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Research about New Zealand

Source-linked reports with geographic coverage including New Zealand.

At least 109 records · Page 6Linked to original sources
USGS1998

The Whakamaru group ignimbrites, Taupo Volcanic Zone, New Zealand: Evidence for reverse tapping of a zoned silicic magmatic system

The Whakamaru group ignimbrites are widespread voluminous welded ignimbrites which crop out along the eastern and western margins of the Taupo Volcanic Zone (TVZ), New Zealand. The ignimbrites have a combined volume exceeding 1000 km 3 , and were erupted from a large caldera in the central TVZ around 340 ka, following a c. 350 ka hiatus in caldera-forming activity in TVZ. Analysis of individual pumice clasts identifies five distinct magma types (rhyolite types A to D, and high alumina basalt) and significant gradients in temperature, water content, and Sr isotopic composition in the pre-eruptive Whakamaru magmatic system. There is a marked variation in mineral assemblage with composition; type A low-silica rhyolite pumices contain plagioclase, quartz, orthopyroxene, hornblende, biotite, and magnetite/ilmenite with distinctive large rounded quartz phenocrysts. High-silica (types B and C) pumices contain quartz (smaller, subhedral phenocrysts), plagioclase, sanidine, biotite, and magnetite/ilmenite. Type D pumices are rich in plagioclase and biotite phenocrysts, and have anomalously high Rb contents (>200 ppm) relative to all other pumice types. Rhyolite types B and C are related to type A magma by a two-stage crystal fractionation process, probably by side wall crystallisation and convective fractionation. The first stage involved 30–40% fractionation of a plagioclase-dominated (sanidine-free) assemblage to produce a type B magma, which in turn underwent fractionation of a plagioclase/quartz/sanidine assemblage to produce the highly evolved, but relatively Ba-depleted, type C magmas. Stratigraphic variations in modal proportions of mineral phases, and calculated Fe–Ti oxide equilibrium temperatures indicate that eruptions commenced with the hottest, least evolved magmas, and more evolved magmas became important at a later stage in the eruption along with a high alumina basalt component. This reverse-zoned sequence precludes simple sequential tapping of a large zoned magma chamber, and indicates a complex magma chamber configuration and/or withdrawal dynamics during eruption. Type D magma, which appears to be unrelated to either types A or B by crystal fractionation, may have formed a separate subjacent chamber that was ruptured and incorporated into the eruption. The Whakamaru magma system provides clear evidence that (less evolved) low silica rhyolites undergo significant fractionation at shallow crustal levels in central TVZ, to produce the generally more evolved rhyolites more commonly erupted at the surface, and suggests large ignimbrite eruptions may tap multiple magma chambers.

Journal of Volcanology and Geothermal Research↗
USGS1995

Volcanic and structural evolution of Taupo Volcanic Zone, New Zealand: A review

The Taupo Volcanic Zone (TVZ) in the central North Island is the main focus of young volcanism in New Zealand. Andesitic activity started at c. 2 Ma, joined by voluminous rhyolitic (plus minor basaltic and dacitic) activity from c. 1.6 Ma. The TVZ is c. 300 km long (200 km on land) and up to 60 km wide, as defined by vent positions and caldera structural boundaries. The total volume of TVZ volcanic deposits is uncertain because a sub-volcanic basement has not been identified, but present data suggest bulk volumes of 15–20,000 km 3 , and that faulted metasediments form most of the immediate subvolcanic basement. Rhyolite (≥15,000 km 3 bulk volume, typically 70–77% SiO 2 ) is the dominant magma erupted in the TVZ (mostly as calderaforming ignimbrite eruptions), andesite is an order of magnitude less abundant, and basalt and dacite are minor in volume (< 100 km 3 each). The history of the TVZ is here divided into ‘old TVZ’ from 2.0 Ma to 0.34 Ma, and ‘young TVZ’ from 0.34 Ma onwards, separated by the Whakamaru eruptions, which obscured much of the evidence for older activity within the zone. The TVZ shows a pronounced segmentation into northeastern and southwestern andesite-dominated extremities with composite cones and no calderas, and a central 125-km-long rhyolite-dominated segment. Eight rhyolitic caldera centres have so far been identified in the central segment, of which two (Mangakino and Kapenga) are composite features, and more centres will probably be delineated as further data accumulate. These centres account for 34 inferred caldera-forming ignimbrite eruptions, in the c. 1.6-Ma lifetime of the central TVZ. The modern central TVZ is the most frequently active and productive silicic volcanic system on Earth, erupting rhyolite at c. 0.28 m 3 s −1 , and available information suggests this has been so for at least the past 0.34 Ma. The rhyolites show no major compositional changes with time, though the extent of magma chamber zonation may have changed with the incoming of rifting and crustal extension in the past c. 0.9 Ma. Within the central TVZ, non-rhyolitic compositions have been erupted apparently irregularly in time and space; in particular there is no evidence for a geographic separation of basalts from andesites. Between 0.9 and 0.34 Ma, a major episode of uplift affected areas around the TVZ, while at the same time the main focus of activity may have migrated eastwards within the TVZ accompanying rifting along the axis of the zone. The modern TVZ is rifting at rates between 7 and 18 mm a −1 and restoration of the thin (15km) ‘crust’ ( V p ≤ 6.1 km s −1 ) beneath the central TVZ to its pre-rifting thickness (25 km) implies that rifting at such rates may have begun only at c. 0.9 Ma. The TVZ is a rifted arc, but its longitudinally segmented nature, high thermal flux and voluminous rhyolitic volcanism make it unique on Earth.

Taupo Volcanic Field↗
USGS1995

Chronology and dynamics of a large silicic magmatic system: Central Taupo Volcanic Zone, New Zealand

The central Taupo Volcanic Zone in New Zealand is a region of intense Quaternary silicic volcanism accompanying rapid extension of continental crust. At least 34 caldera-forming ignimbrite eruptions have produced a complex sequence of relatively short-lived, nested, and/or overlapping volcanic centers over 1.6 m.y. Silicic volcanism at Taupo is similar to the Yellowstone system in size, longevity, thermal flux, and magma output rate. However, Taupo contrasts with Yellowstone in the exceptionally high frequency, but small size, of caldera-forming eruptions. This contrast reflects the thin, rifted nature of the crust, which precludes the development of long-term magmatic cycles at Taupo.

Bay of Plenty, Taupo Volcanic Zone↗
USGS1994

Physical geology and eruptive history of the Matahina Ignimbrite, Taupo Volcanic Zone, North Island, New Zealand

The Matahina Ignimbrite is a 280 ka ash‐flow sheet that erupted from Haroharo Caldera in the Okataina Volcanic Centre, northern Taupo Volcanic Zone, North Island, New Zealand. The ignimbrite underlies a 2000 km 2 area mainly east of the caldera, ranges in thickness from 5 to 200 m, and has a outflow volume of c. 120 km 3 , equivalent to c. 75 km 3 of magma. It is a multiple‐flow, compound cooling unit consisting of a basal tephra (fallout) member and three ash‐flow members, designated lower, middle , and upper , that record three eruptive pulses separated by brief time intervals, estimated from cooling and compaction noddling to range from 20 to 60 days. Distribution of coarse lithic clasts, together with local interbedded co‐ignimbrite lag breccias and tephra layers east of the Puhipuhi Easin, confirm Haroharo Caldera as the eruptive source. Over most of its extent on the Kaingaroa Plateau, the outflow s leet thickens eastward away from its source and attains its greatest thickness in the elongate, north‐trending, fault‐a ngle trough formed between the gently east sloping surface of the plateau and the western front of the Ikawhenua Fange. Difference in thickness of the ignimbrite across the fault bounding the west front of the Ikawhenua Range suggests that during the short time interval between emplacement of the lower and middle ash‐flow members, a major tectonic event caused at least 10 m displacement on the fault locally. Circumstantial evidence supporting this early syneruptive tectonic event is found along the Bay of Plenty coast where penecontemporaneous liquefaction structures, possibly seismically induced, occur in the distal subaqueous facies of the lower ash‐flow member. The presence of such 1 quefaction structures in the Matahina and other coastal New Zealand ignimbrites suggests a possible close association between tectonism and major ignimbrite eruptions.

North Island, Taupo Volcanic Zone↗
USGS1992

40 Ar/ 39 Ar dating of Quaternary feldspar: Examples from the Taupo Volcanic Zone, New Zealand

Using a continuous laser and resistance furnace, we have measured ages on Quaternary plagioclase with an absolute precision of about ±30 ka and on Quaternary sanidine with a relative precision of better than 1%. Such precision was achieved by using low-temperature heating steps to remove much of the nonradiogenic argon contamination. Plagioclase is one of the most common mineral phases in volcanic rocks; thus, these procedures will be widely applicable to many problems for which precise radiometric age control has not been available. We studied plagioclase and plagioclase-sanidine concentrates from the oldest and the three largest silicic ash-flow deposits of the Taupo Volcanic Zone, New Zealand, one of the world's largest and most active volcanic systems. The results are in close agreement with new magnetostratigraphic data, suggest that existing fission-track age determinations significantly underestimate the age of older units, and shift the inception of Taupo Volcanic Zone volcanism back to at least 1600 ka. The improved precision has permitted the first correlations between proximal and distal units; previous correlations with deep-sea ash flows in the western Pacific require major revision.

Geology↗
USGS1991

K‐Ar ages from the Western Dome Belt and associated rhyolitic lavas in the Maroa‐Taupo area, Taupo Volcanic Zone, New Zealand

The Western Dome Belt is a 32 km long belt of rhyolitic lava domes west of Maroa caldera. New K‐Ar age data suggest that the belt was a significant locus of extrusive volcanism between the voluminous pyroclastic Whakamaru eruption(s), and the onset of caldera formation at Maroa, during which time it marked the western boundary of rhyolitic volcanism in Taupo Volcanic Zone. A smaller, younger cluster of lava flows and domes to the south at Ben Lomond station forms part of a transitional region between the youthful Maroa and Taupo calderas.

Maroa, Taupo↗
USGS1991

Effect of hunting on annual survival of grey ducks in New Zealand

We used band recovery data from grey ducks ( Anas superciliosa ) banded in New Zealand between 1957 and 1974 to test 2 null hypotheses: (1) hunting mortality is completely additive to natural sources of mortality, and (2) hunting mortality is completely compensated by changes in natural mortality. We modeled annual survival as a function of survival in the absence of hunting and the probability of death from hunting. The complete compensation hypothesis was rejected, but we were unable to reject the completely additive hypothesis. There was no evidence of sex- or age-specificity for the relationship between kill rate and annual survival rate. We used simulated data to evaluate model performance. Parameter estimates were unbiased despite the inclusion of estimates that lay outside the bounds of the parameter space, although model-based variance estimates were consistently less than empirical variances. Our results imply that harvest-restrictions may be useful in effecting change in annual survival rates of grey ducks.

Journal of Wildlife Management↗
USGS1991

Survival and band recovery rates of sympatric grey ducks and mallards in New Zealand

We used band recovery data from grey ducks ( Anas superciliosa ) and mallards. ( A. platyrhynchos ) banded sympatrically during 1957-74 to estimate annual survival and recovery rates. Young birds tended to have higher recovery rates and lower survival rates than adults for both species. Both species showed strong evidence of year-to-year variation in annual survival rates. Survival rates of male mallards were higher than those in females, as is typical for this species in North America, but there was no evidence of sex-specific survival differences in grey ducks. Recovery rate estimates for grey ducks were high and were significantly higher than those for mallards. However, survival rates did not differ significantly between the 2 species within any age-sex class. The similar survival rates, when mallard populations were increasing and grey ducks were decreasing, suggest that mallard reproductive rates have been greater than those of grey ducks.

Journal of Wildlife Management↗
USGS1990

Survival and band recovery rates of mallards in New Zealand

Mallards ( Anas platyrhynchos ) were banded at 4 discrete study areas in New Zealand. We used hunting season recoveries in conjunction with band recovery models to estimate annual survival and recovery rates and to test hypotheses about sources of variation in these rates. Recovery rates varied among the 4 areas and from year to year within areas. Recovery rates were generally higher for young mallards than for adults, and recovery rates of males were higher than those of females. Survival rates varied among the 4 areas and from year to year within some areas. Survival rates of females were lower than those of males, but survival rates of young birds were not consistently lower than those of adults. Average survival rates over all 4 areas were generally lower than averages for North American mallards.

Journal of Wildlife Management↗
USGS1989

Chemical affinities between the solvent extractable and the bulk organic matter of fossil resin associated with an extinct podocarpaceae

Analyses by GC-MS and GC-IR of resin associated to Dacridiumites mawsonii deposits, an extinct species of Podocarpaceae occurring on the South Island of New Zealand during the Bortonian (Middle Eocene), have revealed that dehydroabietic acid is the predominant component of the solvent soluble fraction. Accordingly, this diterpenoid has been selected as the principal component material for spectroscopic comparison with the bulk resin using IR and CP/MAS 13 C NMR.

South Island↗
USGS1988

Age and height distribution of holocene transgressive deposits in eastern North Island, New Zealand

Holocene transgressive deposits are frequently exposed near the present-day coastline of the study area along eastern North Island, New Zealand. They occur in sites of former estuaries that were filled during the postglacial rise in sea level. We present one hundred radiocarbon dates of Holocene transgressive deposits from the study area, ranging in age from ca. 10,000 to 5500 yr B.P. Relative sea level curves up to ca. 6000 yr B.P. were reconstructed for six locations. The curves have similar slopes prior to about 7000 yr B.P., indicating that sea level rise was much more rapid than any tectonic uplift at that time. The postglacial rise in sea level in New Zealand is considered, in general, to have culminated at about 6500 yr B.P. but the upper limit ages of transgressive deposits in our study area vary from ca. 5500 to 7000 yr B.P. At sites where the uplift rate is high the postglacial transgression culminated rather earlier than ca. 6500 yr B.P., and at sites where there is subsidence or there is very low uplift the culmination is later than ca. 6500 yr B.P. Nine of fourteen dates from fossil trees in growth position, that grew in and were buried by estuarine silt, cluster in the age range ca. 8000–8400 yr B.P. These data support the view that there was a minor regression or stillstand in the eustatic sea level rise at that time. Eleven tectonic subregions are recognized in the study area on the basis of average uplift rate. Most of these subregions coincide with those established from the number and ages of younger Holocene marine terraces of probable coseismic origin.

North Island↗
USGS1988

Limestone and chert in tectonic blocks from the Esk Head subterrane, South Island, New Zealand

The Esk Head subterrane is a continuous belt, generally 10-20 km wide, of tectonic mélange and broken formation on the South Island of New Zealand. This subterrane separates older and younger parts of the Torlesse terrane which is an extensive accretionary prism composed mostly of quartzo-feldspathic, submarine-fan deposits ranging from Permian to Early Cretaceous in age. The Torlesse is the most Pacific-ward of several Permian and Mesozoic accreted terranes in New Zealand that record tectonic amalgamation and ultimate accretion against the Pacific-facing Gondwana margin. The Esk Head subterrane of the Torlesse is especially informative because it includes within it conspicuous tectonic blocks of submarine basalt and a variety of basalt-associated seamount and sea-floor limestones and cherty rocks thought to be representative of the subducted plate. Limestones in tectonic blocks are of Late Triassic and probably Jurassic ages and include (1) submarine-cemented, pelagic-bivalve, geopetal packstone-grainstone; (2) brachiopod-bryozoan encrinite; and (3) radiolarian, pelagic lime mudstone. Most of the Triassic blocks have been dated using conodonts which have remarkably low color alteration index (CAI) values (<1.5). An incomplete sampling of cherts in tectonic blocks and from Holocene gravels derived from the Esk Head subterrane yields radiolarian-based ages of Late Triassic, Early Jurassic, Middle Jurassic, and Late Jurassic. Paleogeographic inferences drawn from megafossils, bioclasts, and radiolarians, as well as from carbonate cements, indicate deposition of the oceanic sedimentary rocks at paleolatitudes somewhat lower than that of the New Zealand part of the Gondwana margin, but higher than paleoequatorial latitudes. These oceanic sediments and their basaltic substrates were evidently emplaced in the Torlesse accretionary prism following off-scraping from an extensive subducting oceanic plate, probably the Phoenix plate, which was obliquely convergent with the northwest-trending Gondwana margin during Late Jurassic and/or Early Cretaceous time.

Geological Society of America Bulletin↗
USGS1987

Tectonostratigraphic terranes of the Croissilles Harbour region, South Island, New Zealand

The boundary between Hokonui and Te Anau assemblages is flanked by a broad (10–20 km) zone of imbricated slabs of late Paleozoic and Mesozoic lithostratigraphic terranes. Five terranes are mapped, three of predominantly sedimentary character (Dun Mountain‐Maitai, Rai, Pelorus) are separated by two consisting of ophiolitic melange (Patuki, Croisilles). A regional stratigraphy is mapped within the Late Permian Maitai Group, but formational subdivision of Rai and Pelorus rocks is not attempted because of degree of deformation and the more monotonous aspect of these graywacke‐dominated suites. Sandstone petrography and petrochemistry indicate provenance of sands mainly from dissected and undissected arc sources. Each of the three sedimentary belts possesses its own lithic character and we can see no evidence for original stratigraphic interrelations. The two ophiolitic melanges are similar, but not identical. They probably formed through tectonic disruption of the Dun Mountain ophiolite. Correlation seems more likely for these but must await further evidence. Each terrane possesses distinctive structural style, metamorphic grade, and probably metamorphic timing. The Croisilles area represents a complex zone of rocks formed under both convergent and divergent conditions; their evolution began early in the Permian and continued until achieving the present relationship, probably by middle Mesozoic time. Original relations between the five terranes remain equivocal and they should be regarded as suspect terranes until further constraints are available.

South Island↗
USGS1984

Eyewitness account of the 1931 great earthquake at Hawke’s Bay, New Zealand

No part of New Zealand is far from a known earthquake origin. The magnitude 7.9 earthquake of 1931 at Hawke's Bay, North Island, on February 3, 1931, was the most serious event recorded in New Zealand hsitory. It was responsible for 256 deaths. The Modified Mercalli intensity reached XI in Napier, a city of 35,000 people, and hence, caused considerable destruction to property.

Hawkes Bay↗
USGS1981

Earthquake-triggered landslides form lakes in New Zealand

Eleven small lakes were formed by landslides caused by the 1929 Buller earthquake in New Zealand; four others were formed by other historic earthquakes in this country. At least nine other New Zealand lakes are dammed by landslides and were probably formed by prehistoric earthquakes. Earthquake-dammed lakes could provide an estimate of paleoseimicity for the past few hundred or thousand years.

Earthquake Information Bulletin (USGS)↗