a new late holocene sea level record from the mississippi delta evidence for a climate sea level connection abstract a detailed relative sea level rsl record was constructed for the time interval 600 1600 ad using basal peat to track sea level and containing 16 sea level index points that capture 60 cm of rsl rise the study area is in the mississippi delta where the spring tidal range is 0 47 m the impact of ocean currents on sea surface topography is limited and crustal motions are well constrained age control was obtained by ams 14 c dating and most ages represent weighted means of two subsamples sample elevations were determined by combining differential gps measurements with optical surveying all index points were plotted as error boxes using 2 confidence intervals for the ages plus all vertical errors involved in sampling and surveying as well as the indicative range of the samples a striking clustering of sea level index points between 1000 and 1200 ad suggests a possible acceleration in the rate of rsl rise removal of the long term trend 0 60 mm yr 1 allows for the possibility of a sea level oscillation with a maximum amplitude of 55 cm however given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out comparison of the new rsl record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes including the medieval warm period and the little ice age however given the error margins associated with this reconstruction it is stressed that this causal mechanism is tentative and requires corroboration by high resolution sea level reconstructions elsewhere

seeing the wood from the trees reconstructing past climates is important if we are to distinguish anthropogenic warming from natural variability in the climate system briffa and osborn 1 discuss a recent study by mann et al that has extended their northern hemisphere climatic reconstruction to a d 1000 and explain why there are large uncertainties in the reconstruction of medieval and earlier temperatures on large spatial scales thus although the 20th century was almost certainly the warmest of the millennium the amount of anthropogenic warming remains uncertain 1 http www sciencemag org cgi content full 284 5416 926

onset of recent rapid sea level rise in the western atlantic ocean a high resolution record of sea level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2 m thick salt marsh peat sequence at chezzetcook nova scotia canada former mean tide level positions are reconstructed with a precision of 0 055 m using a transfer function derived from distributions of modern salt marsh foraminifera our age model for the core section older than 300 years is based on 19 ams 14c ages and takes into account the individual probability distributions of calibrated radiocarbon ages the past 300 years is dated by pollen and the isotopes 206pb 207pb 210pb 137cs and 241am between ad 1000 and ad 1800 relative sea level rose at a mean rate of 17 cm per century apparent pre industrial rises of sea level dated at ad 1500 1550 and ad 1700 1800 cannot be clearly distinguished when radiocarbon age errors are taken into account furthermore they may be an artefact of fluctuations in atmospheric 14c production in the 19th century sea level rose at a mean rate of 1 6 mm yr between ad 1900 and ad 1920 sea level rise accelerated to the modern mean rate of 3 2 mm yr this acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming 2005 elsevier ltd all rights reserved

coupling instrumental and geological records of sea level change evidence from southern new england of an increase in the rate of sea level rise in the late 19th century 1 we construct a high resolution relative sea level record for the past 700 years by dating basal salt marsh peat samples above a glacial erratic in an eastern connecticut salt marsh to test whether or not the apparent recent acceleration in the rate of sea level rise slr is coeval with climate warming the data reveal an average slr rate of 1 0 0 2 mm year from about 1300 to 1850 a d coupling of the regional tide gauge data 1856 to present with this marsh based record indicates that the nearly three fold increase in the regional rate of slr to modern levels likely occurred in the later half of the 19th century thus the timing of the observed slr rate increase is coincident with the onset of climate warming indicating a possible link between historic slr increases and recent temperature increases

relative sea level rise and climate change over the last 1500 years we constructed a detailed relative sea level rise curve for the last 1500 years using a novel approach i e charting the rate of relative sea level rise using microfaunal and geochemical data from a coastal salt marsh sequence clinton ct usa the composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively the resulting sea level rise curve with age control from 14c dating and the onset of anthropogenic metal pollution shows strong increases in the rate of relative sea level rise during modern global warming since the late nineteenth century but not during the little climate optimum ad 1000 1300 there was virtually no rise in sea level during the little ice age ad 1400 1700 most of the relative sea level rise over the last 1200 years in clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years changes from slow to fast rates of relative sea level rise apparently occurred over periods of only a few decades we suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea level rise along the northeastern usa seaboard relative sea level rise in that area is currently faster than the worldwide average which may result partially from an ocean surface effect caused by hydrodynamics our data show no unequivocal correlation between warm periods on a decaal to centennial time scale and accelerated sea level rise one period of acclerated sea level rise may have occurred between about ad 1200 and 1450 which was the transition for the little climate optimum to the little ice age i e a period of cooling at least in northwestern europe local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea level however the second period of accelerated sea level rise occurred during the period of modern global warming that started at the end of the last century

peralkaline granitoid magmatism in the mongolian transbaikalian belt evolution petrogenesis and tectonic significance article i nfo the central asian orogenic belt caob is well known for its massive generation of juvenile crust in the phanerozoic in eastern caob voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanics were emplaced in three stages from early permian to late mesozoic 295 270 ma 230 190 ma and 150 120 ma they occur as huge granitoid belts in extensional tectonic settings and form a complex network of about 12 million km 2 in area among them the 2500 km long mongolian transbaikalian belt mtb is the most spectacular and it comprises more than 350 granite syenite plutons and stocks with numerous co genetic volcanic fields the three stages of granitoids have similar chemical compositions but show temporal variation in nd isotopic composition initial end t values range from 1t o 5 for the early permian 0 to 4 for the early mesozoic and 2t o 3 5 for the late mesozoic granitoids the negative end t values observed in the mtb are not typical of the caob granitoids which are generally characterized by positive values however several pieces of evidence suggest that the mtb peralkaline and alkali feldspar granitoids were produced from enriched mantle derived sources the evidence includes 1 felsic and mafic rocks formed in the same stage have similar initial nd sr isotopic ratios and sm nd model ages tdm 2 the granitoid belts extend over thousands of kilometers and intersect distinct crustal provinces but no correlation is found in chemical compositions between the granitoids and country rocks 3 the abundant syenites are considered to be cogenetic or in some cases parental to the granites experimental and isotope data argue for the derivation of syenites from an enriched mantle source thus the granites and comendites are regarded as mantle derived 4 a study of melt inclusions in quartz phenocrysts of comendite indicates a high liquidus temperature of 1000 1100 c for the magma generation this suggests that the silicic magma was generated in an unusually high temperature condition which is likely produced by basaltic magma that underplated the lower crust the generation of voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanic rocks represents an important addition of juvenile crustal mass to the earth s continental crust during a time span of about 150 ma from late paleozoic to late mesozoic

surface distributions of salt marsh foraminifera from connecticut usa modern analogues for high resolution sea level studies abstract salt marsh foraminifera are routinely used as sea level indicators since their vertical distribution is closely linked with elevation relative to the tidal frame the precise nature of these relationships is variable in time and space and the accuracy of sea level reconstructions depends upon the selection of appropriate modern analogues that reliably reflect past fauna environment associations the marshes of connecticut usa are sites of ongoing research seeking to produce high resolution records of sea level change yet little published data regarding their modern foraminiferal distributions exist this paper presents new surface foraminiferal data from three connecticut salt marshes and evaluates their suitability as modern analogues for past sea level changes the results indicate that significant intra and inter site variability between these marshes and those of neighbouring states exists as a consequence of this the extrapolation of fauna environment relationships developed from marshes with different hydrographic physiographic vegetative or climatic characteristics may produce erroneous reconstructions even when adjusted for variations in tidal range these errors are potentially greatest if single indicator species are used since the relative abundance of individual taxa does not vary consistently with elevation even in high marsh environments from the same site whilst cluster analysis demonstrates that foraminiferal assemblages from connecticut are vertically zoned with respect to mean high water mhw the composition elevation and height range of these zones is variable between sites this spatial heterogeneity results in reconstructions of relatively low and variable precision that restricts their utility in high resolution sea level research new studies seeking to distil decimetre scale changes in relative sea level will need to employ quantitative methods capable of combining multi site information to develop fauna environment relationships that capture this spatial variability reconstructions will be most precise when employing local foraminiferal distributions but may require the collection of additional modern analogue samples from other regions when the extant foraminiferal population of a site differs in composition from its sub fossil counterpart

relative sea level rise across the eastern border fault branford connecticut evidence against seismotectonic movements abstract basal peat age depth data from four salt marsh sites located 500 1500 m south of the eastern border fault ebf near branford connecticut document an error envelope for the lower limit of relative mean high water mhw rise during the past 3300 yr the long term rate of relative lower limit mhw rise during the past 3000 yr 1 1 mm yr 1 corresponds with late holocene rates of relative mhw rise found elsewhere in coastal connecticut 0 9 1 2 mm yr 1 this result invalidates repeated claims that multiple seismotectonic lowering of a crustal block towards the south has occurred along a segment of the ebf near branford shortly after 815 cal yr bc and during the past 1200 yr and calls for a non tectonic interpretation of biostratigraphic evidence of local short term sea level variations

contemporary foraminiferal distributions of a mangrove environment great barrier reef coastline australia implications for sea level reconstructions abstract contemporary foraminiferal samples and associated environmental information were collected from cocoa creek a mesotidal fringing mangrove environment on the great barrier reef gbr coastline australia to elucidate the relationship of the foraminiferal assemblages with elevation and environment there is a strong and highly significant relationship between elevation and the foraminiferal assemblages supporting the intertidal vertical zonation concept which suggests that the distribution of foraminifera in the intertidal zone is usually a direct function of elevation with the most important controlling factors being the duration and frequency of subaerial exposure multivariate analyses separate the intertidal foraminiferal assemblages into three elevational zones with zone i the highest and zone iii the lowest zones i and ii are dominated by agglutinated species trochammina inflata and miliammina fusca respectively and zone iii is dominated by calcareous species notably ammonia tepida and elphidium discoidale multiloculum these assemblage zones are similar to those found in both tropical and temperate intertidal environments a predictive transfer function has been developed to allow reconstruction of former sea levels for tropical environments based upon the relationship between foraminiferal assemblage and elevation results suggest that a precision of 0 07 m should be attainable superior to most similar studies from temperate mid latitude environments our work has produced the first foraminifera based transfer function for environmental interpretations for tropical australia and allows the potential development of a new generation of high resolution sea level reconstructions for the post glacial sequences of the gbr shelf

central city colorado the upper part of an alkaline porphyry molybdenum system the distribution of molybdenite fluorite rhodochrosite enargite and telluride minerals together with anomalous quantities of cu pb zn and mo in rocks and variations in stable isotope ratios define a complex zoned hydrothermal system in the central city mining district the molybdenite mineralization is centered on a laramide quartz bostonite or alkali rhyolite breccia pipe that occurs at the intersection of the dory hill fault and the idaho springs ralston shear zone stream sediment geochemistry suggests that significant amounts of w may be present in the system uranium base and precious metal mineralization of a similar age but with a distribution different from the molybdenite mineralization is also present and is considered to be a part of the same hydrothermal system fluid inclusion data for the molybdenite and precious and base metal mineralization indicate that fluid inclusions associated with early molybdenite veins are of two types co 2 rich and rare halite bearing with respective homogenization temperatures of 340 degrees to 420 degrees c and 240 degrees to 340 degrees c inclusions associated with precious metal bearing pyrite and base metal veins are aqueous two phase types with homogenization temperatures in the range of 220 degrees to 380 degrees c those from late molybdenite veins are aqueous two phase inclusions with homogenization temperatures of 200 degrees to 280 degrees c salinities as equiv wt nacl are between 34 to 42 for halite bearing inclusions and 2 to 12 for all other types no evidence of boiling has been found trapping pressures of co 2 rich inclusions are 0 46 to 0 75 kb which suggest an emplacement depth of about 2 km for the molybdenite mineralization respective quartz delta 18 o and fluid inclusion delta d values are 1 early molybdenite veins 9 3 to 14 3 per mil and 87 to 66 per mil 2 precious metal bearing pyrite and base metal veins 8 4 to 15 9 per mil and 90 to 47 per mil and 3 late molybdenite veins 10 1 to 15 4 per mil and 77 to 69 per mil with associated fluorite having fluid inclusion delta d values of 70 to 57 per mil a late telluride vein has a quartz delta 18 o value of 11 2 per mil and fluid inclusion delta d value of 86 per mil these data suggest that all except the telluride ore fluids contained large proportions of a d rich magmatic fluid the distribution of fluid inclusion delta d values defines two distinct anomalies each zoned with delta d enrichment occuring inward toward centers which correspond to the areas of known molybdenite occurrences and precious and base metal mineralization likewise delta d values for sericites developed during early hydrothermal activity increase inward toward the quartz bostonite pipe various intrusive breccias and molybdenite mineralization in the district there is no indication at central city of negative delta 18 o anomalies in the precambrian country rock within or peripheral to the centers of mineralization suggesting that ore fluids were thus essentially confined to discrete fractures it is concluded that molybdenite and other mineralization in this classic gold mining district may be related and may represent the upper part of an alkaline porphyry molybdenum system

north atlantic climate ocean variations and sea level in long island sound connecticut since 500 cal yr a d abstract a record of detrended mean high water mhw variations from hammock river marsh connecticut is extended from ca 850 to ca 500 cal yr a d and correlated with summer temperature reconstructions from northern fennoscandia and northern eurasia greenland ice sheet project 2 18 o and greenland ice core project borehole temperature variations from central greenland a sargasso sea sea surface temperature sst record and a proxy record for deep ocean flow south of iceland the records from northern fennoscandia eurasia and central greenland document century scale intervals of warming four and cooling three since ca a d 850 the mhw fluctuations lag behind these climate intervals by 0 100 yr with the two larger mhw rises corresponding to the two larger temperature increases this positive correlation suggests that surface air temperature sat is a dominant variable controlling sea level in the northwestern north atlantic since ca a d 850 the sst variations parallel the mhw fluctuations back to ca 950 cal yr a d a positive correlation is found also for sub century scale sat and mhw variations during the period a d 500 850 but this result is less firm mhw sst correlation over this time interval is not consistent

quantifying the contribution of sediment compaction to late holocene salt marsh sea level reconstructions north carolina usa abstract salt marsh sediments provide accurate and precise reconstructions of late holocene relative sea level changes however compaction of salt marsh stratigraphies can cause post depositional lowering pdl of the samples used to reconstruct sea level creating an estimation of former sea level that is too low and a rate of rise that is too great we estimated the contribution of compaction to late holocene sea level trends reconstructed at tump point north carolina usa we used a geotechnical model that was empirically calibrated by performing tests on surface sediments from modern depositional environments analogous to those encountered in the sediment core the model generated depth specific estimates of pdl allowing samples to be returned to their depositional altitudes after removing an estimate of land level change error in variables changepoint analysis of the decompacted and original sea level reconstructions identified three trends compaction did not generate artificial sea level trends and cannot be invoked as a causal mechanism for the features in the tump point record the maximum relative contribution of compaction to reconstructed sea level change was 12 the decompacted sea level record shows 1 71 mm yr 1 of rise since ad 1845

the sweet home rhodochrosite specimen mine alma district central colorado the porphyry molybdenum fluorine connection intermediate sulfidation veins containing quartz sphalerite tetrahedrite rhodochrosite fluorite in the sweet home mine alma district colorado were originally mined for silver starting in 1873 for the last 13 years up until 2004 however the mine has produced world class rhodochrosite specimens some of these specimens are considered to be among the finest mineral specimens ever produced and the finest of their species with values well over 1 million us dollars the extraction preparation and marketing techniques pioneered at the sweet home operation have revolutionized the minerals specimen industry the sweet home deposit is interpreted as a single pulse variant of a climax type hydrothermal system evidence for this includes 1 an age of mineralization 25 8 0 3 ma that coincides with the age of the end stages of mineralization of the climax molybdenum deposit approximately 7 5 km to the northeast 2 a geochemical mn w f and mineralogical topaz fluorite hubnerite greisen muscovite signature typically associated with climax type systems 3 the presence of porphyry rhyolite dikes a breccia dike and local quartz molybdenite veins in the nearby area 4 a small pegmatite within the mine with an age 25 9 0 3 ma coincident with mineralization which also contains minor amounts of disseminated molybdenite and 5 the presence of similar appearing gemmy red rhodochrosites at climax and other high silica rhyolite systems a significant difference is that unlike climax type systems the sweet home hydrothermal system appears to have consisted of a single relatively small pulse of magmatic fluid that slowly cooled and diluted with groundwater this is inferred to have occurred at moderate depths in the order of 1 5 2 5 km below the surface the fluids that formed the sweet home veins were dilute salinity in the order of 2 4 wt nacl equivalent high temperature temperatures of homogenization up to 370 c and initially of magmatic origin gem quality ruby red rhodochrosite at the sweet home mine is nearly pure manganese carbonate with minimal solid solution with fe 2 ca or mg it formed at higher temperatures and salinities in comparison to lower value pink rhodochrosite gemmy ruby red rhodochrosite is distinctly associated with highly evolved silica rich igneous hydrothermal systems the high fluorine content typical of such systems suggests that mn was transported in solution as fluoride complexes which in turn favored rhodochrosite deposition at above average temperatures and with minimal cation contamination

salt marsh reconstructions of relative sea level change in the north atlantic during the last 2000 years abstract sea level changes record changes in the mass balance of ice sheets and mountain glaciers as well as dynamic ocean atmosphere processes unravelling the contribution of each of these mechanisms on late holocene timescales ideally requires observations from a number of sites on several coasts within one or more oceans we present the first 2000 year long continuous salt marsh based reconstructions of relative sea level rsl change from the eastern north atlantic and uniquely from a slowly uplifting coastline we develop three rsl histories from two sites in north west scotland to test for regional changes in sea level tendency a positive tendency indicating an increase in the proximity of marine conditions and a negative tendency the reverse whilst at the same time highlighting methodological issues including the problems of dataset noise when applying transfer functions to fossil salt marsh sequences the records show that rsl has been stable 0 4 m during the last two millennia and that the regional sea level tendency has been negative throughout most of the record lengths a recent switch in the biostratigraphy of all three records indicating a regional positive tendency means we cannot reject the hypothesis of a 20th century sea level acceleration occurring in north west scotland that must have exceeded the rate of background rsl fall 0 4 mm yr 1 but this signal appears muted and later than recorded from the western north atlantic

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

mangrove pollen of indonesia and its suitability as a sea level indicator we investigated the mangroves of southeast sulawesi indonesia to assess their potential as proxies for reconstructing sea level during the holocene initial investigations confirmed that the mangrove species demonstrate zonations parallel to the shoreline and are dominated by the family rhizophoraceae with avicennia heritiera and sonneratia also important constituents of the mangroves we investigated the vertical distributions of pollen assemblages at three sites partial cca analysis demonstrated that at all three sites elevation was a significant control on the distribution of pollen assemblages in surface samples we combined the three contemporary transects to develop a regional transfer function to explain the relationship between the surface assemblages and elevations using the maximum likelihood ml method the developed transfer function indicated mangrove pollen can be used as a precise indicator of past sea levels with an error of 0 22 m the transfer function was applied to two fossil cores from the wakatobi marine national park and evaluated using the modern analogue technique both cores showed similar patterns in changes of palaeo mangrove elevation and had modern analogues in the contemporary training set we conclude that mangrove pollen is a suitable proxy for reconstructing sea level in tropical environments

distribution of modern salt marsh foraminifera in the albemarle pamlico estuarine system of north carolina usa implications for sea level research abstract we described the distributions of foraminifera from ten physiographically distinct salt marshes in the albemarle pamlico estuarine system north carolina using 193 surface samples we defined elevation dependent ecological zones at individual sites using cluster analysis and detrended correspondence analysis additionally seven principal biozones of salt marsh foraminifera were identified that have distinctive spatial distributions reflecting a pattern of salinity regimes caused by the current configuration of barrier island inlets high salinity sites along the southern outer banks are associated with sub tidal calcareous assemblages low marshes dominated by miliammina fusca and high marsh environments defined by haplophragmoides wilberti trochammina inflata and arenoparrella mexicana in contrast lower salinity marshes have ammobaculites spp in sub tidal settings miliammina fusca dominated low marshes and high marsh settings characterized by jadammina macrescens spatial variation of foraminiferal populations and the potential for biozones to migrate in response to changing inlet configuration and salinity suggests that datasets of modern salt marsh foraminifera from multiple environments would be appropriate for reconstructing holocene relative sea level in north carolina

sea level variability in the northwest atlantic during the past 1500 years a delayed response to solar forcing 1 numerical experiments with a coupled oceanatmosphere model ecbilt have shown that centennial variations in sea level sl in the northwest atlantic may be associated with deep ocean salinity anomalies generated by solar forced variations in the north atlantic overturning circulation here we compare simulated sl curves for the gulf stream region with reconstructed late holocene sl records from connecticut usa simulated sl variations lag the solar forcing record by ca 120 year this lag is found to be robust over a small number of different experiments the reconstructed sl curves visually match the solar forcing optimally when lagging it by ca 125 yr a quantitative test shows that the correlation is significant while this result is not sensitive to dating uncertainties the temporal response pattern of the simulated sl curves compares reasonably well with the reconstructions index terms 4556 oceanography physical sea level variations 1650 global change solar variability 4255 oceanography general numerical modeling 4267 oceanography general paleoceanography 3030 marine geology and geophysics micropaleontology citation van de plassche o g van der schrier s l weber w r gehrels and a j wright sea level variability in the northwest atlantic during the past 1500 years a delayed response to solar forcing geophys res lett 30 18 1921 doi 10 1029 2003gl017558 2003

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

contrasting records of sea level change in the eastern and western north atlantic during the last 300 years we present a new 300 year sea level reconstruction from a salt marsh on the isle of wight central english channel uk that we compare to other salt marsh and long tide gauge records to examine spatial and temporal variability in sea level change in the north atlantic our new reconstruction identifies an overall rise in relative sea level rsl of c 0 30 m since the start of the eighteenth century at a rate of 0 9 0 3 mmyr 1 error in variables changepoint analysis indicates that there is no statistically significant deviation from a constant rate within the dataset the reconstruction is broadly comparable to other tide gauge and salt marsh records from the european atlantic demonstrating coherence in sea level in this region over the last 150 300 years in contrast we identify significant differences in the rate and timing of rsl with records from the east coast of north america the absence of a strong late 19th early 20th century rsl acceleration contrasts with that recorded in salt marsh sediments along the eastern usa coastline in particular in a well dated and precise sea level reconstruction from north carolina this suggests that this part of the north carolina sea level record represents a regionally specific sea level acceleration this is significant because the north carolina record has been used as if it were globally representative within semi empirical parameterisations of past and future sea level change we conclude that regional scale differences of sea level change highlight the value of using several regionally representative rsl records when calibrating and testing semi empirical models of sea level against palaeo records this is because by using records that potentially over estimate sea level rise in the past such models risk over estimating sea level rise in the future

the climax alma granite batholith of oligocene age and the prophyry molybdenum deposits of climax colorado u s a abstract the porphyry molybdenum deposits of climax colorado are stockworks of quartz molybdenite veinlets they are apical to intrusive cupolas of leucocratic rhyolite granite porphyry of oligocene age 33 to 24 ma the upper parts of the orebodies are overprinted by overlying zones of phyllically altered rocks and by stockworks of greisen like veinlets containing quartz pyrite topaz and huebnerite the phyllic and or greisen like zones are surrounded by a propylitic zone characterized by quartz chlorite hematite veinlets and chlorite after biotite late veins radial and peripheral to the intrusive center are common but widely scattered and discontinuous such veins typically contain quartz fluorite rhodochrosite pyrite dark sphalerite galena tetrahedrite and traces of huebnerite molybdenite argentite native gold and or electrum the alma district 4 to 10 km southeast of climax contains widely scattered clusters of veins and replacement deposits the veins cut chloritized to sericitized silicate host rocks and the replacement deposits are in carbonate host rocks the ore and gangue mineral assemblages of the veins of the alma district resemble those of veins peripheral to the climax molybdenum deposits veins of the alma district cut dikes of late white rhyolite 35 ma which resemble the rhyolite porphyries of climax a swarm of such dikes is parallel to the long axis of an elliptical drainage pattern which bounds a structural dome here called the outer alma dome the outer alma dome 8 12 km surrounds an inner alma dome 6 8 km veins of the alma district generally are axial and or marginal to the outer alma dome and or radial to the inner alma dome veins and alteration minerals associated with the outer alma dome formed between 35 and 27 ma ago those associated with the inner alma dome formed about 27 ma ago as indicated by fission track age determinations on thermally annealed zircon grains from hydrothermally altered rocks within and around the inner alma dome negative bouguer gravity anomaly patterns indicate 1 a regional northeast trending gravity low associated with the composite monzonite granodiorite granite b batholith of the colorado mineral belt average density about 2 62 g cm3 2 a semi regional gravity trough within the gravity low of the colorado mineral belt extending northeastward across the mosquito range 3 an oval pattern of gravity lows coincident with the alma domes and 4 a closed gravity low associated with the climax stock density about 2 56 g cm3 tweto and case 1972 behrent and bajwa 1974 corry 1981 the semi regional gravity trough is interpreted as the gravimetric expression of a granite batholith here called the climax alma batholith the gravity lows of the climax and alma districts are interpreted as expressions of cupolas on this granite batholith the highly differentiated rhyolite granite intrusions of climax plunge toward the alma domes the climax intrusions are interpreted as products of apical differentiation of the inferred climax alma granite batholith magmatic hydrothermal fluids associated with highly differentiated apical magmas produced the climax molybdenum orebodies most of the veins and replacement deposits of the alma district are associated with lower broader cupolas of the inferred granite batholith the shape of the composite climax alma magmatic hydrothermal system resembles that of a teapot with climax above the spout and the alma district above the lower broadly domed lid

sea level climate correlation during the past 1400 yr we present a new mean high water curve for hammock river marsh clinton connecticut obtained by improving the age model for an existing record of relative marsh elevation based on foraminiferal analysis of a 1 8 m long peat core unlike the earlier curve the new curve confirms trend changes in mean high water rise during the past 1400 yr as noted for salt marshes 15 km farther west suggesting a regional cause these trend changes and century scale mean high water variations in the clinton record correlate positively with large scale regional variations in sea surface and summer air temperature indicating a link between sea level and the climate ocean system on the basis of the clinton mean high water curve we conclude that real sea level oscillated centimeters to decimeters on a century time scale over the past 1400 yr was 25 25 cm higher ca a d 1050 medieval warm period than ca a d 1650 little ice age and rose at a mean rate of 1 mm yr 1 over the past 350 yr there was little or no rise during the cool 1800s

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

sm nd dating of scheelite and tourmaline implications for the genesis of archean gold deposits val d or canada sm nd analyses of 19 scheelite samples from auriferous quartz carbonate tourmaline scheelite gold veins from three mines in the val d or gold camp in the abitibi greenstone belt in western quebec the sigma pascalis north and siscoe extension mines yield a linear array on an isochron diagram with a mean square weighted deviation mswd of 3 6 corresponding to an age of 2596 or 33 ma and epsilon sub nd 1 2 5 eight scheelite samples from the pascalis north mine alone define an excellent linear array with an mswd 0 31 an age of 2593 or 18 ma and epsilon sub nd 1 2 7 these ages are interpreted to represent the age of quartz carbonate tourmaline scheelite vein hosted gold mineralization in the three mines sampled sm nd analyses of tourmaline suggest that this mineral may also be useful for sm nd dating of hydrothermal mineralization the sm nd scheelite age of ca 2600 ma is in good agreement with u pb ages obtained from mineralization related rutile and titanite in the val d or area these results indicate that the quartz carbonate tourmaline scheelite vein hosted gold mineralization was emplaced approximately 70 m y later than the youngest observed premineralization magmatic activity and approximately 60 m y later than peak regional metamorphism in the val d or area these ages do not support hypotheses for deposit formation which involve fluids derived from spatially related intrusive rocks or metamorphism although they do not preclude an earlier stage of introduction of gold into the val d or area the scheelite sm nd age and depleted mantlelike epsilon sub nd 1 and the mineralogy and alteration of the quartz carbonate tourmaline veins are consistent with the derivation of the mineralizing fluids from a relatively homogeneous external source and introduction into the upper crust as part of a single large hydrothermal system the formation of the val d or gold deposits also appears to be broadly synchronous with the growth of zircon in high grade metamorphic rocks of the lower crust underlying the greenstone belt material suggesting that these may be related processes

the direction of the earth s magnetic field at london 1570 1975 the observations of magnetic declination and dip made in london over the past 400 years comprise one of the longest and most complete series of such data for anywhere in the world they give an indication of secular change on a time scale intermediate between that of recent observatory measurements and of archaeomagnetic measurements we have attempted to catalogue all direct measurements of declination and dip paying particular attention to completeness in the earlier years and tracing the data to their original source wherever possible sufficient details of the observations are given for an assessment of their reliability and accuracy the data are then corrected to a single site fitted with a continuous smooth curve and discussed

assessing sea level data from connecticut usa using a foraminiferal transfer function for tide level concerns surrounding possible future climate change sea level rise and their potential impacts on coastal environments have stimulated research seeking to elucidate the relationship between ocean levels and climate at the sub century scale the need for increasingly precise reconstructions of relative sea level change has in turn driven the development of new methodologies capable of resolving fine scale variability within salt marsh sedimentary sequences the use of salt marsh foraminifera as precise indicators of past tide levels has played a central role in this process and is exemplified by a number of detailed studies conducted in connecticut usa in this paper we apply the most recent methodological advance in the reconstruction of relative sea levels using salt marsh foraminifera we develop a foraminiferal transfer function for tide level derived from the modern foraminiferal distributions of four connecticut salt marshes in contrast to existing approaches that employ site specific interpolations of local vertical foraminiferal assemblage zones this transfer function can provide objective quantitative and reproducible estimates of palaeomarsh surface elevation with explicitly stated error terms for marshes throughout connecticut irrespective of differences in tidal range we demonstrate the foraminiferal transfer function approach by employing it to reconstruct changes in palaeomarsh surface elevation from three cores recovered from hammock river marsh connecticut the resulting reconstructions which are precise to f0 09 m are tested using an independent dataset from the neighbouring state of maine and are used to assess a pivotal record of mean high water mhw change from this site we conclude that the transfer function reconstructions show good general agreement with previous records of palaeomarsh surface elevation but with the advantages of quantified error terms and a transparent reproducible methodology this replicability will assist in the comparison or combination of local records of mhw change to infer large scale regional sea level variations d 2003 elsevier b v all rights reserved

hydraulic back flood model for the archaeological stratigraphy of the connecticut river alluvial lowland central connecticut usa abstract state mandated archaeological investigations associated with urban renewal in downtown hartford led to the development of a mechanistic model for holocene floodplain sedimentation in central connecticut our model is based on historic flood hydrometeorology and geomorphologic mapping the lithologic magnetic pollen and archaeological stratigraphy exposed in sixteen deep boreholes and 24 hydraulic push cores the chronology provided by sixteen ams radiocarbon ages and diagnostic historic artifacts ranging from 10 030 cal bp to the present we conclude that the alluvial stratigraphy in this part of the lowland resulted from bottom up changes in hydraulic ponding at a bedrock outlet rather than from top down responses of the watershed to changes in climate vegetation or human activity our model provides a geologically based time space framework for the distribution of known archaeological sites and carries implications for future research

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

a sea level rise curve from guilford connecticut usa abstract high resolution stratigraphic studies based on sediment chemistry lithology macroflora and benthic foraminiferal assemblages in three peat cores from coastal salt marshes at guilford connecticut show that coastal marshes are ephemeral environments marsh wide environmental variations were common and century long episodes of relative submergence alternated with emergence despite about 2 m of relative sea level rise rslr in connecticut over the last 1500 years the marshes have expanded both landwards and seawards and marsh accretion has been outpaced only marginally by rslr we used radiocarbon dating and the level of anthropogenic markers metal pollution as dated with 210 pb in the cores for age control for most of the last 1000 years the rate of rslr was between 1 3 and 1 8 mm yr but over the last 300 400 years it increased to 2 9 3 3 mm yr and has been faster than the accretion rate especially in the middle marsh the net submergence rate or submergence index ratio of the rate of rslr and marsh accretion rate averaged about 1 15 over the last 1000 years and increased to about 1 5 over the last 200 years the rate of rslr was very sluggish during the early part of the little ice age but we found a slightly higher rate during the little climate optimum this excursion is close to the noise level however the most significant observation is that rslr increased strongly around a d 1650 the onset of this acceleration falls in the middle to end of the little ice age and thus preceded the period of modern global warming that started late last century and that has been tentatively correlated with anthropogenic emissions of greenhouse gases

seasonal fluctuations in sea level on the south carolina shelf and their relationship to the gulf stream near bottom pressure measurements obtained over a 9 month period in 1978 on the outer continental shelf off south carolina document that sea level rose 35 to 50 cm between july and october records of coastal sea level showed a similar rise when the pressure and coastal sea level records were corrected for the effects of wind stress and temperature the largest portion of the rise in the two variables remained the amplitude of the change in residual sea level was largest at the shelf break 28 cm and decayed to 22 cm at the coast the relatively small magnitude of the decay suggests that alongshelf pressure gradients imposed at the shelf break have minimum alongshelf wavelengths of 2000 km the changes in residual sea level were seasonal and associated with seasonal changes in the transport of the gulf stream the 3 years of residual sea level records examined here indicate that the amplitude of a typical decrease in transport of the gulf stream off south carolina between july and october has a strong interannual variability the change in transport can be 50 lower to over 100 higher than the historical average the residual sea level records also suggest that a change in transport of the gulf stream is not strongly related to the onshore offshore position of the gulf stream

rapid sea level rise in the gulf of maine usa since ad 1800 two sea level records from salt marshes in coastal maine are derived from foraminiferal analyses and ams 14 c 210 pb 137 cs and pollen chronology both records cover the period from ad 800 until the present and show corresponding patterns of sea level change when corrected for trends which could accommodate millennial scale isostatic adjustments the records provide a detailed sea level chronology for the last few centuries and thus link the instrumental tide gauge record with the long term geological record of sea level change results show that sea level was relatively stable between ad 800 and 1300 and reached a lowstand around ad 1800 which was preceded by an oscillation in the eighteenth century since ad 1800 sea levels in the gulf of maine have risen by 0 3 0 4 m the onset of this rise corresponds with regional climatic warming and could be interpreted as thermal expansion of the gulf of maine and north atlantic sea surface sea level rise possibly slowed temporarily during the mid nineteenth century but twentieth century rates are unprecedented in the last millennium and correspond with hemispheric warming

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

timing and processes of late mesozoic mid lower crustal extension in continental ne asia and implications for the tectonic setting of the destruction of the north china craton mainly constrained by zircon u pb ages from metamorphic core complexes abstract late mesozoic large scale crustal extension occurred across the northeastern section of continental asia and metamorphic core complexes mccs are the major features in this region this paper presents new zircon u pb and ar ar ages of biotite and hornblende for pre or syn mylonitized and post kinematic unmylonitized intrusions from these mccs and attempts to determine the timing of initiation duration and termination of the mid lower crustal ductile extension by integrating with geochronological data from previous studies these mccs have similar 40 ar 39 ar biotite and hornblende ages 130 to 110 ma mainly from 130 to 120 ma which are interpreted as the cooling ages and represent the timing of the late stage formation of the mccs zircon u pb ages for syn to post kinematic intrusions from some mccs suggest that the mid lower crustal extension probably initiated at ca 150 145 ma with a peak occurring 145 130 ma and continued to 130 120 ma which is older than that suggested by 40 ar 39 ar ages by 10 20 ma the early ductile extension most likely initiated in mongolia and northern china during the late jurassic 150 145 ma at a deeper level then propagated southwards 140 130 ma and finally developed throughout the entire continental ne asia 130 120 ma based on the timing and processes of the extension a geodynamic model and tectonic setting of the destruction of the north china craton ncc are proposed

a paleomagnetic study from the late jurassic volcanics 155 ma north china implications for the width of mongol okhotsk ocean abstract a new paleomagnetic study has been carried out on the tiaojishan formation effusives in the chengde area north china block ncb the age of the tiaojishan formation volcanics was recently dated from 153 ma to 161 ma by u pb and 40 ar 39 ar a total of 154 samples from 16 sites within the tiaojishan formation were collected detailed stepwise thermal demagnetization allows us to isolate two components from 77 oriented drill core samples a low temperature component identified in most samples falls close to the present local earth field direction characteristic remanent directions obtained from high temperature pass reversal test yield a pole position at 240 3 e 59 9 n with 95 6 8 combined with coeval paleopoles obtained from the siberia block sib these results show a significant paleolatitude displacement between the ncb and sib which indicates that the mongol okhotsk ocean was still open with 3000 km width in its eastern part at ca 155 ma

fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising fluids the naturally occurring noble gas isotopes 40ar 36ar 84kr and 129xe and halogens cl br i have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits pcd bingham canyon utah and silverbell ray mission pinto valley and globe miami in arizona in addition analyses of 3he 4he have been obtained from sulphide minerals hosted by the quartz veins at silverbell ray pinto valley and globe miami the majority of pcd fluids studied have br cl and i cl ratios that overlap those of fluids included in mantle diamond suggesting that the salinity had a juvenile origin the high i cl 121 10 6 mole m in samples from the propylitic zone of silverbell is attributed to the presence of sedimentary formation water 3he 4he ratios have r ra values in the range 0 3 to 1 72 and provide evidence for the involvement of a crustal component in addition to mantle volatiles 40ar 36ar ratios vary from meteoric values of 317 in the propylitic zone of bingham canyon and 323 in the skarn alteration of mission up to 3225 in the potassic zone of pinto valley fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end member comprising meteoric water and air and a high salinity end member consisting of a mixed mantle and crustal fluid the 40ar cl ratio of fluid inclusions at pinto valley 10 4 m is similar to values obtained previously for mantle fluids the 40ar cl value is two orders of magnitude lower at bingham canyon where a depleted 36ar concentration 0 2 10 6 cm3 g below that of air saturated water asw and a range of highly fractionated noble gas compositions f84kr 13 and f129xe 160 indicate that boiling and pulsed fluid flow have occurred

on the unpredictability of geomagnetic secular variation abstract various methods for the prediction of secular variation are tested by applying them to data for a single element at a single station none of them is of any use for more than a few years

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

a geochemical study of the sweet home mine colorado mineral belt usa hydrothermal fluid evolution above a hypothesized granite cupola deposition of quartz molybdenite pyrite topaz muscovite fluorite and subsequent hubnerite and sulfide fluorite rhodochrosite mineralization at the sweet home mine occurred coeval with the final stage of magmatic activity and ore formation at the nearby world class climax molybdenum deposit about 26 to 25 m y ago the mineralization occurred at depths of about 3 000 m and is related to at least two major fluid systems 1 one dominated by magmatic fluids and 2 another dominated by meteoric water the sulfur isotopic composition of pyrite strontium isotopes and rey distribution in fluorite suggest that the early stage quartz molybdenite pyrite topaz muscovite fluorite mineral assemblage was deposited from magmatic fluids under a fluctuating pressure regime at temperatures of about 400 c as indicated by co2 bearing moderately saline 7 5 12 5 wt nacl equiv fluid inclusions la icpms analyses of fluid inclusions in quartz demonstrate that fluids from the sweet home mine are enriched in incompatible elements but have considerably lower metal contents than those reported from porphyry cu au mo or climax type deposits the ore forming fluid exsolved from a highly differentiated magma possibly related to the deep seated alma batholith or distal porphyry stock s sulfide mineralization marking the periphery of climax type porphyry systems with fluorite and rhodochrosite as gangue minerals was deposited under a hydrostatic pressure regime from low salinity co2 bearing fluids with low metal content at temperatures below 400 c the sulfide mineralization is characterized by mostly negative 34s values for sphalerite galena chalcopyrite and tetrahedrite highly variable 18o values for rhodochrosite and low ree contents in fluorite the pb isotopic composition of galena as well as the highly variable 87sr 86sr ratios of fluorite rhodochrosite and apatite indicates that at least part of the pb and sr originated from a much more radiogenic source than climax type granites it is suggested that the sulfide mineralization at the sweet home mine formed from magmatic fluids that mixed with variable amounts of externally derived fluids the migration of the latter fluids that were major components during late stage mineralization at the sweet home mine was probably driven by a buried magmatic intrusion

marine sediments from southeastern brazilian continental shelf a 1200 year record of upwelling productivity abstract a sediment core from the cabo frio coastal shelf 23 19 s 41 8 w 117 m depth was analyzed for toc c n ratio organic petrography and planktonic foraminiferal content to evaluate variations in local productivity caused by changes in upwelling intensity and its relation to regional and global climatic variations during the last millennium the cabo frio core recorded the last 1200 years of sedimentation with rates varying from 0 11 to 0 32 mm yr 1 foraminiferal and organic geochemical analyses indicate the occurrence of three distinct periods of productivity from 850 ad until 1070 ad foraminifera fluxes consisting primarily of turborotalita quinqueloba indicate stronger south atlantic central water sacw transport onto the shelf which induced high biological productivity that was also recorded by high toc and marine palynomorphs content and a low c n atomic ratio this period coincided with a northward displacement of the atmospheric intertropical convergence zone itcz and south atlantic high sah systems driven by positive temperature anomalies in the north atlantic ocean during the medieval climate anomaly mca from 1070 until 1500 ad low toc flux and planktonic foraminifera fluxes and high c n atomic ratios suggest a reduction in marine productivity probably driven by reduced transport of sacw associated with the southward displacement of the sah and weakening of northeasterly winds the period between 1500 and 1830 ad which corresponds to the little ice age is marked by increased fluxes of planktonic foraminifera principally of globigerina bulloides and globigerinita glutinata these species mark an increase in productivity linked to sacw upwelling supported by the enhancement of northeasterly winds and southward displacement of the itcz and sah

isotope geochemistry and geochronology of the niujuan silver deposit northern north china craton implications for magmatism and metallogeny in an extensional tectonic setting the niujuan breccia type silver deposit forms part of the north hebei metallogenic belt along the northern margin of the north china craton the hercynian baiyingou coarse grained granite and the yanshanian er daogou fine grained granite are the major mesozoic intrusions exposed in this region here we investigate the salient characteristics of the mineralization and evaluate its genesis through zircon u pb and fluorite sm nd age data and pb s o h he and ar isotope data the orebodies of the niujuan silver deposit are hosted in breccias which contain angular fragments of the baiyingou and er daogou granitoids the 34s values of pyrite from the silver mineralized veins range from 2 4 to 5 3 the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of the sulfide minerals show ranges of 16 837 16 932 15 420 15 501 and 37 599 37 950 respectively the 3he 4he and 40ar 36ar ratios of the fluids trapped in pyrite are 0 921 4 81ra and 299 34 303 84 respectively the 18o and 18dw values of the ore forming fluids range from 0 6 to 4 15 and from 119 4 to 98 7 respectively our isotopic data suggest that the ore forming fluids were originally derived from the subvolcanic plutons and evolved into a mixture of magmatic and meteoric water during the main hydrothermal stage the ore forming materials were primarily derived from the lower crust with limited incorporation of mantle materials the emplacement time of the er daogou granite is constrained by la icp ms zircon u pb geochronology at 145 5 2 1 ma five fluorite samples from the last hydrothermal stage yielded a sm nd isochron age of 139 2 3 8 ma indicating the upper age limit for the silver mineralization these ages correlate with the formation of the niujuan deposit in an extensional setting associated with the closure of the mongol okhotsk ocean and the subduction of the paleo pacific oceanic plate beneath the north china craton

zoned base metal mineralization in a porphyry system origin and evolution of mineralizing fluids in the morococha district peru porphyry related base metal vein and replacement mineralization i e cordilleran polymetallic mineralization in the morococha district central peru is part of a large magmatic hydrothermal system associated with the emplacement of several late miocene porphyry intrusions and formation of important cu mo mineralization zn pb ag cu veins overprint the giant toromocho porphyry cu mo deposit in the center of the district and display a typical concentric base metal zonation cu zn pb ag covering an area of approximately 50km2 a detailed fluid inclusion study supports the hypothesis that base metal mineralization precipitated from cooled and evolved metal rich intermediate density porphyry type fluids in early stages of cordilleran base metal vein formation fluid inclusions have low salinities of 2 to 5 wt nacl equiv co2 contents of 3 to 10mol and homogenization temperatures th of 380 to 340 c they are similar to intermediate density fluid inclusions trapped in a milky quartz vein predating cordilleran polymetallic mineralization with similar low salinities 3 0 3 8 wt nacl equiv and low co2 contents 6 5 8 mol but higher th of 420 to 410 c during cooling of the intermediate density fluids from 400 to 300 c the lithostatic pressure regime changed to a hydrostatic one the fluids underwent pressure drop as well as phase separation i e unmixing and lost most of their co2 they acquired moderate salinities in some cases intermediate up to 16 wt nacl to brine compositions however the bulk of the magmatic fluid retained low salinity while it continued to cool under open system conditions and precipitated tennantite tetrahedrite chalcopyrite enargite sphalerite and galena upon cooling below 270 c the fluids deposited abundant rhodochrosite and quartz while following the boiling curve toward lower p t conditions these data record an evolution of mineral precipitation from deep minimum depth of 2 1 5 km to shallow environments 300 800 m oxygen hydrogen and carbon stable isotope data indicate that the hydrothermal fluids have a dominantly magmatic signature and were diluted by meteoric waters during the carbonate stage copper 5 000 18 000 g g sulfur up to 12 000 g g and iron 2 100 6 000 g g concentrations in the intermediate density fluid inclusions in the milky quartz veins are approximately 5 to 10 times higher than in intermediate density inclusions of the early cordilleran base metal veins the base metals zn pb and mn have comparable concentrations between 100 and 1 000 g g for both types of fluid these findings suggest that the fluids identified in cordilleran polymetallic veins are compositionally similar to the porphyry type fluids and could have derived from the latter after precipitation of cu and fe bearing sulfides in a deeper porphyry environment the new data explain the commonly observed base and precious metal zonation patterns encountered in porphyry centered districts e g bingham butte and show that both porphyry and polymetallic mineralization can precipitate from similar magmatic hydrothermal fluid pulses

mineralogy and fluid inclusion study of the southern amethyst vein system creede mining district colorado ag mineralization occurs as vein fillings and disseminations confined to areas of high fracture density and brecciation in the hanging wall of the amethyst fault and vein paragenesis is divided into two main stages 1 is a sulfide poor assemblage characterized by rhodochrosite quartz barite and an absence of silver 2 represents a complex event made up of three substages disseminated mineralization in the study area appears to be related to stage 2 analysis of fluid inclusions in stage 2 vein quartz showed that average homogenization temperatures and salinities decrease in a regular manner from lower to upper levels of the mine inclusions in stage 2 quartz from the lower mine levels had an average t h 238 degrees c and an average salinity of 9 8 equivalent weight percent nacl those in the uppermost level had an average t h 170 degrees c and an average salinity of 6 5 equivalent weight percent nacl the rapid drop in temperature and dilution of hydrothermal solutions which was a result of mixing with near surface waters caused the deposition of the high grade ag ores in the southern amethyst vein system modified journal abstract

evidence for oxygen isotope disequilibrium in selected geothermal and hydrothermal ore deposit systems abstract there is ample evidence from geothermal systems that temperatures estimated from the oxygen isotope fractionation between alteration phases and coexisting aquifer fluids agree closely 25 c with measured bore hole temperatures conversely many hydrothermal systems exhibit varying degrees of apparent fluid rock oxygen isotope disequilibrium measured rock water equilibrium rock water a comparison of data from a variety of hydrothermal systems indicates that an increase in the degree of isotopic equilibration can be related in a general way to an increase in the temperature salinity and intensity of fracturing this relationship is entirely consistent with calculations carried out for a simple closed system model that estimates the fraction of isotope exchange between rock and fluid as a function of temperature rock type salinity of the fluid grain size water rock ratio and the rate of isotope exchange the fact that many silicate fluid reactions and their isotopic counterparts are fast leads us to conclude that observed variations in the degree of exchange may have resulted from local self sealing of the fracture network prior to equilibration the ability for fractures to remain open or to propagate allowing continued fluid flow may be the deciding factor in the attainment of isotopic equilibration

sea level change during the last 2500 years in new jersey usa relative sea level changes during the last w2500 years in new jersey usa were reconstructed to test if late holocene sea level was stable or included persistent and distinctive phases of variability foraminifera and bulk sediment d 13 c values were combined to reconstruct paleomarsh elevation with decimeter precision from sequences of salt marsh sediment at two sites using a multi proxy approach the additional paleoenvironmental information provided by bulk sediment d 13 c values reduced vertical uncertainty in the sea level reconstruction by about one third of that estimated from foraminifera alone using a transfer function the history of sediment deposition was constrained by a composite chronology an ageedepth model developed for each core enabled reconstruction of sea level with multi decadal resolution following correction for land level change 1 4 mm yr four successive and sustained multi centennial sea level trends were objectively identified and quantified 95 confidence interval using error in variables change point analysis to account for age and sea level uncertainties from at least 500 bc to 250 ad sea level fell at 0 11 mm yr the second period saw sea level rise at 0 62 mm yr from 250 ad to 733 ad between 733 ad and 1850 ad sea level fell at 0 12 mm yr the reconstructed rate of sea level rise since w1850 ad was 3 1 mm yr and represents the most rapid period of change for at least 2500 years this trend began between 1830 ad and 1873 ad since this change point reconstructed sea level rise is in agreement with regional tide gauge records and exceeds the global average estimate for the 20th century these positive and negative departures from background rates demonstrate that the late holocene sea level was not stable in new jersey

stratigraphy pollen history and geochronology of tidal marshes in a gulf of maine estuarine system climatic and relative sea level impacts abstract sedimentologic and stratigraphic characteristics of five tidal marshes in great bay estuary new hampshire which is located on the western boundary of the gulf of maine were assessed from 20 vibracores detailed descriptions of surficial environments pollen analyses and radiocarbon dating modern marsh sequences in great bay estuary initiated with a time transgressive basal peat that formed at the upland brackish marsh boundary the oldest basal peat deposit sampled during this study was dated at 4560 cal yr b p based on an age of 4060 40 14 c yr b p the original tidal marshes that formed in great bay estuary apparently were unable to accrete at a high enough rate to allow seaward expansion resulting in a transgressive sequence of low marsh or mudflat sediments overlying the basal peat the transgressive tidal marsh sequence is capped by high marsh sediments that corresponded to a slowing of relative sea level rsl rise in the region and regressive seaward expansion of the tidal marshes however significant variations from these transgressive regressive sequences occur in the great bay tidal marshes as a result of more recent marsh expansion and tidal channel migrations detailed pollen analyses of a vibracore taken in a tidal marsh along squamscott river with a sedimentary record spanning the last 3900 cal yr b p exhibit five well documented marker horizons including 1 an increase of tsuga hemlock 2 the appearance of picea spruce 3 tsuga and fagus beech declines 4 an increase in ambrosia ragweed coupled with a sudden decrease in quercus oak and 5 the castanea chestnut decline using published ages for these pollen horizons and a calibrated 14 c age obtained during this study for a basal peat accretion rates for this marsh system over five time intervals were calculated 1 0 4 to 0 5 mm yr 1 from 3900 to 2850 cal yr b p 2 0 6 mm yr 1 from 2850 to 1960 cal yr b p 3 0 8 mm yr 1 from 1960 to 580 cal yr b p 4 0 7 to 0 8 mm yr 1 from 580 to 210 cal yr b p and 5 0 8 to 0 9 mm yr 1 over the last 210 years the long term accretion rate for the entire sequence based on the calibrated 14 c age of the basal peat was 0 6 to 0 7 mm yr 1 this result agrees with accretion rates determined from calibrated 14 c ages from two other tidal marsh systems in great bay estuary with accretion rates between 0 6 to 0 8 mm yr 1 higher accretion rates were obtained at a nearby tidal marsh with 1 2 mm yr 1 for just the marsh and 1 3 mm yr 1 for the marsh and underlying subtidal sediment the results of this study indicate that the sedimentology and stratigraphy of moderate size tidal marshes in rocky glaciated coasts are highly variable and are strongly influenced by complex interactions among rsl climatic variations and anthropogenic influences for instance the early development of many of the marshes in the great bay estuary area were likely driven by changes in rates of rsl resulting in transgressive onlap boundaries subsequently overlain by regressive intertidal marsh sequences however more recent changes in tidal marsh sediment composition deposited during a relatively slow steady rsl rise likely result from other forcings such as changes in minerogenic and orogenic sediment inputs due to anthropogenic effects tidal channel migrations major storms causing erosion of the marsh or climatic changes causing shifts in sediment delivery or vegetation

sultan mountain mine western san juan mountains colorado a fluid inclusion and stable isotope study the sultan mountain mine in the western san juan mountains of colorado has produced cu pb zn ag au ores from the mid 1870s until the 1950s production was from veins filling faults and fissures along the southern margin of the silverton caldera the principal host rock to the veins is a quartz monzonite stock five periods of hypogene mineralization have been recognized i early quartz pyrite ii quartz pyrite iii rhodochrosite siderite iv main ore stage chalcopyrite tetrahedrite galena sphalerite and gold and v quartz fluorite evidence of open space filling banding crustification vugs is widespread heating studies of fluid inclusions in quartz rhodochrosite siderite sphalerite and fluorite indicate temperatures were approximately 200 degrees c for stages i to iv and 186 degrees c for stage v stages i ii and iv show evidence of boiling crushing studies indicate that high pressure gas probably co 2 is present in the fluid inclusions freezing point depression estimates of salinity corrected for co 2 indicate a range of 13 6 to 1 3 wt percent nacl equiv these data together with p v t data for saline solutions and p sub co 2 38 bars give a minimum depth of formation of 600 m the delta 18 o values at 200 degrees c of water calculated for oxygen isotope composition of quartz range from 5 63 to 8 8 per mil and the values for rhodochrosite siderite are 0 05 and 0 35 per mil the delta 18 o values of whole rocks adjacent to the champion and alletha veins range from 2 65 to 6 10 per mil these data suggest hydrothermal fluids were predominantly composed of meteoric water which underwent isotopic exchange with the quartz monzonite the delta 13 c values for rhodochrosite siderite range from 6 9 to 7 3 per mil carbon isotope data are inconclusive as to the source of the carbon the delta 34 s values for sulfides range from 2 9 to 6 1 per mil and these limited data suggest a paleozoic evaporite source for most of the sulfur stable isotope data indicate isotopic control of the fluid by the surrounding country rocks geologic and geochemical studies suggest a model of sultan mountain ore deposition in which predominantly meteoric hydrothermal solutions restricted mostly to the sultan mountain area scavenged metals from the precambrian basement and the tertiary volcanic and intrusive rocks sulfur was derived mostly from solution of paleozoic evaporites however the sulfur isotope data indicate some of the sulfur may have been derived from the quartz monzonite stock the primary mechanism of precipitation of the ore was an increase in ph as a result of boiling

reinterpretation of past sea level variation of the bay of fundy reports of shifts in rates of aggradation in a salt marsh deposit at amherst point nova scotia have been linked with fluctuations in eustatic sea level crustal subsidence and possibly changes in tidal amplitude however evidence for the most recent fluctuation is an artifact of early acadian land reclamation that occurred in the seventeenth century at amherst point acadian settlers had constructed dikes to prevent regular tidal flooding but probably allowed occasional flooding of the surface by tidal waters thus maintaining the salt marsh signature of the deposit statistical analysis of the pollen assemblage from the uppermost deposit inter preted as a regressive sequence aligns critical depths with pollen assemblages retrieved from modern soils of diked and drained marshes inspection of historical aerial photographs confirms that the dikes persisted on the site until at least 1939 interpretations of earlier fluctuations recorded in deposits below this regressive sequence remain valid it is possible that the bay of fundy experienced a regressive period just prior to acadian diking but future research on unexamined salt marsh deposits here or elsewhere must include an exhaustive search of historical documents to avoid misinterpretation of anthropogenic modifications

some problems in the reconstruction of mean sea level and its changes with time the ocean level is constantly changing and there are many different forcing functions today we realize that a rise in one area may in fact correspond to a fall in another area a number of prob

late holocene sea level change around newfoundland differential sea level change in formerly glaciated areas is predicted owing to variability in extent and timing of glacial coverage newfoundland is situated close to the margin of the former laurentide ice sheet and the orientation of the shoreline affords the opportunity to investigate variable rates and magnitudes of sea level change analysis of salt marsh records at four sites around the island yields late holocene sea level trends these trends indicate differential sea level change in recent millennia a north south geographic trend reflects submergence in the south very slow sea level rise in the northeast and a recent transition from falling to rising sea level at the base of the northern peninsula this variability is best explained as a continued isostatic response to deglaciation

temporal variations of strength and location of the south atlantic anomaly as measured by rxte abstract the evolution of the particle background at an altitude of 540 km during the time interval between 1996 and 2007 is studied using the particle monitor of the high energy x ray timing experiment on board nasa s rossi x ray timing explorer a special emphasis of this study is the location and strength of the south atlantic anomaly saa the size and strength of the saa are anti correlated with the 10 7 cm radio flux of the sun which leads the saa strength by 1 year reflecting variations in solar heating of the upper atmosphere the location of the saa is also found to drift westwards with an average drift rate of about 0 3 yr following the drift of the geomagnetic field configuration superimposed to this drift rate are irregularities where the saa suddenly moves eastwards and where furthermore the speed of the drift changes the most prominent of these irregularities is found in the second quarter of 2003 and another event took place in 1999 we suggest that these events are previously unrecognized manifestations of the geomagnetic jerks of the earth s magnetic field

the jiaodong type gold deposits characteristics origin and prospecting abstract the jiaodong type comprises a unique class of gold mineralisation which includes the linglong type quartz vein hosted and the jiaojia type fracture disseminated style deposits although the type area is in the jiaodong peninsula in ne china where some of the world s richest gold reserves occur we identify similar occurrences in other parts of china and elsewhere in the world under this category the ore fluids migrated upwards forming quartz vein type of gold ore linglong type wherever the ore controlling fractures are at high angles fluid infiltration into the surrounding wall rocks and generation of the jiaojia type disseminated style deposits resulted where the ore bearing fluids encountered low angle fractures on a regional scale the jiaodong type gold mineralisation occurs along the margins of reactivated cratons within the interior of cratons along paleosuture zones or along the junctions of micro blocks and is distinctly different from the classic orogenic gold in terms of their tectonic setting ore characteristics and genetic history unlike skarn and porphyry type of deposits the jiaodong type gold deposits do not always show close spatial relationship with magmatic intrusives and some of the deposits occur distal to plutons 10 km in this paper we evaluate the salient geological geochronological geochemical and isotopic features of the jiaodong type gold deposits and propose some general guidelines for gold prospecting based on case studies we predict that the gold lodes in the jiaodong type mineralised zones might extent vertically up to 3000 m with only minor mineralogical and geochemical variations

microblock amalgamation in the north china craton evidence from neoarchaean magmatic suite in the western margin of the jiaoliao block abstract the archaean earth is considered to have been characterized by microcontinents that formed dominantly through the accretion of oceanic arcs and plateaus the north china craton ncc provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the archaean here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks the jiaoliao block that forms part of the composite eastern block of the ncc we present petrological geochemical and zircon u pb geochronological data from the taipingzhai charnockite suite and associated amphibolites metagabbros and orthogneisses from the qianxi complex geochemically the rocks show a wide range of sio 2 charnockite suite 52 57 75 50 wt metagabbro 43 71 wt amphibolite 50 24 wt garnet bearing biotite 63 73 wt and mgo charnockite suite 0 89 5 01 wt metagabbro 3 99 wt amphibolite 6 23 wt garnet bearing biotite 2 08 wt the composition of the felsic units straddle from diorite through syeno diorite to granite with both alkalic and subalkalic affinity with dominantly magnesian composition and arc related features their immobile trace element relationships suggest calc alkaline affinity they show positive pb ba la nd and gd and negative nb ta sr th and ti anomalies with slightly negative anomalies of ce and y attesting to arc related features in tectonic classification diagrams the rocks plot in the vag syn colg field or the vag area suggesting subduction related origin the dominant population of zircons in all these rocks displays magmatic crystallization features including high th u values with core rims textures indicating subsequent thermal events the zircon u pb data yield upper intercept ages of 2587 10 ma to 2543 17 ma and 207 pb 206 pb mean ages of 2578 7 3 ma to 2536 8 ma for the charnockite suite marking the timing of emplacement of the arc magmas the overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207 pb 206 pb ages between 2533 ma to 2490 ma zircons in the metagabbro preserve upper intercept ages of 2556 20 ma representing the crystallization age of this rock the younger ages of 2449 58 ma upper intercept age and 1845 25 ma 207 pb 206 pb spot age are interpreted to represent subsequent multiple thermal events in this area zircons in the amphibolite preserve the 207 pb 206 pb mean age of 2539 9 ma representing the crystallization age of this rock the garnet bearing biotite gneiss shows an upper intercept age of 2562 10 ma mswd 0 66 n 36 and the 207 pb 206 pb mean age of 2561 9 ma mswd 0 63 n 33 which is taken to represent the crystallization age of this rock some inherited zircons are also identified with 207 pb 206 pb ages of 2664 26 ma and 2628 26 ma zircon lu hf data show dominantly positive ehf t values and combined with crustal residence ages the results suggest mesoarchean to neoarchean juvenile crust formation in the ncc we interpret the data presented here to represent a phase of major late neoarchaean arc magmatism along the western margin of the jiaoliao block related to the birth of microcontinental nuclei within the ncc our data suggest that the western and eastern blocks might not have existed as discrete crustal blocks and that the construction of the ncc is a result of the assembly of several microblocks or terranes at the end of archaean similar archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early earth

fallen arches dispelling myths concerning cambrian and ordovician paleogeography of the rocky mountain region high resolution sedimentologic biostratigraphic and stable isotope data from numerous measured sections across colorado reveal a complex architecture for lower paleozoic strata in the central cordilleran region a lack of precise age control in previous studies had resulted in misidentification and miscorrelation of units between separate ranges corrections of these errors made possible by our improved data set indicate the following depositional history the quartz rich sandstone of the sawatch formation was deposited during onlap of the precambrian erosion surface in the early late cambrian the overlying dotsero formation a regionally extensive carbonate and shale rich succession records blanket like deposition with only minor facies changes across the state an extremely widespread meter scale stromatolite bed the clinetop bed caps the dotsero formation in most areas however a latest cambrian erosional episode removed 9 11 m of the upper dotsero formation including the clinetop bed from just east of the homestake shear zone in the sawatch range eastward to the mosquito range the overlying manitou formation differs in character and thus in member stratigraphy on the east vs west sides of the state these differences were previously interpreted as the result of deposition on either side of a basement high that existed within the central colorado embayment or colorado sag a region of major breaching across the transcontinental arch this paleogeographic reconstruction is shown herein to be an artifact of miscorrelation biostratigraphic data show that the northwestern members of the manitou formation are older than the members exposed in the southeastern part of the state and that there is little or no overlap in age between the two areas this circumstance is the result of 1 removal of older manitou formation strata in the southeast by an unconformity developed during the rossodus manitouensis conodont zone and 2 erosion of younger manitou strata in central and western colorado along middle ordovician and devonian unconformities deciphering these complex stratal geometries has led to invalidation of long held views on western laurentian paleogeography during the cambrian and earliest ordovician specifically the existence of the colorado sag and a northeast trending high within the sag that controlled depositional patterns on either side the mid rossodus uplift and resultant unconformity eliminated any and all upper cambrian and lower ordovician deposits in southern colorado and northern new mexico and thus their absence should not be misconstrued as evidence for earlier nondeposition in this region lithofacies distribution patterns and isopach maps provide no evidence that highlands of the transcontinental arch existed in colorado prior to the mid rossodus age uplift event in fact regional reconstructions of earliest paleozoic paleogeography along the entire length of the purported transcontinental arch should be reevaluated with similarly precise biostratigraphic data to reconsider all potential causes for missing strata and to eliminate topographic elements not supported by multiple stratigraphic techniques this study illustrates how seriously paleogeographic reconstructions can be biased by the presumption that missing strata represent periods of nondeposition rather than subsequent episodes of erosion particularly in thin cratonic successions where stratigraphic gaps are common and often inconspicuous

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

sea level changes in iceland and the influence of the north atlantic oscillation during the last half millennium abstract we present a new diatom based sea level reconstruction for iceland spanning the last 500 years and investigate the possible mechanisms driving the sea level changes a sea level reconstruction from near the icelandic low pressure system is important as it can improve understanding of ocean atmosphere forcing on north atlantic sea level variability over multi decadal to centennial timescales our reconstruction is from vi arholmi salt marsh in snaefellsnes in western iceland a site from where we previously obtained a 2000 yr record based upon less precise sea level indicators salt marsh foraminifera the 20th century part of our record is corroborated by tide gauge data from reykjavik overall the new reconstruction shows ca 0 6 m rise of relative sea level during the last four centuries of which ca 0 2 m occurred during the 20th century low amplitude and high frequency sea level variability is super imposed on the pre industrial long term rising trend of 0 65 m per 1000 years most of the relative sea level rise occurred in three distinct periods ad 1620 1650 ad 1780 1850 and ad 1950 2000 with maximum rates of 3 2 mm yr during the latter two of these periods maximum rates were achieved at the end of large shifts from negative to positive of the winter north atlantic oscillation nao index as reconstructed from proxy data instrumental data demonstrate that a strong and sustained positive nao a deep icelandic low generates setup on the west coast of iceland resulting in rising sea levels there is no strong evidence that the periods of rapid sea level rise were caused by ocean mass changes glacial isostatic adjustment or regional steric change we suggest that wind forcing plays an important role in causing regional scale coastal sea level variability in the north atlantic not only on multi annual timescales but also on multi decadal to centennial timescales

world magnetic charts for 1985 spherical harmonic models of the geomagnetic field and its secular variation summary the 1980 world magnetic charts published by the uk hydro graphic department and by the us defense mapping agency hydrographic topographic center have been produced jointly they are based on spherical harmonic models of the main geomagnetic field 168 coefficients and of the secular variation 80 coefficients these models are presented here with a discussion of the methods used to derive them and of the data on which they are based positions of the dip poles the geomagnetic poles and the eccentric dipole together with their rates of change are derived from the models