Along-strike Transitions in Subduction Characteristics, Hikurangi Margin, New Zealand
Abstract
The Hikurangi subduction margin, North Island, New Zealand, shows systematic variation in subduction characteristics moving along strike. With many features observable at relatively shallow depths, the margin is an excellent natural laboratory for observing and subsequently trying to understand the effects of different physical relationships on subduction behaviour. Moving south to north along strike, many subduction features change: convergence rate at the trench doubles from ~30 mma-1 to ~60 mma-1 coupled with rotation of the margin and onset of back-arc extension; the accretionary wedge narrows from ~200 km to only ~10 km wide with steep seafloor topography; sediment cover on the subducting Pacific plate decreases; plate roughness increases; and, the interface transitions from locked to un-coupled inter-seismic behaviour. Offshore multi-channel seismic (MCS) reflection data have characterised the structural differences between the accretionary margin to the south and non-accretionary margin to the north, and we have recently documented a pronounced steepening in dip of the shallow interface moving north about a kink in the subducting slab, with correlated steeper seafloor topography and greater overall wedge taper. In addition to a few deeper events, shallow (<15 km) slow slip events (SSE) are characteristic of the margin, clustered in the northern Hawke Bay and offshore Gisborne region (4 events), and offshore south of Cape Kidnappers (2 events). For the Gisborne events, reflection characteristics in MCS data have been used to show that second-order corrugations of the interface superimposed on the first-order plate interface kink may focus fluid flow and facilitate SSE. Here we review some of these observations, particularly from MCS data, and examine MCS data on the southern margin in the vicinity of the southern shallow SSEs and the transition from plate interface inter-seismic locking to slipping. We note a highly reflective wedge of imbricate thrust slices of old rocks coring the inner-to-outer wedge transition and speculate on its significance for subduction characteristics of the southern margin.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T23B1906B
- Keywords:
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- 3025 MARINE GEOLOGY AND GEOPHYSICS / Marine seismics;
- 3060 MARINE GEOLOGY AND GEOPHYSICS / Subduction zone processes;
- 8170 TECTONOPHYSICS / Subduction zone processes