composition of chondrule silicates in ll3 5 chondrites and implications for their nebular history and parent body metamorphism our petrologic studies of 75 type ia and type ii porphyritic olivine chondrules in nine selected ll group chondrites of type 3 3 to type 5 and comparisons with published studies of chondrules in semarkona ll3 0 show that compositions of silicates and bulk chondrules but not overall chondrule textures vary systematically with the petrologic type of the chondrite these compositional trends are due to diffusive exchange between chondrule silicates and other phases e g matrix such as those now preserved in semarkona during which olivines in both chondrule types gained fe2 and mn2 and lost mg2 cr3 and ca2 in a given ll4 5 chondrite the olivines from the two chondrule types are identical in composition enrichments of fe2 in olivine are particularly noticeable in type ia chondrules from type 3 3 3 6 chondrites especially near grain edges chondrule rims grain boundaries and what appear to be annealed cracks compositional changes in low ca pyroxene lag behind those in coexisting olivine consistent with its lower diffusion rates with increasing petrologic type low ca pyroxenes in type ia chondrules become enriched in fe2 and mn2 and depleted in mg2 cr3 and a13 these compositional changes are entirely consistent with mineral equilibration in chondritic material during metamorphism from these compositional data alone we cannot exclude the possibility that chondritic material was metamorphosed to some degree in the nebula but we see no evidence favoring nebula over asteroidal metamorphism nor evidence that the chondrule reacted with nebular gases after crystallization modelling of the equilibration of chondrule olivines suggests that heterogeneous feo concentrations in olivine could be preserved after cooling from 600 c at rates of 1 10 c ma for at least tens to hundreds of millions of years this is consistent with published estimates for the maximum metamorphic temperatures in type 3 chondrites thermal histories derived from metallographic and fission track cooling rates and 4 4 ga 40ar 39ar ages for ordinary chondrites since the lifetime of the solar nebula was not more than 106 years and there is abundant evidence that meteorite parent bodies were heated some even above their melting point we confidently conclude that the formation of type 3 3 5 ordinary chondrites from type 3 0 material by metamorphism occurred in parental asteroids not the solar nebula

peak metamorphic temperatures in type 6 ordinary chondrites an evaluation of pyroxene and plagioclase geothermometry quantifying the peak temperatures achieved during metamorphism is critical for understanding the thermal histories of ordinary chondrite parent bodies various geothermometers have been used to estimate equilibration temperatures for chondrites of the highest metamorphic grade type 6 but results are inconsistent and span hundreds of degrees because different geothermometers and calibration models were used with different meteorites it is unclear whether variations in peak temperatures represent actual ranges of metamorphic conditions within type 6 chondrites or differences in model calibrations we addressed this problem by performing twopyroxene geothermometry using quilf95 on the same type 6 chondrites for which peak temperatures were estimated using the plagioclase geothermometer nakamuta and motomura 1999 we also calculated temperatures for published pyroxene analyses from other type 6 h l and ll chondrites to determine the most representative peak metamorphic temperatures for ordinary chondrites pyroxenes record a narrow overlapping range of temperatures in h6 865 926 c l6 812 934 c and ll6 874 945 c chondrites plagioclase temperature estimates are 96 179 c lower than pyroxenes in the same type 6 meteorites plagioclase estimates may not reflect peak metamorphic temperatures because chondrule glass probably recrystallized to plagioclase prior to reaching the metamorphic peak the average temperature for h l and ll chondrites 900 c which agrees with previously published oxygen isotope geothermometry is at least 50 c lower than the peak temperatures used in current asteroid thermal evolution models this difference may require minor adjustments to thermal model calculations

ideal mixing of divalent cations in mafic magma and its effect on the solution of ferrous oxide in this study three sets of aluminosilicate liquids are equilibrated with metallic iron under controlled oxygen fugacity to determine the compositional dependence of the activity of ferrous oxide in petrologically interesting melts the liquids lie in three ternary systems of the type matrix feo mgo that contain synthetic analogs of standard diabase w 1 morb and high tio2 mare basalt respectively using 218 runs with both high and low iron starting materials the ternaries are contoured at afeo 0 1 intervals by bracketing each isoactivity curve the results demonstrate that the relation aternaryfeo amg freefeo fe fe mg accounts for the variation of afeo at constant mole fraction of matrix xmatrix 1 xfeo xmgo in these ternaries this suggests that ferrous iron and magnesium mix ideally on the sites they occupy in mafic magmas extending this approach demonstrates that the compositional dependence of afeo in a wide range of mafic melts is temperature insensitive and is consistent with anorthite as in a norm calculation being a component of the matrix and the remaining ca behaving like fe mn and mg importantly these findings greatly facilitate determination of the effect of melt chemistry variations on solidliquid distribution coefficients

thermodynamic constraints on the formation conditions of winonaites and silicate bearing iab irons abstract silicate inclusions in iab irons and related winonaite meteorites have textures mineralogies and mineral chemistries that indicate a complex formation history of heating followed by brecciation and metamorphism using olivine orthopyroxene chromite assemblages in five iab iron silicate inclusions caddo county campo del cielo copiapo lueders and udei station and one winonaite winona we calculated closure temperatures and oxygen fugacities for these meteorites calculated olivine chromite fe mg exchange temperatures are compared to two pyroxene temperatures olivine chromite closure temperatures range from 590 c to 700 c while two pyroxene temperatures range from 900 c to 1200 c oxygen fugacities of these meteorites determined for the first time in this study range from 2 3 to 3 2 log units below the fe feo buffer and define a line between the fe feo and cr cr 2 o 3 buffers highly variable temperatures were experienced by these rocks on the hand sample and sometimes even the thin section scale consistent with the idea that the winonaite iab iron parent body experienced collisional fragmentation and reassembly after peak temperatures were reached although modest reduction likely occurred during cooling the oxygen fugacities and mineral compositions recorded at peak metamorphic temperatures suggest that the chondritic precursor for this parent body was initially more reduced than ordinary chondrites

phosphate minerals in ll chondrites a record of the action of fluids during metamorphism on ordinary chondrite parent bodies ordinary chondrites contain two phosphate minerals merrillite and chlorapatite both of which are secondary minerals that developed in response to metamorphism on the chondrite parent bodies we have studied the phosphate mineralogy of four ll chondrites of petrologic types 3 9 6 in order to determine the petrogenesis of the two minerals and interpret the conditions under which they formed characterization of merrillite and apatite includes textural observations mineral compositions determined by electron probe microanalysis and ion microprobe analyses of trace element and volatile anion elemental abundances initial formation of phosphate minerals during mild metamorphism to petrologic type 4 conditions resulted in oxidation of p that was originally incorporated in metal and growth of merrillite as inclusions within metal grains subsequent development of both phosphate minerals occurred in response to diffusional equilibration possible precipitation from fluids as well as replacement reactions resulting from interactions with fluids porosity and vein filling textures in both merrillite and chlorapatite as well as textures indicating replacement of merrillite by chlorapatite support a model in which fluid played a significant role and suggest an interface coupled dissolution reprecipitation mechanism during metasomatism some associations of phosphate minerals with chromite plagioclase assemblages suggest that phosphate minerals could also be related to impact processes either as precipitation from an impact melt or as a result of interactions with a fluid or vapor derived from an impact melt fluid compositions may have been water bearing initially at low temperatures of metamorphism but later evolved to become halogen rich and very dry late stage halogen rich fluids that dominated during cooling of ll chondrite material may have been derived from vaporization of partial melts in the interior of the parent body overall the ll chondrite parent body underwent a complex chemical evolution in which metasomatism played a significant role

magmatic sulfides in the porphyritic chondrules of eh enstatite chondrites abstract the nature and distribution of sulfides within 17 porphyritic chondrules of the sahara 97096 eh3 enstatite chondrite have been studied by backscattered electron microscopy and electron microprobe in order to investigate the role of gas melt interactions in the chondrule sulfide formation troilite fes is systematically present and is the most abundant sulfide within the eh3 chondrite chondrules it is found either poikilitically enclosed in low ca pyroxenes or scattered within the glassy mesostasis oldhamite cas and niningerite mg fe mn s are present in 60 of the chondrules studied while oldhamite is preferentially present in the mesostasis niningerite associated with silica is generally observed in contact with troilite and low ca pyroxene the sahara 97096 chondrule mesostases contain high abundances of alkali and volatile elements average na 2 o 8 7 wt k 2 o 0 8 wt cl 7100 ppm and s 3700 ppm as well as silica average sio 2 62 8 wt our data suggest that most of the sulfides found in eh3 chondrite chondrules are magmatic minerals that formed after the dissolution of s from a volatile rich gaseous environment into the molten chondrules troilite formation occurred via sulfur solubility within fe poor chondrule melts followed by sulfide saturation which causes an immiscible iron sulfide liquid to separate from the silicate melt the fes saturation started at the same time as or prior to the crystallization of low ca pyroxene during the high temperature chondrule forming event s protracted gas melt interactions under high partial pressures of s and sio led to the formation of niningerite silica associations via destabilization of the previously formed fes and low ca pyroxene we also propose that formation of the oldhamite occurred via the sulfide saturation of fe poor chondrule melts at moderate s concentration due to the high degree of polymerization and the high na content of the chondrule melts which allowed the activity of cao in the melt to be enhanced gas melt interactions thus appear to be a key process that may control the mineralogy of chondrules in the different classes of chondrite

measured and simulated flow near a submerged spur dike to improve knowledge of the flow and scour processes associated with spur dikes three dimensional flow velocities were measured at 2 592 points using an acoustic doppler velocimeter over a fixed flat bed with a trapezoidal shaped submerged spur dike in a laboratory flume general velocity distribution and detailed near field flow structures were revealed by the measurements and numerical simulations performed using a free surface turbulent flow model with a k e closure scheme the three dimensional flow separation characterized in this study was found to yield forces on the bed that were significantly different from nonsubmerged vertical obstructions that have been measured in other studies values of bed shear stress derived from both measured and simulated values were similar but indicated that local scour would be initiated in one rather than in the two locations of initial local scour measured in previous experiments with a similar flow

flume experiments on scour downstream of wood stream restoration structures abstract river restoration aims to improve physical natural form and processes of a river techniques to control the riverbed stabilize channel alignment protect stream banks and rebuild the natural habitat are an important part of river restoration projects rivers can be stabilized and habitat restored through techniques such as rebuilding meanders and pool riffle sequences and managing large wood structures that limit channel width to accelerate the normal flows through the constricted section are referred to as stream deflectors single wing double wing and triangular deflectors are the most commonly used types of this measure log frame deflectors consist of a triangular log frame filled with rock deflector constructions singly or in series in low gradient meandering streams divert base flows toward the center of the channel and under certain conditions increase the depth and velocity of flow thereby creating scour pools and enhancing fish habitat scour characteristics and morphologies downstream of log frame deflectors have been analyzed at the hydraulic laboratory of the university of pisa all experiments have been carried out in clear water conditions the results showed that the tailwater depth plays an important role on scour characteristics in addition it was experimentally proven that using log frame deflectors instead of log deflectors result in a better river bank protection in this case for all the tested hydraulic conditions the scour hole never occurred close to the channel bank useful empirical relationships have been proposed in order to evaluate the main features of the scour geometry

three dimensional numerical model for flow and bed deformation around river hydraulic structures this paper describes a numerical model developed to simulate flow and bed deformation around river hydraulic structures the model solved the fully three dimensional reynolds averaged navier stokes equation expressed in a moving boundary fitted coordinate system to calculate the flow field with water and bed surfaces varying in time a nonlinear k e turbulence model was employed in order to predict flow near the structure where three dimensional flow is dominant the temporal change in bed topography was calculated by coupling a stochastic model for sediment pickup and deposition using a momentum equation of sediment particles in order to account for the effect of nonequilibrium sediment transport in validating the numerical model a spur dike and a bridge pier which are considered to be typical river engineering structures were selected by comparing the numerical results with observed laboratory experimental data the model was found to reproduce flow and scour geometry around these structures with

an investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel 1 conditions corresponding to the initiation of the erosion and deposition process 1 the present study investigates the flow physics and the role played by the main coherent structures in the scouring processes around a vertical spur dike in a straight channel at conditions corresponding to the start flat bed of the scouring process large eddy simulation les is performed at a relatively low channel reynolds number re 18 000 in the range where most flume studies with clear water scour conditions are conducted similar to these studies the incoming flow is fully turbulent and contains realistic turbulence fluctuations visualization experiments are conducted to better understand the nature of the interactions between the dominant coherent structures playing a role in the erosion process it is found that the structure of the horseshoe vortex hv system at the base of the spur dike changes considerably in time and in vertical sections perpendicular to the trajectory defined by the axis of the main necklace vortex however its intensity is the largest at vertical sections situated around the tip of the spur dike it is in this region that the core of the main necklace vortex oscillates aperiodically between two preferred modes in one of them zero flow mode the necklace vortex is closer to the spur dike and more compact and the near bed jet flow beneath it is weak in the other one back flow mode a strong near bed jet flow convects the primary necklace vortex away from the spur dike and its core is more elongated and less compact this explains the large amplification by about 1 order of magnitude compared to the surrounding turbulent flow of the turbulent kinetic energy and pressure fluctuations inside the hv system in the region situated around the tip of the spur dike and the double peak distribution of the turbulent kinetic energy past the spur dike in the legs of the necklace vortex the intensity of the bimodal oscillations decreases such that they are not observed in spanwise sections situated at more than one channel depth behind the spur dike it is found that the legs of the horseshoe vortices can interact at times with the vortex tubes shed in the detached shear layer dsl and with the tip of the spur dike these events typically result in a significant change in the coherence of the hv system the largest bed shear stress values in the mean flow are present in the strong acceleration region near the tip of the spur dike but high bed shear stress values are also observed beneath the upstream part of the dsl the bed shear stress fluctuations around the local mean values can be very high especially in the region situated beneath the upstream part of the dsl at random times some of the vortices shed in the dsl merge or interact with eddies from the recirculation region this leads to an increase in their strength and to a large increase of the bed shear stress along their path

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2

late formation of a comet wild 2 crystalline silicate particle pyxie inferred from al mg chronology of plagioclase we examined the al mg isotope systematics of plagioclase in a feo poor ferromagnesian wild 2 particle c2092 7 81 1 0 named pyxie using a 2 m spot three analyses show average 27al 24mg ratio of 65 and excess 26mg value of 0 1 4 5 0 1 4 5 2 indicating no resolvable 26mg excess in the particle the inferred initial 26al 27al 0 ratio of plagioclase in pyxie is estimated as 0 6 4 5 10 6 0 6 4 5 10 6 with an upper limit of 4 10 64 10 6 the result is very similar to that of the feo rich ferromagnesian particle iris ogliore et al 2012 assuming homogeneous distribution of 26al in the early solar system pyxie formed at least 2 6 ma after the oldest ca al rich inclusions this minimum formation age is marginally younger than formation ages of most chondrules in type 3 0 chondrites but comparable with those of mg 98 chondrules in cr3 chondrites considered in conjunction with similar oxygen isotope ratios between pyxie and iris and mg 98 chondrules in cr3 chondrites it is inferred that the ferromagnesian wild 2 particles and mg 98 chondrules in cr3 chondrites formed late in local disk environments that had similar oxygen isotope ratios and redox states

sensitivity of the elastic anisotropy and seismic reflection amplitude of the eagle ford shale to the presence of kerogen the eagle ford shale of central and south texas is currently of great interest for oil and gas exploration and production laboratory studies show that the eagle ford shale is anisotropic with a correlation between anisotropy and total organic carbon organic materials are usually more compliant than other minerals present in organic rich shales and their shapes and distribution are usually anisotropic this makes organic materials an important source of anisotropy in organic rich shales neglecting shale anisotropy may lead to incorrect estimates of rock and fluid properties derived from inversion of amplitude versus offset seismic data organic materials have a significant effect on the pp and ps reflection amplitudes from the austin chalk upper eagle ford interface the upper eagle ford lower eagle ford interface and the lower eagle ford buda limestone interface the higher kerogen content of the lower eagle ford compared with that of the upper eagle ford leads to a negative pp reflection amplitude that dims with offset whereas the ps reflection coefficient increases in magnitude with increasing offset the pp and ps reflection coefficients at the austin chalk upper eagle ford interface the upper eagle ford lower eagle ford interface and the lower eagle ford buda limestone interface all increase in magnitude with increasing volume fraction of kerogen

formation of unequilibrated r chondrite chondrules and opaque phases abstract sulfide assemblages are commonly found in chondritic meteorites as small inclusions in the matrix or in association with chondrules these assemblages are widely hypothesized to form through pre accretionary corrosion of metal by h2s gas or through parent body processes we report here on two unequilibrated r chondrite samples that contain large chondrule sized sulfide nodules in the matrix both samples are from mount prestrud pre 95404 chemical maps and spot and broad beam electron microprobe analyses empa were used to assess the distribution stoichiometry and bulk composition of sulfide nodules and silicate chondrules in the clasts oxygen isotope data were collected via secondary ion mass spectrometry sims to assess the relationship of chondrules to other chondrite groups scanning electron microscopy sem focused ion beam fib and transmission electron microscopy tem analyses were used to assess fine scale features and identify crystal structures in sulfide assemblages thermodynamic models were used to assess the temperature sulfur fugacity fs2 total pressure dust to gas ratio and oxygen fugacity fo2 conditions during sulfide nodule and chondrule formation the unequilibrated clasts include a mixture of type i and type ii chondrules as well as non porphyritic chondrules chondrule oxygen isotopes overlap with ordinary chondrite chondrules sulfide nodules average 200 m in diameter have rounded shapes and are primarily composed of pyrrhotite pentlandite and magnetite some are deformed around chondrules in a petrologic relationship similar in appearance to compound chondrules both nodules and sulfides in chondrules include phosphate inclusions and cu rich lamellae which suggests a genetic relationship between sulfides in chondrules and in the matrix ni co ratios for matrix and chondrule sulfides are solar while fe and ni are non solar and inversely related we hypothesize that sulfide nodules formed via pre accretionary melt processes during chondrule formation precursors composed of a mixture of silicate and sulfide material were heated to form immiscible melt droplets which separated and cooled to form si rich chondrules and s rich nodules sulfide melt was stabilized by a high total pressure 1 atm in a dust or ice enriched environment heating of this material contributed to a high fs2 2 10 3 atm at 1138 c and high fo2 iw 1 to iw 4 in an environment with peak temperatures between 1539 c and 1750 c oxygen isotopic compositions in this region were similar to those recorded by the ll chondrite chondrules

local scour associated with angled spur dikes a series of experiments were conducted in which the volume of the scour hole associated with model spur dikes was measured in a laboratory flume under clear water overtopping flows spur dike models were angled at 45 90 and 135 to the downstream channel sidewall with contraction ratios of 0 125 and 0 250 the main goals of the experiments were to evaluate the effect of the three angles on the volume of scour and potential aquatic habitat and on minimizing erosion adjacent to the streambanks the experiments showed that of the three angles tested the least erosion of the bed in the near bank region was associated with the spur dikes with 90 angles while the greatest volume of the scour hole was associated with the 135 spur dikes it was concluded that spur dikes with 135 angles showed the best potential for providing improved aquatic habitats while minimizing the potential for erosion of the channel bank

paleomagnetism of rumuruti chondrites suggests a partially differentiated parent body abstract different types of magnetic fields were at work in the early solar system nebular fields generated within the protoplanetary nebula solar fields and dynamo fields generated within the solar system solid bodies paleomagnetic studies of extraterrestrial materials can help unravel both the history of these magnetic fields and the evolution of solar system solid bodies in this study we studied the paleomagnetism of two rumuruti chondrites pca 91002 and lap 03639 these chondrites could potentially bear the record of the different fields solar nebular dynamo fields present during the early solar system the magnetic mineralogy consists of pseudo single domain pyrrhotite in lap 03639 and pyrrhotite plus magnetite in pca 91002 paleomagnetic analyses using thermal and alternating field demagnetization reveal a stable origin trending component of magnetization fields of 12 t or higher are required to account for the magnetization in pca 91002 but the timing and exact mechanism of the magnetization are unconstrained in lap 03639 considering various chronological constraints on the parent body evolution and on the evolution of the different sources of magnetic field in the early solar system an internally generated dynamo field of 5 t recorded during retrograde metamorphism is the most likely explanation to account for the measured magnetization this result indicates the existence of an advecting liquid core within the rumuruti chondrite parent body and implies that as proposed for cv and h chondrites this chondritic parent body is partially differentiated

the formation and alteration of the renazzo like carbonaceous chondrites ii linking o isotope composition and oxidation state of chondrule olivine abstract to better understand the formation conditions of type i and type ii chondrules in the renazzo like carbonaceous cr chondrites an in situ major and minor element and o isotope study was conducted twenty one ferromagnesian chondrules from three cr chondrites gra 95229 gra 06100 and que 99177 were analyzed to establish an internally consistent data set from this study we infer that type ii chondrule precursors contained enhanced s bearing dust and ice abundances relative to type i chondrules there is a relationship between the o isotope composition and oxidation state of olivine which may be related to the amount of 16 o poor ice and reduced carbon accreted by chondrule precursors before melting type ii chondrules formed under h 2 o h 2 ratios of 230 740 times solar in contrast type i chondrules formed under more reducing conditions with lower h 2 o h 2 ratios of 10 100 times solar we find a relationship between type ii chondrule petrology relict free vs relict grain bearing and o isotope composition which is due to degree of melting and exchange with a 16 o poor gas reservoir the 16 o poor gas that interacted with both type i and type ii chondrules is estimated to have an isotopic composition between 18 o g 13 27 and 17 o g 10 22 different from the o isotope composition of the water accreted by the cr chondrite parent body due to partial melting type i chondrules and relict grain bearing type ii chondrules exchanged with the 16 o poor gas to a lower degree than relict free type ii chondrules

radar enabled recovery of the sutter s mill meteorite a carbonaceous chondrite regolith breccia doppler weather radar imaging enabled the rapid recovery of the sutter s mill meteorite after a rare 4 kiloton of tnt equivalent asteroid impact over the foothills of the sierra nevada in northern california the recovered meteorites survived a record high speed entry of 28 6 kilometers per second from an orbit close to that of jupiter family comets tisserand s parameter 2 8 0 3 sutter s mill is a regolith breccia composed of cm mighei type carbonaceous chondrite and highly reduced xenolithic materials it exhibits considerable diversity of mineralogy petrography and isotope and organic chemistry resulting from a complex formation history of the parent body surface that diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to c class asteroids are interpreted

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

geometry of scour holes associated with 90 spur dikes the stable pools formed by spur dikes can be a significant factor for improving aquatic habitat in unstable degraded streams prediction of the volume and geometry of the scour hole associated with a spur dike yields information that is valuable for assessing the potential benefit to the aquatic habitat volumes of the scour hole in the vicinity of model spur dikes were measured in a laboratory flume under clear water overtopping flows spur dike length flow depth and shear velocity ratio were varied in the experiments and found to significantly influence the volume of the scour hole for overtopping flows the ratio of the flow depth to the spur dike height was found to be an important control on the geometry of the resulting scour hole at higher flow depth to spur dike height ratios the location of the maximum depth of scour changed from the upstream point of the dike toward the channel bank and caused a secondary scour zone to form downstream of the spur dike a preliminary technique is proposed to predict the volume of scour for spur dikes perpendicular to the bank

comparing wild 2 particles to chondrites and idps we compare the observed composition ranges of olivine pyroxene and fe ni sulfides in wild 2 grains with those from chondritic interplanetary dust particles idps and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular wild 2 olivine has an extremely wide composition range from fa096 with a pronounced frequency peak at fa1 the composition range displayed by the low calcium pyroxene is also very extensive from fs48 to fs0 with a significant frequency peak centered at fs5 these ranges are as broad or broader than those reported for any other extraterrestrial material wild 2 fe ni sulfides mainly have compositions close to that of fes with less than 2 atom ni to date only two pentlandite grains have been found among the wild grains suggesting that this mineral is not abundant the complete lack of compositions between fes and pentlandite with intermediate solid solution compositions suggests but does not require that fes and pentlandite condensed as crystalline species i e did not form as amorphous phases which later became annealed while we have not yet observed any direct evidence of water bearing minerals the presence of ni bearing sulfides and magnesium dominated olivine and low ca pyroxene does not rule out their presence at low abundance we do conclude that new investigations of major and minorelement compositions of chondrite matrix and idps are required

widespread evidence for high temperature formation of pentlandite in chondrites abstract by investigating the compositional and textural evolution of sulfides within a wide range of relatively pristine aqueously altered and thermally metamorphosed chondrites we constrain the equilibration temperatures of sulfide minerals and compare them to the metamorphic history of their host meteorite sulfides in mighei like carbonaceous chondrites are complex as they equilibrated mostly between 100 and 135 c but some may have equilibrated at temperatures up to 600 c this is consistent with some cm chondrite sulfides forming at high temperature during chondrule cooling and others during low temperature aqueous alteration and or annealing karoonda like carbonaceous chondrite sulfides equilibrated between 500 and 230 c which is consistent with formation during cooling and annealing after thermal metamorphism sulfides in the ll chondrites equilibrated between 600 and 230 c and are consistent with formation during chondrule cooling for semarkona ll3 00 and during cooling after thermal metamorphism for the equilibrated samples types 4 6 sulfides in the rumuruti like r chondrites equilibrated between 600 and 500 c and are consistent with formation after thermal metamorphism the sulfides within the brachinite equilibrated between 600 and 400 c consistent with formation during cooling after thermal metamorphism contrary to the assertion that pentlandite is solely the product of low temperature aqueous alteration in many chondrite groups this study suggests that most sulfides in chondrites are formed at or upon cooling from high temperature the evaluation of a single mineral system within samples that retain petrographic context is vital to the interpretation of formation and alteration processes recorded by small extraterrestrial samples such as those that have been returned by the spacecraft missions stardust and hayabusa and will be returned by osiris rex and hayabusa2

the nanoscale mineralogy of fe ni sulfides in pristine and metamorphosed cm and cm ci like chondrites tapping a petrogenetic record we have sampled sulfide grains from one pristine cm2 chondrite yamato y 791198 one thermally metamorphosed cm2 chondrite y 793321 and two anomalous metamorphosed cm ci like chondrites y 86720 and belgica b 7904 by the focused ion beam fib technique and studied them by analytical transmission electron microscopy tem our study aims at exploring the potential of sulfide assemblages and microstructures to decipher processes and conditions of chondrite petrogenesis complex exsolution textures of pyrrhotite crystallographic nc type with n 6 troilite and pentlandite occur in grains of y 791198 and y 793321 additionally polycrystalline 4c pyrrhotite pentlandite magnetite aggregates occur in y 791198 pointing to diverse conditions of gas solid interactions in the solar nebula coarser exsolution textures of y 793321 grains indicate higher long term average temperatures in the 100 c range compared to y 791198 and other cm chondrites sulfide mineralogy of y 86720 and b 7904 is dominated by aggregates of pure troilite and metal indicating metamorphic equilibration at sulfur fugacities fs2 of the iron troilite buffer absence of magnetite in equilibrium with sulfide and metal in y 86720 indicates higher peak temperatures compared with b 7904 in which coexistence of troilite metal and magnetite constrains metamorphic temperature to less than 570 c nc pyrrhotite occurs in both meteorites as nm wide rims on troilite grains and together with frequent anhydrite indicates a retrograde metamorphic stage at higher fs2 slightly above the fayalite magnetite quartz pyrrhotite buffer fine grained troilite olivine intergrowths in both meteorites suggest the pre metamorphic presence of tochilinite serpentine interlayer phases pointing to mineralogical cm affinity pseudomorphs after euhedral pyrrhotite crystals in y 86720 in turn suggest ci affinity as do previously published o isotopic data of both meteorites

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

phase relations involving pyrrhotite below 350 degrees c a hydrothermal recrystallization method was employed to determine the phase relations in the fe s system involving pyrrhotite between 350 degrees and 115 degrees c the superstructures of pyrrhotite as designated by nakazawa and morimoto 1970 1971 are considered to be thermodynamic phases the solvus between pyrite and hexagonal 1c 1 pyrrhotite continues below 325 degrees c along the slope established by toulmin and barton 1964 to 308 degrees c where a discontinuity marks the upper stability of the mc superstructure the solvus then continues along a similar slope to 262 degrees c where with the onset of the na superstructure there is a discontinuity and the curve reverses slope sharply at 254 degrees c monoclinic 4c pyrrhotite becomes stable in the peritectoid reaction hexagonal na pyrrhotite 47 30 at fe pyrite monoclinic 4c pyrrhotite 47 25 at fe monoclinic pyrrhotite exists over a range of compositions the maximum being 46 4 to 46 9 at percent fe at 115 degrees c hexagonal pyrrhotite is separated from monoclinic pyrrhotite by a narrow miscibility gap down to the upper stability limit of the nc superstructure at 209 degrees c below 209 degrees c the miscibility gap widens with hexagonal nc pyrrhotite of 47 3 at percent fe coexisting with monoclinic pyrrhotite of 46 9 at percent fe at the sulfur rich limit of the stability field monoclinic pyrrhotite coexists with pyrite the phases greigite smythite and marcasite were not encountered our results are in reasonable agreement with those obtained previously by hydrothermal synthesis methods but they are in disagreement with some results obtained in dry experiments which have produced metastable phase assemblages the phase diagram is compatible with natural pyrrhotite occurrences and in particular with those from geothermal boreholes at broadlands new zealand from which samples were recovered at known quench temperatures on the other hand our studies cast considerable doubt on the validity of the pyrrhotite geothermometer as applied to ores

evidence for aqueous activity on comet 81p wild 2 from sulfide mineral assemblages in stardust samples and ci chondrites abstract the discovery of nickel copper and zinc bearing iron sulfides from comet 81p wild 2 wild 2 represents the strongest evidence in the stardust collection of grains that formed in an aqueous environment we investigated three microtomed tem sections which contain crystalline sulfide assemblages from wild 2 and twelve thin sections of the hydrothermally altered ci chondrite orgueil detailed structural and compositional characterizations of the sulfide grains from both collections reveal striking similarities the stardust samples include a cubanite cufe 2 s 3 grain a pyrrhotite fe ni 1 x s pentlandite fe ni 9 s 8 assemblage and a pyrrhotite sphalerite fe zn s assemblage similarly the ci chondrite sulfides include individual cubanite and pyrrhotite grains cubanite pyrrhotite assemblages pyrrhotite pentlandite assemblages as well as possible sphalerite inclusions within pyrrhotite grains the cubanite is the low temperature orthorhombic form which constrains temperature to a maximum of 210 c the stardust and orgueil pyrrhotites are the 4c monoclinic polytype which is not stable above 250 c the combinations of cubanite and pyrrhotite as well as pyrrhotite and pentlandite signify even lower temperatures the crystal structures compositions and petrographic relationships of these sulfides constrain formation and alteration conditions taken together these constraints attest to low temperature hydrothermal processing our analyses of these minerals provide constraints on large scale issues such as heat sources in the comet forming region aqueous activity on cometary bodies and the extent and mechanisms of radial mixing of material in the early nebula the sulfides in the wild 2 collection are most likely the products of low temperature aqueous alteration they provide evidence of radial mixing of material e g cubanite troilite from the inner solar system to the comet forming region and possible secondary aqueous processing on the cometary body

impact of groyne on channel morphology and sedimentology in an ephemeral alluvial river of bengal basin numerous groynes had been constructed on the dwarkeswar river to improve bank protection among them groynes adjacent to the village rautara of khandaghosh block west bengal have been studied which were constructed in the year of 2009 this study investigates the alteration of channel morphology sedimentology and flow characteristics influenced by emerged groynes through micro level field study an extensive field survey has been made with a dumpy level and fifty nine sediment samples were collected from the field different channel parameters such as degradation aggradation ratio braided index channel instability and bar occupied area indices have been used from 2003 to 2018 the simulation of channel flow has been done using hec ras it has been found that width depth w d ratio bankfull channel width channel area and sand bed length of the river decrease due to groyne construction on the other hand channel maximum bankfull channel depth depositional rate the difference between average depth maximum depth and braided index drastically increased increasing flow velocity flow deflection with coarse and poorly sorted multimodal sediments near the tip of the groynes as well as decreasing flow velocity curve flow path accelerated sedimentation with elevating river bed have been observed altogether result indicates that the emerged groynes are effective in protecting the river banks at the cost of channel degradation

fe ni metal and sulfide minerals in cm chondrites an indicator for thermal history abstract cm chondrites were subjected to aqueous alteration and in some cases to secondary metamorphic heating the effects of these processes vary widely and have mainly been documented in silicate phases herein we report the characteristic features of fe ni metal and sulfide phases in 13 cm and 2 cm related chondrites to explore the thermal history of these chondrites the texture and compositional distribution of the metal in cm are different from those in unequilibrated ordinary and co chondrites but most have similarities to those in highly primitive chondrites such as ch cr and acfer 094 we classified the cm samples into three categories based on metal composition and sulfide texture fe ni metal in category a is kamacite to martensite category b is characterized by pyrrhotite grains always containing blebs or lamellae of pentlandite opaque mineral assemblages of category c are typically kamacite ni co rich metal and pyrrhotite these categories are closely related to the degree of secondary heating and are not related to degree of the aqueous alteration the characteristic features of the opaque minerals can be explained by secondary heating processes after aqueous alteration category a cm chondrites are unheated whereas those in category b experienced small degrees of secondary heating cms in category c were subjected to the most severe secondary heating process thus opaque minerals can provide constraints on the thermal history for cm chondrites

p to s conversion for a thin anisotropic zone produced by vertical fracturing point source synthetic seismic responses for a thin fractured bed are generated interpreted and processed the synthesis is carried out for a compressional source and multicomponent surface receivers the anisotropy considered has hexagonal symmetry with a horizontal symmetry axis and represents oil and gas filled aligned vertical fractures for a broad range of fracture densities and aspect ratios p to s reflected conversions recorded on the horizontal geophones show both kinematic and dynamic anomalies that increase with increasing fracture density and are only weakly dependent on aspect ratio in contrast the vertical component p wave reflections provide a much poorer diagnostic of fracturing analytic expressions for the eigenvalues and eigenvectors of a vertically fractured system are presented that have the same simplicity as those for transverse isotropy new linearized expressions for mode converted amplitudes are developed for small angles of incidence and are used to interpret the synthetic response

siderophile element anomalies in ck carbonaceous chondrites implications for parent body aqueous alteration and terrestrial weathering of sulfides abstract ck chondrites constitute the most oxidized anhydrous carbonaceous chondrite group most of the fe occurs in magnetite and in feo rich mafic silicates the two observed ck falls karoonda and kobe along with thirteen relatively unweathered ck finds have unfractionated siderophile element abundance patterns in contrast a sizable fraction of ck finds 9 of 24 investigated shows fractionated siderophile abundance patterns including low abundances of ni co se and au the most extreme depletions are in ni 0 24 of normal ck and au 0 14 of normal ck this depletion pattern has not been found in other chondrite groups out of the 74 ck chondrites listed in the meteoritical bulletin database 2006 excluded considerably paired specimens see http tin er usgs gov meteor metbull php we analyzed 24 and subclassified the ck chondrites in terms of their chemical composition and sulfide mineralogy sl siderophiles low six samples for large depletions in ni co se and au 50 of sulfides lost sm siderophiles medium two cks for moderately low ni and co abundances sulfides are highly altered or partly lost sh siderophiles high one specimen for enrichments in ni co se and au normal for unfractionated samples 13 samples the sole sh sample may have obtained additional sulfide from impact redistribution in the parent asteroid we infer that these elements became incorporated into sulfides after asteroidal aqueous processes oxidized nebular metal thermal metamorphism probably also played a role in their mineral siting the siderophile losses in the sl and sm samples are mainly the result of oxidation of pentlandite pyrite and violarite by terrestrial alteration followed by leaching of the resulting phases some antarctic ck chondrites have lost most of their sulfides but retained ni co se and au presumably as insoluble weathering products

shock and annealing in the amphibole and mica bearing r chondrites mil 11207 r6 and lap 04840 r6 contain hornblende and phlogopite mil 07440 r6 contains accessory titan phlogopite and no hornblende all three meteorites have been shocked mil 11207 contains extensive sulfide veins pyroxene that formed from dehydrated hornblende and an extensive network of plagioclase glass mil 07440 contains chromite plagioclase assemblages chromite veinlets and blebs pincer shaped plagioclase patches but no sulfide veins lap 04840 contains olivine grains with chromite bleb laden cores and opaque free rims rare grains of pyroxene that formed from dehydrated hornblende and no sulfide veins these meteorites appear to have been heated to maximum temperatures of approximately 700 900 c under conditions of moderately high ph2o perhaps 250 500 bars all three samples underwent postshock annealing during this process olivine crystal lattices healed giving the rocks the appearance of shock stage s1 and diffusion of fe and s from thin sulfide veins to coarse sulfide grains caused the veins to disappear in mil 07440 and lap 04840 this latter process apparently also occurred in most s1 s2 ordinary chondrites of high petrologic type the pressure temperature conditions responsible for forming the amphibole and mica in these rocks may have been present at depths of a few tens of kilometers as suggested in the literature a giant impact or a series of smaller impacts would then have been required to excavate the hornblende and biotite bearing rocks and bring them closer to the surface it was in that latter location where the samples were shocked deposited in a hot ejecta blanket of low thermal diffusivity and annealed

shock and thermal history of northwest africa 4859 an annealed impact melt breccia of ll chondrite parentage containing unusual igneous features and pentlandite abstract northwest africa 4859 nwa 4859 is a meteorite of ll chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite the most obvious unusual feature is a high proportion of large 3 cm diameter igneous textured enclaves lites interpreted as shock melts that were intruded into an ll chondrite host one such lite appears to have been produced by whole rock melting of ll chondrite initial rapid partial crystallization and subsequent slow cooling of the residual melt in the host to produce a differentiated object other unusual features include mm sized overgrowth objects fine grained plagioclase rich bands and coarse troilite 7 mm across grains all these features are interpreted as having crystallized from melts produced by a single transient shock event followed by slow cooling a subsequent shock event of moderate s3 intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype pentlandite together with associated troilite in nwa 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature 230 c following the second shock event nwa 4859 is interpreted to be an unusual impact melt breccia that contains shock melt which crystallized in different forms at depth within the parent body

chondrules in ck carbonaceous chondrites and thermal history of the cv ck parent body ck chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6 it is commonly reported than 15 vol of ck4 6 samples are composed of chondrules the modal abundance of chondrules estimated here for 18 ck3 6 including 5 ck3s ranges from zero totally recrystallized to 50 5 although almost all chemically re equilibrated with the host matrix we recognized in ck3s and tanezrouft tnz 057 ck4 up to 85 of chondrules as former type i chondrules mean diameters of chondrules range from 0 22 to 1 05 mm for karoonda ck4 and tnz 057 ck4 respectively up to 60 of chondrules in ck3 4 are surrounded by igneous rims from 20 m to 2 mm width zoned olivines were found in unequilibrated chondrules from dag 431 ck3 an nwa 4724 ck3 8 nwa 4423 ck3 9 and tnz 057 ck4 we modeled fe mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the ck parent body metamorphism and proposed a two stage diffusion process in order to account for the position of inflection points situated within chondrules time scales inferred from fe mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred of thousand years from 50 to 70 000 years for peak metamorphic temperatures of 1140 and 920 k respectively these durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay using the concept of a continuous cv ck metamorphic series which is reinforced by this study we estimated peak metamorphic temperatures 850 k for cv 850 920 k for ck3 and 920 1140 k for ck4 6 chondrites considering a duration of 70 000 years

intermineral oxygen three isotope systematics of silicate minerals in equilibrated ordinary chondrites high precision oxygen three isotope ratios were measured for four mineral phases olivine low ca and high ca pyroxene and plagioclase in equilibrated ordinary chondrites eocs using a secondary ion mass spectrometer eleven eocs were studied that cover all groups h l ll and petrologic types 4 5 6 including s1 s4 shock stages as well as unbrecciated and brecciated meteorites sims analyses of multiple minerals were made in close proximity mostly 100 m from several areas in each meteorite thin section to evaluate isotope exchange among minerals oxygen isotope ratios in each mineral become more homogenized as petrologic type increases with the notable exception of brecciated samples in type 4 chondrites oxygen isotope ratios of olivine and low ca pyroxene are heterogeneous in both 18o and 17o showing similar systematics to those in type 3 chondrites in type 5 and 6 chondrites oxygen isotope ratios of the four mineral phases plot along mass dependent fractionation lines that are consistent with the bulk average 17o of each chondrite group the 18o of three minerals low ca and high ca pyroxene and plagioclase are consistent with equilibrium fractionation at temperatures of 700 1000 c in most cases the 18o values of olivine are higher than those expected from pyroxene and plagioclase suggesting partial retention of premetamorphic values due to slower oxygen isotope diffusion in olivine than pyroxene during thermal metamorphism in ordinary chondrite parent bodies

petrography stable isotope compositions microraman spectroscopy and presolar components of roberts massif 04133 a reduced cv3 carbonaceous chondrite here we report the mineralogy petrography c n o stable isotope compositions degree of disorder of organic matter and abundances of presolar components of the chondrite roberts massif rbt 04133 using a coordinated multitechnique approach the results of this study are inconsistent with its initial classification as a renazzo like carbonaceous chondrite and strongly support rbt 04133 being a brecciated reduced petrologic type 3 3 vigarano like carbonaceous cv chondrite rbt 04133 shows no evidence for aqueous alteration however it is mildly thermally altered up to approximately 440 c which is apparent in its whole rock c and n isotopic compositions the degree of disorder of c in insoluble organic matter low presolar grain abundances minor element compositions of fe ni metal chromite compositions and morphologies and the presence of unequilibrated silicates sulfides within type i chondrules from rbt 04133 appear to be pre accretionary i e did not form via aqueous alteration providing further evidence that some sulfide minerals formed prior to accretion of the cv chondrite parent body the thin section studied contains two reduced cv3 lithologies one of which appears to be more thermally metamorphosed indicating that rbt 04133 like several other cv chondrites is a breccia and thus experienced impact processing linear foliation of chondrules was not observed implying that rbt 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism presolar silicates are still present in rbt 04133 although presolar sic grain abundances are very low indicating that the progressive destruction or modification of presolar sic grains begins before presolar silicate grains are completely unidentifiable

the formation and alteration of the renazzo like carbonaceous chondrites iii toward understanding the genesis of ferromagnesian chondrules to better understand the formation conditions of ferromagnesian chondrules from the renazzo like carbonaceous cr chondrites a systematic study of 210 chondrules from 15 cr chondrites was conducted the texture and composition of silicate and opaque minerals from each observed feo rich type ii chondrule and a representative number of feo poor type i chondrules were studied to build a substantial and self consistent data set the average abundances and standard deviations of cr2o3 in feo rich olivine phenocrysts are consistent with previous work that the cr chondrites are among the least thermally altered samples from the early solar system type ii chondrules from the cr chondrites formed under highly variable conditions e g precursor composition redox conditions cooling rate with each chondrule recording a distinct igneous history the opaque minerals within type ii chondrules are consistent with formation during chondrule melting and cooling starting as s and ni rich liquids at 988 1350 c then cooling to form monosulfide solid solution mss that crystallized around olivine pyroxene phenocrysts during cooling fe ni metal crystallized from the s and ni rich liquid and upon further cooling mss decomposed into pentlandite and pyrrhotite with pentlandite exsolving from mss at 400 600 c the composition texture and inferred formation temperature of pentlandite within chondrules studied here is inconsistent with formation via aqueous alteration however some opaque minerals fe ni metal versus magnetite and panethite present in type ii chondrules are a proxy for the degree of whole rock aqueous alteration the texture and composition of sulfide bearing opaque minerals in graves nunataks 06100 and grosvenor mountains 03116 suggest that they are the most thermally altered cr chondrites

insights into solar nebula formation of pyrrhotite from nanoscale disequilibrium phases produced by h2s sulfidation of fe metal lauretta 2005 produced sulfide in the laboratory by exposing canonical nebular metal analogs to h 2 s gas under temperatures and pressures relevant to the formation of the solar system the resulting reactions produced a suite of sulfides and nanophase materials not visible at the microprobe scale but which we have now analyzed by tem for comparison with interplanetary dust samples and comet wild 2 samples returned by the stardust mission we find the unexpected result that disequilibrium formation favors pyrrhotite over troilite and also produces minority schreibersite daubreelite barringerite taenite oldhamite and perryite at the metal sulfide interface tem identification of nanophases and analysis of pyrrhotite superlattice reflections illuminate the formation pathway of disequilibrium sulfide we discuss the conditions under which such disequilibrium can occur and implications for formation of sulfide found in extraterrestrial materials

two dimensional depth averaged model simulation of suspended sediment concentration distribution in a groyne field summary river training structures such as spur dikes are effective engineered methods used to protect banks and improve aquatic habitat this paper reports the development and application of a two dimensional depth averaged hydrodynamic model to simulate suspended sediment concentration distribution in a groyne field the governing equations of flow hydrodynamic model are depth averaged two dimensional reynold s averaged momentum equations and continuity equation in which the density of sediment laden flow varies with the concentration of suspended sediment the depth averaged two dimensional convection and diffusion equation was solved to obtain the depth averaged suspended sediment concentration the source term is the difference between suspended sediment entrainment and deposition from bed surface one laboratory experiment was chosen to verify the simulated flow field around a groyne and the other to verify the suspended sediment concentration distribution in a meandering channel then the model utility was demonstrated in a field case study focusing on the confluence of the kankakee and iroquois rivers in illinois united states to simulate the distribution of suspended sediment concentration around spur dikes results demonstrated that the depth averaged two dimensional model can approximately simulate the flow hydrodynamic field and concentration of suspended sediment spur dikes can be used to effectively relocate suspended sediment in alluvial channels

the distribution of platinum group elements pge and other chalcophile elements among sulfides from the creighton ni cu pge sulfide deposit sudbury canada and the origin of palladium in pentlandite concentrations of platinum group elements pge ag as au bi cd co mo pb re sb se sn te and zn have been determined in base metal sulfide bms minerals from the western branch 402 trough orebodies of the creighton ni cu pge sulfide deposit sudbury canada the sulfide assemblage is dominated by pyrrhotite with minor pentlandite chalcopyrite and pyrite and they represent monosulfide solid solution mss cumulates the aim of this study was to establish the distribution of the pge among the bms and platinum group minerals pgm in order to understand better the petrogenesis of the deposit mass balance calculations show that the bms host all of the co and se a significant proportion 40 90 of os pd ru cd sn and zn but very little 35 of the ag au bi ir mo pb pt rh re sb and te osmium and ru are concentrated in equal proportions in pyrrhotite pentlandite and pyrite cobalt and pd 1 ppm are concentrated in pentlandite silver cd sn zn and in rare cases au and te are concentrated in chalcopyrite selenium is present in equal proportions in all three bms iridium rh and pt are present in euhedrally zoned pge sulfarsenides which comprise irarsite irass hollingworthite rhass pge ni rich cobaltite coass and subordinate sperrylite ptas2 all of which are hosted predominantly in pyrrhotite and pentlandite silver au bi mo pb re sb and te are found predominantly in discrete accessory minerals such as electrum au ag alloy hessite ag2te michenerite pdbite and rhenium sulfides the enrichment of os ru ni and co in pyrrhotite pentlandite and pyrite and ag au cd sn te and zn in chalcopyrite can be explained by fractional crystallization of mss from a sulfide liquid followed by exsolution of the sulfides the early crystallization of the pge sulfarsenides from the sulfide melt depleted the mss in ir and rh the bulk of pd in pentlandite cannot be explained by sulfide fractionation alone because pd should have partitioned into the residual cu rich liquid and be in chalcopyrite or in pgm around chalcopyrite the variation of pd among different pentlandite textures provides evidence that pd diffuses into pentlandite during its exsolution from mss the source of pd was from the small quantity of pd that partitioned originally into the mss and a larger quantity of pd in the nearby cu rich portion intermediate solid solution and or pd bearing pgm the source of pd became depleted during the diffusion process thus later forming pentlandite rims of coarse granular veinlets and exsolution flames contains less pd than early forming pentlandite cores of coarse granular

sensitivity of three component 3d finite difference elastic seismic modeling to inclusion parameters in hti and tti media with high inclusion density parameters associated with the presence of inclusions cracks or vugs significantly influence seismic responses the t matrix method is used to define approximate anisotropic effective elastic stiffness tensors for media with inclusions this allows 3d three component eighth order staggered grid finite difference modeling to simulate the seismic responses of anisotropic media with high inclusion density various aspect ratios spatial distributions and orientations of inclusions and fluid content the model parameters are chosen to represent aligned inclusions ranging from vertical cracks to vugs in a carbonate reservoir encased in clastics the magnitude of anisotropy increases with increasing inclusion density for p and s waves cracks in a high velocity carbonate reduce the stiffnesses and correspondingvelocities this results in smaller contrasts with the surrounding lower stiffness clastics and hence smaller reflection coefficients s wave splitting and the anisotropy of vp vs are clearly

cm and co chondrites a common parent body or asteroidal neighbors insights from chondrule silicates abstract by investigating the petrology and chemical composition of type ii feo rich chondrules in the mighei like carbonaceous cm chondrites we constrain their thermal histories and relationship to the ornans like carbonaceous co chondrites we identified feo rich relict grains in type ii chondrules by their fe mn ratios their presence indicates chondrule recycling among type ii chondrules the majority of relict grains in type ii chondrules are feo poor olivine grains consistent with previous studies chemical similarities between cm and co chondrite chondrules indicate that they had similar formation conditions and that their parent bodies probably formed in a common region within the protoplanetary disk however important differences such as mean chondrule size and the lower abundance of feo poor relicts in cm chondrite type ii chondrules than in co chondrites suggest cm and co chondrules did not form together and they likely originate from distinct parent asteroids despite being aqueously altered many cm chondrites contain pre accretionary anhydrous minerals i e olivine that are among the least thermally metamorphosed materials in chondrites according to the cr 2 o 3 content of their ferroan olivine the presence of these minimally altered pre accretionary chondrule silicates suggests that samples to be returned from aqueously altered asteroids by the hayabusa2 and osiris rex asteroid sample return missions even highly hydrated may contain silicates that can provide information about the pre accretionary histories and conditions of asteroids ryugu and bennu respectively

iron and iron nickel sulfides in chondritic interplanetary dust particles abstract we report the results of a study of iron and iron nickel sulfides in chondritic anhydrous and hydrated interplanetary dust particles idps the idps were characterized using chemical and mineralogical techniques including energy dispersive x ray analyses and transmission electron microscopy it is widely believed that the first sulfur containing mineral to form in the early solar nebula should have been stoichiometric fes troilite and that pyrrhotite is of secondary origin all examined interplanetary dust particles both anhydrous and hydrous types contain more pyrrhotite than troilite suggesting that the former was a common possibly predominant nebular condensate phase pyrrhotite could form from sulfidation of troilite after the latter had exfoliated from substrate metal grains in contrast to anhydrous idps hydrated ones contain ni rich sulfides including pentlandite which are probably of secondary origin

mean flow and turbulence around a laboratory spur dike the three dimensional turbulent flow field around a spur dike in a plane fixed bed laboratory open channel was studied experimentally using a microacoustic doppler velocimeter mean and turbulence characteristics in all three spatial directions were evaluated at upstream and downstream cross sections near the dike results showed that the primary flow separated in both lateral and vertical directions two counter rotating flow circulations consisting of the lateral and vertical velocity components originated at the dike section downstream of the dike the circulation in the flow separation zone is stronger than the one in the contracted primary flow zone the maximum bed shear stresses estimated using reynolds stresses is about three times as large as the mean bed shear stress of incoming flow

oxygen isotope and chemical compositions of magnetite and olivine in the anomalous ck3 watson 002 and ungrouped asuka 881595 carbonaceous chondrites effects of parent body metamorphism we report in situ o isotope and chemical compositions of magnetite and olivine in chondrules of the carbonaceous chondrites watson 002 anomalous ck3 and asuka a 881595 ungrouped c3 magnetite in watson 002 occurs as inclusion free subhedral grains and rounded inclusion bearing porous grains replacing fe ni metal in a 881595 magnetite is almost entirely inclusion free and coexists with ni rich sulfide and less abundant ni poor metal oxygen isotope compositions of chondrule olivine in both meteorites plot along carbonaceous chondrite anhydrous mineral ccam line with a slope of approximately 1 and show a range of 17o values from approximately 3 to 6 one chondrule from each sample was found to contain o isotopically heterogeneous olivine probably relict grains oxygen isotope compositions of magnetite in a 881595 plot along a mass dependent fractionation line with a slope of 0 5 and show a range of 17o values from 2 4 to 1 1 oxygen isotope compositions of magnetite in watson 002 cluster near the ccam line and a 17o value of 4 0 to 2 9 these observations indicate that magnetite and chondrule olivine are in o isotope disequilibrium and therefore not cogenetic we infer that magnetite in ck chondrites formed by the oxidation of pre existing metal grains by an aqueous fluid during parent body alteration in agreement with previous studies the differences in 17o values of magnetite between watson 002 and a 881595 can be attributed to their different thermal histories the former experienced a higher degree of thermal metamorphism that led to the o isotope exchange between magnetite and adjacent silicates

heavily metamorphosed clasts from the cv chondrite breccias mokoia and yamato 86009 metamorphosed clasts in the cv carbonaceous chondrite breccias mokoia and yamato 86009 y 86009 are coarse grained granular polymineralic rocks composed of ca bearing up to 0 6 wt cao ferroan olivine fa34 39 ferroan al diopside fs9 13wo47 50 approximately 2 7 wt al2o3 plagioclase an37 84ab63 17 cr spinel cr cr al 0 19 0 45 fe fe mg 0 60 0 79 nepheline pyrrhotite pentlandite ca phosphate and rare grains of ni rich taenite low ca pyroxene is absent most clasts have triple junctions between silicate grains indicative of prolonged thermal annealing based on the olivine spinel and pyroxene thermometry the estimated metamorphic temperature recorded by the clasts is approximately 1100 k few clasts experienced thermal metamorphism to a lower degree and preserved chondrule like textures the mokoia and y 86009 clasts are mineralogically unique and different from metamorphosed chondrites of known groups h l ll r eh el co ck and primitive achondrites acapulcoites brachinites lodranites on a three isotope oxygen diagram compositions of olivine in the clasts plot along carbonaceous chondrite anhydrous mineral line and the allende mass fractionation line and overlap with those of the cv chondrule olivines the 17o values of the clasts range from about 4 3 to 3 0 we suggest that the clasts represent fragments of the cv like material that experienced metasomatic alteration high temperature metamorphism and possibly melting in the interior of the cv parent asteroid the lack of low ca pyroxene in the clasts could be due to its replacement by ferroan olivine during iron alkali metasomatic alteration or by high ca ferroan pyroxene during melting under oxidizing conditions

3d flow and sediment dynamics in a laboratory channel bend with and without stream barbs abstracta series of laboratory flume experiments were performed to study the effect of stream barbs on flow field dynamics and sediment erosion in a 135 mobile bed channel bend stream barbs also known as spur dikes or submerged groynes are low profile linear rock features that redirect high velocity flow away from the outer bank of channel bends unlike emergent groynes the submerged nature of these structures creates a unique combination of horizontal shear plunging type flow and vertical shear at the groyne tip spatially dense high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three dimensional 3d velocity throughout the bend and in the vicinity of the stream barbs this paper demonstrates that the outer bank region particularly between barbs may still be at risk of erosion or even increased erosion greater than the same case without barbs if stream barbs generate excessive secondary velocities because of their size and layout that are op

3 d flow and scour near a submerged wing dike adcp measurements on the missouri river 1 detailed mapping of bathymetry and three dimensional water velocities using a boat mounted single beam sonar and acoustic doppler current profiler adcp was carried out in the vicinity of two submerged wing dikes located in the lower missouri river near columbia missouri during high spring flows the wing dikes become submerged creating a unique combination of vertical flow separation and overtopping plunging flow conditions causing large scale three dimensional turbulent flow structures to form on three different days and for a range of discharges sampling transects at 5 and 20 m spacing were completed covering the area adjacent to and upstream and downstream from two different wing dikes the objectives of this research are to evaluate whether an adcp can identify and measure large scale flow features such as recirculating flow and vortex shedding that develop in the vicinity of a submerged wing dike and whether or not moving boat single transect data are sufficient for resolving complex three dimensional flow fields results indicate that spatial averaging from multiple nearby single transects may be more representative of an inherently complex temporally and spatially variable three dimensional flow field than repeated single transects results also indicate a correspondence between the location of calculated vortex cores resolved from the interpolated three dimensional flow field and the nearby scour holes providing new insight into the connections between vertically oriented coherent structures and local scour with the unique perspective of flow and morphology in a large river

mineralogy and texture of fe ni sulfides in ci1 chondrites clues to the extent of aqueous alteration on the ci1 parent body to better understand the role of aqueous alteration on the ci1 parent body we have analyzed the texture composition and mineral associations of iron nickel sulfides in four of the five known ci1 chondrites the most commonly occurring sulfide present in the ci1 chondrites is the iron deficient fe ni sulfide pyrrhotite fe ni 1 xs that has a composition close to that of stoichiometric troilite fes three of the ci1s alais ivuna and tonk also contain pentlandite fe ni 9s8 although pentlandite is a rare phase in ivuna cubanite cufe2s3 was found in both alais and ivuna in this study although it has also been reported in orgueil macdougall and kerridge 1977 the pyrrhotite grains in all four chondrites form hexagonal rectangular or irregular shapes and show no evidence of ni or co zoning the pyrrhotite grains in orgueil and ivuna are in general smaller and show more corrosions or embayments than those in alais or tonk we suggest that the precursor sulfide present in the ci1 chondrites was troilite which during brecciation and oxidation on the parent body at a temperature of 100 c or less converted the troilite to magnetite and pyrrhotite with pentlandite inclusions subsequently continued alteration on the parent body removed pentlandite partially from alais tonk and ivuna completely from orgueil leaving behind pyrrhotite with spaces corrosions where the pentlandite had been ni derived from the pentlandite was incorporated into ferrihydrite onto the surface of which the ni na sulfate ni bloedite formed based on the size and abundant corrosions within pyrrhotite grains combined with observations from other authors we conclude that orgueil and ivuna have undergone a greater degree of alteration than alais and tonk further work is needed to assess the conditions under which pentlandite would be dissolved preferentially to pyrrhotite as the study of terrestrial literature indicates that the latter mineral is preferentially removed

relict chondrules in primitive achondrites remnants from their precursor parent bodies abstract we studied the petrography analyzed the chemical compositions constrained the closure temperatures via geothermometry and determined the oxidation states of relict chondrules in campo del cielo iab iron meteorite graves nunataks gra 98028 acapulcoite and netschaevo iie iron meteorite to constrain their formation conditions and investigate links to known meteorite groups despite having been thermally metamorphosed mineral phases within relict chondrules retain information about their precursor compositions the sizes and textures of relict chondrules and silicate and chromite compositions indicate that campo del cielo gra 98028 and netschaevo had distinct parent bodies that were similar to but different from known chondrite groups to determine the utility of relict chondrule sizes in thermally metamorphosed meteorites we determined the chondrule size distributions in the ll chondrites semarkona ll3 00 soko banja ll4 siena ll5 and saint severin ll6 and the h chondrites clovis no 1 h3 6 kesen h4 arbol solo h5 and estacado h6 as expected mean chondrule diameters increase with degree of thermal metamorphism we find that campo del cielo and gra 98028 were reduced during thermal metamorphism consistent with previous studies indicating that their precursors were initially more feo rich than their current compositions in contrast to previous studies we find no evidence for reduction of silicates in netschaevo normal zoning of olivine in netschaevo is consistent with crystallization and suggests its silicates are near their primary feo contents the presence of elongated chromite grains along olivine grain boundaries in netschaevo indicates formation during thermal metamorphism under oxidizing conditions due to the absence of reduction and the composition of chromite being distinct from that of metamorphosed h chondrites we conclude that netschaevo and by extension the iie iron meteorites are not from the h chondrite parent body

sulfide mineralogy and geochemistry introduction and overview the metal sulfides are the raw materials for most of the world supplies of non ferrous metals and therefore can be considered the most important group of ore minerals although there are several hundred known sulfide minerals only a half dozen of them are sufficiently abundant as to be regarded as rock forming minerals pyrite pyrrhotite galena sphalerite chalcopyrite and chalcocite see bowles and vaughan 2006 these mostly occur as accessory minerals in certain major rock types with pyrite being by far the most important volumetrically it is also important to note that the synthetic analogs of certain sulfide minerals are of interest to physicists and materials scientists because of their properties electrical magnetic optical and have found uses in various electronic or opto electronic devices recently this interest has been directed towards the use in such devices of metal sulfide thin films and of sulfide nanoparticles topics touched upon in chapter 3 but not discussed in detail in this volume but see for example fuhs and klenk 1998 bernede et al 1999 trindade et al 2001 the importance of sulfide minerals in ores has long been and continues to be a major reason for the interest of mineralogists and geochemists in these materials determining the fundamental chemistry of sulfides is key to understanding their conditions of formation and hence the geological processes by which certain ore deposits have formed this in turn may inform the strategies used in exploration for such deposits and their subsequent exploitation in this context knowledge of structures stabilities phase relations and transformations together with the relevant thermodynamic and kinetic data is critical as with many geochemical systems much can also be learned from isotopic studies the practical contributions of mineralogists and geochemists to sulfide studies extend beyond areas related to geological applications the mining

a relict grain bearing porphyritic olivine compound chondrule from ll3 0 semarkona that experienced limited remelting chondrule d8n in ll3 0 semarkona is a porphyritic olivine po chondrule 1300 1900 m in size with a complicated thermal history the oldest recognizable portion of d8n is a moderately high feo po chondrule that is modeled as having become enmeshed in a dust ball containing a small intact low feo porphyritic chondrule and fine grained material consisting of forsterite kamacite troilite and possibly reduced c the final chondrule melting event may have been a heat pulse that preferentially melted the low feo material and produced a low feo opaquerich exterior region 45 140 m in thickness around the original chondrule at one end of the exterior region a kamacite and troilite rich lump 960 m in length formed during the final melting event the coarse moderately ferroan olivine phenocrysts within the original chondrule appear to have been partly resorbed these relict phenocrysts have the highest concentrations of feo mno and cr2o3 7 5 0 20 and 0 61 wt respectively in d8n narrow olivine overgrowths crystallized around the phenocrysts following final chondrule melting their compositions seem to reflect mixing between melt derived from the exterior region and the resorbed margins of the phenocrysts during the melting event feo in the relict phenocrysts was reduced producing numerous small blebs of ni poor metallic fe along preexisting curvilinear fractures the reduced olivine flanking the trails of metal blebs has lower feo than the phenocrysts but virtually identical mno and cr2o3 contents subsequent parent body aqueous alteration in the exterior region of the chondrule formed pentlandite and abundant magnetite

sulfide rich metallic impact melts from chondritic parent bodies sacramento wash 005 saw 005 meteorite hills 00428 met 00428 and mount howe 88403 how 88403 are s rich fe ni rich metal meteorites with fine metal structures and homogeneous troilite we compare them with the h metal meteorite lewis cliff 88432 phase diagram analyses suggest that saw 005 met 00428 and how 88403 were liquids at temperatures above 1350 c tridymite in how 88403 constrains formation to a high temperature and low pressure environment the morphology of their metal troilite structures may suggest that met 00428 cooled the slowest saw 005 cooled faster and how 88403 cooled the quickest saw 005 and met 00428 contain h chondrite like silicates and saw 005 contains a chondrule bearing inclusion that is texturally and compositionally similar to h4 chondrites the compositional and morphological similarities of saw 005 and met 00428 suggest that they are likely the result of impact processing on the h chondrite parent body saw 005 and met 00428 are the first recognized iron and sulfide rich meteorites which formed by impact on the h chondrite parent body which are distinct from the iie iron meteorite group the morphological and chemical differences of how 88403 suggest that it is not from the h chondrite body although it likely formed during an impact on a chondritic parent body

the geomorphic and ecological effectiveness of habitat rehabilitation works continuous measurement of scour and fill around large logs in sand bed streams abstract geomorphologists ecologists and engineers have all contributed to stream rehabilitation projects by predicting the physical effect of habitat restoration structures in this study we report the results of a stream rehabilitation project on the snowy river se australia that aims to improve fish habitat and facilitate migration associated with scour holes around large wood in the streambed whilst engineering models allow us to predict maximum scour the key management issue here was not the maximum scour depth but whether the holes persisted at a range of flows and if they were present when fish actually required them this led to the development of a new method to continuously monitor scour in a sand bed using a buried pressure transducer in this study we monitored fluctuations in the bed level below three large logs 1 m diameter on the snowy river each log had a different scour mechanism a plunge pool a horseshoe vortex analogous to a bridge pier and a submerged jet beneath the log the continuous monitoring demonstrated a complex relationship between discharge and pool scour the horseshoe vortex pool maintained a constant level whilst contrary to expectations both the plunge pool and the submerged jet pool gradually filled over the 12 months filling was associated with the average rise in flows in winter and occurred despite several freshes and discharge spikes the plunge pool showed the most variation with bed levels fluctuating by over 1 m a key factor in pool scour here may not be the local water depth at the log but the position of the log in relation to larger scale movements of sand waves in the stream these results question assumptions on the relative importance of small floods or channel maintenance flows that lead to beneficial scour around large wood in sand bed streams further the continuous measurement of scour and fill around the logs suggested the presence of pool scour holes would have met critical requirements for australian bass macquaria novemaculeata during the migration period whereas less frequent monitoring typical of rehabilitation trials would have suggested the contrary the results of this study have demonstrated that geomorphic effectiveness is not always synonymous with biological effectiveness whilst physical models emphasise extreme changes such as maximum scour the key biological issue is whether scour occurs at the critical time of the life cycle continuous measurement of sand levels is an example of a geomorphic technique that will help to develop models that predict biologically meaningful processes not just extremes

a petrologic thermodynamic and experimental study of brachinites partial melt residues of an r chondrite like precursor abstract the primitive achondrites provide a window into the initial melting of asteroids in the early solar system the brachinites are olivine dominated meteorites with a recrystallized texture that we and others interpret as evidence of partial melting and melt removal on the brachinite parent body we present a petrologic thermodynamic and experimental study of the brachinites to evaluate the conditions under which they formed and test our hypothesis that the precursor material to the brachinites was feo rich compared to the precursors of other primitive achondrites petrologic analysis of six brachinites brachina allan hills alh 84025 hughes 026 elephant moraine eet 99402 northwest africa nwa 3151 and nwa 4969 and one brachinite like achondrite nwa 5400 shows that they are meteorites with recrystallized texture that are enriched in olivine 80 vol and depleted in other minerals with respect to a chondritic mineralogy silicates in the brachinites are feo rich fa 32 36 brachinite like achondrite northwest africa 5400 is similar in mineralogy and texture to the brachinites but with a slightly lower feo content fa 30 thermodynamic calculations yield equilibration temperatures above the fe ni fes cotectic temperature 950 c for all meteorites studied here and temperatures above the silicate eutectic 1050 c for all but two brachina formed at an f o 2 of iw and the other brachinites and nwa 5400 formed at iw 1 all the meteorites show great evidence of formation by partial melting having approximately chondritic to depleted chondritic mineralogies equilibrated mineral compositions and recrystallized textures and having reached temperatures above that required for melt generation in an attempt to simulate the formation of the brachinite meteorites we performed one atmosphere gas mixing partial melting experiments of r4 chondrite lapaz ice field 03639 experiments at 1250 c and an oxygen fugacity of iw 1 produce residual phases that are within the mineralogy and mineral compositions of the brachinites these experiments provide further evidence for the formation of brachinites as a result of partial melting of a chondritic precursor similar in mineralogy and mineral compositions to the r chondrites