Earth Sciences - Theses, Dissertations, and other Required Graduate Degree Essays

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Modelling hard rock pillars using a Synthetic Rock Mass approach

Author: 
Date created: 
2014-03-20
Abstract: 

Rock pillar strength and the characterisation of pillar failure mechanisms are of major importance in mine design. The recently developed Synthetic Rock Mass (SRM) approach provides a state-of-the-art numerical technique to more accurately characterize the mechanical properties of rock pillars. The SRM approach used in this thesis is based on a combination of two well accepted numerical methods, a Particle Flow Code (PFC3D) incorporating a Discrete Fracture Network (DFN). This research presents the results of a systematic study of the use of SRM modelling for hard rock pillars. The effect of assumed joint set characteristics (orientation and persistence) is first investigated through comparison of the numerical results from a series of conceptual pillar models. The joint set properties are shown to have important controls on the pillar peak strength, deformation modulus, lateral stiffness and the pillar strain-softening gradient in the post-peak stage. The effect of pillar confinement is then examined using two conceptual pillar models with varied slenderness (Width/Height ratio). The pillar confinement effect is investigated by comparing the axial and lateral stresses at the pillar core and pillar boundaries, and this effect attributed to the lateral restraint due to the loading platens. The confinement effect is further examined using a series of triaxial compression test simulations in which the pillar peak strength, residual strength and post-peak strain-softening gradient are quantified. Simulations of the development of 3D cracks in two jointed pillar models, including wing cracks, large scale crack coalescence and step path failure are presented. A 3D visualisation of internal pillar failure mechanisms is illustrated by examining crack development and the changes in the localised stresses within the pillar model. Research presented will contribute significantly to the development of a more robust SRM approach for rock pillar design.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Doug Stead
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Diachronous deformation, metamorphism and exhumation in the northern Canadian Cordillera: revealed from pressure-temperature-time deformation paths of former mid-crustal rocks

Date created: 
2014-03-26
Abstract: 

The lowest structural and stratigraphic levels of the Yukon-Tanana terrane and the structurally underlying parautochthonous North American margin rocks were metamorphosed at similar conditions (7.5 – 9 kbar; 600 – 680 °C) and share a common style of deformation, characterized by the transposition of lithologic contacts and primary compositional layering into a regional ductile foliation (ST) with at least one generation of intrafolial isoclinal folds. Equilibrium assemblage modeling and in situ U-Th-Pb SHRIMP dating of monazite are used to place quantitative constraints on the conditions and timing of deformation, metamorphism and subsequent decompression. These data reveal that these fabrics, and the associated metamorphism, did not develop during a single tectono-metamorphic event. Rather, ductile deformation and high-grade metamorphism developed diachronously. Rocks deformed and metamorphosed in the Permo-Triassic and Early Jurassic were exhumed in the Early Jurassic, while rocks to the northeast in the Finlayson domain were buried, heated and ductiley deformed at mid-crustal levels (~25 km depth) from the Middle Jurassic to Early Cretaceous (c. 169 – 142 Ma). Metamorphism continued at an even deeper crustal level (~ 30 km depth, as recorded in the Australia Mountain domain), propagating downward into the parautochthonous North American crust in the Early Cretaceous (c. 146 – 118 Ma). Together, these data reveal a spatial and temporal pattern of structurally downward younging deformation and metamorphism that corresponds with the foreland-directed growth of a critically tapered orogenic wedge. In this model, rocks in front of the wedge are episodically underthrust downward into a distributed, high-grade transposition shear zone at 25 to 30 kilometres depth near the base of the overriding wedge. Rocks previously underthrust, buried and metamorphosed are progressively exhumed to higher structural levels within the wedge, as the upper crust enters a state of extension in order to maintain a critically tapered wedge. Rocks that occupied the mid-crustal shear zone in the Middle Jurassic and Early Cretaceous (Finlayson and Australia Mountain domains) were exhumed in the mid-Cretaceous along southeast-directed (orogen-parallel) extensional faults, from beneath a supracrustal ‘lid’ that had previously been metamorphosed and ductiley deformed at amphibolite facies in the Permo-Triassic and Early Jurassic.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Dan Gibson
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Late Holocene history of Squamish River north of Brackendale, British Columbia

Date created: 
2014-03-14
Abstract: 

Laminated silt, organic-rich silt, and peat exposed in the banks of Squamish River north of Brackendale, British Columbia, provide evidence for a lake impounded behind Cheekye Fan during the late Holocene. The lake gradually filled with sediment as Squamish River advanced its delta and floodplain southward toward the fan. Radiocarbon ages on detrital and growth-position plant fossils provide evidence that the lake reached up to 9 km upstream of Cheekye Fan about 3400 years ago and persisted until about 2300 years ago. Geomorphic observations and the distribution of fine-grained facies indicate that both Cheakamus and Squamish rivers contributed sediment to the lake; consequently, different depositional environments existed near Cheekye Fan than farther upstream. Debris flows that travelled down Cheekye River to Cheakamus River provided fine-grained sediment that accumulated in the deepest part of the lake just north of the fan. Farther upstream, organic-rich silt was deposited in fens and marshes surrounding the lake. Squamish River is confined by steep banks of cobble-boulder gravel 1.5–2 km north of the present Cheakamus-Squamish confluence, suggesting that coarse sediment transported by Cheakamus River controlled the lake outlet and, accordingly, lake level. As sediment delivery from Cheakamus and Cheekye rivers declined through the late Holocene, the lake outlet was progressively lowered and the lake drained. Sedimentation in Squamish Valley upstream of Cheekye Fan is also influenced by landslides at Mt. Cayley, 45 km upstream. A large landslide at Mt. Cayley about 1100 years ago produced a sediment pulse that propagated downstream and caused the floodplain above Cheekye Fan to aggrade. Sand buried the remaining fens that covered part of the low-gradient floodplain, leading to their replacement by coniferous and riparian forest. The model that I use to interpret Squamish River sedimentary environments can be applied to other low-gradient floodplains influenced by alluvial fans.

Document type: 
Thesis
File(s): 
Senior supervisor: 
John Clague
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Paleoenvironmental interpretation and depositional process classification of allomembers D and E, lower Horseshoe Canyon Formation, Alberta, Canada

Date created: 
2014-03-04
Abstract: 

Outcrops of allomembers D and E of the Late Cretaceous, Horseshoe Canyon Formation comprise marginal-marine units deposited on the western margin of the Western Interior Seaway. Associated facies are grouped into seven element complexes (EC; equivalent to facies associations) and 3 larger-scale element complex assemblages (ECA; equivalent to a depositional setting). Allomember D is classified as a tide-dominated, fluvial-influenced (Tf) ECA, and comprises two element complexes: Tf-tidal flat EC and F-onshore EC. Allomember E1 forms a tide-dominated, fluvial-influenced, wave-affected (Tfw) ECA that is composed of four ECs: Twf-tidal flat, Ft-channelized-A, Ft-channelized-B and F-onshore ECs. Allomember E2 forms a wave-dominated, tide-influenced, fluvial-affected (Wtf) ECA that consists of four ECs: Wtf-lobe, Wft-mouthbar, Tf-tidal flat EC and F-onshore ECs. Through classification of the element complexes within the allomembers, lateral and vertical changes in hydraulic processes are recorded and analyzed, highlighting the depositional variability within single parasequences and between parasequence sets in marginal-marine environments.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Shahin Dashtgard
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

The northern Cache Creek terrane: record of Middle Triassic arc activity and Jurassic-Cretaceous terrane imbrication

Author: 
Date created: 
2014-01-24
Abstract: 

The northern termination of the Cache Creek terrane in the Cordillera contains oceanic crustal lithologies including subalkaline mafic intrusive rocks with an arc geochemical signature, mafic volcanics with arc to back-arc signatures, and an arc-flanking volcaniclastic succession informally termed the Michie formation. This formation contains unimodal zircon populations with U-Pb dates of 245.85 ± 0.07 and 244.64 ± 0.08 Ma. These dates differ from the dominant detrital zircon age population of ca. 190 Ma found in the adjacent Whitehorse trough, but are similar to igneous crystallization ages of the Kutcho arc of northern British Columbia. Two main faults record oppositely verging deformational events: 1) The Judas Mountain thrust, a west-verging structure that emplaced Cache Creek terrane rocks above Stikinia and the Whitehorse trough, and 2) the Mount Michie thrust, an east-verging second phase structure that imbricated Stikinia and Whitehorse trough rocks onto and replaced them over the Cache Creek terrane.

Document type: 
Thesis
Senior supervisor: 
Dan Gibson
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Multiphase flow and reactive transport modelling of CO2 storage in heterogeneous reservoirs

Date created: 
2013-12-06
Abstract: 

This study addresses how physical heterogeneity, representing different sedimentary rock layers and the relationships between those layers, impacts the distribution of CO2, and thus the type and extent of mineral dissolution and precipitation reactions during CO2 geologic storage in deep saline aquifers. Numerical multiphase flow (TOUGH2) and reactive transport codes (TOUGHREACT) were used to construct a series of reservoir scale simulations to investigate how the flow controlling parameter values, distribution, and grid refinement of various hydrostratigraphic units (HSUs) affect the distribution of CO2, pH and mineral reactions. Physical heterogeneity is critical for controlling the distribution of supercritical and dissolved CO2, the redistribution of ions from geochemically reactive materials to more stable portions of the reservoir, mixing and dilution of CO2-rich waters, and the extent of mineral dissolution and precipitation reactions. The highest magnitude of carbonate mineral precipitation occurs at the sandstone-siltstone interface and along the extent of the CO2-water contact.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Dirk Kirste
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Facies Modelling of a Tide-Influenced, River-Dominated Delta, Fraser River Delta, British Columbia, Canada

Author: 
Date created: 
2014-01-27
Abstract: 

The Fraser River delta is a tide-influenced, river-dominated delta that exhibits distinct asymmetry in sedimentological and neoichnological character between the updrift (south) and downdrift (north) sides of the delta front and upper prodelta (< 200 m water depth). The updrift portion consists mainly of sands and heterolithic sand and mud bedsets with low bioturbation intensities (BI 0-3). Trace suites are sporadically distributed and include elements of the Skolithos Ichnofacies. The downdrift portion is composed of homogeneous mud beds and bedsets with significantly higher intensity of bioturbation (BI 3-6). Trace suites are attributable to the Cruziana Ichnofacies. The asymmetrical distribution of sediment and burrows on the delta is primarily controlled by strong northward-directed tidal currents. Physical sedimentary processes differ significantly between updrift and downdrift sides of the delta. The updrift delta is mainly an area of erosion in which strong tidal currents scour previously deposited sediments. This scouring reveals underlying sandy paleo-distributary channel deposits. The downdrift delta, on the other hand, is an area of net sediment (predominantly mud) accumulation. Sandy material eroded from the updrift delta is trapped within a deep submarine channel and does not get redistributed to the downdrift delta. This results in contrasting substrate types between the updrift and downdrift delta. The asymmetrical character of the Fraser River delta is similar in its sedimentological signature, but ichnologically distinct, from the wave-dominated asymmetric delta model. Neoichnological trends are opposite to that observed in wave-dominated asymmetrical deltas, in that the trace diversity and density are higher on the downdrift side of the delta front than the updrift side. Based on the results presented herein, a new tidally asymmetric delta model is proposed which, overall, leads to a more robust asymmetric delta model. The most important aspect of this new model is that tidally-influenced asymmetric deltas are not depth-dependent, and therefore, they have greater potential to develop in deep water settings than wave-dominated asymmetric deltas.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Shahin Dashtgard
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Flood hazard and risk in Lillooet River valley, British Columbia, Canada

Author: 
Date created: 
2013-09-09
Abstract: 

This thesis examines flood hazard in Lillooet River valley in the southern Coast Mountains of British Columbia, Canada. My research is multi-disciplinary: I used earth science methods to estimate pre-historical flood frequency and sediment yield, as well social science theory to study the process of knowledge transfer between the scientific community and local stakeholders. The results from this thesis contribute to and complement previous earth science and natural hazard studies in Lillooet River valley, while furthermore providing knowledge for river and floodplain management. The results also shed a light on the communication of scientific knowledge to local emergency managers and the use of such information at the local level.My thesis comprises three studies. First, I compiled a varve chronology spanning 825 years (AD 1179-2004) from annually layered sediments (varves) recovered from Lillooet Lake. I compared twentieth-century discharge records of Lillooet River to the contemporary part of the varve chronology to determine the relation between river discharge and varve thickness. Based on this relation, I examined the entire 825-year varve chronology for the floods it might record. Second, I made annual sediment yield estimates for the period AD 1629-1997 and compared them to estimates derived from Lillooet Lake cores by previous researchers. I compared times of anomalously high sediment yield to ages of large landslides and floods in the watershed, and to times of marked glacier advance and retreat in order to understand controls on sediment delivery. I assessed the persistence of high sediment input episodes using statistical methods. Third, I assessed the history and current flood management policy landscape at the federal, provincial, and local levels. In the context of the transfer of flood management responsibility from the British Columbia Government to municipalities in 2003, I interviewed local floodplain and emergency managers on their use of scientific knowledge in preparing for flooding in Lillooet River valley.

Document type: 
Thesis
File(s): 
Senior supervisor: 
John Clague
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Boiling as a mechanism for colour zonations observed at the Byrud emerald deposit, Eidsvoll, Norway

Date created: 
2013-12-13
Abstract: 

The Byrud emerald deposit was first discovered in the early 1860s, near Lake Mjøsa, southern Norway. From a geological, gemmological, and geochemical perspective, the Byrud emeralds are of great interest as they are vanadium-rich rather than chromium-rich, which is uncommon for the majority of emeralds worldwide. The emerald deposit genesis is consistent with a typical granite-related emerald vein system from dominantly magmatic fluid sources. Emerald mineralization occurs within pegmatite veins which are hosted within Cambrian black shale and Late Carboniferous quartz syenite sills, and intruded by a Permo-Triassic alkaline granite. Muscovite from an emerald-bearing pegmatite at Byrud yielded an Ar-Ar plateau age of 233.4 ± 2.0 Ma. The emerald display colour zonation alternating between emerald and beryl. Two dominant fluid inclusions types are identified: two-phase (vapour+liquid) and three-phase (brine+vapour+halite) fluid inclusions. Raman analyses indicate molar gas fractions for CO2, N2, CH4, and H2S are approximately 0.8974, 0.0261, 0.0354, and 0.0410, respectively. Formational temperatures and pressures of approximately 160 °C to 385 °C and below 1000 bars were derived from fluid inclusion data and lithostatic pressure estimates from fluid inclusion studies within the Oslo Paleorift.The emerald from the Byrud mine displays growth zoning and banding from green emerald to colourless beryl. The use of chemical analyses, fluid inclusions and petrography is consistent with boiling as a mechanism for this distinct ‘striped’ colour zonation or banding. These zones are due to enrichment of vanadium and chromium in the green bands which host salt-saturated aqueous primary fluid inclusions with an overall 31 mass percent NaCl equivalent salinity. Vapour-rich primary fluid inclusions dominate within the colourless bands of the zoned emerald. The chemical compositions of the salt-saturated and the vapour-rich inclusions indicate they represent the coexisting liquid and vapour portions of a two-phase boiling system. This “boiling” formational model has application to not only other emerald deposits, but also other zoned gem deposits worldwide.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Dan Marshall
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Deep-seated gravitational slope deformations near the Trans-Alaska Pipeline, east-central Alaska Range

Date created: 
2013-09-03
Abstract: 

I investigated active deep-seated gravitational slope deformation (DSGSD) near the Trans-Alaska Pipeline and Richardson Highway in the east-central Alaska Range, Alaska, USA. I documented the presence, spatial extent, and rates of DSGSD using field-geology methods and optical, SAR, and D-InSAR remote-sensing images. I also documented and mapped many of the morphological, geological, and structural characteristics of slopes undergoing DSGSD, and constructed conceptual numerical models to better understand potential deformation mechanisms. Results confirm that many large DSGSD slopes in the study area are actively deforming. Deformation rates range from less than a millimetre per month to more than ten centimetres per month, and are spatially and temporally varient within each slope. Deforming slopes are characterized by differential movement of kilometre-scale rock blocks. Recent climatic changes and strong seismic shaking, especially during the recent 2002 Denali Fault earthquake, have exacerbated ongoing deformation. Study-area DSGSDs should be considered capable of generating long-runout rock avalanches that could directly sever the Trans-Alaska Pipeline and Richardson Highway, or that could dam up valleys and lead to the buildup and catastrophic failure of landslide-dammed lakes capable of impacting said infrastructure.

Document type: 
Thesis
Senior supervisor: 
John Clague
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.