trace and minor elements in galena a reconnaissance la icp ms study minor and trace elements can substitute into the crystal lattice of galena at various concentrations in situ la icp ms analysis and trace element mapping of a range of galena specimens from different deposit types are used to obtain minor trace element data aimed at achieving insight into factors that control minor trace element partitioning the previously recognized coupled substitution ag bi sb 3 2pb2 is confirmed however the poorer correlation between ag and bi sb when the latter elements are present at high concentrations 2000 ppm suggests that site vacancies may come into play 2 bi sb 3 3pb2 galena is the primary host of tl in all mapped mineral assemblages along with cu tl is likely incorporated into galena via the coupled substitution ag cu tl bi sb 3 2pb2 tin can reach significant concentrations in galena 500 ppm cd and minor hg can be incorporated into galena the simple isovalent substitution cd hg 2 pb2 is inferred this paper shows for the first time oscillatory and sector compositional zoning of minor trace elements ag sb bi se te tl in galena from two epithermal ores zoning is attributed to slow crystal growth into open spaces within the vein at relatively low temperatures the present data show that galena can host a broader range of elements than previously recognized for many measured elements the data sets generated display predictable partitioning patterns between galena and coexisting minerals which may be dependent on temperature or other factors trace element concentrations in galena and their grain scale distributions may also have potential in the identification of spatial and or temporal trends within individual metallogenic belts and as markers of ore formation processes in deposits that have undergone superimposed metamorphism and deformation galena trace element geochemistry may also display potential to be used as a trace minor element vector approach in mineral exploration notably for recognition of proximal to distal trends within a given ore system

inherited smnd isotope components preserved in monazite inclusions within garnets in leucogneiss from east antarctica and implications for closure temperature studies abstract application of the sm nd dating technique using garnet can be hampered by the presence of minor microscopic to submicroscopic ree rich inclusions in particular monazite and to a lesser extent zircon an acid leaching method using a mixture of hno 3 hcl has been used to tackle the monazite contamination problem with this leaching technique we demonstrate that inherited monazite inclusions have been preserved in garnet formed under high grade metamorphic conditions even very low levels of monazite contamination 0 001 wt have a profound effect on the sm nd system in the garnet analysis of a garnet from a leucogneiss dyke in the northern prince charles mountains eastern antarctica reveals that unleached garnet concentrates and the monazite inclusions as represented by the leachates define an apparent isochron of 1150 30 ma mswd 1 88 which represents a mixing age of inclusions preserving their inherited sm nd isotopic systematics in contrast analyses of the leached garnet concentrates yield much younger ages of 630 to 555 ma model calculations show that the presence of as little as 0 01 wt of monazite inclusions would swamp the sm nd isotope signature of the garnet concentrates this very low level of contamination is beyond the reach of physical purification processes and without leaching contamination is inevitable in inclusion bearing garnets such contamination can lead to older apparent ages than those of garnet formation and thus has profound implications for sm nd as well as u pb garnet chronometry

major and trace element zoning in garnets from calcareous pelites in the nw shelburne falls quadrangle massachusetts garnet growth histories in retrograded rocks

high precision microsampling and preparation of zoned garnet porphyroblasts for sm nd geochronology abstract zoned garnet porphyroblasts contain one of the longest continuous records of tectonic processes with growth histories spanning many millions of years well known challenges exist in the physical preparation purification and geochronologic analysis of zoned garnets which have limited the progress and application of this potentially powerful geochronologic tool here we present details of an integrated methodology specifically for the acquisition of high resolution sm nd geochronologic records from zoned garnets that overcome these challenges we develop and demonstrate our methods on large test garnets from a shear zone in the tauern window in western austria chemically contoured microdrilling permits physical sampling of many discrete age annuli each as narrow as 100 m within a single garnet refined hno 3 hf hclo 4 partial dissolution methods cleanse coarse crushed 75 150 m size garnet annuli of detrimental inclusions yielding high 147 sm 144 nd ratios 0 9 to 4 6 and consequently accurate and precise ages experiments on powdered garnet 147 sm 144 nd 143 nd 144 nd with 10 20 ppm 2 rsd precision good enough for 147 sm 144 nd 1 0 in total this integrated sampling and analytical protocol permits the acquisition of 3 11 discrete high precision

garnets recording deep crustal earthquakes syn eclogite facies pseudotachylytes of the bergen arcs western norway were formed during co seismic faulting at a depth of 60 km during caledonian continent collision concurrent with fluid induced partial eclogitization of precambrian anorthositic granulites the pseudotachylytes contain the high pressure assemblage omphacite garnet and kyanite and formed in the metastable granulites at the border of eclogitized areas rock volumes corresponding to outcrops of 100 m2 in area were shattered by pseudotachylytes associated with ultramylonites cataclasites and shear zones the granulite facies garnets unzoned and inclusion free away from the pseudotachylyte veins display planar and curved fractures brecciation and melting with decreasing distance from the veins sieve textured garnet developed by the disintegration of granulite facies garnet crystallization of eclogite facies mineral inclusions and welding together of garnet fragments fractured granulite facies garnets trend to more almandine rich compositions with variable grossular contents in the pseudotachylyte veins a second generation of minute 10 200 m euhedral or dendritic garnets has a higher femg ratio than the granulite facies garnet and a wide range in grossular content grs11 grs89 suggesting rapid growth and cooling fracturing of garnet and its preferential disappearance in the pseudotachylyte show that garnet has a relatively low fracture toughness seismic faulting caused enhanced reaction rates during ongoing fluid induced eclogitization of the deep crust by increasing the surface to volume ratio of garnet and its dislocation density the sudden volume reduction associated with eclogitization of metastable crust may have nucleated further faulting and pseudotachylyte formation

interface coupled dissolution reprecipitation in garnet from subducted granulites and ultrahigh pressure rocks revealed by phosphorous sodium and titanium zonation garnet zonation provides an unparalleled record of the pressure temperature time fluid evolution of metamorphic rocks at extreme temperature conditions 900 c however most elements preserve little zonation due to intracrystalline diffusional relaxation under these conditions slowly diffusing trace elements including p na and ti have the best chance of recording metamorphic histories here we map dramatic zoning patterns of these elements in subducted high pressure felsic granulite saxon granulite massif and ultrahigh pressure diamondiferous saidenbachite saxonian erzgebirge bohemian massif the results show that garnet replacement via interface coupled dissolution reprecipitation can strongly affect garnet compositions in subduction zones and that p na and ti record burial and exhumation histories that are otherwise lost to diffusion in these samples p diffuses the slowest and ti the fastest

the effect of fluid and deformation on zoning and inclusion patterns in poly metamorphic garnets within the bergen arcs of w norway caledonian eclogite facies assemblages t 650 c p 15 kbar have formed from grenvillian granulites t 800 900 c p 10 kbar along shear zones and fluid pathways garnets in the granulites grti pyr56 40 alm45 25gro19 14 are unzoned or display a weak ca 1 wt feo over 1000 m zoning the eclogite facies rocks contain garnets inherited from their granulite facies protoliths these relict garnets have certain areas with compositions identical to the garnets in their nearby granulite but can be crosscut by bands of a more almrich composition grtii pyr31 41alm40 47gro17 21 formed during the eclogite facies event these bands orientated preferentially parallel or perpendicular to the eclogite foliation may contain mineral filled veins or trails of eclogite facies minerals omphacite amphibole white mica kyanite quartz and dolomite steep compositional gradients up to 9 wt feo over 40 m separate the two generations of garnets indicating limited volume diffusion the bands are interpreted as fluid rich channels where element mobility must have been infinitely greater than it was for the temperature controlled volume diffusion at mineral interfaces in the granulites the re equilibration of granulite facies garnets during the eclogite facies event must therefore be a function of fracture density deformation and fluid availability the results cast doubts on modern petrological and geochronological methods that assume pure temperature controlled chemical re equilibration of garnets

the p t deformation path for a mid proterozoic low pressure terrane the reynolds range central australia the proterozoic low pressure high temperature lpht terrane of the reynolds range occurs in a 130 km long nw trending belt in the central part of the arunta block central australia the reynolds range has been affected by two mid proterozoic tectonic cycles di and dii associated with two metamorphic events mi and mii di mi effects are restricted to the older of two sedimentary successions the lander rock beds which are separated from the younger reynolds range group by an angular unconformity the dominant structural metamorphic features formed during dii mii affected both sedimentary successions and the various granites that intruded them and reworked most di mi effects the dii deformation history can be subdivided into one prograde two peak and one retrograde stage average p t calculations in the southeastern half of the range indicate a peak metamorphic pressure of 4 1 0 3 kbar because the calculated values are derived from the same stratigraphic level corresponding to the base of the reynolds range group which is exposed throughout the area it is likely that pressures were similar in the entire range in fact however the peak metamorphic temperature shows a dramatic increase from greenschist facies c 400 c in the northwest to granulite facies 740 60 c in the southeast indicating that mii was associated with anomalously high heat flows the p t path is anticlockwise with isobaric cooling from the metamorphic peak indicated by corona textures however the evidence of a prograde increase in pressure is indirect and based on the compressional nature of the structures peak metamorphic mineral assemblages and retrograde mineral assemblages in amphibolite facies shear zones show the same metamorphic zonation suggesting they formed in response to the same thermal event if this is true the implication is that a thermal perturbation external to the crust was maintained for a considerable period of time 110 ma based on zircon dating as it is not clear whether proterozoic asthenosphere active thermal perturbations operated for this long the alternative interpretation must be considered namely that the peak metamorphic events are separate from the shear zone event associated with reheating of the area

rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth we present laser ablation microprobe inductively coupled mass spectrometry analyses of y yb er dy and gd in garnet crystals from high grade metamorphic and migmatitic rocks from the sierras pampeanas of argentina these rocks contain large garnet porphyroblasts 4 mm that are compositionally zoned rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores a notable feature of this zonation is the inversion of yb er and yb dy ratios from 1 in the cores to 1 in the rims we show quantitatively that the spatial distribution of these trace elements in garnet can be most simply and effectively explained as arising from rayleigh fractionation during garnet growth we also analyzed a small garnet crystal 2 mm representative of a garnet population that is associated with migmatitic leucosomes this crystal displays uniformly low concentrations of all trace elements that are virtually identical in both absolute and relative magnitudes to those in the rims of the larger garnet porphyroblasts the small crystals and perhaps part of the porphyroblast rims are likely to be peritectic products of incongruent melting reactions we argue that melts formed from garnet bearing sources may generally be unable to equilibrate with metamorphic garnet cores and may thus be more strongly depleted in heavy rare earth elements and y than modeling based on bulk source rock abundances of these elements would indicate

petrology and geochemistry of feldspathic impact melt breccia abar al uj 012 the first lunar meteorite from saudi arabia abar al uj aau 012 is a clast rich vesicular impact melt im breccia composed of lithic and mineral clasts set in a very fine grained and well crystallized matrix it is a typical feldspathic lunar meteorite most likely originating from the lunar farside bulk composition 31 0 wt al2o3 3 85wt feo is close to the mean of feldspathic lunar meteorites and apollo fan suite rocks the low concentration of incompatible trace elements 0 39ppmth 0 13ppm u reflects the absence of a significant kreep component plagioclase is highly anorthitic with a mean of an 96 9 ab 3 0 or 0 1 bulk rock mg is 63 and molar feo mno is 76 the terrestrial age of the meteorite is 33 4 5 2kyr aau 012 contains a similar to 1 4x1 5mm 2 exotic clast different from the lithic clast population which is dominated by clasts of anorthosite breccias bulk composition and presence of relatively large vesicles indicate that the clast was most probably formed by an impact into a precursor having nonmare igneous origin most likely related to the rare alkali suite rocks the im clast is mainly composed of clinopyroxenes contains a significant amount of cristobalite 9 0 vol and has a microcrystalline mesostasis although the clast shows similarities in texture and modal mineral abundances with some apollo pigeonite basalts it has lower feo and higher sio2 than any mare basalt it also has higher feo and lower al2o3 than rocks from the fan or mg suite its lower mg 59 compared to mg suite rocks also excludes a relationship with these types of lunar material

a simple mechanism for mid crustal shear zones to record surface derived fluid signatures ion microprobe analyses of garnet porphyroblasts from three separate splays of the mid crustal walter outalpa shear zone curnamona province south australia indicate homogeneous 18 o values of 18 o values in deeply exhumed shear zones may therefore be indicative of fault structures that have a prior history of surface exposure weathering burial and re exposure

the nolans bore rare earth element phosphorus uranium mineral system geology origin and post depositional modifications nolans bore is a rare earth element ree u p fluorapatite vein deposit hosted mostly by the 1805 ma boothby orthogneiss in the aileron province northern territory australia the fluorapatite veins are complex with two stages 1 massive to granular fluorapatite with inclusions of ree silicates phosphates and fluoro carbonates and 2 calcite allanite with accessory ree bearing phosphate and fluoro carbonate minerals that vein and brecciate the earlier stage the veins are locally accompanied by narrow skarn like garnet diopside amphibole wall rock alteration zones shrimp th pb analyses of allanite yielded an age of 1525 18 ma interpreted as the minimum age of mineralisation the maximum age is provided by a 1550 ma shrimp u pb age for a pegmatite that predates the fluorapatite veins other isotopic systems yielded ages from 1443 to 345 ma implying significant post depositional isotopic disturbance calculation of initial end and 87sr 86sr at 1525 ma and stable isotope data are consistent with an enriched mantle or lower crust source although post depositional disturbance is likely processes leading to formation of nolans bore began with north dipping subduction along the south margin of the aileron province at 1820 1750 ma producing a metasomatised volatile rich lithospheric mantle wedge about 200 million years later near the end of the chewings orogeny this reservoir and or the lower crust sourced alkaline low degree partial melts which passed into the mid and upper crust fluids derived from these melts which may have included phosphatic melts eventually deposited the nolans bore fluorapatite veins due to fluid rock interaction cooling depressurisation and or fluid mixing owing to its size and high concentration of th 2500 ppm in situ radiogenic heating caused significant recrystallisation and isotopic resetting the system finally cooled below 300 c at 370 ma possibly in response to unroofing during the alice springs orogeny surface exposure and weathering of fluorapatite produced acidic fluids and intense near surface kaolinitised zones that include high grade supergene enriched cheralite rich ores

effects of diffusional modification of garnet growth zoning on p t path calculations the effect of intragranular diffusion on chemical zoning in garnet and on p t paths calculated from that zoning was evaluated using a numerical model of multicomponent diffusion in combination with simulations of garnet growth syn and post growth diffusion of mg fe mn ca species in garnet was calculated for a model pelitic assemblage over a range of temperatures from 485 to 635 c compositions from zoned garnet as modified by diffusion hypothetical inclusions of plagioclase within garnet and matrix phases were used to reconstruct pressure temperature p t paths from isobaric and polybaric model histories p t path calculations based on numerical simulations conducted over an input isobaric heating path that reached peak temperatures between 585 and 635 c show that relaxation of garnet compositional gradients by diffusion can induce modest to appreciable curvature in the inferred paths retrieved paths also indicated somewhat smaller overall temperature changes relative to the actual temperature difference of the input path the magnitude of these distortions is shown to depend upon the heating and cooling rate and garnet crystal size as well as the actual peak temperature condition the effect of diffusion on path trajectories in simulations with thermal histories that also included cooling were comparable to heating only models that reached peak temperatures approximately 15 30 c higher compositions of garnets with radii less than 1 mm that reached actual peak temperatures of 605 c along temperature time histories characteristic of regional metamorphism experienced sufficient diffusional relaxation to introduce errors of hundreds of bars to in excess of one kilobar in path trajectories path distortions were significant at heating cooling rates less than 10 c ma but rapidly diminished for rates faster than this in polybaric simulations diffusion effects were least noticeable when the actual pressure temperature conditions changed in a clockwise sense i e convex to higher p and higher t but apprecciable modification was seen in path models that underwent counterclockwise changes in p and t reequilibration of garnet rim compositions occurred during cooling on all paths and temperature maxima obtained from garnet biotite geothermometry underestimated actual peak conditions by 40 to 70 c calculations suggest that p t path trajectories calculated from garnets of at least 1 mm size and that experienced actual thermal maxima below 585 c are not likely to be distorted by diffusional effects during regional metamorphism however p t path reconstructions based on garnet zonation with smaller grains or higher temperatures may lead to misinterpretation of crystallization history the partitioning record of peak metamorphic temperatures may be destroyed by diffusional reequilibration of garnet rim compositions during cooling seriously complicating the task of quantitatively estimating diffusion effects on path calculations

the basil cu co deposit eastern arunta region northern territory australia a metamorphosed volcanic hosted massive sulphide deposit abstract the basil cu co deposit harts range central australia is hosted by the riddock amphibolite a sequence that has been metamorphosed at upper amphibolite to granulite facies conditions at 480 460 ma larapinta event and subsequently reworked at amphibolite facies conditions 450 300 ma as a result many of the primary mineralization textures and other features that could characterise ore genesis have been obliterated however preserved textures and mineral relationships in the mineralized zone allow some constraints to be placed on the genetic history of the deposit using mineralogical petrographic and geochemical studies of host rocks and sulphides results of this study permit at least two genetic models to be ruled out firstly whole rock geochemistry and garnet compositions suggest that the deposit is not a skarn system secondly the lack of any significant ni signature and the presence of abundant zircons in the host amphibolite indicating that not all host rocks are mafic in composition and or magmatic in character make an orthomagmatic ni cu pge system unlikely alternatively basil is assigned to a volcanic hosted massive sulphide vhms style of mineralization formed on the seafloor within basaltic and sedimentary host rocks typical of deposits occurring in such settings the lack of a recognisable hydrothermal alteration zone is consistent with either destruction of the alteration zone during metamorphism or detachment of the ore from alteration during later deformation the occurrence of sulphide inclusions within garnet and amphibole indicates that the sulphides must be syn metamorphic or earlier partitioning of trace elements between pyrite and co existing pyrrhotite suggests that re crystallization occurred under equilibrium conditions the composition of sphalerite coexisting with pyrite and pyrrhotite indicates crystallization at pressures of at least 10 kbar consistent with peak metamorphism during the early ordovician larapinta event zr in titanite geothermometry indicates peak temperatures of 730 745 c

chromium and manganese zoning in pelitic garnet and kyanite spiral overprint and oscillatory zoning patterns and the role of growth rate x ray composition maps and quantitative analyses for mn ca and cr have been made for six pelitic and calc pelitic garnet crystals and al fe and cr analyses maps have been made for two kyanite crystals from lower and mid upper amphibolite facies rocks from the grenville province of western labrador using an electron microprobe analyser and a laser ablation icp ms garnet with spiral snowball internal fabrics si has spiral zoning in major elements implying that growth was concentrated in discrete regions of the crystal at any one time spiral zoning cr zoning is parallel to si in low amphibolite facies garnet with both straight and spiral internal fabrics indicating that the garnet overprinted a fabric defined by cr rich mica chlorite epidote and cr poor quartz plagioclase layers during growth overprint zoning and that cr was effectively immobile in contrast in mid upper amphibolite facies garnet porphyroblasts lacking si cr zoning is concentric implying that cr diffusion occurred cr zoning in kyanite porphyroblasts appears superficially similar to oscillatory zoning with up to three or four annuli of cr enrichment and or depletion present in a single grain however the variable width continuity cr concentration and local bifurcation of individual annuli suggest that an origin by overprint zoning may be more likely the results of this study explain previously observed nonsystematic cr zoning in garnet and irregular partitioning of cr between coexisting metamorphic mineral pairs in addition this study points to the important role of crystal growth rate in determining the presence or absence of inclusions and the type of zoning exhibited by both major and trace elements during fast growth inclusions are preferentially incorporated into the growing porphyroblast and slow diffusing elements such as cr are effectively immobile whereas during slow growth inclusions are not generally included in the porphyroblast and cr zoning is concentric

diffusion limited ree uptake by eclogite garnets and its consequences for lu hf and sm nd geochronology garnets from the zermatt saas fee eclogites contain narrow central peaks for lu yb tm er and at least one additional small peak towards the rim the ree sm eu gd tb dy are depleted in the cores but show one prominent peak close to the rim these patterns cannot be modeled using rayleigh fractionation accompanied by mineral breakdown reactions instead the patterns are well explained using a transient matrix diffusion model where ree uptake is limited by diffusion in the matrix surrounding the porphyroblast observed profiles are well matched if a roughly linear radius growth rate is used the secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to temperature increase during prograde metamorphism the model predicts anomalously low 176lu 177hf and 147sm 144nd ratios in garnets where growth rates are fast compared to diffusion of the ree and these results have important implications for lu hf and sm nd geochronology using garnet

boron isotope record of peak metamorphic ultrahigh pressure and retrograde fluid rock interaction in white mica lago di cignana western alps this study presents boron b concentration and isotope data for white mica from ultra high pressure uhp subduction related metamorphic rocks from lago di cignana western alps italy these rocks are of specific geological interest because they comprise the most deeply subducted rocks of oceanic origin worldwide boron geochemistry can track fluid rock interaction during their metamorphic evolution and provide important insights into mass transfer processes in subduction zones the highest b contents up to 345 g g b occur in peak metamorphic phengite from a garnet phengite quartzite the b isotopic composition is variable 11b 10 3 to 3 6 and correlates positively with b concentrations based on similar textures and major element mica composition neither textural differences prograde growth zoning diffusion nor a retrograde overprint can explain this correlation modelling shows that b devolatilization during metamorphism can explain the general trend but fails to account for the wide compositional and isotopic variability in a single well equilibrated sample we therefore argue that this trend represents fluid rock interaction during peak metamorphic conditions this interpretation is supported by fluid rock interaction modelling of boron leaching and boron addition that can successfully reproduce the observed spread in 11b and b taking into account the local availability of serpentinites as potential source rocks of the fluids the temperatures reached during peak metamorphism that allow for serpentine dehydration and the high positive 11b values 11b 20 5 modelled for the fluids an influx of serpentinite derived fluid appears likely paragonite in lawsonite pseudomorphs in an eclogite and phengite from a retrogressed metabasite have b contents between 12 and 68 g g and 11b values that cluster around 0 11b 5 0 to 3 5 white mica in both samples is related to distinct stages of retrograde metamorphism during exhumation of the rocks the variable b geochemistry can be successfully modelled as fluid rock interaction with low to moderate 3 fluid rock ratios where mica equilibrates with a fluid into which b preferentially partitions causing leaching of b from the rock the metamorphic rocks from lago di cignana show variable retention of b in white mica during subduction related metamorphism and exhumation the variability in the b geochemical signature in white mica is significant and enhances our understanding of metamorphic processes and their role in element transfer in subduction zones

trace element mapping by la icp ms assessing geochemical mobility in garnet a persistent problem in the study of garnet geochemistry is that the consideration of major elements alone excludes a wealth of information preserved by trace elements particularly the rare earth elements rees this is despite the fact that trace elements are generally less vulnerable to diffusive resetting and are sensitive to a broader spectrum of geochemical interactions involving the entire mineral assemblage including the growth and or dissolution of accessory minerals we outline a technique for the routine acquisition of high resolution 2d trace element maps by la icp ms and introduce an extension of the software package xmaptools for rapid processing of la icp ms data to visualise and interpret compositional zoning patterns these methods form the basis for investigating the mechanisms controlling geochemical mobility in garnet which are argued to be largely dependent on the interplay between element fractionation mineral reactions and partitioning and the length scales of intergranular transport samples from the peaked hill shear zone reynolds range central australia exhibit contrasting trace element distributions that can be linked to a detailed sequence of growth and dissolution events trace element mapping is thus employed to place garnet evolution in a specific paragenetic context and derive absolute age information by integration with existing u pb monazite and sm nd garnet geochronology ultimately the remarkable preservation of original growth zoning and its subtle modification by subsequent re equilibration is used to see through multiple superimposed events thereby revealing a previously obscure petrological and temporal record of metamorphism metasomatism and deformation

origins of yttrium and rare earth element distributions in metamorphic garnet highly variable distributions of yttrium and rare earth elements y rees are documented in pelitic garnet from the picuris mountains new mexico and from passo del sole switzerland and in mafic garnet from the franciscan complex california the wide variety of these y ree zoning patterns and those described previously in other occurrences imply diverse origins linked to differing degrees of mobility of these elements through the intergranular medium during garnet growth in the picuris mountains large early nucleating crystals have radial profiles of y ree dominated by central peaks and annular maxima in patterns that vary systematically with atomic number superimposed on these features are narrow spikes in hrees and mrees located progressively rimward with decreasing atomic number in contrast profiles in small late nucleating crystals contain only broad central maxima for all y rees in garnet from passo del sole y ree zoning varies radically from sample to sample in some rocks crystals of all sizes display only central peaks for all y rees in others profiles exhibit irregular fluctuations in y ree contents that match up with small scale patchy zoning in y and ca x ray maps in the franciscan complex y ree in garnet cores fluctuate unsystematically but mantles and rims display concentric oscillatory zoning for both major elements and y rees our interpretation of the complexity of y ree distributions in metamorphic garnet centres on the concept that these distributions vary primarily in response to the length scales over which these elements can equilibrate during garnet growth very short length scales of equilibration due to low intergranular mobility produce overprint zoning characterized by small scale irregularities higher but still restricted mobility yields diffusion controlled uptake characterized by patterns of central peaks and annular maxima that vary with atomic number and are strongly influenced by t t paths during garnet growth still greater mobility permits progressively greater potentially rock wide equilibration with major and accessory phase assemblages leading to mineralogical controls an unchanging mineral assemblage during garnet growth produces bell shaped profiles resembling those produced by rayleigh fractionation whereas changes in major and or accessory phase assemblages produce profiles with distinct annuli and sharp discontinuities in concentration the very high mobility associated with influxes of y ree bearing fluids can cause these element distributions to be dominated by factors external to the rock yielding profiles characterized by abrupt shifts or oscillations that are not correlated to changes in mineral assemblages

experimental investigation of eclogite rheology and its fabrics at high temperature and pressure eclogite plays an important role in mantle convection and geodynamics in subduction zones an improved understanding of processes in the deeper levels of subduction zones and collision belts requires information on eclogite rheology however the deformation processes and associated fabrics in eclogite are not well understood incompatible views of deformation mechanism have been proposed for both garnet and omphacite we present here deformation behaviour of eclogite at temperatures of 1027 1427 c confining pressures of 2 5 3 5 gpa and strain rates of 1 10 5 s 1 to 5 10 4 s 1 we obtained a power law creep for the high temperature and pressure deformation of a dry eclogite 50 vol garnet 40 omphacite and 10 quartz with a 103 3 1 0 n 3 5 0 4 e 403 30 kj mol 1 and v 27 2 cm3 mol 1 the two principal minerals of eclogite have greatly different strengths progressive increase of garnet results in a smooth increase in strength analysis by electron back scattered diffraction shows that 1 garnet displays pole figures with near random distributions of misorientation angle under both dry and wet conditions 2 omphacite shows pronounced lattice preferred orientations lpos suggesting a dominant dislocation creep mechanism further investigation into the water effects on eclogite show 3 water content does not influence the style of omphacite fabric but increases slightly the fabric strength 4 grain boundary processes dominate the deformation of garnet under high water fugacity or high shear strain conditions yielding a random lpo similar to that of non deforming garnet despite the strong shape preferred orientation spo observed 110 001 slip may dominate the deformation of rutile quartz displays complicated and inconsistent lpos in eclogite these results are remarkably similar to observations from deformed eclogites in nature

hardness toughness and modulus of some common metamorphic minerals studies of the hardness and toughness of minerals have historically focused on minerals of the mohs scale although with the exceptions of quartz orthoclase and calcite mohs phases are not common rock forming minerals we report new hardness h toughness resistance to fracture k ic and indentation modulus e data obtained by microhardness and depth sensing indentation dsi or nanoindentation experiments for common metamorphic minerals sillimanite kyanite andalusite garnet quartz and orthoclase feldspar because the experimental techniques involve indentation induced cracking as well as depth sensing indentation the new data set can be used to investigate a range of plastic behavior for minerals in the crust and mantle the three al2sio5 polymorphs have similar h values 10 12 gpa kyanite has the largest values and andalusite the smallest these values are similar to that of quartz 12 gpa and greater than that of orthoclase 7 gpa garnet h values vary with composition for grossular h 13 gpa and for almandine pyrope h 15 gpa although h values for the minerals we analyzed span a range of 10 gpa most fracture toughness values are between 1 1 8 mpa m garnet is much harder than al2sio5 but has a similar to slightly lower k ic grossular 1 2 mpa m almandine pyrope 1 4 mpa m andalusite 1 8 mpa m sillimanite 1 6 mpa m kyanite k ic is difficult to measure owing to the ease with which kyanite cleaves garnet has properties similar to those of cubic zirconia zro2 which we measured as a reference another reference mineral periclase mgo has the lowest h 5 gpa and the highest k ic 4 mpa m of minerals we measured among the silicates e varies significantly from orthoclase 89 gpa to quartz 117 gpa to garnet 245 260 gpa and al2sio5 has intermediate values kyanite 186 253 gpa sillimanite 207 gpa andalusite 232 gpa

yttrium zoning in metamorphic garnets abstract yttrium zoning has been measured in garnets from the straits schist connecticut usa using the synchrotron x ray fluorescence sxrf microprobe sxrf compositional maps for mn and fe show that the major elements are concentrically zoned about the gannet core in the classic bell shaped profiles considered indicative of growth zoning yttrium however displays oscillatory zoning which varies three orders of magnitude in abundance from about 3 to 4000 ppm and is correlated with textural zoning in garnet the major element abundances by contrast display no visible inflection related to textural zoning at this time it is not possible to unequivocally identify the mechanism which has produced this oscillatory zoning most likely this reflects either the breakdown of y enriched phases changes in the rate of garnet growth with time or changes in the effective y concentration of matrix phases due to breakdown and reprecipitation of garnet as the equilibrium reactions involving gannet change this study demonstrates that the sxrf microprobe provides excellent spatially resolved compositional maps for trace elements in porphyroblasts something other analytical techniques have been unable to do it also suggests that the diffusion rates for y in garnet are probably significantly slower than those for major cations such as mn fe mg and ca as a result trace element mapping potentially provides a clearer record of the reaction history of the rock provides details of how chemical zoning in garnet is produced and allows evaluation of assumptions about chemical equilibrium between minerals

zircon solubility in alkaline aqueous fluids at upper crustal conditions field evidence and thermodynamic data at ambient conditions suggest that complexing of zr with hydroxyl ions at high ph enhances the solubility of zircon we tested this hypothesis by measuring the solubilities of the assemblages zircon zrsio 4 baddeleyite z b and zircon quartz z q in neutral to alkaline fluids at 0 2 gpa and 450 750 c in neutral to alkaline fluids 0 0 1 1m naoh zircon dissolved incongruently in quartz undersaturated fluids to form baddeleyite at 450 c various na zr silicates precipitated from fluids saturated and undersaturated in quartz we observed no significant dependence of solubility on temperature the measured solubilities of zircon in pure h 2o at 600 and 750 c are only slightly higher than the procedural blank of 3 3 10 7 m zr however the measured solubility of zircon increases with increasing aqueous silica suggesting that zirconium complexes with silica in the fluid at 600 c linear regression of experimental results yielded ln zr 0 25 2 9 ln si where terms in parentheses represent molal concentrations zircon solubility also seems to increase with increasing hydroxyl concentration in the fluid enhanced solubility in silica rich alkaline fluids may cause dissolution reprecipitation of zircon and resetting of its isotopic clocks suggesting that some zircon u pb ages may correspond to fluid events

deformation enhanced metamorphic reactions and the rheology of high pressure shear zones western gneiss region norway microstructural and petrological analysis of samples with increasing strain in high pressure hp shear zones from the haram garnet corona gabbro give insights into the deformation mechanisms of minerals rheological properties of the shear zone and the role of deformation in enhancing metamorphic reactions scanning electron microscopy with electron backscattering diffraction sem ebsd compositional mapping and petrographic analysis were used to evaluate the nature of deformation in both reactants and products associated with eclogitization plagioclase with a shape preferred orientation that occurs in the interior part of layers in the mylonitic sample deformed by intracrystalline glide on the 0 0 1 1 0 0 slip system in omphacite crystallographic preferred orientations indicate slip on 1 0 0 0 0 1 and 1 1 0 0 0 1 during deformation fine grained garnet deformed by diffusion creep and grain boundary sliding ilmenite deformed by dislocation glide on the basal and at higher strains prism planes in the a direction relationships among the minerals present and petrological analysis indicate that deformation and metamorphism in the shear zones began at 500 650 c and 0 5 1 4 gpa and continued during prograde metamorphism to ultra high pressure uhp conditions both products and reactants show evidence of syn and post kinematic growth indicating that prograde reactions continued after strain was partitioned away the restriction of post kinematic growth to narrow regions at the interface of garnet and plagioclase and preservation of earlier syn kinematic microstructures in older parts layers that were involved in reactions during deformation show that diffusion distances were significantly shortened when strain was partitioned away demonstrating that deformation played an important role in enhancing metamorphic reactions two important consequences of deformation observed in these shear zones are i the homogenization of chemical composition gradients occurred by mixing and grain boundary migration and ii composition changes in zoned metamorphic garnet by lengthening diffusion distances the application of experimental flow laws to the main phases present in nearly monomineralic layers yield upper limits for stresses of 100 150 mpa and lower limits for strain rates of 10 12 to 10 13 s 1 as deformation conditions for the shear zones in the haram gabbro that were produced during subduction of the baltica craton and resulted in the production of hp and uhp metamorphic rocks

timing relationships between pegmatite emplacement metamorphism and deformation during the intra plate alice springs orogeny central australia in the harts range central australia the upper amphibolite facies to lower granulite facies c 480 460 ma harts range metamorphic complex hrmc and the upper amphibolite facies c 340 320 ma entia gneiss complex are cut by numerous generally peraluminous pegmatites and their deformed equivalents the pegmatites have previously been interpreted as locally derived partial melts however shrimp u pb monazite and zircon dating of 29 pegmatites or their deformed equivalents predominantly from the hrmc reveal that they were emplaced episodically throughout almost the entire duration of the polyphase c 450 300 ma intra plate alice springs orogeny episodes of pegmatite intrusion correlate with the age of major alice springs age structures and with deposition of syn orogenic sedimentary rocks in the adjacent centralian superbasin similar alice springs ages have not been obtained from anatectic country rocks in the hrmc suggesting that the pegmatites were not locally derived instead they are interpreted as highly fractionated granites and imply that much larger parental alice springs age granites exist at depth the mechanism to allow repeated felsic magmatism in an intraplate setting where all exposed rock types had a previous high temperature history is enigmatic however we suggest that episodic underthrusting and dehydration of unmetamorphosed centralian superbasin sedimentary rocks allowed crustal fertility to maintained over a c 140 ma interval during the intra plate alice springs orogeny

the flow of surface derived fluids through alice springs age middle crustal ductile shear zones reynolds range central australia the south east reynolds range central australia is cut by steep north west trending alice springs age c 334 ma shear zones that are up to hundreds of metres wide and several kilometres long with reverse senses of movement amphibolite facies 550 600 c 500 600 mpa shear zones cut metapelites while greenschist facies shear zones 420 535 c 400 650 mpa cut metagranites the sheared rocks commonly underwent metasomatism implying that the shear zones were the pathways of significant fluid flow altered granites within greenschist facies shear zones have gained si and k but lost ca and na relative to their unsheared counterparts suggesting that the fluid flowed down temperature and hence probably upward through the shear zones time integrated fluid fluxes calculated from silica addition are up to 2 1 1010 mol m 2 c 4 2 105 m3 m 2 similar time integrated fluid fluxes are also estimated from changes in k and na the sheared granitic rocks locally have 18o values as low as 0 which is much lower than the 18o values of the adjacent unsheared granites 7 to 9 implying that the fluid which flowed through these shear zones was derived from the surface for the estimated time integrated fluid fluxes the fluids would be able to retain their isotopic signature for many tens to hundreds of kilometres the flow of surface derived fluids into the ductile middle crust with subsequent expulsion upwards through the shear zones may have been driven by seismic activity accompanying the alice springs deformation

lu hf geochronology on cm sized garnets using microsampling new constraints on garnet growth rates and duration of metamorphism during continental collision menderes massif turkey abstract this study shows lu hf geochronology of zoned garnet crystals contained in mica schists from the southern menderes massif turkey selected samples are four 3 5 cm large garnet megacrysts of which several consecutive garnet shells have been sampled with a micro saw and analyzed for dating the results are used to extract growth rates of garnet and also to improve the time constraint for alpine aged overprint of the pan african basement in the menderes massif lu hf ages of the sampled garnet shells are determined by two point garnet only isochrons using the garnets lu depleted rim compositions this yields a consistent decrease of age information from core to rim segments of individual garnet crystals and the calculated isochron ages propose a time frame of growth between 42 6 1 9 and 34 8 3 1 ma major element profiles in the investigated garnets characterize zoning patterns indicative of prograde conditions rayleigh fractionated bell shaped mn and decreasing fe fe mg are recorded by the garnets core to rim compositions therefore the obtained lu hf ages record timing of early prograde growth for the cores of the garnets two of the large garnet crystals also yield isochron ages of 58 83 0 69 and 50 16 0 84 ma in their innermost cores which appear to record an early nucleation event this view however is not in concordance with the observed major element profiles of these garnets and therefore is interpreted with caution termination of the garnet growth period is determined through the calculation of radial growth rates based on the size of the garnets and the lu hf ages obtained for consecutive shells extrapolation of these rates potentially constrains the total duration for garnet growth terminating at 31 6 ma comparison of the growth rates calculated for individual crystals shows a variety of slow and fast growing garnets and similar results have been previously obtained with the rb sr and sm nd isotope systems the new data provides a precise age determination for prograde barrovian metamorphism in the southern menderes massif which so far was placed between 63 and 27 ma on the basis of mica rb sr and ar ar dating this study provides new constraints crucial to the understanding of the tectonic evolution of southwest anatolia and the aegean realm as it yields a shorter outline for alpine aged continental collision

garnets as open systems during regional metamorphism if a garnet fractures during metamorphism its interior will be in chemical communication with matrix phases solids and fluids and may participate in late prograde or retrograde metamorphic reactions the core of a growth zoned garnet is unlikely to be in equilibrium with matrix phases and may react locally in the vicinity of fractures or extensively resulting in dissolution and reprecipitation of the garnet interior and or production of new phases the results of petrologic techniques such as thermobarometry pressure temperature path calculations and geochronometry may be misinterpreted if sites of garnet and mineral inclusion compositional modification are not identified brittle fracturing of garnet during regional metamorphism may be facilitated by the presence of mineral inclusions the conditions at which differential expansion of an inclusion relative to its host garnet are sufficient to cause radial cracking around the inclusion vary as a function of peak pressure retrograde pressure temperature path and thermoelastic properties of the inclusion and garnet inclusion induced fracturing is favored by nearly isothermal decompression a common metamorphic pressure temperature path other fractures may form as a result of propagation of an inclusion host boundary or by mechanisms external to the garnet

scales of disequilibrium and rates of equilibration during metamorphism mounting evidence suggests that partial disequilibrium meaning disequilibrium for some elements but not for others may be a common but rarely detected phenomenon during metamorphic mineral growth even in ordinary prograde reactions that progress to completion detailed examination of compositional variations in garnet crystals over a range of metamorphic grade suggests distinctly different scales of equilibration for common elements with strong temperature dependence under lower greenschist facies conditions fe and mg may equilibrate at hand sample scale whereas mn and ca may not equilibrate even at millimeter scale although mn may achieve hand sample scale equilibration under upper greenschist facies conditions ca and many trivalent cations e g rees may not do so until temperatures exceed those of the middle amphibolite facies even in the lower granulite facies some elements e g y yb show indications of disequilibrium at sub centimeter scales during garnet growth analysis and numerical modeling of undisputed disequilibrium textures demonstrate that the most common impediment to equilibration during metamorphism is the sluggishness of intergranular diffusion the same mechanism known to govern porphyroblast crystallization in many metamorphic environments despite this importance to petrology few quantitative determinations exist of inter granular diffusion rates under metamorphic conditions using numerical simulations of coupled intergranular and intracrystalline diffusion processes in coronal textures around partially resorbed garnet crystals from the llano uplift u s a a very precise and relatively accurate estimate is obtained for the rate of intergranular diffusion of al in fluid undersaturated systems this result and an earlier estimate for fluid saturated systems provide bracketing values for al diffusivity during metamorphism

assessing the geochemical and tectonic impacts of fluid rock interaction in mid crustal shear zones a case study from the intracontinental alice springs orogen central australia the reynolds anmatjira ranges central australia form part of a high grade basement terrane dissected by intensely metasomatized transpressional shear zones active during the ordovician carboniferous alice springs orogeny unlike typical retrograde structures associated with discrete fluid flow the mid crustal setting and intracontinental nature of these shear systems present significant problems for the source and ingress mechanism of the fluid involved in their rehydration to address these issues we describe two detailed traverses across deformed and metasomatized basement rocks in this region and interrogate their record of fluid rock interaction from various perspectives both traverses combine structural and petrological observations with zr in rutile and ti in quartz thermobarometry oxygen and hydrogen stable isotope analysis and major trace and rare earth element mobility trends each technique is critically evaluated for its utility in this study and its more widespread applicability to alternative field areas providing a strategic framework for the general investigation of fluid affected shear zones ultimately the integrated data sets specify pressure temperature conditions of 530 c and 4 5 kbar implying average apparent thermal gradients of 29 36 c km 1 and depths of 14 18 km other characteristic features to emerge include strongly variable element mobilities and pronounced isotopic depletion fronts consistent with the alteration effects of an externally derived non equilibrium fluid this is confirmed by calculated fluid compositions indicative of contributions from a fluid of meteoric origin with estimated 18o and d values as low as 2 3 and 59 8 respectively we propose that these surficial fluid signatures are imposed on the mid crust by the prograde burial and dehydration of hydrothermally altered fault panels produced during pre orogenic basin formation progressive fluid release with continued subsidence then leads to the accumulation of increasing fluid volumes in the vicinity of the brittle ductile transition promoting extensive hydration metasomatism and reaction softening at the locus of stress transmission from plate boundary sources the sustained injection of externally derived fluids into refractory crustal material may thus stimulate a critical reduction in the long term strength of the lithosphere providing strong impetus for the initiation and advancement of intracontinental orogenesis

arsenopyrite pyrite association in an orogenic gold ore tracing mineralization history from textures and trace elements laser ablation inductively coupled plasma mass spectrometry la icp ms spot analysis and element mapping coupled with high resolution focused ion beam scanning electron microscopy fib sem imaging has been performed on au hosting sulfides from a proterozoic orogenic gold deposit tanami gold province north central australia gold distribution patterns in the arsenopyrite pyrite assemblage which probably crystallized toward the end of the au forming event suggest a process of initial scavenging of au into arsenopyrite and subsequent remobilization of that au following brittle fracture gold expelled from the sulfide lattice during the remobilization event is reconcentrated around the margins of the same arsenopyrite grains and within swarms of crosscutting microfractures the distribution of pb bi and ag closely mimic au indicating that these elements were also reconcentrated preservation of oscillatory zonation patterns for co ni sb se and te in arsenopyrite imply however that no significant degree of sulfide recrystallization took place residual concentrations of invisible gold in grain centers are 5 ppm in arsenopyrite and 1 ppm in coexisting pyrite the presence of submicron sized pores is suggestive of a fluid driven process rather than solid state diffusion micron scale 2 10 m remobilized gold is accompanied by fine particles 200 nm 2 m and nanoparticles 200 nm of gold the extensive variation of au concentrations within single arsenopyrite grains underlines the significance of textures when using trace element data to understand how gold ores evolved

rates of fe mg mn and ca diffusion in garnet extraction of the thermal and chemical histories preserved by modified compositional zoning in garnet is compromised by large uncertainties in experimentally determined diffusion coefficients for principal divalent cations some of this uncertainty derives from long down temperature extrapolations but much of it arises from an inability to account accurately for large variations in diffusivity as a function of garnet composition numerical simulation of stranded diffusion profiles in partially resorbed natural garnets constrains diffusivities at low temperature and reveals a systematic dependence of diffusion rates on host garnet composition a comprehensive model incorporating a simple compositional dependence allows accurate prediction of diffusion rates for fe mg mn and ca for nearly all garnet compositions across the full range of geologically relevant temperatures pressures and oxygen fugacities

diffusional homogenization of light ree in garnet from the day nui con voi massif in n vietnam implications for sm nd geochronology and timing of metamorphism in the red river shear zone abstract high grade migmatitic and mylonitic gneisses from the day nui con voi massif in northern vietnam record temperatures of 760 810 c at pressures of 6 10 kbars high temperature conditions have resulted in the development of major element diffusional profiles in garnet laser ablation icp ms analyses of trace elements indicate that ree and hf closely followed rayleigh like fractionation trends but underwent significant post crystallization modification light ree and to a lesser extent hree rim to rim zonation profiles show progressive flattening with the decreasing garnet size nd and sm are completely homogenized in the crystals smaller than 1 5 mm while lu always preserves variable degrees of core to rim concentration gradient the observed ree patterns are interpreted as resulting from the combination of protracted garnet growth of progressively smaller crystals and intracrystalline diffusion this had profound influence on sm nd geochronology and resulted in isochron ages ranging from 50 to 32 ma the youngest age was obtained for a sample where all garnet crystals are smaller than 2 mm in which light ree profiles are completely or nearly completely homogenized thus only the youngest age represents geologically meaningful event and 31 7 0 9 ma age is interpreted as the best estimate of the resetting episode due to high temperature diffusional homogenization of light ree during early oligocene metamorphism older sm nd ages reflect mixed analyses of variably reset individual garnet crystals lu hf isotopic analyses of bulk garnet fractions despite yielding high parent daughter isotopic ratios appeared very scattered and did not allow defining isochron ages instead apparent ages defined by whole rock and individual garnet fractions range from c 80 to 160 ma very old apparent ages are interpreted as being the consequence of intracrystalline lu diffusion and preservation of the original hf distribution which leads to lower 176 lu 177 hf ratios and thus steeper older isochrons back diffusion of lu during commonly observed resorption played a subordinate role in modifying isotope systematics

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

deciphering high pressure metamorphism in collisional context using microprobe mapping methods application to the stak eclogitic massif northwest himalaya the stak massif northern pakistan is a newly recognized occurrence of eclogite formed by the subduction of the northern margin of the indian continent in the northwest himalaya although this unit was extensively retrogressed during the himalayan collision records of the high pressure hp event as well as a continuous pressure temperature p t path were assessed from a single thin section using a new multiequilibrium method this method uses microprobe x ray compositional maps of garnet and omphacitic pyroxene followed by calculations of 200 000 p t estimates using appropriate thermobarometers the stak eclogite underwent prograde metamorphism increasing from 650 c and 2 4 gpa to the peak conditions of 750 c and 2 5 gpa then retrogressed to 700 650 c and 1 6 0 9 gpa under amphibolite facies conditions the estimated peak metamorphic conditions and p t path are similar to those of the kaghan and tso morari high to ultrahigh pressure hp uhp massifs we propose that these three massifs define a large hp to uhp province in the northwest himalaya comparable to the dabie sulu province in china and the western gneiss region in norway

yttrium zoning in garnet coupling of major and accessory phases during metamorphic reactions the concentration of yttrium in pelitic garnets as a function of metamorphic grade has been examined in relation to the distribution of xenotime ypo 4 in samples from new england and british columbia samples with xenotime present only as inclusions in garnet generally possess high y cores and concentrations that drop off discontinuously along zoning shoulders of variable width to low y outboard regions samples with matrix xenotime are restricted to the garnet zone y concentration of these garnets generally decreases smoothly from core to rim xenotime may also be present in reaction zones around garnet in xenotime bearing samples y g r t is strongly temperature dependent and ranges from 5000 ppm in the garnet zone to 150 ppm in the sillimanite zone measured yttrium zoning profiles in xenotime absent samples are reproduced with both rayleigh fractionation and diffusion models but p t histories of the samples examined favor the rayleigh model with garnet volume bulk rock yttrium and mode of y hree accessory phases controlling the profile shape high yttrium annuli in staurolite zone samples may form by garnet overgrowth of proximal matrix enriched in yttrium due to garnet consumption during discontinuous staurolite forming reactions an increase in y g r t and hree g r t in garnet from anatectic samples is related to dissolution of phosphates in vapor absent peraluminous melt with partitioning of highly compatible y and hree into garnet grown during anatexis textural analysis reveals that phosphates are absent from regions of garnet grown in equilibrium with melt a main result of this study is identification of an intimate coupling between major pelite phases and accessory phases during reaction progress this coupling is of great advantage in that it may be used to 1 calibrate sensitive geothermometers and geobarometers 2 identify particular regions of garnet grown in different garnet producing reactions over a range of grades and 3 reveal portions of pelite reaction history invisible to major elements

fluid mediated partial alteration in monazite the role of coupled dissolution reprecipitation in element redistribution and mass transfer monazite ce lree th u ca p si o4 with complex zoning in th and other elements is commonly observed in metamorphic and igneous rocks the hypothesis that this alteration is a product of fluid mediated element mass transfer has been tested in the piston cylinder press caf2 assembly cylindrical graphite oven at 1 000 mpa and 900 c and in cold seal autoclaves on a hydrothermal line at 500 mpa and 600 c experiments included a relatively homogeneous monazite ce 7 8 wt tho2 from a heavy mineral sand plus a series of alkali bearing fluids including 2n naoh 2n koh and na2si2o5 h2o experiments were conducted using bse imaging emp analysis and both tem and hrtem a subset of monazite grains from each experiment show evidence of partial alteration in the form of areas enriched in th si with sharp curvilinear compositional boundaries extending from the grain rim into the monazite interior these thsio4 enriched textures are similar to those commonly seen in natural examples of metasomatised monazite in both magmatic and metamorphic rocks in the na2si2o5 h2o experiments scarce inclusions of britholite formed in the altered monazite the altered monazite is also characterised by strong depletion in pb ca and y thorium and si mobility coupled with the formation of britholite inclusions during partial alteration in the monazite grain is considered to be the product of fluid aided coupled dissolution reprecipitation as opposed to solid state diffusion since other fluids including nacl and kcl brines do not result in the formation of these textures the experimental replication of thsio4 enriched areas in the monazite strongly suggests that similar textures in monazite observed in nature are fluid induced specifically by alkali bearing fluids if true complex metasomatically induced textures in monazite could yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of the metasomatic event presuming that all the original radiogenic pb has been removed

burial rates during prograde metamorphism of an ultra high pressure terrane an example from lago di cignana western alps italy abstract estimation of burial rates and duration of prograde metamorphism of ultra high pressure uhp rocks t 590 630 c p 2 7 2 9 gpa of the zermatt saas ophiolite from lago di cignana italy may be made through combined lu hf and sm nd garnet geochronology in conjunction with petrologic estimates of the prograde p t path we report a lu hf garnet omphacite whole rock isochron age of 48 8 2 1 ma from the uhp locality at lago di cignana which stands in contrast to the sm nd age of 40 6 2 6 ma amato et al earth planet sci lett 171 1999 425 438 obtained from the same sample and mineral material the sm nd and lu hf ages as well as other ages determined on metamorphic garnet zircon and white mica amato et al earth planet sci lett 171 1999 425 438 mayer et al eur union geosci 10 1999 abstr 809 rubatto et al contrib mineral petrol 132 1998 269 287 dal piaz et al int j earth sci 90 2001 668 684 from lago di cignana and elsewhere in the zermatt saas ophiolite lie within a range of 50 38 ma which we interpret to encompass the duration of prograde metamorphism and possibly the duration of garnet growth the difference in measured sm nd and lu hf ages from cignana can be accounted for by expected core to rim variations in lu hf sm and nd the measured yttrium content in garnet which may be a proxy for lu is highest in garnet core and lowest in the mineral rim generally following a profile that is predicted by rayleigh fractionation preferential enrichment of lu in the core produces a lu hf age that is weighted toward the older garnet core sm nd ages as predicted by rayleigh fractionation of sm and nd during garnet growth however reflect later grown garnet as compared to lu hf ages the difference in sm nd and lu hf ages from a single sample should therefore be a minimum estimate for the duration of garnet growth and prograde metamorphism so long as sm nd and lu hf blocking temperatures were not exceeded for a long period of time based on the 12 myr duration of prograde garnet growth estimated in this study burial rates for rocks at lago di cignana were on the order of 0 23 0 47 cm yr these values correlate with continuous shortening rates of 0 4 1 4 cm yr between the european plate and the african adriatic promontory between 50 and 38 ma which is on the order of that calculated for plate velocities from plate reconstructions suggesting that the zermatt saas ophiolite may have remained well coupled to the down going slab to uhp conditions

the geological evolution of the reynolds range central australia evidence for three distinct structural metamorphic cycles the reynolds range is affected by three distinct structural metamorphic cycles di mi dii mii anddiii miii which represent the local expressions of a series of orogenic events that affected large sections of the arunta block central australia the tectonic cycles recognized in the reynolds range correlate extremely well with similar events in the nearby anmatjira range di mi took place around 1820 ma and only affected the nw reynolds range dii mii occurred between 1760 and 1650 ma and involved ne sw shortening with identical timing relationships between the deformations and metamorphism along the entire reynolds range dii commenced with the formation of a fabric sii1 preserved as inclusion trails in porphyroblasts sii1 formed early during a progressive event dii1 2 which involved the formation and tightening of upright nw se trending isoclinal folds a penetrative subvertical nw se trending fabric sii2 developed axial planar to these folds the general symmetry of dii2 microstructures suggests that fii2 folds were formed during progressive coaxial deformation under plane strain conditions dii3 structures are associated with conjugate sets of crenulation bands within the macroscopic crenulation bands large sections of earlier folds and fabrics are rotated to a near recumbent position the dominant set of crenulation bands is upright and trends ene wsw while the conjugate to this set trends nw se no penetrative fabric formed during dii3 dii4 is associated with a system of amphibolite grade ne dipping thrusts interconnected by numerous smaller shear zones the sense of movement is ne over sw during dii essentially penetrative coaxial deformation dii2 evolved into essentially localized non coaxial deformation dii3 dii4 dii deformation occurred concomitant with a low pressure granulite facies metamorphic event mii 1730 ma peak metamorphic sillimanite cordierite orthopyroxene ilmenite spinel garnet k feldspar quartz assemblages define sii2 oriented sillimanite biotite assemblages that formed early during dii3 and unoriented andalusite chlorite muscovite assemblages that formed late during dii3 indicate that cooling of mii was initially isobaric during dii4 thrusting staurolite garnet biotite quartz and biotite kyanite quartz assemblages defining the mylonitic fabric overprint the late dii3 andalusite assemblages dii4 shear movement is therefore accompanied by a slight rise in pressure dii4 shear zones gradually increase in grade eastward along the reynolds range this trend coincides with the variation in peak metamorphic grade attained during mii indicating that the rocks had not yet fully cooled when dii4 thrusting commenced diii miii is late devonian to carboniferous in age and caused minor differential movement 100 m and retrogression along dii4 shear zones

diffusion control of garnet growth harpswell neck maine usa a detailed analysis of chemical zoning in two garnet crystals from harpswell neck maine forms the basis of an interpretation of garnet nucleation and growth mechanisms garnet apparently nucleates initially on crenulations of mica and chlorite and quickly overgrows the entire crenulation giving rise to complex two dimensional zoning patterns depending on the orientation of the thin section cut contours of ca zoning cross those of mn fe and mg indicating a lack of equilibrium among these major garnet constituents zoning of fe mg and mn is interpreted to reflect equilibrium with the rock matrix whereas ca zoning is interpreted to be controlled by diffusive transport between the matrix and the growing crystal image analysis reveals that the growth of garnet is more rapid along triple grain intersections than along double grain boundaries moreover different minerals are replaced by garnet at different rates the relative rate of replacement by garnet along double grain boundaries is ordered as muscovite chlorite plagioclase quartz flux calculations reveal that replacement is limited by diffusion of si along double grain boundaries to or from the local reaction site it is concluded that multiple diffusive pathways control the bulk replacement of the rock matrix by garnet with si and al transport being rate limiting in these samples

a combined chemical isotopic and microstructural study of pyrite from roll front uranium deposits lake eyre basin south australia abstract the common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at pepegoona pepegoona west and pannikan lake eyre basin south australia combined chemical isotopic and microstructural analysis of pyrite indicates variation in fluid composition sulfur source and precipitation conditions during a protracted mineralization event the results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low temperature hydrothermal systems in situ micrometer scale sulfur isotope analyses of pyrite demonstrated broad scale isotopic heterogeneity 34 s 43 9 to 32 4 vcdt indicative of complex multi faceted pyrite evolution and sulfur derived from more than a single source preserved textures support this assertion and indicate a genetic model involving more than one phase of pyrite formation authigenic pyrite underwent prolonged evolution and recrystallization evidenced by a genetic relationship between archetypal framboidal aggregates and pyrite euhedra secondary hydrothermal pyrite commonly displays hyper enrichment of several trace elements mn co ni as se mo sb w and tl in ore bearing horizons hydrothermal fluids of magmatic and meteoric origins supplied metals to the system but the geochemical signature of pyrite suggests a dominantly granitic source and also the influence of mafic rock types irregular variation in 34 s coupled with oscillatory trace element zonation in secondary pyrite is interpreted in terms of continuous variations in fluid composition and cycles of diagenetic recrystallization a late stage oxidizing fluid may have mobilized selenium from pre existing pyrite subsequent restoration of reduced conditions within the aquifer caused ongoing pyrite re crystallization and precipitation of selenium as native selenium these results provide the first qualitative constraints on the formation mechanisms of the uranium deposits at beverley north insights into depositional conditions and sources of both sulfide and uranium mineralization and an improved understanding of pyrite geochemistry can also underpin an effective vector for uranium exploration at beverley north and other sedimentary systems of the lake eyre basin as well as in comparable geological environments elsewhere

dissolution reprecipitation of zircon at low temperature high pressure conditions lanzo massif italy abst r a c t an eclogite facies meta plagiogranite from the lanzo massif western alps italy contains crystals of zircon intimately associated with allanite zircon displays different microtextures ranging from pristine euhedral and magmatic to fractured porous varieties with mosaic zoning and pervasive recrystallization into euhedral microcrystals fractures and voids in the recrystallized zircon microcrystals are mainly filled by high pressure na rich pyroxene electron backscattered diffraction analysis revealed a similar crystallographic orientation for primary magmatic zircon crystals and microcrystals with less than 2 misorientation among neighboring microdomains the textural change is coupled with chemical and isotopic modifications recrystallized zircon domains contain significantly less th and light to mid ree but are richer in sr than magmatic zircon crystals magmatic zircon preserves the protolith u pb age of 163 5 1 7 ma whereas zircon microcrystals have a mean age of 55 1 ma the coexisting allanite also contains inclusions of na rich pyroxene and has chemical features elevated sr and ni contents and lack of eu anomaly indicating formation at high pressure despite being associated texturally with zircon allanite yields a younger th pb age of 46 5 3 0 ma suggesting that the lanzo unit remained at relatively high pressure conditions for 8 m y zircon recrystallization proceeded with volume reduction and loss of material to an alkaline metamorphic fluid that acted as the agent for a coupled dissolution reprecipitation process recrystallization occurred with minimum transport in a low strain environment and was not significantly enhanced by metamictization the source of the fluid for zircon recrystallization is most probably related to prograde devolatilization reactions in the surrounding serpentinite

the slump breccias of the toquepala porphyry cu mo deposit peru implications for fragment rounding in hydrothermal breccias intrusive hydrothermal breccias have long attracted interest e g bastin and hill 1917 farmin 1934 bryner 1961 mayo 1976 due in part to their widespread occurrence in association with many types of ore deposits in porphyry copper centers such breccias may host a substantial proportion of the mineralization but even where barren they provide critical information on the physical evolution of the magmatic hydrothermal environment most salient aspects of ore related breccias are addressed by sawkins and sillitoe 1985 burnham 1985 emphasized the enormous release of energy concomitant with the near surface intrusion of water bearing magmas and its role in breccia development and since the proposals of reynolds 1954 most workers have accepted an involvement of fiuidization processes in the emplacement of the fragmental materials among the more intriguing features of hydrothermal breccias is the occurrence of rounded clasts particularly in the so called pebble breccias these have generally been attributed to shearing rotation and attrition of originally angular rock fragments during transport in a particle charged gaseous tream see boothroyd 1971 thus in the patch breccia pipe central city colorado bastin and hill 1917 record a correlation between fragment rounding and the juxtaposition of diverse rock types extensive downward e g at leadville colorado emmons et al 1927 or upward e g at tintic utah farmin 1934 movement of clasts in breccia pipes has been well documented in several mining districts in an allied context williams 1936 established a correlation between the degree of rounding of fragments and the extent of their upward translation in pliocene diatremes in nevada

cation diffusion kinetics in aluminosilicate garnets and geological applications the compositional properties of garnet probably preserve the most extensive records of the pressure temperature time p t t history of metamorphic rocks there are a number of cation exchange and discontinuous reactions involving garnet that have been extensively used to decipher the p t conditions or p t paths of the host rocks as these were buried and exhumed e g ganguly and saxena 1987 spear 1993 however as metamorphic garnets commonly show compositional zoning the choice of composition within a zoned garnet to retrieve peak metamorphic conditions requires consideration of its diffusion kinetic properties dasgupta et al 2004 2009 as does the issue of whether the peak condition is at all preserved in the compositional property of a garnet of a given grain size e g spear 1991 ganguly and tirone 1999 tirone and ganguly 2010 diffusion kinetic modeling of the major element compositional zonings of garnets leads to important constraints on the time scales of metamorphic processes such as heating and cooling rates e g florence and spear 1993 ganguly et al 2000 faryad and chakraborty 2005 augue and baxter 2007 from which one may infer the burial and exhumation rates respectively e g ganguly et al 2000 faryad and chakraborty 2005 and time scales of deformation camacho et al 2009 in addition the presence of garnet in the source region of a basaltic magma imparts a characteristic signature often referred to as the garnet signature to its rare earth element ree pattern in addition to providing an important constraint on the depth of the source region of a basaltic magma since garnet is stable below 50 km depth in the earth s interior e g saxena and eriksson 1983 the ree pattern of basaltic magma with garnet signature is often used to infer

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

models of garnet differential geochronology abstract rayleigh distillation models are developed to describe theoretical growth zoning of lu hf rb sr sm and nd in typical garnet crystals from metapelites and metabasites effects of diffusion limited transport within the matrix and intracrystalline diffusion are also considered qualitatively theoretical zoning profiles show strong depletions of lu in garnet rims compared to cores but virtually invariant hf rb sr sm and nd profiles generally consistent with natural profiles for lu and hf and previously published models theoretical isochron diagrams for lu hf exhibit distinctive arcuate distributions and high mswds consistent both with himalayan data and with expectations that garnet growth durations exceed chronologic resolution by as much as an order of magnitude predicted isochron diagrams for sm nd and rb sr exhibit vertical arrays for garnet and high mswds that are generally lower than for lu hf in metapelites inherent chronologic resolution for bulk separates is best for lu hf in metapelites and rb sr but analytical considerations favor rb sr or sm nd for chronologic zoning studies diffusion limited transport in the rock matrix strongly influences zoning profiles but does not change the main trends on isochron diagrams intracrystalline diffusion will initially rotate lu hf isochrons to steeper slopes giving older apparent ages the natural himalayan data indicate growth of garnet in one rock from the greater himalayan sequence at 34 ma consistent with previously measured monazite ages from the same rock data from another himalayan rock suggest polymetamorphism that includes a paleozoic component

rare earth diffusion kinetics in garnet experimental studies and applications abstract we determined the diffusion coefficient of sm in almandine garnet as function of temperature at 1 bar and fo 2 corresponding to that of wustite iron buffer and to a limited extent that of a few other selected rare earth elements in almandine and pyrope garnets both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields the experimental diffusion profiles were analyzed by secondary ion mass spectrometry and in addition by rutherford back scattering spectroscopy for two samples transmission electron microscopic study of an almandine crystal that was diffusion annealed did not reveal any near surface fast diffusion path using reasonable approximations and theoretical analysis of vacancy diffusion the experimental data were used to develop an expression of rare earth element ree diffusion coefficient in garnet as a function of temperature pressure fo 2 ionic radius and matrix composition calculation of the closure temperature for the sm nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently modeling of the ree evolution in melt and residual garnet suggests that for dry melting condition the ree pattern in the melt should commonly conform closely to that expected for equilibrium melting however for much lower solidus temperatures that would prevail in the presence of a h 2 o co 2 fluid the concentration of light ree in the melt could be significantly lower than that under equilibrium melting condition a reported core and rim differences in the ree content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the ree zoning was a consequence of entrapment in a magma derived from an external source for 32 000 yr before the eruption

decadal vegetation succession from modis reveals the spatio temporal evolution of post seismic landsliding after the 2008 wenchuan earthquake abstract strong earthquakes especially in continental mountainous areas can trigger extensive mass wasting producing large amounts of debris that accumulates along the hillslopes or in drainage channels the coseismic deposits and disturbed slopes are prone to be reactivated or remobilized by heavy rainfalls in the subsequent years after the earthquake predicting how long post seismic landslide activity will return to the pre earthquake level is a key to risk assessment and management however this is still poorly understood and lacks quantitative prediction approach the 2008 wenchuan earthquake triggered an unprecedented number of landslides creating an extraordinary natural laboratory to investigate the evolution of post seismic landslides and their impacts on environment using the vegetation recovery rate as an indicator we present the observational evidence of the post seismic landslide evolution based on modis ndvi time series between 2000 and 2018 using a simple vegetation recovery rate vrr function we quantify the rate of vegetation regrowth in the wenchuan earthquake affected area and discuss the decaying trend of post seismic landslide activities our findings show that 83 of the co seismic landslides become inactive within a decade the ndvi trend suggests that landslide activity may return to the pre earthquake level within 18 years the sensitivity of vegetation regrowth to post seismic landsliding thus offers a great potential to improve our understanding of the spatio temporal evolution of the post seismic landslide activities

crystal growth and the formation of chemical zoning in garnets a crystal growth model is developed which generalizes the rayleigh fractionation process the new growth model allows some insight into the interpretation of nonequilibrium behavior of minerals primarily the chemical zoning profiles exhibited by metamorphic minerals a nonlinear equilibrium term for exchange of constituents between a growing mineral and a reservoir is initially incorporated into the usual isothermal fractionation model criteria are established to decide when a simple distribution term is sufficient to describe the growth and exchange process the model is then extended to allow for temperature changes during a cooling or heating event finally an exact solution is obtained for the temperature dependent case incorporating a time dependent growth rate the growth models are successfully used to obtain growth rates of 0 01 to 0 09 cm million year and describe the magnesium and iron zoning profiles of garnets from phillipston massachusetts the generalized model confirms the development of zoning during the retrograde growth of garnet in the late stages of the acadian orogeny

trace element distributions in silicates during prograde metamorphic reactions implications for monazite formation to assess the petrogenetic relationship between monazite and major silicates during prograde metamorphism ree were measured across coexisting zoned silicates in garnet through kyanite grade pelitic schists from the great smoky mountains western blue ridge terrane southern appalachians to establish ree concentrations and distributions before and after the monazite in isograd and to identify the role major silicates play in the formation of monazite results indicate significant scavenging of light rare earth elements lree from silicates during the monazite in isograd reaction however the absolute concentration of lree hosted in the silicates was insufficient to produce monazite in the quantity observed in these schists monazite must have formed mainly from either the dissolution of allanite or some other source of concentrated lree possibly adsorbed onto grain boundaries even though direct evidence for allanite is lacking in a majority of the samples laser ablation icp ms analyses and theoretical thermodynamic calculations show that monazite may have formed as a result of contributions from both allanite and major silicates allanite breakdown initially formed monazite and monazite production drew lree liberated from allanite major silicates and possibly from crystal boundaries in many rocks the reaction was further promoted by the staurolite in reaction allowing for rapid isogradic monazite growth

lu hf geochronology and trace element distribution in garnet implications for uplift and exhumation of ultra high pressure granulites in the sudetes sw poland combining lu hf garnet geochronology with in situ trace element analyses in garnet allowed its to gain new insight into the metamorphic evolution of uhp uht rocks in the stary gieraltow region in the polish sudetes prograde garnet growth recorded by rayleigh type heavy ree hree zoning in the felsic granulites indicates that the obtained 386 6 4 9 ma lu hf age represents the time of garnet crystallization on a prograde uhp metamorphic path the surrounding rocks were metamorphosed at the same time as indicated by 381 2 6 7 ma sm nd garnet age obtained for the mid crustal metapelites the second metamorphic episode which affected most of the lower crust in the orlica snieznik massif osm occurred at ca 340 ma as determined by u pb zircon and sm nd garnet dating of granulites in this and previous studies is interpreted as a high temperature event which took place on a retrograde path trace element distribution in garnets from the layered granulites showed significant differences in distribution of medium and hree in garnets from mafic and felsic protoliths over the course of the metamorphic evolution this had strong impact on the isotopic dating results and led to decoupling of the sm nd and lu hf clocks which recorded timing of the two different metamorphic episodes separated by as much as 40 ma moreover the preservation of the hree growth zonation profile in garnets from the felsic granulites whose minimum metamorphic temperature was established at 900 degrees c implies that the lu hf system under relatively dry conditions does not undergo significant diffusional re equilibration even at such extreme temperatures and therefore it sill provides the age of prograde garnet growth under hydrous conditions at least some resetting will take place as documented by the partially relaxed hree zonation profile in the amphibolitised mafic granulite which yielded a 10 ma younger age the hree distribution study appeared to be a particularly valuable and essential tool which allowed us to distinguish garnet growth from post growth complexities and hence provide improved age interpretation medium ree on the other hand did not show any obvious correlation with the isotopic signature of garnet two distinct metamorphic episodes recorded in the stary gieraltow region show that buoyancy driven uplift of uhp rocks can be arrested at the base of a continental crust if not supported by any additional force in our case study the uhp rocks would have never reached the surface if their uplift had not been resumed after a long pause under a different tectonic regime the multistage discontinuous uplift revealed by the uhp rocks of the osm provides a new scenario for the exhumation of continental crust from mantle depths distinct from the fast track exhumation histories recognized in uhp terranes elsewhere c 2006 elsevier b v all rights reserved

high resolution la icp ms trace element mapping of igneous minerals in search of magma histories we report experiments on optimisation of la icp ms mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals the experimental design was refined with maps on clinopyroxene and amphibole macrocrysts mainly antecrysts from a porphyritic lamprophyre in ne spain as well as on a high precision metal wire grid in terms of spatial resolution we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0 4 and 0 7 mu m of material depending on ablation parameters maps were produced with square laser beam spots of 12 and 24 mu m it was found that complexities can be resolved in the sample even though they are smaller than the beam diameter e g 7 10 mu m discontinuities using 12 mu m laser beam resolution in x and y was found to be identical probably reflecting the fast washout of the two volume ablation cell and the short total dwell time of the analyte menu selected due to the excellent stage reproducibility and the limited ablation depth it is feasible to re ablate the identical map area many times employing different instrument parameters or analyte menus on the magmatic crystals la icp ms maps define very sharp compositional zoning in trace elements highlighting complex crystallisation histories where normal magmatic fractionation is not the only process events of mafic recharge are easily recognised as zones enriched in compatible metals such as cr ni or sc further trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data these include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones therefore la icp ms mapping opens a new window of opportunity for analysis of magmatic histories the wide combination of instrumental parameters such as laser beam size scan speed and repetition rate make it possible to carry out experiments at different levels of detail we recommend a two step approach to mapping the initial step involves rapid maps to gain an overview of potential complexities in the sample this enhances representativeness of the analysed materials as a large number of crystals and trace elements can be tested in little time subsequently detailed maps can be carried out on areas of interest an additional functionality is to create 1d profiles from 2d maps the potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond c 2015 elsevier b v all rights reserved