Abstract The c. 450 km-long Brook Street Terrane (pre-Alpine Fault displacement) sheds light on processes of arc magmatism and related sedimentation. A very thick (up to 15 km) succession accumulated south of the Alpine Fault in the Takitimu Mountains during the Early Permian. Predominant arc-flank talus is intercalated with basic extrusive and intrusive igneous rocks. Volcaniclastic sediments mainly accumulated by mass-flow and turbidity current processes. The sediments were mostly derived from differentiated, arc-core, basaltic–andesitic rocks, contrasting with less evolved arc-flank flows and minor intrusions. Some igneous rocks are mildly enriched, supporting an extensional back-arc setting. After volcanism ended, Middle–Late Permian mixed carbonate–volcaniclastic gravity-flow deposits were derived from a non-exposed carbonate platform. Other volcanogenic successions in the south (Bluff, Riverton) represent smaller eruptive centres. In contrast, north of the Alpine Fault (e.g. Nelson), volcanism began with mostly felsic tuffaceous gravity-flow deposits, followed by extrusion/intrusion of clinopyroxene-rich, primitive magmas, related to arc rifting, and ended with an accumulation of a mixed basic–felsic volcaniclastic forearc apron. Taking account of regional comparisons, the Early Permian arc is interpreted as having formed adjacent to Gondwana (on accreted or trapped oceanic lithosphere), whereas the lithologies north of the Alpine Fault represent contrasting Late Permian continental arc magmatism.

Abstract Graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization. We examine processes of graphitic carbon emplacement and deformation in the active Alpine Fault Zone, New Zealand by analysing samples obtained from Deep Fault Drilling Project (DFDP) boreholes. Optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain. Raman spectroscopy allowed interpretation of the degree of graphite crystallinity, which reflects both thermal and mechanical processes. In the amphibolite-facies Alpine Schist, highly crystalline graphite, indicating peak metamorphic temperatures up to 640°C, occurs mainly on grain boundaries within quartzo-feldspathic domains. The subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions (500–600°C), resulting in clustered (in protomylonites) and foliation-aligned graphite (in mylonites). In cataclasites, derived from the mylonitized schists, graphite is most abundant (<50% as opposed to <10% elsewhere), and has two different habits: inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon. Tectonic–hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences. The increasing abundance of graphite towards the fault zone core may be a significant source of strain localization, allowing fault weakening. Supplementary material: Raman spectra of graphite from the Alpine Fault rocks is available at https://doi.org/10.6084/m9.figshare.c.3911797

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.

Abstract Reconnaissance 2D seismic reflection data intended to investigate the petroleum potential of New Zealand’s marine territories have contributed many insights into the geological evolution of the large continental block that surrounds New Zealand. These include: definition of a back-thrust system to the Mesozoic Gondwana subduction margin along the Northland–Reinga Basin and the transition to back-arc rifting; the development of a Mesozoic back-arc rift system through the present New Caledonia and probably the Bounty troughs; the Early Cretaceous cause, at least locally, of the cessation of subduction along the New Zealand sector of the Gondwana margin; evidence for anticlockwise rotation of eastern New Zealand relative to the west in Late Eocene time; an explanation for the development of the Alpine Fault and the South Island compressional strike-slip margin between the Pacific and Australian plates through South Island.