transmission electron microscope analyses of alteration phases in martian meteorite mil 090032 abstract the nakhlite group of martian meteorites found in the antarctic contain varying abundances of both martian and terrestrial secondary alteration phases the aim of this study was to use transmission electron microscopy tem to compare martian and terrestrial alteration embodied within a single nakhlite martian meteorite find mil 090032 martian alteration veins in mil 090032 are composed of poorly ordered fe smectite phyllosilicate this poorly ordered smectite appears to be equivalent to the nanocrystalline phyllosilicate hydrated amorphous gel phase previously described in the martian alteration veins of other nakhlites chemical differences in this nanocrystalline phyllosilicate between different nakhlites imply localised alteration which occurred close to the martian surface in mil 090032 both structurally and compositionally the nakhlite nanocrystalline phyllosilicate shows similarities to the amorphous poorly ordered phase recently discovered in martian soil by the mars curiosity rover at rocknest gale crater terrestrially derived alteration phases in mil 090032 include jarosite and gypsum amorphous silicates and fe oxides and hydroxides similarities between the mineralogy and chemistry of the mil 090032 terrestrial and martian alteration phases suggest the alteration conditions on mars were similar to those in the antarctic at both sites a small amount of fluid at low temperatures infiltrated the rock and became acidic as a result of the conversion of fe2 to fe3 under oxidising conditions

the weathering of micrometeorites from the transantarctic mountains abstract micrometeorites are cosmic dust particles recovered from the earth s surface that dominate the influx of extraterrestrial material accreting to our planet this paper provides the first in depth study of the weathering of micrometeorites within the antarctic environment that will allow primary and secondary features to be distinguished it is based on the analysis of 366 particles from larkman nunatak and 25 from the transantarctic mountain collection several important morphological categories of weathering effects were identified 1 irregular and faceted cavities 2 surface etch pits 3 infilled cavities 4 replaced silicate phases and 5 hydrated and replaced metal these features indicate that congruent dissolution of silicate phases in particular olivine is important in generating new pore space within particles comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration precipitation of new hydrous phases within cavities in particular ferrihydrite and jarosite results in pseudomorph textures within heavily altered particles glass in contrast is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios metal is variably replaced by fe oxyhydroxides and results in decreases in ni fe ratio in contrast sulphides within metal are largely preserved magnetite an essential component of micrometeorites formed during atmospheric entry is least altered by interaction with the terrestrial environment the extent of weathering in the studied micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type despite these differences we propose a weathering scale for micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases the compositions and textures of weathering products however suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits

quantifying noble gas contamination during terrestrial alteration in martian meteorites from antarctica we investigated exterior and interior subsamples from the martian shergottite meteorites allan hills alh a77005 and roberts massif rbt 04261 for secondary minerals oxygen isotopes ar ar and noble gas signatures electron microprobe investigations revealed that rbt 04261 does not contain any visible alteration even in its most exterior fractures whereas fracture fillings in alha77005 penetrate into the meteorite up to 300 m beyond which the fractures are devoid of secondary minerals light noble gases seem to be almost unaffected by terrestrially induced alteration in both meteorites thus a shock metamorphic overprint of 30 35 gpa can be deduced from the helium measurements in rbt 04261 oxygen isotopes also seem unaffected by terrestrially weathering and variations can easily be reconciled with the differences in modal mineralogy of the exterior and interior subsamples the measurements on irradiated samples ar ar showed a clear martian atmospheric contribution in alha77005 but this is less apparent in our sample of rbt 04261 exterior and interior subsamples show slight differences in apparent ages but the overall results are very similar between the two in contrast krypton and xenon are severely affected by terrestrial contamination demonstrating the ubiquitous presence of elementally fractionated air in rbt 04261 although seemingly contradictory our results indicate that rbt 04261 was more affected by contamination than alha77005 we conclude that irrespective of on which planet the alteration occurred exposure of martian rocks to atmosphere or brine introduces noble gases with signatures elementally fractionated relative to the respective atmospheric composition into the rock and relationships of that process with oxygen isotopes or mineralogical observations are not straightforward

ancient meteorite finds and the earth s surface environment abstract the flux of meteorites to the earth over the last 50 000 yr has remained approximately constant most meteorites that fall in temperate or tropical areas are destroyed on a time scale which is short compared to the rate of infall however in arid regions both hot deserts and the cold desert of antarctica weathering is slower and accumulations of meteorites may occur the initial composition for many meteorite groups is well known from modern falls and terrestrial ages may be established from analyses of the abundance of cosmogenic radionuclides providing an absolute chronology for recording terrestrial processes as samples are falling constantly and are distributed approximately evenly over the earth meteorites may thus be thought of as an appropriate standard sample for studying aspects of the terrestrial surface environment studies involving 14 c and 36 cl terrestrial ages of meteorites 57 fe mossbauer spectroscopy to quantify the degree of oxidation in samples stable isotopes and determination of halogen abundances are yielding information on the terrestrial history of meteorites i terrestrial age and oxidation frequency distributions for populations of samples allow the ages of surfaces to be estimated ii differences in the weathering rate of samples between sites allows constraints to be imposed on the effect of climate on rock weathering rates iii carbon isotopic compositions of generations of carbonate growth within meteorites allows in some cases temperatures of formation of carbonates to be estimated iv structure in the oxidation terrestrial age distribution for meteorites from some arid accumulation sites specifically the nullarbor of australia appears to be linked to previous humid arid cycles v meteorite accumulations in antarctica have been used to constrain aspects of the quaternary evolution of the ice sheet and terrestrial age and oxidation data have been used to constrain ice flow

phyllosilicates in the matrix of the unique carbonaceous chondrite lewis cliff 85332 and possible implications for the aqueous alteration of ci chondrites abstract the fine grained matrix of the unique unequilibrated carbonaceous chondrite lewis cliff lew 85332 has been studied by scanning electron microscopy sem electron probe microanalysis epma and transmission electron microscopy tem compositionally lew 85332 has a matrix that is more fe rich than typical ci chondrites but has elemental abundance ratios that appear to be closer to ci matrices than to cm or cr chondrites the mineralogy of the matrix is dominated by phyllosilicate phases that are predominantly interlayered fe rich serpentine saponite anhydrous silicate phases such as olivine and pyroxene are rare minor magnetite troilite and ferrihydrite also occur associated with the phyllosilicates despite the high degree of weathering in lew 85332 the phyllosilicates appear to have an extraterrestrial origin but the highly variable mg fe ratios of saponite may be the result of partial terrestrial oxidation of fe rich saponite to a more mg rich saponite and ferrihydrite alternatively some of the ferrihydrite may have formed as a result of terrestrial weathering of fe ni metal the compositional and mineralogical data suggest that the matrix of lew 85332 may represent a very early stage in the type of aqueous alteration experienced by the ci chondrites although it is improbable that lew 85332 was a precursor to the ci chondrites because of its high abundance of chondrules the absence of carbonates the high fe content of the matrix and phyllosilicate phases and relatively low abundance of magnetite all indicate that the degree of oxidation and leaching of lew 85332 matrix was significantly less than that experienced by the ci chondrites the absence of clear evidence for alteration of chondrules suggests that either the formation of the hydrous phases in the matrix occurred prior to accretion or that alteration occurred on a parent body and involved limited amounts of fluid such that the reactions took place preferentially and exclusively within the fine grained anhydrous matrix materials

carbonates in antarctic ordinary chondrites inferred from infrared diffuse reflectance spectra examination of antarctic ordinary chondrites was made through use of infrared diffuse reflectance spectroscopy the spectra of all the antarctic ordinary chondrites measured show weak absorption bands near 1350 cm 1 7 4 m which are caused by carbonates probably hydrated carbonates the band is not present after acid dissolution consistent with the carbonate identification the carbonates were probably produced by terrestrial weathering since the spectra of recently fallen non antarctic chondrites nuevo mercurio h5 and la criolla l6 do not show the 1350 cm 1 7 4 m band infrared diffuse reflectance spectroscopy is useful for easily detecting the presence or absence of the weathering produced carbonates in meteorites

the geological history of northeast syrtis major mars abstract as inferred from orbital spectroscopic data northeast syrtis major bears considerable mineral diversity that spans the noachian hesperian boundary despite its small geographic area in this study we use observations from the high resolution imaging science experiment supplemented with context camera imagery to characterize and map the lateral extent of geomorphic units in northeast syrtis major and constrain the geomorphic context of the orbital identified mineral signatures using recent observations we confirm previous mineralogy identified with the compact reconnaissance imaging spectrometer for mars and greatly extend the lateral extent of visible to near infrared investigation utilizing the greater coverage analysis of thermal emission imaging system observations reveals further physical properties and distribution of the geomorphic units the stratigraphy which spans the noachian hesperian boundary displays significant morphological heterogeneity at the decameter scale but it is unifiable under five distinct geomorphic units our paired morphological and mineralogical analysis allows us to construct a detailed geological history of northeast syrtis major several geological events that occurred in northeast syrtis major including the formation of the post isidis crust the emplacement of an olivine rich unit the formation of sulfate minerals and the emplacement of the syrtis major volcanics can be related to regional and global processes constraining the local chronology other mineralogical indicators particularly the formation of al phyllosilicates are difficult to place in the temporal sequence they are observed in isolated patches on the post isidis crust not as a distinct stratigraphic unit as observed elsewhere in nili fossae suggesting their formation via isolated leaching or through alteration of initial compositional heterogeneities within the crust exposures of an olivine rich unit are intermittently observed to form quasi circular landforms suggestive of emplacement in circular depressions which may indicate a period of cratering between the formation of the isidis basin and the deposition of the olivine rich unit we identify and discuss intriguing large linear features of the olivine rich unit reminiscent of dyke fed volcanism that have raised bounding ridges suggestive of contact metamorphism with the crust we compile review and discuss many of the outstanding questions and running hypotheses relevant to our mapping area a synthesis of our geomorphic mapping with recent literature reveals a well defined geological history with extensive aqueous activity at northeast syrtis major that is amassed in a stratigraphic sequence spanning a time likely greater than 250 million years of geological history our geomorphic and spectral analyses confirm that northeast syrtis major exhibits considerable geomorphic and mineralogic diversity within a relatively small geographic area that is representative of the geologic processes occurring throughout the broader nili fossae region during the noachian and hesperian northeast syrtis major adds to this sequence by exposing the diverse environmental history of this region as observed through the presence of alteration minerals not present in this fidelity or proximity elsewhere in nili fossae

effect of coal weathering on some geochemical parameters abstract the effect of coal weathering on some geochemical parameters was studied seven pairs of fresh and altered samples were selected from different venezuelan coal deposits the following analyses were performed water and ash percent heating value bitumen content and composition infrared spectroscopy n alkane distribution and humic substances concentration hs as weathering proceeds there is a corresponding change in hs concentration most geochemical parameters show small changes with hs concentrations below 15 for intense weathering all parameters measured show important modifications such changes are due to the breaking of the coal s macrostructure

martian microfossils in lunar meteorites one of the five lines of evidence used by mckay et al 1996 for relic life in the martian meteorite allan hills alh 84001 was the presence of objects thought to be microfossils these ovoid and elongated forms are similar to structures found in terrestrial rocks and described as nanobacteria folk 1993 mcbride et al 1994 using the same procedures and apparatus as mckay et al 1996 we have found structures on internal fracture surfaces of lunar meteorites that cannot be distinguished from the objects described on similar surfaces in alh 84001 the lunar surface is currently a sterile environment and probably always has been however the lunar and martian meteorites share a common terrestrial history which includes many thousands of years of exposure to antarctic weathering although we do not know the origin of these ovoid and elongated forms we suggest that their presence on lunar meteorites indicates that the objects described by mckay et al 1996 are not of martian biological origin

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

compositions and taxonomy of 15 unusual carbonaceous chondrites abstract we used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification acfer 094 type 3 0 ungrouped cm related belgica 7904 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes wisconsin range wis 91600 dhofar 225 and yamato 86720 dar al gani dag 055 and its paired specimen dag 056 anomalous reduced cv3 like dag 978 type 3 ungrouped dominion range 03238 anomalous magnetite rich co3 1 elephant moraine 90043 anomalous magnetite bearing co3 graves nunataks 98025 type 2 or type 3 ungrouped grosvenor mountains gro 95566 anomalous cm2 with a low degree of aqueous alteration hammadah al hamra hah 073 type 4 ungrouped possibly related to the coolidge loongana c l 001 grouplet lewis cliff lew 85311 anomalous cm2 with a low degree of aqueous alteration northwest africa 1152 anomalous cv3 pecora escarpment pca 91008 anomalous metamorphosed cm queen alexandra range 99038 type 2 ungrouped sahara 00182 type 3 ungrouped possibly related to hah 073 and or to c l 001 and wis 91600 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes belgica 7904 dhofar 225 and y 86720 many of these meteorites show fractionated abundance patterns especially among the volatile elements impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies the metamorphosed cm chondrites comprise two distinct clusters on the basis of their 17o values approximately 4 for pca 91008 gro 95566 dag 978 and lew 85311 and approximately 0 for belgica 7904 and wis 91600 these six meteorites must have been derived from different asteroidal regions

high resolution body wave tomography beneath the svekalapko array ii anomalous upper mantle structure beneath the central baltic shield high resolution body wave tomography beneath the svekalapko array ii anomalous upper mantle structure beneath the central baltic shield

regional power and local ecologies accumulated population trends and human impacts in the northern fertile crescent archaeological data tend to be gathered at the local level human agency also operates at this scale by combining data from multiple surveys conducted within a larger area it is possible to use local datasets to obtain a perspective on regional trends in settlement population and human activity here we employ data derived from nine archaeological surveys in the northern and western regions of the fertile crescent west and north syria se turkey and northern iraq to show how local trends aggregate to create a general proxy record of settlement and regional population in addition we use geoarchaeological data from a region extending from homs in the west to northern iraq in the east to outline historical trends in alluvial fill development both settlement and alluviation trends are then related to palaeoclimate proxy data from soreq cave and lake van settlement geoarchaeological signatures and climate are then examined side by side in order to assess long term human interactions

earthquake location genetic algorithms for teleseisms kennen b l n and sambndge m s 1992 earthquake location genetic algorithms for teleselsms phys earth planet inter 75 103 110 the location of earthquakes requires the estimation of the spatial and temporal components of the hypocentre this can he achieved by a direct mmlmtsatlon of a measure of the misfit between observed and calculated travel times and also slownesses and azimuths if array data are available an efficient means of carrying out this optlmlsatlon procedure is to make use of genetic algorithms this technique is based on the use of many estimates of the hypocentre location at once and the properties of the cluster of estimated locations in four dimensions are exploited m the course of the optlmtsatlon process each estimate of the hypocentral location is represented on a local discrete grid by a bit string and successive iterations generate new bit strings and hence location estimates by operations based on biological analogues these operations are the replication of the best fining bit strings the cross over of reformation between pairs of bit strings and the mutation of indwldual bits in a string the non local character of the information on the misfit function carried in the cloud of hypocentral estimates is usually sufficient to prevent the location being trapped in local minima of the misfit surface convergence to the global misfit minimum can be achieved with a very limited sampling of the original spatml and temporal grid no derivatives of the seismic phase information are reqmred and so the technique is easily generahsed to three dimensional velocity models and can be used with any statable measure of the quahty of an earthquake location by the choice of the misfit criterion between observed and calculated quantities

generation of abnormal trace element abundances in antarctic eucrites by weathering processes abstract based on rees antarctic eucrites can be divided into two groups those showing normal trace element characteristics e g similar to juvinas and those showing abnormal trace element abundances many antarctic eucrite polymict eucrite and basaltic clast samples show the abnormal trace element abundances with ree patterns exhibiting positive ce anomalies sometimes negative ce anomalies positive eu anomalies and low abundances of the remainder of the rees with the lrees generally being at lower relative abundances than the hrees most samples of crystalline clasts from the polymict eucrites lew85300 lew85302 and lew85303 show the abnormal patterns while the glassy matrixes of these meteorites show normal patterns exterior samples generally show more abnormal patterns larger anomalies greater depletions than interior samples from the same meteorites comparison of all basaltic eucrite literature data combined with our data shows that positive and negative ce anomalies and positive eu anomalies are found in about 61 of antarctic eucrite analyses and are virtually unknown in non antarctic eucrite analyses further positive ce anomalies and positive eu anomalies are commonly associated with antarctic eucrites having low ree concentrations consideration of mineral melt partition coefficients shows that it is unlikely that ce anomalies are magmatic features from the hed parent body cerium anomalies on earth are generally restricted to the weathering zone where the relative ease of oxidizing ce to the 4 state allows for fractionation of ce from the 3 rees we believe the unusual ree patterns of abnormal antarctic eucrites arise from weathering effects generated in or on the antarctic ice our suggested scenario involves formation of melt water and its equilibration with the atmosphere which promotes dissolution of ree rich phosphates and oxidation of ce tetravalent ce can then be fractionated from the trivalent ree in solution the details of the weathering process are unclear and will require detailed chemical and sem investigations of eucrites for their elucidation we predict that rapidly chilled eucrites with glassy rather than crystalline mesostases will be more likely to survive the antarctic environment without alteration of their ree patterns occasional s se and k enrichments are likely due to weathering in the antarctic environment as well but these enrichments are not well correlated with ce anomalies

homogeneous distribution of fe isotopes in the early solar nebula to examine the iron fe isotopic heterogeneities of ci and ordinary chondrites we have analyzed several large chips approximately 1 g from three ci chondrites and three ordinary chondrites ll5 l5 and h5 the fe isotope compositions of five different samples of orgueil one from ivuna and one from alais ci chondrites are highly homogeneous this new dataset provides a 56fe average of 0 02 0 04 2se n 7 which represents the best available value for the fe isotopic composition of ci chondrites and probably the best estimate of the bulk solar system we conclude that the homogeneity of ci chondrites reflects the initial fe isotopic homogeneity of the well mixed solar nebula in contrast larger up to 0 26 in 56fe isotopic variations have been found between separate approximately 1 g pieces of the same ordinary chondrite sample the fe isotope heterogeneities in ordinary chondrites appear to be controlled by the abundances of chondritic components specifically chondrules whose fe isotope compositions have been fractionated by evaporation and recondensation during multiple heating events

alteration minerals fluids and gases on early mars predictions from 1 d flow geochemical modeling of mineral assemblages in meteorite alh 84001 clay minerals although ubiquitous on the ancient terrains of mars have not been observed in martian meteorite allan hills alh 84001 which is an orthopyroxenite sample of the early martian crust with a secondary carbonate assemblage we used a low temperature 20 c one dimensional 1 d transport thermochemical model to investigate the possible aqueous alteration processes that produced the carbonate assemblage of alh 84001 while avoiding the coprecipitation of clay minerals we found that the carbonate in alh 84001 could have been produced in a process whereby a low temperature 20 c fluid initially equilibrated with the early martian atmosphere moved through surficial clay mineral and silica rich layers percolated through the parent rock of the meteorite and precipitated carbonates thereby decreasing the partial pressure of co 2 as it evaporated this finding requires that before encountering the unweathered orthopyroxenite host of alh 84001 the fluid permeated rock that became weathered during the process we were able to predict the composition of the clay minerals formed during weathering which included the dioctahedral smectite nontronite kaolinite and chlorite all of which have been previously detected on mars we also calculated host rock replacement in local equilibrium conditions by the hydrated silicate talc which is typically considered to be a higher temperature hydrothermal phase on earth but may have been a common constituent in the formation of martian soils through pervasive aqueous alteration finally goethite and magnetite were also found to precipitate in the secondary alteration assemblage the latter associated with the generation of h 2 apparently despite the limited water rock interaction that must have led to the formation of the carbonates 3 9 ga ago in the vicinity of the alh 84001 source rocks clay formation would have been widespread

ephemeral liquid water at the surface of the martian north polar residual cap results of numerical modelling abstract gypsum a mineral that requires water to form is common on the surface of mars most of it originated before 3 5 gyr when the red planet was more humid than now however occurrences of gypsum dune deposits around the north polar residual cap nprc seem to be surprisingly young late amazonian in age this shows that liquid water was present on mars even at times when surface conditions were as cold and dry as the present day a recently proposed mechanism for gypsum formation involves weathering of dust within ice e g niles p b michalski j 2009 nat geosci 2 215 220 however none of the previous studies have determined if this process is possible under current martian conditions here we use numerical modelling of heat transfer to show that during the warmest days of the summer solar irradiation may be sufficient to melt pure water ice located below a layer of dark dust particles albedo 0 13 lying on the steepest sections of the equator facing slopes of the spiral troughs within martian nprc during the times of high irradiance at the north pole every 51 ka caused by variation of orbital and rotational parameters of mars e g laskar j et al 2002 nature 419 375 377 this process could have taken place over larger parts of the spiral troughs the existence of small amounts of liquid water close to the surface even under current martian conditions fulfils one of the main requirements necessary to explain the formation of the extensive gypsum deposits around the nprc it also changes our understanding of the degree of current geological activity on mars and has important implications for estimating the astrobiological potential of mars

the use of principle component analyses in characterising trace and major elemental distribution in a 55 kyr peat deposit in tropical australia implications to paleoclimate abstract the lynch s crater peat deposit in ne australia is a sensitive environmental archive located in the tropical southern hemisphere this unique deposit illustrates that local and regional changes had a profound effect on the local australian ecosystem over the past 55 kyr to obtain a proxy of past climate changes trace and major element geochemistry analyses were applied to a 13 m peat core from the crater principle component analysis pca was used to identify the main factors that control elemental distribution in the peat and to add interpretative strength to the geochemical behavior of selected major and trace elements for example sc al cu and pb were found to be related to increased erosion of the basin soils and from this several periods of significant flux from atmospheric input and or terrigenous run off were identified geochemically mobile elements during rock weathering and pedogenesis such as mg ca and sr helped to identify the peat ombrotrophic minerotrophic boundary at 1 5 m depth and offered important information about fluxes of these nutrients to the mire and their dynamics within the deposit arsenic and v comparisons between the peat record high concentrations in some peat sections and in local basin rocks very low concentrations suggested the presence of a long range atmospheric dust source early in the formation of the mire the lynch s crater peat record presents a continuous record of environmental change in tropical australia and contributes new understanding to geochemical processes in peatlands

high temperature mass spectrometric degassing of enstatite chondrites implications for pyroclastic volcanism on the aubrite parent body wilson and keil 1991 argued that a few hundred ppm of expanding volatiles present in early partial basaltic melts on the aubrite parent body or on other differentiated asteroids 925 c principally co 1580 2830 ppm n2 110 430 ppm cl 120 450 ppm s see discussion for abundance are indigenous the precise host phases and host sites of the indigeneous volatiles are uncertain 2 2 n2 release appears to be associated with the melting of the fe ni sulfide cotectic at 950 c the amounts of gas released are not unlike those previously measured for iron meteorites and sulfides in irons but exceed by several orders of magnitude the equilibrium n2 solubility in metallic fe ni for solar nebula pressures this suggests that either partial pressures during n2 incorporation were much higher than solar values or n2 is trapped in lattice defects and microcracks possibly in sulfides 3 3 co release over a narrow temperature interval of 1025 1255 c is violent and results in pronounced vesiculation of the residue co may be trapped in microvesicles and cracks in silicates or less likely may form by a reduction reaction during heating between carbon graphite and the minor ferrosilite in the enstatite 4 4 cl release beginning at 950 eh s and 1025 c el s appears not to be associated with lawrencite which should sublime at t as low as 325 c in eh s some may be released from djerfisherite 5 5 gas release and textural studies suggest that metamorphic reheating of eh s and el s was to less than about 950 c el s did not form during metamorphic reheating of eh s by draining of cotectic fe ni sulfide liquid 6 6 sinoite present in some el6 s did not form by condensation from the solar nebula but during parent body metamorphism at t 950 c via the reaction of sio2 gaseous n2 and si in solid solution in the metallic fe ni 7 7 as little as 1 by volume partial melting in an asteroid of any size will generate excess pressures in the melt much greater 10 s of mpa than the tensile strength of silicate materials and will initiate formation of cracks this process will be enhanced by expansion of any exsolved or trapped gas phase in the asteroid and will lead to the formation of pathways cracks growing into dikes for melt migration 8 8 the pressure gradients implied when these pathways intersect the asteroid surface coupled with the observed amounts of indigenous volatiles released from eh s and el s are easily sufficient to drive the pyroclastic volcanic eruptions envisaged by wilson and keil 1991

terrestrial weathering of antarctic stone meteorites formation of mg carbonates on ordinary chondrites abstract white efflorescences of weathering origin occur superposed on fusion crusts or along fractures in the interiors of approximately 5 of all meteorites in the us antarctic collection efflorescences from equilibrated ordinary chondrites consist of the hydrous mg carbonates nesquehonite hydromagnesite x ray diffraction and scanning electron microscope studies of efflorescences from lew 85320 h5 show abundant elongate prismatic crystals of nesquehonite idiomorphic not pseudomorphous after lansfordite with minor local encrustations of hydromagnesite abundances of na k ca and rb in efflorescences from lew 85320 suggest that the observed contents of these elements would require only modest fractionation of chondritic composition whereas extensive fractionation would be required to derive the observed cation ratios from terrestrial sea salts therefore cations in evaporite minerals on antarctic meteorites are most likely not products of contamination by terrestrial marine salts the mg in the efflorescences probably originated from weathering of meteoritic olivine other cations in the efflorescences are also of meteoritic provenance thermodynamic analysis of the reaction forsterite water carbon dioxide nesquehonite silica at antarctic temperatures and pco 2 indicates spontaneity for all water activities greater than 0 65 compatible with the presence of liquid water as brines and or thin films

hydration bands near 3 μm and weathering of some antarctic meteorites abstract we studied the degree of weathering of some antartctic meteorites using the integrated intensity of absorption bands hydration bands near 3 m due to the presence of hydrous minerals the allan hills meteorites measured show stronger integrated intensities than the yamato meteorites measured although the number of meteorites we measured is small this suggests that the allan hills meteorites are more weathered than the yamato meteorites the allan hills meteorites show greater terrestrial ages than other antarctic meteorites on the basis of cosmic ray produced nuclide data our results are consistent with the terrestrial age data because weathering produces hydrous minerals integrated intensities near 3 m vary widely among the antarctic meteorites reported to be relatively little weathered under microscopic observation the integrated intensity of hydration bands near 3 m may have the potential for quantifying the degree of weathering these quantified data may help in selecting less weathered meteorites from among the antarctic meteorite collection and may be combined with terrestrial age data to study terrestrial histories of antarctic meteorites

the preservation state of organic matter in meteorites from antarctica the recovery of large numbers of meteorites from antarctica has dramatically increased the amount of extraterrestrial material available for laboratory studies of solar system origin and evolution yet the great age of antarctic meteorites raises the concern that significant amounts of terrestrial weathering has corrupted their pre terrestrial record organic matter found in carbonaceous chondrites is one of the components most susceptible to alteration by terrestrial processes to assess the effects of antarctic weathering on both non antarctic and antarctic chondritic organic matter a number of cm chondrites have been analyzed mossbauer spectroscopy has been used to ascertain pre terrestrial and terrestrial oxidation levels while pyrolysis gas chromatography mass spectrometry was used to determine the constitution of any organic matter present increased oxidation levels for iron bearing minerals within the non antarctic chondrites are likely to be a response to increased amounts of parent body aqueous alteration parent body processing also appears to remove ether bonds from organic material and alkyl side chains from its constituent units the iron in antarctic chondrites is generally more oxidized than that in their non antarctic counterparts reflecting terrestrial weathering antarctic weathering of chondritic organic matter appears to proceed in a similar way to parent body aqueous alteration and simply enhances the organic responses observed in the non antarctic data set degradation of the record of preterrestrial processes in antarctic chondrites should be taken into account when interpreting data from these meteorites

geogenesis pedogenesis and multiple causality in the formation of texture contrast soils abstract coarse over fine vertical texture contrasts vtc are common in soils and weathering profiles in a variety of environmental settings including many where inheritance or surficial processes alone cannot account for them a multiple causality model is presented here which shows that texture contrasts can form in response to a combination of ubiquitous phenomena there are six key elements downward translocation by water erosional winnowing soil mixing by bioturbation the tendency for surface clay additions to be mobilized while subsurface clays are more likely to remain in place and biological facilitation of moisture flux no element alone is sufficient to create a vtc but not all are necessary in any given regolith the model is illustrated by application to case studies in the ouachita mountains arkansas ridgetops in eastern kentucky the lower coastal plain of north carolina and the upper coastal plain of east texas the implications for interpretation of soils paleosols and weathering profiles is that the presence of a textural contrast by itself does not connote any particular set of geogenic or pedogenic processs or controls texture contrasts may be geogenic pedogenic or both given the widespread occurrence of the mechanisms of the multiple causality model vertical texture contrasts are inevitable

differences between antarctic and non antarctic meteorites an assessment abstract the discovery of a statistically significant number of meteorites in antarctica over the past 20 years has posed many questions one of the most intriguing suggestions that came up during the study of the antarctic samples was that there might be a difference between the parent populations of antarctic and non antarctic meteorites this interpretation was put forward after the detection of a significant difference in the abundances of volatile and mobile trace elements in h l and c chondrites and achondrites other major differences include the occurrence of previously rare or unknown meteorites different meteorite type frequencies petrographic characteristics oxygen isotopic compositions and smaller average masses in addition antarctic meteorites have greater terrestrial residence ages and have collected on the ice shield over several 10 5 years the reality of numerous such differences has now been established beyond doubt however the main question regarding the cause of these differences remains it seems that they have a wide variety of origins ranging from pre terrestrial traits to collection recovery effects and terrestrial weathering studies of terrestrial weathering have shown that over the long time the meteorites spend in and on the ice even subtle processes can produce substantial effects for future investigations it will be important to pay more attention to the weathering status of samples and to develop a more reliable and quantitative weathering index e g based on infrared reflectance spectrometry or differential scanning calorimetry not all differences between the antarctic and non antarctic meteorite populations can be explained by weathering pairing or different collection procedures variable trace element abundances and distinct differences in the thermal history and thermoluminescence characteristics have to be interpreted as being pre terrestrial in origin such differences imply the existence of meteoroid streams whose existence poses problems in the framework of our current knowledge of celestial mechanics however several independent studies support the existence of such meteoroid streams thus being consistent with the suggestion of a time variable influx of extraterrestrial material to earth the generally smaller average size of antarctic meteorites may be the cause for the different meteorite type frequency and the higher abundance of rare samples because smaller meteorites may come from a slightly different parent population in this paper we summarize the contributions in this series and provide a review of the current state of the question for the reality and cause of differences between antarctic and non antarctic meteorites

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

the significance of biogenic element cycling in ancient tropical soils many lateritic tropical soils on stable cratonic areas have developed over millions to 10 s of millions of years some elements e g alkalies alkaline earths si are extremely depleted by leaching and others a1 fe ti are greatly enriched commonly this enrichment is regarded as merely the accumulation of insoluble constituents but inspection of the soil shows development of pisolites nodules and other features indicating extensive dissolution precipitation of feand al oxides and hydroxides this paper suggests that cycling of elements through vegetation is an important part of soil development in these ancient soils this project was initiated to investigate the processes forming lateritic gold deposits in which a relatively small primary vein or similar au deposit in bedrock mushrooms in the soil to become a significant au enrichment in the laterite zone davy and e1 ansary 1986 lecomte and colin 1989 the site of our investigation is the gold deposit of igarape bahia in the serra carajas mining region para province brazil in this region a very ancient plateau surface furnishes the environment for major fe mn and a1 deposits of the carajas district beisiegel 1982 machamer et al 1991 as well as a lateritic gold deposit at igarape bahia the plateau surface is interpreted to have been developed in cretaceous or early tertiary beisiegel 1982 kotschoubey and lemos 1985 the entire region is covered by dense tropical rain forest at the igarape bahia au deposit a narrow primary zone of au cu mineralization at depth gives rise to a relatively rich au deposit in lateritic soil the deposit appears analogous to other lateritic au accumulations in which the initial primary agbearing gold grains are etched and become smaller and new grains of ag poor gold grow in the laterite lecomte and colin 1989 a preliminary study indicated that considerable au was present in vegetation over the deposit so in a later sampling expedition an extensive group of vegetation samples was collected along with soils and waters andrade et al 1991 bliss 1991 machesky et al 1993 vegetation sampling was concentrated along a traverse across the unmined f30 deposit a satellite au deposit 1 km from the main igarape bahia deposit additional samples were collected at three background sites 1 10 and 30 km from the deposit at the f30 deposit and at the 1 km background site all species of tree and shrub were collected with leaves twigs and bark being collected from most species five specific species a large tree two bamboo species and two bushes were sampled along the traverse and at the background sites samples were washed dried chopped homogenized and analyzed for 40 elements by neutron activation activation laboratories ltd ancaster ontario and xray fluorescence materials characterization lab penn state university

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

clay mineraloid weathering products in antarctic meteorites abstract clay mineraloids are associated with gypsum k fe sulfates possibly jarosite cryptocrystalline rust and possibly with zeolites and or secondary alkali feldspars as terrestrial weathering products in stony meteorites from the allan hills alh and elephant moraine eet collection areas in victoria land antarctica weathering formed fracture fillings in fusion crusts of eucrites eeta79004 and eeta79005 diogenites alha77256 and eeta79002 shergottite eeta79001 and h5 chondrite alh82102 and decomposition products of glass and plagioclase in interior samples of achondrites clay mineraloids displayed massive to incipient vermicular forms with elemental compositions that suggest smectite and mica like phases deposits were too small to yield pure material for phase identification although x ray diffractometry and differential scanning calorimetry of bulk samples suggested that the clay mineraloids were not well crystallized a typical structural formula calculated on a smectite basis follows k 0 26 ca 0 04 al 0 97 ti 0 02 fe 3 0 77 mg 0 03 si 4 00 o 10 oh 2 n 2 o net charge 0 28 excessions 0 58 si 0 02 cl 0 09 so 4 0 02 po 4 hydrocryogenic diagenesis can initiate clay mineral formation on timescales of 10 4 10 6 y even with only limited supplies of liquid water cosmochemists must take care not to confuse possible weathering induced elemental and isotopic fractionations in antarctic meteorite samples with signatures of pre terrestrial cosmic processes given proper sample selection and testing though occurrence of clay mineraloid and other weathering products should probably not impede progress in studies of antarctic meteorites

corrosion of fe ni alloys by cl containing akaganeite beta feooh the antarctic meteorite case a suite of 12 iron and 8 stony meteorites from various environments and locations in antarctica was studied representing a range of compositions metallographic structures and degrees of weathering polished sections of meteoritic metal with adhering corrosion products were examined microscopically with the electron microprobe and sem and were used as samples for x ray diffraction examination the major corrosion products are cl containing akaganeite up to 5wtper thousand cl and goethite with minor amounts of lepidocrocite and maghemite cl is not native to the meteorites but owing to the electrochemical nature of the corrosion of fe ni alloys is attracted from the snow and ice or rocky soil environment that contains low amounts of cl akaganeite precipitates near the reaction front incorporating cl ions into ion exchange sites where they may be retained made available for further depassivating corrosive action or become flushed from the system with time and distance from the reaction surface akaganeite ages and transforms to mainly goethite and maghemite it is again argued that lawrencite fecl 2 is not a mineral in meteorites in the stormy antarctic wind blown terrestrial particles may become attached to the weathering products on the meteorite and in time themselves decompose delivering terrestrial ions to the meteorite corrosion system the ions may move a significant distance from the surface and in particular cl may be found along almost invisible cracks in the deep interior trace element work and age determinations 36 cl should take this problem into account

origin of crystalline cold desert salts in the mcmurdo region antarctica abstract the distribution of crystalline salt minerals in deposits in the mcmurdo region of antarctica has been examined to study the origin of these salts sulphate chloride sodium and calcium salts are most frequently encountered salts containing chloride and sodium ions become less common away from the coast sulphate salts are more regularly distributed but tend to be related isotopically to sea water sulphate salts containing magnesium ion tend to exist mainly on substrates composed of basic igneous rocks whereas calcium and carbonate salts are present on all rock types in the region these distributions show that salts of marine origin are regionally and quantitatively most important but that chemical weathering of mafic materials in rocks and soils is also significant however biological volcanic and hydrothermal processes are or have been active contributing to salts in local areas that include penguin rookeries and eastern taylor valley the summit area of erebus volcano and subsurface rocks respectively

the flux of meteorites to the earth and weathering in hot desert ordinary chondrite finds abstract the abundance of ferric iron produced by weathering in ordinary chondrites collected from hot desert regions is related to their terrestrial age enabling a variety of processes involved in meteorite weathering to be deduced fe0 fe2 fe3 content was measured quantitatively by 57fe mossbauer spectroscopy it is observed that meteorites from different regions are oxidised at different rates we also propose the tentative hypothesis that one source of scatter in total oxidation versus terrestrial age for a region is climatic change a mechanism to explain the variable response to climatic conditions involves the high initial porosity of samples being reduced as ferric oxides and other alteration products are produced reliable recovery data from a meteorite accumulation site roosevelt county new mexico usa and a quantitative measure of weathering and terrestrial age permit an estimate of the flux of meteorites to the earth s surface having established a decay constant for meteorites and accounting for the area of searches and pairing we estimate an accumulation rate of 159 falls of mass greater than 20 g per 106 km2 per yr this calculation is distinct from but in broad agreement with previous estimates from camera observations suggesting that the accumulation rate of meteorite falls to the earth s surface has remained essentially unchanged over the last 50 000 years at between 59 and 159 falls of mass exceeding 20 g per 106 km2 per yr the error for both methods is approximately a factor of 2

the geochemistry of antarctic streams and their role in the evolution of four lakes of the mcmurdo dry valleys abstract major ion concentrations are reported for nineteen meltwater streams in the mcmurdo dry valleys antarctica and for the four lakes fed by these streams the most important solute acquisition processes for these flowing waters are dissolution of marine derived salts dissolution of calcite coatings derived from chemical weathering of parent rock and direct weathering of silicates although lakes joyce hoare and fryxell have undergone significant evaporative concentration the only simple salt which is predicted to form at present is calcite the shallow waters of all four lakes were supersaturated with respect to this mineral but were undersaturated with respect to other simple salts geochemical budgets however indicate that so4 k and mg in addition to ca and hco3 have been removed from some of these lakes over recent geological time bacterial sulfate reduction followed by precipitation of metal sulfides is likely to be a sink for sulfate sinks for mg and k are more problematic but may include formation of mgcalcites and in the case of k reverse weathering reactions the ages of the contemporary water columns as indicated by chloride budgets are relatively young and these lakes could have evolved their chemical compositions over a few thousand years of present stream flows it is not necessary to invoke trapped seawater or other salt sources to explain their evolution

geochemical investigations to explain iodine overabundances in antarctic meteorites abstract iodine bromine and chlorine concentrations were determined in different antarctic meteorite specimens eucrites high iron and low iron chondrites with isotope dilution mass spectrometry in all antarctic meteorites i overabundances have been analysed compared with the concentrations for non antarctic meteorites of the same class half of the antarctic specimens show especially high concentrations of more than 1 g a similarly high enrichment effect in antarctic meteorites was not found for br and cl but smaller cl excesses could be observed in some eucrites and high iron chondrites by analysing different types of antarctic rocks a significant decrease of the i concentration but not of the br and cl concentration was determined from the surfaces to the centers of the rocks this shows that atmospheric i compounds interact with the surfaces of antarctic rocks and therefore with those of antarctic meteorites as well analyses of atmospheric halogens show that the gaseous compound ch 3 i is probably responsible for the i overabundance in antarctic meteorites and rocks chloride and bromide are found in particles derived from sea spray in antarctic aerosols deposition of halogens in antarctic snow near the coast shows i cl ratios 10 190 higher than the average value for seawater the corresponding br cl ratios are in the same range as seawater on the basis of our results and of other reported data we construct a preliminary hypothesis for a geochemical i cycle in antarctica taking into consideration long distance and short distance transportation of different i compounds from the coast to inland antarctica

low temperature aqueous alteration on the cr chondrite parent body implications from in situ oxygen isotope analyses the presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early solar system however the process of aqueous alteration is still poorly understood renazzo like carbonaceous cr chondrites are particularly well suited for the study of aqueous alteration samples range from being nearly anhydrous to fully altered essentially representing snapshots of the alteration process through time we studied oxygen isotopes in secondary minerals from six cr chondrites of varying hydration states to determine how aqueous fluid conditions including composition and temperature evolved on the parent body secondary minerals analyzed included calcite dolomite and magnetite the o isotope composition of calcites ranged from 18o 9 to 35 dolomites from 18o 23 to 27 and magnetites from 18o 18 to 5 calcite in less altered samples showed more evidence of fluid evolution compared to heavily altered samples likely reflecting lower water rock ratios most magnetite plotted on a single trend with the exception of grains from the extensively hydrated chondrite mil 090292 the mil 090292 magnetite diverges from this trend possibly indicating an anomalous origin for the meteorite if magnetite and calcite formed in equilibrium then the relative 18o fractionation between them can be used to extract the temperature of co precipitation isotopic fractionation in al rais carbonate magnetite assemblages revealed low precipitation temperatures 60 c assuming that the cr parent body experienced closed system alteration a similar exercise for parallel calcite and magnetite o isotope arrays yields global alteration temperatures of 55 to 88 c these secondary mineral arrays indicate that the o isotopic composition of the altering fluid evolved upon progressive alteration beginning near the al rais water composition of 17o 1 and 18o 10 and becoming increasingly 16o enriched toward a final fluid composition of 17o 1 2 and 18o 15

aqueous corrosion of olivine in the mars meteorite miller range mil 03346 during antarctic weathering implications for water on mars abstract several nakhlites clinopyroxenite meteorites from mars contain olivine phenocrysts with corrosion features identical in size shape and distribution to the smaller etch pits of well characterized weathered terrestrial olivine miller range mil 03346 is an antarctic nakhlite find recovered after long exposure to antarctic conditions the distribution of discrete olivine etch pits almost exclusively within a few hundred microns of allocation mil 03346 171 s documentably exposed surface suggests that they formed by terrestrial weathering in antarctica the small size of olivine etch pits in mil 03346 171 relative to commonly much larger etch pits in even incipiently weathered terrestrial examples suggests that the duration of its exposure to weathering conditions was short or the weathering conditions to which it was exposed did not favor olivine corrosion in the form of etch pit formation or both time scales for the formation of etch pits estimated from experimentally determined dissolution rates of olivine over a range of phs are comparable to the measured terrestrial age of the meteorite and short relative to the time available for possible similar corrosion on mars etch pits of the observed size on mil 03346 olivine phenocrysts would be relatively easy to form supraglacially under brief episodic acidic antarctic conditions but the terrestrial age of mil 03346 is long enough that its olivine might have been weathered to the observed state by englacial films of alkaline antarctic water the paucity of similar etch pits in olivine from the interior of mil 03346 suggests that olivine in this mars meteorite was exposed to even less aqueous alteration after iddingsitization during its 1 3 billion years on mars than its exterior was subjected to during its pleistocene holocene exposure to antarctic weathering conditions

pedogenesis and clay mineralogical investigation of soils formed on gypsiferous and calcareous materials on a transect southwestern iran abstract this study examined pedogenesis as well as the clay mineralogy of soil and rock samples obtained from a transect of gypsiferous and calcareous materials the main objectives of this research were to study the relationship between clay minerals and physiographic units as well as the relative importance of key pedogenic processes in controlling clay mineralogy palygorskite chlorite illite smectite quartz and interstratified minerals were observed in both soil and rock samples using xrd tem and edx analyses illite chlorite and interstratified minerals are inherited largely from parent rocks most of the smectite is inherited from highly smectite marl formations although some may be the product of palygorskite weathering and transformation of illite particularly at the surface horizons neoformation of palygorskite as a result of calcite and gypsum precipitation seems to be a major pathway for the occurrence of this mineral especially on plateau physiographic units although inheritance has less importance gypsiferous soils showed more pedogenic palygorskite as compared to calcareous soils three morphological forms of palygorskite related to degree of weathering were identified in the studied pedons new great groups and subgroups of ustepts aridic gypsiustepts and aridic calcic gypsiustepts are suggested to be included in soil taxonomy based on the properties of some of the studied pedons dissolution and transport of anhydrite from outcrops is considered the main source of pedogenic gypsum in these soils micromorphological studies including thin section observations and sem analyses indicated variable habits of gypsum crystals suggested a dynamic soil environment

an oxygen isotope dichotomy in cm2 chondritic carbonates a sims approach abstract we present petrologic and secondary ion mass spectrometry sims oxygen isotope analyses of ca carbonate within a group of paired antarctic cm2 chondrites the carbonates can be grouped into two isotopically and morphologically distinct populations type 1 grains small matrix grains possess average 18 o of 33 7 2 3 1 and average 17 o of 0 81 0 90 1 type 2 grains calcite aggregates possess distinct oxygen isotopic compositions average 18 o of 19 4 1 5 1 and average 17 o of 1 98 0 9 1 these differences are interpreted to indicate that the two populations of calcite formed under different conditions at different times the carbonates have textural features that suggest an extraterrestrial origin the data presented here fall within error of a previously measured array for carbonates from cm falls benedix et al 2003 the presence of two generations of carbonate suggests carbonate formation in two discrete events on the parent body of these meteorites the oxygen isotopic data presented here deviate from prior bulk carbonate measurements undertaken for these meteorites most likely this deviation is because bulk carbonate analyses included vein carbonate which formed during terrestrial weathering

geochemistry of the onyx river wright valley antarctica and its role in the chemical evolution of lake vanda the onyx river wright valley antarctica is a dilute meltwater stream originating in the vicinity of the wright lower glacier it acquires a significant fraction of its salt content when glacial meltwaters contact wright valley soils at lake brownworth and the concentrations of all ions increase with distance along the 28 km channel down to lake vanda average millimolar concentrations of major ions at the vanda weir during the 1980 1981 flow season were ca 0 119 mg 0 061 na 0 212 k 0 033 q 0 212 so4 0 045 hco3 0 295 and sio2 0 049 based on the flow measurements of chinn 1982 this amounts to an annual flux in moles to lake vanda of ca 0 238 106 mg 0 122 106 na 0 424 106 k 0 066 106 cl 0 424 106 so4 0 09 106 hco3 0 59 106 sio2 0 098 106 in spite of the large salt input from this source equilibrium evaporation of onyx river water would have resulted in early calcite deposition and in the formation of a na mg cl hco3 brine rather than in the ca na mg cl waters observed in lake vanda the river alone could not have produced a brine having the qualitative geochemical features of the lower saline waters of lake vanda it is proposed that the vanda brine is instead the result of past 1200 yrs bp mixing events between onyx river inflows and calcium chloride rich deep groundwaters derived from the don juan basin the mixing model presented here shows that the onyx river is the major contributor of k hco3 so4 and possibly mg found in the lake and a significant contributor approximately one half of the observed na calcium and cl on the other hand came largely from deep groundwater sources in the don juan basin all concentrations except mg are well predicted by this model the chemical composition of the geologically recent upper lake is explained in terms of ionic diffusion from the pre formed brine coupled with onyx river inflow ionic ratios calculated from this latter model are in very good agreement with those observed in the lake at 35 meters

locating regional seismic events with global optimization based on interval arithmetic more than 1000 seismic events in northern europe at distances of up to 400 km from the detecting network are located using an optimization method in which the global minimum of the traveltime function residuals is searched for using an interval arithmetic ia method epicentres are determined using p waves detected by the finnish national seismic network up to 15 stations were used in the analysis the ia results coincide with locations provided by the university of helsinki bulletins with a median location bias of 7 6 km a second data set of 59 explosions in the siilinjarvi mine in central finland was examined in detail because the locations of the explosions were known exactly in this case the median difference of ia locations was 3 8 km from the average location of mine explosions while all 59 events were located within 9 km of the true epicentres the corresponding median error of the university of helsinki locations was smaller 3 2 km but some helsinki locations were well over 10 km from the mine the convergence towards the global optimum using interval arithmetic was fast when compared with the conventional least squares approaches for epicentre determinations

teleseismic epicentre locations from arrival times at regional networks summary arrival time reportings from local and regional networks can be used for preliminary epicentre location of teleseismic events via slowness and azimuth estimation robust techniques for doing so are presented and their relative performance tested on isc listed p arrival times of fennoscandian stations aperture ca 10 for the 10 events analysed the most efficient technique a variant of geiger s method for fitting arrival times to traveltime tables gave average location errors of less than 1 for distances from 15 to 85

evaluation of meteorites as habitats for terrestrial microorganisms results from the nullarbor plain australia a mars analogue site unambiguous identification of biosignatures on mars requires access to well characterized long lasting geochemical standards at the planet s surface that can be modified by theoretical martian life ordinary chondrites which are ancient meteorites that commonly fall to the surface of mars and earth have well characterized narrow ranges in trace element and isotope geochemistry compared to martian rocks given that their mineralogy is more attractive to known chemolithotrophic life than the basaltic rocks that dominate the martian surface exogenic rocks e g chondritic meteorites may be good places to look for signs of prior life endemic to mars in this study we show that ordinary chondrites collected from the arid australian nullarbor plain are commonly colonized and inhabited by terrestrial microorganisms that are endemic to this mars analogue site these terrestrial endolithic and chasmolithic microbial contaminants are commonly found in close association with hygroscopic veins of gypsum and mg calcite which have formed within cracks penetrating deep into the meteorites terrestrial bacteria are observed within corrosion cavities where troilite fes oxidation has produced jarosite kfe so oh where terrestrial microorganisms have colonized primary silicate minerals and secondary calcite these mineral surfaces are heavily etched our results show that inhabitation of meteorites by terrestrial microorganisms in arid environments relies upon humidity and ph regulation by minerals furthermore microbial colonization affects the weathering of meteorites and production of sulfate carbonate fe oxide and smectite minerals that can preserve chemical and isotopic biosignatures for thousands to millions of years on earth meteorites are thus habitable by terrestrial microorganisms even under highly desiccating environmental conditions of relevance to mars they may therefore be useful as chemical and isotopic standards that preserve evidence of life thereby providing the possibility of universal context for recognition of microbial biosignatures on earth mars and throughout the solar system

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

opaque assemblages in cr2 graves nunataks gra 06100 as indicators of shock driven hydrothermal alteration in the cr chondrite parent body we have studied the petrologic characteristics of sulfide metal lodes polymineralic fe ni nodules and opaque assemblages in the cr2 chondrite graves nunataks gra 06100 one of the most altered cr chondrites unlike low petrologic type cr chondrites alteration of metal appears to have played a central role in the formation of secondary minerals in gra 06100 differences in the mineralogy and chemical compositions of materials in gra 06100 suggest that it experienced higher temperatures than other cr2 chondrites mineralogic features indicative of high temperature include 1 exsolution of ni poor and ni rich metal from nebular kamacite 2 formation of sulfides oxides and phosphates 3 changes in the co ni ratios and 4 carbidization of fe ni metal the conspicuous absence of pentlandite may indicate that peak temperatures exceeded 600 c opaques appear to have been affected by the action of aqueous fluids that resulted in the formation of abundant oxides fe rich carbonates including endmember ankerite and the sulfide silicate phosphate scorzalite we suggest that these materials formed via impact driven metamorphism mineralogic features indicative of impact metamorphism include 1 the presence of sulfide metal lodes 2 the abundance of polymineralic opaque assemblages with mosaic like textures and 3 the presence of suessite initial shock metamorphism probably resulted in replacement of nebular fe ni metal in chondrules and in matrix by ni rich co rich fe metal al ti cr rich alloys and fe sulfides while subsequent hydrothermal alteration produced accessory oxides phosphates and fe carbonates an extensive network of sulfide metal veins permitted effective exchange of siderophile elements from pre existing metal nodules with adjacent chondrules and matrix resulting in unusually high fe contents in these objects

chemical studies of h chondrites 4 new data and comparison of antarctic suites we report data for the trace elements au co sb ga rb ag se cs te zn cd bi tl and in ordered by putative volatility during nebular condensation and accretion determined by neutron activation analysis in 13 h5 chondriles from victoria land and 20 h4 6 chondrites from queen maud land antarctica these and earlier results provide antarctic sample suites of 34 chondrites from victoria land and 25 from queen maud land treatment of data for the most volatile 10 elements rb in in these suites by multivariate statistical techniques more robust as well as more conservative than conventional linear discriminant analysis and logistic regression demonstrates that compositions differ at marginally significant levels this difference cannot be explained by trivial terrestrial causes and becomes more significant despite the smaller size of the database when comparisons are limited to data from a single analyst and when all upper limits arc eliminated from consideration the victoria land and queen maud land suites have different mean terrestrial ages 300 kyr and 100 kyr respectively and age distributions suggesting that a time dependent variation of chondritic sources with different thermal histories is responsible as a result these two antarctic suites are on average chemically distinguishable from each other since h chondrites serve as a paradigm for other meteorite classes these results indicate that the near earth populations of planetary materials varied with time on the 105 year timescale

the geochemistry of calcareous forest soils in sulaimani governorate kurdistan region iraq abstract the properties of and processes in calcareous soils are important in the context of dryland soil management and moderation of atmospheric co2 by carbonate weathering this study was conducted to determine the major and trace elemental composition in soils of the kurdistan region of iraq and their geochemical features soil samples were taken from seven pedons five of them from forest soils and two others from non cultivated soils selected physical properties total concentrations of elements and mineralogical properties were determined on samples from each horizon weathering processes in the soils are characterised by loss of ca sr and several trace elements and accumulation of less mobile elements such as zr ti and al the progress of carbonate weathering was best expressed using ba sr and rb sr ratios principal components analysis confirmed that distinctive geochemical differences for two profiles significantly higher mg co cr mn and ni were likely to represent control by parent material a conclusion reinforced by both mineralogical differences and the location of profiles relative to surficial geology the other main geochemical processes differentiating the pedons were chemical weathering of carbonates and accumulation of residual elements calculation of absolute mass flux values showed that for some profiles concentration of mobile elements such as na and k by evapotranspiration was potentially important despite evidence for clay eluviation in most profiles absolute loss of several elements was also correlated with increased weathering as measured by ba sr ratios none of the forest soils showed enrichment depletion profiles for fe or al consistent with podzolisation this study highlights useful geochemical approaches to understanding chemical weathering and pedogenesis in calcareous soil profiles

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

alteration assemblages in the miller range and elephant moraine regions of antarctica comparisons between terrestrial igneous rocks and martian meteorites the weathering products present in igneous terrestrial antarctic samples were analyzed and compared with those found in the four miller range nakhlite martian meteorites the aim of these comparisons was to determine which of the alteration phases in the miller range nakhlites are produced by terrestrial weathering and what effect rock composition has on these phases antarctic terrestrial samples mil 05031 and eet 96400 along with the miller range nakhlites mil 03346 and 090032 were found to contain secondary alteration assemblages at their externally exposed surfaces despite the difference in primary mineralogy the assemblages of these rocks consist mostly of sulfates jarosite in mil 05031 jarosite and gypsum in eet 96400 and iddingsite like fe clay as neither of the terrestrial samples contains sulfur bearing primary minerals and these minerals are rare in the miller range nakhlites it appears that so42 possibly along with some of the na k and ca in these phases was sourced from wind blown sea spray and biogenic emissions from the southern ocean cl enrichment in the terrestrially derived iddingsite of mil 05031 and mil 03346 and the presence of halite at the exterior edge of mil 090032 can also be explained by this process however jarosite within and around the olivine bound melt inclusions of mil 090136 is present in the interior of the meteorite and therefore is probably the product of preterrestrial weathering on mars

mechanisms of weathering of meteorites recovered from hot and cold deserts and the formation of phyllosilicates abstract petrographic mineralogical and chemical analysis of naturally weathered equilibrated ordinary chondrites collected from hot deserts and antarctica has revealed striking similarities and also pronounced differences in weathering between the two environments terrestrial weathering in all meteorites studied is dominated by oxidation and hydration of fe ni metal producing fe oxides and oxyhydroxides that have partially replaced the metal grains and have also occluded primary intergranular pores to form veins troilite weathers readily in hot desert environments but undergoes very little alteration under antarctic conditions most of the primary porosity of ordinary chondrites has been occluded by the time that 15 to 25 of the initial fe 0 and fe 2 has been oxidised to fe 3 in both environments results from modelling the volume changes upon alteration of primary minerals to a range of weathering products demonstrates that the primary porosity of most meteorites is sufficient to accommodate weathering products dilation of primary pores and brecciation which has been observed in parts of some meteorites will only occur if the meteorite is especially metal rich or has a low primary porosity these weathering products are absent from recent falls but have formed in a fall after 100 yr of museum storage cl bearing akaganeite and hibbingite are common weathering products in antarctic finds but occur in abundance in only one hot desert meteorite daraj 014 the majority of fe rich weathering products in meteorites from both environments contain low but variable concentrations of si mg and ca in most meteorites a proportion of these elements are inferred to be present as a very finely crystalline mineral with a 1 0 nm lattice fringe spacing where seen within intragranular fractures this mineral has a topotactic relationship with olivine and orthopyroxene in the heavily weathered antarctic finds alha 78045 and 77002 si is concentrated in cronstedtite a fe rich phyllosilicate an unidentified hydrous si fe ni mg mineral or gel has also partially replaced taenite in alha 78045 in addition to fe rich weathering products hot desert meteorites contain sulphates ca carbonate and silica whereas such minerals are largely absent from antarctic finds the abundance of silicate weathering products in antarctic meteorites is unexpected and indicates that olivine and pyroxene undergo significant chemical weathering in these environments as preterrestrial cronstedtite is abundant in cm2 carbonaceous chondrites the antarctic environment may be a powerful analog for aqueous alteration in the asteroidal parent bodies of primitive meteorites

assessment of alteration processes on circumstellar and interstellar grains in queen alexandra range 97416 abstract insight into the presolar and interstellar grain inventory of the co3 chondrite queen alexandra range que 97416 is gained through correlated secondary ion mass spectrometry sims transmission electron microscopy tem and synchrotron based x ray absorption near edge structure spectroscopy xanes only one presolar silicate grain o 17 o 16 9 96 0 75 10 4 o 18 o 16 19 49 0 96 10 4 that may have formed in a low mass red giant or asymptotic giant branch star occurs in the coarse grained matrix of que 97416 no other presolar grains were identified although presolar grains are rare in que 97416 numerous 898 259 ppm 15 n rich domains n 15 1447 to 3069 occur in the thin section based on tem of an extracted section two 15 n rich domains are amorphous c bearing and texturally uniform and they are embedded in a ferromagnesian silicate matrix with varied grain sizes the individual 15 n rich organic regions with high n 15 2942 107 and 2341 140 exhibit diverse carbon functional groups such as aromatic vinyl keto amidyl and carboxylic functionality while the nitrogen xanes reveals traces of nitrile functionality que 97416 appears to have escaped aqueous alteration based on the absence of hydrated minerals but is thermally altered which could have resulted in the destruction of presolar grains however this process at 400 c metamorphic temperatures was inefficient in destroying the carriers of n isotope anomalies which may indicate the resistant nature of the organic carriers and or the limited extent of thermal metamorphism on the que 97416 parent body

hydrous carbonates on mars evidence from mariner 6 7 infrared spectrometer and ground based telescopic spectra absorption features at 2 28 and 5 4 m identified in mariner 6 7 infrared spectrometer and terrestrial telescopic spectra are consistent with the spectra of hydrous magnesium carbonates such as hydromagnesite and artinite spectral characteristics of these hydrous carbonates are different from those of the anhydrous carbonates as the former do not have the strong spectral features typically associated with anhydrous carbonates such as calcite and siderite theoretical mixing indicates that depending on the type of hydrous carbonate 10 20 wt can be incorporated into the regolith without contradicting the spectral observations or the viking x ray fluorescence chemical analysis hydrous carbonates form as weathering products of mafic minerals in the presence of h2o and co2 even in the antarctic their formation as evaporite minerals from either original magmas or hydrothermally altered rocks is consistent with the martian environment provided liquid water is or has been at least transiently present on earth formation of hydrous mg carbonates is associated with the production of amorphous iron oxides which is consistent with both the environment and the inferred surface mineralogy of mars these minerals are about 60 wt h2o co3 and oh if they are abundant everywhere at the 10 level then about 6 of the surface weight could be volatiles bound in this type of mineral although the stability of hydrous carbonates in a martian environment is uncertain there may be kinetic factors inhibiting the dehydration of these minerals which may persist metastably in the current environment although the spectroscopic evidence for anhydrous carbonates is scant the possible presence of hydrous carbonates provides an appealing mechanism for the existence of carbonates on mars

chemical studies of h chondrites ii weathering effects in the victoria land antarctic population and comparison of two antarctic populations with non antarctic falls abstract we report rnaa data for 14 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in sb se te tl u zn in interior portions of 45 different h4 6 chondrites 49 samples from victoria land antarctica and 5 h5 chondrites from the yamato mts antarctica relative to h5 chondrites of weathering types a and b all elements are depleted 10 at statistically significant levels in extensively weathered types b c and c samples probably by leaching on the ice sheet surface contents of 8 elements in extensively weathered samples may provide a qualitative ranking for terrestrial surface residence chondrites of weathering types a and b seem compositionally uncompromised and as useful as contemporary falls for trace element studies when data distributions for these 14 trace elements in non antarctic h chondrite falls and unpaired samples from victoria land and from the yamato mts queen maud land are compared statistically numerous significant differences are apparent concentrations of 8 elements differ significantly in the victoria land and non antarctic h5 chondrite populations essentially the same compositional differences and 53 mn content and shock history differences appear when h4 6 populations are compared contents of 8 elements differ when queen maud land and victoria land populations are compared and 5 for the queen maud land non antarctic comparison these and other differences give ample cause to doubt that the various sample populations derive from the same parent population the observed differences do not reflect weathering chance or other trivial causes a preterrestrial source must be responsible the least unlikely of these involves a temporal variation in the source regions from which meteoroids derive

weathering of olivine under co2 atmosphere a martian perspective abstract recent analyses from the curiosity rover at yellowknife bay gale crater mars show sedimentary rocks deposited in a lacustrine environment and containing smectite clays thought to derive from the alteration of olivine however little is known about the weathering processes of olivine under early martian conditions and about the stability of smectite clays in particular here we present a 3 month experiment investigating the weathering of forsteritic olivine powders fo 90 under a dense co 2 atmosphere and under present day terrestrial conditions for comparison the experiment also evaluates the potential effects of hydrogen peroxide h 2 o 2 as a representation of the highly oxidizing compounds produced by photochemical reactions throughout martian history the weathered samples were characterized by means of near infrared spectroscopy nir x ray diffraction xrd transmission electron microscopy with energy dispersive x ray spectrometry tem edx mossbauer spectroscopy and thermogravimetry the results show that a mg rich smectite phase formed from the weathering of olivine under co 2 conditions although in lower abundance than under terrestrial conditions the main secondary phase formed under co 2 turns out to be a silica rich phase possibly acting as a passivating layer with a non diagnostic near infrared spectral signature the use of h 2 o 2 highlights the critical importance of both the redox conditions and fe content of the initial olivine on the nature of the secondary phases

mechanisms for chemostatic behavior in catchments implications for co2 consumption by mineral weathering a r t i c l e i n f o article history concentrations of weathering products in streams often show relatively little variation compared to changes in discharge both at event and annual scales in this study several hypothesized mechanisms for this chemostatic behavior were evaluated and the potential for those mechanisms to in uence relations between climate weathering uxes and co2 consumption via mineral weathering was assessed data from loch vale an alpine catchment in the colorado rocky mountains indicates that cation exchange and seasonal precipitation and dissolution of amorphous or poorly crystalline aluminosilicates are important processes that help regulate solute concentrations in the stream however those processes have no direct effect on co2 consumption in catchments hydrograph separation analyses indicate that old water stored in the subsurface over the winter accounts for about one quarter of annual stream ow and almost one half of annual uxes of na and sio2 in the stream thus ushing of old water by new water snowmelt is an important component of chemostatic behavior hydrologic ushing of subsurface materials further induces chemostatic behavior by reducing mineral saturation indices and increasing reactive mineral surface area which stimulate mineral weathering rates co2 consumption by carbonic acid mediated mineral weathering was quanti ed using mass balance calculations results indicated that silicate mineral weathering was responsible for approximately two thirds of annual co2 consumption and carbonate weathering was responsible for the remaining one third co2 consumption was strongly dependent on annual precipitation and temperature these relations were captured in a simple statistical model that accounted for 71 of the annual variation in co2 consumption via mineral weathering in loch vale published by elsevier b v

the 1925 meteorite fall near ellemeet and serooskerke the netherlands two meteorites impacted in 1925 around the town of serooskerke on the isle of schouwen the netherlands the largest mass is widely known as the ellemeet diogenite while a second mass heavily weathered due to environmental exposure also survived until the present day this work aims to reconstruct the history of the 1925 fall and for the first time documents the second mass known as the serooskerke by integrating a historical and experimental approach the study of historical news archives and cadastral records redefined the 1925 impact site at n 51 42 086 e 3 49 789 environmental exposure experiments reproducing the effects of rainfall and frost weathering identified the latter as the main cause for the second mass reported disintegration in the field sometime during the 1925 1926 winter the bulk mineralogy of the second mass was established using xrd powder diffraction for a 2 range of 3 70 and was found to be identical to an ellemeet reference sample uv vis nir spectroscopy 300 2500 nm was subsequently used to broadly compare the second mass to hed clan meteorites bouvante eet87503 johnstown and asteroid 4 vesta in order to corroborate its vestan origin the historical and geographic relationship of the two masses and the comparable bulk mineralogy supported the pairing of these two meteorites this makes the serooskerke a valuable legacy of the 1925 fall especially as the location of 50 of the remaining ellemeet mass is presently unknown

in situ sequestration of atmospheric co2 at low temperature and surface cracking of serpentinized peridotite in mine shafts abstract the investigation of carbonate formation at low temperature during weathering of ultramafic rocks has become increasingly important as it represents an analog study for a cost efficient carbon disposal strategy here we present new insight into carbonate formation under subarctic surface conditions obtained from extensively carbonated chromite mine shafts in the feragen ultramafic body e norway carbonation proceeded by formation of mm to cm thick carbonate surface coatings on the serpentinized peridotite host rock the surface coatings consist in most cases of pure lansfordite mgco 3 5h 2 o and sometimes nesquehonite mgco 3 3h 2 o heavy o and c isotopes are strongly enriched in the carbonate coatings relative to drip water samples from the mines and water samples from subaerial ponds the major element composition of the water samples reveal that infiltrating rainwater reacts rapidly with the peridotite mainly due to brucite dissolution within the mines discharging alkaline water forms thin films on walls and ceilings that evaporate upon circulation of cold dry air in mines with only one opening the carbonation is limited to the entrance area in mines with a more efficient air circulation due to multiple entrances carbonation is found throughout the mine evaporation of the mine water results in lansfordite saturation and precipitation and is accompanied by a rayleigh type distillation effect causing enrichment of the heavy c and o isotopes in the liquid from which the carbonates precipitate formation of the carbonate coatings involved fragmentation of the underlying serpentinite substrate fragmentation proceeded by subcritical cracking i e by a combination of substrate weakening due to brucite dissolution and stress build up due to lansfordite precipitation in fractures close to the surface reaction induced fracturing represents a positive feedback mechanism as it creates additional reactive surface area during the carbonation mining operations in the area ceased in the mid 1920s indicating that the described carbonation occurs on a time scale relevant for the disposal of anthropogenic co 2

relict soil evidence for profound quaternary aridification of the atacama desert chile abstract a relict soil on a late tertiary early quaternary gravelly alluvial fan in the southern atacama desert was studied to determine if evidence of quaternary climate change was evident in the profile stratigraphic relations of soil morphological features indicated that the initial phase of soil development was extensive chemical weathering with the loss of si na etc and the formation of secondary clay this was then followed by a prolonged period of carbonate accumulation that has discontinuously impregnated the earlier formed argillic horizons the carbonate accumulation occurred both as fine grained accumulations that engulfed and expanded the gravelly soil matrix and as carbonate that formed dense and continuous coatings on gravel bottoms overlying the carbonate is a holocene calcareous sand unit stable c and o isotope profiles of the disseminated carbonate show that this material appears to have formed under conditions of low to modest plant cover and significant soil water evaporation very similar to soils presently found at higher latitudes and altitudes in modern argentina seven transects of the carbonate laminations on the gravels at 10 m scale reveal that all show a nearly 4 increase in 13 c values with time over distances of approximately 150 mm and variable 18 o values the shift in c isotope values which is unlikely to be due to significant changes in c3 vs c4 vegetation reflects a profound and prolonged aridification with a corresponding lowering of plant density and soil respiration the precise beginning of the aridification is unknown due to a lack of carbonate dating methods amenable to the time frame involved when all changes are considered this remarkable soil indicates that local rainfall declined from somewhere between 500 to 1000 mm y 1 in the late tertiary early quaternary to the present climate of about 25 mm y 1 future work will focus on developing more precise geochronological controls but this initial study reveals the enormous potential that carbonate bearing relict soils have for understanding climate change

1 200 myr impact melting age and trace element chemical features of the yamato 790964 chondrite 1 200 myr impact melting age and trace element chemical features of the yamato 790964 chondrite

the tatahouine diogenite mineralogical and chemical effects of sixty three years of terrestrial residence comparison between clasts of the tatahouine diogenite collected the day of the fall in 1931 and 63 years later in 1994 allows the evaluation of mineralogical and chemical effects of terrestrial residence on meteorites secondary minerals are found in the 1994 samples iron stains and carbonate rosettes major and trace element abundances have been determined on fallen and found clasts no significant differences have been observed for most elements with the exception of rb sr and in a single case the light rare earth elements lree in this case the ree pattern of a 1994 clast displays a weak positive ce anomaly probably linked to the presence of iron hydroxide the contents of rb and sr are significantly higher in the 1994 samples than in the 1931 clasts and reflect the formation of calcite inside some of the clast fractures these results demonstrate that weathering processes may change the chemistry of meteorites in a very short time

argillic horizon development in calcareous soils of arid and semiarid regions of southern iran abstract ten representative pedons with argillic horizons from southern iran were selected for micromorphological and mineralogical study they were classified as haploxeralfs haplustalfs argixerolls argiustolls and argigypsids with thermic hyperthermic and mesic temperature regimes some of the argillic horizons were probably formed in a less arid previous climate during which carbonate migrated through the profile thus allowing clay to illuviate into deeper horizons thin sections showed few to no clear clay coatings in argillic horizons with greater clay content where shrink swell has disrupted them clay coatings superimposed on carbonate coatings and in turn covered by calcite indicate recalcification calcite depletion pedofeatures were the most striking features in these soils sodium may have played an important role in the dispersion of clay and formation of argillic horizons within two of the pedons studied a micromorphological index of soil evolution in highly calcareous arid and semiarid conditions is proposed it correlates with the content of free fe2o3 fedcb in fine earth the colour index the clay illuviation index and the smectite chlorite illite ratio the index can be useful for correlation of soils with argillic horizons formed on highly calcareous parent material in different landscape units new subgroups of haploxeralfs and argiustolls are suggested for inclusion in soil taxonomy based on the properties of some of the studied profiles

replacement of olivine by serpentine in the carbonaceous chondrite nogoya cm2 abstract coarse chondrule and isolated olivine in some cm chondrites is replaced by serpentine in both centripetal and meshwork replacement textures locally preserved textures formed by partial replacement of coarse olivine by serpentine in the carbonaceous chondrite nogoya cm2 establish unique associations between each individual mass of serpentine and the specific olivine from which that serpentine formed electron probe microanalyses show that the composition of serpentine replacing coarse olivine is uniform throughout all analyzed volumes of nogoya and is independent of the composition of the olivine being replaced if as previously proposed late stage alteration fluids were mg rich because fe source minerals were depleted in earlier stages then the uniform mg rich composition of the serpentine replacing large silicate grains during advanced stages of alteration may indicate diffusional homogenization of the aqueous solutions over progressively larger spatial scales enabled by long timescales and previously proposed stagnant or slow moving fluids the range of olivine compositions replaced in nogoya is even larger than previously reported from alh 81002 cm2 this militates against hypotheses of strong primary mineral control on the compositions of alteration products at least at advanced stages of alteration the serpentine formed by olivine replacement in nogoya is more magnesian than the counterpart serpentine replacing all anhydrous primary silicates in alh 81002 this intermeteorite heterogeneity of replacement serpentine composition between alh 81002 and nogoya indicates that the aqueous solutions in which the olivine serpentine replacement reactions occurred were of different compositions in the two different cm parent body volumes sampled by alh 81002 and nogoya the more magnesian character of serpentines in nogoya than in alh 81002 indicates that the nogoya aqueous alteration environment was even more highly evolved toward mg rich solutions than the environment indicated by the composition of the serpentine in alh 81002 persistence of primary silicate remnants within centripetal and meshwork serpentine indicates that either the aqueous alteration episodes in the parent body volumes represented by individual meteorites were too short to allow complete replacement of olivine by serpentine or one or more reactants most likely water were completely consumed before the coarse primary silicate was completely replaced seemingly incompatible arguments for and against primary mineral control of serpentine composition during cm chondrite alteration may be reconciled by considering the different grain sizes and reaction timescales that likely existed in different textural settings

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

terrestrial alteration of carbonate in a suite of antarctic cm chondrites evidence from oxygen and carbon isotopes the oxygen 18o 17o and carbon 13c fmod14c the fraction of modern 14c isotopic compositions of carbonate were measured for a set of paired antarctic cm chondrites eet 96006 eet 96016 eet 96017 and eet 96019 while the oxygen isotopic compositions do not plot on the terrestrial fractionation line and indicate that a component of the carbonate minerals has an extraterrestrial origin they also do not fall on the array defined for carbonates by cm falls and are thus consistent with the presence of a terrestrial carbonate component the 13c and fmod14c measurements of carbonate suggest the presence of at least two carbon sources carbonate derived from atmospheric co2 that is inferred to have been produced as a result of silicate weathering reactions and carbonate derived from another carbon source that is either old or non atmospheric the relationships between oxygen and carbon isotope data provide additional constraints on the weathering process and allow the possibility that rock dominated weathering of the meteorite caused the oxygen isotopic composition of antarctic water added to the meteorite to evolve away from the terrestrial mass fractionation array leading to formation of low temperature terrestrial alteration products that do not lie on the terrestrial fractionation line

climate and rock weathering a study of terrestrial age dated ordinary chondritic meteorites from hot desert regions abstract ordinary chondrites oc recovered from the desert areas of roosevelt county new mexico the nullarbor region of western australia and the algerian and libyan sahara for which 14c terrestrial ages have been determined were examined by 57fe mossbauer spectroscopy oc were chosen as a standard sample to investigate weathering processes as their well constrained trace and bulk element chemistry normative mineralogy and isotopic composition define a known pre weathering starting composition given that terrestrial ages are known it is possible to compare initially very similar samples that have been subsequently weathered in a range of climatic regimes from the present day to 44 ka bp in addition recently fallen equilibrated oc contain iron only as fe0 and fe2 thus the abundance of ferric iron is directly related to the level of terrestrial weathering mossbauer spectroscopy identifies two broad types of ferric alteration paramagnetic phases akaganeite lepidocrocite and goethite and magnetically ordered principally magnetite and maghemite oc finds show a range in the percentage of total fe existing as fe3 from zero to over 80 however oxidation is comparable between fragments of the same oc separated since their time of fall i e paired meteorites our results indicate several features of meteorite weathering that may result from climatic or geomorphologic conditions at the accumulation site 1 saharan samples are overall less weathered than non saharan samples which may be related to the relatively recent age ca 20 ka of the saharan accumulation surface 2 broad differences between sites in the rate of weathering arising from regional differences in climate 3 consistent differences in the weathering products between samples that fell during humid periods and those that fell during more arid periods those falling during humid periods contain a higher proportion of magnetically ordered ferric oxides 4 one region the nullarbor that shows a variation in the total amount of ferric species that closely matches the climatic record for this area of australia for the last 30 ka points 3 and 4 may be related to the identification of a rapid initial weathering phase the majority of weathering occurs in the first few hundred years after fall followed by passivation of weathering by porosity reduction porosity reduction and the associated restriction in the ability of water to penetrate the sample appears to be the mechanism whereby a weathering assemblage formed during the brief initial period of oxidation is preserved through subsequent climatic cycles over the terrestrial lifetime of the sample

characteristics of dust deposited along a transect between central iran and the zagros mountains abstract few studies have been reported on the characteristics of dust particles deposited in arid regions of the middle east the objective of this study was to identify the variations in physical chemical and mineralogical composition of dust particles deposited along an elevational transect lying between central iran and the zagros mountains in the west dust samples were collected at 12 localities during september 2008 and july 2009 with and without transboundary dust storms respectively samples were examined for their grain size distribution and their mineralogical and chemical composition surface soils were also sampled from the vicinity of the dust sampling sites and their total elemental compositions were determined the results indicated that dust deposition rate mean particle diameter and concentration of soluble ions in samples from both sampling periods decreased with altitude with a significantly lower gradient for samples of july 2009 than for those of september 2008 the similarity observed in dust samples taken during september 2008 and those reported by previous studies or measured in local soils and sediments suggests that local soils greatly contribute to the atmospheric dust along the transect in periods with no dust storms during such periods dust deposits in the high altitude zagros mountains where annual precipitation is higher and temperature lower only receive a minor contribution from arid soils of central iran however in july 2009 when a heavy dust storm took place significant differences were observed between local soils and dust samples along the transect particularly at high altitudes in terms of their physicochemical and mineralogical characteristics these findings together with satellite images and patterns of wind frequency and direction clearly indicate the major contribution of a transboundary dust storm probably originating from iraqi arid land to atmospheric deposition in the zagros area and central iran when dust storms blow from across the borders the contribution of local soils and sediments to aerosols drastically decreases with elevation if dust storms originating from outside the country continue to occur not only will they influence the surface soil properties in the zagros region but will also induce environmental problems in the region

modelling soil genesis in calcareous loess abstract the soilgen1 model was developed to simulate soil development in calcareous loess at holocene 15 000 bp present temporal extent we used the leachc model as a core and added process formulations to describe the effect of vegetation and soil macrofauna on various soil properties a limited calibration was done on the calcite solubility constant by comparing decarbonization rates in various leaching climates with values predicted by the metamodel of egli and fitze egli m and fitze p 2001 quantitative aspects of carbonate leaching of soils with differing ages and climates catena 46 35 62 soil profiles of c and ph after 15 000 years compared well with measurements in a belgian loess profile that was never under agriculture taking the composition of the c horizon as uniform parent material scenarios with and without agriculture with varying degrees of bioturbation and for documented holocene climatic and vegetation evolutions in belgium and hungary were simulated and compared results show a clear effect of bioturbation on soil development especially in the continental climate evolution of hungary indicators for the possible occurrence of clay migration and disturbance of lateglacial morphology were calculated and these also show the importance of bioturbation

molecular and isotopic indicators of alteration in cr chondrites the cr group of carbonaceous chondrites may represent some of the most primitive extraterrestrial materials available for analysis however in contrast to other chondrite groups the cr organic fraction is poorly characterized the carbonaceous chondrite literature shows that relatively anhydrous thermal processing results in a condensed poorly alkylated o poor macromolecular material while for aqueous processing the converse is true such characteristics can be used to discern the alteration histories of the carbonaceous chondrites we have performed bulk elemental and isotopic analysis and flash pyrolysis on four cr chondrites renazzo al rais elephant moraine eet 87770 and yamato y 790112 to determine the nature of their organic component renazzo al rais and y 790112 release qualitatively similar pyrolysis products although there are some variations al rais macromolecular structure contains substantially higher relative abundances of alkylated and oxidized species and relatively lighter 15n suggesting that it has endured more extensive aqueous processing than the other cr chondrites renazzo appears relatively unprocessed with a low degree of alkylation a lack of detectable nitrogen bearing components and low methylnaphthalene ratio eet 87770 s low abundance of alkylated species suggests its macromolecular structure may be relatively condensed with condensation potentially assisted by a period of mild thermal alteration

evidence for mechanical and chemical alteration of iron nickel meteorites on mars process insights for meridiani planum 1 the weathering of meteorites found on mars involves chemical and physical processes that can provide clues to climate conditions at the location of their discovery beginning on sol 1961 the opportunity rover encountered three large iron meteorites within a few hundred meters of each other in order of discovery these rocks have been assigned the unofficial names block island shelter island and mackinac island each rock presents a unique but complimentary set of features that increase our understanding of weathering processes at meridiani planum significant morphologic characteristics interpretable as weathering features include 1 a large pit in block island lined with delicate iron protrusions suggestive of inclusion removal by corrosive interaction 2 differentially eroded kamacite and taenite lamellae in block island and shelter island providing relative timing through crosscutting relationships with deposition of 3 an iron oxide rich dark coating 4 regmaglypted surfaces testifying to regions of minimal surface modification with other regions in the same meteorites exhibiting 5 large scale cavernous weathering in shelter island and mackinac island we conclude that the current size of the rocks is approximate to their original postfall contours their morphology thus likely results from a combination of atmospheric interaction and postfall weathering effects among our specific findings is evidence supporting 1 at least one possible episode of aqueous acidic exposure for block island 2 ripple migration over portions of the meteorites 3 a minimum of two separate episodes of wind abrasion alternating with 4 at least one episode of coating forming chemical alteration most likely at subzero temperatures

redistribution and mobilization of titanium zirconium and thorium in an intensely weathered lateritic profile in western australia abstract the mobility of titanium zirconium and thorium elements commonly considered insoluble during supergene weathering is still not well understood especially in intensely weathered regolith thus an intensely weathered lateritic profile jg developed on meta granitoids in jarrahdale western australia was investigated the mobility of ti zr and th has been assessed at both mineral assemblage and profile scales and the mode of occurrence has been investigated through the combined use of geochemical data from bulk regolith particle size fractions and sequential extractions with in situ data determined by electron probe micro analyzer and synchrotron x ray powder diffraction neoformed poorly crystalline phases containing trace to minor amounts of zr ce and th unassociated with silicates or phosphates were identified on the walls of al fe rich pores in the ferruginous duricrust this implies that some mobilization and redistribution of zr and th occurs within a sample scale breakdown of primary thorite and rare earth element rich fluorocarbonates is thought to be the source for zr and th in the neoformed phases rather than zircon thus the mineral hosts of zr ti and th in the parent rock and their relative susceptibility to weathering are the fundamental controls on subsequent mobility during initial weathering trace amounts of th in secondary phases such as rhabdophane and florencite show translocation of th at the mineral scale while strong partitioning of th into gravel rather than matrix reflects redistribution of th at the profile scale the absence of primary sphene from the regolith and the presence of partially dissolved ilmenite and rutile grains in the ferruginous mottled zone suggest mobilization and translocation of ti at a mineral assemblage scale furthermore the fluctuation of ti zr in the ferruginous zone is in contrast to the consistency of zr hf throughout the profile in general within the range of parent meta granitoid this suggests that ti and zr fractionate from each other and partition between gravel and matrix during extreme weathering and advanced lateritization this study demonstrates that ti zr and th are mobile at a variety of scales an important consideration that is often overlooked when calculating element mass flux in intensely weathered regolith