Subduction Evolution And Dynamics (SEAD)

A proposed seismic reflection-refraction experiment of the Tonga-Kermadec subduction and back-arc system

Call for expression of interest

Proposed date of acquisition: Summer 2005-2006
Project leader: Stuart Henrys
Part of a FRST-funded program The Effects of Plate Tectonics on New Zealand
Program leader: Rupert Sutherland

Global Science motivation

• The subduction of oceanic plates provides the main driving force for global plate motions, but how subduction zones initiate and then evolve to a stable geometry remains poorly understood.
• The Tonga-Kermadec system is one of the few places on Earth where many features of present and past subduction systems can be studied, including: oceanic plateau, trench, accretionary prism, axial range, active andesite volcanoes, back-arc rift, fold and thrust belt and foreland basin.
• Australia-Pacific plate motion is well constrained over the last 43 million years period and better understanding the structure of subduction system, will provide an important constraint on the and the dynamics of convergent margins.
• Determining crustal structure of northern New Zealand will help to solve the enigma of plate reconstruction in the south west Pacific - a vital cog in global plate circuit.

Please contact Stuart Henrys for further information

Figure 1. Proposed transect lines,
shown on gravity anomaly map.

Structures	Target depths (km)	MCS1	OBS2	O-O3	Tele- seismics 4	Comment
Pacific Plate subduction interface	5 - 20	*	*
Back-arc rifted structures	5 - 30	*	*
Miocene Subduction interface	10-40	*	*	*		Postulated north-eastward facing system offshore Northland
Volcanic intrusions/melt conduit	5 - 40			*	*	Active volcanic field beneath Auckland City
Sedimentary reflections and sediment-basement contact	1 - 8	*	*
Allochthon structures	5 - 20	*	*	*

1 Multichannel Channel Seismic: Airgun source > 8000 cu in Hydrophone array with ~ 6 km offset 2 Ocean Bottom Seismometer deployment ~ 25 km spacing 3 Onshore-offshore deployment: onshore receiver spacing ~1 km 4 Receiver function analysis of teleseismic events will provide further constraints on crustal models