oxygen diffusion in amphiboles the kinetics of oxygen isotope self diffusion in natural samples of hornblende tremolite and richterite have been measured samples were run under hydrothermal conditions using 18o enriched water profiles of 18o 16o 18o vs depth into the crystal were obtained using an ion microprobe the depths of sputtered holes were measured using an optical interferometer at 1000 bars 100 mpa water pressure the activation energies q and pre exponential factors d0 for diffusion parallel to c are d0 cm2 sec q kcal gm atom t c hornblende 1 20 1 10 741 6 650 800 tremolite 2 30 2 10 8 39 5 650 800 richterite 3 5 2 10 4 57 2 650 800 the diffusion coefficient d for hornblende at 800 c and 1000 bars water pressure measured parallel to the c crystallographic direction is at least ten times greater than that parallel to the a or b directions an increase in water pressure from 200 to 2000 bars increases d by a factor of 2 7 for diffusion parallel to c at 800 c the d value for hornblende at 800 c is about 0 01 that for quartz and 0 001 that for anorthite as a result closure temperatures for oxygen exchange in natural primary amphiboles are significantly higher than for quartz or feldspars it is unlikely that amphiboles will exchange oxygen isotopes by diffusion under most crustal conditions

fluid flow and mass transport at the valentine wollastonite deposit adirondack mountains new york state the valentine wollastonite skarn in the north west adirondack mountains new york is a seven million ton deposit which resulted from channellized infiltration of hzo rich silica bearing fluids the wollastonite formed by reaction of these fluids with non siliceous calcite marble the skarn formed at the contact of the syenitic diana complex and was subsequently overprinted by grenville age granulite facies metamorphism and retrograde hydrothermal alteration during uplift calcite marbles adjacent to the deposit have generally high 6 o values c 21 0 typical of grenville marbles which have not exchanged extensively with externally derived fluids carbon isotopic fractiona tions between coexisting calcite and graphite in the marbles indicate equilibration at 675 c consistent with the conditions of regional metamorphism oxygen isotopic ratios from wollastonite skarn are lower than in the marbles and show a 14 variation 1 to 13 some isotopic heterogeneity is preserved from skarn formation and some represents localized exchange with low4 0 retrograde fluids detailed millimetre to centimetre scale isotopic profiles taken across skarn marble contacts reveal steep 8i8o gradients in the skarn with values increasing towards the marble the gradients reflect isotopic evolution of the fluid as it reacted with high 6 o calcite to form wollastonite calcite in the marble preserves high 6 o values to within 5 mm of the skarn contact the preservation of high 6 o values in marbles at skarn contacts and the disequilibrium fractionation between wollastonite skarn and calcite marble across these contacts indicate that the marbles were not infiltrated with significant quantities of the fluid thus the marbles were relatively impermeable during both the skarn formation and retrograde alteration skarn formation may have been episodic and fluid flow was either chaotic or dominantly parallel to lithological contacts although these steep isotope gradients resemble fluid infiltration fronts they actually represent the sides of the major flow system because chromatographic infiltration models of mass transport require the assumption of pervasive fluid flow through a permeable rock such models are not applicable to this hydrothermal system and by extension to many other metamorphic systems where low permeability rocks restrict fluid migration pathways minimum time integrated fluid fluxes have been calculated at the valentine deposit using oxygen isotopic mass balance reaction progress of fluid buffering reactions and silica mass balance all three approaches show that large volumes of fluid were necessary to produce the skarn but silica mass balance calculations yield the largest minimum flux and are hence the most realistic

fluid flow and volume loss during mylonitization an origin for phyllonite in an overthrust setting north carolina u s a abstract in the western blue ridge province of the southern appalachians north carolina granite gneisses are converted to phyllitic mylonites phyllonites along the base of the rector branch thrust sheet the mylonites show evidence for fluid infiltration and large volume losses with decreasing distance from the thrust and local shear zones feldspars undergo grain size reduction by cracking followed by chemical breakdown to muscovite sericite and zoisite the following reaction was important during mylonitization 3 k feldspar 2 h muscovite 2 k 6 sio 2 quartz displays evidence for dynamic recrystallization whereas feldspar deforms brittely which together with the secondary mineral assemblages suggest that deformation occurred at temperatures of between 300 c and 500 c in the presence of a fluid the mylonites are enriched by a factor of at least 2 5 in elements such as tio 2 p 2 o 5 zr y v la ce and depleted in sio 2 in comparison to their protolith gneisses the immobile element enrichments are attributed to enrichment in residual phases such as ilmenite zircon apatite and epidote in the mylonites and are interpreted as due to minimum volume losses of 60 mass balance calculations based on major element chemistry indicate the mylonites lost large amounts of sio 2 and smaller amounts of alkalies and were infiltrated by fluid rock weight ratios of between 10 2 and 10 3 phyllonitization as a process involves several deformation mechanisms including cataclasis and solution of feldspar as well as dislocation creep of quartz and micas reaction enhanced softening was apparently important in strain localization

isotopic and chemical alteration of zircon by metamorphic fluids u pb age depth profiling of zircon crystals from barrow s garnet zone northeast scotland u pb isotopic analyses were done using ion microprobe depth profiling on zircon crystals from dalradian rocks in barrow s garnet zone northeast scotland to determine the timing of metamorphic fluid infiltration and investigate fluid zircon interactions zircon crystals collected from altered metasedimentary rock adjacent to a cross cutting quartz vein and from relatively unaltered continuously equivalent layers distal to the vein indicate that paleozoic fluid influx caused isotopic and chemical alteration along zircon crystal surfaces and internal fractures ion drilling into natural zircon crystal faces yielded u pb depth profiles with 50 100 nm spatial resolution that permitted u pb isotopic age analysis of thin grain rims affected by fluid mediated growth recrystallization at 500 550 c we interpret the measurements to indicate that fluid influx at 462 8 8 ma caused the growth recrystallization of new zircon along pitted crystal surfaces and fractures in archean zircon grains our age estimate overlaps the accepted age range ca 467 464 ma for peak barrovian garnet growth confirming that metamorphism and fluid influx were contemporaneous the new zircon was enriched in u th and common pb relative to host grains suggesting that u th and pb were actively transported by upper greenschist facies metamorphic fluids we present the first field based evidence that common pb in zircon can serve as an indicator of metamorphic fluid infiltration archean ages for some detrital zircons suggest contributions from a lewisian scourian provenance

an investigation of the relationship between bulk composition inferred reaction progress and fluid flow parameters for layered micaceous carbonates from maine usa reaction progress exhibited by multivariant assemblages in micaceous limestones can provide an excellent record of metamorphic fluid flow however it is necessary to understand the sensitivity of these assemblages to bulk composition parameters here analysis of bulk composition on different scales and pseudosection construction are used to draw conclusions on relationships between bulk composition fluid flow and reaction progress issues addressed include the effects of bulk composition on the mineralogical evolution of micaceous carbonates the sensitivity of bulk composition to bulk composition sampling methods the magnitude of cross layer fluid composition gradients the potential for metasomatism to drive reaction progress and the relative timing of reaction in adjacent layers pseudosections successfully represent observed mineral assemblages constrain the position of reactions in t x co2 space and allow assessment of the sensitivity of reaction position inferred reaction progress and calculated fluid fluxes to uncertainties in bulk composition the scale of bulk composition sampling affects bulk compositions calculated modes predicted mineral assemblages and calculated fluid compositions larger samples record an average of different lithological subdomains while point count derived bulk compositions are subject to uncertainties related to the small number of sample points the optimum bulk composition for pseudosection purposes probably lies between measured bulk compositions results suggest that reaction progress in some extensively reacted layers was driven by infiltration of h2o rich fluid which flowed or diffused parallel to layering perpendicular to layering in response to fluid composition gradients and out of veins small variations in fluid composition across layering x co2 0 02 were maintained by internal buffering by the mineral assemblages internal buffering must also have driven samples up a sequence of narrow low variance fields in t x co2 space and so reaction in adjacent layers must have close to simultaneous metasomatic effects on reaction progress are likely to have been small so long as the porosity was low

actualistic models of mantle metasomatism documented in a composite xenolith from dish hill california major and trace element whole rock and mineral variations in composite hornblendite peridotite xenolith ba 2 1 from dish hill ca are due to a single event of metasomatism in the mantle the hornblendite is the crystallized selvage of a dike conduit charged with incompatible element enriched hydrous mafic magma the magma infiltrated the refractory peridotite wallrock reacted with its constituent minerals and simultaneously deposited amphibole the systematic data from this study show considerable variation in isotopic values and trace elements these data provide insight into a mantle process that was defined previously from samples without context lacking evidence about the number or source of metasomatic events in the contact zone of ba 2 1 peridotite is enriched in fe ti co2 and h2o clinopyroxene and amphibole also are enriched in fe and ti but clinopyroxene appears slightly depleted in cao compared to chondrites peridotite clinopyroxene and probably amphibole are enriched in light rare earth lreecn and other incompatible trace elements values of 87sr86sr and 143nd144nd in the contact zone are close to isotopic equilibrium with the dike whole rock and constituent clinopyroxene compositions change to those of refractory peridotite with distance from the contact these compositional variations were modelled using gresens equation for whole rock major and minor elements and calculations for isotopic ratios and rees which emulate the effects of chromatographic fractionation the choice of endmembers was restricted to compositions actually present in mantle samples from dish hill model results indicate that 1 1 the variations can be explained as the result of a single metasomatic event probably a single pulse of previously fractionated liquid 2 2 the ratio of total interacting liquid to peridotite was at least 1 3 by weight in the contact zone and 3 3 the composition of the metasomatic liquid changed progressively as it infiltrated beyond that zone the small distance over which variations occur is due to the small amount of liquid that infiltrated only in the contact zone was peridotite wallrock saturated by a liquid composition similar to the dike comparison of the ba 2 1 data with those of another xenolith from dish hill suggests that the compositional variations of mantle metasomatism result from both the compositional contrast between the metasomatizing liquid and wallrock and the relative abundances of each compositional and volumetric variations of mantle partial melts and their fractionates and repeated events of melting and reaction in contiguous mantle can create broad ranges of metasomatic signatures from the same process

rate and mechanism in prograde metamorphism for a given rate of heat input into a prograde metamorphic sequence the extent of overstep of reaction temperature disequilibrium depends on the slowest of three sequential steps a surface detachment of reactant minerals b transport of material to the site of mineral growth and c nucleation and growth of the product mineral we have developed analytical expressions which enable determination of the rates of mineral dissolution and growth and of advective and diffusive mass transport during metamorphism the dissolution and growth steps are linear functions of the driving force g of the overall reaction while diffusion may take place either through a grain boundary fluid film or through the disorganized grain boundary itself

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

isotopic evidence for closed system anatexis at midcrustal levels an example from the acadian appalachians of new england we have investigated the sr and o isotope systematics of granitoid and metasedimentary samples from the central maine terrane cmt of new england granitoid samples were taken from interior and contact zones within the acadian aged 410 m y synmetamorphic and syntectonic kinsman quartz monzonite kqm which is a member of the new hampshire plutonic series metasedimentary samples were taken from silurian and devonian formations hosting the kqm initial sr isotope ratios sri and 18o values for the kqm range from 0 70799 to 0 71246 and 1 6 to 12 9 respectively and sri and 18o values of the metasedimentary rocks range from 0 70770 to 0 75008 and 6 2 to 14 1 respectively we observe a linear and slightly positive correlation between sri and 18o for interior kqm samples that can be duplicated by a mixing curve calculated for metasedimentary endmembers whereas the sri and 18o values of contact kqm samples cluster near the sri and 18o values of the metasedimentary rocks with which they are in contact mixing calculations provide no evidence for a measurable primitive mantle component in either interior or contact kqm samples and we conclude that the sr o isotopic composition of the kqm is most likely a reflection of isotopic heterogeneities inherited from a complex package of midcrustal metasedimentary source rocks we propose that the kqm is the product of midcrustal partial melting that was initiated due to excess thermal energy from the decay of anomalously high concentrations of heat producing elements in silurian source rocks within the cmt because we see no isotopic evidence for a lower crustal or mantle component in the kqm we suggest that midcrustal anatexis may have occurred as a closed system process requiring no accompanying mantle derived magma or above normal mantle heat flow

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

rock buffered fluid rock interaction in deformed quartz rich turbidite sequences eastern australia quartz vein 18o 16o ratios across a 500 km transect through the lachlan fold belt of southeastern australia are remarkably uniform 1 1 5 permil at both local centimeter to meter and regional over 104 km2 scales they define isotopic zones that correlate with the tectonic divisions of the cambrian through devonian dominantly ordovician quartz rich turbidites determined by regional mapping from west to east these divisions are 1 stawell 18o 14 7 1 1 47 samples 2 bendigo ballarat 18o 17 5 1 3 204 samples 3 melbourne 18o 19 0 1 6 80 samples 4 tabberabbera 18o 16 3 1 9 12 samples and 5 omeo 18o 14 4 1 0 26 samples isotope profiles across zone boundaries and intrazone fault zones particularly within the bendigo ballarat zone show steps indicating abrupt changes across faults with little or no evidence of fluid mixing within the fault zones 18o values of veins are insensitive to relative age type of vein and immediate host rock lithologies the 18o values of coexisting vein and host rocks show nonequilibrium relationships which can be explained in terms of rock buffering under conditions of low fluid rock ratios water rock 1 limited d h determinations on fluid inclusions fall mainly in the range 70 and 100 with one value as low as 140 these low deuterium values when considered in the context of paleolatitude may have been inherited from deutrium depleted detrital minerals and do not necessarily require the direct penetration of meteoric fluids to midcrustal depths the work suggests that vein formation is possible in regions where the integrated water rock w r ratio is very low w r 1 as long as a pervasive fluid phase is present this fluid appears to achieve a steady state isotopic composition on scales of hundreds of meters and once a quasi steady state has been reached the isotopic compositions of the resultant quartz veins are rather insensitive to the diachronous and nonisothermal conditions under which vein growth occurs advective cycling of the fluid on this scale is by episodic dilatancy pumping in fracture networks associated with localized faulting

the effect of heterogeneous stress and strain on metamorphic fluid flow mary kathleen australia and a model for large scale fluid circulation in the proterozoic mary kathleen fold belt northern australia infiltration of large volumes of externally derived fluid occurred synchronously with regional amphibolite facies metamorphism and deformation this paper develops a model of structurally controlled fluid migration by comparing the distribution of fossil fluid pathways with the inferred stress and strain patterns during the deformation intense fluid flow was localized within strong relatively brittle meta intrusive bodies and in discrete veined brecciated and altered zones around their margins in metasediments folded in a ductile manner outside these areas fluid infiltration was negligible the direct correlation between structural styles and the magnitude of veining and metasomatism suggests control of permeability enhancement and hence fluid flow by deformation finite difference modelling of a strong body in a weaker matrix has been used to evaluate the variation of stresses during the deformation from which it is clear that stress and strain heterogeneities have systematically influenced the development and maintenance of metamorphic fluid pathways particular regions in which mean stress may be significantly lower than the average lithostatic pressures include the strain shadow zones adjacent to the strong bodies other dilatant zones around the bodies and the bodies themselves this geometry is favourable not only for localized brittle deformation under amphilobite facies conditions but also for focused fluid flow in the low mean stress regions as evidenced by the abundance of veins fluid access through these metamorphic aquifers occurred during tensile failure episodes with particularly large dilations and decimetre scale veining in areas of strain incompatibility it appears likely that fluid circulated many times through the fold belt with flow concentrated in the metamorphic aquifers a model is developed that explains both the structurally focused fluid flow and the postulated multi pass recirculation by dilatancy pumping the pump engines comprising the low mean stress zones

principles involved in mobilization and remobilization abstract many orebodies result from appropriate combinations of fluid flow chemical environment pressure temperature and rock structure within the context of mobilization and possibly remobilization this is largely because solid state diffusion is too slow to allow transport of materials over distances in the order of kilometres within appropriate time frames advective mass transport involving large fluid rock ratios is the only viable mechanism of solution transfer that satisfies distance time frame requirements despite removal of metal species from a source region and their emplacement in otherwise barren rock being influenced by transport mechanism and fluid chemistry it is the porosity and permeability mechanical and chemical of source region and emplacement site and the need for focussed flow that are fundamental to forming ore concentrations and constitute important exploration guides thee processes and recognition of mechanically enhanced permeability are related to crack seal vein systems critical vein systems subcritical joints and vein breccias the only significant differences between the basic principles of mobilization and remobilization are the lesser need for focussing of circulating fluids and the local role of solid state remobilization in highly ductile massive sulphide by definition the chemical environment associated with fluid state mobilization and remobilization must differ from that of previous deposition and this generally means that the associated metamorphic conditions will differ

textural and isotopic variations in graphite from plutonic rocks south central new hampshire graphite occurs in two distinct textural varieties in syntectonic granitoids of the new hampshire plutonic series and in associated metasedimentary wall rocks textural characteristics indicate that coarse graphite flakes were present at an early stage of crystallization of the igneous rocks and thus may represent xenocrystic material assimilated from the wall rocks the range of 13c values determined for flake graphite in the igneous rocks 26 5 to 13 8 overlaps the range for flake graphite in the wall rocks 26 0 to 16 7 and spatial correlation of some 13c values in the plutons and wall rocks supports the assimilation mechanism the textures of fine grained irregular aggregates or spherulites of graphite on the other hand indicate that they formed along with secondary hydrous silicates and carbonates during retrograde reactions between the primary silicates and a carbon bearing aqueous fluid phase relative to coexisting flake graphite spherulitic graphite shows isotopic shifts ranging from 1 9 higher to 1 4 lower in both igneous and metasedimentary samples

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

strontium isotopic equilibration during metamorphism of tillites from the ogcheon belt south korea the ne sw trending ogcheon belt formed during the mesozoic by deformation and metamorphism of a sedimentary sequence which includes tillite formations of late precambrian or lower palaeozoic age in this study rb sr isotopic data are reported from cm scale sampling of clasts and matrix in these tillites which underwent metamorphism at grades ranging from the biotite zone to the kyanite zone sr isotopic disequilibrium between clasts and matrix persists up to the highest grade but in four out of five rocks the matrix samples approximate to isochrons mswd s 12 the mechanism for this selective isotopic equilibration is considered to be related to the metamorphic reactions in the matrix which were probably accompanied by a substantial fluid flow the matrix isochrons for three of the rocks together with separated white micas from associated schists suggest that metamorphism took place in the trias approximately 200 myr ago metamorphism was followed by slow cooling and biotite closure temperatures were not reached until 190 150 myr these results suggest that where high fluid rock ratios can be demonstrated on independent petrological grounds the analysis of small scale whole rock samples may allow effective rb sr dating of metamorphism

fluid flow and alkali transport within a metamorphic terrane western north carolina abstract this paper presents preliminary results from study of a metasedimentary terrane near the great smoky mountains of north carolina grade of metamorphism ranges from garnet to staurolite kyanite zone the stratigraphic section is dominated by metasandstone but contains thick pelitic horizons over the central portion anakeesta formation of the studied interval metasandstone beds contain numerous isolated calcite concretions these react to form leucocratic calc silicate rock at variable grade of metamorphism metasandstones themselves are unreactive study of calc silicate reaction permits the following statements regarding fluid flow and alkali transport within the studied terrane within unreacted concretions the typical mineral assemblage is quartz oligoclase muscovite biotite calcite reaction between micas and calcite proceeded through several stages forming as prograde minerals andesine bytownite clinozoisite zoisite garnet hornblende and chlorite reaction occurred in the presence of a fluid phase containing a h2o co2 ratio of 9 and resulted in massive expulsion of na2o k2o and co2 since postulated reactions would have produced on average a fluid phase whose h2o co2 ratio is only one flow of water rich fluid through the concretions accompanied reaction rough estimate suggests a volumetric ratio of external fluid to rock of at least 1 1 the metamorphic grade at which concretions undergo reaction is controlled by stratigraphic position of the host metasandstone relative to metashale within the anakeesta formation and overlying strata extensive reaction occurs near the pelitic staurolite and kyanite isograds within massive metasandstones of the underlying strata reaction is delayed to the middle staurolite kyanite zone 5 km upgrade some reaction occurs within the upper garnet zone but this is restricted to certain thin metasandstone beds interlayered with metashale study of dehydration reactions within metashale demonstrates that calc silicate reaction was coupled to production of h2o rich fluids within pelitic strata transport of h2o rich fluids beyond outcrop scale was by advection diffusion was limited to outcrop distance on most outcrops all isolated concretions show the same degree of reaction but at larger scale separate metasandstone packets bounded by metashale show differing degrees of reaction also all rocks underwent some degree of penetrative deformation during time of reaction the suggestion is made that advective flow was in fact channelized into fractures within metasandstone and that diffusion between fractures promoted reaction within outcrop size volumes of rock overall direction of fluid transport was in part upsection and in part channelized within metasandstone strata downsection flow was limited for the most part alkalis liberated by calc silicate reaction appear to have left the terrane metasandstones do not appear to constitute a sink for alkalis and no sink of any sort was found for sodium potassium metasomatism of pelitic rock did occur and is marked by conversion of chlorite to biotite but such k deposition is limited to sections within which metashale and calc silicate rock are within outcrop distance no sink is evident for most liberated potassium it is within conjecture that the liberated elements caused alkali metasomatism elsewhere within the metamorphic belt but such an event has yet to be demonstrated

internally consistent geothermometry and h 2 o barometry in metamorphic rocks the example garnet chlorite quartz temperature and h2o activity can be determined with high precision using metamorphic mineral assemblages that define both a dehydration equilibrium and a temperature sensitive cation exchange equilibrium such determinations are obtained by applying the gibbs method and then integrating two resulting differential equations as illustrated here for the assemblage garnet chlorite quartz the first equation a geothermometer that monitors temperature based upon fe mg exchange between garnet and chlorite was calibrated using rocks at pecos baldy new mexico 0 0 05 p bars 19 02 t k 4607 ln kd 24 156 with errors of 8 c based upon analytical precision the second equation monitors differences in the activity of water between specimens 1 and 2 0 0 1 xmg chl 1 2 05 p2 p1 33 02 5 96 ln xfe chl 1 xalm 1 t2 t1 2 67 rt1ln a h2o 2 a h2o 1 5 96 t1ln xfe chl 2xalm 1 xfe chl 1xalm 2

tremolite and h 2 o activity attending metamorphism of hornblende plagioclase garnet assemblages estimation of the activity of tremolite component atr in calcic amphiboles is an important problem in igneous and metamorphic petrology because equilibria involving tremolite are used in the estimation of the activity of h2o attending crystallization of igneous and metamorphic rocks estimated values of atr from hornblende analyses using both ionic and coupled substitution crystalline solution models can be compared to values of atr calculated from vapor absent mineral equilibria in addition these values of atr can be used in calculations of ah2o for rocks for which there is an independent estimate of ah2o the values of atr calculated from vapor absent equilibria are generally consistent with those estimated from the different crystalline solution models but uncertainties in the calculations preclude choosing a preferred solution model from computed mineral equilibria it is clear that mineral assemblages with low values of atr can be in equilibrium with high values of ah2o consequently the low values of ah2o estimated from hornblende bearing high grade rocks with low values of atr may be real rocks from mica creek british columbia probably achieved extremely low values of ah2o by vapor absent metamorphism

stable isotope geochemistry of marbles from the coesite uhp terrains of dabieshan and sulu china abstract marbles from dabieshan and sulu china suffered ultra high pressure uhp metamorphism in the coesite eclogite facies at approximately 700 c and 30 kbars during triassic continental collision and subduction the marbles range in isotopic composition from 7 to 25 18 o vsmow and from 0 to 6 13 c vpdb high 13 c values are representative of unmodified protoliths and are similar to those of 13 c enriched sinian carbonate rocks from the yangtze craton high oxygen isotope ratios reflect pristine protoliths but the low values may have been caused by infiltration of low 18 o meteoric water during diagenesis and dolomitization by fracture controlled infiltration of water during subduction by metamorphic mineral reactions or by a combination of these processes no evidence of regional isotopic transport during uhp metamorphism has been found sampling on scales of 1 to 100 m shows marbles to be inhomogeneous in both carbon and oxygen isotopes only samples separated by less than 10 cm have equilibrated oxygen and carbon isotope compositions limited isotopic equilibration between adjacent rocks is consistent with the preservation of unaltered uhp minerals and indicates that the metamorphic fluid rock system was rock dominated during and following peak metamorphism a freely flowing pervasive fluid phase was not present during uhp metamorphism there is no evidence of isotopic exchange between marble and the upper mantle into which it was subducted correlation of geochemical similarities of uhp marbles with sinian limestones implies that the subducted edge of the yangtze craton extends at least as far north as the coesite eclogite facies rocks of dabieshan deposition of protolith carbonates may have taken place in a cold climate either preceding or following but not coincident with neoproterozoic glaciation

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

evidence from mossbauer spectroscopy for intense localization of metamorphic fluid flow during the formation of spaced cleavage arenites in the low grade metasedimentary rocks of the stirling barren group western australia contain discrete spaced cleavages these in part are pure white mica but up to 30 of the cleavage zones consists of fine grained quartz resulting from crystal plastic deformation a modified gresens analysis shows that the cleavage domains formed by a 50 volume loss associated primarily with sio2 and mgo concentration decreases of 58 and 37 respectively and a 12 decrease in fe2o3 mossbauer spectroscopy shows that the fe2 fe3 ratio from lithon to cleavage changed from 50 so to 15 85 this substantial difference cannot be accounted for by loss of iron the data are best explained by the focusing of a highly oxidizing fluid through the cleavage domains where volumetric fluid rock ratios around 150 to 1 are indicated in this example advectic processes appear to be important in low grade regional metamorphism

the role of fluids in syntectonic mass transport and the localization of metamorphic vein type ore deposists abstract in low to medium grade metamorphic environments the mobilization of species is closely associated with the operation of solution precipitation creep processes during foliation development such deformation processes involve dissolution of material from source sites which are usually discrete dissolution surfaces having orientations controlled by the applied stress and displacement fields mass transfer occurs via solute diffusion in an essentially static fluid network or by transport of dissolved species in a migrating fluid precipitation of material removed from dissolution sites occurs in a variety of sink sites including pore surfaces grain scale microcracks and veins sink sites may be close to or distantly removed from source sites the transport of material during deformation involving solution precipitation creep is largely controlled by the mobility of metamorphic fluids in regions of high fluid mobility significant mass transfer may occur over large distances fluid flow mass transfer paths and the development of sink sites in such cases are constrained by the structurally controlled development of high fluid pressure domains and the consequent mechanical enhancement of permeability by hydraulic fracture processes and the development of grain scale dilatancy these processes may result in focussed fluid flow and precipitation of mobilized species in restricted regions a proportion of syntectonically mobilized material is precipitated to form vein type deposits in hydraulic fracture arrays which develop in high fluid pressure environments the microstructures developed in minerals deposited in these sites reflect the interaction of a range of nucleation and growth processes which usually involve multiple generations of fracture growth and mineral crystallization the formation of syntectonic gold quartz vein deposits in central victoria australia illustrates the importance of structural controls on both the large scale migration of metamorphic fluids and the development of sites suitable for the precipitation of metamorphically mobilized species

garnet composition as a petrogenetic indicator an example from a marble calc silicate granulite interface at kondapalle eastern ghats belt india thep t fluid histories of aluminous garnet clinopyroxene bearing calc silicate granulites are commonly constrained through interpretation of sequential reaction textures based on activity corrected petrogenetic grids for model systems for example the widely used cas co2 h2o topologies application of these topologies to calc silicates of diverse bulk composition is limited by the fact that the role of clinopyroxene and hence of garnet composition in the garnet forming reactions is ignored or not adequately considered in this contribution the complexities that arise from the involvement of clinopyroxene in the garnet forming reactions are critically evaluated as an example the paragenetic relations and compositional features of clinopyroxene and coronitic garnet across paired scapolite and wollastonite dominated reaction zones scp cpx qtz cal qtz wo cal cpx scp developed between marble layers cal cpx wo scp and their host calc silicate granulite cpx pl qtz scp at an exposure in the high grade eastern ghats belt india are examined the microtextural features and systematic changes of modal and phase compositions across the profile indicate that clinopyroxene scapolite plagioclase quartz and calcite as well as wollastonite participated in the garnet forming reactions using the sub assemblage qtz cal cpx scp grt v in the system cao feo al2o3 sio2 co2 it is demonstrated that at the ambient p t xfluid conditions the reaction coefficients of the participating phases are uniquely defined by the garnet composition as a result the p t slope of a garnet forming reaction changes with the garnet composition with sharp changes at singular points across which one or more phases change their sides with respect to garnet in a given reaction to consider the consequences of these complexities on the reaction topology of calc silicate granulites a new petrogenetic grid for the system cao feo al2o3 sio2 co2 involving clinopyroxene has been constructed the effects of fluid composition co2 h2o o2 fluid pressure pfluid

quantifying rates of methanogenesis and methanotrophy in lake kinneret sediments israel using pore water profiles full seasonal sets of chemical and isotope profiles from the pore water of lake kinneret sea of galilee israel were produced to study methanogenesis and methanotrophy processes and the couplings between methane ch4 sulfur and iron sulfate is depleted within the upper 10 cm of the sediment mainly by traditional bacterial sulfate reduction by organic matter maximum sulfate reduction rates calculated from sulfate concentration profiles are found at the water sediment interface 0 1 cm 2 1 4 3 10212 6 0 2 3 10212 mol cm23 s21 ch4 concentrations and modeling of dissolved inorganic carbon dic and its stable carbon isotope d13cdic suggest that maximum methanogenesis rates of 2 5 3 10213 6 1 5 3 10213 mol cm23 s21 occur at 5 12 cm depth in the sediments and that it ends at 20 cm of the produced ch4 50 75 is converted to gas bubbles of ch4 before it reaches the bottom water model results suggest the occurrence of anaerobic oxidation of ch4 aom in the deep sediments of the lake below the zone of methanogenesis methane ch4 is an important greenhouse gas with emissions from anthropogenic and natural sources roughly estimated to be around 350 and 120 tg c yr 21 tg 2 1 3 1012 g respectively wuebbles and hayhoe 2002 among the natural sources continental emissions contribute more than 70 wuebbles and hayhoe 2002 however the parameters controlling these emissions are not well understood therefore it is essential to resolve the rate of the processes behind ch4 emissions from continental systems this study aims at this objective investigating lacustrine environment using a geochemical approach ch4 in its natural sources is produced mainly through microbial processes methanogenesis chemical profiles in pore water of organic rich sediments indicate that various microbes use a series of electron acceptors during the remineralization of organic matter in the order of decreasing chemical potential and methanogenesis accounts for the last stage of the microbial respiration in stratified lakes developing an anoxic hypolimnion methanogenesis and sulfate reduction are key terminal

structural controls on syntectonic metasomatic tremolite and tremolite plagioclase pods in the molanite valley mt isa australia abstract in the molanite valley west of mt isa tremolite bearing metasomatic pods showing sharp contacts with enclosing rocks occur over a strike length of 7 4 km in the biotite zone bortala formation in relatively low strain rocks of the western part of the valley plagioclase tremolite pods have replaced psammite or mica schist surrounding the terminations of buck quartz veins whereas in intensively sheared rocks to the east pods of medium to coarse grained massive tremolite commonly containing greater than 95 tremolite have replaced marble quartzite and psammite talc chlorite schists formed by dissolution of carbonates during shearing of marble are associated with some of the massive tremolite pods the direct relationship between structural domains and metasomatism suggests that migration of externally derived fluids was controlled by fractures and the shear zone the fluids having migrated along fractures interacted with wall rocks to produce plagioclase tremolite pods in the shear zone buck quartz veins some tremolite bearing show no obvious geometric relationship to massive tremolite pods it is postulated that the metasomatic fluids fluxed through shear domains and penetrated progressive shortening domains to replace the host rocks and form the massive tremolite pods both styles of metasomatic rocks developed from late s 2 to early s 3 during a progressive e w shortening event which corresponds to the regional metamorphism the metasomatic rocks represent only a small part of widespread metasomatism across the mt isa inlier

fluid flow metasomatism and amphibole deformation in an imbricated ophiolite north cascades washington abstract metasomatic tremolite rich mylonites are widespread in imbricate thrust slices of ultramafic rocks of the ophiolitic ingalls complex in washington state protoliths for these amphibolite facies mylonites were peridotite and serpentinite abundant syntectonic tremolite veins in the ultramafites record narrowly channelized flow of infiltrating fluids whereas metasomatic mylonite zones record more pervasive flow fluids were probably released mainly by prograde devolatization reactions within serpentinite and mafic ophiolitic rocks that experienced earlier hydrothermal metamorphism olivine apparently deformed by dislocation creep in the mylonites in the tremolite rich rocks locally preserved amphibole porphyroclasts deformed mainly by microfracturing acicular tremolites which dominate the mylonites form syntectonic overgrowths on porphyroclasts and probably record diffusive mass transfer which may have accompanied cataclasis acicular tremolites subsequently were folded and define both post crystalline crenulations and polygonal arcs fluid flow deformation and metamorphism were apparently complexly interrelated in the imbricate zone thrusts juxtaposed contrasting rock types that were sources and sinks for fluids and shear zones focused fluid flow metamorphism probably facilitated deformation through the release of fluids during dehydration reactions high fluid pressure may have led to hydraulic fracturing and may have controlled strain softening in the tremolitic mylonite zones as it favored microcracking and diffusive mass transfer over dislocation creep infiltrating metasomatic fluids probably play an important role in the evolution of shear zones in many ultramafic bodies during medium grade metamorphism

magnetic fabric in the biella and traversella stocks periadriatic line implications for the mode of emplacement abstract the biella and traversella stocks forming part of the intrusions along the periadriatic line intruded into the sesia lanzo zone italian western alps 30 ma ago samples were collected from 12 localities in the traversella massif diorites and 22 in the biella massif granites syenites monzonites in most localities the fabric is primarily planar with a distinct foliation of intermediate to subvertical dip the magnetic lineation is less developed its plunge is very variable marking a girdle pattern the mean foliations and lineations per locality are scattered this is probably due to the fact that the outcropping parts of the two stocks are summital i e nearer the roof and hence the magma movements may have been less regular in the structurally deepest part of the biella massif the magnetic foliation dips regularly to the northwest its direction could reflect the pattern of the deep fractures along which the magma rose the classic models of owens to describe the process of magnetic mineral orientation do not apply to the features of these two stocks a new model has been constructed to take account of the differences in viscosity contrast between the magnetic mineral crystals and the matrix referred to as the ductile model it offers a suitable representation of the typical situation of crystal mushes and is the most appropriate for the biella and traversella stocks

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

local and regional differences in the chemical potential of water in amphibolite facies pelitic schists mineral assemblages in different samples of amphibolite facies pelitic schists collected from two separate outcrops in the moosilauke area nh record differences in the chemical potential of water during metamorphism mineralogical petrological and field relations indicate that mineral assemblages at both outcrops equilibrated at 520 c and 3 5 4 0 kbar thermodynamic analysis of the mineral assemblages demonstrates that maximum chemical potential differences at each outcrop were of the order of 150 calories over distances of 10 20 m the differences in the chemical potential of water recorded in both bed to bed and outcrop to outcrop relations are consistent with the following conclusions 1 mineral assemblages on a specific outcrop did not equilibrate with an external reservoir of fluid of fixed composition 2 the relatively small magnitude of the chemical potential differences suggests little or no infiltration of externally derived fluid 3 these differences on the outcrop scale are probably related to initial compositional variations and the buffer capacity of the mineral assemblage and 4 the different values of the chemical potential of water exhibited by the various mineral assemblages permits an understanding of the effects of variable h2o for amphibolite facies pelitic schists

oxygen and hydrogen isotope study of minerals from metapelitic rocks staurolite to sillimanite zones mica creek british columbia oxygen and hydrogen isotope analyses have been made of coexisting quartz ilmenite muscovite and biotite from late precambrian metapelitic rocks staurolite kyanite to k feldspar muscovite sillimanite zones from mica creek british columbia the 18o and d values of these minerals are generally uniform and do not decrease significantly with increasing metamorphic grade this implies that there has not been significant infiltration of deep crustal possibly magmatic fluids into the metapelites that has been suggested for other high grade metamorphic terranes the uniformity of oxygen isotope compositions of the mica creek metapelite rocks may reflect isotopic uniformity in the sedimentary protolith rather than widespread exchange with an isotopically homogeneous metamorphic pore fluid temperature estimates based upon 18o exchange thermometry for samples below the sillimanite zone are in reasonable agreement with the results of garnet biotite fe mg exchange thermometry in the higher grade rocks the oxygen isotope and garnet biotite thermometry yield results which disagree by about 100 c the highest temperatures recorded by oxygen isotope thermometry 595 c are at least 60 c below the minimum temperatures required by phase equilibria these discrepancies appear to result from pervasive equilibrium retrograde exchange of oxygen isotopes between coexisting minerals in addition there are problems with calibration of garnet biotite thermometry at higher temperatures retrograde oxygen isotope exchange may be a general characteristic of high grade metamorphic rocks and oxygen isotope thermometry may not usually record peak metamorphic temperatures if they significantly exceed 600 c

fluid heterogeneities and hornblende stability in interlayered graphitic and nongraphitic schists tauern window eastern alps the assemblage hornblende white mica occurs in graphite free schists at two localities in the southwest corner of the tauern window eastern alps in interbedded graphitic layers 1 mm to 1 m thick however hornblende is typically replaced by pseudomorphs of biotite plagioclase epidote chlorite staurolite in the presence of white mica garnets adjacent to these pseudomorphs have pronounced growth discontinuities near their rims in contrast to the continuously zoned garnets in nongraphitic layers these observations imply that reactions of the type hbl white mica gar bio plag epid chl staur h2o occurred in the graphitic samples but that hbl white mica remained stable in graphite free layers calculation of the equilibrium constants for solid phases in five dehydration equilibria at locality 1 indicates thata h2o in the nongraphitic layers was 6 to 11 times greater thana h2o in the graphitic layers similar calculations involving six dehydration equilibria at locality 2 show no difference ina h2o between layers at the conditions of final equilibration initial differences in fluid composition maintained between the graphitic and nongraphitic layers caused the hbl white mica reaction to occur at differentp t conditions in different horizons of the schists these data indicate that systematic differences in fluid composition were generated during metamorphism of the interlayered graphitic and non graphitic schists but were subsequently homogenized at locality 2 the heterogeneities could initially have been produced while the rocks were in thep t field of co2 h2o immiscibility development of a penetrative layer parallel shear foliation at this time would have prevented subsequent mixing of the fluids across layers after temperatures exceeded the consolute temperature in the co2 h2o system late stage homogenization of fluids at locality 2 is thought to reflect loss of the buffer capacity of the mineral assemblage in response to total consumption of hornblende

a regional gradient in the composition of metamorphic fluids in pelitic schist pecos baldy new mexico two metamorphic isograds cut across graphitic schist near pecos baldy new mexico the southern isograd marks the first coexistence of staurolite with biotite whereas the northern isograd marks the first coexistence of andalusite with biotite the isograds do not record changes in temperature or pressure instead they record a regional gradient in the composition of the metamorphic fluid phase ortega quartzite which contains primary hematite lies immediately north of the graphitic schist mineral compositions within the schist change gradually toward the quartzite reflecting gradients in mu text o text 2 and mu text h text 2 text o the chemical potential gradients locally as high as 72 cal m in mu text o text 2 and 9 cal m in mu text h text 2 text o controlled the positions of the two mapped isograds the staurolite biotite isograd records where x text h text 2 text o fell below 0 80 at f text o text 2 near 10 23 bars the andalusite biotite isograd records where x text h text 2 text o fell below 0 25 at f text o text 2 near 10 22 bars dehydration and oxidation were coupled by graphite fluid equilibrium the chemical potential gradients apparently formed during metamorphism as graphite in schist reacted with hematite in quartzite local oxidation of graphite formed co2 which triggered dehydration reactions along the schistquartzite contact this process created a c o h fluid which infiltrated into overlying rocks upward infiltration local fluid rock equilibration and additional infiltration proceeded until the composition of the infiltrating fluid evolved to that in equilibrium with the infiltrated rock this point occurs very close to the staurolite biotite isograd pelitic rocks structurally above this isograd show no petrographic evidence of infiltration even though calculations indicate that volumetric fluid rock ratios may have exceeded 15 and thin rare calc silicate beds show extensive k metasomatism and quartz veining

granulite facies metasomatism zoned calc silicate boudins from the rauer group east antarctica calc silicate boudins from the rauer group east antarctica were metamorphosed under granulite facies conditions during late proterozoic ca 1 000 ma m3 metamorphism boudin cores contain low to moderate aco2 assemblages including wollastonite grossularandradite grandite garnet clinopyroxene scapolite plagioclase quartz calcite petrological and stable isotopic evidence suggests that these core assemblages resulted from pre peak m3 infiltration of water rich fluids there is no evidence for a pervasive fluid phase under peak m3 conditions the boudins are separated from the surrounding fe rich pelites and semi pelites by a series of concentric high variance reaction zones developed under peak m3 conditions variations in mineral assemblage mineral composition and whole rock composition across these zones suggest that they formed by diffusional masstransfer controlled principally by a chemical potential gradient in ca across the original calc silicate paragneiss lithological boundary as a consequence of the nearcomplete decarbonation of the calc silicatesbefore the m3 peak development of the diffusion controlled reaction zones did not liberate significant co2 during granulite facies metamorphism similar calcite poor low aco2 calc silicate horizons in other granulite facies terrains are unlikely to have been important local fluid sources during deep crustal metamorphism

sulfides oxides and sphene in high pressure schists from new caledonia in the new caledonia high pressure schists pyrite pyrrhotite chalcopyrite rutile and sphene are common phases while hematite and ilmenite are rare and magnetite is absent the parageneses of these minerals were clarified from their occurrence as inclusions in garnet from phase relations in the cu fe s and fe ti o s systems and from phase rule considerations for the multi component system the sulfur fugacity estimated for pelites and basites containing pyrrhotite pyrite and rutile increased with increasing metamorphic grade the oxygen fugacity in these schists was less than 10 27 6 bars at 400 c 10 kb and 10 22 3 bars at 500 c 11 kb among the other components of the metamorphic fluid in pelites h2o was major ch4 co2 and h2s minor and h2 co cos and so2 rare the fluid composition altered with advancing metamorphic grade such that h2o decreased while co2 ch4 and h2s increased and this change was linked to concurrent massive decarbonization in the rock matrices

an application of cathodoluminescence microscopy to the study of textures and reactions in high grade marbles from connemara ireland upper amphibolite facies dolomite and calcite marbles from the dalradian connemara marble formation of western ireland display a wide range of textures when viewed in cathodoluminescence that are invisible in transmitted light examples observed include growth zones in calcite that appear to represent the infilling of a metamorphic secondary porosity produced by the large reduction in solid volume accompanying growth of tremolite from dolomite and quartz retrograde phenomena are widespread and include both carbonate pseudomorphs after tremolite and coarse veining which is in optical continuity with peak metamorphic calcite but otherwise indistinguishable from it admixture of such widely differing calcite types may account for scatter in some stable isotope studies of marbles

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

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

role of water in hydrocarbon generation from type i kerogen in mahogany oil shale of the green river formation abstract hydrous and anhydrous closed system pyrolysis experiments were conducted on a sample of mahogany oil shale eocene green river formation containing type i kerogen to determine whether the role of water had the same effect on petroleum generation as reported for type ii kerogen in the woodford shale the experiments were conducted at 330 and 350 c for 72 h to determine the effects of water during kerogen decomposition to polar rich bitumen and subsequent bitumen decomposition to hydrocarbon rich oil the results showed that the role of water was more significant in bitumen decomposition to oil at 350 c than in kerogen decomposition to bitumen at 330 c at 350 c the hydrous experiment generated 29 more total hydrocarbon product and 33 more c 15 hydrocarbons than the anhydrous experiment this is attributed to water dissolved in the bitumen serving as a source of hydrogen to enhance thermal cracking and facilitate the expulsion of immiscible oil in the absence of water cross linking is enhanced in the confines of the rock resulting in formation of pyrobitumen and molecular hydrogen these differences are also reflected in the color and texture of the recovered rock despite confining liquid water pressure being 7 9 times greater in the hydrous experiments than the confining vapor pressure in the anhydrous experiments recovered rock from the former had a lighter color and expansion fractures parallel to the bedding fabric of the rock the absence of these open tensile fractures in the recovered rock from the anhydrous experiments indicates that water promotes net volume increase reactions like thermal cracking over net volume decrease reactions like cross linking which results in pyrobitumen the results indicate the role of water in hydrocarbon and petroleum formation from type i kerogen is significant as reported for type ii kerogen

evidence for a regional scale fluid loss event during mid crustal metamorphism how fluid is released from the deep crust during metamorphism remains controversial whereas some authors advocate large scale fluid fluxes due to convective circulation of metamorphic fluid1 others consider that only one way flow is possible2 3 furthermore some flow models imply that fluid moves across and largely independently of sedimentary layering1 2 whereas many fluid based studies find evidence for focusing of flow by particular lithologies2 4 7 here we report a study of metamorphic fluid flow on a regional rather than an outcrop scale using a combination of field geology petrology and theoretical and isotope geochemistry we identify metasomatic lithologies at the top of a dolomitic marble unit which must have drawn in water over a kilometre scale from adjacent pelitic formations we suggest that this flow was part of a single major fluid loss event near the metamorphic peak fluid followed the metasomatic layers to structural highs where it broke out into adjacent schists to form skarns this fluid loss may have changed the rheology of the rock involved and terminated regional folding

assessing metasomatic mass and volume changes using the bootstrap with application to deep crustal hydrothermal alteration of marble a statistically rigorous approach for determining likely errors on estimates of mass and volume change in metasomatic systems is presented and then used to assess mass transfer resulting from hydrothermal alteration of marble during regional metamorphism analysis of metasomatic effects using standard statistical methods designed for unconstrained univariant data often fails to provide useful results for several important reasons 1 the concentration of any constituent in a composition is constrained to be between 0 and 100 wt percent 2 the sum of the concentrations of all constituents must be 100 wt percent the closure constraint compositions are multivariate and provide information only about the relative proportions of constituents 3 the maximum possible mass or volume loss is 100 percent 100 corresponds to complete mass or volume loss 4 rock bulk density must be greater than 0 g cm super 3 5 the underlying probability distributions for mass and volume changes are commonly non normal to address these issues we use statistical procedures recently developed to treat the special properties of compositional data including closure and the bootstrap method to compute accurate confidence intervals for assessing how far in error best estimates of mass and volume change are likely to be the bootstrap deals effectively with non normality and constraints 1 3 and 4 we apply our approach to gain a better understanding of synmetamorphic acadian orogeny hydrothermal alteration of upper greenschist facies and amphibolite facies marble beds of the wepawaug schist connecticut the marbles lost significant amounts of volatiles dominantly co 2 and h 2 o si ti k rb sr and ba best estimates of total mass and volume change are 27 and 32 percent respectively the bulk of the lost mass was volatiles approximately 140 g kg super 1 sio 2 approximately 60 g kg super 1 and k 2 o approximately 15 g kg super 1 numbers are g lost per kg of parent rock volatile loss was probably regional in scope loss of si ti k rb sr and ba occurred over minimum length scales on the order of typical hand sample dimensions maximum length scales remain to be determined the fortran 77 computer code that performs the calculations described herein is available from the senior author

reaction induced fluid flow in synthetic quartz bearing marbles the reaction kinetics and fluid expulsion during the decarbonation reaction of calcite quartz wollastonite co2 in water absent conditions were experimentally investigated using a paterson type gas apparatus starting materials consisted of synthetic calcite quartz rock powders with variable fractions of quartz 10 20 and 30 wt and grain sizes of 10 m calcite and 10 and 30 m quartz prior to reaction samples were hiped at 700 c and 300 mpa confining pressure and varying pore pressures initial porosity was low at 2 7 6 3 depending on pore pressure during hip and the amount and grain size of quartz particles samples were annealed at reaction temperatures of 900 and 950 c at 150 and 300 mpa confining pressures well within the wollastonite stability field run durations were between 10 min and 20 h sem micrographs of quenched samples show growth of wollastonite rims on quartz grains and co2 filled pores between rims and calcite grains and along calcite grain boundaries measured widths of wollastonite rims vs time indicate a parabolic growth law the reaction is diffusion controlled and reaction progress and co2 production are continuous porosity increases rapidly at initial stages of the reaction and attains about 10 12 after a few hours permeability at high reaction temperatures is below the detection limit of 10 21 m2 and not affected by increased porosity this makes persistent pore connectivity improbable in agreement with observed fluid inclusion trails in form of unconnected pores in sem micrographs release of co2 from the sample was measured in a downstream reservoir the most striking observation is that fluid release is not continuous but occurs episodic and in pulses ongoing continuous reaction produces increase in pore pressure which is once having attained a critical value pcrit spontaneously released connectivity of the pore space is short lived and transient the resulting cycle includes pore pressure build up formation of a local crack network pore pressure release and crack closure using existing models for plastic stretching and decrepitation of pores along with critical stress intensity factors for the calcite matrix and measured pore widths it results that pcrit is about 20 mpa patterns of fluid flow based on mineralogical and stable isotope evidence are commonly predicted using the simplifying assumption of a continuous and constant porosity and permeability during decarbonation of the rock however simple flow models which assume constant pore pressure constant fluid filled porosity and constant permeability may not commonly apply properties are often transient and it is most likely that fluid flow in a specific reacting rock volume is a short lived episodic process

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

partial eclogitisation of gabbroic rocks in a late precambrian subduction zone zambia prograde metamorphism triggered by fluid infiltration gabbros and eclogites occur closely associated in a 200 km long and up to 40 km wide area of the zambezi belt in central zambia this area is interpreted to represent part of a late precambrian suture zone with the mafic rocks being relics of subducted oceanic crust gradual stages of prograde transformation from gabbro to eclogite are preserved by disequilibrium textures of incomplete reactions this resulted in kyanite omphacite bearing assemblages for eclogites that have al poor bulk compositions undeformed eclogites typically preserve features of a former gabbroic texture reflected by replacements of plagioclase and magmatic pyroxene by eclogite facies minerals textures of deformed eclogites range from sheared porphyroclastic to porphyroblastic relics of magmatic pyroxene are common and complete eclogitisation occurred only in millimetre to centimetre scale domains in most of the rocks no evidence for prograde blueschist or amphibolite facies mineral assemblages was found in eclogites in contrast the fine grained intergrowth of omphacite garnet kyanite and quartz which replace former plagioclase or was formed in the pressure shadow of magmatic pyroxene relics indicates that eclogitisation might have affected the gabbroic protoliths directly without any significant intervening metamorphic reactions eclogitisation took place under p t conditions of 630 690 degreesc and 26 28 kbar suggesting a large overstepping 10 kbar of reaction boundaries eclogitisation was initialised and accompanied by a channelised fluid flow resulting in veins with large subhedral grains of omphacite kyanite and garnet the gabbro to eclogite transformation was enhanced by a fluid which allowed the necessary material transport for the dissolution precipitation mechanism that characterises the metamorphic mineral replacements the process of eclogitisation was limited by reaction kinetics and dissolution precipitation rates rather than by the metamorphic p t conditions even though ductile deformation occurred and equilibrium phase boundaries were overstepped the infiltration of fluids was necessary for triggering the gabbro to eclogite transformation

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