acid weathering of basalt and basaltic glass 2 effects of microscopic alteration textures on spectral properties this work was funded in part by the nasa 2001 mars odyssey themis project jet propulsion laboratory contract 1228404 through arizona state university and by the arizona state university exploration postdoctoral fellowship the natural sciences and engineering research council of canada the canadian space agency the canada foundation for innovation the manitoba research innovations fund and the university of winnipeg for supporting the establishment and operation of the planetary spectrophotometer facility

tsunami propagation over a wide shallow continental shelf caused by the storegga slide southeastern north sea denmark the large storegga slide which occurred on the norwegian atlantic shelf 8150 yr ago triggered a tsunami that has been identified in sediment deposits along the coasts of greenland norway the faroe islands the shetland islands scotland and the northernmost coasts of england but hitherto not along the southeastern shores of the north sea it has generally been assumed that the shallow continental shelf of the north sea attenuated and dissipated the energy of the tsunami before it reached those coastlines we used radiocarbon and optically stimulated luminescence dating as well as stratigraphic lithologic chemical and palynological analyses of sediment cores to identify tsunami deposits on the barrier island of romo located on the southwestern north sea coast of denmark we show that tsunami sediments were deposited in a freshwater paleolake that is located 16 m below present day mean sea level the tsunami sediment run up was between 1 5 m and 5 5 m above the contemporaneous sea level our results demonstrate that the storegga slide tsunami propagated across the wide 500 km and relatively shallow depth 95 m continental shelf of the north sea and resulted in run up along adjacent coastlines in contradiction to earlier theoretical studies the coastline of the southeastern north sea cannot be regarded as being sheltered from impacts of north atlantic tsunami incidents

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

characteristics distribution origin and significance of opaline silica observed by the spirit rover in gusev crater mars 1 the presence of outcrops and soil regolith rich in opaline silica 65 92 wt sio2 in association with volcanic materials adjacent to the home plate feature in gusev crater is evidence for hydrothermal conditions the spirit rover has supplied a diverse set of observations that are used here to better understand the formation of silica and the activity abundance and fate of water in the first hydrothermal system to be explored in situ on mars we apply spectral chemical morphological textural and stratigraphic observations to assess whether the silica was produced by acid sulfate leaching of precursor rocks by precipitation from silica rich solutions or by some combination the apparent lack of s enrichment and the relatively low oxidation state of the home plate silica rich materials appear inconsistent with the originally proposed hawaiian analog for fumarolic acid sulfate leaching the stratiform distribution of the silica rich outcrops and their porous and brecciated microtextures are consistent with sinter produced by silica precipitation there is no evidence for crystalline quartz phases among the silica occurrences an indication of the lack of diagenetic maturation following the production of the amorphous opaline phase

rock coatings in hawaii basaltic lava flows exposed to semiarid weathering on the island of hawaii develop hydrous silica coatings that thicken and incorporate detrital material with age the nearly pure silica coatings on the younger rocks are colorless but basaltic detritus and its weathering products incorporated into coatings on older flows produce colors ranging from brown to red age rate of supply of material and the mechanical stability of flow surfaces dictate the color and thickness of coatings fresh glassy pahoehoe surfaces support thin as much as 5 m clear silica coatings but break down in a few years to expose the vesicular underlying material at first coloring is concentrated in the open vesicles yielding a dark brown color a mixture of red vesicles and projections of black basalt with age thicker accumulations of silica incorporate layers of oxidized basaltic material the dark basaltic material in kilauea and mauna kea coatings is probably supplied by large explosive eruptions but at mauna loa and kohala the source could be locally derived basaltic weathering products the clear hydrous silica layers are probably the product of leaching of locally derived basaltic dust

thermal infrared analysis of weathered granitic rock compositions in the sacaton mountains arizona implications for petrologic classifications from thermal infrared remote sensing data 1 critical to spectral interpretations of geologic surfaces on the earth and mars is an understanding of the relationship between the composition of weathered rock surfaces and whole rock mineralogy in this study thermal infrared spectroscopic and remote sensing analyses were used to determine the composition of weathered granitoid rock surfaces in the sacaton mountains arizona a linear spectral deconvolution approach was employed to determine the mineralogies of naturally exposed weathered surfaces and artificially exposed fresh rock surfaces deconvolution results from fresh rock surfaces yield similar bulk mineralogy to results from point counting of rock slabs and thin sections deconvolution of weathered rock spectra indicate that compared to fresh samples weathered surfaces are deficient in plagioclase feldspar and are enriched in clay minerals the differential weathering of feldspar minerals impacts the interpretation of whole rock mineralogy and the spectral classification of bedrock geology which for plutonic rocks is dependent on the relative proportions of different feldspars deconvolutions of multispectral remote sensing or laboratory data show a deficiency of total feldspar in the weathered rock units but lack sufficient spectral resolution for the discrimination between different feldspars these results demonstrate that the differential breakdown and removal of primary minerals in rock surfaces due to weathering can affect the interpreted rock petrology from remote sensing studies the relationships observed in our granitic samples could be applied to any rock type and may be important to consider for remote sensing of mars

structural dependence of crystalline silicate hydration during aqueous dissolution abstract by using mev ion beam analytical techniques which provide the depth profiles of incorporated hydrogen and major constituent elements we show that alike glasses crystalline silicates can form surficial hydrated layers upon aqueous dissolution at temperatures up to 200 c the occurrence of such layers depends on both crystal structure and chemical composition tridimensional network silicates containing easily exchangeable alkalis being the most suitable materials this phenomenon could have important implications for the geochemical cycle of certain trace elements since highly hydrolyzable ones tend to accumulate in such hydrated layers

fundamental processes controlling the first stage of alteration of a basalt glass by seawater an experimental study between 200 and 320 c the first stage of alteration of a basalt glass by seawater has been studied experimentally between 200 and 320 c under vapor pressure following both the chemical evolution of the reacting solutions during the experiments and the chemical and mineralogical transformations of the altered glass surface via microprobe scanning transmission electron microscope and resonant nuclear reactions the alteration is controlled by diffusion of dissolved species through an altered layer and not by surface chemical reaction selective removal of cations with respect to sio2 leads to the formation of a thick porous protonated surface layer enriched in sio2 aqueous diffusion of dissolved species from the reacting glass and from solution through the pores of this layer results in the formation of an amorphous silicate gel which is the precursor of normal crystalline clays saponites appearing in a later stage computer simulations of the alteration generated with the eq3 6 computer software package account for the chemical composition of the rim and the sequence of secondary minerals found in the experiments

basalt weathering rates on earth and the duration of liquid water on the plains of gusev crater mars where martian rocks have been exposed to liquid water chemistry versus depth profi les could elucidate both martian climate history and potential for life the persistence of primary minerals in weathered profi les constrains the exposure time to liquid water on earth mineral persistence times range from 10 k y olivine to 250 k y glass to 1 m y pyroxene to 5 m y plagioclase such persistence times suggest mineral persistence minima on mars however martian solutions may have been more acidic than on earth relative mineral weathering rates observed for basalt in svalbard norway and costa rica demonstrate that laboratory ph trends can be used to estimate exposure to liquid water both qualitatively mineral absence or presence and quantitatively using reactive transport models qualitatively if the martian solution ph 2 glass should persist longer than olivine therefore persistence of glass may be a ph indicator with evidence for the ph of weathering the reactive transport code crunchflow can quantitatively calculate the minimum duration of exposure to liquid water consistent with a chemical profi le for the profi le measured on the surface of the exposed martian rock known as humphrey in gusev crater the calculated exposure time is 22 k y which is a minimum due to physical erosion if correct this estimate is consistent with short term episodic alteration accompanied by ongoing surface erosion more of these depth profi les should be measured to illuminate the weathering history of mars

timescales and mechanisms of formation of amorphous silica coatings on fresh basalts at kīlauea volcano hawai i young basalts from k lauea volcano hawai i frequently feature opaque surface coatings 1 80 m thick composed of amorphous silica and fe ti oxides these coatings are the product of interaction of the basaltic surface with volcanically derived acidic fluids previous workers have identified these coatings in a variety of contexts on hawai i but the timescales of coating development coating growth rates and factors controlling lateral coating heterogeneity were largely unconstrained we sampled and analyzed young lava flows of varying ages from hours to 40 years along k lauea s southwest and east rift zones to characterize variation in silica coating properties across the landscape coating thickness varies as a function of flow age flow surface type and proximity to acid sources like local fissure vents and regional plumes emitted from k lauea caldera and pu u silica coatings that form in immediate proximity to acid sources are more chemically pure than those forming in higher ph environments which contain significant al and fe incipient siliceous alteration was observed on basalt surfaces as young as 8 days old but periods of a year or more are required to develop contiguous coatings with obvious opaque coloration inferred coating growth rates vary with environmental conditions but were typically 1 5 m year coatings form preferentially on flow surfaces with glassy outer layers such as spatter ramparts volcanic bombs and dense pahoehoe breakouts due to glass strain weakening during cooling microtextural evidence suggests that the silica coatings form both by in situ dissolution reprecipitation and by deposition of silica mobilized in solution thin films of water acidified by contact with volcanic vapors dissolved near surface basalt then precipitated amorphous silica in place mobilizing more soluble cations additional silica was transported to and deposited on the surface by silica bearing altering fluids derived from the basalt interior

weathering rinds and rock coatings from an arctic alpine environment northern scandinavia coarse rock debris exposed in the subaerial environment of northern sweden displays the development of a wide variety of surface coatings these include weathering rinds as well as a great diversity of geochemical coatings including those dominated by ca fe si and al each of these types of rock coatings displays a high degree of geochemical complexity the weathering rinds exhibit both geochemical and morphologic changes to the parent rock cores including extensive dissolution oxidation and hydration as well as disaggregation fracturing and cementation by secondary geochemical coatings chemical breakdown of the rock to form weathering rinds includes loss of k si mg and ca and buildup of fe weathering rinds are fundamentally the result of dissolution as no clay minerals were identified in the rinds rock coatings are distinguished from rinds by their clear accretionary nature despite the distinction made between weathering rinds and rock coatings it is important to note that often the two are intimately related the presence of rock coatings as well as weathering rinds on rock surfaces amplifies the important role played by geochemical processes in the arctic alpine climate of northern sweden in particular as well as its significance in landscape evolution in such environments in general

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

effects of pure silica coatings on thermal emission spectra of basaltic rocks considerations for martian surface mineralogy 1 on mars silica derived from chemical weathering could precipitate to coat rocks and particles we suggest that rock coatings of secondary amorphous silica may account for a widespread martian surface spectral unit previously modeled as andesite or weathered basalt in a laboratory study we investigated the effects of synthetic silica coatings on thermal infrared tir spectroscopic measurements secondary amorphous silica is spectrally similar to silicate glass and clay spectra used in previous spectroscopic models silica coating and substrate spectra combine nonlinearly to produce a composite spectrum of a coated rock silica coatings 10 m thick effectively mask the spectral contribution of a silicate substrate therefore the capability of volumetrically small amounts of silica present as thin coatings on rocks should be considered when seeking explanations for spectral variability of martian surface materials

silica coatings in the ka u desert hawaii a mars analog terrain a micromorphological spectral chemical and isotopic study high silica materials have been observed on mars both from orbit by the crism spectrometer and in situ by the spirit rover at gusev crater these observations potentially imply a wet geologically active martian surface to understand silica formation on mars it is useful to study analogous terrestrial silica deposits we studied silica coatings that occur on the 1974 kilauea flow in the ka u desert hawaii these coatings are typically composed of two layers a 10 m layer of amorphous silica capped by a 1 m layer of fe ti oxide the oxide coating is composed of 100 nm spherules suggesting formation by chemical deposition raman spectroscopy indicates altered silica glass as the dominant phase in the silica coating and anatase and rutile as dominant phases in the fe ti coating jarosite also occurs within the coatings oxygen isotopic contents of the coatings were determined by secondary ion mass spectrometry cameca 7f and nanosims the measured values 18 o fe ti 14 6 2 1 and 18 o silica 12 1 2 2 relative to smow are enriched in 18 o relative to the basalt substrate the observations presented are consistent with a residual formation mechanism for the silica coating acid sulfate solutions leached away divalent and trivalent cations leaving a silica enriched layer behind micrometer scale dissolution and reprecipitation may have also occurred within the coatings chemical similarities between the hawaiian samples and the high silica deposits at gusev suggest that the martian deposits are the product of extended periods of similar acid sulfate leaching

internal structures and dating of complex zircons from meissen massif monzonites saxony abstract u pb zircon ages were determined for accessory zircons from two monzonites from the meissen massif northern bohemian massif germany by shrimp ion microprobe bse and cl imaging revealed that the monzonite zircons showing oscillatory growth zoning often contain inherited cores raman microprobe measurements showed that zoned rims u 277 1426 ppm th 144 910 ppm are slightly disordered to moderately metamict whereas cores have a wide spectrum of structural states from well crystallized to highly metamict the radionuclide u th content of cores varies from a few hundred to more than 20 000 ppm shrimp ion probe measurements on zoned rims interpreted as zircon growth during crystallization of the monzonite magma gave concordant carboniferous 206 pb 238 u ages of 326 6 ma monzonite from leuben and 330 5 ma monzonite from heidenschanze 95 confidence respectively these ages are consistent with recently published 40 ar 39 ar ages of 329 1 2 8 to 330 4 2 8 ma 2 on amphiboles from the same rocks in contrast shrimp measurements on cores range from slightly discordant proterozoic relic ages in low u and th cores to highly discordant data in the most metamict cores previously obtained 207 pb 206 pb ages single zircon evaporation technique in the range 340 16 to 357 16 ma 1 are probably mixed ages between magmatic and inherited zircon components the u pb ages of the monzonite zircons postdate the upper devonian lower carboniferous subduction and collision events in the area by about 20 ma due to their shoshonitic chemical signature which is typical of rocks from destructive plate boundary settings the meissen massif monzonites might be interpreted as originating during these 350 ma events and the earlier 207 pb 206 pb ages appeared to confirm this interpretation however both the 40 ar 39 ar ages and our current results show that only the enrichment of the lithospheric mantle source but not the monzonite intrusion itself was directly related to these events the monzonite intrusion itself took place 330 ma ago in the framework of strike slip tectonics in the elbe valley zone widely occurring zircon cores are indicative of crustal contamination of the magma causing considerable modification of chemical signatures trace element content of the monzonites

opaline silica in young deposits on mars high spatial and spectral resolution reflectance data acquired by the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism instrument reveal the presence of h 2o and sioh bearing phases on the martian surface the spectra are most consistent with opaline silica and glass altered to various degrees confirming predictions based on geochernicall experiments and models that amorphous silica should be a common weathering product of the basaltic martian crust these materials are associated with hydrated fe sulfates including h 3o bearing jarosite and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the valles marineris canyon system stratigraphic relationships place the formation age of these deposits in the late hesperian or possibly the amazonian implying that aqueous alteration continued to be an important and regionally extensive process on mars during that time

a new structural model for the sw irish variscides the variscan front of the nw european rhenohercynian abstract the variscan front of nw europe has been drawn in the past from belgium across southern england and southern wales towards southern ireland but the term variscan front is not well defined and means different things to different people a tectonic front should represent the outcrop of a frontal thrust or the tip line of the basal detachment in fact such a tectonic front cannot be traced along the so called variscan front in ireland field based studies of the western part of the irish variscides show that the fold and thrust belt continues north of the so called variscan front but deformation decreases gradually therefore we suggest supported by seismic data a detachment which ends as a blind thrust far to the north the tip line of this basal detachment represents the true tectonic front of the variscides in sw ireland shear indicators show locally a dextral shear component near major faults and 3d microstructural strain analyses show varying x axes and oblate deformation indicating transpression during the tectonic evolution of the western irish variscides therefore a thin skinned model associated with dextral shearing and transpression in the hanging wall of the basal detachment is suggested the evolution of the variscan fold and thrust belt in nw europe is related to the west european indentation model but also to pre variscan basement structures as the leinster wales and london brabant massifs finally an attempt is made to outline the variscan front along the entire nw european rhenohercynian fold and thrust belt ftb

fold cleavage relationships as indicator for late variscan sinistral transpression at the rheno hercynian saxo thuringian boundary zone central european variscides abstract the boundary between the rheno hercynian and the saxo thuringian zones of the european variscides is characterized by a ne sw striking late orogenic fold and thrust belt affecting the intervening rheic suture classical models used the first order strike of this zone as an indicator for perpendicular plate convergence i e nw se we present structural data from both sides of the suture focusing on fold cleavage relationships the statistical analysis reveals an orientation maximum of the youngest cleavage that deviates from the strike of the fold and thrust belt by c 22 the presence of clockwise transection of the folds by the cleavage up to 16 indicates pervasive sinistral transpression three types of fold cleavage relationships are observed ne trending folds i with or ii without a transecting cleavage and iii non transected ene trending folds we explain the occurrence of different fold cleavage types by strain partitioning due to nnw convergence obliquely to pre existent ne trending mechanical anisotropies in terms of plate tectonics we propose that the classical boundary of the rheno hercynian and the saxo thuringian zone represents an initial transform plate boundary that was finally affected by sinistral transpression

structural analysis of an accretionary prism in a continental collisional setting the late paleozoic pulo do lobo zone southern iberia abstract models concerning the tectonic evolution of accretionary complexes typically relate outcrop scale to plate scale multiphase deformation as a smooth variation of strain on all scales however at oblique convergent margins regional scale brittle faults in the shallow crust are commonly parallel to the main orogenic grain these faults impose a strong structural anisotropy and can subsequently control deformation at subordinate scales as a result finite strain in each domain may not record local kinematics consistent with the overall orogenic scale motion implying that structural data must be analyzed selectively from a large area in order to relate outcrop scale kinematics to global plate scale dynamics field mapping and preliminary structural analysis of the late devonian pulo do lobo pdl formation and suspect exotic south portuguese zone spz in southern iberia indicate tectonic juxtaposition of diverse deposits such as foreland basin flysch sedimentary and tectonic melange and passive margin sediments showing an overall geometry consistent with an accretionary wedge setting variations in finite strain lithology and regional structure were used as proxies for defining tectonic domains for structural analysis numerous local kinematic indicators within the pdl suggest a complex regional deformation with several enigmatic features that can be explained by sequential compartmentalization of strain during the development of the imbricate stack followed by late stage bulk strain imposed across the entire complex structural data produced by local strain partitioning reveals kinematic indicators which contradict the overall regional structural style e g spatial juxtaposition of sinistral and dextral fabrics when viewed at larger scales i e regional scale however these data indicate that significant sinistral strike slip movement occurred in conjunction with both an extension and shortening outcrop scale deformation in polydeformed domains is controlled by local conditions resulting from brittle deformation coeval with orogenic scale bulk strain the entire pulo do lobo zone is dominated by a pervasive late stage vertical to sub vertical e w cleavage axial planar to chevron folds which overprint earlier deformation in the older passive margin units this overprinting suggests that in the late stages of the evolution of the accretionary complex bulk strain was imposed over the entire complex as a result of internal locking of the accretionary complex and reduced strain rates during the waning stages of collision between gondwana and laurussia stereographic analysis of fabric elements from each distinct tectonic domain together with regional geological constraints support this hypothesis and are indicative of progressive deformation imposed on the pdl during the variscan orogeny

combined use of visible reflected infrared and thermal infrared images for mapping hawaiian lava flows the weathering of hawaiian basalts is accompanied by chemical and physical changes of the surfaces these changes have been mapped using remote sensing data from the visible and reflected infrared and thermal infrared wavelength regions they are related to the physical breakdown of surface chill coats the development and erosion of silica coatings the oxidation of mafic minerals and the development of vegetation cover these effects show systematic behavior with age and can be mapped using the image data and related to relative ages of pahoehoe and aa flows the thermal data are sensitive to silica rind development and fine structure of the scene the reflectance data show the degree of oxidation and differentiate vegetation from aa and cinders together data from the two wavelength regions show more than either separately the combined data potentially provide a powerful tool for mapping basalt flows in arid to semiarid volcanic environments

relative dating of hawaiian lava flows using multispectral thermal infrared images a new tool for geologic mapping of young volcanic terranes the weathering of hawaiian basalts in arid and semiarid environments is accompanied by change in their thermal infrared emittance spectra the spectral differences can be measured and mapped with multispectral imaging systems the differences appear to be related to the degree of development preservation and alteration of glassy crusts the oxidation of iron and the accretion of silica rich surface veneers because the measurements are quantitative and in image format they are useful for estimating relative ages in geologic mapping of lava flows in hawaii this technique is most diagnostic for distinguishing among sparsely vegetated flows less than 1 5 ka in age

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

acid sulfate weathering of synthetic martian basalt the acid fog model revisited the acid fog model has received considerable attention as a model of soil formation on mars previous evaluations of this model have focused on experimental weathering of terrestrial basalt samples however these samples differ significantly from what now is thought to be typical of martian basalt the acid fog model is tested here using synthetic basaltic analogs derived from mars pathfinder soil and rock compositions reaction of synthetic basalt with various acidic solutions and subsequent evaporation has led to the formation of several putative secondary mineral phases many of these phases were not produced in prior experimental studies aimed at aqueous interactions on mars of these alteration phases mg fe ca and al sulfates were identified in addition secondary ferric oxide phases formed via rapid fe oxidation under relatively high ph levels buffered by basalt dissolution amorphous silica is a ubiquitous product in these experiments and has formed by precipitation from solution and by the dissolution of minerals and glasses leaving behind leached surface layers composed of residual silica the secondary products formed in these experiments demonstrate the importance of primary mineralogy when testing models of aqueous interactions on mars new constraints are placed on both the reactivity of primary basalt and the secondary mineralogy present at the martian surface copyright 2004 by the american geophysical union

variscan transpressive inversion in the northwestern central rhenohercynian belt of western germany abstract important orogen parallel strike slip components during the convergence of the variscan orogen of central europe have been increasingly recognized these oblique slip faults often develop from pre existing tectonic boundaries and are influenced by pre existing structural trends in the basement in this paper evidence is presented for a 3 6 km wide distributed shear zone here named the monschau shear zone in epizone metamorphic cambro ordovician and lower devonian clastic rocks of the northwestern rhenohercynian belt kinematic indicators including field observations of anomalous mullion and fold axes patterns a set of two cleavages stretching lineations and shear and kink bands microscopical observations of stretching parallel asymmetric pressure shadows of quartz on prekinematic epizone metamorphic pyrite porphyroblasts and microfabrics of phyllosilicates by x ray texture goniometry point to a sinistral tranpressive shear zone with emplacement of the southeast hangingwall under retrograde conditions coincidence of the anchizone epizone metamorphic boundary with the change along strike from penetrative shearing to distributed thrusting suggests a ductile brittle transition the monschau shear zone is situated on the backlimb of an allochthonous anticlinorium located above a basement ramp that corresponds roughly to a pre orogenic synsedimentary normal fault its continuation shows up clearly in a dekorp seismic reflection profile to a depth of 12 15 km

widespread weathered glass on the surface of mars low albedo sediments cover 10 7 km 2 in the northern lowlands of mars but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations here we use near infrared spectra acquired by the mars express omega observatoire pour la mineralogie l9eau les glaces et l9activite imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron bearing glass and silica enriched leached rinds on glass this interpretation is supported by observations of low albedo soil grains with possible rinds at the phoenix mars lander landing site in the northern lowlands by comparison with the extensive glass rich dune fields and sand sheets of iceland we propose an explosive volcanic origin for these glass rich sediments we also propose that the glassy remnant rinds on the sediments are the result of postdepositional alteration as these rinds are commonly formed in arid terrestrial volcanic environments during water limited moderately acidic leaching these weathered glass rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identified in mid infrared spectra suggesting that they may be representative of global processes our results provide potential confirmation of models suggesting that explosive volcanism has been widespread on mars and also raise the possibilities that glass rich volcaniclastics are a major source of eolian sand on mars and that widespread surficial aqueous alteration has occurred under amazonian climatic conditions

thermal infrared spectral character of hawaiian basaltic glasses multispectral thermal infrared remote sensing of hawaiian basalts younger than a few hundred years old can be used to discriminate basalt lava flows that are difficult to map with visible and near infrared images laboratory thermal infrared reflectance spectra of the exposed surfaces of mauna loa and kilauea basalts show systematic changes with age fresh glass collected from active lava flows shows a broad reflectance feature between 8 and 12 m indicative of a strong degree of disorder after a few weeks of exposure to the environment the spectra of the top surfaces of samples begin to exhibit spectral features suggestive of ordering into silicate chainlike and sheetlike units with progressive aging features of apparent sheetlike structures become the preferred mode as soon as 3 years after emplacement a silica rich coating can begin to develop on the surfaces adding another spectral feature to the laboratory reflectance measurements the thermal infrared multispectral scanner tims with six channels between 8 and 12 m has been used to take advantage of these spectral differences in basalts to map flows in hawaii remote sensing instruments with increased spectral resolution in the thermal infrared would aid in further discrimination of basalts with more subtle differences in age quenching and weathering histories

influence of amorphous silica layer formation on the dissolution rate of olivine at 90 c and elevated pco2 for mitigating against rising levels of atmospheric co2 carbonation of m2 bearing silicates has been proposed as a possible option for sequestering co2 over long time spans due to its rapid far from equilibrium dissolution rate and its widespread occurrence in mafic and ultramafic rocks olivine has been suggested as a potentially good candidate for achieving this goal although the efficacy of the carbonation reaction still needs to be assessed with this as a goal the present study aims at measuring the carbonation rate of san carlos olivine in batch experiments at 90 c and pco2 of 20 and 25 mpa when the reaction was initiated in pure water the kinetics of olivine dissolution was controlled by the degree of saturation of the bulk solution with respect to amorphous silica this yet unrecognized effect for olivine was responsible for a decrease of the dissolution rate by over two orders of magnitude in long term 45 days carbonation experiments with a high surface area to solution volume ratio sa v 24 600 m 1 the final composition of the solution was close to equilibrium with respect to sio2 am independent of the initial concentration of dissolved salts nacl and naclo4 ranging between 0 and 1 m and with an aqueous mg si ratio close to that of olivine no secondary phase other than a ubiquitous thin 40 nm si rich amorphous layer was observed these results are at odds with classic kinetic modeling of the process due to experimental uncertainties it was not possible to determine precisely the dissolution rate of olivine after 45 days but the long term alteration of olivine was indirectly estimated to be at least 4 orders of magnitude slower than predicted taken together these results suggest that the formation of amorphous silica layers plays an important role in controlling the rate of olivine dissolution by passivating the surface of olivine an effect which has yet to be quantified and incorporated into standard reactive transport codes

incongruent and congruent dissolution of plagioclase feldspar effect of feldspar composition and ligand complexation abstract secondary ion mass spectrometry sims was used to characterize the surfaces of plagioclase feldspar two labradorite compositions and one anorthite leached in water ph 5 8 and in 10 4m hcl hf and oxalic acid all at the same ph 4 0 4 1 labradorite an54 and an60 leached at ph 4 for 72 days dissolved incongruently in hcl oxalic acid and hf yielding altered layers strongly depleted in al ca and sr and residually enriched in si the leached layers formed on the more calcic composition an60 were approximately 3 times thicker than those formed on the more sodic an54 composition the thinnest leached layers were produced by hcl up to 1000 a on an54 and up to 3000 a on an60 and the thickest leached layers by hf up to 1700 a on an54 and up to 5000 a on an60 because the h concentration was the same in each solution it was possible to clearly separate the relative importance of proton promoted dissolution in hcl and ligand promoted dissolution in oxalic acid and in hf for a given feldspar composition to do this the sims depth profiles obtained from an60 labradorite leached in oxalic acid and in hf were normalized to those produced in response to hcl this comparison clearly shows that the ligands oxalate and fluoride significantly increased the formation of leached layers compared to the effect of h alone in contrast anorthite an100 leached in the same solutions essentially dissolved congruently in response to hcl only very thin leached layers formed in which al and ca were only weakly depleted relative to si chemical analyses of the output solutions showed that the molar ratio of si to al in solution 1 1 to 1 is equal to the molar ratio of si to al in the fresh solid confirming that the anorthite dissolved congruently while the leached layers found on anorthite leached in oxalic acid and hf were thinner and less intensively depleted compared to the leached layers formed in response to hcl the concentrations of si and al in the output solutions were significantly greater than those in the hcl solutions while oxalate and fluoride again promoted the dissolution of the feldspar si and al were still released to solution in the same molar proportion as they are found in the solid congruent dissolution the early stages of feldspar dissolution therefore may be either incongruent or congruent depending upon the chemical composition of the feldspar

silica in a mars analog environment ka u desert kilauea volcano hawaii airborne visible near infrared imaging spectrometer aviris data acquired over the ka u desert are atmospherically corrected to ground reflectance and used to identify the mineralogic components of relatively young basaltic materials including 250 700 and 200 400 year old lava flows 1971 and 1974 flows ash deposits and solfatara incrustations to provide context a geologic surface units map is constructed verified with field observations and supported by laboratory analyses aviris spectral end members are identified in the visible 0 4 to 1 2 m and short wave infrared 2 0 to 2 5 m wavelength ranges nearly all the spectral variability is controlled by the presence of ferrous and ferric iron in such minerals as pyroxene olivine hematite goethite and poorly crystalline iron oxides or glass a broad nearly ubiquitous absorption feature centered at 2 25 m is attributed to opaline amorphous hydrated silica and is found to correlate spatially with mapped geologic surface units laboratory analyses show the silica to be consistently present as a deposited phase including incrustations downwind from solfatara vents cementing agent for ash duricrusts and thin coatings on the youngest lava flow surfaces a second ti rich upper coating on young flows also influences spectral behavior this study demonstrates that secondary silica is mobile in the ka u desert on a variety of time scales and spatial domains the investigation from remote field and laboratory perspectives also mimics exploration of mars using orbital and landed missions with important implications for spectral characterization of coated basalts and formation of opaline silica in arid acidic alteration environments

mechanism of leached layer formation during chemical weathering of silicate minerals the dissolution of most common multicomponent silicate minerals and glasses is typically incongruent as shown by the nonstoichiometric release of the solid phase components this results in the formation of so called surface leached layers due to the important effects these leached layers may have on mineral dissolution rates and secondary mineral formation they have attracted a great deal of research however the mechanism of leached layer formation is a matter of vigorous debate here we report on an in situ atomic force microscopy afm study of the dissolution of wollastonite casio 3 as an example of leached layer formation during dissolution our in situ afm results provide for the first time clear direct experimental evidence that leached layers are formed in a tight interface coupled two step process stoichiometric dissolution of the pristine mineral surfaces and subsequent precipitation of a secondary phase most likely amorphous silica from a supersaturated boundary layer of fluid in contact with the mineral surface this occurs despite the fact that the bulk solution is undersaturated with respect to the secondary phase our results differ significantly from the concept of preferential leaching of cations as postulated by most currently accepted incongruent dissolution models this interface coupled dissolution precipitation model has important implications in understanding and evaluating dissolution kinetics of major rock forming minerals

effects of chemical weathering on infrared spectra of columbia river basalt and spectral interpretations of martian alteration abstract we investigated the mineralogy of basalt weathering rinds and fresh basaltic rocks using visible near infrared vnir 0 4 2 5 m and thermal emission 6 30 m spectroscopy to 1 constrain the effects of chemical weathering on rock spectra and 2 further understand the context of infrared spectra of mars which may contain evidence for weathered rocks and particulates derived from them vnir spectra of weathered rock surfaces are generally redder and brighter than fresh surfaces thermal infrared spectra of weathered basalts show evidence for aluminous opal and clay minerals or clay precursor mineraloids in natural surfaces supporting vnir observations generally do not show the same evidence for neoformed clays or silica because of their textural occurrence as thin coatings and microfracture fill and possibly due to poor crystallinity of the aluminosilicate weathering products in this context spectral trends observed at mars such as the detection of low to moderate 10 25 abundances of silica and clay that are observed in the thermal infrared but not in the vnir are therefore consistent with trends observed for natural rock surfaces in the laboratory the combined use of thermal infrared and vnir suggest that vast areas of martian dark regions contain sandy rocky basaltic materials with weathering rinds and thin coatings that could have formed in conditions of relatively low water rock ratios

a 3 5 ga record of water limited acidic weathering conditions on mars abstract the secondary mineral budget on earth is dominated by clay minerals al hydroxides and fe oxides which are formed under the moderate ph high water to rock ratio conditions typical of earth s near surface environment in contrast geochemical analyses of rocks and soils from landed missions to mars indicate that secondary mineralogy is dominated by mg fe ca sulfates and fe oxides this discrepancy can be explained as resulting from differences in the chemical weathering environment of earth and mars we suggest that chemical weathering processes on mars are dominated by 1 a low ph sulfuric acid rich environment in which the stoichiometric dissolution of labile mineral phases such as olivine and apatite fe ti oxides is promoted and 2 relatively low water to rock ratio such that other silicate phases with slower dissolution rates e g plagioclase pyroxene do not contribute substantially to the secondary mineral budget at the martian surface under these conditions al mobilization is limited and the formation of significant al bearing secondary phases e g clays al hydroxides al sulfates is inhibited the antiquity of rock samples analyzed in situ on mars suggest that water limited acidic weathering conditions have more than likely been the defining characteristic of the martian aqueous environment for billions of years

the surface of labradorite feldspar after acid hydrolysis abstract after reaction with a ph both the surface area of the reacted feldspar and the porosity increase with acid hydrolysis modeling of nitrogen sorption onto the surface suggests that the pores have a nominal radius of 20 80 a or less this distribution of pore sizes resembles other acid reacted silicate materials such as glass chrysotile and kaolinite although the mineral surface clearly becomes more porous during acid hydrolysis the increase in powder area also does not coincide with an increase in the flux of dissolved si from the powder we thus attribute most of this increase in area to spallation of the silica rich surface from the feldspar upon drying

stylolite controlled layering in an homogeneous limestone pseudo bedding produced by burial diagenesis it is often assumed that layering in many shelf and platform limestones at weathered outcrop is always bedding the layers always beds and the surfaces always bedding planes recognition of bedding is fundamental to facies and basin analysis examination of part of the lower carboniferous high tor limestone of the gower south wales shows that a totally diagenetic layering pseudo bedding resembling and parallel to primary depositional layering true bedding has been produced by the generation of parallel more or less evenly spaced stylolite surfaces during burial diagenesis these stylolite surfaces are picked out by weathering at outcrop and resemble bedding planes evidence that the stylolite surfaces do not mark original bedding planes includes a cross cutting relationship of a stylolite surface to a primary bedding surface lack of lithological change across or sedimentary structures associated with a stylolite surface original bedding that is not coincident with stylolite surfaces and has not suffered pressure dissolution and lack of sedimentological evidence that the layers defined by the stylolite surfaces are true primary depositional beds the generation of parallel and more or less evenly spaced stylolite surfaces could be explained by a mathematical kinetic model based on the relationship between pressure dissolution diffusion and reprecipitation recognition of true bedding depends upon presence of lithological changes and or sedimentary structures it is suggested that pseudo bedding could be confused with true bedding in some open platform shelf lagoon facies where lithological changes or sedimentary structures are scarce or absent

coupled dissolution and precipitation at mineral fluid interfaces reactions occurring at mineral fluid interfaces are important in all geochemical processes and essential for the cycling of elements within the earth understanding the mechanism of the transformation of one solid phase to another and the role of fluids is fundamental to many natural and industrial processes problems such as the interaction of minerals with co2 saturated water the durability of nuclear waste materials the remediation of polluted water and mineral reactions that can destroy our stone based cultural heritage are related by the common feature that a mineral assemblage in contact with a fluid may be replaced by a more stable assemblage

folds and the strain ellipsoid a general model abstract a new general model is proposed to account for non orthogonal relationships of fold axes and axial surfaces to the axes of the finite strain ellipsoid descriptions in the literature of such relationships e g plunge variations and transecting cleavage are reviewed and the development of the model is outlined the model is described in which plane strain k 1 or slight flattening strain k 0 71 or slight constrictional strain k 1 85 are imposed on a suite of layers with oblique orientations to the bulk strain axes x y z folds will initiate perpendicular to the direction of shortening in the layer and develop as non material lines moving through the layer by angular migration at geologically realistic finite strains the folds will be transected by xy cleavage in slight flattening strain folds are likely to be cylindroidal with axes not measurably oblique to xy in slight constrictional strain en echelon periclines are predicted with marked transection by cleavage in some examples the interference of two directions of folding will give rise to severe plunge variations and even downward facing although strain markers frequently indicate finite strains in the flattening field this may result from the superimposition of slightly constrictional tectonic strain on compactional flattening

surface mineralogy of martian low albedo regions from mgs tes data implications for upper crustal evolution and surface alteration 1 mars global surveyor thermal emission spectrometer mgs tes data are used to derive the modal mineralogy of spectrally distinct martian low albedo regions and to identify spatial trends in mineralogic assemblages results from this work are consistent with the major results of previous spectroscopic studies 1 plagioclase and clinopyroxene are the dominant minerals of most southern highlands regions 2 the northern plains exhibit the lowest pyroxene abundance within martian low albedo regions and 3 the highest concentrations of high silica phase s are found in the northern plains solis planum and a few southern high latitude regions low albedo regions may be classified into four units on the basis of relative abundances of plagioclase pyroxene and high silica phase s unit distributions between 45 latitude exhibit moderate correlation with distinct provinces e g syrtis major aonium sinus defined by large scale morphology elevation and to some extent surface age suggesting that the spectral and compositional differences between these units are more strongly controlled by original bedrock mineralogy than by surface atmosphere interactions and alteration syrtis major exhibits a difference in mineralogy from the surrounding highlands suggesting a differing degree of fractional crystallization assimilation or source region composition areas with thick crust near the tharsis plateau exhibit lower abundances of olivine and greater plagioclase pyroxene ratios than surrounding highland terrains suggesting that magmas in this region may have undergone increased olivine fractionation regions where surface alteration is more likely to be the primary control on observed spectral signatures are the high latitude areas 45 where globally surfaces dominated by high silica phase s are most commonly found

contraints on the evolution of the mid german crystalline rise a study of outcrops west of the river rhine several small outcrops along the western rhinegraben escarpment expose rocks which represent the western prolongation of the so called mid german crystalline rise this basement ridge separates the rhenohercynian and saxothuringian zones of the variscan belt of europe and thus marks the boundary between the external and the internal zones the variable rock association includes an orthogneissamphibolite complex weakly deformed low grade sediments devonian and visean and a number of different syn to post orogenic granodioritic to granitic intrusives all crosscut by late lower carboniferous undeformed lamprophyric dikes and unconformable overlain by permian sediments and volcanics

acidic weathering of basalt and basaltic glass 1 near infrared spectra thermal infrared spectra and implications for mars engineering research council of canada the canadian space agency the canada foundation for innovation the manitoba research innovations fund and the university of winnipeg for supporting the establishment and operation of the planetary spectrophotometer facility this work was funded in part by the nasa 2001 mars odyssey themis project jet propulsion laboratory contract 1228404 through arizona state university and by the arizona state university exploration postdoctoral fellowship

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