Abstract This chapter traces the history of understanding the central terranes of New Zealand: Drumduan, Brook Street, Murihiku, Dun Mountain–Maitai and Caples. The terranes, mostly exposed in the South Island, are named from stratigraphic units of Late Paleozoic–Late Mesozoic age, including the Murihiku Supergroup, Brook Street Volcanics and Maitai groups, and the Dun Mountain ophiolite. European geologists in the mid-nineteenth century determined the stratigraphy of these rocks in the extremities of the island but in the succeeding half-century much effort was devoted to understanding widespread poorly fossiliferous ‘greywackes’: the ‘Maitai Controversy’. This was resolved in 1917 by palaeontology and the recognition of major faulting. In the 1940s the Alpine Fault, with an apparent 460 km dextral offset of the rocks at either end of the island, was recognized. In the following two decades, New Zealand was interpreted in terms of the geosynclinal hypothesis and then paired metamorphic belts. With plate tectonics, the basement rocks were assigned to terranes with the implication of being conveyed over considerable distances. The identification of source areas, coupled with the definition of the Cordilleran Median Batholith, has progressed the understanding of the present arrangement of the central terranes in the New Zealand part of Zealandia.

Abstract This contribution considers the fossil content of the three Eastern Province ‘central’ terranes discussed within this Memoir, namely the Brook Street Terrane, the Dun Mountain–Maitai Terrane and the Murihiku Terrane, and reviews the evidence and/or arguments for the current interpretation of their age ranges as determined from fossils. It also briefly considers the Permian–Triassic record of the Western Province. There has been limited new palaeontological discovery in the past few decades but there has been significant new taxonomic and biostratigraphic analysis of New Zealand Permian faunas in light of new research in eastern Australia. This enables refinement of age correlations and greater confidence in the age significance of the New Zealand Permian record.

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 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.

Abstract The Dun Mountain ophiolite, South Island, New Zealand, records complex overprinting of mantle fabrics. Using structural observations, microstructural analysis, geothermometry, geobarometry, geochronology and rheological constraints from the Red Hills and Dun Mountain massifs, we propose that three deformation events occurred during the early stages of subduction initiation along the Permian margin of Gondwana. During the first deformation event, the lineated Two Tarns Harzburgite from the Red Hills formed in a transtensional setting associated with subduction initiation. Deformation was pervasive, homogeneous and simultaneous with boninitic melt migration through the unit; it also occurred at very fast strain rates (10 −9 –10 −8 s −1 ). During the second deformation event, progressive exhumation to c. 5 kbar and cooling to 1000°C led to the localization of melt and deformation into distinct zones (Dun Mountain, and the Plateau Complex, Plagioclase Zone and Ellis Stream Complex of the Red Hills). The third deformation event resulted in continued cooling and exhumation along serpentinized faults. This history provides a rare glimpse of the coupled fabric development and melt migration that sequentially develop in the early mantle wedge during the initiation of a subduction zone.

Abstract The late Early Permian ( c. 278–270 Ma) supra-subduction zone (SSZ) Dun Mountain ophiolite is bordered to the east by the Pataki Melange and to the NE by the Croisilles Melange. In the south, the ophiolite passes into a dismembered incipient oceanic arc (Otama Complex). The above units represent an oceanic forearc generated above a west-dipping subduction zone. Terrigenous sediment reached the subduction trench after the Mid-Permian(?) docking of the oceanic forearc with the long-lived SE Gondwana active continental margin. Mixed terrigenous–volcaniclastic turbidites accumulated in the trench prior to and during melange accretion. Fragments of the overriding oceanic forearc (and incipient arc, locally) detached and mixed to form melange and broken formation. Despite some individual features (e.g. of the basalt chemistry), the Patuki and Croisilles melanges are interpreted as originally representing a single Permian trench–accretionary complex. The more distal (easterly) part was sliced into the adjacent accretionary complex of the Caples Terrane to form the Croisilles Melange (and equivalent Greenstone Melange) probably after the Triassic. The South Island melanges exemplify accretionary processes in which igneous and sedimentary rocks were detached from the overriding plate by subduction–erosion, together with accretion, including seamount material from the subducting oceanic plate, with implications for melanges elsewhere.

Abstract The Dun Mountain ophiolite and related oceanic-arc rocks (Otama Complex) formed above a westward-dipping subduction zone within Panthalassa, with implications for the emplacement of Cordilleran-type ophiolites and arcs elsewhere. The ophiolite is overlain by the Mid–Late Permian Upukerora Formation (up to 850 m), a predominantly very coarse breccia-conglomerate that mainly accumulated by mass flow. Lesser amounts of sediment accumulated from turbidity currents and as background hemipelagic sediments. The succession unconformably overlies ophiolitic basaltic or, rarely, gabbroic rocks after a regional hiatus. Much of the coarse clastic debris was derived from the underlying ophiolite. However, clasts of plagioclase-phyric basalt, felsic volcanics and quartz-bearing intrusive rocks, including plagiogranite, are over-represented compared to the ophiolite. The evolved igneous material was derived from an incipient oceanic arc (the Otama Complex) that bordered or covered the ophiolite, especially in the south. The coarse clastic material accumulated following the activation of north–south-trending, subaqueous, extensional growth faults within the underlying oceanic crust. Large blocks of mainly basalt, diabase and gabbro were also shed down fault scarps from relatively shallow-water to deeper-water settings. Fault-controlled talus accumulated soon after Mid-Permian docking of the ophiolite and oceanic arc with SE Gondwana to initiate the Mid-Permian–Mid-Triassic Maitai continental margin forearc basin.

Abstract The Mid-Late Permian–Mid-Triassic Maitai Group is interpreted as the distal forearc basin of the SE Gondwana active continental margin. The basin initially received very coarse detritus (Upukerora Formation) from the recently emplaced, nearby Dun Mountain ophiolite and related oceanic-arc rocks. Early tectonic subsidence accommodated up to 1000 m of bioclastic gravity-flow deposits from an adjacent carbonate platform, together with terrigenous and volcanic arc-derived material (Wooded Peak Formation). Basin-levelling turbidites then accumulated, composed of mixed terrigenous and arc-derived igneous material, with bottom-current reworking (Tramway Formation). Latest Permian–earliest Triassic gravity-flow deposits (locally absent) are characterized by relatively basic volcanic material (Little Ben Formation). Overlying turbidites accumulated in a relatively oxygen-poor, deeper-water setting (Greville Formation). Fine-grained background sedimentation then switched to well-oxidized, with traction-current reworking (Waiua Formation). The overlying Early–Mid Triassic Stephens Subgroup included the accumulation of lenticular sandstone turbidites, channelized conglomerate, well-oxidized deep-sea mud and felsic tuff. Permian and Early Triassic marginal carbonate platforms collapsed and were emplaced as localized exotic blocks. Extrusive and intrusive clasts within channelized conglomerates (Snowdon Formation) were derived from the adjacent continental margin arc. The forearc basin was subsequently displaced to its present position, possibly with up to 3000 km of southwards translation.

Abstract Major, trace and rare earth element data for sandstones and conglomerates from the Mid-Permian–Mid-Triassic Maitai Group are compared with other tectonostratigraphic units, using discrimination diagrams and comparisons with potential source terranes. Maitai Group sandstones reveal a mainly ophiolitic–oceanic-arc source during the Mid-Permian, followed by a mixed continental margin-arc–terrigenous source during the Late Permian. Latest Permian–Early Triassic sandstones mainly came from little-evolved continental margin-arc extrusives, tending to more evolved (but variable) during the Triassic. Source volcanism of the Murihiku Terrane sandstones was magmatically evolved relative to the Maitai Group generally (except during the Late Triassic). The Maitai Group and Murihiku Terrane are restored as proximal and more distal parts, respectively, of the SE Gondwana forearc basin. The localized Willsher Group shows some Maitai Group affinities. Sandstones in two melanges that formed in an outer forearc–subduction trench setting mainly indicate a mixed terrigenous–continental margin-arc source, similar to the Late Permian Maitai Group. The Caples Terrane, a Triassic accretionary prism, received detritus from little-evolved, to evolved continental margin-arc volcanics and terrigenous sources. Much of the arc-related material in all units is compatible with derivation from the latest Permian–Triassic Median Batholith, or a lateral equivalent along the SE Gondwana active margin.

Abstract Chemical and mineralogical evidence is reported, first for mudrocks from the Mid-Permian–Mid-Triassic Maitai Group and, secondly, for Late Permian(?) mudrocks from the structurally underlying Patuki Melange. Weathering and alteration indices indicate increased source weathering and aluminosilicate input stratigraphically upwards in the Maitai Group. The Maitai Group exhibits an upward change from a relatively enriched continental magmatic arc source (and related country rocks) during the Late Permian, to a relatively depleted continental magmatic arc source (and related country rocks) during the Triassic. The melange mudrocks have a similar provenance to the Late Permian mudrocks of the Maitai Group. The melange mudrocks are, however, generally less altered, probably because of additional, local, ophiolite-related input. Red iron-rich mudrocks accumulated widely in two Triassic Maitai Group formations and also locally in the Patuki Melange. The iron oxide was derived by continental weathering under warm conditions, and then accumulated relatively slowly under oxidizing seafloor conditions. The chemical evidence, as a whole, indicates sources for all of the mudrocks similar to the Median Batholith and associated country rocks, or non-exposed equivalents along the SE Gondwana active continental margin. Accumulation took place during a change from an icehouse to a hothouse world.

Abstract We present the results of U–Pb dating of zircons of two Late Permian igneous rocks from the Dun Mountain–Maitai and Brook Street terranes of New Zealand's South Island. A conglomerate clast of hornblende diorite from the Early–Middle Triassic Stephens Subgroup, Maitai Group, gives an age of 251.1 ± 1.6 Ma. A sample of hypabyssal andesite–microdiorite (Weetwood Formation) that intrudes the Late Permian Productus Creek Group of the Brook Street Terrane gives an age of 258.8 ± 7.9 Ma. The intermediate and subalkaline geochemistry of the two samples is not distinctive of specific tectonic settings, but their ages match plutons of the I-type, subduction-related Longwood Suite of the nearby Median Batholith. Assuming that correlation with the Longwood Suite is correct, the Weetwood sample increases the known areal extent of intrusion of the Longwood Suite; and the Stephens Subgroup Formation clast is consistent with a detrital link between Gondwana and the Dun Mountain–Maitai Terrane by the Middle Triassic. However, because of uncertainties regarding the timing of magmatism along other parts of the Gondwana margin, the data in this paper do not establish any specific provenance links.

Abstract Felsic tuffs play an important role in the Permian–Triassic geology of the Eastern Province in South Island. In the Brook Street Terrane, primary felsic tuff is minor in the south (e.g. Takitimu Mountains) but abundant in the north (Grampian Formation, Nelson area). Felsic fallout tuff dominates one interval of the Maitai Group (Early Triassic Kiwi Burn Formation), south of the Alpine Fault, but is otherwise mainly redeposited by gravity flows. The Murihiku Terrane is characterized by two main intervals of felsic fallout tuff, the Middle Triassic Gavenwood Tuffs and the Late Triassic Bare Hill Tuff Zone, south of the Alpine Fault (e.g. Hokonui Hills and south Otago coast). Counterparts north of the Alpine Fault (Richmond Group) are mainly reworked, with terrigenous admixtures. Tuffaceous sediments are also abundant in the late Middle–early Late Triassic Willsher Group (south Otago coast). Based on combined field, petrographical, semi-quantitative X-ray diffraction (XRD) and chemical evidence, the felsic tuffs of the Brook Street Terrane in the south are interpreted as small-scale eruptions of fractionated oceanic-arc-type magmas. In contrast, the Triassic felsic tuffs of the Murihiku Terrane, Willsher Group and Maitai Group erupted violently and episodically in proximal to distal segments of the SE Gondwana continental margin.

Abstract U–Pb detrital zircon age patterns in sandstones from the Wellington and eastern Cook Strait area have broad Permian–Triassic and Precambrian–early Paleozoic age groups that confirm a previously established Triassic Rakaia Terrane correlation. Along the western Cook Strait coast, meta-psammitic Marlborough Schist samples have zircon patterns with a single age group, either Late Triassic or Jurassic, indicating a Waipapa Terrane ancestry. Similar data from the central Cook Strait region suggest that Waipapa Terrane basement continues northeastwards from Marlborough through Fishermans Rock to Kapiti Island. The Rakaia–Waipapa terrane boundary thus lies east of Kapiti Island and Fishermans Rock. The position of a Caples–Waipapa terrane boundary within the Marlborough Schist is less certain but most of the eastern Marlborough Schist is Waipapa Terrane.

The Western Province is a fragment of the c. 500 Ma SE Gondwana active continental margin. The Eastern Province is a terrane assemblage, which is partly stitched by the Median Batholith. Fragments of the batholith are preserved in the adjacent Drumduan and Brook Street terranes. Permian arc magmatism of the Brook Street Terrane involved both oceanic and continental margin settings. The Permian ( c. 285–275 Ma) supra-subduction zone Dun Mountain ophiolite records subduction initiation and subsequent oceanic-arc magmatism. The Permian Patuki and Croisilles melanges represent detachment of the ophiolitic forearc and trench–seamount accretion. The Murihiku Terrane, a proximal continental margin forearc basin, received detritus from the Median Batholith (or equivalent). The south coast, Early–Late Triassic Willsher Group is another proximal forearc basin unit. The sediments of the Dun Mountain–Maitai Terrane (Maitai basin) represent a distal segment of a continental margin forearc basin. The Caples Terrane is a mainly Triassic trench accretionary complex, dominantly sourced from a continental margin arc, similar to the Median Batholith. The outboard (older) Torlesse and Waipapa terranes are composite subduction complexes. Successively more outboard terranes may restore farther north along the SE Gondwana continental margin. Subduction and terrane assembly were terminated by collision (at c. 100 Ma), followed by rifting of the Tasman Sea Basin.

Abstract This volume presents a set of research papers that provide new data and interpretations of the Permian–Triassic terranes of SE Gondwana, now exposed in South Island, New Zealand. Following an introduction for general readers, a historical summary and a review of biostratigraphy, the individual papers primarily focus on the Permian magmatic arc of the Brook Street Terrane, the classic Permian Dun Mountain ophiolite and the Permian–Triassic Maitai Group sedimentary succession. The new results emphasize the role of subduction and terrane displacement adjacent to the Permo-Triassic Gondwana margin, and present fundamental insights into three crustal processes: subduction initiation, supra-subduction zone oceanic crust genesis and forearc basin evolution. The volume concludes with a wide-ranging summary and synthesis of the regional Cambrian to Early Cretaceous tectonostratigraphy of New Zealand's South Island in relation to the wider areas of Zealandia, East Australia and West Antarctica. The volume will interest geoscientists, including stratigraphers, sedimentologists, palaeontologists, igneous petrologists, geochemists, geochronologists and economic geologists, and is aimed at professional geologists and advanced students of geology.