ca eskola component in clinopyroxene experimental studies at high pressures and high temperatures in multianvil apparatus abstract in order to investigate the pressure implications of silica exsolution from clinopyroxene in ultrahigh pressure metamorphic rocks we have measured systematically the values of the calcium eskola ca esk component of clinopyroxenes over a considerable range of pressure and temperature a series of anhydrous experiments using powdered glass of composition wt sio2 59 29 al2o3 23 12 mgo 5 44 cao 10 37 and na2o 1 78 were conducted in a walker style multianvil apparatus in the p t range of 6 12 gpa and 900 1200 c we find that all clinopyroxenes synthesized in equilibrium with garnet kyanite and sio2 coesite or stishovite are cation deficient the highest value of the ca esk component 32 38 mol is reached at 6 gpa followed by slight decrease beginning at 8 gpa as the pyroxene progressively dissolves into garnet and more rapid decrease at 10 12 gpa when stishovite becomes stable in the assemblage comparison of our data with those available in the literature which all together covers a wider range of p and t shows that the ca esk activity depends strongly on bulk chemistry especially the silica content in general integrated analyses of published experiments on similar compositions show that the ca esk component rises rapidly to its highest values from 1 to 4 6 gpa then slightly decreases to 9 gpa followed by remarkable decrease to 15 gpa culminating in replacement of pyroxene by garnet in equilibrium with stishovite we conclude that the sio2 exsolution lamellae observed in clinopyroxenes from many ultrahigh pressure terranes can be explained by destabilization of the ca esk component during decompression however because silica solubility in clinopyroxene reaches its maximum at 6 8 gpa the practical upper pressure limit that can be inferred from this system is 200 250 km

crystallization environment of kazakhstan microdiamond evidence from nanometric inclusions and mineral associations nanometric solid inclusions in diamond incorporated in garnet and zircon from felsic gneiss of the kokchetav massif kazakhstan have been examined utilizing electron microscopy and focused ion beam techniques host garnet and zircon contain numerous pockets of multiple inclusions which consist of 1 3 diamond crystals intergrown with quartz phengite phlogopite albite k feldspar rutile apatite titanite biotite chlorite and graphite in various combinations recalculation of the average chemical composition of the entrapped fluid represented by multiple inclusion pockets indicates that such fluid contained a low wt of sio2 suggesting a relatively low temperature fluid rather than a melt transmission electron microscopy revealed that the diamond contains abundant nanocrystalline inclusions of oxides rare carbonates and silicates within the 15 diamond crystals studied abundant inclusions were found of sio2 tio2 f e xoy c r 2o3 zrsio4 and single grains of thxoy baso4 mgco3 fecr2o4 and a stoichiometric fe rich pyroxene the diversity of trace elements within inclusions of essentially the same stoichiometry suggests that the kokchetav diamond crystallized from a fluid containing variable amounts of si fe ti cr zr ba mg and th and other minor components such as k na p s pb zn nb al ca cl most of the components in crystals included in diamond appear to have their origin in the subducted metasediments but some of them probably originate from the mantle it is concluded that kokchetav diamond most likely crystallized from a coh rich multicomponent supercritical fluid at a relatively low temperature hence the apparently low content of rock forming elements and that the diversity of major and minor components suggests interactions between subducted metasediments and mantle components

fluid rock interactions during uhp metamorphism a review of the dabie sulu orogen east central china comprehensive review on the characteristics of petrology oxygen isotope fluid inclusion and nominally anhydrous minerals nams for many dabie sulu ultrahigh pressure uhp metamorphic rocks including drill hole core samples reveals that fluid has played important and multiple roles during complicated fluid rock interactions attending the subduction and exhumation of supracrustal rocks we have identified several distinct stages of fluid rock interactions as follows 1 the neoproterozoic supercrustal protoliths of uhp rocks experienced variable degrees of hydration through interactions with cold meteoric water with extremely low oxygen isotope compositions during neoproterozoic snow ball earth time 2 a series of dehydration reactions took place during triassic subduction of the yangtze plate beneath the sino korean plate the released fluid entered mainly into volatile bearing high pressure hp and uhp minerals such as phengite zoisite epidote talc lawsonite and magnesite as well as into uhp nams such as garnet omphacite and rutile 3 silicate rich supercritical fluid hydrous melt existed during the uhp metamorphism at mantle depths 100 km which mobilized many normally fluid immobile elements and caused unusual element fractionation 4 the fluid exsolved from the nams during the early exhumation of the dabie sulu terrane was the main source for hp hydrate retrogression and generation of hp veins 5 local amphibolite facies retrogression at crustal depths took place by infiltration of aqueous fluid of various salinities possibly derived from an external source 6 the greenschist facies overprinting and low pressure lp quartz veins were generated by fluid flow along ductile shear zones and brittle faults during late stage uplift of the uhp terrane

alpe arami a peridotite massif from depths of more than 300 kilometers the abundance of fetio 3 and chromite precipitates in olivine of the alpe arami peridotite massif switzerland requires a much higher solubility for highly charged cations than is found in mantle xenoliths from depths of 250 kilometers three previously unknown crystal structures of fetio 3 were identified that indicate that the originally exsolved phase was the high pressure perovskite polymorph of ilmenite implying a minimum depth of origin of 300 kilometers these observations coupled with the unique lattice preferred orientation of olivine further suggest that the original composition of olivine may reflect that of a precursor phase perhaps wadsleyite that is stable only at depths greater than 400 kilometers

determining the origin of ultrahigh pressure lherzolites the occurrence of coesite and diamond in regional ultrahigh pressure metamorphic rocks requires that rocks formed at pressures of 3 to 4 gpa 100 to 120 km below the earth s surface have been transported back to the surface 1 1 l dobrzhinetskaya et al suggest that garnet lherzolite from

osmotic model to explain anomalous hydraulic heads laboratory experiments have shown that compacted clays act as osmotic membranes when they separate aqueous solutions of unequal ionic concentration theoretically osmotically induced differential hydraulic pressure in groundwater systems can be relatively high the magnitude depends primarily upon concentration differences across the membrane type of ions type of clay and pore size in experiments thin compacted clay membranes commonly exhibit varying degrees of osmotic efficiency due to ion leak age through the clay in natural systems the membrane and the solution containers are not as distinct and well defined as they are in the laboratory moreover the membrane is commonly thick inhomogeneous and composite in a buried triassic basin at the savannah river plant near aiken south carolina it is suspected that osmosis causes the saline water in the basin center to be slightly geopressurized in relation to freshwater in the overlying coastal plain aquifer two wells have heads of 7 88 and 12 98 bars 114 3 and 188 3 psi above the head in the coastal plain aquifer the head in each of these wells approximates the osmotic equilibrium head calculated from solution concentration of water produced by each well 12 000 and 18 500 mg l respectively other wells penetrating the top and edge of the triassic basin probably penetrate a zone where ion leakage gives rise to less saline water thus these wells are not geopressurized

ultrahigh pressure minerals and metamorphic terranes the view from china abstract ultrahigh pressure uhp metamorphism refers to mineralogical modifications of continental and oceanic crustal protoliths associated mafic ultramafic rocks initially formed or emplaced in shallow levels of the lithosphere but which subsequently have experienced p t conditions within or above the coesite stability field 2 7 gpa 700 c typical products include eclogite garnet peridotite and uhp varieties of metapelite quartzite marble paragneiss and orthogneiss uhp metamorphic assemblages require relatively cold lithospheric subduction to mantle depths some recrystallization even occurs under forbidden p t conditions characterized by a geotherm of the current explosion of research on continental uhp terranes reflects their significance for mantle dynamics and the tectonics of continental subduction collision exhumation mantle slab interactions and geochemical recycling a further characterization of uhp phases and positive identification of uhp minerals requires new experimental studies coupled with state of the art analyses for example the very rare occurrence of microdiamond inclusions in zircons from dabie sulu uhp rocks may reflect high f o 2 attending recrystallization inasmuch as epidote is rather common rutile needles within garnets from sulu uhp eclogitic rocks may not be the result of exsolution so in such cases the apparent uhp pressure may have been over estimated hadean igneous microdiamond inclusions in jack hills detrital zircons could have originated from mantle xenoliths whereas abundant detrital phanerozoic diamonds containing inclusions of coesite and other eclogitic minerals from new south wales might have been derived from unexposed uhp metamorphic terranes micro mineral intergrowth and nano size minerals may hold important key to deciphering the actual p t paths of subduction and mantle return flow although most exhumed terranes have returned surfaceward relatively rapidly after short time of uhp condition the long duration of storage at great depth and slow exhumation for the largest uhp terranes remain as major problems

flow system controls of the chemical evolution of groundwater abstract isotopic and major ion analyses of 130 fresh and brackish groundwater samples reveal a strikingly consistent pattern of variation over 28 000 km 2 of the western canada sedimentary basin hydrodynamic interpretations based on drill stem tests and piezometric data reveal a pattern of broad regional flow from south to north however there is some evidence to suggest that patterns of groundwater flow have been influenced in the past by wisconsin glaciation all the permeable units appear to be recharged by meteoric water in the south where they outcrop or come close to the surface samples of groundwater collected down dip in each of six major sandstone units are progressively enriched in d 18 o na and cl for example the deepest waters of the artesian milk river aquifer are enriched by up to 70 and 15 with respect to the d and 18 o of the modern recharge waters the pattern of chemical evolution is strongly related to the hydraulic characteristics of individual units the isotopic composition is determined by the extent to which hydraulic conductivity has facilitated meteoric water flushing of connate water thus more permeable units and permeable zones within a unit tend to be isotopically lighter because of a more complete and more rapid invasion of meteoric water interestingly the largest conductivity values are found in some of the deepest units 1500 m consequently water in these deeper units have d and 18 o values which approach that of the recharge the major ion chemistry is controlled both by this process and a complex set of rock water interactions in addition to providing information about the chemical evolution of groundwater this study can begin to quantify the complex pattern of flushing in a large sedimentary basin

hydrogeology and hydrochemistry of the milk river aquifer system alberta canada a review abstract the milk river aquifer system consists of 30 60 m of cretaceous sandstone located within the milk river formation southern alberta canada the milk river formation is confined below by 500m of shale of the colorado group and above by up to 120 m of shale the pakowki formation the dominant recharge area for the aquifer is the sweetgrass hills montana where the aquifer crops out from the recharge area the groundwater flows to the north east and west calculated groundwater residence times at the north end of the aquifer about 100 km north of the recharge area range from 250 to 510 ka limited hydrological data from the confining shales suggest that cross formational flow does not occur systematic patterns are observed in major ions na cl hco 3 co 3 and so 4 stable isotopes 18 o and deuterium and field ph on a regional scale several mechanisms have been proposed to explain the geochemical evolution of the groundwaters

very high pressure orogenic garnet peridotites mantle derived garnet peridotites are a minor component in many very high pressure metamorphic terranes that formed during continental subduction and collision some of these mantle rocks contain trace amounts of zircon and micrometer sized inclusions the constituent minerals exhibit pre and postsubduction microstructures including polymorphic transformation and mineral exsolution experimental mineralogical petrochemical and geochronological characterizations using novel techniques with high spatial temporal and energy resolutions are resulting in unexpected discoveries of new phases providing better constraints on deep mantle processes

clinoenstatite exsolution in diopsidic augite of dabieshan garnet peridotite from depth of 300 km clinoenstatite exsolution lamellae have been discovered in clinopyroxene grains of garnet peridotite from the bixiling massif of the ultrahigh pressure metamorphic uhpm terrane in the dabie mountains china using transmission electron microscopy we show here that although the lamellae are low clinoenstatite lclen with p 2 1 c space group symmetry they contain nanometer scale antiphase domains indicating that the originally precipitating phase had c 2 c space group symmetry the lamellae are oriented parallel to 010 and 18 to 001 of the host approximately parallel to 401 both the very cold exhumation path of the dabie uhpm terrane and the orientation of the lamellae preclude the possibility that the originally precipitating phase could have been high temperature clinoenstatite htclen we conclude that the lamellae precipitated as high pressure clinoenstatite hpclen and subsequently inverted to lclen analysis of the incomplete high pressure crystallographic data available for compositions approximating those of the lamellae and host suggests a minimum pressure of precipitation of 9 gpa for dabie and about 12 gpa for similar exsolution previously observed in the alpe arami peridotite switzerland the bixiling complex is a crustal cumulate hence this result extends the minimum depth of subduction of continental rocks in the dabie sulu orogen to 300 km p 9 gpa

silica precipitates in omphacite from eclogite at alpe arami switzerland evidence of deep subduction observations of oriented sio2 precipitates in omphacite from eclogite with tholeiitic basalt protolith bordering the alpe arami garnet peridotite massif ticino switzerland and petrological studies of the eclogitic mineral assemblages suggest that this rock was subjected to higher pressure metamorphism than previously realized we employed various calibrations of the fe2 mg exchange thermometer and calculations of equilibria with thermodynamic data considering the calcium tschermak s component caal2sio6 of garnet pyroxene pairs from these calculations it is concluded that the eclogitic lenses have recorded at least four stages of mineral growth corresponding to the following stage i prograde c 2 4 gpa 700 c stage iia maximum recorded grade c 7 0 gpa 1100 c stage iib retrograde c 3 7 gpa 900 c stage iii retrograde c 2 1 gpa 750 c because of the preservation of stage i a relatively rapid subduction and exhumation of alpe arami eclogite is suggested the exhumation path of the eclogitic rock is in good agreement with most exhumation paths inferred for the alpe arami garnet lherzolite proposed previously by several authors based upon a variety of different observations although the eclogite and peridotite exhumation paths may diverge at depths greater than 120 km

clinoenstatite in alpe arami peridotite additional evidence of very high pressure observations by transmission electron microscopy show that lamellae of clinoenstatite are present in diopside grains of the alpe arami garnet lherzolite of the swiss alps the simplest interpretation of the orientation crystallography and microstructures of the lamellae and the phase relationships in this system is that the lamellae originally exsolved as the high pressure c centered form of clinoenstatite these results imply that the rocks were exhumed from a minimum depth of 250 kilometers before or during continental collision

the source and age of groundwater brines in the dead sea area as deduced from 36cl and 14c 36cl and 14c analyses of saline groundwater in the dead sea area were performed in order to study the chloride source of the brines and their age similarity among the 36cl cl ratio in saline groundwater 7 15 10 15 dead sea water 12 8 10 15 and in an halite layer 11 10 15 indicates that they all have a similar chloride source the 36cl cl ratios also suggest a significant contribution of chloride from rain water it is postulated that groundwater brines are the result of direct infiltration of brines from a precursor dead sea lake such as lake lisan which covered the area in the past this lake underwent several evaporation stages precipitating halite and infiltrating brines of varying chemical composition 14c data 3 8 25 8 pmc indicate that the percolation of brines into the sediments took place more than 9 000 years ago

talc magnesite and ti clinohumite bearing ultrahigh pressure meta mafic and ultramafic complex in the dabie mountains china

reply to comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz

radiocarbon and stable isotopes in water and dissolved constituents milk river aquifer alberta canada abstract origin and age of groundwater in the milk river aquifer alberta canada was the focal point of the present study to answer related questions wells in this aquifer were sampled and 2 h and 18 o in water 13 c and 2 h in methane 34 s and 18 o in so 4 13 c and 14 c in dissolved inorganic carbon dic and dissolved organic carbon doc and tritium contents determined stable isotope analyses on ground water permitted the recognition of at least three different zones within the aquifer starting at the recharge zone modern type groundwaters are encountered for the first few kilometers these are followed by groundwater with slightly higher 18 o and 2 h contents i e waters which do not show a glacial signature and were probably recharged under warmer climatic conditions groundwater in the third zone is characterized by higher salinities and a pronounced oxygen isotope shift they show the gradual admixture of far more saline formation waters from the alberta basin sulphate s and sulphate o isotope values indicate a till source for the so 4 however so 4 in wells close to the area where so 4 virtually disappears show isotopic values which suggest that so 4 reduction is occurring although other studies could not find bacterial populations of so 4 reducers methane is present in most wells and based on c and h isotope data has a biogenic origin methane production occurs close to some wells and or it diffuses from the confining shales into the aquifer radiocarbon is measurable only in the first 20 km from the recharge zone however transformation of measured concentrations to water ages is very difficult because of the complexity of the geochemical system comparison with 14 c data on doc was therefore very interesting and this new technique may complement the dic radiocarbon dating two wells near the recharge zone yielded dic doc high molecular weight hmw and doc low molecular weight lmw results the dic dates were much older than doc dates but the differenve in years between the wells for all three types of c were within 1000 a of each other the doc dates led to the conclusion that the initial dic radiocarbon content was as low as 30 modern when the water entered the aquifer the age of the water 20 km from the recharge zone was assessed at 20 000 a resulting in a velocity of 1 m a this result is much higher than estimates by other techniques

nanocrystalline mg fe cr tio3 perovskite inclusions in olivine from a mantle xenolith udachnaya east kimberlite pipe siberia abstract olivine grains from an ilmenite garnet peridotite nodule from the kimberlite pipe udachnaya wostotschnaya siberia have been investigated by tem methods electron diffraction hrem aem eels the nodule is a high temperature garnet peridotite which equilibrated at about 1200 1300 c and 200 km depth tem investigation of several olivine grains revealed nanometre sized inclusions of mg fe cr tio3 perovskite together with ilmenite both types of inclusions exhibit a typical grain size of about 50 nm the crystal structure of the perovskite inclusions is monoclinic with a0 1 095 nm b0 0 5169 nm c0 0 743 nm and the monoclinic angle 95 the orientation relationship between perovskite and olivine is 101 ol 300 per and 010 ol 01 0 per this observation combined with the experimentally determined ilmenite perovskite phase boundary a metha k leinenweber a navrotsky m akaogi calorimetric study of high pressure polymorphism in fetio3 stability of the perovskite phase phys chem minerals 21 1994 207 212 8 allows the use of perovskite in olivine as a geobarometer the presence of perovskite in olivine suggests that the peridotite originated at pressures of 8 10 gpa significantly higher than the pressure of last silicate equilibration 4 5 6 5 gpa

strontium isotopic evidence on the chemical evolution of pore waters in the milk river aquifer alberta canada abstract strontium isotope ratios were measured on 13 rock 18 leachate and 28 pore water samples from the milk river aquifer the confining argillaceous formations and the glacial till mantling the recharge area strontium isotope ratios 87sr 86sr of pore waters from the aquifer confining units and the glacial till ranged from 0 7069 to 0 7082 the 87sr 86sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area and this is interpreted to be the result of mixing and water rock interaction within the aquifer the solute composition of the recharging groundwater is modified by the local lithology causing distinct geochemical patterns along different flow paths within the aquifer whole rock 87sr 86sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone the authigenic carbonate cements and rock forming minerals comprising the major lithologic units had little apparent influence on the pore water sr chemistry carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations feldspar separates from the aquifer sandstone have relatively radiogenic sr isotope ratios whereas bentonites from the milk river and colorado shale formations have whole rock and leachate sr isotope ratios that are relatively unradiogenic ratios of most milk river aquifer pore waters are lower than those of any leachates or whole rocks analyzed except the bentonites the 87sr 86sr ratios of exchangeable sr in the bentonites are similar to ratios found in the more evolved pore waters simple rock water interaction models calculated for the whole rock leachate and exchangeable ion pore water pairs indicate that ion exchange with bentonite clays within the milk river and colorado shale formations appears to influence the isotopic evolution of the pore water sr in each of these units

the displacement of connate water from aquifers a mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers the theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids depending on constraints in the recharge area the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system the former condition is attained when the recharge area incorporates the total depth and breadth of the formation where this condition is not satisfied the concentrations that evolve are controlled by the original concentration of the formation water the composition of recharging meteoric water the dispersion parameters and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike for heterogeneous formations the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity this is demonstrated in the milk river sandstone which is characterized by several extensive zones of dilute water within narrow high conductivity pathways and marked increases in concentration in adjacent lower permeability rock in parts of the aquifer where higher permeability pathways appear to be absent the isochlores form a broad linear band with a marked increase in concentration in the flow direction

experimental support for a predictive osmotic model of clay membranes osmosis has been cited as a mechanism for explaining anomalously high fluid pressures in the subsurface clays and shales act as membranes and osmotic flux across these units may result in pressures sufficiently high to explain these anomalies the theoretical osmotic pressures as calculated solely from solution properties can be quite large however it is not yet resolved whether these geologic membranes are sufficiently ideal to generate such pressures

hyperfiltration of sodium chloride through kaolinite membranes under relatively low heads implications for groundwater assessment abstract three relatively low head hyperfiltration experiments were conducted to investigate clay membrane behavior at lower hydraulic heads dilute cl solutions 187 and 336 mg l were forced through thin layers of kaolinite 0 67 1 62 mm under heads ranging between 1 45 and 1 89 m at the end of each experiment there was a cl concentration increase 15 29 within the cell the concentration increase is attributable to solute sieving by the kaolinite calculated final concentration increases at the membrane face ranged between 1 51 and 1 65 times the initial concentration and the calculated values of the reflection coefficient ranged between 0 35 and 0 40 these experiments show that clays are capable of significant hyperfiltration effects at lower pressure heads more typical of natural aquifers consequently hyperfiltration effects may need to be considered in a broad spectrum of shallow subsurface processes in which these effects have been regarded as inconsequential particularly in perched aquifers

implications of halide leaching on 36cl studies at yucca mountain nevada 1 chlorine 36 was generated from nuclear tests in the 1950s and 1960s and has been used to identify fast flow paths at yucca mountain the proposed repository for high level nuclear waste fabryka martin et al 1997 1998 bomb pulse 36cl brought into the subsurface by infiltrating rainwater presumably resides along fracture surfaces because of the extremely low rock matrix permeability however leaching a rock sample to extract this salt inevitably extracts pore water chloride cl and rock matrix chloride thereby making it difficult to obtain reproducible measurements or detect the specific bomb pulse signatures complexities introduced by these sources of older chloride include dilution of bomb pulse 36cl cl ratios for samples from strata with a high cl concentration variations in measured ratios as a function of leaching time rock chip size and the differing effects of active leaching from those of passive leaching this work provides both a conceptual model and a mathematical solution for the leaching processes and examines the role of sample leaching in the 36cl studies of yucca mountain rocks an analytical solution is derived for the diffusion of cl and 36cl in composite media rock matrix and water to accommodate variable diffusivity this solution is subsequently used to develop a leaching model that takes into account bomb pulse signal matrix pore water and relatively hard to leach components isolated fluid inclusion and mineral boundary salts the model is then applied to samples from stratigraphic units at yucca mountain to obtain leachate concentrations from different setup methods protocols including duration chip size and gravitational settling of the water rock mixture the model results show that the probability of detecting a 36cl cl bomb pulse signal is severely diminished under longer leaching times and smaller rock fragment sizes and that leaching times of 1 to 10 hours are most likely to be successful in detecting a bomb pulse signal bomb pulse 36cl cl ratios are more likely to be observed if pore water cl concentrations were initially low prior to the introduction of bomb pulse carrying water

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

chemical and isotopic signature of old groundwater and magmatic solutes in a costa rican rain forest evidence from carbon helium and chlorine 1 c he and cl concentrations and isotopes in groundwater and surface water in a lowland costa rican rain forest are consistent with the mixing of two distinct groundwaters 1 high solute bedrock groundwater representing interbasin groundwater flow igf into the rain forest and 2 low solute local groundwater recharged in the lowlands in bedrock groundwater high 13c 4 89 low 14c 7 98 pm high r ra for he 6 88 and low 36cl cl 17 10 15 suggest that elevated tracer concentrations are derived from magmatic outgassing and or weathering of volcanic rock beneath nearby volcan barva in local groundwater the magmatic signature is absent and data suggest atmospheric sources for he and cl and a biogenic soil gas co2 source for dissolved inorganic carbon dating of 14c suggests that the age of bedrock groundwater is 2400 4000 years most likely at the lower end of the range local groundwater has 14c 100 pm indicating the presence of bomb carbon and thus ages less than 55 years overall data are consistent with a conceptual hydrologic model originally proposed on the basis of water budget and major ion data 1 large variation in solute concentrations can be explained by mixing of the two distinct groundwaters 2 bedrock groundwater is much older than local groundwater 3 elevated solute concentrations in bedrock groundwater are derived from volcanic fluids and or rock and 4 local groundwater has not interacted with volcanic rock tracers with different capabilities converge on the same hydrologic interpretation also transport of magmatic co2 into the lowland rain forest via igf seems to be significant relative to other large ecosystem level carbon fluxes

precipitation of pyroxenes and mg2sio4 from majoritic garnet simulation of peridotite exhumation from great depth our experimental simulations of the exhumation path of mantle peridotites show that high temperature 1400 c decompression of lherzolite from 14 to 13 and 12 gpa results in exsolution of interstitial blebs of diopside and mg2sio4 wadsleyite lamellae from majoritic garnet at lower pressures from 8 to 5 gpa at t 1400 c only enstatite exsolves as blebs at garnet boundaries continuous high temperature decompression from 14 to 7 gpa produces zoned majoritic garnet containing blebs of exsolved pyroxenes inside garnet rims no intracrystalline precipitation of pyroxene was observed in garnet although such lamellae are found in some natural garnet peridotites the explanation appears to be the three orders of magnitude difference in grain size between experimental and natural specimens our data suggest that mg2sio4 and diopside exsolutions reflect the deepest point of the exhumation path of garnet peridotites whereas enstatite precipitation may be restricted to garnets with less majoritic component at shallower depths

sources of chloride and implications for 36cl dating of old groundwater southwestern great artesian basin australia we investigate the relative importance of a number of processes that affect cl and 36cl distribution in the southwestern flow systems of the great artesian basin australia to provide more precise estimates of age and flow and recharge rates in situ production of 36cl secular variations in the rate of production of 36cl and its subsequent fallout as well as rates of diffusion of stable cl from adjacent aquitards mask the interpretation of rates of decay of 36cl cl along hydraulic gradients and can preclude estimating absolute groundwater ages however mean flow velocities calculated from absolute cl concentrations are 0 24 0 03 m yr and are a more reliable parameter than calculated ages because fewer assumptions and approximations are required recharge rates to the main cadna owie formation and algebuckina sandstone aquifer of the great artesian basin estimated from cl mass balance in the unconfined aquifers are 0 16 0 08 mm yr and were probably up to a factor of 3 higher 30 kyr ago as indicated by decreasing cl and 18o concentrations along the head gradient

differences in groundwater and chloride residence times in saline groundwater the barwon river catchment of southeast australia abstract the residence times of groundwater and chloride and the processes contributing to the development of saline total dissolved solids tds up to 45 379 mg l groundwater within the barwon river catchment of southeast australia were investigated using major ion stable isotope 18 o 2 h and 13 c and radioactive isotope 3 h 14 c 36 cl geochemistry the elevated groundwater salinity in the region is primarily due to evapotranspiration and recycling of solutes in saline lakes with minor contributions from weathering of halite silicate and calcite minerals groundwater residence times estimated from 14 c vary from modern to 20 ka for groundwater with lower 14 c activities the estimated residence times vary significantly depending on the assumed flow model and the 14 c activity of recharge chloride residence times downgradient of lake murdeduke a saline through flow lake in the centre of the catchment are greater than the corresponding groundwater residence times due to the recycling of cl within the lake precise estimates of chloride residence time could not be determined using 36 cl due to r 36 cl in precipitation being lower than that of groundwater this is most likely due to r 36 cl values in rainfall having been higher in the past than they are at present due to climate variability 18 o 2 h and 13 c values also suggest that the region has experienced increasingly more evaporative conditions with time the results of this study demonstrate that while cl is a useful tracer of hydrological processes it must be applied carefully in arid and semi arid regions of the world in particular recharge rates calculated using chloride mass balance may be underestimated where recycling of cl has occurred

dating of syngenetic ice wedges in permafrost with 36cl abstract a new method of permafrost dating with the cosmogenic radionuclide 36 cl is presented in the first application syngenetic ice wedges are dated using the ratio of 36 cl and cl concentrations in ice as the signal 36 cl is produced in the atmosphere by nuclear reactions of cosmic rays on argon stable chlorine enters the atmosphere from the oceans their ratio does not depend on chloride concentration in precipitations and on sublimation of snow in situ production of 36 cl in permafrost ice via cosmic ray induced reactions and neutron capture are calculated and the dating age limit is estimated as 3 million years 36 cl cl ratios in permafrost samples from cape svyatoy nos laptev sea coast north eastern siberia are measured by accelerator mass spectrometry analysis of the first results and the calculated dates support the feasibility of the 36 cl permafrost dating method

trace elements in the gas emissions from the erta ale volcano afar ethiopia high temperature 1084 c fumarolic emissions from a spatter cone at the erta ale north pit crater granted a rare opportunity to collect giggenbach bottles condensates and sublimates from the fumarolic gases of a rift plume volcano in the immediate proximity of degassing lava these results represent the highest temperature gases sampled directly for trace elements and the first high t fumarolic samples for a rift plume volcano sixty seven metals and metalloids were measured quantitatively by icp aes and icp ms in liquid gas condensates and solid sublimates the total amount of trace elements in the gas without si exceeded 170 ppm the ten most abundant elements transported in nonsilicate modes were na 61 ppm fe 41 ppm k 32 ppm br 12 4 ppm cd 3 0 ppm se 2 3 ppm cu 2 0 ppm zn 2 0 ppm te 1 7 ppm and as 1 2 ppm the gases contained 27 ppb re 1 5 ppb au 0 5 ppb pt and 0 27 ppb os rh and pd containing phases were observed in solid sublimates the only metal not detected by all analytical methods was ruthenium chalcophile elements cd cu zn se te as were transported primarily in the gaseous form alkali metals were emitted at least partially as liquid micron size sulfate droplets whereas alkali earths aluminum and ree had a high affinity to silicate aerosol in the form of basaltic microspheres the silicate aerosol content was evaluated at 59 ppm on average but varied within a 7 5 fold range during sampling because of the extremely high temperature refractory elements ca ba ta u and lree showed evidence of transport in the form of gaseous species the so2 flux in january 2011 was evaluated at 91 24 t d for the entire volcano including 31 t d from the north crater and 60 t d from the lava lake the daily output of trace elements from both erta ale craters without si was estimated at 53 kg d including 20 kg of na 13 5 kg of fe 10 5 kg of k 4 5 kg of chalcophile elements 9 g of re 0 5 g of au and 0 17 g of pt the trace element pattern of erta ale fumarolic gases do not possess any distinct geochemical specialization and resemble te patterns from fumarolic emissions of studied arc and plume volcanoes

ultrahigh pressure metamorphic terranes mineral reactions fluids microstructures and deformation a celebration of the career contribution of h w green papers presented during the 33rd international geological congress at uhp symposia 4 and 5 organized by task force iv of the international lithosphere program held in oslo norway 5 14 august 2008

transport modeling applied to the interpretation of groundwater 36cl age 1 we use reactive transport modeling to consider how diffusion and hydrodynamic dispersion cross formational flow and subsurface production affect the steady state distribution in flow regimes of the radioactive isotope 36cl and the relationship of the isotope distribution to groundwater residence time or age the isotope forms naturally in the atmosphere dissolves in rainwater and then decays in the subsurface with a half life of 301 000 years hence it is important for age dating very old groundwater in a simple flow regime composed of an aquifer confined above and below by aquitards isotopic age may correspond rather well with a groundwater s piston flow age this correspondence is favored where the aquifer is thick cross formational flow is insignificant salinity is low and the diffusion coefficient within the aquitards is small the maximum dateable age however is somewhat smaller than expected from the isotope s half life owing to the effect of dead chloride dating based on isotope abundance the 36cl cl ratio may be less accurate than that based on 36cl concentration cross formational flow can strongly affect the 36cl distribution and abundance preventing the rates and even direction of flow within an aquifer from being interpreted using the piston flow model where salinity is moderate or high the isotope distribution is controlled by subsurface production and dating on the basis of the decay of atmospheric 36cl is not possible in models of simple flow regimes the 36cl method fails to predict groundwater age accurately where groundwater chlorinity exceeds 75 150 mg kg 1 reactive transport models hold considerable promise for improving interpretation of the rates and patterns of groundwater flow from radioisotope distributions

factors controlling groundwater quality in eastern united arab emirates a chemical and isotopic approach abstract chlorine 36 along with oxygen and hydrogen isotopes and selected major ions were used to investigate the factors controlling groundwater quality in the eastern part of the united arab emirates two main aquifers occupy the study area the eastern gravel plain aquifer that occurs near the coastal area and the inland ophiolite aquifer previous studies suggest that groundwater particularly in the eastern gravel plain aquifer is affected by seawater intrusion and evaporation samples of groundwater from the eastern gravel plain aquifer cl 1000 mg l have r 36 cl values in the range of 13 3 17 4 10 15 while those from the ophiolite aquifer cl 36 cl values in the range of 20 118 10 15 these values indicate the presence of bomb produced 36 cl and are consistent with recent post 1950 recharge of most of the samples d 18 o relationship plots on a typical evaporation line which suggests potential evaporation of the recharging waters prior to infiltration the r 36 cl values of the coastally bound eastern gravel plain aquifer are lower than the ophiolite aquifer which suggests an additional input of chloride to this aquifer moreover in most cases the chloride concentration is not balanced by the concentrations of other cations such as sodium potassium calcium or magnesium seawater intrusion is thus ruled out measurements of bromide concentrations support the contention that organically bound cl is being released into this environment agricultural practices which are extensive in this region are a possible source also sodium and silica concentrations provide evidence for the release of these elements by the weathering of host rocks

underground production of radionuclides in the milk river aquifer alberta canada abstract most cosmogenic radionuclides that may be used to estimate groundwater ages in excess of 100 ka are also produced underground by in situ nuclear reactions radioactive equilibrium between in situ production and decay would be approached within such long residence times radionuclide production by in situ nuclear reactions within the groundwater and within its host rock has been calculated theoretically and compared with some measured radionuclide contents of the groundwater the fractional transfer of in situ produced 37 ar 39 ar and 222 rn from rock to groundwater necessary to account for the total measured groundwater contents were found to be similar although site specific the implications for radionuclide release mechanisms and for groundwater dating by the use of cosmogenic radionuclides including those which are applicable for very old groundwaters 36 cl 81 kr 129 i are discussed

chlorine 36 dating of very old groundwater 1 the great artesian basin australia chlorine 36 has many advantages as a dating tool for very old groundwater these advantages include a suitable half life 3 01 x 10 sup 5 years simple geochemistry conservative behavior in groundwater and a general absence of subsurface sources at levels comparable to the atmospheric input recent advances in tandem accelerator mass spectrometry have permitted the analysis of sup 36 cl at low abundance expected following residence in the subsurface for 10 sup 6 years or more in order to test the suitability of sup 36 cl for dating very old groundwater the sup 36 cl cl ratios of 26 groundwater samples from the great artesian basin of australia have been measured groundwater ages calculated from the sup 36 cl data compare favorably with ages computed independently from hydrodynamic simulations

radioisotope dynamics the origin and fate of nuclides in groundwater the use of radionuclides as clocks for groundwater dating and as probes to investigate the geometry and spatial extent of the contact area between rocks and water is reviewed subsurface production rates for 222 rn 37 ar 55 kr 39 ar 36 cl 3 he 4 he and 40 ar in various rock types are listed measured rn fluxes from the surface of sandstone grains and from pieces of granite point to scale dependent diffusion coefficients the temporal evolution of subsurface produced 222 rn 37 ar 85 kr and 39 ar activities in groundwaters yields radionuclide escape factors between 0 1 and 9 for the stripa granite sweden and between 1 and 4 for the milk river sandstone canada the combination of 3 h 85 kr 39 ar 14 c 36 cl 4 he in the uk triassic sandstone aquifer allows groundwater dating up to 40 000 a very old groundwaters can be studied using cl 36 cl and 4 he evolution as demonstrated in the milk river aquifer in canada

chlorine isotopes as tracers of solute origin and age of groundwaters from the eastern desert of egypt abstract chlorine 36 abundances and stable chlorine isotope ratios 37 cl 35 cl were analyzed to decipher sources of chloride and to estimate subsurface residence times of groundwaters from the nubian sandstone aquifer system nsas alluvial aquifers and fractured basement aquifers in the eastern desert of egypt chlorine 36 isotopic abundances 36 cl cl ranged from 5 10 15 to 343 10 15 the range in 37 cl values was 0 61 to 0 90 groundwater solute compositions were dominated by na ca cl and so 4 with total dissolved solids ranging from 445 to 13 700 mg l chemical and isotopic data indicate that dry fallout of marine aerosols and evaporated vadose zone residues from precipitation that recharged the aquifers may have been the main sources of groundwater solutes apparent groundwater 36 cl model ages range from 0 40 to 1300 300 180 kyr groundwater from the fractured basement aquifers in the southwestern part of the study area had the youngest apparent ages while that from deep wells tapping the nubian aquifer had the oldest apparent ages shallow alluvial aquifers having anomalously old apparent 36 cl model ages indicate mixing of old nubian aquifer water with modern recharge in alluvial aquifers stable isotope ratios of hydrogen and oxygen support this inferred mixing relationship and allowed quantitative estimation of old young water mixing fractions

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

electron microscope study of the reaction olivine h2o tio2 titanian clinohumite titanian chondrodite synthesized at 8 gpa 1300 k the nucleation and growth processes of titanian clinohumite ti cl and titanian chondrodite ti ch during hydrous alteration of olivine at 8 gpa 1300 k are described in detail we observed two different nucleation sites and orientation relationships for ti cl 1 heterogeneous nucleation at olivine grain or phase boundaries yielding semicoherent 001 lamellae with 001 ol 001 ti cl and 010 ol 010 ti cl 2 formation of coherent nanometer sized nuclei inside olivine with the orientation relationship 100 ol 001 ti cl and 011 ol 020 ti cl only the former for which the interface with olivine facilitates the transport of oh and ti necessary for the formation of the humite group minerals survives to large sizes these results suggest that ti cl should form readily in a ti and h rich environment at mantle temperatures independent of f content from shallow environments to those at depths exceeding 250 km and could play a role in recycling water back into the deep mantle

chlorine 36 in groundwater as a palaeoclimatic indicator the east midlands triassic sandstone aquifer uk the36cl contents of groundwaters from the east midlands triassic sandstone have been used to deduce rainfall its chloride content and evapotranspiration during the late pleistocene at this time the regional precipitation and evapotranspiration would have been reduced relative to the modern and holocene climate it is estimated that the infiltration was reduced by about 40 mm a 1 the method for evaluation of these palaeoclimatic parameters is dependent upon the major cl source being a marine aerosol fall out this is the general case but groundwater east of the exploited zone of the aquifer contains chloride which is derived from saline formation water with a marinecl br ratio and in equilibrium with the in situ neutron flux the fall out of cosmogenic36cl at the geomagnetic latitude 56 2 n is evaluated as 30 6 atoms m 2s 1 and is significantly greater than that estimated from the theoretical fall out curve of bentley et al 1 the bomb peak of36cl remains entirely within the unconfined zone of the aquifer the assessment of groundwater residence time from the36cl chronometer is shown to be impossible for this aquifer

mineralogy of the martian interior up to core mantle boundary pressures in order to determine the mineralogy of the martian interior along a high temperature areotherm multianvil experiments have been performed with a model martian mantle composition up to 23 5 gpa the dreibus and wanke 19851 martian mantle composition yields an upper mantle that consists of olivine clinopyroxene orthopyroxene garnet at pressures up to 9 gpa above 9 gpa orthopyroxene is no longer present the transition zone is marked by the appearance of spinel at 13 5 gpa up to 15 gpa clinopyroxene and majorite coexists with phase and or spinel by 17 gpa clinopyroxene is entirely replaced by majorite and the modal abundance of spinel increases at the expense of phase the dominant assemblage throughout most of the transition zone is spinel majorite two experiments completed in the perovskite stability field indicate that the lower mantle consists of mg fe silicate perovskite magnesiowustite and majorite casio 3 perovskite is not present in these experiments both the presence of a martian lower mantle i e an mg fe silicate perovskite bearing zone and the phase assemblage stable in the martian lower mantle are very sensitive to the temperature profile of the interior a low temperature profile may stabilize stishovite in the lower mantle or it may lead to the absence of the lower mantle because of the higher transition pressure required for forming perovskite at lower temperatures regardless of the temperature profile assumed the martian upper mantle and transition zone will account for a larger proportion of the planet s interior than is the case for the earth s interior because of the smaller size of mars

shock induced minerals in meteorite provide prospecting tools for mineral physics over the last 40 years a combination of seismic data from earth s interior and experimentation at high pressures on materials of composition similar to that in earth s mantle has led to an increasingly accurate picture of what succession of phases must be present at increasing depths during the same time period it has been discovered that many of these phases are present in minute amounts in meteorites that before their arrival on earth were shocked to high pressures and temperatures during collisions between the asteroids from which the meteorites were derived in a recent issue of pnas chen et al 1 reported a previously uncharacterized mineral from such a shocked meteorite and by using diamond anvil experiments and synchrotron x ray analysis derived the stability conditions of that mineral and another closely related one discovered earlier this year from the same meteorite both of these phases are high pressure polymorphs of the mineral chromite fecr2o4 which is a common although minor mineral in peridotites rocks of the upper mantle that are abundantly exposed at the surface and also found as inclusions xenoliths in volcanic rocks some of this volcanism e g kimberlite also carries diamonds and hence must be derived from a minimum depth of 120 km the authors suggest that the newly discovered polymorphs of chromite if found in natural rocks on earth could serve as anchor points for estimation of the depths of origin of rocks transported from great depth the two polymorphs place minimum pressures of 12 13 gpa cafe2o4 structure and 20 gpa cati2o4 structure these pressures are equivalent in earth to depths of 400 km and 680 km respectively however is there any reason to believe that any rocks presently at the surface have ever seen such pressures

the solubility of tio2 in olivine implications for the mantle wedge environment abstract one characteristic of many subduction zone garnet peridotites is that they contain titanium bearing phases not otherwise found in mantle rocks in particular titanoclinohumite tich and or its breakdown assemblage consisting of symplectic intergrowths of olivine and ilmenite is common in many of these bodies the alpe arami garnet lherzolite of the lepontine alps while lacking tich displays instead large numbers of fetio 3 rod shaped precipitates in the oldest generation of olivine amounting to approximately 1 by volume indicating that at some time in its past the peridotite experienced conditions under which the solubility of tio 2 in olivine was greater than 0 6 wt in order to test the hypothesis that the environment of very high solubility of tio 2 in olivine is to be found at very high pressures we have conducted experiments on lherzolite compositions with added ilmenite at pressures between 5 and 12 gpa and temperatures of 1350 1700 k our results on anhydrous compositions show that whereas solubility of tio 2 was not detected in olivine at 5 gpa 1400 k where it coexists with rutile when rutile disappeared from the paragenesis the solubility climbed to 0 5 wt at 8 and 10 gpa and to 1 wt at 12 gpa all at 1600 k these results support our previous interpretations from titanate morphology and abundance that the alpe arami massif has surfaced from depths 300 km corresponding to pressures 10 gpa but remove the need to suggest a deeper origin and possible precursor phase such as wadsleyite they also support the hypothesis that garnet peridotites with unusual ti bearing phases reflect a unique mantle environment occurring in the mantle wedge overlying subduction zones 2000 elsevier science b v all rights reserved

age differentiated subduction regime an explanation of regional scale upper mantle differences beneath the alps and the variscides of central europe abstract the upper mantle beneath the alps and the variscides of central europe has a varied seismic structure as a result of the accretionary and evolutionary processes that have shaped it natural earthquake data the raypaths of which pass beneath these regions have enabled the calculation of travel times out to 3000 km the source receiver geometry ensured there was broadband station coverage at offsets between 900 and 3000 km enabling the detection of the appropriate upper mantle phases over an azimuthal span embracing the studied structures the resulting data allowed us to model first order discontinuities to a depth of about 420 km we have used modelling based on ray tracing in a cylindrical coordinate system reflecting the geometry of the wave propagation medium the data allow determination of the thickness of the upper mantle low velocity zone lvz beneath the alpine orogen it appears to be thicker than beneath surrounding areas with its upper lid at a depth of about 90 km and its base the lehmann discontinuity being depressed to 220 km such thickening of the lvz is typical below young orogens a seismic discontinuity at a depth of around 300 km with the p wave velocity increasing to 9 km s has been observed for all the sub alpine raypaths we consider this discontinuity to have originated as a result of alpine orogen subduction this is responsible not only for changes in the thermal field as a result of transporting colder material to depths probably exceeding 200 km but also for delivering the necessary amounts of excess silica required for the coesite stishovite phase transition for rays passing beneath the variscides there is a scatter in travel times over the 8 15 distance range however the scattering does not indicate significant thickening of the lvz as identified beneath the alpine orogen and the lehmann discontinuity at the base of the lvz does not exceed 200 km depth also in contrast to the alps no high velocity phases are observed for a discontinuity near 300 km depth this supports our contention that the 300 km discontinuity is a regional feature ascribed to the subduction regime beneath the younger orogen for all azimuths from which structures beneath the alps are illuminated we clearly observe both the refraction as well as the reflection branch from the 410 km discontinuity

titanium solubility in coexisting garnet and clinopyroxene at very high pressure the significance of exsolved rutile in garnet exsolution microstructures including ilmenite garnet in clinopyroxene and rutile in garnet are common in clinopyroxenite and eclogite from the sulu ultrahigh pressure uhp terrane in order to understand the phase relations and ti solubility in both garnet and clinopyroxene in a natural tio2 bearing system several experiments at 5 15 gpa 1000 1400 c were carried out using the multianvil high pressure apparatus the hujianlin ilmenite rich garnet clinopyroxenite showing exsolution microstructure was selected as starting material because it closely approaches a composition lying in the tio2 cao mgo feo al2o3 sio2 system except for minor melt in one experiment at 1400 c and 5 gpa other run products contain majoritic garnet clinopyroxene ilmenite or rutile and exhibit neoblastic texture with increasing pressure ti and ca mg and si contents of neoblastic garnet increase with decreasing al the principal coupled substitutions are ca2 ti4 2al3 and si4 mg2 2al3 responding to majorite component increase titanium solubility 0 8 4 5 wt as tio2 in garnet and grtti cpxti ratio have a pronounced positive correlation with pressure between 5 and 15 gpa on the other hand the coexisting clinopyroxene contains low ti 0 17 0 53 wt as tio2 and shows no significant pressure effect rutile exsolution in garnet is coupled to that of pyroxene exsolution both are exsolved from majoritic garnet on decompression therefore the amount of such exsolved lamellae is a potential indicator of high pressure metamorphism in exhumed rocks whereas the tio2 content of clinopyroxene coexisting with garnet is not sensitive to pressure change

quantitative 3d measurement of ilmenite abundance in alpe arami olivine by confocal microscopy confirmation of high pressure origin a critical aspect of the debate about the origin and conditions of metamorphism of the alpe arami aa peridotite is the disagreement over how much ilmenite is contained in the older generation of olivine and therefore how much tio 2 might have been dissolved at high pressure and temperature we have now determined quantitatively the 3 dimensional distribution of ilmenite in aa olivine by confocal laser scanning microscopy clsm the clsm measurements show an average concentration of 0 31 vol of ilmenite in olivine with individual grains containing up to 1 2 vol this translates into average and maximum concentrations of 0 23 and 0 9 wt tio 2 in olivine respectively and confirms the original estimation of maximum concentration of 1 vol tio 2 the vast majority of ilmenite in aa olivine is distributed randomly although topotactically oriented and in all cases is accompanied by chromite in a ratio of 4 1 these observations are consistent with an origin of the ilmenite and chromite by exsolution from an olivine solid solution at p 9 12 gpa and temperatures above the stability field of titanian clinohumite but are not consistent with suggested breakdown of titanian clinohumite combining these results with other recent findings suggests that exsolution followed deformation under relatively high fugacity of h 2 o and that the high solubility of tio 2 is probably explained by pressure induced accommodation of ti in the tetrahedral site of silicates

isotope palaeohydrology and the prediction of long term repository behaviour there are considerable well recognized difficulties involved in the investigation of very low permeability rocks by conventional measurements of water potentials and spatial distribution of hydrological parameters such as permeability and effective porosity therefore most studies of predictive behaviour are based on models which when unconstrained by data are often worse than no model at all geochemistry and environmental isotope geochemistry are techniques well suited for hydrological investigations of potential sites of nuclear waste isolation and for constraining predictive models stable isotopes constitutive of the water molecule 2h and 18o may give information on the origin of the water especially 2h which is practically uninvolved in isotope exchange with rock forming minerals variations in stable isotope contents can be related to palaeohydrological and palaeoclimatic conditions whereas 3h is indicative of recent recharge the 13c content of dissolved carbon is related to its origin s and the 14c activity gives a time scale however the initial carbon isotope contents can be modified by various diagenetic effects such as precipitation dissolution of secondary calcite and oxidation of reduced carbon the heavy isotope content of the total dissolved inorganic carbon tdic cannot be interpreted without a detailed knowledge of the carbon chemistry and of the mineralogy and isotope contents of secondary carbonates species of dissolved organic carbon doc with high molecular weights hmw can generally be attributed to soil derived compounds their 14c content may be measured by ams accelerator mass spectrometry thus providing an estimate of the time elapsed since recharge took place chlorine 36 is an interesting potential tool for dating old ground waters because of its long half life 301 kyr and its hydrophilic behaviour it can be also produced in situ in significant amount if the rocks are rich some tens of ppm in u and th in such cases this time dependent build up provides a more systematic radiochronometer of ci residence time in the rock than the decay of cosmic input 36ci provided no cl is leached from the rock the isotopic composition of aqueous sulphur compounds depends on their origin and on their diagenetic evolution the redox reactions of so2 4 reduction or of s2 oxidation are marked by strong isotope effects especially when generated by bacteria sulphate reduction by organic matter is a potential source of dissolved inorganic carbon and may thus interfere with 14c age interpretations after discussion of the possible age and origin of waters and solutes some scenarios of evolution of local and regional palaeohydrological conditions are proposed examples are given with special emphasis on detailed results from the fennoscanian shield stripa project and from northern switzerland

ultra depleted peridotite xenoliths in the northern taihang mountains implications for the nature of the lithospheric mantle beneath the north china craton abstract we report the finding of peridotite xenoliths in the early cretaceous longmengou olivine bearing diabase 138 ma in the northern taihang mountains in the central north china craton based on the modal proportions of olivine clinopyroxene amphibole and anorthite these peridotite xenoliths can be divided into three zones clinopyroxene bearing olivine zone coz olivine clinopyroxene zone ocz and amphibole bearing anorthite clinopyroxene zone aacz the core of olivine grains in clinopyroxene bearing olivine zone have higher mg 95 sio2 41 80 42 53 wt and lower cao 95 and lower nio content

synthesis of skeletal diamonds implications for microdiamond formation in orogenic belts diamond was synthesized at high temperature and pressure in a walker style multianvil apparatus from various supercritical c o h rich fluid compositional systems depending on the type and amount of impurities added to the system diamonds of vary ing morphology and bearing solid oxide inclusions were found within the run product these characteristics bear a striking re semblance to metamorphic microdiamonds recovered from the kokchetav massif kazakhstan these natural diamonds share mor phological traits with our synthesized diamonds and both the nat ural and synthesized diamonds contain similar solid oxide inclu sions our data favor formation of kokchetav diamonds via crystallization from a supercritical c o h fluid rather than from carbonate or carbonatite melt as others have suggested

application of isotopic methods to dating of very old groundwaters milk river aquifer alberta canada the aim of this joint project was to evaluate the usefulness of available geochemical and isotope techniques for dating very old groundwater this paper represents a synthesis of an iaea sponsored study for which purpose the milk river aquifer groundwaters were sampled from 16 wells during 1985 and subsequent years for the following measurements 2h 3h 13c 18o 14c 39ar 81kr 85kr noble gases including222rn 36cl 129i and u isotopes the milk river aquifer was selected for this study because several preceding investigations had established that this groundwater system contains waters whose ages range from recent to 1ma the present study has established that the milk river aquifer system is very complex both in terms of groundwater origin and in terms of the evolution of its chemical and isotopic contents however this apparent complexity proved to be an interesting challenge with respect to the use of different and complementary approaches to interpretation of the geochemical and isotope data in terms of groundwater residence time thus the groundwater ages based on the hydrodynamic model should be considered as a lower limit of the average groundwater age in the milk river aquifer 0 25ma while those based on the36cl cl data uncorrected for any dilution by dead cl should be considered as an upper limit 2ma the milk river aquifer international project is an excellent illustration of the variety of insight and increased confidence possible in flow system analysis when multiple independent dating methods are combined with detailed hydrogeological studies the conclusion of the present study is that the potential for dating of very old groundwaters by a variety of isotope techniques is very high provided a combination of methods is applied never a simple method by itself

analytical electron microscopy of nanometer scale hornblende lamellae low temperature exsolution in cummingtonite cummingtonite from central massachusetts which has experienced pervasive exsolution of hornblende contains numerous hornblende precipitates lamellae and discs ranging in thickness from 2 5 mm to 4 nm that represent multiple generations of exsolution the smallest precipitates were investigated using transmission electron microscopy and analytical electron microscopy to characterize the coherent cummingtonite hornblende solvus at low temperature in contrast to older coarser generations of exsolution lamellae which are 0 5 2 5 mm in width planar and extend across entire grains the youngest generation consists of nanometer scale discs 4 80 nm thick and 10 1000 nm long that represent exsolution at approximately 300 8c klein et al 1996 quantitative energy dispersive x ray analyses were obtained from discs as small as 20 nm in thickness providing compositional data for coherent exsolution of hornblende at 300 8c surprisingly these tiny discs have a lower ca content and a higher al content than the coarser higher temperature lamellae these compositions appear to lie well within miscibility gaps of the equilibrium and coherent solvi for cummingtonite hornblende in terms of ca fe 21 exchange at low temperatures and may represent a more tschermakitic hornblende coexisting with cummingtonite with excess al relative to ca the composition of the cummingtonite host between nanometer scale discs is very low in both ca and al relative to bulk cummingtonite analyses that were obtained from electron microprobe analyses of 1 2 mm areas compositional profiles across host areas were measured to help interpret the unexpected chemistries of the nanometer scale discs a profile across the precipitate free zone between a coarse hornblende lamella and a group of nanometer scale hornblende discs shows downward concavity for ca and al as expected for incomplete diffusion between the precipitation zone and the pre existing hornblende lamellae a profile measured between two nanometer scale discs shows downward concavity for al and nearly constant to slight upward concavity for the ca content suggesting incomplete al diffusion before completion of the exsolution process but a near equilibrium state for ca however the ca profile could also represent incomplete diffusion if the hornblende discs had started coarsening at the expense of other shrinking discs by means of the gibbs thomson capillary effect the observed profiles suggest that relative to al ca was the faster diffusing element when the exsolution and coarsening processes stopped

comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz the milk river aquifer in southern alberta combines apparently simple classical confined aquifer hydrodynamics with somewhat enigmatic groundwater geochemistry of conservative solutes over the past 10 years five major papers have focused on the geochemistry of milk river aquifer groundwater most recently hendry and schwartz 1988 have proposed a different mechanism aquitard diffusion to explain the milk river geochemistry they described and evaluated previously proposed geochemical processes especially ion filtration hendry and schwartz 1988 concluded that ion filtration and the other proposed mechanisms were not supported by the data they then described the aquitard diffusion mechanism and used a simple analytical model to simulate observed aquifer trends in cl sup minus and sup 18 o from the results of this exercise they concluded that diffusion from the aquitards was controlling the solute distributions in the aquifer finally they interpreted previously published sup 36 cl data and new profiles of cl sup minus in the aquitards in terms of the diffusion model upon review the authors do not find the arguments against ion filtration to be as damaging as hendry and schwartz indicate nor do they find the evidence for aquitard diffusion to be as persuasive in this study they will first evaluate hendry andmore schwartz s arguments against ion filtration then they will review the arguments in favor of aquitard diffusion and finally the authors will address the implications for the interpretation of the vertical cl sup minus profiles and the sup 36 cl data less

pseudobrookite group oxide solutions and basaltic melts abstract orthorhombic bbmm r2 1 x 3 rx2 ti1 xo5 r3 r2 ti m1 ti r2 r3 2m2o5 solid solutions were first recognized in lunar rocks and then identified as such on earth even though they are less common than ilmenite and magnetite s l there is strong field experimental and theoretical evidence that they are not geological oddities besides pseudobrookite oxide solutions may have had a critical role in the petrogenesis of the mare basalts and lunar picritic glasses as a source of tio2 and may be present in other planetary bodies as well as materials they are of particular theoretical and practical interest because of the cation order disordering phenomena that affect their physical and mechanical properties and participation in the tio2 slag smelting process x ray crystallography and spectroscopy studies have shown that all the cations are in octahedral coordination occupying two nonequivalent sites with a 1 2 ratio evaluation of site fractions configurational entropy in r2 1 x 3 rx2 ti1 xo5 solutions and of the known properties of pseudobrookite group mgti2o5 suggests that r23 tio5 solutions may reach cation random distribution and thus entropy maxima at lower temperatures than r2 ti2o5 rich solid solutions as a result the entropy contribution to their thermodynamic stability may depend upon the r 2 r 3 ratio on the basis of computations experiments and chemography of mineral equilibria it is inferred that 1 assemblages of pseudobrookite group ti oxide ilmenite rutile olivine and pyroxene s should be expected under lower crust and upper mantle conditions in the earth and conceivably in other planetary bodies including the earth s moon 2 reactions between pseudobrookite group ti oxide and olivine orthopyroxene and pseudobrookite group ti oxide or ilmenite can produce ilmenite or olivine saturated ti enriched liquids 3 lack of either ilmenite or pseudobrookite group ti oxide saturation in melts which are in equilibrium with orthopyroxene and olivine enriches these melts in tio2 4 the assemblage olivine orthopyroxene rutile has a large stability field and is probably replaced by olivine orthopyroxene ilmenite with increasing pressure and temperature and olivine orthopyroxene pseudobrookite group ti oxide with decreasing pressure and increasing temperature 5 lunar source regions nominally saturated in olivine orthopyroxene and pseudobrookite group ti oxide or ilmenite may produce the range of tio2 content in the lunar pristine glasses which apparently cannot be derived by partial melting of model late stage lunar magma ocean oxide silicate assemblages or equivalent bulk compositions

dissolved gases in the milk river aquifer alberta canada abstract geochemical relations between the noble gases 40 ar 36 ar ratio n 2 and ch 4 contents of groundwaters from the milk river aquifer albert canada have been investigated the ch 4 contents for many of the groundwaters are several times their n 2 contents and cause degassing to occur as the hydrostatic pressure decreases during their ascent in the wells recharge temperatures derived for those groundwaters that were not degassed indicate that the youngest groundwaters were recharged under cooler climatic conditions than prevailed during earlier recharge this conclusion is supported by the stable isotope compositions of the groundwater the 4 he concentration in the groundwater varies with depth according to the theoretical concentration depth profile for accumulated radiogenic 4 he in the aquifer and its adjacent shales the corresponding flux of 4 he to the atmosphere is 4 he production rate excess radiogenic 40 ar is associated with ch 4 and both gases originated within the adjacent shales the ch 4 is biogenic and was produced in an aqueous environment which ranged from marine to freshwater as the connate fluids in these marine shales were replaced the degassing process has been modelled to explain the residual dissolved gas contents of the groundwater and to show that the ch 4 n 2 ratio in situ was 12

estimating groundwater age in the cambrian ordovician aquifer in iowa implications for biofuel production and other water uses deep confined water from the cambrian ordovician c o aquifer is being increasingly used for ethanol production in iowa in this study we used isotopic age dating to estimate the age of groundwater in the aquifer and assess how groundwater use for all purposes including ethanol production may be affecting the long term sustainability of the aquifer eight municipal wells located across the extent of the aquifer in iowa were sampled for major and minor ions stable isotopes 18o and d and the radioactive isotope 36cl multiple lines of evidence from this study suggest that groundwater in the c o aquifer is older than 10 000 years with results from 36cl analyses suggesting groundwater travel times in the aquifer ranging from approximately 70 000 to nearly 180 000 years old from northern to central iowa our study suggests that pumping from the c o aquifer for all uses including ethanol production is extracting old groundwater from the aquifer to mitigate long term impacts we recommend that expansion of new ethanol production should be based on accessibility of sustainable groundwater resources rather than siting facilities where deep groundwater reserves are needed for production

control of 36cl production in carbonaceous shales by phosphate minerals abstract when using 36cl to date very old groundwater in regional aquifer systems knowledge of the subsurface 36cl input into the aquifer system is essential although 36cl can be produced through nuclear reactions in the subsurface in many situations the input of 36cl into sedimentary aquifer systems by this avenue of production can be neglected this is a valid assumption when investigating long flowpath groundwater systems composed of sandstones limestones and shales of typical composition these rock types are not sufficiently enriched in radioactive elements to produce significant 36cl in the deep subsurface carbonaceous shales on the other hand can concentrate the radioactive elements necessary to produce significant 36cl in the deep subsurface chlorine 36 ratios 36cl cl for a suite of late devonian and pennsylvanian carbonaceous shales were calculated from bulk rock chemistry as well as measured using accelerator mass spectrometry the poor agreement between calculated and measured ratios is the result of the assumption of chemical homogeneity used by the calculation algorithm an assumption that was not satisfied by the carbonaceous shales in these shales organic matter clay minerals and accessory minerals are heterogeneously distributed and are physically distinct on a micron order scale although organic matter and clay minerals constitute the overwhelming bulk of the shales it is the phosphate minerals that are most important in enhancing and suppressing 36cl production minerals such as apatite and carbonate apatite francolite by including uranium rare earth elements rees and halogens have an important impact on both neutron production and thermal neutron absorption by incorporating both uranium and fluorine phosphate minerals act as neutron production centers in the shale increasing the probability of 36cl production by incorporating rees and chlorine phosphate minerals also act to shield 35cl from the thermal neutron flux effectively suppressing the production of 36cl to reconcile the measured 36cl ratios with the ratios calculated assuming chemical homogeneity the shales were artificially split into three fractions organic clay mineral and phosphate mineral neutron production was calculated separately for each fraction and the calculation results demonstrated that the phosphate fraction exerted much more control on the 36cl ratio than the organic or clay mineral fractions by varying the uranium and chlorine contents in the phosphate fraction a new heterogeneous 36cl ratio was calculated that agreed with the measured ratio for the overwhelming majority of the carbonaceous shales when using rock chemistry to calculate the 36cl ratio rock types that show mineralogical heterogeneity on a micron scale can be divided into bulk fractions and accessory fractions for separate calculations of neutron production and neutron absorption in this manner a more accurate heterogeneous 36cl ratio can be calculated for the rock as a whole

groundwater dating by estimation of groundwater flow velocity and dissolved 4he accumulation rate calibrated by 36cl in the great artesian basin australia abstract we tested two methods for dating groundwaters that cannot be reliably measured by 36cl dating alone one based on groundwater flow velocity plus distance along a flow path and the other based on 4he accumulation rates calibrated with 36cl dates we sampled groundwaters along six inferred regional groundwater flow paths in the great artesian basin gab of australia we selected three groundwater paths where the decrease in 36cl was largely controlled by cosmogenic 36cl radioactive decay without a significant increase in chloride concentration the extrapolated groundwater velocities were 0 133 0 018 m y to 0 433 0 140 m y the estimated residence time of 1 06 106 y at the discharge area around lake eyre was comparable to the estimate of 1 2 2 106 y in previous studies on the other hand our estimated 4he accumulation rates for the selected three groundwater flow paths 1 85 0 31 10 11 to 1 51 0 63 10 10 ccstp cm3 y were approximately 2 15 times lower than previously reported rates for the central gab our estimated rate of 1 51 10 10 ccstp cm3 y 1 in the western gab is compatible with previous estimates based on 81kr ages the groundwater residence time estimated from the 4he accumulation rate was approximately 7 105 y near the discharge area at lake eyre finally both estimations were mutually compatible with a 30 error