T68 Convergent Margin Systems

Sunday, 15 October 2023
1:30 PM - 5:30 PM
326

NEW INSIGHTS INTO HIKURANGI SUBDUCTION INPUTS, ACCRETIONARY WEDGE, AND PLATE INTERFACE HOST ROCKS SPANNING ALONG-STRIKE CHANGES IN FAULT SLIP BEHAVIOR, NEW ZEALAND

Paper number: T68-16
Program: Technical Sessions
Time: 4:55 PM – 5:10 PM

Authors

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-391426

© Copyright 2023 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.