fluid flow in metamorphic environments the study of fluid flow in metamorphic environments progressed over the last quadrennium mainly from a focus on the tenets of continuum mechanics in which rock properties such as porosity and tortuosity that control flow are assumed to be homogeneous over a specified finite volume advances have been afforded by these principles not only from their direct application but also from tests of their veracity assumptions inherent in the continuum approach are based on the scale of observation and in conjunction with the advent of new analytical technologies have given new impetus for examining mechanisms of material transfer between fluids and metamorphic rocks at smaller and smaller scales thus even as continuum mechanics has laudably come to be widely utilized in the study of metamorphic fluid flow the empirical adequacy oreskes et al 1994 of the methodology is being assessed through access to previously unattainable scales of observation

strontium and oxygen isotope decoupling in the hercynian trois seigneurs massif pyrenees evidence for fluid circulation in a brittle regime systematic shifts of oxygen isotopic compositions in the higher grade parts of the high temperature low pressure hercynian metamorphic sequence exposed in the trois seigneurs massif have previously been explained as a result of an influx of surface derived water during the prograde part of the metamorphic cycle it has been suggested that this caused a regional lowering of 87sr 86sr in the metamorphic sequence mapping of strontium isotopic compositions across a 15 m meta carbonate horizon in the higher grade pelite psammite sequence shows that strontium isotopic compositions were homogenised over length scales of metres or less during the hercynian metamorphism which brought the carbonate and pelite psammite to oxygen isotopic equilibrium with a common fluid comparison of model pre hercynian 87sr 86sr profiles across the carbonate based on a depositional diagenetic age of 450 ma and initial 87sr 86sr ratio of 0 7086 given by 10 m length scale averaging with the post hercynian 87sr 86sr profile calculated from analysed 87sr 86sr and rb sr compositions implies strontium isotopic diffusion distances of ca 0 4 m in the carbonate and ca 7 m in the pelite psammite the limited sr isotopic diffusion distance of 0 4 0 7 m within the carbonate is compatible with pervasive oxygen isotopic exchange over distances restricted to 4 15 m if fluid strontium concentrations were between 4 and 50 ppm the strontium isotopic transport distances are not compatible with pervasive oxygen isotopic alteration over the observed 5 km regional scale either the flow was perfectly layer parallel or more probably the regional scale alteration of oxygen took place by fluid circulation in the brittle regime early in or prior to the hercynian metamorphic event flow along cracks with incomplete diffusive exchange between fluid and wall rock would allow greater decoupling of oxygen and strontium isotopic transport than pervasive advective transport with local fluid solid equilibrium

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

reactive dispersion of stable isotopes by mineral reaction during metamorphism abstract the process of reactive dispersion is introduced whereby reaction in one chemical system imparts hydrodynamic dispersion to another apparently unrelated reactive transport system reactive dispersion is illustrated with a one dimensional finite difference model for coupled heat flow fluid flow mineral reaction and oxygen isotopic exchange during contact metamorphism of siliceous dolomite infiltration driven decarbonation reactions impart isotopic heterogeneity to an initially homogeneous system the effect on fluid composition is explored using a breakthrough curve that tracks fluid composition through time the corresponding effects on rock composition are illustrated with plots of isotopic alteration vs distance reactive dispersion is especially efficient during infiltration of h 2 o into carbonate rocks because 18 o is strongly fractionated between co 2 and h 2 o and because mineral reactions may buffer the co 2 h 2 o content of fluid the spatially heterogeneous isotopic alteration predicted to develop during decarbonation reactions in a homogeneous protolith is similar in magnitude and distribution to that observed downstream of the isotopic depletion front in contact metamorphic aureoles

fluid evolution and transport during metamorphism evidence from the llano uplift texas a field petrologic and stable isotopic investigation of the marbles and calc silicates of the 1 15 b y valley spring gneiss documents the dilution of internally evolved co2 rich fluids by externally derived aqueous fluids introduced along channelways reaction textures within calcsilicates record the evolution through time of initially co2 rich fluids toward increasingly more aqueous compositions assemblage zonations within calc silicates require equilibration within local gradients of the mole fraction of co2 in the fluid and suggest that the infiltration of aqueous fluids was largely channelized along more permeable lithologies localized depletions in 13c and 18o corroborate petrologic evidence for channelized infiltration isotopic compositions reflect both devolatilization and the introduction of low 18o fluids estimated minimum oxygen equivalent fluid to rock ratios are near unity both mineralogical and stable isotopic systematics document the essential role of infiltration in driving decarbonation reactions during calc silicate formation the calc silicate assemblages which equilibrated with fluids of the lowest mole fraction of co2 record isotopic exchange equilibrium with fluids of 18o typical of those derived from normal granites as do the granitic aplites and pegmatites which transect most calcsilicate occurrences thus the infiltrating fluids are believed to be genetically linked to the intrusion of a suite of granitic plutons emplaced after the peak of regional metamorphism

coals of the brazil formation pennsylvanian in indiana observations of correlation inconsistencies and their implications the coals of the upper part of the mansfield brazil and the lower part of the staunton formations atokan and desmoinesian pennsylvanian in indiana illinois basin are characteristically thin and discontinuous as a result problems with correlation and identification of the seams have persisted for both researchers and industry these discrepancies affect coal exploration mine planning and subsequently coal fired utilities this study presents exploration and operational examples demonstrating some of the correlation problems associated with the coals of the brazil formation and the upper block and lower block in particular and the surrounding upper part of the mansfield formation and lower part of the staunton formations based on exploration boreholes mine scale observations and coal quality and petrographic data this study suggests that 1 the coal mapped as the upper block coal member of clay county may in fact be the same seam as the lower block coal member of daviess county and 2 the lower block coal of clay county is not present south of the switz city area of central greene county in

three dimensional geometry of metamorphic fluid flow during barrovian regional metamorphism from an inversion of combined petrologic and stable isotopic data inverse calculations reveal the three dimensional geometry of time integrated fluid flux over a 120 km2 area during peak barrovian regional metamorphism in southeastern vermont prograde changes in whole rock co2 18o and 13c and calculated fluid compositions at the peak of metamorphism were inverted assuming tracer mass balance to obtain the time integrated fluid flux in three dimensions peak metamorphic fluid flow was spatially nonuniform with flux magnitudes ranging from 0 to 3 105 mol fluid cm2 rock and flux directions ranging from vertical upward and downward to horizontal averaged over the entire study area the magnitude of the time integrated metamorphic fluid flux vector is 3 4 104 mol fluid cm2 rock the average flux vector trends 45 to the southwest and points upward at 36 from the present horizontal parallel to formation boundaries on a regional scale fluids in the terrain carried 3 103 mol co2 cm2 rock toward earth s surface during the peak of metamorphism results suggest that local cross layer transport processes are secondary to terrain scale metamorphic fluid flow in driving prograde decarbonation reactions regional structure exerts a first order control on the gross geometry of peak metamorphic fluid flow

oxygen isotope map of the giant metamorphic hydrothermal system around the northern part of the idaho batholith u s a abstract determinations of 18o values from 100 outcrops of belt supergroup wallace fm metasedimentary rocks in the idaho panhandle reveal a regular regional pattern that was produced by pervasive fluid infiltration and isotopic exchange low grade argillites at large distances 60 km from the idaho batholith have high 18o values 15 compatible with their probable primary values pelitic rocks with anomalously low 18o values of 8 7 to 12 7 occur in the following zones 1 in a 5000 km2 zone of schist and gneiss peripheral to the idaho batholith generally coincident with high grade sillimanite bearing assemblages 2 in high grade metasedimentary roof pendants within the idaho batholith 3 peripheral to small cretaceous stocks and 4 within and near the scapolite bearing zone south west of st regis on 18o 18o plots data from coexisting minerals define trends with unit slopes indicating that the reductions in 18o occurred under high grade metamorphic conditions this metamorphism culminated in the emplacement of the idaho batholith probably as a consequence of profound crustal thickening associated with the cretaceous accretion of the wallowa seven devils arc terranes with north america the huge low 18o region is bounded by a steep 18o gradient 0 1 0 5 km that occurs in low grade rocks along and near the lewis and clark line well below the biotite isograd this boundary zone may be analogous to but is not nearly as sharp as those of meteoric hydrothermal systems in many regions the important ore deposits of the coeur d alene district are located in this peripheral zone suggesting that the metamorphic hydrothermal system may have been intimately involved in their formation in addition the metamorphic hydrotermal system in idaho is larger deeper and higher in temperature than typical meteoric hydrothermal systems and it involved fluids with much higher 18o values that were probably dominantly derived from formation waters accordingly this system produced rocks with 18o values similar to those of the idaho batholith and mineral assemblages that approach isotopic equilibrium under high temperature conditions

oxygen isotope constraints on metamorphic fluid flow townshend dam vermont u s a fluid rock interaction during amphibolite facies metamorphism has been investigated for rocks exposed in a single 400 m long lithologically heterogeneous outcrop near townshend vermont usa oxygen isotopic compositions have been measured in profiles across single garnet crystals from thirteen samples and from hornblende and garnet separates from thirty three fine grained samples this outcrop was previously studied who measured large oxygen isotope gradients 3 per thousand in garnets from one sample and inferred large amounts of pervasive fluid flow all of the garnets that we have analyzed show less isotopic zonation le 1 per thousand twelve of them have zonation 0 5 per thousand and the mineral separate data imply both a strong correlation of isotopic composition with rock type and large gradients in peak metamorphic fluid isotopic compositions although devolatilization reactions in these rocks must have produced metamorphic fluids the data preclude cross foliation time integrated fluid fluxes greater than 300 600 cm sup 3 cm sup 2 during prograde amphibolite facies metamorphism the isotopic trends can all be interpreted in terms of closed system behavior channeled fluid flow or diffusive exchange of oxygen in an interconnected grain boundary fluid and within uncertainty cross strike advective fluxes could have been zero any significant flow at this locality was dominantly either layer parallel or channeled out of the system in veins more if all fluid flow occurred in veins then their spacing must have been less than 300 600 m the data are inconsistent with massive and pervasive metamorphic fluid flow across strike but do not address layer parallel flow less

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

new insights from 2 and 3 d numerical modelling on fluid flow mechanisms and geological factors responsible for the formation of the world class cigar lake uranium deposit eastern athabasca basin canada the cigar lake uranium deposit in the athabasca basin is the world s second largest high grade unconformity related uranium deposit its distinct geological architecture includes heterogeneous basement lithologies a local basement high and sub vertical faults the sub vertical faults are classified further into two sub types faults that are restricted to the basement termed basement faults and faults that are distinctly related to post athabasca fault reactivation in that they extend upward into the sandstone termed extended basement faults this study aims to evaluate the effects of the aforementioned geological factors on the fluid flow patterns under two different driving forces buoyancy due to variation of fluid density or thermal convection and deformation or a combination of them and to determine the most probable fluid flow scenarios for the formation of the deposit the numerical results show that fluid flow is strongly affected by the two types of faults while the basement faults represent fluid paths with complex fluid flow patterns depending on the driving forces providing favourable physical conditions for different chemical processes such as fluid fluid and fluid rock interactions the extended basement faults enhance the permeability of an e w corridor within the sandstone and significantly strengthen the overall upwelling flow above the basement faults promoting sandstone hosted mineralization the numerical results also suggest that the main deposit likely formed via fluid convection during tectonically quiet periods although faulting played a critical role in increasing permeability in turn enhancing thermal convection

simple models of co2 release from metacarbonates with implications for interpretation of directions and magnitudes of fluid flow in the deep crust simple one dimensional models of coupled advection hydrodynamic surroundings can account for basic t fluid composition reaction dispersion reaction are used to investigate processes of co2 release progress relationships observed in much of the acadian orogen of from metacarbonate beds during deep crustal 8 kbar acadian new england the results provide an alternative to up t flow prograde metamorphism in new england usa two broad models scenarios that account for these relationships by large pervasive in which reaction progress is controlled by gradients in h2o co2 horizontal fluid fluxes up regional t gradients fluid composition between diverent rock types are presented in the first divusional exchange of volatiles across lithologic contacts is significant co2 generated during prograde temperature t rise is transported away from metacarbonate layers to surrounding 1 metapelitic layers which generate h2o by dehydration and or 2 key words metamorphism fluid flow flow direction carbon dioxide

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

high temperature retrogression of granulite facies marbles form the reynolds range group central australia phase equilibria isotopic resetting and fluid fluxes reynolds range group rocks underwent granulite facies metaintroduction morphism m2 at 1 6 ga 5 kbar 750 800 c and were the uplift history of high grade metamorphic belts comsubsequently retrogressed in narrow strike parallel zones at 1 59 monly involves partial re equilibration of mineral as1 57 ga within these zones metacarbonates that initially equisemblages to lower temperature and pressure conditions librated at x 2 0 8 during m2 were mineralogically reset this re equilibration is facilitated by fluid rock interby the infiltration of water rich fluids x 2 0 02 0 3 at action and new mineral assemblages are often best 650 700 c and 3 4 kbar do carb values of the retrogressed developed in discrete zones of extensive retrogression metacarbonates were variably reset during fluid infiltration with the e g van reenen 1986 cartwright 1988 peters lowest values 10 13 suggesting that the fluids that caused wickham 1994 cartwright buick 1995 petrological retrogression were exsolved from segregated partial melts themselves studies of retrograde mineral assemblages may provide derived from the underlying granulite facies metapelites minimportant information about the tectonics and hydroeralogical and isotopic resetting were locally accompanied by silica geology of the lower and middle crust metasomatism the mineralogically reset marbles record time inhowever although there have been many recent quantegrated fluid fluxes of typically 10 10 m m and metasomatic titative studies of metamorphic fluid rock interaction in rocks record time integrated fluid fluxes as high as 10 10 m contact aureoles cartwright valley 1991 ferry m for upward flow of high temperature fluids through the marbles dipple 1991 young morrison 1992 jamveit et al over a distance of 200 m in 18 ma the observed mineralogical 1992 davis ferry 1994 and during prograde regional and isotopic resetting and metasomatism require intrinsic permetamorphism bickle baker 1990a 1990b ferry meabilities between 10 and 10 m that vary across strike 1992 stern et al 1992 leger ferry 1993 cartwright on a centimetre to metre scale indicating that fluid flow was strongly et al 1995 buick cartwright 1996 there have been channelled relatively few studies of high temperature retrogression vennemann stuart smith 1992 peters wickham 1994 cartwright buick 1995 therefore the origins of the retrograde fluids and the absolute timing of

stable isotope evidence for regional scale fluid migration in a barrovian metamorphic terrane vermont usa we measured the c and o isotopic composition of carbonate minerals in the waits river formation eastern vermont to determine the extent of fluid infiltration during regional metamorphism over an approx 2000 km2 area in a deep seated 25 km barrovian terrane from a petrologic study of this terrane ferry proposed the existence of a large regional metamorphic hydrothermal system with two first order features 1 on the scale of the entire terrane fluid flow was focused into the axes of two major antiforms of regional extent 2 on a smaller scale about 100 km2 flow was further focused around synmetamorphic granitic plutons that intruded along the axes of the antiforms we find isotopic evidence for both the regional hydrothermal activity along the antiforms and the more intense fluid flow around synmetamorphic plutons the evidence for hydrothermal activity around the plutons is large heavy isotope depletions up to 6 9 in 18ocarb and 13ccarb in diopside zone rocks adjacent to the plutons these isotopic shifts are greater than can be explained solely by prograde metamorphic reactions we find two lines of evidence for the more diffuse regional flow that was focused into axes of the antiforms first 18ocarb and 13ccarb within individual outcrops become increasingly homogeneous with increasing grade towards antiform axes indicating that the rocks equilibrated with a permeating fluid second there are depletions in 18o near the margins of the waits river formation which can be interpreted as a dispersed advective infiltration front displaced toward the antiform axes these fronts were modelled using eq 13 of bickle and baker and imply time integrated fluid of 105 106 cm3 cm2 which are consistent with values derived by ferry from measured progress of prograde devolatilization reactions

axial and off axial heterogeneity of basaltic rocks from the east pacific rise at 12 35 n 12 51 n and 11 26 n 11 30 n surface ship operations and 40 submersible dives have provided a large amount of field observations and rock samples from two segments of the epr at 12 35 n 12 51 n and at 11 26 n 11 30 n and from four adjacent seamounts centered at less than 18 km from the rise axis the basaltic samples show a great variety of morphological features and a diversity in the proportions of early formed mineral phases and chemical composition there is no correlation between lava flow morphology geological settings and compositions based on mineral and compatible element composition these basalts were classified into three types the least evolved olivine basalts and highly phyric plagioclase basalts type a have high fo87 89 high mg 66 70 and high ni 100 contents the most evolved plagioclase olivine basalts with or without pyroxene type b and c have relatively low fo78 86 low mg 55 65 and low ni 60 100 ppm contents simple crystal fractionation 3 18 accounts for some of the observed compositional range however based on their incompatible element contents the above basalts are divided into three groups the various types a to c are found in each group depleted basalts with low k ti 0 04 0 15 ratios low zr 100 ppm and low nb 0 4 ppm contents undepleted basalts with the highest k ti 0 25 0 46 zr 150 170 ppm and nb 8 16 ppm contents and the transitional basalts having compositions between these two extremes these three basaltic groups occur within limited portions of the axial graben and its limbs in areas of less than 10 km in length and less than 3 4 km in width near 12 43 n 12 51 n on the epr similar volcanic diversity in a more limited area 3 km2 is observed on off axial seamounts and other constructional features centered up to 6 and 18 km from the rise axis depleted and undepleted melts are believed to have been formed during sequential batch melting of a composite mantle the transitional basalts probably result from a mixing of depleted and undepleted liquids which have undergone variable degrees of crystal fractionation two distinct mantle sources are distinguishable by their incompatible element contents and their susceptibility to melting we suggest that a lherzolitic mantle with minerals having a variable behavior under partial melting constitutes this type of composite mantle indeed clinopyroxene enriched in incompatible elements will be consumed at an earlier stage of melting than the olivine plus orthopyroxene eruption of compositionally distinct magma batches in close proximity on axial and off axial structures implies periods of quiescence between successive magmatic stages and cycles

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

determining the direction of contact metamorphic fluid flow an assessment of mineralogical and stable isotope criteria one dimensional fluid advection dispersion models predict differences in the patterns of mineralogical and oxygen isotope resetting during up and down temperature metamorphic fluid flow that may in theory be used to determine the fluid flow direction with respect to the palaeotemperature gradient under equilibrium conditions down temperature fluid flow is predicted to produce sharp reaction fronts that separate rocks with isobarically divariant mineral assemblages in contrast up temperature fluid flow may produce extensive zones of isobarically univariant mineral assemblages without sharp reaction fronts however during contact metamorphism mineral reaction rates are probably relatively slow compared with fluid velocities and distended reaction fronts may also form during down temperature fluid flow in addition uncertainties in the timing of fluid flow with respect to the thermal peak of metamorphism and the increase in the variance of mineral assemblages due to solid solutions introduce uncertainties in determining fluid flow directions equilibrium down temperature flow of magmatic fluids in contact aureoles is also predicted to produce sharp 18o fronts whereas up temperature flow of fluids derived by metamorphic devolatilization may produce gradational 18o vs distance profiles however if fluids are channelled significant kinematic dispersion occurs or isotopic equilibrium is not maintained the patterns of isotopic resetting may be difficult to interpret the one dimensional models provide a framework in which to study fluid rock interaction however when some of the complexities inherent in fluid flow systems are taken into account they may not uniquely distinguish between up and down temperature fluid flow it is probably not possible to determine the fluid flow direction using any single criterion and a range of data is required

the relative permeabilities of quartzites and schists during active metamorphism at mid crustal levels the hot spot near bristol new hampshire was an area of high fluid flow during metamorphism in order to determine the mechanisms of fluid flow through the area we made a detailed study of the 18o values of quartz from an outcrop of interlayered quartzites and schists results indicate that the permeability of the quartzite was very low in comparison to that of the schist the 18qtz values from schist layers are remarkably homogenous 15 5 15 8 in contrast to the 18qtz values of schist units outside of the hot spot which vary widely quartz veins that cut the quartzites and pinch out in the schists have the same 18o values 15 7 as quartz from the schists in the quartzites 18qtz values immediately adjacent to the veins and schists are similar to those in the veins and schists but decrease by 1 permil in the centers of the layer we interpret these results to indicate that fluid flow in the hot spot was mainly through the schists and fractures in the quartzites the oxygen isotope exchange fronts in the quartzites prove that there was some flow from the the schists and the fractures into the quartzites comparisons of the shapes of these exchange fronts with exchange fronts predicted by two different models of fluid flow in rocks indicate that fluid transport in the quartzite was predominantly by advection and that the kinetic rates of isotope exchange were fast relative to the advective velocity of the fluid infiltrating the system considering the slow rate of oxygen isotope exchange between quartz and a fluid this implies that fluid flow from the schist and vein fracture into the quartzite was extremely limited

fluid rock interaction during low pressure polymetamorphism of the reynolds range group central australia marbles and metapelites from the reynolds range group central australia were regionally metamorphosed at low pressure during m at 6 go m ranged in grade from gnenschist to granulite fades along the length of the reynolds range and overprinted l 78 ga granites and their contact aureoles in the reynolds range group metasediments at all m 2 grades the marbles and metapelites have highly variable oxygen isotope ratios marbles 5i8o carb 14 20 o metapelites b180 6 14 o similarly l 78 ga granites have highly variable oxygen isotope ratios 8i8o 5 13 o with the lowest values occurring at the granite margins in all rock types the lowest oxygen isotope values are consistent with the infiltration of channelled magmatic and or meteoric fluids the variable lowering of oxygen isotope values resulted from pre mi2 contact metamorphism and fluid rock interaction around the l 78 ga granites in contrast mineral assemblages in the marbles define a trend of increasing xco with increasing grade from 0 05 gnenschist fades to 0 71 0 granulite fades this together with the lack of regionally systematic resetting of oxygen isotope ratios implies that there was little fluid rock interaction during prograde regional metamorphism key word law pressure polymetamorphism fluids stable isotopes petrology

oxygen isotope geochemistry of hydrothermally altered synmetamorphic granitic rocks from south central maine usa hydrothermally altered mesozonal synmetamorphic granitic rocks from maine have whole rock 18o smow values 10 7 to 13 8 constituent quartz feldspar and muscovite have 18o in the range 12 4 to 15 2 10 0 to 13 2 and 11 1 to 12 0 respectively mean values of q f 18oquartz 18ofeldspar 2 4 and q m 18oquartz 18omuscovite 3 3 are remarkably uniform standard deviations of both are 0 2 measured q f and q m values demonstrate that the isotopic compositions of the minerals are altered from primary magmatic 18o values but that the minerals closely approached oxygen isotope exchange equilibrium at subsolidus temperatures analyzed muscovites have d smow values in the range 65 to 82 feldspars in the granitic rocks are mineralogically altered to either a muscovite calcite b muscovite calcite epidote c muscovite epidote or d muscovite only a consistent relation exists between the assemblage of secondary minerals and the oxygen isotope composition of whole rocks quartz and feldspar rocks with assemblage a have whole rock 18o 12 1 and contain quartz and feldspar with 18o 13 8 and 11 4 respectively rocks with assemblages b c and d have whole rock 18o 11 4 and contain quartz and feldspar with 18o 13 1 and 11 0 respectively the correlation suggests that the mineralogical alteration of the rocks was closely coupled to their isotopic alteration three mineral thermometers in altered granite suggest that the hydrothermal event occurred in the temperature range 400 150 c 100 150 c below the peak metamorphic temperature inferred for country rocks immediately adjacent to the plutons calculations of mineral fluid equilibria indicate that samples with assemblage a coexisted during the event with co2 h2o fluids of text x text co text 2 0 03 0 13 and 18o 10 8 to 12 2 while samples with assemblages b c or d coexisted with fluids of text x text co text 2 leqslant 0 03 and 18o 9 4 to 10 1 compositional variations of the hydrothermal fluids were highly correlated fluids enriched in co2 were also enriched in 18o because co2 was added to the granites during hydrothermal alteration and because fluids enriched in co2 were enriched in 18o some or all of the variation in 18o of altered granites may have been caused by addition of 18o to the rocks during the hydrothermal event the source of both the co2 and 18o could have been high 18o metasedimentary country rocks the inferred change in isotopic composition of the granites is consistent with depletion of the metacarbonate rocks in 18o close to the plutons and with large volumes of fluid that were inferred from petrologic data to have infiltrated the metacarbonate rocks during metamorphism a close approach of minerals to oxygen isotope exchange equilibrium in altered mesozonal rocks from maine is in marked contrast to hydrothermally altered epizonal granites whose mineral commonly show large departures from oxygen isotope exchange equilibrium the difference in oxygen isotope systematics between altered epizonal granites and altered mesozonal granites closely parallels a differences between their mineralogical systematics both differences demonstrate the important control that depth exerts on the products of hydrothermal alteration deeper hydrothermal events occur at higher temperature and are longer lived minerals and fluid have sufficient time to closely approach both isotope exchange and heterogeneous chemical equilibrium shallower hydrothermal events occur at lower temperatures and are shorter lived generally there is insufficient time for fluid to closely approach equilibrium with all minerals

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