Paper No. 68-12
Presentation Time: 4:55 PM
NEW INSIGHTS INTO HIKURANGI SUBDUCTION INPUTS, ACCRETIONARY WEDGE, AND PLATE INTERFACE HOST ROCKS SPANNING ALONG-STRIKE CHANGES IN FAULT SLIP BEHAVIOR, NEW ZEALAND
BARNES, Philip1, DAVIDSON, Sam R.2, GASE, Andrew C.3, HENRYS, Stuart A.4, MOUNTJOY, Joshu J.1, BASSETT, Dan4, CRUTCHLEY, Gareth J.5, WALLACE, Laura M.6, ELLIS, Susan4 and UNDERWOOD, Michael B.7, (1)Ocean Geology, National Institute of Water and Atmospheric Research (NIWA), 301 Evans Bay Parade, Greta Point, Wellington, 6021, New Zealand, (2)Ocean Geology, National Institute of Water and Atmospheric Research (NIWA), 301 Evans Bay Parade, Greta Point, Wellington, 6021, New Zealand; School of Earth and Environment, University of Canterbury, Christchurch, 8140, New Zealand, (3)Department of Geology, Western Washington University, Bellingham, WA 98225, (4)GNS Science, Lower Hutt, 5040, New Zealand, (5)GEOMAR Helmholtz Centre for Ocean Research, Wischhofstr. 1-3, Kiel, 24148, Germany, (6)Institute for Geophysics, University of Texas at Austin, PO Box 7456, Austin, TX 78713; GEOMAR Helmholtz Centre for Ocean Research, Wischhofstr. 1-3, Kiel, 24148, Germany, (7)Department of Earth & Environmental Science, New Mexico Institute of Mining & Technology, Socorro, NM 87801
The Hikurangi subduction margin exhibits well documented spatial variations in convergence rate, trench sediment, accretionary wedge structure and geomorphology, and fault slip behavior ranging from stick-slip megathrust earthquakes to slow slip events (SSEs) and creep. Precisely what controls the fault slip behavior is not well understood, but variations in lithology, physical properties, subducting plate relief, and pore pressure regime have been implicated. Previous studies have interpreted (i) a northern margin impacted by subducting seamounts, and a weakly coupled plate interface comprising volcaniclastic and calcareous rocks that host fault creep phenomena including SSEs, and (ii) a wider, low tapered central - southern margin inboard of thick subduction inputs and a strongly coupled plate interface that, for up to 75 km landward, appears to be hosted in the plateau’s sedimentary cover sequence. Given that megathrust slip behavior and upper plate thrust faulting have implications for earthquake and tsunami hazard, it is vital to improve understanding of the sequences that host the plate interface, accrete, and subduct.
Prior to International Ocean Discovery Program (IODP) Expeditions 372 and 375, the incoming plate and cover sequence at the deformation front had never been drilled and directly dated. Regional seismic reflection profiles tied to drilling data and core from IODP Site U1520 in the northern Hikurangi Trough provide new insights into the composition and structure of the subduction inputs, accretionary wedge, and plate interface spanning along-strike changes in fault slip behavior. We observe (i) widespread extensional faulting and late-stage volcanism in the subducting Hikurangi Plateau, (ii) current-influenced sedimentation, erosional surfaces, and polygonal faulting in the Paleogene-Neogene calcareous pelagic cover, (iii) thick (0.5-6 km) Plio-Pleistocene clastic trench turbidites that are younger than previously inferred, implying higher rates of sedimentation and tectonic shortening, (iv) clay mineral assemblages that vary strongly with time, (v) a plate interface that smoothens southwards across the region of transitional slip behavior, and (vi) a southern interface widely hosted at the base of smectite-rich calcareous mudstones immediately overlying chalk.
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