b'Education matters hidden processes can be revealed. ThisMonte Carlo is proposed. Based upon theEmily Lewis, University of Adelaide. process of taking observable data andwork of El Moselhy and Marzouk (2012),Bottom-up exploration: Imaging resistivity inferring the underlying mechanisms issolving the Bayesian inference problemof a mineral system from source to sink.formally known as solving the inversecan be expressed as nding a map problem, and this reverse way ofthat transports the prior distribution thinking is foundational for much of ourto the posterior. While this concept understanding of the internal structureis not new, a novel implementation and dynamics of the planet. is developed. The mapping method-ology is then found to be well suited Whilst processes that behave in a linearfor prior sampling tasks, where a full fashion can generally be well understoodunderstanding of the inverse problem within an inversion framework, moreis developed before observations are complex non-linear problems are notmade. A simple test problem is explored, so straightforward. Developing newand promising initial results found.techniques to address the issues arising from non-linear processes is thereforeThrough the various concepts discussed a topic of considerable interest withhere, and in the wider literature, OT is Ore deposits are broadly defined as far-reaching consequences acrossfound to have a multitude of uses forgeochemical anomalies that have been seismology, geodynamics, geodesy,solving non-linear inverse problems,concentrated from significantly larger geomagnetism, and many more. Recentmany of which are yet to be exploredvolume sources at depth. This requires a attention has developed around the usedeeply in a geophysical context. mineral system process through which of optimal transport (OT) in solving suchelements in the lower crust or mantle are inverse problems (Engquist and Froese,Sinan zaydn, Affiliation: Macquarieentrained and moved to the surface. In 2014) (El Moselhy and Marzouk, 2012).University: Three-dimensionalvarious locations around the world, the OT gives a new perspective on bothmagnetotelluric constraints onsource region of a mineral system has optimisation-based and probabilisticcompositional variations of the Southernbeen shown to have a distinct electrical inversion techniques. African mantle. resistivity signature as a result of past In this study, we rst consider themagmatic fluid processes which have OT-derived Wasserstein distance asleft a geochemical overprint. This project a measure of mist, seeking to avoidfocuses on the Curnamona Province, a the suboptimal convergence that isPaleo-Mesoproterozoic craton which frequently encountered in non-linearextends across South Australia and inversion. The procedure is derived in aNew South Wales with approximate general setting, feasibly allowing a varietydimensions of 300 km east-west and of inverse problems to be considered.300 km north-south. A previous broadband We reframe the minimisation of themagnetotelluric (MT) (102 to 0.01 Hz) Wasserstein distance as a least-squarestraverse of 60 stations spaced 2 km across problem and solve it using the Gauss- the Curnamona Province identified a 2D Newton optimisation method. To the bestgeophysical signature with a footprint of our knowledge, this is the rst time thesimilar to that below the IOCG Olympic problem has been cast in this manner andDam deposit in the Gawler Craton. In this may allow numerous other techniquesproject, broadband MT measurements from classical least-squares to be applied.(104 to 0.01 Hz) were collected along four An application of tting Raman spectraparallel lines of 1 km spaced sites, and with for volcanic glasses with mixture modelsline separation of 5 km to develop the 3D is considered as a test case. This simplecontext. We image a discrete low-resistivity example provides a vital building blockIn the absence of significant thermalzone on three of the lines, which extends for more complex mixture modellinganomalies, the electrical conductivityfrom the surface down to 20 km depth, tasks in the future. A more intricatedistribution in the cratonic mantle is stillwhere it is linked to a conductor of 1m. It waveform tting task is then explored.highly variable, which indicates the highlyappears to be bound between two resistive Two key innovations are made here: adiffering chemical and physical propertiesblocks and is not laterally continuous. The new method for converting arbitraryof the mantle. It is not well understoodoutcomes of this model are comparable signals into a form compatible with OTwhich forms and styles of chemicalto pathways across the Gawler Craton. We is developed, and the sliced Wassersteindifferences (metasomatism) are relatedshow a very strong relationship between distance introduced as a mist measureto observed electrical conductivitydeep crustal conductors and narrow for inversion, seemingly for the rst time.distributions in magnetotelluric models.pathways, inferring a signature which is We see that these two concepts can workThe primary aim of this thesis is to unravelresponding to past magmatic events.in tandem to avoid cycle-skipping whensuch relationships between electricalFletcher Howell, Australian National considering simple waveform functions. conductivity distribution and mantleUniversity: Constraining the nature of composition in Southern Africa, whichdynamic topography to guide inverse We then consider the alternativeis chosen as the study field because notgeodynamical models.Bayesian approach for non-linearonly it has excellent magnetotelluric data, inversion. A transport-based samplingbut also it is rich in kimberlite-hostedOceanic lithosphere is formed at a mid-method to compete with Markov chainxenoliths and xenocrysts. ocean ridge and subsides as it spreads 43 PREVIEW DECEMBER 2021'