School of Earth Sciences - Theses
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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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ItemThe stratigraphy and palaeontology of Cape Vani, Milos, Greece( 2005)Milos, dominated by Pliocene-Recent explosive calc-alkaline volcanics, is in the active Aegean Arc. This project investigated the microfauna and depositional environment of a sequence associated with the only terrestrial white smoker field in the world. White smokers occur in a volcaniclastic-hosted Mn-Fe-Ba deposit in a 1 km2 rift basin associated with dacite intrusives. Although the sediments are extensively hydrothermally altered, they have sedimentary structures and yield a variety of micro- and macrofossils. The typical microfaunal assemblage comprises Miliolinids (e.g. Quinqueloculina spp.; Triloculina spp.) and Elphidiids (Elphidium spp.). In the absence of any planktonic foraminifera, this assemblage is typical of inner shelf palaeodepths from around 10-50m. The occurrence of this fauna with echinoderm spines indicates an open marine setting with normal salinity levels. The associated coarse-grained burrowed facies with symmetrical ripples and hummocky cross stratification and a macrofauna of molluscs (e.g. pectinids, Mytilus, fish teeth) further indicates a shallow marine setting. Terrestrial artiodactyl megafauna occur at three levels in tuff and trough cross-laminated fluvial deposits suggesting close proximity to a regressive shoreline. Macrofauna were probably killed by tephra, rapidly disarticulated and removed into a shallow marine environment. The sequence is unconformably overlain by coarse-grained alluvial fan to braided river deposits deposited when Milos became emergent. Barite-silica white smokers derive from the ingress of and leaching by seawater into basement and overlying volcanics. Palaeontological-boiling data shows the fluid was at 165-140°C and the extremophile echinoderm spicule microfauna dominated because forams were unable to live in warm silica-laden turgid fluids with a high heavy metal content.
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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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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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ItemGeology of the Club Terrace district, East Gippsland( [1983])The mapping and laboratory projects are a combined study of the Club Terrace district. Part of the laboratory project will involve structural analysis of drill core, obtained from the study area by Samedan of Australia, in an attempt to relate the mineralization to structural and sedimentological features. (From Introduction)