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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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 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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ItemGeology of the Dookie District (Part I) & Trace element distributions within some major stratiform orebodies (Part II)( 1973)Part I: The Cambrian rocks outcropping in the Dookie district consist of a series of altered igneous rocks (diabases), a variety of pyroclastic rocks and cherts. The igneous rocks are thought to have been originally tholeiitic, having undergone low grade burial metamorphism, hydrothermal alteration and possibly contact metamorphism. Field evidence indicates that at least one of the igneous bodies is intrusive, probably a sill. The relation between these rocks and Cambrian rocks elsewhere in Victoria is discussed. The lithology and structure of an area of folded Ordovician and Silurian — L. Devonian sediments outcropping to the south of the main Cambrian massif is reviewed. Part II: Trace elements Tl, Ag and Au abundances in whole rock samples from a number of important stratiform basemetal orebodies have been determined by neutron activation analysis. Suites of samples were taken from the HYC Zn-Pb-Ag deposit at McArthur River, N.T., the Cu-Pb-Zn deposit of Rosebery, Tasmania and a Karoko type orebody from Shakanai, Japan. While the distribution of Au and Ag in the three deposits were found to closely follow those of Cu and Pb respectively, a higher Ag/Au ratio is apparent in the HYC deposit. In the other deposits, probably formed at temperatures greater than 200°, high concentrations of Au are explainable in terms of high temperature transport via chloride or thiocomplexing, while in the HYC deposit, formed below 150°, hydrothermal transport of comparable amounts of Au is considered unlikely. In response to lower temperature, strongly reducing conditions and restricted circulation, Tl concentrations in the HYC deposit are markedly greater than those in the remaining deposits. At McArthur River, significant enrichments in Tl occur up to, 250 metres stratigraphically above the main ore shales, and the geochemical significance and practical value of such metal haloes about stratiform orebodies are discussed.
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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.
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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.