Geometry of the Hikurangi subduction thrust and upper plate, North Island, New Zealand
Abstract
We use 2800 line km of seismic-reflection data to map the offshore character and three-dimensional geometry of the Hikurangi subduction thrust and outer forearc wedge to depths of c. 15 km. Several first order subduction characteristics (e.g., convergence rate, apparent plate locking, margin morphology) vary systematically over relatively short along-strike distances on the Hikurangi margin, making it an excellent natural laboratory for studying subduction tectonics assessing the significance of variations in subduction thrust geometry. For 200 km along-strike south of Hawke Bay, the subduction thrust is relatively smooth, dips less than 8 degrees, and the wedge is characterised by accretion of young sediment and topographic slopes of less than 3 degrees. In Hawke Bay and north for 200 km, a kink in the subduction thrust is apparent, with a down-dip increase in dip to angles greater than 8 degrees at depths of 10-15 km; there is a corresponding steepening of the topographic slope to greater than 3 degrees outboard of the kink and the wedge is characterised by lithified sedimentary rock and slope failure. We suggest that the kink in the subduction thrust is caused by a combination of a northward change in subducting lithosphere chemistry and subduction rate that, in turn, controls fluid release rates and intra-slab deformation patterns. The subduction thrust geometry, in combination with a northward increase in subducting plate roughness and decrease in sediment cover, causes the observed spatial change in character of the subduction thrust and forearc wedge.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T23A1998B
- Keywords:
-
- 3025 Marine seismics (0935;
- 7294);
- 3060 Subduction zone processes (1031;
- 3613;
- 8170;
- 8413);
- 8104 Continental margins: convergent;
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413)