contact metamorphism and depth of emplacement of the manaslu granite central nepal implications for himalayan orogenesis abstract the manaslu massif central nepal provides a well exposed example of a deeply eroded pluton its contact aureole can be followed from the base to the top along medium to low grade mesozonal to anchizonal tethyan metasediments contact metamorphic mineral assemblages and thermobarometric estimations suggest that the granite was emplaced at 18 21 km for the base and 9 13 km for the roof calculated temperatures within the aureole at 550 40 c are compatible with the intrusion temperature of a leucogranitic magma microstructural evidence shows that the temperature remained high 500 c at the base of the massif during and after granite emplacement whereas towards the top of the granite deformation proceeded rapidly at lower temperature heating of the abundant calcareous rocks in the contact aureole released a local co2 rich fluid whereas a h2o and boron rich fluid seems to have pervaded the whole zone this fluid is probably exsolved from the granitic melt during its crystallization the depth of emplacement of the massif has an important implication for the reconstruction of the himalayan geodynamic evolution implying a burial of the tethyan metasediments by a major refolding of the sedimentary cover or more probably by extensive development of the north himalayan nappes towards the south for more than 70 km before granite emplacement i e before the miocene the young age of the granite and its depth of emplacement suggest a rapid tectonic denudation in the order of 1 mm a 1 probably by normal faulting north of the massif during its cooling

assessment of grain scale homogeneity and equilibration of carbon and oxygen isotope compositions of minerals in carbonate bearing metamorphic rocks by ion microprobe abstract nineteen samples of metamorphosed carbonate bearing rocks were analyzed for carbon and oxygen isotope ratios by ion microprobe with a 5 15 m spot three from a regional terrain and 16 from five different contact aureoles contact metamorphic rocks further represent four groups calc silicate marble and hornfels 6 brucite marble 2 samples that contain a reaction front 4 and samples with a pervasive distribution of reactants and products of a decarbonation reaction 4 the average spot to spot reproducibility of standard calcite analyses is 0 37 2 standard deviations sd for 18 o and 0 71 for 13 c ten or more measurements of a mineral in a sample that has uniform isotope composition within error of measurement can routinely return a weighted mean with a 95 confidence interval of 0 09 0 16 for 18 o and 0 10 0 29 for 13 c using a difference of 6sd as the criterion only four of 19 analyzed samples exhibit significant intracrystalline and or intercrystalline inhomogeneity in 13 c at the 100 500 m scale with differences within individual grains up to 3 7 measurements are consistent with carbon isotope exchange equilibrium between calcite and dolomite in five of six analyzed samples at the same scale because of relatively slow carbon isotope diffusion in calcite and dolomite differences in 13 c can survive intracrystalline homogenization by diffusion during cooling after peak metamorphism and likely represent the effects of prograde decarbonation and infiltration all but 2 of 11 analyzed samples exhibit intracrystalline differences in 18 o up to 9 4 intercrystalline inhomogeneity in 18 o up to 12 5 and or disequilibrium oxygen isotope fractionations among calcite dolomite calcite quartz and calcite forsterite pairs at the 100 500 m scale inhomogeneities in 18 o and 13 c are poorly correlated with only a single mineral dolomite in a single sample exhibiting both because of relatively rapid oxygen isotope diffusion in calcite intracrystalline inhomogeneities in 18 o likely represent partial equilibration between calcite and fluid during retrograde metamorphism calcite is in oxygen isotope exchange equilibrium with forsterite in one of four analyzed samples in equilibrium with dolomite in none of six analyzed samples and in equilibrium with quartz in neither of two analyzed samples there are no samples of contact metamorphic rock with analyzed reactants and products of an arrested metamorphic reaction that are in oxygen isotope equilibrium with each other the degree of departure from equilibrium in analyzed samples is variable and is often related at least in part to alteration of 18 o of calcite during retrograde fluid rock reaction in situ sub grain scale carbon and oxygen isotope analyses of minerals are advisable in the common applications of stable isotope geochemistry to metamorphic petrology correlation of sub mm scale stable isotope data with imaging will lead to improved understanding of reaction kinetics reactive fluid flow and thermal histories during metamorphism

the stable isotope signature of kilometre scale fracturedominated metamorphic fluid pathways mary kathleen australia abstract large calcite veins and pods in the proterozoic corella formation of the mount isa inlier provide evidence for kilometre scale fluid transport during amphibolite facies metamorphism these 10 to 100 m scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 10 km mary kathleen fold belt despite the isotopic heterogeneity of the surrounding wallrocks the fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks the pods have 13ccalcite values of 2 to 7 and 18ocalcite values of 10 5 to 12 5 away from the pods metadolerite wallrocks have 18owhole rock values of 3 5 to 7 and unaltered banded calc silicate and marble wallrocks have 13ccalcite of 1 6 to 0 6 and 18ocalcite of 18 to 21 in the alteration zones adjacent to the pods the 18o values of both metadolerite and calc silicate rocks approach those of the pods large calcite pods hosted entirely in calc silicates show little difference in isotopic composition from pods hosted entirely in metadolerite thus 100 to 500 m scale isotopic exchange with the surrounding metadolerites and calc silicates does not explain the observation that the 18o values of the pods are intermediate between these two rock types pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc silicates these data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the corella formation at the presently exposed crustal level although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc silicates or thermal fluctuations attending deformation and metamorphism the overall l shaped trend of the data on plots of 13c vs 18o is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc silicate rocks localization of the vein systems in dilatant sites around metadolerite calc silicate boundaries indicates a strong structural control on fluid flow and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km the ultimate source for the external fluid is uncertain but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism

contrasting fluid flow patterns at the bufa del diente contact metamorphic aureole north east mexico evidence from stable isotopes impure limestones with interstratified metachert layers were contact metamorphosed and metasomatized by the bufa del diente alkali syenite massive marbles exhibit mineralogical and stable isotope evidence for limited fluid infiltration confined to a 17 m wide zone at the contact influx of magmatic brines along most metacherts produced up to 4 cm thick wollastonite rims according to calcite cc quartz qz wollastonite wo co2 and were observed at distances of up to 400 m from the contact the produced co2 exsolved as an immiscible low density co2 rich fluid chert protolith isotope compositions were 18o qz 27 30 and 18o cc 24 27 many wollastonites in infiltrated metacherts have low 18o ranging from 11 17 and confirm that decarbonation occurred in presence of a magmatic signatured fluid large gradients in 18o wo across the rims may reach 6 the 18o of remaining quartz is often lowered to 15 20 whereas caleites largely retained their original compositions the isotopic reversals of up to 10 between quartz and calcite along with reaction textures demonstrate non equilibrium between infiltrating fluid in the aquifer and the assemblage calcite quartz wollastonite this is compatible with the assumption of a down temperature flow of magmatic fluids that occurred exclusively in the remaining quarzite layer the 13c cc and 18o cc of marble calcites measured perpendicular to two metachert bands reveal significant isotopic alterations along distances of 4 5 cm and 7 5 cm from the wollastonite marble boundary only into the hanging wall marble suggesting an advection process caused by a fluid phase which movel upwards covariation trends of 13c cc and 18o cc across the alteration front indicate that this fluid was co2 rich mass balance calculations show that all co2 rich fluid produced by the decarbonation reaction was lost into overlying marble the metachert aquifers did not leak with respect to water rich fluids

extraction and carbon isotope analysis of co2 from scapolite in deep crustal granulites and xenoliths abstract carbon isotope compositions of scapolite from granulite facies gneisses and lower crustal xenoliths document the composition and constrain the source of carbon in scapolite from the lower crust co 2 is extracted from scapolite without fractionating carbon isotopes by reaction with phosphoric acid at 25 or 75 c thus partial yields of co 2 from scapolite are sufficient for accurate carbon isotopic analysis isotopic compositions of coexisting scapolite and calcite in high grade calc silicate gneisses and marbles and consideration of the crystal chemical environment of co 3 in the scapolite structure indicate little fractionation of 13 c 12 c between scapolite and calcite 0 1 1 2 at equilibrium conditions of 650 800 c the carbon isotope composition of co 2 extracted from scapolite in twenty nine samples of regional granulite facies gneisses amphibolites calc silicate gneisses and crustal xenoliths yield values of 13 c that range from 10 to 1 pdb high grade marbles and graphitic paragneisses are precluded as major sources of carbon for scapolite in the high grade rocks analyzed in this study as the former are isotopically enriched and the latter isotopically depleted in 13 c 12 c relative to the range of isotopic compositions determined here the 13 c values for mafic granulites and amphibolites in granulite terranes composed of supracrustal sequences 10 1 to 4 0 may reflect the isotopic composition of diagenetic carbonate present in their basaltic protoliths the values of 13 c for scapolite in mafic xenoliths and some granulite facies orthogneisses 8 2 to 1 2 are consistent with crystallization of the scapolite from a mafic melt or derivation of co 2 from mafic melts emplaced in the lower crust or upper mantle the values of 13 c for scapolites from calc silicate gneisses and calc silicate xenoliths 10 0 to 2 9 may result from depletion of 13 c 12 c as a result of decarbonation of calcite bearing protoliths during prograde metamorphism

combined oxygen isotope compositional studies of some granitoids from the grenville province of ontario canada implications for source regions oxygen isotopic compositions of whole rocks and coexisting quartz feldspar pairs have been determined for nine pre and syn to late kinematic granitoid plutons in the grenville province of ontario these new data demonstrate that granitoid rocks algonquin mulock in migmatite terrain of the ontario gneiss segment possess normal 18o values 9 0 in accord with previous results in the algonquin sodic suite a gross covariance of 18o with compositional indices is present from 6 4 sio2 50 5 wt gabbro to 8 7 sio2 72 wt trondhjemite resulting from combined assimilation fractional crystallization mafic members of the sodic suite are 18o enriched overall 5 8 7 9 relative to fresh tholeiites 5 7 0 3 implicating some 18o contamination of the protolith the dispersion of 18o values in the

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

resetting of oxybarometers and oxygen isotope ratios in granulite facies orthogneisses during cooling and shearing adirondack mountains new york the petrography petrology and oxygenisotope geochemistry of granulite facies granitic and syenitic orthogneisses of the diana and stark complexes adirondack mountains new york show that the extent and nature of resetting of isotopic and mineralogic systems is highly variable there is a strong correlation between retrogression and shearing and the rocks may be divided texturally into 1 unsheared lithologies that preserve little retrogressed pyroxene or hornblendebearing peak metamorphic mineralogies and 2 sheared rocks that underwent retrogression marked by the growth of late biotite in centimetre to metre wide shear zones after the peak of metamorphism oxygen fugacities in the unsheared lithologies were estimated for reintegrated mineral compositions from magnetiteilmenite mt ilm and ferrosilite magnetic quartz fs mt qtz equilibria mt ilm yields logfo2mt ilm values of 15 9 to 17 6 0 6 to 1 3 log units below the fayalite magnetite quartz buffer fmq and temperatures of 670 745 c that agree with those from other geothermometry and phase equilibria studies these data suggest that aside from oxyexsolution of ilmenite from magnetite the fe ti system underwent only minor resetting during cooling and the fe ti oxides yield good estimates of peak metamorphic temperatures and fo2 in unsheared ilmenite magnetite orthopyroxene quartz assemblages values of logfo2mt ilm are lower than logfo2fs mt qtz by an average of 0 6 when the orthopyroxene activity model of sack and ghiorso is used minor resetting of the fe ti oxides analytical errors and errors in the placement of end member reactions probably account for this relatively small difference in fo2 values whole rock 18o values of unsheared diana and stark lithologies range from 4 0 to 10 3 reflecting pre regional metamorphic oxygen isotope ratios peak metamorphic minerals preserve high temperature oxygen isotope fractionations and in many samples the effective diffusion of oxygen in minerals ceased at higher temperatures than predicted from wet experimental diffusion data these data suggest that the rocks did not contain an aqueous fluid phase during cooling the combination of petrologic isotopic and textural data also permits a detailed study of shearing and retrogression ilmenites in the sheared lithologies underwent greater degrees of hematite loss than in the unsheared rocks resulting in logfo2mt ilm values as low as 24 1 3 1 log units below fmq and mt ilm temperatures that are up to 175 c below regional estimates sheared rocks also have higher 18o values up to 13 3 during shearing 18o values of biotite k feldspar and magnetite reset readily while the degree of isotopic resetting of quartz correlates with the intensity for recrystallization

fractured controlled fluid flow and metasomatism in the contact aureole of the marulan batholith new south wales australia the late silurian bungonia limestone was contact metamorphosed adjacent to the early devonian glenrock granodiorite at 500 580 c and 0 7 2 2 kbar at 60 m from the granodiorite contact the limestone is pure calcite marble closer to the contact it was extensively metasomatised to form metre scale dykes of garnet and clinopyroxene massive wollastonite skarns decimetre thick veins dominated by vesuvianite and distinct breccia zones that contain millimetre wide veinlets of vesuvianite garnet these skarns and veins represent channel ways for aqueous si mg fe al bearing metasomatic fluids of magmatic origin the 18o values of the marble are typically little reset 20 even within millimetres of the skarn breccias and only within tens of centimetres of the thicker skarns the pattern of metasomatism and isotope resetting observed around and within the skarn zones does not accord with simple flow models that assume fluid flow from the granodiorite into marble that initially contained a connected fluid filled porosity instead the data are most compatible with hydrofracture of corrosive metasomatic fluids into initially dry rocks in short duration flow events

geochemical evidence for a revised precambrian sequence in the northwest adirondacks new york middle proterozoic metasedimentary and metavolcanic rocks in the northwest adirondacks are assigned into four lithostratigraphic units basal hyde school gneiss that herein is given formational status lower marble popple hill gneiss formation and upper marble a variety of stratigraphic columns have been proposed for this complexly deformed terrane the most recent being a column by wiener and others 1984 their basal formation the alexandria bay gneiss is defined from rocks that include the rockport granite gneiss near rockport ontario and alexandria bay new york as well as leucogneisses in 14 structural domes throughout the northwest adirondacks we believe that these rocks have a diverse origin one being intrusive the other volcanic ash their uppermost formation the pleasant lake gneiss includes granitoid gneisses near rossie village and pleasant lake that they suggest are illitic arkoses but we give field geochemical and geochronological evidence for an intrusive origin the gneisses near rossie village have a whole rock rb sr age of 1 160 42 m y ir 0 7036 0 0004 and similar gneisses near antwerp village are 1 197 53 m y ir 0 7034 0 0005 these ages are younger than the zircon u pb ages of 1 280 1 250 m y generally obtained for metasedimentary and metavolcanic rocks in the central metasedimentary belt of ontario we urge abandonment of the five formations and two groups proposed by wiener and others 1984 on the basis of an intrusive origin for the gneisses near rockport and rossie villages and on stratigraphic correlations of recent studies the stratigraphy of four formations proposed herein with a generalized geologic map of the northwest adirondacks may lead to correlation with carbonate sequences in the central metasedimentary belt and with rocks of the adirondack highlands to the east

preservation of premetamorphic oxygen isotope ratios in granitic orthogneiss from the adirondack mountains new york usa the adirondack mountains new york expose a diverse group of proterozoic igneous rocks that were metamorphosed to granulite facies conditions during the ottawan phase of the grenville orogeny oxygen isotope data for seventy whole rock samples of gabbroic to granitic meta igneous rocks primarily from the charnockite suites from the tupper and saranac sheets in the central adirondacks demonstrate a correlation between 18 o wr and major element composition within continuous mappable meta plutonic units no such relationship is seen among nonconsanguineous granitoids variations in mineral 18 o values and large differences in 18 o between rocks with nonconsanguineous protoliths but similar bulk composition demonstrate that these rocks were not infiltrated by or isotopically equilibrated through a pervasive metamorphic fluid values of 18 o for mineral separates preserve generally high temperature fractionations indicative of dominantly closed system retrograde exchange values of 18 o wr in adirondack orthogneisses were not significantly shifted during granulite facies metamorphism and were dominantly controlled by processes active during premetamorphic magmatism values of 18 o wr may thus serve as a petrogenetic indicator allow discrimination of rock units and serve as a source constraint for meta igneous rocks fayalite meta granites with low 18 o values can be discriminated from surrounding granitoids having high 18 o values a record of assimilation in the evolution of differentiated granitic units is preserved the preservation of primary igneous 18 o values in granulite facies orthogneiss imposes constraints on the synmetamorphic and postmetamorphic fluid history of the adirondack highlands oxygen isotopic compositions at the hand sample scale have been preserved through granulite facies metamorphism fluid absence or low fluid rock ratios on a regional scale are indicated

the role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the hida metamorphic terrain central japan display typical metamorphic fluid enhanced isotopic zonations isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion enhanced isotopic exchange may control these profiles carbon and oxygen isotopic behaviour in grain boundaries is remarkably different oxygen isotopic troughs 18o depleted rims around the calcite grain boundaries are widely observed in this contact aureole demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite in contrast no difference is observed in carbon isotopic profiles obtained from grain cores and rims there is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation carbon chemical species such as co2 and co3 ions in metamorphic fluid migrate mainly through lattice diffusion the carbon and oxygen isotope profiles may be modelled by diffusion into a semi infinite medium empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes and oxygen grain boundary diffusion is ten times faster than oxygen lattice diffusion oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer from the stability of wollastonite and the attainment of oxygen isotopic equilibrium we suggest that diffusion of oxygen occurred through an aqueous fluid phase the timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0 76 106 years using the experimentally determined diffusion constant

arrested kinetic li isotope fractionation at the margin of the ilimaussaq complex south greenland evidence for open system processes during final cooling of peralkaline igneous rocks li contents li and isotopic composition 7 li of mafic minerals mainly amphibole and clinopyroxene from the alkaline to peralkaline ilimaussaq plutonic complex south greenland track the behavior of li and its isotopes during magmatic differentiation and final cooling of an alkaline igneous system li in amphibole increase from b10 ppm in caamphiboles of the least differentiated unit to n3000 ppm in na amphiboles of the highly evolved units in contrast li in clinopyroxene are comparatively low b85 ppm and do not vary systematically with differentiation the distribution of li between amphibole and pyroxene is controlled by the major element composition of the minerals ca rich and na rich respectively and changes in oxygen fugacity due to li incorporation via coupled substitution with ferric iron during magmatic differentiation 7 li values of all minerals span a wide range from 17 to 8 with the different intrusive units of the complex having distinct li isotopic systematics amphiboles which dominate the li budget of whole rocks from the inner part of the complex have constant 7 li of 1 8 2 2 2 n 15 this value reflects a homogeneous melt reservoir and is consistent with their mantle derivation in agreement with published o and nd isotopic data clinopyroxenes of these samples are consistently lighter with 7 liamph cpx as large as 8 and are thus not in li isotope equilibrium these low values probably reflect late stage diffusion of li into clinopyroxene during final cooling of the rocks thus enriching the clinopyroxene in 6 li at the margin of the complex 7 li in the syenites increases systematically from 2 to high values of 14 this coupled with the observed li isotope systematics of the granitic country rocks reflects post magmatic open system processes occurring during final cooling of the intrusion although the shape and magnitude of the li isotope and elemental profiles through syenite and country rock are suggestive of diffusion driven isotope fractionation they cannot be modeled by one dimensional diffusive transport and point to circulation of a fluid having a high 7 li value possibly seawater along the chilled contact in all this study

stable isotopic and petrological constraints on scapolitization of the whitestone meta anorthosite grenville province ontario the whitestone anorthosite wsa located in the central gneiss belt of the south western grenville province ontario exhibits a nearly concentric metamorphic envelope characterized by an increase in modal scapolite hornblende epidote and garnet developed around a core of granulite facies clinopyroxene orthopyroxene garnet meta anorthosite scapolite and hornblende bearing assemblages develop mainly at the expense of plagioclase and pyroxene within the envelope stable isotopic and petrological data for scapolite bearing mineral assemblages within meta anorthosite constrain the source of carbon responsible for co3 scapolite formation and the extent of fluid rock interaction between the anorthosite and adjacent lithologies stable isotopic data indicate increasing 18o and 13c from core to margin of the meta anorthosite and for samples from the southern extension of the wsa where it is ductilely deformed within the parry sound shear zone pssz the average 18osmow value whole rock for the wsa core is 6 9 increasing to 11 5 where the wsa is in tectonic contact with marble breccia the average 13cpbd value of scapolite in meta anorthosite from the centre of the wsa is 3 4 increasing to 0 5 at the eastern marble contact average values of 13c for scapolite and whole rock 18o for samples from the shear zone are 1 0 and 8 0 respectively marbles have average 18o and 13c values of 19 2 and 0 4 respectively the sulphate content of texturally primary scapolite decreases from the core of the wsa xso4 0 48 to the eastern contact 0 05 texturally late scapolite after plagioclase and garnet tends to be co3 rich relative to texturally primary scapolite and some scapolite grains show zoning in the anion site with co3 enriched rims scapolite composition may vary at any scale from a single grain to outcrop the pattern of isotopic enrichment in 13c and 18o preserved in the eastern margin of the wsa is consistent with marble as the major source of fluid contributing to the formation of the metamorphic envelope the decrease in xso4 and increase in xco3 in scapolite toward the margin of the wsa indicate that the volatile content was reset by or developed from a co2 bearing fluid assuming derivation of fluid from marble minimum fluid rock values at the margin of the wsa range from 0 03 for the least enriched to 0 30 for the most isotopically enriched samples although marble is not found in immediate contact with samples of sheared meta anorthosite from the pssz a marble source is also consistent with the c and o isotope composition and anion chemistry of scapolite within these samples

the role of synmetamorphic igneous rocks in the metamorphism and partial melting of metasediments northwest adirondacks field and petrologic studies along the adirondack lowlands highlands boundary near harrisville ny indicate that heat from the synmetamorphic intrusion of the diana syenite complex intrusion temperature of 1 050 c played a major role in the local metamorphic thermal regime and was responsible for extensive partial melting of adjacent metasedimentary units major paragneiss of engel and engel metamorphic temperatures inferred from two feldspar and spinel quartz assemblages decrease from 850 950 c along the diana metasediment contact to 650 700 c 2 3 km away from the contact metamorphic pressures are 7 0 5 kb as determined from coexisting plagioclase garnet sillimanite quartz kyanite sillimanite and garnet rutile ilmenite sillimanite quartz grail in the paragneiss migmatites consisting of quartz microcline perthite sodic plagioclase leucosomes are generally concordant with the melanosome consisting of biotite sillimanite garnet spinel plagioclase corundum cordierite qualitatively the amount of partial melt and occurrences of corundum bearing assemblages decrease away from the diana contact activity of h2o inferred from coexisting biotite sillimanite quartz garnet k feldspar ranges from 0 01 to 0 17 and is five to ten times lower in corundum bearing rocks

steep oxygen isotope gradients at marble metagranite contacts in the northwest adirondack mountains new york usa products of fluid hosted diffusion steep gradients in oxygen isotope ratios are recorded from two contacts between grenville marbles calcite 18o 21 24 and metamorphosed granitic intrusives whole rock 18o 11 12 in the northwest adirondacks oxygen and carbon isotope fractionations between coexisting minerals in the marbles and the metagranites are consistent with isotopic equilibration at peak metamorphic temperatures the 18o profiles are sigmoidal with inflection points at the contacts and are developed over 5 6 m quantitative fluid infiltration diffusion modeling suggests that the isotopic gradients are best explained as the result of fluid hosted diffusion for porosities of 10 3 to 10 6 the profiles could have formed in 103 107 years via an interconnected grain boundary fluid the granites were probably emplaced at shallow crustal levels prior to the regional grenville metamorphism and isotopic exchange is most likely to have occurred at that time contact metamorphism at these localities involved devolatilisation of the marbles and the time estimates may reflect the periods over which fluid producing reactions took place and an enhanced porosity was maintained in the marbles there is a progressive increase in the percentage of diopside and k feldspar at the expense of phlogopite and tremolite towards the metagranites these mineralogical changes probably occurred due to the temperature increase associated with granite intrusion and diffusion of h2o from the granite the two localities lie on either side of the regional metamorphic amphibolite to granulite facies transition the preservation of isotopic profiles formed during contact metamorphism suggests that there was little pervasive fluid flow at this crustal level during the regional metamorphism or at any time thereafter steep isotopic gradients are present at orthogneiss marble contacts elsewhere in the adirondacks suggesting that this conclusion may be generally applicable to this terrain

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

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

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

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

raman spectroscopic characterization of h2o in co2 rich fluid inclusions in granulite facies metamorphic rocks abstract water h2o has been identified during raman analyses at 150 200 c of fluid inclusions from granulites that were previously thought to contain pure co2 at room temperature h2o in a co2 rich fluid inclusion forms an optically unresolvable liquid wetting the inclusion walls during heating the h2o phase evaporates into the co2 phase to produce a homogeneous h2o co2 fluid throughout the inclusion volume and the h2o raman peak at 3640 cm 1 is clearly resolvable at elevated temperatures to test and confirm the method synthetic h2o co2 fi of known composition 87 5 mol and 95 mol co2 were also analyzed previously studied granulite samples from the adirondack mountains usa and from the kerala khondalite belt sittampundi complex and sevitturangampatti india were tested for the presence of h2o in co2 rich fluid inclusions traces of h2o were found in co2 rich fluid inclusions in quartz crystals from the adirondacks and from the kerala khondalite belt h2o was not detected in co2 rich secondary fluid inclusions in garnet from the sittampundi complex and from sevitturangampatti rather hydrogarnet was detected along the walls of inclusions in garnet as evidenced by a peak at 3661 cm 1 the hydrogarnet is interpreted to be a step daughter phase that formed by reaction of the h2o in the fluid inclusion with the garnet host during retrogression these observations confirm the presence of an h2o bearing co2 rich fluid at some time during granulite petrogenesis but do not resolve the question of whether these co2 rich fluids were trapped at peak metamorphic conditions or during retrogression or whether the fluid inclusions have reequilibrated following entrapment

on the causes of 18 o depletion and 18 o 16 o homogenization during regional metamorphism the east humboldt range core complex nevada previous stable isotope studies at lizzies basin revealed that metasedimentary rocks are 18o depleted relative to protolith values particularly in the lower parts of the section lower zone where the rocks are also isotopically homogeneous on a scale of hundreds of meters quartz 18o 9 0 to 9 6 per mil in contrast metasedimentary rocks at higher levels at lizzies basin upper zone are less 18o depleted and more heterogeneous in 18o in order to understand more fully the isotopic evolution of this terrane a series of detailed meter scale traverses across various metamorphic and igneous lithologies were completed at lizzies basin and at the structurally higher angel lake locality traverses in the lizzies basin lower zone and in the lower parts of angel lake angel lake lower sequence across various silicate lithologies including abundant granitoids reveal similar degrees of homogeneity although the average 18o values are higher at angel lake in contrast traverses which include substantial thicknesses of marble and calc silicate gneiss and very little granitoid have more heterogeneous quartz 18o values 11 9 to 13 4 per mil and also have a higher average 18o 12 9 per mil than observed elsewhere the scale of 18o 16o homogeneity in quartz observed at lizzies basin and angel lake meters to hundreds of meters requires fluid mediated isotope exchange which accompanied tertiary metamorphism there is a correlation between the degree of 18o depletion in metasedimentary rocks 18o 16o homogenization between lithologies and the proportion of granitoids leucogranites in particular within any part of the section and a corresponding anticor relation with the proportion of marble this points to a causal relationship whereby the leucogranites as well as the tertiary hornblende diorite and biotite monzogranite acted as both a relatively low 18o reservoir and a source of fluids to enhance exchange while the marbles hindered isotope deplction and homogenization by acting as relatively high 18o reservoirs and impermeable layers material balance calculations help delineate the plausible mechanisms of exchange between granitoids and metasediments single pass infiltration of magmatic fluids from the granitoids is not capable of reproducing all of the observations fluidmediated exchange by convective recirculation of magmatic fluids on a scale of meters is the mechanism which explains all of the observations the generalized model for the isotopic evolution of the east humboldt range core complex provides and excellent opportunity to establish the main causes and controlling factors of 18o depletion and 18o 16o homogenization during regional metamorphism

oxygen grain boundary diffusion in natural and hot pressed calcite aggregates abstract oxygen grain boundary diffusion rates were experimentally determined in natural solnhofen limestone and hot pressed calcite aggregates at 300 to 500 c and 100 mpa water pressure the solnhofen limestone was pre annealed for 24 h at 700 c and 100 mpa confining pressure under anhydrous conditions to produce an equilibrium microstructure for the diffusion experiments the synthetic calcite aggregates were formed by hot isostatic pressing of an intimate mixture of 1 2 m calcite grains plus 5 wt 0 3 m alumina grains at 700 c and 200 mpa for 3 10 days values for the product of the grain boundary diffusion coefficient d and the effective grain boundary diffusion width were determined from 18 o concentration profiles measured with an ion microprobe there is no measurable difference between d values obtained for pre annealed solnhofen samples and hot pressed calcite aggregates the temperature dependence for oxygen grain boundary diffusion at 100 mpa is described by the arrhenius parameters d 0 3 8 10 14 m 3 s and q 127 17 kj mol comparison of the results of this study with previously published data show that the rate of oxygen grain boundary diffusion in calcite aggregates is four to five orders of magnitude greater than that of volume diffusion in calcite single crystals and the activation energy is less grain boundary diffusion of oxygen in calcite aggregates is five to six orders of magnitude greater than that of calcium when the latter is extrapolated to the temperature range of this study in addition oxygen grain boundary diffusion rates in calcite aggregates are about a factor of 4 10 and 100 times greater than that in feldspar and quartz aggregates respectively under similar experimental conditions

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

u pb zircon geochronology of the adirondack mountains and implications for their geologic evolution u pb zircon studies of metamorphosed igneous rocks in the adirondack mountains have yielded preliminary ages within the range 1420 990 ma several geochronologically and geochemically distinct episodes of igneous intrusion and at least one pre granulite facies dynamothermal metamorphic event are documented this information is consistent with recent field and geochronological studies throughout the grenville province and suggests that a complex sequence of events occurred in the adirondack mountains prior to the widespread deformation and metamorphism commonly attributed to the approximately 1100 1000 ma ottawan phase of the grenvillian orogenic cycle

oxygen self diffusion in calcite dependence on temperature and water fugacity oxygen self diffusion in natural calcite single crystals was studied hydrothermally at 400 800 c and 10 350 mpa confining pressure diffusion coefficients d were determined from18o concentration profiles measured with an ion microprobe at 100 mpa confining pressure the arrhenius parameters yield an activation energy q 173 6 kj mole and pre exponential factor d0 7 10 9 m2 s over the temperature range 400 800 c and there is no measurable anisotropy constant temperature experiments at 700 c indicate that there is a strong linear correlation slope 0 9 of d with water fugacity over the range 4 240 mpa consistent with the interpretation that in the presence of water the dominant oxygen bearing transport species in calcite is molecular water a sample containing 1180 ppm mn shows a marked increase in observed d values at temperatures below 600 c however when pre annealed at 700 c the d values obtained at 550 c are within a factor of four of the value obtained for the low 100 ppm mn sample the results of this study confirm that in contrast to carbon oxygen diffusion rates in calcite are greatly enhanced when water is present the difference in the effect of water on doxygen and dcarbon in calcite may provide valuable information for evaluating the role of fluids in the thermal histories of calcite bearing rocks

oxygen and carbon isotopic constraints on the development of eclogites holsnoy norway abstract eclogite formation on the island of holsnoy required the addition of water to anhydrous granulite facies protoliths in order to assess this process oxygen and carbon isotope ratios of whole rock powders and mineral separates from eclogites and granulites have been measured whole rock oxygen isotope ratios range from 7 3 to 6 0 smow in granulites average 6 38 and 7 2 to 6 1 in eclogites average 6 55 field relations permit identification of the granulite protolith of eclogites oxygen isotope measurements show shifts of up to 0 5 between some eclogites compared to their corresponding granulite protoliths indicating open system and locally heterogeneous fluid behavior mineral pair fractionations in the eclogites show disequilibrium are incompatible with slow cooling and diffusive exchange between phases and suggest that open system fluid movement continued after eclogite facies metamorphism carbonate is also present in some of the eclogites as a primary mineral dolomite and as part of a retrograde assemblage calcite textural evidence suggests that carbonate formation occurred during and after eclogite formation however all measured carbonate is out of isotopic equilibrium with eclogite facies minerals due to the influx of retrograde fluids massive calcite marble pods containing amphibolite facies cale silicate minerals have average 18 o of 9 5 0 6 while calcite in retrograded eclogites has 18 o 17 7 2 7 the 13 c 4 0 8 is indistinguishable between these two groups both whole rock and carbonate stable isotope data are interpreted as indicating a continued history of fluid infiltration during and after peak eclogite facies metamorphism the most probable source of fluids are from dewatered sediments tectonically juxtaposed during the caledonian orogeny

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

high 18o granitic plutons from the frontenac axis grenville province of ontario canada abstract 18 o 16 o ratios have been determined for whole rock as well as coexisting minerals from nine syn to post tectonic monzonite and quartz monzonite plutons in the westport gananoque area covering approximately 2500 km2 the plutons fall in two distinct isotopic groups 1 i low 18o group 8 0 11 2 rideau lake westport and wolfe lake plutons and 2 ii high 18o group 12 7 16 2 lyndhurst perth road battersea gananoque south lake and crow lake plutons the 18 o 16 o ratios of granitic rocks from the latter group are among the highest ever reported in the literature the isotopic compositions of samples within each pluton bear no relationship to the sample distance from the intrusive contacts nor are they affected by the types of country rocks marbles vs pelitic gneisses into which they are emplaced oxygen isotope fractionations among coexisting quartz feldspar biotite and magnetite all show normal plutonic values thus all lines of evidence suggest that the monzonite and quartz monzonite plutons did not acquire their characteristic 18 o 16 o ratios at the present level of exposure either by isotopic exchange with the surrounding metasedimentary country rocks or by any post crystallization low temperature alteration processes the distinct 18o 16o ratios observed in the high and low 18o groups probably reflect the difference in the isotopic compositions of the source materials the most plausible source for the high 18o group plutons is the grenville supergroup metasedimentary rocks and that for the low 18o group plutons the grenville basement gneisses mixed with a small amount of grenville supergroup metasedimentary rocks

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

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

stable isotope and petrologic evidence for the origin of regional marble hosted magnetite deposits and the zinc deposits at franklin and sterling hill new jersey highlands united states mesoproterozoic marble in the new jersey highlands hosts small magnetite deposits that occur in discrete groups along linear trends and are concentrated mainly in the western part of the region magnetite also forms a layer structurally beneath the zn fe mn orebody at the franklin mine marble host rocks are interlayered at fe and zn fe mn deposits with bimodal metavolcanic rocks amphibolite and rhyolitic gneiss that were deposited synchronously in a back arc basin developed on the eastern margin of laurentia between 1 3 and 1 25 ga magnetite in the deposits ranges from massive to disseminated and is characterized by low ti variable mn and locally high s concentrations of as v sb and zn are enriched in magnetite compared to marble host rocks and associated metavolcanic rocks carbon and oxygen isotope ratios of the marbles are consistent with water rock interaction between the marble protolith and a mixture of igneous fluids and seawater regional geology petrology and isotope data indicate that fe was introduced into the carbonate protolith as low temperature fe oxides and hydroxides via hydrothermal fluids discharged along basinal fracture zones on the sea floor related marble hosted zn fe mn deposits at franklin and sterling hill contain the assemblage willemite zincite franklinite stable isotope compositions of the zn deposits are consistent with alteration of host rocks by water rich fluids preserving protolith carbon isotope ratios stable isotope modeling suggests that zn silicate oxides or hydroxides represent an appropriate protolith for the high grade zn ores alteration of metavolcanic rocks at the fe deposits combined with the isotope data and other petrologic and geochemical evidence document the presence of an extensive hydrothermal system of grenville age centered in the western highlands metals precipitating from this hydrothermal system were responsible for fe in the marble hosted magnetite deposits and zn in the deposits at franklin and sterling hill from the same or a related hydrothermal system underplating of the back arc by mafic magma provided the heat to melt the lower crust and drive the hydrothermal system resulting in carbonate hosted fe and zn ore deposits and associated bimodal volcanism

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

diffusion obstacles and opportunities in petrochronology many of the approaches in petrochronology are rooted in the assumption of equilibrium diffusion is an expression of disequilibrium the movement of mass in response to chemical potential gradients and isotopes in response to isotopic gradients it is extremely important that we be aware of how the effects of diffusion can place obstacles across our path towards petrochronologic enlightenment conversely the effects of diffusion also provide opportunities for understanding rates processes and conditions experienced by rocks the enormity of the field does not permit us to provide a comprehensive review of either the mathematics of diffusion or quantitative data that have been obtained relevant to the interpretation of diffusive processes in rocks and minerals many resources cover these topics including rimg volume 72 diffusion in minerals and melts zhang and cherniak 2010 and several textbooks crank 1975 glicksman 2000 particularly relevant to the discussion of petrochronology are summaries of the theory and controls on diffusion brady and cherniak 2010 zhang 2010 as well as diffusion rates in feldspar cherniak 2010a accessory minerals cherniak 2010b garnet ganguly 2010 mica pyroxene and amphibole cherniak and dimanov 2010 and melts zhang and ni 2010 zhang et al 2010 rather than duplicate that material our goal is to explore the obstacles and opportunities presented by the effects of diffusion as they inform the rates of petrologic processes to achieve this goal we emphasize key principles and illustrative examples quantitative interpretation of the effects of diffusion assumes predictability of numerous factors that may affect chemical or isotopic transport including temperature initial and boundary conditions water and oxygen fugacities activities of other components multiple mechanisms of diffusion and crystal chemistry coupling of the substitution of elements into different crystallographic sites additionally the extraction of meaningful ages durations of events and temperatures requires

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

tension vein arrays in progressive strain complex but predictable architecture and major hosts of ore deposits abstract most en echelon vein arrays are extensional and can be termed tension vein arrays tvas tvas in major fault and shear zones fszs are subject to progressive deformation this deforms the initial tva whose geometry is well documented in the literature via discrete stages first into progressively more complex architecture involving folding of the tension veins then into progressively more simple architecture ultimately forming pipes during this progression the tva axis new definition rotates within the shear plane from normal to parallel to the displacement vector the deforming tva axis has simpler geometry than the complex tension veins and it can be employed to precisely track the deformation state of the fsz its displacement vector and shear sense through all the strain stages five structural metasomatic stages are defined by discrete steps in the strain evolution tvas are difficult to recognise and are under recognised in ore systems for a number of inherent geological reasons orebodies founded on dilation form parallel to the tva axis which is also parallel to dilational jogs in the parent fsz orebodies formed early in the fsz history are normal to the displacement vector and in progressive shear rotate with the tva axis toward the displacement vector orebodies formed late in the fsz history overprint apparently complex to chaotic vein stockwork which nevertheless has analysable geometry tva hosted orebodies are not necessarily parallel to the displacement vector of the host fsz but occupy elongate orientations over a 90 range within the fsz large orebodies are favourably developed in tvas in unfoliated fszs type 1 shear zones which may form fluid superhighways type 1 shear zones form in predictable circumstances involving particularly host rocktype and crustal position strike slip fszs possess a downdip tva axis and are especially able to tap deep crustal fluid tva hosted orebodies form a major deposit style exploration requires careful analysis of the prospect geometry at an early stage and recognition of the multi faceted tva architecture the relationship between the parent shear zone or fault including fault veins and the component tension veins is complex and search strategies depend critically on the strain stage the type of host fsz and the type of exposure deciphering the architecture of tvas involves a combination of vector orientational parameters and scalar angular relationship parameters this permits ready analysis in oriented rock outcrop and oriented drillcore and in unoriented rock unoriented drillcore mine dumps and float

stable isotopic signatures of superposed fluid events in granulite facies marbles of the rauer group east antarctica the role of volatiles in the stabilization of the lower granulite facies crust is contentious opposing models invoke infiltration of co2 rich fluids or generally vapour absent conditions during granulite facies metamorphism stable isotope and petrological studies of granulite facies metacarbonates can provide constraints on these models in this study data are presented from metre scale forsteritic marble boudins within archaean intermediate to felsic orthogneisses from the rauer group east antarctica forsteritic marble layers and associated calcsilicates preserve a range of 13c and 18o depleted calcite isotope values 13c 9 9 to 3 0 pdb 18o 4 0 to 12 1 smow a coupled trend of 13c and 18o depletion 2 5 respectively from core to rim across one marble layer is inconsistent with pervasive co2 infiltration during granulite facies metamorphism but does indicate localized fluid rock interaction at another locality more pervasive fluid infiltration has resulted in calcite having uniformly low carbonatite like 18o and 13c values a favoured mechanism for the low 18o and 13c values of the marbles is infiltration by fluids that were derived from or equilibrated with a magmatic source it is likely that this fluid rock interaction occurred prior to high grade metamorphism other fluid rock histories are not however ruled out by the available data coupled trends of 13c and 18o depletion are modified to even lower values by the superposed development of small scale metasomatic reaction zones between marbles and internally folded mafic interlayers the timing of development of these layers is uncertain but may be related to archaean high temperature 1000dc granulite facies metamorphism

isotopic constraints on emplacement age of anorthositic rocks of the marcy masiff adirondack mts new york the igneous emplacement age of anorthositic rocks comprising the marcy massif have been constrained by fixing minimum and maximum ages for their intrusion minimum ages have been fixed by a u pb dating of cores of air abraded zircons from the anorthosite 1113 ma b u pb dating of baddeleyite within the anorthosite 1087 ma c u pb dating of baddeleyite from an olivine metagabbro crosscutting marcy massif anorthosite 1109 ma d u pb zircon dating of jotunitic rocks crosscutting the marcy anorthosite massif 1143 pm 31 ma maximum emplacement ages are based upon a sheets of anorthositic rock crosscutting mangeritic charnockitic gneiss dated by u pb zircon at 1125 pm 10 ma 1134 pm 4 ma and 1135 pm 43 ma and b anorthosite related pyroxenite dikes crosscutting mangerite that contains xenoliths of identical pyroxenite these results constrain emplacement of the marcy anorthosite to 1113 1138 ma with the most probable age in the interval 1125 1135 ma this time of in