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STRUCTURAL AND KINEMATIC EVOLUTION OF THE MIDDLE CRUST
DURING LATE CRETACEOUS EXTENSION IN WESTERN NEW ZEALAND
A Thesis Presented
by
Williams C. Simonson
to
The Faculty of the Graduate College
of
The University of Vermont
In Partial Fulfillment of the Requirements
for the Degree of Master of Science
Specializing in Geology
October, 2003
Accepted by the Faculty of the Graduate College, The University of Vermont, in partial
fulfillment of the requirements for the degree of Master of Science, specializing in
Geology.
Thesis Examination Committee:
Advisor
Keith A. Klepeis, Ph.D.
Barry Doolan, Ph.D
Tracy Rushmer, Ph.D.
Chairperson
Donna Rizzo, Ph.D.
David S. Dummit, Ph.D.
Date: August 28, 2003
Special Assistant,
to the Provost for
Graduate Eductation
CITATION
Material in this thesis will be submitted for publication in the geologic and geophysical
journal, Tectonics, pending the arrival of geochronologic data, in the following form:
Simonson, W.C., and Klepeis, K.A., (in prep.), Structural evolution of the middle crust
during exhumation by continental extension: The Paparoa Metamorphic Core Complex,
South Island, New Zealand. Tectonics.
ii
ACKNOWLEDGEMENTS
This thesis would not exist without the help of many. In no particular order I am grateful to:
My parents, Pat and Ric Simonson, who have been educating me for my entire life. Thank you
so much for everything that you have given me (TPS, AC). I promise to repay you with love and
understanding.
My teachers, far too numerous to list, who have challenged and pushed me. Thank you for your
time and energy.
Keith Klepeis, my mentor, who has taken me so many places I never expected to see. Keith,
under your guidance I achieved things I was sure were never possible…drawing the WHC xsection, giving a talk at GSA, writing a paper…Thank you is clearly not enough. I'll get you back
somehow.
The geology faculty at the University of Vermont, for supporting me and advising me on how
to improve my story.
The geology faculty at Amherst College, who put me in the position to do what I have done for
the last two years.
The National Science Foundation, for funding my travel to New Zealand
Mrs. Catherine Suiter, for funding the Suiter Award, which covered the cost of my travel to
GSA in Denver, CO.
Dave, Gabi, Denise, and Ian, for allowing me to share your toys and your work space.
Steve Marcotte, for taking so many measurements in the field and taking part in many, many
discussions about all things structural.
Kenny Oldrid, for being Kenny Oldrid during the summer of 2003
Dave West at Middlebury College, for allowing me to use his brand new Spectroscope.
UVM Geology students, thanks for the fun times and moral support.
J. Renee, for your love.
The Institute for Geological and Nuclear Sciences, in Dunedin, NZ, for kind hospitality and
permission to use the rock saw.
The University of Vermont, for funding my GTF stipend and paying for my summer research in
2002
Pat Frank, for helping with all those little details
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TABLE OF CONTENTS
CITATION……………………………………………………………………………….ii
ACKNOWLEDGEMENTS…………………………………………………………….iii
LIST OF FIGURES……………………………………………………………………viii
CHAPTER 1: Introduction…………………………………………………………….…1
1.1 STATEMENT OF PURPOSE AND SIGNIFICANCE………………………….…1
1.2 APPROACH………………………………………………………………………...2
1.2.1 Study area selection ……………………………………………………………...2
1.2.2 Field Techniques……………………………………………………………...…..3
1.2.3 Laboratory Techniques …………………………………………………………..3
1.3 THESIS OUTLINE…………………………………………………………………..4
CHAPTER 2: Literature Review…………………………………………………………6
2.1 INTRODUCTION…………………………………………………………………..6
2.2 CONTINENTAL EXTENSION………………………………………………….…6
2.3 METAMORPHIC CORE COMPLEXES…………………………………………10
2.4 EVOLUTION OF DETACHMENT ZONES AND LOWER PLATE ROCKS…..12
2.5 WESTERN NEW ZEALAND AS AN EXTENSIONAL SETTTING…………...15
2.6 CASE STUDIES OF SYN, POST-OROGENIC EXTENSION…………...……...25
CHAPTER 3: Manuscript prepared for submission to Tectonics:
"Structural evolution of the middle crust by exhumation during continental
extension: The Paparoa Metamorphic Core Complex, South Island, New
Zealand"………………………………………………………………………………….26
3.1 INTRODUCTION……………………………………………………………….…27
3.2 PREVIOUS WORK………………………………………………………………..28
3.2.1 Regional geologic and structural relationships………………………………...28
3.2.2 Paparoa metamorphic core complex…………………………………………...32
3.2.3 Lower plate cooling history…………………………………………………….42
3.3 DUCTILE DEFORMATION IN THE LOWER PLATE………………………….35
3.3.1 Zone of mylonitic fabrics……………………………………………………….35
3.3.2 Central core zone……………………………………………………………….39
3.3.3 Ductile deformation on the northern border of the core……………………….41
3.4 BRITTLE AND SEMI-BRITTLE DEFORMATION……………………………..44
3.4.1 Brittle faults…………………………………………………………….………45
3.4.2 Semi-brittle faults……………………………………………………………….50
3.5 KINEMATIC ANALYSIS………………………………………………………...50
3.5.1 Kinematic analysis of mylonitic rocks………………………………………….50
3.5.2 Kinematic analysis of ductile fabrics outside the mylonitic zone………………57
3.5.3 Kinematic analysis of fault-slip data…………………………………………...58
3.6 CORRELATION OF STRUCTURES AND DEFORMATION SEQUENCE…...60
3.7 GEOCHRONOLOGY……………………………………………………………..61
3.7.1 Sample locations………………………………………………………………..61
3.7.2 U-Pb Ages………………………………………………………………………62
3.8 DISCUSSION……………………………………………………………………..62
3.8.1 Three-dimensional strain and kinematic evolution of the middle crust………...62
3.8.2 Extensional mechanisms………………………………………………………..65
3.9 CONCLUSIONS…………………………………………………………………..67
CHAPTER 4: Strain and Kinematic Analysis………………………………………….69
4.1 INTRODUCTION…………………………………………………………………69
4.2 STRAIN……………………………………………………………………………69
4.2.1 Background……………………………………………………………………..69
4.2.2 Methods…………………………………………………………………………72
4.2.3 Results…………………………………………………………………………..74
4.3 KINEMATIC ANALYSES………………………………………………………..83
4.3.1 Background and methods……………………………………………………….83
4.3.2 Kinematic vorticity analysis…………………………………………………….86
4.3.3 Shear-sense determinations …………………………………………………....89
4.3.4 Results of kinematic vorticity analysis………………………………………….92
4.4 SUMMARY AND CONCLUSIONS……………………………………………...93
CHAPTER 5: THESIS SUMMARY AND CONCLUSIONS…………………………95
5.1 SUMMARY AND CONCLUSIONS……………………………………………….95
5.2 SUGGESTIONS FOR FUTURE WORK……………………………………………97
COMPREHENSIVE BIBLIOGRAPHY……………………………………………...99
APPENDICES…………………………………………………………………………115
APPENDIX A: KINEMATIC INDICATORS………………………………………..116
APPENDIX B: IGNS PETLAB DATABASE SPREASHEET………………………128
APPENDIX C: STRUCTURAL DATA……………………………………………..137
LIST OF FIGURES
Page #
Figure 2.1. End member models showing predicted styles of deformation
produced by continental extension………………………………………………………..8
Figure 2.2. Metamorphic core complex model after Lister & Davis (1989) and
Reynolds et al., (1990)…………………………………………………………………...14
Figure 2.3. Paparoa Metamorphic Core Complex after Tulloch & Kimbrough (1989).
Map includes data compiled from Bowen (1964), Hume (1977), Nathan (1978) and
White (1987) Abbreviations in caps refer to structural transects and sample suites; CF Cape Foulwind, CH - Charleston, WHC - White Horse Creek, PS - Pike Stream, BR Buller River, BG - Buckland
Granite…………………………………………………………………………………....17
Figure 2.4. Thermal history for the syntectonic Buckland Granite (lower plate intrusion)
in the northern Paparoa Range. U/Pb data from Muir et al. (1994), Musc Rb/Sr ages
from Graham & White (1990), Apatite FT data from Seward (1989), Ar/Ar
ages from Spell et al. (2000)……………………………………………………………..21
Figure 3.1. Paparoa Metamorphic Core Complex after Tulloch & Kimbrough (1989).
Map includes data compiled from Bowen (1964), Hume (1977), Nathan (1978) and
White (1987) Abbreviations in caps refer to structural transects and sample suites; CF Cape Foulwind, CH - Charleston, WHC - White Horse Creek, PS - Pike Stream, BR Buller River, BG - Buckland
Granite…………………………………………………………………………………....29
Figure 3.2. White Horse Creek structural transect. a.) Map of structural data; b.) Crosssection showing the folded mylonitic front and WHC strain gradient ; c.)-e.) Outcrop
scale field sketches of F2,F3 folds; f.)-i.) Lower hemisphere, equal-area projections of
structural data; j.) Block diagram illustrating the geometry of F2-F4 in the highest strain
zone………………………………………………………………………………………36
Figure 3.3. Charleston structural transect. a.-c.) Lower hemisphere projection of fabric
data; a.) site CH1, b.) CH2, c.) CH3-7. Circles - poles to foliation; triangles lineations………………………………………………………………………..………..40
Figure 3.4. Buller River structural transect. Contact relationships after Tulloch &
Kimbrough (1989)……………………………………………………………………….42
Figure 3.5. Cape Foulwind structural transect. a.) - d.) Lower hemisphere
projections of fabric data, circles - poles to foliation; triangles - mineral lineations.
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a.) CF1,4 b.) CF3 c.) CF2, d.) CF5-6. Horizontal scale for cross-sections is
b.) equal to the vertical scale….…………………………………………………………43
Figure 3.6. Brittle fault geometries for the northern domain. a.) View looking SSW at
NE and SW dipping faults, site CH1 b.) Looking down on what may have been the
Slip surface of a low-angle normal fault, now dissected by steep, smaller faults. c.)-f.)
Fault planes and straie for data sets CF 1 regional and CF 1 block, respectively. d. -h.)
X and Z axis contours (see text)…………………………………………………………46
Figure 3.7. Fault-fan style of normal faulting observed in the central core zone at site
CH7 a.) Faults and straie b.) Z axis contour c.) X axis contour d.) Sketch of framed
area in photograph………………………………………………………………………47
Figure 3.8. Vertical profile of site WHC1 showing upright, open (F3) folding and
conjugate brittle faulting. a.) Poles to foliation (circles) and mineral lineations b.) Fault
planes and straie c.),d.) X and Z axis contours…………………………………………..48
Figure 3.9. Outcrop and thin section scale kinematic indicators. a,b.) Mylonitic fabric
photographed in the field. S-C fabric and large beta-type feldspar clast directly below
pencil indicate dextral motion, parallel to the pencil (lineation); c.) S-C fabric,
imbricated, antithetically microfaulted feldspar in the center of field of view, sigma-type
clast in the upper left-hand corner indicate dextral motion.Photograph taken under
crossed polars with the gypsum plate inserted; d,f.) Plagioclase feldspar porphyroclasts
sampled from site WHC3. Large beta-type clast in the upper third of "d."; sigma-type and
delta-type clasts in the upper third of "f."; g,h.) S-C fabrics developed in the Foulwind
Granite at sites CF2 and CF3. These fabrics are interpreted as related to semi-brittle
faulting. "g." indicates sinistral motion as C planes are oriented NE-SW and S planes are
oriented NW-SE. Large beta-type clast in center of field of view. "h." displays well
developed dextral S-C fabric…………………………………………………………….51
Figure 3.10. Kinematic vorticity analysis. a.) Field photo showing plagioclase
porphyrocasts b.) Feldspar Rf/phi data (see text) c.)-e.) Hyperbolic nets showing clast
distribution, plots rotated parallel to foliation as seen in (a.) f.) Beta clast in plane light g.)
Sigma clast in plane light g.) Delta clast in plane light……….…………………………55
Figure 3.11. Kinematic fault plane solutions for brittle faults affecting lower plate rocks.
Solutions are based on the scatter of X and Z axes (squares and circles, respectively)…59
Figure 3.12. Schematic block diagrams illustrating the structural evolution, (D1 - D5), of
the metamorphic core during exhumation. a.) D1-D2; b.) D3; c.) D4-D5. Bold arrows
indicate the orientations of stretching and extension axes remained nearly parallel
during deformation and exhumation of the middle crust...……………………………...64
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Figure 4.1. Principle planes determined in accordance with the orientations of fabric
elements………………………………………………………………………………….73
Figure 4.2. Three-dimensional strain results from the quartz analysis. Lower hemisphere
plots show the orientation of the principle ellipsoid axes (X,Y,and Z) determined using
the program Strain 3D and Rf/φ data from three perpendicular planes….………………75
Figure 4.3. Three-dimensional strain results from the feldspar analysis. Lower
hemisphere plots show the orientation of the principle ellipsoid axes (X,Y,and Z)
determined using the program Strain 3D and Rf/φ data from three perpendicular
planes…………………………………………………………………………………….78
Figure 4.4. a.) Flinn plot describing illustrating the three dimensional strain geometry
determined from strain analysis; b.) Shapes of feldspar grains measured in threedimensional feldspar strain analysis……………………………………………………..80
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CHAPTER 1: Introduction
1.1
STATEMENT OF PURPOSE AND SIGNIFICANCE
After the general acceptance of plate tectonics, the focus of many studies became the
thermal and mechanical evolution of continental crust as it was affected by changing
plate boundary conditions. Contractional structures, such as fold and thrust belts and
vertically thickening ductile shear zones, have been observed in regions where collisional
tectonics is thought to have increased (sometimes by more than a factor of two) the
thickness of the Earth’s crust. Extensional structures, including high and low angle
normal faults, detachment faults, metamorphic core complexes and vertically thinning
ductile shear zones have been observed in regions which have experienced extension and
crustal thinning.
While crustal thickening is nearly always attributed to plate collision, a consensus
regarding the dominant mechanism of continental extension (post-orogenic extension) in
thickened orogens, however, has yet to be reached. A variety of models have been
proposed in the recent literature pointing to a range of potential causes for large-scale
lithospheric extension. Popular models invoke gravitational instability (Burchfiel et al.,
1992), crustal thickening (Coney & Harms, 1984), and thermal weakening due to partial
melting (Vanderhaeghe & Teyssier, 1997) as extensional mechanisms. The purpose of
this study is to make a contribution to the debate, as we add data from a region of
continental crust extended during the late Cretaceous breakup of the Gondwana
supercontinent. We show, here, that extensional deformation and crustal thinning may
1
take place without significant weakening of the middle and lower crust, and that it may
be driven dominantly by a change in regional plate boundary dynamics.
Among the specific questions addressed in this thesis are: (1) How was deformation
partitioned among mid-crustal rocks during the late Cretaceous extensional event? (2)
What was the kinematic evolution of the middle crust as it passed through the brittleductile transition zone? (3) What were the dominant mechanisms for extension in the
region? Addressing these issues is important for developing a complete understanding of
continental lithospheric evolution during extension.
1.2 APPROACH
1.2.1
Study area selection
Previous work on the South Island's "West Coast" by numerous workers
(Shelley, 1969; 1972; Nathan, 1978; Tulloch and Kimbrough, 1989; Tulloch and Palmer,
1990; Spell et al., 2000) allows this study to address specific questions regarding the
structural history of the region and place them in the context of a system with well
understood boundary conditions. Tulloch and Kimbrough’s (1989) conception of the
“Paparoa Metamorphic Core Complex” provides an excellent starting point for this
research, as these workers describe and locate the regional characteristics that define the
system. However, some questions about the structural and kinematic evolution of
deformation in the plutonic and metamorphic core of the complex remain. Thanks largely
to previous mapping, we were able to select specific transects along the coast and inland
within the creeks where core deformation could be measured and documented. Structural
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transects are named in accordance with their geographical position; Pike Stream (PS),
White Horse Creek (WHC), Charleston (CH), Cape Foulwind (CF), Buller River (BR)
(Figure 2.3). These abbreviations are also used for sample identification.
1.2.2
Field techniques
Field work is arguably the most critical component to a study such as this. The
most critical objectives while in the field are: (1) Collecting enough structural data over
a large enough area to understand the structural and kinematic evolution of the system.
Structural data includes sketches, form cross-sections, photographs and measurements of
foliation, lineation, fold axes, fold axial planes, fault planes, slickenlines, orientation of
S-C fabrics and other kinematic indicators observed in the field. (2) Collecting enough
samples over a large enough area to document changes in microtexture and understand
microscale kinematics and deformation mechanisms. Samples collected in the field are
oriented so geometrical elements may be understood in real space.
1.2.3
Laboratory techniques
Laboratory analyses generally fall into two categories, those involving field data
(including structural measurements, sketches and sections) and those involving samples
(including strain analysis, kinematics, and microtextural analysis). Field data are
generally processed immediately after thin section preparation, and involve the
organization of regional structural data into specific forms (i.e. lower hemisphere equalarea projections for planar and linear data). Form cross-sections drawn in the field are
digitized using Adobe IllustratorTM. Regional cross sections are drawn, digitized and
3
keyed to strip maps. Fault and slickenline populations are plotted and kinematic solutions
generated using the program “Faultkin v.4.1” written by Rick Allmenginger
(www.geo.cornell.edu/geology/faculty/RWA/maintext.html)(Allmendinger et al.,
1989). Clast orientation (Rf/φ for kinematic vorticity analysis) are plotted using
hyperbolic nets. (See Chapter 4 for a description of methods)
A total of 40 oriented samples were collected in the field. Each was cut into cubes
using a diamond-studded rock saw, such that thin section faces are parallel to the XZ
plane (parallel to lineation, perpendicular to foliation, Figure 4.1). On some samples thin
sections were made for the YZ (perpendicular to lineation, foliation) and XY (parallel to
foliation) planes as well. Thin sections were prepared by Spectrum Petrographics, inc. at
a moderate cost. Thin section analysis included documentation of microstructure, bulk
kinematics, and three-dimensional strain. (See Chapter 4 for a complete discussion)
1.3 THESIS OUTLINE
This thesis is written following the University of Vermont Graduate College
guidelines for a journal article thesis. Chapter 1 provides a general introduction to the
study. Here, the purpose, approach and methods are outlined and the significance of
studying extension in western New Zealand as it relates to contemporary issues in the
fields of Tectonics and Structural Geology are presented.
Chapter 2 provides a review of recent literature that addresses both topical and
regional issues. Topics reviewed include mechanisms and styles of continental extension,
metamorphic core complexes and geometry of mylonitic zones. The studies discussed in
4
this portion of the chapter include some of the key models tested by the results of this
study. Additionally, a review of literature discussing the elements and nature of mid-late
Cretaceous extension in western New Zealand are presented, so the reader may clearly
understand what was known prior to the undertaking of this study. Finally, characteristics
of previously studied collapsed orogenic belts are presented and their extensional
mechanisms are discussed.
Chapter 3 contains a manuscript prepared for submission to the journal Tectonics,
pending the arrival of geochronologic data from the University of Arizona. The paper
focuses on the structural and kinematic evolution of the mid-crustal core of the Paparoa
metamorphic core complex. The orientation and evolution of ductile and brittle structures
throughout the core are presented, as are rigorous kinematic analyses including kinematic
vorticity. A discussion of the results focuses on the dominant processes accommodating
extension at a variety of scales.
Chapter 4 presents the methods, results, and interpretations for strain and kinematic
analyses. While kinematic analyses are presented as part of Chapter 3, they are expanded
upon here and include a full discussion of background and assumptions. A threedimensional strain analysis conducted on both quartz and feldspar grain shapes is
presented here, complete with a discussion of background and assumptions as well.
Chapter 5 is a summary of the most important conclusions drawn from this study,
and includes a section on suggestions for future work.
5
CHAPTER 2: Literature Review
2.1 INTRODUCTION
After the general acceptance of plate tectonics, the focus of many studies became
the evolution of continental crust as it became involved in a wide variety of tectonic
settings (see below for examples). Of particular interest became the mechanisms and
manifestations of continental extensional tectonics in the Earth’s crust. Geologists began
investigating areas of active extension, such as in the Red Sea and in east Africa, as well
as areas where extensional deformation affected older rocks in the record such as
collapsed mountain belts and passive continental margins. Significant attention was paid
to the effects (thermal, structural, and chemical among others) the construction and
collapse of mountain belts exerted on continental lithosphere. In general, these studies
may be divided into two domains: those examining deformation associated with the
contractional phase of orogenesis, i.e. mountain building, and those examining the
extensional phase, or orogenic collapse. This thesis is concerned with the “structural
fingerprint” left on the continental crust below present day New Zealand as it became
involved in a major plate boundary reorganization and transition from crustal contraction
to crustal extension. This chapter provides a brief history of thinking on the mechanisms
by which continental crust structurally reaponds to extension under both ductile and
brittle P-T conditions.
2.2 CONTINENTAL EXTENSION
6
Early workers in continental extensional terranes argued extension was
accommodated by large-scale pure shear and igneous dilation of the lithosphere (Proffet
1977; Wright and Troxel 1969, 1973; Anderson 1971; Armstrong 1968, 1972) (Figure
2.1). According to these models, the crust is thermally weakened by magmatic activity,
then flattened and deformed dominantly by coaxial strain. Stretching of the lithosphere in
this manner was supported by McKenzie (1978) in his study of normal fault bounded
sedimentary basins. McKenzie suggests sedimentary basins produced by stretching and
slow cooling of the lithosphere are likely to be found in two geological environments:
rifted margins and back arc basins.
An alternative to the pure shear stretching model was proposed by Brian
Wernicke (1985) known as “uniform-sense normal simple shear” of continental crust
(Figure 2.1). The basis of this model was the discovery of many low-angle faults in the
Basin and Range province with large-scale (tens to hundreds of kilometers), of normal
offset (Wernicke, 1981). Wernicke suggested these low-angle extensional faults may be
rooted deep in the lithosphere as ductile shear zones forming a continuous, curved
dislocation through tens of kilometers of crust. His hypothesis was a mechanism for
generating very large amounts of extension without generating excessive relief. Wernicke
eloquently writes in his concluding remarks, “Thus, one cannot conclude that the mantle
lithosphere and lower crust penetratively flatten directly beneath discontinuous uppercrustal normal fault systems… (and) There is no means of theoretically predicting what
the strain field of a compositionally heterogeneous, extending lithosphere will be, and it
is therefore worthwhile to entertain any hypothesis that is consistent with observations
7
that bear directly on strain geometry.” (Wernicke, 1985 p. 122). Wernicke’s words nicely
sum up why there is still healthy debate surrounding the style of extensionally deformed
continental crust.
Shortly after Wernicke’s low-angle normal fault hypothesis was published in the
journal Nature, Wernicke and Burchfiel (1982) published a review of structures, mainly
brittle structures, found to accommodate extension in the Earth’s crust. They decided to
establish two classes of structures: rotational and non-rotational. Rotational structures are
those in which extension is accommodated by rotation of geological features, namely
bedding planes. Wernicke and Burchfiel (1982) argue that two fault geometries are
possible for this class, planar and listric (curved). Extension by motion on listric,
rotational faults generally produces a series of imbricate, normal fault bounded slices.
Syntectonic sedimentary “growth basins” are also commonly associated with this type of
faulting. Non-rotational extension does not require curved fault planes, thus all faults
associated with this mechanism are planar. Wernicke and Burchfiel (1982) show field
examples of both classes of extensional structure, exposed in the Basin and Range
province and interpreted from seismic profiles.
A number of key conclusions were drawn by Wernicke and Burchfiel (1982)
regarding modes of extension. (1) Extended and actively extending terranes usually
accommodate tensile stresses by a combination of rotational and non-rotational
structures, and thus by a combination of curved and planar, high-angle and low-angle
normal faults. From this analysis, followed the burden of the field geologist to prove that
faults belonged to one class or the other, as incorrect diagnosis leads to large errors in
9
calculated values of extension. (2) Large-scale extension is accommodated by large
displacements on planar, low-angle normal faults (non-rotational) and contemporaneous
rotation of imbricate fault blocks bound by listric and planar faults.
In April, 1985 the Geological Society of London held a conference on continental
extensional tectonics. One of the most interesting papers to come out of this event was
written by J.A. Jackson (1987) who discusses the nature of brittle faults directly related to
seismic activity in extensional regimes. Jackson’s data set includes first motion analyses
of earthquakes in extensional settings around the globe including Greece, Turkey,
western USA, NE China, Yunnan and East Africa. He concludes that the “overwhelming
majority” of seismically induced normal faults nucleate in the depth range 6-15 km, and
dip between 30 and 60°. Jackson also indicates the faults in his study, where exposure or
seismic lines are good enough, appear to be approximately planar from the surface
through the upper crust.
Jackson’s work calls into question, but does not refute, the claims made by
Wernicke and Burchfiel (1982) that large scale extension is accommodated by slip on
low angle (10-20°), planar normal faults. The theories may be reconciled, if slip on lowangle faults could be proven to be aseismic, or if planar low-angle normal faults exposed
at the surface today represent the exhumation of shallow dipping, ductile shear zones
below the nucleation depth of most extension induced earthquakes. A third hypothesis
suggested by Davis (1987) is that some low angle normal faults may have been uplifted
by large scale, range bounding steep normal faults.
2.3 METAMORPHIC CORE COMPLEXES
10
A decade before Wernicke presented his model for Basin and Range evolution, a
team of geologists in western North America were discovering a new structural/tectonic
province: the metamorphic core complex (e.g. Armstrong, 1972; Coney, 1973a,b, 1976,
1978, 1979; Davis and Coney, 1979; Crittenden et al., 1980). In general, metamorphic
core complexes are terranes characterized by a heavily eroded, brittley deformed upper
plate separated from a generally younger ductiley deformed lower plate by a shallow
dipping detachment fault. The upper plate generally consists of low grade to
unmetamorphosed cover rocks deformed by populations of planar, “domino” style and
listric normal faults (Crittenden et. al., 1980). These normal faults always splay into the
underlying detachment or “decollement”. Graben and half-graben structures are common
in the upper plate, as are fault bounded sedimentary basins (Crittenden et. al., 1980).
Lower plate rocks, sometimes referred to as “basement” or “core” rocks, comprise
deformed plutonic and metamorphic rocks of varying age and protolith (Crittenden et. al.,
1980). Metamorphic grade in lower plate rocks is distinctly higher than in the upper
plate; kyanite, sillimanite, and andalusite bearing assemblages are not uncommon
(Reesor, 1970; Armstrong, 1968; Compton and others, 1977; Tulloch and Kimbrough,
1989). Recent work in the footwall of the Snake Range decollement in eastern Nevada
and western Utah indicates stable mineral assemblages such as:
quartz+muscovite+biotite+garnet+plagioclase+staurolite±kyanite±tourmaline±apatite,
suggesting peak metamorphic pressures of 810 ± 70 MPa (30 ± 3 km) and temperatures >
600° C (Lewis et al., 1999). Lower plate rocks are characterized by localized zones of
high ductile strain, where core rocks become mylonitized and generally display an arched
11
regional foliation pattern where maximum dips on the flanks of arches rarely exceeds 2030°. Lineations generally plunge shallowly, parallel to inferred motion of upper plate
transport and locally sub-parallel to the axes of regional arching. Ductile deformation in
lower plate rocks is overprinted by brecciation and other brittle structures with increasing
proximity to the detachment surface. Ductile fabrics are truncated, abruptly, in some
cases by the detachment surface owing to late stage movement on the decollement
(Coney, 1974). Granitic plutons of varying composition and size intrude the lower plate
at different stages during deformation. These plutons are useful for both deformation
studies and thermal studies of evolving core complexes.
2.4 EVOLUTION OF DETACHMENT ZONES AND LOWER PLATE ROCKS
While most metamorphic core complexes identified in the field display the
general characteristics described in the preceding section, significant variety exists when
examining detailed styles of deformation in both upper plate and lower plate rocks. Of
particular interest to this study are the evolution of lower plate structures recording the
multistage development of core/footwall exhumation.
In 1986, Gregory Davis, Gordon Lister and Stephen Reynolds, attempted to
interpret many of the observations found in metamorphic core complexes by proposing a
model for the structural evolution of the Whipple and South mountains in California and
Arizona (Davis et al., 1986). Their model suggests a five stage development beginning
with (1) the formation of a sub-horizontal zone of mylonitic fabrics of variable thickness
(3.5 km in the Whipples and less than 200 m thick in the South Mountains) within lower
plate rocks. This event may rotate any previously formed structures into parallelism with
12
mylonitic fabrics and structures. Mylonitic fabrics may also cut older fabrics
discordantly. (2) A later generation of mylonitic fabrics forming narrow (0.1-10 cm thick)
zones of high shear strain cuts and/or rotates early formed fabrics (including mylonites)
at high angles. (3) A zone of chloritic breccia up to 300 m thick (in the Whipples) forms
as a result of shearing, brecciation, and retrograde alteration of kinematically inactive
mylonites and non-mylonitic lower plate rocks. Pseudotachylite veins may splay off from
subhorizontal breccia surfaces. Davis and others (1986) suggest this may be the result of
seismically related fault melts. (4) Formation of throughgoing, discrete, low-angle
detachment faults underlain by thin zones (< 1 m) of microbreccia or ultracataclasite. (5)
The last stage involves shallow level detachment faulting and the formation of fault
gouge in upper plate rocks directly above the detachment. This model is useful for
describing the evolution of lower plate rocks in a general sense, however the geometry of
ductile structures such as the “mylonitic front” and polyphase folds are not addressed
here.
Mylonitic front
The term “mylonitic front” was introduced by Davis and others (1980) to describe
the structure of lower plate rocks affected by penetrative foliations and lineations.
Mylonites are characterized by ductility contrasts between mineral constituents, namely
quartz and feldspar, where the former behaves plastically through grain boundary
migration and dynamic recrystallization and the latter behaves brittley through
microfracture. In the Whipple and Buckskin Mountains of southeastern California and
western Arizona, other minerals shown to flow ductiley include micas and some
amphiboles while brittle deformation mechanisms occur in some amphiboles, epidote,
13
and sphene (Davis et al., 1980). Lithological units that become mylonitized include both
basement rocks and well as syntectonically injected granitic plutons (Davis et al., 1980).
As a result, mylonites may differ in hand sample texture, grain size, and composition.
Davis (1980) emphasizes that the mylonitic front is a well-defined, mappable structural
boundary between mylonitic and non-mylonitic rocks, and that it is not a discrete fault
surface.
Based on field observations from the South Mountains, Santa Catalina, and
Harcuvar core complexes in southern Arizona, Reynolds and Lister (1990) proposed a
model for the structural geometry and kinematic evolution of the mylonitic front. In each
of these core complexes, the mylonitic front is folded, characterized by a gently dipping
limb sub-parallel to the overlying detachment and a steeper, back-dipping limb (Figure
2.2). Kinematic indicators present in the fabric on both limbs reveal that rocks preserving
sense of shear information were crystallized prior to folding of the mylonitic front. For
example normal, top to the NE fabrics on the gently dipping limb are accompanied by
reverse, top to the NE fabrics in the back dipping zone. Additionally, mylonitic fabrics in
the back-dipping zone are cut by steeper, antithetic shear zones characterized by
retrograde mineral assemblages. Reynolds and Lister (1990) attempt to interpret these
observations by evaluating a series of potential models for the structural and kinematic
evolution of the mylonitic front.
2.5 WESTERN NEW ZEALAND AS AN EXTENSIONAL SETTING
Prior to the undertaking of this study, it was recognized that northwest Westland
(Figure 2.3) had experienced regional continental extension in the Late Cretaceous
15
(Tulloch and Kimbrough, 1989; Tulloch and Palmer, 1990; Bishop, 1992; Spell et al.,
2000). By the time Tulloch and Kimbrough (1989) presented their core complex model
for extensional deformation, the local geology was well mapped and age data suggesting
a major metamorphic/cooling event in the late Cretaceous has already been proposed for
the lower crust exposed in Fiordland (Gibson and Ireland, 1988). Northwest Westland
contains the following elements characteristic of an extended continental terrane:
Structures
1. Two, opposite dipping, low angle (10-15°) normal faults, or detachment faults of the
type described by Wernicke (1981)(Figure 2.3). These were identified by Tulloch and
Kimbrough (1989), who suggested on the basis of new age data determined for the
Charleston Metamorphic Group, that the faults were the dominant structures in a
symmetrical metamorphic core complex. In the hanging walls of both faults rests the
Greenland Group, a sedimentary sequence characterized by greywackes and argillites and
containing Ordovician graptolite fossils (Laird, 1972; Nathan, 1978). Ductile deformation
in the footwall of these faults suggests motion was top to the NE in the northern half of
the core (exposed in Buller Gorge) and top to the SW in the southern half of the core
(exposed in Pike Stream). A maximum estimate for displacement on the northern fault
(Ohika detachment of Tulloch and Palmer, 1990) using a 14-18 km emplacement depth
for the Foulwind Granite (Spell et al., 2000) and assuming a continuous, planar slip
surface is 60-80 km.
16
2. Offshore and onshore, WNW-ESE trending, normal fault bound basins occupied by
up to 5 km thick sequences of Mid-Cretaceous, nonmarine breccia-conglomerates and
fluvial sedimentary rocks of the Pororari group (Nathan et al., 1986; Bishop, 1992).
Deformed granitic clasts in the Hawk’s Crag Breccia (northern Paparoa range) studied by
Tulloch and Palmer (1990) are believed to be derived from Early Cretaceous source
plutons. Syn-extensional sedimentary deposits are separated from younger rift deposits
by a major regional unconformity of early Haumurian age (Nathan et al., 1986). The age
of the unconformity is just younger than the age of the oldest ocean crust in the Tasman
sea (Weissel & Hayes, 1977) causing some workers to favor a breakup unconformity
model marking the transition from rift to drift (Falvey, 1974; Braun & Beaumont, 1989;
Bishop, 1992).
Magmatism
Igneous activity, both intrusive and extrusive, played a significant role in the
events leading up to rifting of the Pacific margin of Gondwana (Tulloch and Kimbrough,
1989; Bishop, 1991; Waight et al., 1998a; Waight et al., 1998b). Subduction related
magmatism associated with the contractional phase of orogenesis produced the Western
Fiordland Orthogneiss (WFO) in Fiordland and the Separation Point Suite (SPS) in
Westland. These rocks have ages in the range of ∼125-114 Ma, and are characterized
geochemically by distinctive alkali-calcic, sodic compositions, high Sr content and high
Sr/Y ratios (Muir et al., 1995). This geochemical signature is described as “adakitic”, and
is thought to represent melting of a mafic crustal underplate of garnet amphibolite or
18
eclogite composition beneath a thickened arc (Muir at al, 1995). The SPS is well east of
the PMCC and does not bear a penetrative ductile fabric.
Early to Middle Cretaceous plutonism in the western and southern regions of
Westland is dominated by the I-S type Rahu Suite (Tulloch, 1983; Tulloch &
Braithwaite, 1986). Rahu Suite plutons have crystallization ages as old as 114 Ma
(Tulloch and Kimbrough, 1989). These plutons are generally granitic in composition and
display evidence for crustal contamination (Graham & White, 1990). Plutons such as the
Buckland Granite (Figure 2.3) in the northern Paparoa Range display evidence for synextensional deformation, uplift and cooling during a ∼30 m.y. period beginning ∼112-110
Ma (Tulloch and Kimbrough, 1989; Tulloch and Palmer, 1990; Spell et al., 2000). Mid
Cretaceous magmatism is dominated by the Hohonu Suite, dated at ∼114-110 Ma
(Waight et al., 1998a). Hohonu Suite plutons are characterized by amphibolite-biotite
tonalite to muscovite-biotite monzogranite compositions and are typically calc-alkaline
(Waight et al., 1998). The emplacement of the Hohonu Suite overlaps in time with the
end of subduction related magmatism (SPS) and the onset of crustal extension (Waight et
al., 1998a).
Mid-Cretaceous dikes have been described in numerous localities in Westland
(Nathan, 1978; Tulloch and Kimbrough, 1989; Bishop, 1992; Waight et al., 1998b).
These dikes are dominantly alkaline and have been described as lamprophyres. The
Hohonu Dike Swarm in the Hohonu Range, dated at ∼84 Ma (Waight et al., 1998b), has
been interpreted as synchronous with extension as it coincides with the generation of the
first ocean crust in the Tasman Sea. Bishop (1992) compiled orientation data for 393
19
dikes thought to be Cretaceous in age and found a bimodal distribution, where the
dominant trend is 120° (WNW-ESE) and the secondary trend is 020° (NNE-SSW). The
dominant trend measured in the study is consistent with a NE-SW extension direction.
Thermochronologic evolution
Isotopic studies performed on samples from plutons that intruded the lower plate
during deformation allow for lower plate cooling histories to be reconstructed (Tulloch
and Palmer, 1990; Muir et al., 1994, 1995, 1997; Ireland and Gibson, 1998; Spell et al.,
2000). A 109.6±1.7 Ma crystallization age for the Buckland Granite by Muir et al.,
(1995) and a 111.0±0.8 Ma monazite Th/Pb age was determined by Ireland and Gibson
(1998). Spell et al., (2000) show the Buckland Granite was unroofed immediately after
emplacement, cooling at a rate of ∼35°-60°C/Myr until ∼92 Ma, when the rates slowed
considerably to an average of 8°C/Myr. A similar cooling history was reconstructed by
Spell et al., (2000) for the Okari granitic gneiss in the southern Paparoa range. These
samples indicate rates of ∼50°C/Myr between ∼110 and 90, then slower cooling at a rate
of ∼5°C/Myr through ∼80 Ma.
Tulloch and Palmer (1990) presented a variety of isotopic results obtained from
clasts in the Hawk’s Crag Breccia , a member of the Pororari Group in the northern
Paparoa range. The petrology of the clasts led Tulloch and Palmer to propose the
Buckland Granite, the Blackwater Pluton and possibly the Steele Pluton as sources.
Muscovite K-Ar age data suggest the source was uplifted through the 350°C isotherm at
20
∼112 Ma. This age is slightly older than the ages determined by Spell et al., (2000).
Using an age for the Hawk’s Crag Breccia of ∼104 Ma (Raine, 1984; Nathan et al.,
1986) Tulloch and Palmer (1990) suggest uplift to the surface (a 10 km vertical distance
assuming a geothermal gradient of 35°C/km) was accomplished in less than ∼7 Ma,
suggesting a minimum uplift rate of 1.4 mm/yr (or 1.1 mm/yr at a gradient of 45°C/km).
Sericite ages obtained from hydrothermally altered samples close to the Ohika and Pike
detachment faults indicate ages of ∼98 Ma and ∼85 Ma respectively. Tulloch and Palmer
(1990) interpret these results as evidence the Pike detachment remained active longer
than the Ohika detachment, and suggest the ∼85 Ma age links motion on the Pike
detachment to continental rifting and the opening of the Tasman Sea.
The reconstructed thermal histories determined by previous workers are
consistent with an initial period of rapid cooling followed by protracted cooling rates
preceding continental rifting at ∼84 Ma. This trajectory is common to other metamorphic
core complexes, however overall cooling rates tend to vary. For example, the South
Mountains metamorphic core complex in Arizona cooled from ∼700°C to ∼100°C in less
than 5 million years, equating to an average rate of 192 ±74° C/Myr (Livaccari, 1995).
The PMCC displays a cooling history that lasted 4 to 5 times longer. The Shuswap
Metamorphic Core Complex in southern British Columbia, has a thermal history akin to
the PMCC. A rate of 50°C/Myr persisted for the first ∼8 Ma, followed by slower cooling
at 16°C/Myr for the next ∼12 Ma (Vanderhaeghe et al., 2002). While initial cooling rates
for the Shuswap and the PMCC are nearly identical, the second phase of cooling differs
by a factor of two. In sum, the PMCC thermal history displays the characteristic core
22
complex trajectory of initial rapid cooling followed by slower rates, however, overall the
PMCC is an example of a core complex that cooled relatively slowly.
2.6 CASE STUDIES OF POST-OROGENIC EXTENSION
Extensional deformation of continental crust may occur in a wide range of
tectonic settings: continental rift valleys, back arc basins, collapsed orogenic belts, or
regions of anamolously high heat flow. For the purposes of this study extensional
deformation may be grouped into two categories: (1) deformation produced by a period
of continental extension that followed a period of contraction and crustal thickening; (2)
deformation produced during continental extension that did not follow a period of
contraction and thickening. This study is interested in the styles of deformation produced
during the former, as western New Zealand records a phase of contractional deformation
contemporaneous with subduction and terrane accretion during a ∼15 Ma period
beginning around ∼129 Ma (Hollis et al., 2003). In this section, styles of extensional
deformation in other collapsed mountain belts, namely the Himalaya, the Canadian
Cordillera, and the Scandinavian Caledonides are presented for comparison with the data
presented in Chapter 3.
Many theories have been proposed for how mountain belts accommodate
extension. The signature of the tectonic shift from contraction to extension, the focus of
this study, is linked to the mechanism or cause of collapse. Coney and Harms (1984),
suggest that the collapse of the Canadian Cordillera was caused by compressional crustal
thickening and associated plutonism. This study is based on palinspatic reconstructions of
continental crust along decollment surfaces, which reveal the presence of a 60 km thick
23
crustal welt in the hinterland. P-T conditions at the base of the welt were sufficient to
produce crustal melts. According to this study, injection of these magmas effectively
reduced intraplate stress and accommodated extension by gravitational collapse.
Burchfiel et al., (1992) and Edwards et al., (1996) present evidence for synorogenic extension in the high Himalaya. E-W striking, low-angle detachment faults in
the upper crust were found by these workers to be contemporaneous with and parallel to
contractional faults and shear zones in the lower crust. Burchfiel’s (1992) model
attributes syn-orogenic extension to the gravitational instability of overthickened crust.
Edwards et al. (1996) build on Burchfiel’s work by suggesting that extension in the
Himalaya, so far, has occurred in two distinct periods separated by folding, major
plutonism and uplift.
Vanderhaeghe and Teyssier (1997; 2001b; 2002) emphasize partial melting,
thermal weakening, and buoyancy forces as factors which strongly influence the shift
from contraction to extension. These workers favor a model in which the generation of a
partially molten layer during mountain building controls the evolution of the crustal
column. They suggest the presence of a partially molten layer leads to mechanical
decoupling of the upper and lower plate during subduction, a result which allows orogens
to flow independently. The effects of partial melting during mountain building have been
studied in the Tibetan Plateau, the Shuswap range in the Canadian Cordillera, the French
Massif, and in the Greek isles (Vanderhaeghe and Teyssier, 1997; 2001).
The Scandinavian Caledonides formed as a result of Late Silurian-Early Devonian
collision between Baltica and Laurentia during what is known as the Scandian orogeny
24
(Stephens & Gee, 1985). The resultant architecture of the belt is a series of stacked
nappes, where the farthest traveled exotic terranes represent the uppermost allochthons
(Roberts, 1988). The thickness of the Caledonide Orogen is thought to have reached 100120 km, as peak metamorphic conditions are indicated by microdiamond and coesite
bearing eclogites in the Western Gneiss Region of western Norway (Smith, 1984;
Dobrzhinetskaya et al., 1995). The dominant mechanism for extension in the region is
still under debate, however many studies have identified extensional shear zones that
nucleated at nappe contacts (Norton, 1986; Fossen, 1992, Fossen & Dunlap, 1998;
Osmundensen et al., 1998; Osmundsen et al., 2003). In this case, pre-existing anisotropies
in the architecture of the mountain belt exerted a strong influence on the style of
extensional deformation.
25
CHAPTER 3: Tectonics manuscript
STRUCTURAL EVOLUTION OF THE MIDDLE CRUST DURING
EXHUMATION BY CONTINENTAL EXTENSION: THE PAPAROA
METAMORPHIC CORE COMPLEX, SOUTH ISLAND, NEW ZEALAND
ABSTRACT
During the period ∼112-84 Ma, regional extension affected the Pacific margin of
the Gondwana supercontinent. This event produced the Paparoa Metamorphic Core
Complex in Westland (northwest South Island) New Zealand, where mid-crustal rocks in
the core have been exhumed by NE and SW dipping, low-angle detachment faults. Core
rocks, exposed in discontinuous sections along the NW coast of the South Island, record a
history of at least five events (D1-D5) of ductile, semi-brittle and brittle deformation. We
used these exposures to determine the structural and kinematic evolution of the middle
crust during Late Cretaceous regional extension.
Ductile deformation (D1-D4) is distributed heterogeneously throughout the core.
In the north, foliations developed in deformed granitoids are regionally folded about
shallow E plunging axes; mineral lineations generally plunge ENE. In the south, the most
intense ductile deformation is focused and exposed along a 5 km coastal section near
White Horse Creek (WHC). Multiple generations of folds, foliations and lineations
developed in the Charleston Metamorphic Group gneisses are interfolded with a thin (<
50 m thick) section of protomylonites, mylonites and ultramylonites. At least three
generations of coaxial NE-SW-plunging folds (F2,F3,F4) are developed within the main
mylonitic zone. A strain gradient within the WHC transect is defined by an increase in
fold tightness and fold axis rotation (F2,F3) towards the direction of maximum extension.
Kinematic vorticity (Wk) analysis using systems of rotated plagioclase feldspar
porphyroclasts, indicates the main mylonitic zone was characterized by thinning in the
vertical (XZ) plane, and by an environment of general shear where simple shear
dominated over pure shear (0.74 < Wk < 0.78). Sense of shear analysis on planes parallel
to gently plunging mineral lineations and perpendicular to foliation suggests normal
motion, top down to the SW and NE. Based on the orientation of D1-D4 structures, the
WHC strain gradient and Wk results, a three-dimensional environment of deformation
characterized by constriction (X-extension; Z,Y-shortening) is proposed. D5 deformation
produced a series of NE, SE, and SW dipping semi-brittle and brittle faults that cut all
previously formed ductile structures. Kinematic analysis of fault-slip data indicates
strains produced during faulting were characterized by vertical shortening and subhorizontal (NE-SW) extension. These results suggest the directions of maximum
extension (X) and shortening (Z), as well as sense of shear stayed constant during the
transition from ductile to brittle deformation in the middle crust.
26
3.1 INTRODUCTION
Previous work in extensional terranes has shown that low-angle detachment faults
and the formation of metamorphic core complexes are common products of continental
extension (e.g. Crittenden et al., 1980; Wernicke, 1981; Lister and Davis, 1989).
Detachment faults are capable of exhuming deep (>20 km) crustal levels rapidly
(>2mm/yr) without requiring extreme topographic relief because of their low-angle
orientations (e.g. Wernincke, 1981; Lewis et al., 1999). Studies have shown ductile
deformation in the footwall of detachments and brittle deformation in the hanging wall
are temporally and kinematically related (e.g. Lister and Davis, 1989; Tulloch and
Palmer, 1990; Bishop, 1992). However, determining how structural and kinematic
patterns change as rocks move from mid-crustal levels to upper crustal levels, is an
important process that has received less attention. This aspect is less well known,
partially because in most exposures of deformed middle crust the inadequate memory of
rocks leads to a lack of preservation of structural changes and strain history during rapid
uplift and exhumation.
In this paper, we present the structural and kinematic evolution of the mid-crustal
core of the Paparoa Metamorphic Core Complex (PMCC) in Westland, New Zealand,
where structures record the transition from ductile to brittle deformation during the period
∼112-84 Ma (Tulloch and Kimbrough, 1989). The prolonged cooling history (>25 M.y.)
recorded by lower plate rocks (Tulloch and Palmer, 1990; Spell et al., 2000), as compared
to some other core complexes (e.g. South Mountains MCC, ∼5 M.y.) may account for the
preserved structural changes (Livaccari et al., 1995) (Figure 2.4). We build on previous
27
studies of crustal structure in the core of the PMCC (Shelley, 1970; Shelley, 1972;
Tulloch and Kimbrough, 1989) and show continental extension resulted in the formation
of a narrow (< 50 m thick) mylonitic shear zone characterized by vertical shortening and
sub-horizontal (NE-SW) stretching. As the ductile middle crust was exhumed into the
brittle upper crust, stress was relieved by slip on systems of conjugate, brittle normal
faults. We use fault-slip data to develop kinematic solutions describing strain geometry
during brittle deformation, and develop a kinematic model for the progressive
deformation of exhumed middle crust by comparing these results to the geometry and
kinematics of ductile deformation. This results of this study add a critical component, the
structural and kinematic evolution of the middle crust, to published models that document
the extensional system that dominated crustal evolution in New Zealand during the Late
Cretaceous.
3.2 PREVIOUS WORK
Field observations, isotopic analyses, geophysical data and plate reconstructions
indicate that northern Westland experienced a period of regional continental extension
during the period ∼112-84 Ma. This section summarizes the results of this previous work.
3.2.1 Regional geologic and structural relationships
Rocks north of the Alpine Fault on New Zealand’s South Island comprise faultbounded terranes of early Paleozoic to Mesozoic age belonging to both the Eastern and
Western provinces (Landis and Coombs, 1967). Eastern and Western province rocks are
28
separated by the Median Tectonic Zone (MTZ), a region of plutonism and deformation
that probably formed in situ, adjacent to the Western province (Mortimer et al., 1999).
This study is predominantly concerned with extensional structures affecting Western
province rocks, most specifically those belonging to the Buller terrane (Cooper, 1979).
The dominant lithologies within the Buller terrane are quartzite, quartz rich turbidites and
black shales of the Greenland group (Figure 3.1). Graptolite bearing sedimentary rocks
indicate a Cambrian-Ordovician age of deposition. The paleo-Pacific, passive continental
margin of Gondwana has been suggested as the environment of deposition.
Buller terrane rocks were intruded by two main pulses of granitic magmatism, one
in the Devonian which produced the S-type Riwaka complex and one in the Cretaceous
which produced the I-S type Rahu suite (Tulloch, 1983; Tulloch and Brathwaite, 1986;
Tulloch, 1988). The Foulwind granite, exposed along the Tasman coast south of Cape
Foulwind, may be related to the Devonian pulse, as Muir reported a U/Pb ion probe
zirocn age of 327 +/- 6.2. Spell et al., (2000) reported Ar/Ar ages of 109.0 +/- 1.0, 101.1
+/- 1.1, 97 Ma for hornblende, biotite, and k-feldspar respectively. These data suggest
crystallization in the Devonian followed by a Cretaceous metamorphic event.
Variably deformed plutons of the Cretaceous age Rahu suite, mixed with
metasedimentary rock of uncertain affinity crop out along the Tasman coast in the
Charleston region and inland in the southern Paparoa range. Common to these exposures
is a ductile fabric of varying strength, which led Nathan (1975) to propose the term
Charleston Metamorphic Group (CMG) for the granites, orthogneisses and paragneisses.
Thus, these rocks were first grouped on the basis of texture rather than age. Early workers
30
considered the CMG to be as old as Precambrian although Aronson (1968) reported a RbSr mineral age of 104-212, suggesting metamorphism in the Cretaceous. Tulloch and
Kimbrough (1989) reported a conventional U/Pb zircon age of 114 +/- 18 for four
orthogneiss samples collected near Charleston, and suggested an early Cretaceous
crystallization age for at least some of the CMG. This conclusion was supported by
Ireland and Gibson (1998) who reported U/Pb age of 119 +/- 2 Ma on a zircon core
from a sample near Charleston, and a 109 +/- 5 Ma rim using an ion microprobe.
Excellent age control indicates the portion of the CMG most central to this study is
characterized by crystallization in the early Cretaceous followed by metamorphism
within 5 Ma.
Unconformably overlying the Cambro-Ordovician rocks and the meta-igneous
basement are mid to late Cretaceous sediments deposited in onshore and offshore fault
bounded basins, which trend dominantly WNW-ESE and NNE-SSW. (Nathan, 1986;
Bradshaw, 1989; Bishop, 1992). Basin fill includes alluvial fan, fluviatile and lacustrine
sediments and reaches thicknesses > 4 km (Bradshaw, 1989). In the study area these are
dominated by the mid-Cretaceous Pororari Group which comprises breccia
conglomerates or “fanglomerates” (Nathan, 1986). Laird (1990) showed that Pororari
Group deposits were derived from active normal fault scarps and deposited in half
grabens trending WNW-ESE. Bishop (1992) on the basis of onshore and offshore basin
geometry concluded that WNW-ESE trending basins were temporally associated with
Cretaceous NE-SW extension, and NNE-SSW trending basins may postdate continental
rifting and the opening of the Tamsan Sea at 84 Ma. A major “break up” unconformity
31
and marine transgression mark this transition. Volcanic rocks intrude many of the
Cretaceous-Paleocene sedimentary basins suggesting volcanism was coeval with
extension (Gage, 1952; Nathan, 1978; Newman, 1985; Sewell et al., 1988).
Late Cretaceous lamprophyre dikes of alkaline, basic and acidic compositions
intrude older rocks in many localities in north Westland (Hamil, 1971; Nathan, 1978).
Bishop (1992) compiled dike orientation data presented by Suggate (1957), Warren
(1967), Hamil (1972), Nathan (1978), Grindley & Oliver (1979), White (1987), Laird
(1988), and Roder & Sugggate (1990) and showed the distribution to be bimodal with a
main trend at 120° and a secondary trend at 020°. The dominant orientation is consistent
with a NE-SW extension direction.
3.2.2 Paparoa metamorphic core complex
The unconformable, older over younger contacts of Greenland Group turbidites
and CMG gneisses, complemented by new age data for CMG units led Tulloch and
Kimbrough (1989) to propose a metamorphic core complex model for crustal extensional
deformation. Many geological attributes of the PMCC make it generally conformable to
the core complex model synthesized from observations made in western North America
(Crittenden et al., 1980). The most significant departure from this model, is, that the
PMCC is characterized by two opposite-dipping crustal detachments, making it a
“symmetrical” core complex. Ductile deformation in lower plate rocks near detachment
surfaces indicates upper plate transport down to the NE on the northern end of the core
and down to the SW on the southern end of the core (Tulloch and Kimbrough, 1989).
Tulloch and Palmer (1990) have shown that motion on the Ohika (northern) detachment
32
may have ceased before motion on the Pike (southern) detachment. These workers
suggest, on the basis of an 85 Ma age for a hydrothermally altered mylonite below the
Pike detachment, that motion on the Pike detachment is linked to continental rifting and
the opening of the Tasman Sea at 84 Ma. If this assertion is true, deformation should
strongly favor the southern end of the core. We test this hypothesis by presenting
rigorous structural and kinematic data from both the northern and southern ends of the
core.
3.2.3 Cooling history of the PMCC
Isotopic studies performed on samples from plutons that intruded the lower plate
during deformation allowed previous workers to reconstruct cooling histories (Tulloch
and Palmer, 1990; Muir et al., 1994, 1995, 1997; Ireland and Gibson, 1998; Spell et al.,
2000). A 109.6 +/- 1.7 Ma crystallization age for the Buckland Granite by Muir et al.,
(1995) and a 111.0 +/- 0.8 monazite Th/Pb age was determined by Ireland and Gibson
(1998). Spell et al., (2000) show the Buckland Granite was unroofed immediately after
emplacement, cooling at a rate of ∼35°-60°C/Myr until ∼92 Ma, when the rates slowed
considerably to an average of 8°C/Myr. A similar cooling history was reconstructed by
Spell et al., (2000) for the Okari granitic gneiss in the southern Paparoa range. These
samples indicate rates of ∼50°C/Myr between 110 and 90, then slower cooling at a rate of
∼5°C/Myr through 80 Ma.
Tulloch and Palmer (1990) presented a variety of isotopic results obtained from
clasts in the Hawk’s Crag Breccia (member of the Pororari Group). The petrology of the
clasts led Tuloch and Palmer to propose the Buckland Granite, the Blackwater Pluton and
33
possibly the Steele Pluton as sources. Muscovite K-Ar age data suggest the source was
uplifted through the 350°C isotherm at ∼112 Ma. This age is slightly older than the ages
determined by Spell et al., (2000). Using a depositional age for the Hawk’s Crag Breccia
of ∼104 Ma (Raine, 1984; Nathan et al., 1986) Tulloch and Palmer (1990) suggest uplift
to the surface (a 10 km vertical distance assuming a geothermal gradient of 35°C/km)
was accomplished in less than ∼7 Ma, suggesting a minimum uplift rate of 1.4mm/yr (or
1.1 mm/yr at a gradient of 45°C/km). Sericite ages obtained from hydrothermally altered
samples close to the Ohika and Pike detachment faults indicate ages of ∼98 Ma and ∼85
Ma respectively.
The reconstructed thermal histories determined by previous workers are
consistent with an initial period of rapid cooling followed by protracted cooling rates
preceding continental rifting. This trajectory is common to other metamorphic core
complexes, however cooling rates tend to vary. For example, the South Mountains
metamorphic core complex in Arizona cooled from ∼700°C to ∼100°C in less than 5
million years, equating to an average rate of 192 +/- 74°C/Ma (Livaccari, 1995). The
PMCC displays a cooling history that lasted 4 to 5 times longer. The Shuswap
Metamorphic Core Complex in southern British Columbia, has a thermal history akin to
the PMCC. A rate of 50°C/Ma persisted for the first 8 Ma, followed by slower cooling at
16°C/Myr for the next 12 Ma (Vanderhaeghe et al., 2002). While initial rates for the
Shuswap and the PMCC are nearly identical, the second phase of cooling differs by a
factor of two. In sum, the PMCC thermal history displays the charcteristic core complex
34
trajectory of initial rapid cooling followed by slower rates, however overall the PMCC is
an example of a core complex that cooled relatively slowly.
3.3 DUCTILE DEFORMATION IN THE LOWER PLATE
The metamorphic core of the PMCC is exposed in the central region of the Paparoa
range, and along the northwest coast of the South Island. Discontinuous exposure occurs
for approximately 10 km between Cape Foulwind south of Charelston (Figure 3.1). In
this section we present the ductile structure of the metamorphic core based on detailed
structural transects, cross-cutting relationships and regional correlations.
3.3.1 Zone of mylonitic fabrics
Detailed structural mapping within a 4 km long coastal transect (WHC on Figure
3.1) south of Morrissey Creek (Figure 3.2) reveals variably deformed CMG gneisses and
a polyphase folded sequence of protomylonitic-ultyramylonitic rocks. CMG gneisses
south of White Horse Creek are characterized by granitic compositions that include
plagioclase, quartz, biotite ± muscovite. CMG gneisses south of WHC are characterized
by a gneissic foliation (S1) that dips to the SSE and mineral lineations (L1) that plunge
moderately to the SE. Minor, asymmetric (s-type, z-type, and m-type) folds (F3) of this
gneissic layering are visible at many locations along the coast (Figure 3.2). Fold hinges
range from being curved to kinked. Wavelengths are on the order of tens of centimeters.
South of WHC, F3 fold axes plunge to the SE and axial planes dip moderately to the S.
North of WHC, F3 fold axes plunge to the SW-NE and axial planes dip to the N. At site
WHC 12 (Figure 3.2) two additional styles of folding affect the CMG. Earlier, tight to
35
Figure 3.2. White Horse Creek structural transect. a.) Map of structural data; b.) Crosssection showing the folded mylonitic front and WHC strain gradient ; c.)-e.) Outcrop
scale field sketches of F2,F3 folds; f.)-i.) Lower hemisphere, equal-area projections of
structural data; j.) Block diagram illustrating the geometry of F2-F4 in the highest strain
zone.
36
isoclinal folds (F2) of compositional layering in the gneiss are characterized by subhorizontal axial planes, display sheared out limbs, and are
refolded about a younger, upright open fold (F3). The upright, open fold is characterized
by a moderately NNW dipping axial plane, and its upright limb is affected by minor kink
folding. Thus, this single outcrop displays three generations of superposed, coaxial
(shallow NE-SW plunging) folds in non-mylonitized CMG gneiss.
Protomylonitic-ultramylonitic rocks, classified using clast:matrix proportion as
suggested by Passchier and Trouw (1996), crop out discontinuously along the WHC
transect. Mylonitic rocks are characterized by grain boundary reduction and dynamic
recrystallization in quartz (Figure 3.10), planar alignment of micaceous minerals into
well developed S and C surfaces, and feldspar porphyroclasts that commonly are rotated
and fractured. Mylonites generally display well-developed foliations, defined by aligned
quartz ribbons and biotite ± muscovite crystals, and lineations, defined by quartz rodding,
quartz-mica aggregates, and feldspar rodding. Strain appears to be partitioned
heterogeneously along the coast, based largely on the percentage of quartz
recrystallization and fold tightness (Figure 3.2). The highest strain zone is located
between sites WHC3-4, where the most spectacular mylonites and ultramylonites are
visible at low tide.
Detailed structural mapping of mylonites exposed along the coast and Coast
Road, together with the aforementioned non-mylonitized CMG structures, allowed us to
propose the geometry for the mylonitic shear zone shown in Figure 3.2. Map pattern
variation in the dominant mylonitic foliation (S2) within the WHC transect suggests a
38
thickness of ∼50 m for the mylonitic front. A variety of structures affect rocks within the
mylonitic front. Early, tight to isoclinal (interlimb angle < 10°) intrafolial folds (F2) with
axes that plunge shallowly to the SW and NW are present within the highest strain zone
(Figure 3.2). Folds of S2 occur in four dominant styles: (1) Tight to isoclinal, intrafolial
folds (F2) that plunge shallowly NE-SW. (2) Asymmetric, tight-is s and z type folds (F3)
of foliation display both rounded and chevron type hinges and plunge SW-NE. (3)
Upright open folds of foliation (F3) with moderate NNW dipping axial planes and
shallow WSW plunging axes (Figures 3.2, 3.8). (4) Regional scale (wavelength = tens to
hundreds of meters) gentle warps in the foliation (F4) about shallow WSW-ENE punging
axes (Figure 3.2). These relationships suggest a sequence of at least four events of
deformation, beginning with pre-mylonitic structures south of WHC, followed by the
development of mylonitic fabrics and penecontemporaneous F2 folds, outcrop scale F3
folding and regional scale F4 warping.
3.3.2 Central core zone
CMG orthgneisses and paragneisses crop out discontinuously on headlands, cliffs,
and bays north and south of Charleston forming a ∼10 km long, measurable structural
section.(Figure 3.3). Penetrative ductile fabrics dominate the northern portion of the
transect while in the south only weak foliations, mineral and intersection lineations are
present. On a regional scale, the foliation is folded into two broad arches with shallow
ESE and ENE plunging axes. Mineral lineations defined by quartz-mica aggregates
plunge in accordance with the arch axial surface, generally NNE-SSW. Three styles of
39
folding are observed in the central core zone. Cross-cutting relationships allowed us to
determine the following sequence: (1) Asymmetric, tight-intrafolial folds of foliation and
compositional layering (F2). (2) Asymmetric, s and z type parasitic folds (wavelength <
10 cm) of foliation (F3 ). (3) Regional scale warping of the foliation and earlier formed
axial planes. F2 folds tend to plunge S, SE, and NE while F3’s plunge shallowly to the W.
F4, regional arches plunge shallowly ENE-WSW.
3.3.3 Ductile deformation along the northern border of the core
In the northern Paparoa Range, the Greenland and Pororari Groups are separated
from lower plate rocks by the NE dipping Ohika detachment fault (Tulloch and
Kimbrough, 1989; Tulloch and Palmer, 1990). Evidence of ductile deformation in lower
plate rocks exposed along the road parallel to the Buller River is limited to a few exposed
outcrops (Figure 3.4). Foliations dip to the WNW and mineral lineations plunge to the
NE and NW. These outcrops are <500 m from the mapped detachment fault, yet neither
penetrative ductile fabrics nor mylonites are present in exposures along the road.
Approximately 3 km of nearly continuous coastal exposure south of the Cape
Foulwind lighthouse is dominated by the Foulwind Granite of Nathan (1975) (Figure
3.5). Two texturally distinct intrusive phases of the Foulwind Granite are found along the
beach south of Cape Foulwind. A megacrystic variety rich in potassium feldspar crops
out north of Siberia Bay and on Tauranga Bay’s bounding headlands. This unit, Kf1b of
Nathan (1976), is also rich in biotite which defines the local foliation planes, and quartz
that has deformed plastically to form subgrains with undulose extinction. Potassium
41
feldspar megacrysts locally display asymmetric tails, useful for kinematic interpretation
(see section 3.5). South of Cape Foulwind, foliation is folded about two broad arches that
plunge shallowly ENE. Quartz-mica mineral lineations plunge gently to the E in the south
and SW-NE in the north. In contrast to areas farther south, no intrafolial or single outcrop
scale folds are found anywhere along the transect.
A finer grained granitic phase crops out along the coast for less than 1000m
beginning on the headland north of Siberia Bay. This phase is devoid of a penetrative
ductile fabric, however thin (<5 m thick) proto-ultramylonite zones are developed within
the granite (CF2,3). Ductile foliations in deformed rocks dip north and mineral lineations
plunge to the NE. Texturally, these samples stand out in marked contrast from the
deformed megacrystic phase. Quartz microtextures in samples collected from site CF3
indicate near complete recrystallization, similar to samples collected from the White
Horse Creek mylonite zone. Feldspar grains are deformed dominantly by microfracture
and rotation. Quartz deformation textures in the megacrystic Foulwind Granites include
subgrains, seriate grain shapes, and undulose extinction, however dynamic
recrystallization is not observed. We discuss the localized development of mylonitic
fabrics on the Foulwind transect in the next section.
3.4 BRITTLE AND SEMI-BRITTLE DEFORMATION
Brittle and semi-brittle faults affect lower plate rocks exposed along the coast in the
north, south and center of the metamorphic core. In general, two styles of faulting are
observed: (1) A strictly brittle phase dominated by SW, NE and SE dipping fault planes
and slickenlines that plunge down-dip and obliquely down-dip. Offsets on these faults are
44
on the order of tens of centimeters. (2) A “semi-brittle” phase, so named because these
faults are associated with localized development of ductile fabrics (discussed in the
previous section) ranging from weakly deformed granitoid to ultramylonite. The
magnitude of offset on the semi-brittle phase is difficult to constrain because of the
absence of appropriate markers. In this section, we present fault-slip data from three
domains within the core, southern central and northern. These data are used to generate
kinematic solutions for brittle fault populations (Figures 3.6-3.8).
3.4.1 Brittle faults
Brittle faults cut all generations of ductile structure in lower plate rocks at numerous
locations within the core (CF1, CH6-7, WHC1,4,10). We measured the orientations of
these faults and found that most faults tend to occur in narrow zones, or groups. Here we
describe fault geometries observed in the northern, central and southern domains within
the core.
Northern domain
The first headland north of Siberia Bay contains an intensely faulted exposure of
the Foulwind Granite. The exposure photographed in Figure 6a allowed us to measure a
large population of minor (offset 5-10cm) faults in three dimensions. Most of the faults
measured in this population lie within the hanging wall or footwall of a low-angle, NE
dipping master fault. The exposed length of this fault is approximately 10 m; the fault
zone is characterized by localized development of ductile strain and pseudotachlyte.
45
Brittle faults affecting this block generally dip moderately to the E and SE; slickenlines
commonly plunge ENE and SSW. We grouped faults within 20 m of site CF1 into a data
set and plotted them for comparison. Faults in this latter group (CF1 regional) dip
preferentially to the SE and NE, slickenlines plunge to the NE and SSW.
Central domain
CMG gneisses within the Charleston transect are affected by two distinct styles of
brittle faulting. A low-angle variety cuts coastal exposure between sites CH6-7. Most
faults dip to the NE, and slickenlines plunge approximately down-dip. Ductile
deformation in footwall rocks increases with proximity to the fault, and a thin (<5 cm
thick) zone of protomylonite is common in the fault zone.
At site CH7 a block of CMG gneiss is cut by a series of SW dipping normal faults
displaying a litsric “fault fan” geometry. Steeply dipping early faults splay into a slightly
bowed-up, listric master fault. Slickenline orientation suggests motion was nearly down
dip. A deformed pegmatite dike indicates meter-scale offset on the minor faults.
Southern domain
At site WHC1 along the Coast Road, brittle faults dip moderately to the SW and
steeply to the NE dissecting the limbs of an upright open synform (F3) composed of
protomylonites (Figure 8). Brittle faults also cut asymmetric s-folds (F3) and gently
dipping crushed zones. Slickenlines on S-dipping faults generally plunge approximately
down dip, while slickenlines on N-dipping faults tend to be shallow and obliquely down-
49
dip. A syn-tectonic pegmatite indicates offset is normal and on the scale of tens of
centimeters.
3.4.2 Semi-brittle faults
Based on field observations (presented in section 3.2) and kinematic analysis
(presented in section 3.5) we suggest the presence of a “semi-brittle” (semi-ductile)
structure capable of producing meter scale thicknesses of moderate to highly deformed
rocks. The term semi-brittle, describes structures which accommodate stress by a
combination of brittle and ductile deformation mechanisms, such as a brittle fault and a
strain softened, ductiley deformed fault zone. We suggest at least two locations within the
core (sites CF2,3) may have been affected by such structures. Texturally, rocks at these
sites bear little resemblance to the massive, fine grained, undedformed phase of the
Foulwind Granite to which they belong (Figures 3.5, 3.9). Instead they are chacterized by
localized, spatially distinct thicknesses of high strain rocks. Kinematic interpretations
regarding semi-brittle structures are made in the next section.
3.5 KINEMATIC ANALYSIS
The structurally diverse, variably deformed metamorphic core of the PMCC
provided an excellent opportunity to perform a scale independent kinematic analysis of
ductile, semi-brittle, and brittle deformation. Here we present the techniques and results
of this analysis.
3.5.1 Kinematic analysis of mylonitic rocks
50
Figure 3.9. Outcrop and thin section scale kinematic indicators. a,b.) Mylonitic fabric
photographed in the field. S-C fabric and large beta-type feldspar clast directly below
pencil indicate dextral motion, parallel to the pencil (lineation); c.) S-C fabric,
imbricated, antithetically microfaulted feldspar in the center of field of view, sigma-type
clast in the upper left-hand corner indicate dextral motion.Photograph taken under
crossed polars with the gypsum plate inserted; d,f.) Plagioclase feldspar porphyroclasts
sampled from site WHC3. Large beta-type clast in the upper third of "d."; sigma-type and
delta-type clasts in the upper third of "f."; g,h.) S-C fabrics developed in the Foulwind
Granite at sites CF2 and CF3. These fabrics are interpreted as related to semi-brittle
faulting. "g." indicates sinistral motion as C planes are oriented NE-SW and S planes are
oriented NW-SE. Large beta-type clast in center of field of view. "h." displays well
developed dextral S-C fabric.
51
Excellent coastal exposure and extensive sampling of mylonitic rocks allowed us
to establish the kinematics of ductile flow associated with the main mylonite zone north
of White Horse Creek (Figure 3.2). In the field, three-dimensional exposures facilitated
the identification of S and C surfaces on faces perpendicular to foliation and parallel to
mineral stretching lineation (XZ plane, where X is parallel to stretching lineation and Z is
perpendicular to foliation). Easily visible (cm scale) asymmetric, sigma, beta, and delta
type plagioclase feldspar porphyroclasts served as a check on sense of shear deduced
from S/C relationships alone (Figure 3.9). Sense of shear information deduced in the field
was cross-referenced with and complemented by results from a microscale analysis. At
the scale of a thin section, kinematic indicators used include: S-C relationships, mica fish,
asymmetric porphyroclast geometry, synthetic and antithetic microfaults affecting
feldspars, and LPO in quartz. Our goal was to collect enough data to compare the
kinematic signature of the main mylonitic shear zone within the PMCC to previously
identified mylonitic zones, particularly those in the western North America (e.g.
Reynolds et al., 1990).
Our results indicate that the sense of shear in most samples within the mylonitic
front was normal, top down to the S, SW or NE. Because all measurements were made on
the XZ plane, sense of shear is also parallel to the gently plunging mineral lineation (SWNE). These results are consistent with 2D, NE-SW sub-horizontal flow. One significant
exception to this general trend occurs at site WHC11 (Figure 3.2), where the mylonitic
fabric dips N and the mineral lineation plunges NE (consistent with observations made by
Tulloch and Kimbrough,1989). Here, meso and microscale kinematic indicators suggest a
53
reverse, top to the SW sense of shear. This zone may be analogous to back-dipping
mylonite zones in western North American core complexes, that commonly display sense
of shear reversals. These reversals have been attributed to folding of mylonite zones postcrystallization of ductile kinematic information (e.g. Reynolds et. al., 1990).
Kinematic vorticity analysis
In addition to recording sense of shear distributions among the mylonites, we
measured the axial ratios, long axis orientations and tail types on coarse grained
plagioclase feldspar porphyroclasts, which are a ubiquitous feature of the highest strain
zones (WHC3-4). Measurements were made on multiple outcrops within this zone,
spanning a horizontal distance of approximately 40 m. We use this data set,
complemented by an identical analysis on the microscale, to estimate the kinematic
vorticity, or rotational component of flow within the main mylonitic shear zone (Simpson
& DePaor, 1993). Such an analysis requires that (1) clasts behave rigidly and rotate
passively within the deforming matrix, and (2) results are interpreted two-dimensionally.
We address the first of these assumptions using deformation microtextures. All mylonites
analyzed in this study are characterized by a strong ductility contrast between quartz and
feldspar (this study; Tulloch and Kimbrough, 1989) where the former deformed through
grain boundary migration and dynamic recrystallization and the latter deformed
dominantly through microfracture and rotation. While localized deformation twinning in
feldspar is present in some samples, Rf/φ (axial ratio/long axis orientation) data for 283
54
feldspar clasts measured on all three (XZ, YZ, XY) principle planes indicates Rf values
are close to 1 on nearly all planes (Figure 3.10). This result supports rigid clast rotation.
A fundamental problem with using kinematic vorticity to completely describe
deformation in shear zones is that vorticity results are two-dimensional measurements of
flow fields that are commonly three-dimensional (Tikoff and Fossen, 1995; Jiang and
Williams, 1999; Jiang, 1999). Thin sections in this study examined on the XY and YZ
planes display weakly developed asymmetries suggesting flow was three-dimensional,
however, the plane of dominant asymmetry is consistently the XZ plane. As a result, we
use the results to determine the relative contributions made by pure and simple shear, in
the near vertical XZ plane.
We measured 100 clasts from planes parallel to lineation and perpendicular to
foliation over a 40 meter section along the coast. The technique involves measuring the
values for the long (X) and short (Z) axes of clasts, as well as the orientation (Φ) of the X
axis relative to a fixed reference line. Along the WHC transect we found that foliation
(S2) served as a convenient reference line. We completed the same procedure on an
oriented thin section where we measured 70 more clasts. We plotted the Rf/Φ data on
three hyperbolic nets and after constructing eigenvectors following the technique outlined
in Simpson & De Paor (1993) we determined Wk, the kinematic vorticity number, to be
between 0.74-0.78 (Figure 3.10). A value of approximately 0.71 represents a shear zone,
which has received equal contributions from pure and simple shear (Tikoff & Fossen,
1995; Law, 2002). The value we obtained is scale independent, and indicative of a shear
56
zone that has experienced thinning in the vertical plane where simple shear dominates
over pure shear.
The domainal character of the core rocks exposed along the WHC transect
allowed us to identify a strain gradient, defined by changes in , degree of rotation and
transposition of D1, D2 structures, and the evolution of quartz and feldspar
microstructures. In general, strain increases down-section (lowest strain - WHC6; highest
strain - WHC3,4) as F2, F3 folds become tighter (Figure 3.2) and grain size reduction in
quartz increases. Additionally, the direction of maximum elongation (tracked by the L1,
L2 stretching lineation) rotates from a position plunging shallowly SE in moderately
deformed CMG gneisses to shallowly SW plunging in the main D2, D3 mylonitic zone.
The geometry of the WHC strain gradient, charcterized by vertical shortening, subhorizontal extension and rotation, is consistent with Wk results that suggest thinning in
the near vertical (XZ) plane.
3.5.2 Kinematic analysis of ductile fabrics outside the mylonite zone
Using the same methods as outlined above for outcop and thin section scale sense
of shear determination, we were able to establish the kinematics of ductile flow outside
the main mylonitic zone. North of Siberia Bay (Figure 3.5), field observation of S-C
fabrics together with rotated, coarse potassium feldspar grains which commonly display
tails composed of biotite ± muscovite and quartz indicate top down to the ENE and SW
shear on opposite limbs of the warped foliation. On the southern coast of Siberia bay, at
sites CF2 and CF3, local development of protomylonite, mylonite, and ultramylonite is
characteristic of the NE dipping fabric. Protomylonitic rocks observed at site CF2 contain
57
well-developed S-C fabrics indicative of top down to the NE shear. Site CF3 indicates an
increase in fabric intensity from protomylonite to ultramylonite over a vertical distance of
1 meter. The total thickness of high strain rocks at this site is approximately 3 meters.
Rotated feldspar porphyroclasts in the mylonites indicate sense of shear was top down to
the NE. Less than 500m south of this outcrop, the granites become megacrystic again
with penetrative ductile foliations and lineations. On the headland just north of Tauranga
Bay S-C fabrics, rotated feldspar grains, and E plunging lineations indicate sense of shear
was top down to the E.
One sample collected from the lower Buller gorge (site BR2, Figure 3.4)
displayed a visible S-C fabric in outcrop and thin section (Figure 3.9). These
relationships, together with NE plunging lineations, indicate a top down to the NE sense
of shear. Taken together, kinematic analysis of ductile fabrics in the north indicate sense
of shear was dominantly top down to the NE. While ductile fabrics are common in the
north, their intensity is greatly subdued when compared to fabrics observed in the
southern end of the core. As a result, our understanding of the three-dimensional
characteristics of ductile flow in these rocks is limited.
3.5.3 Kinematic analysis of fault-slip data
Using the program “Faultkin v.4.1” we calculated the principle axes of instantaneous
shortening (Z) and extension (X) for the incremental strain tensor associated with each
fault measured in this study (Figures 3.6, 3.7, 3.8, 3.11)
(www.geo.cornell.edu/geology/faculty/RWA/maintext.html)(Allmendinger,1993)
58
(Allmendinger et al., 1989). These are calculated using measurements of fault plane
attitude, straie orientation, and sense of displacement. The program constructs an
instantaneous
strain ellipse for each fault within the plane perpendicular to the entered fault plane and
parallel to straie orientation. In general, calculated Z axes were steep or sub-vertical,
while calculated X axes plunge shallowly to the WSW-ENE. These data indicate the
kinematics of brittle faulting are characterized by vertical shortening and sub-horizontal,
NE-SW extension.
3.6. CORRELATION OF STRUCTURES AND DEFORMATION SEQUENCE
Based on cross-cutting relationships, we break out a sequence of five events (D1D5) that may have occurred progressively or in a non-steady fashion during regional
continental extension. D1 describes structures that formed prior to D2 mylonite
generation. We interpret SE dipping foliations (S1) , SE plunging lineations (L1) and SE
plunging fold axes (F3) within CMG gniesses south of WHC as older than the mylonites,
based on their orientation and position within the strain gradient. Tight to isoclinal folds
observed at site WHC12, previously termed F2’s based on fold tightness and refolded
geometry, may represent flattened asymmetric folds observed south of this site,
previously termed F3’s based on their geometry (Figure 3.2). Should this be true, the tight
to isoclinal folds would also be F3s. In either case, structures south of WHC are
interpreted to represent early stages of extension based on deformation textures and an
oblique (∼90°) orientation with respect to the dominant extension direction.
60
Within the central core zone, early SE plunging folds (F2 ) may have also been
part of D1 deformation. Ductile fabrics (S2, L2) exposed south of Cape Foulwind may
have predated mylonite development, however stretching lineations plunge exclusively to
the ENE-SW. This orientation is parallel to L2 myl in the south. Because of their
geometrical similarity, we group ductile fabrics in the megacrystic Foulwind Granite with
mylonitic structures (S2, L2, F2) and refer to them collectivecly as D2. Additionally,
central core zone fabrics, S2 ,L2 are included because of their orientation.
D3 deformation involves folding of the mylonitic front and its host rocks. This
event produced the upright, open F3 folds visible at sites WHC 12 (Figure 3.2) and WHC
1 (Figure 3.8). D4 describes the regional E-W arching about sub-horizontal axes
displayed throughout the core, that folds axial planes of earlier formed structures (F4). D5
includes both semi-brittle and brittle faulting, as these cut all previously formed fabrics
and structures.
3.7 GEOCHRONOLOGY
We determined U-Pb zircon ages for three samples within the core of the PMCC.
In this section we present the results and discuss how these data allow time constraints to
be placed on D1- D5.
3.7.1 Sample locations and cross-cutting relationships
Sample 03-whc-1
61
Extracted from a granitic pegmatite on a roadcut along the Coast Road, < 1km south of
White Horse Creek. The pegmatite cuts the folded (F3) mylonitic fabric (S2) at site
WHC1, but is cut by a series of NE and SW dipping normal faults (Figure 3.8). This age
places a minimum on the age of brittle faulting (D5) on the southern side of the core
complex.
Sample 03-ch-2
Extracted from a granitic dike cross-cutting the locally folded (F3) gneissic fabric
developed in the coastal exposure below, and west of the Charleston Cemetary. This age
places a maximum on the age of fabric development and folding within the CMG in the
central core zone.
Sample 03-whc-13
Extracted from a granitic pegmatite folded sub-concordantly with the local mylonitic
fabric. This age places a minimum on folding (F3) within the mylonitic shear zone.
3.7.2 U-Pb Ages
3.8. DISCUSSION
In this section we discuss the results of our structural and kinematic analysis in
the context of published models for regional extension.
3.8.1 Three-dimensional strain and kinematic evolution of the middle crust
62
Our structural analysis of the main mylonitic shear zone (WHC transect) suggests
ductile deformation (D1-D4) included a three-dimensional flow pattern and may have
been characterized by constriction (X - extension; Z - shortening; Y- shortening).
Evidence for constriction is based largely on the orientation of linear features (lineations,
fold axes) as they are tracked through progressive deformation (section 5). Pre-mylonitic
(D1) folds regardless of tightness, and lineations (L1) progressively rotate into parallelism
with the D2 strain field as the highest strain zone is approached from the south. These
changes occur as strain is increasing within the WHC strain gradient. Three generations
of coaxial, superposed folds (F2-F4) within CMG gneiss parallel to the dominant
stretching direction at site WHC12 illustrate this geometry, and serve as an excellent
qualitative indicator of constrictional strain. Additionally, within the mylonitic front north
of site WHC12, F2, F3, and F4 myl folds have parallel, NE-SW plunging axes, parallel to
the dominant stretching direction. (Figure 3.2). F4 folds found elsewhere in the core tend
to have E-W sub-horizontal axes. This geometry implies a component of NNW-SSE
shortening during extension, as F4 folds do not re-orient kinematic information
crystallized during D2 or D3 deformation. These geometric relationships, together with
independent determinations of the orientations of X and Z strain axes (kinematic
vorticity) suggest three-dimensional strain in the ductile field was characterized by
vertical shortening (Z axis), sub-horizontal, NE-SW extension (X axis), and NNW-SSE
shortening (Y axis)(Figure 3.12).
Kinematic analysis of brittle fault-slip data indicates the orientations of maximum
shortening and extension axes during D5 were parallel to those observed during ductile
63
deformation, (D1-D4). This result suggests the kinematics of ductile flow and brittle
faulting, and the orientation of X and Z strain axes remained constant during the
transition from ductile to brittle deformation.
3.8.2 Extensional mechanisms
Published models describing post-orogenic extensional mechanisms emphasize
the role of : (1) gravity-driven extension as a response to overthickened crust and reduced
intra plate stress (Coney & Harms, 1984; Burchfiel et al., 1982) as in the North American
Cordillera and the Himalaya; (2) thermal weakening of a broad zone of middle crust by
partial melting, and extension related, melt-enhanced deformation (Vanderhaghe &
Teyssier, 1997; Vanderhaghe & Teyssier, 2001) in regions such as the Shuswap
Metamorphic Core Complex in southern British Columbia. The Paparoa Metamorphic
Core Complex in western New Zealand is an excellent place to test aspects of these
models because the region was charterized by regional contraction and crustal thickening
during a ∼20 Ma period directly before the onset of regional extension at ∼112-108 Ma.
Post-orogenic extension in western New Zealand is somewhat unique, however, because
extension eventually led to continental rifting and the opening of a new ocean basin.
The styles of crustal thickening and thinning during the period of Cretaceous
orogenesis recorded by the rocks in western New Zealand sugggest that weakening of the
middle crust caused by partial melting was not a dominant mechanism during the
extensional process. Voluminous syn-tectonic magmatism during contraction and
extension was likely important in reducing intra plate stress prior to and during extension,
however migmatites recording melt-enhanced deformation are nearly absent at mid-upper
65
crustal levels. This observation is consistent with the mid-crustal architecture of a
collapsed orogen composed domiantly of magmatic rocks as opposed to an orogen
dominated by fertile, melt-producing meta-pelites. Tulloch and Palmer (1990) suggest the
thickness of the crust in western New Zealand may have reached 45-55 km in the Early
Cretaceous. These workers suggest crustal thickening may have been important for the
generation of syn-extensional granitic magmatism in the metamorphic core of the PMCC,
represented by plutons of the Rahu Suite. Deformation in these rocks is consistently
solid-state, suggesting extension was not driven by the collapse of the upper crust over a
weak horizon in the middle crust. Data presented here and elsewhere suggest the
dominant mechanism for extension in the PMCC was not related to a mechanical
weakening of the middle crust caused by partial melting.
Late Cretaceous extension in western New Zealand coincided with a major
change in plate boundary dynamics that affected the entire Pacific margin of Gondwana.
We suggest this change was the driving force behind and dominant mechanism for
extension in the region. Two results in the recent literature help support this
interpretation. First, shear zones affecting Cretaceous and older rocks shift from
contractional style, vertically thickening pure shear dominated zones to extensional zones
recording retrogression and vertical thinning at middle and lower crustal levels by 112108 Ma (Klepeis, 2002; Tulloch and Palmer, 19990; Gibson & Ireland, 1988; this study).
Second, thermal studies of lower crust exposed in Fiordland, indicate the lower crust was
cooling rapidly and strong during the shift from contraction to extension (Daczko et al.,
2002; Klepeis et al., 2003). Additionally, partial melting in the middle and lower crust
66
produced low volumes of melt, particularly when compared to voluminous migmatites
common where metapelites are subjected to heat and burial. We suggest the narrow,
focused style of ductile thinning in the mid-crustal core of the PMCC is primarily the
result of changing regional stress conditions in a column of lithosphere characterized by a
strong lower crust and a plastic middle crust. We acknowledge that the middle crust was
likely weakened to some degree by syn-extensional magmatism, but reject gravitational
instability due to partial melting in the middle crust as a dominant mechanism driving
extension.
An extensional model driven by plate boundary change is supported,
additionally, by isotopic analyses of hydrothermally altered mylonites in the footwall of
the Pike detachment fault (Tulloch and Palmer, 1990). A sericite age of ∼85 Ma has been
suggested to represent the last stage of motion on the Pike detachment just prior to
continental rifting and the opening of the Tasman Sea. It follows then, that the driving
force behind late Cretaceous extension and the exhumation of mid-crustal rocks in the
PMCC may have been the same force that drove continental rifting and the generation of
new ocean crust.
3.9. CONCLUSIONS
We recognize five events (D1-D5) of deformation within the core of the Paparoa
Metamorphic Core Complex produced during regional extension on the Pacific margin of
Gondwana in the Late Cretaceous. D1-D4 comprises a ductile history characterized by
polyphase folding and fabric development in mylonitic (southern domain) gneissic
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(central core zone) and granitic (northern domain) units. D5 describes semi-brittle and
brittle faults that cut all previously formed ductile fabrics.
In the southern half of the core, D1-D4 produced a 4 km long section of
interfolded mylonites and host rocks. Within the highest strain zone, three generations of
folds (F2,F3,F4) have axes parallel to the orientation of the mineral stretching lineation
and regional extension direction. Fold axes and mineral lineations oriented oblique (∼90°)
to the extension direction are recorded by lower strained rocks within the WHC strain
gradient. Sense of shear analysis of mylonitic fabrics indicates sub-horizontal stretching
during top down to the NE and SW normal motion. Kinematic vorticity analysis of D2
mylonites performed on a suite of three sites in the field and a fourth on the microscale
indicate 0.74 < Wk < 0.78. This result is consistent with a shear zone that has
experienced thinning in the vertical (XZ) plane. Two-dimensional kinematic analyses,
together with the geometry of D1-D4 structures, suggest a three-dimensional environment
characterized by constrictional strain where the direction of maximum shortening (Z axis)
is vertical and maximum extension (X axis) is sub-horizontal, NE-SW. Kinematic
analysis of brittle fault-slip data indicates D5 was also characterized by vertical
shortening and NE-SW sub-horizontal extension. We interpret these results as evidence
that structural and kinematic parameters, namely sense of shear and the orientation of
maximum extension and shortening axes, remained constant during the transition from
ductile to brittle deformation in the middle crust during extension.
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CHAPTER 4: Strain and kinematic analysis
4.1 INTRODUCTION
Any comprehensive study of rock deformation would be incomplete without an
analysis of finite strain and the kinematics of flow. Strain analysis allows for the
estimation and comparison of the magnitude and orientation of deformation parameters.
Kinematic analysis is important for reconstructing displacement history and interpreting
the evolution of flow regimes. This chapter describes the background, methodology,
results and analysis of a finite strain and kinematic analysis performed on ductiley
deformed rocks during the Late Cretaceous extensional event in western New Zealand.
4.2 STRAIN
4.2.1 Background
Finite strain is the end result of one or more episodes of shape change, rotation, or
translation experienced by a volume of rock (e.g. Davis & Reynolds, 1984; Twiss &
Moores, 1992). A common goal of structural geologists working with deformed rocks is
the determination of the magnitude and orientation of the finite and incremental twodimensional strain ellipse or three-dimensional strain ellipsoid for a sample, outcrop, or
region. The concept of the strain ellipse and ellipsoid are fundamental to structural
geology, and are based on the idea that an unstrained object may be represented as a
circle or sphere, and any subsequent strain accumulated by that circle or sphere will result
in the formation of an ellipse or ellipsoid. Implicit here is the concept of the instantaneous
or infinitesimal strain ellipse, which records the shape change, rotation or translation of a
69
potentially infinite number of incremental strains. The end product of one or more
episodes of incremental strain is the finite strain state of an object.
The challenge for field geologists working in deformed terranes became the
identification of “strain markers” or objects that accurately record incremental and finite
strain. A diverse and creative assortment of strain markers have been used by workers
during the last three decades including shape change in ooids, boudins, and feldspar
grains and rotation of veins and reaction zones (e.g. Fry, 1979; Sen and Mukherjee, 1972;
Borradaile, 1979; Klepeis et al., 1999). Choosing an appropriate strain marker in the field
is difficult because natural objects often do not originate as circles or spheres, and shape
change histories commonly deviate from the simple circle to ellipse morphology.
Based on these fundamental principles, a set of assumptions exists for any strain
analysis performed on naturally deformed rocks. First, the nature of strain accumulation
makes it difficult to determine, in the absence of external data, whether the strain being
measured represents an infinitesimal or a finite strain, particularly in polyphase deformed
terranes. For this reason, strain studies commonly are comparative analyses and the
results are not necessarily viewed as true finite strains but rather as apparent strains. The
aim of this strain analysis is to quantify a strain gradient defined by textural changes in
deformed granitoid rocks, an increase in fold tightness, and rotation of structures toward
parallelism with the dominant stretching lineation and extension direction. It is
acknowledged, that while a strain gradient defined by external observations is used, the
results likely do not represent true strains.
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True strains are not calculated in this study because of the nature of the strain
markers and the environment of deformation. This study fails to satisfy an important
second assumption, that strain markers deform homogeneously. As indicated above, we
measured the strain exhibited by granitoid rocks in a strain gradient associated with the
White Horse Creek high strain zone. Microtextural evidence suggests the conditions of
deformation did not exceed 500°C, as feldspars deform dominantly by microfracture and
quartz behaves by grain boundary migration during dynamic recrystallization. Studies
have shown that at low strain rates, quartz deformation textures include undulose
extinction and subgrain formation. Subgrains have been shown to form in a variety of
orientations, from near circular to moderately elliptical. With increasing deformation,
subgrains undergo grain boundary area reduction and finally, in mylonitic rocks, dynamic
recrystallization. The shapes of quartz grains and subgrains were used as strain markers
in this study, despite the admission that their deformation paths were likely
heterogeneous.
A third and final important assumption to note is that factors other than
deformation may influence the shapes and orientations of strain markers, resulting in
apparently incorrect finite strain results. Volume loss can be a very important external
factor to consider when using mineral grains as strain markers, particularly when using
feldspars in low-temperature regimes. Dissolution of feldspar may cause grains to change
shape before, during or after deformation, masking the true finite strain state. Knowledge
of volume loss becomes critical when attempting to interpret three-dimensional strains.
Three dimensional strain ellipses have prolate (cigar-shaped) and oblate (pancake-
71
shaped) end member geometries. These ellipsoids are determined by combining twodimensional strain results for three perpendicular faces. A Flinn diagram illustrates these
concepts (Flinn, 1979), where each ellipsoid plots as a point somewhere in the field of
constriction, flattening or plane strain. Volume loss in a sample shifts the K = 1 division
(a line with a slope of 1), where K > 1 indicates constriction and K < 1 indicates
flattening. The more volume lost in a system, the farther to the right the line will shift.
Hence, without considering volume loss results may be interpreted as flattening when
they are really constrictional.
4.2.2 Methods
This study employed the methods of Lisle (1985) and Ramsay and Huber (1983)
in order to track the changes in magnitude and orientation of the finite strain ellipsoid
through the White Horse Creek strain gradient. Two different analyses were performed;
one suite of three samples using quartz as a strain marker and one suite of three samples
using feldspar. The second analysis was conducted to produce a quantitative check on
microtextural evidence suggesting feldspar behaved brittley during deformation. If quartz
and feldspar truly deformed by different deformation mechanisms, a comparison of the
results of these anlyses should reflect the behavioral variation.
In samples where quartz was used as a strain marker, ellipses were drawn around
deformed, but not recrystallized, quartz grains and subgrains. Relic grains were used
where they could be identified. In samples where feldspar was used, ellipses were drawn
around whole feldspar grains. The methodology involved taking oriented, digital images
of whole thin sections from three perpendicular planes (XY,XZ, and YZ, Figure 4.1),
72
importing these images into Adobe IllustratorTM, and tracing grains using the Illustrator
ellipse tool. Axial ratios (ratios of long axis:short axis) and the φ angle (angle between
the long axis and an arbitrary reference line) are calculated in the program (AI), then
transferred to ExcelTM data sheets where harmonic and vector means are calculated.
Ramsay and Huber (1983) indicate that obtaining harmonic mean of Rf analyses is an
acceptable technique for rapid determination of tectonic strain (Rs). This information
allows the magnitude and orientation of sectional, two-dimensional strain ellipses to be
calculated. The magnitude and orientation of the three-dimensional finite strain ellipsoid
is calculated by entering the data for three sectional ellipses into the program Strain3D
written by Basil Tikoff (University of Wisconsin) that uses the least squares of Means
(1984) method to compute six possible ellipsoidal geometries. Thus, the result of each
sample analysis is a lower hemisphere, equal-area projection showing the trend and
plunge of six possible X (direction of maximum elongation), Z (direction of maximum
shortening) and Y (direction of intermediate shortening/elongation) orientations. A robust
analysis is one where X,Y and Z orientations form three tight clusters.
4.2.3 Reults
Quartz
Despite the behavioral heterogeneity quartz displays during deformation, Rf/φ
analysis of grains from deformed granitoid rocks in the White Horse Creek strain
gradient indicates a modest, but detectable quantitative increase in strain (Figure 4.2).
Sample WHC6, the low strain sample collected in the field, dislpays the lowest Rf
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Figure 4.2. Three-dimensional strain results from the quartz analysis. Lower hemisphere
equal-area plots show the orientation of the principle ellipsoid axes (X,Y,and Z)
determined using the program Strain3D and Rf/φ data from three perpendicular planes.
75
harmonic mean values (least elliptical). The XZ plane from this sample yielded a mean Rf
of < 2, where 1 is a perfect circle. Sample WHC5 yielded higher mean Rf values; the XZ
plane for this sample = 2.14. Sample WHC2, taken from a low strain pod within the
mylonitic front near Morrissey Creek (Figure 3.2), yielded the highest mean Rf value for
XZ planes at 2.56. While these results clearly do not represent true strains, they do
confirm what was observed in the field, the presence of a measurable strain gradient.
Three-dimensional strain analyses yielded the ellipsoids shown in Figures 4.2 and
4.3. An example of how to read one of these diagrams is given here for Sample WHC6.
The X-axis (direction of maximum stretch), the longest axis of the ellipsoid, is steep and
plunges to the SW. The Z axis (direction of maximum shortening), the shortest axis of the
ellipsoid, plunges shallowly to the NE. The Y axis, or intermediate axis, plunges
shallowly to the SE. The relative lengths of the X, Y, and Z axes are directly proportional
to the Rf values determined for the three sectional XZ , YZ and XY, strain ellipses.
Sample WHC5 shows a change in geometry, where the Z-axis is nearly vertical and
maximum extension is shallow to the NW. WHC2 shows a third stage in the geometrical
evolution, with a steep Z-axis and maximum extension shallow to the SW. The results of
the three-dimensional strain analysis suggest that as strain was increasing from site
WHC6 to WHC2, the shape and orientation of the strain ellipsoid was evolving. The final
orientation of the ellipsoid, recorded by sample WHC2, contains a direction of maximum
extension parallel to the orientation of the mineral stretching lineation in the main
mylonitic zone and the dominant regional extension direction (NE-SW). Three
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Figure 4.3. Three-dimensional strain results from the feldspar analysis. Lower
hemisphere equal-area plots show the orientation of the principle ellipsoid axes (X,Y,and
Z) determined using the program Strain3D and Rf/φ data from three perpendicular planes.
78
Figure 4.4. a.) Flinn plot illustrating the three-dimensional strain results. After volume
loss is accounted for, samples would likely plot in the field of constriction; b.) Shapes of
feldspar grains measured in three-dimensional feldspar strain analysis.
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dimensional strain results may also be plotted on a Flynn diagram, which places ratios of
harmonic mean of Rf values determined in sectional analysis on the x and y axes such
that y = Rf xy and x = Rf yz (Figure 4.4). Samples that plot in the upper half of the
diagram display a constrictional strain geometry, samples which plot in the bottom half
indicate flattening strains. As discussed in the background, volume loss in the system will
shift the plane strain line separating the two fields to the right. Microstructural evidence
from this study suggests volume loss was present in the system, thus making the shift a
reality in this system. Depending on exactly what percentage of volume was lost, samples
from this study would either plot well into the field of constriction or near the boundary
indicating plane strain.
Feldspar
An identical analysis was performed on three samples containing abundant
plagioclase feldspar porphyroclasts. These data indicate that Rf for feldspar grains is
generally less than 1.5 (Figure 4.3). Additionally, ellipticity decreases towards the high
strain zone; the inverse of what the quartz analysis indicated. These results suggest
feldspar was not deforming by ductile processes during deformation. Comparison of all
XY and YZ sectional Rf data suggests that the shapes of feldspar grains are both prolate
and oblate (Figure 4.4).
Despite the conclusion that feldspar deformed by brittle deformation mechanisms
during deformation, three-dimensional analysis of feldspar Rf/φ data yielded ellipsoids
that indicate a preferred alignment of long axes on principle planes. While the orientation
82
of X and Y axes are variable, Z axes are generally steep to vertical. This is the same
orientation as the Z axis in the finite strain ellipsoid determined by the quartz analysis.
4.3 KINEMATIC ANALYSES
4.3.1 Background and methods
Kinematic analyses, mainly sense of shear determination and kinematic vorticity
(rate of rotation in a flow field) analysis , play a significant role in this study. These are
powerful tools which may be very useful in describing the environment of deformation
for a given shear zone (Lister and Williams, 1983; Simpson and De Paor, 1993; Passchier
& Trouw, 1996). However, due to the complex behavioral patterns in heterogeneous
naturally deforming systems, a certain amount of caution is required when interpreting
the results of kinematic analyses. This section first describes the fundamental
assumptions inherent in general kinematic analysis, then discusses these assumptions
with particular reference to the kinematic vorticity analysis used in this study.
Kinematic analyses of ductile fabrics are the measurement of instantaneous and
finite flow in rocks. Rocks deformed through tectonic processes are generally termed
“tectonites” and may be dominated by planar (S-tectonite), linear (L-tectonite) or a
combination of planar and linear elements (L-S tectonite). L-S tectonites allow for the
identification of principle, XY, YZ, and XZ planes, based on the orientation of the
stretching lineation and the foliation. The XZ plane (Figure 4.1), the plane parallel to
lineation and perpendicular to foliation, has been long thought to be the plane where the
most asymmetry occurs. Asymmetrical relationships formed on the XZ plane, have been
used as kinematic indicators under the assumption that the stretching lineation is parallel
83
to the transport, or shear direction (eg. Hanmer and Passchier, 1991). This assumption
may not always be valid, as will be discussed later in this section. Asymmetrical
relationships which have been used as sense of shear indicators include S/C fabrics, mica
fish, oblique foliations, asymmetric tails developed on porphyroclasts, synthetic and
antithetic microfaulted grains, and preferred orientation of mineral c-axes (Hanmer and
Passchier, 1991). This study employs macroscopic and microscopic S/C fabrics and
porphyroclast tails, as well as synthetic and antithetic microfaulted feldspar grains. As a
result of this kind of analysis, two-dimensional sense of shear is determined and is always
parallel to the stretching lineation for a given sample.
These techniques have been used by numerous workers in deformed terranes and
are occasionally interpreted as relating to the orientation of an applied tectonic stress,
such as the emplacement of an allochthon. However, two important assumptions must be
discussed before such interpretations may be made. The first of these assumptions
concerns the deformation path followed by naturally deforming rocks. For some
kinematic interpretations to be valid, a progressive (as opposed to a time-separated)
deformation path must be assumed. For example, in the case of the emplaced allochthon,
if fabric asymmetry indicates reverse motion on a 30° plunging lineation, an
interpretation assuming progressive deformation might suggest this fabric was related to
the thrusting. However, if a time-separated deformation path is assumed, there are an
infinite variety of paths that may lead to a certain finite deformation (Jiang and White,
1995; Jiang and Williams, 1999).
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The progressive vs. time-separated deformation path complication to kinematic
analysis may be addressed by invoking corroborating evidence, often in the form of field
data, which allows for a sequence of events and/or a strain gradient to be established. In
this study, the White Horse Creek strain gradient allows this assumption to be
satisfactorally addressed. Fold axes and lineations plunge moderately to the SE south of
White Horse Creek in deformed, though not mylonitized granitoid rocks. North of WHC
still within the same unit, multiple generations of folds are present with axes plunging
gently to the NE-SW. Continuing north, granitoids are mylonitized with stretching
lineations and F2,F3 folds plunging gently SW-NE. These relationships suggest that the
ISA, or instantaneous stretching axis, evolved from an orientation plunging shallowly SE
to one plunging shallowly SW and NE. The occurrence of earlier or later stages of ductile
deformation, however, may not be ruled out.
The second assumption that is owed discussion is based on the theory that every
deforming system has the potential to be characterized by three-dimensional flow. This is
not to say that all deformation is three-dimensional, nor does it mean that twodimensional analyses are not useful. Studies have shown that assuming a twodimensional strain field may increase the likelihood of incorrect interpretation (Lin et al.,
1998; Williams, 2002). Lin (1998) showed that changes in the orientation of the main
stretching lineation in a shear zone indicate the strain field was likely three-dimensional
and deformation likely triclinic. Williams (2002) showed that in some cases, the ISA
(instantaneous stretching axis) may not be parallel to lineations measured in the field.
85
These factors effectively shift the burden toward disproving a three-dimensional
environment of deformation.
The results of this study are consistent with a three-dimensional, evolving strain
field during Late Cretaceous extensional deformation. Microstructural investigation of all
three principle planes for many samples confirms the assumption that the XZ plane is the
dominant plane for asymmetry. Additionally, the XZ planes measured in this study are
characterized by the highest Rf values. However, auxiliary planes did record changes in
strain, suggesting a three-dimensional flow field. Three-dimensional strain analysis
indicates that strains were likely constrictional, and that ellipsoids had prolate
geometeries with maximum extension oriented SW-NE in the final state. Additionally,
the orientation of F2, F3, and F4 fold axes within the mylonitic front suggests constriction
as a first order approximation. In sum, this study (1) acknowledges the assumption that
strain fields are likely three-dimensional, and (2) describes the 3D kinematic evolution of
the strain field during extension.
4.3.2 Kinematic vorticity analysis
The aim of any kinematic vorticity analysis is to quantify the relative
contributions of pure shear (coaxial deformation) and simple shear (non-coaxial
deformation) in a system. Passchier and Trouw (1996) summarize a number of sensitive
vorticity gauges including deformed sets of veins, lattice-preferred orientations, mantled
porphyroclasts, and oblique foliations. This study employs the rigid rotation of
porphyroclasts and the geometry of asymmetric σ-type, β-type, and δ-type tails. It is
generally accepted that rigid objects embedded in a viscous medium will rotate during
86
non-coaxial flow in accordance with the bulk kinematics of the system. Passchier (1987)
showed that during two-dimensional general shear, rigid porphyroclasts whose axial ratio
is above a critical value may become stationary at high strain as they rotate into
parallelism with the asymptotic flow apophyses. Passchier used this critical value, below
which no stable clast orientations exist, as a measure of kinematic vorticity. Simpson and
De Paor (1993) describe the technique for measuring kinematic vorticity using systems of
rigid porphyroclasts containing asymmetric tails. Rf and positive or negative φ are plotted
on a hyperbolic net (Figure 3.10). The cosine of the acute angle between the first
eigenvector (parallel to the reference line, S2 in this study) and the second eigenvector
(forms the limit of the field of backrotation) is Wk, the kinematic vorticity number. The
equation is written:
Wk = cos(v)
where v = angle between eigenvectors
An increasing v value indicates an increase in the contribution of pure shear to the
system. A system completely dominated by pure shear has a Wk of 0, and a system
dominated completely by simple shear has a Wk of 1. General shear describes all values
between 0 and 1. When Wk = .71 the system has received roughly equal contributions
from pure and simple shear (Tikoff & Fossen, 1995).
Kinematic vorticity analysis has been proven to be useful for describing flow
regimes in two-dimensional strain fields characterized by monoclinic symmetry and
steady-state deformation (e.g. Passchier, 1998, Holcombe and Little, 2001). However, a
problem with all determinations of Wk is that it may have been variable over a volume of
87
rock and may have changed with time. As a result, some workers have suggested the term
mean vorticity, or Wm, as a more appropriate description of the result. For simplicity, this
study consistently describes kinematic vorticity as Wk.
Passchier and Trouw (1996) suggest these difficulties may be addressed by
measuring vorticity using a variety of gauges that re-equilibrate at different rates. For
example, LPO in quartz is a gauge which re-equilibrates much faster than a deformed
vein set, particularly if the veins pre-date deformation. This approach seeks to define
changes in Wk during progressive deformation. A variety of gauges applied to a scale
independent sampling and measuring strategy is the most thorough method to date for
determining Wk.
An additional limitation of kinematic vorticity anlaysis is that it is a twodimensional measurement of a three-dimensional flow field. While in many cases it can
be argued that the XZ plane is the dominant asymmetric plane, a two-dimensional
analysis is, by definition, not completely accurate. Successful application of vorticity
measurement techniques to the third dimension has yet to be achieved (Tikoff and
Fossen, 1995). Tikoff and Fossen (1995) have shown that assumptions made during twodimensional analysis are not valid in a three dimensional system. These workers indicate
knowledge of the orientation of the flow apophyses and instantaneous strain axes with
respect to the shear zone boundary is not sufficient for determining three-dimensional
Wk. Despite these assumptions, this study includes the results of scale independent, twodimensional kinematic vorticity analysis. This analysis is useful on account of the
following: (1) This study has produced a detailed account of the environment of
88
deformation, i.e. good understanding has been reached regarding the deformation
mechanisms favored by the participating mineral constituents; (2) This study has tracked
the orientation of the ISA (instantaneous stretching axis) during deformation, using
mineral stretching lineation as a proxy and by performing an Rf/φ analysis on a strain
gradient defined in the field. The final observed orientation of the ISA is parallel to the
mineral lineation, transport direction, and inferred shear zone boundary; (3) This study is
interested in using the results of the analysis for a two-dimensional interpretation of
whether the shear zone was thinning or thickening in the vertical, or Z direction.
4.3.3 Shear sense determinations
Shear sense analysis results
Analysis of macroscopic and microscopic fabrics in the field and in the lab
indicates the kinematics of flow were characterized by sub-horizontal,normal motion
parallel to the plunge of the mineral stretching lineation. On the northern half of the core,
Cape Foulwind and the Buller Gorge, this generally meant top down to the E-NE motion.
In the southern half of the core, WHC and Pike Stream, fabrics suggest both top down to
the SW and top down to the NE shear. In general, these results are consistent with a NESW extension direction
Discussion
Excellent exposure along the coast north and south of White Horse Creek allowed
us to track the orientation of shear sense indicators through the main mylonitic zone
associated with the Pike detachment fault. Models describing the structural evolution of
89
the mylonitic front associated with metamorphic core complexes make predictions
regarding the orientation and distribution of kinematic indicators as well as the gross
structure of the mylonitic zone (see Chapter 2 for discussion of models). Detailed
observation of kinematic indicators in the field and in samples examined microscopically
in this study allow for comparison with these models, particularly the model proposed by
Reynolds and Lister (1990) (Figure 2.2). In this model, the mylontic front is folded
asymmetrically such that a shallow dipping mylonitic zone has synthetic kinematics with
the main detachment fault, and a steeper back dipping limb displays opposite (or apparent
reverse) kinematics. Reynolds et al. (1990) suggest the apparent reverse kinematic
indicators are evidence the mylonitic front was folded after the crystallization of
kinematic information. Our results suggest some agreement with this model (Figure 3.2).
Between site WHC1, the first mylonitic exposure driving north along the Coast Road,
and site WHC11 structural and kinematic data suggests a geometry consistent with the
folded geometry proposed by Reynolds and Lister (1990). Site WHC1 is folded at the
mesoscale about a W-plunging axis and contains top down to the SSW kinematics. Site
WHC11 dips to the NNW and contains NE-plunging mineral lineations. Kinematic
indicators from this site are consistent with reverse, top to the SW motion. The mylonitic
front disappears below the surface north of this site, re-emerging at site WHC4 where it
dips to the SSW. The reverse-sense conclusion at site WHC11 is drawn from kinematic
indicators observed in the field and checked under the microscope.
North of site WHC11, the mylonitic front is shallowly warped about NE-SW
plunging axes, and contains both SW and NE shallowly plunging mineral lineations.
90
Kinematic indicators in this region are consistent with top down to the SW and top down
to the NE normal motion. This geometry may suggest the influence of syn-extensional
magmatism on the gross geometry and kinematics of the core complex. Buoyant, granitic
magmatism is known to have accompanied extension (e.g. Buckland Granite). Synextensional magmatism during exhumation is known to “bow” the lower plate during
extension, often resulting in a dome-and-basin pattern (e.g. Lister and Davis, 1988). This
process may help explain NE plunging lineations and top down to the NE kinematic
indications in a zone dominated by top to the SW shear. Thus, the proposed geometry and
kinematics of the mylonitic front associated with the Pike detachment fault is in
agreement with some features of published models as well as generally accepted styles of
extensional deformation.
Exposure in the northern half of the core allowed us to analyze fabrics for
kinematic interpretation at Cape Foulwind and in the Buller Gorge. The level of
deformation in the north does not equal the level observed in the south on a penetrative
scale, however isolated, thin mylonitic zones are observed. These mylonites contain S/C
fabrics and rotated porphyroclasts consistent with top down to the NE motion. The
Foulwind Granite (megacrystic variety) is affected by N-dipping foliations and mineral
lineations that plunge from E to N. Kinematics are consistently top down to the E-NE,
save for one site near the Foulwind lighthouse where a fold reverses the kinematic trend.
The exposure on the roadside on the southern bank of the Buller River reveals only one
site with a fabric suitable for kinematic analysis. Here, a well developed S/C fabric
91
indicates top down to the NE normal motion. These results are consistent with top down
the NE motion on the Ohika detachment fault.
4.3.4 Results of kinematic vorticity analysis
Thin section, outcrop, and multiple outcrop scale measurements of rigid particles
in a once viscous matrix enabled this study to report on Wk within the main mylonitic
zone associated with the Paparoa metamorphic core complex (Figure 3.10). The
distribution of the 175 plagioclase feldspar clasts measured allowed for determination of
the first and second eigenvectors of flow (Simpson & De Paor, 1993). The limit of the
field of backrotation, bound by the second eigenvector, displays a range between 38° and
42°. The greater the area displayed by the field of backrotation, the greater the
contribution from pure shear to the system. A second eigenvector at 90° to the first
suggests a Wk of 0. Thus, our results indicate 0.74 < Wk < 0.78, where Wk = 0.71 (Tikoff
& Fossen, 1995) describes a shear zone which has received equal input from pure and
simple shear.
Discussion
These results suggest that the main mylonitic zone within the core of the PMCC was
characterized, during its final phase of movement in the ductile field, by vertical thinning
and sub-horizontal stretching. A value for Wk between 0.74 and 0.78 suggests conditions
approximated general shear, however simple shear seems to have been the dominant
process. This result proves ductile thinning of the middle crust was an important
mechanism of extension during early stages of deformation.
92
4.4 SUMMARY AND CONCLUSIONS
Efforts made by this study to quantify finite strain state, infer strain paths and
establish the kinematics of flow complement a rigorous structural analysis and together
these data contribute to a near complete understanding of structural, kinematic and
deformational processes at multiple length scales. This study shows that the dominant
deformation mechanisms at the grain scale are grain boundary migration and dynamic
recrystallization in quartz and rigid rotation accompanied by microfaulting in feldspars.
Strain analysis shows that Rf values for all feldspars are generally close to 1 with no
significant spatial variation. Rf/φ analyses using quartz show a quantitative increase in
strain with proximity to the zone dominated by mylonitic fabrics. Additionally, quartz
analyses indicate a finite strain ellipsoid characterized by NE-SW horizontal stretching
and vertical shortening. Quartz results plotted on a Flinn diagram indicate that three
dimensional strains were likely constrictional, consistent with qualitative results
(structural geometry of F2,F3,F4) interpreted from field data. Kinematic vorticity analysis
indicates that the main mylonitic zone (WHC) was characterized by general shear (0.74 <
Wk < 0.78) though simple shear was dominant. The range of Wk indicates the main
mylonitic zone was characterized by thinning in the vertical plane and NE-SW, subhorizontal extension. These results are interpreted here as an indication that ductile
thinning of the middle crust was an important mechanism during Late Cretaceous
extension.
The data and interpretations presented in this section are consistent with field
studies in other extensional metamorphic core complexes (Fletcher and Bartley, 1994). In
93
the central Mojave metamorphic core complex (CA, USA) Fletcher and Bartley (1994)
show, using a combination of finite strain and fold orientation, constrictional strains
produced by a non-coaxial shear zone. Syn-mylonitic folds have orientations parallel to
the stretching lineation in the main shear zone, suggesting a component of compression in
the Y direction. These workers also show that the geometry of folds in a vertical strain
gradient evolves from upright and open and tight and isoclinal (also consistent with this
study and others e.g. Harris et al., 2002). Hence, the results presented here and elsewhere
make predictions about structural geometries and strain patterns in continental
extensional terranes, or at least in metamorphic core complexes. These may include, but
are not restricted to:
•two-dimensional, non-coaxial strain
•three-dimensional, constrictional strain
•superposed, extension parallel folding
•ductile shear zones characterized by vertical thinning
94
CHAPTER 5: Thesis Summary and Conclusions
5.1 SUMMARY AND CONCLUSIONS
This study adds structural and kinematic data from the metamorphic core within
the Paparoa Metamorphic Core Complex to a growing body of knowledge regarding late
Cretaceous extension in western New Zealand. This thesis describes the geometry,
kinematics and sequence of deformation in the middle crust, as it was exhumed during
regional extension between ∼112-84 Ma. The methods used to characterize the style of
extensional deformation incorporate field data and lab analyses including: (1) a structural
analysis of structures recorded by mid-crustal core rocks; (2) a rigorous kinematic
analysis of ductile and brittle phases of deformation including kinematic vorticity; (3) a
detailed analysis of ductile and brittle deformation mechanisms as well as threedimensional strain analysis.
Results from the structural analysis indicate five events (D1-D5) of deformation
within the core of the Paparoa Metamorphic Core Complex were produced during
regional extension on the Pacific margin of Gondwana. D1-D4 comprises a ductile history
characterized by polyphase folding and fabric development in mylonitic (southern
domain), gneissic (central core zone) and granitic (northern domain) units. D5 describes
semi-brittle and brittle faults that cut all previously formed ductile fabrics.
In the southern half of the core, D1-D4 produced a 4 km long section of
interfolded mylonites and host rocks. Within the highest strain zone, three generations of
folds (F2,F3,F4) have axes parallel to the orientation of the mineral stretching lineation
and regional extension direction. Fold axes and mineral lineations oriented oblique (∼90°)
95
to the extension direction are recorded by lower strained rocks within the WHC strain
gradient. Sense of shear analysis of mylonitic fabrics indicates sub-horizontal stretching
during top down to the NE and SW normal motion. Kinematic vorticity analysis of D2
mylonites performed on a suite of three sites in the field and a fourth on the microscale
indicate 0.74 < Wk < 0.78. This result is consistent with a shear zone that has
experienced thinning in the vertical (XZ) plane. Two-dimensional kinematic analyses,
together with the geometry of D1-D4 structures, suggest a three-dimensional environment
characterized by constrictional strain where the direction of maximum shortening (Z axis)
is vertical and maximum extension (X axis) is sub-horizontal, NE-SW. Kinematic
analysis of brittle fault-slip data indicates D5 was also characterized by vertical
shortening and NE-SW sub-horizontal extension. We interpret these results as evidence
that structural and kinematic parameters, namely sense of shear and the orientation of
maximum extension and shortening axes, remained constant during the transition from
ductile to brittle deformation in the middle crust during extension.
Results from this study are consistent with ductile thinning of the middle crust
within narrow focused zones as a dominant mechanism for extension under ductile P-T
and strain rate conditions. This style of deformation contrasts sharply with the style of
post-orogenic extension characterized by weakening of the middle crust by partial
melting during crustal thickening (Shuswap Metamorphic Core Complex, BC). While
both core complexes developed after a period of crustal thickening, deformation in the
Shuswap MCC is distributed over a broad, diffuse zone and directly related to the
collapse of the upper crust over a weak layer in the middle crust. As a result of these
96
observations, weakening of the middle crust is not considered to be the driving force
behind late Cretaceous extension in the PMCC.
Regional extension coincided with a major change in plate boundary dynamics
that affected the entire Pacific margin of Gondwana in the mid-late Cretaceous. We
suggest the narrow, focused style of ductile thinning in the mid-crustal core of the PMCC
is primarily the result of changing regional stresses in an extending column of lithosphere
characterized by a strong lower crust and a plastic middle crust. Additionally, we suggest
extension was not controlled by buoyancy forces in a weak, gravitationally unstable
middle-crust. An extensional model driven by plate boundary change is supported,
additionally, by isotopic analyses of hydrothermally altered mylonites in the footwall of
the Pike detachment fault (Tulloch and Palmer, 1990). A sericite age of ∼85 Ma obtained
from these rocks has been suggested to represent the last stage of motion on the Pike
detachment just prior to continental rifting and the opening of the Tasman Sea. Thus, the
driving force behind late Cretaceous extension and the exhumation of mid-crustal rocks
in the PMCC may have been the same force that drove continental rifting and the
generation of new ocean crust.
5.2 SUGGESTIONS FOR FUTURE WORK
Future work on extensional deformation in western New Zealand should focus on
establishing the link between the PMCC (extension in the middle crust) and the Doubtful
Sound Shear Zone, an extensional shear zone that cuts lower crustal rocks. Extensional
processes on a full crustal scale are not completely understood. Questions to pursue
include: How do we reconcile a SW directed, dominant extension direction in the middle
97
crust and a NE directed, dominant extension in the lower crust? If no other detachments
are found, a full-crustal “conjugate” system may be a possible model to test. Efforts
should be focused on attaining a better understanding of extensional processes between
the lower and middle crust.
Lastly, conclusions drawn in this study regarding indicate a major plate boundary
change as the dominant mechanism driving Late Cretaceous extension in Western New
Zealand. If this is true, then one must ask why a spreading center was born on the Pacific
margin of Gondwana at that time? One hypothesis to test might focus on the end of
subduction related magmatism coeval with the accretion of an island arc terrane in the
Early Cretaceous. Slab break-off at this time may have been an important process that
perturbed convection currents in the upper mantle, and caused the plate boundary to
reorganize.
98
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114
APPENDICES
115
APPENDIX A: KINEMATIC INDICATORS
116
Figure A-2-3. This sample from the Cape Foulwind transect shows the characteristic,
megacrystic, protomylonitic fabric within the Foulwind Granite. An S-C fabric is
defined by aligned biotite grains indicating dextral motion
119
APPENDIX B: IGNS PETLAB DATABASE SPREADSHEET
128
03-cf-1b
03-cf-3a
03-whc-4b
03-br-8
03-br2a-xy
03-cf-2a
03-cf-2
03-cf-4b
03-cf-1a
03-br2a-yz
03-cf-3b
03-ps-3
03-ps-2
03-br2a-xz
03-whc-17
03-ps-4
03-whc-8
03-br-2
03-whc-4a
03-ch-7
COLL_TYPE COLL_NUM
a
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
COLLECTORS
aa
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
COLL_DATE
2-Jan-2004
1/20/07
1/20/07
1/30/07
1/21/07
1/21/07
1/20/07
1/20/07
1/20/07
1/20/07
1/21/07
2/2/07
1/20/07
2/2/07
1/21/07
30-Jan-2007
2-Feb-2007
30-Jan-2007
21-Jan-2007
30-Jan-2007
28-Jan-2007
FIELDNUMBEIN_SITU
a
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
03-cf-1b
03-cf-3a
03-whc-4b
03-br-8
03-br2a-xy
03-cf-2a
03-cf-2
03-cf-4b
03-cf-1a
03-br2a-yz
03-cf-3b
03-ps-3
03-ps-2
03-br2a-xz
03-whc-17
03-ps-4
03-whc-8
03-br-2
03-whc-4a
03-ch-7
LOC_TYPE
M
SHEET
A44
K29
K29
K30
K29
K29
K29
K29
K29
K29
K29
K29
K31
K31
K29
K30
K31
K30
K29
K30
K29
EAST
1
2382000E
2382000E
2378000E
2402000E
2403000E
2382000E
2382000E
2382000E
2382000E
2403000E
2382000E
2385000E
2385000E
2403000E
2377000E
2385000E
2378000E
2403000E
2378000E
2379000E
NORTH
1
5938000N
5937000N
5913000N
5929000N
5929000N
5938000N
5938000N
5938000N
5938000N
5929000N
5937000N
5888000N
5888000N
5929000N
5911000N
5888000N
5912000N
5929000N
5913000N
5921000N
COUNTRY
Afghanistan
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
LOC_METHOD
Surveyed
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
PRECISION
0.1
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
50
SITE_DESCRIPTION
ROCK_DESCRIPTIO
a
a
Headland north of Siberia B megacrystic granite
Southern end of Siberia Baymegacrystic granite
WHC beach
porphyroclastic mylo
Buller Gorge rd.
deformed granite
Buller Gorge rd.
deformed granite
Siberia Bay
deformed granite
Siberia Bay
megacrystic granite
South of Foulwind lighthous megacrystic granite
South of Foulwind lighthous megacrystic granite
Buller Gorge rd.
deformed granite
Southern end of Siberia Baymylonite
within Pike Stream
mylonite
within Pike Stream
deformed granite
Buller Gorge rd.
deformed granite
WHC beach
mylonite
within Pike Stream
mylonite
WHC beach
granitic gneiss
Buller Gorge rd.
deformed granite
WHC beach
deformed granite
Charleston Coast
deformed granite
STRATIGRAPHIC_UNIT
a
Foulwind Granite
Foulwind Granite
Charleston Metamorphic Group
Berlins Porphyry, Railway Quartz Diorite
Buckland Granite
Foulwind Granite
Foulwind Granite
Foulwind Granite
Foulwind Granite
Buckland Granite
Foulwind Granite
Charleston Metamorphic Group
Charleston Metamorphic Group
Buckland Granite
Charleston Metamorphic Group
Charleston Metamorphic Group
Charleston Metamorphic Group
Buckland Granite
Charleston Metamorphic Group
Charleston Metamorphic Group
STRATAGE_MIN
Quaternary
Carboniferous
Carboniferous
Cretaceous
Cretaceous
Cretaceous
Carboniferous
Carboniferous
Carboniferous
Carboniferous
Carboniferous
Carboniferous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
STRATAGE_MAX
Quaternary
Carboniferous
Carboniferous
Cretaceous
Cretaceous
Cretaceous
Carboniferous
Carboniferous
Carboniferous
Carboniferous
Carboniferous
Carboniferous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
ROCK_CODESAMPLE_TYPANALYSIS_T ARCHIVE_SIT
a
a
a
Gracefield
grnt
TS
other
Other
grnt
TS
other
Other
mylon
TS
other
Other
grnt
TS
other
Other
grnt
TS
other
Other
grnt
TS
other
Other
grnt
TS
other
Other
grnt
TS
other
Other
grnt
TS
other
Other
grnt
TS
other
Other
grnt
TS
other
Other
mylon
TS
other
Other
mylon
TS
other
Other
grnt
TS
other
Other
mylon
TS
other
Other
mylon
TS
other
Other
gneiss
TS
other
Other
grnt
TS
other
Other
mylon
TS
other
Other
TS
other
Other
gneiss
JOBNUM
a
COMMENTS_REPORTS_PAPERS
a
a
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
AZIMUTH
DIP
1
96
220
239
39
151
44
56
82
54
88
47
65
175
22
45
206
102
64
1
1
49
85
75
56
5
77
84
38
73
80
83
90
28
80
79
76
58
DIP_DIR
N
N
NW
NW
SE
SW
NW
NW
SE
NW
N
NW
SE
W
SE
NW
SE
NE
90
81 E
MARKED
Topside
PETROGRAPHY_BY
a
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
PET_DATE
2-Jan-2004
HAND_SPECIMEN_DESC
a
megacrystic granite
megacrystic granite
porphyroclastic mylonite
deformed granite
deformed granite
deformed granite
megacrystic granite
megacrystic granite
megacrystic granite
deformed granite
mylonite
mylonite
deformed granite
deformed granite
mylonite
mylonite
granitic gneiss
deformed granite
deformed granite
deformed granite
MINERALOGY_DESCRIPTION
a
TEXTURAL_DESCRIPTION
a
Plagioclase feldspar + quartz + biotite +/- mus megacrystic granite
Plagioclase feldspar + quartz + biotite +/- mus megacrystic granite
Plagioclase feldspar + quartz + biotite +/- mus porphyroclastic mylonite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus megacrystic granite
Plagioclase feldspar + quartz + biotite +/- mus megacrystic granite
Plagioclase feldspar + quartz + biotite +/- mus megacrystic granite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus granitic gneiss
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
03-cf-6
03-cf-4
03-whc-15b
03-whc-11
03-whc-15a
03-ch-6a
03-whc-19b
03-whc-19
03-ps-1
03-whc-16
03-br-3
03-br-4
COLL_TYPE COLL_NUM
a
P
P
P
P
P
P
P
P
P
P
P
P
COLLECTORS
aa
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
03-cf-6
Yes
03-cf-4
Yes
03-whc-15b Yes
03-whc-11 Yes
03-whc-15a Yes
03-ch-6a
Yes
03-whc-19b Yes
03-whc-19 Yes
03-ps-1
Yes
03-whc-16 Yes
03-br-3
Yes
03-br-4
Yes
COLL_DATE FIELDNUMBEIN_SITU
2-Jan-2004 a
Yes
20-Jan-2007
20-Jan-2007
30-Jan-2007
30-Jan-2007
30-Jan-2007
28-Jan-2007
30-Jan-2007
30-Jan-2007
2-Feb-2006
30-Jan-2007
21-Jan-2007
21-Jan-2007
LOC_TYPE
M
SHEET
A44
K29
K29
K30
K30
K30
K29
K30
K30
K31
K30
K29
K29
EAST
1
2379000E
2382000E
2378000E
2378000E
2378000E
2379000E
2377000E
2377000E
2385000E
2378000E
2405000E
2403000E
NORTH
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
New Zealand
COUNTRY
1 Afghanistan
5921000N
5938000N
5913000N
5912000N
5913000N
5921000N
5911000N
5911000N
5888000N
5914000N
5928000N
5928000N
LOC_METHOD
Surveyed
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
Map - 1:50,000 scale
ROCK_DESCRIPTIO
a
Tauranga Bay
megacrystic granite
South of Foulwind lighthous megacrystic granite
WHC beach
mylonite
WHC beach
mylonite
WHC beach
mylonite
Charleston Coast
deformed granite
WHC beach
mylonite
WHC beach
mylonite
within Pike Stream
protomylonite
WHC beach
protomylonite
Buller Gorge rd.
deformed granite
Buller Gorge rd.
deformed granite
PRECISION SITE_DESCRIPTION
0.1 a
50
50
50
50
50
50
50
50
50
50
50
50
Other
Other
Other
Other
Other
Other
Other
Other
Other
Other
Other
Other
STRATAGE_MIN STRATAGE_MAX ROCK_CODESAMPLE_TYPANALYSIS_T ARCHIVE_SIT
Quaternary
Quaternary
a
a
a
Gracefield
other
other
other
other
other
other
other
other
other
other
other
other
STRATIGRAPHIC_UNIT
a
gneiss
grnt
mylon
mylon
mylon
grnt
mylon
mylon
mylon
mylon
grnt
grnt
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
Carboniferous
Carboniferous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Carboniferous
Carboniferous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Cretaceous
Foulwind Granite
Foulwind Granite
Charleston Metamorphic Group
Charleston Metamorphic Group
Charleston Metamorphic Group
Charleston Metamorphic Group
Charleston Metamorphic Group
Charleston Metamorphic Group
Charleston Metamorphic Group
Charleston Metamorphic Group
Berlins Porphyry, Railway Quartz Diorite
Berlins Porphyry, Railway Quartz Diorite
JOBNUM
a
COMMENTS_REPORTS_PAPERS
a
a
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
Simonson & Klepeis, in prep.
AZIMUTH
1
288
42
230
36
240
290
220
45
40
250
241
52
DIP
SE
NW
NW
NW
NE
NW
SE
SE
NW
SW
SE
DIP_DIR
1N
36
64
74
74
84
50
86
90
78
75
72
81
MARKED
Topside
PETROGRAPHY_BY
a
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
W.C. Simonson
PET_DATE
2-Jan-2004
MINERALOGY_DESCRIPTION
a
TEXTURAL_DESCRIPTION
a
HAND_SPECIMEN_DESC
a
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus protomylonite
Plagioclase feldspar + quartz + biotite +/- mus protomylonite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus deformed granite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus mylonite
Plagioclase feldspar + quartz + biotite +/- mus megacrystic granite
Plagioclase feldspar + quartz + biotite +/- mus megacrystic granite
megacrystic granite
megacrystic granite
mylonite
mylonite
mylonite
deformed granite
mylonite
mylonite
protomylonite
protomylonite
deformed granite
deformed granite
APPENDIX C: STRUCTURAL DATA
137
02WHC1
strike
115
90
100
142
147
157
142
152
140
125
115
130
105
140
162
156
165
150
158
162
95
118
152
dip
40
87
70
34
32
25
15
20
15
30
70
49
62
30
35
47
15
20
24
22
8
15
28
foliation
dip direction
sw
s
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
sw
lineation
trend
158
169
175
188
187
177
182
179
172
190
180
190
167
180
165
182
plunge
14
10
5
15
15
26
11
12
2
43
22
20
1
5
6
7
02WHC2-4
strike
204
196
207
187
203
196
206
208
200
199
225
198
190
205
195
205
196
186
52
60
48
85
79
70
212
94
212
185
185
dip
21
19
20
15
18
10
24
20
15
17
8
11
12
20
16
15
18
17
43
21
30
21
22
43
26
20
32
15
16
foliation
dip direction
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
s
s
s
s
s
s
n
s
n
w
w
plunge
245
225
231
229
232
237
228
235
225
trend
lineation
trend
10
9
19
5
20
14
7
13
16
6
14
16
24
10
15
9
11
13
8
15
9
8
12
3
6
9
9
4
5
8
02WHC2-4
210
218
192
225
239
224
226
212
215
205
209
208
202
221
225
229
240
235
225
230
252
223
234
232
230
222
228
224
220
218
75
65
13
80
5
0
240
285
13
75
24
strike
lineation
plunge
25
30
40
32
24
35
64
15
40
44
40
dip
foliation
plunge
trend
15
38
40
15
16
30
20
02WHC5,6
8
16
13
11
18
26
11
23
15
208
170
187
210
220
135
115
se
se
se
se
se
e
se
s
se
s
se
strike
35
46
40
24
18
9
20
6
11
36
20
26
27
27
43
47
48
19
33
35
30
7
15
55
25
26
35
32
36
37
dip
03WHC7-12
85
72
122
101
41
49
44
310
301
90
59
72
79
57
77
47
76
90
110
56
32
36
282
15
7
65
78
66
9
68
foliation
lineation
plunge
162
138
131
149
138
174
160
75
45
154
325
125
138
146
154
143
162
200
143
135
125
trend
85
85
42
34
10
9
10
54
59
2
11
11
10
3
30
24
36
26
20
36
14
44
36
51
50
dip
plunge
foliation
strike
20
14
17
32
20
11
15
27
37
11
10
30
15
22
15
20
33
30
22
20
10
7
16
17
03WHC14,15
146
46
207
217
219
85
66
201
170
97
49
65
120
85
77
205
205
192
80
110
160
203
184
210
14
4
17
8
9
10
9
7
2
3
9
8
19
7
17
7
6
7
14
13
12
17
7
3
5
2
trend
lineation
228
46
260
219
223
212
210
211
45
206
219
224
228
60
235
236
233
225
221
222
226
232
230
220
217
40
plunge
34
66
25
218
230
215
211
205
207
220
207
30
39
52
41
211
48
32
38
219
223
212
210
211
trend
lineation
dip
9
4
16
2
10
21
20
17
17
3
0
2
5
1
8
2
11
10
6
8
9
10
9
7
foliation
strike
5
4
15
5
14
21
24
20
17
19
15
5
6
2
6
1
11
3
20
19
9
17
9
7
19
9
03N of WHC15
320
349
345
115
89
121
152
152
90
120
65
205
300
24
348
313
338
30
23
355
291
63
160
292
181
182
03WHC11
strike
03WHC16
strike
100
0
85
320
322
293
324
310
340
243
156
60
87
146
46
207
132
dip
dip
foliation
foliation
35
12
16
15
14
11
11
6
10
18
26
20
20
20
14
17
51
plunge
plunge
2
7
6
16
14
16
7
9
8
12
14
4
35
17
lineation
trend
205
60
48
46
57
43
28
44
30
lineation
trend
228
228
46
185
260
dip
320
0
358
316
315
80
45
310
321
311
317
288
61
252
276
316
strike
foliation
strike
32
30
6
21
21
12
15
19
21
11
25
11
24
5
15
34
32
26
20
19
22
18
32
27
15
12
14
17
22
20
CF1,4
42
45
15
267
6
80
55
70
95
295
70
90
315
265
330
270
75
58
46
11
16
24
48
312
322
291
320
185
216
274
dip
trend
56
70
54
90
16
65
65
110
61
65
40
340
29
240
244
215
250
230
256
237
247
14
37
37
34
75
62
34
15
34
plunge
17
17
14
5
15
7
7
2
25
31
15
27
17
10
trend
40
58
62
42
42
47
213
225
40
17
47
43
37
233
plunge
lineation
15
19
11
17
11
11
20
24
25
19
29
22
43
16
19
15
10
15
10
21
19
6
15
21
4
30
35
5
34
21
6
24
5
16
15
15
19
22
16
11
14
11
9
19
13
18
strike
CF2
52
36
25
27
22
19
19
27
26
24
32
27
32
31
27
30
31
29
33
dip
foliation
38
36
21
23
21
19
22
30
27
27
32
27
31
32
36
32
31
34
37
trend
55
36
45
37
85
56
47
45
42
37
35
45
45
41
52
52
44
46
52
plunge
lineation
300
331
10
355
335
316
308
295
315
340
280
355
332
298
303
307
312
311
320
dip
CF3
strike
plunge
23
35
16
15
17
34
7
11
16
17
27
trend
56
57
55
62
62
63
46
46
52
46
35
310
315
320
292
346
315
355
336
338
335
322
23
26
16
11
17
32
9
12
16
16
27
foliation
lineation
CF5
strike
48
60
51
60
55
54
62
72
56
60
70
80
66
67
61
76
73
82
84
64
64
dip
26
40
20
36
20
32
28
34
37
37
27
40
37
42
46
46
43
30
32
53
55
foliation
trend
75
85
85
100
77
75
85
65
74
82
79
83
72
84
74
77
plunge
lineation
15
22
19
15
14
29
15
10
15
4
17
13
3
5
11
34
CF6
strike
40
26
25
24
23
36
27
dip
foliation
plunge
65
51
62
55
64
72
62
trend
100
89
73
84
92
84
70
lineation
29
36
9
11
11
11
5
trend
24
23
22
15
22
17
13
22
20
20
11
20
20
244
plunge
lineation
dip
25
25
21
26
23
18
14
12
12
25
17
26
26
5
foliation
strike
59
30
24
23
17
21
19
16
17
16
27
16
26
27
12
22
BR 2
35
273
264
252
271
265
274
273
262
262
266
276
266
271
68
66
strike
BR6
42
31
32
31
dip
foliation
dip
foliation
210
199
194
196
stike
7
24
20
21
5
4
18
5
11
13
16
6
30
10
21
25
24
20
22
19
CH3-8
325
265
270
125
40
0
80
76
348
280
328
325
260
195
252
272
262
262
267
270
4
326
78
281
253
32
15
25
30
34
45
10
trend
lineation
plunge
59
85
25
45
221
225
90
96
87
93
74
54
70
57
52
14
358
352
348
336
112
CH3-8
11
22
23
2
8
4
12
7
14
13
3
5
0
15
20
26
24
21
23
16
15
14
25
dip
96
53
strike
20
16
19
16
14
24
25
35
22
16
16
16
20
16
9
14
CH9-10
135
148
120
90
101
112
68
105
80
55
26
85
42
30
42
10
foliation
CH1
dip
9
30
11
27
12
16
15
24
17
20
16
foliation
trend
strike
89
245
126
95
102
192
120
89
84
116
111
plunge
169
32
28
185
193
216
198
186
198
202
200
lineation
11
15
6
27
12
13
14
14
16
19
15
CH2
strike
260
265
246
275
315
266
252
310
350
278
306
284
295
307
282
341
338
348
325
310
270
dip
46
19
16
11
34
24
9
21
35
31
27
26
26
27
13
25
28
26
24
32
26
foliation
plunge
30
21
7
21
21
12
24
27
4
20
32
20
21
22
12
8
20
25
22
20
25
lineation
trend
22
16
356
9
350
330
356
27
29
55
46
54
32
60
52
285
55
52
45
56
8
strike
225
180
255
185
190
320
322
338
180
202
175
188
325
186
315
192
176
192
Pike Stream
dip
10
30
37
53
35
37
40
17
42
30
22
36
26
19
24
34
40
36
foliation
trend
lineation
plunge
215
223
196
210
223
200
214
203
205
210
210
206
215
210
230
203
190
191
Pike Stream
31
10
16
14
27
30
37
12
27
15
16
10
24
10
27
10
11
11
plunge
30
18
126
280
279
281
2
36
21
trend
CH1-2 F2,3
10
15
31
11
16
12
4
36
14
plunge
245
79
50
226
240
59
224
220
238
270
225
235
200
202
23
225
235
trend
All F3 kinks
11
5
9
11
11
1
10
9
35
39
37
20
13
18
7
17
17
axes
axes
plunge
303
252
263
trend
N of WHC3 F3
7
17
22
plunge
245
79
50
226
240
59
224
220
trend
WHC11-4 F3
11
5
9
11
11
1
10
9
plunge
231
225
250
260
268
245
255
230
trend
WHC3-4 F2
11
30
22
24
9
12
19
16
axes
axes
axes
14
18
18
14
7
7
14
16
16
5
15
17
21
7
17
22
17
12
20
24
248
265
275
305
195
252
250
283
264
310
285
305
292
303
252
263
228
21
235
255
WHC7-10 F3
plunge
36
35
29
21
33
10
20
12
24
26
trend
axes
114
110
120
125
136
55
30
165
172
124
WHC 1
Sense
of Slip
NR
NL
NR
NR
NR
NL
NL
NL
NR
NR
NL
NR
NL
NR
NL
NR
NR
NL
NL
NR
Fault
Strike
145
120
128
142
130
335
355
155
162
110
168
304
316
120
138
141
116
122
132
314
Fault
Dip (rhr)
51
48
46
68
67
80
75
87
21
59
51
74
66
46
46
40
75
56
57
80
Striae
Trend
240
45
240
265
335
350
42
115
255
245
105
50
45
222
222
235
225
119
222
44
Striae
Plunge
51
45
44
64
49
56
70
87
21
50
37
73
66
45
46
41
75
51
57
80
T-axis
Trend
237
138
49
242
263
39
74
243
74
219
358
38
46
216
225
53
210
174
222
44
T-axis
Plunge
6
11
0
22
23
28
29
44
24
10
4
29
21
1
1
5
30
12
12
35
P-axis
Trend
35
37
319
29
14
278
283
67
257
332
92
207
227
312
118
257
19
68
42
224
P-axis
Plunge
84
44
79
64
41
45
58
45
66
65
39
61
69
84
87
85
59
51
78
55
WHC 10
Sense
of Slip
NL
NL
NL
NL
NL
NR
NL
NL
NL
NL
CH7 fan
Sense
of Slip
NR
NL
NL
NR
NR
NR
NL
NL
NR
Fault
Strike
Fault
Strike
290
72
278
287
230
205
206
330
94
97
123
149
152
110
130
115
134
124
147
Fault
Dip (rhr)
Fault
Dip (rhr)
67
60
76
78
60
60
63
50
68
76
58
28
29
45
40
67
40
55
63
Striae
Trend
Striae
Trend
20
123
290
298
320
325
267
320
104
119
233
232
218
262
263
226
213
200
260
Striae
Plunge
Striae
Plunge
67
53
41
41
60
56
60
48
24
56
57
28
27
25
32
66
40
55
61
T-axis
Trend
T-axis
Trend
20
146
335
343
320
307
286
15
144
163
221
54
46
55
65
211
38
208
245
T-axis
Plunge
T-axis
Plunge
22
12
17
18
15
14
17
6
1
24
13
17
17
12
10
22
5
10
17
P-axis
Trend
P-axis
Trend
200
26
230
238
140
79
144
277
53
41
4
224
194
309
312
10
171
62
34
P-axis
Plunge
P-axis
Plunge
68
67
39
38
75
70
69
52
33
49
74
73
70
53
66
67
83
78
70
CF1 block
Sense
of Slip
TR
NL
NL
NR
NL
NL
NL
NR
NR
NL
NL
NR
NL
NL
NR
NL
NR
NR
NR
NR
NL
NL
NL
NL
NR
Fault
Strike
123
218
279
15
20
28
31
185
291
219
22
192
172
24
282
32
78
79
84
80
24
32
30
62
65
Fault
Dip (rhr)
30
49
38
68
50
62
51
80
60
50
53
70
17
45
86
43
40
32
30
42
45
43
53
22
36
Striae
Trend
140
239
290
200
60
85
80
346
82
223
70
22
175
63
103
42
238
242
232
235
63
42
35
55
211
Striae
Plunge
10
22
8
29
37
58
43
61
40
5
45
61
1
32
32
10
16
10
17
21
32
10
6
2
22
T-axis
Trend
110
90
139
151
265
106
101
297
49
79
92
311
11
266
53
253
31
38
33
29
266
253
252
256
10
T-axis
Plunge
47
11
27
5
1
16
2
30
6
23
4
29
42
7
20
23
20
28
24
16
7
23
21
41
18
P-axis
Trend
343
192
255
244
357
331
6
66
147
184
353
77
158
9
152
4
277
273
264
278
9
4
354
35
250
P-axis
Plunge
29
47
41
33
62
68
68
48
54
31
67
47
43
61
24
40
47
47
55
51
61
40
30
41
57
CF1 reg
Sense
of Slip
NR
NL
NL
NR
NL
NL
NR
NR
NR
NR
NL
NR
NR
NL
NL
NR
NR
NR
NR
Fault
Strike
97
310
295
190
20
355
327
322
65
56
75
87
284
325
334
180
244
103
86
Fault
Dip (rhr)
30
19
35
50
34
35
80
82
35
34
37
35
74
67
54
14
24
44
39
Striae
Trend
231
12
12
328
45
60
204
222
167
159
117
273
16
34
10
342
352
248
251
Striae
Plunge
23
17
34
39
16
32
76
80
34
33
27
6
74
66
39
4
23
29
12
T-axis
Trend
36
199
197
124
248
250
67
54
342
334
316
62
14
49
38
150
167
44
43
T-axis
Plunge
20
28
10
1
23
12
45
46
10
11
14
33
29
22
2
39
22
10
24
P-axis
Trend
263
359
346
33
10
23
231
231
191
182
75
301
193
251
305
356
5
298
288
P-axis
Plunge
62
61
78
64
51
73
44
44
78
77
62
38
61
67
59
48
67
58
44
CH6-7
Sense
of Slip
NL
NR
NL
NR
NR
Fault
Strike
351
338
332
285
310
Fault
Dip (rhr)
18
29
19
12
19
Striae
Trend
49
70
50
57
52
Striae
Plunge
15
29
19
9
19
T-axis
Trend
237
249
233
230
229
T-axis
Plunge
29
16
26
36
26
P-axis
Trend
36
72
44
66
58
P-axis
Plunge
59
74
63
53
63