Shear zones of the Maud Belt, Antarctica : kinetics and deformation mechanisms
Master Thesis
2014
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University of Cape Town
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Abstract
The rocks of the Maud Belt, western Dronning Maud Land, Antarctica, have experienced at least two deformation phases related to the Grenvillian and Pan- African orogenies. Deformation is heterogeneous and strain is commonly localized within shear zones. The two study areas H.U. Sverdrupfjella and Neumayerskarvet mainly consist of paragneisses and orthogneisses and in places migmatites and granite intrusions. The orthogneisses and paragneisses mainly consist of coarse to medium grained quartz, feldspar and biotite and in places hornblende, garnet and epidote. The rock types only differ in the proportion of these minerals, the paragneisses having a higher proportion of biotite than the orthogneisses. Both study areas contain well developed lineations, defined by elongated quartz grains and in places hornblende and epidote, and a S₁+₂ foliation defined by biotite. The foliation is related to the shear zones in the region which are commonly sub-horizontal but locally sub-vertical in eastern Neumayerskarvet. In eastern Neumayerskarvet the paragneisses wrap around the competent orthogneiss units, resulting in sub-vertical strike-slip shear zones alongside the competent orthogniess units. Two differently orientated lineations are found in the study areas, a weak, shallow plunging, E-trending lineation that occurs within the host rock and always alongside a well developed, shallow plunging, SE-trending lineation. Within the shear zones only the SE-trending lineation is found. The presence of only the SE-trending lineation in the shear zones implies that the SE-trending lineation is associated with a more recent deformation phase, D₂, and that the weak Etrending lineation is associated with an older deformation phase, D₁. Two major collisional events affected the region, the Grenvillian (~1300 Ma to ~900 Ma) and the Pan-African (~600 Ma to ~450 Ma). D₂ is therefore likely associated with the Pan-African orogeny and D₁ with the older Grenvillian orogeny. Evidence for D₁ is distributed broadly within the host rock and is absent from the shear zones. If D₁ localized shear zones did exist, they have been overprinted by D₂. The presence of only D₂ in the shear zones implies that strain in D₂ was localized. The strain partitioning into narrow shear zones during the more recent deformation phase could be due to pre-existing fabrics from an earlier deformation phase. Superposition of later deformation into zones of pre-existing fabrics could be typical of areas that have experienced multiple deformation phases.
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Includes bibliographical references.
Reference:
McGibbon, D. 2014. Shear zones of the Maud Belt, Antarctica : kinetics and deformation mechanisms. University of Cape Town.