petrogenesis of the elephant moraine a79001 meteorite multiple magma pulses on the shergottite parent body abstract the eeta 79001 achondrite consists of two distinct igneous lithologies joined along a planar non brecciated contact both are basaltic rocks composed primarily of pigeonite augite and maskelynite but one contains zoned megacrysts of olivine orthopyroxene and chromite that represent disaggregated xenoliths of harzburzite both lithologies probably formed from successive volcanic flows or multiple injections of magma into a small shallow chamber many similarities between the two virtually synchronous magmas suggest that they are related possible mechanisms to explain their differences involve varying degrees of assimilation fractionation from similar parental magmas or partial melting of a similar source peridotite of these assimilation of the observed megacryst assemblage seems most plausible however some isotopic contamination may be required in any of these petrogenetic models the meteorite has suffered extensive shock metamorphism and localized melting during a large impact event that probably excavated and liberated it from its parent body both basaltic lithologies and the inferred ultramafic protolith of the megacryst assemblage are petrologically similar to other members of the shergottite group and all may have been derived from a volcanic plutonic complex on a planetary body

analysis of upper mantle structure using wave field continuation of p waves wave field continuation transforms seismic record section data directly into velocity depth space simultaneously providing an estimate of model nonuniqueness this inversion previously used for reflection and refraction data converts readily to spherical earth problems through simple adjustments in each of the two linear transformations the slant stack and downward continuation because the time resolution inherent in the data transforms to depth resolution in the model space this method is extremely useful for analysis of data compatibility with preexisting models and direct comparison between data sets as well as the complete inversion of raw data for structure wave field inversion demands densely sampled digital data and assumes source coherency and lateral homogeneity along the profile we test this technique for upper mantle analysis using a previously studied large array recorded data set representative of structure beneath the gulf of california we compare slant stacks and downward continuations of both synthetic and data record sections to illustrate the method s resolution capability wave field continuation proves particularly useful in comparing entire data sets to various models even subtle structural differences are resolvable given good data quality

on the origin of gypsum in the mars north polar region 1 we describe the distribution and concentration of the largest martian gypsum deposit discovered to date by the mars express omega observatoire pour le mineralogie l eau les glaces et l activite imaging spectrometer its relationship to the late amazonian aged north polar dunes in which it is found and its likely origin gypsum has not been discovered anywhere within the north polar region outside of the olympia undae dune sea in the areas of highest gypsum a concentration 35 pure gypsum grains of a few tens of micrometers in size mixed with 65 millimeter sized gypsum grains containing dark spectrally featureless inclusions best fit the omega observations the gypsum rich dunes contain no significant average albedo temperature or morphological anomalies we propose that water emanating from nearby channels carved during melting of the polar layered deposits infiltrated the eastern end of the polar dune sea percolating through the dunes deposits of gypsum resulted from a combination of direct in situ alteration of sulfide and high calcium pyroxene bearing dunes and from formation of evaporitic gypsum crystals in the pore spaces of these dunes this gypsum deposit formed in a unique local environment and is disconnected from sulfate forming events elsewhere on mars which are thought to have occurred much earlier during the late noachian and hesperian by various means sulfates have not been discovered in any other collection of dunes on mars

hydrothermal jarosite and hematite in a pyroxene hosted melt inclusion in martian meteorite miller range mil 03346 implications for magmatic hydrothermal fluids on mars low temperature aqueous processes have been implicated in the generation of jarosite and hematite on the martian surface but little is known regarding the role that high temperature magmatic fluids may have played in producing similar assemblages on mars we have identified jarosite and hematite in a clinopyroxene hosted melt inclusion in martian meteorite mil 03346 that shows evidence of having been hydrothermally precipitated in addition to jarosite and hematite the melt inclusion contains titanomagnetite pyrrhotite potassic chlorohastingsite an iron rich silicate glass and possibly goethite these phases were identified and characterized using scanning electron microscopy sem con focal raman spectroscopy and electron probe microanalysis epma based on observed textural relationships and the compositions of the hosted phases we report that the jarosite bearing melt inclusion in mil 03346 has recorded a fluid rich history that began in the magmatic stage and continued to low temperatures this history begins at entrapment of a volatile rich silicate melt that likely reached fluid saturation after only minor crystallization within the melt inclusion this fluid rich in chlorine reacted with surrounding silicate material to produce the potassicchlorohastingsite as cooling proceeded the liquid phase eventually became more oxidized and reacted with the pyrrhotite sulfide oxidation resulted in so4 2 formation and concomitant acid production setting the stage for jarosite formation once the fluid cooled beyond the upper thermal stability of jarosite 200 c as the fluid cooled below 200 c jarosite continued to precipitate with hematite and or goethite until equilibrium was established or reactions became kinetically unfavorable this work suggests an additional jarosite hematite formation pathway on mars one that may be important wherever magmatic hydrothermal fluids come into contact with primary sulfide grains at the martian surface or subsurface moreover hydrothermal fluids rich in chlorine sulfur and iron are important for ore forming processes on earth and their indirect identification on mars may have important implications for ore formation on mars

efflorescence as a source of hydrated sulfate minerals in valley settings on mars abstract a distinctive sulfur cycle dominates many geological processes on mars and hydrated sulfate minerals are found in numerous topographic settings with widespread occurrences on the martian surface however many of the key processes controlling the hydrological transport of sulfur including sulfur sources climate and the depositional history that led to precipitation of these minerals remain unclear in this paper we use a model for the formation of sulfate efflorescent salts mg ca na sulfates in the rio puerco watershed of new mexico a terrestrial analog site from the semiarid southwest u s to assess the origin and environmental conditions that may have controlled deposition of hydrated sulfates in valles marineris on mars our terrestrial geochemical results s 34 of 36 0 to 11 1 show that an ephemeral arid hydrological cycle that mobilizes sulfur present in the bedrock as sulfides sulfate minerals and dry wet atmospheric deposition can lead to widespread surface accumulations of hydrated sulfate efflorescences repeating cycles of salt dissolution and reprecipitation appear to be major processes that migrate sulfate efflorescences to sites of surface deposition and ultimately increase the aqueous so 4 2 flux along the watershed average 41 273 metric tons yr we suggest that similar shallow processes may explain the occurrence of hydrated sulfates detected on the scarps and valley floors of valles marineris on mars our estimates of salt mass and distribution are in accord with studies that suggest a rather short lived process of sulfate formation minimum rough estimate 100 to 1000 years and restriction by prevailing arid conditions on mars

investigation of the near infrared spectral character of putative martian chloride deposits 1 putative chloride salt deposits observed throughout the southern highlands of mars by the compact reconnaissance imaging spectrometer for mars crism display featureless red slopes in near infrared ratio spectra it is hypothesized that the admixture of anhydrous chlorides or unoxidized sulfides with silicate rocks or minerals could imitate this spectral behavior three different sets of spectra were collected 1 simple mixtures of halite with labradorite and flood basalt at multiple concentrations 2 halite crusts formed on both labradorite and flood basalt and 3 simple mixtures of 25 and 50 wt acid washed pyrite with labradorite and flood basalt in all three instances multiple grain sizes were used to evaluate the effect of particle size on spectral results spectra of the mixtures and crusts were divided by pure labradorite and flood basalt spectra of the same grain size to produce ratio spectra comparable to the crism ratio spectra our study rules out pyrite as a possible component of these deposits whereas flood basalt mixtures with halite reproduced the observed red slope under some conditions this allows us to place some broad constraints on halite proportions and the effective grain sizes of these deposits

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

evaluating the role of sulfide weathering in the formation of sulfates or carbonates on mars orbital and landed missions to mars have revealed complex sulfate and fe oxide bearing mineralogical assemblages which have been interpreted as the result of a late planet wide acidic period due to large so2 emissions however this global scenario does not explain the recent discovery of hesperian and noachian aged carbonates in several regions because they should have been dissolved by the acidic conditions nor the restriction of sulfate occurrences in preferential regions here we present the results of a 4 year long experimental study designed to test the impact of fe sulfides pyrrhotite fe0 9s on the weathering of basaltic silicates olivine clino and orthopyroxene under an early martian like co2 rich atmosphere our weathered silicate sulfide mixtures showed complex parageneses containing elemental sulfur hydrated sulfates gypsum hexahydrite jarosite and fe oxy hydroxides olivine only samples produced nesquehonite an mg carbonate precursor of hydromagnesite and magnesite these secondary phases are similar to those observed in the martian sulfate and carbonate bearing deposits therefore we propose a geochemical model in which on the one hand martian sulfates mainly formed from weathering of sulfide enriched basalts producing locally acidic environments and on the other hand carbonates were preserved and could even have formed in regions initially devoid of sulfides thereby resolving the apparent paradox arising from the possible coeval formation of the two types of minerals these results raise doubts on the need for a global acidic event to produce the sulfate bearing assemblages suggest that regional sequestration of sulfate deposits is due to regional differences in sulfide content of the bedrock and pave the way for reevaluating the likelihood that early sediments preserved biosignatures from the earliest times

chemical systematics of the shergotty meteorite and the composition of its parent body mars abstract we report chemical data for 60 elements by inaa and rnaa in two bulk samples for 30 elements in various mineral separates of shergotty and results of leaching experiments with 1m hcl on powdered aliquots of shergotty and beta 79001 lithologies a and b shergotty is homogeneous in major element composition but heterogeneous with respect to lil trace elements 20 the heterogeneity is even greater for volatile and siderophile trace elements the mineral data including three clinopyroxene fractions with variable feo contents maskelynite and minor phases ti magnetite ilmenite quartz k rich phase show that major minerals do not account for the rare earth elements ree in the bulk meteorite instead the ree are to a large extent concentrated in accessory whitlockite and apatite shown by leaching with 1m hcl together with the majority of ree la 96 yb 70 cl and br are quantitatively dissolved by leaching the ree patterns of the leachate of shergotty and eeta 79001 are different the shergotty leachate may consist of two components component l is similar to that of eeta 79001 leachate whitlockite component 2 is enriched in light ree and may be responsible for the higher lree contents of shergotty in comparison to the other shergottites there is some evidence that shergotty was an open system and component 2 was introduced after crystallization the ree patterns of the residues of shergotty and eeta 79001 are identical indicating that the parent magmas of both meteorites are compositionally similar based on cpx separates with the lowest ree content the ree pattern in the shergotty parent magma was calculated it is enriched in lree and has a subchondritic nd sm ratio the negative eu anomaly in the phosphates indicates that at least some plagioclase crystallized before phosphate based on several element correlations in snc meteorites it was suggested dreibus and wanke 1984 that both the shergotty parent body spb very probably mars and the earth accreted from the same two chemically different components component a highly reduced and devoid of volatile elements and an oxidized component b containing also volatile elements the spb mars mantle is 2 4 times richer in volatile and moderately siderophile elements than the earth indicating a higher portion of component b in the spb the concentrations of chalcophile elements in the spb mantle are low reflecting equilibration with a sulfide phase and subsequent segregation of sulfide into the core unlike the earth wanke 1981 the spb mars may therefore have accreted almost homogeneously

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

mineral chemistry of the shergottites nakhlites chassigny brachina pallasites and urelites the mineral chemistry is compared for selected achondrites olivine in the alha 77005 and eeta79001 shergottites olivine rich chassigny and brachina and the nakhlites contains ni indicative of oxidizing conditions whereas pallasitic and ureilitic olivines contain much lower ni due to reducing conditions the brachina olivine and pyroxene have distinctively higher fe mn than the shergottites and chassigny further indicating that brachina is unique the chassigny and 77005 olivines contain lower cr2o3 0 03 wt than the brachina and 79001 olivines values of fe mn for cumulus augites in nakhlites are higher than for the shergottites whereas those for ferropigeonites are not the 77005 shergottite contains troilite fes in contrast to 79001 shergotty zagami and chassigny which contain pyrrhotite further analyses are needed but the present survey indicates that at least brachina is not chemically cogenetic with the other oxidized achondrites and that the fe mn ratio of the cumulus augites in nakhlites is a problem for the assignment of the nakhlites shergottites and chassigny to a single genetic group

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

surge deposit misidentification at spor mountain utah and elsewhere a cautionary message for mars abstract before base surges were described in association with nuclear blasts and explosive volcanic eruptions especially the 1980 eruption of mount st helens washington laminar and cross bedded volcanogenic surge deposits were commonly misinterpreted as being of fluvial or aeolian origin one well documented example involves the water laid tuffs in and near the spor mountain beryllium mine utah other examples abound in light of how frequently volcanogenic surge deposits have been misinterpreted on earth extreme caution is urged for mars studies contrary to what has been claimed the markedly cross bedded salty deposits at meridiani planum on mars need not have been formed by a combination of aeolian and aqueous processes and their contained hematitic spherules need not have formed as aqueous concretions given the lack of indications of volcanism in the vicinity and the planet wide abundance of impact craters deposition by surges associated with distant impact targets consisting of brine soaked locally sulfidic regolith is a reasonable explanation for all features observed especially if diagenesis and weathering are considered the uniformly sized and shaped ni enriched blue gray hematitic spherules would then be some type of vapor condensation spherules including accretionary lapilli a similar interpretation is possible for deposits in the home plate area gusev crater unlike on the dry and atmosphereless moon salty impact surge deposits containing spherules should be common and well preserved on mars

the parental magma of the nakhla achondrite ultrabasic volcanism on the shergottite parent body the nakhla meteorite is an augite rich igneous cumulate rock magma trapped among the cumulus grains is now represented by fine grained mesostasis and post cumulus overgrowths on cumulus grains the composition of the intercumulus magma calculated by mass balance is ultrabasic sio2 45 and enriched in incompatible elements lalu 6 ci the cumulus augite and intercumulus magma were in chemical equilibrium implying that the intercumulus magma is a sample of nakhla s parental magma complex processes like infiltration metasomatism were therefore unimportant nakhla contains olivine crystals which are as large or larger than the cumulus augite crystals the largest olivine crystals probably xenocrysts preserve core compositions too fe rich to have been in equilibrium with the intercumulus magma other smaller olivine grains may have been phenocrysts the closest terrestrial analogs to nakhla and the other nakhlites are pyroxene rich cumulate layers in differentiated picrite and komatiite flows and shallow sills spinel or garnet was fractionated from the parental magmas of the nakhlites or their parental mantle based on the superchondritic caoal2o3 ratio of nakhla s intercumulus magma and its lack of an eu anomaly the three nakhlites and chassigny are half of the known samples of the shergottite parent body spb one may tentatively infer that ultrabasic volcanism was much more important on the spb than on the moon eucrite parent body or present day earth

ferric sulfates on mars evidence is presented for the possible formation and existence of ferric sulfato complexes and hydroxo ferric sulfate minerals in the permafrost on mars acidic groundwater derived from atmospheric oxidation of volcanogenic h2s to h2so4 aerosols promoted chemical weathering of fayalitic olivines iron rich pyroxenes plagioclase feldspar and pyrrhotite pentlandite mineral assemblages in crustal ultramafic and basic igneous rocks the acidic groundwater entered into electrochemical reactions with the iron sulfides yielding dissolved feso4 fe so4 2 and feoh2 complex ions and the precipitation of basic ferric sulfate minerals such as those belonging to the roemerite copiapite botryogen and jarosite alunite groups these phases are stabilized at low temperatures and ph in martian permafrost the occurrence of jarosites in terrestrial arid regions suggests that they could also survive on the surface of mars melting of the permafrost and raising of the ph may have initiated the hydrolysis of dissolved ferric sulfato complex ions and led to the precipitation of feooh which reacted with precipitated silica to form phyllosilicates alternatively degradation of the hydrolysate feooh to fe2o3 during sublimation of permafrost exposed on mars surface may account for the presence of eolian maghemite suspected to be the magnetic mineral observed on the viking landers

alteration assemblages in the miller range and elephant moraine regions of antarctica comparisons between terrestrial igneous rocks and martian meteorites the weathering products present in igneous terrestrial antarctic samples were analyzed and compared with those found in the four miller range nakhlite martian meteorites the aim of these comparisons was to determine which of the alteration phases in the miller range nakhlites are produced by terrestrial weathering and what effect rock composition has on these phases antarctic terrestrial samples mil 05031 and eet 96400 along with the miller range nakhlites mil 03346 and 090032 were found to contain secondary alteration assemblages at their externally exposed surfaces despite the difference in primary mineralogy the assemblages of these rocks consist mostly of sulfates jarosite in mil 05031 jarosite and gypsum in eet 96400 and iddingsite like fe clay as neither of the terrestrial samples contains sulfur bearing primary minerals and these minerals are rare in the miller range nakhlites it appears that so42 possibly along with some of the na k and ca in these phases was sourced from wind blown sea spray and biogenic emissions from the southern ocean cl enrichment in the terrestrially derived iddingsite of mil 05031 and mil 03346 and the presence of halite at the exterior edge of mil 090032 can also be explained by this process however jarosite within and around the olivine bound melt inclusions of mil 090136 is present in the interior of the meteorite and therefore is probably the product of preterrestrial weathering on mars

petrography and mineralogy of two basalts and olivine pyroxene spinel fragments in achondrite eeta79001 three lithologies occur in shocked achondrite eeta79001 a1 exotic irregular crystals and clusters of coarse grained olivine fo81 55 cao 0 2 cr2o3 0 06 nio 0 5 wt low ca pyroxene en82wo2 en58wo12 and low ti chromite cr2o3 59 feo 27 tio2 0 7 wt a2 basaltic host to a1 containing pyroxene mainly pigeonite en67wo12 en52wo13 maskelynite an61 55or0 7 high ti chromite some rimming low ti chromite whitlockite minor cl apatite ilmenite pyrrhotite and mesostasis and b a homogeneous basalt containing augite laths en40 50wo25 35 in a matrix of pigeohite augite maskelynite an62 56 or1 2 ulvospinelilmenite intergrowth whitlockite cl apatite and mesostasis mineral compositions indicate an oxidation state similar to that of shergottites lithology a1 represents an unmetamorphosed cumulate that was disrupted and partly resorbed by a basaltic magma incorporation of low ca magnesian pyroxenes and olivine increased the mg fe ratio of the basaltic magma responsible for a2 and resulted in abundant crystallization of pigeonite lithology b was generated from a distinct magma lacking fragments of a1 the parental spinel harzburgite of a1 was not annealed and is probably a near surface igneous cumulate from a shergottite type basalt ringwood and majorite were found in shock veins

theoretical prediction of phase relationships in planetary mantles calorimetric and phase equilibrium data have been used to establish an internally consistent thermodynamic data base for the silica undersaturated part of the system na2o feo cao mgo al2o3 sio2 this data base has been used to calculate the stability fields of assemblages involving the phases olivine ol orthopyroxene opx clinopyroxene cpx spinel sp plagioclase plag and garnet gt at high pressures and temperatures in the six component system all these phases are solid solutions their mixing properties were also obtained from phase equilibrium and calorimetric data in the model system cao mgo al2o3 sio2 cmas the stable assemblages are ol opx cpx plag at pressures less than 8 kb at 1300 c and less than 6 kb at 900 c above these pressures spinel replaces plagioclase until pressures of 16 kb at 1300 and 14 kb at 900 c are reached at higher pressures garnet lherzolite ol opx cpx gt is stable stable phase assemblages have also been calculated for sodium and iron bearing compositions postulated as possible martian mantles the mcgetchin smyth composition would not contain orthopyroxene and a low pressure assemblage of plag ol cpx sp would be replaced by gt ol cpx sp at pressures above 13 kb in contrast the morgan anders composition has stability fields of plagioclase iherzolite p 8 kb and a small field of spinel iherzolite at about 6 kb at temperatures below 900 c

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

mossbauer mineralogy of rock soil and dust at meridiani planum mars opportunity s journey across sulfate rich outcrop basaltic sand and dust and hematite lag deposits additonal co authors p gutlich e kankeleit t mccoy dw mittlefehldt f renz me schmidt b zubkov sw squyres re arvidson

evolution of sulfide mineralization on mars the presence of komatiitic igneous rocks on marks based on geochemical evidence from snc meteorites and viking x ray fluorescence analyses of the regolith suggests that massive and disseminated iron sulfide mineralization occurs near the martian surface analogies are drawn between possible ultramafic fe ni sulfides on mars and terrestrial pyrrhotite pentlandite ore deposits associated with archean komatiites formed during early crustal development on earth partial melting of the mantle as a result of high radiogenic heat production then extrusion of turbulent high temperature ultramafic lavas segregation of immiscible fes melts during cooling gravitational settling and fractional crystallization of sulfide minerals in magma chambers or lava flows produced massive and disseminated sulfide mineralization associated with terrestrial komatiites comparable processes probably occurred on mars where on account of the inferred higher fe fe mg ratio of the x ray mantle estimated to contain approximately 4 5 wt s iron rich basaltic magmas were produced by partial melting at depths and temperatures exceeding 165 km and 1 400 degree c respectively adiabatic diapiric emplacement of these iron rich very low viscosity basaltic melts transported significant concentrations of dissolved sulfur as s sup 2 minus and hs sup minus from the mantle ensuing sulfide mineralization may have been either thinly disseminated within ultramafic lavas eruptingmore over large areas of mars or concentrated locally at the base of structural depressions cumulate ore deposits several meters thick may occur at the base of intrusions or in near surface magma chambers the evidence for insignificant plate tectonic activity on mars and minimal interactions of martian mantle with crust hydrosphere and atmosphere has restricted the evolution of sulfide ore deposits there less

emplacement and cooling of komatiite lavas we propose that komatiite lavas were emplaced as turbulent flows accompanied by vigorous forced convection with cooling rates often in excess of hundreds of c h 1 they melted and assimilated up to 10 of the ground over which they flowed forming deep channels nickel sulphide mineralization may have resulted from incorporation of sulphur rich sediment after emplacement high cooling rates persisted resulting in spinifex textures due to compositional convection

the geology of the kambalda nickel field western australia the kambalda nickel field contains the major concentration of volcanic peridotitc associated nickel ores in the archean of australia it occupies an area of 400 km 2 underlain by two sequences of ultramafic mafic and felsic volcanics and sedimentary rocks which can be broadly correlated with previously erected regional stratigraphic sections most ores occur in the lower kambalda sequence at the base of the kambalda ultramafic rocks the ultramafic rocks of the upper bluebush sequence contain only minor mineralization four phases of deformation occurred over an interval of more than 300 m y resulting in a dominant north northwest structural trend faulting was active during original volcanism and continued intermittently until after mafic felsic dike intrusion the ultramafic rocks have been serpentinized and all rocks have exerienced low strain upper greenschist to lower amphibolite facies metamorphism and variable carbonation and potash metasomatism the kambalda ultramafic rocks are of variable thickness and in places exceed 1 000 m the lower member of the ultramafic rocks occupying approximately one third of the sequence comprises thicker high magnesium flows i e generally 36 volatile free mgo commonly separated by sulfidic quartz albite sediments thinner lower magnesium flow units characterize much of the upper member the ores occur in 24 shoot complexes each containing multiple ore surfaces caused by structural dislocation of a few grouped ribbonlike original orebodies eighty percent is contact ore occurring at the base of the lowermost ultramafic flow and generally occupying elongate troughs in the footwall basalt ultramafic contact these troughs are thought to be original volcanic depressions which focused later deformation the remainder is hanging wall ore usually occurring directly above contact ore at the base of the second or third ultramafic flow hanging wall orebodies occasionally grade into stratigraphically equivalent interflow sediments the ores contain varying proportions of massive matrix and disseminated sulfides the hypogene mineral assemblage is pyrrhotite pentlandite pyrite chalcopyrite but millerite is locally significant the massive ores in particular are commonly severely deformed and some have been remobilized tens of meters from their original contact position metamorphism has caused recrystallization of the ores and some redistribution of elements there is commonly marked variation of mineralogy and s ni ratios between contact and overlying hanging wall ores and within and between original ore surfaces within shoots but the relative contributions of primary composition and metamorphism to this variation are uncertain in ore environments the footwall basalt ultramafic contact is more deformed than in non ore environments the basal ultramafic flows are thicker and richer in magnesium the trend toward lower magnesium flows upward through the ultramafic formation is less well developed and there is better textural development and compositional differentiation within flows non ore environments usually contain interflow sediments whereas there is generally a sediment free prism of ultramafic rocks above ore environments most ores are interpreted to have originated by either simultaneous or sequential extrusion of sulfide melts and ultramafic lavas rich in olivine phenocrysts along active linear fissures in a basaltic ocean floor volcanic exhalations probably contributed to minor ore in sulfidic sediments

sulfide mineralogy and redox conditions in some shergottites magmatic sulfide mineralogy has been studied in 2 olivine phyric shergottites dag 476 and sau 005 and 4 basaltic shergottites zagami shergotty los angeles and nwa 480 modal abundances of magmatic sulfides as estimated by image analysis on thin section are high 0 16 to 0 53 area percent and correlate positively with abundances of fe ti oxides sulfides are mesostasis minerals being mostly interstitial grains or locally enclosed in post cumulus melt inclusions e g sau 005 in olivine sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of cu sulfides chalcopyrite and or cubanite hot desert finds e g dag 476 show abundant fracture filling iron oxy hydroxides of probable terrestrial origin unaltered sulfides show metal rich hexagonal pyrrhotite compositions with metal sulfur m s ratio ranging between 0 936 0 005 and 0 962 0 01 this compositional range corresponds to the two phase structural domain 2c nc of the fe s system however the high temperature disordered hexagonal 1c pyrrhotite structure would be in better agreement with magnetic properties of shergottites ni contents in pyrrhotite increase from los angeles 0 05 at to shergotty zagami and nwa 480 0 2 0 5 at and dag 476 and sau 005 up to 3 at the higher ni values of pyrrhotite in olivine phyric shergottites correlate with the abundance of pentlandite exsolutions both reflecting more primitive ni rich sulfide liquids where abundant olivine crystallized this result and the strong correlation between sulfide abundances and fe ti oxides argue for a primary magmatic origin of these sulfides although they reproduce the trend of magmatic oxygen fugacity conditions determined from fe ti oxide pairs observed pyrrhotite compositions are systematically more metaldeficient compared to those calculated from the fe s o system this suggests post magmatic oxidation during cooling on mars followed by terrestrial weathering for hot desert finds

geological context of water altered minerals in valles marineris mars 1 greater than 15 000 km2 of the layered deposits within valles marineris are associated with water altered minerals yet their origin and history of alteration remain a mystery there are numerous competing hypotheses for the formation of the interior layered deposits including aeolian lacustrine and volcanic recent orbiter spectroscopic data have indicated that water has played a role in their geological history thermal emission spectrometer tes measurements have revealed significant crystalline hematite bearing deposits within valles marineris typically related to interior layered deposits these hematite deposits found with a wide range of albedo values are associated with relatively steep bedrock exposures but can also be seen downslope on flat surfaces where they may be a lag deposit more recently observatoire la mineralogie l eau les glaces et l activite omega data have shown hydrated sulfates covering more than 13 000 km2 area of valles marineris sulfates are found in numerous topographic settings and geological units but are typically located along the flanks of interior layered deposits and nearby low lying floor units here we study the detailed morphologies of hematite and sulfate bearing units such as mantled wall units mass wasting blocky deposits massive floor deposits and tectonically altered floor units all of these terrains have diverse erosional styles and varied crater populations in both hematite and sulfate bearing units occasionally found in conjunction with one another formation processes require contributions from water the results indicate a wide range of diversity within an individual mineral class between mineral classes and also among morphological types the diversity of geological settings and properties suggest that any single unified formation mechanism is improbable

speculations on the thermal and tectonic history of the earth summary the connection between the earth s thermal history and convection in the mantle is exploited to elucidate the early evolution of the earth it appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the earth s history only in boundary layers at the surface and at a depth of 650 700 km is conduction likely to be important the resulting evolution appears to be consistent with geological observations on early precambrian rocks various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km the large scale flow is related to the motion of major plates and must be ordered over distances of more than 5000 km its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the earth s surface and to reconcile the geophysical observations with the results of numerical experiments though the existence of the small scale flow is at present speculative various tests of its presence are proposed

zinc and germanium in the sedimentary rocks of gale crater on mars indicate hydrothermal enrichment followed by diagenetic fractionation zinc and germanium enrichments have been discovered in sedimentary rocks in gale crater mars by the alpha particle x ray spectrometer on the rover curiosity concentrations of zn 910 840 ppm and ge 65 58 ppm are tens to hundreds of times greater than in martian meteorites and estimates for average silicate mars enrichments occur in diverse rocks including minimally to extensively altered basaltic and alkalic sedimentary rocks the magnitude of the enrichments indicates hydrothermal fluids but curiosity has not discovered unambiguous hydrothermal mineral assemblages we propose that zn and ge rich hydrothermal deposits in the source region were dispersed in siliciclastic sediments during transport into the crater subsequent diagenetic mobilization and fractionation of zn and ge is evident in a zn rich sandstone windjana zn 4000 ppm ge 85 ppm and associated cl rich vein stephen zn 8000 ppm ge 60 ppm in ge rich veins garden city zn 2200 ppm ge 650 ppm and in silica rich alteration haloes leached of zn 30 200 ppm in moderately to highly altered silica rich rocks ge remained immobile relative to leached elements fe mn mg and ca consistent with fluid interaction at ph 7 in contrast crosscutting ge rich veins at garden city suggest aqueous mobilization as ge f complexes at ph 2 5 multiple jarosite detections by the chemin x ray diffractometer and variable zn concentrations indicate diagenesis of lower mount sharp bedrock under acidic conditions the enrichment and fractionation of zn and ge constrains fluid events affecting gale sediments and can aid in unraveling fluid histories as curiosity s traverse continues

iron sulfur mineralogy of mars magmatic evolution and chemical weathering products models for the evolution of sulfide minerals on mars and reaction pathways to their oxidative weathering products in martian regolith have been proposed based on petrogenetic associations between komatiitic rock types viking geochemical data snc meteorites and terrestrial fe ni sulfide deposits to test the weathering model komatiitic pyrrhotites and olivines were exposed to sulfuric acid solutions with and without dissolved ferric iron added to simulate deep weathering processes and the reaction products were identified by mossbauer spectroscopy secondary fes sub 2 pyrite or marcasite feooh goethite and possibly jarosite were formed from pyrrhotite while olivine was oxidized to nanophase goethite these results suggest that on mars acidic groundwater induced pyrrhotite yields fes sub 2 yields feooh jarosite oxidative weathering reactions particularly in the presence of dissolved fe sup 3 such gossaniferous materials occurring in martian regolith were derived mainly from fe ni sulfides associated with komatiitic basalts and not from sulfides occurring in calc alkaline porphyry copper deposits granitic hydrothermal veins sediment hosted pbs zns ores etc which presumably did not evolve on mars due to the virtual lack of plate tectonic activity there

an astrobiological perspective on meridiani planum sedimentary rocks exposed in the meridiani planum region of mars record aqueous and eolian deposition in ancient dune and interdune playa like environments that were arid acidic and oxidizing on earth microbial populations have repeatedly adapted to low ph and both episodic and chronic water limitation suggesting that to a first approximation the meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place on the other hand the environmental conditions inferred for meridiani deposition would have posed a challenge for prebiotic chemical reactions thought to have played a role in the origin of life on earth orbital observations suggest that the combination of sulfate minerals and hematite found in meridiani rocks may be unusual on the martian surface however there is reason to believe that acidity aridity and oxidizing conditions were broadly distributed on ancient mars when these conditions were established and how much environmental heterogeneity existed on early mars remain to be determined because sulfates and iron oxides can preserve detailed geochemical records of environmental history as well as chemical textural and microfossil signatures of biological activity meridiani planum is an attractive candidate for mars sample return

nickel sulfide deposits in western australia a review the nickel sulfide deposits of western australia consist of many intrusive dunite associated and volcanic peridotite associated deposits of late archean age a few small gabbroid associated deposits of archean or proterozoic age and some other rare types some 96 percent of the nickel metal resource is contained in deposits concentrated in the curvilinear folded and strike faulted supracrustal belts of the eastern yilgarn block very magnesian ultramafic rocks and sulfidic metasediments abound in these belts which have commonly been metamorphosed to greenschist or lower amphibolite facies conditions major strike faults probably influenced the nature and distribution of volcanism and sedimentation later tectonometamorphic styles and nickel mineralization intrusive dunite associated deposits occur in semiconcordant lenses of peridotite to olivinite composition and of komatiitic affinities which are restricted to curvilinear zones 100 km or more long nickel sulfides occur centrally or marginally in the thickest part of the lens low grade 1 ni sulfides are abundant and enclose smaller bodies of higher grade disseminated and massive or breccia ores which may be in part tectonically displaced the ni content of the sulfide fraction is about 10 percent although low grade sulfides may be ni rich with ranges in ni cu of 19 to 70 and ni co of 30 to 70 the lenses may have been emplaced 1 passively as subvolcanic sills which fractionated olivine and sulfides and gave rise to associated komatiitic lavas and or 2 dynamically as dikelike bodies of sulfidic olivine rich crystal mush volcanic peridotite associated deposits are best developed at or near the base of volcanic komatiitic ultramafics occurring between metabasalts and at low stratigraphic levels in the succession there is little or no geographical coincidence between these deposits and the intrusive dunite associated deposits the ultramafics are mainly lavas ranging from picrite to olivine peridotite in composition with thicker and more magnesian flows dominating the lower mineralized part of the piles where thin interflow sulfidic metasediments are also common about 90 percent of the mineralization is at the base of the lowermost olivine peridotite flows which appear to be tongue shaped and to occupy original depressions in basalt surfaces devoid of sulfidic sediment thin discontinuous massive sulfides resting on metabasalt are overlain by thicker continuous and more extensive matrix to disseminated sulfides some massive and breccia ores are tectonically displaced the ni content of the sulfide fraction varies from 5 to 23 percent with an accompanying increase in ni cu from 10 to 16 and ni co from 40 to 65 on eruption of sulfidic komatiitic magma sulfide segregation under differential flow and gravity would probably result in the observed cross sections through the ore but with subsequent physical modification of the ore during metamorphism gabbroid associated deposits occur in layered or composite intrusions of gabbronorite with lesser pyroxenite peridotite and anorthosite which crystallized from basaltic magma of uncertain affinity the rocks are incompletely hydrated low grade disseminated or blebby sulfides form layers or irregular bodies associated with lenses or veins of matrix massive or breccia sulfides the ni content of the sulfide fraction is up to about 6 percent with a range of ni cu ratios of 1 to 7 and an ni co ratio average of about 25 the bulk chemistry of the intrusions and the sulfides and sulfide silicate textures are consistent with the existence of immiscible sulfide liquids at the magmatic stage layered sedimentary associated and vein type arsenical deposits are rare but indicate the possible involvement of nickel in volcanic exhalative and metamorphic hydrothermal processes respectively a complex history of weathering and supergene alteration has affected the deposits and presents major difficulties in exploration the recognition of siliceous limonitic cappings some with pseudomorphic textures led to the discovery of most deposits many problems remain before a more complete understanding of the genesis of the parental sulfidic magmas and their mode of ascent and emplacement into the crust is possible these are discussed with particular reference to the intrusive dunite and volcanic peridotite associated deposits which seem to be restricted to ca 2 7 b y old archean terrains worldwide

compositional investigation of the proposed chloride bearing materials on mars using near infrared orbital data from omega mex 1 several hundred occurrences of chloride bearing salt deposits have been proposed in terrains within the southern highlands of mars on the basis ofthermal emission imaging system and thermal emission spectrometerinfrared observations the spectral identification of chloride salts by remote sensing is challenging because they are transparent over much of the thermal infrared portion of the spectrum further ambiguity arises from the diverse geologic settings in which the putative chloride bearing materials are found in order to better constrain the composition of these unique compositional units we perform a global survey of these materials in the near infrared nir domain with theobservatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer the spectral signatures of the deposits are consistent with although not specific of chlorides we do not observe olivine to be associated with the deposits which confirms that sulfides are an unlikely alternative candidate our systematic search reveals the global lack of association with hydrated minerals phyllosilicates sulfates hydrated silica except for a few deposits noteworthy in northwestern terra sirenum where a small fraction of chloride material overlaps fe mg rich clay bearing terrains even in these locations the morphology and crosscutting relationships of the deposits suggest two separate episodes of mineralization first phyllosilicates then chlorides followed by subsequent formation of sulfates our study shows that local groundwater upwelling seems to be the most frequent source for the water involved in the formation of chloride rather than surface runoff

laboratory simulated acid sulfate weathering of basaltic materials implications for formation of sulfates at meridiani planum and gusev crater mars 1 acid sulfate weathering of basaltic materials is a candidate formation process for the sulfate rich outcrops and rocks at the mer rover opportunity and spirit landing sites to determine the style of acid sulfate weathering on mars we weathered basaltic materials olivine rich glassy basaltic sand and plagioclase feldspar rich basaltic tephra in the laboratory under different oxidative acid sulfate conditions and characterized the alteration products we investigated alteration by 1 sulfuric acid vapor acid fog 2 three step hydrothermal leaching treatment approximating an open system and 3 single step hydrothermal batch treatment approximating a closed system in acid fog experiments a1 fe and ca sulfates and amorphous silica formed from plagioclase rich tephra and mg and ca sulfates and amorphous silica formed from the olivine rich sands in three step leaching experiments only amorphous si formed from the plagioclase rich basaltic tephra and jarosite mg and ca sulfates and amorphous silica formed from olivine rich basaltic sand amorphous silica formed under single step experiments for both starting materials on the basis of our experiments jarosite formation in meridiani outcrop is potential evidence for an open system acid sulfate weathering regime waters rich in sulfuric acid percolated through basaltic sediment dissolving basaltic phases e g olivine and forming jarosite other sulfates and iron oxides aqueous alteration of outcrops and rocks on the west spur of the columbia hills may have occurred when vapors rich in so 2 from volcanic sources reacted with basaltic materials soluble ions from the host rock e g olivine reacted with s to form ca mg and other sulfates along with iron oxides and oxyhydroxides