School of Earth Sciences - Theses
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ItemThe geology and geochemistry of the Agnew Intrusion: implications for the petrogenesis of early Huronian mafic igneous rocks in Central Ontario, Canada( 1996-07)The Early Proterozoic Agnew Intrusion is a well-preserved leucogabbronoritic to gabbronoritic layered intrusion that is a member of the East Bull Lake suite of layered intrusions (ca. 2490-2470 Ma) occurring in central Ontario. These intrusions are related to the development of the Huronian Rift Zone, which may be part of a much more widespread rifting event that involved the Fennoscandian Shield. Structural data suggest that these intrusions have been subjected to ductile deformation and are erosional remnants of one or more sill-like bodies originally emplaced along the contact between Archaean granitic rocks of the Superior Province and an Early Proterozoic Huronian continental flood basalt sequence in the Southern Province.
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ItemThe development of a high quality historical temperature data base for Australia( 1996)A high quality, historical surface air temperature data set is essential for the reliable investigation of climate change and variability. In this study, such a data set has been prepared for Australia by adjusting raw mean annual temperature data for inhomogeneities associated with station relocations, changes in exposure, and other problems. Temperature records from long-term stations were collaborated from the set of all raw data held by the Australian Bureau of Meteorology. These long-term records were extended by combining stations and manually entering previously unused archived temperature measurements. An objective procedure was developed to determine the necessary adjustments, in conjunction with complementary statistical methods and station history documentation. The objective procedure involved creating a reference time series for each long-term station, from the median values at surrounding, well-correlated stations. Time series of annual mean maximum and mean minimum temperatures have been produced for 224 stations, and the adjusted dataset has been made available to the research community. The adjusted data are likely to be more representative of real climatic variations than raw data due to the removal of discontinuities. The adjusted data set has been compared with previously used temperature data sets, and data sets of other parameters. The adjusted data set provides adequate spatial coverage of Australia back to 1910. Additional adjusted data are available prior to this date at many stations. Trends in annual mean maximum, minimum, the mean of the maximum and minimum, and the range between the maximum and minimum, have been calculated at each site. Maximum and minimum temperatures have increased since about 1950, with minimum temperatures increasing faster than maximum temperatures.
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ItemDeformation and the thermobaric history of the eastern coast of Williams Island( 1997)Williams Island is located off the southern coast of the Eyre Peninsula of South Australia where the Palaeoproterozoic rocks of the Lincoln Batholith intrude a portion of an Archaean basement complex. The structures of the eastern coast of Williams Island are controlled by the rheological contrast between the mafic dykes and the felsic granite gneisses that comprise the batholith. Planes of rheological weakness exist at the dyke margins along which strain is localised. The plane of failure and the kinematics along it depends upon the orientation of the dyke with respect to the stress field. Displacements at cross-cutting dyke margins indicates the occurrence of three significant deformation events, D 1, D2 and D3. By comparison, the D1 is localised to a region of outcropping Jussieu Dykes, the D2 is pervasive and the D3 is confined to the discrete Northern and Southern Shear Zones. Associated with the latter two deformations is an increase in temperature and strain rate which controls the relative strength of the metabasic and the granite gneiss rocks. Brittle extensional structures, such as boudinage, form when the mafic dykes behave in a more competent manner relative to the host, whereas ductile extensional features, like pinch and swell, infer a greater homogeneity between the rock types. The rheological contrast is inverted with a preferential increase in strain resulting in granite boudinage. The D2 fabrics arc predominantly defined by a granulite two-pyroxene assemblage and the structural elements of D3 are characterised by minerals associated with amphibolisation. Average pressure calculations of representative assemblages give 7 ± 1 kbar for M2/D2 and 12 ± 2 kbar for M3/D3, which suggests crustal thickening over D2 - D3 time. Exhumation of the crustal block therefore occurred after peak D3.
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ItemA structural analysis of Wanna, South Australia: the comparative behaviour of Mafic dykes and granite during deformation( 1996)Strain localisation that produces varying foliation development, folding, and patterns of boudinage has led to structural features within, and between, the two main lithologies at Wanna, South Australia at amphibolite facies, these lithologies being the megacrystic granite gneiss of the Donington Granitoid Suite, and the Tournefort dykes which cross-cut the gneiss. The structural elements differ between, and within each lithology-for example, the megacrystic granite gneiss has a reasonably pervasive foliation, whereas deformation features in the Tournefort dykes tend to be localised into areas of high strain. Cross-cutting relationships are used to constrain the temporal relationships between structural elements, and the development of the different structural features explained in terms of rheological behaviour of the lithologies. The relative rheological behaviour of the principal lithologies was thus found to vary over space, as well as over time. Geothermometry of mafic assemblages was used to constrain the temperatures at which different structural features developed, which were all found to be in the order of about 720°C and occurring under fluid-rich, upper amphibolite conditions.
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ItemProterozoic strain localisation during the Kimban Orogeny: a structural analysis of Williams Island, Eyre Peninsula, South Australia( 1997)Strain localisation and shear zone development is spatially controlled by rheological inhomogeneity of the crust. Shear zone development is found to be localised by the distribution of mafic dykes within the deformed Palaeoproterozoic granitoids and orthogneisses of the Lincoln Batholith, outcropping on Williams Island, southern Eyre Peninsula, South Australia. These granitoids have experienced regional upper amphibolite metamorphism, episodic ductile deformation and exhumation of the Lincoln Batholith during the Kimban Orogeny (c. 1850-1700 Ma). In the area mapped, crustal shortening has been accommodated by dextral strike-slip transport along the dyke-hosted Williams Shear Zone, and by the transferring of strain into oblique south-up thrusts. Strain analysis of granite orthogneiss was undertaken using both finite strain methods and by examination of strain-induced orthogneiss fabric development. It was found that large strains have been localised within mafic dykes, whilst comparatively little strain has been accommodated within the host rock. Although finite strain estimation met with limited success, results demonstrate a partitioning of flattening and constrictional strain between granite gneisses and the mafic dykes and an asymmetry of strain intensity across dyke-hosted shear zones. Temporal evolution of the granite/dyke rheological contrast results in a progression of boudinage structures which may be used to chart the variation or temperature and strain rate during metamorphism and deformation. Such evolution is mimiced within orthogneiss fabric by changes in the quartz/feldspar rheology contrast and grain-scale microstructure. Placing the deformation observed on Williams Island into a regional perspective has proven difficult due to the limited scale of mapping and an incoherence of kinematic data from previous work within the batholith. It seems plausible that the strike-slip movement recorded on the Williams Shear Zone occurred in response to regional exhumation of the Lincoln Batholith during the Kimban Orogeny.
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ItemStructural and metamorphic constraints on Kimban Orogenesis from southern Eyre Peninsula, South Australia( 1997)Archaean to Mesoproterozoic lithologies at Whalers Way on southern Eyre Peninsula present a unique cross section of episodic deformation and magmatism within the Gawler Craton. D2 and D3 at Whalers Way were coaxial phases of progressive fold-thrust deformation. Progressive D2 deformation resulted in the formation of east dipping shear zones along which nappes with NW directed vergence were stacked coeval with the Kimban metamorphic peak. Domains of upright and recumbent D3 structure can be identified based on the orientation of S3. Domains of recumbent D3 structure retain transitions from open folds not associated with an axial planar foliation through to recumbent antiforms bound by shallow west dipping shear zones. S3 within domains of recumbent structure is non-pervasive and well developed only within D3 shear zones. In contrast a pervasive S3 developed within domains of upright D3 structure. Systematic variation in the pitch of L3 imply vertical strain was partitioned into domains of upright structure. Tectonic foliations have been used to establish linkages between the structural and metamorphic histories of Whalers Way. Assemblages that define S2 (M2) equilibrated at 6-7 kbar and 800-820°C (M2) whereas S3 (M3) assemblages equilibrated at 3-5 kbar and 700°C (M3). M2 and M3 peak temperatures were in excess of those which could result solely from thermal relaxation of an overthickened crust. Transient Kimban heat input is consistent with rapid post-D3 cooling implied by K-Ar geochronology. D2 and D3 were the earlier and latter phases of a single episode of transpressional deformation in which the change in kinematics from NW to NE directed transport was associated with a 90° swing in the orientation of the subhorizontal principal compressive stresses. The consistency of kinematic data and the temporal sequence of magmatism relative to deformation across the Eyre Peninsula suggest syn-D3 decompression at Whalers Way reflects regional scale processes. Because the terrain is inferred to have cooled rapidly, the presence of near isothermal decompression textures implies exhumation must also have been rapid and suggests significantly non-plane strain flow within steeply oriented crustal scale shear zones is an efficient mechanism for exhumation of the mid to lower crust.
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ItemGeology of the lookout area, Eyre Peninsula, South Australia( 1996)The Lookout Area, southern Eyre Peninsula, South Australia forms part of the Lincoln Batholith with outcropping Donington Granitoid Suite units of Palaeo-Proterozoic age (l840-1800Ma) and both syn-plutonic and intrusive mafic dykes. The area was surveyed and mapped at 1:500 to produce a detailed geological map including the form surface trend of structural features. The units, incorporating felsic, intermediate and mafic gneisses intruded by the mafic dyke sequences, preserve high strain mylonitic deformational features with well developed fabrics in the felsic units. The Mafic dykes are boudinaged and display asymmetries attributed to antithetic back-rotation due to extensional shear. Kinematic indicators including shear band formation, parasitic folding and strain shadows suggest a kinematic history of initial sinistral deformation post-dated by dextral west-up oblique shear associated with the formation of the principal foliation. This is in turn post-dated by local sinistral shearing. The strain associated with the deformation can be measured by use of porphyroclast shape and distribution. These results indicate that the strain is locally variable, from constrictional to flattening, but generally constrictional with an extensional ratio of approximately 6:1. The metamorphic conditions preserved by the mineral assemblages analysed through the average PT method using THERMOCALC are; 700-850°C and 5.8-6.8 kbar. This mineral assemblage indicates metamorphism in the area has achieved upper-arnphibolite to lower granulite facies metamorphism at some stage in the PT history of the area.
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ItemOccurrence of nitrate in soil and groundwater in the Corangamite area, Western Victoria( 1996)Soil and groundwater samples taken from two areas of different land use in the Corangamite Region, 200 km west of Melbourne, were analysed for nitrate and ammonium, and in some cases chloride. Both sites are located on the Later Newer Volcanics 'stone rises', and groundwater was sampled from nested bores which intersect the shallow unconfined aquifer and deeper semi-confined aquifer at both sites. The Carpendeit site is an area of native Eucalypt forest, and the Purrumbete North site is a pasture for grazing dairy cows. Low concentrations of nitrate (< 1 mgN/L) in groundwater at Carpendeit correspond to low soil nitrate concentrations (< 3 µgN/cm3 ). Higher groundwater nitrate concentrations occurred in the shallow unconfined aquifer at Purrumbete North, (up to 3 mgN/L), but not in the lower semi-confined aquifer, and corresponds to higher nitrate concentrations in soil (1 to 60 µgN/cm3 ). Elevated nitrate concentrations also occurred in groundwater discharge at McVeans Springs, in the range 2.61 to 4.72 mgN/L, and at Ettrick Springs in the range 8.08 to 16.07 mgN/L, greater than the limit of 10 mgN/L for drinking water specified in ANZECC water quality guidelines. Nitrate in soil under the pasture is probably derived primarily from the activity of nitrogen fixing bacteria associated with subterranean clover introduced to the pasture. Soil nitrate distributions suggest intense return of nitrogen in dung and urea occurs at 'camps' locations on the pasture, where cows tend to gather for shelter. Transport of nitrogen to shallow groundwater is stimulated by cracks and channels in the basalt clay soils. Local groundwater flow includes interaction with the many lakes and temporary ponds 'which form in surface depressions at times of high rainfall. The ponds probably serve as an effective nitrate supply in recharge to the shallow aquifer.
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ItemTransport, attenuation, and degradation of organic chemicals in a basaltic aquifer system near Melbourne, Australia( 1996)Groundwater in the Pliocene to Pleistocene fractured and jointed Newer Volcanics basaltic aquifer system beneath Melbourne's industrialised western suburbs is extensively contaminated by a wide variety of organic and inorganic compounds. Groundwater in Tertiary sediments underlying the Newer Volcanics is probably also contaminated by the same sources. The main objectives of this research were 1) to assess the types, concentrations, and distribution of contaminants in the Newer Volcanics aquifer system in Melbourne's western suburbs and at a selected contaminated site and 2) to determine contaminant transport, attenuation, and degradation processes affecting organic contaminants in this aquifer system. Contaminants detected in the Newer Volcanics aquifer system during this research include phenols, volatile organic compounds, polynuclear aromatic hydrocarbons, polychlorinated biphenyls, metals, and inorganic anions. The groundwater flow system in the study area comprises a single heterogeneous and anisotropic unconfined aquifer, and includes both the Newer Volcanics and underlying sedimentary units (the Brighton Group and the Werribee Formation), although hydraulic connection of these units to the volcanics is irregular. Groundwater flow in the Newer Volcanics is through vesicular and/or scoriaceous lava flow tops and bottoms, in intercalated fluvial deposits, and through the fractured and jointed lava flows. Locally (scale of less than I km square), the basaltic aquifer system may consist of hydraulically separated shallow and deep aquifer zones that are connected on a larger scale. The deep aquifer zones may be semi-confined to confined. Groundwater in the study area is recharged via throughflow from upgradient and infiltration of rainfall. Discharge from the Newer Volcanics in the study area is primarily to underlying sedimentary formations, but also to surface water features and directly to Port Phillip Bay. Several mechanisms which reduce contaminant concentrations are possible in the Newer Volcanics aquifer system. These include volatilisation, dispersion and diffusion, transient storage, matrix diffusion, sorption, hydrolysis, and biodegradation. However, the nature of porosity in the Newer Volcanics may significantly extend the lifetime of contaminant plumes via the processes of transient storage and matrix diffusion. The primary mechanisms of attenuation and degradation of organic contaminants in the Newer Volcanics aquifer system are probably biodegradation, matrix diffusion, sorption, and dispersion (for non-reactive contaminants) in order of decreasing effect. Biodegradation at the water table and discharge areas will also be significant because of atmospheric contact and increased dissolved oxygen concentrations. Because of the relative lack of organic carbon in the basaltic aquifer system, sorption will occur mainly to mineral surfaces in clay-rich zones and within the rock matrix (concurrent with matrix diffusion). In some cases, relatively undiluted contaminants may be transported along preferred flow paths to discharge locations where they may pose a potential threat to the environment prior to degradation or attenuation. It was found, at least with phenols and volatile organic compounds in groundwater at a study site, that contaminants are degraded and/or attenuated rapidly, probably via biodegradation, matrix diffusion, and sorption. Biodegradation testing of groundwater at this study site confirmed the existence of microorganisms in the aquifer system capable of aerobic degradation; indirect evidence may indicate the presence of anaerobes.