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

Cretaceous coals and coal measures onshore and offshore New Zealand record a period of great tectonic change in the region. Coal measures accumulated mainly within fault-controlled depressions resulting from a complex early rifting history during the breakup of eastern Gondwanaland. Lithofacies relationships and coal properties reflect a complex interplay between paleoenvironmental and contemporaneous tectonic influences. Mid-Cretaceous terrestrial sediments up to 4,500 m thick accumulated in narrow fault-angle depressions interpreted as failed rifts. Fan breccias and conglomerates predominate, with minor fine-grained sediments and thin, uneconomic coal seams. Latest Cretaceous coal measures in the order of 1,000 m thick accumulated mainly as floodplain deposits in generally more extensive basins, some probably exceeding 60 km along their axes. The coal measures are lithologically variable, with sandstone and conglomerate dominant in most basins, many of which contain economically important coalfields. Seams are characterized by marked lenticularity and maximum thicknesses of 20 to 30 m. Some latest Cretaceous coal measures were deposited in near-shore environments as a consequence of marine transgression, which also influenced coal measure deposition in some tectonically controlled basins. Coal properties vary, although ash and sulphur contents are commonly low. A range of coal rank from lignite to low-volatile bituminous results from different burial histories. The most extensive mid- to Late Cretaceous coal measures are in offshore basins. Up to 2,000 m of lithologically variable coal measures with numerous seams accumulated in rapidly subsiding basins up to a few hundred kilometers in extent.

The Westland dike swarm of South Island, New Zealand, consists of a variety of ultrabasic, alkaline rock types including camptonite lamprophyres, ouachitite peridotites, and carbonatites. At least part of the swarm is as young as Oligocene-Miocene age. The majority of Nd and Sr isotope analyses for 16 dikes ε Nd = +3.5 to +5.2, 87 Sr/ 86 Sr i = 0.7028 to 0.7035) fall to the left of the mantle array in Nd-Sr isotope correlation diagram. The data are similar to the ocean islands St. Helena and Tubuai and to some continental volcanics and mantle nodules (Menzies and Wass, 1983). The dikes contain radiogenic Pb ( 206 Pb/ 204 Pb = 19.19 to 20.59, 207 Pb/ 204 Pb = 15.64 to 15.71, 208 Pb/ 204 Pb = 39.0 to 40.2), which also is similar to the most radiogenic Pb in ocean islands. The trace element and isotope data are consistent with an origin involving a Paleozoic enrichment event, which added CO 2 , Sr, light rare-earth elements, and U to a depleted mantle. We propose that this first event was the manifestation of a deep-seated intrusion of carbonated hyperalkaline magma. A second event triggered the melting of this newly metasomatized mantle and the emplacement of the Westland dikes.