a unifying framework for particle entrainment 1 a new framework is presented that describes the hydrodynamic entrainment of sediments the framework is derived from the general equations of particle stability and fluid motion and covers a wide range of scales from that of the individual particle to en masse entrainment at the scale of the stream reach particle entrainment is explicitly shown to be driven by the combination of instantaneous fluid stress and pressure gradients particle surface contact forces particle submerged weight and the weight and motion of particle associated fluid of these factors bed shear stresses across particle differences in pressures and fluxes of momentum and sediment bed characteristics are found to be key factors in particle entrainment the conventional shields entrainment parameter is shown to be applicable to averaged en masse entrainment by steady uniform 2 d flows this nondimensionalized bed shear stress at threshold is further demonstrated to be a function of interparticle forces and bed normal hydrodynamic forces and thereby sediment size and other fluid sediment and bed characteristics observed shields parameter dependencies are discussed the presented framework which includes all relevant particle and fluid characteristics and flow dynamics may aid understanding of entrainment mechanics the design and analysis of further studies of entrainment the design of parameterizations that lead to the solution of entrainment problems and numerical modeling of combined fluid and sediment dynamics

stable isotope geochemistry and phase equilibria of coesite bearing whiteschists dora maira massif western alps peak metamorphic temperatures for the coesite pyrope bearing whiteschists from the dora maira massif western alps were determined with oxygen isotope thermometry the 18o smow values of the quartz after coesite 18o 8 1 to 8 6 n 6 phengite 6 2 to 6 4 n 3 kyanite 6 1 n 2 garnet 5 5 to 5 8 n 9 ellenbergerite 6 3 n 1 and rutile 3 3 to 3 6 n 3 reflect isotopic equilibrium temperature estimates based on quartz garnet rutile fractionation are 700 750 c minimum pressures are 31 32 kb based on the pressure sensitive reaction pyrope coesite kyanite enstatite in order to stabilize pyrope and coesite by the temperature sensitive dehydration reaction talc kyanite pyrope coesite h2o the a h2o must be reduced to 0 4 0 75 at 700 750 c the reduced a h2o cannot be due to dilution by co2 as pyrope is not stable at x co2 0 02 t 750 c p 30 kb in the absence of a more exotic fluid diluent e g ch4 or n2 a melt phase is required granite solidus temperatures are 680 c 30 kb at a h2o 1 0 and are calculated to be 70 c higher at a h2o 0 7 consistent with this hypothesis kyanite jadeite quartz bands may represent a relict melt phase peak p t f h2o estimates for the whiteschist are 34 2 kb 700 750 c and 0 4 0 75 the oxygen isotope fractionation between quartz 18o 11 6 and garnet 18o 8 7 in the surrounding orthognesiss is identical to that in the coesitebearing unit suggesting that the two units shared a common final metamorphic history hydrogen isotope measurements were made on primary talc and phengite d smow 27 to 32 on secondary talc and chlorite rite after pyrope d 39 to 44 and on the surrounding biotite d 64 and phengite d 44 gneiss all phases appear to be in nearequilibrium the very high d values for the primary hydrous phases is consistent with an initial oceanicderived connate fluid source the fluid source for the retrograde talc chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization the similar d but dissimilar 18o values of the coesite bearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium but not oxygen isotope equilibrium the unusual hydrogen and oxygen isotope compositions of the coesite bearing unit can be explained as the result of metasomatism from slab derived fluids at depth

predicting incipient motion including the effect of turbulent pressure fluctuations in the bed 1 incipient motion of particles on a river bed can in principle be understood and predicted from a balance of the forces acting on the particles on a natural river bed the exposure of particles to the flow is variable the effect of exposure on the initiation of motion including the case of deep embedding is studied in this paper so far the turbulence induced lifting force has been derived exclusively from examinations of the surface flow the understanding of destabilization processes of the riverbed is improved when turbulence induced vertical pressure gradients in the upper sediment layer are included this is particularly important for particles that lie in the lee of larger ones an analytical solution for the critical shields parameter of spherical particles is found including the effects of pressure fluctuations in the bed macroscale flow structures average bed slope and shallow flow existing laboratory data designed to test the effect of exposure and roughness conditions are in excellent agreement with the new model

do critical stresses for incipient motion and erosion really exist the concept of critical stress for the initial motion of noncohesive sediment beds under turbulent flow conditions is reviewed observational definitions of incipient motion are many and not entirely compatible some laboratory flume observations of sediment movement suggest that no true threshold exists current understanding of turbulent fluid motion at a sediment bed suggests that some particle movement must occur at all nonzero time mean velocities a combined model for flume flow and sediment transport having no threshold is seen to explain features of data that have been previously used to support the threshold concept

lithium isotopes in island arc geothermal systems guadeloupe martinique french west indies and experimental approach abstract we report lithium li isotopic measurements in seawater derived waters that were discharged from geothermal wells thermal springs and sub marine springs located in volcanic island arc areas in guadeloupe the bouillante geothermal field and martinique lamentin plain and the diamant areas while li isotopic signatures of the geothermal fluids collected from deep reservoirs were found to be homogeneous for a given site the 7li signatures for each of these reservoirs were significantly different the first low temperature 25 250 c experiments of li isotope exchange during seawater basalt interaction confirmed that li isotopic exchange is strongly temperature dependent as previously inferred from natural studies li isotopic fractionation ranged from 19 4 solution solid at 25 c to 6 7 at 250 c these experiments demonstrated the importance of li isotopic fractionation during the formation of li bearing secondary minerals and allowed us to determine the following empirical relationship between isotopic fractionation and temperature solution solid 7847 t 8 093 application of experimental results and literature data to the bouillante area suggested that geothermal water was in equilibrium at 250 260 c it likely has a deep and large reservoir located in the upper sheeted dike complex of the oceanic crust just below the transition zone between andesite volcanic flows and the basaltic dikes the upper dike section from which li is extracted by hydrothermal fluids was characterized by light li isotopic values in the rocks indicating retention of 6li by the altered rocks for the lamentin and diamant areas the geothermal fluids appeared to be in equilibrium with reservoir volcano sedimentary rocks at 90 120 c and 180 c respectively further evidence for this argument is provided by the fact that only the na li thermometric relationship determined for sedimentary basins yielded temperature values in agreement with those measured or estimated for the reservoir fluids this suggests the importance of a sedimentary signature in these reservoir rocks altogether this study highlights that the use of li isotopic systematics is a powerful tool for characterizing the origin of geothermal waters as well as the nature of their reservoir rocks

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

the variability of critical shear stress friction angle and grain protrusion in water worked sediments the erodibility of a grain on a rough bed is controlled by among other factors its relative projection above the mean bed its exposure relative to upstream grains and its friction angle here we report direct measurements of friction angles grain projection and exposure and small scale topographic structure on a variety of water worked mixed grain sediment surfaces using a simple analytical model of the force balance on individual grains we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography the friction angle projection and exposure of single grain sizes vary widely from point to point within a given bed surface the variability within a single surface often exceeds the difference between the mean values of disparate surfaces as a result the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution rather than a single value on a given bed the crtitical shear stress distributions of different grain sizes have similar lower bounds but above their lower tails they diverge rapidly with smaller grains having substantially higher median critical shear stresses large numbers of fines trapp ed within pockets on the bed or shielded by upstream grains are effectively lost to the flow our calculations suggest that critical shear stress as conventionally measured is defined by the most erodible grains entrained during transient shear stress excursions associated with the turbulent flow this implies a physical basis for the indeterminacy of initial motion these observations suggest that transport rate shear stress relationships may be controlled in part by the increasing numbers of grains that become available for entrainment as mean shear stress increases they also suggest that bed textures and grain size distributions may be controlled within the constraints of an imposed shear stress and sediment supply regime by the influence of each size fraction on the erodibility of other grain sizes present on the bed

double averaging concept for rough bed open channel and overland flows theoretical background the goal of this paper is to discuss the spatial averaging concept in environmental hydraulics and develop it further by considering transport equations for fluid momentum passive substances and suspended sediments the averaging theorems the double averaged in time and in space fluid momentum equation and advection diffusion equations for a passive substance and suspended sediments are introduced and their limitations and applications for modeling rough bed flows experimental design and data interpretation are discussed the suggested equations differ from those considered in terrestrial canopy aerodynamics and porous media hydrodynamics by accounting for roughness mobility change in roughness density in space and time and particle settling effects for the case of suspended sediments we show that the form of the double averaged equations may depend on the type of decomposition of flow variables and that this difference may have important implications for modeling we also show that the suggested methodology offers better definitions for hydraulic characteristics variables and parameters such as flow uniformity flow two dimensionality and bed shear stress

channelized fluid flow and mass transfer along a rift related detachment fault eastern alps southeast switzerland remnants of a rift related low angle detachment system are spectacularly exposed in the continental err nappe and occur discontinuously in the underlying oceanic platta nappe in southeast switzerland rocks along the detachment fault exhibit systematic changes in mineralogy fabrics and structures that are related to deformation and hydration of granite to form cataclasite and subsequent gouge structural mineralogical and geochemical data indicate a continuous evolution of fluid flow and mass transfer along the detachment fault mass balance calculations together with stable isotope data suggest 1 an altered seawater source and local interaction with mantle rocks 2 limited fluid rock interaction and mass transfer during initial cataclasis at deeper crustal levels and temperatures of 150 to 200 c 3 increased fluid flux and mass transfer at slightly lower temperatures 100 150 c during gouge formation at shallower crustal levels and 4 strongly localized fluid rock interaction at low temperatures 65 80 c near the sea floor at a final stage of detachment faulting we propose a model in which seawater dominated fluids penetrated and locally interacted with mantle rocks before they were caught and channelized along large scale detachment faults flow direction is upward along the detachment from higher to lower temperatures suggesting that the driving force of fluid flow was thermal fluid convection associated with mantle exhumation our study suggests that this large scale detachment fault is a good analog for extensional structures along present day nonvolcanic rifted margins such structures along ocean continent transitions are important in controlling fluid pathways and mass transfer between mantle and continental crust

experimental evidence for diamond facies metamorphism in the dora maira massif the peak metamorphic conditions of subducted continental crust in the dora maira massif western alps have been revised by combining experimental results in the kcmash system with petrologic information from whiteschists textural observations in whiteschists suggest that the peak metamorphic assemblage garnet phengite kyanite coesite talc originates from the reaction kyanite talc garnet coesite liquid in the experimentally determined petrogenetic grid this reaction occurs above 45 kbar at 730 c at lower pressures talc reacts either to orthopyroxene and coesite or together with phengite to biotite coesite and kyanite the liberated liquid contains probably similar amounts of h2o and dissolved granitic components the composition of the liquid in the whiteschists at peak metamorphic conditions a major unknown in earlier studies was probably very similar to the liquid composition produced in the experiments therefore the experimentally determined petrogenetic grid represents a good model for the estimation of the peak metamorphic conditions in whiteschists experimentally determined si isopleths for phengite further constrain peak pressures to 43 kbar for the measured si 3 60 of phengite in the natural whiteschists all these data provide evidence that the whiteschists reached diamond facies conditions the fluid absent equilibrium 4 kyanite 3 celadonite 4 coesite 3 muscovite pyrope has been calibrated on the basis of garnet and phengite compositions in the experiments and serves as a geothermobarometer for ultra high pressure uhp metapelites for graphite bearing metapelites and kyanite phengite eclogites forming the country rocks of the whiteschists peak metamorphic pressures of about 44 3 kbar were calculated from this barometer for temperatures of 750 c estimated from garnet phengite thermometry therefore the whole ultra high pressure unit of the dora maira massif most likely experienced peak metamorphic conditions in the diamond stability field while graphite is common in the metapelites diamond has not been found so far the absence of metamorphic microdiamonds might be explained by the low temperature of metamorphism the absence of a free fluid phase in the metapelites and a short residence time in diamond facies conditions resulting in kinetic problems in the conversion of graphite to diamond

superzoned garnets in the coesite bearing brossasco isasca unit dora maira massif western alps and the origin of the whiteschists abstract rare centimeter sized superzoned garnets szgs were discovered in two coesite bearing whiteschists of the brossasco isasca unit biu southern dora maira massif dmm western alps the superzoned garnet consists of a reddish brown almandine core crowded with inclusions of staurolite chloritoid kyanite chlorite and paragonite and of a pinkish pyrope rim with sporadic inclusions of kyanite and magnesian chlorite the core rim contact is relatively sharp and marks the termination of the inclusion rich portion the core composition of the superzoned garnet is almost identical to or slightly richer in mg than that of the rim of porphyroblastic garnet in metapelites from the same unit in the rim of the superzoned garnet mg fe ratio increases abruptly towards the outermost rim whose composition is identical to that of the common pyrope in the whiteschist at the core rim boundary there is no chemical gap chloritoid and staurolite are common inclusions in the core of the superzoned garnet in the whiteschist and in the porphyroblastic garnet in the metapelite the staurolite composition si 2 00 and total r 2 grt cld chl the resulting petrogenetic grid suggests that the core of the superzoned garnet contains incompatible assemblages such as st cld chl vs cld chl ky new and literature data and results of experiments in the kfash system suggest that 1 the superzoned garnet was formed under a single prograde high pressure ultra high pressure hp uhp alpine metamorphism 2 the almandine inclusion rich core of the superzoned garnet crystallized at disequilibrium in a pelitic composition system at around 600 c and less than 16 kbar probably from a former metapelite xenolith included in a variscan granitoid and 3 the chemical environment of the host rock suddenly changed from the normal pelite to the whiteschist composition by a metasomatic process during the rim growth i e at a stage close to the uhp climax

lithium isotopes in global mid ocean ridge basalts abstract the lithium isotope compositions of 30 well characterized samples of glassy lavas from the three major mid ocean ridge segments of the world spanning a wide range in radiogenic isotope and elemental content and sea floor physical parameters have been measured the overall data set shows a significant range in 7li 1 6 to 5 6 with no global correlation between li isotopes and other geochemical or tectonic parameters the samples with the greatest lithophile element depletion n morb k2o tio2

behavior of li and its isotopes during serpentinization of oceanic peridotites analyses of li and li isotopes in serpentinized peridotites have been performed using thermo ionisation mass spectrometry tims and secondary ion mass spectrometry sims techniques on samples collected from the southwest indian ridge swir in the bulk samples li concentrations range from 0 6 to 8 2 ppm while whole rock 6li values range from 2 9 to 14 in situ analyses display a greater range in both li concentration 0 1 19 5 ppm and li isotopic composition 27 to 19 with the serpentinized portions having higher li concentrations than the associated relict phases these variations may reflect changes in li partitioning and isotopic fractionation between serpentine and fluid with temperature and water rock ratio they may also be explained by changes in the composition of the serpentinizing fluid over the course of serpentinization as the serpentine forms by interaction with a circulating fluid it preferentially removes 6li causing the li in the fluid to become isotopically heavier the isotopic composition of the initial hydrothermal fluid is dominated by basalt derived li which easily overwhelms the very low li content originally present in seawater as this fluid circulates through ultramafic rocks it induces the formation of serpentine that incorporates this mantle derived li hence li in serpentine is mainly derived from oceanic crust rather than from seawater and serpentinization involves li recycling within this crust consequently li isotopes are good tracers of the hydrothermal contribution in serpentinizing fluid these results imply that serpentinized peridotites are probably only a minor sink of oceanic li

mg metasomatism of metagranitoids from the alps genesis and possible tectonic scenarios terra nova 24 423 436 2012 abstract mg metasomatic rocks e g whiteschists leucophyllites derived from post variscan granitoids are common in the alps previously reported field petrological geochemical and fluid inclusion data are combined to trace the genetic processes and the associated tectonic scenarios many common features can be recognised in all of the continental mg metasomatic rocks indicating that the genetic process is likely common in the entire range of the alps this process assumes highly channelised fluids derived from ultramafic rocks previously interacting with seawater that infiltrated the continental crust along strain zones and produced chromatographic fractionation of major and trace elements three tectonic scenarios involving distinct mantle sources are proposed rift related ocean continent transition continental subduction and continent continent collision all these data suggest that the mg metasomatism was diachronous and occurred at different structural levels during the alpine history

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

lithium and its isotopes as tracers of subduction zone fluids and metasomatic processes evidence from the catalina schist california usa abstract the catalina schist well studied for its tectonometamorphic history and geochemical evolution provides a field area in which to evaluate the extent of li mobility in subduction zone fluids and the degree to which li isotopes can trace metamorphic fluid rock interactions a suite of 63 samples of the catalina schist that represent a range of metamorphic grades and diverse lithologies was analyzed for li concentration and isotope composition metasedimentary rocks show no evidence for significant loss of li with increasing metamorphic grade despite the wide range of prograde p t histories represented by the five tectonometamorphic units with the highest grade rocks having experienced peak temperatures near 750 c metamafic rocks similarly show no change in li concentration as a function of grade that can be directly related to varying degrees of devolatilization the li concentrations and 7 li of metasedimentary rocks appear to best correlate with a chemical alteration index that likely reflects differential extents of weathering in the sediment sources the 7 li of most metamafic rocks including gabbroic metaconglomerate cobbles veins and melange matrix reflects overprinting of the li isotope compositions derived through transfer of li in fluids from sedimentary lithologies in the same tectonometamorphic units thus it appears that li was mobilized in fluids released from metasedimentary rocks but that the loss was insufficient to affect the bulk 7 li and li content of the metasedimentary rocks veins and melange matrix have the highest li concentrations of all samples analyzed ranging up to 70 ppm some veins and amphibolite grade mafic rocks have low 7 li suggestive of li diffusion through an intergranular fluid taken together these observations suggest mobilization of li during high pressure temperature p t fluid rock interactions that also resulted in enrichments in b n and some large ion lithophile elements k rb cs ba in the veins melange matrix and cobbles this study demonstrates that although li is mobile in high p t metamorphic fluids it does not partition into fluids to the extent demonstrated for n b and cs the latter elements showing large depletions in the higher grade catalina schist metasedimentary rocks thus even in relatively warm subduction zones deeply subducted metasedimentary rocks are expected to largely retain their li inventory to depths of at least 40 km the maximum depth at which units of the catalina schist experienced peak metamorphism

mg metasomatism and formation conditions of mg chlorite muscovite quartzphyllites leucophyllites of the eastern alps w hungary and their relations to alpine whiteschists the lower austroalpine orthogneiss micachist complex of the sopron fertorakos area of w hungary contains mg chlorite muscovite quartzphyllites leuco phyllite and mg chlorite bearing kyanite quartzites whose chemical compositions differ greatly from their surrounding rocks formation of leucophyllites took place in shear zones and was associated with depletion in alkalies and iron and enrichment of magnesium and h2o mg zonation of relict igneous muscovites of leucophyllites and changes in the whole rock chemical compositions suggest mg metasomatism material gains and losses have been assessed using the composition volume relationship approach proceeding from metagranite through transition rocks to leucophyllites mgo h2o feo and alkalies show continuously increasing dispersion in isocon plots with mg enrichment even in sheared gneiss not in contact with leucophyllite the metasomatic processes that formed the mg rich rocks may be similar to those responsible for the formation of high pressure whiteschists in the central and western alps the geochemical characteristics of the dora maira whiteschists italy and their country gneisses are very similar to those of the sopron leucophyllites supporting the theory that mg metasomatism produced the whiteschist chemistry on the basis of oxygen isotope compositions of relict igneous muscovites the precursor granitic rock had a 18o value around 13 proving its crustal anatectic origin the leucophyllites have whole rock oxygen isotope compositions around 8 5 which is in conflict with the theory of an mg rich sedimentary protolith rather the low 18o values reflect fluid rock interaction with a low 18o fluid quartz mineral oxygen isotope fractionations yield a metamorphic temperature of 560 30 c which agrees with earlier estimates from mineral stabilities silicon contents of phengites correspond to a metamorphic pressure of 13 gpa at this temperature indicating eclogite facies metamorphism the fluids in equilibrium with leucophyllites had oxygen isotope compositions around 7 9 similar to those calculated for the ultrahigh pressure dora maira whiteschists 7 6 further supporting the genetic link between the leucophyllites and whiteschists hydrogen isotope compositions of mixed white mica chlorite samples from leucophyllites range from 40 to 35 correlating with chlorite contents the calculated endmember chlorite and white mica have d values of 30 and 40 respectively the similar d values of the white micas in leucophyllites gneisses and metagranites suggest an overall equilibration with respect to h isotopes the calculated d value of the fluid is approximately 0 suggesting a seawater origin this conclusion was also reached for the dora maira whiteschists a possible fluid source that satisfies both metasomatic and isotopic data is dehydration of hydrothermally altered oceanic crust the mafic ultramafic complex of the alpine penninic unit underlying the austroalpine nappes is a likely candidate the subduction and subsequent dehydration of the ophiolite series would supply the mg rich fluids whose migration brought about the metasomatic alteration of the overlying gneiss micaschist complexes

interactions between serpentinite devolatilization metasomatism and strike slip strain localization during deep crustal shearing in the eastern alps the greiner shear zone in the tauern window eastern alps changes from a zone of distributed dominantly sinistral shear in supracrustal rocks to a series of narrow gully forming dextral splays where it enters basement gneisses within these splays granodiorite is transformed into quartz poor biotite and or chlorite schists reflecting hydration removal of si ca and na and concentration of fe mg and al stable isotope analyses show a prominent increase in d and a decrease in 18o from granodiorite into the shear zones these changes indicate significant channelized flow of an externally derived low 18o high d fluid through the shear zones the shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the greiner zone and the stable isotope data support alteration via serpentinite derived fluid monazite in schist from one shear zone yields spot dates of 29 20 ma indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the alpine orogeny c 30 ma we suggest that alpine metamorphism of serpentinites released large amounts of high d low 18o si undersaturated fe mg saturated fluids that became channelized along prior zones of weakness in the granodiorite infiltration of this fluid facilitated growth of chlorite and biotite which in turn localized later dextral strain in the narrow splays via cleavage parallel slip this dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the eastern alps this study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis

may the shields theory be extended to cohesive and adhesive benthic sediments 1 a threshold criterion for incipient motion of cohesive adhesive sediments based on moment balance and dimensional considerations is here developed the criterion discriminates between single particles and flocs critical conditions and induces a modification to the traditional shields curve commonly adopted for noncohesive particles this modification is particularly effective for the smaller size particles but tending to vanish for the larger ones the proposed approach is validated on the basis of experiments performed on sediment cores sampled at different depths from seven lakes with different trophic conditions and organic matter content the incipient motion conditions are evaluated by means of an original procedure based on image analysis techniques which enables the entrainment between single particles and flocs to be distinguished the adhesion force which is mainly due to the biological activity at the sediment water interface is estimated following the proposed criterion and it is found to depend on the organic matter content in particular the cores sampled in the littoral photic zone are characterized by a bell shaped dependence between adhesion coefficient and organic matter content which is typical for indicators of biological activity of the littoral ecosystems

subelement form drag parameterization in rough bed flows spatial averaging of the reynolds averaged navier stokes equations gives the double averaged navier stokes equations for which boundary drag appears naturally and explicitly in momentum conservation equations increasing use of the double averaged equations e g for relating flows to three dimensional bed roughness for evaluation of profiles of flow stresses and velocities in ecologically significant regions below roughness tops and for modeling purposes requires parameterization of boundary drag at subelement scales based on seven flows over repeated square rib roughness and ten flows over repeated fixed simulated sand waves with measured velocities and bed pressures expressions for form drag coefficient cd f elevation below roughness top relative roughness submergence roughness steepness are obtained for each of the two dimensional roughness types using these equations form drag variation with elevation below roughness tops can be calculated using either the double average of the square

lithium abundance and isotope systematics of forearc serpentinites conical seamount mariana forearc insights into the mechanics of slab mantle exchange during subduction 1 variable lithium contents and contrasting li isotopic signatures are evident in the serpentininite muds and clasts extruded at conical seamount in the mariana forearc the muds have high li contents compared to mantle values 3 7 ppm and a mean 7li value of 6 the clasts are generally lower in li and 7li varies from 6 to 10 with higher 7li correlating broadly to higher lithium contents the diverse 7li in the serpentinite clasts suggests li exchanges between mantle rocks and evolving slab derived fluids from different depths producing a subarc mantle that is zoned in terms of li abundances and 7li mariana forearc li isotopic signatures reach values as high as those reported in mariana arc lavas but neither mariana lavas nor lavas from other mature arcs show the variability observed in the serpentinites although elevated serpentinite li contents indicate forearc releases of li large differences in 7li are not evident in the slab outputs at forearc versus arc depths in the marianas despite evidence for changes in other alkaline species e g ba sr k it is thus possible that the li sampled by mariana arc volcanoes is in large part li which was released in the forearc and transported in the mantle via convection to arc depths as has been proposed to explain b isotopic variations straub and layne 2002 the uniform 7li signatures observed in mature volcanic arcs tomascak et al 2002 are consistent with higher overall fluxes of slab fluids which generate larger melting anomalies including both modified and nonmodified mantle wedge domains high or low 7li in lavas from anomalous arcs e g panama tomascak et al 2000 may indicate that the volumes of mantle sampled in these magmatic events are smaller and thus more likely to reflect the signatures of hydrated plums e g allegre and turcotte 1986 phipps morgan and morgan 1999 with extremely high or low 7li

zircon geochemical constraints on the protolith nature and metasomatic process of the mg rich whiteschist from the western alps abstract the mg rich silicic crustal rocks characterized by high sio2 and mgo contents are widespread in the alps providing rare targets to investigate the origin of mg rich fluids in the continental subduction zone however it is a prerequisite to elucidate the protolith nature of such mg rich rocks including the possible alteration process experienced before the alpine metamorphism for this purpose we carried out a detailed study of trace elements o hf isotopes and u pb ages for zircons from the coesite bearing whiteschist and its country rock metagranite at dora maria in western alps the whiteschist is characterized by much higher mgo contents than the adjacent metagranite relict magmatic zircons from the two types of rocks give essentially the same u pb ages of 262 ma similar ree contents and patterns the same range of ehf t1 values from 6 4 to 2 8 and 18o values from mostly 9 to 11 these features provide compelling evidence that the whiteschist and metagranite share the same protolith i e the permian granite all the above geochemical compositions are consistent with the argument that the high mgo content of the whiteschist was acquired from high mg fluids from dehydration of the serpentinized peridotite at the slab mantle interface in the continental subduction channel the hypothesis of a pre alpine hydrothermal alteration of the granitic protolith to cause the mgo enrichment is not favorable zircon in the metagranite does not show any metamorphic overgrowth during the alpine orogeny in contrast to the extensive overgrowth of metamorphic rims at 35 ma in the whiteschist the metamorphic rims show relatively low ree contents with variably flattened hree patterns different from the relict magmatic zircons that exhibit relative high ree contents with steep hree patterns this difference suggests that the breakdown of hydrous minerals plays a crucial role in dictating mineral reactions for zircon growth during the continental subduction zone metamorphism this interpretation is also consistent with the local occurrence of garnet coronae along the grain margins of biotite in the metagranite therefore this study provides not only the constraints on the protolith nature and metasomatic process of mg rich whiteschist from the western alps but also insights into the role of metamorphic fluids in controlling mineral reactions for the metamorphic growth of both zircon and garnet in the continental subduction zone

experiments on particle turbulence interactions in the near wall region of an open channel flow implications for sediment transport a high speed video system was used to study the interaction between sediment particles and turbulence in the wall region of an open channel flow with both smooth and transitionally rough beds in smooth flows particles immersed within the viscous sublayer were seen to accumulate along low speed wall streaks apparently due to the presence of quasi streamwise vortices in the wall region larger particles did not tend to group along streaks however their velocity was observed to respond to the streaky structure of the flow velocity in the wall region in transitionally rough flows particle sorting was not observed coherent flow structures in the form of shear layers typically observed in the near wall region interacted with sediment particles lying on the channel bottom resulting in the particles being entrained into suspension although there has been some speculation that this process would not be effective in entraining particles totally immersed in the viscous sublayer the results obtained demonstrate the opposite the entrainment mechanism appears to be the same independent of the roughness condition of the bottom wall smooth or transitionally rough in the latter case however hiding effects tend to preclude the entrainment of particles with sizes finer than that of the roughness elements the analysis of particle velocity during entrainment shows that the streamwise component tends to be much smaller than the local mean flow velocity while the vertical component tends to be much larger than the local standard deviation of the vertical flow velocity fluctuations which would indicate that such particles are responding to rather extreme flow ejection events

flume study of the effect of relative depth on the incipient motion of coarse uniform sediments an experimental study of the incipient motion of coarse uniform sediments was undertaken in an 8 m long by 0 3 m wide tilting flume the concept of critical shear stress for the initial motion of streambeds has been linked to the probability of sediment entrainment through the intensity of sediment transport the experiments have revealed that critical flow conditions for uniform sediment motion are dependent not only on the grain size but also on the ratio of flow depth to grain diameter a revised shields diagram relating critical stress grain reynolds number and depth to grain size ratio has been derived this has implications for the calculation of sediment transport rates design of stable alluvial channels and physical hydraulic modeling

threshold for particle entrainment into suspension laboratory observations regarding the limit conditions for particle entrainment into suspension are presented a high speed video system was used to investigate conditions for the entrainment of sediment particles and glass beads lying over a smooth boundary as well as over a rough bed the results extend experimental conditions of previous studies towards finer particle sizes a criterion for the limit of entrainment into suspension is proposed which is a function of the ratio between the flow shear velocity and particle settling velocity observations indicate that particles totally immersed within the viscous sublayer can be entrained into suspension by the flow which contradicts the conclusions of previous researchers a theoretical analysis of the entrainment process within the viscous sublayer based on force balance considerations is used to show that this phenomenon is related to turbulent flow events of high instantaneous values of the reynolds stress in agreement with previous observations in the case of experiments with a rough bed a hiding effect was observed which tends to preclude the entrainment of particles finer than the roughness elements this implies that as the ratio between particle and roughness element sizes becomes smaller progressively higher bed shear stresses are required to entrain particles into suspension on the other hand an overexposure effect was also observed which indicates that a particle moving on a smooth bed is more prone to be entrained than the same particle moving on a bed formed by identical particles

critical shear stress of natural sediments the critical shear stress of individual fractions ci in unimodal and weakly bimodal sediments shows little variation with grain size and depends only on the mean grain size bf the mixture for strongly bimodal sediments ci increases with grain size an apparent result of a lateral segregation of the finer and coarser fractions on the bed surface that causes ci to deviate from size independence in the direction of unisize shields values a quantitative definition of mixture bimodality may be used to estimate the degree of mixture bimodality beyond which a substantial size dependence of ci is observed and to predict the variation of ci with grain size in bimodal sediments because properties of sediment grain size distributions other than bimodality appear to have little influence on ci the trends presented here for 14 unimodal and bimodal sediments may be quite general

lithium and lithium isotope profiles through the upper oceanic crust a study of seawater basalt exchange at odp sites 504b and 896a abstract ocean drilling program odp hole 504b near the costa rica rift is the deepest hole drilled in the ocean crust penetrating a volcanic section a transition zone and a sheeted dike complex the distribution of li and its isotopes through this 1 8 km section of oceanic crust reflects the varying conditions of seawater alteration with depth the upper volcanic rocks altered at low temperatures are enriched in li 5 6 27 3 ppm and have heavier isotopic compositions 7li 6 6 20 8 relative to fresh mid ocean ridge basalt morb due to uptake of seawater li into alteration clays the li content and isotopic compositions of the deeper volcanic rocks are similar to morb reflecting restricted seawater circulation in this section the transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization li enrichment in this zone is accompanied by relatively light isotopic compositions 0 8 2 1 which signify influence of basalt derived li during mineralization and alteration li decreases with depth to 0 6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high temperature reaction zone rocks in the dike complex have variable isotopic values that range from 1 7 to 7 9 depending on the extent of hydrothermal recrystallization and off axis low temperature alteration hydrothermally altered rocks are isotopically light because 6li is preferentially retained in greenschist and amphibolite facies minerals the 7li values of the highly altered rocks of the dike complex are complementary to those of high temperature mid ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage the inventory of li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of li in the ocean on balance the upper 1 8 km of oceanic crusts remains a sink for oceanic li the observations at 504b and an estimated flux from the underlying 0 5 km of gabbro suggest that the global hydrothermal flux is at most 8 109 mol yr compatible with geophysical thermal models this work defines the distribution of li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle

li and li isotopic composition of hydrothermally altered sediments at middle valley juan de fuca li and li isotopes have been measured in the clay fraction of sediments recovered from the middle valley hydrothermal site on the juan de fuca ridge the li content of pure detrital clays is 51 ppm while hydrothermal clays and carbonates have lower li 22 11 ppm however there is no clear relationship between the mineralogy of the hydrothermal alteration products and their li content the 7li value of the detrital clays is 5 8 hydrothermal clays and carbonates have 7li in the range of 3 9 to 7 8 these values do not seem to be dependent on the temperature at which they formed modelling of the li and li isotope systematics indicates that the fluid from which the alteration products form is significantly enriched in li higher than 10 000 mol kg 1 relative to pore fluids recovered from within the sediments up to 589 mol kg 1 wheat c g m j mottl 1994 data report trace metal composition of pore water from sites 855 through 858 middle valley juan de fuca ridge in mottl m j davis e e fisher a t slack j f eds proc odp sci res 139 749 755 and that this li is derived from sediment thus the alteration products are not in equilibrium with their conjugate pore fluids rather the alteration minerals formed at lower water sediment ratios this suggests that fluid flow pathways at middle valley were more diffuse in the past than they are today

diffusion driven extreme lithium isotopic fractionation in country rocks of the tin mountain pegmatite abstract lithium concentrations and isotopic compositions in the country rocks amphibolites and schists of the tin mountain pegmatite show systematic changes with distance to the contact both li and 7 li decrease dramatically along a 10 m traverse from the pegmatite into amphibolite with li concentration decreasing from 471 to 68 ppm and 7 li decreasing from 7 6 to 19 9 rubidium and cs also decrease from the pegmatite contact into the country rock but only within the first 2 m of the contact after which their concentrations remain constant neither mixing between pegmatite fluids and amphibolite nor li isotope fractionation by rayleigh distillation during fluid infiltration is a likely explanation of these observations due to the extremely light isotopic composition required for the amphibolite end member in the mixing model 7 li 20 and the similarly extreme isotopic fractionation required in a rayleigh distillation model rather these variations are likely due to isotopic fractionation accompanying li diffusion from the li rich pegmatite li 450 to 730 ppm into amphibolites li 20 ppm the fact that other alkali element concentrations vary only within 2 m of the contact reflects the orders of magnitude faster diffusion of li relative to heavier elements quartz mica schists in contact with the pegmatite also show large variations in both li and 7 li as a function of distance from contact 1 wt to 70 ppm and 10 8 to 18 6 respectively but over a longer distance of 30 m lithium concentrations of the schist decrease from 1 wt adjacent to the contact to 70 ppm 300 m from the contact the latter is a typical concentration in metapelites the nature of the 7 li variations in the schists is different than in the amphibolites schists within the first 2 m of the contact have nearly identical 7 li of 10 which mimics that of the estimated bulk pegmatite 8 to 11 at a distance of 30 m the 7 li reaches the lowest value in the schists of 18 6 similar to the lowest amphibolite measured at a distance of 300 m the 7 li climbs back to 2 5 which is within the range of 7 li of other schists in the region and metapelites worldwide the behavior of li in the schists can also be modeled by li diffusion with the effective diffusion coefficient in the schist being 10 times greater than that in the amphibolite the effective diffusion coefficients of li in the amphibolite and schist are 2 orders of magnitude greater that those in minerals which implicates the importance of fluid assisted grain boundary diffusion over solid state diffusion in transporting li through these rocks

lithium isotope evidence for light element decoupling in the panama subarc mantle the systematics of fluid mobile trace elements in arc lavas from panama relative to their li isotopic compositions provide unique evidence for the fertilization and subsequent differential extraction of mobile species from the subarc mantle calc alkaline lavas that crystallized between 20 and 5 ma old group that possess 7 li as high as 11 2 have low b be otherwise identical and similarly old calcalkaline lavas with high b be to 23 have mid ocean ridge basalt morb like 7 li 4 7 to 5 6 adakite lavas 3 ma young group possess 7 li from 1 4 to 4 2 and have consistently lower b be than old group lavas consistent with derivation from melting of a devolatilized morb slab if li and b had comparable fluid mobility in the subarc mantle then slab fluids would carry both high b concentrations and elevated 7 li signatures into arc sources and samples with the highest 7 li would also have the highest b be our data suggest that although both li and b are initially derived from the slab older 7 li signatures may be preserved in the mantle beneath arcs as a result regions of the lithospheric mantle will develop li isotope signatures that are heavier than typical morb mantle

lithium isotopic compositions of post collisional mafic ultramafic rocks from dabieshan china implications for recycling of deeply subducted continental crust abstract lithium li isotopes are potential tracers of processes related to crust mantle interaction and recycled crustal materials previous studies have reported that li isotopic compositions of island arc lavas are similar to those of fresh mid ocean ridge basalts morbs although the former are expected to record high slab derived 7li values caused by fluid metasomatism however it is unclear whether li isotopic signatures of subducted continental crust were transported to mantle depths and preserved there for clarification we determined whole rock major and trace element and li isotopic compositions of post collisional mafic ultramafic rocks from northern dabieshan china the analyzed samples have high mgo up to 20 67 wt and low sio2 41 06 56 20 wt contents and arc like trace element distribution patterns suggesting derivation by partial melting of fertile mantle sources the samples have 7li values of 2 9 to 7 2 average 2 7 n 42 and li concentrations of 2 50 to 28 1 g g average 9 20 g g both of which are beyond the relatively limited ranges of mantle values 7li 2 9 to 4 3 average 3 5 1 0 and li 1 20 0 10 g g excluding possible effects of wall rock assimilation and contamination magmatic crystallization and li isotopic fractionation during subduction exhumation processes the observed li isotopic heterogeneity is most likely related to the recycling of crustal materials based on a comparison with li isotopic compositions of ultrahigh pressure uhp metamorphic rocks from the dabie sulu orogenic belt and terrestrial sediments we suggest that the recycled continental crustal materials likely comprised gneisses sediments eclogites and or minor carbonate rocks i e marbles our study demonstrates that li isotopes may provide a novel means of tracing deeply subducted continental materials

limited lithium isotopic fractionation during progressive metamorphic dehydration in metapelites a case study from the onawa contact aureole maine the major trace element and li isotopic compositions of granodiorite and metapelites from the onawa pluton and surrounding contact aureole have been measured to document the behavior of li and its isotopes during progressive metamorphic dehydration major andtraceelementconcentrationsinmetapelitesofthecontactaureolechangelittle whilelossonignition loi decreaseswithincreasing metamorphic grade which ranges from regional chlorite zone metamorphism far removed from the pluton to partially melted rocks adjacent to the pluton lithium concentrations in metapelites from all zones correlate with loi and abundances of the main li bearing minerals chlorite biotite muscovite decreasing by a factor of two from 130 ppm far removed from the pluton to 64 ppm adjacent to thepluton incontrast liisotopiccompositionsremainrelativelyunchangedacrosstheaureole 7 li 3 5to 1 0 andarecomparable to the range observed in schists and unmetamorphosed shales compared to the surrounding metasediments the granodiorite has a lower li content 45 ppm and a comparable 7 li value of 0 2 similar to those of other granites and the average upper crust 0 2 these observations are consistent with the removal of li from metapelites via rayleigh distillation during progressive metamorphic dehydration with isotopic fractionation factors between fluids and rocks ranging between 1 001 and 1 004 these values are similar to thoseofarecentexperimentalstudyandproduceisotopicfractionationthatisbarelybeyondanalyticaluncertainty 1 fortheobserved degree ofli depletion the good correlationsbetweenli concentrations and loiwithmineralogicalabundancesreflecttheimportanceof mineralogyincontrollingliconcentrationsandisotopiccompositionsofmetamorphicrocks comparisonoftheseresultswiththosefrom a study of a contact halo around the tin mountain pegmatite suggests that the nature of the intrusion plays a critical role in controlling the behavior of li in country rocks large diffusive driven isotopic fractionation over a small scale is expected to occur when rocks are infiltrated by li rich magmatic fluids while metamorphic devolatilization results in minor isotopic fractionation on the aureole scale published by elsevier b v

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

lithium isotope fractionation during incongruent melting constraints from post collisional leucogranite and residual enclaves from bengbu uplift china abstract lithium li elemental and isotopic compositions of the jurassic jingshan leucogranites including garnet rich mafic enclaves and wall rock wuhe gneisses from the southeast margin of north china craton ncc were investigated to understand the behavior of li isotopes during post collisional magmatism the jingshan leucogranites have distinct u shape ree patterns with y and ree concentrations significantly lower yet sr y ratios higher than their presumed source rocks i e the dabie sulu gneisses trace element modeling of ree and sr y suggests these elemental signatures of the jingshan leucogranites can be consistently explained by a fluid present crustal incongruent partial melting bt qz pl h 2 o grt melt leaving mainly grt bt with minor allanite in the residuum the mafic enclaves show identical sr nd isotopic compositions with their host leucogranites contrasting with the wuhe gneiss and the exposed regional lower crust the garnet rich mafic enclaves are thus interpreted as entrained residual phases formed by this incongruent partial melting the jingshan leucogranites show relatively high 7 li values 4 0 to 9 0 and low li concentrations 4 7 11 3 ppm in comparison to published data for worldwide granites in contrast the residual enclaves show low 7 li values as low as 0 6 and high li concentrations as high as 118 ppm garnet separated from residual enclaves is characterized by a narrow range of low 7 li values 1 5 to 0 1 with high li concentrations from 32 9 to 81 7 ppm by contrast coexisting quartz shows relatively high 7 li values 15 0 to 16 6 with very low li concentrations 1 ppm biotite from both leucogranite and residual enclaves shows high li concentrations 195 382 ppm and relatively heavy li isotope compositions 3 2 to 7 5 the li elemental and isotopic signatures of the residual enclaves can be modeled as a grt bt rich residuum mixed with leucogranite melt in various proportions this work indicates that the li isotopic compositions for magmatic rocks that are derived from anatexis of mid to lower crustal gneisses may not be a faithful source indicator as commonly suggested

mg o isotopes trace the origin of mg rich fluids in the deeply subducted continental crust of western alps abstract fluids are important for mass transfer at the slab mantle interface in subduction zones however it is usually difficult to trace fluids from specific sources in a subducting slab especially those derived from dehydration of serpentinite coesite bearing whiteschist at dora maira in the western alps is characterized by strong mg enrichment relative to the country rocks which requires infiltration of mg rich fluids into the supracrustal rock in order to constrain the origin of such mg rich fluids we have performed an integrated study of whole rock mg and o isotopes zircon u pb ages and o isotopes for the whiteschist and related rocks zircons in the whiteschist show two groups of u pb ages at 262 ma and 34 ma respectively for relict and newly grown domains the permian u pb ages of relict magmatic domains are consistent with the protolith age of host metagranite suggesting that their common protolith is the permian granite the tertiary u pb ages occur in coesite bearing metamorphic domains consistent with the known age for ultrahigh pressure metamorphism the metamorphic domains have 18o values of 5 8 6 8 whereas the relict magmatic domains have high 18o values of 10 such high 18o values are also characteristic of the metagranite indicating that the whiteschist protolith underwent metasomatism by metamorphic fluids with low 18o value of 2 4 the whiteschist mostly has whole rock 26mg values of 0 07 to 0 72 considerably higher than country rock 26mg values of 0 54 to 0 11 thus the metamorphic fluids are not only rich in mg but also heavy in mg isotopes they were probably derived from the breakdown of mg rich hydrous minerals such as talc and antigorite in serpentinite at the slab mantle interface in the subduction channel therefore the dehydration of mantle wedge serpentinite during the subduction and exhumation of continental crust can provide the mg rich fluids responsible for the metasomatism of crustal rocks at subarc depths

uraniferous diagenetic xenotime in northern australia and its relationship to unconformity associated uranium mineralisation stratabound uraniferous diagenetic xenotime cements provide a minimum depositional age of 1 632 3 ma for the sedimentary birrindudu group in the killi killi hills tanami region in northern australia the age of xenotime formation is broadly coeval with that recently proposed 1 650 1 600 ma for uranium mineralisation in the unconformity associated deposits of the pine creek inlier northern australia and athabasca basin canada the geological setting and formation model for the uraniferous xenotime crystals are similar to those widely proposed for unconformity associated uranium deposits suggesting a genetic link between the two however xenotime formation in the birrindudu group occurred during an apparently earlier stage of diagenesis compared to late diagenetic formation of unconformity associated uranium deposits this could be explained by variations in the thickness of sediment cover and diachronous diagenesis across the basin at the time of the basin wide uranium mobilisation event herein dated at ca 1 630 ma in such a scenario stratabound uraniferous xenotime cements could represent the remote distal zones of a more deeply buried uranium mineralising system alternatively the xenotime layer represents a precursor to or a source for later unconformity associated ore deposition in this case the presence of diagenetic uraniferous xenotime in an area prospective for unconformity associated uranium mineralisation would be an indication of and still provide an approximate age for uranium mobilisation within the cover sequence xenotime is a far more robust mineral than uraninite for u pb geochronology and can potentially provide a more reliable and precise timeframe for uranium mineralisation and subsequent recrystallisation events if present in the immediate uranium ore environment

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

fluvial entrainment of protruding fractured rock fluvial entrainment of fractured rock assessed in terms of bed shear stress stream power and time averaged bed uplift pressures indicates that rock block stability reduces with increasing protrusion and decreasing surface length in the direction of flow with protrusion of only a nominal portion of the block required to significantly decrease block stability variations in block uplift pressure coefficient with normalized block protrusion and block surface length can be used to predict the height of a block of protrusion p and known surface lengths at the point of entrainment for an open channel flow of average depth h and velocity u alternatively entrainment of prismoidal particles of square section in plan by fully turbulent open channel flows of 100 can be predicted using c0 002 0 0015 pvb l 1 where c is the critical dimensionless shear stress is the grain reynolds number l is the particle upper surface side length and pvb is the particle protrusion relative to the virtual bed level at which the average flow velocity is zero approximately the tops of the supporting or surrounding particles for the present prismoidal blocks owing to the potential occurrence of cavitation on prototype block surfaces it is recommended that quantitative scaling of the present results be conservatively limited to prototype average velocities u of less than approximately 6 m s with scale ratios l 29 in contrast to existing practice particle protrusion needs to be accounted for when assessing the erodibility of a channel bed using stream power based methods such as the erodibility index method reported by annandale in 1995

lithium isotope fractionation between li bearing staurolite li mica and aqueous fluids an experimental study abstract we determined the lithium isotope fractionation between synthetic li staurolite and aqueous fluids containing excess licl or lioh at 3 5 gpa between 670 and 880 c and between li mica and similar fluids at 2 0 gpa and 300 to 500 c in all experiments for the system li staurolite fluid 7 li was weakly partitioned into li staurolite whereas for li mica fluid 7 li preferentially fractionated into the fluid the difference in the li isotope fractionation behaviour results from different li coordination in staurolite li 4 and mica li 6 for the system li mica fluid fractionation is about half as large along the same t range as for spodumene fluid wunder b meixner a romer r l heinrich w 2006 t dependent isotopic fractionation of lithium between clinopyroxene and high pressure hydrous fluids contrib mineral petrol 151 112 120 this behaviour is consistent with differences in the bonding strengths of the li octahedra in li mica and spodumene subduction and concomitant dehydration of metabasic oceanic crust containing chlorite and clinopyroxene with li in six fold coordination releases fluids enriched in li and 7 li into the fore arc and arc mantle and thus introduces a light li component into the deeper mantle ongoing dehydration and li loss along the subduction path produces fluids with increasingly lower li concentrations and lighter lithium isotope compositions however as staurolite is the most important carrier of li in metapelitic assemblages the inverse fractionation of li isotopes relative to fluids enables staurolite to transport high li concentrations in combination with an isotopic composition enriched in 7 li into the mantle thus depending on the li contents and li isotope signature of the protolite breakdown of li bearing staurolite at high p and t can release fluids with high li contents and isotopically heavy li into the deep mantle wedge

discrete particle modeling of entrainment from flat uniformly sized sediment beds the stability of randomly deposited sediment beds is examined using a discrete particle model in which individual grains are represented by spheres the results indicate that the threshold shear stress for flat beds consisting of cohesionless uniformly sized grains cannot be adequately described by a single valued parameter rather it is best represented by a distribution of values physically this result stems from the localized heterogeneity in the arrangement of surface grains for uniformly sized beds geometric similarity exists such that the critical entrainment shear stress distributions scale directly with grain size a shields parameter of 0 06 is commonly used to define threshold conditions and it was found that this corresponds to a point on the distributions where approximately 1 4 by weight of the surface is mobile furthermore the analysis includes a comparison of the contributions of sheltering to variation in critical entrainment shear stress it was found that remote sheltering ind

measurement of fluctuating pressures on coarse bed material bed protections are usually characterized by low mobility transport conditions and nonequilibrium turbulence profiles as the present knowledge of the influence of turbulence on stability of cover layer units is minimal an in depth investigation was undertaken regarding the influence of turbulence on the stability of rough granular beds detailed measurements of fluctuating pressures on a bed element are used to evaluate certain concepts that are often used in modeling the entrainment of bed material from hydraulically rough beds three pressure transducers are placed in a cube that is part of a rough granular bed under open channel flow and velocities are measured using laser doppler velocimetry the measurements show that the magnitude of the fluctuating pressure at a certain point of the cube is a function of the exposure relative to the stones upstream of the cube a quadrant analysis reveals that the drag force is not only directly dependent on the horizontal near bed velocity but on the vertical velocity as well further the effect of small scale eddies shedding from the stone during large scale increases of longitudinal velocity is shown the fact that large scale velocity fluctuations create a large part of the pressure or force variance indicates that downstream of a roughness transition these fluctuations have to be taken into account in order to evaluate the stability of the bed

stochastic incipient motion criterion for spheres under various bed packing conditions incipient motion criteria based solely on time averaged bed shear stress may underpredict sediment transport the focus of this study is on the stochastic aspect of the problem of incipient motion specifically the role of near bed turbulent structures and bed packing density on the commencement of sediment motion is investigated the cornerstone of the proposed model is based on the concept that the particle motion is governed by the intermittent nature of near bed turbulence based on this mechanism in this article we provide a quantitative model for predicting the commencement of sediment entrainment for the first time under three representative bed packing densities corresponding to the isolated wake interference and skimming flow regimes the performance of the proposed model is compared to published experimental data and the conventional approach that is based on the consideration that flow parameters are statistically well represented by a normal distribution

the effect of chrysotile nanotubes on the serpentine fluid li isotopic fractionation we determined the lithium isotope fractionation between synthetic li bearing serpentine phases lizardite chrysotile antigorite and aqueous fluid in the p t range 0 2 4 0 gpa 200 500 c for experiments in the systems lizardite fluid and antigorite fluid 7li preferentially partitioned into the fluid and 7li values followed the t dependent fractionation of li bearing mica fluid wunder et al 2007 by contrast for chrysotile fluid experiments 7li weakly partitioned into chrysotile this contrasting behavior might be due to different li environments in the three serpentine varieties in lizardite and antigorite lithium is sixfold coordinated whereas in chrysotile lithium is incorporated in two ways octahedrally and as li bearing water cluster filling the nanotube cores low temperature ir spectroscopic measurements of chrysotile showed significant amounts of water whose freezing point was suppressed due to the li contents and the confined geometry of the fluid within the tubes the small inverse li isotopic fractionation for chrysotile fluid results from intra crystalline li isotope fractionation of octahedral li 6 with preference to 6li and lithium within the channels li ch of chrysotile favoring 7li the nanotubes of chrysotile possibly serve as important carrier of li and perhaps also of other fluid mobile elements in serpentinized oceanic crust this might explain higher li abundances for low t chrysotile bearing serpentinites relative to high t serpentinites isotopically heavy li bearing fluids of chrysotile nanotubes could be released at relatively shallow depths during subduction prior to complete chrysotile reactions to form antigorite during further subduction fluids produced during breakdown of serpentine phases will be depleted in 7li this behavior might explain some of the li isotopic heterogeneities observed for serpentinized peridotites

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

35 ma old ultrahigh pressure metamorphism and evidence for very rapid exhumation in the dora maira massif western alps abstract ion microprobe shrimp data on zircons from various rock types of an ultrahigh pressure uhp metamorphic whiteschist type pyrope quartzite lens of the dora maira massif dmm consistently show domains giving a late eocene age of 35 4 1 0 ma which is taken as the age of uhp metamorphism these domains partially replace the older oscillatory zoning pattern of the zircons formed during primary magmatic crystallization at about 275 ma zircons of a metagranitic country rock next to the uhp metamorphic lens have these primary features best preserved all zircons measured also yield intermediate ages between 275 and 35 ma with a statistical concentration between 260 and 210 ma thus the uniformity of the initial zircon population both in the lens and the country rock evidences a common protolith that is a granite intruded during the late herynian while the intermediate ages are at least partly due to incomplete resetting of the zircons during uhp metamorphism those in the 260 210 ma range may be related to rifting episodes in the permotriassic the mg rich chemistry of the whiteschist lenses is due to local metasomatic alterations of the granite perhaps by fluids derived from evaporitic sediments dating as early as the permotriassic as well the more pervasive resetting of zircon ages during uhp metamorphism in the pyrope quartzite lenses is explained by the ubiquity of fluids and or melts produced during subduction by a series of dehydration reactions that occurred only in the more hydrous mg rich protoliths and not in their drier granitic neighborhood fission track ages determined partly on the same zircon samples yielding 29 9 1 4 ma mark the time when the uhpm unit had reached about 290 c at a shallow location within the crust thus exhumation over a vertical distance of about 120 km must have occurred within about 5 6 ma indicating an average uplift rate of about 20 24 km ma and an average cooling rate of about 85 100 c ma the radiometric data obtained do not lend any support to an eo alpine cretaceous subduction event so that deep subduction and immediately following exhumation all took place during early to mid tertiary time this scenario seems to apply to large portions of the western and central alps as well calling for drastic geodynamic reinterpretations of these parts of the alps

serpentinite derived low δ7li fluids in continental subduction zones constraints from the fluid metasomatic rocks whiteschist from the dora maira massif western alps abstract whole rock lithium li and li isotopic compositions of coesite bearing whiteschists and their country rock metagranites from the dora maira massif in the western alps were investigated to understand their behavior during fluid rock interaction in mantle depths of continental subduction zones the whiteschists reveal relatively low 7li values 6 4 to 2 4 with an average value of 2 1 in comparison to the country rock metagranites 7li 1 2 to 3 6 with an average value of 1 4 the 7li values of whiteschists do not show any correlations with major elements e g mg fe li or isotopes i e 26mg and 18o values and cannot be explained by kinetic fractionation hence the low 7li values of whiteschists result from interactions with metasomatic fluids containing isotopically light li that occurred in deep portions of a continental subduction zone fluid rock interaction modeling suggests that the metasomatic fluids contain low 7li values down to 4 and moderate li concentrations 50 to 150 ppm which were probably derived from the dehydration of serpentinites in the subduction channel the presence of such low 7li fluids in deep subduction zones could cause li isotopic heterogeneity in the earth s interior

stochastic prediction of sediment transport in sand gravel bed rivers classical deterministic bedload transport predictors are applied to sand gravel bed rivers the turbulent bed shear stress is modeled according to a probability distribution to obtain realistic bedload transport rates at incipient motion in extending the predictors to stochastic predictors for nonuniform sediment many parameters that represent near bed turbulence and the particle size distribution must be chosen the parameters that give realistic results are chosen by analyzing the results of a new experimental flume dataset with relatively large water depths choosing other combinations of parameters may give equal total bedload transport rates but at the cost of large errors in fractional transport rates attention is given to the hiding exposure phenomenon and a hindrance effect related to nonuni form sediment validation based on two independent field datasets shows that successful predictions of particle sizes near the threshold for motion are feasible using the stochastic approach while the deterministic approach gives successful predictions well above incipient motion

pb sr nd isotopic behavior of deeply subducted crustal rocks from the dora maira massif western alps italy ii what is the age of the ultrahigh pressure metamorphism pb nd and sr isotope data are reported from two localities on mineral separates from mg rich metapelites and associated rocks that have been subducted to depths of at least 100 km for which metamorphic conditions are estimated at 28 33 kilobars pressure and 700 800 c and then returned to the surface initial isotope ratio data from the granitoid country rock are similar to those found in the metapelites the initial ratios indicate predominantly recycled aged granitic crustal materials for the sources of all of the samples five zircon samples 4 from pyrope megacrysts and 1 from fine grained pyrope quartzite lenses in the metapelites accurately define a chord yielding intercept ages of 304 10 and 38 0 1 4 ma in a concordia diagram zircon from the country rock also plots along the chord the zircon data together with initial nd and sr data indicate that the sedimentary sources of the rocks were derived mainly or entirely from sialic hercynian rocks ellenbergerite from pyrope megacrysts and monazite from the fine grained ground mass yield slightly younger ages of 30 34 ma apparently reflecting lower blocking temperatures than that of zircon sm nd data from a pyrope megacryst give an errorchron corresponding to an age of 38 ma in agreement with the zircon date a major question concerns the timing of the ultrahigh pressure metamorphism experimental data suggest that pyrope and quartz coesite as well as ellenbergerite formed by various metamorphic reactions if as generally assumed the ultrahigh pressure metamorphism occurred ca 100 ma ago our data require that the zircon did not experience measurable lead loss at that time but lost major amounts of lead 38 ma ago during late alpine metamorphism estimates of diffusion rates for nd in pyrope further suggest that the apparent sm nd age of 38 ma for the megacryst is not consistent with that model those problems are resolved if the ultrahigh pressure metamorphism occurred 38 40 ma ago but problems remain from ar ar dates of 100 ma on phengite an inferred 120 ma age for zircon lead loss from another study and possibly by the very rapid uplift required if the metamorphism is that young