time space modeling of the dynamics of santorini volcano greece during the 2011 2012 unrest the 2011 2012 unrest of santorini thera volcano aegean sea greece was associated with microseismicity confined to the kameni line kl a major tectonovolcanic lineament and has been regarded as a single magmatic episode produced by a spherical source derived from inversion of gps data however such a source is a few kilometers away from the kl and cannot explain observed microseismicity for this reason we divided the unrest episode into five periods based on the fluctuations of seismicity and deformation rates and investigated the connection between seismicity and two spherical magmatic point sources for each period based on a new inversion algorithm and consistent gps data we recognized during the volcano unrest episode an unstable pattern of intrusions correlating with both the kl and columbo line cl a second major tectonovolcanic lineament intrusions correlating with cl appear relatively persistent aseismic small and shallow which is consistent with marine geophysical evidence for arrested shallow dykes and geodetic evidence from a previous inflation episode during the two periods of intense seismicity sources close to the kl explaining seismicity were obtained this unstable pattern of intrusions explains both the well observed location and timing of seismicity as well as ground deformation and is consistent with results of an okada type inversion for a sill and a dyke the stress interactions between the two sources agree with coulomb failure stress models santorini appears to be affected by concurrent offset magma pulses and only recent activity from a magma pulse below the kl produced microseismic swarms

backarc rifting constructional volcanism and nascent disorganised spreading in the southern havre trough backarc rifts sw pacific high resolution multibeam em300 and seabeam data of the southern havre trough sht combined with observations and sample collections from the submersible shinkai6500 and deep tow camera are used to develop a model for the evolution and magmatism of this backarc system the havre trough and the associated kermadec arc are the product of westward subduction at the pacific australian plate boundary detailed studies focus on newly discovered features including a seamount saito seamount and a deep graben ngatoroirangi rift 4000 m water depth floored with a constructional axial volcanic ridge 5 km in length and in excess of 200 m high both of which are characterised by pillow and lobate flows estimated at elongate volcanic ridges at 35 15 s and 34 30 s and backarc seamounts 35 30 s 178 30 e occur at the eastern margin of the sht similar seafloor morphology is observed in the central and western portions of the basin suggesting that recent volcanism may be broadly distributed across the backarc mass balance modelling indicates a maximum crustal thickness of 11 km to 4000 m spreading systems these discontinuous spreading systems are characterised by failed rifts rift segmentation and propagation successive episodes of magmatic intrusion into thinned faulted arc basement results in defocused asymmetrical accretion cross arc volcanic chains isolated volcanoes and underlying basement plateaus are interpreted to represent a cap of recent extrusives however they may also be composed entirely of newly accreted crust and the spatially extensive basement fabric of elongated volcanic ridges may be the surface expression of pervasive dike intrusion that has thoroughly penetrated and essentially replaced the original arc crust with newly accreted intrusives

dike intrusion and displacement accumulation at the intersection of the okataina volcanic centre and paeroa fault zone taupo rift new zealand abstract we examine the relationship between dike emplacement and normal fault displacement along the south western margin of okataina volcanic centre new zealand at this location dikes including a basaltic dike up to 5 m wide at the ground surface intruded during the 1886 ad tarawera eruption formed over the last 22 kyr in the tarawera linear vent zone within a few kilometres of the paeroa fault zone displacement analysis and mapping of fault scarps indicate that fault and dike extension are complementary over time periods of tens of thousands of years extension that is primarily accommodated by faulting outside the volcanic complex is achieved by dike intrusion and faulting within it historical observations following the 1886 ad eruption and previously published active fault trenching collectively indicate however that dike intrusion generally does not induce slip within the paeroa fault zone close to the lateral dike tip we suggest that displacement in the paeroa fault zone outside the okataina volcanic centre is generally not triggered by eruptions and that this fault is principally tectonic in origin

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 11 refs 4 figs 1 tab

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

evolution of a dynamic paleo hydrothermal system at mangatete taupo volcanic zone new zealand abstract recent quarrying and active faulting at mangatete taupo volcanic zone tvz new zealand illuminate a rare spatial and temporal window on a dynamic late quaternary geothermal system detailed geological mapping stratigraphic logging ams 14 c dating and textural and mineralogical analyses were used to construct a complex history of hydrothermal volcanological and tectonic activity from 36 to 2 ka extinct surface hydrothermal manifestations occur over a 2 km 2 area and include in situ siliceous sinters distributed on normal fault terraces an inferred hydrothermal eruption breccia heb containing acid etched sinter blocks another probable heb that was bathed in silicifying thermal fluids and sinter clasts that were entrained in a debris flow associated with a volcanic ash event preserved sinter textures typical of near neutral ph alkali chloride spring discharge channels aprons terraces and affiliated marshes comprise plant rich palisade tufted bubble mat and domal stromatolitic fabrics in addition a packed fragmental sinter facies is shown herein to constitute silicified microbial mats that were broken transported and deposited as point bar deposits in thermal spring fed streams moreover four unusual siliceous sinter fabrics vuggy globular spongy scalloped and arcuate wavy layered are interpreted to have formed from local acid sulfate chloride thermal springs possibly associated with paleo fumaroles the reconstructed history of paleo hydrothermal activity indicates that the oldest sinters 36 ka at mangatete developed in alkali chloride hot springs but then underwent post depositional alterion overprinting by acid sulfate steam condensate and were dismembered possibly by a hydrothermal eruption low ph hot spring discharges forming the unusual inferred acid sinter fabrics were localized in the same area a shift in paleo hydrology is evidenced by unaltered alkali chloride sinters dated between 22 and 3 ka a cluster of sinter dates between 22 7 and 20 7 ka denote thermal fluid emissions around the time of the okareka eruption 22 1 ka an 11 kyr gap in sinter ages followed which overlaps with a time of relative quiescence in local fault movement in between the rotorua and rotoma eruptions as determined from previous paleo seismicity studies on the whirinaki fault in the mangatete area at 9 4 ka hot spring activity in thermally fed streams slightly post dated the rotoma eruption 9 5 ka the locations and ages of the youngest post 9 4 ka alkali chloride sinters and silicified paleosols in relation to whirinaki fault movements indicate an overall westward migration of siliceous spring discharge dated charcoal 1 8 kyr in ash at the base of a locally extensive volcaniclastic debris flow containing sinter blocks of a range of ages and mineralogical maturity suggests its affiliation with the taupo eruption mangatete sinters occur along sw ne striking faults parallel to the regional trend of the tvz which dissect the topography into stepped terraces inferred basement cross faults in the study area i e structural lineaments orthogonal to this trend may have served as fluid pathways at depth initiating and maintaining hydrothermal activity at mangatete for more than 30 kyr within the larger ngakuru graben 150 km 2 the ages and distributions of sinters and hydrothermal eruption breccias including those at mangatete show that significant hydrothermal activity occurred for more than 60 kyr in an area lacking such activity today thus mangatete retains a rare stratigraphic record within the tvz sinter archive of changing geothermal fluids resulting from shifts in paleo phreatic water levels moreover although limited the presented age data imply a relationship among seismic activity volcanic ash fall events and the occurrence of permeable pathways for upward migration of thermal fluids finally whereas currently active tvz geothermal fields appear to be stable over tens of thousands of years or more the fossil hydrothermal systems in the wider mangatete area demonstrate the possibility of much greater temporal variability in the lateral expression of local surface manifestations of thermal fluid discharge through time

characteristics and consequences of lava dome collapse at ruawahia taupo volcanic zone new zealand the eruption of large rhyolitic lava domes may be accompanied by the formation of large block and ash flows this may be linked to the style of dome extrusion whether it forms a series of individual lobes flows or spines exogenous or grows by internal inflation endogenous lava domes can transition from one extrusive style to another as a result of a change in extrusion rate or the formation of facilitating structures such as shear zones how this change can affect large rhyolitic lava domes is unclear as there are few historically recorded rhyolitic dome eruptions here we present structures at ruawahia lava dome a well exposed 700 year old lava dome how these facilitating structures enable exogenous extrusion at ruawahia dome and link this to collapse episodes along the fringes of the dome during growth ruawahia dome is part of the tarawera dome complex a chain of domes running parallel to regional structures across the okataina caldera complex in the taupo volcanic zone new zealand ruawahia dome consists of 1 a high porosity 44 52 crystalline 65 dre locally brecciated carapace facies with rare bread crusting and ropey flow textures 2 a core facies of dominantly low to moderate porosity 20 25 with elongate vesicles that mark weak flow bands and 3 thin 5 m thick interior breccia zones flow bands at ruawahia are complex and do not fit with hypothesised flow band orientations attributed to a single phase of exogenous or endogenous dome growth inward dipping flow bands on ramp structures on the flow surface suggest a flow like coulee morphology however steeply dipping and multidirectional flow bands on the edges of the dome challenge this hypothesis widespread block and ash flow deposits have been sourced from the leading dome fronts to the nw and se these collapse events left behind inflated and bread crusted outcrops on these dome fronts suggesting syn eruption collapse events that led to expansion of a hot pressurised dome interior we consider ruawahia erupted from multiple aligned vents either as lobes confined within the crater of a pyroclastic cone formed during the initial plinian phase of the eruption or those able to flow down the cone flank the confined lobes formed steep internal breccia zones as individual dome lobes extruded past one another lobes that were able to overcome the pyroclastic cone rim or where the vent was outside the crater were able to flow down the flanks as bulldozing thickening flows with dominantly ductile interiors and brittle exteriors these flows collapsed as the front thickened possibly due to a decrease in gradient producing widespread block and ash flows the removal of lava associated with collapse generated a decompression event which resulted in fragmentation cracking and vesiculation in the hot interior of the lava flows these events left behind a re vesiculated and bread crusted lava flow front and produced block and ash flows with abundant breadcrust bombs that reached the base of tarawera

analysis of late holocene faulting within an active rift using lidar taupo rift new zealand abstract high quality light detection and ranging lidar data collected across the rangitaiki plains the fastest extending section of the onshore taupo rift new zealand reveal 122 active fault traces and provide new constraints on displacements displacement rates and paleoearthquakes of the normal faults in the rift the identified lineaments are scarps that record vertical offset of geomorphic surfaces e g beach ridges meander channel floors river terraces etc and trend parallel or sub parallel to other active faults in the rift these lineaments are interpreted to be active faults active fault traces trend 060 and their lengths range from 0 25 to 6 km they mainly traverse and displace a diachronous landscape of

modelling ground deformation patterns associated with volcanic processes at the okataina volcanic centre abstract the okataina volcanic centre ovc is one of two large active rhyolite centres in the modern taupo volcanic zone tvz in the north island of new zealand it is located in a complex section of the taupo rift a tectonically active section of the tvz the most recent volcanic unrest at the ovc includes the 1315 ce kaharoa and 1886 tarawera eruptions current monitoring activity at the ovc includes the use of continuous gps receivers cgps lake levelling and seismographs the ground deformation patterns preceding volcanic activity the ovc are poorly constrained and restricted to predictions from basic modelling and comparison to other volcanoes worldwide a better understanding of the deformation patterns preceding renewed volcanic activity is essential to determine if observed deformation is related to volcanic tectonic or hydrothermal processes such an understanding also means that the ability of the present day cgps network to detect these deformation patterns can also be assessed the research presented here uses the finite element fe modelling technique to investigate ground deformation patterns associated with magma accumulation and diking processes at the ovc in greater detail a number of fe models are produced and tested using pylith software and incorporate characteristics of the 1315 ce kaharoa and 1886 tarawera eruptions summarised from the existing body of research literature the influence of a simple ring fault structure at the ovc on the modelled deformation is evaluated the ability of the present day continuous gps cgps geonet monitoring network to detect or observe the modelled deformation is also considered the results show the modelled horizontal and vertical displacement fields have a number of key features which include prominent lobe based regions extending northwest and southeast of the ovc the results also show that the ring fault structure increases the magnitude of the displacements inside the caldera in particular in the vicinity of the southern margin as a result some of the cgps stations in the vicinity of the ovc are more important for measuring deformation related to volcanic processes than others the results have important implications for how any future observed deformation at the ovc is observed and interpreted

contemporary ground deformation in the taupo rift and okataina volcanic centre from 1998 to 2011 measured using gps the taupo volcanic zone tvz is one of the world s most productive regions of rhyolitic volcanism and contains the highly active okataina volcanic centre ovc within the tvz intra arc extension is expressed as normal faulting within a zone known as the taupo rift the ovc is located within a complex part of the rift where volcanism and deformation is considered influenced by rift structure and kinematics there has been significant research on the structural volcanic and geophysical properties of the rift and ovc but less focus on deformation using geodetic data the limited studies that have utilized geodetic data do not clearly resolve the distribution of deformation and strain rates within the rift and ovc this is essential to ensure that deformation signals from volcanic processes at the ovc are correctly identified and distinguished from those related to regional tectonic or local hydrothermal processes within the rift in this paper we present a picture of contemporary deformation at the ovc and within the surrounding rift in detail using existing and new gps campaign and continuous gps cgps data collected between 1998 and 2011 the results show a highly heterogeneous deformation and strain rate field both extension and shortening through the study area partitioned into different parts of the rift our results agree well with earlier geodetic studies as well as identify new features but some deformation patterns conflict with long term geological observations in the ovc we observe a locally rotated horizontal velocity field significant vertical deformation and variable strain rates across the caldera in the tarawera rift we identify elevated extension and shear rates which may have significant implications for volcanism there a shortening pattern is identified through the central rift which is unexpected in an intra arc rifting environment we attempt to explain the source s of shortening and extension and discuss their implications for geodetic monitoring efforts in the ovc

dike induced faulting in rift zones of iceland and afar geodetic data and field observations demonstrate that the emplacement of dikes in volcanic rift zones frequently generates normal faulting and graben subsidence at the earth9s surface elastic modeling of the vertical ground surface displacements above dikes and faults indicates that the extent of graben subsidence can be achieved only if fault slip extends virtually to or beyond the dike plane at depth a mechanical model that includes dikes and frictional faults shows that dike opening tends to compress and lock faults located to either side of the dike therefore slip extending into or beyond the dike cavity must occur either 1 on faults that intersect the dike near its top above the zone of dike induced compression or 2 on faults that slip ahead of the dike as it propagates laterally data from iceland indicate that slip occurred on deep faults that presumably slipped in advance of the laterally propagating dike

evolution of the quaternary alluvial fan system in the himalayan foreland basin implications for tectonic and climatic decoupling abstract the quaternary evolution of an alluvial fan system in the himalayan foothills reveals two distinct phases the early quaternary siwalik system i and the late quaternary intramontane piggy back system ii have been studied in detail in the subathu sub basin of nw himalaya with system i followed by system ii sedimentary architecture and facies analysis from chronologically constrained sections using magnetostratigraphy and tl osl indicate that systems i and ii although developed in similar hinterland basin settings indicate contrasting aggradation and entrenchment system i is characterised by predominant fan aggradation in contrast to the variable aggradation entrenchment response in time and space for system ii system i is time transgressive laterally from east to west with the central part remaining as the uplifted inter fan domain further confinement of system i along the basin margin indicates its syn orogenic evolution linked to the intra foreland thrusting this continued with the formation of the piggy back basin of system ii glacial interglacial cycles influenced the evolution of both alluvial fan systems however greater sediment yield and larger accommodation space favored aggradation during system i in contrast in system ii insufficient accommodation space relative to sediment yield and ongoing upliftment and reduced subsidence resulted in aggradation at the fan head during incessant precipitation followed by entrenchment during low precipitation the latest phase late quaternary to recent is characterised by two level terraces at ca 16 and 5 ka within the entrenched streams due to variation in water budget and sediment load governed by glacial interglacial cycles this study thus demonstrate the variable importance of accommodation space base level change and magnitude of tectonic and climatic forcing as controlling factors on aggradation and entrenchment in quaternary alluvial fan systems of the himalayan foreland basin

fault slip accumulation in an active rift over thousands to millions of years and the importance of paleoearthquake sampling abstract the catastrophic earthquakes that recently september 4th 2010 and february 22nd 2011 hit christchurch new zealand show that active faults capable of generating large magnitude earthquakes can be hidden beneath the earth s surface in this article we combine near surface paleoseismic data with deep 1 ma timescales in the taranaki rift new zealand our analysis shows that the integration of different timescale datasets provides a basis for identifying active faults not observed at the ground surface estimating maximum fault rupture lengths inferring maximum short term displacement rates and improving earthquake hazard assessment we find that fault displacement rates become increasingly irregular both faster and slower on shorter timescales leading to incomplete sampling of the active fault population surface traces have been recognised for

spatio temporal associations between dike intrusions and fault ruptures in the tongariro volcanic center new zealand abstract crustal extension of the southern portion of the taupo rift in the central north island of new zealand is mostly accommodated by normal faulting and rare dike intrusions to better understand how extension is accommodated and how volcanoes and faults interact we provide a new integration of the tectonic and volcanic history of this young section of the taupo rift from geological evidence fault acceleration and deceleration apparently coincide with episodes of voluminous volcanic eruptions during the last 100 ka using geological data we detect three modes of volcano fault interactions active during different periods 1 increased volcanism eruptive volume coupled with increased fault slip rate e g 26 11 cal kyr bp 2 increased volcanism but decreased adjacent fault activity e g 11 10 cal kyr bp pahoka mangamate unzipping period and 3 decreased volcanism low rates and volumes but increased fault slip rate e g 45 25 cal kyr bp the availability of melt production at depth is a first order factor controlling the geodynamic processes of coeval fault slip rate and magma volume variations within this rift we hypothesize that progressive shallowing of magma drives transition of mode 1 to 2 i e maintaining high volcanic rates but decreasing fault slip second order interactions such as stress transfer is modelled by simple coulomb stress transfer scenarios to other faults and volcanoes surrounding rift elements our results strongly suggest that fluctuations in magma input through time strongly influence both eruption frequency and seismic cycles in volcanic rifts time dependent seismic hazard models must consider the influence of magmatic processes in fault parameters e g temporal slip rate variations in continental rifting environments

the mount wright arc a cambrian subduction system developed on the continental margin of east gondwana koonenberry belt eastern australia abstract the mount wright arc in the koonenberry belt in eastern australia is associated with two early to middle cambrian lithostratigraphic groups developed onto the late neoproterozoic volcanic passive margin of east gondwana the gnalta group includes a calc alkaline basalt andesite dacite suite mount wright volcanics interpreted to represent the volcanic component of the arc volcaniclastic gnalta group rocks now buried in the bancannia trough represent the continental back arc developed immediately behind the arc in a manner analogous to the modern taupo volcanic zone of new zealand east of the gnalta group is the ponto group a deep marine sedimentary package that includes tholeiitic lavas bittles tank volcanics and felsic tuffs interpreted as part of a fore arc sequence the configuration of these units suggests the mount wright arc developed on continental crust in response to west dipping subduction along the east gondwana margin in contrast with some models for cambrian convergence on other sections of the delamerian orogen which invoke east dipping subduction and arc accretion by arc continent collision this convergent margin was deformed by the middle cambrian delamerian orogeny which involved initial co axial shortening followed by sinistral transpression and oroclinal folding around the edge of the curnamona province

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

shear wave velocity variation across the taupo volcanic zone new zealand from receiver function inversion summary the taupo volcanic zone tvz new zealand is a region characterized by very high magma eruption rates and extremely high heat flow which is manifest in high temperature geothermal waters the shear wave velocity structure across the region is inferred using non linear inversion of receiver functions which were derived from teleseismic earthquake data results from the non linear inversion and from forward synthetic modelling indicate low s velocities at 6 16 km depth near the rotorua and reporoa calderas we infer these low velocity layers to represent the presence of high level bodies of partial melt associated with the volcanism receiver functions at other stations are complicated by reverberations associated with near surface sedimentary layers the receiver function data also indicate that the moho lies between 25 and 30 km deeper than the 15 2 km depth previously inferred for the crust mantle boundary beneath the tvz

the importance of microearthquakes in crustal extension of an active rift a case study from new zealand received 24 august 2012 revised 29 november 2012 accepted 19 december 2012 1 the amount of extension accommodated in active rifts by earthquakes that do not rupture the ground surface e g mw 5 5 is often poorly constrained the matata earthquake sequence mes a high quality dataset of 2563 relocated microearthquakes 1 mw 4 7 that ruptured the taupo rift in new zealand over a period of 49 months has been used to quantify the proportion of extension produced by small to moderate sized earthquakes analysis shows that the extension rate across the rift due to the mes is 2 4 0 7 mm yr at 1s standard deviation an average extension rate for small to moderate magnitude earthquakes which also prevailed during the preceding 28 years 1977 2004 and represents up to 30 of the total contemporary deformation recorded across the north taupo rift by gps 15 5 mm yr the bulk of the mes 94 occurred at depths of 1 5 to 6 5 km and may not be observed in geological datasets e g as displacements of the ground or near surface horizons small scale faulting associated with microseismicity may thus record strains not measured by geological datasets and constitute an important component of the 3 10 mm yr disparity between geological and gps rates of extension across the taupo rift

interdependence of fault displacement rates and paleoearthquakes in an active rift paleoearthquakes at earth s surface often generate faults with variable displacement rates over short time intervals e g 18 k y the nature and origin of these variations and the extent to which they result from systematic and therefore predictable earthquake processes is unresolved we examine the processes underlying fluctuations in displacement rates by charting the accumulation of displacement over the last 60 k y on 25 normal fault traces distributed across the taupo rift new zealand displacement rates become more stable with increasing fault size and are uniform when aggregated across the entire rift the increased stability of fault displacement rates at greater spatial scales suggests that each fault is a component of a kinematically coherent system in which all faults interact and their earthquake histories are interdependent fault interdependencies generate short term complex 18 k y fluctuations in the timing and magnitude of earthquakes but also ultimately result in the stability of displacement rates on million year time scales

a volcanotectonic cascade activation of range front faulting and eruptions by dike intrusion mono basin long valley caldera california 1 stratigraphic data suggest that during the north mono inyo eruption sequence of 1350 a d a series of strong earthquakes occurred near the end of the north mono explosive phases and the beginning of the inyo explosive phases the temporal proximity of these events suggests the possibility of a causal relationship geological and geomorphic features of the hartley springs fault are consistent with rupture of the fault during the eruption sequence these features include steep central slope segments on several fault scarps and a fault scarp and stratigraphic offset since the deposition of 1200 year old tephra we hypothesize that the inyo dike found by drilling underneath the main inyo vents neared the hartley springs fault as it propagated southward from the mono basin circa 1350 a d we demonstrate that once the lateral distance between dike and fault was sufficiently small the mechanical interaction between them could have triggered the slip observed on the fault the slip in turn could have reduced the horizontal confining pressure in a region near the southern tip of the fault the presence of the main inyo vents in this region suggests that the reduction in confining stress was sufficient to allow magma to propagate to the surface the results suggest that a volcanotectonic cascade of eruptions and earthquakes is a possible mechanism by which a large section of a range front or rift system can be activated because of the positive feedback provided by each element to continued activity

water mass analysis and alongshore variation in upwelling intensity in the eastern great australian bight 1 a study of climatological and conductivity temperature depth ctd data for 2004 is made to provide a conceptual model of upwelling for the eastern region of the great australian bight in particular the data and other studies provide strong evidence that shelf break upwelling is confined to the southwest kangaroo island region and does not occur farther to the west off the eyre peninsula rather the upwelled water is likely to remain in a kangaroo island pool until subsequent upwelling events draw the water to the shallower and surface coastal regions of the eastern bight in this manner the surface upwelling apparent off the bonney coast kangaroo island and the eastern great australian bight gab can appear to be simultaneous moreover it appears likely that the water within the kangaroo island pool remains nutrient rich support for this model comes from ctd sections collected in 2004 that show that the upwelled signal cool 26 kg m 3 diminishes in width and intensity with increasing distance from kangaroo island the pattern of fluorescence is similar to that for temperature in the upwelled plume and indicates that the kangaroo island pool remains nutrient rich relatively low oxygen concentrations may indicate a previous bloom the warmest water is found near the shelf break along with very low values of fluorescence and relatively higher levels of oxygen suggesting nutrient limited growth of phytoplankton these data also support the notion that the upwelled nutrient rich water is supplied from the kangaroo island pool and not by shelf break upwelling in the eastern gab anomalously salty and fresh water is identified as resulting from evaporation in coastal bays and groundwater aquifer discharge

fault controls on the geometry and location of the okataina caldera taupo volcanic zone new zealand abstract okataina caldera is located within the taupo rift and formed due to collapse following eruptions at 325 and 61 ka gravity seismic reflection topographic and geological data indicate that active rift faults pass into the caldera and have influenced its location and geometry the caldera has a minimum gravity anomaly of 50 mgal is elongate north south with an inferred minimum depth to caldera floor of 3 0 5 km at the rift axis and occupies a 10 km hard linked left step in the rift the principal rift faults 55 75 dip define the location and geometry of the northwest and southeast caldera margins and locally accommodate piecemeal collapse segments of the east and west margins of the caldera margin are near vertical 70 90 dip trend north south and are inferred to be faults formed by the reactivation of a pervasive mesozoic basement fabric i e faults and or lithological contacts the fault sets which define the caldera geometry predate it while the step in the rift across the okataina volcanic centre ovc is at least as old as the caldera within the ovc displacement on rift faults induced by gravitational caldera collapse at 61 ka exceeds tectonic displacement since this time by at least a factor of two collapse along pre existing rift faults and in particular mesozoic basement fabric are important for caldera formation elsewhere in the taupo volcanic zone

crustal spreading due to dikes and faults in southwest iceland abstract a 30 km long profile extending from 3 million year old pleistocene rocks to the holocene rocks of the rift zone in southwest iceland is dissected by 443 dikes and 156 normal faults nearly all the dikes are basaltic with an average strike of n26 e which is subparallel to the trend of fractures in the nearby rift zone their average dip is 69 and average thickness 1 37 m both values much lower than averages for regional tertiary dike swarms in iceland many dikes are seen to change into sills the great majority of the faults are pure dip slip with an average throw of 10 2 m their average strike n37 e is different from the average strike of the dikes in this area and the fractures in the nearby rift zone their average dip is 75 2 which is somewhat steeper than in the tertiary areas but the dips are less in the interbedded sedimentary layers than in the lava flows growth faults are very rare in the area and most of the faults appear to have completed their growth in less than 10 000 years in subsections crustal dilation due to dikes is 0 4 3 7 that due to faults is 0 6 5 3 and that due to both dikes and faults is 1 04 6 44 in these subsections average fault spacing is one fault per 170 563 m spacing decreases toward the active rift zone it is concluded that in typical fissure swarms of the rift zone the dilation at the surface is almost entirely due to extensional fractures and gaping vertical normal faults in the depth range of a couple of hundred metres to perhaps 1 km the non vertical faults contribute most to the dilation at deeper crustal levels however dilation due to dikes becomes dominant

the ad1315 tarawera and waiotapu eruptions new zealand contemporaneous rhyolite and hydrothermal eruptions driven by an arrested basalt dike system a series of large hydrothermal eruptions occurred across the waiotapu geothermal field at about the same prehistoric time as the ad1315 kaharoa rhyolite magmatic eruptions from tarawera volcano vents 10 20 km distant triggering of the waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent ngapouri fault the kaharoa rhyolite eruptions are now recognised as primed and triggered by multiple basalt intrusions beneath the tarawera volcano a 1000 t day pulse of co2 gas is recorded by alteration mineralogy and fluid inclusions in drill core samples from waiotapu geothermal wells this co2 pulse is most readily sourced from basalt intruded at depth and although not precisely dated it appears to be associated with the waiotapu hydrothermal eruptions we infer that the hydrothermal eruptions at waiotapu were primed by intrusion of the same arrested basalt dike system that drove the rhyolite eruptions at tarawera this dike system was likely similar at depth to the dike that generated basalt eruptions from a 17 km long fissure that formed across the tarawera region in ad1886 fault ruptures that occurred in the waiotapu area in association with both the ad1886 and ad1315 eruptions are considered to be a result rather than a cause of the dike intrusion processes

insights into caldera and regional structures and magma body distribution from lava domes at rotorua caldera new zealand abstract lava domes emplaced after caldera forming eruptions are often the only clue to the structure of the caldera and to the regional structure at the time of caldera formation this is because the deposits from the subsequent eruptions commonly bury subsidence controlling caldera faults and regional cross faults within calderas other calderas and lava domes in the taupo volcanic zone tvz new zealand have been previously reported to show strong regional control at rotorua caldera there is a general lack of surface expression of faults but rhyolite lava domes are well exposed and aligned with regional structures that have been mapped outside of the caldera our summary of published data and new observations allows these lava domes to be subdivided into three groups based upon their petrology geochemistry relative age and spatial distribution 1 the kaikait huna group of pre collapse 451 ka crystal rich domes at the caldera boundary 2 the utuhina group of crystal poor high alkali post collapse domes c 200 ka surrounding the locus of collapse and directly related to the earlier 240 ka mamaku ignimbrite eruption and 3 the ruamata group of crystal rich more calcic less devitrified post collapse 60 36 ka domes further out from the collapse locus mapping of the morphology and internal structures of the utuhina group domes shows an ene wsw elongation direction and vent alignment which is parallel to and down strike of a the extensional rift orientation independently mapped either side of the caldera b the local caldera morphology and c structures mapped at nearby okataina caldera complex a second nw se trending orientation in the caldera morphology is parallel to a pre collapse basement fabric and has partially controlled the locations of the domes a third orientation is hinted at through consistent n s striking flow bands within ngongotaha dome which are parallel with a gravity anomaly we suggest that this orientation is a n s section of a caldera ring fault that links regional structures and was utilised during caldera collapse a subsequent dike intrusion also used this structure erupting a fissure style dome that contains radiating flow bands which mimic the orientation of the feeder dike however the structure morphology and location of post collapse lava domes generally echo the unburied regional structures outside the caldera indicating that dike intrusion also occurred along regional structures we suggest that the regional structures at rotorua caldera which are similar to those at okataina caldera complex show that the kink in the orientation of the rift across the tvz to the se of rotorua was active to at least 240 ka and possibly earlier this kink is significant due to its proximity and influence on both rotorua and okataina caldera systems and their associated geothermal fields we conclude that internal structures such as flow bands and morphology of lava domes are direct consequences of the shape and location of the feeder dike which in turn is controlled by the structure of the caldera and region we also suggest that lava dome eruptions at rotorua were from a series of small related nestled magma bodies a key outcome of this study is the reconstruction of the wider structure of the caldera and surrounding structure based upon the localised internal features distribution and morphology of related lava domes

basalt triggering of the c ad 1305 kaharoa rhyolite eruption tarawera volcanic complex new zealand abstract the ad 1305 kaharoa eruption episode of tarawera volcanic complex was the largest 4 km3 magma eruption in new zealand in the last 1000 years high silica 76 sio2 rhyolite was erupted from seven vents along an 8 km linear zone to form pumiceous pyroclastic deposits and lava domes initial vent clearing explosions were followed by a series of plinian pumice eruptions that spread tephra downwind and pyroclastic density current deposits over the volcano slopes the early pyroclastic eruptions were followed by extrusion of a dome in the summit vent and the migration of further plinian activity to adjacent vents the episode finished with the extrusion of three summit lava domes accompanied by block and ash flows two main types of rhyolite were erupted 1 a low zr low sr high rb type comprising the early plinian pyroclastics and 2 a high zr high sr low rb type comprising the late eruptives including the summit domes basaltic material basalt and basaltic andesite is commonly present as free clasts within the kaharoa pyroclastic deposits along with rare clasts of granodiorite diorite gabbro and olivine clinopyroxenite the basaltic clasts are often veneered by kaharoa rhyolite basaltic material is also common as inclusions within rhyolite pumices along with olivine and augite xenocrysts derived from the basalt the basaltic clasts and inclusions contain complexly zoned plagioclase and corroded olivine commonly with a reaction rim consistent with disequilibrium caused by magma mixing some basaltic clasts and inclusions are hornblende free others contain groundmass hornblende plumes of brown glass often extend from hornblende bearing basaltic inclusions into the surrounding rhyolite these plumes demonstrate magma mixing as does the presence of rhyolitic glass and quartz xenocrysts in some basaltic inclusions most basaltic inclusions have crenulate boundaries suggesting they were fluidal when coming into contact with the rhyolite magma diorite gabbro and olivine clinopyroxenite clasts have mineralogy similar to the basalts commonly contain patches of fine grained basaltic material and are considered co magmatic with the basalts intrusion of basalt magma into the base of the rhyolite magma chamber appears to have occurred for some time before the kaharoa eruptions began allowing considerable mixing with the rhyolite magma transfer of water to some basalt inclusions and formation of hornblende in their groundmass conversely the hornblende free basalt inclusions did not have time to react with the rhyolite magma and must have been intruded shortly before the start of the eruption intrusion of this hornblende free basalt appears to have triggered the kaharoa eruption after the magma chamber had been primed by the earlier intrusions

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

three dimensional distribution of seismic anisotropy in the hikurangi subduction zone beneath the central north island new zealand 1 we use earthquake arrival time data in the central north island new zealand in inversion for 3 d vp azimuthal anisotropy it is parameterized with an isotropic component and two azimuthal anisotropy parameters for each node and local earthquake shear wave splitting observations define the initial anisotropy model our results suggest that mantle flow either within the mantle wedge or below the subducted slab is not the primary source of anisotropy in the hikurangi subduction zone the largest region of anisotropy that we image is within the subducted slab where anisotropy is consistently trench parallel and 5 9 magnitude from 32 to 185 km depth bending induced yielding in the slab offshore and as it passes through the trench provides an explanation for this slab anisotropy beneath the taupo volcanic zone tvz there is 1 4 trench normal anisotropy within 30 km of the surface of the slab within a region entrained with motion of the slab in contrast only very weak 0 2 anisotropy is imaged in the region of high temperature partial melt arising from active corner flow in the mantle wedge in the crust geologic structure is important with the largest crustal anisotropy 14 related to schist we image significant anisotropy aligned with the margins of the tvz related to extensive fracturing on the margins as the tvz actively extends within the heavily intruded and underplated tvz lower crust the orientation of anisotropy switches to align with the extension direction this orientation is consistent with other geophysical data suggesting the presence of connected melt in this region

patterns of tectonic fault interactions captured through geostatistical analysis of microearthquakes 1 historical earthquakes are often strongly clustered in space and time this clustering has been attributed to static stress triggering associated with tectonic fault interactions and or to fluid migration discrimination between these two models requires detailed information on the timing location and size of earthquakes the matata earthquake sequence in the taupo rift new zealand provides a unique opportunity to chart spatial and temporal patterns of earthquakes along individual faults and their relations to other faults in the system over timescales of days to years this is possible because there are 2563 accurately relocated within 5 5 earthquakes that occur over thousand year timescales e g 60 kyr

dike induced contraction along oceanic and continental divergent plate boundaries the axis of divergent plate boundaries shows extension fractures and normal faults at the surface here we present evidence of contraction along the axis of the oceanic ridge of iceland and the continental main ethiopian rift contraction is found at the base of the tilted hanging wall of dilational normal faults balancing part of their extension our experiments suggest that these structures result from dike emplacement multiple dike injection induces subsidence above and uplift to the sides of the dikes the transition in between is accommodated by reverse faults and subsequent peripheral inward dipping normal faults our results suggest that contraction is a direct product of magma emplacement along divergent plate boundaries at various scales marking a precise evolutionary stage and initiating part of the extensional structures extension fractures and normal faults

a back arc basin formed within continental lithosphere the central volcanic region of new zealand abstract the central volcanic region is an area of quaternary volcanism and tensional tectonics within the north island of new zealand that appears to be a direct continuation of a young oceanic back arc basin the havre trough into the continental structure of new zealand volcanism is predominantly rhyolitic yet the region possesses many of the geophysical characteristics often associated with oceanic back arc basins upper mantle seismic velocities are low pn and sn velocities of 7 4 and 3 95 km s respectively the crust is anomalously thin for its continental setting and the heat flow almost all of which is expressed in the discharge of hot water through geothermal systems is about 700 mw m2 i e some twelve times greater than normal continental heat flow in order to account for such a high heat flow a large scale mass transfer of heat is required it is proposed therefore that the central volcanic region represents a site of active back arc spreading within a continental lithosphere

reconstruction of the geology and structure of lake rotomahana and its hydrothermal systems from high resolution multibeam mapping and seismic surveys effects of the 1886 tarawera rift eruption abstract present day lake rotomahana is one of the two focal points of the most destructive eruption in new zealand s historical record i e that of mt tarawera on 10 june 1886 with devastating loss of life and presumed destruction of the iconic pink and white terraces that adorned the margins of the lake basaltic dikes are considered to have ascended near surface in the area intruding into hydrothermally altered and water saturated ground beneath the existing lake the consequential hydrothermal and phreatomagmatic eruptions ejected 0 5325 km 3 of material from the lakefloor and below plastering the nearby landscape for several kilometers with mud and other debris the eruption buried the natural outlet of the lake with the bottom of the craters becoming filled by water within months and completely concealed from view within years today lake rotomahana has depths up to 118 m high resolution 0 5 m bathymetric mapping when combined with a 2 d seismic reflection survey enables us to see details of the maar craters on the lakefloor including those parts subsequently buried by sediment the large rotomahana crater described by workers immediately after the eruption measures 2 5 km in diameter near its southwestern end and excavated ground to 155 m below present day lake level the vent system as revealed by the present study forms an array of right stepping dextral craters with the main crater being host to two sub craters rotomahana west crater and rotomahana east crater today buried beneath the lakefloor and which are in filled by 36 and 37 m of sediment respectively subordinate craters along the same 057 tarawera rift trace include hochstetter crater 11 m of infill waingongongongo crater 14 m and rotomakariri crater 26 m these craters host a total 0 0268 km 3 of sediment other features highlighted by the bathymetric data include craters not filled by sediment sediment fan deltas volcanic ridges and dikes submerged wave cut terraces formed during times of lower lake levels and gas pockmarks all either related to the 1886 eruptive episode or post eruption hydrothermal and erosional processes application of results from bubble plume co 2 flux magnetic and heat flux surveys of lake rotomahana to this study when combined with regional earthquake relocation analysis and broadband magnetotelluric data suggest an explanation in terms of a magmatic heat source located south of waimangu and a corresponding convective water heat transport system extending thence to beneath the western end of the lake a holistic approach has provided a coherent context for the eruption and its effect on the historical pink and white terraces hydrothermal system that appears to have been the eastern most extension of a larger system that lay beneath the waimangu area before the eruption the newly named pink terraces hydrothermal system 1 5 km 2 is a continuation of the historical hydrothermal activity that was concentrated on the western shores of the old lake and together with the formation of the new post 1886 patiti hydrothermal system 1 km 2 located sw of patiti island mark the two distinct areas of hydrothermal activity in the lake today

rapid evolution of subduction related continental intraarc rifts the taupo rift new zealand the evolution of the continental intra arc taupo rift in the north island new zealand is rapid significantly faster than comparative intra continental rifts such as the african rifts based on our faulting data and published geological geophysical and borehole data we show that activity in the 2 ma taupo rift has rapidly and asymmetrically narrowed via inward and eastward migration of faulting at rates of ca 30 km my 1 and 15 km my 1 respectively and has propagated southwards along its axis 70 km in 350 kyr the loci of voluminous volcanic eruptions and active faulting are correlated in time and space suggesting that a controlling factor in the rapid rift narrowing is the presence of large shallow heterogeneities in the crust such as large rhyolitic magma bodies generated by subduction processes which weaken the crust and localize deformation eastward migration of faulting also follows the eastward migration of the volcanic arc which may be related to rollback of the pacific crust slab at the hikurangi subduction zone southward propagation of the rift is linked with southward migration of the hikurangi plateau chatham rise subduction point and occurs episodically aided by stress changes associated with voluminous local volcanism the large magma supply during early continental intra arc rift stages explains faster evolution from tectonic to magmatic than intracontinental rifts however the fast changes in magma supply from the subduction zone can also lead to evolution reversals more evolved magmatic stages reverting to less evolved tectonic stages rift cessation and thus failed continental break up

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

surface deformation and shallow dike intrusion processes at inyo craters long valley california the inyo craters are the two largest of four phreatic craters that lie within a 2 5 km long 500 to 700 m wide n s trend of faults and fissures at the south end of the inyo volcanic chain in eastern california the alignment of these features with dike fed silicic volcanic centers of the same age a few kilometers to the north suggests that they were produced during intrusion of a dike at about 650 550 yr b p e w extension south of south inyo crater is ten to several tens of meters suggesting that the dike is at least that thick to understand how the faults and fissures developed we mapped and studied the fault and fissure pattern used a theoretical boundary element model to determine the surface strain profile above a shallow dike in a purely elastic medium and conducted physical model experiments of fault and fissure growth results of the field studies and experiments indicate that deformation develops according to the following sequence 1 extension fractures and perhaps other inelastic deformation develop immediately above the dike top and on the limbs of a shallow syncline which forms above the dike 2 fissures form along two parallel trends at the surface on opposite sides of the dike plane leaving a relatively unfractured region in between 3 dip slip movement on subsurface fractures and linkage of these fractures with surface fissures produces inward facing normal fault scarps that bound a nested graben above the dike experimental graben widths are up to several times narrower than predicted from the locations of theoretical strain maxima above a dilating crack in a linearly elastic medium this fact is apparently due to the growth of a zone of inelastic deformation above the experimental dike top in the subsurface if the ratio between the depth to the dike top and the distance between the outermost surface fissures at inyo craters is within the range of ratios measured experimentally then the depth to the dike top is between 250 m and several times that a slant hole drilled in the summer of 1987 by the department of energy office of basic energy sciences intersected three breccia bodies of possibly intrusive origin directly below the center of south inyo crater between 550 m and 610 m below the crater rim no intact juvenile igneous rock was intersected suggesting that the hole passed above the magma filled dike top perhaps passing through the zone of inelastic deformation which is inferred to exist from our model results

repeating earthquakes in the yellowstone volcanic field implications for rupture dynamics ground deformation and migration in earthquake swarms abstract we evaluated properties of yellowstone earthquake swarms employing waveform multiplet analysis thirty seven percent of the earthquakes in the yellowstone caldera occur in multiplets and generally intensify in areas undergoing crustal subsidence outside the caldera in the hedgen lake tectonic area the clustering rate is higher up to 75 the yellowstone seismicity follows a succession of two phases of earthquake sequence the first phase is defined between swarms it is characterized by a decay of clustering rate and by foreshock aftershock sequences the second phase is confined to swarms and is characterized by an increase in clustering rate and dominant aftershock sequences this phase reflects tectonic swarms that occur on short segments of optimally oriented faults for example the largest recorded swarm in yellowstone occurred in autumn 1985 on the northwest side of the yellowstone plateau which was initiated as a tectonic source sequence fitting experimental dependence of fluid injection with intrusion migration suggests that the 1985 swarm involved after 10 days hydrothermal fluids flowing outward from the caldera the 2008 2009 yellowstone lake swarm exhibited a high migration rate of 1 km day a decrease in clustering rate without a main shock and appears to be associated with magma injection of 1 to 5 m 3 s in a succession of migrating magma fronts that incrementally solidify and fracture at its brittle edges the 2010 madison plateau earthquake swarm on the west side of the caldera initiated as a tectonic sequence but the expansion of the swarm front was associated with hydrothermal fluid migration

a multiple approach radiometric age estimate for the rotoiti and earthquake flat eruptions new zealand with implications for the mis 4 3 boundary abstract pyroclastic fall deposits of the paired rotoiti and earthquake flat eruptions from the taupo volcanic zone new zealand combine to form a widespread isochronous horizon over much of northern new zealand and the southwest pacific this horizon is important for correlating climatic and environmental changes during the last glacial period but has been the subject of numerous disparate age estimates between 35 1 2 8 and 71 6 ka all errors are 1 s d obtained by a variety of techniques a potassium argon k ar age of 64 4 ka was previously determined on bracketing lavas at mayor island volcano offshore from the taupo volcanic zone we present a new more precise 40ar 39ar age determination on a lava flow on mayor island that shortly post dates the rotoiti earthquake flat fall deposits of 58 5 1 1 ka this value coupled with existing ages from underlying lavas yield a new estimate for the age of the combined eruptions of 61 0 1 4 ka which is consistent with u th disequilibrium model age data for zircons from the rotoiti deposits direct 40ar 39ar age determinations of plagioclase and biotite from the rotoiti and earthquake flat eruption products yield variable values between 49 6 2 8 and 125 3 10 0 ka with the scatter attributed to low radiogenic ar yields and or alteration and or inheritance of xenocrystic material with inherited ar rotoiti earthquake flat fall deposits occur in new zealand in association with palynological indicators of mild climate attributed to marine isotope stage mis 3 and thus used to suggest an age that is post 59 ka the natures of the criteria used to define the mis 4 3 boundary in the northern and southern hemispheres however imply that the new 61 ka age for the rotoiti earthquake flat eruption deposits will provide the inverse namely a more accurate isochronous marker for correlating diverse changes across the mis 4 3 boundary in the southwest pacific