effects of h2o ph and oxidation state on the stability of fe minerals on mars 1 on mars there is evidence that solutions may have been present on the surface episodically in the past these solutions were derived by weathering minerals such as olivine and sulfides found in mafic ultramafic rocks and possibly sulfates and meteorite fragments upon removal of water and or supersaturation of solutions secondary minerals formed we present a theoretical model for the formation of the solutions and the subsequent precipitation of fe bearing phases the first fe bearing phases to weather via oxidation are sulfides troilite or pyrrhotite which produce secondary fe hydr oxides or fes 2 pyrite or marcasite and fe 2 sulfates such as melanterite melanterite may be replaced by fe sulfates that have decreasing h 2 o 3fe 3 2fe 2 increasing oxidation and increasing bulk oh oh 2so 4 at meridiani planum the presence of jarosite indicates that the solutions were oxidized with ph 4 5 the solutions were likely fe mg ca s04 cl rich and precipitated fe hydr oxides fe phosphates fe sulfates with low oh oh so 4 ca mg sulfates and possible halides along with si rich phases the minerals indicating an acid environment were preserved by either removing components such as salts or water from the system e g in dust storms or episodic aqueous events isolating the mineral surfaces from fluids using disequilibrium processes or a combination at other localities jarosite is below detection limits and schwertmannite may be present if schwertmannite is present the solution had near neutral ph 4 ph 10 and fe hydr oxides would have crystallized rapidly leaving mg na ca s04 cl rich solutions that likely precipitated ca phosphates ca mg na sulfates fe sulfates with moderate high oh oh so 4 halides si rich phases and possibly fe mg ca carbonates

hydrothermally altered impact melt rock and breccia contributions to the soil of mars samples of melt rock and breccia from 12 terrestrial impact craters were examined to identify alteration minerals and their conditions of formation the dominant assemblage in most cases is clay silica k feldspar zeolite indicating hydrothermal alteration at low pressures and temperatures of 100 300 c the clays are predominantly fe chlorites and smectites in most cases depleted in al and enriched in fe and mg relative to their source rocks alteration of impact glass is often complete while alteration of crystalling melt rock is limited to a few percent of the rock volume impact breccia is altered to only a small extent compared to the alteration of glass impact induced hydrothermal alteration is to be expected at martian impact sites if significant quantities of ground ice and or water are present the alteration products are likely to resemble the clays found at terrestrial craters al fe fractionation similar to that observed on earth is strongly suggested by the viking soil analyses the quantitative contribution of hydrothermal clays to the soil of mars is estimated based on a model which predicts the generation of the equivalent of a 61 m thick blanket of impact melt planet wide the inefficiency of melt production in small craters and the inefficiency of alteration in large craters limit the expected production of clay to a few percent of this figure clays produced by impact induced hydrothermal alteration may be expected to contribute to the fines on mars but this contribution is probably not dominant relative to other suggested sources

sulphur dioxide particle and elemental emissions from mount etna italy during july 1987 sulphur dioxide emission rates were measured at mount etna italy during july 1987 while the volcano was undergoing relatively quiet activity the so2 flux averaged 930 587 1 mg d excluding 19 july when the flux was 3200 1730 1 mg d rising magma and or an influx of less degassed magma could explain the increased so2 flux the high so2 flux did not correlate with changes in observed volcanic activity this suggests that so2 monitoring may be useful as an indicator of shallow magmatic activity but not as a predictor of future eruptions of mount etna

chaotic obliquity and the nature of the martian climate recent calculations of the martian obliquity suggest that it varies chaotically on timescales longer than about 107 years and varies between about 0 and 60 we examine the seasonal water behavior at obliquities between 40 and 60 up to several tens of centimeters of water may sublime from the polar caps each year and possibly move to the equator where it is more stable co2 frost and co2 h2o clathrate hydrate are stable in the polar deposits below a few tens of meters depth so that the polar cap could contain a significant co2 reservoir if co2 is present it could be left over from the early history of mars also it could be released into the atmosphere during periods of high obliquity causing occasional periods of more clement climate

an unusual spectral unit in west candor chasma evidence for aqueous or hydrothermal alteration in the martian canyons abstract high spatial resolution observations made by orbiting spacecraft from the viking and phobos missions suggest the local development of crystalline ferric oxides in a small area in mars valles marineris canyon system quantitative color analysis of viking orbiter multispectral images identifies two spatially coherent regions of unique hue among the interior layered deposits in western candor chasma the anomalous color indicates a local compositional difference between these regions and the surrounding high albedo materials the unusual appearance of the unit in the viking color observations could be explained by a small increase in the degree of crystallinity or abundance of hematite near infrared spectra obtained by the ism imaging spectrometer aboard phobos 2 confirm a local enrichment in ferric oxides or oxyhydroxides in the region and suggest the presence of another phase in addition to hematite in high resolution the spectral unit can be seen to occur within two 20 km long depressions on the margins of an hesperian aged layered deposit which forms a plateau on the chasma floor water is implicated in the formation of the iron oxides since the same sedimentary layers seen in the depressions are exposed on steep surfaces elsewhere on the plateau but show no evidence of unusual coloration this suggests that the mineralization occurred through secondary alteration of preexisting rocks and developed locally in association with the depressions which could have ponded surface runoff or groundwater seepage

210pb 230th and 10be in central indian basin seamount sediments signatures of degassing and hydrothermal alteration of recent origin 1 isotopic 210pb 238u 230th 10be major and trace elements and micromorphological and microchemical data were used to identify recent 100 yrs hydrothermal alteration of a 200 kyr sedimentary record from the flank of a seamount in the central indian basin located at the edge of the 75 30 e fracture zone alteration effects are also reflected in 1 the depleted sedimentary organic carbon 2 dissolution features of radiolarian skeletons 3 the presence of altered minerals such as smectite and zeolites and 4 distinctly different magnetic properties in the altered sediments we interpret a predominant influence of neutral chloride type hydrothermal fluids this is the first report of recently occurring sediment alteration by shallow circulating sub surface fluids along the indian ocean intra plate seamount environment

on water detection in the martian subsurface using sounding radar several radar experiments are planned to map the martian subsurface down to several kilometers searching for subsurface liquid water reservoirs using different concepts and techniques all based on the penetration property of radio frequency waves in arid soils the penetration depth of low frequency radar is mainly related to the electromagnetic properties of the investigated medium thus a good knowledge of the martian subsurface dielectric profile along the first few kilometers is necessary for future water identification and data interpretation in this work we have investigated the electrical and magnetic properties of the martian surface and subsurface using terrestrial laboratory analogues in the frequency range 1 500 mhz covering the frequency domain of the mars advanced radar for subsurface and ionosphere sounding marsis experiment on board the mars express mission esa 2003 the netlander ground penetrating radar gpr cnes 2007 and future sounding radar that may be updated to the mars exploration program in the follow the water strategy in our approach we constructed experimentally the most common dielectric profile representative of the martian subsurface by measuring the electric permittivity and magnetic permeability of well defined mixtures of basaltic volcanic and sedimentary materials that have been reported for mars we also considered iron oxides hematite and maghemite and evaporites that may be present such as gypsum and their mixtures with representative amounts of the martian geological context under the most common petrophysical and geophysical conditions along the subsurface profile this led to synthetic representative samples of the martian subsurface materials under adequate conditions of porosity and temperature that should exist in the first 2 5 km of the upper crust dielectric measurements show that the first layers of the martian subsurface a few hundred meters which are mainly composed of volcanic iron rich materials could dramatically decrease the radar penetration depth initially foreseen thus limiting deep subsurface exploration we also investigated the constraints on subsurface water detectability in a radar lossy medium and its dielectric identification among surrounding geological materials

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

the sudbury structure controversial or misunderstood the origins of the sudbury structure and associated igneous complex have been controversial most models call for a major impact event followed by impact induced igneous activity although totally igneous models are still being proposed much of the controversy is due in our opinion to a misunderstanding of the size of the original sudbury structure by analogy with other terrestrial impact structures the spatial distribution of shock features and huronian cover rocks at the sudbury structure suggest that the transient cavity was 100 km in diameter which places the original final structural rim diameter in the range of 150 200 km theoretical calculations and empirical relationships indicate that the formation of an impact structure of this size will result in 104 km3 of impact melt more than sufficient to produce a melt body the size of the igneous complex present volume 4 8 103 km3 for the igneous complex to be an impact melt sheet it must have a composition similar to that of the target rocks evidence for this has been presented previously for sr and nd isotopic data which suggest a crustal origin here we also present new evidence from least squares mixing models that the average composition of the igneous complex corresponds to a mix of archean granite greenstone terrain with possibly a small component of huronian cover rocks this is a geologically reasonable mix based on the interpreted target rock geology and the geometry of melt formation in an impact event of this size the igneous complex is differentiated which is not a characteristic of previously studied terrestrial impact melt sheets this can be ascribed however to its great thickness and slower cooling that large impact melt sheets can differentiate has important implications for how the lunar samples and the early geologic history of the lunar highlands are interpreted if this working hypothesis is accepted namely that both the sudbury structure and the igneous complex are impact in origin then previous hybrid impact igneous hypotheses can be discarded and the sudbury structure can be studied specifically for the constraints it provides to large scale cratering and the formation of basin sized multiring impact structures

hematite pyroxene and phyllosilicates on mars implications from oxidized impact melt rocks from manicouagan crater quebec canada visible and near ir reflectivity mossbauer and x ray diffraction data were obtained on powders of impact melt rock from the manicouagan impact crater located in quebec canada the iron mineralogy is dominated by pyroxene for the least oxidized samples and by hematite for the most oxidized samples phyllosilicate smectite contents up to 15 wt were found in some heavily oxidized samples nanophase hematite and or paramagnetic ferric iron is observed in all samples no hydrous ferric oxides e g goethite lepidocrocite and ferrihydrite were detected which implies the alteration occurred above 250 c oxidative alteration is thought to have occurred predominantly during late stage crystallization and subsolidus cooling of the impact melt by invasion of oxidizing vapors and or solutions while the impact melt rocks were still hot the near ir band minimum correlated with the extent of aleration fe3 fetot and ranged from 1000 nm high ca pyroxene to 850 nm bulk well crystalline hematite for least and most oxidized samples respectively intermediate band positions 900 920 nm are attributed to low ca pyroxene and or a composite band from hematite pyroxene assemblages manicouagan data are consistent with previous assignments of hematite and pyroxene to the 850 and 1000 nm bands observed in martian reflectivity spectra manicouagan data also show that possible assignments for intermediate band positions 900 920 nm in martian spectra are pyroxene and or hematite pyroxene assemblages by analogy with impact melt sheets and in agreement with observables for mars oxidative alteration of martian impact melt sheets above 250 c and subsequent erosion could produce rocks and soils with variable proportions of hematite both bulk and nanophase pyroxene and phyllosilicates as iron bearing mineralogies if this process is dominant these phases on mars were formed rapidly at relatively high temperatures on a sporadic basis throughout the history of the planet the manicouagan samples also show that this mineralogical diversity can be accomplished at constant chemical composition which is also indicated for mars from analyses of soil at the two viking landing sites

spectral evidence for the mineralogy of high albedo soils and dust on mars because of the lack of direct mineralogic data available for mars spectral remote sensing techniques and in particular earth based reflectance spectroscopy remain the primary source of this information presented here are laboratory observations which further constrain the mineralogy and origin of the high albedo soils and dust earth based observations show the reflectance spectra of classical bright regions to be fairly uniform with a strong fe3 o2 charge transfer absorption edge extending from the near uv through the visible this absorption is relatively smooth unlike those observed for crystalline ferric oxides which have superimposed fe3 crystal field bands dilution of ferric oxide with a spectrally more neutral medium montmorillonite weakens the charge transfer and crystal field absorptions together and does not serve to make the ferric oxide spectrum more mars like smoother nontronite ferric iron bearing smectite clay was also investigated for spectral agreement with telescopic observations pure nontronite has fe3 absorptions analogous to but different from ferric oxides as in the previous case the absorptions are very distinct and inappropriate for mars admixture of neither montmorillonite nor ferric oxide serves to improve the nontronite spectrum the conclusion is that nontronite is not a major component of martian soils although the presence of other iron poor clays cannot be totally excluded based on currently available observational data the best spectral analogs known for high albedo soil and dust are a specific type of palagonite from hawaii x ray amorphous weathering products of mafic volcanic glass the indication is therefore that ferric iron on mars is likely to occur in poorly defined crystallo graphic sites such as found in these amorphous materials these materials form slowly under semiarid conditions at ambient temperature even low temperature hydrothermal alteration of glass might provide enough ion mobility to favor some formation of crystalline clays over amorphous gels and may therefore not be the primary mechanism responsible for soil formation on mars the amorphous hawaiian soils exist metastably for thousands of years on earth similar materials on mars would be expected to survive considerably longer under the present cold and dry climatic conditions

mixed hydrothermal fluids and the origin of the martian soil the martian soil consists mainly of weathered basaltic rock and a salt component enriched in volatile and mobile elements primarily sulfur chlorine sodium and potassium since the discovery of this mobile element component by the viking x ray fluorescence spectrometer volcanic aerosols have been considered a likely source for these enrichments alternative sources of the mobile element component are fluids supplied to the surface by hydrothermal processes related to impact craters and volcanism we show that a mixed hydrothermal fluid model can successfully explain the composition of the mobile element component of the soil this model is constructed using terrestrial analogs constrained by the viking and pathfinder measurements of the martian soil chemistry the potential hydrothermal fluid contributions to the soil are tightly constrained because the relative abundances of the mobile elements in hydrothermal fluids are nearly constant the two end member types of hydrothermal fluids considered in the model are the neutral chloride and the acid sulfate type the neutral chloride fluids have high cl and na contents and a significant amount of k but their s abundance relative to cl s cl ratio is too low to match the martian soil however acid sulfate hydrothermal systems characterized by substantial vapor transport and high s cl ratios are likely on mars due to the low abundance of water indeed as the availability of water declines in a hydrothermal system the neutral chloride system can evolve to a vapor dominated acid sulfate system a combination of the two types of fluids can quantitatively explain the s and cl abundance in the soil and provide reasonable abundances of other mobile elements including na k and br without predicting an excess of any element measured in the soil however the hydrothermal fluids are unlikely to be involved in the formation of the magnetic minerals in the soil because the fe contents of the fluids are too low although the acid sulfate fluids have fe concentrations a factor of 100 larger than the neutral chloride fluids the acid sulfate fluids would contribute less than 1 of the total fe in the soil the volcanic aerosol models are poorly constrained in contrast to the hydrothermal fluid models because in volcanic aerosols the relative abundances of the mobile elements are highly variable therefore while volcanic aerosols can explain the mobile element component of the soil significant contributions from other sources cannot be excluded determining the relative contributions of hydrothermal components compared to volcanic aerosols will require measurements in the martian soil of trace elements that provide signatures of the hydrothermal fluids such as high lithium contents that are associated with neutral chloride fluids

a case for ancient evaporite basins on mars observations indicate that a martian analog to the earth s salt pans and saline lakes of arid regions may have existed in crater basins during mars early noachian epoch terraced and channelized crater basins point to ponding of surface water as well as possible prolonged and evolving base levels in addition supportive evaporite basin analogs are offered for three other morphologic features of martian crater basins an evaporite basin model for crater basins on mars has major implications for the mechanical chemical and even biological processes that potentially have operated in mars past and represent a spectrum of potential mineral resources

tes and themis study of proposed paleolake basins within the aeolis quadrangle of mars 1 several studies have described photogeologic evidence for paleolacustrine basins on mars mostly within impact craters if these basins contained persistent standing water subsequently lost through evaporation they may have contained deposits of evaporite minerals if still present and sufficiently exposed these evaporites would be detectable in orbital thermal infrared spectra using data from mars orbiter thermal emission imaging system mo themis and mars global surveyor thermal emission spectrometer mgs tes we examined proposed paleolake basins within aeolis quadrangle including gusev and gale craters gusev crater is dominated by units with a spectrally intermediate to thick layer of dust mantling the surface tes linear deconvolutions of the low albedo deposits which have a thinner dust mantling include surface type 1 basalt materials when sulfates are included in the end member library otherwise the linear deconvolution uses surface type 2 andesite or weathered basalt themis surface emissivity spectra for the low albedo deposits do not display sufficient contrast to distinguish between surface types gale crater is relatively dust free except for the mound variably covered in a spectrally intermediate to thick layer of dust tes linear deconvolutions of crater floor and less dusty portion of the mound are consistent with a mixture of surface types 1 and 2 themis surface emissivity spectra are consistent with surface type 1 or a mixture of surface types 1 and 2 for the crater floor and surface dust for the mound these results do not discriminate between several previously suggested origins fluvial lacustrine aeolian or volcanic deposition for the mound layers we find no spectral evidence for evaporite deposits that might substantiate paleolakes existed in these craters

gale crater and impact processes curiosity s first 364 sols on mars abstract impact processes at all scales have been involved in the formation and subsequent evolution of gale crater small impact craters in the vicinity of the curiosity msl landing site and rover traverse during the 364 sols after landing have been studied both from orbit and the surface evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate and disrupted fractured sedimentary layers which are not obviously displaced by erosion impact ejecta blankets are likely to be present but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary volcaniclastic breccia and conglomerate deposits the occurrence of individual blocks with diverse petrological characteristics including igneous textures have been identified across the surface of bradbury rise and some of these blocks may represent distal ejecta from larger craters in the vicinity of gale distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material possible examples of impactites in the form of shatter cones shocked rocks and ropy textured fragments of materials that may have been molten have been observed but cannot be uniquely confirmed modification by aeolian processes of craters smaller than 40 m in diameter observed in this study are indicated by erosion of crater rims and infill of craters with aeolian and airfall dust deposits estimates for resurfacing suggest that craters less than 15 m in diameter may represent steady state between production and destruction the smallest candidate impact crater observed is 0 6 m in diameter the observed crater record and other data are consistent with a resurfacing rate of the order of 10 mm myr considerably greater than the rate from impact cratering alone but remarkably lower than terrestrial erosion rates

fluidization and hydrothermal alteration of the suevite deposit at the ries crater west germany and implications for mars the formation cooling and alteration of the impact ejecta deposits at the ries crater are an analog for impact processes and the formation of regoliths and soils on mars we have studied the suevite deposit an impact melt bearing breccia found outside of the crater rim this suevite contains large numbers of chimney like degassing pipes apparently formed by high gas pressures in the hot 500 c fluidized suevite immediately after deposition of the suevite the likely sources of the gas are volatiles from the melted and shocked basement inclusions the suevite outside of the crater rim contains about 15 wt clay indicating a large amount of alteration of the suevite the clay is an fe rich montmorillonite with less than 5 interstratified illite indicating that the temperature at which most of the alteration occurred was less than 100 130 c the duration of this low temperature period may have been extended by additional heating from the exothermal alteration reactions the surfaces of the degassing pipes are not altered to clays however but have a thin fe rich oxide or hydroxide coating the absence of alteration in the pipes suggests that the main alteration event outside the crater occurred under unsaturated conditions such that the walls of the pipes were dry suevite deposits are likely to exist on mars because of the presence of volatile rich target rock martian suevites may have also been fluidized and hydrothermally altered contributing significantly to the formation of the clay like phases inferred to exist in the martian soil

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

mobile element analysis by secondary ion mass spectrometry sims of impactite matrix samples from the yaxcopoil 1 drill core in the chicxulub impact structure the concentrations of the fluid mobile trace elements lithium beryllium boron and barium were measured in samples of the altered matrix of several impactite breccias of the yaxcopoil 1 drill core using secondary ion mass spectrometry sims to determine the extent of transport due to aqueous or hydrothermal processes three of the elements li be and b have higher concentrations in the upper suevite impact breccias than in the lower impact melt deposits by factors of 3 5 2 2 and 1 5 respectively lithium and b are the most enriched elements up section and appear to have had the greatest mobility the similar fractionation of li and b is consistent with fluid transport and alteration under low temperature conditions of less than 150 c based on published experimental studies in contrast to li be and b the concentration of ba in the altered matrix materials decreases upward in the section and the concentration of ba in the matrix is an order of magnitude less than the bulk concentrations likely due to the presence of barite the origin of the elemental variations with depth may be related to different protolith compositions in the upper versus the lower impactite units a different protolith in the altered matrix is suggested by the mg rich composition of the lower units versus the al rich composition of the upper units which largely correlates with the mobile element variations the possibility that vertical transport of mobile elements is due to a postimpact hydrothermal system is supported by published data showing that the sediments immediately overlying the impactites are enriched in mobile elements derived from a hydrothermal system however the mobile elements in the sediments do not have to originate from the underlying impactites in conclusion our data suggests that the impactites at this location did not experience extensive high temperature hydrothermal processing and that only limited transport of some elements including li be and b occurred

acidic volatiles and the mars soil large portions of mars surface are covered with deposits of fine homogeneous weathered dusty soil material nanophase iron oxides silicate mineraloids and salts prevail in the soil the mode of formation of this somewhat peculiar type of soil is still far from being clear one scenario suggests that weathering took place during early epochs when mars may have been warm and wet the properties of the soil are not easily reconciled with this scenario we propose another possible scenario that attributes in part the peculiar nature of the martian dust and soil to a relatively young weathering product formed during the last few hundreds of millions of years in a process that involves acidic volatiles we tested this hypothesis in an experimental study of the first step of acidolytic weathering of a partly palagonitized volcanic tephra of hawaiitic lava origin using sulfuric hydrochloric and nitric acids and their mixtures the tephra effectively neutralize the added acidity the protonic acidity added to the tephra attacks the primary minerals releasing fe al and mg which control the ph acting as lewis acid species of varying acid strengths the full amount of acidity added to the tephra is stored in it but only a very small fraction is preserved as the original protonic acidity the majority of the added sulfate and chloride were present as salts and easily solubilized minerals well crystallized sulfate salt minerals of aluminum and calcium were detected by powder x ray diffractometry whereas secondary magnesium and iron minerals were not detected due probably to lack of crystallinity the presence of gypsum caso4 2 h2o and alunogen al2 so4 3 17 h2o is probably responsible for the observed increased hygroscopicity of the acidified tephra and their tendency to form hardened crusts we suggest that if this mechanism is of importance on mars then the chemically weathered component of the martian soil consists of a salt rich mineral mixture containing the salts of the anionicligands so4 and cl resulting from volatiles emitted from volcanoes during more recent eruptions up to 109 years b p the lack of liquid water on mars surface during that time slowed or halted mineralogical evolution into highly crystallized minerals having large mineral grains the chemically weathered components are mixed with the products of physical weathering the recently formed soil may cover and coat more evolved hydrothermally modified mineral deposits formed in earlier epochs of mars

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

nickeliferous pyrite tracks pervasive hydrothermal alteration in martian regolith breccia a study in nwa 7533 martian regolith breccia nwa 7533 and the seven paired samples is unique among martian meteorites in showing accessory pyrite up to 1 by weight pyrite is a late mineral crystallized after the final assembly of the breccia it is present in all of the lithologies i e the fine grained matrix icm clast laden impact melt rocks climr melt spherules microbasalts lithic clasts and mineral clasts all lacking magmatic sulfides due to degassing pyrite crystals show combinations of cubes truncated cubes and octahedra polycrystalline clusters can reach 200 lm in maximum dimensions regardless of their shape pyrite crystals display evidence of very weak shock metamorphism such as planar features fracture networks and disruption into subgrains the late fracture systems acted as preferential pathways for partial replacement of pyrite by iron oxyhydroxides interpreted as resulting from hot desert terrestrial alteration the distribution and shape of pyrite crystals argue for growth at moderate to low growth rate from just saturated near neutral 6 fmq 2 log units it is inferred from the maximum ni contents 4 5 wt that pyrite started crystallizing at 400 500 c during or shortly after a short duration relatively low temperature thermal event that lithified and sintered the regolith breccias 1 4 ga ago as deduced from disturbance in several isotope systematics

an assessment of the meteoritic contribution to the martian soil the addition of meteoritic material to the mars soils should perturb their chemical compositions as has been detected for soils on the moon anders et al 1973 and sediments on earth kyte and wasson 1986 using the measured mass influx at earth and estimates of the mars earth flux ratio we estimate the continuous planet wide meteoritic mass influx on mars to be between 2700 and 59 000 t yr if distributed uniformly into a soil with a mean planetary production rate of 1 m b y consistent with radar estimates of the soil depth overlaying a bouldered terrain in the tharsis region christensen 1986 our estimated mass influx would produce a meteoritic concentration in the mars soil ranging from 2 to 29 by mass analysis of the viking x ray fluorescence data indicates that the mars soil composition is inconsistent with typical basaltic rock fragments but can be fit by a mixture of 60 basaltic rock fragments and 40 meteoritic material clark and baird 1979 the meteoritic influx we calculate is sufficient to provide most or all of the material required by the clark and baird 1979 model particles in the mass range from 10 7 to 10 3 g about 60 200 m in diameter contribute 80 of the total mass flux of meteoritic material in the 10 13 to 106 g mass range at earth hughes 1978 on earth atmospheric entry all but the smallest particles generally 50 m in diameter in the 10 7 to 10 3 g mass range are heated sufficiently to melt or vaporize mars because of its lower escape velocity and larger atmospheric scale height is a much more favorable site for unmelted survival of micrometeorites on atmospheric deceleration we calculate that a significant fraction of particles throughout the 60 1200 m diameter range will survive mars atmospheric entry unmelted thus returned mars soils may offer a resource for sampling micrometeorites in a size range which is not collectable in unaltered form at earth

possible precipitation of ice at low latitudes of mars during periods of high obliquity most of the old cratered highlands of mars are dissected by branching river valleys that appear to have been cut by running water1 2 yet liquid water is unstable everywhere on the martian surface in the equatorial region where most of the valleys are observed even ice is unstable3 4 it has been suggested therefore that mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water5 here we suggest instead that during periods of very high obliquities ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards at low latitudes the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed the mechanism is efficient only at the very high obliquities that occurred before formation of tharsis very early in the planet s history but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet s history partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system

magnetic study of an antarctic weathering profile on basalt implications for recent weathering on mars abstract in order to better interpret the martian surface weathering related mineralogy we focused on a relevant analogue of the martian subsurface in terms of lithology and paleoclimate the jurassic aged ferrar dolerite priestley glacier transantarctic mountains weathered in cold and dry climate together with chemical and mineralogical studies rock magnetic properties were investigated and completed with mossbauer measurements weathering of the decimetric block is evidenced by chemical profiles showing an increase in fe content from 10 5 in the core to 13 wt in the surface and a decrease in si from 57 to 53 wt respectively according to mineralogical thermomagnetic and hysteresis properties the main opaque mineral is inherited titanomaghemite with a concentration about 1 enhancement in low field magnetic susceptibility from 4 10 6 to 10 10 6 m 3 kg respectively and saturation magnetization from 0 44 to 0 96 am 2 kg respectively indicates the neoformation of metastable maghemite neoformed red ferric oxy hydroxides are abundant in the surface high field susceptibility normalized to iron concentration and mossbauer spectra indicate a replacement of fe 2 from primary silicates pyroxene by poorly crystalline antiferromagnetic fe 3 oxy hydroxides thus highly magnetic titanomaghemite and maghemite coexist with nanosized ferric oxy hydroxides and primary silicates in accordance with martian in situ observations therefore this study supports the formation of the martian regolith as resulting from a slow weathering process in near present day conditions

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

the valley of ten thousand smokes katmai klaska a unique geochemistry laboratory abstract during june 6 8 1912 a new vent novarupta near mt katmai in the aleutian range of alaska released the largest volcanic eruption of this century and the largest rhyolitic eruption in nearly twenty centuries spectacular fumaroles developed in the ash flow sheet prompting robert f griggs who discovered the steaming valley in 1916 to name it the valley of ten thousand smokes vtts the katmai scientific drilling project was developed to advance understanding of the physical and chemical processes involved with explosive volcanism through an interdisciplinary investigation of the novarupta vent and fissure fumaroles present in the ash flow sheet novarupta vent represents a unique target for subsurface geophysical and coring studies of structures and lithologies produced by explosive volcanism panel on volcanic studies at katmai national academy of sciences 1989 scientific expeditions sponsored by the department of energy the national science foundation and the u s geological survey were conducted during the summers of 1989 and 1990 most of the surface studies are now complete and drilling is planned for 1994 contingent on successful completion of the national environmental policy act process one of the main objectives of this ambitious study is to determine the source mechanisms and thermal and chemical conditions of the fumarolic transport of elements that occurred following ash flow emplacement as part of the surface investigation prior to drilling a detailed geochemical study has been initiated involving the mass flux of nearly fifty major minor and trace elements using samples from fumarolic deposits located in distal rhyolitic and proximal dacitic and andesitic portions of the ash flow sheet significant enrichments are observed in s br cl f zn pb cu sn cr ni as sb and au in various portions of the fossil fumaroles these enrichments correlate well with those determined in active high temperature fumarolic sublimates and indicate that most of these elements were transported to the surface early in the vapor phase

anisotropic radio wave scattering from englacial water regimes mýrdalsjokull iceland colinear polarized 5 mhz radar profiling data were obtained on m rdalsjokull a temperate glacier in iceland radar transects and therefore polarization planes were aligned approximately parallel transverse and oblique to the ice flow direction echoes from the shallower half to two thirds of the ice were 10 20db stronger on the oblique and longitudinal transects than those on the transverse transects anisotropy as a function of depth is clearly seen at the sites where the transects cross strong scattering on longitudinal transects apparently caused extinction of a radar reflecting layer that was continuously profiled on the transverse transects a radio wave scattering model shows that scattering from a longitudinal water filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo we conclude that low frequency mhz radio waves can help to characterize englacial water regimes

geochemical components in martian soil abstract trends in element compositional variation among samples at the viking lander sites on mars provide evidence for multiple geochemical components in the soils a simple two component model can explain all pair wise trends of eight elements analyzed component a contains si and most or all the al ca ti and fe component b which is 16 3 by weight of the total contains s and most or all the cl and mg these results constrain several models of martian soil mineralogy but are consistent with a mixture of silicates and salts

experimental epithermal alteration of synthetic los angeles meteorite implications for the origin of martian soils and identification of hydrothermal sites on mars 1 the dissolution behavior and secondary minerals generated by experimental alteration of a synthetic los angeles basaltic shergottite la were evaluated at epithermal 75 c conditions starting ph values of 1 1 and 3 6 and water rock ratios ranging from 100 to 2000 were studied using flow through and batch reactor experimental apparatus dissolution of plagioclase dominates effluent solution chemistry under all experimental conditions little mg is released to solution because nearly 100 of the mg in unaltered la is contained in pyroxene m1 sites which are relatively resistant to dissolution secondary minerals generated include siliceous residue amorphous sio2 lepidocrocite and ferrihydrite anhydrite alunogen rhomboclase ferrinatrite halite and unidentified ca and na sulfates the dominance of alteration products of plagioclase suggests that la type basalts have not contributed significantly to the martian soils the search for hydrothermal sites by remote sensing may be hampered by the general similarity of the alteration products found in the near surface epithermal environment to those thought to exist in martian soils sulfates iron oxyhydroxides amorphous silica however the unique chemical composition of secondary products formed by la alteration may make detection of recent hydrothermal alteration of evolved basaltic rocks more straightforward in addition alteration in terrestrial epithermal environments associated with mafic to intermediate volcanic rocks generally produces abundant sulfides and kaolinite two potentially unique mineral phases which might also indicate the presence of active or extinct hydrothermal systems

mixing relationships in the martian regolith and the composition of globally homogeneous dust abstract comparison of the chemical compositions of martian soils reveals distinct mixing trends resulting from admixture of variable amounts of sulfate chloride cement at viking landing sites and of the local andesitic rock fragments at the mars pathfinder site these trends most easily visualized in plots of oxides versus so 3 intersect approximately at a common composition thought to represent a global dust that has been homogenized by pervasive aeolian activity the source rocks that were weathered to produce the global dust are inferred to have been basalts rather than felsic rocks based on the observation that the dust lies along well established chemical weathering trends for terrestrial basalts the basaltic protolith was chemically similar e g high fe mg low al 2 o 3 to basaltic shergottite meteorites chemical changes during the weathering of martian basaltic rocks are apparently not as drastic as in terrestrial weathering perhaps because of evaporation of hydrous fluids that leave soluble components behind in the residue comparison with chemical trends for previously proposed martian soil formation mechanisms suggests that palagonitization of basalts more readily explains the dust composition than do hydrothermal alteration at higher temperatures or reactions of rocks with an acid fog produced by volcanic exhalations local or temporal processing of dust into soil involves not only cementation by salts and mixing with rock fragments but also chemical fractionations of fe 2 o 3 tio 2 presumably resulting from aeolian sorting by grain size and density if the global dust represents a broad average of the martian surficial or upper crustal composition the planet s surface geology is dominated by basaltic volcanic rocks and evaporitic salts

impact crater lakes on mars the robotic search for life on mars centers on identifying accessible environments where the biological catalyst water has existed the formation of large impact craters on mars 65 km diameter may have resulted in the creation of ice covered impact crater lakes which would not freeze for thousands of years even under present climatic conditions water could be supplied from deep confined aquifers penetrated by the impact craters without the need for surface melt water freezing of the lakes is postponed owing to heat from impact generated melt bearing deposits from impact related uplift of hotter rocks from depth and from the latent heat of freezing of a deep crater lake abundant morphologic evidence for ancient crater lakes has not been found in viking images except for craters associated with outflow channels however ice covered crater lakes could have formed and further searches for evidence of these lakes are warranted the lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from mars

sulfur bearing phases detected by evolved gas analysis of the rocknest aeolian deposit gale crater mars the sample analysis at mars sam instrument suite detected so2 h2s ocs and cs2 from 450 to 800 c during evolved gas analysis ega of materials from the rocknest aeolian deposit in gale crater mars this was the first detection of evolved sulfur species from a martian surface sample during in situ ega so2 3 22 mol is consistent with the thermal decomposition of fe sulfates or ca sulfites or evolution desorption from sulfur bearing amorphous phases reactions between reduced sulfur phases such as sulfides and evolved o2 or h2o in the sam oven are another candidate so2 source h2s 41 109 nmol is consistent with interactions of h2o h2 and or hcl with reduced sulfur phases and or so2 in the sam oven ocs 1 5 nmol and cs2 0 2 1 nmol are likely derived from reactions between carbon bearing compounds and reduced sulfur sulfates and sulfites indicate some aqueous interactions although not necessarily at the rocknest site fe sulfates imply interaction with acid solutions whereas ca sulfites can form from acidic to near neutral solutions sulfides in the rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source the presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering the possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage understanding the sulfur mineralogy in rocknest materials which exhibit chemical similarities to basaltic fines analyzed elsewhere on mars can provide insight in to the origin and alteration history of martian surface materials

mount st augustine volcano fumarole wall rock alteration mineralogy zoning composition and numerical models of its formation process abstract intensely altered wall rock was collected from high temperature 640 c and low temperature 375 c vents at augustine volcano in july 1989 the high temperature altered rock exhibits distinct mineral zoning differentiated by color bands in order of decreasing temperature the color bands and their mineral assemblages are a white to grey tridymite anhydrite b pink to red tridymite hematite fe hydroxide molysite fecl 3 with minor amounts of anhydrite and halite and c dark green to green anhydrite halite sylvite tridymite with minor amounts of molysite soda and potash alum and other sodium and potassium sulfates the alteration products around the low temperature vents are dominantly cristobalite and amorphous silica with minor potash and soda alum aphthitalite alunogen and anhydrite compared to fresh 1986 augustine lava the altered rocks exhibit enrichments in silica base metals halogens and sulfur and show very strong depletions in al in all alteration zones and in iron alkali and alkaline earth elements in some of the alteration zones to help understand the origins of the mineral assemblages in altered augustine rocks we applied the thermochemical modeling program gasworks in calculations of a reaction of the 1987 and 1989 gases with wall rock at 640 and 375 c b cooling of the 1987 gas from 870 to 100 c with and without mineral fractionation c cooling of the 1989 gas from 757 to 100 c with and without mineral fractionation and d mixing of the 1987 and 1989 gases with air the 640 c gas rock reaction produces an assemblage consisting of silicates tridymite albite diopside sanidine and andalusite oxides magnetite and hercynite and sulfides bornite chalcocite molybdenite and sphalerite the 375 c gas rock reaction produces dominantly silicates quartz albite andalusite microcline cordierite anorthite and tremolite and subordinate amounts of sulfides pyrite chalcocite and wurtzite oxides magnetite sulfates anhydrite and halides halite the cooling calculations produce a anhydrite halite sylvite b cu mo fe and zn sulfides c mg fluoride at high temperature 370 c d chlorides fluorides and sulfates of mn fe zn cu and al at intermediate temperature 170 370 c and e hydrated sulfates liquid sulfur crystalline sulfur hydrated sulfuric acid and water at low temperature

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

equatorial and midlatitude distribution of chlorine measured by mars odyssey grs 1 the 2001 mars odyssey gamma ray spectrometer grs has made the first measurement of the equatorial and midlatitude distribution of cl at the near surface of mars a mean concentration value of 0 49 wt cl has been determined from a grand sum of grs spectra collected over the planet excluding high latitude regions cl is significantly enriched within the upper few tens of centimeters of the surface relative to the martian meteorites and estimates for the bulk composition of the planet however cl is not homogeneously distributed and varies by a factor of 4 even after smoothing of data with a 10 arc radius filter several contiguous geographically large 20 regions of high and low cl concentrations are present in particular a region centered over the medusae fossae formation west of tharsis shows significantly elevated cl a large region north of syrtis major extending into utopia planitia in the northern hemisphere shows the lowest cl concentrations on the basis of hierarchical multivariate correlations cl is positively associated with h while negatively associated with si and thermal inertia we discuss four possible geologic mechanisms aeolian volcanic aqueous and hydrothermal that may have affected the cl distribution seen by grs while some of the distribution may be due to cl rich dust deposits transported by aeolian processes this mechanism does not appear to account for all of the observed variability we propose that reactions with volcanic exhalations may have been important for enriching cl in medusae fossae formation material

geochemistry of metallic trace elements in fumarolic condensates from nicaraguan and costa rican volcanoes metallic trace element composition of volcanic gas from cerro negro momotombo san cristobal telica and masaya volcanoes in nicaragua and poas volcano in costa rica is indicated by analyses of fumarolic condensates for alkalis alkaline earths transition elements precious metals halogens and sulphate the temperatures of the fumaroles varied from 85 to 852 c element concentrations range from 104 to 10 3 ppm statistical tests indicate that the trace element constituents of the condensates are log normally distributed although there are variations in element concentrations in individual condensates the general order of decreasing elemental abundances in nicaraguan and costa rican fumarolic gas is cl so4 certain igneous rock forming elements si al fe ti f and alkalis li na k alkaline earths mg ca ba br and transition elements cr mn co ni cu zn other ore forming elements mo cd sn pb semi metals as sb sc hg and precious metals au ag li mn cr and pb were found to be near or below detection limits in many of the condensates analyzed so4 ti al k na zn sn cr and br all tend to decrease in abundance as mean fumarolic temperature between volcanoes decreases the remaining elements remain constant in abundance or behave erratically the metallic trace element composition of the nicaraguan and costa rican fumarolic condensates is very similar to condensates from subduction zone volcanoes around the pacific margin and the mediterranean metals in volcanic gas are postulated to have been transported as halogen sulphate and oxide compounds chloride and fluoride compounds are considered to be the primary transporters of metals in volcanic gas correlations between metal and halogen content vary considerably between volcanoes statistically significant correlations between metal content and both chlorine and bromine are found in the cerro negro and between metal content and bromine and fluorine in the momotombo condensates metal bearing compounds in volcanic gas are postulated from correlation matrices bromine though seldom reported in condensates is a minor but important constituent of volcanic gas with concentrations similar to those of fluorine metal bromide compounds have higher volatilities than fluoride compounds and volatilities similar to chloride compounds significant correlations between bromine content and metal concentration suggests that bromide compounds play a role in the transportation of metals in volcanic gas

chemical components of the martian soil melt degassing hydrothermal alteration and chondritic debris on the basis of measurements by the viking and soviet phobos missions the fine grained surficial drift material on mars is enriched in moderately volatile and mobile elements such as s cl k and br the compounds of these elements may amount to as much as 16 wt of the soil while the bulk of the soil appears to consist primarily of crustal material whose composition is similar to that of the basaltic mars meteorites clark 1993 three possible geochemical sources melt degassing hydrothermal alteration and accretion of chondritic material may have contributed to the enrichments we have evaluated possible chemical signatures for these sources by examining the relative abundances of chemical elements in the different components to the measured k abundance in the mars soil and have identified characteristic elements for each component the relative abundances of mobile elements in the different components are much less variable than their absolute abundances which strongly depend on conditions such as temperature and water composition the volatility controlled elemental signature of the melt degassing process includes enrichments of zn mo cd ba and w relative to the elemental abundances in the other components and martian meteorites hydrothermal alteration of minerals and glass controlled by low temperature solubility makes up a second component with a characteristic lithium enrichment signature a chondritic component is enriched in siderophile and chalcophile elements including ni compared to material derived from the martian mantle which was depleted in siderophile elements due to core formation unfortunately the existing data for the mars soil do not include any of these key signature elements and the uncertainties for the viking analyses could allow large amounts of each of these elements the mars pathfinder inorganic analysis experiment and the 2001 orbital gamma ray experiment have the potential to determine some of these characteristic elements and to reveal the possible contributions to the soil the enriched components of the soil especially cd and pb could also be a potential hazard for future martian explorers who will be exposed to the dust carried into their habitats on their space suits

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

mineralogic and compositional properties of martian soil and dust results from mars pathfinder mars pathfinder obtained multispectral elemental magnetic and physical measurements of soil and dust at the sagan memorial station during the course of its 83 sol mission we describe initial results from these measurements concentrating on multispectral and elemental data and use these data along with previous viking snc meteorite and telescopic results to help constrain the origin and evolution of martian soil and dust we find that soils and dust can be divided into at least eight distinct spectral units based on parameterization of imager for mars pathfinder imp 400 to 1000 nm multispectral images the most distinctive spectral parameters for soils and dust are the reflectivity in the red the red blue reflectivity ratio the near ir spectral slope and the strength of the 800 to 1000 nm absorption feature most of the pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide s sometimes mixed with small but varying degrees of well crystalline ferric and ferrous phases darker soil units appear to be coarser grained compacted and or mixed with a larger amount of dark ferrous materials relative to bright soils nanophase goethite akaganeite schwertmannite and maghemite are leading candidates for the origin of the absorption centered near 900 nm in imp spectra the ferrous component in the soil cannot be well constrained based on imp data alpha proton x ray spectrometer apxs measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average viking derived soil elemental composition differences exist between viking and pathfinder soils however including significantly higher s and cl abundances and lower si abundances in viking soils and the lack of a correlation between ti and fe in pathfinder soils no significant linear correlations were observed between imp spectral properties and apxs elemental chemistry attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions we attempted to use the pathfinder results to constrain a number of putative soil and dust formation scenarios including palagonitization and acid fog weathering while the pathfinder soils cannot be chemically linked to the pathfinder rocks by palagonitization this study and mcsween et al 1999 suggest that palagonitic alteration of a martian basaltic rock plus mixture with a minor component of locally derived andesitic rock fragments could be consistent with the observed soil apxs and imp properties

incipient hydrothermal alteration of basalts and the origin of martian soil the martian soil is a fine grained regolith that is chemically basaltic in character with evidence for both gains and losses of volatile and mobile elements compared to martian basalt compositions these chemical fractionations provide clues to geochemical processes on the surface of mars geochemical processes contributing to the soil proposed in the past include the chemical and mechanical breakdown of rocks under surface conditions the addition of volcanic aerosols containing s and cl compounds and the alteration of basaltic glass to palagonite our studies of terrestrial analogs suggest that hydrothermal alteration processes involving impact craters and volcanism could also contribute to the major element trends observed in martian soil data from viking pathfinder and the current mer missions consistently show that relative to basaltic martian meteorite compositions the major element compositions of the soils are 1 depleted in the fluid mobile element calcium 2 generally similar or somewhat enriched in iron oxide and magnesium but mgo depleted compared to gusev rocks 3 locally variable in potassium 4 possibly poorer in aluminum and 6 very enriched in chlorine and sulfur the major element trends aside from the cl and s enrichment could be explained by the formation or addition of palagonite according to mcsween and keil 2000 but the missing cao remains a problem the chlorine and sulfur are probably derived from other processes such as volcanic aerosols and hydrothermal fluids mcsween and keil 2000 also argued that hydrothermal alteration of basalts produce alteration trends that are inconsistent with the mars soil but this study concludes otherwise we have used quantitative mass balance mixing models to investigate possible models involving mixtures of basaltic compositions with different types of alteration materials including palagonite we show that the mars soil composition can be matched with a combination of unweathered basaltic martian meteorites with basaltic feo rich cao poor alteration products palagonite is a possible but not a necessary component of successful model mixtures the hydrothermal alteration materials that form successful model mixtures are formed in low temperature low water rock ratio environments and they can reproduce the required geochemical trends because they are poorer in cao but not in feo compared to their respective protoliths these results argue that material altered by hydrothermal processes could be a plausible component of the soil and that removal of cao from the soil into some undiscovered reservoir after its formation is not required the current soil on mars therefore did not have to undergo an episode of in situ aqueous alteration but could represent a sink for materials that experienced aqueous processes in a different setting before erosion to form the soil the soil can also represent a sink for mobile elements e g s cl and br derived from other sources such as volcanic aerosols and hydrothermal fluids