an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

molybdenum and tungsten in volcanic rocks and in surface and 100 c ground waters in iceland abstract the concentrations of mo and w in tholeiite series basaltic to silicic volcanics in iceland increase with the concentrations of incompatible magmatic elements in normal mid ocean ridge basalt morb mo and w levels are as low as 0 03 and 0 01 ppm but in rhyolites they are up to 4 and 1 3 ppm respectively in the slightly evolved tertiary tholeiites of the main study area of skagafjordur northern iceland mo and w concentrations are 1 01 and 0 32 ppm respectively on average surface waters in this area typically contain 10 000 years waters in river and ground waters the average mo w ratio is the same as that of the basalt host rock on the other hand in peat soil waters the average mo w ratio is higher due to adsorption processes involving w in river and ground waters both mo and w display conservative behavior progressive water rock interaction leads to successively lower aquatic b mo and b w ratios however the b mo and b w ratios of the most reacted waters are considerably higher than those of the basalt due to non stoichiometric rock dissolution b is dissolved preferentially to both mo and w because b is largely present in a soluble form but mo and w are concentrated in the fe ti oxides these minerals are stable under both surface and sub surface conditions i e the waters are over saturated with respect to these minerals the main supply of mo and w to surface waters is from dissolution of plagioclase and pyroxene as well as volcanic glass olivine is not an important source due to its scarcity in the basalts in

high resolution sims analysis of common lead an evaluation of the sims technique for precise analysis of common lead in natural materials has been undertaken the instrument used is a new generation of high resolution high transmission ion probe the isolab 120 two glass standards nbs 610 and waterford have been characterised for their pb isotope composition by tims repeated sims analyses of these materials have failed to reveal any resolvable mass discrimination of pb isotopes the mass discrimination is shown to be 0 2 amu 1 in all cases comparison of sims pb analyses of natural ferromanganese samples with tims pb isotope analyses on adjacent portions are in good agreement and support the conclusion that mass discrimination is minimal the basic performance characteristics of the instrument operated at high mass resolving power are detailed in terms of transmission extraction efficiency pb ion yield from different materials and repeatability of measurements the precision and accuracy of common pb isotope ratio measurement by sims approaches that of tims to the point where application to palaeo oceanographic problems for example become entirely feasible

re assessing the surface cycling of molybdenum and rhenium we re evaluate the cycling of molybdenum mo and rhenium re in the near surface environment world river average mo and re concentrations initially based on a handful of rivers are calculated using 38 rivers representing five continents and 11 of 19 large scale drainage regions our new river concentration estimates are 8 0 nmol kg 1 mo and 16 5 pmol kg 1 re natural anthropogenic the linear relationship of dissolved re and so 2 4 in global rivers r 2 0 76 indicates labile continental re is predominantly hosted within sulfide minerals and reduced sediments it also provides a means of correcting for the anthropogenic contribution of re to world rivers using independent estimates of anthropogenic sulfate approximately 30 of re in global rivers is anthropogenic yielding a pre anthropogenic world river average of 11 2 pmol re kg 1 the potential for anthropogenic contribution is also seen in the non negligible re concentrations in precipitation 0 03 5 9 pmol kg 1 and the nmol kg 1 level re concentrations of mine waters the linear mo so 2 4 relationship r 2 0 69 indicates that the predominant source of mo to rivers is the weathering of pyrite an anthropogenic mo correction was not done as anthropogenically influenced samples do not display the unambiguous metal enrichment observed for re metal concentrations in high temperature hydrothermal fluids from the manus basin indicate that calculated end member fluids i e mg free yield negative mo and re concentrations showing that mo and re can be removed more quickly than mg during recharge high temperature hydrothermal fluids are unimportant sinks relative to their river sources 0 4 mo and 0 1 pre anthropogenic re we calculate new seawater response times of 4 4 10 5 yr smo and 1 3 10 5 yr sre pre

pb isotopic evidence for an early enriched crust on mars abstract martian meteorite nwa 7533 is a regolith breccia that compositionally resembles the martian surface measured by orbiters and landers nwa 7533 contains monzonitic clasts that have zircon with u pb ages of 4 428 ga the pb isotopic compositions of plagioclase and alkali feldspars as well as u pb isotopic compositions of chlorapatite in the monzonitic clasts of nwa 7533 have been measured by secondary ion mass spectrometry sims the u pb isotopic compositions measured from the chlorapatite in nwa 7533 yield an age of 1 357 81 ga 2 the least radiogenic pb isotopic compositions measured in plagioclase and k feldspar lie within error of the 4 428 ga geochron these data indicate that the monzonitic clasts in nwa 7533 are a product of a differentiation history that includes residence in a reservoir that formed prior to 4 428 ga with a value 238 u 204 pb of at least 13 4 1 7 2 and a value 232 th 238 u of 4 3 this value is more than three times higher than any other documented martian reservoir these results indicate either the martian mantle is significantly more heterogeneous than previously thought value of 1 14 vs 1 5 and or the monzonitic clasts formed by the melting of martian crust with a value of at least 13 4 therefore nwa 7533 may contain the first isotopic evidence for an enriched differentiated crust on mars

pb evolution in the martian mantle abstract the initial pb compositions of one enriched shergottite one intermediate shergottite two depleted shergottites and nakhla have been measured by secondary ion mass spectrometry sims these values in addition to data from previous studies using an identical analytical method performed on three enriched shergottites alh 84001 and chassigny are used to construct a unified and internally consistent model for the differentiation history of the martian mantle and crystallization ages for martian meteorites the differentiation history of the shergottites and nakhla chassigny are fundamentally different which is in agreement with short lived radiogenic isotope systematics the initial pb compositions of nakhla chassigny are best explained by the late addition of a pb enriched component with a primitive non radiogenic composition in contrast the pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the martian mantle that can be modeled based on recent results from the sm nd system the shergottites have been linked to a single mantle differentiation event at 4504 ma thus the shergottite pb isotopic model here reflects a two stage history 1 pre silicate differentiation 4504 ma and 2 post silicate differentiation to the age of eruption as determined by concordant radiogenic isochron ages the values 238u 204pb obtained for these two different stages of pb growth are 1 of 1 8 and a range of 2 from 1 4 4 7 respectively the 1 value of 1 8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto earth suggesting this is the initial value for inner solar system bodies when plotted against other source radiogenic isotopic variables sri 187 os e 143 nd and e 176 hf the second stage mantle evolution range in observed mantle values display excellent linear correlations r 2 0 85 and represent a spectrum of martian mantle mixing end members depleted intermediate enriched

geochemistry of atmospheric aerosols generated from lava seawater interactions 1 trace elements were measured in the aerosol plume produced by lava seawater interactions along the shoreline of kilauea volcano hawaii plume concentrations were normalized relative to hawaiian basalt composition and showed a linear log log covariation with their emanation coefficient an indicator of element volatility normalized aerosol concentrations also consistently covaried with corresponding normalized concentrations in dilute fumarolic gas from kilauea volcano and fumarolic gas condensates from kudryavy and merapi volcanoes despite different mechanisms of element volatilization conservatively estimated regional ocean deposition rates of cu cd ni pb mn zn fe and p were 50 times background rates thus upper ocean volcanism may be an important source of both toxic and nutrient elements to the surrounding ocean it appears unlikely however that shallow ocean volcanism can exert a significant impact on the global ecosystem even during massive lava emplacements

the concept of joint saturation and its application two of the major joint driving mechanisms are joint normal stretching and poroelastic shrinkage and these lead to joint sets commonly associated with structural bending and natural hydraulic fracturing respectively regardless of joint driving mechanism joint infilling is a nonhomogeneous poisson process in the presence of stress shadows through probability modeling we show that in all cases joint spacing is best fit with gamma distributions the shape parameter of the best fit gamma distribution to joint spacing data is a quantitative means to assess the extent of saturation which is represented in a new parameter the joint saturation ratio jsr to test the utility of jsr we call upon published structural bending joint data elk basin lilstock and rives plate bending experiment the shape parameters for these well developed structural bending joints are equal to around three corresponding to a jsr of approximately 30p using the same analysis on the spacing of natural hydraulic fractures collected from outcrops in the gas prone devonian sections of the appalachian basin we find that natural hydraulic fractures differ in two aspects from structural bending joints first the joint spacing is proportional to bed thickness in bedded rocks but not in gas shale sections second the joint saturation of natural hydraulic fractures is generally lower than in well developed structural bending joints thus the jsr is a means to distinguish the joint driving mechanism and to represent joint saturation level independent of bed thickness effects it can be used to distinguish natural fractures from drilling induced fractures and to improve the fracture network modeling

new insights on natural hydraulic fractures induced by abnormally high pore pressures in this paper i identify a mechanism by which high pore pressures acting alone can cause natural hydraulic fractures and keep them open for extended time periods such fractures may occur in tectonically extensional neutral or compressional settings although the fractures orientations will be governed by the regional stress field they can form and remain open without a horizontal stress differential large enough to induce regional scale dilation rather these fractures are a result of compression or shrinkage of the host rock s solid constituents grains as such grain shrinkage caused by a pore pressure increase is analogous to grain shrinkage caused by temperature decreases a process that also causes extension fractures in rocks i call these fractures hydra lic shrinkage fractures to distinguish them from other types of hydraulic fractures that may be induced by intrusive fluids other than the dominantly present pore fluid i present sample calculations to demonstrate the theoretical basis for these fractures and include various examples to show how fracture potential and orientation are affected by the host rock s mechanical properties and different geological processes these examples indicate that pore pressure magnitude cannot be used alone as a fracture criterion instead fracture potential and orientation depend on the geologic processes causing the excess pore pressures and the mechanical properties of the unfractured rock in general vertical shrinkage fractures are favored and should occur at lower pore pressures in less compressible rocks buried in basins with lower geothermal gradients

solving the martian meteorite age conundrum using micro baddeleyite and launch generated zircon the age of the representative martian meteorite nwa 5298 is determined using spatially correlated electron beam nanostructural and uranium lead isotopic measurements of microminerals resolving a paradox of different age interpretations for the evolution of martian crust a few of the many meteorites that fall to earth are of martian origin the true age of these rare samples of the martian surface has been the subject of a decades long debate with interpreted ages differing by up to 4 billion years desmond moser and colleagues resolve this problem using a new approach to dating meteorite launch events through nanoscale investigation of crystal growth zoning and structures their analysis of the resistant micromineral baddeleyite and host igneous minerals in the highly shocked martian meteorite northwest africa 5298 reveals it as a crystallization product of martian volcanism of the past 400 million years previous estimates of a 4 billion year age of formation have actually dated a remnant signature of the ancient mantle melting event from which the magma was derived these findings confirm the presence of an ancient non convecting mantle beneath a relatively young volcanic martian crust invaluable records of planetary dynamics and evolution can be recovered from the geochemical systematics of single meteorites1 however the interpreted ages of the ejected igneous crust of mars differ by up to four billion years1 2 3 4 5 6 a conundrum7 due in part to the difficulty of using geochemistry alone to distinguish between the ages of formation and the ages of the impact events that launched debris towards earth here we solve the conundrum by combining in situ electron beam nanostructural analyses and u pb uranium lead isotopic measurements of the resistant micromineral baddeleyite zro2 and host igneous minerals in the highly shock metamorphosed shergottite northwest africa 5298 ref 8 which is a basaltic martian meteorite we establish that the micro baddeleyite grains pre date the launch event because they are shocked cogenetic with host igneous minerals and preserve primary igneous growth zoning the grains least affected by shock disturbance and which are rich in radiogenic pb date the basalt crystallization near the martian surface to 187 33 million years before present primitive non radiogenic pb isotope compositions of the host minerals common to most shergottites1 2 3 4 do not help us to date the meteorite instead indicating a magma source region that was fractionated more than four billion years ago9 10 11 12 to form a persistent reservoir so far unique to mars1 9 local impact melting during ejection from mars less than 22 2 million years ago caused the growth of unshocked launch generated zircon and the partial disturbance of baddeleyite dates we can thus confirm the presence of ancient non convecting mantle beneath young volcanic mars place an upper bound on the interplanetary travel time of the ejected martian crust and validate a new approach to the geochronology of the inner solar system

molybdenum isotope behaviour in groundwaters and terrestrial hydrothermal systems iceland abstract molybdenum mo isotopes have proved useful in the reconstruction of paleoredox conditions their application generally relies upon a simplified model of ocean inputs in which rivers dominate mo fluxes to the oceans and hydrothermal fluids are considered to be a minor contribution to date however little attention has been paid to the extent of mo isotope variation of hydrothermal waters or to the potential effect of direct groundwater discharge to the oceans here we present mo isotope data for two icelandic groundwater systems m vatn and eistareykir that are both influenced by hydrothermal processes relative to nist 3134 0 25 the cold n 13 show little if any fractionation from the host basalt 98 95 mobasalt 0 16 to 0 12 and are on average lighter than both global and icelandic rivers in contrast waters that are hydrothermally influenced 10 c possess isotopically heavy 98 95mohydrothermal values of 0 25 to 2 06 n 18 with the possibility that the high temperature endmembers are even heavier although the mechanisms driving this fractionation remain unresolved the incongruent dissolution of the host basalt and both the dissolution and precipitation of sulfides are considered regardless of the processes driving these variations the 98mo data presented in this study indicate that groundwater and hydrothermal waters have the potential to modify ocean budget calculations

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

researching the earth and a few of its neighbors during my career our knowledge of erupting geysers and volcanoes in the solar system has exploded in this prefatory i tell how i became fascinated with high speed processes through studying meteorite impact dynamics and then how my initial idea of studying old faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of mount st helens in 1980 but also on geysers erupting on io a fiery satellite of jupiter triton a frigid satellite of neptune and enceladus an active satellite of saturn unforeseeably the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the grand canyon this is a narrative not a formal review article but the reader can find references in the related resources section to explore topics in more detail

extent and isotopic composition of fe and mo release from two pennsylvania shales in the presence of organic ligands and bacteria abstract isotopic fractionation of fe and mo during weathering could contribute toward the isotopic signatures of river and ocean waters to investigate weathering processes batch experiments were carried out at ph 6 under oxygenated conditions to investigate the influence of a nitrogen fixing soil bacterium and organic ligands on the extent and isotopic signature of fe and mo release from two pennsylvania shales with different mineralogies an olive to grey shale rose hill and a black shale marcellus results of these studies showed that fe and mo were mainly released from illite chlorite vermiculite and fe oxides in the rhs and from pyrite in the ms dissolution rates of the clays estimated from our batch experiments are broadly consistent with published estimates release of fe from both shales was only enhanced by the hydroxamate siderophore desferrioxamine b dfam in contrast none of the treatments enhanced release of mo furthermore release of this metal was measurable only for the black shale for both shales fe that was released in the presence of dfam was depleted in 56 fe as compared to the bulk rock in contrast leachate solutions were enriched in the heavier mo isotope as compared to the bulk marcellus in all experiments with and without organic ligands and the bacterium the isotopic fractionations in fe and mo are broadly consistent with previously reported fractionation effects during sorption onto precipitating fe mn oxides the observed mo isotope fractionation is also consistent with all published studies of rivers i e riverine mo is enriched in heavy mo isotopes the observed fe isotope fractionation is likewise consistent with published studies for some rivers i e riverine fe is sometimes depleted in 56 fe our experimental results are consistent with sorption of fe and mo onto fe oxyhydr oxides during weathering as a possible explanation for the isotopic signatures of these metals in many rivers

description of new shock induced phases in the shergotty zagami nakhla and chassigny meteorites the shergottite nakhlite and chassignite snc meteorites shergotty zagami nakhla and chassigny have been studied by analytical transmission electron microscopy new phases characteristic of strong shock conditions have been discovered calcium rich majorites in shergottty wadsleyite with anomalously elevated iron content in chassigny and impact melts in shergotty zagami and nakhla cristobalites and polymorphs observed in shergotty and zagami may also be related to shock and are interpreted as back transformation products of post stishovite silica polymorphs shocks corresponding to pressure and temperature conditions characteristic of the earth s transition zone and lower mantle have occurred in those meteorites moreover impact melts indicate high temperature conditions in localized areas on the other hand no massive impact melting is observed in those meteorites consistent with previous descriptions these observations provide evidence of highly heterogeneous shock conditions at the scale of few micrometers in these meteorites strongly heterogeneous conditions such as those suggested by the present study may help to explain the preservation in martian meteorites of phases practically unaffected by shock being very close to strongly shock metamorphized minerals

chemical weathering mass loss and dust inputs across a climate by time matrix in the hawaiian islands we determined the total mass loss and rate of chemical weathering from three minimally eroded hawaiian lava flows that are 10 170 and 350 ka old using a backhoe we sampled the entire weathering zone at 28 sites and measured the depletion or enrichment of each major element in each soil horizon relative to parent material we were able to assess the influence of both climate and substrate age on chemical weathering because each flow crosses a precipitation gradient from 600 to 2500 mm yr 1 mass loss rates were highest for the 0 10 ka interval under the wettest climatic conditions 54 t km 2 yr 1 and decreased to near zero in the wet sites during the 10 170 and 170 350 ka intervals not surprisingly weathering rates were lower in drier sites 24 t km 2 yr 1 from 0 10 ka to b 2tk m 2 yr 1 thereafter however the effects of precipitation were non linear there was a precipitation threshold below which mass loss was relatively small and above which mass loss was substantial but insensitive to increased rainfall chemical weathering rates depend on tectonic uplift erosion climate rock type or some combination thereof by working on stable uneroded surfaces of a single rock type across a well constrained precipitation gradient we were able to identify another potential driver the rate of dust deposition although hawai i is one of the least dusty places in the northern hemisphere dust inputs reached 82 of the total mass loss from the weathering zone at some sites and averaged 30 on the 170 ka flow this highlights the potential importance of dust as a component of observed weathering fluxes from catchments worldwide

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

constraints on the u pb isotopic systematics of mars inferred from a combined u pb rb sr and sm nd isotopic study of the martian meteorite zagami uranium lead rb sr and sm nd isotopic analyses have been performed on the same whole rock mineral and leachate fractions of the basaltic martian meteorite zagami to better constrain the u pb isotopic systematics of martian materials although the rb sr and sm nd systems define concordant crystallization ages of 166 6 ma and 166 12 ma respectively the u pb isotopic system is disturbed nevertheless an age of 156 6 ma is derived from the 238u 206pb isotopic system from the purest mineral fractions maskelynite and pyroxene the concordance of these three ages suggest that the 238u 206pb systematics of the purest zagami mineral fractions have been minimally disturbed by alteration and impact processes and can therefore be used to constrain the behavior of u and pb in the zagami source region the value of the zagami source region can be estimated with some confidence from the 238u 206pb isochron to be 3 96 0 02 disturbance of the u pb isotopic systems means that this represents a minimum value the value of the zagami source is significantly lower than the values estimated for most basaltic magma sources from earth and the moon this is surprising given the high initial 87sr 86sr ratio 0 721566 82 and low initial end value 7 23 0 17 determined for zagami that indicate that this sample is derived from one of the most highly fractionated reservoirs from any known planetary body this suggests that mars is characterized by a low bulk planet u pb ratio a feature that is consistent with its relatively volatile rich nature the leachates contain terrestrial common pb that was probably added to the meteorite during handling curation or sawing the mineral fractions particularly those with significant amounts of impact melt glass contain a second contaminant the presence of this contaminant results in pb pb ages that are older than the crystallization age of zagami indicating that the contaminant is characterized by a high 207pb 206pb ratio such a contaminant could be produced by removal of single stage pb from a relatively high martian reservoir before 1 8 ga and therefore could be an ancient manifestation of hydrous alteration of martian surface material

molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain the application of the molybdenum mo isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types and remains constant however it has recently been shown that the 98 95mo composition of global rivers varies between 0 15 and 2 4 and is therefore systematically heavier than the average composition of the continental crust 0 in order to understand the processes that control mo isotope fractionation during weathering this study presents 98 95mo and mo abundance data for rivers and estuarine samples from iceland that drain predominantly basaltic terrains resolvable differences are observed in the isotopic composition of the riverine mo sources ice 98 95moice 1 8 basaltic bedrock 98 95mobedrock 0 0 and hydrothermal waters 98 95mohydrothermal 3 4 systematic changes in the dissolved mo isotope composition are also observed within river catchments with 98 95mo values increasing from 0 in glacial rivers close to the source to 1 downstream consistent with mo isotopes being fractionated during weathering analysis of other riverine phases bedload colloids and iron precipitates demonstrates that these phases preferentially incorporate light mo isotopes and remain coupled to the dissolved load during riverine transportation a 98 95mo profile through the borgarfjor eth ur estuary exhibits a predominantly conservative mixing behaviour but suggests that the release of isotopically light mo from the particulate and or colloidal phases may occur in the low salinity part of the estuarine mixing zone 2010 elsevier b v

ejection of martian meteorites we investigated the transfer of meteorites from mars to earth with a combined mineralogical and numerical approach we used quantitative shock pressure barometry and thermodynamic calculations of post shock temperatures to constrain the pressure temperature conditions for the ejection of martian meteorites the results show that shock pressures allowing the ejection of martian meteorites range from 5 to 55 gpa with corresponding post shock temperature elevations of 10 to about 1000 c with respect to shock pressures and post shock temperatures an ejection of potentially viable organisms in martian surface rocks seems possible a calculation of the cooling time in space for the most highly shocked martian meteorite allan hills alh 77005 was performed and yielded a best fit for a post shock temperature of 1000 c and a meteoroid size of 0 4 to 0 6 m the final burial depths of the sub volcanic to volcanic martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for martian meteorites during the impact of a small projectile 200 m as defined by numerical modeling artemieva and ivanov 2004 a comparison of shock pressures and ejection and terrestrial ages indicates that on average highly shocked fragments reach earth crossing orbits faster than weakly shocked fragments if climatic changes on mars have a significant influence on the atmospheric pressure they could account for the increase of recorded ejection events of martian meteorites in the last 5 ma

rates of relative plate motion during the acadian orogeny based on the spatial distribution of black shales devonian mississippian black shales apparently were deposited in foreland basins formed in response to deformational loading in the acadian orogen these black shales were deposited in a succession of partially overlapping basins separated from each other by coarser clastic units which migrated episodically south westward in time parallel to the orogen if foreland basins are results of an isostatic response to deformational loading in the orogen migration of successive basins along the orogen must reflect concomitant shift of orogeny and hence relative plate motion in the same direction these black shale deposits then not only demonstrate the diachronous nature of the acadian orogeny a fact previously indicated by other lines of evidence but also enable approximation of rates of relative plate motion to be made using three different dating schemes the black shale deposits indicate late devonian plate motion along an 800 km segment of the orogen during approximately 11 ma for an average rate of

mechanism for joint saturation in mechanically layered rocks an example from southern israel abstract over 700 joint spacings were measured along a 190 m scanline within a single limestone bed of the turonian gerofit formation southern israel by investigating joints belonging to a single systematic set confined to a bed of uniform thickness one can factor out the major influences of bed thickness lithology and mechanical properties on joint set development joint spacing distributions and fracture spacing ratios fsr vary dramatically along the length of the scanline and correlate directly with throughgoing fracture zones belonging to the same tectonic stress regime regions cross cut by fracture zones display narrower median joint spacings fsr of 1 3 and unimodal joint spacing distributions where fracture zones are absent joint spacings have wider medians fsr of 0 8 and multimodal distributions because fracture zones most likely represent areas of high strain and laboratory experiments demonstrate a systematic decrease in fracture spacing with increasing strain regions of the bed cross cut by fracture zones are likely at a more advanced stage of joint set development and hence closer to saturation than other regions joint saturation in the gerofit formation may be achieved by a shift in scale from single layer to multi layer jointing as the development of throughgoing joints prevents the formation of additional bedding confined joints

u pb isotopic systematics of shock loaded and annealed baddeleyite implications for crystallization ages of martian meteorite shergottites abstract shock recovery and annealing experiments on basalt baddeleyite mixtures were undertaken to evaluate shock effects on u pb isotopic systematics of baddeleyite shock pressures up to 57 gpa caused fracturing of constituent phases mosaicism of olivine maskelynitization of plagioclase and melting but the phase transition from monoclinic baddeleyite structure to high pressure temperature polymorphs of zro 2 was not confirmed the u pb isotopic systems of the shock loaded baddeleyite did not show a large scale isotopic disturbance the samples shock recovered from 47 gpa were then employed for annealing experiments at 1000 or 1300 c indicating that the basalt baddeleyite mixture was almost totally melted except olivine and baddeleyite fine grained euhedral zircon crystallized from the melt was observed around the relict baddeleyite in the sample annealed at 1300 c for 1 h the u pb isotopic systems of baddeleyite showed isotopic disturbances many data points for the samples annealed at 1000 c plotted above the concordia both radiogenic lead loss uranium gain and radiogenic lead gain uranium loss were observed in the baddeleyite annealed at 1300 c complete radiogenic lead loss due to shock metamorphism and subsequent annealing was not observed in the shock loaded annealed baddeleyites studied here these results confirm that the u pb isotopic systematics of baddeleyite are durable for shock metamorphism since shergottites still preserve fe mg and or ca zonings in major constituent phases i e pyroxene and olivine the shock effects observed in martian baddeleyites seem to be less intense compared to that under the present experimental conditions an implication is that the u pb systems of baddeleyite in shergottites will provide crystallization ages of martian magmatic rocks

the age of the martian meteorite northwest africa 1195 and the differentiation history of the shergottites samarium neodymium isotopic analyses of unleached and acid leached mineral fractions from the recently identified olivine bearing shergottite northwest africa 1195 yield a crystallization age of 347 13 ma and an end143 value of 40 1 0 9 maskelynite fractions do not lie on the sm nd isochron and appear to contain a martian surface component with low 147sm 144nd and 143nd 144nd ratios that was added during shock the rb sr system is disturbed and does not yield an isochron terrestrial sr appears to have affected all of the mineral fractions although a maximum initial 87sr 86sr ratio of 0 7016 is estimated by passing a 347 ma reference line through the maskelynite fraction that is least affected by contamination the high initial end143 value and the low initial 87sr 86sr ratio combined with the geologically young crystallization age indicate that northwest africa 1195 is derived from a source region characterized by a long term incompatible element depletion the age and initial sr and nd isotopic compositions of northwest africa 1195 are very similar to those of queen alexandra range 94201 indicating these samples were derived from source regions with similar sr nd isotopic systematics these similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano the meteorites yamato 980459 dar al gani 476 sayh al uhaymir 005 008 and dhofar 019 also have relatively old ages between 474 and 575 ma and trace element and or isotopic systematics that are indicative of derivation from incompatible element depleted sources this suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible element depleted sources closed system fractional crystallization of this suite of meteorites is modeled with the melts algorithm using the bulk composition of yamato 980459 as a parent these models reproduce many of the major element and mineralogical variations observed in the suite in addition the rare earth element systematics of these meteorites are reproduced by fractional crystallization using the proportions of phases and extents of crystallization that are calculated by melts other shergottites that demonstrate enrichments in incompatible elements and have evolved sr and nd isotopic systematics have some geochemical systematics that are similar to those observed in the depleted group most notably although they exhibit a very limited range of incompatible trace element and isotopic compositions they have highly variable major element compositions this is also consistent with evolution from a common mantle source region by variable amounts of fractional crystallization if this scenario is correct it suggests that the combined effects of source composition and fractional crystallization are likely to account for the major element trace element and isotopic diversity of all shergottites

the impact of igneous bedrock weathering on the mo isotopic composition of stream waters natural samples and laboratory experiments abstract river waters have been shown to be systematically enriched in the heavy molybdenum mo isotopes when compared to typical granites and basalts which generally possess mo isotopic compositions 98 95 mo of around 0 this inconsistency has been used to argue against weathering of crustal rocks as the cause for heavy riverine 98 95 mo signatures incongruent dissolution of primary bedrock however may be an important process by which the anomalous mo signatures of the river dissolved load are produced this study therefore investigates the effect of igneous crustal rock weathering on the aquatic 98 95 mo signal by comparing stream water and bedrock mo isotope data to results of bulk rock leach experiments for this purpose stream water and bedrock orthogneiss granite basalt as well as soil and vegetation samples were collected in a small catchment in the french massif central in accordance with the results of earlier studies on riverine mo both streams are isotopically heavier 98 95 mo 0 5 1 1 than the typical granites and basalts the excellent agreement of these data with those of mo released during experimental leaching of the basalt bedrock 0 6 1 0 identifies a predominance of basalt weathering over the stream water mo geochemistry while other processes i e soil formation secondary mineral precipitation and adsorption are subordinate in this catchment given that the basalt bulk rock 98 95 mo reflects a value typical for crustal magmatic rocks ca 0 1 mo isotope fractionation during the incongruent dissolution of basalt can explain the observed isotopically heavy aquatic mo signatures laser ablation analyses demonstrate that the volumetrically minor magmatic sulfides can be highly enriched in mo and mass balance calculations identify the sulfide melt inclusions as the principal mo source for the leach solutions these data suggest that the magmatic sulfides possess a distinctly heavier 98 95 mo signature than the coexisting silicate melt in this case mo would behave like fe by showing a detectable isotope fractionation at magmatic temperatures incongruent crustal bedrock weathering may thus cause a preferential release of heavy mo isotopes this effect however is highly dependent on the primary bedrock mineralogy consequently the average continental runoff may have been significantly affected by incongruent weathering during periods when the earth system was exceptionally far from steady state e g large glaciations with enhanced physical weathering or large subaerial basalt eruptions such as the deccan and the siberian plateau

noble gases and chemical composition of shergotty mineral fractions chassigny and yamato 793605 the trapped argon 40 argon 36 ratio and ejection times of martian meteorites we report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene maskelynite mesostasis glass and bulk material of shergotty and of bulk samples from chassigny and yamato 793605 the 40k 40ar isochron for the shergotty minerals yields a gas retention age of 196 ma which is within errors in agreement with previously determined rb sr internal isochron ages argon that was trapped at this time has a 40ar 36ar ratio of 1100 for chassigny and y 793605 we obtain trapped 40ar 36ar ratios of 1380 and 950 respectively using these results and literature data we show that the three shergottites shergotty zagami and que 94001 the lherzolites alh 77005 lew 88516 and y 793605 as well as chassigny and alh 84001 contain a mixture of martian mantle and atmospheric ar whereas the trapped 40ar 36ar ratio of the nakhlites nakhla lafayette and governador valadares cannot be determined with the present data we show that martian atmospheric trapped ar in martian meteorites is correlated with the shock pressure that they experienced hence we conclude that the martian atmospheric gases were introduced by shock into the meteoritic material for the shergotty minerals we obtain 3he 21ne and 38ar based cosmic ray exposure ages of 3 0 ma and for the lherzolite y 793605 4 0 ma which confirms our earlier conclusion that the lherzolites were ejected from mars 1 ma before the shergottites chassigny yields the previously known ejection age of 11 6 ma

molybdenum sources and isotopic composition during early stages of pedogenesis along a basaltic climate transect abstract molybdenum mo is an essential micronutrient and redox sensitive trace metal that has the potential to be a tracer of pedogenic processes globally riverine 98mo values based on 98mo 95mo relative to nist srm 3134 are heavier relative to bedrock suggesting weathering processes preferentially retain light mo isotopes however the mechanisms governing this process in soils are poorly understood we investigated soil mo abundance and isotopic composition as a function of climate along a well constrained climosequence on a 10 kyr lava flow in hawaii receiving 660 to 2100 mm year 1 mean annual precipitation map we assessed mo abundance and isotopic composition as a function of soil organic matter om content short ranged ordered sro iron fe oxyhydr oxide abundance and mo loss gain we find net accumulation of mo across all soils up to 139 gain that is positively correlated with increasing map the highest mo gains are in surface soil horizons and are correlated with high om content the isotopic composition of soil mo deviates from underlying basaltic bedrock which ranges from 98mo values of 0 11 to 0 26 soil mo isotopic values are lightest at the dry sites 98mo 0 63 and become heavier with increasing precipitation up to 98mo 0 03 samples with the heaviest 98mo values are from horizons with the largest net gains of mo relative to bedrock and have higher om content in order to further constrain mo fluxes into and out of the soil system we measured mo isotope ratios in local rainwater average 98mo 1 11 groundwater average 98mo 0 14 and vegetation 98mo values between 0 18 and 0 64 based on these data we propose that mo in these soils is substantially augmented by additions from precipitation volcanic fog and potentially anthropogenic inputs of mo and that retention of these inputs within soils is likely related to mo om interactions the large atmospheric inputs of mo strongly modulate the 98mo values of dissolved mo fluxes from soil to values only slightly heavier than bedrock these patterns illustrate the potential for mo as a tracer of atmospheric inputs and pedogenic processes in soils and help elucidate the mechanisms that drive heavy 98mo values in the global riverine mo flux

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

the pb isotopic evolution of the martian mantle constrained by initial pb in martian meteorites the pb isotopic compositions of maskelynite and pyroxene grains were measured in alh84001 and three enriched shergottites zagami roberts massif 04262 and larkman nunatuk 12011 by secondary ion mass spectrometry a maskelynite pyroxene isochron for alh84001 defines a crystallization age of 4089 73 ma 2 the initial pb isotopic composition of each meteorite was measured in multiple maskelynite grains alh84001 has the least radiogenic initial pb isotopic composition of any martian meteorite measured to date i e 206pb 204pb 10 07 0 17 2 assuming an age of reservoir formation for alh84001 and the enriched shergottites of 4513 ma a two stage pb isotopic model has been constructed this model links alh84001 and the enriched shergottites by their similar value 238u 204pb of 4 1 4 6 from 4 51 ga to 4 1 ga and 0 17 ga respectively the model employed here is dependent on a chondritic value 1 2 from 4567 to 4513 ma which implies that core segregation had little to no effect on the value s of the martian mantle the proposed pb isotopic model here can be used to calculate ages that are in agreement with rb sr lu hf and sm nd ages previously determined in the meteorites and confirm the young 170 ma ages of the enriched shergottites and ancient 4 ga age of alh84001

unusually heavy stable mo isotope signatures of the ottawa river causes and implications for global riverine mo fluxes abstract the accurate use of mo isotope mass balance modelling of ancient oceans relies on the assumption that the 98mo of modern riverine inputs represents a reasonable estimate of the past a growing number of studies of global rivers have demonstrated significant variation in 98mo from the bedrock sources of mo the ottawa river canada was previously identified as having an anomalously heavy mo isotope composition with a 98mo signature close to seawater 2 3 for a seemingly pristine natural river to further explore this unusual signature we collected and filtered 29 water samples from the ottawa river tributaries and small lakes and analysed them for mo isotopes as well as major and trace elements here we fully document heavy 98mo signatures throughout the ottawa river and its absence in surrounding areas of the wider ottawa river basin orb our results reveal a progressive upstream increase in both mo concentration and 98mo signatures in the ottawa river towards values even heavier than seawater up to 3 13 the heaviest mo isotopic signature of river water measured to date in contrast the tributaries and lakes display far lighter and more consistent 98mo signatures within the range previously found in other rivers weathering of an isotopically heavy bedrock source fractionation during weathering and retention of light isotopes in soils have all been proposed as sources of heavy 98mo in rivers however none of these mechanisms can satisfactorily explain our new observations colloidal and particulate processes that remove elements downstream as inferred from some trace element proxies also cannot explain the decreasing 98mo since the preferential removal of light mo isotopes is predicted from these processes similarly the downstream trends show no apparent relationships with constructed dams or known potential industrial sources therefore our findings from the ottawa river are best explained as the dilution of a yet unidentified point source of heavy mo upstream of sampling or a significant permanent sink for light isotopes existing only in the upper reaches of the catchment in both cases anthropogenic contribution from a large mining district in the headwaters of the river must be considered and should be explored further fractionation of mo in waste rock storage facilities have been previously identified and may provide an unnatural sink for isotopically light mo through the rayleigh type fractionation of dissolved mo on oxyhydr oxide mineral surfaces the implied anthropogenic alteration of the natural mo cycle highlights the significant and wide reaching effects of unnatural point sources of mo on the cumulative 98mo signatures of the catchment and emphasises the necessity for detailed geochemical screening of anomalous river water isotope signatures before natural isotope compositions are inferred

origin and evolution of the nakhla meteorite inferred from the sm nd and u pb systematics and ree ba sr rb and k abundances analyses of sm nd and u th pb systematics ree ba sr rb and k concentrations were carried out for whole rock and mineral separates from the nakhla meteorite the 1 26 07 b y sm nd age obtained in this work is in good agreement with those previously obtained by the rb sr and ar ar methods the high initial nd value of 16 suggests that nakhla was derived from a light ree depleted old planetary mantle source u th pb data after correction for pre analytical terrestrial pb contamination assuming an age of 1 26 b y suggest that the age of the nakhla source is 4 33 b y the agreement in the age determined by three independent radiometric methods and the high initial nd value strongly suggest that the 1 3 b y age dates one thorough igneous event in the parent body which not only reset these isotopic systems but also established the chemical and petrologic characteristics observed for the nakhla meteorite using a three stage sm nd evolution model in combination with lil element data and estimated partition coefficients we have tested partial melting and fractional crystallization models to estimate lil element abundances in a possible nakhla source our model calculations suggest that partial melting of the light ree depleted source followed by extensive fractional crystallization 50 of the partial melt could account for the ree abundances in the nakhla constituent minerals the estimated source is depleted in the light ree ba rb and k and therefore may resemble the morb source in the earth s upper mantle or the upper 60 300 km of the moon the significantly younger age of nakhla than the youngest lunar rock the young differentiation age inferred from the u th pb data and the estimated lil element abundances including those of k u and th in the source suggest that the nakhla meteorite may have been derived from a relatively large well differentiated planetary body such as mars

precipitation of molybdenum from euxinic waters and the role of organic matter abstract molybdenum preserved in organic rich shales is a key archive employed in studying earth s past oxygenation and life s evolution in these shales positive correlations between mo and corg are common and have been attributed to mo scavenging from seawater by organic shuttles here we argue that known organic ligands are too weak or too scarce to capture more than minor amounts of mo from seawater especially in competition with sulfide alternatively we demonstrate that mo corg correlations can arise simply from microbially mediated oxidation of corg by so42 this process produces sulfide and lowers ph triggering precipitation of femos4 which soon transforms irreversibly to femos2 s2 in euxinic basins the extent of sulfate reduction progress increases with depth and can be modeled as an empirical function of biological productivity and water replacement time the response of dissolved mo to sulfate reduction progress occurs in three stages identified by a thermodynamic model in stage i progress is too small to precipitate mo from waters that are only mildly sulfidic in stage ii the flux of mo to sediments is promoted by sulfate reduction progress giving rise to positive mo corg correlations in sediments due to fluctuations in biological productivity in some cases precipitation in this stage begins before mos42 becomes the predominant dissolved mo species in which case femos4 with negative 98mo can be produced in stage iii the flux of mo becomes independent of further sulfate reduction progress and mo corg correlations degrade as reported in extremely corg rich shales even though the model omits a number of potentially important processes its predicted mo profiles in waters of several modern euxinic basins are qualitatively reasonable and are consistent with observed reduction of movi in water to moiv in sediments according to the model spikes in atmospheric pco2 will markedly increase mo accumulation and lower 98mo in euxinic basin sediments this appears to have occurred repeatedly during the phanerozoic and may be commencing now as a result of fossil fuel combustion minimal deposition of mo in organic rich shales during the archean has been attributed to low moo42 in seawater but seems more likely to be due to low so42

molybdenum isotope fractionation in glacial diamictites tracks the onset of oxidative weathering of the continental crust abstract molybdenum isotopes in twenty four composites of glacial diamictites spanning depositional ages of 2900 to 300 ma show a systematic shift to lighter compositions and a decrease in mo concentration over time the diamictites fall into three age groups relative to the great oxidation event goe pre goe 2 43 2 90 ga syn goe 2 20 2 39 ga and post goe 0 33 0 75 ga pre goe composites have an average 98 monist3134 of 0 03 0 18 syn goe composites average 0 29 0 60 and post goe composites average 0 45 0 51 these groups are statistically different at p 0 05 we use the pre goe data to estimate the average archean upper continental crust ucc 98 mo signature as 0 03 0 18 2 which falls within the range of previous estimates of modern igneous rocks as the diamictites represent a mixture of igneous and weathered crust the shift to lighter mo values over time likely reflects mo isotope fractionation during oxidative weathering and increased retention of light mo isotopes in weathered regolith and soils we hypothesize that this fractionation is due to the mobilization of oxidized mo following the goe and subsequent adsorption of light mo onto fe mn oxides and or organic matter in weathered regolith we conclude that mo isotopes in continental weathering products record the rise of atmospheric oxygen and onset of oxidative weathering as the regolith formed under oxidative conditions is isotopically lighter than average continental igneous rocks mass balance dictates that mo isotope fractionation during oxidative weathering should result in isotopically heavy groundwater and river water which is observed in modern systems

martian meteorite chronology and the evolution of the interior of mars abstract the earth moon and mars are the only three planets for which satellite and ground observations can be confronted with extensive chronological and geochemical observations of rock samples here we use new pb isotope data on shergottites nakhlites chassigny and the alh 84001 orthopyroxenite to reassess chronological evidence and discuss its bearing on the evolution of the interior of mars we find that the depleted shergottites formed at 4 3 ga i e 170 ma after the last equilibration of pyroxene rich cumulates with the magma ocean while the younger enriched and intermediate shergottites as well as alh 84001 formed 200 ma later at 4 1 ga after the residual part of the mantle had been largely mixed back into these cumulates we also demonstrate that the th u ratios inferred from pb isotopes require shergottite ages older than 4 0 ga we finally reexamine the implications of this new chronological framework for the interpretation of 142 nd and 182 w anomalies in martian meteorites we conclude that shergottites represent samples that derived from a volcanic basement subsequently shattered by the 3 9 ga late heavy bombardment lhb although the magmatic activity of mars had strongly declined by the time of the lhb the new chronology of martian meteorites proposed here allows the martian mantle to be convective until today the 1 3 ga old emplacement of nakhlites and chassignites corresponds to decompression melting of ilmenite rich mantle domains and not to renewed global magmatic activity of the planet with the exception of this event the history of the interior of mars therefore somewhat resembles that of the moon

determination of molybdenum isotope fractionation by double spike multicollector inductively coupled plasma mass spectrometry 1 molybdenum isotopic compositions are precisely determined by mc icp ms measurements using a mo double spike the double spike is added prior to chemical purification so that laboratory and instrumental mass fractionations are separated from natural mass dependent fractionation fractionation is determined on four mo mass ratios providing an internal consistency check the external standard reproducibility is at 0 06 per mil on the 98mo 95mo ratio 2 standard deviation using a normal microconcentric nebuliser with a cyclonic spray chamber the minimum quantity of mo is 1 g for high precision results a hydrothermal molybdenite shows fractionation of 0 3 per mil on the 98mo 95mo ratio relative to our standard johnson matthey 1000 g ml 0 3 icp standard solution lot 602332b fine grained sediments show fractionation of 0 1 and 0 3 per mil on the 98mo 95mo ratio the observed mo isotope fractionation is small but resolvable with the presented high resolution technique

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

molybdenum mo stable isotopic variations as indicators of mo attenuation in mine waste rock drainage abstract measurements of molybdenum mo stable isotopes 98mo were applied along with conventional geochemical analyses of water and rock samples at a mo mine in the usa to assess controls on mo mobility in two unsaturated waste rock storage facilities wrsfs that are differentiated by acidic and alkaline drainages unweathered waste rock mo ore and mine tailings from the site were also analyzed to constrain the isotopic composition of the source of mo entering mine drainage via weathering processes the surfaces of weathered waste rock samples were sequentially leached using a two step chemical extraction to determine the distribution and isotopic composition of mo among primary and secondary mineral assemblages the observed variation in 98mo among all samples exceeded 5 the 98mo of mo rich 340 g l mine process water and pit wall runoff ranged from 0 6 to 0 7 which was equal within error to the average 98mo of waste rock tailings and ore samples and indicated negligible isotopic fractionation during molybdenite oxidative dissolution in contrast drainage from the base of both waste rock storage facilities was isotopically heavier ranging from 1 6 to 1 9 coupled 98mo and mo so42 ratios in mine drainage and sequential chemical extractions of weathered waste rock surfaces indicated that mo adsorption onto mineral surfaces was most likely driving the increase in 98mo in drainage from both wrsfs molybdenum stable isotope data provided a powerful tracer of processes controlling mo mobility when used in conjunction with conventional geochemical analyses

insights into the chemical diversity of the martian mantle from the pb isotope systematics of shergottite northwest africa 8159 abstract shergottite northwest africa nwa 8159 is a basaltic rock derived from a mantle source with chemical characteristics that are unique in the martian meteorite suite to further investigate this source reservoir the pb isotope compositions of plagioclase maskelynite pyroxene phosphates and shock melt glass in nwa 8159 have been measured in situ by secondary ion mass spectrometry sims due to the limited spread in pb isotope data these pb isotope compositions have been used to calculate an imprecise pb pb isochron age of 3 4 2 1 ga 2 which is broadly consistent with the crystallization age of 2 37 0 25 ga determined previously by 147sm 143nd the lack of radiogenic in growth within individual minerals since 2 4 ga means that this sample is depleted in u which is in agreement with nwa 8159 s positive initial e143nd an initial pb composition was calculated using an x y weighted average of the least radiogenic pb isotope population measured in the sample this initial pb composition is not consistent with the model for pb growth in the shergottite mantle at 2 4 ga this composition is however consistent with the model for the nakhla chassigny mantle using the latter model a source 238u 204pb of 2 6 0 6 has been calculated this value is in contrast with the other depleted shergottites 1 4 1 5 and falls significantly off the array of source e143nd vs defined by the rest of the martian meteorite suite and thus necessitates a differentiation history distinct from the other martian meteorites sequestering pb in sulphides during differentiation is the only mechanism to fractionate u from pb and create a low reservoir consequently the relatively high value of the source of nwa 8159 is in contrast with the positive initial e143nd and indicates that its mantle source region likely lacked significant sulphur this is consistent with the lack of sulphides in the sample itself and could have played a role in its complicated oxidation history

unique meteorite from early amazonian mars water rich basaltic breccia northwest africa 7034 we report data on the martian meteorite northwest africa nwa 7034 which shares some petrologic and geochemical characteristics with known martian meteorites of the snc i e shergottite nakhlite and chassignite group but also has some unique characteristics that would exclude it from that group nwa 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent rover and orbiter missions it formed 2 089 0 081 billion years ago during the early amazonian epoch in mars9 geologic history nwa 7034 has an order of magnitude more indigenous water than most snc meteorites with up to 6000 parts per million extraterrestrial h2o released during stepped heating it also has bulk oxygen isotope values of 17o 0 58 0 05 per mil and a heat released water oxygen isotope average value of 17o 0 330 0 011 per mil suggesting the existence of multiple oxygen reservoirs on mars

limited iron isotope variations in recent lateritic soils from nsimi cameroon implications for the global fe geochemical cycle laterites are oxidized fe rich soils covering one third of the continents and are drained by half of the continental waters they therefore represent a key component of the iron geochemical cycle at the earth s surface yet no iron isotope study has been conducted on recent laterites so far building on previous integrated morpho pedological studies of soils located in an equatorial rainforest southern cameroon we have undertaken a mineralogical elemental and isotopic study of iron in two lateritic profiles one is a borehole 3620 cm deep going to the parent granodioritic rock located at the top of a hill whereas the other is 675 cm deep and is located downhill mossbauer spectroscopy reveals that typically geq 96 of the soil s iron is held in nanocrystalline hematite and goethite iron isotope measurements performed by plasma source mass spectrometry show that fe isotopic equilibrium was rarely reached between these iron oxide and hydroxide despite their small size overall it is found that most samples display iron isotope signatures very close to the mean crustal value with a maximum range of 0 2 in delta 57 fe given that lateritic soils evolve over millions of years show large variations in fe concentrations and mineralogical abundances this range is surprisingly small when compared to other fe isotope studies of soils from different climatological contexts that can easily show delta 57 f e ranges in excess of 1 at the bulk sample scale the most likely explanation of this finding is that despite notable vertical and lateral fe mobility in the studied laterites from cameroon as computed using the open system mass fraction transport function tau fe w iron remained mostly in the oxidized form as shown by mossbauer pectroscopy this probably results from the strong bioturbation and pedoturbation of these lateritic soils that lead them to remain porous over a large thickness and facilitated the flow of oxygenated waters from the surface down to the saprolite horizon this study therefore reveals that soils that remained as an open system for iron do not necessarily show large fe isotopic variations it is suggested that the fe drained from such lateritic soils should have delta 57 fe values within sim 0 1 of that of the continental crust this is in contrast with previous soil studies notably from sites located at higher latitudes that imply that these soils should release isotopically more variable fe to surface waters such possible contrasted isotopic signatures from different surface waters will likely lead to an isotopically heterogeneous ocean given the short residence time of fe in seawater

sulfidity controls molybdenum isotope fractionation into euxinic sediments evidence from the modern black sea molybdenum mo isotope fractionation has recently been introduced as a new proxy in oceanography and biogeochemistry it is therefore fundamental to understand the processes controlling mo partitioning into modern marine environments this study identifies the availability of dissolved sulfide as the dominant control on overall mo removal from the water column in euxinic systems mo isotopic composition of surface sediments from different localities of the black sea demonstrates complete fixation of mo only below 400 m water depth above a critical concentration of 11 mol l 1 aqueous hydrogen sulfide in the bottom water the mo isotopic composition of these sediments reflects the homogeneous seawater isotopic composition of 2 3 in contrast significant mo isotope fractionation into less euxinic sediments is evident at shallower depths in the black sea as well as in temporarily euxinic deeps of the baltic sea consistent with the observed lower maximum sulfide concentrations in the respective water columns therefore mo isotope signatures in the modern black sea constrain the processes responsible for global mo removal from the ocean by euxinic sediments furthermore models of past ocean anoxia reconstruction have to consider that the seawater mo isotopic composition is not per se archived in euxinic sediments

the molybdenum isotopic composition in river water constraints from small catchments we report molybdenum isotope compositions and concentrations in water samples from a variety of river catchment profiles in order to investigate the influence of anthropogenic contamination catchment geology within river precipitation and seasonal river flow variations on riverine molybdenum our results show that the observed variations in 98 95mo from 0 to 1 9 are primarily controlled by catchment lithology particularly by weathering of sulfates and sulfides erosion in catchments dominated by wet based glaciers leads to very high dissolved molybdenum concentrations in contrast anthropogenic inputs affect neither the concentration nor the isotopic composition of dissolved molybdenum in the rivers studied here seasonal variations are also quite muted the finding that catchment geology exerts the primary control on the delivery of molybdenum to seawater indicates that the flux and isotope composition of molybdenum to seawater has likely varied in the geologic past

the age of snc meteorites and the antiquity of the martian surface we report new sm nd lu hf and pb pb mineral and whole rock isotope data for the basaltic shergottite zagami as well as pb pb whole rock isotope data for the basaltic shergottite los angeles the lherzolitic shergottite dar al gani 476 dag 476 and the clinopyroxenite nakhla in agreement with previous findings our new sm nd and lu hf mineral ages on the martian meteorite zagami are young 155 and 185 ma respectively the 207pb 206pb 204pb 206pb compositions of the insoluble fractions of shergottites zagami los angeles and literature data for shergotty and eeta79001 form an excellent alignment indicative of a 4 0 ga crystallization age the range of pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial pb and argues against mixing relationships the age of 4 048 0 017 ga mswd 1 5 provided by the pb isotope compositions of the zagami whole rock and residues is therefore taken to date the crystallization of this rock which so far was believed to be only not vert similar 180 ma old based on this result we argue that the lithosphere of mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the martian surface this interpretation is consistent with photographic interpretations of erosional features on mars it also relieves the constraint imposed by the presence of anomalies of 142nd and 182w both products of extinct radioactive nuclides that the martian mantle should have preserved primordial isotopic heterogeneities thus allowing for the planet interior to be actively convecting

northwest africa 8694 a ferroan chassignite bridging the gap between nakhlites and chassignites abstract the origin s of the chassignites and nakhlites closely related martian olivine and augite cumulates respectively are much debated northwest africa nwa 8694 is the third chassignite to be discovered and the most ferroan containing 85 olivine fo54 its o isotope compositions 18o 4 4 17o 0 30 are typical of other martian meteorites it has adcumulate texture and contains cumulus chromite poikilitic pigeonite en56fs37wo7 and mesostasis trapped interstitial liquid the latter contains pyroxene and plagioclase an23 ab70 or8 plus rare k feldspar or74 and has a trachyandesitic to trachytic bulk composition melt inclusions in olivine contain a variety of phases including biotite and rare amphibole olivine chromite and pigeonite compositions are intermediate between those of the other chassignites and those of the nakhlites augite which appears to mantle pigeonite has a composition overlapping that in nakhlite nwa 998 and some other nakhlites at en41 40wo38 39 the augite lamellae in pigeonite 1 2 m in apparent width and the survival of ca zoning in olivine suggest a near surface cooling environment the bulk rock ree concentrations in the three chassignites do not correlate with mg but depend on the abundance of trapped liquid the form of ree patterns calculated for olivine subtraction is very like those of nakhlite mesostases but the observed concentrations of lree in nwa 8694 trapped liquid have a very steep slope this is explained by undersampling of baddeleyite and zirconolite that occur near olivine contacts with mesostasis though pyroxene is unzoned its trace element variations indicate fractional crystallization the range of olivine compositions in the three chassignites fo79 54 is too large to result from the crystallization sequential growth of olivine from a single magma undergoing fractional crystallization the ge si ratios show degassing of nwa 8694 which sets this chassignite apart from other chassignites and nakhlites implying a unique batch of magma for its genesis many potential parent liquids are capable of generating the nwa 8694 olivine composition though not its alkaline mesostasis we calculated that nakhla parent liquid na01a stockstill et al 2005 with 10 nakhla core olivine added would produce both olivine crystals and alkaline daughter liquids with compositions matching those of nwa 8694 this meteorite is a chassignite cumulate containing nakhlitic mesostasis a direct link between the chassignites and the nakhlites and the association of dunitic to trachytic compositions is reminiscent of terrestrial shield volcanoes chassignites and nakhlites were possibly formed when solidification fronts on chamber walls were disrupted mainly as side eruptions of olivine charged magmas from the deeper zones and augite charged fractionated magmas from nearer the summit of a volcano resembling piton de la fournaise on earth

chemical weathering controls on variations in the molybdenum isotopic composition of river water evidence from large rivers in china abstract mo isotopic composition in large rivers is very important for understanding global mo cycle at present temporal variation signatures in the 98 95 mo in large rivers have not been investigated which hinder a comprehensive understanding on the mechanism for the variations of mo isotopic compositions in river water in this study we report a one year long time series march 2010 to march 2011 of the 98 95 mo of both the water and suspended particulates collected at guiping from the middle reaches of the xijiang river xjr and of the water 98 95 mo from the lower reaches of the huanghe river hhr or yellow river collected at lijin china the results indicate that the temporal variations in the concentration and 98 95 mo of dissolved mo in the xjr range from 4 32 to 10 5 nmol l mean 7 31 nmol l and 1 04 to 1 31 relative to nist 3134 mean 1 20 respectively but that the particulates have a lower 98 95 mo 0 18 to 0 58 analysis of the suspended particulates and other chemical parameters of the river water suggests that the weathering of silicates and sulfides is the main contributor to the dissolved mo content in the xjr subsequently the highly efficient preferential trapping of lighter 98 95 mo by weathering products such as clay minerals fe mn oxides and organic materials in soils and saprolites which are abundant in the tropical catchment is the key to the heavy mo isotope signatures in the xjr furthermore it seems that neither mo scavenging by suspended particulates during riverine transportation nor the weathering of sulfates significantly influences the 98 95 mo of the xjr water cross comparison among the 98 95 mo in the waters of the three largest rivers in china the changjiang cjr hhr and xjr indicates that the hhr has the highest mo concentrations but the lightest 98 95 mo the xjr has the lowest mo concentrations but the heaviest 98 95 mo and the values for the cjr are intermediate between those for the other two rivers this supports the conclusion that the efficiency of the selective trapping of mo by soils and saprolites is the main factor controlling 98 95 mo in these large rivers the tropical subtropical xjr catchment experiences intense chemical weathering the semi arid temperate hhr catchment experiences very little and the cjr catchment falls somewhere between the two such a relationship between water mo concentrations and 98 95 mo agrees with previous observations from many large rivers worldwide it is therefore suggested that chemical weathering on continents is the key to variations in the isotopic composition of mo in the waters of large rivers

accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances hawaiian soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs including sea salt aerosols and asian dust we use soil mineralogy and radiogenic isotope geochemistry sr and nd to evaluate the impact of asian dust on a chronosequence of hawaiian soils dust becomes an important constituent of soils 20 ky and older near surface 50 cm depth horizons contain as much as 30 quartz a mineral absent from local parent material basaltic sr and nd isotope signatures in these horizons have been completely overprinted by asian dust signatures with 87sr 86sr ratios as high as 0 723 and end values as low as 7 ree patterns in these soils are indistinguishable from that of average upper continental crust quartz abundance and nd isotopes provide two independent tracers of long term dust additions to the chronosequence soils the two tracers indicate a minimum long term average dust accretion rate of 125 mg cm 2 ky 1 at the 150 ka chronosequence site roughly a factor of three higher than holocene dust accumulation rates estimated from north pacific sediment cores we find that the mass of dust preserved in these soil profiles does not increase with age in soils 150 ka and older requiring a loss mechanism for accreted dust on the basis of the geomorphic stability of these sites observed preferential loss of dust derived mica relative to quartz and estimates of soil si leaching rates we argue that chemical weathering is the dominant loss mechanism for dust from these soils dust has a profound effect on the budgets of elements that are susceptible to leaching losses dust becomes the dominant source of soil nutrients si and p in the oldest most intensely weathered soils we calculate a dust derived p input flux of 0 8 mg cm 2 ky 1 and a dust derived si input flux of 35 mg cm 2 ky 1 si leaching fluxes are high 1400 mg cm 2 ky 1 in the youngest 2 ka soils and drop systematically with soil age to a value that closely balances the dust derived si input flux by 4100 ka extremely refractory elements such as nb which are concentrated in soils by residual enrichment processes are much less readily impacted by dust addition although dust has had a pronounced impact on sr and nd isotopic budgets and on soil mineral composition at the 150 ka site dust cannot have contributed 4 of the total nb contained in this soil profile

absence of molybdenum isotope fractionation during magmatic differentiation at hekla volcano iceland this study investigates the behaviour of molybdenum mo isotopes during magmatic differentiation molybdenum isotope compositions as well as concentrations of rare earth elements and a selection of trace elements have been determined for a well characterised sequence of lavas from hekla volcano iceland covering a compositional range from basalt to rhyolite 46 72wt sio2 and thought to have developed by differentiation and mixing of melts derived from a cogenetic source all samples have identical mo isotopic compositions with an average 98mo of 0 15 0 05 2 s d n 23 there is therefore no resolvable mo isotope fractionation during magmatic differentiation at hekla this finding is supported by the fact that mo remains highly incompatible in hekla lavas increasing from 1 3 to 4 6 g g from basalt to rhyolite indicating that the crystallising phases are extracting only limited amounts of mo from the magma and therefore that significant fractionation of mo isotopes is unlikely it has previously been proposed that cerium ce and mo have similar bulk distribution coefficients and are equally incompatible during mantle melting while both ce and mo remain incompatible in hekla lavas the ce mo ratio decreases from 50 to 36 during magmatic differentiation indicating that mo is more incompatible than ce comparison of mo with other incompatible trace elements indicates that mo is as incompatible as la and slightly less incompatible than k sulphur s decreases strongly from 200 to as low as 2 g g from basalt to andesite and more evolved compositions yet this has no effect on the mo isotopes therefore mo does not exhibit significant chalcophile behaviour in hekla magmas the mo isotopic signature therefore may be used as an indicator of parent magma composition and a potential discriminant of assimilation processes

molybdenum vanadium and uranium weathering in small mountainous rivers and rivers draining high standing islands abstract rivers draining high standing islands hsis and small mountainous rivers smrs are known to have extremely high sediment fluxes and can also have high chemical weathering yields which makes them potentially important contributors to the global riverine elemental flux to the ocean this work reports on the riverine concentrations ocean flux and weathering yields of molybdenum mo vanadium v and uranium u in a large number of small but geochemically important rivers using 338 river samples from ten lithologically diverse regions these redox sensitive elements are used extensively to infer paleo redox conditions in the ocean and mo and v are also important rock derived micronutrients used by microorganisms in nitrogen fixation unlike in large river systems in which dissolved mo has been attributed predominately to pyrite dissolution mo concentrations in these rivers did not correlate with sulfate concentrations v was found to correlate strongly with si in terrains dominated by silicate rocks but this trend was not observed in primarily sedimentary regions many rivers exhibited much higher v si ratios than larger rivers and rivers draining young quaternary volcanic rocks in nicaragua had much higher dissolved v concentrations mean 1306 nm than previously studied rivers u concentrations were generally well below the global average with the exception of rivers draining primarily sedimentary lithologies containing carbonates and shales fluxes of u and mo from igneous terrains of intermediate composition are lower than the global average while fluxes of v from these regions are higher and up to two orders of magnitude higher in the nicaragua rivers weathering yields of mo and v in most regions are above the global mean despite lower than average concentrations measured in some of those systems indicating that the chemical weathering of these elements are higher in these smr watersheds than larger drainages in regions of active boundaries with andesite dacite lithologies rivers draining young pleistocene rocks had higher concentrations than did older miocene pliocene rocks of a similar composition this work shows that weathering yields of mo v and u from smrs are slightly higher than from large rivers and the age of igneous lithologies in these regions exhibits a measurable control on riverine concentrations of these elements

the isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans despite important biological and biogeochemical consequences of extensive ocean anoxic events their identification is controversial the marine isotope geochemistry of molybdenum can help quantify the past oxygenation state of the ocean if the riverine input of mo isotopes is known analysis of a set of rivers that account for 28 of global river runoff suggests more variable mo isotopic ratios in rivers that are also isotopically enriched in the heavy isotopes suggesting near total anoxia in the proterozoic ocean and during mesozoic ocean anoxic events despite its important biological and biogeochemical consequences1 2 3 the identification of extensive oceanic anoxia in the geological record is controversial in particular global anoxia is difficult to distinguish from spatially restricted anoxia in the deep ocean or in tectonically isolated basins such as the modern black sea the marine isotope geochemistry of molybdenum mo can help quantify the past oxygenation state of the ocean4 5 6 7 8 9 10 11 12 13 14 because to first approximation under oxic conditions lighter isotopes of mo are preferentially removed to sediments whereas in euxinic conditions quantitative removal leads to no fractionation however the isotopic composition of the mo input from rivers the main contributor of mo to the oceans is poorly constrained and had been assumed to be isotopically comparable to the narrow range found in a small dataset of continental rocks4 5 6 7 8 9 10 11 12 13 14 here we present an isotopic analysis of mo in a set of rivers that together account for 22 of the global riverine water discharge we find a broad range of variability in the mo isotopic composition of these rivers with almost all samples enriched in the heavy isotopes compared with continental rocks our data remove key uncertainties associated with the marine mo isotope budget14 and strongly suggest near total anoxia in the mid proterozoic ocean8 as well as during mesozoic ocean anoxic events13

multiple sources of lead in soils from a hawaiian chronosequence abstract we report lead isotopic ratios and concentrations from a basaltic soil chronosequence in hawaii substrate ages at the sites range from 300 years to 4 1 million years all soils show a net addition of pb above the contributions made by basaltic weathering indicating that atmospheric deposition of natural or pollutant sources is important across the sequence isotopic ratios from the chronoseqence soils indicate a mixture of basalt mineral aerosol and anthropogenic pb sources derived from both long range and local inputs locally derived anthropogenic pb dominates young soils intermediate age soils in remote locations have a strong mineral aerosol signature and likely contain some anthropogenic lead of asian origin older soils have undergone extensive leaching of both basaltic and eolian lead while the anthropogenic inputs in most sites are from less radiogenic local and asian sources we find evidence of j type lead of north american origin in a remote soil on kauai the diversity of anthropogenic lead sources suggests that at least two different weather patterns dominate atmospheric pb transport across the hawaiian island chain

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

transient liquid water and water activity at gale crater on mars liquid water on equatorial mars is inconsistent with large scale climatic conditions humidity and temperature measurements by the curiosity rover support the formation of subsurface liquid brines by hydration of perchlorates during the night

kinematic implications of joint zones and isolated joints in the navajo sandstone at zion national park utah evidence for cordilleran relaxation 1 at zion national park znp the landscape is a consequence of differential weathering of the navajo sandstone where closely spaced vertical joints constitute joint zones that erode to form regularly spaced half kilometer slot canyons striking 351 between these joint zones is a set of isolated joints striking 339 fracture interaction and horsetail wing crack development indicate that the 339 striking joint set is younger than the 351 striking joint zones despite the lateral extent of stress reduction shadows in the vicinity of the large scale joint zones in addition to an older less pervasive 020 joint set this sequence of jointing records a counterclockwise rotation of the regional extension directed from wnw to wsw in the navajo sandstone at znp znp is located at the western margin of the colorado plateau 100 km east of the major normal faults of the northeastern central basin and range subprovince extension within the eastern central basin and range initiated during the miocene and exhibited a wsw extension direction anderson 1971 wernicke et al 1988 snow and wernicke 2000 the correlation between nearby basin and range extension and the extension direction for the 351 tending joint zones of znp is so close that the jointing at znp is interpreted as evidence for modest yet pervasive basin and range extension in the western margin of the colorado plateau

the behaviour of cu and zn isotopes during soil development controls on the dissolved load of rivers abstract the stable isotopes of copper cu and zinc zn are finding increasing applications in surface earth geochemistry an important early observation is that aqueous pools of cu rivers and oceans are isotopically heavier than rocks of the continental crust for zn the global average 66 zn for rivers is identical to estimates of the upper continental crust but the oceans are slightly heavier here we study cu and zn abundances and isotopes in soils to assess how processes in the weathering environment control isotopic values of rivers and ultimately the oceans we investigated a range of soils developed on granitoid scotland and basaltic hawaiian islands rock substrates representing soil development times from 0 1 to 400 kyr mean annual temperatures of 6 16 c and mean annual precipitation map of 1060 5050 mm soils developed on the island of maui over 400 kyr and under high rainfall show the clearest chemical weathering signatures here in oxic soils cu and zn are both depleted by 50 90 with preferential loss of heavy cu 65 cu up to 1 2 lower than parent material and small shifts in 66 zn we attribute this to equilibrium fractionation between aqueous organic species that are removed from the soil versus sorption to residual fe oxyhydroxides in soils that are 0 1 150 kyr old in scotland and hawaii this same pattern is overprinted by biological cycling and the addition of mineral aerosol cu and zn with heavier isotope compositions in reducing soils on maui developed under the highest rainfall cu and zn are almost completely stripped from the soil leaving a very small residual pool with 65 cu and 66 zn values that range from those for the oxic soils back to and beyond parent material this removal of the light sorbed cu seen in oxic soils is attributed to the dissolution of fe oxides under anaerobic conditions perhaps microbially mediated leaving a very small residual isotopically heavier pool overall these data suggest that processes in soils create significant variability in cu isotopes with the heavy isotope exported from oxic soils in contrast small isotope fractionations of zn are generated in the soil environment these observations are consistent with those made previously for cu and zn isotopes in rivers but the maximum amount of cu and zn stored by world soils equates to only 30 130 years of the dissolved riverine flux soils cannot be the ultimate repository of the residual cu and zn required balancing the riverine flux and this must ultimately reside in the erosive products of soil formation in continental and ocean margin sediments

a pb isotopic resolution to the martian meteorite age paradox abstract determining the chronology and quantifying various geochemical reservoirs on planetary bodies is fundamental to understanding planetary accretion differentiation and global mass transfer the pb isotope compositions of individual minerals in the martian meteorite chassigny have been measured by secondary ion mass spectrometry sims these measurements indicate that chassigny has mixed with a martian reservoir that evolved with a long term 238u 204pb value two times higher than those inferred from studies of all other martian meteorites except 4 428 ga clasts in nwa7533 any significant mixing between this and an unradiogenic reservoir produces ambiguous trends in pb isotope variation diagrams the trend defined by our new chassigny data can be used to calculate a crystallization age for chassigny of 4 526 0 027 ga 2 that is clearly in error as it conflicts with all other isotope systems which yield a widely accepted age of 1 39 ga similar trends have also been observed in the shergottites and have been used to calculate a 4 ga age or alternatively attributed to terrestrial contamination our new chassigny data however argue that the radiogenic component is martian mixing occurred on the surface of mars and is therefore likely present in virtually every martian meteorite the presence of this radiogenic reservoir on mars resolves the paradox between pb isotope data and all other radiogenic isotope systems in martian meteorites importantly chassigny and the shergottites are likely derived from the northern hemisphere of mars while nwa 7533 originated from the southern hemisphere implying that the u rich reservoir which most likely represents some form of crust must be widespread the significant age difference between snc meteorites and nwa 7533 is also consistent with an absence of tectonic recycling throughout martian history

geochronology of the martian meteorite zagami revealed by u pb ion probe dating of accessory minerals abstract the precise chronology of geological events on mars is hampered by the lack of absolute ages for the martian timescale and the significant uncertainties that result from the extrapolation of the lunar timescale to mars hartmann and neukum 2001 martian meteorites represent the only samples of mars currently available attempts to identify source craters for the meteorites have thus far proven inconclusive hamilton et al 2003 lang et al 2009 mouginis mark and boyce 2012 precluding their use in constraining the absolute martian timescale the majority of the known martian meteorites are basalts shergottites all dated shergottites have mineral separate rb sr or sm nd ages of borg et al 2005 here we report a 238u 206pb age of 182 7 6 9 ma by ion microprobe analysis of baddeleyite zro2 grains in the zagami shergottite there is no correlation between discordancy and baddeleyite grain location relative to shock metamorphism mineral petrography demonstrates that baddeleyite is the result of late stage igneous crystallization and raman spectroscopy shows that baddeleyite has not been transformed by shock into preservable high pressure polymorphs supported by an age of 153 81 ma for phosphate grains obtained using the same method we conclude that zagami crystallized at 180 ma in agreement with previous results from mineral separate geochronology therefore the shergottites represent igneous rocks preferentially ejected from young terrains on mars in a small number of ejection events

changing sources of strontium to soils and ecosystems across the hawaiian islands abstract strontium isotope ratios assist ecosystem scientists in constraining the sources of alkaline earth elements but their interpretation can be difficult because of complexities in mineral weathering and in the geographical and environmental controls on elemental additions and losses hawaii is a natural laboratory where a number of important biogeochemical variables have either limited ranges or vary in systematic ways providing a unique opportunity to understand the impact of time climate and atmospheric inputs on the evolution of base cation sources to ecosystems there are three major sources of strontium sr to these ecosystems each with distinct isotopic compositions basalt lava asian dust and rainfall we present sr isotope and concentration data on both bulk soil digests and nh4ac extracts from soil profiles covering a wide range of environments and substrate ages bulk soil material from dry climates and or young substrate ages with 80 g g 1 sr retain basalt like sr isotopic signatures whereas those with sr concentrations 40 by mass at elevated dust levels lava derived sr is low and dust derived sr is the dominant control of 87sr 86sr in bulk soils however 87sr 86sr of nh4ac extractable sr largely reflects atmospheric deposition of marine aerosol in these situations overall whole soil sr isotope values are controlled by complex interactions between sr provided by lava weathering but partially lost by leaching and sr provided by dust but held in more resistant minerals the isotopic composition of nh4ac extractable sr and of the biota is controlled by lava weathering and rainfall contribution of sr with only minor contributions from radiogenic dust sources

the age of dar al gani 476 and the differentiation history of the martian meteorites inferred from their radiogenic isotopic systematics samarium neodymium isotopic analysis of the martian meteorite dar al gani 476 yields a crystallization age of 474 11 ma and an initial end143 value of 36 6 0 8 although the rb sr isotopic system has been disturbed by terrestrial weathering and therefore yields no age information an initial 87sr 86sr ratio of 0 701249 33 has been estimated using the rb sr isotopic composition of the maskelynite mineral fraction and the sm nd age the sr and nd isotopic systematics of dar al gani 476 like those of the basaltic shergottite que94201 are consistent with derivation from a source region that was strongly depleted in incompatible elements early in the history of the solar system nevertheless dar al gani 476 is derived from a source region that has a slightly greater incompatible enrichment than the que94201 source region this is not consistent with the fact that the parental magma of dar al gani 476 is significantly more mafic than the parental magma of que94201 and underscores a decoupling between the major element and trace element isotopic systematics observed in the martian meteorite suite combining the end142 end143 isotopic systematics of the martian meteorites yields a model age for planetary differentiation of 4 513 0 033 0 027 ga using this age the parent daughter ratios of martian mantle sources are calculated assuming a two stage evolutionary history the calculated sources have very large ranges of parent daughter ratios 87rb 86sr 0 037 0 374 147sm 144nd 0 182 0 285 176lu 177hf 0 028 0 048 these ranges exceed the ranges estimated for terrestrial basalt source regions but are very similar to those estimated for the sources of lunar mare basalts in fact the range of parent daughter ratios calculated for the martian meteorite sources can be produced by mixing between end members with compositions similar to lunar mare basalt sources two of the sources have compositions that are similar to olivine and pyroxene rich mafic cumulates with variable proportions of a rb enriched phase such as amphibole whereas the third source has the composition of liquid trapped in the cumulate pile i e similar to kreep after 99 crystallization correlation between the proportion of trapped liquid in the meteorite source regions and estimates of fo2 suggest that the kreep like component may be hydrous the success of these models in reproducing the martian meteorite source compositions suggests that the variations in trace element and isotopic compositions observed in the martian meteorites primarily reflect melting of the crystallization products of an ancient magma ocean and that assimilation of evolved crust by mantle derived magmas is not required furthermore the decoupling of major element and trace element isotopic systematics in the martian meteorite suite may reflect the fact that trace element and isotopic systematics are inherited from the magma source regions whereas the major element abundances are limited by eutectic melting processes at the time of magma formation differences in major element abundances of parental magma therefore result primarily from fractional crystallization after leaving their source regions

importance of atmospheric inputs and fe oxides in controlling soil uranium budgets and behavior along a hawaiian chronosequence abstract a long term budget of uranium calculated for a chronosequence of hawaiian soils demonstrates the importance of mineral aerosol deposition as a geochemical pathway a series of sequential extractions on the same soils shows a strong association between fe oxides and uranium especially the amorphous and poorly crystalline fe oxides present in intermediate age soils 20 and 150 ka despite intense leaching conditions soil u contents were found to increase between 20 fold and 60 fold with age along the chronosequence from 9 to 17 g cm 2 at 0 3 ka sites to 344 543 g cm 2 at the 4100 ka site an open system transport function comparing u to an index least mobile element nb was used to calculate u gains or losses from the soils relative to the input from parent material weathering results show small losses or small gains 25 of u occurred in soils 150 ka and younger while gains of up to 531 u occurred in soils older than 150 ka highlighting the importance of mineral aerosol dust deposition at the older sites in the 4100 ka soil the ratio of dust derived u inputs to parent material derived u inputs is approximately 6 sequential extractions show that between 0 1 and 1 2 of the total u in the soils was extracted with ammonium acetate indicating that very little u exists as exchangeable cations a second extraction employing citrate dithionate and hydroxylamine hydrochloride was performed to extract u associated with fe oxides average percent occurrences for u in the fe oxide extraction for each profile are 7 at 0 3 ka 53 at 20 ka 40 at 150 ka and 17 at 4100 ka illustrating an increase with age to 20 ka followed by a subsequent decline this parallels the trend observed in amorphous fe oxide content suggesting that adsorption on amorphous fe oxides is the dominant control on u in the intermediate age soils

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

thrust fault modeling and late noachian lithospheric structure of the circum hellas region mars the circum hellas area of mars borders hellas planitia a giant impact 4 0 4 2 ga old making the deepest and broadest depression on mars and is characterized by a complex pattern of fracture sets lobate scarps grabens and volcanic plains the numerous lobate scarps in the circum hellas region mainly formed in the late noachian and except amenthes rupes have been scarcely studied in this work we study the mechanical behavior and thermal structure of the crust in the circum hellas region at the time of lobate scarp formation through the modeling of the depth of faulting beneath several prominent lobate scarps we obtain faulting depths between 13 and 38 km depending on the lobate scarp and accounting for uncertainty these results indicate low surface and mantle heat flows in noachian to early hesperian times in agreement with heat flow estimates derived from lithospheric strength for several regions of similar age on mars also faulting depth and associate heat flows are not dependent of the local crustal thickness which supports a stratified crust in the circum hellas region with heat producing elements concentrated in an upper layer that is thinner than the whole crust

trace element geochemistry of volcanic gases and particles from 1983 1984 eruptive episodes of kilauea volcano compositional data have been obtained for volcanic gases and particles collected from fume emitted at the pu u o o vent on the east rift zone of kilauea volcano the samples were collected by pumping fume through a filter pack system consisting of a front stage particulate filter followed by four base treated filters 7lioh particles and condensed phases are trapped on the particulate filter and acidic gases are collected on the treated filters the filters are analyzed for 30 elements by instrumental neutron activation analysis fume samples were collected from the pu u o o vent for two eruptive episodes 1 7 days after episode 11 cooling vent samples and 2 the waning stage of episode 13 active vent samples additional samples were collected by aircraft from the gas plume released during the lava fountaining phase of episode 17 aircraft samples element concentrations in the vent gases were 104 g m 3 for s cl and f enrichment factors efs for the volcanic fume versus the source magma were calculated using the volatile element br as the reference element for normalization and the u s geological survey standard bhvo 1 as the magma standard this removes the ash dilution effect obtained by using an ash constituent al sc or mg as the reference element bromine normalized efs 105 range from 101 to 102 for na k and cu 102 to 105 for zn w sb in ir ag f and as and 105 for au cd re cl se and s the highest enrichment factors are for aircraft samples collected during the most gas rich phase of an eruption cycle metal and volatile element data form two groups 1 elements showing little or no variation in abundance ratios with sample type group 1 cl br and re and 2 elements that show significant variation in abundance ratios by sample type group 2 zn w sb in ir au and cd bivariate plots of elements of the first group versus elements of the second group separate by sample type the separation corresponds to samples collected during eruptive activity versus samples collected during repose periods monitoring trace metal ratios in volcanic fume could provide an additional tool for predicting volcanic eruptions the f cl ratio of cooling vent samples is higher than those of active vent or aircraft samples and the ratio is inversely correlated with efs for most volatile metals

halogens and trace metal emissions from the ongoing 2008 summit eruption of kīlauea volcano hawai i volcanic plume samples taken in 2008 and 2009 from the halema uma u eruption at k lauea provide new insights into k lauea s degassing behaviour the cl f and s gas systematics are consistent with syn eruptive east rift zone measurements suggesting that the new halema uma u activity is fed by a convecting magma reservoir shallower than the main summit storage area comparison with degassing models suggests that plume halogen and s composition is controlled by very shallow 77 as gaseous elemental mercury at the point of emission sulphate is an important aerosol component modal particle diameter 0 44 m aerosol halide ion concentrations are low compared to other systems consistent with the lower proportion of gaseous hydrogen halides plume concentrations of many metallic elements rb cs be b cr ni cu mo cd w re ge as in sn sb te tl pb mg sr sc ti v mn fe co y zr hf ta al p ga th u la ce pr nd sm eu gd tb dy er tm are elevated above background air there is considerable variability in metal to so2 ratios but our ratios generally at the lower end of the range previously measured at k lauea support assertions that k lauea s emissions are metal poor compared to other volcanic settings our aerosol re and cd measurements are complementary to degassing trends observed in hawaiian rock suites although measured aerosol metal s ratios are about an order of magnitude lower than those calculated from degassing trends determined from glass chemistry plume enrichment factors with respect to hawaiian lavas are in broad agreement with those from previous studies allowing similar element classification schemes to be followed i e lithophile elements having lower volatility and chalcophile elements having higher volatility the proportion of metal associated with the largest particle size mode collected 2 5 m and that bound to silicate is significantly higher for lithophiles than chalcophiles many metals show higher solubility in ph 7 buffer solution than deionised water suggesting that acidity is not the sole driver in terms of solubility nonetheless many metals are largely water soluble when compared with the other sequential leachates suggesting that they are delivered to the environment in a bioavailable form preliminary analyses of environmental samples show that concentrations of metals are elevated in rainwater affected by the volcanic plume and even more so in fog however metal levels in grass samples showed no clear enrichment downwind of the active vents

uranium lead isotope systematics of mars inferred from the basaltic shergottite que 94201 abstract uranium lead ratios commonly represented as 238u 204pb calculated for the sources of martian basalts preserve a record of petrogenetic processes that were active during early planetary differentiation and formation of martian geochemical reservoirs to better define the range of values represented by the source regions of martian basalts we completed u pb elemental and isotopic analyses on whole rock mineral and leachate fractions from the martian meteorite queen alexandra range 94201 que 94201 the whole rock and silicate mineral fractions have unradiogenic pb isotopic compositions that define a narrow range 206pb 204pb 11 16 11 61 in contrast the pb isotopic compositions of weak hcl leachates are more variable and radiogenic the intersection of the que 94201 data array with terrestrial pb in 206pb 204pb 207pb 204pb 208pb 204pb compositional space is consistent with varying amounts of terrestrial contamination in these fractions we calculate that only 1 7 contamination is present in the purified silicate mineral and whole rock fractions whereas the hcl leachates contain up to 86 terrestrial pb this terrestrial pb contamination generated a 206pb 207pb array in the que fractions that appears to represent an ancient age which contrasts with a much younger crystallization age of 327 10 ma derived from rb sr and sm nd isochrons borg l e nyquist l e taylor l a wiesmann h and shih c y 1997 constraints on martian differentiation processes from rb sr and sm nd isotopic analyses of the basaltic shergottite que 94201 geochim cosmochim acta 61 4915 4931 despite the contamination and accepting 327 10 ma as the crystallization age we use the u pb data to determine the initial 206pb 204pb of que 94201 to be 11 086 0 008 and to calculate the value of its mantle source to be 1 82 0 01 the value calculated for the que 94201 source is the lowest determined for any martian basalt source and when compared to the highest values determined for martian basalt sources indicates that values in martian source reservoirs vary by at least a factor of two additionally the range of source values indicates that the value of bulk silicate mars is approximately three the amount of variation in the values of the mantle sources 2 4 is greater than can be explained by igneous processes involving silicate phases alone we suggest the possibility that a small amount of sulfide crystallization may generate greater extents of u pb fractionation during formation of the mantle sources of martian basalts

rb sr sm nd and ar ar isotopic systematics of martian dunite chassigny abstract isotopic analysis of the martian meteorite chassigny yields a rb sr age of 1406 14 ma with an initial 87 sr 86 sr ratio of 0 702251 0 000034 a sm nd age of 1386 28 ma with an initial e 143nd value of 16 9 0 3 and an 39 ar 40 ar age of 1360 40 20 ma the concordance of these ages and the rb sr and sm nd initial isotopic signatures suggest that chassigny crystallized from low rb sr light rare earth element depleted source materials 1390 ma ago the ages and e 143nd values of chassigny and the nakhlites governador valadares and lafayette overlap suggesting that they could have come from very similar mantle sources nakhla northwest africa 998 and yamato 000593 appear to be from similar but distinct sources chassigny and all nakhlites so far studied have undergone similar evolution histories that is chassignites nakhlites were derived from a region where volcanism lasted at least 50 ma and crystallized from different lava flows or subsurface sills they probably were launched from mars by a single impact event the trapped martian atmospheric 40 ar 36 ar ratios in chassigny nakhlites and shergottite impact glass are similar and possibly indicate minimal change in this ratio over the past 600 ma

influence of atmospheric deposits and secondary minerals on li isotopes budget in a highly weathered catchment guadeloupe lesser antilles abstract to better constrain li dynamics in the tropics we sampled critical zone compartments of a small forested andesitic catchment in guadeloupe soils parent rock atmospheric dust plants soil solutions stream and rain waters the aims of this study are to identify the origin of li in the different compartments and to better characterize the behavior of li and its isotopes during water rock interaction in a highly cation depleted soil the li isotope signature 7li of throughfall samples varies between 11 2 and 26 4 as this is lower than the seawater signature 31 and vegetation does not fractionate li isotopes our data indicate that saharan dust 0 7 significantly contributes to the throughfall signature li isotope composition measured in a 12 5 m deep soil profile varies from 3 9 near the surface to 13 5 at 11 m depth compared to unweathered andesite 5 the deep soil signature is in agreement with preferential incorporation of light li into secondary minerals in the top soil however our results also emphasized that atmospheric deposition wet and dry is a main source of li to the soil the decreasing 7li with increasing depth is consistent with a vertical gradient of incorporation of heavy atmospheric li this input being maximal near the surface at the catchment scale throughfall and total atmospheric inputs sea salts saharan dust provide 12 1 and 23 9 g li yr 1 respectively to the quiock creek catchment these fluxes represent 34 and 67 respectively of li exported at the outlet indicating that atmospheric deposition is one of the main li inputs to the critical zone li concentration and isotopic mass balance at the catchment scale indicate that in addition to atmospheric deposition secondary mineral phase dissolution is a major solute source and that andesite no longer participates in significant production of li

formation ages and evolution of shergotty and its parent planet from u th pb systematics the isotopic composition of lead was determined in different phases from shergotty zagami and eeta 79001 using phases with low 238 u 204 pb the initial leads of these meteorites could be well defined and are distinct from each other and have high 204 pb 206 pb from 0 0652 to 0 0739 these leads evolved in different reservoirs over most of solar system history in a low 238 u 204 pb 5 environment it follows that the parent planet of the shergottites has a high 204 pb concentration relative to u and must also be high in other volatiles if the parent planet of the shergottites is mars then this planet must be volatile rich compared to the earth by a factor of 1 8 this implies that mars lost its original atmosphere and that the present atmosphere was derived from a previously outgassed martian upper mantle the u th pb isotopic relationships involving phases with high 238 u 204 pb are quite regular and give ages for three shergottites which indicate an event of u th pb fractionation at 200 m y the initial leads at that time were highly evolved relative to the primordial lead the absence of substantial additions of radiogenic lead above the initial lead in high u phases precludes an older age for the u th pb fractionation however details of the data arrays are complex the young age is in general agreement with some of the ages obtained by other methods but precise concordance between the different methods is not established it is suggested that the shock event that produced maskelynite may possibly be associated with the late stage breakup at 2 5 m y and not necessarily related to the 180 m y record the major event of chronometer resetting is taken to be 180 m y this event does not appear to be an endogenic igneous event but an almost complete equilibration during a major impact on more ancient igneous rocks which were contained in the target problems of the polymetamorphic history of meteorites appear as complicated as those of polymetamorphic terrestrial terranes

integrated pb and s isotope investigation of sulphide minerals from the early archaean of southwest greenland we present high spatial resolution secondary ion mass spectrometry sims measurements of pb and s isotopes in sulphides from early archaean samples at two localities in southwest greenland secondary pyrite from a 3 71 ga sample of magnetite quartz banded iron formation in the isua greenstone belt which has previously yielded unradiogenic pb consistent with its ancient origin contains sulphur with a mass independently fractionated mif isotope signature delta 33 s 3 3 parts per thousand this reflects the secondary mineralization of remobilized sedimentary s carrying a component modified by photochemical reactions in the early archaean atmosphere it further represents one of the most extreme positive excursions so far known from the early archaean rock record sulphides from a quartz pyroxene rock and an ultramafic boudin from the island of akilia in the godth a over circle bsfjord have heterogeneous and generally radiogenic pb isotopic compositions that we interpret to represent partial re equilibration of pb between the sulphides and whole rocks during tectonothermal events at 3 6 2 7 and 1 6 ga both these samples have delta 33 s 0 within analytical error and therefore show no evidence for mif sulphur these data are consistent with previous interpretations that the rock cannot be proven to have a sedimentary origin our study illustrates that sims s isotope measurements in ancient rocks can be used to elucidate early atmospheric parameters because of the ability to obtain combined s and pb isotope data but caution must be applied when using such data to infer protolith when information from geological context petrography and chronology i e by pb isotopes is combined and fully evaluated delta 33 s signatures from sulphides and their geological significance can be interpreted with a higher degree of confidence c 2005 elsevier b v all rights reserved