School of Earth Sciences - Theses

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    Heat flow modelling in the Adelaide Geosyncline, South Australia and implications for geothermal resource exploration
    Musson, Alexander James ( 2008)
    The central theme of this research is the continental heat flow at the surface of the Earth. Radioactive heat production in the lithosphere and heat flux from convection in the asthenosphere are first order controls on surface heat flow. Accurate heat flow determinations are essential in understanding the geodynamics of the lithosphere and refining resource exploration models, in particular those related to geothermal resources. The focus of this investigation is confined to the understanding of heat refraction as a result of the heterogeneity and anisotropy of the geological subsurface, under a steady-state heat conduction regime. Within the South Australian Heat Flow Anomaly, an area of particular significance for geothermal resource exploration is the deep seated Torrens Hinge Zone, a strip of tectonic transition between the Archaean Gawler Craton to the west and the Neoproterozoic to Cambrian sedimentary cover of the Adelaide Geosyncline to the east. (For complete abstract open document)
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    Deformation and the thermobaric history of the eastern coast of Williams Island
    Marks, Bianca ( 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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    Geologic and geomorphic applications of Aster satellite imagery, northern Flinders Ranges, South Australia
    Harper, Katherine Louise ( 2002)
    Multispectal ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite data has been evaluated for geologic and geomorphic interpretations within the northern Flinders Ranges, South Australia. ASTER is a new remote sensing imaging system on board NASA’s Terra satellite, launched in December, 1999. ASTER measures the reflectance of the Earth’s surface within 14 bandwidths of the visible, near infrared, short wave infrared and thermal infrared sections of the electromagnetic spectrum, with a minimum spatial resolution of 15 m. ASTER has the ability to produce digital elevation models (DEM), important for understanding the dynamics of the landscape by draping false colour images over topography. The northern Flinders Ranges is one of the most diverse geological settings on the Australian continent, making it an ideal ‘test site’ to demonstrate the capabilities of the ASTER instrument. The area contains a range of geology from Precambrian basement to Quaternary desert landforms. The ability of ASTER Level 1B data to discriminate between the large range of lithologies is assessed. Geomorphic interpretations made from exploiting the high resolution ASTER data and DEM has revealed a significant record of post Pliocene landscape development, attributed to a combination of climatic and tectonic factors. Such features as incision morphology and the identification of palaeodrainages have enabled constraints to be placed on the Quaternary degradational and aggradational events. For example, estimates of Quaternary sediment flux rates in some areas of the study area are essentially extracted from ASTER DEM data. ASTER has persisted to be extremely useful in the study of aeolian landform morphology in regions surrounding the northern Flinders Ranges. The short wave infrared has proved useful for identifying areas of high surface moisture, directly relating to the depth to water table. The application of principal component analysis to ASTER short wave infrared data is used to accurately identify specific mineralogical character.
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    Metamorphism of granulite facies metapelites
    Tong, Laixi ( 2004)
    This thesis involves a study of metamorphism and partial melting in granulite facies metapelites from three regions, the Larsemann Hills and the Rauer Group of east Antarctica, and Fishery Bay in southern Eyre Peninsula of South Australia. Along with the metamorphic study, $^40Ar/^39Ar$ thermochronological dating was also undertaken for the first two areas to constrain the timing of tectonothermal events and syn- to post-tectonic cooling history. (From Abstract)
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    The Mine Creek region, Eyre Peninsula, South Australia: a structural analysis of the Kalinjala Shear Zone
    Karner, Tamara ( 2000)
    Mine Creek, located in the Eastern Eyre Peninsula, South Australia, exposes a natural cross section through the Kalinjala Shear Zone where it juxtaposes a sequence of granulite facies metasediments to the west from upper amphibolite granite gneisses to the east. The lithologies include biotite-garnet schists, forsteritic marbles, biotite-hornblende amphibolite, banded iron formation and quartz +feldspar +biotite +hornblende ± garnet megacrystic granite gneisses. These rocks preserve evidence of at least two deformation events. D1 formed a layer- parallel S1 foliation defined by peak garnet +biotite +quartz +feldspar assemblages, with no recognised folding. Associated with this deformation was the initiation of the NE-SW oriented, dextral transpressive, Kalinjala Shear Zone, which is up to 3km wide and 300km long. The shear zone is characterised by high-grade assemblages, steeply plunging stretching lineations (L1) and dextral kinematic indicators. The formation of S^C, fabrics, C' shear bands and local ultramylonitic zones indicates intense shearing and high-strain. D2 developed isoclinal F2 folds and a localised NE-SW orientated S2 axial planar cleavage, that was not pervasive. Progressive deformation and retrogression and subsequent tectonic reworking has created a highly recrystallised and structurally complex environment. A strain analysis of the augen gniess was undertaken using both finite strain methods and by qualitative examination of gneissic fabric intensity. Although finite strain estimation met with limited success, results demonstrate a significant component of flattening was responsible for producing strongly oblate strain markers. Analysis of shear zone fabric development reveals strain insensitive composite fabrics that do not accurately reflect the total amount of strain accommodated by the rock. Instead their oblique orientation, relative to the shear zone boundaries reflects non-coaxial strain and may be used as an important kinematic indicator. Deformation fabric analysis resolves the intensely strained nature of the lithologies of Mine Creek, these are dominated by S^C orthogneiss and layered mylonite fabrics. Low-strain fabric features in the granite gneisses are not preserved.
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    Proterozoic strain localisation during the Kimban Orogeny: a structural analysis of Williams Island, Eyre Peninsula, South Australia
    Harrowfield, Mathew ( 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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    Structural and metamorphic constraints on Kimban Orogenesis from southern Eyre Peninsula, South Australia
    Berman, David ( 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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    Sedimentology of the late Neoproterozoic Patsy Springs Canyon, Flinders Ranges, South Australia
    Mornane, Kate ( 2003)
    The Neoproterozoic Patsy Springs Canyon is located within the northern portion of the Adelaide Geosyncline, South Australia. The sedimentary structures found within the canyon fill are consistent with a deep marine origin, and include syn-sedimentary marine phosphates, marine cements, sandstones with partial Bouma sequences, abundant mudstones and various mass flow deposit types (including grain flows, debris flows and slumps). Structures indicative of tidal activity (previously interpreted to be of shallow water origin) are interspersed with Bouma sequences and mass flow deposits and are here interpreted as having been produced by deep-water tidal bottom currents. Rare structures resembling hummocky cross stratification are here interpreted as similarly being of deep-water origin. This deep water interpretation for the canyon fill contradicts previous shallow water models and alleviates the need for extraordinary changes in base level, required by such shallow water models. A deep-water submarine origin for the canyon is also more consistent with the lack of canyon-synchronous basin-wide unconformity and is more consistent with an open-ocean palaeogeography. This study has resolved some of the ambiguity surrounding the origin of the Wonoka canyons by providing sedimentological evidence to suggest that they may in fact represent ancient submarine canyons.
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    Physical and chemical hydrogeology of the Otway Basin, southeast Australia
    Bush, Angela L. ( 2009)
    The Otway Basin of southeast Australia is the subject of this thesis, which incorporates pre-existing geological, hydraulic and major element hydrogeological data with new isotope hydrogeochemical investigations. The region is an Upper Cretaceous–Tertiary basin, filled with siliciclastic and calcareous aquifers and aquitards and characterised by late volcanic activity, pervasive faulting and karstification. (For complete abstract open document.) As part of this study, an hydrogeological database is compiled for the Otway Basin region from existing distinct datasets from the states of Victoria and South Australia. Utilising this new resource, the data are reinterpreted into a 3D model of the hydrostratigraphy for the basin in GoCAD, and interpolated surfaces of hydraulic head and electrical conductivity are created for 5 aquifers/aquitards. The Victorian hydraulic head data is analysed for long term declining or inclining trends and hydrograph trend maps are created for different aquifer systems. The data are also compiled into representative cross sections of flow and chemical composition, with one section located in each of the three major sub-basins. The records of groundwater chemistry from the Victorian section of the Otway Basin are used to plot the relative concentration of major cations and anions for the main aquifers. More than 120 groundwater samples were taken for analysis of major and minor ion concentration and/or oxygen, hydrogen, carbon, strontium and chlorine isotope composition. These data are used to characterise the hydrogeochemical evolution of the groundwater and to identify the processes that the groundwater drives or experiences in the system. The potentiometric maps and cross sections reveal the interconnected nature of the flow in all aquifers and the relationship between local and regional flow systems. Regional flow paths originate inland near basement highs or the basin margins. In the shallower aquifers they terminate at the coastline where the groundwater mixes with ocean water at a diffuse interface and density differences induce groundwater discharge at the land surface or the ocean floor. In the deeper confined aquifers, discharge is submarine via several possible mechanisms, which include: diffuse intergranular leakage to overlying units; flow along faults or volcanic conduits; and/or seepage directly to the ocean from exposed sections of the aquifer, e.g. in submarine canyons. These mechanisms may be operating up to 50 km offshore but the interface is currently migrating landward, which will result in a shortening of that estimated distance. Local-scale flow lines are complex and may be oriented against the direction of regional coastward flow. Local hydraulic divides are often associated with volcanic eruption centres, which have elevated topography and relatively high hydraulic head, making them important recharge zones. These zones contain low salinity groundwater because infiltration is relatively rapid. Conversely, basalt flows that have developed clay horizons through weathering reduce drainage and allow significant evapotranspiration which concentrates the cyclic salts in solution. Many local flow systems discharge mainly via evapotranspiration, which acts again to concentrate the cyclic salts in solution. Other local discharge zones are rivers, creeks and lakes or lagoons that receive baseflow and seeps and springs associated with geological contacts or boundaries and faults. Evaporitic concentration of solutes in surface water bodies and shallow groundwater affects the quality of water recharging the underlying aquifers and aquitards. This quality has changed over the last 50,000 years or so due to fluctuations in climate and hence variation of the precipitation/evaporation ratio. Stresses on the aquifers are climate fluctuations, sea level change, land use change and groundwater extraction. These stresses have resulted in the system being out of hydraulic equilibrium in many cases. Lags in response to these changes in boundary conditions are identified and/or hypothesised. In particular, the confined aquifer’s response to sea level change could be subject to a lag in the order of millennia. The stress on an aquifer is often transferred to its adjacent units, in some cases inducing cross-formational leakage, which is possibly supported by radiocarbon dating evidence. The area of the Otway Ranges appears to have escaped the effects of stress to date because of its stable microclimate, its distance from the ocean and from groundwater extraction. Increase in demand on groundwater resources, development of geothermal, sequestration and hydrocarbon industries and future climate change may yet have a detrimental effect on the groundwater of the Otway Basin. Isotopic composition of the groundwater confirms its meteoric origin and chlorine isotopes from several samples of the deep groundwater indicate that accumulation of solutes along the flow path is not due to diffusion or dissolution of connate salt. Thus, the salinity of the water is sourced from cyclic salts and solutes from water-rock interaction, both of which may be concentrated by evapotranspiration. Water-rock interaction is dominated by dissolution of carbonates and weathering of silicates as a result of the surficial geology being dominated by calcarenite or limestone and young basalt. The volcanic activity has produced gas that has interacted with the groundwater, and continues to do so, fractionating oxygen, hydrogen and carbon isotopes and contributing fluorine, boron and sulphur to solution. The addition of volcanic CO2 creates an uncommon situation for water-rock interaction, where continued dissolution of carbonate and silicate minerals along the deeper flow paths is demonstrated by the silicon/chloride ratios and strontium isotopic composition of the groundwater. These water-rock interaction processes, with the addition of cation exchange, are responsible for the development of a relatively fresh Na+HCO− 3 type water that is characteristic in parts of the deep aquifer. The study confirms the existing hydrogeological understanding of the Otway Basin and forms new conclusions regarding the history of the groundwater and the processes of flow and chemical evolution by integrating numerous lines of evidence. Significant contributions of this work which improve current scientific knowledge include these findings: the maps and cross sections of hydraulic head and electrical conductivity reveal the connected nature of flow systems within all the aquifers and aquitards; geological features can induce discharge, e.g. at contacts or faults, and recharge, e.g. volcanic eruption centres; the changes to the surface drainage system as a result of the eruption of basalt flows have affected the water chemistry and flow systems in all the underlying units; there is a lag in aquifers’ responses to sea level change and therefore future migration of the interface is expected regardless of further boundary changes; climate change has influenced surface water quality by changing the regional water balance, and therefore has affected groundwater quality; the discharge from the confined aquifer is submarine via various pathways, interaction between the groundwater and volcanic gas has occurred in the past and is ongoing, and consequently mineral dissolution persists at deep levels; the origin of high salinity of brackish groundwater in all Tertiary aquifers and aquitards is concentrated solutes from water rock interaction and cyclic deposition.