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

eruptible magma for those who remember the classic disaster docudrama supervolcano bbc discovery channel 2005 the adjective eruptible is likely to ring a bell set in the near future and generally quite scientifically literate the movie envisions volcanologists trying desperately to evaluate the near term threat posed by the giant yellowstone magmatic system at the heart of their mission and of the drama is their quest to determine the mass of eruptible magma under yellowstone that is how much material that is capable of erupting is down there right now fortunately the scientists have at their disposal virgil a seismic tomography system that is based upon but greatly upgraded from existing systems virgil can reliably detect eruptible magma but unfortunately it is just coming on line and when they discover that there is in fact an enormous reservoir beneath them that can erupt the scientists lack context given a gigantic mass of eruptible magma what if any sort of eruption or eruptions is likely to occur how soon will it begin how long will it last how explosive will it be and how should scientists and the government respond supervolcano doesn t turn out well despite the heroism of the scientists in pnas the search for context is at the heart of research presented by barboni et al 1 geophysical techniques as represented by virgil and its less sophisticated present day tomographic counterparts and by magnetotelluric and gravity surveys provide a real time glimpse of where magma is or may be stored within the crust 2 results to date are intriguing but frustrating surveys suggest the presence of molten material beneath a growing number of volcanoes in fact gigantic volumes of the crust beneath yellowstone and the washington cascade volcanoes st helens rainier and adams appear to contain melt 3 4 however these zones are interpreted to mostly contain very small melt 1 1email calvin miller at vanderbilt edu 1 xref corresp 1 1

aqueous fluid connectivity and chemical transport in clinopyroxene rich rocks abstract in order to assess the efficacy of fluid assisted chemical transport in deep seated pyroxene rich rocks two types of experiment involving synthetic clinopyroxenites were performed at 900 950 c and 1 5 gpa 1 annealing of ferrosalite camg 0 4 fe 0 54 mn 0 06 si 2 o 6 or diopside camg 0 94 fe 0 06 si 2 o 6 powder in the presence of aqueous fluids water nacl cacl 2 or co 2 to produce near equilibrium fluid crystal dihedral angles s and 2 diffusion couple experiments in which an h 2 o bearing cylinder of fe rich clinopyroxenite ferrosalite was placed against one of mg rich clinopyroxenite diopside control diffusion experiments on fluid free clinopyroxenite and on single clinopyroxene crystals were also carried out the dihedral angle experiments consistently yielded median apparent values i e in 2d section of 65 69 well above the pinch off value of 60 and independent of additives nacl cacl 2 and co 2 in all cases however the frequency distributions were broad enough to suggest a range of real s on either side of the median the textures were also complicated by frequent crystal faceting at pore margins the diffusion couple experiments carried out with 0 0 6 1 3 2 7 4 0 and 8 0 vol h 2 o at run p and t showed no fe mg interdiffusion for all but the most fluid rich 8 couple this result is consistent with the determinations in showing that for geologically realistic fluid abundances aqueous fluids in clinopyroxenite form isolated noninterconnected pores this conclusion implies that aqueous fluids play no role in larger than grain scale chemical transport in pyroxene rich rocks under conditions of mechanical equilibrium the results also allow the possibility that water can be deeply subducted as a separate but trapped phase beyond the stability limit of amphibole

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

the notch peak contact metamorphic aureole utah petrology of the big horse limestone member of the orr formation the upper cambrian big horse limestone member of the orr formation is contact metamorphosed by the jurassic notch peak quartz monzonite in the central portion of the house range utah two lithologic types were sampled from specific stratigraphic horizons within the member over a lateral distance of 6 km at locations reflecting a range in metamorphic grades the rocks were metamorphosed at 2 kbar on the basis of estimates of stratigraphic overburden at the time of intrusion the lithologies are relatively pure dolomitic limestones and impure argillaceous limestones argillites the progressive metamorphism has resulted in the successive appearance of talc tremolite scapolite diopside and forsterite in the meta limestones and the appearance of biotite tremolite diopside plagioclase scapolite vesuvianite grossular and wollastonite in the argillites mineral assemblages of the limestones compared with isobaric 2 kbar phase equilibria in the cao mgo sio 2 h 2 o co 2 system suggest that 1 fluid buffering by metamorphic reactions has occurred 2 domains of equilibrium are small and 3 the limestones behaved as relatively closed systems during metamorphism maximum temperatures and x co 2 composition consistent with assemblages in the limestone are see pdf for table temperatures estimated by the calcite dolomite geothermometer are consistent with these temperature estimates temperatures estimated from limestone mineral assemblages are used to establish the sequence of prograde reactions in the multi component argillite system compositions of fluids in equilibrium with low grade argillites are poorly constrained but may have reached a maximum x co 2 of 0 75 fluid compositions in equilibrium with medium to high grade argillites were more h 2 o rich than x co 2 0 20 indicated primarily by the presence of wollastonite at temperatures between 475 and 600 c therefore the argillites were either initially more water rich than limestones at the same grade or they were more open to h 2 o rich fluids during metamorphism

aqueous fluid connectivity in pyrope aggregates water transport into the deep mantle by a subducted oceanic crust without any hydrous minerals abstract the effect of pressure and temperature on the dihedral angles of aqueous fluid in a pyrope matrix was investigated experiments were performed on an h 2 o pyrope system in a multianvil apparatus over the pressure and temperature ranges of 4 13 gpa and 900 1200 c respectively the dihedral angle of the fluid in contact with the pyrope exhibited a significant change at pressures around 8 9 gpa the dihedral angles increased with increasing pressure up to 9 gpa at pressures above 9 gpa the dihedral angles were greater than 60 at temperatures below 1000 c therefore the efficient percolation of aqueous fluid in a pyrope matrix is not feasible in the upper mantle and the transition zone the fluid released from the breakdown reactions of the hydrous minerals lawsonite and phengite exists in the oceanic crust which mainly consists of garnet in the upper mantle and transition zone we conclude that a part of the aqueous fluid released from the hydrous minerals may be retained in the subducted oceanic crust and transferred into the deep mantle by the subduction process

vapour loss boiling as a mechanism for fluid evolution in metamorphic rocks the calculation of fluid evolution paths during reaction progress is considered for multicomponent systems and the results applied to the ternary system co2 h2o nacl fluid evolution paths are considered for systems in which a co2 rich phase of lesser density vapour is preferentially removed from the system leaving behind a saline aqueous phase liquid such boiling leads to enrichment of the residual aqueous phase in dissolved components and for certain reaction stoichiometries to eventual saturation of the fluids in salt components distinctive textures particularly radiating growths of prismatic minerals such as tremolite or diopside are associated with saline fluid inclusions and solid syngenetic salt inclusions at a number of field localities the most thoroughly studied of these localities is campolungo switzerland where metasomatic rocks have developed in association with fractures and veins at 500 c and 2 000 bars of pressure the petrography of these rocks suggests that fluid phase separation into liquid and vapour has been an important process during metasomatism fracture systems with fluids at pressure less than lithostatic may facilitate the loss of the less dense vapour phase to conditions of the amphibolite facies

evolution of the blueschist and greenschist facies rocks of sifnos cyclades greece the metamorphism on the island of sifnos is characterized by the eocene development of a coherent highpressure blueschist terrane and an early miocene greenschist facies overprint this study documents the metamorphic evolution of the blueschist assemblages still preserved in the northern parts of the island and their subsequent transformation into greenschists in the central and southern parts the oxygen isotope geothermometry is based on calibrations for quartz pyroxenes and magnetite matthews et al 1983a augmented by revised calibrations for the minerals muscovite qz mu 1 55 106 t 2 epidote qz ep 1 56 1 92 ps 106 t 2 and rutile qz ru 4 54 106 t 2 oxygen isotope analyses of minerals from the blueschist unit of northern sifnos give consistent fractionations which are independent of rock type an average temperature of 455 c was obtained although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred the minerals and whole rocks of the greenschists of central sifnos are systematically enriched in 18o relative to the blueschist assemblages chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of ca2 and co2 the petrologic isotopic and chemical evidence favour a metamorphism governed by the infiltration of 18o co2 enriched aqueous solutions it is reasonable to assume that this is connected with the miocene magmatic activity observed throughout the cyclades the marbles separating the blueschist from the greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation the pressure of the blueschist metamorphism is estimated at 14 2 kbar corresponding to a depth of ca 50 km the structural style and stratigraphy of sifnos are suggestive of the subduction of a continental margin sequence it is clear that the considerable tectonic depression may be associated with continental collision and underthrusting

electrical conductivity and temperature in the canadian cordilleran crust abstract high electrical conductivity and high heat flow coexist in much of the canadian cordillera a region of recent accretion of crustal terranes to north america the relationship between temperature and electrical conductivity in the crust is investigated by means of results from 251 heat flow determinations and 301 magnetotelluric mt soundings we first compared maps of mt phase at period 10 s and of heat flow larger phases correlate with higher heat flows in some areas but the relationship is complicated by other causes of variation in these two parameters to give a more focussed comparison we map the depth d 450 to the 450 c isotherm for two assumed distributions of reduced heat flow and the depth d c to the top of the lower crustal conductor at mt sites away from major fracture zones the map of d c visually resembles both of the maps of d 450 and readings at 76 points of a grid give correlation coefficient 0 80 this supports a relationship between high conductivity in the crust and temperatures above 450 c both the lower crustal conductor and the 450 c isotherm occur at depths near 30 km above the subducting oceanic plate under vancouver island at 15 20 km in the intermontane belt and of 10 15 km in the omineca belt if there is an upcurrent in the mantle beneath the continent behind the subduction as proposed elsewhere its axis may now be under the omineca belt this location is in harmony with evidence of recent extension and uplift there

the effect of fluid chemistry on quartz microcrack lifetimes abstract metamorphic porosity consists of a branching hierarchy of primary features grain boundaries secondary features 3 and 4 grain junction tubules tertiary features microcracks and higher order features fractures while some of these features are rarely open to bulk fluid flow e g boundaries higher order features are open to fluid flow for timescales which vary significantly as a function of temperature pressure and fluid and rock chemistry the kinetics of microcrack healing in quartz between 300 600 c at 200 mpa increases as a function of fluid chemistry in the following order co 2 h 2 o 2 o m nacl 2 m cacl 2 6 m nacl changes in fluid chemistry which increase quartz solubility correlate with increased rates of healing these observations suggest that local redistribution of quartz occurs by solution precipitation driven by gradients in curvature along the crack surface and is possibly rate limited by pore fluid diffusion however the effect of crack geometry is larger than the effect of fluid chemistry at elevated temperatures and pressures aqueous fluids with elevated nacl concentrations can penetrate pervasively into polycrystalline quartz along a branching hierarchy consisting of episodically open fractures connected to 3 and 4 grain junction tubule networks while pure water or h 2 o co 2 fluid can only infiltrate pervasively along episodically open fractures 1 at lower temperatures and pressures 3 and 4 grain tubule networks in polycrystalline rocks may be closed to all fluids limiting fluid infiltration to microfacture networks lifetimes of quartz microcracks in all these fluids p fluid p confining is geologically short even at temperatures as low as 200 c

isotopic and petrological evidence for the infiltration of water rich fluids during the miocene m2 metamorphism on naxos greece abstract a detailed carbon and oxygen isotopic study in conjunction with petrological work has been carried out across calcite dolomite marble layers in the high grade metamorphic sequence on the island of naxos greece the purpose of this study is to examine fluid flow during the miocene barrovian metamorphic event individual marble bands show two dominant styles of isotopic alteration from core values of 22 to 29 in 18o and 1 to 3 in 13c firstly contacts between the marble bands and surrounding pelitic rocks have altered isotopic ratios across a metre wide boundary layer the isotopic values of the marble along the contacts drop to 15 to 17 in 18o and 1 to 5 in 13c secondly there is a drop in the isotopic composition of the marbles along vein networks associated with the development of calc silicates the isotopic compositions in these veins drop to 14 to 16 in 18o and 3 to 4 in 13c cross cutting relationships observed between these two alterations allow the relative timing of infiltration to be determined the development of boundary layers is shown to result from the infiltration of fluids with isotopic signatures of 12 to 16 in 18o and 3 to 12 in 13c and an xco2 less than 0 3 these fluids are derived from dehydration of graphite bearing pelites during the prograde metamorphism these conclusions are at odds with those of previous workers who suggested that the prograde metamorphism was a result of the pervasive influx of mantle derived fluids with xco2 greater than 0 5 the alteration associated with vein networks results from peak to post peak infiltration of fluids which drive decarbonation reactions at least some of these fluids have an xco2 less than 0 05 but this is obscured by the production of co2 during the decarbonation reactions these fluids were most probably produced from the crystallising partial melts formed during the prograde metamorphism these infiltrating fluids are thought to have 18 o 10 and 13c of 5 to 7

stable isotopic and trace element evidence for restricted fluid migration in 2 gpa eclogites mineral stable isotopic and trace element studies in 2 gpa banded eclogites of the tauern window eastern alps record mm to cm scale heterogeneities that reflect compositional variations in the accompanying metamorphic fluids a close correlation between dolomite mode and dolomite 18o is consistent with equilibrium partitioning among coexisting minerals and fluids small variations in dolomite 13c values correspond with 18o variations but an overall decrease in dolomite 13c by c 1 o across a 12 cm sample is a relict feature that pre dates eclogite equilibration garnet omphacite and clinozoisite rims show little systematic mineral mineral partitioning behaviour for ti v cr y sr or zr major elements however are well equilibrated among these same minerals despite the apparent lack of mineral mineral trace element equilibration most of the trace elements vary systematically with water activity calculated in each layer trace element behaviour during the eclogite metamorphism thus appears to have been controlled largely by mineral fluid interactions along grain boundaries shallow structural levels in other subduction complexes c 10 45 km typically exhibit fracture controlled permeability and extensive metasomatism but there is no field or geochemical evidence for extensive fluid advection during high pressure metamorphism in the tauern eclogites because most dewatering and devolatilization during tectonic burial occurs prior to eclogite conditions the volumetric fluid rock ratio in eclogites should generally be low low fluid rock ratios coupled with the possible non wetting nature of the fluids permits the production and preservation of fine scale chemical heterogeneities in deeply subducted eclogites and associated fluids however the eventual breakdown at greater depth of volatile bearing dolomite phengite clinozoisite zoisite or amphibole could lead to renewed fracture controlled fluid release from the subducted rocks to regions appropriate for arc magma generation

p t x effects on equilibrium carbonate h 2 o co 2 nacl dihedral angles constraints on carbonate permeability and the role of deformation during fluid infiltration fluid solid solid dihedral angles in the nacl h2o co2 calcite dolomite magnesite system have been determined at pressures ranging from 0 5 to 7 kbar and temperatures from 450 c to 750 c at 1 kbar and 650 c both dolomite and magnesite exhibit a dihedral angle minimum for intermediate h2o co2 fluids similar to that previously determined by the present authors for calcite but the depth of the minimum is smaller being above the critical value of 60 for both dolomite and magnesite for all fluid compositions calcite calcite brine dihedral angles at 650 c have been determined in the pressure range 1 5 kbar angles decrease with increasing salt content of the fluid tending towards a constant value of about 65 for strong brines at pressures above 2 kbar there is a general increase of angle with increasing pressure which is most marked for strong brines a positive correlation of angle with pressure is also observed in calcite h2o co2 fluids the position of the minimum moving towards higher angles and towards h2o rich fluids with increasing pressure the permeability window previously observed by the present authors at 1 kbar and intermediate fluid compositions closes at about 1 5 kbar the results demonstrate that the permeability of carbonates to grain edge fluid flow is only possible at low pressures and for fluids of restricted h2o co2 nacl compositions however geochemical evidence from metamorphic terrains suggests that pervasive infiltration does occur under conditions where impermeability is predicted from examination of published studies of infiltrated carbonates we conclude that deformation plays a critical role in enhancing carbonate permeability possible mechanisms for this include shear enhanced dilatancy micro cracking fluid inclusion drag by deformation controlled grain boundary migration and dynamically maintained transient grain boundary fluid films

regional metamorphism of the vassalboro formation south central maine usa a case study of the role of fluid in metamorphic petrogenesis progressively metamorphosed carbonate rocks of the vassalboro formation serve a natural laboratory for the investigation of fluid rock interactions during metamorphism an integrated study of their whole rock chemistry mineralogy mineral chemistry and mineral abundances has led to the following results a prograde mineral reactions involved hydrolysis as well as dehydration and decarbonation the hydrolysis reactions have resulted in an almost quantitative extraction of k and na from high grade metacarbonates b prograde mineral reactions buffered the x co 2 of coexisting metamorphic fluid during almost all of the rocks metamorphic history c the carbonate rocks were infiltrated by large volumes of h 2 o rich fluid while the buffering reactions progressed during the metamorphic event some high grade metacarbonates were infiltrated by at least 3 rock volumes of fluid combined buffering and infiltration appears to be a general metamorphic phenomenon in carbonate bearing rocks to depths of 30 km in the crust d there is an excellent positive correlation between the heat budget of individual metacarbonate rock samples and calculated fluid rock ratios convective heat transfer by metamorphic fluids is therefore likely to be an important item in the heat budget of metamorphic terrains consideration of these results leads to a model of regional metamorphism which involves infiltration of rock by large volumes of acid h 2 o rich fluid large scale acid infiltration metasomatism in this model the infiltrating fluid exerts enormous control over the mineralogical evolution of the carbonate rocks during the metamorphic event it drives mineral reactions it changes whole rock chemistry and it supplies heat

contrasting rock permeability in the aureole of the ballachulish igneous complex scottish highlands the influence of surface energy the ballachulish igneous complex in the scottish highlands part of a widespread group of late caledonian calcalkaline intrusions was emplaced at a depth of 10 km into dalradian metasediments resulting in melting of the country rocks near the intrusive contact the greatest extent of melting occurred in the leven schist in the 400 m wide so called chaotic zone which experienced infiltration of aqueous fluids from the pluton in contrast adjacent to the chaotic zone the feldspar bearing appin quartzite underwent significant melting only within a few metres of the intrusion despite both being in contact with the same fluid source as the leven schist and having a similar wet melting point the permeability of the appin quartzite and quartz horizons in the leven schist to pervasive grain edge infiltration of aqueous fluids was determined by measuring the equilibrium quartz h2o dihedral angle for the p t conditions of contact metamorphism addition of powdered samples of both rock types to the pure quartz h2o system results in a linear decrease of the quartz h2o dihedral angle with increasing temperature the rate of this decrease for the leven schist is greater than that for the appin quartzite and the angle decreases below 60 some 30 c below the wet solidus 670 c at 0 3 gpa charges bearing appin quartzite had dihedral angles greater than 60 at all temperatures below the wet solidus 690 c at 0 3 gpa these results demonstrate that quartz rich horizons in the leven schist would have been permeable to infiltration of aqueous fluids close to the solidus permitting extensive h2o fluxed melting to occur the appin quartzite would have remained impermeable to grain edge flow consistent with the observed differences in the extent of partial melting of the two lithologies

short paper textures of forsterite calcite marbles from the beinn an dubhaich aureole skye and implications for the structure of metamorphic porosity in the aureole of the beinn an dubhaich granite forsterite grew with dihedral angles of less than 110 against calcite but was progressively and variably annealed towards the equilibrium dihedral angle of 165 new experimental estimates of calcite calcite fluid dihedral angles are presented ranging from 50 90 the early low angles may be due to rapid olivine growth into a fluid filled porosity the preservation of a range of textural states in the beinn an dubhaich aureole has the potential to provide information on the kinetics of grain boundary readjustments in metamorphic rocks which control pore geometry and permeability

metasomatism of gabbro mineral replacement and element mobilization during the sveconorwegian metamorphic event widespread metasomatism affected the 100 km long and 25 km wide proterozoic bamble and modum kongsberg sectors south norway resulting in the chemical and mineralogical transformation of wide segments of continental crust scapolitization was associated with veining and was followed by albitization transforming metagabbros pervasively over large areas fluids played an active role in these reactions forming h2o co2 and cl bearing phases at the expense of the primary volatile free minerals causing depletion in fe and infiltration of k mg na b and p the transformation of gabbro to scapolite metagabbro is observed as a fluid front replacing the primary magmatic mineral assemblage in three stages during an incipient amphibolitization stage the primary mafic minerals were replaced by anthophyllite or hastingsite followed by pargasitic and edenitic ca amphibole magnetite was dissolved while rutile formed by the breakdown of ilmenite plagioclase was replaced by cl rich scapolite me19 42 reflecting cl saturation while k and mg saturation produced phlogopite enstatite sapphirine and rare corundum the high modal contents of chlorapatite and tourmaline in the scapolite metagabbro imply infiltration of b and p the albitites consist dominantly of albite ab95 98 with varying generally small amounts of chlorite calcite rutile epidote and pumpellyite they formed from a h2o co2 fluid rich in na the gabbro yields a zircon u pb age of 1149 7 ma and tonalite 1294 38 ma whereas rutile from scapolite metagabbro and albitite has u pb ages of 1090 1084 ma and phlogopite produced during scapolitization rb sr ages of 1070 1040 ma temperature conditions for the scapolitization are inferred to have been 600 700 c the reported ages combined with mineralogical and petrographic observations and inferred p t conditions indicate that the metasomatism was a part of the regional sveconorwegian amphibolite facies metamorphic phase initial 87sr 86sr of the scapolite ranges from 0 704 to 0 709 the sr signature the cl and b rich environment and regional distribution of lithologies suggest that the fluid may have originated from evaporites that were mobilized during the regional metamorphism

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

relations among net transfer reaction progress 18 o 13 c depletion and fluid infiltration in a clinohumite bearing marble a siliceous dolomitic marble xenolith within a mid crustal jurassic diorite exhibits mineralogical and stable isotopic evidence for infiltration of water rich fluid adjacent to endoskarn which bounds the xenolith forsterite has been replaced by clinohumite as a result of a devolatilization reaction driven by addition of aqueous fluid and extraction of heat isotopic compositions of calcite also record infiltration of aqueous fluid concentrated near contacts with endoskarn marble calcite 18osmow values range from 19 5 at the center of the xenolith to 12 6 adjacent to endoskarn calcite 13cpdb decreases sympathetically from 3 0 to 1 4 the calculated equilibrium composition of coexisting c o h f fluid and a quantitative characterization of the whole rock reaction which produced clinohumite and consumed graphite are used to place inequality contraints on the composition of the infiltrated fluid continnum mechanical transport models based on the resulting fluid compositions suggest that a small time integrated darey flux of 44 cm3 cm2 coupled with diffusive transport in the fluid was sufficient to produce both the isotopic shifts and the net transfer reactions evidenced in the xenolith the calculations demonstrate the importance of graphite as an indicator of time integrated flux the maximum possible ch4 content of the infiltrated fluid is sufficiently high to impart a 2 0 uncertainty in the 13c of the fluid the isotopic composition of the fluid is consistent with a magmatic origin when this uncertainty is taken into account

quantification of lower crustal synmetamorphic fluid fluxes in the kapuskasing structural zone based on oxygen isotope profiles across two paragneiss mafic gneiss contacts detailed oxygen isotope profiles were measured across two very similar amphibolite grade paragneiss mafic gneiss contacts located 2 km apart within the kapuskasing structural zone the first profile is asymmetrical about die contact 18 o values for whole rocks and minerals are homogeneous in the paragneiss whole rock 18 o 10 4 to 11 4 smoothly decrease by about 2 over 2 5 m moving into the mafic gneiss and are homogeneous in the remainder of the mafic gneiss whole rock 18 o 7 0 to 7 4 the second profile is flat with homogeneous whole rock and mineral 18 o values in bom lithologies and mafic gneiss values whole rock 18 o 8 7 to 9 8 that are higher by about 3 relative to typical mafic gneiss values mineral mineral isotopic fractioations are fairly constant in all samples and are typical of high grade metamorphic rocks despite their differences both profiles can be explained by the advection of a mixed h 2 o co 2 fluid in equilibrium with the paragneiss across the contact into the mafic gneiss coupled with diffusion of oxygen in the fluid modeling constrains the net fluid flux required to form me first profile to be 1 3 m 3 m 2 and for me second profile to be 10 m 3 m 2 thus the net fluid flux during metamorphism varied probably by at least a factor of five over 2 km these fluxes could have been generated locally within the kapuskasing structural zone during metamorphism either by metamorphic devolatilization reactions or by the release of volatiles from crystallizing magmas

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

genesis and mobility of the h2o co2 fluid phase during regional greenschist and epidote amphibolite facies metamorphism a petrological and stable isotope study in the scottish dalradian during high pressure low temperature greenschist and epidote amphibolite facies metamorphism in dalradian rocks of the sw scottish highlands mineral assemblages in metabasites and calcareous metasediments were dominantly controlled by infiltration of hydrous fluids consequently mineral assemblages capable of buffering the fluid phase composition were rare equilibrium prograde h 2 o co 2 fluids usually contained less or much less than about 1 2 mol co 2 three fluid infiltration events are recognized during prograde greenschist facies metamorphism metabasic sills were infiltrated by large volumes of co 2 bearing hydrous fluid carbon isotope studies indicate that the co 2 was locally derived by widespread oxidation of graphite or other organic carbon in adjacent metasediments this may have occurred under approximately lower greenschist facies conditions as a result of mixing of fluids of varying f o 2 initiated by thermal expansion of water during heating decompression and consequent hydraulic fracturing in the epidote amphibole facies garnet zone dehydration reactions in metabasites generated large quantities of water which removed carbonate from metabasites on a regional scale and infiltrated calcareous metasediments to produce assemblages containing grossular diopside k feldspar amphibole clinozoisite and sphene a late retrograde infiltration of co 2 bearing hydrous fluid under lower greenschist facies conditions generated assemblages containing k feldspar chlorite rutile dolomite in calcareous rocks and albite prophyroblast schists in zones of intense secondary deformation large scale infiltration of fluid into greenschist facies metadolerite sills was intimately related to and possibly controlled by penetrative deformation and in the absence of a penetrative deformation grain boundary diffusion by itself was an ineffectual mechanism of fluid transport

experimental constraint on grain scale fluid connectivity in subduction zones abstract the dihedral angle between olivine and aqueous fluid is a critical parameter in identifying the grain scale fluid connectivity which controls the distribution and migration of aqueous fluids in subduction zones besides physical properties of mantle wedges recent magnetotelluric observations have suggested the occurrence of significant fluid circulation in deep fore arc regions which can be explained by infiltration of saline fluid with a low in the mantle wedge huang et al 2019 along with the salt component non polarized gas such as co2 is a crucial constituent of subduction zone fluids co2 is known to increase the olivine fluid under conditions in which the olivine does not react with co2 which is in contrast to the effect of nacl on for a better understanding of the connectivity of multicomponent fluid in the mantle wedge we experimentally constrained in olivine h2o co2 fluid and olivine h2o co2 nacl multicomponent fluid systems at 1 4 gpa and 800 1100 c for the h2o co2 system we found that co2 tends to increase at 1 gpa and 800 1100 c and at 2 gpa and 1100 c in contrast co2 reduced even below 60 at relatively high pressure p and low temperature t conditions in which the olivine partly reacts with co2 to form magnesite and orthopyroxene opx the consumption of non wettable co2 components in aqueous fluid alone cannot explain lower than those in a pure h2o system additional experiments on olivine magnesite h2o and olivine opx h2o systems showed that the presence of magnesite or opx decreased the olivine fluid which implies that coexisting minerals affect the olivine fluid interfacial energy by changing the fluid chemistry the results of the multicomponent system showed that the effect of nacl on is much more significant than that of co2 strikingly was smaller than 60 in all the magnesite and opx bearing multicomponent systems our results suggest that slab derived fluid can infiltrate into the deep fore arc mantle wedge through an interconnected network even in a co2 bearing multicomponent system at pressures above 2 gpa which facilitates significant fore arc fluid circulation the contrasting effects of aqueous fluid and silicate melt on the seismic wave velocity in a wide condition may allow for the possibility of mapping partial melt in the mantle wedge

immiscible fluids in metamorphism implications of two phase flow for reaction history fluid immiscibility between a co 2 rich fluid and brine has been described from several medium to high grade marbles and calcsilicates here we also report evidence for ch 4 h 2 o immiscibility in low grade metamorphic rocks from wales and suggest that the flow of such immiscible fluids may be comparable to that of water oil or water gas mixtures in petroleum reservoirs this analogy implies that where one fluid is being produced by reaction it will flow out of the rock while the other remains immobile except insofar as it is soluble in the more abundant fluid phase hence extensive reaction may take place in the presence of coexisting immiscible fluids each having high activities it is proposed that this type of flow behavior not only accounts for the development of salt saturated fluids in marbles but also may be responsible for the elimination of carbonate and extensive loss of graphite from pelites in the lower part of the greenschist facies

the effect of feldspar on quartz h 2 o co 2 dihedral angles at 4 kbar with consequences for the behaviour of aqueous fluids in migmatites an investigation was made of the effect of trace amounts of feldspar na and or k on dihedral angles in the quartz h2o co2 system at 4 kbar and 450 1050 c quartz quartz h2o dihedral angles in feldspar bearing quartz aggregates are observed to be the same as those in pure quartz aggregates at temperatures below 500 c above this temperature they decrease with increasing temperature until the solidus the final angle at the inception of melting is about 65 for microcline quartz h2o and microcline albite quartz h2o and much less than 60 the critical value for formation of grain edge fluid channels in an isotropic system for the albite quartz h2o system co2 was observed to produce a constant quartz quartz fluid dihedral angle of 97 in feldspar bearing quartz aggregates at all temperatures studied also examined were the dihedral angles for the two co existing supersolidus fluids in quartz aggregates in all systems the quartz volatile fluid angle is greater than 60 whereas the quartz melt angle is lower than 60 both supersolidus angles decrease with increasing temperature the transition from nonconnected to connected porosity with increasing temperature observed in the quartz albite h2o system some tens of degrees below the solidus termed a permeability transition if a common feature of rocks near their melting points will play an important role in controlling the permeability of high grade rocks to aqueous fluids

silicate oxide and sulphide trends in neo archean rocks from the nilgiri block southern india the role of fluids during high grade metamorphism the nilgiri block southern india represents an exhumed section of lower late archean 2500 ma crust the northern highlands of the nilgiri block are characterized by metagabbros with pyroxenite inlayers a two pyroxene granulite zone acts as a transition between the metagabbros and charnockites which are exposed in the central and southern part of the nilgiri highlands thermobarometry results indicate a sw ne regional trend both in temperature similar to 650 800 degrees c and in pressure 700 1100 mpa over the nilgiri highlands in the charnockites composite rutile ilmenite grains are the dominant oxide assemblage in the two pyroxene granulites hemo ilmenite magnetite is dominant with coexisting rutile ilmenite composite grains in a few samples in the vicinity of the boundary with the charnockites in the metagabbros hemo ilmenite magnetite is the dominant oxide assemblage the principal sulphide mineral in the charnockite is pyrrhotite with minor pyrite chalcopyrite exsolution lamellae or blebs in the two pyroxene granulites and the metagabbros the principal sulphide assemblage consists of discrete pyrite grains with magnetite rims and pyrite pyrrhotite chalcocopyrite associations from these observations a specific oxidation trend is seen the northern granulite facies metagabbros and two pyroxene granulites of the nilgiri highlands are highly oxidized compared with the charnockites from the central and southern regions this higher oxidation state is proposed to be the result of highly oxidizing agents probably as so3 in low h2o activity grain boundary nacl saline fluids with a dissolved caso4 component present during granulite facies metamorphism of the metagabbros and two pyroxene granulites eventually these agents became more reducing owing to the inherent buffering of the original tonalite granodiorite granitoids at the graphite co2 buffer such that s took the form of h2s during the granulite facies metamorphism of the charnockites at the same time these saline fluids were also responsible the solid state conversion of biotite and amphibole to orthopyroxene and clinopyroxene in the metagabbro two pyroxene granulite and charnockite

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

fluid immiscibility in natural processes use and misuse of fluid inclusion data abstract many occurrences of fluid immiscibility in natural geologic systems have been reported recently most often from fluid inclusion studies however the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology in the tpx space of natural fluid systems for such reasons some authors have been misled to erroneous interpretations the term chemical immiscibility is unambiguously redefined as a multiphase multicomponent equilibrium the consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters temperature pressure volumes compositions to each other these equations already put constraints on the topology of the phase equilibria in fluid systems a particular expression of the phase rule is proposed which takes into account the multiphase constant bulk volume constant bulk composition constraints in fluid inclusions the consequences of such an expression are of major importance in fluid inclusion studies the phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed h2o nacl co2 ch4 h2o co2 h2o co2 nacl the effects of these topologies and of the supplementary constraints constant bulk composition and constant bulk volume assumed for fluid inclusions isopleth isochoric systems are discussed

petrologic phase equilibria and stable isotope fractionations of carbonate silicate parageneses from granulite grade rocks of sri lanka abstract the calc silicate rocks and marbles of central and southern sri lanka can be characterized by three groups of parageneses cc dol phl fo spl di acc in the northern and eastern part of the highland complex di scp spn cc acc following to the west and wo di scp spn cc acc in the most southwestern part this distribution mirrors the compositional variation of the sedimentary precursors and the regional pressure gradient during prograde metamorphism decarbonation with internal fluid buffering increased xco2 to 0 75 graphite precipitation at near peak metamorphic conditions at constant oxygen fugacity reduced xco2 to 0 5 the variation of 18o 26 to 9 and 13c 4 to 5 of carbonates can largely be explained by primary differences in the isotopic composition and in the silicate carbonate contents of the protoliths the particular light isotopic compositions are due to fractionation processes during decarbonation of the rocks the dolomite free scapolite bearing rocks in general are isotopically lighter than dolomite bearing parageneses calcite graphite temperatures in the range of 750 900 c were calculated using the experimentally derived thermometer of scheele 1991 calcite silicate temperatures 150 900 c were calculated with the increment method hoffbauer et al 1994 these temperatures reflect near peak equilibrium as well as different degrees of retrograde isotope resetting

wetting properties of anorthite aggregates implications for fluid connectivity in continental lower crust 1 the connectivity of c h o fluids in anorthite aggregate was assessed by measurements of the dihedral angle at conditions of 800 1000 c and 0 8 1 2 gpa for duration of 1 21 days the longer duration experiments show reduction of the effect of crystal anisotropy on pore geometry especially fluid filled small pores 5 m in anorthite aggregate quickly approach to textural equilibrium controlled by minimization of surface energies in 3 days anorthite aggregates with co2 fluid show large dihedral angle over 120 in the anorthite aggregates with aqueous fluid the dihedral angles are over 60 at pressure of 1 0 gpa and decrease across critical angle of 60 with increasing pressure over the range of experimental conditions isopleths of dihedral angle show nearly zero to negative dp dt slope with increasing temperature the observed reduction in dihedral angle with increasing pressure and temperature may be attributed to increase in plagioclase solubility in aqueous fluid natural anorthite with small amounts of albite component shows smaller dihedral angle than pure anorthite at higher temperature conditions the anorthite content of the run products deviates progressively from that of starting material this suggests that preferential solubility of albite component relative to anorthite affects the equilibrium fluid distributions of plagioclase by aqueous fluid experimental results point to the likelihood that plagioclase rich lower continental crust will not allow intergranular fluid flow of c h o fluids even in the presence of high geothermal gradient

a paleoproterozoic nappe on meso archean gneisses exhumed by a cretaceous metamorphic core complex in northeastern north china craton the paleoproterozoic jiao liao ji orogenic belt provides key evidence of evolution from an early rift basin or back arc basin to final collision of the longgang block eo meso archean granitic gneiss and the nangrim block in the liaodong peninsula northeastern north china craton a structural investigation of schists and phyllites in the langzishan formation of the north liaohe group reveals two new major structures 1 a sub horizontal nappe on meso archean granitic gneiss belonging to a 1 95 1 9 ga paleoproterozoic d1 2 fold thrust system produced by terminal collision from the south basin to the north basement the metamorphic gradient transferred from greenschist facies metamorphism into amphibolite facies produced by crustal thickening in the paleoproterozoic orogenesis the intensity of deformation was also increasing from south to north the pure shearing style changed into simple shearing 2 a metamorphic core complex the gongchangling metamorphic core complex formed during cretaceous extension and doming enabled delamination and diapiric rise and exhumation in the core complex this extensional delamination event affected a wide area of the orogenic belt as part of the delamination of the northeastern half of the north china craton this is the first example of the paleoproterozoic thrust nappe tectonics exhumed and preserved by cretaceous diapirism in northeast china

contrasting stable isotope behavior between calcite and dolomite marbles lone mountain nevada late proterozoic to cambrian carbonate rocks from lone mountain west central nevada record multiple post depositional events including 1 diagenesis 2 mesozoic regional metamorphism 3 late cretaceous contact metamorphism related to the emplacement of the lone mountain granitic pluton and 4 tertiary hydrothermal alteration associated with extension uplift and intrusion of silicic porphyry and lamprophyre dikes essentially pure calcite and dolomite marbles have stable isotopic compositions that can be divided into two groups one with positive 13c values from 3 1 to 1 4 pdb and high 18o values from 21 5 to 15 8 smow and the other with negative 13c values from 3 3 to 3 6 and low 18o values from 16 9 to 11 1 marbles also contain minor amounts of quartz muscovite and phlogopite brown and blue luminescent clear smooth textured quartz grains from orange luminescent calcite marbles have high 18o values from 23 9 to 18 1 while brown luminescent opaque rough textured quartz grains from red luminescent dolomite marbles typically have low 18o values from 2 0 to 9 3 the 18o values of muscovite and phlogopite from marbles are typical of micas in metamorphic rocks with values between 10 4 and 14 4 whereas mica d values are very depleted varying from 102 to 156 no significant lowering of the 18o values of lone mountain carbonates is inferred to have occurred during metamorphism as a result of devolatilization reactions because of the essentially pure nature of the marbles bright luminescence along the edges of fractures quartz cements and quartz overgrowths in dolomite marbles low d values of micas negative 13c values and low 18o values of calcite and dolomite and depleted 18o values of quartz from dolomite marbles all indicate that meteoric fluids interacted with lone mountain marbles during the tertiary partial oxygen isotopic exchange between calcite and low 18o meteoric fluids lowered the 18o values of calcite resulting in uniform quartz calcite fractionations that define an apparent pseudoisotherm these quartz calcite fractionations significantly underestimate both the temperature of metamorphism and the temperature of post metamorphic alteration partial oxygen isotopic exchange between quartz and meteoric fluids also resulted in 18o depletion of quartz from dolomite marbles this partial exchange was facilitated by an increase in the surface area of the quartz as a result of its dissolution by meteoric fluids the negative 13c values in carbonates result from the oxidation of organic material by meteoric fluids following metamorphism stable isotopic data from lone mountain marbles are consistent with the extensive circulation of meteoric hydrothermal fluids throughout western nevada in tertiary time