School of Earth Sciences - Theses

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    Synthesising uncertainties of transient sea level rise projections
    Nauels, Alexander ( 2017)
    Global sea levels increased by around 0.2 m over the 20th century and will continue to rise during the 21st century and far beyond. This has profound implications for coastal populations, infrastructure and ecosystems around the globe. Efforts to assess future impacts on low-lying coastal areas need to be based on robust projections capturing the latest physical understanding of sea level drivers. This PhD research project provides an efficient and robust modelling tool that more consistently links the future sea level response to plausible emission scenarios and allows for extensive uncertainty assessments of long-term sea level projections until 2300. The new MAGICC sea level model is consistent with the Fifth Assessment Report (AR5) of the IPCC. It has been extended to also account for more recent research suggesting additional Antarctic discharge dynamics. In the IPCC AR5 consistent setup, global mean sea levels in 2100 are projected to rise between 0.4 and 0.6 m (66% range) under RCP 2.6 and between 0.7 and 1.0 m under RCP8.5, relative to 1986-2005. Global Mean Sea Level Rise (GMSLR) projections for the year 2300 yield median responses of around 1.1 m for RCP 2.6, 1.8 m for RCP 4.5, 2.4 m for RCP 6.0, and 4.8 m for RCP 8.5. If additional Antarctic rapid dynamics are included, we project 2300 median GMSLR of around 1.0 m under RCP 2.6, 3.3 m under RCP 4.5, 5.3 m under RCP 6.0, and 13.4 m under RCP 8.5. For the new Shared Socioeconomic Pathways (SSPs) without dedicated climate mitigation, 2100 GMSLR is projected to range between 1.0 and 1.9 m (66% range) for a 21st century storyline of high fossil-fuel use and energy demand. SSP pathways staying below 2 degC of warming relative to pre-industrial levels with a likely chance yield 2100 median GMSLR between 0.3 and 0.8 m. 2100 median SSP GMSLR could be limited to around 0.5 m if 2050 cumulative CO2 emissions since pre-industrial stayed below 850 GtC and the global coal phase-out was nearly completed by that time. The analysis of GMSLR under Paris Agreement climate targets clearly points to the need for early and stringent CO2 emission reductions between 2020 and 2035 for limiting 2300 GMSLR to around 1 m relative to 1986-2005. The Antarctic ice sheet represents the most uncertain but also potentially largest future sea level contribution, followed by the Greenland ice sheet and ocean thermal expansion. Due to its great scenario flexibility and robust 2300 projection capability, the MAGICC sea level model would be well suited to feed into regional sea level rise and coastal impact assessments.
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    Reactive barrier formation as CO2 leakage mitigation technology
    Castaneda-Herrera, Cesar Augusto ( 2017)
    Global climate change driven by the emission of carbon dioxide (CO2) to the atmosphere is one of the grand challenges of our time. Energy from the use of fossil fuels is the main source of anthropogenic CO2 emissions. While renewable energies are emerging, fossil sources are expected to continue providing a large portion of our energy needs into the foreseeable future. One way to mitigate emissions from fossil fuel usage is through Carbon Capture and Storage (CCS). This involves capturing CO2 by engineered methods and storing it in a high porosity-high permeability geological formation overlain by a low permeability shale (or caprock). It is expected that these formations will be able to hold CO2 for thousands of years. However, in some instances CO2 leakage through the caprock cannot be entirely precluded, e.g. through undetected zones of higher permeability including natural fractures. This thesis proposes the use of a chemical reactive barrier formation as a technology to mitigate and remediate CO2 leakage successfully. The proposed technology consists of injecting an alkaline sodium silicate solution that reacts with the leaking CO2 or CO2-saturated water, leading to silica gel formation. This work was conducted in three main research phases. Firstly, experimental and modelling studies were undertaken to evaluate the properties of the sodium silicate solution and geochemical viability of the chemical reaction. The second phase involved experiments in a flow-through unconsolidated sand-packed column at ambient conditions. During this phase, variables such as flow rate, temperature and incubation times were evaluated under different scenarios. Finally, core-flood experiments were carried out at reservoir conditions. CO2­saturated fluid and supercritical CO2 (scCO2) were injected into a sandstone saturated with silicate at high pressure and temperature. Reduction in permeability and the retention of silica in the column were used as measures of barrier formation in the last two experimental phases. The first phase of work showed that 7.15 wt% sodium silicate solution proved to be the most practical for applications in subsequent experiments. The modelling also showed that at this concentration the reaction is predicted to happen at different geochemical reservoir conditions. During the second phase, the formation of the silica barrier was found to be controlled by the mixing gradient of the two reactants, where the reaction resulted in reduction of permeability by at least one order of magnitude for mitigation and remediation scenarios. Moreover, the results of the core-flood experiments demonstrated that the formation of the silica barrier under CO2 reservoir conditions is possible and viable for a mitigations scenario. These results showed a significant reduction in permeability of two or three orders of magnitude and that the barrier was still strong a month after completing the test. In conclusion, results of this thesis suggest that the silica barrier formation is a promising technology to abate CO2 leakage from a geological carbon storage reservoir and provides useful findings for further research.
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    Climate justice: can we agree to disagree? Operationalising competing equity principles to mitigate global warming
    Robiou du Pont, Yann ( 2017)
    With the Paris Agreement, the international community has agreed to limit global warming to well below 2 °C and to pursue efforts to stay below 1.5 °C (UNFCCC 2015a) to avoid dangerous climate impacts. Staying within these boundaries requires important emissions mitigation efforts from all countries (Rogelj et al 2015). Equitable distribution across countries of mitigation efforts, or equivalently of emissions rights, consistent with global mitigation objectives is a contentious issue that involves divergent interpretations of distributive justice (Winkler and Rajamani 2014a). The latest Intergovernmental Panel on Climate Change (IPCC) report categorises equity approaches from the scientific literature in five groups (Clarke et al 2014). At climate negotiations, most countries tend to support the approach that requires the least efforts on their behalf (Fleurbaey et al 2014, Lange et al 2010). With the absence of consensus on an effort-sharing approach, current negotiations under the United Nations Framework Convention on Climate Change (UNFCCC) follow a self-interested, or ‘bottom-up’, approach to target setting (Andresen 2015, Bodansky 2016) where each country decides its own effort following its understanding of fairness. As a result, the sum of all parties’ announced contributions is not consistent with limiting global warming to 2 °C, let alone 1.5 °C (Rogelj et al 2016a). Under the Paris Agreement, countries committed to increase the ambition of their post-Kyoto climate pledges through a ratcheting-up process that begins in 2023. With the disagreement on effort-sharing approaches, the international community relies on diverging metrics to evaluate the adequacy of national pledges with the global warming thresholds. Since the beginning of climate negotiations under the United Nations, a rich literature has modelled allocations of emissions rights to countries using various effort-sharing approaches with uncoordinated parameterisation. At the start of this PhD work, no study modelled the effort-sharing categories presented in the last IPCC report under a common parameterisation. Additionally, the literature on the combination of effort-sharing approaches remained thin and consisted of averaging the emissions allocations of multiple effort-sharing approaches. This PhD thesis addresses these gaps with the modelling of a new emissions allocation framework, the ‘PRIMAP-Equity’ framework, and with the suggestion of a new combination of effort-sharing approaches. Firstly, this thesis quantifies allocations of emissions rights to countries in a manner that reflects the existing literature on distributive justice. An emissions allocation framework is developed to derive national emissions allocations that reflect the five equity categories of the fifth IPCC report. This modelling framework is applied to derive emissions allocations, under each of the five equity categories, consistent with the emissions mitigation goals of the G7 Elmau agreement signed in June 2015. The allocation framework is then used to derive national emissions trajectories aligned with the recent Paris Agreement goals of both well below 2 °C and 1.5 °C, consistently with the five equity categories . This work represents the first quantification of equitable national trajectories to achieve 1.5 °C goal and informs scientists and government experts in the preparation of the IPCC Special Report on 1.5 °C (IPCC 2017). The Nationally Determined Contributions (NDCs), countries’ national pledges, of 171 Parties are then evaluated in order to determine which, if any, categories of equity they are consistent with. As well, the thesis highlights the consistency of G20 countries’ pledges with equity allocations. This is discussed in the context of the statement on fairness contained in each pledge. This PhD thesis then addresses the apparent incompatibility between the global warming thresholds and countries’ self-interested visions of effort-sharing by suggesting a new quantitative approach. Doing so, this PhD thesis provides a new metric, inclusive of all international positions, to assess the ambition of the NDCs under the Paris Agreement. This new ‘hybrid’ allocation method reconciles the ‘bottom-up’ approach of equity with the ‘top-down’ climate threshold that they commonly agreed. Under this ‘hybrid’ approach, each country follows the least stringent effort-sharing approach – out of the five that reflect the equity categories presented in the last IPCC report – to achieve the Paris Agreement. The aggregation of current national pledges is found to align with such a ‘bottom-up’ combination of approaches and lead to a warming of up to 2.3 °C in 2100 (with a 50% chance). Conversely, an enhanced ‘bottom-up’ approach – ‘hybrid’ – of global emissions scenarios leading to 1.1 °C and 1.3 °C warmings results in the achievement of the Paris Agreement mitigation goals of 1.5 °C and well below 2 °C, respectively. Ultimately, this study quantifies a compromise where each country can choose an equity approach to determine its effort, but does directly use that approach to assess other countries’ pledges. Finally, the application of this ‘hybrid’ approach provides a temperature assessment for all countries’ climate pledges, indicating the consistency of countries’ ambition in light of the global temperature goals. The NDCs of India, the EU, the USA and China are in line with global ‘bottom-up’ situations leading to warmings of 2.6 °C, 3.2 °C, 4 °C and over 5.1 °C, respectively. The results of this thesis can inform public opinions and decision makers through the ratcheting-up process on what constitutes fair and ambitious pledges to achieve the Paris Agreement following a range or combination of equity approaches. Additionally, the assessments of the adequacy of countries’ pledges with international agreements can inform courts when ruling ‘climate cases’ where governments are sued for their lack of ambition in mitigating emissions (Sabin Center for Climate Change Law 2018).
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    Thermochronological insights into the morphotectonic evolution of Zimbabwe, southern Africa
    Mackintosh, Vhairi ( 2017)
    The Zimbabwe Craton and surrounding mobile belts that make up Zimbabwe form the north-eastern part of the Southern African Plateau, which is of great scientific interest due to its anomalous elevation. The Phanerozoic history of Zimbabwe is largely unresolved and is difficult to unravel using conventional field methods due to the fragmentary nature of the preserved geological record and lack of structural controls in the dominantly granitic lithologies. Low-temperature thermochronology systems provide an invaluable toolkit for understanding upper crustal processes and in turn deciphering cryptic morphotectonic histories. Despite their value, thermochronology studies within Zimbabwe are considerably lacking, especially within the cratonic interior. In this work, a multiple low-temperature thermochronology approach— including the first apatite and zircon (U-Th)/He data and a more spatially extensive apatite fission track dataset—is employed together with inverse thermal history modelling to unravel the Phanerozoic histories of the different tectonic provinces of Zimbabwe. The data reveal that structural reactivation, largely caused by stress transmission and associated with uplift and denudation of different crustal blocks, has played a major role in the morphotectonic evolution of Zimbabwe, albeit spatially and temporally variable. The new dataset allows for a more clearly defined spatial and temporal structural reactivation pattern and suggests that the cratonic interior experienced reactivation in the Paleozoic but has since remained tectonically stable. Cratonic Zimbabwe preserves a Pan-African signature associated with Gondwana amalgamation, whereas the eastern cratonic margin and neighbouring mobile belts are dominated by Jurassic Gondwana breakup signals. The spatial extent and trend of the Pan-African rejuvenation signature suggest that the anomalous topography of Zimbabwe may have an ancient component. The regional dataset suggests unroofing of a previously more extensive sedimentary cover over the craton that began in the Paleogene. The zircon (U-Th)/He dataset in this work provides significant methodological insight. The unexpectedly recurrent ‘inversion’ of low-temperature thermochronology ages suggests that moderately-extremely radiation-damaged zircons can, in certain geological settings, act as ultra-low-temperature thermochronometers and provide insight into the more recent morphotectonic history. However, at present, the current zircon α-radiation damage accumulation and annealing model (ZRDAAM) does not adequately capture the He diffusion behaviour of the majority of the dated zircons. The exact source of this issue in the zircon (U-Th)/He system is uncertain, but could be associated with a ZRDAAM calibration issue, an unaccounted source of error and/or a currently unrecognised factor affecting He diffusion and retentivity within zircon.
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    Uncertainties in runoff projections in southwest Western Australia and central Chilean catchments
    Barria Sandoval, Pilar Andrea ( 2017)
    Important runoff reductions have been reported in mid-latitude, Mediterranean-like climate catchments of the Southern Hemisphere (SH), in particular in the southwest of Western Australia (SWA) and in central Chile (CC). These changes have been driven by decreases in rainfall since the mid-1970s. Despite regional rainfall and runoff projections from Global Climate Models (GCMs) indicating that the observed trends are expected to continue during the 21st century, the projections are affected by large uncertainties that limit their utility to decision makers. The main source of uncertainty in runoff projections are the GCMs used to produce future climate projections. However, uncertainties arise from the observations of the climate variables, the statistical methodology to downscale the GCM simulations to the catchment scale and the hydrological model used to simulate runoff. In particular, the short length (<50 years) and poor spatially distributed observed climatological variables in mountainous catchments, characterized by steep topography, hampers a deep analysis of runoff trends and runoff variability, such as the case of CC mountainous catchments. The impact of the GCM uncertainty on runoff projections has mainly been assessed through comparison of multi-model runs of future climate with little exploration of uncertainties inside the models due to different parameterisations. This thesis seeks to investigate the uncertainty response of projected runoff due to both: perturbed physics parameter variations within a GCM using a novel 2500-member ensemble from the HadCM3L model, the climaprediction.net data (CPDN), termed the within-GCM uncertainties, and from a multi-model ensemble of different GCMs collated by the CMIP5 project, termed the between-GCM uncertainties. The impact of GCM uncertainties on runoff modelling for pluvial regimes in southwest Western Australian and Central Chilean catchments was assessed. Both regions share similar trends and climatic features, with major decreases in winter precipitation and runoff since the mid-70s that have been related to a displacement of the Southern Hemisphere storm track. Nonetheless one important difference between SWA and CC catchments, is the presence of nivo-pluvial regimes located at the foothills of the Andes in CC, whose hydrology is poorly understood mainly due to the lack of well distributed and long gauge records that represent its variability. The results presented in this thesis show that the impact of within-GCM uncertainties on runoff projections in SWA catchments is very large; larger than previous estimates of within-GCM uncertainties impact on runoff. The perturbed physics approach indicates that current water management assessments underestimate uncertainties in runoff projections. Regarding the comparison of the impact of between-GCM and within-GCM uncertainties on runoff projections in SWA catchments quantified as the difference between the 5th and the 95th percentile of simulations, the impact of within-GCM uncertainties on runoff projections range between 39% and 65%. Whereas the impact of between-GCM uncertainties on runoff projections range between 44% and 83% for the Representative concentration pathway 4.5 (RCP4.5) scenario and about 38% and 72% under the RCP8.5 for the period between 2050-2080 compared to 1970-2000. Regarding CC catchments, between-GCM uncertainties of about 55% and 51% in runoff projections using the RCP4.5 and the RCP8.5 scenarios were found. The results here reported indicate that the impact of within-GCM and between-GCM uncertainties in SWA catchments runoff projections is very similar. The results also indicate that because some GCMs in the CMIP5 ensemble have multiple runs, using different initial conditions, CMIP5 gives some insight into within-GCM uncertainty as well. For these reasons and because CMIP5 provides runs that represent all regions of the world, it is recommended for use in hydrological assessments of climate change impact and the uncertainties around the projections.
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    The composition of altered oceanic crust: Implications for mantle evolution
    Kuo, Tzu-Ying ( 2017)
    The geochemical characterisation of oceanic crust, in its dual role as a mantle-derived melt and a subducted material, is an essential component in understanding the evolution of the Earth’s mantle. Interaction of newly formed crust with seawater, however, producing ‘altered oceanic crust’ (AOC), provides a degree of complexity in this undertaking. This study aims to conduct a global survey of trace element and Sr-Nd-Hf-Pb isotopic compositions of AOC by compiling high quality literature data and adding new analyses where appropriate to address identified gaps in the record. Ten representative DSDP/ODP/IODP sites were selected for the new analyses. In total 93 samples for homogeneous portions and 19 samples for heterogeneous portions of AOC were analysed. These results are combined with all available data for these ten sites as well as geochemical data from other locations that also cored AOC samples. Prior to any assessment of alteration effects, variations due to magmatic processes are considered. Comparison of alteration-insensitive elements and isotope ratios of AOC, grouped by rock type, crustal age and ocean basin (i.e. spreading rate) reveals the relative importance of these parameters on AOC composition. The results show that rock type provides the first order control on trace element variations. Alteration-insensitive trace element compositions are not correlated with either crustal age or ocean basin/spreading rate, whereas Nd and Hf isotope ratios do show trends with crustal ages, mirroring the evolution of the mantle source over the past 170 Ma. In addition, the compositions of lower crustal rocks from slow-spreading ridges are significantly more variable than those from fast-spreading ridges. This is because the lower crust at slow-spreading ridges is generated from multiple magma pulses compared to that at fast-spreading ridges that generally forms more homogeneous magmas derived from larger magma chambers In terms of alteration effects compositional variations in the upper and lower crust are considered separately because of their very different nature. The alteration in homogeneous parts of the upper AOC varies with crustal age. This is consistent with the correlation between the oxidation state, which plays an important role in upper crust alteration, and crustal age. The alteration in homogeneous parts of the lower AOC, however, is better linked with spreading rate. In heterogeneous parts of AOC, such as breccias and veins, compositional variation is principally dependent on the phases themselves instead of crustal age or spreading rate. The compiled results, with the controls on compositional variation revealed, are used to calculate the global compositions of eight AOC types, namely fast-upper AOC, slow-upper AOC, fast-lower AOC, slow-lower AOC, fast-total AOC, slow-total AOC, global AOC and global AOC-plume free. Site medians are calculated first and the crustal age- and spreading rate-weighted averages are determined for upper and lower crust, respectively. The global AOC compositions are then calculated using the proportion of fast- and slow-spreading crust worldwide. Also, the compositions of plume-free global AOC are also estimated by removing some of plume-influenced sites. The results are then compared with previous estimates of AOC composition revealing some differences. The results of this investigation encompass a greater number of drill sites with a more detailed understanding of the controls on variation, and are therefore likely a more accurate representation than previous estimations. The newly derived AOC compositions can be used to test models for the involvement of subducted AOC in generating Ocean Island Basalt (OIB) compositional variation, in particular the origin of the ‘high-Mu’ (HIMU) signature. As an example a preliminary test was performed using source and recycling ages of 3 and 2 Ga, respectively. The model results show that 1) subduction modification is essential for AOC to generate HIMU signals and 2) the upper crustal components are most likely to generate HIMU signals in all isotope systems after subduction modification (dehydration) with adjusted mobility of Th. However, a more detailed determination of element mobility is required in order to obtain more reliable modelling results. Intriguingly, four analysed samples have extremely unradiogenic Pb isotope compositions, unlike anything previously recovered from the ocean floor. These are compared with similar signals observed in peridotites but show different trends, indicating a different source or magmatic origin. They might also be caused by the occurrence of secondary sulfides, but this aspect requires further investigation.
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    Deep seawater circulation through oceanic crust stimulates the subseafloor biosphere
    Cox, Toni ( 2017)
    The deep subseafloor hosts the largest prokaryotic biomass on Earth, with cell abundances 3-4 orders of magnitude higher than the overlying ocean. Oxidant concentrations in the subseafloor are consumed sequentially by respiring microorganisms. However, studies show that seawater can flow through hydrologically conductive basalt and deliver oxidants upwards into overlying sediments. Our knowledge of how these fluids may influence biogeochemical cycles both within the oceanic basement and deeply-buried sediments is limited. Recent investigations have focused on more easily accessible sites (e.g. hydrothermal vents, mid-ocean ridges, ridge flanks, and continental margins), while buried subducting oceanic crust is less well studied. This thesis aims to address, through 16S rRNA and functional gene-level investigations, the question of how recirculating crustal fluids have affected deeply buried microorganisms in the subducting Philippines Sea plate. Through amplicon sequencing and functional gene analyses (dsrAB, mcrA) of a deep sediment anaerobic oxidation of methane zone, an inverted redox ladder is revealed that supports sulfate reduction at a greater depth than methanogenesis. Subseafloor microorganisms are intrinsically linked to the production of natural resources (e.g. natural gas, oil and metal ore); therefore, scientists need to understand how these biogeochemical systems run. Moreover, the reinvigoration of bacterial sulfate reduction coupled to hydrogen oxidation in sediments buried ~480 meters below the seafloor (mbsf) may explain the observed low methane concentrations at this site. Geochemical investigations at the sediment-basement interface (SBI) identified the presence of bioavailable metals released via basement alteration. These interpretations were supported by geochemical modelling and an abundance of 16S rRNA genes closely related to metal-cycling bacteria at the SBI. Additionally, substantial water rock reactions drove an increase in salinity, which corresponded with an increase in Halobacteria in the basement. Together these findings indicate the basement aquifer is delivering oxidants and microorganisms through the SBI of the subducting sea plate and influencing in situ microbial ecosystems. These communities offer insights into potential adaptations for microbial survival in deeply buried sediments. Lastly, this thesis extends the current subseafloor habitability database to regions where the ocean crust is being consumed by subduction.
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    Isotopic disequilibrium in granitic systems: the origins of heterogeneity in granites and implications for partial melting in the crust and petrogenetic models
    Iles, Kieran Anthony ( 2017)
    Unravelling the processes involved in granite magmatism is essential to our understanding of the continental crust, its formation and evolution. Radiogenic isotope systems are commonly employed to this end, but the behaviour of these systems may not be as simple as is often assumed. Understanding the causes of isotopic complexity in granite suites is the aim of this research. By modelling the disequilibrium partial melting of isotopically heterogeneous protoliths the different compositions of the melt, source and restite for a range of hypothetical scenarios have been calculated. Results demonstrate that the melt produced may have Sr, Nd and Hf isotope compositions distinct from both the protolith and restite. A corollary is that restite-bearing magmas may exhibit different isotope compositions than their melts, a feature which should be preserved as a difference between the Hf isotope compositions of bulk-rock samples and their magmatic zircon populations. The same modelling also suggests that a single source rock can produce melts with diverse isotope compositions. The predictions of this modelling have been tested by analysing S- and I-type granites from the Lachlan Fold Belt, southeastern Australia, including iconic examples of restite-bearing rocks. Comparisons of Hf isotope compositions between bulk-rocks and their magmatic zircons reveal discrepancies (ΔεHfbulk-zircon) ranging from -0.6 to +2.5 ε units for I-type granites. This intra-sample Hf isotopic heterogeneity is interpreted to represent disequilibrium between the melt and restite assemblage. The ΔεHfbulk-zircon values are consistent with calculated ΔεHfmagma-melt values (from -4.2 to +7.4) based on the disequilibrium amphibole dehydration melting of 0.5-1.0 Ga meta-igneous protoliths. S-type granites also record differences between their bulk-rock and magmatic zircon Hf isotope compositions; however, the disparity is more subtle. Both positive and small negative ΔεHfbulk-zircon values are observed, consistent with modelling the partial melting of isotopically heterogeneous meta-sedimentary protoliths. In addition to low-temperature granites, case studies of two high-temperature I-type granitoid suites (Boggy Plain and Wallundry) have also been conducted. Both display a weak coupling between geochemical parameters that have been interpreted previously to indicate the involvement of assimilation and fractional crystallisation (AFC) processes. Positive ΔεHfbulk-zircon values obtained in the Boggy Plain Suite support the existing petrogenetic model in which basaltic melt becomes variously contaminated by material derived from the continental crust. The positive value is explained by retention of earlier-crystallised, more radiogenic phases in isotopically evolved, more felsic samples. In contrast, the Wallundry Suite is characterised by negative ΔεHfbulk-zircon values caused by the presence of unmelted components of its contaminant. A complex interplay of contamination, crystallisation, melt segregation and interaction between magma batches is required to account for the Wallundry Suite isotope data. The results of this study indicate that disequilibrium partial melting can produce within-suite isotopic variability without recourse to assimilation or mixing processes (1) in mafic to felsic samples caused by the progressive separation of melt from its isotopically distinct restite assemblage; and (2) via the extraction of multiple batches of isotopically distinct melts produced from a single source as anatexis proceeds. Furthermore, the isotope variation resulting from restite unmixing may be distinguished from magma mixing by decoupling of the Rb-Sr, Sm-Nd and Lu-Hf isotope systems. Importantly, the isotopic discrepancy between bulk-rock granite samples and their magmatic zircon populations suggests that the most mafic bulk-rock granite samples of a given suite, not magmatic zircon, provide the most accurate estimate of source rock Hf isotope compositions. This raises concerns regarding the ubiquitous use of zircon Hf isotope data to constrain crustal growth models.
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    Fire weather in two regions of the Southern Hemisphere
    Pazmiño, Daniel ( 2017)
    This thesis investigated fire weather in Victoria, Australia and the Ecuadorian Andes. The selection of these areas considered several criteria. First of all, bushfires cause significant impacts in these two regions. Victoria has endured some of the most catastrophic bushfire events in Australian history (e.g. “Black Friday” (1939), “Ash Wednesday” (1983), “Black Saturday” (2009)). On the other hand, bushfires in Ecuador destroy every year large areas of national parks in one of the most biodiverse countries in the world. Secondly, the El Niño- Southern Oscillation (ENSO) is a strong climate driver in the two study areas. Finally, Victoria and Ecuador share the Eucalyptus as the dominant bushfire-prone species. The aim of this thesis is to better understand the drivers and evolution of fire weather in these two regions of the Southern Hemisphere. Specifically, it examined three aspects. First of all, it investigated fire weather spatial patterns in Victoria and their relationship with associated events like heatwaves. Subsequently, the study explored long-term fire weather variability and changes. Finally, the investigation evaluated the influence of ENSO and other climate drivers over fire weather. The analyses used three groups of data: bushfire records, meteorological and climate indices data. Consistent bushfire records were available only for Victoria during the period 1961-2010. Additionally, the investigation required observations from weather stations in Victoria and the Ecuadorian Andes. This research also analysed reanalysis data from the Twentieth Century Reanalysis Project (20CR) and the European Reanalysis of Global Climate Observations ERA-Clim project (ERA-20C). The study had a stronger emphasis on ENSO since it affects both regions. This research used two indices to represent fire weather. The first index was the McArthur Forest Fire Danger Index (FFDI). This Australian metric was designed for an Eucalyptus environment. Therefore, this investigation applied the FFDI for Victoria and Ecuador. Additionally, this thesis proposes an alternative fire weather index for Victoria: the “Victorian Seasonal Bushfire Index” (VSBI). The VSBI combines local meteorological variables and sea surface temperature in ENSO regions to represent—and predict—extreme fire weather. The investigation of fire weather in Victoria and the Ecuadorian Andes yielded several findings. First of all, bushfire and heatwave weather patterns display differences from one another in Victoria. These comparisons used synoptic climatologies with reanalysis data during the period 1961-2010. Additionally, the investigation showed that Victoria experienced an increase in fire danger during the period 1974-2010. There is also weaker evidence suggesting an increasing trend since 1920. “El Niño” events are the leading remote driver of fire activity in Victoria. In fact, the incorporation of ENSO indicators in a simple index (VSBI) shows skill to forecast extreme fire weather in this region. For the Ecuadorian Andes, this research indicates that its fire danger season (July-September) is longer than reported. October and November also display “high” fire danger during the period 1997-2012. Finally, “El Niño” events increase fire risk in the Ecuadorian Andes.