aqueous alteration in the northwest africa 817 nwa 817 martian meteorite samples of a new martian meteorite of the nakhlite family nwa 817 contain traces of an iron rich alteration product textural arguments indicate that this alteration product has been formed on the parent body of the meteorite mars the chemical composition and structural data x ray diffraction transmission electron microscopy and vibrational spectroscopy show that the alteration mineral is a hydrous phase from the smectite family major elements and rare earth elements suggest that the formation of the alteration phase is related to the circulation of an aqueous fluid which composition is controlled by the dissolution of feldspars to account for a positive eu anomaly olivine and possibly apatite hydrogen isotope data display negative deltad values ranging from 60 to 280parts per thousand in olivine and pyroxenes and from 140 to 181parts per thousand in the alteration phase the values of deltad for the alteration product show a small scatter with a mean value of 170 14parts per thousand these values are lower than those previously obtained on other martian meteorites which give mainly positive deltad values these positive values have been interpreted as resulting from the interaction of the martian meteorites with water from the martian atmosphere ruling out the effect of terrestrial alteration it is suggested that alteration in the nwa 817 meteorite was likely produced on mars by the circulation of an aqueous fluid originating from a chemical reservoir such as the martian mantle which has not equilibrated with a fractionated martian atmosphere c 2002 elsevier science b v all rights reserved

stable isotope compositions of serpentinite seamounts in the mariana forearc serpentinization processes fluid sources and sulfur metasomatism the mariana and izu bonin arcs in the western pacific are characterized by serpentinite seamounts in the forearc that provide unique windows into the mantle wedge we present stable isotope o h s and c data for serpentinites from conical seamount in the mariana forearc and s isotope data for torishima seamount in the izu bonin forearc in order to understand the compositions of fluids and temperatures of serpentinization in the mantle wedge and to investigate the transport of sulfur from the slab to the mantle wedge six serpentine mineral separates have a restricted range of 18o 6 5 8 5 antigorite separates have d values of 29 5 to 45 5 that reflect serpentinization within the mantle wedge whereas chrysotile has low d values 51 8 to 84 0 as the result of re equilibration with fluids at low temperatures fractionation of oxygen isotopes between serpentine and magnetite indicate serpentinization temperatures of 300 375 c two late cross fiber chrysotile veins have higher 18o values of 8 9 to 10 8 and formed at lower temperatures as low as 100 c aqueous fluids in equilibrium with serpentine at 300 375 c had 18o 6 5 9 and d 4 to 26 consistent with sediment dehydration reactions at temperatures 200 c in the subducting slab rather than a basaltic slab source three aragonite veins in metabasalt and siltstone clasts within the serpentinite flows have 18o 16 7 24 5 consistent with the serpentinizing fluids at temperatures 250 c 13c values of 0 1 2 5 suggest a source in subducting carbonate sediments the 34s values of sulfide in serpentinites on conical seamount 6 7 to 9 8 result from metasomatism through variable reduction of aqueous sulfate 34s 14 derived from slab sediments despite sulfur metasomatism serpentinites have low sulfur contents generally 164 ppm that reflect the highly depleted nature of the mantle wedge the serpentinites are mostly enriched in 34s median 34ssulfide 4 5 consistent with a 34s enriched mantle wedge as inferred from arc lavas

hydrogen isotope evidence for loss of water from mars through time 1 the high d h of the martian atmosphere 5 6 terrestrial is considered strong evidence for the loss of martian water to space the timing and magnitude of the loss of water from mars can be constrained by measurements of d h in martian meteorites previous studies of martian meteorites have shown a large range in d h from terrestrial values to as high as the current martian atmosphere here we show that the ancient 4 ga mars meteorite alh84001 has a d h 4 terrestrial and that the young 0 17 ga shergotty meteorite has a d h 5 6 terrestrial we also find that the young los angeles shergottite has zoning in d h that can be correlated to igneous growth zoning strongly suggesting assimilation of d enriched water during igneous crystallization near the martian surface in contrast to previous studies we find higher and less variable d h ratios in these three meteorites our results suggest a two stage evolution for martian water a significant early loss of water to space prior to 3 9 ga followed by only modest loss to space in the last 4 billion years the current martian atmospheric d h has remained essentially unchanged for the last 165 ma

basalt and olivine dissolution under cold salty and acidic conditions what can we learn about recent aqueous weathering on mars 1 to test which variables may be important for weathering on mars the effects of temperature 22 c 6 c and 19 c high ionic strength and oxygen concentrations were investigated in batch dissolution experiments containing forsterite fayalite and basalt glass cacl2 nacl h2o brine can remain liquid to temperatures of 55 c and thus may be liquid in the cold dry climate that currently characterizes mars to understand weathering under such conditions dissolution rates were measured in experiments in distilled water with and without cacl2 and nacl as observed by others dissolution rates increased with temperature and only fayalite dissolution was significantly affected by the presence or absence of oxygen enhanced fayalite dissolution under anoxic conditions suggests that fe rich olivine would dissolve more rapidly than mg rich olivine on mars dissolution in the two most dilute experimental solutions deionized water and cacl2 nacl h2o solution of ionic strength 0 7 m were the same within uncertainty but apparent dissolution rate constants in cacl2 nacl h2o brines were significantly slower steady silica concentrations are decreased in the brines consistent with other work and precipitation rates of silica decrease with decreasing temperatures these results suggest that enhanced silica precipitation could be an indicator of high ionic strength solutions on mars consistent with these observations weathering of basalt has been observed to sometimes be accompanied by precipitated layers of silica in cold dry environments on earth if dissolution on mars occurs or occurred under conditions similar to our experiments cation leaching would be expected to be accompanied by silica precipitates on weathering surfaces

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

spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of mars mineral abundances derived from the analysis of remotely sensed thermal emission data from mars have been interpreted to indicate that the surface is composed of basalt surface type 1 and andesite surface type 2 1 the global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient heavily cratered crust in the southern hemisphere basalt from younger lowland plains in the north andesite 1 but the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of mars here we reinterpret martian surface rock lithologies using mineral abundances from previous work1 and new mineralogies derived from a spectral end member set representing minerals common in unaltered and low temperature aqueously altered basalts our results continue to indicate the dominance of unaltered basalt in the southern highlands but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite the coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre

noble gases in iddingsite from the lafayette meteorite evidence for liquid water on mars in the last few hundred million years we analyzed noble gases from 18 samples of weathering products iddingsite from the lafayette meteorite potassium argon ages of 12 samples range from near zero to 670 91 ma these ages confirm the martian origin of the iddingsite but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40ar in any case because iddingsite formation requires liquid water this data requires the presence of liquid water near the surface of mars at least as recently as 1300 ma ago and probably as recently as 650 ma ago krypton and xe analysis of a single 34 g sample indicates the presence of fractionated martian atmosphere within the iddingsite this also confirms the martian origin of the iddingsite the mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas our strongest conclusion is that the iddingsite in lafayette formed on mars in agreement with the microstratigraphic arguments of gooding et al 1991 and treiman et al 1993 a preterrestrial origin of the iddingsite is required both by the many non zero k ar ages and by the presence of xe that is isotopically distinct from any terrestrial xe the xe is accompanied by kr but the kr and xe have been fractionated if they are derived from the present martian atmosphere this is presumably the result of either incorporation via interaction with liquid water drake et al 1994 bogard and garrison 1998 or by adsorption from the martian atmosphere perhaps accompanied by shock see also gilmour et al 1998 1999 although the iddingsite is enriched in kr and xe compared to whole rock analyses it is not clear whether iddingsite is the dominant carrier of the atmospheric derived gas drake et al 1994 or merely a minor carrier gilmour et al 1999 our 40ar 39ar experiment was disappointing in that it mostly served to confirm that the iddingsite which contains fine grained clays is susceptible to recoil loss of 39ar during irradiation only one sample of five gave a clear signal of radiogenic or extraterrestrial 40ar and that was only by 3 potassium argon ages of the second set of samples were more successful ranging from near 0 to 670 91 ma it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration the fact that a rb sr experiment shih et al 1998 gave an apparent age for iddingsite of 679 66 ma 2a suggests that perhaps formation of iddingsite occurred or began 650 ma ago and that some samples either formed or were thermally altered later the ages could be even younger than 650 ma if the samples have incorporated martian atmospheric 40ar this means that liquid water was certainly present on mars in the last 1300 ma the formation age of lafayette and probably within the last 650 ma

40ar 39ar studies of whole rock nakhlites evidence for the timing of formation and aqueous alteration on mars 20 25 mg whole rock samples of the nakhlites lafayette and nakhla have been analyzed via the 40ar 39ar technique in part to verify their formation ages but primarily in an attempt to determine the timing of aqueous alteration in these martian meteorites as in previous studies plateaus in apparent age are observed at about 1300 ma 1322 10 for lafayette 1332 10 and 1323 11 for nakhla presumably corresponding to crystallization ages the plateaus are not entirely flat perhaps reflecting the effects of recoil during creation of 39ar in the nuclear irradiation the first 5 20 of the k derived ar released from all three samples give apparent ages 1300 ma coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance we believe the low temperature pattern represents more recent than 1300 ma formation of martian aqueous alteration products such as iddingsite no low temperature plateaus are observed this is consistent with petrographic evidence for multiple formation events although the lack of low temperature plateaus is far from conclusive on the other hand if there was a single time of alteration we believe that it will be difficult if not impossible to determine it using the k ar system

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

insights into martian water reservoirs from analyses of martian meteorite que94201 the martian atmospheric d h value of 5 2 times terrestrial is significantly higher than any found on earth and has been ascribed to preferential loss of h relative to d from the atmosphere through jeans escape over time here based on ion microprobe analyses of apatite grains from martian meteorite que94201 it is shown that the pre jeans escape martian water reservoir has a d h value twice that of terrestrial water rather than the terrestrial value that has been assumed in prior work the data support a two stage history for martian volatiles in which early hydrodynamic escape enriched martian water to 2x terrestrial d h values subsequent jeans escape to produce the current atmospheric values has thus been responsible for less d enrichment than previously thought a martian crust containing 2 3 times more water than previously proposed is implied by the results

evolution of water reservoirs on mars from d h ratios in the atmosphere and crust ancient fluvial networks on the surface of mars suggest that it was warm and wet over three billion years ago surface features resembling massive outflow channels provide evidence that even more recently the martian crust contained the equivalent of a planet wide reservoir of water several hundred metres deep but arguments based on the isotopic fraction and present day escape rate of hydrogen in the martian atmosphere require only 0 5 metres of crustal water today and about six metres in the past an additional constraint on the evolution of the isotopic composition of martian water has recently been obtained from measurements of the deuterium to hydrogen ratio of hydrous minerals in the snc meteorites meteorites that almost certainly originated on mars here i show that these new data require that the modern crustal reservoirs of martian water must be quite large at least several metres in global equivalent depth the deuterium enrichment of the present martian atmosphere then implies that the reservoir of crustal water on ancient mars was several hundred metres deep consistent with the geological evidence

the sources of water in martian meteorites clues from hydrogen isotopes abstract h isotope measurements of carbonate phosphate feldspathic and mafic glasses and post stishovite silica phase in the shergottites zagami shergotty sau 005 dag 476 alha 77005 and eeta 79001 as well as in chassigny and alh 84001 show that all these phases contain deuterium enriched water of extraterrestrial origin the minerals and glasses analyzed may contain an initial primary hydrogen component but their isotopic composition was modified to varying degrees by three different processes interaction with a fractionated exchangeable water reservoir on mars hydrogen devolatilization by impact melting and terrestrial contamination positive correlations between d and water abundance in feldspathic glass and post stishovite silica in zagami shergotty and sau 005 is indicative of mixing of a high d component 3000 4000 and a less abundant low d component 0 the high d component is primarily derived from the martian exchangable reservoir but may also have been influenced by isotopic fractionation associated with shock induced hydrogen loss the low d component is either a terrestrial contaminant or a primary magmatic component the negative correlation between d and water abundances in mafic and feldspathic glasses in alh 84001 alha 77005 and eeta 79001 is consistent with the addition of a low d terrestrial contaminant to a less abundant high deuterium martian component the low d of magmatic glass in melt inclusions suggests that the d of martian parent magma was low and that the initial h isotope signature of mars may be similar to that of earth

the elmore ranch and superstition hills earthquakes of 24 november 1987 introduction to the special issue on 24 november 1987 two significant earthquakes occurred along the southern san jacinto fault zone and related structural elements in southern california not far from the international border these two events the elmore ranch earthquake m 6 2 at 0154 gmt and the superstition hills earthquake m 6 6 at 1315 gmt both moment magnitudes from sipkin 1989 and their aftershocks have yielded a rich harvest of geological seismological and engineering data pertinent to the cause and effect of earthquakes in this region where the southern san jacinto fault zone enters the salton depression from the peninsula ranges bordering it on the southwest fig 1 this special issue of the bulletin presents 18 geologic and seismologic investigations of these earthquakes a collection of papers born in el centro california on 8 and 9 february 1988 at a meeting attended by approximately 60 scientists interested in these earthquakes for one reason or another

an integrated multi scale 3d seismic model of the archaean yilgarn craton australia abstract the collection of a range of different seismic data types has greatly improved our understanding of the crustal architecture of australia s archaean yilgarn craton over the last few years these seismic data include broadband seismic studies seismic receiver functions wide angle recordings and mine scale to deep seismic reflection transects each data set provides information on the three dimensional 3d tectonic model of the yilgarn craton from the craton scale through to the mine scale this paper demonstrates that the integration and rationalisation of these different seismic data sets into a multi scale 3d geological seismic model that can be visualised at once in a single software package and incorporating all available data sets significantly enhances this understanding this enhanced understanding occurred because the integrated 3d model allowed easy and accurate comparison of one result against another and facilitated the integrated questioning and interrogation across scales and seismic method as a result there are feedback questions regarding understanding of the individual seismic data sets themselves as well as the yilgarn craton as a whole the methodology used including all the data sets in the model range had to allow for the wide range of data sets frequencies and seismic modes at the craton scale p wave s wave and surface wave variations constrained the 3d lithospheric velocity model revealing noticeable large scale velocity variations within and across the craton an interesting feature of the data easily identified in 3d is the presence of a fast s wave velocity anomaly 4 8 km s 1 within the upper mantle this velocity anomaly dips east and has a series of step down offsets that coincide approximately with province and terrane boundaries of the yilgarn craton one dimensional receiver function profiles show variations in their crustal velocity across the craton these crustal velocity variations are consistent with the larger scale geological subdivision of the craton and provide characteristic profiles for provinces and terranes the receiver function results and the deep seismic reflection data both agree on the depth to the moho and both indicate an increase in moho depth to the east the 2d seismic refraction results in the south west of the craton provide crustal thickness information an indication of middle and lower crustal compositions and information regarding the broad scale architectural framework at the province and terrane scale the deep seismic reflection data and the mine scale seismic data provide geometric constraints on crustal architecture in particular the orientation of the region s fault systems as well as variations in the thickness of the granite greenstone succession integration of the results from wide angle seismic refraction data coincident with the deep seismic reflection data provided additional constraints on likely upper crustal lithologies the integrated 3d seismic model implies the dominant geodynamic process involved the development of an orogenic belt that developed with a series of contractional folding and thrusting events separated by equally important extensional events the seismic reflection data in particular suggests that extensional movement on many shear zones was more common than previously thought the seismic reflection data suggest that the dominant mineral systems involved deeply sourced fluid flowing up crustal penetrating shear zones these deeply sourced fluids were further focussed into sites located above fault breached domal regions in the upper crust

petrology of the miller range 03346 nakhlite in comparison with the yamato 000593 nakhlite we petrologically examined the miller range mil 03346 nakhlite the main phase modal abundances are 67 7 vol augite 0 8 vol olivine and 31 5 vol mesostasis among all known nakhlites mil 03346 s modal abundance of olivine is the smallest and of mesostasis is the largest augite occurs as cumulus phenocrysts having a homogeneous core composition en36 38fs24 22wo40 which is identical with other nakhlites they accompany thin ferroan rims divided into inner and outer rims with a compositional gap at the boundary between the two rims olivine grains have magnesian cores fa 55 and show normal zoning toward ferroan rims fa 84 mesostasis consists mostly of glass 26 0 vol with minor skeletal fayalites skeletal titanomagnetites acicular phosphate massive cristobalite and sulfides we conclude that mil 03346 is the most rapidly cooled nakhlite among all known nakhlites based on the petrography we obtain the intercumulus melt composition for mil 03346 from the mass balance calculation using the modal abundances and discuss the crystallization sequence of mil 03346 in comparison with that of yamato y 000593 although magnesian olivines of y 000593 are phenocrystic magnesian olivine grains of mil 03346 seem to have texturally crystallized from the intercumulus melt after the mil 03346 magma intruded upward to the martian surficial zone the magnesian olivine crystallized and then the ferroan inner rim formed on phenocrystic core augite the outer rim of phenocrystic augites formed after the crystallization of skeletal fayalites and skeletal titanomagnetites resulting in a compositional gap between the inner and outer rims finally glassy mesostasis formed from the residual melt this crystallization sequence of mil 03346 is different from those of other nakhlites including y 000593

geochemical and mineralogical indicators for aqueous processes in the columbia hills of gusev crater mars 1 water played a major role in the formation and alteration of rocks and soils in the columbia hills the extent of alteration ranges from moderate to extensive five distinct rock compositional classes were identified the order for degree of alteration is watchtower clovis wishstone peace backstay the rover s wheels uncovered one unusual soil paso robles that is the most s rich material encountered clovis class rocks have compositions similar to gusev plains soil but with higher mg cl and br and lower ca and zn watchtower and wishstone classes have high al ti and p and low cr and ni peace has high mg and s and low al na and k backstay basalts have high na and k compared to plains adirondack basalts and paso robles soil has high s and p some rocks are corundum normative indicating that their primary compositions were changed by loss and or gain of rock forming elements clovis materials consist of magnetite nanophase ferric oxides npox hematite goethite ca phosphates ca and mg sulfates pyroxene and secondary aluminosilicates wishstone and watchtower rocks consist of fe oxides oxyhydroxides ilmenite ca phosphate pyroxene feldspar mg sulfates and secondary aluminosilicates peace consists of magnetite npox mg and ca sulfates pyroxene olivine feldspar apatite halides and secondary aluminosilicates paso robles consists of fe3 mg ca and other sulfates ca phosphates hematite halite allophane and amorphous silica columbia hills outcrops and rocks may have formed by the aqueous alteration of basaltic rocks volcaniclastic materials and or impact ejecta by solutions that were rich in acid volatile elements

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

what we know about mars from its impact craters martian impact craters provide insights into formation ages of terrain units nearsurface properties and the planet s degradational history crater size frequency distribution analyses allow determination of terrain unit relative ages and extrapolation of the lunar crater chronology can provide estimates of absolute ages for these units such analyses indicate that mars has been geologically active throughout its history but it also retains extensive regions dating back to ca 4 ga higher cratering rates during the late heavy bombardment lhb helped to create the martian regolith and formation of large impact basins helped to erode the initially denser martian atmosphere and may have created the hemispheric dichotomy low global degradation rates since the end of lhb ca 3 8 ga resulted in well preserved impact crater morphologies the presence of layered ejecta blankets and central pits associated with fresh to moderately eroded craters suggests a volatile rich crust impact crater depth diameter relationships allow estimation of the vertical extent of crustal volatiles to depths greater than those probed by current spacecraft instrumentation temporal changes in subsurface ice reservoir depths are revealed by differences in layered ejecta onset diameter as a function of crater age an understanding of the morphology and morphometry of pristine impact craters facilitates efforts to determine the amount and types of degradation and the periods over which they operated impact craters therefore play a major role in unraveling the climatic and geologic history of mars

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

hydrogen isotopic compositions in allan hills 84001 and the evolution of the martian atmosphere hydrogen isotopic compositions of carbonate and maskelynite in allan hills alh 84001 were measured by secondary ion mass spectrometry sims the delta d values of both minerals show considerable deviation the deviation seems to be caused by addition of varying amounts of terrestrial water in the case of carbonate in the case of maskelynite h is heterogeneously distributed and the deviation in delta d values seems to be due to mixing of this indigenous heavy h with isotopically normal h present in the sims chamber the indigenous delta d value in alh 84001 seems to be approximately 2000 carbonate rather than maskelynite seems to be the main carrier of h in alh 84001 because alh 84001 is approximately 4 ga old the h isotopic composition suggests that a large fraction of the initial martian atmosphere had already escaped by 4 ga

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

high resolution reflectance spectra of mars in the 2 3 μm region evidence for the mineral scapolite spatially resolved reflectance spectra of mars in the 2 2 to 2 4 m spectral region were obtained in august 1988 using the nasa 3 m infrared telescope facility the spectra show weak absorption features due to martian atmospheric carbon monoxide and a surface mineral both co and the mineral absorptions are composed of overlapping narrow features but in many locations such as hellas chryse eden and moab the mineral absorptions are quite strong at least 3 times stronger than at the most absorbing wavelengths of co near 2 33 m therefore co complicates the analysis of the surface mineral but does not always overwhelm its signature model removal of the martian atmospheric co has been performed and the remaining absorption bands are identified as scapolite relatively strong absorptions that match bands in the spectrum of scapolite and have little or no co absorption interference are seen near 2 41 2 39 and 2 29 m absorption also occurs at the scapolite bands at 2 36 and 2 33 m but the analysis is complicated by uncertainty in the atmospheric co removal at these wavelengths weaker scapolite bands are seen at 2 44 and 2 23 m where there is virtually no atmospheric interference the scapolite bands observed on mars are due to hco3 and hso4 ions in the scapolite structure the bicarbonate and bisulfate contents appear to vary with location the scapolite in hellas is more bisulfate rich relative to that in the chryse moab eden area other locations contain little arabia syrtis major hellespontica and isidis or no scapolite e g margaritifer ausonia and erythraeum the calculated abundances are unconstrained because the amounts of hco3 and hso4 in the martian scapolites as well as their grain sizes are not known if the scapolites contain about 3 wt of each near the maximum possible the scapolite abundances probably range from about 5 wt scapolite at eden and hellas 3 5 at chryse moab and oxia palus 2 3 at arabia syrtis major and isidis to less than 2 at hellespontica syrtis minor and margaritifer assuming a relatively large grain size of 50 100 m if the characteristic grain sizes are smaller or the hco3 and hso4 contents are lower the scapolite abundances required to match the observed band depths would be higher the mineral bands are apparent in many of the mars spectra measured so it appears to be widely but not uniformly distributed the newly observed fine structure also varies greatly in both depth and spectral detail with location on mars thus there appears to be regional variations in composition the mineral phases appear to reflect local or regional geology and are not primarily contained in the homogeneous globally redistributed aeolian dust higher spectral resolution martian spectra in the 2 3 m region as well as at 3 9 m are needed to confirm the scapolite identification and to constrain its abundance

comparisons of the four miller range nakhlites mil 03346 090030 090032 and 090136 textural and compositional observations of primary and secondary mineral assemblages abstract petrological and geochemical analyses of miller range mil 03346 indicate that this meteorite originated from the same augitic cumulate layer s as the nakhlite martian meteorites but underwent rapid cooling prior to complete crystallization as with the other nakhlites mil 03346 contains a secondary alteration assemblage in this case consisting of iddingsite like alteration veins in olivine phenocrysts fe oxide alteration veins associated with the mesostasis and ca and k fe sulfate veins we compared the textural and mineralogical compositions of mil 090030 090032 and 090136 with mil 03346 focusing on the composition and raman spectra of the alteration assemblages these observations indicate that the meteorites are paired and that the preterrestrial olivine bound alteration assemblages were produced by weakly acidic brine although these alteration assemblages resemble similar assemblages in nakhla the absence of siderite and halite in the miller range nakhlites indicates that the parental alteration brine was comparatively hco3 depleted and less concentrated than that which altered nakhla this indicates that the miller range nakhlite alteration brine experienced a separate evolutionary pathway to that which altered nakhla and therefore represents a separate branch of the lafayette nakhla evaporation sequence thin sections cut from the internal portions of these meteorites away from any fusion crust or terrestrially exposed edge contain little ca sulfate identified as gypsum and no jarosite whereas thin sections with terrestrially exposed edges have much higher sulfate abundances these observations suggest that at least the majority of sulfate within the miller range nakhlites is terrestrially derived

sulfates in the north polar region of mars detected by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer observed the northern circumpolar regions of mars at a resolution of a few kilometers an extended region at 240 e 85 n with an area of 60 kilometers by 200 kilometers exhibits absorptions at wavelengths of 1 45 1 75 1 94 2 22 2 26 and 2 48 micrometers these signatures can be unambiguously attributed to calcium rich sulfates most likely gypsum this region corresponds to the dark longitudinal dunes of olympia planitia these observations reveal that water alteration played a major role in the formation of the constituting minerals of northern circumpolar terrains

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

hydrogen isotope analyses of alteration phases in the nakhlite martian meteorites abstract secondary alteration phases such as carbonates smectite clays and fe oxides are found within the martian meteorites if these meteorites were seen to fall the assumption can be reasonably made that the secondary phases have a martian origin however for martian meteorite finds this is not the case deuterium hydrogen d h ratio analysis can be used to distinguish between terrestrial and martian secondary alteration phases the martian atmosphere is currently five times enriched in deuterium compared to terrestrial seawater producing a deuterium enrichment in the martian alteration phases large enough to be detected with modern ion microprobe techniques we aimed to measure the d h ratio of the iddingsite like alteration veins in the nakhlite martian meteorites nakhla mil 03346 mil 090030 and y 000593 to help confirm the martian origin of this material and determine the relative amounts of terrestrial contamination in each meteorite as an observed fall nakhla is nominally uncontaminated by terrestrial alteration and shows elevated d values in its alteration veins however even the highest of these values is much below that of the martian atmosphere indicating that terrestrial contamination probably combined with fractionation effects between the martian atmosphere and the alteration material have reduced the d values of these veins the speed of hydrogen isotope exchange in the nakhlite iddingsite like alteration veins is demonstrated by the purely terrestrial d values in the veins of nakhla 110 a thin section exposed to the terrestrial atmosphere since its preparation in 1998 mineralogical heterogeneity also affects the hydrogen isotope exchange rate in these veins the wide variation in d within the veins of nakhla and y 000593 appears to be due to the heterogeneous nature of the vein material where some phases exchange hydrogen with the atmosphere at a faster rate than others

a halite siderite anhydrite chlorapatite assemblage in nakhla mineralogical evidence for evaporites on mars we report the results of a study of a halite siderite anhydrite chlorapatite assemblage in the shergotty nakhla chassigny snc martian meteorite nakhla these minerals are found associated with each other in interstitial areas with halite often being adjacent to or enclosing siderite we suggest the halite and other minerals are martian in origin because 1 the conditions of fall preclude significant amounts of terrestrial contamination or weathering having taken place 2 textures indicate that the minerals within this assemblage crystallized at the same stage as some silicate and oxide minerals within the nakhla parent and 3 the association with siderite which previous studies have shown has c and o isotopic compositions incompatible with an origin on the earth siderite has the range of compositions caco3 0 1 5 7 mgco3 2 0 40 9 feco3 23 2 87 0 mnco3 1 0 39 9 mol there are two compositional groupings high mnco3 30 mol and low mnco3 high feco3 with a gap identified between the two this may be a miscibility gap or alternatively the two compositional groupings may mark separate generations of carbonate we have not found any textural evidence for the latter explanation but acceptance of the presence of a miscibility gap would require independent work on fe mn carbonates to verify its existence trace element abundances have been determined by ion microprobe analysis on three siderite and one anhydrite grains siderite has light rare earth elements 2 2 7 3 c1 greater than heavy rare earth elements 0 32 0 79 c1 without ce or eu anomalies and the anhydrite has a similar pattern these abundances reflect the source composition rather than partitioning or complexing controls they are not typical of hydrothermal signatures which generally do not have such smooth ree abundance patterns the nature of the mineral assemblage suggests that its source rocks on mars were evaporites these may be common in the craters and flood plains of the martian southern highlands two models are suggested in this paper to explain the incorporation of evaporitic material into the nakhla igneous parent it may have happened as a low temperature process 200 c by crystallisation from an aqueous fluid an origin at low temperature is compatible with the available experimental data on siderite stability alternatively we suggest evaporitic material may have been incorporated into the nakhla parent while melt was still present and crystallized 800 c the latter model can more readily explain the trace element abundances and also the siderite textures that imply intergrowth with residual interstitial melt both high and low temperature models are consistent with the presence of evaporite sediments on mars