long term atmospheric deposition as the source of nitrate and other salts in the atacama desert chile new evidence from mass independent oxygen isotopic compositions abstract isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the atacama desert in northern chile has shown anomalous 17 o enrichments in both minerals 17 o values of 14 21 in nitrate and 0 4 to 4 in sulfate are the most positive found in terrestrial minerals to date modeling of atmospheric processes indicates that the 17 o signatures are the result of photochemical reactions in the troposphere and stratosphere we conclude that the bulk of the nitrate sulfate and other soluble salts in some parts of the atacama desert must be the result of atmospheric deposition of particles produced by gas to particle conversion with minor but varying amounts from sea spray and local terrestrial sources flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200 000 to 2 0 m years during hyper arid conditions similar to those currently found in the atacama desert correlations between 17 o and 18 o in nitrate salts from the atacama desert and mojave desert california indicate varying fractions of microbial and photochemical end member sources the photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture biologic activity and nitrogen cycling these isotopic signatures have important implications for paleoclimate astrobiology and n cycling studies

sulfur isotopic compositions of individual sulfides in martian meteorites alh84001 and nakhla implications for crust regolith exchange on mars atmospheric chemical reactions on mars have been invoked to explain non mass dependent 33s anomalies 33s 33s 0 516 34s reported from bulk analyses of martian meteorites to explore this signature in detail a new ion microprobe multi collector technique was developed to obtain precise in situ 32s 33s and 34s measurements of individual sulfide grains from martian meteorites alh84001 4 0 ga and nakhla 1 3 ga this technique permits high precision simultaneous measurement of multiple isotopes to uniquely evaluate 33s at the grain scale 30 m our data reveal resolvable non mass dependent 33s anomalies in two separate alh84001 pyrite grains 33s 0 74 0 39 and 0 51 0 38 2 none were detectable in nakhla pyrrhotite total range in 33s 0 4 0 5 to 0 07 0 5 2 our results might reflect a difference in how these meteorites exchanged sulfur with the martian regolith and or differences in their sources atmospheric versus meteoritic of anomalous sulfur nebular heterogeneities in sulfur isotope composition are indicated by 33s anomalies preserved in for example the ureilites the 33s anomalies in alh84001 pyrite could suggest that early pre 4 ga additions of a meteoritic component carried isotopically anomalous sulfur to the martian regolith and was stored there as seen in the detection of 33s anomalies from bulk measurements of nakhla therefore meteoritic contributions should also be considered in addition to atmospheric effects when explaining the large non mass dependent anomalies seen in martian meteorites these studies provide insight into how hydrothermal systems have facilitated exchange between volatile reservoirs on mars a planet that lacks efficient crustal recycling mechanisms and preserves ancient and anomalous 33s signatures

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

a 4 gyr shock age for a martian meteorite and implications for the cratering history of mars analyses of meteorites that originated on mars provide important insights into the geological and atmospheric evolution of the planet such analyses have hitherto been restricted to relatively young martian rocks1 the oldest martian meteorites have an age of approximately 1 3 billion years but the recently recognized2 martian meteorite allan hills 84001 which is distinct from the other martian meteorites2 4 shows evidence for a much older age5 6 here we report an analysis of the shock alteration history of this meteorite based on argon isotope dating from which we derive a shock age of 4 0 0 1 billion years the age and geological history of this meteorite suggest that it came from the heavily cratered noachian age terrains of mars s southern hemisphere and it may thus provide an absolute chronology for this region of the planet independent of that inferred from the cratering record the shock age of the meteorite also coincides with that of the so called lunar cataclysm a relatively short period during which many of the craters on the moon are believed to have formed supporting the idea7 that intense bombardment was widespread throughout the inner solar system between 3 9 and 4 1 billion years ago

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

snc meteorites are they martian rocks snc shergottite nakhlite chassignite achondrites are similar in many respects to terrestrial basaltic and ultramafic rocks several independent geochemical and petrological characteristics suggest that they formed on mars these include young 1 3 b y crystallization ages evidence for a magmatic history too complex for an asteroid possibility of garnet in the source region calculations of the magnitude of the gravity field necessary for crystal accumulation by settling presence of trapped gases similar to the the martian atmosphere and other features consistent with what is known about mars however the dynamical difficulties of ejecting meteorites from planetary surfaces are formidable

oxygen isotopic record of silicate alteration in the shergotty nakhla chassigny meteorite lafayette samples from a suite of shergotty nakhla chassigny snc meteorites were analyzed for their o isotopic ratios by a modified version of the laser fluorination technique measured isotopic ratios 17o 16o and 18o 16o from bulk samples of the shergottites eeta79001 shergotty and zagami the nakhlite lafayette and chassigny are similar to those reported in the literature as are those from olivine and pyroxene mineral separates from lafayette iddingsite a preterrestrial alteration product of lafayette was measured for the first time as a separate phase oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum 18o of 14 4 for a 90 separate based on these measurements end member iddingsite has a 18o of 15 6 which places it among other 18o enriched secondary phases carbonate and silica observed in snc meteorites the relatively large difference in 18o between iddingsite and the olivine and pyroxene it replaces 11 is typical of low temperature alteration products a range of crustal fluid 18o values can be interpreted from the 18o for end member iddingsite assuming isotopic equilibrium was achieved during low temperature hydrous alteration 100 c treiman et al 1993 the calculated range of values 15 to 5 depends on many factors including 1 the modal mineralogy of iddingsite 2 potential isotopic exchange among other o bearing phases such as host silicate and carbonate and 3 exchange with evolved or exotic o reservoirs on mars despite the lack of constraints the calculated range is consistent with isotopic exchange and possibly equilibria among components of the co2 carbonate iddingsite h2o system at low temperature the snc meteorite samples in this study have 17o values that are indistinguishable from bulk mars 0 30 except for a single small sample of iddingsite that has an anomalous 17o of 1 4 while analytical difficulties make isotopic measurements for this sample problematic the 17o is similar in direction to 17o reported for waters extracted from bulk samples of lafayette karlsson et al 1992 if the 17o for iddingsite is confirmed it can be concluded that evolved or exotic fluids on mars have contributed volatiles to the o reservoir from which iddingsite formed 130 to 700 ma ago

sulfate oxygen 17 anomalies in desert varnishes rock varnishes are ubiquitous in arid regions on earth and are believed to be commonly present on mars here we report high water soluble sulfate and nitrate contents in desert varnishes from the death valley region of southwestern u s a and that sulfate in varnishes possess 17o 18o ratios that do not fall on terrestrial mass dependent fractionation line sulfate from wet and dry atmospheric deposition is probably the source of the 17o anomalies the anomalies are only moderately lower than that of aerosol sulfates collected from the greater los angeles area indicating probably more than half of the sulfate in desert varnish is supplied by atmospheric deposition this finding suggests that earth surface environments are constantly accumulating 17o anomalous sulfate from the atmosphere arid and stable conditions facilitate the preservation of these atmospheric signatures this finding also indicates that different 17o 18o ratios found in different components in the martian meteorites may result from atmospheric chemical processes

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

evidence for recent volcanism on mars from crater counts impact craters help characterize the age of a planetary surface because they accumulate with time they also provide useful constraints on the importance of surface erosion as such processes will preferentially remove the smaller craters earlier studies of martian crater populations revealed that erosion and dust deposition are important processes on mars they disagreed however on the age of the youngest volcanism these earlier studies were limited by image resolution to craters larger than a few hundred metres in diameter here we report an analysis using new images obtained by the mars global surveyor spacecraft of crater populations that extend the size distribution down to about 16 m our results indicate a wide range of surface ages with one region lava flows within the arsia mons caldera that we estimate to be no older than 40 100 million years we suggest that volcanism is a continuing process on mars

pliocene 3 2 2 4 ma ostracode faunal cycles and deep ocean circulation north atlantic ocean ostracode assemblages from deep sea drilling project sites 607 western mid atlantic ridge and 610 southeast rockall plateau show rapid systematic shifts during late pliocene glacial interglacial cycles that reflect deep sea environmental change progressive decreases in north atlantic deep water taxa and increases in southern ocean taxa occur from 3 4 to 2 4 ma and high amplitude faunal cycles begin near 2 8 ma four ostracode assemblages each with a characteristic phase relative to 41 k y obliquity glacial interglacial 18 o cycles characterize the benthic faunal record at site 607 cross spectral analysis shows that the site 607 glacial assemblage has a 41 k y periodicity significant at the 95 level other assemblages show a less significant but still obvious concentration of variance at 41 k y faunal patterns suggest climatically controlled reorganization of deep sea benthic communities during glacial interglacial cycles due to oscillating deep sea environments

carbonate formation events in alh 84001 trace the evolution of the martian atmosphere carbonate minerals provide critical information for defining atmosphere hydrosphere interactions carbonate minerals in the martian meteorite alh 84001 have been dated to 3 9 ga and both c and o triple isotopes can be used to decipher the planet s climate history here we report 17o 18o and 13c data of alh 84001 of at least two varieties of carbonates using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the martian atmosphere hydrosphere geosphere interactions and surficial aqueous alterations these results indicate the presence of a ca rich carbonate phase enriched in 18o that formed sometime after the primary aqueous event at 3 9 ga the phases showed excess 17o 0 7 that captured the atmosphere regolith chemical reservoir transfer as well as co2 o3 and h2o isotopic interactions at the time of formation of each specific carbonate the carbon isotopes preserved in the ca rich carbonate phase indicate that the noachian atmosphere of mars was substantially depleted in 13c compared with the modern atmosphere

petrogenesis of the nakhlite meteorites evidence from cumulate mineral zoning abstract a simple igneous petrogenesis for the meteorite nakhla has previously been called into question because mg fe ratios in olivine indicate substantial disequilibrium between the predominant cumulus minerals olivine and augite comparative analyses of simulated diffusive zoning and the observed cumulus mineral zoning for all three nakhlites nakhla governador valadares and lafayette show that their current compositions do not necessarily reflect parental magma compositions instead diffusion has altered primary cumulus compositions to varying degrees nakhla being the least affected and lafayette being almost completely re equilibrated only the cores of augite grains in nakhla and governador valadares appear to have preserved their original compositions mineral zoning in each meteorite is strongly concentric around mesostasis areas suggesting that reaction with intercumulus liquid has controlled the observed zoning the presence of pigeonite and orthopyroxene overgrowths in nakhla and governador valadares and of poikilitic orthopyroxene enclosing olivine relicts in lafayette indicate substantial late magmatic reactions two pyroxene geothermometry for lafayette indicates temperatures around 950 c suggesting subsolidus equilibration as well the nakhlites appear to be a series of relatively simple cumulate rocks which have undergone various amounts of late magmatic and subsolidus diffusion possibly reflecting their relative positions in a cooling cumulate pile

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

the parent magma of the nakhlite meteorites clues from melt inclusions abstract several forms of trapped liquid found within nakhlite meteorites have been examined including interstitial melt and magmatic inclusions within the cores of large olivine grains differences in the mineralogy and texture between two types of trapped melt inclusions and between these inclusions and the mesostasis indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early forming olivine and augite parent liquids were calculated from the mineralogy of large inclusions in nakhla and governador valadares using a system of mass balance equations solved by linear regression methods the chosen parental liquids were cosaturated in olivine and augite and had mg fe values consistent with measured augite liquid kd s these parental magma compositions are similar to other published compositions for nakhla chassigny and shergotty parental melts and may correspond to a significant magma type on mars

the history of allan hills 84001 revised multiple shock events the geologic history of martian meteorite allan hills alh 84001 is more complex than previously recognized with evidence for four or five crater forming impacts onto mars this history of repeated deformation and shock metamorphism appears to weaken some arguments that have been offered for and against the hypothesis of ancient martian life in alh 84001 allan hills 84001 formed originally from basaltic magma its first impact event i1 is inferred from the deformation d1 that produced the granular textured bands crush zones that transect the original igneous fabric deformation d1 is characterized by intense shear and may represent excavation or rebound flow of rock beneath a large impact crater an intense thermal metamorphism followed d1 and may be related to it the next impact i2 produced fractures fr2 in which carbonate pancakes were deposited and produced feldspathic glass from some of the igneous feldspars and silica after i2 carbonate pancakes and globules were deposited in fr2 fractures and replaced feldspathic glass and possibly crystalline silicates next feldspars feldspathic glass and possibly some carbonates were mobilized and melted in the third impact i3 microfaulting intense fracturing and shear are also associated with i3 in the fourth impact i4 the rock was fractured and deformed without significant heating which permitted remnant magnetization directions to vary across fracture surfaces finally alh 84001 was ejected from mars in event i5 which could be identical to i4 this history of multiple impacts is consistent with the photogeology of the martian highlands and may help resolve some apparent contradictions among recent results on alh 84001 for example the submicron rounded magnetite grains in the carbonate globules could be contemporaneous with carbonate deposition whereas the elongate magnetite grains epitaxial on carbonates could be ascribed to vapor phase deposition during i3

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

ion microprobe measurements of 18o 16o ratios of phosphate minerals in the martian meteorites alh84001 and los angeles abstract oxygen isotope ratios of merrillite and chlorapatite in the martian meteorites alh84001 and los angeles have been measured by ion microprobe in multicollector mode 18o values of phosphate minerals measured in situ range from 3 to 6 and are similar to martian meteorite whole rock values as well as the 18o of igneous phosphate on earth these results suggest that the primary abiotic igneous phosphate reservoir on mars is similar in oxygen isotopic composition to the basaltic phosphate reservoir on earth this is an important first step in the characterization of martian phosphate reservoirs for the use of 18o of phosphate minerals as a biomarker for life on mars cumulative textural major element and isotopic evidence presented here suggest a primary igneous origin for the phosphates in los angeles and alh84001 textural and chemical evidence suggests that phosphates in alh84001 were subsequently shock melted in a later event

negative δ18o values in allan hills 84001 carbonate possible evidence for water precipitation on mars the martian meteorite alh84001 contains 1 by weight of carbonate formed by secondary processes on the martian surface or in the shallow subsurface the major form of this carbonate is chemically and isotopically zoned rosettes which have been well documented elsewhere this study concentrates upon carbonate regions 200 m across which possess previously unobserved magnesium rich inner cores interpreted here as rosette fragments surrounded by a later stage cement containing rare ca rich carbonates up to ca81mg07fe04mn07 intimately associated with feldspar high spatial resolution ion probe analyses of ca rich carbonate surrounding rosette fragments have 18ov smow values as low as 10 these values are not compatible with deposition from a global martian atmosphere invoked to explain alh84001 rosettes the range of 18o values are also incompatible with a fluid that has equilibrated with the martian crust at high temperature or from remobilisation of carbonate of rosette isotopic composition at martian atmospheric temperatures the small co2 gas co2 ice fractionation makes meteoric co2 an unlikely source for 10 carbonates in contrast closed system rayleigh fractionation of h2o can generate 18oh2o 30 as observed at high latitudes on earth we suggest that atmospheric transport and precipitation of h2o in a similar fashion to that on earth provides a source of suitably 18o depleted water for generation of carbonate with 18ov smow 10

a nitrogen and argon stable isotope study of allan hills 84001 implications for the evolution of the martian atmosphere the abundances and isotopic compositions of n and ar have been measured by stepped combustion of the allan hills 84001 alh 84001 martian orthopyroxenite material described as shocked is n poor n approximately 0 34 ppm delta 15n approximately 23 although during stepped combustion 15n enriched n delta 15n approximately 143 is released in a narrow temperature interval between 700 degrees c and 800 degrees c along with 13c enriched c delta 13c approximately 19 and 40ar cosmogenic species are found to be negligible at this temperature thus the isotopically heavy component is identified in part as martian atmospheric gas trapped relatively recently in the history of alh84001 the n and ar data show that alh84001 contains species from the martian lithosphere a component interpreted as ancient trapped atmosphere in addition to the modern atmospheric species and excess 40ar from k decay deconvolution of radiogenic 40ar from other ar components on the basis of end member 36ar 14n and 40ar 36ar ratios has enabled calculation of a k ar age for alh 84001 as 3 5 4 6 ga depending on assumed k abundance if the component believed to be martian palaeoatmosphere was introduced to alh 84001 at the time the k ar age was set then the composition of the atmosphere at this time is constrained to delta 15n or 200 40ar 36ar or 17 x 10 5 in terms of the petrogenetic history of the meteorite alh 84001 crystallised soon after differentiation of the planet may have been shocked and thermally metamorphosed in an early period of bombardment and then subjected to a second event this later process did not reset the k ar system but perhaps was responsible for introducing recent atmospheric gases into alh 84001 and it might mark the time at which alh 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages

petrography and composition of martian regolith breccia meteorite northwest africa 7475 the northwest africa nwa 7475 meteorite is one of the several stones of paired regolith breccias from mars based on petrography oxygen isotope mineral compositions and bulk rock compositions its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten other clast types include crystallized impact melt rocks evolved plutonic rocks possible basalts contact metamorphosed rocks and siltstones impact spherules and vitrophyre shards record airborne transport and accreted dust rims were sintered on most clasts presumably during residence in an ejecta plume the clast assemblage records at least three impact events one that formed an impact melt sheet on mars 4 4 ga ago a second that assembled nwa 7475 from impactites associated with the impact melt sheet at 1 7 1 4 ga and a third that launched nwa 7475 from mars 5 ma ago mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to 5 and 15 gpa the mild postshock heating that resulted from these shock pressures would have been insufficient to sterilize this water bearing lithology during launch magnetite maghemite and pyrite are likely products of secondary alteration on mars textural relationships suggest that calcium carbonate and goethite are probably of terrestrial origin yet trace element chemistry indicates relatively low terrestrial alteration comparison of mars odyssey gamma ray spectrometer data with the fe and th abundances of nwa 7475 points to a provenance in the ancient southern highlands of mars gratteri crater with an age of 5 ma and an apparent diameter of 6 9 km marks one possible launch site of nwa 7475

mars volatile evolution implications of the recent measurement of 17o in water from the snc meteorites escape of oxygen to space on mars is capable of producing a fractionation of oxygen isotopes in the remaining oxygen which is off of the fractionation line produced by the usual mass dependent exchange processes the magnitude of fractionation which can occur can be larger than that which was measured in oxygen in water derived from the snc meteorites thought to have come from mars in conjunction with the apparent lack of fractionation of 18o in the atmosphere this result suggests that less than 25 of the oxygen in the martian climate system has been lost over geologic time other mechanisms also might be able to produce such a fractionation so that this conclusion is not unique however it is consistent with other lines of evidence there is no requirement for an initial volatile inventory with an isotopic composition different from that of the bulk planet as might be the case for a late veneer of volatile rich material

the age of the carbonates in martian meteorite alh84001 the age of secondary carbonate mineralization in the martian meteorite alh84001 was determined to be 3 90 0 04 billion years by rubidium strontium rb sr dating and 4 04 0 10 billion years by lead lead pb pb dating the rb sr and pb pb isochrons are defined by leachates of a mixture of high graded carbonate visually estimated as approximately 5 percent whitlockite trace and orthopyroxene approximately 95 percent the carbonate formation age is contemporaneous with a period in martian history when the surface is thought to have had flowing water but also was undergoing heavy bombardment by meteorites therefore this age does not distinguish between aqueous and impact origins for the carbonates

oxygen cycle of the martian atmosphere regolith system δ17o of secondary phases in nakhla and lafayette oxygen isotope fractionations among silicates carbonates and sulfate from nakhla and lafayette can be used to resolve how multiple oxygen isotope reservoirs formed and evolved on mars and to gain insight into the environment and processes that led to the formation of the snc carbonates and other secondary minerals carbonates and sulfate from nakhla and lafayette carry an imprint of atmospheric chemistry analogous to that documented on earth but reflect an inhospitable environment where ozone hydrogen peroxide and odd oxygen compounds transferred their signature of atmospheric oxygen isotope fractionations to water ice and minerals that formed in the regolith at low temperature such an environment would not be conducive to the preservation of easily oxidized organic compounds its existence provides an abiotic isotopic benchmark biotic processes should produce isotopic fractionations that lie on a coherent mass fractionation line and not the mass independent fractionation relationships observed in the present study

implications from sulfur isotopes of the nakhla meteorite for the origin of sulfate on mars abstract the isotope geochemistry of sulfur in the snc shergottite nakhlite chassignite meteorites may carry important implications for the origin and chemistry of sulfates and sulfides in the martian surface and subsurface we report measurements of the sulfur isotope composition for three sulfur bearing components of the nakhla meteorite these results yield a negative 33 s signal of 1 25 and a near zero 36 s signal for total sulfate as well as a small nonzero 33 s of 0 09 for sulfide phases the 33 s of total sulfate measured here is more negative than the 33 s reported previously for water soluble sulfate and points to sulfur isotopic heterogeneity in the sulfate of nakhla current understanding of mass independent isotope effects associated with sulfur oxidation reactions rules out hydrothermal oxidation mechanisms for producing nonzero 33 s and points to a significant role for photochemical effects including hyperfine chemistry likely located in the martian atmosphere the near zero 36 s signal allows for the possibility of hyperfine chemistry because of the relationship between snc sulfate and the sulfate deposits seen on mars these results place constraints on the generation of sulfur vi at the martian surface and provide a case for future direct measurements of 33 s and 36 s of martian sulfate

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

source of copper in the giant shimensi w cu mo polymetallic deposit south china constraints from chalcopyrite geochemistry and oxygen fugacity of ore related granites abstract porphyry type copper mineralization is generally considered to be related to ore forming fluid exsolution from oxidized magnetite bearing intermediate to felsic magmas however copper deposits associated with ilmenite bearing per aluminous evolved granites also exist and their origin remains obscure the shimensi w cu mo polymetallic deposit located in the northern segment of the jiangnan orogen south china composed mainly of the neoproterozoic shuangqiaoshan group meta sediments volcanic rocks and biotite granite is one of the largest tungsten deposits in the world the w cu mo polymetallic orebodies occur at the contact zone between the mesozoic ilmenite bearing fluorite bearing f rich highly fractionated granite and the neoproterozoic granite the reason for the accompanying cu mineralization within ilmenite bearing granites is unclear in this paper we present a detailed study of chalcopyrite geochemistry including s pb isotopes trace elements and nd isotopes and oxygen fugacity fo2 of ore related granites in the shimensi deposit to constrain the origin of copper sulfur isotope values of the sulfides give a narrow 34s interval of 3 3 to 0 5 mean 1 5 n 32 suggesting the ore forming fluid is of magmatic origin the similarity of pb isotopes of the majority of sulfides and k feldspars from mesozoic granites indicates their genetic relationship however chalcopyrite samples show a wider range of pb isotopic compositions than that of k feldspars suggesting an extra source for the ore forming fluids chalcopyrite from the ore deposit show features of lree enriched patterns variable eu negative anomalies eu eu 0 26 0 75 and la sm n values 0 77 5 93 while the two figures for the mesozoic f rich evolved granites are eu eu 0 18 0 45 and la sm n 2 42 4 09 this along with and the larger range of end values 12 4 to 2 7 of the chalcopyrites than for the mesozoic granites and neoproterozoic granite therein 8 6 to 6 2 suggest that the ore forming fluids cannot be attributed to the mesozoic granites alone the local cu enriched neoproterozoic shuangqiaoshan group rocks should have contributed to the mineralization the low bulk rocks fe3 fe2 ratios 0 02 1 00 average 0 22 fe2 enriched biotite compositions fe2 fe3 5 64 143 average 22 combined with the low ce4 ce3 ratios 3 509 average 142 negative eu anomalies eu eu 0 05 0 56 average 0 25 and low fo2 fmq 3 4 1 9 fmq 1 5 1 7 for the mesozoic magmatic zircons suggest that the granites in the shimensi deposit are relatively reduced the low oxygen fugacity below nno of granites is favorable for significant tungsten mineralization accompanying by minor cu mineralization