high resolution sr ca records in sclerosponges calibrated to temperature in situ ratios of strontium to calcium have been analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms in a skeletal section of the sclerosponge ceratoporella nichol soni the growth period representative of 3 yr was stained in the skeleton with a fluorochrome calcein temperatures were record ed at 2 h intervals within the shallow cryptic reef enclosure that the sclerosponge inhabited on the northern coast of jamaica al lowing the formulation of a direct empirical relationship between sr ca and temperature to verify this calibration sr ca ratios of two sclerosponges of the same species from depths of 67 m and 136 m in exuma sound bahamas were analyzed by la icp ms and compared to the temperatures from these depths over a decade prior to collection the result is an independently verified high resolution empirical calibration for the temperature sensitivity of sr ca ratios in the aragonite skeletons of sclerosponges from ja maica and the bahamas the calibration is a first for c nicholsoni and indicates that sclerosponges are more sensitive temperature recorders than zooxanthellate corals it represents an important step in establishing skeletal geochemistry of sclerosponges as a proxy of temperature in the upper 250 m of the ocean

evidence for preindustrial variations in the marine surface water carbonate system from coralline sponges 1 coralline sponge skeletons are excellent tools for reconstructing the carbon isotope history of dissolved inorganic carbon dic in tropical surface waters carbon isotope records from coralline sponges clearly reflect the industrial 12c increase in atmospheric co2 with a precision that permits quantitative interpretations we find from a set of 13c records of four caribbean sponge specimens that the isotopic response of surface water dic to the changing isotopic composition of atmospheric co2 varied dynamically during the last century depending on the rate of atmospheric change three of our sponges provide 600 year long 13c records for the first time we can reconstruct surface water 13cdic for the full history of the industrial co2 release as well as the preceding preindustrial period back to the beginning of the little ice age this provides a well founded estimate of the anthropogenically uninfluenced preindustrial background level of surface water 13c 12c ratios our records show small but systematic variations that appear to be linked to the climate fluctuations of the little ice age

improved calibration of the sr ca temperature relationship in the sclerosponge ceratoporella nicholsoni re evaluating sr ca derived records of post industrial era warming abstract although the sr ca ratio in the skeletons of sclerosponges appears to be robustly correlated with water temperature the measurement of sr ca ratios from several specimens by different workers yields unexpectedly large up to 5 c increases in temperature over the past 150 years this is considerably greater than spatially and temporally averaged observational temperature increases one possible culprit for the larger than anticipated temperature changes in these samples arises from the calibration between temperature and sr ca ratios of the skeleton that was derived from specimens grown in a relatively narrow range of high temperatures 26 to 30 c in order to improve the calibration we acquired a number of samples of sclerosponges collected at lower average water temperatures different localities and deeper water depths and combined measurements of the sr ca ratios from bulk samples representing the last 15 years of growth with the previous calibration dataset analyses of these samples have produced a revised relationship between temperature and sr ca ratios in the skeletons of sclerosponges application of this new calibration equation to published sclerosponge data reduces the magnitude of the increase in temperature reconstructed from sr ca ratios to values in better agreement with spatially and temporally gridded observational ocean temperature data sets however the acceleration of warming indicated by nearly all caribbean sclerosponge records over the last several decades remains unchanged by this revised calibration

crustal outgassing and lile enrichment in major lithosphere structures archean abitibi greenstone belt evidence on the source reservoir from strontium and carbon isotope tracers major structural discontinuities in the abitibi greenstone belt acted as conduits for outgassing of the archean crust as reflected in fixation of a select group of lithophile elements including si c k rb ba li cs b and pb in metasomatized faults for two of the largest structures the destor porcupine dp and kirkland lake cadillac kc fault zones 6 1015 g si 3 1015 g co2 and 1015 g k were introduced into the faults during expulsion of an estimated 6 1018 g aqueous fluids strontium isotope ratios of tourmaline piemontite actinolite and scheelite mineral separates characterized by rb sr 0 02 are concordant with respect to 87sr 86sr initial ratios over local sectors of the faults the sr isotope data record geographic variations which from east to west on the kc fault is 0 7031 0 7041 val d or 0 7008 0 7022 bourlemaque 0 7017 0 7019 bousquet 0 7029 0 7031 noranda and 0 7013 to 0 7015 kirkland lake at timmins on the pd fault 87sr 86sr initial ratios cluster at 0 7010 to 0 7020 metasomatised fault zones are systematically more radiogenic than contiguous host lithologies and imply a source reservoir 0 7010 to 0 7041 generally more radiogenic than the upper mantle at 2690 ma 0 700 0 001 or contemporaneous volcanic rocks of mafic to ultramafic composition 0 700 to 0 7012 whereas certain minerals are concordant and retentive rb sr isochrons based on suites of rocks at progressive intensities of metasomatism have been systematically reset over an elpased time of 200 ma after termination of outgassing due to disturbance accompanying incremental displacements on structures

sclerosponges as a new potential recorder of environmental changes lead in ceratoporella nicholsoni lead concentrations have been analyzed on a 223 yr profile through the aragonitic skeleton of the reef building caribbean sclerosponge ceratoporella nicholsoni by using laser ablation inductively coupled plasma mass spectrometry a parallel study of the 13 c distribution in the skeleton validates the previously established mean annual growth rate of 230 m yr at least for long term important environmental changes the pb trend in the specimen displays a general increase from 0 30 ppm ca a d 1760 to 2 15 ppm ca a d 1984 a major threefold increase occurred after 1930 this pb profile is analogous to results acquired from ice or coral cores and clearly highlights the potential of sclerosponges as a new proxy of environmental changes for time series extending over several centuries

past and recent changes in the large scale tropospheric cycles of lead and other heavy metals as documented in antarctic and greenland snow and ice a review abstract the investigation of the occurrence of lead and other heavy metals in antarctic and greenland ancient ice and recent snow is of great interest in reconstructing the past natural tropospheric cycles of these metals and determining to what extent these cycles have now been altered by man because concentrations to be measured are exceedingly low down to the sub pg g level reliable data can however be obtained only if full control of contamination is achieved from field sampling to laboratory analysis the available data show that the past natural concentrations of pb cd zn cu and hg in antarctic ancient ice are highly dependent upon climatic conditions the highest values occurring during the coldest periods of the ice ages especially during the last glacial maximum about 18 000 years ago human activity has led to an increase in lead concentrations during recent centuries both in antarctica tenfold increase and in greenland two hundredfold increase this last increase was followed by a 7 5 fold decrease during the past two decades mainly as a consequence of the rapid fall in the use of lead alkyl additives in the usa as confirmed by recent isotopic data

grain growth kinetics in olivine aggregates abstract grain growth kinetics were studied in hot pressed fine grained olivine aggregates experimental conditions include pressures of 0 1 mpa 300 mpa and 1 gpa and temperatures of 1473 1573 and 1673 k with or without the presence of water at the initial stage of grain growth growth of larger grains occurs rapidly consuming smaller grains which results in significant pore entrapment almost homogeneous grain size distribution is established in this process after this stage grain size distribution remains almost homogeneous in most cases it was found that the presence of water enhances the grain growth kinetics when the amount of water is limited however when the amount of water is large the water containing pores significantly inhibit the grain boundary migration therefore the enhancement of grain growth due to the presence of water is due to the role of dissolved water in olivine rather than the mass transport through water abnormal grain growth was found in some samples in these cases normal grain growth was inhibited by the presence of a significant amount of water filled pores or grains with significantly larger size than the rest occurred in the starting materials in 0 1 mpa runs significant porosity developed and the grain growth rates were significantly lower than in those at high confining pressures these results show that both water and pores have important effects on grain growth kinetics in olivine when the effects of pores or secondary phases in inhibiting grain growth are unimportant the grain growth rate in olivine is very fast growth to 100 m size will occur in 102 to 103 hours at 1500 k thus fine grain size in olivine will be maintained only for a short geological time unless the grain boundaries are effectively pinned by secondary particles

surface ocean variability at galapagos from 1936 1982 calibration of geochemical tracers in corals a variety of geochemical tracers has been developed in reef corals as a means of reconstructing the natural variability of the tropical surface ocean over wide ranging time frames the purpose of this paper is to calibrate the performance of five of these tracers in a modern coral colony over an extended period a 47 year growth interval 1936 1982 in a colony of pavona clavus taken from san cristobal island galapagos islands was sectioned into 187 quarterly intervals and analyzed for 18o 13o ba ca cd ca and mn ca the resulting time series are compared with eastern pacific sea surface temperatures one of few instrumental data bases available for calibration over this time period linear least squares regressions of four of the tracers 18o 13o ba ca cd ca against peruvian sst show highly significant correlations p 0 0001 over the annual biennial and enso 3 8 years frequency bands cross spectral comparisons show even stronger coherency with sst frequently accounting for 70 80 of the variance in these tracers these results as well as the phase relationships determined from the spectral analyses suggest that the coupling between sst and 18o and the nutrientlike tracers ba and cd is controlled principally by seasonal upwelling cycles and interannual interruptions of these cycles brought about by el nino and anti el nino phenomena an inverse relationship between sst and 13c has its primary origins in the co occurrence of the warm sst phase with high light levels during the first half of the calendar year the association with sunlight derives from the photosynthetic response of algal symbionts which results in fractionation of light and heavy carbon isotopes between soft tissues and caco3 skeleton the fifth tracer the transition metal mn exhibits poorer correlations against both sst and the other tracers slight shifts in phasing of the historical mn ca annual cycle suggest that the general water column distribution of this tracer which is the reverse of a nutrient may not be stable the erratic behavior of mn illustrates how complex hydrography near galapagos may influence tracers with diverse source signatures

natural variability of skeletal elemental phosphorus p ca lead pb ca and barium ba ca in the western pacific sclerosponges acanthoceatetes wellsi and astrosclera welleyana

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

grain growth in partially molten olivine aggregates grain growth rates in partially molten olivine aggregates were determined experimentally at a pressure of 1 gpa the aim of the experiments with fine grained starting material solution gelation derived fo90 olivine with a grain size of 1 m with 2 and 4 wt added basaltic glass was to determine growth rates during steady state grain growth a series of experiments was conducted at a fixed temperature of 1 350 c for durations from 2 to 700 h and a second series at fixed duration 168 h at temperatures from 1 250 to 1 450 c the resulting activation energy e 390 kj mol and growth exponent n 4 3 are comparable to melt free results nichols and mackwell 1991 the observed grain size distributions are broader than those predicted for normal grain growth or ostwald ripening and most similar to the log normal distribution the observed melt distribution is influenced by the continuous rearrangement of neighboring grains during growth the relatively large growth exponent observed in this study and by nichols and mackwell 1991 where secondary phases are present suggests that grain growth in the upper mantle is slower than predicted by karato 1989

decoding nonlinear growth rates in biogenic environmental archives 1 the record of an environmental proxy along a growth axis in biogenic carbonates can reflect changing environmental conditions experienced during the lifetime of the organism when a chronology of the growth axis is not available a method based on anchor points is commonly used to introduce a time grid between these anchor points a constant growth rate is generally assumed despite the fact that growth rates change during life in most organisms here we present a method which refines the constant growth rate assumption at least in situations where the environmental proxy has a periodic component in its signal a nonlinear growth rate can then be estimated enabling the construction of a more realistic time base the anchor point method and the method proposed here are first compared on a synthetic record it is shown that the choice of the anchor points which is always a subjective one is largely influenced by the stochastic noise on the data record this results in biased growth rate profiles and biased time grids next we apply the method on the mg record in the bivalve isognomon ephippium on three samples of the clam saxidomus giganteus from washington state and on the vanuatu coral stable isotope record the method developed is applicable to a wide range of proxy records which are measured along an indirect time grid and are complicated by nonlinear accretion rates furthermore this method which takes variable growth rates into account opens perspectives on quantitative modeling of the relationship between environmental proxies recorded by accretive archives and the instrumental record like temperature or salinity

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

volcanism of shoshonite to high k andesite affinity in an archean are environment oxford lake manitoba volcanic rocks of the archean oxford lake group are characterized by a stratigraphic progression from mafic to felsic compositions accompanied by a systematic decrease in incompatible element abundances this coupled with high abundances of sr rb k2o and la high la yb n and unfractionated flat to concave heavy ree rare earth element profiles distinguishes these rocks as an archean shoshonite to high k andesite dacite rhyolite series directly comparable to modern analogues formed in convergent tectonic settings the trace element data support a model of petrogenesis in which an archean mantle source region was modified by volatiles rich in large ion lithophile elements the modified mantle was subjected to partial melting forming a parental liquid of shoshonitic character and this liquid principally underwent amphibole fractionation to form the evolved rock compositions this process is envisaged as terminal magmatism during the final senile stage of activity in an arc setting the rb sr

neoarchean evolution of differing convergent margin assemblages in the wabigoon subprovince geochemical and geochronological evidence from the lake of the woods greenstone belt superior province northwestern ontario abstract the neoarchean lake of the woods greenstone belt is subdivided into three lithostratigraphic assemblages a lowermost mafic volcanic assemblage a compositionally diverse predominantly volcanic middle assemblage and a predominantly sedimentary uppermost assemblage the secular evolution and geodynamic settings of these assemblages are constrained with detailed geochronological and geochemical data the lower keewatin is the oldest assemblage with a zircon u pb age of 2738 2 0 ma it consists of mg and fe tholeiitic basalts mg number 30 65 with flat to slightly enriched rare earth elements ree la yb cn 0 9 1 6 elevated large ion lithophile elements lile and undepleted high field strength elements hfse the tholeiites do not appear to have exact modern analogs but do have some similarities to primitive arc tholeiites and back arc basin basalts suggesting an archean destructive margin setting the upper keewatin assemblage disconformably overlies the lower keewatin assemblage it consists of volcanic and sedimentary groups two geochemically distinct volcanic suites are recognized the dominant suite consists of compositionally diverse calc alkalins basalt to rhyolite felsic end members have yielded zircon u pb ages ranging from 2712 to 2723 ma the suite exhibits highly fractionated ree la yb cn 4 35 elevated lile and nb and ta depletion anomalies which are very similar to modern island arc volcanic rocks developed in proximity to continental margins a coeval suite of mafic to ultramafic volcanic rocks consists of mg tholeiite komatiitic basalt and ultramafic komatiite mg numbers 45 80 the suite exhibits depleted lree la yb cn 0 6 1 0 slightly elevated lile and undepleted to slightly enriched hfse suggesting that this geochemically primitive suite was produced by partial melting of a refractory mantle source perhaps as second stage melts of the same mantle source from which the lower keewatin assemblage basalts were previously derived the electrum assemblage unconformably overlies the upper keewatin assemblage in the northern part of the belt it consists of conglomerates sandstones and minor volcanic rocks having detrital ages indicating deposition after 2699 ma the volcanic rocks consists of andesite to rhyolite with shoshonitic to calc alkaline geochemical affinity as indicated by highly fractionated ree la yb cn 12 112 highly enriched lile and pronounced nb ta and ti depletion anomalies samples from the syenitic falcon island pluton appear to be coeval with electrum assemblage volcanics having an u pb isotopic age of 2694 ma and similar but even more alkaline chemistry consisting of highly fractionated lree and lile trace elements with very pronounced nb ta and ti depletion anomalies these late tectonic suites are geochemically similar to modern shoshonites with a continental influence formed in the late stages of a mature island arc or a continental arc setting

interpreting environmental signals from the coralline sponge astrosclera willeyana coralline sponges sclerosponges have been proposed as a new source for paleo subsurface temperature reconstructions by utilizing methods developed for reef building corals however unlike corals coralline sponges do not have density variations making age determination difficult in this study we examined multiple elemental rations b mg sr ba u in the coralline sponge astrosclera willeyana we also measured skeletal density profiles along the outer living edge of the sponges and this data indicates significant thickening of skeletal material over intervals of 2 3 mm or 2 3 years this suggests that any skeletal recovered environmental record from astrosclera willeyana is an integration of signals over a 2 3 year period sponge sr ca seemed to hold the most promise as a recorder of water temperature and we compared sr ca from 2 sponges in the great barrier reef and one from truk in micronesia to their respective sea surface temperature record the correlations were not that strong approx r 0 5 but they were significant it appears that the signal smoothing due to thickening or perhaps even some biologic control on sr skeletal partitioning limits the use of sr ca as an indicator of water temperature in astrosclera willeyana

diffusion creep of dry melt free olivine 1 deformation experiments were conducted on fine grained 3 6 m fully synthetic fo90 olivine aggregates in a gas medium apparatus at 300 mpa confining pressure and temperatures of 1150 1360 c the strain rates of the solution gelation derived and therefore genuinely melt free dry samples are about two orders of magnitude lower than the strain rates for nominally melt free aggregates at the same pressure and temperature conditions and grain size benchmark deformation tests with anita bay dunite and mild steel reproduce published data the creep strength of melt added sol gel olivine is similar to the published creep strength of dry melt bearing olivine derived from natural rocks nonlinear least squares fits to the melt free deformation data give an activation energy of 484 kj mol a stress exponent of 1 4 and a grain size exponent of 3 over a range of stresses from 15 to 210 mpa these results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water however a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments

archaean orogenic ultrapotassic magmatism an example from the southern abitibi greenstone belt the clericy pluton in the southern abitibi greenstone belt of quebec is a syenitic intrusion cross cut by nordmarkitic dykes it is probably one of the oldest known ultrapotassic intrusions about 2 7 ga it crystallized in a crustal environment under low ph20 2 5 kbar and low fo2 conditions most trace elements behaved as compatible elements suggesting that sphene and apatite were involved together with clinopyroxene during low pressure crystal fractionation the large range of initial isotopic ratios calculated for 2 68 ga nd 1 9 to 2 3 as well as the trace element distribution suggest that the syenitic pluton is the product of differentiation from a parental magma with a composition similar to that of timiskaming type archaean shoshonites contaminated by a crustal component on the other hand the nordmarkitic dykes are probably the result of crustal anatexis of metasedimentary rocks and some addition of the syenitic magma the clericy peralkaline syenite differs chemically from typical intraplate syenites in being saturated with respect to quartz and displaying lower ti and hfse contents it is related to an ultrapotassic volcano plutonic event which characterized the last 20 ma of igneous activity in the abitibi greenstone belt it may represent an increased rate of convergence of small heterogeneous plates during a subduction driven accretion tectonic event which possibly marked the culmination of the kenoran orogeny in the superior province of the canadian shield

reproducibility of trace element profiles in a specimen of the deep water bamboo coral keratoisis sp abstract bamboo corals order gorgonacea family isididae are attractive prospects for deep sea paleoceanographic reconstruction capturing trace elements in their calcitic skeletons that may serve as environmental proxies with subdecadal resolution over multi century timescales we study the reproducibility and fidelity of trace element profiles ba mg sr mn u pb in a 420 year old specimen of the bamboo coral keratoisis sp from the se usa using laser ablation icp ms to obtain multiple replicate profiles we use spectral techniques to distinguish noise and irreproducible variations from fully reproducible geochemical fluctuations that are candidates for environmental signals by quantifying variability between profiles we assess the fidelity with which the corals potentially record environmental information barium is the most reproducible element in the skeleton with large fluctuations along different growth radii reproducing to within 4 both mg and sr have very uniform levels within the coral but display low amplitude irreproducible variations that might represent an internal biological process in the case of mg which has been proposed as a paleotemperature proxy this irreproducibility would represent an intrinsic uncertainty of 0 1 to 0 4 c both mn and pb contain some irreproducibility superimposed upon broad reproducible profiles that may be environmental signals some of the irreproducible pb fluctuations correlate with cracks and dark bands in the sample suggesting detrital or surface contamination uranium displays large amplitude variations which are not reproducible along different radii this suggests that uranium cannot be used for paleoenvironmental reconstruction and may show signs of early diagenesis a possibility that could complicate attempts to date young keratoisis sp samples by u series geochemistry the highly reproducible ba signal allows precise alignment of profiles and thus we can show that growth rate along one radius can vary by a factor of two relative to growth along a different radius there is no evidence that this large variation in relative growth rate affects either the mg or sr incorporation in addition geochemical anomalies in ba and mg indicate that the very central axis of the specimen may represent a different mode of growth this study suggests that keratoisis sp corals are imperfect recorders of geochemical information but do contain reproducible variations which are good candidates for environmental signals

geochemistry of archean alkalic volcanic rocks from the crystal lake area east of kirkland lake ontario canada abstract twelve samples of timiskaming volcanics from the crystal lake area were analyzed for major and trace elements ta th zr hf v cr sc rare earth elements ree y etc by x ray fluorescence and instrumental neutron activation analysis techniques the samples which include mafic trachytes trachytes and leucite trachytes represent several batches of archean alkalic magmas differentiated at shallow depths the cr sc cr systematics and ree zr th and zr y characteristics show however that their primary magmas generated at great depths in the enriched mantle where garnet remained in the refractory residue of partial melt the chemical similarity between the timiskaming samples and modern alkalic rocks in mature volcanic arcs strongly implies that the timiskaming volcanism represents the last stage of a late archean island arc volcanism present in the southwestern abitibi belt superior province the occurrence of timiskaming type alkalic rocks is not rare in archean greenstone belts thereby suggesting that a tectonic setting similar to modern volcanic arc system might have been common in late archean time

eastern pacific sea surface temperature since 1600 a d the δ18o record of climate variability in galapagos corals we measured stable oxygen isotope ratios and skeletal growth rates in the massive corals pavona clavus and p gigantea from the west coast of isabela island galapagos to assess interannual to decadal climate variability in the eastern pacific comparisons of instrumental data sets show that sea surface temperatures sst in the galapagos region are representative of a broad portion of the eastern equatorial pacific the site is especially well suited for long term studies of the el nino southern oscillation enso phenomenon as it lies within the eastern pacific center of action for thermal anomalies associated with enso the p gigantea isotope record is nearly monthly in resolution spans the period 1961 1982 and shows strong correlation with a galapagos instrumental sst record r 0 90 for annual averages cross spectral analysis shows that sst can explain greater than 80 of the variance in 18o at both the annual cycle and within the high frequency portion of the enso band 3 5 years the p clavus record is annual in resolution extends from 1587 to 1953 a d and was obtained from a 10 m diameter colony preserved within the urvina bay uplift because seawater 18o variations in the region are very small we interpret the urvina bay coral 18o record in terms of annual average sst the isotopic record appears to be a very good but not perfect indicator of enso events and shows good correspondence with the historical enso reconstruction of quinn et al 1987 a number of low 18o excursions that we observe during the 17th and 18th centuries very likely represent enso events that are missing from the historical tabulations most interannual 18o variations between 1607 and 1953 a d represent annual average temperature excursions of 1 to 2 5 c during the little ice age the annual 18o series correlates well with many north american tree ring records and shows low temperatures during the early 1600s and early 1800s and relatively warmer conditions during the 1700s unlike most northern hemisphere tree ring and instrumental records we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling 28 of the total variance the main enso mode is centered at 4 6 years and accounts for 12 of the total variance additional significant oscillations occur at periods of 3 3 6 8 11 17 22 and 34 years both annual growth rate and 18o show variance at periods equivalent to the solar and solar magnetic periods e g 11 and 22 years respectively in addition the amplitude of the 11 year 18o cycle generally varies with the amplitude of the solar cycle supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics the dominant oscillatory modes both within the enso and interdecadal frequency bands shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s this may reflect major reorganizations within the tropical ocean atmosphere system and suggests that tropical pacific climate variability is linked across timescales ranging from years to decades

the effect of melt distribution on the rheology of plagioclase rocks abstract synthetic plagioclase aggregates were fabricated by hot isostatic pressing glass powder with an60ab40 composition at a confining pressure of 300 mpa and a temperature of 1223 k the residual glass content 15 vol was reduced to 1 3 vol by annealing the specimens at temperatures between 1423 and 1523 k at 0 1 mpa high resolution electron microscopy showed that the residual glass was confined to grain triple junctions when these samples were annealed at 0 1 mpa and above the solidus 1620 k they also contained silica rich amorphous phases at grain boundaries other samples were hot pressed at 1423 k they often have grain boundaries containing thin amorphous films 5 50 nm wide the chemical composition of the films differs from pure labradorite with up to 80 wt sio2 the volume fraction of si rich glass increases up to 2 vol for samples that contain 1 wt water uniaxial creep experiments were performed at temperatures of 1373 1638 k and stresses between 2 and 50 mpa the plagioclase aggregates deformed by grain size sensitive creep with a stress exponent n 1 the activation energy for grain boundary diffusion controlled creep of the partially molten aggregates was 400 20 kj mol 1 it remained unchanged with varying glass content and glass topology the strength of samples containing glass along grain boundaries is 4 10 times less than without amorphous grain boundary films the transition between diffusion and dislocation creep is shifted towards higher stresses for samples that contain glass films at grain boundaries

constraining initial 230th activity in incrementally deposited biogenic aragonite from the bahamas the 230th content of subsurface bahamas seawater has been estimated from incrementally deposited aragonite skeletons of sclerosponges using u series age models which imply syndepositional incorporation of 230th first order age models assuming constant growth rate and zero initial 230th activity display an average surface age of 63 18 y despite the fact that the surfaces of the organisms were known to be alive at the time collection in the 1990s a knowledge of the initial 230th activity is necessary to incorporate the surface age constraint into an age model in the bahamas this approach estimates an initial 230th 232th activity ratio of 4 3 1 1 when applied to several individuals of the caribbean sclerosponge ceratoporella nicholsoni these results differ from the same approach applied to previous work on jamaican sclerosponges accreting aragonite in an environment closer to crustal sources and with less carbonate substrate we report new measurements of jamaican sclerosponge suggesting initial activity ratios of 230th 232th of 1 albeit with a high amount of uncertainty indicating a regional difference in initial thorium activities the estimates of initial 230th 232th activity ratios in the bahamas are similar to the dissolved ratio rather than the particulate ratio and can be explained by mixing of open ocean water and bank top surface water however no information regarding temporal changes in the amount of initial 230th 232th activity available for incorporation into biogenic aragonite can be constrained using this approach growth rates do not change after correction for initial thorium and they display an inverse relationship with depth although this paper deals uniquely with sclerosponge aragonite it is likely that the approach can be used on any incrementally deposited biogenic aragonite provided information is known a priori about the first order growth model and there is evidence that initial thorium incorporation is representative of ambient environment rather than individual physiology

lead pb profiles in red coral skeletons as high resolution records of pollution in the mediterranean sea 26 lead concentrations in long lived corallium species of known age from the mediterranean 27 sea atlantic and pacific oceans were determined by laser ablation inductively coupled 28 plasma mass spectrometer la icpms lead concentrations in a 2000 year old sub fossil 29 mediterranean c rubrum are ca 0 09 0 03 g g for the period 1894 1955 lead 30 concentrations in c rubrum skeletons from the mediterranean are stable within the range 0 2 31 0 4 g g concentrations increase to about 1 1 2 g g during the period 1960 1978 then 32 decrease progressively to stabilize and reach values in the range 0 2 0 4 g g in present day 33 corals these variations can be related to the lead gasoline pollution event that 1 started in 34 the early 1950s with the increase of the numbers of cars in the world and 2 was mitigated 35 by the implementation of new regulations starting in 1975 leading to a return to pre 1950 36 levels in 2000 in the pacific lead concentrations in c japonicum and c konojoi are lower 37 than in the mediterranean c rubrum with values close to 0 17 0 03 g g the lowest lead 38 concentrations in present day samples 0 11 g g are found in c johnsoni and c niobe from 39 the azores islands in the atlantic and in a mediterranean c rubrum from montecristo island 40 one of the least accessible and most protected areas in the mediterranean sea using lead 41 concentrations in c rubrum and in the mediterranean seawaters a partition coefficient kd 42 pb ca calcite pb ca seawater of 13 3 is estimated it allows calculating past and present lead 43 contents in seawater in which corals grew application to corallium species indicates that 44 values endangering human health or threatening the preservation of aquatic ecosystem on 45 long terms were nearly reached or exceeded in mediterranean seawaters at the maximum of 46 the lead gasoline pollution event in the 1980s measurements in c rubrum from different 47 places in the mediterranean indicate that present day seawater concentrations vary between 48 2 40 and 200 pmol kg as expected the lowest concentrations come from protected areas 49 insulated from human activities while the highest come from places close to lead mining or 50 processing sites 51

minor and trace elements in sclerosponge ceratoporella nicholsoni biogenic aragonite near the inorganic endmember abstract the trace and minor element composition have been investigated in the accretionary skeletons of two specimens of the caribbean sclerosponge species ceratoporella nicholsoni one from tongue of the ocean bahamas toto and the other from pear tree bottom jamaica ptb both sclerosponges were analyzed at high resolution using laser ablation icp ms la icp ms and verified using wet chemical methods icp oes the shallow ptb sclerosponge 25 m was analyzed for a short temperature calibrated record of trace and minor elements while the toto sclerosponge 146 m was analyzed for a century long record from subsurface waters the resulting ba ca mg ca pb ca and u ca ratios were compared with sr ca ratios which have been shown to reliably record seasonal scale temperature change in sclerosponges close to equilibrium precipitation of inorganic aragonite sclerosponge aragonite incorporates minor and trace elements according to general mineralogic constraints with less vital effects than other calcium carbonate secreting organisms this is perhaps most obvious in the behavior of mg ca ratios which show an inverse correlation to temperature unlike any other calcite or aragonite organism despite having mg concentrations 1 mmol mol within published estimates of equilibrium aragonite ratios of mg ca and ba ca show a strong positive correlation despite large differences in ionic radii and u ca values 3 15 mol mol are 2 5 higher in sclerosponge aragonite than in aragonite from corals supporting earlier work ratios of u ca show an insignificant correlation with temperature dependent sr ca ratios r 2 0 05 supporting existing theories that temperature signals recorded by u ca ratios can be convolved with ph co 3 2 and phosphate signals differences between sclerosponge aragonite and other calcium carbonate arising from siliceous spicule contamination are unlikely because of the small mole percent of silicon in the aragonite small differences between the two sclerosponges were noticed in pb ca and sr ca because of the average ages of the sampled material and average temperatures of the ambient environment respectively anomalies between la icp ms and icp oes were noticed in measurements of ba ca and pb ca due to standardization differences for la icp ms ba ca and measurements close to the instrument detection limits of pb icp oes

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

bulk flow strength of forsterite enstatite composites as a function of forsterite content creep experiments have been conducted to investigate the effect of varying forsterite content vfo on the bulk flow strength of dry forsterite enstatite fo en aggregates in order to evaluate the applicability of existing theoretical models to two phase rocks as well as to understand the rheology of polyphase systems in general the experiments were performed at temperatures of 1423 1593 k stresses of 18 100 mpa oxygen fugacities of 10 14 10 2 5 mpa and 0 1 mpa total pressure the fine grained fo 10 17 mm en 14 31 mm composites of various fo volume fractions vfo 0 0 2 0 4 0 5 0 6 0 8 and 1 were synthesized by isostatically hot pressing in a gas medium apparatus at 1523 and 350 mpa our experiments show that flow strength contrasts between fo and en are in the range of 3 8 at the given experimental conditions with fo as the stronger phase the measured stress exponent n and activation energy q values of the fo en composites fall between those of the endmembers the n values show a nearly linear increase from 1 3 to 2 0 while the q values display a non linear increase from 472 to 584 kj mol with en volume fraction from 0 to 1 0 there is no clear dependence of creep rates on oxygen fugacity for the fo en composites the mechanical data and tem microstructural observations suggest no change in deformation mechanism of each phase when in the composites compared to when in a single phase aggregate the en deformed mainly by dislocation creep while the fo deformed by dislocation accommodated diffusion creep for our grain sizes and experimental conditions comparisons between the measured composite strengths and various theoretical models indicate that none of the existing theoretical models can give a precise predication over the entire vfo range from 0 to 1 however the theoretical models based on weak phase supported structures wps yield a good prediction for the flow strengths of the composites with vfo 0 6 no model gives a good prediction for the bulk strength of two phase composites in the transitional regime vfo 0 4 0 6 applications of the wps and sps based models in the transitional regime result in under and over estimations for the composite flow strength respectively thus the effect of rock microstructure should be taken into consideration in modeling the bulk flow strengths of the crust and upper mantle using laboratory determined flow laws of single phase aggregates d 2001 elsevier science b v all rights reserved

petrological evolution of the crust and mantle in its simplest form crust mantle evolution can be thought of as a study of the processes by which material is lost from the mantle and forms new crust the overall goal is achievement of mass balance between the average composition of material known to have been added to the crust and the estimated average composition of the entire crust attainment of this goal for the earth has been elusive primarily because the materials available for study have generally been involved in several stages of evolution including fractionation within both the crust and mantle and recycling of material from crust to mantle thereby complicating the interpretation of available data although the overall composition of the continental crust generally has been modelled as andesitic taylor and mclennan 1981a the present upper continental crust is granodioritic and requires a more mafic lower crust it has been proposed taylor and mclennan 1981a that originally the archean crust had an andesitic composition throughout its volume and that partial melting in the lower crust developed more felsic melts that rose to enrich the upper crust leaving a more mafic residuum of lower crust this concept has been challenged by weaver and tarney 1981a who argue that the granulites of presumed lower crustal origin do not have the correct compositions for this model if one considers more recent additions to the crust from the mantle over the past several hundred million years it appears that these latest additions are basaltic with very little if any granitic additions in fact barker 1981 in his introduction to a special issue of jgr on granites and rhyolites states to date no one has demonstrated that such magmas may form in the mantle indeed much experimental and geochemical work indicates that such siliceous liquids cannot originate there therefore such magmas must be generated in the crust in island arc environments where the average composition of added material normally is thought to be andesitic a anderson 1982 has shown that the parent melt is basaltic not andesitic in addition kay 1980 has shown that the k content of the newly added material is less than the average k content of the previously existing crust in the oceanic crust the additions from the mantle are basaltic and according to o hara 1982 probably are derived from very mafic picritic melts as parents continental flood basalts which have also added material from mantle to crust also are clearly derived from basaltic parental melts basaltic volcanism study project 1981 thus the evidence for the nature of material subtracted from the mantle and added to the crust for the past several hundred million or perhaps a billion years points to very mafic melts this contrasts significantly with the overall andesitic composition of continental crust it implies furthermore that if the overall archean crustal composition was andesitic as estimated by taylor and mclennan 1981a then additions to the crust have become more mafic with time a concept in direct conflict with most models in which secular trends are from mafic to felsic with time veizer and jansen 1979 and mclennan et al 198o a question which is beginning to appear either explicitly or implicitly is whether crustal volcanic rocks or the crust as a whole really represents the parent melt that formed in the mantle a anderson 1982 o hara 1982 and nisbet and walker 1982

lead concentrations in the northeast pacific evidence for global anthropogenic perturbations lead concentrations were determined by isotope dilution mass spectrometry in 34 surface and deep water samples collected in the northeast pacific between hawaii and california and off the california coast using a deep water sampler protected against fouling by contamination from the ship and hydrowire measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90 or more of the total lead is in a dissolved form lead concentrations are about 10 fold higher in surface and thermocline waters than in deep waters values drop as low as 1 ng kg 5 pmol kg below 3500 m depth lead profiles thus appear different compared to those of most trace metals which show enrichment in deep waters compared to surface concentrations lead concentrations in surface waters increase from 5 to 15 ng kg 25 to 75 pmol kg along a transect starting from a location 200 km off the california coast and continuing towards the center of the north pacific gyre this increase is congruent with that observed for 210 pb concentrations in the same waters sampled at the same time lead is supplied to the open north pacific largely from the atmosphere at a rate of about 60 ng cm 2 yr which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold this excess originates from emissions from smelters and combustion of leaded gasoline overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers vertical lead concentration profiles below the surface mixed layer are probably not in steady state there concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters based on an estimated 10 fold input and concentration increase since the mid eighteenth century in the surface mixed layer in the central northeast pacific it is calculated that the 10 ng kg average concentration between 100 and 900 m is 2 to 5 times larger and the 1 8 ng kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid eighteenth century profiles of lead concentrations in the north atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the north pacific because of the effects of greater industrial lead contamination while lead concentration profiles in the south pacific are expected to be shifted generally to lower values compared to the north pacific by about this same factor because of the effects of lesser industrial lead contamination

flow behavior of fine grained synthetic dunite in the presence of 0 5 wt h2o the deformation behavior of synthetic dunite mg forsterite plus 2 5 vol enstatite with a grain size of 1 m has been investigated in combined constant displacement rate and temperature stepping experiments at temperatures of 850 to 1000 c strain rates of 10 7 to 10 5 s 1 and a confining pressure of 600 mpa nominally dry material behaved purely elastically in contrast samples with 0 5 wt added water flowed at stresses between 9 and 81 mpa reaching strains up to 12 fitting a dorn type power law to the wet data yielded stress exponents n of 1 7 0 4 and apparent activation energies in the range 302 22 kj mol 1 the wet deformed samples showed polygonal grains no crystallographic preferred orientation no subgrains low dislocation densities and evidence for grain boundary cavitation grain growth was minor it is concluded that the wet samples probably deformed by a grain size sensitive grain boundary sliding dominated mechanism though the nature of the accommodation process remains unclear and the possibility of transitional behavior between dislocation creep and diffusion creep cannot be eliminated application of the results to upper mantle shear zones supports previous speculation that the presence of such zones can lead to a significant weakening of the top 10 to 20 km of the upper mantle during extension of the continental lithosphere

rubidium strontium age and origin of uraniferous granite molson lake red sucker lake area northwestern superior province manitoba late archean post kinematic uraniferous granite and alaskite occur as several discrete large and small bodies in the 250 km long molson lake red sucker lake batholithic belt in the western god

archean tectonic and metallogenic evolution of the superior province of the canadian shield abstract the superior province of the canadian shield has mainly experienced an archean tectonic history comprising several cycles of volcanism plutonism and tectonism although the rocks of the superior province span more than 500 million years of archean time most mineral deposits formed in an interval of 100 million years or less corresponding to a period of accretion of oceanic and pre existing continental fragments in the late archean at 2 7 ga in accord with recent tectonic syntheses which argue for the accretionary origin of the superior province the metallogenic history of the superior province can also be interpreted in the same context provided secular anomalies in the early history of the earth are acknowledged for relatively unique deposit types such as komatiitic nickel deposits and voluminous iron formations volcanogenic massive sulphide iode gold and granitoid associated deposits as well as ni cu pge cr and ti deposits associated with mafic ultramafic intrusions are readily interpreted in terms of the construction and accretion of late archean island arcs

the cosmos greenstone succession agnew wiluna greenstone belt yilgarn craton western australia geochemistry of an enriched neoarchaean volcanic arc succession abstract the geodynamic setting of the neoarchaean eastern goldfields superterrane egs of the yilgarn craton is the subject of debate some authors propose plume models while others advocate variants on a subduction accretion model for the origin of mineralised greenstone belt sequences felsic volcanism in the kalgoorlie terrane the westernmost terrane of the egs is considered to have a tonalite trondhjemite granodiorite dacite ttg d geochemical affinity the cosmos greenstone succession which lies in the agnew wiluna greenstone belt awb of the kalgoorlie terrane contains several komatiite hosted nickel sulphide deposits the volcanic footwall to which consists of an intercalated succession of fragmental and coherent rocks ranging in composition from basaltic andesite to rhyolite light rare earth elements lrees and large ion lithophile elements liles are strongly enriched relative to high field strength elements hfses across all volcanic units and the rocks display strong positive pb and negative nb anomalies these geochemical characteristics resemble closely those of modern high k calc alkaline to shoshonite continental arc successions contrasting ree lile and hfse concentrations coupled with assimilation fractional crystallisation afc modelling shows that the intercalated dacitic and andesitic volcanic rocks within the footwall succession are not co genetic xenocrystic zircons within the felsic volcanic lithologies indicate that some assimilation of older continental crust contributed to the generation of the footwall volcanic sequence the geochemical characteristics of the cosmos volcanic succession indicate that parental melts were derived via partial melting of enriched peridotite that had been contaminated by subducted crustal material within the mantle wedge of a subduction zone in contrast two younger felsic porphyry intrusions which cross cut the volcanic succession have a distinct ttg d affinity therefore these intrusions are considered to be generated via partial melting of a subducting slab and are related to local high ca granitoid intrusions the cosmos volcanic succession represents the first extrusive high k calc alkaline to shoshonitic volcanic arc sequence described in the kalgoorlie terrane and coupled with age dating of the stratigraphy is indicative of formation in a long lived volcanic arc setting active from 2736 ma to later than 2724 ma the composition and geochemical affinity of the volcanic footwall succession to the cosmos komatiite hosted nickel sulphide deposits contrasts with the majority of felsic volcanic rocks within the awb and also the wider kalgoorlie terrane suggesting that the overall architecture of this region is more complex than is currently thought our conclusions not only have consequences for recent models of the tectonic evolution of the egs but also contribute to the debate on the operation of plate tectonics during the late archaean in general the arc affinity of the cosmos volcanic succession containing abundant high k calc alkaline andesite lavas provides further support for the operation of plate tectonics in the neoarchaean

long term variability in the stable carbon isotopic composition of porites corals at the northern gulf of aqaba red sea abstract to study long term variations in surface ocean 13c we investigated coral skeletal 13c records of 20 colonies of the shallow water coral porites spp from the northern gulf of aqaba and the northern red sea the coral colonies represent different water depths a wide range of different periods last interglacial holocene the last centuries the last decades and various growth rates records from modern and fossil corals show irregular seasonal cycles attributed mainly to the seasonal cycle of light no attenuation in the amplitude of the seasonal skeletal 13c cycle with depth is evident and no significant correlation between mean annual coral 13c and water depth was observed in the modern corals the mean coral extension rates show no clear relationship with mean skeletal 13c values the average skeletal 13c value of modern corals was 2 74 0 49 offset from both calcite and aragonite equilibrium values by about 5 22 and 6 26 respectively modern corals reveal a clear trend toward lighter skeletal 13c values since the year 1974 at longer timescales the skeletal 13c values from last interglacial and holocene corals and from coral records extending back to the mid to late 18th century reveal much heavier 13c values compared to values from 1960 to the present the trend toward lighter skeletal 13c values over the last decades can be attributed to changes in the 13c of the dissolved inorganic carbon of the ambient seawater due to the addition of anthropogenically derived co2 13c suess effect to the atmosphere other factors such as the metabolic effects of corals may account for the modulation of skeletal 13c on shorter timescales a centuries long coral record from the northern red sea reveals a magnitude of decrease in skeletal 13c comparable to global trends 1960 1990 whereas a centuries long coral record from the northern gulf of aqaba indicates a larger decrease over the same period probably due to local effects in conclusion the combined carbon isotope records obtained from porites spp corals from the northern red sea seem to be suited to provide information on long term world wide changes in atmospheric co2

geological evolution of the northwestern superior province clues from geology kinematics and geochronology in the gods lake narrows area oxford stull terrane manitoba the study of lithology geochronology and structure in the oxford stull terrane in particular in the gods lake narrows area has led to the recognition of three distinct supracrustal sequences 2 8 2 9 ga volcanic rocks a 2720 ma fault bounded package of volcanics and sandstones and 2705 ma conglomerate and alkaline volcanic rocks of the oxford lake group detrital zircon as old as 3647 ma is present in the oxford lake group an early generation of folding and shearing occurred prior to deposition of the oxford lake group and was probably synchronous with emplace ment of 2721 ma tonalite dykes the second generation of deformation caused south over north thrusting of volcanic rocks over the oxford lake group the youngest fabric resulted from east southeast trending dextral south over north shearing the youngest rock dated in the area is the 2668 1 ma magill lake pluton which records crustal melting following deformation the pattern of sedimentation and deformation in this area is similar to

tropical seasonality in the late campanian late cretaceous comparison between multiproxy records from three bivalve taxa from oman abstract geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub annual timescales however the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment in this study records of multiple proxies in three bivalve taxa from the same late campanian locality in oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment micro x ray fluorescence mapping allows the localization discussion and evasion of diagenetically altered parts of the fossil shells x ray fluorescence line scanning calibrated with laser ablation inductively coupled plasma mass spectrometry is used to measure trace element profiles through well preserved calcitic parts of the shells records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high resolution trace element concentration profiles to study sub annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale spectral analysis routines are used to detect cyclicity in stable isotope 18o and 13c and trace element mg ca sr ca s ca and zn ca records differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species specific physiological effects stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8 c around an annual mean of 28 c with the shell of the rudistid torreites sanchezi milovanovici yielding slightly higher average temperatures the discussion of the application of various mg ca palaeotemperature calibrations on mg ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species it shows that long term changes in mg ca ratios in ocean water need to be taken into account and that mg ca ratios in bivalves might be influenced by vital effects sr ca and s ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell although an influence of local salinity on strontium to calcium ratios cannot be excluded sub annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column

ejecta megaregolith accumulation on planetesimals and large asteroids megaregolith accumulation can have important thermal consequences for bodies that lose heat by conduction as vacuous porosity of the kind observed in the lunar megaregolith lowers thermal conductivity by a factor of 10 i have modeled global average ejecta accumulation as a function of the largest impact size with no explicit modeling of time in conjunction with an assumed cratering size distribution exponent b the largest crater constrains the sizes of all other craters that significantly contribute to a megaregolith the largest impactor mass ratio is a major fraction of the catastrophic disruption mass ratio and in general the largest crater s diameter is close to the target s diameter total accumulation is roughly 1 5 of and proportional to the target s radius global accumulations estimated by this approach are higher than in the classic housen et al 1979 study by a factor of roughly 10 this revision is caused mainly by higher typical largest crater size for b 2 the single largest crater typically contributes close to 50 of the total of new nonrecycled ejecta megaregolith can be destroyed by sintering a process whose pressure sensitivity makes it effective at lower temperature on larger bodies planetesimals 100 km in diameter may be surprisingly well suited about as well suited as bodies two to three times larger in diameter for attaining temperatures conducive to widespread melting a water rich composition may be a significant disadvantage in terms of planetesimal heating as the shallow interior may be densified by aqueous metamorphism and will have a low sintering temperature

siliceous deep sea sponge monorhaphis chuni a potential paleoclimate archive in ancient animals abstract the deep sea sponge monorhaphis chuni forms giant basal spicules which can reach lengths of 3 m they represent the largest biogenic silica structures on earth that is formed from an individual metazoan the spicules offer a unique opportunity to record environmental change of past oceanic and climatic conditions a giant spicule collected in the east china sea in a depth of 1110 m was investigated the oxygen isotopic composition and mg ca ratios determined along center to surface segments are used as geochemical proxies for the assessment of seawater paleotemperatures calculations are based on the assumption that the calculated temperature near the surface of the spicule is identical with the average ambient temperature of 4 c a seawater temperature of 1 9 c is inferred for the beginning of the lifespan of the monorhaphis specimen the temperature increases smoothly to 2 3 c to be followed by sharply increased and variable temperatures up to 6 10 c in the outer part of the spicule the inferred seawater temperature is about 4 c the lifespan of the spicule can be estimated to 11 000 3000 years using the long term trend of the inferred temperatures fitted to the seawater temperature age relationships since the last glacial maximum specimens of monorhaphis therefore represents one the oldest living animals on earth the remarkable temperature spikes of the ambient seawater occurring 9500 3100 years b p are explained by discharges of hydrothermal fluids in the neighborhood of the spicule the irregular lamellar organization of the spicule and the elevated mn concentrations during the high temperature growth are consistent with a hydrothermal fluid input

seismic properties of anita bay dunite an exploratory study of the influence of water as a pilot study of the role of water in the attenuation of seismic waves in the earth s upper mantle we have performed a series of seismic frequency torsional forced oscillation experiments on a natural anita bay dunite containing accessory hydrous phases at high temperatures to 13008c and confining pressure pc o f 200 mpa within a gas medium high pressure apparatus both oven dried and pre fired specimens wrapped in ni fe foil within the poorly vented assembly were recovered essentially dry after 50 100 h of annealing at 13008c followed by slow staged cooling the results for those specimens indicate broadly similar absorptionband viscoelastic behaviour but with systematic differences in the frequency dependence of strain energy dissipation q 1 attributed to differences in the small volume fraction of silicate melt and its spatial distribution in contrast it has been demonstrated that a new assembly involving a welded pt capsule retains aqueous fluid during prolonged exposure to high temperaturescallowing the first high temperature torsional forced oscillation measurements under high aqueous fluid pore pressure pf at temperatures 410008c a marked reduction in shear modulus without concomitant increase in q 1 is attributed to the widespread wetting of grain boundaries resulting from grain scale hydrofracturing and the maintenance of conditions

annually resolved δ13cshell chronologies of long lived bivalve mollusks arctica islandica reveal oceanic carbon dynamics in the temperate north atlantic during recent centuries abstract the ability of the ocean to absorb carbon dioxide is likely to be adversely affected by recent climate change however relatively little is known about the spatiotemporal variability in the oceanic carbon cycle due to the lack of long term high resolution dissolved inorganic carbon isotope 13 c dic data especially for the temperate north atlantic which is the major oceanic sink for anthropogenic co 2 here we report shell carbon isotope values 13 c shell a potential proxy for 13 c dic of old grown specimens of the long lived bivalve mollusk arctica islandica this paper presents the first absolutely dated annually resolved 13 c shell record from surface waters of the north atlantic iceland gulf of maine covering the time interval between 1753 and 2003 according to our results the 13 c shell data were unaffected by trends related to ontogenetic age however the shell carbonate was precipitated with a constant offset from expected equilibrium by 1 54 to 2 7 0 2 corresponding to a 6 2 to 10 8 0 8 contribution of respiratory co 2 25 the offset did not appear to vary through the lifetime of individual specimens and among specimens therefore the 13 c shell data of this species can very likely be used as a measure of 13 c dic furthermore shell stable carbon isotope chronologies exhibited habitat specific differences and a significant inter annual and decadal variability related to the natural carbon cycle in addition a distinct negative 13 c shell shift was found reflecting the oceanic suess effect i e the admixture of anthropogenic co 2 however this shift only occurred after the early 1920s when a major climate regime shift led to a northward movement of the oceanic polar front in the nordic seas and a large scale reorganization of atmospheric and oceanic currents in the north atlantic this likely resulted in a reduced admixture of cold polar water onto the north icelandic shelf through the east iceland current and the gulf of maine through the labrador current with an increased volume of warmer isotopically well equilibrated atlantic waters our shell based 13 c dic proxy record provides the basis to quantitatively assess natural and anthropogenically induced patterns of carbon uptake in the north atlantic

sr ca ratios and oxygen isotopes from sclerosponges temperature history of the caribbean mixed layer and thermocline during the little ice age we investigate aragonitic skeletons of the caribbean sclerosponge ceratoporella nicholsoni from jamaica 20 m below sea level mbsl and pedro bank 125 mbsl we use d18o and sr ca ratios as temperature proxies to reconstruct the caribbean mixed layer and thermocline temperature history since 1400 a d with a decadal time resolution our age models are based on u th dating and locating of the radiocarbon bomb spike the modern temperature difference between the two sites is used to tentatively calibrate the c nicholsoni sr ca thermometer the resulting calibration points to a temperature sensitivity of sr ca in c nicholsoni aragonite of about 0 1 mmol mol k our sr ca records reveal a pronounced warming from the early 19th to the late 20th century both at 20 and 125 mbsl two temperature minima in the shallow water record during the late 17th and early 19th century correspond to the maunder and dalton sunspot minima respectively another major cooling occurred in the late 16th century and is not correlatable with a sunspot minimum the temperature contrast between the two sites decreased from the 14th century to a minimum in the late 17th century and subsequently increased to modern values in the early 19th century this is interpreted as a long term deepening and subsequent shoaling of the caribbean thermocline the major trends of the sr ca records are reproduced in both specimens but hardly reflected in the d18o records

secular variation in greenstone sequence development emphasizing superior province canada abstract evidence from the superior province of the canadian shield suggests the existence of several distinct lithostratigraphic associations in greenstone belts 1 quartz arenite and carbonate bearing sequences 2 mafic ultramafic volcanic sequences 3 mafic to felsic volcanic cycles and 4 timiskaming type sequences of fluviatile sediments and calc alkaline to alkaline volcanics recently recognized quartz arenite bearing sequences in the sachigo and wabigoon subprovinces are from base to top quartz arenite stromatolite bearing carbonate oxide facies iron formation and komatiite or tholeiite primary structures in the quartz arenites indicate shallow water deposition and represent mature sedimentation granitoid provenance of these sediments is postulated based upon petrography of coarse arenites and clasts of associated conglomerates the few dated superior province quartz arenite bearing sequences are 2 85 ga the shallow water origin of the primary structures and biota and the areal extent of the quartz arenite and carbonate sequences invite comparison with platform sediments at passive margins platform sequences unconformably overlie 3 ga granitoid rocks and older mafic volcanics where original lower contacts are preserved in two localities mafic volcanic sequences contain sheet flows iron formations and deep water argillites based on physical volcanology and sedimentology these sequences are compared to modern deep water mafic plain and hawaiian volcanism they generally underlie mafic to felsic volcanic cycles and overlie platform sequences mafic sequences are 2740 2700 ma in age mafic to felsic volcanic cycles consist of deep water tholeiitic flows overlain by shallow water to subaerial intermediate to felsic pyroclastics and flows the facies style of volcanism petrography and geochemistry of the mafic to felsic cycles most closely resemble the characteristics of crust in continental magmatic arc systems this type of lithostratigraphic association varies in age from 2775 to 2700 ma in the superior province with minor exceptions timiskaming type sequences consist of fluviatile conglomerate immature arenites and wackes with subaqueous to subaerial volcanics of variable chemistry longitudinal and lateral variation within fault bounded basins is extreme and the sequences have generally been affected by only late stages of deformation the combination of rock types facies distribution the fault bounded nature of the repositories and the locus of sedimentation along zones of transcurrent displacement suggest timiskaming sequences are best compared with modern pull apart basins superior province timiskaming sequences are within the superior province platform sequences are the earliest postorogenic lithostratigraphic unit in greenstone belts followed by mafic plain sequences arc volcanics and pull apart basins we suggest that platform sequences based upon limited evidence are preceded by an orogeny and that pull apart basins represent a subsequent orogeny the lithostratigraphic units above have distinct metallogenic associations 1 platform sequences based upon compilation of several shields may contain detrital au and u and oxide facies iron formations associated felsic volcanics contain no recognized volcanogenic cu zn deposits in the superior province the following metallogenic associations are noted 2 mafic plain sequences contain komatiite flow related ni deposits cu ni and platinum group deposits are associated with flows and coeval intrusions 3 arc volcanic sequences contain volcanogenic cu zn sulphide deposits and scarce deposits of porphyry type cu mo and 4 timiskaming sequences and related plutonism are related to lode au

shear wave attenuation and dispersion in melt bearing olivine polycrystals 2 microstructural interpretation and seismological implications 1 the torsional forced oscillation tests of melt bearing olivine aggregates reported by jackson et al 2004 consistently show a peak in attenuation that is absent from melt free aggregates tested under similar conditions and grain sizes characterization by sem shows that the melt resides in triple junction tubules and larger pockets as previously described tem imaging and eds analysis reveals that olivine olivine grain boundaries are characterized by a region 1 nm wide which is structurally and chemically distinct from olivine grain interiors from the possible mechanisms that can produce an anelastic attenuation peak melt squirt can be eliminated for our samples and experimental conditions we attribute the observed attenuation peak to elastically accommodated grain boundary sliding requiring that the grain boundaries are weak relative to olivine grain interiors but have a significantly higher viscosity than bulk melt while the nanometer scale grain boundary structure in the melt bearing aggregates is essentially the same as for melt free aggregates studied previously elastically accommodated sliding in the latter is apparently inhibited by tight three grain edge intersections the exponentially increasing high temperature background attenuation in both types of aggregate is attributed to diffusionally accommodated grain boundary sliding extrapolation to mantle grain sizes shows that the broad peak may be responsible for nearly frequency independent attenuation in partially molten regions of the upper mantle

carbon isotope records from extant caribbean and south pacific sponges evolution of δ13c in surface water dic stable isotope records of demosponges from the caribbean and coral sea are described for the purpose of studying the influence of fossil fuel co2 on the carbon isotopic composition of dissolved inorganic carbon dic in surface water the slow growing sponges precipitate calcium carbonate in isotopic equilibrium with ambient sea water and are used to detect changes in 13cdic from pre industrial times early 19th century to the present we observed similar shapes and ranges in 13c curves measured on caribbean specimens collected from water depths of 25 84 and 91 m as well as a specimen collected in shallow waters off new caledonia the records reveal a highly significant correlation with atmospheric 13cco2 13cdic values for caribbean and coral sea surface waters were calculated using the 13c sponge records while 13c of atmospheric co2 decreased by about 1 4 from the early 19th century to 1990 13cdic of caribbean and coral sea surface waters decreased by 0 9 0 2 and 0 7 0 3 respectively no isotopic equilibrium between surface water dic and atmospheric co2 was observed either during the pre industrial steady state or during the last 100 years the lower amount of depletion in the surface water 13cdic with respect to the atmospheric anthropogenic signal is explained by the dilution of the surface waters by biologically altered subsurface water dic the lower 13c decrease in the coral sea points to a stronger influence of the subsurface water source compared to the caribbean

lead in corals reconstruction of historical industrial fluxes to the surface ocean twentieth century environmental lead chronologies for the western north atlantic pacific and indian oceans have been reconstructed from annually banded scleractinian corals measurements of lattice bound pb in sequential coral bands reveal temporal changes in surface water pb concentrations and pb isotopic distributions perturbations are observable in all specimens studied attesting to global augmentation of environmental pb by industrialization in the western north atlantic pb perturbations have occurred in direct response to the american industrial revolution and the subsequent introduction and phasing out of alkyl pb additives in gasoline surface ocean conditions near bermuda may be reliably reconstructed from the coral data via a lead distribution coefficient of 2 3 for the species diploria strigosa based on210pb measurements a similar distribution coefficient may be characteristic of corals in general surface pb concentrations in the pre industrial sargasso sea were about 15 20 pm concentrations rose to near 90 pm by 1923 as a result of metals manufacture and fossil fuel combustion beginning in the late 1940 s increased utilization of leaded gasoline eventually led to a peak concentration of 240 pm in 1971 representing an approximate 15 fold increase over background surface ocean concentrations are presently declining rapidly 128 pm in 1984 as a result of curtailed alkyl pb usage lead isotopic shifts parallel the concentration record indicating that characteristic industrial and alkyl pb source signatures have not changed appreciably in time industrial releases recorded in the florida keys reflect a weaker source and evidence of recirculated pb 5 6 years old from the north atlantic subtropical gyre an inferred background concentration of 38 pm suggests influence of shelf and or resuspended inputs of pb to these coastal waters in remote areas of the south pacific and indian oceans industrial signals are fainter and the corals studied much younger than their atlantic counterparts contemporary pb concentrations implied by coral measurements assumingkd 2 3 are 40 50 pm for surface waters near tutuila and galapagos in the south pacific and 25 29 pm near mauritius in the indian ocean a single coral band from fiji 1920 5yr implies a pre industrial surface water concentration of 16 19 pm pb for the south pacific in view of reported surface water measurements and the north atlantic coral data the pacific coral extrapolations may be slightly high this could be a result of small variations inkd among different coral genera or incorporation of diagenetic pb by corals sampled in coastal environments

lead concentration and isotopic composition in the pacific sclerosponge acanthochaetetes wellsi reflects environmental lead pollution we measured pb ca and pb isotopes with high resolution in the high mg calcite skeleton of a pacific sclerosponge acanthochaetetes wellsi collected from the reef edge off the western coast of kume island east china sea to investigate its potential to be used as a proxy for lead contamination in the environment and atmospheric transportation and fallout over the last few decades skeletal pb ca ranged from 58 to 1642 nmol mol 10 higher than that of the aragonite skeleton of pacific corals and 2 5 higher than that of the aragonite skeletons of caribbean sclerosponges the pb ca timeseries recorded from 1967 through 2007 ce correspond to historical changes in atmospheric lead flux in anthropogenic aerosols pb isotopes 206pb 207pb and 208pb 207pb in the sclerosponge skeleton document that the main source of lead emissions shifted from japan 1970 1980 ce to china 1995 2005 ce as expected from the timing of legislation against the use of leaded gasoline in japan and china our results indicate that the skeleton of the pacific sclerosponge is a powerful proxy to monitor environmental lead pollution applying this methodology to long living and or fossil specimens could be useful in determining the interannual variability of atmospheric transport and dynamics over geologic time scales

influence of mineral fraction on the rheological properties of forsterite enstatite during grain size sensitive creep 2 deformation experiments 1 in order to understand the effects of secondary minerals on the flow properties of rocks we have conducted uniaxial compression experiments on polycrystalline forsterite fo enstatite en samples at constant temperature and strain rate the flow stress of the samples decreases with increasing enstatite volume fraction fen for samples with 0 fen 0 5 and increases with increasing fen for samples with 0 5 fen 1 the values of the preexponential term stress and grain size exponents and activation energy in the constitutive equation for a wide range of fen were determined samples with a low fen 0 03 deformed at strain rates of 2 10 5 to 2 10 4 s exhibit creep characteristics that correspond to dislocation accommodated grain boundary sliding creep i e stress exponent n 3 whereas diffusion accommodated grain boundary sliding creep is typical of high fen samples i e stress exponent n 1 the change of flow strength as a function of fen during grain size sensitive creep is primarily due to changes in grain size of both phases and secondarily due to changes in the volume fraction of phases with different flow strengths viscosities of all samples can be reproduced in a viscosity model that takes into account 1 the grain sizes estimated by the grain growth laws established in our part 1 paper and 2 flow laws determined for the individual phases in this case forsterite and enstatite furthermore we demonstrate that our model can be extended to make predictions of viscosity in other mineral assemblages

deformation of peridotite at high pressure in a new molten salt cell comparison of traditional and homologous temperature treatments abstract we have conducted a series of constant strain rate experiments on a synthetic peridotite composed of isostatically hot pressed olivine and orthopyroxene over a pressure range of 700 2200 mpa and a temperature range of 1250 1700 k by using a sample assembly in which specimens are surrounded by molten salt the data are of much higher quality than previously obtained in solid pressure medium apparatus we find that both the temperature and pressure dependence of creep in our experiments can be combined quantitatively as the homologous temperature dependence of creep this quantitative relationship between creep and melting greatly simplifies the thermodynamic treatment of creep and provides a simple model for the extrapolation of laboratory creep data for peridotite to conditions throughout the earth s upper mantle

intra annual variation in the stable oxygen and carbon and trace element composition of sclerosponges 1 this paper presents data to support the presence of 1 intra annual signals in the chemical composition 18o and sr ca of the skeletons of sclerosponges from the bahamas and 2 variable rates of skeletal accretion these conclusions are based on data obtained by using a microsampling method for the stable oxygen and carbon isotopes in which material was extracted at a resolution of one sample every 34 m and a laser microprobe which obtained trace element data every 20 m sr mg and pb an age model was established using a combination of changes in the concentration of pb the change in the 13c of the skeleton of the sclerosponges and u th isotopic measurements these methods yield a mean growth rate of 220 m yr but suggest that the growth rate in this particular sclerosponge was not constant the calculated growth rate is within error identical to that determined by u th methods the variable growth rate was confirmed through spectral analysis of the 18o and sr ca data that showed peaks corresponding to the annual cycle in these parameters as well as peaks corresponding to growth rates of approximately 128 212 270 and 400 m yr the presence of these additional frequencies suggests a growth rate between approximately 100 and 300 m yr these conclusions were supported by modeling of oxygen isotopic data measured on a scleractinian coral as well as model isotope data generated on synthetic time series these findings have important implications for the use of sclerosponges as proxies of paleoclimate because they emphasize the need for a precise yearly chronology in order that proxy data can be compared with climatic variables

accretion of japanese island arcs and implications for the origin of archean greenstone belts the present day region of arc arc collision between the izu bonin arc and mainland japan honshu arc in the western pacific called the izu collision zone or icz provides a useful kinematic model for the development of many archean greenstone belts the compositional assemblage thermal structure and structural style of the crust in the icz are very similar to those inferred for many archean greenstone belts in both cases thick young and flaky arc crust with a high heat flux is in collision with another crustal block the icz has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms many archean greenstone belts show similar geological features and we suggest that the incremental imbrication of the crust was a common tectonic style in some archean convergent margins

deposition of atmospheric heavy metals to the greenland ice sheet from the 1783 1784 volcanic eruption of laki iceland abstract in order to assess better the influence of major volcanic events on the large scale atmospheric cycles of heavy metals greenland ice dated from the time of the fallouts from the great 1783 1784 eruption of laki volcano in iceland has been analysed for pb cd cu zn and sulphate the concentrations of the four heavy metals investigated are found to be greatly enhanced in the ice layers which correspond to the fallouts from the eruption confirming that such events do modify the atmospheric cycles of heavy metals cumulative fallout of heavy metals to the whole greenland ice cap from the 1783 1784 laki eruption ranges from 1 t for pb and cd to 40 t for zn for cd cu and zn it represents a few percent of the cumulative anthropogenic fallout to the ice cap from the industrial revolution to the present

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

lead concentrations and isotope ratios in speleothems as proxies for atmospheric metal pollution since the industrial revolution abstract lead concentrations and isotope ratios from two speleothems from the han sur lesse cave in southern belgium were measured in order to study the ability of speleothems to act as archives of atmospheric pollution to address this aim we analyzed trace elemental al and pb compositions by la icp ms and icp ms as well as pb isotopes by mc icp ms the results help to identify three intervals characterized by particularly high enrichment of pb from 1880 to 1905 ad from 1945 to 1965 ad and from 1975 to 1990 ad the speleothem record shows similar changes as the known historical atmospheric pollution level in belgium lead isotope ratios discriminate between pb sources and confirm that coal and gasoline combustion combined with regional metallurgical activities were the predominant pb pollution sources in the stalagmites during the last 250 years this study opens possibilities to determine anthropogenic versus natural metal sources in well dated speleothem archives

silicon diffusion in forsterite aggregates implications for diffusion accommodated creep silicon diffusion rates were determined in fine grained 4 5 m hot pressed forsterite aggregates at 900 to 1200 c and 0 1 mpa using a 30si tracer and standard sims analysis there is no measurable difference in diffusion rates between samples buffered by excess mgo or sio2 nor samples run in dry n2 or h2 co2 the results yield the arrhenius parameters d0 bulk 5 4 10 9 m sec and q 203 36 kj mol at 1200 c the grain boundary diffusion rate of 30si is similar to 26mg si 10 times greater 10 less than fe and 105 less than o in addition the 30si grain boundary diffusion rate is 109 greater than the si volume diffusion rate and indicates that diffusional transport of si in forsterite aggregates is dominated by grain boundaries

meso and neoarchean evolution of the island lake greenstone belt and the northwestern superior province evidence from lithogeochemistry nd isotope data and u pb zircon geochronology abstract the island lake greenstone belt is located on the northern margin of the north caribou terrane a large reworked mesoarchean crustal block in the northwestern superior province the belt experienced a long and complex geological history manifested by an older mesoarchean 2 897 2 852 ga and a younger neoarchean 2 744 ga volcanic assemblages comprising chronologically and geochemically distinct mafic and felsic volcanic rocks and associated plutonic rocks the mafic volcanic rocks in these assemblages are subdivided into two groups with distinct geochemical signatures 1 enriched in th and lree and with pronounced negative nb ta and ti anomalies and 2 with broadly flat ree patterns without apparent nb ta and ti anomalies the geochemical characteristics of these mafic volcanic rocks are interpreted to have formed in magmatic arc settings with a protracted history consistent with nd isotope data that require variable inputs of an older ca 3 0 ga crustal source i e the north caribou terrane for their formation crustal contamination appears to decrease with decreasing age in the volcanic assemblages and associated plutonic rocks together these data suggest that the meso and neoarchean volcanic assemblages are parts of a primary volcanic stratigraphic sequence built on the same ca 3 0 ga basement and have autochthonous relationships with each other u pb zircon id tims geochronology constrained the ages of two episodes of deformation d 1 and d 2 in the belt two dykes crosscutting an older foliation place a minimum age of ca 2 723 ga on the d 1 deformation and two syn kinematic dykes dated movement along d 2 transpressional shear zones at ca 2 70 ga geological geochemical and geochronological data indicate that the tectonic evolution in the island lake greenstone belt and in the northwestern superior province took place in three main stages the first two stages involved the generation of meso and neoarchean volcanic assemblages and contemporaneous plutonic rocks which is interpreted to be due to southward dipping subduction under the north caribou terrane this plate tectonic model is in contrast with well documented northward dipping subduction south of the north caribou terrane the third stage involved movement along late transpressional shear zones at ca 2 70 ga at the end of this geodynamic process the hudson bay terrane was terminally docked to the north caribou terrane along the north kenyon fault