Scott Philip Cheadle MSc thesis abstract

Thesis Title: 
A Gravity Study of an Archean Crustal Segment Near Thunder Bay, Ontario
Scott Philip
Cheadle
MSc
1982

A gravity survey in an area involving portions of the Quetico and Shebandowan subprovinces of the Superior structural province resulted in the establishment of 350 new gravity stations in addition to 50 previously established stations.

For the purposes of this study the bedrock was divided into 4 major units including the metavolcanic rocks, metasedimentary rocks, assorted gneissic rocks and a group of intrusive igenous bodies.

Based on gravity modeling of these principal units, the following subsurface structure results.  The metavolcanic rocks vary in depth extent from 6 km to 12 km and typically occupy a trough-shaped structure flanked by a domical feature of granitoid gneisses to the south.  To the north of the metavolcanic unit, the metasedimentary rocks form a basin-like structure of variable depth extent.  The contact between these two units is modeled as dipping steeply southward.

The Quetico granitoid gneisses to the north of the metasedimentary unit form a southward dipping wedge which extends to depths of 10 km in the model structure profiles.  These gneisses are modeled as being underlain by a denser substratum representative of more basic gneiss and amphibolite.  The basal surface of this unit is gently convex upward, and the unit as a whole thickens toward the north and dips toward the south in a tapered wedge extending to a depth of 10 km.  This unit is inclined slightly from east to west, and is exposed at the present erosion surface in the eastern portion of the study area only.

A number of quartz monzonite plutons have been emplaced near the northern portion of the metasedimentary unit and outcrops above the southern most edge of the dense substratum underlying the Quetico gneisses.

A tectonic model put forward synthesizes the available information regarding Archean crustal evolution and the data from this study.  The proposed model consists of a basin-like structure (Quetico subprovince) which received sedimentary and volcanic debris from a mature volcanoplutonic terrane to the north (Wabigoon subprovince).  Additional sedimentation into the basin was provided from the less mature volcanoplutonic terrane to the south (Shebandowan subprovince).  Subsequent deformation accompanied by high grade metamorphism resulted in a general upwarping of the basin, producing the structures now observed in this part of the Quetico subprovince.

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Ali R. Tabrez MSc thesis abstract

Thesis Title: 
A Comparison of the Late Quarternary Sedimentary Sequence and Paleomagnetic Record of the North Bay Outlet and a Baffin Island Fiord
Ali R.
Tabrez
MSc
1983

The lithology of the Late Quaternary lacustrine sequences of five lakes in the North Bay area differs from one lake to another.  However, chronostratigraphically equivalent sections of cores taken from the same lake do show similarities in mean grain size, sand percentage and organic and carbonate carbons.  The lithology of the Late Quaternary fiord sedimentary sequence of McBeth Fiord, Baffin Island exhibits a slightly higher sand content and lower organic carbon content than the North Bay lacustrine sediments.

The magnetic mineral grains deposited on the bottom of lakes and fiords tend to align in the direction of the earth's magnetic field at the time of deposition creating a remanent magnetic field in the sediments.  The sedimentary sequences of lakes in the North Bay and McBeth Fiord, Baffin Island areas provides a record of the direction and intensity of the earth's magnetic field for these regions during the Late Quaternary.  The declination and inclination values of oriented samples taken from soft-sediment cores of the Late Quaternary lacustrine sequences of the North Bay area and the fiord sequences of McBeth Fiord can be compiled into paleodeclination and paleoinclination logs.  The oscillations of the relative paleodeclination logs show a similar character for cores taken from the five lakes and the fiord as do the paleoinclination logs.  Marker horizons picked on the character of either the paleodeclination or paleoinclination logs provide a method for chronostratigraphic correlation from one core to another within the North Bay area and also for the McBeth Fiord area.

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Adel Mohamed Hassan El Tawashi MSc thesis abstract

Thesis Title: 
A Study of the Depositional Environments of The Halfway Formation British Columbia
Adel Mohamed Hassan
El Tawashi
MSc
1983

The upper sands of the discontinous Halfway Formation to the northeast of Fort St. John were formed as barrier islands deposited perpendicular, or nearly perpendicular to the dip of the paleoslope of the Western Canadian Sedimentary Basin.  These upper sands of the area of study were deposited during a transgressive phase of the Triassic sea to the northeast, and formed the basal unit of an onlapping sequence comprising the Halfway and the Charlie Lake Formations that disconformably overstepped the erosional surface on the silty dolomite of the Doig Formation.  The Weasel sand body was deposited during a pause in the transgression, and then was submerged by a rapid rise in sea level.  The Wildmint to Beatton barrier islands trend was deposited during a second pause in the transgression.  These barrier islands would appear to have been deposited under arid conditions resulting in restricted lagoonal environments.  The lower sands of the discontinuous Halfway Formation which only occur at a few locations in southern Willow and Wildmint, would appear to have resulted from tidal inlet action that eroded channels into the Doig Formation below the base of the upper sands forming the barrier island complex.  These later were filled with sand.  Then this barrier island trend was submerged by renewed transgression of the Triassic sea.  The source of the sediments comprising the discontinous Halfway Formation probably was to the north and northeast of the area of study. 

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Myra Carolyn Kennedy MSc thesis abstract

Thesis Title: 
The Quetico Fault in the Superior Province of the Southern Canadian Shield
Myra Carolyn
Kennedy
MSc
1984

The Quetico fault is a major transcurrent fault in the southern Superior Province of the Canadian Shield.  Along part of its length the fault forms the boundary between the Quetico and Wabigoon subprovinces.  Dextral motion on the fault is indicated by dextral microfaults and approximately asymmetrical quartz c-axis petrofabrics.

The fault comprises a zone of dynamically metamorphosed rocks - primarily mylonitic rocks with some cataclastic rocks and pseudotachylite.  A transition from predominantly ductile deformation to brittle deformation occurred during the time the fault was active.

The ductile deformation of quartz within the fault zone is the result of crystal-plastic processes, predominantly slip on prism planes in the a-direction and slip on rhomb planes in the a-direction, accompanied by dynamic recovery and syntectonic recrystallization.  Feldspar grains are commonly deformed in a brittle manner by fracture processes.  Particulate flow appears to have made a significant contribution to deformation in the fault zone.

The harmonic mean of deformed grain axial-ratios and strain determinations by the all object-object separations method indicate that flattening strain is predominant within the fault zone.  The magnetic susceptibility anistropy ellipsoid is also flat-shaped and coaxial with the strain ellipsoids.  The characteristics of microfaults and folds within the fault zone indicate that flattening may have been accompanied by or followed by shearing.  The harmonic mean of deformed quartz grain axial ratios yields a minimum strain estimate of 130% extensions in X, 58% extension in Y, and 71% shortening in the Z direction.

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G. Heather Brown MSc thesis abstract

Thesis Title: 
A Structural and Stratigraphic Study of the Keewatin-Type and Shebandowan-Type Rocks West of Thunder Bay, Ontario
G. Heather
Brown
MSc
1985

Detailed mapping was carried out in the Shebandowan Lakes area and eastward to the Kaministiquia River to study the structural and stratigraphic relationships between the Keewatin and Timiskaming rocks (herein referred to as Keewatin-type and Shebandowan-type, respectively, to avoid connotations of time-stratigraphic equivalence with type areas) of the region.

It is believed that the Shebandowan-type rocks are younger than the Keewatin-type rocks.  Although no actual contact between the two has been seen in outcrop in the study area, the trend of their contact is discordant with the trend of cleavage in the Shebandowan-type rocks.  This, along with the less recrystallized appearance of the Shebandowan-type rocks, and the presence of clasts of jasper in conglomerates of the Shebandowan-type sequence similar in appearance to the jaspilitic iron formation interbedded with the Keewatin-type mafic volcanics, leads to the conclusion that an unconformity separates the two groups of rocks.  Recent geochronological work on some of the rocks in the region, carried out by the Ontario Geological Survey, supports this theory.

The macroscopic, microscopic and sub-microscopic structure of both groups of rocks was examined in detail.  The minor structures seen in outcrop, the examination of thin sections, scanning electron microscope work, and the determination of the magnetic fabric of the rocks all show that the rocks in the present study area contain a single, penetrative, primary cleavage, which has a consistent trend across the whole area.  The regional structural picture which emerges from the data is characterized by close-spaced, isoclinal folding with sub-vertical fold axial traces trending roughly east-west.  Local variations exist in the eastern portion of the study area where more widely-spaced and open folding is more common.  No evidence of a second, significant period of deformation in the present study area has been found.

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Dennis C. Arne MSc thesis abstract

Thesis Title: 
A Study of Zonation at the Nanisivik ZN-PB-AG Mine, Baffin Island, Canada
Dennis C.
Arne
MSc
1985

Zn-Pb-Ag mineralization at Nanisivik, northwest Baffin Island, is hosted by Proterozoic, laminated dolostone of the Society Cliffs Formation.  Mineralization of the Main Orebody is highly variable in terms of texture and mineralogy exhibiting both replacement and open space filling textures.  Sulfides are generally coarsely crystalline and banding, consisting of interlayered pyrite, sphalerite, galena and sparry dolomite, is common along the margins of the Upper Lens of the Main Orebody.  The eastern and central portions of the Upper Lens are characterized by laterally extensive mine units, which are distinguished on the basis of texture and mineralogy.  Contacts between units are generally sharp.

The physical and chemical parameters responsible for the textural and mineralogical variations have been evaluated through a study of fluid inclusions, sulfur isotopes and ore mineralogy.  Fluid inclusion homogenization temperatures from simple, two-phase primary and pseudo-secondary inclusions in sphalerite and sparry dolomite gangue indicate initial temperatures of ore formation from 150-210°C in the eastern Upper Lens when the estimated pressure of ore formation is taken into consideration.  The temperature of ore formation decreased to 100-150°C in the western portion of the Upper Lens.  Freezing studies indicate that the ore-forming fluid was a brine containing 20-37 equivalent weight percent CaCl2.  The sulfur isotopic compositions of late and main stage pyrite crystals range from δ34s = +27.4€ to + 28.0€, suggesting relatively constant temperature, fluid source and dominant sulfur species in the ore fluid during ore formation, providing there has been no subsequent re-equilibriation of sulfur isotopes.  The iron content of sphalerite varies from 14 mole % to 0 mole % from crystal centers to rims respectively, corresponding to well developed colour zonation.  Sphalerite iron contents constrain the oxygen activity of the ore fluid from 10-46 to 10-41 at 200°C during sphalerite precipitation.  The best developed zoning and, thus, the highest oxygen activities occur within sphalerite adjacent to carbonate wall rock.  Under high oxygen activities, conditions were favorable for the generation of sulfanes considered necessary for precipitation of marcasite.  X-ray diffraction studies indicate that primary marcasite has inverted completely to pyrite.  The stability of the simplest sulfane, H2S2, constrains the maximum allowable pH of the ore fluid at the time of marcasite precipitation to 5.0.  The presence of interbanded marcasite pseudomorphs and sparry dolomite indicate that the ore fluid fluctuated around pH = 5.0.

Comparison of solid organics extracted from the Society Cliffs dolostone to bitumen associated with mineralization suggests that organics within the host formation have played a role in sulfate reduction.  The model of ore formation therefore proposed involves the in situ reduction of a hot, saline, metal-bearing ore fluid by hydrocarbons liberated by the replacement and dissolution of wall rock.  Sulfate reduction was probably concentrated at the wall rock orebody interface along a replacement front that migrated away from the orebody.  Banding was likely the result of repetitive sulfate reduction, metal precipitation and wall rock dissolution in response to the pulsatory influx of ore fluid.  Gross textural and mineralogical variations are probably a result of slight variations in the oxidation state of the ore fluid, the availability of H2S and, to a lesser extent, temperature.

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Perry Sarvas MSc thesis abstract

Thesis Title: 
The Structure and Magnetic Fabric of the Quetico Metasedimentary Rocks in the Calm Lake - Perch Lake Area, near Atikokan, Northwestern Ontario
Perry
Sarvas
MSc
1987

The Quetico metasedimentary rocks are the metamorphosed equivalents of a turbidite sequence, comprised of a repetitive interstratification of sandstones and mudstones.  The rocks are metamorphosed to lower greenschist facies, but metamorphic grade increases progressively from north to south.  Anchimetamorphosed phyllites and slates in the north part of the present study area grade progressively into biotite schists in the south part.

Interpretation of structural features in the study area, mainly bedding (S0) - cleavage (S1) relationships and structural facing directions, has led to the delineation of a number of major F1 folds.

These are tight to isoclinal, asymmetric sheath folds, with axial planes arranged en echelon and slightly oblique to the dominant east-west, vertically-dipping, structural trend.  The orientation, geometry and disposition of the F1 fold suggest the Quetico rocks of the present study area have experienced a regional dextral transpressional tectonic evolution, with components of north-south regional shortening and east-west regional dextral shear, with a possible component of vertical (south side up) displacement.

The Quetico metasedimentary rocks have a polyminerallic magnetic mineralogy comprised of significant proportions of a ferromagnetic (magnetite and pyrrhotite) and a paramagnetic (chlorite, biotite, muscovite) component.  The rocks possess a predominantly tectonic magnetic fabric, which consists of a deformational, and a metamorphic, magnetic fabric.  In some rocks (especially coarse-grained sandstones with wide-spaced cleavage planes) a depositional magnetic fabric is partially preserved.  The complexities involved in having component deformational, metamorphic and depositional magnetic fabrics indicate that the principal magnetic susceptibility directions of the rock's magnetic susceptibility anisotropy cannot be considered reliable indicators of principal finite strain directions in the Quetico metasedimentary rocks.  Great care must be taken in interpreting the significance of principal magnetic susceptibility directions.

A copy of the thesis can be downloaded here

Douglas Bruce McKay MSc thesis abstract

Thesis Title: 
Aspects of Gallium Geochemistry in Upper Mantle-Derived Lherzolite Xenoliths and Continental Alkaline Volcanic Rocks
Douglas Bruce
McKay
MSc
1987

Various aspects of the geochemistry of Ga in upper mantle-derived garnet lherzolite xenoliths (from the Bultfontein Floors mine dump in Kimberly, South Africa), spinel lherzolite xenoliths (from Mount Pordnon, Australia), and continental alkaline volcanic rocks (from the Freemans Cove, Balcones, Urach and Hegau suites of Canada, the U.S.A., and Germany, respectively) have been investigated.  Ga abundances were determined by RNAA.  The feasibility of using epithermal INAA to generate accurate Ga data was investigated.  Analysis of U.S.G.S. standard granite G-2 suggests that epithermal INAA utilizing 630.1 KeV72Ga data has the potential to produce geologically useful Ga data.

The abundance of Ga in the lherzolite xenoliths varies by a factor of approximately 10 from 0.52 ± 0.14 ppm to 5.23 ± 0.44 ppm.  The spinel lherzolite xenoliths contain appreciably more Ga (2.78 ± 0.26 ppm to 5.23 ± 0.44 ppm) than the garnet lherzolite xenoliths (0.52 ± 0.14 ppm to 1.44 ± 0.18 ppm).  The sequence of enrichment of Ga in the minerals comprising the lherzolites is, from lowest to highest Ga content, olivine (0.20 ± 0.04 ppm to 0.72 ± 0.11 ppm), clinopyroxene (1.31 ± 0.13 ppm to 4.92 ± 0.32 ppm), garnet, if present (3.17 ± 0.16 ppm to 6.03 ± 0.48 ppm) phlogopite, if present (7.65 ± 0.21 ppm), and spinel, if present (43.49 ± 0.91 ppm to 65.91 ± 2.10 ppm).  Ga mineral/mineral distribution coefficients have been calculated.  Preliminary results suggest the distribution of Ga between certain mineral pairs (e.g., DGaopx/pcx) is temperature dependent and might be profitably utilized as a geothermometer.

The abundance of Ga in the continental alkaline volcanic rocks varies by a factor of approximately 3.5 from 12:14 ± 0.32 ppm to 41.97 ± 1.20 ppm.  Ga behaved as an incompatible trace element during the genesis of these rocks.  Model-derived constraints for Ga bulk-solid/melt distribution coefficients vary from 0.16 (Balcones suite) to 0.28 (Hegau suite).  Intrasuite variations in the Ga/Al ratios of the mafic continental alkaline volcanic rocks range from approximately 14% (Hegau and Urach suites) to approximately 20% (Freemans Cove suite).  Ga/Al ratios of primary melts from the Freemans Cove and Balcones suites decrease slightly (from 2.86 ± 0.16 top 2.28 ± 0.13, and from 4.12 ± 0.24 to 3.35 ± 0.19 respectively) with increasing degrees of partial melting.

A copy of the thesis can be downloaded here

Jonathan Ross Devaney MSc thesis abstract

Thesis Title: 
Sedimentology and Stratigraphy of the Northern and Central Metasedimentary Belts in the Beardmore-Geraldton Area of Northern Ontario
Jonathan Ross
Devaney
MSc
1987

The northern and central metasedimentary belts (NMB, CMB) are east-trending, regional (formation- to group-scale) lithostratigraphic units within the Beardmore-Geraldton Archean terrane of northern Ontario's Superior Province.

Gravelly braided rivers deposited the lithofacies assemblage of clast-supported polymict conglomerate and interbedded sandstone that comprises most of the NMB.  Felsic volcanic pebbles and cobbles are the most abundant clast lithology.

The CMB contains several east-trending lithofacies assemblages that together form a generally northward-coarsening sequence.  The southern CMB is composed of mudstone, iron formation and sandstone with common graded beds.  This fine-grained assemblage is paralleled to the north by a horizon of rhythmically bedded and cross-bedded sandstone units, and a heterogeneous, conglomerate-rich assemblage.  The northern CMB strata are mostly a conglomeratic assemblage similar in form (lithofacies) and composition (provenance) to the NMB.  Some fine-grained units (mudstone, iron formation, graded sandstone) of relatively minor regional extent are present near the north margin of the CMB.

The CMB's southern (lower) fine-grained subaqueous facies are apparently capped at different sites by:  1) rhythmic delta front couplets;  2) sandy braided river deposits with very rare associated intertidal strata;  and 3) a conglomerate submarine fan or fan-delta front resedimented assemblage.  The northern (upper) CMB is a gravelly braided river deposit, with minor aquabasinal facies.

The CMB is probably a 1 - 2 km thick structurally modified homoclinal sequence.  Relative positions of its depositional paleoenvironments, as deduced from lithofacies assemblages, suggest that the epiclastic portion of the CMB is the record of a dominantly coarsening-upward, subaqueous to subaerial trend that was produced by a prograding clastic system(s), likely a number of fan-deltas.

The extreme eastern part of the CMB is composed of generally oligomict, coarse (conglomerate) felsic pyroclastic and/or reworked volcaniclastic facies which are probably subaerial deposits.

Similar clast compositions and several sedimentological criteria, including average maximum deformed clast size, strongly suggest that highly proximal fluvial facies in the NMB and more distal fluvial and aquabasinal facies in the CMB were originally part of a continuous coarse clastic wedge or sheet.

A copy of the thesis can be downloaded here

Owen J. Steele MSc thesis abstract

Thesis Title: 
A Theoretical and Experimental Investigation of Pressure Solution
Owen J.
Steele
MSc
1988

Consideration of the existing thermodynamic theory of pressure solution (PS) shows that this theory is applicable to the development of PS structures as well as to local grain-scale diffusive transfer.  Local precipitation of pressure solved material ceases when pores are reduced to equilibrium size, if not before by kinetic considerations.  Longer range diffusion may then occur if a site of non-equilibrium porosity is available.  Such porosity may be generated by particulate flow or by hydraulic fracturing.  Long range diffusion may also depend on greater ease of diffusion, as may occur along stylolites.

Measurement of PS strain rates was attempted by stress relaxation tests (SRTs) at room temperature of both Carrara marble and compacted aggregates of calcite and quartz sands.  Neither material gave results indicative of PS although strain rates as low as 10-8.5s-1 were obtained.  Work hardening during loading resulted in alternating increase and decrease of strain rate concomitant with steadily declining differential stress during the SRTs.  The variation in strain rate, termed cycling, was interpreted to be the result of non-steady state flow during loading.  Thermal expansion and contraction were shown to be the cause of pressure fluctuation in a long term quantitative experiment on PS begun during this study.  Such expansion and contraction should be avoided in quantitative studies, particularly at low strain rates.

A copy of the thesis can be downloaded here

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