Doctor of Philosophy in Geological Sciences (PhD)
Pb isotopic and trace element signatures in honey: Environmental proxy for pollutant source-tracking
Geochemistry of the Hawaiian mantle plume - trace element modelling, time evolution and relation to the deep mantle geophysical anomalies.
Honey, salmon as bioindicators - see also UBC Excellence Research Cluster, BeeHIVE: https://beehive.ubc.ca/
Indigenous/Science - see also UBC Excellence Research Cluster, Indigenous/Science at UBC: Partnerships in the Exploration of History and Environments: https://indigenousscience.ubc.ca/
G+PS regularly provides virtual sessions that focus on admission requirements and procedures and tips how to improve your application.
Another shout-out for my #GreatSupervisor Dr Dominique Weis at #UBC! Dominique's desire to explore nature, stand by her students, and think outside the box makes the @PCIGR a great place to work, learn, and expand horizons!
It’s #GreatSupervisor week at #UBC and I want to take this moment to give a tremendous thank you to Dr Dominique Weis from @PCIGR, who's always encouraging us to be the best possible scientists we can be! Thanks for believing and supporting us, while always pushing us to succeed!
Big thanks and much appreciation for my #GreatSupervisor Dr. Dominique Weis at #UBC, whose passion for a challenge, support for her students, and leadership of the @PCIGR team is endlessly motivating!!
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.
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.
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 (
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.
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.
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 =
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 (1.5 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
Barkley Sound and Alberni Inlet, located on the west coast of Vancouver Island, British Columbia, are home to economically important oyster farms. The headwaters of Alberni Inlet are proximal to the city of Port Alberni, where industrial activities (e.g., paper mills, recycling plants) release significant quantities of heavy metals into Alberni Inlet annually. The distribution of As, Cd, and Pb and Pb isotopic composition of Pb were studied in surface and cored sediments collected downstream from the paper mill using quadrupole and multi collector inductively coupled plasma mass spectroscopy (Q-ICP-MS, MC-ICP-MS). Surface and core sediment concentrations of As, Cd and Pb generally decrease downstream from Port Alberni, with the exception of a Pb spike observed in Barkley Sound. Alberni Inlet and Barkley Sound display ranges of 3.8-24 and 3.5-21.6 ppm for As, from 0.03-0.87 and 0.2-1.1 ppm for Cd, and 4.1-18 and 2.9-24.2 ppm for Pb, respectively. Scavenging of dissolved metals is observed at the distance of 10-25 km downstream from Port Alberni. Based on comparison to Sediment Quality Guidelines, the environmental impact of trace metals in the sediment on bottom dwelling organism is low. Major elements compositions determined using Aluminum as an elemental normalizer indicated that the sediment corresponds to a source predominantly from Vancouver Island bedrock. The isotopic composition for surface sediment ranges from 1.17020 to 1.21602 for ²⁰⁶Pb/²⁰⁷Pb, and 2.0397 to 2.0835 for ²⁰⁸Pb/²⁰⁶Pb. In core samples, the range is from 1.16571 to 1.19109 for ²⁰⁶Pb/²⁰⁷Pb and 2.06883 to 2.08533 for ²⁰⁸Pb/²⁰⁶Pb. Lead isotope fingerprinting indicates that sediments derived from Vancouver Island were contaminated with trace metals by a source displaying the Pb isotopic signature of the Sullivan Ore, the primary anthropogenic Pb source for British Columbia. This is consistent with paper mill effluent from Port Alberni. Sediments from the lower inlet and Barkley Sound also show a contribution from Chinese loess. Other human activities are most likely responsible for the spike in Pb concentrations in Barkley Sound. This study demonstrates that the combination of trace metal analysis and high precision Pb isotopic data are effective tools for monitoring anthropogenic input into the environment.
The Neoproterozoic (ca. 723 Ma) Franklin large igneous province (LIP) located on Victoria Island, Arctic Canada, consists of the Natkusiak Formation continental flood basalts and a sill-dominated feeder system exposed in the Minto Inlier. The Franklin LIP is temporally linked with the breakup of Laurentia from Siberia and the Sturtian glaciation or “Snowball Earth”. Recent mapping shows that the Natkusiak Formation, preserved in two lobes (northern and southern), has a thin basal unit, ~50 m thick, followed by two ~500 m thick cycles (1 and 2) of basaltic sheet-flows. Sr-Nd-Pb-Hf isotopic compositions, major element oxides, and trace element concentrations of the Natkusiak basalts allow for the characterization of mantle source components and the extent of crustal contamination. Four geochemical groups (southern low- and high-Ti basalts; northern low- and high-Ti basalts) are defined. The basal basalts (low-Ti, 1.0-1.2 wt.% TiO₂) are distinguished from the overlying cycle 1 and 2 basalts (high-Ti, 1.2-1.8 wt.% TiO₂). The high-Ti basalts are characterized by a narrow range in ⁸⁷Sr/⁸⁶Sri (0.7027-0.7045), high εNdi and εHfi, and relatively low ²⁰⁶Pb/²⁰⁴Pbi, ²⁰⁷Pb/²⁰⁴Pbi, and ²⁰⁸Pb/²⁰⁴Pbi compared to the low-Ti basalts (⁸⁷Sr/⁸⁶Sri = 0.7033-0.7057). The northern (low- and high-Ti) basalts are isotopically distinct from the southern (low- and high-Ti) basalts with lower εNdi values for a given ⁸⁷Sr/⁸⁶Sri. The chemistry of the coeval Franklin intrusions mainly overlaps that of the northern basalts and they show only limited isotopic correlation with the southern basalts, which indicates that the southern basalts were fed from a separate feeder system. Significant major and trace element and isotopic differences between the low- and high-Ti basalts are inconsistent with the effects of crustal contamination and are related to different mantle source compositions, with a garnet-bearing source for the low-Ti basalts and a spinel-bearing source for the high-Ti basalts. A shift in mantle source region, likely reflected by an episode of syn-volcanic extension, occurred after the emplacement of the low-Ti basalts, which represent the earliest volcanic products of the Franklin LIP.