HR: 1330h
AN: T52C-0283    [PDF]
TI: The Dynamics of Deformation across the Southern Hikurangi Margin
AU: * Hall, L S
EM: lisa.hall@earth.ox.ac.uk
AF: COMET, Department of Earth Sciences Oxford University Parks Road, Oxford, OX1 3PR United Kingdom
AU: Lamb, S H
EM: simon.lamb@earth.ox.ac.uk
AF: COMET, Department of Earth Sciences Oxford University Parks Road, Oxford, OX1 3PR United Kingdom
AB: New Zealand lies on the plate boundary between the obliquely converging Australian and Pacific Plates. Off the east coast of the North Island, this motion is accommodated by subduction of the Pacific Plate along the Hikurangi Margin. This system terminates northeast of the South Island, where the motion is transferred onto the transpressive Marlborough Fault System. At this transition between subduction and continental collision, a portion of the convergent component of relative plate motion is accommodated across a fold-and-thrust belt, which lies above the plate interface with the subducted slab. Regional structural and geomorphic data indicates that the deformation, both in this fold-and-thrust belt and further north along the margin, has accelerated within the last 1--2 Myr. This cannot be explained by changes in the relative plate motion and, as little is understood about the dynamics of this system, there are currently no constraints on why it has begun to deform more actively. In this study critical wedge modelling, topographic buoyancy stress calculations and heat flow data are used to better constrain the dynamic properties of the fold-and-thrust system. Of the three different rheological critical wedge models tested, a bulk plastic rheology best describes the surface topography and strain partitioning observed. The models also show that the relative strength of the underlying plate interface compared to the wedge is rather higher than in other subduction systems, in agreement with published seismic and geodetic data. The wedge modelling results, combined with buoyancy stress contrast calculations along the length of the Hikurangi Margin, give a estimate for the shear stress on the underlying plate interface of between 12--18 MPa. The dynamic framework of these models is used to provide plausible explanations for the recent acceleration in deformation. These include increased rates of erosion and sediment accretion in association with climate change over the last $\sim$ 0.8 Myr, or a change in the buoyancy of the subducted slab.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8158 Plate motions--present and recent (3040)
DE: 8168 Stresses--general
DE: 9355 Pacific Ocean
SC: Tectonophysics [T]
MN: 2003 Fall Meeting