holocene glacial activity and climatic variations in the swiss alps reconstructing a continuous record from proglacial lake sediments cores recovered from proglacial lake silvaplana swiss alps were investigated to examine the influence of holocene glaciers on lacustrine sedimentation during times of glacial activity in the catchment the sedimentation in the lake is dominated by the input of silt and clay sized material delivered by glacial meltwaters the deposition of fine grained material and the formation of varves reflect the existence of glaciers in the catchment and can therefore be used for the reconstruction of glacial history sedimentation rates are up to nine times higher in the varved than in the non varved sediments indicating significantly higher erosion rates under glaciated catchment conditions glacial varves were deposited in lake silvaplana during glacial retreat in the latest pleistocene and early holocene until 9400bp non varved deposits having a higher organic content and coarser grain sizes accumulated at lower rates when glacial activity was absent or negligible within the catchment between 9400 and 3300 bp

geochemical and fluid dynamic modeling of compositional variations in archean komatiite hosted nickel sulfide ores in western australia stratigraphic volcanological petrological and fluid dynamic studies suggest that archean komatiite associated nickel sulfide deposits in western australia formed by thermal erosion of unconsolidated sulfidic sediments beneath channelized lava flows geochemical and nd isotope data for the type area at kambalda suggest that mineralized lava channels are less contaminated than barren flanking segments of the flow owing to high discharge rates and continuous replenishment within the channel this interpretation has several implications for the mode of emplacement of sulfides their degree of equilibration with the host komatiite and the compositions of sulfide ores 1 the solubility of sulfur in komatiite is relatively low so most of the sulfide in eroded sediments will be melted and remain as a dense layer at the base of the flow or be incorporated into the turbulently flowing komatiite as immiscible sulfide droplets 2 sulfide ores will not necessarily be in equilibrium with overlying komatiites but will record equilibration with variably contaminated lavas during initial stages of emplacement and crystallization and 3 ore compositions will vary from channel to channel shoot to shoot depending on i the composition of the hybridized komatiite ii the fluid dynamics of the system and the effective magma sulfide ratio r factor and iii the sulfide silicate partition coefficients under the prevailing conditions of temperature and f sub o 2 f sub s 2 the size of immiscible droplets and the interface between two immiscible layers are affected by inertial forces during turbulent flow turbulence causes coalescence of small droplets and breakup of large droplets leading to an equilibrium droplet size if the average size of the droplets is small and or the flowage rate is high they may be carried in suspension in the flowing komatiite droplets have a large surface area to volume ratio and will be effective in scavenging chalcophile elements since they are carried by the turbulent motion of the flowing komatiite if the average size of the droplets is large or if the flowage rate is low they will settle and collect at the base of the komatiite komatiite and sulfide liquids may continue to flow but the sulfide layer will have a low surface area to volume ratio and will be ineffective in extracting chalcophile elements from the overlying komatiite layer thus the initial stages of emplacement when sulfides are initially melted and are most likely to be in suspension if at all control the effective r factor and therefore the tenor of the sulfide ores numerical modeling of the observed variations in ore compositions constrained by known komatiite compositions and experimentally or empirically determined distribution constants indicates that the observed range of ore compositions in western australian komatiite associated nickel sulfide deposits can be accounted for primarily by variations in the effective sulfide silicate ratio 500 r 100 although required variations in the partition coefficient for ni 200 d ni 100 suggest that f sub o 2 f sub s 2 may also have varied systematically assimilation of h 2 o fes rich sediments should increase f sub o 2 f sub s 2 because of the relative abundances of the two components in the magma and unconsolidated sediments if low tenor ores represent equilibration at lower r and higher f sub o 2 f sub s 2 and high tenor ores represent equilibration at higher r and lower f sub o 2 f sub s 2 as suggested by the modeling then d ni appears to decrease with increasing f sub o 2 f sub s 2 as suggested by doyle and naldrett 1987 the range of calculated r values is relatively low suggesting that low tenor sulfides were not entrained into the komatiite lava but remained as a segregated layer at the base of the flow and that high tenor sulfides were not transported long distances in suspension but settled rapidly to the base of the flow magma compositions vary only slightly from an inferred parental komatiite low tenor ores appear to have equilibrated with only slightly more evolved contaminated and fractionated lavas

geochemistry of the dundonald komatiite basalt suite and genesis of dundeal ni deposit abitibi subprovince canada the genesis of konatiites basalts and associated ninineralization in the dundonald township area on tario is critical to understanding the metallogenic evolution of the kidd munro assemblage one of the most primitive volcanic assemblages in the world the 2 5 kin thick stratigraphic succession has a basal calc alkalic basalt dacite rhyolite sequence 2716 8 2 1 ma u pb zircon cut by the dundonald peridotite gabbro sill 27077 ma u pb zircon overlain by komatiitic and basaltic flows containing magmatic ni sulfide mineral ization which are in turn overlain by chemically distinctive low ti basalt flows the dundonald komatiites correlate with komatiites in the footwall of the giant kidd creek volcanic associated massive sulfide deposit 40 km to the west but are slightly older than the komatiites of munro township which are 40 km to the east the dundonald komatiites comprise a munro type al undepleted komatiite suite with liquid compositions having a120 ffio o 18 to 22 and mgo up to 30 3 vet percent anhydrous n 24 most samples in the ko matiite suite have slightly depleted light bee contents with lan smn 0 6 to 1 1 and lan ybn 0 4 to 0 9 n 21 and negligible ti ti and zr zr anomalies their major and trace element geochemistry is consistent with a derivation by sigfificant partial melting of a chemically primitive mantle with little or no influence of majoritc garnet flows that are host to the dundeal and alexo ni deposits have distinctively high thpm nbpm ratios 1 7 n 3 suggesting crustal contamination and peperite textures that are consistent with contami nation from nearby graphitic argillite the chemically distinctive lmv ti basalts have 49 to 53 percent sios 4 5 to 9 5 percent mgo 18 8 to 21 5 percent a1203 0 30 to 0 37 percent tios moderately depleted light ree con tents with lan smn 0 9 to 1 2 and la n ybn 0 4 to 0 6 high ni cr and ba contents 570 6 800 390 630 90 320 ppm respectively n 6 their high ai203 contents place them in the calc alkalic field on a jensen cation plot although their trace element ratios zr y la yb are more consistent with a tholeiitic affinity they are compositionally identical to and they correlate with low ti basalts in the kidd creek volcanic complex their geochemistry is consistent with a derivation by partial melting of a refractory harzburgitic mantle that has undergone a previous melt extraction possibly influenced by a large ion lithophile enriched hydrous phase the empire flow is the thickest and most primitive komatiite flow and is host to the dundeal ni deposit re source of 0 4 mt at 2 0 ni the empire flow contains an elongate dunite peridotite basal unit interpreted as the core of a flow that thermally eroded into footwall heterolithic breccias and pillowed andesites the main dundeal ni horizon overlies part of the basal dunite peridotite unit within the flow channel and extends over the cutbank wall the dundeal deposit and the nearby dundonald south ni deposit have lo v total sulfide con tents and high ni s ratios 0 9 and 1 0 respectively in comparison to most komatiite hosted magmatic sulfide deposits the high ni tenor in sulfide is believed to be due to assimilation of reducing carbonaceous sediment which causes greater ni partitioning into the magmatic sulfide phase

late pleistocene holocene surface processes and landscape evolution in the central swiss alps abstract the european alps are a geomorphologically active region and experience a number of gravity driven hillslope processes soil and landscape formation in the alps has consequently undergone several minor and major traceable changes of developmental trajectories during the holocene soil development is hypothesised to be often non linear with time and characterised by stages of progressive and regressive evolution caused by upbuilding formation profile deepening and erosion profile shallowing several cold and warm climate phases are identified during the holocene but it is largely unknown which effects these might have had on slope processes by using datable moraines 10 be and mires 14 c we have constructed a temporal framework for these processes using the geochemical imprint of mires in the alpine setting of the goschener valley of the central swiss alps we reconstructed general mostly erosional landscape processes for the last ca 10 ka as this is the type locality for the goschener cold phase we assumed that this phase goschener cold phase i and ii 1 5 and 2 5 ka bp should have left easily recognizable traits after deglaciation 11 12 ka bp soil evolution was progressive beginning around 8 ka bp we detect a distinct increase in erosion here together with a vegetation change towards tundra vegetation and the highest measured rates of carbon sequestration other phases of high geomorphic activity were recognised ca 5 6 ka bp 4 ka bp and to a lesser extent 1 3 ka ago the cold phase at 5 6 ka bp corresponds to a less distinct change in vegetation and lessened erosion human impact is increasingly obvious since about 2 4 ka bp which overlaps with the goschener cold phase nonetheless erosion processes were not extraordinarily high during this period and a climate effect cannot be distinguished we detect evidence of increasing human disturbance regressive soil evolution for about the last 1 ka we also detect an increase in dust flux during the last ca 4 5 ka presumably due to the landscape change s in the sahara during this time

paleosea floor volcanic associated massive sulfide mineralization related to a cooling komatiite flow abitibi subprovince canada paleosea floor volcanic associated massive sulfide mineralization has been discovered 50 to 150 m upsection from a late archean peridotitic komatiite flow where the flow is thickest in a thermal erosion channel the terminus massive sulfide occurrence is within carbonaceous argillites that are intercalated with basaltic komatiite flows and flow breccias it contains appreciable zn and cu contents and is associated with silicification and chlorite epidote alteration ultramafic magmas are ideal heat sources for hydrothermal convective systems because of their extremely high liquidus temperatures and their tendency to become less permeable during serpentinization which impedes advective cooling heuristic calculations indicate that there is sufficient enthalpy in the peridotitic komatiite flow to drive the hydrothermal system responsible for the terminus mineralization this hypothesis is tested using two dimensional finite element heat and fluid flow simulations the results suggest that under the right circumstances 1 relatively thick komatiite flows may take hundreds of years to cool 2 komatiite flow driven hydrothermal systems can form sea floor or subsea floor deposits comparable in mass to those along the mid atlantic ridge 3 much of the metal leaching by hydrothermal fluids occurs below and adjacent to the flow and 4 the shape of heat source komatiite flows or subsea floor magma chambers affects the locus and distribution of hydrothermal upwelling similar base metal precipitating paleohydrothermal systems are present above ponded komatiite flows broadly along strike at the potter zn cu deposit in munro township ontario these paleohydrothermal systems and the calculations presented here suggest that thick ponded basaltic flows on the modern sea floor have sufficient enthalpy to form significant hydrothermal sulfide accumulations

palaeodistribution modelling of european vegetation types at the last glacial maximum using modern analogues from siberia prospects and limitations we modelled the european distribution of vegetation types at the last glacial maximum lgm using present day data from siberia a region hypothesized to be a modern analogue of european glacial climate distribution models were calibrated with current climate using 6274 vegetation plot records surveyed in siberia out of 22 initially used vegetation types good or moderately good models in terms of statistical validation and expert based evaluation were computed for 18 types which were then projected to european climate at the lgm the resulting distributions were generally consistent with reconstructions based on pollen records and dynamic vegetation models spatial predictions were most reliable for steppe forest steppe taiga tundra fens and bogs in eastern and central europe which had lgm climate more similar to present day siberia the models for western and southern europe regions with a lower degree of climatic analogy were only reliable for mires and steppe vegetation respectively modelling lgm vegetation types for the wetter and warmer regions of europe would therefore require gathering calibration data from outside siberia our approach adds value to the reconstruction of vegetation at the lgm which is limited by scarcity of pollen and macrofossil data suggesting where specific habitats could have occurred despite the uncertainties of climatic extrapolations and the difficulty of validating the projections for vegetation types the integration of palaeodistribution modelling with other approaches has a great potential for improving our understanding of biodiversity patterns during the lgm

sedimentary evidence of landscape and climate history since the end of mis 3 in the krkonose mountains czech republic abstract a sedimentary core recovered from the cirque basin of labsk d l valley 1039 m a s l in the krkonose mountains reflects the environmental history for approximately the last 30 000 years analyses of magnetic susceptibility carbon content pollen assemblages and macrofossil data in a 15 m thick sediment sequence provide the first continuous record of lateglacial and holocene vegetation history in sudetes region of the czech republic the succession of sedimentary units in the lower part of the core suggests that the cirque was ice free before the onset of the last glaciation at the beginning of marine isotope stage 2 highly variable climate prevailed during this period with cold conditions culminating about 18 cal ka bp cold climates persisted until the lateglacial period evidenced by an identified warming and subsequent cooling event correlated with the younger dryas period sparse treeless vegetation dominated in the catchment area at that time the sequence of interrupted thinly laminated silts reflects the retreat and temporary readvance of a local glacier in the cirque during 12 5 10 8 cal ka bp subsequently the alpine treeline ecotone gradually shifted above the cirque floor palaeoclimatic conditions in the early holocene fluctuated strongly whereas since 5 1 cal ka bp conditions have been more stable pollen based climate reconstructions suggest significant cooling at around 9 8 9 3 7 7 7 5 and 4 0 3 3 cal ka bp spruce forests have dominated the site since 5 0 cal ka bp when the vegetation became similar to the modern one two phases of increased sedimentation were identified within the holocene culminating about 9 2 7 5 cal ka bp and 5 8 5 5 cal ka bp sediment yield was as high as 2 4 mm yr 1 during the period reflecting environmental changes during the atlantic sub boreal transition

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

an analysis of eemian climate in western and central europe on the basis of 31 pollen diagrams and additional data for botanical macrofossils an analysis is made of the last interglacial eemian climatic history in western and central europe the main tool for this analysis is the climatic indicator species method only selected woody species are used for the quantification of data partial climatic range diagrams are presented for abies alba acer monspessulanum acer tataricum buxus sempervirens tilia tomentosa the problem of time correlation and pollen zonation of the eemian is discussed the climatic analysis itself is based on an improved version of the indicator species method in this version not every site is analysed for its climatic values instead maps and tables on the migrational history of hedera ilex buxus abies and species of acer tilia and abies are the basis for climatic maps showing respectively january and july isotherms for the periods of the corylus zone e4a and the carpinus zone e5 it is concluded that mean january temperatures were as much as 3 c higher at amsterdam the netherlands than at present and mean temperatures in july were 2 c higher however the thermal maximum in winter was later zone e5 than the summer thermal maximum zone e4a winter temperatures changed parallel to rise and fall of global sea level precipitation changes are more difficult to estimate in the first part of the eemian precipitation must have been relatively low but from zone e4b onward it increased to higher values reaching 800 mm and probably substantially more in zones e5 and e6 hence the eemian climate was in its beginning relatively more contintental and later from e4b onward more oceanic however as compared with the holocene the eemian climate was generally speaking more oceanic

cirque overdeepening and their relationship to morphometry abstract shape and size characteristics of cirques and their changes and mutual relationships include not only spatial and descriptive aspects but also genetic attributes the goals of this article were to define an application of k curve sensu haynes 1968 that describes the extent of cirque overdeepening and to identify k curve equation input variables the k values depend on the profile location and hence a clear definition of the cirque profile position is necessary therefore ideal profiles were delineated through the steepest part of the cirque headwall k steepest k s or through a point on the cirque crest that had a maximal elevation k highest k h knowledge of the cirque headwall height allows for the mathematical theoretical calculation of cirque overdeepening i e the maximum depth of the cirque floor sedimentary filling of the cirque floor further the goal of this study was to analyse and compare cirque classification methods according to the extent of overdeepening and standard morphometric characteristics as a training data set 27 example cirques of the bohemian massif giant mts sumava mts and hrub jesenik mts and a total of 12 morphometric characteristics were used in the analyses cirques were classified into two groups using cluster analysis based on the extent of overdeepening k values k h and k s a mutual relationship between cluster analysis classifications and classifications based on morphometric characteristics l w h and 3d 2d was determined using general discriminant analysis the classification of cirques based on other characteristics corresponded closely in total 81 for the first group and the cross validation group with cirque classifications based on the degree of overdeepening k value

the tepla saxothuringian suture in the karkonosze izera massif western sudetes central european variscides the southern and eastern karkonosze izera massif northern bohemian massif exposes blueschist facies rocks and morb type magmatic complexes during late devonian to early carboniferous times these were overthrust within a nappe pile toward the nw onto the pre variscan saxothuringian basement composed of the izera kowary metagranitoids and their envelope the lowermost nappe or parautochthonous unit of the pile is the low grade metamorphosed jest d complex comprising a devonian to early carboniferous sedimentary succession of the saxothuringian passive margin this is tectonically overlain by the south karkonosze complex which represents ordovician silurian volcano sedimentary infill of the saxothuringian basin affected by late devonian hp metamorphism the uppermost nappe is the early palaeozoic epidote amphibolite grade leszczyniec morb like complex cropping out on the eastern margin of the karkonosze izera massif it probably represents a fragment of obducted saxothuringian basin floor the nappe pile was stacked beneath the overriding upper plate margin now concealed below the intra sudetic basin and hypothesized to represent a fragment of the tepla barrandian terrane the nappe stacking triggered by buoyancy controlled upward extrusion of the subducted continental slab was the main mechanism for the exhumation of hp rocks the final stages of the nw ward nappe stacking were accompanied and followed by se directed early carboniferous extensional collapse the lower plate of the suture zone was uplifted at that time and intruded by the 330 ma old nearly undeformed karkonosze granite pluton as a result of the collapse the tepla barrandian upper plate was downthrown on shear zones and brittle faults and buried under several km thick synorogenic late tournaisian through namurian and post orogenic late carboniferous early permian succession of the intra sudetic basin the south and east karkonosze suture most probably is a fragment of the tepla saxothuringian munchberg tepla suture belt known from the western bohemian massif

multicentury glacier fluctuations in the swiss alps during the holocene subfossil remains of wood and peat from six swiss glaciers found in proglacial fluvial sediments indicate that glaciers were smaller than the 1985 reference level and climatic conditions allowed vegetation growth in now glaciated basins an extended data set of swiss glacier recessions consisting of 143 radiocarbon dates is presented to improve the chronology of glacier fluctuations a comparison with other archives and dated glacier advances suggests 12 major recession periods occurring at 9850 9600 93008650 85508050 77007550 74506550 61505950 57005500 52004400 43003400 28002700 21501850 14001200 cal yr bp it is proposed that major glacier fluctuations occurred on a multicentennial scale with a changing pattern during the course of the holocene after the younger dryas glaciers receded to a smaller extent and prolonged recessions occurred repeatedly culminating around 7 cal kyr bp after a transition around 6 cal kyr bp weak fluctuations around the present level dominated after 3 6 cal kyr bp less frequent recessions interrupted the trend to advanced glaciers peaking with the prominent little ice age this trend is in line with a continuous decrease of summer insolation during the holocene

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

10be exposure age chronology of the last glaciation in the krkonose mountains central europe abstract a new chronology of the last glaciation is established for the krkonose giant mountains central europe based on in situ produced 10be in moraine boulders exposure ages and schmidt hammer rebound values obtained for terminal moraines on the northern and southern flank of the mountains suggest that the oldest preserved moraines represent early phases of the last glacial maximum lgm large moraines at the outlet of the snowy cirques niezne kotly and in the middle part of the upa ob i d l trough were deposited around 21 ka while a series of smaller moraines above the lgm deposits represent readvances that occurred no later than 18 1 0 6 ka 15 7 0 5 ka 13 5 0 5 ka and 12 9 0 7 ka an exposure age of 13 8 0 4 ka obtained for protalus ramparts at the foot of the upska jama cirque headwall indicates that glaciers advanced only in north to east facing cirques during the lateglacial the last glacier fluctuation was synchronous with the younger dryas cold event the timing of local glacier advances during the last glacial episode correlates with the late weichselian glacier phases in the alps and in the bavarian bohemian forest

classification of poorly sorted sedimentary rocks abstract the classification and nomenclature of sandstones has evolved over the years into a system which is now generally accepted as standard however no equivalent system exists for the poorly sorted sedimentary rocks which include grain sizes from clay to gravel a descriptive classification is proposed based on an earlier system but using updated nomenclature and lithological fields such a scheme is needed to clearly define lithological terms currently used in the description of sedimentary sequences

re os isotope systematics of ni cu sulfide ores sudbury igneous complex ontario evidence for a major crustal component sudbury igneous complex sublayer ores from the levack west falconbridge and strathcona mines were analyzed for their re and os concentrations and os isotopic compositions the re os isotope systematics of three ores from the different mines give isochron ages of1 840 60 ma 1770 60 ma and 1780 110 ma suggesting that the re os system became closed at the time of or soon after the 1850 1 ma crystallization age of the complex the os isotopic compositions of different portions of the complex at the time of crystallization varied considerably with initial187os 186os1850 ranging from 4 64 at levack west to 7 55 at strathcona these heterogeneities require that the os and probably also the other platinum group elements contained in the ores were derived from at least two sources in addition the high initial187os 186os ratios indicate that the os was derived predominantly from ancient crust previous studies have suggested that the complex either crystallized from a mixture of mantle derived basaltic melt and ancient continental crust or was derived exclusively from the fusion of ancient continental crust resulting from a meteorite impact results of modelling suggest that if a contemporaneous mantle derived basaltic melt was involved in the origin of the sic it likely contributed 50 of the os to all three ores the large percentage of ancient crust involved in the production of the ores is most consistent with an interpretation of substantial crustal fusion resulting from meteorite impact

pleistocene terraces of the vltava river in the budějovice basin southern bohemian massif new insights into sedimentary history constrained by luminescence data abstract we studied quaternary sediments from the bud jovice basin in southern bohemia now being able to reconstruct the landscape formation of this area during the late pleistocene the main objective of this study was to map fluvial terraces of the rivers vltava and malse in the basin and to constrain their ages by luminescence dating topographic data from a high resolution dem in combination with lithological profiles of more than 1000 boreholes allowed identifying five terrace levels bb 1 to bb 5 with bases ranging from 7 m below to 26 m above the recent mean water level of the vltava river for the lowermost terrace level bb 1 a consistent stratigraphy with ages ranging between 84 5 9 0 ka and 7 9 0 8 ka was constrained additionally we obtained luminescence ages of alluvial fan and colluvial deposits which allow us to better constrain the late pleistocene sedimentation history of the study area based on the spatial distribution of derived ages the terrace level bb 1 represents a complex sediment body incorporating more distinct packages of river aggradation the presence of stacked fluvial deposits of pleistocene age underneath the recent floodplain points to an ongoing subsidence or relative tectonic stability of the bud jovice basin during the late pleistocene

nickel sulfide deposits in australia characteristics resources and potential abstract australia s nickel sulfide industry has had a fluctuating history since the discovery in 1966 of massive sulfides at kambalda in the eastern goldfields of western australia periods of buoyant nickel prices and high demand speculative exploration and frenetic investment the nickel boom years have been interspersed by protracted periods of relatively depressed metal prices exploration inactivity and low discovery rates despite this unpredictable evolution the industry has had a significant impact on the world nickel scene with australia having a global resource of nickel metal from sulfide ores of 12 9 mt five world class deposits 1 mt contained ni and a production status of number three after russia and canada more than 90 of the nation s known global resources of nickel metal from sulfide sources were discovered during the relative short period of 1966 to 1973 australia s nickel sulfide deposits are associated with ultramafic and or mafic igneous rocks in three major geotectonic settings 1 archean komatiites emplaced in rift zones of granite greenstone belts 2 precambrian tholeiitic mafic ultramafic intrusions emplaced in rift zones of archean cratons and proterozoic orogens and 3 hydrothermal remobilized deposits of various ages and settings the komatiitic association is economically by far the most important accounting for more than 95 of the nation s identified nickel sulfide resources the ages of australian komatiitic and tholeiitic hosted deposits generally correlate with three major global scale nickel metallogenic events at 3000 ma 2700 ma and 1900 ma these events are interpreted to correspond to periods of juvenile crustal growth and the development of large volumes of primitive komatiitic and tholeiitic magmas caused by large scale mantle overturn and mantle plume activities there is considerable potential for the further discovery of komatiite hosted deposits in archean granite greenstone terranes including both large and smaller high grade 5 to 9 ni deposits that may be enriched in pges 2 to 5 g t especially where the host ultramafic sequences are poorly exposed analysis of the major komatiite provinces of the world reveals that fertile komatiitic sequences are generally of late archean 2700 ma or paleoproterozoic 1900 ma age have dominantly al undepleted al 2 o 3 tio 2 15 to 25 chemical affinities and often occur with sulfur bearing country rocks in dynamic high magma flux environments such as compound sheet flows with internal pathways facies kambalda type or dunitic compound sheet flow facies mt keith type most precambrian provinces in australia particularly the proterozoic orogenic belts contain an abundance of sulfur saturated tholeiitic mafic ultramafic intrusions that have not been fully investigated for their potential to host basal ni cu sulfides voisey s bay type mineralization the major exploration challenges for finding these deposits are to determine the pre deformational geometries and younging directions of the intrusions and to locate structural depressions in the basal contacts and feeder conduits under cover stratabound pge ni cu cr deposits hosted by large archean proterozoic layered mafic ultramafic intrusions munni munni panton of tholeiitic affinity have comparable global nickel resources to many komatiite deposits but low grades

fractionation of the platinum group elements and gold in some komatiites of the abitibi greenstone belt northern ontario the noble element patterns from four nickel sulfide deposits in komatiites of the abitibi greenstone belt exhibit various degrees of fractionation pd ir ratios for dundonald texmont hart and alexo are 10 5 12 and 116 respectively the noble element patterns could have been affected by metamorphism including hydrothermal alteration contamination of the magma by a sulfide rich sediment crystal fractionation of monosulfide solid solution solubility of os ir alloys and rus2 and timing of sulfur saturation noble element patterns of samples from the deposits dundonald and alexo of the lowest metamorphic grade prehnite pumpellyite facies are smooth and exhibit no or very small au and pt anomalies however some samples from texmont mid greenschist facies metamorphism contain pt and au anomalies further all samples from the hart deposit which has experienced carbonate alteration have large negative pt and au anomalies contamination of the komatiites with fe sulfide rich sediments found in their vicinity will not change the noble element patterns appreciably a 10 percent contamination of the komatiites will change the pd ir ratio of the sulfides from approximately 5 to 7 5 the massive sulfide at the base of the alexo deposit has a pd ir ratio of 44 the overlying net textured ore has a pd ir ratio of 171 this change in pd ir ratios could be due to the fractionation of monosulfide solid solution from the sulfide liquid the difference in noble element fractionation between the four deposits does not appear to be related to differences in the lithophile element composition of the silicate liquid from which the sulfides separated since all four deposits have a similar lithophile chemistry it is proposed that the differences in the fractionation of the noble element between the deposits is the combined result of the timing of sulfur saturation and the lower solubility of os ir and rus2 in the silicate melt compared to rh pt and pd

the evolution of the southern abitibi greenstone belt in light of precise u pb geochronology this paper summarizes u pb zircon ages for the archean southern abitibi greenstone belt and integrates them together with zircon and baddeleyite data for three new samples into a general framework for the evolution of the region new ages are reported for the ghost range gabbroic complex 2713 super 7 sub 5 ma and for a pyroclastic volcanic rock of the gauthier group 2700 or 3 ma a previously determined age of 2701 super 3 sub 2 ma for the felsic volcanic skead group is confirmed by magmatic zircons from a second sample that also contains a xenocrystic component or 2720 ma indicating that the skead volcano was built on top of an older volcanic sequence the compiled ages show that the southern abitibi greenstone belt developed between 2750 and 2670 ma the earliest ages date remnants of volcanic complexes that occur at the periphery of the belt major preorogenic magmatism was confined mainly to the period 2720 to 2700 ma in general each episode was characterized by the essentially coeval formation of komatiitic tholeiitic and calc alkalic igneous rocks taking into consideration the known geologic geochemical and isotopic data this association is consistent with evolution in paired active are and back are systems older crust was absent from the region but it may have interacted with these arcs and rift systems farther to the west the extensional regime was followed by a period of compression that caused folding and thrusting emplacement of calc alkalic plutons and deposition of turbidites between 2700 and 2688 ma the magmatism became predominantly alkalic during the main timiskaming period between 2681 and 2676 ma this event was accompanied by the deposition of alluvial fluvial sequences and was followed by renewed compression that caused polyphase folding and thrusting probably between approximately 2676 and 2670 ma lamprophyre dikes were associated with these final stages of deformation postorogenic activity includes faulting and episodes of hydrothermal activity locally associated with gold mineralization ages in the range 2630 to 2580 ma for hydrothermal minerals e g titanite and rutile camflo suggest a correlation of these events with lower crustal magmatism and metamorphism as recorded for example in the adjacent kapuskasing zone

the langmuir volcanic peridotite associated nickel deposits canadian equivalents of the western australian occurrences the 2 7 b y old abitibi greenstone belt is a crudely s shaped zone of metamorphosed volcanic subvolcanic and sedimentary rocks and associated intrusions through it are scattered a dozen small nickel deposits in volcanic peridotites their hosts are volcanic and subvolcanic ultramafic rocks typically containing 40 to 45 percent anhydrous mgo with spinifex tops and overlain by thinner peridotitic to pyroxenitic flows at least one deposit dumont is hosted by a dunitic intrusion others e g dundonald langmuir 2 are partially hosted in sulfidic iron formations mining of the langmuir 2 deposit permitted extensive underground mapping core logging and sample collecting the other deposits are known mainly from poor surface exposures and drill core the langmuir 1 and 2 deposits provided sufficient data to evaluate models for their origin and to compare them to nickel sulfide deposits associated with volcanic peridotites in western australia a magmatic origin is supported by the localization of the main ore zone in a paleotrough by the presence of a possible volcanic feeder beneath the ore and by the regular sequence through the basal ultramafic flow of massive ore overlain by net textured ore then by barren peridotite and lastly by a spinilex textured cap to the flow an unusual spinilex textured and sulfide bearing rock and skeletal chromite also support a magmatic origin as do the base and precious metal contents of the ores the high s se ratios averge 23 000 and slightly lower sulfur isotopic ratios average 0 5 per mil delta 34 s compared to most magmatic nickel sulfide deposits are similar to the ratios for windarra western australia and may be explained by assimilation of sulfide rich cherty iron formation other features incompatible with a purely maginatic origin include the presence of sheared and breccia ore and the high sulfur content of some ores these features result from deformation and greenschist facies metamorphism but surviving features of an earlier magmatic history argue against the ores being formed metamorphically evidence of contemporaneous fumarolic activity was found at the south end of the mine but its importance as an ore forming process was not supported by detailed petrological and geochemical studies limited data from the other deposits in the abitibi belt suggest a common origin for the langmuir deposits with minor variations attributable to the volume of ultramafic magma emplaced the volume of contained nickel sulfides the presence of sulfidic iron formations and the severity of alteration and metamorphism the deposits in western australia probably were formed by similar processes in particular the langmuir deposits display strikingly similar sulfide chemistries to the windarra deposits which are probably dae to assimilation of sulfide rich cherty iron formation

pb and nd isotopic study of two archean komatiitic flows from alexo ontario isotopic analysis of two archean komatiitic flows from alexo ontario gives a pb pb isochron age of 2690 15 ma and a sm nd isochron age of 2752 87 ma these ages agree well with u pb zircon ages from underlying and overlying volcanics the variations in element ratios that define the isochrons were not produced during crystallization of the lavas the spread in u pb was caused by submarine alteration soon after eruption and the spread in sm nd resulted from a differences in the composition of the residue of melting and b contamination of the upper komatiite flow through thermal erosion of the lower flow the 147sm 144nd ratio of uncontaminated komatiite is 0 25 which reflects the depleted nature of its mantle source the th u ratio of about 3 4 is probably also representative of depleted mantle the initial nd of 2 44 0 51 indicates that the mantle depletion took place long before magma formation

vegetation responses to the 8200 cal bp cold event and to long term climatic changes in the eastern alps possible influence of solar activity and north atlantic freshwater pulses subfossil pollen from two bogs in temperature sensitive high altitude regions were analysed in order to reconstruct early to mid holocene summer temperature fluctuations in the eastern alps the p

a chironomid based holocene summer air temperature reconstruction from the swiss alps we developed a quantitative chironomid july air temperature inference model based on surface sediments from 81 swiss lakes and applied it to the holocene subfossil chironomid record of hinterburgsee a small subalpine lake in the northern swiss alps present day mean july air temperature of 11 3 c after smoothing to reduce the high between sample variability of inferred temperatures the reconstruction indicates july air temperatures of 10 4 10 9 c at the end of the younger dryas of 11 9 12 8 c during the early and mid holocene 11500 4000 cal bp and slightly lower temperatures of 11 5 12 0 c during the late holocene 3500 1000 cal bp a warming trend inferred for the past millennium is most likely an artifact of human impact on hinterburgsee s chironomid fauna rather than a genuine temperature signal the most prominent climatological events during the holocene were two periods of lower temperatures at c 10700 10500 cal bp and 8200 7700 cal bp and an abrupt shift to a cooler late holocene cl

emplacement origins of coarsely crystalline mafic rocks hosted in greenstone belts examples from the 2 7 ga yilgarn craton western australia coarsely crystalline mafic rocks commonly referred to as dolerite and diabase make up a substantial proportion of archean greenstone belts and are hosts to major orogenic gold deposits yet their internal architecture and contact relationships remain poorly documented and their emplacement origins are assumed rather than supported with evidence we present results from drill core logging of several late archean coarsely crystalline packages from the eastern goldfields superterrane of the yilgarn craton western australia including the golden mile dolerite these large mafic bodies comprise mostly medium to coarsely crystalline mafic rocks but also include a variety of other products of differentiation the bodies range from 75 to 460 m thick and extend for tens of kilometers are primarily hosted in mudstones and basalt and appear to be concordant to stratigraphy as such this study excludes mafic dykes and extremely thick and internally complex bodies such as the bushveld complex from base to top the internal stratigraphy generally consists of a lower unit of aphyric basalt dolerite gabbro and peridotite pyroxenite then a voluminous middle dolerite gabbro and an upper quartz dolerite gabbro and a topmost aphyric basalt granophyric veins and domains are common in the upper third of the mafic body contacts are gradational between all lithofacies with the exception of granophric veins which have sharp contacts within this overall stratigraphic framework there is variability in the relative thickness of lithofacies number of lithofacies as well as repetition of some lithofacies several examples also include basalt in the interior in well exposed examples the key evidence for distinguishing intrusions from extrusions is provided by the top contact however the top contact from these examples is ambiguous to overcome this gap we review the character of well studied thick ponded lavas from the literature most aspects of the internal character are not unique to intrusions although the maximum groundmass grain size excluding granophyric veins of the archean examples 3 mm is significantly coarser than that for any known ponded lavas 1 mm the ability to distinguish intrusions from extrusions has important implications for reconstructing archean greenstone stratigraphy and mineral exploration

majorite fractionation and genesis of komatiites in the deep mantle abstract melting experiments of the primitive mantle indicate that majorite fractionation is the key process to determine the geochemical nature of magmas generated in the deep upper mantle and the transition zone a model of petrogenesis of komatiite magma is presented by using the melting relations of the primitive mantle and the partitioning data of lithophile elements between majorite and the liquid alumina depleted komatiite generally observed in the early archean can be generated by any degree of partial melting at depths from 450 to 650 km this type of komatiite is also generated by a relatively low degree of partial melting at depths from 180 to 450 km alumina enriched komatiite can be generated by remelting of the residual mantle after separation of alumina depleted komatiite alumina undepleted komatiite generally observed in the late archean can not be formed by a low degree of partial melting of the primitive mantle at any depths this type of komatiite can be generated only by a high degree of partial melting of the mantle at the depths shallower than 450 km as an alternative model the alumina depleted komatiite can be formed by a high degree of partial melting of the archean upper mantle depleted in majorite such heterogeneity in the archean upper mantle was generated by a global melting event succeeding the accretion of the earth and erased by convection by the later archean hf isotope data seem to favour the former model of the petrogenesis of komatiite i e single stage melting of the primitive mantle at various depths

komatiites i eruption and flow because of their high eruption temperatures and ultrabasic composition komatiite lavas had low viscosities which typically ranged from 0 1 to 10 pa s a major consequence of this low viscosity is that most lavas erupted as turbulent flows an analysis of their ascent through the lithosphere suggests ascent velocities in the range of 1 to over 10ms 1 and reynolds numbers much greater than the critical value of 2000 the lavas would have remained turbulent for most or all of their subsequent flow and emplacement typical horizontal flow rates are estimated to range from 0 5 to 100 m2 s per unit width of flow such turbulent lava flows would have lost their heat by convection to the surroundings at rates which are orders of magnitude greater than the rates for laminar flows which cool by conduction a quantitative analysis of the cooling of komatiites indicates cooling rates from over 1000 c hr to a few c hr 1 while the flows remained turbulent these rates are in an appropriate range to cause phenomena such as high nucleation rates strong supersaturation of the lava delayed nucleation of olivine and skeletal or dendritic crystal morphologies komatiites often flowed over ground composed of rocks with lower melting temperatures it is proposed that the turbulent lavas melted the ground to form deep thermal erosion channels melting rates at the lava source are calculated at several metres per day and deep troughs with depths of several metres to hundreds of metres and lengths of several kilometres probably formed laboratory experiments performed to simulate thermal erosion show qualitative agreement with the theory with channel depth decreasing downstream the experiments also revealed that the channel margins become undercut during thermal erosion to form overhanging sides of the channel some sinuous rilles observed in the mare regions of the moon are thought to have formed by thermal erosion hulme 1973 they provide analogues of the channels postulated to form in komatiite eruptions where conditions were in fact more favourable for thermal erosion an assessment of the role of olivine crystals precipitated in the cooling turbulent flows indicates that they will remain in suspension until the lava has come to rest contamination of komatiite lava by underlying rock can be as much as 10 per cent some illustrative calculations show how the major element and trace element compositions of residual melts can be significantly modified by combined assimilation and fractional crystallization in a moving flow assimilation of tholeiitic basalt into a komatiite can cause incompatible trace element ratios such as ti zr and y zr and the rare earth patterns of derivative lavas to vary substantially some of the variations in such geochemical parameters which are often ascribed to mantle heterogeneity also could have resulted from assimilation of the ground assimilation could have modified the isotope geochemistry of lava suites and led to apparent ages which differ from the true eruption age the thermal erosion model also provides an explanation of the formation of some nickel sulphide ores found at the bottom of thick komatiite flows it is proposed that ores can form by assimilation of sulphur rich sediment which combines with ni from the komatiite to form an immiscible liquid

komatiitic sills and multigenerational peperite at dundonald beach abitibi greenstone belt ontario volcanic architecture and nickel sulfide distribution the density and the tectonic stresses in the deep crust and the physical properties of komatiitic magmas determine the level to which they will rise but once in the near surface environment the density and rheology of the near surface rocks consolidated and dense lava flows and sedimentary rocks versus unconsolidated sedimentary or volcaniclastic deposits govern whether they will be emplaced as lava flows invasive flows or sills where near surface strata are competent i e flow dominated or consolidated sedimentary and or volcaniclastic successions komatiitic magma erupts as flows that form extensive lava shields e g kambalda however where near surface strata are not competent i e unconsolidated volcaniclastic and or sediment dominated successions komatiitic magmas typically are emplaced as high level sills that increase the bulk density of the volcano sedimentary pile and eventually allow the eruption of lava and the construction of complex sub volcanic volcanic lava shields e g dundonald and shaw dome abitibi belt raglan cape smith belt pechenga kola peninsula thompson ni belt manitoba the latter environment is illustrated in the volcano sedimentary succession in dundonald township which is only weakly metamorphosed and deformed and superbly exposed in glacially polished outcrops the volcano sedimentary succession in this area comprises from base to top 1 the mcintosh formation composed of a succession of pillowed and massive intermediate volcanic flows 2 the dundonald formation composed of a lower section of komatiite sills argillites and felsic volcaniclastic deposits and an upper section of komatiite flows komatiitic sills and pillowed intermediate volcanic flows and 3 the frederick house lake formation composed of massive and pillowed mafic flows the distribution and thickness of argillites and felsic volcaniclastic rocks define a synvolcanic graben in which the dundonald south and alexo ni cu pge deposits occur within the center and the margin respectively sills and peperites in the lower komatiitic succession at dundonald beach exhibit a multigenerational emplacement history recording progressive lithification and increases in the bulk density and rheological strength of the unconsolidated argillites which ultimately permitted the eruption of lavas at alexo importantly the nature of the near surface rocks also influences the localization of ni cu pge deposits in lava shields e g kambalda the initial eruptions are typically most voluminous and if erupted at sufficient flow rates form channelized flows conducive to thermomechanical erosion of sulfur rich footwall rocks in sub volcanic volcanic lava shields however channelized units may occur within the subvolcanic plumbing system and or within overlying lavas where only sills are channelized e g thompson mineralization will occur only within the subvolcanic environment where only the flows are channelized e g damba silwane zimbabwe mineralization will occur only within the volcanic environment where both sills and lava flows are channelized e g dundonald shaw dome raglan the distribution of the mineralization is more diverse and may occur as subsea or sea floor ni cu pge deposits

a 3 d backstripping method and its application to the eromanga basin in central and eastern australia summary a general 3 d backstripping method based on a precise model of plate deformation is developed for analysis of the tectonic history of sedimentary basins and it has been applied to the eromanga basin in central and eastern australia the 3 d method is more appropriate when dealing with the subsidence history of basins since it takes into account both the flexural effect of surface load and the stress relaxation in the lithosphere due to viscous creep of mantle material furthermore this method is more accurate than conventional thin plate models it is shown that the 3 d model provides a different yet simple and clear evolving picture of the areal extent of the tectonic subsidence of basins the 3 d analysis results show that the formation of the eromanga basin is characterized by a gradual increase in the extent of sedimentation with localized subsidence from the late triassic to the early cretaceous and a large extension of sedimentation with rapid subsidence during the early to middle cretaceous followed by local and gradual subsidence after the middle cretaceous

improving the time control of the subboreal subatlantic transition in a czech peat sequence by 14c wiggle matching to achieve an optimal time control for a late subboreal to early subatlantic peat sequence from pancavska louka in the czech republic different strategies are applied to convert a series of radiocarbon dates into a calendar time scale the methods of selection and preparation of the samples for ams 14c dating are presented the results of calibrating single radiocarbon dates are compared with a 14c wiggle match strategy as the accumulation rate of the peat was not constant the concentrations of arboreal pollen are used to estimate the accumulation rate changes and to correct for these changes the resulting time control represents the best solution for this peat sequence with the methods currently available

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

reconstruction and palaeoclimatic interpretation of mid holocene vegetation and lake level changes at saint jorioz lake annecy french pre alps pollen and sediment analyses were used to reconstruct vegetation and lake level changes over the mid holocene period at saint jorioz lake annecy northern french pre alps episodes of forest clearings point to neolithic cultural activities in the northern french pre alps from c 6500 cal bp in agreement with other pollen and macrofossils records from eastern switzerland and the jura mountains the lake level record shows rises atc 8300 8200 6400 5900 and after 5730 cal bp the rise at c 8300 8200 cal bp shows a tripartition lower water levels developed before 8300 8200 and 6665 cal bp at c 6050 and 5730 cal bp rises at c 8300 8200 6400 5900 and after 5730 cal bp can be related to the 8200 yr event and north atlantic ice rafted debris ird events occurring at c 6200 5800 and 5500 cal bp respectively using a model based on pollen and lake level data the palaeoenvironmental changes reconstructed at saint jorioz were translated into quantitative climate parameters the results suggest that rises in lake level coincided with increasing annual precipitation runoff and available moisture and decreasing mean summer temperature and shortening of the growing season probably as a result of alternate southward northward displacements of the atlantic westerly jet at saint jorioz the period around the 8200 yr event corresponded to a c 2 5degreesc summer temperature cooling and a c 130 mm p e precipitation evaporation increase in agreement with other european and marine palaeoclimate records a c 4degreesc summer temperature cooling and a rise in annual precipitation by c 175 mm are reconstructed at c 5900 cal bp and after 5730 cal bp i e close to the time of the north atlantic ird events dated at 5800 and 5500 cal bp and are to be tested by further investigations a general trend toward temperature cooling and precipitation increase appears over the period documented by the sediment sequence of saint jorioz possibly related to an orbitally induced reduction of summer insolation

mass fluxes and clay mineral formation in soils developed on slope deposits of the kowarski grzbiet karkonosze mountains czech republic poland abstract weathering mineral formation and transformation processes along slopes are complex in cool mountainous regions undisturbed soil development with a strong vertical leaching element may abruptly change as a result of erosion accumulation lateral water fluxes and aeolian input we investigated soils in the eastern karkonosze mountains that have developed on silicatic slope deposits to date illite vermiculite and chlorite are the minerals that have been detected in the clay fraction although the climate and parent material should be favourable for the formation of smectites expandable phases were not verified so far we investigated if expandable phases could be detected and how they related to elemental fluxes along a short slope sequence 1142 1268 m a s l on the border between the czech republic and poland mass balance calculations indicated intensive mineral weathering together with a significant leaching of mg al ca and mn on the shoulder and foot slope positions in the middle zone which has a concave or undulating surface shape however the mass balances of several elements na k al p revealed a less pronounced leaching corresponding to a lower degree of podsolization and in some cases even accumulation at all sites mass balance calculations and detected soil minerals e g the increase in illite towards the surface together with an increase in al and k indicate some aeolian input kaolinite was detected in all soil horizons its concentration slightly increased towards the soil surface together with the pronounced leaching of ca part of kaolinite originates from plagioclase weathering besides being a weathering product of primary minerals part of the kaolinite is inherited from the parent material and probably is also due to aeolian input in all soils illite was being transformed into vermiculite and smectites through regularly interstratified illite smectite phases in addition the content of chloritic components which increases with depth indicated their concurrent weathering and transformation into smectites amphibole also may have acted as a source of smectites not all smectite is being actively formed in the soil most likely due to slope processes cover beds that affected even the subsoil some smectite has been transferred along the slope part of the smectite also seems to derive from the parent material active formation of expandable clay minerals is related to convex and planar landscape forms this relationship suggests intense element leaching inheritance from the parent material and cover bed mixing processes have contributed to the presence of smectite along the slope zones with predominant vertical transport shoulder foot slopes may repeatedly be interchanged with zones dominated by lateral transport undulating slope concave forms

timing of magmatism and deformation in the kamiskotia kidd creek area western abitibi subprovince canada abstract the kamiskotia kidd creek area comprises well preserved granitoid greenstone belt lithologies of the western most abitibi subprovince similar in composition and structural style to other late archean granitoid greenstone terranes e g kalgoorlie norseman western australia belingwe zimbabwe slave province canada it contains the kidd creek volcanogenic massive sulfide deposit and lesser deposits of the kamiskotia district and lode gold deposits associated with the destor porcupine fault zone near the prolific porcupine gold district the magmatic and tectonic history for the area is provided through detailed structural mapping and high precision u pb geochronology field observations support the following sequence of magmatic and structural events in the kamiskotia area 1 formation of older mafic and intermediate volcanic rocks followed by the emplacement of the kamiskotia gabbroic complex kgc and cogenetic massive sulfide bearing bimodal volcanic rocks kv also accompanied by coeval intrusion of granitoid a into the crystallizing kgc 2 regional bulk rotation about a sub horizontal axis of this stratigraphy to form a ne facing monocline 3 emplacement of three large granitoid intrusions imparting their respective contact strain aureoles on the stratigraphy 4 regional sub horizontal bulk north south shortening that formed a non penetrative east west flattening fabric with an element of 5 late dextral transpression that formed high strain zones related to western destor porcupine fault zone dpfz within less competent volcanic units and 6 emplacement of alkalic dikes associated with the late stages of transpressive deformation u pb ages help substantiate this chronology and aid in the correlation of kamiskotia lithologies across the southern abitibi subprovince zircon ages for the kgc and a kamiskotia rhyolite are 2707 2 ma and 2705 2 ma respectively these ages are coeval with the reid rhyolite with a zircon age of 2706 2 ma but are significantly younger than the kidd creek rhyolite and the prosser rhyolite with zircon ages of 2717 2 ma data refined by the addition of an abraded concordant analysis and 2716 6 3 ma respectively two of the granitoid intrusions have zircon ages of 2696 1 5 and 2694 4 ma the older granitoid intrusion has a titanite population with a 207 pb 206 pb minimum age of 2692 5 ma which may represent a protracted cooling history or a metamorphic event after the setting of the zircon u pb system two zircon fractions from the younger granitoid intrusion exhibit inheritance with 207 pb 206 pb minimum ages up to 2926 ma indicating the presence of significantly older crust in this region timing of north south compression and late transpression may be constrained by a u pb garnet titanite age on a late to post tectonic alkalic dike at 2687 3 ma

geochemistry of mineralised and barren komatiites from the perseverance nickel deposit western australia the perseverance formerly known as agnew and the neighbouring rocky s reward nickel deposits are associated with metamorphosed komatiite flows erupted onto a substrate of felsic crystal tuffs the deposits are overlain by the perseverance ultramafic complex which consists of a central dunite lens 700 m thick by 3 km wide flanked by olivine orthocumulates and spinifex textured komatiites a suite of samples of a zones of komatiite flows from the area has been analysed for major and trace elements rare earth elements and platinum group elements the samples fall into two distinct geochemical groups on the basis of major and rare earth elements 1 1 samples from a zones of spinifex textured flows flanking the central dunite show well constrained linear trends of major and trace elements typical of komatiite suites related by simple olivine fractionation 2 2 samples from the perseverance mine mineralised and basal flows from rocky s reward and from unmineralised flows at the base of the perseverance ultramafic complex all show evidence for lree enrichment relative to the first group they are also generally higher in sio2 and lower in feo for a given mgo content geochemical features of the second group are consistent with the effects of crustal assimilation this is in line with current models for nickel sulphide genesis based largely on kambalda which emphasise the role of thermal erosion of sulphidic footwall sediments the chalcophile element ni ir ru pt pd au and cu concentrations in a zone samples from the study area are typical of komatiites komatiites from the perseverance mineralised units and from rocky s reward show evidence of depletion of the more strongly chalcophile pge relative to ni and cu this feature is also evident in massive and matrix sulphide ore samples although less evident in the main perseverance cloud sulphides quantitative geochemical computer modelling indicates that the major and rare earth element chemistry of the samples analysed is consistent with derivation by combined assimilation of felsic material and crystallisation of olivine from a primitive komatiite magma the parental composition is represented by the spinifex textured units flanking the dunite lens compositions of komatiite liquids sulphides and cumulus olivines can be modelled successfully by varying degrees of batch equilibration between komatiite magma olivine and assimilated sulphidic sediment models involving combined assimilation and fractional crystallisation in which olivine and sulphide are fractionally segregated as they form are much less successful at matching the data in physical terms this suggests that the mineralisation is due to wholesale assimilation of floor rocks close to the site of sulphide accumulation comparison with quantitative computer model trends suggests an average ratio of assimilation to olivine fractionation in the order of 0 5 to 1 in order to generate the observed degrees of lree enrichment in flowtops ni depletion in olivine and pge depletion in sulphides and flow tops

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

geochemistry of volcanic rocks associated with cu zn and ni cu deposits in the abitibi subprovince volcanogenic massive sulfide vhms deposits in the abitibi subprovince are preferentially associated with volcanic successions containing 150 m thicknesses of felsic volcanic rocks approximately 50 by area of volcanic terranes and are found within volcanic sequences of at least three distinct affinities group i which is host to greater than half of the volcanogenic massive sulfide deposits by tonnage and which comprises only approximately 10 percent by area of volcanic terranes is composed of bimodal tholeiitic basalt basaltic andesite and high silica rhyolite the basaltic andesites and high silica rhyolites are characterized by high high field strength element and heavy rare earth element ree contents low light to heavy ree ratios most with la n yb n 0 8 3 and strong negative eu anomalies the kamiskotia matagami and chibougamau lower cycle volcanogenic massive sulfide areas all of which are also underlain by large synvolcanic gabbroic complexes are associated with group i volcanic sequences the kidd creek potter normetal and horne deposits are also included in this category group ii which is host to one third of the volcanogenic massive sulfide deposits by tonnage and which is also approximately 10 percent by area of volcanic terranes is composed of bimodal transitional tholeiitic to calc alkalic andesitc and rhyolite characterized by intermediate high field strength element contents and slightly higher ree ratios la n yb n 1 4 noranda camp excluding the horne deposit and val d or camp group iii is host to only one known deposit the selbaie mine which is unusual in that much of its mineralization cuts stratigraphy the selbaie mine sequence contains calc alkalic andesite rhyolite with relatively low high field strength element and ree contents and higher ree ratios la n yb n 3 9 the vast majority of volcanogenic massive sulfide bearing mafic and felsic volcanic rocks in the abitibi subprovince have la n yb n 5 barren volcanic sequences are group iv calc alkalic basaltic andesite to rhyodacite with low high field strength element and relatively high ree ratios la n yb n 8 20 represented by the upper skead group the quebec hunter mine group and the upper cycle chibougamau rocks and group v mafic to felsic alkalic volcanic rocks with high ree ratios la n yb n 12 62 represented by the timiskaming opemisca and ridout series rocks group i is most similar to thickened oceanic rift suites e g galapagos spreading center iceland east rift group ii is similar to suites in rifled island arcs e g hokuroku district japan and group iii is comparable to continental arc suites e g southern volcanic zone central chile groups iv and v are comparable to arc related suites derived from metasomatized mantle with variable amounts of crustal contamination e g setouchi area japan roman province italy known ni cu deposits in volcanic sequences are hosted exclusively in komatiitic flows and hypabyssal sills represented by chill compositions with high mgo contents 20 35 wt anhydrous very low incompatible element contents and depleted signatures la n sm n 0 5 0 8 zr y 2 5 alexo marbridge and shaw dome deposits in comparison to most barren komatiites in the abitibi subprovince their depleted trace element signatures indicate minimal crustal assimilation which would appear contrary to the widely held view that crustal contamination e g addition of silica sulfur oxygen of a mantle derived melt is necessary for sulfur saturation and magmatic sulfide segregation this problem may be reconciled by considering the dynamics of komatiite flows lesher and arndt 1990 where contaminated present address 23 euclid avenue ottawa ontario canada kis 2w2 komatiite liquid segregated and deposited sulfide and was subsequently swept downstream and replenished by uncontaminated magma over the deposit as the flow ebbed and cooled when considered together with geologic features such as evidence for thermal erosion in the footwall langmuir deposits and the presence of sulfidic footwall rocks shaw dome deposits the distinctive depleted geochemical signature of mineralized komatiites is useful in exploration for ni cu deposits

stratigraphy and u pb zircon geochronology of kidd creek implications for the formation of giant volcanogenic massive sulphide deposits and the tectonic history of the abitibi greenstone belt within the context of a structural stratigraphic analysis of the giant kidd creek cu zn ag deposit precise u pb zircon ages have been obtained for five critical rock units associated with the deposit massive flow banded footwall rhyolite is dated at 2714 3 1 2 ma slightly younger than a previously published age of 2717 2 ma on nearby rhyolite breccia extrusive rhyolite in the immediate hanging wall to the main ore lenses is dated at 2711 5 1 2 ma leaving an interval of one to several million years for the formation of the deposit we consider the demonstrated longevity of the kidd creek hydrothermal system as a major control on its giant size age constraints together with the size of the deposit suggest a time averaged rate of base metal sulphide deposition of about 10 100 t year peak rates were likely one to possibly two orders of magnitude above time averaged rates hence 100 1000 t year or higher detrital zircon ages on greywackes in the structural footwall to the deposit support structu

u pb zircon geochronology in the southwestern abitibi greenstone belt superior province the abitibi belt is the largest continuous greenstone belt in the superior province of the canadian shield it comprises several composite komatiitic tholeiitic calc alkalic and sedimentary sequences that are folded transected by major faults and intruded by various generations of plutonic rocks precise u pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems this paper presents new zircon ages and reassesses previously published ones now refined by the addition of abraded and concordant zircon analyses volcanic and subvolcanic units of the timmins area yield the following ages 2727 1 5 ma for a tuff of the upper deloro formation 2703 1 5 ma for a tuff of the upper tisdale formation and 2698 4 ma for the krist fragmental assigned to the top of the tisdale formation the age of a dunite intrusive into the upper deloro formation is revised at 2707 3 ma whereas the aquarius diorite east of timmins yields a poorly define

glacier response in the european alps to heinrich event 1 cooling the gschnitz stadial the gschnitz stadial was a period of regionally extensive glacier advance in the european alps that lies temporally between the breakdown of the last glacial maximum piedmont lobes and the beginning of the bolling warm interval moraines of the gschnitz stadial are found in medium to small catchments are steep walled and blocky and reflect a snowline lowering of 650 700 m in comparison to the little ice age reference snowline 10 be surface exposure dating of boulders from the moraine at the type locality at trins gschnitz valley tyrol austria shows that it stabilised no later than 15 400 1400 yr ago the overall morphological situation and the long reaction time of the glacier suggest that the climatic downturn lasted about 500 300 yr indicating that the gschnitz cold period began approximately 15 900 1400 yr ago if not somewhat earlier this is consistent with published radiocarbon dates that imply that the stadial occurred sometime between 15 400 14 c yr bp 18 020 19 100 cal yr and 13 250 14 c yr bp 15 360 16 015 cal yr a palaeoclimatic interpretation of the gschnitz glacier based on a simple glacier flow model and statistical glacier climate models shows that precipitation was about one third of modern day precipitation and summer temperatures were about 10 k lower than today in comparison during the younger dryas precipitation in this area was only about 10 less and ts summer temperature was only 3 5 4 k lower than modern values based on the age of the moraine and the cold and dry climate at that time we suggest that the gschnitz stadial was the response of alpine glaciers to cooling of the north atlantic ocean associated with heinrich event 1 copyright 2005 john wiley sons ltd