dinoflagellate cyst assemblages as tracers of sea surface conditions in the northern north atlantic arctic and sub arctic seas the new n 677 data base and its application for quantitative palaeoceanographic reconstruction the distribution of dinoflagellate cyst dinocyst assemblages in surface sediment samples from 677 sites of the northern north atlantic arctic and sub arctic seas is discussed with emphasis on the relationships with sea surface parameters including sea ice cover salinity and temperature of the coldest and warmest months difficulties in developing a circum arctic data base include the morphological variation within taxa e g operculodinium centrocarpum islandinium cezare and polykrikos sp which probably relate to phenotypic adaptations to cold and or low salinity environments sparse hydrographical data together with large interannual variations of temperature and salinity in surface waters of arctic seas constitute additional limitations nevertheless the use of the best analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea surface conditions at the scale of the northern north atlantic and the arctic domain the error of prediction calculated from modern assemblages is 1 3 ca nd 1 8 c for the temperature of february and august respectively 1 8 for the salinity and 1 5 months yr 1 for the sea ice cover application to late quaternary sequences from the western and eastern subpolar north atlantic labrador sea and barents sea provide reconstructions compatible with those obtained using the previous dinocyst data base n 371 which mainly included modern data from the northern north atlantic copyright 2001 john wiley sons ltd journal of quaternary science

les concentrations filoniennes a tungstene etain du massif granitique des zaer maroc central mineralisations et phases fluides associees le gisement de tungstene etain de sokhret allal est situe dans la partie meridionale du granite a deux micas des zaer maroc central la mineralisation est supportee par un faisceau subparallele de veines quartzeuses de direction n 100 e 110 e les filons sont associes spatialement a des bandes d episyenites feldspathiques qui semblent avoir guide leur mise en place les successions mineralogiques ont ete divisees en trois stades i stade a oxyde ii stade intermediaire iii stade a sulfures les inclusions fluides ont ete etudiees dans le quartz massif du stade i par microthermometrie et microsonde raman il se caracterise par des fluides evoluant depuis des vapeurs carboniques 75 a 80 moles h2o 17 a 12 moles co2 0 5 moles ch4 5 a 3 moles n2 2 5 a 2 moles eq nacl t 450 500 c p 800 a 850 bars jusqu a des fluides aqueux 98 a 99 moles h2o 2 a 1 moles eq nacl traces de co2 ch4 n2 t 300 c p 300 bars cette evolution s effectue par le melange de fluides carboniques precoces avec une phase fluide essentiellement aqueuse ce processus de dilution favoriserait le depot des mineralisations les fluides carboniques precoces semblent jouer un role important dans le transport du tungstene

major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

living coccolithophore communities in the norwegian greenland sea and their record in sediments abstract investigation of epipelagic coccolithophore communities along a transect from the voring plateau off norway to scoresbysund east greenland and comparison with coccolith assemblages in underlying surface sediments reveal that sedimentation of coccoliths is dependent on the following factors 1 composition of the coccolithophore communities and their bloom phases 2 grazing and selective destruction by zooplanktonic organisms 3 type of vertical flux in fecal pellets and 4 varying carbonate dissolution in different water masses dissolution increases towards the boundaries of carbonate sedimentation as a result the original composition of the living communities becomes increasingly obscured in the impoverished taphocoenoses however differential resistance to dissolution of the two primary calcareous nannoplankton species emiliana huxleyi and coccolithus pelagicus is such that occurrence and ratio of the two species in surface sediments reflect the various water masses in the norwegian greenland sea

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

metallogenesis at the carris w mo sn deposit geres portugal constraints from fluid inclusions mineral geochemistry re os and he ar isotopes abstract the carris orebody consists of two partially exploited w mo sn quartz veins formed during successive shear stages and multipulse fluid fillings they cut the variscan post d3 geres i type granite the most important ore minerals are wolframite scheelite molybdenite and cassiterite there are two generations of wolframite the earlier generation of wolframite is rare and has the highest wo4mn content 91 mol and the most common wolframite contains 26 57 mol wo4mn re os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 1 2 ma and 280 3 1 2 ma respectively which are in very good agreement with the previous id tims u pb zircon age for the carris granite 280 5 ma 3he 4he ratio of pyrite ranging between 0 73 and 2 71 ra 1 ra 1 39 10 6 and high 3he 36ar 0 8 5 10 3 indicate a mixture of a crustal radiogenic helium fluid with a mantle derived fluid the fluid inclusion studies on quartz intergrown with wolframite and scheelite beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit the first was a low to medium salinity aqueous carbonic fluid co2 between 4 and 14 mol with less than 1 95 mol n2 which was only found in quartz associated with wolframite the other was a low salinity aqueous fluid found in all the four minerals the homogenization temperatures indicate minimum entrapment temperatures of 226 310 c average 280 c for the h2o co2 n2 nacl fluid and average temperatures of 266 c for scheelite and 242 c 190 c and 160 c for the last generations of beryl fluorite and quartz respectively it was estimated that wolframite was deposited 7 km depth assuming a lithostatic pressure probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event precipitation of scheelite and sulphides took place later at the same depth but under a hydrostatic or suprahydrostatic pressure regime and probably caused by mixing between the magmatic hydrothermal fluid and meteoric waters that deeply penetrated the basement during post variscan decompression

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

automated seismic event location by waveform coherence analysis summary automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring since microseismic records are generally characterized bylowsignal to noiseratio automated locationmethods arerequested to be noise robust and sufficiently accurate most of the standard automated location routines arebasedontheautomatedpicking identificationandassociationofthefirstarrivalsofpands waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases although current methods can accurately pick p onsets the automatic picking of the s onset is still problematic especially when the p coda overlaps the s wave onset in this paper we propose a picking free earthquake location method based on the use of the short term average long term average sta lta traces at different stations as observed data for the p phases we use the sta lta traces of the vertical energy function whereas for the s phases we use the sta lta traces of a second characteristic function which is obtained using the principal component analysis technique in order to locate the seismic event we scan the space of possible hypocentral locations and origin times and stack the sta lta traces along the theoretical arrival time surface for both p and s phases iterating this procedure on a 3 d grid we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial coordinates of the seismic event a pilot application was performed in the campania lucania region southern italy using a seismic network irpinia seismic network with an aperture of about 150km we located 196 crustal earthquakes depth 20km with magnitude range 1 1 ml 2 7 a subset of these locations were compared with accurate manual locations refined by using a double difference technique our results indicate a good agreement with manual locations moreover our method is noise robust and performs better than classical location methods based on the automatic picking of the p and s waves first arrivals

textural evidence for quartz and feldspar dissolution as a mechanism of formation for maggs pipe zaaiplaats tin mine south africa shallowly plunging and branching pipe systems in lease and bobbejaankop granite at the zaaiplaats mine are host to major tin mineralization detailed textural study of maggs pipe indicates that dissolution of the granite was a major process in the formation of open space which provided permeability for the passage of hydrothermal fluids and sites for the precipitation of ore and gangue minerals the pipe formation process initiates with the dissolution of granite quartz and subsequently extends to feldspar dissolution particularly in the central portion of maggs pipe spaces created by mineral dissolution are filled by hydrothermal phases and the relict feldspar matrix becomes progressively more altered toward the centre of the pipe the distribution of alteration and infill minerals defines a zoning pattern which from the outer margin to the central core includes calcite quartz chlorite cassiterite albite fluorite and synchisite calcite zones it is postulated that quartz and feldspar dissolution resulted from interaction between the granite and hydrothermal fluids containing alkali chloride fluoride or carbonate complexes which had separated from the granite magma during crystallization preliminary observations on several other pipes at zaaiplaats indicate that quartz and feldspar dissolution was a major procress in forming the pipe systems

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

time reversal imaging of seismic sources and application to the great sumatra earthquake the increasing power of computers and numerical methods like spectral element methods allows continuously improving modelization of the propagation of seismic waves in heterogeneous media and the development of new applications in particular time reversal in the three dimensional earth the concept of time reversal hereafter referred to as tr was previously successfully applied for acoustic waves in many fields like medical imaging underwater acoustics and non destructive testing we present here the first application at the global scale of tr with associated reverse movies of seismic waves propagation by sending back long period time reversed seismograms we show that seismic wave energy is refocused at the right location and the right time of the earthquake when tr is applied to the sumatra andaman earthquake 26 dec 2004 the migration of the rupture from the south towards the north is retrieved therefore tr is potentially interesting for constraining the spatio temporal history of complex earthquakes

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

characterization of multiple fluid granite interaction processes in the episyenites of avila bejar central iberian massif spain episyenites are small granite hosted pipe like masses characterized by hydrothermal alteration and the major loss of silica compared with the host granites such bodies are fairly common in the hercynian granites of western europe this study deals with late hercynian amphibole bearing and biotite granodiorites monzogranites from the central iberian massif using petrological geochemical major oxides trace elements and ree and isotopic o h data to constrain the paragenesis of alteration the apparent changes in bulk composition and the sources and conditions of fluids involved in fluid rock interactions episyenitization leads to reduction of quartz content albitized plagioclases and chloritized ferromagnesian phases and the process results in increasingly ordered alkali feldspars there are noticeable variations in whole rock na20 k2o mgo cao rb and sr contents with sio2 in some cases behaving differently depending on whether the episyenite is hosted in amphibole granite or biotite granite the lree y zr and nb have also been modified in those syenites associated with amphibole bearing granites this being attributed to destabilization of accessory minerals and recrystallization of new stable mineral assemblages the process is complex and two generations of chlorite early high fe and late low fe are observed whole rocks and mineral separates were studied for o and h isotopes the data rule out meteoric fluids as the cause of syenitization and the later resiliciftcation of some and suggest that at least two different fluids were involved in generating the syenites the first is interpreted to be a high temperature 300 450 c late magmatic deuteric fluid as recorded by feldspar o isotope data later a different fluid with 18o 1 4 and d 13 isotopically indistinguishable from seawater on a deglaciated earth produced the chlorite secondary quartz and minor epidote such a fluid was only available for a short period since feldspars did not re equilibrate the fault systems occupied by the episyenites provided suitable pathways for fluids of both shallow and deep origins over a long term during the carboniferous

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

fluctuation in porosity and fluid pressure during hydrothermal events textural evidence in the emuford district australia abstract the upper paleozoic granites of the emu suite north queensland show varying degrees of alteration the petrographic and microstructural survey of albite rich zones reveals the spatial overprint of hydrothermal events which are more correlated with changes in physical conditions permeability fluid pressure and flow regime rather than with chemical variations of the percolating fluids the sequence of alteration events chronologically comprises 1 in situ substitution of primary microline to chessboard albite 2 dissolution of magmatic quartz resulting in the formation of interconnected vugs 3 formation of concentric cracks around some vugs 4 infilling of vugs and 5 development of a dense system of closely spaced sheeted veinlets by a crack seal process the first two stages indicate an increase of the global permeability of the albite zones chemically induced porosity whereas the vug and vein filling stages indicate the reverse resulting in an increase of fluid pressure from nearly hydrostatic to nearly lithostatic values mechanically induced porosity this contrast is discussed from micro and mesostructural arguments and from results of a fluid inclusion investigation it is explained by the progressive focusing of the circulating fluids via grain boundaries then vugs and through tapping by late stage microfracturing

dinocyst based reconstructions of sea ice cover concentration during the holocene in the arctic ocean the northern north atlantic ocean and its adjacent seas abstract sea ice cover extent expressed in terms of mean annual concentration was reconstructed from the application of the modern analogue technique to dinocyst assemblages the use of an updated database which includes 1492 sites and 66 taxa yields sea ice concentration estimates with an accuracy of 1 1 10 holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern north atlantic and arctic seas in the canadian arctic the results show high sea ice concentration 7 10 with little variations throughout the interval in contrast in arctic areas such as the chukchi sea and the barents sea the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs eastern arctic other records show tenuous changes with some regionalism either in trends or sea ice cover variability during the mid holocene and notably at 6 0 5 ka minimum sea ice concentration is recorded in the eastern fram strait northern baffin bay and labrador sea however this minimum cannot be extrapolated at the scale of the arctic and circum arctic the comparison of recent observations and reconstructions suggests larger variations in the arctic sea ice cover during the last decades than throughout the holocene

reverse modelling for seismic event characterization summary the localization of seismic events is of utmost importance in seismology and exploration current techniques rely on the fact that the recorded event is detectable at most of the stations of a seismic network weak events not visible in the individual seismogram of the network are missed out we present an approach where no picking of events in the seismograms of the recording network is required the observed wavefield of the network is reversed in time and then considered as the boundary value for the reverse modelling assuming the correct velocity model the reversely modelled wavefield focuses on the hypocentre of the seismic event the origin time of the event is given by the time where maximum focussing is observed the spatial extent of the focus resembles the resolution power of the recorded wavefield and the acquisition this automatically provides the uncertainty in the localization with respect to the bandwidth of the recorded data the method is particularly useful for the upcoming large passive networks since no picking is required it has great potential for localizing very weak events not detectable in the individual seismogram since the reverse modelling sums the energy of all recorded traces and therefore enhances the signal to noise ratio similar to stacking in seismic exploration the method is demonstrated by 2 d and 3 d numerical case studies which show the potential of the technique events with a s n ratio smaller than 1 where the events cannot be identified in the individual seismogram of the network are localized very well by the method

reconstruction of sea surface conditions at middle to high latitudes of the northern hemisphere during the last glacial maximum lgm based on dinoflagellate cyst assemblages abstract a new calibration database of census counts of organic walled dinoflagellate cyst dinocyst assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the northern hemisphere after standardisation of taxonomy and laboratory procedures the database comprises 940 reference data points from the north atlantic arctic and north pacific oceans and their adjacent seas including the mediterranean sea as well as epicontinental environments such as the estuary and gulf of st lawrence the bering sea and the hudson bay the relative abundance of taxa was analysed to describe the distribution of assemblages the best analogue technique was used for the reconstruction of last glacial maximum lgm sea surface temperature and salinity during summer and winter in addition to sea ice cover extent at sites from the north atlantic n 63 mediterranean sea n 1 and eastern north pacific n 1 three of the north atlantic cores from the continental margin of eastern canada revealed a barren lgm interval probably because of quasi permanent sea ice six other cores from the greenland and norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation at the remaining sites n 54 relatively close modern analogues were found for most lgm samples which allowed reconstructions the new lgm results are consistent with previous reconstructions based on dinocyst data which show much cooler conditions than at present along the continental margins of canada and europe but sharp gradients of increasing temperature offshore the results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea ice cover whereas relatively warm conditions may have prevailed offshore in summer from these data we hypothesise low thermal inertia in a shallow and low density surface water layer

albitization in the antimony line murchison greenstone belt kaapvaal craton a geochemical and geochronological investigation abstract the 3 09 2 97 ga murchison greenstone belt is one of several archean volcano sedimentary belts within the kaapvaal craton in southern africa among the diverse ore deposits found within the belt a set of sb au deposits are located in a major quartz carbonate altered brittle ductile structure known as the antimony line the antimony line is thus clearly related to hydrothermal fluid circulation in this study we focus on albitites that run along the antimony line petrological and geochemical investigations indicate that albitization developed at the expense of a granodioritic protoliths under high fluid rock ratios and also that sb enrichment was concomitant with albitization oxygen isotopes on albitites point to a crustal origin for the hydrothermal fluid responsible for the albitization process geochronology on zircon and hydrothermal monazite identifies a 2 97 2 92 ga magmatic crystallization event disconnected from a ca 2 8 ga hydrothermal alteration and a potentially younger event around 2 0 ga these data highlight a likely magmatic related primary enrichment at 2 97 2 92 ga followed by a secondary metamorphic related mobilization event around 2 8 ga leading to a sb enrichment in the albitites and a last episode of alteration around 2 0 ga

role de la deformation du granite dans la genese des episyenites feldspathiques des massifs de lovios geres galice et des zaer maroc central l etude de la deformation du granite dans les zones encaissant les bandes d episyenites feldspathiques de deux massifs hercyniens a permis de degager un modele tectonique rendant compte des caracteristiques structurales de celles ci les bandes d episyenites feldspathiques se forment lors des phases ultimes de la mise en place des intrusions granitiques sous l effet d un champ de contrainte local susceptible d engendrer des surpressions fluides aboutissant a une fracturation de type hydraulique la genese des mineralisations filoniennes intragranitiques a tungstene etain associees spatialement a ces episyenites doit etre rapportee a des evenements tectoniques et a des circulations fluides posterieures

palaeoproductivity and post depositional aerobic organic matter decay reflected by dinoflagellate cyst assemblages of the eastern mediterranean s1 sapropel abstract in the reconstruction of bioproductivity in surface waters the extent to which a proxy has been diagenetically altered is often a matter of debate here we investigate how organic and calcareous walled dinoflagellate cysts can be used for separately estimating bioproductivity and oxygen related diagenesis this is achieved by studying the cyst content of the most recent eastern mediterranean sapropel s1 that is thought to have been deposited under conditions of increased primary production in surface waters and possible anoxia in the bottom waters based on chemical evidence it has been shown that the visible sapropelic layer represents only the residual lower part of what was initially a much thicker sapropel as a result of post depositional decay of organic matter related to oxygen penetration into the sediments the effect of aerobic organic matter decay on the cyst associations is studied through the comparison of the unaffected lower part of the initial sapropel and the oxidised upper part comparing the unaffected sapropelic sediments with pre and post sapropelic material gives insight into the relationship between fossil cysts assemblages and palaeoproductivity impagidinium aculeatum impagidinium patulum operculodinium israelianum polysphaeridium zoharyi and probably impagidinium spp impagidinium paradoxum and nematosphaeropsis labyrinthus are very resistant against aerobic decay and their accumulation rates appear to be primarily related to productivity in surface waters protoperidinium and echinidinium species on the other hand are shown to be very sensitive and can be used to recognise oxygen related decay the calcareous walled dinoflagellate cysts seem to be unaffected by oxic organic matter decay in mediterranean sediments

a highly unstable holocene climate in the subpolar north atlantic evidence from diatoms a composite record lo09 14 of three sediment cores from the subpolar north atlantic reykjanes ridge was investigated in order to assess surface ocean variability during the last 11 kyr the core site is today partly under the influence of the irminger current ic a branch of the north atlantic drift continuing northwestward around iceland however it is also proximal to the sub arctic front saf that may cause extra dynamic hydrographic conditions we used statistical methods applied to the fossil assemblages of diatoms to reconstruct quantitative sea surface temperatures ssts our investigations give evidence for different regional signatures of holocene surface oceanographic changes in the north atlantic core lo09 14 reveal relatively low and highly variable ssts during the early holocene indicating a weak ic and increased advection of subpolar water over the site a mid holocene thermal optimum with a strong ic occurs from 7 5 to 5 kyr and is followed by cooler and more stable late holocene surface conditions several intervals throughout the holocene are dominated by the diatom species rhizosolenia borealis which we suggest indicates proximity to a strongly defined convergence front most likely the saf several coolings reflecting southeastward advection of cold and ice bearing waters occur at 10 4 9 8 8 3 7 9 6 4 4 7 4 3 and 2 8 kyr the cooling events recorded in the lo09 14 ssts correlate well with both other surface records from the area and the nadw reductions observed at odp site 980 indicating a surface deepwater linkage through the holocene

holocene sea surface conditions in the western north atlantic spatial and temporal heterogeneities 1 holocene records of sea surface conditions in the western nordic seas were obtained from quantitative reconstructions based on dinoflagellate cyst assemblages two sediment cores from the east greenland and the north iceland shelves provide a detailed account of the long and short term dynamics of the opposing flows of arctic versus atlantic waters both marker species and quantitative reconstructions depict an overall trend toward warmer winter temperatures saltier surface waters and decreased sea ice extent the latter is supported by a close relationship between relative abundances of an atlantic dinocyst species nematosphaeropsis labyrinthus and ice rafted debris ird records we propose that the late holocene increased ird delivery in the denmark strait region was primarily induced by a combination of less extensive sea ice cover under increased atlantic water inflow and sustained iceberg calving tied to the readvance of the greenland ice sheet our records thus suggest diminishing polar water supplies throughout the holocene although the timing of regime changes differs between the western and eastern sides of the denmark strait finally comparison of our records with a core from southern greenland points to very heterogeneous sea surface conditions in the western north atlantic which could be explained by the decoupled dynamics of the two irminger current branches similarities between the southern greenland marine record and a continental record nearby suggest a close coupling with atmospheric processes reminiscent of a north atlantic oscillation like climate pattern

common reflection surface stack image and attributes the common reflection surface stack provides a zero offset simulation from seismic multicoverage reflection data whereas conventional reflection imaging methods e g the nmo dip moveout stack or prestack migration require a sufficiently accurate macrovelocity model to yield appropriate results the common reflection surface crs stack does not depend on a macrovelocity model we apply the crs stack to a 2 d synthetic seismic multicoverage dataset we show that it not only provides a high quality simulated zero offset section but also three important kinematic wavefield attribute sections which can be used to derive the 2 d macrovelocity model we compare the multicoverage data derived attributes with the model derived attributes computed by forward modeling we thus confirm the validity of the theory and of the data derived attributes for 2 d acquisition the crs stack leads to a stacking surface depending on three search parameters the optimum stacking surface needs to be determined for each point

evidence from driftwood records for century to millennial scale variations of the high latitude atmospheric circulation during the holocene different holocene sea ice drift patterns in the arctic ocean have been hypothesized by dyke et al from radiometric analyses of driftwood collected in the canadian arctic archipelago a dynamic thermodynamic sea ice model is used to simulate the modes of arctic ocean ice circulation for different atmospheric forcings and hence determine the atmospheric circulations which may have accounted for the inferred ice drift patterns the model is forced with the monthly mean wind stresses from 1968 a year with very large ice export and 1984 very low ice export two years with drastically different winter sea level pressure patterns and with different phases of the nao index the simulations show that for the 1968 wind stresses a weak beaufort gyre with a broad transpolar drift stream tds shifted to the east are produced leading to a large ice export from the arctic similarly the 1984 wind stresses lead to an expanded beaufort gyre with a weak tds shifted to the west and a low ice export these results correspond to the patterns inferred by dyke et al based on the simulations the driftwood record suggests that for centuries to millennia during the holocene the high latitude average atmospheric circulation may have resembled that of 1968 1984 and today s climatology with abrupt changes from one state to the other

constraints regarding gold deposition in episyenites the permian episyenites associated with the villalcampo shear zone central western spain the villalcampo shear zone around 307 ma shows second order shear zones 420 390 c with gold ore bodies hosted by episyenites which consist of albite episyenites albitites and albite kfs episyenites both types with different contents in sulphides and gold mass transfer modelling supports higher fluid rock ratios in albitites than in albite kfs episyenites the study of worldwide barren and gold bearing episyenites reveals abundant sulphides in the latter as a distinguishing feature the electrochemical processes at the surface of sulphide would have enhanced gold precipitation sulphides working as a gold trap a complex fluid history occurred in gold ore bodies hosted by episyenites although in essence it was similar to quartz sealed faults hosting late variscan gold deposits a an early fluid equilibrated with the metamorphic pile with sulphides or with a metamorphic fingerprint resulted in a sulphide deposition and b a shallower fluid reservoir of meteoric origin provided gold deposition in contrast to earlier claims regarding episyenite fluid flow a down temperature and probably an upwards fluid flow are proposed for the episyenitization process also in keeping with the early stages of fluid flow in quartz sealed faults fluid inclusions in albite confirm that the striking coupled quartz leaching albitization processes occurred around 400 c and 60 mpa crosscutting the retrograde solubility field of silica and yielding a vuggy rock initially albite and later quartz and sulphide filled the vugs from the same or a very similar fluid uraninites deposited during the albitization and probably the onset of the sulphide deposition afforded the same age 270 12 ma as other spanish episyenites confirming a synchronous and a regional scale process and ruling out a relationship with the granite cooling history 324 11 ma

comparison of coccolith and dinocyst assemblages in the northern north atlantic how well do they relate with surface hydrography abstract coccolith and dinoflagellate cyst or dinocyst population counts were compiled from existing surface sediment databases as well as new counts in order to establish an 87 sample database for which assemblages of both microfossil groups are known this database allowed a direct comparison of the distribution of coccolith and dinocyst assemblages in the subtropical to subpolar north atlantic in addition the relationship between these assemblages and sea surface environmental parameters was addressed in order to identify possible differences in the ecology of the two plankton groups the comparison highlights an excellent correspondence between dinocyst assemblages coccolith assemblages and the distribution of the surface water masses represented in our database notably in the subtropical and temperate domains in the subpolar domain coccolith assemblages are much less diversified than dinocyst assemblages in terms of species as a result the discrimination between the subpolar water masses based on coccolith assemblages is not as clear as in the subtropical temperate regions whereas dinocyst assemblages show a distribution pattern closely related with surface hydrography canonical correspondence analyses performed on coccolith and dinocyst assemblages show that sea surface temperature is the primary environmental parameter influencing the distribution of both groups dinocyst assemblages also seem to respond to the distance to the coast and may therefore bring additional information compared with coccolith assemblages other significant environmental factors include sea surface salinity and productivity but their relative importance changes depending on the inclusion of samples from extreme environmental settings in the database results suggest that the complexity of the interrelationships between the various environmental parameters makes it difficult to adequately bring to light all the different environments and their associated coccolith dinocyst assemblages in multivariate analyses however each surface water mass represented in our database is characterized by a unique combination of environmental parameters as well as by distinct associations of coccolith and dinocyst assemblages thus showing that these microfossil groups closely relate to sea surface conditions including temperature salinity and productivity

apparent long term cooling of the sea surface in the northeast atlantic and mediterranean during the holocene reconstructions of upper ocean temperature t during the holocene 10 0 ka b p were established using the alkenone method from seven high accumulation sediment cores raised from the northeast atlantic and the mediterranean sea 361n 751n all these paleo t records document an apparent long term cooling during the last 10 kyr in records with indication of a constant trend the apparent cooling ranges from 0 27 to 0 151c kyr 1 records with indication of time variable trend show peak to peak amplitudes in apparent temperatures of 1 2 2 91c a principal component analysis shows that there is one factor which accounts for a very large fraction 67 of the total variance in the biomarker paleo t records and which dominates these records over other potential secondary influences two possible contributions are 1 a widespread surface cooling which may be associated with the transition fromthe hypsithermal interval b9 5 7 ka b p to the neoglaciation b5 7 0 ka b p and 2 a change in the seasonal timing and or duration of the growth period of alkenone producers prymnesiophyte algae the first contribution is consistent with many climate proxy records from the northeast atlantic area and with climate model simulations including milankovitch forcing the second contribution is consistent with the divergence between biomarker and summer faunal paleo t fromearly to late holocene observed in two cores further work is necessary and in particular the apparent discordance between biomarker and faunal t records for the relative stable holocene period must be understood to better constrain the climatic and ecological contributions to the apparent cooling observed in the former records r 2002 elsevier science ltd all rights reserved

the role of passive microseismic monitoring in the instrumented oil field with the current industry trend toward instrumented oil fields and smart well completions the permanent deployment of geophones or other acoustic sensors to complement standard engineering gauges is being promoted as a way to map reservoir dynamics the biggest push is from the time lapse seismic practitioners although the deployment of permanent seismic instrumentation is also potentially an ideal route to monitor passive seismicity

le gisement de tungstene de xihuashan sud jiangxi chine relations granites alterations deuteriques hydrothermales mineralisations le gisement de tungstene de xihuashan sud jiangxi chine est situe sur la bordure d un stock granitique forme de 4 unites intrusives chronologiquement infa sup5 inf2b sup5 inf2c sup5 inf2e sup5 le gite est encaisse dans inf2a sup5 et in2b sup5 don le contact est jalonne par un stockscheider et par la presence sporadique d un facies granitique a grain fin inf2b sup5 les zones d episyenites feldspathiques localisees principalement dans inf2b sup5 correspondent a des zones d alterations du granite elles caracterisent l activite des fluides en relai d actions mecaniques prealables un drainage de liquides residuels sous controle structural le gisement filonien de xihuashan district minier de dayu est du type quartz a wolframite dominante et il est principalement developpe dans inf2b sup5 la densite du systeme filonien et l importance de la mineralisation dans inf2b sup5 s explique par l effet de carapace joue par inf2a sup5 inf2b sup5 et le stockscheider le gite comprend 615 filons a teneur economique teneur moyenne 1 08 en wo3 caracterises par quatre stades de mineralisations un zoning vertical inverse est generalement observe

holocene sea surface conditions in the north atlantic contrasted trends and regimes in the western and eastern sectors labrador sea vs iceland basin abstract two sediment cores from the labrador sea and one from the iceland basin were analysed in order to compare holocene sea surface conditions across the northern north atlantic 18o measurements on meso and epi planktonic foraminifera neogloboquadrina pachyderma left coiling and globigerina bulloides along with sea surface condition reconstructions using transfer functions based on dinoflagellate cyst assemblages were used to document thermohaline properties of the upper water column at the labrador sea sites a decreasing trend in sea surface temperature following an early holocene maximum is observed at the iceland basin site a hiatus between 13 and 8 ka bp prevents us from documenting the entire holocene but a stable to slightly decreasing trend is observed from 8 ka bp onwards sea surface salinity and potential density show little variation at the orphan knoll site in the labrador sea since 7 ka bp whereas they depict a decreasing trend at the two other sites since ca 8 ka bp this shift in values suggests a progressive enhancement of labrador sea water formation and a relative decrease in the nordic seas components of the north atlantic deep water i e denmark strait overflow water and norwegian sea overflow water discrepancies are also observed with regard to millennial frequency oscillations in sea surface conditions at the easternmost site they likely match previously documented cold water pulses in the north eastern atlantic whereas they do not show any clear pattern at the westernmost sites hence the western and eastern areas show different behaviours with respect to both long term and high frequency fluctuations

hypocenter velocity structure coupling in local earthquake tomography abstract local earthquake tomography involves the use of seismic wave arrival times from earthquake sources with uncertain locations for the inference of three dimensional variations in seismic velocity formally this inverse problem contains explicit coupling between the earthquake hypocenters and the velocity structure however many studies fail to treat the hypocenter velocity structure coupling explicitly an examination of previous studies provides evidence that this failure can lead to significant bias in the resulting velocity model a set of simple hypothetical test cases clearly demonstrates the seriousness of the potential bias when coupling is neglected producing models that underestimate the actual velocity perturbations by about a factor of four under the same conditions strict simultaneous inversion and simultaneous inversion with parameter separation both produce accurate inverted models the use of appropriate station corrections and iteration of the solution can improve the results when the coupling is ignored but velocity anomalies will still be underestimated by about a factor of two at best

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

coccolith evidence for instabilities in surface circulation south of iceland during holocene times abstract the coccolith based micropaleontological investigation of an exceptionally thick deep sea holocene sediment core was conducted in order to document the pattern and timing of surface circulation changes south of iceland over the gardar contour drift during the last 12 000 years fluctuations in bulk carbonate content at the core location are primarily driven by the coccolith fraction the observed overall correlation between bottom flow speed as given by the sortable silt mean size index and the bulk coccolith concentration abundance g dry sediment suggests that the accumulation of this fine carbonate fraction is as a first order controlled by processes of sediment redistribution by bottom current the down core variations in coccolith assemblage structure species indicate that changes in properties of surface waters south of iceland occurred as two distinct steps at ca 11 2 and 6 ka the onset of north atlantic drift water influence over the gardar drift after 11 2 ka was associated with excess export flux of coccolith carbonate in the vicinity of an active frontal system the period from 10 to 6 ka saw the progressive warming of the study area which culminated between 6 and 7 ka cooling of the surface waters after 6 ka as indicated changes in the relative abundances of the dominant coccolith species took place in two phases the present hydrological regime being only established after a last cooling step between 3 5 and 2 8 ka these long term reorganisations of the surface hydrology are interpreted as the response of the north atlantic to the combined force of the solar insolation and the waning laurentide ice sheet millennial scale perturbations of the surface hydrology are documented by changes in accumulation of the species emiliania huxleyi these successive decreases in the export fluxes of e huxleyi exhibit a distinct millennial pacing in phase with previously recorded holocene advection of cool ice bearing waters from the greenland iceland seas to the british islands from a clear analogy with the most recent extreme variation in global ocean climate we argue that mechanisms responsible for these observed millennial scale perturbations might be found in long term modulations of the atmospheric processes associated with the north atlantic oscillation nao

late quaternary stratigraphy of the northern rockall trough and faeroe shetland channel northeast atlantic ocean a late quaternary deep water stratigraphic framework has been established for the deep water areas 450m of the northern rockall trough and faeroe shetland channel four stratigraphic units 1 4 are identified these are primarily biostratigraphic units based on dinoflagellate cyst evidence unit 1 represents the late weichselian glacial pre 13 000 yr bp unit 2 the late glacial interstadial 11 000 13 000 yr bp unit 3 is of younger dryas age 10 000 11 000 yr bp and unit 4 represents the holocene interglacial post 10 000 yr bp this stratigraphy is supported by the discovery of the mixed vedde ash 10 600 yr bp and north atlantic ash zone 1 and the saksunarvatn ash 9000 9100 yr bp concentrated in units 3 and 4 respectively the sedimentology indicates that the oceanographic regime underwent a major change between the glacial and interglacial stages this is marked by the onset of strong bottom current activity allied to the restoration of overflow of the norwegian sea deep water into the north atlantic towards the end of the younger dryas stadial despite intense bioturbation and bottom current reworking the basic stratigraphic framework is maintained recognition of two volcanic ash markers enables correlation with established onshore and offshore sequences of marine and non marine environments

multifocusing revisited inhomogeneous media and curved interfaces we review the multifocusing method for traveltime moveout approximation of multicoverage seismic data multifocusing constructs the moveout based on two notional spherical waves at each source and receiver point respectively these two waves are mutually related by a focusing quantity we clarify the role of this focusing quantity and emphasize that it is a function of the source and receiver location rather than a fixed parameter for a given multicoverage gather the focusing function can be designed to make the traveltime moveout exact in certain generic cases that have practical importance in seismic processing and interpretation the case of a plane dipping reflector planar multifocusing has been the subject of all publications so far we show that the focusing function can be generalized to other surfaces most importantly to the spherical reflector spherical multifocusing at the same time the generalization implies a simplification of the multifocusing method the exact traveltime moveout on spherical surfaces is a very versatile and robust formula which is valid for a wide range of offsets and locations of source and receiver even on rugged topography in two dimensional surveys it depends on the same three parameters that are commonly used in planar multifocusing and the common reflection surface crs stack method the radii of curvature of the normal and normal incidence point waves and the emergence angle in three dimensions the exact traveltime moveout on spherical surfaces depends on only one additional parameter the inclination of the plane containing the source receiver and reflection point comparison of the planar and spherical multifocusing with the crs moveout expression for a range of reflectors with increasing curvature shows that the planar multifocusing can be remarkably accurate but the crs becomes increasingly inaccurate this can be attributed to the fact that the crs formula is based on a taylor expansion whereas the multifocusing formulae are double square root formulae as a result planar and spherical multifocusing are better suited to model the moveout of diffracted waves

holocene history of drift ice in the northern north atlantic evidence for different spatial and temporal modes 1 we present new high resolution proxy data for the holocene history of drift ice off iceland based on the mineralogy of the 2 mm sediment fraction using quantitative x ray diffraction these new data bolstered by a comparison with published proxy records point to a long term increasing trend in drift ice input into the north atlantic from 6 to 5 ka toward the present day at sites influenced by the cold east greenland current this feature reflects the late holocene neoglacial or cooling period recorded in ice cores and further terrestrial archives on greenland in contrast a decrease in drift ice during the same period is recorded at sites underlying the north atlantic drift which may reflect a warming of this region the results document that holocene changes in iceberg rafting and sea ice advection did not occur uniformly across the north atlantic centennial scale climate variability in the north atlantic region over the last 4 kyr is linked to the observed changes in drift ice input increased drift ice may have played a role in the increase of cold intervals during the late holocene e g the little ice age cooling

distribution of organic walled dinoflagellate cysts in surface sediments from transects across the polar front offshore southeast greenland the polar front along the southeast greenland margin denotes the contrasting hydrographic properties of the polar and atlantic water masses on either side the remains of planktonic organisms in underlying sediments are expected to reflect these contrasts to test this we quantitatively analysed the organic walled dinoflagellate cyst dinocyst assemblages in surface sediments from transects across the present day polar front on the southeast greenland margin proportional differences are found between the composition of the dinocyst assemblages on either side of the polar front the influence of polar water can be traced in the dinocyst record as high abundances of algidasphaeridium minutum and the presence of pentapharsodinium dalei the influence of atlantic water is reflected in the presence of operculodinium centrocarpum and selenopemphix quanta all samples include taxa from both environments but the quantitative composition of the cyst assemblages clearly reflects the hydrographic features of the overlying surface water masses copyright 2001 john wiley sons ltd

air sea interaction and circulation changes in the northeast atlantic the upper ocean of the rockall trough exhibits coherent interannual variations in temperature and salinity over the past 26 years with highs in the mid 1980s and late 1990s and lows in the late 1970s and early 1990s and with ranges of 0 5 c and 0 05 in salinity the origins of the interannual changes are discussed covering three potential influencing factors the propagation of anomalies developed upstream of the basin the effect of local air sea interaction and the result of changes of regional circulation bringing different water masses into the region the changes in heat and freshwater content of the upper ocean are directly compared to observed variations in air sea heat and freshwater fluxes over the period of the time series it is shown that the role of the atmosphere in locally altering the oceanic properties particularly salinity is relatively small and insufficient to explain the changes two recent hydrographic surveys are analyzed to ascertain how the distribution of water masses to the south of the basin may influence the properties of the northern rockall trough upper ocean and the results are reviewed in the context of historical analyses it is found that the critical factor in determining the properties is the varying amount of relatively cool and fresh north atlantic current water mixing with the dominant water mass the warm saline eastern north atlantic central water at the entrance to the basin variations of inflowing water masses are caused by east west changes in the location of the subpolar front and the relationship of these changes in regional circulation to the north atlantic wind stress field is discussed

tin bearing sodic episyenites associated with the proterozoic a type agua boa granite pitinga mine amazonian craton brazil this paper reports the first occurrence of tin mineralized episyenites in the amazonian craton the agua boa and madeira plutons in the pitinga region are stanniferous proterozoic a type granites of the rapakivi series featuring metasomatic episyenitization the biotite granite facies of the agua boa pluton is metasomatically altered to sodic episyenite and minor potassic episyenite and micaceous episyenite the sodic episyenites formed by a albitization of k feldspar b vug formation by dissolution of magmatic quartz c vug filling by albite chlorite lithian muscovite cassiterite fluorite k feldspar and d deposition of late quartz cassiterite in remaining cavities in the potassic episyenites vugs produced by quartz dissolution are filled by secondary k feldspar which also replaces magmatic phases micaceous episyenites formed by zinnwaldite replacement of secondary albite in the sodic episyenites in contrast to the sodic episyenites the potassic and micaceous episyenites contain only traces of cassiterite relative to unaltered biotite granite the sodic episyenites are strongly depleted in sio2 k2o lree and sr moderately depleted in hree and enriched in na2o al2o3 rb and sn the potassic episyenites resemble the sodic episyenite in sio2 and al2o3but exhibit higher values of k2o ba y and rb their na2o ree and sn concentrations match those of the biotite granite host metasomatic episyenitization is attributed to 1 a high temperature gradient and fluid rock ratio during subsolidus cooling of the agua boa pluton 2 quartz dissolution in the biotite granite facies by reaction with an high temperature silica undersaturated fluid of probable magmatic origin 3 hydrothermal cavity filling by a low temperature silica saturated fluid of meteoric or mixed magmatic meteoric character significant tin values in metasomatic sodic episyenites near the pitinga mine suggest that exploration of similar rocks in other a type granites may be worthwhile

imprints of multiple fluid regimes on episyenites in the bohus granite sweden abstract a number of episyenite occurrences within the neoproterozoic bohus granite southwestern sweden were investigated in order to elucidate their genesis and past associated fluid regimes fluid inclusion microthermometry and o h isotope systematics integrated with information from detailed mineralogy reveal a paragenetic succession within individual episyenites including 1 albitization of plagioclase accompanied by dissolution of quartz with a vuggy feldspathic reservoir rock as a result 2 resumed infilling and replacement of igneous fe ti phases by various phyllosilicates muscovite chlorite and or illite hematite assemblages and quartz due to rift related reactivation and 3 sporadic argillitic alteration and precipitation of fracture calcite although sparse owing to later overprinting there are a few remnants that provide arguments for the involvement of meteoric water shifted to a more 18 o rich composition during the initial stage of dissolution and albitization the main vug filling phase is proposed to be associated with the ingress of surface derived fluids with negative 18 o values during the regional thermal anomaly accompanying the development of the nearby permo carboniferous oslo rift at 250 ma the fluids involved during this event show consistently a marked but variable 18 o depletion and resemble the modern day shield brines with modal salinities of 11 24 wt nacl eq low nacl nacl cacl 2 weight ratios and no discernible co 2 even though no p t path can be defined for this phase the fluid pressure can be restricted to 0 3 0 8 kbar and temperature to 160 280 c assuming a sedimentary overburden of 3 km an overall variability in the 18 o and d data can mainly be ascribed to 1 precipitation from fluids affected by isotopic exchange with the host rock and or sedimentary overburden under highly variable water rock ratios and to some extent with 2 varying degrees of partial re equilibration during subsequent hydrothermal interaction at lower temperatures as emphasized by the presence of fluid inclusions of suspected secondary origin in quartz

north atlantic ocean surface currents 1 close to 1800 surface drifters are used to investigate the 15 m circulation of the north atlantic ocean the data are used to describe structures of the average eulerian circulation and of the associated eddy variability the data resolve scales on the order of 50 km which have hitherto not been systematically described in particular near shelf breaks and near the most intense currents the gulf stream the north atlantic current nac and the frontal currents of the subpolar gyre this reveals a complex series of quasi permanent eddies meanders and recirculation patterns gulf stream intensity is portrayed as changing abruptly near 54 w east of which it is identified as two current branches centered near 39 and 41 5 n the northern one connecting more directly with the nac and the southern one with the recirculation gyre and the azores current ac many features of the currents are controlled by topography in particular currents are often intensified near shelf breaks or parallel to ridges in the subpolar gyre however the largest northward branch of the nac in the icelandic basin is located near the deepest bathymetry not near steep bathymetry other currents in particular in the subtropical gyre are less clearly related to topography for instance the ac is featured as a zonal eastward current extending far west of the mid atlantic ridge mar to at least 55 w and possibly 63 w in the interior and away from topographic features the eddy kinetic energy eke is the largest where the mean currents are the largest in the subpolar gyre there are striking differences in eke between southward flowing currents the labrador and east greenland current and the northward flowing currents west greenland current and branches of the nac which have higher eke the areas of weakest variability are located in the southwest part of the subpolar gyre northeast of iceland and in the eastern atlantic south of 45 n the ac eddies and the mesoscales south of the canary islands transect this eastern eddy desert drifter trajectories are used as realizations of lagrangian particles in the vicinity of current cores these illustrate the variety of paths or connections between different current systems and demonstrate cross stream dispersions

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

spatial and temporal variability of holocene temperature in the north atlantic region the early holocene climate of the north atlantic region was influenced by two boundary conditions that were fundamentally different from the present the presence of the decaying laurentide ice sheet lis and higher than present summer solar insolation in order to assess spatial and temporal patterns of holocene climate evolution across this region we collated quantitative paleotemperature records at sub millennial resolution and synthesized their temporal variability using principal components analysis pca the analysis reveals considerable spatial variability most notably in the time transgressive expression of the holocene thermal maximum htm most of the region but especially areas peripheral to the labrador sea and hence closest to the locus of lis disintegration experienced maximum holocene temperatures that lagged peak summer insolation by 1000 3000 years many sites from the northeastern north atlantic sector including the nordic seas and scandinavia either warmed in phase with maximum summer insolation 11 000 9000 years ago or were less strongly lagged than the baffin bay labrador sea region these spatially complex patterns of holocene climate development which are defined by the pca resulted from the interplay between final decay of the lis and solar insolation forcing

water masses and circulation pathways through the iceland basin during vivaldi 1996 quasi synoptic data from late 1996 spanning the subpolar north atlantic have been used to determine the major pathways of the north atlantic current nac at that time high spatial resolution allows fronts to be accurately positioned on each seasoar section a clearly defined front of the nac the southern branch turns north at around 25 w and continues through the middle of the iceland basin as far as 60 n 20 w a second branch the northern branch or subarctic front turns north around 30 w and retroflects westward north of 54 n to re enter the irminger basin and become part of the irminger current up the western side of the reykjanes ridge a third eastward branch turns sharply northwest at the mouth of the rockall trough to skirt the southwestern margin of hatton bank this branch carries a tongue of saline eastern north atlantic water enaw over hatton bank and in consequence enaw covers the whole of the hatton and rockall banks as well as the rockall trough bounded in the west by the southern branch the most saline water found in rockall trough spills out into the northern iceland basin between rockall and lousy banks this saline weakly stratified tongue can be traced westward to the south of iceland continuing southwestward along the eastern flank of the reykjanes ridge subarctic intermediate water is carried into the iceland basin creating a fresh tongue bounded east and west by the more saline enaw over hatton bank and the eastern flank of the reykjanes ridge respectively

reorganization of the upper ocean circulation in the mid holocene in the northeastern atlantic a micropaleontological investigation was conducted on two sediment cores from the reykjanes ridge rr core lo09 14 59 12 30 n 31 05 94 w and the faroe shetland channel fsc core hm03 133 25 60 06 55 n 06 04 18 w to document hydrographical changes of the north atlantic current nac during the holocene dinocyst and coccolith assemblages were analyzed and quantitative reconstructions of sea surface temperatures ssts and sea surface salinities ssss were conducted based on dinocyst assemblages both proxies suggest a major reorganization of surface circulation patterns in the northeastern north atlantic between 7 and 5 4 ka bp at both sites ssss before 6 5 7 ka bp were lower than during the mid late holocene suggesting dispersal of meltwater through the nac long term trends of ssts however show higher than present summer ssts on the rr from 9 3 to 6 ka bp and lower than present ssts in the fsc until ca 5 4 ka bp the contrasted sst trends at the two sites suggest that decreasing summer

dinoflagellate cysts as indicators of water quality and productivity in british columbia estuarine environments abstract palynological analyses of 60 surface sediment samples from estuarine environments near vancouver island including the georgia strait gs the effingham eff and the seymour belize sb inlets were performed in order to document the distribution of dinoflagellate cyst assemblages and their relationship to hydrographic conditions productivity and nutrient concentrations we tested transfer functions using the analogue method and suggest that dinoflagellate cyst assemblages can be used to reconstruct primary productivity temperature and salinity the eff and sb inlets are characterized by a dominance of autotrophic taxa particularly operculodinium centrocarpum whereas the protoperidinioid and gymnodinial heterotrophic taxa such as quinquecuspis concreta and brigantedinium spp dominate the assemblages of the gs multivariate analysis shows that this distribution is closely linked to primary productivity sea surface temperature sst and spring silica concentration the abundance of autotrophic taxa in the eff and sb inlets is associated with high primary productivity and low summer sst indicating summer upwelling of coastal british columbia whereas the heterotrophic taxa that characterizes the gs assemblages are related to low productivity high summer sst and high silica concentration during spring multivariate analysis shows that the most important environmental parameters related to dinocyst distribution in the restricted embayment of the gs are distance to the shore distance to vancouver harbor spring sea surface salinity sss spring phosphate concentration and spring productivity the autotrophic taxa are generally more common in coastal and shallow waters but spiniferites ramosus and pentapharsodinium dalei show an opposite correlation to spring productivity and salinity p dalei is particularly abundant around vancouver harbor near highly urbanized shores and within the fraser river plume where salinity is low and spring productivity and continental runoff are high s ramosus shows its highest abundance on the western coast of gs protoperidinioid and gymnodinial cysts characterize distal zones within the central and southern gs that are associated with a mixture of brackish waters coming from the fraser river and deep upwelling waters entering the gs via juan de fuca strait the relationship between dinoflagellate cyst assemblages and primary productivity in these estuarine systems differs from that in oceanic and outer neritic zones where the abundance of heterotrophic taxa is commonly associated with upwelling and high productivity

arctic north atlantic oscillation signature in holocene sea surface temperature trends as obtained from alkenone data 1 the variability in alkenone derived sea surface temperatures ssts in the north atlantic realm shows that a continuous sst decrease in the northeast atlantic from the early to the late holocene was accompanied by a persistent warming over the western subtropical atlantic the eastern mediterranean sea and the northern red sea based on the analysis of the instrumental data and of atmospheric general circulation model experiments we show that this variation in ssts during the holocene can be attributed to a continuous weakening of a northern hemisphere atmospheric circulation pattern similar to that of the arctic north atlantic oscillation

mineralogical and geochemical characteristics of hydrothermal alteration and episyenitization in the konigshain granites northern bohemian massif germany the late hercynian granites of konigshain underwent multistage hydrothermal processes extensive high temperature late magmatic alteration is for example indicated by low zr hf and an ree pattern displaying the tetrad effect intensive post magmatic alteration of the granite occurred along brittle structures at least two main stages of post magmatic hydrothermal alteration are involved the first high temperature stage which is characterized by albitization and or quartz leaching episyenitization resulted from fluid rock interaction with late magmatic fluids that very probably mixed with external low salinity fluids quartz dissolution was triggered by vapour condensation and or the cooling of these fluids below 450 c along brittle structures the high porosity resulting from quartz leaching during stage 1 assisted subsequent circulation of low temperature fluids at stage 2 the latter is characterized by the chloritization and illitization of episyenites almost all major and trace elements were enriched or depleted during one of the main alteration stages however zr hf th and ti were immobile during post magmatic alteration the significant depletion of lree and the enrichment of hree in albitized samples is controlled by the dissolution of monazite and the new formation of hree rich polycrase y or aeschynite y during post magmatic stage 1 negative ce anomalies of episyenites are associated with illitization and suggest oxidizing conditions during stage 2

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

constraints from geochemistry and sr nd isotopes for the origin of albitite deposits from central sardinia italy major and trace element contents and sr nd isotope ratios were determined in albitite albitized and unaltered late variscan granitoid samples from the world class na feldspar deposits of central sardinia italy the albite deposit of high economic grade has geological textural and chemical features typical of metasomatic alteration affecting the host granitoids albitization locally accompanied by chloritization and epidotization was characterized by strong leaching of mg fe k and geochemically similar trace elements and by a significant increase of na ca and p were moderately leached in the most metasomatized rocks other major si ti ca and trace elements u th y and zr along with light lree and middle mree rare earth elements behaved essentially immobile at the deposit scale the nd isotope ratios 0 512098 to 0 512248 do not provide information on the emplacement age of the unaltered late variscan granitoids on the other hand their sr isotope ratios fit an errorchron of 274 29 ma 1 error in fair agreement with all published ages of sardinian variscan granitoids the very low rb content of albitized rocks precludes application of the rb sr radiometric system to determine the age of albitization the sm nd system is not applicable either because the 143nd 144nd ratios of albitized rocks and unaltered granitoids overlap the overlap confirms that sm and nd were substantially immobile during albitization on the other hand the measured 87sr 86sr ratios of the albitized rocks are appreciably lower than those of the unaltered host granitoids whereas their initial sr isotope ratios are higher this seems to suggest that a albitization was induced by non magmatic fluids rich in radiogenic sr and b albitization occurred shortly after the granitoid emplacement this conclusion is supported by nd isotopes because unaltered granitoids and albitites fit the same reference isochron at 274 ma the fluids acquired radiogenic sr by circulation through the lower paleozoic metasedimentary basement specifically it is estimated that sr supplied by the non carbonatic basement represents about 22 wt of total sr in albitite

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

sedimentary environment of the faroe shetland and faroe bank channels north east atlantic and the use of bedforms as indicators of bottom current velocity in the deep ocean in the northeast atlantic much of the deep cold water flow between the norwegian sea and the main north atlantic basin passes through the faroe shetland and faroe bank channels generating strong persistent bottom currents capable of eroding and transporting sediment up to and including gravel a large variety of sedimentary bedforms including scours furrows comet marks barchan dunes sand sheets and sediment drifts is documented using sidescan sonar images seismic profiles seabed photographs and sediment cores from the floor of the channel published information on current velocities associated with the various bedforms has been used to reconstruct the pattern of bottom currents acting on the channel floor the results broadly reflect the current pattern predicted on the basis of regional oceanographic observations but add considerable detail the internal consistency of the results suggests that the methods used are robust giving confidence in the fine detail of the observed bottom current structure bottom current velocities in the range 1ae0 m s 1 are indicated by the range of observed bedforms with the strongest currents associated with south west transport of norwegian sea deep water nsdw at water depths of 800 1200 m the main nsdw flow forms a relatively narrow core that follows the base of the faroes slope this core follows the 90 change in trend of the faroes slope at the junction between the faroe shetland and faroe bank channels the strongest currents within the nsdw core are found over the shallowest sill in the faroe shetland channel and in the narrowest part of the channel immediately downstream of the sill and are generated by topographic constriction of the flow eastward flow of deep water along the northern flank of the wyville thomson ridge suggests a complex current pattern with some recirculation of deep water within the deep faroe bank channel basin the observations suggest that coriolis force is the main agent controlling the westward deflection of the nsdwinto the faroe bank channel contradicting a previous suggestion that this was controlled by the topography of the wyville thomson ridge

geometry and brittle deformation of the subducting nazca plate central chile and argentina summary we use data from the chile argentina geophysical experiment charge broad band seismic deployment to refine past observations of the geometry and deformation within the subducting slab in the south american subduction zone between 30 s and 36 s this region contains a zone of flat slab subduction where the subducting nazca plate flattens at a depth of 100 km and extends 300 km eastward before continuing its descent into the mantle we use a grid search multiple event earthquake relocation technique to relocate 1098 events within the subducting slab and generate contours of the wadati benioff zone these contours reflect slab geometries from previous studies of intermediate depth seismicity in this region with some small but important deviations our hypocentres indicate that the shallowest portion of the flat slab is a

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

geology and gold molybdenum porphyry mineralisation of the archean taschereau launay plutons abitibi quebec abstract porphyry gold deposits constitute a new challenge for mineral exploration in archean greenstone belts yet the relationships between intrusive rocks and mineralisation remain poorly understood the messegay gold occurrence is situated in the taschereau launay plutonic complex of the northern volcanic zone of the abitibi greenstone belt the taschereau intrusion 2718 2 ma represents a complex network of sills composed of tonalite with minor amounts of diorite monzonite and gabbro the launay granite which intrudes the taschereau pluton is late orogenic and its emplacement was controlled by an early reverse ductile n s shear zone intrusive rocks have been subjected to four episodes of alteration epidote chlorite carbonate magnetite hematite microcline albite pyrite and sericite quartz shear zone hosted and metasomatic au mo mineralisation is mainly associated with albite pyrite assemblages but also occurs within zones of intense magnetite hematite microcline and sericite quartz alteration the messegay gold occurrence is interpreted as a new type of disseminated gold molybdenum porphyry deposit associated with a zone of magmatic differentiation in a magnetite series pluton

evolution of subpolar north atlantic surface circulation since the early holocene inferred from planktic foraminifera faunal and stable isotope records abstract past changes in the surface flow regime of two main eastern north atlantic warm water pathways toward the nordic seas were reconstructed based on faunal analyses in combination with carbon and oxygen stable isotope measurements in planktic foraminifera the investigated sites in the surroundings of the faroe islands are located in the transitional area where surface waters of subpolar and subtropical origin mix before entering the arctic mediterranean in these areas large amplitude millennial variability in the characteristics of the upper water column appears modulated by changes in the intensity of the subpolar gyre circulation from 7 8 to 6 ka bp faunal records indicate a deep mixed layer which in conjunction with lighter 18 o values suggest that the inflowing atlantic waters were dominated by a relatively cooler and fresher water mass reflecting a strengthening of the subpolar gyre under conditions of enhanced positive nao like forcing and reduced meltwater input a shift in the hydrographic conditions occurred during the mid holocene centered at 5 ka bp at this time increasing upper water column stratification and the incipient differentiation of the stable isotopic signal of the iceland faroe and faroe shetland surface water masses suggest increasing influx of warmer more saline surface waters from the subtropical gyre as subpolar gyre circulation weakened the mid holocene decline in subpolar gyre strength is presumably related to a shift toward a low state of the nao like forcing associated with decreased solar irradiance later in the holocene from 4 ka bp to present the increased frequency and reduced amplitude of the surface hydrographic changes reflect corresponding fluctuations in subpolar gyre circulation these high frequency oscillations in subpolar gyre strength suggest increased surface circulation sensitivity to moderate freshwater fluxes to the labrador irminger sea basin highlighting the importance of the salinity balance in modulating subpolar gyre dynamics particularly under conditions of low nao atmospheric forcing

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

microseismic imaging using a source function independent full waveform inversion method we thank kaust for sponsoring this research we also thank to the team of swag for their help during the research

sea surface temperatures and ice rafting in the holocene north atlantic climate influences on northern europe and greenland abstract the oceanographic conditions in the high latitude north atlantic ocean during the holocene were reconstructed through analyses of sea surface temperature sst alkenone unsaturation ratios and ice rafting mineralogy and grain size from two sediment sequences one recovered from the reykjanes ridge at 59 n and the other from the norwegian sea at 68 n comparison of our records to published ice core and terrestrial proxy climate data sets suggests that atmospheric temperature changes over northern europe and greenland were coupled to sst variability and ice rafting the records outline four major climatic phases i an early holocene thermal maximum that lasted until approximately 6 7 kyr bp ii a distinctly cooler phase associated with increased ice rafting between 6 5 and 3 7 kyr bp iii a transition to generally warmer but relatively unstable climate conditions between 3 7 and 2 kyr bp and iv a second distinct sst decline that took place between 2 and 0 5 kyr bp in contrast to the dominant control of northern hemisphere summer insolation on early holocene climate development via strong seasonality the trigger for the onset of relatively unstable climatic conditions in the north atlantic at 3 7 kyr bp is not straightforward however it is possible that this change was triggered by late holocene winter insolation increase at high northern latitude and or by inter hemispheric changes in orbital forcing the late holocene neoglaciation trend which is characteristic of numerous terrestrial archives in northern europe may not only be attributed to a gradual decrease in orbitally forced summer temperature but also to increase snow precipitation at high northern latitudes during generally milder winters

the metamorphosed molybdenum vein type deposit of the alpeinerscharte tyrol austria and its relation to variscan granitoids the molybdenite deposit of the alpeinerscharte austria is situated in variscan greenschist to amphibolite facies metamorphosed granodiorites and granites of the western tauern window these granitoids represent strongly fractionated calc alkaline i type magmas with minor s type components and reveal post orogenic affinities molybdenum contents average 4 3 ppm are slightly above the general background of average granites molybdenite mineralization is restricted to narrow quartz veins and quartz vein selvages which are presently composed of biotite and almandine grossular garnet these selvages show geochemical features typical of intermediate argillic alteration in a hydrothermal system postdating granite intrusion instability of plagioclase causes removal of na ba sr pb and eu while k and ca remain nearly constant rare earth elements apart from eu and metals are extremely enriched application of fe mg exchange garnet biotite and oxygen isotope quartz garnet quartz plagioclase geothermometers to vein selvage mineral assemblages reveals temperatures of the late alpine 35 55 ma metamorphic overprint 540 c 7 10 kbar leucocratic rocks composed of mainly orthoclase and plagioclase are occasionally spatially related to molybdenite bearing veins they are interpreted as episyenites formed by hydrothermal alteration of the host granite this episyenitic alteration is characterized by a mass loss of ca 30 relative enrichment of plagioclase components extreme depletion of si and minor depletion of fe zn cu and mo

improving the resolution of impedance inversion in karst systems by incorporating diffraction information a case study of tarim basin chinaimpedance inversion with diffraction

distribution of coccoliths in surface sediments in the norwegian greenland sea abstract the distribution of coccoliths has been examined in 20 surface sediment samples along an east west transect in the norwegian sea based on the abundance and species richness of coccoliths three biogeographic zones have been established along this transect the distribution of coccolith assemblages in the surface sediments appears to match closely with the locations of the different surface water masses in the norwegian greenland sea