crystallographic fabrics of omphacite rutile and quartz in vendee eclogites armorican massif france consequences for deformation mechanisms and regimes abstract this study aims at further understanding of the mechanisms how lattice preferred orientations lpo develop during deformation in the main eclogite minerals microstructures and textures of deformed eclogites from the les essarts complex western france were investigated using optical microscopy and electron backscatter diffraction ebsd in the scanning electron microscope microfabric analyses of eclogite facies minerals are used to identify their deformation mechanisms which define the rheology at high pressure metamorphic conditions mechanisms of intracrystalline deformation by dislocation movement dislocation creep result usually in a non linear flow law typically power law while diffusive processes diffusion creep correspond to linear flow laws general microstructural observations may suggest intracrystalline deformation dislocation creep of omphacite the omphacite lpo vary between s and l type and correlate with oblate or prolate grain shape fabrics respectively until now these lpo types have not been understood by plasticity models based on dislocation glide on the known slip systems in clinopyroxene an alternative interpretation is given in terms of anisotropic growth and dissolution with grain boundary diffusion as the rate controlling process there are further indications suggesting diffusion creep with concomitant anisotropic growth and dissolution as a main deformation mechanism in omphacite in omphacite around a hollow garnet crystallographic and shape fabrics align with the c 001 axes parallel to the grain elongations defining the mineral lineation which rotates locally with the inferred flow direction in this part the grain sizes of omphacite and rutile are larger than in the surrounding matrix the geometry of both the shape and crystallographic fabrics is interpreted to represent the local stress regime directions and ratios of the principal stresses the lpo of rutile duplicate the lpo of omphacite and a similar distinction between s and l type was used rutile deformation mechanisms probably involve dislocation creep as well as diffusion creep quartz mainly occurs as an interstitial phase with weak lpo patterns interpreted as random no representative obliquity of the lpo in omphacite nor rutile with respect to foliation and lineation was observed to be used as potential shear sense criteria however the rutile lpo was slightly rotated relative to the omphacite lpo consistently in most samples the results suggest that diffusion processes are strongly involved in the deformation of eclogites a linear flow law should be taken into account in tectonic models where eclogites are incorporated

paragonite hornblende assemblages and their petrological significance an example from the austroalpine schneeberg complex southern tyrol italy paragonite bearing amphibolites occur interbedded with a garbenschist micaschist sequence in the austroalpine schneeberg complex southern tyrol the mineral assemblage mainly comprises paragonite mg hornblende tschermakite quartz plagioclase biotite ankerite ti phase garnet muscovite equilibrium p t conditions for this assemblage are 550 600 c and 8 10 kbar estimated from garnet amphibole plagioclase ilmenite rutile and si contents of phengitic muscovites in the vicinity of amphibole paragonite is replaced by symplectitic chlorite plagioclase margarite biotite assemblages muscovite in the vicinity of amphibole reacts to form plagioclase biotite margarite symplectites the reaction of white mica hornblende is the result of decompression during uplift of the schneeberg complex the breakdown of paragonite hornblende is a water consuming reaction and therefore it is controlled by the availability of fluid on the retrogressive p t path paragonite hornblende is a high temperature equivalent of the common blueschist assemblage paragonite glaucophane in ca bearing systems and represents restricted p t conditions just below omphacite stability in a mafic bulk system while paragonite glaucophane breakdown to chlorite albite marks the blueschist greenschist transition the paragonite hornblende breakdown observed in schneeberg complex rocks is indicative of a transition from epidote amphibolite facies to greenschist facies conditions at a flatter p t gradient of the metamorphic path compared to subduction zone environments ar ar dating of paragonite yields an age of 84 5 1 ma corroborating an eoalpine high pressure metamorphic event within the austroalpine unit west of the tauern window eclogites that occur in the otztal crystalline basement south of the schneeberg complex are thought to be associated with this eoalpine metamorphic event

carbonado revisited insights from neutron diffraction high resolution orientation mapping and numerical simulations abstract one of the most controversial diamond types is carbonado as its origin and geological history are still under debate here we investigate selected carbonado samples using neutron diffraction and high resolution orientation mapping in combination with numerical simulations neutron diffraction analyses show that fine grained carbonado samples exhibit a distinct lack of crystallographic preferred orientation quantitative crystallographic orientation analyses performed on transmission electron microscope tem sections reveal that the 2 10 m grains exhibit locally significant internal deformation such features are consistent with crystal plastic deformation of a grain aggregate that initially formed by rapid nucleation characterized by a high number of nucleation sites and no crystallographic preferred orientation crystal plastic deformation resulted in high stress heterogeneities close to grain boundaries even at low bulk strains inducing a high degree of lattice distortion without significant grain size reduction and the development of a crystallographic preferred orientation observed differences in the character of the grain boundary network and internal deformation structures can be explained by significant post deformation annealing occurring to variable degrees in the carbonado samples differences in intensity of crystal bending and subgrain boundary sharpness can be explained by dislocation annihilation and rearrangement respectively during annealing grain energy is reduced resulting in distinct changes to the grain boundary geometry grain scale numerical modelling shows that anisotropic grain growth where grain boundary energy is determined by the orientation of a boundary segment relative to the crystallographic orientation of adjacent grains results in straight boundary segments with abrupt changes in orientation even if the boundary is occurring between two triple junctions forming a zigzag pattern in addition in diamond anisotropic grain growth results in triple junctions that rarely show 120 angles our results support the interpretation that carbonados may have undergone at least 2 or 3 stages of development with rapid nucleation crystal plastic deformation to low strains and variable degrees of post deformation annealing such a history is commonly observed in earth s crustal or mantle rocks hence for carbonados it is not necessary to invoke an extraordinary and or extraterrestrial origin and history the combination of methods utilized here promises to help advance our understanding of diamond and diamond aggregates in the future

prevalence of growth twins among anhedral plagioclase microlites crystal textures of volcanic rocks record the processes involved in magma storage and eruptive ascent syn eruptive crystallization in which groundmass crystals form and grow according to environmental factors such as thermodynamic undercooling strongly influences the texture of erupted magma this stage is difficult to isolate for study in natural rocks but well suited for laboratory experiments because the chemical compositions and crystallization timescales of eruptive processes can be emulated this study examines the incipient stages of plagioclase crystallization in hydrous rhyodacite magma undergoing decompression driven degassing experimental samples in which crystal growth at both near equilibrium and far from equilibrium conditions were examined using electron backscatter diffraction ebsd analysis to ascertain crystallographic lattice orientations of individual crystals the crystal orientation investigation affirms a common assumption invoked in textural studies of crystal number density contiguous crystals with parallel faces are crystallographically continuous whereas contiguous crystals with non parallel faces have unrelated crystal lattice orientations and as such represent separate crystals in the highly undercooled sample twinning is identified in 87 of the crystals examined in the near equilibrium sample 38 of the crystals are twinned we find that the observed twinning is unlikely to be the result of deformation transformation or synneusis but rather a result of growth defects introduced during the incipient stages of crystallization we suggest internal structural defects twins control macroscopic morphological defects embayments swallowtails and melt inclusions as a result of the high energy of the twin plane boundary formation of twins during the incipient stages of plagioclase crystallization is the single most important factor contributing to anhedral morphologies of feldspar microlites growing during magma decompression and plays a role in the development of some plagioclase hosted melt inclusions

misorientation analysis and the formation and orientation of subgrain and grain boundaries in contrast to the behaviour of individual grains both inter and intra granular boundaries within rocks have received much less attention however many geological processes particularly during deformation e g yielding dislocation creep recrystallisation superplasticity and various fracture mechanisms and petrophysical properties depend to some extent on the nature of boundaries present in a rock in this contribution we consider the role of intergranular and intragranular crystal boundaries a precise characterisation of such boundaries depends on defining the crystallographic and dimensional orientations of the boundary and the misorientation between the adjacent regions i e grains subgrains etc separated by the boundary although several theoretical descriptions of boundary configuration are available practical precision is lacking and approximations are necessary we describe two specific approximations for boundary formation and orientation obtained using the sem electron channelling technique the first is a geometrical interpretation of electron channelling patterns ecp in terms of the likely formation and orientation of the intervening boundary the second considers the misorientation between adjacent regions across a boundary this involves a model which assumes a simple geometrical relationship between crystal slip systems responsible for the rotation and misorientation between adjacent regions and the formation and orientation of the resulting boundary these approximations are capable of a identifying trends in the dispersion of crystallographic directions during deformation b identifying active slip systems c calculating the relative schmid factors for each crystal slip system and therefore the most likely system to be activated d modelling synthetic misorientations and predicting the crystal slip systems and boundary configurations to be expected and e comparing real data with synthetic models our analyses are illustrated via natural examples of dynamic recrystallisation in quartzite and a theoretical simulation of the behaviour of an individual quartz grain during deformation

aligned olivine in the springwater pallasite the mechanism by which olivine grains became embedded within iron nickel alloy in pallasite meteorites continues to be a matter of scientific debate geochemical and textural observations have failed to fully elucidate the origin and history of the olivine crystals however little research attention has been devoted to their crystallographic orientations within the metal matrix using electron backscatter diffraction we have collected crystallographic orientation data for 296 crystals within 65 cm2 sample surface from springwater though no global crystallographic preferred orientation exists very low misorientations are observed among 100 axes of olivine crystals within specific texturally defined domains combined with a thorough characterization of large scale springwater textures the definitively nonrandom spatial distribution of olivine orientations provides clues regarding the nature of the olivine s initial formation environment as well as the sequence of events subsequent to metal incorporation

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

conditioning factors in flooding of karstic poljes the case of the zafarraya polje south spain abstract the zafarraya polje undergoes periodical flooding of which the last episode 1996 1997 was analysed in detail on this paper on the basis of the retention curves of the two lakes that formed in the northwestern and southwestern sectors we calculated the total infiltration capacity of the polje to have a maximum value of 3 3 5 m3 s and so we infer that when the flow of the arroyo de la madre exceeds this figure there will be a risk of flooding in the polje we also propose a model for the 1996 flood that can be extended to other similar occurrences in this and other poljes where we can establish the role played by groundwater and surface water during this flood in response to the heavy precipitation the flow of the arroyo de la madre rose abruptly exceeding the infiltration capacity of the main swallow holes on the polje causing first the northern lake and then the southern lake to form with only surface water supply the water table of the karst aquifer rose sharply reaching a situation of equilibrium between the level in the lakes and the water table in this sector of the karst aquifer that prevented infiltration through the swallow holes in the case of the southern lake there were even cases of swallow holes that began to operate as estavelles during this phase of maximum flooding one single lake was present which was divided into two once more when the water table of the karst aquifer in the polje sector began to fall and surface supply also began to decrease

garnet plasticity in the lower continental crust implications for deformation mechanisms based on microstructures and sem electron channeling pattern analysis abstract elongated garnets which preserved deformational microstructures boudinage pinch and swell structures occur in granulite facies quartzites in the highland complex of sri lanka in spite of these microstructures and in contrast with previous reports on garnet plasticity there are no or only few signs of intracrystalline deformation like subgrains or lattice distortion this can be explained by annealing and slow static cooling from high temperatures sem electron channeling pattern analysis reveals that the garnets have a significant crystallographic preferred orientation aspect ratio grain size analysis shows that the deformation mechanism is grain size sensitive these features indicate a diffusion assisted dislocation glide mechanism with dominant 1 2 110 slip system a comparison of the deformation behavior between garnet quartz and feldspar shows that differences in flow strength are low under the high grade conditions 850 50 c garnet is still the phase with the highest flow strength but dry quartz is slightly stronger than feldspar

an overgrowth model to explain multiple dispersed high mn regions in the cores of garnet porphyroblasts the central portions of garnet porphyroblasts from harpswell neck maine exhibit small discrete regions of high mn content dispersed in three dimensions orientation contrast imaging oci and quantitative crystallographic orientation measurements from electron backscatter diffraction ebsd patterns show that most garnet porphyroblasts contain no variations in crystallographic orientation it is difficult to reconcile these data with a model in which each high mn region represents a discrete garnet nucleus an alternative hypothesis invokes a model of garnet growth in which precursor phases rich in mn are overgrown and their mn is incorporated locally into the garnet structure although this model requires length scales for equilibration of mn during the early stages of garnet growth that are shorter than any previously documented that inference is consistent with the very low temperatures of garnet nucleation in these rocks and with compositional evidence for progressively larger scales of equilibrium as reaction progressed very short length scales for equilibration of mn identified in this study for the lowest grade portion of the history of the rocks call into question the common assumption of rock wide equilibrium for mn during garnet growth at low temperature the absence of rock wide equilibrium for mn at low grade has potential negative implications for all common interpretive methods based in phase equilibria including thermobarometric studies and thermodynamic analysis of the origin and meaning of zoning in low grade garnet

development of garnet porphyroblasts by multiple nucleation coalescence and boundary misorientation driven rotations two types of garnet porphyroblast occur in the schneeberg complex of the italian alps type 1 porphyroblasts form ellipsoidal pods with a centre consisting of unstrained quartz decussate mica and small garnet grains and a margin containing large garnet grains orientation contrast imaging using the scanning electron microscope shows that the larger marginal garnet grains comprise a number of orientation subdomains individual garnet grains without subdomains are small 50 m faceted and idioblastic and have simple zoning profiles with ca rich cores and ca poor rims subdomains of larger garnet grains are similar in size to the individual small garnet grains type 2 porphyroblasts comprise only ellipsoidal garnet with small subdomains in the centre and larger subdomains at the margin each subdomain has its own ca high ca dropping towards subdomain boundaries garnet grains with or without subdomains all have the same ca poor composition at rims in contact with other minerals the compositional zonation patterns are best explained by simultaneous multiple nucleation followed by growth and amalgamation of individual garnet grains the range of individual garnet and garnet subdomain sizes can be explained by a faster growth rate at the porphyroblast margin than in the centre the difference between type 1 and type 2 porphyroblasts is probably related to the growth rate differential across the porphyroblast electron backscatter diffraction shows that small individual garnet grains are randomly oriented large marginal garnet grains and subdomain bearing garnet grains have a strong preferred orientation clustering around a single garnet orientation misorientations across subdomain boundaries are small and misorientation axes are randomly oriented with respect to crystallographic orientations the only explanation that fits the observational data is that individual garnet grains rotated towards coincident orientations once they came into contact with each other this process was driven by the reduction of subdomain boundary energy associated with misorientation loss rotation of garnet grains was accommodated by diffusion in the subdomain boundary and diffusional creep and rigid body rotation of other minerals quartz and mica around the garnet an analytical model in which the kinetics of garnet rotation are controlled by the rheology of surrounding quartz suggests that at the conditions of metamorphism the rotation required to give a strong preferred orientation can occur on a similar time scale to that of porphyroblast growth

the origin of faceted garnets in sandstones dissolution or overgrowth faceted garnets from a wide range of geological ages environments and locations have been studied in polished grain mounts by a combination of backscattered electron microscopy and elemental mapping using energy dispersive x ray analysis in all cases the areas apparently showing positive relief on the faceted garnet surfaces are compositionally identical to the adjacent grain cores despite a wide variation in detrital garnet compositions in one case zoning within the grain core can be traced into the faceted areas on the grain surface thus faceted areas must be considered to form part of the original detrital grains together with previously published studies on experimental garnet etching thermodynamic conditions for garnet growth textural relationships between faceted garnets and authigenic and detrital phases and distribution of faceted garnets in the subsurface this paper provides conclusive proof that faceted garnet surfaces form as a result of dissolution not overgrowth

cataclastic deformation of garnet a record of synseismic loading and postseismic creep abstract microstructural evidence for episodic deformation of the uppermost plastosphere related to failure of the schizosphere in major seismic events has been previously reported from the sesia zone western alps with inferred extraordinarily high stresses and strain rates for the early stages of creep during stress relaxation at temperatures of about 300 350 c in some of these rocks crystals of the high strength mineral garnet embedded in a quartz matrix are intensely fragmented detailed optical electron microprobe and scanning electron microscopic study combined with electron backscatter diffraction techniques suggests that fragmentation of garnet took place quasi instantaneously at very high peak stresses subsequent deformation during stress relaxation caused displacement of the garnet fragments by frictional sliding controlled by dislocation creep in the surrounding quartz matrix in a final stage after restoration of a near lithostatic pore fluid pressure the garnet fragments were pulled apart and the opening cracks were filled by quartz and feldspar precipitated from the pore fluid this record appears to be consistent with the proposed model of synseismic loading and postseismic creep and the related pore pressure changes

the significance of intergranular diffusion to the mechanisms and kinetics of porphyroblast crystallization the spatial disposition compositional zoning profiles and size distributions of garnet crystals in 11 specimens of pelitic schist from the picuris range of new mexico usa demonstrate that the kinetics of intergranular diffusion controlled the nucleation and growth mechanisms of porphyroblasts in these rocks an ordered disposition of garnet centers and a significant correlation between crystal radius and near neighbor distances manifest suppressed nucleation of new crystals in diffusionally depleted zones surrounding pre existing crystals compositional zoning profiles require diffusionally controlled growth the rate of which increases exponentially as temperature increases with time an acceleration factor for growth rate can be estimated from a comparison of compositional profiles for crystals of different sizes in each specimen crystal size distributions are interpreted as the result of nucleation rates that accelerate exponentially with increasing temperature early in the crystallization process but decline in the later stages because of suppression effects in the vicinity of earlier formed nuclei simulations of porphyroblast crystallization based upon thermally accelerated diffusionally influenced nucleation kinetics and diffusionally controlled growth kinetics quantitatively replicate textural relations in the rocks the simulations employ only two variable parameters which are evaluated by fitting of crystal size distributions both have physical significance the first is an acceleration factor for nucleation with a magnitude reflecting the prograde increase during the nucleation interval of the chemical affinity for the reaction in undepleted regions of the rock the second is a measure of the relative sizes of the porphyroblast and the diffusionally depleted zone surrounding it crystal size distributions for the picuris range garnets correspond very closely to those in the literature from a variety of other localities for garnet and other minerals the same kinetic model accounts quantitatively for crystal size distributions of porphyroblastic garnet phlogopite sphene and pyroxene in rocks from both regional and contact metamorphic occurrences these commonalities indicate that intergranular diffusion may be the dominant kinetic factor in the crystallization of porphyroblasts in a wide variety of metamorphic environments

albite crystallographic preferred orientation and grain misorientation distribution in a low grade mylonite implications for granular flow abstract crystallographic orientation data from pure albite domains in a low grade sheared metagabbro from the combin zone of the western italian alps were measured by electron backscatter diffraction crystallographic preferred orientations cpos in four high strain domains are non random and have a triclinic symmetry the clusters of 100 010 and 001 show an angular relationship that corresponds to that of the albite crystal lattice however the orientations of axis clusters to the kinematic axes vary from domain to domain cpos from a low strain domain also show clustered axes with triclinic symmetry but with more intense clustering than those in the high strain domains grain misorientation distributions are presented both for the low strain domain and one of the high strain domains in the high strain domain the distribution of misorientation angles between neighbouring grains displays a peak at about 70 the equivalent distribution in the low strain domain has a peak at 30 for both domains the misorientation axis distributions between neighbouring and non neighbouring grains are random except for some of axes with 160 180 misorientation that exhibit a slight concentration around 010 the diversity of cpos among the domains suggests that these cpos could not be produced by dislocation creep they are likely to have been inherited from plagioclase parents as a result of host control on the nucleation of the new albite grains these cpos do not contain any direct information about the deformation kinematics we interpret that deformation of these domains occurred by granular flow crystallographic axis dispersion due to grain boundary sliding gbs caused weakening of cpos modification of misorientation angle distributions and randomisation of misorientation axis distributions the fact that a cpo can survive gbs even after a high strain indicates that cpo is not always a sensitive indicator of deformation mechanisms misorientation distribution may provide a complementary and possibly a more sensitive indicator of deformation mechanisms

plastic deformation and recrystallization of garnet a mechanism to facilitate diffusion creep elongate and deformed garnets from glenelg nw scotland occur within a thin shear zone transecting an eclogite body that has undergone partial retrogression to amphibolite facies at circa 700 c optical microscopy back scattered electron imaging electron probe microanalysis and electron back scatter diffraction reveal garnet sub structures that are developed as a function of strain subgrains with low angle misorientation boundaries occur at low strain and garnet orientations are dispersed around rational crystallographic axes across these boundaries towards high strain areas boundary misorientations increase and there is a loss of crystallographic control on misorientations which tend towards random in high strain areas a polygonal garnet microstructure is developed the garnet orientations are randomly dispersed around the original single crystal orientation some garnet grains are elongate and ca rich garnet occurs on the faces of elongate grains oriented normal to the foliation commonly the garnet grains are admixed with matrix minerals and where in contact with other phases garnet is well faceted we suggest that individual garnet porphyroclasts record an evolution from low strain conditions where dislocation creep and recovery accommodated deformation through increasing strain where dynamic recrystallization occurred by subgrain rotation to highest strains where recrystallized grains were able to deform by diffusion creep assisted grain boundary sliding with associated rotations

kinetics of diffusion controlled mineral growth in the christmas mountains texas contact aureole chert nodules in limestone in the aureole of the christmas mountains gabbro are rimmed by wollastonite in the interval 102 25 m from the intrusive contact and by tilleyite or spurrite and wollastonite within 25 m of gabbro wollastonite rims thicken from 4 5 mm at 102 m to 7 mm at 80 m to 30 mm at 49 m and diminish in thickness from 79 to 53 mm over the interval 13 2 m from the gabbro wollastonite has two textural components polygonal matrix wollastonite grains coarsen from 0 011 mm at 102 m to 0 053 mm at 46 m to 0 2 0 3 mm within 20 m of the contact whereas scattered wollastonite porphyroblasts appear at 30 m and coarsen to impingement with a diameter of 1 07 mm at 12 m kinetic models for normal grain growth and for layer thickening set a function of the square of the grain diameter or layer thickness equal to the product of a material constant and a temperature time integral that includes the arrhenius function for the diffusion coefficient the time index for non isothermal diffusion controlled mineral growth is the temperature time integral numerically evaluated along t t curves for the thermal history of the contact aureole the thermal history of the christmas mountains aureole is obtained using a numerical model for a cylindrical intrusion radius 823 m that matches maximum temperatures in the contact aureole of 600 940 1000 and 1030 c at 115 23 13 and 0 m by convection for 700 yr followed by crystallization and cooling the log of the t t integral varies linearly with distance from the gabbro with a slope proportional to activation energy and an intercept proportional to the material constant a plot of the log of the square of the grain diameter of matrix wollastonite against distance from the gabbro is linear and the normal grain growth model yields the following arrhenius function for the diffusion of oxygen in wollastonite grain boundaries d gb o 2 9 333 x 10 4 m s exp 185 rt kj mole where is grain boundary width the fixed ratio of tilleyite to wollastonite rim thickness on nodules from the inner aureole yields a molar ratio of tilleyite to wollastonite in c t w q structures of 1t 24w and requires consumption of calcite and quartz in the ratio 29c 26q truncation of fully coarsened impingement wollastonite by columnar tilleyite implies that the tilleyite layer grew at expense of wollastonite and that wollastonite coarsened at temperatures greater than 940 c solution of a system of mass balance conservation and flux ratio equations describing diffusion controlled growth of a c t w q nodule matches the net mass transfer and observed textural features for onsager diffusion coefficient ratios of l cao l sio 2 42 and l cao l co 2 grain diameter of impingement wollastonite varies linearly with the radius of spherical wollastonite nodules that ceased growth on consumption of the quartz core implying that coarsening coincided in time with wollastonite rim growth grain boundary cross section of wollastonite decreased by two orders of magnitude during layer growth coupling of the kinetics of coarsening of impingement wollastonite with diffusion controlled growth of the wollastonite layer yields the following arrhenius function for the onsager diffusion coefficient for diffusion of cao in wollastonite grain boundaries l gb cao 1 731 x 10 4 rt mole 2 j s exp 220 rt kj mole the pre exponential term for grain boundary diffusion of sio 2 in wollastonite is obtained from the relation l cao l sio 2 42 values of the diffusion coefficients derived from analysis of grain coarsening and layer growth in the christmas mountains contact aureole satisfy the diffusion compensation relations for grain boundary diffusion of oxygen and cations in oxides based on laboratory experiment the value of the coefficient for diffusion of cao in tilleyite grain boundaries at 1000 c based on a time integrated aver age temperature is essentially identical to that obtained for wollastonite using the full non isothermal analysis suggesting that the values of onsager coefficients for grain boundary diffusion of a given cation are not strongly dependent on identity of solid phase wollastonite rims grow to 82 to 95 of their ultimate thickness during the period of heating that coincides with magmatic convection because growth of the wollastonite and tilleyite layers does not begin until temperature rises to 600 and 940 c respectively rim growth is not synchronous across the aureole

the strain dependent spatial evolution of garnet in a high pressure ductile shear zone from the western gneiss region norway a synchrotron x ray microtomography study reaction and deformation microfabrics provide key information to understand the thermodynamic and kinetic controls of tectono metamorphic processes however they are usually analysed in two dimensions omitting important information regarding the third spatial dimension we applied synchrotron based x ray microtomography to document the evolution of a pristine olivine gabbro into a deformed omphacite garnet eclogite in four dimensions where the 4th dimension is represented by the degree of strain in the investigated samples which cover a strain gradient into a shear zone from the western gneiss region norway we focused on the spatial transformation of garnet coronas into elongated garnet clusters with increasing strain the microtomographic data allowed quantification of garnet volume shape and spatial arrangement evolution with increasing strain the microtomographic observations were combined with light microscope and backscatter electron images as well as electron microprobe empa and electron backscatter diffraction ebsd analysis to correlate mineral composition and orientation data with the x ray absorption signal of the same mineral grains with increasing deformation the garnet volume almost triples in the low strain domain garnet grains form a well interconnected large garnet aggregate that develops throughout the entire sample we also observed that garnet coronas in the gabbros never completely encapsulate olivine grains in the most highly deformed eclogites the oblate shapes of garnet clusters reflect a deformational origin of the microfabrics we interpret the aligned garnet aggregates to direct synkinematic fluid flow and consequently influence the transport of dissolved chemical components ebsd analyses reveal that garnet shows a near random crystal preferred orientation that testifies no evidence for crystal plasticity there is however evidence for minor fracturing neo nucleation and overgrowth microprobe chemical analysis revealed that garnet compositions progressively equilibrate to eclogite facies becoming more almandine rich we interpret these observations as pointing to a mechanical disintegration of the garnet coronas during strain localization and their rearrangement into individual garnet clusters through a combination of garnet coalescence and overgrowth while the rock was deforming

crystal plasticity of natural garnet new microstructural evidence scanning electron microscope sem orientation contrast images of mantle nodules show that garnets contain cellular domains of different crystallographic orientation electron backscatter diffraction shows small crystallographic mismatches

some garnet microstructures an illustration of the potential of orientation maps and misorientation analysis in microstructural studies the microstructures of two contrasting garnet grains are mapped using automated electron backscatter diffraction in both cases there is a very strong crystallographic preferred orientation with measurements clustered round a single dominant orientation each garnet grain is divided into domains with similar orientations limited by boundaries with misorientations of 2 or more in both samples most of misorientation angles measured across orientation domain boundaries are significantly lower than those measured between random pairs of orientation domains one sample is a deformed garnet that shows considerable distortion within the domains lines of orientation measurements within domains and across domain boundaries show small circle dispersions around rational crystallographic axes the domain boundaries are likely to be subgrain boundaries formed by dislocation creep and recovery the second sample is a porphyroblast in which the domains have no internal distortion and the orientation domain boundaries have random misorientation axes these boundaries probably formed by coalescence of originally separate garnets we suggest that misorientations across these boundaries were reduced by physical relative rotations driven by boundary energy the data illustrate the potential of orientation maps and misorientation analysis in microstructural studies of any crystalline material

mantle garnets a cracking yarn abstract garnets showing variation in chemical composition occur in the metasomatised peridotitic wallrocks to intrusive pyroxenitic dikes in mantle xenoliths from the matsoku kimberlite pipe they have been examined by scanning electron microscope sem and imaged using both high contrast and electron channelling backscattered electron bse methods the images revealed intricate variation in the backscatter coefficient across garnets the pattern of variation is one of very slightly diffuse brightwhite high lines surrounded by paler diffuse auras grading into darker lower areas away from the bright lines the bright lines are usually irregular in detail and show branching and braiding but in some cases they form regularly spaced parallel to subparallel sets which reflect crystallographic orientation electron and ion microprobe analyses including a highly exhaustive 40 000 data point electron microprobe survey across one garnet have correlated the change in the backscatter coefficient with compositional variation the compositional changes largely involve enrichment in fe and ti and decrease in mg of the garnet forming the bright lines and pale auras and are consistent with those of metasomatic garnets identified by previous work on an extensive suite of matsoku xenoliths the high ti and fe garnet is also enriched in y zr mrees and hrees and is considered to have formed by direct crystallisation from the melt causing metasomatism whilst areas away from the high lines show compositions similar to those of garnets in unmetasomatised rock the bright high lines are interpreted as delineating a pattern of fractures along which the metasomatising melt was able to penetrate the garnet and from this melt new garnet crystallised to heal the fractures and form the high fe ti garnet diffusion of elements outward from these melt filled and subsequently healed fractures into the main body of the garnet produced the more diffuse zonation pattern imaged by bse methods on the sem

hydrological explanation of the flow in karst example of the crnojevica spring abstract this paper deals with various methods of solving the complex problems of the hydrological transformation of rainfall into runoff in karst terrains as an example of a typical karst catchment the crnojevica spring located in deep dinaric karst is used to illustrate explain and solve several hydrological problems in karst the introduction deals with the geographical geological and meteorological factors which conditioned a specific system of surface and underground flows typical for karst terrains the paper also explains some basic activities related to the identification of such a system special attention has been paid to the karst terrain of the cetinje polje and its flooding which occurred in february 1986 this flood initiated numerous intensive investigations which made it possible to define the catchment area of crnojevica spring and the volume of the underground karst reservoir

three dimensional patterns of garnet nucleation and growth three dimensional compositional zoning patterns in garnet zone garnets from harpswell neck maine united states suggest complex patterns of nucleation and growth compositional zoning is often asymmetric and core compositions do not always coincide with the geometric center of the garnet in detail garnet zoning patterns show multiple isolated high mno areas that we interpret as sites of garnet nucleation if it is assumed that garnet growth is close to equilibrium and the mn zoning is not significantly modified by diffusion then the mno contours or isosurfaces can serve as a proxy for patterns of garnet nucleation and growth computer generated three dimensional animations of these patchwork mno zoning patterns reveal that many garnets contain multiple nuclei that grew and coalesced to form a single crystal new nuclei often appeared next to preexisting porphyroblasts and became incorporated into the growing crystal contrary to the widely held idea that garnets grow radially outward from a single nucleus we propose that many of the garnets examined in this study grew by the coalescence of multiple nuclei

water exchange and pressure transfer between conduits and matrix and their influence on hydrodynamics of two karst aquifers with sinking streams summary karst aquifers are heterogeneous media where conduits usually drain water from lower permeability volumes matrix and fractures for more than a century various approaches have used flood recession curves which integrate all hydrodynamic processes in a karst aquifer to infer physical properties of the movement and storage of groundwater these investigations typically only consider flow to the conduits and thus have lacked quantitative observations of how pressure transfer and water exchange between matrix and conduit during flooding could influence recession curves we present analyses of simultaneous discharge and water level time series of two distinctly different karst systems one with low porosity and permeability matrix rocks in southern france and one with high porosity and permeability matrix rocks in north central florida usa we apply simple mathematical models of flood recession using time series representations of recharge storage and discharge processes in the karst aquifer we show that karst spring hydrographs can be interpreted according to pressure transfer between two distinct components of the aquifer conduit and matrix porosity which induce two distinct responses at the spring water exchange between conduits and matrix porosity successively control the flow regime at the spring this exchange is governed by hydraulic head differences between conduits and matrix head gradients within conduits and the contrast of permeability between conduits and matrix these observations have consequences for physical interpretations of recession curves and modeling of karst spring flows particularly for the relative magnitudes of base flow and quick flow from karst springs finally these results suggest that similar analyses of recession curves can be applied to karst aquifers with distinct physical characteristics utilizing well and spring hydrograph data but information must be known about the hydrodynamics and physical properties of the aquifer before the results can be correctly interpreted

the use of electron backscatter diffraction and orientation contrast imaging as tools for sulphide textural studies example from the greens creek deposit alaska the greens creek polymetallic massive sulphide deposit is hosted in a typical polyphase deformed lower greenschist facies orogenic setting the structure of the host rocks is well constrained exhibiting a series of three superimposed ductile deformations followed by two brittle episodes the ore is found both in fold hinges where early formed depositional features are preserved and in fold limbs where primary features are typically strongly modified or obliterated samples from both settings have been investigated using electron backscatter diffraction ebsd coupled with forescatter orientation contrast oc imaging in order to observe the effects of deformation and lower greenschist facies metamorphism on pyrite results suggest that colloform pyrite may preserve information relevant to palaeoenvironment that apparently simple textures are generally more complex and that pyrite can deform plastically by dislocation glide and creep processes at lower temperatures and or strain rates than generally accepted this analysis indicates that ebsd and oc imaging provide powerful tools for observing textural relationships in pyrite that are not shown by more traditional methods they should become routine tools for pyrite texture analysis

isotopic chronometry of zoned garnets growth kinetics and metamorphic histories basic information on the chronological and pressure temperature evolution of regional metamorphic terrains may in principle be derived from metamorphic garnets because of the similarly low diffusivities of sm nd and major cations in this mineral we report here smnd and rbsr isotopic and major element data on prograde garnets from regionally metamorphosed pelites from newfoundland the garnets preserve a prograde major element zonation as well as a sympathetic variation in sm nd ratio smnd data for separated portions of the garnet from core to rim provide both upper limits on the time for garnet growth and demonstrate synchronous growth of different garnet grains on a hand specimen scale the rbsr data on the same garnet fractions are in general agreement with these results but in some cases cannot be interpreted in terms of growth a minimum heating rate of 3k ma 1 is derived by combining the estimates for garnet growth time with the apparent temperature interval over which the garnet grew deduced from the major element zonation this value is similar to the minimum suggested by theoretical models for the thermal evolution of thickened continental crust the growth rate is within the range of 1 3 19 mm ma 1 set respectively by the isotopic data and the likely upper limit for heating rate during regional metamorphism these growth rates appear too slow to be controlled by surface reaction and suggest that other factors such as transport may be rate limiting in this case the limits set on the effective diffusion coefficient for material transport to the growth site 0 4 6 1 10 17 m2 s 1 suggest that grain boundary diffusion is probably the transport mechanism for supply of material to the growing garnet

numerical modelling of porphyroclast and porphyroblast rotation in anisotropic rocks abstract the rotational behaviour of rigid objects in a weaker rock matrix during deformation has been the subject of many field experimental and numerical modelling studies often centred on the question whether objects rotate or not in non coaxial deformation with numerical studies gaining increasing popularity and importance we here provide an overview of the results published so far and provide new simulations originally shape and orientation were investigated while the emphasis shifted to rheology and slip between object and matrix in the nineties of the last century due to improved numerical techniques anisotropic rheology has become the focus of most recent studies indicating that it is a primary factor in the rotation behaviour of objects we present new simulations investigating the role of anisotropy on different scales relative to the object and show how this influences the rotation rate as well as the inclusion patterns in case of syntectonically growing porphyroblasts these simulations show that a variety of factors play a role to determine the rate and sense of rotation of objects the variability of the inclusion patterns that can develop necessitates extreme caution in the kinematic interpretation of these structures when observed in the field

ductility of garnet as an indicator of extremely high temperature deformation discoidal shaped garnets alm63 prp33 grs3 sps1 occur in the foliation plane of lineated quartzofeldspathic mylonites of the morin shear zone located along the eastern boundary of the morin anorthosite complex grenville province quebec the flattened shape of garnets records a component of coaxial strain x y z different from the dominant rotational shear strain x y z in this mylonite tem observations indicate dislocation slip and recovery to be the main mechanism for the deformation of garnet extrapolation of available experimentally determined flow laws to natural strain rates shows an inversion of flow strength between quartz feldspar and garnet garnet much stronger than quartz and feldspar at temperatures below 700 c becomes weaker than quartz and feldspar above 900 c the coaxial ductile strain recorded by the garnets could be produced by a local uncharacterized deformation under extremely high temperature conditions at the roof of the rising anorthositic diapir 1155 ma subsequent lower temperature rotational deformation is related to strike slip movement along the morin shear zone 1020 ma

applications of x ray computed tomography in the geosciences x ray computed tomography ct is a technique that allows non destructive imaging and quantification of internal features of objects it was originally developed as a medical imaging technique but it is now also becoming widely used for the study of materials in engineering and the geosciences x ray ct reveals differences in density and atomic composition and can therefore be used for the study of porosity the relative distribution of contrasting solid phases and the penetration of injected solutions as a non destructive technique it is ideally suited for monitoring of processes such as the movement of solutions and the behaviour of materials under compression because large numbers of parallel two dimensional cross sections can be obtained three dimensional representations of selected features can be created in this book various applications of x ray ct in the geosciences are illustrated by papers covering a wide range of disciplines including petrology soil science petroleum geology geomechanics and sedimentology

microstructure and crystallographic preferred orientation of polycrystalline microgarnet aggregates developed during progressive creep recovery and grain boundary sliding abstract optical microscopy electron probe microanalysis and electron backscatter diffraction methods have been used to examine a broad range of garnet microstructures within a high strain zone that marks the western margin of a major transpression zone in the southern new england appalachians garnet accommodated variable states of finite strain expressed as low strain porphyroclasts type 1 high strain polycrystalline aggregates type 2 and transitional morphologies type 3 that range between these end members type 1 behaved as rigid porphyroclasts and is characterized by four concentric ca growth zones type 2 help define foliation and lineation are characterized by three ca zones and possess a consistent bulk crystallographic preferred orientation of 100 symmetrical to the tectonic fabric type 3 show variable degrees of porphyroclast associated with aggregate where porphyroclasts display complex compositional zoning that corresponds to lattice distortion low angle boundaries and subgrains and aggregate cpo mimics porphyroclast orientation all aggregates accommodated a significant proportion of greenschist facies deformation through grain boundary sliding grain rotation and impingement and pressure solution which lead to a cohesive behavior and overall strain hardening of the aggregates the characteristic cpo could not have been developed in this manner and was the result of an older phase of partitioned amphibolite facies dislocation creep recovery including chemical segregation and recrystallization of porphyroclasts this study demonstrates the significance of strain accommodation within garnet and its affect on composition under a range of pt conditions and emphasizes the importance of utilizing ebsd methods with studies that rely upon a sound understanding of garnet

conceptualization and classification of groundwater surface water hydrodynamic interactions in karst watersheds case of the karst watershed of the coulazou river southern france summary over the last two decades groundwater systems and surface water bodies are being more and more considered as a same entity which constitutes a single resource within the hydrologic system understanding groundwater surface water gw sw interactions is necessary to effectively manage the water resources concepts methods of analysis and classifications of these hydrodynamic interactions have thus been developed mostly in case of porous aquifer today gw sw interactions are still often poorly understood in many watersheds particularly in the case of complex aquifers like karst aquifers this study focuses on the influence of groundwater on the genesis and propagation of surface floods in the case of a highly karstified watershed gw sw hydrodynamic interactions are analysed i at a local scale focussing on hydrodynamic interactions between the karst aquifer in the vicinity of the river and the river and ii at a larger scale focussing on hydrodynamic interactions between a karst spring and sinkholes in the riverbed hydrodynamic time series are described using the karst watershed of the coulazou river western montpellier france as a case study results are used to adapt gw sw classifications that are usually devoted to porous media in case of the studied karst aquifer it is shown that the initial groundwater level may be used to forecast the type of hydraulic connection between the river and the saturated zone during flood however initial water level in the karst aquifer does not give any information about the flow direction gaining or losing stream during a flood the latter is found to be also controlled by the limited discharge capacity of karst conduits a conceptual model of karst river interactions during flood is given with concepts that are derived from the analysis of the coulazou watershed but that can be easily applied to most of the karst watersheds

trace element zoning as a record of chemical disequilibrium during garnet growth trace element concentrations in pelitic garnets from the picuris range of new mexico display precipitous changes coincident with abrupt variations in ca concentration these patterns probably arise from the transitory participation of different trace element enriched phases in the garnet forming reaction changes in the reactant and product assemblages occur at different times during the reaction history for crystals of different size so they cannot be the result of any event affecting the entire rock such as a change in pressure temperature or fluid composition instead they reflect kinetic factors that cause ca y yb p ti sc zr hf sr na and li to fail to achieve chemical equilibrium during garnet growth caution is needed to avoid misinterpreting excursions in the concentration of these elements as event markers recording simultaneous rockwide changes in intensive parameters when in fact they may record transient disequilibrium states that are local in scope and not contemporaneous

grain boundary hierarchy development in a quartz mylonite abstract orientation contrast imaging using forescatter detectors and backscattered electron diffraction techniques in the scanning electron microscope have been used to investigate the boundary hierarchy characteristics of a quartz mylonite shear zone from torridon nw scotland the boundary hierarchy is defined as the relationship between the boundary misorientations their enclosed domain size and their frequency distribution by measuring the misorientation across every grain and subgrain boundary the characteristics of the boundary hierarchy can be found two microstructural domains were studied one partially recrystallized low strain domain with large relict grains and one fully recrystallized high strain mylonitic domain our results indicate that the processes of recovery subgrain rotation and grain boundary migration recrystallization each produce identifiable boundary hierarchy signatures in the relict quartz grains we have identified the processes of recovery and subgrain rotation in the recrystallized quartz a cyclic steady state exists between these and other processes coupling these data with traditional microstructural observations allows a more rigorous investigation into the development of a high strain fine grained mylonite from a coarse grained undeformed protolith we suggest that this type of detailed crystallographic microstructural analysis can greatly further our understanding of microstructural development in shear zones and may have implications for the effective use of sub grain size palaeopiezometers

intragranular dynamic recrystallization in naturally deformed calcite marble diffusion accommodated grain boundary sliding as a result of subgrain rotation recrystallization abstract intragranular microshear zones within a greenschist facies calcite marble were studied to try to constrain better the processes of dynamic recrystallization as well as the deformation processes that occur within newly recrystallized grains intragranular recrystallized grains within large twinned calcite porphyroclasts can be related to the host from which they have recrystallized and are the focus of an electron backscatter diffraction study lattice distortions low angle boundaries and some high angle boundaries 15 in the microshears within a porphyroclast have the same misorientation axes suggesting that deformation occurred by climb accommodated dislocation creep involving subgrain rotation recrystallization changes in the ratio of host and twin domain as the deformation zone is entered show that twin boundary migration also occurred recrystallized grains have similar sizes 10 60 m to subgrains suggesting that they formed by subgrain rotation however within the intragranular microshear zones the misorientations between recrystallized grains and porphyroclasts are considerably larger than 15 and misorientation axes are randomly oriented moreover recrystallized grain orientations average around the porphyroclast orientation we suggest that the recrystallized grains once formed are able to deform partly by diffusion accommodated grain boundary sliding which is consistent with predictions made from lab flow laws

experimental formation and significance of etch patterns on detrital garnets the patterns found on the surfaces of etched detrilal garnets are formed by facets that resemble a series of elongated overlapping sharp edged rectangular or rhombohedral building blocks mammilla

flash flood events recorded by air temperature changes in caves a case study in covadura cave se spain summary on 28th september 2012 more than 150 mm rain fell in just two hours in some points of southeastern spain triggering intense flash floods that resulted in the death of ten people and widespread material damage in the gypsum karst of sorbas rainfall intensity reached 33 mm h air temperature monitoring in different levels of covadura cave down to 85 m depth enabled the effect of this extreme episode on the cave microclimate to be evaluated in real time the cave air temperature increased by between 0 9 and 4 1 c as a result of water flow into the cavity and intense mixing of air masses in addition to the displacement of deeper air masses toward shallower levels produced by fast recharge of the surrounding karst aquifer the lag between peak rainfall intensity and the highest cave air temperature was 5 6 h indicating the response time of the karst to this rainfall event no trends with depth were observed suggesting that water not only flowed in through the main cave entrance but also through secondary accesses and fractures furthermore the size of the cave passages and the intensity of air turbulence generated by waterfalls in the cave played an important role in producing these temperature differences even though the rainfall event lasted 10 h cave air temperature did not return to pre flash flood values until more than 20 days later this indicates that while waterflow through the cave might stop a few hours after the rainfall event cave air temperature can be affected over a longer period this can be explained by slow groundwater level decreasing of the surrounding karst aquifer and latent heat liberation produced by moisture condensation on the cave walls our results show how continuous monitoring of air temperature in caves can be a useful tool for evaluating the short term effects of flash floods in subterranean karst systems

disequilibrium for ca during growth of pelitic garnet compositional zoning in hundreds of almandine rich garnets in amphibolite by facies micaceous quartzites from the picuris range north central new mexico usa indicates that although mn mg and fe achieve chemical equilibrium at hand sample scale during garnet growth ca does not instead ca concentrations at the surface of growing garnets appear to depend strongly on kinetic factors that govern the local chemical environment yielding disequilibrium for ca at scales larger than the region immediately surrounding an individual porphyroblast detailed zoning profiles were obtained for 371 garnet crystals in a small volume of a single sample of garnetiferous quartzite and core analyses were made of 97 additional crystals each analysis was made on a section that passed precisely through the morphological centre of the crystal located by means of 3 d imagery from computed x ray tomography the data reveal strong correlations between crystal size and concentrations of mn mg and fe but not ca in garnet cores a relationship between crystal size and isolation rigorous cross correlations among concentrations of mn mg and fe but not ca and systematic variations in ca concentrations as a function of crystal size and core composition that are anomalous in comparison to the behaviour of the other divalent cations we interpret these observations as the result of thermally accelerated diffusion controlled garnet growth in circumstances that promoted rapid intergranular diffusion and thus rock wide equilibration of mn mg and fe but that prevented equilibration at similar scale for ca because of its more sluggish intergranular diffusion the anomalous behaviour of ca is made evident in these garnets by the presence of sharp spikes in ca concentration which are demonstrably not a consequence of any simultaneous rock wide event such as a change in pressure temperature or some other intensive parameter instead ca concentrations probably reflect the local extent of reaction in the immediate vicinity of each porphyroblast to the degree that such kinetic factors introduce departures from chemical equilibrium for ca thermobarometric estimates that involve grossular contents of pelitic garnet will be in error

dynamic recrystallization of garnet and related diffusion processes abstract electron backscatter diffraction and compositional data of permian metapegmatite garnet from the koralpe basement eastern alps austria show the evolution of distinct intracrystalline shear zones in c 10 mm sized almandine spessartine garnet orientation maps reveal continuous distortion of the crystal lattice new garnet grains grain size 20 30 m within intragranular deformation zones oriented subparallel to the main foliation of the metapegmatite have similar crystal orientations to the host garnet whereas recrystallized grains along fractures or along growth heterogeneities show a much weaker crystallographic preferred orientation cpo needles of kyanite as well as inclusions of apatite xenotime and rutile occur along the deformation zones together with the ca variation across the deformation zones these inclusions give evidence of material diffusion related to crystal plastic deformation of garnet the individual garnet porphyroclasts record the evolution of recrystallization microfabrics new grains once formed by subgrain rotation recrystallization are able to deform partly by diffusion accommodated grain boundary sliding resulting in a weakening of the cpo whereas magmatic garnet growth had taken place at lp conditions in equilibrium with andalusite the occurrence of kyanite in some deformation zones triggered by the localized crystal plasticity of garnet indicates that the deformation was related to the cretaceous hp metamorphic event

garnet polycrystals and the significance of clustered crystallization polycrystalline garnets are common in metamorphic rocks and may form as a result of close spacing of nuclei if clustering is early or impingement of larger grains if clustering occurs later in the growth history the timing of clustering relative to garnet growth is relevant to understanding the formation and evolution of porphyroblasts and evaluating the significance if any of clustering electron backscattered diffraction ebsd analysis of garnet bearing metamorphic rocks reveals the presence of polycrystalline garnet in nine localities examined in this study the northern appalachians vermont maine new york usa north american cordillera north cascades range washington snake range nevada usa western rocky mountains british columbia canada southern menderes massif turkey santander massif colombia and the sanandaj sirjan zone hamadan iran in some samples polycrystals comprise 20 30 of garnets analyzed and chemical and textural evidence suggests that early coalescence of garnet polycrystals is common some early coalescing polycrystals exhibit growth zoning that is concentric about the geometric center of the polycrystal in thin section these garnets may be undetectable as polycrystals based on morphology or zoning in some polycrystals zoning is unrelated to the location of internal grain boundaries in others fe mn mg zoning has a different pattern than that of ca zoning patterns may vary on the scale of a single thin section in addition some polycrystals are characterized by high angle misorientation boundaries that may be in special non random orientations an observation that indicates that these polycrystals are not random clusters of grains the presence of internal grain boundaries may affect diffusion pathways and length scales and may facilitate communication of porphyroblast interiors with matrix phases thereby influencing reaction history of the rock and the composition zoning of garnet

crystallographic preferred orientations in eclogites a review abstract during the last decades processes taking place in subduction zones have been a topic of extensive debate there are many models on a tectonic scale but knowledge of deformation at microscopic levels is essential for an understanding of the processes involved crystallographic preferred orientation cpo investigations of minerals in eclogites yield the possibility to study deformation in the crustal part of subducted oceanic lithosphere as well as subducted continental units containing basic intrusions which are frequently exhumed during continental collision from cpo data of omphacite and garnet as well as other constituent minerals in eclogites conclusions on stress and strain at depth in currently active subduction zones can be drawn as the pressure temperature and strain path of the now exhumed rocks can be unraveled this contribution provides an overview of cpo studies of eclogites concerning slip systems deformation strain and other possible cpo forming mechanisms in all major constituent mineral phases in eclogites and the implications of these microstructural data on subduction zone processes are discussed nevertheless there are still many open questions and future research is essential

a garnet population in yellowknife schist canada data are presented on a garnet population in a specimen of garnet biotite plagioclase quartz schist from the cordierite zone of an archaean thermal dome in the southern slave province of the canadian shield garnet crystals are bounded by planar dodecahedral faces and by trapezohedral faces which on the 10 m scale are corrugated crystal distribution as revealed by dissection of a small cubic volume of rock is random the size distribution is normal with a mean diameter of 0 81 mm and a standard deviation of 0 32 mm in the largest crystal of the population mean radius 0 83 mm mn 100 mn fe mg mn ca decreases from 14 5 at the centre to 7 5 and then increases in the outer margin to 8 5 fe increases continuously from 67 at the centre to 77 at the surface mg increases from 12 5 to 13 5 and then falls sharply to 11 ca remains unchanged at 4 0 and then drops to 3 3 progressively smaller crystals have progressively lower mn and higher fe concentrations at their centres while all crystals have the same margin composition growth vectors extending from given concentration contours to crystal surfaces are of equal length regardless of the size of the crystal in which the vector is located a garnet forming model is presented in which reaction was initiated by a rise in temperature nucleation sites were randomly selected the nucleation rate increased with time and then declined crystal faces advanced at a constant linear rate which implies an increase in volume proportional to surface area initially the composition of garnet deposited on crystal surfaces was determined by van laar equations of equilibrium which demanded the withdrawal of mn and fe from within chlorite crystals this transfer reaction was then accompanied by an ion exchange reaction which moved mn and fe to garnet surfaces from biotite in exchange for mg the exchange reaction provides an explanation for the high overall concentration of mn and fe in garnet and for the observed mn and mg reversals in the margins of crystals the increase of garnet volume in the garnet population is found to be parabolic i e v 5

superplasticity in garnet from eclogite facies shear zones in the haram gabbro haramsoya norway study of garnet adjacent to and within shear zones that underwent synkinematic eclogitization reveals microstructures and textures that for the first time indicate grain boundary sliding as the main deformation mechanism in garnet monomineralic garnet layers exhibit characteristic features of superplastic behavior and show little strength contrast to the surrounding minerals the low strength is caused by the synkinematic growth of garnet limiting the grain size to tens of micrometers this behavior may significantly influence rheologic properties of high and ultrahigh pressure shear zones in subduction environments and may play a role during the formation of garnet in the transition zone of the mantle

geochemical characterization of a karst polje an example from sinjsko polje croatia the poljes of the adriatic coast are rath er special features whose like is not found any where else in the world the delineation of this unique landform feature by its geochemical charac teristics has been attempted by using examples from sinjsko polje which represents a typical karst polje in the adriatic coast or the area of the di naric karst factor analysis was performed on 96 samples collected in a regular grid of 1 1k m which covered the entire area of the sinjsko polje valley another factor analysis was performed in a regular grid of 5 5 km that comprised 41 samples in the karstic environment in this manner two fac tor models were created and closely inspected for possible differences due to the peculiar properties arising from two geochemically different environ ments within the polje itself it was possible to evaluate three factors while four factors were iden tified to be significant for the explanation of the geochemical structure of data assessed in the regul ar 5 5 km grid this grid includes the area of sinjsko polje and its wider neighborhood the ba sr index reveals striking differences in drainage patterns between the polje itself and the surround ing area

dispersion of b values in gutemberg richter law as a consequence of a proposed fractal nature of continental faulting depending on the area in which the earthquakes are sampled the exponent b c of the distribution of seismic moment or energy of earthquakes fluctuates from one region to another in a range typically between 0 5 and 1 to explain this observation we propose a general mechanism which accounts for fluctuations in the b c value as being related to the variations of the fractal dimension of the set of faults on which the gutemberg richter law is measured

hydrogeological characterization of dasht e arjan lake zagros mountains iran clarifying a long time question dasht e arjan lake is located in the southern zagros mountain ranges of iran it is a tectonic karst polje fed by a single spring plus local surface runoff and drained by a single ponor the fate of sinking water from the ponor had not been determined before this study previous investigations suggested two alternatives 1 underground flow 24 km southwest to parishan lake and or springs in the kazeron area and 2 underground flow 20 km southeast to springs at domeasb gorge to clarify this question an integrated hydrogeological study including a dye tracer test was undertaken comparison of the discharge into the arjan ponor and the discharge of the domeasb springs shows a reliable correlation further annual water balance analysis reveals that the discharge at the domeasb springs is too great for its topographic catchment requiring a major additional source the dye tracer test using 5 kg of uranine was detected only at the domeasb springs flow through time after the dye injection was 210 h the tracer breakthrough curves are very simple and sharp with a clear peak concentration of 7 ppb the total tracer mass recovery and groundwater flow velocity were estimated to be 58 and 105 m h 1 respectively the results indicate a simple and direct limestone karst hydraulic connection along the geologic strike between dasht e arjan lake and the domeasb springs the results clearly suggest the possibility of designing a dam around the ponor to protect drying up the lake during drought periods

misorientations of garnet aggregate within a vein an example from the sanbagawa metamorphic belt japan in this study the chemistry and microstructure of garnet aggregates within a metamorphic vein are investigated garnet bearing veins in the sanbagawa metamorphic belt japan occur subparallel to the foliation of a host mafic schist but some cut the foliation at low angle backscattered electron image and compositional mapping using epma and crystallographic orientation maps from electron backscattered diffraction ebsd reveal that numerous small garnet 10 100 m diameter coalesce to form large porphyroblasts within the vein individual small garnet commonly exhibits xenomorphic shape at garnet garnet grain boundaries whereas it is idiomorphic at garnet quartz boundaries ebsd microstructural analysis of the garnet porphyroblasts reveals that misorientation angles of neighbour pair garnet grains within the vein have a random distribution this contrasts with previous studies that found coalescence of garnet in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation driven rotation as garnet nucleated with random orientation the difference in misorientation between the two studies is due to the difference in the extent of grain rotation a simple kinetic model that assumes grain rotation of garnet is rate limited by grain boundary diffusion creep of matrix quartz shows that i the substantial rotation of a fine garnet grain could occur for the conditions of the sanbagawa metamorphism but ii the rotation rate drastically decreased as garnet grains formed large clusters during growth therefore the random misorientation distribution of garnet porphyroblasts in the sanbagawa vein is interpreted as follows i garnet within the vein grew so fast that substantial grain rotation did not occur through porphyroblast formation and thus ii random orientations at the nucleation stage were preserved the extent of misorientation driven rotation indicated by deviation from random orientation distribution may be useful to constrain the growth rate of constituent grains of porphyroblast that formed by multiple nucleation and coalescence

creep of garnet in eclogite mechanisms and implications abstract the rheological properties of subducting rocks represent a fundamental parameter in the dynamics of subduction zones making robust predictions about these properties and the general strength evolution of subducting plates is hampered by a relatively restricted understanding of the mechanisms by which rocks deform at high and ultrahigh pressure this uncertainty is relates to the discrepancy between experimental and field based observations of eclogite deformation and in particular the role of garnet to further investigate this important aspect we performed a textural and micro structural investigation applying optical microscopy element mapping and electron backscatter diffraction on deformed garnet polycrystals from an eclogite mylonite the results were compared to those from a study of undeformed polycrystals that formed from a supercooled frictional melt at hp conditions the mylonites polycrystals are flattened parallel to the main high pressure foliation in the rock and individual grains were shortened by an average 15 although dislocation creep is commonly presumed to dominate garnet straining in eclogites no record of this mechanism was found instead the garnet grains have dissolution surfaces indicative of deformation by intergranular pressure solution the observations provide compelling evidence for the role of fluids and syn tectonic porosity in the weakening of garnet a supposedly rigid eclogite component such weakening represents a crucial step in the fundamental feedback loop between fluid ingress metamorphism and near instantaneous competence loss in rocks undergoing deep subduction

the petrological significance of misorientations between grains misorientation analysis quantifies microstructural features in tectonites metamorphic and igneous rocks and allows hypotheses on their formation to be tested the misorientation between two lattices can be expressed by a rotation axis and rotation angle for lattices with symmetry it is conventional to take the minimum angle that enables one lattice to be rotated into the other for a group of lattice measurements two types of misorientation distribution can be calculated selecting random pairs of grains gives the random pair misorientation distribution selecting neighbouring pairs gives the neighbour pair misorientation distribution the forms of both distributions are visualised using histograms or cumulative frequency diagrams they are strongly influenced by any overall crystallographic preferred orientation and by intrinsic crystal symmetry in many rocks the random pair misorientation distribution and neighbour pair misorientation distribution are statistically significantly different quantified using the kolmogorov smirnov test differences between the random pair misorientation distribution and neighbour pair misorientation distribution imply that adjacent grains have physically interacted or are inherited from a precursor microstructure interactions include 1 reduction in surface energy by lattice alignment we show this may have occurred in garnet clusters in schist and olivine in a cumulate it is well known in metals and may be a common geological process 2 nucleation where those nuclei have influenced the orientation of adjacent nuclei 3 mechanical rotations of facetted grains in compacting crystal mushes so that faces become parallel 4 growth twinning inheritance includes 1 subgrain rotation recrystallisation in tectonites deforming by crystal plastic processes 2 mechanical and transformation related twinning 3 domainal microstructures e g where grains have formed from a few large original grains may give rise to spurious correlations when the orientation data cover more than one domain with this proviso misorientation analysis can be used to investigate many important microstructural processes

formation of garnet clusters during polyphase metamorphism pre alpine garnets of variscan age from metapelitic basement units in northern italy were strongly retrogressed at near surface conditions prior to alpine contact metamorphism the replacement by sheet silicates caused a significant volume increase during retrogression producing pervasive fracturing up to several hundreds of angular fragments formed from each crystal electron backscatter diffraction analysis documents a maximum misorientation of 22 of some fragments as a result of local rotation during fracturing new garnet growth is observed on the garnet fragments during contact metamorphic overprinting resulting in garnet clusters fragments can be identified due to calcium rich domains fragment orientations were inherited and only minor new nucleation occurred these garnets develop features typically associated with multiple nucleation models but here they reflect multiple metamorphic events we propose that clusters can be indicative of multiple metamorphic events which were separated by a period of intense retrograde alteration

a methodology for extreme groundwater surge predetermination in carbonate aquifers groundwater flood frequency analysis summary the present paper introduces a methodology devoted to groundwater flooding hazard assessment it focuses on groundwater floodings due to water table rises that are induced by heavy rainfall events this special kind of flooding can cause devastating damages particularly in fractured and karstified carbonate aquifers indeed hydrodynamic conditions prevailing in these heterogeneous formations can involve strong groundwater surges the developed methodology shows how flood frequency analysis methods can be applied in groundwater flood frequency analysis actually it consists in estimating the t year hydraulic head that characterizes the t year groundwater surge given a return period t it also aims at defining the rainfall events likely to cause such extreme groundwater surges this methodology was applied within the framework of a building construction project in a karstic mediterranean aquifer located in southern france the present paper is designated to be a first contribution to groundwater flood frequency analysis this new field of research has to be further developed in order to put forward consensus guidelines for hydrogeologists and decision makers as in flood frequency analysis

three dimensional quantitative textural analysis of metamorphic rocks using high resolution computed x ray tomography part ii application to natural samples three dimensional quantitative textural analysis coupled with numerical modelling has been used to assess the dominant mechanisms governing crystallization of garnet porphyroblasts in rocks from diverse regional metamorphic environments in every case spatial dispositions crystal size distributions and compositional zoning patterns of porphyroblasts indicate the dominance of diffusion controlled nucleation and growth mechanisms nine samples from three geological areas were studied a suite of semi pelitic rocks from the picuris mountains new mexico usa a suite of mafic samples from the llano uplift texas usa and a kyanite schist from mica dam british columbia canada the semi pelitic suite exhibits post deformational garnet growth whereas garnet in the mafic suite and in the kyanite schist grew synkinematically in rocks displaying weak and strong penetrative fabrics respectively for each sample the centres and radii of thousands of garnet crystals were located and measured in three dimensions using images produced by high resolution computed x ray tomography statistical measures of the degree of ordering and clustering of nucleation sites and estimates of crystal isolation for each porphyroblast were then computed from the measured spatial dispositions these measures can be reproduced in simple numerical models only by diffusion controlled nucleation and growth mechanisms normalized radius rate relations computed from compositional zoning patterns in the garnets require thermally accelerated diffusion controlled growth providing independent confirmation of the conclusions based on textural analysis the unexpected similarity of results from all samples indicates that diffusion controlled nucleation and growth mechanisms may govern porphyroblast crystallization in many metamorphic regimes

an integrated epma ebsd study of metamorphic histories recorded in garnet growth histories recorded in garnet grains in metasedimentary rocks from the sanbagawa belt in japan and the mogok belt in myanmar were analyzed using an effective combination of electron backscatter diffraction ebsd and electron probe microanalysis epma data garnet in the sanbagawa metapelite has inner and outer zones that formed in the eclogite and epidote amphibolite facies stages respectively based on epma element mapping this garnet appears to have grown as a single crystal with a temporal break in growth between the inner and outer zones that occurred during exhumation the ebsd data however document that the garnet grain is composed of four domains the misorientation angles of crystallographic orientations between the domains are as large as 59 and domain boundaries crosscut the growth zoning and the compositional boundary between the inner and outer zones sets of quartz grains included in the garnets on either side of the domain boundaries sometimes share the same crystallographic orientation with misorientation angles less than 4 the garnet grains formed via a three step process of prograde crystallization of polycrystalline garnet during the eclogite facies stage inner zone resorption around garnet rims and along domain boundaries during exhumation crystallization of the outer zone and in the domain boundaries during the prograde epidote amphibolite facies stage the garnet porphyroblasts in the mogok pelitic gneisses which formed during prograde metamorphism to the upper amphibolite granulite facies 0 6 1 0 gpa 780 850 c are now separated into segments of various sizes by mosaic or symplectite aggregates of biotite plagioclase and quartz or monomineralic biotite veins the segment texture formed at about 0 3 0 4 gpa 610 650 c or lower grade conditions the ebsd analysis shows that most of the segments share the same crystallographic orientation with misorientation angles less than 4 and show no evidence of deformation and or rotation processes after segmentation these data suggest that the mogok sample did not experience dynamic deformation of the garnet grains after the resorption and segmentation stage and may have been exhumed under static conditions from depths of 9 12 km

unraveling the schneeberg garnet puzzle a numerical model of multiple nucleation and coalescence a quantitative kinetic model for the growth of the different garnet porphyroblast microstructures type 1 and type 2 of the western schneeberg complex wsc is presented these porphyroblasts formed by a multiple nucleation and coalescence mechanism our numerical simulation shows that at constant diffusion rates 1 low interface reaction rates result in a fully amalgamated porphyroblast type 2 2 intermediate reaction rates result in a porphyroblast where coalescence of grains closer to the margin prevented amalgamation of those in the centre similar to type 1 porphyroblasts and 3 high interface reaction rates result in a porphyroblast microstructure with an atoll form all three microstructures are characterised by distinctive cluster size distributions a 2 d cluster size distribution analysis of type 1 porphyroblasts of wsc shows that these did not form because of intermediate interface reaction rates but because the diffusion rate of nutrients was too low to keep pace with the interface reaction rate

ductile deformation of garnet in mylonitic gneisses from the munchberg massif germany abstract mylonitic gneisses from the munchberg massif contain single grains type i and polycrystalline aggregates type ii of garnet displaying a distinct elongation parallel to a macroscopic lineation which is interpreted as the result of ductile deformation lattice preferred orientations of quartz textures symmetrical to the macroscopic foliation and lineation and the lack of rotational microfabrics indicate that the bulk deformation was pure shear at least during the latest strain increments garnet textures measured by ebsd together with microprobe analyses demonstrate that these two structural types of garnet can be related to two different processes of ductile deformation 1 for the single grains stretching can be attributed to diffusion creep along grain boundary zones coble creep the related mass transfer is indicated by the fact that primary growth zones are cut off at the long faces of the grains while the related strain shadow domains do not show comparable chemical zoning pressure solution and precipitation suitable to produce similar structures can be largely ruled out because retrogressive reactions pointing to the presence of free hydrous fluids are missing 2 for the polycrystalline garnet aggregates consisting of cores grading into fine grained mantles dislocation creep and associated rotation recrystallization can be assumed continuous lattice rotation from the core to the outer polycrystalline rim allow a determination of the related dominant slip systems which are 100 and equivalent systems according to the cubic lattice symmetry the same holds for garnets which appear to be completely recrystallized for this type of fine grained aggregates an alternative nucleation model is discussed due to penetrative dislocation glide in connection with short range diffusion and the resulting lattice rotation primary growth zones are strongly disturbed since for the considered rock unit of the munchberg massif peak metamorphic temperatures between 630 and 670 c can be assumed this study clearly demonstrates that the inferred processes of ductile garnet deformation can occur not only in ht regimes as often suggested in the literature even if embedded within a matrix of low strength minerals like quartz feldspars and micas

shape size spatial distribution and composition of garnet crystals in highly deformed gneiss of the otter lake area quebec and a model for garnet crystallization garnet biotite sillimanite gneiss 700 c 7 kbar of the otter lake area in the western grenville province canadian shield occurs as granitic gneiss group 4 that forms a large part of the otter complex and as widely distributed more heterogenous metasedimentary gneiss group 2 in one sample of group 4 gneiss qtz25 pl34 kfs28 bt10 grt2 5 sil1 the true diameter determined by serial grinding of subhedral garnet crystals ranges from 0 2 to 3 0 mm with a mode at 1 0 mm nearest neighbour measurements in this sample and in surfaces of nine additional samples all 5 garnet confirm that garnet crystals are distributed mainly at random slight clustering was detected in two samples in one sample of group 4 gneiss microprobe analyses on sections through crystal centres obtained by serial slicing reveal that small crystals and margins to large crystals contain more fe and mn and less mg than the broad central regions of large crystals based on these and previous results together with theoretical considerations a crystallization model is proposed in which i garnet was produced by the continuous reaction ms bt qtz grt kfs h2o ii nucleation occurred by the random selection of randomly distributed ms bt qtz triple junctions iii the rate of linear growth remained constant and iv as temperature increased the rate of nucleation first increased slowly then remained nearly constant and finally declined within population compositional homogenization was followed on cooling by local fe mg mn exchange with biotite

microstructural chemical and textural records during growth of snowball garnet the growth history of two populations of snowball garnet from the lukmanier pass area central swiss alps was examined through a detailed analysis of three dimensional geometry chemical zoning and crystallographic orientation the first population collected in the hinge of a chevron type fold shows an apparent rotation of 360 the first 270 are characterized by spiral shaped inclusion trails gradual and concentric mn zoning and a single crystallographic orientation whereas in the last 90 crenulated inclusion trails and secondary mn maxima centred on distinct crystallographic garnet domains are observed microstructural geochemical and textural data indicate a radical change in growth regime between the two growth sequences in the first 270 growth occurred under rotational non coaxial flow whereas in the last 90 garnet grew under a non rotational shortening regime the second population collected in the limb of the same chevron type fold structure is characterized by a spiral geometry that does not exceed 270 of apparent rotation these garnet microstructures do not record any evidence for a modification of the stress field during garnet growth concentric mn zoning as well as a single crystallographic orientation are observed for the entire spiral electron backscatter diffraction data indicate that nearly all central domains in the snowball garnet are characterized by one 001 axis oriented sub parallel to the symmetry axis and by another 001 axis oriented sub parallel to the orientation of the internal foliation these features suggest that the crystallographic orientation across the garnet spiral is not random and that a relation exists among the symmetry axis the internal foliation and the crystallographic orientation

formation of garnet polycrystals during metamorphic crystallization garnet polycrystals may form throughout the metamorphic history of a rock starting at the earliest stages of garnet growth when closely spaced nuclei coalesce in mica schist from townshend dam vt electron back scattered diffraction ebsd analysis shows that garnet polycrystals possess two or more distinct lattice orientations separated by high angle boundaries 28 61 the minimum rotational displacements required to bring these lattice orientations into concordance with each other are commonly normal to the same low energy planes that occur as crystal faces of euhedral garnet there is no evidence for intracrystalline deformation and the polycrystals therefore probably represent individual garnet crystals that coalesced during growth the boundaries cross cut growth zoning and inclusion trails of the polycrystals indicating that early formed polycrystals once coalesced behave chemically and physically as single crystals statistical analysis of a 3d high resolution x ray computed tomographic data set of a large sample 912 cm3 of a townshend dam schist combined with microprobe and ebsd analyses of garnet are consistent with a high degree of clustering at all stages of garnet growth the formation and prevalence of polycrystals implies that garnet nuclei impinged on each other and coalesced and that coalescence was a common feature throughout garnet growth in the rock

matrix dependent garnet growth in polymetamorphic rocks of the sesia zone italian alps mushroom and atoll shaped garnet crystals were found in high pressure quartz rich pelitic layers from the monte mucrone area western alps italy these garnet crystals are characterized by a peninsula shaped core surrounded by a partially crystallized dodecahedral external rim textural observations and thermodynamic modelling point towards growth of the atoll garnet from the monte mucrone area during two distinct orogenic cycles the core region and the inner part of the ring forming the edge of the atoll grew under barrovian metamorphic conditions of likely hercynian age while the outer rim of the atoll structure developed under alpine high pressure conditions electron backscatter diffraction analyses indicate that the atoll shaped structure has one single crystallographic orientation despite its complex compositional zoning thermodynamic modelling reveals marked changes in equilibrium assemblage leading to changes in stoichiometry of the garnet forming reaction which in turn explain the characteristic garnet morphology small amounts of quartz are consumed during the earlier stage of garnet growth history whereas the production of garnet requires a much larger amount of quartz during the final stage of its growth this leads to a change from initial poikiloblastic to non poikiloblastic textures this change is responsible for the formation of atoll shaped garnet finally garnet in intercalated mica rich layers forms idiomorphic crystals continuous from the centre to rim this study highlights the importance of the difference between the local matrix composition and the aggregate composition of the reactants needed for the garnet forming reaction finally we show that interaction between matrix and reaction stoichiometry can lead to porphyroblast precipitation inside the already grown porphyroblast

controls on metamorphic equilibration the importance of intergranular solubilities mediated by fluid composition a dramatic demonstration of the role of intergranular solubility in promoting chemical equilibration during metamorphism is found in the unusual zoning of garnet in pelitic schist exposed at harpswell neck maine usa many garnet crystals have irregular patchy distributions of mn cr fe and mg in their inclusion rich interiors transitioning to smooth concentric zoning in their inclusion poor outer rims in contrast zoning of ca and y is comparatively smooth and concentric throughout we re assess the disputed origin of these zoning features by examining garnet growth in the context of the thermal and structural history of the rocks and by evaluating the record of fluid rock interaction revealed in outcrop scale veining and fluid inclusion assemblages the transition in the character of garnet zoning correlates with the onset of a synkinematic simple shear dominated phase of garnet growth and with a shift in the composition of the intergranular fluid from co2 rich to h2o rich compositional variations in garnet are therefore best explained by a two stage growth history in which intergranular diffusive fluxes reflect differences in the concentration of dissolved species in these two contrasting fluids interiors of garnet crystals grew in the presence of a co2 rich fluid in which limited solubility for mn and cr and perhaps fe and mg produced patchy disequilibrium overprint zoning while appreciable solubility for ca and y permitted their rock wide equilibration rims grew in the presence of an h2o rich fluid in which high intergranular concentrations for all elements except cr enabled diffusion over length scales sufficient for rock wide equilibration this striking example of partial chemical equilibrium during reaction and porphyroblast growth implies that thermal effects may commonly be subsidiary in importance to solubilities in the intergranular medium as determinants of length scales for metamorphic equilibration

time series analyses for karst river interactions assessment case of the coulazou river southern france summary in many karst systems throughout the world numerous karst features facilitate the exchange of water between the surface the vadose zone and the saturated zone of the aquifer these interactions play actually a prominent role in the ground and surface waters circulation this study aims at assessing karst river interactions by the way of flood hydrograph analysis and new tools for time series analysis in this field of research as in many others binary karst system the captured waters of the coulazou river travel through conduits and preferential flow paths in the vadose zone and join the saturated zone of the aquifer this river is an ephemeral river in a mediterranean context where rapid and intense floods occur each year this hydrologic behaviour is appropriate to study the transfer of a flood through a karst area the water level in caves the rainfall all over the karst aquifer catchment area the piezometric level within the karst aquifer and the discharge in the river upstream and downstream of the karst aquifer are measured in order to understand the karst river exchanges during a flood the modification of the surface flows in the river is treated as a linear time invariant system lti system correlation and spectral analyses are used to understand how the lti system dissipates or enhances the flood wave energy for several floods the frequency response function estimations are interpreted in term of flood wave modification through the karst area in this way according to the initial state of the karst river system the autogenic and or allogenic recharge of the aquifer may induce surge flows and a significant karst contribution to surface flows

sub critical fracture and associated retrogression of garnet during mylonitic deformation garnets from the alpine fault mylonites are fractured most fractures have a retrogressive fracture fill a small number have garnet fill a detailed sem study has been carried out to elucidate the mechanisms of fracture and associated retrogression wide fracture zones contain free floating islands of garnet in a retrogressive matrix electron channelling patterns show that segments of garnet across such fracture zones rarely show any relative rotations where rotations are observed they are small and systematic some large fractures show clearly that fracture and retrogression occurs by a replacement process fracture surface morphologies are indicative of surface dissolution a model is established where crack tips advance by a process of dissolution at a high stress crack tip whilst precipitation occurs as the tip and its associated stress field advance precipitation of retrogressive fracture fill occurs if fracture occurs out of the field of stability of garnet

on the geometric relationship between deformation microstructures in zircon and the kinematic framework of the shear zone abstract we present novel microstructural analyses of zircon from a variety of strained rocks for the first time multiple plastically deformed zircon crystals were analyzed in a kinematic context of the respective host shear zones our aim was to derive how the orientation of zircon grains in a shear zone affects their deformation based on careful in situ observations for sampling we selected zircon bearing rocks that were deformed by simple shear samples covered a range of p t conditions and lithologies including various meta igneous and meta sedimentary gneisses microstructural analyses of zircon crystals in situ with scanning electron backscatter diffraction mapping show strong geometrical relationships between orientations of i the long axes of plastically deformed zircon crystals ii the crystallographic orientation of misorientation axes in plastically deformed zircon crystals and iii the foliation and lineation directions of the respective samples we assume that zircon crystals did not experience post deformation rigid body rotation and thus the true geometric link can be observed the relationships are the following a plastically deformed zircon crystals usually have long axes parallel to the mylonitic foliation plane b crystals with axes oriented at an angle 15 to the foliation plane are undeformed or fractured zircon crystals that have axes aligned parallel or normal to the stretching lineation within the foliation plane develop misorientation and rotation axes parallel to the 001 crystallographic direction zircon grains with the axis aligned at 30 60 to the lineation within the foliation plane often develop either two low miller indices misorientation axes or one high miller indices misorientation axis host phases have a significant influence on deformation mechanisms in a relatively soft matrix zircon is more likely to develop low miller indices misorientation axes than in a relatively strong matrix these relationships are independent of zircon s grain size and shape and reflect the strong geometric control of the macroscopic kinematic rotation axis on the crystal plastic deformation behavior of zircon and on the geometry of its slip systems we describe previously unknown rheological and crystallographic properties of zircon which suggest a tool for deriving an orientation of the plastically deformed zircon crystals with respect to the associated foliation and stretching lineation additionally relationships between zircon deformation microstructures and the macroscopic kinematic framework have implications for zircon geochronology if deformation events result in zircon distortion and as a consequence partial or complete resetting of the zircon isotopic system the age of deformation can be accurately dated