receiver operating characteristics roc as validation tool for prospectivity models a magmatic ni cu case study from the central lapland greenstone belt northern finland abstract a prospectivity model for magmatic ni cu deposits was created by integrating spatially referenced geophysical and geochemical datasets based on a simple and practical exploration model the study area is the central lapland greenstone belt northern fennoscandian shield finland magmatic nickel deposits are related to rock types that are typically characterized by local magnetic and gravity anomalies these deposit types can also be a source of nickel copper and cobalt anomalies in the overlying glacial till cover this straightforward exploration criterion was translated into a fuzzy logic prospectivity model the model validation is an essential step in justifying the validity of the prospectivity model this was accomplished by using receiver operating characteristics roc technique we used the known ni cu occurrences and deposits as true positive cases and other deposit type locations or random points as true negative cases in the validation process it appears that the roc technique provides a robust model validation and optimization technique providing that suitable validation data exists

the younger dryas termination and north atlantic deep water formation insights from climate model simulations and greenland ice cores results from the gisp2 and grip ice cores show that the termination of the younger dryas yd climate event in greenland was a large and extremely fast climate change a reinitiation of north atlantic deep water formation following a shutdown and its associated winter release of heat to the atmosphere has been suggested as the most likely cause of this climate transition to test this idea two general circulation model experiments using genesis have been completed for yd time 12 000 calendar years ago one with low heat flux in the nordic seas 10 w m deep water shutdown and one with high nordic sea heat flux 300 w m active deep water formation comparison of greenland climate differences between these experiments with the ice core records shows that when deep water is turned on much of the yd termination warming is achieved the increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation which obscures the dominantly wintertime response to the specified forcing the winter storm track shift toward greenland contributes much of the climate change at the yd termination

a review of gold mineralization styles in finland a wide range of styles of gold mineralization has been recognized in finland including orogenic metamorphosed epithermal skarn or epigenetic ironstone hosted intrusion related nonskarn massive sulfide hosted paleoplacer and placer deposits gold production in the past was principally as a byproduct from the mining of paleoproterozoic base metal massive sulfide deposits this situation has changed during the last decade with the closure of some base metal mines and the commencement of production from recently discovered gold only deposits gold mineralization occurred during distinct episodes of crustal evolution in finland several late archean greenstone belts in the karelian craton in eastern and northern finland contain orogenic gold deposits dated at about 2 75 to 2 70 ga suggesting a coherent and pervasive tectonic and metallogenic event in the paleoproterozoic low grade the main accretionary stage of the svecofennian orogeny in finland culminated with metamorphism and deformation between 1 89 and 1 86 ga during that time intrusion related au cu mineralization took place in both syntectonic porphyry stocks and their wall rocks in and close to the archean proterozoic margin orogenic gold mineralization took place at or slightly after the metamorphic peak throughout the svecofennian domain possibly also overprinting massive sulfide and intrusion related occurrences it is notable that the largest orogenic deposits are located within discrete plutons rather than hosted by supracrustal sequences this may be a consequence of the rheological contrasts between plutons and the supracrustal lithologies the paleoproterozoic lapland domain in the northern part of the country records a protracted and complicated evolution involving multiple episodes of rifting magmatism sedimentation and alteration culminating at around 1 9 ga with the collision of the karelian craton the svecofennian fold belt to the south and the kola craton to the north these deformational events led to orogenic gold mineralization throughout the proterozoic greenstone belts of northern finland at about 1 89 to 1 86 ga during and soon after the peak of metamorphism and deformation skarnlike or epigenetic ironstone hosted deposits were also formed during the orogeny in the western and southwestern parts of the lapland domain probably somewhat later at around 1 86 ga the most favorable sites for mineralization are regionally extensive zones of early albitization that predate gold mineralization the deposition of molasselike sediments during the terminal stages of the svecofennian orogeny and weathering of both orogenic and syngenetic sulfide mineralization also prior to 1 8 ga produced placer accumulations now paleoplacers in the conglomerates of the uppermost formation of the central lapland greenstone belt placer deposits of controversial origin and provenance have also been worked for many years in the glaciofluvial sediments of northernmost finland the areas with greatest potential for the discovery of new orogenic gold deposits in finland are the late archean and paleoproterozoic greenstone belts in eastern finland and lapland respectively some fe cu au skarns or epigenetic ironstone hosted deposits have been mined in the past and there may be potential for the discovery of larger iron oxide copper gold systems in the western central lapland greenstone belt for intrusion related nonskarn mineralization the most promising areas are close to the raahe ladoga suture and the potential for additional metamorphosed and deformed epithermal mineralization exists in the tampere schist belt the significant number of gold occurrences already known in these areas highlights the potential for new discoveries

vapour discharges on nevado del ruiz during the recent activity clues on the composition of the deep hydrothermal system and its effects on thermal springs abstract the nevado del ruiz volcano is considered one of the most active volcanoes in colombia which can potentially threaten approximately 600 000 inhabitants the existence of a glacier and several streams channelling in some main rivers flowing downslope increases the risk for the population living on the flank of the volcano in case of unrest because of the generation of lahars and mudflows indeed during the november 1985 subplinian eruption a lahar generated by the sudden melting of the glacier killed twenty thousand people in the town of armero moreover the involvement of the local hydrothermal system has produced in the past phreatic and phreatomagmatic activity as occurred in 1989 therefore the physico chemical conditions of the hydrothermal system as well as its contribution to the shallow thermal groundwater and freshwater in terms of enthalpy and chemicals require a close monitoring the phase of unrest occurred since 2010 and culminated with an eruption in 2012 after several years of relative stability still maintains a moderate alert as required by the high seismicity and so 2 degassing in october 2013 a sampling campaign has been performed on thermal springs and stream water located at 2600 5000 m of elevation on the slope of nevado del ruiz analyzed for water chemistry and stable isotopes some of these waters are typically steam heated low ph and high sulfate content by the vapour probably separating from a zoned hydrothermal system by applying a model of steam heating based on mass and enthalpy balances we have estimated the mass rate of hydrothermal steam discharging in the different springs the composition of the hottest thermal spring botero londono is probably representative of a marginal part of the hydrothermal system having a temperature of 250 c and low salinity cl 1500 mg l which suggest along with the retrieved isotope composition a chiefly meteoric origin the vapour discharged at the steam vent nereidas 3600 m asl is hypothesized to be separated from a high temperature hydrothermal system based on its composition and on literature data on fluid inclusions we have retrieved the p t x conditions of the deep hydrothermal system as well as its ph and f o 2 the vapour feeding nereidas would separate from a biphasic hydrothermal system characterized by the following parameters t 315 c p 15 mpa nacl 10 wt co 2 5 wt and similar proportion between liquid and vapour considering also the equilibria involving s bearing gases and hcl ph would approach the value of 1 5 while f o 2 would correspond to the feo fe 2 o 3 buffer chlorine content is estimated at 10 300 mg l changes in the magmatic input into the hydrothermal system could modify its degree of vapourization and or p t x conditions thus inducing corresponding variations in vapour discharges and thermal waters these findings paralleled by contemporary measurements of water flow rates could give significant clues on risk evaluation

assessment of undiscovered metal resources in finland this paper summarises the results of probabilistic estimates of the amounts of cu zn pb ni co pt pd au ag and mo in undiscovered orogenic au volcanogenic massive sulphide vms porphyry cu outokumpu type cu zn co synorogenic intrusion related ni cu komatiite related ni and layered intrusion hosted contact type and reef type pge deposits in finland the assessments were carried out down to the depth of one kilometre using the three part quantitative assessment method permissive areas tracts within which mineral deposits can exist based on their geological properties were delineated separately for each deposit type total number of tracts delineated was 188 and excluding overlap total area covered by the tracts is 190 700 km2 this means that 57 of the land area of finland holds potential for the discovery of new mineral deposits of the types included in the assessments orogenic au tracts cover the largest area 110 000 km2 and the contact type pge and talvivaara type tracts cover the smallest areas both 310 km2 the number of undiscovered deposits was estimated at several levels of confidence for each permissive tract the total expected number of undiscovered deposits across all permissive tracts is 309 deposits the largest expected numbers of deposits are associated with the orogenic au 90 synorogenic intrusion related ni cu 66 and vms 45 tracts statistical comparisons indicated differences in tonnage and grade values between fennoscandian and global data sets for several deposit types and between global precambrian and phanerozoic porphyry cu deposit data sets the reason for the differences is inconclusive but probably related to both global variations in exploration maturity and availability of grade and tonnage information due to the differences grade tonnage models were constructed using data from well known deposits within the fennoscandian shield for most of the assessed deposit types the orogenic au model was constructed using fennoscandian and north australian deposits and the porphyry cu model using global data on precambrian deposits the sum of median estimates of undiscovered resources across all the assessed deposit types is 9 7 mt cu 5 0 mt ni 1 8 mt zn 0 15 mt pb 0 10 mt mo 86 000 t co 12 000 t pd 5600 t pt 2100 t ag and 1400 t au layered intrusion hosted pge deposits and porphyry cu deposits are estimated to host the largest undiscovered resources containing the majority of the undiscovered cu ni pt pd and mo most of the undiscovered zn is in vms deposits and more than half of the undiscovered au is in orogenic au deposits comparison between discovered and estimated undiscovered resources indicates that practically all mo pt and pd resources and more than half of the au and cu resources in finland exist in undiscovered or poorly known deposits undiscovered resources of ni pb and ag are smaller than the discovered resources most of the total endowment of zn and co appears to be in discovered resources on a global scale the finnish resources are small the discovered resources and estimated total endowment for most of the metals assessed are 1 of the corresponding global identified resources platinum group elements ni co and possibly au might be exceptions to this at least on a european scale as a caveat to the results of this work we stress that a few potentially significant deposit types e g kevitsa and talvivaara types precambrian epithermal au were excluded from the assessments due to the lack of statistically reliable grade and tonnage data

late holocene temperature and precipitation changes in vindelfjallen mid western swedish lapland inferred from chironomid and geochemical data in this article we present results from a palaeolimnological study from lake vuoksjavratje in the mountain tundra region in the vindelfjallen mountains northwest sweden we suggest that the influence of precipitation may be one of the factors causing discrepancies between chironomid based late holocene july temperature julyt reconstructions from fennoscandia we combine quantitative temperature reconstruction using chironomids for the last 5100 years with qualitative analysis of chironomid composition and geochemical analyses such as x ray fluorescence xrf total organic carbon toc and c n analysis the studied sequence is dated by 210pb 137cs and 11 14c datings from terrestrial macrofossils the aim of the study was to use chironomids to reconstruct late holocene summer temperature variation on a multi centennial to centennial timescale and to use geochemical data to identify periods during which the changes in chironomid composition might have been forced by environmental variables other than

the 8 2 ka event abrupt transition of the subpolar gyre toward a modern north atlantic circulation 1 climate model simulations of the 8 2 ka event show an abrupt strengthening of the atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early holocene the freshwater outburst from proglacial lakes and the onset of labrador sea water formation the 8 2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the north atlantic region about 8200 years before present it coincides with a meltwater outburst from north american proglacial lakes that is believed to have weakened the atlantic meridional overturning circulation and northward heat transport followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries marine proxy data however date the onset of deep water formation in labrador sea to the same time the subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease although similarities in timing are compelling a mechanism to reconcile these apparently contradictory events was missing our simulations show that an abrupt and persistent strengthening of the atlantic subpolar gyre provides a plausible explanation the intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation stabilized by internal feedbacks and persistent after the cessation of the perturbation as a direct consequence deep water formation around its center intensifies this corresponds to the modern flow regime and stabilizes the meridional overturning circulation possibly contributing to the holocene s climatic stability

out of tune the dangers of aligning proxy archives abstract tuning is a widespread technique to combine date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives the approach will be reviewed by discussing a number of literature examples ranging from peat and tephra layers to orbital tuning and 18o series from marine and ice deposits potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties and some solutions suggested fossil proxy research could become enhanced if tuning were approached in a more quantitative reliable and objective way and especially if individual proxy archives were non tuned and kept on independent time scales

δ15n of n2 in air trapped in polar ice a tracer of gas transport in the firn and a possible constraint on ice age gas age differences with respect to gas transport the fim near the surface of an ice sheet can be divided into three zones the uppermost is a convective zone located just below the surface of the ice sheet in which the air is rapidly flushed by convective exchange with the overlying atmosphere below the convective zone there is a diffusive air column in which diffusion is rapid but there is no convection between the bottom of the diffusive air column and the bubble close off region there may be a nondiffusive zone in which diffusion is so slow that negligible gas transport occurs the diffusive air column is characterized by progressive enrichment with depth of 15n in n2 and heavy isotopes of gases in general as predicted using the barometric equation in this paper we present data on the 15n of n2 in recently trapped air samples from 12 ice cores along with numerous downcore samples from byrd vostok and dome c bubble close off depths for these cores calculated from a densification model ranged from 51 to 114 meters below the surface mbs we used these data and the barometric equation to calculate the thickness of the diffusive air column and found that it comprised 46 to 93 of the total firn thickness at our study sites paleo close off depths calculated from the densification model for glacial sections of byrd vostok and dome c are 15 25 m deeper than close off depths today diffusive column heights calculated from 15n varied in a more complex manner the diffusive column height at byrd appears to have decreased from 74 m during the last glacial period to 50 m during the holocene at vostok and dome c the diffusive column height calculated from 15n increase from about 65 m during the last glacial period to about 80 m in the holocene we use records of surface temperature and co2 at byrd and vostok along with their respective chronologies to constrain the ice age gas age difference age throughout the section of the vostok ice core corresponding to the last glacial termination in principle age values calculated from these data can be used to discriminate whether gas in the fim mixes to the bubble close off depth or to a depth equivalent to the diffusive column height in practice however uncertainties in the chronology of byrd and vostok are too great to allow us to distinguish between these two possibilities one can only say that at the time of the last termination age for vostok was between 3 and 10 5 kyr previous estimates fall within this range

seismicity at fuego pacaya izalco and san cristobal volcanoes central america 1973 1974 seismic data collected at four volcanoes in central america during 1973 and 1974 indicate three sources of seismicity regional earthquakes with hypocentral distances greater than 80 km earthquakes within 40 km of each volcano and seismic activity originating at the volcanoes due to eruptive processes regional earthquakes generated by the underthrusting and subduction of the cocos plate beneath the caribbean plate are the most prominent seismic feature in central america earthquakes in the vicinity of the volcanoes occur on faults that appear to be related to volcano formation faulting near fuego and pacaya volcanoes in guatemala is more complex due to motion on a major e w striking transform plate boundary 40 km north of the volcanoes volcanic activity produces different kinds of seismic signatures shallow tectonic or a type events originate on nearby faults and occur both singly and in swarms there are typically from 0 to 6 a type events per day withb value of about 1 3 at very shallow depths beneath pacaya izalco and san cristobal large numbers of low frequency or b type events are recorded with predominant frequencies between 2 5 and 4 5 hz and withb values of 1 7 to 2 9 the relative number of b type events appears to be related to the eruptive states of the volcanoes the more active volcanoes have higher levels of seismicity at fuego volcano however low frequency events have unusually long codas and appear to be similar to tremor high amplitude volcanic tremor is recorded at fuego pacaya and san cristobal during eruptive periods large explosion earthquakes at fuego are well recorded at five stations and yield information on near surface seismic wave velocities 3 0 0 2 km sec

seismicity associated with the reactivation of nevado del ruiz colombia july 1985 december 1986 abstract renewed activity of nevado del ruiz was first evidenced in november 1984 by increased fumarolic activity and felt earthquakes this increased activity prompted an installation of seismometers on the volcano in july 1985 earthquakes recorded in 1985 indicate that most of the seismic activity prior to the eruption on november 13 1985 was confined to an l shaped epicentral zone beneath the summit of the volcano a swarm prior to the november eruption originated west of the summit telemetered stations installed after the eruption enabled better locations of post eruptive activity majority of located post eruptive earthquakes originate within 5 km of the summit at a depth less than 7 km and only few exceeded magnitude 3

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

model data comparison for the 8 2 ka bp event confirmation of a forcing mechanism by catastrophic drainage of laurentide lakes abstract to improve our understanding of the mechanism behind the 8 2 ka bp cooling event we compare proxy evidence with climate model simulations in which the thermohaline ocean circulation is perturbed by a freshwater pulse into the labrador sea both the proxy data and model results show a cooling that is mainly concentrated in the north atlantic region ranging from more than 5 c cooling in the nordic seas to about 0 5 1 c over europe and less than 0 5 c over the subtropical north atlantic data and model also indicate a weakening of the summer monsoon and generally a drier circum north atlantic over the south atlantic ocean the model simulates a slight warming mostly less than 0 5 c which falls within the uncertainty of proxy data and thus could not be confirmed to examine in detail the structure of the 8 2 ka bp event we also compare the modeled climatological evolution at two locations with high quality records revealing a generally consistent picture the good model data agreement confirms the hypothesis that the 8 2 ka bp event was forced by a freshwater induced weakening of the thermohaline circulation other forcings are unlikely since they would result in an alternative geographical distribution and expression of the climate response

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

operation of a digital seismic network on mount st helens volcano and observations of long period seismic events that originate under the volcano during 1981 we operated with the cooperation of the u s geological survey a 9 station digital seismic array on mount st helens volcano in washington state one of our stations was placed inside the crater of the volcano six were located on the flanks of the volcano within two km of the crater and two were approximately ten km from the crater four of the instruments recorded three components of motion and the remaining five recorded only the vertical component in addition to the monitoring and recording performed by the digital instruments we carried out a one day experiment during which we complimented our crater monitoring seismometer by the addition of two ink recording instruments during the one day experiment we had six observers including 4 usgs scientists who had significant experience working and making observations in the crater recording times of rockfall felt earthquake occurrences and changes in steam emissions from the dome in the crater using information obtained during the one day experiment we are able to classify seismic events recorded by our digital instruments as earthquakes rockfalls helicopter noise and a type of event that is unique to volcanoes which we call long period waveforms of these long period events have a duration of up to 30 seconds and a spectrum that is peaked at approximately 2 hz the frequency at which the peak in the spectrum occurs is nearly the same at all stations which means that the unique waveform of long period events is due to a source effect not a path effect the peak frequency is fairly insensitive to the amplitude of the signal which means that the size of the source region is constant independent of the signal amplitude long period events were not felt and were accompanied by no visible changes inside the crater which lead us to conclude that they are some sort of seismic disturbance generated inside the volcano

palaeoproterozoic accretionary processes in fennoscandia abstract accretionary processes contributed to major continental growth in fennoscandia during the palaeoproterozoic mainly from 2 1 to 1 8 ga the composite svecofennian orogen covers c 1 10 6 km 2 and comprises the lapland savo fennia svecobaltic and nordic orogens it is a collage of 2 1 2 0 ga microcontinents and 2 02 1 82 ga island arcs attached to the archaean karelian craton between 1 92 and 1 79 ga andean type vertical magmatic additions especially at c 1 89 and c 1 8 ga were also important in the continental growth the palaeoproterozoic crust is the end product of accretionary growth continental collision and orogenic collapse preserved accretional sections are found in areas where docking of rigid blocks has prevented further shortening the pirkanmaa belt represents a composite accretionary prism and other preserved palaeosubduction zones are identified in the gulf of bothnia and the baltic sea areas in the southern segment of the lapland savo orogen collision between the archaean continent lower plate and the palaeoproterozoic arc microcontinent assembly upper plate produced a special type of lateral crustal growth the archaean continental edge decoupled from its mantle during initial collision and overrode the arc and its mantle during continued collision

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

the younger dryas relevant in the australian region an assessment of australian climate during the younger dryas chronozone ydc is presented this review focuses on securely dated records from sites of continuous deposition placing greatest emphasis on temperature reconstructions with records of effective precipitation i e the combined effect of precipitation minus evapotranspiration also considered while there is a paucity of australian records covering the last glacial interglacial transition particularly those which directly infer temperature sufficient data exist to examine ydc climate from southern and eastern australia temperature reconstructions from tasmania based on both chironomid and pollen data show no evidence for younger dryas cooling by contrast there is evidence for cooling associated with the antarctic cold reversal from tullabardine dam pollen data and the sediment organic content from eagle and platypus tarns in tasmania records from a number of eastern australian mainland sites provide no evidence of effective precipitation shifts concurrent with the younger dryas chronozone similarly reconstructions of discharge from the murray darling basin which covers a large proportion 14 of the australian continent and dust transport from a larger portion of the continent also show no evidence of climate shifts concomitant with the younger dryas of research published in the past decade only one study located in the great australian bight claims evidence of a ydc cooling andres et al 2003 by contrast this review suggests that there is no conclusive evidence for cooling or indeed any distinctive climate patterning during the younger dryas chronozone in australia

the greenland 8200 cal yr bp event detected in loss on ignition profiles in norwegian lacustrine sediment sequences high resolution loss on ignition analyses of lacustrine sediment cores from both proglacial and non glacial lakes in southern norway have revealed a specific pattern characterised by a significant two peaked reduction of the loss on ignition values in the basal half of the cores in non glacier fed lakes the loss on ignition variations are interpreted to reflect mainly lake productivity and hence variability in surface summer air temperature sediments deposited in proglacial lakes however reflect mainly the glacier activity in the lake catchment bulk ams radiocarbon dates from the core sequences and the loss on ignition curve pattern suggest that this event correlates with the 8200 cal yr bp event recorded in the grip and gisp2 greenland ice cores termed the finse event in southern norway copyright 2001 john wiley sons ltd

analysis of swarms of high frequency seismic events at nevado del ruiz volcano colombia january 1986 august 1987 development of a procedure abstract the determination of signal properties like frequency amplitude signature of the sequence of arrivals of p and s phases and the subsequent computation of hypocenter parameters are the steps of a procedure in the analysis of swarms of high frequency seismic events from nevado del ruiz volcano which could be useful in other volcanic areas the use of this procedure on ruiz data led to the determination of various seismic source volumes which together with hypocenters of non swarmed events and the identification of geological features such as faults which cross the area alignment of domes and volcanic edifices and the record of low frequency seismic events not centered in the area of the active vent suggest the existence of a magma chamber of a rather complex geometry this hypothesis would suggest that magma emplaced in zones of weakness faults that affect the area may act as the source of seismic activity this demands a revision of the methodology used in the deformation measurements and in the analysis of released energy and event occurrence too the relations between hypocenters sources location and relative energy of the swarms as well as the general volcanic activity tremor ash and gas emission deformation could turn out to be a possible means to assist in the identification of premonitory activity and thus be relevant to the process of monitoring and forecasting

palaeolimnological and sedimentary responses to holocene forest retreat in the scandes mountains west central sweden a suite of analyses was performed on sediments accumulated duringthe last 10 700 years in lake spaime a small hydrologically open water body in the modern alpine tundra zone of the scandes moun tains west central sweden the study aimed to evaluate 1 the nature of climate changes that forced the late holocene loweringof altitudinal tree limit in the region the timingof which is known from prior stu dies based on radiocarbon dating of subfossil wood and 2 the impact of these vegetational changes on an aquatic ecosystem arboreal pollen and plant macrofossil data confirm the persistence of trees in the lake catchment at least from c 9700 cal bp until c 3700 cal bp although growing season temperature is com monly believed to be the dominant factor drivingboreal forest tree limit variations in the reg ion a chir onomid based reconstruction of mean july air temperature suggests that local deforestation during the late holocene was not accompanied by a significant cooling the tree limit retreat was more likely caused by increasing effective moisture and declining length of the growing season the ecohydrological response of lake spaime to this combination of climate and vegetational changes included a decline in primary pro ductivity as indicated by an abrupt decrease in sediment organic matter content while associated increases in organic d 13 c d 15 n and c n point to diminished fluxes and altered balance of catchment derived nutrients followingdeforestation the decline in aquatic productivity is also marked by a distinct change in the mineral magnetic properties from a high magnetic concentration assemblage dominated by fine grained magnetite of biogenic origin to one dominated by background levels of coarse grained detrital magnetite

the accretionary svecofennian orogen insight from the babel profiles abstract the babel profiles b c 1 7 form a 1200 km long nearly continuous cross section through the svecofennides the near vertical marine reflection profiles display a wide range of crustal structures that can be associated with both the accretionary svecofennian orogeny 1 96 1 75 ga and the following subjotnian and jotnian rift stages 1 65 1 11 ga the svecofennian accretionary orogeny took place when a number of micro plates with island arc affinities and surface expression of a large archipelago accreted to the continental karelian plate some of the accreting terranes seem to have had older cores that have acted as crustal indentors during the collision babel profiles 3 and 4 image a series of collisional terrane boundaries between karelian continental margin savo arc sa and central finland arc cfa in the north the karelian margin has been both over and underthrust by the savo arc cfa comprises a folded thrust package on top of a continental nucleus and the savo arc the associated subduction zone and accretionary prism are interpreted to lie to the south underneath the bothnian basin area where prominent ne dipping lower to middle crustal reflections are found along babel profiles 1 and 4 an oblique collision of the central finland arc and the continent resulted in the development of the strike slip fault on the young hot savo arc babel profiles 1 6 7 and c image the internal architecture of the southern and central finland arcs the unusually thick crust 55 60 km hosts unreflective high density mafic intrusions acting as a crustal indentor a highly reflective antiform structure developed on the southern side of it southern finland arc complex sfa is an imbrication structure comprising stacked slices of arc related crust on an older continental nucleus bergslagen nucleus prior to the collision the sfa suffered from gravitational collapse during which the crust was thinned profile b images the architecture of the central and southern swedish svecofennides the sormland terrane sob is interpreted as the accretionary prism of the southern finland arc squeezed between the svecofennian collage in the north and the advancing continent to the south the southern continent island arc is characterised by ne dipping crustal reflections and moho offsets as well as step wise increasing thickness of the crust after the final collision large volumes of mantle derived material intruded the crust as large mushroom shaped plutons they are interpreted as the heat source for the tib magmatism in southern and western scandinavia

automated detection and characterization of harmonic tremor in continuous seismic data harmonic tremor is a common feature of volcanic hydrothermal and ice sheet seismicity and is thus an important proxy for monitoring changes in these systems however no automated methods for detecting harmonic tremor currently exist because harmonic tremor shares characteristics with speech and music digital signal processing techniques for analyzing these signals can be adapted i develop a novel pitch detection based algorithm to automatically identify occurrences of harmonic tremor and characterize their frequency content the algorithm is applied to seismic data from popocatepetl volcano mexico and benchmarked against a month long manually detected catalog of harmonic tremor events during a period of heightened eruptive activity from december 2014 may 2015 the algorithm detects 1465 minutes of harmonic tremor which generally precede periods of heightened explosive activity these results demonstrate the algorithm s ability to accurately characterize harmonic tremor while highlighting the need for additional work to understand its causes and implications at restless volcanoes

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

chironomids as a tool for inferring holocene climate an assessment based on six sites in southern scandinavia abstract chironomid subfossil assemblages from six low alpine and sub alpine holocene stratigraphies are presented and compared they are from five lakes in mid southern and western norway and one in central sweden when comparing the chironomid inferred july air temperatures there are many time segments with a poor among lake fit in inferred temperatures possible environmental variables influencing the fossil chironomid assemblages are discussed using a modern norwegian calibration data set to indicate taxon environment relationships these analyses indicate that local changes in ph water chemistry and productivity at times may have overridden the regional temperature signal in addition other causes of poor among site temperature fit are discussed in particular those related to chronological uncertainties holocene temperature inferences from single cores based on chironomids may not always be able to provide a reliable regional temperature signal but can act as a guide from which hypotheses about past environmental conditions can be tested with the aid of chironomid inferred temperatures from several sites and from other environmental proxies we have obtained a regional picture of holocene summer temperature change by developing a consensus reconstruction based on the overall temperature signal from all six sites this consensus is developed by fitting a smoother through all 330 site specific temperature deviations from the holocene mean the consensus temperature deviations vary from 0 8 c at 8800 cal years bp to 0 8 c at 6500 cal years bp

were last glacial climate events simultaneous between greenland and france a quantitative comparison using non tuned chronologies several large abrupt climate fluctuations during the last glacial have been recorded in greenland ice cores and archives from other regions often these dansgaard oeschger events are assumed to have been synchronous over wide areas and then used as tie points to link chronologies between the proxy archives however it has not yet been tested independently whether or not these events were indeed synchronous over large areas here we compare dansgaard oeschger type events in a well dated record from southeastern france with those in greenland ice cores instead of assuming simultaneous climate events between both archives we keep their age models independent even these well dated archives possess large chronological uncertainties that prevent us from inferring synchronous climate events at decadal to multi centennial time scales if possible comparisons between proxy archives should be based on independent non tuned time scales copyright 2009 john wiley sons ltd

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

seismological aspects of the 1988 1989 lonquimay chile volcanic eruption abstract more than 1600 earthquakes were recorded in a four month period on portable seismographic stations installed in the lonquimay area immediately after the initiation of the volcanic eruption of december 25 1988 hypocentral parameters were calculated on a subset of 150 events showing clear p and s arrivals seismic activity was restricted to a north south elongated region that included the main crater of the lonquimay volcano the new navidad crater lies along the eastern margin of the area of seismicity most of the hypocenters are located at depths shallower than 6 km and none have depths exceeding 10 km the largest earthquakes of the sequence took place on dec 28 m 4 7 jan 12 13 m 4 8 and 5 0 and feb 24 m 5 3 the number of events per day varied it peaked on dec 27 with more than 260 events and more than 200 events were recorded on jan 13 both of which corresponded to the days of large earthquakes the relation of large to small events given by the b value of the magnitude frequency distribution log n a bm is typical of volcanic sequences b 1 7 and much larger than the equivalent for tectonic environments the rate of decay of the number of aftershocks of each large earthquake is proportional to t p with p increasing from 0 63 to 1 08 as the eruption progressed in time initial low values of p indicate a slow stress release in the region larger absolute values of p are comparable with tectonic environments and might be indicators of the last stages of the eruption process the total seismic energy release is 9 6 10 19 ergs about five orders of magnitude less than the estimated thermal energy the spatial distribution of earthquakes suggests that the sources of stress change associated with the eruption are located under and possibly to the south of the main crater of the lonquimay volcano and that the evacuation channels of magma occupied a zone of weakness in the region of the new crater

comment the greenland 8200 cal yr bp event detected in loss on ignition profiles in norwegian lacustrine sediment sequences a nesje s o dahl 2001 journal of quaternary science 16 155 166 comment the greenland 8200 cal yr bp event detected in loss on ignition profiles in norwegian lacustrine sediment sequences a nesje s o dahl 2001 journal of quaternary science 16 155 166

new evidence for episodic post glacial sea level rise central great barrier reef australia abstract we present an extensive database of 364 radiocarbon dates from coastal and marine sediments of the central great barrier reef gbr shelf of which 110 are previously unpublished the elevation data have been reduced to a common datum australian height datum ahd and the various sources of error have been assessed using modern lithological and biological relationships with sea level the elements of the radiocarbon database have been converted into sea level indicators the upper bound of the assembled dataset corresponds to a best estimate sea level curve and the full dataset provides a narrow envelope for sea level rise on the gbr shelf for the last 11 12 kyr not including hydro isostatic crustal flexing the envelope is consistent with episodic rise in post glacial sea levels the rising post glacial sea level probably included stillstands or minor falls at ca 45 m ahd at ca 10 5 kyr b p 5 m 7 8 kyr b p 2 m ca 6 kyr b p and 1 7 m 5 5 kyr b p there is evidence for a significant fall in sea level between stillstands at 11 m 8 5 kyr b p and 17 m 8 2 kyr b p stillstand durations apparently ranged between the vertical spread in the derived sea level data is very wide the use of shell material for dating seems unreliable and prone to large and unpredictable errors data from bulk mangrove muds appear reliable for determination of ancient sea level but may at times result in sea level being placed up to 4 m below the true level in situ biogenic carbonates such as preserved oyster beds and coral micro atolls are the most reliable indicators of sea level position while deposits of mangrove mud give a useful first order approximation of ancient sea levels caution should be used in drawing sea level curves from few data points we conclude that the post 11 12 kyr b p relative rise in sea level was episodic on the central gbr continental margin more data are required to define clearly sea level change up to ca 20 m at 9 kyr b p

the marine record of deglaciation from the continental margin off nova scotia continental margin sediments off nova scotia accumulate at high rates up to 360 cm kyr 1 and contain a history of millennial scale environmental changes which are dominated by the proximity of the laurentide ice sheet during the latest quaternary using stable isotope ratios of oxygen accelerator mass spectrometer radiocarbon dating micropaleontology and sedimentology we document these changes in six piston cores ranging in water depth from 450 to 4300 m we find that maximum 18o in n pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by 1000 years between 13 and 14 ka we find a second peak in abundance of n pachyderma minimum 18o and two pulses of ice rafting the sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper paleozoic and mesozoic red beds by 14 ka in southeastern canada so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the st lawrence valley the younger dry as event is recognized as a peak in abundance of n pachyderma and ice rafting dated as 11 3 ka but meltwater discharge to the gulf of st lawrence was either too small or occurred over too long a time to leave a distinct 18o minimum off nova scotia at 7 1 ka in the middle of holocene warming we find a third peak in abundance of n pachyderma and another 18o minimum but no ice rafting we interpret these data as evidence of a late occurring meltwater event which if correct could have originated in the great lakes in the labrador ungava region or in both the final millennial scale phenomenon off nova scotia is the onset of neoglaciation marked by increased ice rafting and increased n pachyderma beginning about 5 kyr ago

problems with identifying the 8200 year cold event in terrestrial records of the atlantic seaboard a case study from dooagh achill island ireland the northern hemisphere cooling event 8200 years ago is believed to represent the last known major freshwater pulse into the north atlantic as a result of the final collapse of the north american laurentide ice sheet this pulse of water is generally believed to have occurred indepen dently of orbital variations and provides an analogue for predicted increases in high latitude preci pitation and ice melt as a result of anthropogenically driven future climate change the precise timing duration and magnitude of this event however are uncertain with suggestions that the 100 yr melt water cooling formed part of a longer term cold period in the early holocene here we undertook a multiproxy high resolution investigation of a peat sequence at dooagh achill island on the west coast of ireland to determine whether the 8200 year cold event impacted upon the terrestrial vege tation immediately downwind of the proposed changes in the north atlantic we find clear evidence for an oscillation in the early holocene using various measures of pollen indicating a disruption in the vegetation leading to a grassland dominated landscape most probably driven by changes in precipitation rather than temperature radiocarbon dating was extremely problematic however with bulk peat samples systematically too young for the north atlantic event suggesting significant contamination from downward root penetration the sustained disruption to vegetation over hundreds of years at dooagh indicates the landscape was impacted by a long term cooling event in the early holocene and not the single century length 8200 year meltwater event proposed in many other records in the north atlantic region copyright 2006 john wiley sons ltd

scalability of the mineral prospectivity modelling an orogenic gold case study from northern finland abstract one of the key objectives for mineral exploration is to map the most prospective areas for the selected deposit type at a regional scale subsequently narrowing these down to camp size target areas and finally to individual prospects that can be developed into economic mines exploration targeting at all scales is constrained by conceptual mineral system models and requires the integration and interpretation of a variety of geophysical geological and geochemical data geographic information system gis applications are commonly used to integrate spatially referenced data sets to produce mineral prospectivity maps in support of the mineral exploration targeting process a knowledge driven fuzzy logic method is used in this work for data integration and prospectivity modelling for orogenic gold deposits in northern finland the modelling workflow is done in a stepwise manner at three scales each step simulates the successive stage used in mineral exploration from selecting the most prospective belt scale domain to the camp size target area and individual prospects new higher resolution data sets are added at each stage as is typically the case in mineral exploration northern finland was selected as the test area due to the regional scale coverage of publicly available geoscientific data and its proven orogenic gold potential the regional scale prospectivity map outlines the central part of the paleoproterozoic central lapland greenstone belt clgb as the most prospective area for orogenic gold in northern finland the belt scale model of the clgb improves the resolution mapping of several camp sized high prospectivity target areas the camp scale model of one of these a past producing mining camp further narrows down the high prospectivity zones into prospect size targets three models have score area under curve auc values between 0 839 and 0 930 from the receiver operating characteristic roc method validation technique indicating that the models are robust the stepwise approach presented confirms that prospectivity mapping using the knowledge driven fuzzy logic method is a scalable flexible and relatively fast method which can be used for decision making at different stages of the exploration targeting process adding new data and rerunning the prospectivity model with the new data is fast and easy the most important conclusion from the study is that remodelling individual regional and camp scale domains separately is highly recommended for mapping the most prospective target areas even if the data sets used are the same

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

rapid hydrological changes during the holocene revealed by stable isotope records of lacustrine carbonates from lake igelsjon southern sweden a holocene sediment sequence from lake igelsjon south central sweden was studied by stable oxygen and carbon isotope analyses of different carbonate components the deposit which covers the time span from ca 11 500 cal bp to the present was laid down in a small kettle hole lake the hydrological balance of which is presently dominated by groundwater flow isotopic records obtained on bulk carbonates originating mainly from summer produced calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand likely reflecting pronounced hydrological variations corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts probably related to an extended calcification season the isotopic records were complemented by studies of modern isotope hydrology and our interpretations are based on a simplistic climate hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface volume ratio of the basin during the ice free season assumed periods of decreased lake volume in a relatively dry climate low lake level are characterised by enrichment in o 18 and c 13 resulting from increased evaporation inflow ratio and atmospheric equilibration respectively in clear contrast to this situation intervals of more humid climatic conditions give rise to increased lake volume high lake level possibly surface over flow and relatively depleted isotopic ratios relatively humid conditions which may correlate to a wide spread cooling event recorded by various proxies across the north atlantic region are indicated by distinct isotopic shifts at ca 8300 and 8000 cal bp bracketing a period of o 18 depletion the period between ca 8000 and 4000 cal bp was characterised by relatively dry and stable climatic conditions whereas the subsequent part of the holocene experienced a more humid and variable climate following marked and coherent depletions in o 18 and c 13 at ca 4000 cal bp c 2002 elsevier science ltd all rights reserved less

a new approach to calculating holocene winter precipitation by combining glacier equilibrium line altitudes and pine tree limits a case stud from hardangerjokulen central southern norway at hardangerjokulen central southern norway detailed knowledge of the number age and magnitude of holocene glacier fluctuations is used to reconstruct variations in equilibrium line altitude ela for the last 10 000 years present and past elas are based on an accumulation area ratio aar of 0 7 and are adjusted for land uplift a synchronous relationship between advanced glacier positions and the highest pine tree limits pinus sylvestris l is demonstrated for the early to mid holocene in southern scandinavia which indicates that warm summers were compensated for by high winter precipitation based on pine tree limit fluctuations as a measure of mean ablation season temperature holocene variations in winter precipitation at hardangerjokulen have been calculated by substitution in the close exponential relationship between mean ablation season temperature and winter precipitation at the ela of norwegian glaciers setting the winter precipitation during the period ad 1961 1990 at 100 mean values

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

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

vegetation responses to climatic variability in the swiss southern alps during the misox event at the early mid holocene transition sedimentary pollen charcoal and plant macrofossil analyses with high resolution and precision suggest a strong shift in vegetation composition during the early to mid holocene transition in the upper mountain belt at piano mire 1439m above sea level a s l ticino switzerland forests were dominated by abies alba during the early holocene prior to ca 8000cal a bp abrupt collapses of a alba at ca 7800 7400cal a bp enabled the expansion of the light demanding pioneer betula afterwards a alba populations regained their previous abundance in the forests within the dating uncertainties of our record we assume that a unique combination of wet and cold years between 8400 and 7500cal a bp led to repeated lethal disadvantages for abies our record of abies oscillations is in good biostratigraphic agreement with the record that has been used to define the misox cold event pian disignano 1540m a s l whichhas been previouslycorrelated withthe8200cal a bp event giventhe ageestimatesoftheabiescollapsesinourwell datedrecord ourresultssuggestthatadditionaleffortsare needed to understand the linkage between the misox and the 8200cal a bp event they imply a high sensitivity of mountain vegetation far below the tree line 800m to holocene climatic changes of about 28c in annual air temperature copyright 2010 john wiley sons ltd

ice core evidence of abrupt climate changes ice core records show that climate changes in the past have been large rapid and synchronous over broad areas extending into low latitudes with less variability over historical times these ice core records come from high mountain glaciers and the polar regions including small ice caps and the large ice sheets of greenland and antarctica

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

seismicity associated with the 1995 1996 eruptions of ruapehu volcano new zealand narrative and insights into physical processes abstract seismicity associated with the 1995 1996 eruptions of ruapehu reflects processes associated with the intrusion of magma to shallow depth in the volcanic edifice its subsequent eruption and changes in the volcanic plumbing system resulting from the eruptions the sequence consisted of two distinct periods of eruptive activity the first lasting from september 17 1995 until late october or early november 1995 and the second from june 16 1996 until late july 1996 immediately prior to and during the early stages of the 1995 eruptions seismicity was similar to that recorded at ruapehu during the previous 25 years with the exception of the occurrence between september 17 and 25 1995 of sub 1 hz tremor which is thought to represent magmatic intrusion in early october a new pattern of seismicity was established with the disappearance of the 2 hz tremor resonator source and a change to wideband 2 10 hz tremor and wideband volcanic earthquakes this change coincided with the ejection of the last vestiges of crater lake and the change in eruptive style from phreatomagmatic to magmatic seismicity associated with the 1996 eruptions was very similar to that which accompanied the later part of the 1995 activity implying the same eruption processes and that no significant changes had occurred in the volcanic plumbing system during the intervening period geochemical geodetic and seismic precursors to the 1995 eruptions were both minor and inconsistent highlighting the difficulty in forecasting these eruptions furthermore deep volcano tectonic earthquakes were extremely rare throughout the 1995 and 1996 eruptive sequences suggesting that stresses associated with magmatic intrusion were minor this most likely resulted from the existence of either an open or a ductile pathway from the deep magma source to the surface prior to the eruptions and because the volume of magma intruded and subsequently erupted was relatively small 3

unsupervised clustering and empirical fuzzy memberships for mineral prospectivity modelling abstract we propose to increase the role of empirical methods in mineral prospectivity modelling for two reasons 1 to make use of data more effectively and 2 to decrease the effect of subjectivity included in expert interpretation we present two approaches for using known mineral occurrences to define the relationship between observed or measured geoscientific parameters and the occurrence of mineralizations in the first approach we define the fuzzy memberships of each geoscientific parameter separately for fuzzy logic modelling our approach proves to be highly useful for investigating the quality of the data in addition to defining the membership transformation functions in our test case the data are somewhat scattered due to the inherent variability of ore forming environments and manual evaluation was required to guide the computations for the second approach we present a technique for delineating non prospective regions to be able to focus more detailed prospectivity modelling to potentially prospective regions our study not only highlights the advantages of using computational methods in prospectivity modelling but also emphasizes the important role of geological expertise in the modelling process

seismicity at white island volcano new zealand a revised classification and inferences about source mechanism the classification of earthquakes at white island volcano new zealand has been revised to address problems in existing classification schemes to better reflect new data and to try to focus more on source processes seismicity generated by the direct involvement of magmatic or hydrothermal fluids are referred to as volcanic and that generated by fault movement in response to stresses caused by those fluids regional stresses thermal effects and so on are referred to as volcano tectonic spasmodic bursts form a separate category as we have insufficient information to classify them as volcanic or volcano tectonic volcanic seismicity is divided into short duration long period volcanic earthquakes long duration volcanic earthquakes and harmonic and non harmonic volcanic tremor while volcano tectonic seismicity is divided into shallow and deep volcano tectonic earthquakes harmonic volcanic tremor is related to sub surface intrusive processes while non harmonic volcanic tremor originates close to active craters at shallow depth and usually occurs during eruptive activity short duration long period volcanic earthquakes come from a single source close to the active craters but originate deeper than non harmonic volcanic tremor and are not related to eruptive activity long duration volcanic earthquakes often accompany larger discrete eruptions the waveform of these events consists of an initial low frequency part from a deep source and a later cigar shaped part of mixed frequencies from a shallow crater source

late deglaciation of the central labrador coast and its implications for the age of glacial lakes naskaupi and mclean and for prehistory the age of the marine limit and associated deglaciation has been estimated from relative sea level curves for the hopedale and nain areas of the central labrador coast as approximately 7600 200 and 8500 200 yr ago respectively these ages indicate that the ice margin remained on the coast for up to 3000 yr longer than previously estimated because the central coast is due east of glacial lakes naskaupi and mclean the earliest the lakes could have formed was 8500 200 yr ago with their largest phases being fully established only after 7600 200 yr ago this suggests that the age of the lakes and associated deglaciation of the central labrador ungava region is younger by at least 1500 yr than previously estimated a late glacial marine based ice mass in ungava bay that dammed the lakes collapsed ca 7000 yr ago within this time frame therefore the glacial lakes only existed for 500 yr the persistence of the laurentide ice sheet margin on the central labrador coast until 7600 yr ago probably restricted the northward movement of early prehistoric people into northern labrador

biomass burning recorded in the gisp2 ice core a record from eastern canada combustion byproducts from biomass burning are preserved in annually stratified layers in the greenland ice sheet electrical conductivity ecm and ammonium records from the gisp2 ice core in central greenland have been used to develop a 6000 year record of biomass burning although there is some uncer tainty regarding the source area for the combustion byproducts it is likely that the majority of the material originates in eastern canada time periods of high biomass burning activity occurred in 0 150 bp 350 750 bp and 5000 to 6000 bp the period 1150 3250 bp is characterized by moderately elevated levels of biomass burning activity these periods are associated with drier conditions the 5000 to 6000 bp period of high biomass burning activity may also be related to forest successional sequences following the removal of the laurentide ice sheet this paper explains how ice cores can be used to develop records of biomass burning and offers suggestions for future studies

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

the age and origin of the younger dryas climate event in greenland ice cores 230th 234u and 14c dating of barbados corals has extended the calibration of 14c years b p to calendar years b p beyond the 9200 year tree ring series bard et al 1990 this now permits the conversion of 14c chronozones which delimit major climate shifts in western europe to calendar years the younger dryas chronozone defined as 11 000 to 10 000 14c years b p corresponds to 13 000 to 11 700 calendar years b p this calibration affects the interpretation of an intensely studied example of the younger dryas climate event the 18o anomaly between 1785 and 1793 m in dye 3 ice core the end of the 18o anomaly in dye 3 ice core has been dated by measurements of 14c in air bubbles andree et al 1984 1986 and by annual layer counting hammer et al 1986 the older 14c dates fall out of the range of the tree ring calibration series but can now be calibrated to calendar years using the barbados 230th 234u calibration the 14ccorrected age for the end of the 18o event is 10 300 400 calendar years b p compared to the annual layer counting age of 10 720 150 years b p thus the younger dryas event in the dye 3 ice core ends in the preboreal chronozone 11 700 to 10 000 calendar years b p and is not correlative with the end of the younger dryas event identified in pollen records marking european vegetation changes the end of the dye 3 18o event is however correlative with the end of meltwater pulse ib fairbanks 1989 marking a period of intense deglaciation with meltwater discharge rates exceeding 13 000 km yr

confidence intervals for age estimates and deposition times in late quaternary sediment sequences distribution sampling from sequences of radiocarbon ages is used to obtain confidence intervals for intermediate age estimates sediment deposition times and thence pollen deposition rates three

holocene climatic records from agassiz ice cap ellesmere island nwt canada four ice cores from the top of the agassiz ice cap and down a flow line have been variously analysed for 8 18o ecm solid conductivity and ice melt layer stratigraphy stratigraphic correlation

seasonal precipitation timing and ice core records this is a commentary on global circulation model experiments of moisture source changes in greenland urging caution in how they are applied because they have important implications for paleoclimate reconstruction from ice cores the work comes from preliminary find is of a ice core gisp2 of the authors the authors conclude that at present anomalies in greenland ice core records should not be interpreted solely in terms of source region variations the combined use of oxygen 18 d and ionic species in the new summit greenland cores should make it possible to answer empirically some of the questions raised by the gcm experiments as to the interpretation of oxygen 18 records in terms of temperature 4 refs 1 fig

changes in continental and sea salt atmospheric loadings in central greenland during the most recent deglaciation model based estimates by fitting a very simple atmospheric impurity model to high resolution data on ice accumulation and contaminant fluxes in the gisp2 ice core we have estimated changes in the atmospheric concentrations of soluble major ions insoluble particulates and 10 be during the transition from glacial to holocene conditions for many species changes in concentration in the ice typically overestimate atmospheric changes and changes in flux to the ice typically underestimate atmospheric changes because times of increased atmospheric contaminant loading are also times of reduced snowfall the model interpolates between the flux and concentration records by explicitly allowing for wet and dry deposition processes compared to the warm preboreal that followed we estimate that the atmosphere over greenland sampled by snow accumulated during the younger dry as cold event contained on average four seven times the insoluble particulates and nearly seven times the soluble calcium derived from continental sources and about three times the sea salt but only slightly more cosmogenic 10 be

age and structural constraints on the tectonic evolution of the paleoproterozoic central lapland granitoid complex in the fennoscandian shield abstract the paleoproterozoic central lapland granitoid complex clgc forms the northern core of the fennoscandian shield we present here new u pb age data and review the existing ones from plutonic and metasedimentary rocks of the clgc and integrate the results with the structural field observations to decipher the tectonic history of this region granitoids vary in age from 2 43 ga to 1 78 ga whereas metamorphic zircon overgrowths both in granites and metasedimentary rocks vary between 1 90 ga and 1 76 ga with several age peaks indicating prominent metamorphic pulses the almost continuous growth of metamorphic zircon domains favors that the central part of the clgc was near solidus for 100 120 ma a succession of five deformations and associated foliation producing events which were near orthogonal to each other have been identified east vergent thrusting and stacking d1 commenced at ca 1 92 ga and led to the onset of barrovian type metamorphism followed by a radical tectonic shift that yielded e w trending d2 structures exhumation at 1 88 1 87 ga caused decompression melting of thermally evolved thickened crust and led to the emplacement of large volumes of granites and triggering of buchan type metamorphic conditions ne sw collision d3 at the southwestern margin of fennoscandia heterogeneously overprinted the s3 fabric on d2 structures orogen parallel nnw sse buckling at 1 87 1 85 ga formed oroclines in the hot linear arc segments renewed nnw sse shortening d4 at 1 84 1 81 ga produced long wavelength folds and caused the formation of domal structure in the clgc the final 1 78 1 76 ga far field collision d5 in the west overprinted all the pre existing structures this complex multi directional tectonic scenario provoked the intermittent exhumation phases between different contraction events of the clgc

signatures of multiple mineralization processes in the archean orogenic gold deposit of the pampalo mine hattu schist belt eastern finland the hattu schist belt is an emerging gold producing ore district in the western part of the archean karelian province of the fennoscandian shield the belt consists of 2 76 to 2 70 ga tonalite granodiorite and leucogranite intruded into a mafic felsic epiclastic volcanic sequence of an only slightly older age complex and successive folding shearing and hydrothermal processes affected these rocks prior to the lower amphibolites facies peak metamorphism 550 50 c 3 5 kbar at ca 2 70 ga orogenic gold deposits are hosted by the highly strained zones that developed during the archean deformation of the belt however previous k ar and rb sr geochronological studies indicated that a second tectonothermal overprint affected the hattu schist belt between 1 7 and 1 8 ga during the svecofennian orogeny results of our field mineralogical textural and pb isotope studies suggest that ore deposition at pampalo was initiated by hydrothermal processes at the time of the emplacement of feldspar porphyry and tonalite intrusions and dikes at around 2 72 ga albitization and quartz tourmaline biotite muscovite veining characterize this hydrothermal activity the major stage of gold ore deposition can be confined to the subsequent development of high strain zones in an intermediate felsic tuffaceous unit mafic schist characterized by biotite carbonate pyrite alteration ar ar studies revealed the complete resetting of the ar ar system in muscovite and biotite due to the svecofennian orogeny with closure of the isotopic system at 1 81 ga results of pb isotope studies of hydrothermal k feldspar galena and altaite by laser ablation inductively coupled plasma mass spectrometry indicate that k feldspar alteration and remobilization of metals also took place during the svecofennian reactivation of high strain zones the petrographic manifestation of this process is the replacement of albite by hydrothermal k feldspar fluid inclusion data from hydrothermal k feldspar suggest that carbonic aqueous low salinity fluids interacted with the archean ore at 350 to 400 c and 1 8 to 2 4 kbar during the svecofennian overprint results of mass transfer calculations indicate that potassium gain correlates with increase of gold concentrations in the mafic schist and feldspar porphyry units therefore the svecofennian overprint locally also enhanced the grade of gold mineralization mostly along competency differences of the mafic schist and feldspar porphyry blocks dikes later percolation of relatively low temperature 300 c saline basin fluids in some fractures of the crystalline basement also left their pb isotope and fluid inclusion signatures on the mineralization while further modifying the composition of the ore occurrences of hydrothermal proto ores as well as fluid flow events along structures reactivated by overprinting orogenic processes are not exceptional features in archean orogenic gold provinces this study shows that the combination of in situ pb isotope studies of u poor alteration minerals and pb rich ore minerals together with evaluation of relationships between gold enrichment and hydrothermal alteration and fluid inclusion studies can be very useful in determining the significance and conditions of overprinting processes as well as their potential implications for genetic and exploration models

repeated syn and post orogenic gold mineralization events between 1 92 and 1 76 ga along the kiistala shear zone in the central lapland greenstone belt northern finland abstract the central lapland greenstone belt clgb is well endowed with orogenic gold deposits along major shear zones and structural lineaments in the northern part of the belt the kiistala shear zone kisz hosts the suurikuusikko gold deposit kittila mine currently the largest gold producer in europe the iso kuotko deposit is located 10 km to the north of suurikuusikko along the same shear zone gold mineralization at iso kuotko formed in two major stages an early stage refractory gold mineralization with auriferous arsenopyrite with similarities to the ore at suurikuusikko and a late main stage mineralization with free gold in carbonate quartz veins with abundant pyrrhotite native bismuth and other sulphide minerals this latter ore is absent at suurikuusikko based on u pb dating as well as re os and pb isotope systematics of rock forming and hydrothermal minerals we evaluate the relationships between tectonic evolution and formation of gold deposits throughout the late palaeoproterozoic in the northern part of the clgb results from in situ u pb dating of zircon and petrographically well constrained hydrothermal monazite and xenotime by la icpms and model age calculations using re os isotopic data for arsenopyrite and in situ pb isotope data for galena from the iso kuotko deposit provide evidence for multiple episodes of hydrothermal activity along the kisz data suggest coincident felsic magmatism and structurally controlled fluid flow events during wrench fault dominated n s shearing associated with early micro continent accretion ushering in the svecofennian orogeny this includes the formation of refractory gold ores at suurikuusikko 1916 19 ma and iso kuotko 1868 15 ma subordinate barren veining took place at 1830 ma during transient extension between the accretion and final collision stage xenotime in late stage veins with visible gold at iso kuotko yield u pb ages between 1761 9 and 1770 7 ma this time interval is concurrent with widespread granitoid emplacement at the close of the svecofennian orogeny disturbance of the re os system in the early auriferous arsenopyrite can be connected to the late stage mineralizing processes pb isotope data suggest a mixed mantle and lower crust origin for fluids in the post orogenic hydrothermal system in situ u pb dating in polished thin sections in tandem with electron microprobe analyses of mineral compositions and detailed textural observations highlights the utility of xenotime and monazite as robust geochronometers capable of recording repeated hydrothermal events in paleoproterozoic orogenic systems results provide precise temporal constraints for orogenic gold mineralization and vital information to refine the tectonic evolution of the central lapland greenstone belt

4d seismic tomography of nevado del ruiz volcano colombia 2000 2016 abstract to track and analyze temporal changes in the volcanic system of nevado del ruiz colombia repeated three dimensional seismic tomography 4d seismic tomography for p and s wave velocities vp and vs respectively during the period 2000 2016 was performed p and s wave arrival time data were classified on the basis of changes in volcanic activity into five time periods 2000 2006 2007 2009 2010 2012 2013 2014 and 2015 2016 our results showed clear changes in 2013 2014 and 2015 2016 periods of heightened volcanic activity after an episode of unrest in 2010 regions of low vp low vs and high vp vs 1 9 were found beneath and northwest of the active crater at depths of 2 3 km below sea level the enhancement of those anomalies suggests that a new pulse of magma arrived in the volcanic system at that time regions with low vp vs values 1 3 1 6 in the upper part of the volcano at depths from 3 to 2 km are interpreted as the result of vapor accumulation within highly fractured zones of the hydrothermal system the ratios of fractional change of vp and vs in 2015 2016 suggest that partial melting zones were located beneath the active crater at depths of 2 to 0 km our results show that the volcanic system of nevado del ruiz has experienced changes associated with the input of new magma which ascended and interacted with preexisting magma bodies and led to the recent emplacement of a small dome at the bottom of the active crater we combined our results and evidence from previous studies to propose a model of the nevado del ruiz plumbing system from 1985 to 2016

ni cu pge deposits in finland geology and exploration potential abstract several types of nickel sulphide deposits occur in finland some of them are also important sources of cu co and pge the main deposit types are related to archaean and palaeoproterozoic mafic to ultramafic rocks palaeoproterozoic metamorphosed black shales of the talvivaara type or the ultramafic and metasomatic calc silicate rocks of the ophiolitic outokumpu association several komatiite hosted ni cu pge deposits have been discovered in the archaean and paleoproterozoic greenstone belts in northern and eastern finland but only one has been briefly mined in 1989 many 2 44 ga palaeoproterozoic mafic ultramafic layered intrusions in finland host contact type pge ni cu deposits and significant reef type pge deposits typically the ni resources are of low grade but large tonnage the mafic ultramafic magmatism at ca 2 06 ga produced significant ni cu pge resources in the central lapland greenstone belt including the kevitsa and sakatti deposits the svecofennian domain in central and southern finland contains hundreds of small ca 1 88 ga mafic ultramafic orogenic intrusions many of these host nickel mineralization nickel exploration potential was evaluated in general based on identification of critical factors within a mineral system framework and a quantitative assessment of the potential occurrence of undiscovered nickel resources the mgo content of the parental magma was estimated for 28 deposits 6 komatiite hosted occurrences and 22 svecofennian orogenic intrusions the estimated mgo content of the parental magmas for the selected deposits varies from around 7 to 15 in basaltic to komatiitic basalt systems and up to 30 in more magnesian komatiitic systems the ni cu value varies mostly between 0 7 and 12 correlating in general positively with the mgo content of the magma exceptionally high or low ni cu values in some deposits may result from for example copper loss during post magmatic processes serpentinization and or metamorphism or part of the sulphide ore zoned by the ni cu value still being unknown recent advances in understanding of komatiites in finland indicates high exploration potential for nickel within the paleoproterozoic komatiitic formations which typically are also significantly enriched in cu and pge however the quantitative assessment of undiscovered nickel resources in finland suggests that the contact type ni cu pge deposits hosted by 2 44 ga mafic ultramafic layered intrusions in northern finland have the greatest potential for hosting undiscovered resources among the assessed nickel deposit types these occur within restricted areas resulting in a high deposit density finally considerable nickel resources might exist in undiscovered talvivaara kevitsa or sakatti type deposits these deposit types should be assessed as soon as more geological information becomes available