7~-
PEROPABRIC IVJESTIGATION ACROSS THE
DAISY LAKE PAULT, ONOESTON, ONTARIO
by
WALTR JAMES HFIICKS
B.S., Peansylvania State University
( 1956 )
sUMeTTED IN PARTIAL WULFILLtM f
OP THE REQUIRWF2TS FOR THE
1
DEREE OF MASTER 0FsHNST
SCIENCE
at the
MASSACHUSWETS INSTITUTE OF
TECULONGY
June, 1958
Signature ofAuthor *
Department of Geology and Geophysios, May 26, 1958
Certified by .-
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Thesis Supervisor
Aoepted by
Chairmen, Departmenta
Committee
on Grauuate Students
ABSTRClT
A petrofabrio investigation of a failted quartsite-granite section
of the Grenville Prant southwest of Coniston, Ontario has been oarried out.
Quarts orientation in twelve sample showing varying degrees of deformation
has beea studied in ocnsiderble d
.etail
Each sample is characterised by an
S-surfaoe and lineation, as determined by the orientation of quartz lenses
formed during deformation.
From these studies it is ooncluded that in the zone
of strongest deformation quarts has fractured into small needloelike or lena
ahaped fragments which have "flowed" through the rooks.
The behavior of the
quartzites during defxnation was determined mainly by the action of the quarts.
In the granite
the feldepare, in oontsast to the quarts, withstood the deform=tion.
Petrofabrie study reveals a consistent s girdle of quarts axes perpediaular to the lineation.
and e.
Within this girdle minima frequently appear at a
Selective meeasuments of various types of deformed quarts gave no aig-
nificant additional information.
Vein quarts introduoed along S-surfaces gave
nearly random orientation patterns.
A comparison is made of other areas of study which have given similar
petrofabric information, e.g.,
Phillips' study of the goine sohist, Fairbairn's
work on quartz lamelae, and Higgins' mapping of the Pine Greek area in Michigan.
The mechanics of deformation are not completely certain although there is reasonable evidence for the action of a shearing force, or couple.
The orientation of
the major plane of deformation is thought to be parallel with the strike and perpendioular to the lineation.
Penetrative movements within the rooks formed
i
quartz raJ~gmetas whih oriented thamselves with their length
parallal to b.
This b direction served as the axis of rotation, whereas transport took place
in the a direotion.
Quarts maxima which formed in the
_ plane were spread out
into inomplete so girdles as a result of rotation about b.
Grain elongation
in the b direction is thought to be caused by the alignment of quartz needle
lengths in that direction, and by end-to-end coalescence of needles.
The area
studied by Higgins is similar geologioally, and his quarts orientation patterns
closely resemble those which were found at Coniston.
Higgins found direct evi-
dence in the field that a shearing force had produoed tectonio transport parallel to A and presumably rotation about b.
The results of a petrofabrio study by Johnston thirty miles to the
northeast across the Grenville Pront are at Variane with the conElusions
reached with re rd to the rooks at Coniston.
At Coniston tectonic transport
is interpreted as perpendicular to the lineation.
Johnston's quarts fabric 8i-
grams are similar to those at Coniston, but he interprets the tectonic transport
as parallel to the lirieation.
The problem of the direction of totconic trans-
port has therefore not been settled.
More detailed description of Higins' and
Johnston's areas, combined with additional field work at Ooniston would be helpfl
in an attempt to relate field, tertural and petrofabric data.
TABLE OFP 0NT
Absltrat
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Table of Content$
List of
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igures and iaram
Introduction..
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General Geology.
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Results of the Petrofabrio Study
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Interpretation of Fabrio Diagrams .
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Direotion of Teotonic Transport.
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References Cited
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3-6
7-10
11-13
14-24
25-36
37-51
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1-2
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Desoriptions of Hand Speclms and Thin Setions .
SUMmay
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Location and Thin Section Preparation of Specimeas Studied
Method of Investigation
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LIST or FIGUXS iAND
nDIAGRS
Pae
Piguzre 1 - Location Map of Coniston
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igure 2 - Location Map of Tr vese
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?igure 3 - Gographio Orientation of S-surwace and Lineations of Specimens
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Diagram 1-24 - Quartz Orientation Patterns at Coniston
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31-36
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igure 4 - Block Diagram Illustrating The Proper Geogrphioal Orientation
of
b and c atCocaston .
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40
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igure 5A - Block Diagram Illustrating the Deformation of the Moine Sohist
According to Phillips.
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42
Figure 5B - Block Dagram Illustrating the Deformation of the Ajibik
Quartsite According to Pairbair
Figure 5C0
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Block Diagram Illustrating the Deformation of the Pine CreeK
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Area Aeoording to HigtIns
Pigure 6 - Block Diagram Illustrating the Deformation at Coniston
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50
ACKNOWLEJGAMTS
This study was undertakea during the 1957 - 1958 academo year at
Massachusetts Institute of Teohnology in the Department of Geology and Geophysics.
The author's interest in rook deformation was first aroused by
Professor R.P. Niokelsn of Pennsylvania State University, and was increased
at MIT aas a result of Professor H.W, Pairbairn's course in str etural petrology.
Professor Fairbairn consented to the use of thin sections and hand speoimens
whioh he colleoted near 0aniston, Ontario, was thesis supervisor, and gave
numerous helpful suggestions during the course of study.
tributions in this work are gratefully acknowledged.
His counsel and con-
IITROOITION
Certain regions of the earth's orst have at one time or another utndaergone movement.
Evidence of past movements in the earth's arust is afforded
by the existence of land masses high above srrounding land, and by rooks which
over a period of time hame been bent into folds or broken along a fault surfaoe.
Present day orustal movements take place also, as shown by earthquakes.
When
movement takes place within a rook the individual components (mineral grains,
fossil fragments, fragmeats of other rooks,
themselves experience movement.
eto.) which make up the zook will
These components adjust themselves to the over-
all rook movement by moving into different position, by fracturing, or by intracomponental movements ass twinning or gliding.
The area of study is located southwest of Coniston Ontario where preHuronian quartzites have been faulted into contact with younger YKillarn
ite.
Cooke (3),
the area in
gran-
in his study of the problems of Sudrry geology, investigated
1938 and gives detailed reference to earlier work done there also.
H.W. Fairbairn visited the area in
1952 and colledcollected the specimens used in
the
present study; the author of this report has not had the opportunity of visitig
there himself.
To the author's knowledge this is the first petrofabrio study
which has been carried out in this vicinity.
A series of 14 hand specimens across a fault zone, spaced approximately 50 feet apart, formed the basis of this petrofabrio study.
On one
side of the zone is a sheared granite, and on the other side an obviously deformed quartaite.
Five samples from the granite and nine from the quartzite
were available for study.
By use of the universal stage the pattern of or-
ientation of quartz orystallographic axes (hereafter referred to aimply as
quarts axea) in thin sections from 12 of these samples was determined.
The
purpose of this study is to find out the relationship between the petrofabrio
data and field information, and to determine the means by which the rook move*
ment has taken place.
GDTRAL GtLOGY
The location of Coniston with respect to the Sadbury igneous oomplex is shown on igui 1 (after next page); Coniston is about seven miles to
the east of Sudbury.
Slightly over two miles southwest of Coniston is the site
from which the samples studied were taken.
The looation of Pairbairn's trat-
eree to the northwest when he took the samples is
approximately shown by the
solid red line between Datisy and Alice Lakes (Figure 2).
The geology of the area in and around 3Sdbury is shown in Figure 1.
As seen from this figure, Thronian rooks (which were originally sedimentary
but are now in some cases recrystallized) southeast of Sadbury
with younger YKillazy granite along a zone of faulting.
are in contact
The relationships be-
tween granite on the southeast side of the fault and the older sedimentary
rooks on the northwest side are shown in Figure 2 in
greater detail.
Within
the sone of fatlting between Daisy and Baby Lakes, and between Baby and Alice
Lakes, there is abundant evidence that significant movement has taken place.
Both the granite and the oniston series are intensely fractured and breaciated in ma~ places; Cooke (3) found that the Misaieagi quartzite was fraotured also.
The most severe fracturing seems to have taken place close to the
Coniston-granite contact along a valleq between Daisy and Baby Lakes.
How-
ever there is also topographic evidence that movement to a lesser setent has
taken place at several places in the Coniston group northwest of its contact
with the granite.
Cooke gives no mention of deformation of the granite, but
this has clearly taken place.
He places the fault between the Coniston and
the supposedly younger Mississagi quartzsite.
However,
for the suite of rooks
studied in this investigation the most intense defonxatton has taken place
close to the Coiston-gcr
nite oontact, with dereasing deformation in the
Coniston to the northwest.
The Coniston series, therefore, ~ccupies in this
area a zone along which movement has taken place.
Cooke's study indicated to him that several stages of movement
along the fault have taken pl3ce.
In the first movement the northerly of the
two fault blocks moved eastward and down relative to the fault block on the
south; during this stage the greatest oomponent of movement was horizontal.
Cooke's evidence for eastward movement of the northern fault blook is in a
draggirg of the Mississagi quartzite along the fault so that parts of this
formation, instead of striking north 500 east with the regional strike, strike,
east or slightly southeast.
He also suggests that nearly vertical drag folds
in the Coniston indicate dcminantly horisontal movement which was to the
east on the north (Fig. 3A, Cooke).
Baby
Cooke also found in the region between
Daiy Lakes that there were numerous subordinate faults which ex&ad
hibited atriae and which dipped southward at angles of 60 to 70 degrees.
Several faults had two sets of striae; an older one
orrespoding to tohe
movement described above, and a younger dipping 500 west which represents to
Cooke a later upward and eastward movement of the south fault block.
associates this latter movement with the intrusion of the granite.
He
urtther
evidence for a later eastward movement of the southerly fault blook at the
time of granite intrusion are drag folds of numerous little
emplaced originally parallel to bedding.
pegmatite dikes
these drag folds are in such a
direction as to indicate the movement direction described.
The evidence
presented by Cooke for a double movement along the fault may or may not be
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15
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25
Figure 1. Location Map of Coniston.
-~
?-Ty'
DID>
Figure 2. Looation Map of Traverse.
o2 -
PtSc;t3;- V~:~
6
orr*oet.
However, the indications he gives for an initial
horizontal,
alone it
movenent are not unreasonable.
easterly, nearly
Fron the geological field evidncee
will be taken that this, has been the main direction of movement.
An
attenpt will be made to correlate this assumption with the petrofabrio data.
o? sOrFcnms STUmUD
WoIATIOI ArD rIn swIroN mrTN
PPRxo
The specimens collected represeit a single traverse from the deformed
granite into the deformed Coniston quartsite.
The direction of traverse as
seen in Pigure 2 was to the northwest; this was in a direction perpendicular
to the strike of the rooks.
followas
Sample #
Orientation and specing of the samples was as
(The strike of the S-surface,S, for all speoimens was about N50OE.)
Rock Type
Distance fir #1
( in ft
)
Mp of S Direction of Lineation
(L) in
(angle be-
tween L and dip line)
1
Deformed ~grante
0
2
100
3
200
4
5
6
7
Conistan quartzite
*
00
300
'00
350
400
450
500
550
600
8
9
10
o
0
650
12
750
13
850
14
15
Defo * ed granite
91
if
i
"
U
Deformed
granite
100
NO 3-surface or Lineation
S and L probably as in #2
(?) 8
andrt L pctrbaly
cia in #2~;
Samples 14 and 15 were collected on the granite side of the fault
zsne after the traverse had been finished.
Sample 15 has the same character-
istics as ssmples
le 1-,
1-3, but
uas has a more highly developed S-surface and lineation.
Sample 14 represents granite of a more massive variety which is only in the
begiming stages of deformation.
It was collected from a small area within
the deformation zone, but shows no visible S-surface or lineatio
specimen.
No fabric di&agran
tation of the specimens
in
n the hand
were made of samples 14 or 15, and the orien-
s therefore unimportant.
However, the rature of these
rooks - in one instance the least deformed of the granites and in the other
the most deformed - is of interest.
Hand specimen #4 was missing, and for
this reason was omitted from the study.
From each of the 15 specimens it was purposed that thin sections
perpendicular to the S-aurface and lineation would be made,
Three mutually
perpendicular thin seetions of sample 15, the most highly deftomed of the
granite,
were made.
In all rooks except the massive granite the S-surface
could be distinguished by naked eye.
Lineation is present in all samples but
#14 and is seen cegasoopioally except in numbers 8, 9 and 11.
sections are correctly oriented is shown by the consistenoc
gram for these rooks.
That the thin
of the quarts diae
Sample 5 was tnintentionally cut at an angle of about
500 from the lineation, but perpendiEular tp the S-surface.
This can be seen
in the hand specimen, and is reflected in the orientation of quartz axes in
the thin section.
Each of the speimens, therefore, except #5, is perpendic-
ular to the S-surface and to the visible lineation.
Specimen #5 is perpen-
dicular to the S-surfaoe, but not to the lineation.
The orientation of the S-surface (3) and lineation (L), as determined
from the orientation of the hand specimens, is not constant throughout the trwerse.
Although S always dips to the east and strikes about NSOoE, its dip
varies between 500 and 90O . The direction of L in S may vary within 500 on
either side of the direction of the dip of S.
These relationships are shown
9
in Pif
e 3 (nextr
page).
The possible significance of these variations will
be considered in the discussion laters
North
13
L 1
West
L5
3 -3, 5-10
East
L 12
S
12, 13
L 6
L1
L7
L 2, 3, 10
L9
South
Figure 3
Sohmidt net plot of the geographic orientation of S and
L for specimens for which petrofabric diagrams have been
made. The projection is lower hemisphere with a horizontal
plane as the equatorial plane. North is as indicated.
11
MOD OF INVI:STIGATION
The method byr which the quarts axes orientations were determined
and recorded is described by Fairbairn (4).
The main steps in the procedre
aret
1 * Selection of an area and one type of quarts grains to measure in an oriented thin section.
2. Mounting the thin section on a microscope equipped with a universal stage,
and dteterminaton of the orientation of between 100 and 300 quarts axes.
Working at the rate of approximately two grains per minte the measurements
avn reproducible to within 50 . This is sufficient precision for a statistical study of this nature.
3. The quartz axes are plotted on a Sohmidt equal area net,
tusing the lower
hemiasphere as the hemAisphere of projeStion.
4. The quartz dcagram are counted out and contoured as described by air*e
bairn.
In the diarama
of this report the quarts axes concentrations are
represented in decreasing density by the following patterns.
g ram some of the interm=diat
In some dia-
pattrnms are omitted.
Highest concentration
mor
l]
Lowest concentration
5. The diagram may be checked in an approximate way by one or two meanes
a. Extinotion of a large number of grains at the same time when the
amiroscope stage is rotated.
b. Predsmnanoe of a single color in a great number of grains when a gp wn
or sensitive tint plate is inserted.
These tests are useful when there is a consentration of axes in a
girdle perpendicular to the plane of the thin section, or when significant
ssa
ooeur singly or approximately 90 apart.
For the diagrams of samples
1-3, 5-7, and 10 one or both of the above test checked with the diagrams ob
served.
S*me of the diagrams for samples 8 and 9 gave positive tests, while
the rest of the diagrams for these samples gave uncertain tests.
from samples 11-13 gave uncertain tests, and thiss i
in the quartz axes of these diagrams.
Thin sections
reflected in the spread
No diagrams were made for either of
the three mutually perpendicular thin sections of the highly deformed granite
(sample 15) in which S and L are so well developed.
However, under the reason-
able assumption that this sample has an orientation pattern similar to the rest
of the samples of the suite, the three sootions were observed to give positive
tests as to the indication of the same type of pattern aa found in the other
sections. Therefore, thbae
is little doubt that the quarts est
diagrams as
found in the thin sections and presented in this report are true approximate
representations of an existing patter
for quarts orientation within the rooks.
The proper selection of quarts grains to be measured has been eaphasised by Fellows (6), and some of his suggestions were followed in step 1.
Where possible distintion was made between unde
ve
quarts and quarts
which had undergone deformation.
Moreover, where the direction of a band of
fine quarts changed, as when it
enclosed a large feldspar orystal, separate
13e-.~-~11~ -- ----~~
-C
-I
---
-
-
~
rrsIrmr~
Is41~*r~3uaiqll
r
Wfiblll
15
diarams wr
made for different parts of the band.
In the samples (1-7)
elose to the sone of deforaton it was emy to distinguish between the var-
teas types of quarts.
oreasingly diffi
Away from this soae, in samples 8-13, it became in-
lt to distinguih types of quarts, exoept that approximtely
10-15% of it was ex*eedingly fine in grain size.
,ase of these diagram
represent rand m
be seen that the patterns
si
In spite of the fact that
of quartz grains it ean
are similar, although more difftse in nature, to
the patterns in the more highly defoned rooks.
DESCRIPTION OF HAND SPW
AND THIN S TIONS
Five samples of granite were available for study.
Of these, sam-
ples 1-3 were collected at 0, 100 and 200 feet respectively from the starting
point of the traverse.
All three of these rooks exhibit about the same de-
of their S-surface
deelo
gree of deforation, as shown by the doegree of drelopment
and lineation.
Of the two remaining granite sample, sample 15 ashow a some-
what more pronounced S-surface and lineation than samples 1-3, while sample
14 is completely massive in hand specimen.
100 fet
The location of sample 14 is about
from #1, but that of #15 is unlaown.
Sample 14, the massive granite, in hand specimen is a fresh, coarse-
grained granite consisting of 60%pink feldspar orystals from 1/16 to 3/8 inch
in size, 35% quartz grains showing the same size range as the feldspar, and
minor amounts of dark green partially decomposed faromagnesian minerals as
(In band specimen this er;k could represent the "typ-
biotite ard hornblende.
ijol" ooaree-grained granite.)
fomed in varying degree.
The r
grmniteaire hand s
ens are d-
The mineralse can still be readily identified, and
the percentage composition is most likely the same as before.
somewhat schistose, with an S-surface and lineation.
The fabric is
Both of these features
are best shown by elongate quart in thin lena-like or platy fores.
leses are discontinuous, unlike the banding in a gneiss.
The quartz
Nevertheless, the
parallel orientation of these lenses gives the rook its S-surface and lineation.
The feldspar crystals exhibit some degree of flattening into lenses, but not to
the same extent as doe
the qiartz.
Quarts gives the impression of having
flowed through the rock around islands of feldspar orystals.
The size of more
nearly equa t crystals in these rook is approximately the
ive sample.
e as in the mass-
The lens-like orystals represent orystals of about the same sizse
which have been squeezed into lenses.
The means by which ther may be squeezed
into lenses will be discussed later. These lenses of quarts, as mentioned above, are similarly oriented
the ratios of their dimensions are approximately
as showns
Thin sections perpendicular ttthe
lineation were available for
study for all of the deformed granites, together with one section of the var-
iety which was massive.
For sample 15 an additional thin section was made
in each of the two planes perpendicular to the plane of the first
section.
The mineal composition of the rooks as estimated from hand specimen is
approximately the same as seen in thin seotion.
features are of interest.
However, several textural
Be~-nning with the least doformed of the rooks,
sample 14, the early stages of rook deformation are plainly visible in thin
section, although not visible in hand specimen.
are much the same in
appearane as in
The feldspars in
undeformed granite.
this rook
They are ooarse sad
euhedral; both orthoclase and plagioclase axe present but the distinction is
sometimes difficult beeanse of partial decomposition of the feldapars.
In
addition, there may be anywhere up to several hundred flakes or shreds of
white mica (sericite) occurring either along cleavage or twin planes, or in
random positions.
These rowths of mica have the appearance of tiny shreds
or needles of mioa which may be up to .2 mn long,
When a great number is sim-
ilarly oriented along the same Orystallographic plane in the feldspar the
all
ertingish sainltaneously in polarized light.
Ingerson (8) studied a similar
oocurrence of mica in albite orystals occurring In rooks in
the Piedmont.
He
showed that the orientation of the micas closely follows erystallographic
planes in the feldepar.
Ingerson's photographs (Figures 2, 5 and 10) res-
emble what is observed in the feldspars of the granite studied in this report.
Several of the feldspar crystals are crossed by thin fractures
are coftiAnous into the nearty quarts.
This may represent cataolastio texture
Ji the rook, or damage during thin section preparation.
considered the most likely.
of feldspar twn
deformed rook.
bei
the quartz in
The former idea is
In the massive granite no evidence could be found
broken or bent, as might be expected in a moderately
The main indication that the more massive granite has suffered
some deformation is shown by the quarts.
in
which
The following deformation features
this rook and the other granites ares
1. Fracturing of larger (1-5mm) quartz grains: Some grains are out by fractures extending all the way ao*os
the grain, dividing the grain into three
or four portions each of which has the same optical orientation as its neighbor.
Fellows (5) has shown excellent photographs of such fracturing in Plate 8 fig. 2
and Plate 9 fig. i.
2. The occurrence of a few quartz lamellae similar to the ones described by
Fairbairn (4).
These lamallae were observed only n some larger quartz grairs
which had not been crushed into small fragments.
Such uncruahed quartz was
found to comprise about 25% of the massive granite, but only 5-10% of the highly
deformed granites.
3. Undulatory extinction and straining of quartz, producing biaxial interference figures.
4. The occurrence of abundant small fragments of quarts in sizes about as large
as a in head and in ahapes which are fran two to four times as long as wide.
The straight edges of large numbers of these grains in one area gives a mosato
appearance under high magnification.
It
seems fairly evident that this quarts
has come into eristence by crua*ing of large quartz crystals into tiny fragments which in the massive granite may occur in little
nests throughout the
wook or my be locally oriented parallel to one another.
In addition to larger unorshad but highly strained qiarts and finer
crshed quarts grains, the massive granite gives the appearan e that strings
or bands of the crushed grains have begun to coalesce into a single grain.
This could take plaoe through reorystallization and a coalescence of theae
msal
rnah fragments.
leases or streas
Evidence for this is the ocourrene of thin, ourved
of quarts which show undulatory extinction and which contain
outlines of foarmer grains which hae not completely grown together with their
neighbors.
Such partly-coaleseed streams of quartz are sea to a much greater
extent in the more deformed granites.
Fellows (5) has shown photographs of
partially annealed quarts grains (Figure 31 Plate 6 fig. 4; Plate 7 fig. 1-4;
Plate 8 fig. 3-4).
The only other minerals in the masasive graite, and in the sheared
grenitee, are small amounts of sericite, and original mica and hornblende.
The sericite occurs as smail shreds growing between grain,
epars.
It
annd in
the feld-
appears to have been brought into the granite after or during def-
.ormation and grown between crystals, along S*surfaces, or in other crystals.
The mica and hornblende oonstitute about 5% of the rook and tave apparently
not been important in oatrolling the behavior of the rock during deformation.
The textural elements which determined the nature of the deformtion were the
more easily deformed
quartz and the relatively strong feldspar grainse
Several textural features of the granites which are developed to a
lesser exrtent in the massive granite are shown well by the four samples of
deformed granite.
All four samples (1,
2,
3, 15) are similar with regard to
these features; for sample 15 three matually perpendicular thin sections were
studied.
The most striking thing to be seen in these rooks is the manner of
ocurrence of the quartz.
Coarser uncrushed quarts makes up 5-10% of samples
1-3, but less than 5% of the more highly deformed sample 15.
This quarts my
occur in thin lenses or in curved or tear-shaped grains up to 5 mm long.
In some cases a single grain of original quarts has fractured into
several lens-shaped fragments, and the adjaoent pieces can be fitted together
like the fragments of a passle.
same optical orientations.
Sametimes these adjacent fragments have the
This quarts probably represents the first
extensive fracturing of quartz into fine fragments.
The crush quartz
stage in
occurs
as numerous fine grains, and makes up 10-20% of samples 1-3, but 30% of sample
15.
It occurs mostly as S-shaped or curved bands to 1/16 inch wide and 1/2
inch long.
These bands completely enclose the feldspar crystals, and give
the appearance that the many small orushed grains of quartz have literally
flowed through the rook.
The general parallel trend of these quartz bands and
the larger quartz lenses gives to the rook its S-surface and lineation.
streaming of crush quartz through the rock is
(Plate 7 fis. 1-4).
shown by Fellows'
(5)
Such
photographs
The tiny orash pgrans of quartz are generally elongated, presumably
from having broken into minature lens-like or needle-shaped fragments.
dividually these gTains have fairly sharp extinotion positions.
In-
The presence
of several hundred of them in slightly different orientations within a band,
however,
causes various parts of the band to have different extinction positions*
That there is some
xystallographio orientation of quarts fragments within the
bands can be seen by use of the gypum plate.
nmerous
In sample 15 it is appa ent that
of the small quarts fragments and some of the lenses have begun to
grow together.
This has already been discussed.
The Conista series is
represented by a series of 10 samples (4-13)
oollected at 50 or 100 foot intervals traveraing to the northwest of sample.I
The hand specimen for sample 4 is
missing, but its
nifioant differences from the samples near to it.
position of all the samples is
feldspar.
thin section shows no sig*
tnral
The general
com-
quartz, mica and small amounts of pla4oelase
All samples have recognizsable S-urfaces in hand specimen, and
lineation is
readily apparent in all hand specimens ezoept 8, 9, and 11.
Quarts elongation and a single S-surface are apparent in all thin sections.
Away from the szoe of strongest defcrmtion thee ean be seen a gradual decrease in
the deformation of the rooks.
rooks to have more poorly der
This is
shown by a tendency of the
oped S-surfaces and lineation in
less fracturing of the quarts, and much sharper extination in
hand speoimen,
the quartz in
the higher numbered samples.
The transition to less deformed and more massive rooks sems to be
best put after sample 8.
Therefore,
samples 5-8 will be considered alone for
20
desoriptite
purposes, as will samples
9-13.
Samples 5-8 are not truly quarts-
ite in that they may contain up to 30 or 35% mica in small shreds which are
directed along S-surfaces.
A more appropriate nrme, especially for sample 8,
may be quartz-mioa schist
Samples 5-8 and 13 ire dark gray in hand specimen,
with a few bands 1/8 inch wide of lighter quartz or chert.
Samples 9-12 are
true quartzi-tes, contain up to 10% mica, and are white or buff-colored.
Sample
13 is a quartzite, but is gray in color.
Samples 4-8 show varying mias content and differences in grain esize,
but all have the features of schistosity, highly elongated quartz and easily
recognized quarts veinlets.
These samples contain 65-80% quartz in grain sizes
of a maximum of .1mm to Im.
'The quarts occurs in approximately equal amounts
of lenses (aximum elongation: 10 width = length) and finer elongated or irregularly shaped grains between the larger leases.
characteristio of the quarts.
Undulatory extinction is
The ashistosity is marked by Minividual or groups
of larger quarts lenses elongate parallel to schistosity, by thin bands of finer
quarts parallel to schistosity, or by the general trend of mioa as it interlaces its way through the rook.
quartz band.
Fine mica may occur between the grains of a
Mica may show an overall range of orientation within 300 of the
general rock schistosity, but no additional S-surfaces were noted.
The bands
of quarts or mioa causing sohistosity are usually of varying width, continuous
for only I mm to 1 inch, and do not remain striotly parallel to one another.
Sample 5 contains some ban d about 1/8 inch wide of crush quartz
similar to the streams of crush quartz contained in the granites.
In sample 6,
which is coarser grained, individual quartz leases elongated parallel to the
sohistosity may
be up to 1/2 inch long and 1/10 as wide.
the quartz plates referred to by Cooke.
These may represent
It is interesting that sample 6 show-
ing the best-developed quartz lenses also has the most syzmetrioal fabrio diagram (diagram #10).
Sample 7 also contains numerous quartz lenses, but these
are about 1/4 mm in length and mch smaller than those of sample 6.
shows many slivers
to-end fashion.
or lenses of quartz which are growing together in
in
an end-
(Fellows (5) has described this also in his study of Appal-
achian quartzites, and illustrated it
the rook its
Sample 6
in Figure 3 of his report.)
numerous quartz plates, but such an effect is
This gives
not well-developed
any of the other samples.
The mia of samples 5-8 makes up frau 10-35% of the rook, most
commonly 15-20%.
It oecurs as numerous fine flakes which are elongated par-
allel to sohistosity or as a more or les
continuous network of fine flakes
which weaves its way through the rook in the direction of the quartz elongation.
The quarts
veins of samples 5-7 are most often parallel to the sohis-
tosity, and up to 1/4 inch in
width.
Beginning with sample 8 the quarts veins
readily out aoross the more poorly developed S-surfaces.
these veins shows sharp extinction,
in contrast to elongated and deformed quarts.
These veins may represent 25% of the thin section.
grain sizes of up to 3 mm, which is
of elongated quartz.
The quartz of all
The quarts veins show
the average size along the long dimension
Plagioclase feldspar comprises about 3% of these samples.
Some of the feldspar twins are curved or bent.
In none of the quartz
coarse elongated, or fine quartz) was lawllae observed.,
(veinlet,
samples 9-13 contain for the most part about 90% quartz, 8-10%mica
and 1-2%plagioelase feldspar.
Some of the samples show very little schis-
tosity, the rook consisting of unassorted equidimensional (to 1 mm in size) and
elongated (length = 4 times width = lmm) quartz grains in equal proportions,
glong with finer grains of quarts, a few feldspar orystals, and an interlacing
network of mica.
The larger quartz grains make up to 60% of the rock; the
finer quartz to 35%.
Beinning with sample 10 the amount of +ine quarts de-
creases to about 10-15%.
in graingrain size.
show as muoh
The feldspar is plagioclase, and may be up to 1 m
Mica occurs in the sa
way as before.
These samples do not
quartz elongation, particularly samples 10 and 11J
are absent or unrecognizable in samples 10-13.
Qa rtz veins
Quartz lamellae were not observed
in any of these samples.
Summarizing briefly, the important tertural features are:
1. Evidence of movement in the granite, as shown by curved and undulose original quartz, cataclastic texture, crush quartz, and the development of S-surfaces and lineation.
2. Quarts elongation, and resulting sohistosity, and undulatory extinction characterizes the quartites of samples 4-8.
3. Samples 9-13 show a slight increase in quartz content and grain size, along
undulatoy
with a decrease in schistosity and undulatory
xtintion of the quartz.
4. Quartz veins penetrate the quartzite mostly parallel to the schistosity
near the granite, then out across the weaker schistosity of samples 8 and 9,
and are not recognizable beyond this.
The quartz of these veins s&ows sharp
extinction positions, and is for the most part equant in grain shape.
As a result of the petrograp ic
grs
of deformation,
study of these rocks of varying de-
the following sequence of events for the deformation is
suggestedz
I. Initial straining of original coarse quartz grains, as shown by undulatory
extinction and biaxial figures.
place at this stage also.
It
Pormation of lamellae could well have taken
seems that crushing and recrystallization have
destroyed any lamellae which were present except in
2.
the mildly deformed granite.
Camminution of quartz, first into larger lens-like fragments, and eventually
into small crash quartz ~haracteristio of the deformed granites and the quartzIt
ite of sample 5.
is elongated in
is less certain if the fine quartz, and also that which
samples 6-13, formed in this way.
The plates of quartz which
are best seen in sample 6 appear to have formed by coalescing of several slivers
or lenses of quartz.
These slivers are here considered to be the result of
fracturing of the quarts into several elongate fragments, but not representing
oomplete granulation to form crush quarts.
3. Orientation and flowage or streaming of the crash quartz or quartz slivers
In the granites the movement of the quarts
response to movement in the rock.
the rock
grains through/is in places impeded by the larger feldspar crystals in the same
in
way that large boulders in
a stroam divert the flow of water.
4. Partial reoxystallisatiDn of crush or needle quarts, and annealing of the
grains to form some of thelong streaks of quartz as seen in samples 6 and 15.
5. Mi4natic crystallization of sericite in small shrede in S-surfaces or as thin
needles and shreds in
crystallographic planes in feldspar.
Whether the serioite
was as original constituent of the quartzite or was later introduced is not known.
24
6.
Intorductioa of vein quarts into the quartzite along S surfaces or, in rooks
with weaker S-surfaces, along
any penetrable plane.
The undeformed nature of
the vein quarts and the close oontrol of the direotion of quarts veins by the
S-surfaces suggest that most of the rock deformation took place prior to the
introduotion of the quartz veinlets,
_ C_ I~_ I
Proa the petrographio
___ ~_~__~_~_______
ttd
of the thin sections for this
suite
of
rooks there were found three petrofabrio elements whose orintati n seemed to
refleot in same wa
the Aeformation which took place
1. Sericite, white
ais, in ti
tallographi
planes in feldspar.
flakes or shreds along S-surfaces or crysThese tiny shreds are for the most part too
assll and too olosely grown together to have their orientations determined on
the universal stage.
would be expected.
Most
oamonly they are oriented along the S-surfaaep as
However, the miesa
were not observed to mark any S-surface
other than the main S-surfaoe in each rook.
The micas may oeour along cleavage
or twin planes in the feldspars, and reference bas already been wade to Ingerson's (8) study of mia growth
within feldspar crastals.
It is very likely
that after the formation of the S-surfaces the mioas grow within them, and
were possibly introduced along then.
However, this does not preclude the
possibility that the raeas were present in the quartzites prior to deformtion.
2. Undeformed vein quarts which in some samples of quartsite possessing a well-
defined S-surface followsthe 8-surface rather closely
it.
instead of transecting
This relationship is not observed in rooks with weaker 8-surfaces, and it
beoomes diffioult to distinguish between undeformed vein quarts and mildly deformed original quarts.
These relationships, the unstrained oondition of vein
quarts, and the disperse petrofabric diagrams of vein quarts lead to the con-
Olusion that it was introduced into the rooks after the dermation.
3. Qurts which has undergone deformation.
The following types are recognised
&. Very coarse, large grains whose undulatory extinction shows the results
26
of severe straining, but which have not yet been broken into ftne fragments.
Catalastic texture, probably as a result of original deformation, mw or
not be present.
sample.
It
may
This is seen in the granites, most commonly in the massive
may represent original quartz which was strong
ably oriented so that it
could resist deformation.
nough or unfaver-
The only lamellae observed
were seen in these grains.
b. Cush quartz in thousands of very fine grains which may occur as distinct
bands within a rook, as streams or pressure shadows enclosing feldspar orystals,
or as small clusters in the rook gra6tdmss.
These grains give the appearance
of having originated through the fracturing of larger quartz grains.
Alfter
fracturing they became transportable, and have flowed like streams through the
rook.
This type of quarts is best seen in samples 1-5 and 14-15, and to a lesser
extent in 6-8.
Pellows (5)
has described nd photographed this typ, of quarts
in Appalachian quartzites.
The granite samples showing the numerous
o. Elongated or lens-like quartz.
fine grains of crush quarts in bands or streams also give the impresion that
larger single grains of these bands are once again coalescing into larger
single grains which are greatly elongated or perhape lans-like in appearance.
This reorystallization or homogenization has been mentioned earlier in this
report, and also by Fellows (5).
The granite samples give the best evidence
that quartz has behaved in this manner.
quartz, especially sample 6
Samples 5-8 show markedly elongated
saple 5 still has the remains of several bands
sample
of fine crash quartz which has not recrystallized.
elongation of quarts,
Samples 9-13 show some
but not much crush quartz of the type recognised nearer
to the zone of greater deformation.
There arej 0Owever, some small quartz frag-
ments distributed through these rooks.
The origin adopted in this repbrt
for
elongated or lens-like quarts seen in
this uite of rooks is
the quartz has fractured into larger leis-shaped fragments,
twofold.
Either
or regrouping and
recrystallization of crush quartz into lenses and streams has taken place.
some rocks there is
evidence that both processes have taken place.
In
Samples 9-13
do not give as clear an indication as do samples 1-8 and 14-15 that these proceases have been activei
With these various petrofabric elements in
mind, the orientation
patterns of every type of quartz grain have been determined.
made for the platy minerals,
sine
they are difficult to measure and are likely
to be the result of mimetic erystallization.
lower hemnisphere projection is
No diagrams were
used.
For every diagram the Schmidt
The S-surface of all rooks is
about X50E.O
S' refers to surfaces slightly varying from 3, as occurs where a band of crushed
quartz grains wraps around a feldspar crystal.
All diagrams except those for
sample 5 are normal to the maximm elongation (L)
of these diagrams.
in S.
L is
therefore at the center
Sample 5 has the lineation (L) 500 from the center, but still
The diagramns have been made so that L as seen in the diagram is pointing
to the east and down the dip of the S-surface in the oriented hand specimen.
This enables all diagrams to be lower hemisphere projections.
Similarly, the
east end of every diagram is on the right, and north is 500 counterclockwise
from this as measured along the edge of the diagram.
The patterns used to rep-
resent various degrees of quartz concentration have been shown on page 11.
The following quartz orientation diagrams have been mades
SAMPTL#1 - Deformed granite
I
1 - 250 quarts axes from curved band; this part of the band is parallel
to S; mostly fine orush quartz, some reorystallized elongated quarts; Contours:
6, 4, 2,
c.
2 - 132 quarts axes from different part of same urPred as in diagram 1;
&EOea
this part of the band is parallel to S' as shown in the diagram; same typn of
quarts measured; contours: 9, 8, 6, 4, 2, 0O.
#2 - )Deformedgranite
SAMPLE
S
- 480 axes of orush quarts from two separate quarts bands in thin
section; 200 axes from one band and 280 from the other; trend of S is the same
for both
ads, nds, parallel to the hand itself;
2, , 0%.
- Deformed granite
8AWPLE #
rgrM
Contours 5 4,,
,
150 quarts axes from band of crush quarts; tr.nd of band is parallel
4
to 3; Contouras 14, 12 10, 8, 6, 4, 2, 0%.
agrgam5
4-
107 quarts axes of orNsh qart
from band from different part of
slide; this part of the eurved band is parallel to 8;
Contours: 8, 6, 4, 2, 0%.
6 --lagam
80 axes of orush quartz from different part of ourved band of diam
e
gram 5; this part of the band is parallel to S'; Contour
APLE
-
artaite ontaining bands of crush quarts and veins of undeformed
quarts parallel to S (L is
ai
7-
8, 6, 4, 2, 0%.
not at the center of the diagrams)
176 quarts axes of crush quarts; the band is parallel to S3
Contouras
7, 6, 5, 3, 1, 0%.
aieMa
8 - 140 quarts axes from different band of fine orush quarts; the band
is parallel to S; Contours: 14, 11, 9, 8, 6, 4, 2, 0%.
9 --isma
230 quartz axes from coarser, vein quartsz
SMPEE
.K-
contourst 3, 2, 1, 0%.
Quarusite showing extrwme elongation and lensing of quart.
iagBram 10 - 305 quarts axes from coarse quarts, moot of which shows strong
elongation parallel to 8; Coatouras
12, 10, 8, 6, 4, 2, 0%.
APLE
f
- Quartsite showing less elongation and finer grain
ise than sample 6.
11 *- 296 axes of fine quartz, noh of which is elongated; elongation is
na~M
parallel to S; Contours: 5, 4, 3, 2, 1, 0%,
12 - 207 axes of mostly coarse vein quarts; trend of vein is parallel
Di~sa
to S; Contoursr
4, 3, 2, 1, 0%.
- Qusartite with recognizable but an irregular Ses-urface
SAiE
Diaam 11 - 120 axes of fine quartz grains elongated parallel to $ and from
one soetion of Alide; Contours: 5, 4, 3, 2, 1, 0%.
S14 - 212 axes of fine qarts grains elongated parallel to 3, and from
different part of slide than
- 199 axes of largeo
Dinzam 1
diagram 13; Contours: 4, 3, 2, 1, 0%.
quart
grains occurring in thin quarts band;
the quartz band, as well as grain elongation, is parallel to 3; Contoura
6, 5,
4, 3, 2, 1, 0%.
MaNam 16 - 102 axes of fine quarts, not all of which is elongated; grain
elongation is parallel to 3; Oontours 5, 4, 3, 2, 1, 0%.
- More massivquare quartite containing less mioa than #8; S-surface is
SAMPLE
more difficult to recogpise.
17 - 250 axes of coarse, elongated quartaX
ME
agr
elongation is parallel to St
Contours, 5, 4, 3, 2, 1, 0%.
iuagam 18 - 160 axes of fine quarts grains, most of which are not elongated;
Contours: 5*5, 5, 4, 3, 2, 1, 0%.
- QuartSite resubling #9, but showing coarser grain and less elongation
E
of the grnai
tasrr
1
- 160 random mostly coarse quartz ares; elongation is parallel S;
Contoures 6, 5, 4, 3, 2, 1, 0%.
iagram -2 - 240 random mostly coarse quarts axes
SAMfP
GContours: 6, 5, 4, 3, 2, 1, 0%.
#11 - Quartzite resembling #10
-aam
- 211 random mostly coarse quarts axes; elongation is barely de-
teotable in thin seotion, but seems to be parallel to S; Contours: 4, 3, 2, 1, 0%.
SAMPLE 12 - Qartsite resembling #10.
tr~ am 22 - 230 axes of mostly coarse, elongated quarts; elongation is par-
allel to 3; Contours: 5, 4, 3, 2, 1, 0%.
SAMPE Wf3 - Quartzite resembling #10
D
r
23" - 124 axes of coarse, elongated quarts; elongation is parallel to
S3; Contours; 6, 5, 4, 3, 2, 1, 0%.
fas
24 - 283 random axes of ocarse quarts faro
diagram 23
same setion of slide as
Contours; 4, 3, 2.5, 2, 1.5, 1, 0%.
The da
, as the
are pireented h
,rebegin in the defonred
granites (samples 1-3), eontinme in the sone of strangest deformation for the
first two samples in the quartzite (samples 5-6), and then contine aw
this sone in the remainder of the samples.
%
ro
Each suoceeding sample is about
50 or 100 feet to the northwest of the proeedi g sample.
Diagram #1
Diagram #2
Sample #1 - 250 axes of crush qtz
Sample #1 - 132 axes of crush qtz
Contours: 6, 4, 2, 0%
Contours: 9, 8, 6, 4, 2, 0f
Diagram #3
Diagram #4
Sample #2 - 480 axes of crush qtz
Sample #3 - 150 axes of crush qtz
Contours: 5, 4, 3, 2, 1, 05
Contours: 14, 12, 10, 8, 6, 4, 2,
o0
Diagram #5
Sanm,,le '3 - 107 axes of crush Ctz
Contours: 8, 6, 4, 2, 0o
Diagram #7
Sample ir5 - 176 axes of crtsh qtz
Contours; 7, 6, 5, 3, 1, 05
Diagram #6
Sample #3 - 80 axes of crush qis
Contours: 8, 6, 4, 2, Of
Diagram #8
Sample #5 - 140 axes of crush ,ltz-
Contours: 14, 11, 9, 8, 6, 4, 2,
05
Diaram #110
Sample #5 - 230 axes of vein Itz
Contours:
, 2,
1.,
C
Sampnle
-
305 a
s strongly
elongated qtz
Contours: 12,
I0, 8,. 6,
4,
2,
0,
Diarm #1.2
Samile #7 - 296 a~es of file,
elongated itz
Cortolrs:
5, 4, 3, 2,
1,
Samle #-7 - 207 axes of vein kitz
Contours: 4, 3, 2, 1, 0~
0,
Diagram #14
Diagram #13
,mple
#8 - 120 axes of fin.,
, 1 ongated cqtz
Co'tours: 5, ,, 3, 2, 1,
Diagram 415
ample i#8 - 199 axes of larger,
elongated qtz
Co7tours:
6, 5, 4, 3, 2, 1, Or'
Sample -8 - 212 ax . of fl,
el ongated qtz
,Contours:
4, 3, 2, 1, Q
Diaram i.T
Sample ,8 - 102 axes of
n
all of which i~:
Contours: 5, 4, 3, 2, 1, D;
Iz,
ot
Yle
, c^1-.lg
Diarm
Sample
9 - 250 axes of coarse,
elongated qtz
3ampl.e
18
Diaram
#17
19 55,
C.ontous:
60 axes o"f 7
5,
1, 2V
4
,5 4, 3, 29 11 O
........
"-
"r
tJ
3j m
)7:fr-P
I.
c>.rn
?S?3
.
7
1
i'
-4
-
n
e a
-,
.,,
SaY7l
e
3iag~am # 27
- 21- rtdcon qtz axes
3-
Diagram #22
Sample #12 - 230 axes of mostly coarse,
elongated qtz
3'
5. , 3,
5r,:
31Co
DL 3?r
,7
f co r>e,
elonrgatei QM
t" ; - 124 axe.s
p2
t.':.L'S
" 6,
5.
4,
3,
2,
1,
~1
Sa.t
1, Of
.. :of......
,'!3S?°
es...
. rion,
3, 2.5, 2,
.
21- - .oaz
CCotoirs:
j,
,
37
NTWEPRWAXION OF PABRIC DIAGRAMS
The petrofabrio diagrams indioate the following features which demand interpretation:
1. With the eception of Diagrams 9 and 12 there is a tendency towards the
formation af an a girdle of quarts axes around the e4ges of the diagrams, with
one or more maxims somewhere in the girdle.
perpendioular to the girdles.
The observed lineation (L) is
The thin section for Diagram
7, 8, and 9, as
already mentioned, is not perpendicular to L. The girdles for Diagrams 7 and 8
are seen to lie along the ar
of a great circle on the c3hmidt net, and are
likewise nearly perpendicular to the observed lineation.
2. Upon olose inspection of the diagrams it is seen that within the girdles
maRima are absent in zones perpendioular and parallel to S.
Diagram 10 is
the most striking example of this.
3. The petrofrbrio diagrams become more diffuse in samples taken farther awa
from the sOnes of strongest deformation.
The main acne of deformation, as in-
terpreted from hand speoimems, thin sections and petrofabris, is in samples 1-7
(Diagrams I-11).
B
with sample #8 there is a gradual deerease in the
degree of deformation as seen in hand specimen, thin sections and grain orientation.
4. In samples showing only slight elongation of quartz grains ( samples 8-13),
the preparation of selective diagrama
grams 13-16 are all from sample #6.
did not have any noticeable effects.
MSL-
Diagrams 13-15 are for the most part
elongated quartz grains, while #16 is a random selection of quarts.
Elongated
coarse quartz grains, of sample #9 are represented by diagram 18, and fine, equant
quarts of the same sample ty Magram 19.
Similarly, for sample #13 Dagram 23
is for coarse elongated quarts and Diagram 24 for a randol saeection of coarse
Comparson of the diagram
quarts.
shows no consistent tendeny towards in-
creased orientation in selective meaurements.
However, it is worthwhile to
note that grain lengths in the -surfae perpendioular to the lineation in eamrples 8-13 is only on the order of twice the grain width, sinoe the plane of
the thin seetions do not show the direction of greatest elongation.
This
could result in a failure to recognize grains which had experienced significant
elongation parallel to L.
5.
DiMrams 9 and 12, showing the orientation of easily recognized vein quarts,
show little
or no pattern of orientation.
minima to develop in
There may be a tendency for the
these diagrams along 5, but no significance can be
attached to such disperse diagrams.
from the petrofabrio, thin section and
hand specimen inforadtn obtainable os vein quartz, the conclusion is that it
has not undergone deformation; it was introduced into the roocks after the deformation had taken place.
6.
Diagrams 1 and 2 (sample #1),
and 5 and 6 (sample #3),
parts of the same ourved band in the two respective rooks.
of each rock is
gram 1,
are from two diffeent
The main 3-surface
represented by 8, and the curved part of the band by S'.
and Diagram 5, represents the part of the band parallel to S.
2, and Diagram 6, represents the part of the band pPrallel to S*.
in
comparing Diagram I with 2, and 5 with 6,
the latter
Dia-
Diagream
Therefore,
of the two diagrams
should be rotated approximately 300 olockwise until S' is east-west.
There is
not a great difference after this has been done except that the minima 900 from
3 or 3' more nearly correspond in eaoh case.
The only significance attached
to these partial diagras is that they mantain
patial sammetry with respeot
to the S-surface's direotion in the part of the rook represented by the diagram.
Thus, if
the direction of S changes, as it
does when a band of crush quartz
wpys around a feldspar grain, the position of the minima and some of the ma&mat
#aem to change aoordingly so as to maintain approximately the same position
with respect to the direetion of S.
With the exception of features 1 and 2, and in pert 3 and 4, the preceding discussion considers the interpretation of the individual fabrie features
noted in this study.
thir
Since the most significant fabric features are I and 2,
meaning will now be discussed.
The reeognition and definition of fabric t*xe
by Sander in his work in petrofabric studies.
was early %ephasized
His conoepts have been presented
by Fairbairn (4), whose suggestions are followed in this report.
Fabric axes
The
are utilized in order to aid in the description of orientation features.
critical axis, j,
denotes the direction of movement or tectonic transport.
the ecoond fabric axis, is chosen perpendicular to
iation.
In addition, b
~,
and in the plane of fol-
is often assooiated with a lineation.
the third axis, and is perpendicular to the abPlane.
j~,
a is chosen as
The field evidence of
Gooke (3) seems to indicate that the direction of transport in the region being
studied is perpendicular to the lineation (L).
Thus, 1 will tentatively be
chosen as parallel to the lineation, and a paralel to teotonic transport.
These choices are indicated in a block diagram in Figare 4 (next page).
An
attempt will be made to explain these in terms of the field, hand speoimen, thin
section, and petrofabrio evidence.
Figure 4
Block diagram illustrating the proper geographical orientation of a,
b, and c at Coniston. The top ofthe block is a horizontal plane showing
the strike of S as being N50 E. The trace of the fault movement as described,
by Cooke is shown in this plane also. Maximum grain elongation, as shown by
quartz needles, is best seen in a section perpendicular to a (front face of
The S-surface and its traces, and the ac quartz girdles are shown
also. The dip of S may vary between 50oE and 900. b may be oriented 500 on
either side of its indicated orientation as shown by the dotted lines in the
block).
S-surface.
The main petrofabrio evidence which has been obtained in this study
is the existence of ansm girdle of quartz axes with minima at S and 900 from
8 ( in other
msft,
the minima are at
Inn the most
).
and
ymmetricr
l
dia-
gram (#10) the maxima correspond to those of Type II of Fairbairn, if L is
taken as parallel to b.
Imerous examples of so girdles with this type of max-
ima may be cited from geological literature.
Therefore, it
is
worthwhile to
consider several instanoes where petrofabric information similar to that found
in this suite of tocks has been recorded, and to detenmine how well the various
in
author's ideas of the mechanism of deformation explain what has been found
the rocks at Caniston.
The following examples will be noteds (each author's
work is illustrated in blook diagram byPiegures 5 A, 3, and C (next page) .)
1. Phillips' (lO)work on the Moine schist, as explained by Schmidt's flattening
bypothesis.
(Figure 5A)
2. Higgins' (7) mapping of the Pine reek area, Michigan.
3. Fairbairn's (4)
lamellae in
study of quart
( A fourth example - Johnston's (9)
(Pigure 50)
the Aibik quarstzite.
(Figure 53)
study of the Granville-Temiskaming contact -
where an so quarts girdle was found will be considered in
a later section)
Schmidt's bypothesis of rook defomation has been recapitulated by
Tuner (11)
and by Fairbairn (4).
flattening type of deformation.
In brief, it
is
sometimes referred to as a
Sohmidt's ideas as applied to Phillips' work
call upon a fixed compressional force which acts normal to what is now the foliation surface.
As a result of this aompression, individual grains within the
rook will rotate until their glide planes are approximately parallel to the shear
surfaces developed by the compression.
they may glide, but then
Once the grains have reached this position
re in what Turner (II)
(page 257) refers to as
a
Figure 5A
Deformation of the Moine schist according
to Phillips&
1. Symmetry of diagram about foliation.
2. Foliation surface as shown is horizontal
with deforming force (P) normal to it.
3. Development of ac quartz girdles parallel to direction of P.
4. Grain elongation parallel to b.
5. In the field the ac girdles lie in a
NEFSW plane.
Figure 5B.
Deformation of Ajibik
quartz-
ite according to Fairbairn:
1i.L marks the most common quartz lamellae
position as determined'by maxima of the
lamellae poles.
2. Parallel lines in quartz represent lamellas.
3. Top of block is foliation surface.
4. P is assumed orientation-of chief stress.
5. Grain elongation is parallel to a.
Figure 5C. Deformation of Pine Creek area
according to Higgins:
1. Lineation, as seen on top of block, is
marked by intersection of fault plane
and bedding.
2. asc girdle of quartz axes parallel to the
direction of fault movement.
3. Rotation about b axis, produced by the
action of a couple.
4. Direction of grain elongation unknown.
5. In the field b is vertical, and the
fault strikes NE.
43
"mechanically stable position", and the tendency will be for grains to raeain
with their gliding planes in a zone within approximately 450 of the foliation
surface.
This means that the zones between the compressive force and the shear
surfaces tend to become "forbidden" zones for the glide planes.
Schmidt's
bypothesis assumes gliding on prismatic planes in quartz, orientation of prinoipal stress perpendioular to foliation, restricted movement parallel to
is best described as a flattening process.
, and
According to this idea of restricted
flow, major elongation should take place parallel to a.
Shbmidt's ideas as applied to Phillips' work on the Moine sohiat provideaan adequate explanation for that area.
veloped, with ma
a at the expected places.
The a
girdle is partially d -
Moreover, there is a zone perpen-
dioular to the foliation surface which is relatively free of quartz axes.
For
the deformation of the Moine schists, Schmidt's hypothesis is therefore accept-
able.
The petrofabric information found in this study is in part strikingly
similar to that predicted by Schmidt (particularly Diagrams 1, 4, 5, 10; and
to a lesser extent Diagrams 2, 3, 6, 11, 14, 18, and 23).
However, certain
of the diagrame do show concentrations of maxima in the forbidden zones.
Schmidt's hypothesis is correct it
tain maxim
If
could be argued that the diagrams which con-
in the forbidden zone may be erroneous or that alignment and ro-
tation of grains has not gone to completion.
The greatest difficulties in Scbmidt's ideas as applied to the moks
at Coniston is the occurrene of elongate grains whose lengths are parallel to
_, the fact that quarts has definitely undergone fracturing and "flowed" through
the rock, and the apparent conflict with Cooke's field work, if
is reliable.
The microscopi
Cooke's work
evidence indieates that extensive fradturing of
quarts in the granite and sample #5 of the quartzite has taken place.
The be-
havior of small oruah fraents of quarts wam not considered in Scbmidt's bypothesis as originally outlined by him.
his ideas are needed if
Therefore certain modifications of
the present suite of rooks is
The action of a copressional fotoe ating
to be explained.
normal to S can easily
have accounted for the fragmentation of quarts, and flowage through the rook
to produce major elongation parallel to b.
equal stresses in
the ab plane
a lump of clay and arfall
This could be aooomplished by un-
Such a process could be likened to squeesing
restricting its
movement in the a direction.
Ma-
jor movement parallel to 1 would take place, and minor movement or elongation
parallel to a
its
The textural features of quarts fracturing and flowing of
fragments through the rook can be envisioned by this mechanism.
However,
this does not accord very well with Cooke's field evidence, nor with the idea
that major transport has been parallel to
sing
1
.
Cooke's explanation calls for a
motion with transport along what has been defined as a.
In an attempt to explain textural, field, and petrofabric evidence
it
is
of interest to consider what would happen under the action of an exterz al
shearing force, or a couple.
The fact that the process to be described seema
to the author of this report to best fit
the various avenues of evidence does
not mean that the aetion of a compressional force is precluded.
either of the two theories of deformation.
donee for eithr
There is evi-
The following ideas are
presented as a comparison of the Coniston rocks with a geologically similar
area described by Higgins (7)
The geological and petrofabric remablance between Higinsf' area in
Michigan and the 0oniston ares is striking.
Higgins studied a 16 mile long
series of northeast-tren4ing vertical fault contasct
between quartzite and Sran-
ite along thioh shear zones were developed both in the granite and the quartaite.
Higgins' field evidence indicates that the main movement along the faults
has
been in the horizontal diretion, and that a shearing force acting from the
southwest. was responsible for the movement.
He has made georaphically orien-
ted quarts petrofabric diagrams with vertical b axes corresponding with megascopio lineation.
teotonio transport.
a
is thus horizontal, corresponding to the direetion of
The lineation is marked by the interseotion of stratifi-
cation with vertical fault planes.
Higgins found that there was a consistent
tendenoy towards the development of horizontal _s girdles in both the granite
and the quartsite.
The s girdles therefore are oriented perpendicular to
the fault surface, and in particular, perpendioular to b.
With this orien-
tation picture in mind, Higgins considers that the directed shearing force
acted in a nearly hrisontal plane about a vertiat
l axi
of rotation, b.
This shearing has been correlated by Higgins with differential movement of
adjacent fault blocks, the components of any one block being acted upon by a
couple.
Higgins presents a number of individual diagrams for granite and
quartzite, as well as composite diagrws from different parts of his area.
The
oomposite diagrams (Figurea,10 and 11) of Higgins show an abanece of maxima
exactly parallel or perpeandicular to the fault surface, i.e. parallel to a or a.
His composite maxim are oriented from 150 to 600 of the horizontal torae of
-
-
the fault, and the individual d~igam
imately the same relationships.
- r
-
t
--
m~r
_____a.rl~,urn
la~iqi*~
he presents on his asp indicate approx-
Therefore it is
evident that Higgins' results
are similar to those found in the Coniston area, even down to finer detail.
Both studies were conducted in a faulted contact zone of granite and quartsite,
an so girdle of quarts axes perpendicular to the fault or shear surface and
parallel to the direction of movement is present in both areas, and there is
a common tendency for minima to occur within the girdles at
and o.
Unfortunately RH4Iins does not describe in detail the thin sections
or hand specimenas he used other than mentioning that the shezr
onestin both
granite and quartite were breeciated or cleaved along closely spaced planes,
and that crash quarts and undulatory extintion of quarts are present.
However, if
mention of grain elongation was found in Higgins' report.
is
similar to Coniston, maximum grain elongation would be parallel to
No
his area
which
is the axis of rotation and which is vertical.
The final example to be coanaidered here of quarts deformation which
has produced
o girdles with type II maxima of the type found at Comiston (Dia
gram 10) is the work by Fairbairn (4) on deformation lamellae in quartz in the
Ajibik quartaite.
gation parallel to
The Ajibik quartsite contains an S-surface with grain elne-
d
. Qarts diagrams from this give
girdles with maxim
ap~rimaely 450 on either side of S and mini= parallel and perpendicular to
S.
Iamellae poles from the quarts of these rocks have a marked concentration
in a position slightly closer to S than do the quartz axes.
The lamellae thns
appear to be associated with any one of a number of irrational quarts cxyso
tallographia surfaces making an angle of between 70 and 360 with the base.
-w
,..__-
_~_~~_
__,~
8
--
-
I
-b-----e-T
~I
L
'ir~r-igrLLI~_
C9l~CbTIPrZ
Thin section studies show that the lamellae seem to represent surfaces along
which gliding of the quarts could have taken place so as to produce elongation
parallel to
a.±
The relationships of lamellae to optical orientation and grain elon-
gation which Fairbairn shows are of definite interest in the Ajibik quartaite.
The microscope evidenoe in the rocks at Coniston seemsto indicate that the roole
have undergone a greater degree of deforation, in that instead of development
of lamellae the quarts has fracturd.
Original unorshed quarts in the massive
granite, and a single uncrushed grain in
sample 15,
showed lamellae, but other
lamlae were apparently destroyed when the quarts was grmalated
seem that lamellae should be present in
13), but none were observed.
mind, and also the fact tiat
whereas at Coeistn it
is
would
the less-deformed qua rtzites (Samples 9-
The reason for this is not known.
major elongation in
parallel to
It
kb some
the Ajibik is
With this in
parallel to a
mechanism of quarts orientation
other than translation along lamellae a~t have been active.
Up to this point the infcmation which is at hand at Coniston has
been compared with Phillips' work on the Moine sohists as seen in the light of
Solidt's hypothesis of deformation; the close similarity to Higgins' area where
a shearing and rotation &bout a vertical b axis has been active has been noted;
and mention has been made of Pairbairn's explanation by quarts lamellae of the
type of quarts maxima observed at Conistion.
Attention will now be directed
to the author's own idea as to how tne quarts behaved during defora tion, and
what eacternal forces may have been active.
-I
~ .~-__
-Ill~~_l-----l--h~~_,
--- L_
-
I
~--L~Z--~.~-dll*C
- %l~lb~l~*
UG-II-CU~Y~~L
The microscopio evidence as to why quarts in
__
the zone of main defor
mation must be regarded as breaking into small needle-like or lens-shaped frag-
ments has already been mentioned and ummmr ed.
Recent work by Bloos (1) and
by Borg and Maxwell (2) on the experimental deformation of quarts has confirmed
It
previous work mentioned by Pairbairn (4).
has been found that under high
pressures quarts 4ractures into tiny needle-like fragment many of which have
one of the rhombohedral faces (
(1011)
secondary importance is the prism face.
the quartz fragments formed b
or (01i) ) as a bounding plane; of
Borg and Maxwell found that 44% of
high pressure deformation were bounded by one
of the rhombohedral planes, and 19% of the remaining frgments by planes parE
allel to the prisms.
Sander early interpreted quartz orientation dia
reosulting from lengthise alignment of the needles in
the common bounding planes (rhombohedron, prism,
m
as
such a way that one of
or base) was parallel to ab
of the fabrio, while the needle lengths were paralltt to b, the direction of
tectonic transport.
This idneatic interpretation of petrofabrio data has
led Fairbairn to predict which quarts maxima
would be most likely to occur if
Sander's ideas are correct.
In addition to explaining quartzs maxim,
it
was necessary for Sander
to account for the various girdle patterns which have been observed.
The ex-
planation of as girdles is that of a forward movement parallel to ., assooiated
with rotational movement about b.
However,
as fairbairn (4) points out, it
is
difficult to understand why needle-like fragments whose lengths are parallel
to a should rxmain in
the s
plane upon rotation about b.
occupy should be more nearly parallel to b.
about b with the formation of an s
The position ther
(It will be recalled that rotation
girdle was Higgins'
erplanation of his
results in the Pine Creek area.)
Since Higgina'
results in an area nearly the same in every respect to
Conistion indiate rotational moveenat around 1
and Cooke's field work seems
to indicate a mdvawmet similar to that proposed by Higgins, and since quartz
needles themselves appear to be oriented parallel to b# it
is suggested
+here
that the quarts needles originally oriented with their lengths parallel to b
When the penetrative sheI ing movement along the 8-surfaces
rather than to a.
of the rocks took place the needles would essentially roll in response to ro-
tation about b.
A similar effect is produoed by placing a pencil in one hand
perpendioular to the fingers and rubbing the other hand over the pencil in a
direction parallel to the length of the fingers.
for rotation about
Such a mechanism accounts
while elongation in b is taking place.
The question new aR*ses as to what optical orientation patterns would
be expected if
such a sequence of events took place.
second edition, 1949 - page 121) ocours in the ~
III (Fairbairn -
Maximaa
plane at positions 450 on
either side of ab when the needles are oriented parallel to a.
However, if
quartz needles have their long directions parallel to bf Type III maxima will
be seen to fall in the a plane.
now lie in the a . plane.
mazaim
into
o girdles.
In like manner maxima Types V and VIII will
A ~ational movement about b could spread these
Fairbairn has listed Type III maxima as the second
most abundant type to form, sinoe its development depends upon the bounding
plane of the needles being parallel to rhombohedral faces.
Types V and VIII
are less common because of their dependence upon basal and prism faces, respeotively.
It is interesting to note that where maxima are developed (Diagram 10)
they are in the new position of the type III maxima.
Slight rotation of grains
about this maxizam could lead to maxima which were perhaps 100 to 30 away from
a or , whereas if maxima V and VIII did not tend to develop, minima in the so
girdle could be formed at a and c.
Regardless of the less convincing evidence
for the location of the various maxima and minima, this explanatio does satisfactorily account for the development of o girdles by rotation parallel to
b in a rock containing elongated elements whose lengths are parallel to b.
It is likewise possible to picture quartz needles as "flowing through the rook
to produce the observed textures by this prooeas. The relationships are piotured below.
S*-urface is
This diagram is
essentially the same as Figure 4,
and the couple could be acting in
horizontal,
except that the
either sense.
The
important features are enumerated.
1. Quartz needles in mosaio
pattern with their lengths
parallel to b.
2. Rotationofneedles in ab
plane by action of shearing
force (couple).
3. Development of ac quartz
girdles with minima at a
and c.
4. Foliation surface (parallel
to top of block), ab, de-
o
velops parallel to plane of
/shearing.
aI
a
Figure 6. Block diagram illustrating deformation at Coniston.
The mechanism of deformation which is
graphs is
15.
In
the preceding para-
consistent with the textural charactrsitios of samples 1-5, and 14samples 6-13 the textural evidence of the means by which quarts has
less clear.
deformed is
tive if
proposed in
Fracturing, as described above, could have been effec-
this was followed by reorystallisation.
However, it
is
also possible
that gliding alotgthe r(lO1) or s(0111) xhombohedral faces of quarts has taken
place.
The rhnobohedral faces make angles of approximately 400 with the ory.-
tallographic axis of quarts.
If the rhombohedral faces were to lie along the
S-surfaces (the plane of shearing),
gliding could take place in
the direction
of a and maxima could form at angles of approximately 400 from S in the so
plane.
parallel to the S-eur-
Failure of all the rhombohedral planes to lie
face could result in spreading these maxima into girdles with minima at a and
Diagram 10, made from quartsite having extren
me-etrioallylocated
axima 420460 o
either side of S.
elongation, has two
Therefore it is
possible that these maxima are the result of rhombohedral gliding.
The more
diffuse s gi*dles of Diagrams 11-24 could be the result to gliding along rhombohedral planes which were not strictly parallel to S.
The evidence for gliding in
fracturing.
quarts is
not as convincing as that for
From laboratory experiments (Bloos (1),
Borg and Maxwell(2),
and
Fairbairn(4) ) it has beaen found that quarts deforms by fracturing with bounding
planes predominantly rhomabohedral orprismatc, but
been produned.
in
haombohedral gliding has nm
In the rooks at Coniston fracturing has definitely taken place
the sazone of strongest deformation
Either gliding or fracturing (followed
by reorystalliation) could have been effective outside the main deformation sw2a
52
MRIOW OF TETONIC TRASIO
The question of whether tectonic transport is parallel or perpendioular to lineation is frea
entty referred to, and has been discussed by Fair-
bairn (4), and more recently by Turner (12).
From the material presented in
this study the direction to tectonic transport is regarded as being paraioular
to lineation.
Higgins' area also falls into the category of transport perpen-
dicular to lineation, although in his discussion lineation is caused by the
intersection of bedding and fault surfaces.
Unfortunately Hi&ins gives no
mention of the extent or direction of grain elongation.
Johnston's study (9) of the Grenville-Temisk~ning fnult contact is
not in agreement with this conclusion. Johnston did extensive mapping alon the
fron
about 25 miles to the northeast.
The geology in both oases is essentially
the same, except that Johnston finds field evidence that upward rather than
horizontal moveraent along the fault has taken place.
His description and photo-
graph (Plate 3, fig. 3) of quarts deformation are similar to what is found at
Coniston.
Johnston fund that quarts axes formed a girdle perpendicular to lin-
eation, and that within the girdle minima appeared parllel and perpendicular to
the foliation surface.
near Coniston.
These results, therefore
, are the same as those found
Johnston interprets the quarts fabrio as representing teootonic
transport parallel to lineation and perpeeniicular to the quartz girdles.
-is
petrographic evidence describing quartz deformation is not as extensive as
that presented in this study.
Nevertheless, the question of transport par-
allel or perpendicular to lineation is still open.
Further description of John-
ston's thin sections and additional study in Higgin's area where the direction
53
of movement is
known would be of considerable value in solving this problem.
SUMMARY
Whether the rooks within the
one of faulting south of Coniston have
been subjected to a compressional or shearing force cannot be established with
complete uncertainty.
Textural evidence indicates that quarts has undergone
deformation through crushing into small fragments, and apparently these frag-
ments have streamed thrawgh some of the rooks.
The fragments are elongate
par-
allel to b, with a bounding rhomboliedral plane in ab.
Petrofabri
study shows that in the zone of main deformation there
exists an easily recognized ao girdle of quartz axes, often with minima at A
and q.
In an attempt to correlate petrofabric with field and thin section evi-
£ence, it
is
conoluded that a shearing force acting as a couple could sat-
isfactorily account for all of the information.
The shearing force could pro-
duce a rotational motion 41th b as the axis of rotation.
IElongate quartz frag-
ments would have their lengths parallel to b, while transport in the direotion
of a took place.
An ap girdle could result.
A similarly faulted area studied
by Higgins reveals essentially the same petrofabric data as that found at Coniston.
There is
Higgins'
direct field evidence that a shearing force has been active in
area.
He states that various fault blocks in his area behaved as a
unit.
This is
likely what has happened at Coniston where the various b axes
dip in
different directions in
S, and the dip of the S-surface changes.
55
REPFR-EWIS CITED
1. Bloos; "Ansitropy of Quartz Frcture,' Am.
m*ourn. So. 35,
page 214, 1957.
2. Borg and Maxwell; "Interpretation ofFabric of Ekperimentally Deformed Rocks,"
Am. JournSai. 2,
page 71, 1956.
3* Cooke; "Problems of Sudbury Geology, Ontaxio," Canadian Geol. Surveq Bull #3,
1947.
otruotal Petrolo& of Defo_~ed Rocks, 2nd edition, 1949.
4. Fairbairn; S
5. Fellows "Reorysallization and Flowage in Appalachian Quartsite," Bull. Geol.
Soc. Amoer.
,
page 1399, 1943*
6. Fellows; "The Influence of Grain Selection on Quartz Disgrame," Trans. Amer.
Geopbys. Union &, page 653, 1944.
7. Higgins; "Structural Petrology of the Pine Creek Area Dickinson County,
icohigan," Journ of Geol 4,
page 476, 1947.
8. Ingerson; "Albite Trends in the Piedmont," Am. Journ. Soi.
1938*.
j,
page 127,
9. Johnston; "Geology of the Temiskm-ing-Grenville Contact Southwest of Lake
Tenagami, Northern Ontario, Canada," Bull. Geol. Soo* Amer. _,
page 1047,
1954.
10, rhillips; "A Fabric Study of Some Moine Sohists and Assooiated Rooks,*
Quart. Journ. Geol. Soc. London 21, page 581, 1937.
11. 'Turner; "Fvolution of the 1letpmorphic Rooks," Geol Soc. of Amer kem. 30, 1948.
12. Turnmr; "Lineation, Symmetry and Internal aovements in konoclinio Tootonite
ioabrics," Bull. Geol. Soc. Amer. 8,
page 1, 1957.