effects of experimental leaching on rbsr and kar isotopic systems and ree contents of diagenetic illite leaching with 1 n hcl 1 n nh4cl acetone humic acid extracts cation exchange resin and nh4 edta have negligible effects on the rb sr and k ar systems of different size fractions 0 4 and 0 8 2 m of a 1m diagenetic illite none of these treatments including the 1 n hcl treatment induced preferential removal of radiogenic 87sr and 40ar from mineral structures however the 1 n hcl treatment removed significant amounts of sr and ree as compared to the treatments by nh4 edta and cation exchange resin however much of these hcl derived elements resided in non clay minerals such as carbonate and fe oxide phases the k ar and rb sr ages of the samples were not affected by the hcl treatment any more than by the nh4 edta or the cation exchange resin because of potential loss of solid material during elutriation of differentially treated samples the hcl treatment is preferred over other methods allowing sufficient controls on the isotopic and mass balances between the leachate and the corresponding residue of an untreated sample for rb sr isotopic dating purposes of clay minerals from sedimentary and metasedimentary rocks leaching experiments give information about the ambient environment of crystallization analysis of both the leachate and residue under carefully controlled conditions is recommended

effect of calcite precipitation on stable strontium isotopic compositions insights from riverine and pool waters in a karst cave abstract radiogenic and stable sr isotope ratios 87 sr 86 sr 88 86 sr serve as potential tracers for evaluation of weathering sources and associated physicochemical processes in terrestrial environments despite carbonate weathering sourcing two thirds of the total continental sr flux to the ocean however few attempts have been aimed at studying stable sr isotope fractionation in carbonate dominated aquifers here we present a monthly resolved monitoring dataset of major ion concentrations and sr isotope ratios for karst riverine and pool waters at the luofang cave in the central china to understand the potential controls responsible for water 88 86 sr compositions under various climatic conditions with the exception of some pool waters in the dry period significantly heavier 88 86 sr were detected in the riverine and pool waters 0 20 to 0 42 compared to bedrock 88 86 sr 0 24 to 0 28 which can t be interpreted solely by lithology a sequential leaching experiment of the local soils suggests limited stable sr isotope fractionation during incongruent silicate mineral dissolution local plant utilization and biological activity in the soil overlying the cave are possible processes for causing the observed heavier 88 86 sr in cave water however air partial pressure of co 2 in cave monitoring water ph and sr isotopic mass balance calculations suggest that plant utilization is unlikely to be the primary control on the heavier water 88 86 sr on the other hand significant stable sr isotope fractionation was found between the cave dripping waters and calcite precipitates and the 88 86 sr car aq was estimated to be 0 15 0 07 2sd precipitation of secondary calcites might be a potential process responsible for the heavier 88 86 sr in the waters the negative correlation between 88 86 sr and sr na ratios in the cave waters is consistent with a scenario of preferential incorporation of the light sr isotope by solid phase furthermore by combining the calcite saturation states and water ph our results suggest that calcite precipitation is the most likely process controlling 88 86 sr compositions in cave water we demonstrate that secondary calcite precipitation in carbonate dominated catchments could be important in controlling the riverine water 88 86 sr compositions

radiogenic and stable sr isotope ratios 87 sr 86 sr δ 88 86 sr as tracers of riverine cation sources and biogeochemical cycling in the milford sound region of fiordland new zealand this study reports radiogenic sr isotope ratios 87sr 86sr stable sr isotope ratios 88 86sr and major ion concentrations for river rock sediment soil and plant samples collected from the cleddau and hollyford catchments in the milford sound region of fiordland new zealand the catchments primarily drain gabbro but some tributaries access limestone and volcanogenic sediments the goal of the study was to understand controls on riverine 88 86sr values in a landscape with multiple factors that may influence chemical weathering including dense vegetation high rainfall and abundant freshly eroded holocene fluvio glacial and landslide debris rivers draining gabbro have higher 88 86sr values than bedrock by as much as 0 14 and the 88 86sr values strongly correlate with molar ca sr ratios r2 0 69 leaching of rocks and sediment reveals no evidence for the preferential dissolution of minerals having high 88 86sr values and ca sr ratios in stream sr isotope fractionation seems unlikely because comparison against 87sr 86sr and ca sr ratios demonstrates that riverine 88 86sr values conservatively trace water mass mixing the riverine data are best explained by the input of soil water which is distinct from potential bedrock end members i e silicates and carbonates based on 88 86sr but indistinguishable in terms of ca sr and 87sr 86sr while strontium isotope fractionation during secondary mineral formation and pedogenesis is possible clay mineral formation is minor and most soils are poorly developed instead soil water 88 86sr values more likely reflect plant uptake plant samples yielded a wide range of 88 86sr values but on average they are lower than those for bedrock consistent with the expectation that plants preferentially incorporate lighter sr isotopes mass balance constraints together with 87sr 86sr ratios indicate that soil water 88 86sr values are 0 30 higher than bedrock 88 86sr values and mixing calculations show that the plant fractionated soil water pool contributes 27 of the riverine sr for tributaries accessing limestone and volcanogenic sediments ca sr and 87sr 86sr ratios appear consistent with two component mixing between silicate and carbonate weathering but 88 86sr values reveal a third contribution from soil water inputs similar to gabbro catchments the results of this study suggest that sr isotopes behave conservatively during water mass mixing and stream transport but non conservatively in soil where plant uptake can elevate soil water 88 86sr values relative to bedrock plant uptake or related biogeochemical processes such as ion exchange on organic matter surfaces also appear to modify soil water ca sr ratios many studies use 87sr 86sr and ca sr ratios to apportion riverine solutes between silicate and carbonate weathering but ca sr ratios may be non conservative in densely vegetated areas the stable sr isotope tracer shows promise for resolving riverine cation sources as well as effects from biological cycling

study of plasmaspheric evolution using geosynchronous observations and global modeling we examine the dynamics of the outer plasmasphere during a 3 day interval in february 1992 by comparing observations from three widely spaced geosynchronous satellites with the predictions of the magnetospheric specification and forecast model msfm for this study the msfm was modified to include a cold plasmaspheric population subject to the effects of corotation convection and ionospheric refilling the model does a very good job of reproducing the observations in particular it clearly shows the formation and westward transport of duskside plasmaspheric plumes accounting for the progressively earlier local time observations of cold ions following periods of enhanced convection the msfm s ability to model dynamically the evolution of the outer plasmasphere under varying solar wind conditions improves upon previous plasmaspheric models and has aided our understanding of spatially and temporally separated observations of plasmaspheric ions at geosynchronous orbit

effects of bedrock on the chemical and sr isotopic compositions of plants this study was conducted to investigate the relationship between the chemical and isotopic compositions of plants and the lithology of their growth location this relationship is one of the principles underlying the geographical discrimination used for agricultural forestry and food products locations in south korea with solely basaltic jeju granitic gongju and carbonate yeongwol rocks were selected as test sites and bedrocks soils and plants in each location were sampled the multi element compositions and sr isotope ratios 87sr 86sr were analyzed for all samples including various soil fractions exchangeable carbonates silicates and plant parts tree leaves vegetable leaves and fruits based on a preliminary statistical analysis anova ca mg k al sr concentrations and 87sr 86sr ratios were selected as key variables with greater variability with location using these variables a multivariate statistical analysis was conducted and three soil fractions and plant parts were successfully discriminated according to their geographical origin i e bedrock type with statistical significance the results indicated that sr isotope ratios of bedrocks can be preserved in soils except in silicate fractions and plants throughout weathering and plant physiological processes and are the most critical variable in the tracing of bedrock characteristics

40ar 39ar illite dating of late caledonian acadian metamorphism and cooling of k bentonites and slates from the welsh basin u k the vacuum encapsulation laser 40ar39ar technique allows extremely small 10 6 g samples of fine grained materials such as diagenetic clays to be dated here we show that the method can be extended to higher grade clay minerals the integration of transmission electron microscopic tem characterization with 40ar39ar dating of vacuum encapsulated samples permits the resolution of the timing of metamorphic growth cooling from the time of diagenesis we have applied this technique to well characterized lower paleozoic slates and k bentonites from the welsh basin which span the transition from anchizonal to epizonal grade which had been previously studied using rbsr and smnd dating tem observations of epizonal k bentonites and slate showed that illite in these samples is of 2m1 polytype of muscovite like composition and oriented parallel to cleavage suggesting that they are of metamorphic origin total gas ages equivalent to conventional kar ages for encapsulated epizonal k bentonites and slate 340 408 ma are considerably variable the ar retention ages calculated from 39ar and 40ar atoms retained in the sample after irradiation are more consistent 383 411 ma the 39ar recoil losses are minor for illites from whole rock samples of epizonal k bentonites but very significant for clay separates of epizonal slate plateaus in age spectra were observed in epizonal k bentonites and slate the plateau ages 414 421 ma and retention ages 383 411 ma can be correlated with the onset of acadian metamorphism and culmination of uplift and inversion of the welsh basin respectively these ages are significantly younger than the 450 ma ages previously reported for diagenetic clays using the same method suggesting that diagenetic history has been lost in these epizonal k bentonites and slate tem observations of anchizonal slates showed that there are two modes of illite the first mode is similar to that observed in epizonal samples suggesting a metamorphic origin the second mode consists of the 1md polytype has typical diagenetic illite composition and is oriented parallel to bedding suggesting a diagenetic origin total gas ages for encapsulated anchizonal slates vary considerably 361 422 ma the retention ages are more consistent 413 432 ma than the total gas ages the 39ar recoil losses are more significant than those for epizonal k bentonites and slate plateaus in age spectra are generally not observed however the consistent retention ages for the anchizonal slates correspond to the plateau ages for the epizonal samples and are inferred to represent the onset of acadian metamorphism these data when combined with our previously published results for diagenetic shales suggest that thermal conditions near the boundary of anchizonal and epizonal grades are necessary to completely reset ar systems in shales and slates

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

recrystallization or cooling ages in situ uv laser 40ar 39ar geochronology of muscovite in mylonitic rocks the intra grain 40 ar 39 ar age distributions of muscovite from greenschist facies mylonite zones are shown to be sensors of metamorphic history textures compositions and in situ uv laser ablation 40 ar 39 ar data from two extensional shear zones demonstrate that cooling ages can be distinguished from neo or recrystallization ages deformed muscovite porphyroclasts and recrystallized shear band muscovite from the pogallo shear zone ivrea zone southern alps reveal variable intra grain 40 ar 39 ar ages with internal age variations of more than 65 ma the wide range of 40 ar 39 ar ages within compositionally homogeneous grains is consistent with diffusion dominated argon loss controlled by observable intra grain microstructures in contrast intra grain 40 ar 39 ar ages of muscovite fish from proterozoic mylonite of the porsgrunn kristiansand shear zone southern norway display only minor age dispersion and age variations are correlated with changes in muscovite composition the sympathetic age composition correlations in different muscovite microstructures directly relate to sequential neo and recrystallization of muscovite and ultimately provide insight into the protracted recrystallization history during extensional deformation along the porsgrunn kristiansand shear zone

weathering rates and 87sr 86sr ratios an isotopic approach the 87sr 86sr ratios of precipitation throughfall groundwater streamwater and mineral matter were analyzed precipitation strontium ratios are around 0 71 throughfall which is affected by strontium from the mineral soil has ratios of 0 72 0 73 and shallow groundwater in a drug well and runoff have ratios around 0 73 0 74 there is a tendency for this relationship to be reversed for discharge higher ratios are associated with lower discharges water from a fracture zone gave the highest value 0 78 approaching the value of the bedrock around 0 85 a calcium budget which reflects the mean conditions over a few years has been calculated this budget indicates that weathering should be of the order of 8 kg ca ha 1yr 1 to maintain the pool of exchangeable calcium at a constant level the major anion in the runoff is suphate which has entered the system in the form of acid rain sulphur deposition has been rather constant over the last two decades if acidification had an effect on weathering of silicates this would have shown up in a tendency of the strontium isotope ratios toward higher values in the soil pool and in runoff water thus its seems from the observed ratios that at least a major portion of the excess calcium export resulting from sulphur deposition is taken from the soil pool resulting in a gradual acidification of the soil

rio tinto sedimentary mineral assemblages a terrestrial perspective that suggests some formation pathways of phyllosilicates on mars abstract the presence of extensive phyllosilicate deposits from the early noachian of mars are often interpreted as having formed from neutral to subalkaline solutions in this paper we examine the rio tinto fluvial basin an early mars analog that hosts clay production and sedimentation along the entire course of the river at rio tinto phyllosilicate minerals including clays and micas are sourced by volcanosedimentary bedrock of rhyolitic and andesitic composition affected by carboniferous hydrothermal alteration pleistocene to modern acidic weathering of those materials chemically altered the volcanic and sedimentary materials to k na clay montmorillonite smectites kaolinite assemblages in paleosoils and fractures while physical weathering degrades phyllosilicates more resistant to acidic attack during the wet season phyllosilicates are eroded transported and deposited from both acidic headwaters and neutral tributaries during the dry season sulfates and nanophase oxyhydroxides co precipitate late summer storms that cause fast flooding events mix illite quartz feldspars iron oxides and other minerals in fluvial deposits where these minerals are stabilized and aggrade until the following wet season as a result chemical precipitates primary phyllosilicates and secondary clays form mineral admixtures that explain the compositional diversity of the fluvial deposits these deposits reveal the persistence of smectites whose occurrence is explained given that the reaction kinetics under acidic conditions of degradation is lowered by seasonal discharges of the river the longevity of phyllosilicate minerals within fluvial deposits depends on climatic and geochemical conditions and processes which are in turn are correlated to temperature persistence of water hydrological cycling hydrogeochemistry and composition of the source materials in the basement these parameters are universal and have to be characterized in order to understand the distribution of mineral composition on any planetary surface including mars

evidence for stable sr isotope fractionation by silicate weathering in a small sedimentary watershed in southwestern taiwan abstract radiogenic sr isotopes 87 sr 86 sr are robust for provenance identification in hydrology affected mainly by the age of background lithologies and the degree of chemical weathering however there is limited knowledge concerning the fractionation mechanism of stable sr isotopes 88 sr 86 sr in rivers in this study river water was collected on a weekly to monthly basis throughout dry and wet seasons furthermore to study the variations of radiogenic and stable sr isotopes during intense weathering a major flooding event 2000 mm precipitation in three days typhoon morakot water was captured within a small drainage catchment system 161 km 2 along the hou ku river in southwestern taiwan for a better constraint on the end member compositions bedload sediments suspended particles and several host rocks were sampled for a systematic investigation the carbonate and silicate phases of these solids were chemically separated dissolved major elements indicate that the watersheds were predominated by silicate weathering stable sr isotopes show no significant variation 88 sr 0 24 0 31 temporally and spatially with an average of 0 28 additionally all solids showed lower 88 sr values than the river water while the host rocks had higher 88 sr values 88 sr 0 20 0 26 than the residual weathering products 88 sr 0 08 0 22 indicating preferential leaching of heavy sr into the hydrosphere and leaving light sr in the residual solids results of laboratory acid leaching experiments reveal that dissolution of high 88 sr value minerals occurred at an early stage of weathering the variation of weathering intensity does not alter stable sr isotopes in silicate weathering dominated river water which contains higher stable sr isotopes than the associated sediments the silicatic sedimentary rocks preferentially released higher stable sr isotopes into the hydrosphere during chemical weathering thus leaving lower stable sr isotopes in the residual solids

ca sr and ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence in hawaii abstract nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus p and calcium ca from minerals at depth and concentrate those nutrients at the surface here we use soil chemistry and stable isotopes of the alkaline earth elements ca strontium sr and barium ba to test the hypothesis that biolifting of p has been an important pedogenic process across a soil climosequence developed on volcanic deposits at kohala mountain hawaii the geochemical linkage between these elements is revealed as generally positive site specific relationships in soil mass gains and losses particularly for p ba and ca using the ratio of immobile elements titanium and niobium ti nb to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials at sites where p is enriched in surface soils relative to abundances in deeper soils the isotope compositions of exchangeable ca sr and ba in the shallowest soil horizons 10 cm depth at those sites is consistently heavier than the volcanic parent materials the isotope compositions of exchangeable ca and sr trend toward heavier compositions with depth more gradually reflecting increasing leakiness from these soils in the order ba

timing of tectonic events in the alpujarride complex betic cordillera southern spain ar ar and fission track dating from four low grade sections in the alpujarride complex sheds light on the timing of the early contractional history of these high pressure metamorphic units and their subsequent exhumation during the early miocene extensional collapse of the betic orogen white mica grains from the lowest grade rocks yield partly reset detrital ar ar ages where deformation and recrystallization are more intense however they yield reproducible ages as old as c 48 ma which we interpret as the approximate timing of the main contractional event and associated high pressure metamorphism in these units rocks from slightly higher grade sections give reproducible ar ar ages between 30 and 40 ma but these younger ages probably reflect the interplay of growth and cooling in fine grained micas heated to between 300 c and 400 c during prograde metamorphism in each of the four areas studied the low grade rocks are separated by an extensional detachment or shear zone from medium grade rocks below in two areas these detachments have been folded around major overturned north vergent folds ar ar data from structurally below the detachments and fission track ages from all structural levels indicate the onset of significant cooling in the early miocene which corresponds to the age of the extensional event the folds must therefore be early miocene or younger

empirical modeling of the plasmasphere dynamics using neural networks we propose a new empirical model for reconstructing the global dynamics of the cold plasma density distribution based only on solar wind data and geomagnetic indices utilizing the density database obtained using the nurd neural network based upper hybrid resonance determination algorithm for the period of october 1 2012 july 1 2016 in conjunction with solar wind data and geomagnetic indices we develop a neural network model that is capable of globally reconstructing the dynamics of the cold plasma density distribution for 2 l 6 and all local times we validate and test the model by measuring its performance on independent datasets withheld from the training set and by comparing the model predicted global evolution with global images of he distribution in the earth s plasmasphere from the image extreme ultraviolet euv instrument we identify the parameters that best quantify the plasmasphere dynamics by training and comparing multiple neural networks with different combinations of input parameters geomagnetic indices solar wind data and different durations of their time history the optimal model is based on the 96 hour time history of kp ae sym h and f10 7 indices the model successfully reproduces erosion of the plasmasphere on the night side and plume formation and evolution we demonstrate results of both local and global plasma density reconstruction this study illustrates how global dynamics can be reconstructed from local in situ observations by using machine learning techniques

introducing δ88 86sr analysis in archaeology a demonstration of the utility of strontium isotope fractionation in paleodietary studies abstract isotopic methods are widely used in archaeology to investigate paleodiet here we present a new method to identify trophic level in archaeological human populations and to investigate paleodiet we demonstrate that strontium isotope compositions reported as 88 86sr vary in a mass dependent manner with increasing trophic level and can elucidate paleodiet in archaeological human populations we present new mass dependent strontium isotope data from tooth enamel and bone from individuals buried during the late intermediate period c ad 1000 1300 in the large cemeteries of chiribaya alta chiribaya baja san geronimo and el yaral in the ilo and moquegua valleys of southern peru we compare these data to radiogenic strontium isotope data 87sr 86sr and light stable isotope data 15ncol and 13ccol from the same individuals to investigate geologic variability in strontium sources as well as marine food consumption among the chiribaya our results demonstrate the utility of measurements of strontium isotope fractionation as a new tool for archaeological investigation of paleodiet importantly this new technique can be used to generate paleodietary 88 86sr and paleomobility 87sr 86sr data from the same specimen minimizing destructive analyses of invaluable archaeological material and provides a new way to examine paleodiet through hydroxyapatite which is particularly important when collagen is poorly preserved

k ar dating constraints on the tectonothermal evolution of the external humber zone southern quebec appalachians in the external humber zone the emplacement episodes of allochthonous nappes and related low grade metamorphism are mainly based on paleontological ages from the st lawrence lowlands in fact late ordovician flysches are affected by thrusting and it is not clear if the nappe imbrication is the result of the taconian or the acadian deformation along the chaudiere river transect fourteen shales and phyllites of cambrian to ordovician age were sampled for determination of the k ar values of their 2 m size fractions to interpret the k ar data mineral composition and clay mineral crystallinity of the 2 m size fractions and maturation of the organic matter were determined in addition the intensity of deformation was characterized by describing the rock texture at macroscopic and microscopic scale the combined approach used in this study emphasized that nearly all k ar dates are mixed or partly reset values however it can be stated that in the quebec promontory nappe and part of the chaudiere

moon based euv imaging of the earth s plasmasphere model simulations the euv imager on board the chang e 3 lunar lander will image the earth s plasmasphere from a lunar perspective to focus on some of the open questions in plasmaspheric researches i e global structures erosion and refilling of plasmasphere in order to achieve the understanding of the plasmaspheric dynamics in relation to these euv images in lunar perspective the he 30 4nm emission intensities and global structures of the plasmasphere viewed from the moon are investigated using a dynamic global core plasma model embedded with ts07 magnetic field model and w05 electric field model two typical storms observed by the image euv imager are systematically simulated from the perspectives of the moon it is found from the simulations that the maximum emission intensity of the plasmasphere is similar to 12 3 r which is greater than that detected from polar orbit and the global shapes and temporal evolutions of large scale plasmaspheric structures plasmapause shoulder and plume also have different patterns in moon based simulated images it is also shown that the plasmaspheric structures extracted from moon based euv images are in agreement with those from image euv images systematic simulations demonstrate that specific latitudinal distribution of the plasmaspheric structures can only be imaged at specific positions in lunar orbit it is expected that this investigation provides us with an overall understanding on moon based euv images and helps to identify the plasmaspheric structures and evolution patterns in future moon based euv imaging

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

effect of plasmaspheric drainage plumes on solar wind magnetosphere coupling evidence is uncovered that plasmaspheric drainage plumes flowing into the dayside reconnection site mass load the reconnection rate and thereby reduce the coupling of the solar wind to the earth s magnetosphere solar wind magnetosphere coupling is statistically analyzed with the 1963 2003 omni2 data set matched up with the ae au and pci geomagnetic indices times when plasmaspheric drainage plumes are flowing are discerned using multiple spacecraft with plasma detectors in geosynchronous orbit it is found that for a given value of vbz of the solar wind the geomagnetic indices ae au and pci are statistically lower when plasmaspheric drainage plumes are present than when plumes are not present this is taken as a measure of a weakened coupling of the solar wind to the earth s magnetosphere caused by the plumes an addendum examines the effects of polar cap saturation on the auroral electrojet index

k ar dating of magmatic sericite crystallites for determination of cooling paths of metamorphic overprints a combined optical and x ray characterisation of fine grained micas in granodioritic to tonalitic dikes and intrusions of the eastardennes eifel nappe linksrheinisches schiefergebirge germany belgium was completed with k ar dating of separated size fractions from these rocks in each sample the k ar ages decrease with decreasing size fraction but the same size fractions of the different samples yield different ages application of the closure temperature concept to the k ar ages of the various size fractions indicates that the crystallite size expressed as cis fwhmser001ad and coherent scattering domain csd thickness acts as the effective radius of ar diffusion a linear model may describe the correlation between k ar ages and crystallite thickness the ages younger than the model prediction are caused by the occurrence of microcline as an accessory k bearing mineral phase the obtained k ar ages were interpreted as representative of the cooling path of the magmatic components in the eastardennes eifel nappe below 330 c the k ar age of the largest size fraction of the tonalitic dike v11 313 6 7 2 ma is the closest value for the age of the variscan cleavage development the oldest age of the hydrothermally altered tonalitic dike 300 2 8 4 ma might represent an episode of hydrothermal fluid migration after cleavage development it represents at least a minimum age the microcline age 242 8 6 0 ma of the hill intrusion may represent the closure temperature of this mineral at about 140 c

determination of temperature dependent stable strontium isotope 88sr 86sr fractionation via bracketing standard mc icp ms stable strontium isotopes here 88sr 86sr are introduced as a new member of the nontraditional stable isotopes we have developed a bracketing standard method for the determination of 88 86sr using an axiom mc icp ms and normalizing to strontium srm nbs987 for individual measurements the external reproducibility is better than about 25 ppm 1 rsd for the iapso seawater standard a 88 86sr value of 0 381 0 010 2sem was determined for the first time a temperature dependent strontium isotope fractionation during calcium carbonate precipitation could be shown aragonite samples inorganically precipitated under temperature control between 10 and 50 c revealed a 88 86sr temperature dependency of 0 0054 5 c r2 0 987 in contrast for natural coral samples pavona clavus from a proxy calibration study 23 to 27 c we did determine 0 033 5 c r2 0 955 the processes causing this sixfold stronger temperature dependency for the natural coral samples have to be studied in more detail in future studies in a first approach the different slopes can be interpreted as effects of kinetic fractionation of strontium ions with or without a hydrate shell of 22 to 29 water molecules

88 sr 86 sr fractionation and calcite accumulation rate in the sea of galilee abstract this study used the sea of galilee lake kinneret northern israel as a natural laboratory to investigate the fractionation of the stable sr isotope ratio 88 sr 86 sr during precipitation of inorganic primary calcite from the lake s water it was found that the absolute value of the 88 sr 86 sr fractionation factor 88 86 sr increases as a function of calcite accumulation rate 88 86 sr 0 05 to 0 042 log r mol m 2 d 1 where r is the accumulation rate furthermore the 87 sr 86 sr and 88 sr 86 sr ratios in the freshwater and brines that enter the lake were used to calculate the contributions of these sources to the lake sr budget the 87 sr 86 sr and 88 sr 86 sr ratios were measured in primary calcite aragonite shells of live melanopsis lake water and various water sources to the lake while the lake s 87 sr 86 sr ratios are determined by the mixture of freshwater of the jordan river and saline springs the 88 sr 86 sr ratios of the lake reflect a more complex mass balance that includes the effect of isotopic fractionation associated with the precipitation of primary calcite data analysis suggests that long term accumulation of inorganic calcite depleted in the heavy isotope 88 sr results in an increase of the 88 86 sr value of the lake water by 0 05 in contrast to the primary inorganic calcite biogenic aragonite of the melanopsis shells show a rather constant 88 sr 86 sr water caco 3 fractionation of 88 86 sr 0 21 similar 88 86 sr values were reported for the precipitation of coralline and inorganic aragonite from seawater and the precipitation of inorganic calcite from various continental waters the 88 86 sr value of inorganic calcite is modulated by the rate of carbonate precipitation as noted above and shown by precipitation experiments massive precipitation of primary calcite with a wide spread of accumulation rates occurs during the spring phytoplankton bloom in lake kinneret the bloom dictates the degree of calcite saturation in the lake and hence the stable sr isotopic composition of the precipitating calcite the correlation between 88 sr 86 sr and the calcite accumulation rate can be therefore used as a tool to reconstruct environmental and ecological variations in the historical lake by analyzing the 88 sr 86 sr ratio in the primary caco 3 recovered from the lake s sedimentary archives

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

dating incipient metamorphism using 40 ar 39 ar geochronology and xrd modeling a case study from the swiss alps six samples of a single carbonate rich unit of the swiss prealpes progressively metamorphosed from diagenesis to deep anchizone yield 40ar 39ar spectra with variably developed staircase patterns consistent with mixtures of detrital mica and neocrystallized mixed layer illite smectite the lowest temperature heating steps for different size fractions 2 6 m and 6 20 m converge to 40 ma providing an imprecise maximum age of regional metamorphism a method is described for distinguishing and quantifying the amount of pre existing detrital mica versus neoformed illite layer in the illite smectite formed during tertiary alpine metamorphism by comparison of x ray diffraction patterns with newmod simulations in the least metamorphosed samples the illite smectite contains 65 neoformed illite and this illite accounts for approximately 17 of all dioctahedral phyllosilicate minerals in the rock e g detrital mica and illite smectite in contrast the illite smectite from the more strongly metamorphosed samples contains 97 neoformed illite which accounts for 70 to 90 of all dioctahedral phyllosilicate minerals phyllosilicate morphologies viewed by scanning electron microscopy are consistent with these estimates a process of dissolution reprecipitation is inferred as a mechanism for the growth of the neoformed phyllosilicates a plot of neoformed illite content versus 40ar 39ar total fusion age yields a near linear curve with an extrapolated age of 27 ma for 100 neoformed dioctahedral phyllosilicates this age is interpreted as the time of incipient metamorphism and is consistent with independent biostratigraphic constraints model 40ar 39ar age spectra constructed with the xrd simulation results correspond well to the experimental data and illustrate the changes in degassing properties of progressively metamorphosed mixtures of detrital mica and neoformed illite

le complexe d ascot des appalaches du sud du quebec petrologie et geochimie this paper reviews new geochemical data obtained from ordovician volcanics in the ascot complex of the quebec appalachians the ascot complex is divided into three distinctive lithotectonic assemblages the sherbrooke eustis and stokes domains the sherbrooke domain includes basalts pyroclastic breccias and felsic tuffs the eustis domain is composed of volcanoclastic and pyroclastic rocks the stokes domain is an assemblage of rhyolitic tuffs and basalts the geochemical composition of the volcanics varies between basaltic and rhyolitic end members basaltic rocks are arc tholeiites la yb 0 5 2 some basalts found in the sherbrooke domain show a composition very close to that of frontal arc boninites la yb 1 2 and are depleted of rare earth elements felsic rocks from the sherbrooke domain are poorer in light rare earth elements la yb 0 5 0 7 than those from the stokes domain la yb 2 all of the felsic rocks are characterized by a negative eu anomaly eu eu 1 3 3 the stokes felsi

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

in situ uv laser 40ar 39ar geochronology of a micaceous mylonite an example of defect enhanced argon loss muscovite and biotite from a crustal scale mylonite zone pogallo shear zone southern alps were investigated using furnace step heating and in situ uv laser ablation 40ar 39ar geochronology undeformed muscovite porphyroclasts yield 40ar 39ar plateau ages of 182 0 1 6 ma whereas in situ uv laser ablation 40ar 39ar dating and furnace step heating of strongly deformed muscovite and biotite grains display a range of apparent ages that are systematically younger the range of 40ar 39ar ages measured in the deformed muscovite and biotite is consistent with protracted cooling through argon closure in minerals that exhibit variably developed segmentation on the intra grain scale these microstructurally controlled segments are bound by either first order lattice discontinuities sub microscopic structural defects and or zones of high defect density which create variable length scales for intragranular argon diffusion the observed deformational microstructures within muscovite and biotite acted as intra grain fast diffusion pathways in the slowly cooled mylonitic rocks therefore the high spatial resolution 40ar 39ar data record the initial and final closure to argon diffusion over a time span of about 60 ma

characterizing nutrient pathways in quebec canada vineyards insight from stable and radiogenic strontium isotopes abstract soils are a crucial interface of earth s critical zone responsible for the biogeochemical cycling of mineral nutrients while the sources of essential nutrients such as ca and sr in plants have been widely studied the processes by which these nutrients are transferred from the soil to the plants is less clear we present new evidence for systematic nutrient fractionation between soils grapes and wines from five vineyards from the quebec terroir canada using the novel stable sr 88 86sr isotope system we coupled this approach with traditional radiogenic 87sr 86sr measurements on the same samples bulk soils labile fraction of these soils whole grapes and wines from five vineyards from the quebec terroir canada to ensure that variations in 88 86sr values were provoked by processes involved in sr transfer instead of mixing between different sources the 88 86sr values generally decrease from the bulk to the labile fractions of the soils to the grapes a decrease in the difference between the soil fractions 88 86srbulk labile with increasing 88 86sr values in the labile fraction is interpreted to reflect increasing pedogenic mineral precipitation and higher soil fertility the depleted 88 86sr values of the grapes are consistent with a preferential uptake of lighter isotopes by plants this effect is magnified in soils showing higher secondary mineral precipitation an increase in the 88 86sr values from the grapes to the wines reflects the separation of the skin seeds and the juice pulp enriched in 88sr in the winemaking process this mixing relationship is supported by a correlation between the sr concentrations and the 88 86sr values of the wines and grapes these findings suggest promising new applications of stable sr isotopes values for studying soil fertility and the impact of nutrient availability for plant growth in agricultural ecosystems as well as the impact of the maceration processes in the production of wine the overall similarity of 87sr 86sr ratios of the labile soil fractions grapes and wines from the same vineyard support the hypothesis of a same sr source from the soil solution to its transfer to the grape and wine and confirm the potential of the 87sr 86sr ratios as a proxy for geographic provenance of wine however slightly lower 87sr 86sr ratios in the grape pulps by 0 00040 on average compared to the skins and seeds suggest that the sources of nutrients available for plant uptake vary during the vegetative cycle the grape seeds and skins formed in the early growth cycle are characterized by rapid growth due to enhanced rhizosphere activity enhanced mineral dissolution providing higher nutrient levels the enhanced mineral solubility results in higher 87sr 86sr ratios in the skin and seeds derived from enhanced dissolution of 87sr enriched silicate minerals in contrast the pulp develops later in the growth cycle when rhizosphere activity and mineral solubility is reduced resulting in a lesser contribution from silicate minerals and thus reflect a higher proportion of dissolved carbonate contributing to the lower 87sr 86sr ratios of the pulps

pb and sr isotopic compositions of snowpack from quebec canada inferences on the sources and deposition budgets of atmospheric heavy metals elemental concentrations of al ba cd cu mg mn pb rb sr and zn as well as pb and sr isotopic compositions were determined in samples of snowpack obtained along two main transects from the province of quebec canada one north south between 47 n and 55 n 1994 and the other within the st lawrence valley 1997 median enrichment factors relative to upper crustal abundances for cd cu mn pb and zn for all samples range from 300 to 42 000 and are indicative of an anthropogenic origin pb isotope ratios for snow samples retrieved in 1994 are highly variable 206pb 207pb 1 148 to 1 193 and are characterized by the most radiogenic sr isotope values 87sr 86sr 0 710 in contrast the pb and sr isotope results for 1997 snow samples collected along the st lawrence valley below latitude 47 n yield the most radiogenic pb isotope ratios 206pb 207pb 1 180 to 1 190 and 87sr 86sr ratios between 0 708 and 0 710 the former indicate that the atmospheric pollution in this region of quebec is dominated by a mixture of anthropogenic emissions from u s 206pb 207pb 1 20 and canadian 206pb 207pb 1 15 sources pb isotope ratios 206pb 207pb 1 160 to 1 180 for 1997 samples collected north of latitude 47 n indicate input of an additional anthropogenic component possibly that of eurasian pollution being transported over the high arctic during the winter season a comparison of the pb isotope results between lichens and snow samples from identical sample locations indicate that these either overlap along st lawrence valley or are significantly different north south transect the latter discrepancy may be attributed to either 1 different time scales for the integration of the atmospheric signal months for snow vs years for lichens 2 recording of the atmospheric signal at substantially different altitudes or 3 the presence of an important local point source of atmospheric pollution annual depositional budgets have been estimated for pb cd zn cu and mn and average values g km 2 yr 1 are 1500 130 196 000 1900 and 6400 respectively compared to previous depositional fluxes 1993 1994 estimated from adjacent regions in north america those reported here are slightly lower with the exception of mn and zn the nondecrease in depositional fluxes of mn may be attributed to combustion of mn bearing fossil fuels by automotive vehicles the exact cause for the elevated annual depositional values for zn however remains enigmatic

k ar dating of episodic mesozoic fluid migrations along the fault system of gernsbach between the moldanubian and saxothuringian northern black forest germany along the sw ne trending fault zone of gernsbach northern black forest over a distance of about 45 km between baden baden and pforzheim basal series of the sedimentary cover are extensively altered by hydrothermal solutions the fluids were conveyed in the fault zone and because of favourable permeabilities they spread out along the unconformity between the basement and sedimentary cover k ar dates on authigenic white micas illites and hydrothermally altered detrital micas point to the occurrence of two major episodes of fluid migration the extensive alteration along the entire fault system occurred about 150 ma ago during the jurassic in relation to these hydrothermal activities the epigenetic strata bound uranium deposit of mullenbach originated in upper carboniferous sediments near the fault and the fluorite quartz vein type mineralization of kafersteige was formed along the fault about 100 ma ago during the cretaceous the results indicate various geological processes of the fault system of gernsbach which is located between the saxothuringian and moldanubian zone the mobilization of the fluids and the formation of the ore deposits were probably caused by and connected with tectonic activities in mid europe

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk

strontium stable isotopes fractionate in the soil environments abstract this study shows that the stable isotopic composition of strontium the 88sr 86sr ratio expressed as 88 86sr value relative to the nbs987 standard varies significantly in sedimentary terrestrial environments the abundances of 86sr 88sr isotopes were analyzed by mc icp ms nu plasma all studied rocks and waters show 88 86sr values that are distinctly different from the measured nbs987 standard yielding 0 01 0 05 all errors are reported as 2 modern corals from the northern gulf of aqaba red sea yielded significantly different value than seawater 88 86sr 0 22 0 07 compared to 0 35 0 06 respectively in an excellent correlation with the 88 86sr analyses reported by fietzke and eisenhauer fietzke j eisenhauer a 2006 determination of temperature dependent stable strontium isotopes 88sr 86sr fractionation via bracketing standard mc icp ms geochm geophys geosyst 7 no 8 on other coral samples all carbonate samples that originated in the marine environment corals porites and acropora from the northern gulf of aqaba cretaceous limestone and runoff from the judea mountains as well as lacustrine evaporitic aragonite dead sea and red sea and atlantic seawater yield an average 88 86sr value of 0 26 0 1 on the other hand secondary materials products of chemical weathering from the terrestrial environment of the judea mountain such as terra rossa soil and speleothem calcite that derives its sr from the above lying soil yielded significantly lower 88 86sr value of 0 17 0 06 this indicates that strontium isotopes fractionate in the soil environment calling for a possible development of strontium isotopes as a tracer for processes of chemical weathering and pedogenesis

the original swiss flysch a reappraisal of the type deposits in the swiss prealps abstract the flysch sequences of the swiss prealps alpine front ranges are described and interpreted in the light of a decade of study by a group research project at fribourg the geographical and geological settings are illustrated the stratigraphy and sedimentology the sedimentary petrography and the geodynamic setting are discussed correlations within and outside the prealps as well as outstanding problems are treated the flysch units and sequences covered are the gurnigel flysch the medianes flysch helminthoid flysch fouyet manche and mocausa flysch hundsruck flysch niesen flysch and the ultrahelvetic flysch the data from clast framework grain and heavy mineral analysis from micropalaeontology from facies analysis palaeocurrent measurements and stratigraphy allow the interpretation of sedimentary environments source terranes and depositional models in all cases flysch deposits are deep marine detrital accumulations and source areas were undergoing active tectonics individual models are based on the deep sea fan concept but interpretations tend to show significant modifications with respect to simple fan characteristics these departures are to some extent due to available grain size to active structuring of basins or to minor controls such as eustatic variations or climatic influence the integration of sedimentological data with stratigraphy and regional structure furnishes palinspastic reconstructions in map view these provide insights on the palaeogeography of the western alps from mid cretaceous to oligocene and give a picture of the evolution of the western mediterranean tethys during the same period the relationship between flysch deposition and alpine mountain building is confirmed while constraints on basin evolution are established

enrichment of 88 sr in continental waters due to calcium carbonate precipitation abstract 88 86sr data published over the last few years suggest that continental waters are enriched with 88sr as compared to the rocks in their drainage basins in an attempt to understand this phenomenon this study established the fractionation in the 88sr 86sr ratio during precipitation of continental carbonates i e carbonates precipitated on land from surface pedogenic or ground waters and evaluated the contribution of this process to the 88sr enrichment in rivers for this stable and radiogenic sr isotopes 88sr 87sr and 86sr were measured in calcite samples and their precipitating waters collected in various continental environments such as soil cave streams and groundwater the results indicate that continental carbonates are 88sr depleted relative to their precipitating waters placing them as one of the most 88sr depleted reservoirs on earth the average difference in 88 86sr values between waters and solid caco3 tufas or speleothems that they precipitate is carb water 0 218 0 014 1sd an even larger fractionation e carb water 0 285 0 02 was measured in groundwater with particularly high carbonate alkalinity and high carbonate precipitation rate that depleted 65 of the sr in the groundwater resulting in substantial 88sr enrichment in the residual dissolved sr sr 88 86 0 656 results also suggest that pedogenic carbonate precipitation in soil profile removes 50 85 of the sr from the recharging soil water thereby increasing the 88 86sr value of the soil water from 0 18 to 0 3 0 6 similar 88sr enrichment was observed in drip water from a karst cave a maximum removal flux of sr into continental carbonates of about 20 gmol sr y 1 is required to yield the reported 88sr enrichment in global rivers sr 88 86 0 32 relative to their rock sources when using the fractionation factor derived in this study carb water 0 218 and the published 88 86sr composition of marine carbonates of 0 16 this surprisingly large flux requires that 40 of the originally weathered sr should co precipitate with continental carbonates this calculation may suggest that caco3 precipitation is a significant mechanism in the continental sr cycle it is possible however that other mechanisms such as sr uptake by plants or incongruent weathering of silicates could also contribute to the riverine 88sr enrichment alternatively the average 88 86sr value of marine carbonate rock sections undergoing weathering is higher than suggested in current literature it is concluded that additional 88 86sr data on marine carbonate rock sections should be collected to resolve the enigma of the high value of riverine 88 86sr

radiometric age constraints on mineral growth metamorphism and tectonism of the gummfluh klippe brianconnais domain of the prealpes switzerland a combined 40ar 39ar k ar rb sr and stable isotope study has been made of white micas from the gummfluh klippe brianconnais domain of the prealpes switzerland the klippe consists mainly of mesozoic to early tertiary carbonate rocks metamorphosed from anchizonal to epizonal conditions at the base of the klippe is a 10 50 m thick ductilely deformed marble mylonite containing deformed authigenic quartz segregations stable isotope measurements of the coexisting calcite 18osmow 24 5 and quartz 18osmow 28 4 from the mylonite indicate relatively low temperatures 300 c during mylonitization analyses of white mica separates of varying size fractions from the mylonitic rocks by k ar and rb sr techniques yield ages between 57 and 103 ma this variation is correlated with two parameters the size of the mineral fraction and the proportion of 2m1 more phengitic to 1m more muscovitic polytype in the sample the k ar and rb sr ages are generally younger in the smaller size fractions which also containless 2m1 phengite high precision 40ar 39ar age spectra from different size fractions of these micas record three distinct components a small hercynian component ca 200 300 ma a significant eoalpine component 64 80 ma forming 40ar 39ar age plateaus and a very minor tertiary component ca 20 40 ma characterization of the samples by sem indicates the presence of two white mica populations a coarser grained deformed detrital mica that probably corresponds to the 2m1 phengite and a finer grained neoformed 1m mica collectively these observations suggest that the gummfluh samples contain a mixture of detrital phengites of hercynian age together with neocrystallized muscovites grown during the late eoalpine metamorphic event followed by minor argon loss during the tertiary the main geologic episode recorded in the 40ar 39ar age spectra of white micas in the mylonite is of late cretaceous early tertiary age 64 80 ma representing the first reliable eoalpine ages ever to be reported from the prealpes contrary to tectonic models the marble mylonite at the base of the gummfluh klippe appears to be a cretaceous thrust plane and not the thrust surface formed during transport of the klippe into its present position from the penninic alps during the tertiary the late cretaceous thrust developed during marine sedimentation at a depth of 800 m below the seafloor at temperatures of 280 c facilitated by warm fluids along the tectonic discontinuity

radiogenic and stable strontium isotopes in provenance studies a review and first results on archaeological wood from shipwrecks abstract different approaches are used to study wood provenance but most of them are based on tracers in wood that are generally controlled by climatic factors the strontium isotopic ratio 87 sr 86 sr in trees and soils is related to the signature of the local bedrock despite being used in diverse archaeological studies sr isotopes have rarely been used to trace the provenance of archaeological wood and especially wood from shipwrecks in addition recent analytical advances have allowed the detection of mass dependent fractionation of sr isotopes during biogeochemical processes as reflected in the variation of 88 86 sr values between different environmental materials the 88 86 sr values could be used in conjunction with the 87 sr 86 sr isotope ratio to improve constraints on the sources of sr in the archaeological materials being studied this paper discusses the potential and limitations of using both of these sr isotope ratios to trace the provenance of wood from shipwrecks we review the 87 sr 86 sr and 88 86 sr variations in rocks waters soils plants and other living organisms and discuss how to determine the local sr isotopic signature of potential sites we also compile a list of known wood post mortem modifications in seawater possible implications in terms of the modification of the original sr isotope ratios of wood during storage in seawater are illustrated through preliminary observations this paper points out some limitations and perspectives for using sr isotopes in provenancing wood from shipwrecks and suggests future research to test and apply this approach for tracing the origin of archaeological wood

the baltica laurentia connection sveconorwegian grenvillian metamorphism cooling and unroofing in the bamble sector norway the sveconorwegian bamble sector of south norway is a segment of the high grade metamorphic basement of the baltic shield generally considered an integral piece of the global grenvillian orogenic belt in particular the bamble sector is generally directly linked to the grenville province of north america in middle proterozoic tectonic reconstructions however few high precision data exist on the metamorphic chronology of the bamble sector to test such models in this paper high precision u pb data for monazite allanite and titanite indicate that rocks from the bamble sector near arendal underwent granulite facies metamorphism at 1140 ma a second phase of metamorphism may be indicated by u pb titanite ages of 1105 ma or alternatively these may simply record delayed cooling or growth of titanite below temperatures for significant lead diffusion hornblende 40ar 39ar ages indicate cooling of the same rocks below 550 c between 1090 and 1080 ma metamorphic cooling rates of 3 8 c ma between 725 an

calculation of k diffusional rates in bentonite beds zoned k bentonites with illite rich contacts and smectite rich interiors are interpreted as products of potassium k metasomatism during diagenesis a mathematical model is developed to describe both k transport in pore water and k fixation in smectite clays smectite illitization solution of these coupled equations is done using finite difference techniques best fit modeling of mineralogical and k ar data from a 2 5 m thick zoned k bentonite from western montana suggests that diffusional exchange of k for ca is the important transport mechanism in compacted bentonite beds diffusion coefficients d for k ca exchange of about 9 to 13 center dot 10 sup minus 8 cm sup 2 sec best model observed zonations in the 2 5 m bentonite as well as mineralogical zonations observed in bentonites thinner than 2 5 meters this range in d seems to be reasonable when compared with calculated d values for k ca exchange in a highly tortuous medium although the precise burial history for these montana rocks is not well known geologically reasonable burial histories appear to be best modeled by using fifth and sixth order kinetic parameters for illitization the model suggests that illitization occurred for 7 to 9 my at temperatures of about 80 to 90 degree c the model of chemical transport and illitizationmore developed here should have applications in the analysis of the stability of bentonite as a backfill material in a nuclear waste repository less

implications of k ar ages of whole rock and grain size fractions of metapelites and intercalated metatuffs within an anchizonal terrane white mica bearing fractions ranging in grain size from 0 4 m to 6 3 20 m were separated from metapelites and intercalated metatuffs of the eastern rheinisches schiefergebirge frg the stratigraphic age of these rocks is middle devonian eifelian and they contain detrital material of northwestern provenance old red continent probably mainly derived from the caledonian orogen folding in the carboniferous was associated with cleavage formation and an apparently synkinematic anchizonal metamorphism apparent k ar ages of metapelite fractions display a marked positive correlation with grain size illustrating the detrital influence which is diminished with decreasing grain size and increasing metamorphism determined by illite crystallinity contrasting grain morphologies observed by sem enable the interpretation of apparent age grain size relationship for coarse fractions the anticipated lack of detrital mica in metatuffs is confirmed by the fairly consistent apparent k ar ages determined for the coarser than 0 63 m size fractions which date the anchizonal metamorphism at ca 330 ma comparison of metatuff and metapelite apparent ages suggests that the extent of rejuvenation in the latter was largely dependent on grain size rejuvenation was also somewhat controlled by the degree of anchizonal metamorphism as suggested by differences in k ar results of metapelites which were metamorphosed at variable anchizonal conditions fractions 0 63 m from upper anchizonal metapelites record ca 330 ma ages similar to those of the 0 63 20 m sizes in metatuffs together those results confirm the limited applicability of conventional k ar dating on bulk clay fractions 2 m of very low grade anchizonal metamorphic rocks in dating metamorphic events and concomitant cleavage formation

illite k ar dating and crystal growth processes in diagenetic environments a critical review k ar dating of illitic minerals is commonly used in studies of diagenetic series applied to oil prospecting in spite of a great number of specialized papers some problems remain unresolved these are mostly due to a misunderstanding of the argon accumulation process during illitization criteria for identifying detrital authigenic mineral mixtures crystal ripening fast precipitation or continuous nucleation growth processes are discussed using k ar data available in the literature using different parameters such as age agek ar agestrati cryst diagenetic agek ar agestrati or frac agek arfraction agek arfinest it is shown that the k ar age significance depends on the illite nucleation growth processes a diagenetic age is obtained when these processes are rapid the k2o accumulation period is shorter than 2 if lower than this value the k ar ratio depends on the proportions of new and old particles respectively which are controlled by the relative rates of nucleation crystal growth and ripening

excess argon 40are uptake during slate formation a 40ar 39ar uv laserprobe study of muscovite strain fringes from the palaeozoic welsh basin uk syn kinematic pure muscovite strain fringes grew around pyritized graptolites in response to the early devonian acadian closure and uplift of the peri gondwanan welsh basin they record ar isotope information on the timing of low temperature deformation and the mudrock to slate transition here we have applied three different 40ar 39ar laserprobe dating methods to strain fringes from the central welsh basin to test for variations in age and to explore the technical limitations of the method infrared laserprobe step heating analyses yielded only occasional plateau ages varying between ca 403 ma and 422 ma and strong evidence for discordance in the ar system likewise ages from infrared laserprobe total fusion analysis are scattered and range from ca 390 ma to 651 ma by contrast ultraviolet laserprobe intra fringe age profiles revealed a complex pattern of ages across individual strain fringes this is the highest spatial resolution technique available and the resulting age profiles consistently showed an oscillatory pattern comprising troughs or baseline ages that are all within error of ca 397 ma and peaks or apparent ages ranging up to ca 550 ma these apparent ages we interpret as the results of repeated periodic assimilation of excess 40ar 40are during deformation and the mudrock to slate transition here basinal fluids carrying 40are are driven through bulk mudrock during contractional phases of the acadian orogen and 40are is taken up by muscovite strain fringes the concentration of 40are varies with metamorphic grade and is inversely proportional to the temperature of metamorphism and we suggest is controlled by the solubility of ar in water which has potentially quite severe implications for 40ar 39ar dating of k bearing minerals in any mudrock these results provide a first record of ar isotope information in strain fringes and a first record of orogenically driven fluid flow through bulk deforming mudrock they also demonstrate how the high spatial resolution ultraviolet laserprobe 40ar 39ar method can access ar isotope information that is obscured by lower spatial resolution laser analysis or bulk sampling methods

reassessing the stable δ88 86sr and radiogenic 87sr 86sr strontium isotopic composition of marine inputs the stable strontium isotope system 88 86sr has recently been suggested to be a suitable proxy for determining variations in the strength of the marine carbonate system the principal output flux of oceanic sr however in order to be able to interpret carbonate driven variations in 88 86srseawater a robust understanding of 88 86srinput is required surprisingly only a limited amount of 88 86sr data currently exists for rivers and hydrothermal fluids thus this study assesses the variability of 88 86sr and 87sr 86sr in global rivers hydrothermal fluids and porewaters as well as minor marine sr sources such as continental dust rainwater and glacial ice our analyses broadly confirm the findings of krabbenhoft et al 2010 and reveal flux weighted 88 86srriverine and 87sr 86srriverine compositions of 0 32 and 0 71299 respectively the hydrothermal fluids analysed in this study are consistent with an end member 88 86srhydrothermal composition that is the same as the oceanic crust at 0 24 although three samples that display 88 86sr compositions offset from the seawater hydrothermal mixing trend suggest that the precipitation of alteration phases such as anhydrite may drive 88 86srhydrothermal to higher values porewater fluids obtained from sediment cores in the atlantic and pacific oceans have 88 86sr compositions within error of seawater 0 39 implying that the diagenetic flux of sr may not significantly affect the 88 86sr composition of seawater continental loess samples have 88 86sr compositions that are consistently lighter than or equal to terrestrial silicates with their tendency to lower values thought to reflect the preferential removal of heavier sr isotopes into solution during weathering finally rainwater and glacial ice samples have 88 86sr compositions that are also isotopically lighter than their associated water sources a factor that may be attributed to interaction with isotopically light loess and additional sr contributions from the bedrock together the principal marine inputs define flux weighted oceanic 88 86srinput and 87sr 86srinput compositions of 0 32 and 0 71161 these values are consistent with an elevated supply of riverine sr to the oceans due to increased post glacial weathering but require the enhanced weathering of exposed carbonate shelves during glacial periods or significant changes in the rate of carbonate burial to match observed changes in the 87sr 86sr ratio of seawater our results confirm that providing a diagenetically robust proxy can be found the 88 86sr and 87sr 86sr isotope systems should provide a useful proxy for investigating changes in the marine carbonate system through time

long lived plasmaspheric drainage plumes where does the plasma come from long lived weeks plasmaspheric drainage plumes are explored the long lived plumes occur during long lived high speed stream driven storms spacecraft in geosynchronous orbit see the plumes as dense plasmaspheric plasma advecting sunward toward the dayside magnetopause the older plumes have the same densities and local time widths as younger plumes and like younger plumes they are lumpy in density and they reside in a spatial gap in the electron plasma sheet in sort of a drainage corridor magnetospheric convection simulations indicate that drainage from a filled outer plasmasphere can only supply a plume for 1 5 2 days the question arises for long lived plumes and for any plume older than about 2 days where is the plasma coming from three candidate sources appear promising 1 substorm disruption of the nightside plasmasphere which may transport plasmaspheric plasma outward onto open drift orbits 2 radial transport of plasmaspheric plasma in velocity shear driven instabilities near the duskside plasmapause and 3 an anomalously high upflux of cold ionospheric protons from the tongue of ionization in the dayside ionosphere which may directly supply ionospheric plasma into the plume in the first two cases the plume is drainage of plasma from the magnetosphere in the third case it is not where the plasma in long lived plumes is coming from is a quandary to fix this dilemma further work and probably full scale simulations are needed

kar systematics of clay to mica minerals in a multi stage low grade metamorphic evolution the behavior of the ar isotopic system of clay to mica fractions was studied in cambrian greywacke samples along a transect of northwestern morocco these rocks were affected by a progressively increasing metamorphic overprint spanning from diagenetic to epizonal metamorphic conditions k ar isotopic data of 0 2 10 m size fractions recovered from seven samples allowed to recognized three episodes of illite crystallization 1 during an upper ordovician thermal event at 445 ma which is characterized by an illite chlorite mineral paragenesis in the northernmost part of the transect 2 during a carboniferous low grade overprint at 305 ma which is characterized by a similar mineral paragenesis and 3 during a triassic to liassic hydrothermal activity at 205 ma which generated a smectite dominated paragenesis the ages were examined in combining x ray mineralogic and k ar isotopic data in terms of linear arrays in both isochron and harper diagrams to differentiate true isochrons from mixing lines it could also be shown that mixtures of two generations of micaceous minerals can induce different trends in the k ar dates depending whether the first generation of minerals was either or not affected by the event inducing the later generation

neoproterozoic metamorphism and deformation at the southeastern margin of the east european craton uralides russia the eastern margin of the east european craton eec has a long lasting geological record of precambrian age archaean and proterozoic strata are exposed in the western fold and thrust belt of the uralides and are known from drill cores and geophysical data below the palaeozoic cover in the uralides and its western foredeep in the southern uralides sedimentary metamorphic and magmatic rocks of riphean and vendian age occur in the bashkirian mega anticlinorium bma and the beloretzk terrane in the eastern part of the bma yamantau anticlinorium and the beloretzk terrane k ar ages of the 2 m size fraction of phyllites potassic white mica and slates illite give evidence for a complex pre uralian metamorphic and deformational history of the precambrian basement at the southeastern margin of the eec interpretation of the k ar ages considered the variation of secondary foliation and the diagenetic to metamorphic grade in the yamantau anticlinorium the greenschist facies metamorphism of the mesoproterozoic siliciclastic rocks is of early neoproterozoic origin about 970 ma and the s1 cleavage formation of late neoproterozoic about 550 ma the second wide spaced cleavage is of uralian origin in the central and western part of the bma the diagenetic to incipient metamorphic grade developed in late neoproterozoic time in post uralian time proterozoic siliciclastic rocks with a cleavage of uralian age have not been exhumed to the surface of the bma late neoproterozoic thrusts and faults within the eastern margin of the eec are reactivated during the uralian deformation

insights into combined radiogenic and stable strontium isotopes as tracers for weathering processes in subglacial environments this study reports stable and radiogenic strontium isotope behaviour in the dissolved load and suspended sediments from the subglacial outflow of the lemon creek glacier juneau ice field alaska over a single melt season in situ measurements discharge total alkalinity ph and conductivity are combined with elemental concentrations x ray diffraction xrd analysis and radiogenic strontium isotope measurements to interpret the variations observed in stable strontium isotopic ratios the stable sr isotope composition 88sr 86sr ratio expressed as 88 86sr of the dissolved load averages 0 31 0 05 and is heavier than both the suspended sediment 0 18 0 03 as well as local bedrocks 0 20 to 0 26 we attribute the enrichment of heavier isotopes in the dissolved load to the uptake of lighter sr isotopes by secondary weathering minerals driving the dissolved load to heavier values x ray diffraction xrd analysis confirms the presence of clays in the suspended sediments and thermodynamic modelling suggests the presence of iron oxy hydroxide phases although it is not possible to completely rule out the effect of dissolution of primary minerals in controlling sr isotopic compositions of the dissolved load our data indicate that the extent of secondary mineral formation likely plays a significant role the preferential weathering of minerals such as biotite consistent with the mineralogical assemblages found in the suspended sediments as well as the potential presence of radiogenic calcites from metacarbonates derived from the yukon tanana terrain may be driving the small seasonal shifts in 87sr 86sr of the dissolved load to more radiogenic compositions from 87sr 86sr dl 0 71048 to 0 710647 using the combination of stable and radiogenic strontium isotopes to investigate weathering processes shows that radiogenic sr isotopes provide information regarding weathering of primary phases while the stable sr isotope data appear to record information regarding the extent of secondary mineral formation where secondary minerals incorporate the light isotopes driving the dissolved load to heavy values

an extensive survey of dayside diffuse aurora based on optical observations at yellow river station by using 7 years optical auroral observations obtained at yellow river station magnetic latitude 76 24 n at ny alesund svalbard we performed the first extensive survey for the dayside diffuse auroras ddas and acquired observational results as follows 1 the ddas can be classified into two broad categories i e unstructured and structured ddas the unstructured ddas are mainly distributed in morning and afternoon but the structured ddas predominantly occurred around the magnetic local noon mln 2 the unstructured ddas observed in morning and afternoon present obviously different properties the afternoon ones are much stable and seldom show pulsating property 3 the ddas are more easily observed under geomagnetically quiet times 4 the structured ddas mainly show patchy stripy and irregular forms and are often pulsating and drifting the drifting directions are mostly westward with speed 5 km s but there are cases showing eastward or poleward drifting 5 the stripy ddas are exclusively observed near the mln and most importantly their alignments are confirmed to be consistent with the direction of ionospheric convection near the mln 6 a new auroral form called throat aurora is found to be developed from the stripy ddas based on the observational results and previous studies we proposed our explanations to the ddas we suggest that the unstructured ddas observed in the morning are extensions of the nightside diffuse aurora to the dayside but that observed in the afternoon are predominantly caused by proton precipitations the structured ddas occurred near the mln are caused by interactions of cold plasma structures which are supposed to be originated from the ionospheric outflows or plasmaspheric drainage plumes with hot electrons from the plasma sheet we suppose that the cold plasma structures for producing the patchy ddas are in lumpy and are more likely from the plasmaspheric drainage plumes the cold plasma structure for producing the stripy ddas should be in wedge like and is generated by conveying the cold plasmas from lower l shell toward higher l shell with magnetospheric convection and that for producing the irregular ddas is resulted from deforming the wedge like structure by disturbance the throat aurora is supposed to be projection of a newly opened flux of reconnection in addition we also found that structured ddas correspond to structured electron precipitations in the ionosphere which implies that the cold plasma structures in the magnetosphere are magnetically mapped to the ionosphere and act as a duct for producing the structured ddas we argue that we have presented some new observational results about dda in this paper which will be useful for fully understanding the ddas

corrensite and mixed layer chlorite corrensite in metabasalt from northern taiwan tem aem empa xrd and optical studies many chloritic minerals in low grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties expand slightly upon glycolation expandable chlorite and or have excess alvi relative to aliv as well as significant ca k and na contents chloritic minerals with these properties fill vesicles and interstitial void space in low grade metabasalt from northern taiwan and have been studied with a combination of tem aem empa xrd and optical microscopy the chloritic minerals include corrensite which is an ordered 1 1 mixed layer chlorite smectite and expandable chlorite which is shown to be a mixed layer chlorite corrensite corrensite and some mixed layer chlorite corrensite occur as rims of vesicles and other cavities while later formed mixed layer chlorite corrensite occupies the vesicle cores the tem observations show that the mixed layer chlorite corrensite has ca 20 and the corrensite has ca 50 expandable smectite like layers consistent with xrd observations and with their abnormal optical properties the aem analyses show that high si and ca contents high alvi aliv and low fevi fe mg vi ratios of chlorites are correlated with interstratification of corrensite or smectite like layers in chlorite the aem analyses obtained from 200 500 a thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low aliv siiv and low fevi fe mg vi while chlorite has high aliv siiv and high fevi fe mg vi this implies that the trioctahedral smectite like component of corrensite has significantly lower aliv siiv and fevi fe mg vi the ratios of fevi fe mg vi and aliv siiv thus decrease in the order chlorite corrensite smectite the proportions of corrensite or smectite like layers relative to chlorite layers in low grade rocks are inferred to be controlled principally by fe mg ratio in the fluid or the bulk rock and by temperature compositional variations of chlorites in low grade rocks which appear to correlate with temperature or metamorphic grade more likely reflect variable proportions of mixed layered components the assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases such as chlorite corrensite corrensite smectite or chlorite corrensite smectite a model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1 1 ordered mixed layer chlorite smectite

strontium isotope fractionation of planktic foraminifera and inorganic calcite we have investigated the strontium isotope fractionation 88 86srcarb aq between inorganic calcite and aqueous sr2 ions by precipitation experiments at a constant temperature of 25 c and precipitation rates r ranging from 102 3 to 104 2 mol m2 h strontium isotope ratios were measured using the 87sr 84sr double spike technique it was found that strontium isotope fractionation in these calcites is strongly dependent on the precipitation rate view the mathml source the measured 88 86sr values are significantly correlated with previously measured 44 40ca and sr ca values of the same calcite samples 88 86srcarb aq 0 18 44 40cacarb aq 0 01 view the mathml source the slope of 88sr 86sr versus 44ca 40ca fractionation is 0 18 0 04 and compatible with a kinetic fractionation during dehydration of the strontium and calcium ions but not with isotope fractionation in a diffusive boundary layer using published equilibrium 44 40cacarb aq and view the mathml source values we estimate the equilibrium isotope fractionation of strontium to be very close to zero 88 86sreq carb aq 0 01 0 06 this estimate is confirmed by strontium isotope values of natural inorganic calcites that precipitated very slowly in basalts of the ocean crust the results from the inorganic calcites are used to explain strontium isotope fractionation of planktic foraminifera specimens of two warm water species globigerinoides ruber and globigerinoides sacculifer were picked from the holocene section of a caribbean sediment core we found no significant difference in 88 86sr between the two species in addition g ruber specimens from marine isotope stage 2 in the same core show 88 86sr values identical to the holocene specimens the strontium isotopes of both foraminifera species are strongly fractionated 88 86srcarb aq 0 248 0 005 when compared to published data of other major marine calcifiers applying the results from the inorganic precipitation experiments we find that the strong foraminiferal strontium isotope fractionation can be explained by calcification in a largely open system at high precipitation rates comparable in magnitude to rates known from scleractinian reef corals this interpretation is in good agreement with the kinetic calcification model for planktic foraminifera by kisakurek et al 2011 which was based on calcium isotopes and elemental sr ca ratios

magnetosphere preconditioning under northward imf evidence from the study of coronal mass ejection and corotating interaction region geoeffectiveness 1 motivated by recent observations and simulations of the formation of a cold and dense plasma sheet in the tail of the magnetosphere under northward interplanetary magnetic field imf and of the direct influence of the plasma sheet density on the ring current strength this paper aims at 1 highlighting how the coupling of these effects may lead to a preconditioning of the magnetosphere under northward imf and 2 performing first tests of the validity of this hypothesis we have analyzed superposed epoch time series of various parameters to investigate the response of the magnetosphere as indicated by the dst index to the passage of coronal mass ejections cmes and corotating interaction regions cirs we first focused on the difference between the measured dst signature and that predicted by a semiempirical dst model for both cme and cir driven storms the superposed epoch results show that the model dst predictions tend to underestimate the actual storm strength by up to 10 30 for events that are preceded by a substantial interval of northward imf as opposed to those with no such preceding northward imf we also analyzed los alamos geosynchronous spacecraft data for these events the average density and temperature measured at storm onset are substantially higher and slightly lower respectively for the cases with preceding northward imf intervals these results suggest that solar wind structures may be more geoeffective if preceded by a northward imf interval and they are consistent with the hypothesis of a preconditioning by a cold dense plasma sheet a colder and denser plasma sheet may lead to a stronger ring current when that plasma is convected inward during the main phase of an ensuing storm

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

characteristics of the flank magnetopause cluster observations the magnetopause is a current sheet forming the boundary between the geomagnetic field on one side and the shocked solar wind on the other side this paper discusses properties of the low latitude dawn and dusk flanks of the magnetopause the reported results are based on a large number of measurements obtained by the cluster satellites during magnetopause traversals using a combination of single spacecraft and multispacecraft techniques we calculated macroscopic features such as thickness location and motion of the magnetopause the results show that the typical flank magnetopause is significantly thicker than the dayside magnetopause and also possesses a pronounced and persistent dawn dusk asymmetry thicknesses vary from 150 to 5000 km with an median thickness of around 1400 km at dawn and around 1150 km at dusk current densities are on average higher on dusk suggesting that the total current at dawn and dusk are similar solar wind conditions and the interplanetary magnetic field cannot fully explain the observed dawn dusk asymmetry for a number of crossings we were also able to derive detailed current density profiles the profiles show that the magnetopause often consists of two or more adjacent current sheets each current sheet typically several ion gyroradii thick and often with different current direction this demonstrates that the flank magnetopause has a structure that is more complex than the thin one dimensional current sheet described by a chapman ferraro layer

deformation and displacement of the jura cover on its basement abstract the sedimentary cover of the internal jura displaced over its basement conforms well with the model of a thin skinned thrust sheet the wedge shaped sheet which includes a thick sequence of molasse deposited ahead of the alpine front slid over the basement cover interface the alpine crustal thrust sheets created a load at the south east end of the overthrust european plate molasse was deposited on the bent plate and the internal part of the basin was progressively affected by thrusting this process also induced deformation and displacements in the foreland gravity spreading in the internal molasse and a forward motion by rigid slipping movement led to a horizontal push causing deformation by indentation in the internal jura in the plateaux of the external jura there is very little extension in the cover and minimal shortening in the basement this shortening induced a decollement under the plateaux over the bresse graben gravity sliding occurred in the form of huge landslides these contrasts in the origin of the jura structures along a median cross section from thonon to arbois are shown by geophysical data construction of a balanced cross section and calculations of realistic mechanical models for the bending of the foreland plate and for the motion of the cover sheet

controls on stable strontium isotope fractionation in coccolithophores with implications for the marine sr cycle abstract the controls on stable sr isotope fractionation into the calcite produced by the coccolithophore species emiliania huxleyi coccolithus pelagicus spp braarudii and gephyrocapsa oceanica are investigated each species has been cultured under controlled laboratory conditions at a range of temperatures 10 25 c to test the potential of 88 86 sr as a proxy for growth rate and or sea surface temperature coccolithophores are one of the most abundant pelagic calcifiers since sr substitutes to some degree for ca in their calcite coccoliths coccolithophores represent a significant output of sr from seawater potentially influencing the 88 86 sr mass balance in the modern oceans the coccoliths are investigated for their 88 86 sr sr ca and 18 o measured as function of temperature as temperature is increased all species show a negative stable sr isotopic fractionation related to a temperature controlled growth rate we infer the shift of 88 86 sr to lighter values as indicative of a kinetic control on the isotope fractionation revealing the potential of 88 86 sr as a proxy for growth rate which in these experiments is primarily dictated by temperature the results from these experiments indicate that coccolithophore calcite incorporates sr with a very light 88 86 sr isotope composition as low as 0

statistical analysis of the plasmaspheric plume at the magnetopause 1 during times of enhanced magnetospheric convection cold dense plasma from the plasmasphere can form a plume extending sunward toward the dayside magnetopause a statistical study is presented of cold high density plasmaspheric plasma at the magnetopause observations from the time history of events and macroscale interactions themis spacecraft show the plume to be present at the dayside magnetopause during 12 5 148 of 1184 of the crossings its most common location in magnetic local time when contacting the magnetopause is at 13 6 h the magnetopause crossings show evidence for reconnection in 68 of events with the plume while only 47 of events without plume although the plume is more likely to be observed at the magnetopause when reconnection is occurring the typical reconnection jet velocity is lower for plume events than nonplume events indicating the presence of the plume may be slowing the efficiency of the reconnection process

transition from basement to cover a geometric model abstract a new simple geometric model is proposed that explains the possible relationships between superficial thrust sheets and deeper fold nappes it demonstrates that the simultaneous formation of these two types of structures at different levels of the crust is kinematically and geometrically possible the model is based on the difference of rheological behaviour between a lower tectonic unit that will suffer mainly a ductile deformation along a shallow dipping shear zone and an upper and rigid tectonic unit that will deform mostly by bedding parallel slip at constant bed length the difference in rheologic behaviour implies that the horizontal shortening that can be produced within the two units is unequal and therefore leads to a relative movement between them this movement takes place within a detachment level of variable thickness the most efficient layers to enable detachment will consist of ductile sediments like evaporites shales or flysch type sediments recent geophysical data have confirmed the view that compressional mountain belts are mainly the result of continental lithosphere subduction the deformation is essentially localized in the upper part of the down going continental crust this fundamental basally driven mechanism constrains the geometry and kinematics of the proposed model examples from the alps show that it can be applied to many cases where cover thrust sheets are directly related to basement fold nappes

40ar 39ar muscovite dating of thrust activity a case study from the axial zone of the pyrenees abstract the pyrenees belt features well exposed deformation structures that make it ideally suited to study thrust faults in this paper we present the first 40ar 39ar age of the pic de port vieux thrust ppvt located in the south western part of the pyrenean axial zone the ppvt is a secondary thrust related to the major gavarnie thrust gt with a footwall comprising upper cretaceous limestones and a hanging wall made of lower triassic pelites and sandstones a vertical transect in the fault hanging wall was investigated to characterize the deformation mechanism and to date the thrust activity by using 40ar 39ar step heating technique on muscovite petrographic observations confirm that pressure solution and recrystallization dissolution processes in presence of fluids are the main mechanisms that controlled the chemical textural changes in the fault core zone three groups of muscovite are identified in the fault zone i e detrital diagenetic and newly formed muscovites the detrital and diagenetic muscovites are mainly present in the damage zone while the newly formed muscovite is abundant in the core zone and is synkinematic to the fault activity the fractions 50 16 m 16 2 m 2 0 5 m

40ar 39ar geochronology of jarosite the effectiveness of hf in removing silicate contaminants abstract supergene and hypogene jarosite have been dated successfully but accurate dating of weathering derived jarosite and its application to landscape evolution studies has been limited because of difficulties in obtaining high purity mineral separates hydrofluoric acid hf can remove potassium bearing silicates from supergene samples but its effects on jarosite crystal chemistry and age dating are unquantified three experiments were conducted to determine whether hf treatment removes silicates without altering the potassium or argon composition of the jarosite prior to dating using the 40 ar 39 ar method in the first two experiments pure hypogene jarosite from pena blanca mexico pb 9 42 0 22 ma and a mixture of 85 pb 15 fish canyon sanidine fc 2 28 02 ma were crushed and treated with 25 hf for 0 30 240 and 480 min jarosite partially dissolves during hf treatment with grains becoming increasingly pitted and rounded with time in acid but pb s potassium concentration and apparent age remained constant regardless of treatment time fc 2 was absent from all treated samples suggesting that 30 min in hf is sufficient to remove mechanically mixed sanidine crystals from jarosite methods developed during experiments conducted on pb jarosite were applied to fine grained supergene jarosite from the red river valley rrv in northern new mexico rrv jarosite is mixed with oligocene 24 86 ma potassium bearing silicates that make up 50 or more of each sample four rrv jarosite samples that yielded age spectra with clear signs of contamination by older phases were treated with hf for 30 min and re dated despite treatment back scattered electron images show that silicates including sanidine and illite continued to comprise approximately 30 of hf treated rrv samples and the age spectra produced during laser step heating continued to show signs of contamination in higher wattage steps however the integrated ages of these samples were consistently less than 1 ma at least 7 ma younger than the expected integrated age if the 30 70 mixture of rrv silicates and jarosite degassed completely the young ages suggest that young jarosite controls the apparent age of these samples and that these ages can be interpreted as the maximum timing of supergene jarosite formation

an 40 ar 39 ar rb sr and stable isotope study of micas in low grade fold and thrust belt an example from the swiss helvetic alps white micas in carbonate rich tectonites and a few other rock types of large thrusts in the swiss helvetic fold and thrust belt have been analyzed by 40ar 39ar and rb sr techniques to better constrain the timing of alpine deformation for this region incremental 40ar 39ar heating experiments of 25 weakly metamorphosed anchizone to low greenschist samples yield plateau and staircase spectra we interpret most of the staircase release spectra result from variable mixtures of syntectonic neoformed and detrital micas the range in dates obtained within individual spectra depends primarily on the duration of mica nucleation and growth and relative proportions of neoformed and detrital mica rb sr analyses of 12 samples yield dates of ca 10 39 ma excluding one anomalously young sample these dates are slightly younger than the 40ar 39ar total gas dates obtained for the same samples the rb sr dates were calculated using initial 87sr 86sr ratios obtained from the carbonate dominated host rocks which are higher than normal mesozoic carbonate values due to exchange with fluids of higher 87sr 86sr ratios and lower 18o 16o ratios model dates calculated using 87sr 86sr values typical of mesozoic marine carbonates more closely approximate the 40ar 39ar total gas dates for most of the samples the similarities of rb sr and 40ar 39ar total gas dates are consistent with limited amounts of detrital mica in the samples the 18o values range from 24 15 vsmow for 2 6 m micas and 27 16 for the carbonate host rocks the carbonate values are significantly lower than their protolith values due to localized fluid rock interaction and fluid flow along most thrust surfaces although most calcite mica pairs are not in oxygen isotope equilibrium at temperatures of ca 200 400 c their isotopic fractionations are indicative of either 1 partial exchange between the minerals and a common external fluid or 2 growth or isotopic exchange of the mica with the carbonate after the carbonate had isotopically exchanged with an external fluid the geological significance of these results is not easily or uniquely determined and exemplifies the difficulties inherent in dating very fine grained micas of highly deformed tectonites in low grade metamorphic terranes two generalizations can be made regarding the dates obtained from the helvetic thrusts 1 samples from the two highest thrusts mt gond and sublage have all of their 40ar 39ar steps above 20 ma and 2 most samples from the deepest helvetic thrusts have steps often accounting for more than 80 of 39ar release between 15 and 25 ma these dates are consistent with the order of thrusting in the foreland imbricating system and increase proportions of neoformed to detrital mica in the more metamorphosed hinterland and deeply buried portions of the nappe pile individual thrusts accommodated the majority of their displacement during their initial incorporation into the foreland imbricating system and some thrusts remained active or were reactivated down to 15 ma

unexpected calcium sources in deep soil layers in low fertility forest soils identified by strontium isotopes lorraine plateau eastern france forest ecosystems are often found on acid soils where calcium availability depends on two main inputs atmospheric deposition and the weathering of soil minerals and on the biological cycling of nutrients in the context of global change decreasing atmospheric inputs increasing biomass exportation climate change it is important to determine calcium sources to the ecosystem and tree nutrition to better understand how forest ecosystems will respond to these changes over time the aim of this study was to study and compare ca pools and cycling in two mature forest ecosystems clermont en argonne and azerailles developed on two contrasting polycyclic soils lorraine plateau eastern france and identify the ca sources contributing to ecosystem functioning at both sites soil ca pools were measured atmospheric deposition of ca was monitored from bulk precipitation and throughfall chemistry ca biological cycling was assessed by measuring litterfall and by a litter decomposition experiment strontium 87sr 86sr isotope data in the soil profile fine roots exchangeable pool bulk soil was used to estimate the distribution of sr and ca uptake in the soil profile and the relative contribution of mineral weathering in the soil layers to total ecosystems inputs despite important differences in ca availability in the topsoil between both sites tree growth and nutrition indicators showed no significant difference this discrepancy is not explained by the biological cycling of ca but may be partly explained by higher ca deposition at the ca poorer site strontium isotope data enabled to show important differences of ca sources for tree uptake at the ca poorer site deep soil layers 105 cm potentially represent from 32 to 100 of total sr uptake at the ca richer site results suggest that uptake is more evenly distributed in the soil profile sr isotope data coupled with a modeling approach suggest that two different mineral sources exist in the soil profile a radiogenic sr source in the topsoil 87sr 86sr 0 717 and a less radiogenic source in depth 87sr 86sr 0 717 the deep mineral source may represent from 40 to 86 of total sr inputs at the poorer site and from 25 to 86 at the richer site the origin of this deep strontium source is unclear but soil mineralogy suggests an allochthonous origin we hypothesize that this deep source originates from capillary rise of the groundwater aquifer this nutrient input to forest ecosystems is not commonly taken into account but may strongly participate in maintaining the chemical fertility of soils over time

evidence for mass dependent isotopic fractionation of strontium in a glaciated granitic watershed abstract the stable isotope composition of strontium expressed as 88 86sr may provide important constraints on the global exogenic strontium cycle here we present 88 86sr values and 87sr 86sr ratios for granitoid rocks a 150 yr soil chronosequence formed from these rocks surface waters and plants in a small glaciated watershed in the central swiss alps incipient chemical weathering in this young system whether of inorganic or biological origin has no resolvable effect on the 87sr 86sr ratios and 88 86sr values of bulk soils which remain indistinguishable from bedrock in terms of sr isotopic composition although due in part to the chemical heterogeneity of the forefield the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of sr a low degree of chemical weathering is also implied by bulk soil chemistry the isotopic composition of sr in streamwater is more radiogenic than median soil reflecting the preferential weathering of biotite in the catchment streamwater 88 86sr values however are indistinguishable from bulk soil 88 86sr values implying that no resolvable fractionation of sr isotopes takes place during release to the weathering flux in the damma forefield analyses of plant tissue reveal that plants rhododendron and vaccinium preferentially assimilate the lighter isotopes of sr such that their 88 86sr values are significantly lower than those of the soils in which they grow additionally 88 86sr values of foliar and floral tissues are lower than those of roots contrary to observations for ca for which sr is often used as an analogue in weathering studies we suggest that processes that discriminate against sr in favour of ca due to the different nutritional requirement of plants for these two elements are responsible for the observed contrast

present day and future tectonic underplating in the western swiss alps reconciliation of basement wrench faulting and decollement folding of the jura and molasse basin in the alpine foreland abstract the western alps form a geodynamically active mountain belt showing the typical features of an evolving orogenic wedge with its pro wedge geometry to the nnw and its retro wedge structures to the sse renewed tectonic underplating of european continental crust occurred after the orogenic wedge underwent major dynamic disequilibrium following the break off of the southward subducting slab of the european passive margin the most important of these basement imbricates are the mont blanc aiguilles rouges and gastern aar crystalline massifs also forming the alps highest mountains the upper plate present day orogenic wedge of the western alps includes the molasse basin and the jura fold and thrust belt both decoupled from the basement over a basal decollement surface the overall geometry of this wedge appears to be strongly unstable according to simple wedge models in its attempt to regain stability out of sequence thrusts form in the existing basement nappes but also new basement nappes should develop beneath the southern portion of the molasse basin new out of sequence thrusts in the cover trigger higher than average uplift rates concentrated around the newly forming structures and are accompanied by a concentration of earthquakes tectonic underplating is further corroborated by neotectonics and the tectonic structures observed in the prealpes molasse basin and jura similarly uplift rates and earthquakes along the southern edge of the jura mountains seem to witness the development of a new incipient basement nappe at depth partial inversion of former permo carboniferous grabens in the basement a possible spatial coincidence of areas with strong earthquake activity and zones with uplift rates above surrounding values suggest a common mechanism for their origin in the western swiss alpine foreland combined with information from basement geometry and wedge dynamics it is proposed that the common mechanism is the development of basement imbricates by tectonic underplating the proposed model for ongoing and possible future tectonic underplating beneath an active alpine orogenic wedge also allows to reconcile the models of basement wrench faulting in the molasse basin and jura with the distant push theory where the molasse basin and jura develop over a basal decollement horizon

seasonal changes in the radiogenic and stable strontium isotopic composition of xijiang river water implications for chemical weathering seasonal changes in strontium sr isotopic systematics in large rivers can effectively track temporal variations in regional chemical weathering and help to better constrain the sr isotopic budget of global oceans however such records are scarce here we present a year long time series of both radiogenic and stable sr isotope measurements 87sr 86sr and 88sr from river water at guiping in the middle reaches of the xijiang river south china temporal changes in chemical weathering in the drainage basin were investigated by recording seasonal changes in the composition of both sr isotopes and major ions in the river water river water 87sr 86sr values range from 0 708487 to 0 710336 with most values being 0 7092 are generally accompanied by high rb sr ratios and low ph and 13c of dissolved inorganic carbo dic and occur during periods of large river flux this indicates that the contribution to the chemistry of river water from the weathering of silicate rocks is enhanced during rainy seasons seasonal variation in river water 88sr is large from 0 147 to 0 661 with higher 88sr values generally corresponding to higher 87sr 86sr values again low 88sr values 0 3 suggest a dominant contribution from the weathering of carbonate rocks whereas the high 88sr values may represent a contribution from intensive weathering of silicate rocks using the time series data we estimated the flux weighted averages of sr concentration 87sr 86sr and 88sr for the xijiang river to be 1 00 mol l 0 70960 and 0 38 respectively the sr concentration and 87sr 86sr results are close to previous estimates while the 88sr value is amongst the highest recorded for the large rivers of the world and is close to that of seawater our results indicate that large rivers draining through tropical sub tropical regions could play an important role in regulating the stable sr isotopic budget of global oceans

the relation between grain size and 40ar 39ar date for alpine white mica from the siviez mischabel nappe switzerland abstract variations in alpine white mica 40 ar 39 ar dates from the cover units of the siviez mischabel nappe relate to regional variations in the thermal history of the nappe we focus on three regions within the nappe the central siviez mischabel csm the southern siviez mischabel ssm and the eastern siviez mischabel esm our approach weaves together observations of quartz and mica textures in thin section the variation of 40 ar 39 ar date with grain size considerations of the effective diffusion dimension edd of argon in white mica and a comparison of dates with diffusion model results in the csm pressure solution of quartz and dislocation glide in mica accommodated alpine deformation dates record mica growth during nappe emplacement from 40 to 36 ma and do not vary with grain size in the ssm and esm both mica and quartz show textures associated with dynamic recrystallization and dates decrease with grain size in the ssm dates also agree with the timing of nappe emplacement but in the esm dates significantly post date the timing of nappe emplacement a comparison of dates with diffusion model results supports inferences from rock fabrics that the ssm experienced higher peak temperatures than the csm even though dates from both units approximate the timing of mica growth dates obtained from the esm however do not compare well with simple models and the thermal evolution of this region of the nappe in the neighborhood of the simplon fault zone is not well understood

40ar 39ar study of plagioclases from the rogaland anorthosite complex sw norway an attempt to understand argon ages in plutonic plagioclase abstract the combined use of stepwise heating and uv laser ablation 40 ar 39 ar techniques with microprobe analyses on plutonic plagioclase allows the investigation of complex argon release and retention the complexity arises from the multiphase nature of the samples comprising plagioclase k feldspar in antiperthite secondary sericite and various inclusions in which some of the components also exhibit variable ages fragments of plagioclase megacrysts and plagioclase separates from whole rock samples were selected from a well constrained series of anorthosite leuconorite intrusions of the rogaland igneous complex sw norway intruded at ca 930 ma all samples exhibit saddle like staircase shaped argon release spectra ages rise from around 400 600 to 750 900 ma though three samples exhibit excess argon released at high temperatures the most remarkable aspect of this data is however the apparently linear correlation of 40 ar 39 ar with ca k the stepwise heating data reveal late stage cooling ages considerably younger than the intrusive age and low temperature reheating of the rogaland igneous complex during caledonian overthrusting arrhenius plots for the stepwise heated samples show a linear trend of diffusion data at low temperatures followed by a systematic break around 900 1060 c single spot ages obtained using a uv laser show extreme age variations with heterogeneous excess argon contained in inclusions but no correlation of 40 ar 39 ar with ca k this lack of correlation indicates that the two component mixing model with two end members of distinct ages suggested by the stepwise heating data is an artefact resulting from a more complex mechanism of argon release the most apparent interpretation of this data is that both plagioclase and another potassium rich minor component probably k feldspar antiperthite yield variable but correlated ages because the excess argon is found exclusively in samples from marginal leuconorite bodies and never in the core of the megacrysts it is probably derived from the outgassing of the k rich country rock

constraining soil mineral weathering 87sr 86sr for calcium apportionment studies of a deciduous forest growing on soils developed from granitoid igneous rocks abstracts we used 87 sr 86 sr as a proxy for ca to apportion the contribution of atmospheric deposition and soil mineral weathering sources to the ca pools in trees in a small forested watershed of southern quebec the effects of topography and forest stand composition were assessed by dividing the watershed into three study zones representing two elevations and differences in tree species apportionment calculations show that all tree species studied contained ca that is dominantly sourced from soil mineral weathering averaging 85 due to the presence in the soils of easily weathered ca bearing minerals such as calcite and apatite as well as the relatively deep rooting habits reaching the mineral soil of the tree species calcium pools in trees are shifted towards the atmospheric component on hilltops due to the filtering of dry aerosols of the tree canopies which are more exposed to atmospheric circulation than trees at the bottom of the slopes although some variability in soil bulk chemistry and mineralogy in the watershed obscures the full extent of this phenomenon the buildup and recycling of ca in the soil vegetation system with the forest floor acting as the major accessible ca pool for the tree roots must be considered when interpreting apportionment calculations this work supports other ca cycling models in forests suggesting that topography can influence the balance of ca captured from atmospheric sources by trees even in cases where mineral weathering is the dominant source of ca nutrition in trees

variation of illite muscovite 40 ar 39 ar age spectra during progressive low grade metamorphism an example from the us cordillera 40ar 39ar step heating data were collected from micron to submicron grain sizes of correlative illite and muscovite rich cambrian pelitic rocks from the western united states that range in metamorphic grade from the shallow diagenetic zone zeolite facies to the epizone greenschist facies with increasing metamorphic grade maximum ages from 40ar 39ar release spectra decrease as do total gas ages and retention ages previous studies have explained similar results as arising dominantly or entirely from the dissolution of detrital muscovite and precipitation recrystallization of neo formed illite while recognizing the importance of these processes in evaluating our results we suggest that the inverse correlation between apparent age and metamorphic grade is controlled primarily by thermally activated volume diffusion analogous to the decrease in apparent ages with depth observed for many thermochronometers in borehole experiments our results suggest that complete resetting of the illite muscovite ar thermochronometer occurs between the high anchizone and epizone or at roughly 300 c this empirical result is in agreement with previous calculations based on muscovite diffusion parameters which indicate that muscovite grains with radii of 0 05 2 m should have closure temperatures between 250 and 350 c at high anchizone conditions we observe a reversal in the age grain size relationship the finest grain size produces the oldest apparent age which may mark the stage in prograde subgreenschist facies metamorphism of pelitic rocks at which neo formed illite muscovite crystallites typically surpass the size of detrital muscovite grains it is also approximately the stage at which neo formed illite muscovite crystallites develop sufficient ar retentivity to produce geologically meaningful 40ar 39ar ages results from our sampling transect of cambrian strata establish a framework for interpreting illite muscovite 40ar 39ar age spectra at different stages of low grade metamorphism and also illuminate the transformation of illite to muscovite at frenchman mtn nv where the cambrian bright angel formation is at zeolite facies conditions illite muscovite 40ar 39ar data suggest a detrital muscovite component with an apparent age 967 ma the correlative carrara fm is at anchizone conditions in the panamint and resting spring ranges of eastern california and in these locations illite muscovite 40ar 39ar data suggest an early permian episode of subgreenschist facies metamorphism the same type of data from equivalent strata at epizone conditions greenschist facies in the footwall of the bullfrog fluorspar canyon detachment in southern nevada reveals a period of slow to moderate late cretaceous cooling