the role of eddies in solute transport and recovery in rock fractures implication for groundwater remediation a better understanding of solute transport and retention mechanism in rock fractures has been challenging due to difficulty in their direct observations in microscale rough walled fractures six representative troughs in a rough walled fracture were selected for microscale observations of eddy formation with increasing flow velocity and its effect on spatiotemporal changes of solute concentration this experimental study was enabled by a microscale visualization technique of micro particle image velocimetry with increasing flow velocity re 2 86 no eddies were generated and solutes along the main streamlines transported rapidly whereas those near the wall moved slowly a larger amount of solutes remained trapped at all troughs at re 2 86 than re 10 and this flow range could be favourable for efficient remediation

state of the art of modelling two phase flow in fractured rock two phase flow in fractured rock is an important phenomenon for a range of practical problems not the least of which is non aqueous phase liquid napl contamination of groundwater although multiphase systems have long been studied in the petroleum field in the hydrogeological field progress has only just reaches the point where models are being developed scale effect is one of the main issues of concern although models presented in this paper have the potential to provide useful predictions they can only be used to investigate a variety of possible scenarios with parameters being specified in the form of distribution of values the calibration and validation of all but the simplest of these models poses a formidable task with great demands on hydrogeologists and geophysicists to provide adequate data

compositions of large metal nodules in mesosiderites links to iron meteorite group iiiab and the origin of mesosiderite subgroups large mesosiderite metal nodules were studied petrographically and by neutron activation their large sizes minimized the effects of silicate contamination and dilution by fe reduced from feo the remarkable mixture of subequal amounts of metal and basaltic and pyroxenitic silicates in mesosiderites can be explained by the accretion of a core like metal mass from one asteroid onto the surface of another asteroid our data show that the accreted mass had a composition roughly similar to that of the iiiab iron meteorite core consistent with other evidence of close genetic links between these and other related groups the siderophile compositional pattern the very limited compositional range the inferred large projectile target ratio and the electrical interconnectedness of mesosiderite metal indicate that the bulk of the metal was molten when accreted mesosiderites have been divided into plagioclase and tridymiterich subgroup a and orthopyroxene rich subgroup b on the basis of modal silicate mineralogy roughly the same subgroups are defined by metal compositions au as ni and cu are generally higher and w lower in subgroup a than in subgroup b in our sample set a widmanstatten pattern is only observed in nodules from subgroup a a plausible model is that subgroup a best preserves the compositions of the target regolithic silicates and accreted core subgroup b is comprised of these materials together with a minor amount of coremantle materials consisting of olivine and refractory ni poor metal the independent covariation of ga re and ir may in part reflect fractionations during impact heating events the anomalous mesosiderite reckling peak a79015 is strongly depleted in refractory siderophiles and slightly enriched in volatile siderophiles such evolved metal requires a formation distinct from common mesosiderite metal

interpretation of field tracer tests of a single fracture using a transient solute storage model the results and interpretation of five induced gradient tracer tests performed at five different average interborehole fluid velocities in a single fracture in monzonitic gneiss are described the experiments were conducted using radioactive 82br and a fluorescent dye as conservative tracers where the tracers were pulse injected into radial convergent and injection withdrawal flow fields the flow fields were established between straddle packers isolating the fracture in three boreholes over distances of 12 7 29 8 m the tracer breakthrough curves were determined from samples of the withdrawn groundwater and were interpreted using residence time distribution rtd theory and two deterministic simulation models the rtd curves of the tracer experiments were interpreted by fitting to the field data a simple advection dispersion model and an advection dispersion model with transient solute storage in immobile fluid zones both models consider the different flow field geometries associated with injection withdrawal and radial convergent tests comparison of the fits obtained by the simulation models suggest that the initial period of solute transport in single fractures is advection dominated and with increasing tracer residence time or decreasing fluid velocity transport progresses toward more fickian like behavior during the advective dominated period the transient solute storage model is shown to adequately describe the asymmetries and long tails characteristic of the fracture rtds interpretation of the tracer experiments using both simulation models further suggests that induced gradient tracer experiments are likely to underestimate the dispersive characteristics of single fractures under natural flow conditions

poincare wave induced mixing in a large lake a 10 000 km2 hypoxic dead zone forms during most years in the central basin of lake erie to investigate the processes driving the hypoxia we conducted a 2 yr field campaign where the mixing in the lake interior during the stratification period was examined using current meters and temperature loggers data as well as 600 temperature microstructure profiles from which turbulent mixing was computed near inertial poincare waves drive shear instability generating 1 m amplitude and 10 m wavelength high frequency internal waves with 1 mdensity overturns that lead to an increase in turbulent dissipation by one order of magnitude the instabilities are associated with enhanced vertical shear at the crests and troughs of the poincare waves and may be correlated with the local gradient richardson number poincare wave induced mixing should be an important factor when the burger number 0 25 the strong diapycnal mixing induced by the poincare wave activity will also significantly modify the energy flux paths for example we estimate that in lake erie 0 85 of the wind energy is transferred to the lake interior below the surface layer of this 40 is dissipated in the interior metalimnion and 60 is dissipated at the bottom boundary in smaller lakes 0 42 of wind energy is transferred to the deeper water with 90 dissipated in the boundary and 10 in the interior metalimnion 2012 by the association for the sciences of limnology and oceanography inc

preliminary interpretation of tracer experiments conducted in a discrete rock fracture under conditions of natural flow the authors present a preliminary analysis of tracer experiments conducted on a natural horizontal fracture system in shale and limestone at a depth of roughly 10 m an array of 27 boreholes on 5 m spacings was placed into this fracture system and apertures of the fractures were determined hydraulically at each hole a conservative tracer was injected into one borehole and monitored in the array the tracer transport process was modeled by a one dimensional model and indicates that transverse dispersion and diffusion in the matrix are the predominant processes which inhibit tracer migration and result in spreading

sorbing tracer experiments in a crystalline rock fracture at aspo sweden 2 transport model and effective parameter estimation 1 transport and retention of sorbing tracers in a single altered crystalline rock fracture on a 5 m scale is investigated we evaluate the results of a comprehensive field study referred to as

laboratory measurement of hydrodynamic saline dispersion within a micro fracture network induced in granite we report the first measurements of hydrodynamic dispersion in a microfractured granite using a combination of novel techniques a fracture network was induced in a cylindrical plug of ailsa craig micro granite by thermal stressing to produce an isotropic network of fractures with an average aperture of 0 3 m a density of approximately 4 10 4 fractures mm 3 and a permeability of 5 5 10 17 m 2 after saturating the cores with 0 01 m nacl solution a step in the concentration profile to 1 m was advected into the plug at flow rates of 0 07 to 2 13 cm 3 h 1 the longitudinal electrical impedance of the plug was measured continuously as the solute front advected through its length until the plug was saturated with the concentrated electrolyte analysis of the impedance versus time relationships allows the derivation of the longitudinal dispersion coefficient dl and hydrodynamic retardation rh the peclet number dispersion relationship for the micro fracture network is very similar to that predicted for other radically different fracture networks thus dispersion may be more dependent on fracture connectivity and length than fracture density and display a relationship similar to that shown by particle beds and clastic sandstones the high retardation values observed 2 2 4 9 reflect flow behaviour within a fracture network with a proportion of blind sections and demonstrates how such networks can slow the advance of conservative solute components 2007 elsevier b v all rights reserved

formation of mesosiderites by low velocity impacts as a natural consequence of planet formation mesosiderites are an enigmatic class of stony iron meteorites composed of roughly equal amounts of pyroxenitic and basaltic silicates and metallic iron nickel olivine is rare we suggest here that during the period of planet formation mesosiderites originated by the low velocity collisions of large metallic core fragments with the surface of a differentiated asteroid size body relative velocities of the asteroids native to this region were low 1 km s 1 because it was distant from massive protoplanets however a few differentiated asteroids were destroyed by high velocity collisions with interlopers perturbed by protoplanets into highly eccentric orbits these collisions reduced mantles and crusts to small silicate fragments but left cores in the form of large durable metal fragments mesosiderite like pyroxenite basalt metal mixtures were formed when large core fragments accreted at low velocities to the regolith of an intact asteroid the metal contents of other regolithic regions remained low most of the olivine in mesosiderite and howardite breccias we attribute to the mantles of the disrupted parent bodies the low 12 20 mg g 1 olivine contents indicate that the amount of debris accreted from disrupted asteroids was small relative to the volumes of the regoliths

reevaluation of formation of metal nodules in ordinary chondrites compositions of four metal nodules from two ordinary chondrites wis91627 h3 7 and juin h5 were determined by instrumental and radiochemical neutron activation analyses compared with bulk metal fractions the metal nodules are characterized by strong and variable depletion of the refractory siderophile elements re os ir ru pt and rh but normal w and mo some fractionation of co from ni and low cu concentrations these characteristics are difficult to explain by shock induced vaporization followed by fractional condensation a mechanism suggested by widom et al 1986 we propose formation of metal nodules during metamorphism in the parent body refractory siderophile elements such as ir os rh etc are partly locked up in noble metal nuggets and cannot participate in kamacite formation the occurrence of metal nodules in both equilibrated and unequilibrated ordinary chondrites suggests that diffusion along grain boundaries was important in the development of kamacite and taenite in ordinary chondrites

field measurement of radial solute transport in fractured rock the results of a tracer experiment conducted in a single fracture are interpreted using a semianalytical model which accounts for advective dispersion matrix diffusion mixing in the test zones and for tortuosity the experiment was conducted using a conservative tracer which was injected into a steady divergent flow field arrival of tracer was monitored in an array of 13 boreholes intersecting the fracture over a square area of approximately 30 m on a side the arrival of tracer was detected in 11 of the 13 boreholes simulation of the transport process suggests that matrix diffusion may play a significant role in the migration of solutes contrary to previously published results the relative influence of advective dispersion was found to be increasingly diminished with increasing scale fracture apertures determined from the results of the tracer experiment were found to be in general agreement with apertures calculated from independent hydraulic tests the individual advective processes that contribute to advective dispersion remain unresolved on the basis of this experiment

the origin and nebular history of the metal phase of ordinary chondrites abstract we present new inaa results for bulk metal from h and ll chondrites both have characteristic elemental patterns similar to l chondrite metal in particular increasing abundances of w and ga from unequilibrated to equilibrated chondrites but a reverse variation of v and cr abundances these characteristics indicate that metal in ordinary chondrites formed by melting and reduction of highly oxidized material the similarities of melting features and the complementary nature of compositions between metal and chondrules suggest that these two components were derived from a common precursor similar to ci or cm material in redox state and compositionally related to the matrix of highly unequilibrated ordinary chondrites co ni abundance ratios are similarly low for bulk metal in the least metamorphosed ordinary chondrites of all three chemical groups this suggests that metal in ordinary chondrites initially had the same composition and formed under the same melting conditions the chondrites that accreted earliest have preserved their melting characteristics while those that accreted later reequilibrated with the ambient gas at different temperatures the differences in redox state between equilibrated and unequilibrated chondrites show that formation of chondritic metal and chondrules by melting occurred during the accretion of ordinary chondrite parent bodies the initial metal composition established during the melting stage 13 wt ni co ni 0 031 is inferred from the metal in highly unequilibrated chondrites the accretion temperatures of about 600 k for ordinary chondrites are calculated from the reequilibration reaction h chondrites were accreted at the highest temperature and are most reduced among the three ordinary chondrite groups ll chondrites were accreted at the lowest temperature and are most oxidized compositionally the metal component that would account for the fe si fractionation among h l and ll chondrites is different from the metal formed by melting indicating that the different fe s ratios of h l and ll chondrites were established before their accretion

petrogenesis of mesosiderites i origin of mafic lithologies and comparison with basaltic achondrites abstract new petrologic and trace element data on basaltic and gabbroic clasts in mesosiderites and basaltic achondrites combined with existing petrologic and trace element data have served as a basis for interpretation of the petrogenesis of mesosiderite clasts compared with the basaltic achondrites the mesosiderite basaltic and gabbroic clasts contain more abundant modal tridymite and merrillite and more commonly contain augite as a late magmatic phase their pyroxenes tend to be more mgo rich and have lower fe mn ratios which are positively correlated with the fe mg ratio some of the mesosiderite basaltic and gabbroic clasts contain xenocrystic plagioclase the basaltic clasts commonly show super chondritic eu sm ratios and slight lree depletions the cumulate gabbro clasts are extremely depleted in lil have very high eu sm ratios and high lu sm ratios all of these features can be explained by a model in which the mafic lithologies of mesosiderites were formed by remelting of a mixed basalt cumulate gabbro metal source region near the parent body surface reducing agents p c s from the metallic fraction reduce feo out of the silicate melt and result in the positive correlation of fe mn with fe mg observed in pyroxene analyses and the modal abundances of tridymite merrillite and augite xenocrystic plagioclase is a natural consequence of remelting a cumulate gabbro rich source as are the unique ree patterns observed

tail shortening with developing eddies in a rough walled rock fracture understanding fluid flow and solute transport in rough walled fractures is important in many problems such as geological storage of co2 and siting of radioactive waste repositories the first microscopic observation of fluid flow and solute transport through a rough walled fracture was made to assess the evolution of eddies and their effect on non fickian tailing a noteworthy phenomenon was observed that as the eddy grew the particles were initially caught in and swirled around within eddies and then cast back into main flow channel which reduced tailing this differs from the conventional conceptual model which presumes a distinct separation between mobile and immobile zones fluid flow and solute transport modeling within the 3 d fracture confirmed tail shortening due to mass transfer by advective paths between the eddies and the main flow channel as opposed to previous 2 d numerical studies that showed increased tailing with growing eddies

power law breakthrough curve tailing in a fracture the role of advection summary we offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock in this example we limit the model to a single planar fracture of varying aperture flow heterogeneity derives from variable fracture aperture which implies variable transmissivity t the analysis employs a physically based model well suited to strong heterogeneity and relies only upon advective transport the purely advective model is able to explain a power law trend of magnitude 2t o 3 in the breakthrough curve tail a range that has been found in field tracer experiments the principle cause of this trend is the comparatively slow transport in zones of small transmissivity tight aperture slow advection occurs when either heterogeneity variance of ln t i s strong or when the assumed heterogeneity distribution is non gaussian thus we link breakthrough tailing to the statistical parameters for the transmissivity field

geochemistry and oxygen isotope composition of main group pallasites and olivine rich clasts in mesosiderites implications for the great dunite shortage and hed mesosiderite connection evidence from iron meteorites indicates that a large number of differentiated planetesimals formed early in solar system history these bodies should have had welldeveloped olivine rich mantles and consequentially such materials ought to be abundant both as asteroids and meteorites which they are not to investigate this great dunite shortage we have undertaken a geochemical and oxygen isotope study of main group pallasites and dunitic rocks from mesosiderites oxygen isotope analysis of 24 main group pallasites 103 replicates yielded a mean 17o value of 0 187 0 016 2 which is fully resolved from the hed 17o value of 0 246 0 014 2 obtained in our earlier study and demonstrates that both groups represent distinct populations and were derived from separate parent bodies our results show no evidence for 17o bimodality within the main group pallasites as suggested by a number of previous studies olivine rich materials from the vaca muerta mount padbury and lamont mesosiderites and from two related dunites nwa 2968 and nwa 3329 have 17o values within error of the mesosiderite average this indicates that these olivine rich materials are co genetic with other mesosiderite clasts and are not fragments from an isotopically distinct pallasite like impactor despite its extreme lithologic diversity the mesosiderite parent body was essentially homogeneous with respect to 17o a feature best explained by an early phase of large scale melting magma ocean followed by prolonged igneous differentiation based on the results of magma ocean modeling studies we infer that mg rich olivines in mesosiderites formed as cumulates in high level chambers and do not represent samples of the underlying mantle by analogy recently documented mg rich olivines in howardites may have a similar origin although the dawn mission did not detect mesosiderite like material on vesta evidence linking the mesosiderites and heds includes i their nearly identical oxygen isotope compositions ii the presence in both of coarse grained mg rich olivines iii both have synchronous lu hf and mn cr ages iv there are compositional similarities between the metal in both and v mesosiderite like material has been identified in a howardite breccia the source of the mesosiderites remains an outstanding question in meteorite science the underrepresentation of olivine rich materials amongst both asteroids and meteorites results from a range of factors however evidence from pallasites and mesosiderites indicates that the most important reason for this olivine shortage lies in the early catastrophic destruction of planetesimals in the terrestrial planet forming region and the subsequent preferential loss of their olivine rich mantles

geochemistry and origin of metal olivine clasts and matrix in the dong ujimqin qi mesosiderite the dong ujimqin qi mesosiderite is the first recorded fall of a stony iron meteorite in china according to silicate textures and metal composition this meteorite is classified as a member of subgroup ib instrumental neutron activation analyses inaa of metals show that the matrix metal has lower concentrations of os ir re and pt but higher concentrations of ni and au than the 7 5 cm metal nodule present in the meteorite we attribute these compositional differences to fractional crystallization of molten metal studies of olivine clasts show that feo contents are uniform in individual olivine crystals but are variable for different olivine clasts although concentrations of rare earth elements rees change within olivine clasts they all exhibit a vee shaped pattern relative to ci chondrites the relatively high concentrations of rees in olivine and the shape of ree patterns require a liquid high in rees and especially in light rees as such a liquid was absent from the region where basaltic and gabbroic clasts formed mesosiderite olivine must have formed in a part of the differentiated asteroid that is different from the location where other mesosiderite silicate clasts formed

mineralogical characterization of near earth asteroid 1036 ganymed abstract we present a mineralogical assessment of near earth asteroid 1036 ganymed using data obtained may 18 2006 ut combined with 24 color asteroid survey data to cover the spectral interval of 0 3 2 45 m results of the analysis indicate 1036 ganymed is an s vi asteroid with a surface silicate assemblage consisting primarily of orthopyroxene fs 23 5 wo 3 3 consistent with calculated band centers and band area ratios bar 1036 ganymed appears to be once part of a large mesosiderite containing howardite eucrite and diogenite hed pyroxenes mixed with metal that was broken apart and dispersed the calculated composition of the average pyroxenes in the surface material of 1036 ganymed is consistent with mesosiderite pyroxenes in particular the diogenites a second possibility could be 1036 ganymed is not yet represented in the meteorite collection our investigation has confirmed ganymed is not a parent body of the ordinary chondrites and is not genetically related to 433 eros

thermal and shock history of mesosiderites and their large parent asteroid to elucidate the geological evolution of the mesosiderite stony iron meteorites and their 3 4 3 8 gy 40ar 39ar ages we have investigated their shock and thermal histories we have studied shock metamorphism in sixteen mesosiderites and find that none have been shocked to more than 10 gpa shock stage s1 s2 three mesosiderites contain a tiny fraction 0 1 overall of mineral fragments that were shocked to shock stage s3 s6 levels the uniformity of shock features within all fragments shows that these fragments were not shocked in situ our shock data for mesosiderites the absence of evidence of 3 6 3 9 gy impact melt the shock history of impact heated ordinary chondrites and the difficulty in quantitatively removing ar in an impact event all suggest that the mesosiderite parent body did not suffer a major impact event 3 6 3 9 gy ago metallographic cooling rates of 0 03 c my at 400 c were estimated from taenite lamellae in four mesosiderites using the latest diffusion coefficients and fe ni p phase diagram cooling rates of 0 01 c my at 425 325 c were estimated from published compositional data for kamacite grains in four mesosiderites these two techniques and four other semiquantitative metallographic cooling rate indicators show that the mesosiderites cooled slower than any iron meteorite we infer that cooling rates at 400 c were 0 02 0 03 c my and certainly less than 0 5 c my the inferred cooling rate is too slow to allow ar closure before 4 gy all of the shock thermal and age data for mesosiderites are consistent with slow cooling at depth 1 my after metal and silicate were mixed around 4 4 gy ago thermal models indicate that the mesosiderites probably cooled in an asteroid some 200 400 km in radius

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

tracer movement in a single fissure in granitic rock some experimental results and their interpretation radionuclide migration was studied in a natural fissure in a granite core the fissure was oriented parallel to the axis in a cylindrical core 30 cm long and 20 cm in diameter the traced solution was injected at one end of the core and collected at the other breakthrough curves were obtained for the nonsorbing tracers tritiated water and a large molecular weight lignosulphonate molecule and for the sorbing tracers cesium and strontium from the breakthrough curves for the nonsorbing tracers it could be concluded that channeling occurs in the single fissure a dispersion model based on channeling is presented the results from the sorbing tracers indicate that there is substantial diffusion into and sorption in the rock matrix sorption on the surface of the fissure also accounts for a part of the retardation effect of the sorbing species a model which includes the mechanisms of channeling surface sorption matrix diffusion and matrix sorption is presented the experimental breakthrough curves can be fitted fairly well by this model by use of independently obtained data on diffusivities and matrix sorption

a solute transport model for channelized flow in a fracture recent experimental and theoretical investigations of transport in fractures indicate that water flows preferentially through channels in the fracture plane this channeling of flow may imply that solutes transported in large aperture channels have limited exposure to the bulk of the rock matrix surface which contacts the fracture we present a solute transport model for large aperture channels that includes both mass transfer to small aperture regions of the fracture and the adjacent rock matrix to investigate the interaction of solute in large aperture channels with the surrounding rock mass modeling channels similar to those observed in the crystalline rock at the stripa mine show that solute can be retarded considerably due to mass exchange between the channels the small aperture regions of the fracture and the rock matrix the extent of solute retardation is insensitive to the solute capacity in the small aperture regions and the areal spacing between channels in the fracture plane but is very sensitive to the mass transfer rates between the channel and the small aperture region

compositional continuity of enstatite chondrites and implications for heterogeneous accretion of the enstatite chondrite parent body abstract chemical compositions of eleven enstatite chondrites 1 eh5 4 eh3 3 el3 i el5 and 2 el6 and their metal and nonmagnetic fractions determined by instrumental neutron activation analysis are reported the abundances of nonvolatile lithophile elements such as al sc and mg increase from eh to el while those of siderophile and moderately volatile elements decrease in the sequence of eh5 to eh3 el3 and el5 6 the continuity in compositions of enstatite chondrites and in particular the inverse variations of moderately volatile element abundances with petrographic type between eh and el groups demonstrate that enstatite chondrites have been derived from a common parent body the enstatite chondrite parent body formed by heterogeneous accretion of materials available in the accretional region metal was effectively accreted into the core where eh5 chondrites were derived and the abundances of metal decreased as accretion proceeded in complement silicate abundances gradually increased in the layers that accreted later the lack of correlation between volatile element abundances and metamorphic degree demonstrates that losses of moderately volatile elements from enstatite chondrites cannot have resulted from parent body processes furthermore it is expected that during accretion various components would mix and thus erase any early fractionation of moderately volatile elements of a single parent body variations of ambient gas temperatures during accretion are also impossible to produce the volatile element pattern of enstatite chondrites it is suggested that moderately volatile elements in the enstatite chondrites were lost during local heating the chondrule formation process formation of chondrules appears to have proceeded during the accretion of the enstatite chondrite parent body and lasted for a certain period the mineralogical and textural features of enstatite chondrites can be explained in terms of two stages of metamorphism the metamorphic trend from eh3 to eh5 resulted from internal heating whereas the trend from el3 to el6 was due to an external heat source it seems very likely that the eh chondrites were metamorphosed during accretion thus cooled rather rapidly activities of the early sun could serve as an energy source for the external heating

compositional differences between basaltic and gabbroic clasts in mesosiderites two gabbroic pebbles and one pebble with basaltic textural affinities from the vaca muerta mesosiderite were analyzed by instrumental neutron activation analysis and electron microprobe these analyses plus literature data reveal remarkable compositional differences between basaltic and gabbroic clasts in mesosiderites on average basaltic clasts have small 15 depletions in light relative to heavy rare earth elements rees and moderate positive eu anomalies i e h chondrite normalizedla lu 0 85 eu sm 1 30 the meanla lu andeu sm abundance ratios of gabbroic clasts are at least 3 3 smaller and 28 greater respectively intense meteoroid bombardment probably persisted until after the mesosiderite parent body had differentiated near surface mixtures of major amounts of basalt and lesser amounts of cumulate eucritic rocks were essentially totally melted and rapidly cooled accounting for the moderately fractionated ree patterns of most basaltic clasts at greater depths impact heating partially melted cumulate gabbros incompatible element rich eutectic liquids drained away creating large ree fractionations in the residual rocks these rocks cooled slowly and developed gabbroic textures

formation of mesosiderites by fragmentation and reaccretion of a large differentiated asteroid we propose that mesosiderites formed when a 200 400 km diameter asteroid with a molten core was disrupted by a 50 150 km diameter projectile to test whether impacts can excavate core iron and mix it with crustal material we used a low resolution smoothed particle hydrodynamics computer simulation for 50 300 km diameter differentiated targets we found that significant proportions of scrambled core material and hence potential mesosiderite metal material could be generated for near catastrophic impacts that reduce the target to 80 of its original diameter and about half of its original mass the proportion of scrambled core material would be about 5 vol equivalent to 10 vol of mesosiderite like material the paucity of olivine in mesosiderites and the lack of metal poor or troilite rich meteorites from the mesosiderite body probably reflect biased sampling mesosiderites may be olivine poor because mantle material was preferentially excluded from the metal rich regions of the reaccreted body molten metal globules probably crystallized around small cool fragments of crust hindering migration of metal to the core if mantle fragments were much hotter and larger than crustal fragments little metal would have crystallized around the mantle fragments allowing olivine and molten metal to separate gravitationally the rapid cooling rates of mesosiderites above 850 c can be attributed to local thermal equilibration between hot and cold ejecta very slow cooling below 400 c probably reflects the large size of the body and the excellent thermal insulation provided by the reaccreted debris we infer that our model is more plausible than an earlier model that invoked an impact at 1 km s to mix projectile metal with target silicates if large impacts cannot effectively strip mantles from asteroidal cores as we infer we should expect few large eroded asteroids to have surfaces composed purely of mantle or core material this may help to explain why relatively few olivine rich a type and metal rich asteroids m type are known some s type asteroids may be scrambled differentiated bodies

a field example of measuring hydrodynamic dispersion in a single fracture a field example of measuring the dispersive properties of a single fracture in fractured plutonic rock is presented the experimental technique involves injecting a slug of conservative tracer into a steady groundwater flow field established between a pumping and recharging borehole and monitoring the tracer breakthrough by sampling the withdrawal water directly the breakthrough curves from two experiments were analyzed with a model which describes the flow field geometry either analytically or numerically and solves for hydrodynamic dispersion analytically a longitudinal dispersivity of 1 40 m was estimated by fitting the model to each set of field data the magnitude of the dispersion was determined to be independent of dispersive effects created by flow through the borehole instrumentation and thought to be purely hydrodynamic in nature

impact versus internal origins for mesosiderites mesosiderites are very intimately mixed stony iron breccias including little recrystallized and highly recrystallized varieties i iii and a subgroup iv with melted matrix all mesosiderite breccias contained some material that was hot as indicated by pigeonite that inverted at 1150 c subgroup iv contained silicate and metal liquids at temperatures of at least 1300 c and 1350 c respectively cooling rates are not rigorously defined but are approximately 1 year in the high temperature range and 1 m y below 500 c the latter cooling requires a depth of 40 km in an asteroid with a radius of 400 km or less if porous low conductivity surface material is present cratering with metal projectiles appears incapable of generating mesosiderites a normal impact produces rapidly cooled metal poor breccias impacts on a crust in which metal silicate segregation had taken place could generate stony iron breccias but burial under an insulating blanket would be necessary to obtain slow cooling disruption and reassembly of two colliding bodies and accretion of differentiated planetesimals could form stony iron breccias at depth but as with the previous two models the easiest way to explain the low olivine of mesosiderites is to postulate derivation from olivine poor chondritic material two internal processes turbulent metal crust mixing during core formation and crustal blocks sinking into the core provide a deep location and withhold olivine from the breccia however these mechanisms do not explain how the silicate and metal liquids in subgroup iv otherwise interpreted as impact melt rocks could have failed to segregate in a deep slowly cooled environment no single model for mesosiderite origins is wholly satisfactory

analysis of some laboratory tracer runs in natural fissures tracer tests in natural fissures performed in the laboratory are analyzed by means of fitting two different models in the experiments sorbing and nonsorbing tracers were injected into a natural fissure running parallel to the axis of a drill core the models take into account advection dispersion diffusion into the rock matrix and sorption onto the surface of the fissure and on the microfissures inside the matrix for the second mechanism one of the models considers hydrodynamic dispersion while the other model assumes channeling dispersion the models take into account time delays in the inlet and outlet channels the dispersion characteristics and water residence time were determined from the experiments with nonsorbing tracers surface and volume sorption coefficients and data on diffusion into the rock matrix were determined for the sorbing tracers the results are compared with values independently determined in the laboratory good agreement was obtained using either model when these models are used for prediction of tracer transport over larger distances the results will depend on the model the model with channeling dispersion will show a greater dispersion than the model with hydrodynamic dispersion assuming constant dispersivity

the case for a melt matrix in plagioclase poik mesosiderites the plagioclase poik mesosiderites bondoc budulan and mincy have poikilitic matrix textures exactly like igneous rocks including the olivine zone of the palisades sill and apollo 17 mare basalts they contain olivine grains with embayed margins characteristic of resorption in liquid rather than coronas formed during solid state reactions there is a nonrandom i e nonmetamorphic arrangement of pyroxene phases in the matrix orthopyroxene is enclosed poikilitically by plagioclase but inverted pigeonite is interstitial and locally subophitic to plagioclase as in an igneous crystallization sequence these mesosiderites are therefore reclassified from subgroup 3b highly recrystallized matrix to 4b igneous matrix the 4a mesosiderites have fine grained intergranular textures because they are richer in plagioclase than subgroup 4b so that plagioclase crystallized earlier than in 4b but also because they contained abundant nuclei associated with relict plagioclase clasts the only 4a melt rock mesosiderite pinnaroo with an intergranular poikilitic matrix texture transitional between 4a and 4b mesosiderites contains very few plagioclase clasts over half the mesosiderites contain melt matrix or melt rock clasts the heterogeneity within mesosiderites as a whole and within specific mesosiderites e g estherville may be due to variations in the proportions of hot melt and cold clasts incorporated

mesosiderite clasts with the most extreme positive europium anomalies among solar system rocks pigeonite plagioclase gabbros that occur as clasts in mesosiderites brecciated stony iron meteorites show extreme fractionations of the rare earth elements rees with larger positive europium anomalies than any previously known for igneous rocks from the earth moon or meteorite parent bodies and greater depletions of light rees relative to heavy rees than known for comparable cumulate gabbros the ree pattern for merrillite in one of these clasts is depleted in light rees and has a large positive europium anomaly as a result of metamorphic equilibration with the silicates the extreme ree ratios exhibited by the mesosiderite clasts demonstrate that multistage igneous processes must have occurred on some asteroids in the early solar system melting of the crust by large scale impacts or electrical induction from an early t tauri phase sun may be responsible for these processes

effective matrix diffusion in kilometer scale transport in fractured crystalline rock concentrations of tritium 3h and dichlorodifluoromethane cfc 12 in water samples taken from glacial drift and fractured crystalline rock over 4 km2 in central new hampshire are interpreted to identify a conceptual model of matrix diffusion and the magnitude of the diffusion coefficient dispersion and mass transfer to and from fractures has affected the 3h concentration to the extent that the peak 3h concentration of the 1960s is no longer distinguishable because of heterogeneity in the bedrock the sparsely distributed chemical data do not warrant a three dimensional transport model instead a one dimensional model of cfc 12 and 3h migration along flow lines in the glacial drift and bedrock is used to place bounds on the processes affecting kilometer scale transport arid model parameters are varied to reproduce the measured relation between 3h and cfc 12 rather than their spatial distributions a model of mass exchange to and from fractures that is dependent on the time varying concentration gradient at fracture surfaces qualitatively reproduces the measured relation between 3h and cfc 12 with an upper bound for the fracture dispersivity approximately equal to 250 m and a lower bound for the effective matrix diffusion coefficient equal to 1 m2 yr 1 the diffusion coefficient at the kilometer scale is at least 3 orders of magnitude greater than laboratory estimates of diffusion in crystalline rock the large diffusion coefficient indicates that diffusion into an immobile fluid phase rock matrix is masked at the kilometer scale by advective mass exchange between fractures with large contrasts in trarismissivity the measured transmissivity of fractures in the study area varies over more than 6 orders of magnitude advective mass exchange from high permeability fractures to low permeability fractures results in short migration distances of a chemical constituent in low permeability fractures over an extended period of time before reentering high permeability fractures viewed at the kilometer scale this process is analogous to the chemical constituent diffusing into and out of an immobile fluid phase

oxygen isotope variation in stony iron meteorites asteroidal material delivered to earth as meteorites preserves a record of the earliest stages of planetary formation high precision oxygen isotope analyses for the two major groups of stony iron meteorites main group pallasites and mesosiderites demonstrate that each group is from a distinct asteroidal source mesosiderites are isotopically identical to the howardite eucrite diogenite clan and like them are probably derived from the asteroid 4 vesta main group pallasites represent intermixed core mantle material from a single disrupted asteroid and have no known equivalents among the basaltic meteorites the stony iron meteorites demonstrate that intense asteroidal deformation accompanied planetary accretion in the early solar system

transport and retention from single to multiple fractures in crystalline rock at aspo sweden 2 fracture network simulations and generic retention model hydrogeologic characterization of crystalline rock formations on the field scale is important for many applications but still presents a multitude of challenges neuman 2005 in this work we use

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

comparing flux averaged and resident concentration in a fractured bedrock using ground penetrating radar this is the published version copyright 2010 by the american geophysical union all rights reserved

assessing the validity of the channel model of fracture aperture under field conditions in recent investigations of fluid and solute movement in discrete fractures spatial heterogeneity of the fracture aperture has been conceptualized as a series of noninterconnecting constant aperture flow paths or channels two methods of estimating the distribution of the aperture sizes are presented using information from a single hole pumping test and a radially converging tracer test the first method uses the transmissivity of the fracture and mean arrival time of the tracer while the second method uses the mean and variance of the solute arrival time if the fracture can be conceptualized as a series of nonintersecting flow paths of constant aperture the two methods should yield identical estimates for the parameters of the distribution the validity of the channel model can be assessed by comparing the parameters of the distribution that are estimated by the two methods this technique was demonstrated using hydraulic and tracer tests conducted in a discrete areally extensive horizontal fracture in the silurian dolomite in the northeastern illinois a lognormal and a truncated gamma distribution were used to describe the distribution of constant aperture flow paths the lognormal distribution could not reproduce the abrupt rising limb and maximum rate of mass arrival that characterized the tracer tests the gamma distribution more accurately predicted the shape of the breakthrough curves however the two methods of estimating the parameters of the distribution provided significantly different estimates of the variances of the aperture sizes the mean aperture as estimated by the two methods was similar the difference in the variance of the aperture as estimated by the two methods indicates that alternative conceptual models of aperture heterogeneity are required to more accurately describe both fluid and solute movement in this field situation

pt re os systematics of group iiab and iiiab iron meteorites the pt re os isotopic and elemental systematics of 13 group iiab and 23 group iiiab iron meteorites are examined as has been noted previously for iron meteorite groups and experimental systems solid metal liquid metal bulk distribution coefficients d values for both iiab and iiiab systems show dos dre dpt 1 during the initial stages of core crystallization assuming closed system crystallization the latter stages of crystallization for each core are generally characterized by dpt dre dos the processes governing the concentrations of these elements are much more complex in the iiiab core relative to the iiab core several crystallization models utilizing different starting parameters and bulk distribution coefficients are considered for the re os pair each model has flaws but in general the results suggest that the concentrations of these elements were dominated by equilibrium crystallization and subsequent interactions between solid metal and both equilibrium and evolved melts late additions of primitive metal to either core were likely minor or nonexistent the 187re 187os systematics of the iiab and iiiab groups are consistent with generally closed system behavior for both elements since the first several tens of ma of the formation of the solar system consistent with short lived chronometers the re os isochron ages for the complete suites of iiab and iiiab irons are 4530 50 ma and 4517 32 ma respectively and are similar to previously reported re os ages for the lower ni endmembers of these two groups both isochrons are consistent with but do not require crystallization of the entire groups within 10 30 ma of the initiation of crystallization the first high precision 190pt 186os isochrons for iiab and iiiab irons are presented the pt os isochron ages for the iiab and iiiab irons calculated using the current best estimate of the for 190pt are 4323 80 ma and 4325 26 ma respectively the re os and pt os ages do not overlap within the uncertainties the younger apparent ages recorded by the pt os system likely reflect error in the 190pt decay constant the slope from the pt os isochron is combined with the age from the re os isochron for the iiiab irons to calculate a revised of 1 415 10 12 a 1 for 190pt although additional study of this decay constant is still needed

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

models of tracer breakthrough and permeability in simple fractured porous media tailing and bimodal behaviour of tracer breakthrough curves from tracer tests conducted in fractured porous media are commonly presented as deviations from the fickian model for homogeneous porous media tailing is mainly attributed to 1 tracer storage brought about by diffusion between mobile and static regions of fluid 2 a concentration of flow towards the wider aperture and thus more permeable fracture zones and 3 the high variance in fracture conductivity and consequent mixing of tracer bi or multi modality has been attributed to solute following a few highly permeable flow paths systematic numerical simulations of flow and transport in geometrically simple fractured porous media were conducted using a 2d finite difference flow code and a particle tracking transport model as a simplification only advective dispersion was considered the modelling study produced a large variety of tracer breakthrough curves including two patterns commonly seen in field data the backward tailed uni modal type and the gaussian type the study demonstrates that different types of breakthrough might be characteristic of particular sets of conceptual models for heterogeneities and as such may provide a useful pointer in the application and interpretation of tracer tests

discrete fracture network interpretation of field tracer migration in sparsely fractured rock field tracer migration in sparsely fractured rock is analyzed with a discrete fracture network model that has been calibrated on fracture and flow data from the stripa 3d experiment in sweden comparison between transport simulations in the flow calibrated discrete model and tracer tests of the field experiment confirms the fracture network parameters obtained from the flow analysis except for the variance of the fracture conductivities which had to be increased the discrete model reproduces the uneven spatial distribution of flow and tracers the complex dispersive behavior and channeling effects that have been observed in the field experiment as a result of flow channeling transport occurs along preferential paths whose transport properties may substantially deviate from the medium average properties for example porosity and wetted fracture surface area available to sorption may be reduced by almost 2 orders of magnitude compared to the medium average values

chemical characteristics of metal phases of the richardton h5 chondrite abstract the magnetic fraction was separated from the richardton h5 chondrite with a hand magnet and was leached with concentrated hf at high temperature for different periods the resulting metallic fractions and the untreated magnetic fraction were analyzed using mossbauer spectroscopy and instrumental neutron activation analysis inaa leaching in concentrated hf for 1 5 5 min was effective in removing silicates from the magnetic fraction while leaving the metal grains intact leaching with increasing time selectively dissolved kamacite with only little attack of the taenite grains the mossbauer spectroscopy shows that martensite phase iron is present in the richardton metals and is dissolved in hf less easily than kamacite but more easily than taenite the distributions of trace siderophile elements among the different metal phases of richardton were obtained based on the inaa data siderophile elements except for co are enriched in the taenite fraction but with different concentration ratios between taenite and kamacite suggesting that kamacite and taenite were not formed by either oxidation reduction of fe of the fe ni metal or by condensation from the nebula or by metal solid differentiation a more likely explanation is that kamacite and taenite have equilibrated by low temperature diffusion it seems that most trace siderophile elements were once dissolved in the fe ni metal and later distributed among the metal phases by diffusion however ir os and ru may still partly exist as tiny separate grains in the feni metal and their distributions among the metal phases are not completely equilibrated

composition and formation of metal nodules and veins in ordinary chondrites abstract five large metal nodules a composite sample of five small metal nodules one troilite nodule and two metal veins from five ordinary chondrites were analyzed by electron microprobe and neutron activation analysis metal nodules and veins in h chondrites generally consist of large single crystals of kamacite whereas l nodules contain significant taenite most nodules and veins are depleted by large factors ranging up to 240 in refractory siderophiles re os ir pt tungsten normally a refractory siderophile and au as and ga volatile siderophiles have abundance ratios similar to those of the common siderophiles fe co and ni we propose that the metal with extremely low refractory element contents was produced by shock induced vaporization of chondritic material the refractory elements condensed near the point of vaporization and were not transported with the vapor because the shock generated gas was mildly oxidizing w formed volatile oxides the low ni fe ratio and the resulting high kamacite contents may reflect dilution by fe from dissociated fes subsequent condensation of the refractory depleted vapor into fractures and voids formed the metal veins and nodules

olivine coronas metamorphism and the thermal history of the morristown and emery mesosiderites abstract coronas are present on all millimeter sized mineral clasts of olivine in the emery and morristown mesosiderites and are a manifestation of high temperature t 850 1100 c metamorphism these coronas formed by reaction and diffusion between olivine and a mesosiderite like matrix assemblage the bulk composition of the coronas can be approximated by a mixture of 10 25 wt olivine and as 90 75 wt metal free matrix except for p and cr which are significantly enriched in coronas phosphorus and cr diffused relatively rapidly to coronas and were derived from a large volume of matrix most likely from metal that was originally enriched in these elements prior to metamorphism the coronas in both meteorites show a similar zone sequence but are systematically thicker in emery 800 m wide than in morristown 350 m wide suggesting that emery experienced more grain growth and more intensive metamorphism than morristown textural relationships suggest that corona formation and high temperature metamorphism occurred largely after intensive millimeter scale brecciation and after or during metal silicate mixing a local equilibrium model can explain many features of the coronas but chemical equilibrium was maintained only on a very small scale overgrowths are present on plagioclase in the coronas of both mesosiderites and probably formed during high temperature metamorphism the compositional interface between core and overgrowth plagioclase is extremely sharp suggesting that cooling rates were 0 1 c y at the peak temperature of metamorphism consistent with high temperature metamorphism occurring in a near surface region of the parent body

pathogen and chemical transport in the karst limestone of the biscayne aquifer 2 chemical retention from diffusion and slow advection 1 a tracer experiment using a nonreactive tracer was conducted as part of an investigation of the potential for chemical and pathogen migration to public supply wells that draw groundwater from the highly transmissive karst limestone of the biscayne aquifer in southeastern florida the tracer was injected into the formation over approximately 1 h and its recovery was monitored at a pumping well approximately 100 m from the injection well the first detection of the tracer occurred after approximately 5 h and the peak concentration occurred at about 8 h after the injection the tracer was still detected in the production well more than 6 days after injection and only 42 of the tracer mass was recovered it is hypothesized that a combination of chemical diffusion and slow advection resulted in significant retention of the tracer in the formation despite the high transmissivity of the karst limestone the tail of the breakthrough curve exhibited a straight line behavior with a slope of 2 on a log log plot of concentration versus time the 2 slope is hypothesized to be a function of slow advection where the velocities of flow paths are hypothesized to range over several orders of magnitude the flow paths having the slowest velocities result in a response similar to chemical diffusion chemical diffusion due to chemical gradients is still ongoing during the declining limb of the breakthrough curve but this process is dwarfed by the magnitude of the mass flux by slow advection

siderophile elements in brecciated hed meteorites and the nature of projectile materials in hed meteorites abstract petrological mineralogical and geochemical studies were performed on five brecciated hed meteorites alh 76005 eet 92003 lew 85300 lew 87026 and gro 95633 in order to elucidate the nature of impactors on the hed parent body some brecciated hed meteorites contain exotic materials such as feni metal grains with low co ni ratios alh 76005 eet 92003 and gro 95633 and carbonaceous chondrite clasts lew 85300 in a clastic and or impact melt matrix such exotic materials were incorporated during brecciation platinum group element pge abundances vary significantly ci 0 002 0 05 but are higher than those of pristine rocks from the hed parent body the pge ratios for the five hed meteorites are inconsistent with each other implying that the impactor components of each hed meteorites are different from each other the various pge ratios are consistent with those for metals from chondrites and iron meteorites and carbonaceous chondrites this study provides the evidence that iab and iva iron meteorites and carbonaceous chondrites cm co cv ck cb and cr ordinary chondrites l and h and enstatite chondrite el are candidates of the impactor materials on the hed parent body it is highly probable that significant amounts of siderophile elements were incorporated into the inner solar system objects like the hed parent body from both chondritic materials and differentiated materials like iron meteorites during heavy bombardment the hed meteorites in this study and metals from mesosiderite have different pd ir ratios probably implying that hed meteorites and mesosiderites formed either at distinct settings on one common parent body or on similar parent bodies

some anomalous features of flow and solute transport arising from fracture aperture variability model fractures with variable apertures are generated by a statistical method and water flow and tracer transport in these fractures are calculated tracer injection and collection are simulated for parallel and convergent flow fields the impact of the use of different injection flow rates and the different locations of injection and collection points are studied the results show that the transport time dispersion and the so called mass balance fracture aperture are very sensitive to the location of the injection point and the injection flow rate these anomalous effects appear to be consistent with observations in several recent field experiments the implications of the calculated results on the analysis of tracer tests are discussed it is concluded that because of the stochastic nature of variable fracture apertures and their permeabilities a point tracer test in a fracture is not sufficient to characterize the properties of the fracture dispersivities and apertures calculated from different tracer tests in the same fracture may vary by orders of magnitude depending on the flow rate and the location of the injection however a line injection of tracer averaged over a series of adjacent points may avoid some of these problems

metal phases of l chondrites their formation and evolution in the nebula and in the parent body abstract metal phases of six three equilibrated and three unequilibrated l chondrites were studied by inaa sem and mossbauer spectroscopy characteristics retained in the bulk metals of unequilibrated chondrites abundant carbon high contents of cr v mn and low contents of w mo and ga compared to metals of equilibrated chondrites less enrichment of w than mo and fractionation of co from ni demonstrate that chondrite metals are not nebular condensates all those characteristics can be well explained by melting chondrite metals are not melting remnants of previously condensed metals rather they were produced by reduction of ci or cm like material during the melting process the complementarity in composition and the similarity in melting feature suggest that chondritic metals and chondrules are the complementary components of the same melting event distribution of trace siderophile elements between taenite and bulk metal indicates that kamacite and taenite can only be the low temperature diffusion products and must have been developed in the chondrite parent body the difference in the taenite composition between equilibrated and unequilibrated chondrites reveals that the equilibrated chondrites were located near the surface while the unequilibrated chondrites were in the interior if they were derived from the common parent body thus while the exsolution of chondrite metal into kamacite and taenite was due to the internal thermal activity the crystallization of eoc silicates resulted from an external heating the internal metamorphism was mild 400 600 c and long whereas the external heating was intense with a maximum temperature in range of 800 950 c and short tetrataenite is present not only in uocs but also in eocs suggesting that the external heating occurred during the internal metamorphism i e within 100 myr of chondrite formation

evolutionary history of the mesosiderite asteroid a chronologic and petrologic synthesis abstract recent petrologic chemical and isotopic analyses of mesosiderite clasts and whole rocks allow reconstruction of the evolutionary history of the mesosiderite parent body mpb chronologic measurements indicate that initial melting of the mpb occurred shortly after accretion 4 56 ga ago at about the same time that the eucrites and angrites formed significant crustal remelting 4 47 ga ago probably associated with metal silicate mixing is responsible for forming abundant gabbroic clasts with extreme positive eu anomalies localized impact melting 4 5 3 9 ga ago produced quench textured clasts and matrices and may be responsible for causing mesosiderite metamorphism as well as the extensive melting of type 4 mesosiderites collisional disruption and gravitational reassembly 3 9 ga ago is indicated by thorough ar degassing at this time metallographic cooling rates of 1 c ma were likely initiated by this event the history of higher temperature events measured by thermoluminescence was annealed out impact excavation and ejection of deeply buried breccias occurred 3 9 ga ago the 10 160 ma cosmic ray exposure ages of mesosiderites represent the epoch when individual mesosiderites were excavated from the mpb or from a 10 m size fragment it is unlikely that mesosiderites and hed howardite eucrite diogenite samples come from the same parent body there is no evidence for metal silicate mixing with attendant redox effects or major crustal remelting on the hed body bulk howardites have flat chondrite normalized rare earth element ree patterns whereas many bulk mesosiderites have ree patterns with positive eu anomalies and relative enrichments in light ree the nature of the heating mechanism which caused the initial differentiation of mesosiderites and howardites is problematic

olivine and pyroxene from the mantle of asteroid 4 vesta a b s t r a c t a number of meteorites contain evidence that rocky bodies formed and differentiated early in our solar system s history and similar bodies likely contributed material to form the planets these differentiated rocky bodies are expected to have mantles dominated by mg rich olivine but direct evidence for such mantles beyond our own planet has been elusive here we identify olivine fragments mg 80 92 in howardite meteorites these mg rich olivine fragments do not correspond to an established lithology in the howardite eucrite diogenite hed meteorites which are thought to be from the asteroid 4 vesta their occurrence in howardite breccias combined with diagnostic oxygen three isotope signatures and minor element chemistry indicates they are vestan the major element chemistry of these mg rich olivines suggests that they formed as mantle residues in crustal layered intrusions or in mg rich basalts the trace element chemistry of these mg rich olivines supports an origin as mantle samples but other formation scenarios could be possible interpreted as mantle samples the range of mg rich olivine compositions indicates that vesta s structure differs from that predicted by conventional models vesta has a chemically heterogeneous mantle that feeds serial magmatism the range of olivine major element chemistries is consistent with models of an incompletely melted mantle such as in the model proposed by wilson and keil 2013 rather than a whole mantle magma ocean for vesta trace element chemistries of mg rich pyroxenes mg 85 92 provide support that some of these pyroxenes may represent initial

experimental evidence of the anisotropy of tracer dispersion in rough fractures with sheared walls 1 dispersion experiments are compared for two model fractures with identical complementary rough walls but with a relative shear displacement parallel u or perpendicular u to the flow velocity u the flowing fluid is a shear thinning polymer solution with a newtonian behavior at low shear rates for u the mixing fronts display large structures well reproduced by assuming parallel channels of conductance deduced from the aperture field this model also explains the amplification of the structures in the shear thinning regime and the distribution of the local transit times x y for u the front is much flatter the local thickness of the front is characterized by a dispersivity x y its distribution is narrow enough to define an effective value pe only for u and in this case pe has a taylor aris like variation with pe

fracture step structure geometrical characterization and effects on fluid flow and breakthrough curve groundwater flow and solute transport through fractured rock is highly responsive to the hydraulic anisotropy and heterogeneity that are specific to every major fracture a major fracture is modeled as the combination of some primal master fractures and several splay fractures that branch out from primal master fractures step structures or jog parts step structures are commonly observed along a major fracture on various scales master fractures were formed and developed by shear movement while some splay fractures were formed by extension normal to their wall this difference in fracturing process may lead to a permeability difference between master fractures and splay fractures which seems to be one of the major factors controlling flow and solute transport through the fracture networks due to its hydraulic anisotropic and heterogeneous features this study is composed of two major components 1 identification and characterization of a step structure from borehole data 2 evaluation of effect of some idealized step structures on breakthrough curve by numerical simulations the fracture data of four 1000 m boreholes were used to make clear fracture patterns in the tono area of japan some major fractures were identified using stereographic projection technique on the basis of these results several idealized models of a major fracture having a step was constructed for the numerical study the obtained results from numerical simulations clearly imply that geometry of step structure plays an important role in flow and transport through the fracture networks

gravity driven infiltration instability in initially dry nonhorizontal fractures experimental evidence demonstrating gravity driven wetting front instability in an initially dry natural fracture is presented an experimental approach is developed using a transparent analog rough walled fracture to explore gravity driven instability three different boundary conditions were observed to produce unstable fronts in the analog fracture application of fluid at less than the imbibition capacity inversion of a density stratified system and redistribution of flow at the cessation of stable infiltration the redistribution boundary condition analogous to the cessation of ponded infiltration is considered in a series of systematic experiments gravitational gradient and magnitude of the fluid input were varied during experimentation qualitative observations imply that finger development is strongly correlated to the structure of the imbibition front at the onset of flow redistribution measurements of fingertip velocity are used to develop a first order relationship with fingertip length measured finger width is compared to theoretical predictions based on linear stability theory

estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses cappa et al modelling pressure pulses in rock fractures estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses frederic cappa 1 yves guglielmi 2 jonny rutqvist 3 chin fu tsang 3 and alain thoraval 4 geosciences azur university of nice sophia antipolis sophia antipolis france geologie des systemes et des reservoirs carbonates university of provence aix marseille france earth sciences division lawrence berkeley national laboratory berkeley usa ineris ecole national superieure des mines de nancy parc de saurupt nancy france corresponding author fax 33 4 92 94 26 10 e mail address cappa geoazur unice fr f cappa