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

geochemical interactions between constituents in acidic groundwater and alluvium in an aquifer near globe arizona abstract acidic water from a copper mining area has contaminated an alluvial aquifer and stream near globe arizona the most contaminated groundwater has a ph of 3 3 and contains about 100 mmol 1 so4 50 mmol 1 fe 11 mmol 1 al and 3 mmol 1 cu reactions between alluvium and acidic groundwater were first evaluated in laboratory column experiments a geochemical model was developed and used in the equilibrium speciation program minteqa2 to simulate breakthrough curves for different constituents from the column the geochemical model was then used to simulate the measured changes in concentration of aqueous constituents along a flow path in the aquifer the ph was predominantly controlled by reaction with carbonate minerals where carbonates had been dissolved adsorption of h by iron oxides was used to simulate ph acidic groundwater contained little or no dissolved oxygen and most aqueous fe was present as fe ii in the anoxic core of the plume fe ii was oxidized by mno2 to fe iii which then precipitated as fe oh 3 attenuation of aqueous cu co mn ni and zn was a function of ph and could be quantitatively modeled with the diffuse layer surface complexation model in minteqa2 aluminum precipitated as amorphous al oh 3 at ph after the alluvium in the column had reached equilibrium with acidic groundwater uncontaminated groundwater was eluted through the column to evaluate the effect of reactants on groundwater remediation the concentration of fe mn cu co ni and zn rapidly decreased to the detection limits within a few pore volumes all of the gypsum that had precipitated initially redissolved resulting in elevated ca and so4 concentrations for about 5 pore volumes aluminum and ph exhibited the most potential for continued adverse effects on groundwater quality as h desorbed from fe oh 3 ph remained below 4 5 for more than 20 pore volumes resulting in dissolution of alohso4 and elevated aqueous al

the tectonic implications of high pressure metamorphism in the western alps five mineralogical stages are recognized in the metamorphism of alpine ophiolites from one area in the zermatt saas zone constraints on p t values indicate an abrupt change at the metamorphic peak 550 600 c 17 20 kbar from a cold positive slope of 25 c kbar or less to cooling initially without discernible change of pressure correspondence of the prograde path to the p t trend of t in c 150 23 p in kbar shown by a variety of alpine units suggests that they all have p t histories for which an england richardson 1977 relaxation model also england thompson 1984 is inappropriate major tectonism at the peak pressure is indicated by association between minerals kyanite chloritoid lawsonite in eclogite vein growths fluid action and thrust surfaces the proposed metamorphic environment involves thrust repetition subcreting ophiolite to the over riding slab in a thermally mature subduction zone at a depth of approximately 70 km preservation is favoured when ocean closure leads to subduction of sialic crust so providing a combination of buoyant uplift with the continued refrigeration by underthrusting of cold surface materials

deformation and recrystallization mechanisms in naturally deformed omphacites from the sesia lanzo zone geophysical consequences buatier m van r rmund h l m drury m r and lardeaux j m 1991 deformation and recrystallization mechanisms in naturally deformed omphacites from the sesia lanzo zone geophysical consequences teetonophysrc c 195 11 27 naturally deformed omphacites clinopyroxenes from the sesia lanzo zone western italian alps have been studied using light and transmission electron microscopy techniques deformation and recrystallization of omphacite took place at 5 50 600 c and minimum pressures of 14 16 kbar tem reveals isolated free dislocations loops nodal points tiltwalls complex dislocation networks minor twins stacking faults and antiphase domain boundaries the activated slip systems are l z llo llo l llo and al assisted by climb in nodal points and complex dislocation networks dislocations with burgers vector l 2 112 are present in low strain domains most of the subgrain transitional and new grain boundaries subparallel to wl develop from 110 tiltwalls which accommodate lattice bending produced by the l 2 110 110 slip system a component of the misorientation across such newly formed sub grain boundaries is however also formed by sub rain boundary migration grain rotations in the intermediate and high strain domains are more complex but can be explained by the activated slip systems the omphacite microstructures indicate that initial strain induct rec stallisation occurred by a rotation mechanism where single crystals become polycrystals by the development of numerous high angle grain boundaries at a subsequent more advanced stage migration recrystallization is also activated and a different kind of recrystallization mechanism occurs which involves the discontinuous development of new strain free grains these grains are derived from the extremum of the orientations produced by heterogeneous strain and slip system activity the evident ductility of omphacite during low to intermediate eclogite metamorphism is inferred to be facilitated by hydrolitic weakening effects as such the plastic behaviour of omphacite should be incorporated in geophysical flow models dealing with subducted oceanic and or lithosperic plate margins

prograde and retrograde metamorphism of hematitebearing basic schists in the sanbagawa belt in central shikoku the mineral assemblages of hematite bearing basic schists in intermediate high pressure metamorphism are temperature dependent for assemblages with excess hematite albite muscovite and quartz the paragenetic relations can be dealt with in terms of a four component system without omitting or grouping major components in the sanbagawa belt in central shikoku the dominant amphibole in the hematite bearing basic schists changes from winchite via crossite and barroisite to hornblende the stability of amphibole is described chemographically within a pseudoternary system with another excess phase epidote many amphiboles are chemically heterogeneous owing to retrograde reactions which produced low t p amphibole around the prograde amphibole the examination of amphibole zoning makes it possible to draw a retrograde p t trajectory which passes on the lower pressure side of the prograde one

analysis and simulation of reactive transport of metal contaminants in ground water in pinal creek basin arizona abstract large scale mining activities have generated a plume of acidic ground water more than 15 km long in the regional aquifer of the pinal creek basin a one dimensional reactive transport model was developed using phreeqc to aid in the analysis of transport and chemical processes in the plume and to determine the uses and limitations of this type of modeling approach in 1984 the acidic part of the plume had a ph as low as 3 4 and contained milligram per liter concentrations of iron copper aluminum and other metals from 1984 to 1994 concentrations of contaminants in the alluvial aquifer in pinal creek basin arizona decreased as a result of mixing recharge remedial pumping and chemical reactions for reactions involving gypsum and rhodochrosite the equilibrium modeling assumption of a local geochemical equilibrium was generally valid from 1984 to 1990 water along the simulated flow path was at equilibrium or slightly supersaturated with gypsum and gypsum equilibria controlled dissolved concentrations of calcium and sulfate beginning in 1991 water in the acidic part of the plume became increasingly undersaturated with respect to gypsum indicating that the gypsum available for dissolution in the aquifer may have been completely consumed by about 1991 rhodochrosite precipitation was thought responsible for the measured attenuation in dissolved manganese in the neutralized zone for reactions involving calcite the assumption of a local geochemical equilibrium was generally not valid dissolution of calcite in the transition zone was not sufficient to establish equilibrium although following neutralization the calcite saturation index decreased to 1 2 in 1986 calcite undersaturation decreased along the flow path in the neutralized zone and equilibrium was attained about 7 km downgradient of the transition zone the assumption of a local geochemical equilibrium was not valid for oxidation reduction reactions that involved iron oxides and manganese oxides kinetically controlled oxidation reduction reactions continued in the acidic part of the flow path for years following the passage of the transition zone although the equilibrium approach helped to provide an increased understanding of contaminant transport at pinal creek future work will require a kinetic modeling approach to more accurately simulate selected reactions between the plume and aquifer materials

prograde high to ultrahigh pressure metamorphism and exhumation of oceanic sediments at lago di cignana zermatt saas zone western alps pelagic metasediments and morb type metabasalts of the former tethyan oceanic crust at cignana valtournanche italy experienced uhp metamorphism and subsequent exhumation during the early to late tertiary maximum pt conditions attained during uhp metamorphism were 600 630 c 2 7 2 9 gpa which resulted in the formation of coesite glaucophane eclogites in the basaltic layer and of garnet dolomite aragonite lawsonite coesite phengite bearing calc schists and garnet phengite coesite schists with variable amounts of epidote talc dolomite na pyroxene and na amphibole in the overlying metasediments during subduction the rocks followed a prograde hp uhp path which in correspondance with the jurassic age of the tethyan crust reflects the thermal influence of relatively old and cold lithosphere and of low to moderate shear heating inflections on the prograde metamorphic path may correspond to thermal effects that arise from a decrease in shear heating due to brittle plastic transition in the quartz aragonite dominated rocks induced convection in the asthenospheric mantle wedge and or heat consumption by endothermic reactions over a restricted pt segment during subduction after detachment from the downgoing slab some 50 70 ma before present the cignana crustal slice was first exhumed to ca 60 km and concomitantly cooled to ca 550 c tracing back the uhp hp prograde path displaced by 50 80 c to higher temperatures exhumation at this stage is likely to have occurred in the benioff zone while the subduction of cool lithosphere was going on subsequently the rocks were near isothermally exhumed to ca 30 km followed by concomitant decompression and cooling to surface conditions at 500 c 1 gpa during this last stage the uhpm slice arrived at its present tectonic position with respect to the overlying greenschist facies combin zone in contrast to the well preserved hp uhpm record of the coesite glaucophane eclogites the hp uhp assemblages of the metasediments have been largely obliterated during exhumation relics from which the metamorphic evolution of the rocks during prograde hp metamorphism and the uhp stage can be retrieved are restricted to rigid low diffusion minerals like garnet dolomite tourmaline and apatite

relationships between eclogite facies mineral assemblages deformation microstructures and seismic properties in the yuka terrane north qaidam ultrahigh pressure metamorphic belt nw china to understand the relationships between eclogite facies mineral assemblages deformation microstructures and the seismic properties of subducting oceanic crust eclogites from the yuka terrane no

deformation processes in eclogitic rocks evidence for the rheological delamination of the oceanic crust in deeper levels of subduction zones the deformation mechanisms and associated growth processes operating in omphacite during foliation development and veining have been studied in a km scale eclogitic ductile shear zone from the monviso meta ophiolitic complex italian western alps dislocation creep due to multiple slip and or climb is the dominant deformation mechanism whereas 100 and 001 twinning fracturing and intergranular fluid phase diffusional creep are subordinate active slip systems include 110 001 12 110 110 100 001 and 12 010 100 fracturing is interpreted in terms of brittle instabilities arising from strain and pore fluid pressure partitioning between adjacent omphacite domains the transition from plastic to brittle behaviour of rocks is cyclic in nature as the internally generated fluids can be released and trapped repetitively during progressive deformation the significance of the eclogitic shear zone is discussed in terms of a mechanically weak zone that developed during burial or at least prior to the peak of temperature at a minimum depth of 40 km in a subduction zone and which subsequently acted as a zone of detachment during a late stage of the alpine orogeny a rheological model for oceanic crust delamination in deeper levels of subduction zones is presented

quartz exsolution topotaxy in clinopyroxene from the uhp eclogite of weihai china abundant oriented silica precipitates of quartz 4 0 1 0 vol in part coexisting with calcic amphiboles 0 2 vol have been identified in clinopyroxenes of eclogites from the weihai area sulu ultrahigh pressure terrane eastern china electron backscatter diffraction ebsd analyses demonstrate that the majority 97 of quartz precipitates have topotactic relationships with their host clinopyroxenes three types of crystallographic topotactic relationship have been identified between quartz and host clinopyroxene 1 52 quartz precipitates share the same orientation for the c axes with 0001 qz 001 cpx 2 34 quartz precipitates share the same orientation for the a axes with 112 0 qz 001 cpx and 3 11 quartz precipitates share the same orientation for the s planes with 112 1 qz 100 cpx other quartz axes and planes disperse in large or small girdles around the shared axes or planes many quartz rods needles are elongated parallel to the 001 cpx with the long axes of quartz being either 0001 qz or 112 0 qz amphibole precipitates have also a strong crystallographic relationship with host clinopyroxene i e 100 amp 100 cpx 010 amp 010 cpx and 001 amp 001 cpx these results provide quantitative microstructural evidence supporting an exsolution origin for oriented quartz needles rods in clinopyroxene and demonstrate that the exsolution of quartz from clinopyroxene occurred within the stability field of quartz rather than coesite the oriented precipitates of quartz in part coexisting with calcic amphiboles in host clinopyroxene are probably promoted by supercritical fluid or partial melting during the early exhumation of eclogites our results suggest that oriented quartz precipitates in clinopyroxene cannot be used as an indisputable uhp indicator

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

arsenic and metal mobility from au mine tailings in rodalquilar almeria se spain in the old mining area of rodalquilar mine wastes soil and sediments were characterized and the results revealed high concentration of au ag as bi cu fe mn pb se sb and zn in tailings and sediments the contaminant of greatest environmental concern is as the mean concentration in the tailings was 679 9 and 345 mg kg in the sediments of playazo creek the groundwater samples from the alluvial aquifer showed high concentration of al as cd fe hg mn ni pb se sb and zn and very high concentration of chloride and sulfate which were above the concentration defined in the european standards for drinking water the presence of as in groundwater may be caused by the oxidation of arsenian pyrite the possible as desorption from goethite and ferrihydrite and the jarosite dissolution groundwater concentrations of cd fe mn and possibly cu were associated with low values of eh indicating the possible dissolution of oxy hydroxides of fe and mn the mobility of metals in the column experiments show the release of al fe mn cr cu ni v and zn in significant concentrations but below the detected values in groundwater however as cd sb se pb and au are generally mobilized in concentrations above the detected values in groundwater the possible mass transfer processes that could explain the presence of the contaminants in the aquifer and the leachates was simulated with the phreeqc numerical code and revealed the possible dissolution of the following mineral phases jarosite natrojarosite arsenian pyrite alunite chlorite kaolinite and calcite

hydrochemistry mineralogy and chemical fractionation of mine and processing wastes associated with porphyry copper mines a case study from the sarcheshmeh mine se iran abstract the sarcheshmeh is one of the largest oligo miocene porphyry cu deposits in the world comparative hydrochemical mineralogical and chemical fractionation associated with mining efflorescence salts and processing wastes of this mine are discussed hydrochemical results showed that rock waste dumps reject wastes and old impoundments of tailings are the main sources of acid mine drainage waters amd that contain potentially toxic metals such as cd co cu mn ni and zn as well as al episodic fluxes of highly contaminated acidic waters were produced in a tailings dam over a short period of time secondary soluble minerals provide important controls on the quality of amd produced especially in old dry tailings impoundments secondary sulfate minerals such as gypsum magnesiocopiapite hydronium jarosite kornelite and coquimbite were found in rock waste drainages and in old weathered reject wastes highly soluble secondary minerals such as gypsum eriochalcite and bonattite are also observed in an evaporative layer on old tailings impoundments chemical fractionation patterns of potentially toxic elements showed that the geochemical behavior of metals is primarily controlled by the mineralogical composition of waste samples elements such as co cr cu mn ni and zn are readily released into the water soluble fraction from efflorescence salts associated with rock waste drainages as well as from the evaporative layer of old tailings potentially toxic elements such as as mo and pb are principally adsorbed or co precipitated with amorphous and crystalline fe oxides but they may also be associated with oxidizing primary sulfides and residual fractions following the development of the dammed tailings pond the secondary minerals were dissolved producing acidic waters contaminated by al 154 mg l 1 cu 150 mg l 1 cd 0 31 m gl 1 co 2 13 mg l 1 mn 73 7 mg l 1 ni 1 74 mg l 1 zn 20 3 mg l 1 and cl 1690 mg l 1 therefore the potential use of recycled water from the sarcheshmenh dammed tailings pond is diminished by the presence of corrosive ions like cl in highly acidic fluids that promote corrosion of pipes and pumps in the water recycling system

development of lattice preferred orientation in clinoamphiboles deformed under low pressure metamorphic conditions a sem ebsd study of metabasites from the aracena metamorphic belt sw spain the mechanical properties of the lower continental crust are intimately related to the rheology of calcic clinoamphibole naturally deformed clinoamphibole typically shows brittle behaviour under a wide range of deformation conditions whereas crystal plasticity is rarely observed in this study the microfabric of clinoamphiboles from metabasites deformed under low pressure medium to high temperature metamorphic conditions is presented amphiboles from all samples have developed lpo that can be attributed to different deformation mechanisms depending on deformation temperature fluid content structure and phase strength contrasts rigid body rotation of amphibole prisms within a weaker plagioclase matrix corresponds to metabasites deformed under medium deformation temperatures that show a weak layer structure and a high phase strength contrast between plagioclase and clinoamphibole lower temperatures and the presence of fluids mean that one of the studied rocks was affected also by dissolution precipitation creep and cataclastic flow in the final sample dislocation creep was accommodated by recovery and subgrain rotation dynamic recrystallization in monominerallic hornblende layers at higher temperatures which could be representative of the rheology of amphiboles in a lower continental crust at high temperature conditions

exhumation of ultrahigh pressure metamorphic oceanic crust from lago di cignana piemontese zone western alps the structural record in metabasites the metamorphic and deformational history of coesite bearing ultrahigh pressure metamorphic oceanic crust from lago di cignana valtoumanche western alps as recorded along the decompression and cooling path has been resolved to derive constraints on the physical state of the crust during exhumation the following history is proposed eclogites derived from pillow basalts were deformed by dislocation creep of pyroxene at a depth of more than 80 km in the stability field of coesite the deformation was progressively localised into shear bands over the first 40 km of subsequent exhumation the rocks remained essentially unmodified any deformation must have been localised beyond the limits of the present outcrop retrogression first in a closed system started without concomitant deformation at a depth of about 40 km and temperatures of 550 to 500 c subsequently the system size increased fluid infiltration focussed along tensile fractures is documented by the formation of veins vein shapes and orientations indicate high pore fluid pressures and low differential stress after cooling to about 350 450 c at depths of 12 to 18 km localised ductile deformation transformed the retrogressed eclogites into greenschists for that stage the microstructure of the quartz veins indicates deformation by dislocation creep at falling temperatures and increasing differential stress final cooling to below ca 300 c took place at depths of 7 to 12 km as indicated by the density of fluid inclusions later deformation in the brittle field cannot be correlated with the p t path

aspects of the distribution and movement of aluminium in the surface of the te kopia geothermal field taupo volcanic zone new zealand abstract the principal al bearing components of two surface quadrats in the central te kopia geothermal field are the atmosphere substrate 10 wt al in ignimbrite clay and protosoils 0 3 0 6 al wt in sinter vegetation 4 5 g al m 2 and waters 1 4 g g al in semi permanent acid surface waters 6 9 g g in acid pools 10 14 g g in post rain ephemeral streams and pools about 0 7 g ha a of al is received from the atmosphere water transports al in and out of each quadrat and distributes it between the different components during initial alteration of the parent ignimbrite by alkali chloride water in the deep reservoir al either remained within the quadrat boundaries or transfers out were balanced by contemporaneous gains subsequently alteration by acid sulfate fluids redistributes elements into new mineral assemblages but again with no net movement of al in or out of either quadrat the latest surface alteration event involves interaction of all the previously and variously altered rocks by steam gases and steam condensate a primary product of this process is transient hydrated al rich water soluble sulfate efflorescences whose persistence indicates a steady flux of al at the surface the magnitude of this flux depends on available moisture and the activities of h sio 4 4 so 2 4 and k such that variations in the rate of discharge of al alone may be used to detect changes in surface conditions as may result from exploitation of a geothermal field

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

efficient natural attenuation of acidic contaminants in a confined aquifer as the demand for energy grows steadily and fossil fuels are depleted gradually nuclear power will continue to play an important role in meeting energy needs in the future uranium as the fuel for nuclear power generation has experienced the increase in production in recent years acid in situ leach uranium mining is an effective and popular technique to extract uranium without exposure of workers to radioactive ore deposits despite this advantage this technique causes extremely high concentrations of contaminants in confined aquifers after mining is completed these contaminants will undergo natural attenuation while migrating downgradient with regional groundwater mounting concerns have been raised regarding widespread groundwater contamination due to concentrations of contaminants and lack of published studies for comparison in this study the fate of various contaminants was examined to infer the extent of natural attenuation in a confined aquifer in northwest china results indicate the efficiency of natural attenuation in the confined aquifer in addition the contaminant plume migrated much slower than regional groundwater the dual domain theory has been invoked to aid in the interpretation of the decoupling of the plume migration with the regional groundwater flow this study also implies that widespread contamination in confined aquifers is more likely to be caused by external factors e g mechanical failure human errors than post mining spreading of contaminants to be always safe strict monitoring schemes must still be established and operated

variable infiltration and river flooding resulting in changing groundwater quality a case study from central europe summary the changes in groundwater quality occurring in a buried valley aquifer following a reduction in groundwater exploitation and enhanced infiltration due to extensive flooding of the odra river in 1997 were investigated long time series data for the chemical composition of groundwater in a large well field for drinking water supply indicated the deterioration of groundwater quality in the wells capturing water from the flooded area which had been intensively cultivated since the 1960s infiltration of flooded river water into the aquifer is suggested by an elevated chloride concentration although salt flushing from the rewatered unsaturated zone due to the enhanced recharge event is much more feasible concomitantly with chloride increases in the concentrations of sulphate ferrous iron manganese and nickel imply the oxidation of pyrite fes 2 which is abundant in the aquifer the proton production resulting from pyrite oxidation is buffered by the dissolution of calcite while the ca so 4 stoichiometry of the groundwater indicates that pyrite oxidation coupled with nitrate reduction is the dominant process occurring in the aquifer the pyritic origin of so 4 2 is confirmed by the sulphur isotopic composition the resultant fe 2 increase induces mn oxide dissolution and the mobilisation of ni 2 previously adsorbed to mn oxide surfaces the study has a major implication for groundwater quality prediction studies where there are considerable variations in water level associated with groundwater management and climate change issues

fabrics produced mimetically during static metamorphism in retrogressed eclogites from the zermatt saas zone western italian alps abstract lattice preferred orientations lpos are commonly interpreted to form by dislocation creep consequently they are used to infer deformation at the metamorphic grade at which the minerals were stable especially if those minerals show a shape fabric here we show that lpos can occur through mimicry of a pre existing lpo so they formed statically not during deformation omphacite and glaucophane lpos occur in eclogite facies rocks from the zermatt saas unit of the northwest italian alps barroisite grew during greenschist facies retrogression and has an lpo controlled significantly by the eclogite facies omphacite and glaucophane lpos rather than directly by deformation using spatially resolved lattice orientation data from the three key minerals collected using electron backscatter diffraction we deploy a new technique of interphase misorientation distribution analysis to prove this barroisite lpo develops by mimicry of omphacite via a particular lattice orientation relationship and by direct topotactic and epitactic replacement of glaucophane lpo in turn influenced anisotropic grain growth resulting in a barroisite grain shape fabric thus regional retrogression during exhumation of the zermatt saas high pressure rocks was in large part static rather than dynamic as previously interpreted in general the possibility of mimetic fabrics forming during metamorphic reactions must be borne in mind when interpreting direct structural observations and seismic anisotropy data in terms of deformation in both crust and mantle

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

modeling of water rock interactions in an aquitard of sandy clay in the coastal area near beihai china unconsolidated sand gravel and clay deposits near beihai and in the leizhou peninsula in southern china form an unconfined aquifer aquitard and a confined aquifer water and soil samples were collected from the two aquifers in the coastal beihai area for the determination of chemical compositions minerals and soluble ions hydrogeochemical modeling of three flow paths through the aquitard are carried out using phreeqc to determine water rock interactions along the flow paths the results indicate that the dissolution of anorthite fluorite halite rhodochrosite and co2 and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the unconfined aquifer to the confined aquifer cation exchanges between na and ca can also happen along the flow paths

ebsd measured lattice preferred orientations and seismic properties of eclogites we investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities alps norway mali and eastern china through the analysis of their microstructures and lattice preferred orientations lpo these samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions omphacite and garnet lpo were determined from electron backscatter diffraction ebsd technique garnet appears to be almost randomly oriented whereas omphacite develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 010 poles concentrated sub perpendicular to the foliation in order to analyze the deformation mechanisms that produced such omphacite lpo we compare our observations to lpo simulated by viscoplastic self consistent numerical models a good fit to the measured lpo is obtained for models in which the dominant slip systems are 1 2h110i 11 0 001 110 and 001 100 dominant activation of these slip systems is in agreement with tem studies of naturally deformed omphacite seismic properties of eclogite are calculated by combining the measured lpo and the single crystal elastic constants of omphacite and garnet although eclogite seismic anisotropies are very weak less than 3 for both p and s wave they are generally characterized by a maximum p wave velocity sub parallel to the lineation and by a minimum velocity approximately normal to foliation the mean p and s wave velocities are high respectively 8 6 and 4 9 km s the s wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation calculated reflection coefficients show that an eclogite crust interface is generally a good reflector rc 0 1 whereas an eclogite body embedded in the upper mantle would be hardly detectable

microstructural evolution during initial stages of static recovery and recrystallization new insights from in situ heating experiments combined with electron backscatter diffraction analysis we present in situ observations performed using electron backscatter diffraction of static recovery and recrystallization processes occurring in a plastically deformed geological material namely rocksalt static heating experiments carried out in a scanning electron microscope at temperatures of up to 450 c allowed direct detailed observations of grain boundary migration between substructured grains in deformed polycrystalline samples contrary to expectations crystallographic orientation maps reveal that behind slowly migrating grain boundaries new subgrain boundaries form while pre existing subgrain boundaries are sometimes inherited moreover the crystallographic character especially the preferred orientation of misorientation axes of the new substructures reflects the character of the previous deformation history these results imply that substructural features such as subgrain misorientation distributions may be relatively robust indicators of deformation mechanisms and conditions even in tectonites that have undergone late static recrystallization in addition our observations suggest that the process of static grain boundary migration does not necessarily reset earlier deformation microstructures as commonly assumed the kinematic observations of boundary migrations are inconsistent with simple models in which migration is achieved by single atoms jumping across the boundary

some factors affecting tds and ph values in groundwater of the beihai coastal area in southern guangxi china groundwater of low total dissolved solids tds of 10 mg l and low ph ranging commonly from 4 0 to 7 0 occurs in the unconsolidated unconfined and confined aquifers in the coastal plain near beihai guangxi china minerals in the unconsolidated sediment of quaternary are predominated by quartz more than 50 with small amount of clay minerals such as kaolinite illite and chlorite sio2 accounts for most more than 70 of the chemical compositions of the sediments the sediments contain low concentrations of soluble constituents below 300 g g and are predominated by so4 abundant recharge from low tds precipitation and a long time s dissolution of the unconsolidated sediments containing small amount of soluble compositions lead to low tds of the groundwater in the area

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

cation ordering in omphacite and effect on deformation mechanism and lattice preferred orientation lpo we present microstructural data and lattice preferred orientations lpos of omphacites from a suite of eclogites from the adula cima lunga nappe central alps our work shows a surprisingly strong correlation between the measured lpo and the ordering state of cations in omphacite estimates of deformation temperature from metamorphic petrology together with measured omphacite compositions and lpos determine the field ordering state on the omphacite phase diagram into which each sample falls lpos dominated by l type and s type signatures are developed in samples that fall in the p2 n field ordered structure and c2 c field disordered structure respectively dislocations with b 1 2 110 or b 001 are observed in the transmission electron microscope tem in all samples the former change from a perfect dislocation in the c2 c structure to a partial in p2 n any movement of a partial dislocation requires the formation or growth of a stacking fault furthermore in order to pass an obstacle a partial dislocation has to constrict to a unit dislocation the energy to form a constriction is high in omphacite due to the large separation width thus the activity of the b 1 2 110 dislocation is hindered in the p2 n structure relative to the c2 c structure which change the balance between the two and might give rise to the different lpos

the geometry and timing of orogenic extension an example from the western italian alps contacts between rocks recording large differences in metamorphic grade are indicative of major tectonic displacements low p upon high p contacts are commonly interpreted as extensional i e material points on either side of the contact moved apart relative to the palaeo horizontal but dating of deformation and metamorphism is essential in testing such models in the western alps the piemonte ophiolite consists of eclogites t 550 600 c and p 18 20 kbar structurally beneath greenschist facies rocks t 400 c and p 9 kbar mapping shows that the latter form a kilometre wide shear zone the gressoney shear zone gsz dominated by top se movement related to crustal extension rb sr data from micas within different gsz fabrics which dynamically recrystallized below their blocking temperature are interpreted as deformation ages ages from different samples within the same fabric are reproducible and are consistent with the relative chronology derived from mapping they show that the gsz had an extensional deformation history over a period of c 9 myr between c 45 36 ma this overlaps in time with the eclogite facies metamorphism the gsz operated over the entire period during which the footwall evolved from eclogite to greenschist facies and was therefore responsible for eclogite exhumation the discrete contact zone between eclogite and greenschist facies rocks is the last active part of the gsz and truncates greenschist facies folds in the footwall these final movements were therefore not a major component of eclogite exhumation pressure estimates associated with old and young fabrics within the gsz are comparable indicating that during extensional deformation there was no significant unroofing of the hangingwall since there are no known extensional structures younger than 36 ma at higher levels in this part of the alps exhumation since the final juxtaposition of the two units at 36 ma seems to have been dominated by erosion key words deformation age eclogite exhumation rb sr dating tectonic

textural evolution of plagioclase feldspar across a shear zone implications for deformation mechanism and rock strength caledonian amphibolite facies shear zones developed in granulitefacies anorthosites and anorthositic gabbros of the bergen arcs western norway allow a detailed study of the relationships between fluid infiltration mineral reactions the evolution of microstructure and deformation mechanisms a sequence of rocks from the relatively pristine granulites into a shear zone has been studied by optical microscopy electron microprobe microanalysis empa scanning electron microscopy sem electron backscatter diffraction ebsd and transmission electron microscopy tem focusing on the progressive development of microstructure in the plagioclase feldspars leading up to their deformation in the shear zone at the outcrop scale fluid infiltration into the granulites is marked by a distinct colour change in the plagioclase from lilac brown to white this is associated with the breakdown of the intermediate composition plagioclase an50 in the granulite to a complex intergrowth of na rich and ca rich domains ebsd analysis shows that this intergrowth retains the crystallographic orientation of the parent feldspar but that the ca rich domains contain low angle grain boundaries within the shear zone this complex intergrowth coarsens by grain boundary migration annihilating these grain boundaries but retaining the na rich and ca rich zoning pattern analysis of nearestneighbour misorientations of feldspar grains in the shear zone demonstrates that local crystallographic preferred orientation cpo is inherited from the parent granulite grain orientations random pair misorientation angle distributions show that there is no cpo in the shear zone as a whole nor is there significant shape preferred orientation spo in single grains these observations are interpreted in terms of fluid induced weakening and deformation by dissolution precipitation pressure solution creep

high pressure metamorphism of the zermatt saas ophiolite zone switzerland within the zermatt saas ophiolite zone of the western alps a record of polystadial high pressure metamorphism is well preserved early blueschist assemblages retained as inclusions in garnets were succeeded by eclogitic assemblages which in some rocks contained lawsonite kyanite talc and chloritoid these eclogitic assemblages formed by prograde reaction from the early blueschists subsequently reaction of these eclogites with a mixed h 2 o co 2 vapour phase led to the replacement of kyanite by paragonite and the partial replacement of omphacite garnet paragenses by assemblages containing glaucophane paragonite and ankerite high pressure eo alpine metamorphism took place under conditions of 550 600 c and 17 5 20 kbar values of a h 2 o between 0 55 and 1 are high enough to accommodate equilibration with a water rich vapour phase under the highest grade conditions the presence of such a fluid phase is locally indicated by the presence of quartz rich veins containing omphacite and kyanite this vapour phase was absorbed during retrogression later rehydration is limited to areas close to albite veins tectonic contacts and bodies of metasediment the metamorphic conditions determined for the zermatt saas zone are compatible with those suggested for over and under lying units these conditions and the p t path inferred by comparing the reaction histories with a petrogenetic grid for the system na 2 o cao mgo a1 2 o 3 sio 2 h 2 o suggest that metamorphism occurred during subduction to depths of between 60 and 70 km and subsequent exhumation during the alpine orogeny

temperature dependent grain boundary migration in deformed then annealed material observations from experimentally deformed synthetic rocksalt abstract grain boundary migration between strained substructured grains and newly appearing strain free grains has been observed during static in situ annealing of pre deformed rocksalt in the sem with increasing temperature t the migration velocity increases and the character of grain boundary migration changes as temperature increases there is an increase in the length of individual migrating boundary segments that move at similar rates in addition the frequency of migrating boundaries that form traces of a 100 boundary plane of at least one of the crystals involved increases and moving grain boundaries between new and old grains change from highly irregular to smooth straight boundaries at the same time there is a decrease in the influence of the substructure of pre existing strained grains on the grain boundary movement resultant microstructures reflect these changes at 325 350 c the deformed then annealed microstructure is characterized by very irregular grain boundaries a high abundance of 5 50 m scale remnants of old substructured grains within new grains giving a poikilitic microstructure at 350 400 c grain boundaries often exhibit elongate embayments into the strained grains and most remnants of old strained grains are located at former grain boundaries at 400 c grain boundaries between new and old strained grains are straight to smoothly curved the grain boundary velocity observations are explained by the effect of temperature on mobility coupled with local driving force variations additionally at low annealing temperature impurity solute drag and driving force variations are influential while at high temperature the anisotropy in grain boundary energy with crystallographic orientation becomes more important transferring the knowledge from our experiments to geological samples enables us to recognize and interpret similar microstructures in rocks thereby making it is possible to relate microstructural characteristics to the pre annealing and post deformational annealing history

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

rapid exhumation of the zermatt saas ophiolite deduced from high precision smnd and rbsr geochronology sm nd isotope data from garnets in ultrahigh pressure coesite bearing eclogite from the western alps were obtained to determine the age of peak metamorphism and exhumation rates of deeply buried oceanic crust in the zermatt saas ophiolite complex we report an exceptionally well constrained sm nd isochron age of 40 62 6 ma from the lago di cignana eclogite difficulties in dating alpine eclogites using this method were overcome by using an hf acid leaching procedure on garnet to remove mineral inclusions the zermatt saas rocks reached greenschist facies conditions around 38 2m a on the basis of rb sr whole rock phengite isochrons these data combined with existing estimates of the pressure and temperature conditions of the eclogite give an estimate for the initial exhumation rate of 10 to 26 km m y depending on the inferred pressure for the recrystallization of phengite followed by slow exhumation of 0 3 km m y from 34 to 14 ma the initial exhumation rates at lago di cignana are among the highest yet determined for high pressure terranes and are well constrained because the age has been determined directly on the high pressure assemblage the rapid exhumation rates presented here place critical constraints on collisional tectonic models 1999 elsevier science b v all rights reserved

major element geochemistry of recent sediments from the flaje basin krusne hory erzgebirge czech republic abstract the weathering products of the granitic rocks which are poor in base cations and their sediments in the flaje basin in an environment that is strongly influenced by so2 and nox emissions have been studied high deposition of so2 and consequent acidification of the environment causes further depletion of base cations mobilisation of al and modification of the weathering reactions resulting in changes of the geochemical features of recent sediments depletion of the bottom sediments of the flaje basin in base cations and al and their enrichment in si compared to the fresh stream sediments and eluvium suggests a mineralogical modification of the weathering product due to prolonged contact with basin water depletion of the non silicate phase of the sediment in base cations which are replaced with al on the other hand appears to be more effective in eluvium and those sediments which are exposed directly to the effect of acid deposition i e which are not below water level for the major part of the year the water of the basin appears to be the main factor influencing the composition of the recent sediments of the basin in the acidified catchment

amphibole fabric formation during diffusion creep and the rheology of shear zones we conducted experiments to examine the effect of amphibole forming hydration reactions on mineral fabric development and the strength of mafic rocks both hydrostatic and general shear deformation experiments were conducted on powdered basalt with added water at lower continental crust conditions 800 c 1 gpa amphibole that formed under hydrostatic conditions exhibits a random lattice preferred orientation lpo in contrast amphibole formed during deformation exhibits both a strong shape preferred orientation spo and lpo with a 001 maximum aligned subparallel to the shear direction plagioclase in both hydrostatic and deformed samples shows a very weak to random lpo at low effective strain rates 10 5 s 1 to 10 6 s 1 the stress exponent is 1 1 5 consistent with deformation accommodated by diffusion creep the correlation of the spo and lpo coupled with the rheological evidence for diffusion creep indicates that the amphibole fabric results from oriented grain growth and rigid grain rotation during deformation the experimentally produced fabrics are strikingly similar to those observed in amphibolite grade natural shear zones supporting interpretations that such rocks deform by diffusion creep in addition the rheology of the fine grained experimental amphibolite is comparable to that predicted using flow laws for wet anorthite thus both our experiments and field analyses indicate that wet plagioclase rheology provides a good constraint on the strength of hydrated lower crust

mobilization of ag heavy metals and eu from the waste deposit of the las herrerias mine almeria se spain we studied the mobility of silver heavy metals and europium in waste from the las herrerias mine in almeria se spain the most abundant primary mineral phases in the mine wastes are hematite hydrohematite barite quartz muscovite anorthite calcite and phillipsite the minor phase consisted of primary minerals including ankerite cinnabar digenite magnesite stannite siderite and jamesonite and secondary minerals such as glauberite szomolnokite thenardite and uklonscovite the soils show high concentrations of ag mean 21 6 mg kg 1 ba mean 2 5 fe mean 114 000 mg kg 1 sb mean 342 5 mg kg 1 pb mean 1 229 8 mg kg 1 zn mean 493 mg kg 1 mn mean 4 321 1 mg kg 1 cd mean 1 2 mg kg 1 and eu mean 4 0 mg kg 1 the column experiments showed mobilization of ag al ba cu cd eu fe mn ni sb pb and zn and the inverse modelling showed that the dissolution of hematite hausmannite pyrolusite and anglesite can largely account for the mobilization of fe mn and pb in the leaching experiment the mobility of silver may be caused by the presence of kongsbergite and chlorargyrite in the waste while the mobility of eu seems to be determined by eu oh 3 which controls the solubility of eu in the ph eh conditions of the experiments the mineralogy ph eh and geochemical composition of the mine wastes may explain the possible mobilization of heavy metals and metalloids however the absence of contaminants in the groundwater may be caused by the carbonate rich environment of host rocks that limits their mobility

microstructures deformation mechanisms and seismic properties of a palaeoproterozoic shear zone the mertz shear zone east antarctica abstract the mertz shear zone msz is a lithospheric scale structure that recorded mid crustal deformation during the 1 7 ga orogeny we performed a microstructural and crystallographic preferred orientation cpo study of samples from both mylonites and tectonic boudins that constitute relics of the terre adelie craton tac the deformation is highly accommodated in the msz by anastomosed shear bands which become more scattered elsewhere in the tac most of the msz amphibolite facies mylonites display similar cpo thermal conditions intensity of deformation and dominant shear strain preserved granulite facies boudins show both coaxial and non coaxial strains related to the previous 2 45 ga event this former deformation is more penetrative and less localized and shows a deformation gradient later affected by a major phase of recrystallization during retrogression at 2 42 ga both msz samples and granulite facies tectonic boudins present microstructures that reflect a variety of deformation mechanisms associated with the rock creep that induce contrasted cpo of minerals quartz feldspar biotite amphibole and orthopyroxene in particular we highlight the development of an uncommon cpo in orthopyroxene from weakly deformed samples characterized by 010 planes oriented parallel to the foliation plane 001 axes parallel to the stretching lineation and clustering of 100 axes near the y structural direction lastly we computed the seismic properties of the amphibolite and granulite facies rocks in the msz area in order to evaluate the contribution of the deformed intermediate and lower continental crust to the seismic anisotropy recorded above the msz our results reveal that i the low content of amphibole and biotite in the rock formations of the tac and ii the interactions between the cpo of the different mineralogical phases generate a seismically isotropic crust thus the seismic anisotropy recorded by the seismic stations of the tac including the msz must be due to mantle rather than crustal structures

deformation induced clinopyroxene fabrics from eclogites abstract clinopyroxene omphacite microfabric studies in eclogites are useful in characterizing the deformation that has affected deeper parts of subduction zones we present the microfabrics and tem structures of four samples representative of the various deformation types known in eclogites the 001 axis tends to be parallel to the lineation while the 010 plane is close to the foliation but these general features undergo strong variations in relation to the shape fabric in strongly lineated samples 010 tends to be spread out in a great circle normal to the lineation whereas 001 is dispersed in the foliation in the case of strongly foliated samples the slip systems identified by tem are 001 100 001 110 and 1 2 110 110 operation of dislocation creep is testified by the presence of dislocations and dislocation walls but this process alone cannot explain all the observed features particularly some aspects of the crystallographic preferred orientation hence other deformation mechanisms must be involved these may be dynamic migration recrystallization by grain boundary migration as well as mass transfer processes this study illustrates that not every crystallographic mineral preferred orientation can be explained by dislocation glide and or twinning processes alone in addition it also demonstrates that eclogite microfabrics can be used to unravel deformation parameters in subduction and or collision zones

redistribution of trace metals in a mineralized spodosol due to weathering liikavaara northern sweden the till east of the liikavaara ostra ore deposit in northern sweden is in some parts rich in cu and other sulphide associated metals groundwater flowing in this till has higher concentrations of cu than groundwater in a reference area where the till has low concentrations of cu and other metals to understand the processes that release metals from the mineralized till at liikavaara into the groundwater the authors performed a detailed study of the 2 mm fraction of a till profile where the highest metal concentrations in the liikavaara area occur the geochemistry and mineralogy of the till were determined and the soil water was sampled by tension lysimeters the importance of local diffusion of cu bearing airborne dust from the adjacent aitik mine tailings impoundment was quantified and solid speciation of metals in airborne material was performed by sequential extraction the results from liikavaara were compared to results from the reference area glacial ice picked up sulphide rich material from the liikavaara ostra cu ore during its flow this material was deposited in the till east of the ore body when the ice melted the sulphides have been dissolved in the 2 mm fraction during 8 7 ka of weathering since the glacial ice retreated after dissolution of the sulphides cu was redistributed and secondarily retained in association with fe oxyhydroxides and altered biotite other sulphide associated elements such as co ni and zn show the same pattern in the till profile as cu though the concentrations are much lower uptake of cu2 in the biotite through ion exchange with k may be an important mechanism for cu enrichment in biotite at liikavaara the airborne dust is not the source of cu in the till although the soil water at liikavaara has higher concentrations of cu and other metals than the soil water at the reference area the cu concentration is too low for infiltrating soil water to explain the high cu concentrations observed in groundwater the high metal concentrations in the till of cu in particular cause the increased concentrations in the local groundwater a fluctuating groundwater table washes out cu and other metals from the till it is possible that increased cu concentration in the local groundwater is caused by dissolved organic complexes or by colloids 0 45 m rich in organic matter and or fe oxyhydroxides

does cation ordering in omphacite influence development of lattice preferred orientation three mantle eclogite xenoliths from the robert victor mine in south africa were studied the calculated pt conditions are ps4 5 gpa and t between 950 and 1145 8c the clinopyroxene has a jadeite component between 0 19 and 0 52 in situ at these compositions and temperatures clinopyroxene omphacite has the high temperature c2 c structure which has perfect cation disordering the lattice preferred orientation lpo of clinopyroxene in the samples of different microstructure and composition has been measured by ebsd the lpo for all three samples is characterized by a strong alignment of the 001 axes with the lineation typical of the l type or ls type patterns for omphacite these data disagree with a cation ordering model for dislocation slip which predicts a s type lpo pattern with the 001 axes forming a girdle in the foliation plane numerical simulation using the vpsc model has been undertaken to show the influence of the h110i 1 10 slip system on the lpo development in axially symmetric compression and extension and pure and simple shear the activity of the h110i 1 10 system should be very sensitive to changes in the cation ordering as the clinopyroxene goes towards the low temperature fully ordered p2 n structure increasing the critical resolved shear stress on this system from 1 to 10 resulted in a decrease of the slip activity of 80 but produced no significant changes to the lpo the most important slip systems for lpo development are 001 100 100 010 and 001 010 in all simulations the ls index is introduced to quantify the symmetry of omphacite lpo the index is based on the eigenvalues of the 010 and 001 pole figures and has a value of one for the end member l type zero for the end member s type and intermediate values for ls types the naturally deformed omphacite lpos have ls indexes of between 0 61 and 0 85 confirming they are ls types but closer to the l type end member in the vpsc models the s type end member develops in axially symmetric compression ls indexz0 whereas the l type end member develops in axially symmetric extension ls indexz1 in simple and pure shear the ls type fabric develops with ls index of between 0 55 and 0 60 the vpsc simulations show that the ls index is nearly constant with increasing strain for a constant macroscopic velocity gradient which prescribes the constant strain path we conclude that development of s and l type lpos in omphacite is controlled by the strain path and that the ls index is a useful quantitative indicator of fabric symmetry q 2005 elsevier ltd all rights reserved

3d seismic analysis of the coast shear zone in se alaska and western british columbia broadside analysis of accrete wide angle data abstract the multidisciplinary accrete project addresses the question of continental assemblage in southeast alaska and western british columbia by terrane accretion and magmatic addition the previous studies of this project yielded important information for understanding the structures across the coast shear zone csz and the formation of the csz and the coast mountains batholith cmb the present study extends these interpretations into pseudo 3 d by using two additional wide angle accrete seismic lines by analyzing the broadside wide angle data using a series of laterally homogeneous 2 d models we derive a lower resolution 3 d velocity model of the outboard terranes and constrain variations in crustal thickness across and along the csz models of the broadside data confirms major structural and compositional trends extend along strike to the northwest the key features are a a steep moho ramp only 15 km wide is coincident with the csz and divides thin 25 1 km crust to the west below the west vergent thrust belt wtb from thicker 31 1 km crust to the east below the cmb b low velocity mantle 7 7 7 9 km s extends beneath the entire study region indicating high crustal and upper mantle temperatures below the wtb and cmb and c the alexander terrane is characterized by strong mid crustal reflectivity and high lower crustal velocities that are consistent with gabbroic composition this study extends the earlier interpretation and implies that the ramp is indeed likely associated with transpressional tectonics and magmatic crustal addition east of the csz

coupling of oceanic and continental crust during eocene eclogite facies metamorphism evidence from the monte rosa nappe western alps high precision u pb geochronology of ru tile from quartz carbonate white mica rutile veins that are hosted within eclogite and schist of the monte rosa nappe western alps italy indicate that the monte rosa nappe was at eclogite facies metamorphic conditions at 42 6 0 6 ma the sample area indren glacier furgg zone dal piaz 2001 geology of the monte rosa massif historical review and personal comments smpm consists of eclogite boudins that are exposed inside a south plunging overturned synform within micaceous schist associated with the eclogite and schist are quartz carbonate white mica rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist intrusion of the veins at about 42 6 ma occurred at eclogite facies metamorphic conditions 480 570 c 1 3 1 4 gpa based on textural relations oxygen isotope thermometry and geothermobarometry the