chemistry of uranium thorium and radium isotopes in the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal abstract the most comprehensive data set on uranium thorium and radium isotopes in the ganga brahmaputra one of the major river systems of the world is reported here the dissolved 238u concentration in these river waters ranges between 0 44 and 8 32 1 and it exhibits a positive correlation with major cations na k mg ca the 238 u cations ratio in waters is very similar to that measured in the suspended sediments indicating congruent weathering of uranium and major cations the regional variations observed in the 234 u 238 u activity ratio are consistent with the lithology of the drainage basins the lowland tributaries chambal betwa ken and son draining through the igneous and metamorphic rocks of the deccan traps and the vindhyan bundelkhand plateau have 234 u 238 u ratio in the range 1 16 to 1 84 this range is significantly higher than the near equilibrium ratio 1 05 observed in the highland rivers which drain through sedimentary terrains the dissolved 226ra concentration ranges between 0 03 and 0 22 dpm 1 the striking feature of the radium isotopes data is the distinct difference in the 228ra and 226ra abundances between the highland and lowland rivers the lowland waters are enriched in 228ra while the highland waters contain more 226ra this difference mainly results from the differences in their weathering regimes the discharge weighted mean concentration of dissolved 238u in the ganga at patna and in the brahmaputra at goalpara are 1 81 and 0 63 1 respectively the ganga brahmaputra river system constitutes the major source of dissolved uranium to the bay of bengal these rivers transport annually about 1000 tons of uranium to their estuaries about 10 of the estimated global supply of dissolved uranium to the oceans via rivers the transport of uranium by these rivers far exceeds that of the amazon although their water discharge is only about 20 of that of the amazon the high intensity of weathering of uranium in the ganga brahmapura river system can also be deduced from the 232 th 238 u and 230 th 238 u activity ratios measured in the suspended sediments 230th is enriched by about 19 in the suspended sediments relative to its parent 238u the flux of excess 230th supplied to the bay of bengal via these river sediments is 980 1012 dpm a about six times more than its in situ production from seawater in the entire bay of bengal

origin of siderite veins in the western carpathians abstract siderite barite veins of the rud any ore field have precipitated from nacl cacl 2 h 2 o co 2 solutions with cacl 2 weight fractions between 0 05 and 0 38 total salinities between 17 and 35 wt and up to 1 8 mol co 2 homogeneous and heterogeneous trapping modes have been distinguished according to volumetric phase ratios of the fluid inclusions which have been trapped at 175 205 c in veiny siderite at 200 230 c in siderite and quartz from drusy cavities and at 90 180 c in the siderite postdating quartz sulfidic assemblage a sequential re equilibration technique has been developed to locate precisely vapour saturated halite liquidus of individual brine inclusions which normally homogenise by halite dissolution slopes of the vapour unsaturated halite liquidi constrained by isochores of coexisting two phase aqueous inclusions have been approximately three to five times steeper in natural polycomponent brines than those in the experimental nacl h 2 o system fluid pressures between 1 and 2 kbar have been determined using this method in drusy quartz associating with siderite crystals oxygen isotope variations 16 8 19 9 v smow in siderite result from a temperature increase from 175 to 230 c whereas nearly constant 13 c values 3 9 to 4 6 v pdb indicate absence of co 2 devolatilisation carbon isotope composition of the parental fluid changed from 9 5 to 8 8 v pdb while the oxygen isotope ratios remained essentially fixed at 7 7 0 3 v smov during formation of siderite the calculated 18 o fluid value is attributed to formation water enriched in 18 o during isotopic exchange with crustal rocks at low fluid rock ratios the 13 c fluid values probably correspond to a mixture of co 2 from dissolved matrix carbonates and that liberated by thermal decarboxylation of organic acids acetates which normally occur in formation waters leachate chemistry data have corroborated high concentrations of cacl 2 and mgcl 2 in the ore forming brines high br concentrations are similar to halite fractionated basinal brines ca 2 and k concentrations in excess of those in normal basinal brines reflect extensive cation exchange with surrounding low to medium grade metamorphites coincidental with calcite and k feldspar dissolution dolomitisation and albitisation of plagioclases high pressures of the siderite forming fluids 1 2 kbar must be linked with a deep circulation 4 8 km of the basinal brines derived primarily from marine water but significantly modified by interaction with low to medium grade paleozoic rocks at low fluid to rock ratios an anti clockwise crystallisation pt path inferred from fluid inclusion and stable isotope data is inconsistent with the siderite precipitation during extensional tectonic regime coincidental with permian triassic rifting suggested in previous models more likely the progressively increasing fluid pressures and temperatures could be attributed to compression and crustal thickening triggered by jurassic subduction in the meliatic hallstatt oceanic suture the superimposed quartz ankerite sulfidic ores have likely crystallised from brines expelled during compression associated with a continental collision during early to middle cretaceous times

late surge glacial conditions on bakaninbreen svalbard and implications for surge termination 1 bakaninbreen is a polythermal glacier in southern spitsbergen svalbard that last surged between 1985 and 1995 seismic reflection data were acquired during early quiescence in spring 1998 just upstream of the surge front the results were combined with complementary ground penetrating radar data to investigate the glacial structure and basal conditions we find no difference between the ice thickness values determined from the seismic and radar methods suggesting that any layer of basal ice cannot be greater than 5 m thick interpretation of the amplitude of the seismic reflections indicates the presence of permafrost close to the glacier base a thin layer of thawed deforming sediment separates the glacier from this underlying permafrost in an area just upstream of the surge front the permafrost becomes discontinuous and may even be absent the ice being underlain by 10 15 m of thawed sediments overlying deeper bedrock high pressure water is believed to have been required to maintain the propagation of the surge and this area of thawed sediment is interpreted as a route for that water to escape from the basal system when the surge front passed over this thawed bed the escaping water reduced the pressure in the subglacial hydraulic system initiating the termination of the surge surge termination was therefore primarily controlled by the presurge permafrost distribution beneath the glacier rather than any feature of the surge itself this termination mechanism is probably limited to surges in polythermal glaciers but the techniques used may have wider glaciological applications

contrasting chemistry and h o c isotope composition of greenschist facies hercynian and alpine metamorphic fluids western carpathians abstract microthermometry and stable isotope data enable us to distinguish between two contrasting sets of fluids involved in the hercynian and alpine metamorphic events in the western carpathians high temperature smoky quartz 450 500 c was probably formed during the syn kinematic phase of the hercynian metamorphism when chemical and isotopic equilibrium had been established between aqueous solutions and the surrounding rocks this is indicated by fixed na ca ratios and narrow ranges of d and 18o values in the inclusion fluids 59 5 and 7 to 7 5 smow respectively in contrast alpine quartz precipitating at temperatures between 300 and 400 c in extension related structures displayed a non equilibrium signature characterized by a much larger compositional and isotopic variability presence of co2 in quartz from granitoid hosted shear zones indicates externally derived fluids with 13c values between 11 9 to 7 7 pdb these values can be interpreted to reflect an admixture of a lighter co2 generated by decomposition of organic matter in underlying low to medium grade sediments the essentially identical isotopic composition of the inclusion co2 from the presumably hercynian as well as alpine metamorphic quartzes supports the concept of hercynian overthrusting of granitoids onto metamorphites in the crystalline basement of the western carpathians

cretaceous dykes discovered in the falkland islands implications for regional tectonics in the south atlantic new aeromagnetic data resolve the dykes of the falkland islands into three swarms a hitherto unrecognized suite of north south dykes is established as early cretaceous by an ar ar date of about 121 ma swarms of ne sw and east west dykes are both early jurassic the former gives an ar ar age of about 178 ma whereas the latter has been previously dated to about 190 ma the intrusion of the cretaceous dykes marks the onset of oceanic crust generation in the south atlantic and so restricts to mid jurassic the microplate rotation envisaged in most models for the falklands break out from gondwana

occurrence and geochemistry of radium in water from principal drinking water aquifer systems of the united states abstract a total of 1270 raw water samples before treatment were collected from 15 principal and other major aquifer systems pas used for drinking water in 45 states in all major physiographic provinces of the usa and analyzed for concentrations of the ra isotopes 224 ra 226 ra and 228 ra establishing the framework for evaluating ra occurrence the us environmental protection agency maximum contaminant level mcl of 0 185 bq l 5 pci l for combined ra 226 ra plus 228 ra for drinking water was exceeded in 4 02 39 of 971 of samples for which both 226 ra and 228 ra were determined or in 3 15 40 of 1266 of the samples in which at least one isotope concentration 226 ra or 228 ra was determined the maximum concentration of combined ra was 0 755 bq l 20 4 pci l in water from the north atlantic coastal plain quartzose sand aquifer system all the exceedences of the mcl for combined ra occurred in water samples from the following 7 pas in order of decreasing relative frequency of occurrence the midcontinent and ozark plateau cambro ordovician dolomites and sandstones the north atlantic coastal plain the floridan the crystalline rocks granitic metamorphic of new england the mesozoic basins of the appalachian piedmont the gulf coastal plain and the glacial sands and gravels highest concentrations in new england the concentration of ra was consistently controlled by geochemical properties of the aquifer systems with the highest concentrations most likely to be present where as a consequence of the geochemical environment adsorption of the ra was slightly decreased the result is a slight relative increase in ra mobility especially notable in aquifers with poor sorptive capacity fe oxide poor quartzose sands and carbonates even if ra is not abundant in the aquifer solids the most common occurrence of elevated ra throughout the usa occurred in anoxic water low dissolved o 2 with high concentrations of fe or mn and in places high concentrations of the competing ions ca mg ba and sr and occasionally of dissolved solids k so 4 and hco 3 the other water type to frequently contain elevated concentrations of the ra radioisotopes was acidic low ph and had in places high concentrations of no 3 and other acid anions and on occasion of the competing divalent cations mn and al one or the other of these broad water types was commonly present in each of the pas in which elevated concentrations of combined ra occurred concentrations of 226 ra or 228 ra or combined ra correlated significantly with those of the above listed water quality constituents on the basis of the non parametric spearman correlation technique and loaded on principal components describing the above water types from the entire data set and for samples from the pas with the highest combined ra concentrations concentrations of 224 ra and 226 ra were significantly correlated to those of 228 ra spearman s rank correlation coefficient 0 236 and 0 326 respectively activity ratios of 224 ra 228 ra in the water samples were mostly near 1 when concentrations of both isotopes were greater than or equal to 0 037 bq l 1 pci l the level above which analytical results were most reliable co occurrence among these highest concentrations of the ra radionuclides was most likely in those pas where chemical conditions are most conducive to ra mobility e g acidic north atlantic coastal plain the concentrations of 224 ra were occasionally greater than 0 037 bq l and the ratios of 224 ra 228 ra were generally highest in the pas composed of alluvial sands and cretaceous tertiary sandstones from the western usa likely because concentrations of 224 ra are enhanced in solution relative to those of 228 ra by alpha recoil from the aquifer matrix rapid adsorption of the two ra isotopes controlled by the alkaline and oxic aquifer geochemistry combined with preferential faster recoil of 224 ra generates a 224 ra 228 ra ratio much greater than 1 the 228 ra 226 ra activity ratio was locally variable and was generally lower than 1 226 ra rich in samples from pas with carbonate bedrock but was typically greater than 1 228 ra rich in pas composed of unconsolidated sand

new improved equations for and sio2 geothermometers by outlier detection and rejection abstract we present new improved equations for three still widely used na k na li and sio 2 geothermometers obtained by statistical treatment of the data and application of outlier detection and rejection as well as theory of error propagation and compare them with those by fournier and others new equations are also developed for estimating errors associated with the use of these new geothermometric equations and comparing them with the performance of the original equations the errors in the use of the new na k equation for temperatures ranging from 80 to 350 c vary from about 19 to 34 which is lower than the corresponding errors 24 43 for the original fournier equation similarly for temperatures ranging from about 50 to 320 c our new equation for na li geothermometer for cl 2 2 geothermometer we have proposed a linear equation for the temperature range of 210 to 310 c sio 2 295 ppm which shows considerably smaller total propagated errors 2 3 than for the original equation 5 29

226ra contents and 228ra226ra activity ratios of the fenland rivers and the wash eastern england spatial and seasonal trends measurements of 226ra and 228ra in the fenland rivers and the wash show that physical and hydrological factors play an important role in controlling the transport and fate of radium isotopes in the surficial environment higher 226ra contents and lower 228ra226ra activity ratios are found in waters from catchments with a greater proportion of carbonate rich source materuals this relationship is more obvious during periods of high runoff and river discharge when enhanced surficial weathering and regolith saturation takes place in the nearshore zone 226ra content is relatively uniform whilst 228ra226ra activity ratio is controlled by ionic concentrations cl so4 and co3 and the acquisition of marine characteristics the observed 228ra226ra activity ratio trend can be attributed to a combination of conservative mixing and radium desorption from suspended sediments whilst more uniform 226ra contents may reflec bottom sediment diffusion of excess 226ra over a greater area the relative importance of these two processes is controlled by differential input from the freshwater and saline end members of the estuary

hibonite fe fe mg al12o19 a new alteration mineral from the allende meteorite hibonite fe fe mg al 12 o 19 is the fe 2 dominant analog of hibonite caal 12 o 19 discovered in a highly altered ca al rich refractory inclusion from the allende meteorite it occurs as scattered micrometer sized single crystals within an aggregate of hercynite fe mg al 2 o 4 adjacent to nepheline ilmenite ferroan spinel perovskite and hibonite the mean chemical composition determined by electron microprobe analysis of hibonite fe is al 2 o 3 90 05 wt feo 3 60 sio 2 2 09 mgo 1 61 na 2 o 0 55 cao 0 28 tio 2 0 04 v 2 o 3 0 02 sum 98 25 corresponding to an empirical formula of fe 2 0 34 mg 0 27 na 0 12 al 0 11 ca 0 03 0 87 al 11 77 si 0 23 12 00 o 19 hibonite fe is hexagonal p6 3 mmc a 5 613 a c 22 285 a v 608 0 a 3 and z 2 its electron backscatter diffraction pattern is a good match to that of the hibonite structure hibonite fe is apparently a secondary alteration product formed by iron alkali halogen metasomatism whereas hibonite is a primary refractory phase

carbon oxygen isotopic covariation in hydrothermal calcite during degassing of co 2 the effect of the outgassing of co2 from a hydrothermal fluid on the c and o isotopic compositions of calcite which is precipitated from this fluid is quantitatively modelled in terms of batch and rayleigh distillation equations both co2 degassing and calcite precipitation are considered to be the removal mechanisms for dissolved carbon species from the fluid combined degassing precipitation models are then developed by taking h2co3 and hco 3 respectively as the dominant dissolved carbon species a positive correlation array between 13c and 13o values of calcite can be yielded by the precipitation of calcite from a h2co 3 dominant fluid accompanied by a progressive decrease in temperature during co2 degassing whereas calcite precipitated from a hco 3 dominant fluid under the same conditions tends to display much smaller variation in 13c values than in 18o values the combined processes of co2 degassing and calcite precipitation result in lowering the 13c value of calcites with respect to those precipitated in a closed system simply due to temperature effect carbon and oxygen isotopic data for calcite from the kushikino gold mining area in japan illustrate the application of quantitative modelling and degassing of co2 is suggested as a more likely cause for the precipitation of the calcite and quartz in this mining area

radium isotopes in coastal waters on the amazon shelf abstract radium isotope distributions on the continental shelf adjacent to the amazon river are a complex function of salinity the river and seawater endmembers for each radium isotope are low data from intermediate salinities plot as a highly scattered region above the conservative mixing line connecting the river and ocean endmembers spatial and temporal variability in sediment mixing and water residence times cause the scatter in the radium isotope data we have used the distributions of 226 ra 228 ra and 224 ra collected during four cruises representing different conditions on the shelf to construct inventories of radium due to nonconservative additions from sediments using estimates of water residence times we calculate fluxes of these radium isotopes from the amazon system the amount of fresh river sediment entering the system each year is adequate to support the nonconservative flux of 226 ra from the shelf sediments however the ultimate release of 226 ra from the sediments requires weeks to months to support the nonconservative flux of 228 ra from this system sediments of the 1 2 m thick surface mixed layer must be resuspended every two years the resulting flux supports 15 of the 228 ra entering the surface atlantic ocean release of 224 ra from suspended sediments primarily fluid mud is more than adequate to support the inventory of 224 ra on the amazon shelf comparing the amasseds low discharge cruise november 1991 to a low discharge sampling in december 1982 revealed no significant changes in the 226 ra and 228 ra distributions

synthetic fluid inclusions vi quantitative evaluation of the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure has been evaluated using pure h2o synthetic inclusions formed by healing fractures in natural quartz three different modes of non elastic deformation referred to as stretching leakage or partial decrepitation and total decrepitation have been observed the internal pressure required to initiate non elastic deformation is inversely related to inclusion size according to the equation internal pressure kbar 4 26 d 0 423 where d is the inclusion diameter in microns regularly shaped inclusions require a higher internal pressure to initiate non elastic deformation than do irregularly shaped inclusions of similar size heating inclusions through the quartz inversion results in mechanical instability in the quartz crystal and leads to mass decrepitation of inclusions owing to structural mismatches generated by pressure gradients in the quartz around each inclusion long term heating experiments 2 years suggest that the internal pressure required to initiate non elastic deformation does not decrease significantly with time and indicates that short lived thermal fluctuations in natural systems should not alter the inclusion density and homogenization temperature inclusions that do exhibit decreased density higher homogenization temperature are however always accompanied by a change in shape from irregular to that of a negative crystal observations of this study are consistent with elasticity theory related to fracture generation and propagation around inclusions in minerals these results indicate that an inclusion will not be influenced by a neighbouring inclusion or other defect in the host phase as long as the distance between the two is 2 4 diameters of the larger of the two inclusions

distribution and flux of 226ra and 228ra in the amazon river estuary measurements of sup 226 ra and sup 228 ra in the amazon river estuary show that desorption from riverborne suspended particulate matter in the estuary increases the riverine flux of both isotopes to the ocean by a factor of approximately 5 over the flux attributable to radium dissolved in the river water alone the total amazon flux supplies approximately 0 20 of the sup 226 ra and approximately 2 6 of the sup 228 ra standing crops in the near surface atlantic 0 200 m diffusive flux from estuarine and shelf sediments and desorption from resuspended sediments in the region of the estuary approximately double the estuarine sup 226 ra concentration and quadruple the estuarine sup 228 ra concentration above that caused by the dissolved and desorbed river components alone

radium isotopes and their environmental implications in the changjiang river system abstract radium ra isotopes are widely used to trace water motion and nutrient transport in coastal oceans to enhance our understanding of ra behavior from river to ocean this study examines 226 ra and 228 ra activity concentrations in the water column suspended particulate matter and river bed surface sediments along the middle and lower changjiang river cjr basin based on two cruises in 2006 and 2008 the results show that the ra activity concentrations in the cjr basin are comparable with other rivers in the world higher ra activity concentrations and lower 228 ra 226 ra activity ratios are detected in the tributaries i e in the dongting and poyang lakes than in the mainstream the comparison of pre three gorges dam tgd data taken in 1984 and post tgd data this work illuminates the effect that a major dam has on radium transport within the river and into the estuary we estimate a riverine 226 ra flux of 1 04 0 08 tbq yr 1 extended ra datasets collected in the estuary and the east china sea show that the dissolved and sedimentary ra activity concentrations are higher in the estuary but lower in the sea whereas the particulate ra activity concentrations are larger in the river this finding indicates significant ra desorption from particulate to dissolved phase in the brackish estuary where riverborne materials are filtered and trapped overall these results help to elucidate ra transport from river to ocean and assist further application of ra isotopes in land ocean interaction studies such as submarine groundwater discharge mixing and diffusion processes and determination of water mass and or current structures in the estuarine and coastal zones

radium and barium in the amazon river system data for sup 226 ra and sup 228 ra in the amazon river system show that the activity of each radium isotope is strongly correlated with barium concentrations two trends are apparent one for rivers which drain shield areas and another for all other rivers these data suggest that there has been extensive fractionation of u th and ba during weathering in the amazon basin the sup 226 ra data fit a flux model for the major ions indicating that sup 226 ra behaves conservatively along the main channel of the amazon river

radium isotopes in cayuga lake new york indicators of inflow and mixing processes naturally occurring radium isotopes 223 ra 224 ra 226 ra and 228 ra were measured in lake and tributary water of cayuga lake new york during the course of a vernal inflow event in the spring of 2001 a large influx of groundwater probably from a carbonate aquifer entered the lake at its extreme southern end early in the vernal inflow event and spread northward covering an extensive part of the southern end of the lake the low 228 ra 226 ra activity ratio of this water mass compared with bulk lake water allowed its identification through time estimates of mixing with bulk lake water were calculated from changes in the 226

high density nitrogen inclusions in barite from a giant siderite vein implications for alpine evolution of the variscan basement of western carpathians slovakia contrasting compositions and densities of fluid inclusions were revealed in siderite barite intergrowths of the dro diak polymetallic vein hosted in variscan basement of the gemeric unit central european carpathians primary two phase aqueous inclusions in siderite homogenized between 101 and 165 c total salinity ranged between 18 and 27 wt and cacl2 nacl cacl2 weight ratios were fixed at 0 1 0 3 by contrast mono and two phase aqueous inclusions in barite exhibited total salinities between 2 and 22 wt and the cacl2 nacl ratios ranged from nacl to cacl2 dominated compositions the aqueous inclusions in barite were closely associated with very high density 0 55 0 745 g cm 3 nitrogen inclusions in some cases containing up to 16 mol co2 crystallization p t conditions of siderite 175 210 c 1 2 1 7 kbar constrained by the vertical oxygen isotope gradient along the studied vein isochores of fluid inclusions and the k na exchange thermometer corresponded to minimal palaeodepths between 4 3 and 6 3 km assuming lithostatic load and average crust density of 2 75 g cm 3 maximum fluid pressure during barite crystallization attained 3 6 4 4 kbar at 200 300 c and the most dense nitrogen inclusions maintained without decrepitation the residual internal pressure of 2 2 kbar at 25 c contrasting fluid compositions increasing depths of burial 4 14 km and decreasing thermal gradients 40 15 c km 1 during initial mineralization stages of the dro diak vein reflect alpine orogenic processes rather than an incipient permian rifting suggested in previous metallogenetic models siderite crystallized at rising p t in a closed rock buffered hydrothermal system developed in the variscan basement during the north vergent cretaceous thrusting and thickening of the gemeric crustal wedge variable salinities of the barite hosted inclusions reflect a fluid mixing in open hydrothermal system and re equilibration textures lengths of decrepitation cracks proportional to fluid inclusion sizes correspond to retrograde crystallization trajectory coincidental with transpression or unroofing maximum recorded fluid pressures indicate 12 km thick pile of imbricated nappe units accumulated over the gemeric basement during the cretaceous collision

rapid mineral surface weathering beneath the greenland ice sheet shown by radium and uranium isotopes abstract glaciated watersheds are regions of intense physical and chemical weathering in order to gain new insight on subglacial weathering processes we measured uranium and radium isotopes from a proglacial river draining the greenland ice sheet gris time series samples were collected from the spring to mid summer a time period during which subglacial drainage pathways are thought to transition from slow inefficient distributed to fast efficient channelized systems the 228ra 226ra activity ratio of the dissolved load varied from 5 2 0 9 16 9 3 6 which was significantly higher than the 228ra 226ra ratio of a suspended sediment load sample of 2 1 0 07 and crustal values of 1 the high 228ra 226ra in the dissolved load relative to the source rock material is indicative of mineral surface weathering induced by rapid and continuous flushing of the subglacial drainage network during the course of the melt season and those prior the 234u 238u ratio 234u varied between 33 and 106 with a discharge weighted mean of 67 the seasonal evolution of 234u did not correlate to geochemical indicators of subglacial meltwater storage time an experiment designed to measure changes in 234u with increasing meltwater storage times found that 234u in the dissolved phase decreased rapidly with increasing storage time similarly samples collected along a transect moving downstream from the ice sheet terminus had decreasing 234u values from 63 to 15 further indicating that with increased weathering the 234u of meltwater decreases coupled with the relatively low 234u and high 228ra 226ra u appears to be impacted by rapid chemical weathering of subglacial and suspended sediments the leverett river discharge weighted u concentration was 0 13 nm if this system is considered representative of the broader gris then the total dissolved u flux from the gris would be on the order of 6 4 104 mol y using a similar set of assumptions the dissolved 228ra and 226ra flux from the gris was 1 1 1014 dpm y and 5 5 1013 dpm y respectively these estimates suggest that the 226ra flux to the ocean from the gris is globally significant and that the 228ra flux in particular is larger than most river inputs

cretaceous evolution of a metamorphic core complex the veporic unit western carpathians slovakia p t conditions and in situ40ar 39ar uv laser probe dating of metapelites alpine metamorphism related to the development of a metamorphic core complex during cretaceous orogenic events has been recognized in the veporic unit western carpathians slovakia three metamorphic zones have been distinguished in the metapelites 1 chloritoid chlorite garnet 2 garnet staurolite chlorite 3 staurolite biotite kyanite the isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system k2o feo mgo al2o3 sio2 h2o kfmash the isograds are roughly parallel to the north east dipping foliation related to extensional updoming along low angle normal faults thermobarometric data document increasing p t conditions from c 500 c and 7 8 kbar to c 620 c and 9 10 kbar reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies 40ar 39ar data obtained by high spatial resolution in situ ultraviolet uv laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the late cretaceous mean dates are between 77 and 72 ma however individual white mica grains record a range of apparent 40ar 39ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous the reconstructed metamorphic p t t path is clockwise reflecting post burial decompression and cooling during a single alpine orogenic cycle the presented data suggest that the veporic unit evolved as a metamorphic core complex during the cretaceous growth of the western carpathian orogenic wedge metamorphism was related to collisional crustal shortening and stacking following closure of the meliata ocean exhumation was accomplished by synorogenic orogen parallel extension and unroofing in an overall compressive regime

tracing the amazon component of surface atlantic water using 228ra salinity and silica high 228ra 226ra activity ratios characteristic of waters in the amazon estuary provide a sensitive indicator of the presence of these waters in the atlantic ocean a conservative mixing model utilizing the 228ra 226ra activity ratio ar tied to absolute measurements in the estuary allows us to estimate that 20 34 of the surface water east of the antilles during june 5 9 from the same area during december and 15 20 of the eastern caribbean surface water during december are derived from the amazon estuary differences in 228ra input occur in response to variable stratification of water near the river mouth during high discharge intense vertical mixing enriches the water in the estuary in 22sra a large fraction of this water moves to the north and east of the antilles where its relatively high 22sra 226ra ar distinguishes it over 1500 km from its source during low discharge northern hemisphere fall a significant fraction of river water passes northwest of the zone of intense mixing into a vertically stratified region where 228ra gain is lower this water is transported by the guiana current along the coast of south america and into the caribbean

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

behavior of 226ra in the mississippi river mixing zone the behavior of 226ra in the mississippi river mixing zone is strongly nonconservative and includes desorption similar to that reported for the hudson pee dee and amazon rivers however dissolved and desorbed 226ra concentrations in the mississippi are 2 to 5 times greater than in the other rivers at the same salinity radium concentrations vary inversely with the water discharge rate the 226ra desorption maximum occurs at a salinity of 5 0 much lower than the 18 to 28 salinity values for the maxima of the other three rivers high concentrations of dissolved 226ra up to 82 dpm per 100 l and the low salinity values for the desorption maximum in the mississippi river result from three major factors suspended sediments include a large fraction of montmorillonite which gives the sediment a high cation exchange capacity 0 54 meq g the average suspended sediment load is large about 510 mg l and contains 1 9 dpm g desorbable 226ra the dissolved 226ra river water end member 9 6 dpm per 100 l is higher than in surface seawater the annual contribution of 226ra to the ocean from the mississippi river is 3 7 1014 dpm yr based on data from three cruises evidence of flux of 226ra from estuarine and shelf sediments is common in vertical profile sampling of the deltaic waters but is not reflected in calculations made with an apparent river water ra value extrapolated to zero salinity

radium isotopes in the lower mississippi river radium isotopes have been measured in mississippi river water at several locations between st francisville and venice louisiana measured activities averaged 11 1 dpm 100 l disintegrations per minute per 100 l for dissolved 226ra with a 228ra 226ra activity ratio of 1 04 and a 224ra 228ra activity ratio of 1 06 for the section of river above a phosphogypsum waste discharge input down river from this site the dissolved 226ra activity averaged 22 4 dpm 100 l with a 228ra 226ra activity ratio of 0 55 and a 224ra 228ra activity ratio of 0 87 chemical and isotopic reequilibration of the radium in the waste with that in the river water and suspended sediments occurs very rapidly fluxes of 226ra are calculated to be 2 44 1014 dpm yr disintegrations per minute per year for the main stem of the mississippi during phosphogypsum disposal compared to 0 98 1014 dpm yr when no phosphogypsum disposal is occurring 28ra flux is calculated to be 1 06 1014 dpm yr during disposal and 1 01 1014 dpm yr in the absence of disposal the radium flux is estimated to be 45 in the dissolved state and 55 in the adsorbed state

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

carbon and oxygen isotopic covariations in hydrothermal calcites isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes 1 mixing between two different fluids which leads to the precipitation of calcite 2 mixing between fluid and rock a calcite precipitation due to fluid rock interaction b secondary alteration of primary calcite by interaction with a subsequent fluid the models are derived from mass balance equations a distinction among the three mixing processes can be made on a 13c vs 18o diagram which places important constraints on the genesis of hydrothermal mineralization the variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock temperature and dissolved carbon species owing to significant temperature dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid the mixing processes may be distinguished by telltale patterns of isotopic data in 13c vs 18o space in particular caution must be exercised in postulating the fluid mixing as the cause for mineral deposition this is demonstrated for hydrothermal pb zn deposits in the western harz mountains germany a positive correlation between 13c and 18o values is observed for calcites from the bad grund deposit in the upper harz two sample profiles through calcite veins show similar correlations with the lowest values at the center of the veins and the highest values at the vein margins because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike it is assumed that a fluid rock interaction is responsible for the observed correlation and thus for the precipitation of calcite a deep seated fluid is inferred with a 13c value of 7 and a 18o value of 10 as well as h2co3 as the dominant dissolved carbon species precipitation temperatures of the calcites are estimated to be about 280 170 c quite different isotopic distributions are observed for calcites from the st andreasberg deposit in the middle harz an alteration model is suggested based mainly on the isotopic distribution through a calcite vein in addition to a primary fluid which has the same isotopic composition as that in the bad grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides an evolved hco 3 dominant subsurface fluid with 13c about 20 15 and 18o 0 is deduced to alter the primary calcite at low temperatures of 70 40 c

melting behavior of fluid inclusions in laboratory grown halite crystals in the systems naclh2o naclkclh2o naclmgcl2h2o and naclcacl2h2o abstract the chemical composition of aqueous fluid inclusions in crystals of halite can be accurately determined from observed melting behaviors of ice hydrohalite and sylvite some fluid inclusion melting behaviors observed in laboratory grown halite crystals systems nacl h 2 o nacl kcl h 2 o nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o differ from predicted stable equilibrium relations in the nacl h 2 o and nacl kcl h 2 o systems observed first melt temperatures are up to 15 c below the equilibrium eutectic temperatures of 21 2 and 22 9 c respectively the final melting temperature of ice in the presence of hydrohalite and the final melting temperature of hydrohalite are reproducible and match predicted melting temperatures the limit of detection of sylvite daughter crystals in the nacl kcl h 2 o system is approximately 5 wt 1 molal kcl final melting temperatures of sylvite match published equilibrium data to within 0 3 c in the nacl kcl h 2 o system at halite saturation m kcl can be determined from the final sylvite dissolution temperature or from the final melting temperature of hydrohalite fluid inclusions in the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems that form stable salt hydrates mgcl 2 12h 2 o and cacl 2 6h 2 o during freezing first melt within 3 c of predicted eutectic temperatures 37 and 52 c however fluid inclusions with mgcl 2 or cacl 2 may also start melting at temperatures as low as 80 c such low first melt temperatures indicate the presence of metastable salt hydrates presumably mgcl 2 8h 2 o mgcl 2 6h 2 o or cacl 2 4h 2 o the formation of metastable phases during freezing of fluid inclusions can lead to misinterpretation of the chemical composition of fluid inclusions in natural samples this is especially true for fluid inclusions with first melt temperatures below 37 c which may be erroneously interpreted as being rich in cacl 2 the final melting of ice in the presence of hydrohalite may vary by more than 15 c in fluid inclusions of different size but identical bulk composition and occurs at lower temperatures than predicted in fluid inclusions from the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems however the final melting temperature of ice in inclusions which fail to nucleate hydrohalite and the final melting temperature of hydrohalite are reproducible to within 0 1 c and can be used to determine mgcl 2 and cacl 2 molalities

dating thrust events using 87 sr 86 sr an example from the northern apennines italy isotopic and petrographic analyses of the major thrust zone calcare cavernoso in the apuane region of the northern apennines are used to date the timing of motion on that thrust zone and to document the type and the amount of fluid focused there the thrust zone consists of a porous cataclasite composed of polylithologic clasts and finely crystalline dolomite included within a recrystallized calcite matrix that shows no affect of subsequent brittle or ductile deformation 87 sr 86 sr isotopic compositions of clasts and matrix from around the entire apuane region 1000 km 2 are very uniform with values that average 0 70811 the strontium data suggest recrystallization of the entire thrust zone by huge volumes of focused fluid flow that caused complete and uniform resetting of the original triassic sr isotopic signature by oligocene sea water during oligocene thrusting preservation of fragile vein networks that also yield the oligocene sea water sr ratios suggests that significant post th

cathodoluminescence fluid inclusion and stable c o isotope study of tectonic breccias from thrusting plane of a thin skinned calcareous nappe basal hydraulic breccias of alpine thin skinned mura nappe were investigated by means of cathodoluminescence petrography stable isotope geochemistry and fluid inclusions analysis our study reveals an unusual dynamic fluid regime along basal thrust plane during final episode of the nappe emplacement over its metamorphic substratum basal thrusting fluids enriched in 18o silica alumina alkalies and phosphates were generated in the underlying metamorphosed basement at epizonal conditions corresponding to the temperatures of 400 450 c the fluids fluxed the tectonized nappe base leached evaporite bearing formations in hangingwall whereby becoming oversaturated with sulphates and chlorides the fluids further modified their composition by dedolomitization and isotopic exchange with the host carbonatic cataclasites newly formed mineral assemblage of quartz phlogopite albite potassium feldspar apatite dravite tourmaline and anhydrite precipitated from these fluids on cooling down to 180 200 c finally the cataclastic mush was cemented by calcite at ambient anchizonal conditions recurrent fluid injections as described above probably enhanced the final motion of the mura nappe

adiabatic decompression of aqueous solutions applications to hydrothermal fluid migration in the crust adiabatic decompression may result in the heating of geologic aqueous fluids on the order of tens of degrees celsius adiabatic expansion may be either reversible in which case geologically important fluids cool on decompression or irreversible if the irreversible adiabatic expansion involves a significant pressure loss due to internal work generation and kinetic and gravitational effects can be ignored and the joule thompson coefficient is large and negative fluids heat up upon decompression the joule thompson coefficient becomes increasingly negative i e the heating effect dominates at high pressures low temperatures high m nacl and high x co 2 we predict that high concentrations of divalent and trivalent ions in solution will also increase the magnitude of the heating effect

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism