High resolution analysis of slope basins on the Hikurangi subduction margin, Eastern North Island, New Zealand
Abstract
The development and evolution of slope basins on accretionary wedges are strongly related to the activity of subduction. Yet, the relationships between the parameters of subduction and the sedimentary/tectonic records within these basins are poorly constraints. We carried out a high resolution study of slope basins across an oblique convergent margin in order to precise these relationships. The North Island of New Zealand is characterized by the westward subduction of the Pacific plate. The onset of the subduction beneath the North Island, 25 My ago, led to the development of an accretionary wedge. The detailed structural analysis of the emerged part of the margin suggests a succession of major tectonic events rather than an homogeneous continuous deformation since the onset of subduction. It shows a succession of deformational episodes that are dominated by important shortening (25-18 Myr and c. 6-0 Myr) or by extension (e.g. 10-6 Ma). The structural development of the active margin can be constrained from the sedimentary infill of slope basins on the accretionary wedge. Our study focus on the sedimentary record of these basins onshore (characterization of facies, geometry and vertical evolution of sedimentary bodies, subsidence evolution, ...) and offshore (seismic stratigraphy) completed by tectonic analysis at different scales. During early and middle Miocene, for exemple, major sedimentary sequences have been identified within the thick turbiditic infill of the onshore slope basins : 1) olistostromes and flysch (linked to the onset of the subduction 25 Myr ago), 2) settlement of a lowstand system tract which shows at its base a containment of the depositional environment (individualisation of slope basins during shortening at 18.5 Myr), 3) brutal change in the turbidites sequences marked by the deposition of deep sea plain turbidites (major subsidence, beginning of extension at c. 13 Myr ?). Offshore seismic data also present some major unconformities of similar ages. The basins evolution can then be compared with their onshore equivalents. The major angular unconformities are correlated to onshore slope basins. However some local sedimentary discontinuities are identified only onshore. That is a possible signature of local geodynamic processes (e.g. seamounts subduction, strain partitioning) rather than markers of general margin deformation (accretion, tectonic erosion ...).
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....1222B