School of Earth Sciences - Theses

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Start date: 1996 × End date: 1996 × Type: Honours thesis ×

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    A structural analysis of Wanna, South Australia: the comparative behaviour of Mafic dykes and granite during deformation
    Bales, Thomasin ( 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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    Geology of the lookout area, Eyre Peninsula, South Australia
    Annear, Joshua A. ( 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.