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STRUCTURAL ANALYSIS OF A DUCTILE SHEAR ZONE WITHIN THE
MARQUETTE IRON RANGE, UPPER PENINSULA, MICHIGAN

By

Cheryl L. Webster

A THESIS

Submitted to
Michigan State University
In partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Geological Sciences

1999

ABSTRACT

STRUCTURAL ANALYSIS OF A DUCTILE SHEAR ZONE WITHIN THE
MARQUETTE IRON RANGE, UPPER PENINSULA, MICHIGAN

By

Cheryl L. Webster

The Marquette Synclinorium is interpreted as an asymmetric rift-related
basin; truncated stratigraphy on the southern margin and a rollover structure to
the north provides evidence for this interpretation. The Palmer Gneiss (PG)
marks the southern boundary of the trough. Mining operations have exposed the
PG revealing mega-scale shear bands; foliation measurements indicate a
reverse sense of shear. The formation of the Palmer Gneiss was previously
interpreted as the alteration of the Archean gneiss. Whole rock chemical
analysis suggests that the PG rocks are not granitic, but basaltic indicating a
Proterozoic age. The folds measured in the adjacent iron formation consistently
plunge gently towards the WNW, reflecting that they were formed under the
same strain conditions as the shear zone. The NNE-SSW compressive direction
is similar to those measured in previous studies of the area. The Penokean
Orogeny caused closure of the Marquette trough that reactivated preexisting
normal faults and resulted in a reverse dip-slip. Strain was concentrated in a
portion of a metadiabase sill that was rotated into the shear zone causing

alteration and shearing of the rock to form the PG.

ACKNOWLEDGMENTS

I would first like to thank Cleveland Cliffs Mining Services for supporting
me for two summers giving me full access to the mines. Glenn Scott and Helen
Lukey’s aid was always available and proved very helpful. Thanks also to Paul
Nordstrom, Ron Graber, and Tom Waggoner for their support.

Special thanks go to my advisor, Dr. Bill Cambray, for all of his guidance,
advice, and most importantly his patience. My committee members, Dr. Tom
Vogel and Dr. Kaz Fujita, are also appreciated for their time and their quick
review of this thesis. Dr. Lina Patino’s help was also gracious and appreciated.

I thank other graduate students for their friendship and insight into life at
MSU and beyond. I also thank those students that proved instrumental in
finishing this project. In particular, I thank Ed leon for being my first field
partner, Dave Szymanski for all to the answers to my endless questions,
Alexandra de Jong for spending time reviewing several drafts of this thesis, Dave
Boutt for the drafting of one of the figures, and also Chris Martinson who was my
second field partner.

Finally, I would like to thank my mother and my Aunt Lori for all of their

support and giving me a swift kick in the -- when I needed it.

iii

TABLE OF CONTENTS

LIST OF FIGURES

Study Site

REGIONAL GEOLOGY... ..
Marquette Range Supergroup
Penokean Orogeny...

METHODS OF STUDY....................
Field Methods
Lab Methods

SHEAR ZONES...
Tilden Shear Zone... .
Geometry of Shear Zone .
Petrography and Kinematic Analysis
Harvey Shear Zone...

Geometry of Shear Zone

Petrography and Kinematic Analysis

FOLD GEOMETRY IN NEGAUNEE IRON FORMATION... ..

Tilden Mine...
North Hanging Wall

Empire Mine... ..
Southwest Extension

Main Pit.......... ................'.'.'.'.'f.'.'.'.‘f.’.'.'.'.'.'.’.'.'.'.'.'.'.'.'.'.'ff.'.'.'.'.'.'.'.'f.'f.'.'I.'.'..
TILDEN SHEAR ZONE PROTOLITH...............
Whole Rock Geochemistry......................................................

Volume and Mass Changes
Republic Dike ComparIson

DISCUSSION... .. ..
Deformation History
Protolith and Mass-Volume Changes

iv

vi

..vii

.....10
.....11
...13

.15
.. 15
.17

19
.....24
.....25
.....29
32
32

.. 35

.38
.. .....38
Northeast Hanging Wal.I 39

.. 42

.45

.48

49
52
62

.....70
.....70
...74

77

APPENDDQAHHHHHH”unununnnnuuuunnnnuuu”unnnunnnuunm
APPENDD(BHHHHHHm”HUHH””H””Hununnnnunuuunuuuunnu

REFERENCESHHHHHH”H””H“”unnnumnuuuuunuunnnnnununm

79

m86

88

LIST OF TABLES

Table 1. Mean chemical data for metadiabase, Palmer Gneiss, and
the Southern Complex Gneiss. Major oxides in weight
percentage, trace elements in ppm. Line indicates
element concentration below detection limits ............................. 51

Table 2. XRF whole rock major oxides of Republic dike, values are
weight percentages (Zieg, unpublished data)... .....64

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

LIST OF FIGURES

Location map of study region. Both the Empire and
Tilden Mines are located north and west of Palmer,

Michigan, respectively

Map of the Tilden Hematite pit. Lines are contours
of toes and crests of benches. Benches occur at
45 feet intervals with decreasing elevation
towards the center of pit. Arrows represent
anticlinal folds indicating the plunge direction and
amount of plunge of the fold. Numbers represent
the areas studied; area (1) shear zone footwall,
(2) hanging wall bench 1440 and 1530, (3) west
south wall, bench 1260, and (4) Northeast wall
benches 1665 and 1710. One inch approxrmates
550feet... . .. .

Map of the Empire Main pit and Southwest
Extension pit. Dashed lines are contours of the
tops of benches. Benches occur every 45 feet,
elevation decreases towards the center of each
pit. Arrows represent anticlinal folds indicating the
plunge amount and direction of the fold. Numbers
represent the areas studied; area (1) northeast
corner of SW-Extension pit bench 1215, (2) Main
pit Fold One on bench 1080, and (3) Main pit Fold
Two, benches 910 and 990. One inch

approximates 1100 feet

Instantaneous strain ellipsoids of pure (A) and simple

shear (B)

Diagram of heterogeneous strain in a dextral shear zone.
The initial circles become elongate and align themselves

in the X-Y plane offinite strain ellipsoid.....................................

S-C structures (a) and shear bands (b) in a dextral shear
zone. Note the C-foliations are parallel to the shear zone
and the shear bands are at an angle to the zone

boundary

vii

.20

.22

.23

Figure 7. Photograph of the Tilden shear zone. The steep foliation
is the S-foliation, notice it curves into the shear band,
shallower dip. The spacing between the shear bands

approximates 2.5 meters

Figure 8. Diagrammatic sketch of the Tilden Footwall, note the
steep S-foliation curving into the shear band indicating a

reverse sense of motIon

Figure 9. Stereonet plot of the Tilden shear zone. The C' is the
mean pole to the shear bands, the mean 0' plane is the
dashed line. The S is the mean pole to the S-foliation
with the dotted line as the mean S plane. The star
indicates the mean intersection of the C' and the S plane;
solid line is the plane perpendicular to this S-C'
intersection. The long and short dashed line is the top of
the shear zone; triangle represents the plunge of the line
of movement of 046/58. As it is a reverse shear zone,
the movement was up towards the SSW, u is the

upthrown, d is the downthrown Side

Figure 10. Stereonet plot of S-C structures outside of the Tilden
Hematite pit. C represents mean pole to the C-foliation,
short dashed line in the mean C-foliation. The long
dash line equals the S-foliation, and the S is the pole to
that plane. Star indicates the mean S-C intersection
and the solid line is the plane normal to the intersection.

Triangle is the plunge ofthe line of movement..........................

Figure 11. Photomicrograph of the Tilden sheared rock (PG).
Notice the well developed foliation. Scale bar equals

Figure 12. Stereonet plot of a syncline in the Kona Dolomite and
the Mesnard Quartzite exposed in the Harvey Quarry.
Circles are the poles to bedding surfaces with a best fit
great circle; the star represents the fold axis gently

plunging to the ENE

Figure 13. Photograph of the shear zone in the Harvey quarry.
The line labeled C' illustrates the orientation of the shear

band, the line marked S parallels the S-foliation...

viii

.26

.27

.28

.30

31

33

Figure 14. Stereonet plot of the Harvey shear zone within the
Mesnard Quartzite. The C' is the pole to the mean
shear band with the dashed line as the mean C' plane.
The S is the pole to the mean S-foliation with the dotted
line as the mean 8 plane. The star represents the
intersection of the S-C' planes and the solid line is the
plane normal to that intersection. The long and short
dashed line is the shear zone boundary; triangle

represents the movement direction of 316/48... ..

Figure 15. Stereonet plot of the fold on the Tilden Hanging Wall
bench 1440. The circles are poles to bedding with a
thick line representing the best fit great circle. Fold axis
(star) is plunging to the WNW, triangles are the
measured hinge lines and the thin line shows the mean

axial surface dipping to the NNE

Figure 16. Stereonet plot of the Tilden hanging wall bench 1530.
Poles to the bedding are the circles, thick line is the
best fit great circle about the bedding poles. The star is
the fold axis plunging to the WNW. The thin line
indicates the mean axial surface, and the hinge lines

are represented by the tnangles

Figure 17. Stereonet plot of the 1710 bench on the Northeast wall
of the Tilden Hematite pit. Fold axis (star) plunges
towards the WNW as do the measured hinge lines
(triangles). The poles to the bedding (circles) are
distributed about a great circle (thick line), and the

mean axial surface (thin line) dips to the NNE

Figure 18. Stereonet plot of the anticline in the Empire Southwest
Extension pit. The thick line represents the best fit
great circle to the bedding poles (circles), the star is the
fold axis, the triangles are the hinge lines, and the thin
line represents the mean axial surface dipping to the

Figure 19. Stereonet plot of an anticline in Empire Main pit, labeled
Fold One. The axial surface (thin line) dips to the SSW,
hinge line (triangle) plunges to the WNW, the bedding
poles (circles) conform to a great circle (thick line) with

a fold axis (star) plunging to the NW

ix

..36

...40

...41

.43

.46

Figure 20.

Figure 21.

Figure 22.

Figure 23.

Figure 24.

Figure 25.

Figure 26.

Figure 27.

Stereonet plot of a fold in the Empire Main pit, named
Fold Two. The fold axis plunges to the WNW and is
represented by the star. Poles to the bedding (circles)
are distributed about a great circle (thick line). The
hinge lines, represented by the triangles, plunge to the

east. The axial surface, thin line, dips to the NNE ...................... 47

Diagrammatic cross section through the Tilden pit.
Notice the metadiabase (230) sill is rotated next to the

footwall shear zone. From Glenn and Lukey (1999) ................... 50

Plot of major oxides versus Si02 for all samples of
metadiabase (diamond), Palmer Gneiss (square), and
Southern Complex Gneiss (triangle)...

Comparison of major oxides concentrations of

metadiabase (diamond), Palmer Gneiss (square), and

Southern Complex Gneiss (triangle) plotted over a

normal basalt composition...

Ratio of average Palmer Gneiss, sheared rock,

concentration versus the average metadiabase

concentration on a logarithmic scale. Elements

plotting above one are enriched in the sheared rock,

values less than one are depleted in sheared rock ......................

Plot of intersections of composition-volume equations

with the gain-loss line of Gresens (1967). Note the tight
clustering of potassium and aluminum oxides (fv =

0.823) and silica and iron oxides (fv = 0.903)..................

lsocon graph, concentration of elements in altered (Ca)

rock versus concentration of elements in protolith (Co).

The line (slope = 1.143) represents the isocon, equal

chemical concentration.....................

Plot of Al203 versus other major oxides. Line represents

constant mass isocon. Elements above the line were

gained by the system, elements below the line were lost

with respect to Al203......

53

55

.59

.61

.63

Figure 28. Ratio plot of the dike margin, or sheared rock
concentration versus the dike center, or protolith
concentration of a Republic dike on a logarithmic scale.
Elements plotting above one are enriched in the
sheared rock, values less than one are depleted in

sheared rock

Figure 29. Plot of intersection of composition-volume equations

with the gain-loss zero line (x-axis) of Republic dike
alteration. Oxides of silica and magnesium are tightly

clustered together atfv= 0826

Figure 30. lsocon graph of Republic dike. Altered rock element
concentration (Ca) versus element concentration of

protolith (Co). lsocon has a slope of 1017

Figure 31. Schematic diagram of the pre-Penokean Marquette

trough

Figure 32. Schematic diagram of Marquette trough after Penokean

deformation

...65

...67

...69

...72

...73

INTRODUCTION

The Marquette Synclinorium, on the southern margin of the Canadian
Shield in the Upper Peninsula of Michigan, is an asymmetric rift-related basin.
The trough contains a thick sequence of Early Proterozoic metasedimentary
rocks that is situated on Archean basement. The stratigraphy on the southern
edge is truncated; a large, low-grade, reverse dip-slip shear zone, mapped as the
Palmer Gneiss, marks the boundary between the Archean and Early Proterozoic
rocks. The name Palmer Gneiss, representing the Tilden sheared rocks, is
misleading because the rock is a phyllite. The shear zone relates to the regional
structure; it first acted as a major normal detachment fault during initial extension
of the region and was then reactivated as a thrust fault on which the basin
invened.

The Early Proterozoic metasedimentary rocks in the area are known as
the Marquette Range Supergroup (MRSG), which lie unoonformably on top of
Archean gneissic basement. The MRSG is divided into groups separated by
unconforrnities and then subdivided into formal formation units. The oldest part
of the sequence is the Chocolay Group, considered to have been deposited in
platformal, or possibly basinal, environments associated with the onset of a rifted
passive margin (Larue and Sloss, 1980). The Menominee Group unconformably
overlies the Chocolay. The deposition of this group occurred along a rifted
passive margin in a subsiding basin due to the break up of the continent
approximately two billion years ago (Larue, 1981b). The Baraga Group rests

unconformably on top of the Menominee Group. Deposition most likely occurred

on a deeply submerged and regionally subsiding shelf (Larue, 1981b) or in a
foreland basin (Barovich et al., 1989). Associated with the MRSG are numerous
metadiabase sills and dikes, which were intruded into the basin during the
extension phase.

Approximately 1.9 billion years ago, subsequent to sedimentation of the
MRSG, the region experienced a compressional event, the Penokean Orogeny.
This event was the result of the Vlfisconsin magmatic arc colliding with the
southern edge of the Superior Craton. The result was closure of the rift-related
basin, producing folding and faulting within the MRSG as well as greenschist
facies metamorphism. Many workers have investigated the structural history of
the area, leading to an understanding of the depositional environments of the
MRSG (Larue, 1981a;b), the metamorphism associated with the Penokean
Orogeny (James, 1955), as well as strain patterns during deformation (Westjohn,
1990). The purpose of this study is to contribute to the understanding of the
regional evolution during the Penokean Orogeny. The major objectives are: (1)
to interpret the kinematics of the large, low-grade shear zone, (2) to deduce
whether a geometrical relationship between the shear zone and the adjacent
folds within the MRSG exists, and (3) to determine the protolith of the sheared

rock.

STUDY SITE
Research was concentrated in three areas within the Marquette

Synclinorium in the Upper Peninsula of Michigan. Extensive work was

completed at the Tilden and Empire mines located in the south-central portion of
the trough (NI/2 Sec. 26, T. 47 N., R. 27 W.; and Sec. 19, T. 47 N.. R. 26 W.,
respectively), and some measurements were taken in the Harvey quarry (NE%
SW% Sec. 1, T. 47 N., R. 25 W.) on the eastern side of the trough (Figure 1).

Both the Tilden and Empire mines are managed and partially owned by
Cleveland Cliffs Mining Company. The Tilden has two separate pits, the
Hematite and Magnetite pits, but all data were obtained within the Hematite pit
(Figure 2). This pit is approximately 1.65 km wide, 1 km long, and 190 m deep.
The Empire has five different pits: the Main Pit, CD-l, CD-V, Section 20, and the
Southwest Extension; data were collected in the Main pit and the Southwest
Extension (Figure 3). The Empire has been operating longer than the Tilden.
The Empire, with its five pits, encompass a greater area than the Tilden and the
Main pit of the Empire exceeds a depth of 305 meters. The rocks exposed within
the mines are Negaunee Iron Formation, metadiabase sills and dikes.

The town of Harvey is located 5 km south of Marquette. Data and
samples of a shear zone in the Mesnard Quartzite were collected in a small

quarry, just west of US Highway 41.

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Figure 3. Map of the Empire Main pit and Southwest Extension pit. Dashed
lines are contours of the tops of benches. Benches occur every 45
feet, elevation decreases towards the center of each pit. Arrows
represent anticlinal folds indicating the plunge amount and direction
of the fold. Numbers represent the areas studied; area ( 1) northeast
comer of SW-Extension pit bench 1215, (2) Main pit Fold One on

bench 1080, and (3) Main pit Fold Two, benches 910 and 990. One
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REGIONAL GEOLOGY

The Lake Superior region, in the southern portion of the Canadian Shield,
has undergone billions of years of deposition, erosion, and several episodes of
tectonism. Since the discovery of iron ore in the Negaunee area during the mid-
nineteenth century, geological interest in the area has continued. The source of
the iron ore is banded iron formation (BIF), which is a chemical sedimentary rock
that contains more than 15% iron (James, 1954).

The iron formation is underlain by old crystalline basement. Two types of
Archean basement rocks compose the craton in the Lake Superior region: a
younger (2.7 Ga.) granite—greenstone belt in the north is bounded by an older
(3.5 Ga.) gneissic belt to the south (Morey and Sims, 1976). These two terranes
were sutured in the Late Archean, and the boundary came to be known as the
Great Lakes tectonic zone (GLTZ) of Sims et al. (1980). Once the two crustal
segments joined, approximately 2.7 Ga, the boundary was a zone of weakness
and differential displacement. The two terranes behaved differently during their
evolution, the southern gneissic belt did not become tectonically stable until
several million years after the granite-greenstone belt was stable (Sims et al.,
1980). All of the subsequent Precambrian tectonic activity in the Lake Superior
region seems to have been concentrated around the GLTZ, including extension
and compression in the more mobile gneissic belt during the Early Proterozoic
(Morey, 1993) and during the development of the Midcontinent Rift System.

Tectonic activity in upper Michigan and northern Vlfisconsin during Early

Proterozoic (2.5-1.6 Ga) resulted in the juxtaposition of two terranes, a northern

10

terrane and a southern terrane. The northern terrane contains Archean gneissic
basement rocks overlain unconformably by sedimentary rocks of the Marquette
Range Supergroup (MRSG). The southern or VVIsconsin magmatic terrane is
composed mainly of Proterozoic felsic volcanic rocks and calc-alkaline plutons
interpreted as an island arc (Sims et al., 1993). The two terranes became
sutured together during the Penokean Orogeny, as the island arc collided with
the passive margin on the southern edge of the Superior Craton. The Niagara
fault is interpreted to be the collisional suture associated with the orogeny

(Cambray, 1978; Larue, 1983).

Marquette Range Supergroup

The MRSG is an Early Proterozoic metasedimentary sequence of rock
deposited 2.1-1.85 billion years ago (Van Schmus, 1976; Morey, 1983). On the
Marquette range, the MRSG consists of three groups; from oldest to youngest
these are the Chocolay, Menominee, and the Baraga Group. The Chocolay
Group is composed of a basal conglomerate (Enchantment Lake Formation)
overlain sequentially by quartzite (Mesnard), dolomite (Kona), and slate (Wewe).
Deposition of the group is believed to have occurred in cratonic rift basins
(indicated by thick sequences) and on a platforms between the basin areas (thin
sequences; Larue, 1981a). Lying unconformably on top of the Chocolay Group
is the Menominee Group, which includes the Ajibik Quartzite, the Siamo Slate,
and the Negaunee Iron Formation. Deposition is interpreted to have been on a

rifted passive margin with the sea located to the south. The Baraga Group, lying

ll

unconformably on top of the Menominee Group, consists of the Goodrich
Quartzite and an undifferentiated sequence of turbidites, volcanic rocks and iron
formations. Deposition most likely occurred on a deeply submerged and
regionally subsiding shelf (Larue, 1981b) or in a foreland basin (Barovich et al.,
1989). Neodymium isotopes were used by Barovich and others (1989) to
determine the source of the sediments within the MRSG. The Lower MRSG has
an Archean signature, whereas the Upper MRSG has an Early Proterozoic
source, indicating the Baraga Group sediments were shed from the WIsconsin
magmatic terrane. Numerous diabase sills and dikes of Early Proterozoic age
intruded the MRSG.

Vlfithin the study area, the MRSG is mainly constrained by steep-sided,
fault-bounded troughs. Many of these troughs are present in the region,
including the Republic, Felch, Menominee, and the Marquette trough (MT), which
is of particular concern to this study. The basins are all second-order troughs
within the larger Animikie Basin (Morey, 1993) and were created by crustal
instability within the gneissic basement during a period of extension. The MT,
also known as the Marquette Synclinorium, is an east-west trending rift-related
basin that extends for 55 km and is approximately 6 km across. The trough is
asymmetric with truncated stratigraphy on the southern margin and a more
continuous stratigraphic sequence in the north. The thick sequence of
sedimentary rock in the trough (approximately 5500 meters) suggests that it was
undergoing subsidence during deposition (Larue, 1981a; b). Subsidence was

controlled by a normal detachment fault on the south side delineated by the

12

Palmer Gneiss (Cambray, 1992). As the southern margin of the trough was
being uplifted relative to the trough, sediments were shed northward towards the
craton. This is evident from the distribution of clastic lenses that increase in

thickness and frequency towards the south (Breithart, 1983).

Penokean Orogeny

The Lake Superior region was deformed as a result of the Penokean
Orogeny, 1.9 billion years ago (Van Schmus, 1976). The folds developed during
this event are characterized by being generally upn'ght to slightly overturned, and
doubly plunging. Several reconstructive models of the tectonic episode
producing the fold patterns have been proposed. Cannon (1973) argued that the
deformation of the Penokean Orogeny was passively induced and resulted from
vertical movement of the Archean basement in fault-bounded blocks as the
sediments were drape-folded into the troughs. Cannon (1973) also suggested
that the second-order basins are best explained by regional gravity sliding of the
sedimentary rocks. Morey and Sims (1976) proposed that sedimentation of the
MRSG was within an intracratonic basin and that the deposition was followed by
intracratonic deformation. Van Schmus (1976) was the first to offer a plate
tectonic interpretation, and suggested deposition was on a passive continental
margin with the sea extending to the south; deformation subsequently occurred
in a back-arc setting with southward dipping subduction. The most accepted
model of evolution in the Lake Superior region during the Early Proterozoic is an

extension of Van Schmus’ idea; Cambray (1978) suggested that sedimentation

l3

occurred in rift-related basins along a passive margin that subsequently closed

due to a collision of an island arc coming in from the south.

14

METHODS OF STUDY

Field Methods

Field work was conducted in the summers of 1997 and 1998. The field
seasons consisted of measuring bedding and structural features and the
collection of rock samples for further petrographic and chemical study.

Accurate measurements of structural features are difficult to obtain in the
area because of the magnetic anomalies associated with iron in the rocks. To
overcome the limitations of any compass, a new technique was used in the
study; an Electronic Total Station (ETS), a survey instrument, was used to avoid
the problems of traditional techniques. Other advantages this tool provided are
those of accuracy, ease of use, and speed of measurements (Philpotts et al.,
1997). For the first time, accurate measurements of defo‘rmational features
formed in the Early Proterozoic banded iron formation could be measured with
this tool.

Measurements in the field were initiated with station point information
provided by a mine surveyor. Values obtained from the Global Positioning
System (GPS), were given for Easting, Northing, and Elevation based on the
mine coordinate system. The mine GPS system is accurate to the sub-
centimeter level in all three directions. The Leica (TC 600L) Electronic Total
Station (ETS) was set up according to the manufacturer's manual. Once setup,
the ETS measures one point at a time; it is not capable of measuring a dip and
dip direction of a plane or line. Three points were needed to define a plane and

two points to define a line. The reflector was randomly positioned at three places

15

on a particular plane, then measured and recorded. The points for a given plane
or line were entered into a program written in Microsoft Excel to convert the
Eastings, Northings, and Elevations into a dip and dip direction via solving the
“three-point problem.” The program was written by W. F. Cambray and modified
by Ed VVI|son.

Several surveys were conducted at each mine to measure bedding
surfaces, axial planes, and hinge lines. The interest of the mining geologists as
well as the relative safety of the bench wall controlled the particular areas for field
measurement. At the Tilden, four areas were surveyed: (1 ) Shear zone footwall
on the east south wall of the Hematite pit, benches 1305 and 1440, (2) North
hanging wall on benches 1440 and 1530, (3) West south wall on bench 1260,
and (4) North east wall on benches 1665 and 1710 (Figure 2). At the Empire
mine, surveys were conducted in the Southwest Extension pit on bench 1215,
and also on the north and east side of the Main pit on benches 910, 990, and
1080 (Figure 3). Approximately 1000 planes and lines were measured
throughout both summers and mines.

Samples of rock in the area were collected for petrographic and chemical
analysis. At the Tilden mine, four oriented samples (#1-4) were collected outside
the Hematite pit on its eastern side. These rocks are sheared, however, appear
to have experienced less strain than the rocks in the main part of shear zone.
Three oriented samples (#5-7) of the Palmer Gneiss were collected outside of
Empire mine property (Sec. 23, T47N, R27W). Examples of the metadiabase sill

(#8-10) within the Tilden were taken. Number 8 was the freshest sample

16

(furthest from the shear zone), and samples 9 and 10 were progressively more
altered and closer to the shear zone. Oriented samples (#11-12) were collected
from the Harvey quarry. Samples #13-22 (#13-15 oriented) were collected on
the Tilden shear zone wall. During a field trip to the Tilden Mine in May 1999,
more samples of the shear zone were collected along with samples of

metadiabase, and Southern Complex Gneiss.

Lab Methods

Chemical analyses of the rocks from the high and low strained parts of the
shear zone, the diabase sills, the Palmer gneiss, and Southern Complex gneiss
were performed with an automated X-Ray Fluorescence Spectrometer (XRF).
Whole rock major elements, as weight percent oxides, and trace elements were
determined from homogenous glass wafers. Wafers were made by combining 3
g of finely ground rock powder, 9 g of lithium tetraborate (flux), and 0.5 g
ammonium nitrate (oxidant) and heated in a platinum crucible at approximately
1100 °C for 20 minutes. After that time, the homogenous mixture was poured
into a platinum mold and quenched.

Petrographic analyses were conducted of the TIIden sheared rocks, the
metadiabase from the TIlden, and also one from the Mesnard Quartzite in the
Harvey quarry. Oriented thin sections, cut perpendicular to foliation and parallel
to lineation, were made on samples 1, 2, 3, 4, 5, 12, 14, and 15. Randomly
oriented thin sections were cut from samples 8, 9, and 10. Microkinematic
analysis of the sheared rocks was used to support observations made in the

large shear zone. Following Simpson and Schmid (1983), three prospective

17

types of kinematic indicators were investigated for, (1) rotated porphyroclast tails
and asymmetric pressure shadows, (2) fractured and displaced grains, and (3)

asymmetry of quartz crystallographic fabrics.

18

SHEAR ZONES

Shear zones form through crustal deformation and can occur under brittle,
ductile, or any intermediate conditions. Shear zones developed under brittle
conditions will form close to Earth’s surface and show fractured features (T wiss
and Moores, 1992). Ductile shear zones form at a depth of approximately 10-15
km, where the strain is accommodated by strain softening and crystal-plastic
deformation (White et al., 1980). lnterrnediate conditions result in features
having both characteristics of ductile and brittle deformation (T wiss and Moores,
1992). The shear zones in the Tilden Mine and the Harvey quarry were
deformed through ductile deformation, in that the differential displacement in the
shear zone was controlled by ductile flow, thus layers may have changed shape
but did not break apart (Ramsay, 1980).

An ideal shear zone has parallel sides and contains identical displacement
throughout the zone. The displacement field within the shear zone is simple
shear and/or volume change (Ramsay, 1980). Simple shear is a rotational strain
compared to pure shear that is a nonrotational, homogeneous strain. During
pure shear, the Z-axis or the maximum shortening direction is oriented
perpendicular to the shear zone, and the X-axis or the maximum elongation
direction, is aligned parallel to the shear zone (Figure 4a). The orientation of the
strain axes is the same for an instantaneous amount of strain as well as for finite
strain, thus deformation is coaxial. An instantaneous strain ellipsoid of simple
shear (Figure 4b) shows that the maximum elongation direction (X-axis) is

oriented 45° to the shear plane.

19

 

 

 

 

 

    

II

PureShear

Figure 4. Instantaneous strain ellipsoids of pure (A) and
simple shear (B).

20

However, as shear increases, the X-axis rotates towards parallelism with the
shear zone, as the Z-axis rotates normal to the shear plane. The finite strain
ellipsoid is different than the infinitesimal strain ellipsoid, hence, simple shear
deformation is noncoaxial.

Because simple shear is a basic component of many shear zones
(Ramsay, 1980), one side of the shear zone is displaced relative to the other.
Shear sense indicators or kinematic indicators are often preserved in the shear
zone to determine this relative displacement. Useful types of indicators include
grain tails, mica fish, S-C fabrics, and shear bands. The latter two indicators are
of particular interest because they are both observed in the shear zones studied.

S-C fabrics and shear bands are types of foliation patterns. An isotropic
and homogeneous material undergoing simple shear stress will result in the
formation of the S-foliation. This foliation is a preferred Orientation of the grains
that is parallel to the XY plane of the finite strain ellipsoid, see Figure 5 (Ramsay
and Graham, 1970). As shear increases in the zone, the S-foliation continually
rotates towards parallelism with the shear wall, and may become
indistinguishable from the C-foliation, which parallels the shear zone boundary.
The geometry of S-C fabrics in a dextral shear zone is illustrated in Figure 6a; the
acute angle of the S-foliations point in the direction of shear, and the C-foliations
are evenly spaced breaks that help accommodate the strain (Platt, 1984). It
remains uncertain as to whether 8- and C-foliations form simultaneously (Lister
and Snoke, 1984), however, Platt (1984) refers to these foliations as a primary

fabric, ductile shear bands form as a secondary fabric. Shear bands (denoted as

21

 

    

00 90.0900 .09

‘—

Figure 5. Diagram of heterogeneous strain in a dextral shear zone.
The initial circles become elongate and align themselves
in the X-Y plane of finite strain ellipsoid.

22

 

 

 

 

 

 

Figure 6. 8-0 structures (a) and shear bands (b) in
a dextral shear zone. Note the C-foliatlons
are parallel to the shear zone and the shear
bands are at an angle to the zone boundary.

23

C') are also known as extensional crenulation cleavages. The geometry of shear
bands in a dextral shear zone is shown in Figure 6b, which shows that the S-
foliation is broken up by the C'-foliation. Shear bands occur at an angle to the
shear wall. The effect of shear bands is to extend the foliation by ductile normal
faults, in effect, they are small shear zones within a shear zone (Platt and

VIssers, 1980).

Tilden Shear Zone

The stratigraphy on the southem margin of the Marquette Synclinorium is
truncated; the Palmer Gneiss (PG) demarcates the boundary between the
Archean (Southern Complex) gneiss and the Early Proterozoic metasedimentary
rocks of the MRSG. Van Hise and Bayley (1895) first interpreted the PG as a
pulverized, sericitized, and partly silicified phase of the Lower Precambrian
gneiss. Through extensive mapping, Gair and Simmons (1968) concurred with
the previous interpretation and concluded the PG to be an altered rock, an
example of retrograde metamorphism. Since 1968, open pit mining operations at
the Tilden Mine have exposed the rocks that mark the trough boundary, and
have revealed large shear bands that indicate the importance of ductile
deformation during its alteration. For the first time, the exposure also allows a
chance to study the shear zone and obtain reliable data to characterize the

orientation of the last movement along this fault.

24

Geometry of the Shear Zone

In the shear zone, two distinct foliations are recognizable, the S and the
C'-foliation. All foliation surfaces were measured along two different benches on
the south wall of the Tilden Hematite pit. The S-foliations are larger, more
pronounced, more abundant, and easier to measure than the shear bands, which
were both less abundant and less accessible than the S-foliations; therefore
fewer measurements were taken. A list of all measurements can be found in the
Appendix A, Table 1. The steep S-foliation gently curves into the C'-foliation with
spacing between the two approximating 2.5 meters (Figure 7). The geometry of
the shear bands (Figure 8) indicates a reverse sense of motion. To determine
the precise orientation of the reverse motion, the orientation of the S-surface, the
shear bands, their intersections and the top of the shear zone boundary are
compiled on a stereonet (Figure 9). The S-foliation steeply dips to the NNE, and
the C'-foliation shallowly dips to the NNE. A plane perpendicular to the
intersection of the S and C' represents the plane of motion of the shear zone. To
obtain the actual slip direction, the shear zone boundary is necessary. Since the
boundary between the shear zone and the MRSG has been removed by mining,
the top boundary was reconstructed from maps and models generated by the
mining company. The actual slip line is determined by the intersection of the
shear zone boundary and the plane normal to the S-C' intersection, and was
calculated to be 046/58. The principal shortening direction is NNE-SSW.

East of the Hematite pit, a small outcrop is exposed showing a cross

section through part of the PG. The outcrop contains mesoscale S-C structures

25

 

Figure 7. Photograph of the Tilden shear zone. The steep foliation is
the S-foliation, notice it curves into the shear band, shallower
dip. The spacing between the shear bands approximates
2.5 meters.

26

 

\ Shear Zone

Palmer Gneiss

Figure 8. Diagrammatic sketch of the Tilden Footwall, note the
steep S-foliation curving into the shear band indicating
a reverse sense of motion.

27

 
    

Top of shear
zone

Figure 9. Stereonet plot of the Tilden shear zone. The C' is the mean pole
to the shear bands, the mean C’ plane is the dashed line. The S
is the mean pole to the S-foliation with the dotted line as the
mean S plane. The star indicates the mean intersection of the C'
and the S plane; solid line is the plane perpendicular to this S-C’
intersection. The long and short dashed line is the top of the
shear zone; triangle represents the plunge of the line of movement
of 046158. As it is a reverse shear zone, the movement was
up towards the SSW, u is the upthrown, d is the downthrown side.

28

that indicate a reverse sense of motion. The S-foliations are steeply dipping
towards the NNE, and the C-foliations dip to the NNE with a shallower dip (Figure
10). The plane perpendicular to the 8-0 intersection along the C plane indicates
the movement direction, 048/49. The S-C structures support the large shear
bands located in the Hematite pit, and suggest a NNE-SSW compressive

direction during reverse dip-slip.

Petrograph y and Kinematic Analysis

Petrography was conducted to observe the mineralogy, texture, and fabric
of the sheared rock as well as the protolith. Thin sections were prepared on two
oriented samples from the Tilden shear zone and on three, non-oriented samples
of metadiabase. The samples of metadiabase were collected progressively
farther away from the shear zone, the furthest representing the ‘freshest’ sample.

The Tilden sheared rocks have a very well developed foliation. The
mineral assemblage is mainly chlorite with some opaques (hematite, magnetite),
quartz, and a few grains of tourmaline. The opaques are subhedral, fine to
medium-grained and concentrated along planes of foliation. The quartz is
generally fine grained and displays undulatory extinction. Figure 11 shows the
well-foliated texture of the sheared rocks. No microscale kinematic indicators
were found. Strain was concentrated in the development of the large shear
bands.

The petrography of the metadiabase is quite similar to the Republic dikes

described by Weaver (1994). The ‘freshest’ sample is medium to coarse-grained

29

 

Figure 10. Stereonet plot of 8-0 structures outside of the Tilden
Hematite pit. C represents mean pole to the C-foliation,
short dash line is the mean C-foliation. The long dash
line equals the S-foliation, and the S is the pole to that
plane. Star indicates the mean S-C intersection and
the solid line is the plane normal to the intersection.
Triangle is the plunge of the line of movement.

30

 

Figure 11. Photomicrograph of the Tilden sheared rock (PG).
Notice the well developed foliation. Scale bar
equals 0.5 mm.

31

and contains mainly plagioclase, amphibole, biotite, with minor amounts of
chlorite, epidotelclinozoisite, and magnetite-ilmentite. The plagioclase is
twinned, altering to sericite, and is subhedral. The amphiboles are the alteration
product of the original pyroxene, they show yellow to blue-green pleochroism,
and are also subhedral. The opaques are mostly euhedral, however, they are
partially exsolved away. The metadiabase samples become progressively finer
grained as the samples get closer to the shear zone; the mineralogy of the

samples becomes unidentifable.

Harvey Shear Zone

The Marquette trough is a large, east-west trending synclinorium that
extends eastward to Lake Superior. The stratigraphy on the eastern margin,
above the Archean pillow basalt, consists of the Enchantment Lake Formation,
the Mesnard Quartzite, and the Kona Dolomite. The outcrop in the Harvey
quarry reveals the north dipping southern limb of a syncline; approximately 100
meters outside the quarry the northern limb dips to the south (Figure 12). A
ductile shear zone is observable in the quarry and is contained within the
Mesnard Quartzite at the contact with the Archean basement. The shear zone

contains clearly recognizable, mesoscale, shear bands (Figure 13).

Geometry of the Shear Zone

The ductile shear zone, bounded by less strained quartzite, is nearly 1

meter in width and contains the distinguishable foliations, S and C'. Similar to

32

 

 

Figure 12. Stereonet plot of a syncline in the Kona Dolomite and the
Mesnard Quartzite exposed in the Harvey Quarry. Circles
are the poles to bedding surfaces with a best fit great circle;
the star represents the fold axis gently plunging to the ENE.

33

 

Figure 13. Photograph of the shear zone in the Harvey quarry. The line
labeled 0' illustrates the orientation of the shear band, the line
marked S parallels the S-foliation.

 

the Tilden shear zone, the S-foliations curve into the shear bands, and they
steeply dip to the NNW while the C'-foliations shallowly dip to the NNE (Figure
14), see Appendix A, Table 2 for measured data. The spacing between the two
foliations is approximately 10 cm. The geometry of the shear bands indicates a
reverse sense of motion. The intersection of the shear zone boundary with the
plane perpendicular to the S-C' intersection results in a slip direction of 316/48.
This area of high strain formed under a NNW-SSE compressive direction,
different than the Tilden shear zone, it is an angle normal to the boundary of the

trough reflecting local variation in the stress field.

Petrograph y and Kinematic Analysis

One thin section was prepared from the shear zone in the Mesnard
Quartzite to analyze for kinematic indicators. The mineralogy is comprised of
fine-grained white mica (sericite), quartz, and opaques (hematite). Similar to the
Tilden sheared rocks, the sheared rocks in the Harvey quarry are also well
foliated, separated into zones of quartz and zones of fine-grained quartz plus
sericite. The opaque porphyroclasts acted as rigid objects during deformation
producing an inhomogeneous strain pattern around the crystal resulting in
pressure fringes (Spry, 1969). These pressure fringes can be used as kinematic
indicators, however, they are complex and did not form part of this study.
Mesoscale shear bands are also observed in the rock and are distinguished by

the fine mica cutting across the preferred quartz direction representing the S-

35

shearzone
boundary

 

 

Figure 14. Stereonet plot of the Harvey shear zone within the Mesnard
Quartzite. The C' is the pole to the mean shear band with the
dashed line as the mean 0' plane. The S is the pole to the
mean S-foliation with the dotted line as the mean S plane.
The star represents the intersection of the S-C' planes and the
solid line is the plane normal to that intersection. The long
and short dashed line is the shear zone boundary; triangle
represents the movement direction of 316l48.

36

foliation. These indicators also suggest a reverse motion supporting the

mesoscale shear bands.

37

FOLD GEOMETRY IN NEGAUNEE IRON FORMATION

The Negaunee BIF lies adjacent to the Tilden shear zone and is an
extensive unit within the Marquette Synclinorium. The iron formation has been
deformed into many folds observable at the Tilden and Empire Mines. The
exposure of the open pit mines allows for great accessibility to the folds.
Measurements along several walls were used to define some of these folds to
determine if a geometrical relationship exists between the folds and the shear
zone in order to deduce whether the deformation of the two occurred under the
same stress conditions. Data was collected mainly on bedding, but hinge lines
and axial surfaces of drag folds were also measured. Fold axes are determined
from stereonet plots; the pole of the best-fit plane through the poles to bedding
was used to define the fold axis. All of the following data is plotted on an equal

area stereonet using StereoNet version 3.0 for Windows (Steinsund, 1995).

Tilden Mine
North Hanging Wall

In the Hematite pit, measurements were obtained on the north side of the
pit and on the northeast side of the hanging wall; a haul road that connects to the
Magnetite pit separates these two areas (see Figure 2). On the north side, data
was restricted to two benches, 1440 and 1530. The upper bench was directly
above the other, but less data was obtainable due to poorer, and smaller
exposure and the presence of intrusives. Measurements included 138 bedding

planes, 22 axial planes, and 17 hinge lines for the lower bench and 17 bedding

38

planes, four hinge lines and axial surfaces for the upper bench (see Appendix A,
Table 3).

A stereonet plot of the measurements is shown in Figures 15 and 16, and
represents the benches 1440 and 1530, respectively. The axial surface plane
represents a mean value of those planes measured. The small drag folds, which
represent the larger fold, were used to measure hinge lines directly or by
projecting the line out of the wall face. Axial surfaces were determined by
aligning a clipboard adjacent to the axial surface and measuring the board. This
method resulted in some error, which explains why many of the hinge lines do
not fall directly on the axial surface. The geometry of the fold is consistent on
both benches; the poles to bedding conform to a great circle with a fold axis
gently plunging around 28° towards the WNW, subparallel to the trend of the
trough. The axial surface dips to the NNE, indicating the folds are overturned to
the SSW; the hinge line plunges 30° towards the WNW. The orientation
suggests that this fold, illustrated on two benches, formed under a NNE-SSW

compressive direction.

Northeast Hanging Wall

A metadiabase sill is the prominent rock type in the upper northeast side
of the hanging wall. Joint orientations were the key measurements made in this
area, except data were obtained for a mine geologist and are not a concern to
this study. However, bedding, hinge lines, and axial surface information in the

iron formation was available and attained. Measurements on bench 1710

39

 

Figure 15. Stereonet plot of the fold on the Tilden Hanging Wall bench 1440.
The circles are poles to bedding with a thick line representing the
best fit great circle. Fold axis (star) is plunging to the WNW,
triangles are the measured hinge lines and the thin line
shows the mean axial surface dipping to the NNE.

40

 

 

 

Figure 16. Stereonet plot of the Tilden hanging wall bench 1530.
Poles to the bedding are the circles, thick line is the best
fit great circle about the bedding poles. The star is the fold
axis plunging to the WNW. The thin line indicates the mean
axial surface, and the hinge lines are represented by the
triangles.

41

included 35 planes of bedding, 6 hinge lines and 3 axial surfaces (Appendix A,
Table 4).

A summation of the geometry is shown on a stereonet plot, Figure 17.
The poles to the bedding congregate about a great circle with a fold axis plunging
towards the WNW. The hinge lines are also plunging in the same direction and
with the same approximate dip as the axis. The mean axial surface is steeply
dipping to the NNE. Geometry suggests a NNE-SSW principal shortening

direction.

Empire Mine
Southwest Extension

An anticline is exposed on the northeast side of the Southwest Extension
pit. The rocks within this part of the pit are the Negaunee BIF and the Siamo
Slate. The BIF contains many small drag folds whereas the slate is more
massively bedded and contains no minor folds. Measurements were taken in
both formations and started with the 1215 bench and moved up ramp on a main
haul road.

Figure 18 is a stereonet plot of measured data of the anticline. Data
included 152 bedding measurements, 5 hinge lines and 5 axial surfaces
(Appendix A, Table 5). The poles to the bedding are distributed in a great circle
with the fold axis gently plunging at 32° to the WNW. The axial surface dips
steeply to the NNE and the hinge line plunges shallowly to the WNW. A principal
shortening direction of NNE-SSW produced this fold.

42

 

Figure 17. Stereonet plot of the 1710 bench on the Northeast wall
of the Tilden Hematite pit. Fold axis (star) plunges towards
the WNW as do the measured hinge lines (triangles). The
poles to the bedding (circles) are distributed about a great
circle (thick line), and the mean axial surface (thin line) clips
to the NNE.

43

 

 

Figure 18. Stereonet plot of the anticline in the Empire Southwest
Extension pit. The thick line represents the best fit great
circle to the bedding poles (circles), the star is the fold axis,
the triangles are the hinge lines, and the thin line represents
the mean axial surface clipping to the NNE.

Main Pit

In the Main pit, two different folds were measured: one on the east side of
the pit, labeled Fold One, and the other in the southeast corner, Fold Two. Fold
One is exposed on the 1080 bench, and is an upright, symmetrically folded
anticline that appears quite isolated. Fold Two is a large anticline with broad
limbs; it is exposed throughout several benches but only measured on the 910
and 990 benches.

Fifty-two bedding planes on Fold One were measured as well as an
approximation of hinge line and axial surface since no drag folds are present
(Appendix A, Table 6). Bedding conforms to a great circle with a fold axis
plunging to the NW at 30° (Figure 19). The axial surface is almost vertical but
slightly dipping to the SW. This fold was deformed under a NE-SW compressive
direction.

The geometry of Fold Two is similar to all the others. One hundred forty-
one bedding planes straddle a great circle that gently plunges to the WNW
(Figure 20). The mean axial surface dips to the NNE and the three measured
hinge lines gently plunge 15° to the east. This fold was compressed from a NNE-

SSW direction.

45

 

Figure 19. Stereonet plot of an anticline in Empire Main pit, labeled Fold
One. The axial surface (thin line) dips to the SSW, hinge line
(triangle) plunges to the WNW, the bedding poles (circles)
conform to a great circle (thick line) with a fold axis (star)
plunging to the NW.

46

 

 

 

Figure 20. Stereonet plot of a fold in the Empire Main pit, named Fold
Two. The fold axis plunges to the WNW and is represented
by the star. Poles to bedding (circles) are distributed about
a great circle (thick line). The hinge lines, represented by
the triangles, plunge to the east. The axial surface, thin line,
dips to the NNE.

47

TILDEN SHEAR ZONE PROTOLITH

Since 1895, the boundary between the Archean gneisses and the Early
Proterozoic metasedimentary rocks, here described as a reverse ductile shear
zone, has previously been interpreted as the altered equivalent of the lower
Archean gneiss (Van Hise and Bayley, 1895). Gair and Simmons (1968) agreed
with this early interpretation, however, they noted that the external characteristics
of the Palmer Gneiss do not reveal the rock from which it was derived; i.e., it has
a misleading name because it does not look like gneiss. They believed the PG
was an example of retrograde metamorphism and offered three modes of
genesis: (1) alteration and shearing of lower Archean gneiss during faulting, (2)
migration of fluids along the contact between lower and middle Precambrian
rocks, and (3) alteration of a regolith during folding. The recent Tilden Mine
exposure of the PG and the presence of shear bands support Gair and Simmons
(1968) first hypothesis for the rock formation. However, because of the
characteristics of the PG, it is questionable whether the Archean gneiss, a
dominantly granitic rock (Cannon and Simmons, 1973), is the protolith.

Several rock types are possible protoliths of the shear zone including the
Southem Complex Gneiss, banded iron formation, a clastic lens, or a
metadiabase sill. In an attempt to test and interpret the protolith of the PG,
chemical analyses were conducted on several samples collected within the
Tilden Mine area. From the analyses, the possibility of the banded iron formation
as the protolith can be dismissed because of the lack of iron in the PG. No

clastics are found in the PG suggesting that it did not form from the alteration of a

48

clastic lens. The Southern Complex Gneiss, previously interpreted as the
protolith, is a likely candidate because it is directly adjacent to the shear zone but
is also discarded for reasons that will be discussed further on. However, it
should be noted that the Southern Complex Gneiss abutting the PG is altered
and shows a gradational contact into the shear zone. The metadiabase is here
interpreted as the original rock of the PG, which suggests a Proterozoic, not an
Archean age because the metadiabase intruded during the extensional stage in
the Early Proterozoic. The sill is not adjacent to the shear zone, but it is a strong
possibility because it may have been rotated into the shear zone during folding.
Figure 21 shows a cross section through the TIlden Hematite pit interpreted from
drill cores and bench maps; notice the anticlinal shape of the metadiabase (230),
it appears that the southern limb may have been rotated into the footwall during
shearing. With metadiabase as the protolith, the role of volume loss can be
interpreted and then contrasted with a sheared dike of similar age and

composition to the metadiabase sill within the Marquette trough.

Whole Rock Geochemistry

Samples were analyzed using X-ray fluorescence to determine the
concentrations of major and trace elements. The samples included rocks
mapped as PG (outside mine area), the sheared PG, gneisses of the Southern
Complex, and metadiabase adjacent to the shear zone.

The sheared rock chemistry is indicative of a basaltic composition (Table

1). The gneissic rocks are much more silica rich and are slightly different from

49

.88: >33 ucm ::o.0 E2“. .ocou :mocm ..mEoo. 9... o. :6:
6999 m. ...m 6mm. mmmntEoE 65 8.62 .2: :02... 05 :99... 5.83 890 oszEEmmfi. .3 9:9“.

 

 

 

 

 

50

Table 1.

Mean chemical data for metadiabase, Palmer
Gneiss, and Southern Complex Gneiss. Major
oxides in weight percentage, trace elements in
ppm. Line indicates element concentration
below detection limit.

 

 

 

 

 

 

 

Metadiabase Palmer Gneiss Southern Complex

(n=7) ("=14) (”=3)
p (g/cma) 2.85 3.03 2.73
Si02 49.83 51.83 73.15
1102 2 1.09 0.19
Al203 14 15.88 15.37
Fe203 14.12 14.72 2.15
MnO 0.2 0.18 0.05
M90 6.67 10.22 1.53
CaO 8.47 4.22 1.69
NaZO 3.06 0.4 2.48
K20 1.45 1.66 3.35
P205 0.18 0.14 0.05
Ni 69.11 148.13 _
Zn 97.01 104.8 63.9
Rb 30.84 52.85 147.57
Sr 266.76 47.84 94.33
Y 16.14 27.22 27.97
Zr 98.93 85.51 72.7
Ba 1119.36 313.37 422.27

 

 

 

 

51

 

the sheared rock as seen on a plot of Si02 vs. other major oxides, in particular
TiOz, MgO, Fe203, and MnO (Figure 22). The sheared rocks are depleted in
alkalis (Ca, Na) in comparison to either the metadiabase or the gneiss. Overall,
the chemistry of the PG closely resembles that of the metadiabase (Figure 23).
Thus, the major elements of the sheared rock are not consistent with a gneissic
protolith, which suggests that the shear zone is an altered equivalent of the
metadiabase.

Using the metadiabase as the protolith to the sheared rock, variations of
the elements between the two are observed by the ratio of the average sheared
rock/average protolith composition for major and trace elements (Figure 24). Nb
and La were measured but were below detection limits for all samples. The PG
is slightly enriched in SiOz, Al203, Fe203, K20, Zn, Zr, and strongly enriched in
M90, Ni, Rb, and Y; whereas the PG is slightly depleted in MnO, P205, and
strongly depleted in T102, CaO, NaZO, Sr, and Ba. Figure 24 gives an idea of the
chemical changes that occurred. However, because the system was most likely
open to fluids and elements with differing mobility, it gives only a vague insight on

the transfer of components (Hippertt, 1998).

Volume Loss

During deformation of the PG, the rock changed both physically and
chemically. Physically, the coarse-grained metadiabase, containing abundant
feldspar, hornblende, and biotite, altered to well-foliated, fine-grained chloritic

schist. Chemically, the rock changed resulting from elements moving in and out

52

 

 

 

 

 

 

 

 

 

 

 

 

 

 

' 7 I I I
o D
I- I I D d
2 a (g on 10
o 9 o
no, a g: M30
1 a a s
A
A A
l 1 1A A l 1 n A
l I U I I I
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0
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A A
A
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MnO
0 I- a d
1. D CI
% A T ' D A .2
D
A I- °§ A d
I A a P
50 . 7O 50 . 70
so, 810,

Figure 22. Plot of major oxides versus SiO2 for all samples of metadiabase
(diamond), Palmer Gneiss (square), and Southern Complex
Gneiss (triangle).

53

Recklflormal Baa-It

10

 

 

 

 

y

 

0.01

 

 

SIOZ 1102 A1203 F0203 M00 M90 C80 N820 K20 P205

Figure 23. Comparison of major oxides concentrations of metadiabase
(diamond), Palmer Gneiss (square), and Southern Complex
Gneiss (triangle) plotted over a normal basalt composition.

54

 

 

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55

 

metadiabase concentration on a logarithmic scale. Elements plotting above one
are enriched in the sheared rock, values less than one are depleted in sheared rock.

Figure 24. Ratio of average Palmer Gneiss, sheared rock, concentration versus the average

of the system, a common effect shown in a number of mylonites (O’Hara, 1988;
Glazner and Bartley, 1991; Hippertt, 1998; Ring, 1999). Dissolution and solution
transfer are dominant processes that occur in shear zones with a large
component of progressive shearing strain (Bell and Cuff, 1989) and under
conditions of low metamorphic grade (Kerrich et al., 1977). Elements of the
minerals broken down and dissolved may be transferred out of the system
resulting in a volume loss (Hippertt, 1998). Deformation involving volume loss is
common in the upper crust (Bell and Cuff, 1989), and is an effective way of
accommodating the strain (Ramsey and Wood, 1973).

Given the bulk chemical compositions of sheared rock and the protolith,
further interpretations about the behavior of the elements and the amount of
volume loss of the system can be explored. The volume relationship can be
determined in two ways; Gresens’ (1967) composition-volume relationship, and
Grant’s (1986) graphical solution to Gresens’ method. Gresens' method is a
mass balance equation that makes use of the bulk chemical analysis and the
densities of the rocks involved in the metasomatism. According to Gresens’
(1967), some components are likely to be immobile during alteration, and once
these components are recognized, they are used to calculate the total amount of
volume change. This assumes that the volume change is common to the
behavior of all components, and assuming a chemically homogenous protolith.
The basic equation behind Gresens' method is:

x, = [fv(g°/g‘)CnB-cn"11oo

56

where Xn is the amount of mass of a component that is either lost (negative
value) or gained (positive value) in the system relative to the reference
(immobile) component; f" is known as the volume factor; 9 refers to the density of
the rock; C represents the concentration of the component; and the superscripts
A and B refer to the protolith and altered rocks, respectively. The value 100
refers to the reference mass of the original sample used for analyses that are
summed to 100 weight percent. Within this equation, Xn and fv are two unknown
variables. If we assume that some of the components are immobile, assume a
value for fv, than it is possible to solve for the other variable, X...

To determine the immobile elements, a series of composition—volume
equations are solved by rearranging the above equation to find the appropriate
volume factor. Using the average compositions of metadiabase protolith and
sheared rock adjusted to 100% (since all the analyses resulted in low totals), and
densities of 2.85 g/cm3 and 3.03 g/cm3 for protolith and altered rock respectively,
the composition-volume equations are as follows:

fv= 0.01803“), + 0.9041

fv = 0.8709xm, + 1.742

f" = 00592me + 0.8298

fv = 00640me + 0.9028

f" = 5226me + 1.045

f, = 0.0919ngo + 0.6142

f, = 0.2783xc.o + 2.354

fV = 2.351 XNazO + 7.219

57

fv = 0.5632xxzo + 0.8167

f, = 6.719xp,o. + 1.277
These equations represent lines that all cross the zero gain-loss line (x-axis;
Figure 25). The components that cross the x-axis furthest from one represent
the highly mobile elements, while a tight clustering in the mid-portion of the graph
indicates the immobile elements or the appropriater value (Gresens, 1967). If fv
= 1, no volumetric change occurred during alteration; if f, < 1, there was a net
volume loss, and if f, > 1, the volume increased. Note that Al203 and K20 both
cross the x-axis at a f" value of 0.8298 and 0.8167, respectively, suggesting
these are the immobile elements and an appropriater value of 0.823. lnputing
the f, into the previous equations gives values for each oxide and results in the
following mass balance equation that relates the chemistry of the sheared PG to

the metadiabase:

 

1009 protolith + 4.489 Si02+ 2.279 M90 + 0.019 K20 P
87.59 altered rock + 1.069 TiOz + 0.119 Al203 + 1.259 Fe203 + 0.049 MnO
+ 5.59 Ca0 + 2.729 Na20 + 0.079 P205
This equation shows that altering the metadiabase to the shear zone rocks
resulted in an increase in Si02 and M90, a loss in CaO and Na20, and an overall
mass decrease of 12.5%. The volume factor subtracted from one suggests a
volume loss of 17.7%.
The above result seems possible because Al is a low solubility element
under many geologic conditions, and is often considered immobile. The Al in the

plagioclase, hornblende, and biotite remained in the system and became

58

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59

incorporated in the abundant chlorite. Using Gresens’ method has severe
limitations; in particular, Gresens example of choosing the appropriater value
was to develop a graph, such as Figure 25, and to find the immobile elements
clustering somewhere in the central portion of the graph crossing the x-axis. This
is quite arbitrary and can result in significant error; e.9., SiOz and Fe203 also
cluster close together at a higher fV value of 0.903, and this would result in a 4%
decrease in mass with a 9.7% decrease in volume. The choosing of the fv value
is important and should be based on petrological reasoning. The errors
introduced during XRF analysis and density estimates, as well as assuming a fV
value limits the computation of absolute values for volume loss.

The second method, Grant’s (1986) graphical solution to Gresens’
equation, was applied to the same compositional values of protolith and altered
rock. The method is to plot the concentration of the altered rock (0,.) vs. the
concentration of the protolith (Co). An isocon, a line representing equal
geochemical concentration, is drawn by inspection. The isocon is a best-fit line
from the origin through a few points, which represents the immobile elements.
The best-fit line through the data (Figure 26) suggests that both Al and K are
immobile. The slope of the isocon, 1.143, is the inverse of f,,(gB/gA) from
Gresens’ (1967), thus results in the same volume loss, 17.7%.

Grant (1986) noted that the term ‘immobile’ could be interpreted to mean
two different things. First, it could mean that the component has undergone
minimal mass transfer; or second, the concentration of a component has not

changed in relation to another. Given this interpretation of the term ‘immobile’, AI

60

Ca

 

40

 

 

 

D

. .25Ni

30 _ “10
Y
00
U
« .SRb ,
.SSIO2
20 _ c, .22:
Alp, °100Mno
I D
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.lZSZn

.. M o D
10 80 1 (m 02 o 3Ca0

_ lONa,O

D
”.0131: lSr
o T I I I j I I
0 10 20 30 40
Co

Figure 26. lsocon graph, concentration of elements in altered (Ca)
rock versus concentration of elements in protolith (Co). The
line (slope = 1.143) represents the isocon, equal
chemical concentration.

61

and K can be used to define the isocon and be helpful in evaluating the behavior
of the other elements during alteration. In Figure 27, the compositions or
behavior of elements are compared to a constant mass isocon drawn from the
origin through the protolith composition. Elements plotting above the line are
gained by the system, and elements below the line are lost. Magnesium is the
only element gained by the system, whereas all the other oxides are lost with

respect to Al.

Republic Dike Comparison

Adjacent to the Marquette Synclinorium, in the Republic area, many mafic
dikes cut into the Archean gneiss. These dikes were sheared during the
Penokean Orogeny and exhibit sigmoidal shaped foliation patterns indicating the
sense of motion (Myers, 1984). The margins of the dikes are highly strained and
altered, while the center portions exhibit the least amount of strain and alteration.
Michael Zieg (unpublished data) studied one of these dikes and conducted a
chemical analysis across it (Table 2). Because the protolith of the dike is
constrained, and similar to the metadiabase in the Tilden, it is beneficial to
compare this sheared dike to the Tilden shear zone.

Both Gresens’ (1967) and Grant’s (1986) methods were applied to the
data in the same manner as the Tilden shear zone to compare the element
behavior and volume relationships. The center of the dike was used as the
protolith and the margin was used as the altered equivalent. Figure 28 shows

the variation of elements from the ratio of sheared concentration/protolith

62

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Ca 4 / lONa
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5 -i / 1
1 //
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° ' 1 z r r T r 0 ' I r I
0 4 I 12 10 N 0 4 12 10 N
Alp3 Alp,

Figure 27. Plot of N203 versus other major oxides. Line
represents constant mass isocon. Elements above
the line were gained by the system, elements below
the line were lost with respect to Al203

63

Table 2. XRF whole rock major oxides of
Republic dike, values are weight
percentages (Zieg, unpublished

 

 

 

 

 

 

data).

margin center
_L(_9lcm3) 2.5 2.1
Si02 53.4 53.05
1102 0.63 0.71
N203 13.66 12.62
F6203 9.41 10.24
Mn0 0.13 0.17
M90 9.21 9.15
Ca0 4.53 8.66
N320 2.13 1.88
K20 3.76 1.4
P205 0.05 0.07
totals 96.91 97.95

 

 

 

 

 

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65

concentration. Slightly enriched in the margins of the dike are Si02, Al203, M90,
Na20, Ni, Y, Zr and components strongly enriched are K20, Rb, and Ba. The
margins are depleted in Ti02, Fe203, Mn0, Ca0, P205, Zn, and Sr. The element
variation of the dike is not much different than the Tilden shear zone (Figure 24);
the major exceptions are Fe203, Zn, Na20, and Ba. Fe203 and Zn are enriched
in the Tilden shear zone and depleted in the dike, while Na20 and Ba are
strongly depleted in the Tilden zone but slightly to strongly enriched in the dike.

To determine the amount of volume and mass change of the dike,
Gresens (1967) composition-volume equations are as follows:

fv= 0.015%“), + 0.8263

f, = 1292an, + 0.933

f" = 0.0596xmo. + 0.7679

f\, = 00865me + 0.9049

f, = 6.269an0 + 1.075

fv = 0.088xwo + 0.8259

fV = 0.1799xc,o +1.59

f" = 0.3822meo + 0.7338

fv = 0.2165xm + 0.3094

fv = 1628me. + 1.081
Figure 29 shows a plot of the value of the X-intercepts upon crossing the zero
gain-loss line when Xn = 0, suggesting Si and Mg are the immobile elements and
indicate a fv value of 0.826. Thist value leads to the following balanced

alteration equation:

66

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67

1009 protolith + 0.979 Al203 + 0.249 Na20 + 2.399 K20 —>
98.39 altered rock + 0.029 Si02 + 0.089 Ti02 + 0.919 Fe203 + 0.049 Mn0
+ 4.259 Ca0 + 0.029 P205

Alteration of the dikes resulted in a 1.7% decrease in mass, and a 17.4%

decrease in volume. The slope of a best-fit isocon is 1.017, suggesting Si, Mg,

and Ni are immobile, however, many of the other elements plot close to the

isocon, indicating not much mobility of those elements (Figure 30).

68

Ca

40

3O

20

10

Figure 30. lsocon graph of Republic dike. Altered rock element
concentration (Ca) versus element concentration of

 

 

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protolith (Co). lsocon has a slope of 1.017.

69

50

DISCUSSION

Defamation History

Structural analysis of the Tilden shear zone and folds within the Marquette
Synclinorium indicate that they formed under a NNE-SSW principal shortening
direction and are interpreted to have originated at the same time. The
determination of the principle shortening direction confirm a previous study of
sheared mafic dikes in the Republic area (Myers, 1984). Deformation is
attributed to the Penokean Orogeny, when the region underwent compression
due to an island arc colliding with the southern edge of the Superior Craton
(Cambray, 1978). This major tectonic episode occurred 1.9-1.85 billion years
ago (Van Schmus, 1976).

The Tilden shear zone is a large, reverse dip-slip ductile shear zone that
contains mega-scale shear bands indicating a reverse sense of motion. The
movement along this fault displaced the younger Early Proterozoic Marquette
Range Supergroup up over the older Archean Gneisses. In order to thrust
younger over older, the younger, MRSG, must originally have been
stratigraphically lower i.e., deposited in a basin type setting within the Archean
Craton. Much of the Lower MRSG is interpreted to have formed in a subsiding
basin on a rifled passive margin (Larue, 1981; Larue and Sloss, 1980) or in a
foreland basin (Barovich et al., 1989). The pattern of younger over older is not
restricted to the Tilden area, for it is also observed in the Harvey Quarry. The
compressive direction of this shear zone is NNW-SSE, normal to the trough

margin, similar to what Myers (1984) observed in his study.

70

The folds in the adjacent iron formation generally have a consistent
geometry. The axes of the folds plunge to the WNW at approximately 30°. The
axial surfaces dip steeply to the NNE. The orientations of these folds suggest
that they were compressed in a NNE-SSW direction. One fold measured at the
Empire Mine has a slightly different geometry, the fold axis is plunging more to
the NW; this dissimilar geometry may possibly indicate a superimposed folding
event as suggested from the complex folding seen at Jasper Knob.

The Marquette trough is an asymmetric basin, which lies adjacent to the
Great Lakes tectonic zone of Sims et al. (1980). Evidence for the asymmetry of
the basin is the truncated stratigraphy on the southern margin with a more
complete succession on the northern side. The MT is similar to a classic rollover
structure in a rift basin (Figure 31), and is supported by clastic lenses that are
relatively thick in the south and fade out to the north (Breithart, 1983). During the
development of the passive margin, the southern side of the trough was being
uplifted, shedding sediments north into the basin; paleocurrents indicate a NE
transport direction (Lin, 1969).

The end of sedimentation of the Early Proterozoic sediments is accredited
to the progressive onset of the Penokean Orogeny. The compression caused
closure of the basin and the reactivation of preexisting normal faults (Figure 32).
The basin was inverted and resulted in a reverse dip slip along the southern
margin of the trough. Inversion tectonics is a common phenomenon in
Phanerozoictectonies (Jackson, 1980; Gillcrist et al., 1987; Chadwick, 1993).

The strain was concentrated in a portion of a metadiabase sill that was rotated

71

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73

into the shear zone causing alteration and shearing of the rock to form the

Palmer Gneiss.

Protolith and Mass-Volume Changes

The Tilden sheared rocks, PG, are interpreted to have been formed from
the alteration of a metadiabase during shearing. Shear bands indicate ductile
deformation during formation, and the “basaltic” type chemistry as well as
external appearance of the sheared rock suggests that it did not form from the
alteration of granitic gneiss as previously assumed. During metasomatic
alteration, pressure solution and solution transfer can cause chemical
modifications that may result in a mass and/or volume change (Kerrich et al.,
1977; Bell and Cuff, 1989). ‘Some’ bulk chemical changes may occur when
rocks develop a foliation, and it is more likely in a rock with a higher phyllosilicate
content (Bell and Cuff, 1989). The sheared PG rocks at the Tilden have a
pronounced foliation and a high content of chlorite; the rocks have definitely
undergone chemical changes when either of the two possible protoliths is
considered. However, the chemical changes involved from the alteration of the
gneiss to the sheared rocks seems too extreme, whereas the chemical changes
form a metadiabase to sheared rocks is more probable.

The chemical modifications induced during deformation of the
metadiabase are comparable to the chemiwl changes caused in a sheared
Republic dike, which represents a known protolith that underwent shearing. The

margins of the dike are altered relative to the central portion. The chemical

74

changes from the margin to the center are similar to the changes form
metadiabase (within trough) to the PG (Figures 24 and 28) indicating further
evidence that the metadiabase is the protolith to the PG.

A compressional setting, which invokes shortening of the crust, was the
tectonic framework that controlled the formation of the PG. Volume loss is a
means of obtaining crustal shortening (Hippertt, 1998), and is interpreted to have
occurred during alteration; calculations result in a 17.7% volume loss and a
12.5% decrease in mass. These changes in volume and mass are not absolute
and are only approximations.

The approximations of changes were calculated using Gresens’ (1967)
composition-volume equations, and Grant’s (1986) isocon method, a graphical
solution to Gresens. The methods have many limitations that prevent the
determination of absolute changes in volume or mass. ‘ The three main problems
associated with the calculation of the volume and mass changes are (1) the
potential for analytical error, (2) the assumption of homogeneous alteration, and
(3) the choosing of the reference element(s). The problem of analytical error
leads to uncertainties of chemical differences; analyzing several samples slightly
minimized this problem. The second major problem is the assumption that the
alteration was homogeneous. Alteration typically is concentrated along fractures
and is commonly heterogeneous (Baumgartner and Olsen, 1995). The
heterogeneity in the chemistry of the samples collected, i.e., the wide ranges in
compositions among the altered rock samples (Appendix B) indicate that the

alteration was not homogeneous. The problem of heterogeneity was not

75

corrected for by the calculations used. The choosing of the appropriate
reference element, the third problem, can cause the greatest source of error if
the wrong element is chosen.

Low solubility elements such as, Ti, Al, and Zr are typically chosen as
reference elements in many metasomatic alteration studies (0’ Hara, 1988;
Hippertt, 1998; Ring, 1999). Many geologic variables effect element mobility
including the composition of the rock, pressure, temperature, and the presence of
fluids (Ague and van Haren, 1996); thus, to assume one of those elements
immobile for a given alteration may be unjustified because the conditions that
controlled the mobility potential are not known or constrained. Therefore, no
element can always be considered immobile, it is dependent upon the conditions,
and additional information, such as petrographic evidence, is needed to make
and support the appropriate choice of the reference element (Baumgartner and
Olsen, 1995). Despite all the problems associated with the determination of
volume and mass changes, the methods were used in an attempt to give a vague

insight into the alteration of the PG.

76

CONCLUSION

The geometry of the large, low-grade shear zone exposed on the southern
margin of the Marquette Synclinorium is that of reverse dip-slip. The mega-shear
bands indicate a NNE-SSW compressive direction, confirming previous studies
of sheared mafic dikes (Myers, 1984). The shear zone was produced when the
Penokean Orogeny caused closure of the basin, and localized strain in part of
the metadiabase sill that was rotated into the shear zone causing alteration and
shearing to form the Palmer Gneiss.

The appearance and the chemistry of the PG suggest that it did not form
from the alteration of gneiss as previously interpreted, but that it is an altered
equivalent of metadiabase indicating a Proterozoic age. The chemical changes
that occurred in forming the altered PG are comparable to the chemical changes
in a sheared mafic dike of similar origin in the Republic area. Volume and mass
loss accompanied the alteration. The best approximations of loss in the Tilden
shear zone are 17.7% in volume and 12.5% in mass.

A geometrical relationship exists between the shear zone and the folds in
the adjacent Negaunee Iron Formation. This suggests that the folds and the
shear zone were produced at the same time under the same compressional
conditions. The Marquette trough is a Precambrian example of inversion
tectonics. Reactivation of preexisting faults has been noted in many studies in
Phanerozoic settings. This suggests that the tectonics during the Precambrian

were similar to the tectonics taking place today.

77

APPENDIX A

78

Table 1. Measurements of foliations in the Tilden footwall, south side
of Hematite pit. Measurements are dip direction/dip amount.

 

 

 

 

 

 

 

 

 

 

 

'l’llden Footwall

S-fohtion (n == 253) C-folation (n = 77)
020161 039173 009171 342164 014169 014167 351715 355136
016/62 033165 014161 352167 026154 357/66 349/49 347/36
016/65 016173 322/63 346/72 025159 003173 016145 021/26
021164 036/69 026176 007166 026155 036164 009/50 023/20
022/71 032/72 044/61 357/61 025/53 353/71 335/54 003/26
352/70 032167 006/75 006157 029/60 353169 340150 020143
001/55 019/77 011/71 360/61 039/62 026/69 355/46 003134
356149 036162 017/72 001161 036154 354/51 036143 026143
002/53 046160 005/65 357I63 036160 017161 013/51 322130
352156 025172 009/75 029172 022162 009155 041/54 332133
352165 019167 001163 217/90 006164 017176 007/51 014/31
003161 016174 016166 336163 017161 036163 036135 350/32
349170 025175 013166 027170 026176 026153 015131 005131
002167 201/69 012/58 330175 356153 349153 025135 010127
043176 022169 014172 334174 009155 013153 009146 345/36
031160 032165 011162 360170 002160 355156 022119 023145
349166 014169 341159 012171 020166 013156 021149 347134
355157 003/76 315/62 356175 019164 012/66 023151 357137
026166 010/74 357163 351175 016166 013173 016120 017126
003161 014169 353167 350175 019177 016m 067130 343/42
012/63 010169 033163 006169 014169 352156 014139 024141
023153 019176 016159 024164 001164 355159 357147 006150
006166 004169 027173 010166 015156 032164 015133 003136
000161 352155 005163 353162 006167 021166 043149 022137
037174 022165 021166 349163 021167 023172 026131 353146
035171 013156 349149 335165 016163 022159 345136 336155
014177 021174 046166 332162 021I67 006176 006132 020137
010174 011154 023175 033166 356163 225166 009139 003/45
015/66 006172 027169 035161 009161 036179 035146 009156
022161 014166 030169 357159 015102 035/77 007150 352154
030/70 037179 029160 026156 029161 022176 336131 312146
022164 012190 002166 025176 044169 047170 360135 004134
007169 009171 016176 044/66 007170 017173 354151 020152
337/61 007170 001162 011160 025167 356160 341149 357146
015166 054154 014164 012166 032167 346160 356149

032170 341157 027174 026156 009166 037165 003156

015173 346159 025167 016156 023163 012160 001152

016167 353175 021169 006167 012/66 027157 006152

021167 349159 014167 016157 029162 337151

037169 010175 026174 025154 020163 002141

016173 020179 016169 355155 309175 003152

017167 027164 022171 026152 016160 346140

001160 005167 007174 004175 029160 013155

 

79

 

Table 2. Measurements obtained in the Harvey
Quarry, including bedding, S-foliations,
and C’-fo|iations. Dip direction/dip amount.

 

 

 

 

 

 

 

 

 

 

Bedding
(11 = 27)
355141 042/32 005/40 165/77
356/41 019148 023126 164/54
358151 013145 173/79 164169
335147 015131 156/52 165/56
015/40 010130 185/87 163/61
012/39 050/12 186/86 160/65
006137 054/32 170/79

S-foliation C-foiation
(n = 10) (n = 8)
354172 340/80 015140 015118
330/81 355182 016141 015126
344/77 330184 01 1135 024/30
342/88 353181 020135
352175 350/80 027/25

 

 

 

 

80

 

Table 3. Data for benches 1440 and 1530 in the Tilden Hematite pit.
Measurements are dip directions/dip amount of bedding, hinge
lines, and axial surfaces.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bench 1440
bedd'ng h'nge he axial surface
(n=138) (n=17) (n=22)
320/45 031/18 184/78 061/18 220/65 201/82 299121 021165
349157 324134 068157 354142 024142 21 9165 105108 005164
348163 31 1135 178161 322136 203180 21 1184 287115 050183
216113 316144 301141 282/27 203/78 302/57 107108 015177
318125 311/35 293136 355160 206/63 250/58 276106 02617 3
289/14 004/42 347/29 256134 201184 016150 295130 024188
017124 051150 322130 243/43 202182 001171 279123 004184
006158 335/42 321/34 241/43 205169 029143 293149 010163
309121 330142 324/43 235/30 221169 222158 291128 019167
31 9135 341/35 347155 241130 344148 333/66 277/30 254/66
348128 353165 348/53 247/34 193/80 262154 290142 236/80
268126 347135 286/47 237137 010136 321139 293149 280128
359/36 347/47 21 9180 250/30 028/53 336/65 303150 012173
251133 316156 011181 244136 009161 223/60 286137 016176
276144 017132 21 1140 250138 016159 226/46 304146 012178
221/37 348/47 287/39 328/38 041/72 239144 271123 200/88
251141 353144 323156 231132 358164 232/34 293/23 008/77
21 9157 351/44 230152 249/27 349/45 241161 197185
231/51 334/20 214/72 244145 025183 225143 001162
223144 330129 236166 006163 193169 199170 207181
216/50 359/44 265/40 252/44 214177 015179 359170
222156 247/23 264/53 254/34 206/78 202/66 229/84
205/88 348/40 208/65 234149 025189 236151
Be nch 1630
bedding hhge he axial surface
(n=17) (n84) (n84)

179183 355134 185170 21 5165 195185 196167 295123 01 8179
180178 357187 209179 01 8186 183/86 201/72 279138 348172
204179 173185 352160 325165 346135 268/43 324/50
281 132 035185

 

81

 

Table 4. Data for bench 1710 on the northeast side of the Tilden
Hematite pit. Measurement are dip direction/dip amount
of bedding, hinge lines and axial surfaces.

 

 

 

 

 

 

 

[Bench 1710
bedding hhge he axial surfa_c_e_
("=35) (n=6) (n=3)
292/44 229/48 233/45 257/33 310129 010159
258/34 259/36 329/40 294/40 287122 022182
206/20 291/36 285/25 230/60 290/15 013172
295/34 267/45 331/76 238/48 301/40
223/21 274/41 267/22 317/29 278/ 12
270/34 276/34 336130 25911 1 281/30
254/43 227/40 336/30 222146
217173 328135 217168 214158
210/60 308/33 209/74

 

 

82

Table 5. Data for the Empire Southwest Extension pit. Measurements are
dip directions/dip amount of bedding, hinge lines, and axial surfaces.

 

 

 

 

 

 

 

 

 

 

 

 

SW-Exte nslon

bedd'ng hhge he axial surface
(n=152) (n=5) (n=5)
342/43 321/42 269133 238143 274147 240149 259113 335176
333/35 321/38 257/37 258131 266145 260139 233132 042169
325141 342/46 260/35 223129 266146 243/41 260/27 003/78
350145 336146 270136 306/25 271/37 245142 275112 004183
349149 340143 266143 296130 259140 245/35 283132 356146
344140 324136 256136 256137 256/43 251/36

354145 339150 270141 275142 231149 242160

002161 333142 259137 272145 252156 236149

355145 342/81 254/29 225/41 21 1164 213/77

334156 330152 272/37 287/45 193167 238138

330146 326163 240/40 267142 213161 245140

336137 325/38 260134 265151 237/51 253/69

332/37 329/40 228/37 246/42 209162 012160

353143 298/34 236/30 267/42 256134 009174

321136 207/37 240/37 232/42 232/48 007/69

359170 320136 254/43 257134 223141 004/45

320137 300143 246149 243133 213171 014169

329142 294/39 250142 230143 229156 021182

331167 258/36 272/35 236/42 242143 015164

306/31 246/37 267/36 247134 229136 232137

310135 257139 249/39 248/35 260/26 232137

195162 259133 223141 259135 247/55 228/45

317144 256137 245/41 264/42 247/44

320/39 256137 251139 254/40 257/84

210/65 206/60 213/55 231153 223143

216147 209162 211155 220140 217142

 

83

 

Table 6. Data for Fold One and Two in the Empire Main Pit. Measurements

are of bedding, hinge lines and axial surfaces as dip direction/dip

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

amount.
Fold One

boddhg hhge he axial surface
("‘52) (0'1) (0'2)
261136 243/45 342/34 265139 025155 258/34 283/30 214/72
259134 251145 338139 258/35 021174 256136 192/86
262/34 260145 012155 283/41 268/47 262136

259137 255136 350139 267/44 262/38 248/37

260/34 264133 009151 274143 269138 274127

269/33 271/26 358148 270145 259135 273/25

293123 267127 005152 270143 256137 324/33

257136 282126 307122 324/30 253141

331135 248/45 332/34 253/40 255/42

Fold Two

beddhg hhge he axial surface
(nu-141) (n-3) (n- 10)
287/29 319/29 312126 336128 194155 0021?] 091117 016170
294130 325/30 296126 326134 303114 003134 090/ 15 010175
289130 313131 300126 332132 315117 004127 071/14 358171
292128 302128 308147 330132 31 7123 004/58 342/67
288/28 298/30 314129 330129 005142 008141 354162
293/28 306125 323130 349/30 231120 009127 359163
283129 313129 317130 338134 012161 018128 357166
285131 310130 328126 319120 314122 024127 028/77
279/27 320133 325/32 312108 007131 032130 023167
279/31 329132 306124 166163 347/49 049108 012163
274130 315132 313124 337/27 235/23 060136

322131 319128 321/28 321/27 018/54 169167

299129 303135 331131 305125 001137 182184

310126 31 3129 327/29 204/76 320147 189155

319/22 317/12 283/21 228/22 299105 196154

239/04 314118 305120 199127 012132 199182

336120 307/ 15 326/17 218127 245120 254/27

337129 335131 324121 332126 317122 332128

197142 303117 332121 327/22 359117 344131

343131 307/ 19 320/21 320/27 347133 353135

331125 330125 319/16 277/16 324137 358/26

319/29 319/24 317130 009159 012135 360124

322121 327128 248/ 19 312134 359150

330124 328127 315129 311127 008142

 

84

 

APPENDIX B

85

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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86

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87

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