geochemistry of the ungrouped carbonaceous chondrite tagish lake the anomalous cm chondrite bells and comparison with ci and cm chondrites i have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the tagish lake carbonaceous chondrite fall along with bulk samples of the ci chondrite orgueil and of several cm chondrites tagish lake has a mean of refractory lithophile element cr ratios like those of cm chondrites and distinctly higher than the ci chondrite mean tagish lake exhibits abundances of the moderately volatile lithophile elements na and k that are slightly higher than those of mean cm chondrites refractory through moderately volatile siderophile element abundances in tagish lake are like those of cm chondrites tagish lake is distinct from cm chondrites in abundances of the most volatile elements mean ci normalized se co zn co and cs co for tagish lake are 0 68 0 01 0 71 0 07 and 0 76 0 02 while for all available cm chondrite determinations these ratios lie between 0 31 and 0 61 between 0 32 and 0 58 and between 0 39 and 0 74 respectively considering petrography and oxygen isotopic and elemental compositions tagish lake is an ungrouped member of the carbonaceous chondrite clan the overall abundance pattern is similar to those of cm chondrites indicating that tagish lake and cms experienced very similar nebular fractionations bells is a cm chondrite with unusual petrologic characteristics bells has a mean ci normalized refractory lithophile element cr ratio of 0 96 lower than for any other cm chondrite but shows ci normalized moderately volatile lithophile element cr ratios within the ranges of other cm chondrites except for na which is low iridium co ni and fe abundances are like those of cm chondrites but the moderately volatile siderophile elements au as and sb have abundances below the ranges for cm chondrites abundances of the moderately volatile elements se and zn of bells are within the cm ranges bells is best classified as an anomalous cm chondrite

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

mineralogical and spectroscopic investigation of the tagish lake carbonaceous chondrite by x ray diffraction and infrared reflectance spectroscopy abstract we have carried out a sample correlated spectroscopic and mineralogical investigation of samples from seven different collection sites of the tagish lake c2 chondrite rietveld refinement of high resolution powder x ray diffraction xrd data was used to determine quantitative major mineral abundances thermal infrared 400 4500 cm 1 2 2 25 0 m spectra of the same samples were obtained using diffuse biconical reflectance infrared fourier transform spectroscopy drifts our results are in good agreement with previous studies of the mineralogy of the tagish lake meteorite we find however that tagish lake is more varied in major mineralogy than has previously been reported in particular we observed two new distinct lithologies an inclusion poor magnetite and sulfide rich lithology and a carbonate rich siderite dominated lithology in addition to the previously documented carbonate rich and carbonate poor lithologies grain density for each tagish lake sample was calculated from the measured mineral modal abundances and known mineral densities for powders from three originally intact inclusion rich samples the calculated grain density is 2 77 0 05 g cm 3 in excellent agreement with those reported in the literature for other intact inclusion rich tagish lake samples tagish lake disaggregated samples have a significantly higher calculated grain density due to their lower saponite serpentine content likely a result of mineral separation in the meltwater holes from which they were collected the disaggregated samples may not therefore adequately represent bulk samples of the tagish lake meteorite the predominance of very fine grained material in the tagish lake samples investigated in this study is expected to produce infrared spectra representative of asteroidal regolith gypsum and talc have been found by xrd in powders from the inclusion rich intact tagish lake samples in this study and may have been present in the parent body if present these hydrous sulfates would complicate the interpretation of possible hydrated mineral features in asteroid infrared spectra

the oxygen isotopic composition of olivine and pyroxene from ci chondrites the ci chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere however their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the ci parent body precursors to this alteration namely olivine and pyroxene are extremely rare in ci chondrites precluding previous measurements of their oxygen isotopic composition we report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from ci chondrites orgueil and ivuna the ci chondrite olivine and pyroxene grains most likely represent liberated chondrule phenocrysts based on petrographic chemical and isotopic evidence consistent with crystallization from a melt the oxygen isotope data form an array that falls nearly along the carbonaceous chondrite 16o mixing line with 18o values ranging from 9 3 to 12 3 o and 17o from 11 3 o to 7 8 o consistent with nebular processes being the source of the oxygen isotopic compositions the degree of 16o enrichment in orgueil olivines is negatively correlated with feo content but the exact nature and timing of the process that introduced this variation remains unknown the pyroxene oxygen isotopic compositions are similar to those of olivines with 5 mol fayalite the oxygen isotopic analyses of the olivine and pyroxene in ci chondrites have been used to revise previous models for the isotopic evolution of ci materials our data require more complete gas solid equilibration in the nebula and constrain the initial aqueous fluids on the ci parent body to have lower 17o values than previously postulated the refined model indicates that the temperature of aqueous activity on the ci parent body was no higher than 50 c and the fluid rock ratio was significantly less than previously estimated even prior to alteration and formation of secondary minerals the ci chondrites were the most 16o depleted carbonaceous chondrites and thus the solids originally contained in the ci chondrites are the most equilibrated nebular materials represented in the carbonaceous chondrites the data suggest the oxygen isotopic composition of average solar system to be approximately equivalent to average terrestrial oxygen as recorded in the compositions of terrestrial and lunar basalts

refractory forsterite in primitive meteorites condensates from the solar nebula all groups of chondritic meteorites contain discrete grains of forsteritic olivine with feo contents below 1 wt and high concentrations of refractory elements such as ca al and ti ten such grains 52 to 754 g with minor amounts of adhering matrix were separated from the allende meteorite after bulk chemical analysis by instrumental neutron activation analysis inaa some samples were analyzed with an electron microprobe and some with an ion microprobe matrix that accreted to the forsterite grains has a well defined unique composition different from average allende matrix in having higher cr and lower ni and co contents which implies limited mixing of allende matrix all samples have approximately chondritic relative abundances of refractory elements ca al sc and rare earth elements ree although some of these elements such as al do not quantitatively reside in forsterite whereas others e g ca are intrinsic to forsterite the chondritic refractory element ratios in bulk samples the generally high abundance level of refractory elements and the presence of ca al ti rich glass inclusions suggest a genetic relationship of refractory condensates with forsteritic olivine the ca al ti rich glasses may have acted as nuclei for forsterite condensation arguments are presented that exclude an origin of refractory forsterite by crystallization from melts with compositions characteristic of allende chondrules a all forsterite grains have cao contents between 0 5 and 0 7 wt with no apparent zoning requiring voluminous parental melts with 18 to 20 wt cao far above the average cao content of allende chondrules similar arguments apply to al contents b the low feo content of refractory forsterite of 0 2 0 4 wt imposes an upper limit of 1 wt of feo on the parental melt too low for ordinary and carbonaceous chondrule melts c the mn contents of refractory forsterites are between 30 to 40 ppm this is at least one order of magnitude below the mn content of chondrule olivines in all classes of meteorites the observed mn contents of refractory forsterite are much too low for equilibrium between olivine and melts of chondrule composition d as shown earlier refractory forsterites have o isotopic compositions different from chondrules weinbruch et al 1993a refractory olivines in carbonaceous chondrites are found in matrix and in chondrules the compositional similarity of both types was taken to indicate that all refractory forsterites formed inside chondrules e g jones 1992 as refractory forsterite cannot have formed by crystallization from chondrule melts we conclude that refractory forsterite from chondrules are relic grains that survived chondrule melting and probably formed in the same way as refractory forsterite enclosed in matrix we favor an origin of refractory forsterite by condensation from an oxidized nebular gas

oxygen isotopic composition of individual olivine grains from the allende meteorite abstract the oxygen isotopic compositions of individual olivine grains from the allende meteorite were determined by ion microprobe techniques a variety of olivine grains were analysed refractory forsterite grains 26 wt rims and twenty eight individual matrix olivine grains 21 41 wt feo in an oxygen three isotope plot refractory forsterite grains 17o 11 18 o 8 fall on the allende mixing line but are significantly less enriched in 16o than spinel and pyroxene from ca al rich inclusions cais possibly indicating a later formation of forsteritic olivine cores of isolated olivine grains with somewhat higher feo contents iogs have oxygen isotopic compositions similar to those of the refractory forsterites 17 o 12 and 18 o 9 both types of olivine grains have oxygen isotopic compositions significantly different from those of chondrules this clearly demonstrates that these olivine grains are not the result of crystallization of chondrule melts fayalite rich rims of the iogs are less enriched in 16o 17 o 3 18 o 0 than the forsteritic cores arguments are presented that this supports a condensation origin of the rims from a gas phase less enriched in 16o than the gas phase from which the forsteritic cores had formed matrix olivines have oxygen isotopic compositions similar to fayalite rich rims however there are variations in the oxygen isotopic composition of matrix olivines that exceed analytical uncertainties suggesting a more complex origin

direct detection of projectile relics from the end of the lunar basin forming epoch the lunar surface a key proxy for the early earth contains relics of asteroids and comets that have pummeled terrestrial planetary surfaces surviving fragments of projectiles in the lunar regolith provide a direct measure of the types and thus the sources of exogenous material delivered to the earth moon system in ancient 3 4 billion years ago ga regolith breccias from the apollo 16 landing site we located mineral and lithologic relics of magnesian chondrules from chondritic impactors these ancient impactor fragments are not nearly as diverse as those found in younger 3 4 ga to today regolith breccias and soils from the moon or that presently fall as meteorites to earth this suggests that primitive chondritic asteroids originating from a similar source region were common earth moon crossing impactors during the latter stages of the basin forming epoch

light element geochemistry of the tagish lake ci2 chondrite comparison with ci1 and cm2 meteorites we have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the tagish lake carbonaceous chondrite by high resolution stepped combustion mass spectrometry and compared the results with data from the orgueil ci1 eet 83334 cm1 and murchison cm2 chondrites the small chip of tagish lake analysed herein had a higher carbon abundance 5 81 wt than any other chondrite and a nitrogen content 1220 ppm between that of ci1 and cm2 chondrites owing to the heterogeneous nature of the meteorite the measured carbon abundance might be artificially high the carbon inventory and whole rock carbon isotopic composition 13c 24 4 of the chip was dominated by 13c enriched carbon from the decomposition of carbonates between 1 29 wt and 2 69 wt 13c 67 and 18o 35 in the proportions 4 1 dolomite to calcite in addition to carbonates tagish lake contains organic carbon 2 6 wt 13c 9 1033 ppm n 15n 77 a level intermediate between ci and cm chondrites around 2 of the organic material is thermally labile and solvent soluble a further 18 of the organic species are liberated by acid hydrolysis tagish lake also contains a complement of presolar grains it has a higher nanodiamond abundance 3650 4330 ppm than other carbonaceous chondrites along with 8 ppm silicon carbide whilst carbon and nitrogen isotope geochemistry is not diagnostic the data are consistent with classification of tagish lake as a ci2 chondrite

bed load grain velocities and sediment transport rates theoretical consideration of the dynamics of bed load sediment transport leads to expressions for bed grain velocity and sediment transport rate as respectively ub a u u c and ib a tan u u c 0 c agreeing in form with many previous analyses the grain velocity equation agrees well with all experimentally determined velocities of single grains moving over fixed rough beds if a is allowed to vary with bed roughness and saltation height values of u c for such overriding grains are substantially less than normally accepted values the sediment transport rate equation predicts plane bed experimental data well over five orders of magnitude of ib values of a tan increase significantly from lower to upper stage plane beds due to an increase in a with suspended sediment concentration but also due to a decrease in tan with increasing transport stage and grain size as predicted by bagnold

on the relationship between isolated and chondrule olivine grains in the carbonaceous chondrite alha77307 abstract the origin of isolated olivine grains in carbonaceous chondrites has been suggested to be either by direct condensation or by fragmentation of chondrules in an attempt to resolve this debate isolated olivine grains in the carbonaceous chondrite alha77307 have been studied in detail zoning characteristics and minor element compositions of olivines from all isolated and chondrule occurrences are described the data show that a strong relationship exists between isolated olivines and the chondrule population chondrule olivine compositions and zoning properties are consistent with olivine crystallization from the molten chondrules because properties of isolated grains are very similar to chondrule olivines an igneous origin for most if not all isolated grains is proposed large isolated forsterite grains may be derived from fragmentation of macroporphyritic type i chondrules which contain one or very few large olivine grains relic forsterite grains in type ii chondrules and complex isolated olivine grains with forsteritic cores and fayalite rich rims provide evidence that fragmentation and recycling of chondrules and their components was a common and efficient process in the chondrule forming region

mineralogical controls on the oxygen isotopic compositions of uocs abstract we report the results of oxygen isotopic analyses made on mineral separates prepared from chondrules and whole meteorites uocs feldspar glass mainly chondrule mesostasis is more 16o poor than the olivine low ca pyroxene from which it was separated this relationship is true both for chondrules and whole meteorites from the three uoc groups feldspar and glass have exchanged to a higher degree with 16o poor gases than ferromagnesian minerals because of the susceptibility of framework silicates and glass to gas solid diffusion olivine and low ca pyroxene have preserved primitive isotopic compositions in this way mineralogy is the dominant control on the oxygen isotopic compositions of uocs the similarity of chondrule and whole meteorite isotope compositions suggests that for many uocs matrix and chondrules have undergone exchange with the same isotope reservoirs this exchange postdates chondrule formation and is believed to have occurred after consolidation with the surrounding chondrite matrix in a parent body regolith after this gas solid exchange some isotopic equilibration took place between feldspar and the other relatively 16o rich solids as a result of metamorphism a progressive decrease in the values of 18ofeldspar glass 18oolivine pyroxene for bulk meteorites occurs with increasing petrologic subtype from 8 0 00 for a type 3 2 to 2 5 for a type 3 9 a chemical origin for the initial 16o poor gas reservoirs in the h l and ll parent bodies by processes of mass independent fractionation is considered more likely than nucleosynthesis feldspar glass separated from adrar 003 l ll3 2 may be in or close to having isotopic equilibrium with the 16o poor gases for l or ll chondrites on this basis and assuming that the gas was dominated by h2o and its isotopic composition lay along a line of slope 1 corresponding to what has been called the equilibrated chondrite line a tentative upper limit for gas solid isotopic exchange in uocs can be calculated which gives 370 c

the paris meteorite the least altered cm chondrite so far the paris chondrite provides an excellent opportunity to study cm chondrules and refractory inclusions in a more pristine state than currently possible from other cms and to investigate the earliest stages of aqueous alteration captured within a single cm bulk composition it was found in the effects of a former colonial mining engineer and may have been an observed fall the texture mineralogy petrography magnetic properties and chemical and isotopic compositions are consistent with classification as a cm2 chondrite there are 45 vol high temperature components mainly type i chondrules with olivine mostly fa0 2 mean fa0 9 with granular textures because of low mesostasis abundances type ii chondrules contain olivine fa7 to fa76 these are dominantly of type iia but there are iiab and iib chondrules ii a b chondrules with minor highly ferroan olivine and iia c with augite as the only pyroxene the refractory inclusions in paris are amoeboid olivine aggregates aoas and fine grained spinel rich ca al rich inclusions cais the cai phases formed in the sequence hibonite perovskite grossite spinel gehlenite anorthite diopside fassaite and forsterite the most refractory phases are embedded in spinel which also occurs as massive nodules refractory metal nuggets are found in many cai and refractory platinum group element abundances pge decrease following the observed condensation sequences of their host phases mn cr isotope measurements of mineral separates from paris define a regression line with a slope of 53mn 55mn 5 76 0 76 106 if we interpret cr isotopic systematics as dating paris components particularly the chondrules the age is 4566 44 0 66 myr which is close to the age of cai and puts new constraints on the early evolution of the solar system eleven individual paris samples define an o isotope mixing line that passes through cm2 and co3 falls and indicates that paris is a very fresh sample with variation explained by local differences in the extent of alteration the anhydrous precursor to the cm2s was co3 like but the two groups differed in that the cms accreted a higher proportion of water paris has little matrix 47 plus 8 fine grained rims and is less altered than other cm chondrites chondrule silicates except mesostasis cai phases submicron forsterite and amorphous silicate in the matrix are all well preserved in the freshest domains and there is abundant metal preserved metal alteration stage 1 of palmer and lauretta 2011 metal and sulfide compositions and textures correspond to the least heated or equilibrated cm chondrites category a of kimura et al 2011 the composition of tochilinite cronstedtite intergrowths gives a pcp index of 2 9 cronstedtite is more abundant in the more altered zones whereas in normal highly altered cm chondrites with petrologic subtype 2 6 2 0 based on the s sio2 and feo sio2 ratios in pcp or tochilinite cronstedtite intergrowths rubin et al 2007 cronstedtite is destroyed by alteration the matrix in fresh zones has ci chondritic volatile element abundances but interactions between matrix and chondrules occurred during alteration modifying the volatile element abundances in the altered zones paris has higher trapped ne contents more primitive organic compounds and more primitive organic material than other cms there are gradational contacts between domains of different degree of alteration on the scale of 1 cm but also highly altered clasts suggesting mainly a water limited style of alteration with no significant metamorphic reheating

turbulence at a roughness transition in a depth limited flow over a gravel bed turbulence statistics derived from velocity measurements along a longitudinal transect characterized by a roughness transition are presented the bed morphology along the transect is dominated by composite scales of roughness ranging from an armoured bed in the upstream section to the presence of large protuberant clasts superimposed on the bed in the downstream section an array of four electromagnetic current meters operating at a frequency of 20 hz was used to measure the longitudinal and vertical velocities at various heights above the bed surface and at different positions along the transect emphasis is put on the longitudinal and vertical distributions of turbulent flow statistics such as reynolds shear stress uv cross correlation and quadrant analysis of velocity fluctuations the results indicate that the presence of protuberant clasts modifies the turbulence structure increases turbulence intensity and appears to dominate turbulence generation distinct flow zones are observed in particular a clear distinction is made between i a sublayer below the top of the major roughness elements identified by fluid motions predominantly towards the bed surface and characterized by intense eddying with some vortices or rollers possibly being trapped in this near bed flow region and ii an inner layer located immediately above the major protuberant clasts identified by positive vertical velocities and hence upward directed fluid motion the dominant generative mechanism of flow structure appears to be the shedding of vortices from the lee of obstacles interaction of vortices stretched by shear into the main body of flow downstream from major obstacles dominates the turbulence structure in depth limited flows over coarse and irregular bed surfaces

petrography and mineral chemistry of the anhydrous component of the tagish lake carbonaceous chondrite most studies of tagish lake have considered features that were either strongly affected by or formed during the extensive hydrous alteration experienced by this meteorite this has led to some ambiguity as to whether tagish lake should be classified a ci a cm or something else unlike previous workers we have focused upon the primary anhydrous component of tagish lake recovered through freeze thaw disaggregation and density separation and located by thin section mapping we found many features in common with cms that are not observed in cis in addition to the presence of chondrules and refractory forsterite which distinguish tagish lake from the cis we found hibonite bearing refractory inclusions spinel rich inclusions forsterite aggregates cr al rich spinel and accretionary mantles on many clasts which clearly establishes a strong link between tagish lake and the cm chondrites the compositions of isolated olivine crystals in tagish lake are also like those found in cms we conclude that the anhydrous inclusion population of tagish lake was originally very much like that of the known cm chondrites and that the inclusions in tagish lake are heavily altered more so than even those in mighei which are more heavily altered than those in murchison

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

fine grained rims surrounding chondrules in the tagish lake carbonaceous chondrite verification of their formation through parent body processes abstract a petrographic and electron microscopic study of the carbonate poor lithology of the tagish lake carbonaceous chondrite reveals that most chondrules contain many pseudomorphs of opaque nodules and are surrounded by phyllosilicate rich altered zones that were formed by replacing enstatite and opaque nodules along the chondrule peripheries most chondrules and other coarse grained components are surrounded by fine grained rims which are commonly disaggregated and partly lacking the altered zones and the rims are compositionally and texturally similar although they exhibit some differences in secondary minerals in comparison the rims and the host matrix show more significant differences in bulk chemical composition texture and mineralogy the observations suggest that the chondrules and the rims experienced aqueous alteration simultaneously whereas the rims and the matrix experienced aqueous alteration under distinct conditions we also found a clast that contains multiple coarse grained components embedded in a matrix and numerous smaller matrix clasts the coarse grained components in the clast have no rims and the matrices of the clasts are mineralogically identical to the rims the results suggest that the chondrules other coarse grained components and their rims generically referred to as chondrules rims and the clasts originated from a common precursor region in the meteorite parent body that was different from the location where the host meteorite was finally lithified that is the chondrules rims are actually clasts produced by brecciation and later transported and incorporated into the present host matrix the rims are therefore remnants of matrix material that formerly filled interspaces between the chondrules and other coarse grained components this model is essentially consistent with those previously proposed for the carbonate rich lithology of tagish lake and the hydrated chondrules rims in the vigarano and mokoia cv3 chondrites

oxygen isotope compositions of chondrules in cr chondrites abstract we report in situ ion microprobe analyses of oxygen isotopic compositions of olivine low ca pyroxene high ca pyroxene anorthitic plagioclase glassy mesostasis and spinel in five aluminum rich chondrules and nine ferromagnesian chondrules from the cr carbonaceous chondrites eet92042 gra95229 and mac87320 ferromagnesian chondrules are isotopically homogeneous within 2 in 17 o the interchondrule variations in 17 o range from 0 to 5 small oxygen isotopic heterogeneities found in two ferromagnesian chondrules are due to the presence of relict olivine grains in contrast two out of five aluminum rich chondrules are isotopically heterogeneous with 17 o values ranging from 6 to 15 and from 2 to 11 respectively this isotopic heterogeneity is due to the presence of 16 o enriched spinel and anorthite 17 o 10 to 15 which are relict phases of ca al rich inclusions cais incorporated into chondrule precursors and incompletely melted during chondrule formation these observations and the high abundance of relict cais in the aluminum rich chondrules suggest a close genetic relationship between these objects aluminum rich chondrules formed by melting of spinel anorthite pyroxene cais mixed with ferromagnesian precursors compositionally similar to magnesium rich type i chondrules the aluminum rich chondrules without relict cais have oxygen isotopic compositions 17 o 2 to 8 similar to those of ferromagnesian chondrules in contrast to the aluminum rich chondrules from ordinary chondrites those from crs plot on a three oxygen isotope diagram along the carbonaceous chondrite anhydrous mineral line and form a continuum with amoeboid olivine aggregates and cais from crs we conclude that oxygen isotope compositions of chondrules resulted from two processes homogenization of isotopically heterogeneous materials during chondrule melting and oxygen isotopic exchange between chondrule melt and 16 o poor nebular gas

active interactions between turbulence and bed load conceptual picture and experimental evidence 1 this paper reports results from experiments with simultaneous measurement of areal bed load sediment concentration and water velocity horizontal and vertical components made at 1 5 particle diameters above the mean bed the same spatial and temporal scales were employed to measure the kinematic properties of flowing water and sediments the obtained data covering a range of low sediment discharges were analyzed in terms of bulk statistics autocorrelation and cross correlation functions and quadrant decomposition of fluctuations at the lowest transport rates the motion of sediment particles was found to be mostly associated with sweep events however with increasing flow rate and bed load discharge the process mechanics changed and the transport of sediments was also found to be significantly correlated with ejections the obtained results are integrated into a conceptual picture attempting to bridge previous depictions of the bed load transport mechanics

the fall recovery orbit and composition of the tagish lake meteorite a new type of carbonaceous chondrite the preatmospheric mass of the tagish lake meteoroid was about 200 000 kilograms its calculated orbit indicates affinity to the apollo asteroids with a semimajor axis in the middle of the asteroid belt consistent with a linkage to low albedo c d and p type asteroids the mineralogy oxygen isotope and bulk chemical composition of recovered samples of the tagish lake meteorite are intermediate between cm and ci meteorites these data suggest that the tagish lake meteorite may be one of the most primitive solar system materials yet studied

the fall and recovery of the tagish lake meteorite the tagish lake c2 ungrouped carbonaceous chondrite fall of january 18 2000 delivered 10 kg of one of the most primitive and physically weak meteorites yet studied in this paper we report the detailed circumstances of the fall and the recovery of all documented tagish lake fragments from a strewnfield at least 16 km long and 3 to 4 km wide nearly 1 kg of pristine meteorites were collected one week after the fall before new snow covered the strewnfield the majority of the recovered mass was collected during the spring melt ground eyewitnesses and a variety of instrument recorded observations of the tagish lake fireball provide a refined estimate of the fireball trajectory from its calculated orbit and its similarity to the remotely sensed properties of the d and p class asteroids the tagish lake carbonaceous chondrite apparently represents these outer belt asteroids the cosmogenic nuclide results and modeled production indicate a prefall radius of 2 1 2 4 m corresponding to 60 90 tons consistent with the observed fireball energy release the bulk oxygen isotope compositions plot just below the terrestrial fractionation line tfl following a trend similar to the cm meteorite mixing line the bulk density of the tagish lake material 1 64 0 02 g cm 3 is the same within uncertainty as the total bulk densities of several c class and especially d and p class asteroids the high microporosity of tagish lake samples 40 provides an obvious candidate material for the composition of low bulk density primitive asteroids

identification of relict forsterite grains in forsterite rich chondrules from the mokoia cv3 carbonaceous chondrite magnesium rich forsterite grains fo 98 in feo poor chondrules show variations in cathodoluminescence cl intensity that are associated closely with variations in al 2 o 3 and tio 2 contents cl thus can be used to map the distribution of al and ti in individual grains we describe several categories of cl distribution including grains that are homogeneous grains that are zoned continuously grains that show oscillatory zoning and grains that show a heterogeneous distribution of cl intensity heterogeneous cl intensity is interpreted as the result of disequilibrium growth from the chondrule melt cl surveys of individual chondrules help to identify forsterite grains that are potentially relics in their host chondrules i e grains that did not crystallize in situ from the chondrule melt several of these grains show minor element variations that differ from the majority of melt grown grains in their host chondrules this observation supports the inference that they are relics little evidence exists for growth of individual grains in multiple brief heating episodes identification of the abundance of relict grains is important for determining the thermal histories of chondrules as well as the nature of the precursor assemblages from which they formed

primordial oxygen isotope reservoirs of the solar nebula recorded in chondrules in acfer 094 carbonaceous chondrite abstract highly precise and accurate ion microprobe analyses of oxygen three isotope ratios in chondrules from the acfer 094 one of the most primitive carbonaceous chondrites show that chondrules preserve evidence for oxygen isotope heterogeneity in chondrule forming regions of the solar nebula identical 17 o values in most minerals and glass within each chondrule indicate that the oxygen isotope ratio in chondrule melt did not change during or after crystallization nearly half of the chondrules studied contain small amounts of olivine grains that have an oxygen isotope anomaly relative to other minerals and glass in the same chondrule most chondrules in acfer 094 can be classified into two oxygen isotope groups 17 o 2 and 17 o 5 indicating that the final melting of chondrules occurred within two distinct oxygen isotope reservoirs probably representing the local protoplanetary disk immediately before planetesimal formation one of these reservoirs 17 o 2 is observed from chondrules in other carbonaceous chondrites and from crystalline silicates in comet wild 2 suggesting that crystalline silicates formed in an oxygen isotope reservoir of 17 o 2 were widely distributed in the outer asteroid belt and throughout the outer solar nebula oxygen three isotope ratios of minerals in chondrules from acfer 094 are distributed along a newly defined primitive chondrule minerals pcm line which has slope 1 17 o 0 987 0 013 18 o 2 70 0 11 and intersects the terrestrial fractionation line at 18 o 5 8 0 4 these data are distinct from and plot between the ccam and young and russell lines the pcm line is interpreted to represent the mixing trend of extreme oxygen isotope reservoirs in the early solar system that were the primary oxygen isotope reservoir of solids that accreted to form planets including the earth

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

imaging salt with turning seismic waves turning seismic waves which first travel downward and then upward before and after reflection have been recorded in a 3 d seismic survey conducted over an overhanging salt dome careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome when seismic wave velocity increases with depth waves that initially travel downward are reflected and may turn so as to travel upward before reflection a simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com mon midpoint cmp gathers in that reflection time decreases with increasing source receiver offset this abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves the most important step in imaging turning waves assuming that they have been recorded is the migration process simple and inexpensive modifications to the conventional phase shift migration method enable turning waves to be imaged for little additional computational cost the examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes

oxygen isotopes in crystalline silicates of comet wild 2 a comparison of oxygen isotope systematics between wild 2 particles and chondritic materials abstract oxygen three isotope ratios of nine crystalline silicate particles from comet wild 2 were measured to investigate oxygen isotope systematics of cometary materials we are able to analyze particles as small as 4 m using an ion microprobe with a 1 2 m beam by locating the analysis spots with an accuracy of 0 4 m three particles of mn rich forsterite known as low iron manganese enriched lime olivine showed extremely 16 o rich signatures 18 o 17 o 50 similar to refractory inclusions in chondrites the three mn rich forsterite particles may have formed by condensation from an 16 o rich solar nebula gas other particles consist of olivine and or pyroxene with a wide range of mg molar mgo feo mgo from 60 to 96 their oxygen isotope ratios plot nearly along the carbonaceous chondrite anhydrous mineral ccam and young and russell lines with 17 o 17 o 0 52 18 o values of 3 0 to 2 5 these data are similar to the range observed from previous analyses of wild 2 crystalline silicates and those of chondrules in carbonaceous chondrites six particles extracted from stardust track 77 show diverse chemical compositions and isotope ratios two mn rich forsterites feo poor pigeonite and three feo rich olivines with a wide range of 17 o values from 24 to 1 6 these results confirmed that the original projectile that formed track 77 was an aggregate 6 m of silicate particles that formed in various environments the 17 o values of ferromagnesian wild 2 particles including data from previous studies increase from 23 to 2 5 with decreasing mg 17 o values of mn rich forsterite particles mg 98 99 8 cluster at 23 those of feo poor particles mg 95 97 cluster at 2 and those of feo rich particles mg 90 scatter mainly from 1 5 to 2 5 compared to chondrules in primitive chondrites the systematic trend between mg and 17 o among the wild 2 particles is most similar to that reported for cr chondrite chondrules we argue that cr chondrites and some cometary materials share multiple common chemical and isotope characteristics we suggest that many of the crystalline silicate particles formed in the outer regions of the asteroid belt or regions that share the common properties and were transported to comet forming regions and accreted into comet wild 2

a comparison between shields threshold criterion and the movement of loosely packed gravel in a tidal channel observations of the threshold of movement of loosely packed gravel in a tidal current are described for gravel with equivalent spherical diameters d in the range 0 2 d 5 0cm the critical friction velocity u c corresponding to the initiation of sediment transport is given by u c 7 0 d0 2 at large values of d within the quoted range the value u c is significantly lower than would be obtained by a shields experiment u c d0 5 by comparing our values of u c with those obtained under well controlled laboratory conditions the discrepancy with shields is shown to be due to the open spacing between and exposure of individual pebbles on the seabed by comparing our results with those from upland gravel streams and flume experiments it is suggested that shields assumed an excessively large water depth to particle size ratio as a constraint within which the critical sediment entrainment number 0c is valid

oxygen isotopes in chondrule olivine and isolated olivine grains from the co3 chondrite allan hills a77307 we have measured o isotopic ratios in a variety of olivine grains in the co3 chondrite allan hills alh a77307 using secondary ion mass spectrometry in order to study the chondrule formation process and the origin of isolated olivine grains in unequilibrated chondrites oxygen isotopic ratios of olivines in this chondrite are variable from delta 17 o 15 5 to 4 5 parts per thousand and delta 18 o 11 5 to 3 9 parts per thousand with delta 17 o varying from 10 4 to 3 5 parts per thousand forsteritic olivines fa 1 are enriched in o 16 relative to the bulk chondrite whereas more feo rich olivines are more depleted in o 16 most ratios lie close to the carbonaceous chondrite anhydrous minerals ccam line with negative values of delta 17 o although one grain of composition fa 4 has a mean delta 17 o of 1 6 parts per thousand marked o isotopic heterogeneity within one feo rich chondrule is the result of incorporation of relic o 16 rich mg rich grains into a more o 16 depleted host isolated olivine grains including isolated forsterites have similar o isotopic ratios to olivine in chondrules of corresponding chemical composition this is consistent with derivation of isolated olivine from chondrules as well as the possibility that isolated grains are chondrule precursors the high o 16 in forsteritic olivine is similar to that observed in forsterite in cv and ci chondrites and the ordinary chondrite julesburg and suggests nebula wide processes for the origin of forsterite that appears to be a primitive nebular component

origin of chondritic forsterite grains abstract iron poor and refractory lithophile element rle rich forsterite grains occur in all major types of unequilibrated chondrites in our laser ablation inductively coupled mass spectrometry la icpms minor and trace element study we show that refractory forsterites rf from carbonaceous cc unequilibrated ordinary uoc and a rumuruti chondrite rc have similar chemical compositions with high rle concentrations and low concentrations of mn fe co and ni fractionation of rles and rare earth elements rees is in agreement with formation by crystallization from a rle rich silicate melt low concentrations and the fractionation of moderately siderophile elements fe co ni in rfs suggests formation at low oxygen fugacity possibly in equilibrium with primitive fe ni metal condensates in a gas of solar composition anomalously high ti in the parental melt can be explained by ti3 ti4 1 5 supporting formation of rf in highly reducing conditions low mn concentrations indicate formation at high temperatures 1160 k the model of formation of rfs and the accompanying physico chemical conditions during their formation as well as their relation to non refractory olivine are discussed

correlated mineralogy chemical compositions oxygen isotopic compositions and size of chondrules we report results of a study into the size chemical composition mineralogy and oxygen isotopic compositions of 40 chondrules in the size range 1 9 mm diameter separated from chainpur ll3 4 and parnallee ll3 6 these 4 parameters were found to be interdependent the main control on the bulk compositions of chondrules is the relative volatilities of the elements the major elements mg al ti ca show strong correlations among one other and most of the remaining more volatile elements form another grouping increasing proportions of refractory to volatile elements correlate with chondrule size smaller chondrules tend to have more glassy sio2 rich mesostases than larger chondrules which have a higher proportion of mesostasis with feldspathic compositions chondrules with high sio2 glassy mesostases have exchanged with 16o poor gases to a greater degree than low sio2 mesostases containing crystalline feldspar the state of mesostases of the chondrules is the most important control on their oxygen isotopic compositions although there also seems to be a size effect in chainpur smaller chondrules in chainpur have more 16o poor compositions suggesting that the relatively large surface areas of smaller chondrules facilitated gas solid exchange this correlation is obscured in parnallee because it has undergone more extensive devitrification than chainpur leading to an increase in the proportion of crystalline mesostasis the model we propose to explain the interdependence of bulk compositions size and oxygen isotopes is in two stages chondrules which were still partially molten experienced an influx of relatively volatile elements from ambient gases smaller chondrules experienced a relatively greater influx than larger chondrules because of their greater surface area volume ratio the second stage following crystallisation of the chondrules and limited devitrification of the mesostases is the influx of an 16o poor gas which led to the isotopic exchange we believe the most likely setting for the formation of these chondrules and the associated volatile rich and 16o poor gas influxes is a planetary regolith setting

analysis of the time averaged properties of sediment motion in a local scour process 1 we examined the kinematics of sediment particles in the proximity of a vertical plate attached to the side wall of a pressurized duct the laboratory phenomenon investigated was archetypal of local scour near bridge abutments in covered rivers we conducted a clear water scour experiment where we measured the temporal evolution of the local erosion depth the latter was found to follow a logarithmic trend the concentration and velocity of the moving particles were measured on the basis of digital movies taken at various evolution stages of the process the spatial pattern of the sediment motion showed that the action of the principal vortex system becomes progressively more evident with the general lowering of the sediment transport intensity detected as the scour hole increases in time furthermore the phenomenology of local sediment transport was analyzed key findings of the research include 1 the time averaged values of the sediment transport rate are linked with those of concentration and velocity through relationships which are almost invariant regardless of the experimental time and of the location within the scour hole 2 intermittency and irregularity of the sediment fluxes increase as their mean intensity decreases 3 the relative weight of the temporal fluctuations of concentration and velocity in the time mean sediment transport activity is significant throughout the entire process potential implications of the present results for the modeling of local scour processes in pressurized flow conditions are discussed the considerations made are likely to have analogous applicability to local scour with a free surface since the large scale evolutions of the erosion depth in the two conditions may not be greatly different given the qualitative analogy of the present findings with earlier ones obtained for one dimensional bed load it is suggested that similar considerations may hold also for the small scale modeling of a wider class of sediment transport processes

comparison of the trace element composition of tagish lake with other primitive carbonaceous chondrites a meteorite fall on 18 january 2000 was detected by u s defense department satellites which established its pre impact orbit fresh samples were collected from frozen tagish lake in british columbia a week later and some properties of these samples reveal it to be a unique meteorite we characterized tagish lake and 8 other samples using icpms and rnaa data for 47 elements reveal that each of 9 carbonaceous chondrites of different type exhibit the orgueil normalized plateaus expected for members of such types trends evident in tagish lake differ from all other carbonaceous chondrites including ci and cm samples of tagish lake collected later show similar patterns affected by weathering

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

compositions and textures of relic forsterite in carbonaceous and unequilibrated ordinary chondrites several percent of the olivine in the c2 c3 and unequilibrated ordinary chondrites uoc can be distinguished by blue cathodoluminescence cl and an unusual composition for forsterite this olivine has the following textural features 1 1 forms cores in single olivine grains 2 2 shows subhedral to euhedral boundaries against rim olivine 3 3 rarely contains inclusions 4 4 has embayments containing olivine like that of the rim 5 5 occurs within chondrules especially in uoc meteorites the blue olivine is always fe poor 0 25 feo 1 0 and shows the following average and maximum values al2o3 0 25 0 5 tio2 0 05 0 09 cao 0 5 0 8 cr2o3 0 15 0 5 and mno 0 02 0 15 vanadium is present within a single olivine and within all blue olivines al ca and ti are strongly positively correlated as are mn fe and cr in olivine surrounding the blue the blue cores are not zoned but each element shows a marked change at the boundary of the blue with al showing the most rapid change these are interpreted as diffusion profiles between rim and core olivine textures suggest initial free growth probably from a gas and later addition of olivine by liquid crystallization to form single crystals or chondrules the unusual olivine composition indicates high temperature growth from a refractory rich reservoir with al entering olivine in tetrahedral coordination vapor growth is suggested as the process allowing the high minor element levels the occurrence of blue olivine in all primitive meteorites indicates that it is relic material which was widespread prior to chondrule and hence meteorite formation similarities in composition exist between this relic olivine and olivine of cosmic dust and deep sea particles pointing to this olivine being a common component in all primitive extraterrestrial material

a comparison of flow intensities in alluvial rivers characteristics and implications for modelling flow processes this paper compares flow intensity data obtained with different instruments from a variety of fluvial environments it examines associations between the root mean square of longitudinal velocity fluctuations flow intensity local mean velocity relative depth and boundary resistance results indicate systematic differences in the behaviour of flow intensity which scale with respect to position in the boundary layer deep sand bedded rivers boundary grain resistance shallow river environments with coarse beds and possibly form resistance shallower sand bedded rivers preliminary approaches to prediction and modelling of variations in flow intensity are suggested based upon linear regression relationships intensity values are also compared with theoretical and empirical limits to the use of taylor s substitution which allows time and frequency properties of a single point velocity time series to be used to yield a flow length scale in general limits are exceeded in all environments for near boundary flow measurements but are met for y d 0 3 in most cases in sand bed rivers and for y d 0 4 in some gravel bed environments 1998 john wiley sons ltd

variability absorption features and parent body searches in spectrally featureless meteorite reflectance spectra case study tagish lake abstract reflectance spectra of many asteroids and other solar system bodies are commonly reported as featureless here we show that weak but consistently detectable absorption bands are observable in 200 2500 nm spectra of the tagish lake meteorite a likely compositional and spectral analogue for low albedo spectrally featureless asteroids tagish lake presents a rare opportunity to study multiple lithologies within a single meteorite reflectance spectra of tagish lake display significant variation between different lithologies the spectral variations are due in part to mineralogical variations between different tagish lake lithologies ultraviolet reflectance spectra 200 400 nm few of which have been reported in the literature to date reveal albedo and spectral ratio variations as a function of mineralogy similarly visible near infrared reflectance spectra reveal variations in albedo spectral slope and the presence of weak absorption features that persist across different lithologies and can be attributed to various phases present in tagish lake these observations demonstrate that significant spectral variability may exist between different lithologies of tagish lake which may affect the interpretation of potential source body spectra it is also important to consider the spectral variability within the meteorite before excluding compositional links between possible parent bodies in the main belt and tagish lake tagish lake materials may also be spectral compositional analogues for materials on the surfaces of other dark asteroids including some that are targets of upcoming spacecraft missions tagish lake has been proposed as a spectral match for ultra primitive d or p type asteroids and the variability reported here may be reflected in spatially or rotationally resolved spectra of possible tagish lake parent bodies and source objects in the near earth asteroid population a search for objects with spectra similar to tagish lake has been carried out among the near earth asteroids we have identified three possible spectral matches the best of which are asteroids 326732 2003 hb6 and 17274 2000 lc16

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

oxygen isotope heterogeneity in chondrules from the mokoia cv3 carbonaceous chondrite we report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the mokoia oxidized cv3 chondrite bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination and oxygen isotope ratios of individual grains mostly olivine were obtained in situ on polished mounts using secondary ion mass spectrometry sims our results can be compared with data obtained previously for the oxidized cv3 chondrite allende bulk oxygen isotope ratios of mokoia chondrules form an array on an oxygen three isotope plot that is subparallel to and slightly displaced from the ccam carbonaceous chondrite anhydrous minerals line the best fit line for all cv3 chondrite chondrules has a slope of 0 99 and is displaced significantly by 17o 2 5 from the young and russell slope one line for unaltered calcium aluminum rich inclusion cai minerals oxygen isotope ratios of many bulk cais also lie on the cv chondrule line which is the most relevant oxygen isotope array for most cv chondrite components bulk oxygen isotope ratios of most chondrules in mokoia have 18o values around 0 and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values in general it appears that chondrule mesostases have higher 18o values than olivines in the same chondrules our bulk chondrule data spread to lower 18o values than any ferromagnesian chondrules that have been measured previously two chondrules with the lowest bulk 18o values 7 5 and 11 7 contain olivine grains that display an extremely wide range of oxygen isotope ratios down to 17o 18o around 50 in one chondrule in these chondrules there are no apparent relict grains and essentially no relationships between olivine compositions which are homogeneous and oxygen isotopic compositions of individual grains heterogeneity of oxygen isotope ratios within these chondrules may be the result of incorporation of relict grains from objects such as amoeboid olivine aggregates followed by solid state chemical diffusion without concomitant oxygen equilibration alternatively oxygen isotope exchange between an 16o rich precursor and an 16o poor gas may have taken place during chondrule formation and these chondrules may represent partially equilibrated systems in which isotopic heterogeneities became frozen into the crystallizing olivine grains if this is the case we can infer that the earliest nebular solids from which chondrules formed had 17o and 18o values around 50 similar to those observed in refractory inclusions

chondrules precursors and interactions with the nebular gas chondrule compositions suggest either ferroan precursors and evaporation or magnesian precursors and condensation type i chondrule precursors include granoblastic olivine aggregates planetary or nebular and fine grained dustball precursors in carbonaceous chondrites type i chondrule precursors were s free while type ii chondrules have higher fe mn than in ordinary chondrites many type ii chondrules contain diverse forsteritic relicts consistent with polymict dustball precursors the relationship between finer and coarser grained type i chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules fe metal in type i and na and s in type ii chondrules indicate high partial pressures in ambient gas as they are rapidly evaporated at canonical conditions the occurrence of metal sulfide or low ca pyroxene on chondrule rims suggests re condensation in semarkona type ii chondrules na rich olivine cores na poor melt inclusions and na rich mesostases suggest evaporation followed by recondensation type ii chondrules have correlated feo and mno consistent with condensation onto forsteritic precursors but with different ratios in carbonaceous chondrites and ordinary chondrites indicating different redox history the high partial pressures of lithophile elements require large dense clouds either clumps in the protoplanetary disk impact plumes or bow shocks around protoplanets in ordinary chondrites clusters of type i and type ii chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together in carbonaceous chondrites the much less abundant type ii chondrules were probably added late to batches of type i chondrules from different o isotopic reservoirs

bedload transport of fine gravel observed by motion picture photography motion pictures taken at duck creek a clear stream 6 5 m wide and 35 cm deep near pinedale wyoming provide detailed quantitative information on both the modes of motion of individual bedload particles and the collective motions of large numbers of them bed shear stress was approximately 6 pa 60 dynes cm 2 which was about twice the threshold for movement of the 4 mm median diameter fine gravel bed material and transport was almost entirely as bedload the displacements of individual particles occurred mainly by rolling of the majority of the particles and saltation of the smallest ones and rarely by brief sliding of large angular ones entrainment was principally by rollover of the larger particles and liftoff of the smaller ones and infrequently by ejection caused by impacts whereas distrainment was primarily by diminution of fluid forces in the case of rolling particles and by collisions with larger bed particles in the case of saltating ones the displacement times averaged about 0 2 0 4 s and generally were much shorter than the intervening repose times the collective motions of the particles were characterized by frequent brief localized random sweep transport events of very high rates of entrainment and transport which in the aggregate transported approximately 70 of the total load moved these events occurred 9 of the time at any particular point of the bed lasted 1 2 s affected areas typically 20 50 cm long by 10 20 cm wide and involved bedload concentrations approximately 10 times greater than background the distances travelled during displacements averaged about 15 times the particle diameter despite the differences in their dominant modes of movement the 8 16 mm particles typically travelled only about 30 slower during displacement than the 2 4 mm ones whose speeds averaged 21 cm s 1 particles starting from the same point not only moved intermittently downstream but also dispersed both longitudinally and transversely with diffusivities of 4 6 and 0 26 cm 2 s 1 respectively the bedload transport rates measured from the films were consistent with those determined conventionally with a bedload sampler the 2 4 mm particles were entrained 6 times faster on finer areas of the bed where 8 16 mm particles covered 6 of the surface area than on coarser ones where they covered 12 even though 2 4 and 4 8 mm particles covered practically the same percentage areas in both cases the 4 8 and 8 16 mm particles in contrast were entrained at the same rates in both cases to within the statistical uncertainty the rates of distrainment balanced the rates of entrainment for all three sizes and were approximately proportional to the corresponding concentrations of bedload

the oxygen isotope composition of chondrules and isolated forsterite and olivine grains from the tagish lake carbonaceous chondrite abstract the oxygen isotope compositions obtained by laser fluorination of hand picked separates of isolated forsterite isolated olivine and chondrules from the tagish lake carbonaceous chondrite describe a line 17o 0 95 18o 3 24 r2 0 99 similar to the trend known for chondrules from other carbonaceous chondrites the isolated forsterite grains fo99 6 99 8 18o 7 2 to 5 5 17o 9 6 to 8 2 are more 16o rich than the isolated olivine grains fo39 6 86 8 18o 3 1 to 5 1 17o 0 3 to 2 2 and have chemical and isotopic characteristics typical of refractory forsterite chondrules contain olivine fo97 2 99 8 with oxygen isotope compositions 18o 5 2 to 5 9 17o 8 1 to 1 2 that overlap those of isolated forsterite and isolated olivine an inverse relationship exists between the 17o values and fo contents of tagish lake isolated forsterite and chondrules the chondrules likely underwent greater exchange with 16o poor nebular gases than the forsterite the oxygen isotope compositions of the isolated olivine grains describe a trend with a steeper slope 1 1 0 1 r2 0 94 than the carbonaceous chondrite anhydrous mineral line ccamslope 0 95 the isolated olivine may have crystallized from an evolving melt that exchanged with 16o poor gases of somewhat different composition than those which affected the chondrules and isolated forsterite the primordial components of the tagish lake meteorite formed under conditions similar to other carbonaceous chondrite meteorite groups especially cms its alteration history has its closest affinities to ci carbonaceous chondrites

composition and evolution of the early oceans evidence from the tagish lake meteorite abstract laboratory leaching studies of the tagish lake meteorite demonstrate that the most readily leached cations of carbonaceous chondrite meteorites are mg ca na and k with the most readily leached anions being so4 cl and po4 in decreasing order of abundances soluble organics were not analyzed due to limited sample sizes magnesium and sulfate the most abundant solutes leached from tagish lake meteorite are also the most abundant ions of salts lining fractures of aqueously altered meteorites these same ions probably were the most abundant solutes of the first permanent oceans which probably formed during or soon after the late heavy bombardment stage 4 2 to 3 7 ga considering the residence time of cl in modern seawater and the composition of the exposed continental crust to at least 3 3 ga evolution of seawater from mg so4 dominated to nacl dominated would have required about 3 105 yr and could not have been complete until about 3 0 to 3 3 ga the calculations also suggest that the first permanent oceans were more saline than modern seawater and as argued by others these aspects have significant implications for evolution of life many solar system bodies besides earth probably derived a significant proportion of their volatile and soluble constituents from carbonaceous chondrite material therefore primordial solutions similar to those presented here were likely important in the early evolution of aqueous systems throughout the solar system including those present on carbonaceous chondrite parent asteroids and icy outer solar system satellites

oxygen isotopes in forsterite grains from julesburg and allende oxygen 16 rich material in an ordinary chondrite we have used the manchester isolab 54 ion microprobe to make in situ measurements of the 17o 16o and 18o 16o ratios of olivine grains in the julesburg l3 6 and allende cv3 chondrites we have discovered a population of olivines in julesburg characterised by 1 the most 16o rich compositions yet reported for olivine from an ordinary chondrite 2 cores of low fa olivine which frequently shows blue cathodoluminesce 3 thick coats of more fa rich fa 20 olivine which is also 16o enriched in an o isotopic plot the julesburg 16o rich grains form a roughly linear array that is offset from the allende mixing line the presence of very low fa olivine and sometimes well defined fa rich coats indicates that these grains experienced significantly less thermal metamorphism than most of the olivine in the meteorite some 16o rich julesburg grains are associated with minor feldspar or pyroxene and are probably chondrule fragments they are isotopically indistinguishable from forsterite in allende however allende forsterite grains do not have the thick fa20 coats typical of those in julesburg these 16o rich forsterite grains appear to be related to the blue olivine of steele 1986 both cores and coats of 16o rich grains in julesburg are isotopically distinct from olivine in semarkona group a and group b chondrules

mass independent fractionation of oxygen isotopes in the mesostasis of a chondrule from the semarkona ll3 0 ordinary chondrite abstract a large chondrule from semarkona the most primitive ordinary chondrite known has been discovered to contain a record of mass transport during its formation in most respects it is a normal type i group a1 low feo chondrule that was produced by reduction and mass loss during the unidentified flash heating event that produced the chondrules the most abundant structural component in primitive meteorites we have previously measured elemental abundances and abundance profiles in this chondrule we here report oxygen isotope ratio abundances and ratio abundance profiles we have found that the mesostasis is zoned in oxygen isotope ratio with the center of the chondrule containing isotopically heavier oxygen than the outer regions the outer regions being volatile rich from the diffusion of volatiles into the chondrule during cooling the 17o values range from 2 0 to 9 9 while 18o range from 1 9 to 9 6 more importantly a plot of 17o against 18o has a slope of 1 1 0 2 1 and 0 88 0 10 1 when measured by two independent methods co variation of 17o with 18o that does not follow mass dependent fractionation has often been seen in primitive solar system materials and is usually ascribed to the mixing of different oxygen reservoirs we argue that petrographic and compositional data indicate that this chondrule was completely melted at the time of its formation so that relic grains could not have survived furthermore there is petrographic and compositional evidence that there was no aqueous alteration of this chondrule subsequent to its formation although it is possible to formulate a series of exchanges between the chondrule and external 16o rich and 16o poor reservoirs that may explain the detailed oxygen isotope systematics of this chondrule such a sequence of events looks very contrived we therefore hypothesize that reduction devolatilization and crystallization of the chondrule melt may have produced 16o rich olivines and 16o poor mesostasis plotting on a slope one line as part of the chondrule forming process in an analogous fashion to known chemical mass independent isotopic fractionation mechanisms during cooling volatiles and oxygen near the terrestrial line in oxygen isotope composition produced the outer zone of volatile rich and 16o rich mesostasis the chondrule therefore not only retains a record of considerable mass transport accompanying formation but also may indicate that the isotopes of oxygen underwent mass independent fractionation during the process

stable isotope constraints on the al2sio5 triple point rocks from the proterozoic priest pluton contact aureole new mexico usa the priest pluton contact aureole in the manzano mountains central new mexico preserves evidence for upper amphibolite contact metamorphism and localized retrograde hydrothermal alteration associated with intrusion of the 1 42 ga priest pluton quartz garnet and quartz sillimanite oxygen isotope fractionations in pelitic schist document an increase in the temperatures of metamorphism from 540 c at a distance of 1 km from the pluton to 690 c at the contact with the pluton comparison of calculated temperature estimates with one dimensional thermal modelling suggests that background temperatures between 300 and 350 c existed at the time of intrusion of the priest pluton fibrolite is found within 300 m of the priest pluton in pelitic and aluminous schist metamorphosed at temperatures 580 c coexisting fibrolite and garnet in pelitic schist are in oxygen isotope equilibrium suggesting these minerals were stable reaction products during peak metamorphism the fibrolite in isograd is coincident with the staurolite out isograd in pelitic schist and k feldspar is not observed with the first occurrence of fibrolite this suggests that the breakdown of staurolite and not the second sillimanite reaction controls fibrolite growth in staurolite bearing pelitic schist muscovite rich aluminous schist locally preserves the al2sio5 polymorph triple point assemblage kyanite andalusite and fibrolite andalusite and fibrolite but not kyanite are in isotopic equilibrium in the aluminous schist co nucleation of fibrolite and andalusite at 580 c in the presence of muscovite and absence of k feldspar suggests that univariant growth of andalusite and fibrolite occurred kyanite growth occurred during an earlier regional metamorphic event at a temperature nearly 80 c lower than andalusite and fibrolite growth quartz muscovite fractionations in hydrothermally altered pelitic schist and quartzite are small or negative suggesting that late isotopic exchange between externally derived fluids and muscovite but not quartz occurred after peak contact metamorphism and that hydrothermal alteration in pelitic schist and quartzite occurred below the closure temperature of oxygen self diffusion in quartz 500 c