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Author(s): Alexandra Witze An international team of geoscientists has unleashed a full-fledged onslaught to understand New Zealand's biggest earthquake and tsunami hazard. On 8 March, the JOIDES Resolution drill ship [...]

Shortly after travelling through the Waikato in January 1904 environmentalist John Muir wrote to his friend and former colleague Robert Underwood Johnson of his delight in the New Zealand landscapes [...]

The ratite moa (Aves: Dinornithiformes) were a speciose group of massive graviportal avian herbivores that dominated the New Zealand (NZ) ecosystem until their extinction [approximately equal to] 600 years ago. The phylogeny and evolutionary history of this morphologically diverse order has remained controversial since their initial description in 1839. We synthesize mitochondrial phylogenetic information from 263 subfossil moa specimens from across NZ with morphological, ecological, and new geological data to create the first comprehensive phylogeny, taxonomy, and evolutionary timeframe for all of the species of an extinct order. We also present an important new geological/paleogeographical model of late Cenozoic NZ, which suggests that terrestrial biota on the North and South Island landmasses were isolated for most of the past 20-30 Ma. The data reveal that the patterns of genetic diversity within and between different moa clades reflect a complex history following a major marine transgression in the Oligocene, affected by marine barriers, tectonic activity, and glacial cycles. Surprisingly, the remarkable morphological radiation of moa appears to have occurred much more recently than previous early Miocene (ca. 15 Ma) estimates, and was coincident with the accelerated uplift of the Southern Alps just ca. 5-8.5 Ma. Together with recent fossil evidence, these data suggest that the recent evolutionary history of nearly all of the iconic NZ terrestrial biota occurred principally on just the South Island. ancient DNA | Oligocene Drowning | Dinornithiformes | phylogeny | taxonomy doi/10.1073/pnas.0906660106

Displacement rates for normal and reverse faults (n = 57) are generally higher when averaged for the Holocene (~10 ka) than for the late Quaternary (~300 ka) and longer time scales. Holocene acceleration of displacement rates could be attributed to geological processes that produce increases of tectonic tempo. We propose an alternative model in which the observed rate changes arise from variability in earthquake slip and/or recurrence coupled with a sampling bias toward those faults that are best represented at the Earth's surface and that accrued displacement fastest during the Holocene. This model is consistent with displacement rates measured over time intervals of as long as -300 ka for 129 faults from the Taupo Rift, New Zealand. Departures of earthquake parameters and associated displacement rates from their long-term (>300 ka) averages are attributed to fault interactions and occur on time intervals inversely related to these long-term displacement rates and to regional strain rates.

Understanding the timings of interhemispheric climate changes during the Holocene, along with their causes, remains a major problem of climate science. Here, we present a high-resolution [sup.10]Be chronology of glacier fluctuations in New Zealand's Southern Alps over the past 7000 years, including at least tire events during the last millennium. The extents of glacier advances decreased from the middle to the late Holocene, in contrast with the Northern Hemisphere pattern. Several glacier advances occurred in New Zealand during classic northern warm periods. These findings point to the importance of regional driving and/or amplifying mechanisms. We suggest that atmospheric circulation changes in the southwest Pacific were one important factor in forcing high-frequency Holocene glacier fluctuations in New Zealand.

We use a multiproxy approach to determine surface and bottom water temperatures off the coast of New Zealand during the middle Eocene and to constrain the [[delta].sup.18]O of seawater. We use these data to place constraints on the size and variability of global ice sheets at that time. The Hampden Section in South Island is characterized by exceptionally well preserved microfossils and clear sedimentary cyclicity, providing a remarkable window into conditions at paleolatitude ~55[degrees]S in the Pacific Ocean. The cyclicity was studied in detail over a ~4 m section corresponding to an interval of ~70 k.y., ca. 41.7 Ma. The sedimentary cycles are defined by fluctuations in the sand (>63 [micro]m) component, occurring on a wavelength of ~1 m, corresponding to Milankovitch-scale frequency. Analyses of foraminifer oxygen isotopic ([[delta].sup.18]O) and Mg/Ca composition, combined with TE[X.sub.86] analyses from organic carbon, are used to generate records of seawater temperature and oxygen isotopic composition ([[delta].sup.18][O.sub.sw]). These indicate bottom water temperatures of ~11-13 [degrees]C and sea surface temperatures of ~23-25 [degrees]C with good agreement between the proxies. Temperature cyclicity with a magnitude of ~1.5 [degrees]C occurs in both surface and bottom waters, approximately in phase with the sedimentary cycles. Estimates of [[delta.sup.18][O.sub.sw] have a mean value of -1.2% throughout the study section. Taken together, the data suggest a largely ice-free world with orbital-scale cycles expressed as temperature and hydrological variation with little or no ice volume change. Keywords: Eocene, paleoclimate, ice, temperature, cyclicity, New Zealand.

The Waipounamu Erosion Surface is a time-transgressive, nearly planar, wave-cut surface. It is not a peneplain. Formation of the Waipounamu Erosion Surface began in Late Cretaceous time following break-up of Gondwanaland, and continued until earliest Miocene time, during a 60 million year period of widespread tectonic quiescence, thermal subsidence and marine transgression. Sedimentary facies and geomorphological evidence suggest that the erosion surface may have eventually covered the New Zealand subcontinent (Zealandia). We can find no geological evidence to indicate that land areas were continuously present throughout the middle Cenozoic. Important implications of this conclusion are: (1) the New Zealand subcontinent was largely, or entirely, submerged and (2) New Zealand's present terrestrial fauna and flora evolved largely from fortuitous arrivals during the past 22 million years. Thus the modem terrestrial biota may not be descended from archaic ancestors residing on Zealandia when it broke away from Gondwanaland in the Cretaceous, since the terrestrial biota would have been extinguished if this landmass was submerged in Oligocene Early Miocene time. We conclude that there is insufficient geological basis for assuming that land was continuously present in the New Zealand region through Oligocene to Early Miocene time, and we therefore contemplate the alternative possibility, complete submergence of Zealandia. Keywords: Waipounamu Erosion Surface, peneplain, submergence, Cenozoic, Gondwanaland, Zealandia, New Zealand.

The Waipaoa sedimentary system spans ~100 km from terrestrial upland to continental rise. Alluvial buffering has little effect on sediment flux at the outlet of this mesoscale dispersal system, and hinterland-to-margin transport is accomplished rapidly. Because of this synergy, the floodplain and shelf depocenters are sensitive to changes in sediment production in the hinterland, and natural and anthropogenically forced changes in sediment source dynamics that occur at several temporal and spatial scales leave distinctive signals in the stratigraphic record. Manifested as variations in sediment properties, these signals appear in intercorrelated sediment cores from a headwater riparian storage area and the major terrestrial and marine repositories for sediment discharged during the past 2.4 k.y. The signals represent the landscape response to vegetation and land-use change, short-term fluctuations in climate that affect surface properties and processes, and extreme storms and subduction-thrust earthquakes. Extreme storms are the minimum geomorphologically effective event preserved in the sediment records. Lower-magnitude storms that are integral components of the prevailing hydrometeorological regime create high-frequency fluctuations in sediment properties and collectively contribute to event sequences of >100 yr duration. Events and event sequences comprise a hierarchy of temporally sensitive phenomena, the impacts of which are conditioned by frequency and magnitude. By contrast, vegetation disturbance is a spatially sensitive phenomenon that directly impacts sediment source areas and lowers the threshold of landscape sensitivity to erosion. For this reason, the Taupo eruption of 1.718ka and the piecemeal vegetation changes that occurred after the arrival of Polynesian settlers also generated strong depositional signals. After European colonization, deforestation of the hinterland altered landscape sensitivity and precipitated the transition to an erosional regime that impacted sediment production and dispersal across the entire magnitude-frequency spectrum of events, regulating sediment delivery to and transport in stream channels. No other perturbation had such a profound impact on the Late Holocene depositional record. Keywords: sediment dispersal, sediment cores, source to sink, depositional signals, environmental change. doi: 10.1130/B25996.1

Exhumed sections of the middle and lower crust in western New Zealand reveal how deformation was partitioned within a thermally and rheologically evolving crustal column during Cretaceous continental extension. Structural data, P-Tdeterminations, and U-Pb geochronology from central Fiordland and the Paparoa Range in Westland show that extension initiated in the lower crust by ~114 Ma as a period of arc-related magmatism waned. Initially, deformation was localized into areas that were weakened by heat and magma. However, these hot, weak zones were ephemeral. During the period 114-111 Ma, lower crustal fabrics record a rapid progression from magmatic flow to high-temperature deformation at the gamet-granulite facies (T > 700[degrees]C, P = 12 kbar) to cooler deformation at the upper amphibolite facies (T = 550-650[degrees]C, P = 7-9 kbar). Lower crustal cooling and compositional contrasts between mafic granulites and hydrous metasedimentary material resulted in a middle crust that was weak relative to the lower crust. Between circa 111 and circa 90 Ma, focused subhorizontal flow and vertical thinning in a weak middle crust led to the collapse of the upper crust and the unroofing of midcrustal material. During this period, arrays of conjugate-style shear zones transferred displacements vertically and horizontally through the crust, resulting in a structural style that resembles crustal-scale boudinage. The New Zealand example of continental extension shows that a weak middle crust and a relatively cool, highly viscous lower crust can result in a localized style of extension, including the formation of metamorphic core complexes that exhume the middle crust but not the lower crust. doi:10.1029/2006TC002003.

Deformation across the active Hikurangi subduction margin, New Zealand, including shortening, extension, vertical-axis rotations, and strike-slip faulting in the upper plate, has been estimated for the last ~24 Myr using margin-normal seismic reflection lines and cross sections, strike-slip fault displacements, paleomagnetic declinations, bending of Mesozoic terranes, and seafloor spreading information. Post-Oligocene shortening in the upper plate increased southward, reaching a maximum rate of 3-8 mm/year in the southern North Island. Upper plate shortening is a small proportion of the rate of plate convergence, most of which (>80%) accrued on the subduction thrust. The uniformity of these shortening rates is consistent with the near-constant rate of displacement transfer (averaged over [greater than or equal to] 5 Myr) from the subduction thrust into the upper plate. In contrast, the rates of clockwise vertical-axis rotations of the eastern Hikurangi Margin were temporally variable, with ~3[degrees]/Myr since 10 Ma and ~0[degrees]-1[degrees]/Myr prior to 10 Ma. Post 10 Ma, the rates of rotation decreased westward from the subduction thrust, which resulted in the bending of the North Island about an axis at the southern termination of subduction. With rotation of the margin and southward migration of the Pacific Plate Euler poles, the component of the margin-parallel relative plate motion increased to the present. Plate convergence dominated the Hikurangi Margin before ca. 15 Ma, with the rate of margin-parallel motion increasing markedly since 10 Ma. Vertical-axis rotations could accommodate all margin-parallel motion before 1-2 Ma, eliminating the requirement for large strike-slip displacements (for example, >50 km) in the upper plate since the Oligocene. doi: 10.1029/2006TC002090.

The Paleocene-Eocene thermal maximum (PETM) ca. 55.5 Ma was a geologically brief interval characterized by massive influx of isotopically light carbon, extreme changes in global climate, and profound variations in Earth system processes. An outstanding issue is whether it was an isolated event, or the most prominent example of a recurring phenomenon. Recent studies of condensed deep-sea sections support the latter, but this finding remains uncertain. Here we present and discuss lithologic and carbon isotope records across two lower Eocene outcrops on South Island, New Zealand. The PETM manifests as a marl-rich horizon with a significant negative carbon isotope excursion (CIE). Above, in sediment deposited between 54 and 53 Ma, are four horizons with similar though less pronounced expressions. Marl beds of all five horizons represent increased terrigenous sedimentation, presumably linked to an accelerated hydrological cycle. Five corresponding clay-rich horizons and CIEs are found in deep-sea records, although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution. The presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of [sup.13]C-depleted carbon during the early Eocene. Keywords: Paleocene-Eocene thermal maximum, PETM, carbon isotope excursion, CIE.

U--Pb detrital zircon ages (LAM-ICPMS) are reported for 20 greywackes and sandstones from seven major tectono-stratigraphic terranes of the Eastern Province of New Zealand (Cretaceous to Carboniferous) to constrain sediment provenances. Samples are mainly from three time horizons: Late Permian, Late Triassic and Late Jurassic. Age datasets are analysed as percentages in geological intervals, and in histogram and cumulative probability diagrams. The latter discriminate significant zircon age components in terms of terrane, sample stratigraphic age, component age, precision and percentage (of total set). Zircon age distributions from all samples have persistent, large Triassic-Permian, and very few Devonian--Silurian, populations, features which exclude a sediment provenance from the early Palaeozoic, Lachlan Fold Belt of southeast Australia or continuations in New Zealand and Antarctica. In the accretionary terranes, significant Palaeozoic (and Precambrian) zircon age populations are present in Torlesse and Waipapa terranes, and variably in Caples terrane. In the forearc and back-arc terranes, a unimodal character persists in Murihiku and Brook Street terranes, while Dun Mountain--Maitai terrane is more variable, and with Caples terrane, displays a hybrid character. Required extensive Triassic--Permian zircon sources can only be found within the New England Fold Belt and Hodgkinson Province of northeast Australia, and southward continuations to Dampier Ridge, Lord Howe Rise and West Norfolk Ridge (Tasman Sea). Small but significant Palaeozoic (and Precambrian) age components in the accretionary terranes (plus Dun Mountain--Maitai terrane), have sources in hinterlands of the New England Fold Belt, in particular to mid-Palaeozoic granite complexes in NE Queensland, and Carboniferous granite complexes in NE New South Wales. Major and minor components place sources (1) for the older Torlesse (Rakaia) terrane, in NE Queensland, and (2) for Waipapa terrane, in NE New South Wales, with Dun Mountain--Maitai and Caples terrane sources more inshore and offshore, respectively. In Early Jurassic Late Cretaceous, Torlesse (Pahau) and Waipapa terranes, there is less continental influence, and more isolated, offshore volcanic arc sources are suggested. There is local input of plutonic rock detritus into Pahau depocentres from the Median Batholith in New Zealand, or its northward continuation on Lord Howe Rise. Excepting Murihiku and Brook Street terranes, all others are suspect terranes, with depocentres close to the contemporary Gondwanaland margin in NE Australia, and subsequent margin-parallel, tectonic transport to their present New Zealand position. This is highlighted by a slight southeastward migration of terrane depocentres with time. Murihiku and Brook Street terrane sources are more remote from continental influences and represent isolated offshore volcanic depocentres, perhaps in their present New Zealand position. Keywords: U--Pb geochronology, detrital zircon, provenance, New Zealand, Palaeozoic terranes, Mesozoic terranes.

A 2500 [km.sup.2] mountainous river catchment in northern South Island, New Zealand, drained southwards until the late Quaternary. The catchment is being transported laterally at c. 36 mm [a.sup.-1] relative to the southern South Island by dextral strike-slip motion along the Pacific-Australian Plate boundary (Alpine Fault). This lateral motion has moved the eastern half of the catchment from a zone of uplift into a zone of subsidence over the past million years, triggering drainage reversal. Sedimentation from the catchment switched from a sedimentary basin in the SE to a basin in the north. Profiles of river terrace remnants, formed from glacial outwash, show that drainage reversal occurred in the latter stages of deposition of the oldest recognizable terrace. Clast imbrication patterns and clast petrography in that terrace indicate southward flow, whereas flow had a northerly component in younger terraces and a nearby active river. In addition, 1.6% genetic divergence of fish on either side of the new drainage divide is consistent with late Quaternary separation by drainage reversal. The timing of drainage reversal is estimated from regional terrace correlation and the magnitude of the genetic divergence to be between 100 and 200 ka bp.

Laser-ablation [sup.40]Ar/[.sup.39]Ar step-heating analyses of 20 pseudotachylyte veins from a single location along the exhumed central portion of the active Alpine fault of New Zealand yield total gas age values between 1 and 19 Ma. Evidence shows that they are genetically related and were formed during coeval episodes of seismogenic melting at shallow crustal depth, contrasting with a spread in formation ages. The total gas ages show an exponential decrease with increasing proportion of melt matrix and K content, reflecting incomplete degassing and mixtures of radiogenic Ar sources. Calculation of intercepts for all-melted matrix and all-clast end-member components indicate ca. 570 ka (Quaternary) friction-melting ages of ca. 332 Ma (Lower Carboniferous) source rock. Assuming an average exhumation rate of 6-9 mm/yr for uplift and erosion, these results imply that friction melts were generated during major slip episodes at ~3.5-5 km crustal depth. We conclude that reliable dating of young pseudotachylyte can be accomplished by combining chronologic study with clast-matrix quantification of genetically related vein assemblages. Keywords: [sup.40]Ar/[.sup.39]Ar dating, pseudotachylyte, coseismic faults, friction melt, Alpine fault.

The burning of the rangelands of the South Island of New Zealand by pastoralists in the second half of the nineteenth century has become so entrenched in New Zealand's environmental history that critics of burning have felt little need to provide evidence to support their assertions. Archival evidence are used to answer the questions of why the pastoralists burned, how often they burned, and when they burned, thus showing that burning was an important management tool.

The U-Pb thermochronology of titanite, apatite, and rutile from a crustal profile through a Mesozoic magmatic arc in Fiordland, New Zealand, is used to constrain the timing and duration of significant vertical movements during arc construction and evolution. Titanite data from deep-crustal (12-13 kbar) basement and cover rocks of central Fiordland imply that contractional arc thickening (~25 km) occurred by 111.1-113.4 Ma, within a few million years of a major phase of mid- to deep-crustal magmatism. This finding suggests that this cycle of magmatism, arc thickening, and high-grade metamorphism occurred in [less than or equal to] 6.2 m.y. In contrast to rapid burial, significant unroofing of the central Fiordland granulites was more protracted, requiring an additional 40-45 m.y. These new data are consistent with continued residence of the granulites in thickened arc crust for 15-20 m.y., with subsequent major unroofing recorded by futile cooling to Keywords: magmatic arc, U-Pb, thermochronology, burial, exhumation, lower crust.

This 1-year study investigated the effect of dairy cow treading on soil physical properties and sediment and phosphorus (P) loss via overland flow firm pasture and cultivated soil used for wintering dairy cows in southern New Zealand. Treading decreased soil macroporosity and [K.sub.sat], and increased overland flow volumes. Treading increased mean suspended sediment concentration in overland flow in the cultivated + trodden treatment (2.6 g/L) compared with ungrazed pasture (0.44 g/L) and ungrazed cultivated (0.98 g/L) treatments over 2 slope positions. Following grazing in the cultivated + trodden treatment, only 25% more sediment was lost in subsequent overland flow events (2.09 and 2.63 g before and after grazing, respectively), and mean total P (TP) losses increased by >250% (from 0.7 to 2.5 mg P). Meanwhile in the cultivated but ungrazed treatment, sediment and TP loss decreased. The increased loss of sediment and P following grazing in the cultivated + trodden treatment was attributed to P from cattle dung, and soil disturbance. Consequently, wintering of animals on cultivated paddocks with forage crops increases the risk of losing much P, especially in particulate form. Additional keywords: phosphorus, overland flow, treading, particulate P, grazing, pasture., Introduction The loss of phosphorus (P) and sediment from land to surface waters via overland flow is associated with impaired water quality (Nash and Halliwell 1999). Factors that are likely [...]

At subduction plate boundaries, strains accumulate within the overriding plate in response to motion of the down-going plate. To a first approximation, margin-normal interplate slip and shortening in the overriding plate sum to the total plate convergence. Therefore margin-normal interplate slip can be estimated by measuring shortening in the overriding plate and total plate convergence. Here we quantify margin-normal interplate slip by measuring shortening of the upper plate along a profile which extends up to 480 km across, and approximately normal to, the central Hikurangi Margin, New Zealand. Long-term deformation is estimated for periods of millions of years using data from seismic reflection lines and cross sections, while contemporary strain rates are derived from Global Positioning System (GPS) geodetic velocities. These data permit comparison of plate convergence rates determined by seafloor spreading data with the rates of contraction over short (~7 years) and long (~2.5 and 5 Myr) periods of time. On this part of the plate boundary, total margin-normal shortening in the overriding plate over the last ~5 Myr was ~9-28 km and accounts for ~6-19% of the total convergence (145-160 km) at rates of ~2-6 mm/yr. The remaining ~80% or more of plate convergence has been accommodated by slip on the subduction thrust. GPS contraction along approximately the same profile indicates ~14-16 mm/yr of contemporary shortening across the terrestrial part of the upper plate, which is approximately modeled by ~80% interplate coupling on the subduction interface down to depths of ~30 km. The contrasting proportions of inferred interplate coupling for contemporary and geological data sets are consistent with stick-slip behavior on the plate interface and with slip being principally achieved during intermittent large earthquakes. The general shapes of short- and long-term shortening profiles are similar and suggest that the highest strains occur at, or immediately east of, the Mohaka Fault. These strain profiles are consistent with a model where high strains in the upper plate are concentrated near the down-dip end of the contemporary locked zone on the plate interface. This model requires that the down-dip end of the interseismic locked zone has, on average, been approximately stable over a period of at least 2.5 5 Myr. INDEX TERMS: 1206 Geodesy and Gravity: Crustal movements interplate (8155); 8099 Structural Geology: General or miscellaneous; 8150 Tectonophysics: Plate boundary--general (3040); KEYWORDS: shortening, overriding plate, Hikurangi margin.

Contraction, strike slip, and extension displacements along the Hikurangi margin northeast of the North Island of New Zealand coincide with large lateral gradients in material properties. We use a finite-difference code utilizing elastic and elastic-plastic rheologies to build large-scale, three-dimensional numerical models which investigate the influence of material properties on velocity partitioning within oblique subduction zones. Rheological variation in the oblique models is constrained by seismic velocity and attenuation information available for the Hikurangi margin. We compare the effect of weakly versus strongly coupled subduction interfaces on the development of extension and the partitioning of velocity components for orthogonal and oblique convergence and include the effect of ponded sediments beneath the Raukumara Peninsula. Extension and velocity partitioning occur if the subduction interface is weak, but neither develops if the subduction interface is strong. The simple mechanical model incorporating rheological variation based on seismic observations produces kinematics that closely match those published from the Hikurangi margin. These include extension within the Taupo Volcanic Zone, uplift over ponded sediments, and dextral contraction to the south. INDEX TERMS: 8020 Structural Geology: Mechanics; 8159 Tectonophysics: Rheology--crust and lithosphere; 3210 Mathematical Geophysics: Modeling; 8109 Tectonophysics: Continental tectonics extensional (0905); 1206 Geodesy and Gravity: Crustal movements--interplate (8155); KEYWORDS: numerical modeling, Hikurangi trench, subduction interface strength, plate coupling, partitioning.

Ocean Drilling Program Sites 1123 and 1124 provide an unprecedented 12 m.y. record of major rhyolitic eruptions from the Coromandel and Taupo volcanic zones of New Zealand. Macroscopic tephras (n = 197) were dated using magnetostratigraphy, supplemented by geochemical correlation with subaerial tephra, isothermal plateau fission-track ages, and orbitally tuned stable isotope data. Eruptions began in the Coromandel volcanic zone ca. 12 Ma, ~1.6-1 m.y. earlier than previously known. Thereafter, volcanism was fairly continuous with a tempo and intensity that increased through the late Miocene-Pliocene and into the Quaternary, when the Taupo volcanic zone formed. The transition from the Coromandel to the Taupo zone, previously placed as ca. 4-2 Ma, was seamless, without obvious breaks or changes in ash composition. This well-dated history of long-lived and productive volcanism allows for more confident correlation with other circum-Pacific tephra records, thus helping confirm the occurrence of widespread coeval eruptions throughout the region. Keywords: tephra, rhyolites, New Zealand, Ocean Drilling Program.

Climatic fluctuations recorded in Antarctica and Greenland during the last deglaciation (18-10 ka) differ markedly in their timing. It remains controversial whether local climate fluctuations recorded in southern mid-latitudes relate primarily to northern or southern polar records. We present multiproxy results from New Zealand that show strong evidence for a minor cooling or slowdown in the rate of warming at the time of the North Atlantic late glacial interstadial. The Younger Dryas chronozone in New Zealand was a period of resumed warming and increased westerly airflow. Differences between the hemispheres at this time were probably due to a reorganization of the thermohaline circulation system and associated changes in the meridional temperature gradient. Keywords: late glacial, bipolar seesaw, thermohaline circulation, Younger Dryas, Antarctic cold reversal. Bayesian radiocarbon dating.

A Permian (~265 Ma) intrusive complex which formed as a magmatic feeder reservoir to an immature island-arc volcano is fortuitously exposed in southern New Zealand. Known as the Greenhills Complex, this intrusion was emplaced at shallow crustal levels and consists of two layered bodies which were later intruded by a variety of dykes. Cumulates, which include dunite, olivine clinopyroxenite, olivine gabbro, and hornblende gabbro-norite, are related products of parent-magma fractionation. Both primary (magmatic) and secondary platinum-group minerals occur within dunite at one locality. Using the composition of cumulus minerals, mafic dykes and melt inclusions, we have determined that the parent magmas of the complex were hydrous, low-K island-arc tholeiites of ankaramitic affinities. Progressive magmatic differentiation of this parent magma generated fractionated melt of high-alumina basalt composition which is now preserved only as dykes which cut the Complex. Field evidence and cumulus mineral profiles reveal that the magma chambers experienced turbulent magmatic conditions during cumulate-rock formation. Recharge of the chambers by primitive magma is likely to have coincided with eruption of residual melt at the surface. Similar processes are inferred to account for volcanic-rock compositions in other parts of this arc terrane and in modern island-arc systems.

Concentration of erosional activity along transpressional plate boundaries can significantly alter the pattern of mechanical behavior through the influence of exhumation on crustal strength. Three-dimensional numerical modeling of an obliquely convergent orogen shows that a single oblique plate-bounding structure is stable if asymmetric erosion patterns, such as those observed in orographic mountain belts, pertain, and if Earth's crust has a strong-on-weak rheology. In early stages of oblique convergence of an initially laterally homogeneous material, lateral (boundary-parallel) strain is accommodated along a near vertical structure and convergent (boundary-normal) strain is concentrated on structures dipping at moderate angles into the orogen. Exhumation of deep crustal material along the convergent structure results in thermal weakening along this dipping structure. When the upper crust beneath the orogen is significantly weakened by exhumation, lateral strain abandons the vertical structure and shifts to the dipping structure, combining with the convergent strain to form a single oblique fault that accommodates the plate motion in the upper crust, as is the case along the Alpine fault, New Zealand. The process of thermal thinning is controlled by advection and occurs on time frames of ~1-2 m.y. The two components of strain remain separate in the lower crust. During active convergence, exhumation of lower crustal material occurs only along those structures accommodating convergent strain. Consequently, material exhumed from lower regions of ductile deformation, as is the case along the Alpine fault, contains lineations that indicate a greater component of convergence than predicted from the total plate motion. Postorogenic exhumation of the roots of an oblique plate boundary will expose two parallel shear zones, one dominantly convergent and one dominantly strike slip. Widely reported orogen-parallel transport in the late stages of ancient oblique convergence may represent not a change in plate vector, but the exhumation of the lateral transport zone. Keywords: numerical models, transpression, erosion, lineations.

At Taupo volcano (New Zealand), a major young caldera system is superposed on the Taupo Fault Belt, a zone of Late Quaternary extensional normal faulting accompanying rifting. Palaeoshorelines formed at 26.5 and 1.8 ka around intracaldera Lake Taupo highlight contrasts between short-term vertical deformation patterns detected by geodetic and lake-levelling surveys, and longer-term trends recorded by the warped and offset palaeoshoreline levels. Rifting is apparently occurring without the accumulation of long-term vertical offsets and net subsidence on adjacent normal faults of the Taupo Fault Belt. Geomorphic and stratigraphic data indicate that much vertical deformation is episodic and closely related to major volcanic eruptions: at other times, compensation is occurring, possibly by magma accumulation in the crust. However, periods of caldera unrest at Taupo may reflect regional rifting processes made manifest by the presence of the lake, rather than magmatic processes alone. Keywords: Taupo Volcanic Zone, Taupo Fault Belt, rifling, neotectonics, calderas.

Cadmium distribution was determined at a hill country agricultural site with no history of fertiliser application, but where pre-European seabird breeding occurred. Total Cd concentrations were measured in 2 depth profiles on the ridgeline, and in surface soil (0-15 cm; 15 ridgeline and 7 sideslope transects). Concentrations were low (range 0.04-0.13 mg/kg) for New Zealand agricultural soils. Concentrations were independent of stock camps (locations frequented by grazing animals), altitude, soil depth, organic matter, and N and P concentrations. Surface Cd concentrations on the sideslope were significantly higher than the ridgeline. Inventories from the 2 ridgeline profiles (29.9 ± or -] 2.4 mg/[m.sup.2]; 18.4 4 ± 1.5 mg/[m.sup.2]) were higher than the 16 mg/[m.sup.2] and 7 mg/[m.sup.2], respectively, predicted from the loess and basalt parent material concentrations; surface soil concentrations also exceeded those predicted from parent materials. Together, these results suggest that agricultural activity has not significantly redistributed Cd, and that external sources have contributed a large proportion of soil Cd. Atmospheric input was too low to explain all of the observed enrichment. Instead, Cd distribution was consistent with seabird input concentrated in the deeper soils of the sideslope rather than the relatively thin soils of the ridgeline. Additional keywords: Canterbury, Ngai Tahu, procellariid., Introduction Cadmium (Cd) is a ubiquitous trace element, which can cause toxic effects in both wild and domestic animals (Larison et al. 2000). Cd concentrations in New Zealand agricultural soils [...]

Arc-flank volcaniclastic sedimentation in the Murihiku Terrane of New Zealand lasted about 120 million years from Late Permian to Early Cretaceous time. Despite the effects of pervasive zeolite-facies alteration, whole-rock geochemical parameters for sandstones, siltstones and tuffs record changes in source-rock composition, both in time and along the length of the depositional basin. Sandstones are considered to give a more reliable indication of the state of evolution of the source volcanic arc than do the siltstones. The siltstones commonly contain detrital white mica flakes that are generally lacking in the sandstones, and are possibly of distal continental origin. Some also contain, very fine felsic ash particles. Average abundances and normalized multi-element diagrams are used to estimate proportions of three model end-member source constituents, average upper-continental crust (UCC), high-K rhyolite (RHY) and basaltic andesite (AND). Sandstone provenance for the Southland Syncline sector changed from a predominantly basaltic-andesite source in Late Permian to early Middle Triassic time, for example, UCC:RHY:AND = 0:17:83 in the Early to early Middle Triassic, to highly felsic in the Middle to Late Triassic, reaching UCC:RHY:AND = 2:74:24 in the Late Triassic Oretian Stage. A UCC component became increasing significant from latest Triassic upward and the proportion of mafic to felsic volcanism increased again, with UCC:RHY:AND = 15:30:35 in the Middle Jurassic Temaikan Stage. Mix modelling suggests that along-arc source proportions varied, with greater mafic and upper continental crust contributions in the northern Kawhia segment than in the Southland segment. These patterns may be explained by deposition at an oceanic Aleutian-type arc margin, with transition to a continental oceanic arc character induced either by arc evolution and dissection, forearc sliver translation, or underplating of rafted microcontinental fragments. Keywords: geochemistry, sedimentary rocks, provenance, island arcs, New Zealand.

Rates of soil redistribution by water and tillage erosion were determined in 3 fields under long-term continuous vegetable production on clay loam, strongly structured soils derived from volcanic ash at Pukekohe, South Auckland, New Zealand. Erosion and deposition rates were estimated using a mass balance model to convert variation in [sup.137]Cs areal activity within the fields to estimates of erosion and deposition. Caesium-137 areal activity in cropped fields ranged from 171 to 2144 Bq/[m.sup.2], compared with a reference value under permanent pasture of 774 Bq/[m.sup.2]. There was a characteristic pattern of [sup.137]Cs distribution within each field, with differences between the fields related to variation in topography. Lowest values of [sup.137]Cs were found in the upper parts of each field and highest values towards the base of each field. In all 3 fields there was a net loss of [sup.137]Cs, ranging from 13 to 32%, with an average over the 3 fields of 18%. Net rates of soil loss from the fields were 30, 11, and 7 t/ha.year. However, within the fields there was a much wider range of both erosion (up to 92 t/ha.year) and deposition (up to 100 t/ha.year) rates. Most of the soil redistribution is caused by water erosion, with tillage erosion accounting for 10-20% of the soil redistribution. The soil redistribution rates were 2 orders of magnitude higher than sediment export measured at small catchment scale. Soil erosion rates are not reflected in variation in topsoil depth, because frequent tillage and incorporation of organic residues maintains a uniform topsoil depth, but soil deposition rates are closely related to topsoil depth. Additional keywords: caesium-137, water erosion, tillage erosion, topsoil depth, market gardening., Introduction Vegetable production is a very intensive land use, especially where it is practised as a continuous monoculture. It is characterised by frequent tillage using a wide variety of implements, [...]

Phylogenetic analysis of ITS and rbcL sequences show that New Zealand Stylidiaceae fall into two distinct lineages differing in species richness. Each lineage represents a unique dispersal event to New Zealand occurring at different times during the evolutionary history of the family. One lineage comprises seven species of Forstera and Phyllachne, while the other consists solely of Oreostylidium subulatum. The origin of the Forstera/Phyllachne lineage in New Zealand is equivocal; either a South American or a Tasmanian origin is equally parsimonious. Possible sister groups are F. bellidifolia in Tasmania and P. uliginosa in South America. Oreostylidium subulatum has an Australian origin. In our analyses O. subulatum is nested in a clade composed entirely of species of Stylidium, almost all of which are endemic to Australia. Species of Phyllachne share a cushion habit with the outgroup Donatia (Donatiaceae) that may have preadapted them to alpine environments in New Zealand. The New Zealand Stylidiaceae have small, white, actinomorphic flowers that are well adapted to the unspecialized pollinator fauna. Forstera and Phyllachne share this trait with Donatia; however, the small, white flowers of Oreostylidium are a dramatic departure from the colorful, highly specialized flowers of Stylidium. Key words: diversification; DNA; ITS; New Zealand; phylogeny; rbcL; Stylidiaceae.

Masting, the intermittent production of large flower or seed crops by a population of perennial plants, can enhance the reproductive success of participating plants and drive fluctuations in seed-consumer populations and other ecosystem components over large geographic areas. The spatial and taxonomic extent over which masting is synchronized can determine its success in enhancing individual plant fitness as well as its ecosystem-level effects, and it can indicate the types of proximal cues that enable reproductive synchrony. Here, we demonstrate high intra- and intergeneric synchrony in mast seeding by 17 species of New Zealand plants from four family across >150 000 [km.sup.2]. The synchronous species vary ecologically (pollination and dispersal modes) and are geographically widely separated, so intergeneric synchrony seems unlikely to be adaptive per se. Synchronous fruiting by these species was associated with anomalously high temperatures the summer before seedfall, a cue linked with the La Nina phase of El Nino--Southern Oscillation. The lone asynchronous species appears to respond to summer temperatures, but with a 2-yr rather than 1-yr time lag. The importance of temperature anomalies as cues for synchronized masting suggests that the timing and intensity of masting may be sensitive to global climate change, with widespread effects on taxonomically disparate plant and animal communities. Key words: abiotic factors; Chionochloa; cross-correlation; Dacrydium; El Nino--Southern Oscillation; Elaeocarpus; masting; New Zealand; Nothofagus; Phormium; synchrony; temperature.

Ion microprobe analyses of detrital zircons in the Te Akatarawa Terrane, New Zealand, reveal that the age of unfossiliferous turbidites overlying a fusuline- and coral-bearing limestone block olistostromal melange is no older than 255 [+ or -] 4 Ma (Late Permian). This is approximately 15 m.y. younger than the Kungurian age of the fusulinid limestone. We interpret this to indicate collapse of a Permian oceanic seamount as it entered a subduction zone along the Pacific margin of Gondwana. These turbidites differ markedly in composition from adjoining Permian to Middle Triassic sandstones of the Torlesse Terrane. Detrital zircon age data indicate predominantly Permian and Carboniferous ages for source rocks supplying the Te Akatarawa turbidites, but also reveal significant earlier Palaeozoic and Proterozoic components, ranging back to 1.9 Ga. The warm-water setting of limestone blocks and the short 15 m.y. time period between sedimentation and accretion onto a continental margin require the limestone to have formed in a low-latitude position probably off the northeast Australian (New Guinea) margin of Gondwana. Zircons within the sample underwent recrystallization at around 230 [+ or -] 11 Ma which may be related to alteration during accretion in a subduction zone environment. Over a period of 100 to 150 m.y. from 255 Ma the terrane underwent more than 5000 km translation along the continental margin southward to its current location as an exotic mini-terrane enclosed within the New Zealand Torlesse Terrane.

1 We used forest stand history reconstruction to infer the relative roles of disturbance and climate warming on the population dynamics of Nothofagus menziesii (silver beech) dominated tree lines in north Westland, South Island, New Zealand. 2 Stem recruitment in tree line forests over the last 300 years has been episodic, has tended to occur in small, scattered patches, and has been dominated by the production of new stems from existing trees. Pulses of stem recruitment also coincide with episodes of abrupt decline in the radial growth of established trees. These patterns suggest that infrequent natural disturbances form localized canopy openings, damage trees that survive the event, and initiate the establishment of new trees and the production of new stems by surviving trees that fill these openings. 3 Climate warming in New Zealand since 1950 has had little effect on the recruitment of Nothofagus close to the tree line. There is a large seedling pool within the tree line forests, but recruitment will probably require a disturbance-related canopy opening. 4 Natural disturbances drive the population dynamics of Nothofagus tree lines and may modify their response to climate warming. Unlike many Northern Hemisphere tree lines, there has been no recent upward movement of the tree line or increase in seedling establishment. This difference could reflect the greater importance of natural disturbance for recruitment in the abrupt closed-canopy tree lines formed by light-demanding Nothofagus species in the Southern Hemisphere. However, given the ubiquity of disturbance effects in low-altitude forests in both hemispheres, future studies need to consider their role when investigating any tree line response to climate warming. Key-words: beech forest, forest disturbance, climate change, growth suppressions, temporal and spatial patterns

1 Large, infrequent disturbances can exert a dominant influence on the structure and dynamics of forested landscapes and in Westland, New Zealand there is evidence of at least three massive earthquakes within the last 650 years. We reconstructed the history of forest disturbance in two study areas, totalling 1412 ha, to quantify the role of such disturbance in structuring the conifer/hardwood forests. 2 We divided the study area into different land-surface types, aged trees on each land surface and identified cohorts of trees established in response to past disturbance. The type of disturbance (tree fall or erosion/sedimentation event) that initiated cohort establishment was determined from the type of land surface and other physical evidence. We also dated abrupt growth releases or suppressions in tree rings to aid disturbance history reconstruction. 3 Erosion and sedimentation events dominated the disturbance regime, affecting 86% of the study area in the last 650 years. Catchment-wide episodes of forest cohort-initiating disturbances were centred around 1820-30, 1710-20, 1610-20 and 1460 AD. Of the 51 cohorts identified in the study area, 47 were initiated during one of these episodes, when disturbance by erosion or sedimentation affected from 10-50% of the study area. Consequently, over 80% of the forested area currently comprises simple, first generation cohorts of trees established after catastrophic disturbance. Only 14% of the study area is more complex, all-aged forest. 4 Three disturbance episodes coincide with the three most recent Alpine fault earthquakes (c. 1717, 1630 and 1460 AD), while one coincides with earthquakes recorded to the south of the study catchment in 1826 AD. Age structures from throughout Westland show that extensive, similar-aged, post-earthquake cohorts of trees are a feature of the region, suggesting that infrequent, massive earthquakes are the dominant coarse-scale disturbance agent, triggering episodes of major erosion and sedimentation and leaving a strong imprint on the forest structure. Key-words: age/forest cohort, disturbance history reconstruction, erosion and sedimentation, landslides, terraces, tree rings

Forest dwelling browsing mammals, notably feral goats and deer, have been introduced to New Zealand over the past 220 years; prior to this such mammals were absent from New Zealand. The New Zealand forested landscape, therefore, presents an almost unique opportunity to determine the impacts of introduction of an entire functional group of alien animals to a habitat from which that group was previously absent. We sampled 30 long-term fenced exclosure plots in indigenous forests throughout New Zealand to evaluate community- and ecosystem-level impacts of introduced browsing mammals, emphasizing the decomposer subsystem. Browsing mammals often significantly altered plant community composition, reducing palatable broad-leaved species and promoting other less palatable types. Vegetation density in the browse layer was also usually reduced. Although there were some small but statistically significant effects of browsing on some measures of soil quality across the 30 locations, there were no consistent effects on components of the soil microfood web (comprising microflora and nematodes, and spanning three consumer trophic levels); while there were clear multitrophic effects of browsing on this food web for several locations, comparable numbers of locations showed stimulation and inhibition of biomasses or populations of food web components. In contrast, all microarthropod and macrofaunal groups were consistently adversely affected by browsing, irrespective of trophic position. Across the 30 locations, the magnitude of response of the dominant soil biotic groups to browsing mammals (and hence their resistance to browsers) was not correlated with the magnitude of vegetation response to browsing but was often strongly related to a range of other variables, including macroclimatic, soil nutrient, and tree stand properties. There were often strong significant effects of browsing mammals on species composition of the plant community, species composition of leaf litter in the litter layer, and composition of various litter-dwelling faunal groups. Across the 30 locations, the magnitude of browsing mammal effects on faunal community composition was often correlated with browser effects on litter layer leaf species composition but never with browser effects on plant community composition. Browsing mammals usually reduced browse layer plant diversity and often also altered habitat diversity in the litter layer and diversity of various soil faunal groups. Across the 30 locations, the magnitude of browser effects on diversity of only one faunal group, humus-dwelling nematodes, was correlated with browser effects on plant diversity. However, browser effects on diversity of diplopods and gastropods were correlated with browser effects on habitat diversity of the litter layer. Reasons for the lack of unidirectional relationships across locations between effects of browsers on vegetation community attributes and on soil invertebrate community attributes are discussed. Browsing mammals generally did not have strong effects on C mineralization but did significantly influence soil C and N storage on an areal basis for several locations. However the direction of these effects was idiosyncratic and presumably reflects different mechanisms by which browsers affect soil processes. While our study did not support hypotheses predicting consistent negative effects of browsing mammals on the decomposer subsystem through promotion of plant species with poorer litter quality, our results still show that the introduction of these mammals to New Zealand has caused far-ranging effects at both the community and ecosystem levels of resolution, with particularly adverse effects for indigenous plant communities and populations of most groups of litter-dwelling mesofauna and macrofauna. Key words: alien organisms; browsing; decomposer food web; deer; goats; herbivory; macrofauna; mesofauna; microbial biomass; microfauna; New Zealand forests; plant litter.

The article examines four phases of environmental change on New Zealand's Manawatu coastal landscape, focusing on the affects of occupation by the Maori, European settlers, and ecological remediation and conservation practices. The article is part of a special issue celebrating the palynological research of New Zealand geographer John Roger Flenley.

Research describing the control of brushtailed possums in New Zealand by use of poisoned cereal bait is presented. It is shown that cold temperatures contributed to high kill rates.

New Zealand's Southern Alps show a two-step thermochronological process caused by cooling and exhumation. The relevant closure temperature at 5 million years ago was followed by a sharp drop that exposed re-equilibration seen in the modern orogenic regime.

Radiolaria and paleomagnetic data from Deep Sea Drilling Project Sites 595 and 596 indicate that Early Cretaceous seafloor was formed at moderate to high latitudes in the Pacific. This inference requires a Cretaceous spreading ridge south of the Pacific-Phoenix Ridge and substantial dextral strike-slip motion at the Gondwana margin. The previously unrecognized southern oceanic plate, called here the Moa plate, was obliquely subducted beneath the Gondwana margin, and material accreted from it is now part of the Eastern province of New Zealand. Keywords: Pacific, tectonics, Cretaceous, radiolaria, New Zealand.

New Zealand's Darran Complex is intruded by the Mt. Christina-Crosscut irruptives of Mackay granitoids despite the fact that rafts of Christian Gneiss were subject to partial melting during the Cretaceous. The Mt. Crosscut irruptive may have acted as a dike-like roof pendant.

1 Competing theories of community assembly are very difficult to test. Four main theories exist. The Stochastic theory sees species assembly as being random. The Humpty Dumpty/Alternative Stable States (ASS) theory suggests that a community may be unable to reassemble itself from its constituent species. The Deterministic theory suggests there will be convergence to one stable state. The Pre-adaptation theory is similar to the Deterministic theory but emphasizes that many species fit the stable state because of characters acquired elsewhere. 2 The reassembly of a flora into new communities in a different country, or its assimilation as a major component of such communities, offers a means to test these theories. The invasion of British plant species into New Zealand, and their reassembly into roadside communities there, is a good example of such a natural experiment. 3 Plant communities of NZ roadsides were compared to the communities of the British National Vegetation Classification (NVC). British roadside communities were also compared to the NVC as a control. New Zealand roadside communities provided a fit to the NVC communities of only 54.7% on average. After excluding species that are not present in NZ, and therefore could not possibly reassemble, the fit increased to 61.1%. British roadsides gave a 65.8% fit. The NZ figures are similar to the fit obtained with random data (58.7%), indicating that the NZ communities bear little relation to the ones formed by the same species in Britain. 4 Similarity between roadside communities in NZ and Britain was low, forming two almost distinct sets of communities. 5 Some of the predictions of the Stochastic, Humpty Dumpty/ASS and Deterministic models are borne out, but others are not. It is concluded that British species have reassembled into communities in NZ most of which are new, i.e. distinct from those that occur in the native range of the species in Britain. The evidence points to a process of community assembly by pre-adaptation. Keywords: alternative stable states, assembly rules, community reassembly, deterministic structure, exotic species, Humpty Dumpty effect, invasion, NVC, preadaptation, roadside, stochastic model

We estimated survival rates of adult Southern Buller's Albatrosses (Thalassarche bulleri bulleri) from 1948 to 1997 based on a long-term banding and recapture program at The Snares, New Zealand. Annual survival exceeded 0.95 from 1961 to 1968 and from 1992 to 1997 but declined to between 0.913 and 0.928 from 1969 to 1991. Reduced survival may have resulted from incidental mortality associated with longline and trawl fisheries in the foraging areas of these birds, but it must have been counterbalanced by changes in other population parameters because the population increased greatly in number from 1969 to 1997. Increased trawling activity in areas where albatrosses forage may have benefited the population by providing additional food, which may have enhanced the survival rate of recently fledged birds. We found no indication that survival rates differed between males and females, but an age effect occurred in which survival of birds with at least 25 years of breeding experience was lower than that of less-experienced and presumably younger birds.

The determination of 'critical thresholds' is an essential task for informed policy decisions on establishing greenhouse gas emission targets. This paper presents a framework for determining critical thresholds for New Zealand agriculture, focusing on three agricultural crops - kiwifruit, grain maize, and Paspalum dilatatum - as exemplars for the fruit production, arable cropping and dairy production industries in New Zealand. The approach is based on the application of a country-scale, integrated assessment model, called CLIMPACTS. The CLIMPACTS system contains a climate change scenario generator, climate and land data, and sectoral impact models. Importantly, CLIMPACTS allows time-dependent assessments of climate change and its effects, which facilitates the identification and examination of thresholds, which largely relate to spatial changes, over time, in regions of economic importance for these crops. However, whether such thresholds are 'critical' for New Zealand cannot currently be addressed by the CLIMPACTS model. The determination of 'criticality' requires a fully integrated assessment in which the social, economic, and environmental costs and risks associated with these thresholds are comprehensively evaluated.

A discussion is presented regarding several hypotheses for the production of a dilute surge observed in New Zealand's Ruapehu volcano. Evidence is explored for a vertically stratified lahar and for a solitary wave originating in the Whangaehu River.

A criticism is presented of a theory that attributes the extinction of moas, an indigenous bird, to Maori hunters within a single century. Targeted issues include assumptions concerning the amount of moa in the Maori diet, archaeological data regarding the cessation of moa hunting, and questions regarding total population figures.

The earth has less than 200 active geysers and Yosemite National Park has more than half of these. Geysers are also found in Iceland, New Zealand and the Kamchatka Peninsula in Siberia. Descriptions of the activity of the geysers in these areas are given.

The longest chronology from New Zealand so far is from Libocedrus bidwillii Hook. f. (i.e., from AD 1992 back to AD 1140, a span of 853 years). A subset of 11 chronologies was selected from a network of 23 sites to reconstruct past temperatures based on the similarity of significant response functions. A comparison of climate data over different seasons with these 11 chronologies was carded out using a bootstrap transfer function. Average late-summer (February-March) temperature was selected for reconstruction based on independent verification results. The reconstructed temperature was then presented for the period back to AD 1720. The chronologies reconstructed years experiencing hot summers better than cold summers. The power spectrum of the reconstructed temperatures showed periodicities similar to those of the observed temperatures. Reconstructed temperatures were significantly correlated with other proxy climate reconstructions derived from tree rings in New Zealand. However, unlike the other tree ring-based reconstructions, the Libocedrus bidwillii series reconstructed both the 1950s and 1970s warming periods. The results also compared very favourably with other palaeoclimate evidence.

Murihiku Terrane is the least deformed of a series of tectonostratigraphic terranes that have been amalgamated to form the basement underlying New Zealand. Apatite fission-track (FT) thermochronology has been applied to the youngest beds (Late Jurassic, Hettangian-Tithonian Stages) of this terrane, located at Port Waikato in western North Island, which are broadly folded. The apatite FT ages are partially annealed, are younger than their stratigraphic ages, and remarkably, decrease in age upsection. Interpretation and modelling of the maximum palaeotemperatures experienced by the sample horizons and the timing of cooling requires a wedge of Cretaceous sedimentary rocks to have accumulated within the axis of the major fold (Kawhia Syncline). Deposition of Murihiku Terrane sequences continued therefore into the Cretaceous and probably until c. 100 Ma. Deposition may have ended as late as 85 [+ or -] 10 Ma, when cooling via denudation started. The upper parts of the former succession probably accumulated during folding. In addition, interpretation of the FT data require a marked increase in palaeogeothermal gradient from a subnormal value of 15[degrees]C [km.sup.-1] during the Late Jurassic, up to c. 30[degrees]C [km.sup.-1] at 85 [+ or -] 10 Ma. This is attributed to the termination of subduction along the Pacific margin of Gondwanaland, and a transition to a rift-transform tectonic setting in western New Zealand during Tasman Sea spreading. The latest Cretaceous-Palaeocene eastward tilting of the Murihiku basement at Port Waikato may have been accommodated on the Taranaki Fault or another coast-parallel fault; the Waikato Fault probably acted as a transfer fault at that time accumulating a significant amount of throw. Keywords: New Zealand, Murihiku, geothermal gradient, palaeotemperatures, fission track.

Tephrochronology is the study of volcanic ash (tephra) beds for the purpose of correlating and dating volcanic and other geologic events. Large magnitude silicic eruptions can disperse tephra up to thousands of kilometres from the vent, producing a near instantaneous marker horizon. In addition to their geochronological value, tephra beds are a major source of data on the eruption frequency and geochemistry of large rhyolitic volcanoes. The Quaternary Taupo volcanic zone (TVZ) in New Zealand is one of the most frequently active rhyolitic centres on Earth, and for much of the 20th century its tephra beds have been the focus of study. As a result, fingerprinting and dating techniques have been fine-tuned, and tephra beds now under-pin the late Cenozoic chronology for a wide variety of disciplines from volcanology to sequence stratigraphy and archaeology. The key to tephrochronology is the identification and correlation of tephra horizons. In the proximal setting (< 50 km from vent), tephra beds can often be identified by their lithology, stratigraphic position and ferromagnesian mineralogy. Farther from source these features became less diagnostic as units become thinner and mineral depleted, and geochemical fingerprinting must then be employed. Grain-specific techniques are commonly required to assess the compositional homogeneity of the tephra, and to avoid xenolithic and detrital contaminants. Criteria that are valuable for identifying both source volcano and individual eruptive events from grain-specific electron microprobe techniques include: glass and Fe-Ti oxide chemistry, and eruption temperature and oxygen fugacity (estimated from oxide equilibrium pairs). Deposits of the contemporaneously active Taupo, Okataina, Maroa and Mayor Island caldera centres in the TVZ can be distinguished on the basis of such criteria. If a tephra lacks contaminants, trace- and rare earth element (REE) compositions of purified glass separates provide additional criteria. Similar approaches can be used on samples of the chilled, nonwelded bases of ignimbrites, while welded zones often display a characteristic thermal remnant magnetism (TRM) direction that can assist in correlation. Late Miocene and Pliocene rhyolitic tephra from the Coromandel region in New Zealand are compositionally indistinguishable from Quaternary TVZ deposits, but deposits from other SW Pacific provinces such as Antarctica and the Tonga-Kermadec arc are compositionally distinct. In the TVZ, rhyolitic tephra erupted during intervals of 10-20 ka from the same volcano are compositionally similar, while over longer periods or following large-volume eruptions the tephra are compositionally and mineralogically distinct. Most TVZ fall deposits are compositionally homogeneous, and there are no temporal compositional trends for individual volcanoes. Tephra beds are also valuable because they can be dated by a variety of methods, and therefore can provide direct age control for sequences that are not normally amenable to radiometric dating. For late Cenozoic tephra beds that are beyond the range of (super 14)C (ca. 40 ka), and are fine-grained and/or lack K-rich phenocrysts, the isothermal plateau fission-track (ITPFT) method using glass can provide an accurate and precise age. (super 40)Ar-(super 39)Ar can be employed for high-resolution dating, however this may require single crystal laser fusion to detect relict and partially degassed crystals that are common in pyroclastic deposits, even within single pumice blocks. The New Zealand tephrostratigraphic record is not complete in space or time. Only the post-64 ka record is well established. However, there are chronologically well-constrained tephra beds dating back to 10 Ma. Some tephra beds cover most of the North Island of New Zealand, are found in the South Island, and extend as much as 1400 km from vent into the Pacific Ocean. Widespread and/or stratigraphically important units include: Kaharoa (665 years BP); Kawakawa (22 ka); Rangitawa (0.33 Ma); Potaka (1 Ma) and Pakihikura (1.6 Ma). Ages on these and other tephra beds provide a framework for global climatic and sea-level change recorded in New Zealand, and allow direct correlation between the marine and terrestrial realms. Keywords: tephrochronology; volcanic ash; volcanology; geochronology; correlation; Taupo volcanic zone

The Whakamaru group ignimbrites are products of one of the largest caldera-forming eruptions from the central Taupo Volcanic Zone, New Zealand, ca. 340 ka. Imaging of zircons separated from low-silica rhyolite pumice from Whakamaru group ignimbrite reveals a complex magmatic crystallization history; some grains contain resorbed cores. Cores and rims of individual zircons were dated using the sensitive high-resolution ion microprobe. Due to the high U contents of the zircons, (super 206)Pb count rates were sufficiently high to obtain (super 206Pb/(super 238)U ages with precisions of 5%-10% (1 sigma) using longer than usual (super 206)Pb(super +) count times, and this has allowed zircon core and rim ages to be distinguished. Zircon rim and outer growth zone ages range from within 1 (sigma) error of the eruption age to 449 +/- 20 ka, whereas zircon cores produced ages to 608 +/- 20 ka, indicating magmatic residence times exceeding 250 k.y. for some zircons. The data are consistent with a prolonged evolution of the magma system over hundreds of thousands of years, involving magma replenishment and mixing with residual phases of older silicic magma chambers, in addition to crystal fractionation processes, prior to eruption. The study has shown that (super 206)Pb/(super 238)U dating using high-resolution ion microprobe can be used to determine zircon preemptive growth histories in Quaternary lavas and pyroclastic rocks.