ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

submillimeter scale zonation of δ18o in quartz and feldspar isle of skye scotland abstract laser probe analysis of oxygen isotope ratios in submillimeter domains of quartz and feldspar in hydrothermally altered granite reveals complex intragranular zonation that can be contoured within individual grains two samples collected within 10 m of each other in the maol na gainmhich epigranite mge isle of skye scotland are similar petrographically yet display very different 18o zonation patterns sk1 has isotopically zoned quartz 18 o 1 8 8 2 with intragranular gradients of 18o as great as 5 mm and individually homogeneous grains of k feldspar 0 2 which also display a large range of values 18 o 1 7 to 7 3 oxygen isotope gradients of more than 11 mm were measured in this sample in contrast sk4 has homogeneous quartz 18o 5 7 0 3 n 14 and a zoned k feldspar phenocryst 18 o 3 3 to 6 9 isotopic heterogeneity in quartz correlates with the degree of chlorite alteration in adjacent hornblende grains the isotopic heterogeneity revealed by the laser probe in single grains of quartz and feldspar is greater than the entire range of values displayed by bulk mineral analysis of samples collected throughout the mge pluton although the average values of 18o obtained by laser probe are identical to the average bulk values values in k feldspar suggest exchange at 400 c with infiltrating meteoric water 18 o 10 the marked differences in zonation profiles between samples on the outcrop scale suggest that permeability and isotope exchange during hydrothermal alteration was highly heterogeneous these microanalytical data for quartz and feldspar provide the first oxygen isotope evidence from pervasively altered granites that paleopermeability is caused at least in part by intracrystalline microfractures

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

simulating the process of reservoir impoundment induced landslide using the extended dda method abstract in this work three extensions to the traditional discontinuous deformation analysis dda method are tested to simulate the entire process describing the behavior of landslides induced by reservoir impoundment these extensions include the discretization of the area of interest block gluing and the hm hydro mechanical coupling approach several hydraulic boundary conditions are introduced based on the water level during the dry and rainfall seasons as verification the entire processes for two practical landslides the qianjiangping and the majiagou landslides which occurred in the three gorges reservoir tgr of china are simulated the simulation results agree well with the observed failure modes indicating that the proposed methodology can intuitively reproduce the entire reservoir impoundment induced landslide process

optically continuous silcrete quartz cements of the st peter sandstone high precision oxygen isotope analysis by ion microprobe a detailed oxygen isotope study of detrital quartz and authigenic quartz overgrowths from shallowly buried 1 km quartz arenites of the st peter sandstone in sw wisconsin constrains temperature and fluid sources during diagenesis quartz overgrowths are syntaxial optically continuous and show complex luminescent zonation by cathodoluminescence detrital quartz grains were separated from 53 rocks and analyzed for oxygen isotope ratio by laser fluorination resulting

assessing the factor of safety using an artificial neural network case studies on landslides in giresun turkey in this study the calculability of slope stability using the artificial neural networks ann method was examined initially 100 synthetic slope models were created to be used in calculations and the factors of safety of these slopes were calculated by a conventional stability calculation method using slope parameters then factors of safety were calculated by through ann method 80 of the datasets from the generated data were used for training while 20 were used for testing in these calculations with the ann method in both conventional calculation of stability and the ann method input parameters included slope height height of the water level slope angle unit weight cohesion and angle of internal friction while the output parameter was factor of safety sf a good level of consistency was obtained between the sfs calculated through the conventional method and the ann method furthermore sfs were calculated separately via the ann method by assigning range values to unit weight cohesion and angle of internal friction from amongst the parameters that affect sf for giresun landslides eastern turkey the data obtained in this scope revealed that cohesion was the parameter with the highest level of effect on sf consequently it was established that the factors of safety of slopes could be calculated by means of the ann method in a rapid and convenient manner the effects of slope parameters on the factors of safety in landslide were examined and the factors of safety for giresun landslides were calculated through the ann method

effects of cation substitutions in garnet and pyroxene on equilibrium oxygen isotope fractionations high grade metamorphic rocks were used to explore oxygen isotope fractionations between pyroxene and garnet and to investigate the effects on fractionation factors of the cation substitutions fe3 al 1 and ca fe mg 1 recrystallized granulite facies 725 c wollastonite ores from the northern adirondack highlands contain essentially only the minerals clinopyroxene a di hd solid solution garnet a grs adr solid solution wollastonite and exhibit a systematic dependence of measured fractionations on the fe3 content of calcic garnet cpx cagrt 0 14 0 12 0 78 0 20 xadr and wo cagrt 0 15 0 22 0 57 0 33 xadr in eclogites formed at t 650 c measured compositions of ca poor garnet and omphacite combined with experimental data indicate that ca poor fe rich garnet is enriched in 18o compared to both diopside and grossular extrapolating to 1000 k alm di c 0 2 and alm grs c 0 5 orthopyroxene and clinopyroxene from gore mountain new york show a constant fractionation that is independent of rock type as expected if they have the same closure temperature these data imply opx cpx c 0 7 at 1000 k measured fractionations among ca poor garnet orthopyroxene clinopyroxene and hornblende in the gore mountain rocks further indicate an 18o enrichment in ca poor garnet over grs c 0 5 at 1000 k the new measurements are indistinguishable from expected equilibrium values based on experiments for the minerals enstatite diopside grossular wollastonite and feldspar but consistently indicate a significant isotope effect for the simple octahedral cation substitutions fe3 al 1 grs vs adr and ca fe mg 1 ca poor garnet vs grs opx vs cpx neither cation substitution has been directly investigated for its effect on 18o 16o fractionation with experiments in silicates chemical characterization of minerals is required prior to petrological interpretation of oxygen isotope trends

paleomagnetism of the permian wallowa terrane implications for terrane migration and orogeny a sequence of volcanic astic sedimentary and pyroclastic rocks of permian age late leonardian or early guadalupian 260 ma in the wallowa terrane of oregon and idaho has been sampled for paleomagnetic study forty six sites 222 cores were collected from folded laminated siltstone mudstone and tuffaceous sandstone beds exposed along the snake river in hells canyon several stratigraphic sections within the 1500 to 2500 m thick hunsaker creek formation were sampled over a stratigraphic interval of about 700 m thermal demagnetization revealed three components of magnetization the a component has the lowest unblocking temperatures generally less than about 200oc has normal polarity and fails the fold test the b component is removed between heating steps of about 200oc and 550oc is of normal polarity and also fails the fold test the c component observed between heating steps of approximately 550oc and 660oc is always of negative inclination the grouping of this component improves slightly upon unfolding with the optimum grouping occurring at 95 unfolding using sites with n 3 and k 10 k95 ko l 18 or 100 using sites n 3 k95 k0 l 51 this component is interpreted as the characteristic remanent magnetization acquired during deposition of the hunsaker creek formation based on the following observations the better grouping of the high temperature magnetic component after unfolding and the consistent reversed polarity seen in samples from the different sections the resulting paleolatitude calculated using inclination only statistics of 24o 12 o n n 3 k 10 or 26o 9on n 3 sites implies a northern hemisphere position of the wallowa terrane during the early permian and possible southward transport of this terrane with respect to north america if the wallowa terrane was attached to the wrangellia superterrane our result indicates a northern hemisphere location for that superterrane during the permian

oxygen isotope evidence for shallow emplacement of adirondack anorthosite oxygen isotopic analysis of wollastonites from the willsboro mine adirondack mountains new york reveals a 400 ft wide zone of 18o depletion at anorthosite contacts values of 18o vary more sharply with distance and are lower to 1 3 than any yet reported for a granulite fades terrain exchange with circulating hot meteoric water best explains these results and implies that the anorthosite was emplaced at relatively shallow depths 10 km in marked contrast to the depth of granulite fades metamorphism 23 km these 18o depletions offer the first strong evidence for shallow emplacement of anorthosite within the grenville province and suggest that regional metamorphism was a later and tectonically distinct event

anticorrelation between low δ13c of eclogitic diamonds and high δ18o of their coesite and garnet inclusions requires a subduction origin diamond is essentially impermeable and unreactive under many conditions and tiny mineral inclusions within natural diamonds can faithfully preserve information on the chemical and physical conditions during diamond growth the stable isotope ratios of carbon nitrogen oxygen and sulfur in diamonds and their mineral inclusions have been used to constrain models of diamond formation but interpretations of the data have differed dramatically the crux of the controversy lies in the interpretation of the carbon isotope ratios of eclogite suite diamonds which range well outside those expected for typical mantle materials such as peridotites basalts and carbonatites proposed explanations for these anomalous carbon isotope ratios include derivation from primordial mantle inhomogeneities fractionated mantle fl uids and subducted biogenic carbon working with samples from three continents we have analyzed the carbon isotope compositions of eclogite suite diamonds and the oxygen isotope composition of their mineral inclusions primarily by ion microprobe methods we have discovered a previously unrecognized remarkably consistent anticorrelation between these two isotopic systems in that virtually all diamonds with anomalously low carbon isotope ratios have silicate inclusions with anomalously high oxygen isotope ratios this is a fundamental observation that can only be explained by formation of eclogite suite diamonds through subduction of seafl oor altered basalt admixed with marine biogenic carbon into the fi eld of diamond stability

application of wavelet analysis and a particle swarm optimized support vector machine to predict the displacement of the shuping landslide in the three gorges china landslides occur frequently in the three gorges in china posing threats to human life and the normal operation of the three gorges dam a number of preexisting landslides have been reactivated since the initial impoundment of the three gorges reservoir in june 2003 an effective and accurate method of predicting landslide displacement is necessary to mitigate the effects of these disastrous landslides this study carries out a landslide displacement prediction for the shuping landslide using 7 years of monitoring data wavelet analysis and a particle swarm optimized support vector machine pso svm model the landslide s displacement is strongly influenced by periodic precipitation and reservoir level fluctuations and the cumulative displacement curve versus time indicates a step like character based on the deformation characteristics of this landslide the total displacement is divided into its trend and periodic components by means of the wavelet analysis an s curve estimation is used to predict the trend displacement via the curve fitting of the historical displacement versus time five primary factors are used as the input variables for a pso svm model to predict periodic displacement these factors include cumulative precipitation over the previous month cumulative precipitation during a two month period maximum continuous decrement in the reservoir level during the current month and cumulative increments and decrements in the reservoir level during the current month the mean squared error squared correlation coefficient and akaike s information criterion of the wavelet pso svm model at gps monitoring points zg85 and zg87 are 2 45 0 945 and 20 80 and 10 46 80 981 and 36 38 respectively this method can be applied to the prediction of displacement in colluvial landslides in the three gorges this study may provide useful information to engineers and planners involved in landslide prevention and reduction

sequential trace element analysis of zoned skarn garnet implications for multi stage fluxing and flow of magmatic fluid into a skarn system abstract a high resolution fluid flux flow model for a shallow crustal system related to skarn formation was established using oscillatory zoning in garnet in situ analytical methods were used to determine major and trace element contents of andradite rich and lower andradite content garnet zones continuous analysis of pure andradite and87 98 shows these garnets record first and second order fluid fluxes the first order fluid flux exhibits a stepwise increase in sn contents and a decrease in the contents of other elements ti v w as mo y and rare earth elements indicating that pure andradite records a large range changes in fluid flux from the magma the second order flux is evident from oscillatory variations in the contents of sn and other elements reflecting small scale and pulsed changes in the fluid flux from a degassing magma reservoir based on the garnet major and trace element variations and mineral textures these fluid fluxes in the skarn system were controlled by pulsed degassing of a cooling magma continuous analysis of oscillatory zoning in garnet with a lower andradite content and72 81 showed that sn concentrations increase gradually and other element concentrations decrease gradually this garnet crystallized from a fluid that was locally equilibrated with a small scale stagnant fluid thick and low andradite garnet bands and62 76 are observed to have grown between the first order fluid fluxing events these bands are al rich and have retrograde textures indicating prolonged magma residence after the first order fluid flux suggesting that circulating fluids persisted for a relatively long time

a garnet zircon oxygen isotope record of subduction and exhumation fluids from the franciscan complex california tectonic blocks of high grade metamorphic rock hosted by the franciscan me lange commonly preserve textural and geochemical evidence for metasomatism and blueschist facies overprinting within a subduction zone these exhumation events can obscure information on the nature of subduction fluids at depth that might otherwise be preserved by these rocks in this tectonic setting cation and oxygen isotope zoning in garnets from eclogite and garnet hornblende rocks with minimal textural evidence of retrogression reveals separate prograde and retrograde fluid histories garnet cores preserve a homogeneous prograde oxygen isotope history with both high do 11o and low 4o values in different samples probably recording altered ocean crust protolith compositions multiple episodes of garnet resorption and regrowth record a dramatically changing bulk oxygen isotope ratio resulting in 6 7o neoformed garnet rims with sharp core rim boundaries in both samples matrix omphacite and hornblende are in profound oxygen isotope disequilibrium with garnet cores but are in equilibrium with garnet rims despite the appearance of overall textural equilibrium in thin section this cryptic metasomatism found in samples from different locations within the franciscan complex brings into question existing thermobarometry on non inclusion phases for this complex as well as interpretations based on whole rock geochemical data zircon ages and oxygen isotope equilibrium with late forming garnet are consistent with postmetasomatic formation of zircon the ability of garnet and zircon to record multiple fluid events and tie them to p t t fluid history is a powerful tool in gaining an improved understanding of the complex fluid environments within subduction zones

zonation patterns of skarn garnets records of hydrothermal system evolution chemically zoned skarn garnets provide a continuous record of hydrothermal processes in lower paleozoic sedimentary rocks within the contact aureole around the drammen granite in the oslo rift southern norway major and trace element zonation profiles the latter obtained using a scanning high resolution proton microprobe reveal early infiltration controlled growth of relatively grossular rich garnets the major and trace elements compositions being buffered by local mineral dissolution subsequent rapid epitaxial growth of andradite rich garnet on grossular rich cores marks the onset of vigorous and focused fluid flow along high permeability zones during this later stage the hydrothermal fluid composition was to a large extent externally controlled and the andradite precipitating from these fluids was characterized by high as and w contents the zonation patterns of the andradite rich garnets record at least five intermittent growth periods with rapid andradite precipitation from fluid batches with high f o 2 and progressively decreasing as and w contents thin layers poor in fe as and w but relatively high in al and mn represent periods of slow growth rates between the major pulses of hydrothermal fluids the marked rimward decrease in the as and w contents of the garnets may reflect influx of meteoric waters or exhaustion of these elements in the hydrothermal fluid reservoir caused by boiling controlled distillation processes at depth

late cretaceous truncation of the western idaho shear zone in the central north american cordillera the mesozoic boundary separating accreted oceanic rocks and continental north america in west central idaho forms a prominent right angle bend the origin and kinematic significance of which have had a great influence on models for the evolution of the north american cordilleran orogen based on structural and geochronologic relations we conclude that the bend in the steep crustal boundary is formed by the intersection of two shear zones with different ages structural fabrics of the north striking western idaho shear zone are overprinted by penetrative structures of the west northwest striking orofino shear zone u pb sensitive high resolution ion microprobe ages on metaplutonic rocks and late synkinematic leucocratic dikes constrain the age of deformation in the orofino shear zone to ca 90 70 ma distinctly younger than ca 120 90 ma magmatism and deformation within the western idaho shear zone the orofino shear zone is interpreted as a southwest vergent contractional relay structure that linked basement cored foreland thrusts of the middle and southern rocky mountains with the deep crustal duplex of the shuswap complex in the canadian rockies truncation ca 90 ma terminated late cretaceous margin parallel translation of terranes along the western idaho shear zone and required displacement to step outboard to poorly understood structures to the west

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

andradite skarn garnet records of exceptionally low δ 18 o values within an early cretaceous hydrothermal system sierra nevada ca skarn garnets in the mineral king roof pendant of the south central sierra nevada within sequoia national park california usa reveal variable fluid chemistry with a significant component of meteoric water during metasomatism in the early cretaceous sierra nevada batholith we focus on andradite garnet associated with pb zn mineralization in the white chief mine laser fluorination oxygen isotope analyses of 18o of garnet 18o grt from sites along the skarn show a large range of values 8 8 to 4 6 vsmow ion microprobe sims analyses elucidate that individual andradite crystals are strongly zoned in 18o grt up to 7 of variation total rare earth element concentrations ree across individual garnets show progressive depletion of skarn forming fluids in these elements during garnet growth these findings support a skarn model of earliest red high 18o grandite garnet consistent with a magmatic dominated equilibrium fluid 18o h2o as high as 8 later green andradite crystallized in equilibrium with a low 18o fluid indicating a significant influx of meteoric fluid 18o h2o 6 to 5 following a hiatus in garnet growth associated with late stage pb zn mineralization latest orange overprint rims have higher 18o values 18o h2o 0 2 and depleted total rees suggesting influx of high 18o trace element depleted fluid derived from regional metamorphism of the carbonate host remarkably low 18o grt values in the white chief canyon skarn require a significant proportion of meteoric fluid available during 400 c andradite forming metasomatism fluid flow was channelized at the pluton wallrock contact evidenced by the narrow extent of skarn

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

dynamic growth of garnet in granitic magmas in order to improve understanding of how accessory garnet crystallizes in igneous rocks and evaluate it as a mineral recorder of magma history we analyzed 18 o of garnets from the hallowell and togus plutons in south central maine united states by laser fluorination and in situ by ion microprobe two types of garnet are recognized magmatic and locally derived peritectic traverses of some single crystals show both gradual and abrupt changes of 18 o garnet commonly 1 while other garnet grains are isotopically homogeneous rimward increase of 18 o in many crystals indicates that garnet grew while high 18 o metamorphic wall rocks were assimilated peritectic grains have a complementary record of the transfer of high 18 o melts to the plutons in some rocks 18 o varies among neighboring grains evidence that crystals grew episodically or were juxtaposed from different sources during magma mixing garnet faithfully records changing magmatic 18 o and is a valuable tool to decipher magma petrogenesis

strontium and oxygen isotopic evidence for strike slip movement of accreted terranes in the idaho batholith abstract the oxygen and strontium isotope compositions of granitic rocks of the idaho batholith provide insight into the magma source assimilation processes and nature of the suture zone between the precambrian craton and accreted arc terranes granitic rocks of the idaho batholith intrude basement rocks of different age triassic jurassic accreted terranes to the west of the salmon river suture zone and the precambrian craton to the east the age difference in the host rocks is reflected in the abrupt increase in the initial 87 sr 86 sr ratios of granitic rocks in the batholith across the previously defined 0 706 line initial 87 sr 86 sr ratios of granitic rocks along slate creek on the western edge of the batholith jump from less than 0 704 to greater than 0 707 along an approximately 700 m transect normal to the salmon river suture initial 87 sr 86 sr ratios along the slate creek transect do not identify a transition zone between accreted arcs and the craton and suggest a unique tectonic history during or after suturing that is not documented along other transects on the west side of the idaho batholith the lack of transition zone along slate creek may be a primary structure due to transcurrent transpressional movement rather than by contractional thrust faulting during suturing or be the result of post imbrication modification

late acadian alleghenian transpressional deformation evidence from asymmetric boudinage in the casco bay area coastal maine abstract asymmetric competent layer and foliation boudinage in the casco bay area of coastal maine formed during regional f 2 hinge parallel elongation and distributed dextral strike slip movement it consists of backward rotated oblique shear fracture boudinage and forward rotated extension fracture boudinage initially symmetric quartz filled extension fractures were intermittently developed as boudin partings orthogonal to the prominent ductile stretching lineation due to fault related fluctuations in fluid pressure and tectonic stresses modification by concurrent non coaxial deformation related to dextral strike slip movement resulted in the clockwise rotation sinistral slip and vein parallel elongation reflected in the forward rotated asymmetric boudinage discordant planar pegmatite veins and variably oriented boudinaged pegmatite sheets common in these exposures underwent a similar evolution the development of this asymmetric boudinage is attributed to progressive brittle ductile non coaxial deformation related to orogen parallel dextral transpression along the norumbega nonesuch river strike slip fault system during the later stages of the acadian orogeny and subsequent alleghenian deformation

in situ oxygen isotope major and trace element constraints on the metasomatic modification and crustal origin of a diamondiferous eclogite from roberts victor kaapvaal craton a subducted oceanic crustal origin for most eclogite xenoliths in kimberlites has long been a cornerstone of tectonic models for craton development however eclogite xenoliths often have protracted and complex histories involving multiple metasomatic events that could overprint some of the key geochemical indicators typically taken as evidence of a subducted origin e g garnet 18o values and mineral 87sr 86sr compositions to assess the potential for disturbance of oxygen isotopic compositions in mantle eclogites via diamond forming and other possible metasomatic fluids we have conducted a multi technique in situ study of a diamondiferous eclogite xenolith from the roberts victor kimberlite s africa using sims we provide the first texturally controlled in situ measurements of 18o values in eclogitic garnet in close proximity to diamond garnet and clinopyroxene modal proportions are heterogeneous in the xenolith and garnet compositions vary from mg 75 8 79 2 grossular proportions 8 05 10 14 mol and omphacitic pyroxene has jd13 24 and mg 86 6 90 0 rare earth element patterns of minerals across the xenolith including grains close to diamond are typical lree depleted garnets and markedly lree enriched pyroxenes these silicate minerals also record detectable intra and inter grain lree abundance variations clinopyroxenes of the studied xenoliths show hfse and sr abundance variations that are decoupled from lree contents and major element variations mineralogical constraints and bulk rock reconstructions indicate that the studied sample likely experienced selective incompatible element enrichment during small volume 0 03 wt infiltration of metasomatic fluid s potentially linked to ancient diamond evolution intra grain major element lree and hfse variations in clinopyroxene resulted from late stage metasomatism oxygen isotope compositions in garnet are decoupled from all major and trace element variations with garnet 18o values being uniform across the xenolith in a wide variety of textural settings garnet 18o values of 6 5 0 2 are higher than the mean 5 19 0 26 of the mantle garnet range 4 8 5 5 modelling of the buffering effect of mantle peridotite on co2 rich and h2o rich metasomatic fluids at temperatures within the diamond stability field indicates that the likelihood of a metasomatic fluid with exotic oxygen isotopic composition arriving at a mantle eclogite body with its isotopic composition unmodified after percolative flow through dominantly peridotitic mantle at great depth is very low as we find no evidence of metasomatically induced garnet oxygen isotope variations in the studied diamondiferous eclogite xenolith we conclude that the most likely origin for the elevated garnet 18o values is via inheritance from a crustal protolith altered at relatively low temperatures these results have broader relevance and support the hypothesis of a low pressure protolith for mantle eclogite xenoliths demonstrating the robust nature of garnet oxygen isotope compositions even in diamond bearing eclogites

direction and shear sense during suturing of the seven devils wallowa terrane against north america in western idaho a northeast dipping 1 5 km thick mylonite near dworshak dam marks the suture zone between precambrian north america and the seven devils wallowa terrane in western idaho the mylonite formed under amphibolite facies conditions from quartz diorite containing apparently synplutonic mafic and synkinematic pegmatite dikes of the kamiah plutonic complex mylonitic lineations and fold axes have a mean plunge of 48 toward 056 nearly down the dip of the mylonitic foliation shear sense given by offset of late stage crosscutting pegmatites is consistently top to the southwest reverse slip parallel to the mylonitic lineation folds that formed by progressive folding of the mylonitic foliation approach sheath fold geometry axial planes and fold limbs are nearly parallel to the mylonitic foliation mafic dikes that are apparently synplutonic in the undeformed quartz diorite immediately south of the mylonite zone and north of kamiah have variable dips and azimuths in the shear zone however these dikes lie nearly in the mylonitic foliation transposition of the dikes into near concordance with the foliation by simple shear requires high values of shear strain and suggests that cumulative top to the southwest reverse slip displacement across the mylonite zone is at least 27 km and likely more than 80 km this displacement involves underthrusting of the kamiah plutonic complex emplaced within the seven devils wallowa terrane beneath north america during late cretaceous docking with continental north america

extreme oxygen isotope zoning in garnet and zircon from a metachert block in melange reveals metasomatism at the peak of subduction metamorphism

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

oxygen isotope variations of garnets and clinopyroxenes in a layered diamondiferous calcsilicate rock from kokchetav massif kazakhstan a window into the geochemical nature of deeply subducted uhpm rocks calcsilicate and garnet pyroxene rocks with dolomite and mg calcite matrices occur with uhpm dia mondiferous biotite gneisses and schists of the kokchetav massif the calcsilicates are characterized by high dia mond grade k bearing diopside and very high mg garnets mg 77 with variable ca contents ca 42 5 80 a rare calcsilicate sample with alternating layers of different bulk compositions was selected for oxygen isotope and electron probe microanalysis of garnets and pyroxenes a grain of fresh garnet with a brownish yellow luminescent inner domain mg 94 and a non luminescent outer part mg 88 was selected for in situ analysis of d 18 o by ion microprobe 10 lm spot the profile demonstrates a d 18 o gradient of 1 5 200 lm from 11 3 rim to 12 8 core vsmow additional 2 mg samples of hand picked garnet and clinopyroxene fragments from different parts of the same sample selected by color and chemical differences were analyzed for d 18 o by laser fluorination yielding even larger differences in d 18 o 6 3 10 6 in garnets and 6 1 8 1 in clinopyroxenes the zonation in d 18 o among grains of the same mineral in different lithologies may in part reflect initial heterogeneities of the finely layered sedimentary precursors the d 18 o values for the garnets are among the highest observed for uhp origin both for crustal or mantle rocks confirming a sedimentary origin for these carbonate bearing rocks and ruling out a primi tive mantle derived protolith oxygen diffusion in garnet at peak metamorphism temperature 1 000c was arrested by rapid cooling

quartz garnet isotope thermometry in the southern adirondack highlands grenville province new york quartz garnet oxygen isotope thermometry of quartz rich metasedimentary rocks from the southern adirondack highlands grenville province new york yields metamorphic temperatures of 700 800 c consistent with granulite facies mineral assemblages samples from the irving pond quartzite record d 18 o qtz grt 2 68 0 21 1 s d n 15 corresponding to peak metamorphic conditions of 734 38 c this agrees well with the estimates from garnet biotite exchange thermometry similar temperature estimates are obtained from swede pond 682 47 c n 3 and king s station c 700 c the whitehall area records higher temperatures 798 25 c n 3 all of these temperatures are higher than previous regional temperature estimates the c 800 c temperatures near whitehall are consistent with preservation of pre granulite contact temperatures adjacent to anorthosite the preservation of peak metamorphic temperatures in garnet of all sizes is consistent with slow oxygen diffusion in garnet and closure temperatures of at least 730 c peak metamorphic fractionations are preserved in rocks with varying quartz feldspar ratios indicating that the modal percentage of feldspar does not affect retrograde oxygen exchange in these rocks the lack of this correlation suggests slow rates of oxygen diffusion in quartz and feldspar consistent with the results of anhydrous oxygen diffusion experiments

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

ion microprobe survey of the grain scale oxygen isotope geochemistry of minerals in metamorphic rocks abstract the oxygen isotope compositions of calcite diopside dolomite forsterite garnet k feldspar kyanite plagioclase quartz and wollastonite were analyzed in suites of contact and regional metamorphic rocks using an ion microprobe spatial resolution was 10 m precision measured as the standard deviation of working standards averaged over the entire project was 0 13 0 18 for three carbonate standards and 0 11 0 12 for two silicate standards a total of 1176 analyses excluding standards were made of 73 minerals in 23 samples both intercrystalline and intracrystalline variability in 18 o is greater in contact than in regional metamorphic rocks of 27 minerals analyzed in contact metamorphosed rocks 70 exhibit statistically significant grain to grain variability in 18 o over areas 1 41 cm 2 with the largest range in silicates and carbonates in a single sample of 7 4 forsterite and 10 6 dolomite of 88 grains analyzed in two or more places in contact metamorphosed rocks 32 exhibit statistically significant intracrystalline variability in 18 o with the largest range in a single silicate and carbonate grain of 3 1 forsterite and 10 1 dolomite in contrast 44 of 45 minerals in regional metamorphic rocks exhibit significant grain to grain variability in 18 o over areas 1 17 cm 2 with the largest range in silicates and carbonates in a single sample of only 1 1 plagioclase and 0 9 calcite only 6 of 144 grains analyzed in two or more places in regional metamorphic rocks exhibit significant intracrystalline variability in 18 o with the largest range in a single silicate and carbonate grain of only 1 5 diopside and 0 7 calcite the difference in intercrystalline and intracrystalline variability in 18 o between contact and region metamorphic rocks is explained by the longer duration and slower reaction rates of regional metamorphism rather than to differences in temperature there is no significant difference in intercrystalline and intracrystalline variability in 18 o in regional metamorphic rocks among samples from the biotite garnet and kyanite zones calcite inclusions in forsterite and calcite and quartz inclusions in garnet either have 18 o that is statistically indistinguishable from 18 o of the same mineral occurring as nearby matrix grains or have statistically significant lower 18 o no reversed isotope fractionations were measured between coexisting mineral pairs minerals in individual samples however exhibit a wide range in the degree to which they attained and preserve oxygen isotope fractionations consistent with metamorphic temperatures recorded by mineral equilibria processes that account for grain scale departures from isotope exchange equilibrium include a overstepping of prograde mineral reactions b growth zoning in low diffusivity minerals c interaction of rocks with fluids at the peak of metamorphism and or during cooling d retrograde mineral reactions and e closed system isotope exchange between coexisting minerals during cooling this study provides new information about 1 the degree to which a variety of textural changes experienced by rocks during metamorphism are associated with changes in 18 o 2 oxygen isotope homogenization at the outcrop scale among contrasting lithologies 3 changes in 18 o with increasing grade of regional metamorphism and 4 time scales of metamorphic process

high resolution p t t paths from δ18o zoning in titanite a snapshot of late orogenic collapse in the grenville of new york we characterize oxygen isotope zoning within single titanite crystals from the carthage colton mylonite zone ccmz adirondack mountains new york state united states by ion microprobe smooth gradients of 18 o up to 0 6 over 90 m resulted from diffusive exchange of oxygen during cooling from peak metamorphic temperatures of 650 700 c modeling of the observed profile indicates punctuated cooling rates of 30 60 c m y along the ccmz set within long periods of much slower cooling these results indicate a previously unrecognized period of rapid cooling along the ccmz that is interpreted to result from the post ottawan collapse of the grenville mountain belt and exhumation of the central adirondack highlands at ca 1050 ma

new evidence for cretaceous strike slip faulting in the united states cordillera and implications for terrane displacement deformation patterns and plutonism early to mid cretaceous dextral strike slip faulting involving up to 400 km displacement has been documented in the southern sierra nevada of california in western idaho the salmon river suture juxtaposes unrelated oceanic and continen tal rocks along a major near vertical shear zone that was active in the early to mid cretaceous these two structural zones have been treated as separate entities however new data indicate that they likely connect via a structural discontinuity in northwest nevada and southeast oregon herein called the western nevada shear zone wns current structures within the wns record dip slip contractional deformation however regional relations structural and stratigraphic indicate a mismatch in the early mesozoic geology of rocks across the wns that is best explained by dextral strike slip displacement of several 100 km these relations argue that an early strike slip structure along the wns was reactivated and obscured during later regional shortening deformation most likely related to the cretaceous sevier orogeny the wns is along strike and broadly coeval with the salmon river suture zone and strike slip boundaries in the sierra nevada we hypothesize that all these features are related elements of a major structural boundary in the western united states cordil lera this boundary is interpreted to have accommodated significant dextral strike slip displacement of outboard arc terranes of the cordillera in the early cretaceous followed by reactivation as a localized contractional zone in the mid cretaceous during the sevier orogeny cretaceous batholiths of the united states cordillera closely parallel the boundary which we suggest formed a major crustal flaw that localized and facilitated emplacement of arc magmas

evaluation of the effects of composition on instrumental mass fractionation during sims oxygen isotope analyses of glasses significant instrumental mass fractionation imf occurs during measurements of oxygen isotope ratios in magmatic glasses by sims in order to characterise and correct for this fractionation we measured oxygen isotope ratios in a range of international and internal glass standards ranging in composition from basalt 47 wt sio2 to rhyolite 72 wt sio2 and with known major element compositions oxygen isotope ratios were determined by laser fluorination at suerc east kilbride or taken from previously published values a total of 1105 18o measurements were made over nine sessions on a cameca ims 1270 ion microprobe at the university of edinburgh sims measurements on glass standards had external precision better than 0 36 1 and the reference material analysed alongside the unknown samples usgs synthetic glass gsa 1g had an average external precision of 0 14 the selected standards are thus sufficiently homogeneous in 18o to be suitable calibration standards in terms of 18o the sims measurements show that within a single session imf may vary by up to 4 7 from one glass standard to another imf is strongly correlated with sio2 and cao a least squares regression calculation was used to explore potential univariate and multivariate correction schemes for each correction scheme the correction coefficients determined for each session were then used to calculate the imf and correct the measured isotopic ratio of each glass standard a univariate correction scheme using only sio2 to correct for imf reproduced 75 of the glass standards to within 0 2 of their true 18o and 95 to within 0 4 bivariate correction schemes using sio2 cao and feo cao produced similar results but did not significantly improve on the sio2 correction the correction schemes were applied to 18o measurements made on melt inclusions and glasses from the askja volcanic system north iceland the uni and bivariate correction schemes tested produced 18o values within the published range for icelandic basalts we recommend a simple correction scheme based on the sio2 content of appropriate standards which should span a suitable compositional range from basalt to rhyolite

crustal reworking and hydration insights from element zoning and oxygen isotopes of garnet in high pressure rocks sesia zone western alps subduction zones represent one of the most critical settings for fluid recycling as a consequence of dehydration of the subducting lithosphere a better understanding of fluid flows within and out of the subducting slab is fundamental to unravel the role of fluids during burial in this study major and trace element geochemistry combined with oxygen isotopes were used to investigate metasediments and eclogites from the sesia zone in order to reconstruct the effect of internal and external fluid pulses in a subducted continental margin garnet shows a variety of textures requiring dissolution precipitation processes in presence of fluids in polycyclic metasediments garnet preserves a partly resorbed core related to pre alpine high temperature low pressure metamorphism and one or multiple rim generations associated with alpine subduction metamorphism in eclogites garnet chemical zoning indicates monocyclic growth with no shift in oxygen isotopes from core to rim in metasediments pre alpine garnet relics show 18o values up to 5 3 higher than the alpine rims while no significant variation is observed among different alpine garnet generations within each sample this suggests that an extensive re equilibration with an externally derived fluid of distinct lower 18o occurred before or in correspondence to the first alpine garnet growth while subsequent influxes of fluid had 18o close to equilibrium the observed shift in garnet 18o is attributed to a possible combination of 1 interaction with sea water derived fluids during pre alpine crustal extension and 2 fluids from dehydration reactions occurring during subduction of previously hydrated rocks such as the serpentinised lithospheric mantle or hydrated portions of the basement

massive fluid influx beneath the colorado plateau usa related to slab removal and diatreme emplacement evidence from oxygen isotope zoning in eclogite xenoliths

simultaneous batholith emplacement terrane continent collision and oroclinal bending in the blue mountains province north american cordillera the north american cordillera is a classic example of accretionary orogen consisting of multiple oceanic terranes attached to the western margin of laurentia during the mesozoic times although the cordillera is linear for most parts terrane boundaries are at a high angle to the overall structural grain in several segments of the orogen which has been a matter of longstanding controversy as to how and when these orogenic curvatures formed this paper discusses mechanisms kinematics and timing of initiation of one of these major curvatures the blue mountains province in northeastern oregon here magmatic fabric patterns and anisotropy of magnetic susceptibility in the wallowa batholith record three phases of progressive deformation of the host wallowa terrane during early cretaceous first is terrane oblique ne sw shortening interpreted as recording attachment of the amalgamated oceanic and fringing terranes to the continental margin during dextral convergence at 140 ma deformation subsequently switched to pure shear dominated nne ssw shortening associated with crustal thickening caused by continued impingement of the amalgamated blue mountains superterrane into a presumed westward concave reentrant in the continental margin at 135 128 ma upon impingement at 126 ma the northern portion of the superterrane became locked leading to reorientation of the principal shortening direction to nnw sse while its still deformable southern portion rotated clockwise about a vertical axis we thus propose oblique bending as the main mechanism of the orocline formation whereby horizontal compressive forces resulting from plate convergence acted at an angle to the terrane boundaries

eclogite facies fluid infiltration constraints from δ 18 o zoning in garnet in situ analysis reveals that eclogite facies garnets are zoned in 18o with lower values in the core and rims that are 1 5 to 2 5 higher this pattern is present in 9 out of 12 garnets analyzed by sims from four orogenic eclogite terranes and correlates with an increase in the mole fraction of pyrope and mg fe ratio from core to rim indicating prograde garnet growth at the maximum temperatures and the time scales experienced by these garnets calculated intragranular diffusion distances for oxygen are small 5 from two kimberlites are homogeneous in 18o possibly due to diffusive exchange which is possible for prolonged periods at higher mantle temperatures homogeneity of 18o in garnets outside the normal mantle range 5 6 may be common in kimberlitic samples

application of lu hf garnet dating to unravel the relationships between deformation metamorphism and plutonism an example from the prince rupert area british columbia abstract the tectonic history of the prince rupert area is marked by profound crustal thickening from thrusting that produced inverted metamorphic field gradients and transpression in crustal scale shear zones syn tectonic garnet in the prince rupert area has lu hf ages of 102 6 3 7 ma and 108 3 4 1 ma 2 porphyroblast matrix relationships in these samples and samples from the same outcrops indicate syn tectonic garnet growth these relationships imply that the garnet ages directly date the development of the metamorphic foliations a third sample of migmatitic garnet amphibolite from the contact aureole of the 94 90 ma ecstall pluton had complex isotope systematics interpreted to indicate a garnet growth episode 105 ma similar to the ages obtained from the other samples and a growth or equilibration event at 94 ma during pluton emplacement the data show that the older lu hf garnet ages date prograde metamorphism during foliation development and modification during pluton emplacement the ecstall pluton was emplaced 10 to 15 m y after regional metamorphism and thrust stacking in the prince rupert area in order to place our samples in a regional tectonic context we compare our results to patterns of regional deformation metamorphism and plutonism throughout the north american cordillera in the time period between 110 and 85 ma contractional and transpressional deformation occurred throughout much of the north american cordillera at this time from southeastern alaska to the baja peninsula in mexico left lateral transpression dominated the canadian cordillera whereas right lateral transpression affected areas south of the idaho salmon river suture zone including the sierra nevada batholith this reversal in kinematics in the northern and southern cordillera within coeval magmatic belts appears to be a first order feature of the geology of the north american cordillera during the cretaceous

strain rates at high temporal resolution from curved inclusion trails in garnet passo del sole central swiss alps quantitative strain rates at outcrop scale are very difficult to obtain but they may be estimated from crystals with curved inclusion trails by calculating rotation rates from growth rates and corresponding deflections of the internal foliation garnet in a quartzose pelite at passo del sole in the central swiss alps is extraordinarily valuable for calculation of strain rates during alpine orogenesis because the unusual zoning patterns clearly define the kinetics of its nucleation and growth complex concentric zoning patterns can be correlated from one crystal to another in a hand sample based on compositional and microstructural similarities the ubiquity of these features demonstrates that all garnet crystals nucleated at nearly the same time compositional bands whose radial widths are proportional to crystal size provide evidence for growth governed by the kinetics of intergranular diffusion of locally sourced nutrients together these constraints increase the reliability of estimates of rates of garnet growth and the strain rate calculations that depend on them to obtain growth rates p t conditions during garnet crystallization were modelled in a series of pseudosections and compositional evolution was connected to rates of garnet growth by means of an independently determined heating rate these growth rates combined with measured amounts of curvature of inclusion trails indicate that the time averaged strain rate at passo del sole during alpine metamorphism was on the order of 10 14 s 1 strain rates calculated using rotational v non rotational models are similar in magnitude the constraints on crystallization kinetics also allow direct calculation of strain rates during individual stages of garnet growth revealing short term increases to values on the order of 10 13 s 1 these higher strain rates are correlated with the growth of concentric high ca or high mn zones in garnet which implies that strain softening associated with the transient passage of fluids is responsible for acceleration of deformation during these intervals

direct dating of adirondack massif anorthosite by u pb shrimp analysis of igneous zircon implications for amcg complexes the low abundance of igneous zircon in proterozoic massif anorthosites has presented a major obstacle to the acquisition of direct absolute ages of crystallization for these important rocks indirect dating that relies on zircon ages from associated mangerite charnockite granite granitoids assumes that they have a coeval relationship with anorthosite that requires documentation shrimp sensitive high resolution ion microprobe u pb zircon dating techniques provide a powerful means for directly dating the small populations of zircons in anorthositic rocks and for resolving problems with inheritance within the adirondack mountains 10 samples of massif anorthosite have yielded more than sufficient quantities of igneous zircon to establish directly the ages of the region9s classic anorthosite occurrences e g the marcy and oregon dome massifs in addition a ferrogabbro a ferrodiorite and a coronitic olivine metagabbro all crosscutting massif anorthosite were dated the average age of this suite of 13 anorthositic samples is 1154 6 ma mswd mean square of weighted deviates 0 26 probability 0 99 in addition eight associated granitoids have been dated by shrimp techniques and complement another five previously dated by multi grain thermal ionization mass spectrometry tims methods the 13 granitoids yield an average age of 1158 5 mswd 0 89 probability 0 60 and are broadly coeval with the massif anorthosite the overlapping ages provide evidence that these rocks constitute a single composite anorthosite mangerite charnockite granite amcg suite intruded at ca 1155 ma an age corresponding to the ages of major amcg suites in the grenville province in canada e g morin and lac st jean although rocks of the adirondack amcg suite are now documented as broadly coeval it does not follow that the constituent amcg lithologies were comagmatic field relationships and mineral disequilibria in transitional zones are inconsistent with derivation from a single parental magma moreover the presence of older ca 1 2 1 3 ga inherited cores in some zircons from amcg granitoids conflicts with derivation of these rocks from magmas that formed anorthosite gabbro or ferrodiorite or jotunite in which zircons are highly soluble the slightly older ca 1158 ma average age of the mangeritic and charnockitic members of the amcg suite is consistent with an origin as early lower crustal anatectites that left behind pyroxene plagioclase restites this refractory material then reacted by assimilation fractional crystallization afc with ponded mantle derived gabbroic magmas to produce plagioclase rich crystal mushes with crustal isotopic signatures as proposed much earlier by r f emslie these magmas are considered to be parental to the adirondack anorthosite and upon ascent they were emplaced in proximity to still hot earlier mangeritic and charnockitic bodies where they underwent further fractionation the composite nature of the marcy massif documents that this process was repeated in several sequential pulses

application of time series analysis and pso svm model in predicting the bazimen landslide in the three gorges reservoir china abstract the landslide displacement in the three gorges reservoir china experiences step like deformation that is influenced by rainfall and the periodic scheduling of the reservoir in view of the step like characteristic the particle swarm optimization and support vector machine pso svm coupling model based on the response of the induced factors was proposed to predict the landslide displacement the moving average method was adopted to divide the total displacement into trend term and periodic term the trend displacement was controlled by the geological conditions and predicted by polynomial function while the periodic displacement was under the combined control of the triggers and the evolution state of the landslide therefore the pso svm model based on the factors of the precipitation the variation range of the reservoir and the displacements of the prior periods was proposed to predict the periodic displacement the typical step like landslide in the three gorges reservoir which is known as the bazimen landslide was taken as a case study to verify the prediction results the values of the root mean square error and the mean absolute percentage error were 13 28 and 25 95 respectively the results showed that rainfall and reservoir water level were the dominant factors for the step like landslide deformation the evolution state of the landslide was also significant in reflecting the response relationship between the displacement and inducing factors in conclusion the proposed pso svm model can better represent the response relationship between the factors and the periodic displacement which made the predicted values of the total displacement fit with the measured values greatly

westward growth of laurentia by pre late jurassic terrane accretion eastern oregon and western idaho united states a discussion advances in the blue mountains province bmp and adjacent areas of the pacific northwest have required an occasional updating of terms used to express new concepts trans idaho discontinuity yates 1968 sr isotopic boundary armstrong et al 1977 salmon river suture zone lund and snee 1988 western idaho suture zone strayer et al 1989 bourne and greenhorn subterranes ferns and brooks 1995 western idaho shear zone wisz mcclelland et al 2000 salmon river belt gray and oldow 2005 izee basin dorsey and lamaskin 2007 orofino shear zone mcclelland and oldow 2007 salmon river suture lund et al 2008 arc continent boundary lewis et al 2014 as a consequence tracking nomenclatural changes over time has presented periodic challenges to workers familiar with the regional geology to the unfamiliar this task is intensified by a literature fraught with tantalizing terminology understandable by few given the various tectonic elements helwig 1974 and etymological changes in the bmp the probability of miscommunication is high this discussion centers on a recent journal of geology article lamaskin et al 2015 that misuses the salmon river belt srb terminology and modifications thereof when describing the geologic setting of west central idaho since the publication of gray and oldow 2005 various authors have referenced the srb in tectonic models proposed to explain the outboard amalgamation accretion and or truncation of volcanic arc terranes comprising the bmp e g dorsey and lamaskin 2007 mcclelland and oldow 2007 giorgis et al 2008 lamaskin and dorsey 2008 blake et al 2009

pathways and challenges of the application of artificial intelligence to geohazards modelling abstract the application of artificial intelligence ai and machine learning in geohazard modelling has been rapidly growing in recent years a trend that is observed in several research and application areas thanks to recent advances in ai as a result the increasing dependence on data driven studies has made its practical applications towards geohazards landslides debris flows earthquakes droughts floods glacier studies an interesting prospect these aforementioned geohazards were responsible for roughly 80 of the economic loss in the past two decades caused by all natural hazards the present study analyses the various domains of geohazards which have benefited from classical machine learning approaches and highlights the future course of direction in this field the emergence of deep learning has fulfilled several gaps in i classification ii seasonal forecasting as well as forecasting at longer lead times iii temporal based change detection apart from the usual challenges of dataset availability climate change and anthropogenic activities this review paper emphasizes that the future studies should focus on consecutive events along with integration of physical models the recent catastrophe in japan and australia makes a compelling argument to focus towards consecutive events the availability of higher temporal resolution and multi hazard dataset will prove to be essential but the key would be to integrate it with physical models which would improve our understanding of the mechanism involved both in single and consecutive hazard scenario geohazards would eventually be a data problem like geosciences and therefore it is essential to develop models that would be capable of handling large voluminous data the future works should also revolve towards interpretable models with the hope of providing a reasonable explanation of the results thereby achieving the ultimate goal of explainable ai

oxygen isotope and trace element zoning in hydrothermal garnets windows into large scale fluid flow behavior single garnet crystals from a large multicyclic hydrothermal system in far east russia are strongly growth zoned microscale ion microprobe analysis reveals consistent intracrystalline patterns in oxygen isotope composition and boron and iron contents reflecting evolution of the hydrothermal system from magmatic to meteoric dominated conditions and repetitive influx of magmatic fluids large intracrystalline variations in oxygen isotope composition 12 18 o delimit temporal evolution of magmatic and meteoric fluid input within different portions of the hydrothermal system and suggest that fluid flow regimes differed between central and distal portions of the system these results provide compelling evidence that microanalytical data can be extrapolated from intracrystalline scales to study macroscale processes in complex large scale fluid rock systems

a novel hybrid approach for landslide susceptibility mapping integrating analytical hierarchy process and normalized frequency ratio methods with the cloud model abstract landslides which could cause huge losses of lives or property damages result from several different environmental factors whose influences on landslides are very complex therefore it is essential to understand the relationships between these environmental factors and landslides thus the integration of the analytical hierarchy process ahp with the normalized frequency ratio nfr is evaluated for landslide susceptibility analyses however in addition to these complex relationships the randomness and fuzziness always affect landslide susceptibility mapping this study introduces the cloud model cm to improve the integrated ahp nfr method and proposes a novel hybrid ahp nfr cm method for landslide susceptibility analyses which can better address issues of the randomness and fuzziness firstly ten environmental parameters are selected as landslide impact factors and their values for all the landslides identified in the study area are obtained through the remote sensing rs and geographical information system gis technologies the ahp method is used to obtain the weight of each landslide impact factor and the nfr method is used to obtain the weight of each subclass in each landslide impact factor which can reflect the relationship between the landslide impact factor and landslide occurrence after applying an appropriate compositional operation between the weights of the landslide impact factors and the weights of the subclasses of the impact factors a landslide susceptibility index lsi for each grid divided via the attribution based spatial information multi grid method asimg can be computed to solve the inevitable issues of randomness and fuzziness in landslide susceptibility analyses a cloud model that uses three numerical features expectation entropy and hyper entropy to represent the intension of the concept is adopted to improve the methods of ahp and nfr the relative importance of two landslide impact factors is scaled with the cloud model rather than the saaty criteria pair wise comparison matrixes of landslide impact factors given by each expert are described by the normal cloud model and the floating cloud model is used to aggregate all experts judgments the weight of each landslide impact factor is also expressed with the cloud model rather than a certain value in improving the nfr the weight of each subclass of each landslide impact factor is expressed with the cloud model rather than a certain value in the improvement of the landslide susceptibility results the domain of landslide risk assessment results is also displayed with the cloud model instead of a series of definite intervals as the study area examined is large several grids would need to be divided meaning that it would take a considerable amount time to subject the entire study area to landslide susceptibility mapping thus we propose a new attribute based spatial information multi grid asimg division method and introduce grid computing technology to improve the calculation efficiency during the process finally the proposed hybrid ahp nfr cm asimg approach is validated and applied in the study area it s concluded that the new integration of ahp and nfr methods with the cloud model can consider both randomness and fuzziness and therefore can increase the robustness of landslide susceptibility analyses while the asimg technology can enhance the calculation efficiency in regional landslide susceptibility mapping

improvement of the finite element based limit equilibrium method to include changes in groundwater a case study of a deforming bank slope from the three gorges reservoir changes in groundwater are an important factor affecting slope stability in this study the finite element based limit equilibrium method fele which does not require any predetermined assumptions is improved to include groundwater the seepage force in the improved fele is directly regarded as a body force and can be transformed into the equivalent nodal force moreover a practical technique of employing the signed distance function is used to represent the groundwater level making the improved fele insensitive to the mesh an analysis of a benchmark slope is performed to validate the effectiveness of the improve fele and the results show that the seepage force has a significant influence on the stability of the slope moreover a case study of a deforming bank slope from the three gorges reservoir is analyzed by the improved fele to study the relationships between the deformation and changes in the phreatic lines within the sliding body

a hybrid machine learning model to estimate potential debris flow volumes abstract empirical statistical models of debris flow are challenging to implement in environments where sedimentary and hydrologic triggering processes change through time such as after a large earthquake the flexible and adaptive statistical methods provided by machine learning algorithms may improve the quality of debris flow predictions where triggering conditions and the nature of sediment that can bulk flows varies with time we developed a hybrid machine learning model of future debris flow volumes using a dataset of measured debris flow volumes from 60 catchments that generated post wenchuan earthquake mw 7 9 debris flows we input topographic variables catchment area topographic relief channel length distance from seismic fault and average channel gradient and the total volume of co seismic landslide debris into the pso elm adaboost machine learning model created by combining extreme learning machine elm particle swarm optimization pso and adaptive boosting machine learning algorithm adaboost the model was trained and tested using post 2008 mw 7 9 wenchuan earthquake debris flows then applied to understand potential volumes of post earthquake debris flows associated with other regional earthquakes 2013 mw 6 6 lushan earthquake 2010 mw 6 9 yushu earthquake we compared the pso elm adaboost method with different machine learning methods including back propagation neural network bpnn support vector machine svm elm pso elm the comparative analysis demonstrated that the pso elm adaboost method has a higher statistical validity and prediction accuracy with a mean absolute percentage error mape less than 0 10 the prediction accuracy of debris flow volumes trigged by other earthquakes decreases to 0 11 0 16 absolute percentage error suggesting that once calibrated for a region this method can be applied to other regional earthquakes this model may be useful for engineering design to mitigate the risk of large post earthquake debris flows

oxygen isotope thermometry using quartz inclusions in garnet oxygen isotope ratios of quartz inclusions within garnet from granulite and amphibolite facies gneisses in the adirondack mountains ny were analyzed and used to determine metamorphic temperatures primary quartz inclusions for eight of 12 samples have 18o values significantly lower than matrix quartz the primary quartz inclusions retain 18o values representative of thermal conditions during garnet crystallization whereas the 18o values of matrix quartz were raised by diffusive exchange with other matrix minerals e g mica and feldspar during cooling the 18o differences between quartz inclusions and matrix quartz show that garnet a mineral with slow diffusion of oxygen can armour quartz inclusions from isotopic exchange with surrounding matrix even during slow cooling these differences between 18o in matrix quartz and quartz inclusions can further be used to test cooling rates by fast grain boundary diffusion modelling criteria for identifying quartz inclusions that preserve primary compositions and are suitable for thermometry were developed based on comparative tests relations between 18o and inclusion size distance of inclusion to host garnet rim core rim zonation of individual inclusions and presence or absence of petrological features healed cracks in quartz inclusions inclusions in contact with garnet cracks lined by secondary minerals and secondary minerals along the inclusion grain boundary were investigated in this study 61 of quartz inclusions preserve primary 18o and 39 were associated with features that were linked to reset 18o values if 18o in garnet is homogeneous and inclusions are removed laser fluorination 18o values of bulk garnet are more precise more accurate and best for thermometry intragrain 18o grt profiles measured in situ by ion microprobe show no 18o zonation almandine rich garnet alm 60 75 from each sample was measured by laser fluorination mass spectrometry lf ms for 18o and compared with ion microprobe measurements of 18o in quartz inclusions for thermometry the 18o qz grt values for adirondack samples range from 2 66 to 3 24 corresponding to temperatures of 640 to 740 c a qz alm 2 71 out of 12 samples that were used for thermometry nine are consistent with previous estimates of peak temperature 625 to 800 c based on petrological and carbon isotope thermometry for regional granulite and upper amphibolite facies metamorphism the three samples that disagree with independent thermometry for peak metamorphism are from the anorthosite mangerite charnockite granite suite in the central adirondacks and yield temperatures of 640 to 665 c approximately 100 c lower than previous estimates these low temperatures could be interpreted as thermal conditions during late post peak crystallization of garnet on the retrograde path this article is protected by copyright all rights reserved

delta 18 o and yttrium zoning in garnet time markers for fluid flow the relative timing of two discrete pulses of metamorphic fluid flow is constrained based on chemical zoning in several garnet crystals from kvaloya troms northern norway the garnet crystals measured 1 2 cm in diameter and were contained within c 1 6 ga staurolite grade metasediments major element zoning indicates that garnet grew under normal prograde conditions in the garnet and or staurolite zones timing constraints are based on comparisons between major and trace element chemical zoning oxygen isotope 18o zoning and deformational inclusion trail zoning in one of the garnet we interpret at least two pulses of metamorphic fluid flow the first pulse occurred during the syn tectonic growth interval the 18o zoning was reversed relative to normal prograde zoning and the 18o maximum was located within the syn tectonic growth zone displaced 3 4 mm from the garnet core the fluid might have been sourced in neighbouring calcareous pelites and may also have caused formation of an y ring the second and subsequent pulse s occurred during after the post tectonic growth interval 18o was locally increased at the garnet rim particularly where the rim was sheared the incomplete rim was also enriched in calcium transport of oxygen and calcium by metamorphic fluids is well documented transport of y is both problematic and poorly understood but might have been facilitated by complexing with f and or co2

a detailed record of shallow hydrothermal fluid flow in the sierra nevada magmatic arc from low δ18o skarn garnets garnet from skarns exposed at empire mountain sierra nevada california united states batholith have variable 18o values including the lowest known 18o values of skarn garnet 4 0 in north america such values indicate that surface derived meteoric water was a significant component of the fluid budget of the skarn forming hydrothermal system which developed in response to shallow emplacement 3 3 km of the 109 ma quartz diorite of empire mountain values of 18o measured in situ across single garnet crystals by secondary ion mass spectrometry vary considerably up to 7 and sometimes abruptly indicating variable mixing of meteoric magmatic and metamorphic water brecciation in the skarns and alteration of the empire mountain pluton suggests that fracture enhanced permeability was a critical control on the depth to which surface waters penetrated to form skarns and later alter the pluton compared to other sierran systems much greater volumes of skarn rock suggest an exceptionally vigorous hydrothermal system that saw unusually high levels of decarbonation reaction progress likely a consequence of the magma intruding relatively cold wallrocks inboard of the main locus of magmatism in the sierran arc at that time

landslide displacement prediction based on multi source data fusion and sensitivity states abstract owing to the complexity of the coupling relationship between multiple external triggering factors and the internal sensitivity state of landslides it is difficult to accurately predict the displacement response of landslides to triggering factors using existing methods to overcome this setback two new concepts namely the trend sequence and sensitivity states were introduced to quantificationally characterize landslide displacement caused by external factors and the landslide internal states respectively the support vector regression method was used to predict the trend sequence while the long short term memory neural network was employed to predict the sensitivity state thereafter by fusing the predicted trend sequence and the sensitivity state a non linear model for landslide displacement prediction was proposed moreover with the baishuihe landslide located in the three gorges reservoir area as a case study the proposed model was evaluated and validated using a large quantity of rainfall reservoir water level and displacement monitoring data spanning a period of over 11 years based on the results obtained the performance of the proposed model with respect to landslide displacement prediction was satisfactory furthermore compared with three existing traditional prediction models of landslide displacement the proposed model achieved a higher accuracy therefore this study is helpful because it provides new insights that can be used to develop deep data mining approaches for landslide displacement prediction

effects of an increase in reservoir drawdown rate on bank slope stability a case study at the three gorges reservoir china abstract to increase the total power output of the three gorges hydropower station and generate greater economic benefits it is necessary to reduce the time required for the water level of the three gorges reservoir to drop i e to increase the rate at which the water level drops a rapid drop in the reservoir water level might result in a significant change in the reservoir bank environment which can destabilize landslides that extend into the water reactivate old landslide masses and form new landslide masses in the reservoir region a typical slope that extends to the water in the three gorges reservoir region was selected for study we studied the geologic conditions of a selected landslide mass and developed an expression for the hydrodynamic pressure under the effects of groundwater within the slope area and an expression for the normal stress on a sliding surface under the effect of hydrodynamic pressures in addition the evolution of the stability of the slope submerged to various depths under the effects of the lowering of the reservoir level is investigated based on a strictly global analysis a safety factor decreases about 14 as the reservoir level drops with rate of 0 6 m d and about 16 with rate of 1 2 m d at the fall of reservoir water level 30 0 m b an increase in the drawdown rate of the three gorges reservoir from 0 6 m d to 1 2 m d is unfavourable for the stability of the slope that extends into the water but the extent of the decrease in safety factors resulting from this increase in rate is not significant

genesis of metapelitic migmatites in the adirondack mountains new york oxygen isotope ratios and rare earth element ree concentrations provide independent tests of competing models of injection v anatexis for the origin of migmatites from amphibolite and granulite facies metasedimentary rocks of the adirondack mountains new york values of 18o and ree profiles were measured by ion microprobe in garnet zircon pairs from 10 sample localities prior u pb sims dating of zircon grains indicates that inherited cores 1 7 1 2 ga are surrounded by overgrowths crystallized during the grenville orogenic cycle 1 2 1 0 ga cathodoluminescence imaging records three populations of zircon i featureless rounded whole grains interpreted as metamorphic or anatectic and rhythmically zoned igneous cores truncated by rims that are either ii discordant rhythmically zoned igneous or iii unzoned metamorphic or anatectic these textural interpretations are supported by geochronology and oxygen isotope analysis in both the amphibolite facies nw adirondacks and the granulite facies se adirondacks 18o zrc values in overgrowths and whole zircon are highly variable for metamorphic zircon 6 1 13 4 n 95 10 m spot in contrast garnet is typically unzoned and 18o grt values are constant at each locality differing only between leucosomes and corresponding melanosomes none of the analysed metamorphic zircon garnet pairs attained oxygen isotope equilibrium indicating that zircon rims and garnet are not coeval furthermore ree profiles from zircon rims indicate zircon growth in all regions was prior to significant garnet growth thus petrological estimates from garnet equilibria e g p t cannot be associated uncritically with ages determined from zircon the unusually high 18o values 10 in zircon overgrowths from leucocratic layers are distinctly different from associated metaigneous rocks 18o zrc 10 indicating that these leucosomes are not injected magmas derived from known igneous rocks surrounding melanosomes have similarly high 18o zrc values suggesting that leucosomes are related to surrounding melanosomes and that these migmatites formed by anatexis of high 18o metasedimentary rocks

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

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

oxygen isotope heterogeneities and diffusion profile in composite metamorphic magmatic garnets from the pyrenees unusually large 1 8 o heterogeneities 4 within single crystals are reported in garnets from dioritic migmatites in the pyrenees these heterogeneities together with contrasting ca and p zoning allow the identification of different growth zones garnet cores with high 1 8 o values 12 14 are relatively poor in ca 7 9 mol grs and rich in p 400 900 ppm p 2 o 5 in contrast garnet rims with lower 1 8 o values 7 12 o are richer in ca 12 14 grs and poorer in p 100 200 ppm these growth zones can be ascribed to a metamorphic event followed by crustal partial melting and contamination by magmas from the mantle high 1 8 o intra crystalline contrasts result from mineral growth in an open magmatic system involving the interaction of partial melts with distinct 1 8 o signatures at the garnet core rim interface compositional profiles in major divalent cations are consistent with the relaxation of an initial sharp step in ca fe and mg by ca fe mg interdiffusion at the same interface an o isotope profile is documented the analogy of ca and o isotope profiles suggests that the 1 8 o distribution may also result from a diffusion process in this particular case temperature garnet composition oxygen fugacity o diffusion appears to be of the same order of magnitude as ca fe mg interdiffusion considering a duration of 10 ma for the plutono metamorphic event in the pyrenees ca and o diffusivities in the range 10 2 2 m 2 s at 850 c are retrieved from the measured profiles like ca o diffusion in garnet at magmatic temperatures 850 900 c is both slow enough to preserve large 1 8 o heterogeneities and fast enough to generate relaxation profiles

extreme channelization of fluid and the problem of element mobility during barrovian metamorphism geochemical profiles across chemically altered zones selvages surrounding amphibolite facies quartz kyanite veins were investigated to determine major minor and trace element mass transfer and volume strain due to channelized fluid flow the three profiles are perpendicular to two veins cutting the wepawaug schist connecticut u s a which underwent barrovian style metamorphism during the acadian orogeny selvages are highly aluminous with considerably more kyanite staurolite and garnet and less quartz plagioclase and mica than surrounding wallrocks kyanite crystals increase in size toward veins and reach several centimeters in length within veins mass balance analysis indicates 50 silica loss and 34 volume loss from selvages on average silica transferred locally from selvages to veins accounts for 40 to 80 of the vein silica the remainder must have been precipitated from fluids that flowed through the veins during regional devolatilization fluid flow also transported elements into the rock mass which were concentrated in the selvages gains of fe mn y and hree were due to the growth of selvage garnet fe zn and li were sequestered into staurolite kyanite staurolite and garnet growth resulted in al mass gains destruction of mica particularly muscovite and of plagioclase in the selvages resulted in losses of k na ba pb sn and volatiles and losses of na sr and eu respectively thin na and sr enrichment zones associated with increased modal plagioclase are found along the margins between selvages and less altered wallrock and may represent either chemical self organization produced during diffusive mass transfer and reaction or are relics from a possible earlier period of na enrichment in the selvages simple two dimensional numerical modeling of flow in a fractured porous medium indicates that fluxes vary significantly over short distances 1 m adjacent to veins fluids channelized into the high permeability fracture conduits carry the bulk of the fluid flow mass transfer to and from selvages adjacent to the conduits occurred by some combination of diffusion and flow in contrast areas distal to the conduits are impoverished in fluid and undergo much more limited infiltration as a consequence different workers can come to vastly different conclusions about the magnitude of fluid fluxes and element transfer depending on the part of a fractured outcrop studied this extreme spatial variability due to channelization can largely explain contrasting views that have arisen in the literature regarding the nature and intensity of non volatile element mass transfer during barrovian metamorphism determining average time integrated fluid fluxes and levels of element transport across outcrops remains as important research challenges due to the spatial variability of flow

two phase evolution of accretionary margins examples from the north american cordillera abstract the coast mountains orogen southeastern alaska and the salmon river suture zone western idaho record the accretion of oceanic crustal fragments to the north american cordilleran margin structural elements associated with these boundaries include a western accretion related thrust belt and steeply dipping post accretionary shear zone the shear zones the coast shear zone southeastern alaska and western idaho shear zone idaho are steeply dipping crustal scale structures characterized by steep isotopic and geophysical gradients the presence of syndeformational tabular calc alkaline tonalitic plutons concordant with shear zone fabrics locally preserved dextral strike slip indicators and pervasive down dip mineral and elongation lineations are consistent with an intra arc transpressional origin for both structures in addition to strike slip translation the structures accommodated exhumation of high pressure moderate temperature metamorphic rocks within the thrust belt to the west and moderate pressure high temperature batholithic rocks to the east similarities between the structures in alaska and idaho suggest that the observed two stage history of underthrusting of accreting crustal fragments followed by modification by intra arc transpressional shear zones is a common tectonic process our analysis implies that recognition of processes active during the accretion of crustal fragments to continental or cratonal margins is commonly inhibited by post accretion deformation and provides insight into lower crustal processes presently operative under modern strike slip accretionary boundaries in addition the intra arc transpressional shear zones e g the coast and western idaho shear zones are structures that could have accommodated paleomagnetically determined large magnitude transcurrent displacements

anatomy of garnets in a jurassic granite from the south eastern margin of the north china craton magma sources and tectonic implications abstract the late jurassic jingshan granite located at the south eastern margin of the north china craton contains abundant garnets which can be subdivided into three types based on texture and composition i euhedral garnet in mafic biotite and garnet rich enclave grt i ii coarse grained garnet grt ii in the host granite and iii small euhedral garnet in aplite grt iii in general grt i has higher feo cao and lower mno contents than grt ii grt iii has higher mn but lower ca contents than others grt i has lower mree and hree contents than grt ii grt iii has prominent and distinctly negative eu anomaly as well as higher mree composition compared to the others systematic variations in oxygen isotope compositions are observed among the three garnet types with 18 o values of 4 7 in grt iii some of the grt ii and grt iii display two distinct zonings with cores having similar major and trace element compositions to grt i cathodoluminescence cl images revealed that the zircons from different garnet bearing samples possess fine scale oscillatory zoned magmatic rims with inherited cores in situ zircon u pb dating and trace element analyses show that the dark luminescent magmatic rims all have jurassic concordia ages 160 ma and similar trace element patterns most of the inherited cores also display similar triassic ages of 210 236 ma which is similar to the ages of ultrahigh pressure uhp metamorphic rocks of the dabie sulu orogen 230 ma in addition jurassic concordia ages were also found in a zircon inclusion in grt i implying that the grt i was formed shortly before the main magmatic event the age data suggest that the three different garnet types may be genetically related and modified by cogenetic magmatic events based on the zircon u pb ages from different garnet bearing samples the major element trace element oxygen isotope and zoning textures of the three kinds of garnet we suggest that grt i may be peritectic garnet whereas grt ii and iii are probably the results of magmatic dissolution precipitation processes and re equilibration of garnets with changing magmatic conditions during melting differentiation crystallization and cooling within the granite we conclude from the oxygen isotopic character of the garnets and ages of the zircons that the source rocks for the jingshan granites are from dabie sulu orogen representing the south china craton

oxygen isotope analysis of olivine by ion microprobe matrix effects and applications to a serpentinised dunite abstract in order to resolve inter and intracrystalline oxygen isotopic heterogeneities in olivine crystals encountered in mantle peridotites basaltic lavas chondritic meteorites and metamorphic rocks in situ techniques such as ion microprobes are needed accurate ion microprobe analysis requires not only well characterised reference materials but also calibration of the matrix bias for compositional variations within a given mineral we investigated matrix bias effects related to mg fe variations in olivine during in situ analysis of oxygen isotopes with sensitive high resolution ion microprobe shrimp by analysing chemically homogenous olivine samples with forsterite contents in the range fo74 fo100 the isotopic measurements were calibrated against san carlos olivine sco fo91 the repeatability achieved for all samples was 0 21 0 50 standard deviation sd at 95 confidence level c l comparable to that of san carlos olivine 0 31 0 48 sd at 95 c l a matrix bias up to 2 0 was observed in olivine with forsterite content above 92 mol conversely to what has been reported for cameca instruments the relationship between the magnitude of matrix bias and fayalite content mol is described by the quadratic function bias fa 0 0062 fa 2 0 233 fa 1 60 the correction scheme for the matrix bias was applied to chemically zoned olivine crystals from a partly serpentinised dunite from the archean nuasahi massif eastern india olivine cores fo92 preserve their typical mantle like signature with a 18o value of 5 16 0 30 at 95 c l during a low temperature stage of serpentinisation olivine transformed to lizardite1 brucite magnetite olivine rims fo98 18o 1 92 0 60 at 95 c l and the surrounding lizardite2 4 87 0 53 at 95 c l formed during a later stage of rock fluid interaction are in isotopic equilibrium at 405 430 c with a fluid having a 18o of 5 3 6 9 evolved seawater enriched in 18o by isotopic exchange during infiltration could have been responsible for this later serpentinisation stage observed in the nuasahi massif the concomitant analysis of oxygen isotopes at the microscale in both olivine and serpentine represents a powerful tool to constrain the nature and source s of serpentinising fluid s as well as the temperature of serpentinisation

intra and intercrystalline oxygen isotope variations in minerals from basalts and peridotites igneous phenocrysts commonly exhibit zoning in major and trace element composition reflecting and potentially constraining the differentiation and or mixing histories of their parent melts to date little work has been done characterizing zonation of oxygen isotopes in minerals from mafic and ultramafic rocks we present 259 ion probe cameca ims 1280 measurements of 18 o in 34 natural magmatic and mantle olivines and pyroxenes from five hand samples from diverse igneous environments we compare 18 o variations with zonation in other elements especially p analyzed by electron microprobe analysis empa and nano secondary ionization mass spectrometry nanosims there is generally a close average within 0 1 0 2 agreement between average 18 o values of olivines measured by sims standardized against san carlos olivine and independently known values for bulk separates from the same samples measured by laser fluorination these data demonstrate that current ion microprobe techniques are not only precise but also accurate enough for study of sub per mil oxygen isotope variations in silicates within 0 2 provided samples are prepared and analyzed following strict guidelines all but one of the 34 studied grains are homogeneous in 18 o within a small multiple of analytical precision estimated 0 2 1 for most data poorer for a subset of measurements made on small 5 m spots this population of isotopically homogeneous grains includes some with oscillatory micrometer scale p banding the lack of 18 o variations suggests that whatever factors lead to this common mode of trace element zonation have no detectable effect on melt crystal partitioning of oxygen isotopes large 2 oxygen isotope variations are observed in one olivine glomerocryst from mauna kea hawaii this glomerocryst contains p rich domains that are either equant or skeletal or feathery in outline and these p rich domains are systematically low in 18 o compared with adjacent later grown p poor olivine this unusual oxygen isotope zonation pattern might reflect a kinetic fractionation during nucleation and growth of the cores of some olivine phenocrysts we tested this hypothesis through measurements of 18 o distributions in synthetic olivines grown at a range of rates and exhibiting diverse patterns of p zoning these synthetic olivines are homogeneous in 18 o within the limits of our analyses 0 3 0 4 in this case and show no connection between p zonation and oxygen isotope heterogeneity we therefore think it more plausible that unusual o isotope zonation in the mauna kea glomerocryst reflects addition of a low 18 o component to some hawaiian magmas just before nucleation of olivine more generally this study demonstrates the utility of modern sims techniques for in situ study of the subtle 1 range oxygen isotope variations characteristic of common mafic and ultramafic rocks

hydrological factors affecting rainfall induced shallow landslides from the field monitoring to a simplified slope stability analysis abstract rainfall induced shallow landslides can seriously affect cultivations and infrastructures and cause human losses a continuous monitoring of unsaturated soil hydrological properties is needed to understand the effects of pore water pressure and water content on shallow landslides triggering and slope safety factor in this work the impact of water content pore water pressure and hydrological hysteresis on safety factor reconstruction is analyzed by applying two different models lu and godt s and slip models to a monitored slope located in oltrepo pavese northern italy a shallow landslide event in the studied slope during the monitoring allowed for identifying the triggering mechanism and modeling the safety factor changes the conditions of instability mechanism develop in periods with frequent rainfalls the uprising of a perched water table in the soil profile gets nil or positive pore water pressure which linked with the nil effective soil cohesion of some soil horizons allows for the shallow landslide triggering the safety factor trends correctly predicted unstable conditions safety factor 1 0 in correspondence of the shallow landslide triggering time on the basis of both water content and pore water pressure a better prediction gets when the safety factor is modeled considering the hysteresis effects modeling the safety factor on the basis of water content can make a good assessment of shallow failures triggering conditions only for failures in unsaturated soils and for completely saturated soils instead considering pore water pressure it is possible estimating safety factor changes linked with the development of positive pore water pressures which can be linked in some cases to shallow landslide development

monitoring shallow coastal environment using landsat altimetry data under rapid sea level change abstract the caspian sea cs is the largest enclosed inland body of water and eminent for its rapid sea level change from 1929 to 1955 rapid cyclic changes with amplitudes of 3 m led to the formation of large submerged and emerged areas the present study seeks to incorporate multi source sensor data such as the landsat time series data i e mss tm etm and oli alongside radar altimetry products i e topex jason 1 ostm jason 3 as a means for extracting morphological features gorgan bay and gomishan lagoon of the southeastern shorelines of the caspian sea as well as to investigate changes in the shoreline for a given period of 42 years 1975 2016 we also employ particle swarm optimization pso algorithm as an automated method to extract shoreline change in shallow marine environments over the past century the cs has experienced a lowstand in 1977 and a highstand in 1995 despite an approximate 1 5 m drop in sea level from 1995 to 2015 gorgan bay and gomishan lagoon with depths of 4 5 and 2 5 m appear to have outlasted and emerged respectively pso is a highly efficient method capable of defining shorelines and extracting water bodies the surface area estimations using the pso method are consistent with corresponding reference values with an average error of 1 73 and a high coefficient of determination r2 0 99 differences between calculated and reference areas were mainly observed in muddy and swamp sectors of the study area this study highlights the key role of satellite time series in shoreline monitoring and management under rapid sea level change conditions moreover the study demonstrates the capabilities of the pso algorithm as an automated and accurate method for shoreline detection

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

high resolution geochemical record of fluid rock interaction in a mid crustal shear zone a comparative study of major element and oxygen isotope transport in garnet garnet grains from an intensely metasomatized mid crustal shear zone in the reynolds range central australia exhibit a diverse assortment of textural and compositional characteristics that provide important insights into the geochemical effects of fluid rock interaction electron microprobe x ray maps and major element profiles in situ secondary ion mass spectrometry oxygen isotope analyses and u pb and sm nd geochronology are used to reconstruct their thermal temporal and fluid evolution these techniques reveal a detailed sequence of garnet growth re equilibration and dissolution during intracontinental reworking associated with the ordovician carboniferous 450 300 ma alice springs orogeny a euhedral garnet porphyroblast displays bell shaped major element profiles diagnostic of prograde growth zoning during shear zone burial coexisting granulitic garnet porphyroclasts inherited from precursor wall rocks show extensive cation re equilibration assisted by fracturing and fragmentation oxygen isotope variations in the former are inversely correlated with the molar proportion of grossular suggesting that isotopic fractionation is linked to ca substitution the latter generally show close correspondence to the isotopic composition of their precursor indicating slow intergranular diffusion of o relative to fe2 mg and mn peak metamorphism associated with shearing 550 c 5 0 6 5 kbar occurred at c 360 ma followed by rapid exhumation and cooling progressive mn enrichment in rim domains indicates that the retrograde evolution caused partial garnet dissolution accompanying intra mineral porosity production then stimulated limited oxygen isotope exchange between relict granulitic garnet grains and adjacent metasomatic biotite resulting in increased garnet 18o values over length scales 200 m spatially restricted oxygen interdiffusion was thus facilitated by increased fluid access to reaction interfaces the concentration of ca in channelled fracture networks suggests that its mobility was enhanced by a similar mechanism in contrast the intergranular diffusion of fe2 mg and mn was rock wide under the same p t regime as demonstrated by a lack of local spatial variations in the re equilibration of these components the extraction of detailed reaction histories from garnet must therefore take into account the variable length and time scales of elemental and isotopic exchange particularly where the involvement of a fluid phase enhances the possibility of measureable resetting profiles being generated for slowly diffusing components such as ca and o even at low ambient temperatures and relatively fast cooling rates

analysis of baishuihe landslide influenced by the effects of reservoir water and rainfall since the impoundment of the three gorges reservoir in june 2003 a number of new landslides have occurred and existing landslides have been made worse the 1 260 104 m3 baishuihe landslide located at 56 km west of the three gorges dam began to deform more noticeably after the first impoundment in early july 2003 the sliding of the two blocks comprising the landslide one an active block and the other a relatively stable block became apparent after approximately 5 years of monitoring field recordings show that the landslide displacement is affected by the combined effects of the rainfall and water level in the reservoir these effects have been investigated in the present paper including the deformation characteristics movement pattern direction displacement and velocity earmarking the temporal evolution of the active block based on a practical creep model of a large rock slide alert velocity thresholds for pre alert alert and emergency phases have been computed corresponding to the imminence of failure the alert velocity thresholds are being proposed to be included as a part of an early warning system of an emergency plan drawn up to minimize the adverse impact in the event of landslide failure the emergency plan is intended to be implemented as a risk management tool by the relevant authorities of the three gorges reservoir in the near future

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

dehydration melting and fluid recycling during metamorphism rangeley formation new hampshire usa reflect the dewatering of structurally lower levels after nappe emmuscovite and biotite dehydration melting reactions near the peak placement if so then nappe emplacement occurred at t 475 c of metamorphism played a significant role in the reaction and fluid history of the rangeley formation in southwestern new hampshire usa evidence for in situ melting includes 1 the consistency among theoretical phase equilibria observed reaction textures and the inferred p t conditions 2 disseminated centimeter scale

oxygen isotope zoning in garnets from franciscan eclogite blocks evidence for rock buffered fluid interaction in the mantle wedge the oxygen isotope compositions of eclogite and amphibolite garnets from franciscan complex high grade blocks and actinolite rinds encasing the blocks were determined to place constraints on their fluid histories sims oxygen isotope analysis of single garnets from five eclogite blocks from three localities ring mountain mount hamilton and jenner beach shows an abrupt decrease in the 18o value by 1 3 from core to rim at a distance of 120 50 m from the rim in nine out of the 12 garnets analyzed in contrast amphibolite garnets from one block ring mountain analyzed show a gradual increase in 18o value from core to rim implying a different history from that of the eclogite blocks values of 18o in eclogite garnet cores range from 5 7 to 11 6 preserving the composition of the eclogite protolith the abrupt decrease in the 18o values of the garnet rims to values ranging from 3 2 to 11 2 suggests interaction with a lower 18o fluid during the final stages of growth during eclogite facies metamorphism 450 600 c we hypothesize that this fluid is sourced from the serpentinized mantle wedge high mg ni and cr contents of actinolite rinds encasing the blocks also support interaction with ultramafic rock oxygen isotope thermometry using chlorite and phengite versus actinolite of rinds suggests temperatures of 185 240 c at ring mountain and mount hamilton rind formation temperatures together with the lower 18o garnet rims suggest that the blocks were in contact with ultramafic rock from the end of garnet growth through low temperature retrogression we suggest a tectonic model in which oceanic crust is subducted at the initiation of subduction and becomes embedded in the overlying mantle wedge as subduction continues metasomatic exchange between high grade blocks and surrounding ultramafic rock is recorded in low 18o garnet rims and later as temperatures decrease with rind formation