GRSGEN AND PEHQLOGY 0? A 9OR'HON
0? THE EQUTHERN COMPLEX NEAR PALMER,

PMRGUETTE COGNYY, MKMGAN

masts go? i‘gm Degree w? M. 3.
MECEEQRN STRTE UNEVERSET?
Richaard A. Long

1959

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ORIGIN AND PETROLOGY OF A PORTION OF THE
SOUTHERN COMPLEX NEAR PALMER, MARQUETTE COUNTY,
MICHIGAN

by

Richard A. Long

A THESIS

Submitted in partial fulfillment of the requirements for
the Degree of Master of Science in the Department of Geology

Michigan State University
East Lansing, Michigan

1959

ACKNOWLEDGMENTS

The writer wishes to eXpress his sincere thanks to
Drs. Justin Zinn, B. T. Sandefur and James Trow of the
Department of Geology, Michigan State University, and to
Mr. Robert C. Reed of the Michigan Geological Survey for
their valuable assistance throughout this study and their
helpful criticism of the manuscript. Without the help of
these men who gave so freely of their time and knowledge,

the study would not have been possible.

Special thanks to Mr. Robert A. Vehrs and Mr. Armen
S. Sahakian of the Department of Geology, Michigan State
University, whose studies in adjacent sections in the
Palmer area helped a great deal in the interpretation of

the regional geology of the Southern Complex.

ii

ABSTRACT

The writer has mapped a small area south of the New
Richmond Mine in Section 34, T47N, R26w, Marquette County,
Michigan. The area lies on the hilly, heavily wooded
northeastern corner of the Southern Complex at its contact

with basal Huronian formations.

The dominant rock in the area is an Upper Precambrian
orange granite which intrudes Middle Precambrian green slates
and Lower Precambrian gneisses. A Keweenawan olivine diabase
dike cuts the granite, placing an upper limit on its age.

The granite has undergone one major period of deformation
which rendered it slightly gneissose and introduced a well-
developed pattern of joints in the area. Hydrothermal agents
have been active in altering the feldSpar and biotite in the

granite.

The slate is schistose near its contact with the in-
trusion, while the older gneisses had been completely re-

crystallized before the granite was intruded.

The research revealed no mineralization in the area,
but the complex microperthites, complex twin combinations
in the plagioclase, and lines of liquid inclusions in the

quartz are areas in which future study might be of value.

iii

CONTENTS

INTRODUCTION . . . . . . . . . . .
Nature and ScOpe of Research .

Previous Investigations in Area

PETROGRAPHY AND PETRCLOGY . . . .
Granite . . . . . . . . . .
Sample 21 . . . . . . . . .
Sample 15 . . . . . . . .
Sample 4 . . . . . . . . .
Sample 10 . . . . . . . . .
Petrologic Interpretations
Injection Gneiss . . . . . . .
Sample 3 . . . . . . . . .
Slate . . . . . . . . . . . .
Basic Dikes . . . . . . . . .
Sample 23 . . . . . . . . .
Sample 12 . . . . . . . . .

METAMORPHISM . . . . . . . . . . .
CONCLUSIONS . O C O O O C O O C O
RECOMMENDATIONS FOR FURTHER STUDY

REFERENCES 0 O O O O O I O O O O 0

iv

a“.

Page

15
15
16
17
23
24
25
25
26
28

1 BACK OF BOOK

LIST OF FIGURES

Figure

1.

Table

II.

The location of T47N, R26W in the
northern peninsula of Michigan . . .

The location of the area studied
in Section 34, T47N, R26W . . . . . .

Photomicrograph of sample 21 showing
xenomorphic-inequigranular texture of

the granite . . . . . . . . . . . . .

Photomicrograph of sample 21 showing
lines of inclusions in the quartz . .

Photomicrograph of sample 21 showing
euhedral zircon . . . . . . . . . . .

Orientation of lines of inclusions in
quartz in three samples of the granite

Photomicrograph of sample 25 showing
chessboard structure in albite . . . .

Photomicrograph of sample 3 showing
biotite alteration aggregate . . . . .

Tinted photomicrograph of sample 12

showing feldSpar, muscovite, quartz,
biotite, hornblende and ilmenite . . .

Outcrop map of the problem area . . .

LIST OF TABLES

Modal analyses of granite . . . . . .

Modal analyses of the basic dikes . .

V

10

12

14

19

22

24

29

pocket
in back

Page
11

27

1 ix'L‘pw 1) l5 ., TIL i‘;
Aature and Sc0pe of the Research

The writer first became interested in the Frecaerian of
Northern Michigan in the summer oi 1‘34 while an undergraduate
stujent at Michigan State University. A: the UCOlOgy field
camp unoer the direction of Drs. Justin Zinn and 3. F. Sande-
fur there was ample Opportunity to become familiar with some
of the more important geologic problems of the Marquette Dis-
trict. In 1357 when the writer was looking for a problem for
the Master's thesis Dr. Zinn suggested mapping a portion of
the Southern Complex near Palmer. A small area south of the
New Richmond Mine was chosen because it lies near the contact
of the Complex with Huronian metasediments.

The research area covers a portion of the Southern Com-
plex south of the Marquette Synclinorium in Section 34, 147R
RZGN, Marquette County, Michigan, east of a portion of the
Complex called the Palmer Gneiss. If the section is divided
vertically into quarters the research area may be defined as
that part in the second quarter from the west which lies be-
tween Gribben Lake and the old tote road 2 mile north of the
lake (Figures 1, 2).

The area can best be reached by the aSphalt road which
runs east from the town of Palmer to the New Richmond Mine.
Southwest of the mine tote roads can be followed by automobile
nearly to the line between Sections 33 and 34. From this
point it is necessary to walk to the northwest corner of the
area.

The terrain consists of low, rough rock-cored hills with

many outcrops and a few small cliffs 20 to 30 feet in height.

An outcrop which runs along the north shore of Gribben Lake

 

   
      

   

a?

uPER/
AKE S 05
L

 

 

 

FIGURE I. THE LOCATION OF T47N, R26W IN THE
NORTHERN PENINSULA OF MICHIGAN.

 

 

 

 

 

FIGURE 2. THE LOCATION OF THE AREA STUDIED
IN SECTION 34, T47 N, R26 W.

Ki)

rises from a swamp on the west end to an 80 foot cliff on the
east. A few small streams drain eastward into the lake or
into the low swampy areas between the hills.

Elevations in the area range from 1215 feet, the eleva-
tion of the lake, to 1385 feet. The topographic features
have a definite east-west trend, an expression of the regional
topography. The area is heavily covered with mixed hardwoods
and some pines in the higher portions and spruce and alders
in the lower swampy portions. Summers are hot with very cool
nights; fall and spring are mild but have a considerable
amount of rain. Winters are severe, with heavy snowfall and
temperatures that often fall below zero.

The Southern Complex itself covers an area of nearly 1400
square miles and includes Precambrian granites, gneisses, and
schists, with associated aplites and pegmatites and a few
basic intrusives. It is irregular in shape and is bounded
roughly by the towns of Palmer, Beacon, Floodwood, Randville,
Foster City, and Gwinn. It is overlain to the east by flat-
lying Cambrian sediments, but to the south and southwest
granites of the Complex with minor occurrences of other rock
types extend for many miles.

The dominant rocks in the Complex are gneissoid granites,
dull in color and porphyritic, but in the northeastern part
which includes the granite of this study, the granite is red
to orange and is not porphyritic. Some of the granite in the
Northern Complex north of the Marquette Synclinorium resembles
the porphyritic granite in the central portion of the Southern
Complex and is generally considered to be part of the same
body.

Due to the considerable extent and geOIOgical complexity
of the area, the Southern Complex has not been mapped in suf-

ficient detail to warrant more than intelligent guesswork as

to its age and origin. The Complex is typical of many exten-
sive Precambrian areas which stimulate only academic interest
because of their lack of economic minerals.

The writer has mapped a portion of the Complex near its
contact with basal Huronian formations of the Marquette district
south of the New Richmond hine in the belief that even a small
contribution will be of value if it is detailed and unbiased.
The petrOIOgy of the igneous and metamorphic rocks of the area
of study will be presented with possible interpretations as to
their origin and significance. The structures in the area
continue beyond the limits of the mapped area and are too ex-
tensive to be considered in detail in this study.

The field work was done in hay, 1955. The writer set up
a base camp on the north shore of Gribben Lake and ran north-
south traverses to take advantage of the east-west trend of
the topography. Mapping was done by pace and compass, the
only practical method for an area so difficult to traverse.
Approximate mean declination in the area is %°w (USGS, 1952),
a negligible value for pace and compass work. backsighting
was unnecessary as the Negaunee iron formation E mile north
of the area had no effect on the needle, so with the lake to
the south and the tote road to the north, horizontal control
did not present a problem. The USGS tOpographic map and
aerial photographs of the area furnished further control.
Traverses were run 100 yards apart and every outcrop was ex-
amined and sampled. Outcrops are abundant in the entire area
except in the low swampy flats between the hills.

WOrk in the laboratory included a megasc0pic study of
hand specimens from the area and a microsc0pic analysis of
27 thin sections prepared from selected samples. Megasc0pic

examination of hand Specimens gave an overall picture of the

variation in the mineral assemblages of the main rock types,
after which a more intense study with the microscope gave
textural relationships, data on deuteric and hydroth rmal
effects, and accurate mineral percentages. Thin section work
was done with a standard petrographic microscope. nodal anal-
yses were made on a six-barrel integrating stage, using ten

traverses per section.
Previous Investigations in the Area

Van Hise and Bayley (1997), in their monograph on the
Marquette District, divide the Archean basement Complex into
the Southern and Northern Complexes. Although they found
that the granites of the two areas differ in color, degree
of metamorphism and size of porphyritic inclusions, they cor-
relate the granites on the basis of their mineralogy. The
granites in both areas intrude hornblende and biotite schists
which they believe to be "mashed eruptives".

Van Rise and Leith (1911) correlate the ancient schists
of the two areas but state that nowhere are they mappable.
They find some evidence which points to a elastic origin for
the schists.

Lamey (1933, 1935) did a great deal of work in the area,
particularly in a belt of schists and gneisses which is com-
monly known as the Palmer Gneiss. He states that the Palmer
Gneisses are Middle and Upper Huronian sediments and that a
portion of the Southern Complex which he names the Republic
granite intrudes these sediments, proving that the granite
is post-Huronian. Keweenawan dikes which cut the granite
place an upper limit on its age.

Dickey (1936), in an attempt to "unravel the sequence

of granitic intrusions in the area", found three distinct

periods of intrusion: 1) the Keewatin schists intruded by a
Laurentian granite to form the Archean injection eneiss; 2) a
later Laurentian granite nornhyry which makes up the greater
part of the Complex; and 3) a post-Huronian, Precambrian
granite which he called the Killarnev although he could not
establish its relation to rocks of Keweenawan age.

In a later article Dickey (1939) described the Ford River
granite in the southwest corner of the Southern Complex and
dated it post-Lower, ore-Middle Hurenian. James (105?) has
since shown that the quartzite cut by this nranite is not
Sturgeon, but is a pre-Huronian quartzite.

Iyler, Marsden, Grout and Theil (1940) attempted to date
Precambrian intrusives by the type of zircon present; those
containing the hyacinth variety were considered pre-Huronian,
those containine malacon, later nre-Huronian or Huronian. Cn
this basis they found four periods of intrusion in the South-
ern Complex: two pre-huronian, one Huronian, and one post-
Huronian.

gigg (1059) has done a great deal of mappin'7 in fiorthern
Michican, particularly in the Marquette and Iron River Dis-
tricts, and believes that portions of the granite in the
Southern Complex are definitely the same ace as the granite

in the western part of the Northern Complex.

PETRCCRAPKY AND PETRCLCCY

The outcrops in the research area are shown on the map

1

in the secret. The dominant rock is a medium» to coarse-

. I j o
by an olmvrne niabase

crained oranee eranite Which is cut
dike. Near the tote road to the north the oranite is fine-
crained and contains a great deal of quart7; near the lake
to the south it is prey to black and intrudes ancient schists
and aneiss:s. The fine-~rained variety in the northern vor-
tion of the area intrudes a green slate whose slaty cleavage
strikes E-W and dips 7OON.

In the followino description and discussion of the more
important thin sections the rock types will be treated under
four headinns: l) granite, 2) injection nneiss, 3) slate, and

4) basic dikes.
Granite

Local variations within an igneous body may significantly
alter the appearance of the rock, particularly in the area
under consideration, in which the granite intrudes two dif-
ferent rock types within 500 yards. Thus we may find varia-
tions in color and texture which are expressions of varying
conditions within the body during its formation or within
the country rock, or which are perhaps due to mavmatic or
metamorphic differentiation. Further changes may occur lo—
cally or selectively after hydrothermal solutions and reeional
metamorphism have played their part.

The granite ranges in color from lioht red-oranee throneh
a dark oranae and black variety to grey and black. The amount
of biotite present determines whether the rock is light or

dark, a difference in 2 or 3% makinw a striking difference in

'5 - ~~s< A ‘1 \" r ‘ ‘r~v - ,"
he appeaiance or tht bumplcb.
1

'1 - - _ ’— P ‘ -: o a," “ ‘ o 1 f. x "‘ ‘ o «‘5 .. a ',‘ .- _‘
Lheie are four Joirn gdthss in the granite hLlum alt

'IC'OV . -~ [PO-3, g-too -
N, C

o L .. ,.. 1 _1 ’ ’ ‘_ ' . 'u " J
conSistent throughout Lie aIUA. .-D, .4 at“, “a 0, “~‘ ",
I I .w, \wn” “ ':o k“‘ 1', 1 11" , f: 7' o 7 IV ‘ '1. '\‘~..
clobd; and no) u, Lassa. an anemalous u-. plane nipping

steeply to the south gas found in the granite just north of
the lake.

Grain size is medium to coarse except in the fine-grained
chilled zone or aplitic samples. Crientation of the biotite
gives the rock a gneissoid apgearance which is not evid\nt
in the field and can be seen only upon close examination of
a properly oriented fresh Specimen.

Four thin sections of the granite are described. Samples
15 and 21 are orange varieties chosen to illustrate local
variations in composition, sample 4 is the grey variety near
the ancient gneiss, and sample 10 is from the chilled zone.

Minerals evident in the hand Specimen are quartz and
orange feldSpar peppered with aligned flakes of biotite and
a few small crystals of pyrite.

In all thin sections containing two feldSpars, the mi-
crocline is fresh and unaltered while the plagioclase 13‘

I
.L

extensively altered, therefore the ew untwinned felJSpar

crystals present are assigned either to microcline or plag-

C

ioclase on the basis or their degree of alteration. The
possibility that the untwinned "microcline" is orthoclase is
a point in question. The probability that orthoclase and
microcline can even exist in the same rock is an object of
diSpute. Johannsen (1932, pp. 137, 185-llt) states that
they may occur together and gives analyses in which generous

amounts of each are present, while Tuttle (1958, p. 98), in

a discussion of cooling of magmas, states:

"Many authors have reported microcline and orthoclase
coexisting in granites, apparently on the basis of
presence or absence of polysynthetic twinning; in
fact, some have reported Rosiwal analyses in which

-the orthoclase and microcline were differentiated.
This criterion for distinguishing the two types is
not reliable as untwinned microcline is common, and
if some of the grains show a microcline grill prob-
ably all the potassium feldSpar is microcline."

Current thought seems to favor the order-disorder hypo-
thesis of Barth (1934), in which the Al-Si distribution is
ordered in microcline, disordered in orthoclase. Stress may
change the crystal from the disordered to the ordered form,
marked by a decrease in symmetry from the monoclinic to the
triclinic mineral.

Laves (1952) believes that orthoclase is unstable below
a temperature somewhere near 700°C and that environmental
conditions, particularly time and temperature, favor th-
transition to microcline. He states that crystals with in-
termediate optical properties are not uncommon.

The writer prefers the view held by the petrologists to
that of the petrographers and includes the microcline and
possible orthoclase in his analyses under the single heading
"K-feldspar".

Braid and rim micrOperthites are abundant in some thin
sections and are listed as "micrOperthite" in the analyses;
they are not divided into approximate percentages of K-feld-
Spar and plagioclase. The quartz, biotite and other minerals
were identified by conventional Optical methods which need no
explanation here.

Sample 71. In thin section the rock is medium- to coarse-

grained with xenomorphic-inequigranular texture (Figure 3).

lO

 

 

 

Figure 3. Photomicrograph of sample 21
showing xenomorphic-inequigranular tex-
ture of the granite. Crossed nicols,
X54 diameters.

Major constituents include quartz, K-feldSpar, micrOper-
thite, plagioclase and biotite (Table I). Zircon, apatite,
pyrite, magnetite, hematite, paragonite, chlorite, allanite
and kaolinite are present in minor amounts.

The quartz occurs in large elongate masses which roughly
parallel the alignment of the biotite. Patches of quartz
surround and invade the other major constituents and contain
remnants of them. host of the quartz exhibits fracturing
and strain shadows although granulation at boundaries is

rare.

11

TABLE 1

MODAL AKALYSES CF GRANITE
W

3

Sample ho.

 

 

 

analySis Tl 15 a 10
Quartz o o o o o o o 0 o o o o . . . . [$2 3:); 35 40

l\)
H
\J
on)

K'feldsp‘ar o o o o o o o o o a o o o 0

PO

Rwy—a
H
D

kid
(\—
N
,r

K H
\:

Plagioclase (Ab97-An3) . . . . . . . .

l'bicropertliite o o o o o o o o o o o o

Biotitea . . . . . . . . . . . . . . . ; ? 2

Zircon . . . . . . . . . . . . . . . . tr tr tr t1
Pyrite . . . . . . . . . . . . . . . . tr tr tr tr
Magnetite . . . . . . . . . . . . . . tr tr

Hematite, martite . . . . . . . . . . tr tr tr
Nuscovite, sericite, paragonite . . . tr tr 8 tr
Chlorite . . . . . . . . . . . . . . . tr tr
Apatite . . . . . . . . . . . . . . . tr tr tr tr
Kaolinite . . . . . . . . . . . . . . tr tr tr tr
Calcite . . . . . . . . . . . . . . . tr tr tr
Allanite . . . . . . . . . . . . . . . tr tr

 

Total . . . . . . . . . . . . . . . . 98 98 100 99

a-u . o 1 1 -
olOtlte lUClUQeS tne cloudy yellow alteration product.

12

A number of the quartz grains contain lines of highly
birefringent inclusions (Figure 4) which Van hise and Bayley
(1897, p. 210) believe to be liquid inclusions with movable
air bubbles, but the writer was unable to detect the movable
bubbles. The lines often contain 40 to 50 individual inclu-
sions and are roughly parallel, suggesting a study of planes
of liquid inclusions might help in interpreting the metamorphic

history of the rock.

 

 

 

 

Figure 4. Photomicrograph of sample 21 showing
lines of inclusions in the quartz. grossed ni-
cols, X54 diameters.

A few smaller quartz grains interSpersed with feldSpar
between the larger quartz masses may be earlier quartz but
the writer can find no proof of this. There is no evidence
of quartz invading quartz nor is there any difference in the

appearance of the grains.

13

,4

P

K-feldSpar occurs in crystals of medium size whica are
invariably fresh and unaltered. A few untwinned grains are
present as are a number which exhibit the twinning only on a
small corner, but most show the polysynthetic grid twinning
typical of microcline. All but a few contain perthitic
intergrowths of plagioclase. These needle-liar inclusinns
are too small to permit determination of their exact composi-
tion by ordinary flat-stage methods.

The plagioclase is albite with cemposition Ao37oan3. It
occurs in stubby laths which vary greatly in size, all ’n some
stage of alteration to paragonite and kaolinite. Lany crys-
tals though irregular in outline are unaltered on their edges,
givilg the effect of a white zone or reaction rim surrounding
the cloudy grain. Albite twinning is very common, sometimes
in combination with pericline or Carlsbad twins. In most
crystals the twin lamellae are numerous and closely Spaced,
but an occassional one may be found in which there are only
a few widely Spaced lamcllae. In some of the crystals with
unaltered rims the ttin lamellae extend into the rim. A few
rare islands of K-feldspar may be found in some of the larger
albite crystals.

Complex microperthites with the approximate ratio of 1
albite (guest) : 4 K-feld5par (host) are present in small to
medium crystals. They are not very abundant and are all

unaltered. An occasional micro raphi

I
.1

intergrowth or quartz

O

in K-feldSpar may be found.

.r1\ 3 Y‘ I {3 ._ ' . . ." " ‘. _ ‘. -. 1' .‘ 1 ,— .v.,.\ ;-. .. ,u t. n ‘
. lac -J l ‘- L- ' k~ Kr '\- \. C. VJ A- g: ‘- L L _- (AL L _~ ‘- . ,I I l . k.
‘ _b

7 .5 ~* ‘f‘ b: v‘ ‘
L - J U‘“.\ .L \— AL L. {L1 — ‘
n 6'- q ‘ s n .f 3‘. . 4- ’ 'E k" - -‘ ' -. ’ \ -‘ -. u 1" \ O l"‘ . ~ I‘ . ‘. ,-‘ L .7. ' r - .-- ,-‘
.JJ. -ureus garlv LllL-lkn-J ‘. .ILksx VLC‘Ji'j L..-~.. .~ 7' 'x. -'..c t’ 1- ."‘,.'..L e
L
,- . . . .
an." '7'. f‘ .1 . f1 - "-‘ " . 1 b'\r . -—1‘ "'~ ‘« ‘ ' ' q " ‘. ’.-4‘\- .l v a
quorlz. c111.) ACJJJE‘LLLI. o (14---.JJ .' 3.1.1.? 5.) -A ’C"> (31‘. elll'. ( 1.1.". 31"
.,V. J
1 fl ‘ W I
a a i a 4— ~ A +13. 9- - — ’ ~ L- '7 .
Lerlptxa, .. - L.(_4.L..“L 14-L- c. cit ClL/Ll -_ L t 11L; tr- -1 - 1.1.
Q 1 -' a- l‘ i . y
3‘ C u, ‘_f\‘\- « 1 - 1 ‘ ~-‘ ~ I- ' . J >‘l
LO... . -1 jJC-JL.&.LL\.L LubLAJ.OIL. . ‘JgL k,‘ 1 'L‘ .1. } ‘--.‘.: -A'LD;

except for a few pieces which have altered to a yellow-brown
cloudy material. Very little chlorite is present. mirds-eye
structure and pleochroic haloes around zircon inclusions are
common. The other major constituents invade and appear to
replace the biotite, shredding and splintering many of the
smaller laths.
Small clouded crystals of zircon are plentiful not only

as inclusions in the biotite but also scattered throughout

the feldspars. host of the zircons are rounded or football-

h w '3 k "‘- -‘ Cr ‘ ‘ ' 3- ' ‘~-- 1 ’ ’7"- -‘ H“. '1 ‘ --‘ n ~ --—- .- 7 -'
S ape... UUL d 1-..‘\v are: t' _ .:.- ..lJ.L \. i _ '.. ‘ - , . a- _ .1- L DLLl .' 01,2? (’31..
q I. 1 L. - . .'Y L. \.r . ‘4 ‘ , -‘
)7 ' 3 “8.1.1. A J ' J L‘ (1.... 1 4L . .L)’ i-Tjr'H-LE’E OL LI‘ t 1t.\
t r" r F “ 1 - v . r ~ " ‘
an: sex- .a: e ; t.i.l "liantrn 1 *,

 

 

 

 

Figure 5. Photomicrograph of sample 21 showing

euhedral zircon. Plain light, KT25 diameters.

hagnetite, pyrite, hematite and chlorite appear as alter-

ation products of the biotite. Paragonite and haolinite occur

15

as alteration products in cleavage cracks and clouding the
surface of the albite. A few small particles of pyrite are
probably primary constituents of the rock.

Sample 15. The mineral assemblage and textural relation-
ships are similar to those of sample 21. Quartz, K-feldspar,
micrOperthite, albite and biotite are the major constituents.
Zircon, pyrite, magnetite, hematite, paragonite, muscovite,
apatite, kaolinite, allanite and calcite occur in minor
amounts (Table 1).

Extensive granulation at boundaries and the great abun-
dance of lines of liquid inclusions in the quartz of this
sample distinguish it from the quartz of sample 21. The
complex microperthites are more abundant in this sample; some
of the K-feldspar shows Spotty alteration to kaolinite.

Quartz invasion has splintered and shredded the biotite
to a considerable extent. The shreds are more extensively
altered than those of sample 21, mainly to muscovite. Small
patches of calcite result from alteration of the albite.

Sample 4. The texture of this sample is xenomorphic-
inequigranular. The notable absence of large quartz and
feldSpar masses distinguishes the texture from that of the
samples previously described. The mineral assemblage is the
same as that of the previous samples (Table I).

The quartz grains are of medium size and show no fractur-
ing or granulation at boundaries although all exhibit undul-
atory extinction. A few lines of inclusions are present as
in sample 21, but they are not nearly as abundant as in sample
15.

K-feldspar and micrOperthite occur in small to medium
unaltered crystals but are the subordinate feldSpars in the

sample. Albite, much of it untwinned but always with the

16

characteristic positive optic sign, makes up half the rock.
It is more extensively altered than in the orange granites,
exhibiting surfaces clouded with paragonite and occasional
patches of calcite. The white rims around grains are not
present in the albite of this sample.

More than half of the biotite has altered to muscovite;
the remainder, although extremely shredded, shows no altera-
tion to chlorite. A few tiny grains of pyrite occur with the
biotite, but no magnetite or hematite could identified in
this sample. A few small rounded zircons are present.

Sample 10. The texture is xenomorphic-inequigranular,
nearly aplitic. Quartz, K-feldspar and albite occur with
minor amounts of chlorite, kaolinite, paragonite, calcite,
hematite, apatite, zircon and pyrite (Table I).

The quartz occurs in two habits, 1) a few medium to
large masses which fill the spaces between the feldSpars,
and 2) numerous smaller blebs and patches which randomly
dot the feldspars. The larger interstitial masses appear to
have crystallized under normal conditions, but the blebs
were caught in the feldspars during rapid crystallization in
the final stages of cooling of the rock. Both varieties ex-
hibit marked undulatory extinction, and the larger masses
are somewhat fractured. There are no lines of liquid inclu-
sions in the quartz of this sample.

A very small amount of untwinned K-feldspar is present
and contains much quartz in stringy patches. The K-feldspar
is clouded by secondary mica and by hematite staining.
Medium-sized equidimensional crystals of albite make up most
of the rock; many are albite-twinned, some in combination
with Carlsbad and pericline twins. Alteration to paragonite,
calcite and kaolinite and staining by hematite cloud most of
the albite.

17

A very small amount of biotite was originally present
but it has been completely altered to a light green pleochroic
variety of chlorite which is dark grey-brown under crossed
nicols.

A few small crystals of pyrite, some very small rounded
zircons, and numerous tiny needles of apatite complete the
list of accessories. The section contains a great deal of
red opaque hematite staining. Veins of heavily stained cal-
cite cut the rock in an angular pattern which appears to be
due to jointing.

Petrologic interpretations. From the petrographic des-
criptions certain characteristics of the individual minerals
and their relationships to one another present themselves and
may have a bearing on the interpretation of the origin of the
granite. Some of the more significant of these characteristics
should be considered. It is difficult to assign an order of
crystallization of minerals to a rock which has no constituents
which show even subhedral boundaries, but there are certain
consistencies worthy of mention.

As the predominant feldspar in the granite is plagioclase,
a better term for the rock might be granodiorite. However,
this rock and many other granodiorites have been referred to
as granites in the literature, so the writer will not confuse
the issue by changing the name. As the term granite is less
cumbersome and is "deeply entrenched in the literature", there
is no reason to argue over names which have no genetic signi-
ficance.

The large quartz masses appear to be the only quartz
present in the granite and to invade and replace the feldSpar
and biotite. The few smaller masses of quartz in some of the

samples do not differ from the larger in such properties as

18

extinction, granulation or inclusions and probably are part

of the same generation. Blebs of quartz in the feldSpar of
the chilled zone are merely remnants of a nearly solid granite
which cooled too quickly to permit its last liquid constitu—
ents to differentiate in the normal manner.

The orientation of the quartz masses parallel to the
alignment of the biotite indicates a deformational stress
near the area with sufficient power to render the rock gneis-
sose. Further evidence of stress lies in the lines of liquid
inclusions which exhibit a striking consistency in their
orientation within each thin section. The writer has plotted
the linear orientation of the lines of inclusions in each of
three samples. As shown in Figure 6, the maxima of l7, l9
and 14% in 10° intervals with corresponding percentages near
these maxima, and the large areas nearly devoid of shading,
illustrate the pattern. The three samples are not oriented
with respect to one another so the writer can only note the
trend and suggest that someone make a more intense study of
these inclusions in the future.

The K-feldspar question has been considered in an earlier
portion of the paper to explain the writer's feldspar classi-
fication. Until more work is done on the orthoclase to micro-
cline transition there is no reason to separate the two as
earlier petrographers have done. If there are intermediate
stages between the two, the K-feldsPar in this granite which
contains so many crystals twinned only on a small corner may
be an example of one of those stages.

Much of the plagioclase has only the albite twinning al-
though combination Carlsbad-albite twins are fairly plentiful,
and an occasional Carlsbad-albite-pericline twin may be found.

Gorai (1950) and Turner (1951), in separate studies, found

19
Figure 6. Orientation of lines of inclusions

in quartz in three samples of the granite.

SAMPLE I4
72 LINES

 
 
  

, I80°
20 IO 0 IO 20 PERCENT

 

 

SAMPLE I5
I42 LINES

 

 

SAMPLE I8
92 LINES

 

 

20

that there is a tendency for the plagioclase of rocks of meta-
morphic origin to exhibit simple twinning, while plagioclases
in igneous rocks are more complexly twinned. Metamorphic
plagioclase usually is untwinned or is twinned simply accord-
ing to the Albite Law while igneous plagioclases show albite
twinning in combination with Carlsbad and pericline twins,

and occasionally with the rarer Baveno and Mannebach twins.

Certainly many more granites will have to be studied and
demonstrate a fairly rigid pattern before the twinning criterion
can be used without reservation, but if it is found to be valid
the petrologist will have a handy tool at his diSposal. The
theory is offered here as a tentative argument in favor of a
fluid stage sometime in the history of the granite of the
present study. If the theory is not valid and complex twin
combinations commonly exist in granites of metamorphic origin,
it is probable that a force of sufficient magnitude to align
the quartz and biotite can induce Carlsbad and pericline twin-
ning in the plagioclase.

The narrow white rims on the albite may indicate a later
addition of sodic material. Emmons and Mann (1953, p. 53)
state that these rims are common in roof phases of granites
and probably post-date the twinning, as some grains may be
found in which the twinning does not enter the rims. They
state that the rims are of the same composition or are more
sodic than the crystal itself.

Braid and rim micrOperthites of the type present in this
granite are commonly attributed to exsolution, while the tiny
perthitic blades in the K-feldSpar may have a simpler replace-
ment origin or may be the final remnants of the exsolution
process. Tuttle (1952) describes his "exsolution series" in

which we can follow the evolution of the feldSpars from

21

anorthoclase through X-ray perthites and cryptoperthites to
the familiar microperthites, perthites, and finally the
completely differentiated plagioclase and K-feldSpar. He
states that exsolution perthites containing approximately
equal amounts of albite and microcline are "prima facie
evidence of magmatic ancestry".

One point in favor of an exsolution origin for the
complex perthites is the fact that albite rims partially
surrounding grains in many granites tend to be located al-
most exclusively between K-feldspar and plagioclase while
very few are located between other combinations of grains.
Tuttle (1952, p. 116) found in a study of six‘granites which
had these rims that over 90% of the rims lie at Or-Pl bound-
aries, while only a few lie at Or-Or, Pl-Pl and Pl-Q, and
none lie at 0r-Q and 0-0. This would indicate that the
plagioclase rim has unmixed from the K-feldspar.

There are not enough of these partial rims in the gran-
ite of the present study to allow the writer to make a similar
tabulation, but Tuttle's study does offer convincing proof
that braid and rim microperthites indicate exsolution. If
they also indicate a magmatic ancestry as he states, the micro-
perthites in the granite of the present study might point to
an igneous origin.

The biotite is generally unaltered or altered only to
chlorite or muscovite so offers no clues to the history of
the rock but does appear to be invaded and replaced by the
quartz and feldspars in all cases. Its occurrence in large
aligned aggregates of smaller individuals is another indica-
tion of the stress which must have acted upon the granite at

one time.

22

The pegmatites which may be a late phase of the granite
are composed of massive untwinned K-feldSpar with veins of
milky quartz. A possible explanation for the lack of twinning
in the K-feldSpar may be the fact that the deformational
stress changed the orthoclase in the granite to microcline
soon after solidification and the pegmatites were introduced
later, perhaps from another granite intrusion.

In each sample of the granite there are a few micrograph-
ic intergrowths of quartz in feldspar which suggest exsolution.
One sample contains a small grain of albite with the unusual
chessboard structure, which Starkey (1959) attributes to
stress. A thorough search of each of the thin sections re-
vealed only this one grain with well-deveIOped chessboard

structure (Figure 7).

 

 

 

 

Figure 7. Photomicrograph of sample 25 showing
chessboard structure in albite. Crossed nicols,
X225 diameters.

23
Injection Gneiss

Near the north shore of Gribben Lake the granite intrudes
ancient Archean schists and gneisses to form younger injection
gneisses. The invading material has approximately the same
composition as the main intrusion and is part of the same body.
The ancient schists and gneisses are the "hornblende and bio-
tite schists" or "mashed eruptives" of Van Hise and Bayley
(1897), and the "Keewatin schists intruded by Laurentian
granite to form Archean injection gneiss" of Dickey (1936).
They are highly deformed banded rocks and are cut by each of
the granites in the Southern Complex. As they predate the
granite and have no bearing on its origin they are not dis-
cussed in detail. Sahakian (1959) describes them thoroughly
in his study of the area two miles east of Gribben Lake.

The only good exposure of the younger injection gneiss
is on the face of a large cliff just north of the lake in the
eastern half of the area. Most of the exposure is inaccess-
ible but there are places near the top and bottom of the cliff
where it is possible to get a good look at the rock types.

At the top of the cliff stringers of granite and pegma-
tite cut across a highly altered basic dike which apparently
intruded the Archean rocks. The rock near the bottom of the
cliff is made up of thin alternating bands of orange granitic
material and black biotite schist in typical lit-par-lit
structure. Small orange feldspar crystals are scattered
throughout the biotite stringers. As nearly as the writer
can determine, the banding and schistosity strike nearly E-w
and dip to the north. The following description of a thin
section of 3 3/4-inch band of the granitic material will give
the reader an idea of the mineral assemblage in one of the

injected lenses.

24

Sample 3. Large elongate masses of quartz lie in a
groundmass of K-feldspar, microperthite and plagioclase. The
quartz masses are aligned parallel to the lit-par-lit struc-
ture and exhibit no cataclasis or granulation at boundaries
although the usual undulatory extinction is present. Lines
of liquid inclusions are plentiful in the quartz and show a
preferred orientation which obliquely cuts the direction of
banding.

K-feldspar, microperthite and plagioclase are present in
the groundmass in approximately equal amounts and exhibit a
striking lack of twinning, only an occasional grain showing
traces of a grid or the parallel albite structure. The K-
feldSpar is unaltered but the albite grains and stringers in
the microperthite are extensively altered to muscovite, para-

gonite and kaolinite.

 

 

 

/

Figure 8. Photomicrograph of sample 3 showing biotite
alteration aggregate. Plain light, X54 diameters.

25

Large aggregates of magnetite and associated chlorite,
zircon and pyrite result from the alteration of biotite (Fig-
ure 8). A few tiny needles of apatite and small pyrite cubes

with red hematite borders are present in the feldspars.
Slate

In the northern portion of the area the granite intrudes
a green slate with well-develooed slaty cleavage which strikes
E-w, dips 70°N. Lacking any evidence of bedding, a better
name for this rock might be "brown-weathering sericitic
chloritic schist", but the rock has no alianed minerals
which are evident even with the hand lens. Only in one
outcrop in the north central portion of the area has the
slate been altered to a schist with schistosity which strikes
N70°W and dips 56°NE. The slate contains a good deal of py-
rite and is intruded by tiny stringers of granitic material.

Lamey (1935) states that the Palmer Gneiss including
this slate is Huronian, the slate being either Siamo (Middle
Huronian) or a slaty member of the Mesnard quartzite (Lower
Huronian). If he is correct, the slate would help to date
the granite, but Vickers (1956) believes that these rocks

are pre-Huronian.
Basic Dikes

Two basic dikes were found in the map area. One is an
altered olivine diabase which cuts the granite in the north
central portion of the area, the other is an older highly
altered hornblende schist which is cut by the granite on
the large cliff near the lake. A description of each rock
type follows; sample 23 is the olivine diabase, sample 12
is the hornblende schist.

26

Sample 23. Megascopically the rock is a fine-grained
brown-weathering black diabase. It is peppered with small
pyrite crystals and contains numerous epidote aggregates
with an average diameter of 2mm.

In thin section the rock is an aggregate of calcic
plagioclase and basic alteration products with typical dia-
basic texture. No quartz is present. The plagioclase,
labradorite with approximate composition Ab43cAn57, occurs
in short laths and in large subhedral crystals. The laths
are partially altered to epidote and paragonite and exhibit
undulatory extinction and albite twinning, many in combina-
tion with Carlsbad or pericline twins. The larger crystals
have been completely altered to an aggregate of epidote and
paragonite except on a few fresh edges, suggesting zoned
calcic crystals with more sodic borders.

The remainder of the rock consists of serpentine, talc,
chlorite and magnesite (Table IT), products of the complete
alteration of the former basic constituents, probably olivine,
pyroxene and biotite. Ilmenite partially altered to leucoxene
occurs in skeleton crystals; pyrite and apatite are present
in minor amounts.

With the exception of the labradorite all the major
constituents have been altered to such an extent that it is
impossible to determine the exact nature of the original
rock. In hand Specimen the rock resembles the brown-weather-
ing Keweenawan diabase which is a common dike rock in the
Marquette district. The great abundance of serpentine in
sample 23 tends to support this observation; it is unlikely
that a quartz-free diabase with this much serpentine did not
originally contain olivine. At any rate the rock has under-

gone extensive alteration of most of its major constituents

27

TABLE II
MODAL ANALYSES OF THE BASIC DIKES

: Hi W‘W’

 

Sample

 

Quartz . . . . . . . . . . . . . . . . . . . .
Plagioclase . . . . . . . . . . . . . . . . .
Biotite . . . . . . . . . . . . . . . . . . .
Serpentine, talc . . . . . . . . . . . . . . .
Hornblende . . . . . . . . . . . . . . . . . .
Epidote . . . . . . . . . . . . . . . . . . .
Chlorite . . . . . . . . . . . . . . . . . . .
Magnesite . . . . . . . . . . . . . . . . .

Calcite . . . . . . . . . . . . . . . . . .

Muscovite,
Apatite . . . . . . . . . . . . . . . . . . .
Pyrite . . . . . . . . . . . . . . . . . . . .
Ilmenite . . . . . . . . . . . . . . . . . .

Leucoxene . . . . . . . . . . . . . . . . . .

Saussurite . . . . . . . . . . . . . . . . . .

No.

23 No.

_‘
"-

34

57

tr

tr
tr
tr

tr

12

44
27

21

tr

tr

tr
tr
tr

tr

 

Total 0 O O O O O O O O O O O O O O O O O O O

 

28

and has undergone a major deformation as shown by the strain
shadows in the labradorite so is at least as old as the latest
period of deformation in the area.

Sample 12. In hand Specimen the rock is dark green to
black, schistose, and is composed mainly of hornblende and
biotite with some feldspar and pyrite. In USGS Bulletin 62,
Williams (1890, p. 225) Shows a drawing of a thin section of
a similar rock which came from Gabbro Ridge below Lower Quin-
nesec Falls, Menominee River, Michigan. Williams, in his
explanation of the drawing, says,

"The original Structure of this rock has been com-
pletely changed, in spite of its still massive
character. It is now composed of pale green, fibrous
hornblende, saussurite, quartz, calcite, chlorite,
ilmenite and leucoxene. Most of the constituents

are of secondary origin, and in the process of their
formation the form of the primitive minerals has
been so completely obliterated that it is now impos-
sible to say whether the mother-rock was a diabase or
a diorite."

And on page 81,

"As the new minerals have formed they have wandered
from the position occupied by the older ones and

have thus produced a fine-grained and confused aggre-
gate in which the remains of larger rectangular feld-
spars or hornblende crystals are only rarely discern-
ible."

In the schist of the present study only a little saussur-
ite is present and most of the feldSpar, oligoclase with ap-
proximate composition Ab72An28, is fresh and is in general
untwinned. In addition to the minerals listed by Williams in
his sample, the schist of this study contains muscovite, bio-
tite, epidote and apatite (Table II, Figure 9). Lacking
definite information on the nature of the original rock, the

writer can only state that structurally it postdates the

29

Archean gneisses and predates the granite of this study and
that its completely recrystallized character points to a late

Archean age.

 

 

 

Figure 9. Tinted photomicrograph of sample 12
showing feldspar, muscovite, quartz, biotite,

hornblende and ilmenite. Crossed nicols, x54

diameters.

3O
METAMORPHISM

The field and petrographic studies of the granite and
associated rocks reveal certain features which may be help-
ful in the interpretation of the metamorphic history of the
research area. Although the study does not embrace an area
of Sufficient magnitude to include well-defined metamorphic
zones or aureoles, each of the rock types in the area exhib-
its features which are consistent with current theories on
the effects of an intrusion upon the country rocks.

The granite and diabase dike are the youngest rocks in
the area and Show only the effects of hydrothermal alteration
and a single deformational stress. The Slight alignment of
constituents and the presence of the alteration products
serpentine, epidote, muscovite and paragonite point to a low
metamorphic rank and may not in themselves be of sufficient
significance to warrant classifying the granite and diabase
as other than altered igneous rocks.

The slate in the northwestern corner of the area (see
map in pocket) shows little effect of the intrusion of the
granite other than the fact that the intrusion probably
changed it from a shale to a green Slate, but an outcrop in
the north central portion of the area Shows the granite and
a schistose phase of the slate in direct contact. Here the
slate has been altered to a greenschist made up mainly of
aligned flakes of chlorite, placing it in the greenschist
facies. Thus a gradational contact may be inferred from the
limited number of outcrops present although we cannot deter-
mine the exact configuration of the contact or detect the

presence of high temperature minerals.

31

The Archean gneiss and associated hornblende schist
contain hornblende, K-feldSpar, quartz, oligoclase or
andesine, and biotite or chlorite, each in major amounts,
with minor occurrences of accessories. This mineral
assemblage, placing the rocks in the amphibolite facies,
and the completely recrystallized nature of the rocks
point to a higher metamorphic rank than that of the other
rocks in the area. In particular, the fact that the rocks
near the lake can be classified in a higher metamorphic
facies than the greenschist points to the fact that they
may have been through more than one period of intrusion

and deformation and so are probably older than the slate.

32

CONCLUSIONS

From the study of the structural relationships and
petrologic characteristics of the rock types in the area,

the writer has reached the following conclusions:

I) The sequence of geologic events in the area is
as follows:
a) deposition of the ancient Archean
sediments or eruptives

b) fluid invasion of the Archean rocks
to form schists and gneisses.

c) intrusion of the highly altered dike
(hornblende schist)

d) folding of the schists and gneisses
e) deposition of the Shale (green slate)
f) intrusion of the granite

g) intrusion of the olivine diabase dike
h) deformation of the area

2) The granite is igneous, not metamorphic, in origin.
There is no petrologic or Structural evidence in the area
to indicate a metamorphic origin; petrologic relationships
point to the normal crystallization of a fluid magma, and
the intrusion of the magma must have metamorphosed the shale
to form the green slate. Stringers of the magma form the
injection gneisses by invading the Archean gneiss and horn-
blende dike.

3) The exposed granite is the upper portion of the

intrusion. This particular granite intrusion appears at

33

first sight to be small in Size; it is bounded by the lake
to the south1 (Vehrs, 1959) and is on the northeastern
corner of the granite complex. This appearent size factor,
the presence of the large chilled zone near the tote road
to the north, the variations in composition (Table I), and
the presence of sodic rims around much of the plagioclase
(Emmons and Mann, 1953) indicate that the exposed portion
of the granite is near the roof of the intrusion.

4) The granite is post-Huronian. Structural evidence
indicates only that it is post-Archean, pre-Keweenawan but
the petrologic evidence indicates that it is the Killarney
Granite of Dickey. Little or no cataclasis, moderate alter-
ation of constituents, and evidence of having undergone only
one period of deformation lead the writer to this conclusion;
earlier granites of known age in the Lake Superior Region
are more cataclastic, are more highly altered, often contain
large feldspar phenocrysts, and have usually been subjected

to more than one major period of deformation.

 

1. South of the lake in sections 34 and 3 Vehrs
encountered Archean gneisses invaded by string-
ers of the granite.

34

RECOMMENDATIONS FOR FURTHER STUDY

In the course of this study certain problems which
warrant further study have become apparent. Research on
the following field and petrologic problems might shed more
light on the origin and history of the granite.

1) Mapping in Sections 32 and 33 would help to deter-
mine the extent of the intrusion and its relation to the
rocks of the Palmer Gneiss. A study of the age of these
former sediments would help in determining their place in
our present time classification of the rocks of the Lake
Superior Region.

2) Absolute age determination by radioactive dating in
the granites of the Southern and Northern Complexes might
facilitate the problem of correlating the sediments of the
Marquette District with those of other districts. Scarcity
of outcrops in the major portion of the Southern Complex
hampers the study of the structural relationships of its
granites with each other and with the surrounding metasedi-
ments .

3) Further research on the orthoclase-microcline trans-
ition might help to unravel the complex geologic history of
many Precambrian intrusions.

4) Much more information is needed on twinning and
zoning in the plagioclases of igneous and metamorphic rocks.
The work of Gorai (1950), Turner (1952), and the Wisconsin
geologists led by Emmons (1953) is a start in the right
direction.

5) Little is known of the extent to which metamorphism,
particularly through ionic diffusion, may alter the acidic

35

constituents of rocks. Particular emphasis in this area
should be placed on perthitic phenomena such as those
exhibited in the granite of the present study.

6) A petrofabric study of the planes of liquid in-
clusions in the quartz might add a further structural

element to our knowledge of the area.

REFERENCES

Barth, T. F. W. (1934) Polymorphic phenomena and crystal
structure: Am. Jour. Sci., vol. 27, pp. 273-286.

Buerger, M. J. (1948) The role of temperature in mineral-
ogy: Am. Mineralogist, vol. 33, pp. 101-121.

Dickey, R. M. (1936) The granitic sequence in the southern
complex of Upper Michigan: Jour. Geol., vol. 44, pp.
317-340.

(1938) The Ford River granite in the southern com-
plex of Michigan: Jour. Geol., vol. 46, pp. 321-335.

Emmons, R. C., and Mann, V. (1953) A twin-zone relationship
in plagioclase feldSpar, in Emmons, R. C. (Editor),
Selected petrogenic relationships of plagioclase:
Geol. Soc. America Mem. 52, pp. 41-54.

Gorai, M. (1950) Preposal of twin method for the study of

the granite problem: Jour. Geol. Soc. Japan, vol.
56, pp. 149-156.

James, H. L. (1958) Stratigraphy of pre-Keweenawan rocks
in parts of Northern Michigan: U. S. Geol. Survey
Prof. Paper 314-C, pp. 27-44.

Johannsen, A. (1932) A descriptive petrography of the ig-
neous rocks, Volume II, The quartz-bearing rocks:
The University of Chicago Press, Chicago, Illinois.

Lamey, C. A. (1933) The intrusive relations of the Republic
granite: Jour. Geol., vol. 41, pp. 487-500.

Lamey, C. A. (1935) The Palmer gneiss: Geol. Soc. America
31111., V01. 51’ pp. 1137-1161.

Laves, F. (1952) Phase relations of the alkali feldspars,

(1) Introductory remarks: Jour. Geol., vol. 60,
Pp. 436-4500

Sahakian, A. S. (1959) Unpublished master's thesis, Mich-
igan State University.

Starkey, J. (1959) Chess-board albite from New Brunswick,
Canada: Geol. Mag., vol. XCVI, pp. 141-145.

Turner, F. J. (1951) Observations on twinning of plagio-
clase in metamorphic rocks: Am. Mineralogist, vol.
36’ pp. 581-5890

Tuttle, O. F. (1952) Origin of the contrasting mineralogy
of extrusive and plutonic salic rocks: Jour. Geol.,
vol. 60, pp. 107-124.

Tuttle, O. F., and Bowen, N. L. (1958) The origin of granite
in the light of experimental studies: Geol. Soc. of
America Mem. 74.

Tyler, 5. A., Marsden, R. W., Grout, F. F., and Theil, G. A.
(1940) Studies of the Lake Superior pre-Cambrian by
accessory-mineral methods: Geol. Soc. America Bu11.,
vol. 51, pp. 1429-1538.

U. S. Geological Survey (1952) Palmer quadrangle, Michigan:
7.5 minute series tOpographic map.

Van Hise, C. R., and Bayley, w. S. (1897) The Marquette
iron-bearing district of Michigan: U. S. Geol.
Survey Mon. 28.

Van Hise, C. R., and Leith, C. K. (1911) The geology of the
Lake Superior region: U. S. Geol. Survey Mon. 52.

Vehrs, R. A. (1959) Graduate student, Department of Geology,
Michigan State University, personal communication.

Vickers, R. C. (1956) Geology and monazite content of the
Goodrich quartzite, Palmer area, Marquette County,
Michigan: U. S. Geol. Survey Bull. 1030-F, pp. 171-
185.

Williams, C. H. (1890) The greenstone schist areas of the
Menominee and Marquette regions of Michigan: U. S.
Geol. Survey Bull. 62.

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

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OUTCROP MAP OF
THE PROBLEM AREA

LEGEND

UPPER ALTERED
PRECAMBRIAN OLIVINE DIABASE

I APLITIC GRANITE
"CHILLED ZONE"

MIDDLE
PRECAMBRIAN I GRAMTE

 

I SLATE

I HIGHLY ALTERED
LOWER HORNBLENDE SCHIST

PRECAMBRIAN I

 

 

 

 

 

 

\ ANCIENT GNEIss

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Symbols
Area of outcrop fl
. A5
LocatIon of sample
. . 1.6—7.1
Smke and de of slaty cleavage ,
. . I . . 52.55.
StrIke and de of Jomt
. . 69
StrIke and dip of foIia’rIon “T
I
I—
a:
SUBDIVISION OF 3
THE PRECAMBRIAN
AFTER JAMES,|958.

 

 

 

 

 

 

 

”IIIIIIIIIIIIIII

93 031

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