contrasting compositions of mariana trough fallout tephra and mariana island arc volcanics a fractional crystallization link discrete quaternary 400 ka tephra fallout layers mostly 1 cm thick within the siliceous oozes of the central mariana trough at 18 n are characterized by medium k to high k subalkalic volcanic glasses k2o 0 8 3 2 wt with high large ion lithophile elements lile high field strength elements hfse ratios and nb depletion ba la 35 ba zr 3 5 la nb 4 typical for convergent margin volcanic rocks compositional zoning within layers ranges from basaltic to dacitic sio2 48 71 wt mgo 0 7 6 5 wt all layers contain basaltic andesites the tephra layers are interpreted as single explosive eruptive events tapping chemically zoned reservoirs the sources being the mariana arc volcanoes mav due to their proximity 100 400 km and similar element ratios mav ba la 36 7 ba zr 3 5 0 9 the glasses investigated however contrast with the contemporaneous basaltic to dacitic lavas of the mav by being more enriched in tio2 1 2 wt mav 0 8 wt feo 10 wt mav 8 9 wt k2o 1 1 wt mav 0 8 wt and p2o5 0 4 wt mav 0 2 wt semi incompatible trace elements including rare earth elements ree of the basaltic andesitic and dacitic glasses match those of the dacitic mav lavas which became enriched by fractional crystallization moreover the glasses follow a tholeiitic trend of fractionation in contrast to mav transitional trends and have a characteristic p2o5 trend that reaches a maximum of 0 6 wt p2o5 at 57 wt sio2 whereas mav lavas increase linearly in p2o5 from 0 1 to 0 3 wt with increasing silica both explosive and effusive series are interpreted to have evolved in common magma reservoirs by convective fractionation similar parental magmas are suggested to have separated into coexisting si andesitic to dacitic and basaltic melts by in situ crystallization the differentiated melt is interstitial in an apatite saturated crystalline mush of plag px ox ol at the cooler chamber margins in contrast to the less differentiated basaltic to basaltic andesitic magmas which are not yet saturated in apatite and occupy the chamber interior reinjection of interstitial melt into the chamber interior and mixing with larger melt fractions of the interior liquid mixing ratios about 1 8 9 can explain the paradoxical behavior of apatite controlled p and mree variation in the basaltic andesite glasses and their mav dacite like fractionation patterns the process may also account for the exclusively tholeiitic trend of fractionation of the glass shard series but in situ crystallization alone cannot cause their absolute enrichment in semi incompatible elements the newly mixed melt is suggested to form the basaltic end member of the glass shard series however it must have become physically separated from the main mav magma body possibly by density driven convective fractionation in order to allow for further evolution of the contrasting geochemical paths as well as differentiation

fluid inclusions in the stripa granite and their possible influence on the groundwater chemistry fluid inclusions in quartz and calcite of the proterozoic stripa granite central sweden demonstrate that the rock and its fracture fillings have a complex evolutionary history the majority of inclusions indicate formation during a hydrothermal stage following emplacement of the stripa pluton total salinities of quartz inclusions range from 0 18 eq wt nacl for unfractured rock and from 0 10 eq wt for fractured rock vein calcites contain up to 25 eq wt nacl but the inclusion size is larger and the population density is lower homogenization temperatures are 100 150 c for unfractured rock and 100 250 for fractured rock pressure corrections assuming immediate post emplacement conditions of 2 kbar give temperatures about 160 c higher measurements of fluid inclusion population densities in quartz range from about 108 inclusions cm3 in grain quartz to 109 inclusions cm3 in vein quartz residual porosity from inclusion densities has been estimated to be at least 1 which is two orders of magnitude greater than the flow porosity breakage and leaching of fluid inclusions is proposed as an hypothesis for the origin of major solutes na ca cl in the groundwater evidence for the hypothesis is based on 1 mass balance only a small fraction of the inclusions need to leak to account for salt concentrations in the groundwater 2 chemical signatures brcl ratios of fluid inclusion leachates 0 0101 match those ratios for the deep groundwaters 0 0107 3 leakage mechanisms micro stresses from isostatic rebound or mining activities acting on irregular shaped inclusions could cause breakage and provide connection with the flow porosity and 4 experimental studies water forced through low permeability granites leach significant quantities of salt this hypothesis is consistent with the available data although alternate hypotheses cannot be excluded

ce anomalies in the lew85300 eucrite evidence for ree mobilization during antarctic weathering abstract there is abundant evidence for widespread ree mobilization in antarctic eucrites resulting in ce and eu anomalies and lower whole rock ree abundances relative to typical eucrites using secondary ion mass spectrometry sims we investigated the microdistribution of ce anomalies in the antarctic polymict eucrite lew85300 ce anomalies positive and or negative are present in all three of the minerals plagioclase pyroxene and silica analysed the anomalies occur in grains from all four clasts as well as in mineral and lithic fragments from the surrounding matrix thus there appears to be no lithologic association silica which has been heavily shocked and altered exhibits a lree enriched pattern with negative ce and eu anomalies consistent with a derivation of the ree from ca phosphate dissolution trivalent ree are leached from the phosphates with preferential retention of tetravalent ce and redeposited on silica pyroxene is also widely affected by ree mobilization due to an extensive shock induced microcrack network along cleavage planes a tendency for the largest ce anomalies to occur at low lree concentrations suggests that pyroxene itself experienced ree leaching with concomitant ce retention ce anomalies are rare in plagioclase because this mineral lacks an extensive network along which ree can be mobilized the widespread ree mobilization and evidence for other forms of weathering requires that trace element data be used cautiously especially for antarctic eucrites

argon 39 argon 37 and krypton 85 isotopes in stripa groundwaters abstract 39 ar 37 ar and 85 kr activities in groundwater samples from three boreholes in the stripa granite are compared with 222 rn activities and with data from a granitic groundwater in switzerland in situ production rates in bulk granite and in fracture filling minerals are calculated the measured isotopes in groundwater have been produced by nuclear reactions in the rock matrix it was reported earlier that a large fraction of the in situ produced 222 rn can escape to the water phase due to the unusual microscopic distribution of u which seems to be in close contact with the water phase the same conclusion can be drawn for 85 kr with escape factors between 5 and 25 the 39 ar values in stripa groundwaters are the highest measured so far but consistent with the unusually high neutron flux in stripa as compared to granites with lower u and th contents the 37 ar concentrations appear to be quite high but since it is the first time that this isotope has been identified in groundwater the basis for a comparison with different rock formations is still too small it seems possible that calcite fracture fillings in stripa have a major influence on the concentration of 37 ar in groundwater

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

formation of saline groundwaters in the baltic region through freezing of seawater during glacial periods typical ca cl brines occur in crystalline and metamorphic rocks below freshwater horizons at various localities in sweden and finland total dissolved solids tds range in concentration between 2 and 120 gl 1 and have long been thought to derive from water rock interactions the relationships between na cl and br in these brines suggest however that they were derived from freezing of seawater during glacial periods the brines were subsequently diluted by meteoric waters and their ca mg ratio was increased through water rock interactions in the subsurface the hydrogeological model for both the formation of freeze derived marine brines and their lateral intrusion involves restricted inland marine basins in recent and subrecent polar climatic belts seawater in such basins gradually freezes in response to glaciation the solutes which concentrate in the remaining water body are residual after precipitation of a sequence of minerals which include carbonates mirabilite and hydrohalite hydraulic pressure of the growing ice sheet over the frozen seas is gradually added to the ambient hydrostatic pressure exerted on the brines this together with their increased density increases the intrusional potential of the brines as the land ice cannot exert hydraulic pressure on continental groundwater in the aquifers the balance of pressure favours deep landward intrusion of brines post glacial processes cause the subsurface dilution and replacement of the brines both by seawater and fresh waters the presence of such brines also far from present day coastal settings reflects the shifting of coastlines as a result of isostatic movements and eustatic sea level changes associated with glaciation and deglaciation

230th 238u radioactive disequilibria in tholeiites from the famous zone mid atlantic ridge 36 50 n th and sr isotopic geochemistry we analyzed u th and230th 232th activity ratios for a few tholeiites from the mid atlantic ridge famous zone at 36 50 n the results show a fairly wide scatter for both th u and 230th 232th ratios seawater contamination appears to be responsible for this scatter and for the uranium produces an increase in content yielding a 234u 238u ratio greater than 1 and for the th an increase of the 230th 232th ratio which is a very sensitive indicator for contamination also the latter often is selective u th and sr are not affected in the same manner when discarding all data for contaminated samples the famous zone appears to be very homogeneous with ath u ratio value of 3 05 and a 230th 232th ratio value of 1 24 comparison with other active volcanic areas reveals a negative correlation between 230th 232th and87sr 86sr ratios for present lavas which is indicative of a consistency in th u and rb sr fractionation in the source regions of these magmas the th isotopic geochemistry can thus provide useful information for the study of present volcanism information as valuable as that from sr pb or nd isotopes

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

recycling of crystal mush derived melts and short magma residence times revealed by u series disequilibria at stromboli volcano abstract the presence of crystal mushes in the feeding system of active volcanoes is generally revealed by antecrysts representing the crystalline portion of old magmas recycled in the juvenile material but very little is known about the fate of interstitial liquid hosted within the crystal rich mush i e antemelt u series disequilibria measured in magmas erupted in the past 18 years at stromboli volcano provide the first geochemical evidence of the involvement of antemelt and help constraining the timescales of the processes occurring in the plumbing system of the volcano despite almost constant major and trace element composition significant variations in isotope ratios are observed 230 th 232 th decreases with time whilst 238 u 232 th 226 ra 230 th and 87 sr 86 sr are different in the two types of magma erupted magma with low phenocryst content lp is erupted as pumices during paroxysm and is thought to belong to a deep reservoir highly porphyritic magma hp is erupted during the normal strombolian activity as scoria and during the effusive events as lavas and it is considered to derive from the former one within a shallow reservoir through degassing driven crystallisation mixing and incorporation of antecrysts the distinct 238 u 232 th of lp and hp magma requires the involvement of a component with high 87 sr 86 sr and 238 u 232 th deriving from older magmas erupted earlier in the volcano history up to 2 5 ka the incompatibility of u and th in major mineral phases limits the possible effect of antecrysts hence requiring the involvement of a u and th rich antemelt the decrease of 226 ra excess from lp to hp magmas provides further and independent evidence for the involvement of a few thousands years old antemelt the variation with time of 230 th 232 th within lp and hp magmas is exploited to constrain the residence time of magmas in the deep and shallow reservoir of the volcano to 55 yrs inferred reservoir volume 0 5 km 3 and 2 10 yrs inferred reservoir volume 0 02 0 09 km 3 respectively our results show the occurrence of magmatic processes operating at different timescale within the feeding system of a so called steady state volcano such as stromboli we show that while most of the magma is erupted within few years a portion of it made of both crystals antecrysts and residual liquid antemelt can be stored in the plumbing system for thousands of years to be eventually rejuvenated and mixed back into the shallow reservoir the presence of antemelts may also affect the eruptive mechanism by promoting heat transfer in locked crystal mushes hence favouring their remobilisation

why is it so difficult to classify renazzo type cr carbonaceous chondrites implications from tem observations of matrices for the sequences of aqueous alteration abstract a number of different classifications have been proposed for the cr chondrites this study aims at reconciling these different schemes mineralogy based classification has proved particularly challenging for weakly to moderately altered crs because incipient mineral replacement and elemental mobilization arising from aqueous alteration only affected the most susceptible primary phases which are generally located in the matrix secondary matrix phases are extremely fine grained generally sub micron and heterogeneously mixed with primary nebular materials compositional and isotopic classification parameters are fraught with confounding factors such as terrestrial weathering impact processes and variable abundance of clasts from different regions of the cr parent body or from altogether different planetary bodies here detailed tem observations from eighteen fib sections retrieved from the matrices of nine antarctic cr chondrites eet 96259 gra 95229 gro 95577 gro 03116 lap 02342 lap 04516 lap 04720 mil 07525 and mil 090001 are presented representing a range of petrologic types amorphous fe mg silicates are found to be the dominant phase in all but the most altered cr chondrite matrices which still retain significant amounts of these amorphous materials amorphous fe mg silicates are mixed with phyllosilicates at the nanometer scale the ratio of amorphous fe mg silicates to phyllosilicates decreases as 1 the size of phyllosilicates 2 abundance of magnetite and 3 replacement of fe ni sulfides increase carbonates are only abundant in the most altered cr chondrite gro 95577 nanophase fe ni metal and tochilinite are present small abundances in most cr matrices based on the presence abundance and size of phyllosilicates with respect to amorphous fe mg silicates the sub micron features of cr chondrites have been linked to existing classification sequences and possible reasons for inconsistencies among classification schemes are discussed

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

238u decay series systematics of young lavas from batur volcano sunda arc abstract activities of 238u decay series radioisotopes have been determined for both postcaldera basalts erupted between 1849 and 1974 and genetically related young precaldera dacites from batur volcano bali sunda arc all rocks possess 230th 238u 1 within 2 sigma error indicating that little if any fractionation between th and u occurred during their genesis or in their source regions within approximately the last 350 ka both the basaltic and the dacitic rocks possess 230th 232u 0 71 consistent with both having a common mantle source with an unusually high th u weight ratio of 4 4 and with the dacitic magma having formed by closed system convective fractionation of the same basaltic magma from which the postcaldera lavas were derived the historical basalts possess 226 ra 230 th 1 indicating a significant ra enrichment relative to th and u within approximately the last 8 ka the highest degree of 226ra enrichment occurs in the most mafic basaltic lavas which form a cycle of mafic volcanism between 1888 and 1926 if ra enrichments were produced during mantle melting as a result of its greater incompatibility relative to th then variations in 236ra 230th may reflect the presence at batur of a periodically replenished but poorly mixed open system magma chamber in addition this result implies that the primitive batur basaltic magmas take considerably less than about 8 ka to travel from their mantle source through the batur magma chamber to the surface whole rock 210 pb 226 ra 1 in the youngest historical basalts indicates that pb has been enriched relative to ra within about 100 years of their eruption because pb is expected to be less incompatible then ra during mantle melting the enrichments are probably due to late stage processes such as accumulation of 210pb rich plagioclase phenocrysts or post eruptive condensation of volatile pb salts in vesicles

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

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

application of mass balance and flow simulation calculations to interpretation of mixing at aspo sweden the hydrogeology of a vertical fracture zone at 70 m depth at the access tunnel to the aspo hard rock laboratory was monitored over 3 a for hydrochemical changes that could be effected by construction of a deep repository for high level nuclear waste tunnel construction dramatically disturbed the hydrogeological system but this provided an opportunity to integrate hydrogeochemical and hydrological evaluation of the zone the objective of this study was to evaluate hydrogeochemical evolution groundwater flow and surface water intrusion during the experiment using an integrated approach of geochemical mass balance calculations and numerical flow simulations the dilution of major ions was the dominant hydrochemical trend however hco3 and so4 showed significant enrichment increasing activity of 14c suggested that oxidation of organic c was the likely source of hco3 any mineral source dissolving during the experiment seemed insufficient to account for changes in so4 and current intrusion of sea water was excluded according to the data cation exchange as well as minor calcite reactions in fractures were assumed probable in such temporary chemical conditions conservative two end member mixing models with shallow groundwater in the zone and initial groundwater at tunnel level also assumed remarkable mass transfer several mmol l therefore a third so4 rich end member a regional shallow groundwater type which may mix by lateral flow in the system was tested this was also expected from hydraulic measurements and preliminary flow simulations assuming homogeneity three end member mixing calculations using cl and so4 as conservative tracers give a constant proportion of lateral water in all boreholes after 300 days which is consistent with the steady state character of the flow field in the late part of the experiment to predict reactions on plausible levels needs significant adjustments of initial and final waters indicating uncertainties in the hydrochemical information of the fracture zone in the flow simulations the transmissivities were selected so that the chemical mixing proportions would match simulated portions of flow as closely as possible the simulated total recoveries drawdowns differ from the measurements mainly due to overly simple parametrisation of the transmissivity in the fracture zone however integrating hydrochemistry in flow modelling is considered encouraging in producing additional information of the heterogeneity of a flow structure

regional sediment sources versus the indus river system the plio pleistocene of the peshawar basin nw pakistan abstract sedimentary archives within the peshawar basin in northwest pakistan preserve a record of siliciclastic supply patterns during the plio pleistocene epoch the basin fill consists of fluvial floodplain clays overlain by thick lacustrine glaciofluvial rhythmites with deposits of multiple alluvial fans in the southern parts of the basin and topped by loess deposits in ideal vertical successions framework mineralogical composition and bulk sediment geochemical proxies of these sediments indicate detritus derivation from dominantly acidic igneous sources with contribution from medium grade metamorphic rocks there appears to be no significant contribution from ultramafic mafic or very high grade metamorphic sources in addition sediments from the southern part of the basin support supply from low grade metamorphic rocks and carbonate sediments overall sedimentation occurred in an active continental margin setting under conditions of insignificant chemical weathering the uplift of the attock cherat range during the late pliocene 2 8 ma restricted the indus river from shedding its detritus into the basin therefore the sediments of the peshawar basin do not reflect signatures of the indus river siliciclastics and thus lack the basic igneous geochemical signal which is otherwise typical for the himalayas hinterland on the contrary the geochemical signatures of these sediments favour predominant detritus flux from the acidic rocks of the peshawar plain alkaline igneous complex ppaic and associated metasediments therefore the kabul swat river and other local tributaries of this smaller river system that originated within the ppaic and associated mountains are considered the major transporting agents which contributed siliciclastics into the peshawar basin during the plio pleistocene additionally in the southern part of the basin the uplifting attock cherat range appeared to have contributed detritus in the form of alluvial fluvial fan deposits

tracage par 13c 2h i et uranine dans la nappe de la craie senonienne en ecoulement radial convergent bethune france abstract the behaviour of four labelled solutions h213co3 2h2 o i and uranine is analysed through a field experiment solutions are injected using a pulse condition into a dynamic radial flow runs are performed on 10 22m of a semi confined aquifer senonian chalk aquifer in the bethune s france institute of technology area using the form and position parameters of the break through curves pure convective transfer time tc mean residence time t and the dispersivity it is shown that 1 i and 2h2o have a nearly identical behaviour 2 uranine presents a faster convective and dispersive transfer than the other tracers specially 2h2o and 3 the retardation of 13c h13co 3 is greater than those of 2h2 o and i this retardation suggests a fixation of h13co 3 onto the solid matrix furthermore the transfer disparity of these compounds is due to the difference of their diffusion rates to the stationary liquid phase of the chalk matrix which lead to apparent distinct mean velocity for each tracer

assumptions about the presence of natural glasses on mars natural glasses occur not only on earth but also in lunar rocks and in some meteorites on geological grounds natural glasses could be expected on the surface of mars and their presence would have important implications for the weathering and alteration of the near surface layer ultramafic and mafic magmatism rich in iron and some volatiles appears to have been important on mars as has been impact cratering volcanism and possibly hydrothermal alteration available data indicate that we can presume the past or present existence of volcanic basaltic glasses impact glasses formed by thermal fusion of meteorite impact targets and diaplectic mainly maskelynite glasses conditions appear unsuitable for the formation of tektites on the martian surface and the production of measurable amounts of fulgurite or combustion glass seems improbable prospects for the remote and in situ identification of martian glasses and their subsequent weathering products are discussed and include orbital reflectance and thermal emission spectroscopic measurements and mossbauer spectroscopy from a surface lander

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

40ar39ar and kar dating of altered glassy volcanic rocks the dabi volcanics p n g k ar and 40ar39ar ages have been determined for altered submarine tholeiitic and boninite high mg andesite lavas from the dabi volcanics cape vogel peninsula papua new guinea 40ar39ar whole rock total fusion and plateau ages identify a late paleocene age for the tholeiitic lavas 58 9 1 1 ma and also for the boninitic lavas 58 8 0 8 ma apparent k ar ages for the same samples range from 27 2 0 7 to 63 9 4 5 ma and young k ar ages for glassy boninites are probably due to variable radiogenic 40ar 40ar loss these new ages effectively reconcile previously ambiguous age data for the dabi volcanics and indicate contemporaneous tholeiitic and boninitic volcanism occurring in southeast png during the late paleocene smectites developed as alteration products after glass in oceanic lavas commonly do not retain 39ar during or subsequent to irradiation but in some cases may contain 40ar in the absence of other factors modifying k and ar contents samples which have not lost 40ar from smectite and suffer 39ar loss only are interpreted to have been altered immediately subsequent to the crystallization of the lava whereas samples which have lost 40ar as well as 39ar may be the result of either recent alteration or of continuous 40ar loss since the time of crystallization

the nature of martian fluids based on mobile element studies in salt assemblages from martian meteorites the s cl and br abundances determined in salt assemblages in nakhla and lafayette olivine fracture fillings and in gas rich impact melt grim glasses from shergotty and eet79001 lithologies a b using empa eds aps x ray microprobe techniques are compared with the s and cl abundances determined by gooding and coworkers in similar samples using quadrupole mass spectrometric techniques all the analytical methods yield relatively high cl and low so sub 3 abundances in nakhla indicating a so sub 3 cl ratio of approx 0 2 the same ratio in lafayette secondary salts seems to be approx 2 in the case of grim glasses from shergotty and eet79001 lith a lith b the so sub 3 abundance is found to be high whereas the cl abundance is low yielding a so sub 3 cl ratio of approx 5 300 large errors are associated with these ratios because of low cl signals the salts found in nakhla fracturefillings are inferred to have formed from cl rich fluids high ph near nakhlite source region on mars whereas the secondary minerals found in shergottite grim glasses seem to be associated with so sub 3 rich fluids low ph near shergottite source region on mars the cl rich fluids seem to have infiltrated into the nakhlite source region approx 600 ma ago more whereas the so sub 3 rich fluids likely percolated into the shergottite source region at approx 180 ma or less suggesting the possible existence of two types of fluid sources on mars less

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

230 th 238 u disequilibrium in island arcs evidence from the aleutians and the marianas complex models for magma generation in island arcs have recently been proposed which require varying contributions from three possible sources 1 the mantle 2 subducted altered oceanic crust and 3 sediments see for example refs 1 6 these models involve partial melting of metasomatized mantle the metasomatizing liquids derive from the subducted slab and are large ion lithophile lil element bearing fluids or are themselves partial melts further modification of the chemical composition of the lavas may occur by processes such as shallow level fractional crystallization because the th u ratio is quite different for each of the three possible magma sources mentioned above and as th and u may behave differently during fractionation processes particularly if volatile transport is involved studies of 230 th 238 u disequilibrium have great potential in investigations of arc lavas our data given here imply that the th u ratio in the sources of mariana and aleutian island arc lavas is similar to ocean ridge basalt sources although there is a hint of a somewhat lower th u component in the aleutian source the data also confirm and extend the observations by gill and allegre and condomines that oceanic arc lavas are distinguished from magmas erupted in virtually all other volcanic environments by activity ratios 230 th 238 u 1 implying relative enrichment of uranium

introduction to the hydrogeochemical investigations within the international stripa project abstract the international stripa project 1980 1990 has sponsored hydrogeochemical investigations at several subsurface drillholes in the granitic portion of an abandoned iron ore mine central sweden the purpose has been to advance our understanding of geochemical processes in crystalline bedrock that may affect the safety assessment of high level radioactive waste repositories more than a dozen investigators have collected close to a thousand water and gas samples for chemical and isotopic analyses to develop concepts for the behavior of solutes in a granitic repository environment the stripa granite is highly radioactive and has provided an exceptional opportunity to study the behavior of natural radionuclides especially subsurface production extensive microfracturing low permeability with isolated fracture zones of high permeability unusual water chemistry and a typical granitic mineral assemblage with thin veins and fracture coatings of calcite chlorite seriate epidote and quartz characterize the site preliminary groundwater flow modeling indicates that the mine has perturbed the flow environment to a depth of about 3 km and may have induced deep groundwaters to flow into the mine

a field example of measuring hydrodynamic dispersion in a single fracture a field example of measuring the dispersive properties of a single fracture in fractured plutonic rock is presented the experimental technique involves injecting a slug of conservative tracer into a steady groundwater flow field established between a pumping and recharging borehole and monitoring the tracer breakthrough by sampling the withdrawal water directly the breakthrough curves from two experiments were analyzed with a model which describes the flow field geometry either analytically or numerically and solves for hydrodynamic dispersion analytically a longitudinal dispersivity of 1 40 m was estimated by fitting the model to each set of field data the magnitude of the dispersion was determined to be independent of dispersive effects created by flow through the borehole instrumentation and thought to be purely hydrodynamic in nature

porosity and density of ordinary chondrites clues to the formation of friable and porous ordinary chondrites densities and porosities of meteorites are physical properties that can be used to infer characteristics of asteroid interiors we report density and porosity measurements of 42 pieces of 30 ordinary chondrites and provide a quantification of the errors of the gas pycnometer method used in this study based on our measurements we find that no significant correlation exists between porosity and petrologic grade chemical group sample mass bulk and grain density or shock level to investigate variations in porosity and density between pieces of a meteorite we examined stones from two showers holbrook and pultusk examination of nine samples of holbrook suggests relative homogeneity in porosity and density between pieces of this shower measurements of three samples of pultusk show homogeneity in bulk density in contrast to wilkison and robinson 2000 a study that reported significant variations in bulk density between 11 samples of pultusk finally examination of two friable ordinary chondrites bjurbole and allegan reveal variability in friability and porosity among pieces of the same fall we suggest that friable ordinary chondrites may have formed in a regolith or fault zone of an asteroid

uranium and 10 be enrichments by fluids in andean arc magmas volcanic rocks from subduction settings frequently contain 10be enrichments that have been attributed to sediment subduction1 6 and are often characterized by 238u 230th ratios greater than unity in contrast to mid ocean ridge and ocean island basalts7 8 here we report such an excess of 238u over 230th in historic lavas from the southern volcanic zone of chile 33 42 s the greatest uranium excess is found south of 39 s where 10be 9 be ratios are highest and the trench is filled with sediment these features suggest that both u and 10be enrichments result from preferential partitioning of u and be into a fluid phase during dehydration of the recently subducted sediments the presence of strong 238u 230th disequilibria in basaltic magmas of the southern volcanic zone suggests that the timescale for dehydration melting and eruption in this arc is probably less than 20 000 yr

u series isotope data on lau basin glasses the role of subduction related fluids during melt generation in back arc basins new thermal ionization mass spectrometry u series disequilibrium data are presented for 24 basaltic to dacitic glasses from active spreading centres in the back arc lau basin sw pacific together with additional inductively coupled plasma mass spectrometry trace element analyses and sr nd pb isotope data valu fa ridge samples adjacent to the arc front have high u th and 230th 238u 1 implying a recent 350 ka addition of a u rich slab derived fluid the valu fa data can be combined with existing 230th 238u data for the central tonga arc to infer a fluid addition event at 50 ka the similar sources and time scales for fluid transfer beneath the valu fa ridge and beneath the arc itself suggest that the valu fa ridge is propagating into the arc front region central lau basin samples further behind the arc have lower u th and 230th 238u 1 similar to typical mid ocean ridge basalts morb within the central lau basin a water rich subduction component is seen only in samples closest to the arc and this fluid does not have the high u th composition of the fluid at valu fa melt generation in the central lau basin appears to be dominated by normal ridge type processes but the relatively low 230th 238u for these shallow ridges compared with global morb could be a consequence of increased melt productivity as a result of the elevated water contents the transition from 238u to 230th excesses within the back arc basin is not a smooth function of decreasing addition of a u rich fluid moving away from the arc front but also reflects the complex dynamics between two major mantle domains within the mantle wedge pacific beneath valu fa ridge indian beneath the central lau basin

diffusion in the matrix of granitic rock field test in the stripa mine three field experiments in granitic rock were performed at 360 m depth in a mine to investigate diffusion in the undisturbed rock matrix the results from all three experiments showed that tracers had migrated through the disturbed zone close to the injection hole and a distance into the undisturbed rock matrix these results show that it is possible for dissolved compounds to migrate into the rock matrix in its natural stress environment diffusivities and hydraulic conductivities obtained in this in situ experiment compare well with those obtained in laboratory experiments

segmentation fragmentation and jostling of cratonic basement in and near aspo southeast sweden this paper summarizes studies of the structural geology in and around the island of aspo before the excavation of an underground rock laboratory there to explore the problems of storing spent nuclear fuel in swedish bedrock each of the major reorganizations of the plate boundaries around the baltic shield are recognizable as distinctive fabrics or structures in the 1 7 ga proterozoic cratonic basement exposed at aspo this rock mass segmented along ductile shear zones while in the lower crust fragmented along much the same zones as it rose into the upper crust and has been jostled mainly by repeated reactivation of the same brittle fracture zones ever since the first strains were ductile and penetrative and shared by all the rocks of the region subsequent strains became increasingly localized to the boundaries of relatively unstrained blocks ductile gneiss zones that segmented the crust at amphibolite facies narrowed to mylonites and then faults as the rock mass passed through the ductile brittle transition in greenschist facies at 1 4 ga since they have been in the cool upper crust many of the same shear zones have widened to brittle fracture zones fracture infills of decreasing age consist of different combinations of quartz epidote fe oxihydroxides chlorite prehnite and calcite fragmentation generation of new fractures generally gave way to jostling reactivation of preexisting fractures in successive episodes of brittle intracratonic strain at aspo the regional fracture pattern on all scales consists of different combinations of the same five fracture sets by the end of palaeozoic times the aspo bedrock had accumulated fracture zones with a sufficiently wide range of orientations that subsequent strains involved more jostling than fragmentation plate tectonic and glacial strains of sweden anticipated in the next few million years are also likely to occur along long established zones of weakness that are already available for study

aqueous sulphates from the stripa groundwater system abstract the isotopic composition of aqueous sulphate in the groundwater in the stripa pluton reflects the geochemical history of the groundwater as well as the origin of the sulphur or sulphate in shallow modern groundwater sulphate originates from fallout and the oxidation of pyrite or other reduced forms of sulphur at intermediate depths sulphate of surface origin is lost through bacterial reduction the origin of sulphate of the deep and more saline water is not clearly defined but could be derived from a sedimentary brine which was subject to substantial modification through rock water interaction bacterial sulphate reduction also occurs locally at depths below about 800 m

mobility of iron and nickel at low temperatures implications for 60fe 60ni systematics of chondrules from unequilibrated ordinary chondrites abstract the fe and ni isotopic composition of ferromagnesian silicates in chondrules from unequilibrated ordinary chondrites uocs have been used to estimate the initial abundance of the short lived radionuclide 60 fe in the early solar system however these estimates vary widely and there are systematic discrepancies in initial 60 fe 56 fe ratios inferred from in situ and bulk analyses of chondrules a possible explanation is that the fe ni isotope system in uoc chondrules has not remained closed a necessary condition for isotopic dating and fe and ni have been redistributed since the chondrules formed in order to evaluate this we collected high spatial resolution x ray fluorescence xrf maps of uoc chondrules to better understand the distribution and mobility of fe and ni at the low metamorphic temperatures of these chondrites we used synchrotron x ray fluorescence microscopy to map the distribution of fe ni and other elements in portions of 71 chondrules from 8 uocs types 3 00 3 2 the synchrotron xrf maps show clear enrichment of fe and or ni in fractures ranging down to micrometer scale in chondrules from all uocs analyzed for this study regardless of petrologic type and regardless of whether fall or find indicating that there was significant exchange of fe and ni between chondrules and matrix and that the fe ni system was not closed sixty percent of chondrules in semarkona ll3 00 have fe and ni enrichment along fractures while 80 100 of chondrules analyzed from the other uocs show these enrichments mobilization was likely a result of fluid transport of fe and ni during aqueous alteration on the parent body and or during terrestrial weathering in situ and bulk fe ni analyses that incorporate extraneous fe and ni from chondrule fractures will result in lowering the inferred initial 60 fe 56 fe ratios

martian volatiles in shergottite eeta 79001 new evidence from oxidized sulfur and sulfur rich aluminosilicates abstract high vacuum pyrolysis of individual petrologically documented chips of lithology a pyroxenemaskelynite host rock and lithology c glass inclusion from the same interior portion of eeta 79001 produced sulfur in substantially different proportions of oxidized so2 and reduced h2s s2 species sulfur pyrolyzed from lith a possessed a bulk atomic ratio of s ox s red 0 21 whereas sulfur from lith c displayed a bulk ratio of 0 54 and included a component with a ratio of 1 83 that was released at 950 c most of the oxidized sulfur in lith c was probably dissolved or occluded in glass although some of the sulfate probably existed in sulfur and chlorine rich aluminosilicate mineraloids that occurred as trace quantities of 10 m sized grains parallel sem eds and pyrolysis analyses of control samples including weathered exterior chips of eeta 79001 and of eucrite eeta 79004 produced evidence against antarctic weathering as the source of oxidized sulfur and sulfur rich aluminosilicates in lith c oxidized sulfur evolved from control samples including lith a was accompanied by substantial amounts of h2o and co2 although virtually none of the latter species were found in lith c gypsum was abundant in the weathered eucrite and in weathered lith a but was not found in lith c because lith c contains trapped noble gases and nitrogen of martian atmospheric affinity a logical explanation for its oxidized sulfur would be rock atmosphere reactions that occurred on mars prior to or during the melting event that produced lith c bulk elemental compositions of two varieties of sulfur rich aluminosilicates in lith c can be arithmetically mixed to produce a composition that agrees remarkably well with that of surface fines at the viking landing sites suggesting that lith c might actually contain relict grains of martian weathering or alteration products

biological dissolution and activity of the allende meteorite this paper reports on the effect of the allende meteorite on the integrity of biological material and addresses the question whether it can induce cell damage via oxidative stress and cell mortality the reaction mechanisms addressed herein are studied using electron paramagnetic resonance spectroscopy epr high resolution transmission electron microscopy scanning electron microscopy and energy dispersive spectroscopy high resolution x ray diffraction and the assays for thiobarbituric acid reactive substances tbars and cell viability using 3 4 5 dimethylthiazol 2 yel 2 5 diphenyltetrazolium bromide mtt bromide as determined by the tbars assay allende specimens induced cell damage via oxidative stress the contents of tbars in suspensions containing 1000 ppm of allende and fe 1 x s were 6 8 0 7 and 5 8 0 6 nmol mg protein respectively epr experiments conducted on reaction mixtures containing allende 5 5 dimethyl 1 pyrroline n oxide dmpo and h 2 o 2 showed a quartet signal a 1 2 2 1 intensity and hyperfine coupling constants corresponding to a n 1 49 mt and a h 1 49 mt a signature of the dmpo oh adduct the intensity of the signal depended on the concentration of the solids in suspension while the formation of dmpo oh was limited by h 2 o 2 experiments were conducted to test for the production of the dmpo oh adduct from ferric ions and the plausible generation of ho the role of ethanol ch 3 ch 2 oh as scavenger of ho in allende dmpo suspensions was addressed results showed a six line spectra with hyperfine coupling constants a n 15 8 g a h 22 6 g and g 2 0059 consistent with the formation of the dmpo ch oh ch 3 adduct but not dmpo och 2 ch 3 we explain these findings as the result of formation of ho onto or in proximity to the mineral surface with ch 3 ch 2 oh competing with dmpo for ho and ferric iron playing a lesser role in dmpo transformation our findings are congruent with reported radical scavenging experiments for pyrite under anoxic conditions concluding the formation of ho at surface defect sites experiments conducted in allende desferrioxamine b dfo b suspensions showed the inhibition of the formation of ho by means of decreases in the dmpo oh adduct signal accounted for by the reaction between fe ii and ho to form fe iii and competing reaction mechanisms at the structural fe centers confirming that the production of ho radicals is associated with iron centers and contributes to mineral dissolution small sized magnetite domains present were recognized as catalytic sites for the production of ho radicals the fe 3 o 4 domains present in the allende matrix exhibited a submicron range an elongated hexagonal habit and a high degree of crystallinity supporting the presence of biogenic fe 3 o 4 cell viability was found to be susceptible to the distribution and atomic environment of structural fe

isotope palaeohydrology and the prediction of long term repository behaviour there are considerable well recognized difficulties involved in the investigation of very low permeability rocks by conventional measurements of water potentials and spatial distribution of hydrological parameters such as permeability and effective porosity therefore most studies of predictive behaviour are based on models which when unconstrained by data are often worse than no model at all geochemistry and environmental isotope geochemistry are techniques well suited for hydrological investigations of potential sites of nuclear waste isolation and for constraining predictive models stable isotopes constitutive of the water molecule 2h and 18o may give information on the origin of the water especially 2h which is practically uninvolved in isotope exchange with rock forming minerals variations in stable isotope contents can be related to palaeohydrological and palaeoclimatic conditions whereas 3h is indicative of recent recharge the 13c content of dissolved carbon is related to its origin s and the 14c activity gives a time scale however the initial carbon isotope contents can be modified by various diagenetic effects such as precipitation dissolution of secondary calcite and oxidation of reduced carbon the heavy isotope content of the total dissolved inorganic carbon tdic cannot be interpreted without a detailed knowledge of the carbon chemistry and of the mineralogy and isotope contents of secondary carbonates species of dissolved organic carbon doc with high molecular weights hmw can generally be attributed to soil derived compounds their 14c content may be measured by ams accelerator mass spectrometry thus providing an estimate of the time elapsed since recharge took place chlorine 36 is an interesting potential tool for dating old ground waters because of its long half life 301 kyr and its hydrophilic behaviour it can be also produced in situ in significant amount if the rocks are rich some tens of ppm in u and th in such cases this time dependent build up provides a more systematic radiochronometer of ci residence time in the rock than the decay of cosmic input 36ci provided no cl is leached from the rock the isotopic composition of aqueous sulphur compounds depends on their origin and on their diagenetic evolution the redox reactions of so2 4 reduction or of s2 oxidation are marked by strong isotope effects especially when generated by bacteria sulphate reduction by organic matter is a potential source of dissolved inorganic carbon and may thus interfere with 14c age interpretations after discussion of the possible age and origin of waters and solutes some scenarios of evolution of local and regional palaeohydrological conditions are proposed examples are given with special emphasis on detailed results from the fennoscanian shield stripa project and from northern switzerland

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

magma cumulate mixing identified by u th disequilibrium dating magma mixing is believed to be important in magmagenesis1 particularly in volcanic arcs2 where its influence is revealed by heterogeneous phenocryst populations3 and quenched inclusions4 nevertheless isotope studies particularly of uranium series dis equilibria have concentrated on the analysis of bulk rock samples5 9 comprehensive u th mineral separate data from arc volcanics are scarce10 14 here we present the first u th isotopic evidence for mixing between a crystal mush and a magma in an andesite from the island of santorini in the aegean arc the lava contains crystal populations from two sources of distinct thorium isotope composition one from a basic cumulate the other phenocrysts from a dacite magma the crystal populations have statistically indistinguishable crystallization ages of 79 14 12kyr and 93 29 22kyr and are thought to have physically intermingled just before eruption the crystals did not re equilibrate and hence retain the isotopic compositions and ages of the parental materials

hydrogeochemical conditions and evolution at the aspo hrl sweden abstract the overall hydrogeochemical conditions at and in the near vicinity of the underground experimental aspo hard rock laboratory hrl in se sweden have been investigated groundwater data from more than 400 samples have been compiled and evaluated the groundwater samples represent depths down to 1700 m below sea level and sampling has been performed prior to and during the hrl tunnel excavation episodic events have to a great extent influenced the hydrochemical evolution since the last glaciation which ended some 13 ka ago at that time glacial melt water was flushed under hydraulic pressure down into the fracture system to a depth of at least several hundred metres the next episodic event took place when the baltic freshwater lake transformed into the brackish litorina sea some 7 ka ago at this time aspo was covered by the sea and these denser more saline waters partly replaced the glacial water down to a depth where the density equilibrated with the replacement sea water at some time around 3 4 ka ago aspo started to rise above sea level and meteoric water began to infiltrate the rock the overall trend of increasing salinity with depth may easily be misinterpreted as a fairly simple groundwater system evolving from a two component evolution path between non saline and saline groundwaters however when combining the results from environmental isotopes and the chemical parameters using a new modelling tool named m3 multivariate mixing and mass balance calculations a higher resolution was obtained and a more complex groundwater pattern which reflects the present and paleo hydrogeological events can be recognised the measured groundwater composition was modelled to be a mixture of meteoric past and present baltic seawater glacial or cold climate recharge and brine type of waters the modelling result shows that the processes considered to have a dominating impact on the present aspo groundwater chemistry are mixing both in disturbed and undisturbed systems calcite dissolution and precipitation redox reactions and biological processes the undisturbed groundwater conditions prior to the hrl tunnel construction at aspo consisted of 1 a dominating proportion of meteoric fresh water in the upper 250 m of the aquifer 2 a brackish saline water consisting of mixing proportions of present and ancient baltic sea water and glacial melt water present to a depth of 250 600 m 3 saline water still containing proportions of glacial water which could represent even older glaciations and brines a large portion of which have been stagnant for perhaps millions of years below a depth of 600 m during the hrl tunnel construction there were changes in the composition of the water flowing into the tunnel at different locations although the variation in salinity was relatively small the variations in the mixing proportions of the different water types were substantial

trace element geochemistry of martian iddingsite in the lafayette meteorite the lafayette meteorite contains abundant iddingsite a fine grained intergrowth of smectite clay ferrihydrite and ionic salt minerals both the meteorite and iddingsite formed on mars samples of iddingsite olivine and augite pyroxene were extracted from lafayette and analyzed for trace elements by instrumental neutron activation our results are comparable to independent analyses by electron and ion microbeam methods abundances of most elements in the iddingsite do not covary significantly the iddingsite is extremely rich in hg which is probably terrestrial contamination for the elements si ai fe mn ni co and zn the composition of the iddingsite is close to a mixture of 50 lafayette olivine 40 lafayette siliceous glass 10 water concordant behavior among these elements is not compatible with element fractionations between smectite and water but the hydrous nature and petrographic setting of the iddingsite clearly suggest an aqueous origin these inferences are both consistent however with deposition of the iddingsite originally as a silicate gel which then crystallized neoformed nearly isochemically the iddingsite contains significantly more magnesium than implied by the model which may suggest that the altering solutions were rich in mg 2

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

hydrochemical investigations at finnsjon sweden abstract ground water collected from within and around a highly conductive low angle fracture zone in crystaline rock has been studied in relation to drilling and sampling methods water quality and hydrogeochemical interpretation air flush percussion drilling was demonstrated to be efficient down to 200 250 m at greater depths large amounts of drilling debris and increasing groundwater contamination from air dissolution become apparent a stepwise drilling sampling procedure using water flush rotary drilling in combination with water analysis carried out on site using a mobile laboratory is recommended for future studies the chemistry of the finnsjon ground waters shows a sharp contact between saline and non saline compositions this contact corresponding to a highly conductive low angle fracture zone zone 2 this zone is therefore a horizon along which ground waters of contrasting age and chemistry come into contact and partially mix this mixing has produced a highly supersaturated water resulting in the precipitation of calcite this is most evident in fractures within the more conductive upper part of zone 2 thus partly forming a seal between the two groundwater environments comparison of the finnsjon saline waters with other saline environments particularly in the fennoscandian shield has shown that the ground waters are dominantly marine in origin but with clear modifications resulting from water rock interaction apparent radiocarbon ages range from 9000 to 15000 years in those waters containing tritum levels below detection limits these ages are considered too young and are thought to have resulted from mainly carbon 14 dilution caused by groundwater mixing during the holocene when large quantities of glacial melt water were available this mixing process is also supported by the oxygen 18 data

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

understanding groundwater chemistry using mixing models abstract for the last 15 a skb the swedish nuclear fuel and waste management company has been using the aspo hard rock laboratory hrl as the main test site for the development of suitable tools and methods for the final disposal of spent nuclear fuel major achievements have been made in the development of a new groundwater modelling technique the technique described in this paper is used within the ongoing site investigations of forsmark and simpevarp in sweden the limitations of existing geochemical models used at many sites and the need to decode complex groundwater information in terms of origin mixing transport and reactions at site scale necessitated the development of a new modelling tool m3 multivariate mixing and mass balance calculations in m3 modelling the assumption is made that the groundwater chemistry is a result of mixing as well as water rock interactions the m3 model compares groundwater compositions measured in terms of major ionic components stable isotopes and 3h at a site the model differs from many other standard geochemical models which primarily use water rock interactions rather than mixing to determine groundwater chemical evolution the tool is not dependent on thermodynamic databases potentially uncertain redox and ph data and can deal with the effects of biological reactions the results of mixing calculations can be compared or integrated with hydrodynamic models in this paper the m3 method has been applied to two large hydrogeochemical databases for the aspo hard rock laboratory in sweden the underground research laboratory in canada url together with data from the ongoing site investigations of forsmark and simpevarp in sweden decreasing amounts of precipitation and increasing proportions of saline and brine waters are seen with increasing depth in both areas biogenic waters caused by uptake of co2 from organics causing additional formation of hco3 by water rock interaction occur at intermediate depths in both areas but more glacial water is detected in the url area the origin and evolution of the groundwater at the aspo and url sites have been quantified with the aid of m3 in addition the conceptual present post glacial hydrogeological model has been verified

hydrological and reactive processes during rapid recharge to fracture zones the aspo large scale redox experiment abstract the hydrochemical response of fracture zones to enhanced recharge into the upper bedrock environment has been studied during a 3 a project at the aspo hard rock laboratory hrl in southeastern sweden hydrochemical data obtained during the experiment provides a basis for development of a model for the impact of accelerated recharge on groundwater composition and reactive processes during repository construction and operation tunnel construction at the hrl resulted in a 50 fold increase in recharge rates and a 30 fold decrease in groundwater residence times in the fracture zone studied up to 80 dilution of the native groundwater created the greatest impact on groundwater composition in addition comparison of mass balances for solutes with known conservative behaviour and reactive solutes indicates a significant source of hco 3 so 2 4 and na ions and a significant sink for ca 2 ions within the fracture zone these trends are explained by ion exchange processes and microbial degradation of organic c transported from the soil with recharge the increased microbial activity helps maintain anoxic conditions within the fracture zone the enhanced recharge favours the performance of the geological barrier since anoxic conditions help to protect against corrosion of engineered barriers and because long lived isotopes of np tc and u are less soluble under reducing conditions a secondary impact is the strong dilution which affects trace element speciation and also the stability and possible transport of colloids through ion strength effects results from this experiment are primarily significant for national radioactive waste disposal programs that consider potential repository sites in granite geology and for other programs considering disposal in fractured rock

distribution of sulphides and oxidised sulphur components in snc meteorites abstract stepped combustion analysis of sulphur bearing phases in snc meteorites indicates that sulphates and sulphides are widespread at low abundance in these meteorites the amount of sulphate sulphur is highest in shergottites shergotty 190 ppm and alha 77005 90 ppm nakhla and chassigny contain lower sulphate sulphur contents 80 85 ppm compared with shergottites but their oxidised reduced sulphur ratios are significantly greater 1 5 which indicates higher net oxidation states nakhla and chassigny also contain elemental sulphur as an additional oxidised component an origin of the sulphates and elemental sulphur by terrestrial weathering processes cannot be completely rejected but it is considered more likely that the minerals were incorporated into the host rocks as relict grains of weathering or alteration products formed on the surface of the snc parent body

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

high cesium concentrations in groundwater in the upper 1 2 km of fractured crystalline rock influence of groundwater origin and secondary minerals abstract dissolved and solid phase cesium cs was studied in the upper 1 2 km of a coastal granitoid fracture network on the baltic shield aspo hard rock laboratory and laxemar area se sweden there unusually high cs concentrations up to 5 6 g l 1 occur in the low temperature 1 median laxemar 3 7 g l 1 and groundwater with marine origin aspo hrl 4 2 g l 1 overall lower but variable cs concentrations were found in other types of groundwater the similar concentrations of cs in the saline groundwater which had a residence time in the order of millions of years and in the marine groundwater which had residence times in the order of years shows that duration of water rock interactions is not the single and primary control of dissolved cs in these systems the high cs concentrations in the saline groundwater is ascribed to long term weathering of minerals primarily cs enriched fracture coatings dominated by illite and mixed layer clays and possibly wall rock micaceous minerals the high cs concentrations in the groundwater of marine origin are in contrast explained by relatively fast cation exchange reactions as indicated by the field data and predicted by 1d solute transport modeling alkali cations with low energy hydration carried by intruding marine water are capable of nh 4 in particular and k to some extent replacing cs on frayed edge fes sites on illite in the fracture coatings the result is a rapid and persistent at least in the order of decades buildup of dissolved cs concentrations in fractures where marine water flows downward the identification of high cs concentrations in young groundwater of marine origin and the predicted capacity of nh 4 to displace cs from fracture solids are of particular relevance in the disposal of radioactive nuclear waste deep underground in crystalline rock

natural radioelement solution by circulating groundwaters in the stripa granite natural radioelement concentrations in groundwaters from the fracture flow regime in the stripa granite were monitored during the period 1977 1986 uranium concentrations from depths of 80 m or less and in minewaters from above the hydraulic sink produced by the deepest mining level 410 m range from 10 to 90 ppb 234u238u activity ratios are characteristic of chemical leaching processes at the shallower depths whilst at about 350 m groundwaters occur which have an additional component of 234u by alpha recoil processes at greater depths u concentrations are indicative of the changed redox conditions and are subject to activity ratio enhancement by the alpha recoil process groundwater residence times may be estimated from the rate of such recoil solution of 234u in zones where chemical leaching of u is not active the 222rn contents of the minewaters are extremely high and can be related to the 222rn flux from fracture surfaces and the fracture width the fracture apertures range from 10 mm for the shallow groundwater zone 222rn contents m for water from the deepest borehole section 222rn content 100 kbq kg 1 the activity ratios 234th238u 210pb222rn and 210po222rn have been used to estimate residence times for th pb and po isotopes solution of ra is controlled by chemical rather than alpha recoil processes the 226ra content of the groundwater increases with salinity and is well correlated with groundwater ca content the 228ra226ra activity ratios in the groundwaters suggest that water rock interaction occurs predominantly with the average granitic matrix rather than with highly uraniferous fracture mineralisation the behaviour of ra th and po isotopes may be used to assess that of homologous fission product and actinide constituents of nuclear wastes in groundwaters

multivariate mixing and mass balance m3 calculations a new tool for decoding hydrogeochemical information to support and help hydrochemical evaluation a multivariate mathematical tool named m3 multivariate mixing and mass balance calculations has been created within the aspo hard rock laboratory research programme the computer code can be used to trace the origin of the groundwater and calculate the mixing portions and mass balances from ambiguous groundwater data groundwater composition data used traditionally to describe the reactions taking place in the bedrock can now be used to trace the effect from present and past groundwater flow with increased accuracy the m3 model consists of the following 3 steps multivariate analysis called principal component analysis pca is used to summarise the information from the data set the summarised information shown in the pca plots is used for finding relationships patterns extreme waters and for further m3 modelling from the pca plot mixing calculations are used to calculate the effect of the groundwater mixing on the obtained groundwater composition this so called ideal mixing model is used to calculate the mixing proportions given in for all the groundwater samples the final step in m3 calculations is the mass balance calculations deviations from the ideal mixing model are used to trace the sources and sinks of elements given in mg l which can be due to mass balance reactions the tested margin of error of the model is 10 for the aspo site data but depends on the data to be modelled a mixing portion of less than 10 is regarded as under the detection limit of the model and such calculations are therefore uncertain this method can be used to trace the origin and calculate the mixing portions and effects from the reactions on the observed groundwater composition with a higher resolution and convenience compared to many standard methods

230th 238u disequilibrium systematics in oceanic tholeiites from 21 n on the east pacific rise significant disequilibrium occurs between 230 th and its parent 238 u in a suite of fresh basalt glasses from the rise project study area at 21 n on the east pacific rise the 230 th 232 th activity ratios observed for eight of nine samples from the crest of the axis at this site are constant within analytical uncertainty with a value of 1 22 this observed homogeneity of 230 th 232 th has two possible interpretations first the measured 230 th 232 th can be considered to indicate a mantle source for the rise basalts with th u of 2 5 this interpretation however conflicts with the proposed correlation between 230 th 232 th and 87 sr 86 sr 1 which predicts that 230 th 232 th should equal 1 33 at the rise site a second possible interpretation is that radioactive decay of 230 th in the basalts themselves or in a magma chamber has decreased 230 th 232 th from 1 33 to the observed values the required time span is 11 000 to 100 000 years however petrologic arguments rule against long residence time in a magma chamber and the spreading rate of this section of the east pacific rise 6 cm yr predicts that the maximum age for axis basalts is 27 000 years both interpretations of the measured 230 th 232 th imply a low th u ratio for the rise basalt source and suggest that the morb source at this location is depleted in th with respect to u relative to primitive mantle or bulk earth in spite of their constant 230 th 232 th the basalts from 21 n have wide ranges of measured th u and thorium and uranium concentrations in apparent conflict with the common assumption that these two elements have very small similar crystal liquid partition coefficients participation of an accessory phase with high th and u concentrations during partial melting or fractional crystallization appears to be required to explain this anomaly major and other trace element compositions provide more information about petrogenetic processes although fractional crystallization can explain the variations in major element composition a more complex process such as continuous melting is required to account for the observed trends in trace element compositions in addition to its use as a tracer the 230 th 238 u disequilibrium technique is capable of putting some constraints on the timing of fractionation events and it may eventually lead to a method for dating very young mid ocean ridge basalts

deuterium oxygen 18 and tritium in stripa groundwater deuterium oxygen 18 and tritium determinations show that groundwaters in the fractures of the stripa granite are of meteoric origin not affected by secondary isotope effects evaporation or isotope exchange deep ground waters have lower 18o and 2h contents than recent shallow groundwaters the differences are most likely due to recharge during cooler climatic conditions however no age information can be derived because recharge could have occurred before the last major climatic improvement following the last deglaciation during minor climatic variations during the more recent past or could be the result of regional groundwater flow low 18o contents are paralleled by increasing salinities with highest salinities limited to a narrow fracture zone at a depth of about 800 m below ground surface most saline waters sampled appear to represent mixtures of a saline component with an isotopically depleted water and local fresh water the presence of young groundwaters is indicated by bomb produced 3h all surface boreholes contain tritium indicating residence times 35 years however tritium is also found in some boreholes drilled at the 300 m mine levels and its presence may be due to flows induced in response to heater tests low but detectable 3h contents about 0 1 to 1 tu in v2 at about 850 m below groundsurface are discussed either as subsurface production and or as a result of admixtures of small amounts of recent water to old groundwater

anomalously old 40 ar 39 ar ages of antarctic meteorites due to weathering in 1969 the japanese antarctic research expedition found nine meteorites on bare ice near the yamato mountains east antarctica1 since then 5 000 meteorites have been found in antarctica by meteorite search teams2 3 they are generally estimated to have been exposed on the ice sheet surface for 103 104 yr ref 4 and have been shown to have been subject to weathering effects5 8 by comparing the 40ar 39ar age patterns for the inner and outer portions of two antarctic meteorites we have found that the oxidized outer portions show anomalously old 40ar 39ar ages which exceed 4 600 myr in the intermediate temperature fractions of around 800 1 000 c this is contrary to the generally expected tendency as a result of ar loss caused by weathering of a sample because old 40ar 39ar ages are accompanied by an increase of 36ar we attribute the anomalous ages to the incorporation of terrestrial atmospheric ar in some phase like haematite which might be changed from goethite during neutron irradiation

aleutian lead isotopic data additional evidence for the evolution of lithospheric plumbing systems abstract lead isotopic ratios and concentrations have been measured in lavas from the aleutian volcanic centers of adak 12 and atka 12 whereas lavas from atka have very small pb isotopic ranges 206 pb 204 pb 18 78 18 86 207 pb 204 pb 15 55 15 62 208 pb 204 pb 38 31 38 52 those from adak have ranges nearly twice as large 206 pb 204 pb 18 34 18 86 207 pb 204 pb 15 47 15 63 208 pb 204 pb 37 81 38 56 on lead lead isotopic diagrams atka data form tight clusters whereas those from adaak define a well developed linear trend extending from the atka field toward less radiogenic values at a given 206 pb 204 pb the lavas from both islands plot in the morb trend for 208 pb 204 pb but atka lavas plot above the morb 207 pb 204 pb 206pb 204pb trend and those from adak fall both within and above the trend lead contents in lavas from atka increase four fold 5 21 ppm over the compositional range of the volcanic suite 49 68 sio2 in contrast actak lavas 49 65 have concentration levels of 0 6 13 ppm and display no simple correlation with sio2 the lead isotopic data alone can be explained by three different processes model 1 assigns lead isotopic differences to original magma source heterogeneity according to model 2 the isotopic ratios of a primary non radiogenic component from the mantle are elevated by the addition of an isotopically enriched slab derived component in contrast model 3 assumes a primary radiogenic magma produced by melting of the slab is contaminated by a non radiogenic lithospheric component during conduit formation because these models all adequately explain the lead isotopic data supplementary geologic petrographic geochemical and isotopic data must be used to select the most likely model careful consideration of the evidence suggests model 3 best explains our extensive lead isotopic data as well as other characteristics of aleutian lavas our study suggests detailed isotopic studies of individual volcanic centers arc or otherwise can be extremely useful in understanding the complex processes of magma generation extraction ascent and evolution

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 alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

usercalc a web based uranium series calculator for magma migration problems 1 measured departures from secular equilibrium in the uranium series decay chains provide important constraints on the rates of recent mantle and crustal processes nevertheless the inferences drawn from these observations depend upon the models used to interpret them while several useful models for u series exist they are not all equally easy to use and it is often the ease of use rather than the utility of the model that determines which models are applied the purpose of this paper is to level the playing field by making some of the more general u series transport models accessible to a wider community through the usercalc web site available from lamont doherty earth observatory at www ldeo columbia edu mspieg usercalc these models calculate the effects of both melting and melt transport on two u series chains 238u 230th 226ra and 235u 231pa and allow the user to input their own petrological insight and data to explore the behavior of this model the purpose of the site is to provide a tool that can spur additional collaborations between geophysicists and geochemists as well as drive more rapid exploration evolution of u series models

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

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval

differences in the degree of weathering between antarctic and non antarctic meteorites inferred from infrared diffuse reflectance spectra abstract infrared diffuse reflectance spectra were measured for antarctic and non antarctic meteorites to compare the degree of terrestrial weathering by using the integrated intensity of absorption bands near 3 m caused by hydrous minerals and the intensity of absorption bands near 7 4 m 1350 cm 1 probably caused by hydrous carbonates non antarctic ordinary chondrite finds usually show large values of the integrated intensity of the 3 m band whereas non antarctic ordinary chondrite falls show small intensities some antarctic ordinary chondrites are as fresh as non antarctic ordinary chondrite falls in the sense of the integrated intensity of the 3 m band some antarctic eucrites show large values of the integrated intensity of the 3 m band although the degree of weathering on the a b c scale is reported to be a weathering produced hydrous carbonates seem to be ubiquitous in antarctic ordinary chondrites because the spectra of all the antarctic ordinary chondrites measured show the presence of the 7 4 m band non antarctic ordinary chondrite falls show very weak 7 4 m bands suggesting only little weatheringproduced hydrous carbonates diffuse reflectance spectra were also measured for the mixtures of akaganeite goethite artinite or calcite with the nuevo mercurio h5 ordinary chondrite to examine spectral changes and to compare them with those of meteorites absorption bands near 7 m of diffuse reflectance spectra are sensitive to the presence of carbonates

mariana trough basalts mtb trace element and srnd isotopic evidence for mixing between morb like and arc like melts abstract mariana trough basalt mtb glasses from zones of of active seafloor volcanism have incompatible trace element compositions which are intermediate between normal morb and basaltic rocks from the active northern mariana island arc miab the chemical variation is observed in trace elemental abundances and ratios such as lil lil and lil hfs mtb glasses with high lil hfs and ba sm ratios and low k rb k ba and sm nd ratios have more enriched sr and nd isotopic compositions comparison of the sr nd isotopic compositions of mtb and miab suggests that the source region within the mantle wedge is heterogeneous the diverse trace element and isotopic compositions of mtb glasses both within and between dredge sites near 18 n imply small scale source heterogeneity correlation between sm nd and143nd 144nd of the mtb glasses is interpreted as due to recent binary mixing rather than closed system evolution of a common homogeneous source mixing of melts at or near the source region between a mantle component with long term lree and lil element depletion morb like and a relatively enriched component with lower integrated143nd 144nd arc like is suggested by trends of the mtb data on ratio ratio ratio element and element element plots

the porosities of ordinary chondrites models and interpretation densities and porosities for 285 ordinary chondrites have been assembled and analyzed measured chondrite porosities are bimodal finds have an average porosity of 30 we conclude that mild degrees of weathering fill pore spaces lowering grain densities and porosities without significantly changing the bulk size or mass of the sample by assuming an original pristine grain density as a function of the meteorite s mineralogy determined by its class we can derive model pristine porosities these model porosities cluster around an average value of 10 for all classes of ordinary chondrites ordinary chondrites do not show any correlation of porosity model or measured with petrographic grade or sample size over a range from 0 2 g to 2 kg however we do see a correlation between shock state and porosity shock blackened meteorites are less porous than other meteorites furthermore less severely shocked meteorites show a much broader range of porosities with the maximum porosity seen among meteorites of a given shock class falling linearly as a function of that shock class this is consistent with the idea that shock compresses and closes pore space analysis of meteorite porosity provides a lower bound to the fine scale porosity of asteroids our densities even with 10 primordial porosity are significantly higher than inferred densities of possible asteroid parent bodies these asteroids are probably loose piles of rubble

alteration assemblages in the nakhlites variation with depth on mars secondary mineral assemblages in the nakhlite meteorites lafayette governador valadares gv nakhla yamato y 000593 y 000749 have been studied using scanning electron microscopy transmission electron microscopy and electron probe micro analysis the different nakhlites have distinctive secondary assemblages in their olivine grains and mesostases showing compositional fractionation correlated with their relative depths below the martian surface fracture filled veins in lafayette at the bottom of the pile consist of a siderite phyllosilicate fe oxide hydrated silicate gel assemblage corresponding veins in nakhla and gv further up the pile are predominantly a siderite gel assemblage with additional evaporites including gypsum y 000593 y 000749 veins are dominated by gel the gel s mg mg fe ratio decreases from lafayette 0 37 to gv 0 32 nakhla 0 24 and y 000593 0 15 we suggest that hydrothermal fluid flowed up this depth profile initiated by melting of buried h2o co2 ice our results show a complex mix of fe rich phyllosilicate within the veins and mesostasis of lafayette with d spacings of 0 7 1 1 nm suggesting a mixture of smectite and serpentine the phyllosilicate formed at close to neutral ph 150 c we also suggest that water rock ratios w r of 1 10 occurred in lafayette with smaller values for the other nakhlites this is reflected in the volume of alteration minerals 10 of olivine in lafayette to 3 in nakhla textural evidence of rapid cooling together with the w r and likely fluid velocities suggest that the secondary assemblages formed quickly e g within months a model is proposed in which the secondary assemblages formed in an impact induced hydrothermal system terminated by precipitation of the gel and evaporation of soluble salts

a test of a quartz eclogite source for parental aleutian magmas a mass balance approach the observation that magmatic conduits evolve with time has provided a new framework within which to interpret aleutian compositional and isotopic data accordingly a two stage physical model of aleutian magma genesis has been developed and used to model quantitatively geochemical and isotopic mass balance relations parental magmas approximated by high alumina basalts are presumed to be generated by partial melting of eclogite and subducted sediment the incorporation of sediment produces elevated parental magma sr and pb isotopic ratios but lowered epsilon nd relative to morb if these magmas ascend along well established conduits their isotopic characteristics are little changed during ascent in immature conduits interaction with oceanic lithosphere produces significant isotopic variability according to this model the isotopic and geochemical characteristics of parental magmas are fixed by mixing eclogite and sediment melts as a test we have quantitatively examined the mass balance rel

denticles on chain silicate grain surfaces and their utility as indicators of weathering conditions on earth and mars abstract denticulated margins also known in older literature as sawtooth cockscomb or hacksaw terminations are a common feature of pyroxenes and amphiboles visible in optical and electron microscopes denticles are remnants of undissolved material that formerly constituted the walls between elongate etch pits the characteristic aqueous dissolution form of chain silicate minerals denticles occur widely in terrestrial near surface materials that have experienced low temperature aqueous alteration including chemically weathered regoliths soils in a variety of climatic and geomorphic settings sediments and sedimentary rocks ranges of dissolution forms and dimensions commonly tens of microns in length are identical on both pyroxenes and amphiboles in these materials denticles on terrestrial chain silicates are formed by low temperature aqueous alteration denticles on a soil mineral grain of unknown composition at the phoenix mars lander site and on terrestrial pyroxenes naturally weathered in terrestrial low temperature aqueous environments are broadly similar in size shape and orientation relationships between denticles however quantitative morphometric parameters vary among different terrestrially weathered pyroxenes and even between different images of compositionally identical pyroxenes from the same naturally weathered sample such variations are too large to allow simple identification of minerals of unknown composition from morphology alone nevertheless the overall morphological similarities are consistent with a low temperature aqueous corrosion origin of denticles at the phoenix mars lander site

the isotope geochemistry of carbon in groundwater at stripa the carbon isotopic composition of the total dissolved inorganic carbon in groundwater associated with a granitic pluton at stripa sweden reflects both inorganic and organic carbon sources following the uptake of soil carbon dioxide calcite dissolution dominates the geochemical evolution of shallow groundwater calcite saturation is reached at a depth of about 100 m in deeper waters geochemical release of ca and increasing ph cause calcite precipitation radiocarbon contents suggest carbon and water ages in excess of 20 000 years for waters at 300 400 m depth in deep groundwaters with enhanced salinities organic carbon is added to the dissolved inorganic carbon either through bacterial activity e g sulphate reducing bacteria or the oxidation of organic compounds such as methane the lowest radiocarbon contents were measured at the 300 400 meter levels and not in the deepest fluids the distribution of 13c in the deep groundwaters suggests the existence of well defined flowsystems with limited active hydraulic interaction isotope analyses on fracture calcites substantiate the complex geochemical history of the pluton

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

halogen contamination in antarctic h5 and h6 chondrites and relation to sites of recovery abstract the distribution of the elements f cl br and i was analysed in layers removed stepwise from antarctic h5 and h6 chondrites all meteorites show higher concentrations of these elements on their surfaces than in their interiors the degree of halogen enrichment cannot be correlated with the degree of visual weathering and is proportional to the time the meteorites were residing on the surface of the antarctic ice during this period aerosols salts and gaseous components are deposited on the surfaces of the meteorites and diffuse into their interior the observed contamination level of the meteorites is influenced by leaching properties and diffusion behaviour of the individual halogens the major contamination source for f cl and probably br is air borne seaspray for i it is the gaseous compound methyl iodide ch3i produced by biological processes in the sea methyl iodide and its oxidation products formed in the antarctic atmosphere e g i2 can be transported over longer distances to the interior of antarctica than air borne seaspray therefore the ratio of the halogen contamination is related to the collection site of the meteorites all meteorites that were found in the antarctic interior are contaminated to a lesser degree by f cl and br relative to i than those found near the coast the measured enrichment ratio of i f is a function of the distance between the collection site and the open sea and increases from the allan hills to the thiel mountains by revealing the degree of contamination of a meteorite it is possible to determine its maximum surface residence time on the antarctic ice

large scale intrusion of shallow water into a vertical fracture zone in crystalline bedrock initial hydrochemical perturbation during tunnel construction at the aspo hard rock laboratory southeastern sweden on march 13 1991 construction of the entrance tunnel to the aspo hard rock laboratory opened a vertical fracture zone at a depth of 70 m this provides an opportunity to study geochemical changes resulting from shallow water inflow into a crystalline bedrock aquifer as anticipated during construction and operation of a deep repository for spent nuclear fuel chloride ion is a natural conservative tracer for mixing between the dilute cl 10 mg l 1 shallow groundwater and the saline cl 5000 mg l 1 native groundwater of the fracture zone a sharp dilution front corresponding to 80 dilution of the native groundwater indicated arrival of shallow groundwater in the entrance tunnel after 3 weeks in spite of this large input of shallow water the fracture zone remains predominantly anoxic major element hydrochemistry and carbon and oxygen stable isotope data indicate large inputs of alkalinity and biogenic co2 g input of organic carbon with shallow groundwater provides a possible energy and carbon source for anaerobic respiration there is no evidence for sulfate reduction and fe iii oxyhydroxide fracture minerals are the only other dominant electron acceptor observed

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

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

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

laboratory experiments on the weathering of iron meteorites and carbonaceous chondrites by iron oxidizing bacteria batch culture experiments were performed to investigate the weathering of meteoritic material by iron oxidizing bacteria the aerobic acidophilic iron oxidizer a ferrooxidans was capable of oxidizing iron from both carbonaceous chondrites murchison and cold bokkeveld and iron meteorites york and casas grandes preliminary iron isotope results clearly show contrasted iron pathways during oxidation with and without bacteria suggesting that a biological role in meteorite weathering could be distinguished isotopically anaerobic iron oxidizers growing under ph neutral conditions oxidized iron from iron meteorites these results show that rapid biologically mediated alteration of extraterrestrial materials can occur in both aerobic and anaerobic environments these results also demonstrate that iron can act as a source of energy for microorganisms from both iron and carbonaceous chondrites in aerobic and anaerobic conditions with implications for life on the early earth and the possible use of microorganisms to extract minerals from asteroidal material

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

calcium carbonate and sulfate of possible extraterrestrial origin in the eeta 79001 meteorite abstract two varieties of ca carbonate were found in a total of three interior 2 cm depth samples of glass inclusions from the shergottite meteorite elephant moraine antarctica a79001 two of the samples including the largest deposit around a vug near the center of the meteorite 8 cm depth contained veins of granular calcite with significant magnesium avg atomic mg mg ca 0 14 0 15 and phosphorus avg atomic p ca 0 04 either as mg calcite with dissolved p or as calcite with very finely intergrown mg bearing phosphate the second variety which occurred in a third sample with a previously documented high concentration of trapped gases consisted of disseminated 10 20 m anhedral grains of nearly pure caco3 and was intimately associated with laths and needles of ca sulfate possibly gypsum the coexisting carbonate and sulfate appeared to be partially decrepitated relict grains that were trapped during rapid solidification of quench textured pyroxene and glass for at least the latter occurrence textural relationships clearly indicate a pre terrestrial origin for the salts all evidence considered it is probable that both varieties of cacarbonate and the ca sulfate formed on a planetary body probably mars before the meteorite fell on earth

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

isotopic and incompatible element constraints on the genesis of island arc volcanics from cold bay and amak island aleutians and implications for mantle structure reply to a critical comment by m r perfit and r w kay