travertine precipitation in the paleoproterozoic kuetsjarvi sedimentary formation pechenga greenstone belt ne fennoscandian shield abstract precambrian travertines tufas and speleothems either formed rarely or they have not been identified in previous studies in the absence of high pco2 soils in paleoproterozoic karst solution and speleothem formation occurred by processes distinct from those commonly found in present day low temperature karst environments however the high pco2 atmosphere could itself have encouraged karst formation the paleoproterozoic kuetsjarvi sedimentary formation of the pechenga greenstone belt nw russia includes abundant terrestrial carbonate precipitates these precipitates were sampled from a drillcore representing a complete section of the ca 120 m thick formation and were investigated for c and o isotopes acid soluble elemental contents and petrography the newly obtained results were used to constrain the origins of the precipitates and to illuminate different terrestrial carbonate types the investigated drillcore includes abundant small scale cavities and veins which are commonly filled with dolomite and quartz dolomite crusts are found both in the cavities and on bedding erosional surfaces dolomite cements coat uneven surfaces and surficial rock fragments the surficial dolomite crusts form distinct and discrete layers whereas the cements do not the cavity and vein fills are likely post depositional in origin whereas the surficial dolomite crusts and dolomite cements are likely syn depositional precipitates the investigated precipitates often show 13c values lower than those reported from their host rocks suggesting the influence of an external carbon source petrographic features and geochemical data suggest dissolution and precipitation of carbonate material originating from deep sourced co2 bearing fluids likely at high earth surface temperatures

ion microprobe evidence for the mechanisms of stable isotope retrogression in high grade metamorphic rocks retrograde interdiffusion is widely proposed as the dominant factor in producing the stable isotopic fractionation among minerals in slowly cooled igneous and metamorphic rocks mineral zonation consistent with interdiffusion of stable isotopes has never been directly observed however leaving doubt as to the mechanism responsible for the bulk mineral isotopic compositions commonly measured ion microprobe analyses of oxygen isotope ratios in magnetite were combined with conventional bulk mineral analyses and diffusion modeling to document the relationship between mineral zonation and the mechanism of retrogression inferred from bulk mineral data two samples of magnetitebearing quartzo feldspathic lyon mountain gneiss from the adirondack mountains n y were studied in detail conventional stable isotope analysis of both samples indicates that isotope thermometers are discordant and were reset by as much as 200 c from the estimated peak temperature of 750 c the relative order of apparent temperatures recorded by various thermometers differs between the two samples however with t qtz fsp t mt qtz and t mt fsp in one sample and t qtz fsp t mt qtz and t mt fsp in the other diffusion modeling using the fast grain boundary model shows that the former pattern of apparent temperatures is consistent with closed system interdiffusion during cooling whereas the latter is not the modeling predicts that 0 5 mm diameter magnetite grains common to this rock type will contain isotopic zonation of 1 rims lower in 18 o than cores and that the cores of smaller 0 1 mm grains will be similarly lower than to the cores of large 0 5 mm grains ion microprobe analysis reveals that the zoning patterns of magnetite grains from the first sample contain clear core to rim zonation in multiple grains core rim 1 1 0 4 and predicted grain size vs core composition variations consistent with diffusion controlled resetting of bulk mineral fractionations in contrast the second sample shows irregular inter and intra granular variations over an 8 range consistent with open system alteration these results provide direct documentation of the importance of interdiffusion in affecting stable isotope distributions in slowly cooled rocks the correlations of bulk mineral resetting with zonation show that bulk mineral data when interpreted with detailed modeling can be used to determinate what processes controlling retrogression

oxygen isotope trends and anomalies in granitoids of the tibetan plateau abstract extreme transhimalayan oceanic mantle i type and high himalayan anatectic collision s type granitoids in the himalaya kashmir and tibet range in their original oxygen isotope composition from 6 to 7 5 and from 10 to 12 5 18osmow respectively in the sutured paleozoic and mesozoic orogen of the eastern tibetan plateau purely oceanic batholiths seem absent shalouli shan 8 10 but high himalayan values are matched in dongda shan and at luxi towards the east oceanic values are found again only on the margin of the yangtse platform the regional pattern of normal oxygen isotope data provides a background for anomalous feldspars to 1 in lhasa granite and in the active geothermal system at yangbachen recharged by 6000 m a s l meteoric water for lhasa granite oxygen isotope exchange paths and preliminary k ar dating of feldspars suggest exchange with meteoric water from over 3000 m altitude before 20 ma ago

provenance of upper precambrian lower cambrian shales in the central iberian zone spain evidence from a chemical and isotopic study geochemical and isotopic sr nd o data are presented for upper precambrian and lower cambrian shale sequences from the central iberian zone spain in order to define geochemical discriminants between them and to assess the nature of the source regions supplying these basins elemental data especially th sc ratios coupled with endt values of 2 5 suggest that the upper precambrian rocks contain a greater proportion of a much younger more mafic component than the lower cambrian sequence which has high th sc and endt of 7 3 coherent trends between elemental and o isotope data imply a homogeneous recycled source as the dominant provenance for the upper precambrian shales whereas a lack of such coherence for the lower cambrian sediments suggests a more heterogeneous provenance the sedimentological geochemical and isotopic data are consistent with the upper precambrian succession being derived ultimately from a polycyclic mixture of young pre cadomian mafic sources and older 2 ga crust in contrast the lower cambrian sequence was mainly derived from old more felsic crust which would have contributed increasingly greater proportions of material as the younger sources were progressively removed by erosion

contribution of icelandic ice caps to sea level rise trends and variability since the little ice age 1 in total icelandic ice caps contain 3600 km3 of ice which if melted would raise sea level by 1 cm here we present an overview of mass changes of icelandic ice masses since the end of the 19th century they have both gained and lost mass during this period changes in ice volume have been estimated both through surface mass balance measurements performed annually since 1990 and differencing of digital elevation models derived from various satellite and airborne observations while the glaciers showed little mass loss as the 20th century began losses increased rapidly after 1925 peaked in the 1930s and 1940s and remained significant until the 1960s after being near zero or even positive during the 1980s and early 1990s glacier mass budgets declined considerably and have since the mid 1990s shown an average annual loss of 9 5 1 5 gt a 1 contributing 0 03 mm a 1 to sea level rise since 1995 interannual variability in mass loss is high ranging from 2 7 to 25 3 1 5 gt a 1 corresponding to surface mass balances of 0 2 to 2 2 0 15 m we a 1 this variability is driven by climate fluctuations and also by transient reduction of albedo due to volcanic eruptions

oxygen carbon and strontium isotope constraints on the mechanisms of nappe emplacement and fluid rock interaction along the subhorizontal naukluft thrust central namibia the naukluft thrust forms the floor thrust to the naukluft nappe complex a far travelled nappe stack of the pan african damara belt in namibia the thrust tectonostratigraphy comprises three dolomitic components a calc mylonite horizon and a discrete brittle fault stable isotope data indicate that the leading edge is characterized by positive 13 c values whereas the trailing edge is characterized by negative 13 c values there is a significant range in the 18 o values over 15 in different sections with the leading edge showing a larger range than the trailing edge 18 o values are characteristic of burial dolomites and secondary dolomitization is indicated by the presence of networks above and below the naukluft thrust zone the large range in 18 o values and variations in 13 c vs 18 o patterns are interpreted to be the result of interaction between the precursor to the naukluft thrust zone dolomites and fluids derived from different footwall lithologies 87 sr 86 sr isotope ratios indicate that some fluids were derived from the basement the data presented in this study suggest that an original carbonate dominated horizon existed prior to thrusting and that the basal thrust of the nappe complex exploited this horizon

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

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

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

determining the orientation of marine csem receivers using orthogonal procrustes rotation analysis electromagnetic receivers deployed to the seafloor for csem surveys can have unknown orientations because of the unavailability of compass and tilt recordings in such situations only the orientation independent parameters derived from the measured csem field vector can be interpreted and this may result in less structural resolution than possible when the sensor orientations are known an orthogonal procrustes rotation analysis opra technique can be used to estimate the full 3d receiver orientation for inline and off line csem receivers the generality of this method allows it to be easily embedded into nonlinear csem inversion routines so that they iteratively search for both the receiver orientation and a seafloor electrical conductivity model compatible with the data synthetic tests using the opra method jointly with a 1d inversion demonstrate that it can recover the rotation and tilt angles to about one degree accuracy for 1d data and to within a few degrees for 2d data application of this method to real survey data shows good agreement with a previous orientation method that is suitable only for determining the horizontal rotation of inline receivers csem data collected over the pluto gas field offshore the northwest coast of australia were used to demonstrate how the opra method can be used to orient csem receivers prior to inversion of only the inline electric and crossline magnetic field components

deep crustal embrittlement and fluid flow during granulite metamorphism in the limpopo belt south africa deep crustal rocks generally deform in a ductile manner and have a very low permeability however in the southern marginal zone of the limpopo belt solutions fluids have moved through high grade rocks and reacted with these on a regional scale along a major shear zone strike slip environments there have more widespread alteration than thrust fault environments under high grade metamorphic conditions brittle failure and hydraulic fracture processes in particular have occurred in these deep crustal rocks the latter phenomenon provides a mechanism for developing permeability and plumbing systems for the migration of fluids and or liquids through the deep crust modeling of the physical conditions of brittle failure under these unusual conditions would suggest that a mobile phase of low viscosity and water activity participated in the fracture process

processes leading to eclogitization densification of subducted and tectonically buried crust 1 the transformation of subducted and tectonically buried crustal rocks to denser eclogite plays a fundamental role in the dynamics of mountain building and crustal recycling however a complex of partially eclogitized granulites on the island of holsnoy in the western part of the norwegian caledonides reveals that such densification depends in part on the antecedent history of rock masses and that large bodies of untransformed rock can persist metastably even after long residence times in the lower crust the rocks on holsnoy suggest that conversion to eclogite was delayed until lower or subcrustal seismic events allowed aqueous fluids to enter the previously dry and unusually strong granulite complex metamorphism then occurred in a spatially heterogeneous manner with several distinct physical processes involving feedbacks between deformation fluid infiltration and chemical reactions operating simultaneously in different parts of the rock mass field relations show that the introduction of fluids and conversion to eclogite significantly weakened the rocks a reservoir flux systems model is used to represent the various processes contributing to eclogitization of the granulites which operated at vastly different rates over disparate intervals of time the model suggests that the metamorphic process may have been brief 1 myr and ultimately self limiting arrested by the change in rheology associated with the conversion of brittle granulite to ductile eclogite

mudball surface dust and snowball earth deglaciation 1 recent modeling results have raised doubts about the ability to deglaciate from a global glaciation at atmospheric carbon dioxide levels that are realistic for a neoproterozoic snowball earth here we argue that over the lifetime of a snowball event ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation this idea leads to the prediction that clay drapes found on top of neoproterozoic glaciations should be thicker in tropical than extratropical regions we test this idea by running the foam general circulation model gcm with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes snowball deglaciation at pco2 0 01 0 1 bar in a reasonable regime of these parameters we find similar though more nuanced results from a limited number of test cases using national center for atmospheric research s cam gcm

mechanisms of oxygen isotopic exchange and isotopic evolution of 18 o 16 o depleted periclase zone marbles in the alta aureole utah insights from ion microprobe analysis of calcite oxygen isotope ratios have been measured by ion microprobe and millimeter scale dental drill along detailed sampling traverses across the boundary between periclase bearing 18o 11 8 and periclase free 18o 17 2 marble layers in the periclase per zone of the alta stock aureole utah these data define a steep coherent gradient in 18o that is displaced a short distance 4 cm into the periclase free cal fo layer sem and ion microprobe analyses show two isotopically and texturally distinct types of calcite at the grain scale clear well polished calcite grains are isotopically homogeneous within analytical uncertainty 0 27 2sd more poorly polished pitted texturally retrograde turbid looking calcite has lower and more variable 18o values and replaces clear calcite along fractures cleavage traces or grain boundaries despite significant lowering of the 18o values in calcite throughout both layers during prograde metamorphism ion microprobe analyses indicate that individual clear calcite grains are now isotopically homogeneous across the entire gradient in 18o diffusion calculations indicate that conservative time scales required for isotopic homogenization of calcite grains by volume diffusion 30 000 62 000 years at 575 600 c exceed significantly the timescale 1 250 years estimated for the prograde development of the 18o gradient at the boundary between these two marble layers the ion microprobe data and these diffusion calculations suggest instead that surface reaction mechanisms accompanying recrystallization are responsible for the observed oxygen isotope homogeneity of these calcite grains thus the ion microprobe data are consistent with the formation of calcite in oxygen isotope exchange equilibrium with infiltrating fluid during prograde reaction and recrystallization

on the determination of marine magnetotelluric receiver orientation using land magnetic observatory data marine magnetotelluric measurements using free fall instruments without effective compasses suffer from the problem of unknown orientation of the receivers at the seafloor while past works indicate that marine magnetotelluric orientation of the instruments can be estimated by reference to land deployments of known orientation using the transfer tensor method there is limited published information on how this is implemented in practice we document this method and propose a set of new time and frequency domain approaches to solve this orientation problem of the seafloor receivers we test these methodologies in onshore and offshore magnetotelluric data whose orientations are well known and apply these techniques to marine magnetotelluric data with unknown orientation for the controlled tests both timeand frequency domain approaches produce overall comparable results to investigate the effects of the subsurface structure distribution on the orientation process a dimensionality analysis of a controlled dataset is carried out in subsequent analysis using the available disoriented marine magnetotelluric data from offshore brazil and from the vassouras magnetic observatory on the mainland for remote referencing frequency domain methods yield approximate orientation angles among themselves with low standard deviation each time domain results are consistent for most cases but differ from frequency domain results for some situations

origin of ree mineralization in the bastnas type fe ree cu mo bi au deposits bergslagen sweden the bastnas type deposits with mineral assemblages of fe oxides ca mg silicates rare earth element ree silicates ree fluorocarbonates and cu fe mo bi sulfides are associated with marble horizons in a strongly na k and or mg altered metavolcanic succession over a distance of at least 80 km in a sw ne trending zone in western bergslagen two subtypes occur 1 enriched relative to the other type in light ree lree and fe exemplified by the bastnas and rodbergsgruvan deposits and 2 enriched in heavy ree hree y mg ca and f represented by deposits in the norberg district bastnasite hosts primary fluid h2o co2 inclusions with salinities of 6 29 eq wt cacl2 and with total homogenization temperatures th tot of ca 300 400 c subtype 2 has late stage fluorite with fluid inclusions that show 1 16 eq wt nacl and th tot of ca 90 150 c molybdenite re os ages obtained from three deposits are 1 904 6 1 863 4 and 1 842 4 ma nd isotopic data from five different ree minerals yielded no defined isochron but a range in end 1 88 ga of 0 2 to 1 6 the oxygen isotope values 18osmow of dolomite and calcite from the associated ree mineralized skarn and recrystallized carbonate assemblages lie in the range 6 1 8 6 overlapping with those of the host marbles carbon isotope values 13cpdb show typical magmatic signatures of 6 7 to 4 4 while the host marbles group around ca 2 4 the sulfur isotope 34scdt values of associated sulfides range between 10 8 and 0 2 the combined evidence suggests ree mineralization beginning at 1 9 ga from mainly svecofennian juvenile magmatic 400 c fluids carrying si f cl s co2 and the ree in addition to other metals mineralization occurred through reactions with dolomitic layers in the supracrustal units coevally with regional metasomatic alteration associated with fluid circulation through an extensive active volcano plutonic complex

a stable isotope study of retrograde alteration in sw connemara ireland dalradian metamorphic rocks lower ordovician meta igneous rocks mgs and caledonian granites of the connemara complex in sw connemara all show intense retrograde alteration alteration primarily involves sericitization and saussuritization of plagioclase the alteration of biotite and hornblende to chlorite and the formation of secondary epidote the alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs and was the result of a phase of fluid influx into these rocks in hand specimen k feldspar becomes progressively reddened with increasing alteration mineralogical alteration in the mgs and caledonian granites took place at temperatures 275 15 c and in the mgs pfluid is estimated to be 1 5 kbar during alteration the d values of alteration phases are 18 to 29 fluid inclusions 47 to 61 chlorites and 11 to 31 epidotes chlorite 18o values are 0 2 to 4 3 while 18o values for quartz k feldspar pairs show both positively sloped mgs and highly unusual negatively sloped caledonian granites arrays diverging from the normal magmatic field on a plot the stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200 140 c the retrograde fluid had d 20 to 30 in all lithologies but the fluid 18o varied both spatially and temporally within the range 4 to 7 the fo2 of the fluid that deposited the epidotes in the mgs varied with its 18o value with the most 18o depleted fluid being the most oxidizing the d values together with low 0 18o values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin this meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration the variation in retrograde fluid 18o values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid rock interaction infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the galway granite soon after intrusion at 400 ma however convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later

high strain deformation and fluid infiltration diachronism of the middle crust new devonian permian alice springs ages 365 290 ma of shear zones in the strangways metamorphic complex central australia abstract the proterozoic granulite facies strangways metamorphic complex smc in the arunta region of central australia was partially hydrated during the devonian carboniferous 380 320 ma alice springs orogeny by amphibolite greenschist facies high strain deformation stable and radiogenic isotope analyses on coeval muscovite and biotite from shear zone samples of the smc were performed to analyse the composition and date the timing of fluid circulation and cooling stable isotope data 18 o and d indicate that in the south of the smc the source of fluids appear to be the thick successions of neoproterozoic heavitree quartzite while another source in the north and central part of the smc may be related to meteoric fluids the heterogeneous 18 o fluid and homogenous d fluid values for muscovite reflect changes in water rock ratios with initial high values in the south and lower in the north possibly suggesting a migration of fluids from south to north as indicated by the evolving 18 o fluid and homogenous d fluid values rb sr muscovite ages of 365 340 ma approximate the time of crystallization and fluid infiltration they also indicate that the shear zones were active at different times during the alice springs orogeny and that some were active prior to the peak carboniferous amphibolite facies metamorphism 40 ar 39 ar muscovite ages of 350 325 ma are mostly interpreted as cooling ages rb sr biotite ages of 335 290 ma are interpreted as cooling ages at 300 c sr closure temperature for biotite and extend the activity of the alice springs orogeny until the permian cooling histories of the wallaby knob and harry creek shear zones which serve as the tectonic boundaries of the smc to the north and south respectively indicate slow cooling 1 for c 30 ma 360 330 ma at both boundaries continuing until 290 ma in the western portion of the harry creek shear zone this slow cooling is associated with passive exhumation i e erosion rapid cooling 20 10 c ma 1 then occurred over c 10 ma 330 320 ma in the wallaby knob shear zone and in the east portion of the harry creek shear zone this change in cooling rate is associated with the combined initiation in the carboniferous of dextral and thrusting deformation by the pinnacles bore and erontonga shear zones

controls on the mechanisms of fluid infiltration and front advection during regional metamorphism a stable isotope and textural study of retrograde dalradian rocks of the sw scottish highlands vein controlled retrograde infiltration of h2o co2 fluids into dalradian epidote amphibolite facies rocks of the sw scottish highlands under greenschist facies conditions resulted in alteration of calcite rich marble bands to dolomite and spatially associated 18o enrichment of about 10 on a scale of metres fluid inclusion data indicate that the retrograde fluid was an h2o salt mixture with a low co2 content and that the temperature of the fluid was about 400d c detailed petrographic and textural backscattered electron imaging studies at one garnet grade locality show that advection of fluid into marbles proceeded by a calcite calcite grain edge flow mechanism while alteration of non carbonate wall rock is associated with veinlets and microcracks stable isotopic analysis of carbonates from marble bands provides evidence for advection of isotopic fronts through carbonate wall rocks perpendicular to dolomite veins and fluid fluxes in the range 2 4 28 6 m3 m2 have been computed from measured advection distances coincidence of isotope and reaction fronts is considered to result from reaction enhanced kinetics of isotope exchange at the reaction front front advection distances are related to the proportion of calcite to quartz in each marble band with the largest advection distance occurring in nearly pure calcite matrix this relationship indicates that fluid flow in carbonates is only possible along fluid calcite calcite grain edges however experimental constraints on dihedral angles in calcite fluid systems require that pervasive infiltration occurred in response to calcite dissolution initiated at calcite calcite grain junctions rather than to an open calcite pore geometry the regional extent of the retrograde infiltration event has been documented from the high 18o of dolomite ankerite carbonates from veins and host rocks over an area of least 50 50 km in the sw scottish highlands isotopically exotic 18o rich retrograde fluids have moved rapidly upwards through the crust inducing isotopic exchange and mineral reaction in wall rocks only where lithology pore geometry or mineral solubilities pressure and temperature have been appropriate for pervasive infiltration to occur

timescales and mechanisms of fluid infiltration in a marble an ion microprobe study using a recently developed ion microprobe technique a detailed oxygen isotope map of calcite grains in a coarse grained marble has been constructed supported by trace element mn sr fe analysis and cathodoluminescence cl imaging in order to constrain scales of oxygen isotope equilibrium timescales and mechanisms of metamorphic fluid infiltration and fluid sources and pathways results are compared with a previous study of this sample wada 1988 carried out using a cryo microtome technique and conventional oxygen isotope analysis the marble from the high temperature low pressure hida metamorphic belt in north central japan underwent granulite facies followed by amphibolite facies metamorphic events the latter associated with regional granite intrusion the cl imaging indicates two types of calcite a yellow luminescing ylc and a purple luminescing plc variety the ylc which occupies grain boundaries fractures replacement patches and most of the abundant deformation twin lamellae post dates the dominant plc calcite and maps out fluid pathways systematic relationships were established between oxygen isotope and trace element composition calcite type and texture based on 74 18o 16o and 17 trace element analyses with 20 30 m spatial resolution the ylc is enriched in mn and fe and depleted in 18o and sr compared to plc and is much more 18o depleted than is indicated from conventional analyses results are interpreted to indicate infiltration of 18o depleted metamorphic or magmatic fluid initial 18o 9 10 5 along grain boundaries fractures and deformation twin lamellae depleting calcite grains in sr and enriching them in mn and fe the sample is characterised by gross isotopic and elemental disequilibrium with important implications for the application of chromatographic theory to constrain fluid fluxes in metacarbonate rocks

a juvenile oceanic island arc origin for the archean ca 2 97 ga fiskenaesset anorthosite complex southwestern greenland evidence from oxygen isotopes abstract the archean ca 2 97 ga fiskenaesset layered intrusion southwestern greenland consists of an association of anorthosite leucogabbro gabbro hornblendite pyroxenite peridotite and dunite the intrusion is characterized by well preserved igneous layering cumulate texture and primary igneous minerals including olivine pyroxene plagioclase hornblende and chromite we use new whole rock n 36 and mineral n 32 oxygen isotopic data for all major lithologic units from the best preserved stratigraphic section of the fiskenaesset complex at majorqap q va to revisit geodynamic and petrogenetic hypotheses proposed for the origin of archean terranes the fiskenaesset complex has modern mantle like whole rock o isotope compositions o 18 5 8 0 5 average o 18 values increase from peridotite o 18 5 0 through hornblendite o 18 5 7 gabbro o 18 5 8 pyroxene hornblendite o 18 6 0 and leucogabbro o 18 6 3 to anorthosite o 18 6 3 these whole rock isotopic compositions reflect the approximate modal abundances of olivine average o 18 4 9 hornblende average o 18 5 7 clinopyroxene average o 18 6 4 and plagioclase average o 18 6 4 in each rock type as a consequence of mineral fractionation in the magma chamber s field relationships and the absence of crustal contamination suggest that the fiskenaesset complex formed in an oceanic setting subduction zone like whole rock trace element signatures and mantle like o 18 and initial e nd values are consistent with formation of these rocks in a juvenile oceanic island arc setting field and geochemical data from the fiskenaesset region and adjacent terranes suggest that the origin of archean crust in southwestern greenland is consistent with phanerozoic like plate tectonic processes rather than density driven sinking delamination and diapiric processes requiring formation of greenstone belts and anorthosite complexes on pre existing continental crust mantle like o 18 values in the ca 2 97 ga fiskenaesset complex are inconsistent with substantial recycling of continental crust indicating that the fiskenaesset rocks originated distal from continental sources

nitrogen isotope fractionations during progressive metamorphism a case study from the paleozoic cooma metasedimentary complex southeastern australia abstract the well studied paleozoic cooma metamorphic complex in southeastern australia is characterized by a uniform siliciclastic protolith of uniform age with a continuous range of metamorphic grade from subgreenschist to upper amphibolite facies and migmatite grade in an annular pattern around the cooma granodiorite those conditions are optimal for investigating variations of n concentrations and 15 n values during progressive metamorphism nitrogen concentrations decrease and 15 n increases with increasing metamorphic grade sub chlorite zone 120 ppm n 15 n 2 3 chlorite zone 110 ppm n 15 n 3 0 biotite and andalusite zone 85 ppm n 15 n 3 8 sillimanite and migmatite zones 40 ppm n 15 n 10 7 covariation of k and n contents is consistent with n substituting for k as nh 4 in micas observed trends of increasing 15 n values with decreasing nitrogen concentrations can be explained by a continuous release of nitrogen depleted in 15 n with progressive metamorphism which causes an enrichment of 15 n in the residual nitrogen of the rock equilibrium models for rayleigh distillation and batch volatilisation for data of the greenschist and amphibolite facies metasedimentary rocks can be explained by n 2 nh 4 exchange at temperatures of 300 600 c whereas observed large fractionations for the upper amphibolite facies and melt products in the migmatite grade samples may be interpreted as nh 3 nh 4 exchanges at temperature of 650 730 c lower values in the highest grade zones may also stem in part from input of 15 n depleted fluids from the granodiorite the magnitude of isotope fractionation of nitrogen is about 1 2 during progressive metamorphism of metasedimentary rocks from sub chlorite zone to biotite andalusite zone which is consistent with previous studies consequently the large spread of 15 n values in archean greenschist facies metasedimentary rocks of 6 to 30 can be accounted for by variable mixtures of mantle plume dominated volatiles with a 15 n of 5 and a 15 n enriched marine sedimentary kerogen component inherited from a ci chondrite veneer having 15 n of 30 to 42

coupled deformation and metamorphism in the roof of a tabular midcrustal igneous complex the 370 377 ma mooselookmeguntic igneous complex was emplaced at 14 km depth into steeply dipping metaturbidites that were folded and metamorphosed ca 400 405 ma during the acadian orog eny gravity and drill hole data isograd geometry thermal modeling and struc tural measurements all indicate that the eastern aureole of the complex represents an areally extensive roof above the gently east dipping tabular shaped intrusion this roof preserves a classic example of low pressure high temperature metamorphism caused by the underlying intrusion ther mal modeling indicates that the roof is no more than 1000 m thick over an area exceed ing 100 km2 unlike other roofs described in the literature the mooselookmeguntic igneous complex roof preserves a thick 600 m emplacement related strain gradi ent with a deformational fabric that evolved through all stages of crenulation cleavage to become an intense nondifferentiated folia tion approximately parallel to the intrusive contact and perpendicular to the steeply dip ping regional acadian age foliation fabric evolution through all stages of crenulation cleavage requires the vertical growth of the tabular intrusion to have been largely accommodated by dissolution precipitation creep which is a linear viscous deformation mechanism that can occur at lower differ ential stress than for example dislocation creep as the crenulation cleavage evolves a stage is reached where further deformation requires a change in deformation mecha nism which may lead to hardening of the rock development of crenulation cleavage requires a mica rich foliation at an initially high angle to the emplacement related fl at tening plane and this confi guration may be the primary reason why the strain aureole in the mooselookmeguntic igneous complex roof is so well developed compared to other published examples of midcrustal roofs

reference data set of volcanic ash physicochemical and optical properties uncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts in this study we provide a dataset that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents 50 80 wt sio2 we measured and calculated parameters describing the physical size distribution complex shape and dense rock equivalent mass density chemical bulk and surface composition and optical complex refractive index from ultra violet to near infrared wavelengths properties of the volcanic ash and classified the samples according to their sio2 and total alkali contents into the common igneous rock types basalt to rhyolite we found that the mass density ranges between 2 49 and 2 98 g cm3 for rhyolitic to basaltic ash types and that the particle shape varies with changing particle size d 100 m the complex refractive indices in the wavelength range between 300 nm and 1500 nm depends systematically on the composition of the samples the real part values vary from n 1 38 to 1 66 depending on ash type and wavelength and the imaginary part values from k 0 00027 to 0 00268 we place our results into the context of existing data and thus provide a comprehensive dataset that can be used for future and historic eruptions when only basic information about the magma type producing the ash is known

ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites diffusive exchange as a guide to cooling history ion microprobe analysis of magnetites from the adirondack mountains ny yields oxygen isotope ratios with spatial resolution of 2 8 m and precision in the range of 1 1 sigma these analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of 18o at this scale high precision micro analyses of this sort will permit wide ranging new applications in stable isotope geochemistry the analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite magnetites are near to fe3o4 in composition and optically and chemically homogeneous a combination of ion probe plus conventional brf5 analysis shows that individual grains are homogeneous with 18o 8 9 1 smow from the core to near the rim of 0 1 1 2 mm diameter grains depth profiling into crystal growth faces of magnetites shows that rims are 9 depleted in 18o these low 18o values increase in smooth gradients across the outer 10 m of magnetite rims in contact with calcite these are the sharpest intracrystalline gradients measured to date in geological materials this discovery is confirmed by bulk analysis of 150 350 m diameter magnetites which average 1 2 lower in 18o than coarse magnetites due to low 18o rims conventional analysis of coexisting calcite yields 18o 18 19 suggesting that bulk 18o cc mt 9 3 and yielding an apparent equilibration temperature of 525 c over 200 c below the temperature of regional metamorphism consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories the data for oxygen in calcite under hydrothermal conditions at high p h2o indicates that diffusion is faster in magnetite and modelling of the low 18o rims on magnetite would suggest that the adirondacks experienced slow cooling after grenville metamorphism followed by a brief period of rapid cooling possibly related to uplift conversely the data for calcite at low p h2o show slower oxygen diffusion than in magnetite modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals suggesting that the low 18o rims form by exchange with late low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets in either case the ion microprobe results indicate that two distinct events are recorded in the post metamorphic exchange history of these magnetites recognition of these events is only possible through microanalysis and has important implications for geothermometry

ten years of marine csem for hydrocarbon exploration marine controlled source electromagnetic csem surveying has been in commercial use for predrill reservoir appraisalandhydrocarbonexplorationfor10 years althougha recent decrease has occurred in the number of surveys and publications associated with this technique the method has become firmly established as an important geophysical tool intheoffshoreenvironment thisisaconsequenceoftwoimportant aspects associated with the physics of the method first it is sensitive to high electrical resistivity which although not an unambiguous indicator of hydrocarbons is an important property of economically viable reservoirs second although the method lacks the resolution of seismic wave propagation it has a much better intrinsic resolution than potential field methods such as gravity and magnetic surveying which until now have been the primary nonseismicdatasetsusedinoffshoreexploration althoughbymany measures marine csem is still in its infancy the reliability and noise floors of the instrument systems have improved significantly over the last decade and interpretation methodology has progressed from simple anomaly detection to 3d anisotropic inversion of multicomponent data using some of theworld sfastestsupercomputers researchdirectionspresently include tackling the airwave problem in shallow water by applying time domain methodology continuous profiling tools and the use of csem for reservoir monitoring during production

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

fluid rock interactions during ultra high pressure metamorphism dabie shan china oxygen isotope analyses of garnet separates and whole rock samples of gneiss and marble hosted eclogites from the ultra high pressure uhp dabie shan terrain fall in the range 6 76 to 10 76 comparison of the isotopic compositions of the eclogites with those of their host rocks leads to the following conclusions 1 the basaltic protolith of the eclogites had isotopic compositions in the range 2 15 to 4 99 it is proposed that this is the result of contamination of the parent basaltic magma with hydrothermally altered18o depleted source materials 2 18o enriched eclogite compositions resulted from local scale 3 m interaction between this basaltic eclogite protolith and fluids produced by decarbonation of impure marble lithologies during uhp metamorphism 3 18o depleted eclogite and gneiss compositions resulted from regional scale meteoric hydrothermal alteration of the basalts and their host rocks prior to uhp metamorphism epidote separates and whole rocks from the cores and rims of mineralogically zoned eclogite boudins within amphibolite grade biotite gneisses show no distinct isotopic differences this suggests that the preferential recrystallisation of the gneisses and the associated amphibolite grade overprint of the rims of eclogite bodies could not have resulted from regional scale infiltration of significant volumes of fluid during the exhumation of the dabie shan terrain

stable c o and s isotope record of magmatic hydrothermal interactions between the faleme fe skarn and the loulo au systems in western mali the gara yalea and gounkoto au deposits of the 17 moz loulo mining district largely hosted by the kofi series metasediments are located several kilometers to the east of the 650 mt fe skarn deposits in the adjacent faleme batholith the au deposits are interpreted to have formed through phase separation of an aqueous carbonic fluid which locally mixed with a hypersaline brine of metaevaporite origin recognition of an intrusive relationship between the faleme batholith and kofi series opens the possibility that the fe skarns and au deposits are part of the same mineral system in this paper we combine new 13c 18o and 34s data from the karakaene ndi skarn au occurrences along the western margin of the kofi series and zircons within plutonic rocks of the faleme batholith we combine these with existing data from the loulo au deposits to model the contribution of magmatic volatiles to au mineralization c and o isotope compositions of auriferous carbonate quartz sulfide veins from the loulo au deposits have wide ranges 13c 21 7 to 4 5 and 18o 11 8 to 23 2 whereas values from carbonate veins in kofi series au prospects close to the faleme batholith and the karakaene ndi fe skarn deposit have more restricted ranges 13c 16 8 to 3 7 18o 11 4 to 17 2 and 13c 3 0 1 18o 12 6 1 respectively kofi series dolostones have generally higher isotopic values 13c 3 1 to 1 3 and 18o 19 1 to 23 3 pyrite from kofi series au prospects adjacent to the faleme batholith have a wide range of 34s values 4 6 to 14 2 similar to pyrite from the karakaene ndi skarn 2 8 to 11 9 whereas 34s values of pyrite and arsenopyrite from the loulo deposits are consistently 6 comparison of the c and o isotope data with water rock reaction models indicates the loulo au deposits formed primarily through unmixing of an aqueous carbonic fluid derived from the devolatilization of sedimentary rocks with an organic carbon component isotopic data are permissive of the hypersaline brine that enhanced this phase separation including components derived from both kofi series evaporite horizons interlayered with the dolostones and a magmatic hydrothermal brine this magmatic hydrothermal component is particularly apparent in o c and s isotope data from the gara deposit and au prospects immediately adjacent to the faleme batholith

ion microprobe study of marble from naxos greece grain scale fluid pathways and stable isotope equilibration during metamorphism in metamorphic terranes modification of the stable isotope compositions of marbles by fluid infiltration has been extensively modeled to try to constrain both the magnitudes and time scales of metamorphic fluid fluxes we have made a study of key localities on the aegean island of naxos greece in which we combined textural observations with micro scale trace element and stable isotope analysis to test the assumptions upon which modeling of metamorphic fluid flow is based and to identify fluid transport mechanisms integration of ion microprobe analyses of 18 o 16 o 13 c 12 c mn and fe with detailed cathodoluminescence imaging provides evidence that water rich fluids were channeled along cracks and grain boundaries within marble with limited equilibration between the fluid and rock very low values of 18 o smow down to 2 along grain boundaries indicate a meteoric source for fluids rather than a metamorphic source in contrast to previous studies in this example the simplifying assumptions made previously in chromatographic theory to constrain metamorphic fluid fluxes time scales and porosities from bulk isotope data are incorrect by making micro scale measurements we can determine infiltration mechanisms and distinguish separate fluid flow events these observations and measurements provide a basis for constructing more realistic models of metamorphic fluid flow

albedo of dirty snow during conditions of melt the evolution of spectrally averaged albedo wavelengths between 0 28 m and 2 8 m of snow surfaces treated with known initial concentrations of particles of submicron sized soot and air fall volcanic ash was investigated during conditions of natural melt depending on the particle type and concentration the initial applications reduced the surface albedo to values ranging from 0 18 to 0 41 which were substantially lower than the albedo of the untreated natural snow about 0 61 many of the soot particles flushed through the snowpack with the meltwater and surface concentrations of soot greater than about 5 10 7 kg kg did not persist for more than a few days the migration of particles to depth caused the snow to brighten after the initial application thus limiting the amount of albedo reduction and the consequent effects on melting nevertheless the soot remaining near the surface had a substantial long term effect the residual concentration of 5 10 7 kg kg persisted for several weeks and compared to the untreated surface reduced the albedo by about 30 and increased melting by 50 particles of volcanic ash with diameters larger than about 5 m remained at or near the snow surface although many of the smaller particles flushed through the snow with the meltwater the surface albedo was not changed significantly by their removal the different behaviors of the ash and soot are probably related to the difference in their particle size distributions in relation to the thickness of water films that form the transport paths under conditions of partial saturation that are characteristic of melting snow

ion microprobe analysis of oxygen isotope ratios in quartz from skye granite healed micro cracks fluid flow and hydrothermal exchange quartz grains in hydrothermally altered granites from the isle of skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 m scale ion microprobe analysis of one grain shows a gradient of 13 over 400 m and a greater range in 18o than all quartz previously analyzed on the isle of skye other crystals from the same outcrop are homogeneous digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable the ion probe analysis correlates low 18o values on a micro scale to one set of healed cracks thus quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures in contrast to more reactive feldspar that appears to exchange from the grain boundary inward macroscopic models of isotope exchange are not realistic for these rocks the flow of hydrothermal fluids was heterogeneous anisotropic and crack controlled

the correlation of reaction and isotope fronts and the mechanism of metamorphic fluid flow infiltration of a metabasite sill from islay scotland by an h2o co2 fluid caused 1 modification of delta 18 o and 2 carbonation at the sill margins maps of delta 18 o and reaction progress were constructed from a 20 x 47 7 metre sample grid across

a preliminary stable isotope study on mogok ruby myanmar the primary occurrence of ruby in the mogok area northern myanmar is exclusively found in marble along with spinel forsterite bearing marble and phlogopite graphite marble these marble units are enclosed within banded biotite garnet sillimanite oligoclase gneisses samples of these marbles collected for c o stable isotope analysis show two trends of 13c 18o variation resulting most likely from fluid rock interactions ruby bearing marble and phlogopite graphite marble followa trend with coupled c o depletion whereas spinel forsterite bearing marble follows a 18o depletion trend with relatively constant 13c values ruby formation might have resulted from co2 rich fluid rock interaction while spinel forsterite bearing marble was genetically related to co2 poor fluid rock interaction both fluids may have arisen from external sources based on graphite raman spectral thermometry the estimated temperature for phlogopite graphite marble and probably ruby bearing marble was lower than 607 c and for spinel forsterite bearing marble lower than 710 c contrasting c o diffusion between graphite ruby spinel forsterite and calcite local variations of isotopic compositions of newly formed minerals as a result of non pervasive fluid infiltration and open system isotopic disturbance during cooling may have affected c o isotopic fractionations between minerals the estimated high formation temperatures for ruby and spinel forsterite imply that the parental fluidsmay have been related to nearby igneous intrusions and or metamorphic processes whether these two types of fluid were genetically related is unclear based on the present data

is the lomagundi event present on the rae craton a case study from the murmac bay group shortly after the initial rise of atmospheric oxygen in the paleoproterozoic era a major perturbation occurred in the global carbon cycle which is manifested as a long lived positive carbon isotope excursion recorded in 2 22 2 06 ga carbonate rocks known as the lomagundi event beyond its significance for evolving seawater composition this geochemical event can be used as an indirect age marker in paleoproterozoic sedimentary successions documenting further occurrences of this event in other paleoproterozoic carbonate rocks confirms that the event was global and reflects ambient seawater composition this event however has only been documented in two successions in canada despite the ubiquity of paleoproterozoic aged rocks on the canadian shield our study focuses on metacarbonate rocks from the paleoproterozoic aged murmac bay group on the southwestern margin of the rae craton in northern saskatchewan measured 13c values up to 7 8 fall within the range of the lomagundi event but most value

diffusion in carbonates fluorite sulfide minerals and diamond this chapter focuses on diffusion in non silicate minerals that do not fall under any of the other chapter categories this includes minerals that are not oxides fluorite sulfide minerals diamond and those like the carbonates that are not among the oxide minerals discussed in chapter 17 of this volume van orman and crispin 2010 although there are numerous minerals in these categories limited diffusion data exist for many of them so the primary phases that will be considered are carbonates fluorite diamond and sulfide minerals carbonate minerals are major constituents of sediments and many sedimentary rocks fractionation of o and c isotopes between carbonate rocks and fluids can provide insight into paleoclimates and sedimentary histories the behavior of the isotopes of major elements in calcite and aragonite has become of increasing interest due to the important role of co2 and carbonate dissolution precipitation in the oceans and the connections to global climate e g arita and wada 1990 chacko et al 1991 dickson 1991 beck et al 1992 cole 1992 graham et al 1998 cole and chakraborty 2001 ca mg diffusion rates affect the process of dolomitization hardie 1987 fisler and cygan 1999 and characterization of diffusion of these species is important for refinements in application of the calcite dolomite geothermometer e g essene 1982 farver and yund 1996 and better understanding of deformation mechanisms for example calcium isotopic fractionation between seawater and calcite and aragonite has been observed in marine samples zhu and macdougall 1998 de la rocha and depaolo 2000 schmitt et al 2003 with possible applications as a thermometer ca isotopic fractionation also occurs in biologic systems as in the growth of foraminifera skulan et al 1997 zhu and macdougall 1998 diffusion of major elemental species plays an important rate limiting

ophicalcites from the northern pyrenean belt a field petrographic and stable isotope study brecciated and fractured peridotites with a carbonate matrix referred to as ophicalcites are common features of mantle rocks exhumed in passive margins and mid oceanic ridges ophicalcites have been found in close association with massive peridotites which form the numerous ultramafic bodies scattered along the north pyrenean zone npz on the northern flank of the pyrenean belt we present the first field textural and stable isotopic characterization of these rocks our observations show that pyrenean ophicalcites belong to three main types 1 a wide variety of breccias composed of sorted or unsorted millimeter to meter sized clasts of fresh or oxidized ultramafic material in a fine grained calcitic matrix 2 calcitic veins penetrating into fractured serpentine and fresh peridotite and 3 pervasive substitution of serpentine minerals by calcite stable isotopic analyses o c have been conducted on the carbonate matrix veins and clasts of samples from 12 pyrenean ultramafic bodies we show that the pyrenean ophicalcites are the product of three distinct genetic processes 1 pervasive ophicalcite resulting from relatively deep and hot hydrothermal activity 2 ophicalcites in veins resulting from tectonic fracturing and cooler hydrothermal activity and 3 polymictic breccias resulting from sedimentary processes occurring after the exposure of subcontinental mantle as portions of the floor of basins which opened during the mid cretaceous we highlight a major difference between the eastern and western pyrenean ophicalcites belonging respectively to the sedimentary and to the hydrothermal types our data set points to a possible origin of the sedimentary ophicalcites in continental endorheic basins but a post depositional evolution by circulation of metamorphic fluids or an origin from relatively warm marine waters cannot be ruled out finally we discuss the significance of such discrepancy in the characteristics of the npz ophicalcites in the frame of the variable exhumation history of the peridotites all along the pyrenean realm

linking of regional and local hydrothermal systems in the mid crust by shearing and faulting abstract the concentration of mass during regional metamorphism and metallogenesis requires interactions between regional and local hydrothermal systems that are scale and time dependent during regional low to medium temperature metamorphism in which fluid flow is driven by broad thermal or mechanical gradients fluid flow rates are on average 8 m s and are limited by restricted permeabilities and gentle gradients in hydraulic head in contrast coseismic fluid flow rates in major fault zones may reach 10 2 m s as a consequence there may be a limited capacity for individual faults to substantially control fluid flow in the region because of the large contrast in flow rates and permeabilities between faults and low permeability rocks to produce a major epigenetic ore deposit in overpressured crust fluid flow systems with such diverse flow rates must interact in such a way that metal dissolution and transport from regional fluid flow systems culminate in focused fluid flow with metal deposition this is best achieved through two steps one in which km scale hydrothermal systems channel into 100 m scale ductile shear zones largely by reaction and deformation enhanced permeability in the shear zone and a second one in which rapid fluid pressure changes accompanying brittle faulting or intense shearing within the broader shear zones causes metal deposition and ore genesis

decorative marbles from the krkonose jizera terrane bohemian massif czech republic provenance criteria marbles from western part of the krkonose jizera terrane northern part of the bohemian massif have been studied to obtain mineropetrographic and chemical reference data for provenance studies samples from six different quarries were analysed by mineralogical petrographic and geochemical methods optical microscopy x ray diffraction stable isotope ratio analysis cathodoluminescence bulk magnetic susceptibility petrographic characteristics permit a distinction between fine grained to medium grained marbles from the jizera mts amphibolite metamorphic facies and fine grained marbles from the jest d mts low grade greenschist facies the samples studied are mainly calcitic with the exception of those from raspenava in which dolomite is abundant in two types the mineralogical composition of the insoluble residues is clinochlore serpentine tremolite diopside pyrite magnetite in case of the locality raspenava and clinochlore muscovite quartz pyrite rutile haematite in case of the localities from the jest d mts 13c and 18o variations in primary and secondary carbonate phases allow to distinguish genetically different carbonate veins and permit quarry separation in one case raspenava jizera mts the 13c and 18o values of the groundmass range from 1 to 3 and from 8 to 20 pdb respectively the 13c and 18o values of secondary carbonate veins decrease to 3 and reach more negative values up to 26 in case of 18o the fabric of cathodomicrofacies allows the distinction between calcite and dolomite except three localities pilinkov horni hanychov jitrava rose type with majority of quenchers high content of iron in carbonate the genetically different calcite is characterised by a pale and dark orange luminescence distribution serpentine tremolite forsterite opaque minerals and quartz have no luminescence and very dull luminescence respectively the majority of studied marbles exhibits low values of the bulk magnetic susceptibility with the exception of those from raspenava rich in magnetite

natural constraints on metamorphic reaction rates abstract quantitative constraints on the rates at which metamorphic reactions proceed in nature are now available from several sources most common are predictions made on the basis of laboratory kinetic data however the applicability of such laboratory based predictions has long been questioned and many observations in the field now suggest much slower rates here published quantitative field based constraints on high temperature 400 c reaction rates are assembled from a variety of sources reaction rates attending regional metamorphism are four to seven orders of magnitude slower than most laboratory based predictions a general rate law for regional metamorphism has been derived which best describes these field based data log 10 r net 0 0029 t 9 6 1 where r net is the net reaction rate g cm 2 a and t is temperature c at the same time natural reaction rates attending contact metamorphism differ from laboratory based predictions by less than two orders of magnitude and are in close agreement at higher temperatures thus while existing laboratory based kinetic data may be judiciously applied to some contact metamorphic systems laboratory based kinetic predictions clearly misrepresent regional metamorphism to explain this kinetic discrepancy regional metamorphic reaction rates may be limited by slow intergranular transport due to comparatively limited or transient availability of aqueous fluid in the intergranular medium the general field based rate law may be applied to regional metamorphic and other environments i e ultrahigh pressure or ultrahigh temperature metamorphism if similar system characteristics mainly low aqueous fluid content can be inferred

microscale isotopic zoning in calcite and graphite crystals in marble chemical and isotopic zoning in minerals is a clear indication of disequilibrium and provides an important key for elucidating metamorphic processes here i present carbon and oxygen isotope data from calcite and graphite crystals in a marble from the hida metamorphic belt central japan showing isotopic zoning within individual crystals within 100 m of the calcite graphite grain boundary the 13c contents gradually decrease from the constant values of the crystal core to values 1 lower 18o contents in calcite decrease by up to 7 within 200 300 jim of the boundary at a calcite calcite grain boundary similar patterns of 13c and 18o depletions were found whereas the 13c contents of graphites remained constant except in a narrow zone at the calcite contact these isotopic patterns are interpreted as reflecting isotopic exchange with metamorphic fluids that were relatively depleted in 13c and 18o these results strongly suggest that the most accurate geothermometry will be obtained if only the cores of crystals are used and that isotopic zoning may provide another way to elucidate polymetamorphic processes

palaeostress estimation using calcite twinning experimental calibration and application to nature abstract by means of high temperature deformation experiments on calcite rocks of different grain sizes we have established the relationships between differential stress and twinning incidence twin density and volume fraction and the way that these relationships depend on grain size both twinning incidence and volume fraction increase with grain size at a constant level of differential stress log twin density is proportional to stress but is independent of grain size at a given grain size volume fraction of twinning increases non linearly with differential stress twinning activity measured by twinning incidence increases linearly with stress the behaviour of each of these parameters is independent of temperature strain and strain rate these relationships can be used as a basis for the estimation of palaeostress values in naturally deformed calcite rocks this is illustrated by a study of twinning activity in limestones close to thrust faults in the cantabrian zone of the variscan orogenic belt in northwestern spain high peak differential stresses were measured ranging from 150 to 250 mpa using the turner dynamic analysis technique however it is clear that shear stresses resolved parallel to the fault planes were very low the attainment of high stress differences when the resistance to faulting was low is attributed either to bending forces induced during the motion of the non planar surfaces relative to each other or to the stress peak being attained prior to the localization of deformation onto the fault surfaces

are stable isotopic trends in amphibolite to granulite facies transitions metamorphic or diagenetic an answer for the arendal area bamble sector southeastern norway from mid proterozoic carbon bearing rocks the isotopic 3 i3 c and 3 18 0 compositions of primary marbles and secondary veins calcites and primary fahlbands and metapelites and secondary veins graphites sampled across the am phibolite to granulite facies transition in the bamble sector southeast ern norway have been investigated the primary calcites display a regional trend in a 3 i3c 3i80 plot which is the reverse of the expected trend the granulite grade primary calcites essentially preserved most of their initial sedimentary compositions whereas the amphibolite grade calcites have increasingly lower 3 i3 c values the 3 18 0 composi tions of amphibolite grade primary calcites and of some vein tlpes appear to be buffered by the o reservoir of the country rock the 3 1 c of graphite of different types is specific for a certain lithology but not spatially related to the metamorphic zoning reaction progress calculations and rayleigh fractionation model ling prove that prograde metamorphic decarbonation reactions alone cannot be held responsible for the isotopic trend in the marbles the reversed isotopic trend in the marbles themselves combined with the lack of any trend in the primary graphites is not compatible with pervasive flushing with a homogeneous mantle derived co2 rich fluid at granulite facies metamorphism the marble trend and the constant 3 i3 c composition of j rimary graphite throughout the metamorphic zoning are best explamed by low grade processes that did affect the stable isotopic compositions of the marbles but left the graphites unaffected the processes may even occur under diagenetic conditions later amphibolite granulite facies metamorphism preserved the trend despite the production of calcsilicates subsequent retrograde hydro thermal action produced graphite quartz veins and several types of calcite veins without resetting stable isotope systematics on a regional scale

transient convective circulation in a sedimented ridge setting implications for applying geochemical data to estimate permeability 1 for an open sedimented ridge setting we investigate by means of transient numerical simulations hydrologic factors that can influence chemical signatures of mineral alteration and how these features relate to the permeability of the upper oceanic crust the transient state we consider involves three stages 1 starting from a static flow field and a conductive thermal regime flow in basement rocks is initiated as unstable convection 2 with the inflow of seawater to the basement the convection pattern evolves into a stable convection cell linking the recharge and discharge sites on the seafloor and 3 convection weakens through time as the system offsets the initial thermal condition to attain a steady state the duration of each stage and the extent of the region in the basement undergoing fluid exchange with seawater varies with permeability by the end of stage 2 for basement permeabilities between 1 10 14 and 1 10 13 m 2 most of the basement and the deeper sediments surrounding the discharge zone is hydrologically isolated but with active recirculation inside this zone through flow of seawater is restricted to a relatively narrow boundary layer the unstable flow geometry during stages one and two is reflected in fluctuations of recharge and discharge rates into and out of the basement and periodic variations in temperature of the discharging fluids fluid discharge at steady state is approximately one half of the average occurring during stage one changing flow patterns through time lead to a strongly heterogeneous evolution of water rock ratios in the basement average water rock ratios for the basement approach a log log linear correlation with basement permeability as steady state is reached

relationship between footwall composition crustal contamination and fluid rock interaction in the platreef bushveld complex south africa in the northern limb of the 2 06 ga bushveld complex the platreef is a platinum group elements pge cu and ni mineralized zone of pyroxenite that developed at the intrusion margin from north to south the footwall rocks of the platreef change from archaean granite to dolomite hornfels and quartzite where the footwall is granite the sr isotope system is more strongly perturbed than where the footwall is sr poor dolomite in which samples show an approximate isochron relationship the nd isotope system for samples of pyroxenite and hanging wall norite shows an approximate isochron relationship with an implied age of 2 17 0 2 ga and initial nd isotope ratio of 0 5095 assuming an age of 2 06 ga the nd values range from 6 2 to 9 6 ave 7 8 n 17 and on average are slightly more negative than the main zone of the bushveld these data are consistent with local contamination of an already contaminated magma of main zone composition the similarity in isotope composition between the platreef pyroxenites and the hanging wall norites suggests a common origin where the country rock is dolomite the platreef has generally higher plagioclase and pyroxene 18o values and this indicates assimilation of the immediate footwall throughout the platreef there is considerable petrographic evidence for sub solidus interaction with fluids and the plagioclase pyroxene values range from 2 to 6 which indicates interaction at both high and low temperatures whole rock and mineral d values suggest that the platreef interacted with both magmatic and meteoric water and the lack of disturbance to the sr isotope system suggests that fluid rock interaction took place soon after emplacement where the footwall is granite less negative d values suggest a greater involvement of meteoric water consistently higher values of plagioclase pyroxene in the platreef pyroxenites and hanging wall norites in contact with dolomite suggest prolonged interaction with co2 rich fluid derived from decarbonation of the footwall rocks the overprint of post crystallization fluid rock interaction is the probable cause of the previously documented lack of correlation between pge and sulfide content on the small scale the platreef in contact with dolomite is the focus of the highest pge grades and this suggests that dolomite contamination played a role in pge concentration and deposition but the exact link remains obscure it is a possibility that the co2 produced by decarbonation of assimilated dolomite enhanced the process of pge scavenging by sulfide precipitation

migration of reaction and isotopic fronts in infiltration zones assessments of fluid flux in metamorphic terrains abstract criteria are presented for recognising fluid infiltration driven reactions in metamorphic rocks and quantifying the associated fractionations of oxygen and carbon isotopic compositions in medium or high grade metamorphic rocks with local equilibrium between fluid and solid phases reactions or isotopic changes driven by infiltrating fluid are expected to migrate as relatively sharp fronts with limited diffusive broadening fluid leaving such reaction fronts is compositionally buffered by the reacting phases in suitably reactive rocks a series of reaction fronts will develop each driven by infiltration of fluid buffered by the upstream reaction knowledge of the spatial arrangement of such fronts allows calculation of the time integrated fluid fluxes total fluid volume per unit area distinctive stable isotope fractionations are predicted adjacent to infiltration driven reactions with the distribution and magnitude of the fractionation effects dependent upon the relative velocities of the reaction and isotopic fronts the various possibilities are illustrated by reference to a hypothetical infiltration driven decarbonation reaction the calculated isotopic fractionations do not in general resemble those predicted by the open or closed system water rock ratio calculations

optical properties of the ash from el chichon volcano we have measured visible wavelength optical properties of the ash from the 1982 el chichon eruptions these measurements were made on ash samples collected at three surface sites at distances between 12 and 80 km from the volcano the most distant sample is taken as most representative of the silicate ash injected into the stratosphere the measured optical properties are expressed as a complex refractive index n with the aerosol absorption expressed as the imaginary component of the refractive index nim each of these samples showed quite low values of absorption with nim at 500 nm ranging from 1 5 10 3 for the 12 km sample to 1 0 10 3 for the 80 km sample based on these measurements we estimate that n for the stratospheric silicate ash is given by n 1 53 0 001i

the origin of chlorite tremolite carbonate rocks associated with the thalanga volcanic hosted massive sulfide deposit north queensland australia the thalanga polymetallic massive sulfide deposit is hosted by felsic volcanics of the cambro ordovician mount windsor subprovince in north queensland the sheetlike sulfide deposit consists of several semiconnected lenses totaling 6 6 million metric tons mt which lie at a single stratigraphic level between underlying subaqueously emplaced rhyolite and overlying dacitic to andesitic lavas sills and volcaniclastic rocks the ores and host rocks have been deformed and metamorphosed to upper greenschist facies associated with the west thalanga orebody are strata bound lenses composed of chlorite tremolite dolomite and calcite that previously have been interpreted as exhalites they extend up to a few hundred meters along the mineralized horizon and locally also exist in the stratigraphic footwall around the fringes of the deposit rhyolitic volcanics beneath the deposit are extensively altered a pervasive sericite chlorite pyrite zone that extends greater than 200 m into the footwall envelops semistratiform proximal quartz pyrite chlorite stringer zones major and trace element geochemical data indicate that zr ti and al remained essentially immobile in the footwall rocks despite intense hydrothermal alteration involving significant mass transfers of mobile elements the chlorite tremolite carbonate assemblages associated with ore lenses have immobile element ratios identical to those of the altered rhyolites carbonate rich assemblages retain some relict spheroidal and rhombic textures in dolomite which suggest formation at an early hydrothermal stage in a matrix of chlorite or in open spaces the chlorite tremolite carbonate rocks probably represent metamorphic equivalents of hydrothermal chlorite quartz dolomite calcite or mg smectite quartz dolomite calcite assemblages the formation of tremolite by metamorphic reaction of quartz and dolomite is consistent with regional metamorphic conditions with allowance for metamorphic decarbonation carbon and oxygen isotope data from dolomite and calcite are consistent with precipitation of primary dolomite at 170 to 250 c from seawater dominated fluid the chlorite tremolite carbonate rocks at thalanga are consequently reinterpreted as altered rhyolitic volcaniclastics containing variable proportions of hydrothermal carbonate they probably formed in a zone of mixing of hydrothermal fluid and seawater in a permeable substrate close to the paleosea floor siliceous ironstones that are present in distal parts of some thalanga ore lenses have very low immobile element contents and are probably true exhalites

fluid rock history of granulite facies humite marbles from ambasamudram southern india an extensive humite bearing marble horizon within a supracrustal sequence at ambasamudram southern india was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics at peak metamorphic temperatures of 775 73 c based on calcite graphite carbon isotope thermometry the mineral assemblages suggest layer by layer control of fluid compositions clinohumite calcite bearing assemblages suggest xco2 0 9 at 790 c and local wollastonite scapolite grossular bearing zones formed at xco2 of c 0 3 retrograde reaction textures such as scapolite quartz symplectites after feldspar and calcite and replacement of dolomite diopside or tremolite dolomite after calcite forsterite or calcite clinohumite are indicative of retrogression under high xco2 conditions calcite preserves late proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting isotopic zonation of calcite and graphite grains was likely produced by localized co2 fluid infiltration during retrogression contrary to the widespread occurrence of humite marbles related to retrograde aqueous fluid infiltration the ambasamudram humite marbles record a prograde to peak metamorphic humite formation and retrogression under conditions of low xh2o

aerosol radiative forcing from the 2010 eyjafjallajokull volcanic eruptions although the 2010 volcanic eruptions of eyjafjallajokull did not exert a large climate forcing several features of their emissions favored weaker aerosol cooling or stronger warming than commonly attributed to volcanic events these features include a high ratio of fine ash to so2 occurrence near reflective surfaces exposed to strong insolation and the production of very little stratospheric sulfate we derive plausible ranges of optical properties and top of atmosphere direct radiative forcing for aerosol emissions from these events and find that shortwave cooling from sulfate was largely offset by warming from ash deposition to cryospheric surfaces and longwave warming from atmospheric ash and sulfate shortwave forcing from atmospheric ash was slightly negative in the global mean under central estimates of optical properties though this forcing term was uniquely sensitive to the simulated distribution of clouds the forcing components sum to near climate neutral global mean 2010 instantaneous 1 9 mwm 2 and effective 0 5 mwm 2 radiative forcing where the latter is elevated by high efficacy of snow deposited ash ranges in net instantaneous 7 3 to 2 8 mwm 2 and effective 7 2 to 4 9 mwm 2 forcing derived from sensitivity studies are dominated by uncertainty in ash shortwave absorptivity forcing from airborne ash decayed quickly while sulfate forcing persisted for several weeks and ash deposits continued to darken snow and sea ice surfaces for months following the eruption despite small global forcing monthly averaged net forcing exceeded 1 wm 2 in some regions these findings indicate that ash can be an important component of climate forcing from high latitude volcanic eruptions and in some circumstances may exceed sulfate forcing

estimation of seafloor electromagnetic receiver orientation abstractif the orientation of a seafloor electromagnetic em instrument is unknown it has to be estimated afterwards relatively early in the processing here we present a method to estimate the horizontal and vertical orientation of seafloor electromagnetic receivers three component magnetic recordings of the naturally occurring magnetotelluric field are utilized to find the tilt pitch and azimuth angle relative to a given reference estimation of angles is controlled by minimum difference criteria precautionary measures are necessary to eliminate the subsurface response in the recordings of the em field components the proposed method is applied to synthetic and real data demonstrating that even in difficult geologic settings the simple characteristics of the incident natural em field allow us to quickly estimate the orientation of the instruments

equilibrium dihedral angles in the system h2o co2 nacl calcite and implications for fluid flow during metamorphism fluid calcite calcite dihedral angles have been measured for fluids in the system h2o co2 nacl between 1 and 2 kbar and 550 750 c it is found that the calcite calcite h2o dihedral angle decreases steadily with addition of nacl from a value of about 80 pure water to 44 60 wt nacl the co2 h2o system displays a well defined minimum at x co 2 0 5 with a dihedral angle of 50 in contrast to those of pure co2 and h2o which are 90 and 80 respectively experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the co2 h2o nacl system which can be approximately correlated with the compositions of the two fluid phases such bimodality was only observed for immiscible fluids in the h2o nacl system if the quench rate exceeded about 200 c per min this is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching the fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with x co 2 close to 0 5 fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly h2o rich or co2 rich and of low salinity all other fluid compositions in the h2o co2 nacl calcite system will occupy isolated pores the largest of which will grow at the expense of the smallest escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture in contrast previous experimental studies of quartz fluid dihedral angles between 950 and 1100 c watson and brenan 1987 predict that quartz dominated lithologies will permit pervasive flow of h2o nacl fluids but not of h2o co2 fluids documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites psammites and limestones which support the results of the experimental studies are discussed

from jurassic shores to cretaceous plutons geochemical evidence for paleoalteration environments of metavolcanic rocks eastern california volcanic and plutonic rocks exposed in east central california record a long history of metasomatism and or metamorphism within the mesozoic cordilleran continental arc we use whole rock and mineral elemental compositions along with standard and cathodoluminescence petrography to characterize alteration histories of late triassic to middle jurassic metavolcanic rocks in the ritter range white inyo mountains and alabama hills although alkali metasomatism is widespread and pervasive ratios and abundances of ce th tb and ta suggest that mafic protoliths from the white inyo mountains were shoshonitic whereas those from the ritter range were calc alkaline alkali exchange apparently modified the compositions of many metavolcanic rocks much of this metasomatism may have occurred at low temperature t conditions and attended or shortly postdated deposition of the volcanic protoliths high 18 o values for k rich metatuffs from

stable isotope evidence of heterogeneous fluid infiltration at the ubehebe peak contact aureole death valley national park california stable isotope ratios of carbon and oxygen are used to define quantitatively the effects of magmatic fluid infiltration in marbles contact meta morphosed by the 173 ma ubehebe peak quartz monzonite death valley national park california in previous studies of fluid infiltration quantitative interpretation of aureole wide isotopic data has been difficult due to small data sets for this study sampling strategies were developed to obtain a data set that was large and unbiased enough to be statistically representative of the carbonates north of the ubehebe peak intrusion a total of 357 samples of marble were analyzed for bulk carbonate isotopic ratios separate analyses of coexisting calcite and dolomite were also obtained for an additional 31 samples unmetamorphosed samples 1900 3000 m from the intrusion have 18 o permil smow values of 25 5 0 8 1 and 13 c permil pdb values of 0 4 0 6 1 samples in the tremolite zone 750 1900 m have 18 o values ranging from 19 4 to 27 7 permil with a median value of 25 2 permil and 13 c ranges from 5 1 to 0 5 permil with a median value of 0 9 permil forsterite zone samples 0 750 m have isotopic ratios shifted to values as low as 11 1 permil 18 o and 9 1 permil 13 c despite this shift most forsterite zone samples retain sedimentary isotopic compositions with median 18 o values of 25 0 permil and 13c values of 1 2 permil 18o values for igneous minerals show no evidence for interaction with heated meteoric or metamorphic fluids the shifts in isotopic compositions within the marbles are interpreted to be the result of magmatic infiltration the effects of this infiltration were quantified by identifying samples with isotopic alteration that can only be attributed to infiltration the results show that magmatic fluid infiltration was limited in extent and very heterogeneous there is no evidence for infiltration of isotopically reactive fluids beyond 850 m from the intrusive contact and within this 850 m zone only 28 percent of the samples have been infiltratively altered with respect to 18 o and 20 percent are depleted in 13 c compositions the isotopic data when evaluated in conjunction with geostatistical and petrologic data indicate that the geometry of the hydrothermal flow system was mainly vertical and away from the pluton infiltration was restricted to large nearly vertical tube like zones of increased permeability these higher permeability zones likely reflect an initial heterogeneity of the host rocks and show no significant evidence for reaction enhanced permeability given the heterogeneity of the system and a lack of knowledge about many basic parameters controlling fluid infiltration it is shown that the best method of calculating the amount and composition of the infiltrating fluid may be a mass balance approach fluid rock ratio the application of mass balance models is discussed and shown to be valid only under limited conditions since infiltration at ubehebe peak was largely vertical the observed isotope alteration patterns represent an infiltration side and not a front because this precludes the use of traditional mass balance calculations a new infiltration side inside model is proposed that allows the isotopic data to be evaluated the inside model uses the ratio of the areal amounts of infiltrative alteration to calculate a fluid composi tion fluid amounts cannot be obtained from this model results for the ubehebe

toward the snowball earth deglaciation the current state of knowledge suggests that the neoproterozoic snowball earth is far from deglaciation even at 0 2 bars of co2 since understanding the termination of the fully ice covered state is essential to sustain or not the snowball earth theory we used an atmospheric general climate model agcm to explore some key factors which could induce deglaciation after testing the models sensitivity to their parameterizations of clouds co2 and snow we investigated the warming effect caused by a dusty surface associated with ash release during a mega volcanic eruption we found that the snow aging process its dirtiness and the ash deposition on the snow free ice are key factors for deglaciation our modelling study suggests that under a co2 enriched atmosphere a dusty snowball earth could reach the deglaciation threshold

oxygen isotope zoning in garnet a record of volatile transport abstract this study examines oxygen isotope zoning in garnets from a barrovian metamorphic terrane in eastern vermont using a co 2 laser extraction system previous strontium isotopic and structural studies of these garnets have shown that they grew over an approximately 10 ma interval during thrusting and nappe emplacement rosenfeld 1970 christensen et al 1989 our studies show that the garnets are strongly zoned in 18 o this zoning is the result of equilibration of garnet with water derived from dehydration of subjacent pelites during nappe stage deformation the magnitude and nature of 18 o zoning depends upon the garnet s location in the outcrop studied the garnets examined in this study come from an isotopically low 18 o paragonitic schist 18 o whole rock 9 that is adjacent to a relatively high 18 o schist 18 o whole rock 12 5 garnets from the paragonitic schists within 10 m of the contact with the isotopically heavier schists have relatively homogenous 18 o values varying from 9 5 in the core to 10 5 at the rim garnet in the paragonitic schists 85 m from the contact are more strongly zoned with 18 o ranging from a low of 6 0 in the cores to a high of 9 0 at the rims of the garnet these zoning patterns were produced by continuous infiltration of relatively high 18 o waters derived from the subjacent schists into the paragonitic schists during garnet grade metamorphism it is possible to determine the time integrated fluid fluxes by comparison of observed 18 o zoning profiles in garnet with those calculated from the equation describing combined advection diffusion of a tracer using this method we calculate time integrated fluid fluxes of 1 5 10 4 cm 3 cm 2 fluxes of this magnitude could have been produced by dewatering of 1 5 km of schist during garnet grade metamorphism

the accuracy of δ11b measurements of foraminifers values of 11b reported in the literature for holocene samples of the same foraminiferal species show large variability 6 relative to cited precision 1 this is indicative of significant inter laboratory biases and raises concerns about the accuracy of foraminiferal proxy ph records to investigate this problem we have measured the 11b of modern ocean carbonates using several different analytical procedures we have used total evaporation negative thermal ionisation mass spectrometry te ntims with various sample preparation and loading procedures and multi collector inductively coupled plasma mass spectrometry mc icpms the 11b of pure boric acid solutions measured by te ntims and mc icpms agree well demonstrating no fundamental biases between the techniques yet the 11b values measured by te ntims for non foraminiferal carbonates are about 2 lighter than those by mc icpms whereas foraminifers measured by the same standard te ntims procedure are 2 to 6 heavier than those by mc icpms significantly we found that foraminiferal samples kept in acidic solution over several months yielded lower 11b values up to 5 lower and better reproducibility when re measured by te ntims we infer that organic material released on foraminiferal dissolution causes biases in ntims measurements no residual organics should be present in the mc icpms measurements as matrix is separated from sample before analysis moreover we demonstrate by standard addition the absence of any matrix influence in the mc icpms procedure beyond the inherent uncertainties in the standard addition approach 0 35 2sigma degradation of the inferred organic residue either by long term storage in acidic solution or by loading samples in 30 h2o2 reduces but does not totally remove the variable bias between te ntims and mc icpms 11b measurements despite these problems careful analysis of similar samples by ntims may permit data to be obtained with consistent relative differences that still yield valuable proxy records but there is clearly considerable potential for inaccuracies to result in such an approach from hard to detect changes in matrix

origin of co2 and carbonate veins in mantle derived xenoliths in the pannonian basin the origin and evolution of co2 inclusions and calcite veins in peridotite xenoliths of the pannonian basin hungary were investigated by means of petrographic investigation and stable isotope analyses the fluid inclusions recovered in paragenetic olivine and clinopyroxene belong to distinct populations type a texturally early inclusions with regular shapes often with negative crystal forms forming intragranular trails type b texturally late inclusions defining randomly oriented trails that reach grain boundaries type b inclusions are often associated with silicate melt type c inclusions stable carbon isotope compositions in inclusion hosted co2 were obtained by vacuum crushing followed by conventional dual inlet as well as continuous flow mass spectrometry in order to eliminate possible lab artifacts olivines clino and orthopyroxenes of the host peridotite have oxygen isotope compositions from 5 3 to 6 0 relative to v smow without any relationship with xenolith texture some of the xenoliths contained calcite in various forms veins and infillings in silicate globules in veins secondary carbonate veins filling cracks and metasomatic veins with diffuse margins the former two carbonate types have 13c values around 13 relative to v pdb and low sr contents 0 5 wt whereas the third type veins with high temperature metasomatic features have a 13c value of 5 0 and high sr contents up to 3 4 wt in spite of the mantle like 13c value and the unusually high sr content typical for mantle derived carbonate trace element compositions have proven a crustal origin this observation supports the conclusions of earlier studies that the carbonate melt droplets found on peridotite xenoliths in the alkaline basalts represent mobilized sedimentary carbonate the large 13c range and the 12c enrichment in the carbonates can be attributed to devolatilization of the migrating carbonate or infiltration of surficial fluids containing 12c rich dissolved carbon carbon isotope compositions of inclusion hosted co2 range from 17 8 to 4 8 relative to v pdb with no relation to the amount of co2 released by vacuum crushing low 13c values measured by stepwise heating under vacuum suggest that the carbon component is pristine and not related to surficial contamination and that primary mantle fluids with 13c values around 5 were at least partly preserved in the xenoliths tectonic reworking and heating by the basaltic magma resulted in partial co2 release and local 13c depletion

an introduction to marine controlled source electromagnetic methods for hydrocarbon exploration early development of marine electromagnetic methods dating back about 80 years was driven largely by defense military applications and use for these purposes continues to this day deepwater frequency domain electric dipole dipole controlled source electromagnetic csem methods arose from academic studies of the oceanic lithosphere in the 1980s and although the hydrocarbon exploration industry was aware of this work the shallow water environments being explored at that time were not ideally suited for its use low oil prices and increasingly successful results from 3d seismic methods further discouraged investment in costly alternative geophysical data streams these circumstances changed in the late 1990s when both statoil and exxonmobil began modeling studies and fieldtrials of csem surveying in deep water around 1000 m or deeper specifically for characterizing the resistivity of previously identified drilling targets trials offshore angola in 2000 2002 by both these companies showed that

decomposition of electromagnetic fields into upgoing and downgoing components this paper gives a unified treatment of electromagnetic em field decomposition into upgoing and downgoing components forconductiveandnonconductivemedia wheretheelectromagneticdataaremeasuredonaplaneinwhichtheelectricpermittivity magneticpermeability andelectricalconductivityareknown constants with respect to space and time above and below the plane of measurement the medium can be arbitrarily inhomogeneousandanisotropic in particular the proposed decomposition theory applies to marine em low frequency data acquired for hydrocarbon mapping where the upgoing components of the recordedfield guided and refracted from the reservoir that are of interest for the interpretation the direct source field the refracted airwave induced by the source the reflected field from the sea surface and most magnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagneticmeasurements the viability and validity of the decomposition method is demonstrated using modeled and real marine em data also termed seabed logging sbl data the synthetic data are simulated in a model that is fairly representative of the geologic area wheretherealsblwerecollected theresultsfromthesynthetic data study therefore are used to assist in the interpretation of the realdatafromanareawith320 mwaterdepthaboveaknowngas province offshore norway the effect of the airwave is seen clearly in measured data after field decomposition just below the seabed the upgoing component of the recorded electric field has almost linear phase indicating that most of the effect of the airwavecomponenthasbeenremoved

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

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

nitrogen isotope record of fluid rock interactions in the skiddaw aureole and granite english lake district the skiddaw granite and its contact metamorphic aureole in the english lake district provide an excellent opportunity to test the capability of the n isotope system to trace devolatilization and large scale transfer of crustal fluids in the aureole skiddaw group metasedimentary rocks with relatively uniform lithology and major element compositions show a dramatic decrease in n content toward the granite contact from or 800 ppm at distances 2 5 km from the contact to 1 5 km these rocks have extremely uniform delta 15 n air near 3 7 per mil whereas closer to the contact or 1 km delta 15 n is shifted to higher values up to 8 7 per mil the coupled decreases in n content and increases in delta 15 n are compatible with the removal of n having low delta 15 n in fluids during continuous prograde devolatilization reactions involving the break down of white mica and the stabilization of biotite cordierite and andalusite bearing assemblages in the same metasedimentary rocks the lack of obvious trends in major element concentrations including sio 2 tio 2 sio 2 al 2 o 3 and the ratios of other major oxides to tio 2 and al 2 o 3 with distance from the granitic contact is consistent with minimal change in major element composition during the contact metamorphism ratios of whole rock n b rb and ba concentrations to whole rock k 2 o content are believed to reflect the differing fluid mica partitioning and involving varying relative proportions of white mica and biotite of these trace elements during devolatilization reactions greisenized skiddaw granite from a borehole is enriched in n range of 17 225 ppm for whole rocks and white mica separates relative to the unaltered granite whole rock 30 ppm and has delta 15 n of 1 0 to 4 8 per mil the n concentrations and delta 15 n of the wall rocks and greisenized granites combined with c isotopic data carbonate and carbonaceous matter for the same rocks are consistent with the mobilization of fluids having low delta 15 n and delta 13 c pdb values from the devolatilized aureole into the cooling intrusive body such transport is consistent with the predictions of recent theoretical models of late stage hydrothermal evolution in cooling intrusive systems

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

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

surface radiative impacts of ash deposits from the 2009 eruption of redoubt volcano the solar broadband albedo change surface radiative forcing and snowmelt rate associated with ash deposits based on those from the 2009 eruption of redoubt volcano were calculated using the field corroborated loadings from the fall3d and the snow ice and aerosol radiation models the optical properties of ash were calculated from mie theory using size information from the fall3d model two sizes of snow grains were used in order to simulate a young and old snowpack the results show concentrations of aerosol sized ash in snow range from 6 9 104 to 1 108 ppb for the distal edge of the deposits located 100 570 km from the vent to the vent and integrated solar albedo reductions of 0 59 for new snow and 0 85 for old snow these albedo reductions are much larger than those typical for black carbon and are of the same order of magnitude as those reported for volcanic deposits in antarctica the daily mean surface shortwave forcings associated with ash deposits on snow were 0 96 w m 2 from the most distal deposits to the near vent deposits we show that forcings caused by ash deposits can be greater than those caused by dust deposits there were no accelerated snowmelts calculated for the edges of the deposits however for areas of higher ash concentrations daily melting rates were conservatively estimated to be 140 160 higher than those of pure snow we find that ash deposits from midsized volcanic eruptions can be a major agent of deposit induced snowmelt

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

the oxygen isotope anatomy of a slowly cooled metamorphic rock the distribution of o isotope ratios in a slowly cooled metamorphic rock is investigated by a combination of ion microprobe and laser probe techniques the sample has unusually simple geometry centimeter size domains of feldspar and garnet separated by a one millimeter to one centimeter thick layer of millimeter size magnetite grains isotopic zonation at two different scales is documented a sharp decrease in 18 o in the outer 10 100 m of individual magnetite grains is in agreement with modeling of isotopic reequilibration during cooling by interdiffusion between feldspar and magnetite the presence of this zonation in the outer portions of magnetite grains that are adjacent to garnet indicates extensive transport along grain boundaries during diffusive exchange millimeter scale zonation in the polygranular layer of magnetite is caused by the interaction of volume diffusion and grain boundary transport the effects of which depend upon local textures grain boundaries enhance bulk diffusion in polygranular aggregates and allow exchange between nontouching grains the results document a complex textural control to millimeter scale o isotope zonation and geothermometry in slowly cooled rocks and document the importance of fast grain boundary transport in controlling diffusive exchange