School of Earth Sciences - Theses
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ItemAltitudinal distribution of vegetation in the headwaters of the Wongungarra River, Victoria( 1993)Changes in vegetation composition with respect to altitude were investigated in the sclerophyllous forests of the Australian mountain region. Vegetation was surveyed at 148 sites along two transects which were located to maximise variation in altitude and minimise the influence of environmental factors not directly related to altitude. The measurement, simulation, and estimation of environmental variables revealed that this aim was met except at the end-points of the transects where secondary influences are present.
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ItemGeology and tectonothermal history of The Fishery Bay Region, Eyre Peninsula, South Australia( 1998)The Fishery Bay region, southern Eyre Peninsula, South Australia, consists of Archaean charnockitic and paragneissic sequences of the Sleaford Complex intruded by Palaeoproterozoic granitoids and two generations of mafic dykes. These rocks preserve the deformational and metamorphic effects of the Kimban Orogeny and the later Wartakan Event. Within the Fishery Bay area, five separate ductile deformation events (D1-D5) are recognised, the dominant of which (D2-D3) are associated with granulite facies metamorphism. The effects of the D3 event are pervasive throughout the Fishery Bay region, with D1 and D2 preserved only in regions of low-D3 strain. The overprinting nature or D3 is recognised in the reorientation of D2 structures. The dominant response of the area to D3 strain is a series of westerly-dipping dextral oblique reverse shears with west block-up movement. Much of the strain is localised within the paragneisses and along the margins of mafic dykes recognised in the development of a NNE-trending D3 high-strain zone termed the Cape Wiles Shear Zone. D3 observations from the Fishery Bay region correlate well with previous studies conducted on southern Eyre Peninsula which lead to the inference that D3 west block-up exhumation is responsible for the positive pressure gradient that exists from west to east across the Kalinjala Shear Zone. The pressure-temperature conditions preserved in the mineral assemblages of the paragneiss units and mafic dykes record two granulite facies metamorphic events, M2 and M3. Mineral assemblages associated with M2 and M3 are similar and passage from M2 to M3 did not result in reaction textures which indicates the proximity of the thermal conditions of these two metamorphic events. M2 corresponds to the second deformational event (D2) where peak metamorphic conditions reached pressures of 8.6±3.2 kbar at 750-900°C, The second thermobaric event correlates with the third deformation event (D3) and a metamorphic peak of 4.1±1.9 kbar at 750-850°C. The decompression of the Fishery Bay region during D3/M3 is synchronous with crustal thickening of the terrain east of the area.
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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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ItemWestern Victoria lava flow and regolith mapping using Landsat imagery( 1991)The South Ripon area 35 km west of Ballarat was mapped using Landsat TM imagery. The aim of the project was to use the TM data to map the regolith. The regolith forms the majority of the surface. Detailed fieldwork revealed that the regolith could be separated into four main types. These were 1. Later Newer Volcanics (stony rises). 2. Earlier Newer Volcanics. 3. Granites, and 4. Cambro-Ordovician rocks. Of these the granites and stony rises were identified easily as their soil-regolith cover were sufficiently different from the monotonous shades associated with the Earlier Newer Volcanics (ENV) and Cambro-Ordovician rocks. The TM images were treated by several techniques, of which a linear contrast stretch resulted in images comparable with those obtained with principal components and band ratios.
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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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ItemThe geochemistry and petrology of the Enterprise dolerite, Ora Banda, Western Australia( 1998)The Enterprise Dolerite was emplaced as an intrusive tholeiitic sill within the Ora Banda Sequence at Ora Banda in the Eastern Goldfields Province of the Yilgarn Craton. The Enterprise Dolerite is now a metamorphic body with modifications in both the mineralogy and geochemistry of the rocks. Careful analysis of petrographic features integrated with geochemical trends have made it possible to interpret the original igneous characteristics of the sill. It is proposed here that the order of crystallisation in the Enterprise Dolerite is plagioclaseolivine- clinopyroxene-quartz. Furthermore, plagioclase and olivine accumulated through crystal settling before a switch to in-situ crystallisation in the remainder of the sill. The bulk chemistry of the Enterprise Dolerite is equivalent to that of the Mt Ellis Sill which occurs at the same stratigraphic position, and it is proposed here that they are continuations of the same intrusive body. This intrusive body is related to the other mafic members of the Ora Banda Sequence, with all members forming a differentiation trend and in which the Big Dick Basalt represents a primary mantle magma. The Enterprise Dolerite/Mt Ellis Sill has evolved in composition along the trend from this primary magma. Finally, the addition and removal of phases has produced a chemically evolving system with differentiation progressing to maxima in silica and iron concentrations which provide very good conditions tor gold deposition. This study proposes that both the Enterprise Dolerite and the Mt Ellis Sill be examined for future potential gold mineralisation.
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ItemGarnet-bearing metabasic rocks at Mount Joel: an investigation into distribution, petrology and equilibrium thermodynamic modelling( 1998)Garnet-bearing metabasic rocks at Mount Joel, Yilgarn craton, Western Australia, have been studied to determine their distribution, petrography and mineral equilibria. At depth, the orientation of garnet-bearing rocks is approximately 340°N, dipping 60°-70° to the east and mimics that of chloritoid schist and gold mineralisation. Three mineral assemblages at Mount Joel can contain garnet, including: chloritoid-chlorite-plagioclase-quartz-garnet; chlorite-plagioclase-quartz-garnet; chlorite-hornblende-plagioclase-quartz-garnet. Garnets are manganese-rich, composed of up to 23% spessartine. Bulk rock analysis suggests a correlation between manganese enrichment and the appearance of garnet in mineral assemblages. The chemical relationships are consistent with the garnet-bearing rocks being formed from altered basaltic rocks. Thermodynamic calculations have been undertaken using an internally consistent thermodynamic dataset (Powell and Holland, 1990) and THERMOCALC v2.5. Phase diagrams, including Pressure-Temperature (P-T) Projections, P-T Pseudosections and Temperature-Composition (T-X) Pseudosections, have been used to model the mineral equilibria for FeO-MgO-Al2O3-SiO2-H2O (FMASH), Mn-FeO-MgO-Al2O3-SiO2-H2O (MnFMASH)and CaO-Na2O-MnO-FeO-MgO-Al203-Sí02-H2O (CaNaMnFMASH) systems. Upon addition of manganese to a garnet-free system (FMASH), garnet becomes introduced as a new stable phase. As a result, garnet can be present in low pressure and temperature metabasic rocks, such as those at Mount Joel. The variety of mineral assemblages in garnet-bearing rocks at Mount Joel reflects a range in mineral chemistry of the metabasic rocks, possibly due to a range of alteration processes affecting these rocks. The pressure and temperature conditions of formation of garnet-bearing metabasic rocks at Mount Joel have been constrained to about 510 °C at about 3 kbars.
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ItemThe geology of the Pyramid and Tonghi Creek areas, East Gippsland( 1984)A study of the geology of the Club Terrace region is being undertaken with two major aims: 1) to provide a clearer picture of the structural geology and geological history of the region and, using this, 2) to investigate Ag, Cu, Pb, and Zn mineralization present in the region with emphasis on producing a model for ore genesis.
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ItemMobility of base metals through regolith, Broken Hill, N.S.W.( 1993)Regolith profiles over and around zones of Pb-Zn mineralisation were investigated at Maybell and Stirling Vale, located in the Broken Hill region, N.S.W. Metasediments and metavolcanics of the Proterozoic Willyama Supergroup crop out in the study areas, with quartz-gahnite horizons hosting mineralisation. Desert loam soils in the study areas have a transported origin. Locally transported sheetwash deposits overlie a relict aeolian deposit which sits on relatively fresh Proterozoic bedrock. Mineralogy of the regolith profile is consistent with depth and landscape position. Quartz-gahnite horizons form topographic highs in both areas, containing up to 13.5% Zn. Gossanous material is associated with the quartz-gahnite rocks. No base metal containing secondary minerals were present in this weathered material but there were high proportions of iron oxides containing substantial amounts of base metals. Surrounding soils were anomalous in Zn, Cu and their pathfinders Cd and As, which outlines a mobilisation of base metals. Similar anomalies were expressed in stream sediments. Calcrete in the area, contained no anomalous levels of Zn, due to the low solubility of Zn at high pH. The majority of base metals in soils were associated with amorphous iron oxides and silicates (presumably gahnites). These metal bonding sites indicate, dispersion haloes in the regolith are due to a combination of physical and chemical dispersion. In this example of transported regolith profiles in an arid terrain, Zn and Cu are both physically and hydromorphically dispersed from weathering quartz-gahnite horizons.
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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.