Forested streams are closely linked to terrestrial catchments which affects their biogeochemical cycling and carbon inputs. Catchment disturbances alter stream water quality and food webs, including changes in productivity. Such changes in stream conditions can potentially alter consumers’ reliance on autochthonous (in-stream) or allochthonous (terrestrial) sources and mercury bioaccumulation. A recent outbreak of the spruce budworm (SBW) that feeds on spruce and fir trees has provided the unique opportunity to examine stream food web responses across watersheds experiencing a range of defoliation in the Gaspé Peninsula, Québec. This project compares streams in twelve watersheds which were selectively sprayed to control SBW and create a gradient in defoliation. Food web samples (food sources, invertebrates, fish) were analyzed for stable isotopes of carbon and nitrogen in 2019 and 2020 to characterize food web structure, and algal productivity was measured in 2019. Hierarchical partitioning models were used throughout the study to compare the contributions of various local and landscape conditions to stream responses. Models indicated that watershed defoliation contributed to increasing autochthonous production, although some invertebrates were more allochthonous in heavily defoliated watersheds, and brook diets were unaffected by defoliation. Next, food web samples were analyzed for methylmercury (food sources, invertebrates) or total mercury (fish) and trophic magnification slopes were determined for each stream food web. Mercury levels in carnivorous invertebrates and brook trout were driven by dissolved organic carbon (DOC), but not consumer autochthony or watershed defoliation. Additionally, rates of trophic magnification were not related to defoliation severity or DOC. This study found that defoliation contributed to increasing autochthonous production and invertebrate consumer allochthony. However, this disturbance did not increase consumer mercury levels or biomagnification in stream food webs. These findings suggest that intervention to reduce defoliation would mitigate algal responses and dietary shifts, but not mercury cycling as it is influenced by DOC levels in the streams of this region. / Thesis / Master of Science (MSc) / A recent spruce budworm outbreak is causing widespread defoliation of spruce and fir trees, but the impacts to stream environments, including primary production, its consumption, and contaminant levels, are largely unknown. Streams are sensitive to conditions in the surrounding terrestrial environment, as such changes can affect the diets of stream invertebrates and fish and are also linked to increased contaminant levels in aquatic organisms. Specifically, mercury is a metal that is transferred through diet and can reach toxic levels in fish. This study found that defoliation is contributing to increased algal production in streams in the Gaspé Peninsula, Québec. However, some stream invertebrates consumed more terrestrial material in streams that had heavier defoliation. Furthermore, defoliation and algal diets did not increase levels of mercury in aquatic organisms, but this contaminant was affected by increasing concentrations of dissolved organic carbon in the streams. These findings suggest that forest defoliation can alter organisms’ diets but not mercury levels.

<p> S^32/S^34 ratios have been determined between some coexisting sulfides from the Heath Steele B-1 orebody and five other stratiform deposits in the Bathurst-Newcastle area, New Brunswick, and in crushed ore samples and pyrites from three across deposit profiles in the B-1 orebody. Zn, Cu, Pb and Ag abundances have been established across the orebody. Fractionations of S^32/S^34 ratios between coexisting sulfides have been determined in heating experiments at temperatures of 350 to 500°C and isotope effects measured in aqueous precipitation and exchange experiments at 25°C. S^32/S^34 fractionations between given coexisting sulfides from all the sulfide deposits are found to show only small variations. Isotope exchange is generally rapid in dry sulfide systems. Metal sulfides in aqueous solutions are slightly enriched in S^32 relative to the H2S with which they precipitate or communicate. It is concluded that the sulfide deposits have been regionally metamorphosed. The origins that have been proposed for the deposits so far are discussed and a model is suggested to explain the sulfur isotope and base metal abundances in the B-1 orebody.</p> / Thesis / Doctor of Philosophy (PhD)

<p> An age of approximately 55K years was found for the St. Clair basin clays using helium isotope dating. This is about 5 times larger than the date obtained from the more accepted carbon-14 method and from other geological evidence. Diffusion of helium from crustal rocks against a flow of approximately 0.03-0.05 cm a· ' is the primary reason for this discrepancy. Mixing of the groundwater with a meteoric component has an opposite effect tending to lower the helium age. </p> / Thesis / Bachelor of Science (BSc)

<p> The photochemistry of 1,1-diphenylsilacyclobutane has been studied by steady-state and nanosecond laser flash photolysis (NLFP) techniques in order to investigate the mechanism of reaction of a transient silene with alcohols. NLFP of 1,1-diphenylsilacyclobutane (I) in acetonitrile solution at 325 nm results in the formation of 1,1-diphenylsilene (II) derived from excited-state [2+2]-cycloreversion of the silacyclobutane. The transient has a lifetime of 100 ns - 1.2 μS in acetonitrile solution at room temperature, depending on the presence of water in the solvent. Steady-state photolysis in the presence of various σ-bonded nucleophiles such as methanol results in the generation of a single product in each case, consistent with addition of the nucleophile to the silene (II). Absolute rate constants (kq) have been determined by NLFP techniques for reactions of the silene with water, methanol, ethanol, tert-butyl alcohol, 2-propanol, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, and glacial acetic acid. The rate constants (kq) illustrate the following characteristics: linear quenching plots characteristic of second order kinetics, observation of small but detectable deuterium kinetic isotope effects, and an inverse Arrhenius temperature dependence. Two possible mechanisms will be discussed based on these results. (See Mechanisms in Thesis)</p> / Thesis / Master of Science (MSc)

<p> Oxygen and hydrogen isotopic distributions have been studied for rocks from a 100 km transect in the central Superior Province of Ontario, Canada. The transect represents progressively deeper terrains of the Michipicoten Greenstone Belt (MGB), the Wawa Gneiss Terrane (WGT), and the Kapuskasing Structural Zone (KSZ), which correspond to an increase of metamorphic grade and are interpreted as an oblique section through approximately 20 km of crustal thickness. The rocks in the terrains range in age from ~2.76 to ~2.60 Ga, with fewer later intrusions.</p> <p> Equivalent lithologic types have similar δ18O range at middle and lower crustal levels (WGT and KSZ). Tonalitic to granodioritic rocks range from 6.4%o to 9.5o/oo; Dioritic and anorthositic rocks range from 5.5o/oo to 7.6o/oo; a majority of the mafic gneisses (group 1) range from 5.7o/oo to 7.1o/oo, while group 2 mafic gneisses range from 8. 1o/oo to 9.5o/oo. δ18O values of the rocks exhibit a remarkable correlation with SiO2 values, similar to that observed in unaltered plutonic rocks of equivalent composition. Paragneisses have significantly higher δ18O values, 9.3o/oo to 12.2o/oo. Low-grade metavolcanic and metasedimentary rocks of the MGB are 18O-enriched compared to their high-grade equivalents in the KSZ and WGT, 7.4o/oo to 13.3o/oo for mafic to felsic metavolcanic rocks and 11.4o/oo to 14.7o/oo for clastic metasediments.</p> <p> Coexisting minerals from high-grade rocks exhibit 18O-fractionation closely consistent with isotopic equilibrium, suggesting that the isotopic system has not been grossly disturbed. Isotopic thermometers give uniform apparent temperatures, about 553°C to 584°C, across the entire transect, which are lower than the inferred metamorphic temperatures in the highest-grade (KSZ) terrane.</p> <p> The lack of distinctive isotopic differences between equivalent rock types in the KSZ and WGT suggests that there is no significant gradient in δ18O with depth in the crust or with metamorphic grade. The majority of mafic gneisses (Group 1) have δ18O values similar to fresh basalts and appear to have been emplaced either as subaerial extrusives, intrusive sills, or, less likely, as submarine extrusives that were hydrothermally altered at high temperatures. The less abundant Group 2 mafic gneisses have δ18O values typical of greenstones that were altered at low temperature by sea-water, and isotopically resemble low-grade rocks in the Michipicoten and Abitibi belts. In general, no major changes in whole-rock isotopic composition appear to have occurred during granulite facies metamorphism, implying limited flux of water or CO2.</p> <p> The continuous linear gradient in δ18O vs SiO2 in the high-grade rocks cannot be due to differentiation of a mafic source magma. A model involving an association between mantle-derived mafic magma and 18O-enriched crustal materials is more consistent with the oxygen isotopic data.</p> <p> Hydrogen isotope composition of hornblende and biotite has been analyzed from selected rocks. Mafic and anorthositic rocks from the KSZ have δD values from -58 to -62o/oo, suggesting a possible mantle-derived origin of fluid in the system. Two mafic gneisses, which are 18O-enriched, show lower δD values, -89 and -101o/oo. The depletion of deuterium is consistent with the model of low temperature alteration with seawater in a submarine environment. Mafic and tonalitic gneisses from the WGT are also depleted in deuterium, -87 to -109o/oo. Since these rocks intruded into relatively higher level of the crust and commonly contain secondary alteration minerals, it is possible that hydrothermal alteration took place at late- or post-metamorphism stage, and the source of the fluid is likely meteoritic water, The amount of water involved in the exchange was restricted, and was not enough to disturb the oxygen isotopic system in the rocks.</p> / Thesis / Master of Science (MSc)

<p> Sulphur isotope data from coexisting sulphides and sulphates from the 120m level of the Shangtancen ore body of the Taolin Pb-Zn ore deposit have been used to estimate the temperatures of sulphur mineral precipitation. The data indicate that sulphide was the dominant species in solution at both high and low temperatures. The data also show that the 𝛿34S value of total sulphur in solution was close to zero at high temperatures, but had low negative values (about -6.7‰) at low temperatures. This is interpreted in terms of the effects of mineral precipitation on the isotopic 34 composition of the solution. The decrease of the 𝛿34S value of the total sulphur with decreasing temperature was brought about because the removal from the system, by precipitation, of isotopically heavy sulphate exceeded the removal from the system, by precipitation, of isotopically light sulphide.</p> / Thesis / Bachelor of Science (BSc)

<p> Nd isotope analysis is well suited for mapping major tectonic boundaries in highly metamorphosed orogenic belts. In this study, approximately 80 samples have been analyzed to map 2 such boundaries in the Central Gneiss Belt of the Grenville Province of Ontario. In Central Ontario, lithotectonic terranes with mapped outcrops of gneisses intruded by eclogites and/or coronitic metagabbro have Nd model ages less than 1.8 Ga are interpreted as components of the allochthonous polycylic belt. More northerly terranes are comprised of similar gneissic materials, but have different types of mafic intrusives and have model ages greater than 1. 8 Ga. These terranes are interpreted as fragments of the parautochthonous belt. These two belts are divided by a major thrust, termed the Allochthon Boundary Thrust (ABT) (Rivers, et. al., 1989). Continuing to the north, another step in the Nd model ages has been used to identify and map a cryptic suture between Archean and early Proterozoic crustal materials (Dickin & McNutt, 1989). </p> <p> Along the Georgian Bay coastline, between Pointe Au Baril and Parry Sound, the Shawanaga Shear Zone has been interpreted as the location of the ABT (Culshaw, et. al., 1994). Analysis of over 50 samples are used to map the crustal formation ages in this region and have confirmed this interpretation. Orthogneisses of the Britt Domain have Nd model ages in the range 1.8- 1.9 Ga. Reworking of the original crust has given these rocks U-Pb crystallization ages of~ 1.45 Ga, which means that these rocks have been metamorphosed prior to the Grenvillian event. Crossing the ABT, the orthogneisses of the Shawanaga Domain have a younger range of crustal formation ages, 1.4 - 1.7 Ga. The U-Pb crystallization ages of these rocks are ~ 1.36 Ga, and they lack signs pre-Grenvillian metamorphism. To the south of Franklin Island, the location of the ABT is difficult to map, as outcrop lies beneath the waters of Georgian Bay. Results of the Nd isotope analyses suggest that the ABT passes through the western edge of the Snake Islands, rather than to their east, as previously interpreted (Culshaw, et. al., 1994). </p> <p> Approximately 15 Nd isotope analyses were used to investigate a recently proposed location of the ABT (Ketchum & Davidson, 2000) in the vicinity of the Powassan Batholith. Results from near Arnstein, Restoule and Magnetewan agreed with the existing location of the ABT. To the east of the Powassan Batholith, 3 Nd model ages coupled with a lack of mappable eclogites and/or coronitic metagabbros suggest that earlier interpretations of the position of the ABT may be correct and that further studies in this region are necessary. </p> <p> A cryptic suture identified by crustal formation ages has been the focus of several previous studies (Dickin & McNutt, 1989, 1990; Holmden & Dickin, 1995; Dickin, 1998; Guo & Dickin, 1996). This suture has been mapped from the Georgian Bay coast through Lake Nipissing to the Ontario-Quebec border. New Nd isotope analyses and studies of the regional magnetics have identified a thrust slice between the Grenville Front tectonic zone (GFTZ) and the parautochthonous belt. The cryptic suture appears to coincide with a previously undescribed tectonic boundary west of the Key River. To the west of this boundary, straight orthogneisses within the thrust slice have Nd model ages greater than 2.2 Ga. These differ from the orthogneisses and metaplutonic tonalites to the east of this boundary, which exhibit kilometer-scale isoclinal folds and crustal formation ages between 1.8- 2.0 Ga, the previously identified range for the Britt Domain. </p> <p> Major steps in the depleted mantle model ages are observed in all three regions, allowing mapping of the ABT and the Penokean Suture. It is concluded that, in metamorphic orogenic belts, such as the Grenville Province, detailed mapping of major tectonic boundaries is greatly enhanced by the use of Nd isotope analysis. </p> / Thesis / Master of Science (MSc)

<p> The Rio Grande Rift is a major tectonomagmatic feature of the North American craton. Physiographically, the present rift is recognized as a series of grabens and half-grabens which extend for over 1000 km from south-central Colorado into Chihuahua, Mexico. Rift structures, however, are recognized as far north as the Colorado-Wyoming border. Basaltic magmatism within the rift began by 30 Ma in southern New Mexico, and by 25 Ma in northern New Mexico and Colorado. Within-rift magmatism is low in volume in comparison to rift-related activity on the rift shoulders and flanks. </p> <p> Petrologic studies of Rio Grande Rift-related volcanics are numerous, yet focus primarily on suites erupted in north-central New Mexico and Colorado. However, recently published abstracts suggest areas of southern New Mexico are receiving much needed attention. Initial attempts at characterizing the petrologic diversity and mantle sources of rift-related volcanics have concentrated on major and trace element data, as well as the application of Sr and Nd isotopes. Only minor attention has been given to Pb isotope variations. </p> <p> This thesis contains the most recent compilation of Pb isotope data for volcanic rocks erupted within the Rio Grande Rift region. The oldest rocks included in this work are· monzonite stocks erupted c. 60 Ma within the Colorado Mineral Belt. Using Pb isotope data in combination with trace element variations and Sr-Nd isotopes, a model is developed which suggests the stocks were initially derived from mantle sources with geochemical properties similar to those which produced rift-related basaltic volcanics in northwest Colorado beginning at 25 Ma. </p> <p> Two chapters of the thesis are devoted to exploring the utility of Pb isotopes as tracers of crustal influence in continental basaltic volcanism. One deals specifically with documenting Pb isotope variations in the northwest Colorado region, whereas the second focuses on variations in the Espanola Basin of north-central New Mexico. Major results of the northwest Colorado study 1) suggest that the asthenosphere contributed to early rift (25 Ma volcanism), 2) better characterize the geochemical signature of lithospheric and asthenospheric sources during periods of active volcanism, and 3) confirm earlier suspicions regarding the effects of crustal contamination in several rock suites. Work on basaltic components of volcanism in the Espanola Basin indicate that crustal contamination was also an important process in producing the observed Pb and Sr isotopic variations in both early and later rift lavas. </p> <p> The remaining chapter of the thesis is a synthesis of all available rift data, from northern Colorado to southern New Mexico. An analysis of changes in the Pb isotopic corn position of the lithosphere with latitude is presented, as well as a cross-rift transect of the central rift region. Further, a model which combines previously published ideas on the tectonomagmatic development of the Rio Grande Rift and the Basin and Range province is proposed. The most important results of the combined model are the proposition that rifting began earlier than previously thought, and that the timing of extension and magmatism in the Rio Grande Rift is very similar to that of the Basin and Range province. Additional data from the rift, particularly the southern region, will help to confirm or deny this model. </p> / Thesis / Doctor of Philosophy (PhD)

<p> Lead isotope ratios have been determined by a VG.354 thermal ionization mass spectrometer on Sudbury Igneous Complex sulphide ores. The isotopic ratios are contrasted with the lead isotope profile of selected country rocks in the vicinity of the complex. South Range data form a linear array whose slope indicates an age of approximately 1.85 Ga, the published age of the igneous complex. They also indicate North Range data a magmatic origin for lead in the ore. North Range data describe a parallel isochron, with lower 206Pb/204Pb and 207Pb/204Pb ratios. The South and North Range data are similar to the lead-isotope composition of country rocks close to them, and indicate rather different crustal-source rocks for sulphide ores in these regions of the complex. This fact suggests that the Sudbury Igneous Complex was generated by a meteorite impact which occurred at the edge of the Huronian succession overlying the Southeast edge of the Superior Province. </p> / Thesis / Master of Science (MSc)

The Grenville Province and adjacent Makkovik Province represent two long-lived ancient orogenic belts that contain remnants of Paleoproterozoic crust accreted to the southeastern Laurentian margin during the Great Proterozoic Accretionary Orogen (GPAO). However, the addition of juvenile Paleoproterozoic crust to the Archean craton during this period was followed by a span of intermittent ensialic arc magmatism and high-grade metamorphism that overprinted much of the early- to mid- Proterozoic geologic history of the region. As a result, these ancient orogenic belts contain cryptic terrane boundaries that require extensive geochronologic mapping in order to reconstruct the accretionary and collisional growth of the southeastern Canadian Shield. Accreted Proterozoic terranes in the Grenville and Makkovik Provinces have been previously mapped using Nd isotopes in order to determine their crustal formation ages and the boundaries between them. Since the U-Pb isotope system has completely different chemical behaviour to the Sm-Nd system, whole-rock Pb isotope analysis provides an independent method to test the results of Nd isotope analysis. Likewise, Pb isotope mapping acts as a useful tool for determining the exhumation of highly metamorphosed crust, as uranium is preferentially transported from lower crustal levels into the upper crust during regional metamorphism. Therefore, whole-rock Pb isotope analysis was performed on over 200 Archean and Proterozoic gneisses from the SW Grenville Province and Makkovik Province in order to 1) differentiate areas of accreted Paleoproterozoic crust from the reworked Archean margin, 2) test the location of the Archean-Proterozoic suture previously mapped in both regions by Nd model ages, and 3) investigate the variable degrees of crustal burial-uplift within the Archean foreland of the SW Grenville Province that was exhumed during the Grenville orogeny. In the Makkovik Province, whole-rock Pb isotope data from the Cape Harrison domain are comparable with published Pb data from the central Ketilidian mobile belt of southern Greenland. The similarity in Pb signatures between the two belts points to a crustal component in the Cape Harrison domain that was derived from a Proterozoic mantle-derived source with minimal input from older Archean crust. This is largely different from published Pb signatures for the Aillik domain in southeastern Labrador and border zone in southern Greenland that suggests a crustal component comprised of reworked Archean crust analogous to the pre-Makkovikian Laurentian foreland. Comparison of new and published Pb data from the Makkovik Province and southern Greenland in turn helps to constrain a revised single arc accretionary model for the Makkovik Province. Previous Nd isotope mapping in the SW Grenville Province revels a break in model ages inferred by authors as a cryptic collisional suture between the reworked Archean foreland and an accreted Paleoproterozoic arc. However, some workers have suggested that this terrane actually consists of Archean crust that was magmatically reworked in the Mesoproterozoic. Whole-rock Pb isotope data presented in this study points to a crustal component south of the proposed suture in Ontario that was derived from a Paleoproterozoic mantle source and subsequently reworked by ensialic arc magmatism during the Mesoproterozoic. North of the suture, Pb data reveals an Archean crustal component analogous to reworked Superior basement that was exhumed from different crustal levels during the Grenville orogeny. Here, regions of anomalously radiogenic and unradiogenic Pb signatures differentiate the Archean-Proterozoic suture in Ontario from a tectonic duplex in western Quebec. / Thesis / Master of Science (MSc)