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Permian Parapara Group and Triassic Topfer Formation are small clastic sedimentary outliers that rest on Cambrian to Devonian basement terranes in the Western Province of South Island, New Zealand....

Detrital zircon U–Pb and muscovite 39Ar/40Ar ages from sandstones in the fluviatile to shallow marine mid-Jurassic Clent Hills Group and Wakaepa Formation of mid-Canterbury, South Island, New Zeala...

A c. 30 cm thick hydrothermal dike (tuffisite) cuts Early Cretaceous Waipapa Composite Terrane basement on Great Barrier Island. The dike was previously, and erroneously, described as a conglomerate band in the Waipapa Composite Terrane. Zircon from a granite clast in the dike gives a U–Pb age of 17.1 ± 0.6 Ma. The age contributes to a growing dataset of geochronological information from the Miocene Northland Arc.

Detrital zircon ages are presented for 34 early Palaeozoic sandstones from Buller and Takaka terranes, New Zealand, and formerly adjacent parts of Australia–Antarctica. The Buller–Takaka datasets always have two major groups: Ordovician–late Neoproterozoic, 444–700 Ma (but mainly 540–700 Ma), termed ‘Gondwana Assembly’ (GA), and early Neoproterozoic–Mesoproterozoic, 700–1600 Ma (but mainly 900–1200 Ma), termed ‘Rodinia Assembly’ (RA). In both terranes, significant age components within these groups are strikingly similar and also have RA/GA ratios, 0.6–1.8. The Cambrian volcanic arc of the Takaka Terrane has contributed little to the zircon patterns. Proportions of Late Cambrian–Early Ordovician zircons, characteristic of granitoid sources in the Ross–Delamerian Orogen are low. The zircons are predominantly reworked with contemporary zircons only evident in a few Buller datasets. The zircon patterns suggest that two major sources (late Mesoproterozoic and late Neoproterozoic), enduring over 120 Ma, were w...

Detrital zircon U–Pb ages and Rb–Sr metamorphic ages from low-grade Torlesse Supergroup metasedimentary rocks from North Canterbury and Marlborough provide preliminary evidence for a continuation of the Kaweka Terrane of the central North Island into the Torlesse Composite Terrane of the South Island. This would extend from the south side of the Wairau Fault in the upper Wairau River valley southwards to the Lake Tennyson and Lake Sumner areas, and as far as Hawarden. Rb–Sr ages indicate Jurassic metamorphism, 170±24 Ma, with initial 87Sr/86Sr ratios at that time 0.7073±0.0007 i.e. similar to their North Island counterparts. These Kaweka Terrane rocks have detrital zircon ages that follow the distinctive pattern of the Torlesse rocks in general, i.e. substantial (>30%) Permian–Triassic and Precambrian–Early Palaeozoic groupings, but they also have minor youngest age components c. 175–165 Ma which constrain a maximum Early–Middle Jurassic depositional age. In detail, significant, older zircon components ar...

Rb‐Sr isochron ages and associated initial 87Sr/86Sr ratios of metasedimentary rocks of Caples Group in Southland and Otago, Pelorus Group in Nelson and Marlborough, and their minor North Island correlates in Northland and King Country, reveal the essential continuity of a long Caples Terrane throughout New Zealand. The Rb‐Sr ages, in the range 251–117 Ma, record post‐metamorphic, Early Triassic to Early Cretaceous uplift and cooling, whilst their associated range of initial 87Sr/86Sr ratios, 0.7039–0.7053, allows a discrimination from analogous datasets of neighbouring Torlesse and Waipapa Terranes. Some petrographically and geochemically anomalous Caples Terrane rocks in East Otago, and Otago Schists of the Aspiring Terrane, all with initial 87Sr/86Sr ratios >0.7055, compare best with dataseis of Waipapa Terrane of the North Island. Detrital zircon U‐Pb ages of greywackes from Caples Terrane metasediments have youngest zircon age components from 251 to 215 Ma, and a comparison of dataset patter...

Detrital zircon U‐Pb ages in grey wackes and initial 87Sr/86Sr ratios are reported for low‐grade metasedimentary rocks from Torlesse Supergroup, Waipapa Group, and Kaimanawa Schist in the central North Island, New Zealand. The data reveal the presence of a hitherto unsuspected, areally extensive, Jurassic part of the Torlesse composite terrane in the Kaimanawa, Kaweka, and Ruahine Ranges, which we name the Kaweka Terrane. Kaweka rocks have initial 87Sr/86Sr ratios (at metamorphism) and detrital zircon patterns that in part are transitional between Rakaia and Pahau Terrane rocks and in part similar to Waipapa Terrane rocks. Combined detrital zircon age data for all Torlesse and Waipapa Terrane data reveal an essential unity, with a long persistence (260–120 Ma) of predominant Permian‐Triassic sources in the form of a major Cordilleran‐style batholith, a decline in major early Paleozoic‐Precambrian sources between 260 and 220 Ma, and presence of minor Early Carboniferous to Late Devonian sources be...

Rb‐Sr metamorphic and U‐Pb detrital zircon ages are reported for basement metasediments and cover sandstones of the Chatham Islands. Rb‐Sr metamorphic ages of the Chatham Schist are 180–198 Ma (Early Jurassic), with initial 87Sr/86Sr ratios 0.7075–0.7091, grouping this distinctively with Torlesse Supergroup of the Eastern Province of New Zealand. These ages impose an Early Jurassic minimum age for the sedimentary protoliths. Detrital zircons from two Chatham Schist metagrey wackes have principal age peaks in the interval Late Triassic to Late Permian, and the youngest, 230–250 Ma, suggest maximum early Late Triassic to early Early Triassic ages for sedimentation. The patterns of minor, but significant, Paleozoic components and scattered Precambrian ages in these greywackes resemble those of Permian Torlesse Supergroup greywackes, but that in a greywacke from the Forty Fours islets is closer to possible latest Permian Caples Group greywackes in Otago. A Cretaceous cover sandstone from Pitt Island ...

Fifty‐six previously unpublished K‐Ar ages for the Dunedin Volcanic Group and previously published K‐Ar and 40Ar/39Ar ages demonstrate that activity in the centrally situated Dunedin Volcano (here given formal lithostrati‐graphic status) lasted from 16.0 ± 0.4 to c. 10.1 Ma, and that of the surrounding Waipiata Volcanics lasted from 24.8 ± 0.6 to 8.9 ± 0.9 Ma. Apart from a gap at c. 20 Ma, recorded Waipiata activity climaxed at c. 16–14 Ma when activity of the Dunedin Volcano was beginning; it outlasted that of the Dunedin Volcano by c. 1 m.y. The total volume erupted by the Dunedin Volcano may have exceeded that of the largely monogenetic Waipiata Volcanics by an order of magnitude. New major‐ and trace‐element analyses are given for 87 whole‐rock samples and kaersutite. The whole‐rock data demonstrate the exclusively alkalic nature of the group, the Waipiata Volcanics being more strongly alkalic than most of the mafic members of the central volcano. This fractionated to give a much greater volu...

Rb‐Sr ages of low‐grade metasediments of the Waipapa Group (probable Permian‐Jurassic) of Northland and Auckland range from Late Triassic (c. 209–217 Ma) to Middle Jurassic (c. 164–174 Ma), reflecting deformation and metamorphism during the Rangitata Orogeny. K‐Ar ages indicate Middle Jurassic (c. 165–175 Ma) uplift and cooling of the western Omahuta‐Puketi Forest block, and later, Middle‐Late Jurassic (c. 150–160 Ma) cooling of the Helena Bay to Hunua Ranges eastern coastal block. In the intervening Western Bay of Islands block, there is evidence of local Early Cretaceous (c. 135 Ma) metamorphism. Rb‐Sr whole‐rock isochron age (t) and initial 87Sr/86Sr ratio (i) data support the assignment of Waipapa Group of the westernmost, Omahuta‐Puketi block to the Caples Terrane. The remaining data have a consistent (t)‐(i) signature, with (i) values 0.7039–0.7049, unlike Permian‐Cretaceous Torlesse Supergroup metasediments with more radiogenic (i) values, typically >0.7060. They thus support the retention...

Rb‐Sr whole‐rock isochron ages from 33 localities of low‐grade metasediments of the Torlesse Supergroup in Canterbury date two episodes of burial metamorphism. Permian and Triassic metasediments were metamorphosed in latest Permian to Middle Triassic times (255–235 Ma), and in Late Triassic to Early Jurassic times (215–195 Ma), respectively. These data also confirm a consistent age (t), and initial 87Sr/86Sr ratio (i), relationship in both Permian and Triassic groups from Otago in the South Island to the Wellington region in the North Island. The (t)‐(i) data of all Torlesse metasediments are more radiogenic than those in other Eastern Province terranes. In particular, Triassic Torlesse (t)‐(i) data confirm a source area dominated by Late Permian to Early Triassic I‐type granitoids, such as the southern‐central part of the New England Fold Belt of northeastern Australia and its hinterland. Permian Torlesse data are similar but indicate an older and less radiogenic source of predominantly Early Pe...

Rb‐Sr whole‐rock isochron ages of early Paleozoic, Greenland Group (Buller Terrane) metasediments from 17 localities range from 458 ± 9 to 271 ± 26 Ma, in a pattern similar to, but frequently 20–30 m.y. older than, corresponding K‐Ar ages of slates. The ages reflect an original low‐grade regional metamorphism at 450 ± 10 Ma in Late Ordovician times and subsequent cooling, which has then been pervasively overprinted by younger thermal events, most probably associated with the emplacement of Devonian‐Carboniferous granitoids. Initial 87Sr/86Sr ratios (i) at the time of metamorphism (t) increase from c. 0.717 at c. 450 Ma to c. 0.722 at c. 350 Ma—this evolution reflecting a bulk sediment Rb/Sr ratio of c. 1.0. The (t)‐(i) data suggest that the Greenland Group source area is extensive granitoid (mostly S‐type) and older metamorphic complexes, similar to the Wilson Terrane of the Ross and Adelaide Foldbelts of Antarctica and Australia. The New Zealand early Paleozoic data follow the (t)‐(i) trend of o...

Understanding the temporal and spatial development of the early Miocene Northland Volcanic Arc is critical to interpreting the patterns of volcanic activity in northern New Zealand through the late Cenozoic. The northwesterly trending arc is considered to have developed above a southwest‐dipping subduction system. The distribution of its constituent eruptive centres is described in terms of an eastern belt that extends along the eastern side of Northland and a complementary broad western belt which includes subaerial and submarine volcanic edifices. Critical examination of all 216 K‐Ar ages available, including 180 previously unpublished ages, and their assessment against tectonic, lithostratigraphic, seismic stratigraphic, and biostratigraphic constraints, leads us to deduce a detailed chronology of periods of activity for the various early (and middle) Miocene arc‐type volcanic complexes and centres of northern New Zealand: Waipoua Shield Volcano Complex (19–18 Ma, Altonian); Kaipara Volcanic C...

K‐Ar and Rb‐Sr ages of Marlborough Schist and Pelorus Group metasediments show coherent regional metamorphic/cooling age patterns, irrespective of their terrane protolith, in which ages are primarily inversely related to metamorphic grade and, more locally, with distance from the Picton Fault Zone. The oldest ages, from the lowest grade (prehnite‐pumpellyite facies, textural grade 1'IIA) Pelorus Group are mainly in the range 175–200 Ma, indicating regional metamorphism occurred at least in earliest Jurassic or latest Triassic times. Progressive cooling of Marlborough Schist resulted in a spectrum of cooling ages, mainly 110–180 Ma, which reflects slow regional uplift during the Jurassic and Early Cretaceous. Some disruption of this pattern occurred at the Picton Fault Zone where post‐Early Cretaceous movement has juxtaposed high and low structural levels. Initial 87Sr/86Sr isotopic ratios (i) at the time of metamorphism (t), derived from Rb‐Sr whole‐rock isochron data, further characterise terran...

Geochronological studies of the eastern Otago Schist and adjacent metagreywacke sequences are applied to their structural/metamorphic history and schist protoliths. Rb‐Sr whole‐rock isochron and K‐Ar total‐rock ages are inversely correlated with metamorphic grade (both in terms of mineral facies and textural zones), dating the time of peak metamorphism and/or postmetamorphic cooling. On the northern flank of the schists, older ages (200–230 Ma) date initial burial metamorphism and deformation in late Triassic ‐ early Jurassic times. Younger age patterns (to 115 Ma) reflect either (1) higher grade metamorphism during a single event followed by long‐continued uplift, or (2) early burial metamorphism at >200 Ma with a second, regional metamorphism between then and 115 Ma followed by rapid uplift. Initial Sr isotopic ratios derived from isochrons indicate that protoliths originate in two terranes. North of Dunedin, initial 87Sr/86Sr ratios range from 0.7064 to 0.7092, similar to Torlesse Terrane (Rak...

Twenty‐one basanites from a regional dike swarm in the Awatere River, Winterton River and Gladstone Stream, Awatere Valley area, Marlborough, have been analysed (major and trace elements) and dated by the K‐Ar method. K‐Ar ages of the dikes range between 100 and 60 Ma. The younger age extends the previously determined age range of igneous activity in the Awatere Valley (fossil age of volcanic activity; K‐Ar and fission‐track ages of volcanic and plutonic rocks) of 103–90 Ma for another 30 Ma into early Tertiary time. Considering only phenocryst‐free or phenocryst‐poor dikes, SiO2, total alkalis, Ba, Ce, Y, Zr, and Differentiation Index (D.I.) increase with decreasing age, and MgO, CaO, Cr, Cu, Ni, Sc, and Mg number decrease. This variation reflects a time‐dependent evolution of magma composition controlled by early‐stage olivine/pyroxene fractionation, gradually increasing sodic enrichment of plagioclase, and later crystallisation of K‐feldspar.