,
phaneritic matrix of biotite and quartz and plagioclase.
Under the microsc0pe, the granite exhibits a hypauto-
morphic-granular texture with large phenocrysts of microcline
and microperthite. Quartz, andesine, orthoclase, microcline
and perthites are the major constituents. Accessory minerals
include pyrite, apatite, zircon, magnetite and leucoxene.
'Uhe quartz is fractured and shows undulatory extinction.
Andesine constitutes upward of 25 per cent of the thin sec-
'ticwn frequently exhibiting incomplete twinning and some
<iEformation. It is extensively paragonitized. Microcline is
ciol'nmon, often grading to micrOperthite (Figure 11). Graphic
jJutergrowths of feldspar and quartz (Figure 12) and complex
‘Varieties of perthites in veins and braids are significantly

Eyresent (Figure 13). Blebs of quartz are common throughout

22

 

 

Figure 11. Photomicrograph of microcline
surrounded by perthites, quartz and various
types of intergrowths (sample 2). Crossed
nicols, x54 diameters.

 

Figure 12. Photomicrograph of example of
graphic intergrowth (sample 2). Crossed
nicols, x54 diameters.

23

the section. Biotite occurs in random, Sparse flakes,
occasionally showing alteration to chlorite. Muscovite is
rare. Crystals of apatite are unusually large and pris-
matic to rounded and irregular in form.' Hematite staining
is not very prevalent but evident locally. Predominantly
anhedral to subhedral crystals of magnetite, sometimes as
euhedral octahedrons, exhibit alteration to martite. The
rock displays cataclasis. Occasional appearance of clinr.

zoisite and pistacite is noted.

 

 

Figure 13. Photomicrograph of vein and
string perthite. Orthoclase is at ex-
tinction (sample 2). Crossed nicols,
x54 diameters.

24

TABLE II

MODAL ANALYSES CF GRANITE

 

 

 

 

 

 

Sample No.
Analysis

2 6a 15
Quartz . . . . . . . . . . . . . . . . 20 40 40
K-feldspar . . . . . . . . . . . . . 33 28 23
Plagioclase (andesine) . . . . . . . 25 3O . 19
Microcline . . . . . . . . . . . . . . 6 9
Perthite . . . . . . . . . . . . . . 4 7
Biotite . . . . . . . . . . . . . . . 10 tr.
Muscovite . . . . . . . . . . . . . . tr. tr.
Chlorite . . . . . . . . . . . . . . 1 tr. 2
Zircon . . . . . . . . . . . . . . . . tr. tr. tr.
Apatite . . . . . . . . . . . . . . . tr tr. tr.
Magnetite . . . . . . . . . . . . . . tr. tr. tr.
Epidote* . . . . . . . . . . . . . . . tr. tr.
Carbonate . . . . . . . . . . . . . tr.
Leucoxene . . . . . . . . . . . . . tr
Sericite and/or paragonite** . . . . . ** ** **
Total . . . . . . . . . . . . . . . . 99 98 99
* Clinozoisite, pistacite
** Percentage of feldspar altered . . 15 2O 25

25

Noniporphyritic Granite

A third type of granite in the map area is relatively
equigranular, medium-grained, gray, pink to red in appearance.
This rock exhibits few effects of intense deformation although
some cataclasis is locally present. It is characterized by a
lack of porphyritic texture. The writer feels that this
granite can also be referred to the youngest granitic intru-
sion, i.e., the Killarney, as described by Dickey (1936).

He defined the granite as:
"...marked by the presence of red to pink
granite with a broad textural range, vary-
ing from fine-grainec to pegmatitic. The
characteristic color, lack of porphyritic
texture, and absence of cataclasis or mash-
ing produced Hy deformation subsequent to
intrusion makes it readily distinguishable
from the Laurentian granite porphyry."
Sample fa. 1n the hand Specimen, the rock is a light-pink
granite, predominantly feldsnar and quartz. It is melium-
grained in texture.

Microscopic examination reveals the pronounced lack of
any ferromagnesian minerals. The major constituents are
orthoclase, andesine and quartz. Little fracturing is shown
by the quartz crystals, which exhibit undulatory extinction
and commonly contain liquid inclusions. Paragonitization and
sericitization of the feldSpars, as is usually the case, occurs
extensively. Carlsbad, albite and pericline twinning is present.
Secondary calcite occurs sparsely, commonly associated with
quartz veinlets or fracture zones. The presence of iron-stain-
ing is evident as a result of what appears to he the breakdow:
Of magnetite into martite. In contrast to former samples,
there is a positive lack of any epidote. Also, the rock shows

little effects of cataclasis, which is a dominant feature of

the gneisses of the area. Apatite appears in euhedral hexa-
gonal cross-sections and subhedral grains, although compara-

tively scarce.

Sample 15. Although very similar to the last Specimen mega-
scopically, the thin section exhibits distinguishing properties.
hegascopically, the rock is light grayish-pink in color and
shows traces of ferromagnesian minerals, and also, more signi-
ficantly, it does not appear as fresh and undeformed as sample
Ga.

Under the microscope, the major portion of the mineral
constituents is comprised of the feldspars, andesine and
orthoclase, and quartz. The plagioclase shows paragonitization
to a marked degree. Albite twinning is extremely prevalent,
although not always distinct because of paragonite. Micro-
Cline is very common and microperthite is seen occasionally.
Perthite appears in various forms -- patch, vein or braid --
and occurs frequently. Chlorite and epidote (clinozoisite
and pistacite) are observed in a few, intermittent patches
and stringers. As a rule, the biotite content is very low
and it has largely altered to chlorite. There are traces of
small, rounded grains of zircon. Muscovite is extremely rare.
Evidence of cataclasis can be seen only locally, in the form
of mashing and fracturing of quartz crystals, but is signifi-
cantly absent in adjacent feldspars. The texture exhibited by

the thin section is hypautomorphic-granular.

 

 

 

Figure 14. Photomicrograph of thin
section showing breakdown of magnetite
and pyrite into martite and hematite in
granite (sample lc). crossed nicols,
x54 diameters.

General Observations and Possible-lnterpretations. A note-
worthy characteristic of what are considered to be the younger
granites, i.e., those seen cutting the gneiss and non-porphy-
ritic in texture, is the apparent restriction of the more
prominent fracturing and mashing to the quartz. This could
coincide with the mylonitization observed along the contacts
of the latest granitic intrusion and the gneiss. However,

the quartz in the latest granitic intrusions shows little ad-
vanced deformation, so that the above-mentioned fractured
quartz may be the product of an earlier period of deformation.
A separate major period of deformation is exhibited by the

cataclastic nature of both the quartz and the feldspars in

the porphyritic granite. There appears to be no selectivity
in the cataclasis noticed in the thin section. Another major
period of orogeny is evident in the extreme shredding and
mashing often present in the gneiss, which is in turn cut by
the younger granites.

To account for the deformation observed, three major

orogenic periods appear to be necessary.

 

 

 

Figure 15. Photomicrograph illustrating
diabasic texture (sample 12c). Crossed
nicols, x54 diameters.

Metadiabases and Associated Basic Rocks

By far the least abundant of the rock types encountered,
the basic intrusives are found in localized masses,usually as
dikes, and appear to have been intruded prior to the last
major period of folding, i.e., the Killarney Revolution. It
is suggested that the basic rocks are a part of the Huronian

volcanic activity, e.;., the Clarksburg, which underwent later

2f)

metamorphism, notably during the pre-Keweenawan Killarney
orogeny (Zinn, 1959). Although the writer has differentiated
between the metadiabases (Figure 15) and the basaltic-type
rocks (Figure 16), it should be pointed out that gradations
exist between the two, and that it is often difficult to as-

certain the differences.

 

p——— - .._.

 

 

 

Figure 16. Photomicrograph illustrating
felsitic texture in metabasalt (sample 22).
Crossed nicols, x54 diameters.

Sample 19b. On its weathered face, the rock shows the chara-
cteristic intergrowth pattern of plagioclase laths and ferro-
magnesian minerals, which identify the diabasic texture. The
rock is grayish-green in color and appears microphaneritic in
texture.

Microscopically, an ophitic texture is observed. Horn-
blende is the most abundant mineral, frequently exhibiting

Various stages of alteration to chlorite. Large, formless

3O

aggregates of Sphene are common in occurence, often assoc-
iated with magnetite. Pyrite is present in anhedral crystals.
The identification of the plagioclase is complicated by the
heavy replacement by piedmontite and clinozoisite. _Some

zoning is present in the plagioclase laths, as well as some
albite and Carlsbad twinning. The plagioclase has a compo-
sition close to labradorite. The feldspathic laths are
intimately associated with anhedral to subhedral hornblende.
Some quartz can be seen and, if primary, indicates the diabase
to be of the tholeiitic type (Heinrich, 1356). Apatite appears

only sporadically in individual, small, rounded crystals.

Sample 22. This dike-like rock is basaltic in appearance,
dirty green in color and the matrix has an aphanitic texture.
.Disseminated pyrite is noticeable.

In the thin section, the texture is holocrystalline,
with aggregates of epidote and calcite (secondary). Epidote
is present in a variety of forms -- clinozoisite, pistacite
and possibly zoisite. The epidote may be an alteration product
of the augite. The original pyroxene may have also altered
to carbonate or chlorite. Chlorite is the dominant constituent
of the matrix. The determination of the feldSpars is extremely
difficult by usual petrographic means. Quartz is present as
an accessory mineral in insignificant amounts. Accessory
minerals include sphene and pyrite in anhedral crystals, the
former appearing abundantly, especially in irregular strinoers

and patches.

31

PETRCCENIC AND
PETRCLCGIC INTERPRETATIONS

Sericitization and Egragonitization. In the writer's Opinion,
more attention should be focused, than has usually been the
case, on the various patterns and environmental frameworks in
in the confines of which seribitization and paraponitization
are seen to develop. As Eskola summarized (1939), the develop-
znent of sericite, through the action of hydrothermal metasoma-
tism, is dependent on the alkali concentration and the tempera-
tnare of the active solutions.

The question of the actual composition and the nomencla-
tnire of the sericitization of different feldSpars has not been
twesolved. It has been suggested (Johannsen) that naragonite,
an1d not sericite, is the plagioclase alteration product and is
sindlar to sodic mica in composition. The thesis has been
auflvanced that the term sericite should be employed only when
(accuring with orthoclase, and that paragonite should be assoc-
iated with plagioclase. Emmons (1°53), on the other hand,
tnentions that T.O. Patrick is to report on the thesis that
"paragonite characterizes orthoclase and sericite character-
izes plagioclase. These micas need not be 'alteration
'Products'."

Emmons and his co-researchers (1053) came to the follow-
ing conclusions regarding the sericitization of feldspars:

"We regard sericitic alteration in zones of

an oscillatorily zoned plagioclase as conse-
quent to the unmixing of potash on cooling.
Our analyses suggest this by the low potash
content and the excess silica. This seri-
citization takes place at about the time of
twinning. In progressively zoned plagioclase
sericitization is much more general through-
out the crystal. Un these premises we further

conclude that some zones of oscil-
latorily zoned crystals contained more
potash than others and hence carry more
sericite. Cr the hioh potash of some
zones may have been transferred to alter-
nate twin lamellae, and hence alternate
lamellae may carry more sericite -- a
frequent observation."

Emmons (1953) bases his concept of sericitization of the
plagioclases on the premise that, within limits, twinning and
zoning are mutually exclusive in that an increase in the
former results in a roughly proportionate decrease in the
latter.

In discussing the alteration products of feldSpars, the
unriter shall restrict the term sericitization to the K-feldSpars
EHId paragonitization to the Na-feldSpars, rewardless of their
tweSpective compositions. Four main patterns of paragoniti-
zmition were evident in their relationships to plagioclase in
tflwe samples studied by the writer. First, paraeonitization
imas sometimes observed to develOp in alternate lamellae,
Ualnmst obscuring the twinning lamellae. Second, paragoniti-
zation was observed restricted to rims of crystals. Third,
'Daxagonitization was observed confined to what appears as
former zone outlines. Finally, a fourth pattern consisted of
‘Various combinations of the above, such as paraqonitization
'regardless of twinning.

In the first case (Figure 17), it is quite probable that
there are compositional variations between the adjacent
lamellae, which makes possible the selective paragonitization
of alternate lamellae. This difference in composition may be
inherited from the preceding zone structures. Emmons and
Mann (1953) state that "the difference in composition of
cOntiguous twin lamellae, in part at least, substitutes for

the difference in composition between zones."

33

 

 

 

 

_ ,y i .N‘_ ——

ieure l7. Photomicrograph exhibiting
sericitization along twinning lamellae

(sample 4). Crossed nicols, x54 dia-
meters

 

 

 

Figure 18. Photomicrograph showing
partial development of twinning la-
mellae in plagioclase crystal (sample
lc). Crossed nicols, x54 diameters.

34

The second case (Figure 19) might be explained by the
concentration or segregation of potash at the borders of the
crystals, thus establishing a conducive area for the para-
gonitization of the plagioclase. As a case in point, the
non-permanence of a difference in composition, whether between
the lamellae or zones, should not be overlooked. This dif-
ference may be removed with the advancing age of the crystal
(Emmons and Mann, 1953). An agent for the concentration and
segregation of the potash content could be the presence of
hydrothermal solutions. The relative abundance of paragonite
in the borders of a crystal may also be explained through the
migration of the potash as a consequence of periods of viscous
fluidity; however, without the effects of cataclasis (Bradley

and Lyons, 1953).

 

Figure 10. Photomicrograph exhibiting
different zones and intensities of seri-
citization in plagioclase crystal (sample
12b). Crossed nicols, x54 diameters.

35

The reasoning applied to the first example may be
employed in attempting to explain paragonitization with
certain former zone outlines. This must again be due to
differences in composition, resulting in selective para-
gonitization of particular zones (Figure 19).

In the absence of sufficient compositional differences
or other pertinent controlling factors, such as, perhaps,
the absence of twins or zones, or the interruption of para-
gonitization by potash transfer, paragonitization may be
expected to assume a random habit with no particular select-
ivity.

The general tendency in Section 36 of paragonitization
to be characteristically not confined to one or two patterns,
involves the consideration of various possible affecting
factors. It must be emphasized that unlike the orthoclase-
based sericite which appears to attack the crystal in a
more random and non-preferential manner, the paragonitized
plagioclase often displays differing patterns of concentra-
tion, as discussed above, which may perhaps be of additional
use as an aid in the identification of what might be untwinned
plagioclases. Emmons' and Mann's statement (1953), that the
difference in composition between lamellae is not constant
throughout the crystal is significant in that it permits an
explanation of the eccentricities of paragonitization that
have been observed.

Sericitization and paragonitization may help in the rela-
tive dating of rocks in a regionally metamorphosed area. How-
ever, until more exact information is available regarding the
proportional relationships of the composition of the alter-
ation product and the chemical composition of the original

rock, the usefulness of age determination on the basis of

paragonitization and sericitization is of a doubtful nature.
Cf interest here is Emmons' and Gates' view that paragoniti-
zation along twinning lamellae would imply a late date in the

deve10pment of the crystal.

Plagioclases. Turner (1951), in his studies of twinning
patterns, arrived at the tentative conclusion that complex

twin patterns could be attributed to a magmatic ancestry

and, conversely, that relatively simple twinning or no twinning
could be related to a metamorphic origin. This seems to agree,
to a certain degree, with the manifestations of twinning in
what the writer considers as metamorphosed rocks, as Opposed

to twin patterns found in granitic rocks of magmatic origin
which were introduced into the gneisses during various periods
of deformation. Albite, Carlsbad, and pericline twinning and
combinations thereof are evident in the rocks studied, their
relative abundances in the order given. Albite twinning, the
most abundant, often displays thin, straight lamellae, not
infrequently incomplete and covering only part of the crystal.
Typically, the sodic plagioclases studied do not exhibit
sharply defined twins because of the advanced stage of para-
gonitization. Ideally, according to Emmons and hann (1953),
"the twin lamellae of sodic plagioclase are typically straight,
sharply defined, uniform, or nearly so, and narrow." There
also appears to be a relationship between the degree of cata-
clasis evident in the rocks studied and the fineness of
lamellae. The greater the degree of deformation suffered by
the granite, within limits, the more intimate the twinning
appears to be. Emmons and Mann (1953) point out that it is
quite possible that "rapidly applied stress, beloy the
shattering point, will create the most intimate twinning,

i.e., narrow lamellae."

It is interestine to note the remarkable frequency of
sodic feldspar crystals exhibitino incomplete twinnine, c.é.,
twinning only in the center of the crystal. This may he due
to differential stress and cataclasis. Gorai (1050) describes
untwinned plaeioclase as resulting predominantly from condi-
tions prevalent in roof and wall rock areas, and, further,
that untwinned plagioclase belonqs to a metamorphic environ-
ment. It would be exnected then that all decrees of qrada-
tions between twinned and untwinned plagioclases could
possibly be explained in terms of their distance from roof
and wall zones of major igneous bodies. As Emmons stated
(1953), "in roof-rock occurences the lamellae of the core
may not continue into the outer later portions of the
crystal." This seems likely, in the writer's view, since
the samples collected for study are thought to be for the
most part from roof-rock regions. This tendency of twinning
to be confined to the crystal nucleus, and its inability or
failure to grow into the newer portions of the crystal, is
regarded by Emmons and Mann (1953) as an "outstanding chara-
cteristic......which contrasts strongly with those crystals
formed from igneous liquids...." Furthermore, they hypothe-
size that this is also probably due to the frequent occurence
of unzoned plagioclases in these reconstituted rocks. The
reader's attention is drawn to the point that Emmons and
Mann (1953) are of the opinion that "...twinning which forms
late in the history of the crystal and nostdates ionine, is
one of the factors and often a dominant one in the elimina-
tion of zoninc." In other words, the possibility of twinning
and zoning being mutually exclusive is thoucht to be hiehly

probable.

id

8

If nothine else, the variations in the patterns of
twinning encountered in the different granites point to
periods of deformation as one of the geologic aeents at
work. The above discussion is more difficult to apply
to the gneiss proper since the sodic feldsnars in the
gneiss are often obscured by the effects of repeated de-
formation. Incomplete twinnin: in some of the granites
may be taken as an argument aaainst the crystallization

of sodic feldspars from ieneous liquids.

Perthites. In a paper on the netroqenic significance of
'perthite, Gates (1953) states that the "textural variations
are thought to orieinate through two chemical processes --
unmixinq and replacement -- operating almost simultaneously."
Cates attempts to eXplain perthitic features by attributing
it to greater mobility of the plagioclase factor than formerly

believed, and concludes that unmixing (Figure 20) as the sole

 

 

 

Figure 20. Photomicrograph of perthitic
intergrowth, probably due to exsolution
(sample 1a). Crossed nicols, x54 dia-
meters. '

39

instrument of perthitizaticn is hardly sufficient to account
for the textural variations encountered. In Sun, three
theories as to the formation of perthitic textures are den-
erally recoonized. They are: 1) unmixinq, 2) simultaneous
crystallization, and 3) replacement.

Althounh the occurence of perthitic textures in the
area is limited, specifically,to those rock units which are
believed by the writer to be of maematic origin, i.e., the
acidic intrusives, a wide variation is observed between the
divergent types. There is an apparent absence of braid per-
thites; however, examples of vein, string (Figure 13) and
patch perthites can be seen. ESpecially striking are the
large phenocrysts showinq patch perthite, which appear to
support Goldich and Kinser's view (1939) that "by further
replacement of microcline by albite, braid and vein perthites
grade into typical patch perthites." The patch perthites
observed frequently include remnants of the original micro-
cline in one form or another. According to Gates (1953),
"patch perthites and eSpecially extreme examples suggest
local accumulation of sodic materials from a greater distance."
In contrast, he concludes that the origin of the sodic material
necessary for the develOpment of string and film perthite is
of a local nature. In the former case, an underlyine bathe-
lith, which the writer is prooosing as a possible exnlanation
of the structural and magmatic phenomena studied, could pre-
sumably fulfill the role of a distant magmatic source. It
becomes apparent that differential pressures would be a major
factor, e.g., the attraction of a low pressure fracture area --
in a feldsnar -- for unmixinq plagioclase in a mobile state
(Emmons, 1953). It is not improbable then that stress con-

siderations in the area under study are of considerable

importance in the interpretations offered concerning
perthites. In the latter case, given the prevalence of
a variety of forms of intrusive feldSpathic bodies, the
develonment of film and shadow perthites "may be the
result of a hydrostatic pressure change durinq the last
stages of crystallization...." (Gates, 1953).

Tuttle rules out as improbable the possibility of
granitization at low temperatures of rocks containing
perthites of equal albite and microcline composition.
Concurrently, the writer wishes to emphasize that the
perthitic occurence is by no means a major constituent
in the thin sections studied, neither is it found in all
the granite types. Notwithstanding, there appears to be
a tendency in the examples observed for the dependence of
perthitic deve10pment on the degree of stress deformation
present.

Since the main lithologic units in the area deveIOped
under relatively low temperature conditions, Tuttle's con-
clusions would imply the genesis of the granite through
processes other than qranitization. This is in general
agreement with the writer's hypothesis that the granitic
intrusions were introduced either in a liquid state from
an outside source, or formed through metamorphic differ-

entiation.

Plaqigglase andhgpiggte. A persistent characteristic of

'the gneisses in the mapped area is the frequent plagioclase-
epfldote associations observed. This phenomenon may be viewed
éis "saussuritization" which took place in plagioclases that
‘vere retrogressively metamorphosed (Rambere, 1950), since
'epidote represents a low-temperature association relative

to the feldSpars. Accordine to Ramberg, the most common

Al

reactions involvino plagioclase and epidote are indicated

in the following equations:

zCaJ/Igsg‘QZOH + 34/1305 + 35m1 $664,445,;08 4. #10
£75,240 t: (fan/be. on or 1% / t:

. . 7;
«0,41, 5,30,,ou + KflIJStqumH), + 2550, -..=
elbr'dot'e. muscovu‘e, .
96.2431‘51308 + Kin/$50, + #40

0’7 oral}: oft/20c. lose,

It is clear that the above equations presuppose an
adequate supply of Ca in the form of the anorthite content
of plagioclase. The need may be filled by the greater
anorthite content (AbhéAnSA) in the dark bands of the gneiss.
Hence, epidote may form as a result of the loss of Ca in
dark bands upon metamorphism. Below a certain temperature,
Tu, the anorthite content of the plagioclase will react
with potash feldSpar and water, because of the fact that
they are then unstable. The products of this reaction will
be epidote, muscovite and some type of an acid rlaqioclase.
Pertinent to the above are the water-vapor pressure and the
Fe3+/Al3+ ratio. According to Ramberq, the increase of the
water-vapor pressure will favor the formation of epidote and
muscovite and will as a result raise the temperature level,
Tu, of the reaction points in the above equations. In like
manner, an increase in the Fe3+/Al3+ ratio of a rock will
result in an environment favorable to an increase in the
arowth of epidote so as to acain disulace the equilibrium
curves to higher temperatures. The latter phenomenon is
due to the ability of epidote, in contrast to that of plaoio-

clase, to replace laree amounts of Al with Fe3+.

 

A”)

The epidote in the qneisses of the mapped area represents
the latest period of metamorphism, coinciding with the young»
est acidic intrusions. It probably represents a separate
period of metamorphism, comine after the first two major
orogenies resulting in the genesis of the wneiss. However,
if metamorphic differentiation were postulated for the de-
velopment of the gneiss, the epidote veins could be explained
as products of retrograde metamorphism associated with one

major period of metamorphism.

DIFFERENTIATION OF ZIRCONS FOR CORRELATION PURPOSES

In their investigation of zircons of various types
occurinq in the granites of the Lake Superior Rceicn, Tyler
and Marsdcn (1°40) su:¢est that “the hyacinth occurs in the
older eranites, to the almost entire exclusion of malaccn,
whereas the malacon is found in the younger granites..."

The malacon zircons, according to Tyler and Earsdon,
are cha acteristically dull in luster, with a cloudy ap-
pearance and evtremely weak birefricence. The grains common-
ly exhibit striated and etched surfaces, and as a rule are
rounded prismatic in form. Elongate dipyramidal prisms are
rare. They are colorless to pale dirty yellow, sometimes
with dustlike inclusions reminiscent of alteration. Apparent-
ly, there exists a relationship between the malacon and the
igneous and compositional history of an intrusive.

The hyacinth zircon, on the other hand, is characterized
by a "very faint pinkish tint to a deep brownish purple,
purple, and pink" color (Tyler and Harsden, 1050). Unlike
the malacon, the hyacinth is slightly pleochroic ranging
from dark to light purple. The grains are usually observed
as rounded, and prismatic examples with several pyramidal
faces are common.

Tyler and Marsden (1040) arrive at the conclusion that
the hyacinth and malacon zircons characterize eranites of
two ages in the pre-Huronian. The older pre-huronian granite
is represented by the hyacinth variety, whereas the youncer
is represented by the malacon. However, it is not possible
to distinguish some of the Dre-Huronian granite from Huron-
ian igneous rocks, as the malacon is also observed to occur

in igneous intrusives into the Huronian. Therefore, the only

 

 

 

 

 

Figure 21. Photomicrograph of malacon-
type zircon, typically cloudy in appear-
ance, occuring in granite. Alteration
zone along borders (sample 19a). Plain
liaht. x225 diameters.

 

Figure 22. Photomicrograph of rounded
zircon with breakdown along periphery in
granite (sample 14). Plain light, x225
diameters.

45

valid conclusion to be drawn is that hyacinth-bearing
granites are pre-Huronian in age and older than the
granites carrying malacon zircons.

In the thin sections studied, the malacon variety
is the dominant zircon present (Figures 21 and 22). The
zircons are frequently rounded to rounded prismatic. Dull,
cloudy color, abnormally low birefrigence, dust-like in-
clusions and reaction rims are characteristic of the
malacon. Complete, elongate, prismatic sections are
seldom seen. In applying Tyler and Narsden's results,
the writer feels that it would be reasonable to assume
that the granites studied are either late ere-Huronian

or Huronian in age.

 

46

STRUCTURAL GEOLOGY

The outcrops in Section 36 appear to be part of an
elongate belt exhibiting a series of anticlinal folds, the
fold axes of which trend in an E-W to NN-SE direction. A
cross-sectional view of an anticline is evident west of
outcrop XXXIV, directly adjaCent to the road (see location
map in back pocket). Additional evidence of the anticlinal
structure is indirect, but an analysis of the structure can
be made through the examination of structural deformation
phenomena observed. Because of the small area that this
study encompasses, however, a structural picture of the
entire Southern Complex, or that part known as the Palmer

gneiss, will not be possible.

Structural Setting

The outcrops have a predominantly NW-SE trend, and the
foliation of the gneisses in them varies from E-w to Nw-SE
in strike and dips to the south at angles of 450 to 850
(see structure map in back pocket). The most prevalent
value for the dip of the s-surface is 55° to the south.

The gneiss often appears quite distorted, with numerous
small drag folds (Figure 23) and crenulations. These are
local phenomena but may reflect upon the general structure.
The axes of these microfolds frequently trend parallel to
the general strike of the gneissosity. Elliptical quartzo-
feldSpathic concentrations (Figure 24) are common in the
gneiss, and they also trend in the direction of the foli-
ation. Assigning the A-axis to the major axis of the
ellipsoid, the AB plane then parallels the plane of folia-
tion, with the C-axis perpendicular to the s-surface (strik-
ing E-W).

47

The entire area is criss-crossed by a maze of quartzo-
feldspathic intrusions. However, due to their lack of any
continuity or extent, and their extreme haphazard pattern,
these appear to be of little value in deducing any sequence

involving them.

 

 

 

Figure 23. Minor draw phenomena.
Fold axis rouehly parallel to
gneissosity.

 

48

 

 

Figure 24. Quartzose elliptical con-
centrations along gneissosity.

 

 

 

Figure 25. Photomicrograph showing

quartzose ellipsoids in biotite dis-
playing flow structure (sample 20).

Crossed nicols, x54 diameters.

49

 

 

 

 

Figure 26. Strike frequenCy diagram of I68 ioims

 

 

 

 

Figure 27. Strike frequency diagram of acute bisectrices

 

 

 

50

 

44M! ,

FIGURE 28. CONTOUR DIAGRAM OF POLES TO I68 JOINTS. CONTOURS 22-n~6—4-2—i PERCENT

 

 

 

Mr
.6.“

"538

AU
Oi.

A.»

r9569

Sl
Joints and Acute Bisectrices

A study of 16% joints (see structure map in back pocket)
was made of what are thought to be shear joints belonOinw to
conjugate joint systems. Joints belonging to definite con-
jugate systems could not be ascertained in spite of the fact
that the overwhelming percentage of joint planes intersect
one or more other joint planes. The most prominent set of
joints with ?2 per cent maxima (Figures 26 and 28) strike
N 5° W to N 50 E and dip steeply. The two next prominent
sets, with maxima of 11 per cent and 6 per cent strike
roughly from N 300 E to N 75° E and N 10° N to N 60° N

respectively and are also steeply dipping.

 

 

Figure 29. Fissures ascribed to tension.
Note quartz vein intruding alon: fissure,
parallel to major stress direction.

52

Fissures, which appear to be tension joints (Fioure 90),
occur more or less at rieht angles to the proposed major
fold axis, and hence also to the trend of the aneissosity.
These can be ascribed to the AC plane and may be regarded as
resulting from the partial release of stress in a neneral E-N
direction, i.e., parallel to the s-surface.

Assigninv the B-axis to the strike of the foliation and
the AC plane perpendicular to the foliation, we find a decree
of agreement with the predominant direction of the strike of
the shear joints. Examining the contour diagram of the acute
bisectrices (Figures 27 and 30), i.e., the direction of the
major stress, the writer comes to the tentative conclusion
that the structural unit underwent a stress field which
caused release of stress in a general E-W to NW-SE direction
as well as in a'vertical sense. Two sets of acute ti-
seetrices are prominent: trending from N 15° N to N 35° W
and from N to N 300 E. Roth plunoe very rvently.

A contour map of the antles of the conjugate joint
systems (Fiqure 31) proved to be of little value, althou h
it did significantly Show the greater occurence of higher
values of 51 to 39 degrees at the two extremities of the
NW-SE structural belt. This might lead to the assumption
that the beds behaved in a more ductile manner towards the
ends of the structural unit than elsewhere. To explain the
latter, the writer suggests the possibility of an under-
lying batholith, elongate in the general Nw-SE direction,
which while providing the intrusive magma for some of the
later emanations, also acted as a device for the buckling
up of the regional structure

In an article on the mechanical interpretations of

joints, Bucher (1921) stated the important generalization

53

 

 

 

 

PERCENT

12-8-4-2-l

FIGURE 30. CONTOUR DIAGRAM OF ACUTE BISECTRICES. CONTOURS

 

U!
D

"that the anele of shearine of a material is the more acute
the more brittle the substance is and vice verse." bus

the initial problem is that of decidini whether the material
under consideration has the properties of a brittle substance
or those of a ductile substance. Lf course, if the direction
of the nreatest nrincital stress is known, the relative
deeree of ductility at the time of deformation may be arrived
at by an examination o. tte resultind joint planes.

The writer is inclined to helieve, hecnuse of the divers-
ity of angles between join planes in a relatively homogeneous
unit, that the beds behaved in a neither completely ductile nor
completely brittle manner. Rather, the differences in the

angles appear to be due to local limitine conditions of

intimately intruded strata. Laztuna observed that the an‘le
of shearing is independent of the nature and intensitv of the
stresses involved. Fore recently, Seivel (1°50) shows that
fracture in an isotrOpic medium takes nlace "across a tair of
conjugate surface elements, equally inclined to the direction
of the maximum pressure at an anele which is a function of the

limiting stresses as well as constants of the medium." The

greater stress, then, would be in the center.

Quartzo-feldsnathic Ellinseids

The origin of the quart7o-feldsnattic (llifticel in-
clusions (Figures 24 and 25) is clearly due to tie tendencv
f the inclusions (formed during metamorttism) “its growth
anisotropy to orient their najor axes fatallel to the direc-
tion of least growth resistance i.e., in conforwity T“it“ the

trend of foliation. It would appear probable that the
elliptical structures resulted f .ae effects exercised

r
b7 the intrusion of igneous liouids along the s-snrface.

-’ .L

55

 

 

 

 

 

 

 

 

 

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56

However, Ramberg (1952) is of the opinion that deformation
under mechanical stress accounts for the greater part of
anisotropic structures in metamorphic rocks, and apparently
discounts the importance of the role of fluid mechanics
resulting from introduced igneous liquids. It is pointed
out by Ramberg that:

"The crystalloblastic structure in most
metamorphic rocks shows that recrystal-
lization flow is the most important type
of yield in silicate rocks, provided that
they do not contain mainly ductile min-
erals like chlorites, talc and some micas.
It appears then, that the ionic, atomic
or molecular mobility in quartzo-felds-
pathic rocks during regional metamorphism
is, as a common rule, considerably great-
er than this type of mobility in basic
rocks."

In other words, despite the observation that in dry
melts basic bodies are less viscous than acidic bodies,
Ramberg asserts that the crucial factor during regional
metamorphism appears to be the ability or ease with which
a rock can undergo chemical rearrangement or recrystalli-
zation. These, in turn, it is suggested, may be the
controlling factors in the formation of quartzo-feldSpathic
ellipsoids during regional metamorphism. If metamorphic
differentiation were postulated, the elliptical structures
could have formed as a result of lateral secretion into

planes of weakness.

Banding and Foliation

Gneissosity, except in local areas, is clearly exhibited
and trends in a general NW-SE to E-W direction. The prominent
foliation of the gneisses is due to subparallel alignment of

 

57

hornblende and biotite. Alternate layers of mafic minerals
and quartzo-feldspathic ”intrusives” accentuate the banding.
The gneisses frequently display local minor drag structures
(Figure 23). The extreme irregularity of these microfolds,
with included acidic lenses, favors the formation of the
gneisses through the action of introduced acid solutions.
Additional discussion of the gneiss development is included
in the section on rock types.

The plane of the gneissosity (foliation) is roughly
parallel to the B-axis of the major structure, i.e., the
fold axis and generally perpendicular to the major stress
directions. An interpretation of the gneissosity in terms
of the structural deformation phenomena (Figure 32), could
account for the general agreement of the s-surface and the
major fold axis. Successive periods of metamorphism could
result in the development of gneisses in the solid state,
without the necessity of having to undergo the invasion of
fluid magmas of high enough temperature (Ramberg, 1952).

It is the writer's modest opinion, however, that the field
phenomena observed appear to favor an invasion by fluid
magmas of sufficiently high temperatures to account for the
irregularity of drag structures, crenulations and cross-

cutting veins.

58

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59

 

 

 

 

 

 

Figure 33. Photomicrograph showing
fracture and displacement of twinning
lamellae. Quartz crystallization in
fracture zone (sample 14). Crossed
nicols, x54 diameters.

 

 

 

Figure 34. Photomicrograph showing
displacement of twinning lamellae
through stress differentials (sample
14). Crossed nicols, x54 diameters.

60
CONCLUSIONS

A resume of the field and laboratory data pertinent to i
a broader understanding of the geologic agents at work in
Section 36, led the writer to a number of assumptions which
are tentative at best. Limitations in thme and space have
not allowed for as complete and exhaustive a study as would
be desired. However, within the limitations set, the writer
feels free to offer a number of points which.may contribute
to a more complete picture of the Southern Complex.

Three major lithologic units constitute the bulk of the
outcrops observed: 1) gneiss, 2) granite and 3) pegmatitic
and basic intrusives, the above listed in their respective
order of abundance in the field. The writer is inclined to
favor the granitic sequence in the Southern Complex of Upper
Michigan, as proposed by Dickey (1936), with certain reserva-
tions.

The presence of hornblende as the major constituent of
the gneisses studied implies a basaltic composition for the
original rock. The original basalt underwent two major and
one minor periods of metamorphism. These coincided, it is
suggested, with 1) early Laurentian disturbance, 2) the
Algoman Revolution and 3) the Killarney Revolution. The
gneiss was formed through the intrusion of the metamorphosed
basalt by Algoman granite. Observed phenomena could lend
themselves to an explanation of the genesis of the gneiss
on the basis of metamorphic differentiation.

What is referred to as the Algoman granite is the oldest
type granite present and represents the intrusive material of
what has been called the Archean gneiss. The porphyritic

granite is seen to intrude the gneiss and may be classed as

61

younger. A final period of intrusion was the Killarney
granite, characterized by a wide textural range, from fine-
grained to pegmatitic, lack of appreciable cataclasis and
absence of porphyritic texture. The distribution of the
granite, displayed in cross-cutting veins, dikes and
irregular masses, is extremely sporadic and random.

The third major group of rock types, composed of basic
rock types, and quartz and pegmatite veins, merits only a
cursory reference as it appears to be of little significance
in its relationship to the granitic sequence. Suffice it to
mention that those showing evidence of deformation were
probably intruded prior to the Killarney Revolution.

The interpretation of the structural data points to the
presence of a possible anticlinal belt, with the major fold
axis trending in a general E-W to NW-SE direction, i.e.,
perpendicular to the greatest stress direction. However,
the probability of more than one period of deformation
complicates the picture and limits the assumptions that may
be drawn. 0n the other hand, the writer is of the opinion
that the role played by the stress field in the preferential
alignment of the mafic minerals in the gneisses, at right
angles to the proposed major stress direction, is significant.

The mineral assemblages observed can be classed in the
epidote-amphibolite facies, with an approximate temperature
range of from 300 to 500 degrees Centigrade. Manifestations
of retrograde metamorphism may be implied from the occurences
of biotite to chlorite alteration.

Observed relationships led the writer to assume the
presence of hydrothermal alteration as an active partici-
pant in the geologic history of the area. A source area

for the acidic emanations could be realized if the presence

62

of a subsurface batholith were inferred. However, the
occurence of intruding acidic veinlets, stringers and
dikes could also be attributed to the refusion of exist-
ing lithologic units in periods of deformation, the latter
possibly conducive to the necessary pressure-temperature
differentials.

Of primary interest is the fact that the gneiss is
the dominant lithologic unit in the area. Thus, the map
of the Southern Complex and associated rocks by Dickey
(1936) appears to err in ascribing the portion studied by
the writer to the Paleozoic.

The predominance of the malacon-type zircons encounter-
ed in what is commonly referred to as the Archean gneiss
points to a late pre-Huronian or Huronian age for the form-
ation 6f the gneisses. This conclusion is based on the
results of Tyler and Marsden's examination of the zircons

in the Lake Superior Region.

63

SUGGESTIONS FOR FURTHER RESEARCH

As a result of the preliminary study undertaken by the
writer, a number of problems become apparent as necessitating
further investigation. The following are suggestions, thought

worthy of consideration:

1. Extremely detailed mapping of a small area would be
instrumental in the exact definitions of the sequence of

different granitic intrusions.

2. A re-examination of the plagioclases present in light of
the significance that varying twin patterns may hold in re-

lationship to structural phenomena present.

3. The possible interpretation of sericitization and/or
paragonitization patterns as due to limiting environmental

conditions.

4. Examination of the prevalence of untwinned plagioclases,

and their possible relationship to roof-rock regions.

5. A petrofabric study of preferred orientations of quartz
axes may contribute to a more complete understanding of

structural phenomena observed.

6. An intensive investigation of joint patterns, taking
into consideration different periods of deformation that
the area is thought to have undergone, and their effects
on the joints, may be pertinent to the unraveling of

conjugate joint systems.

64
BIBLIOGRAPHY.

Bucher, W. H. (1921) The Mechanical Interpretation of
Joints: Journ. Geology, Vol. XXIX, p. 1-28.

Chudoba, K. and Kennedy, W. Q. (1933) The Determination
of the Feldspars in Thin Section: Thomas Murby and
Co., London.

DeSitter, L. U. (1956) Structural Geology: McGraw—Hill,
New York.

Dickey, R. M. (1936) The Granitic Sequence in the Southern
Complex of Upper Michigan: Jour. Geology, Vol. XLIV,
p. 317-340.

(1953) Selected Petrogenic Relationships of Plagio-
clase, Emmons, R. C. (Editor): Geol. Soc. Amer.,
Mem. 52, p. 137.

Emmons, R. C. (1943) The Universal Stage: Geol. Soc. Amer.,
Mem. 8, p. 205.

(1948) Origin of Granite, Gilluly, J. (Chairman): Geol.
Soc. Amer., Mem. 28, p. 139.

Goldich, S. S. (1941) Evolution of the Central Texas Cranites:
Journ. Geol., Vol. 49, p. 697-720.

and Kinser, J. H. (1939) Perthite from Tory Hill,
Ontario: Amer. Minera1., Vol. 24, p. 407-427.

Gorai, M. (1950) Proposal of Twin Method for the Study of the
"Granite Problem": Geol. Soc. Japan, Journ., Vol. 56,
p0 149'1560

Heinrich, E. W. (1956) Microsc0pic Petrography: McGraw-Hill,
New York.

65

Johannsen, A. (1922) Essentials for the Microscopical
Determination of Rock-forming Minerals and Rocks
in Thin Section: Univ. of Chicago, Chicago.

Ramberg, H. (1952) The Origin of Metamorphic and Meta-
somatic Rocks: Univ. of Chicago, Chicago.

Rogers, A. F. and Kerr, P. F. (1942) Optical Mineralogy:
McGraw-Hill, New York.

Seigel, H. O. (1950) A Theory of Fracture of Materials and
Its Application to Geology: Transactions American Geo-
physical Union, Vol. 31, p. 611-619.

Swanson, C. O. (1927) Notes on Stress, Strain and Joints:
Journ. Geol., Vol. XXXV, p. 193-223.

Turner, F. J. and Verhoogen, J. (1951) Igneous and Meta-
morphic Petrology: McGraw-Hill, New York.

Tuttle, 0. F. (1952) Origin of the Contrasting Mineralogy
of Extrusive and Plutonic Salic Rocks: Journ. Geol.,
V01. 60, p. 107-124.

Tyler, S. A. and Marsden, R. W. (1940) Studies of the Lake
Superior Pre-Cambrian by Accessory-Mineral Methods,

Data from.the South Shore of Lake Superior: Geol. Soc.
MEIR, v01. 51, p. 1437-1483.

wahlstrom, E. E. (1955) Petrographic Mineralogy: John Wiley
and Sons, New York.

Winchell, A. N. and Winchell, H. (1927) Elements of Optical
Mineralogy: John Wiley and Sons, New York.

Zinn, J. (1959) Professor, Dept. Geology, Michigan State
University, personal communication.

 

 

 

 

 

 

 

 

 

 

 

   
  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

m 7 //
// . _ LOCATION OF SAMPLES
/ , .
\ / Palmer- Sands Quadrangles
7/x’ ' Section 36
71/ - Michigan-Marquette County
'7' - 900 290 o 290 FEET
. 7"! g; h
,"/ : 7 l...32 sample numbers
N // ~ -4— foliation
3 7 7’7! ‘ : unimproved dirt road
3 i f’ :21 abandoned dirt road
m \ i ,‘7/ 800 l—XXXIV reference numbers of outcrops
_ 7 #71
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it
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JOINTS 8
Palmer- Sands

Secfion

STRUCTURE

  

   
 

MAP
FOLIATION

Quadrangles
36

Michigan-Marquette County

2 O
?l:
jomt, vertical
joint, dipping

foliation

l...XXXlV reference numbers of outcrops

9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   
      
   
     
 
 

290 FEET

   
    
   
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

lOO

  

O

J! SE Corner

FIRE LANE

 

 

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