microscale isotopic zonation in graphite crystals evidence for channelled co influx in granulites abstract coarse graphite in association with cordierite and quartz within a vein in a metapelite locality at chittikara cht in southern india illustrates precipitation of graphite from co 2 rich fluids carbon isotope traverses within individual graphite crystals using a microsampling technique reveal strong isotopic zonations in graphite crystal from the vein with 13 c values oscillating between 13 in the core and 8 5 in the rim co 2 trapped within fluid inclusions in the cordierite shows 13 c 5 suggesting isotopic equilbrium with the core composition of the graphite a graphite crystal from the metapelite immediately adjacent to the vein is also zoned with a smooth rimward increase in 13 c disseminated graphite flakes in the host metapelites ca 1 m from the vein are however unzoned and possess strongly negative 13 c values 34 4 the rimward increase in 13 c the absence of other carbon bearing phases and the sluggish exchange rates for carbon in graphites preclude diffusive re equilibration and suggest that the different zoning patterns in the coarse graphite flakes within and adjacent to the vein assemblage at cht have resulted from precipitation in different parts of a highly channelled fluid regime where fluids are non wetting and move episodically by a hydraulic fracture mechanism our study provides the first unambiguous insight into graphite precipitation mechanisms and has potential implications for the nature of fluid interconnectivity and co 2 transport and equilibration length scales within the crust

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

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

controls on the mechanisms of fluid infiltration and front advection during regional metamorphism a stable isotope and textural study of retrograde dalradian rocks of the sw scottish highlands vein controlled retrograde infiltration of h2o co2 fluids into dalradian epidote amphibolite facies rocks of the sw scottish highlands under greenschist facies conditions resulted in alteration of calcite rich marble bands to dolomite and spatially associated 18o enrichment of about 10 on a scale of metres fluid inclusion data indicate that the retrograde fluid was an h2o salt mixture with a low co2 content and that the temperature of the fluid was about 400d c detailed petrographic and textural backscattered electron imaging studies at one garnet grade locality show that advection of fluid into marbles proceeded by a calcite calcite grain edge flow mechanism while alteration of non carbonate wall rock is associated with veinlets and microcracks stable isotopic analysis of carbonates from marble bands provides evidence for advection of isotopic fronts through carbonate wall rocks perpendicular to dolomite veins and fluid fluxes in the range 2 4 28 6 m3 m2 have been computed from measured advection distances coincidence of isotope and reaction fronts is considered to result from reaction enhanced kinetics of isotope exchange at the reaction front front advection distances are related to the proportion of calcite to quartz in each marble band with the largest advection distance occurring in nearly pure calcite matrix this relationship indicates that fluid flow in carbonates is only possible along fluid calcite calcite grain edges however experimental constraints on dihedral angles in calcite fluid systems require that pervasive infiltration occurred in response to calcite dissolution initiated at calcite calcite grain junctions rather than to an open calcite pore geometry the regional extent of the retrograde infiltration event has been documented from the high 18o of dolomite ankerite carbonates from veins and host rocks over an area of least 50 50 km in the sw scottish highlands isotopically exotic 18o rich retrograde fluids have moved rapidly upwards through the crust inducing isotopic exchange and mineral reaction in wall rocks only where lithology pore geometry or mineral solubilities pressure and temperature have been appropriate for pervasive infiltration to occur

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

comparison of garnet biotite calcite graphite and calcite dolomite thermometry in the grenville orogen ontario canada the elzevir terrane of the grenville orogen in southern ontario contains metapelites and abundant graphitic marbles that were regionally metamorphosed from the upper greenschist to upper amphibolite facies comparative thermometry was undertaken with widely used calibrations for the systems garnet biotite calcite dolomite and calcite graphite temperatures that are obtained from matrix biotites paired with prograde garnet near rim analyses are usually consistent with those determined using calcite graphite thermometry however calcite graphite thermometry occasionally yields low temperatures due to lack of equilibration of anomalously light graphite application of calcite graphite and garnet biotite systems may yield temperatures up to 70 c higher than calcite dolomite in amphibolite facies rocks calcite dolomite temperatures most closely approach those from calcite graphite and garnet biotite when the samples contain a single generation of dolomite and calcite grains contain no visible dolomite exsolution lamellae however some of these samples yield temperatures considerably lower than temperatures calculated from calcite graphite and garnet biotite thermometry indicating that the calcite dolomite thermometer may have been partially reset during retrogression estimated peak metamorphic temperatures of regional metamorphism between madoc upper greenschist facies and bancroft upper amphibolite facies range from 500 to 650 c these results place the chlorite staurolite isograd at 540 c the kyanite sillimanite isograd at 590 c and the sillimanite k feldspar isograd at 650 c although each thermometer may have an absolute uncertainty of as much as 50 c the 50 to 60 c temperature differences between the isograds are probably accurate to 10 to 20 c an incomplete picture of the thermal gradients can result from the application of only one thermometer in a given area simultaneous application of several systems allows one to recognize and overcome the inherent limitations of each thermometer

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

isotopic evidence for involvement of c0 2 bearing magmas in granulite formation it has been suggested1 2 that co2 bearing magmas play an important part in the formation of granulites these magmas crystallize directly into granulites and also expel fluids which promote the development of granulite facies mineral assemblages in adjacent country rocks direct evidence for carbonic fluids remains elusive however as granulite facies aureoles adjacent to charnockitic intrusives1 may result either from the influx of carbonic fluids derived from the intrusives or simply from extraction of water into a vapour absent melt here we report results of a detailed study of carbon isotope compositions of graphite associated with a charnockite dyke from the ponmudi quarry of south india higher graphite abundances and an anomalously heavy carbon isotopic composition 13cgr 8 1 0 at the dyke margins indicate that externally derived co2 rich fluids were transported into the ponmudi paragneisses by the intrusive and precipitated nearly quantitatively as graphite on encountering reducing country rocks the occurrence of large orthopyroxene crystals along the dyke margins suggests that these fluids also served to dehydrate the country rocks this dyke may thus be representative of the widespread transport of carbonic fluids in this terrain by felsic magmas

calcite graphite isotope thermometry a test for polymetamorphism in marble tudor gabbro aureole ontario canada graphitization and coarsening of organic material in carbonate bearing metasedimentary rocks is accompanied by carbon isotope exchange which is the basis of a refractory pressure independent geothermometer comparison of observed isotopic fractionations between calcite and graphite a13ccal gr with independent petrological thermometers provides the following empirical calibration over the range 400 800 c a13ccal gr 5 81 x lo6 x t k 2 61 this system has its greatest potential in marbles where calcite graphite is a common assemblage and other geothermometers are often unavailable the temperature dependency of this empirical calibration differs from theoretical calibrations reasons for this are unclear but the new empirical calibration yields temperature estimates in better agreement with independent thermometry from several terranes and is preferred for geological applications both calcite graphite isotopic thermometry and calcite dolomite solvus thermometry are applied to marble adjacent to the tudor gabbro in the grenville province of ontario canada the marble has undergone two metamorphic episodes early contact metamorphism and later regional metamorphism values of a13cca gr decrease regularly from c 8 0 in samples over 2 km from the pluton to values of 3 4 within 200m of the contact these samples appear to preserve fractionations from the early thermal aureole with the empirical geothermometer and indicate temperatures of 450 500 c away from the intrusion and 700 750 c near the gabbro this thermal profile around the gabbro is consistent with conductive heat flow models in contrast the distribution of mg between calcite and dolomite has been completely reset during later regional metamorphism and yields uniform temperatures of c 500 c even at the contact graphite textures are important for interpreting the results of the calcite graphite thermometer coarsening of graphite approaching the tudor gabbro correlates with the decrease in isotopic fractionations and provides textural evidence that graphite crystallization took place at the time of intrusion in contrast to isotopic exchange during prograde metamorphism which is facilitated by graphitization retrogressive carbon isotopic exchange appears to require recrystallization of graphite which is sluggish and easily recognized texturally resistance of the calcite graphite system to resetting permits thermometry in polymetamorphic settings to see through later events that have disturbed other systems

constraints on the application of carbon isotope thermometry in high to ultrahigh temperature metamorphic terranes nine marble horizons from the granulite facies terrane of southern india were examined in detail for stable carbon and oxygen isotopes in calcite and carbon isotopes in graphite the marbles in trivandrum block show coupled lowering of 13c and 18o values in calcite and heterogeneous single crystal 13c values 1 to 10 for graphite indicating varying carbon isotope fractionation between calcite and graphite despite the granulite facies regional metamorphic conditions the stable isotope patterns suggest alteration of 13c and 18o values in marbles by infiltration of low 13c 18o bearing fluids the extent of alteration being a direct function of the fluid rock ratio the carbon isotope zonation preserved in graphite suggests that the graphite crystals precipitated recrystallized in the presence of an externally derived co2 rich fluid and that the infiltration had occurred under high temperature and low fo2 conditions during metamorphism the onset of graphite precipitation resulted in a depletion of the carbon isotope values of the remaining fluid calcite carbon reservoir following a rayleigh type distillation process within fluid rich pockets pathways in marbles resulting in the observed zonation the results suggest that calcite graphite thermometry cannot be applied in marbles that are affected by external carbonic fluid infiltration however marble horizons in the madurai block where the effect of fluid infiltration is not detected record clear imprints of ultrahigh temperature metamorphism 800 1000 c with fractionations reaching 1000 c and would be consistent with uht metamorphism

graphite bearing co2 fluid inclusions in granulites insights on graphite precipitation and carbon isotope evolution graphite in deep crustal enderbitic orthopyroxene garnet plagioclase quartz granulites 740 c 8 9 kb of nilgiri hills southern india were investigated for their spectroscopic and isotopic characteristics four types of graphite crystals were identified the first type gri which is interstitial to other mineral grains can be grouped into two subtypes gria and grib gria is either irregular in shape or deformed and rough textured with average 13c values of 12 7 0 4 n 3 a later generation of interstitial graphite grib shows polygonal crystal shapes and highly reflecting smooth surface features these graphite grains are more common and have 13c values of 11 9 0 3 n 14 both subtypes show well defined raman shifts suggesting a highly crystalline nature cores of interstitial graphite grains have on average lower 13c values by 0 5 compared to that of the rim the second type of graphite grii occurs as solid inclusions in silicate minerals commonly forming regular hexagonal crystals with a slightly disordered structure the third type of graphite griii is associated with solid inclusions up to 100 m that have decrepitation halos of numerous small 15 m satellite fluid inclusions of pure co2 with varying density 1 105 to 0 75 g cm3 the fourth type of graphite griv is found as daughter crystals within primary type co2 fluid inclusions in garnet and quartz these fluid inclusions have a range of densities 1 05 to 0 90 g cm3 but in general are significantly less dense than graphite free primary pure co2 fluid inclusions 1 12 g cm3 raman spectral characteristics of graphite inside fluid inclusions suggest graphite crystallization at low temperature 500 c the precipitation of graphite probably occurred during the isobaric cooling of co2 rich peak metamorphic fluid as a result of oxyexsolution of oxide phases the oxyexsolution process is evidenced by the magnetite ilmenite granular exsolution textures and the systematic presence of numerous micron sized rutile and other oxide inclusions in association with fluid inclusions within garnet plagioclase and quartz the carbon isotope compositions of coexisting co2 in fluid inclusions and graphite show a fractionation co2 gr co2 gr of 6 in garnet consistent with the existing theoretical estimates of co2 gr co2 gr at 800 c a subsequent generation of co2 inclusions trapped in matrix quartz and quartz segregation have higher 13c values 4 and 2 9 respectively graphite in quartz segregations also has higher 13c values 9 8 than those in enderbite 12 7 micro graphite crystals included in garnet quartz enderbite and quartz segregation have average 13c values of 11 1 10 4 and 8 7 respectively indicating progressive enrichment in 13c with a decrease in temperature of recrystallization of respective minerals this progressive enrichment is also observed in carbon isotope compositions of fluid inclusion co2 suggesting isotopic equilibrium during graphite precipitation from co2 fluids thus the carbon isotope record preserved in these rocks by the interstitial graphite co2 fluid in enderbite graphite microcrystals graphite in quartz segregation and co2 fluid in quartz segregation suggests a temperature controlled isotopic evolution this evolution is in accordance with a closed system rayleigh type graphite precipitation process which progressively enriched residual co2 in 13c

geochemistry of archean carbonaceous cherts deposited at immature island arc setting in the pilbara block western australia abstract archean carbonaceous meta cherts upper greenschist to amphibolite facies from the nickol well unit the cleaverville group 3 2ga in the roebourne district in west pilbara are characterized by variable al2o3 tio2 zr tio2 and cr th values and by high concentrations of carbon and some trace metals distribution patterns of the cherts on a newly proposed diagram al2o3 tio2 element al2o3 indicate that concentrations of cr v and ni can be explained by contributions of clastic components whereas concentrations of cu zn and pb are much higher than those expected solely from clastic contributions detrital material in the cherts was derived from a wide variety of volcanic sources mafic ultramafic felsic sources consistent with the inferred geological setting of the cleaverville group immature island arc setting excess cu zn and pb are probably from hydrothermal solutions as suggested by positive eu anomalies and enrichment in heavy rare earth elements ree in chondrite normalized patterns high concentrations and light isotopic values of c 17 to 24 per mil in the cherts indicate that the precursory sediments were enriched in organic materials although it is unclear whether the organic material was derived from organic particles that settled from the ocean surface or benthic microbes in either case it is possible that this material played an important role in the accumulation of heavy metals cu zn and pb in the sediments

calcite graphite isotope thermometry in amphibolite facies marble bancroft ontario this study presents calcite graphite carbon isotope fractionations for 32 samples from marble in the northern elzevir terrane of the central metasedimentary belt grenville province southern ontario canada these results are compared with temperatures calculated by calcite dolomite thermometry 15 samples garnet biotite thermometry four samples and garnet hornblende thermometry three samples cal gr values vary regularly across the area from 6 5 in the south to 4 0 in the north which corresponds to temperatures of 525 c in the south to 650 c in the north previous empirical calibration of the calcite graphite thermometer agrees very well with calcite dolomite garnet biotite and garnet hornblende thermometry whereas theoretical calibrations compare less well with the independent thermometry isograds in marble based on the reactions rutile calcite quartz titanite and tremolite calcite quartz diopside span temperatures of 525 600 c and are consistent with calculated temperature x co2 relations results of this study compare favourably with large scale regional isotherms however local variation is greater than that revealed by large scale sampling strategies it remains unclear whether the temperature cal gr relationship observed in natural materials below 650 c represents equilibrium fractionations or not but the regularity and consistency apparent in this study demonstrate its utility for thermometry in amphibolite facies marble

quantification of bioturbation in hemipelagic sediments via thin section image analysis traditional ichnofabric descriptive semiquantitative l schemes rely upon subjective estimates of the degree to which original sedimentary fabrics have been disrupted this paper presents an objective method of quantifying bioturbation in hemipelagic sediments based on a thin section image analysis technique in order to perform these analyses optical or backscattered electron micrographs are processed in order to obtain black and white images in these images black pixels are silt size larger grains and the clay size sedimentary matrix are white pixels once the initial processing has been accomplished an index h is defined to quantify the horizontal orientation of the larger grain size fraction of the sediment h is low for bioturbated fabric and high for laminated sediments in hemipelagic suspension deposits h can he used to quantify bioturbation assuming that no other sedimentary processes have disrupted the original depositional fabric the quantitive bioturbation scheme described here is consistent with existing semiquantitative bioturbation schemes in addition it is objective and provides higher resolution descriptions of biological processes that disrupted the sediment after deposition applying this quantitative scheme should refine future paleoecological reconstruction derived from lacustrine and marine successions

mineralogical and isotopic characterization of graphite deposits from the anatectic complex of toledo central spain graphite is found dispersed in high grade metapelitic rocks of the anatectic complex of toledo act and was mined during the mid twentieth century in places where it has been concentrated guadamur and la puebla de montalban mines some samples from these mines show variable but significant alteration intensity reaching very low t hydrothermal supergene conditions for some samples from the waste heap of the guadamur site 100 c and 1 kbar micro raman and xrd data indicate that all the studied act graphite is of high crystallinity irrespective of the degree of hydrothermal alteration chemical differences were obtained for graphite 13c composition act granulitic graphite shows 13cpdb values in the range of 20 5 to 27 8 indicating a biogenic origin interaction of graphite with hydrothermal fluids does not modify isotopic compositions even in the most transformed samples from mining sites the different isotopic signatures of graphite from the mining sites reflect its contrasted primary carbon source the high crystallinity of studied graphite makes this area of central spain suitable for graphitic exploration and its potential exploitation due to the low carbon content required for its viability and its strategic applications in advanced technologies such as graphene synthesis

multistage graphite precipitation through protracted fluid flow in sheared metagranitoid digana sri lanka evidence from stable isotopes abstract the digana metagranitoid situated within the digana shear zone a critical junction between the highland and wanni complexes of sri lanka hosts a variety of graphite types with structural evidence showing formation during different stages prior to and after deformational events affecting this terrain here we discuss their occurrence association and stable isotopes the carbon isotopes of graphite reported in this study from the sri lankan high grade metamorphic terrain differ significantly from the composition of graphite reported elsewhere in other precambrian terrains the stable isotope composition from random crystals depicts an enriched carbon isotopic composition in the range 1 6 to 8 suggesting precipitation by reduction from co2 rich fluids intracrystalline microscale traverses made on graphite crystals indicate the 13c composition of the rims becoming progressively lighter in 13c in metagranitoid hosted samples with the variation reaching up to 1 5 consistent with the changing fluid regimes induced by decreasing temperature during the graphite growth and shows the preservation of core at higher temperatures a highly enriched carbon isotopic composition 0 6 with a rimward enrichment of 13c observed in migmatites contrary to the values in metagranitoid indicates preferential enrichment of heavy isotopes as a result of the partial melting and dissolution reprecipitation of graphite the oxygen isotopic composition of a quartz calcite vein show values in the range 18 5 to 20 typical for recycled crustal source the tight constraint in the isotopic data from different graphite types studied indicates a homogeneous fluid source for the deposits prolonged fluid flow in this region is envisaged in this study which is related to the multistage deformation of the crustal scale shear zone

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

graphite mineralization in paleoproterozoic khondalites of the north china craton a carbon isotope study abstract graphite mineralization in precambrian supracrustal rocks provide important information on the source characteristics of carbon and has been the focus of studies tracking primitive life in the early earth as well as a geochemical tracer in fluid rock interaction processes here we present results from a high precision carbon stable isotope study of the different associations of graphites from a graphite deposit in the paleoproterozoic khondalite belt of the north china craton our results show that disseminated graphite occurring as stratabound deposits along the compositional planes of the khondalites possess the lowest 13c values of ca 25 5 graphite in the massive ores also show identical composition with 13c values in the narrow range of ca 25 3 to 25 7 coarse graphite flakes in quartz pods and veins show slightly heavier values with 13c in the range of 19 1 to 20 9 such flakes with 13c composition of ca 20 6 were also deposited in some domains of the host khondalites the graphite in melt pockets within felsic leucosomes show the heaviest 13c values in the range of 15 8 to 16 8 micro sampling perpendicular to the c axis of the graphite crystals indicates a remarkable homogeneity of carbon isotopic composition within the individual graphite types the highly negative 13c values of the dominant graphite type in this deposit as well as similar values reported for those from other deposits in the region compare well with the isotopic signature of biogenic carbon occurring in other precambrian terranes and suggest that microbial life was flourishing in the paleoproterozoic oceans that closed during the final assembly of the north china craton the 13c enriched graphite in veins and melt pockets might have been deposited from mixed fluids derived through degassing of organic material during high grade metamorphism and externally derived co2 rich fluids

carbon isotope thermometry in marbles of the adirondack mountains new york carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the adirondack mountains new york eighty nine calcite graphite pairs from the amphibolite grade nw adirondacks change systematically in temperature north westwards from 680 to 640 to 670 c over a 30 km distance reflecting transitions from amphibolite facies towards granulite facies to the north west and to the south east temperature contours based on calcite graphite thermometry in the nw adirondacks parallel mineral isograds with the orthopyroxene isograd falling above 675 c and indicate that regional metamorphic temperatures were up to 75 c higher than temperatures inferred from isotherms based on cation and solvus thermometry bohlen et al 1985 fifty five calcite graphite pairs from granulite grade marbles of the central adirondacks give regional metamorphic temperatures of 670 780 c in general agreement with cation and solvus thermometry data for amphibolite and granulite grade marbles show a 12 oo range in 13ccal and 13cgr a strong correlation between carbon isotopic composition and the abundance of graphite cgr crock indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism the trends seen in 13c vs cgr crock and 13ccal vs 13cgr could not have been preserved if significant amounts of co2 rich fluid had pervasively infiltrated the adirondacks at any time the close fit between natural data and calculated trends of 13c vs cgr crock indicates a biogenic origin for adirondack graphites even though low 13c values are not preserved in marble delamination of 17 graphite flakes perpendicular to the c axis reveals isotopic zonation with higher 13c cores these isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite samples located 2km from anorthosite show a decrease of 0 5 0 8 oo in the outer 100 of the grains while samples at distances over 8 km show smaller core to rim decreases of c 0 2 oo correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism core graphite compositions indicate contact metamorphic temperatures were 860 890 c within 1 km of the marcy anorthosite massif if samples with a significant contact metamorphic effect cal gr 3 2 oo are not included then the remaining 38 granulite facies samples define the relation 13c cal gr 3 56 106t 2 k

evidence for cnidaria like behavior in ca 560 ma ediacaran aspidella comment menon et al 2013 1 regard wrinkles at the base of discoid fossils aspidella terranovica and deformation of laminae in cut slabs as evidence for upward migration of a cnidarian polyp in marine shales but their observations are better explained by a sessile growing organism with growth

carbon isotopic thermometry calibrated by dolomite calcite solvus temperatures abstract the temperature dependence of carbon isotopic fractionations between calcite and graphite and between dolomite and graphite are calibrated by the calcite dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the kasuga area central japan the carbon isotopic fractionations 13ccc gr and 13cdo gr systematically decrease with increasing metamorphic temperature the concordant relationships between the fractionations and solvus temperatures are approximately linear with t 2 over the temperature range 400 to 680 c 13ccc gr 5 6 106 t 2 k 2 4 13cdo gr 5 9 106 t 2 k 1 9 these systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases the equation for the calcite graphite system has a slope steeper than bottinga s 1969 results it is however in good agreement with that of valley and o neil 1981 in the temperature range from 600 to 800 c because of the relatively high sensitivity to temperature these isotopic geothermometers are useful for determining the temperatures in moderate to high grade metamorphosed carbonate rocks

an integrated cathodoluminescence video capture microsampling system a new system is described that permits real time microdrilling of sedimentary grains and crystals within cathodoluminescence zonations low light cathodoluminescence photomicrograph images are captured with a thermoelectrically cooled color video camera and saved on a computer these cathodoluminescence images are then transparently superimposed on a standard color video image of the sample being microdrilled on a 20 m scale using a video mixer this integrated system can be applied to a wide variety of sedimentary rocks and minerals

graphite content and isotopic fractionation between calcite graphite pairs in metasediments from the mgama hills southern kenya abstract amphibolite grade metasediments from the mgama hills region kenya contain conspicuous quantities of graphite most probably derived from organic progenitor materials the highest graphite contents 5 1 20 4 are found in schists whereas calcite marbles intercalated in the sequence contain relatively low amounts 0 1 2 0 the graphitic constituents are consistently enriched in 13 c relative to common sedimentary organic material with the highest isotopic ratios in graphite from the marbles 13 c 7 3 5 0 n 10 carbon isotope fractionations between calcite and graphite mostly vary between 3 3 and 7 1 which comes close to both empirically recorded and thermodynamically calculated fractionations in the temperature range of the upper amphibolite facies 550 650 c however larger values occasionally encountered in the marbles suggest that complete isotopic equilibrium is not always attained in amphibolite facies metamorphism

intercrystalline stable isotope diffusion a fast grain boundary model we formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals and the intragranular distribution of stable isotopes in each mineral as functions of mineral grain sizes and shapes diffusivities modes equilibrium isotopic fractionations and the cooling rate of a rock one of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes this fast grain boundary fgb model describes interdiffusion between any number of mineral grains assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled the model can be used for a rock containing any number of minerals and number of grain sizes of each mineral several grain shapes and any thermal history or domain size desired previous models describing stable isotope interdiffusion upon cooling have been based on dodson s equation or an equivalent numerical analogue the closure temperature of dodson is the average bulk temperature recorded between a mineral and an infinite reservoir by using dodson s equation these models have treated the closure temperature as an innate characteristic of a given mineral independent of the amounts and diffusion rates of other minerals such models do not accurately describe the mass balance of many stable isotope interdiffusion problems existing models for cation interdiffusion could be applied to stable isotopes with some modifications but only describe exchange between two minerals under specific conditions the results of fgb calculations differ considerably from the predictions of dodson s equation in many rock types of interest actual calculations using the fgb model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient and may differ from that predicted by dodson s equation by hundreds of degrees c either or both of two minerals may preserve detectable zonation which may in some instances be larger in the faster diffusing mineral rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone the results of fgb diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations concordant or discordant recorded within any rock in which diffusion could have acted over observable scales the predictions of this model are applicable to thermometry evaluation of open or closed system retrogression and determination of cooling rates or diffusion coefficients

13c 12c exchange between calcite and graphite a possible thermometer in grenville marbles the fractionation of 13c between calcite and graphite cc gr is consistently small 2 6 4 8 permil in 34 assemblages from upper amphibolite and granulite facies marbles of the grenville province in 25 samples from the adirondack mountains new york it decreases regularly with increasing metamorphic temperature the fractionations are independent of absolute 13c values of calcite 2 9 to 5 0 for t 600 800 c the adirondack data are described by cc gr 0 00748t c 8 68 this good correlation between and t suggests that carbon isotope equilibrium was attained in these high grade marbles and that the theoretical calculations of this fractionation by bottinga are approximately 2 permil too large in this temperature range because of the relatively high temperature sensitivity suggested by these results and by bottinga s calculations and the pressure independence of isotope fractionation cc gr may provide a very good thermometer for high grade marbles comparison of this field calibration for cc gr vs temperature with results from other terranes supports the utility of cc gr for geothermometry and suggests that graphite is much more sluggish to exchange than calcite that exchange between calcite and graphite occurs at temperatures as low as 300 c and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500 600 c because 13c exchange is an unavoidable metamorphic process at temperatures above 300 c high values of 13c gr in moderate to high grade carbonate bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite

the calcite graphite isotope thermometer data on graphite bearing marbles from naxos greece abstract graphite bearing marbles occur in the regional metamorphic complex of naxos over a continuous temperature range of 380 to 670 c the graphite is of biogenic origin and changed its original isotopic composition towards values in equilibrium with the calcite partial isotope exchange took place at temperatures as low as 380 c but near equilibrium values were generally not reached below 550 c the data agree better with the theoretically derived fractionation curve of bottinga 1969 than with the empirical curve proposed by valley and o neil 1981 we believe that the system will not provide a good thermometer

equilibrium dihedral angles in the system h2o co2 nacl calcite and implications for fluid flow during metamorphism fluid calcite calcite dihedral angles have been measured for fluids in the system h2o co2 nacl between 1 and 2 kbar and 550 750 c it is found that the calcite calcite h2o dihedral angle decreases steadily with addition of nacl from a value of about 80 pure water to 44 60 wt nacl the co2 h2o system displays a well defined minimum at x co 2 0 5 with a dihedral angle of 50 in contrast to those of pure co2 and h2o which are 90 and 80 respectively experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the co2 h2o nacl system which can be approximately correlated with the compositions of the two fluid phases such bimodality was only observed for immiscible fluids in the h2o nacl system if the quench rate exceeded about 200 c per min this is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching the fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with x co 2 close to 0 5 fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly h2o rich or co2 rich and of low salinity all other fluid compositions in the h2o co2 nacl calcite system will occupy isolated pores the largest of which will grow at the expense of the smallest escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture in contrast previous experimental studies of quartz fluid dihedral angles between 950 and 1100 c watson and brenan 1987 predict that quartz dominated lithologies will permit pervasive flow of h2o nacl fluids but not of h2o co2 fluids documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites psammites and limestones which support the results of the experimental studies are discussed

phosphates and carbon on mars exobiological implications and sample return considerations much of the surface of mars may preserve chemical information contained in rocks from the noachian era with ages that overlap the correspondingly earliest archean geological history of the earth or from before around 3800 ma ma 1 106 years metabolically sophisticated life which utilized phosphate and carbon and was capable of fractionating carbon isotopes was apparently present already on earth by 3800 ma or within 600 ma after the formation of the planet an early appearance of life on earth opens the strong possibility for a similarly early and rapid emergence of life on planet mars this hypothesis remains within the realm of plausibility so long as it can be established that liquid water and energy sources were available there for inchoate life and that the life that emerged reached a level of complexity which could be recognized by its chemical and perhaps morphological remains hypotheses to be used in the search for an ancient martian biosphere from future sample return missions are testable by examining the record of life in ancient terrestrial sedimentary rocks including those that contain rare and recognizable physical microfossils morphofossils identified on the basis of their shape alone and stable authigenic biominerals which include carbonaceous matter having characteristically fractionated carbon isotope signatures here termed chemofossils prior to sample return these tests can be applied to the mineral associations of the snc meteorites a group of meteorites believed to have originated on mars recent claims of a biological origin for secondary minerals and their features as well as for trace organic compounds in the martian meteorite alh84001 are derived in part from the interpretation of putative nanofossil shapes and the nature of the associated mineral assemblage in small carbonate deposits of an igneous rock such igneous samples would not normally be the best candidate to search for evidence of past life even on earth investigations of these mineral occurrences in the martian meteorites and of the oldest geological records on earth provide a useful framework for 1 using mineral phase relationships 2 analytical data of stable carbon isotopic distributions and 3 the problematic task of morphofossil interpretations in the search for life via future sample return missions from the ancient surface of mars

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

dehydration reaction and isotope front transport induced by co2infiltration at nuliyam south india the field relations from a quarry at nuliyam south india illustrate dehydration of an amphibolite facies gneiss to granulite facies charnockite by co2 influx over a scale of 30 m both the calc silicate source of the fluids and the full extent of their penetration into the gneiss are preserved in a continuous section fluid flow is by a hydraulic fracture mechanism but is thought to be pervasive the sharp reaction front predicted by the continuum mechanical theory for advective fluid transport is not observed the front spreading is on too large a scale for either diffusive or dispersive control and is due to local kinetic disequilibrium between the fluid and rock although the divariant nature of the reaction may also have a limited effect the time integrated fluid flux varies from the instantaneous porosity at the fluid front to 20 vol adjacent to the calc silicate carbon isotope budgets suggest that decarbonation of the calc silicate by a rayleigh fractionation process provides a sufficient source for the co2 influxing into the gneiss graphite abundances vary from 0 01 to 0 1 by weight it is principally derived by precipitation from the fluid and may be modelled from phase equilibria carbon isotope fronts coincide with the reaction front on the scale of sampling although isotopic disequilibrium between graphite and inclusion co2 also implies local fluid rock disequilibrium

origin of au rich carbonate hosted replacement deposits of the kassandra mining district northern greece evidence for late oligocene structurally controlled and zoned hydrothermal systems

fluid heterogeneity during granulite facies metamorphism in the adirondacks stable isotope evidence the preservation of premetamorphic whole rock oxygen isotope ratios in adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived hot co2 h2o fluids during granulite facies metamorphism this conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations the data suggest that these rocks were not an open system during metamorphism that fluid rock ratios were in many instances between 0 0 and 0 1 that externally derived fluids as well as fluids derived by metamorphic volatilization rose along localized channels and were not pervasive and thus that no single generalization can be applied to metamorphic fluid conditions in the adirondacks

carbon isotopic study on coexisting calcite and graphite in the ryoke metamorphic rocks northern kiso district central japan carbon isotope fractionation between coexisting calcite and grpahite 13ccc gr has been determined in metamorphosed limestones and calc silicate rocks from the ryoke metamorphic belt in the northern kiso district in this district the ryoke metamorphic rocks ranging from the lower greenschist facies to the upper amphibolite facies are widely distributed the fractionation of 13c 12c between calcite and graphite decreases regularly with increasing metamorphic grade and is independent of absolute 13c values of calcite this evidence suggests that carbon isotopic exchange equilibrium has been attained during metamorphism even in the greenschist facies and isotopic modification possibly caused by retrogressive metamorphism is not distinguished for t 270 650 c the fractionation is expressed by the following equation 13ccc gr 8 9 106t 2 7 1 t in k

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

transport of stable isotopes kinetics dispersive advection and the isotopic fronts of baumgartner and rumble 1988 baumgartner and rumble 1988 apply a kinetic continuum theory for stable isotope transport to unidimensional infiltration of fluid into rock their numerical applications are restricted to the simplified case of rapid isotope exchange between phases where the sharp isotope fronts of pure advection are distended by dispersive mechanisms only however kinetic limitations of isotope exchange are potentially an equally important distending mechanism and it will only rarely be possible to ascribe front gradients to diffusion dispersion alone abrupt isotopic changes at vein boundaries are more often a secondary signal of lithologic change than the expression of a retarded advective front at such boundaries diffusion and dispersion play a role that is comparable to or greater than that of advection so that the detailed shapes of isotope fronts depend upon boundary conditions for the infiltration process zerodimensional box models have legitimate if limited uses in the modelling of fluid rock interaction and are reexamined