coeval sedimentation magmatism and fold thrust development in the trans hudson orogen propagation of deformation into an active continental arc setting wekusko lake area manitoba early structures in the southeastern part of the trans hudson orogen tho wekusko lake area manitoba comprise northwest verging folds and a set of steep southeast dipping faults that occur at a low angle to bedding kinematic indicators are rare however the vergence of the associated folds supports reverse movement on the faults these folds and faults formed prior to the peak of regional metamorphism and therefore must correlate with the widely recognised deformational d2 event which developed pre to syn metamorphism and involved development of a regional south to southwest directed fold thrust belt the d2 folds and reverse faults in the study area are interpreted to have originally formed as gently dipping southwest verging structures i e as inclined folds and thrust faults which were then rotated into a steep northwest verging orientation during later deformation d3 in the southeastern tho regional d2 fold and thrust structures are cut by ca 1839 1830 ma plutons indicating that

anomalous sulfur poor platinum group element mineralization in komatiitic cumulates mount clifford western australia an unusual occurrence of sulfur poor platinum group element pge mineralization has been discovered at mount clifford in the agnew wiluna belt western australia within the lower part of a 1 000 m thick komatiitic dunite body the host body consists primarily of strongly serpentinized olivine adcumulates with accessory chromite high precision whole rock icp ms data show that the pge mineralization extends over tens of meters whereas the lateral extent is unknown palladium and pt abundances are closely associated with base metal sulfides but show offset distribution patterns with maximum concentrations associated with the relatively sulfide poor base of a disseminated sulfide bearing layer whole rock concentrations range up to 4 100 ppb pd and 920 ppb pt iridium rh and ru follow the trends in pd and pt but are strongly depleted ir 0 4 ppb ru 0 5 ppb rh 0 1 ppb platinum group minerals pgm were located in essentially sulfide free serpentine 2 m below the peak in sulfide abundance and can be categorized into three groups pd antimonides pt dominated pgm and pt bearing ni antimonides the pge mineralization zone is underlain by an interval of strong ni depletion within olivine mesocumulates that is characterized by an unusual negative correlation between ni and the mg number of the rock this relationship is interpreted to be the result of an equilibration of olivine of variable forsterite content with a relatively large mass of magmatic sulfide however there is no direct evidence of this sulfide mass anywhere in the entire mount clifford dunite body the ni depletion is accompanied by strong depletion in ipge ir ru and rh the association of the pge zone with a reversal in the mg fe ratio of the host cumulates and a distinctive offset relationship of multiple pt pd and cu s peaks is suggestive of a primary magmatic origin however this is inconsistent with current models for offset reef pge concentrations which involve the onset of sulfide liquid saturation from a previously sulfur undersaturated pge undepleted magma the association of enriched pt and pd with highly depleted ni and ipge in immediately underlying cumulates conflicts with this model we suggest a combination of processes early sulfide segregation at low r values producing ni and ipge depleted olivine partial redissolution and removal of most of this sulfide component during a major replenishment event and subsequent overprint by a migrating pt pd cu rich fluid

regional climate regime classification as a qualitative tool for interpreting multi proxy palaeoclimate data spatial patterns a new zealand case study abstract the precipitation characteristics of three basic circulation types for new zealand weather kidson j w 2000 an analysis of new zealand synoptic types and their use in defining weather regimes international journal of climatology 20 299 316 are explored here as a palaeoclimate reconstruction tool and are utilised as a way to interpret spatial patterns exhibited by diverse multi proxy data assemblages the technique is founded on a modern climate shift analogue for new zealand where regional precipitation spatial changes accompanied the 1976 77 inter decadal pacific oscillation ipo phase change the analysis here indicates multi decadal scale circulation changes both in frequency and strength resulted from the 1976 77 ipo phase change primarily during mid late summer late autumn and late winter and a significant change a zonal regime frequency and strength increase occurred for august from the climatological results the eastern north island along with the western and eastern south island are crucial regions to include in a spatial pattern based palaeoclimate reconstruction because of sensitivities to zonal circulation changes ascribing a climate regime classification to multi proxy data was subsequently attempted for three discrete timeslices in the late holocene and illustrates that many different types of multi proxy terrestrial data can successfully be assimilated with some evident advantages and shortcomings climate regime classification has good potential for highlighting spatial and temporal gaps in regional palaeoclimate proxy networks and in the case of new zealand potential for connecting local and regional palaeoclimate data to conditions associated with westerly circulation changes the ipo and for exploration of australasian and extra tropical palaeoclimate archive connections

landslide occurrence as a response to land use change a review of evidence from new zealand abstract vegetation cover is an important factor influencing the occurrence and movement of rainfall triggered landslides and changes to vegetation cover often result in modified landslide behaviour however it is difficult to relate the occurrence of landslides directly to variations in land use especially in some european countries in contrast new zealand provides a good opportunity to investigate geomorphic responses to anthropogenic land cover changes before european settlers first arrived in the 1840s hilly regions were only marginally influenced by human activity the maoris new zealand s first settlers lived largely on coastal plains or near lakes and rivers they influenced general vegetation cover only through localized burning practices in contrast european settlers moved into the back country and converted extensive hill areas from native forest and bush to pasture this reduced the strength of the regolith and rendered the slopes more susceptible to landslides pulses of natural sedimentation in the pre european period have been related to volcanic activity climatic variability including changes in frequency of cyclonic storms and wind erosion and fluvial erosion following forest fires initiated either by volcanic eruptions or lightning strikes since european deforestation began sediment production has largely been determined by landslide events on unstable slopes thousands of landslides were triggered by high magnitude low frequency climatic events during storms with estimated return periods in excess of 50 years in contrast low magnitude high frequency rainfall events have caused gully and channel erosion examples from different parts of new zealand indicate changes in sediment generating processes following land use modifications after deforestation landslides have contributed significantly to sediment sequences in depositional basins such as lakes swamps estuaries coastal wetlands and the nearshore and offshore zones of continental platforms

platinum group minerals in the limoeiro ni cu pge sulfide deposit brazil the effect of magmatic and upper amphibolite to granulite metamorphic processes on pgm formation the limoeiro ni cu platinum group elements pge deposit is a recent discovery associated with an igneous tubular conduit system in northeastern brazil representative ores from the deposit have been used for platinum group minerals pgm identification and for pge in base metal sulfides bms quantification ninety eighty percent of the pgm in the massive sulfide ores is homogeneous pt ni bi bearing merenskyite pdte2 enclosed primarily by pyrrhotite suggesting that it is formed by exsolution from monosulfide solid solution mss merenskyite gradually but systematically becomes poorer in pt and ni with increasing fractionation which is interpreted to reflect a transition to a more evolved sulfide liquid that segregated in the eastern parts of the intrusion in massive sulfide ores merenskyite forms unusually large up to 5000 m2 euhedral grains commonly in contact with spherical silicate inclusions bms hosts 12 16 of the pd with the remainder hosted by pgm which is interpreted to indicate that merenskyite recrystallized from a pge bearing bismuthotelluride metamorphic melt formed during high grade metamorphism sperrylite ptas2 is the second most abundant pgm 18 of pgm in disseminated ore and in contrast to merenskyite occurs mainly as very small median of 25 m2 inclusions in high temperature silicates and oxides interpreted to have crystallized at high temperatures directly from sulfide blebs that formed and were transported within the limoeiro magma conduit

k 2 o poor aluminous assemblages from the buchan dalradian and the variety of orthoamphibole assemblages in aluminous bulk compositions in the amphibolite facies

structural development of the snow lake allochthon and its role in the evolution of the southeastern trans hudson orogen in manitoba central canada the snow lake allochthon is a zone of tectonic interleaving of sedimentary rocks of an inverted marginal basin kisseynew domain with island arc and oceanic rocks it is located in the southeaster

palaeoenvironmental reconstruction from the last interglacial using phytolith analysis southeastern north island new zealand phytoliths extracted from loess resting conformably on lacustrine sediments in southeastern north island new zealand provide a nearly continuous vegetation climate record spanning the time period from the last interglacial marine oxygen isotope stage 5 to the present phytoliths reveal changes in vegetation patterns following changes in climate correlation between tree shrub phytolith fluctuations and the specmap oxygen isotope curve between marine oxygen isotope stages 1 and 5 suggest that changes in the ratio of arboreal to non arboreal phytoliths directly result from changes in climate these data generally support the existing pollen and diatom record this study confirms the usefulness of phytolith fossils for providing environmental and climate information from the quaternary sedimentary record especially in cases where the deposits contain no fossil pollen or diatoms copyright 2000 john wiley sons ltd

environmental change in northland new zealand during the last glacial and holocene abstract the quaternary vegetation and climatic history of the northernmost region of new zealand northland has long been the subject of speculation although the coverage is incomplete and individual records are punctuated by gaps or marked changes in sedimentation rates poor resolution and dating uncertainties recent work points to environmental changes that differ significantly from those at higher latitudes in new zealand conifer angiosperm forest has been important in northland during most of the last glacial cycle with agathis australis and nothofagus truncata dominated communities prominent during interstadials and stadials respectively fire and effective precipitation appear to have exerted greater influence on vegetation developments than temperature although the latter may control the competitive balance between agathis and nothofagus and will influence the environmental response to precipitation changes with the exception of human impacts during the last millenium the most striking vegetation changes are associated with widespread fires towards the end of the last glacial and the moist preceding interstadial in contrast pre human era holocene environments have been comparably stable although there is some evidence for increasing natural disturbance and a drier slightly cooler climate during the late holocene in several key aspects a glacial maximum to lateglacial dry phase very moist interstadial preceding the last glacial maximum no widespread loss of forest and the importance of fire and precipitation change in vegetation development during the last glacial cycle generally northland shows stronger affinities with south eastern australia than with other regions in new zealand

rapidity of orogenesis in the paleoproterozoic halls creek orogen northern australia evidence from shrimp zircon data cl zircon images and mixture modeling studies combining u pb shrimp zircon geochronology with cathodoluminescence imaging enables the resolution of temporally closely spaced geological events important for understanding tectonothermal processes in the paleoproterozoic halls creek orogen of northern australia the youngest detrital zircon grains from a low grade quartz muscovite psammite of the tickalara metamorphics have a 207 pb 206 pb shrimp age of 1864 or 4 ma defining a maximum depositional age for the unit zircon crystals from a high grade garnet biotite metapelite approximately 5 10 volume percent leucosome from the same sequence are considerably more complex and shrimp analyses form a single large concordant group in the range approximately 1885 to 1830 ma the zircon crystals contain three distinct cl zoning patterns and individual shrimp spots show a corresponding variation in 207 pb 206 pb ages concentric oscillatory zoned zircon dominates pre 1850 ma ages and is interpreted as detritus from igneous source rocks narrow structureless zircon rims infrequently overgrow and truncate the oscillatory zoning these rims comprise most of the post 1850 ma analyses and are inferred to be the product of uppermost amphibolite facies metamorphism reflecting the interaction of a robust pre existing detrital zircon suite with a very limited melt volume in addition some zircon cores of uncertain geological affinity contain large areas devoid of oscillatory zoning with individual analyses clustering around 1850 ma dividing the data into detrital and metamorphic suites solely on the basis of cl imaging yields an older group of 18 analyses 207 pb 206 pb age 1867 or 4 ma and a younger group of 10 analyses 207 pb 206 pb age 1843 or 4 ma not including five shrimp spots within areas of unzoned zircon mixture modeling of all 33 analyses in the post 1900 ma data set resulted in a best fit solution composed of two distinct components 1 an older group of 19 analyses with an age of 1867 or 4 ma and 2 a younger group of 14 analyses with an age of 1845 or 4 ma these results suggest that the unzoned patches of zircon might be related to metamorphism rather than being detrital cores importantly the ages and proportions of populations predicted by mixture modeling are otherwise very similar to those derived from analysis of cl zoning patterns these data imply that high temperature metamorphism occurred in the metasedimentary rocks less than 25 my after the crystallization of the igneous detrital source such rapid rates of erosion deposition and burial have rarely been proposed for proterozoic rocks despite evidence for analogous orogenic processes in the mesozoic and cainozoic on a comparable timescale careful evaluation of geological and geochronological data in proterozoic provinces elsewhere may reveal similar patterns with potential implications for the possible rates of proterozoic orogenesis and crustal evolution

platinum group minerals from the kambalda nickel deposits western australia the relative abundance compositional variability and geologic occurrence of platinum group minerals have been determined by a study of samples from a number of geologic environments in the kambalda nickel deposits these results have been integrated with findings from a previous study by hudson and donaldson 1984 of platinum group minerals in amalgamation residues from the gold recovery circuit of the kambalda nickel mill to give an overall picture of the nature and distribution of platinum group minerals at kambalda the major platinum minerals are sperrylite and moncheite and the major palladium minerals are sudburyite merenskyite stibiopalladinite palladoarsenide michenerite and testibiopalladite palladium also occurs in solid solution in palladian melonite irarsite is the only iridium mineral recognized and no discrete phases have been observed for the other platinum group elements sperrylite occurs within massive pyrrhotite pentlandite ores and is particularly abundant in ores that are rich in chalcopyrite a high proportion of the pt in the kambalda nickel deposits is believed to occur as sperrylite but not all sperrylite is sufficiently coarse in grain size to enable gravity concentration nevertheless sperrylite is the dominant platinum group mineral recovered in gravity concentrates discrete palladium minerals are most abundant in stringers of sulfide in the footwall to the ore in crosscutting sulfide veins or in reaction zones associated with hydrothermal veins and porphyries within the massive and matrix ores coarse discrete palladium minerals are rare and it is concluded that palladium occurs in solid solution or as finely dispersed submicroscopic grains in sulfide minerals predominantly pentlandite the occurrence within the ore zones of pt as sperrylite and pd dispersed in pentlandite is believed to reflect a primary magmatic distribution however the presence of sudburyite moncheite merenskyite michenerite testibiopalladite and palladian melonite in stringers and reaction zones indicates that their formation may be related to postmagmatic processes in particular metamorphic segregation of sulfides and the interaction of ore sulfides with younger hydrothermal fluids

a long late quaternary record from lake poukawa hawke s bay new zealand abstract the lake poukawa basin is a large co seismic depression located at 20 m above mean sea level in hawke s bay in eastern north island new zealand we present a detailed environmental history of the basin for the last c 60 ka based on analyses of the top 105 m of a 200 m core record dating control is provided by radiocarbon optically stimulated luminescence osl and u th disequilibrium ages the chronology is supported by nine tephras of inferred age including marker tephras kawakawa 22 590 230 yr bp at 18 25 m core datum tahuna c 35 43 ka at 33 1 m core datum and rotoehu 45 50 ka at 39 1 m core datum disagreements between some of the older tephra ages and the numerical ages from the osl and u th dating mean that more than one age model can be applied three major lithostratigraphic units are identified a basal calcareous silt with lignitic peats between 105 28 and 98 58 m of marine oxygen isotope stage mis 3 age an extended sequence of detrital shelly sands and silts between 98 58 and 8 m of mis 3 and 2 age and a holocene peat unit mis 1 from 8 to 0 m alternatively but less likely the basal unit may represent stage mis 5a and the detrital shelly sands would then contain an amalgam of mis 4 3 and 2 deposits we propose a notably moist phase represented by the peat which our numerical dating model places near the start of isotope stage 3 this suggests the existence of mild conditions during an interstadial in central new zealand at c 55 50 ka when a podocarp beech broadleaf forest of near interglacial affinity surrounded the basin the interstadial is marked by both lake and peat formation in the basin after 50 ka a thermal decline set in though the climate remained moist initially under these conditions the poukawa basin was rapidly infilled by alluvial fan deposits from the surrounding hills the floor of the basin was occupied by grasses and sedges responding to both the highly disturbed environment and swampy conditions in the basin after the deposition of the rotoehu ash effective precipitation declined markedly and woody shrubs expanded across the previously swampy basin floor the data suggest an apparent thermal decline of c 6 7 c for much of mis 2 and the latter half of mis 3 the holocene was marked by the establishment of fen and lake environments on the basin floor prior to human disturbance podocarp broadleaf forest surrounded the basin

melonite group minerals and other tellurides from three cu ni pge prospects eastern desert egypt abstract melonite group minerals and other tellurides are described from three cu ni pge prospects in the eastern desert of egypt gabbro akarem genina gharbia and abu swayel the prospects are hosted in late precambrian mafic ultramafic rocks and have different geologic histories the gabbro akarem prospect is hosted in dunite pipes where net textured and massive sulfides are associated with spinel and cr magnetite michenerite merenskyite pd bi melonite and hessite occur mainly as inclusions in sulfides typical magmatic textures indicate a limited role of late and post magmatic hydrothermal processes at genina gharbia ore forms either disseminations in peridotite or massive patches in hornblende gabbro in the vicinity of metasedimentary rocks actinolitic hornblende epidote chlorite and quartz are common secondary silicates sulfide textures and host rock petrography suggest a prolonged late magmatic hydrothermal event michenerite merenskyite pd bi melonite altaite hessite tsumoite sylvanite and native te are mainly present in secondary silicates the abu swayel prospect occurs in conformable lens like mafic ultramafic rocks in metasedimentary rocks and along syn metamorphic shear zone the sulfide ore and host rocks are metamorphosed amphibolite facies 550 to 650 c 4 to 5 kbar and syn metamorphically sheared melonite group minerals are represented by merenskyite and pd bi melonite other tellurides comprise hessite altaite and joseite b melonite group minerals and tellurides occur as inclusions in mobilized sulfides and along cracks in metamorphic garnet and plagioclase the different geological history of the three prospects permits an examination of the role played by magmatic late magmatic and metamorphic processes on the mineralogy of melonite group minerals and diversity of tellurides the contents of pge and te in the ore and temperature of crystallization control the mineralogy and compositional trends of the melonite group minerals crystallization of the melonite group minerals over a wide range of temperatures in a te rich environment enhances the elemental substitutions merenskyite dominates the mineralogy of the group at low te activity while pd bi melonite is the common phase at high te activity

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

palaeocirculation across new zealand during the last glacial maximum at 21 ka abstract what circulation pattern drove southern alps glacial advances at 21 ka late 20th century glacial advances in new zealand are commonly attributed to a dual precipitation increase and cooler than normal temperatures associated with enhanced westerly flow that occur under synoptic pressure patterns termed zonal regimes kidson 2000 but was the circulation pattern that supported major southern alps glacial advances during the global lgm similar to the modern analog here a regional climate regime classification rcrc time slice was used to infer past circulation for new zealand during the lgm at 21 ka palaeoclimate information that supported the construction of the 21 ka time slice was derived from the nz intimate climate event stratigraphy ces one new auckland maar proxy record and additional low resolution data sourced from the literature the terrestrial evidence at 21 ka implicates several possibilities for past circulation depending on how interpretations for some proxies are made the interpretation considered most tenable for the lgm based on the agreement between terrestrial evidence marine reconstructions and palaeoclimate model results is an anticyclonic zonal circulation regime characterized by increased influences from blocking highs over the south island during winter and an increase in zonal and trough synoptic types with southerly to westerly quarter wind flow during summer these seasonal circulation traits would have generated lower mean annual temperatures cooler than normal summer temperatures and overall lower mean annual precipitation for new zealand particularly in the western south island at 21 ka the anticyclonic zonal time slice reconstruction presented in this study has different spatial traits than the late 20th century and the early little ice age signatures suggesting more than one type of regional circulation pattern can drive southern alps glacial activity this finding lends support to the hypothesis that temperature over precipitation change is more important as the primary modulator of southern alps ice advances the rcrc approach also demonstrates some subtle advantages of integrating multi proxy data within a palaeocirculation context for new zealand notably because this reconstruction technique enables direct comparisons to coarsely resolved palaeoclimate model outputs that do not have downscaled information

last glacial pollen climate reconstructions from northland new zealand despite wide ranging interest in the vegetation and climate of northland new zealand during the last glacial cycle the region and timeframe lack quantitative climate reconstructions while land based pollen records have tended to be poorly dated and fragmentary the region is also important for geochronology due to the co occurrence of the rotoehu tephra a widely dispersed isochron near the current limits of radiocarbon dating and extensive subfossil wood remains of agathis australis with strong dendrochronological and dendroclimatological potential we present new pollen records and temperature reconstructions from three sites set in coastal dune belts from western mid northland 35 s all containing rotoehu tephra that collectively span the last 70 ka the phases and amplitude of temperature changes broadly align with those reported from elsewhere in new zealand and with marine isotope climate stratigraphic records including maximum temperature depression of 6 8 c during the last glacial maximum we argue that these climatic patterns are intimately linked to shifts in the southern westerly wind belt the northern margins of which extend to the region today correspondence between the northland temperature shifts and atmospheric co2 supports the model of ocean atmosphere co2 flux modulated by latitudinal migration of the southern westerlies copyright 2017 john wiley sons ltd

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

the distribution of pge and the role of arsenic as a collector of pge in the spotted quoll nickel ore deposit in the forrestania greenstone belt western australia the spotted quoll pge bearing ni deposit in the forrestania greenstone belt in the archean yilgarn block in western australia is a komatiite associated massive sulfide orebody tectonically displaced from its original host the brecciated ore contains clasts of quartz and garnet schist and is located along a shear zone overlain by banded iron formation bif and underlain by bif and quartz biotite metasediments the deformation of the ore has destroyed its magmatic textures and it has been sheared and recrystallized at amphibolite facies then the deformed ore has been subjected to a hydrothermal event that concentrated the pge with au and as often at the edge of the ni ore the pge are distributed between pgm and in solid solution in ni sulfarsenides and pd also occurs in pentlandite the pgm include sudburyite pdsb sperrylite ptas2 and irarsite irass all six pge and minor au are hosted in gersdorffite niass two generations of gersdorffite have been recognized a higher temperature magmatic euhedral co rich gersdorffite encloses ir pt and rh bearing pgm surrounded by halos of rh ir and os rich gersdorffite a lower temperature ni rich gersdorffite forms anhedral grains and rims on grains of nickeline nias in this low temperature gersdorffite pge are concentrated toward the mineral edges sudburyite and gold occur associated predominantly with nickeline the pge and gold are now predominantly associated with sulfarsenides that are the controlling factor for their distribution

stratigraphy pollen and 14 c dating of johnston s gum hole a late quaternary fossil kauri agathis australis site northland new zealand johnston s gum hole provides a discontinuous pollen record commencing late in marine isotope stage 5 mis 5 in combination with other published records from the region the aupouri peninsula is reconstructed to have been continuously forested through much of the last glacial cycle with the oscillation of agathis and nothofagus dominated forest corresponding to stadials and interstadials respectively a northward latitudinal expansion of beech forest to 358 s is demonstrated kauri demise at the close of mis 5 appears to have been due to flooding of the site the elimination of kauri in mis 3 was also associated with rewetting of the substrate but could have been a more catastrophic event the presence of both mis 5 and mis 3 kauri wood at the site suggests that other aupouri peat swamps may also preserve timber of these ages and demonstrate the potential of this area for providing mis 3 and mis 5 tree ring records copyright 2008 john wiley sons ltd

a discontinuous ca 80 ka record of late quaternary environmental change from lake omapere northland new zealand we present an integrated record of environmental change from lake omapere northland new zealand based on palaeolimnological analysis of a 7 m long core and eight adjunct cores spanning part of the last 80 calendar cal ka the chronology was developed using tephrochronology palaeomagnetism and radiocarbon dating together with climato and palyno stratigraphy two of 14 tephra layers in the cores provide markers for correlating the record with other new zealand climato stratigraphic sequences deep sea cores and the global marine isotope record pollen diatom palaeomagnetic sedimentologic and pigment analyses show that lake omapere currently 2 m deep has had a discontinuous history occupying a shallow basin perched partly within old basalt lavas the initial alkaline lake formed towards the end of mis 5a at ca 80 cal ka presumably because of blockage of local drainage of a swampy alluvial floodplain inundating peat deposits and forest trees including kauri agathis australis the lake filled rapidly to a level 1 2 m above that at present such filling was probably unrelated to climate but a subsequent phase of variable but generally falling lake levels and increasing dystrophy may have been climatically controlled commencing during mis 4 and culminating in periods early in mis 3 when the lake became swampy or dry conditions of non deposition or non preservation obtained for most of the period after ca 55 cal ka rotoehu ash until formation of the modern lake approximately 600 700 cal years ago or soon after as indicated by the presence of tephra 1 identified in part as kaharoa tephra ad 1314 near the top of the core the modern lake originated possibly through damming of the western outlet as a consequence of accelerated erosion accompanying earliest polynesian deforestation an interpretation supported by maori oral tradition the pollen record indicates that beech nothofagus presumably n truncata was much more common in northland during the last glacial and that for this region the relative abundance of nothofagus vs agathis pollen serves as a better indicator of cooler versus warmer intervals during the quaternary than the ratio of tree to non tree pollen however it seems likely that moisture balance was a more critical factor than temperature in vegetation composition and distribution particularly during the lgm and the long periods of hiatus may also be linked to a drier climate than present correlation coefficients between the pollen curves confirm that several tree species halocarpus bidwillii h biformis and phyllocladus alpinus previously palynologically concealed within generic taxonomic groups occurred about two degrees latitude further north and at a much lower altitude than their current limits during cooler or drier phases of the last glacial a temperature depression in northland of 4 c at various times during the last glacial is inferred from these range expansions nevertheless the persistence of widespread forest cover suggests that the late pleistocene climate of northland was less severe than for most of the rest of new zealand and strengthens the argument for a heightened temperature gradient across northern new zealand during the last glacial

volcanic hazards in auckland new zealand a preliminary assessment of the threat posed by central north island silicic volcanism based on the quaternary tephrostratigraphical record

a 28 000 7600 cal yr bp pollen record of vegetation and climate change from pukaki crater northern new zealand a pollen record of vegetation and climate change representing the interval ca 28 000 7600 cal yr bp was obtained from a 52 5 m sediment core taken from a volcanic explosion crater at present sea level in auckland new zealand 36 59 s this provides one of the few continuous terrestrial records covering marine isotope stage 2 and part of stage 1 from the mid latitudes of the southern hemisphere chronology of the record is underpinned by eight distal taupo volcanic zone rhyolitic tephra of known age augmented by thirteen ams radiocarbon dates the last glacial maximum cooling extended from at least c 28 000 cal yr bp to ca 18 000 cal yr bp when vegetation apparently consisted of patches of beech dominated forest embedded within shrubland and grassland forest patches were probably larger or more widespread than those in central north island to the south but less extensive than further to the north in northland climate warming commenced ca 18 000 cal yr bp marked by the replacement of beech by conifers and angiosperms and by the expansion of forest at the expense of shrubland and grassland no clear late glacial climatic reversal is evident at this site early holocene forest is characterised by the replacement of the dominant forest tree prumnopitys taxifolia by dacrydium cupressinum following breach of the crater rim ca 7600 cal yr bp by rising sea level the maar was rapidly infilled with marine sediments over a period of ca 1000 years

vegetation and climate of auckland new zealand since ca 32 000 cal yr ago support for an extended lgm auckland occupies a climatically sensitive position close to a major biogeographic boundary in the southern mid latitudes a new pollen record from kohuora maar crater auckland displays vegetation and climatic changes for the past ca 32 000 years of particular interest are the inferred climatic patterns for the first part of the interval encompassing the last glacial maximum lgm the kohuora record corresponds closely with pollen records from other auckland sites indicating that the patterns observed are at least regional in extent it is also broadly consistent with a variety of palaeoenvironmental evidence from across new zealand including the glacial record from westland other palynological records from north island other palaeoecological records from the south island and aeolian quartz sequences from western north island these records show that glacial conditions prevailed across most if not all of new zealand during the interval ca 29 19 k cal yr bp longer and earlier than the lgm sensu stricto we suggest that the term extended lgm elgm may be more appropriate for the new zealand region within this predominantly cold interval the auckland pollen records indicate a climatic amelioration for the interval ca 26 24 k cal yr bp also consistent with other palaeocological data from canterbury that fall within a period of climate amelioration recognised between the first two elgm glacial advances in westland we refer to this warming interval as the elgm interstadial the ca 27 k cal yr bp kawakawa oruanui tephra is instrumental in most of these inter site comparisons and occurs after the first peak of elgm cooling in a short lived comparatively mild phase a subsequent return to apparently colder climate in the auckland records may indicate a volcanic cooling effect or more likely widespread landscape disturbance following this major eruption event strong correspondence between biotic responses glacial fluctuations and aeolian quartz deposition linked to major shifts in strength and latitudinal extent of the southern westerlies suggest that both the elgm and elgm interstadial may be more widely registered at least across the southern ocean support for this assertion comes from parallel investigations in western and southernmost south america and isotopic and palaeoecological records from southern ocean marine cores recent reconstructions of the globally averaged ice equivalent sea level history are in line with this evidence from the southern hemisphere suggesting that the elgm may have a global registration in light of these observations we suggest a re examination of the defined timing of the lgm along with renewed effort to establish climatic patterns during this period and understand their causes copyright 2007 john wiley sons ltd

an integrated terrestrial paleoenvironmental record from the mid pleistocene transition eastern north island new zealand abstract a tephra bearing lake sequence from near ormond new zealand provided the opportunity to conduct a multi proxy paleoenvironmental analysis within the mid pleistocene time period a 10 5 m thick section was measured and analysed for pollen spores diatoms macrofossils and tephra geochemistry palynological assemblages in the lower 4 m of the section indicate an ameliorating temperate climate and increased humidity the upper 6 5 m is dominated by diatomite that did not yield sufficient palynomorphs for study the source vegetation was distal lowland mixed broadleaf podocarp forest swamp forest from ca 2 5 4 0 m and proximal scrubland with sporadic forest encroachment abundant freshwater algae in the samples suggest that any brackish influence in the lower part of the section was minor marine dinoflagellates found in the basal pollen samples could be mostly recycled diatomite samples were overwhelmingly dominated by a freshwater but mildly salt tolerant diatom we interpret the section as representing a shallow coastal lowland lake that intermittently had access to the sea the chronology of the section is based on a single glass itpft age of 0 62 0 09 ma from a tephra interbed t8 in the lower part of the section in addition the lowermost tephra in the sequence t1 is geochemically correlated to at 485 preserved in the marine record east of new zealand with an astronomically tuned age of 0 7163 ma this chronology places the basal portion of the ormond section within the brunhes normal chron with sequence deposition occurring during either the ois 18 17 or 16 15 transitions however paleomagnetic data indicate a clear reverse polarity from an equivalent stratigraphic position and at this stage it is difficult to reconcile this age discrepancy

thermal evolution of the kisseynew sedimentary gneiss belt manitoba metamorphism at an early proterozoic accretionary margin

interpreting charcoal in new zealand s palaeoenvironment what do those charcoal fragments really tell us the role of charcoal as a palaeoenvironmental indicator has never been fully or adequately explained charcoal fragments are often interpreted as evidence for natural fires caused by lightning strike during drought or dry climatic conditions generally no evidence is presented to show this to be the case the frequency of lightning strike in new zealand is not high and the extent to which it is a causal factor in generating forest fire is questioned the assumption is often made that charcoal fragments found in sedimentary deposits are local or at least reasonably local in origin this assumption is being challenged fine charcoal fragments appear to be transported regionally within new zealand it is highly likely that fine charcoal fragments are being transported from australia both by thermal convection during fires and during dust storm events to be deposited into new zealand sediments the consequences of this in interpreting new zealand s palaeo history requires researchers to at the very least provide charcoal counts within size parameters this is particularly so for archaeologists who would definitely need to show the presence of large charcoal fragments before interpreting the possibility of people in the landscape

the occurrence of platinum group element and gold minerals in the bon accord ni oxide body south africa two samples from the enigmatic ni oxide body of bon accord barberton greenstone belt south africa have been investigated with the hydroseparation technique to obtain heavy mineral concentrates the concentrates contain abundant pt pd and gold minerals never reported before from the bon accord ni oxide body the grains occur as 1 minute inclusions 3 m in trevorite ideally nife3 o4 and 2 larger 5 70 m free aggregates liberated from the host phase the first group comprises several pgm compounds of pd sb pd sb as pd cu sb pt sb pt as s ru as s ru s along with free grains of ni fe as the second consists of sperrylite ptas2 members of the sobolevskite kotulskite series and electrum these results are in good agreement with previous analyses of pge au in bulk rock paragenetic relationships indicate that the pgm and electrum are of secondary origin probably generated during low temperature metamorphism of the ni rich mineralization they have a terrestrial origin and are related with a low sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic ultramafic bodies the ligands in the newly formed pgm as sb bi te and o probably proceed from the same source of the hydrothermal solutions in this model the metals ni pge au were original components of the primary mineral assemblage of the bon accord precursor whereas as sb bi te and o might have been contributed by the metasomatizing fluids during near surface evolution of the ore body the data on the high grade heavy mineral concentrates obtained by hydroseparation have provided new knowledge about the mineral deportment of pd pt and au

paleovegetation of marine isotope stages 4 and 3 in northern new zealand and the age of the widespread rotoehu tephra abstract paleolake sediment constrained by tephrochronology from onepoto basin volcanic crater in auckland northern new zealand 36 48 s provides one of the few uninterrupted records of paleovegetation for marine oxygen isotope stages mis 4 and 3 76 000 26 000 yr b p in the region this period was characterized by cool temperate conifer hardwood forest that lacked some of the warmer taxa typical of the holocene the period 64 400 60 500 yr b p was marked by opening of forest canopy and expansion of small trees and shrubs and correlates to the thermal minima of mis 4 however the landscape was never as open as the forest shrubland mosaic of the mis 2 the beginning of mis 3 60 500 50 500 yr b p was marked by the dramatic expansion and then decline of conifer hardwood forest dominated by dacrydium cupressinum a species that prefers wetter conditions this forest was succeeded by the typically montane nothofagus at 50 500 yr b p corresponding to a thermal decline thus mis 3 began with an abrupt change to moist cool conditions that lasted about 5000 yr followed by gradual cooling and dryer conditions this supports some interpretations from other parts of the southwest pacific region that mis 3 was a period of increased precipitation the widespread and stratigraphically important rotoehu tephra erupted from okataina volcanic centre has been variously dated at 45 000 65 000 yr b p at onepoto sedimentation rate and paleovegetation reconstruction imply an age of c 44 300 yr b p the tephra provides a correlation horizon in the marine and terrestrial realms during a period mis 3 difficult to date by radiometric methods

a widespread ca 1 1 ma tvz silicic tephra preserved near wellington new zealand implications for regional reconstruction of mid pleistocene vegetation abstract a sequence of terrestrial pollen bearing sediments exposed in transmission gully tg near wellington new zealand contains a prominent ca 20 cm thick silicic tephra bed dated at 1 09 0 12 ma based on itpft dating of glass shards such occurrences are rare in the wellington region the associated palynology overlying tg tephra represents vegetation totally different from any modern assemblage with both warm climate taxa e g lygodium articulatum toronia toru and cool climate taxa e g acaena apiaceae epilobium gentiana lycopodium australianum taraxacum and wahlenbergia occurring together a pollen assemblage 0 4 m above the base of tg tephra comes from a southern beech forest existing under warm temperate conditions with both fuscospora and nothofagus menziesii beeches and an abundance of ferns and lycopods represented beeches rapidly disappeared from around the site of deposition until at 0 6 m above the base of tg tephra beech pollen were rare and the pollen assemblages were dominated by grass ferns and lycopods were still well represented but the dramatic increase in grass pollen suggests that the environment outside the immediate depositional site had become much drier a ca 0 64 m thick gravel layer was then deposited which impeded drainage associated pollen assemblages were then dominated by sedges and grasses in approximately equal percentages although conditions may have still been relatively dry overall the pollen assemblages are indicative of a sedge swamp surrounded by grassland with distant beech forest since the glass itpft age range 1 sd for tg tephra extends over oxygen isotope stages ois 37 to 26 the fossiliferous sequence overlying the tephra should be any of the five periods of relative warmth in spite of the lack of tree pollen and dominance in the profile of herbaceous taxa however geochemical comparison of tg tephra with those preserved in odp site 1124 and two equivalent age sequences in auckland region patiki core site okariha suggest a correlation with ois 35 on this basis the presence of beaupreaidites diversiformis 0 4 m above the base of tg tephra provides a date for the final extinction of the modern new caledonian genus beauprea in new zealand pollen from toronia toru occurs throughout the sequence far further south than in any other pleistocene sequence so far analysed

pressure temperature conditions of early proterozoic metamorphism during the trans hudson orogen as determined from rocks straddling the flin flon kisseynew boundary at niblock and file lakes manitoba the niblock lake and file lake areas straddle the boundary between the kisseynew gneiss belt and the flin flon belt near the town of snow lake manitoba the region contains pelitic schists metamo

pressure and temperature conditions of metamorphism in the vicinity of three massive sulfide deposits flin flon snow lake belt manitoba estimates of pressure and temperature conditions of metamorphism in the vicinity of three massive sulfide deposits of the flin flon snow lake manitoba greenstone belt have been obtained using mineral assemblages in mafic and felsic metavolcanic rocks the flin flon area around the centennial deposit in the western part of the belt has been metamorphosed to low greenschist facies near the spruce point deposit in the central part of the belt the metamorphic conditions are estimated to be of the upper greenschist facies with a temperature of 475 75 c at 2 6 1 2 kbar pressure 1 kbar 0 1 kpa the snow lake area to the west in the vicinity of the anderson lake deposit has been metamorphosed to sillimanite grade in the staurolite biotite sillimanite zone the temperature and pressure conditions were 580 25 c and 5 25 0 75 kbar in the biotite sillimanite almandine zone the temperature was 620 25 c at a maximum pressure of 6 2 kbar based on the temperature and pressure estimates fr