Dominique Weis

Multi-Collector Inductively Coupled Plasma Mass Spectrometers (MC-ICP-MS) are widely used instruments in Earth sciences to measure isotopic ratios in rock and environmental materials with high sensitivity, accuracy, and precision (i.e., sub-ppm range). However, even when samples undergo careful chemical separation treatment and the instrument is properly calibrated and operated, the measured ratios always differ from their “true” value due to fractionation caused by processes inherent to the technique. Traditional correction methods such as fractionation laws and standard-sample-bracketing (SSB) can mostly account for this instrumental bias. However, other sources of fractionation may arise when even slight modifications are made to the instrumental set-up and sample composition. This thesis investigates the instrumental conditions and sample preparation methods that govern some common sources of fractionation. Chapter 2 explores oxide formation fractionation and its effect on Nd isotopic ratios using different instrumental setups, including wet and dry plasma and different sampler and skimmer cone geometries. We provide a quantitative description of the influence of NdO⁺ formation on mass bias and a qualitative mechanism of the different mass bias contributions to Nd isotopic ratios.Chapter 3 investigates how self-induced matrix effects (SIME) affect isotopic ratios for several isotopic systems (Li, Mg, Fe, Zn, Sr, Nd, Hf and Pb) using pure elemental solutions and varying the concentration of the samples within ± 50 % relative to the bracketing standard. This characterization allowed us to create several descriptive equations describing how SIME affects the isotopic offsets in each ratio.Chapter 4 systematically studies SIME and matrix effects when measuring Nd, Hf and Pb isotopic ratios in a Plasma 3 MC-ICP-MS using pure elemental solutions and geological reference materials of different matrices. We also investigate a range of Pb/Tl ratios to assess Tl correction accuracy for different matrices and compositions when measuring Pb ratios. This study highlights the robustness of measurements performed using the Plasma 3.Finally, we provide an extensive data set characterizing how the instrumental mass bias affects the isotopic ratios measured by MC-ICP-MS. We provide comprehensive analytical guidelines for several isotopic systems when addressing Nd oxide formation, SIME and matrix-related fractionation effects.

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The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Ocean island basalts are indirect records of Earth’s mantle chemistry and are fundamentalfor constraining its evolution through geological time. Volcanoes of the ~6000 km-longHawaiian-Emperor chain represent an extraordinary record of Pacific mantle chemistry over thepast ~80 Ma, formed as the Pacific tectonic plate passed over the deeply sourced Hawaiianmantle plume. Hawaiian volcanoes are divided into southwestern (Loa) and northeastern (Kea)geographic and geochemical trends that reflect the chemical structure of the underlying plumeand its deep mantle sources. This dissertation addresses a change in the chemistry of eruptedlavas between the Northwest Hawaiian Ridge and the younger Hawaiian volcanoes using a newdatabase from the northernmost island of Kaua‘i that includes high-precision radiogenic isotopes(Pb, Sr, Nd, Hf), major element oxides, trace element concentrations, and ⁴⁰Ar/³⁹Argeochronology. Western and eastern Kaua‘i erupted at different times and from distinct mantlesources. The distribution of Loa and Kea compositions on Kaua‘i is opposite to the youngerHawaiian Islands and is explained by a more westward trend of plate motion relative to the Loa-Kea compositional boundary in the plume. Loa compositions dominated the geochemistry oferupted lavas for over 2 Ma before the onset of the bilateral Loa and Kea geochemical trends.Loa compositions are isotopically enriched and may be influenced by subducted materialsrecycled in the deep mantle source of the Hawaiian plume that were stored within the thermallyand chemically distinct Pacific large low shear wave velocity province (LLSVP). Thalliumisotopes were used to test whether these materials originally consisted of pelagic sediment andwere measured in 33 samples from the entire geochemical range of Hawaiian lavas. Resultsshow evidence of recycled materials on the Kea side of the plume, implying that the lowermantle is heterogeneous both within and outside of the LLSVP. This dissertation providesimportant insight into the timing and source of two major geochemical components along themost active hotspot system on Earth and expands our knowledge on the chemical structure of theHawaiian plume, its evolution in space and time, and the nature of its deep mantle sources.

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Urban geochemistry is an emerging field in which key scientific and societal challenges,including rapid urbanization and population growth, compel investigation of readily accessiblebiomonitors to determine the source, transport, and fate of metal pollutants in cities. Whenproperly managed, Apis mellifera (the Western honey bee) can thrive in urban environments,making bees, and their products (e.g., honey, bee pollen), useful biomonitoring matrices. Lead(Pb) isotopic compositions, together with a suite of twenty-two metal concentrations, measuredin honey collected systematically throughout Metro Vancouver (British Columbia, Canada)demonstrate that honey can elucidate small‐scale (km-scale) metal distribution within a city,reflecting nearby land use and anthropogenic activities. This work focuses on the neurotoxicmetal Pb since its legacy and distribution in cities is a public health concern and its isotopes areuseful for pollution source apportionment. This research refines the field sampling methods forhoney, provides extensive hive and environmental context for honey by presenting metalconcentrations and Pb isotopic compositions measured in bees, bee pollen, propolis, PM10, andtopsoil (collocated with Metro Vancouver hives), and explores the spatiotemporal implications ofthe data. The methods established in Metro Vancouver were applied to an acute Pb pollutionevent in Paris, France, where Pb fallout from the 2019 fire at Notre-Dame cathedral wasmeasurable in honey collected downwind of the fire. Colleagues and community scientistsaround the world helped collect honey from hives in diverse settings (e.g., New York City andthe Hawaiian Islands) and procured commercially available honey, effectively creating apreliminary, global database for Pb isotopic compositions in honey. Honey falls predictablyalong the global Pb isotope array (as defined by legacy Pb pollution, modern aerosols, and otherconsumer products) depending on its origin and provides global context for future city-scalestudies utilizing honey as a biomonitor. This work offers a comprehensive assessment of theefficacy of honey as a biomonitor using metal concentrations in conjunction with Pb isotopiccompositions. The results demonstrate that honey and honey bees may indeed become essentialbiomonitoring tools in the near future as the dynamics and environmental monitoring needs ofurban environments shift.

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Detailed written records only exist for a very small amount of human history. Researchers must therefore combine Indigenous traditional knowledge with scientific evidence, often collected with geochemical and spectroscopic techniques, to investigate ancient human biology, behaviour, and culture. However, acquiring meaningful scientific information about rare and culturally-sensitive materials without destroying or modifying them is extremely challenging. The four research chapters in this dissertation adapt and develop analytical frameworks for appropriately acquiring key data from archaeological biominerals and mineraloids to address the fundamental question: ‘What was the original context and condition of the archaeological materials we find?’The first two research chapters focus on investigating the post-mortem histories and diagenetic alteration of archaeological bone using our novel ‘Perio-spot’ technique. In Chapter 2, we evaluate the depositional histories, stratigraphic provenance, and thus age of megafauna and Neandertal bones at Scladina Cave (Belgium). In Chapter 3, we assess the taphonomic state of archaeological bones and the effectiveness of acetic acid pre-treatment procedure used to remove diagenetic alteration, documenting that it may actually concentrate post-mortem signals in recrystallized, intensively-altered bones. The last two research chapters focus on enhancing the traditional techniques for sourcing obsidian (volcanic glass) stone tools in the Pacific Northwest. Our step-wise ‘Splitting Obsidian’ approach (Chapter 4) involves non-destructively investigating all artifacts in an assemblage for elemental concentrations and structural characteristics, then analyzing a subset of representative artifacts for lead (Pb) isotope compositions and more precise trace element concentrations using minimally-invasive techniques. In Chapter 5, we apply this approach to a suite of rare archaeological belongings in partnership with xʷməθkʷəy̓əm (Musqueam), an Indigenous community near Vancouver (Canada), and suggest ancient transport of obsidian over distances exceeding 1000 km in western North America. This supports the oral history and continuity of intricate xʷməθkʷəy̓əm social and material networks, providing additional key lines of evidence for how and from where people procured resources in ancient North America.In summary, the contributions made in this dissertation research provide unique and robust scientific techniques and data that support investigations of ancient human history while minimizing the destruction and alteration of valuable archaeological materials and contexts.

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To better understand how our climate will change in the future, we look to past analogues of our current climate and rely on indicators of past fluctuations preserved in marine sediment. One such indicator is the isotopic composition of neodymium preserved in authigenic phases of marine sediment, which has been widely applied to reconstruct water mass distribution through time. However, recent studies have suggested that the Nd isotopic composition of authigenic phases associated with foraminifera and bulk marine sediment is influenced by early diagenesis. This dissertation documents through experiments and numerical modelling that the Nd isotopic composition of these authigenic phases is influenced by Nd released to pore water through lithogenic dissolution. To identify the source of Nd to a synthetic authigenic phase, we use an incubation of sediment and seawater from the local Strait of Georgia. By tagging the seawater with a unique isotopic ratio, we show that pore water primarily determines the Nd isotopic composition of the authigenic phase. Then, we examine core top sediment in the Labrador Sea, which acts as a natural analogue of the incubation experiment. The seawater in the region has a more radiogenic Nd isotopic composition than the sediment which fills the basin, providing two natural end members. Measurements of the Nd isotopic composition of foraminifera and the authigenic phase associated with bulk sediment are significantly more unradiogenic than seawater. These measurements indicate that seawater is not the primary source of Nd to the authigenic phases in this region. By constructing a numerical model of Nd concentration and isotopic composition in pore water, we are able to quantify diagenetic Nd added to authigenic phases and apply this numerical model to a location in the Equatorial Atlantic Ocean. The diagenetic biases that shift the ℇNd of foraminiferal records in this region mimic the expected variations in ocean circulation. While the authigenic phase associated with foraminifera and bulk sediment leachates seems to preserve the ℇNd of modern seawater, this proxy is subject to effects of diagenesis that change in time, and therefore we conclude that it is not a reliable recorder of ocean circulation.

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Mafic layered intrusions in the Earth’s crust are natural laboratories for evaluating differentiation processes of mantle-derived magma. The Mesoproterozoic Kiglapait intrusion (Labrador, Canada) represents a remarkable case study of how these intrusions form under closed-system crystallization of basaltic magma. The Kiglapait intrusion is the largest and youngest troctolitic intrusion contained within the vast Nain Plutonic Suite, one of the best-preserved examples of Proterozoic anorthosite massifs that distinguish magmatic activity in the Earth’s crust from ~1.8 to 0.9 billion years ago. The radiogenic isotope ratios of Pb-Sr-Nd-Hf are powerful geochemical tools for identifying magma sources, detecting contamination, and tracing mixing processes in igneous rocks. To measure accurate and precise isotopic ratios by MC-ICP-MS, the analysis of sample–matrix-matched reference materials is required. A new comprehensive isotope database of mafic to ultramafic reference materials is provided to assess the accuracy of Pb-Sr-Nd-Hf isotopes in Kiglapait samples and to be used as a reference dataset for the isotopic study of other terrestrial, and extraterrestrial, mafic-ultramafic rocks. Integration of Pb-Sr-Nd-Hf isotope and trace element geochemistry of whole rocks and mineral separates allows for definition of the Kiglapait source and parent magma composition. An event of post-crystallization addition of radiogenic Pb is distinguished, the effects of which are effectively leached from plagioclase during sample pre-treatment. An in situ LA-ICP-MS technique is also developed for measuring Pb isotope ratios at high spatial resolution in minerals with very low Pb concentrations, such as plagioclase and clinopyroxene. Combined, the solution-based Pb-Sr-Nd-Hf and in situ Pb isotopic results demonstrate that the primary Kiglapait magma was mantle-derived, with minor assimilation of lower crust during ponding and ascent, and that assimilation of local country rocks, as recorded primarily in Sr isotopic variations, was limited to the uppermost gabbros and ferrosyenites during the final stages of crystallization. This multi-isotopic and trace element geochemical framework developed for the Kiglapait intrusion, and at a larger scale for the entire Nain Plutonic Suite, can be adapted to layered intrusions and Proterozoic anorthosite plutonic suites worldwide to better constrain a wide range of geological issues from mantle heterogeneity to crustal differentiation to Proterozoic geodynamics.

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Oceanic island basalts provide the exceptional opportunity to study deep mantle geochemical reservoirs, mantle geodynamics and, for long-lived systems, the time evolution of their mantle sources. The Hawaiian-Emperor chain represents the geologic record of the long-lived (>81 Ma) and deeply sourced Hawaiian mantle plume. The geochemical record of the entire chain is now complete with analysis of Pb-Hf-Nd-Sr isotopes and elemental compositions of the Northwest Hawaiian Ridge (NWHR), which consists of ~51 volcanoes spanning ~42 Ma between the bend in the chain and the Hawaiian Islands. This segment of the chain previously represented a significant data gap where Hawaiian plume geochemistry changed markedly: only Kea compositions have been observed on Emperor Seamounts (>50 Ma), whereas the Hawaiian Islands (6 Ma) present both Kea and Loa compositions. Statistical analysis of the new isotopic compositions of NWHR shield-stage basalts confirms the ephemeral presence of the Loa composition. The Hawaiian plume sampled only Kea-type material from the deep Pacific mantle during formation of the Emperor Seamounts and most of the oldest NWHR. Plume movement up the gently sloping edge of the large low-shear velocity province (LLSVP) resulted in entrainment of greater amounts of LLSVP-enriched material over time, which explains why the Hawaiian mantle plume strengthens. Geochemical investigation of NWHR postshield and rejuvenated basalts shows that the rejuvenated component is homogeneous and different from both that of postshield basalts and the depleted component sampled by the oldest Emperor Seamounts. The oldest Emperor Seamounts record interaction between the Hawaiian plume and a mid-ocean ridge. The high Hf isotope ratios of rejuvenated basalts require a source imprinted by ancient partial melting. The robustness of Pb isotope analyses is assessed by investigation of a potential contaminant, ferromanganese crusts, precipitated hydrogenetically on NWHR lavas. Lithium isotopes of Hawaiian Island basalts distinguish between Loa trend heterogeneities; the Loa trend represents singular components sampled for finite time periods. These conclusions demonstrate how integrated geochemical and geophysical studies of oceanic island basalts can further resolve mantle heterogeneity and challenge us to rethink models of how mantle plumes sample the lower mantle.

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The isotopic compositions of oceanic island basalts erupted at the Earth’s surface can be used to directly constrain the isotopic signatures of their deep mantle sources. Basaltic rocks are highly susceptible to seawater alteration, which can significantly modify elemental contents and potentially hinder the use of radiogenic isotopes as geochemical tracers. In this study, multi-isotopic (e.g., Pb-Hf-Sr-Nd) analyses on the same acid-leached sample aliquot are shown to produce reliable results for use in the discrimination of mantle source components of oceanic basalts. Application to basalts from the Ninetyeast Ridge in the Indian Ocean and from Mauna Kea volcano on Hawaii in the Pacific Ocean allows for an enhanced resolution of their source components and distribution in the deep mantle. Isotopic geochemistry of the Ninetyeast Ridge sampled during Ocean Drilling Project Leg 121 reveals a Kerguelen and Amsterdam-St. Paul mantle plume origin with the presence of at least three source components and no contribution from an Indian mid-ocean ridge basalt source. The isotopic characteristics of the Ninetyeast Ridge basalts are typical of the Dupal isotopic domain and consistent with recycling of altered oceanic crust and a mixture of pelagic sediments and lower continental crust into their mantle source. This supports a deep origin for the enriched mantle “EM-1”-like Dupal signatures encountered in Indian Ocean island basalts. In the Pacific Ocean, isotopic heterogeneity in basalts from the deepest parts of the Hawai’i Scientific Drilling Project (HSDP2) core on Mauna Kea, combined with prior results from overlying flows, indicate that shield basalts can be explained by mixing of variable proportions of four isotopically distinct components intrinsic to the Hawaiian mantle plume. The “Kea” component is the prevailing composition in Mauna Kea basalts and throughout volcanic activity of the Hawaiian hotspot. The relatively depleted isotopic compositions of this “Kea” component are shared by other Pacific oceanic island basalt groups and are very similar to those of the common mantle component “C”. This suggests that “Kea” may be a common and widespread composition within the deep mantle beneath the Pacific Ocean basin.

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Environmental monitoring and remediation require techniques to identify the source and fate of metals emissions. In this study, Cd and Zn isotopes were evaluated as tools for the identification of metal sources through (1) the assessment of metallurgical processing as a source of Cd and Zn isotopic fractionation and (2) the measurement of isotopic compositions in bivalves from sites receiving variable metal contributions from natural and anthropogenic sources. This study was facilitated by the successful development of a technique to measure Cd and Zn isotopes (MC-ICP-MS) in environmental and anthropogenic samples.Cadmium, Zn and Pb isotopic ratios were measured for samples from an integrated Zn–Pb smelting/refining complex in B.C. (British Columbia, Canada). Significant fractionation of Cd and Zn isotopes during processing is demonstrated by the total isotopic variation in δ¹¹⁴/¹¹⁰Cd (1.04‰) and δ⁶⁶/⁶⁴Zn (0.42‰) among smelter samples. Characterization of Cd and Zn isotopic compositions in emissions as fractionated relative to ores demonstrates the tracing capability of this new tool. Moreover, Pb isotopic signatures may be used to identify sources contributing metals to environmental samples. Combined Cd, Zn and Pb isotope systematics were used to trace the source and distribution of these metals in bivalves from western Canada (B.C.), the USA and France. Variability in δ¹¹⁴/¹¹⁰Cd of bivalves (-1.20 to -0.09‰) is attributed to differences in the relative contributions of Cd from natural and anthropogenic (e.g., smelting) sources between sites. High Cd levels in B.C. oysters are identified as primarily natural, with some additional variability attributed to anthropogenic sources. In contrast, high Cd levels in French bivalves (Gironde estuary and Marennes-Oléron basin) are primarily anthropogenic. Variability in δ⁶⁶/⁶⁴Zn values exhibited by bivalve samples is small (0.28 to 0.46‰), with the exception of oysters from the polluted Gironde estuary (1.03 to 1.15‰). Lead isotopes are used to identify emissions from industrial processes and the consumption of unleaded gasoline and diesel fuel as metal sources to bivalve samples.This study demonstrates the effective use of Cd and Zn isotopes to trace anthropogenic sources in the environment and the benefit of combining these tools with Pb “fingerprinting” techniques.

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The Saint-Urbain and Big Island rutile-bearing ilmenite Fe-Ti oxide deposits are locatedin the composite 450 km² Saint-Urbain anorthosite (1055-1046 Ma, U-Pb zircon) and inthe Lac Allard intrusion (1057-1062 Ma, U-Pb zircon) of the 11,000 km² Havre-SaintPierre anorthosite suite, respectively, in the Grenville Province of Eastern Canada. Slowcooling rates of 3-4°C/m.y. are estimated for both anorthosites, based on combined U-Pbzircon/rutile/apatite and ⁴⁰Ar/³⁹ Ar biotite/plagioclase geochronology, and resulted fromemplacement during the active Ottawan Orogeny. Slow cooling facilitated (1) diffusionof Zr from ilmenite and rutile, producing thin (10-100 microns) zircon rims on theseminerals, and (2) formation of sapphirine via sub-so lidus reactions of the type: spinel +orthopyroxene + rutile ± corundum → sapphirine + ilmenite. New chemical andanalytical methods were developed to determine the trace element concentrations and Hfisotopic compositions of Ti-based oxides. Rutile is a magmatic phase in the depositswith minimum crystallization temperatures of 781°C to 1016°C, calculated by Zr-inrutile thermometry. Ilmenite present in rutile-free samples has higher Xhem (hematiteproportion in ilmenite), higher high field strength element concentrations (Xhem = 30-17;Nb = 16.1-30.5 ppm; Ta 1.28-1.70 ppm), and crystallized at higher temperatures thanilmenite with more fractionated compositions (Xhem = 21-11; Nb = 1.36-3.11 ppm; Ta =0.18 ppm) from rutile-bearing rocks. The oxide deposits formed by density segregationand accumulation at the bottom of magma reservoirs, in conditions closed to oxygen,from magmas enriched in Fe and Ti. The initial ¹⁷⁶Hf/¹⁷⁷ Hf of rutile and ilmenite (SaintUrbain = 0.28219-0.28227, Big Island = 0.28218-0.28222), and the initial Pbisotopic ratios (e.g.²⁰⁶Pb/²⁰⁴ Pb: SU = 17.134-17.164, BI = 17.012-17.036) and ⁸⁷Sr/⁸⁶ Sr(SU = 0.70399-0.70532, BI = 0.70412-0.70427) of plagioclase from the deposits overlapwith the initial isotopic ratios of ilmenite and plagioclase from each host anorthosite,which indicates that they have common parent magmas and sources. The parent magmaswere derived from a relatively depleted mantle reservoir that appears to be the primarysource of all Grenvillian anorthosite massifs and existed for --600 m.y. along the marginof Laurentia during the Proterozoic.

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The Wrangellia flood basalts are parts of an oceanic plateau that formed in theeastern Panthalassic Ocean (ca. 230-225 Ma). The volcanic stratigraphy presently extends>2300 km in British Columbia, Yukon, and Alaska. The field relationships, age, andgeochemistry have been examined to provide constraints on the construction of oceanicplateaus, duration of volcanism, source of magmas, and the conditions of melting andmagmatic evolution for the volcanic stratigraphy.Wrangellia basalts on Vancouver Island (Karmutsen Formation) form anemergent sequence consisting of basal sills, submarine flows (>3 km), pillow breccia andhyaloclastite (1 1cm), and subaerial flows (>1.5 km). Karmutsen stratigraphy overliesDevonian to Permian volcanic arc (~380-355 Ma) and sedimentary sequences and isoverlain by Late Triassic limestone. The Karmutsen basalts are predominantlyhomogeneous tholeiitic basalt (6-8 wt% MgO); however, the submarine part of thestratigraphy, on northern Vancouver Island, contains picritic pillow basalts (9-20 wt%MgO). Both lava groups have overlapping initial EHf and ENd, indicating a common, oceanisland basalt (OIB)-type Pacific mantle source similar to the source of basalts from theOntong Java and Caribbean Plateaus. The major-element chemistry of picrites indicatesextensive melting (23-27%) of anomalously hot mantle (~1500°C), which is consistentwith an origin from a mantle plume head.Wrangellia basalts extend ~450 km across southern Alaska (Wrangell Mountainsand Alaska Range) and through southwest Yukon where 3.5 km of mostly subaerialflows (Nikolai Formation) are bounded by Pennsylvanian to Permian volcanic (312-280Ma) and sedimentary strata, and Late Triassic limestone. The vast majority of the Nikolaibasalts are LREE-enriched high-Ti basalt (1.6-2.4 wt% Ti0₂) with uniform plume-typePacific mantle isotopic compositions. However, the lowest ~400 m of stratigraphy in theAlaska Range, and lower stratigraphy in Yukon, is light rare earth element (LREE)depleted low-Ti basalt (0.4-1.2 wt% Ti0₂) with pronounced negative-HFSE anomaliesand high Elf values that are decoupled from Nd and displaced well above the OIB mantlearray. The low-Ti basalts indicate subduction-modified mantle was involved in theformation of basalts exposed in Alaska and Yukon, possibly from mechanical andthermal erosion of the base of the lithosphere from an impinging mantle plume head.

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