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Preprints
https://doi.org/10.5194/se-2020-80
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-80
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  18 May 2020

18 May 2020

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A revised version of this preprint was accepted for the journal SE and is expected to appear here in due course.

Distribution, microphysical properties, and tectonic control of deformation bands in the Miocene accretionary prism (Whakataki Formation) of the Hikurangi subduction zone

Kathryn E. Elphick1, Craig R. Sloss1, Klaus Regenauer-Lieb2, and Christoph E. Schrank1 Kathryn E. Elphick et al.
  • 1School of Earth and Atmospheric Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia
  • 2School of Petroleum Engineering, University of New South Wales, Sydney, NSW, Australia

Abstract. We analyse deformation bands related to both horizontal contraction and horizontal extension in Miocene turbidites of the Whakataki Formation south of Castlepoint, Wairarapa, North Island, New Zealand. In the Whakataki Formation, four sets of cataclastic deformation bands are identified: (1) normal-sense Compactional Shear Bands (CSBs); (2) normal-sense Shear-Enhanced Compaction Bands (SECBs); (3) reverse-sense CSBs; and (4) reverse-sense SECBs. During extension, CSBs form most frequently with rare SECBs. Extensional CSBs are often, but not exclusively, associated with normal faults. During contraction, distributed SECBs are observed most commonly, sometimes clustering around small reverse faults and thrusts. Contractional CSBs are primarily found in the damage zones of reverse faults. The quantitative spacing analysis shows that most outcrops are characterised by mixed spatial distributions of deformation bands, interpreted as a consequence of overprint due to progressive deformation or distinct multiple generations of deformation bands from different deformation phases. Since many deformation bands are parallel to adjacent juvenile normal- and reverse-faults, bands are likely precursors to faults. With progressive deformation, the linkage of distributed deformation bands across sedimentary beds occurs to form through-going faults. During this process, bands associated with the wall-, tip-, and interaction damage zones overprint earlier distributions resulting in complex spatial patterns. Regularly spaced bands are pervasively distributed when far away from faults. Microstructural analysis shows that all deformation bands form by inelastic pore collapse and grain crushing with an absolute reduction in porosity relative to the host rock between 5 and 14 %. Hence, deformation bands likely act as fluid flow barriers. Faults and their associated damage zones exhibit a spacing of order ten metres on the scale of 10 km and are more commonly observed in areas characterised by higher mudstone to sandstone ratios. As a result, extensive clay smear is common in these faults, enhancing the sealing capacity of faults. Therefore, the formation of deformation bands and faults leads to progressive flow compartmentalisation from the scale of ten metres down to about ten centimetres, the typical spacing of distributed deformation bands.

Kathryn E. Elphick et al.

Kathryn E. Elphick et al.

Kathryn E. Elphick et al.

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Latest update: 01 Dec 2020
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Short summary
We analysed a sedimentary rock package located in Castlepoint, New Zealand, to test the control of the tectonic setting on the observed deformation structures. In extension and contraction, we observed faults and small fault-like structures characterised by complex spatial patterns and a reduction in porosity and grain size compared to the host rock. With these properties, the structures are likely to act as barriers to fluid flow and cause compartmentalisation of the sedimentary sequence.
We analysed a sedimentary rock package located in Castlepoint, New Zealand, to test the control...
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