Kinematic,finite strain and vorticity analysis of the Sisters Shear Zone,Stewart Island,New Zealand |
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| Institution: | 1. Department of Physics, University of North Bengal, Siliguri 734013, West Bengal, India;2. Department of Physics, Chakdaha College, Chakdaha, Nadia 741222, West Bengal, India;3. Department of Physics, Dinhata College, Dinhata, Cooch Behar 736135, West Bengal, India;4. Department of Computer and Information Sciences, SUNY at Fredonia, Fredonia, New York 14063, USA |
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| Abstract: | The Sisters Shear Zone (SSZ) on Stewart Island, New Zealand, is a greenschist-facies extensional shear zone active prior to and possibly during the development of the Pacific–Antarctica spreading ridge at ∼76 Ma. We report quantitative kinematic and rotation data as well as apatite fission-track (AFT) ages from the SSZ. Early kinematic indicators associated with the NNE-trending stretching lineation formed under upper greenschist-facies metamorphism and show alternating top-to-the-NNW and top-to-the-SSE senses of shear. During progressive exhumation lowermost greenschist-facies and brittle-ductile kinematic indicators depict a more uniform top-to-the-SSE sense of shear in the topmost SSZ just below the detachment plane. Deformed metagranites in the SSZ allow the reconstruction of deformation and flow parameters. The mean kinematic vorticity number (Wm) ranges from 0.10 to 0.89; smaller numbers prevail in the deeper parts of the shear zone with a higher degree of simple shear deformation in the upper parts of the shear zone (deeper and upper parts relate to present geometry). High finite strain intensity correlates with low Wm and high Wm numbers near the detachment correlate with relatively weak strain intensity. Finite strain shows oblate geometries. Overall, our data indicate vertical and possibly temporal variations in deformation of the SSZ. Most AFT ages cluster around 85–75 Ma. We interpret the AFT ages to reflect the final stages of continental break-up just before and possibly during the initiation of sea-floor spreading between New Zealand and Antarctica. |
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| Keywords: | Shear zone Structural analysis Kinematic vorticity Finite strain Extensional deformation New Zealand |
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