origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

long term final void salinity prediction for a post mining landscape in the hunter valley new south wales australia opencast mining alters surface and subsurface hydrology of a landscape both during and post mining at mine closure following opencast mining in mines with low overburden to coal ratios a void is left in the final landform this final void is the location of the active mine pit at closure voids are generally not infilled within the mines lifetime because of the prohibitive cost of earthwork operations and they become post mining water bodies or pit lakes water quality is a significant issue for pit lakes groundwater within coal seams and associated rocks can be saline depending on the nature of the strata and groundwater circulation patterns this groundwater may be preferentially drawn to and collected in the final void surface runoff to the void will not only collect salts from rainfall and atmospheric fallout but also from the ground surface and the weathering of fresh rock as the void water level rises its evaporative surface area increases concentrating salts that are held in solution this paper presents a study of the long term water quality trends in a post mining final void in the hunter valley new south wales australia this process is complex and occurs long term and modelling offers the only method of evaluating water quality using available geochemical climate and hydrogeological data as inputs into a mass balance model water quality in the final void was found to increase rapidly in salinity through time 2452 to 8909 mg l 1 over 500 years as evaporation concentrates the salt in the void and regional groundwater containing high loads of salt continues to flow into the void copyright 2004 john wiley sons ltd

temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the cm chondrites aqueous alteration of primitive meteorites was among the earliest geological processes during the evolution of our solar system clumped isotope thermometry of carbonates in the cm chondrites cold bokkeveld murray and murchison demonstrates that they underwent aqueous alteration at 20 71 c from a fluid with 18 o vsmow of 2 0 to 8 1 and 17 o vsmow of 0 1 to 3 0 the 13 c vpdb values of these carbonates exhibit a negative correlation with the 18 o vsmow of their formation waters consistent with formation and escape of 13 c depleted ch 4 during aqueous alteration methane generation under these conditions implies that the alteration fluid was characterized by an eh 0 67 and ph 12 5 or lower at the highest alteration temperatures our findings suggest that methane generation may have been a widespread consequence of planetesimal and planetary aqueous alteration perhaps explaining the occurrence of methane on titan triton pluto and other kuiper belt objects

non nebular origin of dark mantles around chondrules and inclusions in cm chondrites abstract our examination of nine cm chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in cm chondrites are not discrete fine grained rims acquired in the solar nebula as modeled by metzler et al accretionary dust mantles in cm chondrites evidence for solar nebula processes geochim cosmochim acta 56 1992 2873 2897 nebular processes that lead to agglomeration produce materials with porosities far higher than those in the dark mantles we infer that the mantles were produced from porous nebular materials on the cm parent asteroid by impact compaction a process that produces the lowest porosity adjacent to chondrules and inclusions compaction was followed by aqueous alteration that formed tochilinite serpentine ni bearing sulfide and other secondary products in voids in the interchondrule regions metzler et al reported a correlation between mantle thickness and the radius of the enclosed object in yamato 791198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation r2 0 44 if we limit consideration to central objects with radii 35 m a moderate correlation is also found in que 97990 we suggest that impact induced shear of a plum pudding like precursor produced the observed mantles these were shielded from comminution during impact events by the adjacent stronger chondrules and inclusions some mantles in cm chondrites with low degrees of alteration show distinct layers that may largely reflect differences in porosity typically a gray uniform inner layer is surrounded by an outer layer consisting of darker silicates with bse bright speckles the cm chondrite objects characterized as primary accretionary rocks by metzler et al did not form in the nebula but rather on the parent body the absence of solar flare particle tracks and solar wind implanted rare gases in these clasts reflect their lithified nature and low surface volume ratios during the period when they resided in the regolith and were subject to irradiation by solar particles the clasts are analogous to the light colored metamorphosed clasts in ordinary chondrite regolith breccias which also lack solar flare particle tracks and solar wind gas

mineralogy and petrology of chondrules and inclusions in the mokoia cv3 chondrite all objects 100 m in apparent diameter in five polished thin sections of the mokoia cv3 chondrite were studied and classified number and volume percentages and mean apparent size of each type of chondrule and inclusion were determined three major types of olivine chondrules were observed igneous chondrules recrystallized chondrules and chondrules that appear to be accretional aggregates coarse grained cai s have igneous textures and mineral parageneses while fine grained cai s are aggregates containing varying proportions of al rich concentric objects ca rich chaotic material and inclusion matrix chondrules and refractory inclusions in mokoia and allende are broadly similar in texture and mineral chemistry but mokoia refractory inclusions contain phyllosilicates rather than feldspathoids and melilite rich cai s are more abundant in allende we think that most cai s formed during the metamorphism partial melting and incomplete distillation of primitive dust aggregates when they were heated in the solar nebula in the process ca rich melt appears to have been physically separated from al rich residues producing the observed fractionation of ca from al into distinct constituents of cai s some cai s may be aggregates of devitrified amorphous metastable condensates inclusion matrix may have condensed from silicate rich vapors produced during distillation mokoia inclusion matrix contains phyllosilicates that are probably primitive nebular material

phyllosilicates in the mokoia cv carbonaceous chondrite evidence for aqueous alteration in an oxidizing environment abstract most cv chondrites contain little if any phyllosilicate mineralization a petrographic and transmission electron microscopy study of the mokoia cv carbonaceous chondrite shows that the matrix chondrules aggregates and inclusions all contain considerable amounts of phyllosilicates those in the matrix are mostly fe bearing saponite while those in chondrules aggregates and inclusions are both febearing saponite and na rich phlogopite serpentine occurs as minor coherent intergrowths within the phlogopite the saponite resulted from aqueous alteration of fe rich olivine and the phlogopite resulted from alteration of ca rich clinopyroxene anorthite spinel and ca al si rich glass iron rich olivines in the mokoia matrix contain extremely thin planar zones parallel to 100 with diffuse streaks along a in their diffraction patterns such planar zones are not known from terrestrial olivines saponite forms preferentially along these zones with its 001 planes roughly parallel to olivine 100 the planar zones probably consist of precipitates of fe oxide or fe hydroxide that were produced during oxidation of olivine while it cooled from a high temperature by formation of the fe rich precipitates olivine became fe deficient and thus was structurally disturbed during subsequent hydration saponite formed by preferentially replacing these regions in olivine simultaneously part of the fe was mobilized and precipitated as magnetite along the olivine peripheries the mineralogy and occurrence of phyllosilicates in mokoia differ from those in the ci and cm chondrites the differences suggest that aqueous alteration of the three meteorite groups probably occurred under a variety of conditions

three dimensional kinematic and microphysical evolution of florida cumulonimbus part i spatial distribution of updrafts downdrafts and precipitation abstract this paper is the first in a three part study that examines the kinematic and microphysical evolution of florida cumulonimbus and focuses on the convective to stratiform transition of the storm this first paper lays the groundwork for the subsequent papers by defining the problem under study delineating the setting for the storm and describing the spatial distribution of updrafts downdrafts and precipitation high resolution radar data of a typical line of storms associated with the florida sea breeze is the centerpiece of this study the high resolution data reveal details of the internal structure of the squall line that were beyond the resolution of previous squall line studies radar reflectivity filled in between cells at upper levels as the storm evolved reflectivity values were only weakly associated with updraft and downdraft magnitude the updrafts and downdrafts in the storm tended to be irregular in their three dimensional shape and less than 5 km in horizontal extent at any giv

modeling aqueous alteration of cm carbonaceous chondrites results from an inorganic geochemical modeling study support a scenario in which low temperature aqueous alteration of an anhydrous cm asteroidal parent body and melt water from h20 and co ices produces the altered assemblage observed in cm carbonaceous chondrites chrysotile greenalite tochilinite cronstedtite and minor calcite and magnetite we consider a range of possible precursor mineral assemblages varying with respect to the fe oxidation state of the initial anhydrous phases the aqueous solutions produced by this alteration are generally strongly basic and reducing and a large quantity of h2 and possible ch4 gas can be released during aqueous alteration

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

arcuate band texture in a dark inclusion from the vigarano cv3 chondrite possible evidence for early sedimentary processes a dark inclusion in the vigarano cv3 carbonaceous chondrite consists almost exclusively of small 5 pm in diameter grains of fe rich olivine and is devoid of chondrules ca al rich inclusions cais and their pseudomorphs in backscattered electron images this dark inclusion shows an unusual texture com prising a network of arcuate bands two or more bands occur roughly parallel forming a set of succesive parallel bands some crosscutting one another the bands contain slightly higher amounts of relatively small 1 pm olivine grains and so are more densely packed than other areas the olivine grains in the bands are slightly more fe rich than those in other areas the bands commonly show gradation on the concave side due to a decrease in the abundance of the small fe rich olivine grains texturally the arcuate bands closely resemble dish structures that are commonly observed in siltstones and sandstones on earth dish structures are characterized by thin dark colored subhorizontal to concave upward laminations that are rich in relatively fine grained material on earth dish structures form during compaction and dewatering of unconsolidated fine grained sediments they are one of the characteristic sedimentary structures formed through fluidization of fine grains the dark inclusion in vigarano therefore provides the first evidence that sedimentary pro cesses due to water migration may have taken place within planetesimals and further suggests that fluidiza tion may have played a significant role in the formation of the carbonaceous chondrites

numerical simulations initialized with radar derived winds pail ii forecasts of three gust front cases abstract numerical simulations of three gust front cases that occurred in northeastern colorado during the summers of 1991 and 1992 am presented the simulations are initialized with radar derived winds and for the two cases in 1992 measurements from a surface mesonet thermodynamic retrieval is used to calculate the buoyancy in the boundary layer the sensitivity of the retrieved buoyancy to the various constraints of real data was examined in part i of this study in the first case a large scale gust front moved southward over the denver region at a speed of 8 9 m s 1 the retrieved buoyancy field for this case exhibits a broad baroclinic zone with a width of approximately 20 km centered about the radar detected fine line this baroclinic zone collapses to a width of about 5 km as the numerical model is integrated forward the simulated gust front propagates at 7 m s 1 which is slightly less than the observed speed for the second and third cases data from a 50 station surface mesonet were also av

nepheline and sodalite in the matrix of the ningqiang carbonaceous chondrite implications for formation through parent body processes abstract ningqiang is an ungrouped carbonaceous chondrite that chemically and petrologically resembles cv3 chondrites the matrix of ningqiang shows much higher abundances of na k and al by factors of 4 4 2 7 and 1 6 respectively than in cv3 chondrites our scanning and transmission electron microscope observations and synchrotron radiation x ray diffraction measurements reveal that the major proportions of these elements can be attributed to the presence of nepheline and sodalite rietveld refinement of x ray diffraction data shows that the feldspathoids constitute 7 7 vol of all crystalline phases in the matrix nepheline and sodalite occur mostly as discrete equidimensional grains 2 5 m in diameter that are dispersed homogeneously in the matrix most of the grains contain inclusions of fe rich olivine and minor ca pyroxene magnetite troilite and pentlandite despite the high abundances of na k and al in the matrix of ningqiang the bulk meteorite abundances of these elements are comparable to those of the cv group e g rubin et al 1988 this means that the chondrules which constitute a major proportion of the volume other than the matrix in ningqiang are depleted in na k and al in fact our analyses and observations show that the chondrules in ningqiang overall contain very small amounts of these elements our interpretation of these findings suggests that nepheline and sodalite in the ningqiang matrix were originally formed by na metasomatism of the chondrules and ca al rich inclusions in the meteorite parent body afterward they were likely disaggregated and scattered into the matrix however it is difficult to envisage that the disaggregation and scattering occurred in situ in the present setting of the meteorite hence we suggest that the ningqiang meteorite underwent these processes before final lithification

olivine rich rims surrounding chondrules in the mokoia cv3 carbonaceous chondrite further evidence for parent body processes abstract fine grained rims surrounding chondrules and inclusions in the mokoia cv3 carbonaceous chondrite can be divided into phyllosilicate rich and olivine rich types we present a petrographic and electron microscopic study of the olivine rich rims and their host objects referred to as chondrules olivine rich rims the olivine rich rims consist mainly of fe rich olivine and very minor phyllosilicate saponite their host chondrules contain minor saponite and phlogopite which resulted from aqueous alteration of anhydrous silicates mineralogical and compositional characteristics of the chondrules olivine rich rims suggest that they experienced mild thermal metamorphic effects the rims commonly contain veins of coarse grained fe rich olivine magnetite and fe ni sulfides the chondrules show abundant evidence of alteration along their peripheries and the alteration textures suggest a mechanism for rim formation by replacement of the chondrules initially enstatite and opaque nodules preferentially reacted to form coarse platy fe rich olivine crystals which were subsequently divided into finer grains forsterite was also replaced by fe rich olivine as the alteration advanced these fe rich olivines were disaggregated mixed with simultaneously produced saponite and formed rims in contrast the surrounding matrix shows no evidence of such alteration and metamorphism these observations indicate that the chondrules olivine rich rims did not experience these secondary processes in their present setting the results suggest that the chondrules olivine rich rims experienced extensive replacement reactions in an environment in which aqueous fluids existed but only in minor amounts they have probably also undergone simultaneous and or subsequent mild thermal metamorphism we suggest that the chondrules olivine rich rims are actually clasts transported from a relatively dry region in the parent body that was different from the region where mokoia was finally lithified

a clast of bali like oxidized cv material in the reduced cv chondrite breccia vigarano the cv vigarano type chondrites are a petrologically diverse group of meteorites that are divided into the reduced and the ball like and allende like oxidized subgroups largely based on secondary mineralogy weisberg et al 1997 krot et al 1998b some chondrules and calcium aluminum rich inclusions cais in the reduced cv chondrite vigarano show alteration features similar to those in allende metal is oxidized to magnetite low ca pyroxene forsterite and magnetite are rimmed and veined by ferrous olivine fs 40 50 and plagioclase mesostases and melilite are replaced by nepheline and sodalite sylvester et al 1993 kimura and ikeda 1996 1997 1998

application of the zhang gal chen single doppler velocity retrieval to a deep convective storm the zhang gal chen single doppler velocity retrieval sdvr technique is applied to a multicell storm observed by three radars near the orlando florida airport on 9 august 1991 this dataset is unique in that 3min volume scans at very high spatial resolution 200 m are available during a 24 min period the retrieved unobserved wind determined using only the radial wind and reflectivity from one of the radars is compared to the observed winds obtained from a hybrid three dimensional wind synthesis error statistics demonstrate that the retrievals perform best when applied in a reference frame moving with the storm however the results also show that the specification of this frame is problematic the findings also indicate that in an environment where the mean flow has a critical layer the moving reference frame is best defined as a function of height rather than a volume mean the benefit of such a reference frame is case dependent and is best realized in regions such as a surface cold pool or upper level divergence at storm top error statistics demonstrate that the sdvr technique recovers the horizontal wind with greater accuracy than it does the vertical velocity suggesting that for deep convection the absence of dynamical constraints is critical the kinematic and o brien techniques and a new variational technique in which the solution to a second order ordinary differential equation for the vertical velocity is expressed in terms of bessel functions are tested as possible alternatives to the sdvr vertical velocity results indicate that this new technique yields vertical velocities significantly better than those using the other three methods

regolith migration and sorting on asteroid itokawa high resolution images of the surface of asteroid itokawa from the hayabusa mission reveal it to be covered with unconsolidated millimeter sized and larger gravels locations and morphologic characteristics of this gravel indicate that itokawa has experienced considerable vibrations which have triggered global scale granular processes in its dry vacuum microgravity environment these processes likely include granular convection landslide like granular migrations and particle sorting resulting in the segregation of the fine gravels into areas of potential lows granular processes become major resurfacing processes because of itokawa s small size implying that they can occur on other small asteroids should those have regolith

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

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

fayalite in the vigarano cv3 carbonaceous chondrite occurrences formation age and conditions abstract we have performed petrographic characterization 53mn 53cr age determination and thermodynamic stability evaluations of fayalite in vigarano meteorite that belongs to the reduced subgroup of cv3 chondrites vigarano is a breccia consisting of clasts which are separate chondrules surrounded by olivine rich fine grained materials four out of twenty three explored clasts contain fayalites that represent materials of the bali like oxidized subgroup of cv3 chondrites the fayalites fa 80 with grain sizes typically

dynamic adjustment in a numerically simulated mesoscale convective system impact of the velocity field abstract an identical twin methodology is applied to a three dimensional cloud model to study the dynamics of adjustment in deep convective storms the principal goal is to diagnose how mass and velocity fields mutually adjust in order to better understand the relative information content value of observations the physical interdependency among variables and to help in the design of dynamically consistent analyses to ensure smooth startup of numerical prediction models using a control simulation truth or nature run of an idealized long lived bow echo convective system a series of adjustment experiments is created by resetting in various combinations the horizontal and vertical velocity components of the control run to their undisturbed base state values during the mature stage of storm system evolution the integrations then are continued for comparison against the control this strategy represents a methodology for studying transient response to an impulsive perturbation in a manner concept

phyllosilicate rich chondrule rims in the vigarano cv3 chondrite evidence for parent body processes abstract a petrographic and scanning electron microscopic study of the vigarano cv3 carbonaceous chondrite reveals that a small proportion 5 of the fine grained rims surrounding chondrules consist mainly of phyllosilicates saponite and serpentine and minor but variable amounts of ferrihydrite most of the rims consist mainly of fe rich olivine the phyllosilicate rich rims and the chondrules that they enclose show abundant evidence of aqueous alteration low ca pyroxene and olivine at chondrule margins have been partially replaced by phyllosilicate rich materials producing embayments on chondrule surfaces fe ni metal fe sulfide and magnetite in the chondrules have also been partially replaced by fe hydroxide due to preferential replacement of low ca pyroxene and olivine sulfide magnetite and fe hydroxide remain exposed at chondrule margins we discovered a clast 0 7 0 9 mm in size containing several chondrules embedded in a phyllosilicate rich matrix that is almost identical in mineralogy texture and composition to the rims we also found numerous small clasts 20 400 m in size consisting of a similar phyllosilicate rich material in the host vigarano meteorite many of the clasts include fragments of chondrules amoeboid olivine aggregates and ca al rich inclusions these clasts also show abundant evidence of aqueous alteration which is similar to that observed in the rims and their host chondrules from these observations we conclude that the chondrule rim assemblages and the clasts are a part of the same precursor chondrite which was fragmented during brecciation on the meteorite parent body we interpret that a portion or portions of the vigarano parent body was aqueously altered and the interchondrule matrix was largely converted to phyllosilicates and ferrihydrite this hydrated portion was later fragmented and brecciated by impacts as fragmentation occurred preferentially along the phyllosilicate rich porous matrix most of the ejected clasts consisted of a chondrule rimmed by remnant matrix the clasts were rounded by abrasion during brecciation and transportation and finally mixed into an anhydrous portion in the regolith from which the vigarano meteorite was derived some of the phyllosilicate rich rims show evidence for partial dehydration during heating before final incorporation into the regolith these results taken together suggest that the vigarano parent body was spatially heterogeneous in degree of aqueous alteration and thermal metamorphism and the host vigarano meteorite is a breccia consisting of numerous clasts from many different locations

fluid flow and chemical alteration in carbonaceous chondrite parent bodies abstract carbonaceous chondrites are a class of primitive meteorites that likely represent early solar system materials thus providing critical insights about planetary evolution however evidence shows that they have undergone considerable processing elucidating the complex formation history of aqueously altered chondrite groups has been a principal objective of cosmochemistry fulfilling this objective requires understanding the nature of the water rock interactions involved many current alteration models are generally founded upon an assumption of uniform alteration in a closed system in these models different chondrite groups must originate on separate parent bodies contrary to this common view we show that chondrite data are consistent with non uniform alteration in a convecting system so that multiple chondrite groups can form within a single body

extended chronologies of aqueous alteration in the cm2 carbonaceous chondrites evidence from carbonates in queen alexandra range 93005 abstract the antarctic cm2 carbonaceous chondrite que 93005 contains four compositionally distinct carbonates namely breunnerite calcite dolomite and a ca poor dolomite these carbonates can form monomineralic grains or may be intergrown as bimineralic grains consisting of dolomite plus breunnerite and dolomite plus calcite or polymineralic grains containing an intergrowth of breunnerite ca poor dolomite and calcite carbonates in all grain types have inclusions of fe ni sulphides and or mg fe phyllosilicates in the bimineralic grains dolomite crystallised first to be overgrown by breunnerite or partially replaced by calcite polymineralic grains are concentrically layered with breunnerite crystallising first on pore margins to be later etched then overgrown and partially replaced by ca poor dolomite that was itself partly dissolved prior to being overgrown by calcite calcite and dolomite have also cemented fractures that cross cut the fine grained rims to aqueously altered chondrules and were formed by expansion of the chondrules during their hydration overall the sequence of mineralisation in que 93005 was 1 dolomite 2 breunnerite 3 ca poor dolomite then 4 calcite this secular change in carbonate composition and mineralogy reflects changing solution composition and probably also provenance mg fe phyllosilicates replaced dolomite breunnerite and ca poor dolomite prior to calcite crystallisation and most or all of the sulphides formed after both the phyllosilicates and calcite following sulphide crystallisation the edges of carbonate grains were abraded either by impact gardening or as a consequence of fluidisation of the matrix during rapid loss of gas or vapour determination of the crystallisation age of dolomite via the mn cr system indicates that aqueous alteration of que 93005 began on or before 3 93 0 23 ma after the formation of the oldest solar system solids overall the water rock ratio and fo2 during alteration of que 93005 was similar to that of the cm1s and cr1s but the lower degree of alteration of que 93005 overall suggests that alteration timescales were shorter possibly due to loss of intergranular liquid water during fluidisation

storm motion estimates derived from dynamic retrieval calculations abstract description is given of a technique for determining optimal storm reference frame motion based upon application of a dynamic retrieval method to velocity datasets derived from multiple doppler radar observations the method depends upon the necessary consistency between the steady state assumption and assumed reference frame storm motion and uses the quantity e from dynamic retrieval calculations as a measure by which to judge when this consistency is best achieved application of the technique is demonstrated in case examples including an oklahoma squall line a montana hailstorm and an oklahoma tornadic storm in the squall line case the question of the dependence of optimal reference frame motion upon analysis domain e g convective versus stratiform regions of the system is explored similar optimal frame motions for different regions of the system are found optimal frame motion corresponds more closely to cell motion than to line motion in the montana case the dependence upon anal

why aqueous alteration in asteroids was isochemical high porosity high permeability carbonaceous chondrite meteorites are the most compositionally primitive rocks in the solar system but the most chemically pristine ci1 and cm2 chondrites have experienced pervasive aqueous alteration apparently within asteroid parent bodies unfractionated soluble elements suggest very limited flow of liquid water indicting a closed system at scales large than 100 s m consistent with data from oxygen isotopes and meteorite petrography however numerical studies persistently predict large scale 10 s km water transport in model asteroids either in convecting cells or via exhalation flow an open system at scales up to 10 s km these models have tended to use permeabilites in the range 10 13 to 10 11 m2 we show that the permeability of plausible chondritic starting materials lies in the range 10 19 to 10 17 m2 0 1 10 d around six orders of magnitude lower than previously assumed this low permeability is largely a result of the extreme fine grain size of primitive chondritic materials applying these permeability estimates in numerical models we predict very limited liquid water flow distances of 100 s m at most even in a high porosity water saturated asteroid with a high thermal gradient over millions of years isochemical alteration with flow over minimal lengthscales is not a special circumstance it is inevitable once we consider the fundamental material properties of these rocks to achieve large scale flow it would require average matrix grain sizes in primitive materials of 10 s 100 s m orders of magnitude larger than observed finally in addition to reconciling numerical modelling with meteorite data our work explains several other features of these enigmatic rocks most particularly why the most chemically primitive meteorites are also the most altered

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

indicators of parent body processes hydrated chondrules and fine grained rims in the mokoia cv3 carbonaceous chondrite abstract a petrographic and electron microscopic study of the mokoia cv3 carbonaceous chondrite shows that all of the chondrules and inclusions 400 m in diameter and most of their fine grained rims studied referred to as chondrules rims contain various amounts of hydrous phyllosilicates mostly saponite formed by aqueous alteration of anhydrous silicates the rims mainly consist of fine grained olivine and saponite in varying proportions and contain crosscutting veins of fe rich olivine the boundaries between the chondrules and their rims are irregular and show abundant evidence of aqueous alteration interactions between them in contrast the host matrix contains very minor amounts of saponite and shows no evidence of such extensive aqueous alteration the boundaries between the chondrules rims and the matrix are sharp and show no traces of the matrix having been involved in the alteration of the chondrules rims these observations indicate that the aqueous alteration in the chondrules rims did not occur in the present setting we suggest that the chondrules rims are actually clasts transported from a location on the meteorite parent body different from where the mokoia meteorite was from the aqueous alteration of the chondrules rims probably occurred there the veins in the rims were originally fractures produced in an interchondrule matrix by impacts these were later filled by fe rich olivine during aqueous activity this location was then involved in impact brecciation and individual chondrules were ejected as clasts with remnants of the matrix surrounding them during the continuing brecciation those chondrule rim clasts were transported mixed with anhydrous matrix grains and finally lithified to the present meteorite therefore the rims are fragmented remnants of a former matrix textures characterized by fine grained rims surrounding chondrules in chondrites have been widely thought to have formed in the solar nebula before they accreted into their parent bodies however our results suggest that some textures may not be explained by such an accretionary model instead the multi stage parent body process modeled for the mokoia rim formation may be a more plausible explanation

redistribution of chondrules in a carbonaceous chondrite parent body a model abstract carbonaceous chondrites mainly consist of chondrules and inclusions embedded in a fine grained matrix this texture is widely believed to have formed primarily by direct accretion of solar nebular materials although it may have been modified to various extents by subsequent parent body processes recently we studied all chondrules and inclusions larger than 400 m in diameter and their rims referred to as chondrules rims in the mokoia cv3 carbonaceous chondrite using a scanning electron microscope and found that the chondrules rims experienced various degrees of aqueous alteration and that some also exhibit evidence of thermal metamorphism the mineralogical and petrographic characteristics of the chondrules rims suggest that the alteration and metamorphism occurred within the meteorite parent body in contrast however the surrounding matrix does not show evidence of such alteration and metamorphism these findings indicate that the alteration and metamorphism of the chondrules rims did not occur in situ based on these results we proposed a model that the chondrules rims are actually clasts transported from regions in the parent body different from the location where the host meteorite was finally lithified if it can be assumed that the chondrules and inclusions studied are representative of all chondrules and inclusions in mokoia the results and interpretation pose a fundamental challenge regarding the formation of the whole mokoia lithology that is it cannot be explained by either direct accretion of the solar nebula or conventional parent body brecciation we propose a model for the development of the mokoia lithology through formation of chondrules rims and fine matrix grains by fragmentation in different regions in the parent body followed by transportation mixing and accumulation in a fluid state and finally lithification of those objects these processes may have been repeated cyclically within the parent body

single doppler velocity retrievals with phoenix ii data clear air and microburst wind retrievals in the planetary boundary layer abstract a new three dimensional single doppler velocity retrieval is introduced and tested with reflectivity and radial velocity data gathered during the phoenix ii field program near boulder colorado this retrieval is based on reflectivity conservation with provision for raindrop fall speed the incompressibility condition and a temporal constraint on the velocity field two temporal constraints are considered velocity stationarity and taylor s frozen turbulence approximation velocity stationarity in a moving reference frame it is demonstrated that either of these temporal constraints can be used to derive a second conserved scalar from the original conserved scalar reflectivity this two scalar system is in general overdetermined but a least squares formulation reduces the problem to a poisson equation for a pseudostreamfunction the requisite boundary conditions arise naturally from the least squares formulation and require only single doppler measurements for their evaluation the new r

hydrous and anhydrous alterations of chondrules in kaba and mokoia cv chondrites chondrules in the bali like cv chondrite kaba and the allende like portion of the mokoia breccia have been studied to explore the relationship between hydrous alteration to form phyllosilicates and anhydrous alteration resulting in secondary olivine zonation replacement of enstatite by ferroan olivine and formation of feldspathoids nepheline and sodalite all kaba chondrules experienced extensive hydrous alteration whereas anhydrous alteration was minor and resulted only in the olivine zonation on the other hand all of the mokoia chondrules experienced both extensive anhydrous and hydrous alteration bronzite rims formed between relic enstatite grains and phyllosilicates in both kaba and mokoia during the hydrous alteration petrographic observations indicate that phyllosilicates in mokoia postdate formation of the secondary ferroan olivine and feldspathoids we conclude that anhydrous alteration in kaba and mokoia predated hydrous alteration and took place before accretion of chondrules into the cv parent asteroid

petrology of allende dark inclusions abstract bulk compositions acquired by neutron activation analysis are reported for eight allende dark inclusions dis and compared with compositions of five dis previously reported in the literature enrichments of the elements na k br ba au and as are generally correlated with increased proportions of porous aggregates predominantly composed of fine grained platy to fibrous olivine these aggregates have been interpreted by some workers as chondrules and inclusions that first were exposed to aqueous alteration converting anhydrous silicates to phyllosilicates and later were dehydrated by thermal metamorphism converting phyllosilicates to olivine our data support this interpretation and suggest that the aqueous alteration was open system in character feldspathoid grains intergrown with platy to fibrous olivines in porous olivine rich aggregates and inclusions of sodalite nepheline pentlandite ilmenite and spinel in these olivines suggest that phyllosilicates produced during aqueous alteration could accommodate na k ni s etc and are most consistent with a mixture of both saponite and serpentine dehydration of saponite would require that the temperature of thermal metamorphism was higher than previously suggested and may have been as high as 800 900 c nonporous rims containing ca rich minerals andradite hedenbergite surrounding dark inclusions containing highest proportions of porous olivine rich aggregates and slight to moderate depletions of these clasts in ca relative to bulk allende suggest that these rims were also the result of redistribution of some elements during dehydration of these clasts caused by thermal metamorphism

impact induced seismic activity on asteroid 433 eros a surface modification process high resolution images of the surface of asteroid 433 eros revealed evidence of downslope movement of a loose regolith layer as well as the degradation and erasure of small impact craters less than 100 meters in diameter one hypothesis to explain these observations is seismic reverberation after impact events we used a combination of seismic and geomorphic modeling to analyze the response of regolith covered topography particularly craters to impact induced seismic shaking applying these results to a stochastic cratering model for the surface of eros produced good agreement with the observed size frequency distribution of craters including the paucity of small craters

hydrothermal convection in carbonaceous chondrite parent bodies abstract numerical simulations of the thermal evolution of carbonaceous chondrite parent bodies indicate a period of several million years during which convective motion of water could occur the present study considers variations of permeability radiogenic heating and body radius the model accounts for the radial variation of gravity within the body melting of ice freezing of liquid water and variable water properties and incorporates a realistic equation of state for water some regions of a parent body experience no pore water flow while other regions experience hundreds of pore volumes of liquid water flow the spatial heterogeneity in pore water flow reflects the convective pattern in the body hydrothermal alteration of minerals inside the parent body will accordingly vary greatly with location in the body and one parent body could be the source of chemically diverse meteorites