Variation in syn-subduction sedimentation patterns from inner to outer portions of deep-water fold and thrust belts: examples from the Hikurangi subduction margin of New Zealand

The structure and distribution of accommodation in fold and thrust belts vary both laterally and longitudinally. Here we integrate gravity, bathymetry and 2D seismic datasets to investigate the structural and stratigraphic variation in the southern part of the Hikurangi subduction wedge, onshore and offshore North Island, New Zealand. Three morphostructural portions are recognized: The inner portion demonstrates reactivation of inherited structures, producing thick-skinned deformation. Pre-subduction rocks are represented by kilometres of acoustically chaotic seismofacies. Thick-skinned deformation and readily deformable substrate lead to the development of wide trench-slope sub-basins, infilled with >5 km of syn-subduction sediments. The mid portion typically demonstrates thrust faults with connections to deeper structures, leading to the development of an imbricate system with asymmetrical sub-basins typically <5 km thick developed on the back-limb of thrust related folds. An antiformal stack marks the transition from the thick-skinned interior of the basin to the thin-skinned accretionary prism. Beyond this, the relatively non-deformed outer portion demonstrates frontal folds, propagating thrusts and up to 3 km thickness of syn-subduction strata. Structural variation across the subduction wedge controls the generation of accommodation with implications for sediment distribution within fold and thrust belts and for petroleum system development.