FROM OBLIQUE SUBDUCTION TO INTRACONTINENTAL TRANSPRESSION - STRUCTURES OF THE SOUTHERN KERMADEC-HIKURANGI MARGIN FROM MULTIBEAM BATHYMETRY,SIDE-SCAN SONAR AND SEISMIC-REFLECTION

The southern Kermadec-Hikurangi convergent margin, east of New Zealand , accommodates the oblique subduction of the oceanic Hikurangi Plateau at rates of 4-5 cm/yr. Swath bathymetry and sidescan data, together w ith seismic reflection and geopotential data obtained during the GEODY NZ-SUD cruise, showed major changes in tectonic style along the margin . The changes reflect the size and abundance of seamounts on the subdu cting plateau, the presence and thickness of trench-fill turbidites, a nd the change to increasing obliquity and intracontinental transpressi on towards the south. In this paper, we provide evidence that faulting with a significant strike-slip component is widespread along the enti re 1000 km margin. Subduction of the northeastern scarp of the Hikuran gi Plateau is marked by an offset in the Kermadec Trench and adjacent margin, and by a major NW-trending tear fault in the scarp. To the sou th, the southern Kermadec Trench is devoid of turbidite fill and the a djacent margin is characterized by an up to 1200 m high scarp that loc ally separates apparent clockwise rotated blocks on the upper slope fr om strike-slip faults and mass wasting on the lower slope. The norther n Hikurangi Trough has at least 1 km of trench-fill but its adjacent m argin is characterized by tectonic erosion. The toe of the margin is i ndented by 10-25 km for more than 200 km, and this is inferred to be t he result of repeated impacts of the large seamounts that are abundant on the northern Hikurangi Plateau. The two most recent impacts have l eft major indentations in the margin. The central Hikurangi margin is characterized by development of a wide accretionary wedge on the lower slope, and by transpression of pre subduction passive margin sediment s on the upper slope. Shortening across the wedge together with a comp onent of strike-slip motion on the upper slope supports an interpretat ion of some strain partitioning. The southern Hikurangi margin is a na rrow, mainly compressive belt along a very oblique, apparently locked subduction zone.