Rose E. Turnbull

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.

Petlab: New Zealand’s national rock catalogue and geoanalytical database

ABSTRACT The Petlab database is New Zealand’s online national rock and analytical database, and provides an accessible, structured and permanent data repository for the local and global geoscience communities. The database contains locations, descriptions and analyses of rock and mineral samples from onland New Zealand, the offshore New Zealand region, Antarctica and worldwide. It is operated by GNS Science and, as a nationally significant database, currently receives core funding from central government. The major data contributors are GNS Science and Auckland, Massey, Waikato, Victoria, Canterbury and Otago universities, all of whom use the database as a digital catalogue for their rock and mineral collections. Petlab sample information and geoanalytical data can be uploaded, queried, viewed and downloaded at http://pet.gns.cri.nz. Petlab is a valuable tool for geoscientists in research and industry.

Extension-facilitated pulsed S-I-A-type “flare-up” magmatism at 370 Ma along the southeast Gondwana margin in New Zealand: Insights from U-Pb geochronology and geochemistry

New U-Pb zircon geochronology on S-, I-, and A-type granitic plutons in New Zealand refines the magmatic and tectonic history along the mid-Paleozoic Gondwana margin and provides constraints on the episodicity and dynamics of continental arc magmatism under “flare-up” conditions. High-precision isotope-dilution thermal ionization mass spectrometry (ID-TIMS) ages confirm that the voluminous (≥38,500 km3) predominantly S-type granites of the ca. 370–368 Ma Karamea Suite were emplaced within a brief ca. 2.1 Ma window. The Karamea Suite magmatic event represents a short-lived thermal perturbation that resulted in rapid crustal melting and granite emplacement that punctuated the steady-state arc “tempo” of the active Gondwana margin. Recognition of three distinct pulses of silicic magmatism within this ca. 2.1 Ma burst of magmatism, and calculation of flux rates that are comparable to those estimated for Cenozoic ignimbrite “flare-up” events indicate that time scales observed in volcanic complexes at the surface are directly analogous to those observed in plutonic complexes at depth. A genetic association with contemporaneous high-Sr/Y I-type and A-type granitoids suggests a thickened crust immediately prior to, and an extensional setting during Karamea Suite emplacement, respectively. Compositionally, Karamea Suite granites are compatible with an origin by dehydration melting of older infracrustal and supracrustal sources. However, thermal requirements suggest it is unlikely that the overthickened crust was able to reach temperatures hot enough to induce dehydration melting without an additional heat and/or fluid source. Direct involvement of hydrous mantle partial melts (supported by isotopic compositions) and/or an elevated asthenospheric heat flow is therefore advocated as the mechanism that induced extensive melting of the crust. An early postorogenic intra-arc extensional setting is proposed whereby thinning of the crust permitted hot asthenospheric mantle to rise to shallow mantle depths and facilitate melting. Application of laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) has further resolved a distinct zircon inherited (premagmatic) age component within Karamea Suite granites. This inherited age component is interpreted to represent a previously undocumented episode of magmatism along the New Zealand margin of Gondwana at ca. 387 ± 3 Ma, ca. 15 Ma prior to Karamea Suite emplacement. The ca. 387 Ma premagmatic zircon grains were preserved within the ca. 370 Ma Karamea Suite granites as a result of low zircon saturation temperatures ( T Zr < 800 °C). This ca. 387 Ma magmatic episode was volumetrically small, and it may have occurred as a result of Buller-Takaka terrane amalgamation—a crustal thickening event that thermally matured the crust and predisposed it to future melting. Slab rollback and/or delamination of a dense mafic root are suggested as possible triggers that facilitated the rapid change in tectonism from orogenic compression to postorogenic extension. Cessation of voluminous S-type magmatism by ca. 368 Ma was likely caused by depletion of the fertile metasedimentary source rocks that had undergone significant partial melting. Tectonic depletion of the source, by way of stretching the soft, partially melted crust, may also have served to halt production of S-type magmatism, resulting in small-volume production of I- and A-type granites from the less-fertile lower-crustal mafic source rocks.

The petrology, geochronology and significance of Granite Harbour Intrusive Complex xenoliths and outcrop sampled in western McMurdo Sound, Southern Victoria Land, Antarctica

Granite Harbour Intrusive Complex xenoliths in McMurdo Volcanic Group rocks and in situ outcrops have been studied from Mount Morning, western McMurdo Sound, Antarctica. Calc-alkalic samples have whole rock signatures and normative compositions similar to the Dry Valleys 1b suite, and zircon grains in one specimen yield a 545.2 ± 4.4 Ma crystallisation age. This supports subduction-related magmatism initiating in Southern Victoria Land by 545 Ma. A second group of xenoliths is alkalic, with titanite grains in one xenolith from this group dated at 538 ± 8 Ma. Whole rock chemistry, normative compositions and geochronology of the alkalic group are comparable to the Koettlitz Glacier Alkaline Suite (KGAS). The position of a proposed lower crustal discontinuity that may form a significant basement suture in the McMurdo Sound region is newly constrained to the east of Mount Morning, perhaps along the trace of the Discovery Glacier. The boundary between East and West Antarctica may also pass along the trace of the Discovery Glacier if, as previously hypothesised, its location is controlled by the basement suture. A significant basement suture may also have provided the necessary egress for the (regionally) early and sustained magmatic activity observed at Mount Morning over the last 24 million years.

Zetland Diorite, Karamea Batholith, west Nelson: field relationships, geochemistry and geochronology demonstrate links to the Carboniferous Tobin Suite

Abstract Field observations, petrography, geochemistry and U–Pb geochronology of the I-type Zetland Diorite from New Zealands Western Province reveal a Carboniferous age of emplacement and chemical affinity with the Tobin dioritic suite. New U–Pb zircon dating by isotope-dilution thermal-ionisation mass spectrometry (ID-TIMS) provides a robust age of 347.19±0.24 Ma for a sample of Zetland Diorite. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb zircon dating of a Zetland quartz leucodiorite sample is complicated by significant inheritance from Karamea and Paringa granitoid suites but yields an estimated crystallisation age of 350.6±8.7 Ma, consistent with the field evidence for emplacement coeval with the dated mafic dioritic phase. Our results show that Zetland Diorite is at least c. 10 Ma younger and geochemically distinct from the 369–360 Ma I-type dioritic intrusives of the Paringa Suite, including the Riwaka Complex, as well as from the 370–368 Ma Karamea Suite S-type granites with which the Zetland Diorite had previously been deemed coeval. It therefore cannot serve as a mafic end-member source component of the Karamea Suite and its emplacement does not constrain the minimum age of amalgamation of the Buller and Takaka terranes.

Field and petrographical insight into the formation of orbicular granitoids from the Bonney Pluton, southern Victoria Land, Antarctica

The diversity of orbicule types exposed within granitoids of the Bonney Pluton inn southern Victoria Land attests to the dynamic and complex interplay of magmatic processesn that were responsible for their formation. Orbicules formed in small pockets ofn H 2 O-rich silicate melt that was extracted from the crystallizing andn fractionating Bonney Pluton magma and concentrated along the pluton margins. These pocketsn of melt experienced a superheating event that destroyed almost all pre-existing nuclei andn a subsequent delay in crystallization, which led to undercooling conditions that promotedn rapid dendritic crystal growth. Superheating was induced by the injection of hot maficn magmas, evidenced by elevated plagioclase X An , and Mg-Al-Ti-contents inn hornblende that point to a higher temperature and a more mafic composition in the meltn that the orbicule shells crystallized from. Variation in the type and structure ofn orbicules (hornblende-rich versus plagioclase-rich shells) were likely due to repeatedn changes in the composition, H 2 O-content, temperature andn P H 2 O at the crystallizing orbicule boundaryn layer in response to pulses in the movement of magma, competition between crystallizingn phases, episodic vesiculation, degassing and/or second boiling which dictated then composition, texture and size of individual orbicule shells. Brittle fragmentation ofn orbicules occurred in response to vesiculation and fragmented orbicules are often found asn cores within intact orbicules, indicating that multiple phases of orbicule formation weren common. The alignment and compaction of orbicules in ‘pods’ indicates movement ofn orbicules within the melt-rich pockets occurred, prior to resumption of near-equilibriumn crystallization in the host granite.

High‐ to ultrahigh‐temperature metamorphism in the lower crust: An example resulting from Hikurangi Plateau collision and slab rollback in New Zealand

Lower crustal xenoliths erupted from an intraplate diatreme reveal that a portion of the New Zealand Gondwana margin experienced high-temperature (HT) to ultrahigh-temperature (UHT) granulite facies metamorphism just after shallow subduction ceased at c. 110–105 Ma. P–T calculations for the garnet–orthopyroxene-bearing felsic granulite xenoliths indicate equilibration at ~ 815 to 910°C and 0.7 to 0.8 GPa, and garnet-bearing mafic granulite xenoliths yield at least 900°C. Supporting evidence for the attainment of HT and UHT conditions in the felsic granulite comes from re-integration of exsolution in feldspar (c. 900 to 950°C at 0.8 GPa), Ti-in-zircon thermometry on Y-depleted overgrowths on detrital zircon grains (932°C + 24°C at aTiO2 = 0.8 + 0.2), and correlation of observed assemblages and mineral compositions with thermodynamic modelling results (> 850°C at 0.7 to 0.8 GPa). The thin zircon overgrowths, which were mainly targeted by drilling through the cores of grains, yield a U–Pb pooled age of 91.7 + 2.0 Ma. The cause of Late Cretaceous HT-UHT metamorphism on the Zealandia Gondwana margin is attributed to collision and partial subduction of the buoyant oceanic Hikurangi Plateau in the Early Cretaceous. The halt of subduction caused the fore-running shallowly dipping slab roll-back towards the trench position and permitted the upper mantle to rapidly increase the geothermal gradient through the base of the extending (former) accretionary prism. This sequence of events provides a mechanism for achieving regional HT–UHT conditions in the lower crust with little or no sign of this event at the surface. n nThis article is protected by copyright. All rights reserved.

The ultramafic–intermediate Riwaka Complex, New Zealand: summary of the petrology, geochemistry and related Ni–Cu–PGE mineralisation

ABSTRACT The Late Devonian ultramafic–intermediate Riwaka Complex represents a rare example of magmatic-related Ni–Cu–platinum group element (PGE) sulphide mineralisation within a convergent margin setting. We provide a comprehensive review of the petrography, geochemistry, geochronology and associated Ni–Cu–PGE sulphide mineralisation for the dominant lithologies of the Riwaka Complex. This study reveals that the c. 364 Ma Riwaka Complex was likely emplaced within an extensional intra-arc along the paleo-Pacific subduction margin of east Gondwana. Initial primary melts were derived by partial melting of a metasomatised heterogeneous mantle source, and potentially a young oxidised mafic underplate. Primary melts were tholeiitic, S-undersaturated, and enriched in Ni, Cu and PGE. Crystal accumulation (olivine, clinopyroxene, amphibole), fractionation, and minor magma mixing and crustal contamination account for most of the chemical diversity within the Riwaka Complex, and were the processes responsible for inducing S-saturation of the melt. Sulphide mineralisation occurs as disseminated pyrrhotite–pyrite–chalcopyrite–pentlandite in hornblende-bearing clinopyroxenite and gabbro cumulate lithologies, and is restricted to the southern portion of the complex, interpreted to represent the deeper-level conduit system. The northern portion of the complex represents a more evolved higher-level magma chamber.

Polymetallic mineralised veins in ferroan/A-type Cretaceous leucogranite, Stewart Island, New Zealand

ABSTRACT The 140u2009±u20091u2005Ma hypersolvus, ferroan, weakly peralkaline to weakly peraluminous North Red Head leucogranite in northwest Stewart Island is cut by quartz-pyrite-rich veins that contain a wide variety of Mo, Ag, Te, Bi, Au, Co, Cu, Pb, Zn, REE, Nb, Y, Th, U, Zr, Ti, Be and F-bearing minerals. Patchy hematite-pyrite alteration locally overprints leucogranite in the vicinity of the mineralised veins. Individual veins are up to 5u2005m thick and 200+ m long. U–Pb dating and trace-element geochemistry indicate a direct link between leucogranite crystallisation and exsolution of the vein-forming hydrothermal fluid. Mineralised veins developed along transpressional faults within the leucogranite soon after emplacement. Incipiently mineralised quartzu2009±u2009pyrite veins at Waituna Bay and the northern end of West Ruggedy Beach several kilometres from North Red Head are probably part of the same hydrothermal system as the veins at North Red Head. Metal and alteration assemblages at North Red Head most closely resemble those in rare hydrothermal systems associated with oxidised fluorine-rich A-type granites.

Polymetallic mineralisation associated with Carboniferous I-type granitoids in central Stewart Island, New Zealand

ABSTRACT Carboniferous granitoids in central Stewart Island host two metalliferous hydrothermal systems that formed during emplacement of the c. 306u2009±u20092u2005Ma old Euchre Pluton and 303u2009±u20092u2005Ma Hill 267 leucogranitoid, respectively. The Ogles Creek–Silvertown Hydrothermal System (OST) on the eastern side of South West Arm, Paterson Inlet is centred on the scheelite-bearing, ilmenite-syenogranite core of the Euchre Pluton. Here pyritic-potassic alteration and related veins contain Mo, Bi, Ag, Co, Cu, W, Pb, Zn, U–Th and rare Earth element (REE) sulphide, telluride, oxide and phosphate minerals. Peripheral quartz-rich veins contain various Ag, Au, Pb and Zn-bearing sulphide, telluride and oxide minerals. The Hill 267 Hydrothermal System (HHS) is centred on the ridge between the Scott Burn and Forked Creek where strongly altered leucogranitoid riddled with miarolitic cavities contains pyrite, W- and Nb-bearing rutile, molybdenite, tourmaline and 2–10 times background Bi, Ag, Te, Cu and Se. More prospective parts of both systems have probably been removed by erosion, but less deeply eroded correlative hydrothermal systems may be present elsewhere in New Zealand near the outboard margin of the Takaka Terrane.