Dissertations / Theses on the topic 'Phase equilibria forward modelling'

Le métamorphisme est un phénomène majeur affectant la distribution des phases minérales au sein de la croûte continentale et participant à sa stabilisation. L’étude des processus métamorphiques est donc essentielle pour comprendre la formation et l’évolution de la Terre. Ces processus exercent un contrôle sur le potentiel de préservation des roches à sa surface et nous renseignent entre autres sur les conditions de pression–température régnant en profondeur. Ils contrôlent également la production et le stockage de fluides au sein de la croûte ce qui influence les cycles géochimiques au sein de la lithosphère, de l’hydrosphère et de l’atmosphère et a, de fait, des implications importantes sur le climat et l’apparition de la vie sur Terre. La principale source de variabilité au sein de ces systèmes correspond à des changements de composition chimique résultant eux-mêmes de transferts de matière. Les techniques modernes de modélisation quantitative des équilibres de phases permettent de calculer l’assemblage minéralogique stable au sein d’un système à l’équilibre pour lequel les paramètres pression, température et composition chimique sont connus. Ceci étant, les programmes informatiques actuels ne possèdent que de fonctionnalités limitées pour modéliser et appréhender les conséquences de changements de composition chimique du système au cours du métamorphisme. Un nouvel outil informatique (Rcrust) a été développé pour permettre de calculer l’assemblage minéralogique stable dans un système soumis à des variations de composition lors de son évolution dans l’espace multidimensionnel pression–température–composition chimique
The investigation of metamorphic processes in the Earth’s crust is integral to understanding the formation and evolution of the Earth. These processes control the preservation potential of the geochronological rock record and give us insight into, amongst others, the pressure and temperature conditions of the Earth’s interior. Further, they control fluid generation and consumption within the crust which influences global geochemical cycles within the lithosphere, hydrosphere and atmosphere. This has important implications on the global climate and the creation of conditions conducive to life. The dominant mechanism of change both within and between these systems are compositional changes invoked by processes of mass transfer. Modern quantitative phase equilibrium modelling allows the calculation of the stable phase assemblage of a rock system at equilibrium given its pressure, temperature and bulk chemical composition. However, current software programs have limited functionalities for the sophisticated handling of a changing bulk composition. A new software tool (Rcrust) has been developed that allows the modelling of points in pressure–temperature–bulk composition space in which bulk compositional changes can be passed between points as the system evolves

Formation of gas hydrates can lead to serious operational, economic and safety problems in the petroleum industry due to potential blockage of oil and gas equipment. Thermodynamic inhibitors are widely used to reduce the risks associated with gas hydrate formation. Thus, accurate knowledge of hydrate phase equilibrium in the presence of inhibitors is crucial to avoid gas hydrate formation problems and to design/optimize production, transportation and processing facilities. The work presented in this thesis is the result of a study on the phase equilibria of petroleum reservoir fluids containing aqueous salt(s) and/or hydrate inhibitor(s) solutions. The incipient equilibrium methane and natural gas hydrate conditions in presence of salt(s) and/or thermodynamic inhibitor(s) have been experimentally obtained, in addition to experimental freezing point depression data for aqueous solution of methanol, ethanol, monoethylene glycol and single or mixed salt(s) aqueous solutions, are conducted. A statistical thermodynamic approach, with the Cubic-Plus-Association equation of state, has been employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. Predictions of the developed model have been validated against independent experimental data from the open literature and the data generated in this work. The predictions were found to agree well with the experimental data.

Understanding gas hydrate inhibitor distribution in hydrocarbon phases is essential for the economic design of process equipment. In order to build a clear image of the inhibitor’s distribution in various phases, three experimental investigations were devised; solubility in liquid and vapour phase as well as saturation pressure measurements. These data will contribute significantly to the understanding of the partitioning of these components as the data in the open literature are fairly limited. Aiming at filling the experimental gap found in the literature, the solubility of methane in pure methanol and ethanol as well as 70 and 50 wt% aqueous solutions at 238.15 – 298.15 K and 0.3 – 47 MPa were measured. The data from the ethanol/solution solubility measurements were used to optimise the methane-ethanol Binary Interaction Parameters (BIPs) of the CPA-SRK72 Equation of State (EoS). The model calculations showed an absolute average deviation of 5.3% over the full pure data range. To improve the CPA-SRK72 EoS predictions for aqueous solutions, new methane-ethanol BIPs were regressed showing significant improvement for both solubility and quaternary bubble point predictions. In order to determine the inhibitor loss to the vapour phase, the inhibitor content of methane was measured using Gas Chromatography (GC) between 0.7 – 62 MPa and 273.15 – 298.15 K. Additionally, a number of bubble point measurements were conducted for binary, ternary and quaternary systems containing methane, a liquid hydrocarbon phase (C7 – C12), methanol/ethanol and water. This was to investigate the effect of the inhibitor phase in the ternary, and the dominant excess water phase in the quaternary system, on the bubble point pressure as well as evaluating the CPA-SRK72 predictions. The saturation pressures were measured at 253.15 – 313.15 K. The solubility of CO2 in Mono-ethylene glycol (MEG), Di-ethylene glycol (DEG) and Tri-ethylene glycol (TEG) and their aqueous solutions (90, 60 and 40 wt%), at pressures and temperatures ranging from 0.2 – 43.4 MPa and 263 – 343 K, were measured. The solubility of CO2 in pure MEG, DEG and TEG were predicted using the CPA-SRK72 EoS, using a single binary interaction parameter, showing an absolute average deviation of 5.13%, 9.51% and 2.55% respectively. Correlations for the solubility of CO2 in MEG, DEG and TEG aqueous solutions, using aqueous solution regressed BIPs, showed an overall absolute average deviation of 17.5%, 18.2% and 25.16% respectively, a significant improvement from the non-aqueous solution BIP optimised predictions.

Thesis (MScEng)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: During the production of pure Ti02 for the pigment industry, ilmenite, containing 35 - 60 % Ti02, is reduced to high titania slag, containing 85 - 95 % Ti02 and pig iron. These ilmenite smelters are operated in very tight operating windows. Over reducing the slag may lead to the formation of TiC and reducing much of the Ti02 to Th03. According to Namakwa Sands furnace operators, this does not only affect the grade of the product, but it can cause slag foaming and furnace eruptions. In under reducing conditions, the liquid slag is fluxed by the FeO and may corrode the furnace lining and consequently lead to run-outs. The reducing conditions in the furnace are not only controlled by carbon addition, but also by temperature. Standard practise in industrial ilmenite smelters is to operate the furnace with a slag freeze lining to protect the refractory lining from chemical and physical attack by the slag. It is therefore clear that it is of great importance to be able to predict the slag liquidus temperature at different compositions. This can help the operator to avoid dangerous operating conditions. Over the past few decades, a number of solution models have been developed to describe non-ideal solutions. With the rapid increase in computer power, these models became more valuable and practical to use in advanced control and decisionsupport. In this study, some of the better-known models are discussed and evaluated for the Ti02 - Th03 - FeO system, based on a critical review of properties and measurements published in literature. Two of these models, the "modified quasi-chemical" model and the "cell" model were chosen to be applied to the high-titania slag system. Both these models are based on statistical thermodynamics with some differences in the initial assumptions. In this study, the model parameters for the cell model were regressed from experimental data. The high-titania slag produced, consists mainly of titanium in different oxidation states and FeO, placing its composition inside the Ti02 - Th03 - FeO ternary system. Reliable experimental data for this system are very limited. All three binary systems contained in the Ti02 - ThO) - FeO system were considered, namely FeO - Ti02, Ti02 - ThO) and FeO - ThO). Only liquidus data for these three binaries were used to regress the model parameters. Accuracy of the models was determined by calculating the root mean square (RMS) error between the experimental data point and the value calculated using the model and the newly determined model parameters. These errors corresponded weil with the reported experimental error of the datasets for both the models and all the binary systems. Due to the fact that this study focussed on the liquidus surface of the system, the results were also plotted in the form of binary phase diagrams and ternary liquidus isotherms. The cell model uses only binary interaction parameters to describe the ternary system. These parameters are not expanded to higher order polynomials, which makes this model more robust, but also less accurate than other models such as the modified quasi-chemical model.
AFRIKAANSE OPSOMMING: Tydens die produksie van suiwer Ti02 vir die pigmentbedryf, word ilmeniet, wat 35 tot 60 % Ti02 bevat, gereduseer tot 'n hoë titaan slak, met 'n Ti02 inhoud van 85 tot 95 % Ti02, en potyster. Hierdie ilmeniet smeltoonde word binne baie nou bedryfskondisies beheer. Oor-redusering van die slak kan lei tot the formasie van TiC en die redusering van Ti02 tot Th03. Dit affekteer nie net die produk se kwaliteit nie, maar kan volgens Namakwa Sands oond operateurs ook slak skuiming en ontploffings tot gevolg hê. Gedurende onder-reduserende omstandighede in die oond, word die vloeibaarheid van die slak verhoog deur die hoër FeO inhoud in die slak. Dit maak die slak meer korrosief en kan lei tot faling van die vuurvaste stene. Die mate van redusering in die oond word nie net bepaal deur die toevoeging van koolstof nie, maar ook deur die temperatuur van die slak. Dit is 'n standaard praktyk van die industrie om die oond te bedryf met 'n gevriesde slak laag om sodoende die vuurvaste stene te beskerm teen chemiese en fisiese aanval van die slak. Dit is dus duidelik dat dit baie belangrik is om die slak se smeltpunt by verskillende samestellings te kan voorspel. Dit kan die operateur help om die oond binne veilige bedryfskondisies te hou. 'n Hele aantaloplossingsmodelle is oor die afgelope paar dekades ontwikkel vir die beskrywing van nie-ideale oplossings. Hierdie modelle het oor die afgelope paar jaar baie toegeneem in praktiese waarde as gevolg van die snelle toename in rekenaarkapasiteit en -spoed. Dit het veral groot waarde in gevorderde beheerstelsels en besluitneming steun. Sommige van die meer bekende modelle word in hierdie studie bespreek en ge-evalueer vir die Ti02 - Th03 - FeO stelsel, gebaseer op 'n kritiese evaluasie van eienskappe en eksperimentele data gepubliseer in die literatuur. Twee van hierdie modelle, die "gemodifiseerde kwasi-chemiese" model en die "sel" model, is gebruik om die hoë titaan slak stelsel te beskryf. Beide hierdie modelle is gebaseer op statistiese termodinamika en het klein verskille m.b.t. die aanvanklike aannames. Die model veranderlikes vir die sel model is in hierdie studie afgelei vanaf die eksperimentele data. Die hoë titaan slak wat tydens hierdie proses geproduseer word, bestaan hoofsaaklik uit FeO en titaan in sy verskillende oksidasie toestande. Dit plaas die samestelling van die slak reg binne die Ti02 - Th03 - FeO temêre stelsel. Betroubare eksperimentele data vir hierdie stelsel is baie beperk. In hierdie studie word daar gekyk al drie binêre stelsels binne die Ti02 - Th03 - FeO temêre stelsel, naamlik: FeO - Ti02, Ti02 - Th03 en FeO - Th03. Slegs die smeltpunt temperatuur data vir hierdie twee binêre is gebruik in die afskatting van die model veranderlikes. Die akkuraatheid van die modelle is bepaal deur die wortel van die gemiddelde kwadraat van die fout tussen die eksperimentele waardes en die berekende waardes te bepaal. Albei die modelle het 'n relatiewe klein fout in vergelyking met die geraporteerde eksprimentele fout gehad vir al die binêre stelsels. Hierdie studie het gefokus op die smeltpunt temperatuur van die slak en die resultate is daarom ook in die vorm van binêre fasediagramme en isoterme projeksies op die temêre fasediagramme gestip. Die "sel" model gebruik slegs binêre interaksie parameters om die temêre stelsel te beskryf Hierdie parameters word vir die "sel" model nie uitgebrei tot hoër order polinome en dit maak die "sel" model meer robuust, maar minder akkuraat as ander modelle soos byvoorbeeld die "kwasi-chemiese" model.

In this thesis, a new approach to parameterization of the intermolecular potential models of ionic species in electrolyte solutions for the SAFT-VRE Mie theory is presented. Additionally, a predictive approach to the description of the fluid-fluid interface of non-electrolytic, non-associating mixtures is presented. These approaches are intended to support an integrated workflow for the study of the fluid systems relevant for carbon capture and sequestration. The parameterization methodology developed for the intermolecular potential models of ionic species in the SAFT-VRE Mie theory reduces the parameters to be estimated from solution data to a single interaction-energy per solvent-ion pair. This is achieved through the use of literature values for the ion-size parameter, and theoretical estimates for the ion-ion interaction energy. Additionally, the Born diameters of the ion models are taken to be those of Rashin and Honig, and not estimated from data. This approach is applied to the monovalent halides as well as select divalent ions. The resulting models reproduce the solvation energy in H2O to within 5 % error at standard conditions for the monovalent halides. Furthermore, the electrolyte models are demonstrated to provide a fair description of aqueous electrolytes when considering the limited parameterization. The predictive description of the fluid-fluid interface, is achieved by an approach in which the Square Gradient Theory (SGT) and the SAFT-VR Mie EOS are combined. The SGT influence parameter is mapped to the SAFT-VR Mie intermolecular model parameters through the relationship with the direct correlation function. The resulting model is parametrized by matching simulation data for the interfacial tension of λr-6 Mie monomeric fluids. A final evaluation of the model is carried out against non-associating systems of up to 4 species, for which predictive capabilities are demonstrated.

Hydrothermal processes play a major role in transporting mass and energy in Earth’s crust. These processes rely on hydrothermal fluid, which is dissolving, transporting and precipitating minerals and distribute heat. The composition of the hydrothermal fluid is specific for various geological settings, but in most cases it can be approximated by H₂O-NaCl-CO₂ fluid composition. The flow of hydrothermal fluid is controlled by differences in temperature, pressure and/or density of the fluid and hydraulic conductivity of the rock. In my work, I was focused on modeling of the hydrothermal fluid properties and experimental characterization of fluid that formed emerald deposit in North Carolina, USA. The dissertation based on the result of three separate projects. The first project has been dedicated to characterization of the H₂O-NaCl hydrothermal fluid ability to transport mass and energy. This ability of the fluid is defined by a change in fluid density and enthalpy in response to changing pressure or temperature. In this project we quantified the derivatives of mass, enthalpy and SiO₂ solubility in wide range of pressure, temperature and composition (PTx) of H₂O-NaCl fluid. Our study indicated that the PT region in which fluid is most efficiently can transport mass and energy, located in the critical region near liquid-vapor phase boundary and the sensitivity to changing pressure-temperature conditions decrease with increasing salinity. In second project we developed the revised H₂O-NaCl viscosity model. Revised model to calculate the viscosity of H₂O-NaCl reproduces experimental data with ±10% precision in PTx range where experimental data available and follows expected trends outside of the range. This model is valid over the temperature range from the H₂O solidus (~0 °C) to ~1,000 °C, from ~0.1 MPa to ≤500 MPa, and for salinities from 0-100 wt.% NaCl. The third project has been focused on the characterization of formation conditions of the emerald at North American Emerald Mine, Hiddenite, North Carolina, USA. The emerald formation conditions defined as 120-220 MPa, 450-625 °C using stable isotope, Raman spectrometry, and fluid inclusion analysis. Hydrothermal fluid had a composition of CO2-H2O±CH4, which indicates mildly reducing environment of emerald growth.
Ph. D.

Die ternären Systeme Ti/P/Te, Ce/P/Te und Si/P/Te wurden in der vorliegenden Dissertation hinsichtlich der Existenz neuer Verbindungen untersucht. Diese Verbindungen wurden insbesondere in Bezug auf ihre thermochemischen Eigenschaften charakterisiert. Durch Kombination von experimentellen Untersuchungen und thermodynamischen Modellierungen der ablaufenden Festkörper-Gasphasen-Gleichgewichte konnten die Synthesen der neuen Verbindungen optimiert werden. Abschließend erfolgte zudem die physikalische und kristallographische Charakterisierung der gefundenen Phosphidtelluride.

Die ternären Systeme Ti/P/Te, Ce/P/Te und Si/P/Te wurden in der vorliegenden Dissertation hinsichtlich der Existenz neuer Verbindungen untersucht. Diese Verbindungen wurden insbesondere in Bezug auf ihre thermochemischen Eigenschaften charakterisiert. Durch Kombination von experimentellen Untersuchungen und thermodynamischen Modellierungen der ablaufenden Festkörper-Gasphasen-Gleichgewichte konnten die Synthesen der neuen Verbindungen optimiert werden. Abschließend erfolgte zudem die physikalische und kristallographische Charakterisierung der gefundenen Phosphidtelluride.

Lors de l'extraction de l'uranium par lixiviation acide, AREVA fait face à des phénomènes transitoires de précipitation de phases mal cristallisées entrainant un colmatage des installations. Les analyses de ces précipités ont mis en évidence la formation d'un solide jaune minoritaire et d'un blanc majoritaire composé de sulfate de calcium et d'hydroxysulfate d'aluminium. Afin de comprendre les phénomènes menant à la précipitation et pour prévoir, éviter ou limiter leur apparition, les travaux de thèse ont consisté en l'étude expérimentale des équilibres solides-liquide du système complexe Al–Fe–K–P–S–H2O (± Ca et Mg) en milieu acide à 25°C, avec pour objectif l'identification des solides susceptibles d'apparaître en conditions industrielles. Les résultats permettront ainsi de compléter les bases de données thermodynamiques utilisées pour modéliser le comportement global du milieu lors des opérations. Après la mise au point de techniques analytiques appropriées, le travail s'est porté sur la délimitation des équilibres liquide-solides du système relatif au précipité blanc et particulièrement sur l'analyse des ternaires impliquant les hydroxysulfates d'aluminium. Le colmatage se produisant durant la phase d'acidification, l'évolution de la précipitation de ces hydroxysulfates en fonction du pH a été étudiée, afin de caractériser les solides formés en présence de cations minoritaires (Na+, K+, Mg2+, Ca2+) et de définir leurs constantes de solubilités à partir d'un modèle de calcul des coefficients d'activités des ions en solution. Des tests dynamiques sur colonne à partir de minerai naturel ont également été effectués et comparés aux résultats statiques
During the uranium extraction by acid leaching, AREVA observed the precipitation of not well crystallized solid phases, leading to the clogging of various equipment. The analyses of these precipitates highlighted the formation of a minor yellow precipitate and a major white precipitate containing calcium sulphate and aluminium hydroxisulphate. To understand the phenomena leading to the precipitation and to predict, prevent or at least limit their formation, this thesis work consisted of the solid-liquid equilibria experimental study of the Al–Fe–K–P–S–H2O (± Ca and Mg) system in an acidic environment at 25°C, with the identification of solid phases which may appear in natural ore as the major goal. The results could complete the thermodynamic database used to model global behaviour of the environment during acid mining. Based on the observed precipitates, two quaternary systems were defined, such as the H2O-Al3+, Ca2+ // O2-, SO42- system. After the development of appropriate analytical techniques, the work focused on the delimitation of the liquid-solid equilibria of the system based on the white precipitate and particularly on the analysis of the ternaries involving aluminium hydroxisulphates. As clogging occurs during acidification, the hydroxisulphate precipitation depending on the pH was studied in the presence of minority cations (Na+, K+, Mg2+, Ca2+), in order to characterise the solid phases which were formed, and to define their solubility constants. For the solubility constant determination, a calculation model of the ion activity coefficients in solution was used. A dynamic survey on a column containing natural ore was done and compared to static results

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Anglesey in North Wales is considered to contain the oldest exposures of lawsonite-glaucophane blueschist in the world, marking the first appearance of lawsonite in the geological record, and heralding the emergence of truly modern subduction thermal regimes. The blueschists formed in the late Neoproterozoic during subduction beneath Avalonia. Interlayered within the blueschist unit are rare lenses of garnet-bearing metapelite that form part of a lithological association with more voluminous garnet-free metapelites. Detrital U-Pb zircon geochronology of the metapelites indicates that deposition of the protolith occurred ~630-590 Ma ago. The dominant detrital zircon ages correspond to the age of arc magmatism along the inferred margin of Avalonia, suggesting that the bulk of the detritus was derived from erosion of the arc. The presence of less abundant older zircons that range in age up to 2Ga, suggest that the arc was built on an ancient continental margin. This suggestion is supported by Nd isotopic compositions of the metapelites, which indicate derivation from an evolved source. The rare garnet metapelites contain the metamorphic assemblage garnet-muscovite-chlorite-albite-quartz-titanite-rutile-pyrite in which coronas of rutile surround titanite. Phase equilibria forward modelling of the metapelites indicates a prograde burial path that culminated with conditions around 400-450°C, at pressures of 10-12kbar. These conditions give an average thermal gradient of around 40°C/kbar, which is comparatively warm for lawsonite-bearing rocks. This suggests the Anglesey lawsonite-bearing blueschists record the onset of global subduction thermal regimes in the late Neoproterozoic that can stabilise lawsonite, rather than simply being a fortuitous preservation of widely developed refrigerated metamorphic rock systems.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2017

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The Warumpi Province has been interpreted to be exotic and accreted to the Northern Australian Craton (NAC) during the Liebig Orogeny at c.1640Ma. However, phase equilibria modelling of melt-deficient, Mg-Al rich granulite facies rocks at Hill 830, in the Mount Liebig area show contradictory evidence of a decompressional pressure-temperature path and a high metamorphic gradient of 90°Ckbar. This interpretation in conjunction with abundant c.1780- 1740Ma and c.1640Ma magmatism in the southern Aileron and Warumpi Provinces, indicate that the tectonic regime at c.1640Ma may instead be a south-migrating, extensional scenario, compared to the previously accepted collisonal regime; speculating that the Warumpi Province is not ‘exotic’ to the NAC.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2015

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The Ediacaran to Cambrian (600-500 Ma) intraplate Petermann Orogeny significantly affected the crustal architecture of Central Australia, resulting in the exhumation of the Musgrave Province from beneath the Centralian Superbasin. In the western Musgrave Province response to intensive deformation is variable, with pervasive mylonitic reworking and localised migmitisation in the western Mann Ranges, and discrete mylonitisation in the eastern Mann Ranges. The duration of this period of intraplate orogenesis is a currently debated topic. Ti-in-zircon thermometry coupled with SHRIMP U-Pb zircon geochronology indicate that peak temperatures of 733±23°C in the western Mann Ranges occurred at circa 540 Ma. Combined diffusion-cooling modelling, U-Pb rutile and titanite isotopic data and calculated phase equilibria of recrystallised metagranites from the Cockburn Shear Zone and kyanite-bearing mylonites from the Mt. Charles Thrust indicate exhumation driven cooling from peak P-T conditions of 12-14 kbars and 700-750°C to 6-7 kbars and 550-600°C at c. 500 Ma occurred at a rate of 3.75-5.6°C/ My. These results indicate a slow-cooling and long-lived thermal regime and additionally suggests that final exhumation of the Musgrave Province had not occurred by c. 500 Ma, much younger than previously estimated. These findings suggest that granulite-facies metamorphism in the Musgrave Province was regional and that other factors such as fluid, control the variations in style of structural reworking. This study lends support to the notion that the intraplate Petermann Orogeny was long-lived and does not advocate short-lived orogenesis or the theory that shear heating is the driving force for metamorphism.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010

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Electrical anisotropy, defined as the directional dependence of electrical conductivity within a medium, causes changes in the electromagnetic signal measured by magnetotellurics (MT) and as such is an important property to consider when interpreting MT data. This study concentrates on replicating the MT response measured at two distinctively different geological settings using a series of 2 dimensional anisotropic forward models. Results presented in this study show that 2-dimensional anisotropic forward modelling is able to account for subtle differences in subsurface anisotropic resistivity structures. Specifically, 2-dimensional anisotropic forward modelling is able to reproduce the measured difference in MT response between pre- and post fluid injection conditions at the Paralana Geothermal System using an anisotropic fluid volume. A second application in constraining the source of the anomalous phase angles exceeding 90o observed in MT measurements of the Capricorn Orogen, shows that 2-dimensional anisotropic MT models are not able to produce phase angles exceeding 90o in the MT data which has its electric field orientated perpendicular to the geoelectric strike. These findings provide a case supporting the use of 2-dimensional anisotropic forward modelling as a means of modelling changes caused by the flow of a fluid through the crust. In addition, they also highlight issues associated with its application to complicated structures perpendicular to the strike of the profile.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2012

This thesis presents research on high-temperature metamorphic processes. A recent development in petrological modelling of granulite facies rocks is reintegration of melt generated and lost during metamorphism. The aim of melt reintegration is to create bulk compositions suitable for modelling prograde subsolidus evolution. Melt reintegration methodology was applied to a low-pressure granulite assemblage containing unambiguous textural evidence for subsolidus andalusite. Melt reintegration methodology resulted in a bulk composition that stabilised subsolidus and modally correct andalusite, providing validation of this petrological modelling technique. Melting and melt loss modifies rock chemistry and a long-standing paradigm is that melting depletes rocks in heat producing elements (HPEs). However, comprehensive K–U–Th datasets taken from a number of terranes show that in metapelites, melting and melt loss does not deplete U–Th concentrations, with overall terrane averages suggesting bulk heat production partitioning between melt and residuum is essentially 1:1. Modelling of HPE concentrations derived from terrane-scale elemental mapping in central Australia show that low-pressure (150–175 °C/kbar) granulite-facies metamorphism was driven by elevated crustal heat production. This energy source resulted in extremely long-lived (> 150 Ma) low-P–high-T metamorphism. High thermal gradient metamorphism driven by this energy source is characterised by contractional structures, kinematically late temperature maxima, and tight clockwise P–T loops. Petrochronology (the nexus between the isotopic age of a mineral and its compositional controls) is being increasingly used to interrogate the thermobarometric record contained in metamorphic rocks. Combined zircon and monazite REE-isotopic U–Pb compositions from interlayered metapelite and metabasic granulites show essentially identical peak metamorphic assemblages were achieved by substantially different P–T–t paths. The metabasic rock composition reached peak conditions at least 30 Ma before the metapelite. While speculative, the thermal delay recorded by the metapelite may reflect thermal buffering associated with partial melting and persistent structurally focussed melt streaming.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2019