School of Earth Sciences - Theses
Permanent URI for this collection
Search Results
1 - 2 of 2
-
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.
-
ItemThe Mine Creek region, Eyre Peninsula, South Australia: a structural analysis of the Kalinjala Shear Zone( 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.