the classification of micrometeorites due to their small size the mineralogical and chemical properties of micrometeorites mms are not representative of their parent bodies on the centimeter to meter scales that are used to define parent body groups through the petrological study of meteorites identifying which groups of mm are derived from the same type of parent body is problematic and requires particles to be rigorously grouped on the basis of mineralogical textural and chemical properties that reflect the fundamental genetic differences between meteorite parent bodies albeit with minimal bias towards preconceived genetic models specifically the interpretation of mms requires a rigorous and meaningful classification scheme at present the classification of mms is however at best ambiguous a unified petrological chemical classification scheme is proposed in the current study and is based on observations of several thousand mms collected from antarctic ice

the weathering of micrometeorites from the transantarctic mountains abstract micrometeorites are cosmic dust particles recovered from the earth s surface that dominate the influx of extraterrestrial material accreting to our planet this paper provides the first in depth study of the weathering of micrometeorites within the antarctic environment that will allow primary and secondary features to be distinguished it is based on the analysis of 366 particles from larkman nunatak and 25 from the transantarctic mountain collection several important morphological categories of weathering effects were identified 1 irregular and faceted cavities 2 surface etch pits 3 infilled cavities 4 replaced silicate phases and 5 hydrated and replaced metal these features indicate that congruent dissolution of silicate phases in particular olivine is important in generating new pore space within particles comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration precipitation of new hydrous phases within cavities in particular ferrihydrite and jarosite results in pseudomorph textures within heavily altered particles glass in contrast is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios metal is variably replaced by fe oxyhydroxides and results in decreases in ni fe ratio in contrast sulphides within metal are largely preserved magnetite an essential component of micrometeorites formed during atmospheric entry is least altered by interaction with the terrestrial environment the extent of weathering in the studied micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type despite these differences we propose a weathering scale for micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases the compositions and textures of weathering products however suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits

the leonard award address presented 1996 july 25 berlin germany the elemental composition of stony cosmic spherules five hundred stony cosmic spherules collected from deep sea sediments polar ice and the strato sphere have been analyzed for major and some minor element composition typical spherules are products of atmospheric melting of millimeter sized and smaller meteoroids the samples are small and modified by atmospheric entry but they are an important source of information on the composition of asteroids the spherules in this study were all analyzed in an identical manner and they provide a sampling of the solar system s asteroids that is both different and less biased than provided by studies of conventional meteorites volatile elements such as na and s are depleted due to atmospheric heating while siderophiles are depleted by less understood causes the refractory nonsiderophile elements appear not to have been significantly dis turbed during atmospheric melting and provide important clues on the elemental composition of millimeter sized meteoroids colliding with the earth typical spherules have cm like composition that is distinctively different than ordinary chondrites and most other meteorite types we assume that c type asteroids are the primary origin of spherules with this composition type s asteroids should also be an important source of the spherules and the analysis data provide constraints on their composition a minor fraction of the spher ules are melt products of precursor particles that did not have chondritic elemental compositions the most common of these are particles that are dominated by olivine the observed compositions of spherules are in consistent with the possibility that an appreciable fraction of the spherules are simply chondrules remelted during atmospheric entry

accretion rate of cosmic spherules measured at the south pole micrometeorites are terrestrially collected extraterrestrial particles smaller than about 1 mm which account for most of the mass being accreted to the earth1 2 compared with meteorites micrometeorites more completely represent the earth crossing meteoroid complex3 4 and should include fragments of asteroids comets mars and our moon as well as pre solar and interstellar grains3 6 previous measurements of the flux of micrometeoroids that survive to the earth s surface have large uncertainties owing to the destruction of particles by weathering7 8 9 inefficiencies in magnetic collection or separation techniques7 8 9 low particle counts10 11 poor age constraint7 8 9 12 13 or highly variable concentrating processes12 13 here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the south pole water well which supplies drinking water for the scott amundsen station using this collection we have determined precise estimates of the flux and mass distribution for 50 700 m cosmic spherules melted micrometeorites allowing for the expected abundance of unmelted micrometeorites14 in the samples our results indicate that about 90 of the incoming mass of submillimetre particles evaporates during atmospheric entry our data indicate the loss of glass rich and small stony spherules from deep sea deposits7 8 and they provide constraints for models describing the survival probability of micrometeoroids15 16

stratigraphic relations and lithologic variations in the jemez volcanic field new mexico over 100 radiometric dates and recent detailed geologic mapping allow some refinements of the stratigraphic relations of major units and generalization of temporal lithologic variations in the jemez volcanic field volcanism had begun in the area by about 16 5 ma with episodic eruptions of alkaline basalts by 13 ma alkaline volcanism had been replaced with eruptions of more voluminous olivine tholeiite high silica rhyolite derived from melts of lower crust also was erupting by about 13 ma basalt and high silica rhyolite continued to be erupted until about 7 and 6 ma respectively but effusions of dominantly andesitic differentiates of basalt that began as early as about 12 ma volumetrically overshadowed all other eruptive products between 10 and 7 ma from 7 to 3 ma the dominant erupted lithology was dacite which appears to have been generated by mixing of magmas whose compositions are approximated by earlier andesites and high silica rhyolites less than 4 3 ma volcanism was dominated by eruption of rhyolitic tuffs field relations geochemistry and dates specifically indicate the following with regards to stratigraphie relations 1 distinctions among basalt of chamisa mesa paliza canyon formation basalts and lobato basalt for other than geographic reasons are artificial basaltic volcanism was continuous in volcanic field from 13 to 7 ma 2 canovas canyon and bearhead rhyolites form a continuum of high silica rhyolite volcanism from 13 to 6 ma 3 hypabyssal and volcanic rocks of the cochiti mining district probably represent the exhumed interior of a keres group volcano s 4 temporal overlaps exist among the major stratigraphie groups which may imply some genetic relations and 5 the tewa group formation cerro rubio quartz latite may more appropriately be considered part of the tschicoma formation of the polvadera group preliminary analysis of hydrothermal alteration in the context of the volcanic stratigraphy suggests at least three distinct hydrothermal events have occurred in the volcanic field s history

synvolcanic and syntectonic sedimentation of the mixed volcaniclastic epiclastic succession in the miocene janggi basin se korea understanding the variability and complex interplay of volcanism tectonism and sedimentation is crucial for unraveling the evolution of sedimentary basins and volcanotectonic depressions in many settings the miocene janggi basin in se korea formed in association with backarc opening of the east sea sea of japan is filled by abundant volcanic deposits intercalated with fluvio lacustrine sedimentary deposits four lithostratigraphic units units i to iv in ascending order are identified in the southern part of the basin including extensive and voluminous dacitic lapilli tuffs units ii and iv and mixed dacitic volcaniclastic and epiclastic sedimentary deposits units i and iii these units suggest repetitive ignimbrite emplacement onto a braided stream to lacustrine environment paleoflow measurements show that the epiclastic conglomerates were deposited by a north flowing fluvial system that debouched from a drainage area to the south of the basin whereas the ignimbrites were introduced from the east because of the separate source areas the epiclastic and volcaniclastic depositional processes did not interfere with each other resulting in discrete alternations of epiclastic and mostly primary volcaniclastic deposits the studied succession also lacks an aggradation degradation cycle which results from the alternation of periods of rapid volcaniclastic sedimentation and relatively longer periods of fluvial incision the volcaniclastic and epiclastic deposits are therefore interpreted to have accumulated in rapid succession in association with rapid basin subsidence and contemporaneous ignimbrite forming eruptions the studied succession can thus be regarded as a syntectonic sequence in which the stratal geometry was significantly modulated by tectonostratigraphic controls with overprints of syntectonic contemporaneous volcanism

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars the antarctic dry valleys adv are generally classified as a hyper arid cold polar desert the region has long been considered an important terrestrial analog for mars because of its generally cold and dry climate and because it contains a suite of landforms at macro meso and microscales that closely resemble those occurring on the martian surface the extreme hyperaridity of both mars and the adv has focused attention on the importance of salts and brines on soil development phase transitions from liquid water to water ice and ultimately on process geomorphology and landscape evolution at a range of scales on both planets the adv can be subdivided into three microclimate zones a coastal thaw zone an inland mixed zone and a stable upland zone zones are defined on the basis of summertime measurements of atmospheric temperature soil moisture and relative humidity subtle variations in these climate parameters result in considerable differences in the distribution and morphology of 1 macroscale features e g slopes and gullies 2 mesoscale features e g polygons including ice wedge sand wedge and sublimation type polygons as well as viscous flow features including solifluction lobes gelifluction lobes and debris covered glaciers and 3 microscale features e g rock weathering processes features including salt weathering wind erosion and surface pitting equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones some equilibrium landforms such as sublimation polygons indicate the presence of extensive near surface ice identification of similar landforms on mars may also provide a basis for detecting the location of shallow ice landforms that today appear in disequilibrium with local microclimate conditions in the adv signify past and or ongoing shifts in climate zonation understanding these shifts is assisting in the documentation of the climate record for the adv a similar type of landform analysis can be applied to the surface of mars where analogous microclimates and equilibrium landforms occur 1 in a variety of local environments 2 in different latitudinal bands and 3 in units of different ages documenting the nature and evolution of the adv microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on mars

igneous rims on micrometeorites abstract melting of micrometeorites mms due to atmospheric entry heating causes significant changes in the textures mineralogies and compositions of particles that obscure their primary properties and greatly complicate interpretation of these extraterrestrial materials despite the abundance of melted mms the nature of melting processes in these materials is poorly constrained in this study mineralogical textural and compositional data on 77 mms with igneous rims are presented which suggest that fusion of micrometeorites during atmospheric entry occurs initially by surface melting textural and mineralogical evidence are presented that demonstrate unequivocally that igneous rims crystallized from a melt surrounding a largely unmelted core and establish melting as a gradational process the compositions of igneous rims on fine grained mms fgmms are broadly similar to those of the unmelted core except for depletions in volatile and moderately volatile elements produced by partial evaporation and suggest the formation of the rims by melting of the fine grained matrix core enrichments in fe si ni si and mn si in igneous rims compared with unmelted cores within fgmms are suggested to occur due to the migration of fe s eutectic liquids from the core of the particle into the surface melt layer the sulphide liquids are probably generated in the core of the particle under reducing conditions resulting by the pyrolysis of carbonaceous materials the presence of igneous rims on fgmms is enabled by the thermal decomposition of phyllosilicates and therefore indicates that fgmms were hydrated particles prior to atmospheric entry in contrast the compositions of igneous rims on coarse grained mms cgmms are difficult to reconcile with those of the unmelted core and instead closely resemble those of fgmms the igneous rims of cgmms are therefore suggested to form by melting of fine grained matrix that was present on the exterior of these particles prior to atmospheric entry coarse grained mms with igneous rims thus were originally composite micrometeoroids which consist of both fine grained and coarse grained materials and are thought to be samples of chondrule like objects the abundance of composite mms to cgmms allows a first estimate of the mean chondrule radius within the parent bodies of mms of 625 m to be made

catastrophic debris avalanche from ancestral mount shasta volcano california a debris avalanche deposit extends 43 km northwestward from the base of mount shasta across the floor of shasta valley california where it covers an area of at least 450 km 2 the surface of the deposit is dotted with hundreds of mounds hills and ridges all formed of blocks of pyroxene andesite and unconsolidated volcaniclastic deposits derived from an ancestral mount shasta individual hills are separated by flat topped laharlike deposits that also form the matrix of the debris avalanche and slope northwestward about 5 m km radiometric ages of rocks in the deposit and of a postavalanche basalt flow indicate that the avalanche occurred between about 300 000 and 360 000 yr ago an inferred average thickness of the deposit plus a computed volume of about 4 km 3 for the hills and ridges indicate an estimated volume of about 26 km 3 making it the largest known quaternary landslide on earth

etch pit size dissolution rate and time in the experimental dissolution of olivine implications for estimating olivine lifetime at the surface of mars various approaches have been used to estimate when and how long liquid water was present at the surface of mars the olivine dissolution lifetime application suggested by stopar et al 2006 and olsen and rimstidt 2007 is here adapted and tested at the scale of individual etch pits using published data from an experimental system in which the volume of mineral removed and the duration of the mineral removal episode are known different assumptions about the specific geometry of etch pits on olivine result in surface area estimates that vary by less than a factor of two from the simple hemispherical pit used in the calculations given that other sources of uncertainty in mass time relationships of silicate mineral dissolution during natural weathering can be up to four orders of magnitude the effects of differing geometric assumptions about the shapes and surface areas of the etch pits are negligible using compiled experimentally determined forsterite dissolution rates and the imaged etch pit sizes from experiments recovers the duration of the experiment that produced the imaged etch pits to within less than a factor of two this suggests that extensively etched olivine surfaces imply a dominance of the etch pit walls over the bulk surface between the etch pits during olivine corrosion the approach adopted here recovers the timescales of experimental etch pit production on olivine at stp and extreme undersaturation of the solution with respect to olivine in experiments where ph is known continued progress in understanding the fundamentals of olivine dissolution kinetics will narrow the ranges of uncertainty in mineral lifetime estimates at mars surface in support of constraining the compositions and duration of potentially habitable aqueous solutions on mars

terrestrial weathering of antarctic stone meteorites formation of mg carbonates on ordinary chondrites abstract white efflorescences of weathering origin occur superposed on fusion crusts or along fractures in the interiors of approximately 5 of all meteorites in the us antarctic collection efflorescences from equilibrated ordinary chondrites consist of the hydrous mg carbonates nesquehonite hydromagnesite x ray diffraction and scanning electron microscope studies of efflorescences from lew 85320 h5 show abundant elongate prismatic crystals of nesquehonite idiomorphic not pseudomorphous after lansfordite with minor local encrustations of hydromagnesite abundances of na k ca and rb in efflorescences from lew 85320 suggest that the observed contents of these elements would require only modest fractionation of chondritic composition whereas extensive fractionation would be required to derive the observed cation ratios from terrestrial sea salts therefore cations in evaporite minerals on antarctic meteorites are most likely not products of contamination by terrestrial marine salts the mg in the efflorescences probably originated from weathering of meteoritic olivine other cations in the efflorescences are also of meteoritic provenance thermodynamic analysis of the reaction forsterite water carbon dioxide nesquehonite silica at antarctic temperatures and pco 2 indicates spontaneity for all water activities greater than 0 65 compatible with the presence of liquid water as brines and or thin films

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

remote sensing studies of the lomonosov fleming region of the moon 1 lomonosov fleming is a 620 km pre nectarian impact basin centered at 19 n 105 e clementine multispectral images and a variety of spacecraft photographs were used to investigate the composition and origin of geologic units in the region mare basalt deposits in the lomonosov fleming region are small and exhibit varying degrees of highlands contamination four previously unrecognized dark mantle deposits of probable pyroclastic origin were identified and mapped a major expanse of cryptomare was mapped in and around the lomonosov fleming basin spectral and chemical data obtained for dark haloed craters dhc established that these impact craters excavated mare basalt from beneath higher albedo highlands rich surface units the buried basalts exposed by dhcs in the region exhibit a variety of compositions which range from very low titanium basalt to intermediate tio2 mare basalt nectarian aged units with subjacent cryptomare are much more extensive than imbrian aged deposits with underlying basalt at least some of the buried mare basalts in the region may have been emplaced during pre nectarian time while both impact basins and craters played a role in cryptomare formation by transporting highlands material to mare surfaces the evidence indicates that most of the cryptomare inside the basin are of the distal basin ejecta type the enhanced feo and tio2 abundances exhibited by these cryptomare surfaces usually light plains units demonstrate that ballistic erosion and sedimentation played an important role in their formation

lunar volcanic glasses and their constraints on mare petrogenesis abstract volcanic glasses from the apollo 11 14 15 and 16 landing sites have been analyzed for major elements and ni by electron microprobe the 19 varieties of volcanic glass define two distinct chemical arrays that provide new insights into a the petrogenesis of mare basalts and b the structure of the deep lunar interior a simple model is proposed whereby mare basaltic liquids may have been derived from two isolated cumulate systems occurring at depths of 300 km and 400 km each system was itself composed of two lithologic components low ti vs high ti that underwent hybridization assimilation or mixing to generate the large compositional range of magmas observed within each array while the distribution of the two components within each system was locally heterogeneous data indicate that the components themselves were chemically uniform on at least a regional scale the surface correlated volatiles associated with the lunar volcanic glasses seem to have come from some other reservoir within the moon the simplicity of the chemical relationships observed among the lunar volcanic glasses allow specific predictions to be made we believe that they should readily reveal any strengths or weaknesses of this new model

a weathering index for ck and r chondrites we present a new weathering index wi for the metallic fe ni poor chondrite groups ck and r based mainly on transmitted light observations of the modal abundance of crystalline material that is stained brown in thin sections wi 0 95 vol wi 6 significant replacement of mafic silicates by phyllosilicates brown staining reflects mobilization of oxidized iron derived mainly from terrestrial weathering of ni bearing sulfide with increasing degrees of terrestrial weathering of ck and r chondrites the sulfide modal abundance decreases and s se and ni become increasingly depleted in addition bulk cl increases in antarctic ck chondrites probably due to contamination from airborne sea mist

chondritic micrometeorites from the transantarctic mountains abstract on the basis of morphological and petrographic characteristics eight giant unmelted micrometeorites in the 300 1100 m size range were selected from the transantarctic mountain micrometeorite collection victoria land antarctica mineralogical and geochemical data obtained by means of scanning electron microscopy electron probe microanalyses and synchrotron x ray diffraction allow their classification as chondritic micrometeorites the large size of the micrometeorites increases considerably the amount of mineralogical and geochemical information compared to micrometeorites in smaller size fractions therefore allowing a better definition of their parent material a large variety of material is observed five micrometeorites are related to unequilibrated and equilibrated ordinary chondrite one to cv chondrite one to cm chondrite and one to ci chondrite parent materials besides reporting the first occurrence of a cv like micrometeorite our study shows that the abundance of chondritic material supports observations from recent studies on cosmic spherules that a large part of the micrometeorite flux in this size range is of asteroidal origin

dissolution of primary basaltic minerals in natural waters saturation state and kinetics abstract the state of saturation of olivine orthopyroxene and plagioclase of variable composition has been assessed in various types of natural waters in iceland including river waters groundwater and geothermal waters with temperatures up to 250 c the stability of olivine and orthopyroxene decreases with increasing mg content similarly the stability of plagioclase decreases with increasing anorthite content the river waters which are representative of the weathering environment are always undersaturated with both olivine and orthopyroxene the degree of undersaturation being dominated by the water ph all river waters tend to dissolve olivine of the composition encountered in basalts according to the linear rate law and orthopyroxene when the ph is 200 c are undersaturated with olivine orthopyroxene and plagioclase the first two particularly when fe rich and sufficient to cause olivine to dissolve according to the linear rate law at intermediate temperatures 50 150 c the geothermal waters are close to equilibrium with these minerals except for mg rich olivine it seems likely that dissolution of glass from basalt which is very reactive will favor stability of the igneous minerals

unmelted cosmic metal particles in the indian ocean fe ni metal is a common constituent of most meteorites and is an indicator of the thermal history of the respective meteorites it is a diagnostic tool to distinguish between groups subgroups of meteorites in spite of over a million micrometeorites collected from various domains reports of pure metallic particles among micrometeorites have been extremely rare we report here the finding of a variety of cosmic metal particles such as kamacite plessite taenite and fe ni beads from deep sea sediments of the indian ocean a majority of which have entered the earth unaffected by frictional heating during atmospheric entry such particles are known as components of meteorites but have never been found as individual entities their compositions suggest precursors from a variety of meteorite groups thus providing an insight into the metal fluxes on the earth some particles have undergone heating and oxidation to different levels during entry developing features similar to i type cosmic spherules suggesting atmospheric processing of individual kamacites taenite grains as another hitherto unknown source for the i type spherules the particles have undergone postdepositional aqueous alteration transforming finally into the serpentine mineral cronstedtite aqueous alteration products of kamacite reflect the local microenvironment therefore they have the potential to provide information on the composition of water in the solar nebula on the parent bodies or on surfaces of planetary bodies our observations suggest it would take sustained burial in water for tens of thousands of years under cold conditions for kamacites to alter to cronstedtite

meteorite and meteoroid new comprehensive definitions abstract meteorites have traditionally been defined as solid objects that have fallen to earth from space this definition however is no longer adequate in recent decades man made objects have fallen to earth from space meteorites have been identified on the moon and mars and small interplanetary objects have impacted orbiting spacecraft taking these facts and other potential complications into consideration we offer new comprehensive definitions of the terms meteorite meteoroid and their smaller counterparts a meteoroid is a 10 m to 1 m size natural solid object moving in interplanetary space a micrometeoroid is a meteoroid 10 m to 2 mm in size a meteorite is a natural solid object larger than 10 m in size derived from a celestial body that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and that later collided with a natural or artificial body larger than itself even if it is the same body from which it was launched weathering and other secondary processes do not affect an object s status as a meteorite as long as something recognizable remains of its original minerals or structure an object loses its status as a meteorite if it is incorporated into a larger rock that becomes a meteorite itself a micrometeorite is a meteorite between 10 m and 2 mm in size meteorite a solid substance or body falling from the high regions of the atmosphere craig 1849 a mass of stone and iron that ha s been directly observed to have fallen down to the earth s surface translated from cohen 1894 a solid bod y which came to the earth from space farrington 1915 a mass of solid matter too small to be considered an asteroid either traveling through space as an unattached unit or having landed on the earth and still retaining its identity nininger 1933 a meteoroid which has reached the surface of the earth without being vaporized 1958 international astronomical union iau definition quoted by millman 1961 a solid body which has arrived on the earth from outer space mason 1962 a solid bod y which reach es the earth or the moon mars etc from interplanetary space and is large enough to survive passage through the earth s or mars etc atmosphere gomes and keil 1980 a meteoroid that survive s passage through the atmosphere and fall s to earth burke 1986 a recovered fragment of a meteoroid that has survived transit through the earth s atmosphere mcsween 1987 a solid bod y of extraterrestrial material that penetrate s the atmosphere and reach es the earth s surface krot et al 2003

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

copernicus crater central peak lunar mountain of unique composition olivine is identified as the major mafic mineral in a central peak of copernicus crater information on the mineral assemblages of such unsampled lunar surface material is provided by near infrared reflectance spectra 0 7 to 2 5 micrometers obtained with earth based telescopes the composition of the deep seated material comprising the copernicus central peak is unique among measured areas other lunar terra areas and the wall of copernicus exhibit spectral characteristics of mineral assemblages comparable to the feldspathic breccias returned by the apollo missions with low calcium orthopyroxene being the major mafic mineral

using stained glass windows to understand the durability of toxic waste matrices abstract using stained glasses sampled from french and german cathedrals and from different archaeological sites this work presents an estimation of the effect of weathering conditions and glass composition on glass dissolution due to accurate dating we also show that stained glass windows allow the determination of the average dissolution kinetics of many toxic elements contained in the glass including transition and heavy metals actinides lanthanides therefore a significant advantage of using stained glass windows over other natural glasses is that they permit the direct study of non stoichiometric elemental dissolution rates under natural conditions of alteration averaged over more than a thousand years and hence to constrain the long term behaviour of vitrified waste matrices

clay mineraloid weathering products in antarctic meteorites abstract clay mineraloids are associated with gypsum k fe sulfates possibly jarosite cryptocrystalline rust and possibly with zeolites and or secondary alkali feldspars as terrestrial weathering products in stony meteorites from the allan hills alh and elephant moraine eet collection areas in victoria land antarctica weathering formed fracture fillings in fusion crusts of eucrites eeta79004 and eeta79005 diogenites alha77256 and eeta79002 shergottite eeta79001 and h5 chondrite alh82102 and decomposition products of glass and plagioclase in interior samples of achondrites clay mineraloids displayed massive to incipient vermicular forms with elemental compositions that suggest smectite and mica like phases deposits were too small to yield pure material for phase identification although x ray diffractometry and differential scanning calorimetry of bulk samples suggested that the clay mineraloids were not well crystallized a typical structural formula calculated on a smectite basis follows k 0 26 ca 0 04 al 0 97 ti 0 02 fe 3 0 77 mg 0 03 si 4 00 o 10 oh 2 n 2 o net charge 0 28 excessions 0 58 si 0 02 cl 0 09 so 4 0 02 po 4 hydrocryogenic diagenesis can initiate clay mineral formation on timescales of 10 4 10 6 y even with only limited supplies of liquid water cosmochemists must take care not to confuse possible weathering induced elemental and isotopic fractionations in antarctic meteorite samples with signatures of pre terrestrial cosmic processes given proper sample selection and testing though occurrence of clay mineraloid and other weathering products should probably not impede progress in studies of antarctic meteorites

corrosion of fe ni alloys by cl containing akaganeite beta feooh the antarctic meteorite case a suite of 12 iron and 8 stony meteorites from various environments and locations in antarctica was studied representing a range of compositions metallographic structures and degrees of weathering polished sections of meteoritic metal with adhering corrosion products were examined microscopically with the electron microprobe and sem and were used as samples for x ray diffraction examination the major corrosion products are cl containing akaganeite up to 5wtper thousand cl and goethite with minor amounts of lepidocrocite and maghemite cl is not native to the meteorites but owing to the electrochemical nature of the corrosion of fe ni alloys is attracted from the snow and ice or rocky soil environment that contains low amounts of cl akaganeite precipitates near the reaction front incorporating cl ions into ion exchange sites where they may be retained made available for further depassivating corrosive action or become flushed from the system with time and distance from the reaction surface akaganeite ages and transforms to mainly goethite and maghemite it is again argued that lawrencite fecl 2 is not a mineral in meteorites in the stormy antarctic wind blown terrestrial particles may become attached to the weathering products on the meteorite and in time themselves decompose delivering terrestrial ions to the meteorite corrosion system the ions may move a significant distance from the surface and in particular cl may be found along almost invisible cracks in the deep interior trace element work and age determinations 36 cl should take this problem into account

radar probing of planetary regoliths an example from the northern rim of imbrium basin 1 imaging radar measurements at long wavelengths e g 30 cm allow deep up to tens of meters probing of the physical structure and dielectric properties of planetary regoliths we illustrate a potential application for a mars orbital synthetic aperture radar sar using new earth based 70 cm wavelength radar data for the moon the terrae on the northern margin of mare imbrium the montes jura region have diffuse radar backscatter echoes that are 2 4 times weaker at 3 8 cm 70 cm and 7 5 m wavelengths than most other lunar nearside terrae possible geologic explanations are 1 a pyroclastic deposit associated with sinuous rilles in this region 2 buried mare basalt or a zone of mixed highland basaltic debris cryptomaria or 3 layers of ejecta associated with the iridum and plato impacts that have fewer meter sized rocks than typical highlands regolith while radar data at 3 8 cm to 7 5 m wavelengths suggest significant differences between the montes jura region and typical highlands the surface geochemistry and rock abundance inferred from clementine uv vis data and eclipse thermal images are consistent with other lunar terrae there is no evidence for enhanced iron abundance expected for basaltic pyroclastic deposits near the source vents of the sinuous rilles radial to plato the regions of low 70 cm radar return are consistent with overlapping concentric haloes about iridum and plato and do not occur preferentially in topographically low areas as is observed for radar mapped cryptomaria thus we suggest that the extensive radar dark area associated with the montes jura region is due to overlapping rock poor ejecta deposits from iridum and plato craters comparison of the radial extent of low radar return crater haloes with a model for ejecta thickness shows that these rock poor layers are detected by 70 cm radar where they are on the order of 10 m and thicker a sar in orbit about mars could use similar deep probing to reveal the nature of crater and basin related deposits

basin evolution within the kitakami massif northeast japan relationship between sedimentation tectonics and volcanism in an incipient neogene continental back arc basin abstract the ichinohe basin in the western margin of the kitakami massif northeast japan consists of the early to middle miocene yotsuyaku and keiseitoge formations and represents the incipient stage of neogene back arc sedimentation that extends toward the north and northwest megaclast breccias derived from mesozoic basement rocks of the kitakami massif were transported from southern areas as debris flows the debris flow deposits of the yotsuyaku formation grade northwards along the basin axis into clast supported braided stream deposits where floodplains developed in the center of the basin voluminous volcanic eruptives of the keiseitoge formation were derived from eastern and southeastern volcanic ranges and formed transversal distributaries the deposition of both clastic and pyroclastic sediments suggests that volcanism and tectonic uplift took place simultaneously during basin evolution parallel laminated fine grained sediments intercalated with lignite beds suggest lacustrine deposition and large cross beds of volcanic breccias indicate gilbert type progradation into the lakes a number of small lakes in the center of the basin was probably formed as the result of damming tributary mouths by the main drainage from eastern and southeastern volcanoes or the reciprocal blocking by lahars and non volcanic debris flows derived from the southern uplift damming episodes produced by thick lava flows were not recognized in this study the evolution of the n s trending longitudinal ichinohe basin indicates that e w extensional tectonism related to the opening of the sea of japan affected not only the green tuff region to the west of the studied basin but also even the mesozoic basement during the miocene although the mingling of volcanic and basement derived deposits indicates the complexities of sedimentary facies and provenances our view of the stratigraphic architecture has relevance to the interpretation of the evolution of other extensional basin systems

the role of fluidization in the emplacement of pyroclastic flows 2 experimental results and their interpretation abstract although often quoted as being important in the emplacement of pyroclastic flows little relevant experimental fluidization work has been done fluidization processes are first reviewed for a simple system against which ignimbrite samples can be compared results from fluidization experiments on ignimbrite samples show that their behaviour differs radically from any simple system principally because of their extremely poor sorting at a certain gas velocity u ie whose value cannot be predicted some ignimbrite samples begin to expand whilst at a higher gas velocity u mp the samples begin to show segregation structures the minimum fluidization velocity u mf in simple systems is replaced by u mp the value of the latter in pyroclastic materials cannot be easily or reliably predicted from published u mf correlations and a new empirical method for determining u mp is presented from the experimental data during fluidization ignimbrite samples expand much less than more conventional materials due to the bypassing of gas through segregation channels the total amount of expansion is also limited e g a 100 m thick pyroclastic flow will from fairly high gas velocities deflate to form an ignimbrite which is not less than 70 85 m thick during fluidization the poor sorting causes only part of the weight of the ignimbrite samples to be supported by the gas flow the degree of support increasing with an improvement in sorting segregation structures and grain size and compositional variations within fluidized ignimbrite samples show varying behaviour depending on the sorting of the sample after subjecting a sample to high gas velocities the net result is a grain size and compositionally zoned bed which becomes richer upwards in pumice and fine material once formed these features cannot be destroyed under laboratory conditions implying that some segregation structures should be present in any ignimbrite where u mp was exceeded

the geochemistry of antarctic streams and their role in the evolution of four lakes of the mcmurdo dry valleys abstract major ion concentrations are reported for nineteen meltwater streams in the mcmurdo dry valleys antarctica and for the four lakes fed by these streams the most important solute acquisition processes for these flowing waters are dissolution of marine derived salts dissolution of calcite coatings derived from chemical weathering of parent rock and direct weathering of silicates although lakes joyce hoare and fryxell have undergone significant evaporative concentration the only simple salt which is predicted to form at present is calcite the shallow waters of all four lakes were supersaturated with respect to this mineral but were undersaturated with respect to other simple salts geochemical budgets however indicate that so4 k and mg in addition to ca and hco3 have been removed from some of these lakes over recent geological time bacterial sulfate reduction followed by precipitation of metal sulfides is likely to be a sink for sulfate sinks for mg and k are more problematic but may include formation of mgcalcites and in the case of k reverse weathering reactions the ages of the contemporary water columns as indicated by chloride budgets are relatively young and these lakes could have evolved their chemical compositions over a few thousand years of present stream flows it is not necessary to invoke trapped seawater or other salt sources to explain their evolution

moon near infrared spectral reflectance a first good look a positive identification of the minerals olivine plagioclase and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements for example the crater aristarchus is found to have an average pyroxene composition of augite and plagioclase is obviously present a dark mantle deposit in the crater j herschel is at least partly composed of a mixture of 70o7o olivine and 30o7o pyroxene these determinations were possible because the reflectance spectra for 10 20 km diameter lunar areas have been measured for the first time in the ir spectral region 0 65 2 5 m with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands the reflectance for all lunar regions observed over 100 to present continues to increase toward longer wavelengths to at least 2 5 m and several mineral absorption bands appear the telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples the absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques including thermal flux removal and absorption band fitting to produce these mineral identifications detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms

olivine settling in cosmic spherules during atmospheric deceleration an indicator of the orbital eccentricity of interplanetary dust a new type of cosmic spherule is reported with textures suggesting settling of olivine during atmospheric deceleration numerical simulations of entry heating reveal that relict forsterite which survives melting can settle over the 1 2 s of flight at high entry angles and entry velocities up to 16 km s 1 enhanced crystallisation of phenocrysts by heterogeneous nucleation on accumulated relict forsterites is the most likely origin of the observed cumulate textures in cosmic spherules such textures in cosmic spherules reveal interplanetary dust with higher encounter velocity with the earth that correspond to orbital eccentricities 0 3 the relative abundance of cumulate spherules suggests 14 of ordinary chondrite related s iv type asteroid dust over the last 800 kyr had relatively high orbital eccentricity owing to secular and planetary perturbations the textures of cosmic spherules collected from sediments can therefore be used to trace dust orbital variations with time which may influence terrestrial climate

evolution of a plio pleistocene volcanogenic alluvial fan the puye formation jemez mountains new mexico the plio pleistocene puye formation north central new mexico contains 15 km 3 of volcaniclastic alluvial sediments deposited in response to rift margin volcanism associated with the later evolution of the tschicoma volcanic center northeastern jemez mountains stratigraphic and sedimentologic evidence indicates that aggradation of puye deposits was nearly continuous and contemporaneous with graben development and establishment of the rio grande as the through flowing axial drainage system in this region much of the puye sediments debouched into an adjacent subsiding depocenter resulting in near complete preservation of this wedge shaped volcanogenic fan primary pyroclastic and reworked facies in the puye formation exhibit distinctive 5 to 30 m scale cyclicity directly related to volcanic activity in the northeastern jemez highlands reworked pyroclastic and conglomeratic sequences deposited by high energy braided streams sediment charged sheet floods sediment gravity flows and in shallow lakes reflect markedly increased sediment loads during and following explosive eruptions individual sequences change markedly in character with increased distance from the source area analysis of these abrupt lateral and vertical variations reveals that puye sedimentation was controlled by the influences of semiarid climate and syndepositional tectonism although the associations that most characterize the fan resulted largely from explosive volcanism cessation of fan growth is attributed to waning sediment supply as a result of volcanic quiescence and to the onset of basinwide pedimentation associated with downcutting of the ancestral rio grande the puye fan therefore provides a detailed record of rift basin alluvial sedimentation complete with closely spaced tephrostratigraphic control and it records the growth and partial denudation of high standing northeastern jemez mountains volcanoes

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

geochemistry of the onyx river wright valley antarctica and its role in the chemical evolution of lake vanda the onyx river wright valley antarctica is a dilute meltwater stream originating in the vicinity of the wright lower glacier it acquires a significant fraction of its salt content when glacial meltwaters contact wright valley soils at lake brownworth and the concentrations of all ions increase with distance along the 28 km channel down to lake vanda average millimolar concentrations of major ions at the vanda weir during the 1980 1981 flow season were ca 0 119 mg 0 061 na 0 212 k 0 033 q 0 212 so4 0 045 hco3 0 295 and sio2 0 049 based on the flow measurements of chinn 1982 this amounts to an annual flux in moles to lake vanda of ca 0 238 106 mg 0 122 106 na 0 424 106 k 0 066 106 cl 0 424 106 so4 0 09 106 hco3 0 59 106 sio2 0 098 106 in spite of the large salt input from this source equilibrium evaporation of onyx river water would have resulted in early calcite deposition and in the formation of a na mg cl hco3 brine rather than in the ca na mg cl waters observed in lake vanda the river alone could not have produced a brine having the qualitative geochemical features of the lower saline waters of lake vanda it is proposed that the vanda brine is instead the result of past 1200 yrs bp mixing events between onyx river inflows and calcium chloride rich deep groundwaters derived from the don juan basin the mixing model presented here shows that the onyx river is the major contributor of k hco3 so4 and possibly mg found in the lake and a significant contributor approximately one half of the observed na calcium and cl on the other hand came largely from deep groundwater sources in the don juan basin all concentrations except mg are well predicted by this model the chemical composition of the geologically recent upper lake is explained in terms of ionic diffusion from the pre formed brine coupled with onyx river inflow ionic ratios calculated from this latter model are in very good agreement with those observed in the lake at 35 meters

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

chemical weathering and diagenesis of a cold desert soil from wright valley antarctica an analog of martian weathering processes weathering diagenesis and chemical alteration of a soil profile from the dry valleys of antarctica have been studied as an analog to soil development within the martian regolith soil samples from a one meter deep soil pit on prospect mesa wright valley have been examined for their major element concentrations water soluble cations and anions carbon sulfur and water concentrations and related petrographic characteristics of weathering in a cold dry environment petrographic study of the soil samples indicates that most silicate mineral and lithic fragments exhibit some degree of alteration chemical alteration occurs in samples both from above and from within the permanently frozen zone concentrations of water soluble cations na k ca2 and anions cl so42 no3 decrease significantly from the surface to the permanently frozen zone suggesting major movement of water soluble species enrichments in secondary mineral abundances correlate with the water soluble ion concentrations formation of zeolites is observed throughout the soil column and may be potential reservoirs for volatile storage within the regolith from the detailed study of the dry valley soils an idealized soil profile for the regolith has been developed and is suggested as applicable to other planetary surfaces especially the martian nearsurface environment the soil profile consists of four zones aeolian salt active and permanently frozen

ignimbrite depositional facies the anatomy of a pyroclastic flow a model is presented for the depositional regimes in a pyroclastic flow to explain the origin of facies in the taupo ignimbrite and to compare these with other published examples in this model a pyroclastic flow consists of a head a body and a tail the head which is where fluidization caused by air ingestion occurs generates layer 1 deposits on lithological grounds these are divided into layers 1 p which is fines depleted and rich in pumice and 1 h which is fines depleted and rich in lithics and crystals layer 1 p represents material thrown forwards from the flow head and is termed the jetted deposits layer 1 h represents material sedimented from within the flow head and is termed the ground layer the body represents the bulk of the flow and the tail is its trailing part which is slowed by ground friction these parts generate the layer 2 deposits which include the valley pond ignimbrite and its associated ignimbrite veneer deposit localized depositional modes within the body and tail generate distinctive coarse pumice concentration zones and pumiceous lee side lenses behind obstacles at its outer limits all of the flow on interfluves is affected by air ingestion fluidization producing the distant facies which combines features of both layer 1 and 2 deposits one important conclusion of this work is that the thicknesses and compositions of the various facies are not related in any simple way to the thickness and composition of the parent flow

an urban collection of modern day large micrometeorites evidence for variations in the extraterrestrial dust flux through the quaternary we report the discovery of significant numbers 500 of large micrometeorites 100 m from rooftops in urban areas the identification of particles as micrometeorites is achieved on the basis of their compositions mineralogies and textures all particles are silicate dominated s type cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine relict crystals of forsterite and iron bearing olivine within glass four particles also contain ni rich metal sulfide beads bulk compositions are chondritic apart from depletions in the volatile moderately volatile and siderophile elements as observed in micrometeorites from other sources the reported particles are likely to have fallen on earth in the past 6 yr and thus represent the youngest large micrometeorites collected to date the relative abundance ratio of barred olivine to cryptocrystalline spherule types in the urban particles of 1 45 is shown to be higher than a quaternary average of 0 9 suggesting variations in the extraterrestrial dust flux over the past 800 k y changes in the entry velocities of dust caused by quasi periodic gravitational perturbation during transport to earth are suggested to be responsible variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events

volcanic dry avalanche deposits identification and comparison with nonvolcanic debris stream deposits abstract a volcanic dry avalanche deposit is defined as a volcaniclastic deposit formed as a result of a large scale sector collapse of a volcanic cone associated with some form of volcanic activity avalanche transport occurred in response to the gravitational field in a manner similar to the transport of nonvolcanic debris streams e g hsu 1975 such deposits are characterized by megablock structure deformed and fractured large blocks up to several hundreds meters in diameter a megablock preserves original layering intrusive contacts or weathered surfaces of the source volcanic edifice surface topography of the deposit is characterised with hummocky relief ratios of fell height to travel distance for volcanic dry avalanche deposits are between 0 18 and 0 06 this range is similar but smaller than the value of 0 58 to 0 08 for nonvolcanic debris stream deposit this similarity suggests similar transportation mechanisms excessive travel distances as defined by hsu 1975 calculated for volcanic dry avalanche deposits give values larger than for debris stream deposits of the same volume the difference is explained by lower rigidity of the collapsing mass due to the existence of soft pyroclastic layers alteration around the vent development of fractures owing to new cryptodome intrusion and boiling of supercritical fluid contained within the collapsed mass

ages of mare basalts on the lunar nearside the chronology of lunar volcanism is based on radiometric ages determined from apollo and luna landing site samples regional stratigraphic relationships and crater degradation and size frequency distribution data for units largely defined prior to the end of the apollo program here we report on new crater size frequency distribution data for 139 spectrally and morphologically defined basalt units which are exposed in six nearside impact basins australe tranquillitatis humboldtianum humorum serenitatis and imbrium crater size frequency distribution measurements are a statistically robust and accurate method to derive absolute model ages of unsampled regions of the moon compared to crater degradation ages crater size frequency ages performed on spectrally defined units offer significant improvements in accuracy our investigation showed that 1 in the investigated basins lunar volcanism was active for at least 1 5 2 0 b y starting at about 3 9 4 0 b y and ceasing at 2 0 b y 2 most basalts erupted during the late imbrian period at about 3 6 3 8 b y 3 significantly fewer basalts were emplaced during the eratosthenian period 4 basalts of copernican age were not found in any of the investigated basins 5 lunar basin filling volcanism probably started within 100 m y after the formation of the individual basins we also assessed the relationship between impact basin age and the history of mare basalt emplacement in these basins we found that 1 in all pre nectarian basins australe and tranquillitatis as well as in the humboldtianum basin which is of nectarian age the distribution of surface ages is clearly dominated by only a single peak in the number of erupted units at 3 6 3 8 b y 2 in the younger basins humorum serenitatis and imbrium a second peak at 3 3 3 5 b y is observed 3 basalt eruptions younger than 2 6 b y occur only intermittently and 4 in the youngest basins serenitatis and imbrium we see an extended period of active basin filling volcanism 1 5 1 6 b y which is 500 m y longer than in the australe and humorum and even 1 0 b y longer than in tranquillitatis and humboldtianum

compositional analyses of lunar pyroclastic deposits abstract the 5 band clementine uvvis data at 100 m pixel were used to examine the compositions of 75 large and small lunar pyroclastic deposits lpds and these were compared to representative lunar maria and highlands deposits results show that the albedo spectral color and inferred composition of most lpds are similar to those of low titanium mature lunar maria these lpds may have consisted largely of fragmented basalt with substantial components of iron bearing mafic minerals pyroxenes olivine and smaller amounts if any of volcanic glass several smaller lpds also show substantial highland components three classes of very large deposits can be distinguished from most lpds and from each other on the basis of crystallinity and possible titanium content of their pyroclastic components one class has spectral properties that are dominated by high titanium crystallized black beads e g taurus littrow a second consists of a mixture of high titanium glasses and beads with a higher glass bead ratio sulpicius gallus than that of taurus littrow and a third has a significant component of quenched iron bearing volcanic glasses aristarchus with possible moderate titanium contents although areally extensive these three classes of very large pyroclastic deposits compose only 20 of the 75 deposits studied 27 and eruption of such materials was thus likely to have been less frequent on the moon

40ar 39ar dating of the bandelier tuff and san diego canyon ignimbrites jemez mountains new mexico temporal constraints on magmatic evolution abstract the jemez mountains volcanic field jmvf located in north central new mexico has been a site of basaltic to rhyolitic volcanism since the mid miocene with major caldera forming eruptions occurring in the pleistocene eruption of the upper bandelier tuff ubt is associated with collapse of the valles caldera whereas eruption of the lower bandelier tuff lbt resulted in formation of the toledo caldera these events were previously dated by k ar at 1 12 0 03 ma and 1 45 0 06 ma respectively pre bandelier explosive eruptions produced the san diego canyon sdc ignimbrites sdc ignimbrite b has been dated at 2 84 0 07 ma whereas sdc ignimbrite a which underlies b has been dated at 3 64 1 64 ma both of these dates are based on single k ar analyses 40ar 39ar dating of single sanidine crystals from these units indicates revision of the previously reported dates isochron analysis of 26 crystals from the ubt gives a common trapped 40ar 36ar component of 304 5 indicating the presence of excess 40ar in this unit and defines an age of 1 14 0 02 ma isochron analysis of 26 crystals from the lbt indicates an atmospheric trapped component and an age of 1 51 0 03 ma an age of 1 78 0 04 ma based on the weighted mean of 5 individual analyses is indicated for sdc ignimbrite b whereas 3 analyses from sdc ignimbrite a give a weighted mean age of 1 78 0 07 ma evidence for xenocrystic contamination in the sdc ignimbrites comes from analyses of a correlative air fall pumice unit in the puye formation alluvial fan giving ages of 1 75 0 08 and 3 50 0 09 ma the presence of xenocrysts in bulk separates used for the original k ar analyses could account for the significantly older ages reported geochemical data indicate that sdc ignimbrites are early eruptions from the magma chamber which evolved to produce the lbt as compositions of sdc ignimbrite b are virtually identical to least evolved lbt samples differentiation during the 270 ka interval between eruption of sdc ignimbrite b and the lbt produced an array of high silica rhyolite compositions which were erupted to form the lbt mixed pumices associated with eruption of the lbt indicated an influx of more mafic magma into the system which produced shifts in some incompatible trace element ratios lavas and tephras of the cerro toledo rhyolite record the geochemical evolution of the bandelier magma system during the 370 ka interval between eruption of the lbt and the ubt the combined geochronologic and geochemical data place the establishment and evolution of the bandelier silicic magma system within a precise temporal framework beginning with eruption of the sdc ignimbrites at 1 78 ma and define a periodicity of 270 370 ka to ash flow eruptions in the jmvf these intervals are comparable to those in other multicyclic caldera complexes and are a measure of the timescales over which substantial fractionation of large silicic magma bodies occur

mare glasses from apollo 17 constraints on the moon s bulk composition two previously unreported varieties of mare volcanic glass have been discovered in apollo 17 samples twenty three chemical types of volcanic glass have now been analyzed from the six apollo landing sites these volcanic glasses which may be samples of primary magmas derived from the differentiated lunar mantle define two linear arrays that seem to reflect regional if not global regularities among the source regions of these melts additional systematics among these glasses have been used to estimate the bulk composition of the moon the results suggest that the refractory lithophile elements e g ca al ti ree u are present at abundances of 1 7 chondrites the silicate portion of the moon appears to have a major element composition similar to a volatile si na k depleted earth s upper mantle the theory involving an earth fission origin of the moon can be tested further through trace element analyses e g ni on the volcanic glasses and through determination of the n 36ar ratio and noble gas isotopes from primordial lunar gas trapped within vesicles associated with mare volcanic glass

dissolution of olivine during natural weathering abstract naturally weathered olivine occurring as phenocrysts in hawai ian volcanic rocks from several volcanic centers and regolith outcrop settings and as tectonized olivines from several metadunite bodies in the southern appalachian blue ridge are all similarly corroded by natural weathering conical funnel shaped etch pits occur as individual pits base to base pairs of cone shaped pits or en echelon arrays etch pit shapes and orientations in the smallest etch pit arrays visible in conventional scanning electron microscopy resemble even smaller features previously reported from transmission electron microscope investigations of olivine weathering etch pits occur in samples with chemical and or mineralogical evidence of weathering and or are associated with or proximal or directly connected to fractures or exposed outcrop surface and therefore are formed by weathering and not inherited from pre weathering aqueous alteration e g serpentinization iddingsitization of these parent rocks many etch pits are devoid of weathering products natural weathering of olivine is surface reaction limited similarity of corrosion forms from naturally weathered olivine from multiple igneous and metamorphic parent rock bodies suggests that olivine weathers in the same manner regardless of its specific crystallization recrystallization history eruption weathering exposure ages of the olivine s host rock and the local regolith history

explosive activity associated with the growth of volcanic domes abstract domes offer unique opportunities to measure or infer the characteristics of magmas that at domes and elsewhere control explosive activity a review of explosive activity associated with historical dome growth shows that 1 1 explosive activity has occurred in close association with nearly all historical dome growth 2 2 whole rock sio 2 content a crude but widely reported indicator of magma viscosity shows no systematic relationship to the timing and character of explosions 3 3 the average rate of dome growth a crude indicator of the rate of supply of magma and volatiles to the near surface enviornment shows no systematic relationship to the timing or character of explosions and 4 4 new studies at arenal and mount st helens suggest that water content is the dominant control on explosions from water rich magmas whereas the crystal content and composition of the interstitial melt and hence magma viscosity are equally or more important controls on explosions from water poor magmas new efforts should be made to improve current rather limited techniques for monitoring pre eruption volatile content and magma viscosity and thus the explosive potential of magmas

melted micrometeorites from antarctic ice with evidence for the separation of immiscible fe ni s liquids during entry heating we report the discovery of four large 50 m cosmic spherules css and a single scoriaceous micrometeorite smm that contain evidence for the separation of immiscible fe ni s liquids during atmospheric entry heating the particles contain segregated fe rich regions dominated by either ni s bearing fe oxides or iron sulphides and have textural relations that suggest these separated from the silicate portions of the particles as metallic liquids the oxides which may be hydrous are thought to result from alteration of metal and sulphide the compositions of the silicate portions of the css are equivalent to spherules without fe rich regions implying that metallic liquids are exsolved during the heating of most spherules but completely separate the single smm has a very different composition from other scoriaceous particles and the occurrence of an exsolved metallic liquid probably indicates extreme reduction during entry heating the pyrolysis of carbonaceous materials is the most likely explanation for reduction and suggests that the precursor material of this particle was unusually c rich this smm might be therefore an appropriate candidate for a large melted anhydrous or smectite interplanetary dust particle idp the exsolution of immiscible fe ni s liquids during entry heating will result in systematic changes in the compositions of the remaining silicate melt

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

explosive volcanism on mercury analysis of vent and deposit morphology and modes of eruption abstract the messenger mission revealed for the first time conclusive evidence of explosive volcanism on mercury several previous works have cataloged the appearance and location of explosive volcanism on the planet using a variety of identifying characteristics including vent presence and deposit color as seen in multispectral image mosaics we present here a comprehensive catalog of vents of likely volcanic origin our classification scheme emphasizes vent morphology we have analyzed the morphologies of all vents in our catalog and recognize three main morphologies simple vent pit vent and vent with mound the majority of vents we identify are located within impact craters the spatial distribution of vents does not correlate with the locations of volcanic smooth plains deposits in contrast to the moon nor do vents correlate with the locations of large impact basins except for the caloris and tolstoj basins using the degradation state of the vent host crater as a proxy for maximum age we suggest that vent formation has been active through the mansurian and into the kuiperian periods although the majority of vents were likely formed much earlier in mercurian history the morphologies and locations of vents are used to investigate a set of plausible formation geometries we find that the most likely and most prevalent formation geometry is that of a dike stalled at depth which then explosively vents to the surface we compare the vent and deposit size of mercurian pyroclastic deposits with localized and regional lunar pyroclastic deposits and find a range of possible eruption energies and corresponding variations in eruption style localized lunar pyroclastic deposits and the majority of mercurian pyroclastic deposits show evidence for eruption that is consistent with the magmatic foam at the top of a dike reaching a critical gas volume fraction a subset of mercurian vents including the prominent copland rachmaninoff vent to the northeast of the rachmaninoff basin indicates eruption at enhanced gas volume fractions this subset of vents shows a similar eruptive behavior to the lunar orientale dark mantle ring deposit suggesting that the dikes that formed these vents and deposits on mercury underwent some form of additional volatile build up either through crustal volatile incorporation or magma convection within the dike there also exists a population of mercurian vents that no longer retain a visible associated pyroclastic deposit we hypothesize that the visible signature of the pyroclastic deposit has been lost through space weathering and regolith mixing processes together these results provide a comprehensive analysis of explosive volcanism on mercury and inform continued research on the thermal history of mercury and magma composition and evolution

magnetic properties of micrometeorites 1 most micrometeorites are strongly magnetic the signal of a single micrometeorite may exceed the signal of a weakly magnetized standard sediment sample micrometeorites contain abundant magnetite mostly produced by high temperature oxidation during atmospheric entry in this study we carried out measurements on 520 micrometeorites 505 melted cosmic spherules 6 partially melted scoriaceous micrometeorites and 9 unmelted micrometeorites the natural remanent magnetization and the saturation isothermal remanent magnetization have been measured followed by alternating field or thermal stepwise demagnetization the natural remanent magnetization is in the range of 0 4 300 a m for cosmic spherules it is a stable thermal remanent magnetization acquired by quenching in the earth s magnetic field the range is 3 8 16 a m for scoriaceous micrometeorites and 78 525 a m for unmelted micrometeorites which may have preserved a preatmospheric magnetization the magnetic susceptibility is in the range of 0 005 2 9 si for cosmic spherules and is in the range of 0 06 0 12 si for scoriaceous and unmelted micrometeorites temperature dependent susceptibility analyses and thermal demagnetization indicate that magnetite is cation substituted in cosmic spherules different populations of magnetite grains may have different degrees of cation substitution within a single micrometeorite anisotropy of magnetic susceptibility measurements indicates that micrometeorites are strongly anisotropic anisotropy degree 15 and that most have oblate fabrics consistent with the parallel habit of magnetite in barred olivine cosmic spherules

discrimination between maturity and composition of lunar soils from integrated clementine uv visible near infrared data application to the aristarchus plateau the reflectance spectrum of a lunar soil is mainly dominated by the composition and the degree of exposure to space weathering processes such as micrometeorite bombardment and solar wind implantation the spectral alteration effects of space weathering should be removed for accurately investigating the composition of the lunar surface using remote sensing data in this paper we show that the integration of the clementine uv visible uvvis and near infrared nir channels provides an improved evaluation of the spectral alteration the depth of the mafic absorption feature at 0 95 m is also better defined by combining the uvvis and nir data laboratory spectra of lunar soil samples indicate that the continuum slope derived from the 1500 750 nm ratio is closely related to the concentration of fine grained submicroscopic iron is the continuum slope therefore provides an evaluation of the spectral alteration of the surface which can be subtracted from the 1 or 2 m absorption band depths to retrieve compositional information this method has been applied to the aristarchus plateau which exhibits a broad range of mineralogical composition and maturity a nine channel multispectral mosaic of 680 clementine images of the aristarchus plateau has been processed eight telescopic spectra have been used to check the validity of the reduction process for the near infrared bands the 1 m absorption band once corrected for spectral alteration provides an evaluation of the initial feo content in mafic silicates mafic iron lunar soil samples show that it is possible to quantitatively map mafic iron with this technique our results are in good agreement with those obtained using the algorithm of lucey et al 1995 1998a which is based on uvvis bands alone the mafic iron content and total iron content which can be derived from the combined uvvis and nir data sets are less sensitive to local slopes than that derived from lucey et al s method this new method could therefore be useful for investigating areas at middle to high latitudes removing spectral alteration from the 2000 1500 nm ratio also makes possible a better discrimination between olivine and pyroxene within identified mare basalts on the aristarchus plateau

the materials of the lunar procellarum kreep terrane a synthesis of data from geomorphological mapping remote sensing and sample analyses major features of the moon s procellarum kreep terrane include subdued relief and extensive resurfacing with mare basalt consistent with high concentrations of th and other heat producing elements at depth we relate the chemistry of sampled materials to the geomorphology th surface concentrations determined by the lunar prospector 2 pixels and feo and tio2 concentrations derived from clementine ultraviolet visible spectral data on the basis of geologic maps each pixel was classified as mare terra or mixed near the periphery of the terrane terra pixel compositions are relatively feldspathic in the interior they mainly represent imbrium basin rim or ejecta deposits and are mainly incompatible trace element rich norites and presumably represent materials from a thick section tens of kilometers of the pre imbrium crust of the terrane excavated by the imbrium event although imbrium ejecta are the principal source of surface terra materials the imbrium event did not create the th rich procellarum kreep terrane broad continuous expanses of mare pixels are observed with little interruption from protruding terra or terra penetrating craters the mare basalt dominated regoliths of these areas have a wide range of tio2 concentrations 18 leading to the conclusion that the high th concentrations are in the mare basalts and are not present in the regoliths as terra derived materials volcanic glasses and impact glasses of mare basalt composition collected from the procellarum kreep terrane support this conclusion

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

the mineralogy and petrology of i type cosmic spherules implications for their sources origins and identification in sedimentary rocks abstract i type cosmic spherules are micrometeorites that formed by melting during atmospheric entry and consist mainly of iron oxides and feni metal i types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time we report the results of a study of the mineralogy and petrology of 88 i type cosmic spherules recovered from antarctica in order to evaluate how they formed and evolved during atmospheric entry to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks two textural types of i type cosmic spherule are recognised 1 metal bead bearing met spherules dominated by ni poor 100 and suggest that metal from h group ordinary cm cr and iron meteorites may form the majority of particles oxidation during entry heating increases in the series met 80 wt ni comprising a particle mass fraction of

constraining the terrestrial age of micrometeorites using their record of the earth s magnetic field polarity we propose a new nondestructive method that uses the paleomagnetic record of micrometeorites in earth9s polar regions to constrain the age of their fall during atmospheric entry melted micrometeorites acquire a thermal remanent magnetization and record the polar subvertical geomagnetic field when the fall vector can be determined due to the location of bubbles iron nickel droplets or grain size gradients it is possible to ascribe the fall to a normal or reverse polarity interval of the geomagnetic field we tested this concept on a set of eight melted micrometeorites from the transantarctic mountains antarctica two micrometeorites have magnetization directions consistent with a normal polarity of the earth9s magnetic field whereas four others have recorded a reverse polarity and therefore fell to earth at least 0 78 m y ago one micrometeorite has a magnetization that is seemingly unrelated to the inferred entry direction the fall direction could not be determined with certainty for one micrometeorite these results provide new evidence suggesting that the transantarctic mountains micrometeorite traps are 1 2 m y old and confirm that they contain the oldest non fossil micrometeorites available

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

late cenozoic rates of erosion in the western espanola basin new mexico evidence from geologic dating of erosion surfaces erosion surfaces in the espanola basin formed before 350 ka and between 350 and 240 240 and 130 and 130 and 80 ka probably in response to climatic change and regional uplift the surfaces are cut on miocene pliocene and pleistocene deposits and range from about 200 m to 15 m above the present rio chama rio grande system periods when the surfaces formed were dated using varnish cation ratios from exposed clasts the mass of soil carbonate and amino acid ratios in pleistocene gastropods from underlying deposits thorium uranium ages from soil carbonate were used to calibrate a local curve for varnish cation ratios the range in age determined for a given surface although derived from different dating techniques implies that parts of the surface were sites of erosion or aggradation after the surface formed from 1 1 ma to present denudation rates averaged 10 cm 1 000 yr from weakly lithified sandstone less than 7 cm 1 000 yr from indurated tuff and boulder gravel and about 4 cm 1 000 yr from tuff and basalt erosion surfaces were preserved as upland benches and terraces by stream incision during periods of pluvial climate and regional uplift but our data do not permit clear separation of the two causes

diagenetically altered fossil micrometeorites suggest cosmic dust is common in the geological record abstract we report the discovery of fossil micrometeorites from late cretaceous chalk seventy six cosmic spherules were recovered from coniacian 87 1 ma sediments of the white chalk supergroup particles vary from pristine silicate and iron type spherules to pseudomorphic spherules consisting of either single phase recrystallized magnetite or fe silicide pristine spherules are readily identified as micrometeorites on the basis of their characteristic mineralogies textures and compositions both magnetite and silicide spherules contain dendritic crystals and spherical morphologies testifying to rapid crystallisation of high temperature iron rich metallic and oxide liquids these particles also contain spherical cavities representing weathering and removal of metal beads and irregular cavities representing vesicles formed by trapped gas during crystallization both features commonly found among modern antarctic iron type i type cosmic spherules on the basis of textural analysis the magnetite and fe silicide spherules are shown to be i type cosmic spherules that have experienced complete secondary replacement during diagenesis fossilization our results demonstrate that micrometeorites preserved in sedimentary rocks are affected by a suite of complex diagenetic processes which can result in disparate replacement minerals even within the same sequence of sedimentary beds as a result the identification of fossil micrometeorites requires careful observation of particle textures and comparisons with modern antarctic collections replaced micrometeorites imply that geochemical signatures the extraterrestrial dust are subject to diagenetic remobilisation that limits their stratigraphic resolution however this study demonstrates that fossil pseudomorphic micrometeorites can be recognised and are likely common within the geological record

the parent body controls on cosmic spherule texture evidence from the oxygen isotopic compositions of large micrometeorites high precision oxygen isotopic compositions of eighteen large cosmic spherules 500 mu m diameter from the atacama desert chile were determined using ir laser fluorination isotope ratio mass spectrometry the four discrete isotopic groups defined in a previous study on cosmic spherules from the transantarctic mountains suavet et al 2010 were identified confirming their global distribution approximately 50 of the studied cosmic spherules are related to carbonaceous chondrites 38 to ordinary chondrites and 12 to unknown parent bodies approximately 90 of barred olivine bo cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites similarly similar to 90 porphyritic olivine po cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites other textures are related to all potential parent bodies the data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters we propose that the po texture may essentially be formed from a coarse grained precursor having an ordinary chondritic mineralogy and chemistry coarse grained precursors related to carbonaceous chondrites i e chondrules are likely to either survive atmospheric entry heating or form v type cosmic spherules due to the limited number of submicron nucleation sites after total melting ordinary chondrite related coarse grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline cc textures instead of bo textures conversely the bo textures would be mostly related to the fine grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases allowing the preservation of submicron nucleation sites independently of the nature of the precursors increasing peak temperatures form glassy textures

using a mineral lifetime diagram to evaluate the persistence of olivine on mars we present a diagram that shows the effect of ph temperature grain size composition hydrodynamics and the laboratory field discrepancy on the lifetime of olivine grains in weathering environments because the persistence of olivine grains on mars can be used to constrain the duration of liquid water we can use this diagram to predict a range of possible maximum contact times for olivine grains with liquid water before they dissolve away completely depending upon the physicochemical conditions this contact time could range between a few thousand and several million years

ferromagnetic resonance intensity a rapid method for determining lunar glass bead origin ferromagnetic resonance intensity is was tested as a criterion for use as a nondestructive reliable and rapid screening method for distinguishing volcanic from impact glass spherules in the lunar soils this method relies on the absence or presence of single domain fe formed during impact melting by autoreduction of fe2 in the melt extensive scanning electron microscope sem inspection of individual glass bead surfaces provided reliable evidence of the mode of glass genesis ferromagnetic resonance intensity was tested against the type apollo 15 and apollo 17 volcanics additional volcanics were also found during the course of the study ninety four percent of the volcanic glasses had is values less than one implying the absence of single domain fe seventy five percent of impact glasses had elevated is values the remaining impact beads had is values less than one these samples lack single domain fe and could represent impact melts of bedrock with little or no regolith contribution the ability to discriminate bedrock derived impact melts as opposed to impact melts partially or completely derived from regolith and the primary discrimination of volcanic glasses from impact glasses suggests the fmr technique can be important in determining the origin of lunar glass spheres

characteristics and mass distribution of extraterrestrial dust from the greenland ice cap extraterrestrial grains with sizes 50 m can now be extracted in large numbers from terrestrial sediments but their origins are still uncertain at least 99 of these grains have been thought to be spherules1 2 resulting from the melting of their parent bodies in the atmosphere which destroyed their mineralogical composition here we present analyses of extraterrestrial grains extracted from six samples of cryoconite3 black dust collected from the melt zone of the greenland ice cap in addition to families of grains never reported before we have found a surprisingly high abundance of unmelted chondritic fragments in which the nonvolatile component of the parent bodies has been well preserved the mass distribution of the grains is very similar to that of the micrometeorite flux at 1 au ref 4 indicating that most of the grains are micrometeorites and not ablation products of larger meteorites these results yield new constraints on the ablation of such greenland micrometeorites as well as guidelines for using them as glaciological and geological markers

geochronology and thermochronology by the 40ar39ar method ian mcdougall and t mark harrison oxford university press 1988 212p u s 55 00 isbn 0 19 504302 2

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

near infrared spectroscopy of probable impact melt from three large lunar highland craters abstract the composition of small areas within three large lunar highland craters are compared using near infrared earth based telescopic data spectra from many areas in the walls and central peaks of the craters indicate the presence of crystalline components which include olivine two types of pyroxene and sometimes fe bearing feldspar spectra from other regions suspected of being impact melt deposits located on the floors and walls of the three craters have remarkably similar yet anomalous features these features are interpreted to indicate the presence of pyroxene fe bearing glass and fe bearing feldspar pyroxene and feldspar are believed to occur primarily in the form of lithic clasts and rapidly recrystallized impact melt the fe bearing glass is interpreted as impact melt glass

remote sensing of lunar pyroclastic mantling deposits abstract mantling deposits on the moon are considered to be pyroclastic units emplaced on the lunar surface as a result of explosive fire fountaining these pyroclastic units are characterized as having low albedos having smooth fine textured surfaces and consisting in part of homogeneous febearing volcanic glass and partially crystallized spheres mantling units exhibit low returns on depolarized 3 8 cm radar maps indicating an absence of surface scatterers in the 1 to 50 cm size range a number of reflectance spectra from several regional pyroclastic deposits are presented for the first time these data support a previous interpretation that mantling units have a unique spectral signature which is indicative of the presence of a significant fe bearing volcanic glass component the rima bode region is discussed as an example of an area in which several types of remote sensing data including 3 8 cm radar spectral reflectance and multispectral vidicon data were used to reconstruct the geologic events surrounding the emplacement of a regional pyroclastic mantling deposit the recognition of numerous varieties of volcanic glass samples especially relatively high albedo e g green yellow glasses suggests the existence of additional unrecognized mantling deposits with albedos higher than those studied to date on the basis of the remote sensing data summarized and presented five new areas have been identified which may represent higher albedo regional pyroclastic deposits

dissolution of subglacial volcanic glasses from iceland laboratory study and modelling abstract subglacial hyaloclastites from iceland with ages ranging from 2 ka to 2 2 ma have been studied from a mineralogical and geochemical standpoint the chemical composition of palagonite alteration crust formed on the surface of the glass is almost identical with that of the clayey material filling the intergranular spaces of the rock the clayey material is made up of two particle populations the first is si mg and ca rich with a smectite structure while the second is amorphous fe ti and al rich and has a smectite like morphology it is suggested that these two types of particles can be formed simultaneously in the same solution such that it is not necessary to explain their existence by local or temporary equilibria the mineralogical sequences observed in natural samples were reproduced using the geochemical computer code dissol the geochemical mass balances calculated with dissol also fit quite well with those calculated from icelandic samples illustrating the predictive capability of such a calculation code and gives us confidence in applying a similar approach to nuclear waste form glass problems

evidence for silicate dissolution on mars from the nakhla meteorite veins containing carbonates hydrous silicates and sulfates that occur within and between grains of augite and olivine in the nakhla meteorite are good evidence for the former presence of liquid water in the martian crust aqueous solutions gained access to grain interiors via narrow fractures and those fractures within olivine whose walls were oriented close to 001 were preferentially widened by etching along 001 this orientation selective dissolution may have been due to the presence within olivine of shock formed 001 100 and 001 110 screw dislocations the duration of etching is likely to have been brief possibly less than a year and the solutions responsible were sufficiently cool and reducing that laihunite did not form and fe liberated from the olivine was not immediately oxidized the pores within olivine were mineralized in sequence by siderite nanocrystalline smectite a fe mg phyllosilicate and then gypsum whereas only the smectite occurs within augite the nanocrystalline smectite was deposited as submicrometer thick layers on etched vein walls and solution compositions varied substantially between and sometimes during precipitation of each layer together with microcrystalline gypsum the fe mg phyllosilicate crystallized as water briefly returned to some of the veins following desiccation fracturing of the smectite these results show that etching of olivine enhanced the porosity and permeability of the nakhlite parent rock and that dissolution and secondary mineralization took place within the same near static aqueous system

dissolution of primary minerals in natural waters abstract the saturation state of olivine plagioclase clinopyroxene orthopyroxene fe ti oxides and apatite of variable composition has been assessed in natural waters in iceland with temperature ranging from 0 c to 300 c and in situ ph from below 5 to above 10 cold waters are undersaturated with respect to olivine orthopyroxene clinopyroxene and plagioclases indicating that all these minerals tend to dissolve under weathering conditions with increasing ph and temperature the waters approach saturation with pyroxene olivine and plagioclases also the degree of undersaturation of olivine and orthopyroxene decreases with increasing fe content of the minerals and fe rich olivine and orthopyroxene are stable between 50 c and 150 c whereas mg rich ones tend to dissolve natural waters in iceland are saturated with respect to pure albite when above 50 c they are on the other hand undersaturated with ca rich plagioclase up to 250 c where the waters reach saturation pure magnetite and hematite are stable at all temperatures with increasing titanium content the minerals become unstable and the waters are undersaturated with respect to pure ulvospinel at temperatures up to 300 c pure ilmenite is however close to saturation under weathering conditions but undersaturated above 200 c f apatite is close to saturation at all temperatures on the other hand undersaturation with respect to oh apatite is observed at all temperatures the weathering susceptibilities of primary minerals of basalt in icelandic waters in increasing order are mg olivine fe olivine ti rich magnetite ca plagioclase mg orthopyroxene fe orthopyroxene clinopyroxene na plagioclase f apatite ti rich ilmenite ti poor magnetite ti poor hematite

galileo imaging observations of lunar maria and related deposits the galileo spacecraft imaged parts of the western limb and far side of the moon in december 1990 ratios of 0 41 0 56 gin filter images from the solid state hnaging ssi experiment provided information on the titanium content of mare deposits ratios of the 0 76 0 99 gm images indicated 1 gin absorptions associated with fe 2 in mafic minerals mare ages were derived froin crater statistics obtained from lunar orbiter images results on mare coinpositions in western oceanus procellarum and the humorurn basin are consistent with previous earth based observations thus providing confidence in the use of galileo data to extract compositional information mare units in the grimaldi and riccioli basins range in age froin 3 25 to 3 48 ga and consist of medium to medium high titanium 4 to 7 tio2 content lavas the schiller zucchius basin shows a higher 0 76 0 99 gm ratio than the surrounding highlands indicating a potentially higher mafic mineral content consistent with previous interpretations that the area includes mare deposits blanketed by highland ejecta and light plains materials the oldest mare materials in the orientale basin occur in south central mare orientale and are 3 7 ga old youngest mare materials are in lacus autumni and are 2 85 ga old these units are medium to medium high titanium 4 to 7 tio2 basalts thus volcanism was active in orientale for 0 85 ca but lavas were relatively constant in composition galileo data suggest that mendel rydberg mare is similar to mare orientale cryptomare are present as well thus the mare lavas on the western limb and far side to 178oe are remarkably uniform in coinposition being generally of medium to medium high titanium content and having relatively low 0 76 0 99 gin ratios this region of the moon is between two postulated large impact structures the procellarum and the south pole aitken basins and may have a relatively thick crust in areas underlain by an inferred thinner crust i e zones within large basins as at apollo titanium content is often higher however no mare deposits with titanium abundances approaching those of the high titanium 9 to 14 tio2 apollo 11 and 17 basalts nor of the high titanium regions of central oceanus procellarum are seen on the western limb or eastern far side light plains deposits are generally indistinct froin the surrounding highlands in the ssi data and are inferred to be derived primarily from the same material that forins the highlands some of the light plains are too young to be related to basin forming impacts suggesting possible volcanic origin dark mantle deposit compositions derived from ssi data are consistent with earth based observations of similar near side deposits and are interpreted to be pyroclastic materials however the modernitc albedo and 1 gin absorption of the dark mantle deposit on the southwest margin of the orientale basin suggest it is a local pyroclastic deposit contaminated with underlying highland materials from the orientale impact

lava dome growth and explosive volcanism in the jemez mountains new mexico evidence from the plio pleistocene puye alluvial fan abstract the plio pleistocene puye formation north central new mexico is a 200 km2 volcanogenic alluvial fan shed eastward from the tschicoma volcanic center part of the jemez mountains volcanic field the fan contains 15km3 of volcaniclastic material derived from closely spaced lava domes in the northeastern portion of the tschicoma center interbedded in the fan sediments are at least 25 primary pyroclastic units from explosive eruptions of dacitic and rhyolitic lava domes tephra occur mainly as pumice falls but include several pumiceous ignimbrites and two thick proximal block and ash pyroclastic flows the upper part of the fan also contains rhyolitic plinian deposits erupted from sources in the central portion of the jemez field and basaltic ash derived from the central rio grande rift fanglomeratic pyroclastic and epiclastic facies exhibit considerable lateral variation primary tephra deposits however provide a stratigraphic framework for reconstruction of the growth of individual lava domes while only volcanic domes and lava flows are exposed in the tschicoma center puye tephra layers show that vulcanian subplinian and plinian activity and block and ash pyroclastic flows accompanied many dome forming events degradation of these lava domes produced coarse grained debris flows dominated by lava and dome carapace clasts from these epiclasts it is possible to identify lithologies of lavas that are either currently buried or have been obliterated by erosion or by collapse of the valles calderas the preservation of puye deposits reflects very high rates of aggradation and gradual down faulting in the espanola basin of the central rio grande rift this record of pyroclastic and epiclastic deposition allows detailed interpretation of the evolution of a volcanic center from its pyroclastic and erosion products and is the first example of a volcanogenic alluvial fan in an intracontinental rift setting to be described in detail this study emphasizes that interpretation of any ancient volcanic terrain based solely upon data derived from mapping radiometric dating and chemical analysis of lavas or existing denuded edifices is likely to greatly underestimate both the role of explosive volcanism in the build up of volcanic centers and subsequent estimates of the volumes of material produced

fine grained precursors dominate the micrometeorite flux we optically classified 5682 micrometeorites mms from the 2000 south pole collection into textural classes imaged 2458 of these mms with a scanning electron microscope and made 200 elemental and eight isotopic measurements on those with unusual textures or relict phases as textures provide information on both degree of heating and composition of mms we developed textural sequences that illustrate how fine grained coarse grained and single mineral mms change with increased heating we used this information to determine the percentage of matrix dominated to mineral dominated precursor materials precursors that produced the mms we find that at least 75 of the mms in the collection derived from fine grained precursors with compositions similar to ci and cm meteorites and consistent with dynamical models that indicate 85 of the mass influx of small particles to earth comes from jupiter family comets a lower limit for ordinary chondrites is estimated at 2 8 based on mms that contain na bearing plagioclase relicts less than 1 of the mms have achondritic compositions cai components or recognizable chondrules single mineral mms often have magnetite zones around their peripheries we measured their isotopic compositions to determine if the magnetite zones demarcate the volume affected by atmospheric exchange during entry heating because we see little gradient in isotopic composition in the olivines we conclude that the magnetites are a visual marker that allows us to select and analyze areas not affected by atmospheric exchange similar magnetite zones are seen in some olivine and pyroxene relict grains contained within mms

the influence of ephemeral processes on pyroclastic sedimentation in a rift basin volcaniclastic alluvial sequence espanola basin new mexico abstract the plio pleistocene puye formation north central new mexico is a coarse grained conglomeratic wedge of primary and reworked volcanic deposits that prograded eastward into an actively aggrading floodbasin of the central rio grande rift this alluvial system grew in response to the degradation of dacitic and rhyolitic lava domes in the northeastern part of the jemez mountains volcanic field analysis of puye deposits shows that fan sedimentation was governed by the complex interaction of explosive volcanism rift basin tectonics and the highly variable localized ephemeral processes common to arid region alluvial systems preserved in this well exposed sequence are complex associations between primary pyroclastic facies related to explosive eruptions from lava domes and reworked tuffs that record the rapid emplacement of poorly consolidated pumice and ash the sporadic availability of water in this semi arid region and the episodic flood frequency and runoff that accompanied individual eruptions largely controlled puye facies characteristics important among the combined influences of explosive eruptions and ephemeral processes were 1 fluvial transport and reworking of pumice sequences 2 remobilization of loosely consolidated volcanic talus and tuffs by mass flow and 3 marked downslope changes in mass flow deposits and fallout tephra emplaced into lakes

the fluvial and pyroclastic deposits of the cagayan basin northern luzon philippines an example of non marine volcaniclastic sedimentation in an interarc basin the cagayan basin of northern luzon an interarc basin 250 km long and 80 km wide contains a 900 m thick sequence of plio pleistocene fluvial and pyroclastic deposits these deposits are divided into two formations the ilagan and awidon mesa and three lithofacies associations the facies which are interpreted as meandering stream braided stream lahar and pyroclastic flow and fall deposits occur in a coarsening upward sequence meandering stream deposits interbedded with tuffs are overlain by braided stream deposits interbedded with coarser pyroclastic deposits lahars and ignimbrites the coarsening upward volcaniclastic deposits reflect the tectonic and volcanic evolution of the adjacent cordillera central volcanic arc uplift of the arc resulted in the progradation of coarser clastics further into the basin the development of an alluvial fan and migration of the basin depocentre away from the arc the coarsening of the pyroclastic deposits reflects the development of a more proximal calc alkaline volcanic belt in the maturing volcanic arc the cagayan basin sediments serve as an example of the type and sequence of non marine volcaniclastic sediments that may form in other interarc basins this is because the tectonic and volcanic processes which controlled sedimentation in the cagayan basin also affect other arc systems and will therefore control or significantly influence volcaniclastic sedimentation in other interarc basins