nucleation dominated crystallization of forsterite in the ubehebe peak contact aureole california the morphology and number of forsterite crystals in the ubehebe peak california contact aureole vary systematically as a function of metamorphic grade from their first appearance to as close as 150 m from the intrusive contact forsterite crystals are large 5 20 mm and have a tabular habit a c b in contrast forsterite near the contact is equigranular and much smaller 1 mm in diameter the number of crystals per mole of forsterite increases from 3 5 104 at the forsterite in isograd to more than 1 5 108 near the contact this trend is interpreted to result from an increase in the ratio of nucleation rates with respect to growth rates with proximity to the intrusion the change in morphology from tabular to equigranular is explained by kinetic surface roughening the nucleation and growth information gained from this study highlights the important role of nucleation kinetics in the crystallization of forsterite at the ubehebe peak aureole

ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

the governing dynamics of the secondary eyewall formation of typhoon sinlaku 2008 abstractthrough successful convection permitting simulations of typhoon sinlaku 2008 using a high resolution nonhydrostatic model this study examines the role of peripheral convection in the storm s secondary eyewall formation sef and its eyewall replacement cycle erc the study demonstrates that before sef the simulated storm intensifies via an expansion of the tangential winds and an increase in the boundary layer inflow which are accompanied by peripheral convective cells outside the primary eyewall these convective cells which initially formed in the outer rainbands under favorable environmental conditions and move in an inward spiral play a crucial role in the formation of the secondary eyewall it is hypothesized that sef and erc ultimately arise from the convective heating released from the inward moving rainbands the balanced response in the transverse circulation and the unbalanced dynamics in the atmospheric boundary layer along with the positive feedback between these processes

concentric eyewall formation in typhoon sinlaku 2008 part iii horizontal momentum budget analyses abstract this is a follow up work to two prior studies examining secondary eyewall formation sef in typhoon sinlaku 2008 this study shows that in the sef region the majority of the elevated

ion microprobe evidence for the mechanisms of stable isotope retrogression in high grade metamorphic rocks retrograde interdiffusion is widely proposed as the dominant factor in producing the stable isotopic fractionation among minerals in slowly cooled igneous and metamorphic rocks mineral zonation consistent with interdiffusion of stable isotopes has never been directly observed however leaving doubt as to the mechanism responsible for the bulk mineral isotopic compositions commonly measured ion microprobe analyses of oxygen isotope ratios in magnetite were combined with conventional bulk mineral analyses and diffusion modeling to document the relationship between mineral zonation and the mechanism of retrogression inferred from bulk mineral data two samples of magnetitebearing quartzo feldspathic lyon mountain gneiss from the adirondack mountains n y were studied in detail conventional stable isotope analysis of both samples indicates that isotope thermometers are discordant and were reset by as much as 200 c from the estimated peak temperature of 750 c the relative order of apparent temperatures recorded by various thermometers differs between the two samples however with t qtz fsp t mt qtz and t mt fsp in one sample and t qtz fsp t mt qtz and t mt fsp in the other diffusion modeling using the fast grain boundary model shows that the former pattern of apparent temperatures is consistent with closed system interdiffusion during cooling whereas the latter is not the modeling predicts that 0 5 mm diameter magnetite grains common to this rock type will contain isotopic zonation of 1 rims lower in 18 o than cores and that the cores of smaller 0 1 mm grains will be similarly lower than to the cores of large 0 5 mm grains ion microprobe analysis reveals that the zoning patterns of magnetite grains from the first sample contain clear core to rim zonation in multiple grains core rim 1 1 0 4 and predicted grain size vs core composition variations consistent with diffusion controlled resetting of bulk mineral fractionations in contrast the second sample shows irregular inter and intra granular variations over an 8 range consistent with open system alteration these results provide direct documentation of the importance of interdiffusion in affecting stable isotope distributions in slowly cooled rocks the correlations of bulk mineral resetting with zonation show that bulk mineral data when interpreted with detailed modeling can be used to determinate what processes controlling retrogression

the direction of fluid flow during contact metamorphism of siliceous carbonate rocks new data for the monzoni and predazzo aureoles northern italy and a global review periclase formed in siliceous dolomitic marbles during contact metamorphism in the monzoni and predazzo aureoles the dolomites northern italy by infiltration of the carbonate rocks by chemically reactive h2o rich fluids at 500 bar and 565 710 c the spatial distribution of periclase and oxygen isotope compositions is consistent with reactive fluid flow that was primarily vertical and upward in both aureoles with time integrated flux 5 000 and 300 mol fluid cm2 rock in the monzoni and predazzo aureoles respectively the new results for monzoni and predazzo are considered along with published studies of 13 other aureoles to draw general conclusions about the direction amount and controls on the geometry of reactive fluid flow during contact metamorphism of siliceous carbonate rocks flow in 12 aureoles was primarily vertically upward with and without a horizontal component directed away from the pluton fluid flow in two of the other three was primarily horizontal directed from the pluton into the aureole the direction of flow in the remaining aureole is uncertain earlier suggestions that fluid flow is often horizontal directed toward the pluton are likely explained by an erroneous assumption that widespread coexisting mineral reactants and products represent arrested prograde decarbonation reactions with the exception of three samples from one aureole time integrated fluid flux was in the range 102 104 mol cm2 both the amount and direction of fluid flow are consistent with hydrodynamic models of contact metamorphism the orientation of bedding and lithologic contacts appears to be the principal control over whether fluid flow was either primarily vertical or horizontal other pre metamorphic structures including dikes faults fold hinges and fracture zones served to channel fluid flow as well

assessment of grain scale homogeneity and equilibration of carbon and oxygen isotope compositions of minerals in carbonate bearing metamorphic rocks by ion microprobe abstract nineteen samples of metamorphosed carbonate bearing rocks were analyzed for carbon and oxygen isotope ratios by ion microprobe with a 5 15 m spot three from a regional terrain and 16 from five different contact aureoles contact metamorphic rocks further represent four groups calc silicate marble and hornfels 6 brucite marble 2 samples that contain a reaction front 4 and samples with a pervasive distribution of reactants and products of a decarbonation reaction 4 the average spot to spot reproducibility of standard calcite analyses is 0 37 2 standard deviations sd for 18 o and 0 71 for 13 c ten or more measurements of a mineral in a sample that has uniform isotope composition within error of measurement can routinely return a weighted mean with a 95 confidence interval of 0 09 0 16 for 18 o and 0 10 0 29 for 13 c using a difference of 6sd as the criterion only four of 19 analyzed samples exhibit significant intracrystalline and or intercrystalline inhomogeneity in 13 c at the 100 500 m scale with differences within individual grains up to 3 7 measurements are consistent with carbon isotope exchange equilibrium between calcite and dolomite in five of six analyzed samples at the same scale because of relatively slow carbon isotope diffusion in calcite and dolomite differences in 13 c can survive intracrystalline homogenization by diffusion during cooling after peak metamorphism and likely represent the effects of prograde decarbonation and infiltration all but 2 of 11 analyzed samples exhibit intracrystalline differences in 18 o up to 9 4 intercrystalline inhomogeneity in 18 o up to 12 5 and or disequilibrium oxygen isotope fractionations among calcite dolomite calcite quartz and calcite forsterite pairs at the 100 500 m scale inhomogeneities in 18 o and 13 c are poorly correlated with only a single mineral dolomite in a single sample exhibiting both because of relatively rapid oxygen isotope diffusion in calcite intracrystalline inhomogeneities in 18 o likely represent partial equilibration between calcite and fluid during retrograde metamorphism calcite is in oxygen isotope exchange equilibrium with forsterite in one of four analyzed samples in equilibrium with dolomite in none of six analyzed samples and in equilibrium with quartz in neither of two analyzed samples there are no samples of contact metamorphic rock with analyzed reactants and products of an arrested metamorphic reaction that are in oxygen isotope equilibrium with each other the degree of departure from equilibrium in analyzed samples is variable and is often related at least in part to alteration of 18 o of calcite during retrograde fluid rock reaction in situ sub grain scale carbon and oxygen isotope analyses of minerals are advisable in the common applications of stable isotope geochemistry to metamorphic petrology correlation of sub mm scale stable isotope data with imaging will lead to improved understanding of reaction kinetics reactive fluid flow and thermal histories during metamorphism

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

optically continuous silcrete quartz cements of the st peter sandstone high precision oxygen isotope analysis by ion microprobe a detailed oxygen isotope study of detrital quartz and authigenic quartz overgrowths from shallowly buried 1 km quartz arenites of the st peter sandstone in sw wisconsin constrains temperature and fluid sources during diagenesis quartz overgrowths are syntaxial optically continuous and show complex luminescent zonation by cathodoluminescence detrital quartz grains were separated from 53 rocks and analyzed for oxygen isotope ratio by laser fluorination resulting

the concentric eyewall cycle of hurricane gilbert abstract hurricane gilbert of 1988 formed an outer eyewall as it intensified rapidly toward a record minimum pressure of 888 hpa in the western caribbean the outer eyewall strengthened and contracted while the inner eyewall showed some signs of weakening before landfall on the yucatan peninsula remarkably both eyewalls survived passage over land but the storm was much weaker when it entered the gulf of mexico although the primary cause of weakening was passage over land the effect of the contracting outer eyewall may have contributed later the outer eyewall completely replaced the inner eyewall subsequently it contracted steadily but slowly as gilbert maintained nearly constant intensity over the cooler waters of the gulf before final landfall on the mainland of mexico

crystal size distribution of periclase in contact metamorphic dolomite marbles from the southern adamello massif italy crystal size distributions csd of periclase in contact metamorphic dolomite marbles are presented for two profiles near the cima uzza summit in the southern adamello massif italy the database was combined with geochemical and petrological information to deduce the controls on the periclase forming reaction the contact metamorphic dolomite marbles are exposed at the contact of mafic intrusive rocks and are partially surrounded by them brucite is retrograde and pseudomorphs spherical periclase crystals prograde periclase growth is the consequence of limited infiltration of waterrich fluid at t near 6058c stable isotope data show depletion in 13 c and 18 o over a narrow region 40 cm near the magmatic contact whereas the periclase forming reaction front extends up to 4 m from the contact csd analyses along the two profiles show that the median grain size of the periclase crystals does not change but that there is a progressively greater distribution of grain sizes including a greater proportion of larger grains with increasing distance from the contact a qualitative model based on the textural and geochemical data attributes these variations in grain size to changing reaction affinities along a kinetically dispersed infiltration front this study highlights the need to invoke disequilibrium processes for metamorphic mineral growth and expands the use of csds to systems of mineral formation driven by fluid infiltration

prograde and retrograde fluid flow during contact metamorphism of siliceous carbonate rocks from the ballachulish aureole scotland siliceous dolomites and limestones contain abundant retrograde minerals produced by hydration carbonation reactions as the aureole cooled marbles that contained periclase at the peak of metamorphism bear secondary brucite dolomite and serpentine forsterite dolomite marbles have retrograde tremolite and serpentine wollastonite limestones contain secondary calcite and quartz and wollastonite free limestones have retrograde tremolite secondary tremolite never appears in marbles where brucite has replaced periclase or in wollastonite bearing limestones a model for infiltration of siliceous carbonates by co2 h2o fluid that assumes a vertical upwardly directed flow b fluid flux proportional to cooling rate and c flow and reaction under conditions of local equilibrium between peak temperatures and 400 c reproduces the modes of altered carbonate rocks observed reaction textures and the incompatibility between tremolite and brucite and between tremolite and wollastonite except for samples from a dolomite xenolith retrograde time integrated flux recorded by reaction progress is on the order of 1000 mol fluid cm2 rock local focusing of flow near the contact is indicated by samples from the xenolith that record values an order of magnitude greater formation of periclase forsterite and wollastonite at the peak of metamorphism also required infiltration with prograde time integrated flux approximately 100 1000 mol cm2 the comparatively small values of prograde and retrograde time integrated flux are consistent with lack of stable isotope alteration of the carbonates and with the success of conductive thermal models in reproducing peak metamorphic temperatures recorded by mineral equilibria although isobaric univariant assemblages are ubiquitous in the carbonates most formed during retrograde metamorphism isobaric univariant assemblages observed in metacarbonates from contact aureoles may not record physical conditions at the peak of metamorphism as is commonly assumed

mechanisms of oxygen isotopic exchange and isotopic evolution of 18 o 16 o depleted periclase zone marbles in the alta aureole utah insights from ion microprobe analysis of calcite oxygen isotope ratios have been measured by ion microprobe and millimeter scale dental drill along detailed sampling traverses across the boundary between periclase bearing 18o 11 8 and periclase free 18o 17 2 marble layers in the periclase per zone of the alta stock aureole utah these data define a steep coherent gradient in 18o that is displaced a short distance 4 cm into the periclase free cal fo layer sem and ion microprobe analyses show two isotopically and texturally distinct types of calcite at the grain scale clear well polished calcite grains are isotopically homogeneous within analytical uncertainty 0 27 2sd more poorly polished pitted texturally retrograde turbid looking calcite has lower and more variable 18o values and replaces clear calcite along fractures cleavage traces or grain boundaries despite significant lowering of the 18o values in calcite throughout both layers during prograde metamorphism ion microprobe analyses indicate that individual clear calcite grains are now isotopically homogeneous across the entire gradient in 18o diffusion calculations indicate that conservative time scales required for isotopic homogenization of calcite grains by volume diffusion 30 000 62 000 years at 575 600 c exceed significantly the timescale 1 250 years estimated for the prograde development of the 18o gradient at the boundary between these two marble layers the ion microprobe data and these diffusion calculations suggest instead that surface reaction mechanisms accompanying recrystallization are responsible for the observed oxygen isotope homogeneity of these calcite grains thus the ion microprobe data are consistent with the formation of calcite in oxygen isotope exchange equilibrium with infiltrating fluid during prograde reaction and recrystallization

oxygen isotope zoning in garnet oxygen isotope zoning was examined within garnet with the use of the stable isotope laser probe four metamorphic garnets from the regional metamorphic terrane in vermont and the skarn deposit at carr fork utah were examined and were found to be concentrically zoned in 18o values the largest variations in 18o values were observed in the regional metamorphic garnets where 18o values change by 3 per mil from core to rim these oxygen isotope zoning profiles reflect the changes in the 18o values of the rocks during garnet growth which are caused by infiltration of fluids and by dehydration reactions during metamorphism

fluid flow along microfractures in calcite from a marble from east antarctica evidence from gigantic 21 oxygen isotopic zonation across a 1 2 mm wide domain a calcite crystal from a granulite facies marble from east antarctica exhibits microscale oxygen isotope heterogeneity that has been enhanced by channelized fluid flow the oxygen isotope compositions range over 21 a gigantic zonation calcite along a boundary with phlogopite has an average 18 o value of 5 along a profile that extends about 700 m into the grain the oxygen isotope composition remains constant indicating equilibrium with source fluids of meteoric origin analyses of a transect away from the phlogopite show the 18 o values rising to 16 the corresponding carbon isotope variation is only about 0 6 isotope heterogeneity is observed mainly in a phlogopite rich zone where the 18 o values are lower 13 5 than those away from the zone 17 1 we inferred that preferential microfracturing and hydrothermal fluid flow were the causes of the 18 o distribution the constant values of both 18 o and 13 c for the distance of 700 m from the grain boundary suggest a solution reprecipitation mechanism whereas the smoothly increasing 18 o and decreasing 13 c values farther along the profile indicate a diffusion controlled isotope exchange between the reprecipitated calcite and the original grain core our results provide important evidence for the mechanism of isotope exchange between fluids and minerals and have major implications for microfracture controlled fluid flow processes in the earth9s crust

ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites diffusive exchange as a guide to cooling history ion microprobe analysis of magnetites from the adirondack mountains ny yields oxygen isotope ratios with spatial resolution of 2 8 m and precision in the range of 1 1 sigma these analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of 18o at this scale high precision micro analyses of this sort will permit wide ranging new applications in stable isotope geochemistry the analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite magnetites are near to fe3o4 in composition and optically and chemically homogeneous a combination of ion probe plus conventional brf5 analysis shows that individual grains are homogeneous with 18o 8 9 1 smow from the core to near the rim of 0 1 1 2 mm diameter grains depth profiling into crystal growth faces of magnetites shows that rims are 9 depleted in 18o these low 18o values increase in smooth gradients across the outer 10 m of magnetite rims in contact with calcite these are the sharpest intracrystalline gradients measured to date in geological materials this discovery is confirmed by bulk analysis of 150 350 m diameter magnetites which average 1 2 lower in 18o than coarse magnetites due to low 18o rims conventional analysis of coexisting calcite yields 18o 18 19 suggesting that bulk 18o cc mt 9 3 and yielding an apparent equilibration temperature of 525 c over 200 c below the temperature of regional metamorphism consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories the data for oxygen in calcite under hydrothermal conditions at high p h2o indicates that diffusion is faster in magnetite and modelling of the low 18o rims on magnetite would suggest that the adirondacks experienced slow cooling after grenville metamorphism followed by a brief period of rapid cooling possibly related to uplift conversely the data for calcite at low p h2o show slower oxygen diffusion than in magnetite modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals suggesting that the low 18o rims form by exchange with late low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets in either case the ion microprobe results indicate that two distinct events are recorded in the post metamorphic exchange history of these magnetites recognition of these events is only possible through microanalysis and has important implications for geothermometry

timescales and mechanisms of fluid infiltration in a marble an ion microprobe study using a recently developed ion microprobe technique a detailed oxygen isotope map of calcite grains in a coarse grained marble has been constructed supported by trace element mn sr fe analysis and cathodoluminescence cl imaging in order to constrain scales of oxygen isotope equilibrium timescales and mechanisms of metamorphic fluid infiltration and fluid sources and pathways results are compared with a previous study of this sample wada 1988 carried out using a cryo microtome technique and conventional oxygen isotope analysis the marble from the high temperature low pressure hida metamorphic belt in north central japan underwent granulite facies followed by amphibolite facies metamorphic events the latter associated with regional granite intrusion the cl imaging indicates two types of calcite a yellow luminescing ylc and a purple luminescing plc variety the ylc which occupies grain boundaries fractures replacement patches and most of the abundant deformation twin lamellae post dates the dominant plc calcite and maps out fluid pathways systematic relationships were established between oxygen isotope and trace element composition calcite type and texture based on 74 18o 16o and 17 trace element analyses with 20 30 m spatial resolution the ylc is enriched in mn and fe and depleted in 18o and sr compared to plc and is much more 18o depleted than is indicated from conventional analyses results are interpreted to indicate infiltration of 18o depleted metamorphic or magmatic fluid initial 18o 9 10 5 along grain boundaries fractures and deformation twin lamellae depleting calcite grains in sr and enriching them in mn and fe the sample is characterised by gross isotopic and elemental disequilibrium with important implications for the application of chromatographic theory to constrain fluid fluxes in metacarbonate rocks

the role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the hida metamorphic terrain central japan display typical metamorphic fluid enhanced isotopic zonations isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion enhanced isotopic exchange may control these profiles carbon and oxygen isotopic behaviour in grain boundaries is remarkably different oxygen isotopic troughs 18o depleted rims around the calcite grain boundaries are widely observed in this contact aureole demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite in contrast no difference is observed in carbon isotopic profiles obtained from grain cores and rims there is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation carbon chemical species such as co2 and co3 ions in metamorphic fluid migrate mainly through lattice diffusion the carbon and oxygen isotope profiles may be modelled by diffusion into a semi infinite medium empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes and oxygen grain boundary diffusion is ten times faster than oxygen lattice diffusion oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer from the stability of wollastonite and the attainment of oxygen isotopic equilibrium we suggest that diffusion of oxygen occurred through an aqueous fluid phase the timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0 76 106 years using the experimentally determined diffusion constant

metastable prograde mineral reactions in contact aureoles extrapolation of reaction paths and rates of metamorphic mineral growth from experimental to natural systems is complicated by a number of factors many of these factors are difficult to evaluate for natural systems a combination of textural modeling and stable isotope analysis allows for a distinction between several possible reaction paths for olivine growth in a siliceous dolomite contact aureole it is suggested that olivine forms directly from dolomite and quartz the formation of olivine from this metastable reaction implies metamorphic crystallization far from equilibrium stable and metastable reaction paths predict the textures observed calcite haloes around bladed olivine crystals well it is possible to discriminate between individual reaction paths only on the basis of the oxygen isotope compositions of the minerals involved products were found to be in stable isotope equilibrium but in disequilibrium with the reactants only the metastable overall reaction dolomite quartz olivine calcite co 2 produces no dolomite by local reactions and hence agrees with the oxygen isotope data thus significant mineral growth occurred far from equilibrium with respect to the thermodynamically stable reactions of the system this amazing finding implies that metamorphism of contact aureoles has to be reinterpreted in a more complex dynamic fashion involving metastable reactions and metastable equilibria as well the spatial distribution of metamorphic mineral assemblages in a contact aureole cannot be interpreted as a proxy for the temporal evolution of a single rock specimen because each rock undergoes a different reaction path depending on temperature heating rate and fluid infiltration rate

a mineral equilibria study of the hydrothermal alteration in mafic greenschist facies rocks at kalgoorlie western australia the influx of a h2o co2 dominated fluid into actinolite bearing metabasic rocks during greenschist facies metamorphism in the kalgoorlie area of western australia resulted in a zoned alteration halo around inferred fluid conduits that contain gold mineralisation the alteration halo is divided into two outer zones the chlorite zone and the carbonate zone and an inner pyrite zone adjacent to the inferred fluid conduits reaction between the fluid and the protolith resulted in the breakdown of actinolite and the development of chlorite dolomite calcite and siderite in addition rocks in the pyrite zone developed muscovite bearing assemblages as a consequence of the introduction of potassium by the fluid mineral equilibria calculations undertaken using the computer software thermocalc in the model system na2o cao k2o feo mgo al2o3 sio2 h2o co2 show that mineral assemblages in the outer zones of the alteration halo are consistent with equilibrium of the protoliths with a fluid of composition xco2 co2 co2 h2o 0 1 0 25 for temperatures of 315 320 c the inner zone of the alteration halo reflect equilibrium with a fluid of composition xco2 0 25 fluid rock buffering calculations show that the alteration halo is consistent with interaction with a single fluid composition and that the zoned structure of the halo reflects the volume of this fluid with which the rocks reacted this fluid is likely to have also been the one responsible for the gold mineralisation at kalgoorlie

ion microprobe study of marble from naxos greece grain scale fluid pathways and stable isotope equilibration during metamorphism in metamorphic terranes modification of the stable isotope compositions of marbles by fluid infiltration has been extensively modeled to try to constrain both the magnitudes and time scales of metamorphic fluid fluxes we have made a study of key localities on the aegean island of naxos greece in which we combined textural observations with micro scale trace element and stable isotope analysis to test the assumptions upon which modeling of metamorphic fluid flow is based and to identify fluid transport mechanisms integration of ion microprobe analyses of 18 o 16 o 13 c 12 c mn and fe with detailed cathodoluminescence imaging provides evidence that water rich fluids were channeled along cracks and grain boundaries within marble with limited equilibration between the fluid and rock very low values of 18 o smow down to 2 along grain boundaries indicate a meteoric source for fluids rather than a metamorphic source in contrast to previous studies in this example the simplifying assumptions made previously in chromatographic theory to constrain metamorphic fluid fluxes time scales and porosities from bulk isotope data are incorrect by making micro scale measurements we can determine infiltration mechanisms and distinguish separate fluid flow events these observations and measurements provide a basis for constructing more realistic models of metamorphic fluid flow

ion microprobe analysis of oxygen isotope ratios in quartz from skye granite healed micro cracks fluid flow and hydrothermal exchange quartz grains in hydrothermally altered granites from the isle of skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 m scale ion microprobe analysis of one grain shows a gradient of 13 over 400 m and a greater range in 18o than all quartz previously analyzed on the isle of skye other crystals from the same outcrop are homogeneous digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable the ion probe analysis correlates low 18o values on a micro scale to one set of healed cracks thus quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures in contrast to more reactive feldspar that appears to exchange from the grain boundary inward macroscopic models of isotope exchange are not realistic for these rocks the flow of hydrothermal fluids was heterogeneous anisotropic and crack controlled

high precision sims oxygen three isotope study of chondrules in ll3 chondrites role of ambient gas during chondrule formation we report high precision sims oxygen three isotope analyses of 36 chondrules from some of the least equilibrated ll3 chondrites and find systematic variations in oxygen isotope ratios with chondrule types feo poor type i chondrules generally plot along a mass dependent fractionation line d 17 o 0 7 with d 18 o values lower in olivine rich ia than pyroxenerich ib chondrules data from feo rich type ii chondrules show a limited range of d 18 o and d 17 o values at d 18 o 4 5 d 17 o 2 9 and d 17 o 0 5 which is slightly 16 o enriched relative to bulk ll chondrites d 17 o 1 3 data from four chondrules show 16 o rich oxygen isotope ratios that plot near the ccam carbonaceous chondrite anhydrous mineral line glass analyses in selected chondrules are systematically higher than co existing minerals in both d 18 o and d 17 o values whereas high ca pyroxene data in the same chondrule are similar to those in olivine and pyroxene phenocrysts our results suggest that the ll chondrite chondrule forming region contained two kinds of solid precursors 1 16 o poor precursors with d 17 o 1 6 and 2 16 o rich solid precursors derived from the same oxygen isotope reservoir as carbonaceous chondrites oxygen isotopes exhibited open system behavior during chondrule formation and the interaction between the solid and ambient gas might occur as described in the following model significant evaporation and recondensation of solid precursors caused a large mass dependent fractionation due to either kinetic or equilibrium isotope exchange between gas and solid to form type ia chondrules with higher bulk mg si ratios type ii chondrules formed under elevated dust gas ratios and with water ice in the precursors in which the ambient h2o gas homogenized chondrule melts by isotope exchange low temperature oxygen isotope exchange may have occurred between chondrule glasses and aqueous fluids with high d 17 o 5 in ll the parent body according to our model oxygen isotope ratios of chondrules were strongly influenced by the local solid precursors in the proto planetary disk and the ambient gas during chondrule melting events 2010 elsevier ltd all rights reserved

convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 abstracteyewall replacements in mature tropical cyclones usually cause intensity fluctuations one reason for eyewall replacements remaining a forecasting challenge is the lack of understanding of how secondary eyewalls form this study uses high resolution full physics model forecast fields of hurricanes katrina and rita 2005 to better understand potential vorticity pv generation in the rainbands and the role that convectively generated pv played in the formation of a secondary eyewall in hurricane rita previous studies have focused on dynamic processes in the inner core and or the effects of certain specified pv distributions however the initial development of a concentric pv ring in the rainband region has not been fully addressed katrina and rita were extensively observed by three research aircraft during the hurricane rainband and intensity change experiment rainex which was designed to study the interaction of the rainbands and the inner core rita developed a secondary eyewall and went

steep oxygen isotope gradients at marble metagranite contacts in the northwest adirondack mountains new york usa products of fluid hosted diffusion steep gradients in oxygen isotope ratios are recorded from two contacts between grenville marbles calcite 18o 21 24 and metamorphosed granitic intrusives whole rock 18o 11 12 in the northwest adirondacks oxygen and carbon isotope fractionations between coexisting minerals in the marbles and the metagranites are consistent with isotopic equilibration at peak metamorphic temperatures the 18o profiles are sigmoidal with inflection points at the contacts and are developed over 5 6 m quantitative fluid infiltration diffusion modeling suggests that the isotopic gradients are best explained as the result of fluid hosted diffusion for porosities of 10 3 to 10 6 the profiles could have formed in 103 107 years via an interconnected grain boundary fluid the granites were probably emplaced at shallow crustal levels prior to the regional grenville metamorphism and isotopic exchange is most likely to have occurred at that time contact metamorphism at these localities involved devolatilisation of the marbles and the time estimates may reflect the periods over which fluid producing reactions took place and an enhanced porosity was maintained in the marbles there is a progressive increase in the percentage of diopside and k feldspar at the expense of phlogopite and tremolite towards the metagranites these mineralogical changes probably occurred due to the temperature increase associated with granite intrusion and diffusion of h2o from the granite the two localities lie on either side of the regional metamorphic amphibolite to granulite facies transition the preservation of isotopic profiles formed during contact metamorphism suggests that there was little pervasive fluid flow at this crustal level during the regional metamorphism or at any time thereafter steep isotopic gradients are present at orthogneiss marble contacts elsewhere in the adirondacks suggesting that this conclusion may be generally applicable to this terrain

tests of an ensemble kalman filter for mesoscale and regional scale data assimilation part i perfect model experiments abstract through observing system simulation experiments this two part study exploits the potential of using the ensemble kalman filter enkf for mesoscale and regional scale data assimilation part i focuses on the performance of the enkf under the perfect model assumption in which the truth simulation is produced with the same model and same initial uncertainties as those of the ensemble while part ii explores the impacts of model error and ensemble initiation on the filter performance in this first part the enkf is implemented in a nonhydrostatic mesoscale model the fifth generation pennsylvania state university ncar mesoscale model mm5 to assimilate simulated sounding and surface observations derived from simulations of the surprise snowstorm of january 2000 this is an explosive east coast cyclogenesis event with strong error growth at all scales as a result of interactions between convective meso and subsynoptic scale dynamics it is found that the enkf is very effective in keeping th

secondary eyewall formation in wrf simulations of hurricanes rita and katrina 2005 1 an analysis is presented of two high resolution hurricane simulations of katrina and rita 2005 that exhibited secondary eyewall formation sef the results support the notion of vortex rossby waves vrws having an important role in sef and suggest that vrw activity is a defining aspect of the moat sef occurs at a radius of 65 80 km in katrina rita close to the hypothesized stagnation radius of vrws vrw activity appears to be the result of eye eyewall mixing events themselves a product of the release of barotropic instability the convection in the radial region that becomes the moat is mainly in the form of vrws propagating radially outward from the primary eyewall until the negative radial gradient of potential vorticity is no longer conducive for their propagation these convectively coupled waves originating and being expelled from the eyewall are rotation dominated and have the coherency necessary to survive their passage through the strain dominated region outside the eyewall

fluid flow and diffusion in the waterville limestone south central maine constraints from strontium oxygen and carbon isotope profiles oxygen carbon and strontium isotopic profiles across the margin of the waterville limestone member are used to investigate advective and diffusive transport during metamorphism of the waterville formation in south central maine usa rb sr isotopic systematics were homogenized on the 10 cm hand specimen scale at ages that are within error of the 366 6 ma rb sr whole rock age of the syn metamorphic hallowell pluton this is consistent with a plutonic heat source for this low pressure andalusite and sillimanite grade acadian metamorphic terrane advective displacements of all three isotope profiles at the garnet grade blue rock quarry indicate fluid flow to the east into the limestone and the oxygen isotope profile implies a time integrated fluid flux of 3 2 1 5 m 3 m 2 2 error this cross layer flux is insufficient to cause the observed reaction progress of the muscovite ankerite quartz to biotite anorthite in plagioclase calcite reaction in the 100 m thick waterville limestone member and much of the fluid flow responsible may have been layer parallel the isotope profiles indicate advective diffusive homogenization over distances of 1 5 m 13 c to 6 m 18 o and such homogenization distances are difficult to reconcile with observations of order of magnitude variations in reaction progression the centimetre scale or less it is possible that infiltration occurred during events short lived compared with diffusion that the reactions started at different temperatures dependent on bulk composition or that diffusion of water from layers with less reactants to layers with more reactants was important in driving the biotite producing reaction however variations of fluid composition inferred from the mineral assemblages are apparently inconsistent with diffusion driving reactions progress and models of precursor assemblages do not indicate significant compositional control of the temperature of the first appearance of biotite in the rocks irrespective of the details of flow and diffusive exchange on the centimetre scale the average reaction progress in the waterville limestone member requires significant layer parallel fluid fluxes

evidence for dendritic crystallization of forsterite olivine during contact metamorphism of siliceous dolostones alta stock aureole utah forsterite crystals produced during metamorphism of siliceous dolomites in the alta utah contact aureole were investigated in situ and with crystal separates to constrain their aureole scale textural and morphological variability as the contact is approached forsterite crystals increase in abundance but decrease in average size suggesting greater kinetic influence on forsterite nucleation and growth in the inner aureole crystal morphologies vary widely from dendritic to skeletal to euhedral shapes across both periclase and forsterite zones highly skeletal forms of forsterite preserve crystallographically controlled internal scaffolding reentrants and internal void boundaries scanning electron microscope imaging of texturally more mature forsterite crystals reveals the common occurrence of surface features such as hopper structures ridges and terraces features that have been linked to dendritic crystallization of olivine in igneous rocks near end member forsterite crystals fo99 from the middle to outer forsterite zone exhibit complex cathodoluminescence cl patterns which can be linked to grain scale heterogeneities in the trace elements li b p and ti these grain scale cl zoning patterns can be correlated to crystallographic forms typical of forsterite the textural trends morphological characteristics surface features and cl patterns suggest that euhedral forsterite crystals grew by a process of early dendritic crystallization hopper development and infilling of hopper reentrants these results caution against interpreting all grain scale zoning profiles preserved in metamorphic forsterites as simple core to rim time sequences consideration of the possible role of dendritic crystallization in the development of forsterite morphologies is required to interpret 2 d element or isotope zoning profiles preserved in individual forsterite grains

ion microprobe survey of the grain scale oxygen isotope geochemistry of minerals in metamorphic rocks abstract the oxygen isotope compositions of calcite diopside dolomite forsterite garnet k feldspar kyanite plagioclase quartz and wollastonite were analyzed in suites of contact and regional metamorphic rocks using an ion microprobe spatial resolution was 10 m precision measured as the standard deviation of working standards averaged over the entire project was 0 13 0 18 for three carbonate standards and 0 11 0 12 for two silicate standards a total of 1176 analyses excluding standards were made of 73 minerals in 23 samples both intercrystalline and intracrystalline variability in 18 o is greater in contact than in regional metamorphic rocks of 27 minerals analyzed in contact metamorphosed rocks 70 exhibit statistically significant grain to grain variability in 18 o over areas 1 41 cm 2 with the largest range in silicates and carbonates in a single sample of 7 4 forsterite and 10 6 dolomite of 88 grains analyzed in two or more places in contact metamorphosed rocks 32 exhibit statistically significant intracrystalline variability in 18 o with the largest range in a single silicate and carbonate grain of 3 1 forsterite and 10 1 dolomite in contrast 44 of 45 minerals in regional metamorphic rocks exhibit significant grain to grain variability in 18 o over areas 1 17 cm 2 with the largest range in silicates and carbonates in a single sample of only 1 1 plagioclase and 0 9 calcite only 6 of 144 grains analyzed in two or more places in regional metamorphic rocks exhibit significant intracrystalline variability in 18 o with the largest range in a single silicate and carbonate grain of only 1 5 diopside and 0 7 calcite the difference in intercrystalline and intracrystalline variability in 18 o between contact and region metamorphic rocks is explained by the longer duration and slower reaction rates of regional metamorphism rather than to differences in temperature there is no significant difference in intercrystalline and intracrystalline variability in 18 o in regional metamorphic rocks among samples from the biotite garnet and kyanite zones calcite inclusions in forsterite and calcite and quartz inclusions in garnet either have 18 o that is statistically indistinguishable from 18 o of the same mineral occurring as nearby matrix grains or have statistically significant lower 18 o no reversed isotope fractionations were measured between coexisting mineral pairs minerals in individual samples however exhibit a wide range in the degree to which they attained and preserve oxygen isotope fractionations consistent with metamorphic temperatures recorded by mineral equilibria processes that account for grain scale departures from isotope exchange equilibrium include a overstepping of prograde mineral reactions b growth zoning in low diffusivity minerals c interaction of rocks with fluids at the peak of metamorphism and or during cooling d retrograde mineral reactions and e closed system isotope exchange between coexisting minerals during cooling this study provides new information about 1 the degree to which a variety of textural changes experienced by rocks during metamorphism are associated with changes in 18 o 2 oxygen isotope homogenization at the outcrop scale among contrasting lithologies 3 changes in 18 o with increasing grade of regional metamorphism and 4 time scales of metamorphic process

clouds in tropical cyclones abstract clouds within the inner regions of tropical cyclones are unlike those anywhere else in the atmosphere convective clouds contributing to cyclogenesis have rotational and deep intense updrafts but tend to have relatively weak downdrafts within the eyes of mature tropical cyclones stratus clouds top a boundary layer capped by subsidence an outward sloping eyewall cloud is controlled by adjustment of the vortex toward gradient wind balance which is maintained by a slantwise current transporting boundary layer air upward in a nearly conditionally symmetric neutral state this balance is intermittently upset by buoyancy arising from high moist static energy air entering the base of the eyewall because of the radial influx of low level air from the far environment supergradient wind in the eyewall zone and or small scale intense subvortices the latter contain strong erect updrafts graupel particles and large raindrops produced in the eyewall fall out relatively quickly while ice splinters left

microscale isotopic zoning in calcite and graphite crystals in marble chemical and isotopic zoning in minerals is a clear indication of disequilibrium and provides an important key for elucidating metamorphic processes here i present carbon and oxygen isotope data from calcite and graphite crystals in a marble from the hida metamorphic belt central japan showing isotopic zoning within individual crystals within 100 m of the calcite graphite grain boundary the 13c contents gradually decrease from the constant values of the crystal core to values 1 lower 18o contents in calcite decrease by up to 7 within 200 300 jim of the boundary at a calcite calcite grain boundary similar patterns of 13c and 18o depletions were found whereas the 13c contents of graphites remained constant except in a narrow zone at the calcite contact these isotopic patterns are interpreted as reflecting isotopic exchange with metamorphic fluids that were relatively depleted in 13c and 18o these results strongly suggest that the most accurate geothermometry will be obtained if only the cores of crystals are used and that isotopic zoning may provide another way to elucidate polymetamorphic processes

metasomatism and graphite formation at a lithological interface in malaspina alpine corsica france multiple pieces of geologic evidence suggest that interfaces between contrasted lithologies exert a strong control on the fate of volatiles in subduction zones here we present results from a contact between serpentinites and sediments located in corsica and metamorphosed in the blueschist facies during the alpine orogeny it was shown previously that carbonates in the sediments have been reduced to graphitic carbonaceous material within a 5 10 cm thick reaction zone at the contact with serpentinites in an effort to investigate the mechanisms governing this unusual process bulk rock geochemical analyses incorporating a statistical analysis of compositional data are presented observations show that the fate of c was decoupled from that of other elements such as o h and large ion lithophile elements e g k sr ba as that were extensively leached from the reaction zone notably na is strongly enriched in the reaction zone and structurally linked to pectolite reducing conditions manifested by the depletion of o in the reaction zone compared to the bulk metasediment were likely maintained by the presence of fe ii in the serpentinite moreover thermodynamic calculations show that the low solubility of carbon in coh fluids at high pressure and low temperature conditions was the main driver for graphite precipitation synchronously with carbonate destabilization this may have been kinetically favored by the presence of already existing graphitized carbonaceous material and phengite in the metasediment limited lateral flow might have contributed as well to the geochemical and petrological patterns observed in these rocks

oxygen self diffusion in calcite dependence on temperature and water fugacity oxygen self diffusion in natural calcite single crystals was studied hydrothermally at 400 800 c and 10 350 mpa confining pressure diffusion coefficients d were determined from18o concentration profiles measured with an ion microprobe at 100 mpa confining pressure the arrhenius parameters yield an activation energy q 173 6 kj mole and pre exponential factor d0 7 10 9 m2 s over the temperature range 400 800 c and there is no measurable anisotropy constant temperature experiments at 700 c indicate that there is a strong linear correlation slope 0 9 of d with water fugacity over the range 4 240 mpa consistent with the interpretation that in the presence of water the dominant oxygen bearing transport species in calcite is molecular water a sample containing 1180 ppm mn shows a marked increase in observed d values at temperatures below 600 c however when pre annealed at 700 c the d values obtained at 550 c are within a factor of four of the value obtained for the low 100 ppm mn sample the results of this study confirm that in contrast to carbon oxygen diffusion rates in calcite are greatly enhanced when water is present the difference in the effect of water on doxygen and dcarbon in calcite may provide valuable information for evaluating the role of fluids in the thermal histories of calcite bearing rocks

formation and destruction of periclase by fluid flow in two contact aureoles periclase formed in steeply dipping marbles from the beinn an dubhaich aureole scotland and the silver star aureole montana by the reaction dolomite periclase calcite co2 equilibrium between rock and fluids with x co 2 1 requires that reaction was infiltration driven brucite pseudomorphs after periclase occur in the beinn an dubhaich aureole either as bed by bed replacement of dolomite or in a lens along the contact between dolomite and a pre metamorphic dike transport theory predicts that infiltration drove both periclase reaction and 18o depletion fronts which moved at significantly different velocities along the flow path the distributions of brucite and 18o depleted rocks are identical in surface exposures thus indicating upward flow time integrated flux q was 500 mol cm2 and the fluid source was magmatic because periclase and its hydrated equivalent brucite are unaltered to dolomite by retrograde reactions the exposure of brucite marbles accurately images the flow paths of peak metamorphic fluids in the silver star aureole brucite pseudomorphs after periclase exclusively occur in tabular bodies that are beds with elevated mg ca the spatial pattern of 18o depletion requires upward vertical fluid flow estimated prograde q 103 104 mol cm2 and the fluid source was magmatic low mg ca 18o depleted brucite free rocks pose a dilemma because the periclase reaction front should have traveled 18 times further through them than the isotope alteration front the dilemma is resolved by reaction textures that indicate periclase and brucite were destroyed in low mg ca rocks by infiltration driven retrograde carbonation reactions values of retrograde q were 103 104 mol cm2 brucite after periclase was preserved only in high mg ca layers where periclase developed in greater abundance the geometry of brucite marbles at silver star thus reflects the location of high mg ca beds rather than the geometry of fluid flow retrograde reactions must be considered before the mineralogical record of prograde fluid flow can correctly be interpreted in both aureoles fluid flow mineral reaction and isotope depletion were structurally controlled by bedding and lithologic contacts

isotopic evidence for dolomite formation in soils abstract dolomite formation in soils constitute a particular challenge because of 1 scant magnesium content in continental environments as opposed to the marine medium 2 the kinetic problem related to the incorporation of magnesium into the carbonate and 3 the unknown role of soil dolomites in the global carbon cycle pedogenic dolomite formed at deeper soil levels subsoil before the development of petrocalcic horizon barriers was investigated in a semiarid region of se spain guadix baza basin mineralogical characterization textural relationships and isotopic data concerning soil dolomite together with the results of a precipitation experiment provided fuller knowledge of the processes and conditions governing neoformation of dolomite in these soils in the study case dolomite enrichment occurs beyond the limit of major biological activity which coincides with the rooting depth of native perennial plants in the semiarid soils studied textural studies reveal the corrosion of inherited dolomite crystals in the upper soil horizons and the formation of dolomite in depth in relation to a clayey material composed mainly of smectites stable isotope distribution in dolomites throughout the profiles indicates a fractionation with depth this is explained by the formation of dolomites after the dissolution of the pedogenic calcite the calcite detected in the subsoil is interpreted here as a precursor of the neoformed dolomites that transport the isotopic signal associated with biological activity of soils to deeper layers dolomite formation appears to be favoured by the presence of clay minerals in the precipitation media clays retain water during evapotranspiration stages which drastically change the transport properties of the media and promote the incorporation of mg into the structure of the neoformed ca mg carbonate as confirmed by laboratory experiments diffusion controlled crystal growth processes lead to the formation a precursory protodolomite with disordered ca mg distribution from a fluid locally supersaturated in dolomite

intragrain oxygen isotope zoning in titanite by sims cooling rates and fluid infiltration along the carthage colton mylonite zone adirondack mountains ny usa oxygen isotopes are an attractive target for zoning studies because of the ubiquity of oxygen bearing minerals and the dependence of mineral 18 o 16 o ratios on temperature and fluid composi tion in this study subtle intragrain oxygen isotope zoning in titanite is resolved at the 10 lm scale by secondary ion mass spectrometry the patterns of d 18 o zoning differ depending on microstructural context of individual grains and reflect multiple processes including diffusive oxy gen exchange partial recrystallization grain size reduction and grain growth using the chrono logical framework provided by structural relations these processes can be related to specific events during the grenville orogeny titanite was sampled from two outcrops within the car thage colton mylonite zone ccmz a long lived shear zone that ultimately accommodated exhumation of the adirondack highlands from beneath the adirondack lowlands during the ott awan phase 1090 1020 ma of the grenville orogeny titanite is hosted in the diana metasyenite complex which preserves three sequentially developed fabrics an early nw dipping protomylonitic fabric s1 is crosscut by near vertical ultramylonitic shear zones s2 which are locally reoriented by a nnw dipping mylonitic fabric s3 texturally early titanite pre s2 shows diffusion domi nated d 18 o zoning that records cooling from peak ottawan granulite facies conditions numerical diffusion models in the program fast grain boundary yield good fits to observed d 18 o profiles for cooling rates of 50 20 cm a 1 which are considerably faster than the 1 5 cm a 1 cooling rates previously inferred for the adirondack highlands from regional thermochronology high cool ing rates are consistent with an episode of rapid shearing and exhumation along the ccmz during gravitational collapse of the ottawan orogen at c 1050 ma texturally later titanite syn s2 h as higher overall d 18 o and shows a transition from diffusion dominated to recrystallization dominated d 18 o zoning indicating infiltration of elevated d 18 o fluids along s2 shear zones and continued shear ing below the blocking temperature for oxygen 500 c for grain sizes at the study site the tex turally latest titanite post s3 h as growth dominatedd 18 o zoning consistent with porphyroblastic grain growth following cessation of shearing along the harrisville segment of the ccmz

genesis of metapelitic migmatites in the adirondack mountains new york oxygen isotope ratios and rare earth element ree concentrations provide independent tests of competing models of injection v anatexis for the origin of migmatites from amphibolite and granulite facies metasedimentary rocks of the adirondack mountains new york values of 18o and ree profiles were measured by ion microprobe in garnet zircon pairs from 10 sample localities prior u pb sims dating of zircon grains indicates that inherited cores 1 7 1 2 ga are surrounded by overgrowths crystallized during the grenville orogenic cycle 1 2 1 0 ga cathodoluminescence imaging records three populations of zircon i featureless rounded whole grains interpreted as metamorphic or anatectic and rhythmically zoned igneous cores truncated by rims that are either ii discordant rhythmically zoned igneous or iii unzoned metamorphic or anatectic these textural interpretations are supported by geochronology and oxygen isotope analysis in both the amphibolite facies nw adirondacks and the granulite facies se adirondacks 18o zrc values in overgrowths and whole zircon are highly variable for metamorphic zircon 6 1 13 4 n 95 10 m spot in contrast garnet is typically unzoned and 18o grt values are constant at each locality differing only between leucosomes and corresponding melanosomes none of the analysed metamorphic zircon garnet pairs attained oxygen isotope equilibrium indicating that zircon rims and garnet are not coeval furthermore ree profiles from zircon rims indicate zircon growth in all regions was prior to significant garnet growth thus petrological estimates from garnet equilibria e g p t cannot be associated uncritically with ages determined from zircon the unusually high 18o values 10 in zircon overgrowths from leucocratic layers are distinctly different from associated metaigneous rocks 18o zrc 10 indicating that these leucosomes are not injected magmas derived from known igneous rocks surrounding melanosomes have similarly high 18o zrc values suggesting that leucosomes are related to surrounding melanosomes and that these migmatites formed by anatexis of high 18o metasedimentary rocks

oxygen isotope zoning in garnet a record of volatile transport abstract this study examines oxygen isotope zoning in garnets from a barrovian metamorphic terrane in eastern vermont using a co 2 laser extraction system previous strontium isotopic and structural studies of these garnets have shown that they grew over an approximately 10 ma interval during thrusting and nappe emplacement rosenfeld 1970 christensen et al 1989 our studies show that the garnets are strongly zoned in 18 o this zoning is the result of equilibration of garnet with water derived from dehydration of subjacent pelites during nappe stage deformation the magnitude and nature of 18 o zoning depends upon the garnet s location in the outcrop studied the garnets examined in this study come from an isotopically low 18 o paragonitic schist 18 o whole rock 9 that is adjacent to a relatively high 18 o schist 18 o whole rock 12 5 garnets from the paragonitic schists within 10 m of the contact with the isotopically heavier schists have relatively homogenous 18 o values varying from 9 5 in the core to 10 5 at the rim garnet in the paragonitic schists 85 m from the contact are more strongly zoned with 18 o ranging from a low of 6 0 in the cores to a high of 9 0 at the rims of the garnet these zoning patterns were produced by continuous infiltration of relatively high 18 o waters derived from the subjacent schists into the paragonitic schists during garnet grade metamorphism it is possible to determine the time integrated fluid fluxes by comparison of observed 18 o zoning profiles in garnet with those calculated from the equation describing combined advection diffusion of a tracer using this method we calculate time integrated fluid fluxes of 1 5 10 4 cm 3 cm 2 fluxes of this magnitude could have been produced by dewatering of 1 5 km of schist during garnet grade metamorphism

stable isotope evidence of heterogeneous fluid infiltration at the ubehebe peak contact aureole death valley national park california stable isotope ratios of carbon and oxygen are used to define quantitatively the effects of magmatic fluid infiltration in marbles contact meta morphosed by the 173 ma ubehebe peak quartz monzonite death valley national park california in previous studies of fluid infiltration quantitative interpretation of aureole wide isotopic data has been difficult due to small data sets for this study sampling strategies were developed to obtain a data set that was large and unbiased enough to be statistically representative of the carbonates north of the ubehebe peak intrusion a total of 357 samples of marble were analyzed for bulk carbonate isotopic ratios separate analyses of coexisting calcite and dolomite were also obtained for an additional 31 samples unmetamorphosed samples 1900 3000 m from the intrusion have 18 o permil smow values of 25 5 0 8 1 and 13 c permil pdb values of 0 4 0 6 1 samples in the tremolite zone 750 1900 m have 18 o values ranging from 19 4 to 27 7 permil with a median value of 25 2 permil and 13 c ranges from 5 1 to 0 5 permil with a median value of 0 9 permil forsterite zone samples 0 750 m have isotopic ratios shifted to values as low as 11 1 permil 18 o and 9 1 permil 13 c despite this shift most forsterite zone samples retain sedimentary isotopic compositions with median 18 o values of 25 0 permil and 13c values of 1 2 permil 18o values for igneous minerals show no evidence for interaction with heated meteoric or metamorphic fluids the shifts in isotopic compositions within the marbles are interpreted to be the result of magmatic infiltration the effects of this infiltration were quantified by identifying samples with isotopic alteration that can only be attributed to infiltration the results show that magmatic fluid infiltration was limited in extent and very heterogeneous there is no evidence for infiltration of isotopically reactive fluids beyond 850 m from the intrusive contact and within this 850 m zone only 28 percent of the samples have been infiltratively altered with respect to 18 o and 20 percent are depleted in 13 c compositions the isotopic data when evaluated in conjunction with geostatistical and petrologic data indicate that the geometry of the hydrothermal flow system was mainly vertical and away from the pluton infiltration was restricted to large nearly vertical tube like zones of increased permeability these higher permeability zones likely reflect an initial heterogeneity of the host rocks and show no significant evidence for reaction enhanced permeability given the heterogeneity of the system and a lack of knowledge about many basic parameters controlling fluid infiltration it is shown that the best method of calculating the amount and composition of the infiltrating fluid may be a mass balance approach fluid rock ratio the application of mass balance models is discussed and shown to be valid only under limited conditions since infiltration at ubehebe peak was largely vertical the observed isotope alteration patterns represent an infiltration side and not a front because this precludes the use of traditional mass balance calculations a new infiltration side inside model is proposed that allows the isotopic data to be evaluated the inside model uses the ratio of the areal amounts of infiltrative alteration to calculate a fluid composi tion fluid amounts cannot be obtained from this model results for the ubehebe

hurricane intensity and eyewall replacement observations made during the historic 2005 hurricane season document a case of eyewall replacement clouds outside the hurricane eyewall coalesce to form a new eyewall at a greater radius from the storm center and the old eyewall dies the winds in the new eyewall are initially weaker than those in the original eyewall but as the new eyewall contracts the storm reintensifies understanding this replacement mechanism is vital to forecasting variations in hurricane intensity processes in the moat region between the new and old eyewall have been particularly unclear aircraft data now show that the moat becomes dynamically similar to the eye and thus is converted into a region inimical to survival of the inner eyewall we suggest that targeting aircraft to key parts of the storm to gain crucial input to high resolution numerical models can lead to improvements in forecasting hurricane intensity

metasomatic vein formation by stationary fluids in carbonate xenoliths at the eastern margin of the bergell intrusion val sissone italy fluid flow is an important mechanism associated with heat and mass transport within the earth s crust the study of veins which represent channelling of fluids can thus be key in understanding these fluid movements unravelling fluid composition and origin paleo stress regimes and the history of the host rock new stable isotope data on carbonates and silicates have been combined with phase petrology mass balance and field observations to evaluate the formation mechanism of metasomatic reaction veins in dolomitic xenoliths in the bergell tonalites val sissone italy multiple generations of extensional veins can be followed from the contact zone between the dolomites and the intrusion to a few meters within either the tonalites with the epidote quartz veins or within the dolomites where they terminate each type of vein contains a central zone which is formed by open fracture crystallization this central fracture is framed by relatively symmetric replacement zones where the original dolomite reacted to form either forsterite diopside tremolite or talc all accompanied by calcite in either a succession of reaction zones or in simpler bi mineral silicate calcite veins the 18o and 13c values across the veins allow temperatures to be estimated from different mineral pairs silicate calcite and which confirm vein formation along a retrograde cooling path of the intrusion at least four different fluid infiltration events are required the first one around 555 c to form the forsterite calcite veins followed by the epidote quartz veins at temperatures around 430 c then the tremolite calcite veins at around 390 c and finally the talc calcite veins at around 140 c the shape of the 18o and 13c profiles which are flat across the central part and the replacement zones of the veins buffered by the intrusion change substantially over short distances both of these isotope profiles overlap with the equally sharp mineralogical front between the veins and the unreacted dolomites these profiles are interpreted to be the result of an isotopic exchange mechanism driven by dissolution and re precipitation reactions all veins are oriented perpendicular to the contact with the intrusive body except for the late talc veins elevated fluid pressures above the confining pressures caused by the regional and intrusion emplacement stress field are suggested to be responsible for the initial fracturing of the carbonates and intrusive rocks the contact zones between the tonalites and carbonates likely served as fluid conduits where fluids accumulated and the pressure built up until hydrofracturing occurred we propose that the veins formed through episodic pulses of highly reactive fluids that remained stationary during reaction rather than a system where fluids flushed through the veins based on the xco2 constrained mass balance the formation of the veins would only require a relatively small amount of fluid which could potentially originate from the intrusive rocks in vicinity of the xenoliths veining is not ubiquitous around the bergell intrusion suggesting that it only may have been a localized event and thus there is no need to involve a larger convective hydrothermal system for their formation

oxygen isotope fractionation in quartz albite anorthite and calcite laboratory measurements of equilibrium oxygen isotope fractionation in quartz albite anorthite and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600 c and above exchange in these systems is as rapid as exchange between silicates and water fractionation factors can be summarized in the following equations qc 0 38 106t 2 abc 0 57 106t 2 anc 1 59 106t 2 from which the silicate pair fractionations are readily obtained these results are compared with published theoretical estimates as well as data derived from hydrothermal experiments some significant differences are found in particular it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data the new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems

planktonic foraminiferal oxygen isotope analysis by ion microprobe technique suggests warm tropical sea surface temperatures during the early paleogene 1 cool tropical sea surface temperatures ssts are reported for warm paleogene greenhouse climates based on the 18o of planktonic foraminiferal tests these results are difficult to reconcile with models of greenhouse gas forced climate it has been suggested that this cool tropics paradox arises from postdepositional alteration of foraminiferal calcite yielding erroneously high 18o values recrystallization of foraminiferal tests is cryptic and difficult to quantify and the compilation of robust 18o records from moderately altered material remains challenging scanning electron microscopy of planktonic foraminiferal chamber wall cross sections reveals that the basal area of muricae pustular outgrowths on the chamber walls of species belonging to the genus morozovella contain no mural pores and may be less susceptible to postdepositional alteration we analyzed the 18o in muricae bases of morozovellids from the central pacific ocean drilling program site 865 by ion microprobe using 10 m pits with an analytical reproducibility of 0 34 2 standard deviations in situ measurements of 18o in these domains yield consistently lower values than those published for conventional multispecimen analyses assuming that the original 18o is largely preserved in the basal areas of muricae this new 18o record indicates early paleogene 49 56 ma tropical ssts in the central pacific were 4 8 c higher than inferred from the previously published 18o record and that ssts reached at least 33 c during the paleocene eocene thermal maximum this study demonstrates the utility of ion microprobe analysis for generating more reliable paleoclimate records from moderately altered foraminiferal tests preserved in deep sea sediments

secondary eyewall formation and eyewall replacement cycles in a simulated hurricane effect of the net radial force in the hurricane boundary layer abstractmultiple secondary eyewall formations sefs and eyewall replacement cycles ercs are simulated with the fifth generation pennsylvania state university psu national center for atmospheric research ncar mesoscale model mm5 at horizontal grid spacing of 0 67 km the simulated hurricane is initialized from a weak synthetic vortex in a quiescent environment on an f plane after spinup and rapid intensification the hurricane enters a mature phase during which the intensity change is relatively slow convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane s primary eyewall this secondary eyewall se then contracts and strengthens the primary eyewall weakens and is eventually replaced by the se the hurricane grows in size and the radius of maximum wind rmw increases as similar ercs repeat 5 times during the simulation two existing hypotheses on sef are evaluated using the simulation output then model diagnostics are used to revea

formation of wollastonite by chemically reactive fluid flow during contact metamorphism mt morrison pendant sierra nevada california usa quartz calcite sandstones experienced the reaction calcite introduction quartz wollastonite co2 during prograde contact metaflow of chemically reactive fluid may control the minmorphism at p 1500 bars and t 560 c rocks were in eralogy stable isotope composition and trace element equilibrium during reaction with a co2 h2o fluid with xco2 chemistry of rocks during contact metamorphism e g 0 14 the transition from calcite bearing wollastonite free to labotka et al 1988 jamtveit et al 1992a 1992b nabelek wollastonite bearing calcite free rocks across the wollastonite isograd labotka 1993 bowman et al 1994 roselle et al is only several millimeters wide the wollastonite forming reaction 1999 a number of aspects of metamorphic fluid flow was driven by infiltration of quartz calcite sandstone by chemically however remain the subject of debate including the reactive h2o rich fluids and the distribution of wollastonite directly direction of flow labotka et al 1988 ferry dipple images the flow paths of reactive fluids during metamorphism the 1992 ferry 1995a hanson 1995a whether numerical mapped distribution of wollastonite and modeling of an o isotope models that assume uniform rock properties adequately profile across a lithologic contact indicate that the principal direction predict the geometry of fluid flow in aureoles that contain of flow was layer parallel directed upward with any cross layer a variety of anisotropic structural features hanson 1992 component of flow 0 1 of the layer parallel component fluid 1995b cook et al 1997 and the degree to which local flow was channeled at a scale of 1 100 m by pre metamorphic mineral fluid equilibrium is attained lasaga rye dikes thrust and strike slip faults fold hinges bedding and 1993 bolton et al 1999 lasaga et al 2000 these and stratigraphic contacts limits on the amount of fluid based on related questions were addressed in an investigation of minimum and maximum estimates for the displacement of the contact metamorphism in the mt morrison pendant wollastonite reaction front from the fluid source are 0 7 1 9 eastern sierra nevada california the location is an 10 cm fluid cm rock the sharpness of the wollastonite isograd exceptional site for the study of metamorphic fluid flow the consistency of mineral thermobarometry the uniform measured for several reasons first the mt morrison sandstone o o fractionations between quartz and calcite and model the focus of this study is ideal for application of concalculations all argue for a close approach to local mineral fluid tinuum models of coupled fluid flow and reaction because equilibrium during the wollastonite forming reaction it is unusually homogeneous in mineralogy and texture

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

the oxygen isotope anatomy of a slowly cooled metamorphic rock the distribution of o isotope ratios in a slowly cooled metamorphic rock is investigated by a combination of ion microprobe and laser probe techniques the sample has unusually simple geometry centimeter size domains of feldspar and garnet separated by a one millimeter to one centimeter thick layer of millimeter size magnetite grains isotopic zonation at two different scales is documented a sharp decrease in 18 o in the outer 10 100 m of individual magnetite grains is in agreement with modeling of isotopic reequilibration during cooling by interdiffusion between feldspar and magnetite the presence of this zonation in the outer portions of magnetite grains that are adjacent to garnet indicates extensive transport along grain boundaries during diffusive exchange millimeter scale zonation in the polygranular layer of magnetite is caused by the interaction of volume diffusion and grain boundary transport the effects of which depend upon local textures grain boundaries enhance bulk diffusion in polygranular aggregates and allow exchange between nontouching grains the results document a complex textural control to millimeter scale o isotope zonation and geothermometry in slowly cooled rocks and document the importance of fast grain boundary transport in controlling diffusive exchange