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    The Variation of atmospheric carbon dioxide,methane and nitrous oxide during the holocene from ice core analysis
    MacFarling Meure, Cecelia. (University of Melbourne, 2004)
    Recent studies have demonstrated that the atmospheric concentrations of radiatively important greenhouse gases, including methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O) and carbon monoxide (CO), have significantly increased during the past 200 years due to anthropogenic emissions. Analysis of air trapped in polar ice cores allows for past atmospheric variations due to natural climate conditions to be investigated, placing recent changes in a historical context. In this thesis new high- precision, multispecies measurements of atmospheric trace gas concentrations during the Holocene have been produced by analysing the air trapped in the ice at Law Dome, East Antarctica (66�46'08"E, 112�48�28�S). The ice core records are well-dated, have high age resolution and overlap with modem instrumental records due to the high accumulation rate at the drilling sites. The combination of high age resolution, precise dating and high precision measurements allows for subtle, decadal-scale variability to be detected. The multispecies measurement technique allows for biogeochemical causes of variations to be identified. The first part of this study focused on the late Holocene period (AD 0 to 1975). New high-precision records of CH4, CO2, N2O and CO have been produced for this period. The CH4 and CO2 measurements are used to build upon the existing Law Dome records of these gases during the last 1000 years, to validate and further define previously observed variations. The new measurements extend the records of these gases by another 1000 years. As a consequence of the multispecies measurement technique it has been possible to also measure N2O and CO during this period. These new measurements highlight the atmospheric response to the Little Ice Age (LIA) cooling (AD 1550 to 1800), particularly a 10 ppm decrease in atmospheric C02 between AD 1550 and 1600. A stabilization of CO2 during the 1940s was also confirmed in the Law Dome record. Increased data density during this period shows that the atmospheric CO2 mixing ratio stabilized at ~310 ppm between 1937 and 1955. New signals were observed in the extended records, including a 100 ppb increase in the CH4 concentration between AD 0 and 1800, which is probably the result of increasing pre-industrial anthropogenic emissions. The second part of this study focussed on the CO2 and CH4 response to a rapid, abrupt cooling at 8,200 years BP. The Law Dome (DSS) measurements are complemented by four measurements of NorthGRIP (Greenland) ice core. A decrease of at least 52 ppb CH4 is observed in the DSS record, and a decrease of at least 62 ppb is observed at NorthGRIP during the same period. A smaller CO2 response of 4 to 5 ppm is seen in both the records. The CH4 signal is used to improve the chronologies of these ice cores by synchronising with other well-dated CH4 records, specifically GRIP (Greenland) and Dome C (Antarctica).
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    The Variation of atmospheric carbon dioxide,methane and nitrous oxide during the holocene from ice core analysis
    MacFarling Meure, Cecelia. (University of Melbourne, 2004)
    Recent studies have demonstrated that the atmospheric concentrations of radiatively important greenhouse gases, including methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O) and carbon monoxide (CO), have significantly increased during the past 200 years due to anthropogenic emissions. Analysis of air trapped in polar ice cores allows for past atmospheric variations due to natural climate conditions to be investigated, placing recent changes in a historical context. In this thesis new high- precision, multispecies measurements of atmospheric trace gas concentrations during the Holocene have been produced by analysing the air trapped in the ice at Law Dome, East Antarctica (66�46'08"E, 112�48�28�S). The ice core records are well-dated, have high age resolution and overlap with modem instrumental records due to the high accumulation rate at the drilling sites. The combination of high age resolution, precise dating and high precision measurements allows for subtle, decadal-scale variability to be detected. The multispecies measurement technique allows for biogeochemical causes of variations to be identified. The first part of this study focused on the late Holocene period (AD 0 to 1975). New high-precision records of CH4, CO2, N2O and CO have been produced for this period. The CH4 and CO2 measurements are used to build upon the existing Law Dome records of these gases during the last 1000 years, to validate and further define previously observed variations. The new measurements extend the records of these gases by another 1000 years. As a consequence of the multispecies measurement technique it has been possible to also measure N2O and CO during this period. These new measurements highlight the atmospheric response to the Little Ice Age (LIA) cooling (AD 1550 to 1800), particularly a 10 ppm decrease in atmospheric C02 between AD 1550 and 1600. A stabilization of CO2 during the 1940s was also confirmed in the Law Dome record. Increased data density during this period shows that the atmospheric CO2 mixing ratio stabilized at ~310 ppm between 1937 and 1955. New signals were observed in the extended records, including a 100 ppb increase in the CH4 concentration between AD 0 and 1800, which is probably the result of increasing pre-industrial anthropogenic emissions. The second part of this study focussed on the CO2 and CH4 response to a rapid, abrupt cooling at 8,200 years BP. The Law Dome (DSS) measurements are complemented by four measurements of NorthGRIP (Greenland) ice core. A decrease of at least 52 ppb CH4 is observed in the DSS record, and a decrease of at least 62 ppb is observed at NorthGRIP during the same period. A smaller CO2 response of 4 to 5 ppm is seen in both the records. The CH4 signal is used to improve the chronologies of these ice cores by synchronising with other well-dated CH4 records, specifically GRIP (Greenland) and Dome C (Antarctica).
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    The geology, petrology and geochemistry of the granitic rocks of Victoria
    Rossiter, Allan G. (University of Melbourne, 1973)
    In the field the granitic rocks of Victoria show a wide variety of characteristics but chemically all are related and are the result of similar processes that occurred cyclically during the Palaeozoic. The granites may be divided into two groups on the basis of whether or not primary hornblende is present in the more basic members of the suite. Rocks of the hornblende-free series concentrate mainly in central Victoria and usually contain biotite that is red-brown in colour. In the granites of the hornblende-bearing group green-brown biotite is generally present. The two different colours appear to indicate unlike oxygen fugacities in the magmas from which the micas crystallized. The rocks of the hornblende-bearing and hornblende-free provinces also vary slightly in chemistry - the most important difference being that the basic members of the first group contain slightly more Ca than those of the second having comparable silica content. The compositions of the Victorian granites is consistent with their derivation by anatexis of a mixture of basic igneous rocks and sedimentary material. The conclusion is drawn that a combination of Cambrian basalts and dolerites and Cambro-Ordovician sediments constitute the source. The explanation of the fact that two chemical trends are observed in the granites may lie in the possible existence of two chemically distinct groups in the Cambrian igneous rocks - the one having lower Ca predominating under central Victoria.
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    Petrogenesis of the Melba Flats Ni-Cu-PGE Deposit in Western Tasmania: Insights from a Geochemical and Geochronological Investigation
    Phua, Marcus ( 2016)
    Since its discovery in 1893, the Melba Flats Ni-Cu-PGE deposit has produced 10,000 tons of Ni and Cu at an average grade of 9.7% and 4.7% respectively. It is a magmatic sulphide deposit located 8 km north-east of the township of Zeehan, along the eastern margin of the Dundas Trough in Western Tasmania. The deposit is associated with a suite of bifurcating mafic intrusions hosting magmatic Ni-Cu-PGE sulphides intruded into a sequence of volcaniclastic lithic greywackes, which are correlated to the Crimson Creek Formation. U-Pb detrital zircon geochronology was utilized to show that the Melba Flats sediments have a maximum depositional age of c. 582 Ma. The Melba Flats mafic intrusions were formed by primitive magmas with 13 to 16 wt% MgO and a sub-alkaline tholeiitic affinity. 40*Ar/39Ar hornblende geochronology was employed to establish that the mafic intrusions were emplaced at c. 568 Ma, along an attenuated continental margin characterized by a transitional rift setting, analogous to the early Paleogene break-up margin of East Greenland. Melba Flats Ni-Cu-PGE sulphides are characterized by massive-to-semi-massive sulphides that possess high Ni, Cu and PGE tenors and mantle-like δ34S values and S/Se ratios and disseminated sulphides that have low Ni, Cu and PGE tenors, along with crustal δ34S values and S/Se ratios. Geochemical data indicates that the massive-to-semi-massive sulphides were formed at depth before being transported to their current sites, whilst the disseminated sulphides were formed during transport as the primitive magma interacted with the S-bearing crustal rocks.
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    Antarctic sea ice and its interactions with high latitude weather and climate
    Watkins, Andrew Bruce ( 1998)
    Antarctic sea ice plays a major role in the earth system by greatly influencing the high latitude exchanges of heat, moisture and momentum between the ocean and atmosphere, as well as profoundly effecting the salt budget of the ocean, and thus the production of Antarctic Bottom Water, one of the driving mechanisms of worldwide oceanic circulation. With such considerable and far reaching impact, it is important to document its climatology, understand its variability and quantify its influence. Climatologies and trends of the Southern Ocean sea ice pack are presented using the most recent satellite observations available from the Defense Meteorological Program’s (DMSP) Special Sensor Microwave Imager (SSM/I). The analysis of these data show that Antarctic sea ice is highly variable in both time and space. Statistically significant increases in the sea ice extent, open water and ice areas have been determined from the SSM/I data for the 9 year period 1987 to 1996, a result which differs from the Scanning Multichannel Microwave Radiometer (SMMR) observations (1978-1987). The increasing trend in the SSM/I observations can be attributed to the large increases in sea ice observed in 1994-1995, as confirmed by an analysis of data from the ERS-1 satellite. The mean season length during these years has remained relatively unchanged. Regional trends, both in the sea ice concentration and in season length, showed vast spatial inhomogeneity. SSM/I data displayed increasing season length in the central Weddell Sea, Bellingshausen Sea and Balleny Islands regions, with decreasing length in the Amundsen Sea, eastern Ross Sea and in the coastal areas off Wilkes Land. Similar trends are observed in the seasonal sea ice concentration. In most cases, these trends are opposite to those observed in the SMMR data, which may be linked to the shift observed in the Amundsen Sea low after 1990. Comparisons with historical data would suggest that no large scale anomalous change has occurred in the Antarctic sea ice limits over the course of human observation. Furthermore, the degree of variability suggests great care is needed in interpreting large scale changes in sea ice conditions, and hence atmospheric or oceanic change, from locally observed anomalies. Case studies of the effect of individual cyclones upon the sea ice concentration show small but definite modification of the ice conditions. To further diagnose aspects of the thermodynamic and dynamic forcing upon the Antarctic pack, detailed analysis of the sea ice concentration variability has been conducted using spectral techniques, and the spectra have been compared to those of the European Centre for Medium Range Weather Forecasts (ECMWF) temperature and wind data. In all cases, and with the seasonal cycle removed, the sea ice concentration shows a bias towards longer timescales of variability than either the wind stress or surface air temperature. This “red shift” in its frequency spectrum is strongest with the wind stress, and weakest with the temperature. For longer period waves, this may be due to the formation of new ice by surface cooling or the moderation of melting by the cold surface water, whereas for shorter period waves, where wind stress dominates temperature and ice concentration respectively, time is required for winds to draw in warmer or cooler air, as well as to overcome the ice masses inertia and keel friction to open or close leads. Strong intraseasonal variability of the sea ice concentration is observed in the 20-25 day period, reflecting similar timescales of the temperature variability, as well as that of the energetic eddies of the Antarctic circumpolar current. Examination of the latitudinal variation of the sea ice concentration, temperature and wind stress spectra showed not only the importance of the north-south temperature gradient in influencing the variability, but also the seasonal changes in the semi annual oscillation of the circumpolar trough. Regional spectra showed clear differences between location, and reflected the influences of the atmosphere and ocean upon the sea ice pack. This is clearly shown in the Weddell Polynya region and off East Antarctica, with high variability in the synoptic timescales, and in the western Ross Sea where changes occur in timescales of greater than 20 days. In order to determine if satellite derived, real time sea ice concentration and distribution would be of benefit to operational numerical weather prediction (NWP) schemes, the effect of sea ice concentration change upon the atmosphere in synoptic timescales was examined using a general circulation model in conjunction with the Australian Bureau of Meteorology’s GASP analyses. Experiments were conducted with a typical July sea ice concentration and distribution, as well as slab concentrations of 0, 10, 25, 50, 80 and 100%. Results from 5-day numerical weather forecasts show that the central pressure, structure and tracks of individual cyclones are sensitive to the ‘switch on’ of different sea ice conditions. Composites of all forecasts made with each concentration showed considerable, and mostly statistically significant, anomalies in the surface temperatures and turbulent heat fluxes over the sea ice. The magnitudes of these changes varied monotonically with the area of open water. The largest changes were simulated closest to the coast for all concentrations except for the typical July sea ice run, which displayed maxima over the outer pack. Significant westerly anomalies were induced over the ice in all cases, as were reductions in mean sea level pressure. The July sea ice runs displayed a distribution of the mean sea level pressure anomaly different from all others, with maxima occurring in the central to outer pack. All other forecasts displayed maxima at the coast. The results suggest that sea ice concentration does induce anomalies in the atmospheric parameters in timescales of less than five days. Further, the use of a realistic distribution of sea ice concentration produces results distinct from the constant concentration forecasts. Hence it is suggested that real time Antarctic sea ice data may be of considerable benefit to numerical weather prediction models.
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    Neoproterozoic to Permian evolution of the Cape Fold Belt, South Africa: Constraints on sediment provenance and orogenesis from high-precision 40Ar/39Ar dating of detrital and metamorphic micas
    Blewett, Scarlett Caroline Joyce ( 2019)
    The Permian Cape Fold Belt extends 1300 km along the western and southern coastal margins of South Africa. It comprises complexly deformed rocks of the lower-Palaeozoic Cape Supergroup, and Mesozoic parts of the Karoo Supergroup. Large-scale thrusts expose portions of the underlying Saldania Belt; a low-grade metamorphic belt intruded by granites of the ca. 550-500 Ma Cape Granite Suite. Both the Cape Fold Belt and Saldania Belt are segments of ancient continent-scale orogenic systems. The former is thought to be a portion of the Permian Gondwanides Orogen that extended from the Sierra de la Ventana Fold Belt of Argentina, across southern Africa, and into the Falkland (Malvinas) Islands, and Ellsworth-Whitmore Mountains of Antarctica, whereas the latter is considered one of the many Neoproterozoic-Cambrian Pan-African/Brasilliano terranes developed during the amalgamation of west Gondwana. However, fragmentation of Gondwana and separation of the Cape Fold Belt from its neighbouring terranes during the Cretaceous has provided major challenges in understanding both the geodynamic evolution of the poorly exposed Saldania Belt and the mechanics by which the Cape Orogen formed within the Gondwana interior. Gondwanan tectonic models often rely on geochronological provenance studies to not only link sedimentary sources and sinks, but to also correlate sedimentary successions in separated terranes. Previous geochronological provenance studies on the Cape Fold Belt have utilised U-Pb dating of detrital zircons to suggest that sediments of the Saldania Belt and Cape Supergroup were largely sourced from Mesoproterozoic rocks of the Namaqua-Natal Metamorphic Belt to the immediate north and underlying the Cape Fold Belt, as well as undifferentiated Pan-African and/or Brasilliano terranes. However, as zircon is able to survive orogenic recycling and long-distance transport, U-Pb detrital zircon studies have been unable to identify the most recent and proximal sources of sediments. In addition to having only broadly defined sediment provenance, the timing and extent of orogenesis during the Pan-African and Permian periods are poorly constrained. The timing of deformation in the Saldania Belt is only defined relative to the Cape Granite Suite, whereas the Cape Orogeny has been dated in a handful of limited 40Ar/39Ar studies. Early studies attempting to constrain Cape deformation utilised bulk mineral aliquots that yielded largely discordant 40Ar/39Ar age spectra, which the authors interpreted to represent multiple phases of deformation. A more recent study performed 40Ar/39Ar dating of single mica grains and proposed a bi-model evolution for the Cape Orogeny; however, this is based on only eight analyses. In this study, high precision 40Ar/39Ar geochronology is used to constrain the ages of individual detrital and metamorphic micas from low-grade rocks, as well as localised zones of variable deformation intensity in the southern Cape Fold Belt branch. Fundamental to this study, was the collection of detailed structural observations, petrographic and mineral chemistry data used to delineate detrital and neocrystallised mica age populations, from partially reset, altered, and/or complexly intergrown micas. A total of 648 individual mica grains were dated from 57 samples representing a variety of relatively undeformed and deformed Cape Supergroup and eastern Saldania Belt sediments, including crenulated metasediments, axial planar cleavages, thrust planes in duplex structures, and major shear zones. Only seven samples, collected from zones of intense deformation and focused fluid flow, yielded reproducible mica ages indicating that Cape Orogenesis was most pronounced at 257-248 Ma. These samples were located along, or in close proximity to the Worcester and Kango Fault systems, which are considered major decollement structures responsible for thin-skinned deformation of the Saldania Belt and Cape Supergroup sediments inland from the Gondwana margin. Biotite fusion ages of 272-270 Ma from a metamorphosed mafic dyke in the Kaaimans Inlier provide possible evidence for an earlier onset of Cape Orogenesis, preserved only in the Saldania basement. Samples from less deformed zones contained partially recrystallised detrital mica grains, mixed detrital and neocrystallised mica grains, and/or complex micas hosting clay and chlorite intergrowths, resulting in a spread of apparent ages older than the Cape Orogeny. 40Ar/39Ar detrital mica age populations were defined for a number of Saldania Belt and Cape Supergroup samples; these data were integrated with published U-Pb detrital zircon ages for provenance analysis. Detrital muscovite and zircon ages for the Lime Bank sequence and possibly part of the Kleinrivier sequence (Gamtoos Inlier) suggest exclusive provenance from the Mesoproterozoic Namaqua-Natal Metamorphic Belt or the similar-aged Maud Belt of Antarctica. In contrast, detrital ages for the Groenefontein and Huis River formations (Upper Cango Caves Group, Kango Inlier) indicate a source that experienced early Pan-African Orogenesis (580-550 Ma), such as the Sor Rondane Mountains or the Dronning Maud Land sector of the East African-Antarctic Orogen. The Cango Caves Group was folded prior to deposition of the overlying Kansa Group, which hosts abundant 530-510 Ma zircons. This suggests that deformation of the Cango Caves Group is Pan-African in age (i.e. 550-530 Ma) - possibly related to tectonic loading of the Kaaimans Inlier to the south, or the western Saldania Belt and Gariep Belt to the west. Later deformation of the Kango Inlier folded both the Cango Caves and Kansa Group, after which the conglomeratic Schoemanspoort Formation was deposited. A tightly constrained detrital mica age population of 510-500 Ma in the Schoemanspoort Formation represents either cooling/exhumation of the source terrane during the late stages of Pan-African tectonism or a younger tectonic and thermal pulse in the source area. These events could have occurred in the proximal Kaaimans Inlier, and may have been responsible for the combined folding of the Cango Caves and Kansa Groups. In the Kaaimans Inlier, 40Ar/39Ar incremental step-heating of muscovite from a pegmatitic vein suggest that parts of the Saldania Belt were affected by a post-Pan-African Ordovician thermal overprint. This overprint, identified in other Cape Granite Suite intrusives by previous studies, may represent a raised geothermal gradient in the basement as a result of Cape Supergroup sediment load and mantle flow coupled to far-field subduction along the Proto-Andean margin, and/or asthenospheric upwelling in the southern East African-Antarctic Orogen to the east of the Cape Fold Belt. 40Ar/39Ar analysis of individual mica grains from the Cape Supergroup reveals a dominant Ordovician (490-465 Ma) detrital muscovite population, suggesting provenance from orogenic belts possibly associated with the aforementioned Ordovician thermal overprint in the Cape Fold Belt basement; i.e. the Famatinian Orogen of western Argentina and/or the East African-Antarctic Orogen. Lesser detrital muscovite populations of 650-500 Ma and >730 Ma corroborate previous zircon provenance studies suggesting Pan-African and Namaqua-Natal Metamorphic Belts sources, respectively. The sediment provenance investigations presented in this study provide insights into the evolution of late Neoproterozoic to Devonian sedimentation in the Cape Fold Belt, and enable correlation of orogenic terranes spanning South American, African and Antarctic. In addition, well-constrained deformation ages from intensely deformed metasediments and major shear zones permitted formulation of a tectonic model for the Cape Orogeny, considering the onset, duration of deformation, and structural development of the Cape Fold Belt along the southwest Gondwana margin.
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    The origin, composition, and evolution of the Kimberley kimberlites (South Africa)
    Soltys, Ashton ( 2019)
    Kimberlites are deeply derived (i.e., >150 km), small-volume igneous bodies that have been emplaced on all continents throughout the last 2.8 billion years. The typical volcanic expression of kimberlites is a deep irregular root zone and/or feeder dyke system connected to a regular steeply dipping and outwardly tapering pipe-like diatreme, which may be overlain by a crater and extrusive material (when not removed by erosion). The crater and diatreme facies contain pyroclastic rocks, which transition into coherent (sub-volcanic) rocks in the root zone. Kimberlites are of economic value as the major host of gem quality diamonds at the Earth’s surface. They also hold great scientific significance, as the deepest derived melts to reach the surface, with entrained mantle material that provides some of our best information on the structure, composition, and evolution of the sub-continental lithospheric mantle. However, despite over a century of dedicated research, numerous aspects of kimberlite petrogenesis remain poorly understood and contentious. One central issue that this project has addressed is the composition and evolution of kimberlite melts. The composition of kimberlite melts remain poorly constrained because: (1) rocks emplaced near the surface are prone to deuteric and hydrothermal alteration; (2) they have been contaminated by the physical incorporation of xenocrystic and xenolithic material; (3) their parental magmas have been modified by interaction with and partial assimilation of mantle and crustal material; and (4) they undergo syn-emplacement differentiation. Therefore, in this study exceptionaly ‘fresh’ rocks from the well studied kimbeley cluster (the type locality) were examined to gain further insights into kimberlite melt compositions. Better constraints on kimberlite melt compositions are pivotal if we are to move toward a comprehensive understanding of the petrogenesis of these enigmatic rocks. The studied samples derive from the Kimberley cluster (South Africa), which lies within the Western terrane of the Kaapvaal carton. This cluster constitutes the type locality of kimberlites, containing five major kimberlite pipes (The Kimberley mine, De Beers, Dutoitspan, Wesselton, and Bultfontein), numerous smaller pipes, and abundant dyke/sill complexes (e.g., Benfontein, Wesselton Floors, Wesselton Water Tunnels). The Kimberley cluster has been dated by various geochronological techniques yielding emplacement ages of ~80-90 Ma. To provide new insights into the composition and evolution of kimberlite melts, a detailed petrographic study of sub-volcanic (hypabyssal) coherent kimberlites was conducted. This included the investigation of mineralogy, mineral zonation, inclusion populations (mineral, melt, and fluid), and textural relationships between phases, utilizing a range of microscopy techniques. This petrographic data formed the basis of targeted geochemical analysis by electron microprobe. A study of olivine compositions across multiple intrusions of the Kimberley cluster shows that olivine, more than any other mineral, provides the most complete record of kimberlite evolution. This study showed that pre-ascent metasomatism of the lithosphere by kimberlite melts is wide-spread, and that so-called ‘xenocrystic’ olivine is not directly representative of the wider lithosphere due to metasomatism of the conduit by previous pulses of kimberlite magmatism. The composition of kimberlitic liquidus olivine overlaps that of olivine from other mantle-derived carbonate-bearing magmas (orangeites, ultramafic lamprophyres, melilitites), with low Mn/Fe and Ca/Fe, and moderate Ni/Mg ratios. It is suggested that these compositions are typical of olivine in equilibrium with melts derived from carbonate-rich peridotite sources. Compositional zonation patterns indicte that olivine crystallises throughout magma ascent and that its crystallisation continues after emplacement into the upper crust. Magmatic olivine (i.e. crystallised from the kimbelrite magma) displays distinct generations of crystallisation, with increasing Mg, Ca, and Mn contents interpreted as the result of fractional crystallisation and increasing oxygen fugacity (fO2). The stability of olivine at sub-solidus conditions implies that secondary melt inclusions cannot trap primitive melts, but rather evolved residual fluids. Although olivine provides a wealth of information on early kimberlite melt evolution and metasomatism of the surrounding lithosphere, details about the later stages of kimberlite melt evolution are evident in other magmatic groundmass phases. Therefore, detailed petrographic and mineral chemical studies were undertaken on all mineral consistents from a suite of samples from the exceptionally fresh De Beers dyke to determine the crystallisation sequence. In turn, this data yielded insights into melt evolution from the perspective of multiple different magmatic phases. The early stages of kimberlite crystallisation (i.e., olivine, Cr-spinel, Mg-Ilmenite, rutile) are defined by decreasing Mg/Fe ratios. This subsequently reverses (i.e., increasing Mg/Fe) during later groundmass crystallisation, which is attributed to increasing fO2. Comparison with published data shows that the melt parental to early crystallising phases in this dyke are indistinguishable from those in the root-zone intrusions of the Kimberley cluster, meaning that not all dykes are the crystalisation product of magmas that underwent pre-emplacement fractionation. To gain additional insights into the very late stages of kimberlite melt evolution further detailed petrographic and mineral chemical studies were conducted on late-stage groundmass phases (i.e., apatite and mica) from samples of different root zone intrusions and dyke/sill complexes in the Kimberley area. Despite the early crystallising phases (i.e., olivine, Cr-spinel, Mg-ilmenite) being compositional indistinguishable in dykes/sills and root zone kimberlites, the compositions of apatite appear to be controlled by the style of magma emplacement. Apatite from dykes/sills is Si-rich and Sr-poor, whereas apatite in root zone intrusions show the opposite features. The high Si content of apatite in dykes/sills is attributed to the coupled incorporation of silica and a carbonate ion for phosphorus, reflecting higher CO2 contents in the melts parental to dykes/sills. The high Sr content of apatite in root zone intrusions likely requires crystallisation from, or overprinting by, hydrous fluids. These features indicate that dyke/sill kimberlites have higher CO2/H2O ratios than the magma that produced root zone intrusions. This is consistent with petrographic observations, whereby dykes/sills are enriched in carbonates, may contain dolomite, and have lower abundances of serpentine, mica, and monticellite than root-zone kimberlites. These differences in CO2/H2O ratios of the crystallised melt are attributed to differences in emplacement style, whereby a rapid decrease in pressure in root zone kimberlites leads to exsolution of a (CO2-rich) fluid phase, possibly caused by breakthrough to the surface. The knowledge gained through detailed petrographic and mineral chemical studies led to the development a new quantitative method for reconstructing the composition of kimberlite melts. This model allowed for constraints to be placed on the composition of primitive kimberlite melts and their evolution, as they incorporate and assimilate xenocrystic material, undergo fractional crystallisation, and post emplacement alteration. The results of this modelling indicate that the melt parental to the Bultfontein kimberlite was transitional between silicate and carbonate. This composition is consistent with experimental constraints on the amount of CO2 that can be dissolved into kimberlite melts in the upper crust. The reconstructed primitive melt composition is in equilibrium with asthenospheric source rocks. Based on constraints from experimental studies, Kimberley kimberlites could have been produced by ~0.5% melting of carbonated lherzolite in the upper asthenosphere (i.e., 6.0-8.6 GPa and ~1400-1500 degrees Celsius).
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    An Investigation into the Potential of Pliocene Speleothems from the Nullarbor Plain, Southwest Australia, to Preserve Interpretable Palaeoclimate Signals
    Sellman, Safana Louise ( 2019)
    The Pliocene has been identified as a key time interval from which estimates of future climate scenarios can be made. At present there is a significant paucity of Pliocene climate data from the Southern Hemisphere, and moreover, from terrestrial sources therein. This thesis aims to address both of these scarcities through applications of both traditional and novel techniques of palaeoclimate analysis to speleothems from the Nullarbor Plain, southwest Australia. This thesis focuses on two primary stalagmites, as well as several additional speleothems, that grew during the Pliocene as revealed by U-Pb dating. It provides one of the first detailed studies of speleothems of a greater antiquity than the 500 kyr dating limit previously imposed by the U-Th method. This study has provided invaluable insights into the climate of the Nullarbor Plain during the Pliocene, through the application of conventional stable isotope analyses, trace element analyses, fluid-inclusion analyses, clumped-isotope analyses, and modern precipitation isotope analyses. For speleothems of such antiquity, a multi-proxy approach grounded in a site-specific modern isotope study, has provided the means for delineating the key drivers of the geochemical variations present. The use of both traditional and novel speleothem proxies provides key information regarding both temperature and precipitation dynamics in the Nullarbor region during the Pliocene. Conventional stable isotope and trace element records from the speleothems reflect changes in precipitation above the cave and the overlying vegetation dynamics. Modern precipitation analyses enable a comprehensive understanding of the influences on isotopic variation in current precipitation, with applications to the interpretation of the speleothem data. This study indicates that during the Pliocene, precipitation was significantly higher in the Nullarbor region, suggestive of an increase in moisture sourced from NCBs and the Southern Ocean. The increased precipitation resulted in significantly higher vegetation cover compared to present, as supported by both the carbon isotope and trace element signals. These conclusions are in agreement with both modelled estimates of vegetation and precipitation for the Nullarbor Plain, and also with studies of speleothem-derived pollen data from the region. Palaeotemperature estimates were derived from combined fluid-inclusion and clumped-isotope analyses; indicating a temperature range of 18.8 'C +/-1.8 'C to 21.4 'C +/-1.3 'C. While the individual methods provided several additional estimates, the uncertainties associated with each limit the reliability of the absolute temperatures. However, they signify significant temperature variations within the Pliocene, indicating that despite being a period of overall global warmth in comparison to the present day, the Nullarbor region experienced significant fluctuations in average temperatures. This study has identified several areas for focus in future research in order to further develop the novel application of speleothem research to the more distant past, while providing unique and important information regarding the climate dynamics of the Nullarbor Plain during the Pliocene.
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    Age, origin and extent of the Newer Volcanic Province in the Melbourne region, Australia
    Heath, Michael Anthony ( 2019)
    Abstract Intraplate basaltic volcanism is present on every continent, untethered to any specific tectonic setting. The ca. 4.6 Ma – 5 ka Newer Volcanic Province (NVP) in south-eastern Australia is a chemically and morphologically diverse intraplate basaltic province. Its diversity, preservation and accessibility make it an ideal natural laboratory for investigating the causes and evolution of intraplate magmatism worldwide. Previous studies in the NVP have put forward competing magmatic models, but their validity is dependent on a limited geochronological dataset. Furthermore, previous geochronology has seldom been supported by geochemical or geomorphological studies on the same volcanic products, such that there is often a disconnect between the absolute ages of NVP rocks and the extent and composition of their associated lava flows or eruption points. This study utilised a holistic approach to lava flow mapping, with a focus on the diagnostic petrographic and geochemical features of individual basaltic lava flows selected for geochronology. The current study area of Melbourne, which is located at the eastern margin of the NVP, was selected for its age range and geochemical complexity, rivalling those of the entire NVP. Drill core was utilised to trace lava flows at depths of up to 80 m, thereby unravelling complex flow networks and facilitating the construction of a detailed lava flow map for the Melbourne area. Trace element geochemistry was utilised to distinguish between petrographically similar flows, and to investigate the eruption of three chemically distinct magma batches erupted consecutively from Mount Fraser. This mapping and geochemical work is complemented by new, high-precision 40Ar/39Ar age constraints, spanning ~7.9 Ma – 0.8 Ma. The new geochronological constraints on Melbourne lava flows reveal that the earliest activity (~7.9 – 3.8 Ma) was dominated by small-volume eruptions that predominantly produced alkali basalts. From oldest to youngest, these included the Bald Hill, Mount Ridley, Tullamarine, Crowe Hill, Spring Hill, Summerhill Rd, Redstone Hill and Aitken Hill lava flows. After ~3.8 Ma, large-volume eruptions dominated, with Fenton Hill, Mount Kororoit, Tulloch Hill and Mount Fraser producing lavas generally of tholeiitic composition. This progression from alkali basalt to tholeiitic volcanism over time is contrary to the purported province-wide progression from tholeiitic to alkali-rich lavas, indicating either that geochemical evolution in Melbourne was distinct from that of the NVP, or that the conclusions of province-wide studies are based on an unrepresentative sample set. An age of 7.931 +/- 0.038 Ma for the Bald Hill Lava Flow far exceeds the generally accepted maximum age of NVP activity (ca. 4.6 Ma). This lava flow, along with those erupted from Pretty Sally, Green Hill and Mount Cooper, is also geochemically distinct from other Victorian NVP products, but is not dissimilar to lavas of the Cosgrove Leucitite suite, the purported products of a long-lived mantle plume. This raises the possibility that the ‘Cosgrove Plume’ traversed the latitude of Melbourne just after 7.9 Ma, casting doubt on its possible role in the initiation of NVP activity some 3.3 million years later. 11 of the 38 samples selected for 40Ar/39Ar dating produced concordant results, with the remainder exhibiting varying degrees of discordance. The underlying causes of this discordance and implications for accurate age determinations are examined and modelled in age spectra and inverse isochron space. A correlation is found between the proportion of radiogenic 40Ar (40Ar*) released and the nature of discordance exhibited by a sample. 39Ar recoil is suggested as the most likely cause of discordance in high-40Ar* samples, whereas low-40Ar* samples exhibit discordance consistent with the modelled effects of mass-dependent fractionation. Based on modelling results, isochron rotation is the main impact of isotopic disturbance on an inverse isochron plot (39Ar/40Ar vs 36Ar/40Ar), leading to a negative correlation between 40Ar/39Ar ages and (40Ar/36Ar)i values. A new framework for the treatment of 40Ar/39Ar data from basaltic rocks is submitted, optimising the interpretation of inverse isochrons and informing the allocation of age constraints. Finally, a new method of 40Ar/39Ar data treatment, here named the multi-isochron approach to 40Ar/39Ar dating, is introduced. A multi-isochron regression utilises the combined output of all possible inverse isochrons from data of a single aliquant to determine its ideal isochron and eruption age. This method has the potential of transforming 40Ar/39Ar data treatment, allowing eruption ages to be calculated even when isotopic disturbance is severe, and to be reported in cases where this was previously not possible.
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    Investigation of air-sea fluxes over the Southern Ocean using an eddy-covariance technique and parameterization using stability functions
    Chen Reddy, Sushma Reddy ( 2019)
    The Earth is an integrated system that consists of sub-systems that interact and influence each other. These interactions have an important influence on the understanding of weather and climate of the earth system. Air-sea interactions are one such interaction that affects the Earth's system — thus making it essential to understand the physical processes that affect the prediction and forecast of the weather and climate. The present state of art climate and numerical weather prediction models use bulk models which are based on Monin-Obukhov similarity theory and Charnock's relations to determine the fluxes across the air-sea interface. The COARE 3.5 model is the best performing model available, and it is seen that the model underestimates the fluxes at higher wind speeds. Hence, to avoid any assumptions and circular dependencies, we need to build a simple parameterization of coefficients of fluxes to determine fluxes. Eddy Covariance, the purest form of flux calculation, is used to develop the parameterization. Eddy covariance relies on high-frequency 3-D winds, which, on ships, are contaminated by platform motions. However, in the absence of reliable accelerometer data, or a failed collocated accelerometer, calculating these motions is difficult. Here, in this study, we studied if the ship's motion reference data can replace external collocated accelerometer data. We have characterized that for the anemometer mounted on the foremast of the R/V Investigator, and there is a lag of 1.4 sec in the ship's motion reference unit data. Hence, we can correct the wind speeds for platform motions using the ships' motion data after adjusting to the lag. The spectral speak due to the platform motions observed in the measured raw data by anemometer is removed after the corrections performed by the ship's data. Hence, achieving the redundancy of the external collocated accelerometer, GPS receiver, and heading sensors. The fluxes computed from the eddy covariance technique are used to get a simple parameterization to estimate fluxes. Here, we have developed the coefficients of drag, latent heat fluxes in terms of simple functions of Reynolds and bulk Richardson number, which are physically dependent on velocity and stability of the atmospheric boundary layer. The model proposed does not depend on any assumptions or does not have any circular dependencies. The coefficient of sensible heat flux could not be parameterized as we observed that there is no dependence on Reynolds number in the neutral, stable region. The proposed model is performing better compared to that of the COARE 3.5 model at higher wind speeds. Gas transfer across the air-sea interface is challenging to measure, and the existing relationships for the gas transfer velocity with wind speeds have a high variance at high wind speeds. It is essential to measure gas transfer velocities in the Southern Ocean as it is least sampled with the rough environment and high surface waves. It is estimated that the Southern Ocean is the largest sink of anthropogenic carbon dioxide, with about 40% of the total world ocean sink. Gas transfer velocities of CO_2 in the Southern Ocean are measured, and it is found that the results obtained are within the range that is reported by the previous researchers. However, there are no sufficient data points, and the variance in the data is high to get any conclusions from the results obtained.