The Archean komatiites of the Lake of the Woods greenstone belt, Kenora, Ontario formed on the western extension of the Superior Province southern margin and have not been studied using modern analytical methods. Although Archean plate tectonic processes have been the subject of decades of research, the nature of these processes remains the subject of considerable debate. Recent work has investigated the link between komatiites and Archean subduction zones. Komatiites are widespread in Archean terranes and together with spatially associated tholeiitic basalts form an important part of many Late Archean greenstone belts, therefore a better understanding of Archean geodynamic processes and comparison to modern day processes is required.   

Detailed mapping in the Upper Keewatin Assemblage identified komatiites on the southern margin of the Long Bay Group. The komatiites are typically metamorphosed to upper greenschist facies and include a variety of schists that do not show any preserved primary textures or mineralogy. Polyhedrally jointed flow tops were observed in rare locations. Mineral assemblages include dominantly anthophyllite-tremolite-chlorite and serpentine-tremolite-chlorite schists, as well as lesser talc-tremolite-chlorite schists. These units are moderately to intensely foliated with chlorite and lesser amphibole defining the foliation and also include randomly oriented bladed amphibole grains that typically have tremolite cores and anthophyllite rims. The amphiboles show a chemical transition from core to rim with a loss in Ca as anthophyllite appears. Accessory phases include chromite, magnetite, ilmenite and apatite. Ultramafic rocks are very fine-grained and mineralogy has been described using a compilation of petrography, x-ray diffraction and scanning electron microscope analysis. 

Whole-rock  geochemical  analyses  were  conducted  on  110  samples.  The  Upper Keewatin Assemblage is composed of dominantly mafic to intermediate volcanic rocks that are typically of tholeiitic affinity with rare calc-alkalic units. A total of 41 samples were determined to be ultramafic in which the komatiite units are Al-undepleted komatiites that display major and trace element concentrations consistent with melts derived from above the garnet stability zone. They can be subdivided into three suites with primitive mantle patterns that display strong Th and Nb depletions with flat HREEs (heavy rare earth elements), weak Th and Nb depletions with flat HREEs and enriched Th with moderate Nb depletions and flat HREEs. Neodymium isotope analyses, in conjunction with trace element geochemistry, suggests that some units have been weakly to moderately contaminated. Mafic tholeiitic units have low- and high-Ti varieties, in which most units are dark grey to black amphibolites   and   rare   chlorite-tremolite   schists.   The   mafic   units   shows   similar contamination trends to the ultramafic units.

The  tectonic  setting  of  the  Upper  Keewatin  Assemblage  requires  voluminous  mafic magmatism  with  relatively  sporadic  ultramafic  magmatism  in  a  subaqueous  setting  giventhe widespread pillow basalts. The belt evolution is interpreted to represent an initial primitive oceanic arc with subaqueous tholeiitic magmatism followed by calc-alkalic dominant magmatism following arc evolution. Tholeiites originating from the primitive arc display weak Nb depletions, and through geochemical modelling it is possible that they are the contaminant that produced Th-enriched komatiites. Although a hydrous source could not be confirmed for the Nb-depleted komatiites, contamination cannot account for the variation in trace elements. It is likely that plume-arc interactions have occurred, similar to scenarios documented in the Superior Province; however, the mechanisms cannot be determined. Deep-penetrating fractures can accommodate along-strike variations in the dip of subduction zones, which typically segment island arcs into various belts. Large-scale crustal weaknesses would act as potential magma conduits for ascending plumes, resulting in a chemical and isotopic difference between the upwelling asthenosphere and arc magmatism. This  would  result  in  likely  interaction  between  the  rising  plume  and  subduction-derived fluids, producing the Nb-depletions present in komatiite samples within the assemblage.

The Hintikka breccia occurrence is hosted within the Shebandowan Greenstone Belt. The Hintikka breccia is classified based on the key characteristics, most likely as a volcanic breccia, which has been further brecciated by a local fault. The breccia occurrence is very close to the boundary between the Shebandowan intermediate volcanics and the Greenwater mafic volcanics, with a local fault interpreted to be related to the Mokomon fault. The northern and southern areas within the Hintikka property show two different composition breccias. The northern breccia shows characteristics of a mafic flow breccia. The southern breccia has an intermediate composition with randomly oriented felsic and jasper clasts present. It is proposed that the north and south breccias are volcanic flow breccias, which have been potentially further brecciated by the faulting event.

The supracrustal rocks of the Shebandowan Greenstone belt have been subdivided into three main assemblages that have differing ages and distinct lithologic associations. The breccia within the Hintikka property could be associated with either the Greenwater or the Shebandowan assemblage. The Shebandowan has large, unsorted massive volcanic breccias, and is associated with faulting from the D2 event, which likely explains the presence of the fault breccia and the intermediate breccia in the southern part of the property. The northern breccia with more mafic composition can also be associated with the massive unsorted breccia, but with more flow breccia characteristics, which were subsequently influenced by a faulting event. The felsic clasts may be related to the felsic intrusions (such as the Tower Mountain stock) associated with the Shebandowan assemblage. The Kashabowie assemblage cannot be entirely ruled out, as the entire extent of the assemblage is unknown, and it is interleaved with the Greenwater assemblage.

Boreal forest soils represent globally significant stores of carbon, much of which is stabilized in the mineral fraction.  Until recently, carbon stored in the mineral fraction was considered highly stable, cycling on millennial timescales.  Recent research has shown that carbon stored in the mineral fraction is stabilized by a variety of mechanisms with varying strengths.  Despite the frequency of forest disturbance in the Boreal region, relatively few studies have examined  the impacts of wildfire, harvest, and salvage logging on soil organic carbon (SOC) in mineral soils.  Fewer still have focused on the response of stabilization mechanisms therein.  This study examines the effects of wildfire, whole-tree harvest and post-fire salvage logging on mineral-bound SOC and its stabilization mechanisms.  A sequential selective chemical dissolution approach was used to isolate pools of SOC on the basis of stabilization mechanisms.  This study shows the majority of mineral-bound carbon to be stabilized by its interaction with free, polyvalent, metallic cations (the organic non-crystalline colloidal, ONC, pool).  Additionally, a substantial amount of carbon was stabilized in the poorly-understood residual pool. It was found that forest disturbance has a significant effect on SOC stabilized in the ONC pool and the residual pool.  Post-harvest, soils showed a significant increase in both SOC concentration and storage.  Fire appeared to reduce SOC stabilization in the ONC pool at surface, but concentration and storage both recovered with depth. Salvage logging markedly reduced SOC concentration and storage associated with the ONC and residual pools, suggesting that it is highly disruptive to SOC stored in the mineral fraction and may not be in best management practice. SOC concentration associated with secondary crystalline Fe and Al minerals is shown to be constant through the whole profile and across all disturbance types.  This is consistent with the notion of C saturation.  This investigation shows that SOC stabilized in the mineral fraction is not as stable as previously thought and may cycle on much shorter timescales.  Additionally, this research suggests that mineral-stabilized SOC may not be robust to the physiochemical changes in soil wrought by disturbance.  These results demonstrate the need for further research concerning the stabilization mechanisms operating in the mineral fraction and their responses to common disturbances in the Boreal region.

The Albany deposit is an igneous-hosted, fluid-derived, graphite deposit hosted within two intrusive vertical pipe structures, known as the East and West pipes, and is located near Hearst, Ontario.  The deposit is estimated to contain 24 million tonnes of ore with an average grade of 3.98% graphite.  The deposit is found near the southern margin of the Nagagami River Alkalic Complex (NRAC), but the precise location of the NRAC’s contact with the surrounding country rock is difficult to establish based on geophysics.  Therefore, it was previously unknown whether the deposit was hosted within the NRAC, another alkalic complex, or within the country rock of the Marmion/Eastern Wabigoon terrane.

This study focuses on characterising the rocks of the NRAC and the host rocks to the Albany deposit.  The NRAC is comprised dominantly of amphibole-pyroxene syenites, while the host rocks contain syenites, monzonites, granites, diorites, and granodiorites. Geochemical analysis shows that the host rocks to the Albany deposit are comprised of two geochemically distinct groups.  The igneous rocks that comprise the matrix of the East and West pipes that are coeval and post-date mineralization, show a particular similarity to the syenites of the Nagagami River Alkalic Complex, while the second group displays a distinct geochemistry and tectonic signature.

The distinction between these two groups suggests that the Albany graphite deposit is hosted directly on the Nagagami River Alkalic Complex’s southern margin, the pipes themselves are formed from the NRAC’s parent magma, and the host rocks represent a portion of the NRAC as well as the country rock of the Marmion/Eastern Wabigoon terrane.

The Gunflint Formation near Thunder Bay, Ontario has undergone very low grades of metamorphism. In this study, two outcrops of the Gunflint Formation near Thunder Bay were analyzed for their deformation microstructures, which are used to constrain temperature conditions of the Gunflint Formation during deformation.  Common deformation microstructures within this Formation are pressure-solution stylolites, deformed calcite veins, deformed quartz veins and kinked illite-mica laths.  All processes that formed these microstructures operate at temperatures between 150°C to 300°C, providing a temperature constraint of the system during deformation. In addition to deformation microstructures, semi-quantitative x-ray diffraction (XRD) phase analysis was completed on one sample from a hanging wall ramp of the Gunflint Formation.  XRD analysis shows likely minor interlayered illite-smectite, as well as the ordered illite-muscovite 2M1 polytype.  These phases are interpreted to represent metamorphic temperatures between 200°C and 300°C.  Combining this with the deformation microstructures, all structures and phases present are satisfied by a temperature range between 200°C and 300°C, corresponding to the anchizone of metamorphism (sub-greenschist facies metamorphism, specifically the prehnite-pumpellyite facies).

Given this temperature range, and assuming an average geothermal gradient of 30°C/km, the depth of the Gunflint Formation during deformation and metamorphism is shown to be anywhere between 6 km and 10 km.  This depth is consistent with tectonic loading, due to bed-parallel thrust faults.  Based on the findings of this thesis, the Gunflint Formation near Thunder Bay is interpreted to represent an eroded foreland thrust and fold belt.

The Hemlo gold deposit is located 41 km east of the town of Marathon in northern Ontario, Canada.  The deposit was discovered in 1980 and active mining in the camp was initiated in 1985.  The different lithologies hosting gold mineralization at this deposit were classified and assigned names that were acceptable at the time of its discovery and development.  This study revisits and re-interprets the classification and nomenclature of the rocks cropping out west of the C-zone open pit.  This lithological classification is reinterpreted using a modern comprehension of plate tectonic dynamics, in conjunction with, the effects of brittle and crystal plastic deformation mechanisms observed in recent material science studies.  Microstructural investigations of the samples collected suggest that the rocks are a mylonitized coarse-grained quartzo-feldspathic plutonic rock.  Microstructural analyses of the samples under transmitted and reflected light indicate that strain has been preferentially accommodated at different rates and that brittle-ductile deformation was progressive and occurred as numerous incremental events.  Such deformation resulted in rocks exhibiting different textures in hand samples but having homogeneous features when observed microscopically.  A weak schistosity results in abundant and relatively coarse-grained quartz and feldspar porphyroclasts, whereas a strong schistosity results in a low abundance and finer-grained quartz and feldspars porphyroclasts.  The magnitude of strain can be approximated using the porphyroclast size and their abundance.  This study also observed that gold mineralization in the Hemlo gold camp occurs at or near strain gradients and that gold mineralization has an affinity for competency contrast.

The western Lake St. Joseph area in Northwestern Ontario is underlain by Archean metavolcanic and metasedimentary rocks.  The strata, referred to as the Lake St. Joseph Group comprise three formations representative of mafic to felsic volcanic cyclicity.  The Blackstone Formation, stratigraphically the lowest, contains a lower member composed of predominantly high-Mg, low-K tholeiitic pillowed basalts and an upper member composed of rhyliticflows and pyroclastic rocks.  The overlying Western Lake St. Joseph Formation contains a lower member composed of predominantly calc-alkaline massive and pillowed basalts and an upper member composed of dacitic pyroclastic and epiclastic rocks.  The overlying Carling Formation contains a volcanic member and a sedimentary member.  The volcanic member is composed predominantly of high-Fe, low-K tholeiitic pillow breccias and dacitic to rhyolitic epiclastic and pyroclastic rocks.  The sedimentary member consists of basal grewacke turbidites and laminated iron formation of economic potential overlain by chloritic classical turbidites.  These sedimentary rocks are overlain by massive and cross-bedded arkosic greywackes which are in turn overlain by conglomerate and pebbly sandstone.

The deformation of the rocks is expressed by isoclinal folding, most evident on Eagle Island, and development of the regional Lake St. Joseph Fault.  Contact and regional metamorphism (lower to middle greenschist facies) have also affected the rocks.

The primary structures, vertical and lateral variations in the felsic volcanic rocks of the Blackstone and Western Lake St. Joseph Formations indicate deposition on a subaqueous paleoslope.  Similarly the felsic volcanic rocks of the Carling Formation indicate subaqueous deposition on a different paleoslope.

The lithologies, primary structures, vertical and lateral variations of the units in the sedimentary member of the Carling Formation indicate deposition on a prograding submarine fan.  Meyn and Palonen (1980) support this interpretation.

Reconstruction of the paleoenvironment envisages three stages of evolution.  In stage 1 the Blackstone and Western St. Joseph Formations are extruded and deposited on the flank of a volcanic edifice.  In stage 2 the volcanic member of the Carling Formation is extruded from a separate vent and in part deposited upon the degradation products of stage 1.  In stage 3 laminated iron formation is deposited with clastic sediments in a submarine fan-basin plain system to form the sedimentary member of the Carling Formation.

A copy of the thesis can be downloaded here

One or possibly two overlapping periods of deformation are responsible for the structures observed in the rocks in the Seine River area.  This deformation has resulted in the formation of tight to isoclinical, non-plane approximately F₁ folds with steeply dipping E-W striking axial surfaces.  A late stage deformation has resulted in the formation of a crenulation cleavage, kink bands and minor faulting.  There is also limited evidence of a possible pre-F₁ folding event.

Two major litholigical groups are present in the study area: shallow water metasedimentary rocks of the Seine Group and metavolcanic rocks.  The Seine Group metasedimentary rocks are younger than the metavolcanic rocks in the western part of the area but may be older than similar metavolcanic rocks in the eastern part of the area.  Two ages of metavolcanic rocks therefore appear to be present: older metavolcanic rocks in the west which underlie the Seine Group, and younger metavolcanic rocks in the east which overlie the Seine Group.

Regional metamorphism to the chlorite to biotite zone greenschist facies was synkienematic with the deformation of the rocks but may have outlasted the folding in places.

Strain analysis from the metasedimentary rocks reveals that the conglomerate units are more intensely strained than arenite units, although all the stain ellipsoids are of the flattened (K < 1) type.

Average shortening in Z ranges from 52% for arenite units to 75% for conglomerate units.  A new empirical approach suggested  by the writer and Dr. Borradaile for assessing competence contrasts between strain markers and matrix is outlined.  This method uses the effects of competent markers on cleavage traces in the matrix of conglomerates.

A copy of the thesis can be downloaded here

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.

A copy of the thesis can be downloaded here

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.

A copy of the thesis can be downloaded here