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This thesis is a study of Boreal's version of the Tristan legend. Its aim is a better understanding of the romance through an examination of the work itself and of those versions of the legend with which it is associated. Part One of the thesis begins with a survey of the manuscript and of the various editions and goes on to suggest the policy that might be adopted when a more reliable text is sought. (The three appendices are also concerned with textual problems.) There then follow - a review of Tristan scholarship and an appraisal of the relationship between the various representatives of the legend. Beroul's romance is seen as an independent derivative of a lost work and as an influence upon the Folie Tristan of Berne. In Part Two, each of the episodes in Beroul's work is examined. If an episode is also found in other versions, the parallel accounts are scrutinized and emphasis is laid upon those elements which are found to be quite peculiar to our romance. Those episodes in the romance which have no equivalent elsewhere are also examined and suggestions are made as to their possible provenance. At the same time, the structure of the romance is compared with that of other versions. Beroul emerges as a writer who has on occasion re-ordered inherited episodes, in order to present more clearly his own conception of the legend. In the Conclusion, the significance of the parallel versions is ascertained, before Beroul's own conception of the legend is determined. Beroul consistently presents Tristan and Iseut as guilty sinners, but who are yet never beyond redemption, and he draws on theological support in order to suggest that by the end of the romance they are set on the road to salvation.

Hydrogen (H) is the most abundant element in the universe. The original budget and speciation of major volatiles, such as hydrogen and carbon ( C), in the silicate material and atmospheres of rocky bodies in our Solar System was determined during their formation and early evolution. Nearly all the large rocky bodies in the Solar System are thought to have experienced at least one magma ocean phase as an outcome of formation processes. Highly reducing conditions well below the iron-wustite buffer (IW) characterized by a low oxygen fugacity (f02) were likely prevalent during the differentiation stages of rocky bodies. Reducing conditions prevailed during the early stages of planetary evolution and magma ocean solidification, and whilst some bodies like Earth progressively oxidized, others have remained more reducing. The investigation of redox conditions not only has implications for primordial magma oceans, but also for solid terrestrial bodies. Current estimates for the prevalent redox conditions in the silicate reservoirs of Mercury, Venus, the Moon and Mars are more reducing than the Earth. Under highly reducing conditions, the effect of volatile speciation on the mineral/melt partitioning and on H solubility in major silicate minerals such as olivine is largely unknown. After three decades of interest, the influence of pressure, temperature, and composition is fairly well constrained for the storage capacity and solubility of H in olivine. However, considerably less work has been conducted on the effect of f02 on H solubility in olivine, especially at very low /02, and the few available reports on this topic show substantial inconsistency. I present SIMS and Raman data to determine the H content and speciation of C-O-H volatiles in olivine and silicate glasses from experiments at (1-3.5 GPa) and temperature (1435-1750 °C). Using a Cr-Cr2O:3 buffer and hydride-bearing starting material, the /02 is estimated to be - IW-4, which can be directly compared to more oxidi;,;ed experiments run at - IW +4. Results demonstrate the systematic variance of C-O-H speciation, solubility, and partitioning as function of f02, which can be further explored, hut not sufficiently predicted, through C-O-H fluid models. The diminished H contents of olivine under reducing conditions indicates that future work concerning magma ocean crystallization or the reducing deep upper mantle of the Earth must consider the effects of low fO2, high fH2, and the existence of appreciable amounts of C. Whilst there is a substantial body of literature on the nature and consequences of water incorporation in the Earth, we know comparatively less about the 'volatile' budgets of the other rocky planets. Mars is a particularly interesting body to investigate in this regard as there is evidence for the presence of a hydrosphere during its history, and it is also one of the few bodies we have direct (meteorite) samples from. Understanding the Martian H and C budget is crucial since such dissolved volatiles reduce the Martian mantle solidus, may act as drivers for volcanism, and are vital for the development of habitable surface environments. Concentrations of H and C were measured by SLVIS in experimentally produced replications of synthetic Martian systems provided by Dr. Justin Filiberto with clinopyroxene, orthopyroxene, olivine, and coexisting silicate glass phases. Such nominally anhydrous minerals (NAMs) can contain significant amounts of Hand, therefore, serve as important reservoirs for H within the silicate Earth and Mars. The determined values were used to calculate the mineral/melt partition coefficients (D values) for H and C. Experiments were conducted in nominally anhydrous conditions, and H partitioning values obtained here arc significantly greater than those obtained in previous studies. Comparison ·with literature data indicate that melt H/) content has an important additional control on H mineral/melt partitioning for clinopyroxene and orthopyroxene. Experimental DH < px/melt values also differ from previous models for DH < px/melt that are based solely on clinopyroxene compositions and do not account for the activity of H2O in the melt, especially at low activities. Combined with previous literature data on DH < px/melt, a new empirically calibrated model for DH < px/melt is developed based solely on phase composition which allows estimation of DH""x/mcir as a function of pressure and/or temperature. This model is applied to Martian meteorites, such as the nakhlites, which may contain knv water contents. The nakhlitc suite arc augite-rich and minimally shocked meteorites, which arc believed to have formed from lava flows from a single volcano, a shallow intrusion of basaltic magma, or a sill complex on Mars. Using the newly derived DH < px/melt, model, the magmatic water contents of the nakhla parental melt was estimate (and subsequently used to calculate the Martian mantle source H2O content by various equilibrium and fractional (accumulated) melting models. both the parental magmatic and the mantle source H2O contents can be compared to literature estimates for the Miartian mantle derived from other methods. Results suggest the H20 contents of the source regions for the nakhlites is significantly lower than most of Earth's upper mantle, but comparable to the primitive lunar mantle and the Martian depleted and enriched sources. Such limited data from Martian meteorites supports the presence of a partially hydrated Martian mantle, although one with a lower overall 'water' content than Earth, perhaps reflecting marked contrasts in geological processes on the t,vo bodies. Finally, semi-empirical models derived from a thermodynamic starting point are used to further explore the available dataset on H solubility in olivine. The second half of this thesis similarly concerns H and C at subsurface (elevated pressure and temperature) conditions but focuses on astrobiologically important hydrocarbons and organics. If molecular biotic evidence docs exist on Mars, it is likely preserved within or below the crust where it would be protected from surface radiation and photolytic decomposition. Extended CV exposure is expected to result in the eventual destruct.ion of surface organics and diagnostic biomarkers. Molecular biosignatures may also have an advantage over morphological biosignatures (e.g., microfossils) in the subsurface environment. For instance, while mieromorphology can potentially distinguish biotic from abiotic carbonates, carbonates experience significant loss of primary microfabric and destruction of fossil evidence due to pervasive recrystallization during diagenesis. Experimental studies of the interactions between bio-organics and minerals under conditions simulating the harsh Martian environment provide key insights into possible prebiotic processes and the search for life. In general, organic matter analysed from a geologic environment can fall into three categories: abiotic compounds that are not associated with biological organisms, biogenic compounds produced by biological organisms, and thermogcnic compounds derived from the thermal decomposition of biologically generated compounds undergoing diagenetic processes. It is critical that biosignatures used to evidence pa.st or present life on !vfars arc not only biogenic or thermogenic, but discernible from abiotic compounds despite significant diagenetic or fluid alteration processes. Additionally, assessing the evolution of organic molecules in subsurface environments has significant implications for evaluating plausible scenarios for the origins of life and prebiotic chemistry. Despite protection from CV and oxidative degradation, buried biosignatures may undergo diagenetic processes that decrease the concentration of organic matter, as well as other degradation mechanisms as a result of elevated temperatures, pressures, and mineralorganic interactions. I provide a fuller understanding of preservation potential by considering several variables, including pressure, temperature, and the mineral matrix environment. Results inform future in situ searches for life on :\la.rs as well as the interpretation of organic analyses from past missions.

The lanthanoid elements, and in particular the heavier lanthanoids, are essential in the manufacture of advanced technologies due to their unique magnetic, spectral and luminescence properties. However, despite advances in the understanding the behaviour of lanthanoids within chemistry, physics and materials science, the behaviour of these elements within geological systems and in particular the processes by which they become concentrated to form economic ore deposits is still poorly understood. The southern Swedish Norra Kärr lanthanoid-deposit represents a significant European lanthanoid resource of 0.19 Mt T-LnO, with the principal ore domains exhibiting ore-grades between 0.48 - 0.69 % T-LnO. Despite its economic significance, the formation of the Norra Kärr intrusion and its economic ore bodies is still not fully understood. However, the intrusion represents an ideal locality to study the concentration of lanthanoids within a peralkaline magma due to the presence of an economically important ore resource; a particular bias towards the economically important heavy- [Ln]; and zonation between light and heavy-[Ln] within separate ore domains. Previous work on the intrusion has primarily focused on analysing the main ore-domains at the expense of other lithologies with the data collected used to develop models for the whole intrusion. This study has analysed the petrology, minerology and whole rock geochemical characteristics of all the lithologies of Norra Kärr and placed the intrusion into the wider structural context of deformation within the Baltic shield at the time of emplacement. These new data and interpretations have been used to test the existing models and develop a new model for the emplacement of Norra Kärr; to better contextualise the formation of the ore domains; and to offer a new model for the light-[Ln] vs heavy-[Ln] zonation observed within the ore-body as a whole. This study has demonstrated that Norra Kärr was emplaced in two magmatic phases, possibly as a series of dyke intrusions; with the first phase magmas more enriched in [Ln] than the second phase magmas. The ore domains developed as a series of cryptic units due to fractionation of the Grennaite-portion of the first magmatic phase. The [Ln]-concentrations were shown to initially increase from the Contact Grennaite to the Pegmatite-Host Grennaite, before enriching in the light- [Ln] and depleting in the heavy-[Ln] as observed in the Crenulated Grennaite. The second phase magmas (Pulaskite-type) display a different minerology to the first phase partially due to due to higher aHF and a more reduced magmatic chemistry. These second phase magmas may have been emplaced due to the effects of ongoing shearing of the intrusion, with the Lakarpite developing its complex chemistry and petrology due to interaction with the still warm Pegmatite-Host Grennaite. This study has demonstrated that a progressive increase in [Ln] within a melt is possible due to aegirine crystallisation, and that the observed variation in light-[Ln] vs heavy-[Ln] within the ore-domains is due to catapleiite crystallisation. This study has also shown that the volatile evolution within a melt affects the magmatic evolution by dictating the order of Zr-silicate crystallisation. The order of Zr-silicate crystallisation within a magma acts to determine the potential grade of any [Ln]- deposit formed. If eudialyte crystallises first then the ore-grade will decrease with fractionation, whereas if catapleiite crystallises first the grade will increase with a bias towards the light-[Ln].

Large-scale silicic systems are characterised by eruption of rhyolite composition magma in caldera-forming events. This often produces pyroclastic flows, which can travel >100km from the vent. A key question in volcanology is understanding how and why some magmatic systems evolve into producing large volumes of eruptible silicic magma, and others do not. The flux of magma over time must be sufficiently high to allow accumulation of large bodies of partially molten, eruptible material within the crust, as opposed to forming fully solidified plutons. First, priming of the system must occur, by repeated injection of mantle-derived mafic magma into the crust. Therefore, a great volume of mafic material is stored at depth beneath silicic systems, driving the production of silicic magma. However, the dominant erupted products in silicic systems are overwhelmingly rhyolitic in composition, and are subject to large amounts of crustal processing, obscuring primitive mantle-derived features. Therefore, in comparison to our knowledge on silicic processes, our knowledge on the primitive, mafic portion of the magmatic system is limited. The Taupo Volcanic Zone (TVZ), New Zealand (NZ) is one of the most productive silicic systems worldwide. It is a rifted continental arc, where both fluids derived from the subducting slab and decompression from rifting drive production of magma. Rifting aids the eruption of volumetrically minor amounts of basalt, which rise from depth along faults parallel to the main rift axis, and caldera rims. Large amounts of mafic magma in the crust are required to drive the production of silicic magma, but are too dense to erupt without the help of normal faulting. This means that although basalt is volumetrically minor at the surface, its composition and crystal cargo can be used to infer much broader processes occurring in the primitive portions of the magmatic plumbing system. The TVZ is also one of the clearest examples of maturation of a magmatic system, where the shift from andesitic continental arc-type volcanism to rhyolitic volcanism is both spatial and temporal. The arc is propagating southwards with time, and is split into north, central and southern segments. Andesitic volcanism is precursory to rhyolitic volcanism in the TVZ and dominates the south TVZ (S-TVZ), where the onset of volcanism is more recent in comparison with the central TVZ (C-TVZ). Coeval mafic rocks show a shift in whole rock composition coinciding with the shift from andesitic to rhyolitic volcanism. This thesis uses a multidisciplinary geochemical approach to resolve the shift in mafic rock composition between the different segments of the TVZ. We find that basalt in monogenetic eruptions is much more texturally complex than previously assumed. TVZ basalt inherits antecrysts and xenocrysts from a range of sources, including the lithospheric mantle, cognate cumulate mushes, and hydrothermally altered rhyolites. The type of crystals inherited vary between different segments of the arc, allowing us to attribute shifts in the basalt composition to changes in the maturation of the magmatic system. Finally, we successfully reproduce the observed changes in basalt composition through a series of high pressure/temperature experiments. This PhD project gives insight into changes within the mafic portion of the transcrustal magma system through the waxing and waning of one of the most productive large-scale silicic systems on Earth.

Subduction zones are the main drivers of global volatile recycling through the supply of water to the mantle wedge which, in turn, triggers arc volcanism. Serpentinites may contribute greatly to this process due to their high water content and widespread presence in oceanic lithosphere. B isotopes are a powerful tracer of serpentinites due to their distinct signature (delta11B = +5 to +40 permil) and the signature of their expelled fluids (delta11B up to +15 permil), compared to the mantle which has a low delta11B (~-7.1 permil). However, despite its fluid mobile nature, B-rich metamorphic olivine has been found in dehydrated serpentinites in the field as well as in experiments. This retention of B in olivine potentially fractionates B isotopes during serpentinite dehydration, but details of this process remain largely unconstrained. The aim of this thesis is to analyse the B and delta11B distribution between phases in dehydrated serpentinites from two different geological settings: a subduction zone and a contact aureole, in order to constrain B isotope behaviour during deserpentinization. In addition we ran olivine-fluid B partitioning experiments to quantitatively constrain the partitioning behaviour of isotopes between olivine and fluid. This project provides an insight into serpentinite-associated fluid movements during subduction and contact metamorphism and the partitioning of B and its isotopes between olivine and fluid. We find that open system dehydration significantly effects the B isotope signature of dehydrated serpentinites and 11B partitioning preferences are fluid > olivine > serpentine.

It is well established that oxygen fugacity, fO₂ , is one of the key parameters that needs to be quantified in order to understand igneous processes, model the geophysical behaviour of the core and mantle, to understand the exchange of C-O-H-S gases between the atmosphere and the interior of the Earth, and to further our understanding of other terrestrial planets. Despite this it remains one of the most poorly constrained geochemical variables, limiting our understanding of terrestrial systems. Recent work has focused on using accessory minerals for determining magmatic fO₂ , as a probe to constraining conditions in planetary interiors. Accessory minerals are already important petrological tools for providing insight into magmatic conditions. These minerals may concentrate a variety of trace elements, and hence are crucial in understanding the elemental budget of magmas. Accessory minerals such as zircon and apatite are also some of the hardier minerals found in igneous rocks and are, therefore, less likely to be altered by processes such as chemical weathering, metasomatism or crustal anatexis. Furthermore, study of detrital accessory minerals in ancient sedimentary rocks could provide much needed insight into the evolution of the oxidation state of the early Earth. This work aims to assess how the compositions and structures of two accessory minerals, spinel and apatite, respond to variations in magmatic fO₂ and to determine whether these minerals could act as probes of fO₂ in planetary interiors. Focus has been concentrated on the element manganese, as (1) it is a relatively abundant trace element, (2) it can exist in valence states from Mn²⁺ to Mn⁵⁺ in nature, and (3) recent work has suggested that Mn may become preferentially concentrated in apatite under reduced conditions. In an initial investigation, large single crystals of Mn-rich spinel were synthesised under a variety of fO₂ conditions. X-ray absorption near edge structure (XANES) spectroscopy and structural refinements of single crystal X-ray diffraction data were used to determine Mn valence state and coordination. Results show that Mn is present in spinel as both Mn²⁺ and Mn³⁺, distributed over both octahedral and tetrahedral cation sites. However, in contrast to the Fe⁺²/Fe³⁺ ratio, little variation in Mn valence as a function of fO₂ was observed. Results were, however, useful in testing and refining protocols for modelling Mn XANES data in a simple, model system. In contrast to results from spinel, previous studies have indicated that Mn valence may change significantly in the accessory mineral apatite due to variations in magmatic fO₂ . To test this, crystals of apatite in equilibrium with different silicate melt compositions were synthesised at high pressure/temperature. Mn partitioning between apatite and melt was determined by electron probe microanalysis (EPMA), and Mn valence state determined by XANES spectroscopy. Although EPMA data revealed that there is no dependence of Mn partitioning on fO₂ , it was noted that partitioning is dependent on melt composition. In more silica-rich melts, a reduction in proportion of non-bridging oxygen reduces the ability of melts to incorporate Mn. As such, apatite crystallising in more evolved melts is expected to be enriched in Mn. These results are confirmed by XANES data, which indicate that Mn is present in coexisting apatite and silicate melt as Mn⁺⁻¹²³⁴⁵⁺², with no observed variation in Mn valence state with fO₂ . In a final, preliminary investigation, attention was turned to Eu and Ce. Inferred variations in the valence state of these rare earth elements, i.e. En²⁺/En³⁺ and Ce³⁺/Ce⁴⁺, are already of use in petrological modelling. Two series of experiments were conducted to synthesise Eu and Ce-bearing silicate glasses (both Fe-bearing and Fe-free) over a range of fO₂ conditions, and apatite in equilibrium with various silicate melt compositions at high pressure/temperature, again over a range of fO₂ conditions. XANES characterisation of glasses demonstrates systematic variations in En²⁺/En³⁺ ratio with fO₂ . In contrast, Ce is dominantly present in quenched glasses as Ce³⁺ under all fO₂ conditions. In apatite, there is little variation in En²⁺/En³⁺, with Eu dominantly incorporated as En³⁺. Ce in apatite is dominantly incorporated as Ce³⁺. These results indicate that apatite-melt partitioning of Eu should be dependent on fO₂ , potentially providing a probe of magmatic fO₂ once the effects of melt compositions are constrained. Results presented here highlight the potential use of apatite as a petrological indicator. However, in contrast to previous work, I show that apatite-melt partitioning of Mn is largely independent of fO₂ . In fact, observed trends in apatite chemistry previously suggested to indicate variations in magmatic fO₂ can instead be fully explained by the observed influence of melt structure/composition on Mn partitioning. In contrast, En contents of apatite (for example apatite/whole rock ratios) may provide insight into oxidation state in the deep Earth. However, more work is required to constrain the influence of fO₂ on En (and other element) partitioning. Importantly, results here highlight the important influence which melt structure has on element partitioning. This control indicates that it is unlikely that fO₂ in the early Earth can be inferred from the chemistry of detrital minerals in sedimentary rocks, or inherited minerals in igneous/metamorphic rocks, as the composition of magmas from which these minerals crystallised cannot easily be constrained.

This thesis investigates the archaeological potential of masonry mortars throughout North Atlantic Europe, with a particular focus on the buildings and environments of medieval northern and western Scotland. The results of an extensive non-intrusive survey of medieval and later buildings are presented, within which nine multiphase sites were subject to more comprehensive building, environment and materials analysis. The survey suggests that, in general, different mortar-making techniques had well-defined sub-regional distributions which are not simply a correlate of environmental availability, but developed in different ways over time. Moreover, all of the more comprehensively studied buildings contain evidence of striking material contrasts from phases to phase which has great potential in standing building analysis. Material contrasts in masonry evidence between building phases, between neighbouring buildings, between specific buildings and the regional corpus, and between the regions themselves, are then considered as evidence of changing cultural, chronological and environmental context. The relationship between secular and ecclesiastical buildings across the region is a particular concern. Qualitative lab-based and on-site material interpretations made throughout the thesis are supported by a programme of comparative experimentation. This thesis includes the first comprehensive investigation of lime mortars made from marine shells, the first evidence of lime mortars made from coralline algae, results from the first programme of dating medieval buildings in Scotland through radiocarbon analysis of relict mortar fuel, and microstructural analysis of a large range of medieval mortars from Norway to the Isle of Man. Wider research considers the initial emergence of mortared masonry in North Atlantic Europe and the relationship between clay and lime mortars. Ultimately, by placing the upstanding buildings archaeology at the centre of the medieval and later landscape this thesis will demonstrate that masonry mortars have significant potential to inform our understanding of the cultural and environmental context of lordship construction in the North Atlantic, providing a new focus for further interdisciplinary discourse.

The UK Committee on Radioactive Waste Management (CoRWM) recommended, in 2006, that geological disposal coupled with safe and secure interim storage should have been the way forward for the long-term management of the UK’s higher activity wastes. The design of the underground repository contemplates the presence of bentonite plugs to seal access galleries and deposition boreholes and hence the interaction between the clay-based backfill material and the underground water. Remote monitoring of the fluid saturation of the barrier, the waste canisters and of the surrounding subsurface Geological Disposal Facility environment assumes a relevant importance to guarantee the safety of the repository and to increase the confidence and the reliance of the communities living in areas potentially affected by the repository over time. This remote monitoring of the Engineered Barrier System represents a technical challenge due to the unsuitability of some of the traditional geotechnical techniques or to the intrinsic unreliability of many geophysical prospecting techniques in providing information about the evolution of the Thermo-Hydro-Mechanical-Chemical coupling of the system over long timescales up to and including post-closure evolution. In this project, I offer an initial approach to an innovative way of using mineral magnetism, and, in particular, I analyse the possible exploitation of corrosion-induced variations of the magnetic properties of several magnetic materials to monitor water saturation in the Engineered Barrier System and its evolution through time. Initially the reactivity of several natural and synthetic materials is tested under different “extreme” conditions to analyse the feasibility of the research concept and identify the materials more adapt to carry out the job. The effects that the corrosion of the magnetic materials has on the clay matrix is also analysed in detail throughout all the thesis work. The initial tests lead to the identification of specific transitions in the hysteretic behaviour of three of the initial candidates (Nd-Fe-B, AlNiCo and SmCo alloys). These three materials are subsequently tested under conditions closer to a real “evolved” Barrier System, where the groundwater interacts, with cementiferous grout producing hyperalkaline leachates. The final tests consider the temporal evolution (after 4, 8 and 12 months) of the magnetic properties of these materials in a dysoxic environment under imposed fluid-flow. The results show a clear change in the hysteretic properties of the three materials analysed and the feasibility of the monitoring of the Barrier fluid saturation in the short-term. Furthermore, the corrosion of the magnets, under the conditions applied, did not cause formation of non-swelling clays.

Previous research has established that the majority of nominally anhydrous minerals (NAMs) in Earth’s mantle can incorporate water in the form of structurally bound hydrogen and, correspondingly, the mantle is thought to contain a substantial volume of water. Water has been shown to play a key role in the geodynamics of the Earth’s interior and quantifying the amount, and distribution, of water in the mantle is an important step in understanding many deep-Earth processes. One of the parameters highly sensitive to the incorporation of water in the mantle is electrical conductivity, as hydrogen is highly mobile and acts as the dominant charge-carrying species. In theory, this relationship can be used in conjunction with geophysical techniques that measure mantle-scale electrical conductivity to ‘map-out’ the deep Earth’s water content – but accurate interpretation of such data requires full understanding of hydrogen mobility in NAMs under extreme conditions, which remains poorly constrained. The aim of this project is to contribute to the reconciliation of geophysical observations with laboratory measurements of electrical conductivity, by considering hydrogen-deuterium exchange in single crystals. In a novel experimental design, hydrogen in crystals synthesised under mantle conditions (such that the hydrogen defects present correspond to the conditions being studied) exchanges with deuterium from a liquid source under controlled (mantle) pressure and temperature conditions for a specified time period. This results in hydrogen-deuterium exchange profiles that can be characterised by SIMS and subsequently fitted to Fick’s law to calculate hydrogen diffusion coefficients – which in turn can be related to electrical conductivity through the Nernst-Einstein equation. Analysis of the experimental results underlines the complexity of the influence of hydrogen on electrical conductivity in NAMs, and emphasises the need for careful consideration when interpreting and applying the results of diffusion studies. Ultimately, the data obtained in this study provides a useful contribution to understanding hydrogen diffusion in mantle minerals, but the non-trivial nature of both the experimental and analytical aspects mean that the method cannot easily be applied to other mantle phases.

Constraining the behaviour of small fractions of partial melt in a solid silicate matrix has been the focus of numerous experimental petrology studies over several decades, and is an important factor in constraining upper mantle rheology, melt extraction at mid-ocean ridges and mechanisms of core formation in the early solar system. Deformation of partially molten rock has been observed to change melt geometry, and may enhance permeability and interconnectivity of melt otherwise trapped in a solid silicate matrix, although it is uncertain how applicable results of high strain-rate laboratory experiments are to the real Earth. The addition of deformation precludes attainment of textural equilibrium, complicating textural analysis, which has previously relied on extrapolation of 3D textures from quenched and polished 2D sections for hydrostatically annealed samples. X-ray computed tomography gives the potential to visualise sample textures directly in three dimensions, and is becoming popular as a complementary technique for textural analysis in petrologic studies. The aim of this project has been to develop techniques to improve visualisation of small fractions of partial melt within a solid silicate matrix using X-ray CT, to examine textures of various partially molten systems at high PT in hydrostatic, and dynamically deforming systems. Experiments carried out in the FeS-melt, solid olivine system have examined the potential for deformation-enhanced percolation of core forming melts before the onset of silicate melting. Access to the newly designed rotational Paris-Edinburgh Cell (roPEC/rotoPEC) equipment has allowed us to carry out controlled, torsional deformation experiments under PT conditions applicable to planetary interiors. Experiments conducted at lower strain-rates over longer duration than in previously published studies show that deformation enhances connectivity at low melt fractions, at strain-rates down to 10-6s-1. This is in contrast to earlier work suggesting melt textures are unaffected at strain-rates below 10-5s-1. Quenched melt networks have been fully characterised in 3D using multi-scale CT, with voxel sizes down to 70nm for small sample sub-volumes. Results suggest segregation of metallic melt below the silicate solidus could be an efficient process, and should be taken into account in geochemical models of planetary evolution. Experiments on basaltic melt in a solid silicate matrix were conducted in application to upper mantle melting. A heavy element, hafnium, was added to the basaltic glass starting composition to enhance contrast between the basalt and olivine phases during CT scans. In-house micro-CT equipment was used to visualise post-quench run products of hydrostatic and deformation experiments. The doping technique was successful for long-duration, high temperature hydrostatic experiments. Some issues with undissolved / re-precipitated HfO¬2 crystals complicated tomographic imaging of partial melt textures in a number of experiments, particularly those carried out on the rotoPEC equipment, limiting comparison between samples. The doping technique requires further adjustment, but is shown to be a viable way to improve visibility of basaltic melt without significantly affecting melt texture. The X-ray transparent design and fully rotating top and bottom anvils of the rotoPEC allow X-ray tomography to be carried out in-situ while experiments are in progress, enabling collection of 4D datasets. During this project, the rotoPEC equipment was incorporated into two different synchrotron beamlines, to carry out time-resolved studies of textural development within samples of varying composition. The migration of gold melt along fractures with a BN matrix was imaged using 2D radiography, in combination with repeated 3D tomography to fully characterise the 3D fracture geometry. This allowed melt migration velocity to be estimated directly from in-situ observations. These techniques could be developed further to constrain melt migration processes quantitatively for a number of geological systems in the near future.

This research is concerned with the mechanisms of diffusion in the Earth and the implications of such an understanding. Specifically, this work is concerned with one particular aspect of diffusion: Grain Boundary Diffusion (GBD). An experimental investigation of GBD has been conducted by considering three specific scenarios; GBD of H in stoichiometric Mg-spinel, GBD of Ti in Quartz and GBD of Li in olivine. By considering the GBD of three very different elements it has been possible to synthesise an understanding of some of the mechanisms involved in the process. GBD is potentially a very important process within the Earth with wide ranging implications. Grain boundaries may provide fast pathways for transportation of a range of compatible and incompatible diffusing species in the Earth’s interior – potentially acting as storage locations and also as efficient pathways between different geological reservoirs. It is also potentially very important in the application of a number of techniques including dating and geothermometry and geobarometry. Here, an experimental study of the GBD of H has been carried out with the overall finding that GBD appears to occur at slightly greater yet broadly similar rates to lattice diffusion. This finding is considered in terms of the mantle properties which are affected by the presence and transport of H. A follow up series of experiments was conducted looking at Li diffusion. Li was chosen due to its volatile nature and larger atomic radius as compared to H. As such, it provided a useful test of the hypothesis that the radius of a diffusant might affect its chosen method of diffusion. A third set of experiments were carried out to investigate the GBD of Ti in quartz with particular reference to the TitaniQ geothermo(baro)meter. This set of experiments provided a very useful comparison to the data which had previously been obtained from lighter elements. This investigation has found that a combination of factors including charge, diffusant diameter and the specific mineralogical characteristics of the host phase will define the dominant diffusive mechanism and the size of the contribution made by that mechanism towards observed bulk diffusivities. A characterisation of the temperature dependency of diffusion within each setting has also been completed. As such, it also makes a useful contribution to the current dataset for GBD.

Our understanding of the nature of Earth’s D” region was changed significantly by a recent finding by Murakami et al. (2004), who revealed a phase transition from perovskite to post-perovskite structure in MgSiO3 at about 125 GPa and 2500 K, corresponding to conditions of the lowermost mantle. A perovskite to post-perovskite phase transition accounts for many unusual features of the D” region, including its notable seismic anisotropy, and also accounts for the unusual topology of the D” discontinuity. However, the experimentally synthesised post-perovskite phase of MgSiO3 is not quenchable to ambient conditions, which means that many of its physical properties remain difficult to determine. On the other hand, there are several post-perovskite oxides, CaIrO3, CaPtO3, CaRhO3 and CaRuO3, which can be quenched to ambient conditions, maintaining their structure. High pressure synthesis of CaIr1-xPtxO3 solid solutions (x = 0, 0.3, 0.5, 0.7) and CaIr0.5Rh0.5O3 was conducted at the University of Edinburgh and Geodynamics Research Center, Ehime University, and structures and physical properties of these novel post-perovskite materials determined. Substantial [100] grain growth was observed in all solid solutions leading to pronounced texture even in powdered materials. Temperature-independent paramagnetism above 150 K and small magnetic entropy observed in heat capacity measurements suggest that CaIrO3 is an intrinsically weak itinerant ferromagnetic metal, while electrical resistivity measurements show that it is a narrow bandgap semiconductor, possibly due to grain boundary effects. CaIrO3 undergoes a magnetic transition at 108K and possesses a saturated magnetic moment of 0.04 μB. Doping with Pt or Rh induces Curie-Weiss paramagnetism and suppresses the magnetic transition. The anisotropic structure and morphology of CaIrO3 combined with the Ir4+ spin-orbit coupling results in a large magnetic anisotropy constant of 1.77 x 106 Jm-3, comparable to values for permanent magnet materials. A new high-pressure phase of CaIr0.5Pt0.5O3 was synthesised at 60GPa, 1900K using a laser-heated DAC (diamond anvil cell) at GRC, Ehime University. Its Raman spectra resemble those of perovskite phases of CaIrO3 and CaMnO3, implying that CaIr0.5Pt0.5O3 undergoes a post-perovskite to perovskite phase transition with increasing pressure. I estimate an increase in thermodynamic Grüneisen parameter γth across the post-perovskite to perovskite transition of 34 %, with similar magnitude to (Mg,Fe)SiO3 and MgGeO3, suggesting that CaIr0.5Pt0.5O3 is a promising analogue for experimentally simulating the competitive stability between perovskite and post-perovskite phase of magnesium silicates in Earth’s lowermost mantle. Such estimation is reliable since the estimated and directly calculated thermodynamic Grüneisen parameter γth from heat capacity show consistent values. The marked effect that Pt has on stabilising the post-perovskite structure in CaIr1-xPtxO3 solid solutions explains why the post-perovskite to perovskite phase transition has not been observed for CaPtO3 in contrast to other quenchable post-perovskite oxides: CaIrO3, CaRhO3 and CaRuO3.Work presented here demonstrates that CaIrO3 solid solutions can be used to provide new insight into factors stabilising post-perovskite structures in Earth’s lowermost mantle.