Structural Style and Tectonic Evolution of the Hawkes Bay Region, Offshore Eastern New Zealand

Nasaruddin Ahmad¹ and Ken McClay^2
1Exploration Geoscience, Petronas Carigali, Kuala Lumpur, Malaysia
²Fault Dynamics Research Group, Royal Holloway College, University of London, Egham, United Kingdom

The research area is located in the outer forearc and contractional domain of the Hikurangi subduction complex (accretionary wedge). Detailed intrerpretation of long regional 2D seismic lines has indicated that the area underwent rifting in the Cretaceous, thermal sag and subsidence in the Paleogene, followed by contraction and thrusting in the early Miocene, extensional faulting in middle to late Miocene together with continued thrusting and inversion from the Pliocene to Present Day. Within the Neogene section three principal depositional sequences were identified representing growth strata deposited during different deformational phases - a syn-thrusting sequence, a syn-extensional sequence and a syn-inversional growth stratal sequence.

Within the research area three distinct tectono-sedimentary domains were identified based on differences in structural styles and tectono-sedimentary architectures. In the northern part of the region the Raukumara Shelf domain is characterized by thrust fault-related folds at the frontal part of the accretionary prism, together with inverted extensional faults and gravitational sliding structures in the inner (western) part of the domain. In the central domain of Hawkes Bay itself, a series of Present Day active thrust faults occurs associated with folds and inverted extensional faults. The southern structural domain, the North Wairarapa Shelf, is characterized by thrust related folds and gravitational sliding structures.

Fold amplification characteristics, overall shortening and thrust fault spacings indicate that the shortening rates were relatively higher towards southwest of the study area. The prominent extensional faulting in the Raukumara Shelf may indicate that subduction underplating and gravitational collapse of a supra-critical Coulomb wedge in this region.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery