elephant moraine 96029 a very mildly aqueously altered and heated cm carbonaceous chondrite implications for the drivers of parent body processing elephant moraine eet 96029 is a cm carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration a later phase of heating and terrestrial weathering the presence of phyllosilicates and carbonates within chondrules and the fine grained matrix indicates that this meteorite was aqueously altered in its parent body features showing that water mediated processing was arrested at a very early stage include a matrix with a low magnesium iron ratio chondrules whose mesostasis contains glass and or quench crystallites and a gehlenite bearing calcium and aluminium rich inclusion eet 96029 is also rich in fe ni metal relative to other cm chondrites and more was present prior to its partial replacement by goethite during antarctic weathering in combination these properties indicate that eet 96029 is one of the least aqueously altered cms yet described cm2 7 and so provides new insights into the original composition of its parent body following aqueous alteration and whilst still in the parent body regolith the meteorite was heated to 400 600 c by impacts or solar radiation heating led to the amorphisation and dehydroxylation of serpentine replacement of tochilinite by magnetite loss of sulphur from the matrix and modification to the structure of organic matter that includes organic nanoglobules significant differences between samples in oxygen isotope compositions and water hydroxyl contents suggests that the meteorite contains lithologies that have undergone different intensities of heating eet 96029 may be more representative of the true nature of parent body regoliths than many other cm meteorites and as such can help interpret results from the forthcoming missions to study and return samples from c complex asteroids

landscape evolution post lgm surface denudation and soil weathering processes from dickinson park mire wind river range wyoming usa abstract at mid latitudes the transition from the pleistocene to the holocene was characterised by distinct and partially abrupt climatic changes also during the holocene climatic perturbations with sometimes cold dry conditions have occurred how land surfaces and soil development processes in high mountains respond to these climatic oscillations is so far only poorly known we traced the responses of surfaces in the alpine settings of the wind river range wyoming us by using a large mire as natural archive this enabled us to reconstruct environmental conditions and ecosystem changes during the holocene in this montane area although adjacent moraine deposits display 10be exposure ages from the last glacial maximum up to mis16 or even older the accessible sediment deposits covered only the holocene via radiocarbon dating by applying a geoforensic approach and deriving sedimentation rates major climatic signals were detected a higher deposition and consequently erosion rate and thus a higher rate of geomorphic activity was measured for the known cold periods 9 4 10 2 ka bp 4 2 ka bp and 2 5 ka bp during the lia especially rapid aggradation of organic matter organic matter took place here rates of chemical weathering and soil formation seem to have been relatively low until about 5 6 ka bp but have since increased during the late holocene this would fit previous observations of increasing moisture conditions after the mid holocene aridity period in contrast to several other studies no clear signs of major disturbances erosion weathering during the 8 2 ka event could be observed together with the low levels of chemical weathering found here we do not see any evidence that the climate was more humid during this period compared to previous findings more humid conditions seemed to have returned earlier i e about 5 kyr bp in general this landscape displayed a patchy pattern of reaction to environmental changes as all events were not recorded in each mire profile

infrared spectroscopic taxonomy for carbonaceous chondrites from speciation of hydrous components mid infrared absorption spectra for all types of carbonaceous chondrites were obtained in this study to establish a versatile method for spectroscopic classification of carbonaceous chondrites infrared spectra were measured using a conventional kbr pellet method and diamond press method spectra of hydrous carbonaceous chondrites exhibit intense o h stretching vibrations ci chondrites are identifiable by a characteristic sharp absorption band appearing at 3685 cm 1 which is mainly attributable to serpentine x ray diffraction analysis showed the presence of serpentine however yamato y 82162 c1 does not have the band at 3685 cm 1 because of its thermal metamorphism cm and cr chondrites have an intense absorption band at approximately 3600 cm 1 this absorption tends to appear in cm chondrites more strongly than cr chondrites because the intensity ratios of an oh stretching mode at 3520 cm 1 compared to 3400 cm 1 for cm chondrites are in the range of 0 95 1 04 which is systematically higher than those of cr chondrites 0 86 0 88 therefore the two types of chondrites are distinguishable by their respective infrared spectra the spectrum feature of the tagish lake meteorite is attributable to neither ci nor cm chondrites co chondrites are characterized by weak and broad absorption at 3400 cm 1 cv chondrites have weak or negligible absorption of water ck chondrites also have no water induced absorption ch and cb chondrites have a sharp absorption at 3692 cm 1 indicating the presence of chrysotile which is also supported by observations of x ray diffraction and tem the combination of spectroscopic classification and the diamond press method allows classification of carbonaceous chondrites of very valuable samples with small quantities as one example carbonaceous chondrite clasts in brecciated meteorites were classified using our technique infrared spectra for a fragment of carbonaceous clasts 1 g separated from willard b and tsukuba were measured the 3685 cm 1 band found in ci chondrites was clearly detected in the clasts indicating that they are ci like clasts

effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains drummond c n wilkinson b h lohmann k c and smith g r 1993 effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains palaeogeogr palaeoclimatol palaeoecol 101 67 79 oxygen isotopic compositions of upper miocene 9 2 m y lacustrine limestone from northwestern wyoming range from 21 5 to 35 2 0 pdb and are the lightest yet reported for a non marine carbonate sequence these values require that lake water was greatly depleted in 180 relative to modern meteoric precipitation and indicate that most inflow was sourced as meltwater from glaciers in the adjacent gros ventre range assessment of climatic factors influencing the isotopic composition of global meteoric water indicates either that nearly all of miocene precipitation in the southern rocky mountains was derived from large lake systems in the snake river plain and northern great basin to the west or that gros ventre catchment elevations were up to 2300 m higher than at present because erosion rates in modern alpine regions suggest that subaerial denudation could only account for up to 1200 m of post miocene elevation reduction any additional lowering must reflect the influence of post laramide epeirogeny during basin and range extensional tectonism lacustrine isotopic data therefore provide boundary conditions on the timing and magnitude of changes in late cenozoic paleoclimate topography hydrology and tectonism in the western wyoming portion of the rocky mountains

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

high spatial resolution ion microprobe measurements refine chronology of carbonate formation in orgueil aqueous activity on meteorite parent bodies is indicated by the presence of carbonates high spatial resolution ion microprobe analyses of nine individual carbonate grains four dolomites five breunnerites from the orgueil meteorite reveal linear correlations between 53cr excesses and mn cr ratios in all grains indicative of in situ decay of radioactive 53mn half life 3 7 million years the well defined isochrons appear to have chronological significance if this is the case then 53mn 55mn ratios between 2 1 and 4 7 x 10 6 are inferred for the time of carbonate formation and absolute ages of between 4561 and 4565 ma are calculated systematic uncertainty of 2 ma dolomites tend to have formed slightly earlier than the breunnerites our data imply extensive aqueous activity on the orgueil parent body over a period of several million years starting 3 4 myr after formation of the solar system that most likely was the result of impact heating and latent heat from the decay of radioactive 26al and 60fe

suppression of dominant topographic overprints in gravity data by adaptive filtering southern wyoming province in areas of the world with a protracted tectonic history the gravity field may be dominated by anomalies due to individual structural features developed during the latest tectonic event these individual tectonic features often have a topographic expression adaptive filtering techniques can be used to suppress the gravity effects of such features iterative space domain techniques are particularly well suited to these types of problems one such technique the stochastic gradient algorithm allows easy updating of filter coefficients at each spatial step through the data this approach eliminates windowing and spectral estimation problems associated with cross spectral admittance schemes in this study adaptive filtering of bouguer gravity and topography in the southern wyoming province was successful in suppressing gravity signatures of laramide structural features the regional gravity trends due to isostatic effects were significantly absent from the residual anomaly map a large continuous positive gravity anomaly stretching from the southern wind river range to the northern end of the laramie range was another outstanding feature observed in the residual anomaly this positive anomaly is about the same magnitude size and shape as anomalies due to greenstone belts observed in other archcan cratonal areas scattered occurrences of greenstone lithologies are known throughout the area of the anomaly but a continuous feature is absent in outcrop due to the unusual structural history of the area it is possible that such a continuous belt does exist but was buried at shallow crustal levels by laramide thrusting or later collapse of a laramide uplift due to a change in the regional stress field

evolution of stream aquifer hydrologic connectedness during pumping experiment the evolution of the hydrologic relationship between streams and aquifers resulting from groundwater pumping or drainage near a stream is of great interest to the research community and to water management decision makers a stream aquifer ditch sandbox was built to be used to characterize the hydrologic connectedness of the stream aquifer responding to declines of the water table over a vertical profile presumably as a result of increased pumping near the stream we called the position of water table over the vertical profile the water table curve six hydrologic cases were chosen to investigate the behaviors of the water table curve all cases are roughly based on existing and possible real hydrogeological conditions in nature emphasis was placed on the analysis of the dynamic processes of evolution in the stream aquifer system where the stream aquifer changes from a fully connected condition to a disconnected condition the experimental results for the six cases were shown by differences in hydraulic head contours pressure head distributions and the shapes of the water table curve over a vertical profile the thickness of the inverted saturated zone and the induced recharge of groundwater from the stream factors that strongly affect the evolution of stream groundwater relationships are discussed including changes in stream stages the declines of the water table curves stream geometries streambed clogging and aquifer heterogeneity then a new concept of a disconnected stream with aquifer is given according to the evolution of stream groundwater relationships

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

olivine in terminal particles of stardust aerogel tracks and analogous grains in chondrite matrix abstract the dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the wild 2 samples we present 68 analyses of olivine fa 0 97 in the coarse grained terminal particles of stardust aerogel tracks and a comprehensive dataset 10 3 analyses of analogous olivine grains 5 30 m isolated in ci cm cr ch co cv3 oxidized cv3 reduced c3 ungrouped acfer 094 and ningqiang l ll 3 0 4 eh3 and kakangari chondrite matrix these compositions reveal that wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite forming regions the wild 2 olivine includes amoeboid olivine aggregates aoas refractory forsterite type i and type ii chondrule fragments and or microchondrules and rare relict grain compositions in addition we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low temperature aqueous processing in the kuiper belt the generally low cr content of feo rich olivine in the stardust samples indicates that they underwent mild thermal metamorphism akin to a petrologic grade of 3 05 3 15

modal mineralogy of cm2 chondrites by x ray diffraction psd xrd part 1 total phyllosilicate abundance and the degree of aqueous alteration abstract cm carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids using position sensitive detector x ray diffraction psd xrd and a pattern stripping technique we quantify the modal mineralogy of cm2 chondrites mighei murray murchison nogoya and cold bokkeveld there is a narrow range in the combined modal volume vol of the most abundant phases mg serpentine 25 33 and fe cronstedtite 43 50 cold bokkeveld is anomalous in containing more mg serpentine 49 59 than fe cronstedtite 19 27 even including cold bokkeveld the range in modal total phyllosilicate is 73 79 average 75 total phyllosilicate abundance provides a non ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration this reflects pervasive hydration of matrix across cm2 samples apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy for all samples there is a limited range in olivine 6 9 and pyroxene 5 abundances modal abundances of the remaining identified phases also show a limited range calcite 0 1 3 gypsum 0 1 6 magnetite 1 1 2 4 pentlandite 0 2 1 and pyrrhotite 1 3 8 as expected we observe a strong negative correlation in the modal abundance of anhydrous fe mg silicates olivine pyroxene and total phyllosilicate mg serpentine fe cronstedtite consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components the negative correlation in the modal abundance between mg serpentine and fe cronstedtite indicates a mineralogic transformation of fe cronstedtite to mg serpentine by fluid driven recrystallisation or b that these meteorites had different initial abundances of olivine and pyroxene the observed positive correlation in the relative proportion of mg serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly mg rich phyllosilicate during aqueous alteration fe cronstedtite is the dominant phyllosilicate while cm chondrule olivines are forsteritic and will form mg serpentine during aqueous alteration this implies that matrix olivine was more fe rich than chondrule olivine prior to aqueous alteration

modal mineralogy of cv3 chondrites by x ray diffraction psd xrd abstract using position sensitive detector x ray diffraction psd xrd we determine a complete modal mineralogy for all phases present in abundances greater than 1 wt in vigarano efremovka mokoia grosnaja kaba and allende reduced cv3 samples are comprised of vol olivine 83 85 enstatite 6 5 8 1 anorthite 1 1 1 2 magnetite 1 4 1 8 sulphide 2 4 5 1 fe ni metal 2 2 2 the oxidized samples are comprised of olivine 76 3 83 9 enstatite 4 8 7 8 anorthite 1 1 1 7 magnetite 0 3 6 1 sulphide 2 9 8 1 fe ni metal 0 2 1 1 fe oxide 0 2 7 and phyllosilicate 1 9 4 2 when our modal data is used to calculate a bulk chemistry that is compared to literature data a near 1 1 correlation is observed psd xrd data indicates that olivine compositions may span almost the entire fe mg solid solution series in all cv samples and that these contain a component 4 13 of fine grained olivine that is more fe rich fa 60 than is typically reported modal mineralogy shows that there are mineralogic differences between cv3 samples classified as oxidized and reduced but that these sub classes are most clearly distinguished by the relative abundance of metal and ni content of sulphide rather than abundance of magnetite the most significant difference in modal mineralogy observed is the relative absence of phyllosilicate in reduced cv that essentially escaped aqueous alteration fayalite ferrous olivine and magnetite are typically considered secondary alteration products the abundances of these minerals overlap in oxidized and reduced samples and correlate positively supporting common conditions of formation in a relatively oxidizing environment the abundances of fayalite ferrous olivine and magnetite show no relationship to petrographic type and if these abundances were used as a proxy for alteration allende would be the least altered cv contrary to all previous data the implication is that thermal metamorphism on the parent body was de coupled from formation of fe rich secondary minerals low temperature fluid assisted metamorphism can also not easily explain the origin of fayalite ferrous olivine and magnetite since the reduced cvs appear to be largely unaffected by this process parent body models require an anhydrous low temperature mechanism of secondary alteration the alternative is that these phases formed prior to accretion of the final cv parent body

long term tectonothermal history of laramide basement from zircon he age eu correlations abstract the long term 1 ga thermal histories of cratons are enigmatic with geologic data providing only limited snapshots of their evolution we use zircon u th he zircon he thermochronology and age composition correlations to understand the proterozoic phanerozoic thermal history of archean wyoming province rocks exposed in the northern laramide ranges of western north america zircon he ages from the wind river range 54 dates and bighorn mountains 32 dates show negative correlations with effective uranium eu a proxy for radiation damage zircon dates from the bighorns are between 960 ma low eu and 20 ma high eu whereas samples from the wind rivers are between 582 ma low eu and 33 ma high eu we applied forward modeling using the zircon radiation damage and annealing model zrdaam to understand this highly variable dataset a long term t t path that is consistent with the available geologic constraints successfully reproduced age eu correlations the best fit to the wind rivers data involves two phases of rapid cooling at 1800 1600 ma and 900 700 ma followed by slower cooling until 525 ma during the phanerozoic these samples were heated to maximum temperatures between 160 and 125 c prior to laramide cooling to 50 c between 60 and 40 ma data from the bighorn mountains were successfully reproduced with a similar thermal history involving cooler phanerozoic temperatures of 115 c and earlier laramide cooling between 85 and 60 ma our results indicate that age eu correlations in zircon he datasets can be applied to extract long term thermal histories that extend beyond the most recent cooling event in addition our results constrain the timing magnitude and rates of cooling experienced by archean wyoming province rocks between recognized deformation events including the 1 ga period represented by the regionally extensive great unconformity

flexural rigidity of the basin and range colorado plateau rocky mountain transition from coherence analysis of gravity and topography stochastic inversion for flexural loads and flexural rigidity of the continental elastic layer can be accomplished most effectively by using the coherence of gravity and topography however the spatial resolution of coherence analysis has been limited by use of two dimensional periodogram spectra from very large 105 km 2 windows that generally include multiple tectonic features using a two dimensional spectral estimator based on the maximum entropy method the spatial resolution of flexural properties can be enhanced by a factor of 4 or more enabling more detailed analysis at the scale of individual tectonic features this new approach is used to map the spatial variation of flexural rigidity along the basin and range transition to the colorado plateau and middle rocky mountains physiographic provinces large variations in flexural isostatic re sponse are found with rigidities ranging from as low as 8 7x102o n m elastic thickness t 4 6 km in the basin and range to as high as 4 1x1024 n m t 77 km in the middle rocky mountains these results compare favorably with independent determinations of flexural rigidity in the region areas of low flexural rigidity correlate strongly with areas of high surface heat flow as is expected from the contingence of flexural rigidity on a temperature dependent flow law also late cenozoic normal faults with large displacements are found primarily in areas of low flexural rigidity while deformation fronts of mesozoic tertiary overthrusts occur 0 to 100 km east of the low rigidity region the highest flexural rigidity is found within the archean wyoming craton where evidence suggests that deeply rooted cratonic lithosphere may play a role in deter mining the distribution of tectonism at the surface

mineralogical and spectroscopic investigation of enstatite chondrites by x ray diffraction and infrared reflectance spectroscopy 1 the mineralogy and infrared reflectance spectra of 13 enstatite e chondrite meteorite finds spanning the full range of textural alteration grades in both el and eh classes have been investigated rietveld refinement of high resolution powder x ray diffraction xrd data was used to determine quantitative major mineral abundances sample correlated mid infrared 2 0 to 25 0 m 4500 cm 1 to 400 cm 1 reflectance infrared spectra were collected for each meteorite spectral features due to the fundamental lattice vibrations of the silicates primarily enstatite dominate the spectra of these meteorites over most of the spectral range investigated the spectral features related to primary i e pre terrestrial mineralogy include fundamental stretching and bending lattice modes 8 3 25 0 m 1200 400 cm 1 overtones and combinations of the fundamental modes 4 5 6 1 m 2200 1650 cm 1 and the principle christensen feature 8 3 m 1200 cm 1 terrestrial weathering products including fe oxyhydroxides gypsum and carbonates occur in most of these meteorites and contribute to some spectral features particularly an asymmetric feature near 2 6 to 3 8 m 3800 to 2600 cm 1 attributed to adsorbed hydrogen bonded and or structural oh and h 2 o and a feature near 6 2 m 1625 cm 1 attributed to adsorbed hydrogen bonded and or structural h 2 o modal mineral abundances determined by rietveld refinement have been used to calculate model grain densities for each meteorite bulk magnetic susceptibility measurements combined with modal mineralogy and grain densities reveal a trend toward lower grain density and lower bulk susceptibility with increased terrestrial weathering

yamato 86029 aqueously altered and thermally metamorphosed ci like chondrite with unusual textures we describe the petrologic and trace element characteristics of the yamato 86029 y 86029 meteorite y 86029 is a breccia consisting of a variety of clasts and abundant secondary minerals including coarse and fine grained phyllosilicates fe ni sulfides carbonates and magnetite there are no chondrules but a few anhydrous olivine rich grains are present within a very fine grained phyllosilicate rich matrix analyses of 14 thermally mobile trace elements suggest that y 86029 experienced moderate open system thermal metamorphism comparison with data for other heated carbonaceous chondrites suggests metamorphic temperatures of 500 600 oc for y 86029 this is apparent petrographically in partial dehydration of phyllosilicates to incompletely re crystallized olivine this transformation appears to proceed through intermediate highly disordered poorly crystalline phases consisting of newly formed olivine and residual desiccated phyllosilicate and their mixtures periclase is also present as a possible heating product of mg rich carbonate precursors y 86029 shows unusual textures rarely encountered in carbonaceous chondrites the periclase occurs as unusually large fe rich clasts 300 500 m fine grained carbonates with uniform texture are also present as small 10 15 m in diameter rounded to sub rounded shells of ankerite siderite enclosing magnetite these carbonates appear to have formed by low temperature aqueous alteration at specific thermal decomposition temperatures consistent with thermodynamic models of carbonate formation the fine and uniform texture suggests crystallization from a fluid circulating in interconnected spaces throughout entire growth one isolated aggregate in y 86029 also consists of a mosaic of polycrystalline olivine aggregates and sulfide blebs typical of shock induced melt re crystallization except for these unusual textures the isotopic petrologic and chemical characteristics of y 86029 are quite similar to those of y 82162 the only other heated ci like chondrite known they were probably derived from similar asteroids rather than one asteroid and hence may not necessarily be paired

gravity interpretation of the southern wind river mountains wyoming the wind river range is the largest laramide uplift in wyoming and is cored by precambrian rocks thrust over sedimentary rocks of the green river basin to the southwest the origin of these uplifts is in dispute it has been ascribed to horizontal compression along thrusts or vertical movement along high angle reverse faults therefore the attitude of the bounding fault is critical to understanding the mechanics of deformation a gravity study based on 1800 stations has been carried out to attack this question and to complement a cocorp deep crustal reflection study smoothed free air gravity anomalies are highly positive over the wind river range and near zero over the adjacent margins bouguer gravity anomalies range from 252 and 225 mgal in the green river basin and wind river basin respectively to 150 mgal in the basement core of the wind river range the bulk density of sedimentary rocks in the adjacent basins is the critical parameter for gravity interpretation of the deep structure and ranges

a mutli technique search for the most primitive co chondrites as part of a study to identify the most primitive cos and to look for weakly altered cms amongst the cos we have conducted a multi technique study of 16 antarctic meteorites that had been classified as primitive cos for this study we have determined 1 the bulk h c and n abundances and isotopes 2 bulk o isotopic compositions 3 bulk modal mineralogies and 4 for some selected samples the abundances and compositions of their insoluble organic matter iom two of the 16 meteorites do appear to be cms buc 10943 seems to be a fairly typical cm while mil 090073 has probably been heated of the cos dom 08006 appears to be the most primitive co identified to date and is quite distinct from the other members of its pairing group the other cos fall into two groups that are less primitive than dom 08006 and alh 77307 the previously most primitive co the first group is composed of members of the dom 08004 pairing group except dom 08006 the second group is composed of meteorites belonging to the mil 03377 and mil 07099 pairing groups these two pairing groups should probably be combined there is a dichotomy in the bulk o isotopes between the primitive all antarctic finds and the more metamorphosed cos mostly falls this dichotomy can only partly be explained by the terrestrial weathering experienced by the primitive antarctic samples it seems that the more equilibrated samples interacted to a greater extent with 16o poor material probably water than the more primitive meteorites

u pb dating of calcite veins reveals complex stress evolution and thrust sequence in the bighorn basin wyoming usa reply we report u pb absolute ages of calcite cements from a diffuse vein network documented in the bighorn basin wyoming usa where distinct systematic vein sets developed at the front of the thin skinned sevier orogen during laramide layer parallel shortening and during thick skinned laramide thrusting and folding the u pb age distribution illustrates 1 an outward eastward transmission of sevier orogenic stress from 89 7 2 9 ma 2 in the west and from 75 3 2 8 ma in the east and 2 an inward westward development of laramide related fracturing and folding 72 3 0 ma and 45 4 1 8 ma respectively in the east 60 5 4 6 ma and 27 9 1 1 ma respectively in the west which is in accordance with the known sequence of exhumation of the major laramide basement arches our results also show that the stress related to laramide compression first overprinted the stress related to sevier compression in the sedimentary cover around major basement uplifts this study highlights the utility of u pb calcite geochronology as a powerful tool for constraining complex sequences of deformation in orogenic forelands

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

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

the origin of volatile element depletion in early solar system material clues from zn isotopes in chondrules abstract volatile lithophile elements are depleted in the different planetary materials to various degrees but the origin of these depletions is still debated stable isotopes of moderately volatile elements such as zn can be used to understand the origin of volatile element depletions samples with significant volatile element depletions including the moon and terrestrial tektites display heavy zn isotope compositions i e enrichment of 66zn vs 64zn consistent with kinetic zn isotope fractionation during evaporation however luck et al 2005 found a negative correlation between 66 zn and 1 zn between ci cm co and cv chondrites opposite to what would be expected if evaporation caused the zn abundance variations among chondrite groups we have analyzed the zn isotope composition of multiple samples of the major carbonaceous chondrite classes ci 1 cm 4 cv 2 co 4 cb 2 ch 2 ck 4 and ck cr 1 the bulk chondrites define a negative correlation in a plot of 66 zn vs 1 zn confirming earlier results that zn abundance variations among carbonaceous chondrites cannot be explained by evaporation exceptions are cb and ch chondrites which display zn systematics consistent with a collisional formation mechanism that created enrichment in heavy zn isotopes relative to the trend defined by ci ck we further report zn isotope analyses of chondrite components including chondrules from allende cv3 and mokoia cv3 as well as an aliquot of allende matrix all chondrules are enriched in light zn isotopes 500 ppm on 66zn 64zn relative to the bulk contrary to what would be expected if zn were depleted during evaporation on the other hand the matrix has a complementary heavy isotope composition we report sequential leaching experiments in un equilibrated ordinary chondrites which show sulfides are isotopically heavy compared to silicates and the bulk meteorite by ca 0 65 per mil on 66zn 64zn we suggest isotopically heavy sulfides were removed from either chondrules or their precursors thereby producing the light zn isotope enrichments in chondrules

carbonate compositions in cm and ci chondrites and implications for aqueous alteration abstract carbonate minerals in fourteen cm chondrites and two ci chondrites have been analyzed by electron microprobe to provide a better understanding of the aqueous processes that affected carbonaceous chondrite parent bodies calcites in cm chondrites and dolomites and magnesites in ci chondrites display the compositions expected of stable phases formed at low temperatures dolomites in cm chondrites identified here for the first time in five members of the group have small amounts of excess ca which may reflect metastable growth the distribution of fe between dolomite and coexisting serpentine differs in the two chondrite groups if the distributions reflect an approach to chemical equilibrium then the difference implies higher alteration temperatures for the ci group than the cm group in agreement with the results of previously published oxygen isotope thermometry and mineral solubility modeling of the alteration process dolomite fe contents are relatively uniform in the two chondrite groups dolomite mn contents by contrast vary widely the variations may reflect transport controlled coprecipitation of mn resulting from a heterogeneous distribution of the element in the anhydrous precursor material if this interpretation is correct then the altering fluids were essentially immobile while hydration reactions proceeded on the meteorite parent bodies the near closed system character of the alteration process long known from bulk chemical analyses of the meteorites is a direct consequence of the limited mobility of dissolved species

nature and degree of aqueous alteration in cm and ci carbonaceous chondrites we investigated the petrologic geochemical and spectral parameters that relate to the type and degree of aqueous alteration in nine cm chondrites and one ci ivuna carbonaceous chondrite our underlying hypothesis is that the position and shape of the 3 m band is diagnostic of phyllosilicate mineralogy we measured reflectance spectra of the chondrites under dry conditions elevated temperatures and vacuum 10 8 to 10 7 torr to minimize adsorbed water and mimic the space environment for subsequent comparison with reflectance spectra of asteroids we have identified three spectral cm groups in addition to ivuna group 1 the least altered group as determined from various alteration indices is characterized by 3 m band centers at longer wavelengths and is consistent with cronstedtite fe serpentine group 3 the most altered group is characterized by 3 m band centers at shorter wavelengths and is consistent with antigorite serpentine group 2 is an intermediate group between group 1 and 3 ivuna exhibits a unique spectrum that is distinct from the cm meteorites and is consistent with lizardite and chrysotile serpentine the petrologic and geochemical parameters which were determined using electron microprobe analyses and microscopic observations are found to be consistent with the three spectral groups these results indicate that the distinct parent body aqueous alteration environments experienced by these carbonaceous chondrites can be distinguished using reflectance spectroscopy high quality ground based telescopic observations of main belt asteroids can be expected to reveal not just whether an asteroid is hydrated but also details of the alteration state

the isotopic composition of volatiles in the unique bench crater carbonaceous chondrite impactor found in the apollo 12 regolith abstract projectiles striking the moon have modified its crust and delivered volatile elements to its interior and surface direct evidence of impactor origins is recorded by the rare occurrence of sub cm sized meteorite fragments identified in apollo samples and lunar meteorites the bench crater meteorite is a millimetre sized carbonaceous chondrite collected in regolith on the rim of bench impact crater at the apollo 12 landing site transmission electron microscopy has previously shown that bench crater contains abundant hydrated silicates establishing the survivability of hydrated material impacting the lunar surface to provide further information on the volatile inventory of the bench crater meteorite we report here the isotope compositions of hydrogen nitrogen carbon and oxygen this is the first direct isotopic analysis of meteoritic material delivered to the lunar surface and provides context for volatile and organic element signatures in lunar regolith samples and the survivability of volatile material delivered to planetary surfaces during impact bombardment the bench crater meteorite is characterised by d values ranging between 36 40 and 200 40 and bulk average 13 c of 13 30 and 15 n of 40 36 all uncertainties at the 2 confidence level the oxygen isotope compositions measured in situ in matrix silicates and magnetite in bench crater are consistent with those measured in matrix and magnetite in ci and cm chondrite falls altogether these new h c n and o isotope data coupled to mineralogical and geochemical observations suggest that bench crater may have been derived from an asteroidal parent body not represented in the terrestrial meteorite collection this is a crucial outcome in the current context of sample return missions to carbonaceous asteroids and more broadly for investigating the flux of material delivered to the earth moon system through time

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

analysis of ordinary chondrites using powder x ray diffraction 1 modal mineral abundances abstract powder x ray diffraction xrd is used to quantify the modal abundances in wt of 18 h 17 l and 13 ll unbrecciated ordinary chondrite falls which represents the complete petrologic range of equilibrated ordinary chondrites types 4 6 the xrd technique presents an effective alternative to traditional methods for determining modal abundances such as optical point counting and electron microprobe phase emp mapping the majority of chondrite powders in this study were previously prepared for chemical characterization from 8 to 20 g of material which is consistent with the suggested mass 10 g necessary to provide representative sampling of ordinary chondrites olivine and low ca pyroxene are the most abundant phases present comprising one half to three fourths of total abundances while plagioclase high ca pyroxene troilite and metal comprise the remaining xrd measured mineralogy pigeonite may also be present in some samples but it is fitted using a high ca pyroxene standard so exact abundances cannot be measured directly using xrd comparison of xrd measured abundances with calculated cross iddings pirsson washington cipw normative abundances indicates that systematic discrepancies exist between these two data sets particularly in olivine and high ca pyroxene this discrepancy is attributed to the absence of pigeonite as a possible phase in the cipw normative mineralogy oxides associated with pigeonite are improperly allocated resulting in overestimated normative olivine abundances and underestimated normative high ca pyroxene abundances this suggests that the cipw norm is poorly suited for determining mineralogical modal abundances of ordinary chondrites

matrix mineralogy of the orgueil ci carbonaceous chondrite a petrographic and transmission electron microscopic study of the orgueil ci carbonaceous chondrite shows that the matrix consists mainly of fe bearing mg rich serpentine and smectite saponite as well as a poorly crystallized fe rich material that contains minor variable s and ni the fe rich material is probably ferrihydrite a ferric hydroxide the ferrihydrite occurs in small particles 80 a in diameter and the s and ni are probably adsorbed on its surfaces the serpentine and saponite occur in poorly crystallized fine crystallites fine phyllosilicates that are intimately associated with the ferrihydrite coarsely crystallized phyllosilicates coarse phyllosilicates occur in clusters relatively free of ferrihydrite the ferrihydrite is a major matrix constitutent and probably accounts for most of the fe3 as well as the superparamagnetic fraction in the orgueil matrix the textures suggest that the fine phyllosilicates resulted from alteration of the coarse phyllosilicates the alteration probably involved a substantial amount of water and coincided with the period of sulfate vein formation during the aqueous alteration magnetite grains disaggregated from framboids and fe ni sulfides were replaced by ferrihydrite simultaneously aqueous solutions reacted with the coarse phyllosilicates and precipitated ferrihydrite producing intimate pervasive mixtures with the fine phyllosilicates the matrix mineralogy of the orgueil chondrite suggests that orgueil experienced considerably different alteration conditions from the cm chondrites the mineralogical and petrological differences between ci and cm chondrites can not simply be explained as the result of different degrees of aqueous alteration

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

a rapid model for estimating the depletion in river flows due to groundwater abstraction the environment agency of england and wales uses its calibrated regional models to estimate the reduction in river flows resulting from proposed groundwater abstractions where there is no regional model analytical equations can produce quick initial estimates of river flow depletion however users often want more confidence in their estimates by representing more faithfully their understanding of the real river aquifer system this paper shows that when using a numerical model designed to predict river flow depletion it is important to include adjacent catchments and intermittent streams and less important to include river elevations and variations in transmissivity with groundwater head recharge does not usually need to be included unless part of the river becomes disconnected or dry therefore for rivers where stream length is constant and transmissivity variations are small it is valid to use a no recharge depletion model which can be built quickly within a month a case study on the river leith in nw england illustrates the use of such a model to assess the ecological impact of two groundwater abstraction licences under the european union habitats directive

a numerical modelling and neural network approach to estimate the impact of groundwater abstractions on river flows summary evaluation of the impacts of groundwater abstractions on surface water systems is a necessary task in integrated water resources management a range of hydrological hydrogeological and geomorphological factors influence the complex processes of interaction between groundwater and rivers this paper presents an approach which uses numerical modeling of generic river aquifer systems to represent the interaction processes and neural networks to capture the impacts of the different controlling factors the generic models describe hydrogeological settings representing most river aquifer systems in england and wales high diffusivity e g chalk and low diffusivity e g triassic sandstone aquifers with flow to rivers mediated by alluvial gravels the same aquifers where they are in direct connection with the river and shallow alluvial aquifers which are disconnected from regional aquifers numerical model simulations using the shetran integrated catchment modeling system provided outputs including time series and spatial variations in river flow depletion and spatially distributed groundwater levels artificial neural network models were trained using input parameters describing the controlling factors and the outputs from the numerical model simulations providing an efficient tool for representing the impacts of groundwater abstractions across a wide range of conditions there are very few field data sets of accurately quantified river flow depletion as a result of groundwater abstraction under controlled conditions one such data set from an experimental study carried out in 1967 on the winterbourne stream in the lambourne catchment over a chalk aquifer was used successfully to test the modeling tool this modeling approach provides a general methodology for rapid simulations of complex hydrogeological systems which preserves the physical consistency between multiple and diverse model outputs

uplift unbuckling and collapse flexural history and isostasy of the wind river range and granite mountains wyoming two dimensional gravity and flexural models constrain the structure and isostatic compensation of the wind river range and granite mountains wyoming these ranges are asymmetric basement cored laramide uplifts their large positive isostatic gravity anomalies imply that the topography of the uplifts is not locally compensated for the wind river range gravity data are consistent with thrusting along a listric fault which flattens and soles out at 30 km depth with no detectable offset on the moho we model the large bouguer gravity high over the range with high density lower crustal rocks emplaced over lower density middle crustal rocks along the wind river thrust the high positive gravity anomaly over the granite mountains can be modeled as an extension of the south pass greenstone belt from the southern wind river range eastward beneath the emigrant trail thrust a crustal root as required in local airy compensation for either range requires unreasonably high density material in the upper crust to obtain the observed anomaly combined gravity and flexural models show that a flexural rigidity at least 2 55 1022 n m maximum deflection of 2 km of the moho is required to satisfy the gravity data our results are consistent with models of uplift due to horizontal compression and support of the resulting topography by lithospheric strength an otherwise puzzling episode of oligocene uplift of the wind river range can be explained as unbuckling decrease of deflection of lithosphere accompanying release of laramide compressional stresses flexurally supported uplifts will collapse if the lithosphere is weakened a number of laramide uplifts have collapsed primarily east west trending structures such as the granite mountains the southern end of the wind river range and the uinta mountains we propose that collapse has occurred along zones of established weakness in the crust in response to north south extension

seasonal variation in surface subsurface water exchange and lateral hyporheic area of two stream aquifer systems abstract we used two dimensional unconfined transient groundwater flow models to investigate the interface between stream and groundwater flow systems or hyporheic zone of two first order streams that drain catchments with distinctly different alluvial sediments and bedrock lithology particle tracking showed that lateral hyporheic area planimetric area of flow paths lateral to the stream that are recharged by and return to the stream with travel times of 10 days or less differed between the two study streams and varied with discharge within each system at the rio calaveras welded tuff lateral hyporheic area ranged from 1 7 to 4 m 2 over the annual cycle in the aspen creek system sandstone lateral hyporheic area 1 1 5 m 2 was restricted to roughly half of that observed at rio calaveras the size of the hyporheic zone lateral to the streams at both sites decreased by approximately 50 during high flows sensitivity analyses indicated that changes in the hydraulic conductivity of alluvial and streambed sediments and variation in recharge rates have greatest impact on the magnitude direction and spatial distribution of stream groundwater exchange

analyses of crustal structure from bandpass and directionally filtered potential field data an example from western canada application of bandpass and directional filtering to potential field data in northwestern canada allows separation of anomalies due to northwest oriented upper crustal sources that are associated w

carbonaceous chondrites as analogs for the composition and alteration of ceres the mineralogy and geochemistry of ceres as constrained by dawn s instruments are broadly consistent with a carbonaceous chondrite cm ci bulk composition differences explainable by ceres s more advanced alteration include the formation of mg rich serpentine and ammoniated clay a greater proportion of carbonate and lesser organic matter amounts of magnetite sulfide and carbon that could act as spectral darkening agents and partial fractionation of water ice and silicates in the interior and regolith ceres is not spectrally unique but is similar to a few other c class asteroids which may also have suffered extensive alteration all these bodies are among the largest carbonaceous chondrite asteroids and they orbit in the same part of the main belt thus the degree of alteration is apparently related to the size of the body although the ammonia now incorporated into clay likely condensed in the outer nebula we cannot presently determine whether ceres itself formed in the outer solar system and migrated inward or was assembled within the main belt along with other carbonaceous chondrite bodies

petrographic chemical and spectroscopic evidence for thermal metamorphism in carbonaceous chondrites i ci and cm chondrites abstract we present a comprehensive description of petrologic chemical and spectroscopic features of thermally metamorphosed ci like and cm and cm like chondrites only two such ci chondrites have so far been discovered i e y 86029 and y 82162 thermal metamorphism in these chondrites is apparent in their low contents of h2o c and the most thermally labile trace elements partial dehydration of matrix phyllosilicates and abundance of thermally decomposed ca mg fe mn carbonates which apparently resulted from heating of mg fe carbonate precursors the cm chondrites exhibit a wide range of aqueous and thermal alteration characteristics this alteration was almost complete in y 86720 and y 86789 which also escaped alternating episodes of oxidation and sulfidization experienced by the others thermal metamorphism in the cm chondrites is apparent in loss of thermally labile trace elements and also in partial to almost complete dehydration of matrix phyllosilicates heating was less uniform in them than in ci chondrites this dehydration is also evident in strength and shapes of integrated intensities of the 3 m bands except in pca 91008 which experienced extensive terrestrial weathering tochilinite is absent in all but y 793321 probably due to heating textural evidence for thermal metamorphism is conspicuous in blurring or integration fusion of chondrules with matrix in the more extensively heated 600 c cm chondrites like pca 91008 and b 7904 tem and xrd analyses reveal that phyllosilicate transformation to anhydrous phases proceeds via poorly crystalline highly desiccated and disordered intermediate phases in the least and moderately heated 400 600 c carbonaceous chondrites like wis 91600 pca 91008 and y 86029 these findings are significant in that they confirm that these phases occur in meteorites as well as terrestrial samples thermal alteration in these meteorites can be used to identify other carbonaceous chondrites that were thermally metamorphosed in their parent bodies combining rnaa trace element data for experimentally heated murchison cm2 samples with petrographic and spectroscopic data these thermally metamorphosed carbonaceous chondrites can be ordered by severity of open system heating as 400 c y 793321

mn cr ages of dolomites in ci chondrites and the tagish lake ungrouped carbonaceous chondrite abstract 53 mn 53 cr ages have been measured for dolomites in three ci chondrites and an ungrouped c2 chondrite tagish lake for an accurate age determination we utilized in contrast to previous works a matrix matched carbonate standard to appropriately correct the observed mn cr ratios the mn cr data of the dolomites most likely represent isochrons with chronological significances and the obtained ages are concentrated in 4563 8 4562 5 million years ago 4 4 5 7 million years after the birth of the solar system the ages of the ci and tagish lake dolomites are very similar to those of carbonates in cm chondrites although ci and cm chondrites are likely to have different alteration histories the similar carbonate ages in various carbonaceous chondrites suggest that the aqueous activities in hydrous asteroids initiated almost concurrently if this is the case the most plausible heat source for the aqueous alteration is the decay energy of short lived radionuclides especially 26 al we carried out a model calculation for the thermal history of the ci chondrite parent body assuming that 26 al is the dominant heat source by two different approaches to estimate the accretion time of the ci chondrite parent body we conclude that it accreted 3 0 3 9 million years after the birth of the solar system this is also likely to be the case for the cm chondrite and tagish lake parent bodies because the result of the calculation is not sensitive to the ice abundance therefore we stress that near the condensation front of water ice meteorite parent bodies with abundant ice accreted almost simultaneously at 3 4 million years after cai formation combining our mn cr ages of the dolomites with those of breunnerites reported previously the youngest one is 4554 6 million years ago we found that the aqueous alteration in the ci chondrite parent body lasted for at least 9 million years therefore the parent body should be large enough 50 km in radius so that the internal heat had been kept for 9 million years

mineralogy and petrography of c asteroid regolith the sutter s mill cm meteorite based upon our characterization of three separate stones by electron and x raybeam analyses computed x ray microtomography raman microspectrometry and visible ir spectrometry sutter s mill is a unique regolith breccia consisting mainly of various cmlithologies most samples resemble existing available cm2 chondrites consisting ofchondrules and calcium aluminum rich inclusion cai set within phyllosilicate dominatedmatrix mainly serpentine pyrrhotite pentlandite tochilinite and variable amounts of ca mg fe carbonates some lithologies have witnessed sufficient thermal metamorphism totransform phyllosilicates into fine grained olivine tochilinite into troilite and destroycarbonates one finely comminuted lithology contains xenolithic materials enstatite fe crphosphides suggesting impact of a reduced asteroid e or m class onto the main sutter smill parent asteroid which was probably a c class asteroid one can use sutter s mill tohelp predict what will be found on the surfaces of c class asteroids such as ceres and thetarget asteroids of the osiris rex and hayabusa 2 sample return missions which willvisit predominantly primitive asteroids c class asteroid regolith may well contain a mixtureof hydrated and thermally dehydrated indigenous materials as well as a significantadmixture of exogenous material would be essential to the successful interpretation ofmineralogical and bulk compositional data

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

evidence for a shallow highly permeable zone in the chalk of hampshire u k abstract studies of the chalk in the u k in the last 10 15 years have shown that it is generally the top 20 50 m below the water table which provides most of the aquifer yield an investigation in hampshire in connection with a river augmentation scheme using seasonal groundwater abstraction shows the chalk in the area to have a particularly thin and well developed 6 m thick zone possessing both high transmissivity and storativity evidence is put forward to support its existence

post laramide oligocene uplift in the wind river range wyoming in late oligocene time the crest of the wind river range was uplifted from an erosion surface that formed during laramide late cretaceous early eocene deformation this uplift created the highest peaks in the wyoming foreland and is indicated by rejuvenation of the range as a sediment source and by the physiography of the peaks differential movement of basement blocks in the core of the range is identified by apatite fission track data we distinguish this deformation from earlier laramide compression and neogene normal faulting and speculate that it occurred when precambrian shear zones were reactivated in response to local flexural stress in the laramide subsidence uplift couple

modal mineralogy of ci and ci like chondrites by x ray diffraction the ci chondrites are some of the most hydrated meteorites available to study making them ideal samples with which to investigate aqueous processes in the early solar system here we have used position sensitive detector x ray diffraction psd xrd to quantify the abundance of minerals in bulk samples of the ci chondrite falls alais orgueil and ivuna and the antarctic ci like chondrites y 82162 and y 980115 we find that alais orgueil and ivuna are dominated by a mixed serpentine saponite phyllosilicate 81 84 vol plus minor magnetite 6 10 sulphides 4 7 and carbonates 3 this reflects an extended period of aqueous alteration and the near complete transformation of anhydrous phases into a secondary mineral assemblage the similarity in total abundance of phyllosilicate suggests that the ci chondrites all experienced the same degree of aqueous alteration on the parent body in contrast y 82162 contains a highly disordered serpentine saponite phyllosilicate 68 vol sulphide 19 olivine 11 and magnetite 2 this mineralogy is distinct from that of the ci chondrites attesting to both a different starting mineralogy and alteration history the structure and relatively low abundance of the phyllosilicate and the high abundance of olivine are consistent with previous observations that y 82162 represents ci like material that following aqueous alteration suffered thermal metamorphism at temperatures 500 c similarly y 980115 contains disordered serpentine saponite 71 vol sulphide 19 olivine 8 and magnetite 2 confirming that it too is a thermally metamorphosed ci like chondrite we suggest that the ci like chondrites are derived from a different parent body than the ci chondrites which underwent short lived thermal metamorphism due to impacts and or solar radiation

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

a mossbauer spectroscopy and x ray diffraction study of ordinary chondrites quantification of modal mineralogy and implications for redox conditions during metamorphism we present a method that combines mssbauer spectroscopy and x ray diffraction to quantify the modal mineralogy of unequilibrated ordinary chondrites uocs despite being a fundamental tool in the interpretation of geological systems there are no modal mineralogical data available for these meteorites this is due to their fine grained nature highly heterogeneous silicate mineralogy and the presence of poorly characterized phases consequently it has not been possible to obtain accurate modal mineralogy by conventional techniques such as point counting here we use mssbauer spectroscopy as a preliminary identification technique and x ray diffraction provides the quantification for a suite of recent uoc falls we find the most primitive uocs to contain a significant amount of phyllosilicate material that was converted during metamorphism to form ferromagnesian silicates a complete suite of antarctic samples is analyzed by each method to observe mineralogical trends and these are compared with trends shown by recent falls the fact that mineralogical relationships shown by finds and falls are in agreement allows us to be confident that we are observing the products of pre terrestrial alteration mssbauer spectroscopy reveals evidence of steadily increasing reduction with metamorphism in the uocs because this technique allows comparisons to be made between uocs and eocs our reduction sequence can be combined with other evidence showing progressive oxidation in the eocs this yields an integrated model of changing redox conditions on equilibrating ordinary chondrite parent bodies

a terrestrial origin for sulfate veins in ci1 chondrites white sulfate veins are a very well known petrological feature of the chemically primitive ci1 carbonaceous chondrites sulfate veins were first described in the orgueil meteorite in 1961 almost one century after its fall however we have observed such veins to form easily during typical sample storage we suggest that all ci1 sulfate veins formed during the terrestrial residence of these heavily brecciated porous stones reacting with atmospheric water sulfates originally present in the meteorites dissolved and remobilized and or sulfides oxidised filling the many open spaces offered to them by the very porous rock sulfate veins in ci1 chondrites can no longer be used as evidence of a late stage oxidation event in the ci1 parent body or of centimeter scale fluid transport on the parent asteroid

brecciation and chemical heterogeneities of ci chondrites abstract fragments in the size range from 40 m to several hundred m in the ci chondrites orgueil ivuna alais and tonk show a wide range of chemical compositions with variations in major elements such as iron 10 4 42 4 wt feo silicon 12 7 42 2 wt sio 2 and sulfur 1 01 15 8 wt so 3 but also important minor elements such as phosphorous up to 5 2 wt p 2 o 5 or calcium up to 6 6 wt cao these variations are the result of the varying mineralogical compositions of these fragments the distribution of phyllosilicates magnetites and possibly ferrihydrite in particular control the abundances of these elements high ree contents up to 150 times the solar abundances were observed in phosphates while matrix and sulfates are ree depleted the studied 113 fragments were subdivided into eight lithologies with similar mineralogical and thus chemical properties the most common is the cga lithology consisting of a groundmass of mg rich coarse grained phyllosilicates and varying abundances of inclusions such as magnetite the second most abundant lithology is the fga lithology consisting of a groundmass of fine grained fe rich phyllosilicates a rare but important lithology consists of fragments with high contents of phosphates and other minerals the proposed model for the evolution of these lithologies is based on a closed system alteration where mineralogical differences in the lithologies reflect heterogeneities in the starting material comparison of our results with literature data indicates a general similarity of the four ci chondrites analyzed further comparison of bulk analyses suggests that the mass threshold for chemical heterogeneities in ci chondrite samples is smaller than 1 2 g

the parent body controls on cosmic spherule texture evidence from the oxygen isotopic compositions of large micrometeorites high precision oxygen isotopic compositions of eighteen large cosmic spherules 500 mu m diameter from the atacama desert chile were determined using ir laser fluorination isotope ratio mass spectrometry the four discrete isotopic groups defined in a previous study on cosmic spherules from the transantarctic mountains suavet et al 2010 were identified confirming their global distribution approximately 50 of the studied cosmic spherules are related to carbonaceous chondrites 38 to ordinary chondrites and 12 to unknown parent bodies approximately 90 of barred olivine bo cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites similarly similar to 90 porphyritic olivine po cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites other textures are related to all potential parent bodies the data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters we propose that the po texture may essentially be formed from a coarse grained precursor having an ordinary chondritic mineralogy and chemistry coarse grained precursors related to carbonaceous chondrites i e chondrules are likely to either survive atmospheric entry heating or form v type cosmic spherules due to the limited number of submicron nucleation sites after total melting ordinary chondrite related coarse grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline cc textures instead of bo textures conversely the bo textures would be mostly related to the fine grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases allowing the preservation of submicron nucleation sites independently of the nature of the precursors increasing peak temperatures form glassy textures

modeling early titan s ocean composition abstract we model the stability fields of minerals in contact with an interior water ammonia ocean on titan using constraints on the ammonia abundance from titan s orbital state and updated kinetic data we show that earlier pre cassini work by engel et al 1994 was qualitatively but not quantitatively correct we calculate a salinity of the ocean of 1 consistent with the ocean density derived from cassini data on titan s tidal response and within the range found for enceladus ocean we also consider the sources and sinks of the observed 40ar in the atmosphere and conclude that what is observed is only a small fraction of what might be dissolved in the ocean or trapped in clathrate in the crust thus the efficiency of degassing from the core must be much higher than in previous estimates e g mckinnon 2010 to account for what is observed in the atmosphere one self consistent model is that of a partially hydrated core from which much of the potassium has been leached into the ocean as suggested by the thermal model of castillo rogez and lunine 2010 our picture of present day titan is that of a slightly salty ocean about 1 salinity atop an actively heated and hydrated rock core

modal mineralogy of carbonaceous chondrites by x ray diffraction and mossbauer spectroscopy carbonaceous chondrites are among the most analyzed geological materials on earth however despite this attention and unlike most terrestrial rocks little is known on the abundance of individual phases within them here we show how a combination of several novel x ray diffraction xrd techniques including a high brightness x ray microsource and mssbauer spectroscopy allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated fine grained chondrites for all minerals of abundance 1 wt knowledge of the modal mineralogy of a sample also allows us to calculate grain density we analyzed allende murchison tagish lake and orgueil based on our modal data the grain density estimates for allende murchison and orgueil are close to literature values in the case of tagish lake there is no published grain density although a bulk density measurement does exist taking our estimate of grain density and the measured bulk density we calculate an exceptionally high porosity of 41 for this meteorite similar to some chondritic idps and in line with a porosity calculated from an entry model for the tagish lake fireball although it is an oxidized cv magnetite is present in allende at a level of 0 5 wt or 0 3 vol a result that is substantiated by several other instrumental studies this may be an oxidized meteorite but that oxidation is not manifested in abundant magnetite in addition we note appreciable fayalitic olivine in orgueil detected by both xrd and mossbauer we employed microsource xrd to look at heterogeneity in mineral abundance in orgueil and found substantial variation with phyllosilicates varying inversely with olivine the data suggest that orgueil was initially composed primarily of anhydrous materials which have been partially but not completely altered although the data are preliminary comparison between our xrd modal assessment bulk chemistry grain density and mossbauer data suggests that our estimates of mineral abundance are robust the advent of microsource xrd allows similar modal data to be acquired from samples as small as a few hundred micrograms

carbonates in ci chondrites clues to parent body evolution all ci chondrites are regolith breccias consisting of various types of chemically and mineralogically distinct mineral and lithic fragments or units in the ci chondrite ivuna for example four different lithological units were identified and are referred to as lithology i ii iii and iv so far lithologies iii and iv have been identified in orgueil as well it appears that at least ivuna and orgueil consist of the same basic lithologies in different proportions carbonates in cis occur as individual grains within such lithic units or exist as large fragments between them carbonate fragments are remnants of former carbonate veins and in contrast to individual carbonate grains are not genetically linked to lithological units four different types of carbonates dolomite breunnerite calcite siderite occur in cis and they constitute on average 5 vol of each studied section in this study carbonates in the ci chondrites orgueil ivuna alais and tonk were studied petrographically mineralologically and chemically the results clearly indicate that in contrast to most previous studies compositional differences exist between dolomites within and among ci chondrites from these differences it can be derived that 1 several episodes of alteration occurred on the ci parent body 2 physicochemical conditions during carbonate formation must have been different among cis and 3 ci carbonates obviously were formed at low temperatures in equilibrium with surrounding fluid s while local compositional changes in fluid s on a micrometer to millimeter scale as reflected by dolomite compositions within ci chondrites were most likely controlled by the availability of ca2 mg2 fe2 and especially mn2 ions in the aqueous solutions more widespread compositional changes on a meter or even larger scale were controlled by variable ph eh co2 partial pressure and especially temperature conditions as reflected by the compositional variability of dolomites among cis

magnetite in comet wild 2 evidence for parent body aqueous alteration the mineralogy of comet 81p wild 2 particles collected in aerogel by the stardust mission has been determined using synchrotron fe k x ray absorption spectroscopy with in situ transmission xrd and x ray fluorescence plus complementary microraman analyses our investigation focuses on the terminal grains of eight stardust tracks c2112 4 170 0 0 c2045 2 176 0 0 c2045 3 177 0 0 c2045 4 178 0 0 c2065 4 187 0 0 c2098 4 188 0 0 c2119 4 189 0 0 and c2119 5 190 0 0 three terminal grains have been identified as near pure magnetite fe3o4 the presence of magnetite shows affinities between the wild 2 mineral assemblage and carbonaceous chondrites and probably resulted from hydrothermal alteration of the coexisting feni and ferromagnesian silicates in the cometary parent body in order to further explore this hypothesis powdered material from a cr2 meteorite nwa 10256 was shot into the aerogel at 6 1 km s 1 using a light gas gun and keystones were then prepared in the same way as the stardust keystones using similar analysis techniques to the eight stardust tracks a cr2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel

hydraulic properties of a major alluvial aquifer an isotropic inhomogeneous system abstract field observations pump test analyses and three dimensional digital simulations of a portion of the missouri river valley floodplain provided insights about the hydraulic properties of this alluvial aquifer three distinct facies can be recognized in the alluvial sediments a lower cobble facies a middle gravel sand facies and an upper sand silt clay facies type curve solutions and two dimensional finite difference models must be used with caution for such strongly inhomogeneous aquifers three dimensional digital model analyses suggest the alluvium is best simulated as an isotropic but inhomogeneous system ratios of vertical to horizontal hydraulic conductivity obtained from analyses such as delayed yield theory are created by aquifer inhomogeneity and not anisotropy per se empirical power relations showing an increase of hydraulic conductivity with depth provide valid estimates in the absence of field data however these relations do not hold for the beds and banks of the major rivers or their tributaries finally riverstage and observation well data show that groundwater levels are controlled primarily by river stage fluctuations and pumping recharge from precipitation seepage into and out of smaller streams and probably bedrock recharge are all minor influences