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How clay mineral assemblages affect instability on the upper slope of the Hikurangi subduction zone, New Zealand
  • Michael Underwood,
  • Brandon Dugan,
  • Sebastian Cardona
Michael Underwood
New Mexico Institute of Mining and Technology

Corresponding Author:underwoodm@missouri.edu

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Brandon Dugan
Coloardo School of Mines
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Sebastian Cardona
Texas A&M University
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The International Ocean Discovery Program cored Sites U1517 (Tuaheni landslide complex) and U1519 (upper Tuaheni Basin) on the Hikurangi margin, North Island, New Zealand. Strong ocean currents result in unusual amounts of compositional homogeny in the muds. Detrital smectite dominates among clay minerals, with average proportions of 52 wt% at Site U1517 and 53 wt% at Site U1519. Bulk sediment from Site U1517 contains up to ~29 wt% smectite (average = 21 wt%), high enough to reduce the angle of internal friction (on average) to ~6°. There are no compositional excursions along inferred slip surfaces or weak layers. Smectite decreases toward the SW in the “downstream” direction of the East Cape Current, and that spatial trend correlates with lower densities of slide scars.