A Subduction Scissor and Development of the Intervening Plate Collision at South Island, New Zealand
The continental plate collision across South Island, New Zealand is bounded to the north by west-dipping Hikurangi subduction of the Pacific plate and to the south by east-dipping Fiordland-Puysegur subduction of the Australian plate. As such, South Island is in the midst of a type of 'subduction scissor'. The tectonic behaviour of the deep plate portion of South Island (viz., the sub-crustal portion of the lithosphere) is unresolved. Previous studies suggest it may be undergoing subduction-like consumption or Rayleigh-Taylor-type viscous instability. We consider these possibilities but in the three-dimensional tectonic context of the subduction scissor. In particular, using 3D computational geodynamic models we explore how the evolution of the continental plate collision is controlled by the adjacent and opposite-facing subduction zones. In the absence of the subduction forcing, the subduction/drip structure develops as a near-vertical sheet. With imposed subduction on the edges, the plate consumption is still steep, but there is appreciable flow along the strike of the collisional plate boundary that results in localized accumulations and gaps in the consumed plate. The response of the model South Island to the subduction scissor depends largely on the rates of subduction and the continental lithospheric rheology. Recent interpretations of the morphology of deep lithospheric structure beneath South Island from geophysical observables indicate that there may be similar along-strike variations in the consumed plate/blob.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 8104 Continental margins: convergent;
- 8120 Dynamics of lithosphere and mantle: general (1213);
- 8170 Subduction zone processes (1031;