Craig Steven Alford MSc thesis abstract

Thesis Title: 
"Tectonic" Magnetic Fabrics in Pure and Simple Shear: Experimental Investigations
Craig Steven
Alford
MSc
1988

Triaxial compression tests were preformed such that changes in the magnetic susceptibility anisotropy with strain would be represented by experimental approximations of simple shear and pure shear.  Both types of tests were performed on artificial materials of high magnetic susceptibility at room temperature and atmospheric pore fluid pressure.  Experimental displacement-rates and strain-rates were computer controlled during testing.

Two different shear zone materials were employed for the "simple shear" testing, a sand-cement mixture and a calcite-cement mixture.   Three series of simple shear tests were conducted on the sand-cement material at various confining pressures; Series A, at 0.689 kbars, Series B at 1.0 kbar and Series C at 1.5 kbars.  Two series of simple shear tests were conducted on the calcite-cement material, Series 1, at 1.0 kbar confining pressure and Series 2 at 1.5 kbars Pc.  For both materials a constant axial displacement-rate of 5.0 x 10-6 inches.  s-1 (corresponding to a slip displacement-rate on the shear zone walls of 8.7 x 10-6 inches. s-1) was employed.  Final shear strain values ranged from 0.025(to 0.378(. 

One series of pure shear deformation was conducted on the calcite-cement material at 1.5 kbars confining pressure employing a constant natural strain-rate of 5.0 x 10-6s-1.  Final axial strain values ranged from 4.42% to 18.3% shortening.

The development of simulated "tectonic" magnetic fabrics in both pure and simple shear has been achieved.  Principal directions of susceptibility rotate sometimes in complex patterns toward 'tectonically' significant stable orientations.  Magnitudes of susceptibility show progressive changes consonant with the intensity of strain such that there appears to exist a consistent relation between the change in the degree of anisotropy of susceptibility ()P') and the bulk strain ratio (In X/Z) for both the pure and simple shear experiments.

A copy of the thesis can be downloaded here

John Peter Burton MSc thesis abstract

Thesis Title: 
Constraints on the Formation of Depositional Placer Accumulations in Coarse Alluvial Braided River Systems
John Peter
Burton
MSc
1989

Placer accumulations are formed by the preferential sedimentation of heavy minerals from the general population of detritus being transported by a fluid.  The depth, velocity, and grain size conditions under which placers form on beaches, sand-dominated meandering, and braided fluvial systems is at present only partially understood.  Our knowledge of the controls on alluvial placer formation in gravel-dominated longitudinal bars of braided rivers is even more poorly developed despite their obvious economic importance.

The accumulation of heavy minerals in coarse-grained longitudinal gravel bars was studied by examining and sampling surficial and matrix sediments from modern, naturally occurring bars, and by simulating these bars under a variety of controlled flow conditions in a sediment-water recirculating flume.

Two processes dominated the deposition of sediments in both the natural and artificial systems studied:  1) suspension rain out; and 2) avalanche face progradation.  Sediments which were deposited as a result of avalanche face progradation were found to contain significantly higher concentrations of heavy minerals in both the naturally occurring and experimental longitudinal gravel bars.  Data also indicate that the difference in heavy mineral content amongst sediments deposited as a result of these two processes will increase substantially with increasing density of the detrital minerals present.  This suggests that denser heavy minerals are more likely to be deposited amongst less dense surficial sediments whereas less dense heavy minerals are more likely to be vertically distributed throughout the bar sequence.

In the natural systems studied, heavy mineral content was found to be much higher in poorly sorted, coarse-grained sediments deposited amongst pebble sized clasts.  Flume tank experimentation similarly revealed that detrital lead content was highest amongst pebble sized clasts during the fastest velocity runs.  In addition, an increase in clast size resulted in a decrease in the amount of heavy minerals accumulating in surficial sediments.

This study has also highlighted two processes which results in the formation of alluvial depositional placer accumulations in coarse-grained braided river systems.  The first process occurs as a result of heavy minerals in channel bottom sediments becoming progressively enriched through the winnowing of less dense sediments, resulting in the formation of an erosional placer deposit.  Flume experimentation revealed that when high concentrations of heavy minerals armouring the stream-bed were reached, this often resulted in the initiation of their movement downstream.  This process can also be triggered by catastrophic events such as large floods of regional tectonic uplift.  A sudden increase in energy typically associated with such events results in the flushing of erosional placers and their eventual deposition in areas of higher preservation potential.  Therefore, a catastrophic adjustment helps to flush out erosional placer deposits into the basin to form a depositional placer accumulation.  The second process of depositional placer formation results from heavy minerals travelling in bed load transport, while less dense sediments are kept mostly in suspension.  With a decrease in velocity, heavy minerals are sedimented with hydraulically equivalent sized, less dense sediments in open framework gravels.

A copy of the thesis can be downloaded here

Robert Nicholas Spark MSc thesis abstract

Thesis Title: 
Magnetic Fabrics and Boundary Structure at the Quetico/Shebandowan Subprovince Boundary, near Kashabowie, NW Ontario
Robert Nicholas
Spark
MSc
1990

The Quetico metasedimentary subprovince and the volcanic-plutonic Shebandowan belt to the south meet along an east-west steeply dipping boundary that is believed to have been affected by dextral transpressional deformation.   It is also parallel to a steep metamorphic gradient from greenschist facies rocks to the north.

Macroscopic petrofabrics are difficult to observe along the belt to the west of Thunder Bay but magnetic susceptibility fabrics (low-field) are quite consistent.  These define a gently plunging extensional fabric parallel to the belt boundary.  Within the Kashabowie area, general field observations of subhorizontal stretching (and intersection) lineations, and cleavage directions are in agreement with magnetic susceptibility axis directions.  Mineral separation reveals that all samples have multiple sources of magnetic susceptibility, dominated by metamorphic phyllosilicates.  Consequently it is not possible to simply quantitatively relate the magnetic fabrics to strain magnitudes although the magnetic fabrics accurately monitor significant kinematic directions.  Analyses of strain of low-grade detrital quartz grains, magnetic fabrics and general field observations recognize flattened oblate fabrics.  Moreover oblique, subhorizontal lineations favour a transpressive kinematic model with compression normal to the belt boundary.  The obliquity between mineral and magnetic lineations seem to indicate dextral transpressive deformation.

A copy of the thesis can be downloaded here

Scott J. Mooney MSc thesis abstract

Thesis Title: 
Stratigraphy of Two Late Paleozoic Basins: Implications for the Timing of Final Emplacement of the Meguma Terrane
Scott J.
Mooney
MSc
1990

Paleomagnetic studies indicate the Meguma terrane's final emplacement occurred between the Mid-Devonian and Early Permian.  Lithostratigraphic units near the boundary of the terrane were investigated in order to provide constraints on the timing of this compressional event.

North of the Cobequid-Chedabucto Fault (Guysborough Basin), volcanic flows, pyroclastics and related sediments are overlain by gravelly to sandy braided fluvial and lacustrine lithofacies.  East-southeast paleocurrents and variable (non-Meguma) clast lithologies are typical of these units.  South of the Cobequid-Chedabucto Fault (St. Mary's Basin), coarse cobble - rich to sandy braided fluvial lithofacies are dominant.  Paleocurrents indicate flow to the north and clast lithologies are representative of the Meguma terrane.

Post Acadian (Late Devonian) basement fragmentation and associated volcanism modified the area noth of the Cobequid-Chedabucto Fault.  Basement block rotation, east end down, initiated Latest Devonian through Mid-Carboniferous sedimentation in a transtensile tectonic environment.  There is no lithostratigraphic evidence to suggest the presence of the Meguma terrane immediately south of the Guysborough Basin during this time interval.  However, the Meguma terrane was supplying sediment to the St. Mary's Basin by the Early Carboniferous.  Collison and wrench faulting probably initiated formation of this basin in a transtensile tectonic environment.  Subsequent dextral displacement along the Cobequid-Chedabucto Fault and transpressive tectonic conditions resulted in the removal of slices of both the St. Mary's and Guysborough Basins as these two distinct assemblages were juxtaposed.

A copy of the thesis can be downloaded here

Richard Morison McLaughlin MSc thesis abstract

Thesis Title: 
Accessory Rare Metal Mineralization in the Coldwell Alkaline Complex, Northwest Ontario
Richard Morison
McLaughlin
MSc
1990

Accessory rare mineralization has been investigated in seven lithologies in intrusive Centres I and III of the Coldwell alkaline complex.  All units contain minerals that are enriched in a suite of granitophile elements, which typically include Nb, REE, Y, Th, U and Zr.  Mineral abundances, composition, and mode of occurrence differ between units.

Centre III is characterized by crystallization of subhedral-to-euhedral chevkinite, pyrochlore and monazite from late-stage melts or residual pore fluids in the more-evolved quartz and ferro-edenite syenites.  These minerals are invariably altered to fluorocarbonate or recrystallized by later F- and CO32- - bearing deuteric fluids.  The Centre I, ferroaugite syenite minerals exhibit similar morphological and replacement of plagioclase and amphibole by K-feldspar, zircon, fluorocarbonate, Nb-rutile (?), allanite, and rare chevkinite.  Fe-rich fluids under oxidizing conditions are believed to have precipitated Fe3+ - bearing fluorocarbonate in which one third of the (REE.)F layers are replaced by Fe3+ layers. 

Most Centre I rare earth minerals are enriched in the HREE relative to those from centre III, in particular pyrochlore, fluorocarbonate, allanite in the eastern contact pegmatites and the quartz syenite dykes.  Compositional data for adjacent syntaxial intergrown domains of bastnaesite, synchysite, and parasite indicate that HREE-enrichment may, in part, be influenced by the Ca content of the species. 

The highest contents of Ce (4193 ppm), Zr (1613 ppm), Y (650 ppm), Th (223 ppm) and U (428 ppm) were found in the quartz syenite dykes intruding the Craddock Cove syenite and Port Munroe megaxenolith.  The emplacement of the quartz syenite dykes and the introduction of the metasomatizing fluids of the Craddock Cove syenite may be temporally related to the differentiation of residual fluids in the apical zone of the Centre I magma chamber.  Complexing of F- and CO32- with rare metals may have permitted their concentration, transportation and precipitation in structurally favourable settings.  The megaxenoliths have been susceptible to brittle fracturing and should be considered primary targets for further exploration.  The Craddock Cove syenites, although intruded by the dykes, may have been hot during dyke emplacement and therefore not as prone to brittle fracturing.

A copy of the thesis can be downloaded here

John Robert McArthur MSc thesis abstract

Thesis Title: 
Dimensional and Crystallographic Fabric Development in Experimentally Deformed Synthetic Aggregate and Natural Rocks
John Robert
McArthur
MSc
1990

Calcite Portland-cement aggregate samples were deformed triaxially at 25E with confining pressures of 200 Mpa.  The samples were deformed under experimental approximations of pure shear (dry and wet experimental conditions), transpressional shear and simple shear.   The pore fluid pressure during the wet pure shear test was less than 195 MPa.  Extensive grain rotation accompanied by twinning of the calcite grains occurred.

Optical analyses of calcite crystallographic fabrics have been used to infer the orientation of the maximum principal compressive stress (F1).  Stress orientations in the deformed specimens agree well with the externally imposed stresses.  A new method has been successfully used to determine the F1 orientation.  The method used contouring of the lamellae index associated with the compression direction determined from Turner's Dynamic analysis method.

In pure shear, preferred dimensional orientation (PDO) of the calcite grains are produced more efficiently in the presence of a pore fluid pressure.  In dry specimens, transpressional shear is more effective in producing a PDO in the calcite grain than either pure shear or simple shear.  Grain shape fabrics do not conform to the symmetry of the bulk deformation when extensive rotation of calcite grains is involved.  Mean grain alignment is perpendicular to the shortening in pure shear, initially inclined and later parallel to the shear zone wall in transpressional shear, and inclined to the shear zone wall in simple shear.  The mean orientation of the grain-alignment fabrics is, therefore, a reliable kinematic indicator under the conditions investigated.  Transpressional shear and dry pure shear exhibit higher lamellae indices than either wet pure shear or simple shear. 

Strain analysis of calcite grains by Robin's method (1977), the linearization method (Yu and Zheng, 1984) and Harmonic mean method (Lisle, 1977) yields overestimates of the experimental bulk strain in wet pure shear.  These methods fail to take into account interparticle motions that occur in the presence of a high pore fluid pressure.

The triaxial deformation of the Ancaster oolitic limestone was performed with a confining pressure of 200 Mpa, a natural strain rate of 10-5/s and at a temperature of 135EC.  The samples were deformed under dry and wet experimental conditions.  The pore fluid pressure, during the wet test, was less than 60% of the confining pressure.   

A copy of the thesis can be downloaded here

Mark Puumala MSc thesis abstract

Thesis Title: 
An Investigation of the Use of Anisotropy of Complex Magnetic Susceptibility to Analyse Strain in Experimentally Deformed Materials and Massive Sulphides
Mark
Puumala
MSc
1991

Anisotropy of magnetic susceptibility (AMS) has become a widely accepted method of fabric analysis in rocks, especially those which have been deformed tectonically.  The use of anisotropy of complex magnetic susceptibility (ACMS) is a new potential method of fabric analysis in which the imaginary, or out of phase A.C. component of an induction coil used for the measurement of magnetic susceptibility is used to delineate rock fabric.  Complex magnetic susceptibility is a function of electrical conductivity, thus making it potentially useful in the analysis of highly conductive sulphide-rich rocks, some of which are not suitable for AMS analysis.

Preliminary measurements were performed on highly conductive aluminum test specimens of differing shapes to determine the relationship between grain shape anisotropy and ACMS.  A relationship was found in which shape anisotropy and resistive ACMS fabrics were of the same sense, but there was no quantitative correlation.  Pure and simple shear deformation experiments performed on plasticene containing numerous small aluminum disks exhibited a correlation between ACMS fabric anisotropies and strain in most cases, as the ACMS fabrics were controlled by the distribution of the disks, which became well-aligned as flattening proceeded.  Although there was no quantitative relationship between strain and ACMS, they tended to increase together.

Triaxial deformation studies on loose pyrrhotite aggregates and pyrrhotite plus talc mixtures were performed at confining pressures of 150 MPa.  The ACMS fabrics developed in these specimens were compared to AMS fabrics and strain analysis data to determine if the ACMS fabrics change as a function of strain.  As expected, oblate resistive ACMS fabrics developed during these pure shear deformations.  The pyrrhotite aggregates exhibited a complex relationship in which ACMS increased with strain, at least up to a critical strain value, after which ACMS appeared to decrease.  The pyrrhotite plus talc mixtures exhibited an unmistakable increase in ACMS with increased strain probably influenced by the presence of the talc matrix.  The ACMS fabrics developed in these experiments were undoubtedly the result of grain alignment and distribution within the aggregates, with insignificant contributions from crystallographic resistive anisotropy.

Measurements performed on specimens of massive pyrrhotite revealed ACMS fabrics completely different from those observed in the loose pyrrhotite aggregates, with ambiguous relationships between strain and ACMS.  This is because the massive specimens behave electrically as a single grain and anisotropy is almost exclusively crystallographically controlled.  Thus the ACMS properties of single minerals must be understood before ACMS fabrics in massive sulphides can be interpreted.

A copy of the thesis can be downloaded here

David L. Nicol MSc thesis abstract

Thesis Title: 
Deformation of Layered Rocks near the Wawa-Quetico Subprovince Boundary
David L.
Nicol
MSc
1991

A supracrustal sequence of rocks near Manitouwadge, Ontario consists of metavolcanic rocks, including pillow lavas, banded iron formation, amphibolite, and a quartzofeldspathic hornblende-biotite gneiss.  This rock has been given the name bladed gneiss to reflect the blade-like appearance of its mafic components.  Results of a detailed geological investigation of the entire supracrustal sequence suggests that the apparent fragmental appearance of the gneiss, and to a lesser degree the other rock types, is not a primary feature, but rather, the product of deformation.  The rocks were initially part of a layered sequence which became variably fragmented.  The blades are in part the result of the transposition of layers and the variations in blade morphology are attributable to the response of the layers to strain during folding.  Individual layers deform by the development of cuspate-lobate folds, buckle folds, and boudinage.  The extent of fragmentation during deformation is controlled by competency contrasts between adjacent layers, absolute and relative layer thickness, and layer orientation with respect to principal finite strain directions. 

Planar and linear structural elements in the metasedimentary and metavolcanic rocks suggest a deformational history which includes two episodes of folding accompanied by medium grade metamorphism and recrystallization.  Similarities in lithology and structural elements between the rocks of the study area and those of the nearby Manitouwadge synform suggest that parent rock assemblages were closely related and that structures present in both locations developed contemporaneously in response to regional tectonic activity.  "Mobilist" tectonic models for the development of the Superior Province entail northward directed subduction and accretion, and are popular with many workers.  The recumbent nature of F1 folds, the shallow plunging hinge lines of F2 folds, and their coaxial relationship may be related to low angle thrust faults and nappe structures which would be likely consequences in the proposed subduction model.

Many workers have attempted to map subprovince boundaries.  In the region of the present study, the boundary between the Wawa and Quetico Subprovinces is traditionally placed a few miles north of Manitouwadge.  If this is correct, the rocks studied form part of the Wawa Subprovince.  Results of this investigation suggest that, on the basis of lithology and structure, such a placement of the boundary is inappropriate.  It appears more appropriate to suggest that the terrain discussed in this thesis, as well as the rocks of the Manitouwadge synform, is best considered to form a zone of transition between the two subprovinces.

A copy of the thesis can be downloaded here

Susan Craig MSc thesis abstract

Thesis Title: 
Sedimentation Models for Glacial Deltaic Successions in the Thunder Bay Area
Susan
Craig
MSc
1991

The comparison of three mapped successions in northern Ontario to glacial deltas reviewed in the literature results in the definition of four end-member depositional environments for glacial deltaic sedimentation.  Similar processes of sedimentation occur within two main glacial delta types, distal-fed, and ice-contact.  Distal-fed deltas divide into nonglacial and ice-influenced.  The other two end member types defined are subglacial and supraglacial ice-contact deltas.

Fine-grained laminated beds sedimented by interflows and overflows, as well as diamict and subaqueous outwash deposits underlie the glacial deltaic sequences.  The prodelta region consists of multiple reverse-graded beds, massive units, and laminated sediments deposited from interflows and overflows, and minor rippled units indicating intermittent underflows.  Within the delta front underflows deposited rippled and graded units, and occasionally planar cross-stratified units were sedimented by grainflows.  The delta plain contains trough cross-stratified sands and gravels which infill multiple distributary channels.  Dropstone deposition was restricted to the prodelta and delta front regions of ice-influenced distal-fed deltas, and ice-contact deltas.

Distributary mouth bars, large scale cyclic sedimentation, subaqueous outwash systems overlain by a glacial deltaic sequence, multiple processes of sedimentation within the delta front, and reworking of glaciogenic deposits have not previously been documented in glacial deltaic systems.   These deposits and processes, as well as the inability to define the strandline position indicated glacial deltaic systems are complex.

A copy of the thesis can be downloaded here

Barbara Ellen Seemayer MSc thesis abstract

Thesis Title: 
Variations in Metamorphic Grade in Metapelites in Transects Across the Quetico Subprovince North of Thunder Bay, Ontario
Barbara Ellen
Seemayer
MSc
1992

The Quetico subprovince is a northeast-southwest striking linear belt of migmatites, gneisses, and metasedimentary rocks.  These Archean rocks form part of the southern Superior Province.  This study involves an examination of variations in metamorphic grade along cross-strike transects in an area north of Thunder Bay, Ontario.

The rocks of the Quetico subprovince include metasedimentary rocks with well preserved primary structures, knotted schists, gneisses, migmatites, and anatectic granitic rocks.  Metamorphic porphyroblasts include muscovite, biotite, garnet, staurolite, cordierite, andalusite, and sillimanite.  Chemical analyses of garnets, geothermobarometry, and mineral assemblage data were used to determine variations in metamorphic grade in transects across the subprovince.

Mineral assemblages characteristic of low to high grade metamorphism are exposed along an across-strike transect.  Metamorphic grade rises gradually from low grade (521°C) to high grade (714°C) northwards along Highway 527.  North of the peak conditions, the grade drops off sharply.  Garnet-biotite geothermometry confirms this pattern.  Maximum pressure reached in the study area is approximately 5 kbar.  

The model proposed to account for the distribution of metamorphic assemblages and minerals involves transpression of the Quetico accretionary prism between the Wabigoon volcanic cratonic margin to the north and the docking Wawa volcanic complex to the south.  Buckling and folding of the sedimentary rocks was accompanied by thrusting.  Erosion has exposed high grade migmatitic and anatectic rocks within the Quetico fold belt which developed as a result of thermal relaxation of depressed isotherms.  The boundaries between metavolcanic and metasedimentary terranes are structurally complex.  Boundaries may be best described as geometrically complex zones up to several kilometres in extent in which various rock types representative of the adjacent terranes have been folded, faulted, and intruded.

A copy of the thesis can be downloaded here

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