I. M. Turnbull

Plutonic rocks of the Median Batholith in eastern and central Fiordland, New Zealand: Field relations, geochemistry, correlation, and nomenclature

Abstract This paper provides a comprehensive description of all major plutonic rock units in Fiordland between Lakes Poteriteri and Te Anau, and the heads of Doubtful and George Sounds. Plutonic rocks comprise c. 80% of the basement in the area described, the remainder being metase dim entary and metavolcaniclastic rocks. The plutonic rocks, of which c. 50% are granitoids, were emplaced in three phases—at c. 492 Ma, between c. 365 and 318 Ma, and between 168 and 116 Ma. Correlatives of the Devonian Karamea Suite emplaced between c. 375 and 367 Ma, and the Triassic to Early Jurassic part of the Darran Suite emplaced between c. 230 and 168 Ma, are not present in the area described here. The strongly deformed Late Cambrian to Early Ordovician Jaquiery Granitoid Gneiss is one of the oldest plutonic rocks yet discovered in New Zealand and is of similar age to plutonic rocks within the Ross and Delamerian Orogens of Victoria Land and South Australia. Rocks emplaced between c. 365 and 318 Ma include Ridge Suite S‐type granitoids and closely related S/A‐type plutons, Foulwind Suite A‐type mafic and granitoid plutons, Tobin Suite I‐type granitoids, and several unassigned mafic plutons. Rocks emplaced between 168 and 116 Ma include extensive c. 168–128 Ma old calc‐alkaline LoSY gabbros, diorites, and granitoids of the Darran Suite, c. 165–135 Ma old hypersolvus perthitic syenogranites and peralkaline granitoids, c. 125 Ma gneissic diorite similar to the Western Fiordland Orthogneiss, and c. 123–116 Ma old quartz diorites and granitoids of the HiSY Separation Point Suite. Plutons from each suite tend to be concentrated in distinct NNE‐striking parallel belts up to 20 km wide and 110+ km long. These belts are one of the key features which define the regional structural grain of Fiordland basement geology. Their strike remains constant from the Carboniferous through to the Cretaceous. S, S/A, and A‐type plutons of the Carboniferous Ridge and Foulwind Suites are confined to a 125 km long but discontinuous belt in southern and central Fiordland, wholly within the areal extent of early Paleozoic metase dim entary basement. Volumetrically minor Carboniferous Tobin Suite I‐type granitoids are confined to the area east of exposed early Paleozoic metasedimentary basement. Much of eastern Fiordland is underlain by an extensive belt of heterogeneous Darran Suite rocks. Darran Suite rocks extend from Stewart Island to the Darran Mountains of northern Fiordland, forming a belt c. 15 km wide and 300 km long. Correlative Darran Suite rocks also occur further west where they intrude early Paleozoic metasediments, indicating that Jurassic to Early Cretaceous arc‐related plutonism and volcanism occurred inboard of the edge of early Paleozoic basement in some parts of the Median Batholith. Distinctive Jurassic, pink, hypersolvus syenogranite and alkalic granitoids form a narrow discontinuous belt within the wider calcalkaline Darran Suite. Cretaceous Separation Point Suite plutons form two major belts, one in easternmost Fiordland partially covered by Cenozoic sedimentary rocks, and the other stitching inboard and outboard parts of the Median Batholith in central Fiordland.

High-level stratigraphic scheme for New Zealand rocks

We formally introduce 14 new high-level stratigraphic names to augment existing names and to hierarchically organise all of New Zealands onland and offshore Cambrian–Holocene rocks and unconsolidated deposits. The two highest-level units are Austral Superprovince (new) and Zealandia Megasequence (new). These encompass all stratigraphic units of the countrys Cambrian–Early Cretaceous basement rocks and Late Cretaceous–Holocene cover rocks and sediments, respectively. Most high-level constituents of the Austral Superprovince are in current and common usage: Eastern and Western Provinces consist of 12 tectonostratigraphic terranes, 10 igneous suites, 5 batholiths and Haast Schist. Ferrar, Tarpaulin and Jaquiery suites (new) have been added to existing plutonic suites to describe all known compositional variation in the Tuhua Intrusives. Zealandia Megasequence consists of five predominantly sedimentary, partly unconformity-bounded units and one igneous unit. Momotu and Haerenga supergroups (new) comprise lowermost rift to passive margin (terrestrial to marine transgressive) rock units. Waka Supergroup (new) includes rocks related to maximum marine flooding linked to passive margin culmination in the east and onset of new tectonic subsidence in the west. Māui and Pākihi supergroups (new) comprise marine to terrestrial regressive rock and sediment units deposited during Neogene plate convergence. Rūaumoko Volcanic Region (new) is introduced to include all igneous rocks of the Zealandia Megasequence and contains the geochemically differentiated Whakaari, Horomaka and Te Raupua supersuites (new). Our new scheme, Litho2014, provides a complete, high-level stratigraphic classification for the continental crust of the New Zealand region.

Plutonic rocks of Western Fiordland, New Zealand: Field relations, geochemistry, correlation, and nomenclature

Abstract This paper provides a comprehensive description of the plutonic rocks of western Fiordland between Breaksea and Sutherland Sounds. The area is dominated by the Early Cretaceous Western Fiordland Orthogneiss (WFO), but also includes smaller bodies of Paleozoic and Cretaceous granitoid. Plutonic rocks of western Fiordland intrude metasediments of the Western Province, many of whose age and terrane affinities remain undefined. Paleozoic granitoids in western Fiordland include the Pandora Orthogneiss (c. 500 Ma) and widespread related sills within Paleozoic metasedimentary rocks; the All Round Pluton (c. 340 Ma); the Deas Cove Granite (c. 372 Ma); and possibly the Straight River Granite. The Pandora Orthogneiss is one of the oldest plutons yet found in the Median Batholith. Correlatives include the Jaquiery Granite Gneiss in central Fiordland and orthogneiss in Doubtful Sound. Plutonism of Ross/Delamarian age is therefore widespread in those parts of Fiordland where Cambrian or older Western Province metasedimentary rocks form basement. The All Round Pluton and Deas Cove Granite are correlatives of the S‐type Ridge and A/I‐type Foulwind Suites, respectively. The c. 125–116 Ma WFO includes at least seven major dioritic and monzodioritic plutons in western Fiordland, one in central Fiordland, and one in central Stewart Island. Plutons which compose the WFO are distinguished by differences in their age, petrography, structural and metamorphic histories, and geochemistry. The WFO in northern Fiordland and the correlative Walkers Pluton on Stewart Island were emplaced in the mid crust (4–9 kbar) at depths comparable with some Separation Point Suite plutons of similar age. WFO plutons in southern Fiordland were emplaced at greater depths (10–18 kbar). WFO plutons have been variably recrystallised to eclogite; omphacite‐, garnet‐, two‐pyroxene‐, and hornblende‐granulite; and hornblende‐amphibolite facies assemblages, reflecting different PTX conditions during metamorphism of each body. Some parts of the WFO remain undeformed and unmetamorphosed. Evidence of up to c. 6 kbar loading after emplacement is limited to WFO plutons in northern Fiordland and adjacent country rocks. Extensional ductile shear zones previously shown to locally separate the WFO from adjacent rocks are discontinuous later features, commonly localised along earlier intrusive contacts between WFO plutons and metasedimentary country rocks. They do not form a regionally extensive detachment between the upper and lower plates of a metamorphic core complex. The WFO has previously been included in the Separation Point Suite since both units share a high Sr/Y (HiSY) chemistry and were emplaced at broadly the same time. However, the WFO and Separation Point Suite have distinct chemistries. Separation Point Suite rocks generally contain greater Sr, Na, and Al, and have lower Sr/Rb ratios, rare earth element and Y contents, than WFO rocks with comparable amounts of SiO2. Many aspects of the WFO chemistry (aside from its HiSY character) are similar to that of the older Darran Suite rather than the Separation Point Suite. This may reflect a greater amount of partial melting during generation of the SiO2‐poor WFO than the SiO2‐rich Separation Point Suite. Alternatively it may indicate derivation of the WFO and Separation Point Suite from different sources, albeit at depths greater than those where residual plagioclase is stable. Relatively large variations in the major element chemistry of the Separation Point Suite reflect fractionation and/or accumulation of plagioclase, whereas the more limited variability in the major element chemistry of the WFO reflects minor fractionation and/or accumulation of hornblende and/or clinopyroxene.

Plutonic rocks of the Median Batholith in southwest Fiordland, New Zealand: field relations, geochemistry, and correlation

Abstract This paper provides a first description of all major plutonic rock units between Resolution Island and Lake Poteriteri in southwest Fiordland. Plutonic rocks, of which c. 95% are granitoids, comprise c. 60% of the basement in southwest Fiordland. Approximately 50% of the plutonic rocks were emplaced between c. 355 and 348 Ma, 5% at c. 164 Ma, 25%between c. 140 and 125 Ma, and 20% between c. 125 and 110 Ma. These episodes of plutonism occurred in response to terrane amalgamation, continental thickening, and subduction along the convergent margin of Gondwana. Correlatives of Devonian plutonic rocks which occur in Nelson are absent from the area described here. A wide variety of plutonic rocks were emplaced at c. 355–348 Ma. These include relatively small plutons of K‐ and Rb‐rich gabbro‐diorite and members of at least three distinct suites of granitoids. Plutons of two‐mica ± garnet granodiorite, granite, and minor tonalite share affinities with the S‐type Ridge Suite and are the most widespread c. 355–348 Ma old granitoids in southern Fiordland. Plutons rich in Ca, Fe and Zr, depleted in K and Na, and containing quartz diorite, tonalite, and minor granodiorite with the unusual assemblage red‐brown biotite, garnet ± hornblende ± clinopyroxene also occur widely in southern Fiordland. These plutons are similar to peraluminous A‐type granitoids, indicating A as well as I and S‐type plutonism occurred in the Western Province at this time. The Newton River and Mt Evans Plutons have no correlatives amongst c. 355–348 Ma granitoids in southern Fiordland, but their chemistry is similar to that of the older Karamea Suite. Three regional‐scale metasedimentary units—locally fos‐siliferous Fanny Bay Group Buller Terrane rocks in southern Fiordland, Edgecumbe and Cameron Group Takaka Terrane rocks in south‐central Fiordland, and undifferentiated Deep Cove Gneiss high‐grade metasedimentary rocks of western Fiordland—are all stitched by c. 355–348 Ma old plutons, indicating they have been in close proximity since at least c. 355–348 Ma. In south‐central Fiordland, c. 355–348 Ma old plutons cut across fabrics defined by upper amphibolite facies mineral assemblages, indicating low pressure/high temperature metamorphism in this area before this time. The c. 164 Ma old leucocratic Lake Mike Granite is a unique pluton in southwest Fiordland with no obvious correlatives. Plutons emplaced between c. 140 and 125 Ma are similar to the Rahu Suite, although isotopic data are required to confirm this correlation. Rahu Suite plutonism may therefore have begun by c. 140 Ma, rather than c. 120 Ma as previously suggested. Plutons emplaced between c. 125 and 110 Ma have high Sr/Y ratios comparable with the Separation Point Suite. They occur in both an outboard location around Lake Poteriteri and an inboard location around the western end of Dusky Sound. The c. 115 Ma two‐mica garnet granites of the Anchor Island Intrusives #2 probably formed by partial melting of adjacent ortho‐ and paragneisses, indicating that upper amphibolite facies metamorphism in western Dusky Sound occurred during the Early Cretaceous. The Dusky Fault does not pass directly out to the coast through outer Dusky Sound as previously mapped. Instead it merges with the major northeast‐striking Lake Fraser Fault at Cascade Cove, which crosses the outer coast near West Cape. The Last Cove Fault is a minor structure which cannot be traced beyond Last Cove rather than a major fault of regional extent as has been previously suggested.

Pliocene‐Quaternary sedimentation and Alpine Fault related tectonics in the lower Cascade valley, South Westland, New Zealand

Abstract Study of Pliocene and Quaternary sediments west of the Alpine Fault in the Cascade valley, South Westland, New Zealand, has allowed determination of Alpine Fault displacement rate and coastal uplift rate over the last 3.5 m.y. Exposures of the Pliocene Halfway Formation (latest Opoitian‐Waipipian) are composed of marine sand and conglomerate deposited in c. 200–1000 m water depth. Beds are gently dipping and weakly deformed, with the direction of principal shortening oriented at a high angle to the Alpine Fault and plunging gently northwest (c. 107340°). Fiordland‐derived clasts indicate a minimum of 95–100 km of lateral offset on the Alpine Fault since deposition of Halfway Formation. Paleogeographic evidence suggests that first‐order features of the drainage were similar in Pliocene time to those of the present day. Quaternary moraines and fluvioglacial sediments are subdivided on the basis of composition and morphology into five groups: Cl (oldest) to C5 (youngest). The Cl deposits have a prov...

Petrology and geochronology of the volcaniclastic and volcanogenic Mesozoic Loch Burn Formation in eastern Fiordland, New Zealand

Abstract The Loch Burn Formation in eastern Fiordland is the metamorphosed and eroded effusive product of a long‐lived Jurassic to Early Cretaceous volcanic arc. Relict sedimentary features within meta‐volcaniclastic components indicate sedimentation in a mostly terrestrial or shallow‐water environment that was fed by debris flows from proximal granitic and volcanic high points. In the Murchison Mountains, deposition is constrained by a c. 342 Ma granite, which is unconformably overlain by the Loch Burn Formation, and a c. 158 Ma quartz diorite that intrudes the Loch Burn Formation. This latter age is 8–9 m.y. older than a volcanic clast from Loch Burn Formation and a sandstone horizon previously dated from the Stuart Mountains, and therefore supports previous suggestions that the Loch Burn Formation is a long‐lived and time‐transgressive unit. The Carboniferous basement provides a potential source for detrital zircon in metasediment, inherited zircon in the intrusive quartz diorite, and some granitoid clasts within the formation. Geochemical similarities between the quartz diorite, volcanic clasts within the Loch Burn Formation, and nearby Jurassic to Early Cretaceous Darran Suite plutons imply that the Loch Burn Formation is the volcanic equivalent of the Darran Suite. The distinctive lithological, geochemical, age, and internal relationships of the Loch Burn Formation are also seen in the volcano‐sedimentary Largs Group of northern Fiordland and Paterson Group of Stewart Island, suggesting that these three units are lithological and chronological equivalents to one another. The Loch Burn Formation provides a comprehensive record of the tectonic evolution of eastern Fiordland, with several episodes of uplift and burial. These are: uplift and erosion of a Carboniferous plutonic basement by c. 195 Ma; deposition of the older part of the Loch Burn Formation sequence in the Jurassic before burial and intrusion by Darran Suite plutons at 158 Ma; deposition continuing until at least 148 Ma; metamorphism of the entire Loch Burn Formation at greenschist and amphibolite facies conditions; uplift, erosion, and then deposition of the overlying Eocene sediments; reburial to zeolite facies depths beneath the Tertiary Te Anau and Waiau Basins; final uplift in the Pliocene.

Loch Burn Formation, Fiordland, New Zealand: SHRIMP U-Pb ages, geochemistry and provenance

Abstract New SHRIMP U‐Pb ages and geochemical data have been obtained for the volcano‐sedimentary Loch Burn Formation (LBF). A rhyolitic clast from the tops of the Stuart Mountains gave a SHRIMP age of 150.3 ± 1.9 Ma, and a very fine sandstone from the same area was dominated by 147.9 ±2.1 Ma zircons. These ages imply a <148 Ma depositional age for the LBF in this area, in contrast to a previous 195‐1 +3Ma age determination for an intercalated felsic flow in the North Fiord area, c. 1 km distant. Two tonalitic clasts from Cumbrae Island gave ages of 354.6 ± 2.6 and 326.8 ±3.2 Ma, respectively. The c. 47 m.y. difference between depositional ages in the Stuart Mountains and North Fiord indicates that the LBF as currently mapped includes more than one unit. however, volcanic clasts and lavas from the two areas are indistinguishable in terms of major and trace element geochemistry, and there is currently insufficient information to discriminate between the two units. informal units are therefore proposed: the < 148 Ma LBF‐2 unit and the c. 195 Ma LBF‐1 unit. volcanic clasts and lavas from both units are probably derived from the Darran Suite arc. The c. 327 Ma tonalite clast has moderate Zr/TiO2 and chemistry similar to most of the other LBF tonalite samples, whereas the c. 355 Ma tonalitic clast has unusual, very high Zr chemistry. Neither appear to be related to any New Zealand plutonics currently well characterised in the literature, based on differences in major and trace element chemistry. however, recent work indicates that possible correlatives with appropriate age and geochemistry exist for both groups of tonalites. No Western Province material is recorded in any of the LBF samples, but this is not considered to exclude formation adjacent to or within the gondwana margin.

Paleoenvironmental and stratigraphic significance of palynomorphs from Upper Eocene (Kaiatan) Beaumont Coal Measures and Orauea Mudstone, Waiau Basin, western Southland, New Zealand

Abstract Studies of palynomorphs from three surface sections through the Upper Eocene Beaumont Coal Measures and Orauea Mudstone in the Waiau Basin, western Southland, together with sedimentological investigations, allow determination of the distribution of plant communities in relation to sedimentary environment Palynofloras from both formations are dominated by the southern beech, Nothofagus, particularly species representing the brassii group (Nothofagidites matauraensis). Fusca group (Nothofagidites flemingii) is also common, as are Casuarina, Myrtaceae, gymnosperms, and pteridophytes. Within the Beaumont Coal Measures and Orauea Mudstone three fades associations are recognised. The Beaumont Coal Measures and Orauea Mudstone were deposited in fluvio-deltaic and lacustrine environments, respectively. Deposition of the Orauea Mudstone in a lacustrine setting is confirmed by the presence of freshwater algae. Palynofloras from a fluvial channel-floodplain facies within the Beaumont Coal Measures have a hi...

Pleistocene glaciomarine sediments of the Kisbee Formation, Wilson River, southwest Fiordland, and some tectonic and paleoclimatic implications

Abstract Fossiliferous sediments of Kisbee Formation (new name) preserved in the Wilson River east of Puysegur Point, southwest Fiordland, are interpreted as filling a submarine canyon that was incised 160 m into Ordovician metasedi‐ments. The formation reflects deposition in quiet, deep cold water beneath floating ice, transitional into shallower water adjacent to an ice‐marginal environment. The macrofauna and nannoflora indicate deposition within Castlecliffian time, somewhere between 0.5 and 1.2 Ma, at depths estimated to range between 50–150 and >200 m. A sequence of marine terraces adjacent to the Wilson River is correlated to global sea‐level records, constraining the local uplift rate to 0.57 ± 0.04 mm/yr and the minimum age for Kisbee Formation to 0.69 Ma. If, as seems likely, the Matuyama‐Brunhes paleo‐magnetic transition lies within the mapped section, Kisbee Formation is older than 0.78 Ma at the the base, and Limopsis lived in >200 m of water.

Petrogenesis and geochemical characterisation of ultramafic cumulate rocks from Hawes Head, Fiordland, New Zealand

Abstract Early Cretaceous parts of the western Median Batholith (Western Fiordland Orthogneiss) represent the exposed root of a magmatic arc of dioritic to monzodioritic composition (SiO2=51–55 wt%; Na2O/K2O=3.7–8.8 in this study). We characterise for the first time the field relationships, petrography, mineralogy and geochemistry of ultramafic and mafic cumulates at Hawes Head, the largest exposure of ultramafic rocks in western Fiordland. We distinguish three related rock types at Hawes Head: hornblende peridotite (MgO=21–35 wt%); hornblendite (MgO=15–16 wt%); and pyroxenite (MgO=21 wt%). Petrogenetic relationships between the ultramafic rocks and the surrounding Misty Pluton of the Western Fiordland Orthogneiss are demonstrated by: (i) mutually cross-cutting relationships; (ii) similar mafic phases (e.g. pyroxene and amphibole) with elevated Mg-numbers (e.g. olivine Mg/(Mg+Fe)=0.77–0.82); (iii) fractionation trends in mineral geochemistry; and (iv) shared depleted heavy rare earth element patterns. In addition, the application of solid/liquid partition coefficients indicates that olivine in the ultramafic rocks at Hawes Head crystallised from a magma with Mg/(Mg+Fe)=0.54–0.57. The olivine grains therefore represent a plausible early crystallising phase of the adjacent Western Fiordland Orthogneiss (Mg/(Mg+Fe)=0.51–0.55).