QSpace Collection:

Environmental Change in Middle Ordovician carbonates near Little Cataraqui Creek Conservation Area, Kingston ON

2013-05-14T12:15:38Z

Title: Environmental Change in Middle Ordovician carbonates near Little Cataraqui Creek Conservation Area, Kingston ON Authors: Shuster, Sonya Abstract: The Black River Group is a carbonate succession in southern Ontario and northern New York State that was deposited in the Middle Ordovician. The rocks of this Group accumulated in a tropical shallow marine environment. The focus of this study is a 16m succession, exposed in a road cut north of Kingston, Ontario. The section is divided into three main zones. The bottom 10m consists primarily of carbonate mudstones with some calcite nodules and a sparse and highly restricted fossil assemblage of mainly salinity tolerant invertebrates such as ostracods. These rocks are interpreted as being a series of primarily peritidal deposits that were generally stressed and hypersaline. The next 2m is primarily an ooid grainstone, with and without fossils. It is interpreted as having been deposited in a sand shoal. The upper 4m consists primarily of floatstones with a lime-mud or fossil-wackestone matrix as well as some oolites and contains an abundant and diverse fossil assemblage that includes stenohaline organisms such as echinoderms and articulate brachiopods. The upper part is interpreted as being deeper water within the photic zone and contains an ooid sand shoal and a bryozoan biostrome, among other facies. This upper part is generally less stressed and had normal marine salinity. The deepening-upwards trend observed in this outcrop is consistent with the Black River Group as a whole, and is generally regarded as reflecting the regional sea level rise that was occurring at this time due to the passing of the peripheral bulge.

Stable Thallium Isotope Fractionation in Uraninites

2013-05-09T05:18:51Z

Title: Stable Thallium Isotope Fractionation in Uraninites Authors: Tupper, Wynn Abstract: Thallium isotopic ratios, (ε205Tl = 205Tl/203Tl deviation from a reference ratio) are measured in uraninite samples representative of diverse geochemical systems responsible for high grade UO2 precipitation. Notably those deposit styles involve from the reduction of uranium complexes in aqueous solutions, and uraninite precipitation from saline fluids. Measureable isotopic fractionation, ε205Tl, must produce a result that exceeds analytical reference error. Thallium isotopic ratios are obtained by multiple collector-inductively coupled plasma mass spectrometry (MC-ICP-MS). For reliable MC-ICP-MS results require that thallium is extracted entirely from the mineral sample. Digestion of uraninite samples is a series of acid digestions, and consequent thallium separation from ion exchange chromatography conducted by acids with minor (~2%) concentrations of oxidizing agents, such as Br2, to disable ion reduction. Separation of Thallium is done in correspondence with molybdenum separation for a separate study on Mo isotopic ratios. Thallium is sensitive to oxidation changes in fluids. Further, the sampled deposit styles display a spectrum of oxidation conditions, solution compositions, temperatures and pressures, theoretically yielding various detectable ε205Tl values. Data for eight samples are produced, where all ε205Tl are negative relative to NIST, the most negative being -5.5 and the least being -0.7. Correlations with various multi-element data, 234U/238U, 235U/238U, and deposit chemistry are graphed to assess the ability to predict ε205Tl. It appears that ε205Tl data is negatively correlated which uranium and thallium concentration, as well as Fe+Mn concentration in. The explanation of this is the ability of thallium to be present as a trivalent ion within basinal high temperature alkaline solutions, those fluids associated with unconformity related deposit types. However, an alternate explanation is that the depletion of thallium correlated to alteration and subsequent interaction of uraninites by fluids after genesis that result in ε205Tl values near 0 at such low concentrations of thallium. Description: Thallium isotope geochemistry

Characterization and 40Ar/39Ar Dating of Hornblende from the Nelson Plutonic Suite, Southern Kootenay Arc, SE, B.C.

2013-05-04T05:10:32Z

Title: Characterization and 40Ar/39Ar Dating of Hornblende from the Nelson Plutonic Suite, Southern Kootenay Arc, SE, B.C. Authors: Pickett, Jessica Abstract: From Mid-Jurassic to Eocene time the Kootenay Arc in southeastern B.C. experienced several episodes of tectonism, metamorphism and plutonism. The focus of this study is the tectonothermal history of the Mine and Wall stocks (biotite-hornblende-epidote granodiorite; U-Pb dates; 171 and 168 Ma) which are the most easterly plutons of the Nelson Suite in the area. Previous K-Ar and 40Ar/39Ar studies of micas from these plutons revealed cooling and overprinting dates between 166 Ma in the west and 67 Ma in the east. For this study, 11 hornblende separates were prepared from the same rocks, checked for purity by SEM and chemically analyzed by electron microprobe. 40Ar/39Ar age spectra for most of these hornblendes show well defined plateaux with plateau dates of ~170 Ma. Inverse isochron reveal the presence of excess 40Ar and yield better estimates of the time of cooling through the closure temperature of hornblende indicating that most of these plutons had cooled to < 500 oC by ~168 Ma. Only hornblende from the Mine stock east of the Next Creek fault shows evidence of a later thermal disturbance in Cretaceous or later time. New Al-in-Hornblende pressure estimates increase to the north and east, and are in general agreement with previous estimates from pelitic assemblages (4 to 6 Kbar) in the contact aureole. Highest pressures are east of the Next Creek fault near the eastern margin of the Mine stock. This zone marks a sharp decrease in mica dates. West of the fault, mid-Jurassic to Early-Cretaceous dates with no evidence of Eocene overprinting are typical. The higher pressures and Late Cretaceous-to-Eocene dates east of the fault are consistent with east-side-up differential uplift and unroofing related to regional Eocene extension.

Microstructural and crystallographic-preferred orientation analysis of the Okanagan Valley fault system, British Columbia

2013-05-02T04:59:06Z

Title: Microstructural and crystallographic-preferred orientation analysis of the Okanagan Valley fault system, British Columbia Authors: Brown, Danielle Abstract: This study focuses on the structural evolution of the high-grade metamorphic infrastructure of the southeastern Canadian Cordillera exposed in a crustal section between Sicamous and Revelstoke, British Columbia. Of particular interest, in the Omineca morphogeological belt, is the Okanagan Valley fault system (OVfs), which consists of the west-dipping Okanagan Valley detachment fault and its sillimanite-grade footwall gneiss, part of the Shuswap metamorphic complex (SMC) and interpreted to be exhumed during early Cenozoic continental extension. Structural measurements and oriented samples were collected along a sixty-kilometre ENE-WSW oriented profile following the Trans-Canada Highway. Microstructural and quartz crystallographic-preferred orientation (CPO) analysis of the OVfs using standard microscope and Fabric Analyser (FA) techniques are used to characterize the sense of shear, dominant slip systems, ductile flow style, and temperature of deformation across the SMC. Coupled with textural mapping, FA techniques identify a variety of non-coaxial slip systems in the SMC, dominated by prism , rhomb , and prism slips. The recurrence of CPO fabrics moving towards prism slip suggests deformation temperatures greater than 600°C in the SMC. The temperature of deformation is consistent with observed sillimanite-grade metamorphism and quartz deformation regimes. Petrofabric analyses suggest a kinematic shear reversal from top-to-the-west shear dominated at the uppermost structural level of the OVfs to top-to-the-east shear dominated at the base, concurrent with evidence of orogen-parallel, N-S directed flow. The initial kinematic reference frame used to ascertain sense of shear during fieldwork utilized the peak metamorphic mineral (sillimanite) elongation orientation as a proxy for the finite stretching orientation. However, for several samples the quality of the quartz CPO iii fabric vastly improved after rotation of the data, implying that the mineral lineation observed in outcrop does not always coincide with the quartz CPO kinematic stretching direction. The discrepancy between mineral lineation and the quartz CPO stretching direction indicates that either different stages of deformation are being recorded by the quartz and peak metamorphic minerals, perhaps as a function of decreasing temperature within an exhuming shear zone, or that the shear system recorded in the quartz CPO is governed by non-plane strain deformation. There is much debate and uncertainty regarding the exhumation mechanisms that resulted in the exposure of the SMC. It is the aim of this investigation to compile a detailed section of deformation to gain a concrete understanding of the strain partitioning in the SMC. This structural analysis should be integrated in the future with 40Ar/39Ar cooling ages, U-Pb thermochronology, and (U-Th)/He and fission-track dating to help unravel the temperature-deformation history of these rocks, and provide a better understanding of the exhumation processes linked to the OVfs. Description: Co-supervised by Dr. Laurent Godin and Dr. H. Dan Gibson