r
I
F
F
I
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Institute on Lake
Lake Superior
Superior Geology
Geol
Thirty-Third Annual Meeting
THE ICAPUSKASING UPLIFT: ARCHEAN
GREENSTONES AND GRANULITES
n
0
50
km
n
P
a
Wawa,
Wawa, Ontario.
Ontario
Vol.
Vol. 33, Part
Part 55
P
ii
THE
THE KAPUSKASING
KAPUSKASING UPLIFT: ARC-lEAN
ARCHEAN
GREENSTONES
GREENSTONES AND GRANULITES
GRANULITES
3.A.
3.A. Percival
Percival
Geological
Geological Survey of Canada,
Canada,
588 Booth Street
Street
Ottawa
KIA OE4
0E4
Ottawa KIA
Annual Institute
Institute on Lake Superior
Superior Geology
33rd Annual
Geology
Wawa, Ontario
Ontario
Wawa,
Vol.
33, Part 55
Vol. 33,
I
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Ã
I
I
I
TABLE OF CONTENTS
TABLE OF CONTENTS
Page
h U ZI:?GEOLOGICAL
~GE~L-FRAMEWORKOFTHEKAPU~KA~INGUPLIFT
PART
FRAMEWORK OF THE KAPUSKASING UPLIFT
Introduction
Introduction
RegionalSetting
Setting
Regional
Geophysical characteristics of south-central Superior Province
Geophysical
characteristics of south-central Superior Province
General
Geology
ofthe
theWawa
Wawa- Abitibi
Abitibi Region
General Geology of
-
-
1
1
i
1
2
Region
I)1)
Greenstone- Granite
GraniteTerranes
Terranes
Greenstone
2)2 )
WawaGneiss
GneissTerrane
Terrane
Wawa
6
6
9
9
Kapuskas'ingStructural
StructuralZone
Zone
Kapuskasing
Relationshipof
ofKapuskasing
Kapuskasingstructural
structural zone to adjacent subprovinces
Relationship
zone to adjacent subprovinces
Structure
of
the
Kap~crustal
crass-section
Structure of the Kapuskasing crustal cross-section
ATcheanevolution
evolutionofofthe
tileKapuskasing
ingcrustal
crustatstructure
structure
Archean
Uptiftofofthe
theKapuskasing
Kapustasingstructure
structure
Uplift
3)3 )
I
13
13
21
21
25
29
32
PART II: ROAD LOG
Summary
Summary
DayI:1: Stops
Stops1-1
1-ltoto1-10;
1-18;Geology
Geologyof
ofthe
the Wawa subprovince,
Day
Wawa subprovince,
Wawa
to
C
h
a
p
k
u
Wawa to Chapleau
Day
2:
Stops2-1
2-1toto2-9;
2-9sGeology
Geologyofofthe
theKapuskasing
Kapuskasing structural
Day 2: Stops
structural
zone
in
the
Chapteau-Poleyet
area
zone in the Chapleau-Foleyet area
34
34
34
39
ACKNOWLEDGEMENTS
ACKNOWLEDGEMENTS
46
REFERENCES
REFERENCES
t
\^
PARTI
PART
t
Figure1 1
Figure
F i r e22
Figure
Figure3 3
Figure
Figure44
Figure
Figure5 5
Figure
Figure66
Figure
figure7 7
Figure
Eggre88
Figure
1
1
46
LETOF
OFILLUSTRATIONS
BAUSTKATIONS
LIST
Geoiogyof
of central
centralSuperior
SuperiorProvince
Province
Geology
Geologyof
ofthe
theWawa-Chapleau-Foleyet
Wawa-Chapteau-Foleyetarea
area
Geology
Crustedthickness
thicknessininthe
theLake
LakeSuperior
Superiorarea
area
Crustal
Bouguergravity
gravitymap
m p
Bouguer
Pressurebased
basedon
enhornblende
hornblendeAl
A1content
content
Pressure
Geology of
of the
theKapuskasing
Kapuskasing structural
structuralzone
zoneand
andvicinity
vicinity
Geology
Geologyof
of the
theShawmere
Shawmereanorthosite
anorthositecomplex
complex
Geology
Metamorphicmineral
mineralassemblages
assemblagesin
inthe
theChapleau-Foleyet
Chageau-Fokyet area
Metamorphic
2
3
4
5
11
11
12
12
15
15
area 1717
U
Figure 9
Figure 10
Figure 11
Figure 12
Metamorphic reactions and P-I conditions
for Kapuskasing
granulites
Paleo-pressure map for the Chapleau_Foleyet
area
Figure 13
Concorcfia diagram for zircon samples
Gravity profile and crosssection for Kapuskasing
zone in
the Chapleau area
Seismic reflection profile
Figure 14
Figure 15
Restored vertical section
40Ar/39Ar age spectra
Page
19
21
22
23
24
26
32
PART II
Figure 22
Location of outcrops at Stop 2-5
42
3
j
J
st
I
8
PART ft
PART
b GEOLOGICAL
GEOLOGICALFRAMEWORK
FRAMEWORK OF
OF THE
THE KAPUSKASING
KAPUSKASING UPLIFT
INTRODUCTION
The purpose
purposeofofthe
the trip
trip is
is to
to examine
examine the
the characteristics
characteristics and
The
and interrelationships
interrelationships of
of
Archean
high-grade gneiss
gneiss terranes
terranes of
of the Superior
Province. A
Archean greenstone-granite
greenstone-granite and high-grade
Superior Province.
A
300-km long west
transect
westtot oeast
east
transect between Wawa
Wawa and Timmins, Ontario will be
be used ttoo
illustrate
illustrateregional-scale
regional-scale relationships.
Figure
Figure 11 shows the
the major
major geological features
features of the
theSuperior
Superior Province
Province and
and
Figure 22 traces
trip route. The
traces the
the trip
The first
first day
day will
will be spent
spent examining features
features of
of the
the
Michipicoten belt, a dominantly
dominantly metavolcanic
metavolcanic portion of the
theWawa
Wawa subprovince,
subprovince, and
and
contact
of the
contact relationships between the
the Michipicoten
Michipicoten supracrustal
supracrustal rocks and intrusions of
Wawa
domal gneiss
gneiss tterrane.
Wawa domal
Onday
daytwo,
two,the
theWawa-Kapuskasing
Wawa-Kapuskasing boundary
boundary will
willbe
be
e r r a e . On
examined,
features of
examined, as well as features
of the
theKapuskasing
Kapuskasing structural
structuralzone,
zone, including
including the
the
Shawmere anorthosite complex, high-grade
gneisses, and the Ivanhoe Lake cataclastic
cataclastic
high-grade gneisses,
zone separating
zone from
from those of
of the Abitibi
separating rocks of the
the Kapuskasing
Kapuskasing zone
Abitibi Belt.
.
REGIONAL
REGIONAL SETTING
SETTING
The Superior Province
Province is
is an
an Archean
Archean tterrane
composed of
of east-west
east-west trending belts
e r r a composed
of alternate
alternatevolcanic-rich
volcanic-rich and
and sediment-rich
sediment-rich character,
character,termed
termedsubprovinces
subprovinces(Fig.
(Fig. 1).
I).
The continuity
continuity of
of the
the east-west
east-west belts
belts is
is interrupted
interrupted by
by aa northeast-trending
northeast-trending zone
zone of
of highhighgrade metamorphic rocks,
rocks, the Kapuskasing
structural zone
zone (Thurston
(Thurstonet
et al.,
al., 1977).
Kapuskasing structural
1977). At its
its
southern end, the Kapuskasing
structure is fault-bounded
fault-bounded on
on the
the southeast
southeast but
but the
Kapuskasing structure
western contact
contactisiscomplex
complexand
and gradational
gradationalover
over120
120 km to low-grade
low-grade rocks of the
the
Michipicoten belt near
near Lake
Lake Superior
Superior (Percival
(Percivaland
and Card,
Card,1983;
1983;1985)
1985) (Figs.
(Figs. I1and
and 2).
2).
The Kapuskasing
Kapuskasing"high",
"high",aaprominent
prominentnortheasterly
northeasterly gravity and aeromagnetic
aeromagnetic
anomaly, was interpreted
indicate pronounced
interpretedby
byWilson
Wilson and
and Brisbin
Brisbin (1965)
(1965) tto
o indicate
pronounced upwarp of
the
the Conrad
Conrad discontinuity. Bennett
Bennettetetal.
al.(1967)
(1967)concluded
concluded that
that the
theKapuskasing
Kapuskasing structure
structure
is aa complex
complex horst uplifted during
during the Proterozoic.
Proterozoic. The
Theassociation
associationofof1,100-1,000
1,100-1,000 Ma
Ma
alkalic
that the
alkalic rock-carbonatite
rock-carbonatitecomplexes
complexesled
ledBurke
Burkeand
and Dewey
Dewey (1973)
(1973) tto
o suggest that
the
Kapuskasing
structure is a failed arm of the
the Keweenawan
Keweenawan rift structure.
structure. Watson
Watson(1980)
(1980)
Kapuskasing structure
postulated
postulated that
thatthe
theKapuskasing
Kapuskasingzone
zone was
was uplifted
uplifted during
during late
late Archean
Archean or
or early
early
Proterozoic sinistral transcurrent movement.
transition aatt the
movement. The
The low-to-high-grade
low-to-high-grade transition
the
southern
of the
the structure
southern end of
structurehas
has been
been interpreted
interpreted as
asan
an oblique
oblique cross-section of the
crust uplifted along an east-verging
east-verging thrust (Percival and Card,
Card, 1983).
1983). Recent
earthquakes in the region
region indicate that
that the
thestructure
structureisisstill
stillactive
active(Forsyth
(Forsythand Morel,
1982; Forsyth et
et a!.,
al.,1983).
1983).
-2-
Figure1.1. Geology
Geologyof
of the
thecentral
centralSuperior
SuperiorProvince.
Province. Inset:
Inset:positive
positive gravity anomalies
Figure
gravity
anomalies
dark
stipple
b-25
mGal);
limes
(-25
mGal
t
o
-35
mGal);
blank
(<-35
mGal).
dark stipple @-25 mGal); lines (-25 mGal to -35 mGal); blank
(<-35 mGal).
GEOPHYSICALCHARACTERISTICS
CHARACTERISTICSOF
OFSOUTH-CENTRAL
SOUTH-CENTRAL SUPERIOR PROVINCE
GEOPHYSICAL
SUPERIOR PROVINCE
mapshowing
showing apparent
apparent crustal
crustalthickness
thicknessininthe
theLake
Lake Superior region, based on
AAmap
Superior region, based on
seismic
refraction
studies,
was
presented
by
Halls
(1982)
(Fig.
3). These data show that
seismic refraction studies, was presented by Halls (1982) (Fig. 3).
These data show that
— 3—
C
C)
C
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4)
U)
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b
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4)
t
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C)
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(Ti
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4)
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C)
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a)
4.)
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o
C)
C)
Co
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o
III
IllIlillIjillIlIl
lillillIlIl
1.17
— 111,1,1,
—'t t
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r-1
Ci,
C
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a)
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Ct
>1
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C
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E
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111111r11111111,J;
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(0
Ct
—1
J
U
I
Initial 1986). Ellis, and Boland 1986; West, and Northey 1985; al., et
(Northey
interpretation of stages preliminary in still are zone, Kapuskasing the beneath structure
crustal examine to 1984 in conducted study, refraction major a of
Results
velocities. mantle and crustal averaging of necessity the to due partly
and areas some in coverage insufficient of because partly preliminary, as
thickness
crustal apparent of map contour the viewed Halls east. the to km —35 to
abruptly
drop zone Kapuskasing the beneath range km 39 the in Values zone. Kapuskasing
the of boundary eastern the with associated Moho to depth in decrease
step—like a be
to appears there addition, In Timmins. near km 35 to Wawa near
km 45 about of values
from easterly decreases Province Superior the of crust the of thickness apparent the
advised.
was map using in caution extreme and Halls
by listed are data of Sources
1982). Halls, (after area Superior Lake the in crust the of thickness Apparent
3
Figure
1
j
2
U
U
3
j
-4U
-585°
470
810
Figure 4.
Bouguer gravity map superimposed
on simplified geology. (Gravity values in
mGal), with 5 mGal Contour interval
are
from Earth Physics Branch maps 44078,
44084, 48078 and 48084). Checks
- greenstone belts; dots -Kapuskasing
unpatterned_undjyided granitoid rocks.
gneiss;
interpretation indicates that the
crust is at least 48 km thick beneath the Kapuskasing
zone and thins abruptly to about 40 km to the
southeast; high seismic velocities
characterize the high-grade rocks of the Kapuskasing
zone (0. Northey, oral
communication, 1985; Cook, 1985; Fountain and
Salisbury, 1986).
The Bouguer gravity anomaly map for the Wawa-Timmins
region is shown in
Figure 4. In general, areas underlain by
metavolcanic rocks have associated positive
gravity anomalies and granitoid..gneissic
rocks have negative anomalies. The
Kapuskasing structural zone has an assoçiate linear
positive gravity anomaly extending
—6—
from
from James
JamesBay
b y in
in the
the north
north to
t o some
some 50
50 km
km southwest
southwest of
of Chapleau.
Chapleau. In
In the
the WawaWawaChapleau.-Foleyet
Chapleau-Foleyet area, the
the gradient
gradient isisgradual
gradual on
on the
the west
west and
and abrupt
abrupt on the east,
east,
suggesting
contact between
betweenthe
theKapuskasing
Kapuskasing zone and Abitibi
Abitibi
suggesting a west-dipping contact
subprovince.
In this
thisregion,
region,the
thegravity
gravityprofile
profile(Fig.
(Fig.12)
12)shows
shows aa paired
pairedhigh—low
high-low
subprovince. In
anomaly.
anomaly. The
The trough
trough of
of the
the low
low is coincident with the fault
fault at
a tthe
theeastern
easternboundary
boundaryof
of
the
the Kapuskasing
Kapuskasing zone.
zone.
To the north,
as itit coalesces
coalesces with
with the
the
north, the
thepositive
positiveKapuskasing
Kapuskasinganomaly
anomaly broadens
broadens as
east-west
east-west gravity
gravity high
high associated with
with the
the Quetico-Opatica
Quetico-Opatica metasedimentary
metasedimentary
subprovince.
J
j
1 GENERAL
GENERAL GEOLOGY
GEOLOGY OF
OFIL-fE
THE WAWA
WAWA -- ABITIBI
ABITIBI REGION
REGION
Three
Three distinct
distinct types
types of
of terrane
terraneare
arerecognized
recognized in
inthis
thispart
partof
ofthe
theSuperior
Superior
Province:
Province: 1) greenstone-granite
greenstone-granite belts,
belts, 2)
2) regions
regionsdominated
dominated by
by orthogneiss
orthogneiss in
in the
the
amphibolite fades,
facies, and 3)
3)heterogeneous
heterogeneousgneisses
gneisses in
in the
the granulite
granulite to
t oupper
upper amphibolite
amphibolite
fades.
facies. Differences between terranes
terranes in
in metamorphic
metamorphic grade
grade and
and pressure
pressure suggest
suggest that
that
the
the terrane
terranetypes
typesrepresent
representcrustal-scale
crustal-scaleniegalayers
megalayers(Percival
(Peruvaland
andCard,
Card,1985),
1985),the
the
components
components of the
the upper
upper and
and middle
middle continental crust.
crust. The
TheWawa
Wawaand
and Abitibi
Abitibi belts
belts are
are
greenstone-granite terranes;
of terrane type
terranes; the
theWawa
Wawa gneiss terrane is an example of
type 22
and
zone represents type
and the
the Kapuskasing
Kapuskasing zone
type 33 terrane
terrane(Fig.
(Fig. 2).
2).
~
j
j
4.:
1)
1)
Greenstone-Granite
Greenstone-Granite Terranes
Terranes
a
The
partofofthe
thevolcanic-rich
volcanic-richWawa
Wawasubprovince,
subprovince,Isiscomposed
composed
The Michipicoten
Michipicoten belt, part
mainly
IC and
mafic
andfetsic
felsiccomposition
composition(Goodwin,
(Goodwin,
mainly of metavolcanic
metavolcanicrocks
rocksofofultrarnafic,
ultramafic,maf
1962),
with intercalated
intercalated greywacke,
1962), with
greywacke, conglomerate, chert
chertand
andiron
iron formation,
formation,mainly
mainly
siderite.
as well as downward-facing
downward-facing strata
strata
siderite. Dome
Dome and basin structures
structures(Goodwin,
(Goodwin, 1962)
1962) as
and
and overturned
overturned structures
structures(Attoh,
(Attoh, 1980)
1980)have
have been recognized.
recognized. Metamorphic
Metamorphic grade
grade
ranges
amphibolite facies
facies (Fraser
(Fraser et al.,
ranges from sub-greenschist
sub-greenschist to amphibolite
al., [978).
1978). Several
Severalsuites
suitesof
of
intrusive
ranging from
from peridotite
peridotite to
intrusive rocks
rocks include
include synvolcanic
synvolcanic bodies ranging
t o granodiorite,
granodiorite,
younger
younger granodiorite
granodiorite batholiths,
batholiths, and
and still
stillyounger
younger granite
graniteand
andsyenite
syeniteplutons
plutons
(Card,
(Card, 1982).
1982).
The
of the southern part of
The supracrustal rocks
ro
of the
the belt
belt were
weredivided
divided into three
three
major
(1962). A lower
lower cycle,
cycle, consisting of
of roafic
major cycles
cycles by
by Goodwin
Goodwin (1962).
rnafic and felsic
felsic volcanics,
volcanics,
isis capped
iron formation,
formation, mainly
mainly siderite,
siderite, but with lesser pyrite-,
capped by
by Michipicoten-type
Michipicoten-type iron
U
-
7
r
—7-
I
chert- and
and graphite-rich
graphite-rich rocks.
rocks. The
Theassociated
associatedJubilee
JubileeStock,
Stock,aa high-level
high-level subvolcanic
SU~VO~C~N
intrusion, was
was emplaced
emplaced within aa caldera
caldera structure
structure(Sage,
(Sage, 1980).
1980). The middle cycle
cyc
Icvolcanics
volcanicsoverlain
overlain by
byclastic
clastic metasediments
metasediments and
and
comprises maf
comprises
mafic
and felsic tuffs an
breccias. The
breccias.
The clastic
clasticsediments,
sediments, including
including the
the Doré
Dor6 conglomerate,
conglomerate, wacke,
wacke, siltstone,
siltstone, and
an
I
crossbeddedarkose,
arkose,a are
thef facies
equivalentsofof the
the felsic
felsic pyroclastics and
crossbedded
r e the
a d e s equivalents
and are formed
mainly of detritus
detritus eroded
eroded from the
t h e felsic
felsic centres.
centres. The
Theupper
upper cycle
cycle comprises
comprises
intermediate to felsic
-dacite) tuffs
tuffs and
quartz-feldspar porphyry.
porphyry. Recent
felsic (andesite
(andesite -&cite)
and quartz-feldspar
Recent
(pers.comm.,
comm., 1986)
1986)indicates
indicatesonly
onlytwo
twocycles
cycleswithin
within tthe
work by Sage
Sage (pers.
h e main volcanic pile.
The Abitibi
Abitibi subprovince
The
subprovince is
is dominated
dominated by a thick
thick sequence
sequence of volcanic
volcanic and
and
I
J
I
I
I
I
I
fl
of the
sedimentary rocks of
t h e Abitibi
Abitibigreenstone
greenstonebelt
belt(Jensen,
(Jensen, 1981;
1981; 1985).
1985). The supracrustal
successiontypically
typically comprises
comprisessequences
sequencesofofultramafic,
ultramafic, mafic,
mafic, and
and felsic
felsic volcanics.
succession
volcanics.
high proportion of volcanic
volcanic detritus.
detritus.
Intercalated turbiditic
turbiditicsedimentary
sedimentary rocks
rocks contain
contain aa high
In the Abitibi
Abitibibelt,
belt,the
t h euppermost
uppermostgroup,
group, the
t h eTimiskaming,
Timiskaming,isisan
anunconformity-bounded
unconformity-bounded
sequenceofof alkal~c
alkalic volcanics and fluviatile
fluviatile sediments
sediments(Hyde,
(Hyde,1980)
1980) localized
localized along
along major
major
sequence
east-west fault
east-west
faultzones.
zones.
Large areas
areas of
of the Abitibi
Abitibi greenstone
Large
greenstone belt
belt are
aremetamorphosed
metamorphosed to
t o greenschist
greenschist
prehnite-pumpellyite Ifacies
acies rocks
rocks are common
common in
in tthe
Timminsh e Timminsffacies;
a d e s ; subgreenschist,
subgreenschist, prehnite-pumpellyite
Rouyn area
areaand
andnarrow
narrowaureoles
aureolesofofamphibolite
amphibolite ffacies
rocks occur
occur adjacent
adjacent tto
Rouyn
a d e s rocks
o plutonic
plutonic
bodies (Jolly,
(Jolly, 1978).
1978).
The supracrustal
supracrustal rocks
rocks of
of the Abitibi
The
Abitibisubprovince
subprovince display
display evidence
evidence of polyphase
polyphase
orientations.
deformation in the
t h e form
form of
of major
majorand
and minor
minor structures
structuresof
ofseveral
severalages
ages and orientations.
In the Abitibi
Abitibigreenstone
greenstone belt, older northerly-trending folds
folds are
are overprinted
overprinted by
by easteaststructures
west trending major and minor folds, forming
formingmajor
major dome
dome and
and basin
basin structures
(Pyke,
1982). The
Themajor
majorisoclinal
isoclinal folds
folds with
with east-west
east-west striking
striking subvertical
(Pyke, 1982).
subvertical axial
axialplanes,
planes,
steeply-plunging
minor folds,
folds, subvertical axial plane foliation,
foliation, and
steeply-plunging minor
and steeply
steeply plunging
plunging
stretching
stretching lineation
lineation were
were probably
probably formed
formed under
under subhorizontal,
subhorizontal, generally
generally north-south
north-south
major compression.
compression. Toward
Towardtthe
southernmargin
marginofofAbitibi
Abitibi belt the
major
h e southern
t h e major folds are
overturned northward, and
and in the
the adjacent
adjacent Pontiac
Pontiac subprovince,
subprovince; folds
folds are
a r e recumbent.
recumbent.
The
Cadillac-Larder Lake fault
fault zone,
between tthe
Abitibi
The Cadillac-Larder
zone, which constitutes the
the boundary
boundary between
h e Abitibi
and
probably has
hasboth
both transcurrent
transcurrent and
and thrust components
and Pontiac subprovinces,
subwovinces. orobablv
comDonents of
movement.
Several suites of intrusive rocks in the Abitibi subprovince can be distinguished on
I
I
of composition,
composition, structural
structural relationships,
the basis
basis of
relationships, setting,
setting,and
andage
a g e(Card,
(Card, 1982).
1982). The
The
sills, dykes and
and plutons
plutons ranging
rangingin
in composition
composition from
from
oldest suite includes synvolcanic sills,
peridotite
typically quartz diorite
peridotite to
t o granodiorite;
granodiorite; the more
more felsic intrusions aare
r e typically
diorite and
and
trondhjemite. Gneissic
Gneissic plutonic
plutonic rocks
rocks of
of tonalite
tonaliteand
and granodiorite
granodiorite composition,
composition,
—8—
commonly
containing amphibolitic
amphiboliticenclaves,
enclaves, occur
occur in
in the
the northeastern and
commonly containing
and southwestern
southwestern
Abitibi
subprovince. Massive
felsic plutonic
plutonic rocks
rocks intrude
intrude both
both the
the greenstones and the
Abitibi subprovince.
Massive felsic
gneissic rocks in
in the form of simple and
and composite
composite plutons
plutons and
and batholiths.
batholiths. They
They form
several suites,
suites, including
including early
early granodiorites,
granodiorites, younger
younger granite
granite batholiths,
batholiths, and
andstill
stillyounger
younger
syenite-diorite plutons.
plutons. Contacts
Contactsbetween
between the
theplutons
plutons and
and the
the country
country rocks
rocks are
are
commonly
concordant and
and steeply
steeply dipping;
dipping;dominant
dominanteast-west
east-weststructural
structural trends are
commonly concordant
are
locally deflected about
about the
theintrusions.
intrusions.
A time framework for events
events in
in the
theMichipicoten
Michipicoten and
and Abitibi
Abitibi belts
belts can
can be
be
constructed
U-Pb zircon dates. In the western Abitibi
Abitibi belt, volcanic
volcanic rocks
rocks range in
in
constructed from
from U-Pb
age from
Nunes and
and Jensen,
Jensen, 1980),
with late
late
to 2,703
2,703 Ma
Ma (Nunes and Pyke, 1980;
1980; Nunes
19801, with
from 2,725
2,725 to
alkaline
Group) aatt 2685 Ma,
Ma, and
and in
in the
the Michipicoten
Michipicoten belt, from
from
alkaline volcanics
volcanics (Timiskaming
(Timiskaming Group)
2,749
a t 2737,
2737, 2744
2744 (Turek
(Turek et
etal.,
al., 1982)
1982)and
and2745
2745
2,749 tto
o 2,696 Ma, with synvolcanic plutons at
Ma
(Sullivanetetal.,
al., 1985).
1985). A number
numberofoflatelate- ttoo post-tectonic plutons
M a (Sullivan
plutons from
from the
the Abitibi
Abitibi
and Michipicoten
Michipicoten belts have zircon dates
dateswithin
within aafew
fewmillion
million years
yearsof
of2,680
2,680(Icrogh
(Krogh
et
et al.,
al., 1982;
1982;Frarey
Frareyand
and Krogh,
Krogh, 1986).
1986). Thus
Thus the
themain
main Abitibi
Abitibi and
and Michipicoten
Michipicoten
supracrustal
supracrustal sequences
sequences and
and early
earlyintrusions
intrusionsdeveloped
developed between
between 2,750
2,750 and
and 2,700
2,700 Ma
Ma ago.
The dates on volcanics
and late
late plutons bracket the
volcanics and
the age
age of
of deformation
deformation and
and regional
regional
metamorphism
Ma
ago. Major
a ago.
Major volcanic, plutonic, and
metamorphism aatt between
between 2,700
2,700 and 2,680
2,680 M
tectonic
tectonic events
events of
of relatively
relatively brief
brief duration
durationwere
wereessentially
essentiallysynchronous
synchronous throughout
throughout the
Abitibi and Wawa
subprovinces, a region some 1,200
km wide.
wide. The
Wawa subprovinces,
1,200 km long and 200 km
The
lithologic and age similarities
similaritiesbetween
between the
theAbitibi
Abitibiand
andWawa
Wawa subprovinces
subprovinces strongly
strongly
suggest original continuity, now
structural zone.
now interrupted by the Kapuskasing
Kapuskasing structural
Diabase dyke
dyke swarms
swarms of
of late
late Archean
Archean and
and Proterozoic age are present
present
throughout
throughout the region. The
Theoldest
oldestdykes,
dykes, the
thenorth-trending
north-trending Matachewan
Matachewan swarm
swarm of
of the
the
Abitibi subprovince,
Rb-Sr age
age of
of 2633
2633 Ma
Ma (Gates and Hurley,
Hurley, 1973).
1973). NorthwestNorthwestsubprovince, have a Rb-Sr
striking
subprovince are
are petrographically
petrographically similar to
t o and
and have
have been
been
striking diabase
diabase dykes
dykes in
in Wawa
Wawa subprovince
paleomagnetically correlated
correlatedwith
withthe
theMatachewan
Matachewanswarm
swarm(Ernst,
(Ernst,1981;
1981;Ernst
Ernstand
and
paleomagnetically
Halls,
subprovincesare
are thus
thus inferred
inferred ttoo have been tectonically
Halls, 1984).
1984). Abitibi
Abitibi and Wawa
Wawa subprovinces
tectonically
time. Northeast-striking
Northeast-striking tholelltic
tholeiiticdykes
dykesare
areabout
about2105
2105Ma
Ma old
old
stable cratons
cratons by
by this time.
stable
(Gates
1973);northwest
northwest olivine diabase
diabase dykes
(Gates and
and 1-lurley,
Hurley, 1973);
dykes (Sudbury
(Sudbury swarm)
swarm) are
a r e about
about
1250 Ma
Ma old
old (Van
(VanSchmus,
Schmus,1975);
1975);and
andeast-northeast
east-northeast olivine diabase
diabase dykes
dykes (Abitibi
(Abitibi swarm)
swarm)
are
M aold
old(Lowden
(Lowdenand
andWanless,
Wanless,1963).
1963).
are approximately
approximately1100
1100Ma
r
1
2)
2)
4
I
I
I
I
$
I
I
I
I
I
I
I
The
belt is intruded
intruded ttoo the
The Michipicoten
Michipicoten belt
the southeast
southeast by
by tonalitic
tonalitic gneiss and plutons
plutons
of
gneiss terrane
terrane (Fig.
2). The
consist of
of aatt least
of the
theWawa
Wawa domal
domal gneiss
(Fig. 2).
The rocks in this region consist
least
four
four lithologic
lithologic components:
components; (1)
(1)hornblende-plagioclase
hornblende-plagioclase ±+ clinopyroxene
clinopyroxene mafic and rare
rare
paragneiss
paragneiss xenoliths,
xenoliths, ranging
ranging from centimetres
centimetresto
totens
tensofofmetres
metresininmaximum
maximumdimension,
dimension,
making
most
makingup
up55to
to 50%
50% of
of individual
individual outcrops, and enclosed in (2) the volumetrically most
abundant
abundant phase,
phase, hornblende-biotite
hornblende-biotite tonalitic
tonaliticgneiss
gneisswhich
which is
iscut
cutby
by (3)
(3) concordant
concordant to
to
discordant
discordant layers
layers of
of foliated
foliatedto
t ogneissic
gneissicbiotite-hornblende
biotite-hornblende granodiorite,
granodiorite,which
whichin
in turn
turn
are
arecut
cutby
by (4)
(4)late
late discordant
discordant quartz
quartz monzonite
monzonite pegmatite. Xenolith-rich
Xenolith-rich tonalitic
tonaliticgneiss
gneiss
units
units alternate
alternateon
on aa 55 to
to 10
10 km
krn scale with xenolith-poor
xenolith-poor units and can be
be traced
traced for
for
distances
distances of
of at
a tleast
least50
50km.
km. Layering
Layeringininmafic
maficxenoliths
xenolithsisislocally
locallydiscordant
discordant to
tolayering
layering
in
in enclosing
enclosing gneiss.
gneiss. Small
Small folds
folds of
of layering
layering in
in tonalitic
tonaliticgneiss
gneiss are
arecommonly
commonly truncated
truncated by
by
layers
layers of
of foliated
foliatedgranodiorite.
granodiorite. Tonalite
Tonalitegneiss
gneisshas
hasa aminimum
minimumU-Pb
U-Pb zircon
zirconage
ageof
of2707
2707
Ma,
M a(Percival
(Percivaland
andKrogh,
Krogh,
Ma, partly
partly reset
resetby
bythe
theintrusion
intrusionofofgranodiorite
granodioritesheets
sheetsata 2677
t 2677Ma
1983)
1983)(Fig.
(Fig. 5).
5). The
The layers
layers of
of granodiorite
granodiorite on
on the cm
cm to
to km
km scale
scale in the
the gneiss
gneiss terrane
terrane can
can
be
be correlated
correlatedby
byzircon
zircongeochronology
geochronologywith
with discordant
discordantplutons
plutonsof
of 2680
2680Ma
Ma age
age in
in the
the
greenstone
greenstone belts,
belts, suggesting
suggesting that
that the
the plutons
plutons have
have deep roots in the gneissic
gneissic terrane.
In
In the
the area
areabetween
betweenthe
theMichipicoten
Michipicotenbelt
beltand
andKapuskasing
Kapuskasingzone
zone (Fig.
(Fig. 2)
2) the
the
orientation
orientationof
of foliation,
foliation,gneissosity
gneissosityand
and axial
axial surfaces
surfacesof
of small
smallfolds
foldspermit
permitdefinition
definitionof
of
several
severalstructural
structuraldomains
domainscharacterized
characterizedby
bydomal
domalgeometry
geometry(Fig.
(Fig. 6).
6). The
Thespacing
spacing of
of
major
major domal
domal or
or antiformal
antiformalculminations
culminations is
is on
on the
the order
order of
of 20
20 to
t o25
25 km,
km, although
althoughmany
many
smaller
smaller culminations
culminations are
arealso
alsopresent.
present.The
TheHighbrush
HighbrushLake
Lakeand
andRacine
RacineLake
Lakedomes
domeshave
have
cores
coresof
of tonalite-granodiorite
tonalite-granodioritegneiss
gneisswhereas
whereasthe
theChaplin
C h a p lLake
i Lakedome
domeand
andMissinaibi
MissinaibiLake
Lake
arch
planar fabric
fabricin
in the
the
archhave
have granitic
graniticcores
coresflanked
flanked by
by foliated
foliated to
to gneissic
gneissic rocks. AAplanar
homogeneous
homogeneous granitic rocks, defined by
by lenticular quartz
quartz and
and biotite
biotitealignment,
alignment,isis
generally
generally concordant
concordant to
t ogneissosity
gneissosity in
in mantling
mantling gneiss.
gneiss. The
Thestructural
structuraldomes
domesmay
maybe
be
related
relatedtotothe
theemplacement
emplacementofofplutons,
plutons,possibly
possiblyby
bydiapiric
diapiricrise.
rise.The
TheRobson
RobsonLake
Lakedome,
dome,
adjacent
adjacentto
t othe
theKapuskasing
Kapuskasiig structural
structuralzone,
zone, has
has aa core
coreof
of interlayered
interlayeredmafic
maficgneiss,
gneiss,
paragneiss
paragneiss and
and tonalitic
tonaliticgneiss.
gneiss.
InIngeneral,
general,asymmetric
asymmetricsmall
smallfolds
foldsofofgneissic
gneissiclayering
layeringdo
donot
nothave
have aa consistent
consistent
sense
senseof
of asymmetry
asymmetrywith
with respect
respectto
todomal
domalculminations
culminations and
and are
are therefore
thereforenot
notcongruent
congruent
with
withthe
thedomes.
domes. Near
Nearsome
somedomal
domal crests,
crests,the
theorientation
orientationofofgneissic
gneissiclayering,
layering,small
small
folds
are widely variable to chaotic and definee aa pattern
foldsand
and lineations
1
patternof
ofcoalescing
coalescing
domes.
domes.
I
Wawa
Wawa Gneiss Terrane
Terrane
- 10 -
geobarometer for calc-alkaline igneous rocks is based on the Al content of
hornblende (l-lammarstrorn and Zen, 1986):
A
P=
—3.92 +
5.03
Allotal
Application of the barometer to a suite of tonalites from the Wawa gneiss terrane
suggests
suggests that
thatthe
thepressure
pressureofofigneous
igneouscrystallization
crystallizationincreases
increasesfrom
fromabout
about55kbar
kbarininthe
the
central
over
Kapuskasing
6 kbarnear
nearthe
the
Kapuskasingzone
zone(Fig.
(Fig. 5).
5). These
These
centralpart
partofofthe
theterrane
terranetoto
over6 kbar
results
areintermediate
intermediatebetween
betweenindependent
independentpressure
pressureestimates
estimatesfor
forthe
theMichipicoten
Michipicoten
resultsare
belt
basedon
onsphalerite-pyrrhotite
sphalerite-pyrrhotitegeobarometry
geobarometry(Studemeister,
(Studemeister,1983)
1983)and
and
beltof
of2-3
2-3kbar,
kbar, based
for
6-8kbar
kbarbased
basedon
ongarnet-pyroxene-plagioclase_quartz
garnet-pyroxene-plagioclase-quartz
forthe
theKapuskasing
Kapuskasingzone
zoneof
of6-8
barometry
barometry(Percival,
(Percival,1983).
1983).AAvalue
valueofof8 8kbar
kbarnear
nearWawa
Wawaisisderived
derivedfrom
fromaabiotite
biotite
tonalite
tonalhewhich
whichcontains
containshornblende
hornblende only
on adjacent to contacts with amphibolite; the
hornblende
hornblendeisisprobably
probablyxenocrystic.
xenoaystic.
Metasedimentary
Metasedimentaryrocks
rocksoccur
occurini two locations in the eastern Wawa subprovince.
AAdiscontinuous,
discontinuous, antiformal
antiformalto
t odomal
domalbelt
beltofofparagneiss
paragneisswest
westofofthe
theRacine
RacineLake
Lakedome
dome
may
6).
maybe
becontinuous
continuous to
t othe
theeast
eastwith
withparagneiss
paragneissofofthe
theKapuskasing
Kapuskasingzone
zone(Figs.
(Figs.22and
and6).
Stretched-pebble
Stretched-pebble metaconglomerate
metaconglomerateoccurs
occursininassociation
associationwith
withquartz
quartzwacke
wackeand
and
amphibolite
Thepolymictic
polymictic(tonalite,
(tonalite,granodiorite,
granodiorite,metame
amphibolitein
inthe
thevicinity
vicinityof
of Borden
Borden Lake.
Lake. The
andesite,
andesite,metasediments,
metasediments,amphibolite,
amphibolite,vein
veinquartz),
quartz),clast-supported
clast-supported rock
rockcontains
contains
cobbles
cm)with
withaaprominent
prominentshallow
shallow
cobblesranging
rangingfrom
fromequant
equanttotoconstricted
constricted(1.5
(1.5mmx x7 7x x7 7cm)
northeast plunge. In cross-section the clasts vary from equidimensional to northwestdipping ellipses.
The Floranna Lake complex is a strongly lineated and foliated complex crescentic
pluton
plutonof
ofintermediate
intermediatecomposition
compositionthat
thatoccurs
occursbetween
betweenthe
theRobson
RobsonLake
Lakeand
andRacine
Racine
Lake
medium-grained
Lakedomes.
domes. The
Themargins
marginsofofthe
thecomplex
complexare
arefinefine-toto
medium-grainedhypersthene.hypersthenebiotite
contains
medium-grained
biotitegranite,
granite,whereas
whereasthe
thecore
core
contains
medium-grainedrnonzonite
rnonzoniteand
anddiorite
dioritewith
with
rare
raregabbro
gabbroand
andcoarse
coarsebiotite-clinopyroxene
biotite-clinopyroxene melagabbro
melagabbrolayers.
layers. The
Theleast-deformed
least-deformed
interior
igneous(?)
interiorportions
portionscontain
containrelict
relict
igneous(?)clinopyroxene
clinopyroxeneand
andfeldspar
feldsparaugen
augenphenocrysts.
pheno
Migmatitic
Migmatiticquartz
quartzmonzonite
monzonitelayers
layersconstitute
constituteupuptot o10%
10%ofofsome
someoutcrops.
outcrops.The
The
complex
complexhas
hassimilar
similarstructural
structuraland
andlithological
lithologicalcharacteristics
characteristicstotocrescentic
crescenticplutons
plutonsofof
the
theWabigoon
Wabigoonsubprovince
subprovinceof
of northwestern
northwesternOntario
Ontario(Schwerdtner
(Schwerdtneretetal.,
al.,
1979,1983;
1983
1979,
Sutcliffe
1979).
Sutcliffeand
andFawcett,
Fawcett,
1979).
The
donial
region
a semi-continuous
Theeastern
easternlimit
limitofofthe
the
domal
regionis is
a semi-contin"ous zone
zoneofofnorth,
north,
northeast
easterly-dipping
and
northeastand
andnorthwest
northweststriking,
striking,gently
gently
easterly-dippinggneissosity
gneissosity
andeasterlyeasterlyplunging
6)6may
plunginglineation.
lineation. This
Thiscurvilinear
curvilinearfeature
feature(Fig.
(Fig.
) mayrepresent
revresentthe
theeastern
easternextremity
extremity
I
I
I
I
I
I
I
— 11
2.6
0
0
a)
Ia
-0
interior
intermediate
edge
8
S
S.-
I.
U
(3)
¼
I
I
a
S
a2E
6-
(I,
0
4
(4
Lu
—
0
0
•
.40
••
5
A
150
Wowa
I
&ne/ss
Terr one
100
I
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-
—
.
50
L8r()
N
Structural
Zone
I
I
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ao
>'
0
Kop uskasing
S
0
A.4
I
p
p
2
I_
'4' ----------
0
9-1.6
C
Distance
Distance from
from Ivanhoe
Ivanhoe Lake
Lake cataciastic
cataclastic zone, km
km
Al/n
A/ in
Horn
b/en de Barometer
Hornblende
Barometer
............
...,.........
..
b'}
. .. . . .,
Wa wa/ /
4•97
I
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I
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•1 24
0
0
I
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r
0
-S.
1*
I
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—
to 11.0
&ne/ss
V
/
A bit/b
-
V
,
,.
/
Belt
5.1
Terrane
50
0
km
Figure
Figure 5.5. a)a) Plot
Plotof
ofhornblende
hornblende composition
composition vs
vs spatial
spatial distribution.
distribution. Vertical
Vertical array
arrayof
of
points represents
representswithin-sample
within-sample compositional variation.
Hornblende at
a t far
far left
leftisis
points
variation. Hornblende
probably xenocrystic,
xenocrystic, from
from adjacent
adjacent amphibolites
amphibolites of
of Michipicoten
Michipicoten belt. Dashed-line
Dashed-line box
box
probably
representsindependent
independentpressure
pressure estimates
estimatesfrom
fromgranulites
granulitesofofthe
theKapuskasing
Kapuskasing zone.
zone.
represents
b)b) Map
Map showing average pressure in kbar,
kbar, based
based on
on hornblende
hornblende geobarometry
geobarometry
in
in the
theWawa-Chapleau
Wawa-Chapleau area.
area.
63'Oo'
LEGEND
Proterozoic
Alkalic rock—carbonatite complex: I: Lackner Lake complex;
n: Nemegosenda Lake
Lake complex;
comple%s:
a: Shenango
Shenango complex
Complex
1100
t i 0 0 Ma
Ma intrusions
intrusions
Archean
I
m
+
massive granite, granodiorite,
grenodiorite, with minor
minor tonalite
tonalite
diorite—monzonite
intrusive complex; minor hornblendite, granite
diorite-monzonite intrusive
2707-2668 Ma
Me sequence
sequence
2707—2668
foliated
foliated to
to flaser
flaser tonalite
tonalite
I@
tg;4
tonalite—granodiorite
tonelite-granodiorite gneiss;
gneis
metavolcanic
metavolcanic rocks,
rocks, mainly
mainly metabasalt
metabasait
.
::
----------
~....'
-
Shawmere
Shawmere anorthosite
anorthositecomplex:
complex: metamorphosed
metamorphosed gabbroic
gabbroic anorthosite,
anorthosite,
anorthosite,
anorthosite, gabbro,
gabbro, minor
minor tonalite
tonalite
pre—2765
pre-2765 Ma sequence
sequence
Amq
gneiss:
highhigh
Ca,AI
basaltic
composition,
with
gneiss:
Ca,AI
basaltic
composition,
withtonalitic
tonaliticleucosome
ieucosome
"fl-i,maficmafic
lAp
0
'
/
^
2749-2696 Ma sequence
sequence
2749—2696
flaser
ic tonalite
flaser diorite
dioritetotomat
mafic
tonalite— includes
inciudesminor
minorgabbro,
gabbro
.._.:j
.-.--hornbiendite, granodiorite
granodiorite
hornblendite,
"'Bsojl
I
metasedimentary
metasedimentery rocks
rocks (includes
(includes metaconglomerate
metaconglomerste with
with tonalite
tonalite
cobbles
zircon date
date of
of 2664±12
cobbles with
with aa U—Pb
U-Pb zircon
2664±1Ma)
Ma)
paragneiss- quartz-rich
paragneiss—
quartz—richcomposition,
composition,wi
with up to 15% tonalitic leucosome
—
fault;
fault; Ivanhoe
ivanhoe Lake
Lake cataclastic
cstaclasticzone
zone
Figure
Figure 6.
6. Geology
Geologyof
ofthe
theiCapuskasing
Kapuskasing structural
s t r u c t u r a l zone
zone and
and vicinity.
vicinity.
I
I
I
I
I
I
I
-
I
-13of
of aa first-order
first-order dome
domeof
of 75-100
75-100 km
km diameter,
diameter, of
of which
which the
t h e individual
individual structural
structural domains
domains
are
a r e higher-order
higher-order domes
domes of
of similar
similarscale
scaleand
andspacing
spacingtot othose
thoseofofthe
theWabigoon
Wabigoonsubprovince
subprovince
(Schwerdtner
(Schwerdtner and
and Lumbers,
Lumbers, 1980).
1980).
Dome development
development can
can be
be temporally
temporally related
related to
t o the
the formation
formation of
of minor
minor
structures
structuresin
in gneiss.
gneiss. The
Thediscordant
discordant foliations
foliationsin
in mafic
mafic gneiss
gneiss predate
predate the
thegneissic
gneissic
layering
layering in the tonalite-granodiorite
tonalite-granodiorite host.
host. Small
Smallfolds
foldsof
of this
thisgneissic
gneissiclayering
layering in
in turn
turn
predate
layers. Crosscutting
predate intrusion
intrusion of granodiorite layers.
Crosscutting pegmatite
pegmatite dykes
dykes and
and sills are still
still
younger
younger and are
a r e probably
probably the
t h e same
same age
age as
asthe
thehomogeneous
homogeneous plutonic
plutonic rocks
rocks which
which locally
locally
have
by lenticular quartz grains,
have a planar
planar fabric defined by
grains, biotite alignment,
alignment, fracture
fracture
cleavage,
of granulation.
granulation. The
cleavage, or minor
minor planar zones of
The absence
absence of aa consistent
consistent sense
sense of
asymmetry
asymmetry of small
small folds with respect to
t o domal
domal culminations
culminations and the
t h e random
random orientation
orientation
of
of re-orientation
of small
small folds
folds near dome crests argue in favour of
re-orientation of
of pre-existing
pre-existing small
small
folds
layering during
duringthe
the latest
latest doming.
doming. The
folds and gneissic
gneissic layering
The quartz-lenticle foliation
foliation and
and
fracture
plutonic rocks
rocks cannot
cannot be
be readily
readily attributed
attributed to
fracturecleavage
cleavagein
inhomogeneous
homogeneous plutonic
to
magmatic
magmatic flow
flow and therefore suggest
suggest that
that the
the plutons
plutons were
were emplaced
emplaced at their
their present
present
structural
structurallevel
levelat
a tsub-solidus
sub-solidus temperature, possibly
possibly relating to
t o late
l a t e diapiric
diapiric rise.
rise.
3)
Kapuskasing Structural Zone
The
The Kapuskasing
Kapuskasing structural zone
zone comprises
comprises northeast-striking, northwest-dipping
northwestdipping
belts
tonalite, and
belts of
of paragneiss,
paragneiss, mafic
mafic gneiss,
gneiss, gneissic
gneissic and xenolithic tonalite,
and rocks
rocks of
of the
the
Shawmere
Shawmere anorthosite
anorthosite complex
complex (Bennett
(Bennett et
et al.,
al., 1967;
1967; Thurston
Thurston et
et al.,
al., 1977)
1977)
(Figs.
(Figs. 22 and
and 6).
6).
Migmatitic
layered with
with garnet, biotite,
Migmatitic paragneiss
paragneiss is compositionally layered
biotite, quartz-rich
quartz-rich
and
and rare
rare graphitic
graphitic varieties.
varieties. Concordant
Concordanttonalitic
tonaliticleucosome
leucosome constitutes
constitutes up
up to
to
20
Ic gneiss
20 per
per cent
cent of
of many
many outcrops.
outcrops. Enclaves
Enclavesand
andlayers
layersofofmaf
mafic
gneiss in
in paragneiss
paragneiss occur
occur on
on
the
the10
10cm
cm to
t o 11km
km scale.
scale. Migmatitic
Migmatiticmafic
maficgneiss
gneiss isis characterized
characterizedby
by garnetgarnetclinopyroxene-hornblende-plagioclase-quartz-ilmenite+orthopyroxenemineral
mineral
clinopyroxene-hornblende-plagioclase-quartz-ilmenite÷orthopyroxene
assemblages
assemblages and
and generally contains concordant tonalitic
tonalitic leucosome.
leucosome. Layering,
Layering, on
on the
the
i1to
t o10
10cm
c m scale,
scale,isisproduced
produced by
by variable
variable proportions
proportions of minerals.
minerals. Table
Table11presents
presentstwo
two
sets
setsof
of whole-rock
whole-rock analyses
analyses from
from adjacent
adjacentanhydrous
anhydrous (garnet-clinopyroxene-plagioclase(garnet-clinopyroxene-plagioclasequartz)and
and hornblende-bearing
hornblende-bearing layers from mafic gneiss in two different locations.
locations.
quartz)
From
From the
t h e analyses
analyses iti tisisunclear
unclear whether
whether the
t h elayering
layeringisisaapreserved
preservedcompositional
compositional
heterogeneity
heterogeneity or
or aa product
product of
of metamorphic
metamorphic differentiation.
differentiation.The
Thebulk
bulkcomposition
composition
corresponds
correspondsto
t ohigh
highcalcium
calcium(10-15
(10-15wt%
wt%CaO),
CaO),high
high alumina
alumina(13.4-17.2
(13.4-17.2 wt%
wt%A1203)
AIn03) basalt
basalt
-
I
I
I
- 14 Table
Table 1:
1:
e
Si02
Si02
Ti02
1102
A1203
Whole rock chemical analyses of
Whole
of mafic gneiss from the
the Kapuskasing
Kapuskasing zone, with
CIPW
norms. Analyst:
I: granulite layer,
Analyst: R.
R. Charbonneau,
Charbonneau, GSC
GSC Lab. 1:
layer, P79-475
P79-475
CIPW norms.
(Gt-Cpx-Pl-Qz, 5%
2: amphibolite
amphibolite layer, P-475
(Gt-Cpx-PI-Qz,
5% Nb);
Hb); 2:
P-475 (Gt-Cpx-Pl-Qz,
(Gt-Cpx-PI-Qz, 25%
25% Nb);
Hb);
3: granulite
(Gt-Cpx—Pl,trtrQz);
Qz);4:4:amphibolite
amphibolitelayer,
layer, P79-371
granulitelayer,
layer,P79—371
P79-371 (Gt-Cpx-PI,
(Nb 40%,
40%, Gt
Gt 15%,
15%, Cpx
Cpx 15%,
15%,PI
Fl20%);
20%);5:5:average
averageofofthree
three mafic gneisses from
(Hb
the
the KSZ
KSZ (79-84A,
(79-84A, 123,
123, 299); 6:
6: high-alumina basalt
basalt (Ringwood,
(Ringwood,1975).
1975).
1
2
3
4
5
6
47.8
46.6
52.5
43.1
47.8
49.9
1.0
1.3
0.81
0.81
1.81
1.59
15.5
15.6
17.2
13.4
16.2
17.0
Fe203
1.3
2.2
2.2
5.7
3.4
1.5
FeO
FeO
9.1
9.4
8.5
12.8
8.5
7.6
MnO
MnO
0.27
0.19
0.32
0.3
0.32
0.2
MgO
MgO
4.53
5.29
3.64
9.25
5.41
8.2
13.50
11.4
CaO
CaO
Na20
Na20
K20
K2Â
fl20
Co2
C02
Ni
Ni
Cr
Total
Total
QZ
OR
AB
AN
DI
HE
EN
PS
P0
PA
MT
IL
AP
CC
15.4
14.2
11.2
10.0
2.0
2.4
2.8
1.6
2.3
2.8
0.25
0.41
0.12
0.58
0.33
0.2
0.5
1.1
0.3
1.6
0.8
2.3
2.0
0.4
0.1
0.6
0.014
0.014
0.0095
0.0098
0.024
0.019
0.018
0.018
0.014
0.015
100.0
1.5
1.49
17.02
32.77
11.42
12.80
6.05
7.83
1.9
1.55
0.12
5.26
100.4
2.44
20.46
30.81
11.52
10.90
3.64
3.95
3.01
3.60
3.21
1.55
0.14
4.58
100.6
100.6
100.4
CIPW
CIPW Norm
Norm
6.6
6.6
0.71
3.47
0.71
23.63
13.72
13.72
33.92
28.03
28.03
6.99
10.20
8.28
6.41
8.28
5.80
5.39
7.89
3.89
9.26
7.36
3.18
8.37
2.24
3.06
3.06
0.26
0.24
0.26
0.24
0.91
0.46
0.91
0.46
100.2
100.1
100.1
1.95
1.95
19.8
32.97
13.77
13'77
10.58
4.96
4.43
4.43
1.54
1.0
1.0
23.5
33.4
33.4
1-54
4.95
4.95
1.90
0.19
0.19
1.44
1.44
1.21
1.21
18.9
9.4
9.3
2.2
2.2
2.5
2.5
t
I
I
I
I
R
mafic gneiss
in the 95-220
and 1212(Table 1). Nickel and chromium abundances
abundance5 ofof mafic
gneiss aare
r e in
95-220 and
190ppm
ppmranges
rangesrespectively
respectivelyand
andare
arenot
notdefinitive
definitive in distinguishing between
190
between basaltic
igneousand
andmarly
martysedimentary
sedimentaryparentage
parentagefor
for the
the rock
rock type.
type.
igneous
In the
the area
area of
of Figure
Figure 6,
6,four
four linear,
linear, northeast-striking
northeast-striking bodies
bodiesofof flaser-textured
flaser-textured tto
In
o
foliated diorite
foliated
dioriteand
and mafic
mafictonalite
tonaliteoccur
occurdominantly
dominantlywithin
withinparagneiss
paragneiss terranes.
terranes. These
These
ff'
SHAWMERE ANORrHOSITE COMPLEX
Megacrystic qabbrac anorthosile
//
Banded zone cpabbrO/anar I hosite/qarneti let
I'
I
Anorthosite zone
I
5 / hornbleedet
/
'a
Tonahtic racks
Liiiilii Paraqnetss
——
$
—
——
km
——
I
I
I
Ia
p
-
I
I
_—_—_—
1
/
____iii___
±61r'-
/
/
----
—
/
/
-
/ —:——7
a
C'
/
/-';Y/
/
—
:Y /
//
// / -
// / /// -:
Renee
/ _/ /
/
/
,:-:i /
Catty
/
*34B
\/
a-
1
ii /
/r //c/:-///
/
/-/
_—_/
-/
—
/1—-
/—
a
/
J-& -- -
--
I
I
/ /-:j
// 7 // I',)
/
/-;: I
/
z
__ /
_//
/
/
/
/
—
Mat a yneiss. amohibolute
FseIt
___I —
;;/ /ft\/// //
S
Luneament
/
". E::E
J
?-
couNrAt ROCKS
$
/
'1-
/
ronalilic rocks
___
//
C
Border zone-am phibolite. mat'c gnetss
4à2
—
-
-
-yI
/
IMd::y
3 4A
/
// 13.:c::_J
--
—-——
/
' -:
-
—:—:—-- —
-
8300----f ':':nFigure 7.
-
t'
a
/
8230
Geologyof
of the
the Shawmere
Shawmereanorthosite
anorthositecomplex
complex (after
(after Riccio, 1981
and
Geology
1981 and
Percival, 1981).
48
- 16 -
medium- to coarse-grained,
coarse-grained, locally
locally migmatitic
migmatitic rocks
mediumrocks consist
consist of
of hornblende,
hornblende, biotite
biotite and
and
per cent
cent quartz
plagioclase, with up to 10
plagioclase,
10 per
quartz as
as well
well as
as orthopyroxene,
orthopyroxene, clinopyroxene
clinopyroxene and
and
hornblendite and
rare pyroxenite
pyroxenite occur
cm to
garnet. Gabbro,
as layers
layers 10
10 cm
to
rare garnet.
Gabbro, hornblendite
and rare
occur locally
locally as
cii thick, generally within 2 km
km of
of paragneiss contacts.
2
2m
present south
south of
of the
t h e main
main
Discrete belts of
of xenolithic
xenolithic and
and gneissic
gneissic tortalite
tonalite are present
and small
small bodies are present
present to
to the north.
anorthosite complex and
body of the
the Shawmere
Shawmere anorthosite
The southern
southern belt
belt is made
up of
of coarse
coarse garnet-hornblende-biotite-plagioclase-quartz
garnet-hornblende-biotite-plagioclase-quartz
made up
and garnettonalite containing enclaves of
of mafic gneiss, paragneiss, hornblendite and
orthopyroxene-hornblende-biotite rocks.
orthopyroxene-hornblende-biotite
rocks. Southwest
Southwest along
along this belt, garnet decreases
decreases in
composition is
is granodioritic.
granodioritic. Inclusions
abundance and the composition
Inclusions in this area
area are
are amphibolite,
amphibolite,
and cummingtonite-hornblende-biotite
cummingtonite-hornb!ende-biotite rocks.
hornblendite, and
rocks.
The Shawmere
Shawmere anorthosite
anorthosite complex (Thurston et
et al.,
al., 1977)
1977) consists of a main
main
northern body,
measuring 55 xx 15 km.
km. The
50 km and a smaller mass,
mass, measuring
The bodies
bodies taper to
to
body, 15
15 x 50
the northeast and
and thus
thus have
haveconcordant
concordantcontacts.
contacts. Gneissic
and southwest and
Gneissic textures
textures
prevail in
in the
the outer
outerportions
portionsof
ofthe
themain
mainbody,
body,whereas
whereas primary
primaryigneous
igneous minerals
minerals and
and
textures are preserved
preserved in the interior
interior(Simmons
(Simmons et
et al.,
al.,1980).
1980). The
Themain
mainbody
body comprises
comprises
four distinct
(1)aaborder
border zone
zone of
of
distinctlithological-textural
lithological-texturalunits
units(Riccio,
(Riccio,1981;
1981;Fig.
Fig.7):
7):(1)
rnigmatitic, foliated
migmatitic,
foliatedtot ogneissic
gneissicgarnetiferous
garnetiferousamphibolite,
amphibolite,(2)(2)a abanded
banded zone
zone consisting
consisting
of 11 ttoo 30
30 cm-thick layers
layers of anorthosite,
anorthosite, gabbro,
gabbro, garnet-rich, and
and ultramafic
ultramafic rock,
rock, (3)
(3)an
an
anorthosite zone
gabbro and (14)
megacrystic gabbroic
gabbroic anorthosite
(4)aamegacrystic
anorthosite
zone containing
containing minor gabbro
zone with plagioclase phenocrysts
cm and
and minor
minor anorthosite, anorthositic
phenocrysts to
t o 50 cm
anorthositicgabbro,
gabbro,
gabbro and
andmelagabbro.
melagabbro. AA 1 km
km wide
wide body
bodyofoffoliated
foliated garnetiferous tonalite
tonalite is
gabbro
is present
present
within the
the outcrop
outcrop area of the anorthosite.
anorthosite. Its
Itsgenetic
geneticrelationship
relationshipto
t othe
theanorthosite
anorthosite
complex is not clear although
although ititappears
appears to
tobe
be temporally
temporallyrelated
related(Simmons
(Simmonsetetal.,
al.,1980).
1980).
southern body
body consists
consistsdominantly
dominantly of
of coarse
coarse gabbroic anorthosite.
The southern
The orientation
orientation of gneissosity
and lithological
lithological contacts
the prominent
prominent
The
gneissosity and
contacts make
make up
up the
east-northeast structural
structural grain of the
structural zone.
zone. Gneissosity
in all
east-northeast
the Kapuskasing
Kapuskasing structural
Gneissosity in
rock types is folded or warped
gently-plunging (0-25°)
northeast-trending axes.
warped about gently-plunging
(0-25O) northeast-trending
axes.
The folds vary from
from isoclinal
"Z"sense
senseasymmetry
asymmetrywhen
when viewed
viewed toward
toward
isoclinalwith
withconsistent
consistent"Z"
the east to northwest-facing
northwest-facing monoclinal flexures.
flexures. Axial
Axialsurfaces
surfacesare
arerarely
rarelyaccompanied
accompanied
by a foliation
foliation defined
defined by
by flattened
flattened quartz
quartzgrains.
grains. The
Thetrend
trendofoflineations
lineationsand
andfold
foldaxes
axesisis
northeast-southwest throughout
throughout this part of
but plunge
plunge direction
direction
northeast-southwest
of the
theKapuskasing
Kapuskasing zone,
zone, but
varies on
on aa regional
regional scale
scale from
from dominantly
dominantly southeasterly
southeasterly in
in the
the south
south tto
northeasterly in
o northeasterly
the north. Between
lineations are
are within
within 10°
Between these
these areas,
areas, lineations
1O0 of horizontal
horizontal and
and abrupt
changes
plungedirection
direction occur
occur on
on the
the 100 m
m scale.
scale. Both
Both regional
regional and
and local
local plunge
plunge
changes inin plunge
reversals
can be
be related
related to aa gently
gently southeast-plunging
southeast-plunging warp axis.
reversals can
r
LI
I
- 17 -
I
A
A
I
I
I
I
'A
-4-
-s
A
'c
-e
A
Sc
"INDEX
MINERAL'
ISOGRADS
(teeth point
p
up—grade)
0
A
/ Clinopyroxene
/
-f
n
A
A
Garnet — cIinopyroxene
Orthopyroxene
A
A
I
'Lfl
A
A
4,
/
1'
A
A4
A
n
I
I
I
I
I
I
I
I
I
I
I
.
.
LEGEND
LEGEND
1
SYMBOLS
SYMBOLS
Alkalic rock-carbonotite complex
Granitic
Graniticrocks
rocks
'
Anorthositic
Anorthositic rocks
rocks
.
Retrograde
Retrograde greenscllst
greemctist fades
facies
laI
Unsubdivided
—
Unsubdivldedgreenschist
ÇMnSchist
amphibolite
amphibolite facies
facie* supra—
supracrustal
crustal rocks
rocks
Cataclastic
ASSEMBLAGES
ASSEMBLAGES
MAFIC(BASALTIC)
(BASALTIC)GNEISS
GNEISS
MAFIC
C HbHb-P1PI
—Hb—PI
CE Gt
Gt-Hb-PI
nfl Cpx—Hb—PI
Cpx-Hb -PI ttton
ton
Q Gt
Gt—Cpx-Hb-PI
-Cpx-Hb-PI -Qz
-02
GI~t—Cpx
—Qz
ton
-CPX-Hb—PI
-~b-PI
-02—-ton
Gt
-ton
Gt—Opx-Cpx-Hb—PI
-0px-Cpx-Hb-PI—Qz
-02-ton
DIOR ITIC ROCKS
ROCKS
DIORITIC
A Hb—Bt-PI
Hb-Bt-PI -Qz
-02
r
A Hb—Bt
Hb-Bt—P1
-PI—Qz
-02—ton
-ton
AA Cpx-Hb—Bt
Cpx-Hb-Bt—P1
-PI -02
-ton
-Qz -ton
AA Opx-Cpx-Hb—Bt
Opx-Cpx-Hb-Bt—P1
-PI -Qz
-02-ton
-ton
PARAGNEIS
PARAGNEISSS
00 BtBt—P1
-PI —Qz±Hb
-0ztHb(+sfauroliteØ)
(*stniirnl~te
0)
0<SGt—Bt
Gt -Bt -P1
-PI -QztHb
-0ztHb
AA Opx—Gpx—Hb—Pl
±Qz
opx-OPX-H~-PI
to2
CC Gt
Gt-Hb-PI
-Hb-PI
±Qz
Hb-PltQz
C Hb-Pl
e0Opx-Bt-PI
Opx-Bt -PI-Qz
-02
ANORTHOSIT1C ROCKS
ROCKS
ANORTHOSITIC
e0 GtOpxHb-PItQz
Gt-Opx-Hb-PltQz
ULTRAMAFIC
+ULTRAMAFIC
ROCKS
ROCKS
CCGt—Bt-PI
—Qz—ton
Gt-Bt-PI
-02-ton± tHbHb
opx-cpx-~b(+Pp
(<-PI.+)
Opx-Cpx—Hb
4)
cM -Opx-Bt—PI
-Qz—ton(+Kspe)
1
-op~-Bt-pI
-O~-~O~(+KSD:È
Opx-Cpx-Bt-Pl -Qz-ton
zone
.
Figure
Metamorphicmineral
mineralassemblages
assemblagesand
andindex
indexmineral
mineralisograds
isogradsIfor
part of
ofthe
the
Figure8.8. Metamorphic
or part
Chapleau-Foleyet
garnet;Opx
Opx- orthopyroxene;
orthopyroxene;Cpx
CpxChapleau-Foleyet area.
area. Gt
Gt- -garnet;
clinopyroxene;
clinopyroxene;Hb
Hb- hornblende;
hornblende; Bt
Bt- -biotite;
biotite; P1
PI- -plagiocase;
plagiocase;Ksp
Ksp- -feldspar;
feldspar;
Qz
Qz- quartz;
quartz;ton
ton- -tonalitic
tonaliticsegregations.
segregations.(after
(afterPercival,
Percival,1983)
1983)
-
-
-
-
- 18 -
Two high-grade
high-grade metamorphic
metamorphic zones canbe
bedistinguished
distinguishedininthis
this part
part of
of the
the
Two
Kapuskasing
structural zone.
zone. Assemblages
characteristic of
Kapuskasing structural
Assemblages characteristic
of aa lower-grade
lower-grade garnetgarnetclinopyroxene-plagioclase zone
zone are
are developed
developedinin mafic
mafic gneiss.
gneiss. Orthopyroxene,
in
clinopyroxene-plagioclase
Orthopyroxene, present
present in
four areas
(Fig. 8;
areas in most rock types, is
is diagnostic of aa higher-grade
higher-grade orthopyroxene zone
zone (Fig.
Percival, 1983).
1983).
A
continuous
reaction resulting
resulting in
of hornblende
in mafic
A continuous reaction
in decomposition
decomposition of
hornblende in
mafic rocks
rocks to
to
produce garnet
garnet and
and clinopyroxene
clinopyroxene may
may be
bewritten:
written:
hornblende
plagioclase^±garne
± garnet +
clinopyroxene +
+ quartz
quartz +
ll2O
(1)
+ clinopyroxene
+H
20
ornblende ++ plagioclase
(1)
The coexistence
over large areas
areas of
of this divariant
and tonalitic
tonalitic leucosome
xistence over
divariant assemblage
assemblage and
leucosome
veinlets suggests
that the
the reaction
reaction was
liquid over
over aa range
range
veinlets
suggests that
was anatectic
anatecticand
and also
also produced
produced aa liquid
of P-I conditions (Fig. 9):
9):
hornblende ++pplagioclase
garnet +
÷ clinopyroxene
clinopyroxene ++ tonalite
tonalite
hornblende
l a g i o c l a s e±e garnet
(2)
(2)
A
reaction leading
leadingtto
the production
production of
of orthopyroxene
orthopyroxene in
in mafic
mafic rocks is:
is:
A possible
possible reaction
o the
hornblende ++garnet
garnete
± orthopyroxene + clinopyroxene
clinopyroxene ++ H20
H20
hornblende
(3)
(3)
The evolved
evolved water would
The
would presumably
presumably have
have been
been taken up by anatectic
anatecticLiquids.
liquids.
In paragneiss,
paragneiss,aare
reaction producing orthopyroxene
yroxen in the presence of anatectic
melt is:
is:
.
. biotite + quartz ÷ plagioc1ase orthopyroxene + gra.rtodioritic
(4)
' biotite +
+ plagioclase^sorthopyroxene + grandioritic liquid
*
.
-
.. >
..~.
.'. ..,.
diagram summarizing
summarizing continuous
continuous reactions
reactions in
in the mafic
- - ' - : AA P—I
P-T diagram
mafic system
system and
and
apparent metamorphic conditions
on various mineral geothermometers
conditions based
based on
geothermometers and
and
geobarometers, is presented in Figure
Figure 9.
9. Apparent
Apparentpressures,
pressures,based
based on
onNewton
Newtonand
and
geobarometers,
Perkins' (1982)
(1982)garnet-clinopyroxene-plagioclase
garnet-clinopyroxene-plagioclasequartz
quartz barometer,
barometer, are
a r e plotted
plotted on
on aamap
map
Perkins'
have aan
averagevalue
valueofof 6.3
6.3 kbar.
kbar. This
10 and have
n average
This barometer apparently
apparently
in Figure 10
by 1-1.6
underestimates pressure
pressure by
1-1.6 kbar (Newton
(Newton and
and Perkins,
Perkins, 1982;
1982; Ghent et
et al.,
al., 1983)
1983)and
and
hence an
an average
average value
valueof
of 7.8
7.8 kbar
kbar is
is suggested.
suggested. Apparent temperatures,
temperatures, based
based on the
hence
Ellis
garnet-clinopyroxene thermometer
thermometer (Fig. 9)
9)are
a r e in
in the
t h erange
range 700700Ellis and
and Green (1979)
(1979) garnet-clinopyroxene
800°C. Metamorphic
on water
water barometry
80O0C.
Metamorphic fluids
fluidswere
were probably
probably depleted
depleted in H20,
H20, based
based on
(Percival, 1983)
and the
the presence
presenceof
of carbonic
carbonic fluid inclusions
1983) and
inclusions (Rudnick
(Rudnick et
et al.,
al., 1984).
1984).
The assemblage
assemblageaimandine
almandinegarnet-clinopyroxene-plagioclase-quartz
garnet-clinopyroxene-plagioclase-quartz is diagnostic
The
of the regional
egionalhypersthene
hypersthene zone
zone according
according to
t o Winkler
Winkler(1979,
(1979, p.
p. 260,
260, 267-268).
267-268). de
de Waard
Waard
(1965)and
andGreen
Greenand
andRingwood
Ringwood (1967)
(1967)suggested
suggestedthat
that this
this assemblage forms
as an
an
(1965)
forms as
alternative to
anulite-facies
toorthopyroxene-plagioclase
orthopyroxene-plagioclaseduring
during high-pressure
high-pressure gr
granulite-facies
alternative
metamorphism. Turner
attachesaadifferent
different significance
significance to
t o the
theassemblage,
assemblage,
metamorphism.
Turner (1981)
0981) attaches
I
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0)
0)
.5
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11.5
S
0
Gt-Cpx—Hb—PI—Oz
Gt-Cpx- Hb-PI-Qz
C
0 Ct
Gt—Opx—Cpx—Hb—PI
-0px-Cpx-Hb-PI
0
0 Gt—Opx—Bt—PI—Oz
Gt-Opx-Bt-PI-Qz
I.
4.
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0.
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0
3
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0
700
800
Temperature (°C)
Figure
Figure 9.
9.
Summary
of reactions applicable to mafic
Summary of
mafic rocks
rocks arid
and metamorphic pressuretemperature
temperature estimates.
estimates. Temperatures
Temperatures are
arederived
derived from
from the garnet-
clinopyroxene
and Green,
Green, 1979)
1979) and pressures from
clinopyroxene thermometer
thermometer (Ellis
(Ellis and
garnet-pyroxene-plagioclase-quartz
garnet-pyroxene-plagioclase-quartzbarometers
barometers(Newton
(Newtonand
and Perkins,
Perkins, 1982).
1982).
-20regarding
based
ononBinns'
regarding it
it as
as transitional
transitionalfrom
fromamphibolite
amphiboliteto
t ogranulite
granulitefades
fades
based
Binns'(1964)
(1964)
study.
In
the
present
study
area,
the
location
of
the
garnet-clinopyroxene-plagioclase
study. In the present study area, the location of the garnet-clinopyroxene-plagioclase
zone
hornblende-plagioclase÷clinopyroxene rocks
zone between
between hornblende-plagioclase+clinopyroxene
rocks and
and orthopyroxene-bearing
orthopyroxene-bearing
rocks suggests
suggeststhat
that it
it characterizes
amphibolite-granulite facies
transition.
characterizes the
the amphibolite-granulite
facies transition.
rocks
Although
is the
the same
that in
Although the
the assemblage
assemblage is
same as
as that
in the
theAdirondacks
Adirondacks(de
(deWaard,
Waard,1965)
1965) and
and
temperature
Bohlen and Essene,
1977),the
the path
path of
temperature conditions
conditions were
were similar
similar(Cf.
(cf. Bohlen
Essene, 1977),
metamorphism
different. In
In the
the Grenville
Grenville Province,
Province, the
the development
development of
of garnetgarnetmetamorphism was
was different.
clinopyroxene
hasbeen
beenattributed
attributed tto
isobaric cooling
clinopyroxene assemblages
assemblages has
o isobaric
cooling of orthopyroxeneorthopyroxeneand
Schrijver,
plagioclase
granulites
(Martignole
1971;
Whitney,
1978)
whereas in
plagioclase
(Martignole and Schrijver,
Whitney, 1978) whereas
in the
the
Kapuskasing
Kapuskasing zone,
zone, garnet
garnet and
and clinopyroxene formed
formed during
during prograde reactions.
Rounded
zircons of
Rounded zircons
of probable
probable metamorphic
metamorphic origin
origin from
from Kapuskasing
Kapuskking mafic
maficgneiss
gneiss
gave a concordant date
date of
of 2,650
2,650 Ma
Ma and
and from
fromaaleucosome
leucosome layer
layerininparagneiss
paragneiss of 2,627
2,627
Ma
Ma (Percival
(Percival and
and Krogh,
Krogh, 1983;
1983; Fig. 11).
11). Further
Furtherwork
workon
onmetamorphic
metamorphiczircon
zirconhas
has
extended
(Krogh et
et al,
A
al, 1986).
1986). A
extended the
the range
range of
of metamorphic
metamorphic dates
dates to
t o 2696-2616 Ma
Ma (Krogh
minimum
age of
of emplacement
emplacement for foliated tonalite
minimum age
tonalite from
from the
theShawmere
Shawmere complex
complex is
provided by
by zircons (2,765
(2,765 Ma)
Ma)but
butthe
the U-Pb
U-Pb system
system has
has been
been strongly affected
affected by
by the
the
high-grade
Krogh, 1983).
1983). The rocks
rocks intruded by
by tthe
high-grade metamorphism
metamorphism (Percival and Krogh,
h e tonalite
tonalite
are thus
t h e Abitibi
Abitibi and
and Michipicoten
Michipicoten belts.
thus older
older than
than dated
dated volcanic
volcanic rocks
rocks of
of the
Quartz-bearing gabbroic anorthosite contains
contains zircon
zircon with
with two
two habits:
habits: red-stained
red-stained
resorbed grains with
with meta-igneous
meta-igneous appearance,
appearance, and equant, multifaceted, colourless
colourless
grains of probable
probable metamorphic origin. Both
Bothpopulations
populations have
have aa U-Pb
U-Pb age
ageof
of 2649
2649Ma
Ma
(3.A.
Sullivan, unpublished
unpublisheddata),
data),interpreted
interpreted as tthe
(LA. Percival and R.W.
R.W. Sullivan,
h e time
time of
of
metamorphic
The analysis
analysis of
of the coarsest
coarsest resorbed
resorbed grains
grains plots slightly
slightly to the
the
metamorphic cooling.
cooling. The
right
line, suggesting
suggesting an
an older
older component.
component.
right of
of the
the2649
2649Ma
Ma discordia
discordia line,
At least
least two
two swarms
swarms of fresh
fresh mafic
mafic dykes
dykes transect
transect metamorphic
metamorphic rocks
rocks of
of the
the
Kapuskasing
zone. East-northeast-striking,
Kapuskasing zone.
East-northeast-striking, southeast-dipping
southeast-dippingKapuskasing
Kapuskasingdykes
dykes are
are11to
to
10 m
m wide,
wide, sparsely
sparsely plagioclase
plagioclase porphyritic,
porphyritic, mediummedium- to
to fine-grained,
fine-grained, ophitic, green-grey
gabbro. Northeast-trending
Northeast-trending olivine-bearing
olivine-bearing dykes
dykes may
may belong
belong to
t o the
the Abitibi
Abitibi swarm.
swarm.
Several
rock-carbonatite complexes
Several small alkalic rock-carbonatite
complexes are associated with the
the
Kapuskasing
zone. The
Kapuskasing zone.
The more
more northerly
northerlybodies
bodieshave
haveK-Ar
K-Ar dates
datesofof1655
1655tot o1720
1720Ma,
Ma,
whereas those in the
the south
south have
have dates
datesof
of 1050
1050to
t o 1100
1100 Ma
Ma (Gittins et
e t al.,
al., 1967).
1967). Thin
Thin
lamprophyre
dykes and
andaa rare
rare diatreme
diatreme breccia are
are associated
associated with
with the
the complexes;
complexes;
lamprophyre dykes
biotite
biotite from
fromaalamprophyre
lamprophyre dyke
dyke in the Chapleau-Foleyet
Chapleau-Foleyet area gave a K-Ar
K-Ar date
date of
of
1144
I144 +±31
31 Ma (Stevens eta!.,
e t al.,1982).
1982).
4
i
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$
Li
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I
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I
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-21 -
PALEOPRESSURE
PALEOPRESSURE
ESTIMATES
ESTIMATES
Equilibria
Equilibria
I
I
I
032—8.3
/
024-
,+.
29-6.5
21 —& 53 .1W(
DC
0
22— 8.i;9,9 W
06.7
enstatite=1/3 grossular
~ 6 . Anorthite+
7Anorthite+enstatite=1/3
gross
+
2/3
pyrope+quartz
0+ 2/3 pyrope+quartz
(Perkins
(Perkins&SNewton,
Newton,1981)
1981)
2
06.7W
0 6 . 7 ~Garnet—orthopyrOXene
Garnet-orthopyroxene
A
(Wood,
(Wood,1974)
1974)
06.79
06.7~33Anorthite=grOSSUIart
Anorthite=grossular+
2 sillimanite÷ciuartz
(Ghent, 1976)
07-6.7
2 0-6.2
14—'
0
10—6.6
013—4.29.9W
013-L2.9.9W
>20 1 1.3,COW
17-6.5 —
48°00 -
2 1—6.7
0
Chapeat
10
0
40
I
I
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6-7.3
2 3—5.4
06.7
grossular
06.7 Anorthite+diopside=2/a
~northite+diopside=~/s
grossu
÷+ 1/3
pyrope+quartz
V3 pyrope+quartz
I
I
3 1-6.00
km
km
Figure
Figure10.
10. Paleopressure
Paleopressure map
Symbols represent rock
map of
of the Chapleau-Foleyet
Chapleau-Foleyet area.
area. Symbols
type
paragneiss; squares
squares - mafic
mafic gneiss;
gneiss; triangles
triangles - orthogneiss).
orthogneiss).
type (circles
(circles- paragneiss;
Numbers
Numbers to
to the
the right
rightofofthe
thedash
dashare
arepressure
pressure estimaters
estimators(kbar)
(kbar)keyed
keyed to
tothe
the
equilibrium
equilibriumused
used to
t o derive
derive the
t h e value.
value. The
The6.3
6.3 kbar
kbar reference
referenceline
lineisisbased
based on
on
garnet-dinopyroxene-plagioclase-quartz equilibrium.
(afterPercival,
Percival,1983)
1983)
garnet-clinopyroxene-plagioclase-quartz
equilibrium. (after
-
-
-
RELATIONSHIP OF
OFKAPUSKASING
KAPUSKASING STRUCTURAL
STRUCTURAL ZONE
ZONE TO
TOAD3ACENT
ADJACENTSUSPROVINCES
SUBPROVINCES
RELATIONSHIP
The
The contact
contactbetween
between the
theKapuskasing
Kapuskasing structure
structureand
and Abitibi
Abitibisubprovince
subprovinceisis aa zone
zone
of faulting
faultingand
andcataclasis,
cataclasis,the
theIvanhoe
Ivanhoe Lake
Lake cataclastic
cataclasticzone,
zone, that
thatseparates
separates the
the two
two
of
terranes of
of contrasting
contrasting lithological,
lithological, structural,
structural,and
and metamorphic
metamorphic characteristics.
characteristics. The
The
terranes
- 22
—
2O6 b
238
u
0.55
2800
1•
14
'4,
0N
2
0.50
'Ix
Paragneiss
Paragneiss leucosorne
leucosome (
Vv
Mafia
Mafic gneiss
gneiss (2)
(2)
013 Shawmere
Shawmere tonalite
tonalite (3)
(3)
(vanttoe
Ivanhoe Lake
Lake ptuton
pluton (4)
(4)
0a Gneissic
Gneissic tonalite
tonalite (5)
(5)
v-
0¡
'Â
+
OneissicGneissic- foliated granodiorite
granodiorite (6)
(6)
7
0
0.45
ZO7Pb
235u
12.0
13.0
14.0
15.0
Figure
Figure 11.
11. Concordia
Concordia diagram
diagram with
with isotopic
isotopic ratios
ratiosof
of zircon
zircon samples.
samples. Ab:
Ab:abraded
abraded
(Krogh,
N:
non-magnetic (Frantz); MI:
magnetic at
: non-magnetic
MI: magnetic
atj0l oside
side tilt
tilt
(Krogh, 1982);
1982); N
(Frantz);
(Frantzk pr:
pr: prismatic;
prismatic; an:
an: anhedral.
anhedral. Solid
Solidlines
lines are
areempirical
empiricallead-loss
lead-loss
trajectories;
Ma
trajectories;dashed
dashedline:
line: hypothetical
hypothetical lead-loss
lead-loss trajectory
trajectory(projects
(projectstoto0 0Ma
lower
lower intercept);
intercept); dash-dot line: empirical mixing
xing line.
line. (after
(afterPercival
Percivaland
and
Krogh,
Krogh, 1983)
1983)
zone
zone is
is defined
defined in part by
by positive,
positive, linear north-northeast-trending
north-northeast-trending aeromagnetic
aeromagnetic
anomalies
pairedhigh
high(Kapuskasing)
(Kapuskasing) --low
low (Abitibi)
(Ab'itibi)
anomalies and
and coincides
coincideswith
withthe
thetrough
troughofofa apaired
gravity
and12).
12).
gravityanomaly
anomaly(Figs.
(Figs.44and
The Ivanhoe
Ivanhoe Lake cataclastic
zone is
is characterized
characterizedby
bynarrow
narrowveinlets
veinletsof
offinely
finely
The
cataclastic zone
comminuted rock
rock which
which form
form discontinuous,
discontinuous, randomly-oriented
randomly-oriented pods
pods and networks.
networks. Two
Two
comrninuted
foliatedtotomassive,
massive,semi-opaque
semi-opaque
typesof
of fault
faultrocks
rockscan
canbe
bedistinguished.
distinguished. The
Thefirst
firstisisfoliated
types
mylonite, cataclasite
cataclasiteand
andblastomylonite,
blastomylonite, partly
partly or
or totally
totallyrecrystallized
recrystallizedtot ofine
finegrained
grained
mylonite,
epidote, chlorite,
chlorite, carbonate,
carbonate, and
and actinolite.
actinolite. The
Thesecond
secondtype
typegrades
gradesfrom
from cataclasite
cataclasitetoto
epidote,
pseudotachylite with
with aphanitic,
aphanitic,almost
almostopaque
opaquematrix
matrixand
androunded,
rounded,embayed
embayed
pseudotachylite
monomineralic
rnonomineralicporphyroclasts.
porphyroclasts.
r
I
I
o
- 23 -
- -5
It:
.-
>
F
0
-to-
.3c.
-so-
m
CB
-
0
10
kkrn
m
I
I
I
20
Shawmere
Shawmere anorthosite
anorthosite complex
complex
PROTEROZOIC
1100 Ma alkalic-rock complex
ARCHEAN
Massive granite. granodiorite (G2.70)
I
I
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I
I
4
Ivanhoe
Ivanhoe Lake cataclastic
cataclastic zone
zone
1
I
Tonalitic gneiss (G.270)
H
Metavolcanic rocks (Gz2.90)
Anorthositic
rocks (G~2.82)
(G2.82)
Anorthositic rocks
Kapuskasing
gneisses (G2.52)
Kapuskasing zone
zone gneisses
(G=2.82)
Figure
Figure12.
12. Generalized
Generalized west-east
west-east cross-section
cross-section from
fromthe
theWawa
Wawa domal
domal gneiss
gneiss terrane,
terrane,
through
structural zone
zone into
into tthe
Abitibi subprovince,
through the
t h e Kapuskasing
Kapuskasing structural
h e Abitibi
subprovince,
showing
showing gross
gross crustal structure. The
The gravity
gravity model
modelbased
based on
on the
t h e average
average
rock
rock densities:
densities: tonalitic
tonaliticgneiss
gneissand
andgranite:
granite:2.70;
2.70; metavolcanics:
metavolcanics: 2.90;
2.90;
Kapuskasing
structural zone
Kapuskasing structural
zoneand
and lower
lower crust:
crust:2.82
2.82 g/cm
g/cm 3.3.
The
cataclastic zone
The dip of the
the Ivanhoe
Ivanhoe Lake cataclastic
zoneisisnot
notwell
wellconstrained
constrainedgeologically.
geologically.
Although
fault-rock veinlets are
Although some fault-rock
are parallel
parallel to
t ogneissosity
gneissosity and
and therefore
thereforedip
dipgently
gently
northwest,
northwest, many
many others
others have
have random
random orientation. The
Thejuxtaposition
juxtapositionofofhigh-grade
high-grade
against
displacement across
across the
the cataclastic
cataclastic zone.
against low-grade
low-grade rocks indicates reverse displacement
zone. The
The
associated
associated paired
paired gravity
gravity anomaly
anomaly is
i s characteristic
characteristic of
of many
many well-documented
well-documented overthrust
terranes
terranes(Smithson
(Smithsonetetal.,
al.,1978;
1978;Fountain
Fountainand
andSalisbury,
Salisbury,1981)
1981) and suggests that
that the
the
Ivanhoe
cataclastic zone
Ivanhoe Lake cataclastic
zone is
is the
t h esurface
surfaceexpression
expression of
of aanorthwest-dipping
northwest-dipping thrust
thrust
fault
fault(Fig.
(Fig. 12).
12). AAshort
short(10
(10km)
km) seismic reflection survey
survey over the zone indicates aa
reflector
reflectorininthe
t h eappropriate
appropriateposition
positionwith
withaatrue
truenorthwesterly
northwesterlydip
dipofof38-40°
38-40-(Cook,
(Cook,1985;
1985;
Fig.
Fig. 13).
13).
The
boundaryvaries
variesinincharacter
character over
over its
its length.
length. North
The Wawa-Kapuskasing
Wawa-Kapuskasing boundary
North of
of
Bonar
Bonar Lake,
Lake, it
i t is
is aafault,
fault,with
withdistinct
distinctaeromagnetic
aeromagneticexpression,
expression,which
whichdiverges
diverges westward
westward
into
into Wawa
Wawa tonalites
tonalites toward
toward the
thesouthwest.
southwest. South
SouthofofBonar
BonarLake,
Lake,the
t h eboundary
boundaryhas
has
T
_______________
- 24 — 24
a
a
LINE KAP
LINE KAP -
s-P. ____.i
—.
b
—
2I
-1
1sw
5 km
400?
—-.-——----
:200
LINE KAP
b
5.P.
n_fl-
201
-1
5km
W
—
A
—C
N
S
C
—
B
—
——
——
-
A
B
5.0.
Figure 13. a )
Figure 13. a)
Seismic reflection profile over the eastern Kapuskasing zone. The data
Seismic
reflection
profile
on left
the Kapuskasing
continuity of zone.
reflections
is
are plotted
with east
overbecause
the eastern
The data
are
plotted
with
east
on left Reflection
because theAcontinuity
better in this orientation.
is likely from
the Ivanhoeis Lake
of reflections
better
in this zone;
orientation.
cataclastic
reflections
B a r e from
t h e Abitibi
Reflection
A is within
likely from
the subprovince.
Lake
cataclastjc zone; reflections B are from within the Abitibi Ivanhoe
subprovince.
b)
Line drawing interpretation of a ) (after Cook, 1985).
b)
Line drawing interpretation of a) (after Cook, 1985).
'I
-25-
I
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I
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$
gradational lithogical,
structural and
lithogical, structural
and metamorphic
metamorphic characteristics. Mafic
Maficgneiss
gneiss with
with
minor paragneiss
paragneiss is typical of the
minor
the Kapuskasing
Kapuskasing zone but also occurs in
in the
the Robson
Robson Lake
Lake
dome with characteristic structural style
subprovince. GarnetGarnetdome
style of the
the Wawa
Wawa subprovince.
clinopyroxene-hornblende-plagioclase assemblages
are common
commonhere,
here, suggesting
suggestingthat
that the
clinopyroxene-hornblende-plagioclase
assemblages are
metamorphic
similar to that in the
structural zone.
zone. The
metamorphic grade
grade is similar
the Kapuskasing
Kapuskasing structural
The
discontinuous paragneiss
paragneiss belt
belt that extends
30km
kminto
intothe
theWawa
Wawasubprovince
subprovince
extends for
for up
upto
t o30
discontinuous
may also be
be a part of
lithological sequence.
sequence. Tonalitic
of the
the Kapuskasing
Kapuskasing lithological
Tonalitic gneiss
gneiss can be
be
traced eastward
eastward from
from the
the Borden
Borden Lake area, where it
i t has
has the
the complex
complex structures
structures
characteristic of
characteristic
of the
theWawa
Wawa subprovince,
subprovince, into strongly foliated and lineated gneiss typical
of the
the Kapuskasing
Kapuskasing zone.
zone.
The
change in
in structural
structural style
The change
style from
from domal
domal in
in the
the eastern
easternWawa
Wawa subprovince
subprovince to
ENEbelts
belts in
inthe
the Kapuskasing
Kapuskasingstructural
structural zone
zonecan
can be
be used
usedto
to define
define aa transitional
transitional
linear ENE
boundary zone
zone between
betweenterranes
terranes with
with contrasting structural
boundary
structural styles,
styles,but
butno
nosharp
sharpline
linecan
can
drawn on
on this
this bask.
basis. South
be drawn
South of Chapleau, the orientation
orientation of
of gneissic
gneissic layering
layering changes
changes
eastward from horizontal
horizontal near
near the
theHighbrush
Highbrush Lake
Lake dome, through a zone with a
superimposed upright
uprighteasterly
easterly foliation,
foliation, ttoo strong northeast-striking,
superimposed
northeast-striking, northwest-dipping
northwest-dipping
north-south-trending structural
structural culmination coincides with
with the eastern
gneissosity. A north-south-trending
eastern
domes of
of the Wawa
subprovi.nce.East
Eastofof the
the culmination,
culmination, lineations plunge
plunge easterly
easterly
domes
Wawa subprovince.
toward a structural
structuraldepression
depression into
into which
which southwest-trending
southwest-trending lineations of the southern
southern
Kapuskasingzone
zonealso
alsoplunge.
plunge. To
To the
the north, lineations plunging
northeasterly off the
Kapuskasing
plunging northeasterly
the
Lake arch
arch appear ttoo be continuous with
with northeastnortheastnortheastern flank
flank of the
the Missinaibi
Missinaibi Lake
plunging, reclined
reclined folds in
in tthe
structural zone
plunging,
h e northern Kapuskasing
Kapuskasing structural
zone (Percival,
(Percival, 1981
1981a,b).
a,b).
Cataclastic veinlets
veinlets characterize the
the faulted
faulted contact
contactbetween
between mafic
maficgneiss
gneiss and
and tonalitic
tonalitic
gneiss southwest
southwest of
of Kapuskasing
KapuskasingLake.
Lake. To
To the
the south,
south, the
the gradational nature of
gneiss
lithological contacts as well as the structural
lithological
structural and
and metamorphic
metamorphic continuity
continuity between
between
high-grade gneisses
gneissessuggests
suggeststhat
that the
the contacts
contacts were etablished prior
tonalites and high-grade
prior ttoo
metamorphism and doming,
doming, and
and that
that rock units of
of the
theKapuskasing
Kapuskasing zone
zone locally occur
the Wawa
Wawatonalite-granodiorite
tonalite-granodiorite gneiss.
gneiss. Based
structurally below
below the
Based on
on the
the change
change in
in
average rock density
density across
across this
thisdiffuse
diffusesubhorizontal
subhorizontalboundary,
boundary, Percival
Percival(1986)
(1986)
suggested that it could represent an exposed mid-crustal
mid-crustal (Conrad)
(Conrad)discontinuity.
discontinuit
STRUCTURE OF THE
THE KAPUSKASING
KAPUSKASING CRUSTAL CROSS-SECTION
I
$
The
The transition from
from the
the Michipicoten
Michipicoten belt to
t o the
the eastern
eastern boundary
boundary of the
the
- 26 -
0
C
4-.
0
04a.
fl-I
0
5
:::::::::::.
Ct
E
o
.
V
CD
U,
ci)
67 __:::_::.c_:c.:
C s
a,
r
———
i! iiiiii:
::::::::::::::::::::•—
—15
T::::E::::::::::
:::..
— — — ..
— -.
———
a
—
.A>2,765
—
25
\Ivanhoe
Ivanhoe Lake
Lake cataciastic
cataclasticzone
zone
Figure
Figure 14.
14. Restored
Restoredvertical
verticalsection
sectionthrough
throughthe
theMichipicoten
Michipicotenbelt,
belt,domal
domalgneiss
gneiss
terraneand
andKapuskasing
Kapuskasing zone.
zone. Numbers
Numbersare
a r ezircon
zircondates
dates(÷4
(54Ma)
Ma)on
onigneous
igneous
terrane
and meta-igneous rocks (after Percival and Card, 1983).
Kapuskasing
Kapuskasing zone can be interpreted
interpreted as
asan
anoblique
oblique crustal
crustal cross-section
cross-section based
basedon
onthe
the
following:
following: 1)1)metamorphic
metamorphic grade
gradeincreases
increaseseastward
eastwardfrom
fromlow
lowgreenschist
greenschistfacies
faciesininthe
the
Michipicoten
Michipicoten belt
belt(Studemeister,
(Studemeister,1983)
1983)through
through amphibolite
amphibolite facies
faciesin
inthe
theWawa
Wawadomal
domal
gneiss
gneissterrane
terranetotoupper
upperamphibolite
amphiboliteand
andgranulite
granulitefades
faciesininthe
theKapuskasing
Kapuskasing zone;
zone;2)2)the
the
proportion
proportion of
of plutonic
plutonicto
t osupracrustal
supracrustalrocks
rocksincreases
increaseseastward
eastwardininthe
theWawa
Wawasubprovince;
subprovince;
3)3)the
theoldest
oldestrocks
rocks(>2,765
b2.765 Ma)
Ma)are
a r eininthe
theKapuskasing
Kapuskasing zone
zone at
atthe
theinferred
inferredbase
baseofofthe
the
section;
section;4)4)the
thegravity
gravityanomaly
anomalycan
canbebebest
bestmodelled
modelledbybyusing
usingaawest-dipping
west-dipping crustal
crustalslab
slab
(Fig.
(Fig.12);
12);and
and5)5 ) rocks
rockswith
withseismic
seismicvelocities
velocities typical
typicalof
of the
theupper
uppercrust
crustare
a r enot
notpresent
present
r
I
-27the Kapuskasing zone. The three major terrane types recognized in the Abitibi-Wawa
region
can be
be related
region can
related to
t o depth
depth zones
zones in
in the
the crust
crustbased
based on
on metamorphic
metamorphic evidence
evidence and
and
consistent
seismicvelocity
velocitycharacteristics
characteristics of
of the
the crust
consistent with
with known
known seismic
crust of
of the
t h e Superior
Superior
Province.
crust is
of supracrustal
supracrustal rocks
rocks of
of the
the greenstone
Province. Thus
Thus the
the uppermost
uppermost crust
is made
made up
up of
greenstone
belts and
and discordant
discordant plutonic
plutonic rocks.
rocks. Beneath
megalayer made
made up
up of
of variably
variably
belts
Beneath is
is aa megalayer
deformed felsic
felsic ttoo intermediate
deformed
intermediate plutonic
plutonic rocks,
rocks, with
with large-scale
large-scale domal
domal geometry.
geometry. With
With
increasing
depth within
within this
this layer,
layer, the
the attitude
attitude of
from sub-vertical,
sub-vertical,
increasing depth
of gneissosity
gneissosity changes
changes from
near
zone. The
near greenstone
greenstone contacts,
contacts, to
t o sub-horizontal,
sub-horizontal, near
near the
the Kapuskasing
Kapuskasing zone.
The lowermost
lowermost
exposed
megalayer is represented
represented by
exposed megalayer
by the
t h e Kapuskasing
Kapuskasing zone, made
made up of aa heterogeneous
heterogeneous
lithological assemblage
assemblage aatt high
metamorphic grade.
grade. Moderate
high metamorphic
Moderate dips
dips of
of lithological
lithological
layering
lower crustal
crustal attitude
attitude rotated
layering aare
r e interpreted as
as the
t h e dominant
dominant sub-horizontal
sub-horizontal lower
rotated
passively
uplift.
passively during uplift.
Construction of
of a generalized
generalized crustal
crustal cross-section
cross-section (Fig.
(Fig. 14)
14) requires
requires several
several
Construction
assumptions:
1)the
the dip
dip of
of the
the crustal slab is constant; 2)
assumptions: 1)
2) pressure is a function of depth
de
so that estimates
of the
estimates of
of metamorphic
metamorphic pressure
pressure can be used
used to derive tthe
h e thickness of
section; 3) the metamorphic assemblages
assemblages aare
r e the product
product of
of aa single
single metamorphic
metamorphic event;
event;
post-metamorphic vertical displacement on faults within
4) post-metamorphic
and 4)
within the
the section
section is
isnegligible.
negligible.
The highest-grade
highest-grade assemblage from tthe
area is garnet-andalusite in
h e Wawa
Wawa area
in
indicating aa maximum
maximum pressure
pressure of
of 3.3
3.3 kb
kb and
and aa depth of
of
metagreywacke (Ayres,
(Ayres, 1969),
1969), indicating
about 11
km (Carmichael,
(Carmichael, 1978).
11 km
1978). Similar pressures, in the
t h e 2-3
2-3 kb
kb range, are
arebased
based on
on
sphalerite-pyrrhotite geobarometry on rocks
rocks from Gutcher Lake, 30 km
km northwest of
o
Wawa
(Studemeister, 1983).
1983). The
The range
range of
of pressures
pressures estimated
estimated from
Wawa (Studemeister,
from the
t h eKapuskasing
Kapuskasing
garnet-clinopyroxene-plagioclase-quartz
zone, based on Newton
Newton and Perkins'
Perkins' (1982)
(1982) garnet-clinopyroxene-plagioclase-quartz
barometer, is
is 5.4
5.4 to
to 8.4
8.4 kb
kb (average
(average of
of 6.3
6.3 kb,
kb, Percival,
Percival, 1983)
1983) but the
t h e lower
lower values
values may
may
result from re-equilibration
re-equilibration during
during cooling.
cooling. These
These values
values correspond ttoo depths of 18
18 ttoo
km (average
(average 21
21km).
km). The
The minimum
minimumerosion-level
erosion-leveldifference
difference isis therefore
therefore 7 km, but the
28 km
the
closer ttoo 15
km. The
maximumdip
dipestimates
estimates over
over aa
difference is
is probably
probably closer
15 km.
The minimum
minimum and maximum
100.
constantly-dipping slab 120
km long
long aare
constantly-dipping
120 km
r e approximately 5°
5O and lo0.
The dips of
of post-metamorphic
post-metamorphic dykes
dykes in
in the
the Kapuskasing
Kapuskasing zone
zone and
and eastern
easternWawa
Wawa
providean
anindependent
independentestimate
estimateofoft the
tilt of
of tthe
subprovince may
may provide
h e tilt
h e slab in this area.
dykes dip
dip NE
NE at
at 75'
75° ttoo 85°
and ENE
ENE Kapuskasing
Kapuskasing dykes
dykes dip
dip SE
SEaatt 70Â
70° ttoo 85°
85' and
85"'.
Matachewan dykes
'
on measurements
measurements of
of dykes
dykeswith
withvertical
vertical exposure
exposureininroadcuts.
roadcuts. Post-metamorphic
based on
Post-metamorphic
maf Icdykes
dykesinint the
Shieldgenerally
generallyhave
havenear-vertical
near-vertical orientations,
rnafic
h e Shield
orientations, as
asdo
do Matachewan
Matachewan
dykes in the Abitibi subprovince (Thurston et a!., 1977; Mime, 1972). The consistent nonin
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vertical dip may thus have resulted from large-scale crustal rotation. To restore the
dykes
of both
both swarms
swarmsto
to vertical,
vertical, a
dykes of
a 14°
14O counter-clockwise
counter-clockwise rotation
rotation about
about an
an axis
axis
trending 038°
is necessary.
necessary. Thus
14°northwesterly
northwesterly dip
dip is
is indicated
indicated in
in this
trending
038'' is
Thus aa 14"
this eastern
eastern area.
area.
The difference
difference in
The
in dip
dip estimate
estimateprovided
provided by
by these
these two
twomethods
methods may
may be
be due
due to
to
uncertainties
in the
the calculations,
calculations, faulty
or real
uncertainties in
in the
the data
data used
used in
faultyassumptions,
assumptions, or
real differences
differences
in
in dip
dip from
from east
east to
t o west.
west. The
The overall
overall dip
dipmust
must flatten
flattentot othe
thenorthwest
northwestand
andisisreversed
reversed
northwest
northwest of
of the
t h e Michipicoten
h4ichipicoten belt
beltwhere
whereErnst
ErnstU981,
(1981, p.
p. 87;
87; 1983)
1983) reported
reported consistent
consis
85° SW
dipsofof Matachewan
Matachewandykes.
dykes. Therefore,
Therefore, an
an intermediate
intermediate dip
85O
SW dips
dip value
value of
of 10°
10'
If dips
flatten
perpendicular tto
the fault
fault was
for construction
construction of
perpendicular
o the
was chosen
chosen for
of Figure
Figure 14.
14. If
dips flatten
toward the
the northwest,
northwest, this
this will
will result
of the
toward
result in
in over-estimation
over-estimation of
of the
the true
true thickness
thickness of
the
section.
The
generalized section
section is
is a
a valid
valid representation
representation provided
provided that
that(1)
(I)aa single
si
The generalized
regional
event affected
affected all
(2) late
late vertical
vertical
regional metamorphic
metamorphic event
all of
of these
these rocks,
rocks, and
and (2)
displacement along
faults isisnegligible
Wawa
negligiblebetween
betweenthe
theIcapuskasing
Kapuskasingzone
zone and
and eastern
e
displacement
along faults
subprovince. In
subprovince.
In view of
of the
thecomplex
complex relationships
relationships described
described and
and uncertainties
uncertainties involved,
involved,
these simplifications
simplifications may
information which
be
these
may be
be unwarranted;
unwarranted; however,
however, the information
which can
can be
derived from an exposed
exposedcross-section
cross-sectionthrough
throughpart
partofofthe
thecrust
crust is
is potentially
potentially valuable
derived
enough
permit some
enough tto
o permit
some speculation.
The generalized crustal cross-section,
cross-section, constructed
constructedusing
using aa dip
dipof
of10°
10' (Fig.
(Fig.14),
14),has
has
at its
upperamphibolite
amphibolite tto
its base
base a sequence
sequence ofof upper
o granulite
granulite facies
faciesgneiss
gneiss and anorthosite,
unknown,and
andof
ofwhich
whichsome
some55tot o10
10km
km isisexposed
exposed in
i the
the full
fullthickness
thicknessofofwhich
whichisisunknown,
Kapuskasing
zone. Structurally
Kapuskasing zone.
Structurallyabove
aboveand
and separated
separated by
by an
an analogue
analogue of the
the Conrad
Conra
an estimated
estimated 10 tto
km thickness
thicknessof
of tabular
tabular ba
batholiths
discontinuity (Percival,
(Percival, 1986)
1986) is an
o 15 km
of gneissic
and xenolithic tonalite.
sheetsand
anddeepdeepgneissic and
tonalite. Massive
Massivegranitic
graniticrocks
rocksoccur
occurasassheets
rooted plugs
at this
this structural
structural level.
upper 5-10
km, both
both granitic
granitic rocks
level. In the upper
5-10 km,
rocks and
and
plugs at
gneissic migmatitic
migmatitic haloes
surroundthe
thelow-grade
low-gradeMichipicoten
Michipicotenbelt.
belt. The interfaces
gneissic
haloes surround
between the
the adjacent,
adjacent, generally horizontal megalayers
undulating surfaces
surfaces with
with
between
megalayers are undulating
several kilometres
kilometres of
of relief,
domesatatintermediate
intermediate structural
structural levels
as gneiss
gneiss domes
several
relief, manifest
manifest as
and as
as intrusive
intrusive bodies
bodies aatt higher levels.
and
In the western Superior
Superior Province, two seismic
seismic discontinuities
discontinuitiesat
at16-19
16-19and
and 21-22
21-22
km, define upper,
km,
upper, middle and
and lower crust (Hall
(Hall and
and Brisbin,
Brisbin, 1982).
1982). Using
Usingthe
theKapuskasing
Kapuskasing
model,
boundary between
betweenaastructurally
structurally higher
model, the upper
upper discontinuity corresponds
corresponds tto
o the boundary
granitoid gneissic
subjacent heterogeneous
heterogeneous high-grade
high-grade gneiss
gneiss complex,
granitoid
gneissic layer
layerand
and aasubjacent
whereas the lower discontinuity, corresponding to the middle-lower crustal boundary, is
I
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metamorphic isograd (orthopyroxene
(orthopyroxene isograd?) within
withinthe
theheterogeneous
heterogeneous
gneiss.
Woods
(1985)studied
studiedelectrical
electrical conductivity
conductivity in
Woods (1985)
in the
theKapuskasing
Kapuskasing region with
with aa
large-scale
array. Although
large-scale magnetometer
magnetometer array.
Although the
t h elower
lowercrust
crustisisanomalously
anomalously conductive
conductive in
in
the area (Duncan
et al.,
al., 1980),
there is
is no
no conductivity
conductivity anomaly associated
associated with
with the
1980), there
(Duncan et
Kapuskasing
zoneofofmidmid-t otolower
lowercrustal
crustalorigin.
origin. This was
wasinterpreted
interpreted tto
indicate that
that
Kapuskasing zone
o indicate
the conductivity
the result of in
conductivity anomaly
anomaly at depth
depth is the
& situ fluids
fluids which
which were
were lost during
uplift
uplift ofofthe
theKapuskasing
Kapuskasing structure.
Similar
gravity
Similar models
models of mega-layered
mega-layered continental
continental crust
crustare
arebased
based on
on seismic
seismic and
and gravity
data (Smithson
and Brown,
Brown, 1977;
1977;Berry
Berryand
andMair,
Mair,1980).
1980). Other
Other inferred
inferred cross-sections
(Smithson and
cross-sections
through the
the crust
crust (Ivrea
(Ivrea zone,
zone, Pikwitonei
Pikwitoneiregion,
region,Musgrave,
Musgrave, Fraser
Fraser ranges;
ranges; Fountain
Fountain and
and
Salisbury,
haveinincommon
commonaadownward
downwardincreasing
increasingmetamorphic
metamorphic grade
grade and
and aa thick,
thick,
Salisbury, 1981)have
intermediate-depth
intermediate-depth amphibolite-facies
amphibolite-fades section
section of
of quartzofeldspathic
quartzofeldspathicgneiss,
gneiss,
corresponding
gneissterrane
terrane of
of the Wawa
Wawasubprovince.
subprovince. In
In the
the central
corresponding tto
o the domal gneiss
Superior Province section,
intrude and
and assimilate
assimilate both the
section, these
these gneisses
gneisses intrude
the overlying
overlying
supracrustal succession
successionand
andparts
partsofofthe
theunderlying
underlyingcomplex.
complex. The
entire section down
The entire
down tto
o
I
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20
addedt to
the crust
crust in the interval
20 km was
was added
o the
intervalbetween
between 2750
2750and
and 2680
2680 Ma.
Ma. The
The prepreexisting
as thick
thick as present
present continental
continental crust
crust
existing crust
crust may
may have,
have, but
but need
need not have
have been
been as
prior to
to the
the major
major thickening
thickeningevent.
event. The
Thehigh
highmetamorphic
metamorphic grade
grade in
in this
this older
older crust
crust can
can
be accounted
accountedfor
for by
by burial,
burial, first
first by
later by
by intrusion
intrusion of
of
by aa volcanic
volcanic pile
pile and
and somewhat
somewhat later
tonalite
tonalitesheets.
sheets.
ARCHEAN
ARCHEANEVOLUTION
EVOLUTION OF
OF THE
THE KAPUSKASING
KAPUSKASING CRUSTAL
CRUSTAL STRUCTURE
STRUCTURE
I
The
and mafic gneiss
of the
The oldest rocks so far
far recognized,
recognized, paragneiss
paragneiss and
gneiss of
the
Kapuskasing
zone, aare
considered part
part of a sedimentary-volcanic
Kapuskasing zone,
r e considered
sedimentary-volcanic succession
succession deposited
deposited
$
probably also prior to
and probably
probably as
asaastratiform
stratiform body
t o 2765
2765 Ma
M a ago and
body at
a t depths
depths of less
less
than
than 20
20 km, as inferred from
from the
the presence
presence of relict
relictolivine
olivine(Thurston
(Thurstonetetal.,
al., 1977;
1977; Kushiro
Kushiro
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prior
prior to
t o2765
2765 Ma
Ma ago.
ago. The
TheShawmere
Shawmere anorthosite
anorthositewas
was emplaced
emplaced into
intothis
thissuccession,
succession,
and
by Simmons
et al. (1980),
the intrusion
intrusion may represent the
As suggested
suggested by
Simmons et
(1980), the
the
and Yoder, 1966).
1966). As
differentiation
basalt
differentiationproduct
productofoftholeiitic
tholeiitic
basaltmagmas
magmaswhich
whichalso
also erupted
erupted at
a t surface.
surface.
Major
Major eruption
eruption of
ofvolcanic
volcanicrocks
rocksand
anddeposition
deposition of
ofsediments
sedimentsoccurred
occurredbetween
between
al.,1982)
1982)and
andbetween
between 2725
2725 and
and
2749 and 2696
2696 Ma
Ma ago in the Michipicoten
Michipicotenbelt
belt(Turek
(Tureketetal.,
2749and
2703 M
Ma
ago in
in the western Abitibi
a ago
Abitibibelt
belt(Nunes
(Nunesand
and PyRe,
Pyke, 1980).
1980). The lowermost volcanics
are
dated by the U-Pb
are generally
generally mafic
maficand
and so
so have
have not been
been dated
U-Pb zircon method.
method.
- 30 -
including ultramafic,
ultramafic, mafic, and trondhjemitic to
Synvolcanic intrusions, including
Synvolcanic
to
granodioritic
granodioritic bodies, were intruded into
into the
theMichipicoten
Michipicoten and
and Abitibi
Abitibi piles
piles 2750
2750 ttoo
2700 MMa
ago. Large
Large volumes
volumesofoftonalite
tonalite intruded
intruded beneath
beneath and
andadjacent
adjacent tto
the greenstone
2700
a ago.
o the
at this
thistime.
time.The
Theminimum
minimumage
ageofof2707
2707Ma
Mafor
forWawa
Wawa tonalite
tonalh? (Fig.
(Fig. 11)
11)isisgiven
given by
by aa
belts at
concordant point
point and
and is
is therefore
therefore probably
close tto
the age of
of crystallization.
nearly concordant
probably close
o the
The tonalites
tonalites could
could be
be the
the subsurface expression
expression of
of magmas
magmas that
that produced
produced &cites
dacites in the
The
upper parts of the
upper
the volcanic
volcanic piles.
piles. Tonalite
Tonaliteintrusions,
intrusions,now
now gneissic,
gneissic, engulfed
engulfed and
and
represented as
detached fragments of the
the lower
lower parts
parts of
of the
thegreenstone
greenstone succession
succession (now
(now represented
rnafic
mafic xenolith trains), possible
possible older,
older, tonalite
tonalitebasement
basementenclaves
enclaves(e.g.
(e.g. 1-lillary
Hillmy and
and
Ayres, 1980),
1980),and
andthe
thewestern
western parts
parts of
of the Kapuskasing
which extend
extend into the
Ayres,
Kapuskasing zone which
tonalite gneiss
gneiss terrane. The
Thetonalitic
tonaliticrnagmas
magmasmay
mayrepresent
representjuvenile
juvenilemaginas
magmas derived
derived
from the mantle, or may
products of partial
partial melting
melting of
of aa heterogeneous
heterogeneous lower
lower
from
may be the products
crust similar to
zone. The
t o that
that exposed
exposed in
in the
the Kapuskasing
Kapuskasing zone.
The tonalitic
tonalitic intrusions
intrusions have
have
imposed amphibolite-facies
amphibolite-facies aureoles on metavolcanic
metavolcanic host
host rocks;
rocks; considering
considering the
thevolume
volume
imposed
sufficient ttoo account for most of
of tonalite, the
the heat
heat from
fromthese
thesemagmas
magmas was
was probably
probably sufficient
the metamorphism
of the volcanics.
metamorphism of
volcanics. Tonalitic
Tonaliticmagmatism
magmatismthus
thusmay
mayhave
havecoincided
coincided with
with
regional metamorphism
metamorphismand
andacted
actedas
asthe
the main
mainagent
agentofofheat
heat transfer
transfer into the upper
regional
upper crust
(cf Wells,
Wells, 1979).
1979). Isoclinally
Isoclinallyfolded
foldedgneissosity
gneissosityininthe
thetonalite
tonalite demonstrates
demonstrates that major
(cf
major
deformation post-dates
post-dates these
these intrusions.
intrusions.
The age of
of major deformation
Abitibi and
and Wawa
Wawa subprovinces is closely
deformation in
in the
the Abitibi
Ma, the
the approximate
approximate age
age of
of the youngest
volcanics of
of the main
youngest volcanics
main
bracketed between 2696 Ma,
pile, and 2680
Ma,the
the approximate
approximateage
ageofoflatelate- to post-tectonic plutons
plutons (Frarey
(Frarey and
2680 Ma,
In supracrustal
supracrustal rocks
rocks at
at high
high crustal levels, this
this deformation
deformation produced
produced
Krogh 1986).
1986). In
upright to vertically-plunging
structural features
upright
vertically-plunging structural
features as
as well
well as
as thrusts
thrusts and
and nappe-like
nappe-like
structures
etal.,
al.,1981;
1981; Gorman
German et
et al.,
al., 1978;
1978; Thurston and Breaks,
Breaks, 1978).
1978). At
structures(Poulsen
(Poulsen et
deeper structural
structural levels,
levels, the
thedeformation
deformationresulted
resultediningneissosity
gneissosity and
and subsequent
subsequent folds
folds in
in
plutonic rock
rock and
and paragneiss,
paragneiss, followed
followedby
bylater
later doming.
doming. Forceful emplacement of
plutonic
massive plutons
plutons also
also deflected
deflected structural
structural trends
massive
trends in
in country
country rock
rock into
into concordance
concordance with
with
of these bodies.
at 2680
2680Ma,
Ma,
the margins of
bodies. Following
Following intrusion of the
the massive
massive plutons at
subprovinces. There
there was
was relative
relative tectonic
tectonicquiesence
quiesencein
inAbitibi
Abitibi and
and Wawa
Wawa subprovinces.
There is
is
evidence, however, of continued activity
activity in
in the
theKapuskasing
Kapuskasing zone.
zone.
High-grade metamorphic rocks of
of the Kapuskasing
yield concordant U-Pb
High-grade
Kapuskasing zone yield
U-Pb
zircon dates of 2696
Ma. U-Pb
U-Pb zircon dates
dates are
a r e generally
generally considered
considered to
t o record
record
2696 ttoo 2616
2616 Ma.
case are
a r eof
of metamorphic
metamorphic origin.
origin.
the age of crystallization of
of the
the zircons,
zircons, which
which in
in this
this case
interpretation would
This interpretation
would imply
imply tthat
h a t metamorphism
metamorphism in
in the
t h e Kapuskasing
Kapuskasing zone occurred
r
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3
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2696
Ma
ago,up
upt to
60M
Ma
aftertectonic
tectonic stabilization of
of much
much of
of the
the rest of
2696 ttoo 2616
2616 M
a ago,
o 60
a after
of
Superior
province. A discrete burial
and metamorphism
metamorphismevent,
event,restricted
restricted tto
burial and
o the
Superior province.
Kapuskasing zone, could explain the deformed, metamorphosed
metamorphosed conglomerate
conglomerate cobbles
cobbles
from Borden
Lake which
which have
have aa zircon
zircon date
date of 2664
2664 Ma
Ma (Percival et al.,
al., 1981).
1981). However,
However,
Borden Lake
an anomalously
young zircon
zircon date
date of
of 2552 M
Ma
on aa trondhjemitic
trondhjemitic cobble from the
anomalously young
a on
the weakly
weakly
metamorphosed
Ma
Doré conglomerate
conglomerate near Wawa,
reported by
Turek et
et
metamorphosed >2696
>2696 M
a Dore
Wawa, reported
by Turek
al. (1984),
suggests that
that the date
(1984), suggests
date on
on the
theBorden
Borden Lake
Lake conglomerate
conglomerate cobble
cobble may
may not
represent the age of crystallization of the source
source pluton.
pluton. In
In addition,
addition, tectonic
mechanisms which
which could
could lead
lead tto
of the 500
krn wide
wide
o deep burial of
500 km long xx 50
50 km
Kapuskasing
"sliver"are
are unknown
unknownand
andseem
seemt otobe
beunlikely
unlikelyafter
after termination
termination of
of the major
Kapuskasing "sliver"
tectonism
theAbitibi
Abitibiand
andWawa
Wawasubprovinces.
subprovinces. It is more likely that aa single
single
tectonism ininthe
protracted
protracted metamorphic
metamorphic event
eventwas
wasresponsible
responsible for
forproducing
producing the
the observed
observed
characteristics.
One must
must therefore examine the assumption that zircons
zircons are
a r e closed
closed to
t o lead
lead loss
loss
immediately following
crystallization, regardless of the
following crystallization,
the cooling
cooling history. Slowly
Slowly
decreasing
temperatures from
decreasing metamorphic temperatures
from peak levels of 800°C
800° could
could result
result in
in lead
lead
diffusion
years after
after crystallization, provided
that there
diffusion out
out of
of zircon
zircon for several million
million years
provided that
is
temperature" for zircon.
50°C was
was estimated
is some finite "blocking
"blocking temperature"
zircon. AAvalue
value of
of 700
700 ±
-+ 50°
for
this hypothesis ttoo explain
for zircon blocking
blocking by Mattinson (1978).
(1978). Invoking
Invoking this
explain the
theyoung
young
"metamorphic"
"metamorphic" dates
dateswould
would allow
allow aa simpler
simpler geological
geological history
historyinvolving
involving only
only the
the
metamorphism
with later fluid
metamorphism at
at 2700
2700 to
t o 2680
2680 Ma
M a with
fluid circulation and
and possible
possible ductile shear
at
at depth.
depth.
The
east-northeast structural
The prominent
prominent east-northeast
structuraltrends
trendsininthe
theKapuskasing
Kapuskasing zone
zone are
are the
the
result of
of relatively
relatively late
late tectonism.
tectonism. The
Thestructural
structuralgrain
grainisisdefined
defined by
by the orientation
orientation of
inigmatitic
axes. This
nigmatiticand
and gneissic
gneissiclayering
layering folded
folded about
aboutshallow-plunging
shallow-plunging ENE
ENE axes.
This folding
folding
event
event therefore
therefore post-dates
post-dates crystallization
crystallization of
of tonalitic
tonaliticmelts,
melts,thought
thought to
t ocoincide
coincide with
with
the
netamorphic peak.
units that can be
the inetamorphic
peak. Similarly,
Similarly, structurally
structurally complex
complex tonalitic gneiss units
traced
into the Kapuskasing
have a strong,
strong, superimposed
superimposed
traced from
from Wawa
Wawa subprovince into
Kapuskasing zone have
ENE
ENE foliation
foliation and lineation in
in the
theKapuskasing
Kapuskasing zone
zone(Percival
(Peruvaland
andCoe,
Coe,1981).
1981). If the
the
correlation
correlation is
isvalid
valid between
between massive
massive granodiorite dated at
a t 2680
2680 ±
Ma and granodiorite
granodiorite
-+ 3 Ma
gneiss
then the
the ductile
gneiss adjacent to
to the
theKapuskasing
Kapuskasing zone in the Abitibi subprovince,
subprovince, then
strain
strain occurred
occurred after
after2680
2680 Ma
Ma but pre-dated
pre-dated post-metamorphic
post-metamorphic cooling.
cooling. This
This timing
timing is
consistent
that sinistral
sinistral transcurrent
transcurrent movement
consistent with
with the
thesuggestion
suggestion of
of Watson
Watson (1980)
0980) that
movement
occurred
occurredalong
alongthe
theKapuskasing
Kapuskasing zone
zone during
during emplacement
emplacement of
of the
theMatachewan
Matachewandyke
dyke
swarm
swarm at
at 2633
2633 Ma
Ma (Gates and Hurley,
Hurley, 1973).
1973). Late
Late Archean
Archean deformation
deformation could
could have
have
promoted
promoted resetting
resettingofof2700-2680
2700-2680 Ma
Ma zircons
zircons to
toages
agesdown
downto
t o2616
2616Ma.
Ma.
- -
— 32
32 —
UPLIFT
UPLIFT OF
OF THE
THE KAPUSKASING
KAPUSKASING STRUCTURE
STRUCTURE
The age of
of uplift of the Kapuskasing
constrained. Evidence
Kapuskasing zone is not well constrained.
Evidence of
of
late
lateArchean
Archean transcurrent
transcurrentmovement
movementwas
wascited
citedby
byWatson
Watson(1980)
(1980) and Percival
Percival and
and Coe
Coe
(1980),
however its
its magnitude was probably
probably small,
small, judging
judging by
bythe
the minor
minor apparent
apparent offset
(1980), however
offset
of
occurred aatt that
of the
the Abitibi-Opatica
Abitibi-Opatica contact
contact (Fig.
(Fig. 1).
I). Major
Major thrusting
thrusting could
could also
also have occurred
that
time,
time, setting
settingU-Pb
U-Pb and
andK-Ar
K-Ar isotopic
isotopicsystems
systemsininthe
thehigh-grade
high-graderocks
rocksata t2,650-2,250
2,650-2,250 Ma.
Ma.
Geochronological
evidence indicates
indicates activity
activity at
Ma. Three
Three alkalic
alkalic
Geochronological evidence
at 1,655-1,850
1,655-1,850 Ma.
rock-carbonatite
rock-carbonatite complexes
complexesnear
nearKapuskasing
Kapuskasiighave
haveK-Ar
K-Ar dates
datesofof1,655-1,720
1,655-1,720 Ma
Ma
(Gittins
(Gittins et
et a!.,
al., 1967).
1967). AAbiotite-whole-rock
biotite-whole-rock Rb-Sr
Rb-Sr isochron
isochron from tonalite of
of the
the
Shawmere
arid others,
others, 1980).
1,850Ma
Ma (Simmons
(Simmons and
1980). A
A whole-rock
whole-rock
Shawmere anorthosite
anorthositecomplex
complexisis1,850
40Ar/39Ar
analysis
of blastomylonite from
from the Ivanhoe Lake
Lake cataclastic
cataclastic zone gave aa
'+o~r/^~
r
of
date
dateof
of 1,720
1,720Ma
Ma (Percival,
(Percival,1981;
1981;Fig.
Fig. 15).
15).
3-0
25
to
2.0
0)
0l
C
02
Co
a
a
I.e
1.0
0.2
0.4
0.6
0.8
1.0
Fraction
Fraction 39Ar
" ~ rre'eased
released
Figure
Figure15.
15. 40Ar/39Ar
40Ar/39Ar age
agespectra
spectrafor
forhornblende,
hornblende,plagioclase
plagioclaseand
andwhole-rock
whole-rock
separates
separatesfrom
fromnear
near the
theIvanhoe
IvanhoeLake
Lake cataclastic
cataclasticzone.
zone. Increasingly
Increasinglyhigh
high
release
releasetemperature
temperature from
from left
lefttotoright.
right.Width
Widthofofbars
barsare
are2o-uncertainty
2uuncertainty
estimates.
estimates.
ii
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17
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-33rock-carbonatite complexes in the southern
Three alkalic rock-carbonatite
southern Kapuskasing
Kapuskasing zone have
of 1,050-1,100
Ma (Gittins
(Gittins et at.,
K-Ar
K-Ar dates of
1,050-1,100 Ma
al., 1967).
1967). Plagioclase
Plagioclase from
from amphibolite4n
amphibolite-in tthe
he
of tthe
Ivanhoe Lake
Lake cataclastic
cataclastic zone
footwall of
h e Ivanhoe
zone yields a 40Arf39Ar
^O~r/39Arplateau at
at 1107
1107 Ma
Ma
(Fig. 15),
suggestingmild
mildresetting,
resetting, possibly
possiblydue
duet otofaulting.
faulting. Lower
concordia intercepts
intercepts
(Fig.
15), suggesting
Lower concordia
of zircon discordia in tthe
Ma (Percival
(Percival and
and Krogh,
Krogh, 1983)
1983)may
mayrelate
relatetto
of
h e range 827-1,108
827-1,108 Ma
o
ago.
uplift 1,100-1,000
1,100-1,000 Ma ago.
events along
along tthe
structure with major
The coincidence of Proterozoic events
h e Kapuskasing
Kapuskasing structure
orogenic activity
activity elsewhere
Shield suggests
suggeststhat
thatt hthe
structure is
is an
anintracratonic
intracratonic
orogenic
elsewhere in tthe
h e Shield
e structure
basementuplift
uplift related to
possibly an
anearly
early Proterozoic
Proterozoic
basement
t o aa distant
distant compressional
compressional event, possibly
collision in the Churchill Province to
t o the
t h e northwest
northwest (Percival
(Percivaland
andMcGrath,
McGrath, 1986).
1986).
- 34 -
PART lb ROAD LOG
.
KAPIJSKASING UPLIFT:
UPLIFT: ARCHEAN
THE KAPUSKASING
ARCHEAN GREENSTONES
GREENSTONES AND
AND GRANULITES
GRANULITES
SUMMARY
Variousstructural
structural levels within tthe
Various
h e central
centralSuperior
Superior Province
Province will
will be
be examined
examined to
to
demonstrate their characteristics
characteristics and
and interrelationships.
interrelationships. Starting
Startingwith
with the
thelowest-grade
lowest-grade
area, we
we will
will progress up-grade
up-grade through an
rocks in the Michipicoten
Michipicoten belt of the
t h e Wawa
Wawa area,
unbrokenoblique
obliqueccrustal
cross-section into tonalitic gneisses and granulites of the
unbroken
r
Kapuskasing zone.
DAYI
Geology
of the
Geology of
the Wawa
Wawa Subprovince, Wawa ttoo Chapleau
Chapleau
in well-preserved
well-preserved supracrustal rocks of
of tthe
h e Michipicoten
Michipicoten belt
The first day begins in
and ends
ends in
in the
the lowest
lowest structural
structural levels
gneiss terrane (Fig.
and
levels of the
the Wawa
Wawa gneiss
(Fig. 2).
2). Exposures
Exposures
near Wawa
willdemonstrate
demonstrate lithological,
lithological,structural
structural and
and metamorphic
metamorphic characteristics
characteristics of
Wawa will
of
the low-grade
terrane. To
rocks
ocks and
and internal
low-grade terrane.
To the
theeast,
east,the
thetransition
transitiontot ogneissic
gneissicplutonic
pi
characteristics
gneiss terrane will be examined.
W
characteristicsof
of the
t h eWawa
STOP 1-1:
1-1: Doré
STOP
Dore Conglomerate
Conglomerate(E.
(E.and
andW.
W. sides
sidesof
of Hwy
Hwy 17)
17)
The Dore
Doré isis aa thick,
thick, coarse polymictic
polyrnictic conglomerate unit tthat
h a t isis overlain
overlain by
by
The
metavolcanic rocks
at2696
2696 Ma
Ma (Turek
(Turek et
et al.,
al., 1982)
1982)and
and underlain
underlain by
by
rocks of cycle
cycle HI,
111, dated
dated at
older inetavolcanic
metavolcanic rocks.
rocks. Eastward
f a d e s transition
transitionfrom
from Doré
Dore conglomerate
conglomerate
older
Eastward there
there is
is aa facies
of wacke, siltstone, cross-bedded
cross-bedded arkose and conglomerate called the
the
into a sequence of
"Eleanor Slate".
Slate". At this locality, coarse felsic tuff-breccias to
"Eleanor
t o the
t h enorth
north are
aresucceeded
succeeded
southward by
by aa sequence
sequence of
of wacke
wacke (reworked
(reworked tuff?)
tuff?) and
and Dore
Doré conglomerate.
conglomerate. Bedding
southward
Bedding and
foliation dip approximately 45°
45" eastward
eastward and
and may
may face
facedownward
downward (west).
(west).
The Dore
Dare consists of
of pebbles
pebbles and
and boulders
boulders of
of mafic
mafic and
and felsic volcanics,
The
volcanics, quartz
quartz
porphyry, iron
iron formation
formation and
andtrondhjemite
trondhjemiteininaa schistose,
schistose, chloritic
chloritic matrix.
matrix. The
The pebbles
pebbles
porphyry,
aare
r e flattened
flattenedininthe
thefoLiation
foliation plane
plane and
and elongated
elongated in
in the
the east-plunging
east-plunging rodding
rodding lineation.
lineation.
Variations
in pebble
pebblepacking
packingand
andsize
sizedefine
definecrude
crudestratification
stratification units.
units. A
Variations in
A single
trondhjemitic boulder
apparent age
age of
of 2552
2552 Ma
Ma
boulder yielded discordant zircons with an apparent
(Turek et
et al.,
at., 1984),
approximately 150
150M
Ma
youngerthan
thant hthe
stratigraphicage
age of
of the
the unit
unit
1984), approximately
a younger
e stratigraphic
(Turek
likely that
that the source of
of the
based on zircon
zircon dates of bracketing volcanic
volcanic rocks.
rocks. It is likely
based
trondhjemitic boulders
syn—volcanic
M a age.
trondhjernitic
bouldersand
andcobbles
cobblesis is
syn-volcanic plutons
plutonsofof2744—2735
2744-2735 Ma
r
I
1-2: Helen Iron Range Section at McLeod Mine, Algoma Ore Properties Ltd.
The McLeod
Mineextracts
extracts siderite
siderite and
and pyrite
pyrite from
from the base of the
McLeod Mine
the Helen
Helen iron
iron
range. This
1800 m
m thick unit of intermediate to
t o felsic
felsic
Thisiron
iron range
range lies
lies at
a t the
thetop
topof
of aa1800
metavolcanics
metavolcanics consisting of oligomictic and polymictic breccia, thin
thin bedded
bedded to
t o massive
massive
tufts,
flows, and
andcrystal
crystal tuffs.
tuffs. These
tuffs, lapilli
lapilli tuffs,
tuffs, spherulitic
spheruliticflows,
flows, flow
flow banded
banded flows,
These
intermediate
to felsic
felsic metavolcanics
metavolcanics are
areintruded
intruded by
by gabbro
gabbro ttoo quartz
quartz diorite
diorite dykes
dykes and
intermediate to
sills
sills that
that reach
reach290
290m
m thickness.
thickness.
The intermediate
intermediate to
dominantly massive
massive and
and
t o felsic
felsicmetavolcanics
metavolcanicsoverlie
overlieaadominantly
pillowed
of intermediate to
ed sequence of
t o mafic
mafic metavolcanics.
metavolcanics.
The
The mafic to
t o felsic
felsic metavolcanics
metavolcanics are
arebimodal
bimodal in
in composition
composition and represent the
the
oldest cycle
cycleof
ofvolcanism
volcanism(Fig.
(Fig. 14).
14).
The
The iron formation caps the first
firstvolcanic
volcanic cycle
cyclein
in the
theMichipicoten
Michipicoten greenstone
greenstone
belt
belt and
and from
from the
the stratigraphic
stratigraphicbottom
bottom to
totop
t o pconsists
consistsof
of five
fivelithologic
lithologic rock
rock types
types that
that
are
are gradational
gradational into
into each other. Upper
Upper and
and lower
lower contracts are sharp.
sharp. From
From
stratigraphic
stratigraphic bottom
bottom to
t o top
top the
t h eiron
iron formation
formation consists
consists of
of siderite,
siderite, pyrite,
pyrite, banded
banded chert,
chert,
thin
chert-wacke-magnetite, and graphite-pyrite.
thin bedded
bedded chert-wacke-magnetite,
graphite-pyrite. AAU-Pb
U-Pb isotopic
isotopic age
age of
of
approximately
has been
been obtained
obtained from
from the
the crystal
M a has
crystal tuffs
tuffslying
lyingimmediately
immediately below
below
approximately 2749
2749 Ma
the
the iron
iron formation
formation (Turek
(Turek et
et al.,
al., 1982).
1982).
Overlying
intermediate to
Overlying tthe
h e iron formation are massive
massive pillowed
pillowed intermediate
t o mafic
mafic
inetavolcanics
inetavolcanics of
of cycle
cycle two.
two.
The
The area
area of
of the
themine
minedisplays
displays numerous
numerous major and minor faults, and
and contains
contains
several
a1Proterozoic
Proterozoic diabase
diabase dykes that strike
strike northeast
northeast and
and northwest.
northwest.
Beneath
areaofofapproximately
approximately1800
1800mmby
by 750
750 m
m has
has been
been
Beneath the
theiron
iron formation
formationan
anarea
outlined
outlined that
that contains
containschloritoid.
chloritoid. These
Thesecrystals
crystalsare
aregenerally
generallyup
upto
t o22mm
mrn in
in diameter
diameter
and
and are
a r erandomly
randomly oriented with
with respect ttoo the schistosity.
schistosity. Chloritoid
Chloritoid alteration
alterationoccurs
occurs
above
above the
the iron
iron formation
formation as
aswell,
well, in
in less
less abundant
abundant quantities.
quantities.
The
The volcanics
volcanics above
above and
and below
below the
the iron
iron range
range are
arepervasively
pervasivelysoaked
soakedwith
with
carbonate.
carbonate. Carbonate
Carbonatealteration
alterationisisofofregional
regionalextent
extentand
andoccurs
occursin
inall
allrock
rock types,
types,
volcanic,
volcanic. sedimentary,
sedimentary, and
and intrusive.
intrusive.
STOP
il
I
I
I
I
I
I
I
I
I
I
I
I
I
Spherulitic rhyolite
rhyolite(100-200
(100-200 m
m south
south of
of gate
gateon
onMcLeod
McLeod Mine
Mine road)
road)
Stop 1-3
1-3 Spherulitic
Stop
This
This stop
stop contains
containsthe
thebest
bestexposure
exposureofofaaspherulitic
spherulitic(hollow)
(hollow)flow
flowbanded
banded felsic
felsic
&
.
flow
Mine area.
area. The
flow within
within the
the McLeod
McLeod Mine
The spherulitic
spherulitic unit
unit isis overlain
overlain by
by aa flow
flow breccia
breccia
containing well
well developed
developed fiamme
fiamme and
and this
this unit
unit isisin
in turn
turnoverlain
overlainby
by aa massive
massivetuff
tuffwith
with
containing
scattered
scattered lapilli-size
lapilli-size clasts.
clasts. This
Thisexposure
exposure lies
lies in
in the
the lower
lower part of
of the
the felsic
felsic part
part of
of the
the
— 36 -
oldest
oldest cycle
cycle of
of volcanism.
volcanism. Stratigraphic
Stratigraphic tops
tops are
are north
north and
and the
t h esection
sectionisisoverturned,
overturned,
dipping
along
Wawa
atWawa
Wawa
dipping south.
south. Interpreted
Interpretedfaulting
faulting
along
WawaLake
Lakeand
andbeach
beachdeposits
depositsat
prevent
any
estimate
as
to
how
far
above
the
contact
with
the
intermediate
prevent any estimate as t o how far above t h e contact with t h e intermediate to
t o mafic
mafic
pillowed
metavolcanics this
this felsic
felsic section
pillowed and
and massive
massive metavolcanics
section occurs.
occurs.
Return
Return to
t o Hwy
Hwy 101
101
-
00.0
km - Junction
Me, Wawa.
Junction of
of Highway
Highway IOIE
101Eand
and Broadway
Broadway Ave,
Wawa. Proceed
Proceed east
east on
on
00.0 km
Highway
Highway 101.
101.
-
20.9
20.9 km -- Stop
Stop 1-4:
1-k Mafic
Maficgneiss
gneiss - tonalite
tonalitecontact
contactzone
zone(N.
(N.and
andS.S.sides
sides of
of Hwy
Hwy101)
101) ,
A
Ic gneiss
A large
large enclave
enclave of
of maf
mafic
gneiss is enclosed in and
and intruded by tonalitic
tonaliticgneiss
gneissininaa
migmatitic
migmatiticzone
zone marginal
marginal to
t o the
the Michipicoten
Michipicoten greenstone
greenstone belt. The
Thehornblendehornblendeplagioclase
considered tto
represent deformed, metamorphosed
plagioclase gneiss is considered
o represent
metamorphosed Michipicoten
volcanics and
and metagabbro.
metagabbro. In
In this
this exposure
exposurei titisiscut
cut by
byearly
earlytonalitic
tonalitic intrusions,
intrusions, llate
ate
aplitic
apliticand
and pegmatitic
pegmatiticdykes,
dykes, and
and still
stilllater
latermafic
maficand
andlamprophyric
lamprophyricdykes.
dykes. The
Thegneiss
gneiss
displays
subvertical foliation,
foliation, mineral
displays subvertical
mineral lineation,
lineation,and
and tight
tightsteeply-plunging
steeply-plunging isoclinal
isoclinal
minor folds.
45.1
45.1 km
km
Jct.
Jct. Hwy.
Hwy. 651.
651. Continue
Continueeast.
east.
*
,
-
68.5
gneiss
Budd
and
68.5 km Stop
Stop1-5:
1-5: Xenolithic
Xenolithictonalite
tonalite
gneissatat
BuddLake
Lake(N.
(N.
andS.S.sides
sidesofofHwy
Hwy101)
101)
This
This complex
complex outcrop
outcropconsists
consists of
of several
severalphases:
phases: 1)
1) xenoliths of mafic
maficgneiss,
gneiss,
interpreted
interpreted as
asrafts
raftsofofthe
t h eMichipicoten
Michipicotenmetavolcanic
metavolcanicsequence,
sequence, 2)
2)gneissic
gneissic tonalite
tonalite
with small, wispy mafic xenoliths, cut by 3) foliated to gneissic hornblende-epidote-
biotite-sphene tonalite, all cut by 4) pink-white granitic pigmatite. Hornblende from
foliated
wt% ,41203,
A1203, indicating
indicating crystallization
crystallization at
foliated tonalite
tonalite(3)
(3) contains
contains 10.4
10.4 wt%
approximately
approximately5.6
5.6 kbar
kbar(Hammarstrom
(Hammarstromand
andZen,
Zen, 1985).
1985).
Continue east on 101
94.4 km Stop 1-6; Tonalite gneiss and maf Ic dykes (N. and S. of Hsy 101)
Tonalite
northeast-trending mafic
Tonalite gneiss
gneiss iiss cut by northwest- and
and northeast-trending
mafic dykes
dykes with
wit
chilled
dykes
(Ernst
and
chilledmargins.
margins. The
Theolder
oldernorthwest-striking
northwest-strikingHearst
Hearst
dykes
(Ernst
andHalls,
Halls,1980,
1980,1984)
1984)
occur
have aa similar
similar trend and
occur west
west of
of the
t h eKapuskasing
Kapuskasing zone.
zone. The
The dykes
dykes have
and similar
similar
-
r
I
(I
I
I
I
1
I
I
I
I
including plagioclase
plagioclase phenocrysts
phenocrystsand
andtholeiitic
tholeiitic composition,
composition, tto
characteristics, including
o
Matachewan dykes
dykes east
east of
of the Kapuskasing
zone. The
Kapuskasing zone.
The Matachewan
Matachewan dykes
dykes have an Rb-Sr
Rb-Sr
Matachewan
whole-rock age of 2633
± 75 M
Ma
(Gates and
andHurley,
Hurley, 1973).
1973). Ernst and Halls (1980,
a (Gates
(1980, 1984)
1984)
whole-rock
2633 +
also reported
reported similar paleomagnetic poles
poles for
for the two
zone 50
50 km
km wide
wide
also
two swarms.
swarms. InInaa zone
"
zone, the
the Hearst dykes average
average 44 m
m in
in width and
west of the
the Kapuskasing
Kapuskasing zone,
and have
have a
consistent easterly
easterly dip
dip of
of 80Â
80° (Ernst,
(Ernst, 1983;
Percival, 1981).
1981). The
Thetonalitic
tonalitic gneiss
is thinly
thinly
consistent
1983; Percival,
gneiss is
layered and
and has
hassparse
sparsemafic
maficxenoliths.
xenoliths. Gneissosity
appearstto
havechaotic
chaotic orientation
orientation
Gneissosity appears
o have
but is subhorizontal
onaverage.
average. There
Thereisisevidence
evidencefor
forat
at least
least two
two sets
setsofof structure:
structure: an
an
but
subhorizontal on
older gneissosity
gneissosity is
is reoriented
reoriented by
by younger
younger subhorizontal
subhorizontalfoliation
foliation to
t o give
give complex
complex
patterns.
sigmoidal patterns.
Continue east
122.2km
km Stop 1-7:
122.2
1-7: Highbrush
Highbrush Lake
Lake Dome
Dome (N.
(N.side of Hwy
Hwy 101)
101)
Small domes
domesexposed
exposedininroadcuts
roadcutshere
hereare
aretypical
typicalofof the
the local
local and
and possibly
possibly of
of the
the
Small
regional-scalestructural
structural pattern.
pattern. The
rock type is fine-grained,
fine-grained, thinly-layered
thinly-layered
regional-scale
The main
main rock
biotite and
biotite
and hornblende-biotite
hornblende-biotite gneiss
gneiss with
with local
localaugen
augen of potash
potash feldspar.
The outcrop
outcrop consists
consists of
of several
several domes
domesor
orcanoe-shaped
canoe-shapedfolds
foldswith
withaarolling
rolling easteastThe
west mineral
mineral and
andstretching
stretchinglineation.
lineation. Small
parts
west
Small intrafolial
intrafolialfolds
foldsare
arepresent
present in
in some
some parts
as are
areamphibolitic
amphibolitic xenoliths,
xenoliths,locally
locally with
with clinopyroxene.
clinopyroxene. Pink
Pink granitic
granitic
of the outcrop,
outcrop, as
and sills
sills cut
cut gneissic
gneissic layering
layering in
in some
some areas.
areas. Late sub-horizontal highpegmatite dykes
dykes and
are common
commonininthe
the vicinity
vicinity of
strain zones
zones are
of the
thetransition
transitionzone
zonebetween
betweenWawa
Wawa and
and
Kapuskasing gneisses.
gneisses.
Continue east
-
I
131.6km
km - Junction
Junction of
of Highway
andHighway
Highway129.
129. Follow
Follow 101E,
lOlE, 129N
toward
Highway 101
101 and
129N toward
131.6
1
132.9 km
Chapleau
Stop 1-8:
1-8: Xenolithic tonalite
(w. side
side of
of Hwy
Hwy
Stop
tonalite with
withhorizontal
horizontalshear
shear zones
zones (W.
101—129)
101-129)
1
I
I
I
Xenolith alignment and
gneissosityhave
havesub-vertical
sub-verticalorientations
orientations in
in the
the central
central
and gneissosity
thin
part of this
this road-cut.
road-cut. Layering
Layeringbecomes
becomes horizontal
horizontal and
and mafic
mafic xenoliths
xenoliths become
become thin
and bottom
bottom of
of the
mafic layers in 1/2
112 m-thick horizontal
horizontalshear
shear zones
zones near
near the top and
outcrop.
139.5
-
— 38
—
km . Junction
)unction of
of Highways
and 129N:
129N: Proceed north
km
Highways 1OIE
101E and
north on
on Highways
Highways 101-129
101-129
through Chapleau.
Chapleau. Follow
Follow the
t h eMissinaibi
Missinaibi Provincial Park
Park signs north of town
on gravel road.
road. Proceed
Proceednorth
northand
andeast
easton
onpark
parkroad
roadand
andlogging
logging roads
roads
leading ttoo the
the Chapleau
Chapleau River.
River.
-
178.3
FlorannaLake
LakeComplex
Complex
Stop 1-9:
1-9: Floranna
178.3 km - Stop
The Floranna
Floranna Lake
Lake Complex
Complexisisaacomplex
complexcrescentic
crescentic pluton
plutonofof intermediate
intermediate
composition.
composition. The
The western
western margin
margin consists of lineated,
h e a t e d , fine
fine grained
grained granite
granite with
with
orthopyroxene and
and biotite.
biotite. inside
Inside the
the marginal
marginal unit is
is lineated diorite
diorite to
t o monzonite
rnonzonite
containing hornblende-rimmed
augenclinopyroxene
clinopyroxenephenocrysts.
phenocrysts. The
Thecentral
central part of the
hornblende-rimmed augen
the
complex is foliated
hornblende-clinopyroxene-biotitediorite,
diorite, gabbro
gabbroand
and
foliated and
and lineated
lineated hornblende-clinopyroxene-biotite
melagabbi-o.
well-exposed eastern
eastern contact
contact of
melagabbro. The well-exposed
of the
thecomplex
complexshows
shows extremely
extremely
attenuated
attenuatedand
and contorted
contortedlayering
layering in
in granite
granite of
of the
thecomplex
complex adjacent
adjacent to
t o rocks
rocks of
of the
the
Robson
Lake dome
dome tto
the east.
Robson Lake
o the
Clinopyroxene
augen diorite-monzonite
diorite-monzonite
C l i p y r o x e n e augen
These
coarse-grained monzonite.
medium- to coarse-grained
monzonite. RodRodThese rocks are strongly lineated, mediumshaped
shaped clinopyroxene
clinopyroxene phenocrysts, rimmed
rimmed by
by hornblende,
hornblende, make
make up
up some
some 20%
20% of the
the
rock.
rock. Original
Originaloutlines
outlines of
of feldspar
feldspar grains
grains are
arevisible
visible but
but these
theseare
arenow
now polycrystalline
polycrystalline
aggregates.
aggregates.
j-y,
-
179.3 -
Foliated and lineated
h e a t e d diorite
dioritewith
with gabbro
gabbro and
and melagabbro
melagabbro layers
layers
Igneous clinopyroxene with
with hornblende
hornblende overgrowths
overgrowths and
and granitic leucosome
leucosome layers
layers
are
are present.
present.
-
183.2
Granulitegneiss,
gneiss,Robson
Robson Lake
Lake dome
dome
183.2 km - Stop
Stop 1-10:
1-10: Granulite
The
of tthe
complexisisaa foliated
foliated to
to augen-textured,
augen-textured,
The easternmost exposure of
h e igneous complex
xenolithic
porphyritic granite
granite with
with leucogranite
leucogranite veinlets
veinlets parallel ttoo foliation
xenolithic hornblende
hornblende porphyritic
on
on the
the 11 mm-2
mm-2 cm scale.
scale. The
Thelayering
layeringisisfolded
foldedabout
aboutnorthwesterly-plunging
northwesterly-plunging axes.
axes.
Parts
Partsof
of the
theoutcrop
outcropare
a r efine-grained
fine-grained and
andmylonitic
myloniticwith
with highly
highly attenuated
attenuatedlayering.
layering.
To
of interlayered mafic
To tthe
h e west, the
t h e Robson
Robson Lake dome consists of
mafic and
and tonalitic
tonalitic
gneiss.
gneiss. Near
Near the
thecontact
contactwith
withthe
theFloranna
FlorannaLake
LakeComplex,
Complex, the
t h e layering
layering in
in rocks in the
dome
concordant tto
west, however,
however, the
the attitude
attitude is
dome is concordant
o the contact and
and dips steeply west,
is
horizontal
Ic rocks
eastin
in the
thecore
coreof
of the
thedome.
dome. AtAtthis
thisoutcrop
outcropthe
themaf
mafic
rocks consist
consist
horizontal farther
farther east
of
garnet-clinopyroxene-hornblende-plagioclase-quartzassemblages,
assemblages, with
with layering
layering
of garnet-clinopyroxene-hornblende-plagioclase-quartz
defined
and hornblende-rich
defined by
by different
different proportions
proportions of
of minerals,
minerals,including
including garnet-rich
garnet-rich'and
hornblende-rich
varieties.
varieties. Concordant
Concordanttonalitic
tonaliticlayers
layerslocally
locallyhave
havelarge
largeclinopyroxene
clinopyroxenecrystals
crystalsrimmed
rimmed
by
by hornblende,
hornblende, in clots up ttoo 4 cm. The
Thelayering
layering isisfolded
folded about
about upright
upright isoclinal
isoclinal folds
folds
locally.
locally.
r
I
I
I
I
I
I
I
-39inclusions of
of mafic gneiss
gneiss in
in granite
granite
of granite
in mafic gneiss and inclusions
Small dykes of
granite in
indicate an
indicate
an intrusive
intrusivecontact
contactbetween
betweenthe
theFloranna
FlorannaLake
LakeComplex
Complexand
and Robson
Robson Lake
dome.
The interpretation
interpretation of the
Lake dome,
dome,which
whichhas
hasthe
thestructural
structural attributes
attributes
The
the Robson
Robson Lake
of the
domal gneiss
gneissterrane
terraneand
andthe
thelithological
lithological characteristics
characteristics of
t h e Wawa
Wawa domal
of Kapuskasing
Kapuskasing
zone, is
is that rocks
zone underlie
underlie the Wawa
domal
zone,
rocks like
likethose
those exposed
exposed in the
the Kapuskasing
Kapuskasing zone
Wawa domal
terrane
been exposed
exposedhere
hereininaastructural
structural culmination.
culmination.
terrane and
and have
have been
Return to
t o Chapleau
Chapleau
DAY 2
Geologyof
of the Kapuskasing
KapuskasingStructural
Structural Zone
Zone in
in the
the Chapleau-Foleyet
Chapleau-Foleyet Area
Geology
In this
this section we will
will examine
In
examine the
t h e rocks
rocks and
and structures of
of the
t h e Wawa
Wawa domal
doma'
gneiss -- Kapuskasing
Kapuskasingzone
zoneboundary
boundaryand
andofofthe
theKapuskasing
Kapuskasingzone
zoneitself
itself along
along
gneiss
Highway 101.
101.
-
0.0 km
km 0.0
I
I
I
I
I
I
I
*
ii.
and Highway
Highway 129 south
south of
of Chapleau.
Chapleau. Proceed
Junction of Highway
Highway 101E
101E and
Proceed east
on Highway 101.
101.
2-1: Borden
13.0 km
km Stop
101)
Lake conglomerate
conglomerate (S.
(S. side of Hwy 101)
13.0
Stop 2-1:
Borden Lake
This outcrop
outcrop consists
consists of
of stretched-pebble
stretched-pebble metaconglornerate
metaconglomerate with
with aa strong rodding
rodding
This
weak, gently
gently north-dipping
north-dipping foliation.
foliation. The
lineation and
and weak,
The rock
rockisisaaclast-supported
clast-supported
conglomerate containing 10%
10%matrix
matrix of
of garnet-hornblende-biotite-quartz.
garnet-hornblende-biotite-.quartz. The
The cobbles,
cobbles,
conglomerate
which range
range up
uptto
m in
in length,
length, aare
felsic metavolcanics,
metasediments,granodioritegranodioriter e felsic
metavolcanics, metasediments,
which
o 1m
amphibolite, with rare hornblendite
tonalite, plagioclase-porphyritic
plagioclase-porphyritic meta-andesite
meta-andesite and
and amphibolite,
and vein
vein quartz.
quartz. The
and
The metaconglomerate
metaconglomerate is spatially
spatially associated
associated with amphibolite and
and
paragneissto
tothe
the south
southon
onBorden
BordenLake,
Lake,and
andisiscut
cutby
bygranite,
granite, however,
however,tthe
stratigraphic
h e stratigraphic
paragneiss
relations of
relations
of the
thesupracrustal
supracrustal rocks
rocks are
areunknown.
unknown.
An aggegate
aggegateofoftonalitic
tonalitic cobbles
extracted from the
An
cobbles extracted
the metaconglomerate
metaconglomerate yielded
yielded
Ma
(Percival et
et al., 1981).
1981). The
The zircons
zircons have
have aa corroded
corroded
zircons dated at
at 2664
2664 ±+ 12
12 M
a (Percival
appearanceand
andproduced
produceddiscordant
discordantdata
datapoints
pointsand
andhence
hencet hthe
interpretation of
of the
the data
appearance
e interpretation
open. Rather
than recording
recording the
the original
original crystallization
crystallization age
of the source
pluton for
for
is open.
Rather than
age of
source pluton
the cobbles
the zircons
zircons probably
probablydate
dateaalater
later deformation-metamorphic
deformation-metamorphic event.
event. The
cobbles the
The
source pluton
plutonfor
for the
the cobbles
cobblesmay
maybe
besimilar
similart otothat
that which
which provided
providedmaterial
material for
for the
source
Doré conglomerate.
Dor6
— 40
-
Continue east on 101
Continue
. ..
-
..
2-2: Mafic
25.9 km Stop 2-2:
25.9
Mafic gneiss
gneiss xenoliths
xenoliths with
with amphibolitic
amphibolitic margins
margins (N.
(N. side of Hwy
Hwy 101)
101)
This exposure
exposuredemonstrates
demonstrates an
an important
important aspect
aspect of
between the
This
of the boundary
boundary between
Kapuskasingzone
zoneand
andWawa
Wawagneiss
gneiss
terrane. Aside
Asidefrom
fromthe
thelarge-scale
large-scale structural
structural
Kapuskasing
terrane.
terrane and
contrast between
between the
the domal
domal Wawa
Wawa terrane
and the
t h e linear
linear belts
beltsin
inthe
theKapuskasing
Kapuskasing zone,
intrusive relations
relations are also instructive. The
intrusive
Theoutcrop
outcropconsists
consists of
of two
two main
main components:
components:
(1)coarse-grained
coarse-grainedhornblende-biotite
hornblende-biotitetonalite,
tonalite, the
the dominant
dominant rock
rocktype
type tto
the west,
west, and
and
(1)
o the
(2) medium
mediumgrained
grained mafic
mafic gneiss
gneiss consisting
consisting of
of garnet-clinopyroxene-hornblendegarnet-clinopyroxene-hornblende(2)
plagioclase-quartz assemblages.
assemblages. Small
xenoliths of
of mafic
mafic gneiss
gneiss in
intonalite
tonalite have
have
plagioclase-quartz
Small xenoliths
margins, up
up tto
cm thick,
thick, consisting
consisting of
of hornblende-plagioclase.
hornblende-plagioclase. Dykes
Dykesofoftonalite
tonalite
margins,
o several cm
cutting mafic gneiss
gneiss are
are bordered
bordered by mafic rock with hornblende-plagioclase
hornblende-plagioclase
assemblages. The
assemblages.
The interpretation of
of age
age relationships
relationships is that
that the
thehigh-grade
high-grade
metamorphism that
that produced the garnet-clinopyroxene assemblages in mafic gneiss
metamorphism
gneiss
preceded the
the intrusion
intrusion of
of tonalite.
tonalite. Water
preceded
Water in
in the
the tonalite
tonalitemagma
magma was
was presumably
presumably
,.
crystallization and
and hydrated
hydrated the
the adjacent less-hydrous
mafic rock.
rock.
released upon
upon crystallization
less-hydrous mafic
Althoughthe
the tonalite
tonalite at this outcrop has not been dated, iti t probably
either to
Although
probably belongs
belongs either
Ma
tonalite gneiss
gneiss suite
suite or ttoo the 2680
group of
of plutons.
plutons. The high-grade
the >2707
>2707 M
a tonalite
2680 Ma
M a group
high-grade
metamorphismisistherefore
therefore older
olderthan
than 2680
2680Ma.
Ma. This
Thisisisininconflict
conflictwith
withthe
thedirect
direct dates
dates
metamorphism
of metamorphic zircons from the
as 2616
2616 Ma.
Ma.
of
the Kapuskasing
Kapuskasing zone that yield
yield ages
ages of
of as
aslow
low as
The conflict
conflict has led ttoo the
that the
The
the suggestion
suggestion (Percival
(Percival and
and Krogh,
Krogh, 1983)
1983) that
the Kapuskasing
Kapuskasing
gneisses, although
although metamorphosed
metamorphosed prior
prior tto
2680 M
Ma
ago,remained
remainedat
at high
high temperatures
temperatures
gneisses,
o 2680
a ago,
where radiogenic lead diffused readily out of zircon until at least 2616 Ma ago.
Continue east
37.0 km
37.0
2-3: Thinly-layered
Stop 2-3:
Thinly-layered tonalitic gneiss
gneiss and diatreme
diatreme breccia
breccia (N.
(N. side
side of
of Hwy
Iiwy
101)
101)
Fine grained
grained tonalitic
tonalitic gneiss
Fine
gneiss aatt this exposure is strongly foliated and layered on a
1-5mm
mmscale
scalewith
withgarnet,
garnet,hornblende
hornblendeand
andbiotite-rich
biotite-richlayers.
layers. Extremely
Extremelyattenuated
attenuated
1-5
intrafolial folds
folds are
are present
present locally.
locally. Units
foliation
intrafolial
Units characterized
characterized by
by extremely planar foliation
such as
as this
this aare
relatively rare in tthe
zone. Although
the orientation
orientation of
of
such
r e relatively
h e Kapuskasing
Kapuskasing zone.
Although the
foliation in this exposure
exposure is typical
typical for
for the
theKapuskasing
Kapuskasing zone,
zone, most
most Kapuskasing
Kapuskasing gneisses
gneisses
coarse-grained and
andlayered
layeredwith
withdistinctive
distinctiveleucocratic
leucocratic portions.
portions. In
are mediummedium- tto
o coarse-grained
addition, the
the layering
layering in
in the
the typical gneisses
gneisses is
is warped
warped about
about gently
gently northeast
northeast or
or
addition,
southwest-plungingaxes.
axes. The fine grain size and thin
thin planar layering in this outcrop
southwest-plunging
suggest aa relatively
relatively late, high-strain
suggest
high-strain flattening
flattening or shearing
shearing event.
r
—41 -
I?
d
A
A thin
thin diatreme
diatremedyke
dykeoccurs
occursininthis
thissame
sameexposure.
exposure. ItIt has
has not
not been
been dated
dated but
but
presumably
presumably is part of
of aa set
set of
of lamprophyre
lamprophyre dykes
dykes of 1100
. ~ l l 0Ma
0M aage
age(Stevens
(Stevens et
et a!,
al, 1982)
1982)
that
are particularly
particularly common
thatoccur
occurininthe
t h eKapuskasing
Kapuskasing zone
zone and
and are
common in the
the area
area between
between the
I
I
I
Lackner
Lakecomplexes.
complexes. Both
Both the
the matrix
matrix and fragments in the
Lackner and
and Nemegosenda
Nemegosenda Lake
the dyke
dyke
are
be identified.
identified. These
are altered,
altered, but
but some
some fragments can be
These include
include tonalitic
tonaliticgneiss,
gneiss, spinel
spinel
n
Continue
Continue east
east on
on Hwy
Hwy101
101
lherzolite
not occur
occur in the
Iherzoliteand
and massive
massive pink granite. As
Asmassive
massive granite
granite does
does not
Kapuskasing
zone,the
thegranite
granite fragments
fragments are
arerelatively
relatively exotic. Their
Kapuskasing zone,
Theirsource
sourcewas
was
probably below
Kapuskasingzone,
zone,possibly
possiblyiningranite
graniteofofthe
the Abitibi
Abitibi belt,
below the Kapuskasing
belt, which
which
according
according to
t o the
the gravity
gravitymodel,
model, lies
liesvertically
verticallybelow
belowatata adepth
depthofof—15
-15 km.
km.
'
52.1
52.1 km
km
Stop
KapuskasingGneiss
Gneiss (S.
(S. side
side of
of Hwy
Hwy101)
101)
Stop 2-4:
2-4: Kapuskasing
Layered ruafic
in situ tonalitic
tonaliticleucosome,
leucosome,and
and crosscrossmafic gneiss
gneiss with concordant &
cutting
cuttingtonalitic
tonaliticand
andpegmatitic
pegmatiticdykes.
dykes. Layering
Layeringononthe
the5 5tot o1010cm
c mscale
scaleisisgiven
givenby
by
I
alternating
of similar
alternatinghornblende-rich
hornblende-rich and
and garnet-pyroxene-rich
garnet-pyroxene-rich layers
layers(see
(see analyses
analyses of
layers
layers in Table 1).
1). Metre-scale
Metre-scale blocks
blocks of mafic
mafic gneiss
gneiss in breccia give parts of the
outcrop
moutcrop aa chaotic
chaoticappearance.
appearance. These
These structurally
structurallycomplex
complexpanels
panelsare
areseparated
separated by.
bym-
scale high-strain
high-strain zones
with gently rolling, north-dipping,
foliation.
zones with
north-dipping, pronounced
pronounced foliation.
Continue
Continue east
east on
on Hwy
Hwy101
101
59.8
59.8 km Stop
Stop2-5:
2-5: Kapuskasing
Kapuskasinggneisses
gneisses (N.
(N. and
and S.
S. sides
sides of Hwy
Hwy 101)
101)
There are several
several features
features of
of interest
interest at this
this outcrop
outcrop (Fig.
(Fig. 23):
23);
Mafic
Maficgneiss
gneiss is present on the northwest side
side of the
the road.
road. ItIt isis aa coarse
coarse grained
grained
rock
rock consisting
consisting of
of three
threetypes
types of
of layers
layerson
on the
the5-100
5-100 mm
mm scale:
scale: i)i)relatively
relativelyanhydrous
anhydrous
A.
I
I
I
I
I
rnafic
and quartz,
quartz, with some
mafic rock
rock made
made up of garnet, clinopyroxene,
clinopyroxene, plagioclase and
some
hornblende
to analyses
analyses I1 && 3,
3, Table
Table 1);
ii) more
hornblende (analogous
(analogous to
1); ii)
more hydrous
hydrous layers
layers containing
containingless
less
garnet
garnet and
and clinopyroxene
clinopyroxeneand
and more
morehornblende
hornblende (analogous
(analogous to
t o analyses
analyses 22 &&4,
4, Table
Table1);
I); and
and
iii)
iii)tonalitic
tonaliticleucosome
leucosomelayers,
layers, both
both concordant
concordant to
t o layering
layering and
and transverse
transverse in the
amphibole-rich
amphibole-rich mafic rocks.
rocks. Note
Note that
that the
thetonalite
tonalitehas
has no
no retrogressive
retrogressive effect
effect on
on
adjacent anhydrous
mafic gneiss.
gneiss. The tonalitic
tonalitic leucosome
anhydrous mafic
leucosome veinlets are
are considered
considered ttoo be
in situ anatectic
anatecticmelt
meltsegregations
segregationsdeveloped
developed during prograde
prograde metamorphic reactions
of the outcrop, submicroscopic
(see reaction 2).
2). In the western end of
submicroscopic symplectites of
orthopyroxene-plagioclase
identified by
form barely-visible coronas
orthopyroxene-plagioclase identified
by microprobe
microprobe analyses,
analyses, form
coronas
around
garnet, clinopyroxene
clinopyroxene and
andhornblende.
hornblende. Analyses
Analysesofof the
the symplectite
symplectite minerals, at
around garnet,
at
-- 42
42 lower size
size limit
limit of
of microprobe
microprobe resolution,
resolution, aare
reported along
along with
with those
those of
of tthe
tthe
h e lower
r e reported
h e other
minerals in
in the
the rock,
rock, in
in Table
Table 2.2. The
minerals
The rock contains three
three plagioclase
plagioclase compositions.
compositions. An39
Ana9
is present in
in coronas
coronas whereas worm-like
worm-like intergrowths
intergrowths of
of An35
An35 and
and An50
Anro make up tthe
he
matrix plagioclase.
plagioclase.
The mineral
mineral compositions
compositions yield
yieldestimates
estimates of
of 735°C
usingtthe
and Green
Green The
735'C using
h e Ellis and
(1979)garnet-clinopyroxene
garnet-clinopyroxenethermometer
thermometer and
and 6.2
6.2 kbar
kbar using
usingtthe
garnet-clinopyroxene(1979)
h e garnet-clinopyroxene-
plagioclase-.quartzbarometer
barometer (Newton
(Newtonand
andPerkins,
Perkins,1982).
1982).At
Atthe
thesame
sametemperature
temperature tthe
plagioclase-quartz
he
and matrix
matrix garnet yield 9.1
coronal minerals and
9.1 kbar
kbar with tthe
h e garnet-orthopyroxenegarnet-orthopyroxeneplagioclase-quartzz Newton
and Perkins
Perkins barometer.
barometer.
plagioclase-quart
Newton and
Kapuskasing dike
Kapuskasing
dike
1
B,
. .
A
A
orthopyroxeneorthopyroxeneplagioclase coronas
22Dm
0m
0
I
I
I
orthopyroxene bearma
bearing
orthopyroxene
metasedimentary
imentary rock
'7
ic and tonalitic gneiss
Figure 23.
23. Location
Location of
of outcrops
outcrops at
at Stop
Stop 2-5.
2-5.
-
A Kapuskasing
Kapuskasingmafic
maficdyke
dykecuts
cutsthe
theeastern
easternend
endofofthe
theoutcrop.
outcrop. The overal
overall
BB..
A
attitude
SE although
although tthe
h e margin is offset by
by numerous small
attitudeof
of the
t h edyke
dykeisis070/75
070175 SE
sinistral faults. The
Theouter
outer22cm
c mof
of the
themargin
margin isischilled.
chilled. Sparse
Sparseplagioclase
plagioclase phenocrysts
phenocrysts
are present in
olivine-bearing gabbro.
gabbro. Several
in the
t h e dominantly
dominantly medium
medium grained ophitic olivine-bearing
Several
dykes of
of this swarm
been dated by tthe
dykes
swarm have been
h e whole-rock
whole-rock K-Ar
K-Ar method
method and
and yield
yield "ages"
"ages"
and 3649
3649 Ma,
Ma,indicating
indicatingt the
presence of
of excess argon
between 2367
2367 and
h e presence
(Stevens et
et al., 1982).
al, (1986)
(1986)estimated
estimated an age of 2040
2200 Ma
Ma based
based on
(Stevens
1982). 1-lanes
Hanes etet al,
2040 -- 2200
dyke and
and its
its baked
baked country
country rock.
rock.
^40Ar/39Ar
~ r / ^ ~ ranalyses of a Kapuskasing
Kapuskasing dyke
Homogeneousmetasedimentary
metasedimentary rock
C.
Homogeneous
South of the road is a flat outcrop of medium grained rock with the
h e assemblage
.
.
r
I
I
I
I
I
I
I
I
I
I
I
I
I
1
1
I
— 43 -
Table 2.
2. Microprobe
Microprobeanalyses
analyses of minerals
minerals in coronitic
coronitic mafic
mafic gneiss,
gneiss. Stop
Stop 2-5
2-5
1
2
4
3
Si02
Si02
38.01
51.57
49.06
42.29
hO2
Ti02
0.00
0.34
0.03
2.03
A1203
20.99
2.92
4.75
12.98
Cr203
0.22
0.21
0.34
0.08
28.06
11.81
31.20
18.43
0.70
0.81
13.35
1.39
0.17
9.28
8.32
0.00
11.34
22.65
11.41
0 27
0.74
0.52
1.95
Cr203
10*
FeO*
MnO
MnO
MgO
MgO
CaO
CaO
Na
0
Na20
2
K20
K2Â
4.11
0.00
0.08
0.00
0.69
Total
Total
100.67
101.79
101.45
99.31
Si
Si
2.973
1.908
1.885
6.252
Aliv
Aliv
0.00
0.092
0.115
1.748
Alvi
Alvi
1.935
0.035
0.100
0.513
Ti
Ti
0.00
0.009
0.001
0.226
Cr
c
r
0.014
0.008
0.010
0.009
0.0
0.087
0.042
0.288
1.835
Mg
Me
0.040
0.479
0.278
0.003
0.625
0.960
0.026
0.764
Ca
Ca
0.697
0.898
0.057
1.990
0.021
2.044
1.807
Na
Na
0.041
0.053
0.039
0.559
K
K
0.00
0.004
0.00
0.130
3+
pe3
Fe
2÷
2+
Fe
Fe
Mn
Mn
(0)
(0)
*
*
(12)
(6)
(6)
(23)
1:
1: garnet;
garnet; 2:
2: clinopyroxene;
clinopyroxene; 3:
3: orthopyroxene;
orthopyroxene;4:
4: hornblende
hornblende
Total
Fe3 by
Total iron as FeO; Fe3+
bystoichiometry
stojcHiornetry
Specimen
Specimen also
also contains
contains quartz
quartzand
andplagioclase
plagioclase(An33
Art88
in syrnplectite)
symplectite)
Ann8 in
I
1.:jyt-
mntrir.
in matrix,
- 44 -
z. Plagioclase
garnet-orthopyroxene-biotite-plagioclase-quart
garnet-orthopyroxene-biotite-plagioclase-quartz.
Plagioclase occurs
occursas
asporphyroblasts
porphyroblasts
to
is up
uptto
mm. The
t o 22 cm
cm and
and orthopyroxene
orthopyroxene is
o5
5 mm.
The rock
rock has
has the
the same
same mineral
mineral assemblage
assemblage as
as
high-grade
in tthe
zone but
but lacks
lacks tthe
high-grade paragneiss
paragneiss in
h e Kapuskasing
Kapuskashg zone
h e migmatitic
migmatitic layering
layering typical
typical
of
of paragneiss.
paragneiss. Application
Application of
of the
the garnet-orthopyroxene-plagioclase-quartz
garnet-orthopyroxene-plagioclase-quartz geobarometer
geobarometer
yields values
values in
in excess
excess of
and Perkins
yields
of 11
11 kbar
kbar by
by both
both Newton
Newton and
and Perkins
Perkins (1982)
(1982) and
Perkins and
and
Chipera (1985) calibrations.
calibrations.
Chipera
Interlayered mafic
mafic and
tonalitic gneiss
D.
Interlayered
and tonalitic
gneiss
D.
complex relations
relations between
Ic and
and tonalitic
tonalitic gneiss.
outcrop demonstrates
This
This outcrop
demonstrates complex
between maf
mafic
gneiss.
Isoclinal
folds of
of layering
layering are
are truncated
truncated by
Isoclinal folds
by tonalite
tonalitepods
pods and
and dykes,
dykes, suggesting
suggesting multiple
multiple
generations of
of tonalite.
tonalite. Thin
generations
Thinmylonite
mylonite seams
seams are
are sub-parallel
sub-parallel to
t o gneissic
gneissic layers.
layers.
Continue east
67.0 km
km Stop
67.0
Stop 2-6:
2-6: Xenolithic
Xenolithictonalitic
tonaliticgneiss
gneiss(S.
(5.side
sideof
ofHwy
Hwy101)
101)
This outcrop
outcrop consists
consists of
of mediummedium-t to
coarse-grained tonalite
tonalite made up of
of garnet,
garnet,
This
o coarse-grained
hornblende, biotite,
biotite, plagioclase
plagioclase and
and quartz.
quartz. AA variety
hornblende,
variety of
of xenoliths
xenoliths includes
includes mafic gneiss
gneiss
(garnet-.clinopyroxene-plagioclase-quart
z),amphibolite,
amphibolite,biotite-rich
biotite-rich schists and spinel
(garnet-clinopyroxene-plagioclase-quartz),
pyroxenite. Amphibole-rich
rims characterize
characterize the
pyroxenite.
Amphibole-rich rims
t h e high-grade
high-grade inclusions.
inclusions.
Continue east
69.2
km Stop
2-7: Ivanhoe
Lake cataclastic
cataclastic zone
69.2 km
Stop 2-7:
Ivanhoe Lake
zone(S.
(S. side
sideof
ofHwy
Hwy 101)
101)
The outcrop
outcrop is
is on
ont the
western, high-grade
high-grade side
sideofoft the
cataclastic zone and consists
h e western,
h e cataclastic
The
of migmatitic
garnet-clinopyroxene-hornblende-plagioclase-quaitz
of
migmatitic mafic
mafic gneiss
gneiss with
with garnet-clinopyroxene-hornblende-plagioclase-quartz
assemblages. ItIt is
assemblages.
is transected
transactedby
by numerous
numerous small fault offsets
offsetsand
and by
by one
one major
major
cataclasite
thin section,
section, this black
black aphanitic material is
cataclasite vein.
vein. In
In thin
is seen
seen to
t o consist
consist mainly
mainly
of (recrystallized)
(recrystallized) fine
fine actinolitic
actinoliticamphibole
amphibole and
and of porphyroclasts
porphyroclasts of hornblende.
hornblende. AA
39
40Ar/39Ar
whole-rock analysis
of material from
art age
age plateau
plateau at
analysis of
from this
this vein
vein yielded
yielded an
A
r / Ar whole-rock
1720MMa
(Fig.15).
15). On
Ont hthe
west side
sideofoftthe
outcrop aare
rusty-weathering
1720
a (Fig.
e west
h e outcrop
r e thin (3 cm) rusty-weathering
lamprophyre dykes.
dykes. Tonalitic
by cataclasite
cataclasite are
of the
lamprophyre
Tonalitic rocks
rocks cut
cut by
a r eexposed
exposed 150
150 m north of
highway on an overgrown road.
Continue east
r
I
I
U
I
I
metavolcanics, Abitibi
2-8: Mafic
km Stop
70.5 km
70.5
Stop 2-8:
Mafic metavolcanics,
Abitibi subprovince
subprovince (N.
(N. side
sideof
of Hwy
Hwy 101)
101)
on the eastern, low-grade
the IL,CZ
and is
is the
the westernmost
This outcrop is on
low-grade side of the
ILCZ and
belt. It is aa fine
hornblendegrained, layered hornblendeof rnetavolcanics
metavolcanics of
of the Abitibi belt.
fine grained,
exposure of
clinopyroxene rock
rock with
with local
local rusty-weathering
rusty-weathering patches.
plagioclase +
patches.
± clinopyroxene
The
structural characteristics
characteristics of the
east-west strike of
of
The structural
t h e outcrop,
outcrop, including
including east-west
isoclinal small
small folds,
folds,aare
typical of
of the
the Abitibi
layering, vertical dip
dip and steeply-plunging
steeply-plunging isoclinal
r e typical
Abitibi
belt. Chlorite
belt.
Chloriteand
and epidote
epidote are
are common
common tto
o tthe
h e east along strike, where
where the belt is wider,
wider,
suggesting an
an easterly
easterly decrease in metamorphic grade.
grade.
suggesting
40Ar/39Ar
of hornblende
hornblende and
and plagioclase
plagioclase from
from this
this outcrop
outcrop by
by tthe
Analyses of
he A
~ I A ~
method (Fig.
(Fig. 15) show
showaa plateau
plateau for
for hornblende
hornblende at
at 2567 M
Ma
and aa saddle-shaped
saddle-shaped spectrum
spectrum
method
a and
plagioclase with
with aa plateau
plateau at 1107
Ma. The
for plagioclase
1107 Ma.
The plagioclase
plagioclase plateau may
may be due to
t o argon
argon
loss resulting
resulting from
from aa mild
mild thermal
thermal event,
event, possibly
possiblyrelated
related tto
faulting.
loss
o faulting.
72.3 km
km Turn
main road.
road.
72.3
Turn north on
on logging
logging road follow main
side of
87.2 km
km Stop 2-9:
2-9: Shawmere
of road)
87.2
Shawmere gabbroic anorthosite (w.
(W. side
mainly coarse-grained
coarse-grained gabbroic anorthosite
anorthosite with
The outcrop is mainly
with hornblende
hornblende and
I
I
•
I
1
I
I
I
I
I
minerals. Ultramafic
Ultramaficlayers
layersconsisting
consistingof
of orthoortho- and
andclinopyroxene
clinopyroxene
rare garnet as mafic minerals.
with hornblende
hornblende rims
rims and
and sparse
sparse plagioclase
plagioclase to 3 cm, occurs
occurs in
in layers
layers and
and pods
pods up to
to 44 m
m
with
Mafic and
and ultramafic
ultramafic layers are
structures
thick. Mafic
thick.
are locally
locally folded
folded into
into shallow
shallow NE-plunging
NE-plunging structures
with aa prominent
prominent lineation.
lineation. One part of the
with
the outcrop
outcrop is
is a spectacular
spectacular coronitic
coronitic gabbroic
gabbroic
anorthosite with football-sized
football-sized plagioclase megacysts.
megacysts. Coronas
Coronas have
have orthopyroxene
orthopyroxene or
clinopyroxene cores;
cores; orthopyroxene
orthopyroxene has
has successive
successive hornblende
hornblende and
and pale
pale garnet
garnet rims;
clinopyroxene
clinopyroxene has
has hornblende
hornblenderims
rims and
andrare
rare orthopyroxene
orthopyroxene cores.
cores.
clinopyroxene
Return to Hwy 101.
km END
134.1 km
END OF
OF DAY
DAY 2.
2. Return to
t o Wawa.
Wawa.
- 46 ACKNOWLEDGEMENTS
Weberimproved
improvedthe
themanuscript.
manuscript. C.W.
by P.C.
W. Weber
Reviews by
P.C. Thurston and W.
C.W. Jefferson is
thanked for editorial
editorial revisions.
revisions.
. .
.
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