fluid inclusions and hydrothermal alteration on the dixie valley fault nevada footwall rocks of the 1954 rupture segment of the dixie valley fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages an early biotite feldspar assemblage is followed by later fe chlorite and epidote both chlorite and epidote are replaced by hydrothermal sericite and cross cut by calcite hematite and quartz calcite veins biotite is partially replaced by prehnite the latest hydrothermal minerals are stilbite laumontite kaolinite alunite smectite illite and pervasive replacement of rock units with fine grained quartz chalcedony and opal secondary fluid inclusions trapped in healed microfractures in igneous quartz include type i inclusions that contain a moderate salinity aqueous liquid and vapor type ii inclusions that contain a moderate salinity aqueous liquid and co2 type iii inclusions that show eutectic melting temperatures below the nacl h2o eutectic and contain substantial cacl2 and type iv inclusions containing halite and other daughter minerals microthermometric measurements on these inclusions yield variable compositions and homogenization temperatures salinities of type i inclusions vary from 0 1 to 12 9 wt nacl with the mode in the interval 0 to 1 salinities of type ii co2 bearing inclusions range from 0 62 to 6 81 wt nacl relative to h2o and salinities of type iii inclusions with low eutectic melting temperatures are 12 9 to 25 3 nacl equivalent wt salinities of halite bearing inclusions are 30 1 to 39 2 wt nacl homogenization temperatures span the range 120 to 400 c the processes of isochemical cooling with upward displacement of the footwall mixing of cool low salinity water with hotter components and mixing of cool evaporite brine with hotter components could be responsible for variable fluid inclusion compositions homogenization temperatures and densities the p t path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics the path includes a lithostatic fluid pressure at 305 c and 1570 bars along with cooling and escape of co2 from fluids the fluid p t path probably approaches hydrostatic pressure conditions at lower temperatures hydrothermal alteration product minerals fluid temperatures pressures and compositions in the footwall of the dixie valley fault constrain minimum fault age to 20 to 25 ma displacement to 6 km with about 3 km of pre 10 to 13 ma and 3 km of post 10 ma uplift fluid compositions and p t data suggest the following mechanism for rupture initiation and arrest ruptures may be initiated as a result of high fluid pressures then opening of dilatant fractures causes drastic decrease in fluid pressure separation of steam and co2 the drastic reduction in fluid bulk modulus that accompanies volatile phase separation permits propagation of the ruptures even though fluid pressure is reduced in areas where fluid pressure reduction is not accompanied by phase separation fractures are arrested by dilatant hardening

chemical and isotopic effects of retrogression in metamorphic fluid inclusions fluid inclusions may provide compositional and isotopic information about fluids from which the host mineral precipitated as long as the host mineral does not react with the fluid our transmission electron microscope tem investigation of grain boundaries and of fluid inclusions in zoisite and quartz of high pressure metamorphic rocks from dabie shan eastern china demonstrates daughter minerals such as margarite muscovite calcite and anhydrite their precipitation changes 1 the composition of the fluid by selective and mineral specific removal of co2 carbonates h2o sheet silicates hydration of the walls or s gypsum anhydrite sulfides 2 the concentrations and proportions of ions dissolved in the fluid and 3 the isotopic composition of the fluid because of isotopic fractionation between mineral precipitate and fluid and between unmixed fluids fluid leakage from overpressurized fluid inclusions with daughter minerals changes the overall chemical and isotopic composition of the inclusion irreversibly even when the daughter crystals later redissolve such fluid loss yields a wide range of compositionally and isotopically different fluids from a single starting fluid depending on the relation between mineral reactions in and fluid loss from the inclusion the fluid remaining in the inclusion and the fluid lost from the inclusion may appear entirely unrelated

mineral assemblages and oxygen and sulphur fugacities in natural water rock interaction processes abstract several mineral assemblages capable of buffering oxygen and sulphur fugacity and theoretical calculations were used to determine the fugacities of these two gas species over a temperature range between 150 and 350 c computed values were compared with those calculated from the composition of the geothermal fluids of larderello travale bagnore and piancastagnaio italy the geysers usa and cerro prieto mexico the possible hydrothermal mineral assemblages that best fit the field data are those containing minerals frequently found in many geothermal fields epidote chlorite k feldspar quartz and pyrite these assemblages can be used in place of the classical buffers based on iron oxides and sulphides

atmospheric radiocarbon calibration to 45 000 yr b p late glacial fluctuations and cosmogenic isotope production more than 250 carbon 14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from lake suigetsu japan provide a first atmospheric calibration for almost the total range of the radiocarbon method 45 000 years before the present the results confirm the recently revised floating german pine chronology and are consistent with data from european and marine varved sediments and combined uranium thorium and carbon 14 dating of corals up to the last glacial maximum the data during the glacial show large fluctuations in the atmospheric carbon 14 content related to changes in global environment and in cosmogenic isotope production

environmental changes during the holocene climatic optimum in central europe human impact and natural causes abstract the priority programme changes of the geo biosphere aimed to reconstruct the environmental history of central europe with emphasis on the time interval from 9000 to 5500 cal bp time slice ii coinciding with the holocene climatic optimum during this period the onset of human activities such as settlement agriculture and animal husbandry caused environmental changes studies of different landscape units in germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system the investigated archives included laminated lake sediments fluvial sediments colluvia and soils speleothems peat and coastal sediments the different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses together with pollen analysis and dating methods for the establishment of a reliable chronology the results of the various research groups are summarised and critically discussed based on these results the climatic optimum can be subdivided into three periods 1 the early atlantic from 9000 to 7500 cal bp with negligible human impact and stable environmental conditions 2 the late atlantic during early and middle neolithic from 7500 to 6300 cal bp with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records and 3 the late atlantic during the younger neolithic jungneolithikum after 6300 cal bp with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments during the whole climatic optimum natural causes such as minor shifts of temperature did not induce substantial environmental changes though some changes such as temporary droughts may have facilitated and amplified the observed human impact

quantification of biotic responses to rapid climatic changes around the younger dryas a synthesis to assess the presence or absence of lags in biotic responses to rapid climatic changes we 1 assume that the 18o in biogenically precipitated carbonates record global or hemispheric climatic change at the beginning and at the end of the younger dryas without any lag at our two study sites of gerzensee and leysin switzerland 2 derive a time scale by correlating the 18o record from these two sites with the 18o record of the grip ice core 3 measure 18o records in ostracods and molluscs to check the record in the bulk samples and to detect possible hydrological changes 4 analyse at gerzensee and leysin as well as at two additional sites that lack carbonates and hence a 18o record pollen plant macrofossils chironomids beetles and other insects and cladocera 5 estimate our sampling resolution using the grip time scale for the isotope stratigraphies and the biostratigraphies and 6 summarise the major patterns of compositional change in the biostratigraphies by principal component analysis or correspondence analysis we conclude that at the major climatic shifts at the beginning and end of the younger dryas hardly any biotic lags occur within the sampling resolution of 8 30 years and that upland vegetation responded as fast as aquatic invertebrates we suggest that the minor climatic changes associated with the gerzensee and preboreal oscillations were weakly recorded in the biostratigraphies at the lowland site but were more distinct at higher altitudes individualistic responses of plant and animal species to climatic change may reflect processes in individuals e g productivity and phenology in populations e g population dynamics in spatial distributions e g migrations and in ecosystems e g trophic state we suggest that biotic responses may be telescoped together into relatively short periods 50 to 150 years perhaps disrupting functional interactions among species and thus destabilising ecosystems

lateglacial calendar year chronology based on annually laminated sediments from lake meerfelder maar germany abstract annually laminated sediments from lake meerfelder maar mfm in the eifel germany provide an independent calendar year timescale for the last glacial interglacial transition changes in varve thickness and varve facies reflect significant environment variations during this period the general micro facies pattern confirms that diatomaceous organic varves are favoured during warm climatic phases while cold periods generate higher allochthonous sediment fluxes an exception is the significant increase in diatom blooms at the beginning of the younger dryas six lateglacial biozones have been defined by litt and stebich quaternary international 1999 the sediment record comprises two tephra layers as chronomarkers the laacher see tephra 12 880 varve years bp is a continent wide correlation horizon while the ulmener maar tephra provides regional chronological links the beginning of the lateglacial warming is dated at 14 450 varve years vyrs bp which is regarded as the minimum age three abrupt cold spells interrupted the lateglacial interstadial at 13 800 vyrs bp oldest dryas 13 540 vyrs bp older dryas and 12 680 vyrs bp younger dryas the oldest dryas 130 years and the older dryas 190 years were rather short while the younger dryas lasted much longer 1090 years the mfm chronology was compared with ice core timescales from gisp2 and grip there is a good agreement between these timescales with the grip model age ss09 providing the best match to the mfm chronology

bio and chronostratigraphy of the lateglacial in the eifel region germany abstract in recent years enormous success has been achieved in varve counting of the eifel maar lakes but a detailed correlation with the biostratigraphy has been missing in this paper we present new palynological results of the lateglacial sequences from holzmaar lake and meerfelder maar lake based on annually laminated sediments in particular the meerfelder maar has great potential because in contrast to the holzmaar the sequence between the ulmener maar tephra 11 000 varve years bp and the laacher see tephra 12 880 varve years bp including the younger dryas is undisturbed and complete therefore we currently use the meerfelder maar chronology brauer et al 1999b as an independent varve calendar for the biostratigraphy of the lateglacial the palynological signals of both maar lakes are in good agreement and can easily be correlated with one another and with type sections type regions in northwestern germany and jutland the sequences of the eifel maar lakes have the quality of hypostratotypes with regional biozones based on an absolute time scale

evolution and environmental impacts of the eruption of laacher see volcano germany 12 900 a bp abstract laacher see volcano lsv 40 km south of bonn explosively erupted ca 6 3 km 3 of chemically strongly zoned phonolite magma probably during spring 12 900 years ago the resulting eruption column having reached at least 20 km in height the bulk of the laacher see tephra lst was deposited east of the volcano within the neuwied basin lst ashes form the most important stratigraphic marker in lateglacial deposits over much of central europe a minimum of 2 mt total s was calculated to have been released during the eruption by comparing pre and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses because a separate s bearing vapor phase was probably present in the magma prior to eruption as indicated by the high melt h 2 o contents close to saturation level the actual amount of s released during the eruption could have significantly exceeded 2 mt the sulfuric acid aerosol layer resulting from the massive stratospheric s input probably resided in the stratosphere for years and most likely had a significant impact on climate and thus the environment increased precipitation in central europe and or impairment of the vegetation cover for several years is suggested by several proxies especially increased sediment supply into lakes proximal to the eruptive center major environmental impacts include an initial blast that felled trees up to 4 km away from vent fast deposition of huge tephra volumes led to the complete disruption of rhine river within the lower neuwied basin and the damming up of a lake ca 140 km 2 in areal extent sudden collapse of the temporary tephra dam caused a catastrophic flood wave downstream whose deposits are recognized as far north as bonn reworking of unconsolidated tephra deposits over several 100 km 2 was widespread and extensive generating abundant lahars and flood plain deposits a braided river system established in neuwied basin probably persisted up to several years recent reports for a second eruption of lsv are not confirmed

the pumpellyite actinolite and contiguous facies in part of the phyllite quartzite series central northern peloponnesus greece variations in assemblage and composition of the constituent minerals in basic and intermediate metavolcanics encountered in the zarouchla group of the phyllite quartzite series are consistent with a progressive sequence corresponding to temperature conditions estimated at 290 380 c minimum values under a total pressure greater than 3 5kbar and possibly as high as 5 kbar in the absence of more critical evidence the parageneses recorded in the metavolcanic rocks are interpreted as belonging to a prograde facies series from the lawsonite albitechlorite facies through the pumpellyite actinolite facies to the greenschist facies the present distribution of mineral assemblages does not show a simple increase of metamorphic grade in a given direction but is apparently related to the tectonic evolution of the metamorphic sequence

three fragmentation mechanisms for highly viscous magma under rapid decompression abstract analysis of the behavior of viscous magma under short term tensile stresses demonstrates that the strain rates anticipated in the eruptive stages of collapse related events may be high enough under certain circumstances to provide fragmentation of the melt by brittle failure mechanisms of fragmentation of a highly viscous vesicular magma by the propagation of an unloading wave by layer by layer vesicle bursting fragmentation wave propagation and by rapid filtration gas flow are outlined fragmentation scenarios involving possible combinations of the three fragmentation mechanisms are evaluated for two models of magma with isolated and with connected pores experimental results for magma fragmentation under high decompression rates appear to support such mechanisms these mechanisms of highly viscous magma fragmentation by rapid decompression probably have their greatest application in cases of explosive disintegration of lava domes and cryptodomes caused by collapse events

sedimentological proof and dating of the early holocene volcanic eruption of ulmener maar vulkaneifel germany a minerogeniclayer occurs in early postglacial organic sediments from five maar lakes west eifel volcanic field germany the mineralogy and stratigraphic position of this tephra suggests that it is related to the youngest german volcano ulmener maar nearby radiocarbon dating of wood from the base of the ulmener maar tephra at two locations provide ages in agreement with an accelerator mass spectrometer 14c date for the minerogenic layer from sediments of lake holzmaar situated 13 km south west of ulmener maar the mean radiocarbon age is 9 560 years bp dating by varve chronology provides an age of 10017 years vt varve time in years before 1950 or 10 895 years corrected vt based on palynology the ulmener maar tephra was deposited at the end of the preboreal high values of natural remnant magnetization intensity typical of pyroclastic material confirm that this minerogenic layer differs in composition from other clastic deposits of the sedimentary record geochemical analyses reveal increased values of total trace elements for the laacher see tephra and ulmener maar tephra an isopach map based on thickness variations of the ulmener maar tephra at five investigated maar lakes indicates that the tephra was mainly transported to the south west

holocene climate variability in europe evidence from δ18o textural and extension rate variations in three speleothems time series o isotope profiles for three u th dated stalagmites have revealed that for much of the holocene a site on the atlantic seaboard sw ireland exhibits first order 18o trends that are almost exactly out of phase with coupled 18o curves from two southern european sites se france and nw italy in the irish stalagmite cc3 from crag cave sw ireland low 18o at 10 000 cal yr bp reflects cool conditions by the early to mid holocene 9000 6000 cal yr bp 18o had increased reflecting the onset of warmer conditions on the atlantic seaboard this shift to higher 18o was accompanied by a marked increase in the stalagmite extension rate reinforcing our interpretation that this was a period of relative warmth except for an episode of increased extension rate about 5500 yr ago 18o in the crag stalagmite exhibits a gradual decrease accompanied by declining extension rates between 7800 and 3500 cal yr bp interpreted as a cooling trend there is evidence for increases in both 18o and stalagmite extension rate in the period from 3500 cal yr bp to the present day suggesting a return to warmer conditions on the atlantic seaboard in the stalagmite from nw italy er76 grotta di ernesto trentino province the early holocene c 9200 7800 cal yr bp is characterised by high 18o probably indicative of warm and or dry conditions exceptionally low 18o from 7800 to 6900 cal yr bp at this site reflects a well defined wet phase cerin wet phase in the last three millennia this stalagmite exhibits a shift to lower 18o interpreted as some combination of cooler and or wetter conditions unlike the irish stalagmite the italian sample does not show a correlation between 18o and extension rate instead its extension rate correlates roughly with 13c presumably reflecting a climate driven vegetation change in the early holocene 18o in the french stalagmite cl26 grotte de clamouse herault province se france was low relative to its holocene average for much of the period since c 3500 cal yr bp this stalagmite exhibits higher 18o than in the early holocene suggesting warmer conditions like the irish stalagmite the french sample exhibits a well defined correlation between 18o and extension rate had drip water availability been the dominant control on 18o at this semi arid site then higher 18o would have been accompanied by lower not higher extension rates this suggests strongly that temperature rather than rainfall amount was the dominant control at this site while conclusions regarding the patterns of climate variability on a continent scale must remain tentative because of the limited number of stalagmites studied we argue that early holocene warm conditions on the atlantic seaboard irish site coincided with relatively cool conditions at the clamouse site by c 3500 yr ago the pattern appears to have been reversed

alteration and mass transfer in cataclasites and mylonites in 6 6 km of granitic crust at the siljan impact structure central sweden granitic rocks deformed by cataclasis and mylonitization on macro a few meters and micro thin section scales are found at depths down to 6 6km in the siljan impact structure in central sweden granites near fault planes exhibit 1 fracturing kinking fragmentation and recrystallization of feldspars into pure k and na endmember varieties 2 fragmentation polygonization and development of undulose extinction in quartz and 3 kinking appearance of wavy extinction and alteration of biotite chlorite amphibole and alteration of ilmenite and magnetite whole rock chemical analyses of deformed and undeformed rocks show that deformed rocks are enriched in sio2 by about 5 wt and depleted in other oxides by variable percentages apart from rb and co the concentrations of other trace elements including ba sr zn zr pb cd cu cr ni v u th la and li are lower in deformed relative to undeformed rocks mass balance calculations for a 1000 cm3 model granite which were based on modal mineralogy whole rock chemistry and mineral analyses suggest that the break down of primary biotite chlorite and amphibole in deformed zones released elements to circulating fluids these calculations also indicate liberation of water and a doubling of porosity from 1 to 2 during the deformation episodes later precipitation of minerals in shear and tension fractures reduced this porosity within the upper 2000 m of the gravberg 1 well the formation of fracture filling minerals smectite calcite hematite chlorite and albite is impact related and was favored by active circulation of meteoric water fracture filling minerals in the upper 2000 m of the borehole formed at temperatures of 70 to 200 c between depths of 2000 and 3500 m fracture filling mineral assemblages dominated by fe mg chlorite sphene and epidote suggest formation temperatures in the range of 150 to 300 c occurrence of pumpellyite and prehnite in some altered biotite and chlorite of the deformed zones between 3500 and 5500 m suggest preimpact metamorphism and formation temperature above 150 c below 5500 m the mineral assemblages in the fractures are dominated by quartz sphene epidote and some muscovite and chlorite indicating a temperature range between 300 and 450 c one of the possible origins for the ch4 and h2 gases detected in the gravberg 1 well is a combination of hydrogen ions released by decomposition of hydrated silicates biotite chlorite hornblende with carbon the presence of iron in the deformed granitic rocks prevented the resulting ch4 from being oxidized

paleo environment and radiocarbon calibration as derived from lateglacial early holocene tree ring chronologies abstract we present an overview of the extended hohenheim oak chronology hoc and the dendrochronologically dated preboreal pine tree ring chronology ppc both provide an absolute annual time frame of the holocene extending into the younger dryas yd back to 11 919 bp two floating pine and larch chronologies are 14 c dated covering large parts of the lateglacial dendro ecological parameters such as ring width and stable isotope variation are used to infer past environmental conditions 14 c analyses on decadal sections provide a high precision high resolution data set for calibration of the radiocarbon time scale based on a marked change in ring width and growth pattern the yd termination is clearly identified in the german pine chronology its absolute age of 11 570 bp appears synchronous within the errors of the respective chronologies to related signals in the greenland ice cores grip gisp2 and in lacustrine varve sequences the 14 c age of the laacher see tephra lst is determined from a series of decadal tree ring samples to 11 063 12 14 c bp the calibrated range is 13 010 13 200 cal bp the climatic impact of the lst is reflected in the growth pattern of our tree ring chronologies

absolute dating of the late glacial period in switzerland using annually laminated sediments abstract results of a high resolution late glacial ams 14 c chronology from rotsee central switzerland have given evidence that the atmospheric radiocarbon concentration was not constant between 13 000 and 9500 yr b p this resulted in three marked phases of constant radiocarbon age at 12 700 at 10 000 and at 9500 yr b p new results of a late glacial varve chronology from soppensee central switzerland suggest that the younger two phases of constant 14 c age each had a duration of ca 400 calendar years the length of the late glacial chronozones has been calculated on the basis of these replicate varve counts and a comparison with their estimated duration in radiocarbon years shows that the estimated duration of the chronozones bolling ca 800 calendar yr vs 1000 14 c yr and younger dryas ca 900 calendar yr vs 1000 14 c yr agree with the expected time span whereas the estimated duration of the allerod chronozone ca 400 calendar yr vs 1000 14 c yr is substantially shorter than expected furthermore a tentative comparison of varve ages and 14 c ages suggests that the varve chronology is more than 1000 yr offset toward older ages from the radiocarbon chronology during the late glacial period

use of reaction path modeling to identify the processes governing the generation of neutral na cl and acidic na cl so4 deep geothermal liquids at miravalles geothermal system costa rica abstract the eq3 6 software package was used to investigate the irreversible water rock mass exchanges governing the production of neutral na cl and acidic na cl so 4 geothermal liquids circulating at depth into the miravalles geothermal system first we reconstructed the in situ reservoir composition including ph we evaluated the boundary conditions p co 2 p h 2 s and or p o 2 which are necessary for the implementation of reaction path modeling we estimated the thermodynamic affinity of the reservoir liquids with respect to relevant hydrothermal solid phases and we identified possible compositions of the initially acidic meteoric magmatic liquids then we modeled both the interaction between meteoric magmatic fluids and calc alkaline volcanic rocks and the interaction between neutral na cl waters and highly altered volcanic rocks reaction path modeling was performed through a purely stoichiometric approach without considering the kinetics of irreversible mass exchanges results of reaction path modeling suggest that the neutral na cl liquids hosted in the miravalles geothermal reservoirs are produced through interaction between initially acidic magmatic meteoric aqueous solutions and volcanic rocks and represent the final product of this process however the deep acid na cl so 4 liquids of miravalles are not intermediate products in this process they are instead generated through interaction of neutral na cl waters with volcanic rocks affected by advanced argillic alteration representing old solfataras buried by later volcanics as suggested by robert o fournier about 10 years ago

late glacial and holocene history of former salziger see central germany and its climatic and environmental implications an 8 40 m long sediment sequence from the salziger see basin central germany was investigated by a multi disciplinary approach including chronological sedimentological geo and biogeochemical methods radiocarbon dating conducted on ten samples of aquatic and terrestrial fossil remains and the occurrence of the laacher see tephra lst reveal that the sediment sequence comprises the late glacial and holocene lake history since ca 13 800 cal year bp this onset of lacustrine sedimentation is almost 7 000 years earlier as assumed so far the geo and biogeochemical data indicate distinct variations throughout the late glacial which can be correlated with cold and warm periods such as the oldest dryas the bolling the allerod and the younger dryas during most of the holocene minor variations in the geo and biogeochemical data and a high carbonate content due to the formation and precipitation of autochthonous carbonate in the lake indicate relatively stable lacustrine conditions a slight change in the sedimentary conditions between 6 700 and 4 000 cal year bp with lower deposition of carbonate and fine material can be traced back to enhanced subrosion in the basin increased deposition of coarser sediments and a high accumulation of heavy metals document intensive human activity in the region during the past ca 1 000 years

environmental response to climatic and volcanic events in central europe during the weichselian lateglacial this paper reviews major results of the recent german research priority program changes of the geo biosphere during the last 15 000 years a contribution to pages focussing on changes of the geo biosphere during the weichselian lateglacial different continental archives such as annually laminated lacustrine sediments floodplain sediments and speleothems were used to reconstruct environmental response to climatic changes and the laacher see eruption event at ca 12 900 cal bp special emphasis is paid to establish a reliable time control using varve counting high precision radiocarbon dating of tree ring series and ams radiocarbon dating of terrestrial plant macrofossils recovered from lacustrine sediments to correlate and synchronize large scale environmental changes and events in central europe

geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock macraes gold mine otago schist new zealand abstract the macraes gold deposit in the otago schist new zealand formed during late metamorphic fluid flow through a lower greenschist facies shear zone mineralisation occurred near to the brittle ductile transition at about 300 c large volumes of host rock in a shear zone up to 120 m thick have been hydrothermally altered by this fluid activity most alteration is not structurally controlled apart from proximity to the shear zone ductile and brittle microshears traverse the most mineralised rocks and some structural control of fluid flow occurred as well fluid flow was slow similar to that in metamorphic rocks mm year and diffusion through interconnected fluid was a significant chemical process localised extensional hydrofractures m scale are filled with mineralised quartz most alteration of the host rocks was isochemical with respect to the lithophile elements and mineralised rocks have been variably enriched in as au sb w mo and bi but not co or cd addition of sulphur has occurred to both host rocks and mineralised rocks up to 1 wt above a background of 0 1 wt host rock sulphur is mainly pyritic and is not structurally controlled mineralised rocks have pyrite and arsenopyrite along microshears pyrite chalcopyrite sphalerite and galena have formed from sulphidation of silicates with no addition of metals graphite has been added to mineralised rocks along microshears up to 3 wt locally above a background of 0 1 wt noncarbonate carbon graphite deposition may have occurred as a result of mixing of two fluids water methane and water carbon dioxide graphitisation and sulphidation reactions released low d water which accumulated in the slow moving mineralising fluid distinction between this low d reaction water and meteoric water incursion is difficult

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

evolution of the latera geothermal system ii metamorphic hydrothermal mineral assemblages and fluid chemistry abstract the latera field vulsini volcanic complex latium italy is one of the geothermal areas of the peri tyrrhenian belt along which a regional high thermal anomaly has been detected so far nine deep wells have been drilled within the latera caldera and four of them have been productive the geothermal reservoir is located within the fractured carbonatic rocks of the tuscan nappe the overlying volcanic units sealed by hydrothermal minerals mainly calcite and anhydrite act as an impervious cover the fluid produced by the wells comes from a deep aquifer about 1000 1500 m depth which at present is not connected with the shallow aquifer in the volcanoclastic units fluid temperatures range between 200 and 230 c in hole temperatures as high as 343 c at 2775 m depth have been measured in dry wells the study of the newly formed mineral assemblages from both volcanic and sedimentary units as sampled from the geothermal wells can be used to reconstruct the thermal evolution of the geothermal field the intrusion of a syenitic melt up to a depth of about 2000 m dated 0 86 ma represents the major thermal event for the units in the area and is assumed to represent the first step in the geothermal evolution of the latera system the above mentioned newly formed mineral assemblages can be divided into three groups a contact metasomatic calcite anhydrite diopsidic pyroxene grossularitic garnet phlogopite wollastonite or monticellite b high temperature hydrothermal calcite anhydrite k feldspar vesuvianite melanitic garnet tourmaline amphibole epidote sulphides c low temperature hydrothermal calcite anhydrite k feldspar clay minerals sulphides group a minerals are now relics part of b and all of c group are still in equilibrium with the existing conditions in different parts of the geothermal system thermodynamic calculations on the observed mineral assemblages permitted estimates of the p t conditions and gas fugacities

biotite and apatite as tools for tracking pathways of oxidized fluids in the archean east repulse gold deposit australia fluid pathways in hydrothermal ore deposits can potentially be traced through alteration zoning patterns and the chemistry of mineral phases i e major trace elements and isotopic composition which provide insight into the physico chemical gradients within and adjacent to pathways world class neoarchean gold deposits of the eastern yilgarn can be zoned with respect to alteration assemblages but in many cases fluid pathways are poorly understood which makes it difficult to identify the nature and source of fluids this study conducted detailed core logging sem mineral mapping of alteration assemblages and microprobe analysis of biotite and apatite in order to identify chemical gradients across the east repulse gold deposit of the st ives gold camp eastern yilgarn western australia results show that the east repulse deposit is vertically zoned with relatively oxidized sulfate rich alteration in the footwall of the deposit anhydrite celestine and or barite sulfide rich alteration in the core of the deposit pyrite magnetite with minor barite and celestine and relatively reduced sulfide only assemblages pyrite pyrrhotite with minor pentlandite millerite and cobaltite in the hanging wall of the deposit gold was identified as inclusions in pyrite and associated biotite implying a link between biotite pyrite alteration and gold mineralization the abundance of f in biotite and apatite progressively decreases from the footwall of the deposit into the mineralized core this trend of decreasing f in biotite and apatite with decreasing depth is consistent with an hypothesis that oxidized f and k bearing fluids were focused along subvertical pathways beneath the deposit within or subjacent to granitoid dikes the biotite apatite geothermometer shows that these fluids were relatively hot 480 60 c at the time of alteration these relatively high temperature oxidized f and k bearing fluids may have been derived from a proximal magmatic source

high resolution climate signals in the bolling allerod interstadial greenland interstadial 1 as reflected in european tree ring chronologies compared to marine varves and ice core records abstract lateglacial and holocene tree ring chronologies are unique archives which provide various information on past environments on a true annual time scale changes in ring width can be related to past climate anomalies and dendrodated wood provides an ideal source for radiocarbon calibration we present a 1051 year tree ring chronology from the late glacial built from subfossil scots pines pinus sylvestris that grew in different regions of central and southern europe through a series of high precision radiocarbon measurements we obtained a floating radiocarbon chronology which allowed accurate wiggle matching to the intcal98 calibration curve the trees show a coherent pattern in ring width variations throughout central europe and extending into the mediterranean which indicates a strong external climatic factor most probably temperature during the growing season we identified major growth events which appear synchronous with events seen in isotopic and tracer signals in the greenland ice cores and with changes in the strength of upwelling in the cariaco basin

volatile composition of the phonolitic laacher see magma 12 900 yr bp implications for syn eruptive degassing of s f cl and h 2 o a volatile rich and chemically zoned phonolitic magma reservoir was tapped successively during the eruption of laacher see volcano ca 12 900 years bp and produced a tephra sequence consisting of phenocryst poor highly evolved phonolite at the base and phenocryst rich more mafic phonolite at the top the stratospheric volatile loading was estimated by comparing pre and post eruptive s f cl and h2o contents of undegassed glass inclusions and partially degassed matrix glasses glass inclusions 150 1490 ppm s and host matrix glasses 150 820 ppm s both document a strong s decrease during progressive magmatic differentiation which is interpreted to be partially caused by crystallization of hauyne the s6 stotal ratio of the pre eruptive melt increased with differentiation from 8 to 71 as indicated by s k wavelength shift measurements in glass inclusions sulfate rich highly evolved phonolitic magma was erupted during plinian and sulfide rich more mafic phonolitic magma during late phreatomagmatic phases f and cl became enriched during late stages of differentiation glass inclusions 690 4060 ppm f 1770 4400 ppm cl matrix glasses 680 3660 ppm f 2130 4330 ppm cl the most differentiated melts maximum 13 wt na2o occur only as matrix glass and are extremely f enriched 5080 8780 ppm but cl depleted 460 2820 ppm suggesting that f was retained in the melt whereas some cl was lost during pre and or syn eruptive degassing the h2o contents of glass inclusions increase irregularly with differentiation 2 5 5 7 wt matrix glasses are h2o depleted 0 2 2 8 wt compared to most glass inclusions showing that most h2o was released to the atmosphere by explosive degassing a mass balance calculation yields a syn eruptive volatile release of 1 9 tg stotal 6 6 tg cl and 403 tg h2o from the melt this is a minimum estimate since s and cl could have accumulated in a separate fluid phase as indicated by fluid inclusions in hauyne and pre eruption h2o contents close to saturation level at the likely pressure temperature conditions in the laacher see magma reservoir we estimate that at least ca 20 tg so2 were injected into the stratosphere causing a significant negative climate forcing as reflected by several paleoclimate proxies and as shown by recent modeling

epidote group minerals in low medium pressure metamorphic terranes epidote group minerals are common in metamorphosed mafic to intermediate igneous rocks quartzofeldspathic sediments and calc alumina silicate marl rocks of higher grade zeolite to medium grade amphibolite facies of low medium pressure contact and regional metamorphic terranes i e pressure and temperature conditions below the calcite to aragonite transition within any one rock epidote composition in terms of fe3 fe3 al can be variable but in general is limited by whole rock composition such that epidote group minerals in metabasite lithologies are more fe rich than those in marls that tend to be more al rich and typically include zoisite because of their wide range of p t stability epidote group minerals of variable composition may form in a single rock during several stages of metamorphic re equilibration slow rates of intra crystalline fe3 al exchange especially at low temperatures preserve complex zonation patterns in individual grains that can serve as a tape recorder providing evidence for continuous or discontinuous prograde and retrograde reactions and the p t fluid redox conditions of metamorphism thus relic lower grade epidote typically fe rich often form cores over which new typically less fe rich higher grade epidote rims form in such a case the boundary between the two generations of epidote may be sharp or gradational depending on the temperature history of the rock and fe3 al diffusivity often compositional differences are blurred across the boundary in addition to zoning is the spread of individual epidote grain compositions within a rock even on a thin section scale this is related to variation in the composition of coexisting phases or reactants e g quartz ca al silicates such as plagioclase margarite lawsonite mafic silicates such as chlorite pumpellyite amphiboles other ca fe3 silicates such as prehnite andraditic garnet carbonates fe oxides relict volcanic glass which serve as compositional micro domains in which epidote may form

occurrence and origin of marialitic scapolite in the humboldt lopolith n w nevada the occurrence and origin of marialitic scapolite in the humboldt lopolith was investigated in the field and in the laboratory using petrographic and experimental techniques scapolite occurs in three modes as a pervasive replacement of plagioclase and other minerals in gabbro diorite and extrusive rocks as a poikiloblastic mineral in scapolitite dikes and as a fracture filling mineral with analcime albite and sphene in scapolite veins additional secondary minerals associated with scapolite include epidote prehnite hornblende and diopside salite clinopyroxene relations with these minerals suggest that most marialitic scapolite grew at temperatures around 400 c scapolite composition varies from eqan12 to eqan37 containing from 72 to 96 atomic cl in the r position experiments on systems of similar compositions indicate that nacl h2o fluid having more than 40 mol nacl is needed to stabilize the scapolite

multistage hydrothermal alteration of gabbroic rocks from the failed mathematician ridge oxygen isotopic mineralogical and fluid inclusion data are presented for fresh and hydrothermally altered gabbroic rocks from the failed mathematician ridge the mathematician ridge though initially a fast spreading ridge presently has a deep central rift valley more typical of slow spreading rifts the inner rift walls expose rare plutonic rocks uncomplicated by proximity to deep large offset fracture zones undeformed mathematician ridge gabbros preserve most of the original texture and phase compositions and have been only slightly mineralogically or isotopically modified by post crystallization hydrothermal alteration metagabbros have been subjected to a pervasive ductile deformation and recrystallization to foliated rocks composed of aluminous amphibole low calcium plagioclase and ilmenite oxygen isotope and phase chemical data suggest this event began at temperatures of up to 700 c water rock ratios of less than one and produced modified seawater fluids with isotopic compositions of 3 5 6 0 the amphibolites are cross cut by multiple generation quartz epidote veins forming a network replacement of the amphibole grade mineralogies by greenschist grade mineralogies fluid oxygen isotopic compositions of 2 4 and a two phase separation in the fluid captured in conjugate vapor fluid inclusions are all associated with the formation of this network fluid inclusion data for the quartz indicate initial temperatures of over 500 c these samples may represent rocks from the 1 2 km deep plumbing system of black smoker type venting

chemical variations in assemblages including epidote and or chlorite in the fossil hydrothermal system of saint martin lesser antilles abstract epidote and or chlorite are common minerals in the roots of the fossil geothermal system of saint martin lesser antilles they appear in four distinct assemblages 1 epidote actinolite quartz magnetite near the contact between the tuffaceous host rocks andesitic modal composition and the quartz diorite intrusion of philipsburg 2 epidote chlorite quartz in host rocks as far as a lateral distance of about 3 km from the intrusion 3 epidote chlorite haematite quartz locally in iron and manganese rich host rocks 4 chlorite phengite magnetite appearing as late sealing of porosity in fracture controlled quartz veins with strongly phengitized wall rocks all these assemblages constitute a large alteration grading from propylitic alteration to thermal metamorphism actinolite bearing assemblage detailed microprobe studies of epidotes replacing plagioclases and of chlorites replacing glass and mafic minerals reveal notable compositional variations which have been studied with respect to temperature paleogradients estimated from fluid inclusions study distance from the thermal source and fo2 conditions the mean ps pm 100 fe3 mn3 al3 fe3 mn3 of epidotes vary from 21 in the presence of magnetite near the intrusion to 32 in haematite bearing iron and or manganese volcanic and sedimentary formations the intra grain chemical scattering of epidotes increases with increasing distance of the pluton and decreasing temperature of crystallization all the chlorites coexisting with epidote are mg rich xfe

al fe super 3 and ca sr super 2 epidotes in metagreywacke quartzofeldspathic schist southern alps new zealand al fe super 3 or and sr super 2 or bearing epidotes are a common constituent in chlorite and biotite albite zone metagreywacke quartzofeldspathic schist in the southern alps of new zealand on the basis of electron microprobe backscattered electron scanning of complexly zoned grains five generations of epidote growth are recognized first generation epidotes ps sub 29 25 are typically fractured as a result of cataclasis during d1 deformation and presumably represent relics of prehnite pumpellyite and or pumpellyiteactinolite facies conditions of metamorphism second generation epidote ps sub 25 20 rims first generation epidote and replaces fragmented grains third generation epidote involved sr replacement up to 8 5 wt sro of earlier grains along fracture planes and grain margins single grains exhibit a range of sr ca replacement that can vary by up to 4 wt sro fourth generation post d 1 epidote ps sub 20 9 occurs as overgrowths on earlier generation epidotes and as continuously zoned grains within the lowest grade part of the biotite albite oligoclase zone fourth generation epidote cores ps sub 10 13 are overgrown by slightly more fe rich fifth generation rims ps sub 16 14 suggesting involvement of the epidote ca 2 al 3 si 3 o 12 oh component in an oligoclase producing reaction in quartzofeldspathic lithologies epidote disappears at higher grades than the appearance of oligoclase epidote compositions plot within the miscibility gap defined and a discontinuity between compositions of ps 20 and ps 16 in chlorite zone rocks is attributed to the persistence of relic cores due to incomplete fe super 3 al diffusional exchange at low temperature and textural grade with increasing grade there is a decrease in the range of zoning in individual epidote grains resulting in a more homogeneous population of epidote compositions with the most al rich epidotes becoming fe super 3 or rich and the most fe super 3 or rich epidotes becoming more al rich the formation of sr epidote appears to be related to the release of sr into the fluid phase from the breakdown of detrital plagioclase over the pumpellyite clinozoisite isograd during d1 deformation early formed oligoclase in the biotite albite oligoclase zone resulting from the disappearance of epidote contains up to 0 4 sro mobility of sr and ca is indicated by veins containing sr bearing epidote and calcite the complex zoning of epidotes is a function of bulk composition time variation in fluid composition temperature pressure and deformation of the rocks

climate related variations in the composition of the late glacial and early holocene sediments of lake perespilno eastern poland abstract this paper presents an array of analyses of the laminated sediments of lake perespilno eastern poland covering the period between older dryas and preboreal using the varve chronologies pollen and 14 c data the laminated sequence of lake perespilno has been synchronised with that of lake go ciaz the length of the allerod and younger dryas periods derived from lake perespilno sediments agrees well with the previous estimates according to our data the climate in the allerod was relatively mild with some increase of precipitation and humidity after ca 13 2 kyr cal bp the beginning of the younger dryas is marked by drastic changes in temperature as well as humidity thinning of forests facilitated input of allochtonous material to the lake it seems that the groundwater level as well as lake level dropped significantly and the period of lowest water table was prolonged for ca 300 years surprisingly the abrupt warming at the beginning of the holocene is only slightly reflected in the sediments changes in sediment composition at that time seem to be controlled more by the development of surrounding vegetation than by the climate itself

varve chronology and palynology of the lateglacial in northwest germany from lacustrine sediments of hamelsee in lower saxony abstract the hamelsee is a dolina from a collapse over permian salt that occurred at the end of the pleniglacial it is more than 21 m deep and contains 18 m of lacustrine sediments the lateglacial sediments in the central part of the lake consist of 2 7 m from 15 to 17 7 m of sapropelic and silty muds which are mostly laminated and partly bioturbated minor slumps occur mainly during colder phases the subdivision of the lateglacial is based on pollen zones multidisciplinary studies of the microfacies from thin sections geochemistry pollen analysis and rotifer analysis allow environmental and palaeoclimatological interpretations to be made the biozones of the lateglacial and their boundaries are marked by rapid climatic changes though covering comparatively short periods of time they are not monotonous but characterized by minor internal climatic fluctuations the sediments of the meiendorf and oldest dryas are not laminated the allerod sediment is seasonally varved without interruption and encompasses 625 yr the eruption of the laacher see volcano 12 900 cal bp had an impact on the climate during the following 10 yr the transition from the allerod to the younger dryas took some 50 yr and it occurred 200 yr after the eruption of the laacher see volcano the abrupt change at the end of the lateglacial 11 560 cal bp occurred within less than 10 yr however many proxies reacted with a time lapse of 15 to 30 yr

a field chemical and stable isotope study of subseafloor metamorphism of the josephine ophiolite california oregon the josephine ophiolite is a large complete ophiolite generated in a late jurassic back arc basin along western north america the ophiolite underwent subseafloor metamorphism under a steep thermal gradient as indicated by downward changes in mineralogy and 18o values characteristic mineral zonation includes mica orthoclase and hematite in the lower extrusives greenschist facies assemblages in the upper sheeted dikes and amphibolite facies assemblages in the lower sheeted dikes and high level gabbro cumulate gabbros are only incipiently altered but are depleted in 18o indicating high temperature alteration with fluids that evolved at low water w rock r ratios a second off axis circulation system is recorded by metalliferous sediments that occur 8 21 m above the ophiolite alteration in the upper sheeted dike complex and especially the extrusive sequence is heterogeneous at outcrop scale as indicated by large variations in mineralogy chemistry and 18o values within individual pillows and dikes the heterogenity is due to 1 variations in w r ratio and starting material during alteration by downwelling seawater e g pillow cores versus glassy rims and 2 localized discharge mineralization mostly epidosites superimposed on the background recharge alteration epidosites occur largely as dike parallel stringers irregular replacement of pillow and massive lava and replacement of interpillow and pillow breccia matrices the chemistry of most extrusives and sheeted dikes is characterized by loss of ca and gain in na and mg consistent with alteration by downwelling fluids in addition the sheeted dikes are depleted in k2o and the lower sheeted dikes and high level gabbros are depleted in zn and cu the 18o and d values for most samples from the extrusive sequence indicate alteration by seawater at 50 rotation of the entire crustal sequence at the spreading axis suggests that the ophiolite formed at a slow spreading center where magma chambers were episodic

hypersaline fluids generated by high grade metamorphism of evaporites fluid inclusion study of uranium occurrences in the western zambian copperbelt in the pan african lufilian belt western zambian copperbelt uranium mineralizations preferentially scattered in kyanite talc micaschists metamorphosed evaporitic sediments or concentrated along transposed quartz veins provide an opportunity to 1 understand the time space relationship between the ore minerals and the deformation of the host rocks 2 identify the different fluid events associated with specific stages of quartz deformation and 3 characterize the ore fluid geochemistry in terms of fluid origin and fluid rock interactions in the u occurrences studied in lolwa and mitukuluku domes region western zambian copperbelt two mineralizing stages are described the first generation of ore fluids 53 59 wt cacl2 13 15 wt nacl n2 h2 in the gas phase of fluid inclusions circulated during the high temperature quartz recrystallization at 500 700 c this temperature is in agreement with the p t conditions recorded during the crustal thickening related to continental collision at ca 530 ma la icpms analyses show the presence of uranium within this fluid with a concentration mode around 20 ppm the second generation of ore fluid 21 32 wt nacl 19 21 wt cacl2 co2 co in the gas phase of fluid inclusions percolated at lower temperature conditions at the brittle ductile transition between 200 and 300 c this temperature could be related to the exhumation of the high grade metamorphic rocks at ca 500 ma the formation of h2 and co is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions finally a late fluid 14 16 wt naclequiv circulated in the brittle domain but seems unrelated to u re mobilization event

plagioclase and epidote buffering of cation ratios in mid ocean ridge hydrothermal fluids experimental results in and near the supercritical region abstract experiments have been performed with na ca k cl fluids of seawater chlorinity and diabase basalt and plagioclase bearing mineral mixtures at 350 425 c and 250 400 bars to help constrain hydrothermal alteration processes at mid ocean ridges dissolved ca na and ph for all experiments responded systematically to differences in dissolved sio2 concentrations and the compositions of plagioclase reactants diabase alteration at low fluid rock mass ratios 0 5 to 1 produces fluids undersaturated with respect to quartz during hydration of primary olivine and orthopyroxene whereas basalt alteration under similar conditions yields fluids slightly supersaturated with respect to quartz during breakdown of glass to smectite and amphibole fluid chemistry in all experiments appears to approach a partial equilibrium state with the albite and anorthite components in plagioclase and approaches a ph consistent with plagioclase alteration to epidote trace element data from vent fluids specifically b and sr together with major element chemistry ca na sio2 ph provides evidence that the reaction zone for black smoker fluids at mid ocean ridges is composed of only slightly altered diabase and is characterized by small amounts of epidote nearly fresh plagioclase and clinopyroxene and partially to completely hydrated olivine and orthopyroxene fluids reacting with this rock may be undersaturated with respect to quartz so pressure estimates based on the quartz geobarometer should be regarded as minimums using equilibrium between plagioclase the dominant reactant and epidote the dominant reaction product in experiments we estimate that temperatures in reaction zones are in excess of 375 c for most vent systems these temperatures are higher than measured vent temperatures suggesting that hotspring fluids commonly loose heat during ascent to the seafloor

chemical and thermal constraints on focussed fluid flow in the lower oceanic crust the mechanism of heat extraction from the lower oceanic crust near the ridge axis is poorly constrained despite its importance for understanding both the process of accretion of the plutonic complex and the mass fluxes associated with ridge hydrothermal systems we have investigated the role of zones of focussed fluid flow in the plutonic complex of the oman ophiolite in the near axis cooling of the oceanic crust lineaments identified on aerial photographs that occur at 1 km spacing show evidence for extensive hydrothermal fluid flow through regions 10 to 50 m wide fluid flow is initiated in these regions at 800 c and continues at least into the lower greenschist facies strontium isotope analyses indicate that the fluid flux through these zones is sufficient to transport a metasomatic front from the base of the sheeted dike complex to close to the moho computed minimum fluid fluxes to transport a metasomatic front through the focussed fluid flow zones are 1x108 kgm2 modeling of diffusive exchange of calcium from olivine to clinopyroxene indicates enhanced cooling rates adjacent to the focussed fluid flow zones heat fluxes estimated from the enhanced cooling rates are broadly consistent with the fluid fluxes determined from modeling the sr isotopic composition of samples from the focussed fluid flow zones the combination of independent estimates of the fluid and heat fluxes such as these can provide more rigorous constraints on the thermal history than either approach used in isolation our results show that focussed fluid flow could play a major role in the cooling in the lower oceanic crust significant focussed fluid flow in the lower oceanic crust has important implications for predicting the total mass flux associated with hydrothermal circulation at mid ocean ridges this is because fluids flowing through channels become chemically rock buffered at smaller fluid fluxes than those flowing pervasively through a rock mass thus if focussed fluid flow is an important mechanism of heat loss from the lower oceanic crust the chemical fluxes from ridge hydrothermal systems into the oceans may be smaller than currently thought

the northern samail ophiolite an oxygen isotope microprobe and field study geological petrological and oxygen isotopic data are presented for 228 whole rock and mineral samples collected from a 100 20 km area of the northern samail ophiolite in oman most of these samples are from three detailed profiles through the pillow lavas sheeted dikes and layered gabbros of this laterally heterogeneous fragment of cretaceous oceanic crust down to and across the petrologic moho the profiles encompass a range of petrologic and tectonic styles and each profile exhibits distinctive 18 16 o variations compared to one another and to mid ocean ridge basalts as a result of pervasive seawater hydrothermal interaction that varied in intensity along strike in the ophiolite in general 18 o depletions are observed in the layered gabbros and 18 o enrichments in most of the sheeted dikes and pillow lavas similar to results previously observed in the southern part of the ophiolite ibra area where 18 o depletions within the gabbroic section are quantitatively balanced by 18 o enrichments in the shallower parts of the oceanic crust the wadi hilti profile selected as an example of relatively intact crust differs from ibra in having more uniform and slightly higher 18 o in the gabbros 5 4 to 6 3 as well as in containing more hydrous alteration minerals amphibole epidote chlorite and prehnite the profiles in the wadi kanut shafan and wadi rajmi sections are much more complex and reveal the impact of off axis intrusions and deep crustal shearing plagiogranite wehrlite intrusions in the shafan kanut area superimposed a local hydrothermal aureole on the ophiolite evident in dikes highly depleted in 18 o quartz sulfide veins abundant epidote thullite and chlorite in shallower rocks and low temperature hydrous alteration of deeper gabbroic rocks the latter produced an overall increase in whole rock 18 o 6 2 to 6 9 such late stage intrusions are found throughout the northern half of the samail ophiolite the wadi rajmi area which is a possible fossil transform or propagating rift represents the most complex of the three profiles it also contains the most abundant highly deformed and hydrothermally altered rocks together with the deepest and largest zone of 18 o depletion yet found in any ophiolite locally 18 o 2 0 conduits for large volumes of high temperature hydrothermal fluids were provided by fractures now occupied by low 18 o gabbro pegmatites and low 18 o dikes material balance estimates for the regional samples and from the various transects through the ophiolite give crustal bulk 18 o averages 5 9 to 6 3 that are within sampling error almost identical to the average morb basalt value of about 5 8 if both vertical and lateral crustal heterogeneities are integrated into a three dimensional model this supports and amplifies the conclusion of earlier workers that the 18 o of seawater is buffered and controlled by hydrothermal interaction with oceanic crust as long as the cumulative effects both spatial and temporal of all seafloor magmatic hydrothermal processes are considered the very slight out of balance enrichment of the integrated crustal average 18 o compared to morb may be explained by the ubiquitous mineralogical and isotopic evidence for a late low temperature alteration event in the basal gabbros these effects are prominent in the vicinity of the petrologic moho and may indicate exchange with low temperature aqueous fluids during or after detachment of the obducted slab

correlation and synchronisation of lateglacial continental sequences in northern central europe based on annually laminated lacustrine sediments abstract the present study focusses on correlation and synchronisation of weichselian lateglacial varved lake sediments from western germany meerfelder maar eifel region northern germany hamelsee lower saxony central poland lake go ci a z and eastern poland lake perespilno by using varve chronology tephrochronology palynostratigraphy and stable isotopes comparison of the several independent time scales shows that biotic and abiotic parameters respond abruptly and quasi synchronously within the errors of the different chronologies during the younger dryas preboreal transition moreover there is a consensus about the length of the younger dryas cold stage of 1100 1150 varve years in the allerod the prominent laacher see tephra 12 880 varve years bp can be used to fix floating varve chronologies the relative duration of this biozone has been determined in meerfelder maar and hamelsee at between 625 and 670 varve years in the meerfelder maar a combination of continuous varve counting and biostratigraphy has been possible for the almost entire lateglacial the comparison between continental limnic sequences and greenland ice core records should be made on the basis of independent chronologies in both archives it is more practicable to develop regional stratotypes on the continental regions instead of simply using ice cores as stratotypes for the lateglacial for terrestrial european records in this respect annually laminated lacustrine sequences have a great potential

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

evolution of fluid rock interaction in the reykjanes geothermal system iceland evidence from iceland deep drilling project core rn 17b abstract we describe the lithology and present spatially resolved geochemical analyses of samples from the hydrothermally altered iceland deep drilling project iddp drill core rn 17b the 9 3 m long rn 17b core was collected from the seawater dominated reykjanes geothermal system located on the reykjanes peninsula iceland the nature of fluids and the location of the reykjanes geothermal system make it a useful analog for seafloor hydrothermal processes although there are important differences the recovery of drill core from the reykjanes geothermal system as opposed to drill cuttings has provided the opportunity to investigate evolving geothermal conditions by utilizing in situ geochemical techniques in the context of observed paragenetic and spatial relationships of alteration minerals the rn 17b core was returned from a vertical depth of 2560 m and an in situ temperature of 345 c the primary lithologies are basaltic in composition and include hyaloclastite breccia fine grained volcanic sandstone lithic breccia and crystalline basalt primary igneous phases have been entirely pseudomorphed by calcic plagioclase magnesium hornblende chlorite titanite albitized plagioclase vein epidote and sulfides despite the extensive hydrothermal metasomatism original textures including hyaloclastite glass shards lithic clasts chilled margins and shell fragment molds are superbly preserved multi collector la icp ms strontium isotope ratio 87 sr 86 sr measurements of vein epidote from the core are consistent with seawater as the dominant recharge fluid epidote hosted fluid inclusion homogenization temperature and freezing point depression measurements suggest that the rn 17b core records cooling through the two phase boundary for seawater over time to current in situ measured temperatures electron microprobe analyses of hydrothermal hornblende and hydrothermal plagioclase confirm that while alteration is of amphibolite grade it is in disequilibrium and the extent of alteration is dependent upon protolith type and water rock ratio alteration in the rn 17b core bares many similarities to that of type ii basalts observed in mid atlantic ridge samples

hydrothermal alteration associated with magnetite mineralization in the bafq iron deposits iran abstract bafq mining district bmd is an iron mineralization province that contains more than 2 gt of iron ore located in the early cambrian volcano plutonic arc known as the kashmar kerman zone the host rocks of the fe mineralization are granitic and microgranitic rocks and their extrusive equivalents field observations and petrographic studies showed that both sodic and calcic alteration are related to iron mineralization other alteration styles including silicic chlorite epidote and sericite alteration are less important and post dated the mineralization sodic alteration is associated with the formation of chessboard albite whereas the calcic alteration is featured by a mineral assemblage of actinolite tremolite magnetite apatite available evidence suggests that the involved metasomatic fluids could be mainly of evaporitic sources with a minor contribution from magmatic fluids we suggest that mineralization formed at the end of the precambrian in pull apart basins in a magmatic back arc region associated with subduction of the proto tethys oceanic crust under central iranian plate iron ore mineralization may be related to the interaction of granite derived hydrothermal fluids and brine derived fluids sourced from the latest precambrian rizu and dezu evaporitic sequences

fluid inclusions in epidote minerals and fluid development in epidote bearing rocks the widespread occurrence of epidote minerals in metamorphic and igneous rocks as well as in many ore deposit types makes it a promising candidate for fluid inclusion studies apart from high to very high temperature and low to intermediate pressure conditions epidote minerals are stable over a wide range of pressure and temperature in the continental and oceanic crust e g poli and schmidt 1998 yet fluid inclusion studies on epidote minerals are surprisingly scarce even in fluid saturated environments like certain vein type deposits or hydrothermal volcanic vugs and druses for example epidote minerals are not mentioned in the subject index of roedder s 1984 outstanding summary and review of fluid inclusion studies and occurrences which lists more than sixty different host minerals for fluid inclusions nonetheless more recent studies showed fluid inclusions in epidote minerals to be the only direct witness of the physiochemical and compositional fluid evolution during certain geodynamic processes mainly found in fossil geothermal systems ore deposits and high pressure to ultra high pressure rocks the aim of this review is to outline and summarize some aspects and interpretations of geodynamic processes which are based on temperature t pressure p molar volume v and composition x data from fluid inclusions in epidote minerals as well as associated host minerals from various geological environments the review starts with a chapter on some typical mixed volatile solid fluid equilibria involving epidote minerals which are relevant for the here discussed environments this is followed by a short introduction into the basic concepts of fluid inclusion research and the role of epidote minerals the next section covers fluid inclusion studies on epidote minerals from active and fossil geothermal systems as well as low grade metamorphic rocks and constraints on the p t x properties of the fluids present in these systems this is followed by a short introduction

the δ18o record along the greenland ice core project deep ice core and the problem of possible eemian climatic instability over 70 000 samples from the 3029 m long greenland ice core project grip ice core drilled on the top of the greenland ice sheet summit have been analyzed for 8o a highly detailed and continuous 8o profile has thus been obtained and is discussed in terms of past temperatures in greenland we also discuss a three core stacked annual 8o profile for the past 917 years the short term 50 years variability of the annual 8o signal is found to be 1 in the holocene and estimates for the coldest parts of the last glacial are 3 or higher these data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the eemian spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the 8o signal which for the holocene ice is found to be considerably stronger than expected we suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix deconvolution techniques were employed for restoring with great confidence the highly attenuated annual 8o signal in the holocene we confirm earlier findings of dramatic temperature changes in greenland during the last glacial cycle abrupt and strong climatic shifts are also found within the eem sangamon interglaciation which is normally recorded as a period of warm and stable climate in lower latitudes the stratigraphic continuity of the eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile

the evolution of the waiotapu geothermal system new zealand based on the chemical and isotopic composition of its fluids minerals and rocks abstract the waiotapu geothermal system is hosted by silicic rocks of the taupo volcanic zone new zealand exploration drilling in the late 1950s down to 1100 m provided physical information on the system measured temperatures show a boiling profile to 295 c with shallow inversions particularly in the north total discharge fluid samples were collected the geothermometry and measured temperatures show that fluids derive mainly from a shallow 400 m deep reservoir at about 225 c petrologic study of drillcore samples recovered from seven wells reveals an alteration assemblage of quartz and albite adularia with a variable distribution of chlorite pyrite calcite zeolites epidote pyrrhotite sphene leucoxene apatite and minor base metal sulfides white mica is a late overprint particularly well developed at shallow depths surficial alteration of kaolin cristobalite alunite and smectite clays reflect alteration by acid sulfate steam heated waters the activities of components in minerals determined from microprobe analyses and composition activity relations and fluids speciated to reservoir conditions indicate equilibrium now exists between the fluids and white mica the na k ratio of the fluid is being controlled by dissolution of albite and adularia while its h 2 h 2 s ratio is buffered by pyrite replacing pyrrhotite the fluids are now slightly undersaturated with respect to calcite the present deep fluids boil adiabatically from at least 300 c to 230 c at depths of 500 m this ascending chloride fluid is variably diluted by a steam heated water of zero chloride that lies over and occurs on the margin of the system like a discontinuous umbrella the steam heated water is relatively co2 rich 0 1 m the cooling at shallow levels by this mixing has shifted the alteration from albite adularia stability to white mica stability this shift is enhanced by the co2 rich nature of the diluent dilution of ascending chloride fluids by shallow waters is also supported by the oxygen and hydrogen isotopic composition of the mixture with the deep fluid being enriched in 18o and d from local meteoric by 7 and 10 respectively the patterns in whole rock 18o indicate that they were largely shifted in isotopic composition prior to incursion of steam heated waters possibly induced by a series of hydrothermal eruptions 900 years ago in contrast the 18o composition of late vug calcite indicates its formation is related to the initial incursion of steam heated groundwater and subsequent cooling this is supported by fluid inclusion evidence the d shift from local groundwater composition and the 13c composition of co2 determined from calcite 4 to 6 may be evidence for a magmatic input to the meteoric convection cell the shallow portion of the waiotapu geothermal system has recently evolved both chemically and physically by incursion of fluids from a steam heated carapace continued refluxing of these relatively cool hybrid fluids progressively deeper with their recycled co2 content will hasten hydrolytic leaching in contrast to a single pass of adiabatically cooling deep fluids this action accompanied by argillic alteration may eventually seal the deeper portions of the system hastening its demise there is evidence for similar events occurring in the fossil environment at epithermal depths

mineralogical and geochemical characteristics of hydrothermal alteration of basalt in the kuroko mine area japan implications for the evolution of a back arc basin hydrothermal system abstract basalt in the furutobe district of the kuroko mine area in japan is characterized by abundant chlorite and epidote fluid inclusion studies indicate that chlorite is formed at lower temperatures 230 250 c than epidote 250 280 c the seawater basalt mass ratio for the early chlorite rich alteration was high max 40 but that for the later alteration was low 0 1 1 8 the cao na2o and sio2 of the bulk rock correlate negatively with mgo while feo and fe correlate positively with mgo these changes in the characteristic features of hydrothermal alteration from early to late are generally similar to those for a mid ocean ridge geothermal system accompanying basalt alteration the mgo feo ratios of chlorite and actinolite and the fe2o3 concentration of epidote from the basalt are greater than those of mid ocean ridge basalt probably owing to the differences in the fe2o3 feo and mgo feo ratios of the parent rocks the lower cao concentration and the higher na2o concentration of the bulk rock compared with altered mid ocean ridge basalt can be interpreted in terms of the difference in original bulk rock compositions the furutobe basalt as well as other submarine back arc basalts contains more vesicles filled with hydrothermal minerals epidote calcite quartz chlorite pyrite than do the mid ocean ridge basalts the abundance of vesicles plays an important role in controlling the secondary mineralogy and geochemistry of hydrothermally altered submarine back arc basin basalts

equilibrium and disequilibrium processes across the greenschist amphibolite transition zone in metabasites documentation of textures modes and compositions of minerals in metamorphosed basalts across two greenschist to lower amphibolite facies sequences flin flon manitoba and rossland british columbia was combined with a compilation of the literature data to assess equilibrium and disequilibrium processes across this important transition zone at flin flon and rossland the greenschist amphibolite facies transition occurs over a narrow spatial interval marked by hornblende in oligoclase in and actinolite out isograds the data suggest the existence of stable miscibility gaps separating coexisting actinolite and hornblende and coexisting albite and oligoclase in the lowermost amphibolite facies however actinolite and hornblende show a divergence in compositions going upgrade across the oligoclase in isograd suggestive of disequilibrium between the new progressively more aluminous hornblende and metastably persisting actinolite likewise coexisting albite and oligoclase compositions show no evidence for converging compositions at higher temperatures suggesting they do not remain in equilibrium across a miscibility gap compositional gaps within epidote phases are attributed to disequilibrium preservation of lower grade epidote compositions to higher grade conditions rather than the existence of a miscibility gap at greenschist and amphibolite facies conditions recognition of equilibrium and disequilibrium relations highlights the difficulty of using natural compositional datasets to extract information on miscibility gaps and more generally to extract a x relationships the greenschist to amphibolite facies transition is controlled principally by the consumption of chlorite which primarily occurs upon crossing the oligoclase in isograd concomitant with conversion of actinolite to hornblende and albite to oligoclase the result is a focused pulse of devolatilization over a small spatial and thermal interval

chemical interaction of aqueous solutions with epidote feldspar mineral assemblages in geologic systems ii equilibrium constraints in metamorphic geothermal processes thermodynamic analysis of the system na sub 2 o k sub 2 o cao feo fe sub 2 o sub 3 al sub 2 o sub 3 sio sub 2 h sub 2 o hcl co sub 2 at pressures and temperatures to 5 kb and 600 sup 0 c affords quantitative description and interpretation of phase relations among epidote garnet plagioclase and alkali feldspar solid solutions in hydrothermal systems comparison of computed and observed compositions of these minerals and coexisting fluids suggests that the calculations afford close approximation of equilibrium and mass transfer in metamorphic geothermal processes the standard molal enthalpies of decomposition reactions for plagioclase are of the order of 4 to 50 kcal mole sup 1 which requires the activity of the anorthite component of plagioclase coexisting with epidote solid solutions to increase with increasing temperature at constant pressure in contrast because the standard molal volumes of these reactions are also negative a sub caal sub 2 si sub 2 o sub 8 decreases with increasing pressure at constant temperature either stoichiometric epidote or clinozoisite is compatible with plagioclase quartz calcite and an aqueous phase but only at x sub co sub 2 less than or equal to 0 2 the complex zoning commonly exhibited by both plagioclase and epidote solid solutions in geologic systems can be attributed to minor isothermal isobaric changes in the composition of coexisting aqueous solutions logarithmic activity and fugacitymore diagrams constructed with provision for solid solution permit documentation of such changes and facilitate thermodynamic interpretation of mineral and fluid compositions in metamorphic geothermal systems less

epidote bearing veins in the state 2 14 drill hole implications for hydrothermal fluid composition epidote bearing veins in state 2 14 drill core from 900 to 2960 m depth were examined using backscattered electron microscopy and electron probe microanalysis to characterize the mineralogy parageneses texture and composition of vein minerals in order of decreasing abundance minerals in epidote bearing veins are pyrite calcite k feldspar quartz anhydrite hematite chlorite fe cu zn sulfides actinolite titanite and allanite the downhole distribution of minerals in epidote bearing veins pyrite and quartz varies as a function of depth and includes 1 calcite above 2000 m 2 k feldspar between 1700 and 2745 m 3 anhydrite between 2195 and 2745 m 4 hematite sulfides above 2773 m and 5 actinolite below 2890 m where present k feldspar was the first mineral to precipitate in veins followed by epidote in all other veins epidote was the earliest vein mineral to form calcite quartz anhydrite hematite and sulfides were paragenetically later compositional zoning common in most vein epidotes is typically symmetric with al rich cores and fe3 rich rims the minimum mole fraction of ca2fe3si3o12 oh xps in vein epidotes decreases systematically with increasing depth from 0 33 at 906 m to 0 21 at 2900 m and the maximum xps at any given depth is greater than 0 33 thermodynamic analyses of phase relations among vein filling minerals and aqueous solutions at depths near 1867 m and 300 c indicate that the modern reservoir fluid in the salton sea geothermal system is in equilibrium with calcite hematite quartz epidote xps 0 33 anhydrite the predicted fugacity of co2 14 bars for the modern salton sea brine is in close agreement with the calculated value of fco2 for the 1867 m production fluid theoretical phase diagrams in the system cao k2o fe2o3 al2o3 sio2 h2o o2 s2 co2 demonstrate that the mineralogies and mineral parageneses recorded hi epidote bearing veins and the observed variations in al fe3 content of vein epidotes may result from only minor changes in the fugacity of co2 o2 and s2 of the geothermal fluid

high resolution late glacial chronology for the gerzensee lake record switzerland δ18o correlation between a gerzensee stack and ngrip oxygen isotope variations were analyzed on bulk samples of shallow water lake marl from gerzensee switzerland in order to evaluate major and minor climatic oscillations during the late glacial to highlight the overall signature of the gerzensee 18o record 18o records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances then the records were stacked with a weighting depending on the differing sampling resolution to develop a precise chronology the 18o stack was then correlated with the ngrip 18o record applying a monte carlo simulation relying on the assumption that the shifts in 18o were climate driven and synchronous in both archives the established chronology on the gicc05 time scale is the basis for 1 comparing the 18o changes recorded in gerzensee with observed climatic and environmental fluctuations over the whole north atlantic region and 2 comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the bolling allerod period the 18o record of gerzensee is characterized by two major isotope shifts at the onset and at the termination of the bolling allerod warm period as well as four intervening negative shifts labeled gi 1e2 d c2 and b which show a shift of one third to one fourth of the major 18o shifts at the beginning and end of the bolling allerod despite some inconsistency in terminology these oscillations can be observed in various climatic proxies over wide regions in the north atlantic region especially in reconstructed colder temperatures and they seem to be caused by hemispheric climatic variations

87sr 86sr values in groundwaters of the east bull lake pluton superior province ontario canada abstract the east bull lake pluton is a 2 48 ga old layered mafic intrusion located on the southern margin of the superior province precambrian shield in ontario canada the groundwaters have been studied as part of a detailed geological mapping and geochemical study of the pluton for the canadian nuclear fuel waste management program all groundwater samples are dilute the most concentrated na cl type water contains 3 1 g l total dissolved solids present day87sr 86sr values of the rock samples varies from 0 705 to 0 714 and the groundwaters from 0 711 to 0 720 the ca hco3 recharge waters show the greatest range in values in contrast to the deeper na hco3 and deep na cl waters where a narrow range of 0 712 0 713 is found fracture filling laumontite calcite and gypsum have the same isotopic signature as the deep water the ca hco3 water is the youngest component of the groundwater system and its spread in isotopic values reflects local conditions at the surface the na cl water is considered to be the oldest component and its sr isotopic ratio value indicates equilibration with silicate fracture mineral phases the isotopic data suggest that laumontite calcite and gypsum fracture phases have either crystallized from this water or are currently controlling its isotopic composition by dissolution no age can be assigned to the deep waters except that the na cl component may date from the early paleozoic based on geological arguments or more likely be 104 106 years old based on kinetic studies of rock water interaction and other isotopic data if seawater was one component of the na cl water history there is no record of this in the87sr 86sr ratios

sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie l etude detaillee du gisement de niccioleta revele les reactions metasomatiques ayant transforme l anhydrite en grenatite la dolomie en pyroxenite et les micaschistes en epidotite et celles qui ont entraine la reduction du sulfate en pyrite les solutions ferriferes ont lessive na k co2 et partiellement ca mg et s l inertie de al et ti et les deplacements de ca si s et sr precisent les modalites des transformations dont on a evalue les bilans pour un volume restant constant le comportement de s est complexe lessive lors de la grenatisation il est apporte lors de la cristallisation de la pyrite sans que le bilan global soit equilibre l origine de ce s est discutee en liaison avec le contexte evaporitique et un systeme geothermique regional tertiaire en l absence de preuve d eventuelles preconcentrations sulfurees syn sedimentaires le gisement parait resulter d une metasomatose de l anhydrite dans un systeme geothermique semblable a celui de larderello mais a alimentation marine

environmental change and fluvial activity during the younger dryas in central germany abstract late pleistocene climatically induced environmental changes are reconstructed by applying a multidisciplinary approach on floodplain sediments of small to medium sized catchments in central germany radiocarbon dating pollen analysis and the presence of an accurately dated tephra layer allow the establishment of a reliable chronology the beginning of the younger dryas is marked by a change in fluvial activity that lasts for several hundred years during this period gravels and sands were deposited by a braided river system fluvial systems at this time were predominantly controlled by the climatic conditions of the surrounding uplands where the climatic deterioration led to a lowering of the forest limit and enhanced periglacial slope processes an open pine forest prevailed in the basin areas and no evidence of slope wash and solifluction was found the second part of the younger dryas is characterised by a meandering fluvial system and the deposition of overbank fines the rapid transition from younger dryas to preboreal coincides with an increase in organic deposition

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

mineralogy 40ar 39ar dating and apatite fission track dating of rocks along the castle mountain fault alaska abstract the castle mountain fault is a 200 km long right lateral fault that forms the northern boundary of the cook inlet basin and matanuska valley alaska fault gouge and fault rock at six localities contain the clay minerals illite smectite chlorite and interstratified illite smectite at one locality gouge contains deformed illite smectite with very little wall rock chlorite contamination fine 36 24 0 08 ma for fine to coarse sizes respectively argon retention ages obtained from 40ar and 39ar retained in the three size fractions of illite at room temperature during neutron irradiation are 37 36 0 15 42 11 0 14 and 47 20 0 10 respectively apatite fission track ages were measured in arkose at a locality on the fault 60 km west of the gouge locality three samples of arkose were dated one within 10 m of the fault core one 170 m from the fault and one 335 m from the fault the sample nearest to the fault yielded an age of 29 3 2 8 ma but it only had four track lengths at 10 13 m two apatite grains from the intermediate sample yielded a pooled age of 34 3 6 1 ma the distant sample 25 grains counted 101 track lengths yielded an age of 32 0 2 9 ma this sample has a broad distribution of track lengths and a broad distribution of individual grain ages ranging from 14 8 5 1 to 67 8 8 8 ma monte carlo modeling of the apatite age and track length data is consistent with hydrothermal mineralization at 37 39 ma followed by rapid uplift and cooling after 10 ma the 40ar 39ar total gas ages k ar are minimum ages and the argon retention ages are maximum ages the thermal model derived from the fission track data and the argon retention age for the finest illite fraction of 37 ma date a hydrothermal mineralization event on the fault

cyclic deformation and chemical transport in the folson lake fault zone east bull lake anorthosite gabbro complex evidence for seismic pumping abstract the east bull lake anorthosite gabbro a late archean 2472 24ma magmatically layered lopolith at the southern margin of the superior province has experienced regional retrograde metamorphism and is transected by the folson lake fault zone a structure of regional extent the fault zone displays repeated episodes of ductile brittle deformation and vein development it has been extensively metasomatized in domains marked by the sequential development of quartz adularia epidote chlorite laumontite calcite and clay fe oxyhydroxide downhole geochemical profiles through the fault zone show coherent patterns for zr hf zr th ta nb and cr co ni which are interpreted to reflect variations in primary igneous compositions by alteration insensitive elements metasomatism is marked by peaks of sio2 k2o or na2o with al2o3 fe mn and mg and ca plus volatiles corresponding to domains of quartz adularia or albite chlorite and laumontite plus calcite respectively the analogue elements th and u are present at uniformly low levels averaging 1 1 and 0 4 ppm respectively thorium covaries with zr such that variations of abundance reflect primary differences whereas th u ratios scatter between 1 5 to 10 indicating minor remobilization of u strontium has been extensively redistributed within the fault zone and cs covaries with k retrograded areas of the pluton have whole rock 18 values ranging between 4 5 and 7 2 per mil both below and above primary values of 5 7 per mil indicating open system behaviour during regional retrograde metamorphism within the fault zone hydrothermal reservoirs involved in later k metasomatism were at temperatures of 150 250 c where 18 o h2o 2 6 to 1 7 per mil likely representing isotopically and chemically evolved deep pore fluids expelled during crustal activity related to tectonic processes in the nearby grenville province calcite and laumontite developed by the advection through the fault zone of ca rich thermal brines at temperatures around 50 200 c where 18oh2o 15 to 0 per mil such fluids were evolved formation brines with a major component of meteoric h2o expelled in the lower paleozoic the multiple deformation metasomatism events are interpreted in terms of episodic seismic pumping on a fault that was intermittently active over a time scale in excess of 1 ga

regional scale hydrothermal alteration in the central blake river group western abitibi subprovince canada implications for vms prospectivity the late archean blake river group is a thick succession of predominantly mafic volcanic rocks within the southern zone of the abitibi greenstone belt it contains a number of silicic volcanic centers of different size including the large noranda volcanic complex which is host to 17 past producing volcanogenic massive sulfide deposits the noranda complex consists of a 7 to 9 km thick succession of bimodal mafic and felsic volcanic rocks erupted during five major cycles of volcanism massive sulfide formation coincided with a period of intense magmatic activity cycle iii and the formation of the noranda cauldron hydrothermal alteration in these rocks is interpreted to reflect large scale hydrothermal fluid flow associated with rapid crustal extension and rifting of the volcanic complex the alteration includes abundant albite chlorite epidote and quartz silicification which exhibit broad stratigraphic and structural control and correlate with previously mapped whole rock oxygen isotope zonation the mine sequence volcanic rocks are characterized by abundant iron rich chlorite fe fe mg 0 5 hydrothermal amphibole ferroactinolite and coarse grained epidote of clinozoisite composition 10 wt fe2o3 lacking the clinozoisite solid solution alteration in the mine sequence volcanic rocks persists along strike well beyond the limits of the main ore deposits as far as several tens of kilometers and can be readily distinguished from greenschist facies metamorphic assemblages at a regional scale the lack of similar alteration in the pre cauldron sequences is consistent with limited 18o depletion and suggests that the early history of the volcanic complex did not support large scale high temperature fluid flow in these rocks comparisons with a much smaller barren volcanic complex in nearby ben nevis township reveal important differences in the alteration mineralogy between volcanoes of different size with implications for area selection during regional scale mineral exploration the ben nevis complex consists of a 3 to 4 km thick succession of mafic intermediate and felsic volcanic rocks centered on a small subvolcanic intrusion alteration of the volcanic rocks comprises mainly low temperature assemblages of prehnite pumpellyite magnesium rich chlorite fe fe mg 10 wt fe2o3 and calcite actinolite magnetite alteration occurs proximal to the intrusive core of the complex but the limited extent of this alteration indicates only local high temperature fluid circulation adjacent to the intrusion a distal zone of carbonate alteration is located 4 6 km from the center of the volcano although iron bearing carbonates are present locally within this zone the absence of siderite argues against a high temperature origin for this alteration these observations do not offer positive encouragement for the existence of a fossil geothermal system of sufficient size or intensity to have produced a large massive sulfide deposit

high resolution sediment and vegetation responses to younger dryas climate change in varved lake sediments from meerfelder maar germany abstract this work focuses on a 1900 year section of varved sediments from lake meerfelder maar mfm extending from the late allerod to the preboreal varve counting provides the chronological framework and determines the length of younger dryas to 1025 1090 years a strong relation between climate change environment response and depositional processes has been found in consequence varve microfacies variations are a sensitive proxy for environment changes these are reflected for example in erosion processes within the lake s catchment minerogenic input and lake productivity diatom blooms the observed varve changes have been quantified by multiproxy analyses of physical and chemical sediment parameters with a resolution of between 8 and 40 years depending on sedimentation rate in addition high resolution palynological investigations provide the biostratigraphical subdivision based on changes in the vegetation occurring during the same time interval varve observations reveal that environment changes at the beginning and the end of the younger dryas occurred within 20 50 years furthermore sediment and vegetation changes were synchronous within the actual precision of the mfm and grip chronologies divergence of only a few decades terrestrial responses in western europe occurred quasi synchronous to temperature changes in greenland

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

oxygen isotopes of lake marl at gerzensee and leysin switzerland covering the younger dryas and two minor oscillations and their correlation to the grip ice core the ratio of oxygen isotopes is a temperature proxy both in precipitation and in the calcite of lacustrine sediments the very similar oxygen isotope records from greenland ice cores and european lake sediments during the last glacial termination suggest that the drastic climatic changes occurred quasi simultaneously on an extra regional probably hemispheric scale in order to study temporal relations of the different parameters recorded in lake sediments for example biotic response times to rapid climatic changes a precise chronology is required in unlaminated lake sediments there is not yet available a method to provide a high resolution chronology especially for periods with radiocarbon plateaux alternatively an indirect time scale can be constructed by linking the lake stratigraphy with other well dated climate records new oxygen isotope records from gerzensee and leysin with an estimated sampling resolution of between 15 and 40 years match the greenlandic isotope record in many details under the assumption that the main variations in temperature and thus in oxygen isotopes occurred about simultaneously in greenland and switzerland we have assigned a time scale to the lake sediments of gerzensee and leysin by wiggle matching their stable isotope records with those of greenland ice cores which are among the best dated climatic archives we estimate a precision of 20 to 100 years during the last glacial termination

compositional order disorder and stable isotope characteristics of al fe epidote state 2 14 drill hole salton sea geothermal system epidote ca2fe3si3o12 oh ca2al3si3o12 oh is a common hydrothermal mineral in metasediments and veins at depths 900 m in the state 2 14 drill hole of the salton sea geothermal system the mole fraction of ca2fe3si3o12 oh in epidotes xps from this drill hole ranges from 0 11 to 0 42 and complex compositional zoning of octahedral fe3 and al is typical within single grains with increasing depth there is an overall but irregular decrease in the fe3 content of epidotes in metasandstones in most samples vein epidotes are more fe3 rich and exhibit a wider compositional range than metasandstone epidotes from the same depth octahedral fe3 in the m 1 sites in four epidotes evaluated by 57fe mossbauer spectroscopy ranges from 7 5 1 7 to 11 4 1 5 of the total iron the most ordered epidote formed in veins at 2618 m in the biotite zone this epidote has an ordering parameter 1 2xfe3 m 1 of 0 85 0 03 which corresponds to a calculated state of equilibrium order disorder at 390 60 c in close agreement with the probable downhole temperature of 340 c two epidote samples from the chlorite calcite zone 1420 m 265 c 1867 m 300 c are more disordered corresponding to calculated states of equilibrium order disorder of 450 c these data suggest that the analyzed epidotes from the chlorite calcite zone are in a metastable state of substitutional order disorder the measured value of depidote from 1420 m is 96 which is 5 6 lighter than epidotes from 1867 m depidote 90 2227 m depidote 91 and 2618 m depidote 90 when compared to the reservoir fluid from the december 1985 flow test the derived fractionation of hydrogen isotopes between epidote and the geothermal brine is 19 at 1867 m and 340 c this value is in accord with published experimental hydrogen isotope fractionations between iron rich epidote and aqueous electrolyte solutions therefore considering the complexity of the salton sea brine the isotopic temperature is similar to the inferred downhole temperature

mineralogical and fluid inclusion features of rock alterations in the seigoshi gold silver mining district western part of the izu peninsula japan abstract propylitic and advanced argillic alterations occur in the seigoshi gold silver mining district in the western part of the izu peninsula japan the propylitic alteration has the following zonal arrangement from the deeper portion to the shallower portion an epidote prehnite k feldspar chlorite zone a wairakite laumontite zone and a stilbite heulandite montmorillonite zone lateral and vertical zoning is conspicuous in the advanced argillic alteration the inner zone is silica rich and this grades laterally and vertically through alunite to clay rich zones fluid inclusions from the epidote prehnite k feldspar chlorite zone are liquid dominated and filling temperatures of this zone are in the range of 225 285 c filling temperatures for the zeolite zone are variable being in the range of 240 380 c this wide range suggests that boiling of the fluids was responsible for the zeolite zone filling temperatures of the advanced argillic alteration range widely from 210 to 430 c this wide range and the coexistence of liquid and vapor dominated fluid inclusions in a given sample suggest that liquid vapor separation simultaneously occurred during the advanced argillic alteration process it is deduced that the ranges of gaseous fugacity are quite different for each type of alteration for instance f s 2 and f o 2 of the advanced argillic alteration are estimated to be higher than those of the propylitic alteration based on the alteration mineral assemblage chemical composition and mode of occurrence of alteration minerals fluid inclusions estimated ranges of gaseous fugacities and comparison of these features with those of active geothermal systems it is concluded that the propylitic alteration minerals were probably precipitated due to the loss of gases such as co 2 and that the formation of advanced argillic alteration was caused by subsurface mixing of volcanic gas and or condensed hot water with groundwater these coexisting propylitic and advanced argillic alterations are commonly found in the other au ag mining districts in japan

chemographic and thermodynamic analysis of the paragenesis of the major phases in the vicinity of the 6120 foot 1866 m flow zone california state well 2 14 the major phases found in the vicinity of the 1866m flow zone are k feldspar epidote pyrite hematite and chlorite these are found to exist in primarily four two phase assemblages the dominant being k feldspar pyrite epidote pyrite epidote hematite and chlorite pyrite complete reaction relations among these isobaric isothermal divariant phase assemblages oriented in log fo2 ph space are compatible with stable growth at 300 c sensitivity of reaction relations to total sulfur temperature pressure and thermodynamic values is investigated the aqueous fluid sampled at 1866 m is out of equilibrium with the more reducing phase assemblages lying stratigraphically above and below the flow zone as well as pyrite bearing assemblages in the flow zone and shows aspects of mixing with other hotter flow zones high concentrations of co2 may indicate contribution to the fluid of co2 from hotter portions of the system low total sulfur and high total iron are due to possible gas loss during down hole sampling and reaction of the fluid with well casing and lost circulation materials

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation

corundum cr muscovite rocks at o briens zimbabwe the conjunction of hydrothermal desilicification and lil element enrichment geochemical and isotopic evidence monomineralic domains of chlorite corundum and cr muscovite coexist over a kilometer scale within ultramafic schists of the harare greenstone belt 2 73 ga this exotic lithological association includes the conjunction of some of the most aluminous al2o3 88 wt and potassic k2o 10 wt rocks known the paragenetic sequence developed from chlorite corundum corundum diaspore cr muscovite variably overprinted both the corundum and chloritite domains terminal stages were marked by sporadic production of andalusite quartz and finally margarite

tracing the laacher see tephra in the varved sediment record of the trzechowskie palaeolake in central northern poland abstract tephrochronological studies of partly varved sediments of trzechowskie palaeolake in central northern poland led to the finding of the late allerod laacher see tephra lst from the eifel volcanic field for the first time in a very distal site ca 840 km ene from its volcanic source the detection of glass shards of the lst involved a comprehensive combination of techniques i e biostratigraphical constrains high resolution xrf core scanning and areal xrf mapping of impregnated sediment slabs as well as detailed visual inspection of sediments the major element chemistry of volcanic glass confirmed the laacher see tephra composition in trzechowskie palaeolake sediments suggesting a deposition from the middle laacher see tephra mlst c or upper laacher see tephra ulst dispersal fans the finding of the lst in this palaeolake enables direct synchronisation with other high resolution archives in north central europe i e lake meerfelder maar rehwiese palaeolake to investigate regional variations of environmental responses at the onset of the younger dryas along a west east transect through north central europe

influence of late glacial climate changes on sediment transport in the river werra thuringia germany abstract several sedimentary records of floodplain sediments in the werra valley and subcatchments have been analysed in order to investigate the influence of climate change on the sediment transport system in the sedimentary records of the subcatchments a marked change from minerogenic to organic sediments is visible about 14 6 ka b p according to palynological analyses this change occurs in a period with a remarkable rise in arboreal pollen percentages in addition a reverse change from organic to clastic sediments takes place shortly after 12 9 ka b p coincident with a decrease in arboreal pollen percentages during this period assuming that changes in vegetation cover are mainly caused by climate the variations in the sedimentary records are also attributed to these climatic oscillations in contrast to the subcatchments comparable changes in the sedimentary record are not detectable in the floodplain of the werra river this points to the conclusion that the influence of late glacial climate fluctuations on the sedimentary regime of a river with a relatively large and a more heterogeneous catchment seems less pronounced