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We combine recently acquired airborne light detection and ranging (LiDAR) data along a portion of the Alpine fault with previous work to defi ne the ways in which the plate-boundary structures partition at three different scales from <10 6 to 10 0 m. At the fi rst order (<10 6-10 4 m), the Alpine fault is a remarkably straight and unpartitioned structure controlled by inherited and active weakening processes at depth. At the second order (10 4-10 3 m), motion is serially partitioned in the upper ~1-2 km onto oblique-thrust and strike-slip fault segments that arise at the scale of major river valleys due to stress perturbations from hanging-wall topographic variations and river incision destabilization of the hanging-wall critical wedge, concepts proposed by previous workers. The resolution of the LiDAR data refi nes second-order mapping and reveals for the fi rst time that at a third order (10 3-10 0 m), the fault is parallel-partitioned into asymmetric positive fl ower structures, or fault wedges, in the hanging wall. These fault wedges are bounded by dextral-normal and dextral-thrust faults rooted at shallow depths (<600 m) on a planar, moderately southeast-dipping, dextral-reverse fault plane. The fault wedges have widths of ~300 m and are bounded by and contain kinematically stable fault traces that defi ne a surface-rupture hazard zone. Newly discovered anticlinal ridges between fault traces indicate that a component of shallow shortening within the fault wedge is accommodated through folding. A fault kinematic analysis predicts the fault trace orientations observed and indicates that third-order fault trace locations and kinematics arise independently of topographic controls. We constructed a slip stability analysis that suggests the new strike-slip faults will easily accommodate displacement within the hanging-wall wedge, and that thrust motion is most easily accommodated on faults oblique to the overall strike of the Alpine fault. We suggest that the thickness of footwall sediments and width of the fault damage zone (i.e., presence of weaker, more isotropic materials) are major factors in defi ning the width, extent, and geometry of third-order near-surface fault wedges.

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The mantle and crustal sections of the Permian Dun Mountain ophiolite (DMO) in New Zealand's South Island have similar and potentially related tectonic histories. The mantle section records a four-part sequence of mid-ocean ridge basalt, and boninite melt extraction, followed by refertilization from supra-subduction melts and, finally, the intrusion of mafic–felsic island-arc tholeiite dykes. The crustal sequence represents a progression from mid-ocean ridge basalts to transitional island-arc tholeiites and, finally, mafic–felsic, possibly calc-alkaline, lavas; overlain by the 6 km-thick sedimentary Maitai Group. Plagiogranite zircon geochronology shows that the crustal ocean-ridge volcanism had commenced by 277.6 ± 3.3 Ma, and the youngest granites and granodiorites crystallized by 269.3 ± 4.5 Ma. All lithologies of the DMO are inferred to have formed in a broad forearc setting, representing a sequence from subduction initiation to magmatic arc formation. Sedimentary blocks within the structurally underlying ophiolitic Patuki Melange are similar to the Maitai Group, supporting a formational relationship with the DMO.

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