School of Physical Sciences
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This collection contains Honours, Masters and Ph.D by coursework theses from University of Adelaide postgraduate students within the School of Physical Sciences. The material has been approved as making a significant contribution to knowledge.
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Item Open Access The geochronology and palaeoclimates of relict landscapes on Kangaroo Island.(2023) Wyche, W. J.; School of Physical SciencesKangaroo Island preserves multiple un-investigated relict landscapes that provide evidence for important changes to effective precipitation in southern Australia during the Late Pleistocene and Holocene (110ka-0ka). These relict landscapes offer a potential means for expanding the sparse Pleistocene southern Australian palaeoclimate record. Three sites that exemplify these long-term changes in hydroclimatology are a lunette at Birchmore Lagoon which formed by deflation of the exposed lake floor during periods of decreased effective precipitation, as well as a fluvial sequence at MacGillivray Sand Quarry and an alluvial floodplain sequence at Willson River, both of which formed during periods of increased effective precipitation and enhanced surface runoff. This thesis aims to provide a synthesised geochronology (single-grain OSL dating), geochemistry (XRF, XRD) and grain size study of these sites to improve understanding of the nature and timing of long-term effective moisture cycles in southern Australia. Six single-grain OSL samples taken at Birchmore Lagoon lunette, two at MacGillivray Sand Quarry and six at Willson River indicate a wide range of depositional ages ranging between 106-0.1 thousand years (ka). Birchmore Lagoon lunette consists of three distinct depositional periods between 106-22 ka, with deposition episodes centred on MIS (marine isotope stage) 5d, MIS 3 and MIS 2, all indicating lake floor exposure and deflation during glacial stages and cooler interglacial sub-stages. Fluvial deposits at MacGillivray Sand Quarry were formed 83-77 ka in MIS 5a, indicating increased effective precipitation and surface runoff around the peak of a warmer interglacial substage. Alluvial floodplain deposits at Willson River accumulated in MIS 1 between 3.2-0.1 ka, revealing periodic increases in effective precipitation during the late Holocene interglacial, potentially coinciding with intensification of ENSO cycle frequency. The results of this study potentially indicate decreased strength or frequency of frontal rainfall from the Southern Ocean during MIS 5d, MIS 3 and MIS 2 as reflected in drier periods at Birchmore Lagoon, as well as increased strength or frequency of frontal rainfall from the Southern Ocean in MIS 5a and MIS 1 as seen in wetter periods at MacGillivray Sand Quarry and Willson River.Item Open Access The fire below: heat generation in the lower crust(2023) Winckle, T. K.; School of Physical SciencesHeat production within Earth’s lithosphere comes from the decay of heat-producing elements: potassium, uranium and thorium. The distribution of these elements varies by an order of magnitude and with depth. With 30-40% of radioactive decay accounting for heat loss through the continents there are large uncertainties in extrapolated lithospheric temperatures. Consequently, it is critical to improve models of heat production with depth to adequately interpret and model Earth geological processes. In this study I improve estimates of heat-producing elements by focusing on multiple magmatic arcs in geographical regions including: Kohistan-Ladak Arc, Pakistan and India; Talkeetna Arc, Alaska; Sierra Nevada Batholith, California USA; Famatinian Arc, Chile and Argentina; and Fordland’s New Zealand. These arcs were chosen because of their differential exhumation, exposing a range of maximum pressures that extend from the surface into the lowermost crust when these magmatic arcs were active. Heat production within the crust must be estimated by proxy with previous studies commonly using seismic velocity to estimate heat production at depth. I establish a relationship from surface samples by using heat production coupled with maximum pressure estimates to make a quasi-vertical view of crustal heat production in outcrop. This showed that there is a relationship between heat production and SiO2 wt.%. Heat production also varies geographically. Total alkali content creates anomalously high heat production, like that in the Gangdese Arc which has a mean heat production of 𝑙𝑜𝑔!"𝐴 0.95 𝜇𝑊𝑚#$. Overall heat production increases with depth but it is very dependent of the composition of the lithologies within the crust.Item Open Access Copper isotopes tracing metal transport and concentration at the Whakaari embryonic porphyry copper deposit(2023) Tilby, J. T.; School of Physical SciencesThe genesis of porphyry copper deposits (PCD) is difficult to study due volcanic destruction and intense alteration. The stratovolcano Whakaari, in New Zealand, provides a modern analogue of an embryonic PCD, with early-stage transport and concentration mechanisms ongoing and recorded in the rock record. Copper isotope fractionation is heavily influenced by changeable REDOX conditions and fluid interactions, which are thought to be primary processes in PCD formation; copper isotopes present as a powerful tracer of formation mechanisms. A suite of lava samples and crater lake sediments are analysed for comparison between igneous processes and a primary hydrothermal endmember. This study uses whole rock major and trace element analysis, copper isotope analysis and petrography. δ65Cu values range between -0.11‰ and 0.59‰, with all but one sample being considered isotopically heavy. The range of values are not representative of a mantle source and indicate that there are processes affecting copper transport outside of magma ascent. δ65Cu values show insignificant correlation between rock evolution, and do not conform to Rayleigh fractionation modelling that would be indicative of transport via igneous processes. Values are consistent with those expected of sulphide minerals deposited from magmatic brines and are observed in several of the lava samples and sediments. Cu isotope analysis furthers our understanding of metal transport processes at Whakaari and can be applied to a broader understanding of porphyry copper genesis. Analysis of additional hydrothermal endmembers, combined with Sn, Fe and Zn isotopes to investigate REDOX conditions, will supplement the findings presented in this study.Item Open Access Middle Pleistocene palaeoenvironmental reconstruction using stable isotope analysis of macropod teeth and sediment geochemistry from Victoria Fossil Cave, Naracoorte(2023) Stokes, L. I.; School of Physical SciencesUnderstanding how species have responded to long-term climate cycles is important for understanding the impacts of modern, human-driven climate change. The Naracoorte Caves World Heritage Area preserves >500 ka of evidence of past climatic and environmental change in south-eastern South Australia, including sediments and vertebrate fossils. The Fossil Chamber within Victoria Fossil Cave is a highly significant pitfall deposit that spans multiple glacial and interglacial cycles between Marine Isotope Stages 12 to 9 in the Middle Pleistocene (~500 to 220 ka). This study examines local climate and environmental variables, including relative humidity, diet, and weathering, across five depositional units within the Fossil Chamber deposit (Units 8 to 4). Oxygen (δ18O) and carbon (δ13C) stable isotope signatures from grey kangaroo (Macropus giganteus and M. fuliginosus) (n = 24) and Red-Necked Wallaby (Notamacropus rufogriseus) (n = 31) tooth enamel are analysed. X-Ray Fluorescence and X-Ray Diffraction sediment geochemistry analyses are used to better understand depositional processes linked to climate, such as weathering and erosion. Our results indicate that application of these proxies is useful for elucidating habitat and environmental variables across the Middle Pleistocene, providing insight into past climate and environments and their influences on faunal community turnover.Item Open Access A geochronologic, thermobarometric and stable isotopic study into the Kanmantoo Cu-Au Deposit, South Australia(2023) Schmaal, T. H.; School of Physical SciencesThe paragenesis of the Kanmantoo Cu-Au Deposit, South Australia, has been a topic of debate in the literature since research on the site was first published. Due to the deposit’s complicated geological history of metamorphism and deformation, determining the source of ore-forming fluid has been difficult. Two major models have been hypothesised; a post-peak metamorphic model suggesting granitic fluid to be the source of mineralising fluids; and a syn-sedimentary model, hypothesising that the mineralisation occurred in a Sed-ex style while the Kanmantoo Group was still being deposited. This study employs a range of techniques such as, stable oxygen and hydrogen isotopes; Cu, Zn, and Pb trace elements within silicate gangue minerals; xenotime, zircon and monazite geochronology; and mineral equilibria forward modelling in an attempt to constrain the conditions of the ore-forming fluid. From these data, the age of mineralisation has been constrained to 489Ma through the use of xenotime geochronology. Mineral equilibria forward modelling has indicated peak-mineralisation conditions of ~3.5 GPa and 570 °C.Item Open Access Millennial scale hydroclimate variability in New Zealand during the Last Glacial Period: oxygen isotope evidence from Lake Pupuke, Auckland(2023) Orchard, A. C.; School of Physical SciencesThe Southern Westerly Winds exert a dominant control on modern precipitation patterns in New Zealand. However, their location has not been constant throughout the geological past, appearing to migrate in relation to temperatures at the poles. Understanding past patterns of migration is, therefore, key to characterising potential shifts associated with anthropogenic warming. There is a lack of palaeoclimate records in the landmass poor Pacific region able to resolve such migrations. This thesis presents a lacustrine sedimentary record of palaeohydroclimate variability inferred from Lake Pupuke, Auckland, New Zealand, from 47 to 35 ka. These sediments also host direct evidence for the Laschamps Excursion at ~41.5 ka, a significant weakening of the Earth’s magnetic field. The Laschamps Excursion has been proposed to have had a profound impact on Earth’s climate and ecosystems, however no evidence for such an effect was found in the Lake Pupuke sediments. In terms of the hydroclimate, variations in δ18O inferred from biogenic silica suggest a teleconnection between Southern Westerly Wind driven precipitation and Antarctic temperatures such that cold periods caused a northward shift in the westerlies, thereby increasing precipitation over Auckland and vice versa. Cold and wet periods occur between 45-44 ka and 43.5-42 ka while warm and dry periods occur between 44-43.5 and 40-38 ka. These results indicate the sensitivity of the Southern Westerly Winds and, by extension, precipitation in New Zealand to global temperature shifts.Item Open Access High-grade metamorphism in Turkana, Kenya: implications for the evolution of the East African Orogen(2023) McIntyre, A.; School of Physical SciencesThe Lokhone Block metasedimentary belt in Turkana, NE Kenya, lies within an understudied region of the Mozambique Belt on the margin of the Congo-Tanzania craton. Phase equilibria modelling indicates that this high-grade belt comprising intercalated pelitic metasediments and calc-silicate rocks underwent peak granulite-facies metamorphism at pressures of 8.4– 10.6 kbar and temperatures of 750–830°C. Peak metamorphic conditions have been directly dated by Lu – Hf isotopic analysis of garnet (625 ± 7 Ma and 621 ± 5 Ma), and by U – Pb isotopic analysis of metamorphic titanite (604 ± 8 Ma and 622 ± 16 Ma) and metamorphic zircon rims (612 ± 14 Ma). This is coeval with high-grade metamorphism recorded throughout the Mozambique Belt associated with the formation of the East African Orogen during the Neoproterozoic amalgamation of Gondwana. P-T conditions indicate a moderate geothermal gradient of 78 – 98°C/kbar (17-30°C/km), consistent with metamorphism during crustal thickening. U – Pb apatite geochronology yields ages between ca. 540 and ca. 560 Ma, interpreted as post-peak cooling after metamorphism. These data suggest slow cooling of 2.5 - 9.5°C/Myr, consistent with slow exhumation over several tens of million years. U – Pb dating of detrital zircons suggest that at the time of formation, the Lokhone region was not connected to any pre-Neoproterozoic terrane. These findings highlight the complexity of the processes shaping the East African Orogen and provide important constraints with which to improve plate tectonic reconstructions for the Neoproterozoic Earth.Item Open Access The thermal evolution of the east-Gondwanan subduction zone: evidence of long-lived subduction preserved at Port Macquarie, NSW(2023) Lee B. R.; School of Physical SciencesThe thermal evolution of subduction zones is not well understood. Numerical models show that subduction zones thermally evolve from hot temperatures at initiation and then cool over time until they reach a steady state (maturity). These models typically show this occurring over periods of 20–40 Myr. However, these models need to be tested using natural examples. There are relatively few examples of naturally occurring long-lived subduction systems preserving accumulated subduction products over those time ranges but the Port Macquarie Serpentinite Mélange in the southern New England Orogen is one example. The mélange contains a comprehensive and diverse suite of exhumed high-pressure (high–P), low-temperature (low–T) metamorphic rocks, including eclogite, blueschist and meta-conglomerate. U–Pb titanite, garnet Lu–Hf and Rb–Sr phengite geochronology document ~100 Myr of thermal evolution in the east-Gondwanan subduction zone. Mineral equilibria modelling of ca. 490 Ma lawsonite eclogite and ca. 400 Ma meta-conglomerate suggests thermal gradients were 219°C/GPa and 200°C/GPa respectively, revealing that over this extended duration the geothermal gradient was between 6–7°C/km and did not significantly change. The high–P rocks from this long-lived palaeo-subduction system reveal that the east-Gondwanan subduction zone had reached a steady state by ca. 490 Ma, and models suggest that subduction of the palaeo-Pacific oceanic lithosphere beneath the east-Gondwanan margin initiated earlier than the Cambrian.Item Open Access Metal isotope insights into volatilisation during meteorite impact: A Cu isotope study of tektites(2023) Jolly, J. C.; School of Physical SciencesThe enigmatic behaviour of high-temperature element mobility within the solar system and on Earth remains a perplexing scientific phenomenon. This process can be explored through the study of materials formed under analogous conditions, such as high-temperature meteorite ejecta. Tektites thereby provide insight into these processes of metal transport and vaporisation of volatile elements under high temperature conditions. This study uses microscopy, bulk rock compositions, in-situ micro-chemistry, and Cu isotopes for a plethora of tektite shapes and locales to identify, quantify, and chemically assess the distribution of elements within tektites. Furthermore, this study attempts to investigate the chemical heterogeneity of flow banding and shaping for the first time. Examination of tektites through microscopy revealed flow banding of roughly 30 μm thicknesses but vary significantly within each sample. In-situ analysis of these bands indicates favoured extraction and diffusion of moderately volatile elements, such as Cu, Zn, and K, across individual samples on a micron scale. Cu isotope data supports the high temperature fractionation of elements during tektite formation with δ65Cu values (‰) generally increasing with decreasing Cu concentration (ppm). δ65Cu varies across a range of highly fractionated values of 1 to 7‰ and follows Rayleigh fractionation models. This geochemical, and extensive micro chemical analysis presents the first investigation into the composition of flow banding of tektites and heterogeneity between tektite shapes. Furthermore, this study demonstrates that Cu, Zn, and K vary across bands, suggesting intrasample diffusion of elements prior to quenching. Analysis of additional tektites shapes and corresponding in-situ flow banding heterogeneity should be prioritised, accompanied by further investigation into other isotopic systems within tektites.Item Open Access Establishing an interconnected mineralisation history of the Mount Isa Province and the Peake and Denison Domain, northeastern Gawler Craton(2023) Gully, D.; School of Physical SciencesThe Mesoproterozoic period saw extensive IOCG mineralisation of the Mount Isa Province at c. 1550-1490 Ma. Tectonic reconstructions of Paleoproterozoic and early Mesoproterozoic Australia situate the Peake and Denison Domain of the northeastern Gawler Craton at the boundary of the NAC and SAC during this time. Recent geochronology of zircon and titanite suggests an interconnected hydrothermal history between the Peake and Denison Domain and Mount Isa Province during the early Mesoproterozoic. This project presents new U-Pb LA-ICP-MS geochronology of zircon and titanite, and multi-method (U-Pb, Lu-Hf) LA-ICP-MS geochronology of apatite from IOCG-style mineralised core of the Peake and Denison Domain. Zircon analysis interprets a c.1775 Ma upper intercept age for the metasedimentary protolith. Titanite analysis constrains the timing of mineralisation to 1500 Ma. Apatite U-Pb analysis presents mineralisation ages of c.1490-1470 Ma, while Lu-Hf analysis constrains the timing of mineralisation to c.1530-1490 Ma. These results suggests that the c.1550-1490 Ma mineralising systems of the Mount Isa Province also governed the Peake and Denison Domain and subsequent northeastern Gawler Craton, separate from the c.1600-1570 Ma mineralising system of the central Gawler Craton. These interpretations align with the Mesoproterozoic amalgamation of the NAC and SAC. Establishing an interconnected mineralisation history of the Peake and Denison Domain and Mount Isa Province implies that the northeastern portion of the Gawler Craton is likely prospective for Isan-style mineralisation, thereby creating incentive for future mineral exploration.Item Open Access Palaeoenvironmental context for the restoration of traditional land management in McLaren Vale, South Australia(2023) Griffiths, N.; School of Physical SciencesWetlands are significant environments for floral and faunal biodiversity, and key to counteracting human impact. Unfortunately, wetlands are also sensitive to climatic and anthropogenic changes and are at risk of being lost. Conservation and rejuvenation are critical to the survival of wetland environments within agricultural areas. This study explores sediments to reconstruct palaeoenvironmental wetlands at Lot 50 – Kanyanyapilla, a restoration project in the viticultural region of McLaren Vale, South Australia. Sediment from the site is found to contain an assortment of proxies that are used to determine depositional environments including elemental concentrations, mineralogical composition, and organic content. Environment transitions are then associated with climatic or anthropogenic events using geochronology to determine potential triggers. Finally, results from the study are used to suggest potential restoration and conservation options for wetlands in McLaren Vale.Item Open Access Deciphering the origin of high carbon shales: the Amungee organofacies conundrum, Velkerri Formation, Greater McArthur Basin(2023) Edwards, L. E.; School of Physical SciencesThe Mesoproterozoic (1.4 Ga) Velkerri Formation of the McArthur Basin contains a number of intervals rich in organic matter (with TOC values locally >10wt%). These have been used as supporting evidence for a transient middle Mesoproterozoic global oxygenation event. New geochemical data collected from Urapunga-4 were compiled with previously published data to; a) illuminate the origin of these organofacies and to particularly understand why the shale preserved such large fluctuations in TOC over short stratigraphic distances, and to b) address the competing hypotheses. The relationship between TOC and δ13C(org) shows that the TOC peaks in all three high organic shales (A, B, and C shales) in the Amungee Member are interpreted to be caused by primary production. However, the A shale was also interpreted to possibly be due to sediment input outpacing the increased carbon production. The B shale was interpreted to be a result of a small organic bloom that was immediately followed by an increased sediment supply that was likely from a storm event. In addition, organic geochemical data and detrital U-Pb zircon and novel laser Rb-Sr dating from newly accessible core samples in the Beetaloo Sub-basin, combined with detailed sedimentology, were used, along with previously published data from Urapunga-4, to verify whether this new core (ELT002) intersects the Velkerri Formation. The depositional age of the new core and the difference in sedimentology and geochemistry between Urapunga-4 well indicate that this new core likely intersects the Kyalla Formation rather than the Velkerri Formation.Item Open Access Anthropogenic mineral systems: material flow, geochemistry, and mineralogy of the Prominent Hill tailings deposit(2023) Cooke, H. M.; School of Physical SciencesHumans shift the same magnitude of rock around the planet as does nature via geological processes. This, in no uncertain terms, is because we mine. Our exponential extraction of metals to grow modern society is most voluminously archived in mine waste deposits like waste rock dumps and tailings, to which we add 100 billion tonnes of material yearly. As dominant agents of the geosphere we must challenge ourselves on this enormous disposal of mineralogical natural capital. The Prominent Hill tailings storage facility (TSF) is an anthropogenic-geologic waste deposit created at the final stage of material flow of Prominent Hill’s mining processes. Tailings sediment provenance and geochronology, and the TSFs stratigraphy, critical mineral resource potential (e.g., copper (Cu) and rare earth elements (REEs)), can be quantified by engaging with material flow processes. This undertaking ultimately maps an anthropogenic mineral systems approach to characterising TSF resources. Microanalytical characterisation of Cu and REEs in sampled Prominent Hill tailings reveals mineralogical fingerprints that become the geometallurgical basis for mineral reprocessing pathways. The TSF contains 112 million tonnes of tailings which average 0.14% Cu and 0.3% REE. Cu(-Fe) particles are highly enriched in Mo, Ag and Au, and are extensively oxidised to Cu-sulphate, and Fe(-Cu, -S, -Cl) mineral assemblages. Meanwhile, the TSFs REE inventory is dispersed between several types of fluorcarbonates and phosphates with unique light REE (LREE) and heavy REE (HREE) signatures. Monazite contains the highest LREE contents, though magnet REEs (e.g. Pr, Nd, Dy) are concentrated in fluorcarbonates. Apatite is potentially a significant reserve of HREEs. By blueprinting the unique anthropogenic mineral systems of our TSFs, this thesis helps future explorations of tailings deposits as responsible sources of critical raw materials and frames an opportunity to redesign our billion-tonne footprints in the Anthropocene rock record.Item Open Access Mineral textures in the Auckland Volcanic Field: Insights into ascent processes.(2023) Coker, J. L.; School of Physical SciencesThe Auckland Volcanic Field, a prominent monogenetic basaltic field, is characterized by rapid magma ascent from source to surface, yielding a landscape of diverse volcanic morphologies. Despite being extensively studied, the fundamental processes governing this field remain largely enigmatic. This study aims to shed light on these mysteries by scrutinizing mineralogical textures and chemistry at a scale representative of the entire volcanic field. To achieve this, we employed advanced techniques, including Scanning Electron Microscope (SEM) image analysis, Electron Microprobe chemical analysis, equilibrium testing, and thermobarometry. Through these methods, we scrutinized various minerals and identified compelling evidence suggesting fluctuations in magma ascent rates. Notably, we observed variable normal zoning rates in olivine, oscillatory zoning in clinopyroxenes, and the presence of lamellae exsolution, surrounded by unexsolved crystallization of Fe-Ti oxides. These mineralogical features offer crucial insights into the dynamic processes taking place during the ascent of magma beneath the Auckland Volcanic Field. The implications of these findings extend beyond geological curiosity. Understanding the changes in magma ascent rates carries significant implications for the forecasting and early detection of moving magma beneath Auckland. If magmas can be identified during slower ascent stages, this knowledge could serve as an essential precursor to the potentially hazardous rapid ascent phase. This insight is not only valuable for understanding the volcanic field's monogenetic nature but also for enhancing the safety and preparedness of the Auckland region in the face of volcanic activity. In conclusion, our research unveils critical mineralogical evidence of variable ascent rates within the Auckland Volcanic Field, enriching our understanding of this complex geological system. Furthermore, the potential implications for volcanic hazard mitigation underscore the practical significance of this study, as it has the potential to improve volcanic forecasting systems and protect the well-being of the Auckland community.Item Open Access Inferring regolith history via in situ Rb-Sr dating, mineral mapping, and elemental analysis at the Avon River Critical Zone Observatory, Western Australia(2022) Schultz, M.; School of Physical SciencesThe critical zone is the interface between atmo-, bio-, hydro-, and lithospheres which supports all terrestrial life. Within this complex system, regolith forms as weathered bedrock products coalesce on the surface, providing anchorage and accessibility to essential nutrients and water for plants and associated microbiota. Productivity within the regolith therefore has significant implications for all heterotrophic lifeforms. Global establishment of Critical Zone Observatories concentrate efforts on understanding this system and the long-term response to anthropogenic influences. This study contributes to this cause, defining baseline geochemical and mineralogical compositions at bulk- and micro-scales for regolith within the Avon River Critical Zone Observatory. This study also addresses novel in situ Rb-Sr dating as a method to separate abiotic and biotic pedogenic mechanisms. Sodium peroxide fusion and ICP-OES is compared against acid digestion and ICP-MS methods to determine a viable immobile index element. Subsequent ‘normalised’ elemental concentration profiles are produced which account for volume changes and relative loss or gain of elements through vertical section. Elemental profiles reflect gradual, or near complete depletions of all elements, excluding Al, Si and Fe-Al metal-oxide species, that relate to a matured rudimentary mineral assemblage of kaolinite, quartz, and Fe-Al-oxide species. Subsequent Rb-Sr dating of clays (i.e., chlorite, illite), micas and feldspars indicate that biotite within the monzogranitic bedrock is of Neoarchean age (2673.4 ± 56.1 Ma (n = 21)) whilst bordering chlorite and feldspars reflect a younger ‘apparent’ age of 2400.5 ± 60.2 Ma (n = 60). Interestingly, Rb-Sr dating of illite also reflect this younger ‘apparent’ age within error across all lower regolith horizons, suggesting inheritance of (87Sr/86Sr)o ratios during authigenic weathering of feldspar and clay precursors. This concludes that pedogenesis in the lower regolith horizons was of abiogenic origin but absence of illite in the upper horizons does not entirely discount biotic involvement.Item Open Access Unconformity-style rare earth element mineralisation along the Watts Rise-Castella Trend, Tanami Region, Western Australia.(2022) Rowland, J. R.; School of Physical SciencesUnprecedented demand for rare earth elements (REEs), driven by the development of new ‘green energy’ technologies, is driving significant exploration activity globally. Traditionally, REE production has been controlled by unique igneous rocks (e.g., peralkaline volcanics and plutonics) considered relatively minor in the geological record; however, to address demand, new mineralisation styles are being explored. Newly recognised unconformity-style hydrothermal REE (+ Au) mineralisation along the Watts Rise-Castella Trend by PVW Resources Ltd in the Tanami Region of north-western Australia comprises HREE-dominant mineralisation along a regional unconformity, hosted within hematised conglomeratic units of the Paleoproterozoic Pargee Sandstone. Detailed ore mineralogy, petrography, and mineral chemistry (via LA-ICP-MS) of samples from two currently-identified prospects within the exploration area provide insights into REE distribution. Geochronological ages via LA-ICP-MS U-Pb dating for both xenotime and zircon in the Pargee Sandstone constrain both the timing of ore mineralisation and the maximum depositional age of the host rock. Two main REE-bearing minerals are identified: xenotime [(Y,HREE)PO4] and florencite (LREEAl3(PO4)2(OH)6). Xenotime is the major host of HREEs, and occurs in different textural phases. In-situ U-Pb dating of xenotime yielded an age range of mineralisation between ca. 1.65 to 1.60 Ga; this timeframe is absent in local magmatic or orogenic events and is comparable to the timing of other REE occurrences in the region, suggesting a regional scale hydrothermal event in northern Australia. Detrital zircon U-Pb geochronology for the Pargee Sandstone produced a wide range of ages primarily between ca. 2.6 to 1.8 Ga, and a maximum depositional age between 1811 ± 5 Ma and 1832 ± 8 Ma. There is significant potential for discovery of further orebodies of this style, especially in the vicinity of regional unconformities, and given the current surge in exploration for REEs, this investigation will assist in the development of exploration models for equivalent terranes.Item Open Access The geochronology, palaeoenvironments and palaeontology of Robertson Cave inner chamber, Naracoorte.(2022) Robertson, B.; School of Physical SciencesRobertson Cave inner chamber within the Naracoorte Cave Complex (NCC) preserves a 4m sedimentary infill record that is relatively unexplored in terms of geochronology and paleoenvironmental history. The inner chamber of this cave also preserves undated megafauna remains and fossil evidence for long-term overwintering activities of the Southern Bent-Wing bat, a critically endangered species with only two known maternity caves in Australia. This thesis aims to provide a detailed geochronology (single-grain OSL dating) and geochemistry (XRF, XRD) study of the inner chamber to better contextualise the palaeontological, palaeoenvironmental and palaeoconservation significance of the Robertson Cave sedimentary sequence. The suitability of OSL dating in this deep cave setting is demonstrated by examining a modern surface sample and two samples from complex sediment horizons affected by syn-depositional mixing (i.e. entrainment and re-transportation of pre-existing sediments within the closed cave environment). These suitability tests confirm that the OSL signal is fully reset prior to entering the cave, providing a modern age of 0ka, and that it is advisable to employ statistical models (minimum age models) that target the most recently reset grain populations when dating deep cave sediments affected by syn-depositional mixing. Twelve single-grain OSL samples from the Inner Chamber excavation provide stratigraphically consistent ages spanning 74.6-10ka, demonstrating that the infill sequence covers a much longer time period than indicated by radiocarbon dating. The entire sequence was deposited between MIS (marine isotope stage) 4 or late MIS5 to early MIS1, with high sedimentation rates evident in late MIS3 (40.5-32.3ka), the MIS2 glacial (26.5-11.8ka) and early MIS1 (11.5-9.8ka), and disconformities coinciding with major climatic transitions at the MIS4/3, MIS3/2 and MIS2-1 boundaries. Two OSL ages from the lowermost unit constrain the timing of in situ megafauna fossils to 74.6-60.1ka, meaning Robertson Cave inner chamber is one of only three well-dated NCC caves preserving late MIS5 to MIS4 megafauna remains. XRF and XRD analyses indicate the presence of multiple guano-rich layers with elevated sulphate, phosphate, organics, and trace metal concentrations. These results imply complex diagenetic processes and reinforce the fossil bat record by confirming an intermittent geochemical signature of bat overwintering activities at Robertson Cave extending back to the last interglacial complex. The findings of this study have broader implications for understanding how sediment accumulation dynamics of NCC roof window cavities can be closely tied to changing climate conditions associated with glacial-interglacial cycles. The results also reinforce the palaeontological and palaeoconservation significance of Robertson Cave, particularly the long-term resilience of its critically endangered Southern Bent-Wing bat populations and their ability to adapt to widely varying climate regimes prior to European colonisation.Item Open Access Kangaroo Island climate variation over the past 7000 years reconstructed using lake sediment(2022) Kamleh, C.; School of Physical SciencesIn the face of devasting bushfires, droughts and floods in recent years in Australia, geologically recent Australian climate reconstructions provide useful context in understanding the long-term patterns of such events before instrumental records existed. There is a lack of such climate reconstructions in southern Australia. Kangaroo Island’s (KI) recent devastation by bushfires, as well as the presence of semi-permanent lakes on the island, make it a location suited for climate reconstructions using lake sediment to complement the understanding of bushfire occurrence. Existing research has focussed on Lashmars Lagoon in the east of KI, and this thesis adds to Lashmars Lagoon research, while also adding research from Little Grassdale Lagoon in the west of KI. Multiple techniques are used: 210Pb dating, radiocarbon dating, age-depth modelling, X-ray fluorescence (XRF), and mass-spectrometry. It is found that over the past 7000 years, Kangaroo Island entered a drier period after ~3000 years BP. This dry period coincides with the onset of more intense bushfires on Kangaroo Island, as recognised by existing research, suggesting a climatic control on bushfire patterns. The last 2000 years on Kangaroo Island are characterised by more variable climatic conditions, and there are fluctuations between wet and dry climates, within the larger context of a dry period.Item Open Access What is Nundorite? A petrological and geochemical study of an unusual rock of the Mount Arrowsmith Volcanics(2022) Johns-Mead, L. Y.; School of Physical SciencesNundorite is an enigmatic rock, known only from its type locality within the Mount Arrowsmith Volcanics (MAV), Western NSW. Alkaline igneous systems such as the MAV are an important source of critical mineral resources. Nundorite is compositionally unique, being peralkaline and enriched in rare metals (Zr, Nb and REEs), but with low silica and high alumina. Despite these features, there has been limited research on nundorite. This thesis represents the most extensive study of nundorite to date. A combination of field observations, petrography, bulk-rock and mineral geochemistry are used to describe samples and develop an understanding of nundorite’s genesis and evolution. Although nundorite only occurs as a single low outcrop, there is a progression of alteration and deformation over a span of ~250 m across the outcrop. Bulk geochemical composition does not change across this traverse, so this variation is attributed to localised shearing and associated metamorphism. Nundorite’s mineral assemblage is established as aegirine porphyroblasts in a predominantly sodic zeolite-orthoclase matrix with minor albite and nepheline. The primary zeolite changes from natrolite to analcime with proximity to a shear zone. Nundorite hosts a suite of unusual accessory minerals, including zircon, monazite, schizolite, cerite group minerals, fergusonite, fersmite, galgenbergite, epidote-allanite, as well as unidentified Zr and REE minerals. Similar complex arrays of accessory minerals have been described from other peralkaline volcanic systems that host critical minerals. Modelling nundorite to felsic alkaline igneous rocks shows that its unique geochemical composition could be achieved through metasomatism of a highly fractionated member of the MAV. Fractionation caused initial enrichment in alkalis and REEs, this was then concentrated by the removal of silica by an alkaline fluid. There are several avenues for further research on nundorite, including comprehensive mineral identification, further constraining alteration conditions, and evaluating the economic potential of the rock.Item Open Access Architecture and thermochronology of the base Adelaidean unconformity at Arkaroola.(2022) Imbrogno, D. N.; School of Physical SciencesThe Arkaroola unconformity represents a gap of almost 750 Ma, yet as well as being demonstrably erosive, the basement Mount Neill Granite is strongly foliated in a style similar to that reported from extensional core complexes. The architecture and strain along this lithological boundary varies in geometry and intensity, with past research providing limited constraints on the structural relationship between the basement and overlying basin rocks. This thesis maps this strain seen in the basement, investigates the relative timing of the shear strain with respect to macroscopic fold development, examines microstructural record, and dates cooling after strain. Samples were collected over a sequence of the unconformity with an increase of shear strain in the basement approaching this boundary, and into the overlying Paralana Quartzite. Normal shearing kinematic indicators at multiple boundary locations suggest basement foliation pre-dates large scale folding during the Delamerian Orogeny. Orientation of c-axes in quartz grains in the protomylonitic basement proximal to the boundary show evidence for non-coaxial strain, with the quartzite directly above producing a girdle representing pure shear, plane strain deformation. This thesis examines previous thoughts on coeval intrusion and deformation of the Mount Neill Granite, with new evidence for basement foliation developing shortly before deposition and rifting sequences of the Adelaidean Superbasin. Presence of prism [c] slip and dynamic recrystallisation in quartz grains indicates temperatures reached at least 500 °C. In-situ Rb–Sr muscovite ages from this study correlate to cooling after the Delamerian Orogeny, the intrusion of the British Empire Granite, hydrothermal deformation, and localised pegmatite intrusions. This study presents a tectonostratigraphic timeline for the evolution of the boundary, with evidence for a mid-crustal extensional shear zone in early formation of the Adelaide Rift Complex. Future work on additional boundary locations is needed to better understand regional architecture resulting from early basin formation.