Abstract 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.

Abstract: Fault growth could be achieved by (1) synchronous increases in displacement and length or (2) rapid fault propagation succeeded by displacement-dominated growth. The second of these growth models (here referred to as the constant length model) is rarely applied to small outcrop-scale faults, yet it can account for many of the geometric and kinematic attributes of these faults. The constant length growth model is supported here using displacement profiles, displacement–length relationships and tip geometries for a system of small strike-slip faults (lengths of 1–200 m and maximum displacements of 0.001–3 m) exposed in a coastal platform in New Zealand. Displacement profiles have variable shapes that mainly reflect varying degrees of fault interaction. Increasing average displacement gradients with increasing fault size (maximum displacement and length) may indicate that the degree of interaction increases with fault size. Horsetail and synthetic splays confined to fault-tip regions are compatible with little fault propagation during much of the growth history. Fault displacements and tip geometries are consistent with a two-stage growth process initially dominated by propagation followed by displacement accumulation on faults with near-constant lengths. Retardation of propagation may arise due to fault interactions and associated reduction of tip stresses, with the early transition from propagation-to displacement-dominated growth stages produced by fault-system saturation (i.e. the onset of interactions between all faults). The constant length growth model accounts for different fault types over a range of scales and may have wide application.

A substantial portion of the Pacific basin is composed of seafloor formed during the Cretaceous Normal Superchron (CNS). Because this region lacks the magnetic lineations typically required to constrain tectonic reconstructions, we employ additional methods for interpreting CNS Pacific history, involving seafloor fabric, basement paleolatitudes, and age data. We utilize seafloor fabric, including fracture zones and the rift margins of large igneous provinces, to derive quantitative rotations. The timing of such rotations is constrained using rock ages, bounding magnetic isochrons, and estimates of interactions with surrounding terrains. The method relies on high-resolution shipboard bathymetry and rock ages, as much fine-scale seafloor fabric useful for reconstructions is not visible in satellite altimetry data. We show that the Ontong Java, Manihiki, and Hikurangi oceanic plateaus likely originated as one large superplateau, the Ontong Java Nui (OJN). Reconstructions of OJN at 123 Ma reveal large offsets between observed and predicted paleolatitudes. Observed paleolatitudes exhibit a systematic bias, which may be attributed to large-scale rotation of the entire plateau. Such a rotation would imply either that OJN was initially decoupled from the Pacific plate and able to rotate independently or that the orientation of the Pacific plate at 123 Ma differed from conventional model predictions. However, large uncertainties in absolute plate motion models prior to ca. 80 Ma preempt a conclusive interpretation for OJN formation. Given an ~10 km resolution limit for satellite altimetry, continued investments in seagoing research will be needed to investigate tectonic events in magnetic quiet zones.