minor and trace element export from a glacierized alpine headwater catchment haut glacier d arolla switzerland major ion concentrations in meltwaters draining glacial environments have been widely reported however concentrations of minor and trace elements have received scant attention this study presents trace and minor element variations in bulk meltwaters draining haut glacier d arolla switzerland based on twice daily sampling throughout the 1999 ablation season which represents the most detailed meltwater quality dataset to date in order to assess the mode of export from the catchment these elements are partitioned into i dissolved and ii particulate associated minor and trace element components a computer based speciation model phreeqci was applied to the bulk meltwater data suggesting that ba be cd cu li rb and sr exist primarily as mobile monovalent or divalent dissolved cations which may be involved in interactions with suspended sediment surfaces conversely the model predicts the precipitation of fe al mn and cr oxi hydroxides suggesting these species may be predominantly transported as colloids which may remove other minor and trace elements from solution by co precipitation reactions laboratory leaching experiments on suspended sediments and fresh rock powder suggests that minor and trace element concentrations may also be influenced by oxy hydroxide precipitation and adsorption desorption reactions with suspended sediment surfaces the quantity and transport mode of trace and minor elements may influence their bioavailability downstream of glacierized headwater catchments further the enrichment of many dissolved minor and trace elements in meltwaters compared with world stream waters coupled with the timing of water and sediment delivery during the summer months may have implications for downstream aquatic environments copyright 2001 john wiley sons ltd

oxygen isotopes in r chondrite magnetite and olivine links between r chondrites and ordinary chondrites ion microprobe studies yield 17o 17o 0 52 18o values in magnetite from the rumurti chondrite rc pca91241 which is paired with pca91002 of 3 1 to 3 9 slightly higher than that in o from whole rock r samples despite 17o values in whole rock rcs that are much by ca 1 6 higher than in whole rock ll chondrites the 17o in r magnetite is much lower by ca 2 than the values 4 to 7 from ll3 semarkona and ngawi choi et al 1998 the 18o values in pca magnetite 15 to 10 are the lowest known in meteorites well below the range in semarkona 4 to 9 on a 17o 18o diagram both magnetite data sets form linear arrays with slopes of ca 0 7 indicating mixing of o from different isotopic reservoirs the slopes and intercepts of the two arrays are similar enough to permit them to be segments of a single array this suggests that in rcs and ll chondrites magnetite formed from the same raw materials by the same processes probably by aqueous alteration of metal in an asteroidal setting we observed 17o values in olivines and pyroxene from rcs ranging from 1 2 to 2 9 and 18o from 1 4 to 9 1 these compositions scatter in the same general range observed in chondrules from ordinary chondrites the similarity in the o isotopic composition of minerals that preserve a record of formation in the solar nebula supports a model in which rcs formed from nebular components similar to those in h chondrites but with a matrix chondrule ratio several times higher in the rcs and with more extensive aqueous alteration in the rcs than in known h chondrites we postulate that the matrix in r chondrites has 17o higher than whole rock values we suggest that the original 17o value of h2o in the rc body was similar to that incorporated into the ordinary chondrites previously estimated by choi et al 1998 to be ca 7 in the ll parent body

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

seasonal evolution of water contributions to discharge from a greenland outlet glacier insight from a new isotope mixing model the greenland ice sheet gris subglacial hydrological system may undergo a seasonal evolution with significant geophysical and biogeochemical implications we present results from a new isotope mixing model to quantify the relative contributions of surface snow glacial ice and delayed flow to the bulk meltwater discharge from a small 5k m 2 land terminating gris outlet glacier during melt onset may and at peak melt july we use radioactive 222 rn and stable isotopes 18 o deuterium to differentiate the water source contributions atmospherically derived 7 be further constrains meltwater transit time from the glacier surface to the ice margin we show that 1 222 rn is a promising tracer for glacial waters stored at the bed and 2 a quantitative chemical mixing model can be constructed by combining 222 rn and the stable water isotopes applying this model to the bulk subglacial outflow from our study area we find a constant delayed flow stored component from melt onset through peak melt this component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land terminating sections of the gris undergoes a seasonal evolution from a distributed to a channelized system

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

oxygen isotopes in asteroidal materials measurement of the variation of the 17o 16o and 18o 16o ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the solar system this chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material as sampled by meteorites in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios ultimately offering a window back to the very origin of solar system and its primordialoxygen isotopic heterogeneity oxygen is generally a major element in the gas liquid and solid phases that have interacted throughout the evolution of the solar system its chemical properties ensuring that there is abundant opportunity for reactions and exchange the details of which can be recorded in the isotopic ratios of the products such processes can be crudely subdivided into the following six categories early solar nebular isotopic heterogeneity high temperature modifi cation of nebular components metamorphism and melting in asteroids aqueous alteration in asteroids mixing of components brecciation terrestrial weathering it is clear from the isotopic variation in the earliest formed nebular components such as refractory inclusions and chondrules that there was considerable oxygen isotopic heterogeneity in the early solar nebula spanning over 50 and perhaps much greater in both 17o and 18o the origin of this variation is discussed elsewhere in this volume however isotopic exchange between the 16o rich solids and 17o and 18o rich gas phase s resulted in a wide range of isotopic variation in these early formed components offering insight into the conditions of these processes and the evolution of the reservoirs with time and or space once accreted onto the early planetisemals much of the primitive nebular components experienced considerable modification the metamorphism and melting experienced by some of these bodies most probably the result of heating from the decay of short lived radionuclides e g 26al resulted in progressive homogenization within individual bodies of any original isotopic heterogeneity complete homogenization appears to have been achieved in the hed parent body indicating very high levels of melting and the development of a large magma ocean the carbonaceous and ordinary chondrite parent bodies experienced more modest heating sufficient to mobilize water ice that accreted along with the more refractory materials the subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration such as water rock ratio temperature and isotopic signature and thus potentially the origin of the water ice the evolution of the asteroidal bodies has been far from simple and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites the result of breakup reassembly and mixing of different bodies during impact processing the final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering the isotopic compositions of the weathering products depend on location primarily latitude while the magnitude of the weathering is dependent on many factors with some meteorites e g highly reduced enstatite chondrites and the matrix rich co3s particularly susceptible to such effects

r chondrite bulk chemical compositions and diverse oxides implications for parent body processes abstract r chondrites are among the most oxidized chondrite groups they also have the highest 17o values known in whole rock meteorites we analyzed r chondrites six antarctic four hot desert by instrumental neutron activation analysis data for one of the former and three of the latter show large weathering effects but the remainder show only moderate scatter and permit us to determine trends and mean compositions for the group bulk r chondrite compositions are similar to those in h and l chondrites but the concentrations of several volatiles especially se and zn are higher the more volatile the element the higher the enrichment in r chondrites relative to h and l petrologic types in r chondrites extend as low as 3 6 we determined olivine compositional distributions and studied opaque oxides in 15 r chondrite thin sections including a newly discovered r4 clast in bencubbin adding to the diversity of chondritic clasts in this polymict breccia and an r clast in cm2 murchison opaque oxides in r chondrites include nearly pure magnetite al rich chromite magnetite chromite solid solution nearly pure chromite and ilmenite this diverse set of opaque phases reflects differing aqueous alteration conditions the least equilibrated r chondrites contain nearly pure magnetite but the spinels in metamorphosed r chondrites contain additional components e g cr2o3 and al2o3 and some minor cations the nio content in olivine correlates with the magnetite component in magnetite chromite solid solution in equilibrated r chondrites and is a function of the degree of oxidation the absence of metallic fe in a 881988 and lap 031156 indicates a high degree of oxidation the relatively low feo fa35 olivine in these rocks in part reflects the conversion of fe2 to fe3 and its partitioning into magnetite oxidation trends in r chondrites are affected by both aqueous alteration and thermal metamorphism the differing degrees of oxidation in this group reflect differences in local environments on the parent asteroid

nonporphyritic chondrules from equilibrated rumuruti and ordinary chondrites chemical evidence of secondary processing fil varela maria eugenia consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet san juan instituto de ciencias astronomicas de la tierra y del espacio universidad nacional de san juan instituto de ciencias astronomicas de la tierra y del espacio argentina

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

discharges of turbid water during mini surges of variegated glacier alaska u s a discharges of water sediment and dissolved impurities from variegated glacier ala ska were monitored in the early summers of 1980 and 1981 during the occurrence of mini surg es sea sonal trends weat her related eve nts and diurnal variat ions similar to behavior of other temperat e gl acier streams were found the prin cipal effect in the stream associated with mini surge occurrence was a brief discharge of extremely turbi d water the turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini surge at a time and locat ion on the upper glacier known from oth er meas ure ments the mean water velocity in the hydraulic system over the int erven ing distance is thereby determined 0 3 m s i the mean water velocity together with the water discharge 16 m3 s 1 at the terminus places con straints on the distribution of water velocity u and total cros s sectional area at of the flow paths along the gl acier base this leads to the con clusion that within the zone of mini surge occurrence in its unpe rturbed state u is about 0 1 m s 1 or possibly less at is about 10 2 m2 or possibly more and it must be divided into a very large number of small passag eways be blocked by constrict ions or both the total water cro ss se ction corresponds to a layer 0 1 2 m thick when spr ead unifo rmly over the glacier width the water velocity is clos e to or less than the propa gation velo city of the mini s urges bet ween the zone affected by mini surges and the stream a dyna mically less active lower section of the glacier is proba bly underlain by a small number of conduits in which the water velocity may be very high 2 m s i water di scharge follo wing the mini surges puts an upper limit on water storage changes ass ociated with the anomalous ice motion

mineralogical characterization of primitive type 3 lithologies in rumuruti chondrites rumuruti r chondrites constitute a new well established chondrite group different from the carbonaceous ordinary and enstatite chondrites many of these samples are gas rich regolith breccias showing the typical light dark structure and consist of abundant fragments of various parent body lithologies embedded in a fine grained olivine rich matrix unequilibrated type 3 lithologies among these fragments have frequently been mentioned in various publications in this study detailed mineralogical data on seven primitive fragments from the r chondrites dar al gani 013 and hughes 030 are presented the fragments range from 300 in size up to several millimeters generally the main characteristics can be summarized as follows 1 unequilibrated type 3 fragments have a well preserved chondritic texture with a chondrule to matrix ratio of 1 1 chondrules and chondrule fragments are embedded in a fine grained olivine rich matrix thus the texture is quite similar to that of type 3 carbonaceous chondrites 2 in all cases matrix olivines in type 3 fragments have a significantly higher fa content 44 57 mol than olivines in other equilibrated lithologies 38 40 mol fa 3 olivines and pyroxenes occurring within chondrules or as fragments are highly variable in composition fa0 65 and fs0 33 respectively and generally more magnesian than those found in equilibrated r chondrites agglomerated material of the r chondrite parent body or bodies was highly unequilibrated it is suggested that the material that accreted to form the parent body consisted of chondrules and chondrule fragments mainly having mg rich silicate constituents and fe rich highly oxidized fine grained materials the dominating phase of this fine grained material may have been fa rich olivine from the beginning the brecciated whole rocks the r chondrite regolith breccias were not significantly reheated subsequent to brecciation or during lithification as indicated by negligible degree of equilibration between matrix components and mg rich olivines and pyroxenes in primitive type 3 fragments

trace element contents of chondrule rims and interchondrule matrix in ordinary chondrites abstract the abundances of forty elements have been measured in the rims and matrices of the unequilibrated ordinary chondrites semarkona bishunpur chainpur and krymka the rims appear to be mixtures of matrix like material and material that was volatilized during chondrule formation iron silicon manganese and copper all appear to have behaved as volatiles during chondrule formation and their enrichments are generally confined to the rims suggesting recondensation of these elements was rapid and localized this is supported by petrologic observations that show many chondrules were still partially molten or plastic when the rims accreted some rims also exhibit a decrease in both their feo content and the degree of mineral re equilibration away from the chondrule the alkali metals are enriched in both the rims and matrices the alkalis may have recondensed onto the matrix as well as the rims but their mobility is such that they have probably undergone extensive redistribution after accretion some na may even have been able to diffuse back into chondrules either during chondrule cooling or during metamorphism alteration most refractory lithophiles are depleted with respect to a1 in the rims and matrices in all four uocs these depletions are probably due to postaccretional redistribution of these elements into phosphates and other secondary minerals that form in and around metal sulfide grains the matrix is probably composed of chondrule fragments and processed nebular dust but the presence of carbonaceous presolar grains in the matrix indicates that there must be unprocessed presolar silicates present too on average the presolar silicates presumably have a ci like composition but a ci like signature is not seen in the matrix compositions simple estimates suggest that the abundances of carbonaceous presolar grains are consistent with there being at most 10 wt o presolar silicates present in uoc matrix which would be hard to detect in this study

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

oxygen isotopes of chondritic components we review the oxygen isotopic compositions of chondrite components refractory inclusions chondrules and matrix and their inter and intra crystalline oxygen isotopic distributions primary oxygen isotopic compositions acquired before planetesimal accretion are easily disturbed by parent body processes such as aqueous alternation and thermal metamorphism primary or original oxygen isotopic compositions of refractory inclusions ca al rich inclusions and amoeboid olivine aggregates distribute along a slope 1 line on the three oxygen isotope diagram over the range of 60 17 o 18 o 16 o rich and 17 o 18 o rich during refractory inclusion formation on the other hand primary minerals of most chondrules have small isotopic variations and are enriched in 17 o and 18 o relative to refractory inclusions suggesting that chondrule formation occurred in 17 o 18 o rich nebular gas however rare 16 o rich chondrules have been found suggesting some overlap in the timing of formation of chondrules and refractory inclusions in the solar nebula oxygen isotopic compositions of matrix grains distribute along the slope 1 line over the same range as refractory inclusions and chondrules the similarity in oxygen isotopic distributions suggests that matrix was originally a mechanical mixture of nebular dusts co generated with chondrules and refractory inclusions presolar grains with oxygen isotopic compositions that are clearly distinct from those of solar nebular materials are a trace component of chondrite matrices based on these oxygen isotopic characteristics more than 99 5 of the solid materials in the nebula formed locally in the solar nebula and the remainder formed in interstellar space the astrophysical setting of chondrite component formation in the early solar system is also discussed refractory inclusions and 16 o rich matrix dusts formed around the inner edge of the solar nebula on the other hand most chondrules and 17 o 18 o rich matrix dusts seem to have formed elsewhere in the solar nebula efficient large scale radial mixing of the solar nebular materials may have been an essential process in the formation of chondritic planetesimals

hydrogeochemistry of the chhota shigri glacier meltwater chandra basin himachal pradesh india solute acquisition processes dissolved load and chemical weathering rates the chemical compositions of various ions in meltwater of the chhota shigri glacier were analysed during the observation period from may to october 2010 total 164 samples of meltwater were collected in two times a day at 8 0 a m and 6 0 p m bicarbonate and calcium were the dominant anion and cation in meltwater of the investigation area high ratios of ca mg versus tz and ca mg versus na k demonstrate that hydrogeochemistry of the study area was mainly governed by carbonate type weathering the average sulphate mass fraction of meltwater was computed to be 0 31 0 12 showing dominancy of bicarbonate over sulphate this excess bicarbonate would be generated by an alternative proton supply mechanism due to biological activities in the bed rock lithology and sulphide oxidation may be about the same as carbonation as a driver of chemical weathering at chhota shigri glacier in general major ions and total dissolved solid concentrations showed decreasing trend with increasing discharge from the study area the average daily mean dissolved load of this glacier was much lower than that of the gangotri glacier which may be due to low meltwater runoff and lithology of the investigation area the cation weathering rates of study area for early peak and late melt seasons were computed to be 694 1631 and 481 meq m 2 a 1 respectively the average value of chemical denudation rates of the chhota shigri glacier meltwater was found lower than that of the dokriani glacier

geometry and flow conditions of subglacial water at south cascade glacier washington state u s a an analysis of tracer injections tracers were injected into south cascade glacier to determine the flow condition and geometry of the subglacial water system results indicate that two distincts drainage basins on the glacier feed the two main streams flowing from the glacier in the largest basin two parallel drainage networks exist one englacial and the other subglacial

paleomagnetic evidence for late cenozoic glaciations in the mackenzie mountains of the northwest territories canada the mackenzie mountains were affected by montane valley glaciers during the pleistocene and peripherally by the laurentide ice sheet during the last glaciation in this paper we report on magnetostratigraphic dating and correlation of three sections recording late pliocene to late pleistocene glaciations katherine creek little bear river and inlin brook located around 65 n 127 w each section consists of a colluvial unit overlying a pliocene pediment surface cut into proterozoic or paleozoic bedrock or tertiary gravel which is in turn overlain by a stack of five and in places six montane tills usually with soils developed at their surfaces and capped by a laurentide till normal and reversed magnetizations were recognized with single domain magnetite as a dominant remanence carrier the katherine creek section has a normally magnetized colluvium at its base which is overlain by two reversed tills succeeded by three normal tills we interpret the top two tills to be of brunhes age 780 ka

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

olivine in martian meteorite allan hills 84001 evidence for a high temperature origin and implications for signs of life olivine from martian meteorite allan hills alh 84001 occurs as clusters within orthopyroxene adjacent to fractures containing disrupted carbonate globules and feldspathic shock glass the inclusions are irregular in shape and range in size from 40 pm to submicrometer some of the inclusions are elongate and boudinage like the olivine grains are in sharp contact with the enclosing orthopyroxene and often contain small inclusions of chromite the olivine exhibits a very limited range of composition from fo65 to fob6 n 25 the 6180 values of the olivine and orthopyroxene analyzed by ion microprobe range from 4 3 to 4 5 3960 and are indistinguishable from each other within analytical uncertainty the mineral chemistries 0 isotopic data and textural relationships indicate that the olivine inclusions were produced at a temperature so0 c it is unlikely that the olivines formed during the same event that gave rise to the carbonates in alh 84001 which have more elevated and variable 6180 values and were probably formed from fluids that were not in isotopic equilibrium with the orthopyroxene or olivine the reactions most likely instrumental in the formation of olivine could be either the dehydration of hydrous silicates that formed during carbonate precipitation or the reduction of orthopyroxene and spinel if the olivine was formed by either reaction during a postcarbonate heating event the implications are profound with regards to the interpretations of mckay el ul 1996 due to the low diflbsion rates in carbonates this rapid high temperature event would have resulted in the preservation of the fine scale carbonate zoning while partially devolatilizing select carbonate compositions on a submicrometer scale brearley 1998a this may have resulted in the formation of the minute magnetite grains that mckay et ul 1996 attributed to biogenic activity

geochemical and oxygen isotope perspective of a new r chondrite dhofar 1671 affinity with ordinary chondrites dhofar 1671 is a relatively new meteorite that previous studies suggest belongs to the rumuruti chondrite class major and ree compositions are generally in agreement with average values of the r chondrites rcs moderately volatile elements such as se and zn abundances are lower than the r chondrite values that are similar to those in ordinary chondrites ocs porphyritic olivine pyroxene pop radial pyroxene rp and barred olivine bo chondrules are embedded in a proportionately equal volume of matrix one of the characteristic features of rcs microprobe analyses demonstrate compositional zoning in chondrule and matrix olivines showing fa poor interior and fa rich outer zones precise oxygen isotope data for chondrules and matrix obtained by laser assisted fluorination show a genetic isotopic relationship between ocs and rcs on the basis of our data we propose a strong affinity between these groups and suggest that oc chondrule precursors could have interacted with a 17o rich matrix to form rc chondrules i e 17o shifts from 1 to 3 these interactions could have occurred at the same time as exotic clasts in brecciated samples formed such as nwa 10214 ll3 6 parnallee ll3 pca91241 r3 8 6 and dhofar 1671 r3 6 we also infer that the source of the oxidation and 17o enrichment is the matrix which may have been enriched in 17o rich water the abundance of matrix in rcs relative to ocs ensured that these rocks would be apparently more oxidized and appreciably 17o enriched in situ analysis of dhofar 1671 is recommended to further strengthen the link between ocs and rcs

oxygen isotopic evolution of the solar nebula studies of the three oxygen isotopes in chondrite meteorites demonstrate that diverse o reservoirs characterized by their 17o values were present in the solar nebula the discovery that some chondritic materials have o isotopic compositions that cannot be explained by mass dependent fractionation of an initially well mixed reservoir has important implications for the history of the solar nebula on a plot of 17o versus 18o or 17o 16o versus 18o 16o terrestrial samples with the main exception of stratospheric ozone fall along a single line the terrestrial fractionation or tf line having a slope 0 52 an indication that the parental reservoir was homogenized a convenient measure of o isotopic heterogeneity is the deviation from the tf line 17o 17o 0 52 18o a popular model to explain the evolution of chondritic oxygen compositions during nebular and asteroidal aqueous alteration processes calls for the nebula to have formed from solids having 18o 40 and 17o 41 17o 20 and a gas having a composition roughly estimated to be 18o 30 and 17o 24 17o 9 this model encounters serious difficulties when examined in detail in particular it cannot readily account for the o isotopic compositions of both chondrules and refractory inclusions from individual chondrite groups or for the differences between groups particularly in the compositions of chondrules magnetite fe3o4 is a key phase for o isotope studies because during its formation by the oxidation of ferrous metal or fes all o comes from the oxidant probably h2o it appears that most and possibly nearly all magnetite formed during aqueous alteration processes that occurred in asteroids in all chondrite groups studied to date 17o of the magnetite is greater than or equal to that of the chondrule silicates if the h2o originated in the ambient local nebula then at the time of accretion the 17o of the nebular gas was generally higher than that of the solids an alternative view is that the heterogeneity in the o isotopic composition of chondrites indicates that the nebula formed from diverse batches of presolar materials the precise o isotopic composition of the mix varying during the accretion history of the nebula the large compositional gaps between groups suggest that agglomeration of nebular dust to form chondrites did not proceed at a constant rate but that periods with turbulence levels low enough to allow agglomeration were punctuated by periods of high turbulence during which the composition of the inner nebula sampled by chondrites changed appreciably

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

crystal orientation effects in δ18o for magnetite and hematite by sims abstract in situ high precision analysis of oxygen isotope ratios 18 o by secondary ion mass spectrometry sims reveals that instrumental bias in 18 o for magnetite varies due to crystal orientation effects multiple analyses of 18 o have an average precision of 0 4 2sd in single grains of magnetite close to 0 3 that obtained for multiple grains of uwq 1 a homogeneous quartz standard in contrast the average precision is five to ten times worse 2 3 2sd from grain to grain of magnetite due to variation in instrumental bias with crystal orientation electron backscatter diffraction shows that individual grains of magnetite are single crystals and that crystal orientation varies randomly from grain to grain the crystal orientation for each magnetite grain is plotted relative to the incident angle of the sims primary cs beam high values of 18 o are measured when the cs beam is parallel to uv 0 from 110 to 100 preferred channeling and focusing directions for magnetite routine 18 o analysis at wiscsims utilizes a gaussian focused cs primary beam deep pit mode at primary and secondary voltages of 10 kv and 10 kv respectively total impact energy 20 kev four analytical experiments were conducted in attempts to improve the grain to grain precision in measured 18 o for magnetite 1 applying an energy offset of 50 ev 2 using a kohler illuminated beam shallow pit mode 3 reducing the total impact energy and 4 varying the primary and secondary accelerating voltages the best results were obtained in experiment 4 at primary secondary accelerating voltages of 3 kv 10 kv respectively with an incident cs beam angle of 14 the grain to grain precision in measured 18 o for magnetite improves from 2 9 to 0 8 2sd at 10 kv 10 kv and 3 kv 10 kv analysis respectively while precision in single grains is 0 4 for both instrumental bias in 18 o also varies with crystal orientation for hematite at similar levels as is seen for magnetite the grain to grain precision in measured 18 o for hematite improves from 2 1 to 1 0 2sd at 10 kv 10 kv and 3 kv 10 kv analysis respectively while precision in single grains is 0 3 2sd for both importantly crystal orientation effects have not been identified at levels of 0 3 for 18 o in silicates or other minerals analyzed by wiscsims though many minerals remain to be examined

oxygen and magnesium isotope compositions of calcium aluminum rich inclusions from rumuruti r chondrites abstract we report oxygen and magnesium isotope compositions of ca al rich inclusions cais from several rumuruti r chondrites measured in situ using a cameca ims 1280 ion microprobe on a three isotope oxygen diagram 17o vs 18o compositions of individual minerals in most r cais analyzed fall along a slope 1 line based on the variations of 17o values 17o 17o 0 52 18o within individual inclusions the r cais are divided into i 16o rich 17o 23 26 ii uniformly 16o depleted 17o 2 and iii isotopically heterogeneous 17o ranges from 25 to 5 one of the hibonite rich cais h030 l has an intermediate 17o value of 12 and a highly fractionated composition 18o 47 we infer that like most cais in other chondrite groups the r cais formed in an 16o rich gaseous reservoir the uniformly 16o depleted and isotopically heterogeneous cais subsequently experienced oxygen isotope exchange during remelting in an 16o depleted nebular gas possibly during r chondrite chondrule formation and or during fluid assisted thermal metamorphism on the r chondrite parent asteroid three hibonite bearing cais and one spinel plagioclase rich inclusion were analyzed for magnesium isotope compositions the cai with the highly fractionated oxygen isotopes h030 l shows a resolvable excess of 26mg 26mg corresponding to an initial 26al 27al ratio of 7 10 7 three other cais show no resolvable excess of 26mg 26mg the absence of 26mg in the spinel plagioclase rich cai from a metamorphosed r chondrite nwa 753 r3 9 could have resulted from metamorphic resetting two other hibonite bearing cais occur in the r chondrites nwa 1476 and nwa 2446 which appear to have experienced only minor degrees of thermal metamorphism these inclusions could have formed from precursors with lower than canonical 26al 27al ratio

oxygen isotopic constraints on the origin of mg rich olivines from chondritic meteorites chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system the calcium aluminum rich inclusions were condensed from the nebula gas chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk petrographic compositional and isotopic arguments allowed the identification of metal bearing mg rich olivine aggregates among the precursors of magnesian type i chondrules two very different settings can be considered for the formation of these mg rich olivines either a nebular setting corresponding mostly to condensation evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal an ion microprobe survey of mg rich olivines of a set of type i chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the 17o values and the presence of a large range of mass fractionation several within each mode the chemistry and the oxygen isotopic compositions indicate that mg rich olivines are unlikely to be of nebular origin i e solar nebula condensates but are more likely debris of broken differentiated planetesimals each of them being characterized by a given 17o mg rich olivines could have crystallized from magma ocean like environments on partially molten planetesimals undergoing metal silicate differentiation processes considering the very old age of chondrules mg rich olivine grains or aggregates might be considered as millimeter sized fragments from disrupted first generation differentiated planetesimals finally the finding of only a small number of discrete 17o modes for mg rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies

record of low temperature alteration in asteroids most chondritic materials experienced diverse styles of secondary alteration resulting in formation of hydrous and anhydrous oxygen bearing minerals silicates oxides and carbonates phyllosilicates magnetite calcite dolomite breunnerite ferrous olivine hedenbergite wollastonite grossular monticellite forsterite andradite nepheline sodalite brearley 2003 2005 and references therein petrographic mineralogic oxygen and short lived isotope systematics 26al 26mg 53mn 53cr 129i 129xe suggest that alteration occurred in the presence of aqueous solutions under variable physico chemical conditions temperature water rock ratio ph f o2 and fluid compositions in an asteroidal setting it started within 1 2 m y after formation of the cv cais was multistage and lasted up to 15 m y krot et al 2006 and references therein here we review bulk o isotopic compositions of chondritic materials o isotopic compositions of secondary minerals produced during asteroidal alteration and possible effects of fluid assisted thermal metamorphism on o isotopic exchange in primary high temperature minerals melilite and anorthite in the cv and co cais the implications of these data for understanding temperatures of alteration water rock ratios and oxygen isotopic composition of water that probably accreted into chondrite parent bodies in the form of ice are discussed the inferred or measured o isotopic composition of the meteoritic water is close to the terrestrial fractionation line 17o 2 it is very different from the inferred o isotopic compositions of the sun 17o 25 clayton 2002 yurimoto and kuramoto 2004 hashizume and chaussidon 2005 lyons and young 2005 suggesting significant evolution of o isotopic composition of the gaseous reservoir in the inner protoplanetary disk over its short 3 5 m y life time

subglacial hydrology for an ice sheet resting on a deformable aquifer glissements et deformation de la calotte de glace en relation avec le materiau de l aquifere et la densite des chenaux de drainage

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

carlisle lakes and allan hills 85151 members of a new chondrite grouplet carlisle lakes and allan hills 85151 alh85151 are members of a new grouplet of chondrites characterized by feo rich silicates olivine fa 38 41 mol unusual oxygen isotopic composition and abundant 35 vol recrystallized matrix material yamato 75302 is not as well characterized but is probably also a member of this grouplet siderophile elements in carlisle lakes and alh85151 are fractionated relative to ci chondrites refractory and common siderophiles are at 1 ci ga and as are lower 0 6 0 9 ci and au is very low 0 17 ci and 0 36 ci in carlisle lakes and alh85151 respectively the low au abundance may indicate that au resided mainly in fine grained metal particles that were suspended in the nebular gas during the time these chondrites agglomerated the oxidation state of chondrites may be controlled by the presence of oxidizing agents e g magnetite in agglomerated matrix material the high matrix abundance that characterizes this new grouplet may thus be responsible for the high oxidation state of these meteorites

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

tropical glacier meltwater contribution to stream discharge a case study in the cordillera blanca peru original abstract discharge measurements climate observations and hydrochemical samples gathered monthly 1998 99 in the yanamarey and uruashraju glacier fed catchments of the cordillera blanca peru permit an analysis of the glacier meltwater contribution to stream flow these glacier catchments feed the rio santa which discharges into the pacific ocean based on a water balance computation glacier melt contributes an estimated 35 of the average discharge from the catchments for comparison a volumetric end member mixing model of oxygen isotopes shows glacier melt contributes 30 45 to the total annual discharge based on stream geochemistry discharge from the yanamarey glacier catchment provides 30 of the annual volume discharged from the querococha watershed which is 10 glacierized by analogy the larger rio santa watershed also 10 glacierized receives at least 12 of its annual discharge from melting glacier ice tributary watersheds to the rio santa with larger fractions of glacier cover have less variable runoff and enhanced discharge demonstrating that the glaciers effectively buffer stream discharge seasonally with continued glacier melting stream flow will likely become more variable and there will be less dry season runoff

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

comments on the use of chemically based mixing models in glacier hydrology the assumptions involved in the use of chemically based mixing models for analysis of flow routing of meltwaters in glacierized basins are critically evaluated the assumption that glacial drainage systems consist of only two primary flow components is arbitrary and must be supported by independent evidence recent studies of the processes by which meltwaters acquire solute indicate that the assumption that flow components have unique and constant chemical compositions is unlikely to lie correct source water composition and weathering potential will vary over the course of a melt season and the extent of subglacial weathering is strongly dependent upon such factors as meltwater residence time and the availability of reactive sediment both of which are known to vary on diurnal to seasonal time scales mixing of flow components does not appear to be confined to the terminal regions of glaciers and is therefore unlikely to be conservative as assumed a multi parameter mixing model is applied to the analysis of data on the chemistry of waters sampled from bureholes drilled through haut glacier d arolla switzerland to demonstrate the range of dissolved species for which the assumption of conservative mixing is violated the consequences of this violation for quantitative hydrograph separation are shown to be highly significant the utility of mixing models as a tool for the investigation of glacier hydrological systems is questionable and the results of previous studies are unreliable

ion microprobe analyses of oxygen three isotope ratios of chondrules from the sayh al uhaymir 290 ch chondrite using a multiple hole disk the ion microprobe is the only technique capable of determining high precision stable isotope ratios in individual tiny extraterrestrial particles 100 lm in diameter but these small samples present special analytical challenges we produced a new sample holder disk with multiple holes three holes and seven holes in which epoxy disks containing a single unknown sample and a standard grain are cast and polished performance tests for oxygen two isotope analyses using san carlos olivine standard grains show that the new multiple hole disks allow accurate analysis of tiny particles if the particles are located within the 500 lm and 1 mm radius of the center of holes for seven hole and three hole disks respectively using the new seven hole disk oxygen three isotope ratios of eight magnesian cryptocrystalline chondrules approximately 100 lm in diameter from the sayh al uhaymir sau 290 ch chondrite were analyzed by ion microprobe at the university of wisconsin five out of eight chondrules have nearly identical oxygen isotope ratios d 17 o 2 2 0 6 2sd which is consistent with those of magnesian cryptocrystalline chondrules in ch cb and cb chondrites suggesting a genetic relationship i e formation by a common possibly impact heating event the other three chondrules have distinct oxygen isotope ratios d 17 o values from 6 4 to 2 2 given that similar variation in d 17 o values was observed in type i porphyritic chondrules in a ch cb chondrite the three chondrules may have formed in the solar nebula similar to the type i porphyritic chondrules

sodium chlorine rich mesostases in chainpur ll3 and parnallee ll3 chondrules forty six chondrules from chainpur ll3 4 and 39 chondrules and clasts from parnallee ll3 6 have been sectioned and searched for na cl rich phases by electron probe microanalysis epma oxygen isotopic compositions i xe ages and ion probe data were also obtained on some of these chondrules sodium cl rich glass and microcrystalline sodalite na4al3si3o12cl nepheline naalsio4 scapolite na4al3si9o24cl have been identified in 7 of the chainpur and 8 of the parnallee samples these phases are present in chondrule mesostases or in one case the plagioclase of a barred olivine chondrule none of the chondrules contain 5 vol na cl rich phases in the chainpur chondrules they originated through partial devitrification of silica undersaturated rare earth element ree na and cl rich mesostases two processes have been identified that led to the formation of these mesostases in two of the chondrules which consist mainly of low ca pyroxene the extended metastable crystallization of low ca pyroxene created silica undersaturated ree rich residua barium and cl enrichments in nepheline and scapolite of one chondrule suggest that there was also an influx of alkalis and cl during crystallization of the low ca pyroxene similarly another one of the chainpur chondrules mainly composed of olivine phenocrysts is markedly enriched in cl 10 oc as there is no evidence of corrosive metasomatism in any of the chondrules cl and alkali enrichment is believed to have occurred when they were still partially molten the chondrules were derived from normal o isotopic reservoirs so the postulated influx of ba na and cl did not occur on an exotic parent body trace amounts of nepheline and sodalite present in two parnallee chondrules crystallized from small na cl ree rich residua following extended crystallization of anorthite an i xe age of 5 0 ma post bjurbole obtained on one of these parnallee chondrules dates the crystallization of feldspathoid and thus formation of the chondrule

ion microprobe measurements of 18o 16o ratios of phosphate minerals in the martian meteorites alh84001 and los angeles abstract oxygen isotope ratios of merrillite and chlorapatite in the martian meteorites alh84001 and los angeles have been measured by ion microprobe in multicollector mode 18o values of phosphate minerals measured in situ range from 3 to 6 and are similar to martian meteorite whole rock values as well as the 18o of igneous phosphate on earth these results suggest that the primary abiotic igneous phosphate reservoir on mars is similar in oxygen isotopic composition to the basaltic phosphate reservoir on earth this is an important first step in the characterization of martian phosphate reservoirs for the use of 18o of phosphate minerals as a biomarker for life on mars cumulative textural major element and isotopic evidence presented here suggest a primary igneous origin for the phosphates in los angeles and alh84001 textural and chemical evidence suggests that phosphates in alh84001 were subsequently shock melted in a later event

evolution of the internal drainage system in the lower part of the ablation area of storglaci aren sweden during the 1989 melt season ten tracer experiments were conducted to investigate seasonal diurnal and spatial variations in the internal drainage system in the ablation area of storglaciaren sweden dye was injected into moulins and dye concentration and discharge were monitored in two streams at the glacier terminus sydjakk and nordjakk dye emerged only in sydjakk transit velocities ranged from 0 07 to 0 29 m s implying that drainage was through a well defined conduit system velocity and discharge relations suggest that these conduits are part of a multi branched arborescent network of individually braided wide low passages a progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits presumably including a decrease in the degree of braiding and an increase in size the system reached its late season configuration in early august by which time the energy dissipated by the flowing water would have sufficed to melt between 0 7 and 21 m 3 of ice per meter of conduit length depending on conduit size potential closure rates exceed melt rates on conduit walls throughout most of the drainage system and so conduits are probably full of water during periods of higher daily discharge with water pressures exceeding atmospheric pressure variations in tracer return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding in this case resulting from drowning of low divides between channels as discharge increases

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

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

a chondrule like object captured by space exposed aerogel on the international space station abstract here we report on the mineralogy petrography and oxygen isotope compositions of a micrometeoroid captured on the international space station this micrometeoroid has the texture of a porphyritic olivine chondrule because hydrated phases were not identified in the micrometeoroid and because ni rich sulfide in it does not show exsolution of pentlandite on the tem scale the micrometeoroid probably escaped low temperature events such as aqueous alteration on its parent body however the mean value and standard deviation of cr2o3 wt in olivine in the micrometeoroid suggest that the micrometeoroid experienced weak thermal metamorphism oxygen isotope ratios of pyroxene and olivine in the micrometeoroid are similar to those of chondrule like objects in comet 81p wild2 and coarse grained crystalline micrometeorites as well as those in chondrules in major types of carbonaceous chondrites these data suggest that the micrometeoroid is a fragment of a chondrule like object that was derived from a primitive parent body that experienced thermal metamorphism

a hydrological approach to estimating daily glacier ablation reduced meltwater discharge owing to glacier retreat can have severe impacts on downstream water users to assess these impacts it is essential to differentiate between water from glacier melt and other sources we propose a method for doing this on a daily time scale by applying a mixing law to electrical conductivity and proglacial discharge measurements daily ablation is then estimated by applying a recession law to the glacier melt component testing this method on summer hydrology and meteorology measurements from the baounet glacier france taken over six consecutive years 2008 2013 allowed us to reconstruct daily ablation during the ablation period mean ablation rates ranged from 20 to 30 mm day 1 air temperature measurements showed that periods of low ablation during the summer were linked to cooler days and snowfall periods comparisons for three consecutive summers showed that the ablation rates obtained by summing calculated daily ablation were statistically similar to the rates recorded

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

the composition of the englacial and subglacial component in bulk meltwaters draining the gornergletscher switzerland a new method of hydrograph separation for bulk meltwaters draining alpine glaciers is proposed it is based on the two component subglacial and englacial mixing model of collins 1978 but allows the composition of the subglacial component to vary between ascending and descending lines of the hydrograph the mean englacial component can be derived from linear relationships between sulphate concentrations and other ions in bulk meltwaters on certain occasions during the ablation season the maximum concentration of ions in the subglacial component can be determined from the linear relationship between bulk meltwater sulphate concentrations and discharge the bulk discharge is then a direct measure of the mass fraction of the englacial component at maximum discharge the contribution of the subglacial component approaches zero which has implications for the storage and mixing of waters in subglacial reservoirs further the subglacial component is not of constant composition and may itself be a mixture of dilute supraglacial and concentrated subglacial water

feo rich porphyritic pyroxene chondrules in unequilibrated ordinary chondrites abstract a suite of feo rich type ii porphyritic olivine pyroxene pop chondrules has been studied in detail data for ten chondrules from semarkona ll3 0 are emphasized and one chondrule from chainpur ll3 4 and two from parnallee ll3 6 are included as further examples of certain properties the chondrules contain phenocrysts of pyroxene and olivine in varying proportions and have fe fe mg 10 mol in the silicate minerals four pyroxene minerals are present clinoenstatite orthorhombic enstatite pigeonite and augite pyroxene phenocrysts may consist of all four minerals with progressive overgrowths in order of increasing wo content enstatite may occur independently of clinoenstatite but ca rich pyroxenes pigeonite and augite always nucleate on low ca pyroxene phenocrysts pyroxene and olivine phenocrysts may be independent of each other or may be intergrown and commonly show hopper morphologies indicative of rapid growth pyroxenes and olivines are commonly strongly zoned as a result of fractional crystallization of the chondrules in addition low ca pyroxene may contain ghost regions of slightly more feo and minor element rich material in the cores of grains these regions are partially resorbed and appear to be derived from previous crystallization of essentially the same chondrule oscillatory zoning is observed in enstatite in two chondrules and is believed to be the result of disquilibrium kinetic effects relict grains including a forsterite relict and a partially reduced feo rich relict in the same chondrule and clinoenstatite cores of pyroxene phenocrysts in another chondrule are evidence for recycling and mixing of chondrule material all of the chondrules are highly disequilibrium assemblages they appear to have cooled from essentially molten droplets with little volatile loss or recondensation occurring during the heating event peak temperatures were probably close to liquidus temperatures 1500 1700 c and cooling rates were probably of the order of hundreds of degrees per hour this description will serve as a basis for future interpretation of the effects of metamorphism on porphyritic pyroxene rich chondrules

petrologic geochemical and experimental constraints on models of chondrule formation abstract the petrologic and geochemical properties of chondrules as well as results of experimental studies provide strong constraints on chondrule formation models nebular formation is indicated by the non mass fractionated oxygen isotopic compositions of bulk chondrules chondrule formation from a melt is required by the prototypical spheroidal shapes and the presence of euhedral phenocrysts and glassy mesostases incomplete melting is indicated by the abundance of porphyritic chondrules which experiments demonstrate require relict nuclei and coarse relict grains the length of time that chondrules were hot is constrained by their retention of relict grains and moderately volatile elements rapid cooling of chondrules after formation is supported by the presence of zoned phenocrysts isotopic anomalies and dynamic crystallization experiments it is clear from the presence of relict grains enveloping compound chondrules and igneous rims that many chondrules were heated again after cooling the heating mechanism responsible for chondrule formation seems to have operated at varying intensities over large regions of the inner solar nebula for at least the time it took ambient nebular temperatures to cool from above 900 to below 600 k the chondrule formation mechanism provided a repeatable source of energy capable of highly localized melting characteristic of flash heating the occurrence of ferroan microchondrules with low melting temperatures within some chondrule rims indicates that chondrule formation did not occur exclusively in high temperature regions near the sun as required in bipolar outflow models mechanisms for forming chondrules that are consistent with the constraints include various flash heating models nebular lightning magnetic reconnection flares gas dynamic shock waves and radiative heating

fractionated matrix composition in cv3 vigarano and alteration processes on the cv parent asteroid abstract although cv3 vigarano is one of the most primitive cv chondrites it has lost most of the s from the matrix matrix na is also depleted relative to the concentration in bulk cv chondrites we used a matrix grid technique to study thirteen 50 50 m regions in vigarano in each area we used an electron microprobe to gather data with an electron beam 3 m in width we found two end member types of matrix textures one is coarse and porous has lower fe contents and lower analytical totals it appears to be contaminated with comminuted chondrule debris the other is finer grained and appears smooth its mean composition has higher fe but lower s and al contents than the coarse matrix areas our tentative interpretation is that the larger grain size of the coarse areas resulted from the admixing of comminuted chondrule materials and thus that the initial fraction of nebular fines was higher in the fine matrix regions aside from volatiles the overall composition of vigarano matrix is similar to that observed in matrix grid studies of other carbonaceous chondrites al si fe and mn have high whole chondrite normalized abundance ratios ca concentrations are low and highly variable because asteroidal alteration effects are present in our sample it is difficult to resolve nebular signatures in the compositions of the grid areas

the compositional classification of chondrites vii the r chondrite group bulk compositional and petrographic data clearly define the new r rumuruti group of chondrites consisting of rumuruti the only fall alh85151 acfer 217 carlisle lakes dar al gani 013 pca91002 pca91241 y 75302 y 793575 and y 82002 compositional petrographic rare gas and 0 isotopic data strongly suggest that pca91002 and pca91241 are paired the yamato specimens are probably not paired the matrices of the known r chondrites have experienced similar minor degrees of metamorphism petrographic types are 3 8 3 9 with the exception of alh85151 3 6 all except carlisle lakes contain equilibrated r5 r6 clasts petrographically the r chondrites are characterized by a low chondrule matrix modal abundance ratio high states of oxidation reflected by abundant nio bearing olivine with fa37 40 relatively small chondrules mean apparent diameters of 400 abundant up to 11 wt sulfides mainly pyrrhotite and pentlandite and negligible amounts of metallic fe ni refractory lithophile abundances are 0 95 x cl intermediate between those in ordinary chondrites oc and ci chondrites abundances of the volatile elements se and zn are greatly enhanced relative to oc the r chondrites are clearly distinguished from other chondrite groups on the basis of al mn and zn mn abundance ratios the oxygen isotopic data plot roughly along a slope 12 line with whole rock 17o values higher than for any other chondrite group rumuruti acfer 217 alh85151 pca91002 and pca91241 have light dark structures and solar wind implanted rare gases indicating that they are regolith breccias the yamato specimens also have light dark structures and are inferred to be regolith breccias carlisle lakes lacks solar rare gases and is unbrecciated based on similarities in refractory lithophile abundances 00 95 x ci oxygen isotope compositions 17o 0 and refractory inclusion abundances 0 1 vol none have been reported the r chondrites probably belong to a noncarbonaceous superclan of chondrites that also includes ordinary and enstatite chondrites the high oxidation state high matrix chondrule modal abundance ratio relatively low abundance of droplet chondrules and high 17o composition suggest that the r chondrites formed at greater heliocentric distances than the oc

investigations of glacier hydrological systems using dye tracer techniques observations at pasterzengletscher austria a l aide de traceurs colores on a mis en evidence une division laterale du drainage dans le bas de la langue qui n est pas determinee par la direction des crevasses obliques la reapparition de l eau dans les differents moulins est complexe bien qu elle reste constante dans le temps

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

the carlisle lakes type chondrites a new grouplet with high δ17o and evidence for nebular oxidation abstract carlisle lakes alh85151 and y75302 are similar ungrouped chondrites which have petrologic and bulk compositional similarities to the ordinary chondrites but are more oxidized and their oxygen isotopic compositions differ they represent a new grouplet which we call the carlisle lakes type chondrites they have the highest 17o values up to 2 91 measured to date the whole chondrites and most of their chondrules plot on the same mass fractionation line on an oxygen 3 isotope diagram they are olivine rich 70 vol essentially metal free and most olivine is feo rich equilibrated at fa38 rare olivine and pyroxene grains in chondrules and fragments are zoned and these are important in discerning the history of these chondrites the zoning does not appear to have formed during crystallization from a melt droplet chondrule but post dated chondrule formation two hypotheses are postulated to explain the zoning 1 1 parent body thermal metamorphism 2 2 nebular gas solid exchange reactions accompanied by condensation of new feo rich olivine utilizing existing olivine surfaces as nucleation sites the occurrence of steep fe mg compositional gradients of core to rim profiles oscillatory zoning in olivine fayalitic rims of fa45 that exceed instead of approach the equilibrium composition of the matrix fa38 and olivine filled veins in zoned pyroxenes are more compatible with the nebular hypothesis the carlisle lakes type chondrites may have originally been derived from an ordinary chondrite like precursor which was later oxidized prior to its final lithification however the oxygen isotopic compositions of the whole chondrites and most of their chondrules suggest that the precursor probably formed in an oxygen isotopically distinct environment

chemical models of solute acquisition in glacial melt waters chemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria different open and closed system models are defined by variations in the rates of weathering relative to the rate of hydrogen ion supply by the dissolution and dissociation of co2 and can be recognized by characteristic ph and relationships the observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed system conditions result where post mixing weathering reactions occur the final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt the extent of post mixing evolution and opportunity for mixing with ground waters or re equilibration with the atmosphere