Abstract - The Southern Taranaki Basin, located between Taranaki Peninsula and northern South Island, contains sedimentary rocks up to 8km thick that record multiple phases of faulting and folding since ~80Ma. The deformation history provides constraints on New Zealand plate boundary development. It has been examined using 2D and 3D seismic reflection lines to generate fault displacement-time curves and basin-wide isopach maps. Up to 16 seismic reflectors tied to 35 wells have been mapped within the basin, producing a temporal resolution of 1-5Ma since ~22Ma and 5-10Ma prior to the Miocene. Three main phases of tectonic activity have been recognised; Late Cretaceous and Early Palaeogene extension (~80-55Ma), Oligocene and younger contraction and Plio-Pleistocene (~4-0Ma) extension. Most of the largest faults (e.g., Cape Egmont fault) accrued displacement during the Late Cretaceous and were reactivated one or more times during subsequent episodes of deformation. The oldest phase of extension occurred during Gondwana breakup and was ubiquitous throughout the basin. Later contraction may have commenced on the largest faults along the eastern margin of the basin (i.e. Taranaki and Manaia faults) synchronous with the onset of subduction no later than Early Oligocene. Contraction occurred throughout the basin during the Miocene and was episodic on many structures, with Latest Miocene (~8-5 Ma) reverse faults and folds being particularly widespread. This period of accelerated shortening has been observed throughout the Hikurangi subduction margin and could have been triggered by changes in the boundary conditions (e.g., adjustments in the trend and magnitude of the plate motion vector). Plio-Pleistocene extension migrated from the northern Taranaki Basin and was accompanied by southward migration of contraction which is now mainly confined to the northern South Island. This migration could have been due to steepening of the subducting plate and/or to southward movement of the southern termination of the Hikurangi subduction system.
Abstract of talk given to:
Geological Society of New Zealand Annual Conference, Geological Society of New Zealand, Hamilton, November 2012.