the evolution of water in the contact metamorphic aureole of the duluth complex northeastern minnesota contact metamorphism of the rove formation by the duluth complex northeastern minnesota resulted from the discontinuous reaction chlorite muscovite quartz cordierite biotite h 2 o and the continuous reaction muscovite biotite quartz cordierite k feldspar h 2 o bulk compositions of hornfelses and mass balance calculations indicate that metamorphism occurred isochemically except for the loss of 0 6 to 2 7 wt h 2 o calculated values of temperature and f h 2 o indicate that during progressive metamorphism h 2 o evolved from the rocks progressively diluted a co 2 rich fluid phase the relations among temperature x h 2 o and progress of the continuous reaction in an average bulk composition suggest that at t 500 c and p 1 500 bars chlorite muscovite quartz in 1 m 3 of rock reacted with at least 0 5 m 3 of a co 2 rich fluid producing a fluid with x h 2 o 0 15 the continuous reaction buffered the composition of this fluid to a value of x h 2 o 1 0 at t 600 c the relation between x h 2 o and the progress of the continuous reaction suggests that the volumetric fluid rock ratio decreased from a value of 0 55 to essentially 0 0 as temperature increased from 500 c to 600 c the study indicates that multivariate devolatilization reactions can be capable buffers of fluid composition the dynamic variables rate of temperature change rate of h 2 o evolution and rate of reaction were determined by a heat conduction model for contact metamorphism the calculated width of the aureole 180 m and temperature distribution within the aureole 500 to 620 c are consistent with observations the calculated reaction rates for the continuous reactions ranging from 1 2 10 4 to 3 10 2 moles m 3 yr are much lower than reported rates for other reactions minimum permeabilities implied by the rate of h 2 o evolution ranging from 10 12 to 5 10 15 cm 3 sec cm 3 rock are 4 to 7 orders of magnitude lower than measured permeabilities of shales these results strongly support the assumption of chemical equilibrium during metamorphism even in contact metamorphic aureoles where the rate of temperature change is great

the direction of fluid flow during contact metamorphism of siliceous carbonate rocks new data for the monzoni and predazzo aureoles northern italy and a global review periclase formed in siliceous dolomitic marbles during contact metamorphism in the monzoni and predazzo aureoles the dolomites northern italy by infiltration of the carbonate rocks by chemically reactive h2o rich fluids at 500 bar and 565 710 c the spatial distribution of periclase and oxygen isotope compositions is consistent with reactive fluid flow that was primarily vertical and upward in both aureoles with time integrated flux 5 000 and 300 mol fluid cm2 rock in the monzoni and predazzo aureoles respectively the new results for monzoni and predazzo are considered along with published studies of 13 other aureoles to draw general conclusions about the direction amount and controls on the geometry of reactive fluid flow during contact metamorphism of siliceous carbonate rocks flow in 12 aureoles was primarily vertically upward with and without a horizontal component directed away from the pluton fluid flow in two of the other three was primarily horizontal directed from the pluton into the aureole the direction of flow in the remaining aureole is uncertain earlier suggestions that fluid flow is often horizontal directed toward the pluton are likely explained by an erroneous assumption that widespread coexisting mineral reactants and products represent arrested prograde decarbonation reactions with the exception of three samples from one aureole time integrated fluid flux was in the range 102 104 mol cm2 both the amount and direction of fluid flow are consistent with hydrodynamic models of contact metamorphism the orientation of bedding and lithologic contacts appears to be the principal control over whether fluid flow was either primarily vertical or horizontal other pre metamorphic structures including dikes faults fold hinges and fracture zones served to channel fluid flow as well

mineralogical controls on metamorphic fluid flow in metabasaltic sills from islay scotland abstract in this study we show that mineralogy was the primary control of metamorphic fluid flow in the well studied metabasaltic sills in the sw scottish highlands here basaltic sills have been partially carbonated by h 2 o co 2 fluids at greenschist facies conditions this has led to mineral zonation with carbonate poor sill interiors separated from carbonate rich sill margins by reaction fronts although deformation set the stage for metamorphic fluid flow in the sw scottish highlands by causing the preferred alignment of mineral grains metamorphic fluid flow was not coupled with active deformation but occurred later utilizing the pre existing mineral alignment as a means of accessing the sill interiors the sills which were studied were partially carbonated with well preserved reaction fronts they were selected because atypically for the sw scottish highlands they are mineralogically heterogeneous making them ideal for a study of mineralogical controls of metamorphic fluid flow their mineralogical heterogeneity reflects chemical heterogeneity arising from magmatic flow differentiation and spilitization which occurred before greenschist facies metamorphism magmatic flow differentiation resulted in parts of the sill containing large crystals with no preferred alignment large up to 3 cm plagioclase phenocrysts were concentrated in the sill interior whereas large up to 1 cm amphibole after pyroxene grains formed cumulate layers close to the sill margins these large randomly oriented crystals were replaced by an interface coupled dissolution precipitation mechanism replacement is constant volume and with hydration and carbonation affecting the cores of these minerals while the rims are remained intact and unaltered this finding points to intra granular metamorphic fluid flow in contrast inter granular metamorphic fluid flow was facilitated by mineral alignment on different scales pre metamorphic spilitization produced layers of epidote called segregations whereas regional deformation caused preferred alignment mainly of amphibole and chlorite epidote undergoes a series of volume changes during greenschist facies metamorphism this created porosity which produced preferred pathways for metamorphic fluids affecting the advancement of fluid driven reaction fronts preferred alignment of amphibole and chlorite also affected the advancement of reaction fronts in this case fluid flow was preferentially parallel to the foliation in both cases inter granular metamorphic fluid flow utilized a pre existing fabric albeit on different scales these results show intra granular metamorphic fluid flow in unfoliated rock and inter granular metamorphic fluid flow in foliated rock in both cases metamorphic fluid flow occurred after deformation controlled by pre existing mineralogical heterogeneities such as grain composition and shape anisotropy as well as preferred alignment of mineral grains

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

earthquake prediction an empirical approach abstract earthquake precursor data so far accumulated in japan have shown that the larger the main shock magnitude the larger the distance between the epicenter and an observation point where a precursor is observed it is possible to empirically establish an approximate relationship between maximum detectable distance d max and main shock magnitude m the relationship being different from discipline to discipline of precursor when a number of precursors are observed we may draw circles with a radius equal to d max peculiar to each precursor discipline centered at the respective observation points on the condition that m takes on a certain value in that case the epicenter of a future earthquake should be located in the area which is common to all of the circles if m is too small some of the circles do not overlap if it is too large an epicentral area which is too wide to be realistic must be assumed in this way an approximate epicenter location and a rough value of the main shock magnitude can be assessed applying the procedure to the precursors of the izu oshima kinkai m 7 0 1978 and the niigata m 7 5 1964 japan earthquakes remarkable success is achieved probabilities of an earthquake occurring in a specified time interval can be evaluated as a function of time when a precursor is observed for such an evaluation we rely either on the log t m relationship with a prescribed value of m or on the frequency distribution of log t which is empirically obtained depending on precursor disciplines t being the precursor time when a number of precursors are observed one by one changes in synthetic probability of earthquake occurrence can be estimated according to the existing formula utsu 1977 as an example such probability changes with time are estimated making use of the precursor data for the izu oshima kinkai earthquake it turns out that the synthetic probability generally increases as time goes on when a long term precursor happens to be observed however the probability drops discontinuously being followed by a gradual rise again the temporal change in probability therefore shows considerable fluctuations this is especially so when a short interval for probability evaluation is specified because of uncertain preliminary probability involved in the evaluation and an unknown rate of false precursor signals against true ones the absolute value of probability thus evaluated may not be perfectly reliable even so the temporal change in probability may provide some clues for the actual publication of earthquake prediction

prograde and retrograde fluid flow during contact metamorphism of siliceous carbonate rocks from the ballachulish aureole scotland siliceous dolomites and limestones contain abundant retrograde minerals produced by hydration carbonation reactions as the aureole cooled marbles that contained periclase at the peak of metamorphism bear secondary brucite dolomite and serpentine forsterite dolomite marbles have retrograde tremolite and serpentine wollastonite limestones contain secondary calcite and quartz and wollastonite free limestones have retrograde tremolite secondary tremolite never appears in marbles where brucite has replaced periclase or in wollastonite bearing limestones a model for infiltration of siliceous carbonates by co2 h2o fluid that assumes a vertical upwardly directed flow b fluid flux proportional to cooling rate and c flow and reaction under conditions of local equilibrium between peak temperatures and 400 c reproduces the modes of altered carbonate rocks observed reaction textures and the incompatibility between tremolite and brucite and between tremolite and wollastonite except for samples from a dolomite xenolith retrograde time integrated flux recorded by reaction progress is on the order of 1000 mol fluid cm2 rock local focusing of flow near the contact is indicated by samples from the xenolith that record values an order of magnitude greater formation of periclase forsterite and wollastonite at the peak of metamorphism also required infiltration with prograde time integrated flux approximately 100 1000 mol cm2 the comparatively small values of prograde and retrograde time integrated flux are consistent with lack of stable isotope alteration of the carbonates and with the success of conductive thermal models in reproducing peak metamorphic temperatures recorded by mineral equilibria although isobaric univariant assemblages are ubiquitous in the carbonates most formed during retrograde metamorphism isobaric univariant assemblages observed in metacarbonates from contact aureoles may not record physical conditions at the peak of metamorphism as is commonly assumed

permeability generation and resetting of tracers during metamorphic fluid flow implications for advection dispersion models advection dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid saturated medium however whether rocks contain a fluid depends on their reaction history and whether any initial fluid escapes the behaviour of different rocks may be illustrated using hypothetical marble compositions marbles with diverse chemistries e g calcite dolomite quartz are relatively reactive and will generally produce a fluid during heating by contrast marbles with more restricted chemistries e g calcite quartz or calcite only may not if the rock is not fluid bearing when fluid infiltration commences mineralogical reactions may produce a reaction enhanced permeability in calcite dolomite quartz or calcite quartz but not in calcite only marbles the permeability production controls the pattern of mineralogical isotopic and geochemical resetting during fluid flow tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection dispersion models however tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction in the case of very unreactive lithologies e g pure calcite marbles cherts and quartzites the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer centimetre scale layering may lead to the formation of self perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants such layered rocks may show patterns of mineralogical resetting that are not predicted by advection dispersion models patterns of mineralogical and isotopic resetting in marbles from a number of terrains for example chillagoe marulan south reynolds range australia adirondack mountains old woman mountains notch peak usa and stephen cross quarry canada vary as predicted by these models

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

macro anomaly and its application to earthquake prediction abstract macro anomalies preceding a number of large earthquakes in japan are analyzed in relation to maximum detectable distance d max from the epicenter and to precursor time t between anomaly appearance and main shock occurrence these anomalies include anomalous animal behaviour strange detonation unusual light in the sky change in underground water and hot springs and are all things which can be sensed by humans without using scientific instruments the number of anomalies analyzed amounts to 910 as a result an approximate relation between main shock magnitude m and d max is brought out given an m therefore it is possible to draw a circle having a radius equal to d max centering at the spot where an anomaly is observed in that case the epicenter of coming earthquake must lie within that circle when there are multiple anomalies the epicenter should be located somewhere in an area where all the circles overlap it will be shown that such a d max method leads us to an assessment of the approximate epicentral area and main shock magnitude it appears that macro anomalies begin to be observed about 100 days before the main shock anomaly numbers tending to increase at around t 10 days in most cases the maximum frequency of appearance usually occurs around 1 day prior to the main shock the distribution of frequency can well be approximated by a weibull distribution making use of parameters of the distribution changes in probability of earthquake occurrence in a specified time interval can be evaluated when an anomaly is observed when many anomalies are observed successively time changes in the synthetic probability can be evaluated it appears that such a probability tends to increase reaching a value close to 1 as the main shock occurrence approaches and the frequency of anomaly appearances increases although no actual pre earthquake prediction based on macro anomaly data has as yet been conducted it is hoped that the technique developed in this paper will be applied to anomaly data related to coming earthquakes once a well organized data acquisition system comes into operation the authors are of the opinion that macro anomalies may be applied at least to some extent to earthquake prediction despite the traditional view that macro anomalies are so unreliable and contaminated by noise that they cannot be used for prediction

the thermal history of the western irish onshore we present here a low temperature thermochronological study that combines the apatite fission track and u th he dating methods with a pseudo vertical sampling approach to generate continuous and well constrained temperature time histories from the onshore irish atlantic margin the apatite fission track and u th he ages range from the late jurassic to early cretaceous and the mean track lengths are relatively short thermal histories derived from inverse modelling show that following post orogenic exhumation the sample profiles cooled to c 75 c a rapid cooling event to surface temperatures occurred during the late jurassic to early cretaceous and was diachronous from north to south it was most probably caused by c 2 5 km of rift shoulder related exhumation and can be temporally linked to the main stage of mesozoic rifting in the offshore basins a slow phase of reheating during the late cretaceous and early cenozoic is attributed to the deposition of a thick sedimentary sequence that resulted in c 1 5 km of burial our data imply a final pulse of exhumation in neogene times probably related to compression of the margin however it is possible that an early cenozoic cooling event compatible with our data but not seen in our inverse models accounts for part of the cenozoic exhumation supplementary material details on the apatite fission track and u th he methods are available at www geolsoc org uk sup18765

earthquake precursors in japan precursor time and detectability abstract earthquake precursor data amounting to 418 in number accumulated in japan are analyzed most data are obtained under the nation wide earthquake prediction programme the precursor time t versus main shock magnitude m relationship is different for different groups of precursors a linear relation such as log t a bm where a and b are constants seems to hold for precursor disciplines such as land deformation revealed by geodetic survey and tide gauge observation ground tilt observed by a water tube tiltmeter anomalous seismic activity and geomagnetic field change although a similar relationship seems to hold for the disciplines of earth currents radon concentration underground water etc the precursor time is substantially smaller for these disciplines than for the former disciplines the above characteristics of precursor time suggests that precursors closely connected to the dilatancy generation seem to be observed at an earlier stage of seismogenetic activity precursors probably associated with diffusion of underground water into the dilatant region seem to follow for a number of precursor disciplines such as foreshock ground tilt observed by a pendulum tiltmeter resistivity by a variometer and so on no dependence of t on m is found the relationship between m and the logarithmic epicentral distance d measured in kilometers is different from discipline to discipline relying on empirical and theoretical studies of coseismic strain step it turns out that precursors found by geodetic and geomagnetic observations seem to reflect a crastal strain of the order of 10 7 10 6 precursors obtained by a resistivity variometer seem to represent a strain of the order of 10 9 10 8 precursors of other disciplines seem to correspond to a strain of 10 8 10 7 it is clear that precursors can be detected further from the epicenter as the main shock magnitude becomes larger in some favourable cases a precursor can be observed even where the epicentral distance is several times larger than that of the epicentral area

mineralogical evidence for fluid rock interaction accompanying prograde contact metamorphism of siliceous dolomites alta stock aureole utah usa contact metamorphism of siliceous dolomite in the southern part of agrees well with the q m tiff 3 4 10 7 mol m 2 determined by the metamorphic aureole of the alta stock utah usa produced numerical simulation of the temperature and 18 o depletion profiles the prograde isograd sequence talc tc tremolite tr forsterite preserved in the southern aureole the estimates of q m tiff for the fo and periclase per calcite cc dolomite do ge forsterite and tremolite zones have much greater uncertainty but othermometry and phase equilibria define a general prograde t may indicate that fluid flux was considerably lower in these zones x co2 path of decreasing x co2 with rising temperature for than in the periclase zone given the outward down temperature the dolomite high variance assemblages typify the aureole per subhorizontal flow geometry indicated by a variety of petrologic cc and fo cc do characterize the inner aureole per and geochemical and geothermometry evidence presented here and elsefo zones and tr do cc and tc do cc are where this decrease implies that fluid has leaked from the flow widespread in the outer aureole tr and tc zones low variance system between the periclase and tremolite zones assemblages are rare and the thickness of reaction zones coexisting reactant and product minerals at the isogradic reaction fronts are narrow tens of metres or less the mineral assemblages calculated progress of isograd reactions and the prograde t x co2 path all key words alta fluid flow infiltration marble mineralogical indicate that massive dolomite was infiltrated by significant fluxes of water rich fluids during prograde metamorphism and that the fluid flow was down temperature and laterally away from the igneous contact fluid infiltration continued through at least the initial retrograde cooling of the periclase zone down t fluid flow introduction is also consistent with the results of cc do geothermometry and both mineral assemblages and stable isotopes have been patterns of 18 o depletion in this area the close spatial association

formation and destruction of periclase by fluid flow in two contact aureoles periclase formed in steeply dipping marbles from the beinn an dubhaich aureole scotland and the silver star aureole montana by the reaction dolomite periclase calcite co2 equilibrium between rock and fluids with x co 2 1 requires that reaction was infiltration driven brucite pseudomorphs after periclase occur in the beinn an dubhaich aureole either as bed by bed replacement of dolomite or in a lens along the contact between dolomite and a pre metamorphic dike transport theory predicts that infiltration drove both periclase reaction and 18o depletion fronts which moved at significantly different velocities along the flow path the distributions of brucite and 18o depleted rocks are identical in surface exposures thus indicating upward flow time integrated flux q was 500 mol cm2 and the fluid source was magmatic because periclase and its hydrated equivalent brucite are unaltered to dolomite by retrograde reactions the exposure of brucite marbles accurately images the flow paths of peak metamorphic fluids in the silver star aureole brucite pseudomorphs after periclase exclusively occur in tabular bodies that are beds with elevated mg ca the spatial pattern of 18o depletion requires upward vertical fluid flow estimated prograde q 103 104 mol cm2 and the fluid source was magmatic low mg ca 18o depleted brucite free rocks pose a dilemma because the periclase reaction front should have traveled 18 times further through them than the isotope alteration front the dilemma is resolved by reaction textures that indicate periclase and brucite were destroyed in low mg ca rocks by infiltration driven retrograde carbonation reactions values of retrograde q were 103 104 mol cm2 brucite after periclase was preserved only in high mg ca layers where periclase developed in greater abundance the geometry of brucite marbles at silver star thus reflects the location of high mg ca beds rather than the geometry of fluid flow retrograde reactions must be considered before the mineralogical record of prograde fluid flow can correctly be interpreted in both aureoles fluid flow mineral reaction and isotope depletion were structurally controlled by bedding and lithologic contacts

boron metasomatism of the alta stock contact aureole utah evidence from borates mineral chemistry and geochemistry geochemical study of the alta stock and adjacent contact aureole rocks provides information concerning the source composition and physical chemical conditions of infiltrating fluids special emphasis was given to boron b as a tracer of fluid rock interactions due to the occurrence of borate minerals ludwigite kotoite and szaibelyite in skarn deposits around the stock in addition thin section alpha track mapping implies significant b enrichments in fluid altered minerals within the stock stockwork veins and related selvages igneous sills near the stock contact skarns and in marbles up to 500 m from the stock forsterite clinohumite lizardite and malachite contain between 50 and 1200 ppm b diopside calcite clintonite phlogopite brucite hedenbergite tremolite and other minerals host b to a lesser extent aureole b enrichments correlate well with major and other trace element enrichments and support existing models of element transport in magmatic fluids with lateral down temperature flow large variations in mineral b concentrations reflect changes in b concentrations of these fluids through time mass balance calculations indicate that magmatic fluids emanating from the alta pluton could supply most b in the alta aureole it is estimated that the emplaced magma had an initial b concentration between 7 10 ppm indicated exhalative losses of b from the pluton are on the order of 50 we estimate that the exsolved fluids had a time integrated b concentration of 160 40 ppm although much higher concentrations may have attended local borate mineralization

generation of forsteritic olivine fo99 8 by subsolidus oxidation in basaltic flows we identify olivine grains with compositions up to fo99 8 which are found in multiple primitive basaltic lava flows from a monogenetic volcano in the big pine volcanic field california usa in this study we show that the forsterite in these basalts formed by subsolidus recrystallization in a high fo2 environment olivine compositions are bimodal with flows having either all normal compositions fo74 9 94 4 or highly forsteritic fo97 2 99 8 compositions in many grains the subhedral forsteritic olivine has a hematite and clinopyroxene rim and internal parallel oriented planes of hematite clinopyroxene and orthopyroxene results of isotopic chemical crystallographic petrographic and mineralogical analyses show that the forsterite formed through subsolidus oxidation of olivine phenocrysts the forsteritic olivines generally occur in the thinner flows we infer that a rapidly emplaced sequence of thin vesicular spatter fed flows allowed the original olivine phenocrysts to become repeatedly reheated while exposed to air our study required sampling each flow so it was difficult to avoid the altered portions of the thinner flows other studies would tend to avoid such flows which may account for why such forsteritic olivines have not been more widely recognized

immiscible co2 h2o fluids in the shallow crust the significance of a single co2 h2o fluid phase is well known for metamorphic systems and co2 h2o immiscibility is explicit in fluid inclusion literature especially regarding hydrothermal ores complex multiphase co2 h2o behavior exists over wide temperature and pressure ranges overlapping other important geochemical processes the character and physical chemical properties of multiple phases possible for co2 and h2o and the potential impact of these coexisting phases on geochemical processes in the crust are not broadly appreciated we propose that immiscible supercritical co2 fluid and a liquid rich in h2o coexist in the shallow crust to 400 c and 300 mpa and that interactions among the two fluids and host rock are significant processes that produce recognizable geochemical and textural evidence supercritical co2 fluids bring potential complexity to fluid rock systems by influencing aqueous reactions via carbonic acid equilibria penetrating complex geometries inaccessible to aqueous fluid and dissolving and redistributing metals as organometallic compounds the distal margin of a contact metamorphic aureole is one example we discuss in which interaction between two disparate co2 h2o fluids controls h2o activity and the progress and distribution of metamorphic hydration reactions in another example supercritical co2 produces acidity carbonate saturation and silica supersaturation in brine separation and emplacement of this brine into a rock dominated system buffered to neutral ph enhances precipitation of carbonates and quartz chalcedony or amorphous silica in veins other possible examples of co2 h2o fluid immiscibility coupled with multiphase fluid rock interactions are clay desiccation diagenetic and postdiagenetic silicate reactions origin and distribution of carbonate cements in sedimentary basin sandstones fluid mass transfer and anthropogenic co2 sequestration

metamorphic degassing of carbonates in the contact aureole of the aguablanca cu ni pge deposit spain analysis of magmatic and sedimentary rocks of several large igneous provinces has demonstrated that the release of gas during plutonic metamorphic processes may be linked to global climate change and mass extinctions aguablanca one of the largest cu ni pge deposits in europe formed during the variscan orogeny when a mafic magma intruded limestones and shales creating a contact aureole composed of marble skarn and hornfels our petrological and geochemical investigation of the aureole provides evidence that a combination of the two processes led to the formation of the ore deposit the assimilation of terrigenous sediments supplied s to the magma while the assimilation of carbonates changed the oxygen fugacity and decreased the solubility of sulfur in the magma the metamorphic assemblages in the contact aureole are directly related to heterogeneity of the protolith and particularly to the original proportions of calcite and clay we modeled carbon dioxide degassing during contact metamorphism and showed that pure limestone is relatively unproductive because of its high reaction temperature the presence of clay however leads to the formation of calc silicates and significantly enhances co2 degassing our estimations suggest that degassing of the aguablanca contact aureole released about 74 8 mt of co2 a relatively low volume that we attribute to the composition of the host rock mainly a pure limestone a far larger volume of carbon dioxide was emitted by the contact metamorphism of dolostones in the contact aureole of panzhihua part of emeishan large igneous province sw china we propose that the level of emission of carbon dioxide depends strongly on the nature of the protolith and has to be considered when predicting environmental impact during the emplacement of large igneous provinces

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

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

timing and mechanisms of carbon isotope exchange in granulite facies calc silicate boudins rauer group east antarctica mineralogically zoned decimeter diameter calc silicate boudins enclosed within paragneisses from little italy island rauer group east antarctica underwent granulite facies metamorphism p 5 700 900 mpa t 5 840 6 40 8c followed by near isothermal decompression to 200 400 mpa during decompression several mineral reactions occurred in the presence of a pore fluid 0 4 the calc silicate boudins show a general xco2 increase in calcite d 13 c values from core as low as 217 to rim 2 9t o 2 10 by contrast d 18 o values show little variation across the boudins the d 13 c profiles are similar to those predicted to result from diffusion within a sphere that is surrounded by a homogeneous reservoir diffusion of carbon isotopes probably occurred synchronous with the post peak metamorphic mineral reactions at that time centimeter scale diffusion would have been facilitated by the presence of the fluid while isotopic exchange between the minerals and the fluid would have been promoted by recrystallization for metamorphic porosities of 10 25 2 10 23 the d 13 c profiles could have formed in a few thousand to hundreds of thousands of years small millimeter to centimeter scale variations in d 13 c values that may have been initially present within the boudins would have been homogenized on much shorter timescales than those required to form the profiles the calculated timescales may reflect the time over which metamorphic recrystallization occurred and a reactionenhanced porosity was present graphite formed locally in the paragneisses only at margins of the boudins probably reflects the local escape of co 2 bearing fluids from the boudins into relatively low rocks fo2