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. We analyse deformation bands related to horizontal contraction with anintermittent period of horizontal extension in Miocene turbidites of theWhakataki Formation south of Castlepoint, Wairarapa, North Island, NewZealand. In the Whakataki Formation, three sets of cataclastic deformationbands are identified: (1) normal-sense compactional shear bands (CSBs), (2) reverse-sense CSBs, and (3) reverse-sense shear-enhanced compaction bands(SECBs). During extension, CSBs are associated with normal faults. Whenpropagating through clay-rich interbeds, extensional bands are characterisedby clay smear and grain size reduction. During contraction,sandstone-dominated sequences host SECBs, and rare CSBs, that are generallydistributed in pervasive patterns. A quantitative spacing analysis showsthat most outcrops are characterised by mixed spatial distributions ofdeformation bands, interpreted as a consequence of overprint due toprogressive deformation or distinct multiple generations of deformationbands from different deformation phases. As many deformation bands areparallel to adjacent juvenile normal faults and reverse faults, bands are likelyprecursors to faults. With progressive deformation, the linkage ofdistributed deformation bands across sedimentary beds occurs to formthrough-going faults. During this process, bands associated with the wall-,tip-, and interaction-damage zones overprint earlier distributions resultingin complex spatial patterns. Regularly spaced bands are pervasivelydistributed when far away from faults. Microstructural analysis shows thatall deformation bands form by inelastic pore collapse and grain crushingwith 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 9 m onthe scale of 10 km and are more commonly observed in areascharacterised by higher mudstone-to-sandstone ratios. As a result, extensiveclay smear is common in these faults, enhancing the sealing capacity offaults. Therefore, the formation of deformation bands and faults leads toprogressive flow compartmentalisation from the scale of 9 m down toabout 10 cm – the typical spacing of distributed, regularly spaceddeformation bands.

solid earth

Distribution, microphysical properties, and tectonic controls of deformation bands in the Miocene subduction wedge (Whakataki Formation) of the Hikurangi subduction zone