formation of chlorite during thrust fault reactivation record of fluid origin and p t conditions in the monte perdido thrust fault southern pyrenees the chemical and isotopic compositions of clay minerals such as illite and chlorite are commonly used to quantify diagenetic and low grade metamorphic conditions an approach that is also used in the present study of the monte perdido thrust fault from the south pyrenean fold and thrust belt the monte perdido thrust fault is a shallow thrust juxtaposing upper cretaceous paleocene platform carbonates and lower eocene marls and turbidites from the jaca basin the core zone of the fault about 6 m thick consists of intensely deformed clay bearing rocks bounded by major shear surfaces illite and chlorite are the main hydrous minerals in the fault zone illite is oriented along cleavage planes while chlorite formed along shear veins 50 m in thickness authigenic chlorite provides essential information about the origin of fluids and their temperature 18o and d values of newly formed chlorite support equilibration with sedimentary interstitial water directly derived from the local hanging wall and footwall during deformation given the absence of large scale fluid flow the mineralization observed in the thrust faults records the p t conditions of thrust activity temperatures of chlorite formation of about 240 c are obtained via two independent methods chlorite compositional thermometers and oxygen isotope fractionation between cogenetic chlorite and quartz burial depth conditions of 7 km are determined for the monte perdido thrust reactivation coupling calculated temperature and fluid inclusion isochores the present study demonstrates that both isotopic and thermodynamic methods applied to clay minerals formed in thrust fault are useful to help constrain diagenetic and low grade metamorphic conditions

thermal and structural evolution of the external western alps insights from u th sm he thermochronology and rscm thermometry in the aiguilles rouges mont blanc massifs in the western alps the external crystalline massifs ecm are key places to investigate the kinematics and thermal structure of a collisional crustal wedge as their paleo brittle ductile transition is now exhumed at the surface new u th sm he data on zircon and new raman spectroscopy on carbonaceous material rscm data from the aiguilles rouges and the mont blanc massifs coupled to hefty thermal modeling constrain the thermal evolution and exhumation of the massifs in the cover of the aiguilles rouges massif we found that the maximal temperature was about 320 c 25 c close to the maximal temperature reached in the cover of the mont blanc massif 350 c 25 c we show that after a fast heating period the thermal peak lasted 10 15 myrs in the mont blanc massif and probably 5 10 myrs in the aiguilles rouges massif this thermal peak is synchronous with crustal shortening documented in the basement u th sm he data and thermal modeling point toward a coeval cooling of both massifs like other ecm at around 18 ma 1 ma this cooling was related to an exhumation due to the initiation of frontal crustal ramps below the ecm quite synchronously along the western alps arc

microstructural observations on natural syntectonic fibrous veins implications for the growth process abstract syntectonic antitaxial and ataxial fibrous veins were investigated using sem microprobe cathodoluminescence cl and optical microscopy in antitaxial calcite veins fibres and surrounding selvage grew simultaneously with similar growth rates of crystallographically differently oriented grains new material precipitated at the vein margin in antitaxial and bi mineralic ataxial microstructures bridges of country rock material formed during vein growth in an initial en echelon vein system in our antitaxial and bi mineralic ataxial samples the spacing of solid inclusions does not reflect individual crack seal openings

fluid rock interactions related to metamorphic reducing fluid flow in meta sediments example of the pic de port vieux thrust pyrenees spain in orogens shortening is mainly accommodated by thrusts which constitute preferential zones for fluid rock interactions fluid flow mass transfer and mineralogical reactions taking place along thrusts have been intensely investigated especially in sedimentary basins for petroleum and uranium research this study combines petrological investigations mineralogical quantifications and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties nature origin temperature and redox and fluid host rock interactions mass transfers recrystallization mechanisms and newly formed synkinematic mineralization in the pic de port vieux thrust fault zone pyrenees spain we demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low grade metamorphism conditions during thrusting the hanging wall triassic red pelite was locally bleached while the footwall cretaceous dolomitic limestone was mylonitized the results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior tectonic and hydraulic and improve our knowledge of fluid rock interactions in open fluid systems in the crust

cooling induced strain localization in carbonate mylonites within a large scale shear zone glarus thrust switzerland abstract the glarus thrust switzerland offers a great field example of strain localization under retrograde conditions along the thrust mylonitic microfabrics are characterized by a temperature stress controlled balance of grain size reducing mechanisms and grain growth consequently mean grain sizes decrease along the thrust with decreasing metamorphic conditions and towards the thrust contact in an opposite manner calcite twin densities increase towards the contact cpos are strongest between 0 5 and 15 m away from the thrust but become generally weaker in the last centimeters where also cataclasites occur the cpo weakening and grain size reduction towards the shear zone point to a change from predominant dislocation creep to granular flow finally ending in cataclastic deformation the microfabric changes correlate with a decrease in 13c and 18o towards the thrust contact indicating the presence of fluids during cycles of brittle and plastic deformation based on the microfabric changes variations in stable isotopes and cross cut relationships a subdivision into a low and high temperature shear zone can be made the microfabric modifications resulted from changes in deformation conditions due to ongoing thrusting and exhumation induced cooling promoting further strain localization of an existing high strain shear zone

measurements of salinity and volume of brine excluded from growing sea ice the volume of brine excluded from growing sea ice and its salinity were measured using a brine sampler the measurements were made in both laboratory and field under various growth conditions of the sea ice the salinity of the brine becomes higher and the volume flux decreases as the sea ice growth rate decreases consequently the salt flux of the brine decreases with decreasing growth rate in the case of sea ice growth at a constant rate as the sea ice becomes thicker the salinity of the brine excluded increases while its volume flux decreases however the salt flux is nearly independent of the ice thickness increase at least up to a thickness of 15 cm for sea ice growth rates between 1 7 10 5 and 1 4 10 4 cm s 1 and for a seawater salinity of 33 0 the brine salinity ranged from 42 3 to 92 7 the volume flux ranged from 6 3 10 6 to 3 4 10 5 cc cm 2 s 1 and the salt flux ranged from 6 4 0 7 to 1 5 10 6 g cm 2 s 1

on small scale horizontal variations of salinity in first year sea ice measurements of salinity over horizontal distances of 38 to 76 cm in a thick first year ice sheet have revealed significant differences a maximum salinity difference of 2 was observed between ice core segments from the same depth the mean standard deviation for 10 cm thickness increments through the 2 0 m ice sheet was 0 39 between the five closely spaced cores the most likely mechanism for these significant differences in salinity over short distances is differential brine drainage in the ice sheet due to varying locations of brine drainage channels a simple one dimensional model which assumes a normally distributed arrangement of brine drainage channels provides results consistent with the horizontal differences observed

controls of the landfast ice ocean ecosystem offshore barrow alaska ba sed on biophysical ice core data collected in the landfast ice off barrow alaska usa in 2002 and 2003 a one dimensional ice ocean ecosystem model was developed to determine the factors controlling the bottom ice algal community the data and model results revealed a three stage ice algal bloom 1 onset and early slow growth stage before mid march when growth is limited by light 2 fast growth stage with increased light and sufficient nutrients and 3 decline stage after late may as ice algae are flushed out of the ice bottom stages 2 and 3 are either separated by a transition period as in 2002 or directly connected by ice melting as in 2003 when in situ light and nutrient enrichment experiments showed only light limitations the modeled net primary production of ice algae npp ai from march to june is 1 2 and 1 7 g c m 2 for 2002 and 2003 respectively within the range of previous observations model sensitivity studies found that overall npp ai increased almost proportionally to the initial nutrient concentrations in the water column a phytoplankton bloom if it occurs as in 2002 would compete with ice algae for nutrients and lead to reduced npp ai about 45 of the npp ai was exported to the shallow benthos

thin saline ice thickness retrieval using time series c band polarimetric radar measurements the application of time series radar measurements to accurately invert the thickness of saline ice is presented in this study the authors describe briefly some experimental observations from the united states army cold regions research and engineering laboratory hanover nh 1993 crrelex 93 campaign of microwave scattering from sea ice they demonstrate that volume scattering from brine inclusions is an important contribution to the backscatter response of saline ice in this case from the experimental findings and the thermophysics of ice growth they develop an inversion algorithm for the ice thickness based on a dynamic electromagnetic scattering model of saline ice this inversion algorithm uses a parametric estimation approach in which the radiative transfer equation is used as the direct scattering model to calculate the backscattering signatures from ice medium and the levenberg marquardt method is employed to retrieve ice thickness iteratively additional information provided by the saline ice thermodynamics is applied to constrain the electromagnetic inverse problem to achieve a reasonably accurate reconstruction the inversion results using this algorithm and the data from crrelex 93 experiment are compared the accurate thickness retrieval suggests the potential use of this algorithm for retrieving geophysical parameters from satellite remote sensing data

thermometry of quartz mylonites importance of dynamic recrystallization on ti in quartz reequilibration quartz mylonites from the tonale fault zone in the alps northern italy have been investigated by the ti in quartz geothermometer titaniq in order to test its applicability to measure deformation temperatures the eastern part of the tonale fault zone was contact metamorphosed by the synkinematic intrusion of the adamello pluton forming an 800 m wide mylonitic shear zone with a synkinematic temperature gradient from 280 c at the frictional viscous transition to 700 c at the pluton contact as derived from metamorphic mineral assemblages deformation microstructures from quartz mylonite samples systematically collected across the mylonitic shear zone display the entire range of dynamic recrystallization in quartz which comprise bulging recrystallization blg subgrain rotation recrystallization sgr and grain boundary migration recrystallization gbm titaniq geothermometry yields the near peak deformation temperature for quartz mylonites deformed at metamorphic temperatures above 540 c in the zone of gbm however for mylonites formed under lower temperatures in the zones of sgr and blg the preexisting ti concentrations were not reset it is suggested that this is due to the sluggish ti volume diffusion rates below 500 c and the short duration of contact metamorphism and deformation even in the higher temperature samples the reequilibration of ti in quartz content was achieved by grain boundary migration rather than by volume diffusion hence our results show that gbm is crucial for the reequilibration of ti in quartz while quartz mylonites deformed by either blg or sgr which predominate in natural shear zones at greenschist facies metamorphic conditions most likely yield inherited temperatures

some thermal constraints on crustal assimilation during fractionation of hydrous mantle derived magmas with examples from central alpine batholiths following assimilation at different levels in the crust we test by heat and mass balance the extent of assimilation of crustal country rocks in different local plutonic

constraints from 40ar 39ar geochronology on the timing of alpine shear zones in the mont blanc aiguilles rouges region of the european alps the mont blanc and aiguilles rouges massifs which form part of the external crystalline massifs of the western european alps record a young and fast exhumation history as established by an extensive low temperature thermochronology and geochronology data set various kinematic and dynamic models for oligocene to neogene deformation and exhumation of the aiguilles rouges mont blanc system have been proposed however the timing of deformation along major shear zones in and around the massifs which is crucial to these models is still controversial our new 40ar 39ar data from key deformation zones in the mont blanc area show that nw directed thrusting lasted from oligocene to mid miocene times in the mont blanc massif before a nw ward jump of the deformation front to below the aiguilles rouges massif which led to updoming of the aiguilles rouges and mont blanc massifs this deactivated the main nw verging shear zones and caused back folding and back thrusting east of the mont blanc as well as upward extrusion of the aiguilles rouges massif subsequently there was a switch to more coaxial shortening between the aiguilles rouges and mont blanc massifs associated with strain partitioning and related dextral strike slip deformation on the eastern side of the mont blanc massif

fluid migration through thrust faults in the helvetic nappes western swiss alps the 18o 13c and 87sr 86sr values of calcite and organic matter were measured for carbonate mylonites from numerous thrusts in the helvetic alps carbonate mylonites in most of the thrusts retain essentially unaltered protolith 18o and 13c values consistent with there having been little to no advection of isotopically distinct fluid through these faults only carbonate mylonites from the basal thrusts of the largest nappes have 18o and or 13c values that differ from those of their protoliths the zone of isotopic alteration exchange is confined to c 10 to 20 meters of these fault contacts we propose the fluids that migrated through these faults contained variable amounts of organically derived carbon and radiogenic strontium and were probably derived from dewatering of the sedimentary rocks and prograde metamorphic reactions in the nappes root zones apart from the basal thrusts of the largest nappes that behaved as narrow laterally extensive conduits for fluids there is little isotopic evidence that large quantities of fluids passed through most of the carbonate hosted thrusts in the helvetic alps

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

microstructural evolution of syntaxial veins formed by advective flow veins are common in earth s crust and are formed by a wide range of processes which lead to crystal growth in dilation sites the first order processes in vein formation have been identified but it is much less clear how these can be diagnosed from field studies in order to better understand the microstructural evolution during vein growth we grew veins of analogue material alum kal so4 2 12h2o in a transmitted light cell from an advecting supersaturated fluid real time observation shows the effects of flow rate and supersaturation on the evolving microstructure 1 along vein trends in growth rate caused by decreasing supersaturation and 2 growth competition between clear crystals in the absence of nucleation and primary fluid inclusions although the overall trends in growth rate are in agreement with previous work the local effects at the scale of individual grains reported here are less well understood these new data form a basis for better interpretation of natural microstructures to explore the possible effects of experimentally observed processes during vein growth we simulate the growth kinetics of a quartz vein at various conditions of advective flow in earth s crust results show that in general the along vein changes in growth rate occur at length scales much larger than a typical outcrop

simulations of crustal anatexis implications for the growth and differentiation of continental crust there is overwhelming and incontrovertible petrological and geophysical evidence for the significant role played by mantle derived mafic magma in the generation and growth of continental crust likewise intrusion of mafic magmas beneath or into continental crust is very likely the major source of enthalpy that drives intracrustal differentiation a simple dynamical model has been constructed to examine the critical factors that govern the evolution and time scale of crustal anatexic events when driven by basaltic magma underplating or injection into crust critical factors include the intensity of the enthalpy input i e the power dissipated and the rheological properties bulk composition and compositional structure of the source rocks undergoing partial fusion we have performed numerical simulations to evaluate these factors using phase equilibria and thermochemical and transport property data applicable to the binary eutectic system caal2si2o8 camgsi2o6 as a rough analog to study anatexis of mafic lower crust the role of enthalpy power is tested by varying the enthalpy or temperature along the base of the crustal block while maintaining a fixed temperature at the top as ratio tbot ttop increases modestly from 1 05 to 1 15 the average fraction of melt at steady state in the anatexic region increases from 50 to 75 time to attain steady state scales inversely with tbot ttop with an increase by a factor of 2 for a 10 decrease in tbot ttop typical anatexic timescales are in the range 103 to 105 years for length scales in range 102 to 103 m the consequences of different rheological models especially the importance of darcy percolative flow relative to en masse flow within the partial melt region was also investigated a value of the solid fraction called the critical value scrit is set such that for 0 0 5 relatively large volumes of nearly homogeneous melt are rapidly generated in distinction for scrit small more enthalpy is stored in the solid and less melt is produced however the compositional spectrum of liquids generated within the anatexic region is significantly larger for small scrit because of the sensitive dependence of solidi and liquidi on bulk composition melt productivity is related to bulk composition given a particular enthalpy power input and rheological model there is a factor of 2 difference in volume of melt generated when the bulk composition of the source is 10 modal percent less refractory compositionally zoned melts form by melting of either homogeneous or layered sources although composition frequency relations are sensitive to the initial subsolidus compositional structure the effects of anatexic events are to fundamentally reorganize the pattern of compositional structure within the crust intracrustal differentiation is a long term inevitable process associated with the underplating or injection of mafic magma into preexisting crust

observations of brine drainage networks and microstructure of first year sea ice brine drainage networks and the microstructure of first year sea ice have been examined at two locations near barrow northern alaska a method for obtaining full depth sections of ice sheets up to 1 8 m thick is presented and shown to provide information on the spatial distribution and geometry of brine drainage networks on a scale of meters a number of such sections from the two test sites are presented which reveal a greater variety of main channel and side branch configurations than is typically observed in ice grown in the laboratory vertical and horizontal micrographs and thin section photographs were obtained in november 1993 and march and may 1994 at a test site in the relatively protected elson lagoon the resulting time series of photographic records provide detailed information on the size shape and spatial distribution of the brine and gas filled inclusions and a means to quantify their size and shape changes with time an example of the changes with time in inclusion sizes and aspect ratios in the vertical and horizontal directions for a depth of 0 2 m with a given thermal history is also presented

thermo mechanical model for the finite strain gradient in kilometer scale shear zones many kilometer scale crustal shear zones with thrust shear sense exhibit a similar nonlinear decrease of the finite shear strain with increasing distance z from the shear zone s base to explain this strain gradient we use a one dimensional 1 d thermo mechanical shear zone model which considers a dislocation creep flow law with temperature dependent viscosity the model predicts a linear finite strain gradient in ln z space which is quantified by the single dimensionless parameter depends on the activation energy q the temperature at the shear zone s base t 0 and the temperature difference across it t which are often well constrained parameters we apply our model to several shear zones worldwide our model is based on physics and fits the strain data as well as previously published empirical functions the estimates of resulting from fitting the finite strain gradient agree with other independent estimates of using realistic values for q t 0 and t reported for the considered shear zones this agreement of independent estimates indicates that the model is physically feasible and that the dominant cause for the nonlinear strain gradient in kilometer scale shear zones can be the temperature increase toward the shear zone s base and the related decrease in viscosity the model however often underestimates the strain gradient in the lowermost part of natural shear zones this underestimation indicates that additional processes such as grain size reduction or viscous heating not considered in the model play an important role close to the base of the shear zone

evidence of density currents with the potential to promote meromixis in ice covered saline lakes abstract ice covers all but the most saline of the vestfold hills lakes for about 8 12 months of each year and precludes wind induced turbulent mixing over the winter when strong winds are most frequent nevertheless the progressive growth of ice volume through the austral winter and spring months generates haline convection capable of mixing the water column to a depth at least as great as that achieved by wind induced turbulence in the summer ice free period further cold and very saline brines may form at the shallow periphery of a lake and flow downslope penetrating to the lake centre below the convectively mixed layer detailed temperature profiles of hypersaline organic lake provide the first evidence for these density currents in saline lakes of the vestfold hills these data indicate a dynamic responsiveness to periods of relatively cold weather and that the resulting density currents may be sufficiently small in volume to have little effect on the anoxia of bottom layers in these meromictic lakes alternating periods of negative and positive water balance may also be significant in the formation and destruction of meromixis in these saline lakes which lack outflow streams if a lake has been through a period of negative water balance becoming relatively more saline and then begins to be diluted during a subsequent period of positive water balance the winter haline convection will penetrate to progressively shallower depths and deeper layers may stagnate marking the onset of meromixis an increase in the water level of organic lake over ten years indicates the speed with which the vestfold hills lakes may experience significant change in salinity despite the generally small catchments of these lakes

empirical calibration of the oxygen isotope fractionation between quartz and fe mg chlorite abstract an empirical calibration has been made of the oxygen isotope fractionation between chlorite and quartz using samples from localities in metamorphic terrains where the formation temperature has been constrained by independent methods e g fluid inclusion homogenization temperatures mineral assemblages and petrology of the host rocks to the veins thermodynamic modeling and raman spectrometry textural equilibrium of chlorite and quartz was a pre requisite and the chemical composition of chlorite was determined the chlorite analyzed had a range in fe mg varying between 0 35 and 0 7 except for pure mg chlorite fe mg substitution within the range measured does not change the oxygen isotope fractionation between quartz and chlorite measurably the results support a linear correlation for chlorite quartz fractionation over the temperature range given by this study 240 550 c 1000 ln 0 01323 0 002 t c 10 97 0 92 the presently established geothermometer can be applied to quartz chlorite fractionations in low grade metamorphic rocks and may be extrapolated to diagenetic systems

the role of seawater freezing in the formation of subsurface brines abstract several mechanisms evaporation water rock interaction ultra filtration have been suggested to explain the evolution of ubiquitous ca chloride subsurface brines in the present paper the freezing of seawater in polar regions and in even wider areas during glacial periods is proposed as an additional possible path of brine formation four detailed seawater freezing experiments to 14 c resulting in a concentration factor of about 5 were carried out and na k ca mg sr cl so4 and br were analysed in the residual brines and in the ice br and sr whose behavior during the freezing of seawater is reported here for the first time show a conservative behavior throughout the studied temperature range our data and earlier literature show that the high salinities which are common in subsurface brines 300 g l may be obtained by the removal of h2o as ice in the primary glacial environment the decrease in the na cl ratio is caused by the crystallization of mirabilite na2so4 10h2o supplemented by hydrohalite nacl 2h2o sulfate is removed both in mirabilite and by bacterial reduction the brine then migrates to the subsurface heats up under the local geothermal gradient and interacts with the adjacent rocks at this stage it may be diluted by meteoric waters its mg ca ratio decreases dolomitization and chloritization the so 4 cl ratio varies according to the local gypsum anhydrite equilibrium conditions and the ca so 4 hco 3 ratio increases as a result of dolomitization or chloritization the interaction with rocks in the subsurface may affect both the original 87 sr 86 sr and the 18 o 16 o ratios of the brine although several of the processes which lead to the formation of ca chloride brines are common for both the evaporative and the freezing models the na br cl relationship in a given brine can be used to discriminate between the two modes of brine evolution several subsurface brines from the canadian shield and one brine from finland are used as examples of the seawater freezing model and an explanation is proposed for the necessary mass production of brines in glacial environments

diatom induced silicon isotopic fractionation in antarctic sea ice 1 in this study we measure the silicon isotopic composition 29si relative to nbs28 quartz standard of dissolved silicon and biogenic silica collected by sequential melting from spring antarctic pack ice collected near 117 e 64 5 s this work aims to investigate the use of si isotopes to quantify the activity of sea ice diatoms in the different brine structures and the influence of sea ice diatoms on the spring ice edge blooms from three cores with contrasted physico chemical characteristics we report significant isotopic fractionations linked to diatom activity with distinct silicon biogeochemical dynamics between different brine structures the diatoms in snow ice and in brine pockets of frazil or congelation ice have the heavier silicon isotopic composition 0 53 to 0 86 indicating that they grow in a closed system and use a significant fraction of the small dissolved silicon pool available in the brine channels and skeletal layer diatoms display a relatively lower silicon isotopic composition 0 41 to 0 70 although it is still relatively positive compared to expected equilibrium fractionation this suggests that the diatoms have grown in a semi closed system where the dissolved silicon pool i e brine is partially replenished the silicon isotopic composition 0 63 of the sea ice diatoms is much heavier than the one of biogenic silica in the seasonal ice zone mixed layer 0 09 our results suggest that sea ice diatoms either contribute to an insignificant part of the whole diatom biomass in the upper water layer or that they are directly exported below the mixed layer

relation of material exchange between sea ice and water to a coupled ice ocean ecosystem at the hokkaido coastal region of the okhotsk sea 1 in this paper the material exchange between the sea ice and the water just below the ice and its relation to the lower trophic ice system are examined using field observations in the hokkaido coastal region of the okhotsk sea and a coupled ice ocean ecosystem model which in detail formulates the material exchange between the ice and the water the accuracy of the model is confirmed by a comparison of the results of the numerical computation with the observations the estimation of the transport of the organic carbon and nutrients based on the computation demonstrates that the physical coupling effect between the ice and water plays a prominent role in supplying the nutrients from the water to the ice ecosystem and in efficiently releasing the organic matter produced by the primary producer in the ice ice algae as a result this study quantitatively clarifies that the physical coupling effect tidal mixing and biological activity in the ice drive the material cycle in the ice and water under the ice

viscous overthrusting versus folding 2 d quantitative modeling and its application to the helvetic and jura fold and thrust belts abstract this paper presents two dimensional 2 d numerical simulations of the shortening of a stiff viscous layer with a pre existing weak zone that is embedded in a weaker viscous matrix the model bottom remains straight during shortening and represents a detachment surface four deformation styles are observed that depend on the ratio of the layer and matrix viscosities l m the thickness ratio of the bottom matrix and the overlying stiff layer hm hl and the power law stress exponent of the matrix nm the numerical results are used to quantify the conditions for which each deformation style occurs 1 pure shear dominated deformation occurs for l m 50 and hm hl 50 and hm hl 1 and 4 folding and overthrusting occur for a power law viscous matrix and 0 5

modeling the transport of passive tracers in sea ice 1 a model for the vertical transport of passive tracers in sea ice is presented two reynolds flux closure approximations are proposed for the tracer velocity dispersion term in the new ice tracer model icet the schemes enhanced molecular diffusion emd and mixing length diffusion mld are suggested parameterizations of gravity drainage the dominant mechanism of desalination in growing sea ice the performance of icet using each parameterization is tested against two experimental studies simulations i compare profiles of brine salinity with passive tracer concentrations during sea ice growth and melt and simulations ii compare bottom boundary salt and brine volume fluxes with passive tracer fluxes and bottom diffusivities icet behavior is evaluated under three salinity forcing prescriptions both schemes successfully reproduce expected tracer concentrations in simulations i when the salinity forcing evolves logarithmically however in simulations ii the mld scheme outperforms emd in two significant ways 1 growth rate trends in the mld diffusivity parallel measurements of brine volume flux while emd bottom diffusivities remain almost constant and 2 mld bottom tracer concentrations decrease with ice growth rate similar to excluded brine salinity while emd trends are contrary hence enhanced molecular diffusion is highly questionable for implementation in models of reactive passive tracers the icet mixing length diffusivity is a viable choice in sea ice biogeochemical modeling it remains a challenge to assess whether mld can provide quantitative estimates of desalination at each time step for use in forcing icet or for implementation in a model of sea ice salinity

a simple thermo mechanical shear model applied to the morcles fold nappe western alps abstract we present a one dimensional shear zone model with a power law flow law and a temperature dependent viscosity the analytical solution for the velocity profile across the shear zone depends only on the single dimensionless parameter depends on the activation energy of the applied flow law the temperature at the base of the shear zone and the temperature difference across it the solution can describe three types of shear deformation 1 homogeneous simple shear for 1 and 3 heterogeneous simple shear potentially generating fold nappes for 5 10 we perform a systematic parameter search and determine the parameters that provide the best fit between a sheared model line and a reference line representing the first order geometry of the frontal part of the morcles nappe we also apply a more elaborated pressure driven model to test whether published flow laws for calcite and realistic pressure gradients provide realistic velocities and strain rates for the morcles nappe the value of applicable to the morcles nappe is estimated with three independent methods 1 applying reported values for temperatures and activation energy to the analytical formula for 2 fitting the first order geometry of the morcles fold nappe and 3 comparing results of a velocity driven i e kinematic boundary condition and pressure driven i e pressure source term and free surface shear zone model all three methods yield consistent estimates for between 3 and 15 our results show that previously published kinematic models which explain the tectonic evolution of the morcles fold nappe within a crustal shear zone are physically feasible the results further suggest that viscous heterogeneous simple shear played a dominant role during the formation of the morcles fold nappe

visualizing brine channel development and convective processes during artificial sea ice growth using schlieren optical methods two non invasive optical schlieren methods have been adapted to visualize brine channel development and convective processes in experimentally grown sea ice obtained when a nacl aqueous solution is cooled from above in a quasi two dimensional hele shaw cell the two different visualization methods i e traditional and synthetic schlieren optical imaging produce high spatial resolution images of transport processes during ice growth without any external perturbation these images allow observations of the flow dynamics simultaneously within the ice layer around the ice water interface and in the liquid water layer revealing connections between the processes occurring within the two phases results from these methods show that desalination of the growing ice layer occurs by two concurrent yet independent mechanisms 1 boundary layer convection persisting throughout the ice growth period with short fingers present just below the ice water interface and 2 gravity driven drainage from the brine channels producing deep penetrating convective streamers which appear after a given time from the beginning of ice growth the improved visualization and qualitative characterization of these processes show that schlieren optical methods have exciting potential applications for future study of convective processes during sea ice growth

grain coarsening maps for polymineralic carbonate mylonites a calibration based on data from different helvetic nappes switzerland abstract microstructures of carbonate mylonites with 0 40 vol second phase particles from different helvetic nappes switzerland have been analyzed while the mean calcite grain size dcc increases with temperature t second phases pin calcite grain boundaries two types of second phases can be distinguished small second phases included in calcite grains and larger second phases at calcite grain boundaries both coarsening with volume fraction and t these trends are controlled by an interaction of different processes during deformation including diffusion dynamic recrystallization grain growth and pinning in terms of dcc t dependencies the microstructures of the investigated nappes are similar the relationship between dcc and t differs for high t and low t these observations can be explained by a change in the simultaneous activity of dominant mechanisms e g diffusion and dislocation creep as a function of t and second phase content in contrast the relation log dp 1 t dp second phase grain size is linear with constant slope for all nappes indicating that growth processes of second phases are identical despite differences in fluid activity and strain rate between individual nappes the microstructural relationships of dcc second phases and t remain similar therefore grain coarsening maps of second phase and recrystallization controlled calcite aggregates are a representative tool to predict deformation conditions and mechanisms for other shear zones developed under similar physical conditions

modeling brine and nutrient dynamics in antarctic sea ice the case of dissolved silica sea ice ecosystems are characterized by microalgae living in brine inclusions the growth rate of ice algae depends on light and nutrient supply here the interactions between nutrients and brine dynamics under the influence of algae are investigated using a one dimensional model the model includes snow and ice thermodynamics with brine physics and an idealized sea ice biological component characterized by one nutrient namely dissolved silica dsi in the model dsi follows brine motion and is consumed by ice algae depending on physical ice characteristics the brine flow is either advective diffusive or turbulent the vertical profiles of ice salinity and dsi concentration are solutions of advection diffusion equations the model is configured to simulate the typical thermodynamic regimes of first year antarctic pack ice the simulated vertical profiles of salinity and dsi qualitatively reproduce observations analysis of results highlights the role of convection in the lowermost 5 10 cm of ice convection mixes saline nutrient poor brine with comparatively fresh nutrient rich seawater this implies a rejection of salt to the ocean and a flux of dsi to the ice in the presence of growing algae the simulated ocean to ice dsi flux increases by 0 115 compared to an abiotic situation in turn primary production and brine convection act in synergy to form a nutrient pump the other important processes are the flooding of the surface by seawater and the percolation of meltwater the former refills nutrients near the ice surface in spring the latter if present tends to expell nutrients from the ice in summer

transition from thin to thick skinned tectonics and consequences for nappe formation numerical simulations and applications to the helvetic nappe system switzerland abstract we use two dimensional numerical simulations to study the deformation style and the formation of nappes during the shortening of basement cover systems with half grabens we perform simulations with only linear and power law viscous rheology and also thermo mechanical simulations with viscoelastoplastic rheology and temperature dependent viscosities the accumulated area averaged strain is calculated for the sediments es and for the basement eb to quantify the deformation style the results show that the transition from thin skinned dominated es eb 1 to thick skinned dominated es eb 1 deformation is controlled by two effective viscosity ratios the ratio of viscosity at the top of the basement to viscosity at the bottom of the basement and the ratio of viscosity at the top of the basement to viscosity of the sedimentary cover a higher basement internal viscosity ratio favors thick skinned deformation whereas a higher basement cover viscosity ratio favors thin skinned deformation simulations with only viscous rheology show the same first order results as the thermo mechanical simulations the results further show that fold nappe formation is associated with thick skinned dominated deformation and thrust nappe formation with thin skinned dominated deformation fold nappes are formed by shearing and extrusion of sediments during the deformation and closure of half grabens whereas thrust nappes are formed due to the shearing off of sediments from half grabens which are nearly undeformed the results are applied to the morcles fold nappe and the helvetic nappe system switzerland

laser cut rb sr microsampling dating of deformational events in the mont blanc aiguilles rouges region european alps spatial control for in situ dating of mineral phases in fine grained rocks is a significant challenge in geochronology and the precision of microsampling is a crucial factor in obtaining accurate results in this study a new microsampling approach to rb sr geochronology has been applied to greenschist facies mylonitic shear zones in the mont blanc aiguille rouges region of the western european alps using a laser ablation system for microsampling by laser cutting followed by conventional tims rb sr isotopic analysis of g sized samples provides an improved workflow for texturally controlled quasi in situ dating of mineral phases the automated cutting process minimizes material loss and the risk of handling errors while facilitating sampling of complex shapes of almost any size a significant improvement over earlier microscope mounted microdrills the new rb sr white mica calcite ages of between 27 and 30 ma indicate oligocene deformation in alpine shear zones from two specific areas in the mont blanc aiguilles rouges region

regional scale development of opening mode calcite veins due to silica diagenesis the formation and distribution of natural fractures in cretaceous paleogene strata in jordan are strongly tied to diagenetic processes which in turn reflect the lithology of the host material observations collected from subsurface cores show that widespread fracturing began before compaction of the host sediment was complete based on ptygmatic folding of one set of mineral filled fractures veins non folded veins are preferentially developed within heavily cemented layers calcium carbonate is the greatest volumetric component of the host sediment and most fractures are at least partially filled by calcite dolomite and silica bearing fractures are present in dolomitized and silicified host beds respectively horizontal veins are filled by cone in cone calcite or rarely silica or dolomite the stratigraphic arrangement and degree of compaction around ptygmatically folded calcite veins and chert nodules suggest that silica diagenesis was an important driver of early fractures nevertheless those fractures were filled with carbonate cements as they opened based on crack seal texture of the vein fill the volume loss associated with silica diagenesis created fracture porosity which was filled coevally by carbonate cements the distribution of later veins reflects embrittlement of host layers by cementation and is consistent with crustal deformation as the primary fracture driver

on the distribution and separation of crystals in convecting magma abstract fractionation of crystals from magma stands squarely as the central principle of igneous petrology and the critical balance is the competition between crystal settling or rising velocity and magmatic convective velocity a ratio we call s the convective velocity is intimately related to the rate of heat transfer from the system although the theory of sediment distribution in rivers establishes the critical parametric balance and it has been often applied to igneous systems this method turns out to be valid only for small concentrations of crystals and it is not clear if it is accurate for other than turbulent flows where the prandtl number is near unity a generalized theory of particle crystal or bubble behavior is presented scaling of the generalized result shows for the magmatic conditions of small crystallinities small particle reynolds number and newtonian viscosity that the exact distribution of crystals in a convecting magma can be found analytically regardless of the flow field critical retention occurs only for 0 s s 0 for sinking crystals retention is centered in the region of maximum updraft for floating particles retention occurs in regions of downflow which for a simple cellular convective pattern produces a torus shaped retention region against the walls about the midsection of the body for a stack of flattened convective cells which in the crudest sense is analogous to double diffusive convection the zones of retention form depending on the exact flow field either a stack or staggered stack of pillows through the central region crystals settling from top to bottom around this stack take a tortuous path and may exhibit a complex but regular compositional zoning additional effects of fluids possessing a yield strength turbulence particle shape and wall and particle dispersive effects are more qualitatively evaluated for each flow field the amount of retention and the effective settling velocity of all crystals is found as a function of s the critical parameter s controlling retention can be estimated from a parametric representation involving stokes s law and the rayleigh number this shows that some retention probably occurs in all magmas and it increases with approach of the magma to the earth s surface although both crystal settling rate and convection decrease with increasing magmatic viscosity the overall effect is to increase retention decrease s magmas having a viscosity near and beyond about 10 4 poise and chambered in the nearsurface environment should show large degrees of crystal retention retention is however never complete for magmas and the flux of settling crystals leading to differentiation varies as a function of crystallinity this flux or flux probability p f is zero both at the liquidus and the point of maximum packing of crystals which for basalts is about 60 the importance of differentiation is regulated by the amount of time spent in the high crystal flux state and a relative measure of this time is given by the thermal probability p t introduced previously thus the probability of differentiation p d is given by the product p f p t which shows that differentiation must occur over a restricted range of crystallinities from about 20 to 45 for basalts and from about 10 to 30 for rhyolitic magmas the most basic lessons learned here are that the full range of crystallinities is not equally accessible to crystal fractionation and the most fundamental information describing the dynamic state and behavior of magma may well be the distribution of crystal sizes found in lavas

microtectonic and geochemical characterization of thrusting in a foreland basin example of the south pyrenean orogenic wedge spain abstract in orogenic systems thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins metamorphic diagenetic meteoric this study focuses on the monte perdido thrust unit emplaced in the paleogene jaca thrust sheet top basin in the sw central pyrenees we aim to decipher the mechanisms and p t conditions of deformation in fault zones and characterize the related fluid involvement through combined microstructural geochemical and microthermometry analyses two thrust faults cutting platform limestones marls and siliciclastic turbidites of the lower part of the basin fill paleocene lower eocene have been studied the fault zones are characterized by metre thick shear zones with highly deformed foliated clay rich sediments foliation is underlined by preferentially oriented phyllosilicates several generations of shear and extension calcite quartz and chlorite bearing veins attest to fluid rock interactions during a multi stage deformation microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins with mineralizing fluids in equilibrium with the host sediments our results suggest an essentially closed hydrologic system and imply the absence of significant fluid flow along the studied fault zones microthermometric study on fluid inclusions present in calcite and quartz veins and calcite quartz oxygen isotopic fractionation determined for the first generation shear veins allow a geothermal gradient of 34 c km to be estimated analytical results demonstrate an evolution of the fault zones in three stages the first stage was related to the emplacement of the monte perdido thrust unit during the middle eocene at a temperature of 208 c and a burial depth of 5 7 km the second stage corresponds to a fault reactivation at a temperature of 240 c and a burial depth of 6 5 km the latter deformation may have been related to folding of the monte perdido thrust unit during the emplacement of the underlying gavarnie thrust unit during the late eocene early oligocene with deeper burial resulting from aggradation of the thrust sheet top basin fill the last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif

oxygen isotope thermometry of quartz calcite veins unraveling the thermal tectonic history of the subgreenschist facies morcles nappe swiss alps combined structural analysis and oxygen isotope thermometry of syntectonic quartz calcite fibrous veins can be used to correlate the thermal history of deformed rocks with specific structural and tectonic events results are presented for the morcles nappe in the western helvetic alps switzerland where mineral parageneses illite crystallinity and fluid inclusion chemistry record an apparent peak metamorphic temperature gradient that increased across the morcles nappe from anchizonal conditions in the foreland to epizonal conditions in its hinterland root zone twenty seven quartz calcite veins were analyzed in this study in order to determine the temperatures of veining during formation and deformation of the nappe peak metamorphic temperatures ranged from 260 to 290 c in the shallower foreland localities and to 330 to 350 c in the deeper more hinterland localities at the end of s1 foliation formation related to large scale folding temperatures gradually decreased throughout the nappe during subsequent development of the s2 foliation and s3 crenulation cleavage uplift and erosion of the overlying nappe pile resulted in slow cooling of the morcles nappe during the waning stages of the alpine orogeny the dominant foliation forming deformation of the morcles nappe occurred at elevated temperatures over the course of 10 to 15 ma combined structure oxygen isotope analyses of quartz calcite veins yield better temperature and temporal constraints on the thermal histories of subgreenschist vein bearing tectonites than do other geothermometers

syn deformation temperature and fossil fluid pathways along an exhumed detachment zone khao khwang fold thrust belt thailand abstract shale detachment zones their influence on deformational style and their internal mechanisms of deformation are an understudied aspect of fold thrust belts properties such as deformational temperature lithology and mineralogy are often recognized as having a key influence on the rheology and deformational style of detachment zones and overlying fold thrust belts however little work has been conducted on rock properties of known detachment zones a recently described upper level detachment zone in the exhumed khao khwang fold thrust belt of central thailand provides an ideal natural laboratory for investigation of the deformation conditions of the detachment zone and association with its complex deformational style the low grade metamorphic indicator illite crystallinty is used to broadly constrain deformational temperatures while oxygen and carbon stable isotope analysis provides insight into fluid flow history and fluid rock interaction illite crystallinity data indicate deep diagenetic to low anchizonal conditions and temperatures of 160 210 c in the shale detachment interpreted as reflecting peak metamorphic conditions during the triassic indosinian orogeny no trend between the intensity spacing complexity of structures and illite crystallinty is observed however shale shear zones of continuous style deformation and inferred higher finite strain display uniformly higher illite crystallinty than surrounding packages of discontinuously faulted shales we also note a positive association between total organic carbon content in the shales and the spacing and complexity of deformational structures data from limestones and syn tectonic vein fills detail the history of fluid rock interaction during early mesogenesis through to orogenesis the early covariant trend of increasingly negative 13 c and 18 o values is attributed to increasing burial while a divergent orogenic trend of increasingly negative 18 o values is interpreted as the result of a loss of matrix permeability and interruption of fluid rock re equilibration these hottest fluids were concentrated along large thrusts which facilitated fluid movement during orogenesis

discrimination of annealed and dynamic fabrics consequences for strain localization and deformation episodes of large scale shear zones abstract large scale shear zones are often characterized by long lasting deformation with complex strain localization behavior based on a drill core across polymineralic carbonate mylonites of the doldenhorn nappe helvetic alps switzerland the present study uses spatially resolved microstructural variations to discriminate unambiguously deformation microstructures from annealed ones to infer the deformation mechanisms and to reconstruct the strain localization history these goals require quantitative microstructural and textural analyses of sample suites in sections across the shear zone particularly the occurrence of two distinct zener trends i e the relationship between grain size and volume fraction of matrix and second phase grains allows for the identification of annealed from dynamic microstructures the data presented here indicate that continued shearing after peak metamorphic conditions and during exhumation induced cooling resulted in progressive strain localization at the base of the shear zone while the inactive parts of the formerly high temperature shear zone were progressively overprinted by annealing

alpine thermal and structural evolution of the highest external crystalline massif the mont blanc 1 the alpine structural evolution of the mont blanc highest point of the alps 4810 m and of the surrounding area has been reexamined the mont blanc and the aiguilles rouges external crystalline massifs are windows of variscan basement within the penninic and helvetic nappes new structural 40ar 39ar and fission track data combined with a compilation of earlier p t estimates and geochronological data give constraints on the amount and timing of the mont blanc and aiguilles rouges massifs exhumation alpine exhumation of the aiguilles rouges was limited to the thickness of the overlying nappes 10 km while rocks now outcropping in the mont blanc have been exhumed from 15 to 20 km depth uplift of the two massifs started 22 myr ago probably above an incipient thrust the alpine sole thrust at 12 ma the ne sw trending mont blanc shear zone mbsz initiated it is a major steep reverse fault with a dextral component whose existence has been overlooked by most authors that brings the mont blanc above the aiguilles rouges total vertical throw on the mbsz is estimated to be between 4 and 8 km fission track data suggest that relative motion between the aiguilles rouges and the mont blanc stopped 4 myr ago since that time uplift of the mont blanc has mostly taken place along the mont blanc back thrust a steep north dipping fault bounding the southern flank of the range the european roof is located where the back thrust intersects the mbsz uplift of the mont blanc and aiguilles rouges occurred toward the end of motion on the helvetic basal decollement hbd at the base of the helvetic nappes but is coeval with the jura thin skinned belt northwestward thrusting and uplift of the external crystalline massifs above the alpine sole thrust deformed the overlying helvetic nappes and formed a backstop inducing the formation of the jura arc in that part of the external alps nw se shortening with minor dextral ne sw motions appears to have been continuous from 22 ma until at least 4 ma but may be still active today a sequential history of the alpine structural evolution of the units now outcropping nw of the pennine thrust is proposed

in situ th pb dating of monazite in fibrous veins direct dating of veins and deformation in the shallow upper crust of the mexican orogen abstract few methods exist for directly dating orogenic events in the upper crust here we report in situ dates from 10 m diameter monazite grown in quartz calcite fibrous veins which precipitated at very low grade metamorphic conditions about 250 c in volcaniclastic and calcareous rocks of the early cretaceous trancas fm in the zimapan basin central mexico our integrated study includes regional and local structural and kinematic analysis of vein and folds detailed textural and mineralogical characterization of vein bearing minerals and texturally controlled th pb geochronologic analysis of monazite by la mc icpms we find that monazite in the veins preferentially crystallized at the interface between vein forming calcite and quartz fibers as well as at the vein host rock interface monazite ages range from 154 to 68 ma with the youngest sub population yielding a weighted mean age of 76 8 0 8 ma coincident with the age of basin wide folding as earlier constrained by ar ar illite dating the oldest monazite ages coincide with the timing of deposition of the volcaniclastic host rock given that veins are ubiquitous in shallow crustal rocks this approach to dating of veins with enclosed monazite has great potential to improve the constraints on temporal resolution of fluid rock interaction during of deformation

pressure temperature and composition history of syntectonic fluids in a low grade metamorphic terrane analysis of stable isotopes and fluid inclusions in centimeter scale fibrous quartz calcite strain fringes from the taconic thrust belt in vermont and new york allows reconstruc tion of fluid conditions and sources over the course of strain fringe growth oxygen isotope ratios in quartz show regular variations in d 18 o ranging between 19 2 and 20 0 in different parts of strain fringes fluid inclusions have low salinities 2 4 nacl equivalent in all parts of strain fringes and we propose that fluids were derived from clay dehydra tion variations in fluid temperature and pressure derived from stable isotope and fluid inclusion analysis mimic changes in the orientations of fibers indicating a strong corre lation between tectonics and fluids earliest fluids had temperatures of 240 8c temperatures declined over time to 200 8c and rose again to 260 8c fluid pressures began at 1 6 kbar 160 mpa and fell to 0 8 kbar 80 mpa before rising to 2 kbar 200 mpa we interpret these results in the context of thrust faulting and the dynamics of thrust wedges our model begins with thrusting along the bird mountain fault placing rocks from depth on shallower ones and raising the temperature of the footwall increasing temperatures would have stimulated clay dehydration raising fluid pressures and weak ening the rocks within the orogen reduced strength of the taconic accretionary wedge would have required lower critical taper angles stopping motion on the bird mountain fault and stimulating horizontal elongation within the taconic thrust wedge as fluid pressures and temperatures declined increasing strength of the rocks would have de manded higher critical taper angles stimulating renewed bird mountain thrusting and increases in temperature and fluid pressure we cannot uniquely determine the depth of burial during strain fringe growth but we can constrain the depth for different geother mal gradients and evaluate how close fluid pressures were to lithostatic the highest fluid pressures were 70 of lithostatic and could have been higher similar mechanisms tying fluid conditions to tectonics in a feedback loop may be active in accretionary prisms and thrust belts worldwide

mineralization and petrogenesis of the qiongheba porphyry copper deposit in mengxi district east junggar china abstract the qiongheba porphyry cu deposit is characterized by geochemical features of island arc and adakitic intrusions with fractional crystallization playing a key role in the formation of the ore bearing rocks calculated sulfur concentrations in silicate melts at sulfide saturation show that two thirds of the sulfur was exsolved during the fractional crystallization process to contribute to the formation of sulfides the ore bearing rocks in the qiongheba area yielded u pb zircon ages of 414 412 ma coeval with the 412 ma re os age of molybdenite indicating that sulfide mineralization is broadly coeval with magmatic crystallization the color cathodoluminescence of quartz purple and k feldspar pink in the fibrous veins and miarolitic cavities qtz 2 and kfs 2 are the same as those qtz 1 and kfs 1 in the granitic porphyry whereas the hydrothermal quartz qtz 3 and k feldspar kfs 3 are black and green suggesting that the color cathodoluminescence can be used to unravel the paragenesis of pcd the oxygen isotopic values of qtz 1 and qtz 2 range from 9 15 to 10 1 and 8 93 to 10 4 with calculated equilibrium fluid compositions of 9 86 to 11 7 and 10 5 to 12 0 respectively indicating a magma dominated fluid composition whereas qtz 3 veins have very low oxygen isotopic values from 4 60 to 1 25 with corresponding fluid compositions of 3 51 to 0 17 implying that the fluid formed via the mixing of magmatic and meteoric water titanium in quartz thermometry constrains the magmatic crystallization to 580 627 c whereas the magmatic to hydrothermal transition occurred at 523 613 c

microfabrics in carbonate mylonites along a large scale shear zone helvetic alps abstract carbonate mylonites with varying proportions of second phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the morcles nappe helvetic nappes switzerland variations of temperature stress and strain rate changes in chemistry of solid and fluid phases and differing degrees of strain localization and annealing were tracked by measuring the shapes mean sizes and size distributions of both matrix and second phase grains as well as crystal preferred orientation cpo of the matrix field structures suggest that strain rate was constant along the fault the mean and distribution of the calcite grain sizes were affected most profoundly by temperature increased temperature presumably accompanied by decreased stress correlated with larger mean sizes and wider size distributions at a given location the matrix grains in mylonites with more second phase particles are on average smaller have narrower size distributions and have more elongate shapes for example mylonites with 50 vol of second phases have matrix grain sizes half that of pure mylonites changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly temporal variations in conditions such as exhumation induced cooling apparently provoke changes in temperature stress and strain rate along the nappe these changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50 the matrix cpo strengthens with increasing temperature or strain but weakens and rotates with increasing second phase content these fabric changes suggest differing rates of grain growth grain size reduction and development of cpo owing to variations in the deformation conditions and perhaps mechanisms to interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric and in particular second phase minerals

the importance of diffusion advection and host rock lithology on vein formation a stable isotope study from the paleozoic ouachita orogenic belt arkansas and oklahoma more than 600 stable isotope analyses from veins and their metasedimentary host rocks from the ouachita orogenic belt of arkansas and oklahoma provide an opportunity to study fluid rock interaction processes associated with vein formation during deformation and low grade regional metamorphism the 18o values of vein quartz vary from 16 0 to 26 4 whereas coexisting host rocks have a greater range from 12 9 to 27 4 the oxygen isotopic compositions of quartz vein versus those of the coexisting host rocks follow an array described by 18ovein quartz 18owhole rock e where e 8 0 3 18owhole rock this relationship emphasizes the dependence of 18o values of vein quartz on host rock oxygen isotopic composition the e term empirically monitors the difference between the quartz water fractionation factor and the compositional dependence of the bulk rock water fractionation factor vein quartz host rock 18o fractionations are 0 in chert novaculite quartzite and siliceous shale and typically between 1 and 4 in sandstones and shales in quartzite and sandstone units that are bounded by shales and associated with significant quartz crystal deposits vein quartz host rock fractionations are often unusually large near 7 quartz calcite oxygen isotope geothermometry indicates that veins from the ouachita mountains formed over a temperature interval of 100 c consistent with fluid inclusion temperatures previously obtained from quartz crystals individual quartz veins are homogeneous with 0 4 variation for all vein orientations at all scales even though vein formation occurred over a temperature interval in which quartz water fractionation varies by 5 this homogeneity highlights the insensitivity of vein quartz 18o values to temperature when veins form under rock buffered conditions the similarity between vein and host rock 18o values in quartz rich lithologies and between vein and host rock 13c values in calcite bearing rocks indicates that diffusion was an important mass transport mechanism the variability in 18o values between calcite bearing veins and host rocks and large vein quartz whole rock fractionations in some sandstones and quartzites indicates that advection also played a major role in mass transport associated with vein formation this inference leads to the interpretation that veins from the ouachita mountains formed by a combined diffusion advection process whereby 18o and 13c from the host rock was transported into the veins with the assistance of a rock buffered fluid on outcrop scales of 10 100 m

linkages between salinity and brine channel distribution in young sea ice a high resolution study of bulk salinity was undertaken on laboratory grown sea ice to determine the extent of spatial variability of salinity and whether this was associated with brine channel structures ice samples at two different stages of development were compared with respect to physical state brine distribution and brine channel structures cold growing sea ice is shown to have steep bulk salinity gradients and a highly variable brine distribution that is closely linked to the location and morphology of brine channels areas of high bulk salinity are found to correspond directly to the positions of the brine channels and these areas are surrounded by ice that shows significant brine depletion it is observed that redistribution of the brine occurs as the ice cover goes through warming and melting phases the redistribution is attributed to an increase in porosity and pore connectivity permitting migration of brine through the ice the distribution of brine in warm ice is shown to be more homogeneous and independent of brine channel structures a number of mechanisms exploiting the enhanced mobility of brine in warm sea ice are used to explain the changes in the salinity profiles and brine distribution

structural and fluid evolution of saraburi group sedimentary carbonates central thailand a tectonically driven fluid system abstract a stable isotopic study focused on calcite cements vein fill calcite and various bioclasts was conducted on variably deformed and thrusted lower and middle permian carbonates of the saraburi group samples were collected in quarry faces across 3 areas in the saraburi lopburi region of central thailand stable isotope crossplots carbon and oxygen using texture aware isotope samples defined variable but related fluid cement histories which are tied to regional burial and then orogenic overprints driven by the indosinian triassic orogeny this was followed by telogenetic overprints driven by late cenozoic uplift the studied carbonates were deposited along the western margin of the indochina block where they were deposited as isolated calcareous algal sponge and fusilinid rimmed platforms on highs bound by extensional faults the platform areas passed laterally and vertically into more siliciclastic dominated sequences deposited in somewhat deeper waters within probable fault bound lows regional post depositional mesogenetic fluid rock re equilibration of the isotope values in ongoing calcite precipitates occurred until the matrix permeability was occluded via compaction and pressure solution this regional burial regime was followed by collision of the indochina and sibumasu blocks during the indosinian triassic blocks which drove a set of structurally focused thrust plane related increasingly warmer set of fluids through the studied sequences the final diagenetic overprint seen in the isotopic values of the latest calcite cements occurs in a telogenetic uplift setting driven by cenozoic tectonics and isostatic uplift integration of isotope data with its structural setting establishes a clear separation in fluid events related to two time separate tectonic episodes its fluid chemistry defines the permo triassic closure of the paleotethys and its subsequent reactivation during the tertiary collision of india and asia the c o covariant plot fields in the permian carbonates of central thailand are so distinct that it is possible to use their signatures to separate burial from meteoric cements in drill cuttings and hence recognise equivalent subsurface unconformities and likely zone of porosity development in possible buried hill plays in thailand

the use of a combined structural stable isotope and fluid inclusion study to constrain the kinematic history at the northern variscan front zone bettrechies northern france abstract a detailed structural stable isotope and fluid inclusion study of distinct vein generations has been performed in a kilometre scale syncline to correlate the temperature pressure conditions of vein formation with specific deformation episodes the structural relationship of the veins with cleavage folds faults and with one another allows the identification of pre syn and post variscan carbonate vein generations the stable isotope composition of the vein calcites and dolomites is very similar to that of the surrounding limestones and dolostones respectively this indicates that the cements were precipitated from fluids buffered by the host rock and implies that the temperature pressure characteristics of the fluids reflect the thermal history of the deformation history within the syncline microthermometric data of primary fluid inclusions were used to estimate the temperature pressure conditions at precipitation time and thus of the deformation pressure corrected trapping temperatures for the veins show a temperature evolution from pre variscan 310 c to variscan 260 200 c and post variscan 75 c this evolution indicates that the syncline developed not at a specific depth but rather as an active progressive deformation process during transport along the northern variscan thrust front

fluid systems above basement shear zones during inversion of pre orogenic sedimentary basins external crystalline massifs western alps abstract in the inner part of the external alps inherited liassic basins were buried and inverted during the oligo miocene collisional phase of the alpine orogeny in northern oisans during crustal shortening the basement was locally sheared while the cover was disharmonically folded above the main basement shear zones that did not propagate into the cover in this contribution we analyze the witnesses of paleo fluid circulations associated with these crustal deformations focusing particularly on bourg d oisans and mizoen basins external western alps on the basis of structural and microstructural observations coupled to geochemical analyses cathodoluminescence o and c stable isotopes trace elements of vein versus host rock minerals we show that in the cover fluids mainly circulated over short distances closed system however trace element data also show that percolation of small amounts of basement derived fluids occurred over several tens of meters in cover rocks right above basement shear zones indeed the three successive vein sets recognized in the field display enrichments in basement derived ni co and cr which indicate that fluid transfer from the basement was efficient since the beginning of basin inversion therefore confirming the synchronous deformation of cover and basement fluid temperatures and pressures are estimated microthermometry coupled to 18o of vein minerals to about 250 400 c and 2 5 kbar for veins that most likely formed at or close to metamorphic peak conditions these results coupled to literature data are finally integrated into a model of fluid circulation evolution through progressive deformation of the whole external western alps

an 40 ar 39 ar rb sr and stable isotope study of micas in low grade fold and thrust belt an example from the swiss helvetic alps white micas in carbonate rich tectonites and a few other rock types of large thrusts in the swiss helvetic fold and thrust belt have been analyzed by 40ar 39ar and rb sr techniques to better constrain the timing of alpine deformation for this region incremental 40ar 39ar heating experiments of 25 weakly metamorphosed anchizone to low greenschist samples yield plateau and staircase spectra we interpret most of the staircase release spectra result from variable mixtures of syntectonic neoformed and detrital micas the range in dates obtained within individual spectra depends primarily on the duration of mica nucleation and growth and relative proportions of neoformed and detrital mica rb sr analyses of 12 samples yield dates of ca 10 39 ma excluding one anomalously young sample these dates are slightly younger than the 40ar 39ar total gas dates obtained for the same samples the rb sr dates were calculated using initial 87sr 86sr ratios obtained from the carbonate dominated host rocks which are higher than normal mesozoic carbonate values due to exchange with fluids of higher 87sr 86sr ratios and lower 18o 16o ratios model dates calculated using 87sr 86sr values typical of mesozoic marine carbonates more closely approximate the 40ar 39ar total gas dates for most of the samples the similarities of rb sr and 40ar 39ar total gas dates are consistent with limited amounts of detrital mica in the samples the 18o values range from 24 15 vsmow for 2 6 m micas and 27 16 for the carbonate host rocks the carbonate values are significantly lower than their protolith values due to localized fluid rock interaction and fluid flow along most thrust surfaces although most calcite mica pairs are not in oxygen isotope equilibrium at temperatures of ca 200 400 c their isotopic fractionations are indicative of either 1 partial exchange between the minerals and a common external fluid or 2 growth or isotopic exchange of the mica with the carbonate after the carbonate had isotopically exchanged with an external fluid the geological significance of these results is not easily or uniquely determined and exemplifies the difficulties inherent in dating very fine grained micas of highly deformed tectonites in low grade metamorphic terranes two generalizations can be made regarding the dates obtained from the helvetic thrusts 1 samples from the two highest thrusts mt gond and sublage have all of their 40ar 39ar steps above 20 ma and 2 most samples from the deepest helvetic thrusts have steps often accounting for more than 80 of 39ar release between 15 and 25 ma these dates are consistent with the order of thrusting in the foreland imbricating system and increase proportions of neoformed to detrital mica in the more metamorphosed hinterland and deeply buried portions of the nappe pile individual thrusts accommodated the majority of their displacement during their initial incorporation into the foreland imbricating system and some thrusts remained active or were reactivated down to 15 ma

evolution of veins and sub economic ore at strassegg paleozoic of graz eastern alps austria evidence for local fluid transport during metamorphism the north eastern part of the graz paleozoic thrust sheet at strassegg austria is characterised by metamorphic assemblages that reflect increasing temperature conditions from 3008c in hangingwall to around 5508c in footwall units the main quartz andror carbonate vein generation cuts the schistosity at moderate to low angles is folded with the schistosity and is commonly boudinaged there is a correlation between vein and the host rock mineralogy additionally the d 18 o and 13 d c signatures of vein minerals quartz andror carbonates vary systematically with the isotopic signature of the host rock and its minerals within individual units d 18 o of vein quartz has a narrow range of values in contrast with a larger variation in both with d 18 o and d 13 c of carbonates at strassegg the greenschist unit hosts an as au mineralisation arsenopyrite

geochemistry of the adamello massif northern italy the tertiary adamello massif outcropping over an area of more than 550 km2 in the southern alps northern italy is composed mainly of granitoid rocks granodiorite tonalite quartz diorite with minor amounts of diorite and gabbro the major and trace element composition of these rocks is comparable to calc alkaline volcanic rocks of continental margins the granitoid rocks display spatial and temporal variations in their composition particularly in na p sr la nb and y contents and 87sr 86sr ratios the variations were probably produced by concurrent contamination wall rock assimilation and fractional crystallization of high alumina basaltic magma

brine fluxes from growing sea ice it is well known that brine drainage from growing sea ice has a controlling influence on its mechanical electromagnetic biological and transport properties and hence upon the buoyancy forcing and ecology in the polar oceans when the ice has exceeded a critical thickness the drainage process is dominated by brine channels liquid conduits extending through the ice we describe a theoretical model for the drainage process using mushy layer theory which demonstrates that the brine channel spacing is governed by a selection mechanism that maximizes the rate of removal of stored potential energy and hence the brine flux from the system the fluid transport through the sea ice and hence the scaling laws for brine fluxes and brine channel spacings are predicted importantly the resulting brine flux scaling is consistent with experimental data for growth from a fixed temperature surface allowing all parameters in the scaling law to be determined this provides an experimentally tested first principles derivation of a parameterization for brine fluxes from growing sea ice

inorganic carbon transport during sea ice growth and decay a carbon pump in polar seas 1 during sea ice formation in polar areas brine rejection increases the density in the underlying water column and thereby contributes to the formation of deep and intermediate water masses in the world ocean here we present evidence that dissolved inorganic carbon tco2 is rejected together with brine from growing sea ice and that low temperatures may result in a significant change in the ratio of tco2 and alkalinity in arctic sea ice compared with surface waters model calculations show that this sea ice driven carbon pump affects surface water partial pressure of co2 significantly in polar seas and potentially sequesters large amounts of co2 to the deep ocean

assimilation of felsic crust by basaltic magma thermal limits and extents of crustal contamination of mantle derived magmas basaltic magma is the most widely used probe of mantle chemistry and structure chemical characterization of the sources for mantle derived magma is possible only after quantitative evaluation of possible contamination by crustal wall rocks the most commonly invoked contamination mechanisms are the combined processes of crustal assimilation and magmatic fractional crystallization afc because of the energetic link between these processes predicting assimilation and crystallization progress requires modeling both heat and mass transfer in the magma country rock system using the melts software package we modeled isenthalpic heat balanced afc between two common types of basaltic magma and several types of felsic crust at 1 kbar our simulations show that during the early stages of isenthalpic afc the ratio of rates of assimilation to crystallization r may be substantially greater than one 2 0 2 7 allowing assimilation of a mass of country rock up to 5 18 of the initial magma mass with only 3 7 crystallization the second stage of afc beginning with plagioclase and or pyroxene saturation is characterized by lower r 0 5 1 0 the initial high r stage results from suppression of crystallization associated with the change in magma composition as assimilation progresses under certain conditions even small degrees of crystallization of olivine alone coupled with cooling of the magma can accommodate relatively large amounts of crustal assimilation and cause large shifts in isotopic and trace element geochemical indices with little differentiation

growth of and brine drainage from nacl h2o freezing a simulation of young sea ice 1 a numerical simulation is used to predict the early time evolution of the solidification and brine drainage of a binary nacl h2o mixture the mathematical formulation is based on continuum mixture theory as outlined by bennon and incropera 1987 and medjani 1993 results yield a simple relationship between surface temperature and cumulative salt mass draining from the ice additionally a scaling analysis of the energy equation leads to a simple parameterization for ice thickness results compare well with existing laboratory measurements however the delay in onset of brine drainage reported in the literature is not supported by these results images generated using continuum salinity and liquid fraction data overlaid with streamlines generated from velocity data provide a reasonable qualitative resemblance to laboratory observations of nacl h2o ice growth

nd sr isotopic and geochemical characteristics of the southern adamello northern italy intrusives implications for crustal versus mantle origin among the periadriatic tertiary calc alkaline intrusions in northern italy the adamello batholith displays the most convincing evidence for a mafic parentage this is particularly the case for the southern adamello where minor ultramafic to gabbroic bodies form the margins of several distinct and dominantly tonalitic plutons isotopic analyses are presented for the val fredda and blumone ultramafic gabbroic to tonalitic leucoquartzdioritic suites for the more felsic rock types of the spatially predominant re di castello group as well as for a lamprophyre this dike of picrobasaltic composition is thought to represent the parental magma field relations and a large body of petrographic geochemical and mineral chemical data point to a cogenetic origin for all of these rocks and to magmatic differentiation with fractional crystallization and accumulation as the main evolutionary mechanism this is compatible with the isotopic results for the blumone series and the mafic rocks of val fredda with end 3 8 to 1 5 and esr 9 1 to 4 6 a common parental magma similar to the lamprophyre end 3 1 esr 4 4 also seems plausible the isotopically homogeneous felsic lithologies of val fredda end 0 1 to 0 3 esr 2 9 to 0 7 structurally intimately associated with their mafic counterpart indicate crustal contamination incurred prior to their differentiation for the re di castello group progressing crustal affinity of isotopic compositions end of 1 9 to 4 9 and esr of 16 5 to 40 9 with chemical differentiation implies large scale interaction with a granitoid crustal component attempts at quantifying this process reveal individual characteristics and evolution for each pluton the data indicate extraction of this component from a source in the lower crust with time integrated low rb sr esr approximating 50 and en close to 6 corresponding to a 1000 ma crustal residence age if a two stage evolution is assumed formation of a gabbroic reservoir from the above parental melt would require uptake of some 4 12 wt of granitoid component by combined assimilation fractional crystallization whereas subsequent evolution to tonalitic compositions would necessitate admixing of 40 70 wt of granitoid partial melt assimilation thus mainly occurs during evolution from gabbroic to tonalitic compositions when the mafic magma is ponded near the mantle crust boundary and where homogenization prior to resuming buoyant ascent is assured precise locations and more detailed petrography of the samples is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document 91b 002 2 50 payment must accompany order